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The main challenges of the input current control in synchronous DC-DC buck converters are the nonlinear model of the system, changes of the operating point in a wide range, and the need to use an input LC filter for current smoothing, which may result in the instability of the closed-loop system. In this paper, a step-by-step approach is developed for the design and improvement of a PI-feedforward closed-loop controller. It is shown that a linear PI controller cannot stabilize the closed-loop system properly during wide changes in model parameters, e.g., an equivalent series resistance of the input filter. To cope with the stability issues, a fixed-frequency sliding mode controller (SMC) has been developed in this paper for the implementation of an electro-mechanical actuator (EMA) emulator. Moreover, a systematic approach is proposed for controller tuning and the selection of the SMC's gains. To achieve high power efficiency, high-frequency GaN switches are used for the practical implementation of the DC-DC converter. Despite large changes in the load current, the designed nonlinear controller can track the input current reference satisfactorily. Steady-state and dynamic responses of the proposed SMC are compared with conventional linear controllers. Considering the Lyapunov stability theorem, it is proved that the designed SMC can stabilize the closed-loop system in the entire utilizable domain. The proposed nonlinear SMC controller enjoys a very simple control law. Hence, despite having very high switching and sampling frequencies, it can be easily implemented. The experimental response of the designed synchronous DC-DC buck converter is evaluated experimentally by implementing the control strategy in a TMS320F28335PGFA DSP from Texas Instrument. Moreover, the comprehensive comparison of the proposed SMC controller and a PI-feedforward controller proved the superior performance of the developed closed-loop system, in terms of the transient time response, robustness, and stability of the EMA emulator. [ABSTRACT FROM AUTHOR]

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

A new two-stage multi-drive direct power conversion (DPC) topology suited for multi-drive application is proposed, having an input port for a three-phase power supply and several output ports to connect three-phase loads, which are independently controlled and allow for sine wave in-sine wave out operation. This is a cost effective topology compared to a standard matrix converter because the multiple three-phase loads share the cost of the controlled rectification stage. A new method to reduce the high frequency ripple from the input current is also proposed based on interleaving the switching patterns of the inversion stages, which have to form two groups, allowing for size reduction of the input current filter. This is validated by experiments on a realistic laboratory prototype, while its limitations are determined by simulations. Index Terms--Direct power conversion (DPC), high frequency ripple, input current filter, standard matrix converter, three-phase loads.

The new trend in adjustable speed drives (ASD) is to integrate the inverter and the motor into a single unit in order to reduce the production cost, the commissioning time, and the physical size of the equipment. This last issue becomes more important, making the matrix converter topology more attractive. Sinusoidal input currents and bidirectional power flow are other advantages of the matrix converter but it is less immune to power grid disturbances compared to a standard ASD. In hoisting applications, short-term braking capability during a power outage is needed until the mechanical brake engages or to perform more effective a combined braking. This paper proposes a new method to provide short-term braking capability during a power outage for matrix converters. A braking chopper is needed in the clamp circuit, which allows for a drastically reduction of the capacitor size. The power flow in the clamp circuit may be reduced by increasing the harmonic content in the motor currents, which causes higher motor losses. Experiments prove the validity of the proposed method. Index Terms--ASD, braking method, clamp circuit, induction motor, matrix converter, power interruption.

This paper proposes an integrated multiport non-isolated DC–DC converter system for integrating battery–supercapacitor hybrid energy storage with photovoltaics for solar-powered unmanned aerial vehicles applications. Compared to the traditional topologies used, the proposed converter allows a size reduction of at least 20% of the supercapacitor by maximizing the utilization of the rated energy capacity. In addition, by proposing to use a phase-shifted carrier modulation technique, the inductors' current ripple is reduced, which enables a further reduction in the inductor size. These improvements in capability and performance of the proposed topology are experimentally validated on a 500 W PV/battery–supercapacitor integrated power system prototype. [ABSTRACT FROM AUTHOR]

This paper introduces a novel multiport power converter with modular architecture for photovoltaic (PV)-battery based power systems. Compared to conventional centralized multiport converters, the proposed converter significantly improves the utilization of PV available energy and battery capacity as it does not require a high number of series-connected PV and battery modules. The proposed converter also eliminates the need for additional battery cell/module equalizer circuitry by being able to implement directly energy management strategies that consider the different capabilities of battery modules to ensure charge/stress balancing. This makes it a promising solution for interfacing second-life batteries or for systems that utilize batteries with a high degree of mismatch. The modularity of the proposed converter enhances system reliability and fault tolerance and reduces the power/voltage ratings of the power electronic devices. The converter modes of operation, control strategy and design considerations are discussed. A 75 V/1 kW integrated PV-battery power system prototype is built and tested to validate the concept. [ABSTRACT FROM AUTHOR]

This paper presents the design and evaluation of an energy storage system (ESS) for helicopters with the aim to recover the kinetic energy in the rotor available after landing and to be able to control the 270 V DC bus voltage during load disturbances. A study is conducted in order to identify the suitable mix of commercially available energy storage devices with the aim of obtaining the minimum weight, exploring also the possibility to implement a hybrid supercapacitor-battery system. On the converter side, commercially available Silicon and Silicon-Carbide devices have been evaluated to achieve also the smallest size/weight. [ABSTRACT FROM AUTHOR]

The overall performance of battery packs may be affected by imbalances between the series connected cells which is more likely in packs with high number of cells needed to provide a high voltage as needed for example in electric vehicles. In this case, the overall capacity and power capability of the pack are limited by the weakest cell in the stack which results in incomplete utilisation of the pack's capabilities. In traditional centralised battery systems (TCBS), this is addressed by implementing cell active/passive balancing circuitry/techniques which restore some of the pack's energy capability. This paper proposes the use of cascaded modular battery systems (CMBS) to remove the need for extra balancing circuitry and maximises the performance and reliability of a battery system containing unequal matched/aged cells. The analysis is assessing the CMBS overall system efficiency, reliability and weight compared to the TCBS for a design of a 300 V/3.6 kW battery system as a case study. [ABSTRACT FROM AUTHOR]

Nowadays, the existing hierarchical, centrally controlled power grid faces new challenges due to the increase penetration of renewable sources, the need of implementing demand-side management and the 2020 and 2050 environmental targets. A promising concept which can successfully contribute to addressing the environmental concerns and energy challenges of the twenty-first century is the grid-connected decentralised energy systems that embed significant amount of renewable generation and allow reverse power flow from distribution grids into the transmission network. Despite their benefits, decentralised energy storage systems are not yet widely spread due to several implementation and designing barriers. The design obstacle which is being addressed in this study includes the determination of the optimal size of the energy storage system components in terms of battery size and rating of the power converter for a single house application. In order to generalise the findings, nine different real houses were considered. Thus, the most financially beneficial battery and power converter combination for nine existing UK houses with installed PV roof-top system were identified in this study. [ABSTRACT FROM AUTHOR]

This study proposes a dedicated modulation scheme for a bidirectional quasi-Z-source (qZS) modular multi-level converter. The operation principle and a suitable pulse-width modulation method are proposed. The relation between the modulation index and shoot-through duty ratio is derived. A formula for calculating the required value of qZS capacitance is given. The simulation results presented in the study validate the operation and the performance of the proposed topology. [ABSTRACT FROM AUTHOR]

This study presents the experimental evaluation of a proposed new three phase hybrid converter topology for medium voltage applications. The topology is based on the interconnection of a low switching frequency voltage source inverter (VSI), rated at medium voltage, with a high switching frequency low-power rated current source inverter (CSI). The main function of the shunt connected CSI is to cancel the large switching current ripple produced by the VSI while operating at a reduced fundamental voltage enabled by the use of series connected capacitors. The simulations and design procedure outline the possibility of achieving high output grid current quality whilst the added installed power by the CSI remains at <4% compared with the VSI. The experimental results show good correlation between analytical/ simulated targets of 20% maximum CSI voltage stress albeit with added installed power of 6.7% due to a larger amount of current ripple processed. [ABSTRACT FROM AUTHOR]

Interleaved converters with coupled inductors are widely used to share load current in high power applications. It offers high equivalent switching frequency and reduced output current ripples using small size magnetic components. Owing to smaller common-mode inductance, control system can be designed to achieve fast dynamic response. This study proposes eight-channel interleaved DC/DC converter for interfacing super-capacitor energy storage system to a 400 V DC voltage bus. Multi-stage interleaving magnetic circuit with two-phase coupling inductor as a building block is proposed. A methodology is developed to construct the model of the multi-stage magnetic circuit from the basic two-phase coupled inductor model. The derived model is successfully used to evaluate the system power losses and to design the magnetic circuit parameters and its current controller to fulfill the DC/DC converter steady state and dynamic performance specifications. A 20 kW/four stage/8-channel DC/DC converter laboratory prototype has been built to connect a super-capacitor stack to 400 V DC voltage bus. Experimental investigation validates the modelling, the system losses calculations and the design specifications of the system. [ABSTRACT FROM AUTHOR]

This paper proposes a novel integration of wind farm energy storage (ES) systems within microgrids. The main feature of the method is that the voltage and frequency control of the microgrid is shared by the wind generators through droop characteristics. Therefore, the control structure is suitable when the wind generators supply significant part of the load. The paper modifies the standard droop method in order to force the generators to share the load according to their available wind power and not just the generator rating. The paper focuses on islanded microgrid application; however, the method is applicable when there is a controlled connection to the main grid via a power converter, and also for HVDC connection. The proposed control methods are derived for doubly-fed induction generators (DFIGs) and validated using PSCAD/EMTDC simulations. The ride-through in case of a 3-phase fault on the local grid will also be simulated. [ABSTRACT FROM PUBLISHER]

AC/AC power conversion is widely used to feed AC loads with a variable voltage and/or a variable frequency from a constant voltage constant frequency power grid or to connect critical loads to an unreliable power supply while delivering a very balanced and accurate sinusoidal voltage system of constant amplitude and frequency. The load specifications will clearly impose the requirements for the inverter stage of the power converter, while wider ranges of choices are available for the rectifier. This paper investigates the utilization of a buck-type current source rectifier as the active front-end stage of an AC/AC converter for applications that require an adjustable DC-link voltage as well as elimination of the low-frequency common mode voltage. The proposed solution is to utilize a combination of two or more zero current vectors in the Space Vector Modulation (SVM) technique for Current Sources Rectifiers (CSR). [ABSTRACT FROM AUTHOR]

Power converters consisting of naturally commutated thyristors such as cycloconverters and current source inverters were the first to be used in driving electrical motors with variable speed, but now, due to their inferior performance compared to forced commutated converters, their use is restricted in the high voltage/high power range where the performance and cost of forced commutated switching devices are not yet competitive. Hybrid cycloconverters proposed recently are capable of improving the performance of cycloconverters by adding an auxiliary forced commutated inverter with reduced installed power. It will be shown that the new topology is not only able to improve the quality of the output voltage but is also able to enhance the control over the circulating current and, therefore, for some of the cycloconverter arrangements, to improve the input power quality. This paper evaluates the performance of a few standard and hybrid cycloconverter arrangements using both simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a novel integration of doubly fed induction generator (DFIG)-based wind farms within microgrids. The main and probably the best feature of this method is that the voltage and frequency of the microgrid are controlled by the wind generators through droop characteristics. Therefore, this control structure is quite suitable for cases where the wind generators supply significant part of the load. This paper will adjust the standard droop method in order to force the DFIG to share the load according to their available wind powers, not only their ratings. This paper focuses on microgrid application; however, the method is quite applicable for ac grid and HVdc link connections as well. The proposed control methods are validated using PSCAD/4.2.1 Professional/EMTDC simulations. [ABSTRACT FROM PUBLISHER]

This paper analyzes and compares three transformerless photovoltaic inverter topologies for three-phase grid connection with the main focus on the safety issues that result from the lack of galvanic isolation. A common-mode model, valid at frequencies lower than 50 kHz, is adopted to study the leakage current paths. The model is validated by both simulation and experimental results. These will be used to compare the selected topologies, and to explain the influence of system unbalance and the neutral conductor inductance on the leakage current. It will be demonstrated that the later has a crucial influence. Finally, a comparison of the selected topologies is carried out, based on the adopted modulation, connection of the neutral and its inductance, effects of unbalance conditions, component ratings, output voltage levels, and filter size. [ABSTRACT FROM AUTHOR]

This paper presents the development of a supercapacitor energy storage system (ESS) aimed to minimize weight, which is very important for aerospace applications, whilst integrating smart functionalities like voltage monitoring, equalization, and overvoltage protection for the cells. The methodology for selecting the supercapacitor cells type/size is detailed to achieve the safest and most energy-dense ESS. Additionally, the development of the interface electronics for cells' voltage monitoring and overvoltage protection is presented. The proposed design implements a modular distributed architecture coordinated using communication buses to minimize the wirings and associated complexity and to enable system reconfiguration and expansions, as well as fault diagnoses. Validating the proposed ESS functionalities has been done via experimental testing and the results are presented and discussed. [ABSTRACT FROM AUTHOR]