Modular harmonic cancellation in a multilevel STATCOM

This paper presents a three-phase Static Compensator (STATCOM) built-up with two types of single-phase H-bridge power cells. Differently to configurations based on symmetrical units, the proposed structure is assembled using one type of power cells for compensating reactive power at fundamental frequency and another kind of power cells for compensating harmonic currents. Hence, high power - slow semiconductors can be used in power cells to compensate reactive power at fundamental frequency using low switching frequencies and the harmonic compensation is done using power cells that feature low power - faster semiconductors commutated at high frequencies. Thus, the functionality and overall efficiency can be improved while keeping the modularity feature. Moreover, this approach allows decoupling the control objectives and thus, using the superposition principle, independent control strategies can be designed. Additionally, the power cells considered for harmonic compensation can be self adjusted as the load conditions change in order to operate at minimal DC voltage. Simulated static and dynamic results confirm the theoretical considerations.