*4.2. WDIM Simulation Graphics*

The simulation graphics show the main WDIM electrical variables: the frequency per unit (fpu) in Figure 7, the RMS voltage per unit in Figure 8 and the active powers of the DG, WTG, DL and consumer load in Figure 9. Figure 9 shows the active powers produced and consumed with positive and negative values, respectively, so the consumer load and DL plots are always below the 0 kW line. At the beginning of the simulation, the WDIM is in steady state, the DG and WTG produce 108 and 92 kW (for a wind speed of 8 m/s), respectively and the load and DL consume 200 and 0 kW, respectively.

**Figure 7.** WDIM frequency pu.

**Figure 9.** Generated (+)/consumed (-) active powers in the WDIM components.

The wind speed increases at *t* = 0.2 s by 1 m/s to a 9 m/s final value. Figure 9 shows an increasing WTG power from the initial 92 kW to the final 143 KW. The DG consequently decreases its power, and the final DG-produced power is 57 kW. The fpu graph first increases due to the active power excess (1.0059 maximum) and then undershoots (0.9987 minimum), and the voltage pu minimum and maximum are 0.9885 and 1.0039, respectively. The DL is not actuated, and its power is 0 as the DG power remains above 12 kW during the whole 0.2–8 s time interval.

By opening the circuit breaker of Figure 6 at *t* = 8 s, the 90 kW extra load is disconnected, so the consumer load changes to 110 kW, a value below the 143 kW WTG power. The DG reacts by reducing its power, and when its value is below 12 kW, the DL integral control starts ordering power consumption to the DL to prevent the DG reverse power. While the DL increases its consumed power to fit the DG active power in the 12–18 kW interval, both the DG and WTG active powers present oscillations. The initial excess of active power makes the fpu increase (1.0089 maximum), and then the fpu undershoots (0.9991 minimum). The voltage pu minimum and maximum are 0.9873 and 1.0081, respectively. The wind

speed remains constant, so the final WTG power is the initial one at *t* = 8 s. In steady state, the DG produces 16.5 kW (a value in the 12–18 range), and the DL consumes 49.5 kW (the DG minimum load plus the WTG active power excess).

At *t* = 16 s, a negative wind speed step of −2 m/s is applied. The WTG power decreases to 50 KW final value. The DG reacts and increases its power over 18 kW so that the DL decreases its consumed power commanded by its integral control. The DL power reaches and stays at zero as the DG power remains greater than 18 KW. The initial lack of active power makes the fpu decrease (0.9937 minimum), and then it overshoots (1.0012 maximum). The voltage pu minimum and maximum are 0.9875 and 1.0126, respectively. The final active powers for the DG, WTG and DL are 60, 50 and 0 kW, respectively.
