Power converter and energy storage system

Abstract

The present application relates to the technical field of power electronics, and provides a power converter and an energy storage system. In the power converter provided by the present application, a current sampling circuit can sample current which flows through the neutral point of a bus and flows through a clamping diode comprised in a first bridge arm in an NPC three-level balancing circuit. When an external switch transistor in the first bridge arm is turned on, or when an internal switch transistor in the first bridge arm is turned off, if it is detected that the current is large, a control circuit determines that a short-circuit fault has occurred in the clamping diode or internal switch transistor in the first bridge arm. In this case, the control circuit stops outputting a PWM signal to the NPC three-level balancing circuit, such that each switch transistor in the NPC three-level balancing circuit is turned off, thereby avoiding the spreading of the short-circuit fault. Therefore, short-circuit protection for the NPC three-level balancing circuit is achieved, thereby preventing a fire caused by current leakage in the NPC three-level balancing circuit.

Description

Power converters and energy storage systems

[0001] This application claims priority to Chinese Patent Application No. 202411651321.8, filed on November 18, 2024, entitled "Power Converter and Energy Storage System", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of power electronics technology, and in particular to a power converter and energy storage system. Background Technology

[0003] The neutral point clamped (NPC) three-level balanced circuit is a power conversion circuit used to balance the energy of the positive and negative bus capacitors (i.e., the bus capacitor connected to the positive bus and the bus capacitor connected to the negative bus).

[0004] An NPC three-level balanced circuit generally includes: an upper bridge arm and a lower bridge arm connected to each other. The connection point between the upper and lower bridge arms is also called the bridge arm midpoint. Each bridge arm includes: a bus capacitor, an external switch, an internal switch, and a clamping diode. The bus capacitors in the upper and lower bridge arms are connected in series between the positive and negative buses, and the series connection point between the positive and negative bus capacitors is also called the bus midpoint. The external and internal switches in the upper bridge arm are connected sequentially between the positive bus and the bridge arm midpoint. The clamping diode in the upper bridge arm is connected between the bus midpoint and the connection point between the external and internal switches in the upper bridge arm. Similarly, the external and internal switches in the lower bridge arm are connected sequentially between the negative bus and the bridge arm midpoint. The clamping diode in the lower bridge arm is connected between the bus midpoint and the connection point between the external and internal switches in the lower bridge arm. Additionally, the NPC three-level balanced circuit also includes an inductor connected between the bus midpoint and the bridge arm midpoint. In the NPC three-level balanced circuit, each external switch and each internal switch can be periodically turned on and off to balance the voltage on the positive and negative bus capacitors, that is, to balance the energy of the positive and negative bus capacitors.

[0005] However, factors such as abnormal voltage or overheating can cause device failures in the NPC three-level balanced circuit (e.g., short circuit). If protection is not implemented in time, the short circuit fault will spread, and in severe cases, it may even cause leakage in the NPC three-level balanced circuit, leading to a fire. Summary of the Invention

[0006] This application provides a power converter and energy storage system that can solve the problem in related technologies where the inability to implement timely protection against short-circuit faults leads to the spread of faults.

[0007] In a first aspect, a power converter is provided, comprising: a midpoint clamping type NPC three-level balancing circuit, a current sampling circuit, and a control circuit. The NPC three-level balancing circuit includes: a first bridge arm and a second bridge arm, and each of the first and second bridge arms includes: a clamping diode, an external switch, and an internal switch. The current sampling circuit is used to sample a first current flowing through the midpoint of the bus and through the clamping diode in the first bridge arm, where the midpoint of the bus is the midpoint between the positive and negative buses connected to the NPC three-level balancing circuit. The control circuit is used to: when the external switch in the first bridge arm is turned on, if the first current is greater than a first current threshold, stop outputting a pulse-width modulation (PWM) signal to the NPC three-level balancing circuit; or, when the internal switch in the first bridge arm is turned off, if the first current is greater than a second current threshold, stop outputting a PWM signal to the NPC three-level balancing circuit. The second current threshold is greater than or equal to the first current threshold.

[0008] Under normal circumstances, when the external switch in the first bridge arm is turned on or the internal switch is turned off, the DC current supplied by the DC source will not flow through the clamping diode in the first bridge arm. This means the current sampling circuit will not sample the first current flowing through the bus midpoint and the clamping diode. Correspondingly, if the control circuit obtains this first current through the current sampling circuit, and this first current is large, it can be determined that a short circuit fault has occurred in the clamping diode or the internal switch in the first bridge arm. Furthermore, since the control circuit can stop outputting PWM signals to the NPC three-level balanced circuit upon detecting this short circuit fault, thus preventing the NPC three-level balanced circuit from operating, the spread of the short circuit fault can be avoided, achieving short circuit protection for the NPC three-level balanced circuit and preventing leakage current from causing a fire.

[0009] Furthermore, for the first bridge arm, the control circuit directly determines whether a short-circuit fault has occurred in the clamping diode or its internal switching transistor based on the first current flowing through the clamping diode. This first current is not directly affected by half-bus voltage drops or dynamic load changes, thus enabling the control circuit to quickly and reliably identify the occurrence of the short-circuit fault. Consequently, the control circuit can promptly implement protection against the short-circuit fault, resulting in good protection effectiveness.

[0010] Optionally, the current sampling circuit may include a first sampling resistor. One end of the first sampling resistor may be connected to the midpoint of the bus, and the other end of the first sampling resistor may be connected to the positive terminal of the clamping diode in the first bridge arm.

[0011] That is, the first sampling resistor can be used to reliably sample the first current flowing through the midpoint of the bus and through the clamping diode. The structure of this current sampling circuit is simple.

[0012] Optionally, the current sampling circuit can also be used to sample a second current flowing through the midpoint of the bus and through the clamping diode in the second bridge arm. The control circuit can also be used to: when the external switch in the second bridge arm is turned on, if the second current is greater than a third current threshold, stop outputting a PWM signal to the NPC three-level balanced circuit; or, when the internal switch in the second bridge arm is turned off, if the second current is greater than a fourth current threshold, stop outputting a PWM signal to the NPC three-level balanced circuit. The fourth current threshold can be greater than or equal to the third current threshold.

[0013] Similar to the first bridge arm, when the external switch in the second bridge arm is turned on or the internal switch is turned off, under normal circumstances, the DC current supplied by the DC source will not flow through the clamping diode in the second bridge arm. That is, the current sampling circuit will not sample the second current flowing through the bus midpoint and the clamping diode. Correspondingly, if the control circuit obtains this second current through the current sampling circuit, and this second current is large, it can be determined that a short circuit fault has occurred in the clamping diode or the internal switch in the second bridge arm. Furthermore, because the control circuit can stop outputting PWM signals to the NPC three-level balanced circuit when this short circuit fault is detected, thus stopping the NPC three-level balanced circuit from operating, the propagation of the short circuit fault can be prevented, achieving short circuit protection for the NPC three-level balanced circuit and preventing leakage current from the NPC three-level balanced circuit that could cause a fire.

[0014] Furthermore, because the control circuit can also detect short-circuit faults in the clamping diodes or internal switching transistors in the second bridge arm and implement short-circuit protection for such faults, the protection is more comprehensive and effective. Moreover, since the second current in the second bridge arm is not directly affected by half-bus voltage drops or dynamic load changes, the control circuit can quickly and reliably identify the occurrence of short-circuit faults. Consequently, the control circuit can promptly implement protection against these short-circuit faults, resulting in better protection performance.

[0015] Optionally, the current sampling circuit may include: a first sampling resistor and a second sampling resistor. One end of the first sampling resistor may be connected to the midpoint of the bus, and the other end of the first sampling resistor may be connected to the positive terminal of the clamping diode in the first bridge arm; one end of the second sampling resistor may be connected to the midpoint of the bus, and the other end of the second sampling resistor may be connected to the negative terminal of the clamping diode in the second bridge arm.

[0016] In one possible implementation, a first sampling resistor and a second sampling resistor can be used to reliably sample the first current flowing through the clamping diode in the first bridge arm and the second current flowing through the clamping diode in the second bridge arm, respectively. That is, different sampling resistors can be used for sampling the first current and the second current. This allows for independent sampling of the first and second currents with high sampling accuracy.

[0017] Optionally, the current sampling circuit may include a first sampling resistor. One end of the first sampling resistor may be connected to the midpoint of the bus, and the other end of the first sampling resistor may be connected to the positive terminal of the clamping diode in the first bridge arm and the negative terminal of the clamping diode in the second bridge arm, respectively.

[0018] In another possible implementation, a first sampling resistor can be used to reliably sample the first current flowing through the clamping diode in the first bridge arm and the second current flowing through the clamping diode in the second bridge arm. That is, the same sampling resistor can be used for sampling the first and second currents. This reduces the number of components required and saves costs.

[0019] Optionally, the power converter may further include a first voltage sampling circuit. This first voltage sampling circuit can be used to sample a first collector-emitter voltage between the collector and emitter of the external switch in the first bridge arm. The control circuit can also be used to stop outputting a PWM signal to the NPC three-level balanced circuit if the first collector-emitter voltage is less than a first voltage threshold. The first voltage threshold may be less than the first half-bus voltage, which can be the potential difference between the bus connected to the external switch in the first bridge arm and the midpoint of the bus, in both the positive and negative bus configurations.

[0020] Under normal circumstances, the first collector-emitter voltage of the external switch in the first bridge arm is generally not too low. If the first collector-emitter voltage of the external switch is much smaller than the potential difference between the bus connected to the external switch and the midpoint of the bus, the control circuit can determine that a short circuit fault has occurred in the external switch in the first bridge arm. Furthermore, because the control circuit can stop outputting PWM signals to the NPC three-level balanced circuit when it detects this short circuit fault, thus stopping the NPC three-level balanced circuit from operating, the propagation of the short circuit fault can be prevented, achieving short circuit protection for the NPC three-level balanced circuit and preventing leakage current from the NPC three-level balanced circuit that could cause a fire.

[0021] Furthermore, because the control circuit can also detect whether a short-circuit fault occurs in the external switching transistor in the first bridge arm and implement short-circuit protection for such faults, the protection is more comprehensive and the protection effect is better. Moreover, for the first bridge arm, since the first collector-emitter voltage is not directly affected by half-bus voltage drops or dynamic load changes, the control circuit can also quickly and reliably identify the occurrence of the short-circuit fault. Consequently, the control circuit can promptly implement protection against the short-circuit fault, resulting in better protection effectiveness.

[0022] Optionally, the power converter may further include a second voltage sampling circuit. This second voltage sampling circuit can be used to sample a second collector-emitter voltage between the collector and emitter of the external switch in the second bridge arm. The control circuit can also be used to stop outputting a PWM signal to the NPC three-level balanced circuit if the second collector-emitter voltage is less than a second voltage threshold. The second voltage threshold may be less than the second half-bus voltage, which can be the potential difference between the bus connected to the external switch in the second bridge arm and the midpoint of the bus, in both the positive and negative bus configurations.

[0023] Similar to the first bridge arm, under normal circumstances, the second emitter voltage of the external switch in the second bridge arm is generally not too small. If the second emitter voltage of the external switch is much smaller than the potential difference between the bus connected to the external switch and the midpoint of the bus, the control circuit can determine that a short circuit fault has occurred in the external switch in the second bridge arm. Furthermore, because the control circuit can stop outputting PWM signals to the NPC three-level balanced circuit when it detects this short circuit fault, thus stopping the NPC three-level balanced circuit from operating, the propagation of the short circuit fault can be prevented, achieving short circuit protection for the NPC three-level balanced circuit and preventing leakage current from the NPC three-level balanced circuit that could cause a fire.

[0024] Furthermore, because the control circuit can also detect short-circuit faults in the external switching transistors of the second bridge arm and implement short-circuit protection for such faults, the protection is more comprehensive and effective. Moreover, for the second bridge arm, since the second collector-emitter voltage is not directly affected by half-bus voltage drops or dynamic load changes, the control circuit can quickly and reliably identify the occurrence of short-circuit faults. Consequently, the control circuit can promptly implement protection against these short-circuit faults, resulting in better protection performance.

[0025] Secondly, a power converter is provided, comprising: an NPC three-level balancing circuit, a first voltage sampling circuit, and a control circuit. The NPC three-level balancing circuit includes: a first bridge arm and a second bridge arm, and each of the first and second bridge arms includes: a clamping diode, an external switching transistor, and an internal switching transistor. The first voltage sampling circuit is used to sample a first collector-emitter voltage between the collector and emitter of the external switching transistor in the first bridge arm. The control circuit is further used to: if the first collector-emitter voltage is less than a first voltage threshold, then stop outputting a PWM signal to the NPC three-level balancing circuit. The first voltage threshold is less than a first half-bus voltage, which is the potential difference between the bus connected to the external switching transistor in the first bridge arm and the midpoint of the bus in the positive and negative buses connected to the NPC three-level balancing circuit, where the midpoint of the bus is the midpoint between the positive and negative buses.

[0026] Optionally, the power converter may further include a second voltage sampling circuit. This second voltage sampling circuit can be used to sample a second collector-emitter voltage between the collector and emitter of the external switch in the second bridge arm. The control circuit can also be used to stop outputting a PWM signal to the NPC three-level balanced circuit if the second collector-emitter voltage is less than a second voltage threshold. The second voltage threshold may be less than the second half-bus voltage, which can be the potential difference between the bus connected to the external switch in the second bridge arm and the midpoint of the bus, in both the positive and negative bus configurations.

[0027] Thirdly, an energy storage system is provided, comprising: an energy storage battery, and a power converter as provided in the first and second aspects. The power converter includes an NPC three-level balanced circuit for converting direct current supplied by the energy storage battery into alternating current.

[0028] In summary, this application provides a power converter and an energy storage system. The power converter provided in this application includes an NPC three-level balancing circuit, a current sampling circuit, and a control circuit. The current sampling circuit samples the current flowing through the bus midpoint and through the clamping diodes in the first bridge arm of the NPC three-level balancing circuit. The control circuit, when detecting a large current (either when the external switch in the first bridge arm is on or when the internal switch is off), determines that a short-circuit fault has occurred in the clamping diode or the internal switch in the first bridge arm. At this time, because the control circuit stops outputting PWM signals to the NPC three-level balancing circuit, all switches in the NPC three-level balancing circuit are turned off, thus preventing the short-circuit fault from spreading. Therefore, short-circuit protection is achieved for the NPC three-level balancing circuit, preventing leakage current from the NPC three-level balancing circuit and thus avoiding fires. Attached Figure Description

[0029] Figure 1 is a schematic diagram of an energy storage system provided in an embodiment of this application;

[0030] Figure 2 is a structural schematic diagram of a UPS power supply provided in an embodiment of this application;

[0031] Figure 3 is a schematic diagram of a power converter provided in an embodiment of this application;

[0032] Figure 4 is a schematic diagram of another power converter provided in an embodiment of this application;

[0033] Figure 5 is a schematic diagram of another power converter provided in an embodiment of this application;

[0034] Figure 6 is a schematic diagram of another power converter provided in an embodiment of this application;

[0035] Figure 7 is a schematic diagram of another power converter provided in an embodiment of this application;

[0036] Figure 8 is a schematic diagram of another power converter provided in an embodiment of this application;

[0037] Figure 9 is a schematic diagram of another power converter provided in an embodiment of this application;

[0038] Figure 10 is a schematic diagram of another power converter provided in an embodiment of this application. Detailed Implementation

[0039] The power converter and energy storage system provided in the embodiments of this application are described in detail below with reference to the accompanying drawings. First, the key terms involved in the embodiments of this application are introduced.

[0040] Busbar: The trace connecting the input terminal of the NPC three-level balanced circuit to the DC source. The DC source typically includes a positive and a negative terminal. Correspondingly, the busbar generally includes a positive busbar BUS+ and a negative busbar BUS-. The positive busbar BUS+ is connected to the positive terminal of the DC source, and the negative busbar BUS- is connected to the negative terminal of the DC source.

[0041] Half-bus: The input terminals of the NPC three-level balanced circuit typically employ a series capacitor scheme, meaning two bus capacitors are connected in series between the positive bus (BUS+) and the negative bus (BUS-). The connection point between these two capacitors is also called the bus midpoint. A half-bus refers to the connection from either the positive bus (BUS+) or the negative bus (BUS-) to the bus midpoint. For example, the connection from the positive bus (BUS+) to the bus midpoint can be called the positive half-bus or upper half-bus, and the connection from the negative bus (BUS-) to the bus midpoint can be called the negative half-bus or lower half-bus.

[0042] NPC three-level balancing circuit: A power electronic device used for energy conversion. By adding a midpoint clamp, the NPC three-level balancing circuit can output three different levels—positive, negative, and zero—at the midpoint of the topology. Through the operation of the three-level topology, the unbalanced energy on the positive and negative buses can be transmitted and regulated until the energy on the positive and negative buses is balanced, thus achieving energy equilibrium of the positive and negative bus capacitors.

[0043] Waveform blocking: Energy storage systems typically include an inverter circuit and a control circuit. The control circuit outputs a PWM signal to the inverter circuit to control the switching transistors in the inverter circuit, driving its operation. This PWM signal is also called a PWM wave. Correspondingly, outputting a PWM signal from the control circuit refers to generating a wave, while wave blocking refers to the control circuit stopping the output of the PWM wave, thus causing the inverter circuit to stop working.

[0044] The NPC three-level balancing circuit provided in this application is widely used in energy storage systems. Figure 1 shows a schematic diagram of an energy storage system. As shown in Figure 1, the energy storage system includes an energy storage battery and a power converter (also called an energy storage power converter). The power converter may include an NPC three-level balancing circuit, which can convert the DC power provided by the energy storage battery into AC power. Furthermore, the NPC three-level balancing circuit in the power converter can also output the converted AC power to a load or the power grid. Accordingly, referring to Figure 1, it can also be seen that the power converter can be connected to the energy storage battery through the positive bus BUS+ and the negative bus BUS-, and the power converter can be connected to the load or the power grid through its output terminal. Moreover, as described above, the NPC three-level balancing circuit in the power converter can also transfer and regulate the unbalanced energy on the positive and negative buses during voltage conversion until the energy on the positive and negative buses reaches balance, thus balancing the energy of the positive and negative bus capacitors.

[0045] It is understood that an energy storage system refers to a device used to store electrical energy or other forms of energy. Its main function is to store electrical energy and release it to supply power to loads or the power grid when needed. Of course, the NPC three-level balancing circuit described in this application is not limited to energy storage systems. For example, in some other embodiments, the NPC three-level balancing circuit can also be applied to a power generation system. A power generation system is used to convert one form of energy (e.g., solar energy provided by photovoltaic modules) into electrical energy and output it to loads or the power grid to supply power to them. Alternatively, in some other embodiments, the NPC three-level balancing circuit can also be applied to inverters, rectifiers, or uninterruptible power supplies (UPS), often designed as power supply equipment. Uninterruptible power supplies, also known as UPS power supplies, are mostly used in data centers to provide power to loads within the data center.

[0046] For example, taking the NPC three-level balanced circuit applied to a UPS power supply as an example, Figure 2 shows a schematic diagram of a UPS power supply structure. As shown in Figure 2, the UPS power supply can include multiple power modules, bypass modules, and a load terminal. Each power module's power input includes an AC input and a DC input. The AC input is connected to the mains input to receive electrical energy from the mains; the DC input is connected to the battery to receive electrical energy from the battery. The bypass module's power input is connected to the bypass input to receive electrical energy from a generator. Continuing to refer to Figure 2, it can be seen that the power output of each power module and the power output of the bypass module are both connected to the load terminal H, which is used to connect to the load. Furthermore, each power module internally includes a rectifier circuit (also called a rectifier), an inverter circuit (also called an inverter), and a DC-DC converter circuit (also called a DC-DC converter). The rectifier circuit can be connected to the mains input, the inverter circuit can be connected to the rectifier circuit and the load terminal H respectively, and the DC-DC converter circuit can be connected to the rectifier circuit, the inverter circuit, and the battery respectively. The rectifier circuit rectifies the DC power input from the mains circuit and outputs it to the inverter circuit. The DC-DC converter circuit converts the DC power from the battery and outputs it to the inverter circuit. The inverter circuit may include an NPC three-level balancing circuit, which converts the received DC power into AC power and outputs it to the load via the load terminal H. Furthermore, the inverter circuit can be connected to the rectifier circuit and the DC-DC converter circuit via the positive bus BUS+ and the negative bus BUS-. During voltage conversion, the NPC three-level balancing circuit in the inverter circuit can also transfer and regulate the unbalanced energy on the positive and negative buses until the energy on the positive and negative buses is balanced, thus ensuring the energy balance of the positive and negative bus capacitors.

[0047] Furthermore, it is understandable that in the field of power electronics, the control circuit can periodically output PWM signals to the NPC three-level balancing circuit on a switching cycle basis to control the on / off state of the switching transistors in the NPC three-level balancing circuit, thereby achieving energy balance on the positive and negative buses connected to the NPC three-level balancing circuit. Moreover, because the NPC three-level balancing circuit requires bus balance between the upper and lower halves of the bus (i.e., the voltage or current on the upper and lower half of the bus must be relatively balanced), the reliability requirements for the components included in the NPC three-level balancing circuit are high. Once a component fails, such as a short-circuit fault in a switching transistor in the NPC three-level balancing circuit, if protection is not implemented in time, the fault will spread, leading to serious consequences such as leakage, fire, or even injury.

[0048] Based on this, in some embodiments, the presence of a short-circuit fault in a device within the NPC three-level balancing circuit can be determined by detecting the inductor current or half-bus voltage, thereby enabling necessary protective actions when a short-circuit fault occurs. This protective action may include controlling the NPC three-level balancing circuit to stop operating, thereby reducing losses caused by the short-circuit fault. For example, a short-circuit fault in a device within the NPC three-level balancing circuit is typically determined when the inductor current exceeds the current protection value or the half-bus voltage drops below the voltage protection value. However, since the half-bus voltage will normally decrease and the inductor current will normally increase when there is a half-bus short circuit or dynamic load changes (i.e., dynamic changes in load power demand), even if no device has a short-circuit fault, this embodiment requires setting the current protection value higher and the voltage protection value lower to prevent false protection. This, in turn, often results in multiple switching cycles before a short-circuit fault is detected and protective action is implemented; that is, the switching transistors in the NPC three-level balancing circuit have been switched on and off within multiple switching cycles, leading to a protection delay that may reach milliseconds (ms) or even seconds (s). During this process, the short-circuit fault may have already spread, resulting in poor protection effectiveness.

[0049] The following description uses the NPC three-level balancing circuit applied to an energy storage system as part of the power converter in the energy storage system as an example to illustrate the NPC three-level balancing circuit provided in the embodiments of this application.

[0050] This application provides a power converter capable of achieving short-circuit protection at the single-switch-cycle level, with the protection time shortened to the microsecond (µs) level. This means it can detect short-circuit faults and implement timely short-circuit protection within µs, thereby preventing further propagation of the short-circuit fault and providing good protection. As shown in Figures 3 and 4, the power converter includes: a midpoint clamping type NPC three-level balanced circuit 01, a current sampling circuit 02, and a control circuit 03.

[0051] The NPC three-level balanced circuit 01 includes a first bridge arm 011 and a second bridge arm 012, and each of the first bridge arm 011 and the second bridge arm 012 includes a clamping diode, an external switch, and an internal switch. For distinction, in Figure 3, the clamping diode, external switch, and internal switch included in the first bridge arm 011 are labeled as D01, Q1, and Q2, respectively; and the clamping diode, internal switch, and external switch included in the second bridge arm 012 are labeled as D02, Q3, and Q4, respectively.

[0052] It is understood that an external switch refers to a switch directly connected to either the positive busbar BUS+ or the negative busbar BUS-, while an internal switch refers to a switch directly connected to the midpoint of the bridge arm. That is, for each of the first bridge arm 011 and the second bridge arm 012, the external and internal switches can be sequentially connected between one of the positive or negative busbars BUS+ and the midpoint of the bridge arm. The bridge arm where the external and internal switches are sequentially connected between the positive busbar BUS+ and the midpoint of the bridge arm can also be called the upper bridge arm; the bridge arm where the external and internal switches are sequentially connected between the negative busbar BUS- and the midpoint of the bridge arm can also be called the lower bridge arm. Furthermore, for each bridge arm, a clamping diode can be connected between the busbar midpoint N and the connection node between the external and internal switches. Furthermore, in the upper bridge arm, the anode of the clamping diode is connected to the bus midpoint N, and the cathode of the clamping diode is connected to the connection node between the external and internal switching transistors. In the lower bridge arm, the anode of the clamping diode is connected to the connection node between the external and internal switching transistors, and the cathode of the clamping diode is connected to the bus midpoint N. Also, referring to Figure 3, it can be seen that the NPC three-level balanced circuit 01 can also include two bus capacitors C1 and C2 connected in series between the positive bus BUS+ and the negative bus BUS-, and an inductor L connected in series between the bus midpoint N and the bridge arm midpoint. The series connection node of the two bus capacitors C1 and C2 is the bus midpoint N.

[0053] For example, in the NPC three-level balanced circuit 01 shown in Figure 3, the external switch Q1 and internal switch Q2 of the first bridge arm 011 are connected sequentially between the positive bus BUS+ and the midpoint of the bridge arm. The external switch Q4 and internal switch Q3 of the second bridge arm 012 are connected sequentially between the negative bus BUS- and the midpoint of the bridge arm. In Figure 3, the connection node between the external switch Q1 and the internal switch Q2 is marked as A, the midpoint of the bridge arm (i.e., the connection node between the internal switch Q2 and the internal switch Q3) is marked as B, and the connection node between the internal switch Q3 and the external switch Q4 is marked as C. Accordingly, in the embodiments of this application, the first bridge arm 011 can refer to the upper bridge arm, and the second bridge arm 012 can refer to the lower bridge arm. Based on this, continuing to refer to Figure 3, it can be seen that in the first bridge arm 011, the positive terminal of the clamping diode D01 can be connected to the midpoint N of the bus, and the negative terminal of the clamping diode D01 can be connected to the connection node A. In the second bridge arm 012, the positive terminal of the clamping diode D02 can be connected to the connection node C, and the negative terminal of the clamping diode D02 can be connected to the midpoint N of the bus. Of course, in some other embodiments, the first bridge arm 011 can also refer to the lower bridge arm, and the second bridge arm 012 can refer to the upper bridge arm. This application does not limit this.

[0054] Optionally, each of the external and internal switching transistors can generally be an insulated-gate bipolar transistor (IGBT) or a metal-oxide-semiconductor field-effect transistor (MOSFET). Each switching transistor may also include a body diode connected between its collector and emitter. In Figure 3, the body diodes of external switching transistors Q1 and Q4 are labeled D1 and D4, respectively, and the body diodes of internal switching transistors Q2 and Q3 are labeled D2 and D3, respectively. The NPC three-level balanced circuit 01 shown in Figure 3 is a type I NPC three-level balanced circuit.

[0055] As described above, during the normal operation of the NPC three-level balanced circuit 01, the control circuit 03 can output PWM signals to each switch in a switching cycle to control the switching of each switch during each switching cycle. Furthermore, for each switch, when the potential of the PWM signal output by the control circuit 03 to that switch is an effective potential (e.g., a positive pulse), the switch can be turned on; when the potential of the PWM signal output by the control circuit 03 to that switch is an invalid potential (e.g., a zero pulse), the switch can be turned off. Also, when all components in the NPC three-level balanced circuit 01 are functioning normally, when both the external and internal switches in each bridge arm are turned on, current can flow through the current path between the external and internal switches (referred to as current path 1); when the external switch in each bridge arm is turned off and the internal switch is turned on, current can flow through the current path between the clamping diode and the internal switch (referred to as current path 2). Furthermore, for the upper bridge arm, when the external switch is off and the internal switch is on, the current can flow through the clamping diode and the internal switch in sequence. For the lower bridge arm, when the external switch is off and the internal switch is on, the current can flow through the internal switch and the clamping diode in sequence.

[0056] In other words, under normal circumstances, i.e., when no short-circuit fault occurs in any device, for each bridge arm, when the external switch in that arm is turned on, current will not flow through current path 2, nor through the clamping diode in that arm. If current still flows through the clamping diode in that arm, it indicates that the clamping diode may have a short-circuit fault. Similarly, for each switch, when it is turned off, current will not flow through it. If current still flows through it, it indicates that the switch may have a short-circuit fault. For example, for the internal switches in each bridge arm, when the internal switch is turned off, current will not flow through current path 2, nor through the clamping diode or the internal switch in that arm. If protection against this short-circuit fault is not implemented promptly, it can spread and damage the NPC three-level balanced circuit 01, potentially causing a fire in severe cases.

[0057] Referring further to Figure 4, it can be seen that the power converter provided in this embodiment of the application also includes a current sampling circuit 02 and a control circuit 03.

[0058] The current sampling circuit 02 is used to sample the first current I1 flowing through the bus midpoint N and the clamping diode D01 in the first bridge arm 011. The bus midpoint N is the midpoint between the positive bus BUS+ and the negative bus BUS- connected by the NPC three-level balancing circuit 01. That is, the current sampling circuit 02 can sample the current between the bus midpoint N and the clamping diode in one of the upper bridge arms. For example, in a structure where the first bridge arm 011 is the upper bridge arm, as can be seen from Figures 3 and 4, the current sampling circuit 02 can be used to sample the current between the bus midpoint N and the positive terminal of the clamping diode D01.

[0059] Control circuit 03 is used for:

[0060] When the external switch Q1 in the first bridge arm 011 is turned on, if the first current I1 is greater than the first current threshold, the output of pulse width modulation (PWM) signal to the NPC three-level balanced circuit 01 will stop.

[0061] or,

[0062] When the internal switch Q2 in the first bridge arm 011 is turned off, if the first current I1 is greater than the second current threshold, the output of PWM signal to the NPC three-level balanced circuit 01 will stop.

[0063] Accordingly, the control circuit 03 can be connected to the current sampling circuit 02 to obtain the first current I1 sampled by the current sampling circuit 02. The control circuit 03 can be, for example, a microcontroller unit (MCU).

[0064] As described above, when the control circuit 03 turns on the external switch Q1 in the first bridge arm 011, under normal circumstances, current will not flow through current path 2, that is, it will not flow through the clamping diode D01 in the first bridge arm 011. If the current sampling circuit 02 can still sample the current flowing through the bus midpoint N and through the clamping diode D01, and simultaneously detects that this current is greater than the first current threshold, then the control circuit 03 can determine that the clamping diode D01 has a short-circuit fault. When the control circuit 03 turns off the internal switch Q2 in the first bridge arm 011, under normal circumstances, current will not flow through current path 2, that is, it will not flow through the clamping diode D01 in the first bridge arm 011 to the internal switch Q2 and then through the internal switch Q2. If the current sampling circuit 02 can still sample the current flowing through the midpoint N of the bus and through the clamping diode D01, that is, if it samples that the current is still flowing through the clamping diode D01 and the internal switch Q2 in sequence, and at the same time detects that the current is greater than the second current threshold, then the control circuit 03 can determine that the internal switch Q2 has a short circuit fault. That is, in the structure shown in Figure 4, the control circuit 03 can at least detect whether the clamping diode D01 and the internal switch Q2 in the first bridge arm 011 have a short circuit fault.

[0065] In this embodiment, the control circuit 03 can stop outputting PWM signals to each switch in the NPC three-level balancing circuit 01 when it detects a short-circuit fault in the clamping diode D01 in the first bridge arm 011 or a short-circuit fault in the internal switch Q2 in the first bridge arm 011, i.e., it performs a waveform blocking operation. This causes the NPC three-level balancing circuit 01 to stop working, thereby preventing the spread of the short-circuit fault and achieving short-circuit protection for the NPC three-level balancing circuit 01.

[0066] Of course, in some other embodiments, when a short-circuit fault occurs in any device in the NPC three-level balancing circuit 01, the control circuit 03 can also directly shut down the equipment to which the power converter belongs to achieve short-circuit protection. Furthermore, the control circuit 03 can also issue an alarm to alert the user that a short-circuit fault has occurred in the NPC three-level balancing circuit 01, enabling the user to promptly and proactively disconnect the power to achieve short-circuit protection. That is, the short-circuit protection action is not limited to waveform blocking.

[0067] The first and second current thresholds can both be pre-stored current thresholds in control circuit 03, or they can be flexibly designed according to actual conditions. Furthermore, the second current threshold is greater than or equal to the first current threshold. That is, the current threshold used to indicate a short-circuit fault in clamping diode D01 can be relatively small, while the current threshold used to indicate a short-circuit fault in internal switch Q2 can be relatively large. For example, the first current threshold can be approximately 30 amperes (A), and the second current threshold can be approximately 80 A. It is understood that since the response time of a diode is usually faster than that of a switch, by setting the first current threshold to be less than the second current threshold, short-circuit protection can be implemented promptly for short-circuit faults in clamping diode D01, preventing short-circuit current from flowing to the internal switch and causing a fault in internal switch Q2, resulting in better protection.

[0068] Furthermore, in this embodiment, since the control circuit 03 directly detects whether a short-circuit fault has occurred in the clamping diode or internal switching transistor based on the current flowing through the midpoint N of the bus and through the clamping diode in the bridge arm, this current is not directly affected by the half-bus voltage drop or dynamic load changes. Therefore, compared to the above embodiment which determines whether a short-circuit fault has occurred by detecting whether the inductor current exceeds the current protection value or the half-bus voltage drops below the voltage protection value, the current threshold does not need to be set too high. Consequently, the control circuit 03 can identify the short-circuit fault and implement protection action within one switching cycle, with the protection time reaching the microsecond level. This reliably prevents the further propagation of the short-circuit fault due to a long short-circuit time, resulting in better protection.

[0069] In summary, this application provides a power converter. The power converter includes an NPC three-level balancing circuit, a current sampling circuit, and a control circuit. The current sampling circuit samples the current flowing through the bus midpoint and through the clamping diodes in the first bridge arm of the NPC three-level balancing circuit. The control circuit, when detecting a large current (either when the external switch in the first bridge arm is on or when the internal switch is off), determines that a short-circuit fault has occurred in the clamping diode or the internal switch in the first bridge arm. In this case, the control circuit stops outputting PWM signals to the NPC three-level balancing circuit, thus turning off all switches in the NPC three-level balancing circuit and preventing the short-circuit fault from spreading. Therefore, short-circuit protection is achieved for the NPC three-level balancing circuit, preventing leakage current and potential fires caused by the NPC three-level balancing circuit.

[0070] Optionally, as shown in FIG5, in this embodiment, the current sampling circuit 02 can also be used to sample the second current I2 flowing through the bus midpoint N and the clamping diode D02 in the second bridge arm 012. That is, the current sampling circuit 02 can also sample the current between the bus midpoint N and the clamping diode included in the upper bridge arm and another bridge arm in the upper bridge arm. In other words, the current sampling circuit 02 can sample the current between the bus midpoint N and the clamping diode in each bridge arm. For example, in a structure where the first bridge arm 012 is the lower bridge arm, as can be seen from FIG5, the current sampling circuit 02 can be used to sample the current between the bus midpoint N and the negative terminal of the clamping diode D02.

[0071] Control circuit 03 can also be used for:

[0072] When the external switch Q4 in the second bridge arm 012 is turned on, if the second current I2 is greater than the third current threshold, the output of PWM signal to the NPC three-level balanced circuit 01 will stop.

[0073] or,

[0074] When the internal switch Q3 in the second bridge arm 012 is turned off, if the second current I2 is greater than the fourth current threshold, the output of PWM signal to the NPC three-level balanced circuit 01 will stop.

[0075] Similar to the first bridge arm 011, and as described above, when the control circuit 03 controls the external switch Q4 in the second bridge arm 012 to turn on, under normal circumstances, the current will not flow through current path 2, that is, it will not flow through the clamping diode D02 in the second bridge arm 012. If the current sampling circuit 02 can still sample the current flowing through the bus midpoint N and through the clamping diode D02, and simultaneously detects that this current is greater than the third current threshold, then the control circuit 03 can determine that the clamping diode D02 has a short-circuit fault. When the control circuit 03 controls the internal switch Q3 in the second bridge arm 012 to turn off, under normal circumstances, the current will not flow through current path 2, that is, it will not flow from the internal switch Q3 in the second bridge arm 012 to the clamping diode D02 and then through the clamping diode D02. If the current sampling circuit 02 can still sample the current flowing through the midpoint N of the bus and through the clamping diode D02, that is, if it samples that the current is still flowing sequentially through the internal switch Q3 and the clamping diode D02, and simultaneously detects that this current is greater than the fourth current threshold, then the control circuit 03 can determine that the internal switch Q3 has a short-circuit fault. In other words, as shown in Figure 5, the control circuit 03 can also detect whether the clamping diode D02 and the internal switch Q3 in the second bridge arm 012 have a short-circuit fault.

[0076] Furthermore, in this embodiment, the control circuit 03 can stop outputting PWM signals to each switch in the NPC three-level balancing circuit 01 when it detects a short-circuit fault in the clamping diode D02 in the second bridge arm 012 or a short-circuit fault in the internal switch Q3 in the second bridge arm 012, i.e., it performs a waveform blocking operation. This prevents the propagation of short-circuit faults and achieves short-circuit protection for the NPC three-level balancing circuit 01.

[0077] The third and fourth current thresholds can both be pre-stored current thresholds in control circuit 03, or they can be flexibly designed according to actual conditions. Furthermore, the fourth current threshold can be greater than or equal to the third current threshold. That is, similar to the relationship between the first and second current thresholds, the current threshold used to indicate a short-circuit fault in clamping diode D02 can be relatively smaller, while the current threshold used to indicate a short-circuit fault in internal switching transistor Q3 can be relatively larger. Of course, the third current threshold can be the same as or different from the first current threshold, and the fourth current threshold can be the same as or different from the second current threshold. For example, the third current threshold can be approximately 30A, and the fourth current threshold can be approximately 80A. Similarly, it is understood that since the response time of a diode is usually faster than that of a switching transistor, setting the third current threshold to be less than the fourth current threshold allows for timely short-circuit protection against short-circuit faults in clamping diode D02, resulting in better protection.

[0078] By setting up control circuit 03, short-circuit protection is also provided for short-circuit faults in clamping diode D02 and internal switching transistor Q3 in the second bridge arm 012. That is, short-circuit protection is provided for short-circuit faults in clamping diodes and internal switching transistors included in each bridge arm, which provides more comprehensive protection and better protection effect.

[0079] Alternatively, as one possible implementation: as shown in Figure 6, the current sampling circuit 02 may include: a first sampling resistor R1.

[0080] One end of the first sampling resistor R1 can be connected to the midpoint N of the busbar, and the other end of the first sampling resistor R1 can be connected to the anode of the clamping diode D01 in the first bridge arm 011 and the cathode of the clamping diode D02 in the second bridge arm 012, respectively. Accordingly, the first bridge arm 011 can refer to the upper bridge arm, and the second bridge arm 012 can refer to the lower bridge arm. Of course, when the first bridge arm 011 is the lower bridge arm and the second bridge arm 012 is the upper bridge arm, the other end of the first sampling resistor R1 can be connected to the cathode of the clamping diode D01 in the first bridge arm 011 and the anode of the clamping diode D02 in the second bridge arm 012, respectively. The following embodiments are similar and will not be described in detail.

[0081] Based on this structure, the first sampling resistor R1 can be used to sample both the first current I1 and the second current I2. That is, in this possible implementation, the current sampling circuit 02 can be configured to include a sampling resistor, or it can be considered as sampling the first current and the second current, sharing the same sampling resistor.

[0082] Alternatively, as another possible implementation: as shown in Figure 7, the current sampling circuit 02 may include: a first sampling resistor R1 and a second sampling resistor R2.

[0083] One end of the first sampling resistor R1 can be connected to the midpoint N of the bus, and the other end of the first sampling resistor R1 can be connected to the positive terminal of the clamping diode D01 in the first bridge arm 011.

[0084] One end of the second sampling resistor R2 can be connected to the midpoint N of the bus, and the other end of the second sampling resistor R2 can be connected to the negative terminal of the clamping diode D02 in the second bridge arm 012.

[0085] Based on this structure, the first sampling resistor R1 can be used to sample the first current I1, and the second sampling resistor R2 can be used to sample the second current I2. That is, in this other possible implementation, the current sampling circuit 02 can be configured to include two sampling resistors, or it can be considered as sampling the first current and the second current, using different sampling resistors respectively.

[0086] Understandably, compared to the structure shown in Figure 7, the structure shown in Figure 6 reduces the number of components required and saves costs by using a single sampling resistor to sample the first current I1 and the second current I2. Conversely, compared to the structure shown in Figure 6, the structure shown in Figure 7 uses different sampling resistors to sample the first current I1 and the second current I2, enabling independent sampling of both currents and achieving higher sampling accuracy.

[0087] Optionally, based on Figure 6, Figure 8 shows a schematic diagram of another power converter. Based on Figure 7, Figure 9 shows a schematic diagram of yet another power converter. Referring to Figures 8 and 9, it can be seen that in the embodiments of this application, the power converter may further include: a first voltage sampling circuit 04.

[0088] The first voltage sampling circuit 04 can be used to sample the first collector-emitter voltage VCE1 between the collector and emitter of the external switch Q1 in the first bridge arm 011. The first collector-emitter voltage VCE1 can refer to the potential difference between the collector and emitter of the external switch Q1.

[0089] The control circuit 03 can also be used to: stop outputting PWM signals to the NPC three-level balancing circuit 01 if the first emitter voltage VCE1 is less than the first voltage threshold.

[0090] Correspondingly, the control circuit 03 can also be connected to the first voltage sampling circuit 04 to obtain the first collector-emitter voltage VCE1 sampled by the first voltage sampling circuit 04.

[0091] The first voltage threshold can be less than the first half-bus voltage. The first half-bus voltage can be the potential difference between the bus connected to the external switch Q1 in the first bridge arm 011 and the bus midpoint N. For example, referring to Figures 8 and 9, in a structure where the first bridge arm 011 is the upper bridge arm and the external switch Q1 is connected to the positive bus BUS+, the first half-bus voltage can be the potential difference between the positive bus BUS+ and the bus midpoint N. The first half-bus voltage is also called the positive half-bus voltage. The first voltage threshold can also be a voltage threshold pre-stored in the control circuit 03 or can be flexibly designed according to actual conditions. For example, the first half-bus voltage can generally be about 300 volts (V), and the voltage range of the first voltage threshold can be about 50V to 100V, such as 80V. When the first collector-emitter voltage VCE1 of the external switch Q1 is less than the first voltage threshold, that is, much less than the first half-bus voltage, the control circuit 03 can determine that the external switch Q1 has a short-circuit fault. That is, with the structure shown in Figures 8 and 9, the control circuit 03 can also detect whether the external switch Q1 in the first bridge arm 011 has a short circuit fault.

[0092] In this embodiment, the control circuit 03 can stop outputting PWM signals to each switch in the NPC three-level balanced circuit 01 when a short-circuit fault is detected in the external switch Q1 in the first bridge arm 011, i.e., it performs a waveform blocking operation. This prevents the propagation of the short-circuit fault and achieves short-circuit protection for the NPC three-level balanced circuit 01. Furthermore, by setting the control circuit 03 to also provide short-circuit protection for short-circuit faults in the external switch Q1 included in the first bridge arm 011, the protection is more comprehensive and the protection effect is better.

[0093] Optionally, as can be seen from Figures 8 and 9, in the embodiments of this application, the power converter may further include: a second voltage sampling circuit 05.

[0094] The second voltage sampling circuit 05 can be used to sample the second collector-emitter voltage VCE2 between the collector and emitter of the external switch Q4 in the second bridge arm 012. The second collector-emitter voltage VCE2 can refer to the potential difference between the collector and emitter of the external switch Q4.

[0095] The control circuit 03 can also be used to: stop outputting PWM signals to the NPC three-level balancing circuit 01 if the second emitter voltage VCE2 is less than the second voltage threshold.

[0096] Correspondingly, the control circuit 03 can also be connected to the second voltage sampling circuit 05 to obtain the second emitter voltage VCE2 sampled by the second voltage sampling circuit 05.

[0097] The second voltage threshold can be less than the second half-bus voltage. The second half-bus voltage can be the potential difference between the bus connected to the external switch Q4 in the second bridge arm 012 and the bus midpoint N. For example, referring to Figures 8 and 9, in a structure where the second bridge arm 012 is the lower bridge arm and the external switch Q4 is connected to the negative bus BUS-, the second half-bus voltage can be the potential difference between the negative bus BUS- and the bus midpoint N. The second half-bus voltage is also called the negative half-bus voltage. The second voltage threshold can also be a voltage threshold pre-stored in the control circuit 03 or can be flexibly designed according to actual conditions. Furthermore, the second voltage threshold and the first voltage threshold can be the same or different. For example, the second half-bus voltage can generally be about 300V, and the voltage range of the second voltage threshold can be about 50V to 100V, such as the second voltage threshold being 80V. When the first collector-emitter voltage VCE2 of the external switch Q4 is less than the second voltage threshold, i.e., much less than the second half-bus voltage, the control circuit 03 can determine that the external switch Q4 has a short-circuit fault. That is, in the structure shown in Figures 8 and 9, the control circuit 03 can also detect whether the external switch Q4 in the second bridge arm 012 has a short-circuit fault.

[0098] In this embodiment, the control circuit 03 can stop outputting PWM signals to each switch in the NPC three-level balancing circuit 01 when a short-circuit fault is detected in the external switch Q4 of the second bridge arm 012, i.e., it performs a waveform blocking operation. This prevents the propagation of the short-circuit fault and achieves short-circuit protection for the NPC three-level balancing circuit 01. Furthermore, by setting the control circuit 03 to also provide short-circuit protection for short-circuit faults in the external switch Q4 included in the second bridge arm 012, that is, short-circuit protection is provided for short-circuit faults in the external switches included in each bridge arm, resulting in more comprehensive protection and better protection effect.

[0099] Similarly, in this embodiment, since the control circuit 03 directly detects whether a short circuit fault has occurred in the external switching transistor based on the collector-emitter voltage of the external switching transistor, and this voltage is not directly affected by the half-bus voltage drop or dynamic load changes, compared to the above embodiment which determines whether a short circuit fault has occurred by detecting that the inductor current exceeds the current protection value or the half-bus voltage drops below the voltage protection value, the voltage threshold does not need to be set too low. Furthermore, the control circuit 03 can identify the short circuit fault and implement protection action within one switching cycle, with the protection time reaching the microsecond level. This reliably prevents the further propagation of the short circuit fault due to a longer short circuit time, resulting in better protection.

[0100] Optionally, each of the voltage sampling circuits in the first voltage sampling circuit 04 and the second voltage sampling circuit 05 may include an operational amplifier to reliably sample the collector-emitter voltage of the external switching transistor.

[0101] As described above, in the power converter provided in this application embodiment, for the first and second bridge arms, a current sampling circuit and a control circuit can be configured to work together to quickly detect short-circuit faults in at least one clamping diode and internal switching transistor in the bridge arm, and to promptly implement short-circuit protection for such faults. Furthermore, a voltage sampling circuit and a control circuit can also be configured to work together to quickly detect short-circuit faults in at least one external switching transistor in the bridge arm, and to promptly implement short-circuit protection for such faults. The protection time is short, the protection effect is good, and the protection is comprehensive.

[0102] Optionally, as mentioned above, the NPC three-level balanced circuit 01 is not limited to power converters, but can also be applied to rectifiers or uninterruptible power supplies (UPS), also known as UPS power supplies, and is often designed as a power supply device.

[0103] In summary, this application provides a power converter. The power converter includes an NPC three-level balancing circuit, a current sampling circuit, and a control circuit. The current sampling circuit samples the current flowing through the bus midpoint and through the clamping diodes in the first bridge arm of the NPC three-level balancing circuit. The control circuit, when detecting a large current (either when the external switch in the first bridge arm is on or when the internal switch is off), determines that a short-circuit fault has occurred in the clamping diode or the internal switch in the first bridge arm. In this case, the control circuit stops outputting PWM signals to the NPC three-level balancing circuit, thus turning off all switches in the NPC three-level balancing circuit and preventing the short-circuit fault from spreading. Therefore, short-circuit protection is achieved for the NPC three-level balancing circuit, preventing leakage current and potential fires caused by the NPC three-level balancing circuit.

[0104] This application also provides a power converter. As shown in FIG10, the power converter includes: an NPC three-level balancing circuit 01, a first voltage sampling circuit 04, and a control circuit 03.

[0105] The NPC three-level balanced circuit 01 includes: a first bridge arm 011 and a second bridge arm 012, and each of the first bridge arm 011 and the second bridge arm 012 includes: a clamping diode, an external switch transistor and an internal switch transistor.

[0106] The first voltage sampling circuit 04 is used to sample the first collector-emitter voltage VCE1 between the collector and emitter of the external switch Q1 in the first bridge arm 011.

[0107] The control circuit 03 is also used to: if the first collector voltage VCE1 is less than the first voltage threshold, stop outputting the PWM signal to the NPC three-level balancing circuit 01, wherein the first voltage threshold is less than the first half bus voltage, the first half bus voltage is the potential difference between the bus connected to the positive bus BUS+ and the negative bus BUS- connected to the NPC three-level balancing circuit 01, and the bus midpoint N, where the external switch Q1 in the first bridge arm 011 is the midpoint between the positive bus BUS+ and the negative bus BUS-.

[0108] Optionally, referring further to Figure 10, the power converter may also include a second voltage sampling circuit 05.

[0109] The second voltage sampling circuit 05 is used to sample the second collector-emitter voltage VCE2 between the collector and emitter of the external switch Q4 in the second bridge arm 012.

[0110] The control circuit 03 is also used to: if the second emitter voltage VCE2 is less than the second voltage threshold, stop outputting the PWM signal to the NPC three-level balancing circuit 01, wherein the second voltage threshold is less than the second half bus voltage, the second half bus voltage is the potential difference between the bus connected to the positive bus BUS+ and the negative bus BUS- and the bus midpoint N of the bus connected to the external switch Q4 in the second bridge arm 012.

[0111] That is, in one embodiment, the power converter may at least be equipped with a voltage sampling circuit to cooperate with the control circuit to quickly detect a short circuit fault in an external switch in at least one bridge arm, and implement short circuit protection in a timely manner for the short circuit fault.

[0112] It is understood that since this power converter has essentially the same implementation method and technical effect as the power converter described in the foregoing embodiments, for the purpose of brevity, the implementation method and technical effect of this power converter will not be described again here.

[0113] In the embodiments of this application, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The term "at least one" refers to one or more, and "multiple" refers to two or more.

[0114] The above description is merely an optional implementation of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A power converter, characterized by, The power converter includes: a midpoint clamping type NPC three-level balanced circuit, a current sampling circuit, and a control circuit; The NPC three-level balanced circuit includes: a first bridge arm and a second bridge arm, and each of the first bridge arm and the second bridge arm includes: a clamping diode, an external switching transistor and an internal switching transistor; The current sampling circuit is used to sample the first current flowing through the midpoint of the bus and through the clamping diode in the first bridge arm, wherein the midpoint of the bus is the midpoint between the positive bus and the negative bus connected by the NPC three-level balanced circuit; The control circuit is used for: When the external switch in the first bridge arm is turned on, if the first current is greater than the first current threshold, the output of pulse width modulation (PWM) signal to the NPC three-level balanced circuit will stop. or, When the internal switch in the first bridge arm is turned off, if the first current is greater than the second current threshold, the output of the PWM signal to the NPC three-level balanced circuit is stopped, wherein the second current threshold is greater than or equal to the first current threshold.

2. The power converter of claim 1, wherein, The current sampling circuit includes: a first sampling resistor; One end of the first sampling resistor is connected to the midpoint of the bus, and the other end of the first sampling resistor is connected to the positive terminal of the clamping diode in the first bridge arm.

3. The power converter of claim 1, wherein, The current sampling circuit is also used to: sample the second current flowing through the midpoint of the bus and through the clamping diode in the second bridge arm; The control circuit is also used for: When the external switch in the second bridge arm is turned on, if the second current is greater than the third current threshold, the output of the PWM signal to the NPC three-level balanced circuit will stop. or, When the internal switch in the second bridge arm is turned off, if the second current is greater than the fourth current threshold, the output of the PWM signal to the NPC three-level balanced circuit is stopped, wherein the fourth current threshold is greater than or equal to the third current threshold.

4. The power converter of claim 3, wherein, The current sampling circuit includes: a first sampling resistor and a second sampling resistor; One end of the first sampling resistor is connected to the midpoint of the bus, and the other end of the first sampling resistor is connected to the positive terminal of the clamping diode in the first bridge arm; One end of the second sampling resistor is connected to the midpoint of the bus, and the other end of the second sampling resistor is connected to the negative terminal of the clamping diode in the second bridge arm.

5. The power converter of claim 3, wherein, The current sampling circuit includes: a first sampling resistor; One end of the first sampling resistor is connected to the midpoint of the bus, and the other end of the first sampling resistor is connected to the positive terminal of the clamping diode in the first bridge arm and the negative terminal of the clamping diode in the second bridge arm, respectively.

6. The power converter of any one of claims 1 to 5, wherein, The power converter further includes: a first voltage sampling circuit; The first voltage sampling circuit is used to: sample the first collector-emitter voltage between the collector and emitter of the external switch in the first bridge arm; The control circuit is further configured to: if the first collector voltage is less than the first voltage threshold, stop outputting the PWM signal to the NPC three-level balancing circuit, wherein the first voltage threshold is less than the first half-bus voltage, and the first half-bus voltage is the potential difference between the bus connected to the external switch in the first bridge arm and the midpoint of the bus in the positive bus and the negative bus.

7. The power converter of any one of claims 1 to 6, wherein, The power converter further includes: a second voltage sampling circuit; The second voltage sampling circuit is used to: sample the second collector-emitter voltage between the collector and emitter of the external switch in the second bridge arm; The control circuit is further configured to: if the second collector voltage is less than the second voltage threshold, stop outputting the PWM signal to the NPC three-level balancing circuit, wherein the second voltage threshold is less than the second half-bus voltage, and the second half-bus voltage is the potential difference between the bus connected to the external switch in the second bridge arm of the positive bus and the negative bus and the midpoint of the bus.

8. A power converter, characterized by, The power converter includes: an NPC three-level balanced circuit, a first voltage sampling circuit, and a control circuit; The NPC three-level balanced circuit includes: a first bridge arm and a second bridge arm, and each of the first bridge arm and the second bridge arm includes: a clamping diode, an external switching transistor and an internal switching transistor; The first voltage sampling circuit is used to: sample the first collector-emitter voltage between the collector and emitter of the external switch in the first bridge arm; The control circuit is further configured to: if the first collector voltage is less than the first voltage threshold, stop outputting the PWM signal to the NPC three-level balancing circuit, wherein the first voltage threshold is less than the first half-bus voltage, the first half-bus voltage is the potential difference between the bus connected to the external switch in the first bridge arm and the midpoint of the bus in the positive and negative buses connected to the NPC three-level balancing circuit, and the midpoint of the bus is the midpoint between the positive bus and the negative bus.

9. The power converter of claim 8, wherein, The power converter further includes: a second voltage sampling circuit; The second voltage sampling circuit is used to: sample the second collector-emitter voltage between the collector and emitter of the external switch in the second bridge arm; The control circuit is further configured to: if the second collector voltage is less than the second voltage threshold, stop outputting the PWM signal to the NPC three-level balancing circuit, wherein the second voltage threshold is less than the second half-bus voltage, and the second half-bus voltage is the potential difference between the bus connected to the external switch in the second bridge arm of the positive bus and the negative bus and the midpoint of the bus.

10. An energy storage system characterized by, The energy storage system includes: an energy storage battery, and a power converter as described in any one of claims 1 to 9; The NPC three-level balancing circuit in the power converter is used to convert the DC power provided by the energy storage battery into AC power.

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