阅读说明：本技术 一种用于开关磁阻电机的多电平功率变换器 (Multilevel power converter for switched reluctance motor ) 是由 蔡燕 董中山 于 2021-08-12 设计创作，主要内容包括：本发明适用于功率变换器技术领域,提出了一种用于开关磁阻电机的多电平功率变换器,应用于开关磁阻电机调速系统(SRD)。所提出的多电平功率变换器包括：直流供电电源、稳压电容C1、升压电容C2、纵向桥和横向桥。通过控制开关管的导通与关断,可使开关磁阻电机工作在七种电平状态,既能实现传统功率电路的常压励磁(+1)、退磁(-1)和零压续流(0),也能实现高压快速励磁(+2)和高压快速退磁(-2),以及由升压电容C2充放电而施加到绕组上的-U-(C2)和+U-(C2)两种电平。提出的多电平功率变换器具有多电平等级、高控制自由度、可快速励磁和快速退磁,以及通过桥臂扩展适用于任意相数电机的优势,可以提高开关磁阻电机调速系统(SRD)的整体控制性能。(The invention is suitable for the technical field of power converters, and provides a multi-level power converter for a switched reluctance motor, which is applied to a speed regulation System (SRD) of the switched reluctance motor. The proposed multilevel power converter comprises: the device comprises a direct current power supply, a voltage stabilizing capacitor C1, a boosting capacitor C2, a longitudinal bridge and a transverse bridge. The switch reluctance motor can work in seven level states by controlling the on-off of the switch tube, not only can realize the normal-pressure excitation (+1), demagnetization (-1) and zero-pressure follow current (0) of the traditional power circuit, but also can realize the high-pressure rapid excitation (+2) and the high-pressure rapid demagnetization (-2), and-U applied to the winding by the charging and discharging of the boost capacitor C2 C2 And + U C2 Two levels. The multi-level power converter has multi-level grades, high control freedom degree, quick excitation and quick demagnetization,and the advantage that the bridge arm extension is suitable for the motor with any number of phases can be used for improving the overall control performance of the switched reluctance motor speed regulating System (SRD).)

1. A multilevel power converter for a switched reluctance motor, characterized by: the motor is composed of a direct current power supply, a voltage stabilizing capacitor C1, a passive boosting capacitor C2, longitudinal bridges and transverse bridges, wherein the number of the longitudinal bridges is equal to the number of phases of the motor, and only one transverse bridge is provided;

the multilevel power converter for the switched reluctance motor is characterized in that: the direct current power supply can be a rectification power supply for rectifying alternating current into direct current, and can also be other types of high-power direct current power supplies and storage batteries;

the multilevel power converter for the switched reluctance motor is characterized in that: the positive pole and the negative pole of the voltage-stabilizing capacitor C1 are respectively connected with the positive pole and the negative pole of a direct-current power supply in parallel, and the negative pole of the passive boosting capacitor C2 is connected with the positive pole of the voltage-stabilizing capacitor C1 in series;

the multilevel power converter for the switched reluctance motor is characterized in that: the three buses are provided, the bus A is led out from the anode of the passive boosting capacitor C2, the bus B is led out from the midpoint of the series connection of the capacitors C2 and C1, and the bus C is led out from the collector of the switch tube VTZ;

the multilevel power converter for the switched reluctance motor is characterized in that: the switching tubes VTZ, VTX1, VTX2 and VTX3(X represents different phases of the motor, for example, for a three-phase motor, X represents A, B, C) adopt a fully-controlled power switching tube;

the multilevel power converter for the switched reluctance motor is characterized in that: the longitudinal bridge consists of switching tubes (VTX1, VTX2 and VTX3), diodes (VDX1, VDX2 and VDX3) and X-phase motor windings; the collector of the switch tube VTX1 is connected with a bus A, the emitter of the VTX1 is connected with the collector of the switch tube VTX2 and is connected with the cathode of a diode VDX1, and the anode of the diode VDX1 is connected with a bus B; an emitter electrode of the switching tube VTX2 is connected with one end of an X-phase winding of the motor and is connected with a negative electrode of a diode VDX3, and a positive electrode of the diode VDX3 is connected with a negative electrode of a direct-current power supply; the collector of the switching tube VTX3 is connected with the other end of the X-phase winding of the motor and is connected with the anode of a diode VDX2, the emitter of VTX3 is connected with the cathode of a direct-current power supply, and the cathode of the diode VDX2 is connected with a bus A;

the multilevel power converter for the switched reluctance motor is characterized in that: the said transversal bridge is composed of a switching tube VTZ and a diode VDZX (X stands for a different phase of the machine, for example for a three-phase machine X stands for A, B, C); the emitter of the switching tube VTZ is connected to the midpoint of the series connection of the capacitors C2 and C1, and the collector of VTZ is connected with a bus C which is used as a common normal-pressure demagnetization channel; the negative pole of the diode VDZX is connected with a bus C, and the connecting end of the motor X-phase winding and the collector of the VTX3 is connected with the positive pole of the diode VDZX.

2. The multilevel power converter for a switched reluctance machine of claim 1 wherein: when the switch tubes VTA1, VTA2 and VTA3 are turned on and VTZ is turned off, the power converter has seven working states for each phase winding, and when the switch tubes VTA1, VTA2 and VTA3 are turned on, the bus bar A voltage (+ (U) is applied to the phase winding_C2+U_DC) Excitation, high voltage rapid excitation is realized ("+ 2" state); when the switching tubes VTA2 and VTA3 are on and VTA1 and VTZ are off, the bus B voltage (+ U) is applied to the phase winding_DC) Excitation, realizing normal-pressure excitation (a state of plus 1); when only VTA3 is conducted and other switch tubes are all turned off, the phase motor winding works in a zero-voltage freewheeling state (0 state); when only VTZ is conducted and other switch tubes are all turned off, the phase motor winding feeds back electric energy to the capacitor C1 through the bus C, and normal-voltage demagnetization is achieved (a "-1" state); when the switching tube VTA1,VTA2, VTA3 and VTZ are all turned off, then this phase winding feeds back the electric energy to electric capacity C1 and C2 through bus A, realize the high-pressure fast demagnetization ("-2" state); when the switching tubes VTA1, VTA2 and VTZ are turned on and VTA3 is turned off, the boosting capacitor C2 energizes the phase winding ("+ U_C2"state"), capacitor C2 discharges; when only VTA2 is on and the other switching tubes are off, the phase winding feeds back power to boost capacitor C2 ("-U_C2"state"), the capacitor C2 charges.

3. The seven operating states of claim 2, wherein: the selection of two excitation modes of high-voltage quick excitation and normal-voltage excitation is realized by controlling the on-off of a switching tube VTX1 to control the potential of a collector terminal of VTX 2; the two demagnetization modes of normal-pressure demagnetization and high-pressure quick demagnetization are selected by controlling the on-off of the switching tube VTZ to control the potential of the phase winding end of the motor.

4. The seven operating states of claim 2, wherein: the + U_C2The state refers to that forward voltages at two ends of the boost capacitor are added at two ends of a motor winding, and the demagnetization energy of the motor recovered by the boost capacitor is used for winding excitation and can be used for realizing the discharge balance and overvoltage protection of the boost capacitor; said "-U_C2The 'state' means that the winding feeds back demagnetization energy to the boosting capacitor, and the voltage at two ends of the winding is-U at the moment_C2And the demagnetization of the winding is realized, and the method can be used for realizing the charge balance and the undervoltage protection of the boost capacitor.

5. The seven operating states of claim 2, wherein: the multi-level power converter can be used as a five-level power converter and mainly works in five working states of +2, 0, 1 and 1, namely high-voltage quick excitation, high-voltage quick demagnetization, zero-voltage follow current, normal-voltage excitation and normal-voltage demagnetization; when the circuit is used as a five-level circuit, the circuit has a combined working mode of any two states except a combination of "-1" and "-2", and actually the combined mode of the two states of "-1" and "-2" is not needed when adjacent two-phase motor windings are overlapped and conducted, so that independent operation between phases can be realized when the circuit is used as a five-level circuit.

6. The seven operating states of claim 2, wherein: the proposed multi-level power converter can be used as seven-level (when the voltage U is applied across the boost capacitor)_C2Less than the supply voltage U_DCWhen in use), the device works at +2 "," -2 "," 0 "," +1 "," -1 "," + U_C2"and" -U_C2The magnetic excitation device comprises seven working states, namely high-voltage quick excitation, high-voltage quick demagnetization, zero-voltage follow current, normal-voltage excitation, normal-voltage demagnetization, low-voltage excitation and low-voltage demagnetization.

7. A multilevel power converter for a switched reluctance machine according to claim 1 wherein: the proposed multilevel power converter can be adapted to motors of any number of phases by increasing the number of longitudinal bridge arms and the extension of the transverse bridge arms.

Technical Field

The invention relates to a power converter of a motor, in particular to a multi-level power converter for a switched reluctance motor.

Background

The switched reluctance motor has the advantages of simple and firm structure, low cost, large starting torque, multiple controllable parameters, good speed regulation performance and the like, and has wide application range due to a series of advantages. The switched reluctance motor speed regulating System (SRD) is composed of a switched reluctance motor, a power converter, a controller, a position detector and the like, wherein the power converter is used as a main component for driving the switched reluctance motor speed regulating system and plays a vital role in the performance of the whole speed regulating system. In order to optimize the performance of the speed regulating system of the switched reluctance motor, the research on the multilevel power converter of the switched reluctance motor is of great significance.

A conventional asymmetric half-bridge three-level power converter is widely used due to its advantages of simple structure, few switching devices, and simple control, as shown in fig. 1. Taking phase a as an example, there are three total operating states, corresponding to those shown in fig. 2, when VTA1 and VTA2 are turned on, a positive voltage of a power supply is applied across the winding, exciting (+1) the winding; when the VTA1 and the VTA2 are switched off, the winding freewheels through a diode VDA1 and a VDA2, and the residual magnetic energy is fed back to a capacitor C1 to realize demagnetization (-1); when one switching tube is kept on, and the other switching tube is kept off, the winding continues current through the upper bridge arm or the lower bridge arm at zero voltage (the upper bridge arm at zero voltage continues current is taken as an example in the figure). However, when the motor runs at a high speed, the traditional asymmetric power converter is difficult to overcome the counter electromotive force to quickly establish current in the excitation stage by normal-pressure excitation (+1) because the counter electromotive force is large and the effective excitation and demagnetization time is short; in the demagnetization stage, normal-pressure demagnetization (-1) hardly inhibits trailing current to generate negative torque, so that the output of the motor is influenced and the efficiency is reduced.

In view of these disadvantages, the researchers at home and abroad have conducted research on the multi-Level power Converter of the switched reluctance motor based on the asymmetric half-bridge, and the document "a Novel Four-Level Converter and instant Switching Angle Detector for High Speed SRM Drive" is improved based on the traditional asymmetric half-bridge circuit, and a Four-Level power Converter using a passive boost capacitor is proposed, as shown in fig. 3, although the circuit can overcome the large back electromotive force at High Speed by capacitor boost, realize fast excitation, accelerate current drop, and realize fast demagnetization, when any phase works in the fast excitation state (+2), the Q is turned on_CDWill cause VD_CDCut off, thereby forcing other phases to work only in a fast excitation state (+2) when being excited, and also working in a normal-pressure excitation state (+1) when one phase works in a normal-pressure excitation state (+1), and Q_CDAnd is off, at which time the power converter cannot provide high voltage excitation. General assemblyWhen two phases are conducted to multiple phases in an overlapping mode, the inter-phase restriction exists, so that the level state of each phase cannot be independently switched, and the application of the multi-level power converter is limited.

The document "asymmetry 7-Level Neutral Point Clamped Converter for Switch transistors" proposes a seven-Level power Converter, as shown in fig. 4, in which a phase bridge is composed of four switching tubes and two diode groups, is powered by a battery pack, and seven Level states of "+ 1", "+ 2/3", "+ 1/3", "0", "-1/3", "-2/3", and "-1" are provided by controlling the on/off of the corresponding switching tubes. The power converter can realize independent operation of seven level states of each phase, but the topology structure cannot provide high voltage exceeding the maximum power supply voltage level, namely, the topology structure has no boosting capacity, and the topology structure is originally designed to be applied to an electric automobile with a battery pack and has limited application.

Disclosure of Invention

The invention provides a multilevel power converter for a switched reluctance motor, aiming at the defects of the prior art. The invention has multiple level grades, can realize normal-pressure excitation, demagnetization and zero-pressure follow current of the traditional power converter, can also realize high-voltage rapid excitation and high-voltage rapid demagnetization, and can provide two low-voltage level states (when the voltage U at two ends of the boost capacitor is in a state of being in which the voltage U at two ends of the boost capacitor is in a state of being in which the passive boost capacitor is properly selected and being reasonably charged and discharged through appropriate type selection of the passive boost capacitor_C2Less than the supply voltage U_DCTime), thereby low-voltage excitation and low-voltage demagnetization can be realized. The invention aims to effectively reduce the torque pulsation of the motor, improve the operation efficiency of the motor and widen the speed regulation range of the motor by utilizing the advantages of multi-level grade, high control freedom degree, quick excitation and quick demagnetization of the multi-level power converter.

The technical scheme of the invention is as follows: a multi-level power converter for a switched reluctance motor is composed of a direct-current power supply, a voltage stabilizing capacitor C1, a passive boosting capacitor C2, longitudinal bridges and transverse bridges, wherein the number of the longitudinal bridges is equal to the number of phases of the motor, and only one transverse bridge is provided.

The direct current power supply can be a rectification power supply for rectifying alternating current into direct current, and can also be other types of high-power direct current power supplies and storage batteries;

the positive pole and the negative pole of the voltage-stabilizing capacitor C1 are respectively connected with the positive pole and the negative pole of a direct-current power supply in parallel, and the negative pole of the passive voltage-boosting capacitor C2 is connected with the positive pole of the voltage-stabilizing capacitor C1 in series;

the multi-level power converter for the switched reluctance motor is provided with three buses, wherein a bus A is led out from the positive electrode of a passive boosting capacitor C2, a bus B is led out from the middle point of the series connection of capacitors C2 and C1, and a bus C is led out from the collector electrode of a switch tube VTZ;

the switching tubes VTZ, VTX1, VTX2 and VTX3(X represents different phases of the motor, for example, for a three-phase motor, X represents A, B, C) adopt a fully-controlled power switching tube;

the longitudinal bridge consists of switching tubes (VTX1, VTX2 and VTX3), diodes (VDX1, VDX2 and VDX3) and X-phase motor windings; the collector of the switching tube VTX1 is connected with a bus A, the emitter of the VTX1 is connected with the collector of the switching tube VTX2 and is connected with the cathode of a diode VDX1, and the anode of the diode VDX1 is connected with a bus B; the emitter of the switching tube VTX2 is connected with one end of the motor X-phase winding and is connected with the cathode of a diode VDX3, and the anode of the diode VDX3 is connected with the cathode of a direct-current power supply; the collector of the switching tube VTX3 is connected with the other end of the X-phase winding of the motor and is connected with the anode of a diode VDX2, the emitter of VTX3 is connected with the cathode of a direct-current power supply, and the cathode of the diode VDX2 is connected with a bus A;

the said transversal bridge is composed of a switching tube VTZ and a diode VDZX (X stands for a different phase of the machine, for example for a three-phase machine X stands for A, B, C); the emitter of the switching tube VTZ is connected to the midpoint of the series connection of the capacitors C2 and C1, and the collector of VTZ is connected with a bus C which is used as a common normal-pressure demagnetization channel; the negative pole of the diode VDZX is connected with a bus C, and the connecting end of the motor X-phase winding and the collector of the VTX3 is connected with the positive pole of the diode VDZX.

The multi-level power conversion for the switched reluctance motorWhen the switch tubes VTA1, VTA2 and VTA3 are turned on and VTZ is turned off, the bus bar A voltage (+ (U) is applied to each phase winding_C2+U_DC) Excitation, high voltage rapid excitation is realized ("+ 2" state); when the switching tubes VTA2 and VTA3 are on and VTA1 and VTZ are off, the bus B voltage (+ U) is applied to the phase winding_DC) Excitation, realizing normal-pressure excitation (a state of plus 1); when only VTA3 is conducted and other switch tubes are all turned off, the phase motor winding works in a zero-voltage freewheeling state (0 state); when only VTZ is conducted and other switch tubes are all turned off, the phase motor winding feeds back electric energy to the capacitor C1 through the bus C, and normal-voltage demagnetization is achieved (a "-1" state); when the switching tubes VTA1, VTA2, VTA3 and VTZ are all turned off, the phase winding feeds back electric energy to the capacitors C1 and C2 through the bus A, and high-voltage rapid demagnetization is realized (a "-2" state); when the switching tubes VTA1, VTA2 and VTZ are turned on and VTA3 is turned off, the boost capacitor C2 energizes the phase winding ("+ U_C2"state"), capacitor C2 discharges; when only VTA2 is on and the other switching tubes are off, the phase winding feeds back power to boost capacitor C2 ("-U_C2"state"), the capacitor C2 charges.

The selection of two excitation modes of high-voltage quick excitation and normal-voltage excitation is realized by controlling the on-off of a switching tube VTX1 to control the potential of a collecting electrode end of VTX 2; the two demagnetization modes of normal-pressure demagnetization and high-pressure quick demagnetization are selected by controlling the on-off of the switching tube VTZ to control the potential of the phase winding end of the motor.

The + U_C2The state refers to that forward voltages at two ends of the boost capacitor are added at two ends of a motor winding, and demagnetization energy recovered by the boost capacitor is used for winding excitation and can be used for realizing discharge balance and overvoltage protection of the boost capacitor; said "-U_C2The 'state' refers to that the winding feeds back demagnetization energy to the boosting capacitor, and the voltage at two ends of the winding is-U at the moment_C2And the demagnetization of the winding is realized, and the method can be used for realizing the charge balance and the undervoltage protection of the boost capacitor.

The multi-level power converter for the switched reluctance motor can be used as a five-level power converter, and mainly works in five working states of +2 ', -0', "+ 1 'and" -1', namely high-voltage rapid excitation, high-voltage rapid demagnetization, zero-voltage follow current, normal-voltage excitation and normal-voltage demagnetization; when the five-level circuit is used, the circuit has a combined working mode of any two states except a combination of "-1" and "-2", and actually the combined mode of the two states of "-1" and "-2" is not needed when adjacent two-phase motor windings are overlapped and conducted, so that independent operation between phases can be realized when the five-level circuit is used.

The multi-level power converter for the switched reluctance motor can be used as seven levels (when the voltage U is applied to two ends of the boost capacitor)_C2Less than the supply voltage U_DCWhen) is operated at "+ 2", "-2", "0", "+ 1", "-1", "+ U_C2"and" -U_C2The magnetic excitation device comprises seven working states, namely high-voltage quick excitation, high-voltage quick demagnetization, zero-voltage follow current, normal-voltage excitation, normal-voltage demagnetization, low-voltage excitation and low-voltage demagnetization.

On the basis of the multi-level power converter for the switched reluctance motor, the number of longitudinal bridge arms is increased and the number of transverse bridge arms is increased, so that the multi-level power converter can be suitable for motors with any number of phases.

Compared with the prior art, the invention has the following beneficial effects: the multi-level power converter adopts the passive boost capacitor to bring two variable levels of high voltage (a +2 state and a' -2 state), realizes high-voltage rapid excitation and high-voltage rapid demagnetization, can accelerate the rise of excitation current and avoid the generation of demagnetization trailing current, and can effectively improve the performance of the motor during high-speed stage operation. The normal-pressure excitation, normal-pressure demagnetization and zero-pressure follow current states of the traditional power converter are reserved, and the requirement of the motor during low-speed operation can be met. The proposed multilevel power converter can also provide + U_C2and-U_C2The low-voltage excitation of the motor winding can be realized by the excitation of the boosting capacitor C2 to the winding and the demagnetization process that the winding energy is fed back to the boosting capacitor C2 at two levels of voltageAnd low-voltage demagnetization; and through the process, the balance control of the voltage of the boost capacitor can be realized, and compared with the multi-level power converter adopting the passive boost capacitor in the prior art, the circuit has better controllability on the voltage of the boost capacitor.

The multilevel power converter for the switched reluctance motor is designed under the condition of ensuring high phase independence of the power converter and reducing the using quantity of switching devices, and four level states (a +2 state, a-2 state, a 0 state and a +1 state) provided by a longitudinal bridge and one level state (a-1 state) provided by a transverse bridge have great combination freedom in a two-phase overlapped conduction interval, because two adjacent phases of the motor do not need to be conducted simultaneously in two combined states of '-1' and '-2', the other conducting combinations of the five level states can be realized, the running independence between the phases is ensured, enabling more flexible control strategies to be developed to further optimize the performance of the switched reluctance motor.

Meanwhile, the topological structure ensures multi-level and reduces the use of switching devices as much as possible so as to reduce switching loss and manufacturing cost, and the topological structure is applicable to motors with any number of phases by increasing the number of longitudinal bridges and expanding transverse bridge arms, and is a more commonly applicable structure.

Drawings

Fig. 1 is a schematic diagram of a prior art asymmetric half-bridge power converter.

Fig. 2 is a schematic diagram of three operating states of an asymmetric half-bridge power converter in the prior art.

Fig. 3 is a schematic diagram of a prior art four-level power converter.

Fig. 4 is a schematic diagram of a prior art seven-level power converter.

Fig. 5 is a schematic diagram of a multilevel power converter for a switched reluctance motor in accordance with the present invention.

Fig. 6(a) to 6(g) are schematic diagrams of seven level states of the proposed power converter, taking phase a as an example, and fig. 6(a) is the "+ 2" state; FIG. 6(b) shows "+ 1"status; FIG. 6(c) is the "0" state; FIG. 6(d) is the "-1" state; FIG. 6(e) is the "-2" state; FIG. 6(f) is "+ U_C2"status; FIG. 6(g) is "-U_C2"status".

Fig. 7(a) and 7(b) are two auxiliary zero states of the proposed power converter, both usable for zero-voltage freewheeling, for example phase a, and fig. 7(a) is the upper arm zero state; fig. 7(b) is another zero state of the composition.

Fig. 8(a) to 8(i) are schematic diagrams of 9 combination patterns of a substantially five-level two-phase overlap conduction interval, taking A, B two-phase overlap conduction as an example, and fig. 8(a) is a combination pattern (+2, + 1); FIG. 8(b) is a combination pattern (0, + 1); FIG. 8(c) is a combination pattern (0, + 2); FIG. 8(d) is a combined pattern (-2, + 1); FIG. 8(e) is a combined pattern (-2, + 2); FIG. 8(f) is a combined pattern (-2, 0); FIG. 8(g) is a combination pattern (-1, + 1); FIG. 8(h) is a combined pattern (-1, + 2); FIG. 8(i) is a combined pattern (-1, 0).

Detailed Description

The present invention provides a multilevel power converter for a switched reluctance motor, and the invention is further described with reference to the accompanying drawings.

As shown in fig. 5, the present invention provides a multilevel power converter for a switched reluctance motor, which is composed of a dc power supply, a voltage stabilizing capacitor C1, a passive boost capacitor C2, a vertical bridge, and a horizontal bridge. The direct current power supply can be a rectification power supply for rectifying alternating current into direct current, and can also be other types of high-power direct current power supplies and storage batteries; the positive electrode and the negative electrode of the voltage stabilizing capacitor C1 are connected with the positive electrode and the negative electrode of the direct current power supply in parallel, and the negative electrode of the passive boosting capacitor C2 is connected with the positive electrode of C1 in series. The proposed multilevel power converter has three busbars, busbar a, busbar B and busbar C, corresponding to the thickened conductors in fig. 5.

In the present embodiment, a three-phase motor is taken as an example, and since the circuit structures of the longitudinal bridges are the same, the a-phase motor is taken as an example for explanation, as shown in a longitudinal dotted line frame in fig. 5, the longitudinal bridges are composed of switching tubes (VTA1, VTA2, and VTA3), diodes (VDA1, VDA2, and VDA3), and a-phase motor windings, the number of the longitudinal bridges is equal to the number of phases of the motor, the collector of the switching tube VTA1 is connected to the bus a, the emitter of the VTA1 is connected to the collector of the switching tube VTA2 and to the cathode of the diode VDA1, and the anode of the diode VDA1 is connected to the bus B; an emitter of the switching tube VTA2 is connected with one end of the phase winding A of the motor and is connected with the negative electrode of the diode VDA3, and the positive electrode of the diode VDA3 is connected with the negative electrode of the direct-current power supply; the collector of the switching tube VTA3 is connected with the other end of the phase winding of the motor A and is connected with the anode of a diode VDA2, the emitter of VTA3 is connected with the cathode of a direct current power supply, and the cathode of a diode VDA2 is connected with a bus A.

As shown in the horizontal dashed box of fig. 5, the horizontal bridge is composed of a switching tube VTZ and a diode VDZX; the emitter of the switch tube VTZ is connected to the midpoint of the series connection of the capacitors C2 and C1, and the collector of VTZ is connected with a bus C which is used as a common normal-voltage demagnetization channel; the negative pole of diode VDZX is connected with bus C, and the connection end of motor X phase winding and the collector of VTX3 is connected with the positive pole of diode VDZX.

The power converter has seven working states when each phase winding is electrified, and the following description is made by taking the phase A as an example:

"+ 2" state: when the switching tubes VTA1, VTA2 and VTA3 are on and VTZ is off, current flows as shown in the loop of FIG. 6(a) by applying bus A voltage (+ (U) to the phase A winding_C2+U_DC) Excitation, fast excitation is achieved.

"+ 1" state: when the switching tubes VTA2 and VTA3 are on and VTA1 and VTZ are off, current flows as shown in the loop of FIG. 6(B) by applying bus B voltage (+ U) to the phase A winding_DC) And (4) excitation is carried out, and normal-pressure excitation is realized.

The "0" state: when only VTA3 is turned on and the other switching tubes are turned off, the current flows to the circuit shown in fig. 6(c), and the a-phase winding operates in a zero-voltage freewheeling state, which is referred to as a "lower arm 0" state.

The "-1" state: when only VTZ is turned on and other switch tubes are all turned off, the current flows to the loop shown in fig. 6(d), the phase a winding feeds back the electric energy to the capacitor C1 through the bus C, and normal-voltage demagnetization is realized.

The "-2" state: when the switching tubes VTA1, VTA2, VTA3 and VTZ are all turned off, the current flows to the loop shown in fig. 6(e), and the phase a winding feeds back the electric energy to the capacitors C1 and C2 through the bus a, so that the fast demagnetization is realized.

“+U_C2"state: when the switching tubes VTA1, VTA2 and VTZ are turned on and VTA3 is turned off, the current flows as shown in fig. 6(f) by applying the forward voltage (+ U) of the boosting capacitor to the a-phase winding_C2) And (6) excitation.

“-U_C2"state: when only VTA2 is turned on and other switching tubes are turned off, the current flows to the voltage boosting capacitor C2 through the bus a in the phase a winding, so that demagnetization is realized.

The proposed power converter also has two auxiliary zero states, an "upper arm 0" state and another zero state ("new 0" state) similar to a conventional asymmetric half-bridge circuit. When the switching tubes VTA1 and VTA2 are on and VTA3 and VTZ are off as shown in fig. 7(a) for the "upper arm 0" state, current flows to the windings freewheeling via the upper arm as shown. When the switching tubes VTA2 and VTZ are on and VTA1 and VTA3 are off as shown in fig. 7(b) for the "new 0" state, current flows to the circuit shown and the windings freewheel through the circuit shown.

The degree of freedom in control of a power converter can be measured by the combined degree of freedom of the level states of the overlapping conduction intervals, and the power converter has great degree of freedom in control if the level states applied to each phase winding can operate independently without interference. The two phases of the proposed power converter are turned on in an overlapping manner to verify its control freedom.

Fig. 8(a) to 8(i) show two-phase overlapped conduction cases of substantially five levels (+2, +1, 0, -2, -1), and there are 10 combinations of five levels states according to permutation combination, and the proposed power converter has 9 combinations, namely (+2, +1), (0, +2), (-2, +1), (-2, +2), (-2, 0), (-1, +1), (-1, +2), and (-1, 0). For the 10 th combination mode (-1, -2), the phases can be operated independently since this mode is not usually required when two adjacent phases are turned on one another. Two kinds of matching exist for each combination, and each combination mode is analyzed one by taking one matching when the two phases AB are overlapped and conducted as an example.

As shown in fig. 8(a), in a combined mode (+2, +1), when VTZ is turned off, the switching tubes VTA1, VTA2 and VTA3 of the a phase are turned on, and the positive superposition voltage of C1 and C2 is applied to two ends of the winding of the a phase, so that quick excitation is realized; and the switching tubes VTB2 and VTB3 of the B phase are switched on, VTB1 is switched off, and the forward voltage at the end C1 is applied to two ends of the winding of the B phase, so that normal-voltage excitation is realized.

As shown in fig. 8(b), in the combined mode (0, +1), when VTZ is turned off, only the switching tube VTA3 is turned on in phase a, and the winding operates in a zero-voltage freewheeling state; the phase B is excited under normal pressure in the same operating state as phase B in fig. 8 (a).

As shown in fig. 8(c), the combined mode (0, +2) is shown, the phase a is the same as the phase a in fig. 8(b) in the operating state, and is zero-pressure continuous flow; the phase B is fast excited as the phase a in fig. 8 (a).

As shown in fig. 8(d), in a combined mode (-2, +1), when VTZ is turned off, all the switching tubes of the a phase are turned off, and the winding feeds back the electric energy to the capacitors C1 and C2 through the diodes VDA2 and VDA3, so that fast demagnetization is realized; the phase B is excited under normal pressure in the same operating state as the phase B in fig. 8 (B).

As shown in fig. 8(e), the combined mode is (-2, +2), and the phase a is the same as the phase a in fig. 8(d) in the operating state, i.e., fast demagnetization; the phase B is fast excited as the phase B in fig. 8(c) operates in the same state.

FIG. 8(f) shows a combined mode (-2, 0), in which the phase A is fast demagnetized when the phase A is in the same working state as in FIG. 8 (e); the phase B is identical to the phase a in fig. 8(c) in operation state and is zero-pressure freewheeling.

As shown in fig. 8(g), in the combined mode (-1, +1), VTZ is turned on, all the switching tubes of the a phase are turned off, and the winding feeds back the electric energy to the capacitor C1 through the switching tube VTZ and the diodes VDZA and VDA3, thereby realizing normal-voltage demagnetization; the phase B is excited under normal pressure in the same operating state as phase B in fig. 8 (d).

FIG. 8(h) shows a combined mode of (-1, +2), in which the phase A is identical to the phase A in FIG. 8(g) in working condition, and normal-pressure demagnetization is performed; the phase B is fast excited as the phase B in fig. 8(e) operates in the same state.

FIG. 8(i) shows a combined mode (-1, 0), in which the phase A is demagnetized under normal pressure when the phase A is in the same working state as in FIG. 8 (h); the phase B is identical to the phase B in fig. 8(f) in working state and is zero-pressure freewheeling.

Through the above 9 combined mode analyses, it can be seen that the proposed multilevel power converter operates independently from phase to phase when used as a five-level converter, and can fully exert the advantage of multilevel, thereby facilitating adoption of a more flexible control strategy and further improving the performance of the SRD.

The power converter provided by the invention adopts the passive boost capacitor C2 to obtain high voltage, which is a simple and cost-saving scheme, and in the specific working process, the series connection of the C2 and the C1 can be used for recovering the feedback energy of a winding to realize quick demagnetization, and the energy can also be used for quick excitation, so that the running efficiency of the motor can be effectively improved. Plus U additionally provided by boost capacitor C2_C2"and" -U_C2The two level states play a good balance control role for the two level states. When the voltage across the boosting capacitor C2 is too high, the stored energy can be released to reduce the voltage by exciting the winding in the state of +2, and the voltage can also be reduced by + U_C2The "state" energizes the winding to discharge the stored energy and reduce the voltage. Similarly, when the voltage across the boost capacitor C2 is too low, besides the demagnetization of the winding can be realized through the ' -2 ' state, and the demagnetization energy is used for the energy storage boost voltage of the capacitors C1 and C2, the voltage can also be increased through ' -U_C2The state realizes the demagnetization of the winding, and the demagnetization energy is fed back to the boosting capacitor C2 to realize the voltage boosting. Generally speaking, the passive boost capacitor has the functions of overvoltage and undervoltage protection while the balance of the passive boost capacitor is controlled.

The multi-level grade of the power converter can meet the requirements of low speed and high speed of the switched reluctance motor, and can mainly work in three working states of +1, 0 and-1 during normal operation to meet the requirements of general working conditions. In a high-speed stage, a high back electromotive force is overcome by using a quick excitation mode so as to quickly establish current; in the demagnetization stage, the rapid demagnetization mode is utilized to rapidly demagnetize so as to inhibit trailing current and improve the output and the operating efficiency of the motor, and the multi-level advantages of the multi-level power circuit can be utilized to effectively reduce torque pulsation and improve the dynamic response of the motor.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all technical solutions and embodiments similar to the technical solutions can be designed without creativity in the layout manner of other similar components or other components without departing from the spirit of the present invention.