*4.1. MPPT-Based Techniques*

#### 4.1.1. Conventional MPPT

### 1. Modified Perturb and Observe (P&O) technique

The conventional P&O MPPT method has limitations during partial shading; hence, overcoming this limitation is required to track the global peak. Figure 7 depicts the flow chart of a modified P&O proposed by [109], where two routines are used. The first routine is the main program and sets a reference voltage close to the open circuit voltage. The main routine scans almost 80% of the P–V curve not to miss the potential global peak. The second is the global peak-tracking routine, which is called into action after executing the main program. Although the proposed method efficiently tracks the international peak, the tracking speed is compromised since the algorithm scans almost the entire P–V curve. Another modified P&O, by comparing two instantaneous power values presented in Equation (8), is proposed in [110].

$$\frac{P\_m(t) - P\_{ref}(t)}{P\_m(t-1)} < \varepsilon \tag{8}$$

where

*Pm*(*t*) is the instantaneous measured power and *Pref*(*t*) is the instantaneous reference maximum power.

The algorithm efficiently tracks the global peak; however, new coefficients are introduced that complicate the overall MPPT process. The authors in [111] proposed another modified P&O MPPT method by periodically changing the PV array voltage from maximum to minimum. A microcontroller is used to store the operating voltage and current. The P&O is used to maintain the operation of the PV system after identifying the region of the global peak.

#### 2. Modified Incremental Conductance (IC)

The conventional incremental conductance fails to track and recognize the true MPP as the method is based on derivative characteristics. In both global and local peaks, the derivatives dP/dV or dP/dI are zero; hence, the IC method should be modified to identify the true MPP. A two-stage IC method similar to the modified P&O is proposed in [112], wherein in the first stage, the value of the maximum voltage and current are used to force the PV system to operate close to the global peak. Equation (9) describes the first stage as:

$$R\_{MP} = k \frac{V\_{MP}}{I\_{MP}} \tag{9}$$

where

*k* is the correction factor, and

*VMP* and *IMP* are approximately 80% of *VOC* and 90% of *ISC*, respectively.

*VOC* and *ISC* are the open circuit voltage and short circuit current, respectively.

The second stage moves the operating point toward the global peak. A linear function to track the global peak is presented in [113] and is expressed as:

$$V\* = \frac{V\_{grid}}{I\_{out}} I(k) \tag{10}$$

where

*Vgrid* is the output grid voltage and *Iout* is the output grid current.

**Figure 7.** Modified P&O.

Equations (11) and (12) are used to detect the occurrence of partial shading and activation of the linear function.

$$V(k) - V(k-1) < V\_{thr} \tag{11}$$

$$\frac{I(k) - I(k-1)}{I(k-1)} < I\_{thr} \tag{12}$$

Although the proposed technique efficiently tracks the global peak, it can be applied only for grid-connected PV systems.

#### 3. Modified Hill Climbing (HC)

Like the other conventional methods, the hill climbing method also fails to track the global peak. Several authors proposed a modified HC method to track the maximum available power under partial shading. A modified HC method based on sweeping the duty cycle is presented in [114]. Equation (13) is used to determine the initial value of the duty cycle as:

$$D = 1 - \sqrt{\frac{R\_{MP}}{R\_{Load}}}\tag{13}$$

where *RLoad* is estimated using the rating of the PV array.

Similar to the modified IC, this method must also scan over 80% of the P–V curve. A multiple-input boost converter for micro-inverters based on modified HC is discussed in [115].
