Method for the determination of a control scheme for a NPC VSC, in particular as an active power filter

摘要

Proposed is a method for the determination of a control scheme for a neutral point clamped (NPC) voltage source converter (VSC) with at least 3 levels, in particular as a shunt active power filter, with a topology of three bridge legs (21-23) between each of three phases (R,S,T) of a grid (11) and a neutral point (24), each leg (21-23) comprising at least four active switches (T1-T4), wherein there is provided a clamping carrier modulator (1) synchronized with the grid (1) for the control of no-switching intervals, said method comprising at least the following steps: analyzing the waveform of the grid and/or a load voltage (ILR) and determination of windows (3) defining an allowed period for no switching of the corresponding bridge leg; operating or simulating the operation of the voltage source converter with different clamping carrier modulator frequencies, and then analyzing the balance in the operating junction temperatures and/or power losses across the active switches and also analyzing the total losses of the voltage source converter; comparing the balance and the total losses of different clamping carrier modulator frequencies and selecting either the clamping carrier modulator frequency according to showing, as primary criterion, the better balance and, as secondary criterion, the lower total losses; operating or simulating the operation of the voltage source converter with the selected clamping carrier modulator frequency, while iteratively changing at least one of the following operating parameters of the voltage source converter: switching frequency, DC-link voltage reference, duty cycle of clamping carrier modulator, phase shift of the clamping carrier modulator relative to the grid, and optimizing the balance in the operating junction temperatures and/or power losses across the active switches and the total losses of the voltage source converter as a function of the adjustment of these operating parameters until reaching optimum operation parameters for the control scheme.