No abstract

Recently, the awareness of the severe consequences of greenhouse gases on the environment has escalated. This has encouraged the world to reduce the usage of fossil fuels for power generation and increase the use of cleaner sources, such as solar energy and wind energy. However, the conventional power system itself was designed as a passive power system, in which power generation is centralised, and power flows from substations towards the loads. Decentralised renewable energy sources, also called distributed generators, were introduced to create an active power system in which power generation can occur anywhere in the power system. Decentralised power generation creates challenges for the conventional power system, such as voltage fluctuations, high voltage magnitudes, reverse power flow, and low power factor. In this paper, an adaptive control system that coordinates different distributed generators for voltage regulation and power factor correction is introduced and designed. The control system will decrease the total reactive power that flows in the transmission network through a reactive power exchange between distributed generators. Therefore, power factor will improve, power system losses will reduce, and the total apparent power on lines will reduce, giving more room to active power to flow. The results obtained showed that the control system is effective in regulating voltage and improving the power factor when multiple distributed generators are connected.

Summary In this paper, a voltage regulation system is proposed that improves the voltage regulation process in power distribution networks with a high penetration of embedded generation. The principle of the proposed system is to alter the existing and conventional substation busbar monitoring technique of the on‐load tap changer (OLTC) commonly implemented in medium voltage power distribution networks. The system alternatively uses measured multiple voltage magnitudes on different vital locations on the power distribution network, it thereafter isolates the uppermost and the lowermost measured voltage magnitudes from all voltage inputs received. The sampled uppermost and lowermost voltage magnitudes are compared with predetermined set voltage limits, and the OLTC will change its tap settings to keep the uppermost and lowermost voltage magnitudes within the set voltage limits. To avoid tap hunting when set voltage limits cannot be maintained, the system will reduce the active power generated by the embedded generator to a predetermined value. On the other hand, the system will monitor the load on the feeder in which the embedded generator is connected and then increase the embedded generator active power generation again when the load start increasing. The proposed voltage regulation system was tested on a typical South African power distribution network consisting of a substation with an OLTC equipped power transformer that is simultaneously regulating voltage of three medium voltage feeders. The voltage regulation system managed successfully to keep feeder's voltages within the acceptable limits.

The South African power distribution network is characterized by long power distribution lines with low short circuit capacity, and when distributed generation is introduced to these lines, voltage magnitudes are severely impacted. The existing voltage regulation methods of the on-load tap changer and step voltage regulator cannot successfully regulate voltage in long distribution lines with distributed generation since their control philosophy was designed for networks without distributed generation. Therefore, a dynamic system is proposed in this paper that coordinates the on-load tap changer, step voltage regulator, distributed generators, and the battery energy storage system to control voltage in long distribution lines with distributed generation. Their coordination will be based on response time and robustness. Unlike the conventional method, the proposed novel system will calculate a reference voltage that the on-load tap changer and the step voltage regulator must follow, based on the real time average voltage of the section of the network they each regulate. The system will also control the charging and discharging of a battery energy storage system based on the point of connection voltage and the average voltage of the feeder which it is connected to. Reactive power from distributed generators will also be used to enhance voltage regulation and refine the network power factor. When voltage magnitudes cannot be successfully brought within acceptable range, the proposed scheme will decrease the active power produced by distributed generators. The proposed system is examined on a South African 22kV network built in Matlab/Simulink.