Abstract
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.
Highlights
To support the “carbon emission peak in 2030 and carbon neutrality in 2060” goal of China, photovoltaic wind power and other new energy power generations will grow explosively as the energy supply system is changing from coal to diversification [1,2].The total installed capacity of photovoltaic and wind power in China reaches 252 GW in 2020 and is expected to reach 1.2 billion kilowatts by 2030, in an effort to peak CO2 emissions by 2030
Case 3: The voltage controlled virtual synchronous generator (VVSG) with direct power control algorithm is connected to a strong utility grid at 1.5 s, and the active power command increases from 0 kW to 60 kW at 1.6 s
Case 4: The VVSG with direct power control algorithm is connected to a strong utility grid at 1.5 s, and the active power command increases from 0 kW to 60 kW at 1.6 s
Summary
To support the “carbon emission peak in 2030 and carbon neutrality in 2060” goal of China, photovoltaic wind power and other new energy power generations will grow explosively as the energy supply system is changing from coal to diversification [1,2]. In the high-penetration new energy power generation system, the requirements of new energy generation efficiency pose new challenges to control flexibility of new energy converter It should simulate synchronous generator characteristics to support voltage and frequency of regional grid or grid nodes, but should meet the active power fast following requirement to track new energy maximum power point or power dispatching command [17]. A voltage-controlled converter achieves higher system stability in the weak grid; as its output active power responds slowly, it generally spends at least a dozen of fundamental periods before the active power command is followed.
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