Microgrids

Abstract

A microgrid is an aggregation of distributed generating units, distributed energy storage, sensitive and non-sensitive loads, smart switches, communication facility, automation capability, and centralized/decentralized control system. It is capable of operating in grid-connected as well as islanded mode. The remotely located load centers are highly benefitted with the development of microgrid at these locations. Solar and wind energy can be harnessed using the power electronics-based converters with an associated control system. Additionally, energy storage devices in the microgrids improve the power supply reliability during generation deficit conditions in the islanded mode of operation. This chapter addresses the attributes of such systems, its architecture, control issues, and developments around the world.

A. K. Sinha: Deceased on 31 March, 2017.

Appendix

The family of PID controllers is the simplest of the controllers. The gains of the controller have different impacts on the closed-loop response of the plant in a microgrid.

Assuming a plant to be represented by a closed-loop transfer function given as:

$$ G = \frac{20}{{s^{4} + 12s^{3} + 40s^{2} + 55s + 30}} $$

(1.42)

The effect of the P controller when only $K_{\text{p}}$ is varied independently is shown in Fig. 14. It is observed that the steady state error reduces with increase in $K_{\text{p}}$. However, the damping reduces and overshoot increases with increase in $K_{\text{p}}$.

Fig. 14

Typical P controller behavior with increasing proportional gain

The integral gain is separately varied keeping P and D gains as zero, as shown in Fig. 15. The overshoot is seen increasing, and damping reduction is observed with increasing $K_{\text{i}}$.

Fig. 15

Typical I controller behavior with increasing integral gain

The derivative controller alone fails to control the controlled variable when $K_{\text{p}}$ and $K_{\text{i}}$ are zero, as observed in Fig. 16.

Fig. 16

Typical derivative controller behavior with increasing derivative gain

The effect of the PID controller with fixed P and D gains but increasing $K_{\text{i}}$ is observed in Fig. 17. The steady state error is almost eliminated with increase in the integral gain. However, the overshoot increases and damping reduces with its increase.

Fig. 17

Typical PID controller behavior with increasing integral gain ($K_{{\text{p}}} = \, 1$, $K_{{\text{d}}} = 1$)

The effect of the PID controller with fixed P and I gains and increasing $K_{\text{d}}$ can be observed in Fig. 18. The derivative gain reduces overshoot significantly.

Fig. 18

Typical PID controller behavior with decreasing derivative gain ($K_{\text{p}} = 1$, $K_{\text{i}} = 1$)

The overall impact of increasing the gains of the PID controller is illustrated in Table 2.

Table 2 Effect of increasing $K_{{p}}$, $K_{{i}}$, and $K_{{d}}$ independently in PID controller