Fuzzy System In Matlab

Fuzzy System In Matlab

1. Introduction

In our Arabian nation peopled areas is very small comparing to total area because fresh water resources concentrate in these areas. Now, the existing fresh water almost enough for our needs, but in the near future with increasing in people numbers it will be huge problem. On the other hand we have shining sun all the year, so we can use stand alone PV-powered water pumping system to get water in non peopled areas. Unfortunately the actual energy conversion efficiency of PV module is rather low. So to overcome this problem and to get the maximum possible efficiency, the design of all the elements of the PV system has to be optimized.

In order to increase this efficiency, MPPT controllers are used. Such controllers are becoming an essential element in PV systems. A significant number of MPPT control have been elaborated since the seventies, starting with simple techniques such as voltage and current feedback based MPPT to more improved power feedback based MPPT such as the perturbation and observation (P&O) technique or the incremental conductance technique [1] and [2]. Recently intelligent based controls MPPT have been introduced.

In this paper, an intelligent control technique using fuzzy logic control is associated to an MPPT controller in order to improve energy conversion efficiency.

2. The proposed system

The proposed system in this paper is stand-alone DC water pumping without backup batteries. As shown inFig. 1, the system is very simple and consists of subsystems:

Fig. 1. Block diagram of the proposed PV water pumping system.

2.1. PV module

BP Solar BP SX 150S PV module is chosen for a MATLAB simulation model. The module is made of 72 multi-crystalline silicon solar cells in series and provides 150 W of nominal maximum power [14]. Table 1shows its electrical specification.

Table 1. Module electrical characteristics data of PV module taken from the datasheet [14].

Electrical characteristics

Maximum Power (Pmax)

150 W

Voltage at Pmax (Vmp)

34.5 V

Current at Pmax

4.35 A

Warranted minimum Pmax

140 W

Short-circuit current (Isc)

4.75 A

Open-circuit voltage (Voc)

43.5 V

Maximum system voltage

600 V

Temperature coefficient of Isc

(0.065 ± 0.015)%/°C

Temperature coefficient of Voc

-(160 ± 20)mV/°C

Temperature coefficient of power

-(0.5 ± 0.05)%/°C

NOCT5

47 ± 2 °C

2.2. DC-DC Cúk converter

The basic operation of Cúk converter and derivation of the voltage transfer function is explained in Fig. 2:

Fig. 2. Cúk converter waveforms: (a) switch off; (b) switch on [15].

The voltage transfer function of Cúk converter is written as [15]:

(1)

Its relationship to the duty cycle (D) is:

• If 0 < D < 0.5 the output is smaller than the input.

• If D = 0.5 the output is the same as the input.

• If 0.5 < D < 1 the output is larger than the input.

Here, a Cúk converter is designed based on the specification shown in Table 2.

Table 2. Design specification of the Cúk converter [5].

Specification

Input voltage (Vs)

20-48 V

Input current (Is)

0-5 A (<5% Ripple)

Output voltage (Vo)

12-30 V(<5% Ripple)

Output current (Io)

0-5 A (<5% Ripple)

Maximum output power (Pmax)

150 W

Switching frequency (f)

50 KHz

Duty cycle (D)

0.1 ? D ? 0.6

2.3. FL controller

This is the main subject of this paper; I will discuss it in the next sections.

2.4. DC water pump

Fig. 3 shows the relationship between flow rate of water and total dynamic head for the Kyocera SD 12-30 solar pump to be modeled. It has the normal operating voltage of 12-30 V and the maximum power of 150 W.

Fig. 3. Kyocera SD 12-30 water pump performance chart [16].

3. Maximum power point tracking algorithms

When a PV module ...