Читать книгу Smart Solar PV Inverters with Advanced Grid Support Functionalities - Rajiv K. Varma - Страница 19

1  Exchange of Active Power: The influence of active power exchange on voltage regulation is discussed in this section. A simple power system is considered with a solar PV system connected at the PCC as illustrated in Figure 1.5. The system has an equivalent source voltage E, whereas V is the voltage at PCC. The network has equivalent reactance and resistance X and R, respectively. The current I injected by the PV system is considered to be purely resistive IR, i.e., at unity power factor. Impact of this active current injection on systems with different X/R ratios is now investigated. Figure 1.6a,b depicts the phasor diagram for systems with X/R = 3, and 1/3, respectively. Active power injection is seen to increase the voltage in both cases. However, the rise in voltage is more in the network having X/R = 1/3 than in network having X/R = 3. This implies that active power injection will result in a greater voltage rise in primarily resistive networks. Similarly, active power absorption, as in energy storage systems, will be more effective in decreasing the voltage in resistive networks.

2 Exchange of Active and Reactive Power: In this case, the solar PV system is considered to perform both active power injection and reactive power exchange. A simple explanation of the impact of active and reactive power is described here. The complex current injected by the solar PV system is denoted by I, and the complex power injected by the solar PV system is expressed by P + jQ. Assuming the open‐circuit voltage E remains constant, the change in PCC voltage due to this current injection is given by:(1.1) (1.2) since V is chosen to be the reference phasor with angle = 0.Substituting Eq. (1.2) in Eq. (1.1), the change in voltage is obtained as(1.3) (1.4) It is noted that Q can be either inductive or capacitive. Also, P can be either positive, if injected as in case of PV system, or negative if absorbed by an Energy Storage System.Figure 1.5 A simple power system with a PV solar system connected at PCC.Equation (1.4) demonstrates that the PCC voltage is influenced by both active and reactive power exchange from the DER [7]. The magnitude of voltage change is dependent on the system short circuit impedance and its X/R ratio.