Electromagnetic transient study on flexible control processes of ferroresonance

Ferroresonance, which is a common phenomenon in power systems, have threatened the security of power systems for a long time. Although several ferroresonance suppression measures have been applied in power systems, ferroresonance still occurs occasionally. In this study, a flexible control strategy to control different ferroresonant modes is proposed. The behavior of a typical ferroresonant circuit acquired from a ferroresonance testing system to obtain the electromagnetic transient and control details of the control method is also investigated. The key parameters in the control module are determined, including the switching frequency and the coefficients of the proportional-integral (PI) controller. Then, six typical ferroresonant overvoltages are selected as control systems using the proposed method. Given the effect of a damping resistor and fully controllable power electronic switches with a gate signal controlled by a proportional-integral (PI) control system, these six typical ferroresonant overvoltages can all be suppressed in 0.12 s to the non-ferroresonant state after the controller is activated. The electromagnetic transients, including the essential system state quantity transients in the control process, are also investigated. At last, a laboratory prototype is implemented, and the experimental results show that the proposed method is useful for ferroresonant overvoltage control.