CONTROL SCHEMES OF UTILITY INTERACTIVE MULTIFUNCTIONAL DISPERSED GENERATION Il-Yop Chung, Sung-Woo Park, Joon-Ho Choi, Seung-Il Moon, and Jae-Eon Kim School of Electrical Engineering & Computer Science #013 Seoul National University Shinlim-dong, Kwanak-gu, Seoul, 151-742, Korea iryop@powerlab.snu.ac.kr Abstract: In this paper, control schemes of utility interactive Multifunctional Dispersed Generation (MDG) are proposed to improve the power quality and the continuity of the electric power supply. The proposed MDG is designed to compensate the power quality event, for example, voltage sag and harmonic distortion, and to supply electric power in parallel operation with power gird. It is also designed to serve a local load for improving the power quality and the continuity of the electric power supply when it is isolated from the power gird. To cope well with this, the instantaneous power theory is used to control the series and shunt DC/AC inverter of the MDG. A numerical formulation of the proposed control scheme is presented. Case study shows the effectiveness and flexibility of the proposed control schemes of the proposed MDG configuration for the multifunctional purpose. Copyright © 2002 IFAC Keywords: Custom Power, Dispersed Generation (DG), Distribution System, Instantaneous Power Theory, Power Quality, and PWM Inverter. 1. INTRODUCTION Recently, there are two important issues in the power distribution system: power quality and power system deregulation. Power quality means the ability to keep voltage and current near to constant sinusoidal waveform lest customer equipments should fail or operate incorrectly. Sag, interruption and harmonics are the representative power quality problems. There are many researches about solutions of power quality. Specially, custom power devices including power electronic interface can be the effective solution because they can provide fast response and flexible compensation required by customers. Custom power devices have various types of structure depending on their inverter connection to the grid, that is, series-connected device, shunt- connected device, and series-and-shunt-connected device. The last device is usually called Unified Power Quality Conditioner (UPQC) and it has almost all remedies about power quality problem including voltage quality and current quality. Although there have been several control schemes of UPQC, the instantaneous power theory is the most effective scheme (Akagi, et al., 1984; Aredes, et al., 1998; Li, et al., 2000). However, UPQC cannot supply large active power to customers steadily due to the limitation of power storage. On the other hand, the opening of the energy market under deregulation brings about the interest in Dispersed Generation (DG) because it can provide independence and flexibility to the customer in planning and developing the installation and can give economic benefits in many cases (Joos, et al., 2000). The most fundamental function of DG is to maintain the reliability of electricity supply even though utility cannot supply sufficient power due to faults or other conditions. This function has several sub-operating rules about sharing active power with grid during paralleling mode, maintaining load voltage constantly and controlling frequency during the islanding operating mode (Barsali, et al., 2002). However, DG has the negative effects and the positive effects to the existing power system. The employment of DG in the existing power system can cause several potential operation problems, i.e. negative effects of DG, such as voltage variation (Choi, et al., 2001a), protection, and harmonics (Choi, et al., 2001b). The recent trend of DG is to use power electronic inverter in order to interface various types of DGs like micro-gas turbines, fuel cells, and wind power stations (Lasseter, et al., 2001). Shunt connected inverter interface is mostly used because it is insensitive to the grid parameter variation and easy to share active power with the utilities (Marei, et al., 2002). In addition, the recent DG needs to have multiple functions to solve various problems such as reliability and power quality. This paper proposes Multifunctional Dispersed Generation (MDG) that has not only shunt inverter but also series inverter. Therefore MDG can inject both voltage and current to the grid more freely than other dispersed generations that have only one inverter connection. Furthermore, MDG can control both the power quality and quantity during paralleling mode and islanding mode. Moreover, in this paper, the novel control scheme of MDG is represented for the purpose of paralleling