【Practical Exercise】Simulation of Photovoltaic Solar Panels Based on MATLAB Simulink (Circuit)

## 2.1 The Physical Principle of Photovoltaic Solar Panels

### 2.1.1 The Photovoltaic Effect and PN Junction

The photovoltaic effect refers to the phenomenon in certain semiconductor materials where photons with energy greater than the material's bandgap are absorbed, producing electron-hole pairs. Electrons and holes move in opposite directions under the influence of an electric field, generating a photoelectric current.

The PN junction is the boundary between two differently doped regions (P-type and N-type) within semiconductor materials. In the depletion zone of the PN junction, carrier concentration is low, creating a potential barrier that prevents current flow.

### 2.1.2 Current-Voltage Characteristic Curve

The current-voltage (I-V) characteristic curve of photovoltaic solar panels describes the current output at various voltages. A typical I-V curve has the following features:

***Open-circuit Voltage (Voc):** The maximum voltage generated by the panel under open-circuit conditions.
***Short-circuit Current (Isc):** The maximum current generated by the panel under short-circuit conditions.
***Maximum Power Point (MPP):** The point at which the panel outputs the most power, located above the I-V curve.
***Fill Factor (FF):** Measures the ratio of the area between the I-V curve and an ideal rectangle, indicating the panel's efficiency.

# 2 Photovoltaic Solar Panel Modeling Fundamentals

### 2.1 The Physical Principle of Photovoltaic Solar Panels

#### 2.1.1 The Photovoltaic Effect and PN Junction

The photovoltaic effect occurs in semiconductor materials when photons are absorbed, causing electrons to jump from the valence band to the conduction band, producing free electrons and holes. This effect is particularly pronounced in PN junctions, which are formed by connecting P-type and N-type semiconductors.

In P-type semiconductors, doping with trivalent elements such as boron results in a higher concentration of holes and a lower concentration of electrons. In N-type semiconductors, doping with pentavalent elements such as phosphorus results in a higher concentration of electrons and a lower concentration of holes.

When P-type and N-type semiconductors are connected, a depletion layer forms at their junction, devoid of free charge carriers. When photons hit the PN junction, they are absorbed by the semiconductor material, producing free electrons and holes. These free electrons and holes, under the influence of the electric field in the depletion layer, diffuse towards the N-type and P-type semiconductors, respectively, creating a photoelectric current.

#### 2.1.2 Current-Voltage Characteristic Curve

The current-voltage (I-V) characteristic curve of photovoltaic solar panels describes the output current at various voltages. The I-V characteristic curve is typically nonlinear and has a maximum power point (MPP).

The MPP is the point at which the panel outputs the most power under specific operating conditions. Before the MPP, as voltage increases, so does current, and output power increases. After the MPP, as voltage continues to increase, current decreases, and output power also decreases.

### 2.2 Modeling Photovoltaic Solar Panels in MATLAB Simulink

#### 2.2.1 Current Source Model

The current source model is a simplified photovoltaic solar panel model that treats the panel as an ideal current source in parallel with a diode. The output current of the current source is proportional to the intensity of light and inversely proportional to the panel's temperature.

% Current source model
I_ph = 10; % Photocurrent (in amperes)
R_sh = 100; % Shunt resistor (in ohms)
R_s = 0.1; % Series resistor (in ohms)
V_d = 0.7; % Diode forward voltage drop (in volts)
n = 1; % Diode ideality factor

% Current-voltage characteristic curve
V = linspace(0, 10, 100); % Voltage range (in volts)
I = I_ph - (V + R_s * I) / R_sh - (V - V_d) / (n * R_s);

% Plot I-V characteristic curve
plot(V, I);
xlabel('Voltage (V)');
ylabel('Current (A)');
title('Photovoltaic Solar Panel Current Source Model I-V Characteristic Curve');

**Logical Analysis:**

The code implements the current source model of a photovoltaic solar panel. The photocurrent (`I_ph`) is proportional to the intensity of light, and the shunt resistor (`R_sh`) and series resistor (`R_s`) are used to simulate the panel's internal losses. The diode forward voltage drop (`V_d`) and ideality factor (`n`) are used to simulate the nonlinear behavior of the diode.

The `I-V` characteristic curve is obtained by calculating the output current at various voltages. The curve shows the panel's output power at different voltages and can determine the panel's maximum power point (MPP).

#### 2.2.2 Diode Model

The diode model is a more accurate photovoltaic solar panel model that considers the panel's nonlinear characteristics. The diode model treats the panel as an ideal diode in parallel with a resistor.

% Diode model
I