Power converter and power supply system

Abstract

The application provides a power converter and a power supply system. By changing the boost conversion circuit into a parallel relationship, the energy difference between the positive bus and the negative bus can be greatly reduced when the DC source is working normally, and the voltage of the positive bus and the negative bus can be evened out, so that the balancing circuit does not need to work, the power of the balancing circuit can be greatly reduced, the balancing energy required by the balancing circuit is greatly reduced or even zero, thereby the balancing circuit can be designed to be lightweight, the number of power semiconductor devices used is reduced, the cost is effectively reduced, and the problem of circuit layout difficulty is solved.

Description

Technical Field

[0001] This application relates to the field of power technology, and in particular to a power converter and power supply system. Background Technology

[0002] Currently, power converters used in power supply systems are developing towards higher density. Within the width constraints of standard servers, the output power of power converters is gradually evolving from 30kW, 50kW, and 100kW to 200kW, 300kW, and even higher. As power increases, heat dissipation becomes crucial, resulting in a large number of power semiconductor devices, large heat sinks, and their cooling equipment occupying the majority of the limited space within the power converter.

[0003] Furthermore, power converters are critical power supply components in equipment such as data centers, requiring high reliability. Failures can lead to incalculable losses, or even catastrophic consequences. The complexity of a power converter's circuit topology largely determines its reliability. Therefore, improving reliability through a minimalist design approach, using relatively fewer power circuits or loads, can effectively reduce system failure rates and extend equipment lifespan. Summary of the Invention

[0004] This application provides a power converter and power supply system for reducing the balanced power within the power converter.

[0005] In a first aspect, this application provides a power converter, including: a first boost converter circuit, a second boost converter circuit, a positive bus capacitor, a negative bus capacitor, and a balancing circuit.

[0006] The midpoint of the bridge arm of the first boost converter circuit is connected to the positive output terminal of the first DC source. The two ends of the bridge arm are connected to the positive bus and the neutral line, respectively. The negative output terminal of the first DC source is connected to the negative bus. The first boost converter circuit is used to implement boost discharge and buck charging functions for the first DC source. The midpoint of the bridge arm of the second boost converter circuit is connected to the negative output terminal of the second DC source. The two ends of the bridge arm are connected to the negative bus and the neutral line, respectively. The positive output terminal of the second DC source is connected to the positive bus. The second boost converter circuit is used to implement boost discharge and buck charging functions for the second DC source BAT2. The positive bus capacitor is connected between the positive bus and the neutral line, and the negative bus capacitor is connected between the negative bus and the neutral line. The balancing circuit is connected between the positive bus and the negative bus. The balancing circuit is used to: discharge the energy of the positive bus capacitor to the negative bus capacitor when the voltage of the positive bus is higher than the voltage of the negative bus, and discharge the energy of the negative bus capacitor to the positive bus capacitor when the voltage of the negative bus is higher than the voltage of the positive bus.

[0007] In this application, the DC source connected to the power converter can be an energy storage battery or a photovoltaic module, etc. Furthermore, the first DC source and the second DC source can be of the same type; for example, they can both be energy storage batteries (which are battery clusters including one or more battery packs) or both be photovoltaic modules. Alternatively, the first DC source and the second DC source can be of different types, for example, one is an energy storage battery and the other is a photovoltaic module. In the following description, this application uses the example of the first DC source and the second DC source both being energy storage batteries.

[0008] In this application, since the two ends of the bridge arm of the first boost converter circuit are connected to the positive bus and the neutral line respectively, and the two ends of the bridge arm of the second boost converter circuit are connected to the negative bus and the neutral line respectively, the bridge arm of the first boost converter circuit and the bridge arm of the second boost converter circuit are connected in series, and the connection point of the series connection is the neutral line. Compared to the parallel connection of the first and second boost converter circuits in existing technologies, this application changes the parallel connection to a series connection. This ensures that when both the first and second DC sources are present, the energy discharged from the first DC source to the negative bus capacitor after being boosted by the first boost converter circuit is greater than the energy discharged to the positive bus capacitor, and the energy discharged from the second DC source to the positive bus capacitor after being boosted by the second boost converter circuit is greater than the energy discharged to the negative bus capacitor. By adjusting the discharge efficiency of the first and second boost converter circuits, the energy obtained on the positive and negative bus capacitors can be roughly symmetrically distributed. This allows the balancing circuit to operate at low power or not at all in most scenarios, thus reducing or even eliminating the power current of the balancing circuit, thereby reducing the power of the balancing circuit, effectively reducing losses, improving efficiency, and also reducing the probability of failure. When only the first or second DC source is present, the total power of the power converter is half of the total power P when both DC sources are operating, i.e., P / 2. If the corresponding boost converter circuit operates at maximum voltage gain, most or even all of the boosted energy will be transferred to a single bus capacitor, resulting in a maximum power of only P / 4 for the balancing circuit. Reducing the power of the balancing circuit significantly reduces the current stress on the power semiconductor devices used, thereby reducing the number of devices required, effectively lowering costs, and solving the problem of complex circuit layout. Specifically, the specifications of the selected devices can be lowered; for example, low-cost and high-efficiency low-voltage devices can be used instead of high-voltage devices. DC film capacitors and fuses can be used to isolate and protect vulnerable points in the power converter, improving reliability.

[0009] In some embodiments of this application, when the first DC source and the second DC source provide the same voltage, the switching transistors in the first boost converter circuit and the second boost converter circuit that are switching between on and off can be controlled to have the same duty cycle, so as to achieve a roughly symmetrical distribution of energy on the positive and negative bus capacitors, so that the balancing circuit can not work, thereby eliminating the power current of the balancing circuit, thereby reducing the power of the balancing circuit, effectively reducing losses, improving efficiency, and also reducing the probability of failure.

[0010] In some embodiments of this application, the first boost converter circuit specifically includes: a first inductor, a first switching transistor, and a first diode. The first terminal of the first inductor is connected to the positive output terminal of the first DC source, and the second terminal of the first inductor is connected to the anode of the first diode and the first electrode of the first switching transistor. The cathode of the first diode is connected to the positive bus, and the second electrode of the first switching transistor is connected to the neutral line. The first DC source, the first inductor, the first switching transistor, the first diode, and the positive and negative bus capacitors constitute a boost circuit. During boost discharge, the first switching transistor, as a power transistor in operation, is controlled by the controller to switch between on and off states. When the first switching transistor is on, the current in the power converter flows in the following direction to form a freewheeling loop: current from the positive output terminal of the first DC source → first inductor → first switching transistor → negative bus capacitor and → negative output terminal of the first DC source, so that the energy of the first DC source is only discharged to the negative bus capacitor. When the first switch is turned off, the current in the power converter flows in the following direction to form a loop: the current flows from the positive output terminal of the first DC source → the first inductor → the first diode → the positive bus capacitor → the negative bus capacitor → the negative output terminal of the first DC source, so that the energy of the first DC source is discharged to both the positive bus capacitor and the negative bus capacitor at the same time.

[0011] In some embodiments of this application, to achieve the charging function, the first boost converter circuit may further include a second switch and a second diode. The anode of the second diode is connected to the positive bus, the cathode of the second diode is connected to the first electrode of the second switch, and the second electrode of the second switch is connected to the second terminal of the first inductor. During boost discharge, the second switch is always in the off state; during charging of the first DC source, the second switch is either turned on or off.

[0012] In some embodiments of this application, when the voltage of the negative bus is less than a set threshold, it indicates that the negative bus has failed. The controller is used to control the first switch to be in the conducting state, so that the first DC source continuously provides energy to the negative bus capacitor through the first switch in the conducting state, so that the energy stored in the negative bus capacitor provides a large current to the negative bus for a short time.

[0013] In some embodiments of this application, the second boost converter circuit specifically includes a second inductor, a third switch, and a third diode. The first terminal of the second inductor is connected to the negative output terminal of the second DC source, and the second terminal of the second inductor is connected to the second electrode of the third switch and the negative terminal of the third diode. The positive terminal of the third diode is connected to the negative bus, and the first electrode of the third switch is connected to the neutral line. The second DC source, the second inductor, the third switch, the third diode, and the positive and negative bus capacitors constitute another boost circuit. During boost discharge, the third switch, as a power transistor in an operating state, is controlled by the controller to switch between on and off states. When the third switch is on, the current in the power converter flows in the following direction to form a freewheeling loop: current from the positive output terminal of the second DC source → positive bus capacitor → third switch → second inductor → negative output terminal of the second DC source, so that the energy of the second DC source is discharged only to the positive bus capacitor. When the third switch is turned off, the current in the power converter flows in the following direction to form a freewheeling loop: the current flows from the positive output terminal of the second DC source → positive bus capacitor → negative bus capacitor → third diode → second inductor → negative output terminal of the second DC source, so that the energy of the second DC source is discharged to both the positive bus capacitor and the negative bus capacitor at the same time.

[0014] In some embodiments of this application, to achieve the charging function, the second boost converter circuit may further include a fourth switch and a fourth diode. The positive terminal of the fourth diode is connected to the second terminal of the second inductor, the negative terminal of the fourth diode is connected to the first electrode of the fourth switch, and the second electrode of the fourth switch is used to connect to the negative bus. During boost discharge, the fourth switch is always in the off state; during charging of the second DC source, the fourth switch is turned on or off.

[0015] In some embodiments of this application, when the voltage of the positive bus is less than a set threshold, it indicates that a fault has occurred in the positive bus. The controller is used to: control the third switch to be in the conducting state, so that the second DC source continuously provides energy to the positive bus capacitor through the third switch in the conducting state, so that the energy stored in the positive bus capacitor can provide a large current to the positive bus for a short time.

[0016] In some embodiments of this application, the balancing circuit includes: a first bridge arm and a second bridge arm connected in series, a third inductor, a fifth diode, and a sixth diode. A first terminal of the third inductor is connected to the neutral line, and a second terminal of the third inductor is connected to the series connection point of the first and second bridge arms. The anode of the fifth diode is connected to the first terminal of the third inductor, and the cathode of the fifth diode is connected to the midpoint of the first bridge arm. The cathode of the sixth diode is connected to the first terminal of the third inductor, and the anode of the sixth diode is connected to the midpoint of the second bridge arm.

[0017] In this application, by changing the connection relationship of the boost converter circuit from the existing parallel relationship to the series relationship, the energy of the positive and negative bus capacitors can be balanced in most scenarios. The balancing circuit can be not working or operate at low power, and the power current of the balancing circuit can be reduced or even eliminated, thereby reducing the power of the balancing circuit. Therefore, in the circuit topology design of the balancing circuit, the AC resonant thin film capacitor that occupies a large area of ​​the circuit board can be removed, and diodes with lower cost and smaller size can be used to achieve the current balancing function.

[0018] Specifically, the balancing circuit provided in this application can control the switches in both the first and second bridge arms to be off when the voltage of the positive bus is equal to the voltage of the negative bus, i.e., when the energies of the positive and negative bus capacitors are the same. When the voltage of the positive bus is higher than the voltage of the negative bus, i.e., when the energy of the positive bus capacitor is greater than the energy of the negative bus capacitor (e.g., when only the second DC source exists), the switch in the first bridge arm can be turned on or off, while the switch in the second bridge arm is turned off, allowing the energy stored in the positive bus capacitor to be transferred to the negative bus capacitor for energy balance. When the voltage of the positive bus is lower than the voltage of the negative bus, i.e., when the energy of the positive bus capacitor is less than the energy of the negative bus capacitor (e.g., when only the first DC source exists), the switch in the second bridge arm can be turned on or off, while the switch in the first bridge arm is turned off, allowing the energy stored in the negative bus capacitor to be transferred to the positive bus capacitor for energy balance.

[0019] When a short-circuit fault occurs at the output of the positive or negative bus, such as when a short-circuit fault occurs at the downstream power distribution switch of the power converter, i.e., at a certain customer terminal, the balancing circuit of this application can operate in a gradual current-limiting state. Combined with the energy provided by the positive and negative bus capacitors and the short-term conduction state of the power transistor, it can continuously output current for a period of time, such as 10ms, which can greatly improve the ability to clear short-circuit faults.

[0020] When a system load fault occurs on the positive bus, the power converter needs to provide a certain amount of current to clear the short-circuit fault. When the power converter's controller detects that the voltage on the positive bus is less than a set threshold, it indicates that a fault has occurred on the positive bus. The controller can then control the balancing circuit to transfer the energy stored in the negative bus capacitor to the positive bus capacitor, allowing the positive bus capacitor to continuously output current and continuously provide energy to the positive bus to clear the short-circuit fault.

[0021] When a system load fault occurs on the negative bus, the power converter needs to provide a certain amount of current to clear the short-circuit fault. When the power converter's controller detects that the voltage on the negative bus is less than a set threshold, it indicates that a fault has occurred on the negative bus. The controller can then control the balancing circuit to transfer the energy stored in the positive bus capacitor to the negative bus capacitor, allowing the negative bus capacitor to continuously output current and continuously provide energy to the negative bus to clear the short-circuit fault.

[0022] In some embodiments of this application, when the voltage of the positive bus is less than a set threshold, the switch in the second bridge arm can be controlled to turn on or off, and the switch in the first bridge arm can be controlled to be in the off state. When the voltage of the negative bus is less than a set threshold, the switch in the first bridge arm can be controlled to turn on or off, and the switch in the second bridge arm can be controlled to be in the off state.

[0023] In some embodiments of this application, when the voltage of the positive bus is higher than the voltage of the negative bus, or when the voltage of the negative bus is less than a set threshold, the switch of the lower bridge arm in the second bridge arm can be turned on after the switch of the upper bridge arm in the second bridge arm is turned on, and the switch of the upper bridge arm in the second bridge arm can be turned off after the switch of the lower bridge arm in the second bridge arm is turned off.

[0024] In some embodiments of this application, when the voltage of the positive bus is lower than the voltage of the negative bus, or when the voltage of the positive bus is less than a set threshold, the switch of the upper bridge arm in the first bridge arm is turned on after the switch of the lower bridge arm in the first bridge arm is turned on, and the switch of the lower bridge arm in the first bridge arm is turned off after the switch of the upper bridge arm in the first bridge arm is turned off.

[0025] Secondly, this application provides a power supply system, including: the power converter provided in the first aspect and a plurality of DC sources, the DC sources including a first DC source and a second DC source. The positive output terminal of the first DC source is connected to the midpoint of the bridge arm of a first boost converter circuit in the power converter, and the negative output terminal of the first DC source is connected to a negative bus; the positive output terminal of the second DC source is connected to the midpoint of the bridge arm of a second boost converter circuit in the power converter, and the negative output terminal of the second DC source is used to connect to a positive bus.

[0026] In some embodiments of this application, the first DC source and the second DC source may both be battery clusters comprising one or more battery packs.

[0027] The technical effects that can be achieved in the second aspect mentioned above can be described with reference to the technical effects that can be achieved by any possible design in the first aspect mentioned above, and will not be repeated here. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of a power converter in the prior art;

[0029] Figure 2a This is a schematic diagram of a power converter provided in an embodiment of this application;

[0030] Figure 2b This is another schematic diagram of the power converter provided in the embodiments of this application;

[0031] Figure 3a A schematic diagram of a circuit structure for a power converter provided in an embodiment of this application;

[0032] Figure 3b This is a schematic diagram of another circuit structure of the power converter provided in the embodiments of this application;

[0033] Figure 4a A schematic diagram of the current flow direction of the power converter when the first DC source is working, provided in an embodiment of this application;

[0034] Figure 4b A schematic diagram of the current flow direction of the power converter when it is operating from the second DC source, as provided in the embodiments of this application;

[0035] Figure 5a A schematic diagram of the current flow direction of a power converter when a fault occurs on the positive bus, provided in an embodiment of this application.

[0036] Figure 5b This is a schematic diagram of the current flow direction of the power converter provided in this application when a fault occurs on the negative bus. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. The specific operational methods in the method embodiments can also be applied to the device embodiments or system embodiments. It should be noted that in the description of this application, "at least one" refers to one or more, where "multiple" refers to two or more. Therefore, in the embodiments of this invention, "multiple" can also be understood as "at least two". "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / ", unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship. Furthermore, it should be understood that in the description of this application, terms such as "first" and "second" are only used for distinguishing the descriptive purpose and should not be construed as indicating or implying relative importance or order.

[0038] Currently, in power supply systems, multiple energy storage batteries (packs) are connected in series to form a DC source. A power converter enables charging and discharging, and also provides current sharing, current limiting, and protection functions. Specifically, the power converter includes a boost converter circuit and a balancing circuit. The number of boost converter circuits corresponds one-to-one with the multiple DC sources. The boost converter circuit acts as the front-end circuit to perform boost discharge and buck charging functions on the energy storage batteries. During boost discharge, the boost converter circuit forms a boost circuit. After boosting, the energy distribution between the positive and negative bus capacitors is unbalanced, thus requiring a subsequent balancing circuit to equalize the energy. The balancing circuit is used to achieve energy balance between the positive and negative bus voltages and provides energy when a short circuit occurs in the load connected to the positive and negative buses. The load can be connected to three terminals of the positive bus, negative bus, and neutral line, or any two terminals.

[0039] Reference Figure 1 The boost converter circuit specifically includes: the midpoint of the bridge arm of the first boost converter circuit connected to the positive output terminal of the first DC source BAT1, and the midpoint of the bridge arm of the second boost converter circuit connected to the positive output terminal of the second DC source BAT2. The negative output terminals of both the first DC source BAT1 and the second DC source BAT2 are connected to the negative bus BUS-. Both ends of the bridge arms of the first and second boost converter circuits are connected between the positive bus BUS+ and the neutral line N. The first and second boost converter circuits are connected in parallel. The two ends of the bridge arm of the first boost converter circuit and the A, B, and C nodes corresponding to the negative output terminal of the first DC source BAT1 are respectively connected to the two ends of the bridge arm of the second boost converter circuit and the D, E, and F nodes corresponding to the negative output terminal of the second DC source BAT2.

[0040] The maximum voltage gain of a boost converter circuit is typically 2. Therefore, when the DC source voltage is low, most or even all of the boosted energy will be transferred to one bus capacitor, such as the negative bus capacitor C2, while the other bus capacitor, the positive bus capacitor C1, receives no energy during a single switching cycle of the boost converter circuit. For two-wire loads that need to draw power from both the positive and negative buses, and for three-wire loads that need to draw power from the positive, negative, and neutral buses, the load needs to draw energy from both the positive bus capacitor C1 and the negative bus capacitor C2 simultaneously. Therefore, the balancing circuit needs to transfer half of the energy from the negative bus capacitor C2 to the positive bus capacitor C1. In this case, the power of the balancing circuit is half of the total output power P of the boost converter circuit, i.e., P / 2. Generally, low-power balancing circuits cannot meet this power requirement, necessitating a larger topology design in the balancing circuit, which can lead to unmet space layout requirements.

[0041] Currently, the balancing circuit in power converters consists of a series inductor-capacitor (LC) resonant circuit. Under steady-state conditions, the LC resonant circuit can achieve soft switching, and the balancing current can be relatively large. During normal operation, the LC resonant circuit has a very large balancing current, typically around 240A, while the inductance is small, usually around 1uH. The ripple current of the resonant capacitor is very large. This necessitates the use of many AC resonant film capacitors in the balancing circuit, such as 40pcs*5, resulting in high cost and a large footprint on the circuit board, making it difficult to complete the circuit layout within the limited space of the circuit board. Furthermore, when a short circuit occurs in the load connected to the positive and negative buses, the balancing circuit needs to provide a large amount of energy, requiring a large current output in a short time, which is practically impossible for the LC resonant circuit. Especially when the voltage difference between the positive and negative buses reaches a certain value, the circuit current will resonate to the protection point within a few switching cycles, causing the balancing circuit to stop working and unable to continuously output current, thus failing to achieve the fault clearing function.

[0042] Based on this, the power converter provided in this application changes the internal circuit connection topology. By changing the existing parallel relationship of the boost converter circuit to a series relationship, the energy of the positive and negative bus capacitors is balanced. In most scenarios, the balancing circuit can be inactive or operate at low power, reducing or even eliminating the power current of the balancing circuit, thereby reducing the power of the balancing circuit, effectively reducing losses, improving efficiency, and also reducing the probability of failure. Simultaneously, this application optimizes the operating timing, significantly reducing the current stress on the power semiconductor devices used, reducing the number of power semiconductor devices required, effectively reducing costs, and solving the problem of difficult circuit layout. Specifically, the specifications of the selected devices can be reduced; for example, low-cost and high-efficiency low-voltage devices can be used instead of high-voltage devices. DC thin-film capacitors and fuses are used to isolate and protect vulnerable points in the power converter, thereby improving reliability.

[0043] The power converter provided in this application can be adapted to different application scenarios. The power converter can be used in data center short-term backup power systems and energy storage systems, such as data center systems, industrial and commercial energy storage systems, and tandem photovoltaic and energy storage systems.

[0044] Reference Figure 2aThe power converter provided in this application specifically includes: a first boost converter circuit, a second boost converter circuit, a positive bus capacitor C1, a negative bus capacitor C2, and a balancing circuit. The midpoint of the bridge arm of the first boost converter circuit is connected to the positive output terminal of the first DC source BAT1. The two ends of the bridge arm of the first boost converter circuit are connected to the positive bus BUS+ and the neutral line N, respectively. The negative output terminal of the first DC source BAT1 is connected to the negative bus BUS-. The first boost converter circuit is used to implement boost discharge and buck charging functions for the first DC source BAT1. The midpoint of the bridge arm of the second boost converter circuit is connected to the negative output terminal of the second DC source BAT2. The two ends of the bridge arm of the second boost converter circuit are connected to the negative bus BUS- and the neutral line N, respectively. The positive output terminal of the second DC source BAT2 is connected to the positive bus BUS+. The second boost converter circuit is used to implement boost discharge and buck charging functions for the second DC source BAT2. The positive bus capacitor C1 is connected between the positive bus BUS+ and the neutral line N, and the negative bus capacitor C2 is connected between the negative bus BUS- and the neutral line N. A balancing circuit is connected between the positive bus BUS+ and the negative bus BUS-. The balancing circuit is used to: discharge the energy of the positive bus capacitor C1 to the negative bus capacitor C2 when the voltage of the positive bus BUS+ is higher than the voltage of the negative bus BUS-, and discharge the energy of the negative bus capacitor C2 to the positive bus capacitor C1 when the voltage of the negative bus BUS- is higher than the voltage of the positive bus BUS+.

[0045] In this application, the DC source connected to the power converter can be an energy storage battery or a photovoltaic module, etc. Furthermore, the first DC source and the second DC source can be of the same type; for example, they can both be energy storage batteries (which are battery clusters including one or more battery packs) or both be photovoltaic modules. Alternatively, the first DC source and the second DC source can be of different types, for example, one is an energy storage battery and the other is a photovoltaic module. In the following description, this application uses the example of the first DC source and the second DC source both being energy storage batteries.

[0046] In this application, since the two ends of the bridge arm of the first boost converter circuit are connected to the positive bus BUS+ and the neutral line N respectively, and the two ends of the bridge arm of the second boost converter circuit are connected to the negative bus BUS- and the neutral line N respectively, the bridge arms of the first boost converter circuit and the bridge arms of the second boost converter circuit are connected in series, and the connection point of the series connection is the neutral line N. Compared to the parallel connection of the first and second boost converter circuits in the prior art, this application changes the parallel connection to a series connection. This ensures that when both the first DC source BAT1 and the second DC source BAT2 are present, the energy discharged from the first DC source BAT1 after being boosted by the first boost converter circuit to the negative bus capacitor C2 is greater than the energy discharged to the positive bus capacitor C1. Similarly, the energy discharged from the second DC source BAT2 after being boosted by the second boost converter circuit to the positive bus capacitor C1 is greater than the energy discharged to the negative bus capacitor C2. By adjusting the discharge efficiency of the first and second boost converter circuits, the energy obtained on the positive and negative bus capacitors can be roughly symmetrically distributed. This allows the balancing circuit to operate at low power or not at all in most scenarios, thus reducing or even eliminating the power current of the balancing circuit, thereby reducing the power of the balancing circuit, effectively reducing losses, improving efficiency, and also reducing the probability of failure. When only the first DC source BAT1 or the second DC source BAT2 is present, the total power of the power converter is half of the total power P when both DC sources are operating, i.e., P / 2. If the corresponding boost converter circuit operates at maximum voltage gain, most or even all of the boosted energy will be transferred to a single bus capacitor, resulting in a maximum power of only P / 4 for the balancing circuit. Reducing the power of the balancing circuit significantly reduces the current stress on the power semiconductor devices used, thereby reducing the number of devices required, effectively lowering costs, and solving the problem of difficult circuit layout. Specifically, the specifications of the selected devices can be lowered; for example, low-cost and high-efficiency low-voltage devices can be used instead of high-voltage devices. DC film capacitors and fuses can be used to isolate and protect vulnerable points in the power converter, thereby improving reliability.

[0047] In this embodiment, the boost converter circuit and the balancing circuit can be composed of devices such as switching transistors, diodes, and inductors. The operating states of the boost converter circuit and the balancing circuit can be adjusted by regulating the operating states of these devices. Specifically, the operating states of the above-mentioned devices can be regulated by a controller; that is, the power converter can also include a controller that can control the boost converter circuit to perform boost discharge or buck charging, and control the balancing circuit to discharge energy from the positive bus capacitor to the negative bus capacitor or discharge energy from the negative bus capacitor to the positive bus capacitor. In specific implementation, the controller can be any of a microcontroller unit (MCU), a central processing unit (CPU), or a digital signal processor (DSP). Of course, the specific form of the controller is not limited to the examples above.

[0048] Reference Figure 2a This application embodiment only illustrates the example of a power converter connected to two DC sources BAT1 and BAT2. In practical applications, the power converter can connect to three, four, or even more DC sources. Correspondingly, the power converter includes boost converter circuits that correspond one-to-one with the number of DC sources. The specific connection relationship of the boost converter circuits can be the connection relationship between the first boost converter circuit and the second boost converter circuit. For example, refer to... Figure 2bThe power converter connects to four DC sources BAT1, BAT2, BAT3, and BAT4. Correspondingly, the power converter includes a first boost converter circuit, a second boost converter circuit, a third boost converter circuit, and a fourth boost converter circuit. The midpoint of the bridge arm of the first boost converter circuit is connected to the positive output terminal of DC source BAT1, and the two ends of the bridge arm of the first boost converter circuit are connected to the positive bus BUS+ and the neutral line N, respectively. The negative output terminal of DC source BAT1 is connected to the negative bus BUS-. The midpoint of the bridge arm of the second boost converter circuit is connected to the negative output terminal of DC source BAT2, and the bridge arm of the second boost converter circuit... The first boost converter circuit has its two ends connected to the negative bus BUS- and the neutral line N, respectively. The positive output terminal of DC source BAT2 is connected to the positive bus BUS+. The midpoint of the third boost converter circuit's bridge arm is connected to the positive output terminal of DC source BAT3. The two ends of the third boost converter circuit's bridge arm are connected to the positive bus BUS+ and the neutral line N, respectively. The negative output terminal of DC source BAT3 is connected to the negative bus BUS-. The midpoint of the fourth boost converter circuit's bridge arm is connected to the negative output terminal of DC source BAT4. The two ends of the fourth boost converter circuit's bridge arm are connected to the negative bus BUS- and the neutral line N, respectively. The positive output terminal of DC source BAT4 is connected to the positive bus BUS+. The bridge arms of the first and second boost converter circuits are connected in series, with the series connection point being the neutral line N. The bridge arms of the third and fourth boost converter circuits are connected in series, with the series connection point being the neutral line N.

[0049] Reference Figure 3a In some embodiments of this application, the first boost converter circuit may specifically include: a first inductor L1, a first switch Q1, and a first diode D1. The first terminal of the first inductor L1 is connected to the positive output terminal of the first DC source BAT1, and the second terminal of the first inductor L1 is connected to the anode of the first diode D1 and the first electrode of the first switch Q1. The cathode of the first diode D1 is connected to the positive bus BUS+, and the second electrode of the first switch D1 is connected to the neutral line N. To achieve the charging function, the first boost converter circuit may further include: a second switch Q2 and a second diode D2. The anode of the second diode D2 is connected to the positive bus BUS+, the cathode of the second diode D2 is connected to the first electrode of the second switch Q2, and the second electrode of the second switch Q2 is connected to the second terminal of the first inductor L1. During boost discharge, the second switch Q2 is always off; during charging of the first DC source BAT1, the second switch Q2 is either on or off. In other embodiments of this application, the positions of the second diode D2 and the second switch Q2 may be interchanged.

[0050] Reference Figure 3aIn some embodiments of this application, the second boost converter circuit may specifically include: a second inductor L2, a third switch Q3, and a third diode D3. The first terminal of the second inductor L2 is connected to the negative output terminal of the second DC source BAT2, and the second terminal of the second inductor L2 is connected to the second electrode of the third switch Q3 and the negative electrode of the third diode D3. The positive electrode of the third diode D3 is connected to the negative bus BUS-, and the first electrode of the third switch Q3 is connected to the neutral line N. To achieve the charging function, the second boost converter circuit may further include: a fourth switch Q4 and a fourth diode D4. The positive electrode of the fourth diode D4 is connected to the second terminal of the second inductor L2, the negative electrode of the fourth diode D4 is connected to the first electrode of the fourth switch Q4, and the second electrode of the fourth switch Q4 is connected to the negative bus BUS-. During boost discharge, the fourth switch Q4 is always in the off state; during charging of the second DC source BAT2, the fourth switch Q4 is either turned on or off. In other embodiments of this application, the positions of the fourth diode D4 and the fourth switch Q4 may also be interchanged.

[0051] Reference Figure 3b In other embodiments of this application, multiple branches can be provided in both the boost converter circuit and the balancing circuit according to the actual power requirements. Figure 3b The following explanation uses the example of the first boost converter circuit, the second boost converter circuit, and the balancing circuit, each of which includes four branches.

[0052] Reference Figure 4a In the first boost converter circuit, the first DC source BAT1, the first inductor L1, the first switch Q1, the first diode D1, and the positive and negative bus capacitors constitute a boost circuit. During boost discharge, the first switch Q1, as a power transistor in the working state, switches between on and off. When the first switch Q1 is on, the current in the power converter flows in the direction of the arrow shown in ①, forming a freewheeling loop: the current flows from the positive output terminal of the first DC source BAT1 → the first inductor L1 → the first switch Q1 → the negative bus capacitors C2 and C4 → the negative output terminal of the first DC source BAT1, so that the energy of the first DC source BAT1 is only discharged to the negative bus capacitors C2 and C4. When the first switch Q1 is turned off, the current in the power converter flows in the direction of the arrow shown in ② to form a freewheeling loop: the current flows from the positive output terminal of the first DC source BAT1 → the first inductor L1 → the first diode D1 → the positive bus capacitors C1 and C3 → the negative bus capacitors C2 and C4 → the negative output terminal of the first DC source BAT1, so that the energy of the first DC source BAT1 is simultaneously discharged to the positive bus capacitors C1 and C3 and the negative bus capacitors C2 and C4.

[0053] Reference Figure 4bIn the second boost converter circuit, the second DC source BAT2, the second inductor L2, the third switch Q3, the third diode D3, and the positive and negative bus capacitors constitute another boost circuit. During boost discharge, the third switch Q3, as a power transistor in operation, switches between on and off. When the third switch Q3 is on, the current in the power converter flows in the direction of the arrow shown in ①, forming a freewheeling loop: the current flows from the positive output terminal of the second DC source BAT2 → positive bus capacitors C1 and C3 → third switch Q3 → second inductor L2 → negative output terminal of the second DC source BAT2, so that the energy of the second DC source BAT2 is only discharged to the positive bus capacitors C1 and C3. When the third switch Q3 is turned off, the current in the power converter flows in the direction of the arrow shown in ② to form a freewheeling loop: the current flows from the positive output terminal of the second DC source BAT2 → positive bus capacitors C1 and C3 → negative bus capacitors C2 and C4 → third diode D3 → second inductor L2 → negative output terminal of the second DC source BAT2, so that the energy of the second DC source BAT2 is discharged to the positive bus capacitors C1 and C3 and the negative bus capacitors C2 and C4 at the same time.

[0054] In this application, when the first DC source BAT1 and the second DC source BAT2 operate simultaneously and provide the same energy (i.e., the same power), the duty cycles of the power transistors (i.e., the first switch Q1 and the third switch Q3) in the first and second boost converter circuits can be controlled to be exactly the same. Due to the symmetry of the first and second boost converter circuits, the energy of the positive and negative bus capacitors is also exactly the same, eliminating the need for energy balancing. The balancing circuit does not need to operate; that is, the switches in the balancing circuit are all in the off state. Therefore, the power current of the balancing circuit can be eliminated, thereby effectively reducing losses, improving efficiency, and also reducing the probability of failure.

[0055] In this application, when only the first DC source BAT1 or the second DC source BAT2 is present, the total power of the power converter is half of the total power P when both DC sources are working, i.e., P / 2. Based on the boost ratio and output power, the power required by the balancing circuit is P1. Even if the duty cycle of the power transistor in the boost converter circuit is 1, the power of the balancing circuit is only P / 4, i.e., P1 is at most P / 4.

[0056] In this application, when there is a difference in the power provided by the first DC source BAT1 and the second DC source BAT2, the power required by the balancing circuit is P2 based on the energy ratio and output power provided by the first DC source BAT1 and the second DC source BAT2. Taking each DC source as an example consisting of eight battery packs connected in series, if it is permissible to damage one battery pack when the DC source is working, then P2 is at most P / 16.

[0057] In this application, the first switch Q1 is connected in series to the positive bus BUS+ through the first diode D1, and the third switch Q3 is connected in series to the negative bus BUS- through the third diode D3. Therefore, the voltage flowing through the first switch Q1, the first diode D1, the third switch Q3, and the third diode D3 is only half of the bus voltage. For example, if the maximum bus voltage is 800V, considering the switching spikes caused by stress, the above power semiconductor device only needs to be a 650V or 600V withstand voltage device, instead of the 1200V withstand voltage device in the prior art.

[0058] Reference Figures 3a to 4b In some embodiments of this application, multiple positive bus capacitors C1 and C3 can be provided between the positive bus BUS+ and the neutral line N, and multiple negative bus capacitors C2 and C4 can be provided between the negative bus BUS- and the neutral line N, according to actual power requirements. Specifically, positive bus capacitor C1 and negative bus capacitor C2 can be provided between the boost converter circuit and the balancing circuit, and positive bus capacitor C3 and negative bus capacitor C4 can be provided between the balancing circuit and the output terminal of the power converter. The positive and negative bus capacitors can specifically use low-cost and small-sized DC film capacitors to replace the AC resonant film capacitors in the existing balancing circuit, thereby saving costs and facilitating circuit layout. Furthermore, when the first switch Q1 in the first boost converter circuit fails and short-circuits, the first DC source BAT1 can achieve short-circuit isolation through the negative bus capacitors C2 and C4, improving reliability. Similarly, when the third switch Q3 in the second boost converter circuit fails and short-circuits, the second DC source BAT2 can achieve short-circuit isolation through the positive bus capacitors C1 and C3, improving reliability.

[0059] Reference Figures 3a to 4b In some embodiments of this application, the balancing circuit may specifically include: a first bridge arm and a second bridge arm connected in series, a third inductor L3, a fifth diode D5, and a sixth diode D6. The first bridge arm may include a fifth switch Q5 as the upper bridge arm and a sixth switch Q6 as the lower bridge arm; the second bridge arm may include a seventh switch Q7 as the upper bridge arm and an eighth switch Q8 as the lower bridge arm. The first terminal of the third inductor L3 is connected to the neutral line N, and the second terminal of the third inductor L3 is connected to the series connection point of the first and second bridge arms. The anode of the fifth diode D5 is connected to the first terminal of the third inductor L3, and the cathode of the fifth diode is connected to the midpoint of the first bridge arm. The cathode of the sixth diode D6 is connected to the first terminal of the third inductor L3, and the anode of the sixth diode D6 is connected to the midpoint of the second bridge arm.

[0060] In this application, by changing the connection relationship of the boost converter circuit from the existing parallel relationship to the series relationship, the energy of the positive and negative bus capacitors can be balanced in most scenarios. The balancing circuit can be not working or operate at low power, and the power current of the balancing circuit can be reduced or even eliminated, thereby reducing the power of the balancing circuit. Therefore, in the circuit topology design of the balancing circuit, the AC resonant thin film capacitor that occupies a large area of ​​the circuit board can be removed, and diodes with lower cost and smaller size can be used to achieve the current balancing function.

[0061] Specifically, the balancing circuit provided in this application can control the switches in the first and second bridge arms to be in the off state when the voltage of the positive bus BUS+ is equal to the voltage of the negative bus BUS-, that is, when the energies of the positive bus capacitor C1 and the negative bus capacitor C3 are the same. Specifically, the fifth switch Q5, the sixth switch Q6, the seventh switch Q7, and the eighth switch Q8 are in the off state. When the voltage of the positive bus BUS+ is higher than the voltage of the negative bus BUS-, that is, when the energy of the positive bus capacitor C1 is greater than the energy of the negative bus capacitor C2, for example, when only the second DC source BAT2 exists, the switches in the first bridge arm can be controlled to be turned on or off. Specifically, the fifth switch Q5 and the sixth switch Q6 are controlled to switch between being on and off, while the switches in the second bridge arm are controlled to be in the off state. Specifically, the seventh switch Q7 and the eighth switch Q8 are in the off state, so that the energy stored in the positive bus capacitors C1 and C3 is transferred to the negative bus capacitors C2 and C4 for energy balance. When the voltage of the positive bus BUS+ is lower than the voltage of the negative bus BUS-, that is, when the energy of the positive bus capacitor C1 is less than the energy of the negative bus capacitor C2, for example, when only the first DC source BAT1 exists, the switching transistors in the second bridge arm can be controlled to be turned on or off, that is, the seventh switching transistor Q7 and the eighth switching transistor Q8 can be controlled to switch between being on and off, while the switching transistors in the first bridge arm are controlled to be in the off state, that is, the fifth switching transistor Q5 and the sixth switching transistor Q6 are in the off state, so that the energy stored in the negative bus capacitors C2 and C4 is transferred to the positive bus capacitors C1 and C3 for energy balance.

[0062] The switching transistors in the boost converter circuit and balancing circuit provided in this application embodiment can include diodes and transistors connected in parallel. Specifically, the switching transistor can be a metal oxide semiconductor field-effect transistor (MOSFET), which inherently has a reverse diode function. The switching transistor can also be an insulated gate bipolar transistor (IGBT) or a bipolar junction transistor (BJT) with a built-in diode. The switching transistor can also be one or more of various types of transistor devices, such as independent diodes connected in parallel with gallium nitride (GaN) field-effect transistors and silicon carbide (SiC) power transistors. This application embodiment will not list them all.

[0063] Specifically, each switching transistor may include a first electrode, a second electrode, and a control electrode, wherein the control electrode is used to control the switching transistor to turn on or off. When the switching transistor is on, current can be transferred between the first electrode and the second electrode; when the switching transistor is off, no current can be transferred between the first electrode and the second electrode. Taking a MOSFET as an example, the control electrode of the switching transistor is the gate, the first electrode of the switching transistor can be the source, and the second electrode can be the drain; alternatively, the first electrode can be the drain, and the second electrode can be the source.

[0064] When a short-circuit fault occurs at the output of the positive bus BUS+ or the negative bus BUS-, such as when a short-circuit fault occurs at the downstream power distribution switch of the power converter, i.e., at a certain customer terminal, the balancing circuit of this application can operate in a gradual current-limiting state. Combined with the energy provided by the positive and negative bus capacitors and the short-term conduction state of the power transistor, it can continuously output current for a period of time, such as 10ms, which can greatly improve the ability to clear short-circuit faults.

[0065] Reference Figure 5a When a system load fault occurs on the positive bus (BUS+), the power converter needs to provide a certain amount of current to clear the short-circuit fault to the positive bus (BUS+). When the power converter controller detects that the voltage of the positive bus (BUS+) is less than a set threshold, it indicates a fault has occurred on the positive bus (BUS+). For a short time, the current to clear the short-circuit fault can flow through the fault point through the following loops: a large current is provided to the positive bus (BUS+) for a short period using the energy stored in the positive bus capacitors C1 and C3, as described above. Figure 5a The circuit shown in section ⑤ uses a balancing circuit to transfer the energy stored in the negative bus capacitors C2 and C4 to the positive bus capacitors C1 and C3, allowing the positive bus capacitors C1 and C3 to continuously output current. (Refer to...) Figure 5a The circuits shown in ①, ②, and ③ are described; the second DC source BAT2 continuously provides energy to the positive bus capacitors C1 and C3 through the third switch Q3, which is in the on state. Figure 5a The circuit shown in ④ above continuously supplies energy to the positive bus BUS+ through the cooperation of the three current loops.

[0066] Specifically, when the energy stored in the negative bus capacitors C2 and C4 is transferred to the positive bus capacitors C1 and C3 through the balancing circuit, the switching transistors in the first bridge arm can be controlled to be in the off state, that is, the fifth switching transistor Q5 and the sixth switching transistor Q6 are always in the off state, and the switching transistors in the second bridge arm can be controlled to be on or off, that is, the seventh switching transistor Q7 and the eighth switching transistor Q8 are both switching between on and off. For example, within one switching cycle, the on / off state of each switching transistor can be switched in the following order: the seventh switching transistor Q7 is turned on to form... Figure 5a The circuit shown in ② is then turned on to form the eighth switch Q8. Figure 5a In the circuit shown in ①, the negative bus capacitors C1 and C3 discharge energy to the third inductor L3, causing the inductor current of the third inductor L3 to increase, thus turning off the eighth switch Q8 to disconnect the circuit. Figure 5a The circuit shown in ① is then turned off to disconnect the seventh switch Q7. Figure 5a The circuit shown in ② is Figure 5a The circuit shown in ③ discharges the energy of the third inductor L3 to the positive bus capacitors C1 and C3, and the inductance current of the third inductor L3 decreases accordingly.

[0067] Reference Figure 5b When a system load fault occurs on the negative bus (BUS-), the power converter needs to provide a certain amount of current to clear the short-circuit fault to the negative bus (BUS-). When the power converter controller detects that the voltage on the negative bus (BUS-) is less than a set threshold, it indicates a fault has occurred on the negative bus (BUS-). For a short time, the current to clear the short-circuit fault can flow through the fault point through the following circuits: a large current is provided to the negative bus (BUS-) for a short period using the energy stored in the negative bus capacitors C2 and C4, as described above. Figure 5b The circuit shown in section ⑤ uses a balancing circuit to transfer the energy stored in the positive bus capacitors C1 and C3 to the negative bus capacitors C2 and C4, allowing the negative bus capacitors C2 and C4 to continuously output current. (Refer to...) Figure 5b The circuits shown in ①, ②, and ③ are described below; the first DC source BAT1 continuously provides clearing energy to the negative bus capacitors C2 and C4 through the second switch Q2, which is in the on state. (Refer to...) Figure 5b The circuit shown in ④ above continuously supplies energy to the negative bus BUS through the cooperation of the three current loops.

[0068] Specifically, when the energy stored in the positive bus capacitors C1 and C3 is transferred to the negative bus capacitors C2 and C4 through the balancing circuit, the switching transistors in the second bridge arm can be controlled to be in the off state, that is, the seventh switching transistor Q7 and the eighth switching transistor Q8 are always in the off state, and the switching transistors in the first bridge arm can be controlled to be on or off, that is, the fifth switching transistor Q5 and the sixth switching transistor Q6 are both switching between on and off. For example, within one switching cycle, the on / off state of each switching transistor can be switched in the following order: the sixth switching transistor Q6 is turned on to form... Figure 5b The circuit shown in ② is then turned on by the fifth switch Q5 to form... Figure 5b In the circuit shown in ①, the positive bus capacitors C1 and C3 discharge energy to the third inductor L3, causing the inductor current of the third inductor L3 to increase, thus turning off the fifth switch Q5 to disconnect the circuit. Figure 5b The circuit shown in ① is then turned off to disconnect the sixth switch Q6. Figure 5b The circuit shown in ② is Figure 5b The circuit shown in ③ discharges energy from the third inductor L3 to the negative bus capacitors C1 and C3, and the inductance current of the third inductor L3 decreases accordingly.

[0069] Based on the same inventive concept, this application also provides a power supply system comprising: the power converter described above and a plurality of DC sources. The DC sources include a first DC source and a second DC source. The positive output terminal of the first DC source is connected to the midpoint of the bridge arm of the first boost converter circuit in the power converter, and the negative output terminal of the first DC source is connected to the negative bus. The positive output terminal of the second DC source is connected to the midpoint of the bridge arm of the second boost converter circuit in the power converter, and the negative output terminal of the second DC source is connected to the positive bus.

[0070] The power converter and power supply system provided in this application can significantly reduce the energy difference between the positive and negative buses when the DC source is working normally by changing the boost converter circuit to a parallel relationship, and even balance the voltage of the positive and negative buses. This eliminates the need for the balancing circuit to work, significantly reducing the power of the balancing circuit. The balancing energy required by the balancing circuit is greatly reduced or even zero, thereby enabling lightweight design of the balancing circuit, reducing the number of power semiconductor devices used, effectively reducing costs, and solving the problem of difficult circuit layout.

[0071] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A power converter, characterized in that, include: The circuit consists of a first boost converter circuit, a second boost converter circuit, a positive bus capacitor, a negative bus capacitor, and a balancing circuit. The two ends of the bridge arm of the first boost converter circuit are connected to the positive bus and the neutral line, respectively; the two ends of the bridge arm of the second boost converter circuit are connected to the negative bus and the neutral line, respectively; the bridge arm of the first boost converter circuit and the bridge arm of the second boost converter circuit are connected in series, and the connection point is the neutral line. The midpoint of the bridge arm of the first boost converter circuit is used to connect to the positive output terminal of the first DC source, and the negative output terminal of the first DC source is used to connect to the negative bus. The midpoint of the bridge arm of the second boost converter circuit is used to connect to the negative output terminal of the second DC source, and the negative output terminal of the second DC source is used to connect to the positive bus. The balancing circuit is connected between the positive bus and the negative bus. The balancing circuit is used to: discharge the energy of the positive bus capacitor to the negative bus capacitor when the voltage of the positive bus is higher than the voltage of the negative bus, and discharge the energy of the negative bus capacitor to the positive bus capacitor when the voltage of the negative bus is higher than the voltage of the positive bus.

2. The power converter as described in claim 1, characterized in that, The first boost converter circuit includes: a first inductor, a first switching transistor, and a first diode; The first end of the first inductor is used to connect to the positive output terminal of the first DC source, the second end of the first inductor is connected to the positive terminal of the first diode and the first electrode of the first switching transistor, the negative terminal of the first diode is used to connect to the positive bus, and the second electrode of the first switching transistor is used to connect to the neutral line. The power converter further includes: a controller; the controller is used for: When the first DC source is in a discharging state, the first switch is controlled to be turned on or off; when the first switch is turned on, the energy of the first DC source is discharged to the negative bus capacitor; when the first switch is turned off, the first DC source discharges to the positive bus capacitor and the negative bus capacitor.

3. The power converter as described in claim 2, characterized in that, The controller is also used for: When the voltage of the negative bus is less than a set threshold, the first switch is turned on, so that the first DC source discharges to the negative bus capacitor.

4. The power converter as described in claim 2 or 3, characterized in that, The first boost converter circuit further includes: a second switching transistor and a second diode; The positive terminal of the second diode is connected to the positive busbar, the negative terminal of the second diode is connected to the first electrode of the second switching transistor, and the second electrode of the second switching transistor is connected to the second terminal of the first inductor. The controller is used to: control the second switch to turn off when the first DC source is discharging; and control the second switch to turn on or off when the first DC source is charging.

5. The power converter according to any one of claims 1-4, characterized in that, The second boost converter circuit includes: a second inductor, a third switching transistor, and a third diode; The first end of the second inductor is used to connect to the negative output terminal of the second DC source, and the second end of the second inductor is connected to the negative terminal of the third diode and the second electrode of the third switching transistor respectively. The positive terminal of the third diode is used to connect to the negative bus, and the first electrode of the third switching transistor is used to connect to the neutral line. The power converter further includes: a controller; the controller is used for: When the second DC source discharges, the third switch is controlled to be turned on or off; when the third switch is turned on, the second DC source discharges to the positive bus capacitor; when the third switch is turned off, the second DC source discharges to both the positive bus capacitor and the negative bus capacitor.

6. The power converter as described in claim 5, characterized in that, The controller is also used for: When the voltage of the positive bus is less than a set threshold, the third switch is turned on, so that the second DC source discharges to the positive bus capacitor.

7. The power converter as described in claim 4 or 5, characterized in that, The second boost converter circuit also includes: a fourth switching transistor and a fourth diode; The positive terminal of the fourth diode is connected to the second terminal of the second inductor, the negative terminal of the fourth diode is connected to the first electrode of the fourth switching transistor, and the second electrode of the fourth switching transistor is used to connect to the negative busbar. The controller is used to: control the fourth switch to turn off when the second DC source is discharging; and control the fourth switch to turn on or off when the second DC source is charging.

8. The power converter according to any one of claims 1-7, characterized in that, Also includes: Controller; The controller is used for: When the first DC source and the second DC source provide the same voltage, the switching transistors controlling the switching between on and off in the first boost converter circuit and the second boost converter circuit have the same duty cycle.

9. The power converter according to any one of claims 1-8, characterized in that, The balancing circuit includes: a first bridge arm and a second bridge arm connected in series, a third inductor, a fifth diode and a sixth diode; The first end of the third inductor is connected to the neutral line, and the second end of the third inductor is connected to the series connection point of the first bridge arm and the second bridge arm. The positive terminal of the fifth diode is connected to the first terminal of the third inductor, and the negative terminal of the fifth diode is connected to the midpoint of the first bridge arm. The negative terminal of the sixth diode is connected to the first terminal of the third inductor, and the positive terminal of the sixth diode is connected to the midpoint of the second bridge arm. The power converter further includes: a controller; the controller is used for: When the voltage of the positive bus is higher than the voltage of the negative bus, or when the voltage of the negative bus is less than a set threshold, the switch in the first bridge arm is controlled to be turned on or off, and the switch in the second bridge arm is controlled to be in the off state. When the voltage of the positive bus is lower than the voltage of the negative bus, or when the voltage of the positive bus is less than a set threshold, the switch in the second bridge arm is controlled to be turned on or off, and the switch in the first bridge arm is controlled to be in the off state. When the voltage of the positive bus is equal to the voltage of the negative bus, the switching transistors in the first bridge arm and the second bridge arm are both in the off state.

10. The power converter as described in claim 9, characterized in that, The controller is specifically used for: When the voltage of the positive bus is higher than the voltage of the negative bus, or when the voltage of the negative bus is less than a set threshold, the switch of the lower bridge arm in the second bridge arm is turned on after the switch of the upper bridge arm in the second bridge arm is turned on, and the switch of the upper bridge arm in the second bridge arm is turned off after the switch of the lower bridge arm in the second bridge arm is turned off. When the voltage of the positive bus is lower than the voltage of the negative bus, or when the voltage of the positive bus is less than a set threshold, the switch of the upper bridge arm in the first bridge arm is turned on after the switch of the lower bridge arm in the first bridge arm is turned on, and the switch of the lower bridge arm in the first bridge arm is turned off after the switch of the upper bridge arm in the first bridge arm is turned off.

11. A power supply system, characterized in that, include: The power converter and the plurality of DC sources as described in any one of claims 1-10, wherein the DC sources include a first DC source and a second DC source; The positive output terminal of the first DC source is connected to the midpoint of the bridge arm of the first boost converter in the power converter, and the negative output terminal of the first DC source is connected to the negative bus. The positive output terminal of the second DC source is connected to the midpoint of the bridge arm of the second boost converter in the power converter, and the negative output terminal of the second DC source is used to connect to the positive bus.

12. The power supply system as described in claim 11, characterized in that, Both the first DC source and the second DC source are battery clusters that include one or more battery packs.

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