Impact Assessment of New Energy Characteristics on Regional Power Grid Considering Multiple Time Scales

[Introduction] With the development of new energy, the influence of new energy uncertainty and time characteristics on power grid is increasing day by day. Traditional new energy indexes are difficult to describe the interaction between power grid and new energy. It is necessary to establish evaluation system and index to quantify the impact of new energy on power grid. [Method] Construct the evaluation system from multi-dimensional and multi-scale and establish new energy output characteristic index, electric quantity characteristic index, peak regulation characteristic index and flexibility demand index to analyze the new energy output characteristics, the relationship between new energy output and electric quantity, the influence of new energy on peak regulation and the influence of new energy fluctuation on power grid at critical moments. Typical scene features were mined by applying indexes from different time scales such as year, season, month, day and hour. [Result] All kinds of indexes of the evaluation system has been calculated by taking the actual wind power, PV power and load in a certain area as an example. The results show quantitatively the influence of regional new energy on power grid and its distribution characteristics at different time scales. The engineering practicability of the proposed index system is verified. [Conclusion] The proposed index calculation method is quick and simple and the physical meaning of indexes is clear and intuitive and helpful to guide the planning and dispatching of new energy

Research on Direct Power Control Strategy Based on Voltage Controlled Virtual Synchronous Generator

To support the “carbon peak and carbon neutrality” goal, new energy is poised to explode, and new energy power generation converter is simultaneously facing new challenges. The conventional current-controlled new energy converter can quickly transmit active power on the DC bus to the power grid. However, for the weak grid, the stability margin of the converter grid-connected system is reduced on the one hand, which can easily cause resonance oscillation; on the other hand, the current controlled converter cannot actively respond to system frequency and voltage fluctuation to offer support. The voltage controlled virtual synchronous generator (VVSG) is used to improve system small signal stability and frequency stability; however, its power response speed is too slow to meet the requirements of fast following power command. Although a voltage/current dual-mode switching control scheme is put forward to achieve characteristics complementary of current controlled converter and voltage-controlled converter, the control structure switching and intermediate variable following is required to realize mode switching, which is prone to large power shocks and switching failures. In view of the problem, a direct power control strategy based on VVSG is proposed. The control structure is raised based on a conventional VVSG outer active power control loop, and the output active power and frequency characteristics are analyzed. Compared with the voltage and current dual-mode control, VVSG with direct power control can perform large inertia characteristic in the weak grid and fast power following characteristics in the strong grid by adjusting λ, and without control structure switching and intermediate variable following. Moreover, the two characteristics can be smoothly transited. In addition, the active support ability of voltage source can be maintained under both characteristics. Finally, the effectiveness of the proposed control strategy is verified through simulation results.</jats:p

Research on Direct Power Control Strategy Based on Voltage Controlled Virtual Synchronous Generator

To support the “carbon peak and carbon neutrality” goal, new energy is poised to explode, and new energy power generation converter is simultaneously facing new challenges. The conventional current-controlled new energy converter can quickly transmit active power on the DC bus to the power grid. However, for the weak grid, the stability margin of the converter grid-connected system is reduced on the one hand, which can easily cause resonance oscillation; on the other hand, the current controlled converter cannot actively respond to system frequency and voltage fluctuation to offer support. The voltage controlled virtual synchronous generator (VVSG) is used to improve system small signal stability and frequency stability; however, its power response speed is too slow to meet the requirements of fast following power command. Although a voltage/current dual-mode switching control scheme is put forward to achieve characteristics complementary of current controlled converter and voltage-controlled converter, the control structure switching and intermediate variable following is required to realize mode switching, which is prone to large power shocks and switching failures. In view of the problem, a direct power control strategy based on VVSG is proposed. The control structure is raised based on a conventional VVSG outer active power control loop, and the output active power and frequency characteristics are analyzed. Compared with the voltage and current dual-mode control, VVSG with direct power control can perform large inertia characteristic in the weak grid and fast power following characteristics in the strong grid by adjusting λ, and without control structure switching and intermediate variable following. Moreover, the two characteristics can be smoothly transited. In addition, the active support ability of voltage source can be maintained under both characteristics. Finally, the effectiveness of the proposed control strategy is verified through simulation results

Analytic of VSC-HVDC Interconnected Power Systems from a Perspective of Frequency Security

Abstract In the interconnected power systems with VSC-HVDC (Voltage Source Converter-High Voltage Direct Current) transmission links, the failures of VSC-HVDC system can cause large power imbalance for both sending-end and receiving-end power systems. In this paper, the reliability model of the VSC-HVDC system is developed based on series-parallel structure recognition. The frequency dynamics of the power systems are characterized considering the frequency regulation of the power systems in response to the power imbalance arise from the component failures. Moreover, the Monte Carlo simulation method is applied to analyze the frequency dynamics in different contingencies. The indices measuring the frequency stability and the reliability of the interconnected power systems are introduced.</jats:p