A Voltage Equalizing Circuit for DC Capacitor Bank of Multilevel Converter

Abstract

A multi-level converter DC capacitor bank voltage sharing circuit outputs m levels, wherein m>=3; the DC capacitor bank is formed by connecting m-1 DC capacitors Ci in series, wherein i=1, 2.., m-1; m-2 voltage-sharing circuits are configured, thus realizing voltage balance of the multi-level converter DC capacitors; two random adjacent capacitors of the DC capacitor bank are respectively connected with one voltage-sharing circuit unit; according to a current limiting inductance current direction, when an auxiliary voltage sharing capacitor voltage is bigger than a reference voltage, the auxiliary voltage sharing capacitor discharges power to the DC capacitor bank through the current limiting inductance; when the auxiliary voltage sharing capacitor voltage is smaller than the reference voltage, the DC capacitor bank charges the auxiliary voltage sharing capacitor through the current limiting inductance, thus controlling voltage balance of the DC capacitor bank. A control algorithm with the overcurrent restriction capability is employed, so the voltage sharing circuit can ensure the multi-level converter DC capacitor bank voltage balance under a random modulation ratio and power factors.

Description

technical field [0001] The invention relates to a voltage balancing device of a DC capacitor bank of a multilevel converter, in particular to a voltage balancing device of a DC capacitor bank of a diode-clamped multilevel converter. Background technique [0002] The DC capacitor bank of the diode-clamped multilevel converter is composed of multiple DC capacitors connected in series. Both ends of the DC capacitor bank are connected to the DC power supply. connected to the clamping diode network of the leveling converter. The bridge arm of the multilevel converter is composed of a plurality of power switching devices connected in series and corresponding clamping diode networks, and the control terminals of the power switching devices are connected with the control device of the multilevel converter. By changing the switching state of the power switching device of the bridge arm through the control device, multiple level values ​​generated by the voltage of the DC capacitor g...

AI Technical Summary

Problems solved by technology

However, similar to the circuit described in literature [1], this circuit still realizes energy transfer between DC capacitors through energy storage inductors, and its disadvantages are: (1) The introduction of floating capacitors is mainly used to balance the voltage stress of power switching devices; (2) The voltage balance of the DC capacitor is still realized by transferring energy through the energy storage inductance in the equalizing circuit unit. The introduction of the floating capacitor increases the volume and weight of the system; (3) After the introduction of the floating capacitor, the equalizing circuit unit The voltage stress of the inductance element is still a quarter of the DC bus voltage, so it is still necessary to set a larger energy storage inductor to limit the rate of change of the energy storage inductor current

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