WO-2026091841-A1 - CONTROL METHOD FOR POWER CONVERSION CIRCUIT, AND INVERTER

WO2026091841A1WO 2026091841 A1WO2026091841 A1WO 2026091841A1WO-2026091841-A1

Abstract

A control method for a power conversion circuit, and an inverter. The power conversion circuit comprises a driver, a bootstrap unit, an upper switch transistor, and a lower switch transistor. The method comprises: on the basis of the maximum loss of a bootstrap diode and the voltage of the bootstrap diode, obtaining a target duty cycle for turning on/off an upper switch transistor or a lower switch transistor; obtaining a half cycle on the basis of the target duty cycle and the voltage of a bootstrap capacitor, two half cycles forming one working cycle; and controlling a driver to drive the upper switch transistor to be turned on at the target duty cycle in a first half cycle of each working cycle and turned off in a second half cycle of each working cycle, and to drive the lower switch transistor to be turned off in the first half cycle of each working cycle and turned on at the target duty cycle in the second half cycle of each working cycle, such that the bootstrap capacitor is charged. Thus, damage to the bootstrap diode caused by excessive inrush current can be reduced.

Inventors

WANG, HUA
LI, YANLONG
LI, JUN

Assignees

浙江艾罗网络能源技术股份有限公司

Dates

Publication Date: 20260507
Application Date: 20250902
Priority Date: 20241031

Claims (10)

A control method for a power conversion circuit, characterized in that the power conversion circuit includes a driver, a bootstrap unit, an upper switching transistor, and a lower switching transistor, wherein the upper switching transistor and the lower switching transistor are connected in series and both are connected to the driver, and the power supply terminal of the driver is connected to the midpoint of the connection between the upper and lower switching transistors through the bootstrap unit, wherein the bootstrap unit includes a bootstrap capacitor and a bootstrap diode connected in series; the control method includes: The target duty cycle for switching on or off the upper or lower switch is obtained based on the maximum loss of the bootstrap diode and the voltage of the bootstrap diode. A half-cycle is obtained based on the target duty cycle and the voltage of the bootstrap capacitor, and two half-cycles constitute one working cycle. The driver controls the upper switch to turn on with the target duty cycle in the first half of each operating cycle and turn off in the second half of each operating cycle, and controls the lower switch to turn off in the first half of each operating cycle and turn on with the target duty cycle in the second half of each operating cycle, so as to charge the bootstrap capacitor.
The control method for the power conversion circuit according to claim 1, characterized in that, obtaining the target duty cycle for the on/off state of the upper or lower switch based on the maximum loss of the bootstrap diode and the voltage of the bootstrap diode, includes: The relationship between the target duty cycle and the maximum loss of the bootstrap diode is obtained based on the current of the bootstrap capacitor and the voltage drop across the bootstrap diode. The current of the bootstrap capacitor is obtained based on the voltage of the zero-state response of the bootstrap capacitor during charging. The target duty cycle is obtained based on the correspondence and the current of the bootstrap capacitor.
The control method for the power conversion circuit according to claim 2 is characterized in that, obtaining a half-cycle based on the target duty cycle and the voltage of the bootstrap capacitor, and two half-cycles constituting a working cycle, includes: obtaining the voltage of the bootstrap capacitor based on the charging voltage of the bootstrap unit and the charging expectation coefficient.
The control method for the power conversion circuit according to claim 1 is characterized in that a current limiting unit is provided between the bootstrap diode and the bootstrap capacitor; The step of obtaining the target duty cycle for switching on or off the upper or lower switch based on the maximum loss of the bootstrap diode and the voltage of the bootstrap diode further includes: The target duty cycle is obtained based on the switching frequency of the upper or lower switch and the resistance value of the current limiting unit.
The control method for the power conversion circuit according to claim 1, characterized in that, the step of obtaining a half-cycle based on the target duty cycle and the voltage of the bootstrap capacitor, wherein two half-cycles constitute one operating cycle, further includes: Gradually increase the target duty cycle to obtain multiple different work cycles.
The control method for the power conversion circuit according to claim 1 is characterized in that the power conversion circuit includes a first driver, a second driver, a first bootstrap unit, a second bootstrap unit, a first upper switch transistor, a second upper switch transistor, a first lower switch transistor, and a second lower switch transistor. The first upper switch and the first lower switch are connected in series and are both connected to the first driver. The power supply terminal of the first driver is connected to the midpoint between the first upper switch and the first lower switch through the first bootstrap unit. The first bootstrap unit includes a first bootstrap capacitor and a first bootstrap diode connected in series. The second upper switch and the second lower switch are connected in series and are both connected to the second driver. The power supply terminal of the second driver is connected to the midpoint between the second upper switch and the second lower switch through the second bootstrap unit. The second bootstrap unit includes a second bootstrap capacitor and a second bootstrap diode connected in series. The first upper switch transistor and the second upper switch transistor are connected; The control method for the power conversion circuit also includes: In the first time interval, the first driver is controlled to drive the first upper switch to be turned on with the target duty cycle in the first half of each working cycle and turned off in the second half of each working cycle, and to drive the first lower switch to be turned off in the first half of each working cycle and turned on with the target duty cycle in the second half of each working cycle, so as to charge the first bootstrap capacitor. In the second time interval, the second driver is controlled to drive the second upper switch to be turned on with the target duty cycle in the first half of each working cycle and turned off in the second half of each working cycle, and to drive the second lower switch to be turned off in the first half of each working cycle and turned on with the target duty cycle in the second half of each working cycle, so as to charge the second bootstrap capacitor; the second time interval is different from the first time interval and is continuous.
The control method for the power conversion circuit according to claim 6, characterized in that the control method for the power conversion circuit further includes: Control the first driver to stop outputting drive signals during the second time interval; The second driver is controlled to stop outputting drive signals during the first time interval.
An inverter, characterized in that it comprises: a power conversion circuit, the power conversion circuit including a driver, a bootstrap unit, an upper switching transistor and a lower switching transistor, the upper switching transistor and the lower switching transistor being connected in series and both connected to the driver, the power supply terminal of the driver being connected to the connection midpoint between the upper switching transistor and the lower switching transistor through the bootstrap unit, the bootstrap unit including a bootstrap capacitor and a bootstrap diode connected in series; The controller is configured as follows: The target duty cycle for switching on or off the upper or lower switch is obtained based on the maximum loss of the bootstrap diode and the voltage of the bootstrap diode. A half-cycle is obtained based on the target duty cycle and the voltage of the bootstrap capacitor, wherein two half-cycles constitute one working cycle. The driver controls the upper switch to turn on with the target duty cycle in the first half of each operating cycle and turn off in the second half of each operating cycle, and controls the lower switch to turn off in the first half of each operating cycle and turn on with the target duty cycle in the second half of each operating cycle, so as to charge the bootstrap capacitor.
The inverter according to claim 8 is characterized in that the controller is further configured to: gradually increase the target duty cycle to obtain multiple different operating cycles when a half-cycle is obtained based on the target duty cycle and the voltage of the bootstrap capacitor.
The inverter according to claim 8 is characterized in that the power conversion circuit includes a first driver, a second driver, a first bootstrap unit, a second bootstrap unit, a first upper switch transistor, a second upper switch transistor, a first lower switch transistor, and a second lower switch transistor. The first upper switch and the first lower switch are connected in series and are both connected to the first driver. The power supply terminal of the first driver is connected to the midpoint between the first upper switch and the first lower switch through the first bootstrap unit. The first bootstrap unit includes a first bootstrap capacitor and a first bootstrap diode connected in series. The second upper switch and the second lower switch are connected in series and are both connected to the second driver. The power supply terminal of the second driver is connected to the midpoint between the second upper switch and the second lower switch through the second bootstrap unit. The second bootstrap unit includes a second bootstrap capacitor and a second bootstrap diode connected in series. The first upper switch transistor and the second upper switch transistor are connected; The controller is also configured to: In the first time interval, the first driver is controlled to drive the first upper switch to be turned on with the target duty cycle in the first half of each working cycle and turned off in the second half of each working cycle, and to drive the first lower switch to be turned off in the first half of each working cycle and turned on with the target duty cycle in the second half of each working cycle, so as to charge the first bootstrap capacitor. In the second time interval, the second driver is controlled to drive the second upper switch to be turned on with the target duty cycle in the first half of each working cycle and turned off in the second half of each working cycle, and to drive the second lower switch to be turned off in the first half of each working cycle and turned on with the target duty cycle in the second half of each working cycle, so as to charge the second bootstrap capacitor; the second time interval is different from the first time interval and is continuous.

Description

Control methods for power conversion circuits and inverters This application claims priority to Chinese Patent Application No. 202411547325.1, filed on October 31, 2024, entitled "Control Method and Inverter for Power Conversion Circuit", the entire contents of which are incorporated herein by reference. Technical Field This application relates to the field of power electronics technology, and in particular to a control method for a power conversion circuit and an inverter. Background Technology Currently, in the half-bridge or full-bridge power conversion circuits of photovoltaic inverters, bootstrap circuits are typically used to power the high-side drive. Since the initial voltage of the bootstrap capacitor in the bootstrap circuit is 0V, the inrush current flowing through the bootstrap circuit can become excessive during its initial operation, easily damaging the bootstrap diodes and affecting their lifespan. In related technologies, to reduce the damage to bootstrap diodes caused by excessive inrush current, methods such as connecting a current-limiting resistor in series in the bootstrap circuit or reducing the size of the bootstrap capacitor are commonly used. However, while the method of connecting a current-limiting resistor in series has a certain limiting effect on the peak value of the inrush current, it is still difficult to reduce the energy of the inrush current that causes damage to the bootstrap diode. Reducing the size of the bootstrap capacitor can reduce the inrush current, but it is easily limited by the operating environment of the bootstrap capacitor. For example, if the operating voltage of the bootstrap capacitor is lower than the high-side drive voltage, the high-side drive will not function properly. Summary of the Invention Therefore, this application provides an auxiliary power supply and inverter with a relatively simple circuit structure, which can reduce costs. In view of the above, it is necessary to provide a control method and inverter for a power conversion circuit, which can reduce the problem of excessive inrush current damaging the bootstrap diode when the bootstrap unit is working. This application provides a control method for a power conversion circuit. The power conversion circuit includes a driver, a bootstrap unit, an upper switch, and a lower switch. The upper and lower switches are connected in series and are both connected to the driver. The power supply terminal of the driver is connected to the midpoint between the upper and lower switches through the bootstrap unit. The bootstrap unit includes a bootstrap capacitor and a bootstrap diode connected in series. The control method includes: obtaining a target duty cycle for the upper or lower switch based on the maximum loss of the bootstrap diode and the voltage of the bootstrap diode; obtaining a half-cycle based on the target duty cycle and the voltage of the bootstrap capacitor, with two half-cycles constituting one operating cycle; controlling the driver to drive the upper switch to conduct with the target duty cycle in the first half-cycle of each operating cycle and turn off in the second half-cycle of each operating cycle, and driving the lower switch to turn off in the first half-cycle of each operating cycle and conduct with the target duty cycle in the second half-cycle of each operating cycle, so as to charge the bootstrap capacitor. In some embodiments, obtaining the target duty cycle for switching on or off the upper or lower switch based on the maximum loss of the bootstrap diode and the voltage of the bootstrap diode includes: obtaining the correspondence between the target duty cycle and the maximum loss of the bootstrap diode based on the current of the bootstrap capacitor and the voltage drop of the bootstrap diode; obtaining the current of the bootstrap capacitor based on the voltage of the zero-state response of the bootstrap capacitor during charging; and obtaining the target duty cycle based on the correspondence and the current of the bootstrap capacitor. In some embodiments, a half-cycle is obtained based on a target duty cycle and the voltage of the bootstrap capacitor, and two half-cycles constitute a working cycle, including: obtaining the voltage of the bootstrap capacitor based on the charging voltage of the bootstrap unit and the charging expectation coefficient. In some embodiments, a current limiting unit is provided between the bootstrap diode and the bootstrap capacitor; the target duty cycle of the upper or lower switch is obtained based on the maximum loss of the bootstrap diode and the voltage of the bootstrap diode, and further includes obtaining the target duty cycle based on the switching frequency of the upper or lower switch and the resistance value of the current limiting unit. In some embodiments, a half-cycle is obtained based on a target duty cycle and the voltage of the bootstrap capacitor, and two half-cycles constitute a duty cycle. The method further includes gr