Showing papers in "Iet Power Electronics in 2019"

Modular-multilevel converter topologies and applications – a review

Abstract: Recently developed modular-multilevel converter (M-MC) has a major attention in the industry and research works which is moving into feasible technology for many medium and high-power applications. M-MCs have been improved by existing power conversion technology in several aspects, including efficiency, modular structure, power quality, transformerless operational capability, fault tolerant and redundancy operations having a low expense, standard components utilisation, high availability, excellent quality of output wave forms. However, as several challenges combined with M-MC topologies, include reduced voltage stress, compact size, and substantially lower semiconductor losses. These attributes the lower operating cost for high-power applications such as distribution systems and high-voltage direct current (HVDC) transmission systems. The main contribution of this study is to bring the scrutiny of M-MC applications and different circuit topologies. These M-MC configurations consist of converter structures with sub-module converters and M-MC family members. In such a way, the M-MC applications are generalised and it results the size and cost halved, reduced conduction and switching losses and increases system reliabilities. Moreover, in each application of M-MC, drawbacks, and advantages have been discussed in detail. This review presents the latest performance of M-MC with respect to the mentioned research areas and new applications.

Survey on magnetic resonant coupling wireless power transfer technology for electric vehicle charging

Abstract: Wireless power transfer (WPT) technology makes it possible to supply power through an air-gap, without the need for current-carrying wires. One important technique of WPT technology is magnetic resonant coupling (MRC) WPT. Based on the advantages of MRC WPT, such as safety and high power transfer efficiency over a long transmit distance, there are many possible applications of MRC WPT. This study provides a comprehensive, state-of-the-art review of the MRC WPT technology and wireless charging for electric vehicle (EV). A comparative overview of MRC WPT system design which includes a detailed description of the prototypes, schematics, compensation circuit topologies (impedance matching), and international charging standards. In addition, this study provides an overview of wireless EV charging including the static wireless EV charging and the dynamic wireless EV charging, which focuses on the coil design, power transfer efficiency, and current research achievement in the literature.

Non-isolated buck–boost dc–dc converter with quadratic voltage gain ratio

Abstract: A new transformer-less buck-boost converter is proposed, which owns a quadratic voltage gain ratio. The proposed converter (a) has only one active switch, which makes the implementation of the gate driver and control system simpler; (b) has a quadratic voltage gain without using a transformer, which equips the designers to obtain a high-voltage gain ratio and avoid the complexity of magnetic utilisations; (c) works both in step-up or step-down mode, while most of the existing quadratic topologies are able to work either in step-up or step-down mode; and (d) shares a common ground between the input and output terminals. The operating states of the proposed converter along with its steady-state performance are analysed. Then, the small-signal modelling and the power loss analysis are performed. A comparison shows the unique features of the converter, specifically in terms of voltage gain ratio and the count of power switches. Finally, the experimental results of a laboratory prototype, as well as the simulation results from PSIM software, are used for validation. The converter was tested in different conditions to inspect its transient response and to record its efficiency. The maximum recorded efficiencies in boost and buck modes, respectively were 94.7 and 93%.

High step-up DC–DC converter with coupled inductor suitable for renewable applications

Abstract: In this study, a new non-isolated high step-up DC-DC converter is presented with high-voltage gain which is suitable for renewable applications. The proposed converter uses coupled inductor and voltage multiplier cell (diode capacitor) for increasing the voltage level. The voltage gain of the proposed converter can be increased by selecting the appropriate turns ratio of coupled inductor. Voltage multiplier cell consists of two diodes and two capacitors which are used to obtain high-voltage gain. The diode-capacitor cell is used as a clamp circuit, which leads to reducing the voltage stress across the semiconductors. The proposed converter has a single power switch which causes the control of the proposed converter is simple. Also, the power switch is used with lower ON-state resistant ( R DS-ON ). The zero-current switching of the diode is obtained in OFF state. Therefore, the conduction losses are decreased with lower normalised voltage stress across semiconductors. To prove the performance of the proposed converter, theoretical analysis and comparison with other converters are provided. To confirm the benefits of the proposed converter, a laboratory prototype with 20 V input voltage, 200 V output voltage and about 200 W power level at operating 25 kHz is built and tested.

Modular multilevel converters technology: a comprehensive study on its topologies, modelling, control and applications

Abstract: A modular multilevel converter (MMC) is one of the perfect topologies for high power and medium-/high-voltage energy conversion systems. The MMC has attractive features such as modularity, voltage and current scalability, transformerless operation, fault blocking capability, reduced filter size, a reduced ripple of the output current, high efficiency, and low expense on redundancy. These features attracted industries over the past few years, notable research has been carried out on MMC topologies, their operation, and control. This study presents a review of MMC topologies and their mathematical models. Furthermore, their control schemes (classical as well as model predictive controls) and modulation techniques are discussed. Finally, MMC applications and their future challenges are highlighted.

Torque ripple suppression of permanent magnet synchronous machines by minimal harmonic current injection

Abstract: Reducing torque ripples in a permanent magnet (PM) synchronous machine (PMSM) system has been an essential requirement in some high-performance applications. To suppress the torque ripples caused by time harmonics and spatial harmonics, an approach based on injecting minimum harmonic currents is proposed here. The proposed method extracts torque ripples from speed fluctuations, and the gradient descent optimisation (GDO) is utilised to determine the injected harmonic currents which are the commands of the harmonic current regulators. Using the torque ripple minimisation and the injected harmonic current minimisation as the two objectives, the GDO not only minimises the torque ripples of the PMSM system but also guarantees that the magnitude of the injected harmonic currents is minimal. The proposed method is simple to implement in the hardware and does not require complex computation. Its effectiveness is verified by experimental results.

Sliding-mode control of a boost converter under constant power loading conditions

Abstract: The cascade connection of two dc-dc switching converters for constant power supply is studied. The source converter is of boost type while the load converter is of buck type. The natural unstable behaviour of the cascade connection for both on and off states of the boost converter is counteracted by a sliding-mode control strategy that combines unstable trajectories to generate a stable one for the regulated boost converter dynamics. Experimental results using an electronic load to emulate a buck converter-based constant power load are in good agreement with the theoretical predictions. A similar agreement is later obtained when a buck converter with a dynamic behaviour close to an instantaneous constant power load is employed instead of the electronic load.

Comparison among different analysis methodologies for LLC resonant converter

Abstract: The LLC resonant converters have been widely used in many applications due to their features such as wide input voltage range, high efficiency, and high power density. Therefore, the analysis methodology for the LLC resonant converter is of great importance. Based on the existing literature, there are mainly four analysis methodologies: (i) fundamental harmonic analysis; (ii) frequency domain with time domain partial correction; (iii) frequency domain with time domain complete correction; (iv) time domain analysis or operation mode-based analysis. However, there is no systematic view and study on different LLC analysis methodologies. Therefore, the main purpose and contribution of this study are to make a comprehensive study and comparison of these analysis methodologies and to provide guidance on analysing and designing of the LLC resonant converter to the readers. In this study, the principles of these four analysis methodologies are introduced briefly. Then, by introducing gain error and peak gain frequency error as definitions, comprehensive comparison studies on these four different methodologies for different conditions are implemented. Recommended applications for each methodology are summarised; finally, an experimental prototype is built to verify the theoretical analysis, and a conclusion is drawn.

Multi-port DC–DC converter for bipolar medium voltage DC micro-grid applications

Abstract: In this study, a new bipolar DC-DC converter based on the combination of a multi-port dual active bridge and a neutral point clamp topology is proposed. This topology provides the integration of multiple renewable energy sources, with different types and capacities, to a bipolar medium voltage DC micro-grid. The main advantages of the proposed topology are its high power density and the reduced number of switches with respect to the combination of different converters. Moreover, it provides isolation which is crucial for some micro-grid power conditioning converters. The proposed converter is employed for a typical hybrid generation system consisting of a photovoltaic (PV) system, a fuel cell (FC), and a battery (BAT) considering the characteristics of each power generation system like maximum power point tracking of PV, optimum operating region of FC and over-charge/discharge of BAT. In addition, the proposed converter is simulated in different power sharing modes in MATLAB/Simulink software environment. Eventually, the theoretical and simulation analyses are validated by experimental prototype results.

Active disturbance rejection control of DC–DC boost converter: a review with modifications for improved performance

Abstract: This study provides a comprehensive review of existing active disturbance rejection control (ADRC) techniques for the control of non-minimum phase (NMP) DC-DC boost converter (DBC). A boost converter presents a challenging control task due to its non-linear and NMP dynamics while operating in continuous conduction mode. ADRC schemes, specifically those that claim improved performance for NMP systems, have been experimentally evaluated for voltage control of DBC. Additionally, a new way of incorporating known system dynamics into the control structure is proposed through a modified scheme. An averaged non-linear model of DBC is used in the simulation to analyse the effectiveness of control schemes and the results are experimentally validated on hardware. It is shown that the proposed method outperforms the reported model-assisted ADRC techniques while utilising only the system pole information.

Review of model predictive control strategies for matrix converters

Abstract: Matrix converters are a well-known class of direct AC-AC power converter topologies that can be used in applications, where compact volume and low weight are necessary. For good performance, special attention should be paid to the control scheme used for these converters. The model predictive control strategy is a promising, straightforward and flexible choice for controlling various different matrix converter topologies. This work provides a comprehensive study and detailed classification of several predictive control methods and techniques, discussing special capabilities they each add to the operation and control scheme for different matrix converter topologies. This study also considers the issues regarding the implementation of model predictive control strategies for matrix converters. This survey and comparison are intended to be a useful guide for solving the related drawbacks of each topology and to enable the application of this control scheme for matrix converters in practical applications.

Detection and identification of multiple IGBT open-circuit faults in PWM inverters for AC machine drives

Abstract: This study proposes a new scheme for online detection and identification of single and multiple insulated-gate bipolar transistor (IGBT) open-circuit faults in three-phase pulse-width modulation (PWM) inverters of AC machine drives, which is based on Park's vector of machine phase currents. First, the switch open-circuit faults are detected by monitoring dwell times of the vector of the actual phase currents expressed in the stationary reference frame in each sector, where the normalisation of the current to its reference value is utilised, by which the immunity to the false alarms in transient conditions is improved significantly. Then, the IGBT open-circuit faults are identified, where leg open-circuit conditions are in the first place determined based on the average values of the normalised line-to-line currents. Next, the single open-circuit IGBT is located from the polarity of the corresponding phase current. By the proposed diagnosis method, the fault detection time is at the longest about 52.3 and 54% of a fundamental period in the simulation and experimental tests, respectively, and the 27 possible cases of IGBT open-circuit faults combined for all IGBTs in the inverter can be identified. In addition, this algorithm can be implemented without any additional hardware and computational burden.

New family of non‐isolated step‐up/down and step‐up switched‐capacitor‐based DC–DC converters

Abstract: Here, a new family of non-isolated step-up/down and step-up switched-capacitor (SC)-based DC-DC converters are proposed possessing many advantages as lower voltage stress on capacitors and higher voltage gain compared to previously introduced DC-DC converters. The proposed converter structures have multiple capacitors which are based on principles of DC-DC SC converters. Therefore, the amount of power transfer from the input to the output is higher in the proposed converters. Generally, the proposed converters are more suitable for industrial applications, especially for generating high-voltage gains in lower duty-cycles. For proving the analysis, comprehensive comparisons and precise experiments have been performed which show remarkable performance of the proposed converter topologies.

Improved hybrid algorithms-based MPPT algorithm for PV system operating under severe weather conditions

Abstract: This study aims to provide a comparison between several maximum power point tracking (MPPT) algorithms for PV system under severe weather conditions. Two MPPT hybrid algorithms are proposed, namely (a) hybrid combination of fuzzy logic controller (FLC) and the incremental conductance (IC) and (b) MPPT controller integrates FLC and perturb and observe (P&O) method. The two developed hybrid algorithms combined the strength of both P&O, IC with FLC in single framework. MATLAB/Simulink is used to investigate the response of both algorithms. Several weather conditions are simulated: (i) uniform irradiation, (ii) sudden changing, and (iii) partial shading. Under partial shading on PV panel, multi-peaks appear in power–voltage characteristics of the panel. Simulation results showed that ability of FLC to track MPP degrade significantly when testing at weather conditions far from those used for training. Finally, the proposed hybrid algorithms successfully eliminate the previous limitations associated with FLC, IC, and P&O algorithms individually with efficiency exceeds 97%.

Switched Z-source networks: a review

Abstract: This study reviews and categorises different structures of switched Z-source networks. Generally, these structures are divided into two groups of basic switched Z-source networks and switched Z-source networks with the capability of high boost. Each of these groups is divided into several subgroups and different structures are introduced. For each subsection, the general power circuit is proposed and the extraction method from general power circuit for each structure is obtained. This study also provides a complete analysis of structures by using a conventional control method with two shoot-through and non-shoot-through modes. Small signal analysis for structures with a basic switched Z-source network is conducted and the general signal flow graph is extracted. A comprehensive analysis of all structures with a switched Z-source network is done and the tree diagram for the division of these structures is provided. Finally, different industrial applications and outlook of Z-source networks are introduced.

Modelling and analysis of the distortion of strongly-coupled wireless power transfer systems with SS and LCC–LCC compensations

Abstract: Accurate modelling is necessary for designing a wireless power transfer (WPT) system and currently, first harmonic approximation (FHA) is widely used. However, it is not accurate for WPT systems with a strong coupling, such as fast charging of electric vehicles with a coupling coefficient of 0.80, compared to the conventional wireless charging with a coupling coefficient of 0.15-0.30. This study develops accurate models for WPT systems with series-series (SS) and LCC-LCC compensations. For the SS compensation with a strong coupling, the transmitter and receiver currents are distorted, leading to much larger values than the estimations from FHA, which determines the selection of power switches and resonant capacitors. For the LCC-LCC compensation, the transmission coil currents are only highly distorted with rich third-order harmonics at the vicinity of the 0.889 coupling coefficient, leading to low efficiency and large coil current ratings. For the experimental prototype, the efficiency drop can be over 3%, which is significant, especially for high-power systems. The WPT system with the LCC-LCC compensation should avoid operation in the vicinity of this particular coupling coefficient. Furthermore, experiments are conducted, and the results perfectly match the calculations, demonstrating the accuracy of the proposed models.

Application of artificial neural networks for transistor open-circuit fault diagnosis in three-phase rectifiers

Abstract: This study deals with the transistor open-circuit fault diagnosis technique based on the grid current processing. In accordance with the proposed method, in the first stage, the defect of the power electronics converter is recognised. For this purpose, the zero current periods are registered in each converter phase circuits. The faulty transistors are identified calculating the average values of differences between predicted and measured phase currents. The novelty of the presented technique is an application of a neural network for the grid current prediction in the active rectifier. In fact, the transistor open-circuit faults do not affect the predicted grid currents immediately as soon as the transistor defects happen. Therefore, the differences between the predicted currents and the measured ones increase which are used for the faulty transistors identification. In the comparison to the switch open-circuit fault diagnostic techniques, which are known from the scientific literature survey, the method presented in this study is insensitive to load changes no matter a direction of the energy flow in the power conversion system.

Ultra-step-up dc–dc converter with low-voltage stress on devices

Abstract: This study suggests a novel ultra-step-up dc-dc converter with low normalised voltage stress across the power devices. The proposed converter incorporates the conventional boost converter with a self-lift circuit and charge pump concept and utilises a voltage multiplier cell at the output side. In the input side, two inductors are magnetised during the switch on-time. During the switch off-time, the stored energy in these inductors, charge pump capacitor and input source, is delivered to the load. Accordingly, the proposed converter is capable of providing high voltage gains with a small duty cycle. Besides, the voltage stress across the power devices is low. Therefore, the MOSFET switch with low R DS-on and devices with reduced nominal voltage can be used which in turn reduces the conduction and turn-on losses. The analysis of the voltage and current stresses is accomplished. The circuit performance is compared with other solutions in the literature in terms of voltage gain and normalised voltage stress of the semiconductors. Eventually, to validate the theoretical analysis, the experimental results are given.

Modified model predictive torque control for a PMSM-drive with torque ripple minimisation

Abstract: This paper presents an improved model predictive torque control (MPTC) scheme for a permanent magnet synchronous machine (PMSM). In conventional finite set model predictive control (FS-MPC), the optimal voltage space vector (VSV) is selected for application in the voltage source inverter (VSI) by the evaluation and minimisation of a cost function; however, the application of a single VSV in the whole control cycle leads to a relatively high torque ripple and a high sampling time is necessary to overcome this issue. In order to reduce these shortcomings without sacrificing torque reaction performance, a modified MPTC is proposed. First, in order to reduce the computational burden, a switching table is introduced for a reduction in the selection of the possible VSVs; further, to reduce the torque ripple, the duty cycle optimisation of a subset of VSVs available from the VSI is performed. The conventional FS-MPC and the proposed control scheme are implemented using a field programmable gate array, and are experimentally compared in terms of torque and flux ripple, current harmonics, and computational effort.

A step-up switched-capacitor multilevel inverter based on 5-level T-type modules

Abstract: The paper presents a new transformer-less step-up multilevel inverter structure with a single DC source. The concept was based on cascaded connection of bipolar T-type 5-level modules. Proper charging and discharging of capacitors across the load in prearranged time durations would make a nearly sinusoidal staircase voltage. The output voltage amplitude was several times greater than the DC input depending on the number of modules and charging mode of the capacitors. Multiplying the input voltage, self-balancing, generating bipolar voltage waveform, easy circuit expansion and considerably low THD (Total Harmonic Distortion) were found to be the advantages of the proposed topology. The paper also adds operating principle, simulation and experimental results of a 29-level prototype based on the presented inverter structure.

Underwater wireless power transfer system with a curly coil structure for AUVs

Abstract: An underwater wireless power transfer system with a curly coil structure is proposed to adapt to the cylindrical symmetric hull of the autonomous underwater vehicles (AUVs). The unipolar and bipolar curly coils are optimised to minimise the weight of the receiver with the same output power. It is revealed that the bipolar curly coil structure has a heavier receiver than the unipolar curly coil structure. However, the electromagnetic field radiation in the AUV of the bipolar curly coil structure is much smaller than that of the unipolar curly coil structure, which means that the bipolar curly coil structure has a smaller influence on the electronics components in the AUV. Therefore, the bipolar curly coil is adopted for the prototype. The series−series (SS) and double-sided inductor−capacitor−capacitor (LCC−LCC) compensation topologies for the bipolar curly coil structure are also investigated. A prototype was built and the experimental results showed that distorted coil currents are generated in the SS compensation topology, while the LCC−LCC compensation has a nearly sinusoidal coil current. The efficiencies of the SS and LCC−LCC compensation topologies are approximately the same, at ∼95%, which indicates that the proposed curly coil structure is applicable.

Dual input–dual output DC–DC converter for solar PV/battery/ultra-capacitor powered electric vehicle application

Abstract: Utilisation of more than one energy source in the electric vehicle (EV) ensures the reliable riding of the vehicle without range anxieties. Solar PV, battery and ultra-capacitor are viable sources to power the EV. A novel dual input–dual output dc–dc converter is proposed for the integration of the above sources for the EV application. The converter can be used to transfer power between the input sources and loads/utility grid/other EVs. The proposed converter can be operated in ten different modes using the same structure by controlling the appropriate switches. The equivalent circuits with the analytical waveforms of significant modes of operation of the converter are discussed in this study. The output equations of all ten modes are derived. The theoretical analysis of the converter is verified experimentally using a 1 kW laboratory prototype and the observed experimental results are shown in the study. A strategy for selecting a mode according to the status of the vehicle, grid, battery etc. is developed. The loss breakdown analysis and efficiency profile of the converter are presented. Finally, the performance comparisons of the proposed converter with the reported converters are carried out in terms of component counts, a number of operating modes etc.

Overview of wireless charging and vehicle-to-grid integration of electric vehicles using renewable energy for sustainable transportation

Abstract: The quest for energy conservation is a thought-provoking conundrum to researchers. Time to time they contributed towards this pursuit. In the 19th century, it was a fascinating idea about electric vehicles (EVs). As most of the developing countries depend on conventional energy sources, integration of EVs with renewable energy sources justified the cause. The parking slots became transformed into unlimited sources of clean energy. For the comfort of charging and better energy management, wireless power transfer technology was introduced to the charging station. As a fulfilment of the technology, the vehicle-to-grid (V2G) integration was implemented. It helped the bi-directional power flow between the vehicle and the grid with renewable energy. This study presents an extensive review of the renewable energy powered wireless charging and V2G integration of EVs. Various topologies are discussed with mathematical explanations and block diagrams. Concepts are validated with PSIM simulations.

Frequency-domain modelling and stability analysis of a DFIG-based wind energy conversion system under non-compensated AC grids: impedance modelling effects and consequences on stability

Abstract: Impedance-based frequency-domain method is an effective tool for the stability assessment of a doubly fed induction generator (DFIG) system. Several impedance models have been proposed recently; however, these models are usually associated with model reductions since the complexity in achieving a detailed DFIG model. This may lead to unreliable stability results under certain conditions, and a clarification of this modelling effect is lacking in the literature. Therefore, this study aims to address this issue by developing a detailed DFIG impedance model. To achieve this target, a modular modelling technique is proposed instead of the conventional linearisation by parts, for which the components of a DFIG system are modelled as multi-port modules. Through this method, the detailed DFIG model together with four types of reduced-order models can be derived efficiently. The detailed DFIG model is verified by the measured frequency responses in PSCAD™/EMTDC™, along with its correctness in Nyquist-based stability analysis. Subsequently, four types of the reduced-order models are compared with the detailed one in terms of Nyquist plots, so that their performance and effectiveness for stability analysis are clarified. Besides, conclusions regarding the reduced-order models are also verified by time-domain simulations.

Hybrid field oriented and direct torque control for sensorless BLDC motors used in aerial drones

Abstract: In this study, a sensorless hybrid control scheme for brushless direct current (BLDC) motors for use in multirotor aerial vehicles is introduced. In such applications, the control scheme must satisfy high-performance demands for a wide range of rotor speeds and must be robust to motor parameter uncertainties and measurement noise. The proposed controller combines field-oriented control (FOC) and direct torque control (DTC) techniques to take benefit of the advantages offered by each of these techniques individually. Simulation results demonstrate the effectiveness of the proposed control scheme over a wide range of rotor speeds as well as good robustness against parameter uncertainties within -5to + 10% for inductance and -5to + 5% for resistance parameters. The proposed hybrid controller is robust also against noise in voltage and current measurements. In order to verify the results from simulation, the proposed hybrid controller is implemented in hardware using the TI C2000 Piccolo Launchpad and TI BOOSTXL-DRV8305EVM BoosterPack. Testing is done with a Bull Running motor typically used in aerial drones. Testing experiments demonstrate that the hybrid controller reduces the rotor speed ripple when compared to DTC while operating in steady-state mode and decreases the response time to desired speed changes when compared to FOC.

New tri‐switching state non‐isolated high gain DC–DC boost converter for microgrid application

Abstract: High efficiency is an important requirement from DC–DC converter in DC microgrid system when integrated with renewable energy sources. This study proposes a new tri-switching state non-isolated high gain boost converter for 400 V DC microgrid applications. The proposed converter developed by modifying the conventional boost converter with advantageous features such as; high-voltage gain operation with two different duty pulses to overcome the restriction of high duty ratio and continuous input current. Moreover, semiconductor components in the proposed converter are subjected to reduced voltage stress for a shorter duration when compared to conventional existing topologies. Steady state (with and without non-idealities consideration) and performance analysis are presented to validate the viability of the proposed converter for high gain operation in grid-connected systems. For experimental validation, a prototype model of the proposed converter is developed for 31 V/400 V, 500 W and operated at 50 kHz switching frequency. The converter is tested for a power range of 100–500 W for two different duty range (case: 1–k 1 kept fixed and k 2 is varied, case: 2–k 2 kept fixed and k 1 is varied) to validate the consistency in output voltage. Hardware results obtained validates superior performance and higher efficiency compared to conventional existing topologies.

Mixed model-based and signal-based approach for open-switches fault diagnostic in sensorless speed vector controlled induction motor drive using sliding mode observer

Abstract: This study deals with a mixed model-based and signal-based approach for sensorless speed-controlled induction motor drive (IM) and insulated-gate bipolar transistors open-switch fault diagnosis. In comparison to the classical sensored drive systems, this structure presents particular characteristics in post-fault operation mode which can be taken into account for fault detection and identification process designing. Firstly, the fault effects analysis is achieved in the abc frame of the IM. Based on such analysis, a diagnostic algorithm, using the measured and estimated currents, is used to define the fault indices, which allow the detection of single open-switch, multiple open-switch and open-phase faults. The sensorless control algorithm used for rotor speed estimation, as well as the fault diagnostic algorithm, are all based on a first-order sliding mode observer. In addition to the simplicity and the fast fault detection, there are no-additional sensors or extra-hardware used by the proposed method. Experimental results, based on a dSPACE DS1104 controller board and a 3-kW induction machine, are shown to validate the proposed strategy.

Ultra-high step-up two-input DC–DC converter with lower switching losses

Abstract: In this study, a novel isolated ultra-high step-up two-input DC–DC converter with low-voltage stress across semiconductors is presented. In the proposed converter, outputs are isolated from the inputs by a high-frequency transformer and the leakage inductance of the transformer is used to soft switching (zero-current switching) of the power switches when they are turned-on and alleviate the reverse recovery problems of the diodes. This converter can be operated as an interleaved single-input converter with a 180° phase shift. The converter benefits from the advantages of both the conventional boost converter and diode-capacitor voltage multiplier (VM) stages. The primary side of the transformer consists of two-input cells based on the conventional boost converter and the secondary side consists of diode-capacitor VM stages which are used to increase the voltage gain and decrease the nominal voltage stress across semiconductors. To confirm the converter performance, the mathematical analysis and simulation result are presented, in addition, the comparison between the proposed converter and other converters which are presented in recent studies is presented. An experimental prototype 410 V/280 W of the converter with 40 and 45 V input voltages is provided to illustrate the correct operation of the presented converter.

Modified virtual inertia control method of VSG strategy with improved transient response and power-supporting capability

Abstract: Virtual synchronous generator (VSG) controlled grid-tied converters could increase power overshoot and oscillation if real power reference disturbance (PRD) occurs. Existing VSG methods can mitigate the power oscillations, but they may reduce the supporting capability of grid contingency. To cope with the issue, a modified virtual inertia control method of VSG strategy is proposed. The proposed modified VSG method introduces two frequencies of point of common coupling into the virtual inertia control. The estimated frequency is used to mitigate the power oscillations and the measured frequency aims to provide extra power supporting. The formulated parameters design principles are given according to the transient characteristics. Stability analysis of power and frequency response is carried out to evaluate the proposed method. Besides, the transient power and frequency response of the PRD case and grid-frequency disturbance (GFD) case are studied. The power overshoot of the proposed modified VSG method decreases by 52.5% under the PRD case and the power support peak increases by 34.3% under the GFD case. Experimental results show that the transient performance of the proposed modified VSG controlled grid-tied converters is improved.

Review of technologies for DC grids – power conversion, flow control and protection

Abstract: This article reviews dc transmission technologies for future power grids. The article emphasizes the attributes that each technology offers in terms of enhance controllability and stability, resiliency to ac and dc faults, and encourage increased exploitations of renewable energy resources (RERs) for electricity generation. Discussions of ac/dc and dc/dc converters reveal that the self-commutated dc transmission technologies are critical for better utilization of large RERs which tend to be dispersed over wide geographical areas, and offer needed controllability for operation of centralized and decentralized power grids. It is concluded that the series power flow controllers have potential to restrict the expensive isolated dc/dc converters to few applications, in which the prevention of dc fault propagation is paramount. Cheaper non-isolated dc/dc converters offer dc voltage tapping and matching and power regulation but they are unable to prevent pole-shifting during pole-to-ground dc fault. To date hybrid dc circuit breakers target dc fault isolation times ranging from 3ms to 5ms; while the resonance-based dc circuit breakers with forced current zeros target dc fault clearance times from 8ms to 12.5ms.