This chapter first reviews the fundamentals of active and reactive power control using STATCOMs. Then, two current control algorithms, namely selective/ resonant controllers and repetitive controllers, are presented that provide a STATCOM with the capability of controlling the harmonics of the current injected into the PCC. Finally, the use of synchronously-rotating reference frames is generalized so that current harmonic control can also be achieved using PI controllers. An efficient application of the last technique is explained in detailed and a number of experimental results are presented. It will be demonstrated that versatile control of STATCOMs is straightforward using this technique even if the grid frequency varies. This technique can be applicable to both, traditional, strong and centralised electric power systems and those to come in the future with large amounts of distributed generation.Keywords STATCOM Á VSC Á Harmonic control Á Selective control Á Repetitive control Á Multiple reference frames M. Ochoa-Giménez Á A. García-Cerrada (&) Á J. Roldán-Pérez Á J.L. Zamora-Macho Á P. García
IntroductionSTATCOMs are typical shunt power electronics-based devices (see Fig. 7.1), used in power systems for multiple purposes [1]. Originally, STATCOMs were intended for reactive power control as a superior alternative to thyristor-controlled devices such as Thyristor-Controlled Reactors (TCRs) or Thyristor-Switched Capacitors (TSCs) [2]. Reactive power compensation in TCRs and TSC depends on the point of common coupling (PCC) voltage unlike in STATCOMs which could overcome this limitation thanks to the use of electronic switches capable of controlled ON-OFF and OFF-ON commutation. Also thanks to their controlled commutation, STATCOMs provide a much faster dynamic performance [3]. STATCOMs rapidly evolved from square wave multi-pulse converters [4-6] to pulse width modulation (PWM)-controlled converters [7][8][9] making it possible a fast and accurate active and reactive power control at the PCC.Nowadays STATCOMs are used for reactive power compensation mainly, in applications such as improving fault-ride-through of wind generators [10] or compensating voltage drops at the transmission level or voltage fluctuations at the distribution level [11,12]. When STATCOMs are used in distributions systems they are often called Distribution Static Compensators (DSTATCOMs) [13].The most classical approach to the control of a STATCOM [9] (reactive power control) only addresses the control of the fundamental components of the current injected in the PCC: the positive-sequence current of the grid frequency. Meanwhile, the same shunt-connected components in Fig. 7.1 (left) namely, a voltage source converter (VSC), a transformer (optional) and a connection filter, are.1 STATCOM schematics (left) and simplified model (right), nomenclature: p and q are the instantaneous real and reactive power injected by the STATCOM into the PCC, p R is the power lost in the filter resistance, p L is the power consumed in the filter plus ...