Mahmoud A. Sayed

All Nodes Voltage Regulation and Line Loss Minimization in Loop Distribution Systems Using UPFC

Voltage regulation and line loss minimization in distribution networks are challenging problems, particularly when it is not economic to upgrade the entire feeder system. This paper presents a new method for achieving line loss minimization and all nodes voltage regulation in the loop distribution systems, simultaneously, by using unified power flow controller (UPFC), one of the most important FACTS devices. First, the line loss minimum conditions in the loop system are presented. Then, load voltage regulation is applied under line loss minimum conditions. Reference voltage of the controlled node is determined based on the assumption that this voltage can subsequently improve all node voltages to be within the permissible range. Also, the proposed control scheme of the UPFC series converter, to regulate all node voltages under line loss minimization, is presented. The effectiveness of the proposed control scheme has been experimentally verified.

Line Loss Minimization in Isolated Substations and Multiple Loop Distribution Systems Using the UPFC

This paper presents the line loss minimum condition in isolated substations and same substation multiple loop distribution systems by using the unified power flow controller (UPFC). In each case, the mathematical model is presented and the line loss minimum conditions are obtained based on the line parameters of the distribution feeders. Since multiple loop distribution system is fed from same substation, the line loss minimization can be achieved by compensating the summation of the line reactance voltage drop. In an isolated substation loop distribution system, the line loss minimization can be achieved by compensating the summation of the line reactance voltage drop in addition to the voltage difference of the substations. Realization of both cases can be achieved if the loop current is eliminated from the loop system. The series compensation technique applied by the UPFC is used to eliminate the loop current from the loop distribution system and hence minimize the total line loss. The effectiveness of the proposed control schemes of the UPFC have been verified experimentally.

Line Loss Minimum Control of Loop Distribution Systems Using UPFC

This paper presents an elaborated mathematical analysis of the line loss minimum condition of loop distribution systems. In order to achieve this condition, the unified power flow controller (UPFC), a typical FACTS (flexible AC transmission systems) device that is capable of instantaneous control of transmission and distribution power flow, is used. Also, the available control schemes of the UPFC to minimize the total line loss of the loop distribution system are presented. The authors propose the line inductance compensation control and the line voltage compensation control which can be applied to the loop distribution system according to the line parameters. The effectiveness of the proposed control scheme, line inductance compensation control, has been verified experimentally using laboratory prototype in a 200 V, 6 kVA system.

Load voltage regulation and line loss minimization of loop distribution systems using UPFC

This paper presents a new method for achieving line loss minimization and voltage regulation in the loop distribution systems, simultaneously. First, the fine loss minimum conditions in the loop distribution systems are presented. Then, load voltage regulation by using the shunt compensation is presented. In order to achieve these two objectives, simultaneously, the unified power flow controller (UPFC) is used. The UPFC shunt converter is used as a shunt compensator to regulate the load voltage, and the UPFC series converter is used to control the power flow to achieve line loss minimization. Also, the proposed control schemes of the UPFC series and shunt converters are investigated. The effectiveness of the proposed control schemes of the UPFC has been verified experimentally using laboratory prototype in a 200 V, 6 kVA system.

Independent Control of Input Current, Output Voltage, and Capacitor Voltage Balancing for a Modular Matrix Converter

This paper presents a novel control scheme for the modular matrix converter (MMxC), in terms of balancing capacitor voltages in addition to controlling output voltage and input current along with a comprehensive mathematical model. The proposed technique has been designed based on a fully decoupled current control of the positive-, negative-, and zero-sequence components of each MMxC subconverter in addition to the feedforward instantaneous power control to suppress the capacitor voltages fluctuation. The frequency of the zero-sequence is the output frequency for the load. Therefore, the positive-sequence current component is used to control the input current to achieve unity input power factor, the negative-sequence current component is used to balance the capacitor voltages among all MMxC arms, and the zero-sequence current component is used to control the output voltage. The effectiveness of the proposed control scheme for controlling the MMxC has been verified theoretically, using simulation software, and experimentally, using a laboratory prototype based 3 kVA, 200 V.

Single-phase five-level inverter with less number of power elements for grid connection

Recently, the emergence of single phase multilevel inverter has been increased due to its advantages over traditional one. This paper proposes a single-phase five level pulse width modulation (PWM) inverter for grid connection employing PI controller to perform unity power factor. Two triangular carrier signals identical to each other with an offset equivalent to the amplitude of the reference signal were used to generate PWM signals for the switches. The proposed inverter has the advantage of less number of components. Operational principles with switching functions are analyzed. A digital proportional integral current control algorithm is implemented in FPGA XC3S400 to control the injected current into the grid to be almost sinusoidal. The inverter offers much less total harmonic distortion and can operate at near-unity power factor. Some switches operate at fundamental frequency and others operate at switching frequency. The proposed inverter has been compared with the conventional single-phase five-level PWM inverter. The effectiveness of the proposed inverter and its control technique has been verified theoretically, using PSIM simulation program, and experimentally, using laboratory prototype system.

All nodes voltage regulation and line loss minimization in loop distribution systems using UPFC

Voltage regulation and line loss minimization in distribution lines are challenging problems, particularly when it is not economic to upgrade the entire feeder system. This paper presents a new method for achieving line loss minimization and all nodes voltage regulation in the loop distribution systems, simultaneously. First, loop system line loss minimum conditions are presented. Then, load voltage regulation is applied under line loss minimum conditions. Reference voltage of the controlled node is determined based on the assumption that this voltage can subsequently improve all node voltages to be within permissible range. Reference angle of the controlled node voltage is the main factor that can be used to minimize total line loss during load voltage control. In order to achieve these two objectives, simultaneously, the UPFC, a FACTS device, is used. Also, the proposed control scheme of the UPFC to regulate all node voltages under line loss minimization is presented. The effectiveness of the proposed control scheme has been verified experimentally.

Grid-connected single-phase multi-level inverter

Recently, great attention has been addressed for multilevel inverters, as they exhibit low total harmonic distortion (THD) in the output voltage and low electromagnetic interference (EMI). This paper proposes a single-phase five-level pulse width modulation (PWM) inverter for grid connection. The proposed PWM technique has some switches operated at fundamental line frequency and the others operate at inverter switching frequency. The proposed inverter has advantages of less number of components and low THD compared with the conventional multilevel inverter. The inverter operational principles and the switching functions are analyzed in this paper. Moreover, a proportional integral (PI) current control algorithm is designed and implemented in DSPACE DS1103 to keep the current injected into the grid sinusoidal and in-phase with the grid voltage for unity power factor. Simulation and experimental results prove the powerful merits of the proposed multi-level inverter and the capabilities of the proposed PWM technique.

New PWM technique for grid-tie isolated bidirectional DC-AC inverter based high frequency transformer

This paper presents a new PWM switching technique for controlling a bidirectional isolated DC-AC-AC inverter along with its soft-switching technique. The proposed PWM technique has the ability to control the input DC current and to inject a sinusoidal three-phase current to the grid at unity power factor. In the first stage, an H-bridge converter is used to convert the DC voltage to a high-frequency square-wave single-phase voltage. In the second stage, a matrix converter is used to convert the high-frequency voltage waveform to conventional three-phase voltage synchronized with the grid. Therefore, a high-frequency transformer is used to link the H-bridge output voltage to the matrix converter input voltage. The proposed soft-switching technique is achieved by connecting shunt capacitors across the DC-AC-AC converter switches. The mathematical model and the circuit operation for soft-switching are presented along with the voltage controllable limits. The effectiveness of the proposed technique has been verified experimentally using a laboratory prototype.

PWM Control Techniques for Single-Phase Multilevel Inverter Based Controlled DC Cells

This paper presents a single-phase five-level inverter controlled by two novel pulse width modulation (PWM) switching techniques. The proposed PWM techniques are designed based on minimum switching power loss and minimum total harmonic distortion (THD). In a single-phase five-level inverter employing six switches, the first proposed PWM technique requires four switches to operate at switching frequency and two other switches to operate at line frequency. The second proposed PWM technique requires only two switches to operate at switching frequency and the rest of the switches to operate at line frequency. Compared with conventional PWM techniques for single-phase five-level inverters, the proposed PWM techniques offer high efficiency and low harmonic components in the output voltage. The validity of the proposed PWM switching techniques in controlling single-phase five-level inverters to regulate load voltage is verified experimentally using a 100 V, 500 W laboratory prototype controlled by dspace 1103.