Flying capacitor pre-charging circuit, control method and three-level converter

Abstract

The present application relates to a pre-charging circuit, a control method and a three-level converter for a flying capacitor. The pre-charging circuit switches the connection between the lower bus capacitor and the first clamping unit or the second clamping unit through a switching unit, and forms a corresponding forward pre-charging circuit and a reverse pre-charging circuit with the same boost power conversion unit, so as to select a preset pre-charging method to charge the flying capacitor according to the relationship between the supply voltage and the bus voltage. The connection between the lower bus capacitor and the first clamping unit or the second clamping unit is switched by the switching unit. When the pre-charging circuit is not working properly, the current loop that charges the input unit and generates a floating voltage at the input end is cut off, and when the pre-charging circuit is working properly, the abnormal current loop that charges the lower bus capacitor is cut off, so that the voltage of the flying capacitor can be equal to half the bus voltage. Through this application, the problems of low-frequency pulsating current, floating voltage at the input end and easy breakdown of semiconductor devices in the flying capacitor boost circuit are solved.

Description

Technical Field

[0001] The present application relates to the technical field of flying capacitor pre-charging, and in particular to a flying capacitor pre-charging circuit, a control method, and a three-level converter. Background Art

[0002] In the dual-diode clamped flying capacitor boost circuit of the related technology, when there are multiple flying capacitor boost circuits in parallel, when at least one of the flying capacitor boost circuits charges the bus capacitor, for the flying capacitor boost circuit that has not yet been powered on, the bus voltage has been established before the circuit is started. At this time, there is a current path to charge the input capacitor, causing a floating voltage to be formed at the input end. The higher floating voltage can easily cause the unpowered flying capacitor boost circuit to start up incorrectly, and there is a risk of electric shock. At the same time, the flying capacitor boost circuit in the related technology also has the problems of low-frequency pulsating current, easy voltage imbalance between the upper and lower bus capacitors, and large voltage stress of the corresponding semiconductor devices when the circuit is started, which can easily cause the corresponding semiconductor devices to break down.

[0003] There is no effective solution to the problems of low-frequency pulsating current, floating voltage at the input end, and easy breakdown of semiconductor devices in the flying capacitor boost circuit in the related art. Summary of the Invention

[0004] The present application provides a flying capacitor pre-charging circuit, a control method and a three-level converter to at least solve the problems of low-frequency pulsating current, floating voltage at the input end and easy breakdown of semiconductor devices in the flying capacitor boost circuit in the related art.

[0005] In the first aspect, the present application provides a pre-charging circuit for a flying capacitor, comprising an input unit, a boost power conversion unit, a flying capacitor, a first clamping unit, a second clamping unit, a switching unit, an upper bus capacitor and a lower bus capacitor, wherein the input unit is electrically connected to a power supply unit, a bus and the boost power conversion unit, respectively, and is used to transmit the power supply voltage provided by the power supply unit to the bus and the boost power conversion unit; when the power supply voltage is greater than the bus voltage of the bus, the boost power conversion unit is electrically connected to the flying capacitor, the first clamping unit, the switching unit and the lower bus capacitor in sequence and A forward pre-charging circuit is formed; when the supply voltage is lower than the bus voltage, the boost power conversion unit is electrically connected to the flying capacitor, the second clamping unit, the switching unit and the lower bus capacitor in sequence to form a reverse pre-charging circuit, wherein the forward pre-charging circuit is used to charge the flying capacitor based on the supply voltage, and the reverse pre-charging circuit is used to charge the flying capacitor based on the half-bus voltage corresponding to the intermediate connection point between the upper bus capacitor and the lower bus capacitor; the switching unit is used to selectively electrically connect the intermediate connection point to the first clamping unit or the second clamping unit.

[0006] In some embodiments, the pre-charging circuit further includes a control module, the switch switching unit includes a controlled switch, the controlled switch includes a first input end, a first controlled end, a first output end, and a second output end, the first input end is electrically connected to the lower bus capacitor, the first controlled end is electrically connected to the control module, the first output end is electrically connected to the output end of the first clamping unit, and the second output end is electrically connected to the input end of the second clamping unit, wherein the control module is configured to output a corresponding enable signal to the controlled switch; and the controlled switch is configured to control the first input end to selectively connect to the first output end or the second output end according to the received enable signal.

[0007] In some embodiments, the switch switching unit further includes a current limiting unit, a first end of the current limiting unit being electrically connected to the lower bus capacitor, and a second end of the current limiting unit being electrically connected to the first input end of the controlled switch, wherein the current limiting unit is used to limit the magnitude of a current flowing through the controlled switch, the first clamping unit, and the second clamping unit.

[0008] In some embodiments, the controlled switch includes a bistable relay, which includes a first port, a second port, a third port, a fourth port and a fifth port, wherein the first port is connected to the first input end, the second port is connected to the first output end, the third port is connected to the second output end, the fourth port is connected to the first controlled end, and the fifth port is electrically connected to the first power supply, wherein the bistable relay is configured to control the first port to be connected to the second port when the level of the enable signal received at the fourth port is a preset high level, so that the intermediate connection point is connected to the first clamping unit, and to control the first port to be connected to the third port when the level of the enable signal received at the fourth port is a preset low level, so that the intermediate connection point is connected to the second clamping unit.

[0009] In some embodiments, the boost power conversion circuit includes an inductor L, a first diode D1, a second diode D2, a first switch transistor T1, and a second switch transistor T2; the input unit includes an input capacitor Cin and a bypass diode D3; one end of the input capacitor Cin is electrically connected to the anode of the bypass diode D3 and the first end of the inductor L, respectively; the second end of the inductor L is electrically connected to the input end of the first switch transistor T1 and the anode of the second diode D2, respectively; the output end of the first switch transistor T1 is electrically connected to the input end of the second switch transistor T2, the first end of the flying capacitor, and the input end of the first clamping unit, respectively; the output end of the second switch transistor T2 is connected to the other end of the input capacitor Cin; the controlled end of the first switch transistor T1 and the controlled end of the second switch transistor T2 are both electrically connected to the control module; the cathode of the second diode D2 is electrically connected to the anode of the first diode D1, the second end of the flying capacitor, and the output end of the second clamping unit, respectively; and the cathode of the first diode D1 and the cathode of the bypass diode D3 are both electrically connected to the bus.

[0010] In some embodiments, the first clamping unit and the second clamping unit are both diodes.

[0011] In a second aspect, the present application provides a control method for a pre-charging circuit, which is applied to the pre-charging circuit of the flying capacitor described in the first aspect, and the control method includes:

[0012] Determining whether the supply voltage is greater than the bus voltage;

[0013] When it is determined that the supply voltage is greater than the bus voltage, the switching unit is enabled to connect the first clamping unit to the lower bus capacitor, and to charge the flying capacitor based on the supply voltage through a forward pre-charging circuit corresponding to a first preset charging mode until the voltage of the flying capacitor is greater than a preset starting voltage, wherein the forward pre-charging circuit is composed of the inductor L, the first switch T1, the second diode D2, the first clamping unit, the switching unit, and the lower bus capacitor;

[0014] When it is determined that the supply voltage is lower than the bus voltage, the switch switching unit is enabled to connect the second clamping unit to the lower bus capacitor, and the flying capacitor is charged based on the half bus voltage through a reverse pre-charging circuit corresponding to a second preset charging method until the voltage of the flying capacitor is greater than a preset starting voltage, wherein the reverse pre-charging circuit is composed of the input capacitor Cin, the inductor L, the freewheeling diode TD1 corresponding to the first switch tube T1, the second switch tube T2, the second clamping unit, the switch switching unit and the lower bus capacitor.

[0015] In some embodiments, during the process of charging the flying capacitor based on the supply voltage through the forward pre-charging circuit corresponding to the first preset charging mode, the control method includes:

[0016] Sending a first pulse signal with a preset duty cycle to the first switch tube T1 within a first preset time;

[0017] When the first switch tube T1 controls the input terminal and the output terminal of the first switch tube T1 to be connected according to the first pulse signal received by the controlled terminal, the inductor L, the first switch tube T1, the first clamping unit, the switching unit, and the lower bus capacitor form an energy storage loop corresponding to the forward pre-charging loop, and stores energy in the inductor L based on the supply voltage. When the first switch tube T1 controls the input terminal and the output terminal of the first switch tube T1 to be disconnected according to the first pulse signal received by the controlled terminal, the inductor L, the second diode D2, the flying capacitor, the first clamping unit, the switching unit, and the lower bus capacitor form a discharge loop corresponding to the forward pre-charging loop, and charges the flying capacitor based on the supply voltage.

[0018] After the flying capacitor is charged for the first preset time, the voltage of the flying capacitor is less than the preset starting voltage. After waiting for a preset interval time, the first pulse signal is again transmitted to the first switch tube T1, and the flying capacitor is charged based on the supply voltage through the forward pre-charging circuit.

[0019] During the first preset time, the voltage of the flying capacitor is greater than the preset starting voltage, the first pulse signal is stopped from being transmitted to the first switch tube T1, and the switch switching unit is enabled to connect the second clamping unit to the lower bus capacitor.

[0020] In some embodiments, during the process of charging the flying capacitor based on the half-bus voltage through the reverse pre-charging loop corresponding to the second preset charging mode, the control method includes:

[0021] transmitting a second pulse signal with a preset duty cycle to the second switch tube T2 within a second preset time;

[0022] When the second switch tube T2 controls the input terminal and the output terminal of the second switch tube T2 to be connected according to the second pulse signal received by the controlled terminal, the second switch tube T2, the flying capacitor, the second clamping unit, the switching unit, and the lower bus capacitor form a first reverse charging loop corresponding to the reverse pre-charging loop, and charges the flying capacitor based on the half-bus voltage; and when the second switch tube T2 controls the input terminal and the output terminal of the second switch tube T2 to be disconnected according to the second pulse signal received by the controlled terminal, the input capacitor Cin, the inductor L, the freewheeling diode TD1, the flying capacitor, the second clamping unit, the switching unit, and the lower bus capacitor form a second reverse charging loop corresponding to the reverse pre-charging loop, and charges the flying capacitor based on the half-bus voltage;

[0023] After the flying capacitor is charged for the second preset time, the voltage of the flying capacitor is less than the preset starting voltage. After waiting for the preset interval time, the second pulse signal is again transmitted to the second switch tube T2, and the flying capacitor is charged based on the half bus voltage through the reverse pre-charging circuit.

[0024] During the second preset time, the voltage of the flying capacitor is greater than the preset starting voltage, and the second pulse signal is stopped from being transmitted to the second switch tube T2 to stop charging the flying capacitor.

[0025] In a third aspect, the present application provides a flying capacitor three-level converter, comprising the flying capacitor pre-charging circuit described in the first aspect.

[0026] Compared with the related art, the present embodiment provides a pre-charging circuit, a control method and a three-level converter for a flying capacitor. The pre-charging circuit of the flying capacitor is provided by setting an input unit, a boost power conversion unit, a flying capacitor, a first clamping unit, a second clamping unit, a switch switching unit, an upper bus capacitor and a lower bus capacitor, and providing voltage to the bus and the boost power conversion unit through the input unit, switching the connection between the lower bus capacitor and the first clamping unit or the second clamping unit through the switch switching unit, and forming a corresponding forward pre-charging circuit and a reverse pre-charging circuit with the same boost power conversion unit, so as to realize the selection of a preset pre-charging method to charge the flying capacitor according to the relationship between the supply voltage and the bus voltage, and at the same time, switching the upper bus capacitor and the lower bus capacitor through the switch switching unit. The middle connection point of the line capacitor is connected to the first clamping unit or the second clamping unit. When the pre-charging circuit is not working properly, the current loop that charges the input unit and generates the floating voltage at the input end is cut off. When the pre-charging circuit is working normally, the abnormal current loop that charges the lower bus capacitor is cut off, so that the voltage at the middle connection point is maintained at half the bus voltage. This solves the problems of low-frequency pulsating current, floating voltage at the input end and easy breakdown of semiconductor devices in the flying capacitor boost circuit in the related technology, and achieves the beneficial effects of eliminating the low-frequency pulsating current and floating voltage at the input end in the dual-diode clamped flying capacitor boost circuit, reducing the voltage stress of the upper diode and the lower switch tube when the flying capacitor boost circuit is started, and avoiding overvoltage breakdown of semiconductor devices.

[0027] The details of one or more embodiments of the present application are set forth in the following drawings and description to make other features, objects, and advantages of the present application more readily apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0030] Figure 1 This is a logic block diagram of a pre-charging circuit for a flying capacitor provided in an embodiment of the present application;

[0031] Figure 2 1 is a topological diagram of a pre-charging circuit of a flying capacitor provided in an embodiment of the present application;

[0032] Figure 3Schematic diagram of the current conduction path of the energy storage circuit corresponding to the forward pre-charging circuit provided in an embodiment of the present application;

[0033] Figure 4 Schematic diagram of the current conduction path of the discharge circuit corresponding to the forward pre-charge circuit provided in an embodiment of the present application;

[0034] Figure 5 Schematic diagram of the current conduction path of the first reverse charging circuit corresponding to the reverse pre-charging circuit provided in an embodiment of the present application;

[0035] Figure 6 Schematic diagram of the current conduction path of the second reverse charging circuit corresponding to the reverse pre-charging circuit provided in an embodiment of the present application;

[0036] Figure 7 is a flow chart of a method for controlling a pre-charging circuit according to an embodiment of the present application;

[0037] Figure 8 4 is a flow chart of a method for controlling a pre-charging circuit according to a preferred embodiment of the present application. DETAILED DESCRIPTION

[0038] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0039] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0040] Figure 1 This is a logic block diagram of a flying capacitor pre-charging circuit provided in an embodiment of the present application. Figure 2 is a topological diagram of a pre-charging circuit of a flying capacitor provided in an embodiment of the present application, Figures 1 to 2 The flying capacitor pre-charging circuit shown in the figure switches the connection between the lower bus capacitor C2 and the first clamping unit 300 or the second clamping unit 400 through the switch switching unit 500. When the pre-charging circuit is not working properly, the current loop that charges the input unit 100 and generates the input floating voltage is cut off. When the pre-charging circuit is working properly, the abnormal current loop that charges the lower bus capacitor C2 is cut off, so that the voltage between the middle connection point of the upper bus capacitor C1 and the lower bus capacitor C2 (which is also the bus midpoint of the corresponding flying capacitor three-level boost circuit) and the bus negative electrode BUS- is maintained at half the bus voltage, thereby making the voltage across the flying capacitor Cf half the bus voltage.

[0041] See also Figures 1 to 2 The flying capacitor pre-charging circuit provided in the embodiment of the present application includes an input unit 100, a boost power conversion unit 200, a flying capacitor Cf, a first clamping unit 300, a second clamping unit 400, a switch switching unit 500, an upper bus capacitor C1 and a lower bus capacitor C2, wherein:

[0042] The input unit 100 is electrically connected to the power supply unit (external power source for providing DC voltage, such as a solar cell array), the bus BUS and the boost power conversion unit 200, respectively, and is used to transmit the power supply voltage Vin provided by the power supply unit to the bus BUS and the boost power conversion unit 200.

[0043] In this embodiment, the positive electrode BUS+ of the bus BUS is the bus voltage output end, which is also the high-voltage side of the flying capacitor three-level boost circuit, corresponding to "1" in the three-level voltage level. The middle connection point between the upper bus capacitor C1 and the lower bus capacitor C2 is the zero potential point, corresponding to "0" in the three-level voltage level. The negative electrode BUS- of the bus BUS is the low-voltage side of the flying capacitor three-level boost circuit, corresponding to "-1" in the three-level voltage level, and the negative electrode BUS- of the bus BUS is electrically connected to the low-voltage side of the power supply unit and the pre-charging circuit.

[0044] In this embodiment, the input unit 100 includes an input capacitor Cin and a bypass diode D3. After the current pre-charging circuit is powered on, the supply voltage Vin provided by the power supply unit will raise the voltage of the bus BUS to the bus voltage V_bus through the bypass diode D3. That is, the bus voltage V_bus is established by the supply voltage Vin. At the same time, the supply voltage Vin will synchronously transmit a corresponding voltage to the boost power conversion unit 200 to pre-charge the flying capacitor Cf. When the supply voltage Vin is greater than the bus voltage V_bus, the bus voltage V_bus is generated by the supply voltage Vin. The voltage Vin is established; when multiple pre-charging circuits are connected in parallel in a photovoltaic system, the bus voltage has been established for a pre-charging circuit that is not powered on, but the input voltage of this pre-charging circuit has not yet been established, so Vin < V_bus. At this time, it is necessary to consider which pre-charging method to use to charge the flying capacitor Cf. It should be noted that the parallel connection of multiple pre-charging circuits in a photovoltaic system means that the output end of the previous pre-charging circuit is connected in parallel to the bus, and the input end of each pre-charging circuit is connected to the solar cell array (the solar cell array corresponds to the power supply unit). The boost power conversion unit is also coupled and electrically connected to the flying capacitor Cf, the first clamping unit 300, and the second clamping unit 400 respectively. The switching unit 500 is also coupled and electrically connected to the first clamping unit 300, the second clamping unit 400, and the lower bus capacitor C2 respectively. The end of the lower bus capacitor C2 electrically connected to the switching unit 500 is also electrically connected to the upper bus capacitor C1, and the upper bus capacitor C1 is also connected to the positive electrode BUS+ of the bus BUS.

[0045] When the supply voltage Vin is greater than the bus voltage V_bus of the bus, the boost power conversion unit 200 is electrically connected to the flying capacitor Cf, the first clamping unit 300, the switch switching unit 500 and the grounded lower bus capacitor C2 in sequence to form a forward pre-charging loop; when the supply voltage Vin is less than the bus voltage V_bus, the boost power conversion unit 200 is electrically connected to the flying capacitor Cf, the second clamping unit 400, the switch switching unit 500 and the lower bus capacitor C2 in sequence to form a reverse pre-charging loop, wherein the forward pre-charging loop is used to charge the flying capacitor Cf based on the supply voltage Vin, and the reverse pre-charging loop is used to charge the flying capacitor Cf based on the half-bus voltage corresponding to the intermediate connection point between the upper bus capacitor C1 and the lower bus capacitor C2 (actually the voltage between the intermediate connection point and the bus negative pole BUS-).

[0046] In this embodiment, the first clamping unit 300 includes a diode D4 , and the second clamping unit 400 includes a diode D5 .

[0047] In this embodiment, the first clamping unit 300 and the second clamping unit 400 are respectively used to perform voltage clamping on the semiconductor devices of the boost power conversion unit 200 close to the negative electrode BUS- of the bus BUS and close to the positive electrode BUS+ of the bus BUS. Specifically, the first clamping unit 300 is used to Figure 2 The second switch tube T2 shown in FIG is used to perform voltage clamping. The second clamping unit 400 is used to clamp the voltage of the second switch tube T2. Figure 2 The first diode D1 shown in FIG. 1 performs voltage clamping, thereby reducing the voltage stress of the first diode D1 and the second switch tube T2 before the voltage of the flying capacitor Cf reaches a preset starting voltage.

[0048] The switch switching unit 500 is used to selectively electrically connect the back ground end of the lower bus capacitor C2 to the first clamping unit 300 or the second clamping unit 400, so that the voltage between the two ends of the flying capacitor Cf can be maintained at half the bus voltage or the current loop for reverse charging to the input unit 100 is cut off.

[0049] In this embodiment, when a forward pre-charging circuit is used to charge the flying capacitor Cf, the switching unit 500 connects the first clamping unit 300 to the lower bus capacitor C2. When a reverse pre-charging circuit is used to charge the flying capacitor Cf, the switching unit 500 connects the second clamping unit 400 to the lower bus capacitor C2. In this embodiment, when the voltage of the flying capacitor Cf of the current pre-charging circuit reaches a set starting voltage, the switching unit 500 connects the second clamping unit 400 to the lower bus capacitor C2. When the pre-charging circuit operates normally, the abnormal current loop charging the lower bus capacitor C2 is cut off, and the voltage on the flying capacitor Cf can be controlled to half the bus voltage, eliminating pulsating current. At the same time, when there are multiple pre-charging circuits connected in parallel, before the unpowered pre-charging circuit is powered on, the switching unit 500 connects the first clamping unit 300 to the lower bus capacitor C2, cutting off the current loop that reversely charges the input unit 100 and preventing the generation of floating voltage at the input end.

[0050] It should be noted that the embodiment of the present application is provided with an input unit 100, a boost power conversion unit 200, a flying capacitor Cf, a first clamping unit 300, a second clamping unit 400, a switching unit 500 and a lower bus capacitor C2, and the input unit 100 provides a voltage to the bus BUS and the boost power conversion unit 200, and the switching unit 500 switches the connection between the lower bus capacitor C2 and the first clamping unit 300 or the second clamping unit 400, and forms a corresponding forward pre-charging circuit and a reverse pre-charging circuit with the same boost power conversion unit 200, and selects a preset pre-charging method to charge the flying capacitor Cf according to the relationship between the supply voltage Vin and the bus voltage V_bus, and at the same time, switches the lower bus capacitor C2 through the switching unit 500. 2 is connected to the first clamping unit 300 or the second clamping unit 400. When the pre-charging circuit is not working properly, the current loop that charges the input unit 100 and generates the floating voltage at the input end is cut off. When the pre-charging circuit is working properly, the abnormal current loop that charges the lower bus capacitor C2 is cut off, so that the voltage between the two ends of the flying capacitor Cf can be equal to half the bus voltage. This solves the problems of low-frequency pulsating current, floating voltage at the input end, and easy breakdown of semiconductor devices in the flying capacitor boost circuit in the related art. It achieves the beneficial effects of eliminating the low-frequency pulsating current and floating voltage at the input end in the dual-diode clamped flying capacitor boost circuit, reducing the voltage stress of the upper diode and the lower switch tube when the flying capacitor boost circuit is started, and avoiding overvoltage breakdown of semiconductor devices.

[0051] In order to realize that the switch unit 500 selectively electrically connects the lower bus capacitor C2 to the first clamping unit 300 or the second clamping unit 400, in some embodiments, reference is made to FIG. Figure 1 and Figure 2 The pre-charging circuit further includes a control module 600, the switch switching unit 500 includes a controlled switch S1, the controlled switch S1 includes a first input terminal, a first controlled terminal, a first output terminal, and a second output terminal, the first input terminal is electrically connected to the lower bus capacitor C2, the first controlled terminal is electrically connected to the control module 600, the first output terminal is electrically connected to the output terminal of the first clamping unit 300, and the second output terminal is electrically connected to the input terminal of the second clamping unit 400, wherein,

[0052] The control module 600 is configured to output a corresponding enable signal to the controlled switch S1 .

[0053] In this embodiment, when the flying capacitor Cf is charged using a forward pre-charging circuit, the control module 600 outputs an enable signal to the controlled switch S1 to connect the first clamping unit 300 to the lower bus capacitor C2. When the flying capacitor Cf is charged using a reverse pre-charging circuit, the control module 600 outputs an enable signal to the controlled switch S1 to connect the second clamping unit 400 to the lower bus capacitor C2. In this embodiment, when the voltage of the flying capacitor Cf of the current pre-charging circuit reaches a set starting voltage, the control module 600 outputs an enable signal to the controlled switch S1 to connect the second clamping unit 400 to the lower bus capacitor C2. When multiple pre-charging circuits are connected in parallel, before the unpowered pre-charging circuits are powered on, the control module 600 outputs an enable signal to the controlled switch S1 to connect the first clamping unit 300 to the lower bus capacitor C2.

[0054] In this embodiment, the control module 600 includes a microcontroller, which includes one of the following: a single-chip microcomputer, a digital signal processor (DSP), a field-programmable gate array (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, and discrete hardware components.

[0055] The controlled switch S1 is used to control the first input terminal to selectively connect to the first output terminal or the second output terminal according to the received enable signal.

[0056] In some of these embodiments, reference Figure 2 The switch switching unit 500 further includes a current limiting unit, a first end of the current limiting unit being electrically connected to the lower bus capacitor C2, and a second end of the current limiting unit being electrically connected to the first input end, wherein the current limiting unit is a current limiting resistor R1, and the current limiting unit is used to limit the current flowing through the controlled switch S1, the first clamping unit 300, and the second clamping unit 300, thereby protecting the controlled switch S1, the first clamping unit 300, and the second clamping unit 400 from breakdown.

[0057] In some embodiments, the controlled switch S1 includes a bistable relay, which includes a first port, a second port, a third port, a fourth port, and a fifth port. The first port is connected to the first input terminal, the second port is connected to the first output terminal, the third port is connected to the second output terminal, the fourth port is connected to the first controlled terminal, and the fifth port is electrically connected to the first power supply VDD. The bistable relay is configured to control the first port to be connected to the second port when the level of the enable signal received at the fourth port is a preset high level, so that the lower bus capacitor C1 is connected to the first clamping unit 300, and to control the first port to be connected to the third port when the level of the enable signal received at the fourth port is a preset low level, so that the lower bus capacitor C2 is connected to the second clamping unit 400.

[0058] In some of these embodiments, reference Figure 2-6 The boost power conversion circuit 200 includes an inductor L, a first diode D1, a second diode D2, a first switch tube T1 and a second switch tube T2, and the input unit 100 includes an input capacitor Cin and a bypass diode D3; in this embodiment, the first switch tube T1 and the second switch tube T2 both include NPN transistors; Figure 2 In the topological circuit diagram shown, one end of the input capacitor Cin is electrically connected to the anode of the bypass diode D3 and the first end of the inductor L, respectively. The second end of the inductor L is electrically connected to the input end of the first switch tube T1 (corresponding to the collector of the transistor) and the anode of the second diode D2, respectively. The output end of the first switch tube T1 (corresponding to the emitter of the transistor) is electrically connected to the input end of the second switch tube T2 (corresponding to the collector of the transistor), the first end of the flying capacitor Cf, and the input end of the first clamping unit 300 (corresponding to the anode of the diode D4), respectively. The output end of the second switch tube T2 (corresponding to the emitter of the transistor) is connected to the other end of the input capacitor Cin (that is, the negative electrode BUS- of the bus BUS, which corresponds to the low-voltage side of the corresponding flying capacitor three-level boost circuit, corresponding to "-1" in the three-level). The controlled end of the first switch tube T1 and the controlled end of the second switch tube T2 are both electrically connected to the control module 600 (refer to Figure 2 The cathode of the second diode D2 is electrically connected to the anode of the first diode D1, the second end of the flying capacitor Cf and the output end of the second clamping unit 400 (corresponding to the cathode of the diode D5), and the cathode of the first diode D1 and the cathode of the bypass diode D3 are both electrically connected to the bus.

[0059] In this embodiment, when the switch unit 500 connects the diode D4 to the lower bus capacitor C2, the inductor L, the first switch tube T1, the diode D4 and the lower bus capacitor C2 form an energy storage circuit corresponding to the forward pre-charge circuit (refer to Figure 3), and based on the supply voltage Vin, the inductor L stores energy; the inductor L, the second diode D2, the flying capacitor Cf, the diode D4 and the lower bus capacitor C2 can also form a discharge circuit corresponding to the forward pre-charge circuit (reference Figure 4 ) to charge the flying capacitor Cf based on the supply voltage Vin.

[0060] In this embodiment, when the switch unit 500 connects the diode D5 to the lower bus capacitor C2, the second switch tube T2, the flying capacitor Cf, the diode D5 and the lower bus capacitor C2 form a first reverse charging loop corresponding to the reverse pre-charging loop (refer to Figure 5 ), and charges the flying capacitor Cf based on the half bus voltage; the input capacitor Cin, inductor L, freewheeling diode TD1, flying capacitor Cf, diode D5 and lower bus capacitor C2 form a second reverse charging loop corresponding to the reverse pre-charging loop (reference Figure 6 ), and charges the flying capacitor Cf based on the voltage at the middle connection point between the upper bus capacitor C1 and the lower bus capacitor C2.

[0061] In some optional embodiments, the first switch tube T1 and the second switch tube T2 are both MOS tubes or insulated gate bipolar transistors (IGBTs).

[0062] It should be noted that the first switch transistor T1 and the second switch transistor T2 in the embodiments of the present application include, but are not limited to, MOS transistors and IGBTs. Furthermore, based on the disclosure of this application, those skilled in the art will readily appreciate the possibility of modifying the controlled switch disclosed in this application into a controlled switch suitable for the specific selection of the switch transistor. Therefore, the present application can be implemented regardless of whether the switch transistor is an N-channel or P-channel MOS transistor, or a single-bridge IGBT, a half-bridge IGBT, or a full-bridge IGBT, and is not limited in the embodiments of this application.

[0063] The present invention also provides a method for controlling a pre-charging circuit. Figure 7 Flowchart of a control method of a pre-charging circuit according to an embodiment of the present application. Figure 7 As shown, the control method of the pre-charging circuit is applied to the pre-charging circuit in the above embodiment, and the control method includes the following steps:

[0064] Step S701: Determine whether the power supply voltage Vin is greater than the bus voltage V_bus.

[0065] In this embodiment, whether the power supply voltage Vin is greater than the bus voltage V_bus is determined by installing an electronic device such as a main control module or microcontroller of a photovoltaic inverter, which is equipped with a flying capacitor Cf and a corresponding pre-charging circuit in the embodiment of the present application. In addition, the corresponding electronic device detects the power supply voltage Vin and the bus voltage V_bus based on existing related technologies. Those skilled in the art should understand that the corresponding technical means belong to existing or known technologies and do not constitute a limitation to the present application.

[0066] In step S702, when it is determined that the power supply voltage Vin is greater than the bus voltage V_bus, the switch switching unit is enabled to connect the first clamping unit to the lower bus capacitor, and the flying capacitor is charged based on the power supply voltage through a forward pre-charging circuit corresponding to the first preset charging method until the voltage of the flying capacitor is greater than the preset starting voltage, wherein the forward pre-charging circuit is composed of an inductor L, a first switch tube T1, a second diode D2, a first clamping unit, a switch switching unit and a lower bus capacitor.

[0067] In step S703, when it is determined that the supply voltage Vin is less than the bus voltage V_bus, the switch switching unit is enabled to connect the second clamping unit to the lower bus capacitor, and the flying capacitor is charged based on the half bus voltage through a reverse pre-charging circuit corresponding to the second preset charging method until the voltage of the flying capacitor is greater than the preset starting voltage, wherein the reverse pre-charging circuit is composed of an input capacitor Cin, an inductor L, a freewheeling diode TD1 corresponding to the first switch tube T1, the second switch tube T2, a second clamping unit, a switch switching unit and the lower bus capacitor.

[0068] In some embodiments, during the process of charging the flying capacitor based on the supply voltage through the forward pre-charging circuit corresponding to the first preset charging mode in step S702, the following steps are further performed:

[0069] Step 21 : Send a first pulse signal with a preset duty cycle to the first switch tube T1 within a first preset time.

[0070] Step 22: When the first switch tube T1 controls the input terminal and the output terminal of the first switch tube T1 to be connected according to the first pulse signal received by the controlled terminal, the inductor L, the first switch tube T1, the first clamping unit, the switch switching unit and the lower bus capacitor form an energy storage circuit corresponding to the positive pre-charge circuit (refer to Figure 3 ), and based on the supply voltage, the inductor L is charged with energy. When the first switch tube T1 controls the input terminal and the output terminal of the first switch tube T1 to be disconnected according to the first pulse signal received by the controlled terminal, the inductor L, the second diode D2, the flying capacitor, the first clamping unit, the switch switching unit and the lower bus capacitor form a discharge circuit corresponding to the positive pre-charge circuit (reference Figure 4) to charge the flying capacitor based on the supply voltage.

[0071] Step 23: After the flying capacitor is charged for the first preset time, the voltage of the flying capacitor is less than the preset starting voltage. After waiting for the preset interval time, the first pulse signal is again transmitted to the first switch tube T1, and the flying capacitor is charged based on the power supply voltage through the positive pre-charging circuit.

[0072] Step 24: within the first preset time, the voltage of the flying capacitor is greater than the preset starting voltage, the first pulse signal is stopped from being transmitted to the first switch tube T1, and the switch switching unit is enabled to connect the second clamping unit to the lower bus capacitor.

[0073] In some embodiments, during the process of charging the flying capacitor based on the half bus voltage through the reverse pre-charging circuit corresponding to the second preset charging mode in step S703, the following steps are further performed:

[0074] Step 31: Send a second pulse signal with a preset duty cycle to the second switch tube T2 within a second preset time;

[0075] Step 32: When the second switch tube T2 controls the input terminal and the output terminal of the second switch tube T2 to be connected according to the second pulse signal received at the controlled terminal, the second switch tube T2, the flying capacitor, the second clamping unit, the switching unit, and the lower bus capacitor form a first reverse charging loop corresponding to the reverse pre-charging loop, and the flying capacitor is charged based on the half-bus voltage. When the second switch tube T2 controls the input terminal and the output terminal of the second switch tube T2 to be disconnected according to the second pulse signal received at the controlled terminal, the input capacitor Cin, the inductor L, the freewheeling diode TD1, the flying capacitor, the second clamping unit, the switching unit, and the lower bus capacitor form a second reverse charging loop corresponding to the reverse pre-charging loop, and the flying capacitor is charged based on the half-bus voltage corresponding to the intermediate connection point.

[0076] Step 33: After the flying capacitor is charged for the second preset time, the voltage of the flying capacitor is less than the preset starting voltage. After waiting for the preset interval time, a second pulse signal is again transmitted to the second switch T2, and the flying capacitor is charged based on the half bus voltage through the reverse pre-charging circuit.

[0077] In step 34, within the second preset time, if the voltage of the flying capacitor is greater than the preset starting voltage, the second pulse signal is stopped from being transmitted to the second switch tube T2 to stop charging the flying capacitor.

[0078] Figure 8 This is a flow chart of a control method for a pre-charging circuit according to a preferred embodiment of the present application, and the following reference is made to Figures 1-8 The working process of the pre-charging circuit of the flying capacitor in the embodiment of the present application is described as follows:

[0079] The flying capacitor pre-charging circuit proposed in the embodiment of the present application pre-charges the flying capacitor Cf according to two preset pre-charging modes, and the selection of the pre-charging mode is determined according to the magnitude of the power supply voltage Vin and the bus voltage V_bus.

[0080] Specifically, when Vin≥V_bus, at this time, the bus voltage V_bus is established by the power supply voltage Vin; when the power supply voltage Vin reaches the starting voltage (the starting voltage refers to the size of the power supply voltage Vin reaching the set value), the forward pre-charge circuit is used to charge the flying capacitor Cf. The current flow path under this method is referenced Figure 3 and Figure 4 By outputting a first pulse signal to the first switch tube T1, the conduction and shutdown of the first switch tube T1 are controlled. The duty cycle of the first pulse signal is fixed and the switching frequency is fixed. The duration of outputting the first pulse signal to the first switch tube T1 is set to a first preset time, recorded as T sw1 , the first pulse signal includes several narrow pulses; when the first switch tube T1 is turned on, the current will pass through the inductor L, the first switch tube T1, the diode D4, the switch switching unit 500, the current limiting resistor R1, and the lower bus capacitor C2 in sequence to store energy in the inductor L; when the first switch tube T1 is turned off, the current will pass through the inductor L, the diode D2, the flying capacitor Cf, the diode D4, the switch switching unit 500, the current limiting resistor R1, the lower bus capacitor C2, and charge the flying capacitor Cf; set to the starting voltage V of the flying capacitor Cf start_cf =0.45V_bus; at the first preset time T sw1 The first pulse signal is sent to the first switch tube T1. If the voltage Vcf on the flying capacitor Cf is greater than V start_cf , the first pulse signal transmitted to the first switch tube T1 is turned off in advance, and the controlled switch S1 is enabled to switch its first port (corresponding to Figure 2 K point in the middle) and the third port (corresponding to Figure 2 The boost circuit corresponding to the flying capacitor Cf starts to work normally; at the first preset time T sw1 The first pulse signal is sent to the first switch tube T1. If the voltage Vcf on the flying capacitor Cf is less than V start_cf , then wait for a while, for example 10T sw1 After a certain time, the first pulse signal is again transmitted to the first switch tube T1 to charge the flying capacitor Cf.

[0081] When Vin is less than V_bus, that is, when the pre-charging circuits of multiple flying capacitors are connected in parallel, when the flying capacitor Cf is started and the pre-charging circuits are working normally, at least one of the multiple pre-charging circuits charges the bus capacitor. For the pre-charging circuits of the flying capacitor that has not been powered on, the bus voltage V_bus has been established before the circuit is started. When Vin reaches the starting voltage, the controlled switch S1 is enabled to turn its first port (corresponding to Figure 2 K point in the middle) and the third port (corresponding to Figure 2 The flying capacitor Cf is charged by the reverse pre-charging circuit corresponding to the second pre-charging method. The current flow path under this method is referenced. Figure 5 and Figure 6 By transmitting a second pulse signal to the second switch tube T2 to control the conduction and shutdown of the second switch tube T2, the duration of transmitting the second pulse signal to the second switch tube T2 is set to a second preset time, recorded as T sw2 , the second pulse signal is a square wave with a fixed duty cycle and a switching frequency that is the same as the normal operating frequency; when the second switch tube T2 is turned on, the current will flow through the current limiting resistor R1, the switch switching unit 500, the diode D5, the flying capacitor Cf, the second switch tube T2 (reference Figure 5 ) to charge the flying capacitor Cf; when the second switch tube T2 is disconnected, if Vin≥Vc2 (lower bus capacitor voltage), the diode D5 is in the cut-off state, and there is no charging current loop. If Vin<Vc2, the current will flow through the current limiting resistor R1, the switch switching unit 300, the diode D5, the flying capacitor Cf, the freewheeling diode TD1 of the first switch tube T1, the inductor L, and the input capacitor Cin (corresponding to the reference Figure 6 ) to charge the flying capacitor Cf; in the second preset time T sw2 The second pulse signal is sent to the second switch tube T2. If the voltage Vcf on the flying capacitor is greater than V start_cf When the voltage Vcf on the flying capacitor Cf is greater than V start_cf , the second pulse signal transmitted to the second switch tube T2 is turned off in advance, and the boost circuit corresponding to the flying capacitor Cf starts to work normally; at the second preset time T sw2 The second pulse signal is sent to the second switch tube T2. If the voltage Vcf on the flying capacitor Cf is less than V start_cf , then wait for a period of time, for example 10T sw1 After a certain time, the second pulse signal is again transmitted to the second switch tube T2 to charge the flying capacitor Cf.

[0082] The present application also provides a flying capacitor three-level converter, including the flying capacitor pre-charging circuit of the above embodiment.

[0083] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0084] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not intended to be limited to the embodiments shown herein, but is intended to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A flying capacitor pre-charging circuit, characterized in that: It includes an input unit, a boost power conversion unit, a flying capacitor, a first clamping unit, a second clamping unit, a switch unit, an upper bus capacitor and a lower bus capacitor, wherein: The input unit is electrically connected to the power supply unit, the busbar and the boost power conversion unit respectively, and is used to transmit the power supply voltage provided by the power supply unit to the busbar and the boost power conversion unit; When the supply voltage is greater than the bus voltage of the bus, the boost power conversion unit is electrically connected to the flying capacitor, the first clamping unit, the switch switching unit and the lower bus capacitor in sequence to form a forward pre-charging loop; when the supply voltage is less than the bus voltage, the boost power conversion unit is electrically connected to the flying capacitor, the second clamping unit, the switch switching unit and the lower bus capacitor in sequence to form a reverse pre-charging loop, wherein the forward pre-charging loop is used to charge the flying capacitor based on the supply voltage, and the reverse pre-charging loop is used to charge the flying capacitor based on the half bus voltage corresponding to the middle connection point between the upper bus capacitor and the lower bus capacitor; The switch unit is used to selectively electrically connect the intermediate connection point to the first clamping unit or the second clamping unit.

2. The flying capacitor pre-charging circuit according to claim 1, wherein: The pre-charging circuit further includes a control module, the switch switching unit includes a controlled switch, the controlled switch includes a first input terminal, a first controlled terminal, a first output terminal, and a second output terminal, the first input terminal is electrically connected to the lower bus capacitor, the first controlled terminal is electrically connected to the control module, the first output terminal is electrically connected to the output terminal of the first clamping unit, and the second output terminal is electrically connected to the input terminal of the second clamping unit, wherein, The control module is configured to output a corresponding enable signal to the controlled switch; The controlled switch is used to control the first input end to selectively connect to the first output end or the second output end according to the received enable signal.

3. The flying capacitor pre-charging circuit according to claim 2, wherein: The switch switching unit further includes a current limiting unit, a first end of the current limiting unit being electrically connected to the lower bus capacitor, and a second end of the current limiting unit being electrically connected to the first input end of the controlled switch, wherein the current limiting unit is used to limit the magnitude of a current flowing through the controlled switch, the first clamping unit, and the second clamping unit.

4. The flying capacitor pre-charging circuit according to claim 2, wherein: The controlled switch includes a bistable relay, which includes a first port, a second port, a third port, a fourth port, and a fifth port. The first port is connected to the first input terminal, the second port is connected to the first output terminal, the third port is connected to the second output terminal, the fourth port is connected to the first controlled terminal, and the fifth port is electrically connected to the first power supply. The bistable relay is configured to control the first port to be connected to the second port when the level of the enable signal received at the fourth port is a preset high level, so that the intermediate connection point is connected to the first clamping unit; and to control the first port to be connected to the third port when the level of the enable signal received at the fourth port is a preset low level, so that the intermediate connection point is connected to the second clamping unit.

5. The flying capacitor pre-charging circuit according to claim 2, wherein: The boost power conversion unit includes an inductor L, a first diode D1, a second diode D2, a first switch transistor T1, and a second switch transistor T2. The input unit includes an input capacitor Cin and a bypass diode D3. One end of the input capacitor Cin is electrically connected to the anode of the bypass diode D3 and the first end of the inductor L, respectively. The second end of the inductor L is electrically connected to the input end of the first switch transistor T1 and the anode of the second diode D2, respectively. The output end of the first switch transistor T1 is electrically connected to the input end of the second switch transistor T2, the first end of the flying capacitor, and the input end of the first clamping unit, respectively. The output end of the second switch transistor T2 is connected to the other end of the input capacitor Cin. The controlled end of the first switch transistor T1 and the controlled end of the second switch transistor T2 are both electrically connected to the control module. The cathode of the second diode D2 is electrically connected to the anode of the first diode D1, the second end of the flying capacitor, and the output end of the second clamping unit, respectively. The cathode of the first diode D1 and the cathode of the bypass diode D3 are both electrically connected to the bus.

6. The flying capacitor pre-charging circuit according to claim 5, wherein: The first clamping unit and the second clamping unit are both diodes.

7. A control method for a pre-charging circuit, applied to the pre-charging circuit of a flying capacitor according to claim 5, characterized in that: The control method includes: Determining whether the supply voltage is greater than the bus voltage; When it is determined that the supply voltage is greater than the bus voltage, the switching unit is enabled to connect the first clamping unit to the lower bus capacitor, and to charge the flying capacitor based on the supply voltage through a forward pre-charging circuit corresponding to a first preset charging mode until the voltage of the flying capacitor is greater than a preset starting voltage, wherein the forward pre-charging circuit is composed of the inductor L, the first switch T1, the second diode D2, the first clamping unit, the switching unit, and the lower bus capacitor; When it is determined that the supply voltage is lower than the bus voltage, the switch switching unit is enabled to connect the second clamping unit to the lower bus capacitor, and the flying capacitor is charged based on the half bus voltage through a reverse pre-charging circuit corresponding to a second preset charging method until the voltage of the flying capacitor is greater than a preset starting voltage, wherein the reverse pre-charging circuit is composed of the input capacitor Cin, the inductor L, the freewheeling diode TD1 corresponding to the first switch tube T1, the second switch tube T2, the second clamping unit, the switch switching unit and the lower bus capacitor.

8. The control method according to claim 7, characterized in that: In a process of charging the flying capacitor based on the supply voltage through a forward pre-charging circuit corresponding to a first preset charging mode, the control method includes: Sending a first pulse signal with a preset duty cycle to the first switch tube T1 within a first preset time; When the first switch tube T1 controls the input terminal and the output terminal of the first switch tube T1 to be connected according to the first pulse signal received by the controlled terminal, the inductor L, the first switch tube T1, the first clamping unit, the switching unit, and the lower bus capacitor form an energy storage loop corresponding to the forward pre-charging loop, and stores energy in the inductor L based on the supply voltage. When the first switch tube T1 controls the input terminal and the output terminal of the first switch tube T1 to be disconnected according to the first pulse signal received by the controlled terminal, the inductor L, the second diode D2, the flying capacitor, the first clamping unit, the switching unit, and the lower bus capacitor form a discharge loop corresponding to the forward pre-charging loop, and charges the flying capacitor based on the supply voltage. After the flying capacitor is charged for the first preset time, the voltage of the flying capacitor is less than the preset starting voltage. After waiting for a preset interval time, the first pulse signal is again transmitted to the first switch tube T1, and the flying capacitor is charged based on the supply voltage through the forward pre-charging circuit. During the first preset time, the voltage of the flying capacitor is greater than the preset starting voltage, the first pulse signal is stopped from being transmitted to the first switch tube T1, and the switch switching unit is enabled to connect the second clamping unit to the lower bus capacitor.

9. The control method according to claim 7, characterized in that: In a process of charging the flying capacitor based on the half bus voltage through a reverse pre-charging loop corresponding to a second preset charging mode, the control method includes: transmitting a second pulse signal with a preset duty cycle to the second switch tube T2 within a second preset time; When the second switch tube T2 controls the input terminal and the output terminal of the second switch tube T2 to be connected according to the second pulse signal received at the controlled terminal, the second switch tube T2, the flying capacitor, the second clamping unit, the switching unit, and the lower bus capacitor form a first reverse charging loop corresponding to the reverse pre-charging loop, and charges the flying capacitor based on the half-bus voltage; and when the second switch tube T2 controls the input terminal and the output terminal of the second switch tube T2 to be disconnected according to the second pulse signal received at the controlled terminal, the input capacitor Cin, the inductor L, the freewheeling diode TD1, the flying capacitor, the second clamping unit, the switching unit, and the lower bus capacitor form a second reverse charging loop corresponding to the reverse pre-charging loop, and charges the flying capacitor based on the half-bus voltage corresponding to the intermediate connection point. After the flying capacitor is charged for the second preset time, the voltage of the flying capacitor is less than the preset starting voltage. After waiting for the preset interval time, the second pulse signal is again transmitted to the second switch tube T2, and the flying capacitor is charged based on the half bus voltage through the reverse pre-charging circuit. During the second preset time, the voltage of the flying capacitor is greater than the preset starting voltage, and the second pulse signal is stopped from being transmitted to the second switch tube T2 to stop charging the flying capacitor.

10. A flying capacitor three-level converter, characterized in that: A pre-charging circuit comprising a flying capacitor according to any one of claims 1 to 6.

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