A power conversion device and control method of NPC topology

Abstract

The application provides a power conversion device of an NPC topology and a control method, and relates to the technical field of power electronics. The device comprises a three-phase NPC three-level inverter, a first switch, a second switch, a controller, a first-phase bridge arm output end connected with a first-phase output end, a second-phase bridge arm output end connected with a second-phase output end through the first switch, and a third-phase bridge arm output end connected with a third-phase output end. When the first switch connects the second-phase bridge arm output end with a zero line and the second switch is off, the first-phase bridge arm, the second-phase bridge arm and the third-phase bridge arm output a first alternating voltage, a second alternating voltage and a third alternating voltage respectively, a target single-phase output voltage is output from between the third-phase output end and the zero line, the amplitudes of the third alternating voltage and the second alternating voltage are equal, the phases are 180 degrees apart, and the first alternating voltage is equal to 0. The technical scheme of the application improves the stability of the single-phase output voltage of the NPC three-level topology inverter.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a power conversion device and control method of an NPC topology structure. Background Art

[0002] With the rapid advancement of power electronics technology, the demand for electronic devices in modern industry, transportation, healthcare, communications, and other fields is trending towards diversification and integration. This trend has not only driven the rapid development of electronic devices but also raised higher standards for power and current requirements. In particular, in applications with high voltage, high power, and high harmonic requirements, the NPC (Neutral Point Clamped) three-level topology has demonstrated its unique advantages and application value in inverter products. As an advanced power electronics technology, the NPC three-level topology's greatest feature is its ability to achieve efficient and stable energy conversion under high voltage and high power conditions. By introducing neutral point clamping technology, this topology effectively addresses the bottleneck problem of traditional inverters in high-voltage applications, enabling stable operation over a wider voltage range. However, single-phase output NPC three-level topology inverters can be affected by various factors during operation, such as grid voltage fluctuations and load changes. This can lead to large voltage fluctuations in single-phase output, resulting in poor stability. This not only shortens the life of the capacitors but also has a direct impact on the quality of the output power. It can be seen that the single-phase output voltage of the NPC three-level topology inverter in the related art has the problem of poor stability.

[0003] With respect to the technical problem of poor stability of single-phase output voltage existing in the related art, no effective solution has been proposed so far. Summary of the Invention

[0004] The present application provides a power conversion device and control method with an NPC topology structure, so as to at least solve the technical problem of poor stability of single-phase output voltage existing in the related art.

[0005] In a first aspect, the present application provides an NPC topology power conversion device, comprising: a three-phase NPC three-level inverter, a first switch, a second switch, and a controller, wherein the input end of the three-phase NPC three-level inverter is connected to a DC power supply, the first-phase bridge arm output end of the three-phase NPC three-level inverter is connected to the first-phase output end, the second-phase bridge arm output end of the three-phase NPC three-level inverter is connected to the second-phase output end through the first switch, and the third-phase bridge arm output end of the three-phase NPC three-level inverter is connected to the third-phase output end, wherein the first switch is configured to allow the second-phase bridge arm output end to be connected to the second-phase output end or the second-phase bridge arm output end to be connected to the neutral line output end, and the neutral line output end is connected to the midpoint potential end of the three-phase NPC three-level inverter through the second switch; the controller is connected to each of the three-phase NPC three-level inverters. Each power switching device in the phase bridge arm is connected, and the controller is also connected to the first switch and the second switch respectively, wherein the controller is used to control the on and off of each power switching device in each phase bridge arm so that each phase bridge arm outputs a different AC voltage, and the controller is used to control the on and off of the first switch and the second switch; when the first switch is set to connect the second phase bridge arm output end with the neutral line output end, and the second switch is disconnected, the controller uses SPWM technology to control the first phase bridge arm output end to output the first AC voltage, control the second phase bridge arm to output the second AC voltage, and control the third phase bridge arm to output the third AC voltage, so that the target single-phase output voltage is output between the third phase output end and the neutral line output end, wherein the amplitude of the third AC voltage and the second AC voltage are equal, and the phase difference is 180 degrees, and the first AC voltage is equal to 0.

[0006] By adopting the above technical solution, the power conversion device with an NPC topology structure includes a three-phase NPC three-level inverter, that is, it includes three-phase bridge arms, and the output end of each phase bridge arm corresponds to a phase output end of the AC voltage. For example, the output end of the first phase bridge arm corresponds to the first phase output end, the output end of the second phase bridge arm corresponds to the second phase output end, and the output end of the third phase bridge arm corresponds to the third phase output end, wherein a first switch is provided between the output end of the second phase bridge arm and the second phase output end. The first switch can connect the output end of the second phase bridge arm to the second phase output end, and can also connect the output end of the second phase bridge arm to the neutral line output end. The neutral line output end is connected to the midpoint potential end of the three-phase NPC three-level inverter through the second switch. When the first switch is turned to the neutral line output end and the second switch is disconnected, the controller uses SPWM (sinusoidal pulse width modulation) technology to control the switching state of each power switching device in each phase bridge arm, so that the first phase bridge arm output end outputs a first AC voltage, the second phase bridge arm output end outputs a second AC voltage, and the third phase bridge arm output end outputs a third AC voltage. Since the amplitudes of the third AC voltage and the second AC voltage are equal and the phase difference is 180 degrees, the target single-phase output voltage obtained between the third phase output end and the neutral line output end can overcome the problems of large bus capacitor current ripple and bus voltage imbalance in related technologies, which lead to large fluctuations in the single-phase output voltage, thereby achieving the effect of improving the stability of the single-phase output voltage of the NPC three-level topology inverter. Using a three-phase NPC three-level inverter, each phase bridge arm can be independently controlled, which helps to more accurately adjust the output voltage waveform and reduce harmonics and ripple. The controller is connected to each power switch device in each phase bridge arm of the inverter, as well as the first switch and the second switch, and can accurately control their on and off. This precise control helps to reduce current ripple and voltage imbalance. The use of SPWM technology can generate a high-quality AC voltage waveform, reduce harmonic content, and thus reduce the current ripple on the bus capacitor. The controller makes the AC voltage amplitude of the third and second phase outputs equal and the phase difference is 180 degrees, while the voltage of the first phase output is 0. This control strategy may help to offset current ripple because the currents of the second and third phases can offset each other in certain periods, thereby reducing the impact on the bus capacitor. The NPC topology power conversion device in this technical solution solves the problems of large bus capacitor current ripple and bus voltage imbalance in NPC topology single-phase output through a specific switch configuration and control strategy, thereby improving system stability and power quality.

[0007] Optionally, the first switch is a single-pole double-throw switch, the fixed end of the first switch is connected to the second phase bridge arm output end, the first moving end of the first switch is connected to the second phase output end, and the second moving end of the first switch is connected to the neutral line output end.

[0008] By adopting the above technical solution, the first switch is a single-pole double-throw switch. The controller can control the first switch to switch two different circuit paths, one is the path between the second-phase bridge arm output terminal and the second-phase output terminal, and the other is the path between the second-phase bridge arm output terminal and the neutral line output terminal. The single-pole double-throw switch provides more connection options, enabling the system to adapt to different loads and grid conditions, thereby enhancing the adaptability and flexibility of the system.

[0009] Optionally, the controller controls the first phase bridge arm, the second phase bridge arm and the third phase bridge arm to output the following AC voltages respectively: U1=0, Among them, U1 represents the first AC voltage, U2 represents the second AC voltage, U3 represents the third AC voltage, U M represents the preset voltage amplitude of the target single-phase output voltage, and ω represents the angular frequency of the target single-phase output voltage.

[0010] By adopting the above technical solution and precisely controlling each power switch device in each phase bridge arm, the first phase bridge arm, the second phase bridge arm, and the third phase bridge arm each output the above-mentioned specific AC voltage waveform. Because the AC voltage waveforms output by the second phase bridge arm and the third phase bridge arm have equal amplitudes and a phase difference of 180 degrees, the problems of large bus capacitor current ripple and unbalanced bus capacitor voltage in the NPC three-level inverter can be effectively overcome, thereby achieving the effect of improving the stability of the power conversion device with an NPC topology.

[0011] Optionally, when the first switch is set to connect the second phase bridge arm output terminal with the second phase output terminal and the second switch is closed, the controller controls the first phase bridge arm output terminal to output a fourth AC voltage, controls the second phase bridge arm to output a fifth AC voltage, and controls the third phase bridge arm to output a sixth AC voltage, so that the target three-phase output voltage is output from the first phase output terminal, the second phase output terminal, and the third phase output terminal; wherein the amplitudes of the fourth AC voltage, the fifth AC voltage, and the sixth AC voltage are equal, and the phase difference between the three is 120 degrees.

[0012] By adopting the above technical solution, when the first switch is turned to the second phase output terminal, that is, the path between the second phase bridge arm output terminal and the second phase output terminal is connected, and the second switch is closed, that is, the neutral line output terminal is connected to the midpoint potential terminal of the three-phase NPC three-level inverter, the NPC topology power conversion device can output the target three-phase output voltage, wherein the amplitude of the AC voltage output by each phase is equal and the phase difference is 120 degrees. By precisely controlling the output voltages of the first, second and third phase bridge arms (i.e., the fourth, fifth and sixth AC voltages), ensuring that they have equal amplitudes and a phase difference of 120 degrees between each other, a high-quality three-phase output voltage is achieved. This is crucial for situations requiring a stable and balanced three-phase power supply. The NPC topology structure in the related art generally can only directly output three-phase voltage, but cannot output single-phase voltage, or the output single-phase output voltage fluctuates greatly. The NPC topology power conversion device in the present technical solution can output both three-phase output voltage and single-phase output voltage.

[0013] Optionally, the controller controls the first phase bridge arm, the second phase bridge arm, and the third phase bridge arm to output the following AC voltages respectively: U5=U M Sin(ωt), Among them, U4 represents the fourth AC voltage, U5 represents the fifth AC voltage, U6 represents the sixth AC voltage, U M represents the preset voltage amplitude of the target three-phase output voltage, and ω represents the angular frequency of the target three-phase output voltage.

[0014] By adopting the above technical solution and precisely controlling each power switching device in each phase bridge arm, the first phase bridge arm, the second phase bridge arm, and the third phase bridge arm respectively output the above-mentioned specific AC voltage waveform. Since the AC voltage waveforms output by the first phase bridge arm, the second phase bridge arm, and the third phase bridge arm have equal amplitudes and a phase difference of 120 degrees, a high-quality three-phase output voltage is achieved.

[0015] Optionally, the first phase bridge arm comprises a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a first diode and a second diode, wherein the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are connected in series, the first end of the first switch tube is connected with the positive pole of the input DC power supply, the second end of the fourth switch tube is connected with the negative pole of the input DC power supply, the connection point of the first switch tube and the second switch tube is connected with the negative pole of the first diode, the positive pole of the first diode is connected with the negative pole of the second diode, the connection point of the third switch tube and the fourth switch tube is connected with the positive pole of the second diode, and the connection point of the second switch tube and the third switch tube serves as the output end of the first phase bridge arm; the second phase bridge arm comprises a fifth switch tube, a sixth switch tube, a seventh switch tube, an eighth switch tube, a third diode and a fourth diode, wherein the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube are connected in series, the first end of the fifth switch tube is connected with the positive pole of the input DC power supply, the second end of the eighth switch tube is connected with the negative pole of the input DC power supply, the connection point of the fifth switch tube and the sixth switch tube is connected with the negative pole of the third diode, the positive pole of the third diode is connected with the negative pole of the fourth diode, the connection point of the seventh switch tube and the eighth switch tube is connected with the positive pole of the fourth diode, and the connection point of the sixth switch tube and the seventh switch tube serves as the output end of the second phase bridge arm; the third phase bridge arm comprises a ninth switch tube, a tenth switch tube, an eleventh switch tube, a twelfth switch tube, a fifth diode and a sixth diode, wherein the ninth switch tube, the tenth switch tube, the eleventh switch tube and the twelfth switch tube are connected in series, the first end of the ninth switch tube is connected with the positive pole of the input DC power supply, the second end of the twelfth switch tube is connected with the negative pole of the input DC power supply, the connection point of the ninth switch tube and the tenth switch tube is connected with the negative pole of the fifth diode, the positive pole of the fifth diode is connected with the negative pole of the sixth diode, the connection point of the eleventh switch tube and the twelfth switch tube is connected with the positive pole of the sixth diode, and the connection point of the tenth switch tube and the eleventh switch tube serves as the output end of the third phase bridge arm; the three-phase NPC three-level inverter further comprises a first capacitor and a second capacitor, wherein the first capacitor and the second capacitor are connected in series and then connected in parallel to the input DC power supply, the connection point of the first capacitor and the second capacitor serves as the midpoint potential end, the positive pole of the first diode, the positive pole of the third diode and the positive pole of the fifth diode are all connected with the midpoint potential end; the third end of each of the first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube, the seventh switch tube, the eighth switch tube, the ninth switch tube, the tenth switch tube, the eleventh switch tube and the twelfth switch tube serves as the control end and is connected with the controller.

[0016] By adopting the above technical solution, the structure of a three-phase NPC three-level inverter is described in detail. Specifically, the first phase bridge arm includes a first switching tube, a second switching tube, a third switching tube, and a fourth switching tube connected in series, and a first diode and a second diode connected between the connection between the first and second switching tubes and the connection between the third and fourth switching tubes. In addition, the first end of the first switching tube is connected to the positive electrode of the input DC power supply, the second end of the fourth switching tube is connected to the negative electrode of the input DC power supply, and the connection between the second and third switching tubes serves as the output end of the first phase bridge arm. The second and third phase bridge arms have similar structures to the first phase bridge arm. The device also includes a first capacitor and a second capacitor, which can be referred to as bus capacitors. They are connected in series and then connected in parallel to the two ends of the input DC power supply. The connection between the first and second capacitors serves as the midpoint potential terminal, and the positive electrode of the first diode is connected to the midpoint potential terminal. The controller uses SPWM technology to independently control the switching state of the switching tubes in each phase bridge arm. When the first AC voltage output from the output end of the first bridge arm is controlled to be 0, the amplitude of the second AC voltage and the third AC voltage are equal and the phase difference is 180 degrees, it can overcome the problems of large bus capacitor current ripple and unbalanced bus voltage in related technologies. In this way, the target single-phase output voltage output from the third phase output end and the neutral line output end is relatively stable.

[0017] Optionally, the first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube, the seventh switch tube, the eighth switch tube, the ninth switch tube, the tenth switch tube, the eleventh switch tube and the twelfth switch tube are all IGBT switching devices, each switch tube has a corresponding freewheeling diode, the positive pole of each freewheeling diode is connected to the second end of the corresponding switch tube, and the negative pole of each freewheeling diode is connected to the first end of the corresponding switch tube.

[0018] By adopting the above technical solution, each switch tube in the three-phase NPC three-level inverter is an IGBT (Insulated Gate Bipolar Transistor) switch device, and a corresponding freewheeling diode is integrated inside each switch tube. By using IGBT switch devices as power switch tubes, due to the advantages of IGBT such as high switching speed and low conduction voltage drop, the power consumption of the system is reduced and the overall efficiency of the inverter is improved. The power conversion device of this NPC topology structure can achieve efficient power conversion and is suitable for various power conversion applications requiring high efficiency and stability. The design of the built-in freewheeling diode effectively prevents voltage spikes and resonance that may be generated during the switching process, reduces the risk of component damage, and improves the long-term operation reliability of the system.

[0019] Optionally, the power conversion device with an NPC topology structure further includes a filter, wherein the filter is connected between the output end of each phase bridge arm and the corresponding phase output end.

[0020] By adopting the above technical solution and providing a filtering circuit between the output end of each phase bridge arm and the corresponding phase output end, these harmonics can be effectively filtered out, thereby improving the purity of the output voltage and current of the power conversion device, solving the harmonic interference problem in the NPC topology power conversion device, improving the power quality, enhancing the system compatibility, and helping to extend the service life of the equipment and the power grid.

[0021] Optionally, the filter includes a first inductor, a second inductor, a third inductor, a third capacitor, a fourth capacitor, and a fifth capacitor, wherein the output end of the first phase bridge arm is connected to the first phase output end through the third inductor, and the fifth capacitor is connected between the first phase output end and the midpoint potential end; the output end of the second phase bridge arm is connected to the first switch through the second inductor, and the fourth capacitor is connected between the connection between the second inductor and the first switch and the midpoint potential end; the output end of the third phase bridge arm is connected to the third phase output end through the first inductor, and the third capacitor is connected between the third phase output end and the midpoint potential end.

[0022] By adopting the above technical solution, an LC filtering circuit is provided between each phase bridge arm output end and the corresponding phase output end, which can filter out harmonics and improve waveform quality, making the power output by the power conversion device purer and more stable. By introducing capacitors (third capacitor, fourth capacitor, fifth capacitor) between the midpoint potential end and each phase output end, these capacitors not only play a filtering role, but also help to balance the midpoint potential and reduce the impact of midpoint potential offset on system performance. The introduction of inductance elements (third inductance, second inductance, first inductance) can effectively suppress the propagation of high-frequency harmonics and further reduce the interference of harmonics on the power grid and other equipment.

[0023] In a second aspect of the present application, a control method for a power conversion device with an NPC topology structure is also provided, which is applied to any of the above-mentioned power conversion devices with an NPC topology structure, comprising: when it is determined that a target single-phase output voltage needs to be output, controlling the first switch to be turned toward the neutral line output terminal, and controlling the second switch to be disconnected; using SPWM technology to control the switching state of each power switching device in each phase bridge arm of a three-phase NPC three-level inverter, so that the output terminal of the first phase bridge arm outputs a first AC voltage, the second phase bridge arm outputs a second AC voltage, and the third phase bridge arm outputs a third AC voltage, wherein the third AC voltage and the second AC voltage have the same amplitude and a phase difference of 180 degrees, and the first AC voltage is equal to 0; and obtaining the target single-phase output voltage between the third phase output terminal and the neutral line output terminal.

[0024] By adopting the technical scheme, the controller controls the first switch to be switched to the zero line output end and controls the second switch to be turned off, then controls the switching state of each power switch device in each phase bridge arm of the three-phase NPC three-level inverter through the SPWM technology, so that the first phase bridge arm output end outputs the first alternating voltage (the value of which is equal to 0), the second phase bridge arm outputs the second alternating voltage, and the third phase bridge arm outputs the third alternating voltage. The third alternating voltage and the second alternating voltage have equal amplitudes and a phase difference of 180 degrees, so that the target single-phase output voltage can be obtained from between the third phase output end and the zero line output end. The technical scheme allows flexible output of a specific single-phase voltage in the power conversion device with the NPC topology, instead of only three-phase voltage, which is very useful in some application scenarios, such as loads or systems that require single-phase power supply.

[0025] In summary, the one or more technical solutions provided in the embodiments of the application have at least the following technical effects or advantages:

[0026] 1. The power conversion device with the NPC topology in the application solves the problems of large bus capacitor current ripple and bus voltage imbalance in NPC topology single-phase output through specific switching configuration and control strategy, improves the stability and power quality of the system;

[0027] 2. By controlling the on-off of the first switch and the second switch, the device can flexibly switch between three-phase output and single-phase output, meet the needs of different application scenarios, and improve the flexibility and adaptability of the system. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a framework diagram of a power conversion device with an NPC topology provided by the embodiments of the application;

[0029] Figure 2 is a control method flow chart of a power conversion device with an NPC topology provided by the embodiments of the application;

[0030] Figure 3 is a circuit schematic diagram of a power conversion device with an NPC topology provided by the embodiments of the application;

[0031] Figure 4 is an example diagram of three-phase output voltage provided by the embodiments of the application;

[0032] Figure 5 is an example diagram of single-phase output voltage provided by the embodiments of the application.

[0033] Explanation of reference signs:

[0034] Q1 - first switching tube, Q2 - second switching tube, Q3 - third switching tube, Q4 - fourth switching tube, Q5 - fifth switching tube, Q6 - sixth switching tube, Q7 - seventh switching tube, Q8 - eighth switching tube, Q9 - ninth switching tube, Q10 - tenth switching tube, Q11 - eleventh switching tube, Q12 - twelfth switching tube, D1 - first diode, D2 - second diode, D3 - third diode, D4 ​​- fourth diode, D5 - fifth diode, D6 - sixth diode, C1 - first capacitor, C2 - second capacitor, C3 - third capacitor, C4 - fourth capacitor, C5 - fifth capacitor, L1 - first inductor, L2 - second inductor, L3 - third inductor, K1 - first switch, K2 - second switch. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this specification will be clearly and completely described below in conjunction with the drawings in the embodiments of this specification. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments.

[0036] In the description of the embodiments of this application, words such as "for example" or "for instance" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as "for example" or "for instance" in the embodiments of this application should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "for example" or "for instance" is intended to present the relevant concepts in a concrete manner.

[0037] In the description of the embodiments of the present application, the term "plurality" means two or more. In addition, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of such features. The terms "include," "comprise," "have" and their variations all mean "including but not limited to," unless otherwise specifically emphasized.

[0038] This application provides a power conversion device with an NPC topology structure, such as Figure 1 As shown, Figure 1This is a framework diagram of an NPC topology power conversion device provided by an embodiment of the present application, the device including: a three-phase NPC three-level inverter, a first switch K1, a second switch K2, and a controller, wherein the input end of the three-phase NPC three-level inverter is connected to a DC power supply, the first-phase bridge arm output end of the three-phase NPC three-level inverter is connected to the first-phase output end, the second-phase bridge arm output end of the three-phase NPC three-level inverter is connected to the second-phase output end through the first switch K1, and the third-phase bridge arm output end of the three-phase NPC three-level inverter is connected to the third-phase output end, wherein the first switch K1 is configured to allow the second-phase bridge arm output end to be connected to the second-phase output end or the second-phase bridge arm output end to be connected to the neutral line output end, and the neutral line output end is connected to the midpoint potential end of the three-phase NPC three-level inverter through the second switch K2; the controller is connected to the three-phase NPC three-level inverter. Each power switching device in each phase bridge arm is connected, and the controller is also connected to the first switch K1 and the second switch K2 respectively, wherein the controller is used to control the on and off of each power switching device in each phase bridge arm so that each phase bridge arm outputs a different AC voltage, and the controller is used to control the on and off of the first switch K1 and the second switch K2; when the first switch K1 is set to connect the output end of the second phase bridge arm with the neutral line output end, and the second switch K2 is disconnected, the controller uses SPWM technology to control the output end of the first phase bridge arm to output the first AC voltage, control the second phase bridge arm to output the second AC voltage, and control the third phase bridge arm to output the third AC voltage, so that the target single-phase output voltage is output between the third phase output end and the neutral line output end, wherein the amplitude of the third AC voltage and the second AC voltage are equal, and the phase difference is 180 degrees, and the first AC voltage is equal to 0.

[0039] In the above embodiment, the power conversion device of the NPC topology structure includes a three-phase NPC three-level inverter, that is, it includes three-phase bridge arms, and the output end of each phase bridge arm corresponds to a phase output end of the AC voltage. For example, the output end of the first phase bridge arm corresponds to the first phase output end, the output end of the second phase bridge arm corresponds to the second phase output end, and the output end of the third phase bridge arm corresponds to the third phase output end. Figure 1As shown, A, B, and C are the first, second, and third phase output terminals, respectively. A, B, and C may correspond to one phase of the three phases U, V, and W in the three-phase alternating current, respectively. N represents the neutral line output terminal, and DC+ and DC- represent the input DC power supply. A first switch K1 is provided between the second-phase bridge arm output terminal and the second-phase output terminal. The first switch K1 can connect the second-phase bridge arm output terminal to the second-phase output terminal, or connect the second-phase bridge arm output terminal to the neutral line output terminal. The neutral line output terminal is connected to the midpoint potential terminal of the three-phase NPC three-level inverter through the second switch K2. When the first switch K1 is turned to the neutral line output end and the second switch K2 is disconnected, the controller uses SPWM (sinusoidal pulse width modulation) technology to control the switching state of each power switch device in each phase bridge arm, so that the first phase bridge arm output end outputs a first AC voltage, the second phase bridge arm output end outputs a second AC voltage, and the third phase bridge arm output end outputs a third AC voltage. Since the amplitudes of the third AC voltage and the second AC voltage are equal and the phase difference is 180 degrees, the target single-phase output voltage obtained between the third phase output end and the neutral line output end can overcome the problems of large bus capacitor current ripple and bus voltage imbalance in related technologies, which lead to large fluctuations in the single-phase output voltage, thereby achieving the effect of improving the stability of the single-phase output voltage of the NPC three-level topology inverter. Using a three-phase NPC three-level inverter, the bridge arm of each phase can be independently controlled, which helps to more accurately adjust the output voltage waveform and reduce harmonics and ripple. The controller is connected to each power switch device in each phase bridge arm of the inverter, as well as the first switch K1 and the second switch K2, and can accurately control their on and off. This precise control helps to reduce current ripple and voltage imbalance. The use of SPWM technology can generate a high-quality AC voltage waveform, reduce harmonic content, and thus reduce the current ripple on the bus capacitor. The controller makes the AC voltage amplitude of the third and second phase outputs equal and the phase difference is 180 degrees, while the voltage output of the first phase is 0. This control strategy may help to offset current ripple because the currents of the second and third phases can offset each other in certain periods, thereby reducing the impact on the bus capacitor. The NPC topology structure in the related art faces the problems of large bus capacitor current ripple and bus voltage imbalance when single-phase output is used. These problems not only affect the life of the capacitor, but also directly affect the quality of the output power. Using PWM control technology to precisely control the switching time of the inverter, reducing output voltage fluctuations and improving system stability can, to a certain extent, solve the problems of large bus capacitor current ripple and bus voltage imbalance, thereby improving system stability and reliability. The NPC topology power conversion device in this application solves the problems of large bus capacitor current ripple and bus voltage imbalance during NPC topology single-phase output through a specific switching configuration and control strategy, thereby improving system stability and power quality.The NPC three-level inverter significantly reduces the harmonic content of the output voltage through multi-level output, making the output voltage waveform closer to a sine wave, improving the power quality, and reducing the impact on the power grid and load. By controlling the on and off of the first switch K1 and the second switch K2, the device can flexibly switch between three-phase output and single-phase output to meet the needs of different application scenarios and improve the flexibility and adaptability of the system. Since the output voltages of the third phase and the second phase are opposite in phase and equal in amplitude, their current components at the zero line output end (i.e., the neutral point) will cancel each other (or mostly cancel each other), thereby reducing the current ripple through the bus capacitor. This is because the bus capacitor mainly plays the role of filtering and stabilizing the DC bus voltage, and the AC component (especially high-frequency harmonics) will cause the current ripple on the capacitor to increase. By controlling the phase and amplitude of the output voltage, the current distribution can be optimized and the ripple can be reduced.

[0040] In an optional embodiment, the first switch K1 is a single-pole double-throw switch, the fixed end of the first switch K1 is connected to the second phase bridge arm output end, the first movable end of the first switch K1 is connected to the second phase output end, and the second movable end of the first switch K1 is connected to the neutral line output end.

[0041] In the above embodiment, the first switch K1 is a single-pole double-throw switch. The controller can control the first switch K1 to switch two different circuit paths, one is the path between the second-phase bridge arm output terminal and the second-phase output terminal, and the other is the path between the second-phase bridge arm output terminal and the neutral line output terminal. The single-pole double-throw switch provides more connection options, enabling the system to adapt to different loads and grid conditions, thereby enhancing the adaptability and flexibility of the system. By introducing a single-pole double-throw switch as the connection point between the second-phase bridge arm and the second-phase output terminal and the neutral line output terminal, the flexibility and controllability of the system are significantly improved. By using a single-pole double-throw switch, the connection mode of the second-phase bridge arm can be flexibly switched according to system requirements, thereby helping to adjust the voltage of each phase and reduce imbalance. The embodiment of the present application can achieve single-phase voltage output in a three-phase system through specific switch control and inverter topology, meet the power requirements of specific application scenarios, and improve the flexibility and efficiency of power conversion.

[0042] In an optional embodiment, the controller controls the first phase bridge arm, the second phase bridge arm and the third phase bridge arm to output the following AC voltages respectively: U1=0, Among them, U1 represents the first AC voltage, U2 represents the second AC voltage, U3 represents the third AC voltage, U M represents the preset voltage amplitude of the target single-phase output voltage, and ω represents the angular frequency of the target single-phase output voltage.

[0043] In the above embodiment, by precisely controlling each power switch in each phase arm, the first, second, and third phase arms each output the aforementioned specific AC voltage waveforms. Since the AC voltage waveforms output by the second and third phase arms are equal in amplitude and 180 degrees out of phase, this effectively overcomes the large bus capacitor current ripple and bus capacitor voltage imbalance issues of the NPC three-level inverter, thereby improving the stability of the NPC topology power conversion device. By precisely controlling the output voltage waveforms of each phase arm (U1 = 0, U2 and U3 are specific sinusoidal waveforms), a single-phase output voltage close to an ideal sine wave can be generated, reducing harmonic content and improving power quality. This allows the NPC three-level inverter to generate a single-phase output voltage without the need for additional equipment (such as a single-phase inverter), enhancing system configuration flexibility and cost-effectiveness. This enables the NPC three-level inverter to output a voltage waveform similar to a single-phase voltage, making it particularly suitable for applications requiring high-quality single-phase output voltages, such as certain single-phase power supply systems and power quality control equipment.

[0044] In an optional embodiment, when the first switch K1 is set to connect the second phase bridge arm output terminal with the second phase output terminal and the second switch K2 is closed, the controller controls the first phase bridge arm output terminal to output a fourth AC voltage, controls the second phase bridge arm to output a fifth AC voltage, and controls the third phase bridge arm to output a sixth AC voltage, so that the target three-phase output voltage is output from the first phase output terminal, the second phase output terminal, and the third phase output terminal; wherein the amplitudes of the fourth AC voltage, the fifth AC voltage, and the sixth AC voltage are equal, and the phase difference between the three is 120 degrees.

[0045] In the above embodiment, when the first switch K1 is switched to the second phase output terminal, that is, the path between the second phase bridge arm output terminal and the second phase output terminal is connected, and the second switch K2 is closed, that is, the neutral line output terminal is connected to the midpoint potential terminal of the three-phase NPC three-level inverter, the NPC topology power conversion device can output the target three-phase output voltage, wherein the AC voltage output of each phase has equal amplitude and a phase difference of 120 degrees. By precisely controlling the output voltages of the first, second, and third phase bridge arms (i.e., the fourth, fifth, and sixth AC voltages), ensuring that they have equal amplitude and a phase difference of 120 degrees, a high-quality three-phase output voltage is achieved. This is crucial for applications requiring a stable and balanced three-phase power supply. NPC topologies in related art generally can only directly output three-phase voltage, but cannot output single-phase voltage, or the output single-phase output voltage fluctuates greatly. When the NPC topology in related art outputs single-phase, this topology faces the problems of large bus capacitor current ripple and unbalanced bus voltage. These problems not only affect the life of the capacitor but also directly affect the quality of the output power. The NPC topology power conversion device in the embodiments of the present application can output both three-phase and single-phase output voltages. Because the output three-phase voltage has a stable amplitude and phase relationship, this helps enhance system stability and reduce system problems caused by voltage imbalance or fluctuations. By precisely controlling the waveform and phase of the output voltage, the harmonic components in the output voltage can be significantly reduced, improving power quality and meeting application scenarios with high power quality requirements. By controlling the on / off states of the first switch K1 and the second switch K2, the embodiment of the present application can flexibly achieve single-phase or three-phase output voltages based on a three-phase NPC three-level inverter. In particular, when a three-phase system needs to be converted to a single-phase system, no additional conversion equipment is required, thereby improving the system's flexibility and integration.

[0046] In an optional embodiment, the controller controls the first phase bridge arm, the second phase bridge arm, and the third phase bridge arm to output the following AC voltages respectively: U5=U M Sin(ωt), Among them, U4 represents the fourth AC voltage, U5 represents the fifth AC voltage, U6 represents the sixth AC voltage, U M represents the preset voltage amplitude of the target three-phase output voltage, and ω represents the angular frequency of the target three-phase output voltage.

[0047] In the above embodiment, by precisely controlling each power switching device in each phase bridge arm, the first phase bridge arm, the second phase bridge arm, and the third phase bridge arm respectively output the above-mentioned specific AC voltage waveform. Since the AC voltage waveforms output by the first phase bridge arm, the second phase bridge arm, and the third phase bridge arm have equal amplitudes and a phase difference of 120 degrees, a high-quality three-phase output voltage is achieved. The balance and stability of the three-phase output voltage help enhance the stability of the entire power conversion device. When the load changes or the power grid fluctuates, the system can restore the balance state more quickly to ensure a continuous and stable power supply. The high-quality three-phase output voltage provides users with a more stable and reliable power supply. In application scenarios such as motor drive and electric transmission, users will be able to experience a smoother and quieter operation, thereby improving the overall user experience.

[0048] In an optional embodiment, if Figure 3As shown, the first phase bridge arm includes: a first switching tube Q1, a second switching tube Q2, a third switching tube Q3, a fourth switching tube Q4, a first diode D1 and a second diode D2, wherein the first switching tube Q1, the second switching tube Q2, the third switching tube Q3 and the fourth switching tube Q4 are connected in series in sequence, the first end of the first switching tube Q1 is connected to the positive electrode of the input DC power supply, the second end of the fourth switching tube Q4 is connected to the negative electrode of the input DC power supply, the connection point between the first switching tube Q1 and the second switching tube Q2 is connected to the negative electrode of the first diode D1, the positive electrode of the first diode D1 is connected to the negative electrode of the second diode D2, and the connection point between the third switching tube Q3 and the fourth switching tube Q4 is connected to the positive electrode of the second diode D2. The connection between the second switch tube Q2 and the third switch tube Q3 serves as the output end of the first phase bridge arm; the second phase bridge arm includes: a fifth switch tube Q5, a sixth switch tube Q6, a seventh switch tube Q7, an eighth switch tube Q8, a third diode D3 and a fourth diode D4, wherein the fifth switch tube Q5, the sixth switch tube Q6, the seventh switch tube Q7 and the eighth switch tube Q8 are connected in series in sequence, the first end of the fifth switch tube Q5 is connected to the positive electrode of the input DC power supply, the second end of the eighth switch tube Q8 is connected to the negative electrode of the input DC power supply, the connection between the fifth switch tube Q5 and the sixth switch tube Q6 is connected to the negative electrode of the third diode D3, the positive electrode of the third diode D3 is connected to the negative electrode of the fourth diode D4, and the seventh switch tube Q8 is connected to the negative electrode of the fourth diode D4. The connection point of the ninth switching tube Q7 and the eighth switching tube Q8 is connected to the anode of the fourth diode D4, and the connection point of the sixth switching tube Q6 and the seventh switching tube Q7 serves as the output end of the second phase bridge arm; the third phase bridge arm includes: a ninth switching tube Q9, a tenth switching tube Q10, an eleventh switching tube Q11, a twelfth switching tube Q12, a fifth diode D5 and a sixth diode D6, wherein the ninth switching tube Q9, the tenth switching tube Q10, the eleventh switching tube Q11 and the twelfth switching tube Q12 are connected in series in sequence, the first end of the ninth switching tube Q9 is connected to the positive electrode of the input DC power supply, the second end of the twelfth switching tube Q12 is connected to the negative electrode of the input DC power supply, and the connection point of the ninth switching tube Q9 and the tenth switching tube Q10 is connected to the negative electrode of the input DC power supply. The cathode of the fifth diode D5 is connected, the anode of the fifth diode D5 is connected to the cathode of the sixth diode D6, the connection point of the eleventh switch tube Q11 and the twelfth switch tube Q12 is connected to the anode of the sixth diode D6, and the connection point of the tenth switch tube Q10 and the eleventh switch tube Q11 serves as the output end of the third phase bridge arm; the three-phase NPC three-level inverter also includes: a first capacitor C1 and a second capacitor C2, wherein the first capacitor C1 and the second capacitor C2 are connected in series and then connected in parallel to the two ends of the input DC power supply, the connection point of the first capacitor C1 and the second capacitor C2 serves as a midpoint potential end, and the anode of the first diode D1, the anode of the third diode D3, and the anode of the fifth diode D5 are all connected to the midpoint potential end;The third terminal of each of the first switching tube Q1, the second switching tube Q2, the third switching tube Q3, the fourth switching tube Q4, the fifth switching tube Q5, the sixth switching tube Q6, the seventh switching tube Q7, the eighth switching tube Q8, the ninth switching tube Q9, the tenth switching tube Q10, the eleventh switching tube Q11, and the twelfth switching tube Q12 is connected to the controller as a control terminal.

[0049] In the above embodiment, the structure of a three-phase NPC three-level inverter is described in detail. Specifically, the first phase bridge arm includes a first switch Q1, a second switch Q2, a third switch Q3, and a fourth switch Q4 connected in series, and a first diode D1 and a second diode D2 connected between the junction of the first and second switches and the junction of the third and fourth switches. In addition, the first end of the first switch Q1 is connected to the positive electrode of the input DC power supply, the second end of the fourth switch Q4 is connected to the negative electrode of the input DC power supply, and the junction between the second switch Q2 and the third switch Q3 serves as the output end of the first phase bridge arm. The second and third phase bridge arms have similar structures to the first phase bridge arm. The device also includes a first capacitor C1 and a second capacitor C2, which can be referred to as bus capacitors. They are connected in series and then connected in parallel across the input DC power supply. The junction of the first capacitor C1 and the second capacitor C2 serves as the midpoint potential terminal, and the anode of the first diode D1 is connected to the midpoint potential terminal. This structure enables the power conversion device to output three-level voltages (positive, zero, and negative), thereby solving the problems of poor output voltage waveform quality and high harmonic content in traditional two-level inverters. By connecting a first capacitor C1 and a second capacitor C2 to the midpoint potential terminal and connecting the positive electrodes of the diodes (such as D1, D3, and D5) connected to the upper half bridge arm in each phase bridge arm to the midpoint potential terminal, the balance of the midpoint potential can be effectively controlled. The stability of the midpoint potential is crucial to the normal operation of the NPC three-level inverter, because the deviation of the midpoint potential can lead to imbalance in the output voltage and increase in harmonics. The controller independently controls the switching state of the switching tubes in each phase bridge arm through SPWM technology. When the first AC voltage outputted from the output terminal of the first bridge arm is controlled to be 0, and the second AC voltage and the third AC voltage have equal amplitudes and a phase difference of 180 degrees, the problems of large bus capacitor current ripple and bus voltage imbalance in the related art can be overcome. In this way, the target single-phase output voltage outputted from the third phase output terminal to the neutral line output terminal is relatively stable.

[0050] In an optional embodiment, if Figure 3As shown, the first switching tube Q1, the second switching tube Q2, the third switching tube Q3, the fourth switching tube Q4, the fifth switching tube Q5, the sixth switching tube Q6, the seventh switching tube Q7, the eighth switching tube Q8, the ninth switching tube Q9, the tenth switching tube Q10, the eleventh switching tube Q11 and the twelfth switching tube Q12 are all IGBT switching devices. Each switching tube has a corresponding freewheeling diode. The anode of each freewheeling diode is connected to the second end of the corresponding switching tube, and the cathode of each freewheeling diode is connected to the first end of the corresponding switching tube.

[0051] In the above embodiment, each switch in the three-phase NPC three-level inverter is an IGBT (Insulated Gate Bipolar Transistor) switch device, and each switch has a corresponding freewheeling diode integrated inside. By using IGBT switch devices as power switches, due to the advantages of IGBT such as high switching speed and low on-state voltage drop, the power consumption of the system is reduced and the overall efficiency of the inverter is improved. The power conversion device of this NPC topology structure can achieve efficient power conversion and is suitable for various power conversion applications requiring high efficiency and stability. The design of the built-in freewheeling diode effectively prevents voltage spikes and resonance that may be generated during the switching process, reduces the risk of component damage, and improves the long-term operation reliability of the system. Using IGBTs as switch tubes in the NPC topology structure can significantly improve the efficiency of power conversion and reduce energy loss. The design of the built-in freewheeling diode allows the current to continue to flow through the freewheeling diode when the switch tube is turned off, avoiding the voltage spikes and resonance problems that may be caused by sudden current interruption, thereby improving the stability and reliability of the system. By integrating the freewheeling diode, the number of external components is reduced, the circuit layout is simplified, and the complexity and cost of the system design are reduced. IGBTs and their built-in freewheeling diodes generally have good thermal management performance, and can maintain a low operating temperature under high-power operating conditions, thereby extending the service life of the device.

[0052] In an optional embodiment, the power conversion device with an NPC topology structure further includes a filter, wherein the filter is connected between the output end of each phase bridge arm and the corresponding phase output end.

[0053] In the above embodiment, by providing a filter circuit between the output end of each phase bridge arm and the corresponding phase output end, these harmonics can be effectively filtered out, thereby improving the purity of the output voltage and current of the power conversion device. The filter can smooth the waveform of the output voltage and current, reduce waveform distortion, and make the output waveform closer to the ideal sine wave or other required waveform, thereby meeting more stringent power quality standards, solving the harmonic interference problem in the NPC topology power conversion device, improving power quality, enhancing system compatibility, and helping to extend the service life of the equipment and the power grid.

[0054] In an optional embodiment, if Figure 3 As shown, the filter includes a first inductor L1, a second inductor L2, a third inductor L3, a third capacitor C3, a fourth capacitor C4, and a fifth capacitor C5, wherein the output end of the first phase bridge arm is connected to the first phase output end through the third inductor L3, and the fifth capacitor C5 is connected between the first phase output end and the midpoint potential end; the output end of the second phase bridge arm is connected to the first switch K1 through the second inductor L2, and the fourth capacitor C4 is connected between the connection between the second inductor L2 and the first switch K1 and the midpoint potential end; the output end of the third phase bridge arm is connected to the third phase output end through the first inductor L1, and the third capacitor C3 is connected between the third phase output end and the midpoint potential end.

[0055] In the above embodiment, an LC filter circuit is provided between each phase bridge arm output terminal and the corresponding phase output terminal to filter out harmonics and improve waveform quality, making the power output of the power conversion device purer and more stable. By introducing capacitors (third capacitor C3, fourth capacitor C4, and fifth capacitor C5) between the midpoint potential terminal and each phase output terminal, these capacitors not only perform filtering functions but also help balance the midpoint potential, reducing the impact of midpoint potential offset on system performance. The introduction of inductors (third inductor L3, second inductor L2, and first inductor L1) can effectively suppress the propagation of high-frequency harmonics, further reducing harmonic interference with the power grid and other equipment. Due to the use of targeted filtering design, the output of each phase can be more effectively filtered, thereby significantly reducing the harmonic content in the output voltage and current and improving power quality. The balance of the midpoint potential is crucial for power conversion devices with NPC topology. By connecting capacitors between the midpoint potential terminal and the phase output terminal, the offset of the midpoint potential can be effectively reduced, improving the stability and reliability of the system. The balance of the midpoint potential is crucial for power conversion devices with NPC topology. Connecting a capacitor between the midpoint potential terminal and the phase output terminal effectively reduces midpoint potential deviation, improving system stability and reliability. Improving filtering and midpoint potential stability can enhance the overall performance of power conversion devices, including higher conversion efficiency, lower energy loss, better dynamic response, and longer service life. Reducing harmonic interference and waveform distortion helps reduce thermal stress on the power grid and electrical equipment, thereby extending the service life of these devices and improving the energy efficiency of the entire power system, as harmonic currents can cause additional energy loss.

[0056] The present application also provides a control method for a power conversion device with an NPC topology structure, which is applied to the power conversion device with the aforementioned NPC topology structure, such as Figure 2 As shown, Figure 2is a control method flow chart of a power conversion device with NPC topology provided by the embodiment of the application, and the flow chart comprises the following steps:

[0057] In step S201, when it is determined that the target single-phase output voltage needs to be output, the first switch is controlled to be switched to the zero line output end, and the second switch is controlled to be turned off.

[0058] In step S202, the SPWM technology is used to control the switching state of each power switch device in each phase arm of the three-phase NPC three-level inverter, so that the first phase arm output end outputs the first alternating voltage, the second phase arm outputs the second alternating voltage, and the third phase arm outputs the third alternating voltage, wherein the amplitude of the third alternating voltage and the second alternating voltage is equal, and the phase difference is 180 degrees, and the first alternating voltage is equal to 0.

[0059] In step S203, the target single-phase output voltage is obtained from the third phase output end and the zero line output end.

[0060] Through the above steps, the controller controls the first switch K1 to be switched to the zero line output end and controls the second switch to be turned off, and then controls the switching state of each power switch device in each phase arm of the three-phase NPC three-level inverter through the SPWM technology, so that the first phase arm output end outputs the first alternating voltage (whose value is equal to 0), the second phase arm outputs the second alternating voltage, and the third phase arm outputs the third alternating voltage. Among them, the amplitude of the third alternating voltage and the second alternating voltage is equal, and the phase difference is 180 degrees, so that the target single-phase output voltage can be obtained from the third phase output end and the zero line output end; through the accurate control of the SPWM technology, the waveform quality of the output voltage can be optimized, the harmonic content can be reduced, and the power quality can be improved. The technical solution allows flexible output of specific single-phase voltage in the power conversion device with NPC topology, not just three-phase voltage, which is very useful in some application scenarios, such as loads or systems that need single-phase power supply. Thus, the application range of the system is expanded, and its flexibility is enhanced. By using the SPWM technology, the waveform of the output voltage is closer to a sine wave, the harmonic content is low, which helps to improve the power quality of the power grid and reduce the interference to other equipment.

[0061] It should be noted that the above described embodiments are only part of the embodiments of the present application, not all the embodiments. The present application will be described in detail below in combination with specific embodiments.

[0062] This application provides an NPC three-level topology single-phase output device and method. The NPC topology single-phase output system mainly consists of a three-phase bridge inverter and a DC power supply. By controlling the switching state of the inverter, the output voltage and current are effectively regulated. The main features of the NPC topology structure are its simple structure, ease of implementation, high voltage utilization and low harmonic content. However, with the continuous development of power systems, NPC topology single-phase output systems also face some challenges, such as output voltage fluctuations, efficiency loss and other problems.

[0063] The purpose of the present invention is to avoid the problems of large bus capacitor current ripple and unbalanced bus voltage when an NPC topology inverter has unidirectional output.

[0064] Figure 3 is a circuit diagram of a power conversion device with an NPC topology structure provided in an embodiment of the present application, such as Figure 3 As shown, K1 is a single-pole double-throw switch and K2 is a single-pole single-throw switch.

[0065] (1) When the output is three-phase, K1 is switched to point a and K2 is closed. At this time, the potentials of points R and U, S and V, T and W, and N0 and N are the same. The waveforms of UN, VN, and WN are sinusoidal waves with a phase difference of 120 degrees, as shown below:

[0066] U VN =U SN0 =U M Sinωt,

[0067]

[0068] The output waveform is as follows Figure 4 As shown, in the above formula, UM represents the preset voltage amplitude, that is, the amplitude of the desired output voltage.

[0069] (2) When UN requires single-phase output, K1 is switched to point b and K2 is disconnected. At this time, S and N are at the same potential. When controlling the output, the phase difference between RN0 and SN0 is set to 180 degrees, the amplitude is half of the set output value, and the output voltage of TN0 is 0.

[0070]

[0071] U TN0 =U WN0 =0,

[0072] The output waveform is as follows Figure 5 shown.

[0073] Through the embodiments of the present application, through specific switch configurations and control strategies, the current and voltage distribution during single-phase output is optimized, thereby reducing the bus capacitor current ripple and solving the problem of bus voltage imbalance. This optimization not only improves the stability of the system, but also extends the life of the capacitor and improves the quality of the output power. The technical effect of the optimized and improved NPC topology single-phase output system in the embodiments of the present application has been significantly improved. First, in terms of stability, the optimized SPWM control technology greatly reduces the output voltage fluctuation and significantly enhances the system stability; secondly, in terms of efficiency, the introduction of advanced power semiconductor devices reduces system power consumption and improves efficiency.

[0074] By optimizing and improving the NPC topology single-phase output system, its technical effectiveness can be significantly enhanced, providing strong support for the stable operation and efficient energy utilization of modern power systems. In the future, with the continuous advancement of science and technology, we expect the NPC topology single-phase output system to play an even greater role in practical applications and make greater contributions to the sustainable development of society.

[0075] Through the description of the above implementation methods, those skilled in the art can clearly understand that the method according to the above embodiment can be implemented by means of software plus the necessary general hardware platform, and of course it can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk), and includes a number of instructions for enabling a terminal device (which can be a mobile phone, computer, server, or network device, etc.) to execute the methods described in each embodiment of the present application.

[0076] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0077] In the several embodiments provided in this application, it should be understood that the disclosed devices can be implemented in other ways. For example, the device embodiments described above are merely schematic, such as the division of units, which is only a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some service interface, and the indirect coupling or communication connection of devices or units can be electrical or other forms.

[0078] Units described as separate components may or may not be physically separate, and components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0079] In addition, the functional units in the various embodiments of the present application may be integrated into a single processing unit, or each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0080] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable memory. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a memory and includes several instructions for enabling a computer device (which can be a personal computer, server or network device, etc.) to execute all or part of the steps of the various embodiments of the present application. The aforementioned memory includes various media that can store program codes, such as USB flash drives, mobile hard drives, magnetic disks or optical disks.

[0081] The foregoing is merely an exemplary embodiment of the present disclosure and is not intended to limit the scope of the present disclosure. In other words, any equivalent variations and modifications made in accordance with the teachings of the present disclosure are still within the scope of the present disclosure. Those skilled in the art will readily conceive of other embodiments of the present disclosure after considering the disclosure in this specification and practice.

[0082] This application is intended to cover any modifications, uses or adaptations of the present disclosure that follow the general principles of the present disclosure and include common knowledge or customary technical means in the technical field not described in the present disclosure.

Claims

1. A power conversion device with an NPC topology, characterized in that: include: Three-phase NPC three-level inverter, first switch, second switch, controller, wherein, The input end of the three-phase NPC three-level inverter is connected to a DC power supply, the first-phase bridge arm output end of the three-phase NPC three-level inverter is connected to the first-phase output end, the second-phase bridge arm output end of the three-phase NPC three-level inverter is connected to the second-phase output end through the first switch, and the third-phase bridge arm output end of the three-phase NPC three-level inverter is connected to the third-phase output end, wherein the first switch is configured to allow the second-phase bridge arm output end to be connected to the second-phase output end or to allow the second-phase bridge arm output end to be connected to the neutral line output end, and the neutral line output end is connected to the midpoint potential end of the three-phase NPC three-level inverter through the second switch; The controller is connected to each power switch device in each phase bridge arm of the three-phase NPC three-level inverter, and the controller is also connected to the first switch and the second switch respectively, wherein the controller is used to control the on and off of each power switch device in each phase bridge arm so that each phase bridge arm outputs a different AC voltage, and the controller is used to control the on and off of the first switch and the second switch; When the first switch is set to connect the second phase bridge arm output terminal to the neutral line output terminal and the second switch is disconnected, the controller uses SPWM technology to control the first phase bridge arm output terminal to output a first AC voltage, controls the second phase bridge arm to output a second AC voltage, and controls the third phase bridge arm to output a third AC voltage, so that a target single-phase output voltage is output between the third phase output terminal and the neutral line output terminal, wherein the third AC voltage and the second AC voltage have the same amplitude and a phase difference of 180 degrees, and the first AC voltage is equal to 0.

2. The power conversion device of the NPC topology structure according to claim 1, characterized in that: The first switch is a single-pole double-throw switch, a fixed end of the first switch is connected to the output end of the second phase bridge arm, a first movable end of the first switch is connected to the second phase output end, and a second movable end of the first switch is connected to the neutral line output end.

3. The power conversion device of the NPC topology structure according to claim 1, characterized in that: The controller controls the first phase bridge arm, the second phase bridge arm, and the third phase bridge arm to respectively output the following AC voltages: U1＝0， Wherein, U1 represents the first AC voltage, U2 represents the second AC voltage, U3 represents the third AC voltage, and U M represents the preset voltage amplitude of the target single-phase output voltage, and ω represents the angular frequency of the target single-phase output voltage.

4. The NPC topology power conversion device according to claim 1, characterized in that: When the first switch is set to connect the second phase bridge arm output terminal with the second phase output terminal and the second switch is closed, the controller controls the first phase bridge arm output terminal to output a fourth AC voltage, controls the second phase bridge arm to output a fifth AC voltage, and controls the third phase bridge arm to output a sixth AC voltage, so that the target three-phase output voltage is output from the first phase output terminal, the second phase output terminal, and the third phase output terminal; wherein the amplitudes of the fourth AC voltage, the fifth AC voltage, and the sixth AC voltage are equal, and the phase difference between the three is 120 degrees.

5. The power conversion device of the NPC topology structure according to claim 4, characterized in that: The controller controls the first phase bridge arm, the second phase bridge arm, and the third phase bridge arm to respectively output the following AC voltages: U5=U M That(ωt), Wherein, U4 represents the fourth AC voltage, U5 represents the fifth AC voltage, U6 represents the sixth AC voltage, and U M represents the preset voltage amplitude of the target three-phase output voltage, and ω represents the angular frequency of the target three-phase output voltage.

6. The NPC topology power conversion device according to claim 1, characterized in that: The first phase bridge arm includes: a first switching transistor, a second switching transistor, a third switching transistor, a fourth switching transistor, a first diode, and a second diode, wherein the first switching transistor, the second switching transistor, the third switching transistor, and the fourth switching transistor are connected in series in sequence, a first end of the first switching transistor is connected to the positive electrode of an input DC power supply, a second end of the fourth switching transistor is connected to the negative electrode of the input DC power supply, a connection point between the first switching transistor and the second switching transistor is connected to the negative electrode of the first diode, an anode of the first diode is connected to the negative electrode of the second diode, a connection point between the third switching transistor and the fourth switching transistor is connected to the positive electrode of the second diode, and a connection point between the second switching transistor and the third switching transistor serves as an output end of the first phase bridge arm; The second-phase bridge arm includes: a fifth switching transistor, a sixth switching transistor, a seventh switching transistor, an eighth switching transistor, a third diode, and a fourth diode, wherein the fifth switching transistor, the sixth switching transistor, the seventh switching transistor, and the eighth switching transistor are connected in series in sequence, a first end of the fifth switching transistor is connected to the positive electrode of the input DC power supply, a second end of the eighth switching transistor is connected to the negative electrode of the input DC power supply, a connection point between the fifth and sixth switching transistors is connected to the negative electrode of the third diode, an anode of the third diode is connected to the negative electrode of the fourth diode, a connection point between the seventh and eighth switching transistors is connected to the positive electrode of the fourth diode, and a connection point between the sixth and seventh switching transistors serves as an output end of the second-phase bridge arm; The third phase bridge arm includes: a ninth switching tube, a tenth switching tube, an eleventh switching tube, a twelfth switching tube, a fifth diode, and a sixth diode, wherein the ninth switching tube, the tenth switching tube, the eleventh switching tube, and the twelfth switching tube are connected in series in sequence, a first end of the ninth switching tube is connected to the positive electrode of the input DC power supply, a second end of the twelfth switching tube is connected to the negative electrode of the input DC power supply, a connection point between the ninth switching tube and the tenth switching tube is connected to the negative electrode of the fifth diode, an anode of the fifth diode is connected to the negative electrode of the sixth diode, a connection point between the eleventh switching tube and the twelfth switching tube is connected to the positive electrode of the sixth diode, and a connection point between the tenth switching tube and the eleventh switching tube serves as an output end of the third phase bridge arm; The three-phase NPC three-level inverter further includes: a first capacitor and a second capacitor, wherein the first capacitor and the second capacitor are connected in series and then connected in parallel to both ends of the input DC power supply, the connection point between the first capacitor and the second capacitor serves as the midpoint potential terminal, and the anode of the first diode, the anode of the third diode, and the anode of the fifth diode are all connected to the midpoint potential terminal; A third end of each of the first switching tube, the second switching tube, the third switching tube, the fourth switching tube, the fifth switching tube, the sixth switching tube, the seventh switching tube, the eighth switching tube, the ninth switching tube, the tenth switching tube, the eleventh switching tube and the twelfth switching tube is connected to the controller as a control end.

7. The NPC topology power conversion device according to claim 6, characterized in that: The first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube, the seventh switch tube, the eighth switch tube, the ninth switch tube, the tenth switch tube, the eleventh switch tube and the twelfth switch tube are all IGBT switch devices, and each switch tube has a corresponding freewheeling diode. The positive electrode of each freewheeling diode is connected to the second end of the corresponding switch tube, and the negative electrode of each freewheeling diode is connected to the first end of the corresponding switch tube.

8. The NPC topology power conversion device according to claim 1, characterized in that: The power conversion device of the NPC topology structure further includes a filter, wherein the filter is connected between the output end of each phase bridge arm and the corresponding phase output end.

9. The NPC topology power conversion device according to claim 8, characterized in that: The filter includes a first inductor, a second inductor, a third inductor, a third capacitor, a fourth capacitor, and a fifth capacitor, wherein: The first phase bridge arm output end is connected to the first phase output end through the third inductor, and the fifth capacitor is connected between the first phase output end and the midpoint potential end; The output end of the second phase bridge arm is connected to the first switch via the second inductor, and the fourth capacitor is connected between the connection point between the second inductor and the first switch and the midpoint potential end; The third-phase bridge arm output end is connected to the third-phase output end through the first inductor, and the third capacitor is connected between the third-phase output end and the midpoint potential end.

10. A control method for a power conversion device with an NPC topology structure, characterized in that: The power conversion device of the NPC topology structure applied to any one of claims 1 to 9 comprises: When it is determined that the target single-phase output voltage needs to be output, the first switch is controlled to be turned toward the neutral line output terminal, and the second switch is controlled to be disconnected; Using SPWM technology to control the switching state of each power switch device in each phase bridge arm of a three-phase NPC three-level inverter, so that the output end of the first phase bridge arm outputs a first AC voltage, the second phase bridge arm outputs a second AC voltage, and the third phase bridge arm outputs a third AC voltage, wherein the third AC voltage and the second AC voltage have the same amplitude and a phase difference of 180 degrees, and the first AC voltage is equal to 0; The target single-phase output voltage is obtained between the third-phase output terminal and the neutral line output terminal.

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