Back-to-Back MMC based Power Electronic Transformer has recently been proposed for the integration of wind energy systems, renewables and storage to medium voltage grid with advantages of decreased transformer size, increased efficiency, potential for virtual inertia to the grid and others. The unique arrangement of the High-frequency link MMC(HF-MMC) interfaced to the two-level voltage source converter(2L-VSC) at the HF-link presents the need to synthesize design equations targeting the required performance during operation. Design of the HF link parameters are discussed to simultaneously satisfy maximum power transfer, soft-switching at 2L-VSC, HF-link current THD, unity displacement power factor(DPF) operation at the HF-link and DC bus utilization. Expressions for the soft-switching current for the 2L-VSC, minimum and maximum transformer turns ratio, power transfer at unity DPF operation have been derived to aid in the design process and provide insights into the operation of the topology. Extensive simulation results in MATLAB/SIMULINK and real-time simulations in OPAL-RT HIL have been presented to validate the design and analysis.

Cascaded H-bridge (CHB) based electric vehicle chargers are widely recognized for their modularity, scalability, and robust fault-tolerant capability. Such converters are often modulated using level-shifted carrier-based PWM (LSPWM) schemes due to computational simplicity and ease of implementation, but results in significant power imbalance among the modules. This power imbalance can be mitigated by reassigning carriers to modules, called Carrier-Reassignment PWM (CR-PWM). A First-In-First-Out (FIFO) based CRPWM is very easy to implement and provides some improvement over LSPWM, but fails to achieve perfect power balance. This paper proposes a novel carrier-reassignment scheme specifically designed for a 17-level CHB stage with eight reassignments per fundamental cycle, resulting in near-perfect power balance among modules. The redistribution of power also results in improvements in semiconductor losses - both conduction and switching loss. Loss models for the semiconductor devices were created through hardware double-pulse tests, SPICE and PLECS models, and integrated with MATLAB/Simulink to validate the proposed PWM scheme.

The Cascaded H-Bridge (CHB) multilevel inverter is a modular topology that uses multiple series-connected submodules (SMs) fed by individual DC sources. The commonly used level-shifted-carrier PWM scheme causes vast disparity in the share of power processed by various SMs, resulting in an unequal electrical and thermal stress, thereby reducing SM reliability. Ensuring equal power processing among all SMs is critical especially in applications such as battery and solar photovoltaics. This paper proposes two computationally efficient and easy to implement carrier-reassignment PWM techniques that result in perfect power balance under unity power factor (UPF) and zero power factor (ZPF) conditions. Mathematical analysis of real and reactive power is used to develop these modulation schemes, followed by validation using MATLAB/Simulink models. A comparison of real and reactive power balance are also provided for various PWM schemes at various power factors.

Recent surge in the adoption and grid-integration of renewable distributed energy resources (DERs) at utility scale has spurred the interest in power-electronic architectures for interface at medium-voltage (MV) grid. The constant endeavor to achieve higher power densities has brought forth the need for multi-port converter topologies capable of integrating heterogeneous energy resources through a common interface scheme. In this paper, a novel high-frequency link transformer based multi-port power converter termed Distributed-Phase-MMC (DP-MMC) is proposed for the grid-integration of DERs at MV level. The topology has several advantages such as modularity at sub-module as well as sub-system level, decoupled/independent power flow through its input ports and reduced voltage stresses in the HF-transformer windings. A simplified equivalent circuit and a phasor-based analysis are proposed for the system, which provide qualitative and quantitative insights into the power transfer mechanism across different ports. In addition, a control scheme is proposed based on this analysis for the operation of the system while injecting the required active/reactive power to the grid. The proposed scheme achieves the critical objective of unifying dispatchable storage systems with intermittent renewable energy systems at MV-level. Detailed MATLAB-Simulink results validate the overall operation and control of the proposed multi-port DP-MMC architecture.

In recent times, wind power generation has become one of the most promising technologies to generate electricity from the renewable energy sources. This paper presents an extremely low-cost wind turbine-generator emulator (WTGE), a scaled down model of an actual 1MW wind turbine-generator. It consists of: real-time wind speed profile, mathematical model of the turbine, PMSM under vector control and its control to achieve maximum power point across varying wind speed. This system was designed using a proprietary custom designed model based numerical simulation and rapid real-time prototyping platform called Workbench. This platform seamlessly allows transitioning from simulation to real-time. The simulation results are validated with the help of hardware setup and are presented in this paper.

This paper presents a carrier based implementation of Space Vector Pulse Width Modulation (SVPWM) of dual matrix converters (MCs) using synchronously rotating vectors. Usage of only synchronously rotating vectors ensures the elimination of differential and average common mode voltages which lead to circulating currents and electromagnetic interference (EMI) problems respectively. The proposed strategy is an alternative way to achieve SVPWM, but it doesn't involve the knowledge of space vectors once it is derived. Also, it avoids any trigonometric and division operations that could be needed to implement the SVPWM using the general space vector approach.

In this paper, the three-port Ćuk converter interfaces one unidirectional input power port (envisioned to be a DC power source such as PV, or fuel cell) and two bidirectional output ports, representing the grid-tied inverter dc bus and a storage port respectively, and combines all the magnetics into a single core. The well-known property of the basic Ćuk converter that emulates an ideal dc-dc transformer (zero ripple terminal currents) is extended to three ports and is analyzed in detail. Two methods, one involving the physical structure of the core, and the other, a circuit-based dual approach, which is directly related to the core structure, are applied to solve the zero-ripple problem, and the accuracy of one of them over the other is verified with simulation results. Three different power transfer modes in this three-port converter are compared using the two methods mentioned above.

This paper presents a single stage, bi-directional multi-level converter topology with a multi-winding medium frequency transformer (MFT) isolation to interface a low voltage DC with a 3-phase high voltage grid. The proposed topology can be used for integrating 3-ph utility grid with various low voltage renewables like solar photovoltaic, fuel cells etc. The transformer secondary windings in each phase have unequal turns ratio. This asymmetry introduced in the transformer turns ratio allows to generate more output voltage levels, using less number of semiconductor switches leading to a reduced footprint. The transformer secondary side has AC-AC converter modules which are pulse width modulated. This results in the elimination of the harmonics at multiples of grid frequency, resulting in reduced size of filter inductance. The paper also shows the winding procedure to interleave the windings resulting in lower leakage inductance to minimize the problem of leakage commutation. The proposed topology is simulated using MATLAB/Simulink.

This paper presents a novel DC-AC inverter based on a high frequency power electronic transformer. It makes use of an adapted push-pull converter on the primary side of the transformer to apply a high frequency alternating voltage. This keeps the transformer flux low and transformer size small, reducing the cost of materials but at the same time keeping the power density high. The secondary side is a set of two bi-directional switches that synthesize the desired output voltage in a cycloconverter manner, helping to reduce the total harmonic distortion. A state space control strategy and commutation of the secondary side is also presented. The topology and control strategy has been confirmed with simulation results.

This paper presents the design, characterization, and modeling of a power electronic converter based around Silicon Carbide (SiC) MOSFETs. A practical characterization procedure is proposed which takes a circuit-level approach, as opposed to a device-level approach, using only the power electronic circuit and no additional test circuitry. The converter circuit is general enough that it can represent a dc chopper circuit or an output phase of an inverter. The design of the converter, including the SiC-specific gate drive circuit, is described. The hardware setup was operated at frequencies up to 200 kHz and efficiencies up to approximately 99% were recorded. A model for predicting converter and driver losses at different load currents, dc bus voltages, and operating temperatures was constructed; the predictions from the model were in good agreement with the measurements.

Grid integration of multiple renewable energy sources using a power electronic transformer (PET) topology is presented in this paper. A modular multilevel converter (MMC) is proposed as the power converter on the high voltage grid side to generate high frequency sinusoidal voltages. A single multi-winding high frequency transformer (HFT) interfaces different wind generators/photovoltaic arrays using many H-bridge converters and PWM inverters. The leakage inductance of the transformer acts as the smoothening filter for the current through the HFT. With sinusoidal voltages and smooth currents through the transformer, there is significant reduction in transformer losses and also natural commutation of leakage energy is obtained. The operating principle, modulation and control of the proposed PET is validated by simulations in MATLAB/Simulink.

A three-port converter (TPC) based on the Ćuk topology is proposed in this paper. The proposed converter interfaces one unidirectional input power port (envisioned to be a DC power source such as PV, or fuel cell) and two bidirectional output ports, representing the grid-tied inverter dc bus and a storage port respectively. This converter utilizes a single integrated magnetic core on which all the inductor and the transformer windings are wound. The proposed structure utilizes only three power switches, and does not require output capacitors on the output ports on account of the zero-ripple property. Depending on utilization state of the battery, three different power operation modes are defined for the converter. The features of the proposed converter are analyzed and then verified by means of simulation results for different operation conditions.

Power Electronic Transformers (PETs) have been proposed for future power distribution systems as well as for use in adjustable speed drives where space and weight are at a premium. This paper investigates the commutation of Matrix Converter (MC) based PETs where finite leakage inductance is present at the input of the matrix converter and it is no longer purely a voltage port. A PET with reduced number of switches on the primary side is selected for the presented research. This paper compares modulation based on carrier comparison and space vector along with commutations using four-step and dead-time. All these combinations of modulation and commutation are implemented efficiently in a single FPGA chip and some of the experimental results are presented.

A novel hybrid indirect multi level matrix converter has been proposed in this paper. In comparison to the conventional matrix converter the proposed converter makes available the input phase voltages and half phase voltages in addition to the line voltages at the converter output. This increased level comes at the cost of additional bi-directional switches and clamp capacitor. Indirect space vector modulation scheme, for synthesizing the required input current and the output voltage while balancing the input and clamp capacitor voltage, is presented. This converter offers reduced THD and lowered switching stress compared to conventional matrix converter. The effectiveness of the proposed converter has been verified by means of simulation.

This paper presents an analysis and comprehensive comparison between the passive filter component requirements of a matrix converter and a DC-link based back-to-back converter. Proper design of the filter components requires the estimation of the switching frequency components present in various voltages and currents. An accurate estimation of different ripple quantities is presented by simple analytical expressions and verified by MATLAB/Simulink simulations. The filters are designed and a quantitative comparison of the passive components is done.

Modular multilevel converters have emerged as a viable solution over conventional voltage source converters (VSC) for applications in high voltage direct current (HVDC) transmission. Due to modular structure, the converter can reach high number of voltage levels resulting in low switching frequency and near sinusoidal voltage waveforms. This paper proposes new submodule topologies which can result in even higher voltage levels with reduced voltage stress across some switches and lower semiconductor losses. A modified modulation scheme and voltage balancing algorithm is proposed for the new topology and is validated by MATLAB/Simulink simulations. A comprehensive comparative analysis with other available submodule topologies is presented to show the added benefits.

The design and construction of a permanent magnet thrust bearing for a bearingless motor is presented and a measurement technique is proposed to characterize the bearing. Optimal design of a bearingless motor requires the machine designer to be aware of the axial bearing's performance under simultaneous axial and radial displacement. A simple, low-cost test setup which requires only two single-axis load cells is proposed and evaluated to make these measurements on the magnetic bearing stator. The measurement data are found to be in reasonable agreement with finite element calculations and to satisfy Earnshaw's theorem, where the sum of stiffnesses in the three axes must be zero. The measurement technique displayed good test-retest reliability, with repeated radial force data having an average standard deviation of 2.1% for radial displacements greater than 0.5 mm and axial force data having a typical error of 0.9%.

A direct power converter based variable frequency drive with three-level input/output waveforms is presented. The proposed drive generates common-mode free output voltages while drawing sinusoidal input currents. Like the conventional matrix converter, the input and output quantities are controlled simultaneously with one controller. Unlike the conventional matrix converter, the circuit always provides a freewheeling path for the load and source currents, thus eliminating the clamp circuit. Further, zero voltage switching (ZVS) of the front-end is naturally achieved. Functional operation of the converter is demonstrated using a hardware prototype. The drive is evaluated for the output common-mode voltage as well as its performance to load and source transients. Extension of the presented drive to an open-end winding drive with enhanced voltage gain is also discussed in context of previous research.

This paper presents a users' perspective of simulation in power electronic and motion control systems. The rationale for simulation in research, education and in the design process, and the details of how simulation is carried out are discussed. Characteristics of a reliable simulation program are outlined and the hierarchical approach to simulation is stressed. Numerical solution issues in the simulation of "stiff" systems such as power electronics and motion control are discussed in general terms. A brief overview of the widely used simulation programs is provided along with the challenges in modeling the semiconductor devices. In conclusion, observations are made with respect to the future role and nature of computer simulations.>