Suppression control of DC current component in SVC originated from even-order voltage harmonics

The geomagnetic disturbance is one of risks in the AC transmission systems. It induces current component of very low frequency and affects the transformer magnetization. As one of effects, the even-order voltage harmonics appear in the AC voltage, which possibly generate the DC current component in the current of the Thyristor Controlled Reactor, TCR, a type of Static Var Compensator, SVC. Without any mitigation, when the transformer is connected to the TCR, the transformer magnetization condition may be further worsened. Then, for stable operation of the AC system, the SVC is sometimes required to suppress the DC current component. The paper, first, discusses mechanism of the DC current component generation from the even-order voltage harmonics. Secondly, based on the discussion, the paper proposes a practical estimation algorithm of the DC current component. The estimation uses only the AC voltage information. The proposed algorithm does not use the TCR current information and then offers an economical advantage to eliminate cost impact of DC current sensors for high voltage circuits. Furthermore, the practical estimation method is proved to show high accuracy. Thirdly, the paper proposes a simple algorithm to suppress the DC current component using the estimated value. The simple algorithm offers another practical advantage, feasible to install in the actual SVC controller. The performance of the suppression control is verified by the digital simulation. Then, the algorithm is installed in the actual SVC controller and has been verified to function as expected through the simulator tests. The proposed suppression control is already used in actual SVC installations.