Harmonic and Balance Compensation using Instantaneous Active and Reactive Power Control on Electric Railway Systems A. Bueno, J. M. Aller and J. Restrepo Grupo de Sistemas Industriales de Electrónica de Potencia Universidad Simón Bolívar Caracas 1080A, Venezuela T. Habetler School of Electrical and Computer Engineering Georgia Institute of Tecnology Atlanta, Georgia Abstract—This work presents a general filtering and unbalance compensation scheme for electric traction systems. The proposed method uses an active filter controlled with the instantaneous active and reactive power, to reduce the harmonic current distortion and the negative sequence obtained by the system under unbalanced operation in steady state. The proposed filter is evaluated using open delta (V-V) and Scott transformers in the power substation. The scheme has been simulated and experimentally validated. Experimental and simulation results show the controller advantages and the applicability of the proposed method in railway systems . Index Terms—Harmonics, Active filter, Transformer, Locomo- tive, Traction application. I. I NTRODUCTION Electric traction systems for passengers and goods use different power transformer configurations, in order to feed single phase systems from the three phase supply. In gen- eral, three-phase to two single phase conversion schemes use transformers connected in open delta (V − V ), Scott or Le Blanc configurations [1]. In a practical application, the load associated with each single-phase circuit does not compensate each other, due to the variable demands in the transport system and railroad line profile. Also, the use of uncontrolled rectification to feed the traction load contribute to the total unbalance seen from the three phase supply. This unbalance is due mainly to the injection of current harmonics to the main three-phase system depending on the transformer connection and harmonic order [2]. It is then required the use of filters and unbalance com- pensators to ensure proper system operation and to raise the power quality [3]. These problems are usually addressed, in practice, with the use of passive power quality compensators such as reactive power compensation capacitors and passive filters, and they are single-phase equipment installed in each feeder of the traction substation. Usually, the coupling factor between two feeders is negligible due to the independent operation of each passive compensator. Moreover, passive equipment does not have the dynamic capability to adjust to changes in load, where over and under compensation happen frequently as a result of continuous change in load conditions. Different active power quality compensators have been proposed in [4]–[6] to solve the unbalance problem. All of them employ two single-phase converters that have a common DC bus and the simultaneous compensation of harmonic content and unbalance can not be achieved with these schemes. Also, when the compensation is made from the single phase side, the instantaneous active and reactive power definition is difficult to use in the compensation of harmonics and power unbalance [7] [8]. In this work a compensation scheme is proposed to pro- vide simultaneous correction of harmonic content and load unbalance for railroad systems using open delta or Scott transformers in the power substation. This scheme is based on the instantaneous active and reactive power description of the system [9], using space vector representation of the state variables, and the application of direct power control (DPC) to attain the required correction by minimizing a cost function obtained from the instantaneous active and reactive mismatch [10]–[12]. The control strategies presented in this work are both, simulated using a state variables model representation and experimentally validated using a DSP based modular power electronic system able to emulate the electric traction system operating conditions, the open delta, the Scott transformer, the filtering and the load balancing converters [13]. The generality of the proposed filtering technique using instantaneous active and reactive power can be extended to any other transformer configuration in the power substation. Multilevel converter technology can facilitate the industrial implementation because reduces the specifications of the power electronics switches and the voltage stress ( dv dt ) on the magnetic components like coupling transformers and/or inductors [14]. II. HARMONIC AND UNBALANCE COMPENSATION SYSTEM Figure 1 shows the proposed control scheme. A shunt active filter is used, directly connected to the power system using a voltage rising transformer. The active filter uses a power converter configured as an active three-phase PWM rectifier, connected to the three-phase side. 978-1-4244-4783-1/10/$25.00 ©2010 IEEE 1139