Peak Current Control Method Research Articles

고효율 및 슬림형 전압 평형 3-레벨 벅 컨버터

The 3-level buck converter features half the switch voltage stress of the conventional synchronous buck converter. The operating frequency of the output inductor is also twice the switching frequency. The slope of the inductor current can be reduced as well due to the flying capacitor voltage, which can greatly reduce the size of the output inductor. Therefore, the 3-level buck converter can achieve high efficiency and high power density. The flying capacitor voltage must be half the input voltage to achieve the abovementioned strength. Most conventional control schemes for the voltage balance of the flying capacitor adopt a peak or valley current mode control method using real-time current sensing. Therefore, the control algorithm is complicated, and high performance and expensive digital controller is required. This study proposes an independent two-loop voltage mode control scheme that can guarantee the flying capacitor voltage to be half of the input voltage. The proposed control scheme can be simply implemented without current detection and does not require complicated control algorithms. Thus, simple and low-cost micro controller can be used. Experimental results from a rated prototype of 500 W are provided to verify the performance of the proposed control scheme.

A Constant Current Digital Control Method for Primary-Side Regulation Active-Clamp Flyback Converter

Constant current controlled flyback converter is widely used in low power applications for its simple structure and low cost. In order to further improve the output power and the efficiency, active-clamp flyback converter with soft-switching technique is always used. To avoid the nonlinearity and temperature drift of opto-coupler in the feedback circuit, a constant current digital control method is proposed for a primary-side regulation active-clamp (PSRAC) flyback converter in this article. Soft-switching technique is realized in discontinuous conduction modulation mode with a modified active-clamp technique. To compensate the nonlinearity of the secondary diode current with primary-side regulation, a new output current estimation algorithm is put forward based on the charge balance principle. The output current is predicted from primary current and the auxiliary winding voltage, and constant output current control is realized with primary peak current control method. The cost is low as only one low speed digital-to-analog converter, three comparators and a digital controller are required. The proposed control scheme was verified by a field-programmable gate array controlled 5.4-10.8 V/1.80 A PSRAC flyback converter. The output current accuracy is within in 1.2% in different input and output condition and the peak efficiency is improved by 3.6% after active-clamp technique is used.

A Constant Current Control Scheme for Primary-Side Controlled Flyback Controller Operating in DCM and CCM

Primary-side regulation (PSR) flyback converters operating in discontinuous conduction mode (DCM) are widely used in low-power applications. In DCM, the peak current control method for PSR flyback is generally adopted to achieve constant current (CC) output. However, there are few effective schemes suitable for DCM and continuous conduction mode (CCM) operation of PSR flyback converters due to the difficulty in estimating the output information correctly, especially in the case of analog circuit control. In this article, a control scheme based on midpoint sampling method is proposed to achieve a high-precision CC control, which operates seamlessly as the operating mode switched between DCM and CCM. In order to verify the feasibility and performance of the proposed control, a control IC with the proposed CC control scheme has been implemented in 0.18 μm 5 V/40 V BCD process. The experimental results show that the deviation of the output current is within ±1.93% under different input and load conditions.

Asymmetric slope compensation for digital hybrid current mode control of a three-level flying capacitor buck converter

The three-level flying capacitor (3LFC) buck converter has the potential to provide better efficiency and higher power density as compared to the traditional buck converter. However, due to the flying capacitor?s instability issues, control is challenging. In this paper, the digital hybrid current mode (DHCM) control method, which combines the average and peak current mode control techniques, is modified and implemented to a 3LFC buck converter. For flying capacitor (FC) voltage balancing, a novel asymmetric slope compensation (ASC) technique is presented. The proposed ASC technique achieves FC voltage balancing by adjusting the slope compensation of the two switching pairs asymmetrically, and therefore is applicable to any type of digital peak current mode control (PCM) method. The ASC technique for DHCM control of the 3LFC buck converter is verified in simulations and experimentally with an ARMbased mixed-signal microcontroller on a 250-kHz, 24-V input, and 35-W/4-A output prototype. The overall control method enables the implementation of the 3LFC buck converter for accurate and fast current regulation, and therefore is especially advantageous for LED and laser diode driver applications.

Stability Analysis of Constant Current-Controlled Primary-Side Regulation Flyback Converter

In low power applications, primary-side regulation (PSR) flyback converter with discontinuous conduction modulation (DCM) mode is widely used to realize constant output current for its simple structure and low cost. In peak current control method, the output current can be predicted from the primary peak current, demagnetization time, and switching period. Based on the current prediction, a pulsewidth modulation (PWM) mode and a pulse frequency modulation (PFM) mode are used. However, as the output current cannot be sampled directly in PSR flyback converter, traditional small-signal modeling method based on the control and output variables cannot be used. Moreover, there is no stability analysis for these constant current (CC)-controlled PSR flyback converters. In this article, a discrete matrix analysis method is proposed to analyze the stability of CC-controlled PSR flyback converter. An iterative matrix of the control and output variable perturbations is obtained, and the stability can be acquired from the eigenvalues. Oscillation occurs in the above PWM mode, and a stable control is realized in PFM mode. An improved PWM mode is thus proposed and analyzed for stable control. The analysis is verified in a PSR flyback converter with 1.92 A.

Multi-Harmonic Currents Control Strategy for Five-Phase Permanent Magnet Machine with non-sinusoidal back-EMF

This paper describes an optimal torque per peak current control method for a five-phase permanent magnet (PM) machine considering both 3rd and 5th harmonic currents. These optimal ratios to the fundamental component are analytically derived to maximize the output torque. It is found that except for the 3rd harmonic current contributing to the output torque, the 5th harmonic current can also produce the additional positive torque. However, the 5th harmonic is zero sequence component for the five-phase machines, which does not exist in the phase windings. Hence, the neutral point is required to connect the middle point of the DC link capacitors for constructing flowing path. The conventional vector space decomposition (VSD) control is extended to zero sequence sub-plane, which can quantitatively control 5th harmonic current. For a prototype five-phase PM machine, the average torque can be increased by 21.4% with 3rd harmonic current injection. Meanwhile, 10.7% additional positive torque is achieved together with 3rd and 5th harmonic injection. The torque ripple remains similar to that without harmonics injection. Finally, the experiments are given to demonstrate the theoretical analysis.

Peak Current Control-Based Power Ripple Decoupling of AC–DC Multichannel LED Driver

AC–DC light-emitting diode (LED) drivers suffer from short lifetime because of the low-lifetime electrolytic capacitors used for dc bus decoupling. In this paper, a primary-side peak current control method applied for driving a two-stage multichannel LED driver is proposed. The LED driver consists of an ac–dc boost power factor correction stage and an isolated dc–dc nonresonant stage. A long-lifetime and small film capacitor is used for implementing the intermediate dc bus. The proposed method, which controls the peak value of the primary-side current of the transformers, is applied to the dc–dc stage to ensure constant dc current output of LEDs in spite of the widely varying dc bus voltage due to low bus capacitance. The proposed method compensates the effect of the large dc bus voltage ripple by varying the switching frequency of the primary-side switches. Detailed design procedure, theoretical analysis, and experimental results of the LED driver operating at 180 W with the proposed method are provided. The LED driver with the proposed control method is proved to have high overall efficiency.

Efficiency Improvement of Multichannel LED Driver With Selective Dimming

There is a widespread application of selective dimming of multichannel LED drivers. In this article, two new selective dimming methods to improve the efficiency of multichannel LED drivers are proposed. The proposed methods are based on a two-stage multichannel LED driver that consists of an ac–dc boost power factor correction converter at its front-end and a dc–dc non-resonant converter at its second stage. Primary side digital peak current control method is applied to the dc–dc converter to control the LED peak currents during selective dimming operation. The auxiliary back-to-back switches are connected across each transformer winding either at the primary side or secondary side to perform selective dimming. The duty ratios of these auxiliary back-to-back switches are varied at lower than switching frequency of dc–dc converter to control the brightness of LED loads. The proposed topologies offer high efficiencies in both full load and during selective dimming operations, and meet the IEEE 1789 recommendation with 3 kHz dimming frequency. The design of the proposed dc–dc converters, modes of operation as well as detailed theoretical analysis are presented in this article. A 150-W prototype of the proposed LED driver with a non-DSP microcontroller is implemented to verify the feasibility of such LED drivers. Comparisons between the proposed methods and the converters reported previously are presented in the article.

Design of a single-stage Flyback LED Constant current Driving Power Supply

In order to solve the problems of high cost and low efficiency of current LED driving power supply, a single-stage flyback LED constant current driving circuit is designed. The power supply adoptes OZ8027 as the main control chip in the critical conduction mode, which uses the peak current control method. A wide range of input voltage of 85~265V is designed, the output current is 200mA, and the actual output power target value is 13W. It is suitable for an AC input type for flyback constant current driving circuit whose light source board owns LEDs for 2-series and 5-parallel. This research describes the working principle of a single-stage flyback LED constant current drive circuit. The detailed design and analysis of the various components of the driving power supply circuit. The test shows that the circuit works normally, and the output current can be obtained after testing. The current is stable at 200mA, output power is 12.7W, output ripple ratio is 1.65%, and the conversion efficiency is as high as 92.33%. The experimental results show that the designed LED driving power supply is stable and reliable, low cost, high efficiency and meets the design standards of LED driving power supply.

A Low-Cost Constant Current Control Method for DCM and CCM in Digitally Controlled Primary-Side Regulation Flyback Converter

Primary-side regulation (PSR) flyback converter with a discontinuous conduction modulation (DCM) mode is widely used in small-power applications. To introduce higher output power, a continuous conduction modulation (CCM) mode is used in which an analog to digital converter of high cost is always required. In this paper, to reduce the cost, a novel digital peak current control method is proposed to realize constant output current control in both DCM mode and CCM mode. However, there exists a time length calculation error that cannot be avoided in the critical condition between DCM mode and CCM mode. The output current will be lower than the nominal output current. Thus, a hysteretic multimode control method with two pulse width modulation modes and two pulse frequency modulation modes is utilized to eliminate the time length calculation error. In the proposed control, only a low-speed digital to analog converter and three comparators are used, which greatly reduced the cost, and high accuracy of output current can be obtained. The proposed control scheme was then verified through a field-programmable gate array (FPGA)-controlled 3.76–15 V/3.76 A PSR flyback converter. In the prototype, the accuracy of the output current is within ±1.5% for the universal load range.

Analysis and Optimization of Variable-Frequency Soft-Switching Peak Current Mode Control Techniques for Microinverters

This paper presents a detailed power loss model for a microinverter with three different zero voltage switching boundary conduction mode (BCM) current modulation methods. The model is used to calculate the optimum peak current boundaries for each modulation method. Based on the power loss model, a dual-zone modulation method is proposed to further improve the microinverter efficiency. The proposed modulation method provides two main benefits: the addition of one more soft switching transition and low inductor peak current. The additional soft switching transition reduces switching losses by means of zero current switching. The lower peak current boundary reduces inductor rms current and conduction losses as well as allowing the output filter inductor to be smaller and more efficient. An improved BCM peak current control method was proposed and implemented on a microinverter prototype. The control circuit provides a highly accurate representation of the filter inductor current waveform and also provides galvanic isolation that simplifies control circuit design. The experimental results on a 400-W three-phase half-bridge microinverter validate the theoretical analysis of the power loss distribution and demonstrate that further improvement in efficiency can be achieved by using the proposed dual-zone modulation method.

A grid-tied flyback-based PV inverter with BCM variable frequency voltage mode control

The modularized microinverter, which can feed small power to the grid directly, has the merit of increasing the conversion efficiency and installed flexibility of the renewable power generation system. This paper proposes a control method for a microinverter derived from the conventional AC-DC boundary conduction mode (BCM) PFC converter. The variable frequency peak current mode control method and the variable frequency voltage mode control method are proposed for the control of a flyback-based inverter. Modeling of the inverter and quantitative controller design of the variable frequency voltage mode control method is presented. A 120 W experimental system with PV module for generating power is built. The effectiveness of the proposed method is confirmed via simulations and measured results.

Design and implementation of a grid‐tied wind power micro‐inverter

Small wind turbine generator (WTG) below 300 W capacity is suitable to generate power in residential or city area, where no large space for installing kilowatt scale WTG. The modularised micro-inverter which can feed WTG power to the grid directly has the merit of increasing the installed flexibility and omitting the battery in this application. This study proposes a grid-tied micro-inverter combining the boost and flyback-based inverter topology and specially designed for the small WTG with permanent magnetic (PM) generator. The boost converter is used to step up the input voltage and track the maximum power point (MPP) of the WTG. The flyback-based inverter is used to feed power to the grid with unity power factor. A fast MPP tracking (MPPT) method is presented to track the wind power to fit for the wind speed with fast variation. The variable frequency peak current mode control method is adopted for the control of the flyback-based inverter. An interleaving technique is also applied to the inverter for increasing its power capacity. Quantitative controller design of the boost converter with the WTG input and the grid-tied flyback-based inverter is presented. A 240 W experimental system is built. A WTG emulator implemented with the M–G set is developed for testing the proposed system. Some simulation and measured results are provided for demonstrating the effectiveness of the proposed system.