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Based on the comparisons of several inverter configurations in the aspects of efficiency, response, volume, current distortion, and price, in this article, we present a feasible three-phase four-wire (3Φ4W) grid-connected hybrid-frequency parallel inverter system (HbFPIS) with ripple compensation to achieve low current distortion and fast response. An HbFPIS consists of a low-frequency-high-power inverter (LFHPI) and a high-frequency-low-power inverter (HFLPI) connected in parallel. An LFHPI design results in higher power output with lower frequency (LF) switching devices, such as insulated gate bipolar transistors (IGBTs) being more cost-effective. An HFLPI design can reduce switching loss by lowering the power requirement of high-frequency (HF) switching devices while increasing dynamic response. With the direct digital control and ripple compensation, LF current ripples are attenuated by the HFLPI to a smaller level, remaining mainly HF current ripples and, thus, resulting in smaller filter size and weight. The design of an HbFPIS ensures that the system has high power output with cost-effective devices, fast response, and smaller output filters. Ripple attenuation, current tracking capability, and inverter stability are analyzed in the article. Low current distortion and fast current tracking performance are validated by the 300-kW simulated and the 10-kW experimental results of a 3Φ4W HbFPIS in grid-connected and active power filter modes. [ABSTRACT FROM AUTHOR]

One of the modular multilevel converter (MMC) applications with scalability is renewable energy generation. Nowadays, renewable energy is especially the source of momentum, which stimulates the energy transition and reduction of greenhouse gas emissions. However, its existing control schemes may not precisely reveal the inherent mannerism of MMCs. The aim of this article is to optimize the cell voltage, arm current, and circulating current of converter arms in MMCs based on the Lagrange multiplier of an energy cost function and arm current tracking control law. Meanwhile, determination of the capacitors and switch ratings in each cell still has a big challenge, and it can result in cell-voltage fluctuations under unbalanced grid-connection conditions. This article presents unique approaches to derive cell-voltage expression in terms of arm currents, which reduces cell-voltage fluctuations by injecting zero-mean current, and the duty-ratio control laws. Moreover, tradeoff between cell voltage and circulating current can be also conducted. Experimental and simulated results from a 3-kW single-phase MMC have verified the functionality of the proposed control method, analysis, and comprehensive discussion. [ABSTRACT FROM AUTHOR]

This paper presents bidirectional grid-connected modular multilevel converters (MMC) with direct digital control and division-summation processes to achieve power-injection and rectification functions. A direct digital control is developed to track current references, regulate dc-bus voltage and cell voltage, and balance the upper and lower dc-bus voltages. It can accommodate wide filter-inductance variation and take care of source voltage harmonics to achieve tight current tracking and low distortion output current. Based on the power-balance principle, the commands of arm currents can be determined directly. In this paper, the MMC configuration is introduced first, and then the control laws for current tracking and voltage regulation are derived in detail. Experimental and simulated results obtained from two 50 kW MMCs operated in power-injection and rectification modes have verified the analysis and discussion. [ABSTRACT FROM AUTHOR]

This paper presents a sinusoidal pulsewidth modulation (SPWM) based direct digital control with average-voltage model (AVM) and division–summation process for paralleled three-phase three-wire (3φ3W) grid-connected converters to reduce circulating currents. With the direct digital control, plant of each single-phase converter can be derived directly, and a controller is then designed to cover the variation effects of filter inductance and grid voltage. Based on SPWM and AVM over a switching cycle, each 3φ3W converter can be decomposed into three single-phase converters and each converter is controlled individually to track its sinusoidal reference current tightly, reducing circulating currents significantly. Equal current sharing is therefore also achieved. The control laws for achieving grid connection are derived in detail. In the design and implementation, the inductances corresponding to various inductor currents are measured offline and stored in the controller for scheduling loop gain cycle by cycle. Experimental and simulated results from a three-converter system confirm the analysis and discussion of the proposed control approaches. [ABSTRACT FROM AUTHOR]

Soft magnetic powder cores with their high saturation flux density and low core loss are excellent alternatives for filter inductors in inverter-based applications. However, their nonlinear current-dependent inductance characteristics pose a challenge for control of grid-connected inverter with LCL filter. In this paper, the variable inductance conundrum is discussed and a modified direct digital control method based on a variable-structure inductance estimation model that takes into consideration wide nonlinear variation in both inverter- and grid-side inductances is proposed. The proposed method is shown to have better grid-voltage harmonic rejection and improved stability margins. However, investigation of stability which is conventionally based on nominal values of filter inductors cannot predict instabilities over the entire range of inductance variation. Hence, a parametric approach to conventional stability methods with a parameter space defined by variation in actual and estimated inductance is explored in this paper. The effect of line impedance on stability is also investigated with impedance-based stability criterion by considering line inductance as an additional dimension in the parameter space. A pattern in stability margins is observed due to inductance variation, with inductance at its minimum being most vulnerable to instability. Experimental results measured from a 5 kW single-phase grid-connected inverter with various LCL filters have verified the feasibility of the proposed control method. The experimental results also match the analytical results with reasonable accuracy. [ABSTRACT FROM AUTHOR]

Resonant frequency of an LCL filter in a grid-connected inverter is an important factor for control stability and grid-injected current quality. However, the constraints on resonant frequency are usually considered as an afterthought in conventional filter design methods. The fact that resonant frequency is affected by both internal and external factors during operation makes it even more critical. Hence, an improved resonant frequency based systematic LCL filter design method is presented in this paper. A resonant frequency band is identified by considering grid-voltage harmonics and control stability boundary. The variation in resonant frequency due to inductive line impedance as well as magnetic permeability of inductor core is taken into account to define the constraints on LCL parameters. The LCL parameters are then systematically derived from the identified constraints with almost no iteration. A division–summation (D-Σ) digital control method is used to validate the design method. Experimental results measured from a 5-kW single-phase grid-connected inverter have verified the effectiveness of the LCL filter design method over conventional methods. [ABSTRACT FROM PUBLISHER]

This paper presents a three-phase back-to-back transformerless inverter for online uninterruptible power supply applications. The inverter consists of a three-phase three-wire input rectifier stage and a three-phase four-wire output inverter stage with their ground wires tied together. Both of the two stages are with sinusoidal pulse width modulation based division-summation (D-∑) digital control. The input stage controls the power flow between utility grid and dc link, regulates the dc-link voltage, and fulfills power factor correction. While the output stage tracks three-phase ac reference voltages. The proposed control laws derived based on the D-∑ digital approach take into account the effects of dc-link voltage fluctuation, grid-voltage distortion, and inductance variation due to different current levels. Thus, distortion of input current and output voltage, and filter inductor core size can be reduced significantly. Moreover, circulating current through their common ground can be suppressed effectively. Simulated and experimental results from a three-phase back-to-back transformerless inverter have confirmed the analysis and discussion of the proposed control approach. [ABSTRACT FROM PUBLISHER]

Pulse-width-modulated (PWM) converters have been widely applied for power processing, and they are typically the stems of other types of converters, such as quasi-resonant, Z-source, and switched-inductor hybrid converters. Development of PWM converters has been spanning over a century, starting from the buck converter. The well-known PWM converters include buck, boost, buck–boost, Ćuk, single ended primary inductive converter (SEPIC), zeta, Z-source, quasi-Z source, etc. Many attempts have been proposed to develop these converters based mostly on canonical cell concepts and by introducing extra LC filters to the cells. This paper presents an enhancement to the layer and graft schemes by introducing the ideas of dc voltage/current offsetting, capacitor/inductor component splitting, diode grafting, and inverse operation of PWM converters. The PWM converters, which can be operated in continuous conduction mode (CCM) or discontinuous conduction mode (DCM), therefore can be synthesized systematically according to decoded transfer gains. Decoding and synthesizing PWM converters uniquely bridge transfer gains to converter topologies and provide readers a comprehensive understanding of PWM-converter evolution from the original converter, the buck converter. Additionally, in this paper, the Ćuk, SEPIC, and zeta converters all with the same transfer gain of $D/(1 - D)$ are proved to be equivalent to the buck–boost converter with an extra LC filter. For further illustrating the proposed approaches, various types of Z-source converters, switched-capacitor/switched-inductor hybrid converters, and a single-stage interleaved converter are reviewed, and new PWM converters are developed. [ABSTRACT FROM AUTHOR]

A division–summation (D-\mathbf\Sigma) digital control for three-phase inverters to achieve active and reactive power injection has been presented. It can overcome the limitation of abc to dq frame transformation. However, the D-\mathbf\Sigma control requires four sets of control laws to cover four quadrant operations, namely, grid connection (power factor (PF) 1 $\sim\pm$0.866), rectification with PF correction, PF leading (0 \sim$ 0.866), and PF lagging (0 \sim$ −0.866). Moreover, the switching sequences for the four modes are also different from each other, increasing complexity of firmware programming. In this paper, improvement of the control law derivation and region selection for the (D), which can obtain the control law directly. Measured results from a 10-kVA 3 $\phi$ bidirectional inverter have been presented to confirm the improvement. [ABSTRACT FROM PUBLISHER]

This paper presents a division-summation (D-\Sigma) digital control for a three-phase inverter to achieve active and reactive power injection to the ac grid. The proposed D-\Sigma approach summarizes the inductor-current variations over one switching cycle to derive control laws directly, which can overcome the limitation of d–q transformation. The inverter with this control can achieve various power factors (PFs) leading or lagging, by taking into account wide filter-inductance variation and grid-voltage distortion, reducing core size significantly. The control laws for achieving the desired features are derived in detail, and they are expressed in general forms for readily software programming. With the enhancement work of previous research, active and reactive power injection with PF from 0 to 1 can be controlled effectively, so that these control laws can be extended to wide current-tracking applications, such as static synchronous compensator and active power filter. In the design and implementation, the inductance values corresponding to various inductor currents were measured at the startup and stored in the controller for scheduling loop gain cycle by cycle. Measured results from a 10-kVA 3 \phi inverter have confirmed the analysis and discussion of the proposed control approaches. [ABSTRACT FROM PUBLISHER]

A bidirectional isolated full-bridge dc–dc converter with a conversion ratio around nine times, soft start-up, and soft-switching features for battery charging/discharging is proposed in this paper. The converter is equipped with an active flyback and two passive capacitor–diode snubbers, which can reduce voltage and current spikes and reduce voltage and current stresses, while it can achieve near zero-voltage-switching and zero-current-switching soft-switching features. In this paper, the operational principle of the proposed converter is first described, and its analysis and design are then presented. A 1.5-kW prototype with a low-side voltage of 48 V and a high-side voltage of 360 V has been implemented, from which measured results have verified the discussed features. [ABSTRACT FROM PUBLISHER]

This study is focused on integration and operation of a single-phase bidirectional inverter with two buck/boost maximum power point trackers (MPPTs) for dc-distribution applications. In a dc-distribution system, a bidirectional inverter is required to control the power flow between dc bus and ac grid, and to regulate the dc bus to a certain range of voltages. A droop regulation mechanism according to the inverter inductor current levels to reduce capacitor size, balance power flow, and accommodate load variation is proposed. Since the photovoltaic (PV) array voltage can vary from 0 to 600 V, especially with thin-film PV panels, the MPPT topology is formed with buck and boost converters to operate at the dc-bus voltage around 380 V, reducing the voltage stress of its followed inverter. Additionally, the controller can online check the input configuration of the two MPPTs, equally distribute the PV-array output current to the two MPPTs in parallel operation, and switch control laws to smooth out mode transition. A comparison between the conventional boost MPPT and the proposed buck/boost MPPT integrated with a PV inverter is also presented. Experimental results obtained from a 5-kW system have verified the discussion and feasibility. [ABSTRACT FROM AUTHOR]

This paper presents two-phase modulated digital control for a three-phase bidirectional inverter with wide inductance variation in dc distribution systems. The bidirectional inverter can fulfill both grid connection and rectification with power factor correction. With the proposed control, the inverter can track its sinusoidal reference currents, and it is allowed to have wide inductance variation, reducing core size significantly. The control laws based on space-vector pulsewidth modulation are first derived with either an accurate approach or an approximated one, and the gate signals were then derived based on two-phase modulation for lower switching loss and switching noise spectra. Determination of control parameters and stability analysis are also presented. In the design and implementation, the inductances corresponding to various inductor currents were measured and tabulated into a single-chip microcontroller for tuning loop gain cycle by cycle, ensuring system stability. Measured results from a 10 kVA 3φ bidirectional inverter have been presented to confirm the feasibility of the discussed control approaches. [ABSTRACT FROM AUTHOR]

This paper presents dc-bus voltage control with a three-phase bidirectional inverter for dc distribution systems. The bidirectional inverter can fulfill both grid connection and rectification modes with power factor correction. The proposed control includes two approaches, one line-cycle regulation approach (OLCRA) and one-sixth line-cycle regulation approach (OSLCRA), which take into account dc-bus capacitance and control dc-bus voltage to track a linear relationship between the dc-bus voltage and inverter inductor current. Since both of the approaches require the parameter of dc-bus capacitance, this paper first presents determination of dc-bus capacitor size and an online capacitance estimation method. With the OLCRA, the inverter tunes the dc-bus voltage every line cycle, which can reduce the frequency of operation-mode change and current distortion. The OSLCRA adjusts current command every one-sixth line cycle to adapt to abrupt dc-bus voltage variation. The two approaches together can prevent dc-bus voltage from wide variation and improve the availability of the dc distribution systems without increasing dc-bus capacitance. Experimental results measured from a three-phase bidirectional inverter have verified the feasibility of the discussed control approaches. [ABSTRACT FROM AUTHOR]

This paper presents power loss comparison of single- and two-stage grid-connected photovoltaic (PV) systems based on the loss factors of double line-frequency voltage ripple (DLFVR), fast irradiance variation + DLFVR, fast dc load variation + DLFVR, limited operating voltage range + DLFVR, and overall loss factor combination. These loss factors will result in power deviation from the maximum power points. In this paper, both single-stage and two-stage grid-connected PV systems are considered. All of the effects on a two-stage system are insignificant due to an additional maximum power point tracker, but the tracker will reduce the system efficiency typically about 2.5%. The power loss caused by these loss factors in a single-stage grid-connected PV system is also around 2.5%; that is, a single-stage system has the merits of saving components and reducing cost, and does not penalize overall system efficiency under certain operating voltage ranges. Simulation results with the MATLAB software package and experimental results have confirmed the analysis. [ABSTRACT FROM PUBLISHER]

This paper presents design and implementation of a 5-kW single-phase bidirectional inverter with wide inductance variation. For dc-microgrid applications, the bidirectional inverter has to fulfill grid connection and rectification with power factor correction to regulate the dc bus to a certain range of voltages. In the inverter operation, inductor current can vary from 0 to 32 A in one line cycle. This will result in wide inductance variation, around seven times for an inductor constructed with a molybdenum permalloy powder core, and thus, high current ripple and fluctuation. In this paper, we take into account this variation while designing controller and selecting key components to ensure inverter normal operation. Additionally, to adopt a cost-effective microcontroller for the inverter, the sensitivities of the control to various parameters are investigated and presented in this paper. Experimental results measured from a 5-kW single-phase prototype have verified the feasibility of the designed inverter. [ABSTRACT FROM PUBLISHER]

This paper presents single-stage regulators with power-factor correction (PFC) based on an asymmetrical half-bridge topology. The proposed regulator is formed from a boost converter with two coupled inductors and an asymmetrical half-bridge converter with the synchronous switch technique, and it is controlled with pulsewidth modulation to achieve zero-voltage switching (ZVS). The boost converter is operated in discontinues conduction mode to achieve PFC. With the coupled inductors, input current ripple and power factor can be improved significantly. The proposed regulator has the features of constant-frequency operation, ZVS, and low voltage stress imposed on the active switches. Moreover, the regulator can achieve high power factor, high power density, high efficiency, low switching loss, and low component count, which makes its applications at medium-power levels feasible. Experimental results have verified the discussed features of the proposed regulator. [ABSTRACT FROM AUTHOR]

Provides information on a study that presented a switch-mode approach to efficiently and flexibly generating reset waveforms for alternating current plasma display panels. Methodology of the study; Results and discussion on the study; Conclusions.

Presents a study which examined the design of a series-resonant parallel-loaded inverter applied to electronic dimming ballasts with bifrequency and fuzzy logic control. Component values of the power stage; Steady-state analysis of the power stage; Possibility of applying the proposed control scheme in practical electronic dimming ballasts.

Presents a study which discussed improved scenario for electronic ballast derived with synchronous switch technique. Merits of electronic ballast; Results; Conclusion.

Presents information on a study which proposed a single-stage converters (SSC) for application of photovoltaic powered lighting system (PPLS). Overview on synchronous switch technique; Derivation of SSC for PPLS application; Results; Conclusion.

Presents information on a study that described a robust-controlled single-stage converter (SSC) operating either in discontinuous conduction mode or in continuous conduction mode to achieve high power factor for universal line voltage. Derivation of the proposed SSC; Analysis of the SSC power stage; Design consideration and small-signal modeling; Experimental results and discussion; Conclusion.

Presents information on a study which introduced an electric dimming ballast with a lead-lag tank operation (LLTO) having the properties of high efficiency and low stress. Analysis of the proposed circuit operation scheme; Outline of the design procedure; Presentation of a design example of electronic dimming ballast with the LLTO scheme for a two-fluorescent-lamp lighting system.

Presents a study on the design, analysis and practical consideration of a single-stage electronic dimming ballast with unity power factor. Methodology used in the study; Results of the study; Conclusions.

Presents information on a unified approach to developing single-stage power converters (SSCs) which can fulfill multifunctions. Details on the previous use of high frequency power converters which has been utilized in electronic products; Features in which converters are configured; Configuration of synchronous switches.

Provides information on the presentation of a systematic and unified approach to modeling pulsewidth modulated (PWM) dc/dc converters based on the graft scheme. Information on a review of the graft scheme; Detailed information on the representation of small signal models in general forms; Conclusion reached.

Presents information pertaining to the off-line applications with single-stage converters (SSC's). Description of approach used in synthesizing the SSC's; What are the functions of SSC's; Reference to the application of prototypes of SSC's.

Analysis the design and practical consideration of a single-stage electronic ballast with dimming feature and unity power. Details on the use of a pulse-width modulation (PWM); Reference made to the hardware measurements conducted on the ballast which showed that desired performance can be achieved feasibly; Methodology used in the analysis; Implications of the findings.

A 2-degree-of-freedom (2DoF) induction machine realizes rotary, linear, and helical motions, exhibiting the merits of integrated structure and high material utilization. Compared with traditional electric machines, one of the special factors affecting the electromagnetic performances is the helical motion coupling effect (HMCE). This article systematically investigates its production mechanism based on the proposed HMCE model first. Then, a comprehensive comparison of the torque performances between the rotary and linear motion parts is conducted to evaluate the HMCE in two motion parts, and then the results are verified by 3-D finite element model. Besides, resistant torque and force ratios are proposed and calculated to assess the extent of the HMCE. It can be concluded that the torque performances of the rotary motion component are weakened more than those of the linear motion component by the HMCE. Further, two methods to suppress the coupling effect, namely adjustment of linear motion slip ratio and change of linear motion frequency, are discussed. Experimental results have validated the analytical results and effectiveness of the suppression strategies. [ABSTRACT FROM AUTHOR]

Current-fed bidirectional dc–dc converters have attracted much attention in battery energy storage system applications due to their zero-voltage-switching performances and greater degree of control freedom. However, high efficiency cannot be achieved for both light and heavy load ranges with the present modulation schemes for a current-fed bidirectional dc–dc converter, especially with low battery voltages. A new modulation scheme is proposed to improve the conversion efficiency over a wide load range and with variations in the battery voltage. The relationship between the duty cycle of the secondary full bridge and the phase-shift angle was investigated to lower the power losses with the wide load variations. Based on the operation mode analysis, the control loop with the proposed pulse wide modulation plus phase-shift modulation scheme was developed. Comparisons of the switch conduction loss and the core loss in the series inductor for the previous modulation schemes and the proposed modulation scheme were carried out. The results show that lower power losses occur with the proposed scheme. The experimental results verify the theoretical analysis and effectiveness of the proposed modulation scheme on loss reduction. [ABSTRACT FROM PUBLISHER]

The objective of this paper is to propose a feedforward delta modulation (FDM) control for switching-mode power converters. The operation principle and mathematical derivation for both the conventional delta modulation (CDM) and the FDM are presented. The proposed FDM uses the control signal to generate the variable integrating slope to obtain better control ability. By comparing to the CDM, the proposed FDM can improve the performance of the dc–ac inverter. The advantages include the following features: 1) wider switching frequency range with smaller electromagnetic interference; 2) larger fundamental component with less harmonics; 3) higher duty-ratio linearity; and 4) elimination of asymmetrical operation. In addition, the proposed FDM can be applied to the dc–dc converter, which cannot be done by using the CDM. It can achieve the fast transient response with voltage-mode control. The FDM controller design strategy for the dc–dc converter is given in this paper, followed by a design example. Finally, experimental results are shown to verify the performance of the proposed FDM for both the dc–dc inverter and the dc–dc converter. [ABSTRACT FROM PUBLISHER]