Power converter

Abstract

The application provides a power converter, and belongs to the technical field of power electronics. Since the controller can control the fifth switch tube to be always off during the process that the second switch tube in the bridge arm is turned on and the first switch tube is periodically turned on and off, that is, during the process that the current flows out of the bridge arm through the series connection of the first switch tube and the second switch tube, and since the first switch tube is connected with the positive direct current bus and the fifth switch tube is connected between the midpoint of the bus and the series connection point of the first switch tube and the second switch tube, the positive direct current bus can be prevented from being short-circuited due to the connection of the positive direct current bus and the midpoint of the bus when the first switch tube is short-circuited.

Description

Technical Field

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

[0002] A power converter is a circuit used to convert direct current (DC) to alternating current (AC). A power converter typically includes a positive DC bus, a negative DC bus, and multiple switching transistors connected between the positive and negative DC buses. By controlling the on / off states of these switching transistors, the power converter can achieve the DC-to-AC power conversion.

[0003] However, when a certain switching transistor is short-circuited, it can cause a bus short circuit due to the switching of other switching transistors. Summary of the Invention

[0004] A power converter is provided that can solve the problem of bus short circuits easily occurring on the positive DC bus and negative DC bus in related technologies.

[0005] In a first aspect, a power converter is provided. The power converter includes: a bridge arm, a positive DC bus, a negative DC bus, a positive DC bus capacitor, a negative DC bus capacitor, and a controller. The bridge arm is used to convert DC power from photovoltaic modules or energy storage batteries into AC power, and includes a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch. The first, second, third, and fourth switches are connected in series between the positive and negative DC buses. The fifth switch is connected between the series connection point of the first and second switches and the sixth switch. The sixth switch is also connected between the series connection point of the third and fourth switches and the fifth switch. The positive and negative DC bus capacitors are connected in series between the positive and negative DC buses, and the series connection point of the positive and negative DC bus capacitors is the bus midpoint. The bus midpoint is connected to the series connection point of the fifth and sixth switches. The controller is used to keep the fifth switch off while the second switch is turned on and the first switch is periodically turned on and off.

[0006] Based on the connection method of each switch, it can be seen that during the process of the second switch being turned on and the first switch being periodically switched on and off, current can flow out of the bridge arm through the first and second switches, and the power converter can operate in the positive half-cycle and current outflow mode. At this time, by always controlling the fifth switch, which is a complementary switch to the first switch, to be turned off, it is possible to prevent the positive DC bus from being connected to the bus midpoint, thereby preventing a bus short circuit in the positive DC bus.

[0007] Optionally, the controller can be configured to: keep the fifth switch off during the periodic switching of the second switch and the periodic switching of the first switch, and when the current flowing out of the bridge arm through the first and second switches is greater than a first current threshold. The first current threshold is 5% to 10% of the rated current flowing out of the bridge arm.

[0008] In other words, the controller can not only use the process of the second switch being turned on and the first switch being periodically turned on and off as a trigger condition to control the fifth switch to be normally off, but it can also refer to the current magnitude, and can only control the fifth switch to be normally off when the current is relatively large during this process. In this way, it can prevent the current from reversing during the commutation process when the current is small, and it can avoid the situation where the current cannot flow normally due to the fifth switch being normally off, thereby ensuring the normal operation of the power converter.

[0009] Optionally, the controller can also be used to: control the sixth switch to turn on first, then control the second switch to turn off, and control the third, fourth and fifth switches to remain off during the process of the second switch being turned on and the first switch being periodically turned off, and in the case of the first switch being short-circuited.

[0010] In the event of a short circuit in the first switch, the controller first turns on the sixth switch, then turns off the second switch, and keeps the third, fourth, and fifth switches off. This allows the current to flow out sequentially through the freewheeling diodes of the sixth and third switches, preventing the short circuit fault from spreading inside the power converter.

[0011] Optionally, the controller can also be used to: control the sixth switch to turn on first, then control the second switch to turn off, then control the third switch to turn on, and control the fourth and fifth switches to remain off during the process of the second switch being turned on and the first switch being periodically turned off, and in the case of the first switch being short-circuited.

[0012] In the event of a short circuit in the first switch, the controller first turns on the sixth switch, then turns off the second switch, then turns on the third switch, while keeping the fourth and fifth switches off. This allows the current to flow out sequentially through the sixth and third switches, thus preventing the short circuit fault from spreading inside the power converter.

[0013] Optionally, there can be multiple bridge arms, and these multiple bridge arms can be connected in parallel. The controller can also be used to: in the event that the first switch of any one of the multiple bridge arms is short-circuited, control all switches of the other bridge arms to be turned off.

[0014] When the first switch in any bridge arm is short-circuited, the controller can prevent the short-circuit fault from spreading to other bridge arms by controlling all switches in the other bridge arms to be turned off.

[0015] Secondly, a power converter is provided. This power converter includes: a bridge arm, a positive DC bus, a negative DC bus, a positive DC bus capacitor, a negative DC bus capacitor, and a controller. The bridge arm is used to convert DC power from photovoltaic modules or energy storage batteries into AC power, and includes a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch. The first, second, third, and fourth switches are connected in series between the positive and negative DC buses. The fifth switch is connected between the series connection point of the first and second switches and the sixth switch. The sixth switch is also connected between the series connection point of the third and fourth switches and the fifth switch. The positive and negative DC bus capacitors are connected in series between the positive and negative DC buses, and the series connection point of the positive and negative DC bus capacitors is the bus midpoint. The bus midpoint is connected to the series connection point of the fifth and sixth switches. The controller is used to keep the first switch off while the second switch is turned on and the fifth switch is periodically turned on and off.

[0016] Based on the connection method of each switch, it can be seen that during the periodic switching of the second switch and the fifth switch, current can flow into the bridge arm through the second and fifth switches, and the power converter can operate in the positive half-cycle with current flowing in. At this time, by always controlling the first switch, which is complementary to the fifth switch, to be turned off, it is possible to prevent the positive DC bus from connecting to the bus midpoint, and thus also to prevent the positive DC bus from short-circuiting.

[0017] Optionally, the controller can be used to: keep the first switch off during the periodic switching of the second switch and the periodic switching of the fifth switch, and when the current flowing into the bridge arm through the second and fifth switches is greater than a second current threshold. The second current threshold is 5% to 10% of the rated current flowing into the bridge arm.

[0018] In other words, the controller can not only use the process of the second switch being turned on and the fifth switch being periodically turned on and off as a trigger condition to control the first switch to be normally off, but it can also refer to the current magnitude, and can only control the first switch to be normally off when the current is relatively large during this process. In this way, it can prevent the current from reversing during the commutation process when the current is small, and it can avoid the situation where the current cannot flow normally due to the first switch being normally off, thereby ensuring the normal operation of the power converter.

[0019] Optionally, the controller can also be used to: control the second switch to remain on while the fifth switch is periodically switched on and off, and in the case of a short circuit in the fifth switch, control the first switch, the third switch, the fourth switch and the sixth switch to remain off.

[0020] In the event of a short circuit in the fifth switch, the controller keeps the second switch on and keeps the first, third, fourth, and sixth switches off, allowing current to flow sequentially through the second switch and the short-circuited fifth switch, thus preventing the short-circuit fault from spreading inside the power converter.

[0021] Optionally, the controller can also be used to: control the second switch to turn off during the periodic switching of the second switch and the fifth switch, and in the case of a short circuit in the fifth switch, control the first and fourth switches to remain off, and control the sixth and third switches to turn on.

[0022] In the event of a short circuit in the fifth switch, the controller turns off the second switch, keeps the first and fourth switches off, and turns on the sixth and third switches. This allows the current to flow through the third and sixth switches in sequence, thus preventing the short circuit fault from spreading inside the power converter.

[0023] Optionally, there can be multiple bridge arms, and these multiple bridge arms can be connected in parallel. The controller can also be used to: in the event that the fifth switch of any one of the multiple bridge arms is short-circuited, control all switches of the other bridge arms to be turned off.

[0024] Similarly, if the fifth switch in any bridge arm is short-circuited, the controller can prevent the short-circuit fault from spreading to other bridge arms by controlling all switches in the other bridge arms to be turned off.

[0025] In summary, this application provides a power converter. Because the controller can keep the fifth switch normally off while the second switch in the bridge arm is on and the first switch is periodically switched on and off—that is, while current flows out of the bridge arm through the first and second switches connected in series—and because the first switch is connected to the positive DC bus and the fifth switch is connected between the bus midpoint and the series connection point of the first and second switches, it can prevent a short circuit in the bus caused by the positive DC bus connecting to the bus midpoint when the first switch is short-circuited. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the working scenario of a power converter provided in an embodiment of this application;

[0027] Figure 2 This is a schematic diagram of the structure of a power converter provided in an embodiment of this application;

[0028] Figure 3 This is a schematic diagram of the operating mode of a power converter provided in an embodiment of this application;

[0029] Figure 4 This is a schematic diagram of another power converter provided in an embodiment of this application;

[0030] Figure 5 This is a schematic diagram of another power converter operating mode provided in the embodiments of this application;

[0031] Figure 6 This is a schematic diagram of the working process of a power converter provided in an embodiment of this application;

[0032] Figure 7 This is a schematic diagram of the operating timing of a power converter provided in an embodiment of this application;

[0033] Figure 8 This is a timing diagram of another power converter provided in an embodiment of this application. Detailed Implementation

[0034] The power converter provided in the embodiments of this application is described in detail below with reference to the accompanying drawings. First, the key terms involved in the embodiments of this application are introduced.

[0035] Photovoltaic modules, also known as photovoltaic panels, are devices used to convert solar energy into direct current (DC) electricity through the photovoltaic effect.

[0036] Energy storage battery: an electrochemical device that can store electrical energy and release it when needed.

[0037] Power grid: The entire system of substations and transmission and distribution lines of various voltages in a power system, also known as the public power grid.

[0038] Box-type substation: also known as box-type substation or box-type transformer, is an integrated power distribution device that can realize the transformation and distribution of electrical energy.

[0039] Power conversion system (PCS): A device used to convert and control electrical energy; it is a type of power converter. The electrical energy conversion here includes the conversion from direct current (DC) to alternating current (AC) and from AC to DC.

[0040] Inverter: A device used to convert direct current (DC) from a direct current source into alternating current (AC), and is a type of power converter. The DC source can be, for example, a photovoltaic (PV) module; accordingly, the inverter is also called a photovoltaic inverter.

[0041] ANPC circuit: A multi-level inverter topology used in photovoltaic inverters and energy storage converters (PCS) to convert direct current (DC) to alternating current (AC). Common ANPC circuits include three-level and five-level circuits. As the names suggest, a three-level ANPC circuit provides three voltage levels (positive, zero, and negative); a five-level ANPC circuit provides five voltage levels (two positive, zero, and two negative).

[0042] Busbar: The wiring connecting the power converter to the DC source. The DC source typically includes a positive terminal and a negative terminal. Correspondingly, the busbar generally includes the positive DC bus (also called the positive bus) BUS+ connected to the positive terminal and the negative DC bus (also called the negative bus) BUS- connected to the negative terminal.

[0043] Pulse-stopping: Power converters typically consist of bridge arms and a controller. Bridge arms include multiple switching transistors. The controller can output pulse-width modulation (PWM) signals to the switching transistors in the bridge arms to control their on / off states. This PWM signal is also called a PWM wave. Correspondingly, the controller outputting a PWM signal means emitting a wave, while pulse-stopping means the controller stops outputting the PWM wave.

[0044] Defensive PWM (DEPWM) modulation: a technique that improves the anti-interference capability and operational reliability of power converters by optimizing the generation and control strategy of PWM signals.

[0045] Taking a power converter including an ANPC circuit as an example, as mentioned earlier, an ANPC circuit typically includes multiple switching transistors, usually insulated-gate bipolar transistors (IGBTs), meaning IGBTs are frequently used as the power semiconductor devices in ANPC circuits. Because IGBTs in ANPC circuits often operate under high-frequency, high-voltage, or high-current conditions, their failure rate is relatively high. Furthermore, IGBTs in some locations experience even greater stress, resulting in correspondingly higher failure rates. For example, some IGBTs are external switching transistors used in the DC connection bus of a photovoltaic inverter. In addition, the losses of external switching transistors are generally relatively high. All of these factors make external switching transistors prone to short-circuit failure. If other switching transistors are then operated normally, it can lead to serious faults such as a bus short circuit, and in severe cases, even cause the fault to propagate. Of course, the switching transistors can also be metal-oxide-semiconductor field-effect transistors (MOSFETs).

[0046] Based on this, this application provides a DEPWM modulation method for power converters to avoid short-circuit faults by controlling the switching transistors in the power converter. It also allows for online detection of short-circuit faults and implementation of safety blocking, thus achieving short-circuit protection. Optionally, the power converter may include a three-level ANPC circuit or a five-level ANPC circuit. The following embodiments use a three-level ANPC circuit as an example.

[0047] Figure 1 A schematic diagram of a possible scenario is shown. (Reference) Figure 1 This scenario includes a DC source, a power converter, a transformer substation, a power grid, and loads. The DC source can include photovoltaic (PV) modules and energy storage batteries. The power converter can include an inverter and a power storage converter system (PCS). The DC source can provide direct current (DC). The inverter in the power converter can convert the DC power provided by the PV modules into alternating current (AC), which is then fed into the power grid and loads via the transformer substation to supply power to the grid and loads. The PCS in the power converter can convert the DC power provided by the energy storage batteries into AC, which is then fed into the power grid and loads via the transformer substation; alternatively, it can convert AC from the grid into DC and output it to the energy storage batteries for energy storage.

[0048] Figure 2 This is a schematic diagram of a power converter provided in an embodiment of this application. Figure 2As shown, the power converter includes: bridge arm 01, positive DC bus BUS+, negative DC bus BUS-, positive DC bus capacitor C1, negative DC bus capacitor C2, and controller 02. Wherein:

[0049] Bridge arm 01 is used to convert the direct current (DC) from photovoltaic modules or energy storage batteries into alternating current (AC). Bridge arm 01 includes a first switch T1, a second switch T2, a third switch T3, a fourth switch T4, a fifth switch T5, and a sixth switch T6. The first switch T1, the second switch T2, the third switch T3, and the fourth switch T4 are connected in series between the positive DC bus BUS+ and the negative DC bus BUS-. The fifth switch T5 is connected between the series connection point of the first switch T1 and the second switch T2 and the sixth switch T6. The sixth switch T6 is connected between the series connection point of the third switch T3 and the fourth switch T4 and the fifth switch T5. The positive DC bus capacitor C1 and the negative DC bus capacitor C2 are connected in series between the positive DC bus BUS+ and the negative DC bus BUS-. The connection point of the positive DC bus capacitor C1 and the negative DC bus capacitor C2 is the bus midpoint N. The bus midpoint N is connected to the connection point of the fifth switch T5 and the sixth switch T6.

[0050] Based on this, it can be seen that the first switch T1 and the fourth switch T4 are the external switches mentioned above. The second switch T2 and the third switch T3 can be called internal switches. The fifth switch T5 and the sixth switch T6 can be called clamping switches. Furthermore, bridge arm 01 can be divided into the upper half of the bridge arm connected between the positive DC bus BUS+ and the bus midpoint N, and the lower half of the bridge arm connected between the negative DC bus BUS- and the bus midpoint N. The first switch T1, the second switch T2, and the fifth switch T5 can be respectively the external switch, the internal switch, and the clamping switch in the upper half of the bridge arm, and the fourth switch T4, the third switch T3, and the sixth switch T6 can be respectively the external switch, the internal switch, and the clamping switch in the lower half of the bridge arm.

[0051] In addition, refer to Figure 2 As can be seen, bridge arm 01 may also include a diode D (also called a freewheeling diode) connected between the emitter and collector of each switching transistor. Figure 2 The diodes connected between the terminals of the first switching transistor T1 to the sixth switching transistor T6 are labeled D1 to D6 respectively.

[0052] Controller 02 is used to control the fifth switch T5 to remain off during the period when the second switch T2 is turned on and the first switch T1 is periodically switched on and off. That is, for the upper half of the bridge arm, controller 02 can control the clamping switch to remain off during the period when the internal switch is turned on and the external switch is periodically switched on and off.

[0053] Understandably, in combination Figure 3 In one embodiment, during the periodic switching of the first switch T1 and the second switch T2 being turned on and off, current can flow out of bridge arm 01 sequentially through the first switch T1 and the second switch T2. At this time, it can be considered that the power converter is operating in the positive half-cycle and current-outflow mode, and the power converter is used to convert DC to AC.

[0054] In some embodiments, as described in the background, the first switch T1 and the fifth switch T5 in bridge arm 01 are complementary switches, that is, the external switch and the clamping switch in the upper half of the bridge arm are complementary switches. When the first switch T1 is turned on, the fifth switch T5 is turned off; and when the first switch T1 is turned off, the fifth switch T5 is turned on. This would cause the positive DC bus BUS+ to connect with the bus midpoint N due to the conduction of the fifth switch T5 in the event of a short circuit in the first switch T1, thereby causing a bus short circuit in the positive DC bus BUS+.

[0055] In the embodiments of this application, the following combination is continued. Figure 3 Because controller 02 can consistently turn off the fifth switch T5, which is complementary to the first switch T1, during the periodic switching of the second switch T2 and the periodic switching of the first switch T1, it ensures that even if the first switch T1 is short-circuited, the positive DC bus BUS+ and the bus midpoint N will not be connected through the fifth switch T5, thus preventing a bus short circuit caused by a short circuit in the first switch T1. This also reduces the fault propagation efficiency of the switch short circuit, allowing sufficient time to detect whether a short circuit has occurred in the first switch T1.

[0056] Furthermore, by keeping the fifth switch T5 normally off, not only will the normal operation of the power converter not be affected, but the operation of the fifth switch T5 can also be reduced, thereby reducing the loss of the fifth switch T5.

[0057] It is understandable that while the fifth switch T5 remains off, its connected diode D5 can also be turned off. That is, in the embodiment of this application, when the power converter is operating in the positive half-cycle and current is flowing out, i.e., during the periodic switching of the external switch in the upper half-arm while the internal switch is conducting, a clamping switch complementary to the external switch and its corresponding diode are kept normally off to prevent a short circuit on the positive DC bus BUS+. This method can also be called a DEPWM modulation.

[0058] It is also understandable that controller 02 could output a PWM signal to the switching transistor in units of switching cycles to control the switching transistor to periodically turn on and off, that is, to control the normal switching of the switching transistor. Furthermore, when the potential of the PWM signal output by controller 02 to the switching transistor is a valid potential (e.g., a positive pulse), the switching transistor can be turned on; when the potential of the PWM signal output by controller 02 to the switching transistor is an invalid potential (e.g., a zero pulse), the switching transistor can be turned off. Alternatively, controller 02 could also control the switching transistor to turn off by stopping the input PWM signal.

[0059] Optionally, the controller 02 can be used to: control the fifth switch T5 to remain off during the process of the second switch T2 being turned on and the first switch T1 being periodically turned on and off, and when the current flowing out of the bridge arm 01 through the first switch T1 and the second switch T2 is greater than the first current threshold.

[0060] The first current threshold can be 5% to 10% of the rated current flowing out of the bridge arm. The rated current refers to the maximum current allowed to flow through the bridge arm when the power converter is operating normally and can maintain stable operation. At this time, the current flows out of bridge arm 01 sequentially through the first switch T1 and the second switch T2. Furthermore, this first current threshold can be a threshold preset in the controller 02, or it can be flexibly adjusted.

[0061] In other words, the triggering conditions for controller 02 to keep the fifth switch T5 off include not only the process of the second switch T2 being turned on and the first switch T1 being periodically switched on and off, but also the magnitude of the current flowing out of bridge arm 01 during this process. Only when the current is large will controller 02 keep the fifth switch T5 off; otherwise, controller 02 can control the fifth switch T5 to also be periodically switched on and off, and control the fifth switch T5 and the first switch T1 to be complementary in their switching on and off states. This prevents current reversal during commutation when the current is small. If the fifth switch T5 is kept constantly off at this time, the current will not flow normally, affecting the normal operation of the power converter. This embodiment of the application, by controlling the fifth switch T5 and the first switch T1 to be complementary in their switching on and off states when the current is small, can avoid current reversal, thereby ensuring the normal operation of the power converter.

[0062] Of course, the triggering method is not limited to the process of the second switch T2 being turned on and the first switch T1 being periodically switched on and off. It can also be triggered based on the current magnitude to control the switching on and off of the fifth switch T5. For example, the triggering can also be achieved by high-speed sampling of the current.

[0063] Optionally, in one implementation, the controller 02 can also be used to: during the process of the second switch T2 being turned on and the first switch T1 being periodically turned on and off, and in the case of the first switch T1 being short-circuited, first control the sixth switch T6 to be turned on, then control the second switch T2 to be turned off, and control the third switch T3, the fourth switch T4 and the fifth switch T5 to remain off.

[0064] Alternatively, in another optional implementation, the controller 02 can also be used to: during the process of the second switch T2 being turned on and the first switch T1 being periodically turned on and off, and in the case of the first switch T1 being short-circuited, first control the sixth switch T6 to be turned on, then control the second switch T2 to be turned off, then control the third switch T3 to be turned on, and control the fourth switch T4 and the fifth switch T5 to remain off.

[0065] That is, in the operating mode where the power converter is in the positive half-cycle and current is flowing out, the controller 02 can also detect whether an external switch in the upper bridge arm is short-circuited. Furthermore, if this external switch is short-circuited, the controller 02 can achieve short-circuit protection by controlling the switching on and off of other switches. For example:

[0066] Controller 02 can control the switching of other switching transistors according to one of the optional implementations described above. This allows current to be first introduced into the lower half-bridge arm, and then flow out of the bridge arm sequentially through the clamping switch and the diodes of the internal switching transistors (i.e., T6 and D3) in the lower half-bridge arm. This allows current to be commutated from the external and internal switching transistors (i.e., T1 and T2) in the upper half-bridge arm to the clamping switch and the diodes of the internal switching transistors in the lower half-bridge arm, preventing short-circuit faults from propagating within the power converter. Correspondingly, the internal switching transistors in the upper half-bridge arm and the external switching transistors (i.e., T2 and T4) in the lower half-bridge arm can withstand the voltages of the positive DC bus BUS+ and the negative DC bus BUS-, respectively, without overvoltage breakdown. Alternatively, controller 02 can control the switching of other switching transistors according to another optional implementation described above. In this way, the current can be introduced into the lower half of the bridge arm first, and then flow out of the bridge arm through the clamping switch and the internal switch in the lower half of the bridge arm in sequence, which can also prevent the spread of short circuit faults.

[0067] Optionally, the controller 02 can detect whether the first switch T1 is short-circuited based on the rate of change of the current flowing out of the bridge arm or the magnitude of the current. For example, the controller 02 can determine that the first switch T1 is short-circuited when the rate of change of the current flowing out of the bridge arm is greater than a speed threshold or the current is greater than a current threshold. Both the speed threshold and the current threshold can be the maximum values ​​determined when the first switch T1 is not short-circuited, and can be preset in the controller 02, or can be flexibly adjusted.

[0068] Optionally, such as Figure 4 As shown, the power converter can include multiple bridge arms 01, and multiple bridge arms 01 can be connected in parallel. Figure 4 The diagram schematically illustrates two bridge arms 01 connected in parallel. Based on this structure, the controller 02 can also be used to: in the event of a short circuit in the first switch T1 of any one of the bridge arms 01, control all switches (i.e., T1 to T6) in the other bridge arms 01 (excluding that bridge arm 01) to be turned off. This also prevents the short-circuit fault from spreading to other bridge arms, thereby achieving safe waveform blocking.

[0069] In summary, the embodiments of this application provide a power converter. Because the controller can control the fifth switch to remain normally off while the second switch in the bridge arm is turned on and the first switch is periodically switched on and off, and because the first switch is connected to the positive DC bus and the fifth switch is connected between the bus midpoint and the series connection point of the first and second switches, it can prevent a short circuit in the bus caused by the positive DC bus connecting to the bus midpoint when the first switch is short-circuited.

[0070] This application also provides a power converter, the structure of which can be referred to... Figure 2 This will not be elaborated further here. Controller 02 is used to: keep the first switch T1 off during the period when the second switch T2 is turned on and the fifth switch T5 is periodically switched on and off. That is, for the upper half of the bridge arm, controller 02 can also control the external switch to remain off during the period when the internal switch is turned on and the clamping switch is periodically switched on and off.

[0071] Understandably, in combination Figure 5 In one embodiment, during the periodic switching of the second switch T2 and the fifth switch T5, current can flow into bridge arm 01 sequentially through the second switch T2 and the fifth switch T5. At this time, it can be considered that the power converter is operating in the positive half-cycle and current-flowing mode, and the power converter can be used to convert AC to DC.

[0072] As described above, in some embodiments, the first switch T1 and the fifth switch T5 in bridge arm 01 are complementary switches. This would cause the positive DC bus BUS+ to connect with the bus midpoint N due to the conduction of the first switch T1 when the fifth switch T5 is short-circuited, thus causing a bus short circuit in the positive DC bus BUS+.

[0073] In the embodiments of this application, the following combination is continued. Figure 5Because controller 02 can consistently turn off the first switch T1, which is complementary to the fifth switch T5, during the periodic switching of the second switch T2 and the fifth switch T5, even if the fifth switch T5 is short-circuited, the positive DC bus BUS+ and the bus midpoint N will not be connected through the first switch T1. This prevents bus short circuits caused by the short circuit of the fifth switch T5 and also reduces the fault propagation efficiency of the switch short circuit, thus allowing sufficient time to detect whether the fifth switch T5 has short-circuited. Furthermore, it also reduces the operation of the first switch T1, thereby reducing its losses.

[0074] It is understandable that during the process of the first switch T1 remaining off, its connected diode D1 can also be turned off. That is, in the embodiment of this application, when the power converter is operating in the positive half-cycle and current is flowing in, i.e., during the periodic switching of the clamping switch in the upper half-arm and the conduction of the internal switch, the positive DC bus BUS+ can be prevented from being short-circuited by controlling the external switch complementary to the clamping switch and the corresponding diode to remain off. This control method can also be called a DEPWM modulation.

[0075] Optionally, the controller 02 can be used to: control the first switch T1 to remain off during the process of the second switch T2 being turned on and the fifth switch T5 being periodically turned on and off, and when the current flowing into the bridge arm 01 through the second switch T2 and the fifth switch T5 is greater than the second current threshold.

[0076] The second current threshold can be 5% to 10% of the rated current flowing into bridge arm 01. For details regarding the rated current and current threshold, please refer to the description of the first current threshold above; it will not be repeated here. The second current threshold can be the same as or different from the first current threshold.

[0077] In other words, the triggering conditions for controller 02 to keep the first switch T1 off include not only the process of the second switch T2 being turned on and the fifth switch T5 being periodically switched on and off, but also the magnitude of the current flowing into bridge arm 01 during this process. Only when the current is large will controller 02 keep the first switch T1 off; otherwise, controller 02 can control the first switch T1 to also be periodically switched on and off, and control the first switch T1 and the fifth switch T5 to be switched on and off complementaryly. This also prevents the current from reversing during the commutation process when the current is small, thus avoiding affecting the normal operation of the power converter.

[0078] Optionally, in the first embodiment, the controller 02 can also be used to: control the second switch T2 to remain on while the fifth switch T5 is periodically switched on and off, and control the first switch T1, the third switch T3, the fourth switch T4 and the sixth switch T6 to remain off when the fifth switch T5 is short-circuited.

[0079] Optionally, in the second embodiment, the controller 02 can also be used to: control the second switch T2 to turn off during the periodic switching of the second switch T2 and the fifth switch T5, and in the case of a short circuit of the fifth switch T5, control the first switch T1 and the fourth switch T4 to remain off, and control the sixth switch T6 and the third switch T3 to turn on.

[0080] That is, in the operating mode where the power converter is operating during the positive half-cycle and current is flowing in, controller 02 can also detect whether a short circuit has occurred in the clamping switch in the upper half-bridge arm. Furthermore, if a short circuit occurs in this clamping switch, controller 02 can achieve short-circuit protection by controlling the switching on and off of other switches. For example:

[0081] Controller 02 can control the switching on and off of the other switches according to the first embodiment described above. This allows current to flow sequentially through the internal switches and clamping switches (i.e., T2 and T5) in the upper half-bridge arm, preventing short-circuit faults from propagating within the power converter. Alternatively, controller 02 can control the switching on and off of the other switches according to the second embodiment described above. This allows current to be introduced into the lower half-bridge arm and flow sequentially through the internal switches and clamping switches (i.e., T3 and T6) in the lower half-bridge arm, similarly preventing short-circuit fault propagation.

[0082] Of course, the methods are not limited to those described above. For example, controller 02 can also control all switches in the upper half-bridge arm where a short circuit occurs to be turned off. That is, while controlling the external switch (i.e., T1) in the upper half-bridge arm to remain off, it also controls the internal switch (i.e., T2) in the upper half-bridge arm to be turned off, so that the current flows sequentially through the diode and clamping switch (i.e., D2 and T5) of the internal switch in the upper half-bridge arm. Alternatively, it can control the internal switch (i.e., T2) in the upper half-bridge arm to remain on, and simultaneously control the internal switch and clamping switch (i.e., T3 and T6) in the lower half-bridge arm to be on, so that the current flows sequentially through the internal switch and clamping switch (i.e., T2 and T3) in the upper half-bridge arm, and sequentially through the internal switch and clamping switch (i.e., T3 and T6) in the lower half-bridge arm. Both of these methods can prevent the short circuit fault from spreading.

[0083] Optionally, the controller 02 can also determine that the fifth switch T5 is short-circuited when the rate of change of the current flowing into the bridge arm exceeds a speed threshold or the current exceeds a current threshold. Both the speed threshold and the current threshold can be the maximum values ​​determined when the fifth switch T5 is not short-circuited, and can be preset in the controller 02, or adjusted flexibly.

[0084] Optionally, in Figure 4 Based on the structure, the controller 02 can also be used to: in the event of a short circuit in the fifth switch T5 of any one of the bridge arms 01, control all switches in the other bridge arms 01 to be turned off. This also prevents the short circuit fault from spreading to other bridge arms, thereby achieving safe waveform blocking.

[0085] In summary, the embodiments of this application provide a power converter. Because the controller can control the first switch to remain normally off during the periodic switching of the second switch in the bridge arm and the periodic switching of the fifth switch, and because the first switch is connected to the positive DC bus, and the fifth switch is connected between the midpoint of the bus and the series connection point of the first and second switches, a short circuit can be prevented between the positive DC bus and the midpoint of the bus when the fifth switch is short-circuited.

[0086] It is understood that the above embodiments are all based on the upper half-bridge arm of the power converter, in the operating mode where the power converter operates in the positive half-cycle and current flows in or out, as an example of the protection control method. Since the lower half-bridge arm has the same structure as the upper half-bridge arm, it can be known that for the lower half-bridge arm, in the operating mode where the power converter operates in the negative half-cycle and current flows in or out, the controller 02 can perform the same control to prevent the negative DC bus BUS- from short-circuiting due to a short circuit in the switching transistor, and to prevent the spread of the short-circuit fault when the switching transistor is short-circuited, which will not be elaborated here.

[0087] Optionally, the power converter may also include a current sensing circuit for the controller 02 to detect current. The current sensing circuit may be a Hall element. The controller 02 may be a microcontroller unit (MCU).

[0088] For example, taking the power converter operating in the positive half-cycle as an example, that is, for the upper half-bridge arm, Figure 6 A schematic diagram illustrating the operation of a power converter is shown. Figure 6As shown, when the power converter is operating in the positive half-cycle, controller 02 can first determine whether the current is flowing out of or into the bridge arm. If the current is not flowing out of the bridge arm, controller 02 can control the clamping switch T5 in the upper half-bridge arm to switch normally (i.e., periodically turn on and off), and simultaneously control the external switch T1 in the upper half-bridge arm to remain normally off. If the current is flowing out of the bridge arm, controller 02 can further determine whether the absolute value |i| of the current i is greater than the first current threshold ith. If |i|>ith, controller 02 can control the external switch T1 in the upper half-bridge arm to switch normally, and control the clamping switch T5 in the upper half-bridge arm to remain normally off. Otherwise, controller 02 can control the external switch T1 and the clamping switch T5 in the upper half-bridge arm to complement each other. In this way, the clamping switch T5 is controlled to remain normally off only when the current is large, so as to avoid short circuit of the positive DC bus BUS+ and prevent the current from reversing, thus avoiding affecting the normal operation of the power converter. Afterwards, it is possible to continue detecting whether the external switch T1 in the upper half-bridge arm is short-circuited, and if the external switch T1 is short-circuited, it can be detected by executing... Figure 7 The timing shown is to prevent the spread of short-circuit faults, achieve short-circuit protection, and ensure safe waveform blocking. Figure 6 In the diagram, Y represents a yes result and N represents a no result.

[0089] refer to Figure 7 At this time, the current can be a positive value greater than 0. Flg can be a short-circuit flag, used to indicate whether the external switch T1 in the upper half-bridge arm has been short-circuited.

[0090] When the external switch T1 in the upper half-bridge arm is not short-circuited, the potential of Flg can be low. At this time, controller 02 can normally output a PWM signal to the external switch T1 in the upper half-bridge arm, causing T1 to periodically turn on and off. It can also output a valid potential signal to the internal switch T2 in the upper half-bridge arm, turning it on, and an invalid potential signal to the clamping switch T5 in the upper half-bridge arm, keeping it normally off. This prevents a short circuit in the positive DC bus BUS+ due to a short circuit in the external switch T1. During this process, controller 02 can also output invalid potential signals to the external switch T4, internal switch T3, and clamping switch T6 in the lower half-bridge arm, turning off all switches in the lower half-bridge arm.

[0091] When the external switch T1 in the upper half-bridge arm is short-circuited, the short-circuit flag Flg can be set to a high potential. At this time, after a period ΔT1, controller O2 first outputs a valid potential signal to the clamping switch T6 in the lower half-bridge arm, turning it on. Then, after a period ΔT2, it outputs an invalid potential signal to the internal switch T2 in the upper half-bridge arm, turning it off. Finally, after a period ΔT3, it outputs a valid potential signal to the internal switch T3 in the lower half-bridge arm, turning it on. In this way, current can be commutated to the lower half-bridge arm and flow out sequentially through the clamping switch T6 and the internal switch T3, preventing the short-circuit fault from spreading.

[0092] Example, Figure 8 Another timing diagram is shown, taking the power converter operating in the positive half-cycle with current flowing into the bridge arm as an example. (Reference) Figure 8 At this time, the current can be a negative value less than 0. Flg is also a short-circuit flag, used to indicate whether the clamping switch T5 in the upper half-bridge arm has short-circuited.

[0093] When the clamping switch T5 in the upper half-bridge arm is not short-circuited, the potential of Flg can be low. At this time, controller 02 can normally transmit a signal to clamping switch T5 in the upper half-bridge arm, causing it to periodically turn on and off. It can also output a valid potential signal to internal switch T2 in the upper half-bridge arm, turning it on, and an invalid potential signal to external switch T1 in the upper half-bridge arm, keeping it normally off. This prevents a short circuit in the positive DC bus BUS+ due to a short circuit in clamping switch T5. During this process, controller 02 can also output invalid potential signals to external switch T4, internal switch T3, and clamping switch T6 in the lower half-bridge arm, turning off all switches in the lower half-bridge arm.

[0094] When the clamping switch T5 in the upper half-bridge arm is short-circuited, the short-circuit flag Flg can be set to a high potential. At this time, the controller O2 can continue to output a valid potential signal to the internal switch T2 in the upper half-bridge arm, keeping the internal switch T2 on. It can also output an invalid potential signal to the external switch T1 in the upper half-bridge arm, and to the external switch T4, internal switch T3, and clamping switch T6 in the lower half-bridge arm, keeping the external switch T1 in the upper half-bridge arm and all switches in the lower half-bridge arm off. In this way, current flows sequentially through the internal switch T2 and the clamping switch T3 in the upper half-bridge arm, preventing the short-circuit fault from spreading.

[0095] In addition, Figure 4 Based on the structure, combined with Figure 7and combination Figure 8 When a short circuit occurs in the switching transistor of any bridge arm, the controller 02 can also stop outputting PWM signals to other bridge arms, that is, block the waveform for other bridge arms to prevent the short circuit fault from spreading to other bridge arms and achieve safe waveform blocking.

[0096] Optionally, Figure 7 and Figure 8 In this context, the effective potential is higher than the ineffective potential, and all are represented by setting the potential to high to indicate the blocking of other bridge arms.

[0097] Understandable, Figure 7 and Figure 8 These are all schematic representations of one operating sequence. That is, as mentioned above, controller 02 can also achieve short-circuit protection through other control methods, and the corresponding sequence is not shown here.

[0098] 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.

[0099] The above description is merely an optional embodiment of this application, but the scope 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 this application. Therefore, the scope of this application should be determined by the scope of the claims.

Claims

1. A power converter, characterized by, The power converter comprises a bridge arm, a positive DC bus, a negative DC bus, a positive DC bus capacitor, a negative DC bus capacitor and a controller, wherein: The bridge arm is used to convert DC power of a photovoltaic module or an energy storage battery into AC power, and comprises a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube and a sixth switch tube, wherein the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are connected in series between the positive DC bus and the negative DC bus, the fifth switch tube is connected between a series connection point of the first switch tube and the second switch tube and the sixth switch tube, and the sixth switch tube is connected between a series connection point of the third switch tube and the fourth switch tube and the fifth switch tube; the positive DC bus capacitor and the negative DC bus capacitor are connected in series between the positive DC bus and the negative DC bus, and a series connection point of the positive DC bus capacitor and the negative DC bus capacitor is a bus midpoint, which is connected to a series connection point of the fifth switch tube and the sixth switch tube; The controller is used to control the fifth switch tube to remain off during the process that the second switch tube is turned on and the first switch tube is periodically turned on and off.

2. The power converter of claim 1, wherein, The controller is used to control the fifth switch tube to remain off during the process that the second switch tube is turned on and the first switch tube is periodically turned on and off, and in the case that a current flowing out of the bridge arm through the first switch tube and the second switch tube is greater than a first current threshold value, wherein the first current threshold value is 5% to 10% of a rated current flowing out of the bridge arm.

3. A power converter as claimed in claim 1 or 2, characterised in that, The controller is further used to, during the process that the second switch tube is turned on and the first switch tube is periodically turned on and off, and in the case that the first switch tube is short-circuited, first control the sixth switch tube to be turned on, then control the second switch tube to be turned off, and control the third switch tube, the fourth switch tube and the fifth switch tube to remain off.

4. The power converter of claim 1 or 2, wherein, The controller is further used to, during the process that the second switch tube is turned on and the first switch tube is periodically turned on and off, and in the case that the first switch tube is short-circuited, first control the sixth switch tube to be turned on, then control the second switch tube to be turned off, and control the third switch tube, the fourth switch tube and the fifth switch tube to remain off.

5. The power converter of claim 1 or 2, wherein, The number of the bridge arms is plural, and the bridge arms are connected in parallel; The controller is further used to control each switch tube included in a bridge arm other than the one bridge arm to be turned off in the case that the first switch tube included in the one bridge arm is short-circuited.

6. A power converter, characterized by, The power converter comprises a bridge arm, a positive DC bus, a negative DC bus, a positive DC bus capacitor, a negative DC bus capacitor and a controller, wherein: The bridge arm is used for converting direct current of a photovoltaic module or an energy storage battery into alternating current, and comprises a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube and a sixth switch tube, wherein the first switch tube, the second switch tube, the third switch tube and the fourth switch tube are connected in series between the positive direct current bus and the negative direct current bus in sequence, the fifth switch tube is connected between a series connection point of the first switch tube and the second switch tube and the sixth switch tube, and the sixth switch tube is connected between a series connection point of the third switch tube and the fourth switch tube and the fifth switch tube; the positive direct current bus capacitor and the negative direct current bus capacitor are connected in series between the positive direct current bus and the negative direct current bus, a series connection point of the positive direct current bus capacitor and the negative direct current bus capacitor is a bus midpoint, and the bus midpoint is connected to a series connection point of the fifth switch tube and the sixth switch tube. The controller is configured to control the first switch tube to remain off during the process that the second switch tube is turned on and the fifth switch tube is periodically turned on and off.

7. The power converter of claim 6, wherein, The controller is configured to control the first switch tube to remain off during the process that the second switch tube is turned on and the fifth switch tube is periodically turned on and off, and in the case that a current flowing into the bridge arm through the second switch tube and the fifth switch tube is greater than a second current threshold value, wherein the second current threshold value is 5% to 10% of a rated current flowing into the bridge arm.

8. A power converter as claimed in claim 6 or 7, characterised in that, The controller is further configured to control the second switch tube to remain turned on, and control the first switch tube, the third switch tube, the fourth switch tube and the sixth switch tube to remain off, during the process that the second switch tube is turned on and the fifth switch tube is periodically turned on and off, and in the case that the fifth switch tube is short-circuited.

9. The power converter of claim 6 or 7, wherein, The controller is further configured to control the second switch tube to be turned off, control the first switch tube and the fourth switch tube to remain off, and control the sixth switch tube and the third switch tube to be turned on, during the process that the second switch tube is turned on and the fifth switch tube is periodically turned on and off, and in the case that the fifth switch tube is short-circuited.

10. The power converter of claim 6 or 7, wherein, The number of the bridge arms is multiple, and the multiple bridge arms are connected in parallel; The controller is further configured to control each switch tube included in other bridge arms except for the any bridge arm to be turned off, in the case that the fifth switch tube included in the any bridge arm is short-circuited.

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