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The output voltage of power electronic converters is a very important quantity for dynamic control of power electronic systems. In electrical drives without electromechanical position or speed sensor, the terminal reference voltage is used to obtain the rotor position. Dead-time effects and semiconductor voltage drop lead to distortion in the actual output voltage and degrade the control performance when the back electromotive force magnitude is low. Thus, for stable low-speed operation, output voltage sensing becomes necessary. Due to the switching nature of power electronic systems, this is not a trivial task, especially when instantaneous measurement of the terminal voltage is required. In this paper, an instantaneous switching-period average voltage sensing technique is proposed that utilizes a combined approach of oversampling and filtering. Based on the theoretical analysis of the sampling- and filter-induced measurement distortion, a general solution for an optimal filter design is derived. The additional sensing circuit is integrated into the low-side gate driver of the converter outputs. This paper includes details about the hardware implementation and extensive verification measurements. [ABSTRACT FROM AUTHOR]

This paper proposes a new single-phase single-stage switched-boost inverter with four switches. Like the quasi-Z-source inverter and quasi-switched boost inverter (qSBI), the proposed inverter has the main features as continuous input current, buck/boost voltage with single-stage conversion, and shoot-through immunity. Compared to the qSBI, the proposed inverter uses one more capacitor and one less switch. This paper presents the operating principles, pulse-width modulation control strategy, parameter design guidelines, and simulation results for the proposed inverter. To verify the performance of the proposed inverter, an 800-W prototype was built with an 110 V/50 Hz output voltage in stand-alone and grid-connected modes. The simulation and experimental results matched those of the theoretical analysis. [ABSTRACT FROM AUTHOR]

Conventional finite control set-model predictive control (FCS-MPC) applies single voltage vector within each control period. This leads to relatively high steady-state ripples and requires fast sampling rate. Additionally, enumeration-based optimal vector selection is computationally intensive. Recently, double-vector-based schemes have been proposed to improve the steady-state performance of FCS-MPC. However, they are usually complicated in vector selection and duty ratio calculation. In this paper, a universal multiple-vector-based MPC (UMV-MPC) is proposed, which achieves the same performance as the state-of-the-art double-vector-based MPC, but executes in a much more efficient and universal way. Unlike conventional FCS-MPC, enumerating process and state predictions for candidate voltage vectors are not required in the proposed UMV-MPC to select the best voltage vectors. In UMV-MPC, the optimal vectors and duty ratios are directly constructed from deadbeat control (DBC) based on space vector modulation (SVM), which is easy to follow and quick to use. The proposed UMV-MPC is not only more efficient than prior methods, but also reveals the inherent relationship between double-vector-based MPC and DBC with SVM. A comparative study of UMV-MPC and prior double-vector-based MPC is carried out in this paper. The theoretical analysis as well as simulation and experimental tests on a 2.2-kW induction motor drive are demonstrated to validate the effectiveness of the proposed UMV-MPC. [ABSTRACT FROM AUTHOR]

In this article, the stability of voltage source converter-based autonomous ac microgrids (MGs), which are interconnected through back-to-back converters (BTBCs), is analyzed. The small-signal stability analysis is based on a detailed, comprehensive and generalized small-signal modeling of the ac interconnected MGs (IMGs), which is possible for any number of MGs and interconnections. The large-signal stability of the IMGs is investigated for the case of the initial BTBC dc voltage as a part of paper contribution. A new margin/criterion is determined for the initial dc voltage in different situations of the BTBC operation. According to the proposed criterion, a fundamental difference between very weak MGs and conventional strong grids in the BTBC voltage stability is addressed. Using eigenvalue analysis and participation matrix, the main participating state variables and corresponding parameters in the dominant critical modes are recognized for an equilibrium point. Sensitivity analysis involves changing initial values of the state variables, parameters, and forcing functions to study their different values and find acceptable ranges of the parameters. Particularly, the considerable contribution of the BTBC in the critical modes is found out by analyzing the initial dc voltage, dc voltage controller and PLLs. In order to observe possible unstable situations and verify the transient studies, real-time simulations are provided for two and three MGs interconnected through BTBCs using OPAL-RT digital simulator. The IMGs can be robustly stable only by specifying the stabilizing ranges of the sensitive parameters to the critical modes and selecting their appropriate values. [ABSTRACT FROM AUTHOR]

In this paper, a new structure of nonisolated boost dc–dc converters based on voltage-lift technique is proposed. In comparison with conventional nonisolated boost dc–dc converters, the proposed converter generates higher voltage gain. In this paper, the relations between voltage and current of all elements in continuous conduction mode and discontinuous conduction mode are calculated as well as voltage gain in each mode. Then, the critical inductance and stress of switch current are extracted. Finally, the validity of given theories is examined by using the experimental results. [ABSTRACT FROM PUBLISHER]

The asymmetrical half-bridge (AHB) converter has been deeply analyzed as second stage in ac–dc light emitting diode (LED) drivers. Galvanic isolation, high reliability and high efficiency are their main advantages while a limited duty cycle range (i.e., 0–0.5) and a poor dynamic behavior are their main disadvantages. As second stage of an LED driver, the most demanding requirement for its control loop is cancelling the low-frequency ripple introduced by the first stage. According to its limited maximum attainable bandwidth, this is normally achieved by implementing a feedforward loop. Nonetheless, the static gain of the standard AHB converter presents a nonlinear relation between the output voltage and the duty cycle. As a consequence, the effectiveness of this feedforward loop is limited. In this paper, the use of the zeta AHB converter as second stage of an LED driver is analyzed and an optimized design is proposed. Regarding its advantages, it presents an extended duty cycle range (theoretically, 0–1.0). Besides, it presents a linear relation between the output voltage and the duty cycle. Therefore, although its dynamic behavior is still limited, it can perfectly cancel the low-frequency ripple introduced by the first stage of the LED driver by means of a straightforward feedforward loop. The optimized design proposed in this paper is focused on minimizing the losses in the magnetic components (transformer and inductor) by wisely choosing the value of the two turns ratios of the transformer. [ABSTRACT FROM AUTHOR]

This paper proposes a new battery cell voltage equalization approach using multiple-receiver wireless power transfer (WPT) working at megahertz (MHz). Compared with existing multiwinding transformer, the MHz multiple-receiver WPT system is advantageous in terms of saved weight and space, ease of implementation, and improved safety. In this paper, the unique operating principle of the WPT-based equalization is first explained, through which equalization currents are naturally determined by the battery cell voltage distribution. The currents are also analytically derived. This facilitates the discussion on power amplifier (PA) design. Performance analysis is then provided to investigate the influences of system parameters on the efficiency and equalization ability of the proposed WPT-based equalization system, and thus guide following design and implementation. Considering the uncertainty in PA load due to the random cell voltage distribution, a current-model Class $E$ PA is designed that enables approximately constant PA output current. Experimental results show that the proposed multiple-receiver WPT-based battery cell equalization system can achieve high overall system efficiency (above 71%) when equalizing six lithium-ion battery cells under loosely coupling ( $k$ = 0.065). A good match between the experimental and calculation results also validates the correctness of the theoretical discussion. [ABSTRACT FROM PUBLISHER]

This paper proposes a new bidirectional resonant dc–dc converter suitable for wide voltage gain range applications (e.g., energy storage systems). The proposed converter overcomes the narrow voltage gain range of conventional resonant dc–dc converters, and meanwhile achieves high efficiency throughout the wide range of operation voltage. It is achieved by configuring a full-bridge mode and a half-bridge mode operation during each switching cycle. A fixed-frequency phase-shift control scheme is proposed and the normalized voltage gain can be always from 0.5 to 1, regardless of the load. The transformer root-mean-square (rms) currents in both the forward and reverse power flow directions have a small variation with respect to the voltage gain, which is beneficial to the conduction losses reduction throughout a wide voltage range. Moreover, the power devices are soft-switched for minimum switching losses. The operation principles and characteristics of the proposed converter are firstly analyzed in this paper. Then the analytical solutions for the voltage gain, soft-switching, and rms currents are derived, which facilitates the parameters design and optimization. Finally, the proposed topology and analysis are verified with experimental results obtained from a 1-kW converter prototype. [ABSTRACT FROM PUBLISHER]

Common-mode voltage output is closely associated with switching states in three-phase three-wire neutral point clamped converter. Detailed analysis shows avoiding redundant states can effectively improve the common-mode voltage, so this paper proposes a pulse width modulation (PWM) technique with zero redundant state to reduce the common-mode voltage output, and evaluates their performance with the conventional PWM schemes. This paper also takes the compensation of neutral point potential deviation into consideration. Laboratory test results are presented to verify the effectiveness of the proposed scheme. [ABSTRACT FROM PUBLISHER]

This paper documents a new three-switch, isolated boost dc–dc converter. The major features of the proposed converter are as follows: 1) continuous input current; 2) reduced one active switch, one additional diode, and one additional capacitor; 3) unchanged primary and secondary voltage waveforms of the transformer when the duty cycle is changed; and 4) removal of the snubber circuit. This paper presents the operating principles, analysis, parameter design guidelines, and simulation results for the proposed converter. To verify the performance of the proposed converter, a 400 W prototype was constructed with a 40–60 V dc input. A PID controller was used to maintain the dc output voltage at 400 V. The simulation and experimental results matched those of the theoretical analysis. [ABSTRACT FROM AUTHOR]

Due to the phase delay caused by low-pass filter, device retarding, and software retarding, the extracted sensorless motor commutation signal deviation occurs. Unfortunately, the relationship between the phase shift and inactive phase freewheeling has been scarcely referred to through the published papers, and most of the commutation instant shift compensation methods present slow convergence rate. Therefore, a fast commutation instant shift correction method based on analyzing the back-electromotive force (EMF) harmonic information is proposed in this paper. The method is effective both in the steady-speed control and in variable-speed control. Considering that commutation instant shift may induce inactive phase freewheeling and negative torque in motor windings, the freewheeling condition and motor electric operation condition are analyzed as well. Furthermore, to exactly delay the zero-crossing points (ZCPs) of EMF by 30° and compensate the commutation instant shift, the speed detection accuracy and feedback frequency are enhanced by measuring and summing up the 2 × P consecutive half-period of the ZCPs signal. Finally, the validity of the proposed commutation instant shift correction method is verified through experimental results. [ABSTRACT FROM AUTHOR]

This paper targets the reduction of common-mode voltage in an indirect matrix converter (IMC) through an intelligent space-vector-based modulation technique. This mode of control results in lower dV/dt at the motor terminals, thereby, reducing voltage stress to windings; and reduced output voltage distortion resulting in lower machine losses. The conventional indirect space vector pulse-width modulation method of controlling matrix converters involves independent control of either the rectifying stage or the inverting stage of the converter. However, in this paper, by suitable selection of space vectors, the rectifying stage of the matrix converter generates different levels of virtual dc-link voltage. Therefore, the responsibility of formulating output voltages with a particular magnitude and frequency, which can be translated to different machine speeds, has been transferred solely to the rectifying stage of the IMC. Estimation of the degree of distortion in the three-phase output voltage is another facet discussed in this paper, which aids the sizing and designing of output passive filters. The analysis of output voltage distortion and the proposed modulation strategies have been substantiated by simulations in MATLAB/Simulink and experimentally verified on a scaled down laboratory prototype. [ABSTRACT FROM AUTHOR]

An extended-duty-ratio (EDR) boost converter is studied extensively in this paper for high voltage gain applications with a wide input (and/or output) voltage range. The EDR is a unique combination of an interleaved, multiphase boost converter and switched capacitor configuration that achieves high voltage gain with significantly lower switch voltage stress and switching losses compared to conventional high-gain solutions. Most of the switches in the multiphase EDR experience only a fixed fraction of the output voltage ($1/M, 2/M$ , etc., where $M$ is the number of phases). Through extensive analysis over a wide operating range, it is shown here that the EDR boost converter has inherent current sharing among the phases only in a limited range of duty ratio— $(M-1)/M \leq D \leq 1$. As the duty ratio reduces beyond this range as required in wide input voltage applications, inherent current sharing property is lost. In this paper, techniques to ensure current sharing under all operating zones without requiring current sensors are presented. Instead of having equal duty ratio for each phase, it is adjusted for each phase according to the operating region of the converter. Extensive analysis is presented to derive the required duty ratio changes for the different phases. The proposed concept is validated with experimental results from a 250 W, 3-phase EDR boost, and GaN-based hardware prototype. [ABSTRACT FROM AUTHOR]

Conventional single-phase power-factor-correction (PFC) rectifiers with active power decoupling capability typically require more than three active switches in their circuits. By exploring the concept of power-buffer cell, a new single-stage PFC rectifier with two active switches, one inductor and one small power-buffering capacitor is reported in this paper. The proposed converter can achieve high-power factor, wide output voltage range, and power decoupling function without using electrolytic capacitor. Additionally, an automatic power decoupling control scheme that is simple and easy to implement is proposed in this paper. The operating principle, control method, and design considerations of the proposed rectifier are also provided. A 100-W prototype with ac input voltage of 110 Vrms and a regulated dc output voltage ranging from 30 to 100 V has been successfully designed and practically tested. The experimental results show that with only a 15 μF power-buffering film capacitor, the proposed converter can achieve an input power factor of over 0.98, peak efficiency of 93.9%, and output voltage ripple of less than 3%, at 100-W output power. [ABSTRACT FROM PUBLISHER]

This paper proposes a new-type Tan-Sun coordinate transformation system, which is an extended version of Clarke coordinate transformation system. The main purpose of the proposed coordinate transformation system is to convert three-phase unbalanced alternating-current quantities into two orthogonal alternating-current quantities with equal amplitudes, and further into two direct-current quantities without second harmonic components through Park transformation method. By applying Tan-Sun coordinate transformation system to three-phase unbalanced converters, we can realize the direct-current decoupling of the three-phase unbalanced currents in the direct-quadrature synchronous rotating coordinate system, so the control methods developed for three-phase converters under balanced voltage conditions can be migrated into those under unbalanced voltage conditions directly. Three-phase unbalanced phase-locked loop technique and active and reactive power definition and calculation for three-phase unbalanced power systems based on Tan-Sun coordinate transformation system are also proposed in this paper. The comparison between Tan-Sun coordinate transformation system and the traditional coordinate transformation system under unbalanced voltage conditions both from the aspects of theory analysis and simulation and experimental verification is provided, and these results indicate the superiority of Tan-Sun coordinate transformation system. [ABSTRACT FROM PUBLISHER]

DC/DC converters connected in series or parallel allow low power devices to be used in high power conversions. The input series output series (ISOS) connection is suitable for situations where both the input and output sides are high voltage fields. To ensure that each module shares voltage with the other, this paper proposes an active output voltage sharing (AOVS) control scheme. The scheme introduces sharing control in the output side so that the isolation is not needed between the input and output sides in the control loop. The AOVS control scheme, consisting of a common output voltage loop and individual output voltage sharing loop, has a master–slave structure. To improve the reliability and realize a hot-plug, this paper also provides an automatic master–slave form of the AVOS control scheme. A simulation of the frequency and time domains is used to verify the accuracy of the small signal model, and an ISOS-connected prototype consisting of three forward converters is made to test the steady and dynamic characteristics of the proposed scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a novel unified nonlinear optimization-based speed and position estimation algorithm for interior permanent magnet synchronous motor drives at wide speed range operations. A cost function based on the voltage equations in the stationary reference frame is employed for speed and position estimation. The speed and position can be estimated by minimizing the cost function. At low speed, including the standstill condition, the cost function is modified and high-frequency sinusoidal voltage signals are injected in the estimated magnetic axis. A phase locked loop is combined with the proposed position estimator for reducing the noise of estimation results. Compared with existing sensorless methods, a unified estimator is used at low- and high-speed operations and a better performance is obtained in transient and steady-state conditions. The convexity of the cost functions with respect to the speed and position estimation errors is analyzed in the paper. The feasibility of the proposed estimation algorithm is validated with an experimental test bench. [ABSTRACT FROM AUTHOR]

This paper presents a fault diagnosis technique for high-resistance connection (HRC) in a nine-phase flux-switching permanent-magnet (FSPM) machine based on zero-sequence voltage components (ZSVC), where the neutral-point connection mode is considered. A nine-phase FSPM machine topology is first introduced and no-load back electromotive force waveforms are analyzed. Moreover, the topologies of the nine-phase FSPM drive with different neutral-point connection modes are studied. Then, the mathematical model of a nine-phase FSPM machine with HRC is established with the consideration of the neutral-point connection mode and then the influence of the HRC on the ZSVC is analyzed based on the established model. It is shown that the HRC may be diagnosed by monitoring the change of the spectral contents of the ZSVC. Furthermore, this paper focuses on the situation of the nine-phase FSPM machine with one neutral point. In this case, to remove the influence of the FSPM machine operating point, an effective fault indicator is defined and used for HRC fault detection. Finally, the simulation and the experiment are carried out to validate the proposed method. Both the results show that the proposed method can be applied for the HRC fault diagnosis in a nine-phase FSPM machine. [ABSTRACT FROM AUTHOR]

This paper proposes a battery simulator (BS) based on a Z-source rectifier (ZSR), with the intention of emulating the discharge or charge characteristic of an actual lithium-polymer battery with high voltage and large capacity. The proposed BS is used for power testing for battery applications. The battery model, combined with a Shepherd model and a Thevenin model, is adopted to freely change the properties and specifications of the battery and to replicate the dynamic behavior of the battery, which is discretized to utilize the digital controller of the BS. The closed-loop voltage controller at the dc side of the ZSR is designed to emulate the rapid dynamic characteristics of the battery based on small-signal methods, considering the influence of the components of the impedance network. In this paper, battery voltage control algorithm (BVCA) is also utilized to minimize the voltage stress across switches while controlling two dc-side voltages within a wide range of output voltages. Simulation and experimental results are provided to verify the BS of the new feature and the proposed control method. [ABSTRACT FROM AUTHOR]

A new static synchronous compensator (STATCOM) based on the diode-clamped modular multilevel converter (DCM2 C) is proposed in this paper. In this converter topology, the capacitor voltage is clamped by using a low power rating diode in each submodule. The quantity of voltage sensors is significantly reduced and is free from the number of voltage levels. Furthermore, the voltage balancing control method becomes very simple and the capacitor voltage balance speed is fast. Based on the structure of modular multilevel converter, the DCM2C-STATCOM has the capability of Var compensation and negative-sequence current compensation. The topology characteristics and compensation control method of DCM2C-STATCOM are investigated in this paper. Experimental results obtained from a laboratory prototype validate that the capacitor voltage of the proposed DCM2C-STATCOM can be well balanced and the Var and negative-sequence current compensations are effective. [ABSTRACT FROM AUTHOR]

This paper presents a methodology to control a phase-shifted full-bridge (PSFB) dc/dc converter with variable switching frequency, as a function of the output load power. The main objective of such control is to maximize the conversion efficiency at a wide range of load power levels. By tuning the switching frequency, the net phase of the input impedance of the converter can be manipulated, and thus, at the lower load power operation, the net input impedance can be made highly inductive to achieve zero-voltage switching (ZVS) at the primary-side switches. This paper proposes an efficiency maximization method, which derives an optimum switching frequency based on the load power from a loss-minimization model. In addition, a state-feedback-based control method is proposed for maintaining a tight dynamic regulation over the converter output under a load transient. A 6-kW laboratory prototype of the PSFB converter is developed and designed to validate the proposed control algorithm. The experimental results show a conversion efficiency of 98% at full load and output voltage ripple of ±1%, while ensuring ZVS at all operating points between 100 W and 6 kW. [ABSTRACT FROM AUTHOR]

This paper presents an intensive discussion on a high-voltage direct-current (HVDC) long-distance transmission system combining two modular multilevel double-star chopper-cells (DSCC) converters with dc power cables. Hereinafter, each converter is referred to simply as a DSCC converter, or just as a DSCC for more simplicity. Such an HVDC transmission system is required to provide low-voltage-ride-through (LVRT) capability to enhance system availability. This paper proposes a practical LVRT control characterized by the use of power-line communications between the two DSCC converters. The validity and effectiveness of the LVRT control is verified not only by simulated waveforms obtained from the software package “PSCAD/EMTDC” but also by experimental waveforms from a three-phase 200-V, 400-Vdc, 10-kW, 50-Hz downscaled system with 300-m-long dc power cables. [ABSTRACT FROM AUTHOR]

This paper introduces a new current-programmed controller for non-inverting buck–boost (NIBB) converters. The controller facilitates tight voltage regulation and excellent transient convergence, all carried out through a simple current programmed mode (CPM) controller hardware. Steady-state operation for the full range of conversion ratios is supported with seamless transitions between modes and improved efficiency and ripple characteristics around unity conversion gain. In case of a load transient, an optimized boundary control scheme achieves near-optimal recovery, with programmable constraints for the voltage deviation and inductor current, covering the entire range of conversion ratios. The operation of the controller is experimentally verified on a 2–15 V input to 3.3 V output, NIBB converter, demonstrating a significant improvement in steady-state around unity gain as well as fast convergence for load transients with programmable constraints for the output voltage deviation and inductor current. [ABSTRACT FROM AUTHOR]

This paper proposes a dc-link voltage shaping method for a cascaded H-bridge (CHB) static synchronous compensator (STATCOM). A recently proposed low capacitance-STATCOM system, which intentionally operates with large voltage ripples on the dc-link capacitors, offers the advantage of superior harmonic performance. However, the capacitor voltage ripples decrease when operating at below-rated reactive current, which removes the aforementioned harmonic performance benefit of this system. In addition, such harmonic performance benefit is only achieved in capacitive operation mode. In order to expand the operating region where advantageous voltage ripples are present, a new voltage shaping method is proposed. The proposed method uses a CHB multilevel converter coupled with simple dc–dc converters to shape voltage ripples on the dc-link capacitor regardless of its operating point. This is achieved by controlling the average current of the dc–dc converter using model predictive control. The concept is best applied to an enhanced STATCOM, or E-STATCOM, application in which the STATCOM is integrated with either a renewable energy source or energy storage system. The operational principle of the proposed approach is validated via simulation and experimental results on a five-level single-phase CHB STATCOM. [ABSTRACT FROM AUTHOR]

Symmetrical ac-side current control is widely used for grid-connected modular multilevel converters (MMCs) under grid fault conditions. However, it is revealed that this control method can lead to unbalanced arm currents and consequently asymmetrical electrical stresses and nonuniform temperature distributions. This paper aims to analyze the mechanism of the unbalanced arm currents and propose an effective method to solve this problem. First, the electrical quantities inside MMCs are analyzed under unbalanced grid fault conditions. The analytical expressions of the unbalanced arm currents are derived considering different fault severities and operating conditions to reveal the “side-effects” of the symmetrical ac-side current control. After that, a zero-sequence ac voltage injection method is proposed. The injected voltage is directly derived from negative-sequence ac current controller and ac-side current with pure mathematical manipulations, which can be easily obtained without extra controllers. The effect of the injected voltage on the original modulation index is very limited according to an accurate quantitative analyzation. Moreover, the proposed method does not affect the already achieved symmetrical ac-side current control and the circulating current suppression. The effectiveness and performance of the proposed analysis and control method are verified by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

The three-phase buck rectifier (3ph-BR) is suitable for applications where a voltage step-down function is required. In this paper, an improved 3ph-BR topology is proposed to reduce the voltage stress on the transistors. The freewheeling diode in the conventional topology is split into two diodes in series and the input neutral point is connected to the common point of the two diodes. With the proposed topology and the corresponding modified modulation scheme, the transistors only need to withstand the input phase voltage instead of the line-to-line voltage, bringing about the significant reduction of voltage stress. The proposed topology enables a more cost-efficient and flexible selection of the transistors. Experimental results have verified the validity of the modified topology and associated modulation scheme. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of active zero vector pulsewidth modulation (AZPWM-1) and space vector pulsewidth modulation (SVPWM) on the design of passive common-mode (CM) attenuation methods to reduce CM current and shaft voltage in inverter-fed V/f-controlled induction motor drives. The passive CM attenuation methods examined here are the CM choke, the CM electromagnetic interference (EMI) filter, and the CM transformer. The attenuation requirement of AZPWM-1 and SVPWM is identified to design the passive CM choke and EMI filter. Based on the attenuation requirement, the design guidelines are revisited for SVPWM, and design rules are proposed for AZPWM-1. However, the CM transformer is designed based on the step change in magnitude of CM voltage of both the pulsewidth modulations (PWMs). The limitations in design, regarding switching frequency and component size for each case, are also established. It is shown that to have a similar attenuation in the considered two PWM cases, AZPWM-1 requires smaller passive components compared to SVPWM. The proposed design guidelines are substantiated with experimental results on a 1.1-kW induction motor drive. [ABSTRACT FROM AUTHOR]

Multilevel converters are widely applied in medium voltage (MV) drive systems due to the attractive features, such as the ability to use devices with lower voltage ratings, high equivalent switching frequency, etc. Recently, a multilevel topology, named seven-level hybrid clamped (7L-HC), is proposed for MV drives. It has a competitive number of devices, showing the potential to build low-cost 7L converters. However, to ensure the wide frequency range operation and power quality of MV drives, its dc-link capacitors and floating capacitors must be controlled properly with balanced voltages. In this paper, an active voltage balancing method is proposed for the 7L-HC converter. This method can effectively balance all the capacitor voltages under a wide frequency range. The method is embedded in the PWM procedure without modifying the control strategies. Simulation and experimental results are provided to validate the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a voltage multiplier topology that is a hybrid between a Cockcroft–Walton multiplier and a Dickson charge pump. The Cockcroft–Walton structure exhibits significant output voltage drop under load as the number of multiplier stage increases. This is because all coupling capacitors are connected in series. Dickson charge pump mitigates this issue by connecting all capacitors in parallel. But this solution comes at the expense of large capacitor voltage stress at the last multiplier stage. The proposed hybrid structure arranges some capacitors in parallel and others in series, thereby achieving low output voltage drop and low capacitor voltage stress at the same time. We develop a model that predicts hybrid multiplier's performance and validates it experimentally. We also demonstrate a 60–2.25 kV dc–dc converter based on a 16-stage hybrid voltage multiplier which achieves a voltage gain of 12.8 while keeping the highest capacitor voltage stress to 660 V. [ABSTRACT FROM AUTHOR]

An isolated bidirectional dc–dc converter, which combines parallel-connected two-level converters (TLCs) on the medium-voltage side and a modular multilevel converter (MMC) on the high-voltage side, namely a TLC-MMC converter, is a promising candidate for the interconnection of medium-voltage direct current (MVDC) and HVdc grids. Different from typical phase-shift controlled isolated bidirectional dc–dc converters, transformer currents of a TLC-MMC converter are regulated by the MMC in a closed-loop manner in order to achieve extremely low switching losses and low total device rating of power-semiconductor devices in TLCs. This paper addresses the dedicated operation technique and the voltage-balancing control of the TLC-MMC converter. The MMC in the TLC-MMC converter operates with six-step phase voltages and sinusoidal phase currents. Such an operation makes the MMC present remarkable differences to ac–dc applications. The direct-modulation technique, which is the most-used technique performed to MMCs in line-frequency ac–dc power conversion, has been concluded not applicable to the MMC in a TLC-MMC converter due to the significant sixth-order oscillation resulted in the dc-link voltage. Thus, the indirect-modulation technique is employed, and consequently a closed-loop voltage-balancing control is mandatory for the MMC. Possible measures for voltage balancing have been explored, and effective voltage-balancing control with a simplified implementation is proposed. Validity and effectiveness of the proposed control strategy have been verified by both simulations and experiment using a downscale prototype. [ABSTRACT FROM AUTHOR]

This paper proposes a ripple injection method in a two-stage intermediate bus architecture to overcome the incremental negative-impedance effect in the intermediate bus converter (IBC) induced by the constant power load, which is essentially a tightly regulated point of load (PoL) converter. The proposed method uses the voltage ripple of the intermediate bus in the feedback path for the closed-loop PoL converter while operating the IBC in open loop. The small-signal model is derived and verified using SIMPLIS simulation. The voltage ripple is shown to carry the inductor current information of the PoL converter. Thus, the proposed scheme is expected to retain the superior line regulation of current mode control for the PoL converter even without sensing the inductor current. Load current feed forward can improve the transient response for the PoL converter. Moreover, the load current information is also used to generate the appropriate duty ratio for the IBC during transient recovery. A simple PI controller is used for the PoL converter, which reduces the design complexity using the proposed control scheme. A hardware prototype is made, and the superior performance using the proposed control scheme is experimentally verified. [ABSTRACT FROM AUTHOR]

This paper presents a simple dc-link voltage modulation scheme to minimize the commutation torque ripple in a permanent magnet brushless dc motor (PMBLdcM). Maintaining a constant current in the noncommutating (NC) phase helps to minimize the torque ripple, which can be achieved by boosting the motor input voltage whenever two phase currents are undergoing commutation. At low speeds, since the required ac voltage at commutation is also less than nominal, the standard pulsewidth modulation operation of the inverter with nominal dc-link voltage suffices. However, at higher speeds, a momentary (only during the commutation interval) boost in the dc-link voltage (above the nominal level) is needed to ensure a boost in motor voltage, and hence, a steady current in the NC phase. In the proposed scheme, the dc voltage boost at higher speeds is obtained by connecting two capacitors in series, which are normally connected in parallel, across the dc-link. The proposed scheme is verified for a 1-hp PMBLdcM drive through simulations and experiments in the laboratory. Results exhibit a notable improvement in reducing the torque ripple. [ABSTRACT FROM AUTHOR]

This paper proposes a voltage difference residual-based fault diagnosis approach for three-level converters in electric traction systems. Compared to the existing open-circuit fault diagnosis approaches, the proposed approach cannot only detect and identify the faulty devices among the transistors and clamp diodes in both of rectifier and inverter, but also hierarchically diagnose the leg-level and device-level faults. Furthermore, no additional sensors are required and all of specified parameters can be directly identified. Specifically, the current related term in the dc-link voltage difference equations are analyzed and modeled under the normal case and open-circuit fault cases in the transistors and clamp diodes, respectively. Subsequently, the estimation models of the dc-link voltage difference are developed, and then, the residuals and their evaluation functions between estimation and actual are generated. Furthermore, by analyzing the residual evaluation functions for various cases and building the current similarity functions, the hierarchical diagnosis algorithms are proposed to identify the leg-level and device-level faults. Finally, hardware-in-the-loop experiments are performed. The results show the effectiveness and robustness of the proposed approach. [ABSTRACT FROM AUTHOR]

This paper proposes a high-efficiency three-level (TL) dc–dc converter with reduced circulating current and rectifier voltage stress by using coupled inductor in the rectifier circuit. Because of decreased circulating current, the conduction loss in the primary circuit is reduced. In addition, since the rectifier diodes with low forward voltage drop can be employed due to the small voltage stress, the conduction loss of rectifier diodes can be reduced. Therefore, the efficiency can be increased due to the reduction of the conduction losses in the primary circuit and rectifier diodes. The characteristics of the proposed converter are analyzed and compared with other TL converters. The validity of the proposed converter is verified by the experimental results of the prototype with 540–600 VDC input and 750 W (48 V/15.625 A) output. [ABSTRACT FROM AUTHOR]

The measurement of fast voltage and current transients of Silicon Carbide (SiC) devices requires high bandwidth (BW) probes. Commercially available voltage and current probes can be expensive, and, in addition, the delay introduced by them must be compensated to achieve a proper time alignment (de-skew). Determining this de-skewing value is not a trivial task. In this paper, a simple and affordable measurement method is presented for the simultaneous measurement of the voltage and current transients of SiC devices. The voltage is measured by means of a high BW RC attenuator, while the current is estimated from the voltage drop in the stray inductance of the switching loop. Since both voltages are measured with two equal and matched high BW passive voltage probes, there is no need to apply any de-skew. This is one of the most important advantages of the method. The presented method is experimentally evaluated and used for the estimation of energy switching losses in the tested SiC-mosfet. [ABSTRACT FROM AUTHOR]

Nine-switch converter (NSC) has been presented as a dual-output converter with common frequency (CF) or different frequency (DF) operation modes. This paper proposes a novel space-vector modulation (SVM) method for the NSC that supports both the CF and DF modes. This method is based on the simplification of the space-vector diagram of NSC into that of six-switch converter, and the SVM method for NSC can be done like conventional SSC. The proposed voltage vector selection method without using common logical xor operation and the calculation method for dwelling times of voltage vectors are described in detail. In addition, the modulation indices for two ac terminals of NSC have been analyzed deeply, and the derived fitting equations can guide engineering application. The performance of the proposed SVM is verified by the simulation and experimental results, and the low total harmonic distortions and harmonic components for phase currents prove the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, a dual half-bridge LLC resonant converter with magnetic control is proposed for the battery charger application. The primary switches are shared by two LLC resonant networks, and their outputs are connected in series. One of the LLC resonant converters is designed to operate at the series resonant frequency, which is also the highest efficiency operating point, and the constant output voltage characteristic is achieved at this operating point. The second LLC resonant converter adopts magnetic control to regulate the total output current and voltage during both constant current charge mode and constant voltage charge mode. Meanwhile, the function decoupling idea is adopted to further improve the system efficiency. The significant amount of the power is handled by the LLC resonant converter operating at the series resonant frequency, whereas the second LLC resonant converter fulfills the responsibility to achieve closed-loop control. By carefully designing the resonant networks, the zero-voltage switching for primary switches and zero-current switching for secondary diodes can be achieved for whole operation range. A 320-W experimental prototype is built to verify the theoretical analysis, and the maximum efficiency is measured about 95.5%. [ABSTRACT FROM AUTHOR]

Health monitoring and fault detection are becoming more and more important in electrical machine systems due to the increasing demand for reliability. Winding turn fault is a common fault in permanent magnet (PM) machines, which can cause severe damages and requires prompt detection and mitigation. High resistance connection fault, which results in phase asymmetry may also occur but does not require immediate shutdown. Thus, apart from the fault detection, the classification between the two faults is also required. In this paper, a new technique for detecting and classifying turn fault and HRC fault by utilizing both the high and low frequency components of the zero sequence voltage is proposed with the enhanced sensitivity. The dependence on the operating conditions is minimized with the proposed fault indicators. The effectiveness of fault detection and classification has been verified by extensive experimental tests on a triple redundant fault tolerant PM assisted synchronous reluctance machine. The robustness of the turn fault detection in transient states and under no load conditions has also been demonstrated. [ABSTRACT FROM AUTHOR]

Load-independent output characteristics of inductive power transfer (IPT) systems are increasingly popular in battery charging. This paper proposes a novel variable-parameter T-circuit (VT) for an IPT system charging a battery with constant current (CC) or constant voltage (CV) output. The VT can transfer a CC/CV input to a CC or CV output by using an ac switch and a passive component (inductor or capacitor). An IPT system with a VT for CC–CV charging can reduce the number of passive components and ac switches. Besides, the proposed VT merits more design freedom of charge current/voltage with the constraints imposed by the loosely coupled transformer parameters compared to that of the traditional one. In addition, there are three kinds of VTs for various IPT charging systems with different requirements. A 400 W laboratory-scale prototype with a 150 mm air gap was built to verify the theoretical analyses. Both electronic load and lead-acid battery are utilized to verify the charging profile of the proposed method. The experimental results of the IPT system indicate that the fluctuation of the charging current in CC mode is less than 2%, and the change rate of charging voltage in CV mode is within 2.9%. The maximum overall efficiency 93.93% of the charging system is achieved from a dc 110 V input to a dc 100 V output. [ABSTRACT FROM AUTHOR]

This paper proposes a constrained modulated model-predictive control (M $^{2}$ PC) scheme for an LC-filtered voltage-source converter (VSC). To tackle the coupling effects of the state variables in a second-order LC filter, a dual-objective cost function (CF) is used to explicitly track both capacitor voltage and inductor current references, which can achieve an improved voltage quality. To handle the state and control input constraints of VSCs, a constrained M $^{2}$ PC scheme is proposed with an “online post-correction” constraint-handling technique. First, the unconstrained optimal voltage vector (OVV) is derived. It is generated by seeking the minimum analytical solution of the CF offline, simplifying the online implementation. Then, an “online post-correction” strategy is employed by reconsidering the constraints to correct the precalculated OVV online, which guarantees the future states within the allowed range. Finally, the corrected OVV is synthesized by the space vector modulation, resulting in a fixed switching frequency and low harmonics. Compared with the typical constrained model-predictive control, the presented scheme has the advantages of improved steady-state performance, flexible constraint-handling ability, and lower computational cost. Additionally, design procedures for weighting factor selection in the CF are given. Comparative experiments are investigated to verify the presented control strategy. [ABSTRACT FROM AUTHOR]

In this paper, a method is proposed to eliminate the voltage ringing problem in a phase-modulated dc–ac converter, also known as a micro-inverter. The basic idea is to apply a time-critical two-stepped voltage waveform to the input of the converter bridge connected to the filter inductor. This method is implemented by a new topology that has one more switching leg added to the full bridge voltage fed converter. It produces a second voltage level and adds it to the first by using a transformer. The advantages of the proposed method are as follows. It almost eliminates the requirement of a voltage clamp, there is no circulating current in the freewheeling state, and the secondary side devices have less voltage and current stress compared to a conventional phase-modulated converter. The overall benefit is an improvement in converter efficiency even for a high-voltage conversion ratio application. The proposed topology operates with a secondary side modulation scheme that achieves zero-voltage switching of four devices on the primary side and either zero-voltage switching or zero-current switching of all the devices on the secondary side, over the entire line cycle of the ac output. Finally, the experimental results verify the proposed method. [ABSTRACT FROM AUTHOR]

A fast output voltage equalization control strategy applied to 10-kV/100-kW high power density photovoltaic dc–dc converter system is proposed in this paper. The converter modules in the system have two dynamic priority factor loops for fast response with an inconsistent voltage between modules and a soft start-up circuit to precharge output capacitance for solving inrush current problem in boost circuit. The proposed strategy can realize fast voltage equalization control under inconsistent leakage inductance and parasitic resistance parameters condition between modules compared to the traditional unified duty cycle control strategy. The fast equalization performance is verified by 10-kV/100-kW photovoltaic dc–dc converter system. The converter system adopts an isolated boost full-bridge topology and input parallel output series structure, which meets high conversion ratio and high-power density requirements. [ABSTRACT FROM AUTHOR]

In photovoltaic applications, many previous research works have focused on pulsewidth modulation (PWM) resonant converters in order to achieve a high efficiency with a wide input voltage range. Conventional approaches utilized symmetric boosting modulation at the secondary side rectifier to obtain a symmetric operation, and they utilized two boosting modes in a switching period. Among various rectifier structures, the voltage doubler structure has a strong advantage due to a small number of components. However, it suffers from serious hard switching losses in the secondary side rectifier. In this paper, a new converter with a novel asymmetrical modulation is proposed and verified. The strong point of the proposed converter is that it eliminates hard switching turn-on losses from the rectifier, while maintaining the minimized number of components. Although the proposed converter adopts an asymmetric modulation, the offset current on the transformer becomes zero inherently. Furthermore, a “forced half resonance” operation of the proposed converter keeps rms current stresses at the same level as conventional converter although it has a higher peak current. Accordingly, the proposed converter achieves a superior efficiency with the minimum number of components at 35–25 V input and 380 V/300 W output specification. [ABSTRACT FROM AUTHOR]

In the no-load condition, LLC converter usually fails to regulate its output voltage although it operates at a high switching frequency. Till now, it is hard to obtain the exact relationship between design parameters and the maximum switching frequency for no-load regulation capability. In this paper, a specific criterion for no-load regulation of LLC converter is provided, without using active components or other modulation schemes. By analyzing the macroscopic switching period and microscopic switching transition in the no-load condition, it is shown that not only the peaking resonant current during the switching transition, but also the resonant tank design affect the no-load regulation of the LLC converter, which affects the no-load regulation capability. Furthermore, the relationship among design parameters is analyzed and the design guideline is also provided to achieve no-load regulation at the specified maximum switching frequency. To verify the effectiveness of the proposed design, 400 V input and 50 V/200 W output prototype is built and tested. [ABSTRACT FROM AUTHOR]

This paper proposes an interleaved active-clamp forward (IACF) converter modified for high efficiency without any additional component. To employ high input voltage, the components on one active-clamp forward module are re-arranged from the conventional IACF converter. The proposed converter can significantly reduce the primary conduction loss with large turns-ratio of the transformer due to the higher input voltage of the modified module and the expanded duty ratio at the nominal input voltage. In addition, unlike the existing approaches, the power density is not affected because there is no additional component. Finally, the proposed converter is validated experimentally using a prototype converter with 36–72 Vdc input and 480 W (12 Vdc/40 A) output. [ABSTRACT FROM AUTHOR]

During the unbalance operation of a standalone brushless doubly-fed induction generator (BDFIG), the negative sequence component causes significant unbalanced effect on the voltage and current of the power winding (PW). In this paper, a new control strategy is proposed to minimize the voltage unbalance effect of a standalone BDFIG under unbalanced loads. The proposed control strategy consists of two parts. The first part represents the conventional direct voltage control strategy to control the frequency and magnitude of the positive sequence PW voltage. The second part is the proposed strategy to minimize the negative sequence component in the output voltage of PW with a negative sequence compensator in the machine side converter. The dual second-order generalized integrator is used to extract negative-sequence component of the PW voltage. Proportional integral controllers are used to obtain reference of the control winding (CW) current which compensate the negative sequence component of the PW voltage. The proportional-integral-resonant controller is applied to regulate the CW current in positive reference frame. A prototype 30 kVA BDFIG test platform is developed in the laboratory to verify the proposed strategy. [ABSTRACT FROM AUTHOR]

A systematic method for developing ultra-wide output voltage range power supply based on modular switched-converter principle is proposed in this paper. The basic symmetric switched-converter (SSC) module is composed of two dc–dc modules, two diodes, and one active switch. Multi-stage SSC modules are generated by symmetric cascaded connection method. By controlling the active switches in multi-stage SSC modules, the connections of all the dc–dc modules’ output ports can be changed flexibly among series, parallel, and partial–parallel–partial-series connections. Then segmented regulation can be realized and system output voltage range can be widely extended. Meanwhile, the voltage range of each dc–dc module can be narrowed and the voltage/current stress can be reduced to simplify the design, increase device utilization ratio, and improve overall efficiency. A full-bridge isolated buck–boost converter with a semiactive rectifier, which features soft-switching and wide voltage adjustment range, is adopted as the dc–dc module to realize the proposed system. Input current sharing control strategy is adopted to ensure proper power balancing in all possible operating modes. The stability of the proposed system is also explored. Simulation and experimental results are provided to verify the effectiveness and advantages of the proposed system configuration, the switched-converter principle, and the control strategies. [ABSTRACT FROM AUTHOR]

In the back electromotive force (EMF)-based sensorless control of interior permanent magnet synchronous motor (IPMSM), the inverter nonlinearity and flux linkage spatial harmonics will possibly give rise to (6k ± 1)th harmonics in the estimated back EMF, especially the fifth and seventh harmonics. Those harmonics will consequently introduce (6k)th harmonic ripples to the estimated rotor position, especially the sixth harmonic component. In order to solve this problem, a bilinear recursive least squares (BRLS) adaptive filter is proposed and integrated into a sliding-mode position observer to suppress the dominant harmonic components in the estimated back EMF and as a result, the accuracy of the estimated rotor position can be greatly improved. A unique feature of the BRLS adaptive filter is its ability to track and suppress the specified harmonic components in different steady state and dynamic operational conditions. The proposed method can compensate for harmonic ripples caused by the inverter nonlinearity and machine spatial harmonics at the same time; this method is also robust to machine parameter variation, and the BRLS algorithm itself is machine parameter independent. The implementation of the proposed BRLS filter in the sensorless control of IPMSM is explained in details in this paper. The enhanced drive performances using the BRLS filter have been thoroughly validated in different steady state and dynamic operational conditions on a 1.5-kW IPMSM sensorless drive. [ABSTRACT FROM AUTHOR]

Voltage model observer is a simple and economical technique for flux estimation in induction motor sensorless drives. However, it shows poor performance in low-speed regions. Therefore, in most cases, the use of this observer is limited. On the other hand, using a simple but accurate estimator is important when the control method is sophisticated and requires heavy computation. This issue will be important in predictive control more than the other methods because the accuracy of the prediction is dependent on the flux estimation. In this paper, a modified closed-loop technique based on voltage model observer is proposed for flux estimation. The feedback loop is supported by the proposed model reference adaptive system direct flux magnitude estimation technique. The dependence of the feedback loop on the stator resistance is eliminated. Therefore, the drift error will be avoided. This will allow the method to withstand the high stator resistance error even at low speeds. Also, a new Lyapunov-based technique for the stator resistance estimation via reduced-order model is proposed. By using the proposed observer, the predictive direct voltage control technique is used as the control method in order to achieve a control method that requires low computation. The proposed method is validated through the experimental results. [ABSTRACT FROM AUTHOR]

Unidirectional current H-bridge modular multilevel converter (UCH-MMC) is a variant of full-bridge MMC and uses fewer semiconductor devices. The operating area and operation mode of UCH-MMC differ from those of conventional half-bridge MMC (HB-MMC) because of the unidirectional current and bipolar voltage of UCH-MMC arms. Thus, analyzing the energy storage requirement (ESR) of UCH-MMC differs from that of HB-MMC. This paper proposes a model for calculating the ESR of UCH-MMC. The ESR of the UCH-MMC under the entire operating area is analyzed. A modified operating scheme that dynamically trims the sub-module capacitor voltage to allow the low capacitance operation under the entire operating area is proposed. Results verify that the UCH-MMC has much lower ESR than HB-MMC. Evaluation results also show that the cost and volume of the UCH-MMC are much lower than those of HB-MMC because of the low ESR. The low ESR of UCH-MMC was verified by simulations and experiments. [ABSTRACT FROM AUTHOR]