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For speed sensorless induction motor drives, the unobservable problem of rotor speed at low synchronous speed has not been solved yet. To obtain a unified observable condition, the local weak observability concept is used in this paper. Based on the result of analysis, virtual voltage injection method is proposed. With this method, the states of induction motor, including rotor speed, are locally weakly observable at zero synchronous. The stability of proposed method is proved by Lyapunov's stability theorem. Finally, the feasibility of proposed method is verified by experiments. [ABSTRACT FROM AUTHOR]

In this paper, a simplified robust control is proposed to improve the performance of a three-phase current controlled voltage source inverter connected to the grid through an inductive–capacitive–inductive (LCL) filter. The presence of the LCL-filter resonance complicates the dynamics of the control system and limits its overall performance, particularly when disturbances and parametric uncertainty are considered. To solve this problem, a robust active damping method based on the linear active disturbance rejection control (LADRC) is proposed. The simplification is made possible by order reduction in the plant transfer function using Padé approximation. Simulation results show that the proposed LADRC-based current controller achieves high power quality and good dynamic performance, in the presence of parameters uncertainties as well as external disturbances. An experimental prototype is built to verify the effectiveness and practicality of the proposed control strategy. [ABSTRACT FROM AUTHOR]

Resistive random access memory is promising for next-generation nonvolatile memory, which has high memory density, low power consumption, and fast read/write speed. However, the resistive switching (RS) mechanism in oxide ferroelectric thin film devices is still unclear. In this paper, Pt/BiFeO3/La0.5Sr0.5CoO3(Pt/BFO/LSCO) heterostructures were deposited on (111)SrTiO3(STO) substrates by magnetron sputtering. X-ray diffraction confirmed the epitaxial relationship between (111)BFO//(111)LSCO//(111)STO. Atomic force microscopy (AFM) showed that (111)BFO had an island structure with uniform grain distribution. The Pt/(111)BFO/(111)LSCO heterostructures exhibit obvious ferroelectricity and RS effects. The results of C-V analysis and I-V fitting indicate that the RS is caused by the space-charge-limited conduction mechanism. [ABSTRACT FROM AUTHOR]

Rotor position estimated with high-frequency (HF) voltage injection methods can be distorted by voltage errors due to inverter nonlinearities, motor resistance, and rotational voltage drops, etc. This paper proposes an improved HF square-wave voltage injection algorithm, which is robust to voltage errors without any compensations meanwhile has less fluctuation in the position estimation error. The average position estimation error is investigated based on the analysis of phase harmonic inductances, and deduced in the form of the phase shift of the second-order harmonic inductances to derive its relationship with the magnetic field distortion. Position estimation errors caused by higher order harmonic inductances and voltage harmonics generated by the SVPWM are also discussed. Both simulations and experiments are carried out based on a commercial PMSM to verify the superiority of the proposed method and the investigations in this paper. [ABSTRACT FROM AUTHOR]

Non-line-start permanent magnet synchronous machines (NLSPMSMs) are normally considered not able to operate stably under grid drive. However, this paper proposes an effective control strategy to achieve soft start and synchronous switching of NLSPMSMs from inverter to grid drives so that to extend the application field. The system electromechanical model during switching is deduced and analyzed numerically to verify the stability under grid drive. For the control strategy, model-based sliding-mode observer is adopted during soft start for low-cost position sensorless drive, and two digital phase lock loops are used to obtain the phases of grid and inverter voltages for phase tracking. Experiments are carried out on five NLSPMSMs with different rated powers and velocities, and test results show that all these prototypes can be safely switched to grid drive and robust to load variation. Tested waveforms are coincident with numerical analysis, and the system efficiencies of NLSPMSMs under inverter and grid drives are compared. [ABSTRACT FROM AUTHOR]

Alternating-current motor drive systems consume the majority of global electricity, but most of them are still not efficient enough. This paper proposes a complete solution to the efficiency enhancement of general induction motor (IM) drive systems with the least cost and a high reliability. On the motor side, the squirrel-cage rotors of IMs are replaced with optimally designed interior permanent-magnet (PM) rotors without damping windings; meanwhile, other assemblies remained unchanged. Stators with both wye- and delta-connected windings are investigated, and super premium efficiency (IE4) is achieved on all the remanufactured motors in this paper. On the drive side, the maximum efficiency per ampere algorithm is realized based on the position-sensorless control to better exert the motor efficiency and reduce the system cost. For applications where an original IM is used under a grid drive, this paper safely switches the remanufactured interior PM synchronous motors from an inverter to the grid drive. A total of seven prototypes with different rated powers and velocities are remanufactured, and various experiments are provided as the verifications of the effectiveness and practicability of the proposed solution. [ABSTRACT FROM PUBLISHER]

High-efficiency electric drive systems claim not only optimally designed electric machines but also efficiency-oriented control strategies. Taking machines and drives into synergetic consideration, this paper proposes a novel vector control algorithm named maximum efficiency per ampere (MEPA) control, aiming to maximize the efficiency of permanent-magnet synchronous machines (PMSMs) during operation. Different from conventional id =0 or maximum torque per ampere control, MEPA fully considers the cross effect and iron loss from which the full-order loss model of PMSMs is built. Due to the proposed concise and accurate analytical approach to iron loss calculation, the optimal current phasor angle for MEPA can be quickly found, and the estimation of efficiency is consistent with measurement. Comparison among different control algorithms is drawn from both analytical and experimental results, from which the effectiveness of MEPA is verified. [ABSTRACT FROM PUBLISHER]

The papers in this special section are devoted to the topic of solutions for power quality management. Although the power quality problems, such as, reactive and harmonic currents, distortion and fluctuations in the supply voltage, are not new to power system and power electronics researchers, the ever changing landscapes in the power generation and distribution systems have given rise to additional power quality challenges. The growing interest in the smart grid concepts, vehicle to grid operation, inverter based large scale photovoltaic (PV) and wind integration, distributed generators (DGs) as ancillary service provider, multilevel inverters for high power applications and so on is making the power quality aspects more prevalent. [ABSTRACT FROM PUBLISHER]

Parallel operation is an effective way to improve the capacity of full power converter in permanent-magnet direct-drive wind power generation system. But it causes the zero-sequence circulating-current (ZSCC), which brings current discrepancy, current waveform distortion, power losses, and electromagnetic interference (EMI), etc. The paper proposes a new topology of full power converters which are composed of n full power converters. The n converters have the same structures and are in parallel with each other. Besides, the average models of the system are analyzed and the fundamental mechanism of ZSCC generation is given. Based on the above analysis, the control strategy of the system is designed. The simulation and experiment results of two parallel full power converters show the feasibility of the proposed theory and control scheme. [ABSTRACT FROM PUBLISHER]

Abstract: Classifying power quality (PQ) disturbances is one of the most important issues for power quality control. A novel high-performance classification system based on the S-transform and a probabilistic neural network (PNN) is proposed. The original power quality signals are analysed by the S-transform and processed into a complex matrix named the S-matrix. Eighteen types of time–frequency features are extracted from the S-matrix. Then, after comparing the classification abilities of different feature combinations, a selected subset with 2 features is used as the input vector of the PNN. Finally, the PNN is trained and tested with simulated samples. By reducing the number of features in the PNN''s input vector, the new classification system reduces the time required for learning and the computational costs associated with the features and the PNN''s memory space. The simulation results show that 8 types of PQ disturbance signals with 2 types of complex disturbances were classified precisely and that the new PNN-based approach more accurately classified PQ disturbances compared to back propagation neural network (BPNN) and radial basis function neural network (RBFNN) approaches. [Copyright &y& Elsevier]

A digital control electronic ballast for the metal halide lamp is proposed based on the low-frequency square wave, and a comprehensive control strategy is employed for the zero-voltage-switching quasi-square-wave dual buck converter. To achieve the self-adaptive zero-voltage-switching control, the digital control method is used, which greatly reduces the switching losses of the circuit. A single-cycle-peak-current control method is adopted to restrain the overcurrent generated by reversing during the low-frequency transition from the turn-on to the steady state. The complicated process of igniting is analyzed in detail, and a constant-current control method is proposed to diminish the power overshoot and to decrease the current and voltage stress in the transition stage. A power closed-loop duty ratio control method is adopted, and its correctness is proved. An experimental prototype of 70 W is implemented, and the system can achieve reliable operation from the transient state to the steady state, with the highest efficiency of 92% and with no acoustic resonance occurring. [ABSTRACT FROM AUTHOR]

An integrated zero common-mode voltage (ZCMV) modulation algorithm is developed in this article for dual-parallel neutral-point-clamped (NPC) inverters treated as an integrated system. While the conventional methods achieve CMV elimination with the cost of worse harmonic performance, the proposed method guarantees a ZCMV and better current quality simultaneously by taking advantage of the extra space vectors provided by paralleling. Specially designed switching sequences are developed to maintain a balanced neutral point of dc bus and keep the averaged value of the circulating current to be zero, ensuring the normal function of parallel NPC inverters. In addition, although the switching sequence design is complicated, a simple approach is proposed and implemented on a commonly used digital signal processor. A laboratory prototype is developed to test the system performance under steady-state conditions and dynamic process in grid-connected operation. Compared with the conventional ZCMV modulation, experimental results verify the effectiveness of the integrated modulation in eliminating the CMV, in addition to the dramatically reduced output current distortion. [ABSTRACT FROM AUTHOR]

Due to the low voltage and high randomness of renewable energy, high-performance grid-connected converters are needed. With the advantages of a high boost ratio, flexible design, and simple control, the Y-Source Converter (YSC) is widely concerned. However, there are a few drawbacks to the traditional Y-source converter, including significant switching stress, voltage voltage overshoot, and discontinuous current. To solve the problems above, a series of improved topologies are proposed. Moreover, the voltage gain, current ripple, and soft switching characteristics have also been optimized. So far, the existing literature lacks the collation and comparison of different topologies of Y-source, as well as the analysis of its evolution process. Therefore, this paper provides a comprehensive overview of Y-source converters' topologies. According to their features and applications, different topologies are classified and described, leading to guidance for the selection of YSCs under different scenarios. Meanwhile, the working principle, evolution process, and vital issues are analyzed. By revealing their deductive rules, valuable suggestions are provided for the future development of YSCs. [ABSTRACT FROM AUTHOR]

Under weak grid condition, negative influence is brought in on system stability because the grid impedance and the grid-connected converter control system are coupled to each other. The key factor affecting the stability of the system is the perturbation of the voltage fluctuation at the point of common coupling (PCC) to the phase-locked loop (PLL) and the dc-link voltage loop. In this article, the impedance model of a three-phase grid-connected converter, including the current loop, PLL, and dc-link voltage loop in the dq frame, is adopted, because it includes coupling information of the converter and reflects the transferring relationship among grid-connected system variables. Based on the transferring relationship, this article analyzes the perturbation paths of PCC voltage and proposes the corresponding compensation methods, i.e., the PLL and dc-link voltage loop compensation terms, which are inserted into the q and d axes of the current loop controller, respectively. The impedance analysis results show that the proposed method can effectively improve the system stability. In addition, the experimental results verify the correctness of the theoretical analysis and the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

To overcome the problem of current control effect being reduced by unideal factors in a motor control system, such as motor parameter variation, inverter dead time, nonlinearity of the system, etc., a sliding mode disturbance observer for an interior permanent magnet synchronous motor is proposed in this paper. The model of an interior permanent magnet synchronous motor with unideal factors is designed, and the unideal factors are unified into lumped disturbances of motor stator voltage. Then, the observer for lumped disturbance is designed. A recursive integral sliding surface is used to replace the terminal sliding surface to avoid the noise sensitivity and singularity problem of the traditional terminal sliding mode observer. The observer can estimate the lumped disturbance of the current loop without relying on the accurate system model in finite time. Moreover, the structure of the current loop does not need to be adjusted while using the observer to observe and compensate for disturbances. Experiments are carried out to verify the effectiveness of the proposed observer. [ABSTRACT FROM AUTHOR]

The unstable problem of speed sensorless induction motor drives (SSIMDs) at low synchronous speed range has not been solved yet. In this paper, the reason of this unstable problem is concluded as two key points: 1) there are poles of the transfer function of the SSIMD system owning positive real part at low speed range; and 2) the rotor speed is unobservable at zero synchronous speed. Correspondingly, to guarantee the stability of the SSIMD system at low speed range, the system has to achieve two conditions simultaneously: the transfer function of the SSIMD system is stable (transfer function stability (TFS) condition) and the rotor speed is observable (rotor speed observability (RSO) condition). To satisfy these two conditions, virtual voltage injection is proposed. The unstable problems can be solved by this proposed method. In addition, the robustness of the virtual voltage injection method is analyzed. When motor parameters are inaccurate, the stability of the system will not be influenced. Finally, the feasibility of the proposed method is verified by experiments. [ABSTRACT FROM AUTHOR]

The methodologies applied to speed sensorless induction motor drives (SSIMD) can be divided into two categories. The first category makes use of the fundamental model of induction motor to establish speed and flux observers. However, the rotor speed is unobservable with these methods when synchronous speed is close to zero. The second category makes use of anisotropies of induction motor to observe rotor speed. However, the anisotropies of induction motor are too weak to extract rotor speed information. Consequently, the unstable problem of SSIMD at low synchronous speed (including zero synchronous speed) has not been solved yet by now. In this paper, a virtual voltage injection method is proposed to solve this problem. The voltage is only injected into observer. The observability of rotor speed based on proposed virtual voltage injection is analyzed. Because the injected voltage into observer results in estimated speed error, a compensation method is proposed then. The stability of the system with virtual voltage injection and corresponding compensation method is analyzed by the input-state-stability concept. Finally, the feasibility of the proposed method is verified by experiments. [ABSTRACT FROM AUTHOR]

A 1-MHz-modified single-ended primary-inductor converter (SEPIC) circuit is presented in this paper as an LED driver for automotive headlights. On the basis of traditional SEPIC, only a diode and two capacitors are added; therefore, the circuit structure is relatively simple and the volume is relatively small. High step-up capability is obtained with moderate duty cycle. Compared with traditional step-up circuit such as boost, low-voltage stress is gained which is beneficial to device selection. Zero-voltage switching is achieved at the same time to reduce switching loss. Planar inductors are used with the advantages of low profile and good thermal characteristic. Operational principle and parameters design process are introduced in detail. A 36-W prototype has been designed to demonstrate theoretical analysis. Obtained efficiency was up to 90.91% at full load. [ABSTRACT FROM AUTHOR]

In order to mitigate harmonics of the grid input current, passive filters are applied widely in the power electric systems. The LC resonance and the negative input impedance are important concerns in the reduced dc-link capacitance motor drive system. In this paper, an active damping control method is proposed to suppress the LC resonance by the direct damping current approach, which can formulate the pole distribution of the drive system. Different control laws have been analyzed, and the stability analysis is evaluated by the Routh–Hurwitz criterion. Meanwhile, the active damping control method is realized by the voltage command, which can overcome the limited bandwidth of the current controller. Since the generation of the direct damping current only depends on the dc-link voltage, the proposed active damping control method is robust. Compared with the virtual impedance methods, parameters can be accurately optimized by Bode diagrams after adopting the proposed active damping method. Simulation and experimental results are provided to verify the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

DC-link electrolytic capacitor critically affects the lifetime of the motor drive system. This paper proposes an inverter power control strategy based on dc-link voltage regulation for the electrolytic capacitor-less interior permanent magnet synchronous motor drive system. The dc-link electrolytic capacitor is replaced by a small film capacitor and the power factor correction circuit is also eliminated. Hence, the inverter power should be regulated effectively to achieve high input power factor and low grid current harmonics. The inverter power control loop based on proportional resonant (PR) controller is established to regulate the inverter power into sinusoidal wave. The PR controller can be designed to achieve a high gain at the desired frequency and the parameters are easy to design due to the simple structure. In addition, a power compensation method based on the dc-link voltage regulation is used to diminish the error of inverter power control, which does not depend on the precise calculation and is easy to realize. The effectiveness of the proposed method is demonstrated by the experimental results on an air conditioner. The input power factor can reach 0.992 and the harmonics of grid current are considerably lower than the requirement of EN61000-3-2 standard. [ABSTRACT FROM PUBLISHER]

To extend the lifetime, improve the power density and reduce the system cost, the film capacitor is applied to replace the large-volume electrolytic capacitor in motor drives. As the dc-link voltage fluctuates periodically, the rotor position estimation error and operation stability are necessary to be concerned in the position sensorless control methods. A cross-decoupling complex filtering-based position estimation method is investigated for the reduced capacitance interior permanent magnet synchronous motor drive system. Harmonic components of the extended back electromotive force (EEMF) caused by the dc-link voltage fluctuation are analyzed to evaluate the additional rotor position error. A cross-decoupling complex filter realized by the multiple first-order complex filters with different center frequencies is designed to improve the position estimation precision. Harmonics of the EEMF are suppressed and the position error can be eliminated. The estimation precision and operation ability are improved. Experimental results are performed to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this article, a 2.5m five-stage inductive power transfer (IPT) system based on domino cylindrical solenoid coupler (CSC) compensated, respectively, in layers is proposed. The system is considered to be used as 220 kV post insulators application, transferring power for sensors and measuring instruments of smart grids. The distributed series compensation method is applied to double-layer CSC. Compared with the two types of parallel schemes, this method can significantly reduce the current of the main circuit. Compared with the concentrated series compensation method, this method can effectively reduce the resistance caused by the stray capacitance. The interaction between the post insulator and the magnetic coupling structure is analyzed. The circuit model of the system with constant voltage output characteristics is analyzed. A prototype with a maximum efficiency of 66.7% is built. When the power is transferred to a larger value of 77.8W, the efficiency can still reach 62%. Comparing with previous works, the wireless distance is extended while the efficiency is improved. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMC) have revolutionized the voltage-sourced converter-based high-voltage direct current transmission, but not yet got widespread application in medium-voltage variable-speed motor drives, because of the large capacitor voltage ripples at low motor speeds. In this paper, a novel hybrid MMC topology is introduced, which significantly reduces the voltage ripple of capacitors, particularly at low motor speeds. Moreover, this topology does not introduce any motor common-mode voltage; as a result, there are no insulation and bearing current problems. Additionally, the current stress can remain at rated value throughout the whole speed range; thus, no device needs to be oversized and converter efficiency can be ensured. Operating principle of this hybrid topology is explained, and control schemes are also developed. Validity and performance of the proposed topology are verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

A 1 MHz half-bridge resonant dc/dc converter based on GaN FETs and planar magnetics is proposed in this paper, which improves the system efficiency and power density. The resonant network can achieve satisfactory soft-switching characteristics based on a small impedance angle, which greatly reduces the losses of switches and diodes. The losses characteristics during the turn-on and turn-off transitions are analyzed in detail. The calculation results show that the GaN FETs with low output capacitance and on resistance can achieve fast switching speed and low losses in high-frequency conditions. To reduce the profile and increase the power density of the system, planar magnetics are used in this paper. The response surface methodology (RSM) and modular layer model (MLM) are adopted to help design the planar inductor and transformer, respectively. Both of the methods offer clearer and more effective ways to design the planar magnetics. A 25-W prototype is built to verify the feasibility of the proposed high-frequency converter. [ABSTRACT FROM AUTHOR]

In this paper, a half-bridge resonant DC/DC converter with constant output voltage is proposed, which possesses good soft-switching characteristics. At rated operating point, the switches can operate almost without switching-on and off losses. Further, at whole working range, both zero-voltage-switching mode of switches and zero-current-switching mode of diodes are maintained. Thus, the converter can achieve a high efficiency. Experimental results verify the low switching losses and high efficiency characteristics based on a 200 W prototype. System efficiency is as high as 96% and always above 90% when output power changes from 100% to 20%. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

De-icing of overhead transmission lines is necessary to prevent damage to the transmission system and outages. In this paper, a modular multilevel dc De-Icer (M2D2) is introduced, based on the structure of the modular multilevel converter with full-bridge submodules. The M2D2 exhibits a lot of salient features: high modularity, scalability, compactness, high efficiency, wide dc voltage range, and no harmonic filter requirements, etc. Moreover, during good weather, the M2D2 can be configured as a static synchronous compensator, providing reactive power support to the grid and alleviating power quality problems. Operating principle of the M2D2 is explained, harmonic features under phase-shifted carrier modulation are analyzed, and selections of the phase-shifted angle are derived to achieve best harmonic performance. Control schemes for the M2D2 are also developed, including control of de-icing current, capacitor voltages, and reactive power. Finally, experimental results, utilizing a downscaled prototype, confirm the validity of this topology and effectiveness of the proposed control strategies. [ABSTRACT FROM PUBLISHER]

Passive diode bridge rectifier with LC filter is widely used in wireless power transfer (WPT) system due to its simple structure and uncontrolled characteristics. However, as the load resistance decreases, its input phase angle will also decrease rapidly until it shows obvious capacitive. Therefore, a novel rectifier topology with an input-series inductor (hereafter called ISIR) is proposed in this article to solve this problem. What is more, the ISIR can avoid the duty cycle loss and improve the dc–dc efficiency. First, the mechanism of ISIR is analyzed in detail combined with the operating status of topology. Then, the inductance and compensation parameters are determined based on theoretical calculation and simulation results. Finally, a prototype with a maximum load of 7 Ω is built to validate the feasibility and effectiveness of ISIR, and 88% efficiency is achieved under this condition. Compared with the traditional method, it has increased by 1.05%. The maximum efficiency of WPT system is as high as 91.14% with the proposed ISIR. [ABSTRACT FROM AUTHOR]

Inductive power transmission has been applied in industries, such as electric vehicles, consumer electronics and biomedical fields. However, there is a long-term key problem in this field that has not been solved. This is the adverse effect of the parasitic capacitance of the coil, which will cause the change of the coil inductance, the reduction of the quality factor and the reduction of efficiency. Especially in the field of long-distance wireless power transmission. The existing technologies all adopt the scheme of sacrificing volume in exchange for the quality factor of the coil. As a result, the volume of the system is very large, and the quality factor of the coil is still not high enough because the influence of parasitic capacitance has not been completely eliminated. Here, we found the solution. Connect compensation capacitors in series to the coil sections to short-circuit the parasitic capacitance and reduce its loss. The designed system has a diameter of 502 mm and a thickness of 22 mm, which can transmit 115.2 W of power within a distance of two meters with an efficiency of 29%. [ABSTRACT FROM AUTHOR]

For the induction motor (IM) current loop, the supertwisting sliding-mode control (ST-SMC) has been considered as an effective approach to achieve chattering suppression and steady-state errorless control. However, due to the system disturbance, the conventional ST-SMC suffers from control delay in the convergence trajectory, resulting in decreased antidisturbance capability. To address this problem, this article proposed a ST-SMC with convergence trajectory optimization. First, a nonlinear sliding-mode manifold is designed to achieve the ideal ST-SMC convergence trajectory. Then, a disturbance compensation term is added into the control law to eliminate the system control delay. Compared with the conventional ST-SMC, the studied method can effectively enhance the antidisturbance capability of IM current loop, leading to improved transient performance. Finally, the superiority of the investigated method is verified by the experimental results from a 3.7 kW IM test bench. [ABSTRACT FROM AUTHOR]

The overmodulation strategy plays an important role in the field weakening control for high-speed permanent magnet synchronous motor (PMSM) drives. However, the voltage jumps between the output voltage vectors (OVVs) in high overmodulation regions result in the deterioration of both current performance and loading capability. In order to solve this problem, a novel overmodulation strategy based on the voltage vector space division is proposed. The overmodulation regions are divided by the amplitude and the phase of reference voltage vectors to guarantee the continuity of OVVs. When the overmodulation region changes, the voltage jump can be efficiently suppressed, which contributes to eliminating current ripples. In addition, the proposed parallel projection replaces the traditional center projection to increase the modulation index, which can also improve the fundamental voltage amplitude, and make a reduction of the field weakening current and its current overshoot. By improving the utilization of the dc bus voltage, the higher capability of the output torque can be achieved in the field weakening region. Finally, the effectiveness of the proposed strategy is verified on a high-speed surface-mounted PMSM platform by the experimental results. [ABSTRACT FROM AUTHOR]

High-frequency resonance (HFR) in the modular multilevel converter (MMC) has been reported in recent years frequently, yet, existing focuses on HFR are limited to the specific control strategy or grid condition, from which the conclusion may be not applicable if the control or grid changes. In this article, a unified MMC high-frequency impedance model (UHFIM) is proposed to fill this gap. By changing the gain of the model, UHFIM can reflect the high-frequency characteristics of the MMC under different control strategies in a unified form, which provides a theoretical basis for the general HFR suppression method. Analysis based on UHFIM reveals the worst cases of the HFR risk and the constraint of low-pass filter (LPF) order on the convergence of MMC high-frequency damping. In order to suppress HFR, this article proposes a joint design method for LPF and passive damper, which can completely remove the HFR risk from the entire high-frequency range without sacrificing too much dynamic performance of MMC, and it works no matter how the grid impedance varies. Besides, in the case that the damper cannot be installed, an alternative HFR suppression method based on delay time adjustment is also developed. Finally, the proposed unified model and the HFR suppression methods have been verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

Communication links, as a part of coordinated control in dc microgrids (MGs), play an essential role in achieving high operational performance. In this article, a bipolar topology based on series modular structure of dc MG is designed, and a complementary dual-window dc bus interacting (CDBI) method which combines droop control with antidroop control is proposed to improve the robustness of system and against communication failure. In the proposed CDBI method, distributed generations regard dc buses as common communication channels for information exchange, and the coordinated control within the dc MGs can be realized through predesigned sequences of voltage pulses without extra communication links. Finally, the proposed symmetrical bipolar structure and communication-free coordinated control scheme have been verified in various cases through rapid control prototype. The experimental results show that the bipolar-type dc MG controlled by the proposed CDBI method can supply high-quality power for a long time even in the case of communication failure. [ABSTRACT FROM AUTHOR]

The power density can be improved and the system cost can be saved in the reduced dc-link capacitance motor drive system. The line inductance can also be diminished to reduce the system volume further. In previous research works, the active damping control methods mainly concentrated on the drive system equipped with a larger line inductor. In this article, a dc-link voltage estimation feedback-based active damping method is proposed to suppress the grid current harmonics and improve the drive system stability with low line inductance. The dc-link voltage ripple caused by the LC resonance is analyzed to evaluate the direct dc-link voltage feedback-based active damping control method. To improve the damping performance, the resonant component of the dc-link voltage caused by the LC resonance could be obtained through the grid current to establish the feedback control loop. The sampling delay should be compensated to improve the control performance. The stability of the drive system is evaluated by the Nyquist plots of the impedance model, and the grid current is also analyzed, which could satisfy the harmonic requirements of IEC-61000-3-2. Experimental results are performed to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This article proposes a coordinate impedance compression strategy for high frequency inverter systems. Based on a two parallel inverter structure, the strategy adopts two methodologies: 1) a passive LC network to adjust the current and voltage seen by each inverter module, and 2) an active modulation of the inverter input voltage and output voltage phase to adjust the load current distribution. For the proposed strategy, the resistance and reactance can be compressed coordinately, which can help the inverter to operate in high efficiency load range. The Half-Bridge Class D inverter is taken as an example to be analyzed. A 10-MHz prototype is built and the experimental results verify the correctness and feasibility of the proposed strategy. [ABSTRACT FROM AUTHOR]

Electrolytic capacitorless Vienna rectifiers have many advantages, such as longer lifetime and higher power density. However, the reduced dc-link capacitance aggravates the voltage stress due to the neutral point (NP) fluctuation. In this article, a hybrid modulation strategy combining the modulations of redundant vector and compression vector is proposed, which can realize the NP voltage balance for electrolytic capacitorless Vienna rectifiers. On the basis of analyzing the limitation of NP-balance capability of conventional space vector pulsewidth modulation (PWM) strategy in the region of high modulation index, the negative influence of reduced capacitance on the NP fluctuation and the input current harmonics is revealed. To suppress the NP fluctuation, the compression coefficient is introduced to redistribute the duty cycles of voltage vector, which can reduce the negative effect of medium vector on the NP voltage. In addition, the phase voltage error is modeled to reduce the input current harmonics with the appropriate adjustment factor. The implementation of the proposed strategy is realized by the equivalent carrier-based PWM, which can avoid the sector judgment and angle calculation. By using the proposed strategy, the NP voltage balance and the input current harmonics reduction can be realized simultaneously. The effectiveness of the proposed strategy is verified on an electrolytic capacitorless Vienna rectifier platform. [ABSTRACT FROM AUTHOR]

Sharp LC resonance peak may enlarge inherent harmonics, dominant harmonics of the supply voltage generated by a three-phase diode rectifier, around the resonance frequency, which will intensify fluctuations of the dc-link voltage, and grid currents in motor drives with small dc-link capacitor. In this article, a novel resonance suppression strategy based on inherent harmonics impedance shaping is proposed specially for three-phase input permanent magnet synchronous motor (PMSM) drives with small dc-link capacitor. Instead of increasing the damping of the whole system for resonance suppression, the motor side power disturbance can be reduced by designing the impedance for inherent harmonics around LC resonance frequency based on the new model with the consideration of motor side characteristic. For damping current generation, the angle of the virtual admittance is modified to eliminate the influence of the dc-link voltage sampling delay. Experimental results show the effectiveness of the method on a prototype of electrolytic capacitorless PMSM drive. [ABSTRACT FROM AUTHOR]

It is important to improve the accuracy of rotor position estimation for the high-performance operation of position sensorless permanent magnet synchronous motor (PMSM) drives. To mitigate the position harmonic error caused by the nonideal factors in high-frequency signal injection based methods, an adaptive quasi-proportional-resonant rotor position observer (AQPRO) for sensorless PMSM drives is proposed in this article. The AQPRO can track the estimation error and generate the compensation value, which can realize online suppression for position error. By analyzing the stability and the influence of parameters of the proposed position observer on the suppression performance, a proportional-resonant gain self-tuning strategy is investigated to improve the suppression effect of the position harmonic error for different loads and speeds. The influence of self-tuning regulator parameters is modeled and analyzed in detail. The proposed method does not require offline detection and has a strong suppression ability for different harmonic error components. The effectiveness is verified by experiments on a 2.2-kW PMSM drive platform. [ABSTRACT FROM AUTHOR]

In this article, a shielding scheme based on ferrite magnetic antennas (SS-FMA) is proposed. The scheme can effectively provide a path for the magnetic field lines of three-dimensional couplers to be concentrated and conducted. The SS-FMA is considered to be applied for long range inductive power transfer (IPT) systems of post insulators to powering smart grid sensors and improve the efficiency under the influence of metal components. The negative influence of the aluminum flanges on the magnetic field distribution is analyzed. The suppression effects of the shielding scheme on the abovementioned influence have been analyzed. Parameters of the SS-FMA are optimized. The equivalent circuit model is established, and the abovementioned process is explained from the perspective of the circuit model. A prototype of a post insulator that includes IPT system and SS-FMA has been built. When the coils of the IPT system are attached to the flanges, the efficiency can still reach 47.8% under the influence of SS-FMA, which is an increase of 13.7% compared with no shielding scheme. When the coils are slightly away from the flanges, efficiency of the system including SS-FMA can be quickly improved to 54.3%. [ABSTRACT FROM AUTHOR]

A 1 MHz active-clamp flyback converter for solar street-lighting applications, featuring a partial power processing, is proposed in this article. The secondary-side resonance between the output capacitor and transformer leakage inductor is utilized to reduce rms current and conduction losses. In comparison with the traditional light-emitting diode drivers based on full power converters (FPCs), the proposed approach that uses partial power converters (PPCs) can significantly improve the overall system efficiency by eliminating the redundant power handling process. The universal schemes are discussed and the optimal solution is eventually determined by the partial power ratio. The advantages of PPC compared with FPC in device stress, losses, and regulation capability are demonstrated by simulation. With GaN devices, a 100 W/1 MHz prototype was built to verify the analysis. The experimental results show that the proposed topology can reduce the power rating of the converter by up to about 80% while increasing the system efficiency by up to 95.8%. [ABSTRACT FROM AUTHOR]

Accurate rotor position estimation is important to ensure the high-performance operation of position sensorless permanent magnet synchronous motor (PMSM) drives. To suppress the estimated rotor position harmonic error (ERPHE) caused by inverter nonlinearities, flux spatial harmonics, and the current measurement error in high-frequency signal injection-based schemes, an adaptive iterative learning control-based online suppression method is proposed in this article. This method constructs a P-type iterative learning rotor position observer with the forgetting factor to obtain the tracking error and generate the compensation value in real time. The stability, the convergence, and the parameter sensitivity of this observer are analyzed in detail. To improve the suppression effect of the ERPHE for different loads and speeds, an iterative learning gain self-tuning strategy is investigated. The proposed method does not require the offline detection and the discrimination of harmonic frequencies, which has strong suppression ability for different harmonic error components. The effectiveness is verified by experiments on a 2.2-kW interior PMSM drive platform. [ABSTRACT FROM AUTHOR]

This letter proposes a switched capacitor (SC)-based continuously adjustable modular bidirectional dc–dc converter. The structure of the proposed converter consists of three types of modules, series–parallel SC converter module, regulating module, and resonant SC converters module. A basic configuration of three modules working in buck operating mode is analyzed in detail. The boost mode operation is symmetrical to the buck mode. The regulation module provides all regulation capability, and the other two modules operate at fixed duty cycle and provide the main conversion ratio. A prototype of the basic configuration was built to verify the theory. The peak efficiency of the prototype is 97.15%. [ABSTRACT FROM AUTHOR]

In order to improve the performance of the traction permanent magnet motor drives without weight transducer for direct-drive elevator applications during starting operation, this article proposes a novel control method based on the high-gain nonlinear active disturbance rejection control (HNLADRC) strategy. First, the limitation of linear and nonlinear error decay function of active disturbance rejection control (ADRC) method is analyzed, which is not suitable for the complex situation at starting operation of the traction motor. A high-gain nonlinear error decay function based ADRC method is proposed, which can achieve better performance in the starting operation of the traction motor. Both the high-gain extended state observer (HNLESO) and the high-gain nonlinear error feedback law (HNLEFL) are constructed by the high-gain error decay function to improve the compensation accuracy of the starting torque and the dynamics of the speed loop. By analyzing the error decay performance of the HNLESO and the HNLEFL, it is proved that the HNLADRC method has a faster error decay rate. Experimental results show that the proposed method can obtain a shorter rollback distance and faster response capability. [ABSTRACT FROM AUTHOR]

In meshed high-voltage direct current (HVdc) grid, the current flows through the lines cannot be controlled with sufficient freedom without additional power electronics-based devices, namely current flow controller (CFC). In this article, a novel hybrid modular interline CFC is proposed based on H-bridge submodules and thyristor valves. Due to its modularity, the proposed CFC is particularly suitable for applications requiring high voltage and large power capacity. The circuit structure, operation principle, and parameter design are presented. In addition, a control strategy is developed for the proposed CFC. Simulations are carried out using a four-terminal meshed HVdc grid to verify the effectiveness of the topology and its control strategy. A downscaled prototype is built, which further validates the proposed CFC. [ABSTRACT FROM AUTHOR]

In this article, a high-performance modified Y-source dc–dc converter is proposed. Comparing with traditional Y-source dc–dc converter, the proposed converter can achieve soft switching characteristics. Due to the discontinuous conduction mode operation of one of the coupled inductor windings and the resonant cell constructed by switch parasitic capacitor, the switch can operate in zero voltage switching (ZVS) and diodes realize zero current switching. Also, the voltage gain of the proposed converter is greatly improved. Meanwhile, the control strategy of hybrid pulsewidth modulation and PFM is adopted to guarantee the ZVS operation within a wide range. A 160 W experimental prototype based on planar coupled inductor is built to verify theoretical analysis and efficiency is up to 94.45% under full load condition. [ABSTRACT FROM AUTHOR]

The nonlinearity of the voltage source inverter (VSI) leads to the error between output voltage and reference voltage, and causes the phase current harmonics. It is necessary to compensate its influence in the fields such as parameter identification, sensorless control, and servo drives. In this article, an industrial solution for VSI nonlinear compensation method based on lookup table (LUT) is introduced. The characteristics of semiconductor devices, equivalent dead-time and influence of parasitic capacitance effects are calculated quantitatively though injecting increase and decrease current during self-commissioning process. The critical current value for parasitic capacitor and the variation of equivalent dead time are verified through different distorted voltage curves. Considering dc-link voltage variation is irresistible for industrial products, 3-D linear interpolation is adopted to compensate the variation of VSI nonlinearity under different voltage conditions. Proposed LUT method does not require VSI datasheet and complicated calculation formula during implementation. Experiments are carried out on a commercial permanent magnet synchronous motor drive system to verify the proposed LUT method. [ABSTRACT FROM AUTHOR]

Active disturbance rejection controller (ADRC) possesses the considerable capability of improving the robustness of the permanent magnet synchronous motor (PMSM) drives. Nevertheless, the traditional linear ADRC (LADRC) and nonlinear ADRC (NLADRC) have their specific characteristic disturbance range of application. To further expand the disturbance range so as to improve the robustness against the disturbances, a novel NLADRC is proposed, which replaces the traditional linear function with a nonlinear function (NLF). And it is applied as the speed regulator for PMSM drives. Considering the accuracy and the dynamic performance of the disturbance estimation at the same time, an NLF is developed, and its describing function is established accordingly. Based on the above analysis, the NLADRC employing a cascaded nonlinear extended state observer is constructed to guarantee the relatively rapid and accurate disturbances estimation and compensation. Then, via the describing function technique, the theoretical frequency-domain analysis for the stability, the disturbance estimation performance, and the stiffness of the proposed NLADRC-based sensorless PMSM drive is given. Finally, the validity of the proposed scheme is verified experimentally on a 2.2-kW PMSM drive platform. [ABSTRACT FROM AUTHOR]

Inthis article, a two-phase series capacitor dual-path hybrid dc–dc converter with the step-down ratio of less than 1/6 is proposed for the first time. In this converter, the output current is divided into capacitance- and inductance-path, so the average value and ripple of inductance current are reduced. On the same time, the conduction loss caused by inductance equivalent series resistance (ESR) is also reduced. The addition of series capacitor leads to desirable characteristics, including lower switching stress, switching loss, parasitic output capacitance loss on mosfet, automatic phase current balancing, duty ratio extension, etc. A 120 W prototype has been designed to demonstrate theoretical analysis. Obtained efficiency was up to 93.18% at full load. Experimental results show good agreement with theoretical analysis and high feasibility of proposed converters. [ABSTRACT FROM AUTHOR]

To overcome the challenges of large reactive energy transmission loss and high current stress, which ocurr during the operation of auxiliary commutated circuit (ACC) of novel parallel resonant dc-link inverter (PRDCLI), an improved modulation strategy for reactive energy transmission loss is herein proposed based on the discontinuous pulsewidth modulation (DPWM), which adopts sawtooth carrier wave with alternating positive and negative slopes and shunt dead zone. Compared with the original modulation strategy, based on minimizing the ACC operation frequency, the proposed modulation strategy is able to realize all switches soft-switching, and avoid the superposition of resonant current and load current during the operation of ACC, thus, effectively reducing the reactive energy transmission loss and the current stress of auxiliary switches of the ACC. Under the proposed modulation strategy, the equivalent circuits in different operation modes are divided, and the operation principle, voltage/current stress, loss distribution, and optimal parameter design method of novel PRDCLI are researched. Eventually, the proposed modulation strategy is verified by experiments on a 5-kW/40-kHz prototype made by SiC mosfet. [ABSTRACT FROM AUTHOR]

A CLCL resonant dc/dc converter has been proposed and analyzed in this paper for two-stage light-emitting diode (LED) drivers. The circuit performs zero-voltage-switching (ZVS) turn-on and quasi-zero-current-switching (ZCS) turn-off. Then, a two-stage system has been designed using a power factor correction circuit before the proposed converter. Optimum input impedance angle, dead time, and components parameters have been achieved after thoughtful design, thus obtaining good soft-switching performance and reduced voltage stress. A 100-W prototype has been realized and tested demonstrating its high feasibility and efficiency at full load and during dimming operations. [ABSTRACT FROM PUBLISHER]