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Compared with multilevel space vector modulation, level-shifted multicarrier sinusoidal pulsewidth modulation (SPWM) for nested neutral point-clamped (NNPC) inverters requires much less calculations and implementation efforts, but the existing conventional SPWM cannot suppress the severe flying-capacitor (FC) voltage ripples under low output-frequency conditions. In order to solve this problem, a multicarrier-based PWM strategy with complete voltage balance control (VBC) capacity is proposed in this paper. For NNPC inverters operating under low output-frequency conditions, two preprocessing steps, the zero-sequence injection and the modulation-signal rearrangement, are proposed before the comparisons between level-shifted carriers and modulating signals. These preprocessing steps make the average currents flowing through FCs zero, which is beneficial to greatly reduce the FC voltage ripples under low output-frequency conditions. Together with additional VBC, the proposed modulation can assure the FC voltages balanced under the entire output-frequency conditions. Principles and implementation processes of proposed modulation techniques and VBC methodsare elaborated in detail and compared with conventional modulation methods. Both simulation results from a 5-MVA system and experimental results based on a 5-kVA platform are presented to verify the effectiveness.

Conventional three-level discontinuous pulsewidth modulation (DPWM) templates typically provide maximum switching loss reduction capability for load power factor angles in the range from 30° lagging to 30° leading. This paper proposes three space-vector-based DPWM templates for lower power factors and a generalized DPWM strategy for three-level inverters operating with modulation indices lower than 0.5. For different power factors, the proposed strategy adapts the inverter pulse sequence by combining different portions of the proposed and conventional DPWM templates within one operating fundamental cycle and ensures minimum switching instances when changing templates. Consequently, the strategy aligns the PWM clamping intervals with the respective load-current peaks, achieving around 50% switching loss reduction capability extended to all operating power factor angles (90° lagging to 90° leading). The simulation and experimental results demonstrate the effectiveness of the proposed three-level generalized DPWM strategy over the conventional three-level modulation strategies.

This paper has developed a direct power control (DPC) structure to improve the performance of an active filter. A control algorithm directly uses the instantaneous power terms as control variables to replace the current and voltage variables that are commonly used in proportional-integral (PI) control systems. Compared to the other DPC schemes that have been reported so far, the proposed algorithm is oriented to harmonic current compensation, for which the switching functions are redefined, the bandwidths of the two hysteresis comparators are dynamically adjusted, and consequently, the pulsewidth modulation (PWM) switching frequencies are regulated to eliminate the unnecessary short switching pulses, and the control system can be used directly and effectively for various types of nonlinear load compensation. With the proposed control scheme, full control of the active filter, including the line current and the DC bus voltage, can be realized within an integrated power control loop. The advantages of the proposed control strategy have been verified by simulation and experimental results on a 2-kVA laboratory prototype.

Pulsewidth-modulated (PWM) techniques equip power converters with unique features such as input-output linearity and control flexibility. Nevertheless, frequent switching of semiconductor switching devices causes considerable switching loss, and therefore makes traditional two-level PWM converters inappropriate for high-power applications. Two alternatives for building modular structures, namely multipulse and multimodule PWM converters were introduced to provide not only voltage and current sharing among the semiconductor switching devices, but also a high-quality output voltage at a much lower switching frequency. While multipulse converters offer minimal switching losses, low-order harmonic neutralization, and the best utilization of the inverter, multimodule PWM converters give control flexibility and power structure simplicity. This paper combines these two, and preserves the advantages of both multipulse and multimodule PWM converters. This not only provides an additional degree of freedom for voltage control, but also enables the converter to operate in PWM mode during transient and in single-pulse mode during the steady state. For the PWM switching mode, a special space vector strategy of 3 p.u. switching frequency is presented to maximize the voltage utilization and maintain a linear transfer characteristic. The power structure and control methods are analyzed, and validated by simulation and experimentally.

This paper investigates various random PWM (RPWM) techniques for conventional two-level inverter-fed traction drives and proposes a discrete RPWM technique for acoustic noise reduction. The proposed RPWM technique randomizes within a set of predefined switching frequencies compared with the continuous nature of randomization in conventional RPWM techniques. The proposed method was compared with conventional SVPWM and other RPWM techniques with respect to the A-weighted IEC 61672-2013 standard acoustic noise profile. The proposed RPWM method spreads the narrowband harmonic clusters effectively and, compared to the conventional RPWM techniques, reduces broadband noise by 2–6 dB over the full modulation index range, thus producing a better acoustic noise profile.

Modular multilevel converter (MMC) is a promising topology for medium and high power applications. The MMC system consists a large number of sub-modules (SMs), which take long time to simulate. In a real-time simulator, the MMC model is optimized to have a fast simulation speed for real-time applications, such as hardware-in-the-loop (HIL) tests. The methodology to evaluate model fidelity is important. In this paper, a methodology is proposed to validate an MMC model capable of real time simulation and implemented in central processing unit (CPU) and field-programmable gate array (FPGA). The model is validated in both open-loop and closed-loop control in a simple MMC test system, and compared to a reference detailed model made with SimPowerSystems (SPS) blocks. The effect of the model sampling time on the accuracy is also studied. The results indicate the MMC model optimized for real time simulation with a time step of 25 μs is as accurate as an SPS model with a time step of 0.2 μs.

The use of six-phase motors is an attractive option for electric and hybrid electric vehicles due to its modularity. Demand for high power density and lower costs for electric traction drives has led to the idea of integrating the battery charging function into the traction drive. When the main battery for dual motor type electric and hybrid electric vehicles is being charged, the equivalent power converter system is two converters that act as rectifiers and are connected in parallel. Feeding these converters from the AC grid with interleaved discontinuous PWM schemes can result in the appearance of a significant amount of circulating current flowing between the converters. Such circulating current increases converter component stresses and reduces battery-charging efficiency. In the paper, a PWM scheme based on discontinuous PWM methods is proposed to mitigate this circulating current. The proposed scheme does not require additional passive elements and maintains the benefits of discontinuous PWM. Simulation and experimental results are presented to validate the proposed scheme.

This paper proposes reduced switching random PWM (RPWM) techniques based on Space Vector PWM (SVPWM) technique for conventional two-level inverters. In the proposed RPWM techniques, the switching frequency is randomized within a band lower than the nominal switching frequency at and around the peaks of the three-phase output currents. For the rest of the fundamental cycle, the switching frequencies are randomly selected within a band higher than the nominal switching frequency. The proposed method is able to spread the narrowband harmonic clusters similar to the conventional RPWM techniques and additionally produce less inverter output current distortion than conventional spread spectrum techniques. The proposed technique has been analyzed and has been verified using experimental results.

Force-commutated multiconverter systems have been proposed and recently implemented for high power applications, particularly high-voltage direct current (HVDC) transmission and flexible ac transmission systems (FACTS) devices, including STAtic var COMpensators (STATCOM). This paper demonstrates that pulse-width modulation (PWM) based on space vector modulation (SVM), and using low switching frequencies (a few hundred Hertz) can be implemented in multimodule power converter systems. The proposed scheme is based on a delayed sampling technique and allows output voltage control and minimization of harmonic components. Pattern generation options are analyzed and system waveforms are presented for different switching frequencies and number of modules. Results are validated by simulation and confirmed by experiments on a 5-kVA prototype unit.

This paper introduces a new method of IGBT switching loss reduction on the system level, while leaving the PWM scheme completely unchanged. The switching loss reduction is achieved by designing an IGBT gate driver that dynamically sets the IGBT gate current depending on feedback signals from IGBT current, IGBT voltage, phase load current, and DC link voltage if it is not constant in the application. Factors influencing switching losses will be demonstrated for two types of output driver stages: one with discrete switching speed setting and one with continuously variable switching speed. Comparing to other gate driver types with or without feedback aimed at keeping constant dv/dt, di/dt, and overshoots of IGBT voltage and current, the proposed gate driver not only ensures the operation of an IGBT in the safe operating area (SOA), but also improves the SOA utilization density by tracking the programmed voltage and current limits using peak-detection circuitry while minimizing the switching losses. Adaptive feedback control algorithms have been developed and verified by simulations. Keywords—gate driver; variable current output stage; IGBT switching loss; adaptive control algorithm I. INTRODUCTION Discrete IGBTs and IGBT modules are used in high- voltage applications mainly to perform DC to AC power conversion and vice-versa. The conversion losses dissipated by devices in form of heat consist of three sources: conduction losses, leakage current losses, and switching losses. The first two sources usually cannot be varied as long as appropriate extreme levels of gate-emitter voltage are applied to the IGBT. The switching losses, on the contrary, can be widely varied by using different modulation schemes, switching frequencies, and gate drivers. The topic of this paper is about development of a closed-loop gate driver with the task of minimizing switching losses while keeping the IGBT in the SOA.

This paper presents a variable reactance type series compensator with pulse-width modulation (PWM) capability. On a per-phase basis, it can be represented by a bidirectional force-commutated switch in parallel with a combination of a capacitor in series with another bidirectional force-commutated switch. The equivalent reactance of the capacitor circuit can be continuously varied, with no risk of short-circuiting the capacitor or interrupting the line current. A simple and reliable PWM AC controller which requires only four force-commutated switches and a three-phase diode bridge is proposed for the implementation of the three-phase compensator. The degree of series compensation is controlled by duty cycle variation of a common train of pulses. No low order harmonics are generated since the force-commutated switches can operate at frequencies higher than that of the AC mains. The operating principles are presented and the theoretical analysis is verified by digital simulation and experimental results on a laboratory set-up.

Operating voltage-source pulsewidth-modulated (PWM) inverters in the overmodulation region extends their voltage and power ranges. Proper operation in this region is of particular importance in AC motor drives. This paper presents a classification algorithm for the implementation of the space vector modulation (SVM) in the pulse-dropping region. It is demonstrated that the proposed algorithm allows smooth transitions through the entire operating range up to square wave operation. It does not require approximations and guarantees exact positioning of the switching instants. In addition, it is shown that the harmonic distortion can be kept lower than with conventional techniques in most of the overmodulation region. The technique requires less computational time, when compared with the conventional SVM methods. The results of the theoretical and mathematical analysis are verified on a 2-kVA prototype unit using a digital signal processor (DSP)-based controller.

A zero-voltage-switched (ZVS) pulsewidth-modulated (PWM) boost converter with an energy feedforward auxiliary circuit is proposed in this paper. The auxiliary circuit, which is a resonant circuit consisting of a switch and passive components, ensures that the converter's main switch and boost diode operate with soft switching. This converter can function with PWM control because the auxiliary resonant circuit operates for a small fraction of the switching cycle. Since the auxiliary circuit is a resonant circuit, the auxiliary switch itself has both a soft turn on and turn off, resulting in reduced switching losses and electromagnetic interference (EMI). This is unlike other proposed ZVS boost converters with auxiliary circuits where the auxiliary switch has a hard turn off. Peak switch stresses are only slightly higher than those found in a conventional PWM boost converter because part of the energy that would otherwise circulate in the auxiliary circuit and drastically increase peak switch stresses is fed to the load. In this paper, the operation of the converter is explained and analyzed, design guidelines are given, and experimental results obtained from a prototype are presented. The proposed converter is found to be about 2%-3% more efficient than the conventional PWM boost converter.

Shunt-type static VAr compensators have been shown to be an effective means of increasing the transmission capability of power systems and of increasing the power factor of industrial loads. This paper presents an alternative to the shunt connection consisting of a series-connected transformer-coupled pulsewidth modulation (PWM) inverter. The scheme consists of a current source inverter (CSI) fed from a self-controlled DC current bus and presents the following features: (1) instantaneous series injected voltage control through online PWM of the DC link current; and (2) steady-state modulation index of the PWM pattern near unity through DC link current minimization. The first feature results in fast dynamic response, while the second feature ensures low and fixed injected voltage harmonic distortion and reduced steady-state compensator losses. Operation of the compensator and of the two-loop control scheme are presented. Simulation and experimental results on a 2 kVA laboratory prototype unit confirm the feasibility of the proposed VAr compensator structure.

Pulsewidth modulated (PWM) current-source rectifiers (CSR), among other alternatives, offer marked improvements over thyristor line-commutated rectifiers as a source of variable DC power. Advantages include reduced line current harmonic distortion and complete displacement power factor control, including unity displacement power factor operation. However, due to nonlinearities of the PWM-CSR model, their control has usually been carried out using direct line current control in a three-phase stationary frame (abc). This paper proposes the application of a nonlinear control technique that introduces more flexibility in the control of the rectifier and results in a more straightforward approach to controller design. The proposed technique is based on a nonlinear state variable feedback approach in the rotating frame (dq). The approach allows the independent control of the two components of the line current (active and reactive) with the same dynamic performance, regardless of the operating point. The control strategy also eliminates the need for input damping resistors and rejects the effect of supply voltage variations. Furthermore, a space vector modulation (SVM) technique is used to maximize the supply voltage utilization. This paper includes a complete formulation of the system equations and a controller design procedure. Experimental results on a 2 kVA digital-signal-processor-controlled prototype confirm the validity of theoretical considerations.

Phase-controlled thyristor rectifiers are still the preferred choice in high-power AC/DC converters. This paper shows that their steady-state and dynamic performance can be greatly enhanced for applications requiring high-precision fast-response performance by means of a hybrid structure using a shunt pulse-width modulation (PWM) active filter. In this hybrid structure, the rectifier is designed to handle the bulk of the output power, whereas the PWM converter is only used for harmonic cancellation and current-error compensation under transient conditions. This results in a small power rating for the shunt-active filter. A suitable control scheme is proposed and implemented in this paper for the rectifier and PWM converter. Experimental results are provided to validate the proposed concept.

On-line pulsewidth modulation (PWM) pattern generators for current-source rectifiers and inverters offer a number of control advantages over off-line optimized patterns. However, when implemented using the principles which apply to voltage-source inverter PWM pattern generators, the switching frequency is equal to: (1) the carrier frequency in standard carrier-based implementations and (2) a function of the cycle frequency, sequence of space vectors, and selection of the zero space vector in space vector implementations. This paper shows that this frequency can be reduced to one-half of the respective frequencies. Two pattern generators are investigated: (1) an analog on-line carrier-based technique, namely, the modified dead-band technique and (2) a digital on-line space vector-based technique, where advantage is taken of the extra zero state available in current-source converters. It is shown that the switching frequency reduction is achieved with no penalty in the line current harmonic distortion. Moreover, a significant reduction of AC line current distortion is obtained with the modified dead-band technique for modulation indexes greater than 0.4. The principles of operation of the proposed schemes are explained, Experimental results on a 5 kVA current-source rectifier and a 5 kVA current-source inverter confirm the feasibility and features of the proposed pattern generators.

Standard pulsewidth modulation (PWM) techniques assume a ripple-free DC-link voltage at the inverter input terminals and ideal switches. Most techniques proposed in the literature to compensate the nonideal characteristics require additional and complex circuitry. This paper proposes and analyzes a simple method of generating PWM switching patterns which ensures a high-quality output voltage and inherently compensates for a nonideal DC bus and switching delays. The method is based on maintaining a sinusoidal volt-second distribution at the inverter output by sensing the output voltage and generating the gating pattern online. The principles of operation are explained, and a design procedure is presented. Simulation results illustrating the features of the proposed modulator are verified experimentally on a 3 kVA prototype unit.

Output harmonic minimization in standard pulse width modulation (PWM) pattern generators is based on the assumption that the input DC bus voltage is ripple-free. However, in a practical converter system, a nonideal DC bus deteriorates the quality of the inverter output voltage by introducing undesirable low-order harmonics that may be difficult to filter. The existing compensation techniques often use additional and complex circuitry to eliminate the effect of this ripple on the output voltage. This paper presents an online PWM pattern generator that inherently takes into account the DC bus ripple and generates gating signals required to produce high-quality sinusoidal output voltages. The technique is based on integrating the output voltage at a constant frequency on a pulse-by-pulse basis to ensure a sinusoidal volt-sec (V/s) distribution, irrespective of the input DC bus. The principles of operation are explained, and design equations are derived. The features of the proposed PWM pattern generator are illustrated. Comparison of the output voltage waveforms of those standard sinusoidal PWM (SPWM) techniques illustrate, in particular, the effectiveness of the ripple-rejection mechanism. Experimental results obtained on a 3-kVA laboratory prototype confirm the feasibility and features of the proposed pattern generator.

Many controllers of flexible AC transmission systems (FACTS), such as the STATCOM, the unified power flow controller (UPFC), the PWM asynchronous DC link, the thyristor-controlled series capacitor (TCSC) and the PWM series static VAr compensator have stabilized AC voltage support. Thus, they can be sited at the mid-point of the transmission line, which has been proven by the late E.W. Kimbark, as the optimum location for shunt capacitor compensation. This paper points out that the ability to double the power transfer of the uncompensated line applies also to the aforementioned FACTS devices. The mid-point siting also facilitates the independent control of reactive power at both ends of the transmission line.

The conventional structures used for phase shifters employ quadrature voltage injection controlled by means of on-load tap changers that require considerable maintenance. Line-commutated thyristor structures have been proposed to replace tap changers, but problems related to filter requirements or the number of switches have limited their utilization. This paper proposes a pulse width modulation (PWM) quadrature-booster phase shifter based on a force-commutated AC controller. It offers features such as fast dynamic response, continuous variation of the phase angle with low harmonic injection, and it requires a simple power structure and can be controlled by adjusting the duty cycle of the switches. The operating principles of the proposed phase shifter are analyzed and their feasibility is demonstrated through digital simulation and experimental implementation.

This paper describes possible incorporation of a modular multilevel inverter (MMI) for a low voltage low-medium power electric vehicle drive. The main focus of this work is essentially to justify the MMI topology as a viable alternative to the classical 2-level voltage source inverter in an electric vehicle drive due to its highly efficient operation. MMIs are viable alternatives for use in low and medium power applications due to lower power dissipations in the switches, low harmonic contents, modularity and outputs with lower electromagnetic interference (EMI). The MMI discussed is based on the half-bridge topology. The modes of operation and different control features have been reviewed. The capacitive voltage unbalance phenomenon is discussed and few balancing techniques are reviewed. Different PWM techniques and switch utilization of the half-bridge topology are also reviewed. A comparative study of two level VSI and 3, 5 level MMI is discussed in the context of conduction and switching loss reduction.

Reference/modulating waveform continuity is not a necessary condition for the implementation of switching patterns for three-phase pulse-width modulated (PWM) converters if the load or the source are Y-connected. This is based on the fact that the converter phase-voltages do not need to be sinusoidal and switching pattern discontinuities-"dead-bands"-do not degrade the quality of output/input voltage/current waveforms by introducing low-order harmonics if certain parameters are optimized. This paper discusses general characteristics of various discontinuous switching patterns for PWM converters and shows that they can yield better performance than their continuous counterparts in some operating regions. Performance is defined as harmonic distortion normalized with respect to effective switching frequency and serves as a measure of comparison with continuous PWM techniques, The applications considered include general purpose and application specific solid-state power supplies using voltage source inverters and PWM rectifiers. Theoretical considerations are verified on an experimental unit.

Active front-end rectifiers with reduced input current harmonics and high input power factor will be required in the near future for utility interfaced applications. In order to meet the new and more stringent regulations with force-commutated switches, the voltage source inverter approach is superior to the conventional current source approach, in terms of number of components and control options. However, the straightforward power angle control of the rectifier is characterized by a slow response and potential stability problems. This paper proposes a current-controlled PWM rectifier as an alternative. It provides near sinusoidal input currents with unity power factor and a low output voltage ripple. Moreover, it produces a well-defined input current harmonic spectrum, exhibits fast transient response to load voltage variations, and is capable of regenerative operation. PWM pattern generation is based on a carrier technique and the current controller is implemented in the: (a) stationary (abc) frame; and (b) rotating (dqo) frame. The design and the performance of the two controller options are investigated and compared. >

In this paper, an improved model predictive control (MPC) of the modular multilevel converter (MMC) with reduced computational burden is proposed. A mathematical model of the MMC system based on the sum and difference of arm voltages are derived. Instead of determining the switching state of individual submodule (SM), the voltage levels of MMC are considered as control options based on the assumption that the SM capacitor voltages are well balanced. The further reduction of calculation effort is realized by using the tolerance band of capacitor voltages. The proposed MPC has a hierarchical structure. The cost function taking into account the ac-side current control, circulating current elimination and arm energy balancing is presented. The optimal voltage level, selected by the cost function, provides the voltage reference for the pulse width modulation modulator. The SM capacitor voltage balancing is done using a separate control loop. The proposed control strategy is investigated using an MMC high-voltage direct current system with 200 SMs in each arm in real-time simulation and hardware-in-the-loop tests. The performance of proposed method is verified by both steady-state and transient-state operations.

Standard PWM current source inverters (CSIs) usually operate at fixed modulation index. The proposed modified current source inverter (MCSI) can operate with most pulse width modulation (PWM) techniques and with a variable modulation index, since the DC link inductor current freewheels on itself and not through the CSI. The use of variable modulation index control results in faster response times with no penalty on input power factor as compared to other variable modulation index schemes. This paper confirms this by investigating the input characteristics of the MCSI as seen from the AC mains. The quality of the input AC line currents is examined, and a design procedure for the input filters is given. Power factor and efficiency are discussed. Results are compared to those of other current source inverter topologies. Experimental results obtained from a 5 kVA converter confirm the theoretical considerations. >

A high-performance reactive-power compensator is presented and analyzed. The VAR compensator consists of a three-phase current-regulated pulse width modulated voltage-source inverter connected to a self-controlled DC bus. Reactive-power compensation is achieved by forcing the inverter output current to follow a reactive sinusoidal reference waveform at a constant switching frequency. The main advantages of this scheme are that it reduces the stresses on the switching devices (as compared with other current regulated techniques), and it has a fast response time, which allows almost instantaneous reactive current control, and low harmonic distortion in the line currents. In particular, the authors discuss the proposed scheme in terms of principles of operation, power and control system design, and the analysis under transient operating conditions. Simulated results obtained with the Spice simulating package for steady-state and transient operating conditions are presented and validated on an experimental unit. >

It is shown that it is possible to reduce and stabilize the switching frequency of three-phase delta-modulated PWM (pulse-width-modulated) inverters, while improving performance. This has been achieved by exploiting the characteristics of three-phase systems. The proposed modulator is based on controlling only two inverter legs at any given time, and forcing the switches in the other leg to remain permanently on or off for specified time intervals. The scheme imposes no penalty on the transient performance and the quality of the output waveform does not suffer. The resulting voltage gain of the inverter is also increased to the level of optimized techniques. Implementation of the technique is simple, requiring no additional computation or circuits. Experimental results on a 5 kVA unit confirm the feasibility of the proposed modulator. >

Modular current-source converter (MCSC) structures can enhance the current capacity and improve the power quality of converters in medium-voltage pulsewidth-modulated applications. An MCSC uses individual three-phase modules in a shunt connection to share the total power in a symmetrical manner. The modulation of these units is normally done using optimized patterns such as selective harmonic elimination patterns. However, the optimization is usually performed at the module level. This paper proposes a modulation technique that optimizes the operation of a complete MCSC taking into account all P modules. Thus, from the injected ac current, we remove P times the number of harmonics as compared with the conventional approach using the same switching frequency. A complete mathematical formulation and experimental results validate the proposed approach.

The performance of a three-phase solid-state reactive power compensator with fast dynamic response is analyzed. The compensator consists of a three-phase pulse-width modulated voltage-source inverter connected to a self-controlled DC bus. The principal advantage of this scheme is that it can maintain a near-unity source power factor without sensing and computation of the associated reactive power component. A mathematical model for the compensator connected across a variable power factor load is derived. The frequency response is obtained for open-loop operation. This allows the design of the controller. Predicted results are verified experimentally for both open and closed-loop responses. >

A stand alone, three-phase, delta-modulated, current-source PWM rectifier has been built and has been shown to be capable of operating with near sinusoidal current waveforms, unity power factor. and good DC current regulation. A mathematical model that has been justified against experimental measurements and results from digital simulations is presented. The current waveform distortion limit and the asymptotic stability limit are established. It is shown that the rectifier can operate safely within these limits in the entire range of its power ratings. >

Optimized PWM techniques have been developed and used with good results for voltage source inverters. However, implementation frequently requires complex electronic circuits, usually microprocessor-based, that cannot be justified in low cost applications. The paper examines three phase PWM pattern generators that are simple to implement with low cost circuitry, particularly with analog components. These modulation techniques are based on the model reference adaptive (MRA) technique. They exhibit intrinsic constant Volts/Hertz operation, and do not require frequency synchronization and frequency jumping, making them ideal for low cost inverter driven variable speed ac motor drives. The PWM patterns are generated by forcing the current in the built-in load model to follow a reference, by means of hysteresis control, also known as the delta modulation technique, or error triangulation control. Unlike delta modulation, the latter technique exhibits constant switching frequency and has an output voltage spectr...

This paper develops a direct power control structure to improve the performance of active filters. The PWM switching functions are defined based on the instantaneous power terms and the bandwidths of the two hysteresis comparators are dynamically adjusted to limit the averaged switching frequency. The controller directly uses the instantaneous power as control variables, to replace the current and voltage variables used in multi-loop control systems. It demonstrates that full control of the active filter, including the line current and the dc-bus voltage, can be realized within an integrated control loop. The advantages of the proposed control strategy are verified by simulation and experimental results on a 2 kVA laboratory prototype.

Performance criteria of three-phase PFC converters improve significantly with increasing the switching frequency, and highly depend on the control strategy used. This paper introduces a novel sensorless 60/spl deg/-clamping vector classification PWM technique for three-phase PFC converters. The proposed scheme needs no current sensor and extra calculation for identification the highest current carrying phase that must not be switched. In addition, classification algorithm offers exact positioning of the switching instants with less computational efforts and therefore shorter sampling period and higher switching frequency are possible, when compared with conventional SVM algorithms. In addition, to reduce the switching and conduction losses a novel switching pattern is presented in this paper. Simulation results on PSCAD/EMTDC software program, confirm the validity of the analytical work.

Three-level voltage source pulse width-modulated (PWM) inverters are used in high power industrial drive applications. Operating the converter in the undermodulation range of PWM technique restricts the drive operation in constant torque region. Therefore, an overmodulation strategy to extend the modulation region is essential. This paper is an extension to the operating range of the classification algorithm for the implementation of overmodulation schemes for SVM in three-level converters. Two schemes, depending upon the output voltage level, are developed to continuously increase the output voltage, in a controllable manner, up to the maximum attainable value. The technique requires less computational time, when compared with conventional SVM methods. The mathematical analysis is verified by means of simulation results.

Performance criteria of three-phase power factor correction (PFC) converters improve significantly. with increasing switching frequency, and highly depend on the control strategy used. This paper introduces a novel sensor less 60/spl deg/-clamping vector classification PWM technique for three-phase PFC converters. The proposed scheme needs no current sensor and extra calculation for identification the highest current carrying phase that must not be switched. In addition, the classification algorithm offers exact positioning of the switching instants with less computational efforts. Moreover its implementation is simpler and needs less hardware and software, when compared with conventional SVM algorithms. In addition, to reduce the switching and conduction losses a novel switching pattern is presented in this paper. Simulation results provided, confirm the validity of the analytical work.

Force-commutated PWM controlled multi-converter systems have been proposed for high power applications, particularly reactive power compensation and FACTS devices. Advantages of the space vector modulation make this PWM technique the preferred technique especially for high power applications. This paper presents new low switching frequency SVM strategies that lead to symmetrical and high quality output voltages fulfilling the high power application standards. Pattern generation options are analyzed and system waveforms are presented for different switching frequencies and number of modules. Results are validated by simulation and confirmed by experiments on a 5 kVA prototype unit.

Pulse width modulation is used in power converters to modulate a reference signal into gating pulses, this conversion can be carried out using analog circuits or digital circuits, such as DSPs and microprocessors. A more efficient and faster solution is the use of field programmable gate arrays (FPGAs). This paper demonstrates how to generate a variable PWM waveform based on standard FPGA device, the proposed circuit is incorporated with a DSP to provide a simple and effective solution for high-performance PWM converters. Experimental results are given to prove the design methodologies and theoretical analysis.

The conduction intervals of power semiconductors in static converters connected to the AC mains are dictated by the AC line voltages. Accurate and reliable synchronization signals must therefore be generated despite the significant distortion that can be present in the AC voltage. The authors propose a novel method for obtaining accurate zero-crossing signals, based on the use of switched-capacitor filters. The characteristic frequency of such filters depends on the frequency of an external control signal. Therefore, this frequency can be accurately set and made to track the input frequency variations. The scheme is presented and analyzed, and design criteria are derived. Experimental results demonstrate the superiority of the method over conventional filtering techniques. The scheme has been used successfully for phase-controlled thyristor converters and transistorized four-quadrant PWM (pulse-width modulated) AC/DC converters. >

A model reference adaptive (MRA) pulsewidth-modulated (PWM) technique for invertor switching applications is presented and analyzed. With this technique, the near optimal inverter gating signals are determined through a closed-loop process which compares a reference signal to a feedback signal derived from a built-in reference model of the load. In addition to its simplicity of implementation, the proposed PWM technique has the advantages of inherent controlled constant volts-per-Hertz (V/f) ratio operation and jitter-free operation with free-running carrier. Such features are of importance in variable-speed AC-drive applications where V/f control increases the control-circuit complexity and where carrier frequency jumps cause harmful torque/speed transients. >

An effective DC bus zero voltage switching (ZVS) turn-off method for high-frequency high-power pulse-width-modulation (PWM) voltage source inverters (VSIs) is presented. This method utilizes an innovative simple DC bus commutating subcircuit (consisting of only a DC bus interrupt switch and a capacitor connected across the DC bus) and a compatible PWM scheme. To minimize effective inverter switching frequency, the subcircuit provides ZVS only when needed and as dictated by the PWM scheme. Thus, switching losses and switch stresses are minimized, enabling the PWM to operate at high switching frequencies. Moreover, the DC bus commutation switch can be utilized to isolate the inverter under abnormal operation conditions. Complete circuit analysis, design guidelines, and a design example are also presented. Predicted results are verified by simulation. >

A novel static VAr compensator is presented. To overcome the problems of large low-order harmonics and slow response associated with conventional thyristor-controlled-reactor-based compensators, a pulse-width-modulated (PWM) AC converter is used to control the reactances of switched reactors/capacitors. Compared with the PWM static VAr compensators previously reported in the literature, the proposed compensator has a simpler structure and its switch gatings are easier to implement. Moreover, it does not require synchronization with the AC mains. The proposed concept was verified through a 1 kVAr prototype, and the measured experimental results prove that either leading or lagging reactive power can be achieved through simple duty cycle control. >

A low-loss soft-switching CSI topology, consisting of two parallel switches with a midpoint connected capacitor, is proposed. The structure accomplishes zero voltage switching during turn-off without any additional snubber circuit. It is well suited for high power applications requiring the use of two parallel switches. An analysis and design procedure are presented. Simulation results confirm the feasibility of the topology. >

The authors propose an improved version of the known pulse width modulation (PWM) controller topologies that can become a practical alternative to line-commutated AC controllers. The improvements include the use of typical unilateral switches, typical gating patterns, and reliability enhancing by-pass capacitors. The authors also present the analysis and design of the proposed converter topology, with key theoretical results verified experimentally on a 10 kVA breadboard. >

Voltage unbalance in AC supply systems is typically corrected by means of a shunt connected thyristor-controlled static VAr compensator. This approach has the disadvantage of slow response, harmonic injection into the AC system, and the requirement for large passive components. The proposed system consists of a three-phase PWM voltage source inverter, connected in series with the line through a three-phase transformer. The unbalance compensation is achieved by canceling the negative sequence component of the line-to-line voltages of the source. It is also shown that by having the inverter operate with unbalanced switching functions, it is possible to balance the load voltage and to control the amplitude of the positive sequence component in order to perform load voltage regulation. A complete mathematical description of the method is presented, demonstrating that the compensation can be achieved with low kVA inverters and low harmonic injection. Implementation procedures, design equations, and a design example are also included in order to illustrate the proposed method. Experimental results of a 1.5 kVA laboratory prototype system confirm the feasibility of the technique. >

Typical 6-12 kW switched-mode rectifier (SMR) converters operate at switching frequencies of about 40 kHz, employ FET switches, and utilize pulse width modulation (PWM) power control techniques. These operating conditions create a harsh PWM switching environment which makes the switching to conduction loss ratio approximately 3 to 1, and complicates the task of EMI suppression. A zero-voltage switching (ZVS) SMR high power circuit that improves overall converter efficiency by significantly reducing switching losses while moderately increasing conduction losses is presented. A feature of the proposed converter is that ZVS fixed frequency operation is possible, even with the primary of the transformer disconnected. The modes of circuit operation are presented and analyzed. The feasibility of the proposed converter is demonstrated with experimental results on a 7 kW prototype unit. >

A high-frequency snubber circuit is proposed for a zero-voltage-switched (ZVS) single-switch pulse-width-modulated (PWM) boost converter. It is shown to be effective in reducing switching losses during turn-off in high-voltage applications. The lossless snubber subcircuit consists of an LC resonant circuit and two diodes. The resonant capacitor of this LC circuit is parallel with the switch and discharges directly through the load, thus providing lossless switching and increasing the input-output DC gain of the converter. Experimental verification has shown a better efficiency (5% higher at 2 kW output power) and an increased output-input DC gain (15% to 20%) compared with a similar standard boost converter with a diode-resistance-capacitor (DRC) snubber circuit. No extra switch or special resistor is required to remove the energy of the snubber capacitor. >

The authors propose a topology based on a practical and reliable pulse-width-modulation (PWM) AC controller connected to the line side of the power transformer, the low voltage winding supplying an uncontrolled diode rectifier. The AC controller power circuit structure ensures reliable switch operation, and the equal PWM pattern is efficient and simple to implement. Advantages of the proposed topology include increased power factor, low AC input current and DC output voltage harmonic distortion, high efficiency, and high reliability. The authors describe the operation of the proposed topology and derive the characteristic equations. Simulation results are verified on an experimental 10 kVA prototype unit. >

The authors present a systematic comparison of the current source topology (pulse width modulation, or PWM rectifier) and the voltage source topology (synchronous link power converter) from the point of view of power converter and switch kilovolt ampere ratings. PWM patterns and input and output filtering requirements, power factor, operating regions, and control aspects. Experimental results obtained on laboratory prototypes are used to validate the theoretical considerations. In general, it is concluded that the synchronous link power converter gives a higher performance but is more complicated to operate. Unity power factor and regenerative operation are achieved with closed-loop control. The PWM rectifier provides good performance with simple control strategies. It requires a larger filter to suppress the input line harmonics, but is simple to operate since open-loop operation is possible. >