Masood Moghaddami

A New Topology of Higher Order Power Filter for Single-Phase Grid-Tied Voltage-Source Inverters

In order to reduce the influence of the grid harmonic currents and voltages, harmonic compensation is regularly implemented for a grid-tied inverter. In this study, a new topology of a higher order power filter for single-phase grid-tied voltage-source inverters, named L(LCL)2, is presented. The subscript is added to the name to prevent confusion with the LLCL filter. In the proposed design, the inverter side inductance is divided into three parts, and the grid side inductor is removed. Also, an additional resonant branch at the double of the switching frequency is added to the traditional LLCL filter to attenuate high-frequency harmonics. The overall inductance of the recommended filter is smaller than the LLCL filter. A comparative study and discussions on the subject of the traditional LLCL filter and the proposed L(LCL)2 filter have been conducted and assessed through an experimental hardware implementation on a 700 W, 120 V/60 Hz single-phase grid-tied inverter. Furthermore, a straightforward engineering design benchmark is suggested to discover parameters of the L(LCL)2 filter. Moreover, stability analysis, loss analysis and an optimization of the L(LCL)2 filter parameters have been conducted in this study. The analysis shows that in comparison with the LLCL filter, the L(LCL)2 filter not only has lower voltage drop and less total inductor size, but also has improved performance in decreasing high-order current harmonics.

Single-Stage Three-Phase AC–AC Matrix Converter for Inductive Power Transfer Systems

A direct three-phase ac-ac matrix converter for inductive power transfer (IPT) systems with soft-switching operation is introduced. The proposed topology is expected to have a high reliability and extended lifetime due to the soft-switching operation and elimination of short-life electrolytic capacitors. The soft-switching operation will also reduce switching stress, switching loss, and electromagnetic interference of the converter. A variable-frequency control strategy based on the energy-injection and free-oscillation technique is used to regulate the resonant current, the resonant voltage, and the output power. With the use of reverse-blocking switches, the proposed converter can be built with a reduced number of switches (only seven), which will consequently increase the reliability and efficiency and reduce the cost of the converter. The converter operates in eight modes, which are described in detail. With the use of the proposed converter as the primary converter, simulation analysis and experimental implementations on a case study IPT system show that the current regulation control method can fully regulate the output current and output power around user-defined reference values, thus making it suitable for dynamic IPT applications, where the system has inherent variations.

Finite element based design optimization of magnetic structures for roadway inductive power transfer systems

Design optimization of magnetic structures for roadway inductive power transfer (IPT) systems based on 2D finite element analysis (FEA) is proposed. The proposed method can be used to find the optimal structure for IPT systems based on prioritization of different objectives such as efficiency, cost, etc. A Multi-objective genetic algorithm (MOGA) coupled with 2D FEA is used for the co-optimization of primary and secondary magnetic structures. Also, Electromagnetic field (EMF) emissions of the pads are considered to meet human exposure regulations in compliance with standards as defined by International Commission on Non-Ionizing Radiation Protection (ICNIRP). A 1 kW roadway IPT system is investigated as the case study and the results of the optimization are presented using different objective functions.

Pareto optimization of circular power pads for contactless electric vehicle battery charger

Design optimization of circular power pads for inductive power transfer (IPT) systems with applications in electric vehicle battery charger is proposed. A multi-objective optimization coupled with 2D finite element analysis (FEA) is used to find the Pareto-optimal solutions for circular magnetic structures considering different objective functions, such as power transfer efficiency, material cost, and horizontal misalignment tolerance of the IPT system. 2D FEA is used to calculate self and mutual inductances between primary and secondary pads, ohmic loss in coils, core loss in ferrites, stray loss in aluminum shields and electromagnetic field (EMF) emissions of the system. Practical limitations of the power electronic converters such as frequency, VA rating, operating quality factor, and EMF emissions are all considered in the proposed optimization. A 10 kW electric vehicle battery charger IPT system with circular power pads is investigated as the case study and Pareto-optimal solutions for this system are presented. Experimental test results on one of the Pareto-optimal solutions are in good agreement with the calculations using the proposed method. The proposed design optimization method provides a tool for finding highly efficient, flexible and cost-effective solutions for contactless electric vehicle battery charger.

A single-stage three-phase AC-AC converter for inductive power transfer systems

A three-phase ac-ac matrix converter for inductive power transfer (IPT) systems with soft-switching operation and bidirectional power flow is introduced. The proposed converter can generate high-frequency current directly from a three-phase ac power source without a dc link. Unlike conventional ac-dc-ac converters, the proposed converter can provide a high frequency current without any current sag around ac source zero-crossings for IPT systems. The proposed topology is expected to have high reliability and extended lifetime due to the soft-switching operation and elimination of short life electrolytic capacitors. Soft-switching operation will also reduce switching stress, switching losses, and electromagnetic interference (EMI) of the converter. A simple control strategy based on energy injection and free oscillation technique is used as the control method. The proposed converter is comprised only seven switches, which in turn increase the reliability, efficiency and reduce cost. The converter operates in eight modes, which are described in detail. Theoretical analysis and simulation results on a 2kW IPT system, show that the current control method can fully regulate the output current with low ripple which is suitable waveforms for IPT applications.

Self-Tuning Variable Frequency Controller for Inductive Electric Vehicle Charging With Multiple Power Levels

A self-tuning controller for contactless electric vehicle (EV) charging systems based on inductive power transfer (IPT) with multiple power levels is proposed. The multiple charging levels (consisting of ten charging levels) are achieved by controlling the energy injection frequency of the transmitter coil of the IPT system. The proposed controller is capable of self-tuning the switching operations to the natural resonance frequency of the IPT system, and it benefits from soft-switching operations (zero-current switching), which ensures the maximum performance of the IPT system. The proposed controller has such a simple design, which can be implemented based on a simplified control circuit. The simulation of the proposed controller for an inductive charging system at different charging levels is carried out in MATLAB/Simulink. Also the proposed controller with an ac/dc/ac converter is implemented experimentally on an IPT charging system to verify the effectiveness of the controller at different charging levels. The experimental test results conform with the simulation results and verify that the proposed controller effectively enables self-tuning capability and soft-switching operations at different charging levels for IPT-based contactless EV charging systems.

Reduction of Stray Loss in Power Transformers Using Horizontal Magnetic Wall Shunts

The use of a horizontal arrangement of wall shunts is proposed in this paper as a cost-effective way to reduce the stray losses in power transformers. This paper compares the performance of horizontal wall shunts with the available alternative (vertical shunts). A 3-D finite-element analysis (FEA) is used for the calculation of stray losses in tank walls, and other structural parts. A novel hybrid numerical/analytical method is proposed for the calculation of stray losses inside the magnetic shunts. The proposed method is based on the double Fourier series expansions of the magnetic field distribution at the surface of the shunts, which is determined using 3-D FEA. A 200 MVA power transformer is investigated as a case study where the stray losses are calculated with and without the vertical and horizontal shunts. A parametric FEA is carried out to find the optimal placement of the horizontal shunts on the tank walls. Results show that the proposed horizontal magnetic shunts arrangement are as effective as the conventional vertical shunts in reducing the stray losses while reducing the weight of the shields, therefore providing a cost-effective method for magnetic shielding of the transformer tank walls.

A modified higher order power filter for grid-connected renewable energy systems

In order to reduce the influence of the grid harmonic currents and voltages, harmonic compensation is regularly implemented for a grid-tied inverter. In this paper a new topology of higher order power filter for single-phase grid-tied voltage-source inverters (VSI), named L(LCL)2, is introduced. The subscript is added to the name to avoid confusion with LLCL filter. In the proposed design the inverter side inductance is divided into three parts, and the grid side inductor is removed. Also an additional resonant branch at the double of switching frequency is added to the traditional LLCL filter to attenuate high frequency harmonics. The total inductance of this filter is less than LLCL filter with the amount of the grid side inductor. A comparative study and discussions on the subject of the traditional LLCL filter and the proposed L(LCL)2 filter have been conducted and assessed through both experimental hardware implementation and Matlab/Simulink-based simulation on a 700 W, 120V / 60 Hz single-phase grid-tied inverter. Also, a straightforward engineering design benchmark is suggested to discover parameters of the proposed L(LCL)2 filter. It is concluded that, compared with the LLCL filter, the L(LCL)2 filter not only has less voltage drop and total inductor size, but also has better performance on reducing high order current harmonics.

A self-tuning variable frequency control for multi-level contactless Electric Vehicle charger

This paper proposes a self-tuning controller for a multi-level inductive Electric Vehicle (EV) battery charger application. By controlling the energy injection frequency of the Inductive Power Transfer (IPT) system, multiple charging levels (4 in number) are achieved. Maximum performance is leveraged by the proposed IPT system using its capability of self-tuning the switching operations to the natural resonant frequency of the IPT system, thereby benefiting from soft-switching operations (zero-current switching).Either a digital or analog control circuit can be used to implement the proposed controller. The results are shown by simulating the proposed controller with different charging levels using MATLAB/Simulink. These results show that the proposed controller effectively enables IPT-based contactless EV charging at multiple charging levels, with soft-switching operations. This self-tuning capability is specifically useful in IPT systems that have variable resonance frequency.

Model predictive power control approach for three-phase single-stage grid-tied PV module-integrated converter

This paper presents the concept of the three-phase module-integrated converters (MICs) incorporated in grid-tied large-scale photovoltaic (PV) systems. The current-source converter (CSC) with dc voltage boost capability, namely single-stage power conversion system, is proposed for three-phase PV MIC system. A model predictive scheme with low switching frequency is designed to control the proposed topology in such a way that provides a certain amount of active and reactive power in steady-state operation and also provides a proper ratio of reactive power under transient conditions to meet the low voltage ride through (LVRT) regulations. To predict the future behavior of current control values and switching states, a discrete-time model of the MIC is developed in synchronous reference frame. It is demonstrated that the injected active and reactive power can be controlled using minimizing the cost function introduced in the predictive switching algorithm. The proposed structure is simulated in MATLAB/SIMULINK software. The results verify the desired performance of the proposed control scheme for exchanging of both active and reactive powers between the PV MIC and the grid within different operating conditions.