Quasi-Z-source-based bidirectional DC-DC converters for renewable energy applications

This article presents a design, analysis, and implementation of a novel impedance-source-based bidirectional DC-DC converter. The proposed converter employs an impedance network to the existing dual-active-bridge (DAB) circuit. It inherits all the advantages of the DAB converter along with extra benefits. Compared with the traditional isolated DC-DC converter, the proposed converter improved the boost ability of the converter. Also, the converter can withstand the shoot-through phenomenon in an H-bridge, improving the reliability. The converter can work in the normal buck/boost DAB mode when extra boost is not required. The bidirectional feature is inherent along with soft switching capability. It is therefore well-suited for the applications, where wide range of voltage gains are required such as renewable energy systems. The topological configuration and control strategy of the proposed topology in both operational modes are discussed. Simulation and experiments have been carried out to demonstrate the effectiveness of the proposed converter topology. The peak efficiency 97% was observed at the rated load of 500 W

Implementation of a hybrid AC-AC direct power converter with unity voltage transfer

This paper presents a novel hybrid direct power converter (HDPC) which overcomes the two main disadvantages of matrix converters: limited voltage transfer ratio and low immunity to grid disturbance. The proposed converter is formed by integrating a reversible auxiliary boost converter in the dc link of the two-stage matrix converter. Therefore, the HDPC can provide unity voltage transfer ratio even in the case where the supply voltage is highly unbalanced. The proposed converter also preserves most of the inherent advantages of the conventional matrix converter such as: controllable input power factor, sinusoidal supply currents, and bidirectional power flow. A novel predictive current control technique for the HDPC is also proposed for minimum energy storage in the converter. Important aspects of design, control, and implementation of the new HDPC are presented including theoretical analysis and simulations. Experimental waveforms at unity voltage transfer using a laboratory prototype are presented to confirm the viability of the proposed idea

Modelling and Analysis of DC-DC Converters for Bidirectional EV Charging Applications

This thesis is focused on the modelling and analysis of DC-DC converter topologies used for bidirectional charging of electric vehicles. Bidirectional converters are used in vehicle-to-grid (V2G) systems to allow bidirectional power transfer between the vehicle and the grid. Following the investigation in the literature review of potential converter topologies used in V2G applications and modelling techniques, this research proposes the application of the cyclic-averaging method for analysis of the Dual Active Bridge, 4th order resonant CLLC converter, and series compensated Inductive Power Transfer (IPT) converter. First, the cyclic-averaging method is applied for analysis of a phase-shift modulated Dual Active Bridge converter (DAB). For implementation of the cyclic analysis, the operation of the converter is first analysed using a Spice simulation to determine the system’s operation modes and duty cycles. The cyclic-averaging model is validated against a Spice simulation and employed to predict the converter’s output and to perform harmonic analysis of the inductor current. Following the analysis of the DAB, a 4th order CLLC converter is evaluated considering frequency and phase-shift modulations. The cyclic-averaging model is derived to model the behaviour of the converter’s output and state-variables in steady state. Additionally, a Fundamental Mode Approximation (FMA) model and a novel piecewise-linear state-variable model are also implemented for comparison. The models obtained are validated using Spice and, for the phase-shift modulated converter, experimental results. Finally, the series compensated IPT converter is analysed considering operation under phase-shift modulation. A FMA model is derived and, using circuit transformation, the state-variable and cyclic-averaging models previously defined for the CLLC converter are adapted for the analysis of the IPT converter. A prototype is built for validation of the cyclic model. Overall, for all converters analysed in this research, the cyclic-averaging method showed good performance with considerably fast execution and accuracy similar to Spice simulations

Power Electronics Intensive Energy Management Solutions for Hybrid Electric Vehicle Energy Storage Systems

Batteries, ultra capacitors (UCs), and fuel cells (FCs) are widely being proposed for electric and plug-in hybrid electric vehicles (EVs/PHEVs) as energy sources. The increasing popularity of EVs and PHEVs can be attributed to the savings in fuel costs, compared to conventional internal combustion engine (ICE) vehicles. EVs and PHEVs save energy due to the employment of reverse regenerating braking, during the deceleration cycle. This recuperated energy can be proficiently stored in batteries and/or ultra-capacitors. In general, the design of an intelligent control strategy for coordinated power distribution is a critical issue for ultra-capacitor supported PHEV energy storage systems. Implementation of several control methods have been presented in related literature, with the goal of improving battery life and overall vehicle efficiency. The control objectives vary with respect to vehicle velocity, power demand, and state-of-charge of both the batteries and ultra-capacitors. Hence, an optimal control strategy design is a critical aspect of an all-electric/plug-in hybrid electric vehicle operational characteristic. This thesis deals with the detailed analysis and novel hybrid controller design for bidirectional energy management solutions, using smart power electronic DC/DC converter solutions. More specifically, an intelligently designed novel digital control technique is presented for a 4-quadrant switched-capacitor Luo (4Q SC Luo) DC/DC converter. Features of voltage step-down, step-up, and bi-directional power flow are integrated into a single circuit. The novel control strategy enables simpler dynamics, compared to a standard buck converter with input filter, superior regulation capability, lower source current ripple, ease of control, and continuous input current waveform in buck and boost modes of operation. Furthermore, the proposed novel control strategy depicts high converter power density, high efficiency, and simple structure

Reactive power minimization of dual active bridge DC/DC converter with triple phase shift control using neural network

Reactive power flow increases dual active bridge (DAB) converter RMS current leading to an increase in conduction losses especially in high power applications. This paper proposes a new optimized triple phase shift (TPS) switching algorithm that minimizes the total reactive power of the converter. The algorithm iteratively searches for TPS control variables that satisfy the desired active power flow while selecting the operating mode with minimum reactive power consumption. This is valid for the whole range of converter operation. The iterative algorithm is run offline for the entire active power range (-1pu to 1pu) and the resulting data is used to train an open loop artificial neural network controller to reduce computational time and memory allocation necessary to store the data generated. To validate the accuracy of the proposed controller, a 500-MW 300kV/100kV DAB model is simulated in Matlab/Simulink, as a potential application for DAB in DC grids

Generic closed loop controller for power regulation in dual active bridge DC-DC converter with current stress minimization

This paper presents a comprehensive and generalized analysis of the bidirectional dual active bridge (DAB) DC/DC converter using triple phase shift (TPS) control to enable closed loop power regulation while minimizing current stress. The key new achievements are: a generic analysis in terms of possible conversion ratios/converter voltage gains (i.e. Buck/Boost/Unity), per unit based equations regardless of DAB ratings, and a new simple closed loop controller implementable in real time to meet desired power transfer regulation at minimum current stress. Per unit based analytical expressions are derived for converter AC RMS current as well as power transferred. An offline particle swarm optimization (PSO) method is used to obtain an extensive set of TPS ratios for minimizing the RMS current in the entire bidirectional power range of - 1 to 1 per unit. The extensive set of results achieved from PSO presents a generic data pool which is carefully analyzed to derive simple useful relations. Such relations enabled a generic closed loop controller design that can be implemented in real time avoiding the extensive computational capacity that iterative optimization techniques require. A detailed Simulink DAB switching model is used to validate precision of the proposed closed loop controller under various operating conditions. An experimental prototype also substantiates the results achieved

Generalized small-signal modelling of dual active bridge DC/DC converter

this paper presents a novel generalised approach of the small-signal modelling of dual active bridge (DAB) DC/DC converter. The adopted analysis is based on a per-unit fundamental frequency representation of the DAB. The outcome of the proposed modelling approach is a small signal, linearised, state-space DAB model; which is considered as a main building block for future control applications. The developed small signal DAB model includes all possible degrees of freedom affecting the performance of the DAB; this includes the voltage conversion ratio to allow the study of all DAB operation modes (i.e.: unity-gain and buck/boost modes.). Furthermore, since triple phase shift control (TPS) is used in this development work, the proposed model incorporates phase shift in addition to duty ratios. This feature allows for bridge voltage regulation, which is essential for efficient DAB operation in the case of buck/boost operation. Another key achievement is that the proposed small signal modelling methodology can be applied to any bidirectional DC-DC converter regardless of ratings, parameter values and number of ports. Extensive simulation is carried out to verify the proposed analysis

A Bidirectional Soft-Switched DAB-Based Single-Stage Three-Phase AC–DC Converter for V2G Application

In vehicle-to-grid applications, the battery charger of the electric vehicle (EV) needs to have a bidirectional power flow capability. Galvanic isolation is necessary for safety. An ac-dc bidirectional power converter with high-frequency isolation results in high power density, a key requirement for an on-board charger of an EV. Dual-active-bridge (DAB) converters are preferred in medium power and high voltage isolated dc-dc converters due to high power density and better efficiency. This paper presents a DAB-based three-phase ac-dc isolated converter with a novel modulation strategy that results in: 1) single-stage power conversion with no electrolytic capacitor, improving the reliability and power density; 2) open-loop power factor correction; 3) soft-switching of all semiconductor devices; and 4) a simple linear relationship between the control variable and the transferred active power. This paper presents a detailed analysis of the proposed operation, along with simulation results and experimental verification

System configuration, fault detection, location, isolation and restoration: a review on LVDC Microgrid protections

Low voltage direct current (LVDC) distribution has gained the significant interest of research due to the advancements in power conversion technologies. However, the use of converters has given rise to several technical issues regarding their protections and controls of such devices under faulty conditions. Post-fault behaviour of converter-fed LVDC system involves both active converter control and passive circuit transient of similar time scale, which makes the protection for LVDC distribution significantly different and more challenging than low voltage AC. These protection and operational issues have handicapped the practical applications of DC distribution. This paper presents state-of-the-art protection schemes developed for DC Microgrids. With a close look at practical limitations such as the dependency on modelling accuracy, requirement on communications and so forth, a comprehensive evaluation is carried out on those system approaches in terms of system configurations， fault detection, location, isolation and restoration

Model and Design of a Power Driver for Piezoelectric Stack Actuators

A power driver has been developed to control piezoelectric stack actuators used in automotive application. A FEM model of the actuator has been implemented starting from experimental characterization of the stack and mechanical and piezoelectric parameters. Experimental results are reported to show a correct piezoelectric actuator driving method and the possibility to obtain a sensor-less positioning contro