Nathan Weise

A Single-Stage Dual-Active-Bridge-Based Soft Switched AC–DC Converter With Open-Loop Power Factor Correction and Other Advanced Features

A dual-active-bridge-based single-stage ac/dc converter may find a wide range of emerging applications such as interfacing plug-in hybrid vehicles with the ac grid, interconnection of dc grid, etc. This type of converter can be used due to unique features such as 1) high-frequency isolation resulting in a) high power density and b) safety and voltage matching; 2) bidirectional power flow; 3) soft switching leading to higher efficiency. In this paper, a modulation strategy has been proposed that results in 1) open-loop power factor correction; 2) zero current switching in the ac-side converter for all load conditions; 3) linear power relationship for easy control implementation; and 4) Zero voltage switching in the load side converter. The converter with the proposed control has been analyzed. Simulation and experimental results on a 1-KW prototype confirm the advantages.

Universal utility interface for Plug-in Hybrid electric vehicles with vehicle-to-grid functionality

This paper proposes a novel topology for Electrical Vehicles and Plug-in Hybrid Electrical Vehicles with controllable power factor with 3-phase input and unity power factor with single phase input. The proposed on-board topology provides bidirectional power flow to/from the grid, low weight, low volume, and isolation. A control scheme is devised and a complete simulation of power control is performed over varying loads, varying input voltages, three phase or single phase input, and switching schemes. Simulation results are presented that demonstrate the ability to control power flow and synthesize the grid currents to be sinusoidal.

Advanced modulation strategy for a three-phase AC-DC dual active bridge for V2G

The introduction of Plug-in Hybrid Electric Vehicles (PHEV) and Electric Vehicles (EV) into the consumer market provides opportunities and challenges to implement Vehicle-2-Grid (V2G). V2G is a vehicle that can connect to the grid and consume power to charge its battery pack or supply power to the grid. This paper presents research on a novel converter that implements bidirectional power flow between the grid and a vehicles battery pack. The main advantages of this converter are the following: i) soft switching for all switches of the input converter independent of the load, Zero Current Switching (ZCS) ii) The switching of the input converter is simplified i.e four-step commutation is not required for the four quadrant switches of the input side converter iii) The average power flow through the converter is a linear function of the control variable so the control is simple iv) open loop input power factor correction, v) high power density, vi) isolation. The entire topology has been simulated with the proposed modulation method and simulation results confirm the analytical predictions.

A bi-directional, isolated, single-stage, DAB-based AC-DC converter with open-loop power factor correction and other advanced features

In this paper, a control method for an AC-DC converter is proposed that simultaneously has the following features: a) galvanic isolation b) bi-directional power flow, c) Zero Current Switching (ZCS) for the primary side switches and Zero Voltage Switching (ZVS) turn-on for the secondary side, d) linear power relationship for easy control implementation, e) unity power factor with open-loop control and f) single-stage power conversion. It is thoroughly analyzed by first assuming it to be a DC-DC converter in a push-pull topology and then extending the results to analyze an AC-DC converter. The conclusions of the analysis are confirmed by simulations.

DQ current control of a bidirectional, isolated single-stage AC-DC converter

Electric vehicles provide portable energy storage that can be used in Vehicle-to-Grid (V2G) applications. In order to source power to the grid, the power electronics on-board these vehicles must be bidirectional. A single stage bidirectional isolated AC-DC converter is discussed. A modulation scheme for this topology is proposed to provide control of real and reactive power. A control scheme is coupled with the modulation and allows the topology to act as an inductive or capacitive or load while sinking or supplying power. The proposed modulation scheme can charge the electric vehicle battery as well as provide ancillary services to the grid. The modulation and control scheme are analyzed and discussed. Simulation and hardware results are presented.

A Fast On-Line Diagnostic Method for Open-Circuit Switch Faults in SiC-MOSFET-Based T-Type Multilevel Inverters

On-line condition monitoring is of paramount importance for multilevel power converters used in safety-critical applications. A novel on-line nonintrusive diagnostic method for detecting open-circuit switch faults in silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs)-based T-type multilevel converters is introduced in this paper. The principle of this method is based on monitoring the abnormal variations of the dc-bus neutral-point current in combination with the existing information on instantaneous switching states and phase currents. Advantages of this method include faster detection speed and simpler implementation compared to other existing diagnostic methods in the literature. Moreover, this diagnostic method is immune to the disturbances of inverters dc-bus voltage unbalance and load unbalance. In this method, only one additional current sensor is required for measuring the dc-bus neutral-point current; therefore, the implementation cost is low. Simulation and experimental results based on a lab-scale 20 kVA adjustable speed drive with a three-level SiC T-type inverter validate the effectiveness and robustness of this novel diagnostic method.

A fault-tolerant topology of T-Type NPC inverter with increased thermal overload capability

Reliability of multilevel power converters has received increased attention over the past few years, due to the relatively high component failure probability caused by the large number of switching devices utilized in the converter topologies. Thus, the fault-tolerant operation of multilevel converters plays an essential role in safety-critical industrial applications. This paper introduces an improved fault-tolerant inverter topology based on the conventional three-level T-Type neutral-point-clamped (NPC) inverter. Unlike other existing three-phase four-leg fault-tolerant inverter topologies, the fault-tolerant T-Type inverter topology proposed here can significantly enhance the overall thermal overload capability of the inverter, in addition to providing desired fault-tolerant capability. The operating principle of this proposed fault-tolerant T-Type inverter is detailed in this paper, and simulation results are presented to verify the advantages of this improved inverter topology.

DQ current control of a bidirectional, isolated, single-stage AC-DC converter for vehicle-to-grid applications

Electric vehicles can provide a viable network of distributed energy storage and provide ancillary services to the grid, (Vehicle-to-Grid, V2G), but Electric Vehicle chargers need to be bidirectional in order to provide power back to the grid. In this paper, dq current control is proposed using a novel bidirectional, isolated, single stage AC-DC converter. Unity open loop power factor has been achieved in previous work using the novel topology but relies on a non-distorted voltage waveform to achieve unity power factor and lacks control of reactive power. The single phase input filter equations are transformed into the rotating dq reference frame by generating an imaginary beta axis. The filter dynamics are analyzed and controllers are designed for dq input currents. A phase shift component is added to the modulation scheme allowing control of the phase and magnitude of the converters input current. The topology and control scheme is simulated in PLECS. Simulation results are presented for various operating points and validate the theoretical analysis. The proposed control strategy implements real and reactive power control which is essential for V2G applications and the topology has the advantages of high switching frequency, isolation, voltage matching, high power density, and reduced size compared to the conventional cascaded isolated AC-DC topologies.

DC ripple current rejection in a bidirectional SiC single-phase AC-DC converter for V2G application

Single phase electric vehicle battery charging converters are bulky due to electrolytic capacitors. These capacitors are used to reduce the voltage ripple in the dc bus. These electrolytic capacitors occupy significant volume and suffer from reliability issues. The required capacitance can be greatly reduced by rejecting the ripple current in the dc bus. The ripple current in the dc bus is rejected at the cost of an additional half-bridge inverter. The half-bridge inverter injects a current out of phase in reference to the dc bus ripple current. The current is injected by applying a voltage across an energy storage element (Inductor). The voltage across the energy storage element is controlled by the dutycyle of the half-bridge. A mathematical relationship between the voltage applied across the energy storage element and the ripple current in the dc bus is derived. Analysis of the ripple current rejection is performed on a Dual Active Bridge (DAB) based SiC single phase AC-DC converter capable of sinking or sourcing real and reactive power. Simulation results are presented verifying ripple current rejection in the dc bus for various operating conditions. Average modeling of the inverter leg currents over a switching cycle is also presented to highlight distinct inverter leg current profiles.

A Current-Dependent Switching Strategy for Si/SiC Hybrid Switch-Based Power Converters

Hybrid switches configured by paralleling Silicon (Si) Insulated Gate Bipolar Transistors (IGBT) and Silicon Carbide (SiC) Metal-Oxide Semiconductor Field-Effect Transistors (MOSFET) have been verified to be a high-efficiency cost-effective device concept. In this paper, a current-dependent switching strategy is introduced and implemented to further improve the performance of Si/SiC hybrid switches. This proposed switching strategy is based on a comprehensive consideration of reducing device losses, reliable operation, and overload capability. Based on the utilization of such Si/SiC hybrid switches and the proposed switching strategy, a 15-kW single-phase H-bridge inverter prototype was implemented and tested in the laboratory. Simulation and experimental results are given to verify the performance of the hybrid switches and the new switching strategy.