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This paper presents a direct torque control (DTC) switching scheme based on the direct matrix converter (DMC) using a 12-side polygonal space vector for variable speed control of an induction motor (IM). The conventional DTC scheme-based matrix converter (MC) is limited by 60° sectors of both flux and voltage vectors, which introduce a high torque ripple. The proposed method utilizes twelve 30° sectors of both flux and voltage vectors to increase the degrees of freedom for selection of proper vectors and reduce the torque ripple. The proposed switching scheme for the MC-based DTC of an IM drive select the appropriate switching vectors for control of torque with small variations of the stator flux within the hysteresis band. This improves the degrees of freedom in selecting the vector algorithm and the torque ripple as well. Furthermore, during the large torque demand, the probabilities of transgressing reference vector limits, which are enclosed by 12-side polygonal space vector, are reduced. Extensive simulation and experimental results are presented to verify the effectiveness of the 12-sector space vector switching scheme for the DTC of an IM fed by the DMC. [ABSTRACT FROM AUTHOR]

This paper studies a three-level dc converter for balancing the dc input voltage, which has a similar topology with the conventional three-level dc converter. It can easily build a neutral line for changing a dc voltage source into two dc voltage-level sources. A control strategy of conducting time extension of partial switch devices is also presented for achieving three-level states of each power switch. The operating principle of the converter is analyzed in detail based on the presented control strategy. The small-signal model and the effects of the proposed control strategy are also driven. Finally, a prototype is fabricated and tested in the lab and the experimental results verify the converter to achieve three-level characteristics and to have a good ability of balancing the input voltage. [ABSTRACT FROM AUTHOR]

In modular multilevel converters, there is a tradeoff between the switching frequency and the voltage ripple in the submodule capacitors. The reason for this is that it becomes increasingly difficult to balance the capacitor voltages when the switching frequency is reduced. This paper presents a new submodule circuit, which improves the balancing of the capacitor voltages at low switching frequencies. The proposed submodule circuit consists of two capacitors and eight switches, forming a three-level submodule. Ideally, the voltage and current ratings of the switches can be chosen such that the combined power rating of the semiconductors is the same as for the equivalent solution with conventional halfbridge submodules. The proposed submodule circuit provides the possibility of connecting the two capacitors in parallel when the intermediate voltage level is used. This will reduce the capacitor voltage ripple, especially at low switching frequencies, and thus, allow for a reduction of the size, weight, and cost of the submodule capacitors. The proposed submodule circuit is validated by both simulations and experimental results. It is found that the parallel connection of the submodule capacitors will, in fact, significantly improve the balancing of the capacitor voltages. [ABSTRACT FROM AUTHOR]

By extending a prior-art transformer-isolated structure for driving multiple LED strings, a scalable and modular capacitor-isolated architecture is presented in this paper. The proposed idea is based on first utilizing a daisy-chained transformer structure to share equally the current delivered from a half-bridge switching circuit and supply the shared currents to multiple string networks and then using a capacitor network in each string network to derive the string current and separate the grounds of the input source and the strings. The capacitor networks give further advantage of balancing the string currents, as compared to the prior-art transformer-isolated structure. Dimming function is achieved by adjusting both the switching frequency and duty cycle of the switching devices in the switching circuit. A 21-W prototype with seven strings has been built and evaluated. The lamp can be dimmed to 10% of full output, and the LED string current can be regulated at less than ±1% error, even under significant variations in the string voltages and some LED failures. [ABSTRACT FROM AUTHOR]

Reactor switching is a test duty for circuit breakers (CBs) in special locations. This duty is characterized by a relatively low current but the CB is stressed with high voltages. Furthermore, this is a stress which will appear frequently in breakers used for switching voltage-control elements. The different international standards define test procedures, which should be used to determine the CB characteristic and the withstand capability for the corresponding operating voltages. Usually, HV CBs need to be tested in synthetic test circuits. Due to the strong interaction between CBs and network synthetic test circuits, it is not possible to be used for inductive switching. Also, the direct test circuit may not be available due to the necessary short-circuit power and the required test voltages. Therefore, a test method has been developed to obtain the necessary information in a multistep method combining testing and calculation. Using the proposed method will enable smaller testing stations to give judgment on CB capabilities. For other very high requirements where even no test possibilities may exist, it will provide some evidence avoiding field tests. A validation of the presented multistep method is given in this paper. [ABSTRACT FROM AUTHOR]

Nonlinear, voltage-dependent capacitances of power semiconductor devices are capable of having significant impact on the operation of switched-mode power converters. Particularly at high switching frequency, these nonlinearities play a significant role in determining switching times, losses, and converter dynamics during switching transitions. In order to accommodate the well-established design and analysis techniques commonly used for linear circuits, this paper examines the nonlinear voltage-dependence of switching device capacitances and proposes a circuit-oriented analysis technique that allows the parasitic capacitances to be replaced with linear equivalents. The multitude of developed equivalents are verified through full nonlinear simulation in both MATLAB/Simulink and SPICE, as well as through experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a high step-up converter for fuel cell energy source applications. The proposed high step-up dc-dc converter is devised for boosting the voltage generated from fuel cell to be a 400-V dc-bus voltage. Through the three-winding coupled inductor and voltage doubler circuit, the proposed converter achieve high step-up voltage gain without large duty cycle. The passive lossless clamped technology not only recycles leakage energy to improve efficiency but also alleviates large voltage spike to limit the voltage stress. Finally, the fuel cell as input voltage source 60-90 V integrated into a 2-kW prototype converter was implemented for performance verification. Under output voltage 400-V operation, the highest efficiency is up to 96.81%, and the full-load efficiency is 91.32%. [ABSTRACT FROM AUTHOR]

A systematic method for derivation of a multiport converter (MPC) based on the dc-link inductor (DLI) concept is proposed in this paper. The MPC is generated by interconnecting multiple pulsating voltage cells (PVCs) through the DLIs. The PVCs can be input type, output type, and bidirectional type, and bidirectional MPC topologies can be harvested if all the PVCs are bidirectional type. As a result, a family of novel MPCs, including multiinput converters, multioutput converters, and bidirectional MPCs, are derived. With the proposed MPCs, step-up and step-down voltage conversion between any two of the ports can be implemented. As an example, the three-port bidirectional buck-boost (TP-B 3) converter is analyzed and applied to a stand-alone renewable power system for interconnection of three dc subsystems. The operation principles, pulse width modulation, and feed-back control strategies are presented and analyzed in depth. The analysis indicates that, compared to the traditional common dc-bus-based solution, bulky dc-link capacitor is eliminated and single-stage conversion between any two of the three dc-buses are achieved with the TP-B 3 converter, which is beneficial for higher efficiency, power density, and reliability. Experimental results are given to verify the feasibility and effectiveness of the developed TP-B 3 converter. [ABSTRACT FROM AUTHOR]

This paper introduces two bridgeless resonant ac-to-dc converters to efficiently convert arbitrary input voltages into a regulated dc output voltage. The proposed topologies provide direct ac-dc power conversion with less number of components, in comparison to other resonant topologies. The converters utilize soft-switched LC networks and diodes to convert low-frequency and low-amplitude alternating input voltage into a dc output voltage. Zero-voltage switching (ZVS) and zero-current switching (ZCS) are achieved in switching both power transistors and diodes. High-frequency soft-switching operation due to LC resonance allows smaller footprint for passive components, thereby increasing the circuit power density without suffering from switching losses. A resonant gate drive circuit is designed and utilized to further reduce gating losses under high-frequency switching and light-load condition. The converters operate at a fixed switching frequency, while they regulate the output voltage by using module pulsewidth-modulated (PWM) on-off control with fast transient response. A 5-mm × 6-mm, 100-mg prototype is fabricated, which is operating at 2-MHz switching frequency. The maximum output power of the prototype reaches 650 mW, with a 3- Vrms ac input voltage and a 7.6-V dc output voltage. The converter achieves higher than 70% closed-loop efficiency across wide range of input voltages and output powers. [ABSTRACT FROM AUTHOR]

This paper presents a new hysteresis current regulation strategy for the neutral point clamped and flying capacitor (FC) three-level inverters. The strategy uses the measured average of the switched phase leg output voltage to adjust the controller hysteresis band as the load back EMF varies to maintain a near constant phase leg switching frequency. The phase leg switchings are then fine tuned to a fixed frequency clock to further improve frequency regulation. Next, the zero-crossings of the measured phase leg average voltages are used to select between positive and negative switched output voltage levels, so that only one hysteresis current regulator is required for the full inverter switched output voltage range. For the FC inverter, a state machine is then added to select between redundant switching states to maintain balanced capacitor voltages. Finally, the controller is extended to a three-phase system by subtracting the common mode interacting current from the total phase leg current error before making any switching decision. The resulting controller achieves a line-to-line harmonic performance that is very close to open-loop phase disposition pulse width modulation, while retaining all of the dynamic benefits of hysteresis current regulation. [ABSTRACT FROM AUTHOR]

This paper investigates the different control objectives, such as loss reduction, neutral point (NP) balance and noise reduction of the space vector modulation (SVM), for the three-level neutral point clamped (NPC) converter. A detailed loss model and simulation model is built for quantitative loss and NP voltage ripple analysis. An improved SVM method is proposed to reduce NP imbalance and switching loss/noise simultaneously. The coordinately selected small vectors consider both the NP charge and the pulse sequence so that the minimized NP ripple and switching events are guaranteed in one switching cycle. In addition, the switching events between switching cycles are also considered to reduce the total switching loss. This method ensures an evenly distributed device loss in each phase leg and also a constant system efficiency under different power factors. The control result for NP balance and loss reduction is verified by using both a simulation model and an experimental prototype on a 200-kVA three-level NPC converter hardware. [ABSTRACT FROM AUTHOR]

This paper presents a buck-boost dc-dc converter for LED drivers capable of delivering an output current ranging from 0.1 to 2 A and a variable output voltage ranging between 2 and 5 V, starting from an input voltage spanning from 2.7 to 5.5 V. The dc-dc converter, realized in a 0.18-μm CMOS technology with 5-V option, occupies an area of 4 mm2 including pads. The circuit features automatic mode switching and dynamic sizing of the power transistors to achieve a peak efficiency of 91%. With a switching frequency of 2.5 MHz, the achieved line regulation is lower than 0.1% V-1 and the output voltage ripple is less than 10 mV. The obtained turn-on and load transient settling time are lower than 40 μs, thus allowing pulsed operation of the LEDs, as well as switching among LEDs of different colors. [ABSTRACT FROM AUTHOR]

This paper discusses about the voltage output ripple reduction and error minimization for the direct-drive, linear switched reluctance generator (LSRG)-based wave power generation system. First, the concept of the LSRG-based wave power generation system is studied. According to the characteristics of the LSRG, the suitable drive circuit dedicated to proper current excitation and generation is established. Second, the reasons that cause voltage output ripples are investigated. To reduce the remarkable ripples from phase current commutations, a current distribution function (CDF) is proposed based on the minimized copper loss principle. Third, the dual-loop control strategy with current and voltage as the inner and outer loop is constructed, implemented with the proposed CDF. Theoretical bases of the control strategy are derived. The simulation results prove that the proposed control algorithm is capable of voltage ripple suppression and error reduction within the range of ±0.5 V over the entire operation speed for wave energy extraction, validated by experimental verification. [ABSTRACT FROM AUTHOR]

A method of rapid prototyping of a solar array simulator, based on low cost, off-the-shelf components is proposed in the paper. A commercial constant output voltage switching power supply is utilized as a power stage. It is shown that it is possible to gain control over output voltage of such a device by injecting variable analog voltage into the voltage feedback loop of the supply. As a result, by sensing the power supply output current and varying the injected voltage it is possible to change the output voltage according to a predefined relation and hence any static I-V curve may be emulated by the device. For simulating a solar array output characteristics, the desired I-V curve may be either digitized from a manufacturer provided datasheet, obtained experimentally or estimated from three basic current-voltage pairs (open circuit, short circuit, and maximum power points) using a dedicated algorithm. In order to demonstrate the proposed method, a prototype was designed and built based on available low-cost commercial components. Dynamic characteristics of the prototype were experimentally evaluated and three static I-V curves of a commercial solar panel were simulated. The resulting I-V output characteristics were shown to closely resemble datasheet I-V curves. [ABSTRACT FROM AUTHOR]

In this paper, a predictive direct power control (DPC) method without sector information and voltage vector selection is proposed for three-phase grid-connected converters. Different from conventional predictive direct power controllers, the proposed strategy always adopts fixed voltage vectors, instead of selecting voltage vectors according to the angular information of the grid-voltage vector or the virtual-flux vector. The converter switching time is obtained by minimizing the squared errors of the instantaneous active and reactive power. Switch duty cycles are then calculated and equivalently reconstructed. The proposed strategy not only presents rapid dynamic response due to the use of the predictive controller, but also possesses excellent steady-state performance as a result of duty cycle reconstruction. The main advantage of the proposed control scheme, compared with the classical DPC strategies, is that it is unnecessary to use sector information of the grid-voltage vector, and selection of active voltage vectors is also not required here. Therefore, incorrect selection of voltage vectors and the resulting performance deterioration are surely avoided, without the need of any additional compensation measures. An in-depth comparison and experimental assessment are given to validate the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

This paper proposes a three-phase wound-field switched-flux (WFSF) machine. It is found that this machine has much higher average torque compared with the conventional 12-slot/8-pole machine with a segmented rotor and 12-slot/5-pole WFSF machine under the constraint of the same copper loss. All of those machines have been optimized to achieve the maximum torque for comparison. The performances of four machines, including back electromotive force, cogging torque, and static torque, are analyzed and compared by 2-D finite-element analysis and validated by experiments on the prototype machines. [ABSTRACT FROM AUTHOR]

This paper addresses on-chip solar energy harvesting and proposes a circuit that can be employed to generate high voltages from integrated photodiodes. The proposed circuit uses a switched-inductor approach to avoid stacking photodiodes to generate high voltages. The effect of parasitic photodiodes present in integrated circuits (ICs) is addressed and a solution to minimize their impact is presented. The proposed circuit employs two switch transistors and two off-chip components: an inductor and a capacitor. A theoretical analysis of a switched-inductor dc-dc converter is carried out and a mathematical model of the energy harvester is developed. Measurements taken from a fabricated IC are presented and shown to be in good agreement with hardware measurements. Measurement results show that voltages of up to 2.81 V (depending on illumination and loading conditions) can be generated from a single integrated photodiode. The energy harvester circuit achieves a maximum conversion efficiency of 59%. [ABSTRACT FROM AUTHOR]

This paper presents a new gate drive circuit for driving a series string of insulated-gate bipolar transistors (IGBTs). The proposed quasi-active gate control (QAGC) circuit is simple to implement as it consists of only a few passive components in addition to a standard gate driver. No separate isolation power supply is required for the upper devices in the stack. The proposed QAGC circuit provides an effective way to drive the power devices and control static and dynamic voltage sharing to the devices at the same time. The theoretical switching operation and the oscillation stability analysis allow criteria for component selection to be established. Limitations of the QAGC circuit are also identified. The modification of the circuit to support more power devices in the series stack is discussed with the aid of the simulation results. The switching operation of the circuit is validated from the experimental results using two IGBTs connected in series. The circuit shows an excellent switching operation with well-controlled dynamic and static voltage sharing and comparable gate voltage between the coupled devices. [ABSTRACT FROM AUTHOR]

In this paper, we present a wireless power transfer (WPT) that is adaptive to change in coil separation. For analytic design of the WPT system, a new design method which does not require calculating the voltages and currents in the system is presented. The proposed design method allows us to have perfect impedance matching theoretically for the WPT system using capacitor circuits connected to the sending and receiving coils. Closed-form design equations are provided for straight-forward application of the new design method. In order to compensate the variation of the mutual coupling between the two coils due to the change in separation, we propose a new switchable capacitor array circuit. For verification of the new design method and the new switchable capacitor array circuit, we have fabricated and measured a WPT system operating at 370 kHz. Measured results have shown a good agreement with theoretical responses, and the reflected power ratio smaller than 3% has been achieved by using the proposed switchable capacitor array circuit over the 5:1 change of coil separation. [ABSTRACT FROM PUBLISHER]

The objective of this paper is to investigate an impact of the inrush current on the prestrike and restrike characteristics of vacuum interrupters (VIs) during capacitive current switching duty. Eleven 7.2 kV VIs are used. Their contact parameters are contact gap 4 mm and contact material CuCr25 (25%weight of Cr). A series of 80 CO operations are executed for each test VI. The amplitude of inrush current Iinrush (3800 Hz) is set to 0 kA, 2 kA, 5 kA and 10 kA, respectively. The switching current is less than 1 A rms. The (1-cosωt) shape of the recovery voltage with a peak of 15 kV is applied to the test VI. The experimental results show that the prestrike and restrike phenomena are significantly influenced by the contact surface conditions damaged by the inrush current. The cumulative probability of the prestrike gap dpre follows a 3- parameter Weibull distribution. When Iinrush increases from 2 kA to 5 kA, the prestrike gap increases accordingly. The 10% dpre increases from 0.5 mm to 0.7 mm. The 50% dpre increases from 0.7 mm to 1.0 mm. The 90% dpre increases from 1.0 mm to 1.5 mm. The scale in the Weibull distribution, which can describe the scattering of dpre, is 0.2 mm and 0.6 mm in the case of Iinrush = 2 kA and Iinrush = 5 kA, respectively. It is found that the occurrence frequency of the inrush current interruption increases from 37.9% to 68.3% with the increase of Iinrush from 2 kA to 5 kA. Moreover, the inrush current also has an impact on the restrike types, which are classified into three types according to the waveform features. The average restrike probability increases from 4.6% to 17.9% and further to 30.4% with the increase of the inrush current from 0 kA to 2 kA and 5 kA, respectively. In addition, the higher the inrush current, the restrike tends to occur earlier during the recovery voltage period. [ABSTRACT FROM AUTHOR]

This paper deals with the influence produced by the solar array parasitic capacitance and its solving methods in the sequential switching shunt regulator (S3R). Nowadays, the usage of triple-junction Ga/As solar cells with larger parasitic capacitance has prompted new problems about power losses, steady state, and dynamic response in the S3R, especially for high section current, voltage applications. Effects of parasitic capacitance on voltage ripple, “double sectioning,” phase margin, and output impedance are represented and analyzed, and turn-off delay caused by parasitic capacitance is mathematically modeled. A novel shunt regulator topology passive and active shunt regulator (PASR) with low switching losses, low mass, and short turn-off time delay is proposed. To further reduce the impact of delay, nonlinear control is added in the control loop, achieving better performances in the stability margin, output impedance, and dynamic performance. Simulation and experimental results are provided to validate the proposed PASR together with nonlinear control scheme. [ABSTRACT FROM AUTHOR]

The common-mode voltage (CMV) produced from a converter system is a source of many problems, e.g., in the motor drive system, CMV might appear at the neutral point of the motor stator windings with respect to the ground and induce destructive bearing current. Reduced CMV space-vector modulation (RCMV SVM) methods have been proposed in both voltage-source converter (VSC) and current-source converter (CSC) systems. The available RCMV SVMs reduce the CMV by avoiding using zero-state vectors. However, this will lead to some negative effects, such as shrink of modulation index range, increase of switching frequencies, bipolar line-to-line voltage pulse patterns in VSCs, and power quality performance deterioration. In this paper, a RCMV SVM method for CSCs is proposed. By allowing the use of zero-state vectors, the proposed RCMV SVM still produces much lower CMV. However, its other performance indices, such as switching frequency and harmonic performance, are unaffected and comparable to the conventional SVMs. The effectiveness of the proposed RCMV SVM for CSCs is verified in the simulations and experiments. [ABSTRACT FROM AUTHOR]

Inductive power transfer (IPT) is an emerging technology that may create new possibilities for wireless power charging and transfer applications. However, the rather complex control method and low efficiency remain the key obstructing factors for general deployment. In a regularly compensated IPT circuit, high efficiency and controllability of the voltage transfer function are always conflicting requirements under varying load conditions. In this paper, the relationships among compensation parameters, circuit efficiency, voltage transfer function, and conduction angle of the input current relative to the input voltage are studied. A design and optimization method is proposed to achieve a better overall efficiency as well as good output voltage controllability. An IPT system design procedure is illustrated with design curves to achieve a desirable voltage transfer ratio, optimizing between efficiency enhancement and current rating of the switches. The analysis is supported with experimental results. [ABSTRACT FROM AUTHOR]

A lot of large-scale industrial critical loads suffer from voltage interruptions and sags which can cause a significant financial loss. The thyristor-based solid-state transfer switch (STS) and mechanical-based automatic transfer switch (ATS) are used to protect loads against these power quality problems. However, the STS has a great deal of loss consumption because of the forward voltage drop of the thyristors, and ATS can hardly satisfy the voltage-sensitive load due to the long transfer time. This paper proposes a 400 V/1000 kVA hybrid ATS (thyristor switch in parallel with mechanical switch) (HATS) to realize low power consumption under normal situation and transfer fast when required. The proposed HATS has four transfer strategies which can be chosen according to different applications, it realizes the overlapping transfer of the neutral wire, and it can make a decision to transfer or not according to the different fault locations (transfer on the source side and not transfer on the load side). The design details of the prototype are presented, and laboratory tests and field experiments show the prototype good performance. [ABSTRACT FROM PUBLISHER]

This paper presents analytical expressions for the class-E power amplifier with MOSFET linear gate-to-drain and nonlinear drain-to-source parasitic capacitances at any duty ratio. The maximum operating frequency, output power capability, and element values as functions of the duty ratio are obtained. The element values are directly dependent upon the selection of duty ratio and require a careful duty ratio selection to minimize component power losses and to maximize the total efficiency. Two design examples at 25 and 9 W output power at 4-MHz operating frequency along with the PSpice-simulation and experimental waveforms are presented. It is shown from the derived expressions that the slope of the voltage across the MOSFET gate-to-drain parasitic capacitance during the switch-off state as a function of the duty ratio affects the switch-voltage waveform. Therefore, it is possible to achieve the required peak switch voltage and the class-E ZVS/ZVDS conditions simultaneously by adjusting the duty ratio. The theoretical results and PSpice simulations agreed with experimental results quantitatively, which shows the validity of the presented analysis. [ABSTRACT FROM AUTHOR]

In this paper, a soft-switching dc/dc converter with secondary-side phase-shift control strategy is proposed to improve the conversion efficiency and minimize the primary switch voltage stress in the high input voltage applications. Zero-voltage-switching performance is achieved for both the primary- and secondary-side power devices in a wide load range to reduce the switching losses due to the secondary-side phase-shift control scheme. Furthermore, compared with the conventional phase-shift control mechanism, the circulating current at the freewheeling stage is effectively suppressed as well to minimize the conduction losses. Moreover, the voltage stress of the primary switches is only half of the input voltage by employing the improved three-level structure, which makes the low-voltage rated power devices available to improve the circuit performance. In addition, the converter can work in the buck, balance, and boost modes to achieve a relatively wide input voltage range, which is an expected advantage for the communication power system to minimize the electrolytic capacitors with an acceptable hold-up time. The operation principle is analyzed and experimental results of a 1-kW 100-kHz prototype are provided to verify the effectiveness and the advantages of the proposed converter. [ABSTRACT FROM AUTHOR]

This paper provides a perspective on progress toward realization of efficient, fully integrated dc–dc conversion and regulation functionality in CMOS platforms. In providing a comparative assessment between the inductor-based and switched-capacitor approaches, the presentation reviews the salient features in effectiveness in utilization of switch technology and in use and implementation of passives. The analytical conclusions point toward the strong advantages of the switched-capacitor (SC) approach with respect to both switch utilization and much higher energy densities of capacitors versus inductors. The analysis is substantiated with a review of recently developed and published integrated dc–dc converters of both the inductor-based and SC types. [ABSTRACT FROM AUTHOR]

The sizes of ultra-high-voltage (UHV) towers and substations are related to the air clearances which are usually determined by switching overvoltage. Based on electromagnetic transient simulation of the first 1000-kV UHV ac transmission line in China, this paper extracted the effective wave information in accordance with the concept of the active part of the waveshape from calculated main types of switching overvoltage. Moreover, based on test results of switching impulse flashover voltages, a practical and accurate method to calculate the risk of failure was presented, which considered the variable characteristics of the insulation strength of the transmission line under different switching overvoltage waveshapes. Evaluation of the results focused on the comparison between two new methods and the traditional simplified method considering the effect of the front time. [ABSTRACT FROM PUBLISHER]

An auxiliary capacitor-based balancing approach is adopted in this paper to equalize the dc-link capacitor voltages of a diode-clamped multilevel converter (DCMC). Four balancing circuits, including the generalized, one-level-capacitor, one-capacitor, and simplified one-capacitor-based configurations are discussed for a five-level DCMC system. These configurations are different in connection of the auxiliary circuits and numbers of the capacitors and switches, but they work on the same principle called ping-pong operation by utilizing the auxiliary capacitor as an equalizer between the capacitors of different voltages. The unbalance phenomenon, ping-pong principle, circuit configurations, and their switching schemes are analyzed, respectively. The superiorities of the proposed approach include balancing operation regardless of load power factor and modulation index, control simplicity, and independence from main circuits when compared to the traditional approaches. Simulations and experimental results verified the performances using the proposed balancing circuits and control strategies. [ABSTRACT FROM AUTHOR]

Single-phase three-level neutral point clamped (NPC) converters are widely applied in high-speed railway electrical traction drive systems. A significant problem related to the single-phase three-level NPC converters is the fluctuation of the neutral-point voltage. In this paper, a capacitor voltage balancing technique is proposed that injects an offset voltage into the sinusoidal modulating signals of the conventional carrier-based pulsewidth modulation (CBPWM) method. Furthermore, when the injected offset voltage is maximized, it cannot only balance the dc-link capacitors voltages, but also reduce switching losses. Theoretical analysis has shown that both methods can control the neutral point voltage effectively, but the neutral point voltage controller in the CBPWM with maximum offset voltage injection (CBPWM-MOVI) has a faster dynamic response. It was observed that the high-order harmonics frequencies of the line current are centered around the twice switching frequency in the CBPWM with the offset voltage injection (CBPWM-OVI) but are centered around the switching frequency in the CBPWM-MOVI. And also, the CBPWM-MOVI has switching commutations number at least 25% below that of the CBPWM-OVI in one modulating signal period. The performances of the two strategies were verified by simulation and experimental tests. [ABSTRACT FROM AUTHOR]

A current source inverter (CSI) requires a capacitor filter for the commutation of switching device as well as for attenuating switching harmonics. Hence, the CSI-fed ac machine has a second-order system in the continuous time domain. This paper presents a design methodology for the closed-loop current controller of the CSI-fed ac machine drive system. A multiloop current controller design using a pole/zero cancellation method is employed with a transfer function matrix. To decouple the cross-coupling terms which cause mutual interferences between the d- and q-axes in the synchronous reference frame, two types of controller are proposed and implemented using different decoupling method. Additionally, active damping methods are incorporated to enhance the stability of the system. A stability analysis in discrete-time domain is investigated to verify the feasibility of the proposed closed-loop current controller. To evaluate the effectiveness of the proposed current controller, computer simulations and experimental tests were performed and the results are discussed. [ABSTRACT FROM AUTHOR]

This paper presents a novel modulation strategy for a seven-phase three-level inverter, aimed at variable-speed drive applications. Developed space vector pulsewidth modulation (SVPWM) strategy is based on vector space decomposition (VSD) approach and an analysis of multidimensional space vector projections in mutually orthogonal planes. The algorithm represents an extension of a recently developed five-phase three-level SVPWM algorithm and is considerably more complex, due to the existence of three mutually orthogonal planes in a seven-phase system. The difficulties of generalization of space vector strategies, which stem from the nature of the multiphase systems, are highlighted. Increasing the number of phases from five to seven increases the number of switching states from 3 ^5 = 243 to 3^7 = 2187 and the number of orthogonal planes from two to three. This considerably affects the complexity of the offline calculations. However, the final implementation of the algorithm is simple. Developed SVPWM algorithm is compared to an equivalent carrier-based strategy and it is shown that they yield identical performance. The complexity of the algorithms for real-time implementation is compared. Simulation and experimental results, obtained using neutral-point clamped inverter, verify the theoretical developments. [ABSTRACT FROM AUTHOR]

Common-mode voltages (CMVs) can lead to premature failure of the motor insulation system in medium-voltage current-source-fed drives. By analyzing the CMV values at all switching states under different operating conditions of a current-source-inverter (CSI)-based motor drive, this paper first indicates that the CMV peaks are produced by the zero states in most of the cases. The nonzero-state (NZS) modulation techniques employed in voltage-source converters are adapted for use in a space-vector-modulated current-source converter (CSC) to reduce the CMV magnitude. For NZS modulation in CSCs, the nearest three-state (NTS) modulation sequences are designed with good low-order harmonic performances in their linear modulation region of m _a ≥ 0.67 and with no increase in the device switching frequency. A combined active-zero-state (AZS) modulation technique is also proposed as compensation, for a lower modulation index in the range of 0.4–0.67, when a compromise is made between the dc-link current minimization and high input power factor control. The simulation and experimental results are provided to validate the CMV reduction effects and harmonic performances of the NTS and combined AZS modulation methods in CSI-fed drives. [ABSTRACT FROM AUTHOR]

A new system for switching electrical power using microelectromechanical systems (MEMS) is presented. The heart of the system utilizes custom-designed MEMS switching device arrays that are able to conduct current more efficiently and can open orders of magnitude faster than traditional macroscopic mechanical relays. Up to now, MEMS switches have been recognized for their ability to switch very quickly due to their low mass but have only been used to carry and switch very low currents at extremely low voltage. However, recent developments have enabled suppression of the arc that normally occurs when the MEMS switch is opened while current is flowing. The combination of the arc suppression with the MEMS switch arrays designed for this purpose enables a breakthrough increase in current and voltage handling capability. The resultant technology has been scaled to handle many amperes of current and switch hundreds of volts. Such current and voltage handling capability deliver improved energy efficiency and the capacity to handle fault current levels that are encountered in typical ac or dc power systems. Fault current interruption takes place in less than 10 \mu\s, almost regardless of the prospective fault current magnitude. The properties of the MEMS switch arrays allow the switching mechanism to operate at temperatures in excess of 200 ^\circ\C. The switches also have a vibration tolerance in excess of 1000 G. The combination of fast MEMS switching speed, optimized current and voltage handling capacity of the switch arrays, the arc suppression circuitry, and optimized sensing and control enables a single sensing, control, and switching system to operate in a small fraction of a millisecond. This paper will present the basic physics of the MEMS switches together with recent advances that enable the technology. Some illustrative examples of the ways that the devices may be used to provide protection and control within electrical systems will also be presented. [ABSTRACT FROM AUTHOR]

This paper is the continuation of an earlier work on narrowing the theoretical gap with power theory (or “power definitions”) for nonlinear circuits. The underlying idea is to compute the active and reactive powers of a general single-phase circuit from only the knowledge of the instantaneous voltage and current at the circuit terminals. This is done to shed light on the long-standing controversy on the physical meaning of the various types of powers defined for nonsinusoidal waveforms. Previously, only the power components of nonlinear switching circuits consisting of constant resistive and inductive elements were properly identified. The method is now extended to be suitable for the identification of the power components of general single-phase nonlinear circuits including magnetic nonlinear components with saturation and hysteresis. The Poynting Theorem is applied to correctly identify the energy consumed in electrical elements (Joule losses) as well as the energy stored/restored and consumed in the hysteresis loop of magnetic elements. Numerous examples are presented for illustration and validation of the method. [ABSTRACT FROM AUTHOR]

Flying-capacitor converters (FCCs), like most multilevel converter topologies, require a balancing mechanism of the capacitor voltages. FCCs feature natural voltage balancing when a special modulation technique is used. The classic methods, such as phase-shifted pulse width modulation (PS-PWM), result in very slow balancing for some duty-ratio ranges. Previous work has shown that for a single-leg five-level FCC, one time constant is infinite for a zero desired output voltage. In this paper, a modified PS-PWM scheme for a single-leg five-level FCC is presented, which results in faster balancing over the total duty-ratio range. The modified PS-PWM scheme is studied, resulting in an averaged voltage-balancing model. This model is verified using simulations and experiments. The modified PS-PWM scheme solves the slow-balancing problems of the normal PS-PWM method for odd-level FCCs, while maintaining the passive control property, and it provides a self-precharge capability. [ABSTRACT FROM AUTHOR]

This paper presents a low-cost bidirectional isolated dc–dc converte, derived from dual-active-bridge converter for the power sources with variable output voltage like supercapacitors. The proposed converter consists of push-pull-forward circuit half-bridge circuit (PPFHB) and a high-frequency transformer; this structure minimizes the number of the switching transistors and their associate gate driver components. With phase-shift control strategy, all the switches are operated under zero-voltage switching (ZVS) condition. Furthermore, in order to optimize the converter performance and increase efficiency, optimal design methods and criteria are investigated, including coupled inductors design, bidirectional power flow analysis, harmonics analysis, and ZVS range extension. Based on all the optimal parameters, higher efficiency can be achieved. Finally, prototypes are built in laboratory controlled by digital signal processor for comparison purpose. Detailed test results verify the theoretical analysis and demonstrate the validity of optimization design method. [ABSTRACT FROM PUBLISHER]

This paper proposes an asymmetrical full-bridge converter with high-voltage gain. The control of the proposed converter is implemented with the asymmetrical pulsewidth modulation technique. The proposed converter achieves zero-voltage switching (ZVS) of all power switches. Zero-current switching (ZCS) of output diodes is also achieved. The proposed converter can provide high-voltage gain and the voltages across the semiconductor devices are effectively clamped. Steady-state analysis of the proposed converter is presented. A laboratory prototype of the proposed converter is developed, and its experimental results are presented for validation. [ABSTRACT FROM AUTHOR]

In this paper, the unclamped inductive switching (UIS) behavior of an inverted L-shaped source trench power MOSFET is numerically analyzed and experimentally characterized. The measured avalanche energy absorption at UIS of the new trench power MOSFET is 2.1 times that of the conventional trench power MOSFET. This is explained by numerical simulation, which shows that the voltage drop across the emitter/base junction in the parasitic bipolar junction transistor of the new structure is smaller than that of the conventional structure. The influence of structural and device size variation of the new trench power MOSFET on UIS performance is also investigated. Results show that the avalanche current density at UIS is a strong function of the \p^+-region width and the device size. Furthermore, the effect becomes very significant as the device size becomes very small. [ABSTRACT FROM PUBLISHER]

The linear flux-switching permanent-magnet (LFSPM) machine is a novel linear brushless ac machine with magnets and armature windings in the short mover, which is a competitive candidate for direct-drive applications due to the inherent sinusoidal back-electromotive force and high force capability. However, the resulting cogging force is serious because of the double salient structure. In this paper, a one-tooth model for the cogging force mechanism and a method for cogging force analysis are introduced. Moreover, an optimization method for minimizing the cogging force and an optimized design for the LFSPM machine are proposed. Both the finite-element analysis and the test measurement verify that the analytical method and the optimization technique are correct and effective, and these methods can be applied to cogging force analysis in the other double salient permanent-magnet machines. [ABSTRACT FROM AUTHOR]

Due to the increasing chip temperature and the strong dependency of leakage power on temperature, thermal aware power management has received a considerable amount of attention recently in energy efficient system design. In this paper, we propose a temperature-aware intra-task scheduling algorithm to minimize leakage energy in real-time systems. The basic idea of our algorithm is to run tasks at full speed when the chip temperature is low or the work urgency is high, and switch the processor to a low-power state when the chip temperature is high or the workload is light. Our offline algorithm can achieve the optimal leakage reduction for a given task with the worst-case execution time, while the online algorithm has a very low runtime complexity. The simulation results show that the online algorithm is able to reduce 34% of total leakage energy on average in both real-world and artificial benchmarks. Finally, we demonstrate how to combine our algorithm with existing dynamic voltage scaling technique to optimize the overall energy consumption. [ABSTRACT FROM AUTHOR]

The novel multilevel circuit topologies are proposed in this paper. They are called multilevel circuit topologies based on switched-capacitor and diode-clamped converters (MCT-BSD). The topology structure and the operation principle, including the working states’ transitions of the diode-clamped part, the voltages balancing mechanism of the dc link capacitors, and the pulse width modulated carrier control strategy are given. The switched-capacitor circuits contribute not only to balancing the voltages of capacitors but also to boosting the output voltage with a certain input dc voltage. The validity of the MCT-BSD is verified by simulations and experiments. The results show that balancing the voltages of capacitors, boosting the output voltages, and operating under the three-phase condition are all realized effectively in the MCT-BSD. The simulations also show the generalization of the MCT-BSD for n-level topologies. [ABSTRACT FROM AUTHOR]

The design and characterization in high-voltage (HV)-CMOS technology of an innovative intelligent power switch (IPS) for harsh automotive applications is proposed in this paper. To safely handle the ordinary and extraordinary automotive electrical and environmental conditions, a systematic design flow is followed: several design solutions are presented at the architectural and circuital level, integrating on-chip self-diagnostic capabilities and full protection against the high voltage and reverse polarity, the effects of wiring parasitics, and the over-current and over-temperature phenomena. Moreover, the current slope and soft start integrated techniques ensure a low electromagnetic interference, and the IPS is also configurable to efficiently drive different interchangeable loads. The innovative IPS has been implemented in a 0.35-\mu\m HV-CMOS technology and has been embedded in mechatronic third generation brush-holder regulator system-on-chip for an automotive alternator. The electrical simulations and experimental characterization and the testing at component and on-board system levels prove that the proposed design allows a compact and smart power switch realization facing the harshest automotive conditions. [ABSTRACT FROM AUTHOR]

When small currents are interrupted by a vacuum switch, it is well known that the chopping current and the associated overvoltage are observed. Many investigations on the current-chopping phenomena in alternating-current (ac) circuits have been carried out, but there are no data available on inverter circuits in spite of their recent wide application to synchronous motor systems. In this paper, chopping-current levels and the overvoltages in an inverter circuit under a simple three-level pulsewidth-modulated control are investigated. As a result, the mean chopping-current level is three to four times higher than that in an ac circuit. In particular, high chopping currents occur only when the timing of the current interruption by the vacuum switch synchronizes with that of the inverter's switching, which we call “double chopping.” High chopping current due to double chopping might be harmful since the high overvoltage proportional to the chopping-current level could damage the insulation of electric equipment. However, we experimentally confirmed that a typical surge suppressor could reduce overvoltage. [ABSTRACT FROM AUTHOR]

In this paper, a novel three-phase soft-switching inverter is presented. The inverter-switch turn on and turn off are performed under zero-voltage switching condition. This inverter has only one auxiliary switch, which is also soft switched. Having one auxiliary switch simplifies the control circuit considerably. The proposed inverter is analyzed, and its operating modes are explained in details. The design considerations of the proposed inverter are presented. The experimental results of the prototype inverter confirm the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper investigates the cogging torque and torque ripple features of a permanent-magnet flux-switching integrated starter generator. The effects of the rotor pole arc width on the cogging torque, torque ripple, and output torque are first established using finite-element analysis (FEA). Three torque ripple reduction techniques based on the optimization of three different rotor pole configurations, namely, uniform, step skewed, and axial pairing, are then proposed. The torque characteristics of each rotor configuration at varying load currents and phase angles are studied in detail. A prototype machine with a common stator and the three optimized rotor configurations are built for experimental validation. Both the FEA results and the experimental tests show that the step skewed and axial pairing techniques can alleviate the cogging torque significantly, but the latter is less effective than the former in reducing the overall torque ripple. [ABSTRACT FROM AUTHOR]

A novel zero-voltage-transition high-efficiency bridgeless power-factor-correction (PFC) circuit with a zero-current-switching auxiliary switch was proposed, analyzed, and experimentally verified. An assist circuit, consisting of a resonant inductor, two blocking diodes, a clamping circuit, an autotransformer, and an auxiliary MOSFET switch, was used to reduce the turn-on switching loss of the two main switches of the bridgeless PFC circuit and the turn-off switching loss of the auxiliary switch. The soft commutation of the main switches is achieved without imposing an additional voltage stress on the main switches. Feedback gate-drive signals can be obtained by using an existing converter IC controller modified to fit the purpose. In this paper, a detailed description of the circuit operation will be given. Based on the analysis, the guidelines for the component selection are presented. A prototype of 100-kHz 600-W universal-line PFC bridgeless circuit was built to verify the proposed scheme. In addition, based on the same concept, a family of bridgeless PFC configuration was proposed. [ABSTRACT FROM AUTHOR]

Many static synchronous compensators (STATCOMs) utilize multilevel converters due to the following: 1) lower harmonic injection into the power system; 2) decreased stress on the electronic components due to decreased voltages; and 3) lower switching losses. One disadvantage, however, is the increased likelihood of a switch failure due to the increased number of switches in a multilevel converter. A single switch failure, however, does not necessarily force an (2n + 1)-level STATCOM offline. Even with a reduced number of switches, a STATCOM can still provide a significant range of control by removing the module of the faulted switch and continuing with (2n - 1) levels. This paper introduces an approach to detect the existence of the faulted switch, identify which switch is faulty, and reconfigure the STATCOM. This approach is illustrated on an eleven-level STATCOM and the effect on the dynamic performance and the total harmonic distortion (THD) is analyzed. [ABSTRACT FROM AUTHOR]

A novel high step-up dc–dc converter for a distributed generation system is proposed in this paper. The concept is composed of two capacitors, two diodes, and one coupled inductor. Two capacitors are charged in parallel, and are discharged in series by the coupled inductor. Thus, high step-up voltage gain can be achieved with an appropriate duty ratio. The voltage stresses on the main switch and output diode are reduced by a passive clamp circuit. Therefore, low resistance R DS(ON) for the main switch can be adopted to reduce conduction loss. In addition, the reverse-recovery problem of the diode is alleviated, and thus, the efficiency can be further improved. The operating principle and steady-state analyses of the voltage gain are also discussed in detail. Finally, a 24-V input voltage, 400-V output voltage, and 400-W output power prototype circuit of the proposed converter are implemented in the laboratory to verify the performance. [ABSTRACT FROM AUTHOR]