Abstract
When the large-scale wind power is sent out through the high voltage direct current (HVDC) transmission system and a DC commutation failure occurs, the voltage of AC bus at the sending end decreases first and then increases. Suppose the reactive power supported in the low voltage ride-through process by various reactive resources is not timely returned. In that case, it may aggravate the voltage rise caused by the commutation failure, and the off-grid risk of wind turbine under high-voltage will be aggravated. In order to reduce the off-grid risk of wind turbines caused by the DC commutation failure, a transient voltage control strategy of DC sending-end regulator based on the online sequential extreme learning machine (OS-ELM) voltage prediction model is proposed. Firstly, the influence factors of commutation failures are analyzed. Aiming at the key factors, the real-time voltage comprehensive prediction model based on OS-ELM is used to predict the voltage increase during the commutation failure process and uses the voltage prediction results to optimize the transient response of the synchronous condenser. A large-scale wind farm together with the HVDC system is established in PSCAD to verify the effectiveness of the proposed scheme. Simulation results show that the proposed scheme can reduce the risk of wind power off-grid risk under DC commutation failures and increase the speed of voltage recovery at the point of common coupling.
Highlights
The environmental problems caused by fossil energy consumption have become increasingly serious, and wind power has been widely used worldwide
When wind turbines are connected to the grid via the high voltage direct current (HVDC)
When a commutation failure occurs in a DC system, the reactive power consumed by the DC system increases due to the increase of the direct current at the initial stage of the commutation failure, and the AC bus voltage of the sending-end converter station drops, and the DC power drops sharply
Summary
The environmental problems caused by fossil energy consumption have become increasingly serious, and wind power has been widely used worldwide. Compared with SVC, SVG and other dynamic reactive power compensation devices based on power electronics technology, the synchronous condenser, as a rotating equipment, provides short-circuit capacity for the system, and has better reactive power output characteristics It has unique advantages in reducing transient overvoltage at DC sending end, restraining commutation failure at DC receiving end, and improving system stability by using forced excitation [9]–[13]. A simulation model of the wind power transmission via HVDC is established to study the method; Secondly, the formula of the voltage variation degree during the DC commutation failure is deduced, and the correlation analysis of its influencing factors is carried out; Subsequently, according to the key influencing factors, the real-time voltage during the commutation failure is predicted by OS-ELM method; a reactive voltage control method of the synchronous condenser based on the voltage prediction is proposed. The voltage change at the grid-connected point of the wind turbine is mainly determined by the change in the AC reactive power of the converter station and the system and the short-circuit capacity of the AC system, which can usually be evaluated by the following formula:
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