Control of a line-commutated converter in two-quadrant operation with zero valves

摘要

A line-commutated converter, which operates in two-quadrant operation in a circuit which saves reactive power and has zero valves, is intended to be controlled in such a manner that the switching on and off of the zero valves does not adversely affect the control behaviour of the converter. Continuous moving through the control characteristic, without discontinuities, is achieved in that a) the delay angle ( alpha H) of the main valves calculated from the zero point of the commutating voltage is limited to a value [150 DEG -(u + gamma )max] as long as current is still flowing through one of the zero valves, gamma denoting the turn-off angle and u the overlapping angle during current transfer from the main valve to the zero valve, b) the width of the control pulses of the zero valves is held variably between 120 DEG and 0 DEG , by limiting the duration of these pulses to a time ( alpha 1-30 DEG ) which is fixedly allocated to the line voltage, and c) the delay angle ( alpha H) for the main valves is enabled at values above [150 DEG -(u + gamma )max] if current is flowing through a main valve in the event of a corresponding signal of a higher-level regulator in each commutation group of the converter. <IMAGE>