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Showing papers in "IEEE Transactions on Industry Applications in 2014"


Journal ArticleDOI
TL;DR: This review serves to provide a clear picture of the state-of-the-art research in this area and to identify the corresponding challenges and future research directions for capacitors and their dc-link applications.
Abstract: DC-link capacitors are an important part in the majority of power electronic converters which contribute to cost, size and failure rate on a considerable scale. From capacitor users' viewpoint, this paper presents a review on the improvement of reliability of dc link in power electronic converters from two aspects: 1) reliability-oriented dc-link design solutions; 2) conditioning monitoring of dc-link capacitors during operation. Failure mechanisms, failure modes and lifetime models of capacitors suitable for the applications are also discussed as a basis to understand the physics-of-failure. This review serves to provide a clear picture of the state-of-the-art research in this area and to identify the corresponding challenges and future research directions for capacitors and their dc-link applications.

882 citations


Journal ArticleDOI
TL;DR: In this article, a design methodology of an LCL filter for grid-interconnected inverters along with a comprehensive study of how to mitigate harmonics is presented for small-scale renewable energy conversion systems and may be also retrofitted for medium and large-scale grid-connected systems.
Abstract: The use of power converters is very important in maximizing the power transfer from renewable energy sources such as wind, solar, or even a hydrogen-based fuel cell to the utility grid An LCL filter is often used to interconnect an inverter to the utility grid in order to filter the harmonics produced by the inverter Although there is an extensive amount of literature available describing LCL filters, there has been a gap in providing a systematic design methodology Furthermore, there has been a lack of a state-space mathematical modeling approach that considers practical cases of delta- and wye-connected capacitors showing their effects on possible grounding alternatives This paper describes a design methodology of an LCL filter for grid-interconnected inverters along with a comprehensive study of how to mitigate harmonics The procedures and techniques described in this paper may be used in small-scale renewable energy conversion systems and may be also retrofitted for medium- and large-scale grid-connected systems

601 citations


Journal ArticleDOI
TL;DR: In this article, a theoretical discrete time-analysis framework is presented to identify three distinct regions of LCL filter resonance, namely, a high resonant frequency region where active damping is not required, a critical resonant rate where a controller cannot stabilize the system, and a low resonant level where active wetting is essential.
Abstract: The control of a grid-connected voltage source inverter with an inductive-capacitive-inductive (LCL) filter is a very challenging task, since the LCL network causes a resonance phenomenon near to the control stability boundary. While many active damping methods have been proposed to overcome this issue, the role that pulse width modulation transport delay plays in the effectiveness of these strategies is still not fully resolved. This paper presents a theoretical discrete time-analysis framework that identifies three distinct regions of LCL filter resonance, namely, a high resonant frequency region where active damping is not required, a critical resonant frequency where a controller cannot stabilize the system, and a low resonant frequency region where active damping is essential. Suitable controllers are then proposed for the two stable regions, with gain calculations that allow for the greatest system bandwidth and damping. Simulation and experimental results verify the presented analysis.

447 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reviewed all the major stability criteria for dc distribution systems that have been developed so far: the Middlebrook Criterion, the Gain Margin and Phase Margin (GMP), the Opposing Argument Criterion (OAC), the Energy Source Analysis Consortium (ESAC), and the Three-Step Impedance Criterion.
Abstract: Power-electronics-based dc power distribution systems, consisting of several interconnected feedback-controlled switching converters, suffer from potential degradation of stability and dynamic performance caused by negative incremental impedances due to the presence of constant power loads. For this reason, the stability analysis of these systems is a significant design consideration. This paper reviews all the major stability criteria for dc distribution systems that have been developed so far: the Middlebrook Criterion, the Gain Margin and Phase Margin Criterion, the Opposing Argument Criterion, the Energy Source Analysis Consortium (ESAC) Criterion, and the Three-Step Impedance Criterion. In particular, the paper discusses, for each criterion, the artificial conservativeness characteristics in the design of dc distribution systems, and the formulation of design specifications that ensure system stability. Moreover, the Passivity-Based Stability Criterion is discussed, which has been recently proposed as an alternative stability criterion. While all prior stability criteria are based on forbidden regions for the polar plot of the so-called minor loop gain, which is an impedance ratio, the proposed criterion is based on imposing passivity of the overall bus impedance. A meaningful simulation example is presented to illustrate the main characteristics of the reviewed stability criteria.

347 citations


Journal ArticleDOI
TL;DR: In this article, the LVRT capability of three mainstream single-phase transformerless PV inverters under grid faults is explored in order to map future challenges, and control strategies with reactive power injection are also discussed.
Abstract: Transformerless photovoltaic (PV) inverters are going to be more widely adopted in order to achieve high efficiency, as the penetration level of PV systems is continuously booming. However, problems may arise in highly PV-integrated distribution systems. For example, a sudden stoppage of all PV systems due to anti-islanding protection may contribute to grid disturbances. Thus, standards featuring with ancillary services for the next-generation PV systems are under a revision in some countries. The future PV systems have to provide a full range of services as what the conventional power plants do, e.g., low-voltage ride-through (LVRT) under grid faults and grid support service. In order to map future challenges, the LVRT capability of three mainstream single-phase transformerless PV inverters under grid faults is explored in this paper. Control strategies with reactive power injection are also discussed. The selected inverters are the full-bridge (FB) inverter with bipolar modulation, the FB inverter with dc bypass, and the Highly Efficient and Reliable Inverter Concept (HERIC). A 1-kW single-phase grid-connected PV system is analyzed to verify the discussions. The tests confirmed that, although the HERIC inverter is the best candidate in terms of efficiency, it is not very particularly feasible in case of a voltage sag. The other two topologies are capable of providing reactive current during LVRT. A benchmarking of those inverters is also provided in this paper, which offers the possibility to select appropriate devices and to further optimize the transformerless system.

307 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated principles for converter operation with high torque in the whole speed range and provided experimental results from a down-scaled 12-kVA prototype converter running a loaded motor at various speeds between standstill and the rated speed.
Abstract: Modular multilevel converters are shown to have a great potential in the area of medium-voltage drives. Low-distortion output quantities combined with low average switching frequencies for the semiconductor devices create an ideal combination for very high-efficiency drives. However, the large number of devices and capacitors that have to conduct the fundamental-frequency current require more complex converter control techniques than its two-level counterpart. Special care needs to be taken for starting and operation at low speeds, where the low-frequency current may cause significant unbalance between the submodule capacitor voltages and disturb the output waveforms. In this paper, principles for converter operation with high torque in the whole speed range are investigated. Experimental results from a down-scaled 12-kVA prototype converter running a loaded motor at various speeds between standstill and the rated speed are also provided.

272 citations


Journal ArticleDOI
TL;DR: In this paper, a dual-stator spoke array (DSSA) VPM topology was proposed to achieve high power factor and high torque capability, and the performance of the DSSA VPM was evaluated based on finite element analysis, including power factor, torque density and cogging torque.
Abstract: Vernier permanent-magnet (VPM) machines are well known for high torque density but low power factor. This paper deals with the low power factor of VPM machines. The goal is not obtained by reducing the electrical loading or adjusting current advance angle but by proposing a novel vernier topology, i.e., a dual-stator spoke-array (DSSA) VPM topology. In this paper, the characteristics of the DSSA VPM topology, such as active part, auxiliary mechanical structure, and rotor anisotropy, are analyzed in detail. Performances are evaluated based on finite-element analysis, including power factor, torque density, and cogging torque. The results show that the DSSA VPM topology exhibits high power factor, viz., ~0.9, and significantly high torque capability. The verification of the mechanical structure scheme is also done in this paper. Finally, theoretical analyses are validated by the experimental results by a 44-rotor pole 24-slot DSSA VPM prototype.

269 citations


Journal ArticleDOI
TL;DR: In this paper, the back electromotive force and power equations of a PM vernier motor are accurately derived considering an air-gap permeance function expressed in terms of practical machine dimensions.
Abstract: In this paper, the back electromotive force and power equations of a permanent-magnet (PM) vernier motor are accurately derived considering an air-gap permeance function expressed in terms of practical machine dimensions. Using these equations, the nature of a PM vernier motor is analytically surveyed, and substantial information such as main geometric factors affecting torque and the maximally obtainable torque for a given current are provided, leading to a new relation for torque per air-gap volume. In addition, these equations provide a means to determine the slot and pole combinations to realize greater power density. Finally, the effects of an increased reactance are investigated in respect to machine performance with a given voltage.

269 citations


Journal ArticleDOI
TL;DR: In this article, a fuzzy logic controller (FLC)-based single-ended primary-induction converter (SEPIC) was proposed for maximum power point tracking (MPPT) operation of a photovoltaic (PV) system.
Abstract: This paper presents a fuzzy logic controller (FLC)-based single-ended primary-inductor converter (SEPIC) for maximum power point tracking (MPPT) operation of a photovoltaic (PV) system. The FLC proposed presents that the convergent distribution of the membership function offers faster response than the symmetrically distributed membership functions. The fuzzy controller for the SEPIC MPPT scheme shows high precision in current transition and keeps the voltage without any changes, in the variable-load case, represented in small steady-state error and small overshoot. The proposed scheme ensures optimal use of PV array and proves its efficacy in variable load conditions, unity, and lagging power factor at the inverter output (load) side. The real-time implementation of the MPPT SEPIC converter is done by a digital signal processor (DSP), i.e., TMS320F28335. The performance of the converter is tested in both simulation and experiment at different operating conditions. The performance of the proposed FLC-based MPPT operation of SEPIC converter is compared to that of the conventional proportional-integral (PI)-based SEPIC converter. The results show that the proposed FLC-based MPPT scheme for SEPIC can accurately track the reference signal and transfer power around 4.8% more than the conventional PI-based system.

265 citations


Journal ArticleDOI
TL;DR: In this paper, a slidingmode duty-ratio controller (SMDC) is proposed for dc/dc buck converters with constant power loads, which is able to stabilize the dc power systems over the entire operating range in the presence of significant variations in the load power and input voltage.
Abstract: Incorporating a medium-voltage dc (MVDC) integrated power system is a goal for future surface combatants and submarines. In an MVDC shipboard power system, dc/dc converters are commonly employed to supply constant power to electric loads. These constant power loads have a characteristic of negative incremental impedance, which may cause system instability during disturbances if the system is not properly controlled. This paper proposes a sliding-mode duty-ratio controller (SMDC) for dc/dc buck converters with constant power loads. The proposed SMDC is able to stabilize the dc power systems over the entire operating range in the presence of significant variations in the load power and input voltage. The proposed SMDC is validated by both simulation studies in MATLAB/Simulink and experiments for stabilizing a dc/dc buck converter with constant power loads. Simulation studies for an MVDC shipboard power system with constant power loads for different operating conditions with significant variations in the load power and supply voltage are also provided to further demonstrate the effectiveness of the proposed SMDC.

225 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a new diagnosis method of an open-switch fault and fault-tolerant control strategy for T-type three-level inverter systems, where the location of the faulty switch can be identified by the average of the normalized phase current and the change of the neutral point voltage.
Abstract: This paper proposes a new diagnosis method of an open-switch fault and fault-tolerant control strategy for T-type three-level inverter systems. The location of the faulty switch can be identified by the average of the normalized phase current and the change of the neutral-point voltage. The proposed fault-tolerant strategy is explained by dividing into two cases: the faulty condition of half-bridge switches and neutral-point switches. The performance of the T-type inverter system improves considerably by the proposed fault-tolerant algorithm when a switch fails. The proposed method does not require additional components and complex calculations. Simulation and experimental results verify the feasibility of the proposed fault diagnosis and fault-tolerant control strategy.

Journal ArticleDOI
TL;DR: In this paper, the authors provide details of the design, analysis, and testing of an advanced interior permanent magnet (PM) machine that was developed to meet the FreedomCAR 2020 specifications.
Abstract: Electric drive systems, which include electric machines and power electronics, are a key enabling technology for advanced vehicle propulsion systems that reduce the petroleum dependence of the ground transportation sector. To have significant effect, electric drive technologies must be economical in terms of cost, weight, and size while meeting performance and reliability expectations. This paper will provide details of the design, analysis, and testing of an advanced interior permanent magnet (PM) machine that was developed to meet the FreedomCAR 2020 specifications. The 12-slot/10-pole machine has segmented stator structure equipped with fractional-slot nonoverlapping concentrated windings. The rotor has a novel spoke structure/assembly. Several prototypes with different thermal management schemes have been built and tested. This paper will cover the test results for all these prototypes and highlight the tradeoffs between the various schemes. Due to the high machine frequency (~1.2 kHz at the top speed), detailed analysis of various loss components and ways to reduce them will be presented. In addition, due to the high coolant inlet temperature and the fact that the machine is designed to continuously operate at 180 °C, detailed PM demagnetization analysis will be presented. The key novelty in this paper is the advanced rotor structure and the thermal management schemes.

Journal ArticleDOI
TL;DR: In this article, the authors proposed a dc circuit breaker for voltage source converter (VSC) based high-voltage dc transmission (HVDC) systems, which consists of a number of semiconductor devices in series.
Abstract: This paper proposes a dc circuit breaker for voltage source converter (VSC) based high-voltage dc transmission (HVDC) systems. Technical challenges for applying dc circuit breakers are to increase blocking voltage and to suppress surge voltage at the current clearing. The proposed dc circuit breaker is a solid-state breaker which consists of a number of semiconductor devices in series. It maintains equal voltage balancing among the devices to apply it to high-voltage applications. Moreover, the surge voltage across the circuit breaker is reduced by employing a freewheeling diode. Considering a system rated at 300 MW in power and 250 kV in dc voltage, the conduction loss of the proposed circuit breaker is estimated to be 0.045% of the rated power. The value is smaller than the power loss of the VSCs. A downscaled HVDC system rated at 10 kW in power and 360 V in dc voltage was built and tested. A series of experimental results demonstrates the dc fault clearing and rapid restoration of power transmission.

Journal ArticleDOI
TL;DR: In this paper, reactive power injection (RPI) strategies for single-phase photovoltaic (PV) systems are explored in light of this, and the design and implementation considerations for the characterized RPI strategies are also discussed.
Abstract: As the development and installation of photovoltaic (PV) systems are still growing at an exceptionally rapid pace, relevant grid integration policies are going to change consequently in order to accept more PV systems in the grid. The next-generation PV systems will play an even more active role like what the conventional power plants do today in the grid regulation participation. Requirements of ancillary services like low-voltage ride-through (LVRT) associated with reactive current injection and voltage support through reactive power control have been in effectiveness in some countries, e.g., Germany and Italy. Those advanced features can be provided by next-generation PV systems and will be enhanced in the future to ensure an even efficient and reliable utilization of PV systems. In light of this, reactive power injection (RPI) strategies for single-phase PV systems are explored in this paper. The RPI possibilities are as follows: 1) constant average active power control; 2) constant active current control; 3) constant peak current control; and 4) thermal optimized control strategy. All those strategies comply with the currently active grid codes but are with different objectives. The proposed RPI strategies are demonstrated first by simulations and also tested experimentally on a 1-kW singe-phase grid-connected system in LVRT operation mode. Those results show the effectiveness and feasibilities of the proposed strategies with reactive power control during LVRT operation. The design and implementation considerations for the characterized RPI strategies are also discussed.

Journal ArticleDOI
TL;DR: In this article, a dc-link voltage stabilization algorithm using an active damping is proposed so that the dclink voltage can be stabilized with reduced DC-link capacitors in the motor drive system.
Abstract: In conventional motor drive systems using pulsewidth modulation (PWM) inverters, large electrolytic capacitors are used for stabilization of the dc-link voltage. Since the electrolytic capacitors are bulky and reduce reliability of the system due to short lifetime, there have been many efforts to eliminate or reduce the electrolytic capacitors in the motor drive system. However, the PWM inverter with reduced dc-link capacitor has a problem that the dc-link voltage is less stable compared to the conventional inverter because the capability of storing energy is also reduced. In this paper, a dc-link voltage stabilization algorithm using an active damping is proposed so that the dc-link voltage can be stabilized with reduced dc-link capacitor. To achieve load-/source-independent stabilization, a source state estimator which estimates both source voltage and current is also proposed. The fluctuation of the dc-link voltage due to a step load change can be also suppressed under the tolerance range using the estimated source current. The effectiveness of the proposed methods is evaluated by experimental results.

Journal ArticleDOI
TL;DR: In this article, the authors proposed a load compensator based on the decomposition of output current, in addition to the outer droop-based power controller and the inner voltage and current controllers, which can counteract the harmonic voltage drops across the grid-side inductance of the DG inverter and dampen out harmonic resonance propagation in the microgrid.
Abstract: Harmonic current filtering and resonance damping have become important concerns in the operation and control of the islanded microgrids To address these challenges, this paper proposes a control method for the inverter-interfaced distributed generation (DG) units to autonomously share the harmonic currents and resonance damping burdens The approach employs a load compensator based on the decomposition of output current, in addition to the outer droop-based power controller and the inner voltage and current controllers The load compensator consists of a virtual-fundamental-impedance loop for the enhanced reactive power sharing and a variable-harmonic-impedance loop which allows to counteract the harmonic voltage drops across the grid-side inductance of the DG inverter and also to dampen out harmonic resonance propagation in the microgrid Finally, the laboratory tests on a three-phase islanded microgrid setup are carried out to validate the performance of the proposed control scheme

Journal ArticleDOI
TL;DR: In this article, the authors proposed a new converter for photovoltaic (PV) water pumping or treatment systems without the use of chemical storage elements, such as batteries, to achieve a more efficient, reliable, maintenance-free, and cheaper solution than the standard ones that use dc motors or lowvoltage synchronous motors.
Abstract: This paper proposes a new converter for photovoltaic (PV) water pumping or treatment systems without the use of chemical storage elements, such as batteries. The converter is designed to drive a three-phase induction motor directly from PV energy. The use of a three-phase induction motor presents a better solution to the commercial dc motor water pumping system. The development is oriented to achieve a more efficient, reliable, maintenance-free, and cheaper solution than the standard ones that use dc motors or low-voltage synchronous motors. The developed system is based on a current-fed multiresonant converter also known as resonant two-inductor boost converter (TIBC) and a full-bridge three-phase voltage source inverter (VSI). The classic topology of the TIBC has features like high voltage gain and low input current ripple. In this paper, it is further improved with the use of a nonisolated recovery snubber along with a hysteresis controller and the use of a constant duty cycle control to improve its efficiency. Experimental results show a peak efficiency of 91% at a rated power of 210 W for the dc/dc converter plus the three-phase VSI and a peak efficiency of 93.64% just for the dc/dc converter. The system is expected to have a high lifetime due to the inexistence of electrolytic capacitors, and the total cost of the converter is below 0.43 U$/Wp. As a result, the system is a promising solution to be used in isolated locations and to deliver water to poor communities.

Journal ArticleDOI
TL;DR: A control scheme for the six-step operation of PMSM with enhanced dynamic performance of current control is proposed by collaborative operation of dynamic overmodulation, flux weakening, and a technique for enhancedynamic performance without losing instantaneous current control capability.
Abstract: Six-step operation has many advantages in permanent-magnet synchronous machine (PMSM) drives such as maximum power utilization and widened flux-weakening region. However, due to the maximum utilization of inverter output, saturation of current regulator makes it difficult to maintain instantaneous current control capability. Accordingly, in most of conventional research studies, the six-step operation has been implemented by voltage angle control without current regulation, whose dynamic performance is quite unsatisfactory. This paper proposes a control scheme for the six-step operation of PMSM with enhanced dynamic performance of current control. By collaborative operation of dynamic overmodulation, flux weakening, and a technique for enhanced dynamic performance, the six-step operation is realized without losing instantaneous current control capability. Simulations and experiments are carried out to verify the effectiveness of the proposed control scheme. The experimental results show 17% extension of the constant torque region and 27% enhancement of torque capability at three times of the base speed.

Journal ArticleDOI
TL;DR: In this article, a flux-intensifying permanent magnet type with low-coercive-force magnets is used in the design due to positive Id operation and reduced loaded Iq effects.
Abstract: This paper presents a design approach for interior permanent-magnet (IPM) machines with variable-flux characteristics using low-coercive-force magnets for improved efficiency and extended operating speed range. A flux-intensifying IPM type with is used in the design due to positive Id operation and reduced loaded Iq effects. Design considerations of machine structures and variable-flux machine attributes are discussed. In addition, leakage flux in a rotor is particularly designed to also obtain another flux-varying capability. Evaluation of the designed machine is provided by finite-element analysis simulations and experiments on a proof-of-principle machine. The designed machine shows benefits in increasing efficiency and speed range in a low-torque region when variable magnetization control of the low-coercive-force magnets or the design of the leakage flux proposed in this paper is implemented.

Journal ArticleDOI
TL;DR: A power spectrum of the WTCs in different scales calculated by Parseval's theorem is proposed and presented and it is proved that the proposed algorithm is applicable in multiple load operations of nonintrusive demand monitoring applications.
Abstract: Though the wavelet transform coefficients (WTCs) contain plenty of information needed for turn-on/off transient signal identification of load events, adopting the WTCs directly requires longer computation time and larger memory requirements for the nonintrusive load monitoring identification process. To effectively reduce the number of WTCs representing load turn-on/off transient signals without degrading performance, a power spectrum of the WTCs in different scales calculated by Parseval's theorem is proposed and presented in this paper. The back-propagation classification system is then used for artificial neural network construction and load identification. The high success rates of load event recognition from both experiments and simulations have proved that the proposed algorithm is applicable in multiple load operations of nonintrusive demand monitoring applications.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a sensorless control strategy with the injection of a high-frequency pulsating carrier signal into a stationary reference frame, where the rotor position information can be retrieved from the carrier current response that is amplitude-modulated by the machine saliency.
Abstract: In this paper, a novel sensorless control strategy with the injection of a high-frequency pulsating carrier signal into a stationary reference frame is proposed. Differing from the two most commonly used conventional high-frequency carrier signal injection methods, i.e., the injection of a rotating carrier voltage into a stationary reference frame and the injection of a pulsating carrier voltage into an estimated synchronous reference frame, the new proposed strategy injects a pulsating high-frequency carrier voltage into a stationary reference frame, which is as stable as the rotating carrier signal injection method. Then, the rotor position information can be retrieved from the carrier current response that is amplitude-modulated by the machine saliency, which is as simple as the pulsating carrier signal injection method. The signal demodulation process, the compensation of the cross-saturation effect, and magnetic polarity detection are also discussed and analyzed in detail. The experimental results on an interior permanent-magnet synchronous machine demonstrate that the new proposed strategy has a robust magnetic polarity detection and that it can achieve an accurate rotor position estimation with good steady-state performance and dynamic performance.

Journal ArticleDOI
TL;DR: In this article, different voltage injection schemes for dynamic voltage restorers (DVRs) are analyzed with particular focus on a new method used to minimize the rating of the voltage source converter (VSC) used in DVRs.
Abstract: In this paper, different voltage injection schemes for dynamic voltage restorers (DVRs) are analyzed with particular focus on a new method used to minimize the rating of the voltage source converter (VSC) used in DVR. A new control technique is proposed to control the capacitor-supported DVR. The control of a DVR is demonstrated with a reduced-rating VSC. The reference load voltage is estimated using the unit vectors. The synchronous reference frame theory is used for the conversion of voltages from rotating vectors to the stationary frame. The compensation of the voltage sag, swell, and harmonics is demonstrated using a reduced-rating DVR.

Journal ArticleDOI
TL;DR: In this article, the authors proposed an intelligent workplace parking garage for plug-in hybrid electric vehicles (PHEVs) with a developed smart power charging controller, a 75kW photovoltaic (PV) panel, a dc distribution bus, and an ac utility grid.
Abstract: This paper proposes an intelligent workplace parking garage for plug-in hybrid electric vehicles (PHEVs). The system involves a developed smart power charging controller, a 75-kW photovoltaic (PV) panel, a dc distribution bus, and an ac utility grid. Stochastic models of the power that is demanded by PHEVs in the parking garage and the output power of the PV panel are presented. In order to limit the impact of the PHEVs' charging on the utility ac grid, a fuzzy logic power-flow controller was designed. Based on their power requirements, the PHEVs were classified into five charging priorities with different rates according to the developed controller. The charging rates depend on the predicted PV output power, the power demand by the PHEVs, and the price of the energy from the utility grid. The developed system can dramatically limit the impact of PHEVs on the utility grid and reduce the charging cost. The system structure and the developed PHEV smart charging algorithm are described. Moreover, a comparison between the impact of the charging process of the PHEVs on the grid with and without the developed smart charging technique is presented and analyzed.

Journal ArticleDOI
TL;DR: In this paper, an adaptive interconnection and damping assignment (IDA) passivity-based controller (PBC) with a complementary proportional integral (PI) controller for dc-dc boost converters with constant power loads (CPLs) is proposed.
Abstract: This paper proposes an adaptive interconnection and damping assignment (IDA) passivity-based controller (PBC) with a complementary proportional integral (PI) controller for dc-dc boost converters with constant power loads (CPLs). The plant is modeled as a port-controlled Hamiltonian system (PCHS). A virtual circuit that interprets the parameters of the PCHS is then derived to determine the parameters of the IDA-PBC for the system to work in the underdamping, critical-damping, and overdamping modes. Moreover, a complementary PI controller is designed to eliminate the steady-state output voltage error of the IDA-PBC caused by the load variation. Simulation studies are carried out in MATLAB/Simulink to validate the proposed control algorithm for a dc-dc boost converter with a CPL; results show that the proposed control algorithm ensures the stability and fast response of the system in different modes when the load changes. Experimental results are provided to further validate the design and simulation of the proposed control algorithm.

Journal ArticleDOI
TL;DR: This paper proposes a space-vector modulation (SVM)-based direct-torque control (DTC) scheme for a permanent-magnet synchronous generator (PMSG) used in a variable-speed direct-drive wind power generation system and greatly reduces the flux and torque ripples.
Abstract: This paper proposes a space-vector modulation (SVM)-based direct-torque control (DTC) scheme for a permanent-magnet synchronous generator (PMSG) used in a variable-speed direct-drive wind power generation system. A quasi-sliding-mode observer that uses a relatively low sampling frequency, e.g., 5 or 10 kHz, is proposed to estimate the rotor position and stator flux linkage based on the current model of the PMSG over a wide operating range. The optimal torque command is directly obtained from the estimated rotor speed for the DTC by which the maximum power point tracking control of the wind turbine generator is achieved without the need for wind speed or rotor position sensors. Compared with the conventional DTC, the proposed SVM-DTC achieves a fixed switching frequency and greatly reduces the flux and torque ripples, while retaining the fast dynamic response of the system. The effectiveness of the proposed SVM-DTC scheme is verified by simulation studies on a 1.5-MW PMSG wind turbine and is further verified by experimental results on a 2.4-kW PMSG with a 10-kHz sampling frequency.

Journal ArticleDOI
TL;DR: In this article, a triple-star bridge cell (TSBC) is used to control a multilevel cascade converter for high-power motor drives with regenerative braking, intended to replace a conventional line-commutated cycloconverter using thyristors.
Abstract: This paper presents a modular multilevel cascade converter based on triple-star bridge cells (MMCC-TSBC), devoting itself to control and experiment. The TSBC is one of the direct ac-to-ac power converters capable of bidirectional power flow with three-phase sinusoidal currents with any power factor at both supply (input) and motor (output) sides. Therefore, it is suitable for medium-voltage high-power motor drives with regenerative braking, intended to replace a conventional line-commutated cycloconverter using thyristors. This paper provides an intensive discussion on how to control the whole TSBC system, how to regulate and balance the dc mean voltages of all the dc capacitors, and how to mitigate their ac voltage fluctuations. The validity and effectiveness of the proposed control strategy and tactics are verified by a three-phase 400-V 15-kW downscaled model.

Journal ArticleDOI
TL;DR: In this article, a method for the seamless transition of three-phase inverters switched between grid-tied and stand-alone modes of operation is presented, where only the inverter current and voltage sensors are utilized, and no control over the grid side static transfer switch is needed.
Abstract: A method for the seamless transition of three-phase inverters switched between grid-tied and stand-alone modes of operation is presented in this paper. In this method, only the inverter current and voltage sensors are utilized, and no control over the grid-side static transfer switch is needed. The presented method contains two strategies for grid-tied-to-stand-alone and stand-alone-to-grid-tied transitions. In the stand-alone-to-grid-tied transition strategy, a novel algorithm is presented for estimating the grid angle nearly instantaneously, which allows the three-phase inverter to respond very quickly if the grid and point-of-common-coupling voltages are out of phase. This fast response allows the inverter to effectively eliminate the transient overcurrent that would normally occur if it was connected to the grid without first being synchronized. The fast response also allows the inverter to return to normal operation very quickly after such an event. The strategy for the seamless transition from grid-tied to stand-alone mode is also presented. These strategies have been verified through experiments, and the results are presented in this paper.

Journal ArticleDOI
TL;DR: In this article, a modular multilevel cascade inverter based on double-star bridge cells (MMCI-DSBC) is proposed for grid connections, which is formed by six modular arms, each of which consists of a cascaded stack of multiple full bridge converters.
Abstract: A modular multilevel cascade inverter based on double-star bridge cells (MMCI-DSBC) is expected to be one of the next-generation medium-voltage pulsewidth modulation (PWM) inverters intended for grid connections. This inverter is formed by six modular arms, each of which consists of a cascaded stack of multiple full-bridge converters. The DSBC is different from the traditional two-level PWM inverter in that the ac voltages are independent of the dc link voltage. Hence, the DSBC is suitable for a grid-connected inverter with a time-varying dc link voltage. This paper describes the DSBC with a focus on its operating principles and performance. The validity of the inverter is confirmed by experiments using a three-phase, 200-V, and 10-kW downscaled system.

Journal ArticleDOI
TL;DR: It is shown that the inverter control mode has a direct impact on its fault current levels and duration and an adaptive relaying algorithm is proposed to detect the faults in the presence of IBDGs with various types of controllers.
Abstract: The ever growing penetration of distributed generation (DG) in a distribution network has a profound impact on network protection and stability. Traditional protection schemes and algorithms need to be extensively investigated as more and more DGs get introduced into the network. The current version of IEEE Standard 1547 does not present a comprehensive solution for fault current detection in the presence of various kinds of DGs. Power electronic inverter-based DGs (IBDGs) are of special concern in distribution network protection as they are often incapable of providing sufficient fault current and their controllers play a principal role in the DG behavior. In this paper, the effects of voltage and current controllers for IBDGs on industrial and commercial power system protection schemes are investigated. It is shown that the inverter control mode has a direct impact on its fault current levels and duration. A simplified distribution network model with IBDG operating under voltage and current control modes was tested to verify the effects of these controllers. This paper also proposes an adaptive relaying algorithm to detect the faults in the presence of IBDGs with various types of controllers.

Journal ArticleDOI
TL;DR: In this paper, a boost-derived hybrid converter (BDHC) is proposed, which can supply simultaneous dc and ac loads from a single dc input by replacing the controlled switch of single-switch boost converters with a voltage-source-inverter bridge network.
Abstract: This paper proposes a family of hybrid converter topologies which can supply simultaneous dc and ac loads from a single dc input. These topologies are realized by replacing the controlled switch of single-switch boost converters with a voltage-source-inverter bridge network. The resulting hybrid converters require lesser number of switches to provide dc and ac outputs with an increased reliability, resulting from its inherent shoot-through protection in the inverter stage. Such multioutput converters with better power processing density and reliability can be well suited for systems with simultaneous dc and ac loads, e.g., nanogrids in residential applications. The proposed converter, studied in this paper, is called boost-derived hybrid converter (BDHC) as it is obtained from the conventional boost topology. The steady-state behavior of the BDHC has been studied in this paper, and it is compared with conventional designs. A suitable pulse width modulation (PWM) control strategy, based upon unipolar sine-PWM, is described. A DSP-based feedback controller is designed to regulate the dc as well as ac outputs. A 600-W laboratory prototype is used to validate the operation of the converter. The proposed converter is able to supply dc and ac loads at 100 V and 110 V (rms), respectively, from a 48-V dc input. The performance of the converter is demonstrated with inductive and nonlinear loads. The converter exhibits superior cross-regulation properties to dynamic load-change events. The proposed concept has been extended to quadratic boost converters to achieve higher gains.