Mahmoud I. Masoud

Medium-Voltage 12-Pulse Converter: Output Voltage Harmonic Compensation Using a Series APF

In this paper, compensation of the dc-side voltage harmonics of a medium-voltage (MV) 12-pulse ac/dc converter is achieved using a series active power filter (APF). The output voltage harmonics are dependent on the converter firing delay angles and, consequently, on the specific power locus followed by the ac/dc converter. This power locus ensures minimum fifth and seventh harmonics (total rms) in the input current which provides minimum input current total harmonic distortion when the reactive power is less than 0.5 p.u. The series APF is connected between the load and the converter output via a magnetic amplifier to eliminate the dc current from the APF inverter, thus reducing inverter losses. Voltage harmonic compensation using a series APF, with and without a magnetic amplifier, is examined with both resistive and inductive loads. The simulation results for compensating a 3.3-kV MV 12-pulse converter system are experimentally verified using a scaled prototype 12-pulse converter with a series APF.

Improved Flux Pattern With Third Harmonic Injection for Multiphase Induction Machines

This paper presents an indirect vector control scheme with an improved flux pattern using third harmonic injection. The control objective is to independently control both flux and torque and to generate a nearly rectangular air-gap flux, resulting in improved machine power density. If there is a proportional relation between the third harmonic and fundamental plane currents, variable misalignment between fundamental and third air-gap flux components occurs with varying mechanical loading. Due to this misalignment, saturation may take place. Accordingly, the total flux is saturated and iron loss increases. Hence, coupling results between different sequence planes. Instead of a proportional relation between the current components, direct and quadrature current components of the injected third harmonic current reference are a function of the fundamental direct and quadrature reference current components, respectively. These functions ensure that the air-gap flux is near rectangular with a maximum value of 1 p.u. from no load to full load. Moreover, this controller guarantees complete decoupling between the sequence planes. An eleven-phase induction machine is used to validate the proposed controller experimentally, while supporting simulation results and theoretical analysis use both MATLAB and finite element platforms.

Optimum Flux Distribution With Harmonic Injection for a Multiphase Induction Machine Using Genetic Algorithms

This paper investigates a nontriplen multiphase induction machine when fed with harmonic current injection with different sequences for an open loop optimized flux distribution that produce a quasi-square wave in the machine air gap. This maximizes iron utilization, giving more torque per ampere. The relation between the fundamental and other harmonic components can be determined for the best iron utilization using genetic algorithms where optimum flux distribution with different injected harmonic order can be obtained. This means, the target is to optimize the flux distribution during no-load to determine the optimum constants that guarantee approximate square wave air-gap flux. The paper focuses on an 11-phase machine that can be excited with harmonics up to the ninth. The technique is assessed using both winding function and finite element analysis methods. The prototype machine is fed from an 11-phase inverter. The system DSP control using genetic algorithm produces an optimum flux distribution by using winding sequence and harmonic current injection. Simulation results for the 11-phase dq model and prototype drive experimental results are presented.

Improved Sensorless Operation of a CSI-Based Induction Motor Drive: Long Feeder Case

Various applications, like in underground mines and oil and gas industries, require remote operation of vector-controlled medium-voltage variable speed drives via a long motor feeder. The use of voltage source inverters in such cases leads to motor overvoltage and harmonic quality problems. The current source inverter (CSI) is ideally matched to these applications because of its motor-friendly voltage output. Speed sensorless operation is mandatory due to the long motor feeder. Although the model reference adaptive system (MRAS) is a powerful and proven speed estimation tool, its implementation in long motor feeder drives faces many challenges. Among them, and addressed in this paper, are inherent dc offset in its stator model, the need for actual motor voltage and current values, and oscillations in the estimated speed due to errors in the motor current measurement signals. In this paper, a sensorless CSI vector-controlled drive, suitable for long motor feeder applications, is studied. Improved speed estimation is achieved by proposing 1) a modified dc-offset eliminator for an MRAS speed estimation and 2) a compensation technique for motor currents measurement errors. Intensive experimental results, for a low-voltage scaled model, along with simulations validate the effectiveness of the proposed technique.

Effect of Current Harmonic Injection on Constant Rotor Volume Multiphase Induction Machine Stators: A Comparative Study

Although torque enhancement in multiphase induction machines using harmonic current injection has been addressed in the literature, a detailed assessment of the effect of this enhancement on the design parameters of multiphase machines with different numbers of phases is needed. This paper addresses this topic by performing a detailed comparative study of harmonic injection torque enhancement on multiphase machines with different numbers of phases. Sets of identical dimension and volume rotors differing in their value of the bar skew angle were designed to operate with the various stator designs in order to facilitate the comparative evaluation. A mathematical approach is also introduced to enable the derivation of equivalent multiphase machine parameters based on an existing one. In addition to a detailed finite-element-analysis verification of the results, time domain MATLAB simulations are used to verify the mathematical modeling. The results provide a means to assess the extent to which such harmonic injection may be beneficial by quantifying torque enhancement as well as torque density for various multiphase machines.

Modified Indirect Vector Control Technique for Current-Source Induction Motor Drive

Medium-voltage (MV) drives are generally based on either voltage-source inverters or current-source inverters (CSIs). CSIs feature simple topology, motor-friendly waveforms, power reversal capability, and short-circuit-proof protection; hence, they are widely used as high-power MV drives. Direct vector control (DVC) CSI drives ensure improved performance by decoupled control of the machine flux and torque using two independent control loops. Despite the excellent performance of DVC, this scheme faces practical challenges, like dc offset in the stator model and machine parameter dependence. Conventional indirect vector control (IVC) CSI drives are known for reduced computational burden and less machine dependence. However, conventional-IVC CSI drives exhibit poor dynamic response and transient field misorientation due to the absence of a dedicated flux control loop. In this paper, a modified IVC technique is proposed featuring superior decoupling and field orientation using only two extra proportional-integral current controllers with additional motor current feedback signals. The proposed-technique effectiveness is examined experimentally, on a scaled low-voltage prototype, as well as using simulation results.

A Shunt Active Power Filter for a Medium-Voltage 12-Pulse Current Source Converter Using Open Loop Control Compensation

AC-side compensation for current source converters using a shunt active power filter (SAPF) is affected by delays introduced into the reference signals and/or the actual injected current. The delays should be identified and compensated to eliminate distortion from the supply current extracted from the point of common coupling, such that the total harmonic distortion complies with standards. An improved distortion factor is achieved if the delay for each harmonic order is considered individually. This paper introduces an open-loop control strategy for the SAPF, which is capable of mitigating specific and predetermined harmonic orders and consequently achieves low total harmonic distortion. The delays are minimized or eliminated when extracting the reference current and controlling the filter current. The control technique is applied on a medium-voltage asymmetrically controlled 12-pulse ac to dc current source converter, which follows a specific power locus with the SAPF connected via taps on the star connected secondary winding of the front end transformer, to compensate the mains current dominant harmonics (5th, 7th, 11th, and 13th). Medium voltage simulation results are verified experimentally using a scaled prototype.

A new power locus for the p-q operation of series connected 12-pulse current source controlled converters

The series connected 12-pulse current source converter can operate under controlled p-q operation with symmetrical or asymmetrical firing of the two series connected 6-pulse thyristor converters. The input power factor and input current total harmonic distortion (THD) are dependent on the converter power locus. In this paper, a new p-q locus is introduced where the maximum reactive power absorbed by the converter is halved, simultaneously providing minimum input current THD. The input current THD and power factor of the converter are investigated based on the proposed power locus. A compensation technique is mandatory in order to improve the performance. The proposed power locus reduces the compensator rating. The power locus performance of the 12-pulse converter is simulated and verified experimentally.

Street lighting using solar powered LED light technology: Sultan Qaboos University Case Study

Many nations have started taking steps to meet the required energy demands through different technologies to improve the local impact. As the standard of living is increased, the development of infrastructure should adapt quickly. Street lighting, one of the infrastructure should meet the consumer requirements, expansions, and growth. Countries may have more burden if still using High Pressure Sodium (HPS) lamps for street lighting. Nowadays, LED light technology becomes a candidate as it surpass the HPS lamp from both energy and money saving. The saving and local impact may be enhanced and increased, if solar power system (PV) is engaged with LED lamp for street lighting. This paper gives recommendation and show the local impact to Sultanate of Oman when street lighting is solar powered LED. The results and analysis are made for one of the Sultan Qaboos University (SQU) main roads as a case study.

Steady-State Performance and Stability Analysis of Mixed Pole Machines With Electromechanical Torque and Rotor Electric Power to a Shaft-Mounted Electrical Load

This paper presents the steady-state model, performance, and stability analysis of a mixed pole machine with a new operational mode which provides a rotor torque and an n -phase rotor electrical output power to a shaft-mounted rotating electrical load. The machine operated under this mode can be used in applications that require contactless power, such as in robotics, or applications that require independent control of both rotor torque and rotor electric power, such as for contactless rotational antennas and turret systems. The performance assessment includes electromagnetic torque, electrical efficiency, mechanical efficiency, and total efficiency based on both simulation and experimentation. The effect of electrical loading and stator voltage on both rotor torque and rotor electric power is also considered. The machine steady-state stability is introduced by plotting the machine operating characteristics that determine all stable operating regions of the machine under the proposed mode of operation.