Comparison of Interior Mounted Permanent Magnet Synchronous Motor Drives with Sinusoidal, Third Harmonic Injection, and Space Vector Pulse Width Modulation Strategies with particular attention to Current Distortions and Torque Ripples

Interior Mounted Permanent Magnet Synchronous Motors (IPMs) have become popular in electric vehicle traction applications in recent years due to their superior features such as high efficiency and high power density compared to other machines. Therefore, development of IPM drive systems is an important research area. In this study, three different pulse width modulation (PWM) strategies commonly used in machine drives are compared extensively in IPM drives. Simulations have been carried out with optimum dq-axes currents based on demanded torque from the system, and hence, the simulated drives are efficiency-optimized. Sinusoidal pulse width modulation (SPWM), third harmonic injection pulse width modulation (THIPWM), and space vector pulse width modulation (SVPWM) strategies have been employed in the drives, and comparisons have been made by paying particular attention to the total harmonic distortion (THD) rates of phase currents and torque ripples. It has been validated through extensive simulations that the SVPWM strategy has less THD percentage for IPM drives than SPWM and THIPWM at wide operating points, and hence, the current and torque responses are better with smooth output torque. Simulation results also validate that the current distortions and torque ripples are the highest when SPWM strategy is adopted in the drives, and hence, the THIPWM strategy is superior to the SPWM. © 2023 Istanbul University. All rights reserved

Harmonic Reduction Using THIPWM Switching Technique with Type-2 Fuzzy on 3-Phase Motor

The development of the increasingly advanced industrial world has increased the need and use of electric motors for various purposes. In the industrial world, many electric motors are found as a driving device to drive various equipment needed, including a three-phase induction motor. The induction motor is expected to operate normally by the desired working characteristics. But it is undeniable that in its use, there are disturbances that can cause damage to the work system of the Induction motor, one of which is harmonic interference. The influence of harmonics on the induction motor causes copper and core losses which will reduce the efficiency motor and cause harmonic torque along with fundamental torque to produce vibration and noise, which considerably affect the operation three-phase induction motor. In this study, a 3-phase inverter was used with the Third Harmonic Injection pulse width modulation (THIPWM) method, with the use THIPWM Switching Method expected to increase the output voltage three-phase inverter and reduce the harmonics caused by the three-phase induction motor. In optimizing a 3-phase induction motor's speed regulation, scalar control or voltage/frequency (v/f) regulation is used. With the use THIPWM switching on this three-phase inverter, it is evident from simulation results that the harmonic value of THDV is 55.62%. THDI is 19.04%, as well the acceleration 3-phase induction motor with a rise time value of 48.547ms with steady-state error of 0.08% at set point 1200 rpm and with rise time value of 52.938ms with steady-state error 0% at set point 1000 rpm

A Novel PWM Scheme with Two Switching Frequencies and Wider Carrier to Improve the THD in Voltage Source Converters

The integration of renewable energy resources presents a significant set of technical and infrastructure challenges to power grid operation and control. Besides, it has been proven that it is less harmful to the environment. Power electronics technology has the capability to mitigate the effects of the issues imposed on the power system by the rapid expansion of renewable energy development and increased penetration level at the utility scale. Although power electronics technology is considered a promising potential solution, power conversion efficiency in the rectifiers and inverters must be improved to optimize system performance. A novel pulse width modulation technique is presented to improve the conversion efficiency. This method has two major concepts. First, widening the on-state of the converter's operation will increase the output fundamental component. Inverse sinusoidal pulse width modulation is one of the methods that can achieve this concept. Second, the rate of change in the information at the peak of the sinusoidal reference is relatively small. The modulation of this period has less significance in comparison to the rest of the reference cycle. Hence, a frequency modulation technique is applied to fulfill this task. The novel development and utilization of these two techniques in combination will prove that; in comparison to the sinusoidal pulse width modulation, the fundamental output will increase substantially. Also, this new technique extensively suppresses the harmonic distortion of the converter operation. Furthermore, these results are attained by using lower switching frequency to produce lower switching losses and improves converter operation efficiency

Enhanced Performance Bidirectional Quasi-Z-Source Inverter Controller

A novel direct control of high performance bidirectional quasi-Z-source inverter (HPB-QZSI), with optimized controllable shoot-through insertion, to improve the voltage gain, efficiency and to reduce total harmonic distortion is investigated. The main drawback of the conventional control techniques for direct current to alternating current (DC-AC) conversion is drawn from the multistage energy conversion structure, which implies complicated control, protection algorithms and reduced reliability due to the increased number of switching devices. Theoretically, the original Z-source, Quasi-Z-source, and embedded Z-source all have unlimited voltage gain. Practically, however, a high voltage gain (>2 or 3), will result in a high voltage stress imposed on the switches. Every additional shoot-through state increases the commutation time of the semiconductor switches, thereby increasing the switching losses in the system. Hence, minimization of the commutation time by optimal placing of the shoot-through state in the switching time period is necessary to reduce the switching loss. To overcome this problem, a combination of high performance bidirectional quasi-Z-source inverter with a sawtooth carrier based sinusoidal pulse width modulation (SPWM) in simple operation condition for maximum boost control with 3rd harmonic injection is proposed. This is achieved by voltage-fed quasi-Z-source inverter with continuous input current, implemented at the converter input side which can boost the input voltage by utilizing the extra switching state with the help of shoot-through state insertion technique. This thesis presents novel control concepts for such a structure, focusing mainly on the control of a shoot-through insertion. The work considers the derivation and application of direct controllers for this application and scrutinizes the technical advantages and potential application issues of these methodologies. Based on the circuit analysis, a small signal model of the HPB-QZSI is derived, which indicates that the circuit is prone to oscillate when there is disturbance on the direct current (DC) input voltage. Therefore, a closed-loop control of shoot-through duty cycle is designed to obtain the desired DC bus voltage. The DC-link boost control and alternating current (AC) side output control are presented to reduce the impacts of disturbances on loads. The proposed strategy gives a significantly high voltage gain compared to the conventional pulse width modulation (PWM) techniques, since all the zero states are converted into shoot-through states. The simulated results verify the validity and superiority of the proposed control strategies

Mitigation of DC Current Injection in Transformerless Grid-Connected Inverters

PhD ThesisWith a large number of small-scale PV plants being connected to the utility grid, there is increasing interest in the use of transformerless systems for grid-connected inverter photovoltaic applications. Compared to transformer-coupled solutions, transformerless systems offer a typical efficiency increase of 1-2%, reduced system size and weight, and reductions in cost. However, the removal of the transformer has technical implications. In addition to the loss of galvanic isolation, DC current injection into the grid is a potential risk. Whilst desirable, the complete mitigation of DC current injection via conventional current control methods is known to be particularly challenging, and there are remaining implementation issues in previous studies. For this reason, this thesis aims to minimize DC current injection in grid-connected transformerless PV inverter systems. The first part of the thesis reviews the technical challenges and implementation issues in published DC measurement techniques and suppression methods. Given mathematical models, the performance of conventional current controllers in terms of DC and harmonics mitigation is analyzed and further confirmed in simulations and experiments under different operating conditions. As a result, the second part of the thesis introduces two DC suppression methods, a DC voltage mitigation approach and a DC link current sensing technique. The former method uses a combination of a passive attenuation circuit and a software filter stage to extract the DC voltage component, which allows for further digital control and DC component mitigation at the inverter output. It is proven to be a simple and highly effective solution, applicable for any grid-connected PV inverter systems. The DC link sensing study then investigates a control-based solution in which the dc injection is firstly accurately determined via extraction of the line frequency component from the DC link current and then mitigated with a closed loop. With an output current reconstruction process, this technique provides robust current control and effective DC suppression based on DC link current measurement, eliminating the need for the conventional output current sensor. Results from rated simulation models and a laboratory grid-connected inverter system are presented to demonstrate the accurate and robust performance of the proposed techniques. This thesis makes a positive contribution in the area of power quality control in grid-connected inverters, specifically mitigating the impact of DC injection into the grid which has influences on the network operating conditions and the design and manufacture of the PV power converter itsel

THERMAL STRESS MITIGATION OF SINGLE-PHASE SINEWAVE INVERTER BY USING DOUBLE SWITCH H BRIDGE CONFIGURATION

The increasing demand for renewable energies and the ongoing advancement in the industry require continuously evolving power converters in terms of efficiency, power density, and reliability. Furthermore, power converters’ applications in harsh and remote environments such as offshore wind turbines demand robust and reliable designs to help reduce operational costs. Power switch failure is a critical reliability issue that leads to the converter going out of service, causing an unscheduled maintenance event. The main reason behind power switch failure is thermal cycling. Therefore, the first part of this thesis attempts to develop an effective double switch H bridge inverter topology aiming to lessen thermal cycling subjected to power switches, increasing the expected lifetime of power switches, improving the system\u27s overall reliability, and reducing operational costs. Meanwhile, the second focus of the thesis is to develop a visual interpretation of an empirical lifetime estimation model that enables the evaluation of the proposed inverter topology compared to the conventional topology. This is done by producing a novel lifetime improvement evaluation curve based on a common empirical lifetime estimation model using MATLAB®. Moreover, the interpretation of the empirical lifetime estimation models as a lifetime improvement evaluation curve helps to bridge the gap between any thermal condition change and its impact on the expected lifetime. The percentage reduction in the junction’s median temperature %_ and the percentage reduction in the temperature swing %Δ_ are taken as the main contributors to the change in the switch’s estimated cycles to failure . The effectiveness of the proposed topology was verified via simulation of the thermal parameters for the two topologies via PLECS® software. Several test scenarios were performed to illustrate the impact of shifting from the conventional topology to the proposed topology. Following that, numerous loading conditions were considered to perform an extensive comparative analysis between the proposed and the conventional topologies. Three power factor values were adopted at high, medium, and low values; to compare the two topologies while covering an adequate loading range for each power factor value. The assessment indices, namely, Life Prolonging Factor (LPF), and the average LPF (in a temperature range) obtained promising results, especially for high loading levels conditions. The LPF reached values more than ‘2’ under some conditions, indicating a more than double lifetime increase. Furthermore, the average LPF in a specific temperature range indicated promising results in general for common loading conditions with an advantage for higher loading conditions over lower loading conditions

Development of pulse-width-modulation techniques for multi-phase and multi-leg voltage source inverters

A huge body of work has been published in recent times in the area of multi-phase machines and drives. Many aspects of these drives have been analysed, such as reduction of torque pulsations, increased reliability and fault tolerance, improved power sharing capabilities and possibilities for realisation of series-connected multi-motor drives with supply coming from a single multi-phase voltage source inverter (VSI). Various pulse width modulation (PWM) schemes have been developed for multi-phase machines with concentrated and distributed windings, utilising both carrier-based PWM and space vector PWM (SVPWM) approaches. However, no systematic analysis has been performed in order to determine properties of multi-phase PWM in general, and to establish close correlation between carrier-based PWM and space vertor PWM, for multi-phase VSIs. This thesis presents an analysis and development of multi-phase PWM schemes for sinusoidal output voltage generation with two-level muhi-phase VSIs, which are suitable for multi-phase machines with distributed windings. Therefore, attention is paid to the elimination of low order harmonics. The scope of the thesis has been narrowed down to the continuous PWM schemes and operation in the linear region of the modulation only. Both multi-phase carrier-based PWM and SVPWM schemes are considered, and, in particular, five-phase, seven-phase e-phase systems are addressed in detail. Thus, a strong link between these two different approaches is established, allowing for an easier comparison of the features offered by each method. All PWM schemes are practically implemented in a DSP and experimentally verified through extensive experimentation on the custom-built multi-phase VSI. In addition to the methods of sinusoidal output voltage generation, achieved by means of the synthesis of the reference in only the first plane of the multi-phase system with simultaneous zeroing of voltages in all the other planes

Active current sharing control schemes for parallel connected AC/DC/AC converters

PhD ThesisThe parallel operation of voltage fed converters can be used in many applications, such as aircraft, aerospace, and wind turbines, to increase the current handling capability, system efficiency, flexibility, and reliability through providing redundancy. Also, the maintenance of low power parallel connected units is lower than one high power unit. Significant performance improvement can be attained with parallel converters employing interleaving techniques where small passive components can be used due to harmonic cancellation. In spite of the advantages offered by parallel connected converters, the circulating current problem is still a major concern. The term circulating current describes the uneven current sharing between the units. This circulating current leads to: current distortion, unbalanced operation, which possibly damages the converters, and a reduction in overall system performance. Therefore, current sharing control methods become necessary to limit the circulating current in a parallel connected converter system. The work in this thesis proposes four active current sharing control schemes for two equally rated, directly paralleled, AC/DC/AC converters. The first scheme is referred to as a “time sharing approach,” and it divides the operation time between the converters. Accordingly, in the scheme inter-module reactors become unnecessary, as these are normally employed at the output of each converter. However, this approach can only be used with a limited number of parallel connected units. To avoid this limitation, three other current sharing control schemes are proposed. Moreover, these three schemes can be adopted with any pulse width modulation (PWM) strategy and can be easily extended to three or more parallel connected units since they employ a modular architecture. The proposed current sharing control methods are employed in two applications: a current controller for three-phase RL load and an open loop V/f speed control for a three-phase induction motor. The performance of the proposed methods is verified in both transient and steady state conditions using numerical simulation and experimental testingMinistry of Higher Education and Scientific Research of Iraq

Design and Control of Power Converters for High Power-Quality Interface with Utility and Aviation Grids

Power electronics as a subject integrating power devices, electric and electronic circuits, control, and thermal and mechanic design, requires not only knowledge and engineering insight for each subarea, but also understanding of interface issues when incorporating these different areas into high performance converter design.Addressing these fundamental questions, the dissertation studies design and control issues in three types of power converters applied in low-frequency high-power transmission, medium-frequency converter emulated grid, and high-frequency high-density aviation grid, respectively, with the focus on discovering, understanding, and mitigating interface issues to improve power quality and converter performance, and to reduce the noise emission.For hybrid ac/dc power transmission,• Analyze the interface transformer saturation issue between ac and dc power flow under line unbalances.• Proposed both passive transformer design and active hybrid-line-impedance-conditioner to suppress this issue.For transmission line emulator,• Propose general transmission line emulation schemes with extension capability.• Analyze and actively suppress the effects of sensing/sampling bias and PWM ripple on emulation considering interfaced grid impedance.• Analyze the stability issue caused by interaction of the emulator and its interfaced impedance. A criterion that determines the stability and impedance boundary of the emulator is proposed.For aircraft battery charger,• Investigate architectures for dual-input and dual-output battery charger, and a three-level integrated topology using GaN devices is proposed to achieve high density.• Identify and analyze the mechanisms and impacts of high switching frequency, di/dt, dv/dt on sensing and power quality control; mitigate solutions are proposed.• Model and compensate the distortion due to charging transition of device junction capacitances in three-level converters.• Find the previously overlooked device junction capacitance of the nonactive devices in three-level converters, and analyze the impacts on switching loss, device stress, and current distortion. A loss calculation method is proposed using the data from the conventional double pulse tester.• Establish fundamental knowledge on performance degradation of EMI filters. The impacts and mechanisms of both inductive and capacitive coupling on different filter structures are understood. Characterization methodology including measuring, modeling, and prediction of filter insertion loss is proposed. Mitigation solutions are proposed to reduce inter-component coupling and self-parasitics