Adaptive current-threshold detector for an adaptive on-time Buck converter at light load

The adaptive on-time control technique has been tremendously utilized in DC–DC converters for its fast transient response, easier design and high efficiency at light load. In some applications the output voltage ripple of DC–DC converters has to be maintained within an acceptable level to achieve superior performance, which depends largely on the load current for adaptive on-time buck converters when operating in discontinuous conduction mode. This paper proposes an adaptive current-threshold detection method for reducing the output voltage ripple. An actual detector circuit is presented to implement the method. This circuit monitors the relationship between the peak inductor current and the load current at light load. Then it outputs a logic signal which controls the turn-on time of the main power MOSFET and hence the peak inductor current. Therefore, the magnitude of the output voltage ripple is controlled. The current-threshold detection method has been verified in an adaptive on-time buck converter by simulation and experimental results. The proposed method can also be used in other constant on-time converters.     

On the use of current sensors for the control of power converters

This paper describes the use of current sensors for the control of power converters. No voltage sensor is required in the whole system. The sensed current and the rate of change of the inductor current in different circuit topologies are used to determine the input and output voltages of the converters, and for current programming and maximum current protection. Apart from reducing the number of sensors, the proposed method provides inherent electrical isolation between the power conversion stage and the controller and lessens noise-coupling problems. The proposed technique is illustrated with a current-programmed DC/DC boost regulator with feedforward and feedback control. The regulator's steady state and transient responses under input source and output load disturbances are presented.     

零电流开关大功率DC/DC双全桥变换器设计

提出了一种基于双全桥结构的单向零电流开关大功率（兆瓦级）DC/DC变换器,该变换器通过采用两个全桥变换器来实现零电流开关,实现了较低的功率损耗和输出滤波电感。为了验证提出的变换器在大功率应用中的有效性,构建了小型样机并在大功率直流电网进行了实际测试。实验证明,相比传统的两种单向大功率全桥变换器,提出变换器所需的滤波电感和半导体器件的功率损耗均较少,分别仅为1.72mH和924.5kW。     

Regulation of a PWM rectifier in the unbalanced network state usinga generalized model

This study concerns the modeling and control of a pulse-width-modulated (PWM) rectifier in the case of network variations. The aim is to limit and stabilize variations of DC output voltage and line currents in such circumstances. Network variations can result in costly damage to power converters and their loads but a power converter such as the PWM rectifier, using cascade digital control, offers many capabilities to stabilize the system with optimized control. A generalized model of the PWM rectifier is first presented using the Clarke notation in order to separate the positive and negative sequences. The model is also extended to the harmonics. The cases of harmonic disturbance and an unbalanced network are then analyzed and an optimized regulation is presented for the latter case, validating the generalized model. Experimental results are proposed. The line current compensation loop method coupled with identification of network parameters offers a good solution to stabilize the PWM rectifier in an unbalanced network     

Practical Implementation of a High-Frequency Current-Sense Technique for VRM

To track the inductor current in high-frequency dc/dc converters is not effortless, particularly when high output currents and low output voltages are demanded by the load. This paper proposes a simple technique to obtain a good accuracy in the inductor current measurement in voltage regulator module (VRM) applications. The main idea is to obtain an equivalent voltage image which can be used for the high-frequency pulsewidth modulation controller to generate the converter control law. This strategy of measurement is generic, and it has been previously validated by simulations. Afterward, some experimental results are obtained by using several prototypes of dc/dc converters delivering a very low output voltage and owning several loads from 10-mA to 100-A currents. This wide range covers the power requirements of portable and embedded VRM applications. Moreover, this sense technique has also been validated in a digital high-frequency current-mode-controlled dc/dc converter.      

A unified analysis of PWM converters in discontinuous modes

Three discontinuous operating modes of PWM (pulsewidth modulated) converters are considered: the discontinuous inductor current mode (DICM), the discontinuous capacitor voltage mode (DCVM), and a previously unidentified mode called the discontinuous quasi-resonant mode (DQRM). DC and small-signal AC analyses are applicable to all basic PWM converter topologies. Any particular topology is taken into account via its DC conversion ratio in the continuous conduction mode. The small-signal model is of the same order as the state-space averaged model for the continuous mode, and it offers improved predictions of the low-frequency dynamics of PWM converters in the discontinuous modes. It is shown that converters in discontinuous modes exhibit lossless damping similar to the effect of the current-mode programming     

Comparison of single-sensor current control in the DC link forthree-phase voltage-source PWM converters

This paper presents a technique for reconstructing converter line currents using the information from a single current sensor in the DC link of a converter and comparative evaluation of the performance of single sensor control techniques in the DC link for voltage-source pulsewidth modulation (V-S PWM) converters. When 3φ input currents cannot be reconstructed, three methods to acquire the DC-link current are compared. Two of them are methods of modifying the switching state (I, II), and another is a method of using the predictive state observer. Also, compensation of sampling delay, and a simultaneous sample value of input currents in the center of a switching period are included. Suitable criteria for the comparison are identified, and the differences in the performance of these methods are investigated through experimental results for a typical V-S PWM converter rated at 10 kVA     

Interleaved converters operation based on CMC

A new family of low-ripple DC-to-DC switching converters based on a parallel connection of N-identical boost converters with current-mode control (CMC) is presented. The CMC strategy ensures that all the converters operate at the same duty cycle, sharing an equal amount of input current and forcing the output voltage to be an integer multiple (N) of the input voltage. As a result, the total input current and output voltage ripples are extremely low. The generation of control signals from inductor currents feedback without using external triangular or sawtooth signals is another characteristic of the new converter family     

Inductor voltage control of buck-type single-phase AC-DC converter

A novel inductor voltage control (IVC) method cable 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 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 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 over-current/short-circuit current limit     

A study of active power filters using quad-series voltage-sourcePWM converters for harmonic compensation

An active power filter using quad-series voltage-source pulse-width-modulated (PWM) converters to suppress AC harmonics by injecting compensating currents into the AC system is described. The circuit used to calculate the compensating current references, the compensation characteristics, and the capability of the DC capacitor are discussed theoretically and experimentally. A control circuit for the DC capacitor voltage is proposed. The discussions focus on transient states, based on the instantaneous reactive power theory. A passive LC filter is designed to remove the switching voltage and current ripples caused by the PWM converters at the AC side. Some experimental results that illustrate the details of the study are shown     

连续导电模式下的单电感多输出DC／DC变换器

系统分析了单电感多输出DC／DC变换器结构,及其采用分时复用原理实现多路输出。由于电感共享,各输出支路间存在着严重的交叉影响。当输出支路严格工作在不连续导电模式（DCM）或伪连续导电模式（PCCM）下,可有效抑制交叉影响。文中采用一种新的控制方式,利用各支路输出电压的共模电压、差模电压分别控制输入半桥、输出半桥占空比,在连续导电模式（CCM）模式下实现了几乎没有交叉影响的多路输出。     

Switched link PWM current source converters with harmonicelimination at the mains

Novel switched link pulse-width-modulated (PWM) current source converters are presented. These converters supply a controlled DC current to the load with a concurrent elimination of selected harmonics in the AC mains. The new topologies permit minimal constraints to be formulated resulting in significantly more efficient PWM patterns than hitherto reported in the literature. A higher number of harmonics are thus eliminated at the mains for a given switching frequency while maintaining a control capability of the output DC current in a wide range. Simulation results confirm the theoretical findings. Also discussed in the paper is the selection of capacitor filters to mitigate the residual harmonics     

A novel PWM control for a bi-directional full-bridge DC–DC converter with smooth conversion mode transitions

A novel CMOS integrated pulse-width modulation (PWM) control circuit allowing smooth transitions between conversion modes in full-bridge based bi-directional DC–DC converters operating at high switching frequencies is presented. The novel PWM control circuit is able to drive full-bridge based DC–DC converters performing step-down (i.e. buck) and step-up (i.e. boost) voltage conversion in both directions, thus allowing charging and discharging of the batteries in mobile systems. It provides smooth transitions between buck, buck-boost and boost modes. Additionally, the novel PWM control loop circuit uses a symmetrical triangular carrier, which overcomes the necessity of using an output phasing circuit previously required in PWM controllers based on sawtooth oscillators. The novel PWM control also enables to build bi-directional DC–DC converters operating at high switching frequencies (i.e. up to 10?MHz and above). Finally, the proposed PWM control circuit also allows the use of an average lossless inductor-current sensor for sensing the average load current even at very high switching frequencies. In this article, the proposed PWM control circuit is modelled and the integrated CMOS schematic is given. The corresponding theory is analysed and presented in detail. The circuit simulations realised in the Cadence Spectre software with a commercially available 0.18?µm mixed-signal CMOS technology from UMC are shown. The PWM control circuit was implemented in a monolithic integrated bi-directional CMOS DC–DC converter ASIC prototype. The fabricated prototype was tested experimentally and has shown performances in accordance with the theory.     

A new state feedback based transient control of PWM AC to DCvoltage type converters

This paper presents a new state feedback based control strategy for a PWM AC to DC voltage type converter with phase and amplitude control. In this control strategy the state variables of the LC filter connected to the AC side of the converter are fed back to the PWM pattern generator, thereby eliminating a DC offset of the AC input currents as well as oscillations of the DC output current during transients. Computer simulation of the converter system with the proposed control strategy shows that the transient waveforms of AC input and DC output currents are improved greatly even if the damping effect of the AC side resistance can not be expected. The DC voltage regulation with good dynamic response is also achieved even if DC capacitance is substantially reduced. Experimental results from a low power laboratory model are also included to confirm the simulated results and to demonstrate the effectiveness of the proposed control strategy     

Extension of inductor voltage control to three-phase buck-typeAC-DC converter

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 a 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     

VSS control of unity power factor

Three-phase pulsewidth modulation (PWM) converters, specifically, voltage-source inverters (VSI), are possibly the most frequently used power converters for applications such as industrial motor control, robotics, air conditioning and ventilation, uninterruptible power supplies, electric vehicles, etc. With the introduction of standards on limiting harmonic pollution of electrical power distribution systems, three-phase PWM converters are being considered as prime candidates for interfacing high-power electronic equipment to power supply lines. In these applications, converters can provide input currents without distortion and with unity power factor. In this paper, the idea of using variable-structure system (VSS) control strategy of a boost rectifier in sliding mode is described. A new discrete-time control algorithm has been developed by combining VSS and Lyapunov design. It possesses all the good properties of the sliding mode and avoids the unnecessary discontinuity of the central input, thus eliminating chattering, which has been considered a serious obstacle to applications of VSS. A unified control approach for output DC voltage and input AC currents based on discrete-time sliding mode is developed. The reference tracking performance is demonstrated in terms of transient and steady-state characteristics by simulation and experimental results. The invariance and the robustness features of the proposed control method are verified by experiment in the presence of large uncertainty in parameters and external perturbations     

Spectral characteristics of randomly switched PWM DC/DC convertersoperating in discontinuous conduction mode

This paper addresses a comparative study of the spectral characteristics of four random-switching schemes that apply to the basic pulsewidth-modulation (PWM) DC/DC converters operating in discontinuous conduction mode (DCM). They include randomized pulse position modulation, randomized pulsewidth modulation, and randomized carrier frequency modulation with fixed duty cycle and with fixed duty time, respectively. Mathematical models that characterize the input current and output voltage of the three basic PWM converters operating in DCM are derived. In particular, the effectiveness of spreading the dominant switching harmonics in the input current that normally exist in the standard PWM scheme and the introduction of low-frequency harmonics in the output voltage with respect to the randomness level are investigated. The validity of the models and analyses are confirmed experimentally by using a DC/DC buck converter     

DC characteristics and stability of push-pull and bridge-typezero-current-switched quasi-resonant converter

In the buck-derived, push-pull, and bridge-type topologies the output inductor current during the switched-off interval can free-wheel either through the shorted secondaries of the transformer or through a separate free-wheeling diode (FWD). It is shown that the former method results in highly nonlinear DC voltage-conversion-ratio characteristics for zero-current-switched quasi-resonant converters operating in the half-wave mode. As a result the incremental gain of the power stage of these converters varies with input voltage and load over an extremely wide range, so that it is not possible to achieve stable feedback control with high loop gains using conventional compensation techniques. It is shown that the addition of a FWD not only linearizes the DC characteristics but also reduces current and voltage stresses on semiconductor devices and improves efficiency     

Single-Phase Multilevel PWM Inverter Topologies Using Coupled Inductors

The number of voltage levels available in pulsewidth modulation (PWM) voltage source inverters can be increased by using a split-wound coupled inductor within each inverter leg and interleaved PWM switching of the upper and lower switches. The magnetizing inductance of the symmetrical split-wound inductor filters the high-frequency PWM voltage differences between the upper and lower switches. The same inductor presents a three-level PWM voltage at the inverter output terminals, with the winding leakage inductance being located in series with the low-frequency output current. Deadtime PWM signal delays can be reduced as dc-rail short circuits are not possible: as a result, the quality and voltage range of the PWM output is improved. Since the inductor windings are technically exposed to high-frequency PWM ac voltages with no dc components, device voltage drops help to reduce the buildup of winding dc currents. Theoretical analysis and a sample design case are presented to illustrate how to design suitable inductors for the various topologies. Simulation and experimental results are used to illustrate the operation of the proposed inverter structures.      

A novel instantaneous power control strategy and analytic model forintegrated rectifier/inverter systems

This paper is concerned with the design and implementation of an integrated pulse width modulation (PWM) rectifier/inverter for three-phase induction motor drives. Two identical PWM converters are used to serve as power regulator with unity power factor and servo motor drive using field-oriented control, respectively. A new input-output instantaneous power balancing approach is proposed to improve the dynamic response of input power regulation during output load change in order to minimize the DC-link capacitance. By using the synchronous rotating-frame current regulators, both the input and output currents of the integrated system are characterized with fast current response and low harmonic distortion. The effects of the dynamic response using different input power control methods are compared and the systematic design and analysis of the proposed method are also presented. Theoretical results of the analysis are verified experimentally