International Journal of Science and Research (IJSR) ISSN (Online): 2319-7064 Index Copernicus Value (2013): 6.14 | Impact Factor (2014): 5.611 Volume 4 Issue 11, November 2015 www.ijsr.net Licensed Under Creative Commons Attribution CC BY Comparison of DPC methods Using Two-Level and Three-Level Rectifiers Jawad Lamterkati 1 , Mohamed Khafallah 2 , Lahcen Ouboubker 3 , Aziz Elafia 4 1, 2, 3 Hassan II University, Higher National School of Electricity and Mechanics (ENSEM), Casablanca 8118, Morocco 4 Hassan II University, Higher National School of Arts and trades (ENSAM), Casablanca, Morocco Abstract: This paper contains the evaluation and comparison between DPC methods for two-level (2-L) and three-level (3-L) AC/DC converters, in order to demonstrate de great advantages of using a three level rectifier type NPC. The theoretical principal of this methods as well as the synthesis of the active and reactive power are discussed. The regulation of DC-bus voltage is achieved using PI controller. The effectiveness of this approach is shown by simulation results using Power System Bloc set (PSB) of Matlab/Simulink. Keywords: Direct Power Control, two-level rectifier, three-level rectifier, instantaneous active and reactive power, switching table, corrector PI. 1. Introduction In recent years, the trend of positively using PWM rectifier, as the dc power supplies for voltage-source inverters has been increasing [1,3]. The voltage-source PWM rectifier- inverter has the following advantages: harmonics in input- output waveforms are fewer, input power factor can be controlled to be unity, generation is possible and the capacity of dc capacitor can be reduced etc.., the PWM rectifiers have more and more application such as active power filter (APF), unified power flow control (UPFC) and so on [1,2]. In the recent years, the research interest in three-phase PWM rectifiers is mainly influenced by the update of the control technology with the aim to: [3] 1) Ensure that the ac terminal current THD is less than 5% of the total fluctuation load to reduce the adverse effect on the grid. 2) Guarantee the power factor close to one and regard the rectifier as a „pure resistive load‟ in terms of the grid; 3) Improve the dynamic characteristic for dc-bus voltage regulation, and reduce the dynamic response time, etc. [4, 5]. The high-performance control strategies of PWM rectifiers are mainly the voltage oriented control (VOC) [6] and direct power control (DPC) [7], which are similar to the vector control (VC) and direct torque control (DTC) [8] for AC machines. The VOC control scheme guarantees high dynamic and static performance via internal current control loops. However, the final configuration and performance of the VOC system largely depends on the quality of the applied current control strategy. With DPC there are not internal current control loops and no PWM modulator bloc, because the converter switching states are selected by a switching table based on the instantaneous errors between the commanded and estimated values of the active and reactive power, and voltage position vector. Therefore, the key point of the DPC implementation is a correct and fast estimation of the active and the reactive line power. On the other hand, multi-level inverters have become a very attractive solution for high power application areas [9-10]. The three-level Neutral Point Clamped (NPC) inverter is one of the most commonly used multi-level inverter topologies in high power ac drives. By comparing to the standard two- level inverter, the three-level inverter presents its superiority in terms of lower stress across the semiconductors, lower voltage distortion, less harmonic content and lower switching frequency [11]. The three level inverters present a big interest in the field of the high voltages and the high powers of the fact that they introduce less distortion and weak losses with relatively low switching frequency [12]. This paper presents a brief description and comparison of DPC methods of vector control using two and three-level AC/DC converters, and to demonstrate the great advantages of using three level converters type NPC. The regulation dc-bus output is realized by corrector PI. 2. DPC with Two Level Rectifier DPC block for PWM converter essentially comprises of active and reactive power comparators, power estimators and switching pattern generator. The DPC application in PWM converter is analogous to direct torque control (DTC) in inverter fed three-phase motor drives. Initially, DTC and DPC strategies had been implemented with look-up table based switching pattern generator. 2.1 The principle and modeling of the two level rectifier The topology of three phase bidirectional voltage-source PWM rectifier (VSR) is shown in fig. 1. The VSR is connected to the three phase as source via smoothing L and internal resistance R. The inductance act as a line filter for smoothing the line currents with minimum ripples. Insulated gate bipolar transistors (IGBTs) are used as the VSR power switches since IGBTs have features of high power rating, simple gate drives requirement and suitable for high frequency switching applications. It is assumed that a pure resistive load R L is connected at the dc-link capacitor C. [13] By assuming a balance three-phase and three wires system, the voltage equations of the PWM rectifier can be described by equation (1)-(3). Paper ID: SUB159140 336