Search

In a six-switch three-phase inverter, the conventional pulsewidth modulation (PWM) has six switching times in every switching period based on the average concept. The used multidimensional feedback quantized modulation (MDFQM) strategy selects one switching state and keeps it in every sampling period based on the minimization of filtered voltage errors between the desired voltage commands and the output voltages. The widths of the output voltage pulse are integer times the fixed sampling time in MDFQM. In this paper, two high-efficiency current control methods based on MDFQM are proposed. They integrate the MDFQM strategy and the current control function to minimize the filtered current errors between the desired current commands and the inverter current. Due to the main advantages of less switching numbers and more closed fundamental current, a high-efficiency performance is achieved. The proposed methods are applied to the current control of a three-phase permanent-magnet synchronous motor. The simulation results and experimental results verify the effectiveness of the proposed methods. [ABSTRACT FROM PUBLISHER]

A variable on-time (VOT) control strategy for a critical conduction mode (CRM) flyback power factor correction (PFC) converter with low total harmonic distortion (THD) and high power factor (PF) is proposed in this paper. By using input voltage and the voltage across the auxiliary winding of the flyback transformer to modulate the turn-on time of the switch of the CRM flyback PFC converter, the PF and THD of the converter can be improved. The operation principles of the traditional constant on-time (COT)-controlled CRM flyback PFC converter and VOT-controlled CRM flyback PFC converter are analyzed. The experimental results show that the PF and THD of the VOT-controlled CRM flyback PFC converter are better than those of the COT-controlled CRM flyback PFC converter. [ABSTRACT FROM PUBLISHER]

In this paper, a dedicated pulse width modulation (PWM) technique specifically designed for single-phase (or four wire three-phase) multilevel Cascaded H-Bridge Converters is presented. The aim of the proposed technique is to minimize the DC-Link voltage unbalance, independently from the amplitude of the DC-Link voltage reference, and compensate the switching device voltage drops and on-state resistances. Such compensation can be used to achieve an increase in the waveform quality of the converter. This is particularly useful in high-power low supply voltage applications where a low switching frequency is used. The DC-Link voltage balancing capability of the method removes the requirement for additional control loops to actively balance the DC-Link voltage on each H-Bridge, simplifying the control structure. The proposed modulation technique has been validated through the use of simulation and extensive experimental testing to confirm its effectiveness. [ABSTRACT FROM PUBLISHER]

This paper presents a modulation strategy for symmetrical cascaded multilevel converters that simultaneously balances the individual DC voltages and reduces switching losses by eliminating redundant or unnecessary commutations. The voltage regulation is based on a 1-bit digital signal indicating whether the DC link voltage of each H-bridge is above or below the set point. The system command identifies commutations that can be suppressed without causing output voltage distortion, thus reducing converter losses. The voltage balancing is reached by postponing each switching commutation for a short lapse of time. Simulation and experimental results for an active filter application validate the proposed methods. [ABSTRACT FROM PUBLISHER]

Multilevel converters are known to have many advantages for electricity network applications. In particular, cascaded H-bridge converters are attractive because of their inherent modularity and scalability. Predictive control for power converters is advantageous as a result of its applicability to discrete system and fast response. In this paper, a novel control technique, named modulated model predictive control, is introduced with the aim to increase the performance of model predictive control. The proposed controller addresses a modulation scheme as part of the minimization process. The proposed control technique is described in detail, validated through simulation and experimental testing, and compared with dead-beat and traditional model predictive control. The results show the increased performance of the modulated model predictive control with respect to the classic finite control set model predictive control in terms of current waveform total harmonic distortion (THD). Moreover, the proposed controller allows a multi-objective control, with respect to dead-beat control that does not present this capability. [ABSTRACT FROM PUBLISHER]

In this paper, an effective output voltage control method using adjustable frequency–duty-cycle hybrid control is presented. By using the proposed method, the operating performance of the full-bridge series resonant dc–dc converter applied to the onboard charger in electric vehicles under the constant-voltage charge mode is improved. The proposed control method improves the system efficiency of the charger up to 4% for light load conditions compared with the conventional control method without any extra hardware. A theoretical analysis is described along with a loss analysis in detail, and the validity of the proposed method is verified by experiment with a 3.3-kW prototype onboard charger. [ABSTRACT FROM PUBLISHER]

This paper presents a built-in input matching technique capable of handling a wide variation of multi-array thermoelectric generator (TEG) impedances ranging two decades, from 10 s to 1000 s of ohms. Maximum power point tracking (MPPT) control for a boost converter (BC) is introduced. The analytical expressions derived offer insight on the manner in which MPPT interacts with a BC to achieve best performance. The BC operates in a discontinuous conduction mode under pulse frequency modulation to minimize power consumption and maximize efficiency for light loads. Losses are minimized by implementing a pseudo-zero current switching control via the PMOS switch on/off time, and the output voltage is set using a global clocked comparator. A prototype was fabricated in 0.5 \mu\m CMOS where efficiency measurements showed a maximum value of 61.15% for an RTEG = 33.33\ \Omega, and quiescent power consumption was 1 \mu\W. [ABSTRACT FROM PUBLISHER]

This paper presents a finite control set model predictive strategy and its application to the load voltage control of two-level four-leg inverters. The proposed approach uses the novel discrete-time model of the inverter and output $LC$ filter in order to predict the variables to be controlled. These predictions are carried out for the 16 switching states of the inverter and are evaluated using a cost function. The switching state that forces the load voltages to be closest to their respective references is chosen and applied to the inverter. The behavior of the predictive controller has been investigated, and the changes to both inductive and capacitive filter parameters have been considered. In order to improve the reliability of the fourth leg as well as the overall inverter efficiency, a solution is proposed, which combines hardware and software reconfigurations. The feasibility of the proposed method is verified through simulation and experimental results considering single-/three-phase, balanced/unbalanced, and linear/nonlinear loads. [ABSTRACT FROM PUBLISHER]

In this paper, two new topologies are proposed for multilevel inverters. The proposed topologies consist of a combination of the conventional series and the switched capacitor inverter units. The proposed topologies reduce the number of switches and isolated dc voltage sources, the variety of the dc voltage source values, and the size and cost of the system in comparison with the conventional topologies. In addition, the proposed topologies can double the input voltage without a transformer. There is no need for complicated methods to balance the capacitor voltage. The simulation and experimental results of single-phase 25- and 17-level inverters are given to prove the correct operation of the proposed topologies. [ABSTRACT FROM PUBLISHER]

The widespread use of electric drives has led to an increasing interest in their condition monitoring and fault diagnostics. With respect to power-switch open-circuit fault diagnosis, the majority of the proposed voltage-based approaches require additional hardware, increasing the system cost. As a result, industry acceptance may be low. This paper proposes a new voltage-based approach—without additional sensors—for open-circuit fault diagnosis in closed-loop controlled pulsewidth-modulation (PWM) ac voltage source converters, by using the information contained in the reference voltages available from the control system. The robustness against false alarms of the proposed technique is improved by employing a voltage observer, in order to estimate the actual converter voltages. It has been proven that the algorithm is insensitive to parameter errors; thus, its effectiveness is not compromised. In order to assess the applicability of the diagnostic technique, it is integrated into the control system of a permanent-magnet-synchronous-machine drive, with regenerative capabilities, together with three of the most widely used PWM control strategies: hysteresis current control, direct torque control, and space vector modulation. The technique performance is analyzed in detail by means of several experimental results. [ABSTRACT FROM PUBLISHER]

This paper presents a single-phase transformerless grid-connected photovoltaic converter based on two cascaded full bridges with different dc-link voltages. The converter can synthesize up to nine voltage levels with a single dc bus, since one of the full bridges is supplied by a flying capacitor. The multilevel output reduces harmonic distortion and electromagnetic interference. A suitable switching strategy is employed to regulate the flying-capacitor voltage, improve the efficiency (most devices switch at the grid frequency), and minimize the common-mode leakage current with the help of a novel dedicated circuit (transient circuit). Simulations and experiments confirm the feasibility and good performance of the proposed converter. [ABSTRACT FROM PUBLISHER]

The widespread usage of load compensators for carrying out harmonic and reactive power compensation is constrained by cost and poor efficiency due to switching losses. Hence, it is customary to employ active harmonic filters for harmonic compensation only, while traditional methods comprising of thyristor-switched capacitors are used to carry out reactive power compensation. Load compensators based on one-cycle control (OCC) have gained considerable significance as they do not require the service of a phase-locked loop to synchronize with the utility grid. However, existing OCC-based load compensators do not have the capability to differentiate between the fundamental reactive component and harmonic components of the load currents. Hence, they cannot be employed for harmonic compensation alone as they end up compensating for reactive current as well, leading to an increase in the converter rating. In order to overcome the aforementioned limitation, an OCC-based shunt harmonic filter which is capable of compensating only the harmonic components of the load current is proposed in this paper. The viability of the proposed scheme is confirmed by performing detailed simulation studies and experimental validation. [ABSTRACT FROM PUBLISHER]

This paper presents a multilevel inverter that has been conceptualized to reduce component count, particularly for a large number of output levels. It comprises floating input dc sources alternately connected in opposite polarities with one another through power switches. Each input dc level appears in the stepped load voltage either individually or in additive combinations with other input levels. This approach results in reduced number of power switches as compared to classical topologies. The working principle of the proposed topology is demonstrated with the help of a single-phase five-level inverter. The topology is investigated through simulations and validated experimentally on a laboratory prototype. An exhaustive comparison of the proposed topology is made against the classical cascaded H-bridge topology. [ABSTRACT FROM PUBLISHER]

An architecture of multiple-integrated converter modules sharing an unfolding full-bridge inverter with a pseudo dc link (MIPs) is proposed for grid-connected photovoltaic systems in this paper. The proposed configuration can improve the power conversion, the control circuit complexity, and the cost competitiveness. The proposed MIP is composed of distributed flyback dc–dc converters (DFCs) and an unfolding full-bridge inverter with an ac filter. The DFCs can eliminate the shading effect by using the individual maximum power point tracking. In conventional flyback-type single-phase utility-interactive inverters, discontinuous conduction mode and boundary conduction mode are popular because of the inherent constant current-source characteristics more desirable for grid connection and of the simple procedures for the controller design. However, the operating mode suffers from a large current stress of the circuit components, which leads to the low power efficiency. To avoid this, the DFCs operate under continuous conduction mode that allows reduced current stresses and increased power efficiency, as well as low material cost. The current control loop of the converters employs primary-side regulation contributing to improvement of dynamics as well as the cost reduction significantly due to the elimination of the high-linearity photocoupler device. Development of a new dc-current loop that maintains the level of dc-current injection into the grid within the levels stipulated by IEEE 1547 will be dealt as well. The performance validation of the proposed design is confirmed by experimental results of a 200-W hardware prototype. [ABSTRACT FROM PUBLISHER]

In this paper, a model predictive control strategy is adapted to the cascaded H-bridge (CHB) multilevel rectifier. The proposed control scheme aims to keep the sinusoidal input current in phase with the supply voltage and to achieve independent voltage regulation of the H-bridge cells. To do so, the switches are directly manipulated without the need of a modulator. Furthermore, since all the possible switching combinations are taken into account, the controller exhibits favorable performance not only under nominal conditions but also under asymmetrical voltage potentials and unbalanced loads. Finally, a short horizon is employed in order to ensure robustness; this way, the required computational effort remains reasonable, making it possible to implement the algorithm in a real-time system. Experimental results obtained from a two-cell CHB rectifier are presented in order to demonstrate the performance of the proposed approach. [ABSTRACT FROM PUBLISHER]

In this paper, a model predictive scheme is proposed to control the grid-connected high-power four-level diode-clamped inverter. To predict the future behavior of active and reactive grid power values and dc link capacitor voltages, a discrete-time model of the inverter is developed in synchronous reference frame. The controller uses all the possible switching states of the inverter for the prediction and evaluates them using a cost function. The switching state, which minimizes the cost function, is then chosen and applied at the next sampling interval. The switching frequency minimization is also achieved by including an extra constraint in the cost function. A simplified extrapolation method with reduced computational burden is proposed to safeguard the semiconductor devices during the dynamic changes in reference power values. The performance of the proposed method is investigated with the perturbations in the grid filter and dc link parameters. The feasibility of the proposed method is verified through simulation and experimental results, showing good dynamic and steady-state performance. [ABSTRACT FROM PUBLISHER]

In this paper, multiloop interleaved control (MIC) is proposed, and it is combined with conventional multiloop control and the interleaved pulsewidth modulation scheme. The average behavior of the interleaved three-level switch-mode rectifier (SMR) behaves similar to the conventional boost-type SMR even though two capacitor voltages are imbalanced. It implies that conventional multiloop control can be applied to the interleaved three-level SMRs to achieve the desired power factor correction function. The proposed MIC is digitally implemented and verified in a field-programmable-gate-array-based system. The provided results show that MIC stably works and the capacitor voltages are eventually balanced during the system operations. [ABSTRACT FROM PUBLISHER]

Loads connected to a stiff source cannot be protected from voltage disturbances using a distribution static compensator (DSTATCOM). In this paper, a new control-algorithm-based multifunctional DSTATCOM is proposed to operate in voltage control mode under stiff source. This scheme provides fast voltage regulation at the load terminal during voltage disturbances and protects critical loads. In addition, during normal operation, the generated reference load voltages allow control of the source currents. Consequently, DSTATCOM injects reactive and harmonic components of load currents to make source power factor unity. Simulation and experimental results are presented to verify the efficacy of the proposed control algorithm and multifunctional DSTATCOM. [ABSTRACT FROM PUBLISHER]

This paper presents a power factor corrected (PFC) bridgeless (BL) buck–boost converter-fed brushless direct current (BLDC) motor drive as a cost-effective solution for low-power applications. An approach of speed control of the BLDC motor by controlling the dc link voltage of the voltage source inverter (VSI) is used with a single voltage sensor. This facilitates the operation of VSI at fundamental frequency switching by using the electronic commutation of the BLDC motor which offers reduced switching losses. A BL configuration of the buck–boost converter is proposed which offers the elimination of the diode bridge rectifier, thus reducing the conduction losses associated with it. A PFC BL buck–boost converter is designed to operate in discontinuous inductor current mode (DICM) to provide an inherent PFC at ac mains. The performance of the proposed drive is evaluated over a wide range of speed control and varying supply voltages (universal ac mains at 90–265 V) with improved power quality at ac mains. The obtained power quality indices are within the acceptable limits of international power quality standards such as the IEC 61000-3-2. The performance of the proposed drive is simulated in MATLAB/Simulink environment, and the obtained results are validated experimentally on a developed prototype of the drive. [ABSTRACT FROM AUTHOR]

A systematic method for deriving multiport converters (MPCs) from the full bridge (FB) converter (FBC) and bidirectional dc–dc converters (BDCs) is proposed in this paper through sharing the parasitized switching legs by the BDCs and the FBC. By employing the proposed method, families of FB and BDC-based MPCs (FB-BDC-MPCs), including some existing ones, are developed for renewable generation systems with the merits of simple topology, reduced devices, and single-stage power conversion. Voltage regulations between any two ports can be achieved by employing pulsewidth modulation and phase-angle-shift control scheme. Furthermore, zero-voltage switching for all the switches can be realized in the proposed FB-BDC-MPCs. A typical four-port converter developed by the proposed method, named buck/boost four-port converter (BB-FPC), is analyzed in detail as an example in terms of operation principles, design considerations, and control strategy. Experiments have been carried out on a 500-W prototype of BB-FPC, which demonstrate the feasibility and effectiveness of the proposed topology derivation method. [ABSTRACT FROM AUTHOR]

This paper discusses the operation of a multiphase system, which is aimed at both variable-speed drive and generating (e.g., wind energy) applications, using back-to-back converter structure with dual three-phase machine-side converters. In the studied topology, an asymmetrical six-phase induction machine is controlled using two three-phase two-level voltage source converters connected in series to form a cascaded dc link. The suggested configuration is analyzed, and a method for dc-link midpoint voltage balancing is developed. Voltage balancing is based on the use of additional degrees of freedom that exist in multiphase machines and represents entirely new utilization of these degrees. The validity of the topology and its control is verified by simulation and experimental results on a laboratory-scale prototype, thus proving that it is possible to achieve satisfactory dc-link voltage control under various operating scenarios. [ABSTRACT FROM PUBLISHER]

This paper presents an analytical design method for the dc collector systems of offshore wind farms and proposes an improved topology to overcome the limitations of the conventional series–parallel (SP) topology. During a severe failure in the SP topology, bypassing the faulty units imposes overvoltage on fault-free units and leads to the disconnection of the series branch from the collector system. By providing auxiliary connection paths, the suggested topology reduces the overvoltage of the units and hence maintains fault-free units operational following a severe failure. Hence, the efficiency of a wind farm increases considerably upon any failure occurrence. To show the merits of the suggested topology, the captured power during a failure has been calculated and fairly compared with that of the conventional SP topology, considering the excess cost of the suggested topology due to additional connection paths. To investigate the performances of both topologies and their feasibility, a collector system including 12 wind turbine generators has been simulated in time domain software environment. Then, various failure scenarios have been investigated to evaluate the transient behavior of the dc collector system following slight and severe failures. The study results reveal the feasibility of the proposed topology as a promising structure for future dc collector systems. [ABSTRACT FROM PUBLISHER]

This paper unifies the underlying concepts of all basic single-switch, two-state, dc-to-dc voltage-sourced converters, by duality, as generic related current and voltage-sourced converters. By using ac and dc circuit theory, the three basic converters can be transformed to yield all known transfer functions and realizes a proliferation of 33 topologies, three being previously unidentified topologies with unique characteristics. The circuit based systematic unifying approach offers new insight and an alternative interpretation to the origin of the 33 topologies including the Zeta, Cuk, \pmLuo, CSC, Landsman, and Sepic converters. Converter time-domain simulations and corresponding practical results of the three new topologies extol and culminate the concepts and analysis presented. [ABSTRACT FROM PUBLISHER]

This paper proposes the pulsewidth modulation (PWM) strategy of Z-source inverters (ZSIs) with minimum inductor current ripple. In existing PWM strategy with single-phase shoot-through, the shoot-through time interval is divided into six equal parts, therefore the three phase legs bear the equal shoot-through time interval. In this manner, the allotment and arrangement of the shoot-through state is easy to realize, but the inductor current ripple is not optimized. This causes to use relatively large inductors. In the proposed PWM strategy, the shoot-through time intervals of three phase legs are calculated and rearranged according to the active state and zero state time intervals to achieve the minimum current ripple across the Z-source inductor, while maintaining the same total shoot-through time interval. The principle of the proposed PWM strategy is analyzed in detail, and the comparison of current ripple under the traditional and proposed PWM strategy is given. Simulation and experimental results on the series ZSI are shown to verify the analysis. [ABSTRACT FROM PUBLISHER]

The pulse-train (PT) control technique for switching dc–dc converters is simple to design and benefits from excellent control performance. Up to now, almost all of the works on PT control are focused on switching dc–dc converters operating in discontinuous conduction mode, with few works reported on PT control of switching dc–dc converters operating in continuous conduction mode (CCM). In this paper, a PT-controlled CCM buck converter is studied and a unique low-frequency oscillation phenomenon is revealed, which results in large undesired inductor-current and output-voltage variations. The effect of equivalent series resistance (ESR) output-capacitor on the low-frequency oscillation is examined. The results indicate that such oscillation occurs when the ESR output-capacitor is relatively small and disappears when it is relatively large. However, a larger ESR will result in a large output-voltage ripple. In order to avoid the low-frequency oscillation and, at the same time, to ensure a small output-voltage ripple, the ICRIF circuit is applied. In this way, a small ESR output-capacitor can be used to decrease the output-voltage ripple. Simulation and experimental results are provided to verify the theoretical analysis. [ABSTRACT FROM PUBLISHER]

In this paper, a photovoltaic (PV)-system maximum power point (MPP) tracking (MPPT) control strategy employing a predictive digital current-controlled converter implemented in conventional hardware resources is presented. Two current programmed controllers (finite-state predictive control and valley current control) have been integrated into a system with current- or voltage-oriented MPPT. The modifications applied to the perturb-and-observe algorithm enable the MPP tracker to interact rapidly with the controller accounting also for abrupt irradiance drops by considering voltage and current limitations. The implementation of digital control in PV systems entails significant advantages of speed and accuracy, although the controller converges correctly at the MPP under irradiance variations featuring fast dynamic response. The proposed controller scheme has been experimentally demonstrated on a digitally current-controlled boost converter delivering power from a PV system. [ABSTRACT FROM PUBLISHER]

In the modern point-of-load (POL) applications, a number of low- and medium-power converters are used very close to the actual load. These applications require superior dynamic response and better power processing density to save space on the motherboard. Hysteretic modulators are one of the obvious choices for these applications because of their superior dynamic response with minimal number of filter capacitors. This paper presents a new carrier (synthetic ripple based)-generation-based digital hysteretic modulator for POL converters. The proposed structure creates a piecewise linear synthetic ripple using sensed converter voltages, without the need of direct inductor current sensing. The artificial synthetic ripple is then added to the output voltage and fed as a carrier to the hysteretic comparator, which helps in natural load current feedforward. This proposed digital modulator helps in the reduction of the output capacitors and exhibits superior large-signal dynamics for a POL converter. It is a simple solution and gives immediate fault detection (within one switching cycle) in case of the main switch (top MOSFET) failure of the converter, thus providing adequate protection to the microprocessor load. Analysis, simulation, and experimental results on a 2-V/10-A 20-W single-phase prototype are presented to verify the properties of the proposed modulator. [ABSTRACT FROM PUBLISHER]

This paper presents a novel current-resonant-type dc–dc converter. In general, the current-resonant-type converters have several remarkable features such as high efficiency, small size, low cost, and low noise and are often used in many electronic systems such as personal computers, flat-panel displays, and so forth. The current-resonant-type converters commonly employ the pulse frequency modulation for the regulation of the output voltage, and their magnetizing inductance is set relatively small. For this reason, the magnetizing current through the converter causes nonnegligible power losses under not only the light load but also standby conditions. Therefore, power supply systems using this type of converter have a problem in which the required smaller size is not able to be achieved because an auxiliary converter is necessary for the standby operation. In order to solve this problem, a novel current resonant converter has been proposed, in which two driving methods are employed. In these driving methods, the high-side MOSFET, as one of two main switches, is driven by an auxiliary winding of the transformer; and the low-side MOSFET, as another main switch, is driven by the driving integrated circuit with a low withstand voltage. As a result, it is clarified that the output voltage regulation is performed well in the useful operation modes. The maximum efficiency is 95.4% at the rated output power. [ABSTRACT FROM PUBLISHER]

This paper presents the hybrid seven-level cascaded active neutral-point-clamped (ANPC)-based multilevel converter. The converter topology is the cascaded connection of a three-level ANPC converter and an H-bridge per phase. The voltage of the H-bridge is actively maintained to the required level through selection of the switching states of the converter. The topology is operated under selective harmonic elimination pulsewidth modulation (SHE-PWM), maintaining the switching frequency of the converter to a minimum. The operating principles, voltage balancing methods, and limitations of the converter are analyzed together with extensive simulation results of the topology. Experimental results from a low-power laboratory prototype are presented that verify the operation of the hybrid converter under SHE-PWM. [ABSTRACT FROM PUBLISHER]

This paper presents the modeling and control processes of the single-phase cascade H-bridge multilevel converter used as a shunt active filter. Based on the obtained model, a controller is proposed to compensate for harmonic distortion and reactive power caused by a nonlinear load. These issues are solved by guaranteeing tracking of the line current toward an appropriately defined current reference. In the proposed approach, the current reference has been selected to be a signal proportional to either the line voltage or to its fundamental component; however, the proposed method can also be extended to other reference definitions. The proposed controller also includes voltage loops to guarantee regulation and balance of the involved capacitor voltages toward constant references. Experimental results on a 2-kVA prototype are presented to assess the performance of the proposed controller. [ABSTRACT FROM PUBLISHER]

Unbalanced grids introduce performance deterioration for Vienna rectifier topology by producing twice fundamental frequency ripples in dc-link voltage and input active/reactive power. A common current reference generation for the purpose of eliminating the input power ripple, such as dual-frame hybrid vector control, can maintain constant input power and eliminate ripples in dc-link voltage under light voltage unbalanced grids. Under severe unbalanced grids, this type of a control method will fail to work. This paper first analyzes the theoretical operation area of a constant power control method under unbalanced grids, and then a novel control method is proposed. The proposed control method can work under severe unbalanced grids by injecting a small amount of input power ripple and balance the performance of working area and output dc voltage ripples. Finally, the experiment results using the constant power control method are given and validate the performance of the proposed control method. [ABSTRACT FROM PUBLISHER]

This paper presents the analysis and design of a sliding-mode control of a boost converter operating in continuous conduction mode that minimizes the inrush current and provides output voltage regulation in front of input voltage perturbations and load changes. The analytical expression of the inrush current is obtained, and the conditions to minimize the current peak are derived. The resulting controller is implemented analogically and employs two switching surfaces. Namely, one surface is combined with the conventional auxiliary diode branch for the start-up, while another one is used for the voltage regulation in steady state. Experimental results are in perfect agreement with the theoretical predictions. [ABSTRACT FROM PUBLISHER]

A new scheme for nine-level voltage space-vector generation for medium-voltage induction motor (IM) drives with open-end stator winding is presented in this paper. The proposed nine-level power converter topology consists of two conventional three-phase two-level voltage source inverters powered by isolated dc sources and six floating-capacitor-connected H-bridges. The H-bridge capacitor voltages are effectively maintained at the required asymmetrical levels by employing a space vector modulation (SVPWM) based control strategy. An interesting feature of this topology is its ability to function in five- or three-level mode, in the entire modulation range, at full-power rating, in the event of any failure in the H -bridges. This feature significantly improves the reliability of the proposed drive system. Each leg of the three-phase two-level inverters used in this topology switches only for a half cycle of the reference voltage waveform. Hence, the effective switching frequency is reduced by half, resulting in switching loss reduction in high-voltage devices. The transient as well as the steady-state performance of the proposed nine-level inverter-fed IM drive system is experimentally verified in the entire modulation range including the overmodulation region. [ABSTRACT FROM PUBLISHER]

Cascaded H-bridge multilevel power electronic converters generally require several dc sources. An alternative option is to replace all the separate dc sources feeding the H-bridge cells with capacitors, leaving only one H-bridge cell with a real dc voltage source. This will yield a cost-effective converter. However, the required capacitor voltage balancing is challenging. In this paper, using the phase-shift modulation approach, a new control method for cascaded H-bridge multilevel converters fed with only one independent dc source is presented. The proposed method has a wide voltage regulation range for the replacement capacitors in the H-bridge cells. Experimental and simulation results support the proposed control method. [ABSTRACT FROM PUBLISHER]

This paper describes a research conducted on a single-phase flying capacitor active rectifier. An online process that reduces the total number of switching events, which leads to a reduction of switching losses in the converter, is introduced. This method is based on redundant state selection, which is used to regulate the voltage of flying capacitors. The proposed approach is general and can be applied to flying capacitor converters with any number of levels. Furthermore, in order to control the inrush current at the start of operation and avoid extra voltage and current stress for active switches and capacitors, a start-up procedure that precharges the flying capacitors is proposed. With this precharge procedure, no additional hardware is needed. Simulation and laboratory results demonstrate these new concepts. [ABSTRACT FROM PUBLISHER]

In this paper, a bee colony optimization (BCO) algorithm is adapted to the current control strategy of power factor (PF) correction for a Sheppard–Taylor converter. The control approach is developed to eliminate the input current harmonics in the converter. The BCO algorithm is a new population-based search algorithm which is one of the metaheuristic techniques based on swarm intelligence. This algorithm depends on modeling the natural behavior of real honey bees. In this approach, duty cycles are generated by the BCO algorithm for the Sheppard–Taylor converter switch to obtain unity PF (UPF) and lower total harmonic distortion of the input current. The duty cycles for half a line period are calculated and stored in a lookup table. By synchronizing the memory with the line, near-unity PFs can be achieved in an operating point. The feedforward is also used into the control algorithm with the maximum value of the input voltage. The implementation of feedforward improves the converter performance. The input current of the converter is operated in continuous conduction mode. The simulation and experimental results show that the proposed control strategy works well and the UPF can be achieved with wide input voltage, load, and parameter variation. The results are compatible with the International Electrotechnical Commission (IEC) 61000-3-2 current harmonic standard. [ABSTRACT FROM PUBLISHER]

The five-level active neutral-point (NP)-clamped (ANPC) converter is a newly emerging topology which can overcome the drawbacks of traditional NP-clamped and flying-capacitor multilevel converters. This paper presents a comprehensive theoretical analysis of the NP potential balancing issue and demonstrates that the NP potential can be naturally balanced under ideal and steady conditions. An NP potential balancing method based on zero-sequence voltage injection is presented. By calculating the average NP currents of all key zero-sequence voltages, the most appropriate zero-sequence voltage is selected to generate the demanded NP current, which can also limit the switching frequency of the series-connected insulated-gate bipolar transistors to the fundamental frequency. A three-phase five-level ANPC inverter prototype is built up, and both steady and dynamic experimental results are presented to verify the validity of this method. [ABSTRACT FROM PUBLISHER]

Equivalent series resistance (ESR) of output capacitor has a significant effect on the control performance of constant on-time (COT) controlled switching dc-dc converters. In this paper, a discrete-time model of COT-controlled buck converter, with variable sampling frequency, is established. Based upon which, the dynamical effects of the ESR of output capacitor on COT-controlled buck converter are revealed and analyzed. The time-domain numerical simulations of the exact switched state equations, the bifurcation diagrams, and maximal Lyapunov exponents of the discrete-time model are obtained. These results verified by experimental circuit indicate that the ESR of output capacitor is a critical factor for COT-controlled buck converter, which can eliminate the unique pulse bursting phenomenon and shift operation mode from discontinuous conduction mode to continuous conduction mode, as well as control stability. [ABSTRACT FROM PUBLISHER]

In this paper, a single-phase multilevel inverter with battery balancing is proposed. The input of each individual inverter is directly connected to a battery. The combination of batteries can be controlled according to the batteries' voltages to implement the battery-balancing function. The operational principle of the proposed system is first described, and then, the design equation is derived. Experiments show that the battery-balancing discharge function is achieved. Finally, a prototype is designed and implemented to verify the feasibility and excellent performance. [ABSTRACT FROM PUBLISHER]

A neutral-point-clamped three-level inverter with small dc-link capacitors is presented in this paper. The inverter requires zero average neutral-point current for stable neutral-point voltage. The small dc-link capacitors may not maintain capacitor voltage balance, even with zero neutral-point current. This may happen due to nonlinearities present in the circuit. This requires a fast control of the neutral-point voltage. A simple carrier-based modulation strategy which allows modeling of the neutral-point voltage dynamics as a continuous function of power drawn from the inverter is proposed. This continuous model shows that the neutral-point current is proportional to the power drawn from the inverter, and it enables the use of a well-established classical control theory for the neutral-point voltage controller design. A simple proportional integral controller is designed for the neutral-point voltage control on the basis of the continuous model. The design method for optimum performance is discussed. The implementation of the proposed modulation strategy and the controller is very simple. The controller is implemented in a 7.5-kW induction machine-based drive with only 14 \mu \F dc-link capacitors. Also, the experimental results show that fast and stable performance of the neutral-point voltage controller are achieved and thus verify the validity of the proposed control approach. [ABSTRACT FROM PUBLISHER]

Improved pulse regulation (IPR) control, a novel control technique for switching dc–dc converters, is proposed and studied in this paper. According to the output voltage and load current of the switching dc–dc converter, IPR control technique achieves output voltage regulation by generating control pulse train made up of some preset control pulses with different duty ratios. IPR control needs only comparators, triggers, and some simple logic devices, without error amplifier and the corresponding compensation circuit of pulse width modulation control scheme, thus IPR control scheme is easy to realize, benefits with excellent transient performance and stability. The principle and operation of IPR control scheme are introduced and illustrated with buck converter operating in discontinuous conduction mode as an example. Simulation and experimental results are presented to show that IPR-controlled converter has much lower output voltage ripple and more accurate output voltage regulation than PR converter. [ABSTRACT FROM PUBLISHER]

Parallel operation is an effective way to improve the capacity of full power converter in permanent-magnet direct-drive wind power generation system. But it causes the zero-sequence circulating-current (ZSCC), which brings current discrepancy, current waveform distortion, power losses, and electromagnetic interference (EMI), etc. The paper proposes a new topology of full power converters which are composed of n full power converters. The n converters have the same structures and are in parallel with each other. Besides, the average models of the system are analyzed and the fundamental mechanism of ZSCC generation is given. Based on the above analysis, the control strategy of the system is designed. The simulation and experiment results of two parallel full power converters show the feasibility of the proposed theory and control scheme. [ABSTRACT FROM PUBLISHER]

Reforms in the electricity sector along with various renewable-energy-promotion policies have increased the importance of small grid-connected photovoltaic (PV) systems utilizing single-stage single-phase inverters. Ruggedness, reliability, and cost effectiveness are the desirable characteristics of such inverters used in distributed low-power applications. Schemes based on one-cycle control (OCC) which do not require the service of a phase-locked loop for interfacing the inverter to the grid are increasingly being employed for such applications. However, the OCC-based schemes reported earlier require sensing of the grid voltage which somewhat offsets one of the inherent strengths of OCC-based systems. In an effort to overcome the aforementioned limitation, an OCC-based grid-connected single-stage PV system is proposed in this paper which does not require to sense the grid voltage. Further, it requires less number of sensors (two) as compared to that required (four) in the earlier reported scheme for the implementation of the core controller comprising of OCC and maximum-power-point-tracking blocks. The viability of the proposed scheme is confirmed by performing simulation and experimental validation. [ABSTRACT FROM PUBLISHER]

With the rapid development of high-speed and high-power railway system in China, power quality such as the negative sequence current and harmonic current caused by electric locomotives becomes more and more critical. This paper proposes a half-bridge-converter-based railway static power conditioner (RPC) (HBRPC) which consists of two half-bridge converters connected by two capacitors in series. Compared with the traditional RPC, the HBRPC requires only a pair of power switch legs and two capacitors. Under the premise of accomplishing the same function of RPC, the proposed conditioner can reduce half of the power switches, which can make it with lower cost and hardware complexity. A double-loop control is proposed for HBRPC to keep the dc-link voltage stable and achieve the dynamic tracking of the current reference signals, while a balanced voltage control is proposed to eliminate the error of two capacitor voltages and maintain the normal operation of HBRPC. Finally, simulation and experiment results have verified the proposed structure and its control method effectively. [ABSTRACT FROM PUBLISHER]

This paper proposed a novel predictive variable-structure-switching-based current controller for a three-phase load driven by a power inverter. The design specifications are robustness to load electrical parameters, fast dynamic response, reduced switching frequency, and simple hardware implementation. In order to meet previous specifications, a sliding mode controller has been developed, which is designed as finite-state automata, and implemented with a field-programmable gate array (FPGA) device. The switching strategy implemented within the state transition diagram provides for a minimum number of switches by the three-phase inverter that is confirmed through simulation and experimental results. Its regulation using the proposed control law provides good transient response by the brushless ac motor control. However, this does not limit the wider applicability of the proposed controller that is suitable for different types of ac loads (rectifier and inverter) and ac motors (induction, synchronous, and reluctance). A new logical FPGA torque and speed controller is developed, analyzed, and experimentally verified. [ABSTRACT FROM PUBLISHER]

The increasing number of distributed generation units has led to the development of microgrids, to which the distributed generators are commonly interfaced by means of a voltage-source inverter (VSI). When the microgrid is operating independently of the power system, i.e., in islanded mode, two levels of control can be distinguished for these VSIs: power control and voltage control (frequency and amplitude). The set-point values for the voltage controller are obtained from the power controller. This paper investigates theoretically and experimentally the benefits of using several PID control structures for the voltage control. Theoretical insights into the dynamics of such a system emphasize the benefits of measuring current signals for control purposes and adding voltage measurements to the output of the controllers. Direct voltage control and cascade voltage control are compared both with and without forward compensation of the grid voltage. Simulation and experimental results are given showing that such PID-type controllers on a digital signal processor are simple yet effective strategies for an accurate voltage control in islanded microgrids. [ABSTRACT FROM PUBLISHER]

This paper presents a magnetically coupled feedback-clamped optimal bidirectional battery charger. The proposed charger acts as a current source, i.e., acts in constant-current (CC) mode with a controlled output current in case of deep discharge of a battery, and as a voltage source, i.e., acts in constant-voltage (CV) mode with a controlled output voltage for near-100% battery state of charge. The proposed circuit is universal from the battery voltage point of view, i.e., can charge a battery with any given voltage rating, and adaptive from the optimum charging current requirement viewpoint, i.e., can adapt to the optimum battery charging current. The presented solution uses a magnetically coupled bidirectional converter topology. In order to make the system feedback controlled during the whole cycle of charging, the regulation loop is clamped, and hence, automatic and smooth transition from the CC to CV mode is achieved without the need of any extra switching circuit or control loop. Experimental and simulation results for a 250-W prototype are presented to verify the proposed system. The prototype shows maximum efficiencies of 90.24% under boost mode and 92.7% under buck mode of operation. The performance of the charger is verified using two different 12-V–7-Ah and 12-V–32-Ah lead–acid batteries. [ABSTRACT FROM PUBLISHER]

This paper discusses two overmodulation controls, namely, square wave and trapezoidal, in the indirect matrix converter (IMC) for motor drive application. The differences between these two modulations are analyzed based on the output–input voltage transfer ratio (VTR), the efficiency, and the current total harmonic distortions under two load conditions. Moreover, the performance is then improved by implementing four-step commutation methods in the primary side of the IMC. The validity of the proposed methods will be demonstrated through simulation and experimentally. The experimental results show that the VTR can be improved from 0.866 to 0.97 in the square wave modulation and 0.92 for the trapezoidal wave modulation in an induction motor drive system. [ABSTRACT FROM PUBLISHER]

In this paper, a new cascade active-front-end converter based on dual-boost/buck converters is proposed for an intelligent universal transformer (IUT), which allows adjusting the power factor to control both the active and reactive powers between medium and low voltage levels. Compared to the traditional cascade H-bridge converter, it has much enhanced system reliability owing to no shoot-through problems and lower switching loss with the help of using power MOSFETs. In addition, a unified control scheme is proposed for active–reactive power control and individual voltage balancing control, which is modular and easy to implement. In the end, a laboratory three-unit cascade active-front-end converter based on the half-bridge dual-boost/buck converter is constructed and tested. The experimental results verified the feasibility and effectiveness of the proposed active-front-end converter and the unified control scheme for IUT. [ABSTRACT FROM PUBLISHER]

This paper presents a novel switched Z-source isolated bidirectional dc–dc converter. The converter employs two unique switched impedance networks to couple the main circuit and the power source and load. Compared with the traditional isolated bidirectional dc–dc converter, the proposed converter has a wider regulation range of voltage. In addition, due to the fully symmetrical circuit configuration, there is neither a high-voltage side nor a low-voltage side in the circuit structure, and the sources connected to the dc side of each H-bridge can be both voltage sources and current sources. At the same time, the converter can bear shoot-through phenomenon in H-bridges, so it has high reliability. The topology configuration and operating principle of this converter are analyzed, and a unique phase-shifting shoot-through bivariate coordinated control strategy is designed and implemented. Both simulation and experimental results verify the analytical results. [ABSTRACT FROM PUBLISHER]