Three-level power electronic controller and control method for a magnetic bearing

Abstract

The application discloses a three-level power electronic controller and a control method of a magnetic suspension bearing, and belongs to the field of magnetic suspension bearing control. The three-level power electronic controller comprises 2N winding bridge arms, a common bridge arm, 2N windings and a power supply; wherein N is the number of degrees of freedom of a multi-axis magnetic suspension bearing. The midpoint of each winding bridge arm is connected to the first end of a winding, and the second ends of all the 2N windings are connected together with the midpoint of the common bridge arm; the common bridge arm is used for providing a constant zero midpoint potential for the winding bridge arms, and controls the winding current in cooperation with the winding bridge arms to realize three-level voltage output. The application further provides a common bridge arm midpoint potential control method of self-adaptive hysteresis, which judges whether the common bridge arm is switched from a current mode to another working mode through a hysteresis width condition, an error sign condition, a differential sign condition and a common mode switching criterion, so that active control of the midpoint potential is realized.

Description

Technical Field

[0001] This invention belongs to the field of magnetic levitation bearing control technology, and more specifically, relates to a three-level power electronic controller and control method for magnetic levitation bearings. Background Technology

[0002] Active magnetic bearings possess excellent characteristics such as frictionless operation, low loss, and noiselessness, and are widely used in high-speed rotating machinery. The magnetic bearing controller primarily controls the winding current of the magnetic bearing through the switching action of a power electronic converter, thereby controlling the rotor position. Therefore, the power electronic converter plays a crucial role in the static and dynamic performance of the magnetic bearing system.

[0003] When a magnetic levitation bearing system's rotor is levitated, it is subject to external mechanical disturbances. To counteract these disturbances and maintain the rotor's levitation in a central position, its controller must provide a high current response speed to quickly offset external winding forces. Therefore, the current loop bandwidth of the magnetic levitation bearing controller becomes a decisive factor in its disturbance rejection performance. On the other hand, in equipment such as high-power energy storage flywheels, air-cooled fans, or turbine machinery, the rotor weight of magnetic levitation bearings reaches tons or more. To increase the load-bearing capacity of these heavy-duty magnetic bearings, a stronger magnetic field is required, typically resulting in larger winding inductance and rated winding current. To improve the current response speed and disturbance rejection capability of heavy-duty magnetic bearings, the power electronic converter, acting as a power amplifier, needs to operate at higher voltage levels. Consequently, it faces problems such as high voltage stress on switching devices and large current ripple. Therefore, it is urgent to optimize its power electronic controller to meet the application requirements of high voltage and high dynamic response. Summary of the Invention

[0004] In view of the shortcomings of the existing technology and the need for improvement, the purpose of this invention is to provide a three-level power electronic controller and control method for magnetic levitation bearings. The controller has lower voltage stress on the switching devices, resulting in less current ripple. It can be applied to high-voltage and high-power applications and can achieve automatic balance of the midpoint potential and global optimization of the number of devices.

[0005] To achieve the above objectives, the present invention provides a three-level power electronic controller for a magnetic levitation bearing, comprising 2N winding bridge arms, a common bridge arm, 2N windings, and a power supply; wherein N is the number of degrees of freedom of the multi-axis magnetic levitation bearing;

[0006] The midpoint of each winding bridge arm is connected to the first end of a winding, and the second ends of all 2N windings are connected to the midpoint of a common bridge arm.

[0007] The common bridge arm is used to provide a constant zero-midpoint potential for the winding bridge arm and works with the winding bridge arm to control the winding current.

[0008] Furthermore, the 2N winding bridge arms include two types: forward current winding bridge arms and reverse current winding bridge arms, and the number can be freely configured and combined. Preferably, by configuring N forward current winding bridge arms and N reverse current winding bridge arms, the current flowing into the shared bridge arm can be minimized, thereby reducing its current stress.

[0009] Furthermore, each forward current winding arm includes a first controllable switch S. 1a The second controllable switch S 2a Negative-level freewheeling unidirectional conduction device D 1a Zero-level freewheeling unidirectional conduction device D 2a S 1a The first terminal is connected to the positive terminal of the power supply, S 1a The second end, S 2a The first end, D 2a The cathode, S, and the other two are connected. 2a The second end serves as the midpoint of the bridge arm and D 1a The cathode and the first end of the winding are connected together, D 1a The anode of D is connected to the negative terminal of the power supply. 2a The anode is connected to the midpoint of the common bridge arm.

[0010] Furthermore, each forward current winding arm has three operating modes, including: the first mode, S... 1a S 2a All are activated; second mode, S 1a Shutdown, S 2a Activation; Third mode, S 1a S 2a All are turned off.

[0011] The first mode is the charging mode, where the midpoint of the bridge arm is connected to the positive terminal of the power supply, and the forward current increases.

[0012] The second mode is the freewheeling mode, where the midpoint of the bridge arm remains at zero potential, and the winding is turned on by the zero-level freewheeling unidirectional conduction device D. 2a Continuous streaming;

[0013] The third mode is the discharge mode, where the midpoint of the bridge arm is connected to the negative terminal of the power supply, and the positive current decreases.

[0014] By adjusting the duty cycle of the three modes, the forward current of the winding can be controlled.

[0015] Furthermore, each reverse current winding arm includes a first controllable switch S. 1b The second controllable switch S 2b Positive level freewheeling unidirectional conduction device D 1b Zero-level freewheeling unidirectional conduction device D 2b ;D1b The cathode is connected to the positive terminal of the power supply, S 1b The first end is used as the midpoint of the bridge arm and D 1b The anode and the first end of the winding are connected together, S 1b The second end, D 2b anode, S 2b The first three ends are connected, S 2b The second terminal is connected to the negative terminal of the power supply, D 2b The cathode is connected to the midpoint of the common bridge arm.

[0016] Furthermore, each reverse current winding arm has three operating modes, including: the fourth mode, S... 1b S 2b All are activated; fifth mode, S 1b Activate, S 2b Shutdown; sixth mode, S 1b S 2b All are turned off.

[0017] The fourth mode is the charging mode, where the midpoint of the bridge arm is connected to the negative terminal of the power supply, and the reverse current increases.

[0018] The fifth mode is the freewheeling mode, where the midpoint of the bridge arm remains at zero potential, and the winding is turned on by the zero-level freewheeling unidirectional conduction device D. 2b Continuous streaming;

[0019] The sixth mode is the discharge mode, where the midpoint of the bridge arm is connected to the positive terminal of the power supply, and the reverse current decreases.

[0020] By adjusting the duty cycle of the three modes, reverse current control of the winding can be achieved.

[0021] Furthermore, the shared bridge arm includes a first controllable switch S 1cm The second controllable switch S 2cm The third controllable switch S 3cm The fourth controllable switch S 4cm Four anti-parallel unidirectional conduction devices D 1cm D 2cm D 3cm D 4cm A capacitor; S 1cm The first terminal is connected to the positive terminal of the power supply, S 1cm The second terminal, the first terminal of the capacitor, S 2cm The first three ends are connected, S 2cm The second end serves as the midpoint of the bridge arm and is connected to the second ends of all 2N windings, S 3cm The first three ends are connected, S 3cm The second terminal, the second terminal of the capacitor, S 4cm The first three ends are connected, S 4cmThe second end of the switch is connected to the negative terminal of the power supply. The first end of each of the four controllable switches is connected to the cathode of one of the unidirectional conducting devices. The second end of each of the four controllable switches is connected to the anode of one of the unidirectional conducting devices.

[0022] Furthermore, the shared bridge arm has two operating modes, including: the seventh mode, S... 1cm S 3cm On, S 2cm S 4cm Off; eighth mode, S 1cm S 3cm Shutdown, S 2cm S 4cm Conduction.

[0023] When in the seventh mode, the voltage at the midpoint of the common arm is V. dc / 2-V cap When in the eighth mode, the voltage at the midpoint of the common arm is V. dc / 2+V cap V dc It is the DC power supply voltage, V cap This is the capacitor voltage of the common bridge arm. For the current flowing into the midpoint of the common bridge arm, the seventh mode discharges the capacitor, and the eighth mode charges it. By adjusting the duty cycle of these two modes, the capacitor voltage can be controlled at a constant V. dc / 2, thereby keeping the voltage at the midpoint of the common bridge arm at zero potential.

[0024] Preferably, any one of the controllable switches is an insulated gate bipolar transistor (IGBT), the first terminal of the controllable switch is the collector of the IGBT, the second terminal of the controllable switch is the emitter of the IGBT, and the conduction time of the IGBT is controlled by changing its gate control signal.

[0025] Preferably, any of the unidirectional conducting devices is a diode.

[0026] On the other hand, the aforementioned three-level control device for the reverse current common bridge arm of a magnetic levitation bearing experiences continuous high-frequency changes in the direction of the current flowing into the common bridge arm, making it difficult to control the midpoint potential of the common bridge arm. Therefore, this invention provides an adaptive hysteresis common bridge arm midpoint potential control method, comprising:

[0027] (1) The initial state of the shared bridge arm is set to either the seventh or eighth mode;

[0028] (2) Calculate the judgment conditions for state switching in each control cycle, including: hysteresis width condition, error sign condition, and differential sign condition;

[0029] (3) Generate mode switching criteria based on the above three sub-conditions;

[0030] (4) Determine whether the shared bridge arm has switched from the current mode to another working mode based on the mode switching criterion;

[0031] Furthermore, the hysteresis width condition is:

[0032]

[0033] Where V dc V is the DC power supply voltage. cap For the shared bridge arm capacitor voltage, V* is the configurable hysteresis bandwidth, and P1 is the hysteresis width condition;

[0034] The error sign condition is:

[0035]

[0036] Where V cap (k-1) is the common arm capacitor voltage of the previous control cycle, and P2 is the error sign condition;

[0037] The difference sign condition is:

[0038]

[0039] Where V cap (k-2) is the common arm capacitor voltage two cycles ago, and P3 is the differential sign condition;

[0040] Furthermore, the mode switching criterion is generated as follows: Mode Criterion When the modality criterion is 1, it indicates that the working mode needs to be switched; otherwise, it remains unchanged.

[0041] Compared with the prior art, the above-described technical solutions conceived in this invention can achieve the following results.

[0042] Beneficial effects:

[0043] 1. The reverse current common bridge arm three-level power electronic controller proposed in this invention can be applied to heavy-duty magnetic levitation bearings. This controller can withstand a larger DC bus voltage, enabling the magnetic bearing controller to operate at a higher voltage, thereby effectively improving the current response speed of the magnetic levitation bearing. It has higher anti-interference performance in the face of large external mechanical disturbances. At the same time, the voltage stress of the switching devices is smaller, and the output current ripple is smaller.

[0044] 2. The reverse current common-arm three-level power electronic controller proposed in this invention realizes active control of the three-level midpoint potential by utilizing the flying capacitor bridge arm. At the same time, the flying capacitor bridge arm is reused as the common bridge arm of the winding, which effectively reduces the number of switching devices in the controller and saves costs.

[0045] 3. The adaptive hysteresis common arm midpoint potential control method proposed in this invention can effectively solve the problem of common arm midpoint potential control caused by the continuous high-frequency change of the current direction flowing into the common arm, and improve the control accuracy of the midpoint potential. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the topology of the reverse current common bridge arm three-level controller for magnetic levitation bearings provided by the present invention;

[0047] Figure 2 This is a schematic diagram of the three operating modes of each forward current winding arm;

[0048] Figure 3 This is a schematic diagram of the three operating modes of each reverse current winding arm;

[0049] Figure 4 These are schematic diagrams of two working modes of the shared bridge arm;

[0050] Figure 5 This is a flowchart of an adaptive hysteresis common arm midpoint potential control method provided by the present invention;

[0051] Figure 6 This is a waveform diagram of the forward current winding bridge arm during operation.

[0052] Figure 7 This is a waveform diagram of the reverse current winding bridge arm during operation.

[0053] Figure 8 This is a waveform diagram of the operation process of the common bridge arm. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0055] This invention provides a reverse current common bridge arm three-level control device for magnetic levitation bearings, comprising: 2N winding bridge arms, a common bridge arm, 2N windings, and a power supply; wherein N is the number of degrees of freedom of the multi-axis magnetic levitation bearing;

[0056] The midpoint of each winding bridge arm is connected to the first end of a winding, and the second ends of all 2N windings are connected to the midpoint of a common bridge arm.

[0057] The common bridge arm is used to provide a constant zero-midpoint potential for the winding bridge arm and works with the winding bridge arm to control the winding current.

[0058] Furthermore, the 2N winding bridge arms include two types: forward current winding bridge arms and reverse current winding bridge arms, and their numbers can be freely configured and combined. Preferably, by configuring N forward current winding bridge arms and N reverse current winding bridge arms, the current flowing into the shared bridge arm can be minimized, reducing its current stress. Figure 1 This is a specific implementation example of this configuration.

[0059] Furthermore, each forward current winding arm includes a first controllable switch S. 1a The second controllable switch S 2a Negative-level freewheeling unidirectional conduction device D 1a Zero-level freewheeling unidirectional conduction device D 2a S 1a The first terminal is connected to the positive terminal of the power supply, S 1a The second end, S 2a The first end, D 2a The cathode, S, and the other two are connected. 2a The second end serves as the midpoint of the bridge arm and D 1a The cathode and the first end of the winding are connected together, D 1a The anode of D is connected to the negative terminal of the power supply. 2a The anode is connected to the midpoint of the common bridge arm.

[0060] Furthermore, Figure 2 The three operating modes of each forward current winding arm are shown, including: the first mode, S... 1a S 2a All are activated; second mode, S 1a Shutdown, S 2a Activation; Third mode, S 1a S 2a All are turned off.

[0061] The first mode is the charging mode, where the midpoint of the bridge arm is connected to the positive terminal of the power supply, and the forward current increases.

[0062] The second mode is the freewheeling mode, where the midpoint of the bridge arm remains at zero potential, and the winding is turned on by the zero-level freewheeling unidirectional conduction device D. 2a Continuous streaming;

[0063] The third mode is the discharge mode, where the midpoint of the bridge arm is connected to the negative terminal of the power supply, and the positive current decreases.

[0064] By adjusting the duty cycle of the three modes, the forward current of the winding can be controlled.

[0065] Furthermore, each reverse current winding arm includes a first controllable switch S. 1b The second controllable switch S 2b Positive level freewheeling unidirectional conduction device D 1b Zero-level freewheeling unidirectional conduction device D 2b ;D 1b The cathode is connected to the positive terminal of the power supply, S 1b The first end is used as the midpoint of the bridge arm and D 1b The anode and the first end of the winding are connected together, S 1b The second end, D 2b anode, S 2b The first three ends are connected, S 2b The second terminal is connected to the negative terminal of the power supply, D 2b The cathode is connected to the midpoint of the common bridge arm.

[0066] Furthermore, Figure 3 The diagram illustrates three operating modes for each reverse current winding arm, including: a fourth mode, S... 1b S 2b All are activated; fifth mode, S 1b Activate, S 2b Shutdown; sixth mode, S 1b S 2b All are turned off.

[0067] The fourth mode is the charging mode, where the midpoint of the bridge arm is connected to the negative terminal of the power supply, and the reverse current increases.

[0068] The fifth mode is the freewheeling mode, where the midpoint of the bridge arm remains at zero potential, and the winding is turned on by the zero-level freewheeling unidirectional conduction device D. 2b Continuous streaming;

[0069] The sixth mode is the discharge mode, where the midpoint of the bridge arm is connected to the positive terminal of the power supply, and the reverse current decreases.

[0070] By adjusting the duty cycle of the three modes, reverse current control of the winding can be achieved.

[0071] Furthermore, the shared bridge arm includes a first controllable switch S 1cm The second controllable switch S 2cm The third controllable switch S 3cm The fourth controllable switch S 4cm Four anti-parallel unidirectional conduction devices D 1cm D 2cm D 3cm D4cm A capacitor; S 1cm The first terminal is connected to the positive terminal of the power supply, S 1cm The second terminal, the first terminal of the capacitor, S 2cm The first three ends are connected, S 2cm The second end serves as the midpoint of the bridge arm and is connected to the second ends of all 2N windings, S 3cm The first three ends are connected, S 3cm The second terminal, the second terminal of the capacitor, S 4cm The first three ends are connected, S 4cm The second end of the switch is connected to the negative terminal of the power supply. The first end of each of the four controllable switches is connected to the cathode of one of the unidirectional conducting devices. The second end of each of the four controllable switches is connected to the anode of one of the unidirectional conducting devices.

[0072] Furthermore, Figure 4 Two operating modes of the shared bridge arm are demonstrated, including: the seventh mode, S... 1cm S 3cm On, S 2cm S 4cm Off; eighth mode, S 1cm S 3cm Shutdown, S 2cm S 4cm Conduction.

[0073] When in the seventh mode, the voltage at the midpoint of the common arm is V. dc / 2-V cap When in the eighth mode, the voltage at the midpoint of the common arm is V. dc / 2+V cap V dc It is the DC power supply voltage, V cap This is the capacitor voltage of the common bridge arm. For the current flowing into the midpoint of the common bridge arm, the seventh mode discharges the capacitor, and the eighth mode charges it. By adjusting the duty cycle of these two modes, the capacitor voltage can be controlled at a constant V. dc / 2, thereby keeping the voltage at the midpoint of the common bridge arm at zero potential.

[0074] Preferably, any one of the controllable switches is an insulated gate bipolar transistor (IGBT), the first terminal of the controllable switch is the collector of the IGBT, the second terminal of the controllable switch is the emitter of the IGBT, and the conduction time of the IGBT is controlled by changing its gate control signal.

[0075] Preferably, any of the unidirectional conducting devices is a diode.

[0076] Figure 5The flowchart of an adaptive hysteresis common arm midpoint potential control method provided by the present invention addresses the problem of difficulty in controlling the midpoint potential of the common arm in the aforementioned reverse current common arm three-level control device, where the direction of the current flowing into the common arm changes continuously at high frequency. The method includes the following four steps:

[0077] (1) The initial state of the shared bridge arm is set to either the seventh or eighth mode;

[0078] (2) Calculate the judgment conditions for state switching in each control cycle, including: hysteresis width condition, error sign condition, and differential sign condition;

[0079] (3) Generate mode switching criteria based on the above three sub-conditions;

[0080] (4) Determine whether the shared bridge arm has switched from the current mode to another working mode based on the mode switching criterion;

[0081] Furthermore, the hysteresis width condition is:

[0082]

[0083] Where V dc V is the DC power supply voltage. cap For the shared bridge arm capacitor voltage, V* is the configurable hysteresis bandwidth, and P1 is the hysteresis width condition;

[0084] The error sign condition is:

[0085]

[0086] Where V cap (k-1) is the common arm capacitor voltage of the previous control cycle, and P2 is the error sign condition;

[0087] The difference sign condition is:

[0088]

[0089] Where V cap (k-2) is the common arm capacitor voltage two cycles ago, and P3 is the differential sign condition;

[0090] Furthermore, the mode switching criterion is generated as follows: Modal Criterion When the modality criterion is 1, it indicates that the working mode needs to be switched; otherwise, it remains unchanged.

[0091] Figure 6 This is a waveform diagram of the forward current winding bridge arm operation process. When S 1a and S 2aWhen both are simultaneously conducting, the midpoint potential of the bridge arm is the positive DC bus voltage, and the forward current increases; when S... 1a Shutdown, S 2a When the circuit is on, the voltage at the midpoint of the bridge arm is zero, the winding freewheels through the diode, and the current remains constant; when S... 1a and S 2a When all are turned off, the bridge arm potential is the negative DC bus voltage, and the forward current decreases; the forward current winding bridge arm switches frequently between the three working modes to achieve control of the winding current.

[0092] Figure 7 This is a waveform diagram of the reverse current winding bridge arm during operation. When S 1b and S 2b When both are simultaneously conducting, the midpoint potential of the bridge arm is the negative DC bus voltage, and the winding current increases; when S 1b On, S 2b When turned off, the voltage at the midpoint of the bridge arm is zero, the winding freewheels through the diode, and the current remains constant; when S 1b and S 2b When all are turned off, the bridge arm potential is the positive DC bus voltage, and the winding current decreases; the reverse current winding bridge arm switches frequently between the three operating modes to achieve control of the winding current.

[0093] Figure 8 The waveform diagram shows the common arm operating process. The current flowing into the midpoint varies frequently within a large amplitude range, making capacitor voltage control difficult. The adaptive hysteresis common arm midpoint potential control method proposed in this invention can control the capacitor voltage to approximately half of the DC bus voltage, with smaller fluctuations. During operation, S... 1cm and S 2cm The gate pulse complementarity enables the common arm to switch between the two operating modes mentioned above, thereby achieving capacitor voltage control.

[0094] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A control method for a three-level power electronic controller of a magnetic levitation bearing, the three-level power electronic controller comprising: 2 N One winding bridge arm, one shared bridge arm, 2 N One winding, power supply; Where N represents the degrees of freedom of the multi-axis magnetic levitation bearing; the midpoint of each winding bridge arm is connected to the first end of a winding, and all 2 N The second end of each winding is connected to the midpoint of a common bridge arm; the common bridge arm is used to provide a constant zero-midpoint potential for the winding bridge arm and cooperates with the winding bridge arm to control the winding current; characterized in that, 2 N Each winding bridge arm includes N One positive current winding bridge arm and N A reverse current winding bridge arm; the common bridge arm includes a first controllable switch. S 1cm Second controllable switch S 2cm The third controllable switch S 3cm The fourth controllable switch S 4cm Four anti-parallel unidirectional conduction devices D 1cm , D 2cm , D 3cm , D 4cm One capacitor; S 1cm The first terminal is connected to the positive terminal of the power supply. S 1cm The second terminal, the first terminal of the capacitor, S 2cm The first three ends are connected. S 2cm The second end serves as the midpoint of the bridge arm and connects with all 2 N The second end of each winding, S 3cm The first three ends are connected. S 3cm The second terminal, the second terminal of the capacitor S 4cm The first three ends are connected. S 4cm The second terminal is connected to the negative terminal of the power supply. The first terminals of the four controllable switches are each connected to the cathode of one of the unidirectional conducting devices, and the second terminals of the four controllable switches are each connected to the anode of one of the unidirectional conducting devices. The common bridge arm has two operating modes, including: the seventh mode. S 1cm , S 3cm Conductive, S 2cm , S 4cm Shutdown; eighth mode, S 1cm , S 3cm Turn off, S 2cm , S 4cm Conduction; When in the seventh mode, the voltage at the midpoint of the common arm is V dc / 2- V cap When in the eighth mode, the voltage at the midpoint of the common arm is V dc / 2+ V cap ,in V dc It is the DC power supply voltage. V cap This refers to the capacitor voltage of the common bridge arm. For the current flowing into the midpoint of the common bridge arm, the seventh mode discharges the capacitor, and the eighth mode charges it. By adjusting the duty cycle of these two modes, the capacitor voltage is kept constant. V dc / 2, thereby keeping the voltage at the midpoint of the common bridge arm at zero potential; including: (1) The initial state of the shared bridge arm is set to either the seventh or eighth mode; (2) The judgment conditions for state switching are calculated for each control cycle, including: hysteresis width condition, error sign condition, and difference sign condition; the hysteresis width condition is: in V dc This is the DC power supply voltage. V cap To share the bridge arm capacitor voltage, V * indicates configurable hysteresis bandwidth. P 1 represents the hysteresis width condition; The error sign condition is: in This is the voltage of the common bridge arm capacitor from the previous control cycle. P 2 is the error sign condition; The difference sign condition is: in This is the voltage of the shared bridge arm capacitor two cycles ago. P 3 is the difference sign condition; The mode switching criterion is generated as follows: Mode Criterion When the modality criterion is 1, it indicates that the working mode needs to be switched; otherwise, it remains unchanged. (3) Generate mode switching criteria based on the above three sub-conditions; (4) Determine whether the shared bridge arm has switched from the current mode to another working mode based on the mode switching criterion.

2. The control method as described in claim 1, characterized in that, Each forward current winding arm includes a first controllable switch. S 1a Second controllable switch S 2a Negative-level freewheeling unidirectional conduction device D 1a Zero-level freewheeling unidirectional conduction device D 2a ; S 1a The first terminal is connected to the positive terminal of the power supply. S 1a The second end S 2a The first end D 2a The cathode, the three are connected. S 2a The second end serves as the midpoint of the bridge arm and D 1a The cathode and the first end of the winding are connected together. D 1a The anode is connected to the negative terminal of the power supply. D 2a The anode is connected to the midpoint of the common bridge arm.

3. The control method as described in claim 2, characterized in that, Each forward current winding arm has three operating modes, including: the first mode, S 1a , S 2a All are operational; second mode, S 1a Shut down S 2a Activation; Third Mode S 1a , S 2a All are turned off; The first mode is the charging mode, where the midpoint of the bridge arm is connected to the positive terminal of the power supply, and the forward current increases. The second mode is the freewheeling mode, where the midpoint of the bridge arm remains at zero potential, and the winding is turned on by a zero-level freewheeling unidirectional conduction device. D 2a Continuous streaming; The third mode is the discharge mode, where the midpoint of the bridge arm is connected to the negative terminal of the power supply, and the positive current decreases. By adjusting the duty cycle of the three modes, the forward current of the winding can be controlled.

4. The control method as described in claim 1, characterized in that, Each reverse current winding arm includes a first controllable switch. S 1b Second controllable switch S 2b Positive level freewheeling unidirectional conduction device D 1b Zero-level freewheeling unidirectional conduction device D 2b ; D 1b The cathode is connected to the positive terminal of the power supply. S 1b The first end is used as the midpoint of the bridge arm and D 1b The anode and the first end of the winding are connected together. S 1b The second end D 2b anode, S 2b The first three ends are connected. S 2b The second terminal is connected to the negative terminal of the power supply. D 2b The cathode is connected to the midpoint of the common bridge arm.

5. The control method as described in claim 4, characterized in that, Each reverse current winding arm has three operating modes, including: a fourth mode. S 1b , S 2b All are operational; fifth mode, S 1b Open S 2b Shutdown; sixth mode, S 1b , S 2b All are turned off; The fourth mode is the charging mode, where the midpoint of the bridge arm is connected to the negative terminal of the power supply, and the reverse current increases. The fifth mode is the freewheeling mode, where the midpoint of the bridge arm remains at zero potential, and the winding is turned on by a zero-level freewheeling unidirectional conduction device. D 2b Continuous streaming; The sixth mode is the discharge mode, where the midpoint of the bridge arm is connected to the positive terminal of the power supply, and the reverse current decreases. By adjusting the duty cycle of the three modes, reverse current control of the winding can be achieved.

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