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POWER ELECTRONICS 2016

Category Archives

Grid Current Shaping Method with DC-link Shunt Compensator for Three-Phase Diode Rectifier-Fed Motor Drive System

Abstracts

This paper proposes grid current shaping method using DClink shunt compensator for threephasediode rectifier system without electrolytic DClink capacitor. In the proposed method, the diode rectifiersystem can satisfy the grid regulation IEC61000-3-12 without any power factor correction circuit or heavy grid filter inductor. The proposed grid current shaping method can be realized by applying DSC with reduced-rating components and without electrolytic capacitor, which is connected parallel to theDClink. Since DSC has no electrolytic capacitor, the system with DSC has high circuit reliability. Furthermore, DSC can enhance the system efficiency, especially in flux-weakening area, since themotor drive inverter recovers the reduced modulation index which has been spent in the additional control for small passive components. This paper presents the control method for DSC and analyzes the effect of proposed method. The feasibility of proposed method is verified by simulation and experimental results.


Modeling and Optimization of a Zero Voltage Switching Inverter for High Efficiency and Miniaturization

Abstracts

In a ZeroVoltage Switching (ZVS) inverter, high conversion efficiency and miniaturization are expected since switching loss can be dramatically reduced with proper design. In order to realize ZVS condition, auxiliary components such as inductors, capacitors and switches are embedded to the inverter to implement the function. Since the design of auxiliary components is critical to the ZVS inverter, it is impossible to realize maximum efficiency or minimum size by following the conventional design procedure. This paper introduces an optimized design methodology for a three-phase ZVS inverter with objectives of both high efficiency and miniaturization. Based on the loss models of different commercial IGBT modules under different ZVS conditions, as well as the loss models of auxiliary components and filter inductors, the issue of pursuing highest efficiency is transformed into solving a constrained nonlinear multivariable problem. According to the proposed design methodology, all parameters that influence the efficiency and physical dimensions are considered simultaneously. Thus the optimized selection of the IGBT module, the parameters of the auxiliary components and the filter inductors would be obtained. A 30 kW three-phase ZVS inverter prototype was built to verify the proposed design method. With proposed design method, the improved prototype has achieved both smaller passive components volume and higher efficiency compared to the former prototype.


Improved Power Decoupling Scheme for Single-Phase Grid-Connected Differential Inverter with Realistic Mismatch in Storage Capacitances

Abstracts

Singlephase differential inverter consists of two elementary dc-dc converters, sharing a common dc source and a common ac output terminal. The other ac terminals of the two converters are connectedto the grid, in case of gridconnected applications. The differential inverter has subsequently been shown to have a differential flow path for power transfer and a common-mode path for shifting the usual second-order power oscillation away from the dc source. This capability is referred to as powerdecoupling, which when implemented properly, may prolong the lifespan of the dc source. Existing studies related to power decoupling using a differential inverter have however focused on developing control schemes with equal storage capacitances assumed for the two elementary converters. This is unquestionably not realistic since the two capacitances will vary in practice. It is therefore the intention of this paper to quantify ac and dc imperfections experienced by the differential inverter when storagemismatch occurs. A simple improved scheme is then proposed for raising performance of thedifferential inverter (or differential rectifier where desired). Simulation and experimental results provided have verified the computation and control scheme developed.


Non-linear PWM Controlled Single-phase Boost Mode Grid-Connected Photovoltaic Inverter with Limited Storage Inductance Current

Abstracts

A nonlinear PWM controlled singlephase boost mode photovoltaic gridconnected inverter with limitedstorage inductance current is proposed in this paper. The circuit topology, control strategy, steady state principle characteristic and design criterion for the key circuit parameters of this kind of inverter are investigated in depth, and important conclusions are obtained. The inverter‘s regenerating energy duty ratio 1-D which decreases with the decline of the gridconnected voltage is real-time adapted by sampling and feeding back the inverting bridge modulation current, and the average value of the modulation current in each switching cycle tracks the reference sinusoidal signal to get high qualitygridconnected current. The active control of the energy storage inductance current and the balance of the voltage step-up ratio are realized by adding a by-pass switch connected in parallel with the energystorage inductance and using two kinds of switching pattern namely boost pattern and freewheeling pattern. The theoretical analysis and experimental results of the 1kVA 110VDC/220V50Hz photovoltaicgridconnected inverter prototype show that it has the advantages such as single-stage boostconversion, high conversion efficiency, high quality of gridconnected current waveform, low value of energy storage inductance, simple control etc.


Control of Parallel Three Phase PWM Converters under Generalized Unbalanced Operating Conditions

Abstracts

This paper proposes a new control scheme for parallel three phase pulse width modulation (PWM)converters under generalized unbalanced operating conditions. An average model of the parallelsystem in positive-sequence synchronous reference frame (PSRF) is derived to analyze the influence of generalized unbalanced operating conditions in AC side. It is seen that the unbalance factors in filter inductance will not only give rise to negative-sequence circulating current, but also contribute to generating zero-sequence circulating current(ZSCC). The negative-sequence circulating current can be inhibited by suppressing the negative-sequence components in AC output currents of parallel modules with a proportional integral resonant (PIR) controller. An improved feed-forward strategy and a PIR controller for ZSCC control are proposed for unbalanced operating conditions. The disturbances in ZSCC caused by unbalance factors in filter inductance can be rejected with feed-forward strategy. Because the disturbance in ZSCC is the fluctuation in grid frequency which can be suppressed by resonance controller, so a PIR controller is adopted in ZSCC controller. The proposed scheme can effectively suppress the circulating currents between the parallel modules and as a result, the distortions in output currents can be greatly reduced. Experimental results confirm the performance and effectiveness of the proposed method.


Inverse Nyquist Stability Criterion for Grid-Tied Inverters

Abstracts

A new impedance-based stability criterion was proposed for a gridtied inverter system based on a Norton equivalent circuit of the inverter [18]. As an extension of the work in [18], this paper shows that using a Thévenin representation of the inverter can lead to the same criterion in [18]. Further, this paper shows that the criterion proposed by Middlebrook can still be used for the inverter systems. The link between the criterion in [18] and the original criterion is the inverse Nyquist stability criterion. Thecriterion in [18] is easier to be used. Because the current feedback controller and the phase-locked loop of the inverter introduce poles at the origin and right-half plane to the output impedance of the inverter. These poles do not appear in the minor loop-gain defined in [18] but in the minor loop-gain defined by Middlebrook. Experimental systems are used to verify the proposed analysis.


Impedance-Phased Dynamic Control Method for Grid-Connected Inverters in a Weak Grid

Abstracts

A power distribution grid exhibits the characteristics of a weak grid owing to the existence of scattered high-power distributed power-generation devices. The grid impedance affects the robust stability of gridconnected inverters, leading to harmonic resonance, or even instability in the system. Therefore a study of the stability of gridconnected inverters with high grid impedance based on impedance analysis is presented in this paper. The output impedance modeling of an LCL-type single-phase gridconnectedinverter is derived, where the effects of the PLL loop and the digital control delays on the outputimpedance characteristics have been taken into account. To enhance the stability of gridconnectedinverters with different grid impedance, a novel impedancephased compensation control strategy is proposed by increasing the phase margin of the gridconnected inverters. Specifically, a detailed implementation and parameter design of the impedancephased compensation control method is depicted. Finally, an impedancephased dynamic control scheme combined with online grid impedancemeasurement is introduced and also verified by the experiment results.


Online Transformerless Uninterruptible Power Supply (UPS) System with a Smaller Battery Bank for Low Power Applications

Abstracts

Uninterruptible Power Supplies (UPS) are widely used to provide reliable and high quality power to critical loads in all grid conditions. This paper proposes a non-isolated online uninterruptible powersupply (UPS) system. The proposed system consists of bridgeless PFC boost rectifier, batterycharger/discharger, and an inverter. A new battery charger/discharger has been implemented which ensures the bidirectional flow of power between dc-link and battery bank, reducing the battery bankvoltage to only 24V, and regulates the dc-link voltage during battery power mode. Operating batteries in parallel improves the battery performance and resolve the problems related to conventional batterybanks that arrange batteries in series. A new control method, integrating slide mode and proportional-resonant control, for inverter has been proposed which regulates the output voltage for both linear and non-linear loads. The controller exhibits excellent performance during transients and step changes in load. Operating principle and experimental results of 1kVA prototype have been presented for validation of the proposed system.


A Robot-Soccer-Coordination Inspired Control Architecture Applied to Islanded Microgrids

Abstracts

Nowadays islanded microgrids present a high interest due to the increasing penetration of renewable energy resources, especially in remote areas, or for improving the local energy reliability. A microgrid can operate in gridconnected or islanded mode, being necessary the use of energy storage systems under islanded operation, in order to ensure the generation/consumption power balance and smooth uncertainties in the dynamics of the renewable energy sources. Particularly, in islanded operation at least one of the distributed energy resources should assume the regulation of the common bus. In a microgrid, every distributed energy resource may be able to cooperate with the grid regulation in accordance to its particular operational conditions. In this sense, a centralized unit with a global perception of the load demand, the power provided by the renewable energy sources, and the storage capacity of the energy storage systems, may ensure proper and reliable operation of the microgrid. This paper proposes a structured architecture based on tactics, roles and behaviors for a coordinated operation of islanded microgrids. The architecture is inspired on a robot soccer strategy with global perception and centralized control, which determines the changes among operation modes for the distributed energy resources in an islanded ac microgrid.


A Fixed Frequency Sliding Mode Controller for a Boost Inverter Based Battery-Supercapacitor Hybrid Energy Storage System

Abstracts

The boost inverter based batterysupercapacitor hybrid energy storage systems (HESSs) are a popular choice for the battery lifetime extension and system power enhancement. Various sliding mode(SM) controllers have been used to control the boost inverter topology in literature. However, the traditional SM controllers for the boost inverter topology operate with a high and variable switchingfrequency which increases the power losses and system components design complexity. This can be alleviated by a pulse width modulation (PWM) based fixed frequency SM controller proposed in this paper. The SM controller is implemented using variable amplitude PWM carrier signals generated using the output capacitor voltage and inductor current measurements thus eliminating the requirement of the output capacitor currents measurement. The battery connected inductor reference currents for the SMcontroller are generated by a supercapacitor energy controller which is responsible for the HESS power allocation. First, the theoretical aspects of the SM controller, the operation and parameter selection of the supercapacitor energy controller and the supercapacitor sizing for the HESS are discussed in the paper. Then, the proposed control system is experimentally verified and it is shown that the HESS is able to satisfy the HESS output power requirements while allocating the ripple current and the fast power fluctuations to the supercapacitor while maintaining operation of the supercapacitor within pre-defined voltage limits. The main advantage of the proposed SM controller, as compared with the traditional double loop (DL) control method, is in eliminating possible DC current injection into the grid when the equivalent series resistance (ESR) values of the boost inductors become unequal due to the tolerances and temperature variations.


Design and Analysis of Robust Active Damping for LCL Filters using Digital Notch Filters

Abstracts

Resonant poles of LCL filters may challenge the entire system stability especially in digital-controlled Pulse Width Modulation (PWM) inverters. In order to tackle the resonance issues, many active dampingsolutions have been reported. For instance, a notch filter can be em-ployed to damp the resonance, where the notch frequency should be aligned exactly to the resonant frequency of the LCL filter. However, parameter variations of the LCL fil-ter as well as the time delay appearing in digital control systems will induce resonance drifting, and thus break this alignment, possibly deteriorating the originaldamping. In this paper, the effectiveness of the notch filter based active damping is firstly explored, considering the drifts of the resonant frequency. It is revealed that, when the resonant frequency drifts away from its nominal value, the phase lead or lag introduced by the notch filter may make itself fail todamp the resonance. Specifically, the phase lag can make the current control stable despite of the resonant frequency drifting, when the grid current is fed back. In contrast, in the case of an inverter current feedback con-trol, the influence of the phase lead or lag on the active damping is dependent on the actual resonant frequency. Accordingly, in this paper, the notch frequency is designed away from the nominal resonant frequency to tolerate the resonance drifting, being the proposed robust activedamping. Simulations and experiments performed on a 2.2-kW three-phase grid-connected PWM inverter verify the effectiveness of the proposed design for robust active damping using digital notchfilters.


Electric Vehicle Charging Station with an Energy Storage Stage for Split-DC Bus Voltage Balancing

Abstracts

This paper proposes a novel balancing approach for an electric vehicle bipolar dc charging station at the megawatt level, enabled by a grid-tied neutral point clamped converter. The work uses the presence of an energy storage stage with access to both of the dc buses to perform the complementary balance. It proposes a generic balancing structure that can achieve balance regardless the kind of ESS employed. This is aiming to reduce the hardware requirements of the system and maximize the usage of the ESS, whose main function is to perform the energy management related tasks. To meet this purpose, a three-level dcdc interface is employed, allowing to compensate the dc currents with a single ESS. Furthermore, in order to prevent the appearance of even-order harmonics in the input current during asymmetrical operation, an alternative switching sequence for the central converter is proposed. Results indicate that, without altering dramatically the charging process of the ESS, it is possible to cover the whole load scenario without the need of a balancing circuit. This allows the use of off-the-shelf products both for the rectifier and the fast chargers. In this paper, simulation and experimental results are presented to validate the proposed balancing strategy.


A Quasi-Z-source Integrated Multiport Power Converter as Switched Reluctance Motor Drives for Capacitance Reduction and Wide-Speed-Range Operation

Abstracts

This paper presents a quasiZsource integrated multiport converter (ZIMPC) for switched reluctancemotor (SRM) drives to reduce the dc-link capacitance and enable wide-speed-range operation. In conventional SRM drives, employing multiphase asymmetrical H-bridge (ASHB) topology, large capacitors are necessary to absorb the transient energy during phase current commutation. However, electrolytic capacitors would affect the lifetime, cost, and power density of the drive system. Withswitch multiplexing technique, a ZIMPC is derived to achieve power ripple reduction using relatively small capacitors. The power ripple generation principle and requirement of capacitance in ASHB and ZIMPC are analyzed. The model of the overall system including SRM and the proposed drive is developed using mode analysis. Advanced control method with repetitive control is proposed and developed based on the system model. Also, the ZIMPC can boost the equivalent phase exciting voltage and widen the constant power speed range. At last, simulation and experimental results verify the feasibility of the proposed ZIMPC and its superior performance with smaller capacitance as compared with ASHB.


Analysis, Design, Modelling and Control of an Interleaved-Boost Full-Bridge Three-Port Converter for Hybrid Renewable Energy Systems

Abstracts

This paper presents the design, modelling and control of a threeport (TPC) isolated dc-dc converterbased on interleavedboostfullbridge with pulse-width-modulation and phase-shift control for hybridrenewable energy systems. In the proposed topology, the switches are driven by phase-shifted PWM signals, where both phase angle and duty cycle are controlled variables. The power flow between the two inputs is controlled through the duty cycle, whereas the output voltage can be regulated effectively through the phase-shift. The primary side MOSFETs can achieve zero-voltage switching (ZVS) operation without additional circuitry. Additionally, due to the ac output inductor, the secondary side diodes can operate under zerocurrent switching (ZCS) conditions. In this work, the operation principles of the converter are analyzed and the critical design considerations are discussed. The dynamic behavior of the proposed ac inductor based TPC is investigated by performing state-space modelling. Moreover, the derived mathematical models are validated by simulation and measurements. In order to verify the validity of the theoretical analysis, design and power decoupling control scheme, a prototype is constructed and tested under the various modes, depending on the availability of the renewableenergy source and the load consumption. The experimental results show that the two decoupled controlvariables achieve effective regulation of the power flow among the three ports.


Control of Active Power Exchange With Auxiliary Power Loop in Single-Phase Cascaded Multilevel Converter Based Energy Storage System

Abstracts

Cascaded multilevel converter (CMC) based energy storage system, which consists of cascaded H-bridge converters and energy storage components, is a promising option to compensate fluctuating electric power of renewable energy. This paper proposes a novel singlephase CMC based battery storage system which includes a LC branch. The cascaded converter cells and the LC branch form anauxiliary power loop, which could realize active power exchange between different cells with the proposed dual-frequency phase-shifted carrier PWM (DF-PSC PWM). The principle and effectiveness of DF-PSC PWM and the power transfer mechanism are analyzed. Meanwhile, the design of the tuned filter, output filter and the SOC balancing control system are introduced. The operation principle of thepower exchange in the proposed energy storage system has been successfully verified by simulation and experiment results.


Three-Phase Unbalanced Power Flow Using a Pi-Model of Controllable AC-DC Converters

Abstracts

Microgrids are unique in that they can combine unbalanced threephase systems with other AC and DCnetwork sections, which may include a range of renewable energy sources, energy storage elements, and controllable ACDC converters. Existing unbalanced power flow techniques such as the Ladder Iterative Technique and the threephase Newton-Raphson (NR) method can analyze microgrids in sections but lack a complete system representation. Hence, there is a need for a power flow algorithm that considers the complete system model and solves it. A novel 525 Three Phase Unbalanced Power Flow Using a Pi Model of Controllable AC DC Convertersmodel of a controllable ACDCconverter and a single set of power balance equations for modeling a grid comprising multiple threephase AC and DC sections is proposed. The 525 Three Phase Unbalanced Power Flow Using a Pi Model of Controllable AC DC Convertersmodel of a controllable ACDC converter enables its inclusion into the network bus admittance matrix (YBUS) along with threephase AC and DC network sections. Verification of the 525 Three Phase Unbalanced Power Flow Using a Pi Model of Controllable AC DC Convertersmodel is also described in the paper. The results of power flow studies with threephase balanced and unbalanced AC and DC network sections are presented. The outcome of the 525 Three Phase Unbalanced Power Flow Using a Pi Model of Controllable AC DC Convertersmodel verification study and power flow study show that the proposed 525 Three Phase Unbalanced Power Flow Using a Pi Model of Controllable AC DC Convertersmodel is consistent and accurate. While the proposed model was developed for microgrids, it is applicable for all powersystem analysis applications.


Time Delay Compensation Method Based on Area Equivalence for Active Damping of LCL-Type Converter

Abstracts

Control of the LCLtype three-phase grid-connected converter is difficult due to high resonance peak of the LCL filter. Active damping is the state-of-the-art solution to this problem, but the dampingperformance will be affected by the inherent time delay of digital control, especially for high power low switching frequency applications. Based on a discrete-time stability analysis of an LCLtype converterwith capacitor-current-feedback active damping, a simple and effective time delay compensationmethod, which is based on area equalization concept, is proposed. The method can reduce the negative impact of the computation delay significantly. It has the potential to serve as a general solution to time delay compensation of digitally controlled PWM converter. The validity of the proposed methodis proved by experimental results.


Maximum Boost Control of Diode-assisted Buck boost Voltage Source Inverter with Minimum Switching Frequency

Abstracts

Diodeassisted buckboost voltage source inverter (VSI) achieves high voltage gain by introducing aswitch-capacitor based high step-up dc-dc circuit between the dc source and inverter bridge. As for the unique structure, various pulse width modulation (PWM) strategies are developed with regard to the chopped intermediate dc-link voltage. In order to maximize voltage gain and increase efficiency, this paper proposes a novel PWM strategy. It regulates the average value of intermediate dc-link voltage in one switching time period (Ts) the same as the instantaneous maximum value of three-phase linevoltage by controlling the front boost circuit. Then, the equivalent switching frequency of power devices in the inverter bridge can be reduced to 1/3fs ???????????? fs=1/Ts ???????????? . The operating principle and closed-loop controller design are analyzed and verified by simulations and experiments. Compared with existing PWM strategies, the new control strategy demonstrates less power device requirement and higher efficiency in high voltage gain applications. It is a more competitive topology for wide range dc/ac voltage regulation in renewable energy applications. Furthermore, with new controlstrategy, the dc-side inductor current and capacitor voltage contains six-time the line frequency ripples. To overcome the undesired influence of low frequency ripples, it is also suitable for 400-800Hz mediumfrequency aircraft and vessel power supply system.


Single-Phase Grid Connected Motor Drive System with DC-link Shunt Compensator and Small DC-link Capacitor

Abstracts

The singlephase diode rectifier system with small DClink capacitor shows wide diode conduction time and it improves the grid current harmonics. By shaping the output power, the system meets the gridcurrent harmonics regulation without any power factor corrector or grid filter inductor. However, thesystem has torque ripple and suffers efficiency degradation due to the insufficient DClink voltage. To solve this problem, this paper proposes the DClink shunt compensator (DSC) for small DClinkcapacitor systems. DSC is located on DC-node parallel and operates as the voltage source, improving the system performances. This circuit helps the grid current-shaping control during grid-connection time, and reduces the flux-weakening current by supplying the energy to the motor during grid-disconnection time. This paper presents a power control method and the design guideline of DSC. The feasibility of DSC is verified by simulation and experimental results.


Abnormal Operation State Analysis and Control of Asymmetric Impedance Network based Quasi-Z-Source PV Inverter (AIN-qZSI)

Abstracts

Since its conception, the quasiZsource inverter (qZSI) has been extensively studied, especially in renewable energy applications fields due to its ability to withstand shoot-through and provide continuous current. However, research thus far has only explored symmetric qZSI/ZSI impedance network with large inductances and capacitances. By utilizing next-gen wideband-gap devices at high-switching frequency, the impedance network can be significantly reduced. However, the reduced qZS impedancenetwork will result in abnormal operation modes, in addition to frequency resonances, in several kilohertz range. Thus, this paper first thoroughly explains the occurrence of the abnormal states,analyzes the effects of the abnormal states on the frequency resonance, and then proposes a controlmethod to suppress the resonance that result from the reduced impedance network. A 1-kW prototype is built and experimental results verify the effectiveness of the analysis and proposed control method.


An Evolutional Line Commutated Converter Integrated with Thyristor Based Full-Bridge Module to Mitigate the Commutation Failure

Abstracts

With thyristor based fullbridge module (TFBM) embedded in the converter valve, an evolutional LineCommutated Converter (ELCC) is proposed to enhance the commutation failure (CF) immunity. The operating principle of TFBM and the coordinated control strategy between TFBM and series-connected valve are presented. The voltage-current stress of the TFBM is analyzed, and the method to select the capacitor parameter is also presented. Then, the ELCC-HVDC under the presented control strategy is developed in PSCAD/EMTDC, and its dynamic responses under ac fault condition are compared with that of capacitor-commutated converter based HVDC (CCC-HVDC) and conventional LCC-HVDC. A dual-infeed HVDC system with TFBM embedded in one HVDC link is also developed to further investigate the merits of TFBM. Finally, the increased capital cost and power loss of the ELCC-HVDC are discussed. The results show that, the presented ELCC-HVDC has the ability to reduce the CF risk effectively and also exhibits favorable steady state and dynamic performances.


Simultaneous Microgrid Voltage and Current Harmonics Compensation Using Coordinated Control of Dual-Interfacing-Converters


Least Power Point Tracking Method for Photovoltaic Differential Power Processing Systems

Abstract

Differential power processing (DPP) systems are a promising architecture for future photovoltaic (PV) power systems that achieve high system efficiency through processing a faction of the full PV power, while achieving distributed local maximum power point tracking (MPPT). In the PV-to-bus DPP architecture, the power processed through the DPP converters depends on the string current, which must be controlled to minimize the power processed through the DPP converters. A real-time least power point tracking (LPPT) method is proposed to minimize power stress on PV DPP converters. Mathematical analysis shows the uniqueness of the least power point for the total power processed through the system. The perturband- observe LPPT method is presented that enables the DPP converters to maintain optimal operating conditions, while reducing the total power loss and converter stress. This work validates through simulation and experimentation that LPPT in the string-level converter successfully operates with MPPT in the DPP converters to maximize output power for the PVto- bus architecture. Hardware prototypes were developed and tested at 140 W and 300 W, and the LPPT control algorithm showed effective operation under steady-state operation and an irradiance step change. Peak system efficiency achieved with a 140-W prototype DPP system employing LPPT is 95.7%.


A Novel DBC Layout for Current Imbalance Mitigation in SiC MOSFET Multichip Power Modules

Abstracts

This letter proposes a novel direct bonded copper (DBC) layout for mitigating the current imbalanceamong the paralleled SiC MOSFET dies in multichip power modules. Compared to the traditional layout, the proposed DBC layout significantly reduces the circuit mismatch and current coupling effect, which consequently improves the current sharing among the paralleled SiC MOSFET dies in power module. Mathematic analysis and circuit model of the DBC layout are presented to elaborate the superior features of the proposed DBC layout. Simulation and experimental results further verify the theoretical analysis and current balancing performance of the proposed DBC layout.


A Novel Flexible Capacitor Voltage Control Strategy for Variable-Speed Drives with Modular Multilevel Converter

Abstracts

Modular multilevel converter (MMC) is very popular in medium-voltage applications, such as highvoltage direct current transmission (HVDC), static Var generator (SVG), and motor drives. The armcapacitor voltage of MMC is usually constant and the output voltage is adjusted by regulating the pulse width modulation (PWM) index for switches in previous studies. In this paper, a novel flexible capacitorvoltage control strategy for MMC as motor drives was proposed, with which the arm capacitor voltagewas controlled flexibly according to the motor speed, by regulating the dc component and ac component of the PWM reference signal. And unsymmetrical control was used for the control of the upper arm and the lower arm in MMC. With the proposed control strategy, the circuit efficiency and the precision of the output voltage of the converter could be improved when the motor speed was low, and di/dt and dv/dt of the motor windings could be decreased. These proposals were implemented on a laboratory prototype, and experiments were carried out. The validity of the control strategy under both steady and dynamic states was verified.


High Efficiency Bi-Directional Converter for Flywheel Energy Storage Application

Abstract

A bidirectional converter (BDC) is essential in applications where energy storage devices are involved. Such applications include transportation, battery less UPS, Flywheel Energy Storage (FES) systems etc. Bidirectional power flow through buck and boost mode operation along with high power density and efficiency are important requirements of such systems. This paper presents a new BDC topology using a combination of fast turn off SCR and IGBT with a novel control logic implementation to achieve zero switching losses through Zero Voltage Transition (ZVT) and Zero Current Transition (ZCT) techniques. The proposed scheme ensures Zero Switching Power Loss (ZSPL) for both buck and boost modes of operation of the BDC. The scheme is simple and achieves ZSPL during both turn-on and turn-off of the devices resulting in improved efficiency and reduced EMI problems. The basic principle of operation, analysis, and design procedure are presented for both voltage buck and boost modes of operation of the proposed BDC topology. A design example is presented. Limitations of the system are highlighted. Experimental and simulation results obtained on a 4kW, 340V input prototype with a switching frequency of 15.4 kHz are presented to verify the design.


Robust and Efficient Transistor-level Envelope-Following Analysis of PWM/PFM/PSM DC-DC Converters

Abstracts

The envelopefollowing (EF) simulation of practical DCDC converters is challenging due to the presence of digital behavior, strong nonlinearity, complex frequency module schemes and feedback loops. This paper presents a novel EF method for time-domain analysis of DCDC converters based upon a numerically robust time-delayed phase condition to track the envelopes of circuit states under a varying switching frequency. We further develop an EF technique that is applicable to both fixed and varying switching frequency operations, thereby providing a unifying solution to converters with pulse width modulation (PWM), pulse frequency modulation (PFM) and pulse skipping modulation (PSM). By adopting three fast simulation techniques, our proposed EF method achieves higher speedup without composing the accuracy of the results. The robustness and efficiency of the proposed method are demonstrated using several DCDC converter and oscillator circuits modeled using the industrial standard BSIM4 transistor models. A significant runtime speedup of up to 30X with respect to the conventional transient analysis is achieved for several DCDC converters with strong nonlinear switching characteristics.


A Novel Multiple-Frequency Resonant Inverter for Induction Heating Applications

Abstracts

This paper presents a novel multiplefrequency resonant inverter for induction heating (IH) applications. By adopting a center tap transformer, the proposed resonant inverter can give load switching frequencyas twice as the isolated-gate bipolar transistor (IGBT) switching frequency. The structure and the operation of the proposed topology are described in order to demonstrate how the output frequency of the proposed resonant inverter is as twice as the switching frequency of IGBTs. In addition to this, the IGBTs in the proposed topology work in zero-voltage switching during turn-on phase of the switches. The new topology is verified by the experimental results using a prototype for IH applications. Moreover, increased efficiency of the proposed inverter is verified by comparison with conventional designs.


Model Predictive Based Maximum Power Point Tracking for Grid-tied Photovoltaic Applications Using a Z-Source Inverter

Abstracts

This paper presents a model predictivebased maximum power point tracking (MPPT) method for aphotovoltaic energy harvesting system based on a single-stage gridtied Zsource inverter. First, it provides a brief review of Zsource inverters, MPPT methods and model predictive control. Next, it introduces the proposed model predictivebased MPPT method. Finally, it provides experimental results to verify the theoretical outcomes.


Fuzzy Logic-Based Energy Management System Design for Residential Grid-Connected Micro grids

Abstracts

This paper presents the design of a low complexity Fuzzy Logic Controller of only 25-rules to be embedded in an Energy Management System for a residential gridconnected microgrid including Renewable Energy Sources and storage capability. The system assumes that neither the renewable generation nor the load demand is controllable. The main goal of the design is to minimize the gridpower profile fluctuations while keeping the Battery State of Charge within secure limits. Instead of using forecasting-based methods, the proposed approach uses both the microgrid energy rate-of-change and the battery SOC to increase, decrease or maintain the power delivered/absorbed by the mains. The controller design parameters (membership functions and rule-base) are adjusted to optimize a pre-defined set of quality criteria of the microgrid behavior. A comparison with other proposals seeking the same goal is presented at simulation level, whereas the features of the proposed designare experimentally tested on a real residential microgrid implemented at the Public University of Navarre.


A Wide Load Range ZVS Push-Pull DC/DC Converter with Active-Clamped

Abstracts

A new activeclamped zero-voltage-switching (ZVS) pushpull converter is proposed in this paper. Compared with the conventional pushpull converter, one auxiliary switch Q3 and a clamping capacitor Ca is added in the primary side of the transformer to recycle the energy stored in the leakage inductors and clamp the voltage spike. Owing to the proposed converter which maintains ZVS of all the three switches from full load to very light load condition, switching losses are reduced significantly. The voltage stresses on switches that can be clamped at the input voltage plus the clamping capacitor voltage i.e., Vin+VCa, are much less than those of a conventional pushpull converter that enabling the use of low-voltage, low-performance and lower cost devices. In addition, the proposed topology can eliminate the problems of flux-imbalance existing in the conventional one. Detailed operation, analysis, design, comparative study and experimental results for the proposed converter are presented in this paper. An 800 W prototype was developed in the laboratory to evaluate and demonstrate the validity of the converter.


Non-Isolated Two-Channel LED Driver with Automatic Current Balance and Zero Voltage Switching

Abstracts

In this paper, a nonisolated twochannel light-emitting diode (LED) driver with automatic current balanceand zerovoltage switching (ZVS) is presented. In this LED driver, a dc-blocking capacitor is connected with one side of the coupled inductor. Therefore, based on the ampere-second balance, a currentsource is generated with the average value of the positive current identical to the absolute average value of the negative current. Accordingly, the LED currents can be balanced naturally without extra active components or current sharing transformer. Consequently, the circuit components can keep at a low count. In addition, the proposed LED driver can achieve ZVS turn-on. Thus, the switching loss can be decreased. Above all, the proposed twochannel LED driver can be extended to a multichannel LEDdriver. In this paper, detailed theoretical analyses and experimental results are provided to verify the feasibility and effectiveness of the proposed LED driver.


Dual-Bridge LLC Resonant Converter With Fixed-Frequency PWM Control for Wide Input Applications

Abstracts

This paper proposes a dualbridge (DB) LLC resonant converter for wide input applications. The topology is an integration of a half-bridge (HB) LLC circuit and a full-bridge (FB) LLC circuit. The fixedfrequency PWM control is employed and a range of twice the minimum input voltage can be covered. Compared with the traditional pulse frequency modulation (PFM) controlled HB/FB LLC resonantconverter, the voltage gain range is independent of the quality factor and the magnetizing inductor has little influence on the voltage gain, which can simplify the parameter selection process and benefit the design of magnetic components as well. Over the full load range, zero voltage switching (ZVS) and zero current switching (ZCS) can be achieved for primary switches and secondary rectifier diodes, respectively. Detailed analysis on the modulation schedule and operating principle of the proposedconverter is presented along with the converter performance. Finally, all theoretical analysis and characteristics are verified by experimental results from a 120V-240V input 24V/20A output converterprototype.


A Sensitivity-Improved PFM LLC Resonant Full-Bridge DC-DC Converter with LC Anti-Resonant Circuitry

Abstracts

An LLC resonant circuit-based fullbridge dcdc converter with an LC antiresonant tank for improving the performance of pulse-frequency-modulation (PFM) is proposed in this paper. The proposedresonant dcdc converter, named as LLCLC converter can extend a voltage regulation area below the unity gain with a smaller frequency variation of PFM by the effect of the antiresonant tank. This advantageous property contributes for protecting over-current in the case of the short-circuit load condition as well as the start-up interval in the designed band of switching frequency. The circuit topology and operating principle of the proposed converter is described, after which the design procedure of the operating frequency and circuit parameters is presented. The performances on the soft switching and the steady-state PFM characteristics of the LLCLC converter are evaluated under the open-loop control in experiment of a 2.5kW prototype, and its actual efficiency is compared with aLLC converter prototype. For revealing the effectiveness of the LLCLC resonant circuitry, voltages and currents of the series and antiresonant tanks are analyzed respectively with state-plane trajectories based on calculation and experiment, whereby the power and energy of each resonant tank are demonstrated. Finally, the feasibility of the proposed converter is evaluated from the practical point of view.


Design and Implementation of a High Efficiency Multiple Output Charger based on the Time Division Multiple Control Technique

Abstracts

Multiple output converters (MOCs) are widely applied to applications requiring various levels of outputvoltages due to their advantages in terms of cost, volume, and efficiency. However, most of the conventional MOCs cannot regulate multiple outputs tightly and they can barely avoid the cross regulation problem. In this paper, the recently developed Time Division Multiple Control (TDMC) method, which can regulate all of the outputs with a high accuracy, is used for a multiple output battery chargerbased on the phase shift full bridge topology to simultaneously charge three batteries. The proposedcharger is able to charge three different kinds of batteries or three of the same kind of battery in different state of charges (SOCs) independently and accurately with the constant current/constant voltage (CC/CV) charge method. As a result, the strict ripple specification of a battery can be satisfied formultiple battery charges without difficulty. In addition, the proposed charger exhibits a high efficiencysince the soft switching of all of the switches during the entire charge process can be guaranteed. The operating principle of the converter and the design of the controller, including the state-space average modeling, will be detailed and the validity of the proposed method is verified through experiments.


Quasi-Z-Source Inverter With a T-Type Converter in Normal and Failure Mode

Abstracts

This paper presents a three-phase multilevel quasiZsource inverter (qZSI) topology operating innormal and fault-tolerant operation mode. This structure is composed by two symmetrical quasiZsource networks and a three-phase Ttype inverter. Besides the intrinsic advantages of multilevel voltage source inverters, the proposed structure is also characterized by their semiconductor fault tolerance capability. This feature is only obtained through changes on the modulation scheme after the semiconductor fault and does not require additional extra-phase legs or collective switching states. In certain fault types, the reduction of the output power capacity will be compensated by the boost characteristic of the qZSI. The fault-tolerant behavior of the proposed topology is demonstrated by several simulation results of the converter in normal and fault condition. To validate the characteristics of this multilevel qZSI, an experimental prototype was also built to experimentally confirm the results.


Efficiency Assessment of Modular Multilevel Converters for Battery Electric Vehicles

Abstracts

This paper evaluates the performance of modular multilevel converters with integrated battery cells when used as traction drives for battery electric vehicles. In this topology, individual battery cells are connected to the dc-link of the converter submodules, allowing the highest flexibility for the discharge and recharge. The traditional battery management system of battery electric vehicles is replaced by the control of the converter, which individually balances all the cells. The performance of the converter as a traction drive is assessed in terms of torque-speed characteristic and power loss for the full frequency range, including field weakening. Conduction and switching losses for the modular multilevel converterare calculated using a simplified model, based on the data sheet of power devices. The performance of the modular multilevel converter is then compared with a traditional two-level converter. The loss model of the modular multilevel converter is finally validated by experimental tests on a small-scale prototype of traction drive.


A Novel Flexible Capacitor Voltage Control Strategy for Variable-Speed Drives with Modular Multilevel Converters

Abstracts

Modular multilevel converter (MMC) is very popular in medium-voltage applications, such as highvoltage direct current transmission (HVDC), static Var generator (SVG), and motor drives. The armcapacitor voltage of MMC is usually constant and the output voltage is adjusted by regulating the pulse width modulation (PWM) index for switches in previous studies. In this paper, a novel flexible capacitorvoltage control strategy for MMC as motor drives was proposed, with which the arm capacitor voltagewas controlled flexibly according to the motor speed, by regulating the dc component and ac component of the PWM reference signal. And unsymmetrical control was used for the control of the upper arm and the lower arm in MMC. With the proposed control strategy, the circuit efficiency and the precision of the output voltage of the converter could be improved when the motor speed was low, and di/dt and dv/dt of the motor windings could be decreased. These proposals were implemented on a laboratory prototype, and experiments were carried out. The validity of the control strategy under both steady and dynamic states was verified.


Steady-State Loss Model of Half-Bridge Modular Multilevel Converters

Abstracts

Lesnicar and Marquardt introduced a modular multilevel converter (MMC) topology back in 2003. Although this topology has received a great deal of attention in recent years by both the research community and industry, hitherto no steadystate model has been developed which accurately captured all the relevant power losses while being computationally light. Hence, the aim of this paper is to introduce a fast MMC loss model which captures the key sources of power losses in steadystateoperation. The proposed model was compared to a loss model developed by Marquardt. Both modelspresented similar results under the same assumptions. However, the proposed model captures the switching losses more realistically and considers the temperature of operation of the electronics, as well as the losses of the inductors and cooling system, in the overall efficiency of the MMC. To validate these new additions, the proposed steadystate model was compared to a dynamic model. Once again, the proposed model was able to capture the different sources of power losses. Nonetheless, results demonstrated that the balancing strategy greatly influences the efficiency of the MMC. Therefore, information regarding the envisioned control strategy is necessary to accurately calculate the efficiency curve of the MMC.


A Static Ground Power Unit Based on Improved Hybrid Active-Neutral-Point-Clamped Converter

Abstracts

This paper proposes a new configuration for static ground power unit (GPU) based on the novel 25-level hybrid activeneutralpointclamped (HANPC) converter. The superiority of the proposedconverter, as compared with conventional and other suggested multilevel converters, is significant decreasing the number of switches and minimizing the number of flying capacitors (FC) in converter. This improvement is possible by using suggested low-voltage sub-module converter to ANPCconverter and proposed modulation method. This results in reduction of the size and cost of converterand makes it more feasible and reliable. Applying active voltage balancing method for FC in proposed HANPC converter guaranties fast charging and voltage level regulation of FC without using balance booster circuit. Improving output voltage spectrum leads to inductance reduction of output L-C filter which enhances static GPU performance. The simulation and experimental results verify the validity and feasibility of proposed converter.


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