Method of current control of three-phase modular multilevel converter with inductance changes allowed

摘要

Current of a three-phase multilevel modular converter (MMC) is controlled. The control is a division-summation (D-Σ) method yet uses integration to replace the two steps of division and summation. Common D-Σ characteristic equations are used for all areas. Inductance changes are considered in the characteristic equations. Current source is used to control converter. Therefore, the current of the converter can be traced to sinusoidal reference current even when the inductance changes become big. The modulation method and the capacitor-voltage balancing method are submodule unified pulse width modulation (SUPWM) and sorted voltage-balancing method, respectively. The current control directly obtains a law of the current change on each conducting module of an arm. It does not need complex sector judgments and table look-ups. Thus, the amount of computation and memory for a processor can be relatively reduced.

主权项

1. A method of current control of a three-phase modular multilevel converter (MMC),
wherein the method is execution in a device of the three-phase MMC to control the three-phase MMC and the three-phase MMC has a plurality of inductance values of upper and lower arms at different phases; and wherein the method comprises the following steps:
(a) three-phase reference currents of three-phase mains side are sine functions of a fundamental frequency; after feedback voltages and feedback currents of said three-phase mains side are separately obtained through a voltage feedback circuit and a current feedback circuit, said reference currents in a next control cycle of said three-phase mains side are separately subtracted by corresponding ones of said feedback currents in a present control cycle to obtain current changes of corresponding inductors in said present control cycle; through storing changes of inductance values of said upper and lower arms into a single chip as following said current changes, equivalent inductance values of said mains side are calculated with said corresponding inductance values of three phases of the MMC;(b) an average number of submodules conducted by each one of said upper and lower arms in said present control cycle is calculated by using a digital division-summation (D-Σ) control method;(c) a law of number change of submodules of each one of said upper and lower arms in said present control cycle is figured out by using a method of submodule unified pulse width modulation (SUPWM); and(d) corresponding duty ratios of all switches of each one of said submodules in said present control cycle are calculated by using a voltage-balancing method based on sorted submodule capacitances and the method is looped to execute step (a).