Voltage control of twelve pulse rectifiers fitted with double LC filters

This work describes the output voltage control of a parallel twelve pulse rectifier with four half wave three-phase rectifiers and a double LC output filter. The implementation is made using two control levels: four internal current control loops and one external output voltage control loop, generating the reference current for the internal control loops. To design these control loops new simplified rectifier models are created and verified. These current control loops allow the tight control of each one of the output currents ensuring their equalisation and are designed considering that the filter first capacitor voltage is almost constant. Even though other control techniques such as sliding mode control allow faster response times, they need to measure all the circuit currents and voltages. On the contrary, to run the proposed controller, only the input currents and the output voltage need to be measured, minimising the implementation costs. This, together with the fact that an extremely fast response time is not usually required, makes this controller a good choice for industrial applications. MATLAB simulations and experimental results, are compared and shown to verify the theoretical results and assumptions.