Mehdi Fazeli

A high performance controller for parallel operation of three-phase UPSs powering unbalanced and nonlinear loads

In this paper, a high performance controller for parallel operation of uninterruptible power supplies (UPS) is proposed. The proposed controller is based on synchronous reference frame that is developed for parallel UPSs. Applying master-slave algorithm in this controller, power sharing and voltage regulation are controlled centrally by master UPS and commands are send through CAN bus to slave UPS. But each UPS performs voltage harmonic compensation locally and independently. Virtual impedance technique is used to share harmonic currents perfectly. Controller also is modified for unbalanced nonlinear loads. The performance of the proposed controller has been verified with simulation results for 20KVA, 380V three-phase parallel UPS.

A novel peak and deep current mode control for two switches buck-boost converter

A simple current mode controller is proposed for two switches buck-boost converter which performs conversion with lower stresses than the single switch types. In this approach problem of interference between buck and boost switches operations are solved by determining four operation modes for the converter. The experimental results on an 110 V, 40 KW converter show the ability of the proposed control method. The line and load regulation in different situation is below than 0.9%.

Evaluation of different positive sequence detection structures applied to grid-connected systems

Effects of three different positive sequence detector structures including qPLL, EPLL, and SOGI-PLL on performance of a 10KVA shunt active filter are investigated in this paper. The evaluation is performed through simulation of practical test conditions including balanced and unbalanced grid voltage, frequency variation, and harmonic polluted grid voltage. These studies lead to recognizing the SOGI-PLL as a proper method for grid-connected power applications, especially for the ones with digital control systems.

Simple and efficient design and control of the single phase PWM rectifier for UPS applications

This paper deals with simple design and control of single-phase PWM rectifier which plays an important task in new commercial and low cost uninterruptible power supplies (UPSs). Firstly, a simple and fast single-phase phase locked loop (PLL) is proposed which is one of the main parts of control system. Besides, an efficient design of passive elements of rectifier is proposed to reduce size and cost of hardware system. In addition, due to several benefits of digital signal processors (DSPs) such as fast calculation capability, various peripherals and serial communications, a DSP-based digital controller is adopted to control the rectifier. Several simulation and experimental results are provided to verify the effectiveness of the proposed design manner and control system.

Design procedure and experimental validation of a 30kVA DSP-based PWM rectifier

Nowadays DSPs have been used widely in power electronic applications because of powerful calculation ability, several peripherals and serial interfaces. Three phase PWM rectifiers (TPPR) have been used widely since they can provide unity power factor (PF), a sinusoidal grid current and also higher DC voltage than grid voltage amplitude. Besides, current vector control is a powerful strategy to be used for three phase PWM rectifier to regulate input active and reactive powers separately. Therefore, in this paper, precise design procedure is presented firstly. Secondly, simulation and experimental evaluation of the three phase PWM rectifier is considered based on a digital signal processor (DSP)-based digital controller. An expanded simulation and experimental results are done to verify the effectiveness of complete control system. The results show the low-ripple adjustable DC voltage between 650 to 750v. Moreover, the THD value of the input current is about 2.4% which satisfy international standards such as IEEE Standard 1547.