PWM control of current source converter

The most important feature of a current source converter using self-extinction-type devices is that it is possible to control the output dc current keeping the input power factor equal to unity and input line current waveform sinusoidal. This paper proposes a new PWM pattern which reduces the switching frequency of GTO elements by 30 percent, reduces the harmonic content and is better suited for current control with variable modulation factor as compared with the conventional patterns. In the proposed method, the frequency spectrum of switching function is weighed inversely proportional to the harmonic order utilizing the low pass L-C filter inserted to the power source. The performance function thus derived is used to define, the evaluation function which represents the sum of squares of harmonic amplitudes. The optimal PWM pattern is determined so as to minimize the evaluation function using Park vectors.