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The output voltage of matrix converter (MC) is related to the frequency of input, output, and carrier signals, and these three frequencies are independent of each other. This makes it difficult to give a precise description of the harmonic spectrum with the commonly used methods such as fast Fourier transform (FFT) and the double Fourier analysis. Based on triple Fourier series, this paper proposes an analytical method to determine harmonic components of MC under space vector modulation (SVM). First, combined with the SVM strategy of MC, the expressions of output voltage harmonics are derived. Then the analytical solutions are obtained on the basis of the calculated expressions. From the analytical solutions, the harmonic amplitudes can be determined precisely, and the values of index variables k , p, and q of harmonic frequency ${kf}_{\rm c} \;\pm\; pf_{{\rm{out}}}\pm qf_{{\rm{in}}}$ are confirmed. According to the results, the harmonic distribution characteristics as well as main harmonic components are analyzed. Finally, the feasibility and accuracy of the proposed analysis method is verified by comparative analysis against the FFT results of measured output voltage waveform. [ABSTRACT FROM AUTHOR]

This paper presents a dynamic power flow management system for a solar photovoltaic (PV) system employing a single-stage single-inductor-based dual-input/output dc–dc converter feeding standalone dc loads backed up by a rechargeable battery. A time-sharing voltage-mode control scheme has been proposed for power flow management between solar PV, a battery, and a standalone dc load, and it also maintains a constant dc load voltage and performs maximum power point tracking operation of solar PV. The implementation of the control scheme has been described in detail. The steady-state performance of the single-stage converter has been explained with the relevant analytical expressions derived along with the characteristics. A state-space average model was developed for simulating the transient behavior and validating the working of the system for step changes in the input solar PV power and the dc loads. A hardware prototype of the proposed system has been fabricated, and the proposed controller has been implemented using the dSPACE DS1103 real-time interface board. The working of the proposed scheme for different levels of input solar insolation and dc load power demand has been satisfactorily demonstrated, and the corresponding results are also provided. [ABSTRACT FROM AUTHOR]

Local hardware clocks in physically distributed computation devices hardly ever agree because clocks drift apart and the drift can be different for each device. This paper analyzes the effect that local clock drifts have in the parallel operation of voltage source inverters (VSIs) in islanded microgrids (MG). The state-of-the-art control policies for frequency regulation and active power sharing in VSIs-based MGs are reviewed and selected, and prototype policies are then reformulated in terms of clock drifts. Next, steady-state properties for these policies are analyzed. For each of the policies, analytical expressions are developed to provide exact quantification of the impact that drifts have on frequency and active power equilibrium points. In addition, a closed-loop model that accommodates all the policies is derived, and the stability of the equilibrium points is characterized in terms of the clock drifts. Finally, the implementation of the analyzed policies in a laboratory MG provides experimental results that confirm the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper presents a loss optimization method for phase-shifted LLC resonant converters operating with phase shift. The method features automatic detection of the preferred operational mode from the five possibilities for the topology. For a given power level and voltage transformation ratio it simultaneously determines the values of the resonant elements and transformer turns ratio. This work supplements and extends the available optimization tools for variable frequency operation and extends these to phase-shifted operation. The combined methods allow converters with much wider voltage regulation ranges to be designed. Numerical programming methods to determine the mode boundaries and to solve the steady-state solutions for the different modes of LLC converter are presented. A detailed loss model for a phase-shifted LLC is also discussed. A prototype of 30–403V, 295W is built to validate the optimization results. A comparison is made between an optimized and unoptimized converter. An extension to multipoint optimization, as required to optimize the European Weighted Efficiency is described. [ABSTRACT FROM AUTHOR]

Parallel inverters are commonly adopted in high-power applications, for instance wind energy systems, smart transformers, and power conditioners. Meanwhile, interleaved pulse width modulation is usually considered as an optimal approach to reduce the current ripple and harmonics of the parallel inverters. However, in the case of a common dc link, the problem of circulating current emerges and leads to performance degradation. This paper aims at investigating the influence of different modulation techniques on the circulating current of two neutral-point-clamped (NPC) inverters under interleaved operation. Two modulation techniques, phase disposition (PD) and alternative phase opposite disposition (APOD), have been studied and compared in terms of current ripple, spectrum quality, and circulating current. Though the PD modulation was regarded as the optimum solution in most of the single-NPC cases, it offers worse performance in the two parallel NPC applications due to higher circulating current. Simulation and experimental validations are provided and show that the APOD leads to much lower circulating current and similar current ripple as well as spectrum quality compared to the PD. [ABSTRACT FROM AUTHOR]

Direct linking between the stator of a doubly fed induction generator (DFIG) and the power grid makes this type of generator sensitive to disturbances in the grid voltage, which may lead to high voltage and current on the rotor side. Moreover, modern grid codes, which specify stringent requirements on reactive power compensation, challenge fault ride-through operation even more. In this paper, based on conventional demagnetizing current control, the capability of a DFIG rotor-side converter to ride-through a symmetrical grid fault is calculated in accordance with its current and voltage ratings. Afterwards, an optimized demagnetizing coefficient is designed to guarantee the same rotor current amplitude between the instants of the fault occurrence and the reactive current injection. A reduction of the junction temperature of the power device can thereby be achieved. It is concluded that, regardless of the rotor speed, the demagnetizing coefficient is related only to the dip level. Compared with traditional vector control, a simulation of 2 MW DFIG system agrees with the reduced thermal stress during the fault period, and experimental results in a down-scale DFIG system verify the feasibility of the proposed control strategy as seen from the electrical characteristics. [ABSTRACT FROM AUTHOR]

Gate oxide in power metal–oxide–semiconductor field effect transistors (MOSFETs) degrades over time. The degradation leads to an accumulation of oxide-trapped charges within the gate oxide and an accumulation of interface-trapped charges at the oxide–semiconductor surface of power MOSFETs. Overtime, such charges significantly alter the electrical parameters of power MOSFETs; to observe this, the electrical parameters are utilized as precursors of gate-oxide degradation. The purpose of this paper is threefold: 1) to propose a new online precursor of gate-oxide degradation—the gate plateau time; 2) to demonstrate a simultaneous dip-and-rebound variation pattern of four precursors of gate-oxide degradation: threshold voltage, gate plateau voltage, gate plateau time, and on-resistance; and 3) to compare the shift tendencies of each precursor over the course of gate-oxide degradation. The existing studies of gate-oxide degradation mechanisms and their effects on threshold voltage and mobility reduction were extended to correlate a variation of all four precursors using analytical expressions. The variation patterns were experimentally verified using high-electric field stressing in two different commercial power MOSFETs. The new precursor, the gate plateau time, was found to be a competitive gate-oxide degradation precursor, as it had a higher positive shift than threshold voltage and gate plateau voltage. In addition, the threshold voltage was found to be the most sensitive indicator of the negative shift (dip), while the on-resistance and gate plateau time were found to be the most sensitive indicators of the positive shift (rebound). [ABSTRACT FROM AUTHOR]

LCL-filter-based grid-tie inverters require damping for the current-loop stability. There are only software modifications in active damping, whereas resistors are added in passive damping. Although passive damping incurs in additional losses, it is widely used because of its simplicity. This paper considers the active damping in medium-voltage parallel inverters for wind turbines. Due to cost reasons, only minimal software changes are allowed and no extra sensors can be used. The procedure must be robust against line-inductance variations in weak grids. Double-update mode is needed so the resonance frequency is under the Nyquist limit. The bandwidth reduction when using active damping is also required to be known beforehand. Moreover, the design procedure should be simple without requiring numerous trial-and-error iterations. In spite of the abundant literature, the options are limited under these circumstances. Filter-based solutions are appropriate and a new procedure for tuning the notch filter is proposed. However, this procedure requires that the resistance of the inductors is known and a novel filter-based solution is proposed that uses lag filters. The lag filters displace the phase angle at the resonance frequency so that the Nyquist stability criterion is fulfilled. Simulations and experiments with a 100-kVA prototype validate the analysis. [ABSTRACT FROM AUTHOR]

With the development of silicon carbide (SiC) power devices, the circuit structure of power converter for high-voltage applications would be simpler and more compact because the two-level-based topologies become applicable. This paper proposes a full-bridge (FB) T-type isolated dc/dc converter for the applications with high input voltage and wide input voltage range. The proposed converter is composed of four main power switches with high voltage stress (SiC mosfet) and four auxiliary power switches with low voltage stress (Si mosfet). Comparing with the conventional diode clamped FB three-level isolated dc/dc converters, the proposed FB T-type converter has simpler circuit structure and higher efficiency. A corresponding control strategy including two working patterns is proposed, which can not only realize the zero-voltage switching for the main and auxiliary power switches but also satisfy the wide input voltage range. More importantly, the proposed corresponding control strategy has the ability of balancing the currents among the power switches, which would balance the power losses, thermal stresses among the power switches, and thus improve the reliability of the converter. The characteristics and performances of the proposed converter with the corresponding control strategy are analyzed in detail and verified by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

Small dc-link drive systems, built with film capacitors in the dc-link, present a new trend in many industrial applications and are obtaining increasing interests. It has the advantages of longer lifetime and the possibility to achieve a more compact design of the capacitor bank, especially at medium and high power rates. However, it could exhibit instability problems, mainly in the form of oscillations. The unexpected oscillation may result in overvoltage and shorten the lifetime of the power devices and the dc-link capacitors; increase the total harmonic distortion and also the partially weighted harmonic distortion of the grid supply current. Therefore, active damping methods are usually needed in order to stabilize such drive systems. This paper first analyzes the system characteristics and the principles of existing active damping methods. Then, a new voltage modulation based method named as “virtual positive impedance” method is introduced to guarantee the dc-link stability. This new approach is simple to apply and its implementation does not require the knowledge of system parameters and machine operating conditions. The proposed method is analyzed in details and verified by experiments. [ABSTRACT FROM AUTHOR]

In this paper, a novel buck–boost dc–dc converter with continuous input current is proposed. The voltage gain of the presented converter is higher than conventional converters, such as buck–boost, single-ended primary-inductance converter, Cuk, and Zeta converters. This converter works only by one switch and voltage stress across the switch is low. Input current of the proposed converter is continuous so a large filter at the input is not needed. Furthermore, continuous input current has made this converter suitable for renewable energy and fuel cell applications. In this converter, noninverting output voltage is obtained and high gain of voltage is achieved as well. So it can operate at wide output voltage range only by changing the duty cycle of the power switch pulse. The presented converter can easily controlled in continuous conduction mode operation, because of using only one power switch. In the following, the principle of operation and the mathematical analyses of the proposed converter are explained, finally, validity of the proposed dc–dc converter is verified by the experimental results. [ABSTRACT FROM AUTHOR]

In this paper, a half-bridge (HB) converter, additionally employing a diode compared with the conventional modified duty-cycle-shifted (MDCS) HB converter, is proposed to achieve a high efficiency in wide-input-voltage and low-output-current applications. Since the proposed converter has symmetrical operation, it maintains the advantages such as no transformer dc-offset current, and identical and low-voltage stresses on the secondary diodes. Moreover, due to one additional switch connected in series, the zero-voltage-switching capability of the upper switch is improved. As a result, small resonant inductances are required, which reduces the duty cycle loss, thus the primary conduction losses decrease. In addition, since additional clamping diodes separate external resonant inductor from the resonance path, additional voltage stresses on the secondary diodes can be decreased. Therefore, its snubber loss can be reduced, and it can achieve higher efficiency than that of the MDCS HB converter. To confirm the operation, features, and validity of the proposed converter, a 310–400 V input and 50-V/250-W output laboratory prototype is built and tested. [ABSTRACT FROM AUTHOR]

This paper presents an improved compact model for a discrete silicon-carbide (SiC) MOSFET. This compact model based on the previous model features a new behavioral model of output characteristics and new nonlinear models of internal capacitors. Simulation with the improved compact model is in better agreement with measurement than that with the previous compact model, as well as transient behavior of the drain–source voltage, the drain current, and the leakage current out of a heatsink. Furthermore, the improved model is useful for constructing the accurate compact model that can reproduce the high-frequency characteristics of the transient waveforms of SiC-MOSFET s. This successful validation indicates that the improved compact model would be a promising tool for a full-simulation-based design system of the power converters using SiC-MOSFETs. [ABSTRACT FROM AUTHOR]

In a dc pulsed power supply (PPS), its instantaneous output power is pulsed, and its input power is required to be constant. In order to balance the instantaneous power difference, a storage capacitor is usually connected to the output terminal of the PPS. However, the storage capacitor is extremely large when the pulse repetition frequency (PRF) is relatively low. In this paper, an active capacitor converter (ACC) is adopted in place of the storage capacitor. In the ACC, the storage capacitor is greatly reduced by intentionally increasing its voltage ripple. To improve the tracking ability of the terminal current of the ACC, a current reference feedforward control scheme is proposed, and it is further simplified for avoiding the use of the reciprocal and square root circuits. In order to improve the dynamic response of the PPS when the pulsed load is triggered on and terminated, several methods are proposed. The methods of imposing a negative dc bias on the current reference and peak voltage control for the ACC storage capacitor are aiming for reducing the undershoot and overshoot of the output voltage, and two fast voltage loops are incorporated for limiting the maximum and minimum voltage of the storage capacitor in the ACC. Finally, a prototype with the output peak power of 2 kW, the output average power of 300 W, and the PRF of 150–300 Hz is fabricated and tested to verify the validity of the proposed PPS and control schemes. [ABSTRACT FROM AUTHOR]

Power theories are advancing signal decomposition approaches used for electrical power signal analysis. Currently, they are key tools for designing reliable and efficient power electronic interface controllers. Due to the inherent uncertainty in the power generation within new technology of distributed generation units (such as renewable-based microgrids), most of these theories are not directly applicable in the era of new power engineering systems. Furthermore, the traditional formulations are not appropriate once we face the nonlinearity in the consumption along a weak grid that may not maintain steady voltage or frequency. Therefore, a new signal decomposition method with a higher level of selectivity must be developed to modify the traditional power theories and improve the control strategies from a design viewpoint. This paper describes a novel formulation of an instantaneous power theory, enhanced instantaneous power theory (EIPT), for unbalanced and nonlinear three-phase power systems. EIPT establishes a proper decomposition of current components for cases of balanced, unbalanced, and distorted voltage sources. In addition to mathematical analysis, this research provides comprehensive simulations under different loads and source conditions, which supports the performance of the EIPT in the active filtering methods. Moreover, the performance of the proposed method is compared with the state-of-the-art approach widely known as the conservative power theory. Our results indicate that this new comprehensive approach is helpful in optimizing control strategies for power electronic interfaces and power quality compensators. [ABSTRACT FROM AUTHOR]

In this paper, a new pulse width modulation (PWM) scheme and commutation method is presented for one phase loss operation of three-phase isolated buck matrix-type rectifier. With the proposed PWM scheme, the maximum allowable voltage gain for one phase loss operation can be achieved, which permits the continuous operation of the converter to deliver two-third of the rated power and regulate the output voltage with maximum output voltage drop less than 5% of nominal output voltage. In addition, with the proposed commutation method, a safe transition from one phase loss operation to normal operation and vice versa can occur with minimum commutation steps (two-step) under zero-voltage switching condition. The performance of the proposed PWM scheme and commutation schemes with one phase loss operation is evaluated and verified by simulations and experiments on a 5 kW prototype. [ABSTRACT FROM AUTHOR]

To develop thermoelectric power conditioning systems that are highly efficient over a wide range of input voltages and support medium-rated power, this paper introduces a hybrid resonant dc/dc converter using an active voltage-doubler rectifier. When the input voltage is higher than the preset nominal input voltage, the converter operates in the phase-shift full-bridge series-resonant converter mode, in which it achieves high efficiency by softly switching the primary-side switches and reducing the conduction loss. When the input voltage is lower than the nominal one, it operates in the resonant boost mode that boosts the resonant inductor current. By using the active voltage-doubler rectifier on the secondary side of the converter, we can build the converter with less number of active components. As a result, the proposed converter achieves, at low cost, high boost-ratio and high efficiency over a wide range of input voltages. A detailed analysis of the converter operation is presented along with the design procedure. At 35–55 V, a 600-W/360-V prototype of the proposed converter has been built and tested to demonstrate its effectiveness. [ABSTRACT FROM AUTHOR]

Inductive power transfer (IPT) for battery charging applications has significant advantages over the traditional plug-in system. Since misalignment between the primary and secondary windings is inevitable, it is of significance to improve the misalignment tolerance of IPT systems with constant-current (CC) and constant-voltage (CV) outputs for battery charging. In this paper, the load-independent output characteristic of the hybrid topology and the function switching between CC and CV of the reconfigurable topology are analyzed. Besides, a hybrid and reconfigurable IPT system with 3-D misalignment tolerance for CC and CV outputs is proposed, simplifying or even canceling control schemes. Moreover, a novel parametric design method is given for the IPT system, which can suppress the fluctuation of the output voltage/current within a certain range of misalignment. In order to validate the performance of the proposed topology, a 1-kW prototype is built, and the corresponding experiments are carried out. In the CC/CV mode, the system can operate with the longitudinal misalignment to 50% when the load varies from 36 to 480 Ω, and the fluctuation of the output current/voltage is within 5%. Similarly, the misalignment in Y- and Z-axis is 12.5% and 33.3%, respectively. [ABSTRACT FROM AUTHOR]

In some application circumstances, both positive and negative sequence reactive power compensations are desired from the star-connected cascaded H-bridge static synchronous compensator (CHB STATCOM). However, the imbalanced phase currents/voltages will cause uneven active power flow among three clusters, which makes the cluster voltage balance more challenging. In this scenario, only zero sequence voltage is available to balance the cluster voltages. Although the zero sequence voltage can be calculated in all operating conditions based on the equilibrium of the active power for each phase cluster, the calculation is definitely complicated due to the zero sequence voltage expressed in the form of trigonometric function in the abc or dq0 frame. In this paper, the zero sequence voltage is represented in a dc form in the dq frame through introducing a virtually orthogonal zero sequence voltage. As a result, a linear relationship between the active powers and the zero sequence voltage is established, based on which, a simple zero sequence voltage calculation method is proposed with a small calculation burden. Furthermore, the accurate compensation region for the negative sequence current injection is identified by establishing the relationship between the maximum converter voltage and the negative sequence currents taking into consideration the initial phase angle of the negative sequence currents, while still keeping the cluster voltage balanced by using the zero sequence voltage control. The effectiveness of the proposed control and the compensation region are verified by the simulation and experimental results on a 400 V/±7.5 kVAr star-connected CHB STATCOM. [ABSTRACT FROM AUTHOR]

Due to the increased integration of multiple distributed generation (DG) units into the distribution network, riding through short-term faults and supporting the host grid have been requested by the new grid codes in many countries. However, the literature lacks the detailed dynamic analysis and control coordination of multiple grid-connected converter-based DG units, equipped with advanced controllers in the synchronous reference frame. To fill this gap, this paper initially presents a detailed small-signal modeling framework for typical medium-voltage multi-bus power distribution systems with multiple DG units equipped with grid-support functions to operate under the unbalanced conditions. This model encompasses the positive and negative sequences of the current and voltage and is developed for three stages of the fault (i.e., before, during, and after the fault) to cover a wide range of system operating points. In addition, to precisely study the interactions among DG units, four different control modes in DG units are considered to study the system dynamics under low-voltage and unbalanced conditions and at different grid strengths. Using the proposed detailed state-space models and based on the small-signal stability analyses, different control parameters are redesigned using the eigenvalue analysis on the complete multi-DG system. As a second contribution, sensitivity analyses are performed to study the effects of different system parameters, such as line characteristics, loading levels, and unbalanced fault characteristics, on the stability of the multi-DG system under unbalanced faults. Comparative simulation and experimental results are also reported to show the accuracy and effectiveness of the theoretical analyses. [ABSTRACT FROM AUTHOR]

This paper proposes an adaptive super-twisting algorithm based sliding-mode observer (STA-SMO) for surface-mounted permanent magnet synchronous machine (PMSM) sensorless control, in which voltage source inverter (VSI) nonlinearity is taken into consideration. An adaptive algorithm for online tuning the sliding-mode coefficients of STA-SMO is proposed based on the existing stable conditions. Thus, position estimation error can be reduced by the proposed adaptive algorithm in wide-speed range. Furthermore, voltage distortion due to VSI nonlinearity is online compensated to improve the accuracy of PMSM model. Because mismatch between reference and actual voltage due to VSI nonlinearity may bring large rotor position and speed estimation error, especially in low-speed range where distorted voltages may become dominant compared to actual voltages. Thus, a STA-SMO with adaptive sliding-mode coefficients and accurate voltage value could be obtained. Finally, the effectiveness of the proposed adaptive STA-SMO with online VSI nonlinearity compensation is verified on a surface-mounted PMSM by experiments. [ABSTRACT FROM AUTHOR]

The multiphase machine is a competitive candidate for applications where uninterrupted operation is demanded under postfault conditions. In this paper, the decoupling vector control for a surface mounted five-phase permanent-magnet synchronous machine (PMSM) under single-phase open-circuit fault is investigated. The decoupled mathematical model of the five-phase PMSM under single-phase open-circuit fault is derived. Then, two postfault control strategies are obtained, which are based on the principles of minimum copper loss and equal amplitudes of currents, respectively. The postfault control strategy based on the feed-forward compensation is proposed in order to eliminate the influences of certain factors and decrease the current ripple. The validity of the postfault control strategies is proved by experiments. [ABSTRACT FROM AUTHOR]

The contribution of decentralized generators in the provision of ancillary services, such as voltage and frequency regulations, is currently growing in many power systems. The impact of these new regulations on islanding detection is generally investigated by calculating the nondetection zone (NDZ) of the protective relay located at generator level. This subject has already been studied in the literature, but has been generally treated by means of steady-state calculations only. As demonstrated in the present paper, the analysis yields very different results when the entire time-evolution of the system is taken into account. It is shown that the impact of the studied regulations, i.e., the P(f) and Q(U) controls, on a standard test system is to reduce the NDZ which goes against the conclusion of several previous works based on steady-state calculations. Then the generalization of this result to other loads and generators is investigated. At last, the impact of the dynamics of the grid and the dynamics of the regulations is further investigated through a parametric study which shows that, if the power regulations dynamics are slow enough compared to the voltage and frequency dynamics, then the NDZ is necessarily reduced by the addition of the new regulations. [ABSTRACT FROM AUTHOR]

This paper presents a novel three-phase DC-link multilevel inverter topology with reduced number of input DC power supplies. The proposed inverter consists of series-connected half-bridge modules to generate the multilevel waveform and a simple H-bridge module, acting as a polarity generator. The inverter output voltage is transferred to the load through a three-phase transformer, which facilitates a galvanic isolation between the inverter and the load. The proposed topology features many advantages when compared with the conventional multilevel inverters proposed in the literatures. These features include scalability, simple control, reduced number of DC voltage sources, and less devices count. A simple sinusoidal pulse-width modulation technique is employed to control the proposed inverter. The performance of the inverter is evaluated under different loading conditions and a comparison with some existing topologies is also presented. The feasibility and effectiveness of the proposed inverter are confirmed through simulation and experimental studies using a scaled down low-voltage laboratory prototype. [ABSTRACT FROM AUTHOR]

This paper proposes a three-level bidirectional dc–dc converter with an auxiliary inductor for full-operation zero-voltage switching (ZVS) in high-output voltage applications. The auxiliary inductor is connected across the middle node of the split flying capacitors and the center tap of the secondary winding in the transformer. In this topology, the outer and inner switches in the three-level stage can generate two independent 50% duty-cycle square waveforms, which are used to control the current in the auxiliary inductor to extend the ZVS from no loads to full loads. Considering the phase-shift angle in three-level stage, the ZVS range of the converter is analyzed, and the modulation trajectory to maintain the full-operation ZVS range with low condition loss is proposed. A flowchart implementation can guarantee the seamless transfer in different working modes. Then, the conduction loss in the proposed converter is compared with the previous three-level bidirectional solution, which illustrates that the conduction loss in the proposed converter only increases in light loads. Finally, the experimental results verify the theoretical analyses and ZVS performance across the whole power and voltage range, and the efficiency curves demonstrate the efficiency improvement. [ABSTRACT FROM AUTHOR]

This paper presents a new predictive power-factor-correction (PFC) controller for series-interleaved three-level boost (TLB) converters. Compared to the state-of-the-art TLB PFC controllers, where a two-cycle prediction and a detection of an operating region are necessary, the proposed controller achieves a low total harmonic distortion of the input current by using a single equation to predict the input current in all operating regions of the converter, in just one operating cycle. The average current control is achieved by sampling at the peak of the triangular carrier. The proposed PFC controller significantly reduces the distortion of the input ac current near the zero-crossing points, resulting in a low total harmonic distortion of the input current. The operation of the proposed controller was evaluated, and its stability and robustness to parameter changes was confirmed analytically. The controller operating principles were verified in simulations and validated by experiments on a medium-voltage 50-kW converter prototype. [ABSTRACT FROM AUTHOR]

Because of fast switching speeds and inevitable stray parameters, the efficiency, security, and stability properties of SiC mosfets in practice are challenged by voltage and current ringing and overshoot. In this paper, the turn-on and off behavior of an SiC mosfet regulated by a gate driver are modeled in detail, and insight mechanisms for suppressing the ringing and overshoot by using gate driver are highlighted. Based on a clamped inductive double-pulse test, many control degrees of freedom, including gate resistance, gate–source capacitance, and gate voltage, are considered and verified by comprehensive experimental results. Although these parameters can regulate the ringing and overshoot, the switching speed of the SiC mosfet decreases and its power loss increases. To balance the tradeoff, a preferred gate driver for an SiC mosfet is recommended. [ABSTRACT FROM AUTHOR]

The neutral-point potential fluctuation in single-phase three-level rectifiers leads to coupling between the line current regulation and dc-link capacitor voltage balancing, deteriorating waveform quality of the line current. For addressing this issue, this paper proposes a low-complexity model predictive current control (MPCC) with constant switching frequency, which achieves a decoupling control of the line current and the neutral-point potential under the unbalanced load condition. The switching frequency is fixed by combining the MPCC scheme with predefined switching sequences. The boundary of the durations for voltage vectors in switching sequences is presented to balance the capacitor voltage without worsening the line current quality. The optimal switching sequence and the corresponding optimal durations of voltage vectors in the switching sequence are readily derived without the assessment of the cost function, which dramatically simplifies the complexity of the MPCC scheme. Finally, simulations and experimental results are conducted to verify the effectiveness of the proposed MPCC scheme. [ABSTRACT FROM AUTHOR]

A family of dimmable ac light-emitting-diode (LED) drivers fed from dc voltages, is presented in this paper based on zero-current-switching quasi-resonant converters. The proposed family of drivers is based on replacing the diode in the conventional converter topologies (i.e., buck, boost, or buck–boost) by a string of high-brightness LEDs (HB-LEDs). Hence, the HB-LED string will be working as the rectifier diode and the load, switching at the same frequency of the main switch. In this case, the output current, which is experimentally validated, shows a negative current peak due to the reverse-recovery effect of the HB-LEDs. In order to reduce the reverse-recovery effect on the HB-LEDs, the main switch of the proposed topologies is replaced with a full-wave resonant switch, which makes possible to reduce the di/dt during the turn-off of the HB-LED string, therefore the reverse-recovery effect is eliminated. Moreover, the dimming of the HB-LEDs is done by means of changing the switching frequency of the converter by varying the turn-off, while keeping a constant turn-on time. The proposed converters are suggested to be used in a postregulator stage of an ac–dc converter or as the interface between the low-voltage bus and the HB-LED string in a dc nanogrid. In order to validate the analysis, the proposed topologies have been experimentally tested on a constructed prototype with an output power of 7.5 W, that is able to achieve an electrical efficiency of 94.5% and a luminous efficacy of 110 lm/W at full load. Moreover, the analysis has been extended to a comparison in terms of reliability with the conventional topologies on a 700-h test. [ABSTRACT FROM AUTHOR]

High-frequency (HF) switching and ac-side unbalanced loads challenge smart transformer (ST)-fed hybrid grids (both ac and dc), causing common-mode (CM) voltage variations and dc-link oscillation. The HF switching introduces an HF CM voltage and the ac grid unbalanced loads introduce a fundamental frequency CM voltage in hybrid grids. The CM voltage in ST-fed distributed grids degrades the power quality, threatens the safety of the connected devices, and potentially constitutes a health risk for the operators of such devices. Therefore, this paper systematically analyzes the root causes of the ST CM voltage variations and the impacts on hybrid grids. Based on the two typical configurations (three- and four-leg converters), the performance and requirements of CM inductor filter and bypass CM filter on HF CM voltage suppression are studied in detail. By considering the CM voltage suppression and dc capacitor lifetime, a four-leg converter with improved modulation strategy and small dc bypass film capacitor is proposed. The simulation and experimental results clearly verify the feasibility and correctness of the proposed strategies. [ABSTRACT FROM AUTHOR]

Three-phase AC−DC and DC−AC power converters have been extensively employed as grid-interfaces in various applications, e.g., distributed generation and energy storage systems. In these applications, power converters should always synchronize with the mains grid so that active and/or reactive power can properly be regulated while maintaining desired waveforms of grid currents. Grid synchronization necessitates accurate information of grid voltages, which is normally obtained through phase-locked-loops (PLLs). However, the employment of PLLs may bring in stability concerns. Previous research revealed that the inclusion of PLLs shapes the impedance of power converters into a negative resistance in the quadrature-axis (q-axis), and this should be responsible for instability. To resolve the instability issue caused by PLLs, this paper proposes an impedance controller for reshaping the q-axis impedance into a positive resistance in the low-frequency band. Without any extra burden on system hardware, the proposed controller can easily be implemented by directly relating the q -axis voltage to the q-axis current reference. As a result, the presented three-phase power conversion system can operate stably even under a severely weak grid condition, which are verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

Owing to low cost, small size, and low weight, transformerless inverters became prominent in single-phase grid connected photovoltaic (PV) systems. Key issues pertaining to these inverters include suppression of common mode (CM) leakage current and improvement of conversion efficiency. Achieving higher efficiency in single-phase grid-connected photovoltaic systems depends on the number of stages involved in feeding power to the grid, predominantly, if the PV array voltage is less than the peak value of the grid voltage. In this paper, an integrated dc–dc converter based grid-connected transformerless PV inverter is proposed which is aimed at maintaining high efficiency, even if the PV array voltage falls below the peak value of grid voltage (efficient operation at an extended input voltage range). A modulation strategy is discussed in order to minimize the flow of CM leakage current. Further, the efficiencies of certain transformerless inverter topologies are analyzed and compared with that of the proposed topology. Detailed simulation studies are carried out in MATLAB/Simulink environment to verify the analysis. Experimental results for a scaled down laboratory prototype are included as a proof-of-concept to validate the claims. [ABSTRACT FROM AUTHOR]

In this paper, a modular control approach has been proposed for a single- and three-phase differential-mode Ćuk inverter (DMCI) operating with a recently proposed discontinuous-modulation scheme that offers tangible performance benefits over conventional continuous modulation scheme. The modular control scheme uses a combination of a transformation and adaptive control law to meet tracking requirements in the presence of converter nonlinearity. Experimental results for the single- and three-phase DMCI are provided for startup, steady state, load transition, and total harmonic distortion using different types of loads, which validate the efficacy of the implemented modular tracking controller. Further, detailed stability of the closed-loop DMCI module is provided. [ABSTRACT FROM AUTHOR]

This paper has focused on the novel space vector pulse-width modulation (SVPWM) strategy for the two-level three-phase inverter, which could eliminate the harmonics nearby pulse width modulation (PWM) frequency. Ear-piercing high-frequency electromagnetic noise from motor is common due to PWM technique. The proposed SVPWM is able to remove the high-frequency harmonics located nearby the PWM frequency and other odd multiples by changing the original switching states. The unpleasant acoustic noise could be removed with the novel strategy whose PWM frequency is selected near 10 kHz. By comparison, it is near 20 kHz for conventional SVPWM to achieve the similar performance. Therefore, the switching losses are significantly reduced using the novel method. Furthermore, the proposed technique neither changes the characteristics of the fundamental wave nor employs the additional circuits in the drive. At last, the effectiveness of proposed strategy is verified by simulation and experiment. [ABSTRACT FROM AUTHOR]

Effective battery voltage regulation is fundamental to extend battery lifetime and to avoid overvoltage. However, the design of this regulation is complicated due to the wide battery impedance range, which, when dealing with universal chargers, is dependent not only on the operating point but also on the battery type and size. This paper first shows how the voltage response becomes highly variable when designing the controller as described in the literature. Then, it proposes to emulate virtual impedance in parallel with the battery, making it possible to achieve a voltage control which is independent of battery characteristics. Experimental results are carried out for a new lithium-ion battery with 25 mΩ impedance and an overused lead-acid battery with 400 mΩ impedance. For this large impedance variation, the results evidence the problems of the conventional control and validate the superior performance of the proposed control. [ABSTRACT FROM AUTHOR]

This paper presents a control method that can prevent audible noise generation in an LLC resonant half-bridge dc–dc converter under a light-load condition, while achieving the same input voltage range and power-conversion efficiency ηe as the burst-control method that generates an audible noise. The proposed method reduces switching and conduction losses at light load by skipping several pairs of switch-control pulses, while varying the switching frequency less than the normal-control method does. This skip-control method enables the LLC resonant converter to have a large magnetizing inductance, and to have high ηe over a wide range of load variation. At an input voltage of 385 V, an output voltage of 24 V, and a resonant frequency of 180 kHz, the proposed method achieved η e ≥ 85.46% for an output power range of 7.2–360 W; the highest ηe was 96.08% at $P_o$ = 336 W. [ABSTRACT FROM AUTHOR]

The powder-core-based inductor has a wide inductance variation due to the soft-saturation nature when subjected to varying load current. Under such a condition, the current ripple is influenced, and the conventional inductor design principle may be inaccurate. Besides, the voltage of the inductor is distorted. Also, the bandwidth of the controller is hard to determine. In this paper, the current ripple under the condition of wide inductance variation is analyzed, and its change rule is revealed; then, a new inductance design principle is proposed. The harmonic components for the three-phase converter with the powder core inductor are investigated, and the harmonic characteristic of the input current is analyzed. According to the current harmonic characteristic, the resonance controllers are introduced to eliminate harmonics, and the quality of the current is improved. Besides, the bandwidth of the controller is found to vary with the output power. Then, a compensation method is proposed to eliminate the influence of inductance variation on the bandwidth. The experimental results verify the analysis. [ABSTRACT FROM AUTHOR]

Matrix converter based open-end winding drives modulated with rotating vectors eliminate the high-frequency common-mode output voltage that could otherwise cause motor failure. Unlike back-to-back converters, no intermediate dc bus capacitor is required—better power density and reliability may, therefore, be achievable. A high voltage transfer ratio and input power factor control capability put these open-end winding drives at a significant advantage over conventional matrix converters. At least three realizations of the matrix converter based open-end drive are possible. This paper compares these three realizations to identify the best topology and presents experimental results validating its capabilities. Filter optimization, loss-optimal vector sequences, and other practical considerations are also discussed. Finally, a comparison with the state-of-the-art back-to-back converters is provided to investigate if the potential improvements are in fact attainable. [ABSTRACT FROM AUTHOR]

For railway traction drives, the active front end usually adopts a single-phase rectifier. However, the dc-link voltage of this single-phase rectifier contains a second-order fluctuating component due to the fluctuation of the instantaneous power at both the ac and dc sides. Fed by the fluctuating dc-link voltage, the traction motor suffers from severe torque and current pulsation. The hardware solution with an additional LC resonant filter is simple, but it will reduce the power density of the system. An alternative solution is to eliminate the beat component in the stator voltage/current through modulation ratio or frequency compensation. However, it is difficult to achieve high performance for the conventional feedforward method. In this paper, an improved closed-loop torque and current pulsation suppression method is proposed, which can eliminate the q-axis current pulsation component in the field-oriented control system through frequency compensation. The torque pulsation suppression is also achieved automatically. Simulation and experimental results show that the proposed scheme can effectively reduce the torque and current pulsation in various operation modes compared with the conventional feedforward method. [ABSTRACT FROM AUTHOR]

A family of high-voltage-gain dc–dc converters derived from a generalized structure with two stages is introduced in this paper. On the input side, a two-phase interleaved boost stage boosts the dc input voltage to output a modified square-wave voltage that feeds the second stage. This output of the interleaved boost stage is rectified and further boosted using a voltage multiplier stage. As a result, a high voltage gain is achieved using the proposed converters. The two-phase interleaved boost stage on the input side makes it possible for the converters to be operated using a single source or two independent sources. If a single source is used, the input current drawn is continuous with a very small ripple. Owing to its generalized structure, the proposed family of converters includes both nonisolated and isolated converters with high voltage gains. The high voltage gain and low-ripple continuous input current make these converters appealing in applications like the integration of renewable sources such as solar, fuel cells, etc., on to a 400-V dc bus. [ABSTRACT FROM AUTHOR]

For the purpose of reducing cost and volume, as well as to increase reliability in hostile environments, techniques of reconstructing three-phase current through a single current sensor have been reported for a three-phase alternating current motor vector control system. Based on the phase current reconstruction method, this paper proposes a novel open-circuit fault diagnosis method for the low-power voltage source inverter in the three-phase permanent-magnet synchronous motor drive. Other than sampling the single dc-link current sensor, the zero voltage vector sampling method (ZVVSM) is adopted to implement the fault diagnosis. By placing the single current sensor at a special position, ZVVSM is able to sample current during the two zero voltage vectors and reconstruct the three-phase currents. The reconstructed three-phase currents are used to generate the diagnostic variables that can detect and locate the faulty power switches. The PWM modulation strategy remains unchanged in this method and the reconstructed phase currents are with less waveform distortion and less harmonic contents, which are suitable for the fault diagnosis. The effectiveness of the proposed method is verified by experiments. [ABSTRACT FROM AUTHOR]

Electrical and electromagnetic methods have long played an important role in mineral exploration. For example, in active source prospecting methods, when measuring the values of many electrical parameters, the signal-to-noise ratio can be improved by increasing the transmitting power. In this paper, we present a multifunction borehole ground electromagnetic transmitting system that transmits rectangular waves at a frequency of 0.01–10 kHz with a frequency error less than 10−8 Hz @ 1 Hz (depending on the high-precision temperature compensation crystal) and the initial synchronization error between the transmitter and receiver is less than $ \pm \text{0.1}\,\mu {\text{s}}$. During operation, either the maximum transmitting voltage output can reach 950 V or the maximum transmitting current can exceed 90 A, but both cannot be achieved simultaneously. We tested the transmitting system at its maximum power output continuously for over 8 h and the power output was more than 48 kW at a current above 60 A. The energy was delivered above ground or underground using existing drill casings to produce the high-power transmissions. The field experiments show that the system meets the demands of the controlled-source audio-frequency magnetotelluric and induced polarization methods used in mineral exploration. [ABSTRACT FROM AUTHOR]

This paper proposes a novel modified LLC converter with two split resonant branches for wide input-range applications. It can operate in low-gain (LG) mode or medium-gain (MG) mode. The voltage gain of MG mode is 1.5 times that of LG mode, while they have same range of voltage gain $M_{{\rm{tank\_range}}}$ , i.e., the ratio of maximum voltage gain to minimum one. Therefore, the input voltage can be regulated in a wide range by operating the converter in different modes. To achieve the transition between modes, the required $M_{{\rm{tank\_range}}}$ of the proposed converter is as low as 1.5, resulting in lower magnetizing current and higher efficiency within the entire operation range. Smooth transition can be achieved by adjusting the duty cycles of switches gradually. The proposed LLC converter with primary dual-bridge is analyzed in detail as an example. To verify the theoretical analysis and performance of proposed solution, a 1-kW 400-V output prototype with input voltage ranging from 80 to 200 V is built, tested, and compared with two existing full-bridge LLC converters. Analysis and experimental results indicate that smaller volume of transformers, reduced rectifying diodes, and higher overall efficiency are achieved with the proposed converter. [ABSTRACT FROM AUTHOR]

The information of the initial rotor position is essential for smooth startup and robust control of permanent magnet synchronous machines (PMSMs). RoTating Voltage Injection (RTVI) methods in the stationary reference frame have been commonly adopted to detect the initial rotor position at standstill without any position sensors. However, although the Pulsating sqUare-wave Voltage-Injection (PUVI) method performs better in estimation time and accuracy, it is rarely used because the estimation result may converge to the q-axis. In this paper, this fault convergence is avoided by modifying the initial states of the position observer, and the PUVI method can finally be used for the robust initial rotor position detection. Modified signal processing techniques are proposed for both RTVI and PUVI methods for better implementations in fixed-point processors and easier observer gain designs. Detailed comparisons between these two methods are provided. Furthermore, two position estimation observers, i.e., the proportional–integral observer and the extended state observer are compared, and their parameter tuning methods are studied as well. Both simulation and experimental results are provided for verifications. [ABSTRACT FROM AUTHOR]

This paper presents a model-based method to diagnose single- and multiple-transistor open-circuit (OC) faults in grid-tied three-phase voltage-source inverters (VSIs). The method is based on calculated average bridge arm pole-to-pole (PTP) voltages and error-adaptive thresholds. Only existing signals for closed-loop control are needed; thus, this method can be easily embedded in the system without extra sampling and circuits. Average PTP voltage deviations are chosen as diagnosis variables, which show considerable distinction quickly after fault. Consequently, fast fault diagnosis speed can be achieved. The fault diagnosis time for single fault can be as short as two switching periods. Besides, diagnosis variables show the same faulty characteristics in inverter mode and rectifier mode; thus, this method is effective in both modes. Moreover, for the first time, the variation of inductance caused by conducted current is considered to obtain a more accurate variable-inductance model, and the thresholds are updated according to mathematically estimated diagnosis variable calculation errors from sampling error, inductance error, dead time, and delay time, which maintains high robustness as well as fast speed. Finally, the effectiveness of the proposed method is validated with experiments. [ABSTRACT FROM AUTHOR]

A quasi-Z-source inverter (qZSI) could achieve buck/boost conversion as well as dc to ac inversion in a single-stage topology, which reduces the structure cost when compared to a traditional two-stage inverter. Specifically, the buck/boost conversion was accomplished via shoot-through state which took place across all phase legs of the inverter. In this paper, instead of using traditional dual-loop-based proportional integral (PI)-P controller, a type 2 based closed-loop voltage controller with novel dc-link voltage reference algorithm was proposed to fulfill the dc-link voltage tracking control of a single-phase qZSI regardless of any loading conditions, without the need of inner inductor current loop. A dc–ac boost inverter with similar circuit parameters as a qZSI was used to verify the flexibility of the proposed controller. The dynamic and transient performances of the proposed controller were investigated to evaluate its superiority against the aforementioned conventional controller. The integrated proposed controller and qZSI topology was then employed in static synchronous compensator application to perform reactive power compensation at the point of common coupling. The effectiveness of the proposed approach was verified through both simulation and experimental studies. [ABSTRACT FROM AUTHOR]

In this paper, a new single-stage half-bridge (HB) resonant $LLC$ converter additionally employing one resonant capacitor and two relays with one package is proposed, compared with a single-stage HB $LLC$ converter. Moreover, a center-tapped transformer is replaced with a coupled transformer. Since the proposed converter changes the turns ratio of the coupled transformer using a relay according to low- or high-input-voltage range, it can decrease the range of its needed voltage gain. It means that the proposed converter can be designed with large transformer magnetizing inductance compared with the conventional single-stage HB $LLC$ converter. As a result, the primary conduction and turn-off losses are reduced. Moreover, in low input voltage range, it has smaller total primary wire resistance of the transformer due to parallel connection of the coupled transformer, which decreases its conduction loss. In addition, additionally employed small-sized components can be inserted to the conventional system. To confirm the operation, features, and validity of the proposed converter, universal input with low line and high line and 16.5 V/60 W output laboratory prototype targeting laptop adapters with wide-input-voltage range is built and tested. [ABSTRACT FROM AUTHOR]

This paper proposes a new control technique, which only employs the primary-side controller and load identification approach to adjust charging voltage/current for series–series (SS) and series–parallel (SP) compensated wireless power transfer (WPT) systems. The advantages are that dual-side wireless communication for real-time charging current/voltage adjustment is avoided as well as it is suitable for different charging modes, e.g., constant voltage (CV) and constant current (CC) charging defined by the battery charging profile. The load identification approach, which utilizes reflected impedance theory and quadrature transformation algorithm for calculating the active power, is proposed to estimate the equivalent load resistance of battery. Then, the CV/CC charging for both SS and SP compensation are achieved by the PI-controlled phase-shift H-bridge inverter. The simulation and experimental results validate the feasibility of proposed control method. During the CC charging, 3.01 and 3.03 A for SS and SP compensation with the error of 1.2% and 1.4% are achieved. During the CV charging, 25.8 and 25.7 V for SS and SP compensation with the error of 1.1% and 1.3% are realized. The proposed method improves the performance of both SS- and SP-compensated WPT systems to be more suitable for the applications that require compact and lightweight receiver. [ABSTRACT FROM AUTHOR]

In this paper, a new reference current generation method is proposed for effective harmonics mitigation and reactive power compensation of three-level neutral-point diode clamped inverter-based shunt active power filter (SAPF) under nonideal grid voltage conditions. The proposed method is named as dual fundamental component extraction algorithm. In operation, the proposed algorithm extracts at the same time, the desired fundamental current and voltage components for generating reference current and synchronization phases, respectively. As a result, the proposed algorithm is able to generate reference current that ensures in phase operation of SAPF with the operating power system, without depending on any phase-locked loop elements. Besides, the proposed algorithm employs self-tuning filter (STF) for accurate computation of the fundamental components. Design concept and effectiveness of the proposed algorithm are thoroughly studied and evaluated in MATLAB–Simulink. Additionally, a laboratory prototype utilizing TMS320F28335 digital signal processor is built to validate its feasibility. Encouraging findings obtained from both simulation and experimental works demonstrate effectiveness of the proposed algorithm under both ideal and nonideal grid voltage conditions. [ABSTRACT FROM AUTHOR]

In this paper, a current-mode Class-DE (CMCDE) power amplifier is presented. The CMCDE with linear shunt capacitance under zero-current switching (ZCS) and zero current-derivative switching (ZCDS) conditions at any active time is analyzed, simulated, and fabricated. An analytical theory along with the design simulation and verification by experimental results at active time \tau d= \pi / 2 are given. It was shown that the peak switch voltage can be adjusted with active time \tau d. The proposed amplifier offers several desirable features, such as simple structure and possibility to include the parasitic inductance and shunt capacitance of the mosfet into a load network, so that ZCS condition is maintained. The results show that the switch voltage and current obtained in CMCDE amplifier are inversed in comparison to the voltage-mode Class-DE (VMCDE) amplifier by using a simple output matching network and series inductance. Also, we could control the harmonics in one resonator in comparison to multiple resonators used in some high-efficiency power amplifiers. The measured maximum drain efficiency of 88% and power gain of 22 dB at 42-dBm output power was obtained at 4 MHz for CMCDE amplifier at active time \tau d= \pi / 2. [ABSTRACT FROM AUTHOR]