Digital current control of a voltage source converter with active damping of LCL resonance

LCL-filters offer higher attenuation of harmonics from VSCs than L-filters. However, LCL filters contain a resonant peak which could cause oscillations or instability unless the controller is carefully designed. In this thesis, a control strategy that employs 'active damping' to damp this resonance is explored. A new topology is presented for a discrete-time current controller which combines deadbeat current control with optimal state-feedback pole assignment to produce well-damped, high-bandwidth response, as well as fast transient overcurrent protection. Through numerical analysis the controller is shown to be robust to parameter uncertainty. A brief analysis of a two-converter system suggests that the controller functions well in a multi-converter environment. Simulations and experimental tests verify that fast well-damped transient response and overcurrent protection is possible at low switching frequencies relative to the resonant frequency.