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This paper provides an experimental discussion on a real-time real-power emulator that plays an important role in achieving a total test of medium-voltage, high-power, high-speed induction motor drives. The use of the emulator brings cost and time savings to the test. The test bench including the emulator is characterized by connecting two modular multilevel double-star chopper-cell (DSCC) converters connected in a front-to-front way. This paper designs, builds, and tests a 400- ${\rm V}_{\rm dc}$ , 10-kW downscaled test bench. It mainly consists of the following two identical DSCC converters: 1) one DSCC converter is used as an inverter under test; and 2) the other as a real-time real-power high-fidelity emulator. Experimental waveforms confirm that the emulator can reproduce electrical and mechanical operating performance of the three-phase 200-V, 10-kW, four-pole, 9000-r/min induction motor loaded with a centrifugal compressor. [ABSTRACT FROM AUTHOR]

Unipolar-pulsewidth modulation (UP-PWM) inverter takes advantages of high power efficiency and small output chokes which is widely used in the industry. However, UP-PWM inverters cannot be used in parallel operation due to a current unbalance problem. This paper studies the current unbalance problem of paralleled UP-PWM inverters with common dc bus and ac bus. First, the problem of unbalanced inductor current is defined and analyzed. Second, a technique to eliminate unbalanced currents is proposed. The proposed current balancing technique only requires one more current sensor in an inverter module rather than changing converter topology or modulation method, which makes it possible to apply UP-PWM inverters in parallel-operation while keeping the advantages of unipolar switching. The proposed current balancing method is verified by both simulation and hardware experiment. Experimental verification is performed on two 1 kW, 400 V input, and 120 V/60 Hz output prototypes, which shows a good agreement to the analytical study. [ABSTRACT FROM AUTHOR]

Parallel interleaved two-level (2L) three-phase voltage source inverters (VSIs) are widely used due to their distinct advantages of high power delivery, modularity, low current rating devices, etc. Along with these advantages, the parallel interleaved 2L VSIs could also be analyzed as a single three-level (3L) VSI. Conventionally parallel interleaved 2L VSIs are modulated using the 2L pulsewidth modulation (PWM) techniques. However, implementation of parallel interleaved 2L VSIs using the 2L PWM techniques may generate a higher ac side current ripple as compared to implementing the parallel interleaved 2L VSIs using 3L PWM techniques. This paper proposes a carrier-based method for implementing different 3L discontinuous PWM (DPWM) techniques for parallel interleaved 2L three-phase VSIs. Comparison of different 2L switching sequences for implementing a 3L DPWM switching sequence based on circulating current, line current ripple, and switching loss is also carried out. Simulation and experimental results are also displayed to validate the proposal. [ABSTRACT FROM AUTHOR]

This paper introduces a three-phase grid-connected inverter for commercial-scale photovoltaic systems. The circuit topology combines an ac-inductor-less active bridge with a parallel-connected pulsewidth modulation inverter acting as an instantaneous reactive power compensator. The active bridge, called a 120° conduction inverter, operates at a switching frequency equal to the grid frequency and outputs a 120° rectangular current, while the compensator eliminates the harmonic currents included in the rectangular current. The main advantage of this strategy is the reduction in size of the required ac inductor by a factor of 4, as well as the reduction of power losses in the switching devices. The theoretical analysis clearly shows that the compensator can synthesize a sinusoidal output current by controlling only instantaneous reactive power, thus eliminating the need for electrolytic capacitors. A 5-kW experimental setup validates the operating principle and the control method of the proposed inverter and exhibits an inverter efficiency as high as 99.2% with Si superjunction mosfets. [ABSTRACT FROM AUTHOR]

A switching-capacitor-based buck–boost converter (with common ground) for point of load applications is proposed in this paper. It is capable of operating in stand-alone buck or boost mode in addition to its primary operation of performing the buck–boost conversion. The striking feature of the proposed converter is low source current ripple content irrespective of its mode of operation (buck–boost, buck, or boost). First, feasible pulsewidth modulation schemes for the proposed converter are identified and thereafter the corresponding circuit performance analysis, steady-state analysis, and state-space modelling is established. Through steady-state analysis, voltage gain expressions are formulated and equations defining L-C components are derived in terms of their ripple quantities. The state-space models are used to formulate small-signal analysis and to obtain the relevant transfer functions required in the controller design. A voltage-mode/current-mode controller is designed, with a tradeoff in bandwidth, to control the proposed converter and transit it from buck to boost mode or vice versa seamlessly. A 30–55 W, 100 kHz, prototype point of load converter with 36-V input dc source is built to supply power at constant load voltage of either 48 or 28 V. The proposed converters’ effectiveness is demonstrated experimentally in terms of reduced source current ripple along with seamless transition from buck to boost mode and vice versa. [ABSTRACT FROM AUTHOR]

This paper investigates a multilevel inverter composed of series/parallel-connected H-bridges. The presented structure can be used for applications in which the use of semiconductor switches with low-voltage and low-current ratings is intended. A comprehensive system model, an overall control strategy to adjust the output voltage with constant magnitude and frequency, and a level-shifted PWM (LS-PWM) strategy based on a voltage vectors unidimensional analysis and a plane analysis are presented. The LS-PWM is capable of mitigating the low-frequency circulating current, thus generating multilevel voltage signals with low harmonic distortion, maximum number of levels, and low dv/dt. In addition, considering a wide range of values of voltages and currents and various power levels, the total converter losses are reduced compared with the conventional multilevel converters. Two multilevel conventional inverters with the same number of semiconductor switches are used for comparison. Simulation and experimental results demonstrate the feasibility of the studied converter. [ABSTRACT FROM AUTHOR]

This paper investigates power shunt filter topologies composed of three standard three-leg converters applied in either three or four-wire system. Compared with the usual three-phase shunt filter, the proposed ones allow us to reduce dc-link voltages, harmonic distortion or/and the semiconductor losses, and fault tolerant operation. Suitable control strategies to adjust filter and circulating currents, as well as the three dc-link voltages are presented. Two pulse-width modulation techniques are developed for the proposed topologies in order to achieve the best voltage-pulse pattern. Comparisons between these techniques are carried out in this paper. Simulation and experimental results are presented to validate the theoretical approach. [ABSTRACT FROM PUBLISHER]

Paralleled inverters are not only a suitable approach to increase the power capacity, but also have the capability of common mode voltage (CMV) reduction, or even elimination. The original zero CMV modulation scheme for paralleled inverters suffers from the current jump problem in phase-leg currents. This current jump phenomenon amplifies the peak values of differential-mode circulating current (DMCC) and zero-sequence circulating current (ZSCC), which is adverse for the design of coupled inductor and common-mode inductor. This paper introduces the modified modulation scheme, which can keep volt-seconds balance in whole fundamental period and mitigate the current jump in phase-leg currents. In addition, the reduction effect of the DMCC and ZSCC can be achieved. To verify the analysis, both the simulation and experimental results are presented, which validates the proposed methods and show that they are beneficial for DMCC and ZSCC reduction. [ABSTRACT FROM AUTHOR]

Paralleling power converters is a common practice in industries to enhance total power rating, reliability, and availability of the system. In case of fault occurring in systems with parallel converters, the faulty power converter can be isolated and the system can still be operated at reduced power level. In this paper, a grid-connected power converter consisting of two parallel H-bridge converters with low ground leakage current is considered. Two contingency configurations, that are also of low ground leakage current, are proposed to enhance the availability of the system. This is done by reconfiguring the power circuit to a single H-bridge in the case of failure in one of the bridges. The power converter is experimentally tested with the proposed configurations for experimental validation. The results show that the second configuration has better performance in terms of power loss and current total harmonic distortion when operating at lower power level. [ABSTRACT FROM AUTHOR]

This paper presents a modular push–pull PWM converter (MPC) for a battery energy storage system, which is intended for grid connections to medium- or high-voltage power systems. The converter per phase consists of a center-tapped transformer and two arms based on a cascade connection of multiple bidirectional PWM chopper-cells with floating dc capacitors. This paper discusses the operating performance and control method of the MPC, focusing on voltage balancing of all the floating dc capacitors. Moreover, a comparison is made between the MPC and a modular multilevel converter (MMC), under an assumption that both are used as the same battery energy storage system. The validity of the operating performance and control method is confirmed by both computer simulation using the “PSCAD/EMTDC” software package and experiment using a three-phase, 200-V, 5-kW downscaled model. [ABSTRACT FROM PUBLISHER]

Zero-sequence circulating current (ZSCC) has been a major concern for the operation of paralleled converters. Existing ZSCC reduction methods in the literature either suffer poor performances or are too complicated for modular implementation in an arbitrary number of interleaved converters. This paper investigates the application of interleaved carrier phase-shift (ICPS) pulse-width modulation (PWM) in modular interleaved converter system for ZSCC peak value reduction. The generalized study based on the derived ZSCC analytical expression reveals that the ICPS PWM can achieve superior ZSCC peak value reduction performance regardless the number of interleaved converters. Moreover, the impacts of ICPS PWM on the output voltage and current quality are also analyzed based on double Fourier integral. Compared with the conventional interleaved sinusoidal PWM (ISPWM), the output quality with the ICPS PWM can be comparable or even better. Simulation and experimental results show good agreement with the theoretical analysis, verifying the performance of the ICPS PWM. [ABSTRACT FROM AUTHOR]

In this paper for power factor correction (PFC), a modified Landsman converter is introduced. The application is targeted for high-brightness (HB) projection application with brightness control for HB red–green–blue (HB-RGB) light-emitting diode (LED). A pulse-width modulation (PWM) technique is used for intensity control to achieve brightness control of the LED driver. The proposed PFC converter is used to feed a dual output flyback dc–dc converter that supplies power to the forced cooling unit and the LED module with galvanic isolation. The brightness control of LED is performed by synchronous buck converter. The modified Landsman converter operates in discontinuous output inductor current mode for PFC at universal ac mains. A prototype of the proposed LED driver is experimentally verified. The performance of proposed driver is evaluated at full and light-load condition for universal ac mains (90–265 V) over a full range of brightness. The power quality parameters are found within the acceptable limits of harmonic standard IEC 61000-3-2 for universal ac mains. [ABSTRACT FROM PUBLISHER]

Ground leakage current and electromagnetic interference noise are important challenges during design of grid-connected power converters. Use of common-mode (CM) choke helps to mitigate these issues. A common practice is to use a separate CM filter and a differential mode LCL filter. In this paper, an integrated CM inductor (ICMI) is proposed in which the LCL filter boost inductor and the CM choke are combined into a single component. This results in a reduction in the number of magnetic components required to build the power converter. Steps involving design of the ICMI are provided. The proposed ICMI is fabricated in the laboratory. Experimental test are carried out on a 5-kW single-phase grid-connected power converter to validate the effectiveness of the proposed ICMI. The results show that the use of proposed ICMI along with an added ground capacitor in the power circuit as a CM filter can reduce the electromagnetic interference noise level up to 30 dB. [ABSTRACT FROM PUBLISHER]

In this paper, the switching cell concept is extended to isolated ac–ac converters, and a highly reliable double step-down ac–ac converter is proposed with high-frequency transformer (HFT) isolation. By using the switching cell structure and coupled inductors, the proposed converter has no commutation problem as it is immune from both short-circuit and open-circuit problems, even when all the switches are turned on or turned off, simultaneously. Therefore, it does not require pulse width modulation dead times along with bulky and lossy RC snubbers or voltage-sensing circuitry to implement soft-commutation strategies, resulting in high reliability and high quality output waveforms. The HFT in the proposed converter provides electrical isolation and safety which is required in applications such as dynamic voltage restorer (DVR), solid-state transformer (SST), etc., without the need for external bulky line frequency transformer. Moreover, all the passive components experience twice the switching frequency; therefore, their size can be reduced. The proposed converter is very suitable for application as DVR, to compensate both voltage sags and swells, owing to its ability to provide both inverting and noninverting outputs. A detailed theoretical analysis and operation of the proposed ac–ac converter are provided, and its applications as DVR and SST are also discussed. Experimental results with scaled-down prototype are also provided to verify its performance. [ABSTRACT FROM AUTHOR]

This paper identifies the characteristics of a current source inverter operating in discontinuous conduction mode, and proposes a new multiobjective pulse-width modulation (PWM) method to mitigate voltage boosting and harmonic distortion effects. The method takes into account load impedance effects. Controls are also developed to enable transition between the multiobjective PWM method and conventional PWM as the current source inverter operates in discontinuous and continuous modes of operation. The concept is verified experimentally on a 3 kW test bed. [ABSTRACT FROM AUTHOR]

Inserted between the inverter and the ac motor for the purpose of providing clean sinusoidal voltage at the motor terminals, the pure sine filter (PSF) involves common-mode and differential-mode suppression components. When using PSF in a motor drive and employing advanced pulsewidth modulation (PWM) techniques with discontinuous modulation waveforms, a large common-mode current may circulate through the inverter and the filter resulting in overcurrent stress in the inverter and significant acoustic noise in the filter inductors. This paper first discusses the PSF and advanced PWM techniques, then investigates the performance issues that may arise when combining advanced discontinuous PWM methods with PSF and provides a curement for the overcurrent stress problems by means of a rate of change limiter. The simulations and detailed experimental studies illustrate the inverter overcurrent stress problems and the feasibility of the proposed method to cure the problems. Via experimental performance evaluation of various PWM methods, the paper also suggests, along with PSF, the use of advanced continuous and discontinuous PWM methods with reduced common-mode voltage for the purpose of performance enhancement and filter size reduction. [ABSTRACT FROM AUTHOR]

This paper presents an energy-recycling class-D low-side gate driver integrated circuit (IC), which can also perform 5-to-15-V level upconversion using a bidirectional flyback converter topology. The gate driver itself is a mini switching regulator that operates at 5–15 MHz to generate 1-μs transition time gate-switching waveforms. In order to maintain uniform charging/discharging currents during transitions, the embedded flyback converter operates in a pulse-frequency modulation mode while charging and in a pulse width modulation mode while discharging the gate node. The required pulses with digitally programmable frequencies and duty cycles are efficiently generated by a custom-designed IC fabricated in a 0.25-μm HV CMOS technology. Also, the presented analysis guides a way to achieve the desired transition time with the maximum efficiency. The prototype IC demonstrates 37.5% energy recycling while driving a 15-V insulated-gate bipolar transistor power switch with 105-nC gate charge at 20 kHz. [ABSTRACT FROM PUBLISHER]

This paper presents a single-phase ac–ac converter based on a modular multilevel cascade converter (MMCC) with double-star chopper cells (DSCC). The converter topology is composed of three DSCC legs, in which the middle leg is shared, and it does not present a common dc-link capacitor. It is suitable for nonregenerative or regenerative low-power and medium-power ac–ac conversions. A voltage-balancing control is presented for regulating the floating dc capacitor voltages. Furthermore, a grid current and load voltage control is presented to correct the input power factor and to ensure input/output sinusoidal waveforms. A phase-shifted carrier (PSC) pulsewidth modulation (PWM) commands submodules (SMs) using half of PSCs, preserving the characteristics of conventional modulation. Details about a downscaled prototype rated at 3.3 kW and 220 V are also presented. The experimental results allow validating the control strategies and the effectiveness of the proposed system. [ABSTRACT FROM PUBLISHER]

A new discrete-time state feedback controller is presented, which allows high-bandwidth voltage control of a buck converter for any load condition, whether it operates in discontinuous conduction mode (DCM), continuous conduction mode (CCM), or at the boundary of these regions. This makes the buck converter applicable for a wide range of applications. For the control design process, two large-signal models, which represent the buck converter's discrete time dynamics in CCM and DCM, are developed. A simple proportional-integral regulator is used for the voltage control of the converter. The operation mode is detected and the voltage controller is connected in cascade to a current controller in CCM or to a nonlinear state feedback decoupling structure in DCM. In this paper, the modeling and design of the proposed control topology are introduced and its performance is demonstrated in simulation and experiment. [ABSTRACT FROM PUBLISHER]

Although the operation of a three-phase current source rectifier (CSR) for ac-to-dc conversion using phase control or low-frequency pulse control is well established in a wide variety of applications, CSR realization using high-frequency pulsewidth-modulation control has been recently studied as a potentially competitive alternative to a voltage source rectifier. In the CSR, reverse blocking gate turn-off switches are realized using series-connected diodes, which prevent any reversal of the dc-link current. A significant consequence of this limitation occurs at light load conditions. The dc-link inductor current enters the discontinuous mode of operation and leads to the loss of the control of the output voltage and a highly distorted input current, which compromise the potential advantages of the approach. This paper characterizes the CSR while operating in the discontinuous conduction mode and proposes a modulation strategy that restores the control of the output voltage and ensures a nearly sinusoidal current at light loads. Simulation and hardware results are provided for a 3-kW laboratory-scale prototype system. [ABSTRACT FROM AUTHOR]

This paper provides an intensive discussion on analysis, simulation, and experiment of a back-to-back (BTB) systemunifying two modular multilevel cascade converters based on double-star chopper cells (MMCCs-DSCCs). Each of the twoDSCCs connected back-to-back consists of multiple cascaded chopper cells and a center-tapped inductor per leg. Lowvoltage steps bring significant reductions in harmonic voltage and current to the BTB system. Neither dc-link capacitornor voltage sensor is required for regulating the dc-link voltage and controlling the dc-link current. A three-phase200-V, 10-kW, 50-Hz downscaled BTB system with phase-shifted PWM is designed, constructed, and tested to verify itsoperating principles and performance. Analytical, simulated, and experimental results agree well with each other insteady and transient states. Experimental waveforms confirm the effectiveness of a self-starting/restartingprocedure. [ABSTRACT FROM AUTHOR]

In this paper, analysis of circulating currents of paralleled single-phase boost converter systems is presented. The dc loop and ac loop circulating currents are clearly explained. In order to eliminate the dc loop circulating currents and reduce switching losses, a simplified pulsewidth modulation strategy is adopted in a paralleled single-phase boost converter. Based on the analysis of circulating currents, common-mode circulating current (CMCC) and differential-mode circulating current (DMCC) are defined. Then, CMCC and DMCC compensators are proposed in a centralized control scheme to reduce the common-mode and differential-mode circulating currents in a parallel system operated in both rectifier and inverter modes with different power sharing for microgrid applications. Converter-paralleled system stability analysis is also presented. Finally, a prototype system is constructed to facilitate the theoretical results as verification. From the experimental results, the proposed control scheme can indeed reduce the circulating currents under equal and/or different power rating conditions in the parallel system. [ABSTRACT FROM PUBLISHER]

In this paper, a fully digitalized current sharing strategy without any analog-to-digital converter (ADC) is presented and applied to light-emitting diode (LED) lighting. By doing so, the cost for digital control is reduced significantly due to no ADC used. Aside from this, LED dimming is easy to realize. Above all, the proposed current sharing method has the capability of resisting variations in input voltage and component parameter. Such a control topology is demonstrated by some experiments and hence is very suitable for LED street lighting. [ABSTRACT FROM AUTHOR]

This paper proposes a new dc-voltage-balancing circuit for a five-level diode-clamped inverter intended for a medium-voltage motor drive with a three-phase diode rectifier used as the front end. This circuit consists of two unidirectional choppers and a single coupled inductor with two galvanically isolated windings. The inductor produces no net dc magnetic flux because the individual dc magnetic fluxes generated by the two windings are canceled out with each other. This makes the inductor compact by a factor of six, compared with the balancing circuit including two noncoupled inductors. Moreover, introducing phase-shift control to the new balancing circuit makes it possible to adjust the midpoint voltage. As a result, the dc mean voltages of all the four split dc capacitors can be balanced, independent of inverter control. Experimental results obtained from a 200-V 5.5-kW downscaled model verify the effectiveness of the new balancing circuit. [ABSTRACT FROM PUBLISHER]

This paper proposes a zero-voltage-transition (ZVT) pulsewidth-modulated (PWM) synchronous buck converter, which is designed to operate at low voltage and high efficiency typically required for portable systems. A new passive auxiliary circuit that allows the main switch to operate with zero-voltage switching has been incorporated in the conventional PWM synchronous buck converter. The operation principles and detailed steady-state analysis of the ZVT PWM synchronous converter with a passive auxiliary circuit are presented. All of the semiconductor devices aside from the main switch operate under soft-switching conditions. Thus, the auxiliary circuit provides a larger overall efficiency. The feasibility of the auxiliary circuit is confirmed by the simulation and experimental results. [ABSTRACT FROM PUBLISHER]

Presents a discussion on the paper, “A review of single-phase improved power quality ACDC converters,” (Singh, B. et al), IEEE Trans. Ind. Electron., vol. 50, no. 5, pp. 962–981, Oct 2003 [ABSTRACT FROM AUTHOR]