Control of the low frequency oscillation in AC and HVDC hybrid transmission power system by using PMU's signals

As the power system is interconnected with HVDC transmission, the power oscillation with low frequency appears in the AC transmission lines with weak damping. This paper presents the low frequency oscillation (LFO) phenomenon and its primary cause. The serious LFO limits the transmission power of AC lines and influences the system angle stability. This paper analyzes the LFO's frequency and oscillation mode with the eigenvalue analysis method in small signal stability. A two-area, four-machine model with AC and HVDC in parallel is studied. In this system model, the generator adopts a three-order reduced-model and HVDC mathematical model has a two-order model. The whole system mathematical model is expressed as state equations and the equations are linearized. The eigenvalue of the linearized matrix can be calculated. Therefore, the system oscillation modes with damping ratio can be analyzed. The coordinated control to HVDC supplementary controller based on the phase signals of PMU's output is discussed and the controller is designed with sliding mode control. (5 pages)