Ara Panosyan

Design of a Power-Electronic-Assisted OLTC for Grid Voltage Regulation

High penetration of distributed generation (DG) has led to frequent voltage fluctuations in the distribution network. This paper describes the design of a partially rated, power-electronic-assisted onload tap-changing (OLTC) autotransformer. Positive and negative compensation of the grid voltage can be achieved on feeders that have high distributed generation and/or loading. A novel design of taps comprised of several no-load switches and a single semiconductor-mechanical hybrid switch have been proposed, that requires reduced voltage rating and a number of switches. In steady state, the mechanical switch in the hybrid switch conducts the load current resulting in low steady-state losses. During the tap change process, the OLTC uses semiconductor switches, namely insulated-gate bipolar transistor /metal-oxide semiconductor field-effect transistor, thus achieving arc-free tap change and long lifetime of switches. The OLTC system has been customized for both low-voltage and medium-voltage three-phase distribution networks. An open-delta configuration for the medium-voltage application has been proposed that requires only two OLTC units to control all three line voltages. Simulations are carried out to verify the steady-state and transient operation of the proposed OLTC.

Method of generating sets of PV plant power time series for grid simulation purposes

Power distribution grids with a high share of photovoltaic (PV) generation can be subject to severe voltage issues. The realistic simulation of such systems is therefore important for planning purposes and the evaluation of technical counter measures. This paper suggests a method to generate realistic power time series for a given set of PV generators within a distribution grid to provide the necessary input data for such simulations.

Design, simulation and testing of semiconductor assisted OLTC for a grid voltage regulator

Integration of higher shares of solar and other renewable sources as well as use of heavy domestic loads in the distribution network and growing consumer acceptance of electric vehicles results in frequent voltage fluctuations in the grid leading to an increasing need for voltage regulation. An effective solution for voltage regulation in the distribution grid is the utilization of On-Load Tap Changers (OLTCs) with hybrid switches. Combination of semiconductor switches and no-load mechanical switches form a hybrid switch which can achieve arc free tap changing while the steady state power loss is kept at minimum. This paper describes the design, analysis and testing of semiconductor assisted OLTC used in the low voltage distribution network for series voltage regulation. Details of high current (1000A) hybrid switch using parallel connected low power MOSFETs and its related issues such as current sharing are discussed.