An integrated control strategy of battery energy storage system in microgrid

AN INTEGRATED CONTROL STRATEGY OF BATTERY

ENERGY STORAGE SYSTEM IN MICROGRID

Lei Zhang *, Yipeng Dong , Zhigang Chen *, Xiaorong Xie , Hao Sun *, Zhiwen Liu *

* Guangdong Electric Power Design Institute,China,510600

ЪState Key Lab. of Power Systems, Department of Electrical Engineering, Tsinghua University, Beijing 100084, China

Keywords: Microgrid, BESS, Control strategy

Abstract

As an important smart-grid technology, microgrid is being developed rapidly for its advantages of high reliability, less pollution and improved system flexibility. This paper proposes an integrated control strategy of battery energy storage system (BESS) in a microgrid. It includes three

control strategies, namely, PQ control, Droop control and V/f control. The integrated control strategy can switch among

these three control strategies as required. In this paper, the simulation is performed and the whole model of the microgrid is built. The BESS uses the integrated control strategy, while the rest microsources use PQ control. Through the comparison and analysis, the applicability and effectiveness of the integrated control strategy has been verified in simulation.

1 Introduction

As an important research direction of smart-grid, microgrid is one of the development trends of power system, and it’s also one of the hot issues in research at present. Figure 1 shows the basic structure of a microgrid, containing the BESS. The BESS consists of a battery and an inverter, connecting to the microgrid ac bus with other microsources and loads. The ac bus connects to the large power grid through a transformer

An integrated control strategy of battery energy storage system in microgrid

An integrated control strategy of battery energy storage system in microgrid

Figure 1: Microgrid configuration

The dc side of the inverter of the BESS is connected to the battery, while the ac side connected to the microgrid, and thus the bidirectional energy transfer between the battery and microgrid is achieved. The rest of the paper will be organized as follows: the model of battery will be discussed first. Then in section 3 the implementation of different control strategies

will be studied. An integrated control strategy for the outer loop controller of BESS is designed, to achieve PQ control,

An integrated control strategy of battery energy storage system in microgrid

V/f control and droop control, which makes BESS can be applied in different microgrids using master-slave control or

An integrated control strategy of battery energy storage system in microgrid

peer control. The whole model of the microgrid is built in

An integrated control strategy of battery energy storage system in microgrid

Matlab/Simulink and dynamic simulations are conducted in section 4, with natural condition being constant. Finally, conclusions are drawn briefly. 2 Battery dynamic model As shown in Figure 2, the battery is modelled as a controlled voltage source in series with a fixed resistance [6]. Figure 2: Battery model

In figure 2, the controlled voltage Eb is expressed as:

Eb E0 KQ

t Aexp( Btidt) (1) Q ³³0

idt

Where E0 and K are respectively the rated voltage and polarization voltage of the battery; Q is the capacity of battery; A is exponential zone amplitude and B is exponential zone time constant inverse.

3 BESS model

3.1 The control strategy of BESS

The widely used control strategies of BESS include PQ control, V/f control and Droop control [5]. By decoupling the active and reactive power, PQ control can control them independently, and the output of BESS is equal to the reference value. PQ control is unable to maintain frequency and voltage of the system, so it’s generally used in grid-connected mode.

V/f control is just constant voltage constant frequency control. No matter how the output of BESS changes, the voltage and frequency of the inverter (ac side) remain unchanged. While

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