Читать книгу Smart Grids and Micro-Grids - Umashankar Subramaniam - Страница 44

A MATLAB-Simulink model of the converter system shown in Figure 2.2 is developed with the specification listed in Table 2.3. The controller shown in Figure 2.3 for control of the bidirectional converter is also implemented in the Simulink platform. The components of the dc-dc converter are selected based using relations [12, 13].

(2.14)

(2.15)

(2.16)

Where V_B, I_B are battery voltage and battery current, respectively while ΔV_B, ΔI_B are the ripple in the battery. f_sw, V_dc are switching frequency and microgrid dc voltage, respectively. The commands “Batt – charge, V_dc–ctrl ” along with the power to be exchanged (I_{B(disc, ref)}, I_{B(cha, ref)}) with microgird are sent to the controller from the EMS of microgrid. The feedback signals inductor current (i_L), dc microgrid voltage (V_dc) are also input to the controller.

Table 2.3 Specifications of the boost converter interfacing dc microgrid and battery.

Parameter	Value
Nominal voltage (VB)	240 V
Rated capacity	35 Ah
Initial SOC	60%
Inductance (L) ESR (rL) of inductor	2.6 mH 0.005Ω
Output capacitor (C0)	2200 µF
DC load	400 Ω
DC microgrid voltage	400 V

Figure 2.5 shows the results for the case when V_dc–ctrl = 0, i.e., ESS should be charging or discharging depending on the status of the Batt – charge command. Initially, command V _dc–ctrl = 1, and the battery discharging current reference is set to 35 A. After 5 sec, the discharging current reference is changed to 17.5 A. After 10 sec, command Batt – charge = 1 and the reference of charging current is kept at 35 A, which was subsequently changed to 17.5 A at 15 sec. The controller was able to track the reference current, as evident from the waveform of Figure 2.5. It is also clear from the figure that the SOC was decreasing when the battery was discharging, while SOC was increasing for the case when the battery was discharging. A similar observation can be made about the battery voltage.

For the case, when it is required to maintain the dc voltage level of microgrid, the command V_dc–ctrl = 1 is received from the microgrid. The reference for dc microgrid voltage is set to 400V. To show the performance of controller under such condition, initially V_dc–ctrl = 0, Batt – charge = 0 and the battery discharging current reference (I_{B(disc, ref)} was set to 35 A. At t=5 sec, the V_dc–ctrl = 1 was sent to the controller. Figure 2.6 shows the performance of the controller. It shows that the converter was able to track the reference voltage.