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This paper introduces a unified modeling methodology to describe and explore the loss mechanism of resonant switched-capacitor converter (SCC) operating in a self-commutation zero current switching (ZCS) mode. The conventional equivalent resistance concept, which assumes a single conduction path of the resonant current, is generalized and extended to model the losses in cases where the resonant current is divided across several conduction loops. The new modeling concept is compatible to describe the losses resulting from resistive elements as well as P–N junction devices, offering a solution for the equivalent resistance. Verification of the concept has been carried out by simulations and experiments on 3–30 W unity, double gain and multiphase Fibonacci resonant SCC with free-wheeling ZCS. A very good agreement is obtained between the theoretical calculations, simulations, and experimental results, well demonstrating model capability to identify the loss contributors in each conduction path. [ABSTRACT FROM AUTHOR]

This paper presents an enhanced space vector modulation (SVM) method to drive matrix converters (MCs) with zero common-mode voltage by using the rotating vectors, which are not used in the traditional SVM for MCs. The reference output voltage vector is generated by a combination of the closer rotating vectors in order to minimize the output distortion. Explicit equations are used to develop the switching patterns so that the proposed SVM method can achieve full control of the output voltage vector and input current phase angle with good performance of the input/output current waveforms. Together with the theoretical analysis, the experimental results are provided to validate the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a power converter and its control circuit for high-frequency-fed ac to dc conversion. Based on the resonant technique, the input current is shaped to be sinusoidal and is forced to follow the high-frequency sinusoidal input voltage so as to achieve unity power factor. With the proper selection of the characteristic impedance of the resonant tank, the converter is able to perform the function of a buck, boost, or buck-boost converter. The initial condition of the resonant tank is used to control the output voltage gain of the converter. Since all the switches are operated at the fundamental frequency of the input ac source, the switching loss of the converter is small. A control scheme is also proposed for the converter. A proof-of-concept prototype operating at 400 kHz is constructed and its performance is experimentally measured. Results show that the proposed converter operates as theoretically anticipated. [ABSTRACT FROM AUTHOR]

The control and stabilization of resonant converters are essential problems in power electronics. The conventional controller design and stability analysis for these converters are based on the linearized averaged model. Nevertheless, the state variables in resonant converters have large ac variations and the validity of the linearized average model is violated. Hence, using large signal and nonaveraged models are necessary for controller design and stability analysis. In this paper, a new hybrid controller is presented that is applicable to dc-dc series resonant converters and use neither averaging nor small signal approximation. The dc-dc resonant converters are inherently switched affine systems with constrained switching law. The proposed controller is based on the switched behavior of the converter and the concept of piecewise affine methodology. Moreover, it has switched inner and proportional-integral (PI) outer control loops and does not require a modulator. The large signal and closed loop stability analysis of the resonant converters is presented by a theorem. The minimum phase attribute of the control system is investigated by zero dynamic stability analysis. The proposed controller has less complexity in comparison to other suggested controllers and can be implemented using simple analog circuits. The simulation and experimental results show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Five-level active neutral-point clamped (5L-ANPC) converter is an attractive topology for high-power medium-voltage motor drives. This paper presents a capacitor voltage-balancing method for the 5L-ANPC converter, including the voltage balancing of dc-link capacitors and flying capacitors. In order to ensure that the series-connected or high-voltage switches of the 5L-ANPC converter are operated at fundamental frequency and the other switches are operated at a constant switching frequency, phase-shifted pulse width modulation is used to control this converter. The relationship between the average neutral-point current and zero-sequence voltage is investigated, and an optimum zero-sequence voltage is calculated to regulate the neutral-point potential. The voltage across the flying capacitor is also regulated by adjusting the switching duty cycles of two PWM signals, which varies the operation time of redundant switching states in each switching period. Simulation and experimental results are presented to verify the validity of this method. [ABSTRACT FROM AUTHOR]

This paper introduces a digitally controlled single-phase rectifier with power factor correction (PFC) based on a modified three-level boost converter topology. In comparison with the conventional boost-based systems, the new PFC rectifier has about three times smaller inductor and significantly lower switching losses. The improvements are achieved by replacing the output capacitor of the boost converter with a nonsymmetric active capacitive divider, with a 3:1 division ratio, and by utilizing the downstream converter stage for the capacitive divider's center-tap voltage regulation. The nonsymmetric voltage divider and applied switching sequence effectively provide four-level converter behavior using the same number of components as three-level converters. As a result, a 66% reduction of the inductor compared to the conventional boost-based PFC and a 33% compared to the standard three-level solutions operating at the same effective switching frequencies are also achieved. Experimental results obtained with a 400 W, 200 kHz, universal input voltage (85 Vrms-265 Vrms) PFC prototype demonstrate three times smaller inductor current ripple than that of the conventional boost converter allowing for the same inductor reduction. Efficiency improvements of up to a 6% are also demonstrated. [ABSTRACT FROM AUTHOR]

This paper proposes a new modulated carrier control method for an interleaved continuous conduction mode (CCM) power factor correction (PFC) boost converter. The proposed method allows precise sinusoidal line current shaping for a PFC boost converter operating in CCM. This is accomplished by simply comparing modulated carrier signal with switch current, such that inner current loop compensation design and rectified line voltage sensing are not required. The proposed control method greatly simplifies current sensing and control circuitry of multiphase converters since average current control is available by just sensing the switch current for each module. This also enables simple current balancing between parallel converters by employing modulated carrier signals with same amplitude. The principle of the control method is presented. The performance of the proposed control method is experimentally verified on a 600-W PFC converter. The measured power factor remains above 94.9% down to 20% of a full load for 110-Vrms and 220-Vrms line voltages. The line current harmonics also meet the IEC61000-3-2 Class D standard. [ABSTRACT FROM AUTHOR]

High voltage gain dc-dc converters are required in many industrial applications such as photovoltaic and fuel cell energy systems, high-intensity discharge lamp (HID), dc back-up energy systems, and electric vehicles. This paper presents a novel input-parallel output-series boost converter with dual coupled inductors and a voltage multiplier module. On the one hand, the primary windings of two coupled inductors are connected in parallel to share the input current and reduce the current ripple at the input. On the other hand, the proposed converter inherits the merits of interleaved series-connected output capacitors for high voltage gain, low output voltage ripple, and low switch voltage stress. Moreover, the secondary sides of two coupled inductors are connected in series to a regenerative capacitor by a diode for extending the voltage gain and balancing the primary-parallel currents. In addition, the active switches are turned on at zero current and the reverse recovery problem of diodes is alleviated by reasonable leakage inductances of the coupled inductors. Besides, the energy of leakage inductances can be recycled. A prototype circuit rated 500-W output power is implemented in the laboratory, and the experimental results shows satisfactory agreement with the theoretical analysis. [ABSTRACT FROM AUTHOR]

V2Ic is a ripple-based control with an excellent performance for load transients and reference voltage tracking because it exhibits a feedforward of the load current and the error of the output voltage. However, if V2Ic is modulated with constant frequency, constant on-time or constant off-time, its dynamic response is hindered by delays in the response. This paper proposes a technique that synchronizes the clock of the converter to initialize the duty cycle when a worst-case load transient occurs using the current through the output capacitor to detect load transients. It is exemplified on a V2Ic control but it is applicable to most of controllers as it only acts on the modulator. [ABSTRACT FROM AUTHOR]

This paper presents the derivation and experimental verification of the closed-form subharmonic instability condition of the constant-frequency peak-current-controlled buck converter with closed voltage feedback loop. The well-known open-voltage-loop instability condition becomes a special case. The instability limits in the converter parameter space are readily obtained from the result. It is found that closing the voltage feedback loop tends to degrade the stability margin. One can clearly see the effects of all converter parameters (such as the pole, zero, and gain of the voltage-loop compensator, the equivalent series resistance of the output capacitor, the presence of a second output capacitor, and the switch turn-off delay) on the instability. [ABSTRACT FROM AUTHOR]

Historically, cascaded H-bridge, capacitor-clamped, and neutral point-clamped topologies have been used for medium- to high-voltage applications but the modular multilevel converter (M2LC) is becoming a popular alternative. However, in comparison to other topologies, control of the load current, which is inherently coupled with circulating currents, is more difficult in the M2LC topology. This paper proposes a modified M2LC topology that allows for decoupled control of circulating currents from the load current. Each arm of the modified topology comprises a plurality of half-bridge modules and one full-bridge module. The full-bridge module minimizes harmonic currents within the converter without affecting the load current. A state-space model, which is generalized per arm with an N number of half-bridge modules and one full-bridge module, is presented to accurately predict the behavior of the proposed topology. Theoretical as well as experimental results of a single-phase three-level 800-VA prototype converter are presented with a discussion to demonstrate the viability of both the proposed mathematical model and modified topology. A comparative investigation with respect to a conventional topology reveals that the proposed topology offers superior performance. [ABSTRACT FROM AUTHOR]

This paper deals with a power factor correction (PFC)-based Cuk converter-fed brushless dc motor (BLDC) drive as a cost-effective solution for low-power applications. The speed of the BLDC motor is controlled by varying the dc-bus voltage of a voltage source inverter (VSI) which uses a low frequency switching of VSI (electronic commutation of the BLDC motor) for low switching losses. A diode bridge rectifier followed by a Cuk converter working in a discontinuous conduction mode (DCM) is used for control of dc-link voltage with unity power factor at ac mains. Performance of the PFC Cuk converter is evaluated under four different operating conditions of discontinuous and continuous conduction modes (CCM) and a comparison is made to select a best suited mode of operation. The performance of the proposed system is simulated in a MATLAB/Simulink environment and a hardware prototype of the proposed drive is developed to validate its performance over a wide range of speed with unity power factor at ac mains. [ABSTRACT FROM AUTHOR]

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

This paper presents an optimal lowest-voltage-switching technique for boundary mode power factor correction (PFC) converters. The proposed approach minimizes the switching loss of the power MOSFET without additional discrete components. Optimal zero-voltage-switching or valley-switching can be achieved for universal input range. The gate driver delay can also be taken into account. A boundary mode boost PFC converter with the proposed optimal switching technique has been implemented using a 0.5-μm N-well process. Experimental results show that the proposed approach can realize optimal soft switching, and improve the efficiency of the boost PFC converter. The proposed lowest-voltage-switching technique can be applied to other resonant converters as well. [ABSTRACT FROM AUTHOR]

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

This paper introduces a novel modular multilevel series/parallel converter that allows switching modules dynamically not only in series, as in the traditional modular multilevel converter (M2C), but also in parallel. As in M2C, the semiconductor voltages do not exceed the module capacitor voltage for any module state. While the new topology is a generalization of M2C and could, therefore, be operated identically to it, the additional states provide degrees of freedom that the controller can dynamically employ to achieve several advantages. Whereas in M2C many modules are bypassed if the instantaneous converter voltage is lower than the system's peak voltage, the parallel connectivity enables these modules to contribute to the current load, thus reducing conduction losses. In addition, the parallel configuration of modules can be used for balancing the modules' state of charge (SOC). The parallelization losses are moderate or negligible, dependent on the switching rate. Since the parallel connection of capacitors can ensure balancing, it enables stable operation of a multilevel converter without the need for monitoring the module SOCs. While such economical control hardware may be appropriate for low-power systems, we also present more sophisticated control that uses the additional degrees of freedom to minimize losses. Finally, we point to further extensions of the circuit topology to multipole module connectivity that could enable additional functionality and applications. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) is attractive for medium- and high-power applications because of its high modularity, availability, and power quality. In this paper, the current ripple on the dc link of the three-phase MMC derived from the phase-shifted carrier-based pulse-width modulation scheme is analyzed. A control strategy is proposed for the current ripple elimination. Through the regulation of the phase-shifted angles of the carrier waves in the three phases of the MMC, the current ripple on the dc link of the three-phase MMC can be effectively eliminated. Simulations and experimental studies of the MMC were conducted, and the results confirm the effectiveness of the proposed current ripple elimination control. [ABSTRACT FROM AUTHOR]

In this paper, a simplified nearest level control balancing method for modular multilevel converter is presented. The proposed method neither requires individual sorting of the submodule voltages nor the redundancy of the switching states. Once the sorting of the submodules is done on the basis of the number of the submodules to be switched on, the identifications of the submodules can be carried out throughout the stages of the implementation of the this method. The proposed method also does not require the individual submodule status in the gate pulse generation stage. The gate logic in the presented method can be implemented with the help of the switching states of the voltage levels. Those simplifications and removing of the some of the stages by the proposed balancing method may ease and lead to the less processor time at the implementation level. The pictorial presentation further helps in consolidating the understanding of the different stages of the method. Rigorous simulations are carried out for open and one of the prominent closed-loop applications, i.e., modular multilevel converter-based high-voltage direct current to demonstrate the validity and effectiveness of the proposed simplified balancing method under normal and emergency conditions. [ABSTRACT FROM AUTHOR]

Modular multilevel converters have several attractive features such as a modular structure, the capability of transformer-less operation, easy scalability in terms of voltage and current, low expense for redundancy and fault tolerant operation, high availability, utilization of standard components, and excellent quality of the output waveforms. These features have increased the interest of industry and research in this topology, resulting in the development of new circuit configurations, converter models, control schemes, and modulation strategies. This paper presents a review of the latest achievements of modular multilevel converters regarding the mentioned research topics, new applications, and future trends. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) has been a subject of increasing importance for medium/high-power energy conversion systems. Over the past few years, significant research has been done to address the technical challenges associated with the operation and control of the MMC. In this paper, a general overview of the basics of operation of the MMC along with its control challenges are discussed, and a review of state-of-the-art control strategies and trends is presented. Finally, the applications of the MMC and their challenges are highlighted. [ABSTRACT FROM AUTHOR]

This paper evaluates two different concepts for the control of the modular multilevel converter (MMC). Generally aiming at medium voltage applications, the considered MMC topology has a low number of submodules, and a pulse-width modulation (PWM) scheme is applied. A model predictive control (MPC) algorithm is developed and experimentally compared to a cascaded control scheme based on conventional PI controllers, which has been proposed by Hagiwara and Akagi. Steady-state and dynamic system performance as well as computational power requirements are discussed. The basis for the comparison is a scaled converter test bench operating from 560-V dc voltage. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (M2Cs) are increasingly used in high-voltage direct current (HVDC) systems. The efficiency of M2Cs is influenced by the modulation and cell selecting methods, which determines the switching frequency and capacitor voltage ripple in the converter station. A new approach to modulation of the M2C is presented in this paper. Tolerance band methods are employed to obtain the switching instants, and also cell selection. The proposed methods overcome the modulation problem for converters with few cells on one hand and also reduce the sorting efforts for cell balancing purposes of many cells converter on the other hand. Three different algorithms are also proposed to balance the cell capacitor voltages. The evaluation is done in time-domain simulation by which the performance of each method is studied in both the steady-state and transient cases. It is observed that using tolerance band methods not only reduces the switching frequency but also allows for handling severe fault cases in a grid-connected system. Eventually, the most promising tolerance band method has been implemented and verified in a real-time digital simulator, RTDS®. The average switching frequency of 70 Hz has been achieved for the system under study, while the capacitor voltage ripple is limited to 10% of the nominal cell voltage. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) has become one of the most promising converter topologies for future high-power applications. A challenging issue of the MMC is the voltage balancing among arm capacitors. A good overall control system is also vital for the MMC, which should be based on sound mathematical model, readily adaptable for different applications, and capable of high performance. This paper presents a general control structure for MMC inverters, which is suitable for both voltage-based and energy-based control methods, and includes voltage balancing between the upper and lower arms. A new method for voltage balancing among arm capacitors, which is based on an improved pulse-width modulation, is also presented. The proposed method avoids some major disadvantages found in present voltage balancing methods, such as dependence on computation-intensive voltage sorting algorithms, extra switching actions, interference with output voltage, etc. Furthermore, all switching actions are evenly distributed among power devices. The proposed control system as a whole can serve as a promising solution for practical applications, especially when the number of submodules is fairly high. Simulation and experimental results verify the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

Hybrid multilevel converters are contemplated in an attempt to optimize the performance of voltage source converters in terms of magnitude of semiconductor losses and converter footprint, and to achieve additional features such as dc short circuit proof, which is essential for a high integrity multiterminal HVDC grid. Therefore, this paper considers an emerging hybrid cascaded converter that offers the dc side short circuit proof feature at reduced loss and footprint compared to the existing multilevel and other hybrid converters. Its operating principle, modulation, and capacitor voltage balancing strategies are described in detail. Furthermore, hybrid converter scalability to high voltage applications is investigated. The validity of the modulation and capacitor voltage strategy presented are confirmed using simulation and experimentation. The hybrid cascaded converter is extendable to a large number of cells, making it applicable to high voltage applications, and operation is independent of modulation index and power factor. On these ground, the converter is expected to be applicable for both real and reactive power applications. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (M2LCs) are typically controlled by a hierarchical control scheme, which essentially requires at least two control loops: one to control the load current and another to control circulating currents. This paper presents an M2LC with a single controller, which is based on model predictive direct current control (MPDCC) with long prediction horizons. The proposed MPDCC scheme maintains the load current within tight bounds around sinusoidal references and minimizes capacitor voltage variations and circulating currents. An internal prediction model of the M2LC is used to minimize the number of switching transitions for a given current ripple at steady state while providing a fast current response during transient conditions. A state-space model, which is generalized for an N number of modules per each arm of the M2LC, is also presented to investigate the dynamic behavior of arm currents and capacitor voltages. Simulated performance of the converter, under various operating conditions, is presented in comparison to measured performance of a single-phase, three-level 860-VA M2LC prototype to demonstrate the proposed MPDCC philosophy. [ABSTRACT FROM AUTHOR]

Switched capacitor (SC) converters are becoming quite popular for use in dc-dc power conversion. The concept of equivalent resistance in SC converters is frequently used to determine conduction losses that occur as a result of the load current. A variety of methodologies have been presented to predict the equivalent resistance in hard-switched SC converters. These works, however, did not consider the effect of stray inductance on equivalent resistance. Current power converter design practices favor higher switching frequencies, moving hard-switched SC converters into operating areas in which stray inductance affects converter performance. This paper presents an analytic equation that can be used to evaluate the effects of stray inductance on the equivalent resistance of SC converters. The concepts proposed here were verified by both digital simulation and a prototype converter. The equations presented can be used to evaluate the effects of stray inductance on SC converter performance, thereby helping designers set a maximum operating frequency to limit those effects. [ABSTRACT FROM AUTHOR]

This paper derives a circuit-level analytical model for describing the mechanism of the spurious triggering pulse in the gate-source voltage of the synchronous MOSFET (SyncFET) in the synchronous buck converter. The model takes into account not only the parasitic capacitances and inductances of the control MOSFET (CtrlFET) and the SyncFET, but also the reverse recovery characteristics of the body diode of the SyncFET. An exhaustive investigation into the impact of all these factors on the spurious triggering pulse is conducted. The spurious triggering pulse can be attributed to two factors. The first one is the positive gate voltage caused by the displacement current through the gate-drain capacitance of the SyncFET, due to the increase in the drain-source voltage. The second one is the negative source voltage caused by the voltage drop across the source inductance of the SyncFET, due to the decrease in the drain current. It is discovered that the gate impedance of the SyncFET would exert different influence on the magnitude of the spurious triggering pulse, depending on the contributions of these two factors. Experimental results affirm that variation in the magnitude of the spurious triggering pulse with each parasitic element can be correctly inferred by the proposed model. Design guidelines for enhancing spurious turn-on immunity are advanced. [ABSTRACT FROM AUTHOR]

This paper presents the design of a resonant converter with a switching frequency in the very high frequency range (30-300 MHz), a large step down ratio (ten times), and low output power (1 W). Several different inverters and rectifiers are analyzed and compared. The class E inverter and rectifier are selected based on complexity and efficiency estimates. Three different power stages are implemented; one with a large input inductor, one with a switch with small capacitances, and one with a switch with low on-resistance. The power stages are designed with the same specifications and efficiencies from 60.7-82.9% are achieved. [ABSTRACT FROM AUTHOR]

At a certain level of abstraction, power converters can be represented as linear circuits connected to diodes and controlled electronic switches. The evolutions of the electrical variables are determined by the state-dependent switchings, which complicate the mathematical modeling of controlled power converters. Differently from the complementarity models previously presented in the literature, the model proposed in this paper allows to represent as a linear complementarity system also closed-loop power converters, without requiring the a priori knowledge of the converter modes. A model construction procedure, not dependent on the specific converter topology, is presented. The discretization of the continuous-time model allows to formulate mixed linear complementarity problems for the computation of the control-to-output frequency response and the evolutions of both transient and steady-state currents and voltages. As illustrative examples, Z-source, boost, and buck dc-dc power converters under voltage-mode control and current-mode control operating both in continuous and discontinuous conduction modes are considered. [ABSTRACT FROM AUTHOR]

Based on the concept derivation, this paper proposes an improved synchronous rectifier (SR) driving strategy focusing on the quasi-resonant primary-side regulation (QR-PSR) Flyback converter, for the applications of dc-dc front-end converter and ac-dc PFC converter both, to prevent reverse energy flowing in light-load/standby mode. Three different implementation candidates are exhibited and analyzed. This proposed driving strategy is programmable for the practical design with input voltage feedforward effect and helpful for achieving the rigorous target of low power loss under light output load condition presented by the U.S. Department of Energy (DoE). Two 60 W (12 V/5 A) lab-made prototypes of synchronous rectified QR-PSR Flyback ac-dc PFC converter and dc-dc front-end converter are built up, respectively, to verify the feasibility of this proposed driving strategy. In the lab-made prototype of ac-dc PFC converter, it improves the overall conversion efficiency more than 3% in light-load mode; in the lab-made prototype of dc-dc front-end converter, it saves the light load power loss up to 0.5 W, especially with 110 Vac input. Reliable operation is achieved when the proposed SR driving strategy is practically designed with enough margin; however, too large design margin could decrease the average conversion efficiency. [ABSTRACT FROM AUTHOR]

In this paper, a new voltage source converter for medium voltage applications is presented which can operate over a wide range of voltages (2.4-7.2 kV) without the need for connecting the power semiconductor in series. The operation of the proposed converter is studied and analyzed. In order to control the proposed converter, a space-vector modulation (SVM) strategy with redundant switching states has been proposed. SVM usually has redundant switching state anyways. What is the main point we are trying to get to? These redundant switching states help to control the output voltage and balance voltages of the flying capacitors in the proposed converter. The performance of the converter under different operating conditions is investigated in MATLAB/Simulink environment. The feasibility of the proposed converter is evaluated experimentally on a 5-kVA prototype. [ABSTRACT FROM AUTHOR]

With wide-spread application of power electronic converters in high power systems, there has been a growing interest in system reliability analysis and fault-tolerant capabilities. This paper presents a comprehensive review of conventional fault-tolerant techniques regarding power electronic converters in case of power semiconductor device failures. These techniques can be classified into four categories based on the type of hardware redundancy unit: switch-level, leg-level, module-level, and system-level. Also, various fault-tolerant methods are assessed according to cost, complexity, performance, etc. The intent of this review is to provide a detailed picture regarding the current landscape of research in power electronic fault-handling mechanisms. [ABSTRACT FROM AUTHOR]

This paper describes a complete digitally controlled dc-dc buck converter performed by field-programmable gate array (FPGA) circuitry. The voltage and current-mode control is based on a voltage control oscillator (VCO) performed measurements regarding output-voltage and inductor current, respectively. This measurement principle also uses digital-counters (digital-integrators) in order to obtain integral values for the output-voltage and inductor current. In analog current-mode control, the instantaneous inductor current-value-measurement is used for the switching action. When the VCO is used for the inductor current measurement, the integral is measured during the switching-on time set as an observation interval and the switching action occurs based on this measurement. Such a principle enables full digitalization of the voltage- and current-control loop and also the used measurement principle is capable of rejecting the switching disturbances during current and voltage measurements. All the tasks for current and voltage control were implemented within the FPGA. The algorithm was verified by simulation and experimentation at a switching-frequency of 25kHz. [ABSTRACT FROM AUTHOR]

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

A new single-active-switch-based zero voltage and zero current switching (ZVZCS) tapped boost converter is proposed. For the ZVZCS operation of the converter, three diodes and two capacitors were added to an ordinary tapped boost converter. When turned ON, the active switch is in zero current switching with the help of leakage inductance of a tapped inductor. When turned OFF, the energy of the leakage inductance is transferred to a snubber capacitor through a diode, which results in zero voltage switching of the active switch. Then the energy of the snubber capacitor is retrieved by a recovery capacitor connected to the tapped inductor. Different from most conventional soft switching converters that need at least two active switches, the proposed converter requires only one active switch such as JFET and MOSFET to guarantee ZVZCS operation for wide operating ranges of duty cycle, load current, and input voltage. The voltage stress of the active switch is always less than the load voltage, and soft switching turn-on and off is achieved without cumbersome current or voltage sensing, which could not be obtained from quasi-resonant converters that also have an active switch. Furthermore, the dc voltage gain of the proposed converter is quite robust against load change and is determined only by duty cycle like a canonical boost converter; hence, it can be even open-loop controlled. All the diodes are in ZVZCS as well, and all the components except an output diode have the voltage stress less than the load voltage. In this paper, the voltage stress of the output diode was selected to have two times the load voltage. A detailed analysis for the continuous conduction mode and the design procedures of the proposed converter is fully established, and experimentally verified for a 450-W prototype over the input voltage of 100-250 V, achieving 98.1% of maximum efficiency at the switching frequency of 100 kHz with a SiC JFET. Due to its versatile soft switching characteristics, the proposed scheme can be generally applied to high-frequency and high-efficiency dc-dc converters as well as power factor correctors. [ABSTRACT FROM AUTHOR]

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

In this paper, a new medium voltage power converter topology using a diode rectifier, three-level boost (TLB) converter, and neutral-point-clamped (NPC) inverter is proposed for a high-power permanent magnet synchronous generator-based wind energy conversion system. The generator-side TLB converter performs the maximum power point tracking and balancing of dc-link capacitor voltages, while the grid-side NPC inverter regulates the net dc-bus voltage and reactive power to the grid. A significant improvement in the grid power quality is accomplished as the NPC inverter no longer controls the dc-link neutral point voltage. A model predictive strategy is proposed to control the complete system where the discrete-time models of the proposed power electronic converters are used to predict the future behavior of control variables. These predictions are evaluated using two independent cost functions, and the switching states which minimize these cost functions are selected and applied to the generator- and grid-side converters directly. In order to comply with the high-power application, the switching frequencies of the TLB converter and NPC inverter are minimized and maintained below 1.5 and 1 kHz, respectively. The proposed topology and control strategy are verified through MATLAB simulations on a 3-MW/3000-V/577-A system and dSPACE DS1103-based experiments on 3.6-kW/208-V/10-A prototype. [ABSTRACT FROM AUTHOR]

This paper proposes a novel wide-range soft-switching pulse-width modulation three-level (TL) combined dc-dc converter characterized with no added primary clamping devices and reduced output inductance value. It is well suited for high input voltage dc-dc industrial applications due to following desirable features: all the switches sustain half of the input voltage; off state voltage of the switches is directly clamped by the bulky input capacitors, and no added primary clamping devices such as clamping diodes, flying capacitors, are required; TL waveform before output filter can be achieved, which significantly reduces the value of the output inductance; the modified phase-shift control method can be utilized to achieve wide output range. The converter can obtain zero-voltage switching (ZVS) for all power switches in wide load range; furthermore, less conduction loss is added to achieve ZVS. The operation and theoretical analysis of the proposed converter are presented. Experiments are carried out to validate the proposed converter, and efficiency curves are tested and given. [ABSTRACT FROM AUTHOR]

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

The total harmonic distortion (THD) of a waveform is a standard way to quantify its deviation from a sinusoid. In three-phase systems, we are interested in minimizing 3THD: the component of THD produced by odd nontriplen harmonics. However, its definition involves an infinite sum, making it difficult to evaluate and analyze. This paper solves the problem of finding equivalent closed-form expressions for the 3THD of a staircase waveform. In particular, two expressions are rigorously derived, which reveal 3THD to be a piecewise differentiable function. One expression is shorter but describes the pieces implicitly. The other is longer but describes the pieces explicitly. We minimize 3THD using the closed-form expression and provide a comparison with previous techniques. Finally, we provide experimental results that show close agreement with the theoretical results. [ABSTRACT FROM AUTHOR]

This paper proposes the modeling and controller design of an autonomous PV module (APVM) which is composed of a PV panel and a four-switch buck-boost converter (FSBBC) for series-connected distributed maximum power point tracking (DMPPT) PV system applications. The FSBBC can operate in buck, boost, and buck-boost modes with less passive component counts and noninverted output voltage polarity. The switching strategy of the FSBBC with smooth transition during mode change is explained. The parameter design criteria and the small-signal ac model of the APVM are developed. Moreover, the design of controller based on the developed small-signal ac model and the stability analysis of the APVM are presented. Computer simulation and hardware experiment results are used to verify the accuracy of the small-signal model and the controller performance of the APVM. [ABSTRACT FROM AUTHOR]

Control of the output current of a boost type dc-dc converter is challenging due to the nonminimum phase characteristic between the input duty cycle and output load current, and the nonlinear dynamics of the converter. This paper presents a control strategy which utilizes the method of output redefinition combined with a nonlinear control scheme to regulate the output current of the converter when operating in the continuous conduction mode. The output redefinition concept relies on defining a new output to make the system minimum phase, or marginally minimum phase, so that a robust controller can be designed. To this end, a nonlinear feedback linearization controller is proposed based on a circuit-averaged model of the converter. Furthermore, control in the discontinuous conduction mode is studied and a switching scheme is presented to regulate the output current of the converter regardless of the operation mode. The control scheme can achieve small regulation errors while providing robustness due to the minimum-phase characteristic of the new output. Numerical simulations and experimental results are presented to evaluate and verify the performance of the proposed control scheme. [ABSTRACT FROM AUTHOR]

In this paper, a novel transformer-less adjustable voltage quadrupler dc-dc converter with high-voltage transfer gain and reduced semiconductor voltage stress is proposed. The proposed topology utilizes input-parallel output-series configuration for providing a much higher voltage gain without adopting an extreme large duty cycle. The proposed converter cannot only achieve high step-up voltage gain with reduced component count but also reduce the voltage stress of both active switches and diodes. This will allow one to choose lower voltage rating MOSFETs and diodes to reduce both switching and conduction losses. In addition, due to the charge balance of the blocking capacitor, the converter features automatic uniform current sharing characteristic of the two interleaved phases for voltage boosting mode without adding extra circuitry or complex control methods. The operation principle and steady analysis as well as a comparison with other recent existing high step-up topologies are presented. Finally, some simulation and experimental results are also presented to demonstrate the effectiveness of the proposed converter. [ABSTRACT FROM AUTHOR]

In this paper, a generalized switching technique for cascaded H -bridge (CHB) converters is proposed. To take advantage of both low- and high-frequency modulation techniques, a hybrid modulation method is utilized. The proposed technique employs the low-frequency switching for voltage balancing of the dc-link capacitors, and the high-frequency sinusoidal pulse-width modulation switching for shaping the input ac current. Using the proposed technique, the stable operating region of CHB converters is extended. The proposed technique is capable of maintaining the dc voltages balanced even under critical operating conditions in which the load of one H-bridge cell is removed. The validity and effectiveness of the proposed method is confirmed by several simulation and experimental tests on a seven-level CHB rectifier. [ABSTRACT FROM AUTHOR]

This paper proposes a novel light-emitting diode (LED) driver consisting of a buck-boost converter and a buck converter. Each converter adopts a power MOSFET as the active switch. With no need to use any auxiliary switches or snubber circuits, both active switches can operate at zero-voltage switching on (ZVS) by freewheeling the inductor current of the converters to flow through the intrinsic diodes of the MOSFETS. The buck-boost converter is operated at discontinuous-conduction mode (DCM) to perform the function of power-factor correction to ensure almost unity power factor at the input line. The buck converter steps down the output voltage of the buck-boost converter to drive LEDs. It could be designed to operate at either DCM or continuous-conduction mode. The detailed circuit operations and analysis are provided. A prototype 60-W LED driver was built and tested. Experimental results show that the switching losses can be effectively reduced by operating the active switches at ZVS. The measured power factor and circuit efficiency are as high as 0.99% and 93%, respectively. [ABSTRACT FROM AUTHOR]

Under partially shaded conditions, series connection of photovoltaic (PV) modules results in the flow of lowest current in the string corresponding to the most shaded module, reducing the overall power output. Power output can be maximized by incorporating module-level “distributed” maximum power point tracking (DMPPT) wherein the current of each module is compensated by regulating its voltage at the respective maximum power point (MPP) value by connecting a dc-dc converter in parallel. Existing current compensation schemes are either too complex or inaccurate. This paper proposes a novel DMPPT scheme using current compensation, which is simple to implement and yet provides an accurate compensation, resulting in exact maximum power point tracking (MPPT). In the proposed scheme, each PV module is resonated through a special arrangement in the shunt-connected flyback dc-dc converter. The secondary-side diode in the flyback converter is replaced by a power mosfet with an antiparallel diode. The converter operates in two modes: resonant MPPT mode and normal flyback mode. An intelligent controller tracks the MPP of the modules while they resonate. An output switch decouples the PV source from the grid momentarily, while the MPP is tracked. All the results of this work, including experimental validation, are presented. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) is a newly introduced switch-mode converter topology with the potential for high-voltage and high-power applications. This paper focuses on the design and control methods for fault-tolerant operation using redundant submodules (SMs), which is one of the most important features in the MMC topology. By comparing three design schemes of redundant SMs, the most economic and reliable scheme is identified. In addition, a mathematical model of the MMC with arms containing different numbers of SMs is developed. Based on the identified scheme and mathematical model, an energy-balancing control strategy is proposed to keep the MMC operating normally under SM fault conditions. Finally, time-domain simulations of a 61-level MMC system are performed, using the PSCAD/EMTDC software, while experiments are carried out on a 41-level MMC prototype. The simulation and experimental results validate the design scheme, mathematical model, and proposed energy-balancing control strategy. [ABSTRACT FROM AUTHOR]

The distributed generation (DG) should supply continuous power to the local critical load, even in the condition of utility outage. And many efforts have been made for the three-phase inverter in the DG to transfer between the islanding mode and the grid-tied mode seamlessly. This paper proposes a transfer strategy based on indirect current control for the three-phase inverter in the DG, which is composed mainly of two cascaded feedback loops, i.e., capacitor voltage loop and external grid current loop, in synchronous reference frame. In the grid-tied mode, the grid current is controlled by regulating the capacitor voltage. When islanding happens, the reference of the voltage loop is fixed by the limiter. As the local load is located in parallel with the filter capacitor in the proposed strategy, the load voltage is always controlled by the capacitor voltage loop directly, and the quality of the load voltage can be guaranteed. Besides, the performance of the capacitor voltage loop is further improved by introducing an inner capacitor current loop. Moreover, the steady state and transient state of the system, including the output of the limiter, are comprehensively analyzed, and then the compensators and limiters are designed. Finally, the proposed control strategy is verified by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

In electric vehicle (EV) energy storage systems, a large number of battery cells are usually connected in series to enhance the output voltage for motor driving. The difference in electrochemical characters will cause state-of-charge (SOC) and terminal voltage imbalance between different cells. In this paper, a hybrid cascaded multilevel converter which involves both battery energy management and motor drives is proposed for EV. In the proposed topology, each battery cell can be controlled to be connected into the circuit or to be bypassed by a half-bridge converter. All half-bridges are cascaded to output a staircase shape dc voltage. Then, an H-bridge converter is used to change the direction of the dc bus voltages to make up ac voltages. The outputs of the converter are multilevel voltages with less harmonics and lower dv/dt, which is helpful to improve the performance of the motor drives. By separate control according to the SOC of each cell, the energy utilization ratio of the batteries can be improved. The imbalance of terminal voltage and SOC can also be avoided, fault-tolerant can be easily realized by modular cascaded circuit, so the life of the battery stack will be extended. Simulation and experiments are implemented to verify the performance of the proposed converter. [ABSTRACT FROM AUTHOR]

Fuel cell stacks and photovoltaic panels generate rather low dc voltages and these voltages need to be boosted before converted to ac voltage. Therefore, high step-up ratio dc-dc converters are preferred in renewable energy systems. A new Z-source-based topology that can boost the input voltage to desired levels with low duty ratios is proposed in this paper. The topology utilizes coupled inductor. The leakage inductance energy can efficiently be discharged. Since the device stresses are low in this topology, low-voltage MOSFETs with small RDS(on) values can be selected to reduce the conduction loss. These features improve the converter efficiency. Also, the converter has a galvanic isolation between source and load. The operating principles and steady-state analysis of continuous and discontinuous conduction modes are discussed in detail. Finally, experimental results are given for a prototype converter that converts 25 V dc to 400 V dc at various power levels with over 90% efficiency to verify the effectiveness of the theoretical analysis. [ABSTRACT FROM AUTHOR]