**5. Simulation Results**

In order to verify the feasibility of the PMS and the reliability of the proposed control strategies under communication problems, the simulations based on the PSIM are conducted. Table 2 lists the system parameters used for simulations. The detailed mathematical models of three converters used for the grid agent, WPGS agent, and battery agen<sup>t</sup> can be found in [30–32]. Simulation results are presented in three cases which are the grid-connected case, the islanded case, and the case of communication problems.




**Table 2.** *Cont.*

## *5.1. Grid-connected Case*

In the grid-connected case, the grid agen<sup>t</sup> primarily controls the DCV to maintain the system power balance under variations of wind power and load demand. Table 3 lists the operation conditions used for the simulation tests.


**Table 3.** Operation conditions for simulation test in grid-connected mode.

Figure 10 shows the simulation results for the grid-connected mode with the operation conditions given in Table 3. It is assumed that the load 1 and load 2 are initially connected to the DC-link, consuming the power of 1.5 kW. Although the WPGS works with the MPPT mode, the output power of the WPGS is not sufficient to supply the load. To deal with this power imbalance, the grid agen<sup>t</sup> operates with DCVM-REC to compensate the deficit power by supplying more power from the grid to the DC-link. In this instant, the DCV is controlled to the nominal value of 400 V by the grid agen<sup>t</sup> and the battery agen<sup>t</sup> is in IDLE mode.

**Figure 10.** Simulation results for grid-connected mode. (**a**) *a*-phase grid voltage and current; (**b**) Output power of each agent; (**c**) Battery *SOC*; (**d**) DCV.

At t = 1 s, the load 3 is switched in, which results in an increase of total load demand. To ensure the system power balance, the grid agen<sup>t</sup> further increases the supplied power from the grid to the DC-link. However, since the supplied power is limited by the maximum power of 2 kW, the grid agen<sup>t</sup> switches the operation into CPCM, and sends the data (*Gctrl* = 0) to other agents. As soon as receiving the data, the battery agen<sup>t</sup> switches its operation from IDLE to DCVM-DIS to maintain the system power balance by regulating the DCV.

From t = 1.5 s, as the wind power gradually decreases from 0.5 kW to zero, the battery agen<sup>t</sup> gradually increases the discharging power to compensate for the change of wind power as can be seen in Figure 10b.

At t = 2 s, the wind power suddenly changes from zero to 2 kW. Although the wind power is still lower than the load demand of 3.5 kW, the grid agen<sup>t</sup> can control the DCV with DCVM-REC since the supply power of 1.5 kW from the grid to DC-link is within the maximum power level. As a result, the battery agen<sup>t</sup> moves to IDLE mode after receiving the data (*Gctrl* = 1) from the grid agent.

At t = 2.5 s, the wind power is further increased to 4 kW, which is higher than load demand. Then, the grid agen<sup>t</sup> switches the operation DCVM-REC into DCVM-INV to transfer the surplus power from the DCMG to the grid.

When the load 2 and load 3 are switched out at t = 3 s, the grid agen<sup>t</sup> tries to inject more power to the grid to maintain the supply–demand power balance. However, since the exchange power exceeds the maximum level assigned by GO, the grid agen<sup>t</sup> can transfer only a portion of surplus power to the grid by CPCM, transmitting the data (*Gctrl* = 0) to other agents in DCMG. After receiving the data via communication, the battery agen<sup>t</sup> switches the operation into DCVM-CHA to absorb the remaining surplus power.

At t = 3.5 s, when the battery agen<sup>t</sup> is incapable of regulating the DCV due to battery fault, the battery agen<sup>t</sup> changes the operation into IDLE mode, and transmits the data (*Bctrl* = 0) to other agents. Because both the grid and battery agents cannot control the DCV in this instant, the WPGS agen<sup>t</sup> intervenes with DCVM-LIM to maintain the output power of WPGS to load power. It is shown in Figure 10d that the DCV can be always regulated stably at the nominal value in all the operating conditions regardless of the conditions of the battery, wind power, and load demand.
