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The challenge in controlling a three-phase pulsewidth modulation (PWM) rectifier under balanced conditions arises from the fact that the state-space averaged model reported in literature has a multi-input--multi-output nonlinear structure and furthermore exhibits a nonminimum phase feature. In this paper, a simple single-input-single-output model is constructed by separating the d-axis and the q-axis dynamics through appropriate nonlinear feedforward decoupling while maintaining nearly unity power factor operation. With the proposed model, the nonminimum phase feature inherent in an ac-to-dc rectifier becomes a simple right-half-plane zero appearing in the small-signal control-to-output transfer function. In addition, the model exhibits a close similarity to a dc-dc boost converter under both large-signal and small-signal operating conditions. This makes it possible to extend the system analysis and control design techniques of dc-dc converters to the three-phase PWM rectifier also. The validity of the proposed model has been verified experimentally in the frequency domain under open-loop operation of the PWM rectifier. The usefulness of the model is further demonstrated through closed-loop operation of the rectifier with both voltage mode and inner-current-loop-based schemes. Index Terms--Pulsewidth modulation (PWM) power converters, voltage mode control.

The inherent switching of power devices in a switch mode power supply generates electromagnetic interference (EMI) noise. This noise is dependent on several factors such as component layout, circuit parasitics, and the control techniques implemented. Several methods have been reported in literature to mitigate the EMI problem. However, until now, a metric to characterize and compare the EMI spectra of power converters is not available in literature. This paper proposes a simple metric to measure and characterize the EMI spectrum of power converters. The proposed technique is based upon the specification and thereby the size of an external passive filter required to meet the given EMI standards. The proposed metric is useful in evaluating and comparing the severity of the EMI noise generated by different implementations of a power converter. Thus, it allows the designer to choose the better implementation option from an EMI noise perspective. The use of the proposed metric is demonstrated through the comparison of the quality of spectra of a power converter with two different switching schemes. Index Terms--Common mode (CM), differential mode (DM), electromagnetic interference (EMI).

The purpose of a voltage controller for uninterruptible-power-supply inverters is to produce stable output voltage with low distortion under all loading conditions, particularly under nonlinear loads and load transients. Since the output impedance of the inverter is the source for tracking error caused by load current, this paper proposes a simple digital feedback controller that focuses on reducing the output impedance of inverters by a feedback of the load current. The proposed control strategy ensures high-quality steady-state and dynamic responses from the inverter system. The design of the proposed digital controller is simple and requires only a reasonably accurate knowledge of the output L-C filter parameters. In addition, only the output voltage and the load current are sensed if the dc link voltage is constant. The results of simulations and experiments show that the proposed controller can achieve very low total harmonic distortion and fast dynamic response under varied loads including nonlinear loads with low switching frequency. Index Terms--Digital control, pole-placement, pulse-widthmodulation (PWM) inverter, uninterruptible power supply (UPS).

This paper proposes a controller for uninterruptible power supply inverters based on a particular type of onlinetrained neural network, which is called the B-spline network (BSN). Due to its linear nature and local weight updating, the BSN controller is more suitable for real-time implementation than conventional muitilayer feedforward neural controllers. Based on a frequency-domain stability analysis, a design methodology for determining the two main parameters of the BSN are presented. The model is found to be similar to that of an iterative learning control (ILC) scheme. However, unlike ILC, which requires a complex digital filter design that involves both causal and noncausal parts, the design procedure of the proposed BSN controller is straightforward and simple. Experimental results under various conditions show that the proposed controller can achieve excellent performance, comparable to that of a high-performance ILC scheme developed earlier. The proposed controller is an attractive alternative to both the multilayer feedforward neural controller and iterative learning controller in this and similar applications. Index Terms--Digital control, inverters, iterative methods, neurocontrollers, spline functions, uninterruptible power systems.

High power conversion efficiency is an important requirement of the front-end power-factor-corrected (PFC) boost rectifier that is used in shaping the ac input current in a typical modern switch-mode power supply. A reasonably accurate estimate of the power losses in individual components is essential in order to improve the efficiency of the PFC rectifier. In this paper, difficulties in the measurement of individual component power losses with particular reference to an ac--dc converter are brought out. A method of loss evaluation by measurement of temperatures of individual components and surrounding ambient is presented. Experimental results that are carried out on the front-end boost PFC rectifier of a commercial ac-dc converter are presented to validate the loss estimation method. Index Terms--Loss measurement, power factor, pulsewidth-modulated power converters, rectifiers, switch-mode power supplies.

In this paper, two iterative-learning-based control methods for uninterruptible power system (UPS) inverters, viz., direct iterative learning controller (direct ILC) and hybrid iterative learning controller (hybrid ILC), are proposed. In both methods, a zero-phase filter that is designed in the frequency domain is applied in order to provide compensation for the resonant peak in the system model to ensure error convergence. Furthermore, a 'forgetting factor' is introduced in both control algorithms to increase the robustness of the scheme against measurement noise, initialization error, and/or variation of system dynamics due to any parameter drift. In the direct ILC method, ILC is combined with the feedforward of the reference to improve dynamic performance. This method is shown to be capable of achieving very high steady-state performance although its dynamic response was not very good. In the hybrid ILC method, ILC is combined with a proportional-derivative controller aside from the reference feedforward to improve the dynamic response further. Experimental results show that both proposed controllers can achieve very low total harmonic distortion and fast error convergence under different loads while using only one sensor. The proposed direct ILC is an effective solution for UPS products where high-quality steady-state output voltage is more important than fast dynamic response, while hybrid ILC can result in excellent steady-state performance with a more improved dynamic response than direct ILC. Index Terms--Digital control, inverters, iterative methods, uninterruptible power systems (UPSs).

The asymmetrical half-bridge (AHB) topology discussed in this paper is one of the complementary driven pulse-width modulated converter topologies, which presents an inherent zero-voltage switching (ZVS) capability. In the previous work, the ideal operation of the converter and the ZVS realization process have been analyzed. However, the influence of the circuit parasitics on the output voltage drop and the design constraints of the circuit parameters to ensure the ZVS operation have not been investigated. The minimum load needed to ensure the ZVS operation is also not readily available. This paper presents a detailed and practical design for a 1-MHz AHB converter. A revised voltage transfer ratio of the converter is derived considering the influence of circuit parasitics and the ZVS transition. Two circuit parameters responsible for maintaining the ZVS operation are the transformer leakage inductance and the interlock delay time between the gate signals of two switches. A design method of the two parameters is proposed, which can ensure the ZVS transition. The possible ZVS range of the load variation is also investigated. A 50-W AHB converter with 1-MHz switching frequency was constructed, and a maximum efficiency of 91% was achieved. Index Terms--Asymmetrical half-bridge (AHB) topology, pulse-width modulated (PWM), zero-voltage switching (ZVS).

Recently, there has been an increase in the application of fuzzy logic controllers (FLCs) for control of power electronic converters. Due to the FLCs' complex algorithm, their realization often calls for a compromise between cost and performance. In this paper, it is shown that the rule table of most of the two-input FLCs used with power converters can be approximated into a single nonlinearity. This allows the controller to be easily realized using simple, fast, and inexpensive analog circuits. The simplified 'nonlinear function controller (NLFC)' developed in this manner is shown to be equivalent in performance to the original FLC through simulations. The NLFC concept is then applied to PI-FLC, a type of FLC popular in power converter control applications. This results in the PI-FLC being replaced by a simple 'nonlinear PI controller (NPIC).' Using this simplification, the design of NPICs to obtain good dynamic performance in power converters is explained. An example design of NPIC for controlling a dc-dc boost power converter is presented. Experimental results are also presented to demonstrate the superior dynamic performance of the converter with NPIC versus that of a linear-PI controller. Index Terms--Dynamic response, fuzzy control, fuzzy logic, pulsewidth-modulated (PWM) power converters, switched-mode power supplies, Topelitz matrices.

A tri-state boost converter with an additional boost-inductor free-wheeling interval was proposed earlier to eliminate the right-half-plane (RHP) zero that occurs in the control-to-output transfer function of a classical boost converter under continuous-conduction mode of operation. A 'constant-Do' control scheme, in which the 'capacitor-charging' interval of the converter was kept constant, was employed. This resulted in a relatively large inductor current, especially under high line and load conditions, thereby causing high circuit losses. This paper proposes two variations of a novel dual-mode control (DMC) scheme that vary both the 'boost' and the 'capacitor-charging' intervals. Control analysis, design, and limitations of the proposed DMC schemes are presented. Through computer simulations and hardware experiments the performance of the tri-state boost converter with DMC schemes are compared with those of the tri-state boost converter with 'constant-Do' control scheme, and the classical PI-controlled boost converter. The DMC schemes achieve a significant (about 10%) improvement in converter's efficiency for a wide load range over the 'constant-Do' control scheme. Index Terms--Boost converter, 'constant-Do' control, dc-dc converter, dual-mode control, right-half-plane zero, small-signal analysis, tri-state boost converter.

A challenging problem in the design of boost converters operating in continuous-conduction mode is posed by the dynamically shifting right-half-plane (RHP) zero in the converter's small-signal control-to-output transfer function. The paper proposes a novel tri-state boost converter without such a zero in the transfer function. The additional degree of freedom introduced in the converter in the form of a freewheeling interval has been exploited through an easy control technique to achieve this elimination. The absence of the RHP zero allows the control scheme to achieve larger bandwidth under closed-loop conditions, resulting in fast response. Analytical, simulation and experimental results of the tri-state boost converter have been presented and compared with those of the classical boost converter both under open-loop and under closed-loop operating conditions. The results clearly demonstrate the superior dynamic performance of the proposed converter. The proposed converter can be used in applications wherever fast-response boost action is needed. Index Terms--Boost converter, dc-dc converter, right-half-plane zero, small-signal analysis, tri-state boost converter.

In low-output-voltage dc/dc converters, power losses due to the conduction of rectifying devices are significant. Using synchronous rectifiers instead of the conventional fast recovery diodes or Schottky diodes is an effective solution to this problem in most topologies. However, for synchronous rectifiers to perform effectively, it requires an external gate drive with proper sensing and timing control circuits. This can increase the complexity and cost in converter hardware implementation. For the first time, a smart power synchronous rectifier (SPSR), which is a two-terminal MOS rectifier, is designed to overcome this difficulty. The SPSR integrates a simple control unit with a power MOSFET into a smart module to form a self-controlled synchronous rectifier. It has great advantages over the conventional discrete circuit composition, such as integrated gate control, precise timing switching, and fast transient response, which are suitable for applications in high-frequency pulsewidth modulation (PWM) converter circuits. Index Terms - Power electronic devices, synchronous rectification.

A single-phase high-efficiency near-unity power-factor (PF) half-bridge boost converter circuit, which has been proposed earlier by other researchers, is presented with detailed analysis. This converter is capable of operating under variable PF. However, the focus of this paper is in achieving unity PF operation only. The efficiency of this circuit is high because there is only one series semiconductor on-state voltage drop at any instant. The existence of an imbalance in the voltages of the two dc-link capacitors, which was noted before, is confirmed here. The cause for the imbalance is analyzed using appropriate models, and a control method to eliminate it is discussed in detail. Analysis and design considerations for the power circuit using the fixed-band hysteresis current control (HCC) technique are provided. The analytical results are verified through simulation using switched and averaged circuit models of the scheme and also through experimental work. At 90-V ac input and 300-W 300-V output, the experimental prototype demonstrates an efficiency of 96.23% and a PF of 0.998. This converter, with its relatively high dc-output voltage, is well suited for the 110-V utility supply system. A circuit modification for universal input voltage range operation is also suggested. Index Terms - Half-bridge boost topology, IEC 1000-3-2, power factor correction, switch-mode rectifier.

In this paper, a new converter with two variations is proposed. A novel asymmetrical pulse-width-modulation (PWM) control scheme is used to control the converter under constant switching frequency operation. The modes of operation for both variations are discussed. The dc characteristics, which can be used in the design of the converters, are also presented. Two 50-W converters were built to verify the characteristics of the converters. Due to the zero-voltage-switching (ZVS) operation of the switches and low device voltage and current stresses, the converter has high full- and partial-load efficiencies. They are potential candidates for high-efficiency high-density power supplies application. Index Terms - DC-DC converters, soft-switched converters, zero-voltage switching.

A new constant switching frequency control method for single-phase boost-type ac-dc converters is presented. The on times of the converter switches in each switching period is determined such that the average input current tracks the reference template in every switching cycle. The problems encountered in achieving smooth and stable operation and the modifications made to overcome them are discussed. The simulation studies done on the converter controlled with this method, which is given the name predicted (on-time) equal-charge criterion (PECC) method, indicate stable operation at different input-current and voltage levels and power factors. The method was implemented on an insulated gate bipolar transistor (IGBT) converter rated for 1 kVA using a 80 386 processor system for computations. The experimental results are presented and discussed in this paper. Index Terms - Boost ac-dc converters, constant-frequency power converters, equal-charge criterion control, microprocessor control of converters.

Based on a generalized state-space sampled data modeling, an iterative and efficient algorithm for deriving the small signal transfer functions of any dc-dc converter is proposed. This algorithm is suitable to be implemented in a software program as an analytical tool for automated control analysis of general dc-dc converters. Such a tool would reduce considerably the time needed by research engineers in modeling existing and new topologies and control methods. The algorithm proposed is applicable to different kinds of linear and nonlinear control methods. It has been verified on different converters and control methods.

A new control method - resonant-tank control (RTC) - is proposed for a parallel resonant converter operating above resonance. Using a simple linear combination of tank variables, it has potential for high-frequency dc-dc converter applications. RTC controls the tank in a near time-optimal manner and is shown to have better dynamics compared to conventional frequency control. Experimental results to confirm the superior transient performance of the RTC method are provided. The principle of operation of the RTC may be extended to operation below resonance as well as to series resonant converter control.

A novel inductor voltage control (IVC) method capable of achieving any input power factor including unity is being proposed for buck-type ac-dc pulsewidth modulation (PWM) converters. In this method, the input inductor voltage is kept within a hysteresis band about a sinusoidal template, thus ensuring sinusoidal input current. This control is much less sensitive to parameter and control signal changes than the existing Delta modulation control (DMC). In this paper, the IVC method is applied to a single-phase buck-type converter. Useful design results based on steady-state analysis have been presented. Simulation and experimental results have been provided to verify the theoretical results. The companion paper extends the applicability of the IVC control method to three-phase converters also. The proposed IVC method has potential in applications requiring ac--dc rectifiers with overcurrent/short-circuit current limit. Index Terms--AC-DC power converter, PWM rectifier, unity power factor rectifier.

A novel inductor voltage control (IVC) method capable of achieving near unity power factor is being proposed for buck-type ac-dc pulsewidth-modulated (PWM) converters. In this method, the input inductor voltages are kept within a hysteresis band about a sinusoidal template, thus ensuring sinusoidal input currents. This control method is much less sensitive to parameter and control variations than the existing delta modulation control (DMC) method. A companion paper has introduced the IVC method for the case of a single-phase buck-type converter. In the present paper, problems involved in direct extension of the IVC method to three-phase buck converter are discussed first. Following this, a new switching logic scheme is proposed which enables these problems to be overcome and for IVC (as well as DMC) to be extended to a three-phase converter as well. Detailed simulation and experimental results have been provided to verify the expected good performance with IVC. The proposed IVC method has potential in applications such as those requiring ac--dc rectifiers with current limiting. Index Terms--AC-DC power converter, PWM rectifier, unity power factor rectifier.