Hussain S. Athab

A High-Efficiency AC/DC Converter With Quasi-Active Power Factor Correction

This letter presents a novel ac/dc converter based on a quasi-active power factor correction (PFC) scheme. In the proposed circuit, the power factor is improved by using an auxiliary winding coupled to the transformer of a cascade dc/dc flyback converter. The auxiliary winding is placed between the input rectifier and the low-frequency filter capacitor to serve as a magnetic switch to drive an input inductor. Since the dc/dc converter is operated at high-switching frequency, the auxiliary windings produce a high frequency pulsating source such that the input current conduction angle is significantly lengthened and the input current harmonics is reduced. It eliminates the use of active switch and control circuit for PFC, which results in lower cost and higher efficiency. In order to achieve low harmonic content, the input inductor is designed to operate in discontinuous current mode. Operating principles, analysis, and experimental results of the proposed method are presented.

A Single-Switch AC/DC Flyback Converter Using a CCM/DCM Quasi-Active Power Factor Correction Front-End

This paper discusses the major issues that exist in the single-stage ac/dc converters with power factor correction (PFC) and presents a novel converter based on a quasi-active PFC scheme. Two additional windings wound in the transformer of a conventional dc/dc flyback converter are used to drive and achieve continuous current mode operation of an input inductor. In addition, direct energy transfer paths are provided through the additional windings to improve the conversion efficiency and to reduce the dc bus capacitor voltage below 450 V for universal line applications. The proposed converter can be easily designed to comply with IEC 61000-3-2 Class D requirement and to achieve fast output voltage regulation. By properly tuning the converter parameters, a good tradeoff between efficiency, dc bus capacitor voltage stress, and harmonic content can be achieved. Operating principles, analysis, and experimental results of the proposed method are presented.

Power and Voltage Balance Control of a Novel Three-Phase Solid-State Transformer Using Multilevel Cascaded H-Bridge Inverters for Microgrid Applications

This paper presents a new application of power and voltage balance control schemes for the cascaded H-bridge multilevel inverter (CHMI)-based solid-state transformer (SST) topology. To reduce load on the controller and simplify modulation algorithm, a master-slave control (MSC) strategy is designed for the dual active bridge (DAB) stage. The master controller executes all control and modulation calculations, and the slave controllers manage only device switching and protection. Due to the inherent power and dc-link voltage unbalance in cascaded H-bridge-based SST, this paper presents a compensation strategy based on three-phase dq decoupled current controller. An optimum zero-sequence component is injected in the modulation scheme so that the three-phase grid currents are balanced. Furthermore, to tightly regulate the output voltage of all the DAB modules to target value, a dynamic reference voltage method is also implemented. With this proposed control method, the three-phase grid currents and dc-link voltage in each module can be simultaneously balanced. Finally, simulation and experimental results are presented to validate the performance of the controller and its application to microgrid SST.

PV Isolated Three-Port Converter and Energy-Balancing Control Method for PV-Battery Power Supply Applications

A photovoltaic (PV)-based stand-alone power system is usually used to manage the energy supplied from several power sources such as PV solar arrays and battery and deliver a continuous power to the users in an appropriate form. Traditionally, three different dc/dc converters would have been used. To reduce the cost and improve the power density of the power system, an integrated solution of PV isolated dc/dc three-port converter (TPC) is proposed in this paper. Zero current switching can be achieved for all main diodes and MOSFETs to improve the efficiency, and a continuous input current of solar array is maintained by adding a magnetic switch derived from a fourth winding of the half-bridge transformer. Based on the energy-balancing part formed by boost, the control methods for the single module to realize maximum power point tracking (MPPT), battery charge control, and main bus regulation are proposed. The power system control method for multimodules in parallel is also derived, and the operation of the TPC power system can be transited between conductance mode and MPPT mode automatically. Finally, the experimental results verify that the proposed TPC, together with the proposed control method, meets the requirements of a high-power-density stand-alone PV-battery power system.

An Efficient Single-Switch Quasi-Active PFC Converter With Continuous Input Current and Low DC-Bus Voltage Stress

This paper proposes a novel single-switch quasi-active power factor correction (PFC) converter based on two flyback dc/dc modules. To achieve a high efficiency, part of the input power is directly transferred to the load by the first dc/dc module. The rest of the input power is stored in the dc-bus capacitor and reprocessed by the second dc/dc module. Together, the dc-bus capacitor and the second dc/dc module also serve as a regenerative snubber. Furthermore, a quasi-active PFC circuit is provided to improve the power factor and to ensure the continuous current mode (CCM) operation of the input inductor without the need for sophisticated feedforward sensing and control mechanism. The quasi-active PFC circuit is driven by a magnetic switch, through the tertiary winding of the transformer of the first flyback module. The input current harmonics of the proposed converter meet the IEC 61000-3-2 (Classes A, C, and D) requirements. The dc-bus capacitor voltage is always less than the input voltage regardless of the load condition and is fairly invariant to large variations of the input voltages. High power factor with CCM operation and fast output voltage regulation have been achieved through a single-loop controller. Operating principles, analysis, and experimental results are presented to verify the effectiveness of the proposed converter.

A Transformerless DC–DC Converter With Large Voltage Ratio for MV DC Grids

This paper proposes a transformerless dc-dc converter, which features a large voltage ratio, for medium-voltage dc (MVDC) applications. The proposed converter combines a boost converter with a series-parallel resonant converter which enables soft switching of the power switches and diodes. Further, the power switches and diodes of the proposed converter experience lower voltage stresses compared to the other topologies. The proposed converter is modular and, therefore, permits series and/or parallel connection of multiple units for the desired voltage and/or power ratings. This paper discusses the principles of operation, analysis, and design of the proposed converter. Simulation and experimental results are presented to demonstrate the effectiveness of the proposed converter.

A Cost Effective Method of Reducing Total Harmonic Distortion (THD) in Single-Phase Boost Rectifier

Due to its simplicity, the discontinuous conduction mode boost rectifier is potentially the least expensive active line-harmonics reducing circuit. The line current however, shows considerable distortion when the peak input voltage is close to the output voltage. This paper proposes a simple, low-cost method to reduce the line harmonics. A periodic voltage signal is injected in the control circuit to vary the duty cycle of the boost switch within a line cycle so that the third-order harmonic of the input current is reduced and the THD is improved. The proposed technique eliminates the additional harmonic generator, phase detecting and phase-locking circuits, which is proposed in the literature. Instead we can utilize the output voltage of the rectifier in the boost converter in order to modulate the duty cycle of the boost switch. As a result, the injected signal is naturally synchronized with line current. Simulation and experimental results are presented to confirm the validity of the method.

Electric vehicle charging station using a neutral point clamped converter with bipolar DC bus and voltage balancing circuit

The automotive industry is making important changes towards the electrified transportation. Several Electric Vehicles (EVs) and Plug-in Hybrid EVs are currently on the market offering a clean and environment friendly alternative to conventional vehicles. However, limited mileage capacity and long refueling times have lead to a lukewarm reception from the consumers. In order to reduce the charging time fast charging architectures are being developed, usually as off-board solutions located in public installations. This paper presents a centralized charging station architecture, using a bipolar dc grid to power off-board chargers and integrate of DGs and storage systems. The central converter topology is an NPC and a novel balancing technique is implemented to extend the operating range of the power converter.

Voltage injection switching inductor (VISI) method for fast transient response in switch mode power supplies

A fast transient response to a step load change is very essential in a switch mode power supply. The transient response can be improved by means of feedback control method. There are two feedback control methods widely used for SMPS, they are voltage mode control (VMC) and peak current mode control (PCMC). A simulation study on these feedback control methods has been done using Matlab/Simulink. It is found that the PCMC helps the SMPS for a faster transient response compared to the VMC. However, there are a few disadvantages of the PCMC which make it not possible for further transient response improvement. Hence, in this paper a novel feedback control technique is presented and it is called voltage injection switching inductor (VISI). This feedback control method provides a better transient response compared to PCMC. Detailed explanations of the novel method and simulation results are presented in this paper. The simulation results show improvement in terms of fast transient response.

Single-phase single-switch boost PFC regulator with low total harmonic distortion and feedforward input voltage

The paper proposes a simple harmonic injection technique with feedforward control to modulate the duty cycle of the boost converterpsilas switch. With this technique a low total harmonic distortion (THD) of the rectifier current can be achieved with a good transient performance which reduces the rectifierpsilas output voltage overshoots during step-up line voltage transients. It is found that third-order harmonic, which is the lowest order harmonic, can be attenuated by adjusting the modulation index (m) of the injected signal. The injected duty cycle variations are naturally synchronized with the input voltage without using an additional harmonic generator and expensive phase-detecting, phase-locking circuits. In addition, to obtain nearly constant harmonic content over a wide range of load variation, a modulation index m is used to update the injected signal with a fraction of the feedback output voltage loop, which reflects the load changes. Simulation and experimental results are presented to confirm the validity of the method.