saad@um.edu.my

Projects

1. Title: A New Five Level Active Neutral Point Clamped Converter for Equal Losses Distribution and Voltage Balancing

Abstract: Three-level neutral point (3L-NPC) converter is one of the main topology in the industrial applications and standard converter in medium-voltage applications. However, the balancing losses among the switches and balancing of capacitor is the main problem of this topology. Active neutral-point-clamped (ANPC) converter is advanced family of 3L-NPC, which was originally proposed to solve the drawback of unbalanced power loss distribution among the devices in conventional neutral-point-clamped (NPC) converters. Hence, improving the performance and features of the NPC, and increasing their efficiency. This work presents a new single phase 5-level Active Neutral Point Clamped (ANPC) converter topology. Using a single DC supply and four capacitors create more divisions in the DC link, the proposed structure produce five voltage levels. The proposed topology helps to reduce the circuit size and cost for a given number of levels. Another drawback is the voltage balancing among the DC capacitors. To solve this problem, an addition circuit has been suggested. Moreover, the 5-Level ANPC can be applied to achieve optimal total harmonic distortion. The structure of topology designed in such a way to maintain the equal switching losses among the switches. An analysis of the switching state and the commutation of the converter are also being presented. The simulation has been carried out in MATLAB Simulink to investigate the effectiveness of the proposed topology. The simulation result shows that the proposed topology can achieved better distribution of the total power losses, between two different strategies PWM-2 and PWM-1. Moreover, the floating capacitor voltage is subdivided into four parts and the balancing is achieved by the additional circuit. The experimental results are also presented to justify the validation of the proposed topology. Moreover; a comparative study has been made to show the cost effectiveness of the proposed topology.

2. Title: Transformer-less Online Uninterruptible Power Supply (UPS) system

Abstract: Uninterruptible power supply (UPS) is widely used to supply power to critical load and provides protection against power failure and other anomalies of power line. A transformer less online uninterruptible power supply (UPS) has been proposed in this paper. The proposed system consists of totem-pole bridgeless boost rectifier, battery charger/discharger, and an inverter. The rectifier operates under zero voltage switching (ZVS), provides regulated DC link voltage with power factor correction. The novel battery charger/discharger ensures the transformer-less operation by reducing the battery bank to only 24V, and regulates the DC link voltage during battery power mode. The inverter provides regulated output voltage to the load. By introducing high gain battery charger/discharger, the battery bank is reduced considerable, which minimize the size, weight, and cost of the system. A new cascaded slide mode and proportional-integral control has been proposed. The controller regulates the output voltage for both linear and non-linear load, shows excellent performance during transients and step change in load. Operation principle and experimental results of 1kVA prototype has been presented to verify the validity of the proposed system.

3. Title: A 12 Sector-Based Switching Scheme for Abnormal Grid-Connected Ultra-Sparse Z-Source Matrix Converter Based DTC of IM Drive

Abstract: This research presents a direct torque control (DTC) switching scheme based on ultra-sparse Z-source matrix converter (USZSMC) using 12-side polygonal space vector for variable speed control of an induction motor (IM). The conventional DTC scheme based direct matrix converter (DMC) is limited by 60°sectors of both flux and voltage vectors which introduce high torque ripple. The proposed method utilizes twelve 30°sectors of both flux and voltage vectors to increase the degrees of freedom for selection of proper vectors and reduce the torque ripple. The proposed switching scheme for MC based DTC of IM drive select the appropriate switching vectors for control of torque with small variations of the stator flux within the hysteresis band. This improves the degrees of freedom in selecting the vector algorithm and the torque ripple as well. Furthermore, during the large torque demand, the probabilities of transgressing reference vector limits, which are enclosed by 12-side polygonal space vector, are reduced. The sensitivity of DMC into the abnormal input voltage from a side and limitation of maximum voltage transfer ratio (86.6%) from other side are the most important drawbacks for conventional prototype of DMC. This study illustrates an USZSMC under abnormal input voltage which could properly reduce the total harmonic distortion (THD) of output current equal to 1.10% by applying compensation method in Particle Swarm Optimization (PSO) PI controller. Although, the Z-source network is cause of intensification of low order harmonics in input and output current; the proposed method optimizes the shoot-through timing in order to abate the distortion spectrum and increase the performance. The eliminating of abnormality rate less than 0.15% for output current, 0.32% for output voltage and accumulated phase synchronization are the advantages of aforementioned system where the restriction of maximum tolerated abnormality for input voltage is 40%. Extensive simulation and experimental results are presented to verify the effectiveness of the 12-sector space vector switching scheme for DTC control of IM fed by USZMC.

4. Title: High efficient single-phase grid-tied transformer less PV inverter with low leakage current

Abstract: Recently, there has been an increasing interest on transformerless photovoltaic (PV) inverter due to the benefits of lower cost, smaller size and weight, and higher efficiency compared to the ones with transformer. It is also going to be more widely adopted as the penetration level of PV system into utility grid is continually increasing. However, one of the technical challenges of transformerless PV inverter is the leakage current issue which mostly depends on the inverter topology structure and control scheme have to be addressed carefully. Another important issue of transformerless inverter is the efficiency that can be improved by optimal design of the inverter. In this study, these two main issues are investigated. The dissertation begins with a comprehensive review of transformerless PV inverter topologies with focus on leakage current and efficiency. In order to select a suitable topology, an analysis by highlighting some key features and a comparison table has been presented. An improved topology is then proposed to better eliminate the leakage current which is introduced by the fluctuating common mode (CM) voltage. The effect of switches junction capacitance on CM voltage is investigated and the desired relationship among them to ensure constant CM voltage is proposed. By introducing two additional capacitors, the constant CM voltage is achieved with this topology. However, the losses due to additional capacitors have very low impact on the overall efficiency. Another new topology is proposed by adding two switches and two diodes with the full-bridge (FB) inverter. The proposed circuit structure does not lead itself to the reverse-recovery issues which allow utilizing MOSFET switches, thereby increasing the overall efficiency. Also, the size of the passive filter has been reduced by increasing the switching frequency without compromising the overall efficiency. The CM voltage remains constant during the operation period, thus the leakage current is minimized to acceptable level. Finally, the simulation and experimental results are shown to verify the theoretical explanation. It has shown that the improved topology combines the superior performance of common-mode and different-mode characteristics. The maximum efficiency of the proposed new topology is 98.6% which is slightly higher than the European efficiency of 98.46%, indicating an optimal topology.

5. Title: Three Phase Shunt Hybrid Active Power Filter Based on Modified Synchronous Reference Frame Theory

Abstract: Due to the increase in the number and application of nonlinear power electronic equipment a mass of harmonic current and reactive power flow into the network. It degrades the power quality of a power distribution system. An active power filter (APF) is an effective means to suppress those issues.To make the active filter cheaper, smaller and more practicable in industry applications, a hybrid configuration appears very attractive in power distribution networks. As series hybrid active filters are complex, unreliable and expensive, a shunt hybrid active power filter (SHAPF) topology is considered in this research because of its capability of attenuation, effective operation and simplicity. A hybrid compensator which is a combination of a three phase four wire shunt APF and a parallel passive filter has been presented in this research. The dominant lower order harmonics as well as reactive power can be compensated by passive elements whereas the active part mitigates remaining distortions. Modified phase lock loop based synchronous reference frame control is adopted here for active filtering system. Here, hysteresis current regulator is used to generate switching signals of APF and for maintaining the dc link capacitor voltage; a proportion-integral (PI) controller is introduced. The proposed hybrid line conditioning system can be quite effective for compensating harmonics, reactive power & neutral current under balanced, unbalanced, distorted and unbalance-distorted grid conditions. The simulated results obtained by MATLAB/SIMULINK power system block set are examined in detail for the validity of suggested approach. A laboratory prototype has been built on dSPACE1104 platform to verify the feasibility of the proposed SHAPF controller. From the simulation and experimental results the robustness of the proposed SHAPF controller has been proven

6. Title: Modified Model Predictive Control of Bidirectional AC-DC And Isolated DC-DC Converters for Energy Storage System

Abstract: Energy storage systems have been increasingly employed in utility and transport applications as well as in renewable energy sources to ensure power reliability, active power control, load leveling, frequency control and grid synchronization. This research presents a modified model predictive algorithm to control bidirectional AC-DC and high frequency-linked isolated DC-DC converter, which have been used in energy storage system for power transferring between the three-phase AC supply and energy storage devices. The modified model predictive control (MMPC) algorithm utilizes the discrete behavior of the power converter and predicts the future variables of the system by defining cost functions for all possible switching states. Subsequently, the switching state that corresponds to the minimum cost function is selected for the next sampling period for firing the switches. The proposed model predictive control scheme allows bidirectional power flow with instantaneous mode change capability and fast dynamic response. The performance of the proposed MMPC controlled bidirectional AC-DC converter is simulated with MATLAB/Simulink and further verified with 3.0 kW experimental prototypes. Both the simulation and experimental results show that, the AC-DC converter is operated with unity power factor, acceptable THD (3.3% during rectifier mode and 3.5% during inverter mode) level of AC current and very low DC voltage ripple. Moreover, the proposed MMPC controlled bidirectional DC-DC converter is also simulated with MATLAB/Simulink, which shows that the proposed MMPC algorithm of the DC-DC converter reduces reactive power by avoiding the phase-shift between primary and secondary sides of the high frequency transformer and allow power transfer with unity-power-factor. Finally, the efficiency comparisons have been performed between the proposed MMPC algorithm and conventional MPC method for both the bidirectional AC-DC and high frequency-linked isolated DC-DC converter which ensures the effectiveness of the MMPC controller.

7. Title: Model Predictive Control With Weithing Factor Optimization For Torque Ripple Reduction of Induction Machine Fed by Indirect Matrix Converter

Abstract: A finite control set-model predictive control (FCS-MPC) has emerged as a powerful control tool in the field of power converter and drives system. In this dissertation, a novel approach of weighting factor optimization method for reducing the torque ripples of induction machine (IM) fed by indirect matrix converter (IMC) has been introduced and presented. Therefore, an optimization method is adopted here to calculate the optimized weighting factor corresponding to minimum torque ripple of IM. However, model predictive torque and flux control of IM with conventionally selected weighting factor is being investigated in this dissertation and is compared with the proposed optimum weighting factor based MPC control algorithm. Also, model predictive control of IM fed by IMC has been investigated to control the unity power factor at the input of the IMC. MPC control selects the optimized switching state that minimizes a cost function based on optimized weighting factor to actuate the power converter at the next sampling period. The weighting factor optimization method has improved the simulation results by 6% torque ripple of IM at forward high speed, and 10.37% of torque ripple at reverse high speed. On the other hand, at low forward speed, the proposed method has improved the torque ripple by 5.4%, and the improvement at reverse low speed is found as 13.34% of torque ripple. Also, the proposed method has improved the torque ripple by 24.2% (at high speed) and 25% (at low speed) in the experimentation. To achieve the objectives of this dissertation, the issues have been investigated using MATLAB simulation and experimental study in the DS1104 R&D controller platform which proves the robustness of the MPC control and shows potential control tracking of variables with their respective references. Finally, the proposed optimization method has reduced the torque ripples corresponding to conventional weighting factor based MPC control method in this dissertation.

8. Title: Thermal Performance Enhancement of Evacuated Tube Solar Collector Using Nanofluids

Abstract: Solar energy is the most available, environmental friendly energy source and renewable to sustain the growing energy demand. Solar energy is captured by solar collectors and Heat pipe evacuated tube solar collector (HP-ETSC) is the most efficient and expedient collector among various kinds of solar collectors. ETSCs have outstanding thermal performance, easy transportability and expedient installation and in addition ETSCs are suitable for unfavorable climates. Water, oil, and air are the most common working fluids used in solar energy system but the thermal conductivity of these fluids are relatively low. In contrast, nanofluids which consists base liquid and nanomaterials have enhanced thermophysical properties such as higher thermal conductivity, viscosity, thermal diffusivity and convective heat transfer coefficients. The objective of this research is to investigate the performance of ETSC using various nanofluids.

9. Title: Transformerless Photovoltaic Inverter with MPPT Controller for Photovoltaic Array Under Partial Shading Condition

In order to overcome the self-heating issue in the photovoltaic (PV) module during the partial shading condition, the bypass diode is added into the PV module. But, the use of bypass diode cause the multiple MPPs appear in the power-against-voltage (P–V) curve of the PV array. Conventional local search space algorithm such as perturbation and observation (P&O) and incremental conductance (Inc Cond) may fail to track the global MPP (GMPP) which has the maximum power under partial shading condition. Thus, a modified Inc Cond algorithm is introduced to track the GMPP during partial shading condition. In the proposed algorithm, three consecutive points are tracked continuously. If the MPP which has the maximum magnitude is located in between of the others MPP, the algorithm will terminate the searching process and operates at the GMPP. The tracking process will keep going until the searching reaches the left end or right end of the P–V curve if the maximum magnitude does not located in between of the other MPP. In order to ensure the fast tracking of the three MPPs, a novel voltage perturbation method is introduced to increase the response of the algorithm in tracking the MPPs.

Apart from that, a transformerless PV inverter is also introduced to convert the direct current (DC) source of the PV array into alternating current (AC) source. The transformerless inverter has the advantages such as lower cost, size and higher efficiency as compared to the inverter with transformer. But, there is leakage current issue in the transformerless PV inverter. Thus, a new six switches and two diodes PV inverter which is able to reduce the leakage current is introduced. The effect of the junction capacitance of the switches in the transformerless PV inverter is taken into consideration during the design of the inverter. The proposed inverter has the ability to reduce the leakage current as compared to the conventional H5 topology.

10. Title: Soft-switching Active Clamp Flyback Converter for PV Applications

Grid-connected photovoltaic (PV) system has received a great attention due to the elimination of battery cost in distributed power generation system. The microinverter is superior to other technologies of PV converter in terms of obtaining the highest maximum power point tracking (MPPT) accuracy on each PV module. The microinverters can be classified into isolated and non-isolated type with respect to the presence of galvanic isolation. Isolated types are more preferable in terms of reliability and transferring higher quality of power to the grid. However, the efficiency of the isolated microinverters degrades due to high frequency transformer and high switching losses. Therefore, increasing the efficiency of the PV converter maintaining higher lifetime and lower cost is the most critical job to form a reliable microinverter. This study presents a single-stage and a double-stage active-clamp resonant flyback microinverter for grid-connected PV AC module system. The single-stage microinverter is operated with a hybrid operation of discontinuous conduction mode (DCM) and boundary conduction mode (BCM). The proposed modified hybrid method is based on different variable negative current references for DCM and BCM operation. Hence, the zero-voltage and zero-current switching (ZVZCS) turn-on of the high frequency main switch is achieved by allowing a negative current through the resonant circuit in both conduction modes. A small capacitor is inserted across the primary switch to achieve zero voltage switching (ZVS) turn-off operation. The energy stored in the leakage inductance of the transformer is also recycled and voltage stress of the main switch is reduced. It enables the use of lower voltage rating MOSFET and reduces the switch conduction loss. The mathematical analysis of the proposed hybrid operation modes in different resonant condition is provided for the modelling of the proposed system. The double-stage microinverter is composed of a DC-DC flyback converter with a resonant full-bridge inverter. The flyback converter contains a resonant active-clamp circuit that limits the voltage stress and provides soft-switching operation. Therefore, the switching losses of the high frequency primary switches are negligible. A resonant full-bridge inverter with ZVS of the high frequency switches is adopted that make the overall efficiency high. Moreover, using a film capacitor in the DC link, the lifespan of the microinverter is increased. A 250W prototype of the proposed microinverter has been implemented and the peak efficiencies are found to be 97.1% and 96.5% for the single- and double-stage microinverter respectively. Hence, the proposed active-clamp flyback microinverter confirms the superiority compare to existing topologies.

11. Title: A Frequency Adaptive Phase Shift Modulation Control Based LLC Series Resonant Converter for Wide Input Voltage Application

Bi-directional DC/DC converters (BDCs) are widely used in many electric power applications such as automobiles, electric vehicles, renewable energy sources, uninterrupted power supplies (UPS), DC micro grid with energy storage systems (ESSs) and so on. Among all the BDCs, Bi-directional resonant DC/DC converters (BDRDCs) are considered as the best suitable for minimizing the switching losses, reducing electromagnetic interference and achieving high frequency operation ability. However, BDRDCs have the inherent limitation of zero voltage switching (ZVS) operation for a wide variation of load and input voltages. This study presents an isolated bi-directional LLC series resonant DC/DC converter with novel frequency adaptive phase shift modulation (FAPSM) control, which is capable of maintaining ZVS for wide variation of load and input voltages. This topology is composed of a stacked structure where four switches are connected in series but sharing the same resonance tank and high frequency transformer. The voltage stress across each switch is reduced to half of the input voltage due to the series combination of four switches. It also uses an active rectifier in the secondary side of the transformer and becomes the key component of an energy storage system (ESS) to enable the bi-directional power flow. The proposed control is composed of two control variables: switching frequency and phase shift angle of the secondary switches. The Switching frequency changes with the load in such a way that, it is secured ZVS to the primary side switches for all phase shift angles. Automatically, it maintains the converter gain characteristics identical regardless of load conditions for all phase shift angles. On the other hand, the phase shift changes according to the input variations only. Thus the converter maintains ZVS to all switches for wide voltage gain and load range. The control also makes the converter voltage gain independent of the loaded quality factor. The simultaneous use of two control variables also reduces the circulating current (or reactive power), especially at light load conditions. In addition, Frequency selection for each load condition helps to minimize the series RMS resonance current as compared to fixed frequency operation which improves the light load efficiency significantly. Furthermore, high value of magnetizing inductance is designed (which has no effects on voltage gain) in this converter, which reduces the conduction losses as well as increases the efficiency of the converter. Experimental results of a 1kW prototype converter with 200-400V input and 48V output are presented to verify the performance of the proposed converter. The measured efficiency of the converter at full load condition is 96.5% and 92% for maximum and minimum input voltage respectively during power flow in forward direction.

12. Title: A New Switching Algorithm Based On Single Phase Modulator for Z-Source Inverters With Reduced Computation Time and Enhanced Output Voltage

The inverter is one of the most common power electronics device used in industrial application. The main objective of the inverter is to produce an ac output waveform from a dc source. The main drawback of VSI is that the maximum output voltage obtained can never exceed the dc-link voltage. To obtain an output voltage higher than the input, an additional stage of dc/dc converter is required, which increases the cost of the system and decreases the efficiency. Recently, Z-source inverter (ZSI) is introduced to overcome the aforementioned disadvantages of VSI where a unique impedance network is coupled between the dc power source and the inverter main circuit. The obtained efficiency is higher due to the main feature of ZSI, which combines the advantages of buck/boost in one stage power conversion. Moreover, the reliability is improved due to the inclusion of the shoot-through (ST) interval, which is not allowed in VSI because it destroys the switching devices. The operation of ZSI has an additional ST state to boost the dc-link voltage besides the eight switching states in conventional converters, i.e. six active and two null vectors. This study proposes a new unified control method for the Z-source inverter family (ZSI), also called the One Dimension for Z-Source Inverters (ODZSI) based on the Single-Phase Modulator technique. The attractiveness of the modulation method lies on its extreme simplicity. A simple mathematical model is necessary to develop the ODZSI, and the calculations relative to switching sequence and the duty-cycles determination are highly simplified. The ODZSI is proposed to modulate single-phase H-bridge ZSI. Then, the same concept is extended to modulate three-phase qZSI/ZSI. In addition, the ODZSI can be used to control different impedance-source topologies. To achieve a maximum voltage gain, the ODZSI-MBC_3 is proposed. The shoot-through period is maximized by turning ON all the switches during the zero states, while iii the active states are kept unchanged. The obtained results using the ODZSI-MBC_3 are compared with those obtained with the carrier-based maximum boost control (CB-MBC), showing that the output voltage quality is enhanced with reduced computation burden. In order to reduce the switching losses, the ODZI-MBC_1 is also proposed. By using a carefully selected shoot-through states, the number of the switching transition is significantly decreased as each switch is locked to the positive or negative dc-rail during a period of 2π⁄3. Only two switches of the same leg will turn ON during the shoot through and the three ST times are distributed per two legs per control cycle. Additionally, as compared with space vector techniques, the inverter power losses are decreased, and the total execution time is reduced by 45%. The obtained results ensure the feasibility and validate the performance of the ODZSI. Moreover, due to the simple structure of the proposed control scheme and the reduced total execution time, it can be easily implemented on a slow and cheap controller. The presented concepts have been verified in simulations using Matlab/Simulink and validated experimentally.

13. Title: A Dynamic Wireless EV Charging System with Uniform Coupling Factor and Negligible Power Transfer Fluctuation

To minimize the dependency on the petroleum products, electric vehicles (EV) have been selected as a feasible solution for transportation purpose. EV was introduced with the appearance of the hybrid electric vehicle (HEV), which causes to bring the development of plug-in hybrid electric vehicles (PHEVs). On the other hand, PHEV is responsible for various drawbacks such as the necessity of connecting cables and plug in charger, galvanic isolation of on-board electronics, the weight and size of the charger, and more important safety issues associated with the operation in the rainy and snowing condition. For user friendly and any prevention from the risk by electricity, inductive power transfer (IPT) method has been emerged to charge the EV inductively over the large air gap. There are two types of IPT based EV charging system: stationary and dynamic. High efficiency inductive power transfer (IPT) with low misalignment effect is one of the key issues for dynamic charging electric vehicle (EV) system. This research presents an advanced concept of analysis and design of transmitter and receiver coils with a special arrangement of coil assembly for dynamic charging of EV. In each transmitter coil, large rectangular section is series connected with two zigzag- shaped small rectangular sections. These small sections are back-to-back series connected and located inside the large rectangular section. Adjacent pair of proposed transmitter coil with back-to-back series connection, named as extended DD transmitter is used throughout this paper. One of the contributions of this work is uniform surface magnetic flux distribution, obtained by the zigzag-shaped rectangular sections. Designing of the proposed transmitter and receiver with the simulation results are done by the 2-D finite element analysis (FEA). In case of extended DD transmitter, negligible power transfer fluctuation is the major contribution regardless of the horizontal (x-direction) misalignment of the receiver coil. Justification of the coil design is performed  with the load independent voltage gain and power transfer fluctuation characteristics. A compensation technique named LC-LC2 is used in order to obtain the load independent operation and the better tolerance of the air gap variation. Experimental results prove that, power transfer fluctuation with load independent unique voltage gain is within ±6% and efficiency is about 93% under any horizontal (x-direction) misalignment condition of the receiver coil with an air gap of 140mm

14. Title: Model Predictive Control Based On Lyapunov Function and Near State Vector Selection of Four-Leg Inverter

Due to the evolution of high processing microprocessors, the model predictive control (MPC) has been widely used in power electronic applications. The model predictive control technique utilizes all the available voltage vectors of power inverter to improve the predictive current control performance.  In spite of simplicity, flexibility and fast dynamic response, the conventional model predictive control (C-MPC) has a drawback of computational burden. The computational burden of C-MPC is expensive due to utilize all available voltage vectors of a power inverter to predict the future behavior of the system. This dissertation has focused on Lyapunov model predictive control (L-MPC) methods, in which Lyapunov control law is employed in the cost function to minimize the error between the desired control variables and the actual control variables of a three-phase four-leg inverter to optimize closed-loop system performance. The proposed control algorithm takes advantage of a predefined Lyapunov control law which minimizes the required calculation time by the Lyapunov model equations just once in each control loop to predict future variables. In this dissertation, a near state vector selection-based model predictive control (NSV-MPC) scheme is also proposed to mitigate the common-mode voltage (CMV) with reduced computational burden. The proposed control technique adopts 6 active voltage vectors in the discrete predictive model among 14 available active vectors based on the position of the future reference vector. The position of reference currents is used to detect the voltage vectors surrounding the reference voltage vector in every sampling period. At last, the influencing factor of CMV is revealed based on switching state combination and then the CMV weighting factor is introduced in the cost function to make balance in the ripple content of load currents and the mitigation of CMV. The switching state pattern is selected according to peak to peak value of CMV and CMV weighting factor is related to peak value of CMV and a user defined co-efficient. The stability of the system is ensured through Lyapunov function with the help of backsteping control method.  L-MPC technique improves the digital speed by 23.8% compared to C-MPC and it reduces current tracking error confined within 0.65A and THD in the variation of inverter control parameters of a three-phase four-leg inverter. The CMV can be bounded within one-fourth of the dc-link voltage of a three-phase four-leg inverter using the proposed NSV-MPC technique. MATLAB/Simulink software environment is used for the simulation and the LabVIEW Field programmable gate array (FPGA) rapid prototyping controller is used to validate the proposed control scheme. The results showed that the proposed control techniques had better performance as compared to the C-MPC.

15. Title: Design of A Modified Class EF2 Inverter For Electric Vechile Charging Through Wireless Power Transfer

Wireless power transfer (WPT) also referred as inductive power transfer (IPT) has the huge potentiality to revolutionize our way of electricity usage. This technology has found many applications like charging autonomous mobile devices like mobile phone, autonomous guided vehicles as well as industrial process system, biomedical implant and electric vehicle charging. These applications involve power transfer from small level (1 W) to a high level (10-20 kW) with a large air gap (5-50 cm).

A complete IPT system usually consists of several stages: grid or utility AC to DC conversion, the rectified DC to high-frequency AC conversion, primary compensation, WPT coils (loosely coupled transformer), secondary compensation and AC/DC/DC conversion. Among these, high-frequency DC/AC conversion plays a vital role to transfer high power, to increase gap distance and overall system efficiency. The focus of this research is to design and evaluate a single switch high-frequency resonant inverter for WPT vehicle charging application capable of transferring power up to 3 kW. Single switch resonant inverter topologies are potential for WPT application. The capability of operating with high frequency and high power, ease of control circuit design and compactness are some of the main features of these types of inverters.

In this research, a modified single switch resonant inverter termed as class EF2 will be designed and evaluated for standard vehicle charging system frequency (85-100 kHz). This is the major contribution of this research.  A detail mathematical model is developed which includes the significant parasitic elements of the overall system on this frequency range. Furthermore, a series tuned passive resonant circuit is used for second harmonic termination which reduces the switching stress significantly from all other single switch topology. The placement of this passive resonant circuit for reducing switch stress and input DC-feed inductance characteristic is also analysed. Power transfer capability, switch stress and reactive power circulation during misalignment and coupling variation condition have been evaluated experimentally with constant frequency and with a frequency variation of 5-10%. Finally, inverter efficiency on perfectly align to 30% misalignment and variation of output voltage with load variation will be evaluated.

16. Title: Model Predictive Current and Reactive Power Control Fed by Multilevel Four-leg Indirect Matrix Converter Operating Under Unbaalanced Voltage Supply

This research works focused on model-based predictive current control which was applied to indirect matrix converter. Indirect matrix converter (IMC) is an alternative solution of conventional ac/ac converter. Its energy storage-less structure enables the construction of a compact power converter circuit. The feature of IMC was extended with multilevel concept to improve the output waveform quality by unifying the conventional four-leg indirect matrix converter with a four-switch circuit resembling a dual asynchronous buck-circuit to synthesise the multilevel output voltage. The unbalance voltage supply posed a real challenge in implementing the ac/ac power converter. In practice, the matrix converter is supplied by the utility grid which is prone to become unbalance due to the asymmetric load connected to the grid. Being energy storage-less solution, the unbalance voltage supply has a direct effect on the load current regulation due to the fluctuated active and reactive power. Hence, there is strong mutual coupling between the supply and the output. Any disturbance in the input volt ages can be immediately reflected to the output voltages. For most of the modulation strategies, the unbalanced and non-sinusoidal input

voltages can cause unwanted output harmonic voltages. This study is aimed to maintain excellent load current reference tracking while minimising the instantaneous reactive power for both balance and unbalance voltage supply. In order to achieve this objective, the conventional cost function was properly modified to adapt to the unbalance supply voltage. The predictive algorithm computes the one-step prediction load current and reactive power. The proposed control strategy uses the discrete nature of the system to predict the future load current and reactive power behaviour to perform switching optimisation using a minimum cost function criterion. This study proposed an optimized rectifier switching strategy to ensure positive fictitious dual dc-link voltage at any instant and reduce the computational burden of the controller. In order to evaluate the robustness of the proposed control, different combinations of balance or unbalance supply voltage

with balanced or unbalanced loading conditions were pre-validated using Matlab/Simulink®. It is followed by an FPGA based experimental works to validate the proposed control scheme. The integration of this circuit has resulted in a significant reduction of current harmonics.  the four-leg structure, the proposed topology was adequate for balance or unbalance load. Moreover, the modified cost function enabled an optimum reactive power minimisation throughout the wide range of voltage supply unbalance. The experimental assessment confirmed that the proposed control could cater for the wide range of degree of unbalance. In addition, it revealed an outstanding load current reference tracking with harmonics distortion below 5% while maintaining

relatively small instantaneous reactive power. Findings from this study is that, subject to sufficient active power, outstanding load current tracking was achieved, and the instantaneous reactive power can be optimally reduced. The proposed system exhibits π‘‡π»π·π‘£π‘œbelow 30% and 𝑇𝐻𝐷iπ‘œ% below 5% based on IEEE S td 519™ -2014 and IEC 61000-3-6. This study makes noteworthy contribution to the ac/ac conversion that can be applied to systems such as wind turbine and hydro power plant.

17. Title: Fractional Order Sliding Mode Control for Speed Control of PMSM

A fractional order sliding mode control with PID sliding surface design (FOSMC-PID) is proposed in this research. This controller incorporates fractional calculus which has a slower energy transfer compared to integer order calculus in order to suppress the chattering. Stability of this controller is analyzed using Lyapunov stability theorem. Simulation results proved that the proposed FOSMC speed controller performs as a robust and fast anti-disturbance controller to regulate the speed of a PMSM and proven its advantages against SMC controllers. The proposed sliding surface design also improves the FOSMC in terms of torque ripple reduction, chattering reduction and anti-disturbance properties, compared to FOSMC with PI or PD sliding surface.


Contact Details

POWER ELECTRONIC AND RENEWABLE ENERGY RESEARCH LABORATORY (PEARL)
Department of Electrical Engineering
Faculty of Engineering
University Of Malaya
50603 Bangsar
Kuala Lumpur
Tel: +603 7967 6851
Fax: +603 7967 5361
Email: saad@um.edu.my
Website: pearl.um.edu.my