*5.2. Case 2: Proposed Controllers Performance Analysis in Grid-Tied AC MG Application*

It was essential to analyze the performance of the proposed PVMT-based FLDPC in grid-tied AC-MGs, to ensure that the controller was performing well in MG's different operating modes. In addition, the controller should be capable of operating in different real-world conditions such as varying load, and solar irradiation in MG. To verify these features in this section, the performance of the proposed PVMT-based FLDPC method was validated by varying both solar irradiation and load demand. Finally, a comparison is presented at the end of this section, to prove the superiority of the proposed FLDPC method over conventional MG power control methods for grid-tied VSIs. The results obtained after implementing the proposed controller for active power flow between different sources and loads are depicted in Figure 14 and Table 2. To regulate the power flow between different sources and load, a power management algorithm was adopted from [17].

**Figure 14.** Active power flow from different power sources to loads.

The initial values of solar irradiation and varying load were set to 1000 W/m<sup>2</sup> and 0.14 MW (critical 0.02 MW + non-critical 0.12 MW, respectively). In between 0 and 2 s, PV was generating full power of 0.1 MW, which fulfilled 0.1 MW of the total load, and the remaining 0.04 MW demand was supplied by grid. At this period, the power from battery and diesel generator were nil. The solar irradiation was dropped to 850 W/m<sup>2</sup> between 2 and 4 s and, in contrast, load demand was increased to 0.15 MW. During this

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period, PV provided a maximum of 0.078 MW power support to the load. Since PV power went down from the nominal value, the battery came into operation. In this case, the battery and grid supplied 0.025 MW and 0.047 MW power to fulfil the rest of the load demand. From 4 to 6 s, solar irradiation and load demand reduced to 700 W/m<sup>2</sup> and 0.115 MW, respectively. This situation compelled the grid to supply power of 0.024 MW to the load, since PV (0.066 MW) and battery (0.025 MW) together can support a maximum of 0.091 MW power. During 6–8 s, load demand decreased (0.089 MW) and solar irradiation increased (1000 W/m<sup>2</sup> ). Since the total load demand (0.089 MW) was less than the PV generation (0.1 MW), the remaining power (0.011 MW) from MG was delivered towards grid, and power from battery became zero. At 8 s, solar irradiation level reached 800 W/m<sup>2</sup> and the PV system generated a power of 0.074 MW. During 8–10 s, the load demand was 0.068 MW, which was supplied by the PV system fully, and remaining power (0.006 MW) of MG was supplied to the grid. For this period, power obtained from battery was nil and from 0 to 10 s, since MG was operating in grid-tied mode; therefore, the diesel generator did not provide any power support. The MG started operating in islanded mode at 10 s when the grid disconnected from the MG. During islanding, according to the power management algorithm, if PV and battery cannot fulfill the load demand, then the diesel generator will be activated. From 10 to 12 s, the generation of the PV system was 0.085 MW while the load demand was higher than the PV generation, i.e., 0.097 MW. As the battery had enough power (0.012 MW) to fulfil the remaining load demand, the diesel generator remained inactive during this duration. After 12 s, solar irradiation was reduced to 800 W/m<sup>2</sup> and load demand increased to 0.13 MW. During 12–14 s, the total generation (0.096 MW) from solar and battery (0.071 MW + 0.025 MW) was not sufficient to support the load demand. As a result, diesel generation turned on and supplied 0.034 MW power to fulfil the remaining load demand. Lastly, between 14 and 16 s, the PV generation further reduced to 0.056 MW. However, load demand did not reduce much (0.122 MW), which compelled the diesel generator to continue the power supply as PV, and the battery could not fulfill the total load demand.


**Table 2.** Summary of active power flow from different power sources to loads.

In Figures 15 and 16, the output power, current and voltages of PV and battery VSIs are presented. Figure 15a shows that through the PV-VSI, the amount of delivered power was almost same as the power supplied by the PV with low ripple. In addition, the PV-VSI output current also had less distortion, as shown in Figure 15b, because the PVMT-based

FLDPC was implemented to control the PV-VSI. Similarly, from Figure 15c, it can be observed that the PV-VSI output voltage also had a pure sine wave shape, and negligible ripple. On the other hand, due to the use of PLL-integrated CCS-based controller battery VSI output power, current and voltage had high steady-state oscillations and distortions, which are presented in Figure 16a–c, respectively.

**Figure 15.** AC MG's PV-VSI output (**a**) power, (**b**) current and (**c**) voltage during solar irradiation and load changes.

The THD of PV and battery VSIs' output currents and voltages are depicted in Figure 17a–c, respectively. From the figures, it can be seen that the THD of PV-VSI output current was only 1.585%, whereas battery VSI output current THD was 4.718%, which was higher compared with PV-VSI current THD. In the case of voltages, battery VSI output voltage THD (2.592%) was higher than the PV-VSI output voltage THD (1.44%). The THDs were measured by considering three cycles (5.95–6 s) of current and voltage waveforms, as shown in the zoomed portion of Figure 15b,c and Figure 16b,c. Finally, in Figure 18a–c, grid power, current and voltage are presented, respectively. From the figures, it is clear that the power delivered or absorbed by the grid was according to the MG's requirement, and there were negligible ripples observed in the power. Furthermore, the shape of grid current and voltage were sinusoidal, which maintained 60 Hz frequency and had no distortions.

**Figure 16.** AC-MG's battery VSI output (**a**) power, (**b**) current and (**c**) voltage during solar irradiation and load changes.

(**c**)

**Figure 17.** THD of (**a**) PV-VSI output current and (**b**) battery VSI output current and (**c**) PV and battery VSIs output voltage.

**Figure 18.** Grid (**a**) power, (**b**) current and (**c**) voltage during solar irradiation and load changes.
