CONTROL METHODS FOR THE SYNCHRONISATION OF PARALLEL-CONNECTED POWER CONVERTERS OPERATING IN ACCORDANCE WITH A PULSE WIDTH MODULATION (PWM) STRATEGY

摘要

A method is described for controlling a plurality of parallel-connected power converters 20a, 20b, each of which operates in accordance with a pulse width modulation (PWM) strategy defined by an independent voltage carrier signal and an independently controllable modulating sinusoidal voltage signal which are used to generate a PWM command signal for each PWM strategy. The voltage carrier signals of the PWM strategies have the same switching period and desynchronisation of the PWM command signals causes an unwanted circulating current to flow between the power converters 20a, 20b. The method thus comprises providing the independently controllable modulating sinusoidal voltage signal of the PWM strategy of at least one of the plurality of power converters 20a, 20b with a dc voltage offset to modify the PWM command signal of the at least one power converter and thereby increase the synchronisation of the PWM command signals so that the magnitude of any unwanted circulating current is reduced. The magnitude of the required dc voltage offset is typically determined based on the magnitude of the circulating current flowing between the parallel-connected power converters 20a, 20b.