Modelling and control of a series dual bridge GTO voltage source converter

The authors present the steady state operation, a small signal model, and a control loop structure for a series dual bridge GTO voltage source inverter. Fourier analysis, transformation of a rotating reference frame, and small signal linearization are used in obtaining a standard state space model with all variables in real quantities. The converter is a sixth order system and is open loop stable. From a control standpoint, the system is a three input three output multivariable system and can be decoupled into three single input single output loops. Classical control design methods in the frequency domain can be applied. It is found that although the system is open loop stable the converter has poor relative stability in the regulation of power balance between the two bridges. A structural modification and a more sophisticated control design are suggested to overcome this problem.<>