Operation and Control of Renewable Energy Systems

Chapter 13Control of Grid-Connected Photovoltaic and Wind Energy Systems

13.1 Introduction

In many countries, the renewable generation from wind and solar has increased substantially during the past few years and forms a significant proportion of the total generation in the grid. At present, this renewable generation is concentrated in few areas, which is quite significant. It therefore requires serious consideration to balance the variability of such generation. With further increase in renewable generation, it is quite clear that some changes may be necessary in the operation of grid for large-scale integration of such variable renewable energy sources (RESs), although the demand for electricity, or load, also varies with time, but because it is slow or small, the power system is designed to handle that uncertainty. The short-term changes in load (over seconds or minutes) are generally small and caused by random events that change the demand in different directions. Over longer periods (several hours), changes in load tend to be more predictable. For example, there is a daily pattern of morning and evening load pattern highly correlated with human endeavours. The main difference is that load variations are more predictable than wind and solar variations. In order to maintain a constant frequency, the generation and load must be matched at every instant. The problem arises when there is mismatch between power supply and demand.

But all the generation from RES is not unpredictable. ...