阅读说明：本技术 一种双三相无刷直流电机的飞轮储能系统及其控制方法 (Flywheel energy storage system of double three-phase brushless direct current motor and control method thereof ) 是由 林海 莫乾坤 于 2019-11-04 设计创作，主要内容包括：本发明公开了一种双三相无刷直流电机的飞轮储能系统及其控制方法,双三相无刷直流电机包括六路绕组,两组三相绕组之间通过双向晶闸管连接,两组绕组间相差30度的电角度；双向晶闸管实现一组三相绕组和一组三相逆变器连接,组成第一逆变电路和第二逆变电路；三相逆变器组的每一桥臂与一相绕组之间连接一个断路器QF和熔断器FU,直流母线中分别设置继电器K1,K2闭合触点；能量回馈中采用BOOST电路通过控制开关管实现直流侧电压稳定,在BOOST电路中设置继电器K3,K4常开触点,当绕组电压达到给定值时,继电器K3,K4常开触点闭合,继电器K1,K2闭合触点断开,实现能量切换。本发明适合大容量储能,功率大,使用寿命长,充放电速度快。(The invention discloses a flywheel energy storage system of a double three-phase brushless direct current motor and a control method thereof, wherein the double three-phase brushless direct current motor comprises six windings, two groups of three-phase windings are connected through a bidirectional thyristor, and the two groups of windings have an electric angle difference of 30 degrees; the bidirectional thyristor realizes the connection of a group of three-phase windings and a group of three-phase inverters to form a first inverter circuit and a second inverter circuit; a breaker QF and a fuse FU are connected between each bridge arm and one phase winding of the three-phase inverter group, and relays K1 and K2 are arranged in a direct current bus respectively to close contacts; the direct current side voltage stabilization is realized by adopting a BOOST circuit through a control switch tube in energy feedback, relays K3 and K4 normally open contacts are arranged in the BOOST circuit, when the winding voltage reaches a given value, the normally open contacts of the relays K3 and K4 are closed, the closed contacts of the relays K1 and K2 are opened, and energy switching is realized. The invention is suitable for large-capacity energy storage, and has the advantages of large power, long service life and high charging and discharging speed.)

1. A flywheel energy storage system of a double three-phase brushless direct current motor is characterized by comprising the double three-phase brushless direct current motor and a BOOST circuit, wherein the double three-phase brushless direct current motor comprises six windings, and three windings form a group of three-phase windings; the two groups of three-phase windings are connected through a bidirectional thyristor, and the difference between the two groups of windings is 30 degrees in electrical angle; the bidirectional thyristor realizes the connection of a group of three-phase windings and a group of three-phase inverters to form a first inverter circuit and a second inverter circuit; each bridge arm of the three-phase inverter group comprises two power MOS switching tubes which are connected in series, the connection point is the middle point of the bridge arm, a breaker QF and a fuse FU are connected between each bridge arm and one phase winding, and a relay K1 and a K2 closed contact are respectively arranged in a direct current bus; the direct current side voltage stabilization is realized by adopting a BOOST circuit through a control switch tube in energy feedback, relays K3 and K4 normally open contacts are arranged in the BOOST circuit, when the winding voltage reaches a given value, the normally open contacts of the relays K3 and K4 are closed, the closed contacts of the relays K1 and K2 are opened, and energy switching is realized.

2. The flywheel energy storage system of a dual three-phase brushless direct current motor according to claim 1, wherein in the BOOST circuit, when the switching tube V is turned on, the energy of the power supply flows to the inductor L, and the voltage on the capacitor C supplies power to the power grid; when the switching tube V is in an off state, energy is not output; the switching tube V compares the voltage at the end of the detection winding with the designated voltage, the error is compared with the triangular wave carrier after being subjected to PI regulation to generate a PWM signal, and the PWM signal is used for regulating the duty ratio of the switching tube V to realize stable direct-current voltage output.

3. The flywheel energy storage system of the dual three-phase brushless direct current motor as claimed in claim 1, wherein the inverter comprises a group A and a group B, the group A inverter comprises three legs, the leg La of the inverter comprises a power switch tube S1 and a power switch tube S2, and a circuit breaker QF1 and a fuse FU1 are connected between the legs and the winding; the inverter bridge arm Lb comprises a power switch tube S3 and a power switch tube S4, and a circuit breaker QF2 and a fuse FU2 are connected between the bridge arm and the winding; the inverter bridge arm Lc comprises a power switch tube S5 and a power switch tube S6, and a circuit breaker QF3 and a fuse FU3 are connected between the bridge arm and the winding;

the group B inverter comprises three bridge arms, the bridge arm Lx of the inverter comprises a power switch tube S7 and a power switch tube S8, and a circuit breaker QF4 and a fuse FU4 are connected between the bridge arms and the windings; the inverter bridge arm Ly comprises a power switch tube S9 and a power switch tube S10, and a circuit breaker QF5 and a fuse FU5 are connected between the bridge arm and the winding; the inverter bridge arm Lz comprises a power switch tube S11 and a power switch tube S12, a circuit breaker QF6 and a fuse FU6 are connected between the bridge arm and the winding, and connection points on two sides of the power switch tube after being connected in series are respectively connected with the positive electrode and the negative electrode of the direct-current power supply.

4. The flywheel energy storage system of the double three-phase brushless direct current motor according to claim 3, wherein in the group A inverter, three-phase currents of the stator are detected, then coordinates are converted into current values under two-phase coordinates, alternating-direct axis voltages are obtained through vector control, voltage values on α - β axes are obtained through coordinate conversion, and six paths of signals are output after space vector pulse width modulation to generate six paths of signals to respectively control the corresponding six switching tubes;

in the B-group inverter, the reference signal U is passed_dc ^*And actual detected U_dcAnd comparing to obtain a difference value for PI regulation, wherein the output quantity of the voltage PI regulation is a given value of a current loop, comparing with a current feedback value, performing PI regulation on the obtained difference value, converting decoupling coordinates, comparing with a triangular wave to generate a trigger pulse signal PWM2 signal, and generating six paths of signals to respectively control the corresponding six switching tubes.

5. The flywheel energy storage system of a dual three-phase brushless dc motor of claim 1, wherein the control of the triac is: detection of three-phase winding u by voltage sensor_a,u_b,u_cAnd given a threshold voltage

when the inverter is operating normally, F_u1, systemThe two-phase three-phase motor works in a power supply mode of a traditional twelve-switch inverter, firstly, a bidirectional thyristor VS receives a forward voltage signal to be conducted, and then the two-phase three-phase motor is formed.

6. The method for controlling the flywheel energy storage system of a dual three-phase brushless DC motor according to any one of claims 1 to 5, comprising:

in a charging state, an external power supply supplies power to the motor/generator through the power electronic converter, the motor/generator operates as a motor, the flywheel rotor is driven to accelerate, when the rotating speed of the rotor reaches the maximum working torque, the power electronic device generates a control signal to control the driving motor, and the motor drives the flywheel to operate and realize charging;

in a discharging state, the motor/generator operates as a generator, the flywheel rotor decelerates, mechanical energy is converted into electric energy by the generator, and the power electronic converter adjusts the bus voltage output by the generator to keep the bus voltage constant all the time;

a hold state, in which the flywheel system is in an energy hold phase with neither forward nor reverse flow of energy, in which mode the system operates with minimal losses;

detection three-phase winding u by detection voltage sensor_a,u_b,u_cWith a given voltage value u_oWhen u is compared with_a,u_b,u_cGradually rise to u_oWhen the battery is in a charging state; when u is_oWhen the value gradually drops to a set value, the discharge state is realized, and the working mode is judged as follows:

when the current sensor detects that the port of the armature winding connected with the fault bridge arm has fault and makes fault judgment, the current sensor controls signals to control the six switching tubes of the A group/the B group of the inverter to be simultaneously turned off by controlling the PWM1/PWM2 module, and the inverter stops working.

7. The method of claim 6The method is characterized in that in the charging process, six paths of PWM driving signals are sent out by detecting the zero crossing point of the back electromotive force, and the power switching tube is driven after power amplification, so that the motor reaches the highest rotating speed and is in a holding stage; the control strategy is to control the speed omega of the position^*Comparing with the actually estimated omega to obtain a difference value, and then leading the difference value to pass through a PI controller to obtain a current signal i of a q axis_q ^*While setting the given reference signal of the d-axis to zero; transformed into a current component i by coordinate transformation_dAnd i_qWith its reference signal i_d ^*,i_q ^*Comparing, decoupling by current controller, outputting voltage signal u_d ^*And u_q ^*And after coordinate transformation, the control signal is generated by SVPWM control, so that the charging process is realized.

8. The method according to claim 7, characterized by the specific steps of:

s101, subtracting the given rotating speed omega of the motor from the actual rotating speed omega to obtain a speed error e_ωVelocity error e_ωOutputting given current after passing through a rotating speed PI regulator

S102, referring to the direct current signal and the alternating current signal

S103, rootDetecting stator winding current i of motor according to current sensor_a,i_bCalculating the current i under a two-phase rotating coordinate system_d,i_qFor the calculated reference voltage

And S104, determining the direction of the interval where the reference voltage vector is located, and synthesizing the reference voltage vector by using two adjacent voltage vectors and a proper sector zero vector to realize the modulation of the SVPWM signal.

9. Method according to claim 6, characterized in that in the discharge state, a double closed-loop control system is used, the outer loop being a voltage regulation loop, in which the quadrature-axis current component i is measured_q ^*Limiting, wherein the current inner ring performs current control according to the current output by the voltage ring, and generates a trigger pulse signal PWM2 module by comparing the current with a triangular wave after the decoupling coordinate transformation; the discharge process is realized.

10. The method according to claim 9, characterized by the following specific steps:

s201 and PWM2 modules convert the measured three-phase stationary coordinate system into synchronously rotating two-phase coordinates, and the current value is converted into a current component i after coordinate conversion_dAnd i_q；

S202, adopting a direct current control strategy, and controlling a given reference signal to be compared with an actual value by a voltage outer ring tracking system to realize constant direct current voltage through the output current of a PI regulator;

s203, current control is carried out on the current output by the current inner ring according to the voltage ring, and the current is subjected to decoupling coordinate transformation and then is compared with a triangular wave to generate a trigger pulse signal to control the on and off of the converter;

and S204, in the discharging process, converting mechanical energy into electric energy, boosting a Boost circuit behind an inverter to supply power to a direct current load, comparing the voltage at the end of a detection winding with a specified voltage, comparing an error with a triangular wave carrier after PI regulation to generate a PWM signal to regulate the duty ratio of V, and regulating and outputting direct current voltage.

Technical Field

The invention belongs to the technical field of motor control, and particularly relates to a flywheel energy storage system of a double three-phase brushless direct current motor and a control method thereof.

Background

Energy has been a major problem in human development. In the process of developing and utilizing traditional energy and new energy, the development of energy storage technology can relieve the contradiction between energy production and energy consumption. The hydroelectric generation is responsible for adjusting peak voltage, adjusting frequency, power storage and other tasks, reducing the excessive use of thermal power resources, reducing the cost of a power grid and improving the reliability of the power grid. The development of the parallel operation technology of the flywheel energy storage units is applied to the field of large power grid energy storage, and along with the research of a power grid, a distributed energy system based on the energy storage technology is built, and the development of the energy storage technology is imperative.

The energy storage form is divided into three categories: 1) mechanical energy storage such as flywheel energy storage, compressed air energy storage, energy pumping energy storage and the like; 2) energy storage such as super capacitor energy storage, superconducting energy storage and the like; 3) lead-acid batteries, lithium ion batteries, sodium sulfur batteries, redox flow batteries, and the like.

Among the energy storage technologies mentioned above, those applied in engineering are relatively mature, pumped storage and chemical battery storage. The pumped storage has low comprehensive benefit and high requirement. Chemical batteries are widely used, but have limitations such as the number of charging and discharging times, environmental pollution, and high operating temperature requirements. On the other hand, in recent years, new activities are injected into the development of flywheel energy storage systems for developing advanced composite materials, high-power electronic devices, low-loss advanced bearings and high efficiency and long service life of high-speed permanent magnet motors. The flywheel energy storage system has the advantages of high power density, high energy density, convenience in installation and maintenance, no harm to the environment, long service life, almost no limit to the charging and discharging times, and is superior to the chemical battery energy storage technology.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a flywheel energy storage system of a dual three-phase brushless dc motor and a control method thereof, so as to improve the charging and discharging efficiency of the flywheel energy storage system.

The invention adopts the following technical scheme:

a flywheel energy storage system of a double three-phase brushless direct current motor comprises the double three-phase brushless direct current motor and a BOOST circuit, wherein the double three-phase brushless direct current motor comprises six windings, and a group of three-phase windings are formed by three windings; the two groups of three-phase windings are connected through a bidirectional thyristor, and the difference between the two groups of windings is 30 degrees in electrical angle; the bidirectional thyristor realizes the connection of a group of three-phase windings and a group of three-phase inverters to form a first inverter circuit and a second inverter circuit; each bridge arm of the three-phase inverter group comprises two power MOS switching tubes which are connected in series, the connection point is the middle point of the bridge arm, a breaker QF and a fuse FU are connected between each bridge arm and one phase winding, and a relay K1 and a K2 closed contact are respectively arranged in a direct current bus; the direct current side voltage stabilization is realized by adopting a BOOST circuit through a control switch tube in energy feedback, relays K3 and K4 normally open contacts are arranged in the BOOST circuit, when the winding voltage reaches a given value, the normally open contacts of the relays K3 and K4 are closed, the closed contacts of the relays K1 and K2 are opened, and energy switching is realized.

Specifically, in the BOOST circuit, when the switching tube V is turned on, the energy of the power supply flows to the inductor L, and the voltage on the capacitor C supplies power to the power grid; when the switching tube V is in an off state, energy is not output; the switching tube V compares the voltage at the end of the detection winding with the designated voltage, the error is compared with the triangular wave carrier after being subjected to PI regulation to generate a PWM signal, and the PWM signal is used for regulating the duty ratio of the switching tube V to realize stable direct-current voltage output.

Specifically, the inverter comprises a group A and a group B, the group A inverter comprises three bridge arms, a bridge arm La of the inverter comprises a power switch tube S1 and a power switch tube S2, and a circuit breaker QF1 and a fuse FU1 are connected between the bridge arms and a winding; the inverter bridge arm Lb comprises a power switch tube S3 and a power switch tube S4, and a circuit breaker QF2 and a fuse FU2 are connected between the bridge arm and the winding; the inverter bridge arm Lc comprises a power switch tube S5 and a power switch tube S6, and a circuit breaker QF3 and a fuse FU3 are connected between the bridge arm and the winding;

the group B inverter comprises three bridge arms, the bridge arm Lx of the inverter comprises a power switch tube S7 and a power switch tube S8, and a circuit breaker QF4 and a fuse FU4 are connected between the bridge arms and the windings; the inverter bridge arm Ly comprises a power switch tube S9 and a power switch tube S10, and a circuit breaker QF5 and a fuse FU5 are connected between the bridge arm and the winding; the inverter bridge arm Lz comprises a power switch tube S11 and a power switch tube S12, a circuit breaker QF6 and a fuse FU6 are connected between the bridge arm and the winding, and connection points on two sides of the power switch tube after being connected in series are respectively connected with the positive electrode and the negative electrode of the direct-current power supply.

Further, in the inverter group A, three-phase current of a stator is detected, then coordinates are converted into current values under two-phase coordinates, alternating-direct axis voltage is obtained through vector control, voltage values on an axis α - β are obtained through coordinate conversion, and six paths of signals are output to generate PWM1 signals to respectively control six corresponding switching tubes after space vector pulse width modulation;

in the B-group inverter, the reference signal U is passed_dc ^*And actual detected U_dcAnd comparing to obtain a difference value for PI regulation, wherein the output quantity of the voltage PI regulation is a given value of a current loop, comparing with a current feedback value, performing PI regulation on the obtained difference value, converting decoupling coordinates, comparing with a triangular wave to generate a trigger pulse signal PWM2 signal, and generating six paths of signals to respectively control the corresponding six switching tubes.

Specifically, the control of the triac is as follows: detection of three-phase winding (u) by means of voltage sensors_a,u_b,u_c) And given a threshold voltageThe comparison results in a signal F of the bidirectional thyristor VS_UThe method specifically comprises the following steps:

when the inverter is operating normally, F_uThe system works in a traditional twelve-switch inverter power supply mode, firstly, a bidirectional thyristor VS receives a forward voltage signal to be conducted, and the motor becomes a double three-phase motor.

The other technical scheme of the invention is that the control method of the flywheel energy storage system of the double three-phase brushless direct current motor comprises the following steps:

in a charging state, an external power supply supplies power to the motor/generator through the power electronic converter, the motor/generator operates as a motor, the flywheel rotor is driven to accelerate, when the rotating speed of the rotor reaches the maximum working torque, the power electronic device generates a control signal to control the driving motor, and the motor drives the flywheel to operate and realize charging;

in a discharging state, the motor/generator operates as a generator, the flywheel rotor decelerates, mechanical energy is converted into electric energy by the generator, and the power electronic converter adjusts the bus voltage output by the generator to keep the bus voltage constant all the time;

in the hold state, the flywheel system is in an energy hold phase. It has neither forward nor reverse flow of energy, in which mode the system operates with minimal losses;

detection voltage sensor detects three-phase winding (u)_a,u_b,u_c) With a given voltage value u_oWhen u is compared with_a,u_b,u_cGradually rise to u_oWhen the battery is in a charging state; when u is_oWhen the value gradually drops to a set value, the discharge state is realized, and the working mode is judged as follows:

when the current sensor detects that the port of the armature winding connected with the fault bridge arm has fault and makes fault judgment, the current sensor controls signals to control the six switching tubes of the A group/the B group of the inverter to be simultaneously turned off by controlling the PWM1/PWM2 module, and the inverter stops working.

Specifically, in the charging process, six paths of PWM driving signals are sent out by detecting the zero crossing point of the back electromotive force, and the power switching tube is driven after power amplification, so that the motor reaches the highest rotating speed and is in a holding stage; the control strategy is to control the speed omega of the position^*Comparing with the actually estimated omega to obtain a difference value, and then leading the difference value to pass through a PI controller to obtain a current signal i of a q axis_q ^*While setting the given reference signal of the d-axis to zero; transformed into a current component i by coordinate transformation_dAnd i_qWith its reference signal i_d ^*,i_q ^*Comparing, decoupling by current controller, outputting voltage signal u_d ^*And u_q ^*After coordinate transformation, the control signal is generated by SVPWM controlThe charging process is now present.

Further, the method comprises the following specific steps:

s101, subtracting the given rotating speed omega of the motor from the actual rotating speed omega to obtain a speed error e_ωVelocity error e_ωOutputting given current after passing through a rotating speed PI regulator

S102, referring to the direct current signal and the alternating current signalAnd a direct current, an alternating current i_d,i_qCalculating the current deviation e_d,e_qOutputting reference DC voltage after passing through two current PI regulators

And DC/AC shaft voltage

S103, detecting the stator winding current i of the motor according to the current sensor_a,i_bCalculating the current i under a two-phase rotating coordinate system_d,i_qFor the calculated reference voltage

Calculating reference voltage under three-phase rotating coordinate system

And S104, determining the direction of the interval where the reference voltage vector is located, and synthesizing the reference voltage vector by using two adjacent voltage vectors and a proper sector zero vector to realize the modulation of the SVPWM signal.

In particular, in the discharge state, a double closed-loop control system is adopted, the outer ring is a voltage regulating ring, and a quadrature axis current component i in the voltage regulator_q ^*Limiting, in currentThe ring is subjected to current control according to the current output by the voltage ring, and is compared with a triangular wave after being subjected to decoupling coordinate transformation to generate a trigger pulse signal PWM2 module; the discharge process is realized.

Further, the method comprises the following specific steps:

s201 and PWM2 modules convert the measured three-phase stationary coordinate system into synchronously rotating two-phase coordinates, and the current value is converted into a current component i after coordinate conversion_dAnd i_q；

S202, adopting a direct current control strategy, and controlling a given reference signal to be compared with an actual value by a voltage outer ring tracking system to realize constant direct current voltage through the output current of a PI regulator;

s203, current control is carried out on the current output by the current inner ring according to the voltage ring, and the current is subjected to decoupling coordinate transformation and then is compared with a triangular wave to generate a trigger pulse signal to control the on and off of the converter;

and S204, in the discharging process, converting mechanical energy into electric energy, boosting a Boost circuit behind an inverter to supply power to a direct current load, comparing the voltage at the end of a detection winding with a specified voltage, comparing an error with a triangular wave carrier after PI regulation to generate a PWM signal to regulate the duty ratio of V, and regulating and outputting direct current voltage.

Compared with the prior art, the invention has at least the following beneficial effects:

the invention relates to a flywheel energy storage system of a double three-phase brushless direct current motor, because the power grid does not supply power in the discharging process of the flywheel energy storage system, the speed of the motor gradually decreases, the required discharging depth is not reached, and the terminal voltage of the motor gradually decreases, a Boost circuit needs to be added in front of a load, and meanwhile, in order to stabilize the output voltage of the power grid, the contents of claim 1 are supplemented to explain the advantages and the advantages of the whole energy storage system.

Furthermore, a control signal of a switching tube V in the BOOST circuit is analyzed, the voltage of a detection winding end is compared with a specified voltage, an error is subjected to PI regulation and then compared with a triangular wave carrier to generate a PWM signal, the range of the direct current BOOST transformation ratio is greatly improved compared with that of the traditional direct current BOOST transformation ratio by adopting the mode, and the number of the switching tubes is only one, so that the loss of the circuit is effectively reduced, the working efficiency of the inverter is ensured, and the efficiency of the whole flywheel energy storage system is improved.

Furthermore, a full-bridge controllable circuit formed by six MOS power switching tubes of the bidirectional inverter is analyzed, and the bidirectional inverter is used for inverting direct current into 120-degree square wave current to drive the brushless direct current motor during charging and converting square wave electromotive force into direct current by AC/DC conversion during power generation.

Furthermore, a bidirectional thyristor VS is connected between two groups of three-phase windings of the double three-phase motor, neutral point isolation is achieved, anti-interference performance is effectively improved, and the difference between the two groups of windings is 30 degrees in electrical angle. When VS is conducted, one group of winding and inverter are charged and discharged, and the other group of winding and inverter are charged and discharged. When VS is turned off, the system is changed into two sets of three-phase motors, one set can be normally charged and discharged, and the other set does not work. When one group of inverters fails, the other group can normally realize energy conversion, and when a failure occurs, the failure excess of the system can be realized. The purpose of replacing the fault group is achieved, and the normal energy storage work of the system is achieved.

The invention relates to a control method of a flywheel energy storage system of a double three-phase brushless direct current motor, which improves the charge and discharge power of the flywheel energy storage system under the condition of not increasing the voltage and the current of a bus by driving a flywheel of the direct current motor, reduces the loss of a motor rotor by reducing the content of low-order harmonic, improves the efficiency of the system, realizes the combination of a plurality of motors and the flywheel energy storage system, and has application prospect on the structure composition of the direct current motor and the flywheel energy storage system.

Furthermore, considering the characteristics of large rotational inertia and long charging time of a flywheel energy storage system, the PWM control mode of current hysteresis tracking is adopted to reduce the charging time, eliminate the electromagnetic torque fluctuation of the brushless direct current motor caused by peak current and reduce the noise of the system during charging.

Furthermore, the fact that vector control is adopted in the discharging process is analyzed, the brushless motor achieves energy feedback through the three-phase inverter, and due to the fact that the electric energy changes along with the change of the rotating speed in the discharging state, better utilization of the electric energy is needed, the fact that the converted direct-current voltage is kept unchanged is guaranteed, a BOOST circuit needs to be added behind the inverter to better stabilize direct-current bus voltage, and the method has the advantage that the control mode is easier.

In conclusion, the flywheel energy storage charging and discharging control system is suitable for high-capacity energy storage, has the advantages of high power, long service life and high charging and discharging speed, and has a very wide prospect, so that the flywheel energy storage charging and discharging control needs to be researched.

The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.

Drawings

Fig. 1 is a winding structure diagram of a brushless dc motor of the present invention;

FIG. 2 is a schematic diagram of the flywheel energy storage system of the present invention;

FIG. 3 is a diagram of a flywheel system charging energy storage dual closed loop control system according to the present invention;

FIG. 4 is a control system diagram of the flywheel system discharge double closed loop of the present invention;

FIG. 5 is a schematic circuit diagram of the energy storage system charging of the present invention;

FIG. 6 is a main circuit diagram of an energy storage system of a dual three-phase motor of the present invention;

FIG. 7 is a diagram of a flywheel energy storage system charging model;

fig. 8 is a graph of charging simulation data in which (a) is a conversion of the rotation speed N1000 r/min and (b) is an electromagnetic torque T of 1000r/min_eConversion, (c) is that N is 1000r/min load current i_abc(d) is the conversion of the rotating speed N equal to 2000r/min, and (e) is the load current i equal to 2000r/min_abc(f) N is 2000r/min electromagnetic torque T_eTransforming;

FIG. 9 is a diagram of a flywheel energy storage discharge model;

fig. 10 is a graph of discharge simulation data, in which (a) is a graph of a voltage waveform on the load side of a given voltage U-220V, (b) is a graph of a rotational speed waveform on the load side of the given voltage U-220V, (c) is a graph of a voltage waveform on the load side of the given voltage U-250V, and (d) is a graph of a rotational speed waveform in the given voltage U-250V.

Detailed Description

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

The invention provides a flywheel energy storage system of a double three-phase brushless direct current motor and a control method thereof, wherein mathematical models of the direct current motor under a natural coordinate system and a rotating coordinate system are analyzed, and a double closed-loop control method for controlling the charging and discharging of the system is adopted, wherein the control method comprises a motor model, a PI controller model, a coordinate transformation model and an SVPWM control mathematical model, so that control models of two systems of charging and discharging are obtained; and a double closed-loop control method is adopted, and the direct-current brushless motor is connected with the flywheel and generates two processes of accelerating energy storage and decelerating discharge for the flywheel.

The method comprises the steps that a coordinate transformation module is needed to be used for obtaining the current values and position angles of the double three-phase brushless direct current motors through establishing a three-phase brushless direct current motor mathematical model, coordinate transformation is carried out on the current values of the double three-phase brushless direct current motors according to the position angles of a motor rotor to generate current values of d-q axes of two groups of windings in a rotating coordinate system, and a module is generated. And the PWM module obtains a driving signal through a space voltage vector modulation technology, controls the conduction and the turn-off of the switching tubes of the two groups of inverters, and obtains the realization of system charging and discharging.

Referring to fig. 6, the present invention provides a flywheel energy storage system of a dual three-phase brushless dc motor, including a brushless dc motor, a six-phase inverter, a fuse, a circuit breaker, a relay KM, a bidirectional thyristor, and a BOOST circuit.

Referring to fig. 1, the dual three-phase brushless dc motor includes six windings, and the structure can be divided into three windings to form a set of three-phase windings, and the two sets of three-phase windings form a dual three-phase motor winding part; two groups of three-phase windings are connected through a bidirectional thyristor VS to realize neutral point isolation, and the difference between the two groups of windings is 30 degrees in electrical angle. The bidirectional thyristor can realize the connection of a group of three-phase windings and a group of three-phase inverters A (B) to form two systems of an inverter circuit 1 and an inverter circuit 2; a breaker QF and a fuse FU are connected between each bridge arm and a phase winding in the group A (B) inverter, relays K1 and K2 are arranged in a direct current bus respectively, meanwhile, relays K3 and K4 are arranged in a BOOST circuit, action signals of the relays are obtained by detecting whether the voltage of the winding reaches a given value, when the voltage of the winding reaches the given value, the normally-open contacts of the relays K3 and K4 are closed, and the closed contacts of the relays K1 and K2 are opened, so that the switching process of energy is realized. The motor is characterized in that the outlet end only has 6 phases, and the motor is equivalent to a symmetrical twelve-phase motor system when viewed from the inside, thereby effectively eliminating 5 and 7 harmonic potentials of the traditional three-phase motor, reducing the manufacturing process requirements of the motor and improving the stability of the motor.

Each inverter bridge arm is formed by connecting two power MOS switching tubes in series, and the connecting point is the middle point of the bridge arm. The group A inverter comprises three (La, Lb and Lc) bridge arms, the bridge arm La of the inverter consists of a power switch tube S1 and a power switch tube S2, and a circuit breaker QF1 and a fuse FU1 are connected between the bridge arms and a winding; the inverter bridge arm Lb consists of a power switch tube S3 and a power switch tube S4, and a circuit breaker QF2 and a fuse FU2 are connected between the bridge arm and the winding; the inverter bridge arm Lc consists of a power switch tube S5 and a power switch tube S6, and a circuit breaker QF3 and a fuse FU3 are connected between the bridge arm and the winding; the group B inverter comprises three (Lx, Ly and Lz) bridge arms, the bridge arm Lx of the inverter consists of a power switch tube S7 and a power switch tube S8, and a circuit breaker QF4 and a fuse FU4 are connected between the bridge arm and a winding; the inverter bridge arm Ly consists of a power switch tube S9 and a power switch tube S10, and a circuit breaker QF5 and a fuse FU5 are connected between the bridge arm and the winding; the inverter bridge arm Lz consists of a power switch tube S11 and a power switch tube S12, a circuit breaker QF6 and a fuse FU6 are connected between the bridge arm and the winding, and connection points on two sides of the power switch tube after being connected in series are respectively connected with the positive electrode and the negative electrode of the direct-current power supply.

The group A inverter comprises three (La, Lb, Lc) inverter bridge arms and six switching tubes, the control signals of the group A inverter are (S1, S2, S3, S4, S5, S6) respectively generated by a PWM1 controller, the implementation process of the group A inverter is to detect three-phase current of a stator, then coordinate conversion is carried out on the three-phase current to obtain current values under two-phase coordinates, alternating-direct axis voltage is obtained after vector control, voltage values on α - β axes are obtained through coordinate conversion, and PWM1 signals are output after space vector pulse width modulation, the group B inverter comprises three (Lx, Ly, Lz) inverter bridge arms and six switching tubes, the control signals of the group B inverter are generated by a PWM2 controller to obtain six signals (S7, S8, S9, S410, S11, S12), and the implementation process of the group B inverter is carried out through a voltage reference signal U_dc ^*And actual detected U_dcAnd comparing to obtain a difference value for PI regulation. The output quantity of the voltage PI regulation is used as the given value of the current loop, the given value is compared with the current feedback value, the obtained difference value is subjected to PI regulation, and then the PI regulation is carried out, and the PI regulation is subjected to decoupling coordinate transformation and then compared with a triangular wave to generate a trigger pulse signal PWM2 signal.

1. Detecting a three-phase winding (u) by a voltage sensor according to the control of a triac (VS) in a double three-phase motor winding structure_a,u_b,u_c) And given a threshold voltage

The comparison results in a signal F of the bidirectional thyristor VS_UTo obtain the data under different modes

Bidirectional thyristor F_UThe following were used:

when the inverter is operating normally, F_uThe system works in a traditional twelve-switch inverter power supply mode, firstly, a bidirectional thyristor VS receives a forward voltage signal to be conducted, and then the double three-phase motor is formed. The judgment method of the charging and discharging process comprises the following steps:

detection voltage sensor detects three-phase winding (u)_a,u_b,u_c) With a given voltage value u_oComparison of

When u is_a,u_b,u_cGradually rise to u_oIn time, the charging process is realized.

When u is_oWhen the value gradually drops to a certain value, the discharge process is performed.

Judging the working mode:

the charging and discharging operation of one group of windings and the inverter is realized, the charging and discharging operation of the other group of windings and the inverter can also be realized, and the fault excess of the system is realized when a fault occurs. As shown in fig. 6, the main circuit is divided into an inverter circuit 1 and an inverter circuit 2, the charging process is that the dc bus voltage is disconnected through a relay K1(K2) closing contact K3(K4) normally open contact, after six switching tubes of the inverter a (b) group are controlled to be turned on at different times by a control signal generated by the PWM1(PWM2) module provided by the above claim 3, fuses FU1, FU2, FU3(FU4, FU5, FU6) are closed through three inverter arms, and meanwhile, circuit breaker contacts QF1, QF2, QF3(QF4, QF5, QF6) are closed, so as to realize the charging process of the flywheel. In the discharging circuit part, energy is fed back to a direct current bus when the direct current motor is in a generating state, the feedback energy is controlled to be switched on at different time by a control signal generated by PWM2(PWM1) provided by the claim 3, and then is switched on by fuses FU4, FU5 and FU6(FU1, FU2 and FU3) on three inverter bridge arms, meanwhile, breaker closing contacts QF4, QF5 and QF6(QF1, QF2 and QF3) are closed, and as the actual voltage reaches a given value, a relay acts, the K4(K3) contact is disconnected K2(K1) and electric energy can be stably output through the BOOST circuit.

If the voltage of the winding is detected to be abnormal, F_uBy controlling the thyristor VS to turn off for-1 by giving a reverse voltage signal, when the current or voltage of the detection winding is excessive, the fuse contacts (FU1, FU2, FU3,FU4, FU5, FU6) is automatically turned off. And after the current sensor detects that the port of the armature winding connected with the fault bridge arm has a fault and makes fault judgment, the current sensor controls signals to control six switching tubes of the A group (B group) of the inverter to be simultaneously turned off by controlling a PWM1(PWM2) module, and the inverter stops working. The system is changed into two sets of three-phase motors, one set of three-phase motors can be normally charged and discharged, and the other set of three-phase motors does not work. Assuming that three bridge arms of the A-group inverter (La, Lb and Lc) work normally, a normal charging and discharging process can be realized, the B-group inverter comprises three bridge arms of (Lx, Ly and Lz), when one bridge arm has a fault, such as a short-circuit fault, a breaker (QF4, QF5 or QF6) connected with the bridge arm acts to cut off the bridge arm, and meanwhile, a PWM2 control signal controls the switching tube of the inverter to be cut off.

If the state is 1, a group of charging assumes an inverter circuit 1, and charging adopts i_d ^*The control strategy is that the speed omega of the position is controlled by the control strategy^*Comparing with the actually estimated omega to obtain a difference value e_ωThen the difference value of the q-axis current and the q-axis current is obtained through a PI controller_q ^*While a given reference signal for the d-axis is set to zero. Transformed into a current component i by coordinate transformation_dAnd i_qWith its reference signal i_d ^*,i_q ^*Comparing, decoupling by current controller, outputting voltage signal u_d ^*And u_q ^*After u is transformed by inverse Park_α ^*And

and PWM1 signals are obtained through SVPWM to control the six switching tubes, so that the charging process is realized.

The voltage equation of the positive spin wave permanent magnet synchronous motor under the dq two-phase rotating coordinate system is as follows:

wherein u is_sd、u_sq、i_sd、i_sq、

The stator voltage, the stator current and the stator flux linkage of the motor rotate in dq two phases respectively.

Direct and quadrature components, omega, under the system_rFor rotor angular velocity, stator flux linkage

Expressed as:

wherein L is_d、L_qRespectively a direct axis inductor and a quadrature axis inductor of the positive spin wave permanent magnet synchronous motor,

is a rotor permanent magnet flux linkage.

The motor torque equation under the dq two-phase rotor synchronous rotation coordinate is as follows:

wherein the content of the first and second substances,

referring to fig. 2, the present invention provides a method for controlling a flywheel energy storage system of a dual three-phase brushless dc motor, in which a flywheel rotating at a high speed is used as mechanical energy, and power electronic equipment is used to realize mutual conversion between electrical energy and mechanical energy, including a charging state, a discharging state and a holding state, the charging state is that external power is supplied through a power electronic conversion device to drive the flywheel to rotate, the discharging state is that a flywheel rotor rotating at a high speed is used to drive a motor to rotate, and a working device is used to realize conversion from mechanical energy to electrical energy;

in the charging state, an external power source supplies power to the motor/generator through the power electronic converter, the motor/generator operates as a motor, and the flywheel rotor is driven to accelerate. When the rotating speed of the rotor reaches the maximum working torque, the power electronic device generates a control signal to control the driving motor, and the motor drives the flywheel to operate and realize charging.

In the discharge state, the motor/generator operates as a generator, the flywheel rotor decelerates, mechanical energy is converted into electrical energy by the generator, and the power electronic converter adjusts the bus voltage output by the generator to keep the bus voltage constant all the time.

In the hold state, the flywheel system is in an energy hold phase. It has neither forward nor reverse flow of energy, and in this mode the system operates with minimal losses.

The charging method comprises the following specific steps:

s1, referring to fig. 3 and 5, in the charging process, six paths of PWM driving signals are sent out by detecting the zero crossing point of the back electromotive force, and the power switching tube is driven after power amplification, so that the motor reaches the highest rotation speed and is in the holding stage. The control strategy is to control the speed omega of the position^*Comparing with the actually estimated omega to obtain a difference value, and then leading the difference value to pass through a PI controller to obtain a current signal i of a q axis_q ^*While setting the given reference signal of the d-axis to zero; transformed into a current component i by coordinate transformation_dAnd i_qWith its reference signal i_d ^*,i_q ^*Comparing, decoupling by current controller, outputting voltage signal u_d ^*And u_q ^*After coordinate transformation, the control signal is generated by SVPWM control, so that the charging process is realized; the method comprises the following specific steps:

s101, subtracting the given rotating speed omega of the motor from the actual rotating speed omega to obtain a speed error e_ωVelocity error e_ωOutputting given current after passing through a rotating speed PI regulator

Defining active damping as

_q＝i_q′-B_aω

By using i_dControl strategy of 0 and assuming the motor is in control (T)_L0) on start-up, we get:

coefficient of active damping B_a：

If a conventional PI regulator is used, the expression tacho loop controller is shown as

Parameter k of the PI regulator_pw、k_jwSetting by the following formula:

where β is the desired bandwidth of the band for the speed loop.

S102, referring to the direct current signal and the alternating current signal

And a direct current, an alternating current i_d,i_qCalculating the current deviation e_d,e_qOutputting reference DC voltage after passing through two current PI regulators

And DC/AC shaft voltage

Wherein, K_pd,K_pqIs a proportional constant coefficient, K_id,K_iqIs an integral constant coefficient;

s103, detecting the stator winding current i of the motor according to the current sensor_a,i_bCalculating the current i under a two-phase rotating coordinate system_d,i_qFor the calculated reference voltage

Calculating reference voltage under three-phase rotating coordinate system

Wherein theta is the electric angle of the position of the motor rotor;

s104, to realize the modulation of the SVPWM signal, firstly, the direction of the interval where the reference voltage vector is located is known, and then the reference voltage vector is synthesized by using two adjacent voltage vectors and a proper fan-shaped zero vector.

S1041, sector judgment of reference voltage vector

The purpose of determining the sector in which the voltage space vector is located is to determine the basic voltage space vector u used in this switching cycle_outUsing u_αAnd u_βRepresenting the reference voltage vector u on the axis_outComponent at α, β, define u_ref1、u_ref2、u_ref3Three variables of

The following 3 variables AB C are defined and analyzed:

if u_ref1If the value is more than 0, A is equal to 1, otherwise, A is equal to 0;

if u_ref2If the value is more than 0, B is 0, otherwise B is 0;

if u_ref3If > 0, C is equal to 0, otherwise C＝0。

Let N be 4C +2B + a, the relationship with the sector can be obtained

S1042, calculation of non-zero vectors and zero vector action time

By simple calculation, can become

In the same way, the action time of each vector of other sectors can be obtained, and the order

Can get each sector T₀(T₇),T₄And T₆The time of the action is as follows,

if T is₄+T₆>T_SThen, perform over-modulation processing to order

S1043, sector vector switching point determination

First, define

The switching point T of the three-phase voltage switch time_cm1、T_cm2、T_cm3The relationship with each sector is as follows：

The sector determination of the reference voltage vector, the non-zero vector calculation of each sector, the zero vector action time calculation and the switching point determination of each sector vector form SVPWM, and finally a triangular carrier signal with certain frequency is used, and the switching point of each sector vector is compared, so that a PWM pulse signal can be obtained by a converter.

S2, vector control of the discharging process;

referring to fig. 4, it is shown that if the flywheel system of the present invention is in the state 1, one group of the discharge units includes dc motor, position measurement, voltage detection, current control, coordinate transformation, SVPWM, voltage inverter, BOOST circuit, etc. the double closed loop control system is adopted, the outer loop is a voltage regulation loop, in order to reduce the output voltage of the motor by external load disturbance or rotation speed reduction and maintain the stability of the voltage, the voltage regulator is used for the alternating current component i_q ^*The size is limited because

Ensuring that its value is not greater than the upper limit allowed for the motor. The current inner ring carries out current control according to the current output by the voltage ring, and generates a trigger pulse signal PWM2 module by comparing with a triangular wave after the decoupling coordinate transformation; the control steps for realizing the discharging process of the flywheel energy storage system of the B group inverter and the winding are as follows:

the S201 and PWM2 modules convert the measured three-phase stationary coordinate system into synchronously rotating two-phase coordinates, and the current value is converted into a current component i through coordinate conversion_dAnd i_q；

S202, adopting a direct current control strategy, comparing a given reference signal with an actual value by a voltage outer ring tracking system, and outputting current through a PI regulator to realize constant direct current voltage, constant power and the like;

wherein the content of the first and second substances,

is the input voltage.

S203, current control is carried out on the current output by the current inner ring according to the voltage ring, and the current is subjected to decoupling coordinate transformation and then is compared with a triangular wave to generate a trigger pulse signal to control the conduction and the disconnection of a converter tube;

and S204, in the discharging process, the mechanical energy of the system is converted into electric energy, the permanent magnet brushless current works and the generator state, and the speed of the motor is gradually reduced along with the conversion from the mechanical energy to the electric energy, so that a Boost circuit needs to be added behind the inverter. Meanwhile, in order to stabilize the output voltage, the direct current load is supplied with power after passing through a Boost circuit, the voltage at the end of a detection winding is compared with the specified voltage, the error is regulated by PI and compared with a triangular wave carrier to generate a PWM signal to regulate the duty ratio of V, and therefore the output direct current voltage is regulated.

The boost chopper circuit can control the stability of the voltage at the direct current side by controlling a switching tube, and the switching-on and switching-off conditions of the switching tube V are analyzed; assuming that an inductor L and a capacitor C in the circuit are large enough, when V is conducted, the energy of a power supply flows to the inductor L, and meanwhile, the voltage on the capacitor C supplies power to a load; when the capacitance C is large enough, the output voltage does not become U₀When the V is in the off state, the power supply E and the inductor L charge the capacitor C together to supply power to the load.

V is respectively t_on、t_offWhen the circuit is operating steadily, it is assumed that the current through the inductor L remains substantially unchanged as I₁In one period T, the energy identity is:

where a is the duty cycle of the control switch T, it is seen that as the rotation speed decreases, the back electromotive force decreases, the duty cycle of the switch increases, and the voltage can be kept stable.

The critical inductance value of the current continuous mode in which the Boost circuit can work is as follows:

the capacitance value is:

wherein, Delta U₀Indicating a difference in the required voltages, decreasing the voltage increases the capacitance value.

After the current sensor detects that the port fault of the armature winding connected with the fault bridge arm makes fault judgment, the current sensor controls signals to control six switching tubes of the A group (B group) of the inverter to be simultaneously turned off by controlling a PWM1(PWM2) module, and the inverter stops working. The system is changed into two sets of three-phase motors, one set of three-phase motors can be normally charged and discharged, and the other set of three-phase motors does not work. Assuming that three bridge arms of the A-group inverter (La, Lb and Lc) work normally, a normal charging and discharging process can be realized, the B-group inverter comprises three bridge arms of (Lx, Ly and Lz), when one bridge arm has a fault, such as a short-circuit fault, a breaker (QF4, QF5 or QF6) connected with the bridge arm acts to cut off the bridge arm, and meanwhile, a PWM2 control signal controls the switching tube of the inverter to be cut off.

1. Charging process modeling

Referring to fig. 7, the speed regulation of the motor is performed by a closed loop regulation of the rotation speed, and by an inner loop current loop and an outer loop speed loop control, wherein the reference value of the outer loop speed is the maximum rotation speed ω required by the flywheel, and the actual rotation speed ω acquired from the permanent magnet synchronous motor is compared to obtain a rotation speed difference, and then the rotation speed difference is further processed by a proportional-integral controller to obtain a current reference i_qRegulating the q-axis current i by regulating the actual rotation speed value to approach the given rotation speed continuously_qAnd further controls the electromagnetic torque.

In order to verify the feasibility of the built model, the system comprises a PID module, a speed detection PI, a current detection PI, a coordinate transformation Plark, a Clark module, an SVPWM module, a three-phase voltage type inverter circuit and a three-phase synchronous motor, and simulation setting parameters are as follows: the parameter rotation speed is set to N1000-3000 r/min, the initial load torque T10 N.m, and the load current i_abcSimulation results within t-0.4.

Charging process simulation result analysis

The permanent magnet brushless direct current motor adopts a d and q coordinate method and PARK transformation, and converts a two-phase coordinate system from a three-phase coordinate system to realize motor current control. As shown in fig. 8(a) to (c) are simulation results when N is 1000r/min, and fig. 8(d) to (f) are simulation results when N is 2000 r/min.

As can be seen from fig. 8, when the predetermined rotation speed N is 1000r/min, the rotation speed starts to increase with time, the charging time is short, the control effect is good, overshoot does not occur substantially, and then the control gradually becomes stable. Harmonic disturbance occurs to the electromagnetic torque in a period of time at the beginning, then the torque is directly increased to 10N.m from zero rise, the current is switched back and forth between three phases, a divergent state does not occur, and the control effect is very ideal.

When the given rotation speed is set to be 2000r/min, the rotation speed curve also gradually increases along with the increase of time, an overshoot of 2% occurs, the charging time is longer than before, and the rotation speed is approximately stabilized at 1800 r/min. The current is disturbed for a certain time and then the current oscillates back and forth within 10. The electromagnetic torque may be kept constant at 2n.m until t is 0.03, and then may be stabilized at 2n.m, and when t is 0.2s, the torque gradually increases and finally may be stabilized at about 12 n.m.

From the two sets of simulation graphs, it can be derived that changing the parameter value of the given rotating speed, the stability of the rotating speed is reduced along with the increase of the rotating speed on the load side, the required time is longer, the control effect is reduced along with the increase of the rotating speed, and the control effect is basically kept within a certain value. The change in the rotational speed causes the load current to oscillate. The electromagnetic torque is gradually smoothed.

2. Discharge process modeling

A discharging model of the flywheel energy storage system shown in the figure 9 is established, most importantly, a Boost direct-current voltage stabilizing circuit is adopted, a control loop signal is obtained by obtaining a difference value between a load output voltage feedback quantity and a given reference voltage, an output signal is a required duty ratio signal, and the signal is compared with a carrier signal to finally obtain a signal for controlling the switching-on and switching-off of the Mos tube. The motor/generator parameters were as follows: number of pole pairs 2, stator resistance R_S0.000233, 42.24uH of stator inductance, 0.034V.s of flux linkage, 2000r/s of initial speed, 0.0002N.m.s of friction coefficient and 0.2Kg.M of moment of inertia.

(2) Analysis of discharge simulation results

During the discharging process of the system, the flywheel is in a power generation state, as shown in fig. 10(a) - (f), simulation results of voltage and torque waveform on the load side are given, and the voltage is always stabilized at a certain value along with the reduction of the rotating speed of the motor by adopting a control mode of energy feedback braking in the discharging simulation control. A voltage, torque waveform plot is provided over 1.5 s.

As can be seen from fig. 10(a) to (b), when the given voltage U is 220V, the load voltage gradually increases with time, and becomes stable at 230 at about 0.3s at t, which is a 1% overshoot, and the control effect is good, while the rotational speed gradually decreases at 2000r/min, the graph is relatively smooth, and the decreasing speed is relatively slow.

As can be seen from fig. 10(c) to (d), when the given voltage is set to U of 250V, the voltage gradually increases with time as seen from the voltage waveform diagram, and when t is 0.5s, the voltage reaches about 270V and finally stabilizes at 260V, and there is an overshoot of 1% to 2%, and the rotational speed curve diagram shows that the rotational speed gradually decreases from the given rotational speed of 2000r/min, but the speed of the rotational speed decrease is significantly faster than the given voltage of 220V. The control effect is ideal.

From the two sets of data, it can be obtained that the longer the voltage waveform on the load side tends to be stable with the rise of the given voltage, the voltage has certain loss, the overshoot is also increased, the rotating speed is gradually increased in the descending amplitude under the condition that the given rotating speed is not changed, the curve becomes steep, and the control effect is reduced.

The invention has an inversion circuit in the main discharging circuit and the main charging circuit, and the inversion method is used for the conversion process of the DC voltage to the AC voltage during charging, and the rectification method is used for the conversion process of the AC voltage to the DC voltage during discharging. In the discharging process, the direct current brushless motor works as a generator, and because the flywheel rotates by inertia to drag the direct current brushless motor to generate electricity, the voltage can be reduced along with the reduction of the rotating speed, and the rectifying circuit not only converts the alternating voltage generated by the generator into direct voltage, but also ensures the stability of the output direct voltage.

The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.