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The ultra‐low frequency oscillation (ULFO) imposes an emerging stability challenge to the high proportion of hydropower grids. To suppress ULFO without reducing the primary frequency regulation of the hydro governor, a novel idea to exploit the voltage regulation effect of load is implemented. First, the additional damping controller is designed and configured in static var compensator (SVC), and the frequency analysis model considering the configuration of SVC as well as damping controller is established. Based on the model, the specific influence of SVC and controller on ULFO is analysed through eigenvalue calculation. In addition, the influence of various load models and SVC location on the damping level are further studied. Consequently, a parameter optimization design method for SVC additional damping control is proposed, it is modelled as the optimization problem of damping ratio in ULFO mode under multi‐operation conditions, which is solved by a particle swarm optimization algorithm. Finally, the effectiveness of the designed SVC additional damping controller is verified in the improved four‐machine two‐area power system and the actual power grid in China. [ABSTRACT FROM AUTHOR]

To make clear the influence of renewable energy on ultra-low-frequency oscillation (ULFO) in a hydro-dominant system via an high voltage direct current (HVDC) transmission system, this paper studies the damping characteristics when wind power is integrated into the sending power system. The damping torque method is applied for the mechanism study and risk evaluation of ULFO. The study of the inner cause and outer performance proves that ULFO belongs to frequency oscillation rather than conventional power oscillation. According to the theoretical analysis, the suggested control mode is identified to reduce the risk of ULFO. Moreover, a robust controller is designed for wind units based on mixed H2/H∞ robust control theory, and the control method makes use of the fast response ability of the converter without compromising the primary frequency regulation ability. Finally, a simulation model of a hydro-dominant sending power system with wind integration is established in PSCAD Version 4.6 software. The simulations verify the proposed control can suppress ULFO effectively. [ABSTRACT FROM AUTHOR]

Aiming at the problem of ultra-low-frequency oscillation (ULFO) in power systems, with an oscillation frequency lower than 0.1 Hz, an oscillation suppression control method is proposed. Firstly, the mathematical modeling of the system is carried out, and a cascade correction control method of the governor of hydropower generators is proposed. Secondly, using the ability of photovoltaic (PV) active power to adjust the system frequency, an additional controller for PV active power is proposed. Then, a unified frequency model considering the two controllers is established for multi-hydro and multi-PV systems, and the structural singular value method is used to coordinate the design of the parameters of the hydropower and PV generator controllers to achieve robust performance. Finally, based on a time-domain simulation of single-hydro and single-PV systems and an actual demonstration system located in Sichuan Province, China, the results show that the control method proposed in this paper has a good suppression effect on ultra-low-frequency oscillation under different working conditions, and meets the requirements of robust performance. [ABSTRACT FROM AUTHOR]

The ultra‐low frequency oscillation and poor speed regulation performance caused by the fast power control decrease the stability and efficiency of the variable speed pumped storage unit with a full size converter (FSC‐VSPSU). This paper presents a fast frequency control strategy to solve this problem. The small‐signal model of the FSC‐VSPSU in fast frequency mode is established, and the key parameters for the system stability are studied by the eigenvalue method. Aiming at the coupling oscillation mode caused by the governor and generator side converter (GSC), the corresponding control parameters optimisation method is proposed. In order to solve the power anti‐regulation problem, the strategy of combining rotor kinetic energy release, power slope adjustment, and delay acceleration control is proposed. PSCAD and RTDS simulation results show that the proposed strategy can effectively avoid the ultra‐low frequency oscillation caused by the fast power control and significantly improves the frequency and power control performance. [ABSTRACT FROM AUTHOR]

• This paper establishes a small signal model of variable speed pumped storage unit with full size converter. • The oscillation modes and key influencing factors are clarified. • A coordinated control strategy for suppressing the ultra-low frequency oscillation is proposed. The research on control strategies of the variable speed pumped storage unit with full size converter (FSC-VSPSU), mainly focuses on the rapidity of power regulation. But the speed oscillation and slow speed regulation performance caused by fast power regulation are ignored, which is not conducive to the safe and efficient operation of the unit. This article investigates the dynamic stability characteristics of the FSC-VSPSU in detail. In turn, the stability risks are clarified and serve for the design of its control strategy and the improvement of operational efficiency. The small-signal model of FSC-VSPSU considering the variation of water head and load in fast power mode is established. The dominant instability control link and key parameters are revealed based on the eigenvalue analysis. Oscillation mode analysis shows that the unit has a wide-band oscillation characteristic. The dominant oscillation mode is the ultra-low frequency oscillation (ULFO) caused by the governor control system. To suppress the ULFO and improve the optimal speed tracking performance of the unit to the greatest extent, a coordinated control strategy of governor variable parameter control and governor power system stabilizer (GPSS) is proposed. The electromagnetic transient simulation based on PSCAD verifies the effectiveness of the proposed measures. [ABSTRACT FROM AUTHOR]