Showing papers on "Switched-mode power supply published in 2017"

Modeling of Grid-Connected VSCs for Power System Small-Signal Stability Analysis in DC-Link Voltage Control Timescale

Abstract: With the increasing use of voltage source converters (VSCs) in power electronics dominated power systems, oscillation phenomena in DC-link voltage control (DVC) timescale (around 10 Hz) among multiple VSCs have occurred. Several studies have tried to analyze these oscillation problems, but all associated with the single VSC situation. To consider the dynamic interactions between VSCs in DVC timescale, especially in the weak grid condition, this paper presents a small-signal model to understand VSC external characteristics based on motion equation concept also featured in synchronous generator (SG). Comparisons of time-domain simulation responses and eigenvalues show that the proposed model can hold the main behaviors of concern. The form of the model is very similar to the rotor motion equation in SG, with which power engineers have been very familiar. In addition, by establishing the relationship between the unbalanced powers and state variables of internal voltage (viz., VSC output voltage), the modeling idea introduced in this paper can be applied to other power electronic devices.

Higher Order Compensation for Inductive-Power-Transfer Converters With Constant-Voltage or Constant-Current Output Combating Transformer Parameter Constraints

Abstract: Compensation is crucial for improving performance of inductive-power-transfer (IPT) converters. With proper compensation at some specific frequencies, an IPT converter can achieve load-independent constant output voltage or current, near zero reactive power, and soft switching of power switches simultaneously, resulting in simplified control circuitry, reduced component ratings, and improved power conversion efficiency. However, constant output voltage or current depends significantly on parameters of the transformer, which is often space constrained, making the converter design hard to optimize. To free the design from the constraints imposed by the transformer parameters, this paper proposes a family of higher order compensation circuits for IPT converters that achieves any desired constant-voltage or constant-current (CC) output with near zero reactive power and soft switching. Detailed derivation of the compensation method is given for the desired transfer function not constrained by transformer parameters. Prototypes of CC IPT configurations based on a single transformer are constructed to verify the analysis with three different output specifications.

Electrical power system essentials

Abstract: Preface 1 Introduction to Power System Analysis 11 Introduction 12 Scope of the Material 13 General Characteristics of Power Systems 14 Phasors 15 Equivalent Line-To-Neutral Diagrams 16 Power in Single-phase Circuits 17 Power in Three-phase Circuits 18 Per Unit Normalization 19 Power System Structure 2 The Generation of Electric Energy 21 Introduction 22 Thermal Power Plants 23 Nuclear Power Plants 24 Renewable Energy 25 The Synchronous Machine 3 The Transmission of Electric Energy 31 Introduction 32 Transmission and Distribution Network 33 Network Structures 34 Substations 35 Substation Concepts 36 Protection of Transmission And Distribution Networks 37 Transformers 38 Power Carriers 4 The Utilization of Electric Energy 41 Introduction 42 Types of Load 43 Classification of Grid Users 5 Power System Control 51 Introduction 52 Basics of Power System Control 53 Active Power and Frequency Control 54 Voltage Control and Reactive Power 55 Control of Transported Power 56 Flexible AC Transmission Systems (FACTS) 6 Energy Management Systems 61 Introduction 62 Loadflow or Power Flow Computation 63 Optimal Powerflow 64 State Estimator 7 Electricity Markets 71 Introduction 72 Electricity Market Structure 73 Market Clearing 74 Social Welfare 75 Market Coupling 8 Future Power Systems 81 Introduction 82 Renewable Energy 83 Decentralized Or Distributed Generation 84 Power-electronic Interfaces 85 Energy Storage 86 Blackouts and Chaotic Phenomena Appendices A Maxwell's Laws A1 Introduction A2 Power Series Approach To Time-varying Fields A3 Quasi-Static Field Of A Parallel-plate Capacitor A4 Quasi-Static Field Of A Single-turn Inductor A5 Quasi-Static Field Of A Resistor A6 Circuit Modeling B Power Transformer Model B1 Introduction B2 The Ideal Transformer B3 Magnetically-Coupled Coils B4 The Non-ideal Transformer B5 Three-phase Transformer C Synchronous Machine Model C1 Introduction C2 The Primitive Synchronous Machine C3 The Single-phase Synchronous Machine C4 The Three-phase Synchronous Machine C5 Synchronous Generator In The Power System D Induction Machine Model D1 Introduction D2 The Basic Principle of The Induction Machine D3 The Magnetic Field In The Air-Gap D4 A Simple Circuit Model For The Induction Machine D5 Induction Motor In The Power System E The Representation of Lines And Cables E1 Introduction E2 The Long Transmission Line E3 The Medium-length Transmission Line E4 The Short Transmission Line E5 Comparison of The Three Line Models E6 The Underground Cable References List of Abbreviations List of Symbols Index

DC Grid Voltage Regulation Using New HESS Control Strategy

Abstract: The power generation from renewable power sources is variable in nature, and may contain unacceptable fluctuations in case of the wind power generation. High fluctuations in power generation may negatively impact the voltage stability of the microgrid. This problem can be alleviated by using hybrid energy storage system consisting of batteries and supercapacitors (SCs) at dc grid. A new control scheme is proposed to control the power sharing between batteries and SCs to match the generation-demand mismatch and hence to regulate the grid voltage. In the proposed control strategy, the SC supplies error component of the battery current in addition to the fast transient power demand. This added feature not only improves the dc grid voltage regulation capability but also reduces the stress levels on the battery and hence increases the life span of the battery. The main advantage of the scheme is that, the uncompensated power due to slow dynamics of the battery is diverted to the SC and keeps the state of charge within the limits for longer duration, as compared to the conventional strategy. The proposed scheme is validated through detailed experimental studies.

Optimum Number of Cascaded Cells for High-Power Medium-Voltage AC-DC Converters

Abstract: For power electronic systems to interface medium-voltage grids, e.g., in future electric ships, usually cascaded cells converters need to be employed, whereby either few cells featuring power semiconductors with high blocking voltage capability or a larger number of cells using low-voltage (LV) semiconductors can be used. As shown in this paper, physics-inspired empirical models of the dependence of Insulated-Gate Bipolar Transistor (IGBT) power modules' loss-relevant characteristics on the blocking voltage enable an analytic optimization of the efficiency of a cascaded H-bridges (ac-dc) converter, which is complemented by a full efficiency versus power density ηρ-Pareto optimization. For a 10-kV grid, 1200V or 1700V are identified as optimum blocking voltages, resulting in a suitable trade-off between efficiency and power density. Significant efficiency and power density gains can be realized by replacing silicon IGBTs by LV silicon carbide (SiC) devices in multi-cell systems, whereas single-cell designs based on high-voltage SiC devices suffer from the high dv/dt and di/dt values required to limit switching losses. Reliability is analyzed considering redundancy, showing that the reliability of designs based on lower blocking voltages can be comparable with that of designs using higher blocking voltages, and hence fewer cells, if similar effort concerning additionally installed power capability is considered.

A New Three Input DC/DC Converter for Hybrid PV/FC/Battery Applications

Abstract: In this paper, a new three-port dc/dc converter is presented for hybrid photovoltaic (PV)/fuel cell (FC)/battery applications. The proposed structure comprises a conventional buck-boost and a boost converter. Four power switches and four diodes are employed in the proposed converter. The voltage gain of the presented converter is more than the conventional boost converter. This advantage and having two unidirectional and a bidirectional inputs make the structure a suitable power electronic interface for hybrid generation applications. In addition, there are no limitations in switching the modulation. Therefore, tracking the maximum power of the PV source, setting the FC power, controlling the battery power, and calibrating the output voltage can be equipped by controlling duty ratios of the switches. The input power sources can provide power to the load and either charge or discharge the battery individually or simultaneously. The steady-state analyses of the presented converter are discussed thoroughly in this paper. Finally, in order to validate the feasibility of the presented converter, experimental results are provided.

A High Power Density Series-Stacked Energy Buffer for Power Pulsation Decoupling in Single-Phase Converters

Abstract: A high-efficiency, high-power-density buffer architecture is proposed for power pulsation decoupling in power conversion between dc and single-phase ac. We present an active decoupling solution that yields improved efficiency and reduced circuit complexity compared to existing solutions. In the proposed architecture, the main energy storage capacitor is connected in series with an active buffer converter across the dc bus. The series-stacked capacitor blocks the majority of the dc bus voltage to reduce the voltage stress on the buffer converter, such that fast, low-voltage transistors can be employed for the buffer converter. Moreover, the series capacitor provides the majority of the power pulsation decoupling through a wide voltage swing, and the buffer converter only needs to process a small fraction of the total power of the entire architecture, allowing a very small active circuit volume and very high system efficiency. The circuit operation and design constraints are analyzed in detail. In the proposed buffer architecture, the series stacking of a nearly lossless capacitor and a lossy converter presents a challenge of capacitor voltage balancing and power loss compensation. We propose a control scheme exploiting the small ripple in the bus voltage and dc input current to compensate for the power loss in the buffer converter while maintaining the voltage balance. Light-load techniques are also introduced to ensure that the buffer architecture meets strict ripple requirements while providing sufficient loss compensation. A 2-kW hardware prototype based on low-voltage GaN switches has been built to demonstrate the performance of the proposed solution. A power density of 25 W/cm $^3$ (410 W/in $^3$ ) by rectangular box volume and an efficiency above 98.9% across a wide load range has been experimentally verified.

Delta Power Control Strategy for Multistring Grid-Connected PV Inverters

Abstract: With a still increasing penetration level of grid-connected photovoltaic (PV) systems, more advanced active power control functionalities have been introduced in certain grid regulations. A delta power constraint, where a portion of the active power from the PV panels is reserved during operation, is required for grid support (e.g., during frequency deviation). In this paper, a cost-effective solution to realize delta power control (DPC) for grid-connected PV systems is presented, where the multistring PV inverter configuration is adopted. This control strategy is a combination of maximum power point tracking (MPPT) and constant power generation (CPG) modes. In this control scheme, one PV string operating in the MPPT mode estimates the available power, whereas the other PV strings regulate the total PV power by the CPG control strategy in such a way that the delta power constraint for the entire PV system is achieved. Simulations and experiments have been performed on a 3-kW single-phase grid-connected PV system. The results have confirmed the effectiveness of the proposed DPC strategy, where the power reserve according to the delta power constraint is achieved under several operating conditions.

High Step-Up Interleaved Boost Converter for Distributed Generation Using Renewable and Alternative Power Sources

Abstract: This paper proposes a novel high step-up interleaved boost converter suitable for distributed generation using renewable and alternative power sources. The proposed interleaved boost converter not only lengthens the lifetime of the renewable power source by reducing the input-current ripple but also achieves high step-up conversion. In addition, the voltage stress of the main switches is lowered due to the lossless passive-clamp circuit. Hence, large voltage spikes across the main switches are alleviated and the efficiency is improved. Finally, a prototype circuit with an input voltage of 48 V, an output voltage of 380 V, and an output rated power of 3.5 kW are implemented and tested to demonstrate the functionality of the proposed converter. Moreover, satisfying experimental results are obtained and discussed in this paper; the measured full-load efficiency is 94.7%, and the highest measured efficiency of the proposed converter is 97.3%.

High-Performance Quasi-Z-Source Series Resonant DC-DC Converter for Photovoltaic Module Level Power Electronics Applications

Abstract: This paper presents the high-performance quasi-Z-source series resonant dc-dc converter as a candidate topology for the photovoltaic module-level power electronics applications. The converter features a wide input voltage and load regulation range thanks to the multimode operation, i.e., when the shoot-through pulse width modulation and phase-shift modulation are combined in a single switching stage to realize the boost and buck operating modes, respectively. Our experiments confirmed that the proposed converter is capable of ensuring ripple-free 400 V output voltage within the sixfold variation of the input voltage (from 10 to 60 V). The converter prototype assembled achieved a maximum efficiency of 97.4%, which includes the auxiliary power and control system losses.

Novel Dynamic Voltage Support Capability of Photovoltaic Systems for Improvement of Short-Term Voltage Stability in Power Systems

Abstract: The large integration of photovoltaic (PV) power generation systems into power systems causes deterioration in power system stability. In our previous work, we showed that reactive power control using the inverters of PV systems, known as dynamic voltage support (DVS) capability, is a promising approach to improve the short-term voltage stability in power systems. In this paper, we propose a novel DVS capability as a function of PV inverters. In contrast to the conventional DVS capability, the proposed method uses both active and reactive power injection to improve the short-term voltage stability. Numerical examples show that the proposed DVS capability further improves the short-term voltage stability compared with the conventional DVS capability. Furthermore, the proposed method can alleviate a frequency drop after a fault caused by interruption in PV systems.

Management of Power Quality Issues in Low Voltage Networks Using Electric Vehicles: Experimental Validation

Abstract: As electric vehicles (EVs) are becoming more widespread, their high power consumption presents challenges for the residential low voltage networks, especially when connected to long feeders with unevenly distributed loads. However, if intelligently integrated, EVs can also partially solve the existing and future power quality problems. One of the main aspects of the power quality relates to voltage quality. The aim of this work is to experimentally analyze whether series-produced EVs, adhering to contemporary standard and without relying on any vehicle-to-grid capability, can mitigate line voltage drops and voltage unbalances by a local smart charging algorithm based on a droop controller. In order to validate this capability, a low-voltage grid with a share of renewable resources is recreated in SYSLAB PowerLabDK. The experimental results demonstrate the advantages of the intelligent EV charging in improving the power quality of a highly unbalanced grid.

A Novel Grid-Connected PV System Based on MMC to Get the Maximum Power Under Partial Shading Conditions

Abstract: In the case of partial shading, the output power of the unshaded PV modules will be decreased by the influence of the shaded PV modules in one branch. In order to solve this problem, this paper proposes a novel topology for a PV power generation system by connecting a PV module to the capacitor in each submodule of a modular multilevel converter parallel. As partial shading occurs, the maximum power can be extracted by regulating the capacitor voltage to the maximum power point voltage. With this proposed topology, the maximum power tracking controller, the redundancy module controller, the voltage stability controller, and the grid-connected controller are studied. Simulation and experiment results show that comparing to the traditional topology, the proposed topology can greatly improve the output power of the PV system under the conditions of partial shading and features with low-voltage stress and high efficiency.

Online Condition Monitoring of Power MOSFET Gate Oxide Degradation Based on Miller Platform Voltage

Abstract: The condition monitoring problem of power devices is significant for diagnostics and prognostics of a switched-mode power supply (SMPS) system. For power mosfet , the gate oxide degradation often occurs in various applications. However, there is no online condition monitoring method for gate oxide degradation so far. In this paper, a new precursor that can be used for online condition monitoring of power mosfet gate oxide degradation is proposed. Gate oxide degradation mechanisms and effect are summarized, and the mosfet turn-on process is analyzed. Then, a theoretical model is established to describe the relationship between miller platform voltage and two types of gate oxide defects, and miller platform voltage is identified as a new precursor. The precursor can be extracted without impacting system operation, thus online condition monitoring can be accomplished. The accelerated degradation test is carried out for power mosfet s with both high electric field and gamma irradiation methods, and the degraded devices injection and in situ monitoring of miller platform voltage are conducted on a BOOST circuit to verify the feasibility of the new precursor. Experimental results demonstrate that the new precursor can be applied to online condition monitoring of power mosfet gate oxide degradation in the SMPS system.

Voltage Control with PV Inverters in Low Voltage Networks—In Depth Analysis of Different Concepts and Parameterization Criteria

Abstract: In some rural and sub-urban areas, the hosting capacity (HC) of low voltage networks is restricted by voltage limits. With local voltage control, photovoltaic generators can mitigate the voltage rise partly and, therefore, increase the HC. This paper investigates the effectiveness and general performance of different reactive and active power control concepts. It presents the findings of an extensive simulation-based investigation into the effectiveness of voltage rise mitigation, additional reactive power flows, network losses, and power curtailment. The two most common implementations of reactive power control have a similar effectiveness. The voltage rise can be compensated for by up to 25% and more than 60% for typical cable and overhead (OH) feeders, respectively. By additionally using active power curtailment of up to 3% of the annual yield, the HC can be increased by about 50% and 90% for the considered cable and OH feeder, respectively (purely rural feeders).

Transmission Loss Optimization-Based Optimal Power Flow Strategy by Hierarchical Control for DC Microgrids

Abstract: This paper proposes an efficient power flow sharing and voltage regulation control method based on hierarchical control to minimize the transmission loss of dc microgrids. Different from the conventional optimal power flow algorithm for the dc grids, the proposed approach needs neither prior knowledge of the grid's conductance matrix nor the load distribution matrix, which means improvement of the expansibility and reduction of the cost. At the primary control level, a voltage droop characteristic is set for each converter to improve the stability and reliability of the grid. The secondary control level aims to regulate the power flow of the microgrid to the optimal condition. The two control levels exchange information by low bandwidth communication. The validity of the proposed approach is verified by both simulation results of a dc microgrid based on IEEE 14-bus system and experimental results on a 50-V two-terminal prototype dc microgrid.

Model Predictive Control With Common-Mode Voltage Injection for Modular Multilevel Converter

Abstract: Submodule (SM) capacitor voltage ripple is one of the major concerns in modular multilevel converters (MMCs). Capacitor voltage ripple leads to the double-frequency circulating current (CC) in legs, thereby resulting in a cascading effect of increased peak value of the arm current, semiconductor device stress, and power losses in MMCs. In this study, a model predictive control (MPC) with common-mode voltage (CMV) injection is proposed to minimize capacitor voltage ripple and the magnitude of CC. A discrete-time mathematical model of the MMC with CMV is presented to predict the future behavior of the control variables. The injection of CMV guarantees arm voltage balancing without CC control and long-term stability of MMC without large capacitors. The dynamic and steady-state performances of MPC with CMV injection are verified on an MMC with three-level flying capacitor SMs. A performance comparison between the proposed approach and the conventional MPC is also presented. Simulation and experimental studies show that CMV injection significantly reduces the capacitor voltage ripple and the CC in legs. The proposed approach also improves output voltage and current waveform quality.

Integrated Multiple-Output Synchronous Buck Converter for Electric Vehicle Power Supply

Abstract: This paper proposes a novel integrated synchronous buck converter for the auxiliary power supply system of electric vehicles, which achieves multiple independently regulated outputs with reduced switching components in comparison with the conventional separate buck converters. In order to obtain a better understanding of the proposed converter, operational principle and performance characteristics of a simplified dual-output buck converter are introduced in detail, as an example. The analysis shows that zero-voltage-switching operation and lower conduction losses could be attained. In addition, its dynamic behavior is similar to the conventional buck converter and thus the controller design is simple. Finally, experimental results based on a prototype circuit in which two inductors are integrated into one magnetic core to achieve further reduced cost are demonstrated to verify the advantages.

Relationship Between Two Direct Power Control Methods for PWM Rectifiers Under Unbalanced Network

Abstract: Active power control plays an important role in a pulse width modulation (PWM) rectifier under both balanced and unbalanced network conditions. The prior methods to achieve active power oscillation cancellation (APOC) under unbalanced grid voltages are usually implemented by forcing the grid current to track appropriate current references. They require fine tuning work of a current controller and positive-/negative-sequence extraction of grid voltage/currents and/or converter voltage, which complicates the design of the controller. This paper presents two APOC methods in the frame of direct power control (DPC) for the PWM rectifier and reveals their inherent relationship. In the first method, an appropriate power compensation is added to the original power references without modifying the internal control structure. In the second method, a novel definition of reactive power is employed to replace conventional reactive power, which achieves the aim of APOC automatically. Both methods can be easily integrated with existing DPC schemes with a slight modification. The sequence extraction required in prior methods is eliminated. The inherent relationship between these two methods is investigated, and it is found that they are completely equivalent. The two APOC methods are comparatively studied and implemented in the basic table-based DPC. Simulation and experimental results confirm the theoretical study and the effectiveness of the two methods.

Improved Vehicle-to-Home (iV2H) Operation Mode: Experimental Analysis of the Electric Vehicle as Off-Line UPS

Abstract: This paper presents experimental results of electric vehicle (EV) operation as an off-line uninterruptible power supply (UPS). Besides the traditional grid-to-vehicle and vehicle-to-grid modes, this paper presents an improved vehicle-to-home operation mode. This new operation mode consists of the detection of a power outage in the power grid and the change of the EV battery charger control to operate as an off-line UPS. When the power grid voltage is restored, the voltage produced by the on-board EV battery charger is slowly synchronized with the power grid voltage before a complete transition to the normal mode. This paper presents results of two algorithms to detect a power outage: the root mean square (rms) calculation method based on half-cycle of the power grid voltage, and the rms estimation based on a Kalman filter. The experimental results were obtained in steady and transient state considering two cases with the EV plugged in at home: when charging the batteries and without charging the batteries. This paper describes the EV battery charger, the power outage detection methods, and the voltage and current control strategies.

A Single-Switch AC–DC LED Driver Based on a Boost-Flyback PFC Converter With Lossless Snubber

Abstract: A single-switch ac–dc light-emitting-diode (LED) driver based on boost-flyback power factor correction (PFC) converter with a lossless snubber is proposed. In the proposed LED driver, the boost PFC module is designed to be operated in the discontinuous-conduction mode to achieve a high power factor. The dc–dc flyback module is designed to provide input–output electrical isolation to improve safety. The lossless snubber circuit clamps the peak voltage spike of switch to a low voltage and the leakage inductor energy is recycled via the dc–dc flyback module. Additionally, a low-voltage-rating capacitor can be used as the dc-bus capacitor because some of the input power is directly conducted to the output; the remaining power is stored in the dc-bus capacitor. Therefore, the proposed LED driver can provide a high power factor and a high power conversion efficiency. These results are verified for an output of 48 V and 2 A for the experimental prototype.

A 6.78-MHz Single-Stage Wireless Power Receiver Using a 3-Mode Reconfigurable Resonant Regulating Rectifier

Abstract: A 6.78-MHz wireless power receiver using a 3-mode reconfigurable resonant regulating rectifier for resonant wireless power transfer is presented. The proposed receiver improves power conversion efficiency and reduces die area and off-chip components by achieving power conversion plus voltage regulation in one stage, using only four on-chip power transistors and one off-chip capacitor. Moreover, the proposed 3-mode operation reduces the output voltage ripples and accomplishes switching synchronization easily during mode switching. The proposed pulsewidth modulation controller using ramp-stacking technique and type-II compensation achieves tight voltage regulation in the full loading range with fast transient responses. An adaptive sizing method is also employed to further improve the light-load efficiency of the receiver. Fabricated in a standard 0.35- $\mu \text{m}$ CMOS process using 5-V devices, the receiver regulates the output voltage at 5 V and delivers a maximum power of 6 W. The measured peak efficiency reaches 92.2% when delivering an output power of 3.5 W. For a load step between 0.5 and 5 W, the overshoot and undershoot are less than 300 mV and the settling times are less than 16 $\mu \text{s}$ .

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

Abstract: 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 nonisolated online UPS system. The proposed system consists of bridgeless PFC boost rectifier, battery charger/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 bank voltage to only 24V, and regulates the dc-link voltage during the battery power mode. Operating batteries in parallel improves the battery performance and resolve the problems related to conventional battery banks that arrange batteries in series. A new control method, integrating slide mode and proportional-resonant control, for the inverter has been proposed which regulates the output voltage for both linear and nonlinear loads. The controller exhibits excellent performance during transients and step changes in load. The operating principle and experimental results of 1-kVA prototype have been presented for validation of the proposed system.

Improvement of power quality using a robust hybrid series active power filter

Abstract: The degradation in power quality causes adverse economical impact on the utilities and customers. Harmonics in current and voltage are one of the most commonly known power quality issues and are solved by the use of a hybrid series active power filter (HSAPF). In this paper, a new controller design using sliding-mode controller-2 is proposed to make the HSAPF more robust and stable. An accurate averaged model of a three-phase HSAPF is also derived in this paper. The design concept of the robust HSAPF has been verified through simulation and experimental studies, and the results obtained are discussed.

A DC-voltage Controlled Variable Capacitor for Stabilizing the ZVS Frequency of a Resonant Converter for Wireless Power Transfer

Abstract: Varactors are often used in phase-locked-loop (PLL) circuits for dynamic frequency control. However, the voltage and current ratings of varactors are too low to be used in most power electronic circuits. This paper proposes a transistor-controlled variable capacitor (TCVC), which functions similar to varactors in that its equivalent capacitance can be controlled by a dc voltage. However, TCVC can handle high voltages and currents so that it can be used in dc-ac power converters of wireless power transfer (WPT) systems such as an autonomous push-pull resonant converter to adjust its zero voltage switching (ZVS) frequency so that the operating frequency of the system can be stabilized to simplify the circuit and EMI filter design particularly for WPT systems with multiple power pickups while maintaining soft-switching operation of the converter against magnetic coupling and load variations. The relationship between the equivalent capacitance of the TCVC and the dc control voltage is developed by theoretical analysis and verified by experimental results. A prototype circuit is built with a PLL controller to demonstrate that the soft-switching condition of the converter is maintained when the operating frequency is locked in at 1.65 MHz under load and magnetic coupling variations.

Self-Tuning Power Supply for Inductive Charging

Abstract: Inductive power transfer (IPT) systems for electric vehicle (EV) charging often have to operate under a wide range of coupling factors and loads, potentially mistuning the primary power supply. This is especially a problem in dynamic applications where the vehicles are moving. This paper investigates the design of a self-tuning power supply by utilizing a switchable bank of capacitors with a push-pull tuning topology. The proposed power supply is able to handle operation under a wide range of coupling factors and loading conditions while achieving ZVS operation at a fixed frequency. A mathematical model is developed to model the system and an experimental system is built to test the design. The experimental system is able to deliver a constant 1 kW over a coupling factor range of 0.1-0.33. A detection circuit to monitor the state of tuning of the power supply is presented along with a control scheme to maintain optimal tuning.

Capacitance, dc Voltage Utilizaton, and Current Stress: Comparison of Double-Line Frequency Ripple Power Decoupling for Single-Phase Systems

Abstract: Double-line frequency ripple power is inherent in single-phase rectifiers and inverters, and, if not managed properly, it can be adverse to system performance at both the ac and dc sides. Therefore, numerous active power-decoupling techniques have been introduced to decouple the double-line frequency ripple power. However, no comprehensive comparisons are available on the permitted minimum capacitance for power decoupling, dc voltage utilization, current stress, modulation complexity, and even application evaluations, except for power rating and component counts. All of these aspects are critical when choosing appropriate power-decoupling techniques for different applications. In this article, the minimum capacitance to decouple the ripple power and the current stress of power devices in the main circuit are derived in light of different voltages across energy storage capacitors. By considering the ripple power paths, we investigate the dc voltage utilization of both the main circuit and power-decoupling circuit. Combined with other features, including component counts and modulation complexity, the overall characteristics of different power-decoupling techniques are compared and summarized to effectively evaluate their performance in different applications.

Cascade-Free Model Predictive Control for Single-Phase Grid-Connected Power Converters

Abstract: In a conventional finite control set model predictive control (FCS-MPC) formulation, active and reactive power control loops rely on the predictive controller, whereas the dc-bus voltage is usually governed by a PI-based control loop. This originates from fact that the dynamic equations for describing the predictions of these variables are heavily coupled. In this paper, a cascade-free FCS-MPC for single-phase grid-connected power converters is presented. The proposed control algorithm is formulated in terms of established dynamic references design, which was originally proposed to directly govern active and reactive power, and dc-voltage in three-phase power converters. In this paper, the dynamic reference design concept is extended to control single-phase grid-connected power converters. The proposed control algorithm does not use instantaneous ac-power calculations; instead, it directly formulates the optimal control problem on the grid-current in the original stationary reference frame. The experimental results obtained with a single-phase grid-connected neutral point clamped (NPC) converter confirm a successful design, where system constraints, e.g., maximum power and weighted switching frequency, are easily taken into account.

On-Line Load Sensitivity Identification in LV Distribution Grids

Abstract: This letter proposes a new on-line load sensitivity identification by means of power electronics-based devices. Applying a voltage and frequency perturbation and measuring the consumed power of the loads, the proposed method computes in real time the voltage and frequency dependency of the load active and reactive power. In this letter, a smart transformer application has been proposed, but the method is general for any power electronics converter able to influence dynamically the voltage and frequency in the grid.

Reactive Power Ancillary Service of Synchronous DGs in Coordination With Voltage Control Devices

Abstract: This paper presents an optimal way to control steady-state voltage in distribution feeders using reactive power ancillary service that is provided by synchronous distributed generators (DGs). Based on load forecasts provided one day in advance, DG reactive power is dispatched on the hour in coordination with the switching operations of an on-load tap changer (OLTC) and shunt capacitors (SCs). This aims to reduce not only distribution line power losses but also the number of switching operations of the OLTC and the SCs, which affect the feeder voltage quality and switching device lifetime. For the reactive power dispatch, a mixed-integer nonlinear optimization problem is formulated using a multiobjective function and solved using a particle swarm optimization (PSO) algorithm. Modules using evolutionary and dynamic programming are incorporated into the PSO algorithm to be less susceptible to becoming trapped in local optima and have a better chance of reaching global optimum. Simulation case studies using small- and large-scale distribution networks were performed using MATLAB to demonstrate that the coordinated reactive power support of the DGs, OLTC, and SCs can achieve the objective effectively, resulting in improved voltage quality.