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This paper proposes a new class of topologies of single-stage high-frequency ac-link power converters, which is capable of providing both voltage step up/down within a wide frequency and voltage ranges. The proposed family, which supports bidirectional power flow, can interface various single/multi-port dc and/or single/multi-phase ac systems to provide dc–dc, dc–ac, ac–dc, or ac–ac power conversion. In this family of converter, which offers a very modular structure, a small inductor that forms the link exchanges power entirely or partially between the source and load. The proposed family can function in buck, boost, and/or buck–boost modes of operation, and a combination of these modes of operation is also feasible. In comparison to the parallel inductive four-quadrant link converters, the proposed family features a significantly reduced link peak current, reduced switch ratings, and reduced total number of power switches. These features enhance the efficiency, reduce the total cost, and increase the power density of the system. In order to further improve the overall efficiency of the system, minimize the current/voltage stress over all utilized semiconductor devices, and lower electromagnetic interference (EMI), a small capacitor is placed in parallel with the link inductor to realize soft-switching operation for the proposed configurations. Moreover, the proposed converters have the potential to incorporate a lightweight single-phase high-frequency transformer for electrical isolation. The proposed circuit topologies prevent reverse recovery issues and eliminate losses corresponding to body diodes of power switching devices via utilizing power switches in conjunction with external fast recovery diodes. The proposed family offers a very high level of reliability owing to its immunity from short circuit of input and output terminals and open circuit of the link inductor, which may occur in other power converters due to commutation problem resulting from a short deadtime or an overlap time between switches, unwanted control command, delay in electronic circuits, or EMI noise's misgating on or off, in addition to the absence of electrolytic capacitors in the power circuit. A control approach is also developed to regulate input and output currents in one stage of power conversion. A detailed theoretical analysis, operation, design methodology, and control strategy of the proposed family are provided in this paper, and the effectiveness and performance of the proposed converter family are verified via simulation results and experimentally. [ABSTRACT FROM AUTHOR]

In this paper, a new class of bidirectional partial-resonance power converters is presented. The proposed family can be configured to interface single- or multi-port dc, single- or multi-phase ac systems at input-side and/or output-side. The proposed family offers a very modular structure, which can lead to cost reduction from a common designed module. In this converter, which accomplishes power conversion in a single stage, a small inductor placed in series with the input and output switch-bridges forms the link. This small link inductor is responsible for transferring power between different ports of the system. The proposed topologies can operate in buck, boost, and buck–boost modes of operation to step up and/or step down the voltage. In buck–boost mode of operation, the converter is controlled such that the power is entirely transferred through the link inductor; whereas, in buck or boost modes of operation only a fraction of the power is transferred through the link inductor, and the remaining power is directly transferred from input phases to the output phases. Galvanic isolation, which is typically a prominent factor contributing to power density of a converter, can be provided by means of a compact and lightweight single-phase high-frequency transformer added to the link. In comparison with earlier generations of partial-resonance inductive-link power converters, in the proposed converter, the level of link peak current and consequently power-loss, as well as voltage and current stress of switches are dramatically decreased. A very small film capacitor can be placed in parallel with the link inductor to facilitate zero-voltage-switching (ZVS) operation for all the switches/diodes. Apart from increasing the overall efficiency, minimized dv/dt stress and improvement in power density are achieved by adding the link capacitor. The proposed converter employs four-quadrant switches, i.e., bidirectional-conducting bidirectional-blocking switches, and charges the link inductor in both positive and negative directions in each cycle. In view of this, better utilization of the link inductor and lower total harmonic distortion (THD) are offered. Furthermore, two distinct switching algorithms are developed for the proposed family of converters. In this paper, the detailed behavior of the proposed family is investigated analytically, and simulation and experimental results are presented to evaluate the performance and effectiveness of the proposed converter. A low-power proof-of-concept prototype with input voltage of 59 V/161 V, load voltage of 178 V/73.5 V, maximum switching frequency of 4.9 kHz/3.65 kHz at 215 W/450 W in a step-up/step-down operation is considered for the experimental verification. [ABSTRACT FROM AUTHOR]

In this paper, a new structure for a nonisolated boost dc–dc converter is proposed. The proposed converter generates higher voltage gain than some conventional nonisolated boost dc–dc converters. In this paper, the voltage and current equations of the elements and voltage gain in continuous conduction mode and discontinuous conduction mode are extracted. Then, the critical inductance converter is extracted and the current stresses in the switches are calculated. To achieve high voltage gain, a generalized structure based on the proposed structure generates for dc–dc converters. Meanwhile, the root mean square current relations of devices are obtained for an extended structure. Finally, the results of PSCAD/EMTDC software and laboratory prototype are used to reconfirm theoretical concept. [ABSTRACT FROM AUTHOR]

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

In this paper, two structures are proposed for the switched-inductor quasi-Z-source inverter. In the proposed structures to extend the voltage gain of inverter, two new switched-inductor structures are used. In the proposed structures, voltage across the capacitors in the Z-source network and in the switched-inductor is symmetric and small. The other advantage of proposed inverters is known as achieving higher voltage gain per smaller duty cycle ratio (of shoot-through). Compared with a conventional continuous input current switched-inductor quasi-Z-source inverter at the same gain voltage, there is less of a ripple of input current in the proposed inverters. In this paper, at first the both the conventional and the proposed switched-inductor Z-source inventers are thoroughly investigated to find out their governing relations. Then, the proposed Z-source inverters are compared with the conventional ones by simulating them to assess their performance efficiency. Next, applying the simple boost pulse width modulation the simulation is carried out with PSCAD/EMTDC software. After that, to evaluate the obtained results, the prototypes of the proposed inverters with 48 Vdc input voltage are used. [ABSTRACT FROM PUBLISHER]

This paper presents a new single-phase ac–dc–ac three-level three-leg converter composed of three coupled-inductors and six active switches. The system model, operation principles, and a control strategy are presented and discussed. Additionally, a space-vector pulsewidth modulation technique is developed to double the effective frequency of the grid and load voltages and to reduce the switching losses. The proposed converter is compared to other similar converters in terms of switch count, harmonic distortion, and power losses. The results show that the proposed topology has improved power quality and uses fewer switches and gate drive circuits. These characteristics can potentially reduce the costs and the complexity of the system. In addition, the proposed converter eliminates the requirement for dead time to prevent short circuit of the dc-link. In order to validate the theoretical analysis, simulated and experimental results are presented and discussed. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) systems having rechargeable batteries are prone to be complex and costly because multiple converters are necessary to individually regulate a load, PV panel, and battery. This paper proposes novel nonisolated multiport converters (MPCs) integrating a bidirectional pulsewidth modulation (PWM) converter and phase-shift-switched capacitor converter (PS-SCC) for standalone PV systems. A PWM converter and PS-SCC are integrated by reducing the total switch count, realizing the simplified system and circuit. In the proposed MPCs, two control freedoms of duty cycle and phase shift angle are manipulated to individually regulate the load, PV panel, and/or battery. The detailed operation analysis was performed to mathematically derive gain characteristics and zero voltage switching operation boundaries. For the battery discharging mode, in which the PV panel is not available and the MPC behaves as a single-input–single-output converter with two control freedoms available, the optimized control scheme achieving the lowest rms current is also proposed to maximize power conversion efficiencies. Various kinds of experimental verification tests using a 200-W prototype were performed to verify the theoretical analysis and to demonstrate the performance of the proposed MPC. [ABSTRACT FROM AUTHOR]

A novel PWM full bridge (FB) dc–dc converter for large power industrial applications is proposed in this paper. The soft switching mode of the primary switches can be varied under different input and output conditions to achieve optimum system efficiency. In the zero-voltage and zero-current switching (ZVZCS) mode, the turn-on and turn-off switching loss can be optimized because the soft switching conditions of the turn-on and turn-off instants are well decoupled. In the zero-voltage switching (ZVS) mode, the turn-off switching loss can also be optimized because there is no requirement for light load operation in this mode. Four mosfets with ultra-low on-state resistance are used, thus, the added conduction loss is small. The auxiliary mosfets with high switching frequency are turned on with zero-current and off with zero-voltage, hence, the added switching loss can also be neglected. Furthermore, some drawbacks of the conventional ZVS and ZVZCS converters, e.g., narrow ZVS load range, high primary circulating current, incomplete reset of the primary current, and unreasonable VA rating of the added components, have been well solved. The operation principles and soft switching characteristics are discussed. Experimental results from an 18-kW prototype are provided to verify the proposed converter. [ABSTRACT FROM AUTHOR]

In this paper, a generalized switching modification method is proposed to reduce the root-mean-square (rms) current flowing into a dc-link capacitor in a dc–dc–ac structure consisting of a boost converter and a three-phase inverter. To analyze the current flowing into the capacitor, we analyze the currents at the respective converter and inverter sides. Based on this analysis, we derive an analytical method to find the modification time between the converter and inverter pulsewidth modulation (PWM) carriers through a Fourier series and approximation to facilitate real-time implementation. Real-time implementation of the modification time calculated by the derived method is described. To verify the validity of the proposed method, experimental results are presented based on a 1-kVA dc–dc–ac prototype. The proposed method has a better capacitor rms current reduction performance than the conventional method in various inverter power factors and PWM strategies. Especially, it has an excellent performance in mid-power factor level (0.95–0.1). [ABSTRACT FROM AUTHOR]

This paper proposed a new half-bridge (HB) LLC resonant converter family with pulse-width modulated (PWM) auxiliary switch (sLLC converter) for hold-up mode operation. The proposed sLLC converters could operate with synchronous rectifier, which is suitable for low-output voltage applications. In the proposed converters, an auxiliary switch is added at the primary side to provide charging path for the series resonant inductor. For nominal 400-V input, sLLC achieves same performance as conventional LLC converter, and all the good features such as soft switching are naturally retained. For slight input voltage fluctuation, frequency modulation is used to regulate the output voltage. When the input voltage reduces further, HB switches will operate at constant minimum frequency, and the auxiliary switch will operate in the PWM mode to energize the resonant inductor with the bus voltage directly during hold-up period. Thus, the converter achieves higher voltage gain, and the output voltage can be maintained at desired level. To verify the effectiveness of the proposed sLLC converter, operational principle and equivalent circuits will be carefully explained and analyzed in this paper. A 300-W prototype is built for 250–400-V input 12-V output application. [ABSTRACT FROM AUTHOR]

In this paper, a new soft switching flyback dc–dc converter with a simple zero-voltage and zero-current switching (ZVZCS) cell is proposed. The auxiliary resonant cell consists of one switch, one diode, one inductor, and two capacitors. It provides ZVZCS not only for the main switch but also for the auxiliary switch at both turn-on and turn-off times. In addition, all the auxiliary diodes and body diodes of the switches operate under full ZVZCS except the output diode which turns off only with zero current switching. This soft switching technique makes the proposed converter have less switching losses which leads the converter to operate in higher frequencies and efficiency. Another outstanding feature of the proposed converter is using the auxiliary resonant cell out of the main power path to have lower voltage stress on the switches. In this paper, pulse width modulation (PWM) is employed to control the main switch. A detailed mode analysis of the proposed converter operation is presented along with design procedure. Finally, the accuracy performance of the converter is verified through a 60 W experimental prototype results. [ABSTRACT FROM AUTHOR]

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]

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 proposed a novel family of pulsewidth modulation (PWM) strategies for single-phase quasi-switched boost inverter (qSBI). By combining shoot-through (ST) mode in the inverter's switches and the turning-on state of an additional switch, the qSBI produced a high voltage gain without adding any passive components. Compared to the conventional PWM strategy for the same input and output voltage gain, the introduced PWM strategies for qSBI could reduce voltage stress across semiconductors and capacitor with the following additional merits: having smaller high-frequency inductor current and capacitor voltage ripples, using high modulation index with low ST duty cycle, and having higher efficiency. Circuit analysis, operating theories, and simulation results of the single-phase qSBI with the introduced PWM5 strategy are shown. A 500-W laboratory prototype was constructed and the effectiveness of the introduced PWM strategy was validated. The qSBI with the proposed PWM strategies is suitable for applications where the required voltage gain lies between 2 and 3. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) systems containing a rechargeable battery as an energy buffer require multiple dc–dc converters for PV panel control and battery regulation, and hence, they are prone to be complex and costly. To simplify the system by reducing the number of converters, this paper proposes the nonisolated switched capacitor converter (SCC)-based multiport converter (SC-MPC) for standalone PV systems. The proposed SC-MPC can be derived by integrating a bidirectional pulsewidth modulation (PWM) converter, series-resonant converter (SRC), and an SCC with sharing switches. PWM and pulse frequency modulation (PFM) controls are employed for the PWM converter and SRC, respectively, to regulate either a battery voltage, output voltage, or input power from a PV panel, depending on power balance among the input, battery, and load. The 150-W prototype was built for an experimental verification, and the results demonstrated the output voltage could be regulated independently on the battery voltage or input port of PV panels. [ABSTRACT FROM AUTHOR]

High step-down voltage conversion is necessary to bridge the voltage gap between main power converters and low-voltage auxiliary electronics in power conversion systems. Switched capacitor converters (SCCs) are an attractive candidate as a high step-down converter, but their poor voltage regulation capability may limit their applications. Pulsewidth modulation (PWM) SCCs with adjustable high step-down voltage conversion are proposed in this paper. The proposed PWM SCCs can be derived from traditional SCCs by replacing an energy transfer capacitor with a switched-capacitor-inductor (SCL) cell that comprises inductors, capacitors, and diodes to realize PWM-controllable voltage conversion. The voltage step-down ratio of the proposed PWM SCCs is not only PWM controllable but also adjustable with structures of SCCs and SCL cells. Two representative PWM SCCs were taken as examples to perform the operational analysis. The prototypes of both representative PWM SCCs were built and tested to demonstrate the proposed concept. [ABSTRACT FROM AUTHOR]

In this paper, a three-level quasi-switched boost T-type inverter (3L qSBT2I) is proposed. A new pulse-width modulated (PWM) control method is presented to reduce the inductor current ripple of the qSBT2 I. In the introduced PWM technique, the shoot-through duty cycle is maintained constant to keep the modulation index as high as possible. Then, the only control parameters of the qSBT2I are the duty cycles of the two additional switches. By controlling the duty cycles of the two additional switches, the voltage gain of the proposed qSBT2 I can be improved to a value larger than that of the conventional 3L impedance source inverters. The steady-state analysis, operating principles, and comparisons with the impedance source-based 3L inverters are presented. A 1-kW prototype is constructed to verify the operating principle of the 3L qSBT2I. An indirect dc-link voltage regulator and a capacitor voltage-balance controller are applied to the proposed qSBT2I. Simulation and experimental results are presented. [ABSTRACT FROM AUTHOR]

In order to incorporate the advantage of the $V^{2}$ control scheme and the benefits of digital implementation, this paper proposes a digital $V^{2}$ control with hybrid capacitor current ramp compensation, which includes the estimated output capacitor current ramp and the external ramp. Since capacitor current responds to the load change immediately, the proposed method has faster transient response than either digital inductor current compensation or external ramp compensation. The proposed estimator does not require high sampling rate and avoids the current ramp distortion due to the parasitic resistance and inductance. The small-signal model is derived by describing function to understand the dynamic characteristics of the proposed control scheme. The model provides design criteria of the current feedback gain and the external ramp slope. The effectiveness of the proposed control architecture and the current ramp estimator is verified by simulation and experimental results. Compared with the benchmark, the proposed control has 70% reduction on settling time and 20% reduction on undershoot deviation. [ABSTRACT FROM AUTHOR]

Single-stage power-factor-corrected (S2PFC) power supplies usually suffer from high voltage stress, due to lack of control on the intermediate bus capacitor voltage. In the past, analysis of such voltage stress was mostly based on steady-state condition without providing sufficient explanation during the transient circuit operation. This paper revisits the problem at circuit level and reports that the root cause is due to the inherent negative current feedback property of the output inductor or the transformer operating in continuous conduction mode (CCM). Based on the finding, this paper further proposes a new approach to reducing the voltage stress by adding an auxiliary circuit branch to existing S2PFC converters. The additional circuit branch limits the effect of negative current feedback by suppressing the change of output current slope due to change of load. This assists the pulsewidth modulation controller to track the change of load better such that the bus capacitor voltage range is reduced through duty cycle control. The auxiliary circuit branch also reduces reverse-recovery-related losses of the converter under CCM operation. A laboratory prototype using the popular boost PFC converter combined flyback dc/dc converter was built and tested to confirm the analysis and effectiveness of the approach. [ABSTRACT FROM AUTHOR]

Soft switching pulse-width modulation (PWM) dc–dc full-bridge converter with controlled rectifier on the secondary side of the high-frequency power transformer is presented in this paper. An active secondary switch, including new nondissipative passive energy recovery turn-off snubber on the secondary side and modified PWM control algorithm, provide conditions for zero-voltage and zero-current turn-on and zero-current turn-off of IGBT transistors on the primary side of the high-frequency dc–dc converter. The simple passive energy recovery snubber ensures also zero-voltage turn-off of the transistor on the secondary side of the power transformer. The principle of operation is explained and analyzed and consequently verified on a 2 kW, 50 kHz laboratory model of the converter. [ABSTRACT FROM PUBLISHER]

This paper extends the trans-Z-source concept to ac–ac power conversion and proposes a novel single-phase trans-Z-source ac–ac converter. The proposed converter retains the advantages of its existing Z-source/quasi-Z-source counterparts in which the output voltage can be boosted and in-phase with the input voltage or bucked/boosted and out-of-phase with the input voltage. Meanwhile, a coupled inductor is introduced into the proposed converter, and the turns ratio of the coupled inductor become another control variable beside the duty cycle to obtain extreme voltage gain. Importantly, the input voltage and output voltage share the same ground, and the input current could be continuous, which is a benefit for reducing input current harmonics. Most important of all, the safe-commutation strategy for the proposed converter is deep developed, and analytic expression between the switches state and loop circuit voltage/current condition is derived out. Hence, the current/voltage ripple can be avoided without a loss snubber circuit, which benefits a reduced cost and enhanced reliability. The performance analysis is discussed in consideration of parasitic resistance, and system parameter design is optimized based on theoretic calculation. A laboratory prototype is fabricated, and experiments are performed to verify the validation of the proposed converter. [ABSTRACT FROM PUBLISHER]

This paper proposes a pulse width modulation plus phase-shift (PPS) control for nonisolated high gain soft-switching bidirectional dc–dc converter (HSBDC). The phase-shift angle is used to control the direction and amount of power flow of the bidirectional dc–dc converter, while the duty cycle is used to balance the voltage between two high voltage side (HVS) capacitors. The HSBDC with PPS control has the advantages of simple control structure and symmetrical switching patterns, ensured soft-switching in both forward and backward modes at all load under wide voltage range, and reduced voltage ratings of the HVS capacitors and switches. The operation principle of the HSBDC with PPS control is analyzed in detail. Based on the analysis the passive component is designed to achieve higher efficiency. A 3-kW prototype is implemented and tested to verify the validity of the proposed method. [ABSTRACT FROM AUTHOR]

ZSVM1, ZSVM2, and ZSVM6 are three traditional space vector modulation (SVM) strategies for three-phase Z-source inverter. The shoot-through times of ZSVM1, ZSVM2, and ZSVM6 are divided into two equal parts, four equal parts, and six equal parts, respectively. Although these control strategies are easy to be implemented in program, their inductor current ripples are not optimized, causing large current ripple. This paper proposes new SVM strategies, named ZSVMD6 and ZSVMD1, for reducing inductor current ripples of Z-source inverter. The principle of volt–second balance is used in the proposed strategies to divide shoot-through times in real time. So every divided shoot-through time is not equal, and changing in real time. The divided shoot-through time can ensure that the sum of the inductor charging current ripple and discharging current ripple is zero at each time, therefore reducing the inductor current ripples. The derivation details of the proposed strategies are given. The inductor current ripples of the proposed strategies and traditional ones are compared and analyzed. Simulation and experiment results show that the inductor current ripples of the proposed strategies are much lower than that of the traditional ones, verifying the effectiveness of the proposed strategies. [ABSTRACT FROM PUBLISHER]

This paper proposes a new bidirectional direct pulse width modulation (PWM) three-phase buck-boost ac–ac converter. It requires six switches and three inductors and can provide wide range buck-boost voltage operation. It has high reliability due to no short-circuit and open-circuit risks in the converter. Therefore, it solves the commutation problem without using lossy snubber circuits, soft commutation strategies, and coupled inductors. It can be designed with metal–oxide–semiconductor field-effect transistors (MOSFETs) without their body diodes conducting, which eliminate reverse recovery issues and losses of body diodes. In addition, to reduce the ripples in input and output voltages and currents, the proposed converter can be operated with a PWM strategy-II. The PWM strategy-II is a type of interleaved PWM strategy with dead- and overlap-times operating modes. To validate the effectiveness of the proposed converter extensive analysis followed by detailed experimental results are provided. [ABSTRACT FROM PUBLISHER]

In this paper, a new zero-voltage switching and resonant core reset pulse width modulation forward converter with a simple auxiliary circuit is introduced. The proposed auxiliary circuit can be applied to both single-switch and two-switch forward converters. The main and the auxiliary mosfets of the proposed converters operate under soft switching condition independent of line and load variation. Also, due to the capability of operating at duty cycles higher than 0.5, the proposed converters can be used for wide input voltage applications. In comparison to the existing zero-voltage transition (ZVT) forward converters, this auxiliary circuit has low number of components and also does not require any additional magnetic element which has improved the power density. The proposed converter is compared with exiting ZVT forward converters in details. The converter steady-state operation is analyzed and various operating modes are explained. Also, in addition to a design example, a comprehensive design procedure is presented. The experimental results of a laboratory prototype of the converter with 85–180 V input voltage and 24 V output voltage at 150 W are provided which verify the theoretical analysis and confirm the converter operation. The overall efficiency of 93.5% is achieved for the proposed converter at full load. [ABSTRACT FROM PUBLISHER]

DC–DC converters with voltage boost capability are widely used in a large number of power conversion applications, from fraction-of-volt to tens of thousands of volts at power levels from milliwatts to megawatts. The literature has reported on various voltage-boosting techniques, in which fundamental energy storing elements (inductors and capacitors) and/or transformers in conjunction with switch(es) and diode(s) are utilized in the circuit. These techniques include switched capacitor (charge pump), voltage multiplier, switched inductor/voltage lift, magnetic coupling, and multistage/-level, and each has its own merits and demerits depending on application, in terms of cost, complexity, power density, reliability, and efficiency. To meet the growing demand for such applications, new power converter topologies that use the above voltage-boosting techniques, as well as some active and passive components, are continuously being proposed. The permutations and combinations of the various voltage-boosting techniques with additional components in a circuit allow for numerous new topologies and configurations, which are often confusing and difficult to follow. Therefore, to present a clear picture on the general law and framework of the development of next-generation step-up dc–dc converters, this paper aims to comprehensively review and classify various step-up dc–dc converters based on their characteristics and voltage-boosting techniques. In addition, the advantages and disadvantages of these voltage-boosting techniques and associated converters are discussed in detail. Finally, broad applications of dc–dc converters are presented and summarized with comparative study of different voltage-boosting techniques. [ABSTRACT FROM AUTHOR]

Power systems for exploration rovers tend to be complex as three separate converters are necessary; in addition to a main dc–dc converter and cell equalizer for rechargeable energy storage cells, an equalizer for photovoltaic (PV) modules is desirably equipped in order to preclude negative impacts of partial shading. This paper proposes the pulse width modulation (PWM) converter integrating voltage equalizers for PV modules and energy storage cells. The proposed integrated converter comprises a switched capacitor converter, PWM buck converter, and series-resonant voltage multiplier that perform PV equalization, power conversion from the PV modules to the load, and cell equalization, respectively. Three converters can be integrated into a single unit with reducing the total switch counts, achieving not only system-level but also circuit-level simplifications. The derivation procedure of the integrated converter is explained, followed by the operation analysis. Experimental tests were performed using series-connected supercapacitor (SC) modules and solar array simulators to emulate a partial shading condition. With the integrated converter, the extractable maximum power from the PV modules significantly increased while voltage imbalance of SC modules was adequately eliminated, demonstrating the integrated performance of the proposed converter. [ABSTRACT FROM AUTHOR]

Dynamic voltage restorer (DVR) technology has become a mature power quality product. In high-power applications, DVR using a multilevel converter is commonly used. However, DVR using a multilevel direct pulse width modulation (PWM) ac–ac converter has not been well studied. This paper presents a new DVR topology using a cascaded multilevel direct PWM ac–ac converter. In the proposed scheme, the unit cell of the multilevel converter consists of a single-phase PWM ac-ac converter using switching cell structure with coupled inductors. Therefore, the multilevel converter can be short- and open-circuited without damaging the switching devices. Neither lossy RC snubber nor a dedicated soft commutation strategy is required in the proposed DVR. This improves the reliability of the DVR system. The output voltage levels of the multilevel converter increase with the number of cascaded unit cells, and a high ac output voltage is obtained by using low-voltage-rating switching devices. Furthermore, a phase-shifted PWM technique is applied to significantly reduce the size of the output filter inductor. A 1-kW prototype of single-phase DVR is developed, and its performance is experimentally verified. Finally, the simulation results are shown for a three-phase DVR system. [ABSTRACT FROM AUTHOR]

The positive output elementary superlift-Luo converter (POESLLC) is a type of dc/dc converter. This dc/dc converter has an attractive advantage of a high voltage transfer gain as compared with other conventional dc/dc converters. Because of the voltage and load variations and also switching operation, the dynamic and static performances of the POESLLC are nonlinear and time varying. In order to achieve an excellent performance, a nonlinear controller is required. In this paper, a robust and fast response controller for voltage regulation of a POESLLC is presented. A proportional integral and pulse width modulation sliding mode controller are combined to control a third-order POESLLC. The proposed controller can be applied in the continuous conduction mode. Some simulations and experimental results are presented to show the effectiveness of the developed controller in different operating conditions. Furthermore, it will be shown that the developed controller is successful in suppressing the steady-state error of the output voltage of the POESLLC as well as the number of reduction of sensors. [ABSTRACT FROM PUBLISHER]

A new soft-switching pulse-width-modulated (PWM) full-bridge converter is proposed in this paper. The proposed converter has zero voltage switching (ZVS) in all its switches with fewer conduction losses than other ZVS-PWM full-bridge converters, due to a novel auxiliary circuit scheme. In this paper, the operation of the new converter is explained and analyzed, a design procedure is presented and demonstrated with an example, and experimental results that confirm the feasibility of the converter are also presented. [ABSTRACT FROM AUTHOR]

The Z-source inverter (ZSI) employs an LC impedance network between the main inverter bridge and the power source. The unique feature of the ZSI is that it can operate either in buck or boost mode with a wide range of obtainable output voltages from a given input voltage. This topology also exhibits better electromagnetic-interference noise immunity when compared to a traditional voltage-source inverter (VSI). However, the LC impedance network of ZSI significantly increases the size and cost of the power converter and can make it unsuitable for low-power applications. This paper proposes a novel topology called switched boost inverter (SBI) which exhibits similar advantages of ZSI with lower number of passive components and more active components compared to ZSI. The steady-state and small-signal analyses of SBI, along with its pulsewidth modulation (PWM) control strategies, have been discussed in this paper. This paper also presents a comparison of SBI and ZSI with the same input and output parameters. The theoretical analysis given in this paper has been validated using a laboratory prototype of SBI, and the experimental results are presented for verification. The experimental harmonic spectrum of the inverter's output voltage with the proposed PWM technique is also plotted and compared with that of a traditional VSI. All the experimental results show good correlation between theory and experiments. [ABSTRACT FROM PUBLISHER]

The main objective of this paper is to examine the operation of a fundamental buck-based three-phase single-stage ac–dc full-bridge converter. In this paper, the operation of this fundamental converter is explained and analyzed, and a procedure for the design of its key components is derived and demonstrated with an example. The performance and characteristics of the converter are shown with experimental results that have been obtained from a prototype, and general concluding remarks comparing buck-based and boost-based three-phase single-stage ac–dc full-bridge converters are made. [ABSTRACT FROM PUBLISHER]

This paper focuses on the common dc-link voltage between a three-phase diode rectifier and a modular multilevel cascade inverter based on double-star chopper cells (MMCI-DSCC) for a medium-voltage motor drive. This motor drive can be operated even when no capacitor exists on the dc link. However, a nonnegligible, but predictable, amount of switching-ripple voltage occurs on the dc link. This paper achieves modeling and analysis of the switching-ripple voltage, thus making it possible to design a small-sized dc passive filter consisting of series connection of a film capacitor and a damping resistor. A 400-V, 15-kW down scaled system is used to confirm the effectiveness of the analysis and the dc filter. Experimental results show that the switching-ripple voltage can be attenuated satisfactorily by the dc filter, and that the power loss dissipated in the damping resistor is negligible, compared to the rated power of 15 kW. [ABSTRACT FROM AUTHOR]

This paper proposes a pulse-width modulation three-level converter with reduced filter size using two transformers. The proposed converter has many advantages. All switches sustain only the half of the input voltage and since the secondary rectified voltage is a three-level waveform, the output filter inductor can be reduced. Also, because of the power sharing of transformer and reduced output inductor, high efficiency can be obtained. The operational principle, analysis, and design considerations of the proposed converter are presented in this paper. The validity of this study is confirmed by the experimental results from a prototype with 600 W, 500-600 V input, and 60 V output. [ABSTRACT FROM AUTHOR]

This paper proposes a single-phase, single-stage buck–boost inverter for photovoltaic (PV) systems. The presented topology has one common terminal in input and output ports which eliminates common mode leakage current problem in the grid-connected PV applications. Although it uses four switches, its operation is bimodal and only two switches receive high-frequency pulse width modulation signals in each mode. Its principle of operation is described in detail with the help of equivalent circuits. Its dynamic model is presented, based on which a bimodal controller is designed. Experimental results, in stand-alone and grid-connected mode, obtained with a 300-W laboratory prototype are presented to validate its performance. [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]

This paper introduces a combination of two proposed efficiency improvement techniques for a microinverter with current mode control zero-voltage switching output stages. The first technique is dynamic dead-time optimization wherein pulse width modulation dead times are dynamically adjusted as a function of load current. The second method is advanced phase skipping control which maximizes inverter efficiency by controlling power on individual phases depending on the available input power from the photovoltaic source. Neither of the techniques requires any additional circuit components and both can be easily implemented in digital controller firmware. The two techniques were designed and implemented in a 400-W three-phase microinverter prototype. The experimental results validate the theoretical analysis of these techniques and demonstrate that a significant efficiency improvement can be achieved by combining the two proposed control techniques. [ABSTRACT FROM AUTHOR]

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]

This paper proposes a new type of ac–ac converter which can operate as traditional noninverting buck and boost converters, and inverting buck–boost converter as well. The proposed converter uses six unidirectional current flowing and bidirectional voltage blocking switches, implemented by six reverse blocking insulated-gate bipolar transistors (IGBTs) or series mosfet–diode pairs, two input and output filter capacitors, and one inductor. It has no shoot-through problem of voltage source (or capacitor) even when all switches are turned-on, and therefore, pulsewidth modulation dead-times are not needed resulting in high-quality waveforms, and solves the commutation problem without using bulky and lossy RC snubbers or dedicated soft-commutation strategies. It has smaller switching losses because only two switches out of six are switched at high frequency during each half-cycle of input voltage, and it can use power MOSFETs as body diode never conducts, making it immune from mosfet failure risk which otherwise may occur due to poor reverse recovery problem of body diode. The noninverting buck–boost mode of the proposed converter can be used in applications with both step-up and step-down demand, while the inverting buck–boost mode can also be used in its application as dynamic voltage restorer. Detailed analysis of the proposed converter is given, and experimental results are also provided. [ABSTRACT FROM AUTHOR]

A zero-voltage switching (ZVS) grid-connected full-bridge inverter and its modulation schemes are investigated. A novel sinusoidal pulse width modulation scheme for the ZVS full-bridge inverter (ZVS SPWM) is proposed in this paper. The ZVS SPWM is evolved from the double-frequency SPWM by adding gate drive to the auxiliary switch. The ZVS condition is analyzed and the circulation loss of the resonant branch is optimized by adjusting the energy storage in the resonant inductor. The reverse recovery of the body-diode of MOSFET is relieved and ZVS is realized for both main and auxiliary switches. The filter inductors are significantly reduced with higher switching frequency. The design guideline of resonant parameters and the implementation of ZVS SPWM in DSP controller are introduced. The ZVS SPWM scheme is verified on a 3-kW inverter prototype. According to the experimental result, peak efficiency as 98.8% is achieved. [ABSTRACT FROM AUTHOR]

Soft-start strategy is very important for boost converters to guarantee the stability of the output voltage. However, previous methods may cause large initial inrush current and long output voltage settling time. In this paper, a variable ramp-slope with predefined voltage (VRSPV) soft-start strategy is proposed. As a result, one branch of the initial inrush current is successfully eliminated and the output settling time of the boost converter is shortened by using the variable slope soft-start voltage. Also, an adaptive inrush current suppressing (AICS) technique is designed. The series resistance of the output capacitor is adaptively regulated by AICS technique to further suppress the initial inrush current. Finally, the VRSPV strategy and AICS technique are combined and implemented in a voltage-mode boost converter. The measurement results show that the peak initial inrush current and settling time are decreased by 60% and 40%, respectively. The output voltage of the boost converter increases smoothly during the soft-start period and finally achieves stability. The proposed method of combining VRSPV strategy and AICS technique is very suitable to be integrated on a chip to save the printed circuit board area and cost. [ABSTRACT FROM AUTHOR]

It is known that the ripple-based control of a switching dc–dc converter benefits from a faster transient response than a conventional pulse width modulation (PWM) control switching dc–dc converter. However, ripple-based control switching dc–dc converters may suffer from fast-scale oscillation. In order to achieve fast transient response and ensure the stable operation of a switching dc–dc converter over a wide load range, based on a conventional pulse train (PT) control technique, a peak capacitor current PT (PCC-PT) control technique is proposed in this paper. With a buck converter as an example, the operating modes, steady-state performance, and transient respond performance of a PCC-PT controlled buck converter are presented and assessed. To eliminate fast-scale oscillation, circuit and control parameter design considerations are given. An accurate discrete iteration model of a PCC-PT controlled buck converter is established, based on which the effects of circuit parameters on the stability of the converter operating in a discontinuous current mode (DCM), mixed DCM-continuous conduction mode (CCM), and CCM are studied. Simulation and experimental results are presented to verify the analysis results. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel single-phase ac–ac Z-source converter based on the Γ-structure. The proposed converter uses a coupled transformer to produce the required gain. The obtained gain can be tuned by varying the turn ratio $\gamma _\Gamma$ of the transformer within the narrow range of $1 < \gamma _\Gamma < 2$. Also, the gain factor increases with decrease of the transformer turns ratio, $\gamma _\Gamma$ . Small transformer turn ratio results in more practical topology in some voltage gains. It makes the transformer design easier and reduces construction cost. Also, in the proposed topology, the input and output voltages share the same ground. In order to avoid voltage and current spikes on the switches, a commutation strategy is proposed and safe commutation is achieved without using a snubber circuit. The operating principles and steady-state analyses are presented to verify the operational concept of the proposed topology. Also, experimental results are given to verify the validation of the proposed converter. [ABSTRACT FROM AUTHOR]

In this paper, a family of three-phase direct pulse-width modulated (PWM) ac–ac converters consisting of buck, boost, and buck–boost converters is proposed. The proposed converters have no commutation problem even if all of the switches are turned on or off simultaneously. They do not use lossy snubbers and do not sense the voltage polarity for commutation, and produce high-quality output voltage waveforms. The proposed converters allow the use of power MOSFETs and fast recovery freewheeling diodes independently. The use of power MOSFETs as active switches and freewheeling diodes with extremely fast recovery features lower the switching losses and enable us to reduce the volume of passive components by increasing switching frequency. The input (or output) filter inductor experiences twice of the converter switching frequency and thus can be designed with minimum size. To increase power density of the proposed converters, a three-phase three-limb coupled inductor is proposed. Three-phase coupled inductor integrates three separate coupled inductors of the proposed converters in one three-limb core. In comparison with separate coupled inductors, the three-phase coupled inductor has a smaller size with large current-handling capability. Experimental results obtained for the boost-type converter show the robustness of the proposed three-phase ac–ac converters. [ABSTRACT FROM AUTHOR]

As electrolytic capacitor is apt to fail in power circuits, it is very important to identify its electrical parameters, mainly the equivalent series resistance (ESR) and capacitance (C). A noninvasive online identification method of capacitor's ESR and C for continuous-conduction-mode (CCM) buck converter is proposed in this paper. Based on the ac component of capacitor voltage, the calculation model is founded. By sampling the pulse width modulation signal and output voltage, the method needs no current sensor and is effective for the CCM buck converter operating at different conditions. Implementation of the identification system is presented. The tests are carried out for different aged capacitors and ambient temperatures. The experimental results validate the effectiveness of the method. [ABSTRACT FROM AUTHOR]

The three-level boost power factor correction (PFC) converter has advantages of lower inductor current ripple and lower switch withstanding voltage compared with the boost PFC converter. Interleaved pulsewidth modulation had been used in the multiphase boost PFC converter. In the literature, interleaved current sensorless control (ICSC) for the multiphase boost PFC converters had been proposed. In this paper, the behavior of the three-level boost PFC converter is first analyzed. The results show that three-level converter has the same average equation as the interleaved boost PFC converter. Then, ICSC is modified for the three-level boost PFC converter with considering the voltage imbalance and the zero-crossing current distortion. The proposed modified ICSC (MICSC) is implemented in a field-programmable gate array board. Simulation results and experimental results are also provided to validate the proposed MICSC. [ABSTRACT FROM PUBLISHER]

In this paper, an analysis and calculation of the dc-link current and voltage ripples are presented for a three-phase inverter with unbalanced load. A comparison of the dc-link average and root-mean-square (rms) currents between considering and ignoring high frequency harmonics of the output current is drawn. It is shown that high frequency harmonic currents have little effect on the dc-link current, and therefore, they can be ignored. Based on the symmetrical components method, the dc-link average and harmonic rms currents are derived, and the dc-link voltage ripple is compared between the balanced and unbalanced loads. It can be found that the dc-link current and voltage ripples consist of not only high frequency harmonics but also the double fundamental frequency harmonic, and the voltage ripple is independent of the positive-sequence component and determined by the negative-sequence component, under the unbalanced load. Experimental results are shown to verify the accuracy of the theoretical analysis. [ABSTRACT FROM AUTHOR]