阅读说明：本技术 一种永磁同步电动机同步变频软起动装置及其方法 (Synchronous frequency conversion soft starting device and method for permanent magnet synchronous motor ) 是由 梁业庭 黄启新 史红燕 于磊 陈竹光 史强 吴思思 于 2020-12-21 设计创作，主要内容包括：本发明提出了一种永磁同步电动机同步变频软起动装置及其方法,在起动过程转速精确可控,可满足电机平滑起动要求；并且结构简单,无机械换向器,不会产生火花,便于维护；容易做到大容量,高转速,高电压,晶闸管实现串并联更加可靠,可以方便地实现四象限运行；低速时采用直流脉动技术,周期地将直流环节电流降低到零,完成逆变换相；高速时逆变采用负载感应电势自动换相方式；可连续起动,重复精度高；起动容量小于电机额定容量的1/3；调速范围可以从电机的静止状态到额定转速,在此工作范围内静止变频器工作效率不会降低。(The invention provides a synchronous frequency conversion soft starting device and a synchronous frequency conversion soft starting method for a permanent magnet synchronous motor, wherein the rotating speed is accurate and controllable in the starting process, and the smooth starting requirement of the motor can be met; the structure is simple, no mechanical commutator is arranged, no spark is generated, and the maintenance is convenient; the high-capacity, high-rotating-speed and high-voltage thyristor is easy to realize series-parallel connection, is more reliable, and can conveniently realize four-quadrant operation; the direct current pulse technology is adopted at low speed, the direct current link current is periodically reduced to zero, and the inversion phase change is completed; the inversion at high speed adopts a load induction potential automatic phase change mode; the device can be started continuously, and has high repetition precision; 1/3, the starting capacity is less than the rated capacity of the motor; the speed regulation range can be from the static state of the motor to the rated rotating speed, and the working efficiency of the static frequency converter cannot be reduced in the working range.)

1. The utility model provides a soft starting drive of synchronous frequency conversion of permanent magnet synchronous motor, its includes preceding stage contactor, back stage contactor, bypass contactor and the soft starting drive of frequency conversion, its characterized in that: the variable frequency soft starting device comprises a rectifier bridge, a direct current reactor, an inverter bridge, a controller, a zero-crossing detection circuit and a thyristor drive circuit;

the input end of the preceding stage contactor and the input end of the bypass contactor are respectively connected with a three-phase power grid, the output end of the bypass contactor is electrically connected with the input end of the permanent magnet synchronous motor, the output end of the preceding stage contactor is electrically connected with the input end of the rear stage contactor through a rectifier bridge, a direct current reactor and an inverter bridge which are sequentially connected in series, the output end of the rear stage contactor is electrically connected with the input end of the permanent magnet synchronous motor, the input end of a zero-crossing detection circuit is electrically connected with the input end of the permanent magnet synchronous motor, the output end of the zero-crossing detection circuit is electrically connected with an I/O port of a controller, and the SPWM output end of the controller is electrically connected with control electrodes of thyristors.

2. The synchronous variable frequency soft start device of a permanent magnet synchronous motor according to claim 1, characterized in that: the zero-cross detection circuit includes: the voltage transformer, the zero crossing comparator, the inverter, the diode clamping circuit, the Schmitt trigger and the optical coupling isolator are sequentially connected in series;

the voltage transformer comprises a voltage transformer, a phase inverter, a diode clamping circuit, a positive conducting voltage and a pulse signal, wherein the primary side of the voltage transformer collects the voltage of the input end of the permanent magnet synchronous motor, the alternating current signal is generated at the secondary side of the voltage transformer, the alternating current signal is converted into a square wave signal which has the same frequency and the same phase as the alternating current signal through a zero crossing comparator, the square wave signal is input into the diode clamping circuit after being inverted through the phase inverter, the positive conducting voltage of the diode clamping circuit is clamped at 0.7V, and when the waveform of the inverted square wave signal just crosses a zero point, the diode; and the pulse signal is subjected to waveform stabilization by a Schmidt trigger and then is output to an I/O port of the controller by an optical coupling isolator.

3. A synchronous frequency conversion soft start method of a permanent magnet synchronous motor is characterized in that: the method comprises the following steps:

s1, calculating the initial position of the rotor according to the three-phase stator voltage detected in the process of establishing the exciting current of the permanent magnet synchronous motor;

s2, detecting the rotating speed of the motor in real time after the permanent magnet synchronous motor is statically started, and detecting the position of a rotor by adopting a three-phase irrelevant method and adopting forced commutation control when the rotating speed of the permanent magnet synchronous motor is lower than 5% of the rated rotating speed;

s3, when the rotating speed of the permanent magnet synchronous motor rises to 5% -10% of the rated rotating speed, detecting the position of the rotor based on a voltage zero-crossing detection method, stopping forced phase commutation, and automatically commutation by utilizing counter electromotive force generated at the stator side of the motor;

s4, introducing current closed-loop control, and under the condition that the maximum allowable current and the torque of the motor are limited, fully utilizing the overload capacity of the motor, starting at the maximum acceleration and reaching the rated rotating speed;

s5, when the rotating speed of the permanent magnet synchronous motor rises to 97% of the rated rotating speed, judging whether a grid-connected condition is met, when the grid-connected condition is met, disconnecting the front-stage contactor and the rear-stage contactor, switching on the bypass contactor, generating an additional rotating speed fine-tuning signal according to the difference value of the voltage of the power grid and the voltage frequency of the synchronous motor, automatically adjusting the height of the direct current voltage output by the rectifier bridge, and finely tuning the rotating speed of the synchronous motor;

and S6, the permanent magnet synchronous motor enters power frequency operation and enters a constant power factor control or constant current control state.

4. The synchronous frequency conversion soft start method of the permanent magnet synchronous motor according to claim 3, characterized in that: the S1 specifically includes the following steps: the external world outputs a step-change excitation voltage to a unit of the permanent magnet synchronous motor, the generated excitation current changes along with the excitation voltage, a changing magnetic field generated by the excitation current induces a three-phase induction voltage on a three-phase winding of a stator of the unit, and the initial position of a rotor is obtained by detecting the phase and amplitude of the three-phase induction voltage.

5. The synchronous frequency conversion soft start method of the permanent magnet synchronous motor according to claim 3, characterized in that: the three-phase independent method in the S2 specifically comprises the following steps: the method comprises the steps that the voltage of the input end of the permanent magnet synchronous motor is detected through a zero-crossing detection circuit, digital filtering is carried out on three terminal voltages of the permanent magnet synchronous motor, A/D sampling is carried out, if the sign of one terminal voltage value in the three terminal voltages changes, the voltage of the input end of the permanent magnet synchronous motor is judged to have a zero crossing point, and the current rotor position is obtained according to the relation between the zero crossing point voltage and the rotor position.

6. The synchronous variable frequency soft start method of the permanent magnet synchronous motor according to claim 4, characterized in that: the forced commutation control in S2 specifically includes the following steps:

s101, setting a delay angle of a rectifier bridge to be 150 degrees, enabling the rectifier bridge to enter an inversion state, reducing current of a main loop to be zero, and turning off all conducted thyristors in the inverter bridge;

and S102, after the current of the main loop is reduced to zero, switching the rectifier bridge to a rectification working state again, controlling the conduction of the next group of thyristors to be triggered in the inverter bridge, and reestablishing the current of the direct current loop.

7. The synchronous frequency conversion soft start method of the permanent magnet synchronous motor according to claim 3, characterized in that: the self-commutation of the phase by using the counter potential generated at the stator side of the motor in S3 specifically includes the following steps: all thyristors in the inverter bridge are turned off at the zero crossing point of the permanent magnet synchronous motor, corresponding thyristors are triggered according to a triggering sequence that the phase change lead angle is equal to 60 degrees, and a current signal is immediately blocked, at the moment, the phase change residual angle of the inverter bridge meets the following formula:

wherein, delta is the phase-changing residual angle of the inverter bridge, gamma is the actual phase-changing lead angle in loading, mu is the phase-changing overlap angle,for the commutation lead angle, k is a safety coefficient larger than 1, w is the maximum possible value of the working angular frequency of the inverter bridge, t₀The turn-off time of the thyristor.

Technical Field

The invention relates to the technical field of synchronous frequency conversion soft starting of a permanent magnet synchronous motor, in particular to a synchronous frequency conversion soft starting device and method of the permanent magnet synchronous motor.

Background

The synchronous frequency conversion soft starting device of the permanent magnet synchronous motor is suitable for the permanent magnet synchronous motor with small power (below 500 KW) and is used for the frequency conversion starting of the motor. The main soft starting device of the permanent magnet synchronous motor at present is a voltage source type frequency converter. Because the voltage source type frequency converter adopts a diode device, four-quadrant operation cannot be realized, and the voltage source type frequency converter has the defects that the terminal voltage phase of a motor is not coincident with the phase of a power grid in the grid connection process, so that impact is caused to the power grid. Although the current source type frequency converter has no impact on a power grid, when the current source type frequency converter is used, the turn-off and turn-on time of the thyristor cannot be accurately controlled, so that the current source type frequency converter cannot be used in a permanent magnet synchronous motor. Therefore, the invention provides a synchronous frequency conversion soft starting device and a method thereof for a permanent magnet synchronous motor, wherein a thyristor control signal is generated according to a certain control strategy by adopting a rotating speed and current double closed loop control principle, and the frequency, amplitude and phase of three-phase current output by a frequency converter are controlled, so that the aim of tracking the rotating speed of a rotor by the synchronous rotating speed of a motor is fulfilled.

Disclosure of Invention

In view of the above, the invention provides a synchronous frequency conversion soft start device and a method thereof for a permanent magnet synchronous motor, which generate a thyristor control signal according to a certain control strategy by adopting a rotating speed and current double closed loop control principle, and control the frequency, amplitude and phase of three-phase current output by a frequency converter, so as to achieve the purpose of tracking the rotating speed of a rotor by the synchronous rotating speed of a motor.

The technical scheme of the invention is realized as follows: on one hand, the invention provides a synchronous frequency conversion soft starting device of a permanent magnet synchronous motor, which comprises a front-stage contactor, a rear-stage contactor, a bypass contactor and a frequency conversion soft starting device, wherein the frequency conversion soft starting device comprises a rectifier bridge, a direct current reactor, an inverter bridge, a controller, a zero-crossing detection circuit and a thyristor drive circuit;

the input end of the preceding stage contactor and the input end of the bypass contactor are respectively connected with a three-phase power grid, the output end of the bypass contactor is electrically connected with the input end of the permanent magnet synchronous motor, the output end of the preceding stage contactor is electrically connected with the input end of the rear stage contactor through a rectifier bridge, a direct current reactor and an inverter bridge which are sequentially connected in series, the output end of the rear stage contactor is electrically connected with the input end of the permanent magnet synchronous motor, the input end of a zero-crossing detection circuit is electrically connected with the input end of the permanent magnet synchronous motor, the output end of the zero-crossing detection circuit is electrically connected with an I/O port of a controller, and the SPWM output end of the controller is electrically connected with control electrodes of thyristors.

On the basis of the above technical solution, preferably, the zero-cross detection circuit includes: the voltage transformer, the zero crossing comparator, the inverter, the diode clamping circuit, the Schmitt trigger and the optical coupling isolator are sequentially connected in series;

the method comprises the steps that the primary side of a voltage transformer collects the voltage of the input end of a permanent magnet synchronous motor, an alternating current signal is generated on the secondary side of the voltage transformer, the alternating current signal is converted into a square wave signal which has the same frequency and the same phase with the alternating current signal through a zero crossing comparator, the square wave signal is inverted through a phase inverter and then input into a diode clamping circuit, the forward conduction voltage of the diode clamping circuit is clamped at 0.7V, and when the waveform of the inverted square wave signal just crosses a zero point, the diode clamping circuit is conducted, a pulse signal is output, and zero crossing detection is achieved; and the pulse signal is subjected to waveform stabilization by a Schmidt trigger and then is output to an I/O port of the controller by an optical coupling isolator.

On the other hand, the invention provides a synchronous frequency conversion soft starting method of a permanent magnet synchronous motor, which comprises the following steps:

s1, calculating the initial position of the rotor according to the three-phase stator voltage detected in the process of establishing the exciting current of the permanent magnet synchronous motor;

s2, detecting the rotating speed of the motor in real time after the permanent magnet synchronous motor is statically started, and detecting the position of a rotor by adopting a three-phase irrelevant method and adopting forced commutation control when the rotating speed of the permanent magnet synchronous motor is lower than 5% of the rated rotating speed;

s3, when the rotating speed of the permanent magnet synchronous motor rises to 5% -10% of the rated rotating speed, detecting the position of the rotor based on a voltage zero-crossing detection method, stopping forced phase commutation, and automatically commutation by utilizing counter electromotive force generated at the stator side of the motor;

s4, introducing current closed-loop control, and under the condition that the maximum allowable current and the torque of the motor are limited, fully utilizing the overload capacity of the motor, starting at the maximum acceleration and reaching the rated rotating speed;

s5, when the rotating speed of the permanent magnet synchronous motor rises to 97% of the rated rotating speed, judging whether a grid-connected condition is met, when the grid-connected condition is met, disconnecting the front-stage contactor and the rear-stage contactor, switching on the bypass contactor, generating an additional rotating speed fine-tuning signal according to the difference value of the voltage of the power grid and the voltage frequency of the synchronous motor, automatically adjusting the height of the direct current voltage output by the rectifier bridge, and finely tuning the rotating speed of the synchronous motor;

and S6, the permanent magnet synchronous motor enters power frequency operation and enters a constant power factor control or constant current control state.

On the basis of the above technical solution, preferably, S1 specifically includes the following steps: the external world outputs a step-change excitation voltage to a unit of the permanent magnet synchronous motor, the generated excitation current changes along with the excitation voltage, a changing magnetic field generated by the excitation current induces a three-phase induction voltage on a three-phase winding of a stator of the unit, and the initial position of a rotor is obtained by detecting the phase and amplitude of the three-phase induction voltage.

On the basis of the above technical solution, preferably, the three-phase independent method in S2 specifically includes the following steps: the method comprises the steps that the voltage of the input end of the permanent magnet synchronous motor is detected through a zero-crossing detection circuit, digital filtering is carried out on three terminal voltages of the permanent magnet synchronous motor, A/D sampling is carried out, if the sign of one terminal voltage value in the three terminal voltages changes, the voltage of the input end of the permanent magnet synchronous motor is judged to have a zero crossing point, and the current rotor position is obtained according to the relation between the zero crossing point voltage and the rotor position.

On the basis of the above technical solution, preferably, the forced commutation control in S2 specifically includes the following steps:

s101, setting a delay angle of a rectifier bridge to be 150 degrees, enabling the rectifier bridge to enter an inversion state, reducing current of a main loop to be zero, and turning off all conducted thyristors in the inverter bridge;

and S102, after the current of the main loop is reduced to zero, switching the rectifier bridge to a rectification working state again, controlling the conduction of the next group of thyristors to be triggered in the inverter bridge, and reestablishing the current of the direct current loop.

On the basis of the above technical solution, preferably, the self-commutation of the phase by using the back electromotive force generated at the stator side of the motor in S3 specifically includes the following steps: all thyristors in the inverter bridge are turned off at the zero crossing point of the permanent magnet synchronous motor, corresponding thyristors are triggered according to a triggering sequence that the phase change lead angle is equal to 60 degrees, and a current signal is immediately blocked, at the moment, the phase change residual angle of the inverter bridge meets the following formula:

wherein, delta is the phase-changing residual angle of the inverter bridge, gamma is the actual phase-changing lead angle in loading, mu is the phase-changing overlap angle,for the commutation lead angle, k is a safety coefficient larger than 1, w is the maximum possible value of the working angular frequency of the inverter bridge, t₀The turn-off time of the thyristor.

Compared with the prior art, the synchronous frequency conversion soft starting device and the method thereof of the permanent magnet synchronous motor have the following beneficial effects:

(1) the zero-crossing detection circuit is used for detecting the zero crossing point of the terminal voltage of the permanent magnet synchronous motor to judge the position interval of the rotor, compared with the traditional method, the position of the rotor can be detected by a position-free sensor, and the terminal voltage of the permanent magnet synchronous motor can be effectively detected;

(2) the interference near the zero crossing point can be effectively eliminated by arranging the phase inverter in the zero crossing detection circuit, the zero crossing point voltage can be effectively detected by arranging the diode clamping circuit, the zero crossing point voltage can be effectively detected even under the condition that the voltage waveform of the permanent magnet synchronous motor at the low speed stage is seriously distorted, the Schmitt trigger is arranged to further stabilize the waveform, and the reliability of the device is improved; the optical coupler isolator is arranged to realize electrical isolation, so that the anti-interference capability of the device is improved;

(3) the synchronous frequency conversion soft starting device has the advantages that the rotating speed is accurate and controllable in the starting process, and the smooth starting requirement of the motor can be met; the structure is simple, no mechanical commutator is arranged, no spark is generated, and the maintenance is convenient; the high-capacity, high-rotating-speed and high-voltage thyristor is easy to realize series-parallel connection, is more reliable, and can conveniently realize four-quadrant operation;

(4) the synchronous frequency conversion soft starting device is a static element, so that the maintenance workload is small, the reliability is high, and the equipment installation and arrangement are flexible;

(5) the starting current can be kept below the rated current required by the synchronous motor to run by adopting the static frequency converter for starting, no impact is caused to a power grid, and the soft starting performance is realized;

(6) the static frequency converter motor structure has no special requirements, a plurality of units can share one device, and the requirement of frequent starting in the operation process can be met;

(7) the direct current pulse technology is adopted at low speed, the direct current link current is periodically reduced to zero, and the inversion phase change is completed; the inversion at high speed adopts a load induction potential automatic phase change mode; the device can be started continuously, and has high repetition precision; 1/3, the starting capacity is less than the rated capacity of the motor; the speed regulation range can be from the static state of the motor to the rated rotating speed, and the working efficiency of the static frequency converter cannot be reduced in the working range.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a structural diagram of a synchronous variable frequency soft start device of a permanent magnet synchronous motor according to the present invention;

FIG. 2 is a structural diagram of a zero-crossing detection circuit in a synchronous frequency conversion soft start device of a permanent magnet synchronous motor according to the present invention;

FIG. 3 is a circuit diagram of a zero-crossing detection circuit in a synchronous frequency conversion soft start device of a permanent magnet synchronous motor according to the present invention;

FIG. 4 is a circuit diagram of a rectifier bridge, a DC reactor and an inverter bridge in the synchronous frequency conversion soft starting device of the permanent magnet synchronous motor of the invention;

FIG. 5 is a block diagram of a synchronous frequency conversion soft start control system in the synchronous frequency conversion soft start device of the permanent magnet synchronous motor according to the present invention;

fig. 6 is a flow chart of a thyristor trigger control layer strategy in a synchronous frequency conversion soft start device of a permanent magnet synchronous motor according to the invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

Example 1

As shown in fig. 1, the synchronous variable frequency soft start device of the permanent magnet synchronous motor of the present invention includes a front stage contactor, a rear stage contactor, a bypass contactor, and a variable frequency soft start device.

Preceding stage contactor, back stage contactor: after the frequency conversion soft starting device is started, the front-stage contactor and the rear-stage contactor are disconnected, so that the frequency conversion soft starting device is disconnected from a power supply, and a safety isolation effect is achieved. The input end of the preceding stage contactor is connected with a three-phase power grid, the output end of the preceding stage contactor is electrically connected with the input end of the rear stage contactor through a variable frequency soft starting device, and the output end of the rear stage contactor is electrically connected with the input end of the permanent magnet synchronous motor.

And after the frequency conversion soft starting device is started, the bypass contactor is switched on, and the motor is connected to the grid and enters a power frequency running state. The input end of the bypass contactor is connected with a three-phase power grid, and the output end of the bypass contactor is electrically connected with the input end of the permanent magnet synchronous motor.

The frequency conversion soft starting device adopts a current source type frequency converter to synchronously start a permanent magnet synchronous motor. In this embodiment, the variable frequency soft start device includes a rectifier bridge, a dc reactor, an inverter bridge, a controller, a zero-cross detection circuit, and a thyristor drive circuit; in this embodiment, the output end of the preceding contactor is electrically connected to the input end of the subsequent contactor through a rectifier bridge, a dc reactor and an inverter bridge connected in series in sequence, the output end of the subsequent contactor is electrically connected to the input end of the permanent magnet synchronous motor, the input end of the zero-crossing detection circuit is electrically connected to the input end of the permanent magnet synchronous motor, the output end of the zero-crossing detection circuit is electrically connected to the I/O port of the controller, and the SPWM output end of the controller is electrically connected to the control electrodes of the thyristors in the rectifier bridge and the inverter bridge through a thyristor drive circuit.

The rectifier bridge rectifies the three-phase 50Hz alternating current into direct current; by adopting 6-pulse rectification technology and two loops, the harmonic waves of the input measuring current of the power grid are effectively reduced;

the direct current reactor connects the rectifier bridge and the inverter bridge, limits the current rise rate of a direct current loop and plays a role in flat wave current limiting; due to the current limiting function of the direct current reactor, the direct current waveform of the main loop of the frequency converter is flat and has small pulsation, and the frequency converter has the characteristic of a current source; the direct current reactor has a filtering function, and when a short-circuit fault occurs on the inversion side, the current cannot change suddenly; the inverter bridge inverts the direct current signal output by the rectifier bridge into a three-phase alternating current with a certain frequency and inputs the three-phase alternating current into the synchronous motor to be started. In this embodiment, the structures of the rectifier bridge, the dc reactor, and the inverter bridge are as shown in fig. 4, and compared with the conventional current source type frequency converter, in this embodiment, a step-up transformer and a step-down transformer are not used to convert, then rectify and invert the 380V three-phase ac, but the 380V three-phase ac is directly rectified and inverted.

And the zero-crossing detection circuit is used for detecting whether the terminal voltage of the permanent magnet synchronous motor is at a zero crossing point. In order to solve the above problem, in this embodiment, as shown in fig. 2, the zero-cross detection circuit includes: the circuit comprises a voltage transformer, a zero crossing comparator, a phase inverter, a diode clamping circuit, a Schmidt trigger and an optical coupling isolator which are sequentially connected in series.

And the voltage transformer is used for acquiring the terminal voltage of the permanent magnet synchronous motor and filtering. In this embodiment, the primary side of the permanent magnet synchronous motor collects the voltage at the input end of the permanent magnet synchronous motor, and the secondary side of the permanent magnet synchronous motor generates an alternating current signal.

In order to facilitate the post-stage circuit processing and zero-crossing comparison, in this embodiment, a zero-crossing comparator is provided to convert the ac signal output by the voltage transformer into a square wave signal with the same ac signal frequency and the same phase, and in this embodiment, a circuit diagram of the zero-crossing comparator is shown in fig. 3. The alternating current signal passes through the zero-crossing comparator of the embodiment, so that a square wave signal with the same frequency as the alternating current signal, the same phase and the 12V amplitude can be obtained.

In order to eliminate the interference near the zero crossing point and facilitate the detection of the zero crossing point, in the embodiment, an inverter is provided, and the square wave signal is inverted by the inverter and then input to the diode clamp circuit. In this embodiment, the circuit structure of the inverter may adopt a circuit diagram as shown in fig. 3.

And the diode clamping circuit is used for judging whether the end voltage of the permanent magnet synchronous motor crosses zero points or not. In this embodiment, a circuit diagram of the diode clamp circuit is shown in fig. 3, a forward conduction voltage of the diode clamp circuit is clamped at 0.7V, and when a waveform of the inverted square wave signal just crosses a zero point, the diode clamp circuit is turned on and outputs a pulse signal to realize zero-crossing detection.

In order to prevent the output signal waveform of the diode clamp circuit from being distorted and interfered by the environment, in this embodiment, a schmitt trigger is provided to shape the pulse signal, so as to stabilize the waveform, and then the waveform is output to an I/O port of the controller through an opto-isolator.

And the thyristor drive circuit receives a control signal generated by the controller according to a certain control strategy and controls the conduction of the thyristors in the rectifier bridge and the inverter bridge. Can be implemented by using the prior art, and will not be described in detail herein.

The working principle of the embodiment is as follows: the method comprises the steps that the primary side of a voltage transformer collects the voltage of the input end of a permanent magnet synchronous motor, an alternating current signal is generated on the secondary side of the voltage transformer, the alternating current signal is converted into a square wave signal which has the same frequency and the same phase with the alternating current signal through a zero crossing comparator, the square wave signal is inverted through a phase inverter and then input into a diode clamping circuit, the forward conduction voltage of the diode clamping circuit is clamped at 0.7V, and when the waveform of the inverted square wave signal just crosses a zero point, the diode clamping circuit is conducted, a pulse signal is output, and zero crossing detection is achieved; the pulse signal is subjected to waveform stabilization through a Schmidt trigger and then is output to an I/O port of a controller through an optical coupling isolator, the controller obtains the real position and the rotating speed of the rotor according to the position of a zero-crossing point, then generates a control signal according to a certain control strategy, controls the conduction of thyristors in a rectifier bridge and an inverter bridge, controls the frequency, the amplitude and the phase of three-phase current output by the inverter bridge, achieves the purpose that the synchronous rotating speed of the motor tracks the rotating speed of the rotor, and brings the motor into full speed within a specified time according to a starting rotating speed curve given before starting.

The beneficial effect of this embodiment does: the zero-crossing detection circuit is used for detecting the zero crossing point of the terminal voltage of the permanent magnet synchronous motor to judge the position interval of the rotor, compared with the traditional method, the position of the rotor can be detected by a position-free sensor, and the terminal voltage of the permanent magnet synchronous motor can be effectively detected;

the interference near the zero crossing point can be effectively eliminated by arranging the phase inverter in the zero crossing detection circuit, the zero crossing point voltage can be effectively detected by arranging the diode clamping circuit, the zero crossing point voltage can be effectively detected even under the condition that the voltage waveform of the permanent magnet synchronous motor at the low speed stage is seriously distorted, the Schmitt trigger is arranged to further stabilize the waveform, and the reliability of the device is improved; the optical coupler isolator is arranged to realize electrical isolation, so that the anti-interference capability of the device is improved;

the synchronous frequency conversion soft starting device of the embodiment has the advantages that the rotating speed is accurate and controllable in the starting process, and the smooth starting requirement of the motor can be met; the structure is simple, no mechanical commutator is arranged, no spark is generated, and the maintenance is convenient; the high-capacity, high-rotating-speed and high-voltage thyristor is easy to realize series-parallel connection, is more reliable, and can conveniently realize four-quadrant operation;

the synchronous frequency conversion soft starting device is a static element, so that the maintenance workload is small, the reliability is high, and the equipment installation and arrangement are flexible;

the starting current can be kept below the rated current required by the synchronous motor to run by adopting the static frequency converter for starting, no impact is caused to a power grid, and the soft starting performance is realized;

the static frequency converter motor structure has no special requirements, a plurality of units can share one device, and the requirement of frequent starting in the operation process can be met.

Example 2

The synchronous frequency conversion soft start device of the permanent magnet synchronous motor can determine the electrifying mode and the control mode of the inverter bridge and the frequency and the phase of the output current only after the actual space position of the rotor is detected, so that the output frequency of the inverter bridge and the rotating speed of the motor are always kept synchronous without generating step loss and oscillation. The existing mechanical position sensor is adopted to detect the position of the rotor, although the position of the rotor can be detected, the complexity of the device and the workload of installation, debugging and maintenance are increased, and the reliability of the device is reduced. Therefore, in the embodiment, the zero-crossing detection circuit is used for detecting the terminal voltage zero-crossing point of the permanent magnet synchronous motor to judge the rotor position interval; the specific process is as follows:

on the basis of embodiment 1, in this embodiment, a synchronous frequency conversion soft start method for a permanent magnet synchronous motor is provided, which includes the following steps:

s1, calculating the initial position of the rotor according to the three-phase stator voltage detected in the process of establishing the exciting current of the permanent magnet synchronous motor;

the method specifically comprises the following steps: the method comprises the steps that an external excitation voltage with step change is output to a unit of the permanent magnet synchronous motor, generated excitation current changes along with the excitation voltage, a changing magnetic field generated by the excitation current induces three-phase induction voltage on a three-phase winding of a stator of the unit, and the phase and amplitude of the three-phase induction voltage are related to the initial position of a rotor, so that the initial position of the rotor is obtained by detecting the phase and amplitude of the three-phase induction voltage.

S2, detecting the rotating speed of the motor in real time after the permanent magnet synchronous motor is statically started, and detecting the position of a rotor by adopting a three-phase irrelevant method and adopting forced commutation control when the rotating speed of the permanent magnet synchronous motor is lower than 5% of the rated rotating speed;

in this embodiment, the method for detecting the position of the rotor by using the three-phase independent method specifically includes the following steps: the method comprises the steps that the voltage of the input end of the permanent magnet synchronous motor is detected through a zero-crossing detection circuit, digital filtering is carried out on three terminal voltages of the permanent magnet synchronous motor, A/D sampling is carried out, if the sign of one terminal voltage value in the three terminal voltages changes, the voltage of the input end of the permanent magnet synchronous motor is judged to have a zero crossing point, and the current rotor position is obtained according to the relation between the zero crossing point voltage and the rotor position.

In this embodiment, the forced commutation control specifically includes the following steps:

s101, setting a delay angle of a rectifier bridge to be 150 degrees, enabling the rectifier bridge to enter an inversion state, reducing current of a main loop to be zero, and turning off all conducted thyristors in the inverter bridge;

and S102, after the current of the main loop is reduced to zero, switching the rectifier bridge to a rectification working state again, controlling the conduction of the next group of thyristors to be triggered in the inverter bridge, and reestablishing the current of the direct current loop.

When forced commutation control is adopted, the commutation lead angle of the inverter bridge does not work on commutation, and in order to increase starting torque and reduce torque pulsation, the commutation lead angle of the inverter bridge is generally taken as 0 degree; meanwhile, when forced commutation control is adopted, the current pulsation is large, and the conduction time of the thyristor is relatively long, so that the current of the main loop is limited to 67% of the rated current generally.

S3, when the rotating speed of the permanent magnet synchronous motor rises to 5% -10% of the rated rotating speed, detecting the position of the rotor based on a voltage zero-crossing detection method, stopping forced phase commutation, and automatically commutation by utilizing counter electromotive force generated at the stator side of the motor;

in this embodiment, the self-commutation using the back electromotive force generated at the stator side of the motor specifically includes the following steps: the thyristors in the inverter bridge are all turned off at the zero crossing point of the permanent magnet synchronous motor, the corresponding thyristors are triggered according to the triggering sequence of the phase change lead angle equal to 60 degrees, and the current signal is immediately blocked, at the moment, on one hand, the energizing time of the thyristors is increased due to the influence of the phase change overlap angle mu; on the other hand, due to the influence of armature reaction, the phase of the terminal voltage of the permanent magnet synchronous motor leads the counter potential by a power angle theta, so that the actual commutation lead angle gamma in the load is reduced, and therefore, the commutation residual angle of the inverter bridge satisfies the following formula:wherein, delta is the phase-changing residual angle of the inverter bridge, gamma is the actual phase-changing lead angle in loading, mu is the phase-changing overlap angle,in order to change the phase lead angle, theta is a power angle of phase lead counter potential of the permanent magnet synchronous motor terminal voltage, k is a safety coefficient larger than 1, w is the maximum possible value of the inverter bridge working angle frequency, t₀The turn-off time of the thyristor.

S4, introducing current closed-loop control, and under the condition that the maximum allowable current and the torque of the motor are limited, fully utilizing the overload capacity of the motor, starting at the maximum acceleration and reaching the rated rotating speed;

in the embodiment, the rotating speed and current double closed-loop control is adopted, and the system always maintains the maximum working current output in the starting and accelerating process.

S5, when the rotating speed of the permanent magnet synchronous motor rises to 97% of the rated rotating speed, judging whether a grid-connected condition is met, when the grid-connected condition is met, disconnecting the front-stage contactor and the rear-stage contactor, switching on the bypass contactor, generating an additional rotating speed fine-tuning signal according to the difference value of the voltage of the power grid and the voltage frequency of the synchronous motor, automatically adjusting the height of the direct current voltage output by the rectifier bridge, and finely tuning the rotating speed of the synchronous motor;

and S6, the permanent magnet synchronous motor enters power frequency operation and enters a constant power factor control or constant current control state.

As shown in fig. 5, it is a block diagram of the synchronous variable frequency soft start control system of the permanent magnet synchronous motor of the present embodiment, which corresponds to S1-S6; as shown in fig. 6, a flowchart of the thyristor triggered control layer strategy is shown.

The beneficial effect of this embodiment does: the direct current pulse technology is adopted at low speed, the direct current link current is periodically reduced to zero, and the inversion phase change is completed; the inversion at high speed adopts a load induction potential automatic phase change mode; the device can be started continuously, and has high repetition precision; 1/3, the starting capacity is less than the rated capacity of the motor; the speed regulation range can be from the static state of the motor to the rated rotating speed, and the working efficiency of the static frequency converter cannot be reduced in the working range.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.