An electrolytic capacitor-less power converter for permanent magnet synchronous motor and a control method thereof

Abstract

The application provides a non-electrolytic capacitor power converter for a permanent magnet synchronous motor and a control method thereof. The power converter comprises a rectifier circuit, a power decoupling circuit and a three-phase inverter bridge which are connected in series. The power decoupling circuit comprises a Boost converter and a pulsating power buffer circuit, and the output ends of the two circuits are connected in series with a small-capacity film capacitor of different values to form a DC bus of the non-electrolytic capacitor power converter. The Boost converter is used for controlling power quality of a power grid, and the output capacitor voltage contains DC and AC components. The pulsating power buffer circuit controls pulsating power of the power grid, realizes complementary voltage of the film capacitors of different values, and effectively suppresses DC bus voltage pulsation. In addition, the non-electrolytic capacitor power converter improves DC bus voltage gain and widens the speed range of the permanent magnet synchronous motor.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology and relates to a capacitorless power converter and a DC bus voltage complementary control method. Background Technology

[0002] Permanent magnet synchronous motors (PMSMs) boast advantages such as high efficiency, high power density, high starting torque, and high overload capacity, making them widely used in aerospace, defense, industrial and agricultural production, and daily life. To achieve high-performance operation, large-capacity electrolytic capacitors are required in parallel with the DC bus of the motor drive system to maintain stable bus voltage. However, the short lifespan and poor thermal stability of electrolytic capacitors are the main reasons for the persistently high failure rate of drive systems.

[0003] Electrolytic capacitor-free drive systems replace large-capacity electrolytic capacitors with small-capacity, high-reliability film capacitors, significantly improving the reliability of the drive system and representing one of the current development directions for motor drive systems. However, due to the substantial reduction in decoupling capacitors (only about one-tenth of that in traditional systems), the pulsating power of the power grid causes periodic fluctuations in the bus voltage of electrolytic capacitor-free drive systems. This not only increases the harmonic content of the grid current but also amplifies the motor torque pulsation. More seriously, under dynamic operating conditions, the bus voltage of electrolytic capacitor-free drive systems experiences severe drops or rises, leading to a significant decrease in key performance characteristics such as drive system response speed and torque pulsation. In severe cases, the system may even fail to operate normally.

[0004] To address the aforementioned issues, researchers proposed two solutions. One is to apply control strategies such as field weakening control, virtual impedance control, and harmonic injection to electrolytic capacitor-free drive systems. While this approach results in stable motor speeds and grid quality that meets harmonic standards for grid-connected equipment, such as IEC61000-3-2, the motor's torque ripple and noise are significant because it absorbs some of the grid's pulsating power. Furthermore, the poor dynamic performance and resistance to external disturbances inherent in electrolytic capacitor-free drive systems remain a prominent drawback.

[0005] The second solution is to introduce an active power decoupling circuit into the capacitor-free drive system. Compared to the first solution, this approach further reduces bus voltage ripple and improves the dynamic performance of the drive system. However, compared to traditional drive systems, the DC bus voltage fluctuation problem in capacitor-free drive systems under dynamic conditions remains prominent, limiting the dynamic response capability of capacitor-free drive systems and restricting their application in high-performance applications. Therefore, it is urgent to design an active power decoupling circuit that can effectively stabilize the DC bus voltage under both dynamic and steady-state conditions to achieve high-performance operation of capacitor-free drive systems. Summary of the Invention

[0006] This invention addresses the problems of the second type of electrolytic capacitor-free drive system by proposing a novel electrolytic capacitor-voltage complementary electrolytic capacitor-free power converter. While improving the reliability of the drive system, it can significantly suppress DC bus voltage ripple of the drive system under steady-state and dynamic operating conditions, effectively improve the response speed of the drive system, reduce torque ripple, and achieve a comprehensive improvement in grid power and motor performance of the electrolytic capacitor-free drive system.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A novel electrolytic capacitor-free power converter for a permanent magnet synchronous motor drive system includes a rectifier circuit, an active power decoupling circuit, a three-phase inverter, and a permanent magnet synchronous motor (PMSM) connected in sequence. The active power decoupling circuit consists of a boost converter and a pulsating energy buffer circuit. The unequal-value small-capacity thin-film output capacitors of the active power decoupling circuit are connected in series to form the DC bus of the electrolytic capacitor-free power converter. The positive terminal of the first capacitor (C1) and the negative terminal of the second capacitor (C2) are defined as the DC bus.

[0009] Furthermore, the input terminal of the rectifier circuit is connected to the power grid, the positive terminal of the rectifier circuit output is connected to the positive terminal of the active power decoupling circuit input, and the negative terminal of the rectifier circuit output is connected to the negative terminal of the active power decoupling circuit. The positive terminal of the active power decoupling circuit output is connected to the positive terminal of the DC bus, and the negative terminal of the active power decoupling circuit output is connected to the negative terminal of the DC bus. The positive terminal of the DC bus is connected to the positive terminal of the three-phase inverter input, and the negative terminal of the DC bus is connected to the negative terminal of the three-phase inverter input. The output terminal of the three-phase inverter is connected to the three-phase winding of the permanent magnet synchronous motor (PMSM).

[0010] Furthermore, the rectifier circuit is composed of diodes D1 to D4 forming a single-phase rectifier circuit; the active power decoupling circuit is composed of a first inductor (L1), a second inductor (L2), a first capacitor (C1), a second capacitor (C2), a fifth diode (D5), a sixth diode (D6), a first switch (S1), and a second switch (S2); the three-phase motor inverter is composed of power devices T1 to T6. The positive output of the rectifier circuit unit is connected to one end of the first inductor (L1), and the negative output of the rectifier circuit unit is simultaneously connected to the source of the first switch (S1), the source of the second switch (S2), the negative terminal of the first capacitor (C1), and the negative input of the three-phase inverter bridge. The drain of the first switch (S1) is connected to the other end of the first inductor (L1) and the anode of the fifth diode (D5). The cathode of the fifth diode (D5) is connected to the positive terminal of the first capacitor (C1), the negative terminal of the second capacitor (C2), and one end of the second inductor (L2). The other end of the second inductor (L2) is connected to the drain of the second switch (S2) and the anode of the sixth diode (D6). The negative terminal of the sixth diode (D6) is connected to the positive terminal of the second capacitor (C2) and simultaneously connected to the positive input of the three-phase inverter bridge.

[0011] Furthermore, the DC bus is composed of a first capacitor (C1) and a second capacitor (C2) connected in series; the voltage of the first capacitor (C1) consists of a DC component and a ripple component, and the voltage of the second capacitor (C2) consists of a DC component and a ripple component; the ripple component of the voltage of the first capacitor (C1) and the ripple component of the voltage of the second capacitor (C2) are controlled by an active power decoupling circuit to complement each other and eliminate the ripple voltage of the DC bus; both the first capacitor (C1) and the second capacitor (C2) are small-capacity thin-film capacitors.

[0012] Furthermore, the current of the first inductor (L1) is controlled by the first switching transistor (S1), and the input current of the drive system is controlled to follow the phase change of the grid voltage, so as to achieve high power factor and low current harmonic operation of the drive system.

[0013] Furthermore, the first switch (S1) controls the average voltage of the first capacitor (C1), and the second switch (S1) controls the voltage of the second capacitor (C2) to complement the ripple voltage component of the first capacitor (C1), thereby eliminating DC bus voltage fluctuations.

[0014] The present invention discloses a novel electrolytic capacitor-free power converter control method for a permanent magnet synchronous motor drive system, comprising the following steps:

[0015] When the first switch (S1) is in the ON state: when the first capacitor (C1) and the second capacitor (C2) are connected in series, the DC bus voltage u dcWhen the voltage exceeds the set voltage, the second switch (S2) is turned on, and the first capacitor (C1), the second inductor (L2), and the second switch (S2) form a closed loop. The first capacitor (C1) releases energy to the second inductor (L2), and the voltage of the second capacitor (C1) drops. At this time, the first capacitor (C1) and the second capacitor (C2) provide energy to the motor through the three-phase inverter. The voltage of the second capacitor (C2) drops, and the DC bus voltage drops.

[0016] When the DC voltage u across the first capacitor (C1) and the second capacitor (C2) dc When the voltage is less than the set voltage, the second switch (S2) is turned off, the second inductor (L2) releases energy to the second capacitor (C2), and the voltage of the second capacitor (C2) rises accordingly. The first capacitor (C1) and the second capacitor (C2) supply energy to the permanent magnet synchronous motor through the three-phase inverter, and the voltage of the first capacitor (C1) drops accordingly.

[0017] By using the second switch (S2) to control the complementary voltages of the first capacitor (C1) and the second capacitor (C2), bus voltage ripple suppression can be achieved.

[0018] When the first switch (S1) is in the off state: when the DC voltage u across the first capacitor (C1) and the second capacitor (C2) is... dc When the voltage is greater than the set voltage, the second switch (S2) is turned on, the first inductor (L1) releases energy to the first capacitor (C1), the first capacitor (C1) releases energy to the second inductor (L2), and the voltage of the first capacitor (C1) rises. At this time, the first capacitor (C1) and the second capacitor (C2) provide energy to the motor through the three-phase inverter, and the voltage of the second capacitor (C2) drops accordingly.

[0019] When the DC voltage u across the first capacitor (C1) and the second capacitor (C2) dc When the voltage is less than the set voltage, the first inductor (L1) releases energy to the first capacitor (C1), and the voltage of the first capacitor (C1) rises accordingly; when the second switch (S2) is turned off, the second inductor (L2) releases energy to the second capacitor (C2), and the voltage of the second capacitor (C2) rises accordingly. The first capacitor (C1) and the second capacitor (C2) supply energy to the permanent magnet synchronous motor through the three-phase inverter, and the bus voltage drops.

[0020] By using the second switch (S2) to control the complementary voltage ripple components of the first capacitor (C1) and the second capacitor (C2), bus voltage pulsation suppression is achieved.

[0021] By adopting the above technical solution, this invention proposes an electrolytic capacitor-free power converter where the control of grid power quality and bus voltage ripple suppression are independent. This not only effectively suppresses DC bus voltage fluctuations under dynamic operating conditions but also reduces the design complexity of the controller. Furthermore, the electrolytic capacitor-free power converter proposed in this invention can achieve higher DC bus voltage gain, which helps improve the power density of the drive system and expand the power rating and speed range of the permanent magnet synchronous motor.

[0022] By controlling the complementary voltages of the two capacitors through a pulsating power buffer circuit, DC bus voltage pulsation is suppressed, laying the foundation for high-performance operation of the permanent magnet synchronous motor. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a small capacitor drive system based on a novel power decoupling circuit proposed in this invention;

[0024] Figure 2 yes Figure 1 Schematic diagram of the working principle when the first switch is turned on and the second switch is turned on;

[0025] Figure 3 yes Figure 1 Schematic diagram of the working principle when the first switch is turned on and the second switch is turned off;

[0026] Figure 4 yes Figure 1 Working principle diagram when the first switch transistor is turned off and the second switch transistor is turned off;

[0027] Figure 5 yes Figure 1 Schematic diagram of the working principle when the first switch is turned off and the second switch is turned on;

[0028] Figure 6 This is a block diagram of the control strategy for the active power decoupling circuit proposed in this invention. (a) Grid current power factor correction control strategy; (b) DC link voltage stabilization control strategy;

[0029] Table 1 shows the power device control logic of the active power decoupling circuit proposed in this invention. Detailed Implementation

[0030] The following description, in conjunction with the accompanying drawings and examples, provides a more detailed description of the specific embodiments of the novel electrolytic capacitor-free power converter of the present invention.

[0031] This invention discloses a novel electrolytic capacitor-free power converter for a permanent magnet synchronous motor drive system, comprising a diode rectifier, a novel active power decoupling circuit, and a three-phase motor inverter. Based on a small-capacity thin-film voltage-complementary active power decoupling circuit, it controls the absorption and release of grid pulsating power according to the difference between grid power and motor power, significantly improving the flexibility in handling grid pulsating power. Replacing traditional large-capacity electrolytic capacitors, it effectively eliminates the shortcomings of traditional drive systems such as poor reliability and short lifespan, while significantly reducing DC bus voltage fluctuations, achieving high-performance operation of the motor under both steady-state and dynamic conditions. On the grid side, the active buffer circuit can control the grid output current to track grid voltage changes, exhibiting a power factor of approximately 1 and low total current harmonic content. On the motor side, the active power decoupling circuit significantly improves the lifespan and reliability of the drive system and effectively reduces DC bus voltage fluctuations, thereby achieving motor dynamic and static operating performance essentially consistent with traditional drive systems.

[0032] The rectifier circuit unit A, the novel active power decoupling circuit B, and the three-phase inverter unit C described in this invention together constitute a power converter for a capacitor-free drive system. The input terminal of rectifier circuit unit A is connected to the power grid. The positive output terminal of rectifier circuit unit is connected to one end of the first inductor (L1). The negative output terminal of rectifier circuit unit is simultaneously connected to the source of the first switching transistor (S1), the source of the second switching transistor (S2), the negative terminal of the first capacitor (C1), and the negative input terminal of the three-phase inverter bridge. The drain of the first switching transistor (S1) is connected to the other end of the first inductor (L1) and the anode of the fifth diode (D5). The cathode of the fifth diode (D5) is connected to the positive terminal of the first capacitor (C1), the negative terminal of the second capacitor (C2), and one end of the second inductor (L2). The other end of the second inductor (L2) is connected to the drain of the second switching transistor (S2) and the anode of the sixth diode (D6). The negative terminal of the sixth diode (D6) is connected to the positive terminal of the second capacitor (C2) and simultaneously connected to the positive input terminal of the three-phase inverter bridge. The output terminal of the three-phase inverter C is connected to the three-phase windings of the permanent magnet synchronous motor.

[0033] As attached Figure 1 As shown, the novel active power decoupling circuit of the present invention comprises: a first inductor (L1), a second inductor (L2), a first capacitor (C1) (film capacitor), a second capacitor (C2) (film capacitor), a fifth diode (D5), a sixth diode (D6), and a first switch (S1) and a second switch (S2). The first inductor (L1), under the action of the first switch (S1), controls the grid output current, achieving high power factor and low current harmonic operation of the drive system. The second inductor (L2), under the action of the second switch (S2), controls the current i. L2This allows for the control of the voltage across the second capacitor (C2), making the voltage across the second capacitor (C2) complementary to the voltage across the first capacitor (C1), thereby suppressing DC bus voltage ripple.

[0034] The main control objectives of the small-capacitor active power decoupling circuit described in this invention are to control the grid current and suppress DC bus voltage fluctuations, thereby achieving high-performance operation of the motor under both dynamic and steady-state conditions. The specific implementation process of this invention is as follows:

[0035] The steps to achieve control objective one are: adopt a dual-loop control strategy with an outer loop for DC bus voltage and an inner loop for grid current. Specifically, the process is as follows: first, the DC bus voltage is sampled and obtained; then, it is subtracted from the DC bus voltage setpoint, and the input current error value ΔI is obtained by a PI controller. g The input current reference value is obtained by dividing the motor power by the bus voltage. The input current error value ΔI obtained above g Calculations are performed to obtain the average grid current through a PI controller, and multiply it by the grid phase to obtain the grid reference operating current. Then, this current and the feedback current error from the first inductor (L1) are used by the PI controller to generate a modulation signal, which is compared with a high-frequency triangular wave to generate the control signal for the first switch (S1). When the first switch (S1) is turned on, the current in the first inductor (L1) increases; when the first switch (S1) is turned off, the current in the first inductor (L1) decreases. Therefore, by controlling the first switch (S1), the power quality of the grid can be controlled.

[0036] Table 1

[0037]

[0038] The steps to achieve control objective two are as follows: Specific working states and controls are detailed in the appendix. Figures 2-6 As shown in Table 1, Appendix Figures 2-6 These are the four modes within one operating cycle of the electrolytic capacitor-free power converter.

[0039] Figure 2 Mode 1: Both the first switch (S1) and the second switch (S2) are turned on. The power grid releases energy to the first inductor (L1), increasing the current in the first inductor (L1) and storing the grid's pulsating power. The first capacitor (C1), the second inductor (L2), and the second switch (S2) form a circuit. The first capacitor (C1) releases energy to the second inductor (L2), and the second inductor (L2) stores energy to control the voltage of the second capacitor (C2) in subsequent stages. In this mode, the first capacitor (C1) and the second capacitor (C2) are connected in series to provide energy to the motor through the three-phase inverter. The DC bus voltage decreases, and when the DC bus voltage reaches the set minimum voltage, the second switch (S2) is turned off.

[0040] Figure 3 Mode 2: The first switch (S1) is on, and the second switch (S2) is off. The power grid releases energy to the first inductor (L1), causing the current in the first inductor (L1) to continue increasing and storing more grid ripple power. The second inductor (L2), through the sixth diode (D6), releases the energy stored in Mode 1 to the second capacitor (C2), causing the current in the second inductor (L2) to decrease. In this mode, the voltage across the second capacitor (C2) increases due to the absorption of energy from the second inductor (L2). Simultaneously, since the first capacitor (C1) continues to release energy to the motor, the voltage across the first capacitor (C1) continues to decrease. Theoretically, when the voltages of the first capacitor (C1) and the second capacitor (C2) are complementary, there is no voltage ripple on the DC bus voltage. When the current of the first inductor (L1) exceeds the grid reference operating current, the first switch (S1) is turned off.

[0041] Figure 4 Mode 3: Both the first switch (S1) and the second switch (S2) are off. The power grid and the first inductor (L1) are connected in series to supply power to the first capacitor (C1). The current in the first inductor (L1) decreases, the first capacitor (C1) absorbs the pulsating power from the power grid, and the voltage of the first capacitor (C1) increases. In this mode, the second inductor (L2) still releases the energy stored in Mode 1 to the second capacitor (C2) through the sixth diode (D6). The current in the second inductor (L2) decreases, and the voltage of the second capacitor (C2) increases. When the current in the first inductor (L1) is greater than the power grid reference operating current, the first switch (S1) is off. When the DC bus voltage is higher than the set maximum voltage, the second switch (S2) is on.

[0042] Figure 5 Mode 4: The first switch (S1) is off, and the second switch (S2) is on. The power grid and the first inductor (L1) are connected in series to supply power to the first capacitor (C1). The current in the first inductor (L1) continues to decrease, and the voltage across the first capacitor (C1) further increases. The second inductor (L2) no longer supplies power to the second capacitor (C2), and the first capacitor (C1) releases energy to the second inductor (L2), causing the voltage across the second capacitor (C2) to drop. When the current in the first inductor (L1) exceeds the reference operating current of the power grid, the first switch (S1) turns on.

[0043] In summary, this novel electrolytic capacitor-free power converter utilizes an active power decoupling circuit to replace large-capacity electrolytic capacitors in absorbing grid pulsating power, significantly improving the reliability and lifespan of the motor drive system. The power decoupling circuit is connected in series between the traditional diode rectifier and the DC bus of the drive system. The DC bus voltage is provided by two small-capacity thin-film capacitors with complementary voltages, increasing the bus voltage gain and significantly reducing DC bus pulsation. Based on the complementary cancellation principle, the instantaneous current control strategy rapidly and accurately controls the instantaneous voltage changes of the decoupling capacitors according to the drive system's operating conditions, significantly reducing bus voltage pulsation under various conditions and enabling high-performance operation of the motor drive system under both steady-state and dynamic conditions. The decoupling of grid power quality control and DC bus voltage pulsation suppression based on the small-capacitor active power decoupling circuit effectively reduces the complexity of the system controller, achieving high-performance motor operation while meeting relevant grid power quality harmonic standards.

Claims

1. A novel electrolytic capacitor-free power converter for a permanent magnet synchronous motor drive system, characterized in that: It includes a rectifier circuit, an active power decoupling circuit, a three-phase inverter, and a permanent magnet synchronous motor (PMSM) connected in sequence; the active power decoupling circuit consists of a boost converter and a pulsating energy buffer circuit, and the unequal-value small-capacity thin-film output capacitors of the above active power decoupling circuit are connected in series to form the DC bus of the electrolytic capacitor-free power converter; the positive terminal of the first capacitor (C1) and the negative terminal of the second capacitor (C2) are defined as the DC bus; The input terminal of the rectifier circuit is connected to the power grid. The positive terminal of the rectifier circuit output is connected to the positive terminal of the active power decoupling circuit input, and the negative terminal of the rectifier circuit output is connected to the negative terminal of the active power decoupling circuit. The positive terminal of the active power decoupling circuit output is connected to the positive terminal of the DC bus, and the negative terminal of the active power decoupling circuit output is connected to the negative terminal of the DC bus. The positive terminal of the DC bus is connected to the positive terminal of the three-phase inverter input, and the negative terminal of the DC bus is connected to the negative terminal of the three-phase inverter input. The output terminal of the three-phase inverter is connected to the three-phase winding of the permanent magnet synchronous motor (PMSM). The rectifier circuit consists of diodes D1 to D4 forming a single-phase rectifier circuit; the active power decoupling circuit consists of a first inductor (L1), a second inductor (L2), a first capacitor (C1), a second capacitor (C2), a fifth diode (D5), a sixth diode (D6), and a first switch (S1) and a second switch (S2); the three-phase inverter consists of power devices T1 to T6. The positive output terminal of the rectifier circuit is connected to one end of the first inductor (L1), and the negative output terminal of the rectifier circuit is connected to both the source of the first switch (S1) and the second switch (S2). The source, the negative terminal of the first capacitor (C1), and the negative input terminal of the three-phase inverter bridge are connected; the drain of the first switch (S1) is connected to the other end of the first inductor (L1) and the anode of the fifth diode (D5); the cathode of the fifth diode (D5) is connected to the positive terminal of the first capacitor (C1), the negative terminal of the second capacitor (C2), and one end of the second inductor (L2); the other end of the second inductor (L2) is connected to the drain of the second switch (S2) and the anode of the sixth diode (D6); the negative terminal of the sixth diode (D6) is connected to the positive terminal of the second capacitor (C2) and simultaneously connected to the positive input terminal of the three-phase inverter bridge.

2. The novel electrolytic capacitor-free power converter for a permanent magnet synchronous motor drive system according to claim 1, characterized in that: The DC bus is composed of a first capacitor (C1) and a second capacitor (C2) connected in series. The voltage of the first capacitor (C1) consists of a DC component and a ripple component, and the voltage of the second capacitor (C2) consists of a DC component and a ripple component. The ripple component of the voltage of the first capacitor (C1) and the ripple component of the voltage of the second capacitor (C2) are controlled by an active power decoupling circuit to complement each other and eliminate the ripple voltage of the DC bus. Both the first capacitor (C1) and the second capacitor (C2) are small-capacity thin-film capacitors.

3. A novel electrolytic capacitor-free power converter for a permanent magnet synchronous motor drive system according to claim 1, characterized in that: The first switch (S1) controls the current of the first inductor (L1), and at the same time controls the input current of the drive system to follow the phase change of the grid voltage, so as to achieve high power factor and low current harmonic operation of the drive system.

4. A novel electrolytic capacitor-free power converter for a permanent magnet synchronous motor drive system according to claim 1, characterized in that: The first switch (S1) controls the average voltage of the first capacitor (C1), and the second switch (S2) controls the voltage of the second capacitor (C2) to complement the ripple voltage component of the first capacitor (C1), thereby eliminating DC bus voltage fluctuations.

5. A novel electrolytic capacitor-free power control method for a permanent magnet synchronous motor drive system, which employs the converter as described in claim 1, characterized in that: Includes the following steps: When the first switch (S1) is in the ON state: when the first capacitor (C1) and the second capacitor (C2) are connected in series, the DC bus voltage is... When the voltage exceeds the set voltage, the second switch (S2) is turned on, and the first capacitor (C1), the second inductor (L2), and the second switch (S2) form a closed loop. The first capacitor (C1) releases energy to the second inductor (L2), and the voltage of the first capacitor (C1) drops. At this time, the first capacitor (C1) and the second capacitor (C2) provide energy to the motor through the three-phase inverter. The voltage of the second capacitor (C2) drops, and the DC bus voltage drops. When the DC voltage across the first capacitor (C1) and the second capacitor (C2) When the voltage is less than the set voltage, the second switch (S2) is turned off, the second inductor (L2) releases energy to the second capacitor (C2), and the voltage of the second capacitor (C2) rises accordingly. The first capacitor (C1) and the second capacitor (C2) supply energy to the permanent magnet synchronous motor through the three-phase inverter, and the voltage of the first capacitor (C1) drops accordingly. By using the second switch (S2) to control the complementary voltages of the first capacitor (C1) and the second capacitor (C2), bus voltage ripple suppression can be achieved. When the first switch (S1) is in the off state: when the DC voltage across the first capacitor (C1) and the second capacitor (C2) is... When the voltage is greater than the set voltage, the second switch (S2) is turned on, the first inductor (L1) releases energy to the first capacitor (C1), the first capacitor (C1) releases energy to the second inductor (L2), and the voltage of the first capacitor (C1) rises. At this time, the first capacitor (C1) and the second capacitor (C2) provide energy to the motor through the three-phase inverter, and the voltage of the second capacitor (C2) drops accordingly. When the DC voltage across the first capacitor (C1) and the second capacitor (C2) When the voltage is less than the set voltage, the first inductor (L1) releases energy to the first capacitor (C1), and the voltage of the first capacitor (C1) rises accordingly; when the second switch (S2) is turned off, the second inductor (L2) releases energy to the second capacitor (C2), and the voltage of the second capacitor (C2) rises accordingly. The first capacitor (C1) and the second capacitor (C2) supply energy to the permanent magnet synchronous motor through the three-phase inverter, and the bus voltage drops. By using the second switch (S2) to control the complementary voltage ripple components of the first capacitor (C1) and the second capacitor (C2), bus voltage pulsation suppression is achieved.

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