Distributed Cooperative Control for Photovoltaic Generation Systems

Introduction

In recent years, photovoltaic (PV) power generations have been introduced in large quantities, and PV generation systems are focused as shown in Fig.1. Generally speaking, in PV generation systems, it is important to achieve the power supply and demand balance, i.e. to balance the amount of power supplied with the amount of power consumption. Therefore, suppressing the fluctuation of the PV outputs is necessary due to the change in the weather for achieving the power supply and demand balance in PV generation systems. In addition, it is important to achieve the local generation of electric power for local consumption in terms of self-sufficient in energy.

Then, this study tackles the problem to achieve the power supply and demand balance, and the local generation for local consumption by determining whether or not each PV supplies electric power (ON/OFF) in PV generation systems.


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Fig.1 PV generation systems

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Fig.2 The PV outputs which fluctuates by weather conditions

Purpose

In this study, our approach is to cooperate the distributed controller through information network, which embedded in each PV, and to determine ON/OFF to achieve the following specifications (Fig.3).
Specification
 ① the power supply and demand balance
 ② the local generation for local consumption (Fig.4)
 ③ the reduction in frequency of ON/OFF switching in between the time (Fig.5)
Therefore, the research purpose is to propose the distributed controller for controlling ON/OFF to achieve the specifications ①, ②, ③.


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Fig.3 The power network layer and the information network layer

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Fig.4 The local generation for local consumption

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Fig.5 The reduction in frequency of ON/OFF switching

Problem Formulation

The PVs information, the solar radiation distribution, and the power demand distribution are given for the PV systems. Then, find ON/OFF of each PV to achieve the specifications ①, ②, ③ (Fig.6).


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Fig.6 Problem formulation

Proposed Distributed Controller

Proposed distributed controller Ki is composed of the two sub-controllers Ki1 and Ki2. At the begining, the ON/OFF switching is suppressed to achieve the specification ③ by the controller Ki2. Next, the controller Ki1 determins the ON/OFF by transiting the information in a very short period through the information network to achieve the specification ①, ②.


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Fig.7 The proposed distributed controller

Numerical Example

First, we describe ON/OFF results at a certain time.
Consider the PVs information, the solar radiation, and the power demand as shown in Fig.8. Then, ON/OFF result is shown in Fig.9 and Fig.10. In Fig.9, we can see that ① the power supply and demand balance is achieved. Also, in Fig.10, we can confirm that ② the local generation for local consumption is achieved.

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Fig.8 The PVs information, the solar radiation, and the power demand

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Fig.9 The power supply and demand balance

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Fig.10 ON/OFF

Second, we describe the number of ON/OFF switching of all PVs in between the time in the case of being given a chain of demand power distribution as shown in Fig.11.
We can see that ③ the reduction in frequency of ON/OFF switching is achieved in comparison with not suppressing the ON/OFF switching.

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Fig.11 The number of ON/OFF switching in between the time