BOOST power conversion circuit and control method thereof

Abstract

The invention discloses a BOOST power conversion circuit and a control method thereof. According to the conversion circuit, an initial voltage establishing circuit of a flying capacitor C1 is added onthe basis of an input and output common-ground type three-level Boost converter. The initial voltage establishing circuit is composed of a first resistor R1, a second resistor R2 and a third resistorR3. Initial voltage is established for a first capacitor C1 when the voltage of the input end of the voltage-boosting power conversion circuit is lower than starting threshold voltage Vstart of the voltage-boosting power conversion circuit, and the BOOST power conversion circuit has the effects that firstly, forward voltage of a second switching tube T2 is reduced; and secondly, the reverse voltage borne by the fourth diode D4 is reduced, the second switching tube T2 is further protected, and the fourth diode D4 with smaller reverse voltage stress can be selected.

Description

technical field [0001] The invention relates to the technical field of power electronics, in particular to a photovoltaic grid-connected inverter BOOST boost power conversion circuit and a control method thereof applied to a multi-channel MPPT. Background technique [0002] The boost circuit is a boost power conversion circuit, which can boost the input voltage and output it, thereby realizing power conversion. Usually the Boost circuit includes a two-level Boost circuit and a multi-level Boost circuit. The two-level Boost circuit is generally used in applications with lower voltage levels, and the multi-level Boost circuit is used in applications with higher voltage levels. Compared with the two-level Boost circuit, the multi-level Boost circuit realizes multi-level by improving its own topology, thereby realizing high-voltage and high-power output. For the same input voltage, the outstanding advantage of the multi-level boost circuit is that it can reduce the voltage stre...

AI Technical Summary

Problems solved by technology

[0004] 1. When the power is initially turned on and the input voltage is high, since the initial voltage of the flying capacitor is equal to zero at this time, the input voltage will be fully applied to the second switch tube T2, which will cause overvoltage breakdown of the switch tube T2 in severe cases

For example: Since the front stage of the photovoltaic grid-connected inverter is generally multi-channel MPPT parallel connection (such as Figure 13 ), when the input voltage of one of the MPPTs reaches the initial start-up voltage V of the MPPT start At this time, assuming that the initial voltage of the flying capacitor is equal to zero, the voltage on both ends of the second switching tube T2 is equal to V in , in extreme cases, V in =1500V, it will cause instantaneous overvoltage breakdown of the second switching tube

[0005] 2. When the bus voltage is established and a certain MPPT is not started, since the initial voltage of the flying capacitor voltage is equal to zero, the output bus voltage will be fully applied to the fourth diode D4, which will cause overvoltage breakdown of the diode in severe cases

At this time, it is necessary to choose a diode with a high withstand voltage value, and a diode with a high withstand voltage value has a high tube voltage drop and poor reverse recovery characteristics, which will seriously affect the circuit efficiency when used.

[0006] The above two potential problems will bring serious challenges to the device design of the circuit, so appropriate measures must be taken to obtain a method to ensure the safety of the second switch tube and reduce the voltage stress of the fourth diode to ensure the circuit efficiency, lower system cost

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