Abstract
The on-load tap changer is critical for voltage regulation, however, its voltage regulation philosophy is suitable for one-directional power flow power systems. Since distributed generators introduce bidirectional power flow, the conventional operation of the on-load tap changer will be highly impacted, resulting in high voltage magnitudes that exceed acceptable limits, frequent voltage magnitude fluctuations, and the increase in overall reactive power supply when distributed generators start absorbing/injecting reactive power. Therefore, an adaptive control system is proposed on this paper that alters the existing voltage regulation philosophy of the on-load tap changer and also coordinate the voltage regulation capabilities of distributed generators with those of the on-load tap changer for optimal overall voltage regulation and the reduction of reactive power that flows through the power system, enhancing the power factor thereof. The proposed control system will change the centralized, and single-variable busbar voltage monitoring technique of the conventional philosophy with a decentralized, and multi-variable strategy that controls voltage based on the average voltage of the entire distribution network. The control system will calculate the on-load tap changer and distributed generators setpoints based on the overall average network voltage, average voltage deviation from nominal voltage, generators points of connection voltage and the total reactive power that flows through the power transformer. The control system was tested on a 22kV network modelled in MATLAB SIMULINK and the results attained revealed that the proposed multi-stage control system can successfully control voltage and simultaneously improve power factor.
Highlights
Voltage regulation is a critical criterion of any power system
An advanced voltage regulation scheme is introduced on this paper that allows the medium voltage power distribution network to optimally regulate voltage and improve the power factor when multiple distributed generators (DGs) are connected
While the conventional on-load tap changer (OLTC) voltage regulation philosophy changes substation voltage based on a fixed reference voltage, the proposed control scheme calculates an OLTC reference voltage based on overall average network voltage magnitude
Summary
Voltage regulation is a critical criterion of any power system. Through voltage regulation, the power system can provide minimal voltage magnitude variation as the load on the power system changes with time [1]. The centralized voltage regulation strategy of the OLTC is negatively impacted by the connection of DGs on the power distribution network This is because the excessive reverse power flow creates a network in which the substation busbar is not the location of highest voltage magnitude anymore. The control system proposed on this paper will evaluate and improve voltage regulation on a medium voltage power distribution network with high penetration of DGs. In addition, the designed control system can operate with any type of DG that has reactive power capability. The peak voltage magnitude will shift from one point to the other as the difference between DG generation PG and network load PL changes It is these reasons that renders the static conventional OLTC voltage regulation philosophy that relies on a fixed voltage magnitude for voltage regulation ineffective when DGs are connected. A voltage regulation philosophy is required that will not use a fixed OLTC reference voltage but change the OLTC reference voltage as the network voltage magnitudes are influenced up and down by DGs
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