Primary-side Regulation Research Articles

Wireless Power Transfer System with Constant Voltage/Constant Current Output Performance

Aiming at the problem of unstable output voltage and output current caused by load fluctuation, this paper starts from the perspective of system topology and control strategy for analysis. First, the output characteristics of LCL-S (inductor-capacitor-inductor and series), LCL-P (inductor-capacitor-inductor and parallel), LCL-LCL (inductor-capacitor-inductor and inductor-capacitor-inductor), and LCL-LCC (inductor-capacitor-inductor and inductor-capacitor-capacitor) compensation topologies are analyzed. Combining the advantages of LCL-S and LCL-LCL compensation topology output characteristics, an LCL-LCL/S compensation topology is constructed, and its topology is optimized. Then the influence of parasitic resistance on the output characteristics of LCL-LCL/S compensation topology is derived. A control strategy of primary side regulation is proposed to address the issue of unstable output voltage and current caused by parasitic resistance in the system under variable loads. This method can effectively improve the stability of the output voltage and output current of the wireless power transfer system in the LCL-LCL/S compensation topology under load fluctuations. Finally, a set of experimental prototypes is built to verify the correctness of the theoretical analysis.

A high-efficiency primary-side regulation control strategy for half-bridge LLC resonant converter with wide input voltage range

The requirement of the half-bridge LLC resonant converter with a wide input voltage range is becoming higher in photovoltaic applications because of its simple structure and low switching loss. Conventional frequency modulation (FM) requires a wide switching frequency range and a high-quality factor circuit design, leading to reduced efficiency and large component volumes at light loads. To solve the problems, a high-efficiency control strategy using adaptive pulse-width and frequency modulation (APWFM) is proposed. APWFM adjusts the gain by changing the switching frequency and duty cycle simultaneously. When the output power is below the reference value, the switching frequency decreases linearly as the output power decreases, and the duty cycle is simultaneously modulated to achieve constant output voltage, so the switching frequency variation range is smaller than FM. This results in improved light or medium load efficiency in a limited frequency range while keeping a small volume of magnetic components. Also, the proposed control strategy is realized with primary-side regulation (PSR) to eliminate the optocoupler and simplify the control circuit. Experimental results demonstrate a significant improvement in efficiency at medium and light loads compared to FM, and the average efficiency is improved by 5% based on low cost and simple operation.

An Improved Constant Current Control Scheme for Multimode PSR Flyback Converter

For low cost and wide power range, the constant current (CC) control scheme for multimode primary-side regulation (PSR) flyback converter is prevalent in low and medium power applications. Although some multimode CC control schemes have been presented to raise CC accuracy, the current deviation caused by the mode conversion and inherent propagation delay remains unsolved. An improved CC control scheme is adopted to mitigate the influence of propagation delay or mode conversion on CC accuracy, which can be added into an IC controller with no extra pin penalty. The proposed scheme is implemented in 0.18lm 5V/40V BCD process. The experimental results reveal that the deviation of the output current is within 1 0.8% under different input and load conditions.

Thermal energy storage thermal data processing for heating systems

In order to solve the problem that the traditional industrial control methods cannot control the heating flow and water temperature in a timely and effective manner due to the high delay and complex coupling characteristics of the urban central heating system, the authors propose deep learning-based data processing and management for thermal heating systems. The author analyzes the non-ideality of district heating system and its influence on the application of deep learning technology, and gives solutions, respectively, finally, a primary side regulation scheme of district heating system based on deep learning and automatic control technology is proposed as a whole. The experimental results show that, by comparing the water supply temperature predicted by the equipment model of the primary side heat station with its actual measured value, the mean square error of the prediction results using the model directly is 1.30%, and the mean square error after model correction is 0.094%. The secondary return water temperature was controlled by adjusting the opening of the primary side electric valve, the expected secondary return water temperature in the scheme was compared with the actual secondary return water temperature, and the mean square error was 0.102%. It is proved that the scheme can achieve good control effect in the actual system, and the data result proves that the scheme is feasible.

High Precision Primary Side Regulation Constant Voltage Control Method for Primary and Secondary Resonant Active Clamp Flyback Converter

Active clamp flyback (ACF) converter has been demonstrated that which is better than traditional flyback in high-frequency power-adaptor applications. According to the circuit structure, ACF has two modes, primary resonant ACF (PR-ACF) and secondary resonant ACF (SR-ACF). In order to improve the power density, a high-precision primary side regulation (PSR) constant voltage control method for ACF converter is proposed in this article. The proposed method not only can be effectively adopted in PR-ACF but SR-ACF converter. The high-precision output voltage is predicted by highly accurate sampling points on primary auxiliary voltage. The applied microcontroller environment improves the practicability and increases the power density of the ACF system. To verify the proposed PSR method, a prototype that can be changed into PR-ACF and SR-ACF is designed. The output voltage offset, operation efficiency, and dynamic performance are analyzed. The tested results show that high-precision output is obtained in ACF converter by using the proposed method and the maximum output voltage deviation which are 4% and 3.5% in PR-ACF and SR-ACF converter, respectively. Moreover, SR-ACF has a higher efficiency compared with PR-ACF converter, and a smaller voltage shoot during dynamic process, which needs a larger regulation time since the additional output inductor.

An Active Clamp Flyback Converter With High Precision Primary-Side Regulation Strategy

The active clamp flyback (ACF) converter has been widely adopted because of the feature of isolation, soft-switching, and high conversion efficiency. On the other hand, due to the characteristic of the circuit cost reduction and the fast control response, the primary-side regulation (PSR) has become a popular control method for isolated power converters. However, high precision PSR strategies for ACF converters are not exposed. Therefore, the aim of this article is to propose a high precision PSR strategy for the ACF converter. Relations between the primary-side current and the secondary-side current are analyzed and derived. Both of the continuous conduction mode operation and the discontinuous conduction mode operation will be considered. The output voltage control mode or the output current control mode can be selected via the proposed strategy. In addition, a secondary-side losses compensation (SSLC) strategy is developed to deal with the non-ideal circuit characteristics as well as to enhance the control accuracy. Operational principles and thorough mathematical derivations will also be revealed. Finally, both simulation and experimental results obtained from a 100 W prototype circuit demonstrate the performance and feasibility of the proposed PSR and SSLC strategy. Validations show that the control accuracy of the output voltage and the output current are 98.54% and 98.42%, respectively.

Digital Voltage Sampling Scheme for Primary-Side Regulation Flyback Converter in CCM and DCM Modes

Primary-side regulation (PSR) flyback topology with discontinuous conduction modulation (DCM) mode has been widely used in low-power application due to its high stability, wide input voltage range, low cost, and low standby power. To improve the output power, continuous conduction modulation (CCM) mode is always introduced. However, in CCM mode, conventional PSR voltage-sampling method cannot realize high precision of output voltage or the voltage sampling method requires complex control of high cost. In this paper, a simple digital voltage sampling scheme with two reference voltages outputted from a digital-to-analog converter (DAC) is put forward to trace the “accurate-point” voltage for DCM and CCM modes. In CCM mode, the sampling voltage error of the “knee-point” voltage can be compensated just by inserting DCM switching cycle to obtain the “accurate-point” voltage. Voltage difference between DCM mode and CCM mode will be eliminated, and high precision is easily realized. The proposed method is verified in a 20V, 65W PSR flyback converter. The sampling method only requires a low speed DAC, three comparators and a digital controller. The output voltage precision is within 0.6% with universal input voltage.

A Modified Forward PFC Converter for LED Lighting Applications

A modified forward power factor correction (PFC) converter for light-emitting-diode (LED) lighting applications is proposed in this paper. The proposed circuit topology is an integration of a forward converter and a flyback converter with a multi-windings transformer. The flyback converter is operated as an auxiliary voltage source (AVS) connected in series with the rectified ac grid voltage to achieve low harmonic current distortion and high power factor. The magnetizing inductance energy is recycled to charge the capacitor in the AVS. The commonly used constant on-time control and primary side regulation can be easily adopted to control the proposed LED driver. The operation principle of the proposed converter is presented followed by the mathematical derivation of the parameter design. An 80 W prototype converter was built and tested to verify the performance of the proposed PFC converter. Experimental results show that the proposed PFC converter can comply with the IEC 61000-3-2 standard with high efficiency, low current harmonics, and a nearly unity power factor under universal input voltage range.

Analysis and Design for Output Voltage Regulation in Constant-on-Time-Controlled Fly-Buck Converter

Fly-buck converter is a multi-output converter with the structure of a synchronous buck converter structure on the primary side and a flyback converter structure on the secondary side, and can be utilized in various applications due to its many advantages. In terms of control, the primary side of the fly-buck converter has the same structure as a synchronous buck converter, allowing the constant-on-time (COT) control to be applied to the fly-buck converter. However, due to the inherent energy transfer principle, the primary-side output voltage regulation of COT controlled fly-buck converters may be poor, which can deteriorate the overall converter performance. Therefore, the primary output capacitor must be carefully designed to improve the voltage regulation characteristics. In this paper, a theoretical analysis of the output voltage regulation in COT controlled fly-buck converter is conducted, and based on this, a design guideline for the primary output capacitor considering the output voltage regulation is presented. The validity of the analysis and design guidelines was verified using a 5 W prototype of the COT controlled fly-buck converter for telecommunication auxiliary power supply.

Constant DC‐bus critical conduction mode Zeta converter fed primary‐side regulated LLC resonant converter in LED lighting applications

AbstractThis paper deals with a two‐stage high‐power light‐emitting diode (LED) driving solution for an isolated LED load. The first‐stage DC–DC power conversion is using a nonisolated Zeta converter operating in critical conduction mode to reduce component stress and switching power loss. This power stage is accountable for the power factor correction (PFC) under the universal AC voltage operation and developed a constant DC‐bus voltage for the second stage. In the second stage, half‐bridge LLC resonant converter is dedicated to deliver ripple‐free DC voltage to an isolated LED load. A new primary‐side regulation (PSR) technique is implemented in series with the resonant tank to reduce the component counts in the feedback loop. The stability of the DC‐bus voltage is verified by the state‐space analysis for the critical conduction mode (CrCM) Zeta converter. A 150 W load is driven by a prototype with a nearly unity power factor (PF) and low harmonics distortion in the input current.

Seamless Mode-Switch Control Scheme for Primary Side Regulation Flyback With Capacitorless Self-Adaptive Startup

A seamless mode-switch control scheme for primary side regulation flyback with capacitorless self-adaptive startup is presented in this article to increase the system stability for full-load range and reduce the area cost. Instead of traditional soft-startup, a peak current of primary side (PCPS) control scheme without off-chip capacitor is adapted during the startup process and a homologous startup modeling is built. Including the traditional pulsewidth modulation (PWM), the pulse frequency modulation (PFM), and deep pulsewidth modulation (DPWM) are adapted to reduce the standby power at utralight load. Meanwhile, a seamless control scheme is proposed to assure the continuity among the PCPS, PWM, PFM, and DPWM mode switch. The controller chip is fabricated in 0.18 μm BCD process. The experiment results show that the startup time and overshoot voltage are, respectively, 35 ms and 4 V at 0.8 A load current, 48 ms, and 0.2 V at 0.008 A load current. The accuracy of output voltage is within ±0.98% under different input voltages and loads while the peak power efficiency of 88.52% is achieved.

A Novel Digital Control Method of Primary-Side Regulated Flyback With Active Clamping Technique

Because of the different working principles between conventional flyback and active-clamped flyback (ACF), the existing primary-side regulation (PSR) technology cannot be applied to ACF. And in order to achieve PSR of ACF, a low-cost digital sampling method based on the auxiliary winding of the transformer is proposed. In the conventional peak current mode (PCM) controlled ACF, the sampling resistor of primary current may introduce additional power loss, and high-frequency oscillations during sampling may reduce system's stability. Therefore, a digital feedback-feedforward control (FFC) method is proposed to eliminate the sampling resistor. The stability of the proposed control method and its influence on the dynamic response are studied. In addition, since GaN device has higher power loss during reverse conduction than its Si counterpart, design considerations of reverse conduction time of power switches are also discussed in this paper. All control methods and design considerations are verified on a GaN-based 12V-3A ACF, and the proposed control strategy is implemented by FPGA.

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.

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.

Primary-Side Regulation Scheme for LLC Resonant Converter With Improved Resonant Current Sampling Circuit

A primary-side regulation (PSR) scheme for LLC resonant converter with improved resonant current sampling circuit is presented in this letter. An RC branch together with the auxiliary winding of the transformer is added in parallel with the current sampling resistor. The transformer magnetizing current component in the sampled primary current waveform on the sampling resistor can be offset by the generated voltage waveform on the added capacitor of the RC branch. In this way, PSR control for LLC resonant converter can be realized. Detailed operation principle and deviation analysis on the proposed PSR scheme are presented. Furthermore, a deadtime compensation is introduced to improve the output current accuracy caused by the component tolerance. Finally, a 48-78 V/1.3 A half-bridge LLC prototype has been built up to verify the theoretical analysis.

A Novel Primary-Side Regulation Control Scheme for CCM and DCM LLC LED Driver Based on “Magnetizing Current Cancellation Method”

In this article, the primary-side regulation (PSR) technique to achieve accurate output current in an LLC resonant converter has been studied. A novel PSR control scheme for an LLC light-emitting diode (LED) driver based on the “magnetizing current cancellation method” is proposed. The proposed “magnetizing current cancellation method” can effectively eliminate the effect of magnetizing current in the sampled primary resonant current under both the continuous conduction mode and the discontinuous conduction mode. Thus, the accurate output current can be estimated on the primary side of the LLC resonant converter. The magnetizing current cancellation method for the LLC LED driver with symmetric primary resonant current and asymmetric primary resonant current has been analyzed in detail. Some design considerations have also been presented. Then, an LLC PSR control circuit has been designed based on the theoretical analysis. Finally, a 48-to-78-V/1.3-A laboratory prototype for the LED driver has been built up, and experimental results show that good output current regulation has been obtained.

Flyback CC/CV AC–DC converter with high precision and reliability based on two-winding topology

Due to the rapid development of consumer electronics, the demand for power adapters is increasing. Therefore, a high-precision, high-reliability, low-cost flyback AC–DC converter without auxiliary winding was proposed in this paper. The converter adopted a primary-side regulation (PSR) topology to sample the output voltage and current from the primary inductor, and adjusted the switching frequency to achieve a constant output voltage. By alternately switching the main power BJT and the auxiliary MOSFET, with the advantage of the base charge storage effect, the chip was powered by the primary-side current. A primary-side sampling resistor was placed at the negative terminal of the ground potential of the chip, which approached real-time monitoring of the primary-side current. This improved the reliability and output accuracy of the system. To verify the feasibility and performance of the proposed circuit, an IC controller was designed and fabricated under the NEC 1 μm BCD process. Experimental result showed that deviations of the output voltage and current do not exceed ± 1.4% and ± 2.3%, respectively. These results also showed that the maximum conversion efficiency can reach a level of 78.7%, which satisfies the consumer market very well.

New Digital Control Method for Improving Dynamic Response of Synchronous Rectified PSR Flyback Converter With CCM and DCM Modes

In order to improve the dynamic response of synchronous rectified primary-side regulation (PSR) flyback converter with CCM and DCM modes, a novel digital control method is proposed. In a dynamic process, when output voltage is detected to fluctuate greatly, two special working modes called light-to-heavy mode and heavy-to-light mode are introduced. The output capacitor will be quickly charged and discharged by an optimized control scheme to make the output voltage's dynamic fluctuation smaller. On the other hand, during the dynamic process control, for eliminating overshoot and oscillation when the output voltage returns to the reference voltage, the load is detected by the output voltage slope to determine the appropriate operating mode. With the proposed control method, the dynamic performance can be greatly improved. An field programmable gate array (FPGA)-controlled 20-V/5-A synchronous rectified PSR flyback converter is established to verify the proposed control scheme. In the prototype test, compared to the traditional multimode control, the undershoot voltage and overshoot voltage of the proposed control scheme are improved from 5.02 to 1.63 V and 3.15 to 1.73 V, respectively. The undershoot and overshoot recovery times are reduced from 83.43 to 1.79 ms and 40.32 to 1.85 ms, respectively.

Quasi-resonant flyback PSR converter with adaptive frequency control

In this paper, a quasi-resonant (QR) flyback primary-side regulation (PSR) converter with adaptive frequency control is proposed. The converter adopts the PSR scheme to detect load information through the auxiliary winding. The converter employs the QR control scheme to switch in the valley mode either in CV or CC operation, which greatly reduces the switching loss. In addition, according to the load condition, the converter adaptively reduces the switching frequency and realize valley switching, which achieves better light-load efficiency in the CV mode. The proposed QR converter was implemented using the HHGRACE 0.35 μm BCD process and verified in a 5 V/1A circuit prototype. Experimental results show that the light-load power efficiency of the proposed converter is improved by up to 4.0% when compared to the conventional QR controller. In addition, the valley switching is realized under different load conditions, which improves the system efficiency in the entire range of output load.