Using Electric Water Heaters (EWHs) for Power Balancing and Frequency Control in PV-Diesel Hybrid Mini-Grids

Abstract

ABSTRACT- Electricity is usually supplied by diesel generators in remote communities at high costs. In such a case, renewable energy sources (RESs), such as wind and photovoltaics (PV), can be cost effective to meet part of the energy needs. However, the integration of RESs may lead to large power fluctuations and to the operation of the diesel genset under-loaded. Traditionally, energy storage devices have been used to provide power smoothing and frequency regulations, but this solution is quite costly. In this thesis, electric water heaters (EWH) are used to assist with power balancing and frequency regulation and to prevent the diesel genset from operating under-loaded, in a PV-diesel hybrid mini-grid. The characteristics of the diesel genset, PV, and the EWH are studied. An EWH is modeled using Matlab/SIMULINK. Approximate linear equations are derived and used for estimating the amount of power an EWH can take or drop, by varying the set point temperature Td. A review of methods used to control the EWH are then presented. A basic integrated control of the EWH, which varies the set point temperature (Td), using the system frequency is studied. Issues using this control in a small power system are investigated, and a modified integrated control is proposed to solve them. The effectiveness of basic and modified integrated controls is validated using a hybrid PV-diesel mini-grid benchmark implemented in PSCAD. Moreover, the impact of the PV on fuel consumption, and frequency variations is observed. Simulation results indicate that the modified integrated control is effective for frequency regulations, peak shavings, and for preventing genset operates under loaded.