Simulation And Control Of Transformer Less Unified Power Quality Conditioner For Power Quality Improvement Sruthi Raghunath PG Scholar, Department of EEE Karunya University, Coimbatore, India P.Venkatesh Kumar Assistant Professor, Department of EEE Karunya University, Coimbatore, India Abstract— The major issue in the power distribution system is the power quality. The increase in the proportion of sensitive equipments in production processes also increases the demand of the power quality improvement. With the extensive improvement in power electronics field, the implementation of power electronics to improve power quality provides effective solutions to power quality problems. One of the most effective solutions to power quality issues in the distribution side is the installation of Unified Power Quality Conditioner (UPQC). UPQC is supported for alleviating all the voltage and current related problems. In this paper, the conventional injection transformer is replaced with capacitor which injects voltage to the line. With the use of capacitor, the drawbacks of the injection transformer are reduced and thus are more efficient. The cross phase connected UPQC enables to overcome the problems related to single line faults also. The cross phase connection enables injection to a faulty phase from a healthy phase. The control strategy implemented is much similar to DVRs. This scheme was found beneficial and the simulation (using MATLAB/SIMULINK) results prove that the voltage and current control was found good and the harmonics in the system were also reduced. Keywords: Power Quality; UPQC; Harmonics; Voltage Source Converters (VSC) I. INTRODUCTION Power quality phenomena include all situations in which the supply voltage (voltage quality) or load current (current quality) waveforms deviate from the sinusoidal waveform at rated frequency with amplitude corresponding to peak value for all the phases for any three-phase system. In recent years, the term Power Quality (PQ) has gained significant importance, especially in electrical distribution side. As per international standards, the term power quality can be defined as the physical characteristics of the electrical supply provided under normal operating conditions that do not disrupt or disturb the user's processes. The disturbances in voltage (harmonics, sags, swells) may cause the tripping of sensitive electronic equipment which can lead to disastrous consequences in industrial plants, such as, unexpected results or a termination of the whole production line. These events are common in industrial sectors and cause high economical damage. In the above scenario, it is the source that disturbs the load/ sensitive equipment. To avoid heavy economical losses, the industrial customers often install mitigation devices/ equipments to protect their own plants from such kind of disturbances. The growing use of power electronics based equipments in modern plants is resulting in a load which is sensitive and harmonics producing in nature. Interestingly, these equipments generally produce distortion in currents and/or voltages. Thus, there is a new trend to install mitigating equipments that can serve the dual purpose, to both the utility as well as to the customer. Thus with the implementation of Custom Power Devices in the distribution side, Power Quality is enhanced. One of the most effective solutions to power quality issues in the distribution side is the installation of Unified Power Quality Conditioner (UPQC). UPQC is supported for alleviating all the voltage and current related problems (imbalances, Harmonics etc). Conventional UPQC [1] is constituted of two Voltage Source converters (VSC), an injection transformer and a common dc link. The presence of injection transformer can create problems like offset due to energisation of transformers, increased losses in transformer windings and high cost of the system. Thus there is a need for a better injecting device. A DC isolation circuit was proposed in [4]. This implementation increases the complexity of the system along with the increase in the cost of the system. Thus, here in this paper, injection transformer as well as the DC isolation circuit is replaced with a series capacitor which acts as „Voltage Injecting‟ source to the line. With the use of a series capacitor as injecting device [5], the cost and the complexity of the system is reduced and the system was found more efficient. The conventional UPQC can eliminate three phase faults alone. The system remains idle for single phase faults. The cross phase connected UPQC enables to overcome the problems related to single line faults [6]. The cross phase connection enables injection of voltage to a faulty phase from a healthy phase. The cross connection in phase is given at the load side as shown in Fig. 1. Unlike conventional UPQC, here each phase is implemented with half bridge configuration VSCs and separate DC links for each phase. This configuration provides better control of each phase keeping the cost also minimal. Control scheme of the proposed UPQC is also considered here in this paper. Various control strategies have been proposed for UPQC. Some of them are PQ theory [7], wavelet 740 International Journal of Engineering Research & Technology (IJERT) Vol. 2 Issue 11, November - 2013 ISSN: 2278-0181 www.ijert.org IJERTV2IS110192