Dynamic Voltage Regulation Using Distributed Energy Resources

Many distributed energy (DE) resources are near load centers and equipped with power electronics converters to interface with the grid, therefore it is feasible for DE to provide ancillary services such as voltage regulation, nonactive power compensation, and power factor correction. A synchronous condenser and a microturbine with an inverter interface are implemented in parallel in a distribution system to regulate the local voltage. Voltage control schemes of the inverter and the synchronous condenser are developed. The experimental results show that both the inverter and the synchronous condenser can regulate the local voltage instantaneously, while the dynamic response of the inverter is faster than the synchronous condenser. Also, integrated voltage regulation (multiple DE perform voltage regulation) can increase the voltage regulation capability and reduce the capital and operation costs. INTRODUCTION There are a wide range of ancillary services in the distribution level that can be supplied by distributed energy (DE) resources [1], among which voltage regulation has drawn much interest because of the nonactive power shortage in power systems. Previously, others have reported that the power electronics interface between the DE and the utility can provide several nonactive power services [2]-[3]. The installation of DE and the provision of voltage regulation from DE can have a beneficial impact on transmission stability by supplying nonactive power at the distribution level [4]. The total installed DE capacity for installations smaller than 5 MW in the U.S. is 195,251 MW, among which the nonactive-power-capable DE is estimated at 10% of the total installations [5]. Therefore, there is a large amount of DE resources potentially available for voltage regulation. SYSTEM CONFIGURATION A parallel-connected DE with power electronics inverter interface is shown in Fig. 1. The interface, including the inverter, the DC side capacitor vdc, and the coupling inductor Lc, is referred to as the compensator because voltage regulation from DE is the main topic in this paper. The compensator is connected in parallel with the utility at the point of common coupling (PCC) vt. By generating or consuming nonactive power, the compensator regulates the PCC voltage vt. The compensator current ic only contains the nonactive power component. The system configuration of a parallel-connected synchronous condenser is shown in Fig. 2. The synchronous condenser generates nonactive power at over-excitation, and consumes nonactive power at under-excitation. By controlling the excitation voltage vexcitation, the synchronous condenser regulates the voltage vsystem by changing the nonactive power it provides or consumes. The synchronous condenser current isc only contains the nonactive power component. Two system configurations of the compensator and the synchronous condenser are studied in this paper, which are shown in Figs. 3 and 4. In Fig. 3, the two devices are connected on two different circuits from a 2.4 kV substation. The synchronous condenser is connected to the 480 V Panel A with some other loads through transformer 1, C I R E D 19th International Conference on Electricity Distribution Vienna, 21-24 May 2007