Average Current Mode Control Research Articles

$I^{2}$ Average Current Mode Control for Switching Converters

Constant frequency average current mode (ACM) control is a widely used control scheme for converters requiring precise current control. However, its transient response is relatively slow, while the switching loss and driving loss significantly diminish the light load efficiency. To solve these issues, the I2 control ACM is proposed. By combining the fast direct current feedback and integral feedback, the I2 control achieves both wide bandwidth and accurate current control. As a particular embodiment of this concept, by adopting constant on-time modulation, constant on-time I2 control needs no artificial ramp, and has a fast dynamic response. Moreover, due to the decrease of the switching frequency, constant on-time I2 control improves the efficiency in discontinuous conduction mode. The concept of I2 control can be extended to other modulations. A small-signal model using the describing-function-based equivalent circuit model is proposed. The model is accurate up to 1/2 switching frequency. Based on the model, the design guidelines are discussed. The proposed control is verified with simulation and hardware measurement results.

Unified subharmonic oscillation conditions for peak or average current mode control

SummaryThis paper is an extension of the author's recent research in which only buck converters were analyzed. Similar analysis can be equally applied to other types of converters. In this paper, a unified model is proposed for buck, boost, and buck–boost converters under peak or average current mode control to predict the occurrence of subharmonic oscillation. Based on the unified model, the associated stability conditions are derived in closed forms. The same stability condition can be applied to buck, boost, and buck–boost converters. Based on the closed‐form conditions, the effects of various converter parameters including the compensator poles and zeros on the stability can be clearly seen, and these parameters can be consolidated into a few ones. High‐order compensators such as type‐II and PI compensators are considered. Some new plots are also proposed for design purpose to avoid the instability. The instability is found to be associated with large crossover frequency. A conservative stability condition, agreed with the past research, is derived. The effect of the voltage loop ripple on the instability is also analyzed. Copyright © 2014 John Wiley & Sons, Ltd.

Average Current Mode Control for LLC Series Resonant DC-to-DC Converters

An average current mode control scheme that consistently offers good dynamic performance for LLC series resonant DC-to-DC converters irrespective of the changes in the operational conditions is presented in this paper. The proposed control scheme employs current feedback from the resonant tank circuit through an integrator-type compensation amplifier to improve the dynamic performance and enhance the noise immunity and reliability of the feedback controller. Design guidelines are provided for both current feedback and voltage feedback compensation. The performance of the new control scheme is demonstrated through an experimental 150 W converter operating with 340 V to 390 V input voltage to provide a 24 V output voltage.

A fast-response sliding-mode controller for quadratic buck converter

The switched-mode power supplies are widely used in very low voltage and high-power applications where large conversion ratios are required. In such cases, the quadratic buck converter is the suitable one compared to buck, cascaded buck and multi-phase choppers, because of their limitations in switching frequency and losses. This paper presents mathematical analysis, design and simulation of a quadratic buck converter using fixed frequency Pulse-Width Modulation (PWM)-based Sliding-Mode (SM) controller in order to obtain fast dynamic performance. The design aspects include choice of sliding surface, deriving existing and stability conditions, control parameter selection and their analysis. The performance of the proposed converter is compared with the conventional Average Current-Mode (ACM) controller. In average current mode, the tuning of the PI controller for the inner current loop and outer voltage loop is done using bode plots. The simulation results for the two types of controllers are represented for analysing dynamic performance, as well as line and load regulations.

Zero‐voltage switching current‐fed flyback converter for power factor correction application

Previous research on flyback power factor correction (PFC) converters exposes some inherent shortcomings, such as high-voltage spike on the metal oxide semiconductor field effect transistor (MOSFET), frequency variation, pulsating input current and hard switching operation. This study presents a new topology for PFC applications named zero-voltage switching (ZVS) current-fed flyback converter to not only achieve spike-free voltage, ZVS on the MOSFETs, but also improve the input current quality. By utilising quasi-z-source configuration, the voltage spikes on the MOSFET are effectively eliminated using only a capacitive clamper, resulting in no-loss consumption. Low-voltage MOSFETs with low on-resistance Rds (on) are used to improve the efficiency. In addition, by taking advantage of the average current mode control with the continuous conduction mode operation, the input current perfectly tracks the input voltage. To demonstrate the circuit's feasibility, a 100–140 V input, 28 V/5 A output laboratory prototype was built. The experimental results showed that the proposed topology completely eliminated the voltage spikes on the MOSFETs. The efficiency was improved using low Rds (on) MOSFETs, and ZVS was achieved. In summary, the proposed topology meets the high efficiency and high-input current quality requirements.

Analysis and Design of Average Current Mode Control Using a Describing-Function-Based Equivalent Circuit Model

This paper proposes a small-signal model for average current mode control based on an equivalent circuit. The model uses a three-terminal equivalent circuit model based on a linearized describing function method to include the feedback effect of the sideband frequency components of the inductor current. The model extends the results obtained in peak current mode control to average current mode control. The proposed small-signal model is accurate up to half switching frequency, predicting the subharmonic instability. The proposed model is verified using SIMPLIS simulation and hardware experiments, which show good agreement with the measurement results. Based on the proposed model, new feedback design guidelines are presented. The proposed design guidelines are compared with several conventional, widely used design criteria. By designing the external ramp following the proposed design guidelines, the quality factor of the double poles at half of the switching frequency in the control-to-output transfer function can be precisely controlled. This helps the feedback loop design to achieve wide control bandwidth and proper damping.

Switching regulator using a high step‐up voltage converter for fuel‐cell modules

A typical fuel-cell stack produces a low DC voltage with wide variations; therefore a DC–DC switching converter is required to step up and regulate the output voltage. In this work, a model based on electrical variables is developed for a fuel-cell stack. This model is later combined with the model of a high step-up voltage converter to obtain a combined model that incorporates the behaviour of fuel-cell stack. The resulting model is then used to design an average-current mode controller for a switching regulator. To test the proposed regulator, a power module with polymer electrolyte membrane fuel cells is used as an input source. This module delivers an output voltage between 26 and 42 V depending on the current being drawn. Experimental results exhibit the robustness of the switching regulator to step changes in the output load and the output voltage of the fuel-cell stack.

Modeling and Analysis of Projected Cross Point Control—A New Current-Mode-Control Approach

This paper features the projected cross point control (PCPC) approach which is a recent current-mode control (CMC) technique. PCPC benefits from several advantages including fixed switching frequency, wide stability range, high current loop gain, improved audio susceptibility, and simpler design procedure. An introduction of its principles of operation is followed by detailed discussions about its stability and dynamic response. This paper then describes the development of the small-signal model of PCPC and derives transfer functions, such as current loop gain, audio susceptibility, and output impedance. Finally, simulations and experimental results are presented. Peak, average, and hysteresis CMC schemes are used for comparison.

Modelling of nonisolated high-voltage gain boost converters using the PWM switch model

This paper presents the small-signal models for nonisolated dc–dc boost converters based on the three-state switching cell (3SSC) and voltage multiplier cells (VMCs) by using the concept of pulse-width modulation switch introduced by Vorpérian. Two possible topologies are analysed in the study using one multiplier cell (VMC = 1) and two multiplier cells (VMC = 2). The models are validated by properly comparing the theoretical curves with those obtained in simulation tests. Besides, conventional average current-mode control is implemented in practice for the topology with VMC = 2. An experimental prototype rated at 1 kW is evaluated so that it can be seen that the control system is stable and the dynamic response of the converter is satisfactory.

Closed-Form Critical Conditions of Subharmonic Oscillations for Buck Converters

Based on a general critical condition of subharmonic oscillation in terms of the loop gain, many closed-form critical conditions for various control schemes in terms of converter parameters are derived. Some previously known critical conditions become special cases in the generalized framework. Given an arbitrary control scheme, a systematic procedure is proposed to derive the critical condition for that control scheme. Different control schemes share similar forms of critical conditions. For example, both <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> control and proportional voltage mode control have the same form of critical condition. A peculiar phenomenon in average current mode control where subharmonic oscillation occurs in a window value of pole can be explained by the derived critical condition. A ripple amplitude index to predict subharmonic oscillation proposed in the past research has limited application and is shown invalid for a converter with a large pole comparable to the switching frequency.

Simple analytical approach to predict large‐signal stability region of a closed‐loop boost DC–DC converter

A simple analytical approach to predict large-signal stability region of switching power converters is presented. By the concept of input-output stability, the large-signal stability region is estimated via the small-signal feedback control loops. Therefore the influence of the small-signal loop gains on the large-signal stability region is also revealed. A Boost DC-DC converter with average-current mode control is adopted as the example throughout the study to illustrate the derivation of the presented approach. The effectiveness of the approach is verified by both simulations and experimental results.

Comparison among Chargers of Electric Vehicle Based on Different Control Strategies

The charger of electric vehicle is a power electronic device which consists of rectifying devices and DC-DC converters. This nonlinear diode rectifier circuit has low power factor and high harmonic content. In order to improve power factor and reduce the harmonic distortion rate of the AC side current, single-phase non-controlled rectifier charger needs to install the active power factor correction device. A piece of power system analysis software which is called PSCAD is used in modeling of an EV charger which contains Boost-APFC. By means of simulation and analysis, differences of APFC characteristics between the hysteresis current control mode and average current control mode which has an influence on the power grid are compared. The consequence of simulation shows that the two control strategies achieve power factor correction and harmonic reduction requirements; Boost type power conversion circuit employs the average current control mode is better, which has following features: relatively faster settling time of the output voltage, relatively smaller overshoot, lower current harmonic distortion rate on AC side, lower switching frequency and better control effect.

Fully Digitalized Implementation of PFC Rectifier in CCM Without ADC

As is generally acknowledged, the main drawback of a fully digitalized power factor correction (PFC) rectifier is that too many analog-to-digital converters (ADCs) are used, and hence, the corresponding cost is high. Consequently, in this paper, the information on the desired signal is obtained from two paired saw-toothed waves compared with the sensed signal, without the use of any ADCs. For the PFC rectifier operating in the continuous conduction mode (CCM) under average current mode control, the two proposed formulas used to calculate the average inductor current, together with the strategy for changing sampling points, are applied to accurately sample the average inductor current of the PFC rectifier. At the same time, based on the slope value of the inductor current obtained from the proposed average current calculation formula, another related formula is derived to obtain the input voltage information used to feed the partial feedforward controller. As for the sinusoidal current command, it is generated by a sinusoid table along with a zero-crossing detector. Furthermore, the information on the output voltage is obtained by one simple approximate formula. Therefore, there is no ADC required to realize the full digital control of the PFC rectifier operating in CCM.

Digital Current Sharing Method for Parallel Interleaved DC–DC Converters Using Input Ripple Voltage

This paper describes a new digital current sharing method for parallel interleaved dc-dc converters. The difference between sensed inductor current values can cause unequal current distribution in the parallel dc-dc converters even though they are controlled by the same average current mode controller with a common current reference. To overcome this problem, a simple digital current sharing algorithm using input voltage ripple difference is proposed. The digital current sharing algorithm calculates the required current reference adjustment value using only the input ripple voltage difference information. No additional input current sensing circuit is required. The proposed algorithm achieves equal current distribution between phases of the parallel converters with high parameter insensitivity. For the experimental verification, a 500 W two phase interleaved synchronous buck dc-dc converter which charges a 24 V Li-ion battery is implemented.

Current-controlled switching regulator using a DC–DC converter with high-step-down voltage gain

During the last two decades, a great number of applications for DC-DC converters have been reported. New technologies are requiring low voltages. A possible solution to this problem is to use a transformerless high-step-down voltage converter where the conversion ratio depends on an integer number that indicates the number of times the steady-state duty ratio is multiplied by itself to obtain a high-voltage reduction. A controller design methodology is given in this study for such converter using average current-mode control. The proposed controller scheme employs the inductor current of the input stage and the capacitor voltage of the output stage. The advantage of using the selected current is that changes in the input source will have an immediate effect in the controller. The sensed current can also be used for one cycle overload protection; therefore the full benefits of current-mode control are maintained. The resulting switching regulator is able to provide a high-step-down voltage reduction and a regulated output voltage. Experimental results are given for a switching regulator with a voltage reduction from 48 to 1.5-V where the robustness of the proposed controller is tested under changes on the output load.

Sistema automático para o controle eficiente de iluminação para multiplas lâmpadas fluorescentes

Este artigo apresenta o desenvolvimento e a implementação de um sistema de iluminação automático multi-lâmpadas fluorescentes, com correção ativa do fator de potência de entrada utilizando a técnica dos valores médios instantâneos na forma digital, com capacidade de pré-aquecimento programável dos filamentos dos eletrodos e com controle de luminosidade. Além disso, o sistema proposto permite o gerenciamento e supervisão remota através de uma plataforma computacional amigável ao usuário, onde o sistema opera de forma automática ou manual, de acordo com a necessidade de cada ambiente e/ou do usuário, otimizando o consumo de energia elétrica.

Positive Feed-Forward Control Scheme for Distributed Power Conversion System With Multiple Voltage Sources

This paper presents the positive feed-forward control (PFFC) scheme associated with the average current-mode control (ACMC) scheme for the distributed power conversion system with the multiple voltage sources of different power ratings to protect individual voltage sources from the chain reaction of the undervoltage lockout in order not to cause system voltage collapse. The ACMC scheme has the inherent function of the negative feed-forward control (NFFC) to increase the input current of the converter by increasing the control duty cycle of the converter while the source voltage decreases. However, the undervoltage lockout protection of the employed source or converter can be activated if the source voltage drops below the set threshold value. Therefore, the PFFC+ACMC scheme is proposed to reduce the control duty cycle of the employed converter once the source voltage is less than the set threshold value to avoid system voltage collapse. The input current of the individual converter module is regulated by the proposed PFFC+ACMC mechanism in correspondence with the level of the sensed input terminal voltage. Finally, the prototype circuit of a simple interleaved buck-type converter system is built to validate the proposed PFFC+ACMC function.

Digitally Implemented Average Current-Mode Control in Discontinuous Conduction Mode PFC Rectifier

This paper proposes a digital average current-mode control method in discontinuous conduction mode (DCM) power factor correction rectifier. The proposed control technique does not estimate, but directly senses the average value of the inductor current in each switching cycle. It is implemented by means of a conventional current sensing circuit and a microcontroller. The calculation burden of the microcontroller is the same with that of conventional two-loop-controlled converter because the additional calculation process is not required. The control method achieves lower total harmonic distortion and higher power factor than the conventional technique. Experimental results with a 200-W prototype verify the feasibility and performance of the proposed control method.

A low-cost photovoltaic emulator for static and dynamic evaluation of photovoltaic power converters and facilities

In testing maximum power point tracking (MPPT) algorithms running on electronic power converters for photovoltaic (PV) applications, either a PV energy source (PV module or PV array) or a PV emulator is required. With a PV emulator, it is possible to control the testing conditions with accuracy so that it is the preferred option. The PV source is modeled as a current source; thus, the emulator has to work as a current source dependent on its output voltage. The proposed emulator is a buck converter with an average current mode control loop, which allows testing the static and dynamic performance of PV facilities up to 3 kW. To validate the concept, the emulator is used to evaluate the MPPT algorithm of a 230-W experimental microinverter working from a single PV module. Copyright © 2012 John Wiley & Sons, Ltd.

Analysis of Parameter Effects on the Small-Signal Dynamics of Buck Converters with Average Current Mode Control

In DC-DC Buck converters with average current mode control, the current loop compensator provides additional design freedom to enhance the converter current loop performance. On the other hand, the current loop circuit elements append substantial amount of complexity to not only the inner current loop but also the outer voltage loop, which makes it demanding to quantify circuit and operating parameter effects on the small-signal dynamics of such converters. Despite the difficulty, it is shown in this paper that parameter effects can be analyzed satisfactorily by using an existing small-signal model in conjunction with a newly proposed simplified alternative. As a result of the study, new insight into average current mode control is uncovered and discussed quantitatively. Measurable experimental results on a prototype averaged-current-mode-controlled Buck converter are provided to facilitate the analytical study with good correlation.