Average Current Control Research Articles

Averaged current mode control for maximum power point tracking in high-gain photovoltaic applications

Efficient extraction of the maximum power from photovoltaic (PV) systems under inherently variable weather conditions is a key issue that has been tackled in recent years. Maximum power extraction techniques are relevant for increasing the penetration of PV systems into electric systems. This paper presents an averaged current mode control strategy as a maximum power extraction technique in a photovoltaic high step-up dc–dc converter, which can be applied to dc microgrids or ac networks through power inverters. Since the generated power of a photovoltaic system is related to the terminal voltage, power extraction is given through the regulation of the converter’s input voltage. For this purpose, in the proposed averaged current mode control, the inner current loop uses the inductor current as a feedback signal, which improves the dynamic behavior of the converter with a simple gain. Meanwhile, the outer voltage loop is built with a proportional-integrative controller for regulation. The converter and control strategy are able to track rapid irradiance changes. They are also able to maintain the photovoltaic voltage regulation under dc bus voltage variations. The performance of the proposed control scheme is validated experimentally with a 100 W converter prototype.

Small-Signal Analysis and Control of Soft-Switching Naturally Clamped Snubberless Current-Fed Half-Bridge DC/DC Converter

This paper presents small-signal analysis of a soft-switching naturally clamped snubberless isolated current-fed half-bridge (CFHB) DC-DC converter using state-space averaging. A two-loop average current controller was designed and implemented on a digital signal processor. The complete design procedure is presented here. Simulation results using software PSIM 11.1 are shown to validate the stability of the control system and the controller design. Experimental results for the step changes in load current vividly demonstrated satisfactory transient performance of the converter and validated the developed small-signal model and the control design.

Decoupled Average Current Control of Coupled Inductor Single-Input Dual-Output Buck Converter

Multiple-output dc–dc converters are compact and cost effective as compared to multiple parallel dc–dc converters. This article focuses on a coupled-inductor single-input dual-output (CI-SIDO) buck converter. For the CI-SIDO converter, achieving independent regulation of output voltages and maintaining good dynamic performance are difficult due to cross-regulation and cross-coupling problems. In addition, tuning of controller parameters is challenging. Thus, this article proposes a decoupled average current control (ACC) to suppress cross-coupling and cross-regulation in CI-SIDO buck. It also demonstrates the method of decoupling of inductor currents and the stability issue that exists in ACC of CI-SIDO buck. The analysis shows that decoupling of inductor currents makes the design of controllers independent and simplifies the closed-loop transfer functions. Based on the conditions of decoupling and stability, a systematic design procedure for a Type-II compensator is developed. The proposed control method is compared with the voltage-mode control by using MATLAB/Simulink results. The comparison shows that the proposed ACC exhibits better dynamic performance. Finally, the proposed method is validated using experimental results.

Single-phase unidirectional AC-DC PFC converter with switched capacitors

ABSTRACT A single-phase AC-DC converter based on switched capacitor is proposed. This converter is an integration of basic boost converter and switched capacitors. This rectifier is controlled by an average current control method which comprises of two feedback loops, that is, voltage control loop and current control loop to produce unity power factor. The proposed converter develops a DC voltage more than the peak value of AC supply. Apart from this, all the components are subjected to voltage less than the DC output voltage, that is, almost half. A prototype model with AC voltage of 75 V and output voltage of 300 V with power 75 W is developed to validate the results.

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.

Direct AC–AC Active-Clamped Half-Bridge Converter for Inductive Charging Applications

In this article, a new direct ac-ac active-clamped half-bridge converter feeding a series-series compensated inductive charging system is proposed. The proposed converter eliminates the rectification stage and bulky life-limited electrolytic dc-link capacitors, resulting in an actual single-stage (ac-to-ac) conversion with low component. The operation principles, steady-state analysis, and design considerations of the proposed converter are presented in detail. Moreover, a new predictive dead-beat technique for input current control and a linear average charging current controller are developed for the proposed converter, which enables the unity power factor and charging current regulation. The performance of the proposed battery charger is validated through experimental results on a 1-kW field programmable gate array (FPGA)-controlled silicon carbide based laboratory prototype.

I 2 V 2 Average Current Control for Modular LED Drivers

Present light-emitting diode (LED) drivers often exhibit difficulty in meeting the increasing demand for compact size, flexible multiphase configuration, accurate current regulation, and fast transient response. In this letter, we present an output-capacitorless modular LED driver that simultaneously achieves these attributes by the realization of monolithic integration and the employment of our proposed I 2 V 2 average current control. The proposed control based on pulsewidth modulation, considers the complete LED current profile to obtain the accurate current regulation and combines the feedforward signals of the inductor current, input voltage, and the output voltage to accelerate the transient response. To verify the proposed I 2 V 2 average current control scheme, we monolithically realize a modular LED driver that embodies a tiny 1.8 μH inductor and supports an input voltage range of 5–18 V, output LED current of 1 A, switching frequency of 2 MHz, LED current settling time of 1.3 μs, and the peak power efficiency of 94.5%. When being benchmarked against state-of-the-art counterparts, the proposed design features at least 2.6× smaller output inductor, 2.3× shorter settling time, and 2.5% higher peak power efficiency.

A Computationally Simple Predictive CCM Average Current Controller With Nearly Zero Tracking Error for Boost PFC Converter

Predictive current controllers offer superior control action in power factor correction (PFC) converters, however, cause tracking error in the average inductor current due to the unmodeled circuit parameters and variations which could lead to higher harmonic currents, higher input current THD and impact on the output voltage. Attempts to make the predictive current control equations accurate leads to increased computational complexity, thus limiting the switching frequency of operation or increasing the processing requirements. This article proposes a computationally simple predictive continuous conduction mode average current controller based on the concept of moving averages for the boost PFC converter and achieves nearly zero tracking error in the average inductor current. Additionally, a predictive current controller is derived for performance comparison by considering the effect of major converter nonidealities and digital implementation aspects. The performance of the proposed predictive current controller is compared with that of a PI current controller, an ideal predictive current controller and the derived predictive current controller with nonidealities included. Experimental studies on a boost PFC converter hardware prototype validate the effectiveness of the proposed predictive current controller.

Interleaved bidirectional DC–DC converter for electric vehicle applications based on multiple energy storage devices

Hybrid electric vehicles (HEVs) and pure electric vehicles (EVs) rely on energy storage devices (ESDs) and power electronic converters, where efficient energy management is essential. In this context, this work addresses a possible EV configuration based on supercapacitors (SCs) and batteries to provide reliable and fast energy transfer. Power flow among the aforementioned energy sources and the EV occurs through a dc link associated with an interleaved bidirectional dc–dc converter. This topology presents low component count and high efficiency over a wide load range, consisting of an adequate choice for high-power, high-current levels. A detailed design methodology is presented, which comprises the qualitative and quantitative analysis of the converter and the control system implementation using a simple strategy, i.e., average current mode control. A 2 kW laboratory prototype of the converter using microcontroller dsPIC30f4011 by Microchip is implemented and the system performance is evaluated in terms of some key waveforms. High power density, low component count and increased robustness can be stated as the main advantages of the proposed approach, which can be considered as a viable alternative for practical EV applications.

Average Inductor Current Measure and Control Strategy for Multimode Primary-Side Flyback Converters

Primary-side flyback converter (PSR) is widely used among small and medium power applications for its simplicity and cost effectiveness. However, it is hard to measure the current of secondary side due to the special structure characteristic of PSR. Conventionally, a peak current measurement strategy is adopted to measure the current of primary inductor. However, the sampling method is just for one conduction mode and is affected by the propagation delay between the control signal and actual turn-off instant of mosfet. Thus, a compensation circuit is needed to improve the accuracy, which leads to a large area and cost of the controller. In this work, a kind of average inductor current measure and control strategy for multimode is introduced. The average inductor current measurement strategy is based on the Miller stage to recognize the state of the mosfet, which eliminates the error caused by the mosfet. The average current of primary inductor is obtained and there is no need to estimate the rising slope and the peak value of the inductor current. To verify the feasibility of the proposed method, a controller for charging application is fabricated integrated with the proposed method. Hardware experimental results show that the control system can properly operate in multimode. The accuracy of constant output current is ±1% and the line regulation of the system is 1.6% under the input line voltage ranges from 85 to 265 Vac.

A Single-Inductor Multiple-Output Buck/Boost DC–DC Converter With Duty-Cycle and Control-Current Predictor

A single-inductor multiple-output (SIMO) buck/boost dc–dc converter with average-current control is presented in this article. With the proposed duty-cycle and control-current predictor, fast and robust reference tracking of inductor current is achieved. The conventional charge-balance method is modified together with an auto-tuning-divider-based duty generator to release the cross-regulation to the last channel. Moreover, an anti-right-half-plane zero method is also proposed to suppress cross-regulation during large loading transient when the SIMO dc–dc converter operating in the boost mode. The proposed SIMO buck/boost dc–dc converter has four output channels which are adaptive to both boost and buck operations and is implemented in a standard 0.35-μm CMOS process. Measurement results show that the proposed dc–dc converter achieves a peak efficiency of more than 89% at a total output power of about 0.5 W, load transient's response time of less than 40 μs, cross-regulation within 0.05 V/A when a 300-mA loading transient is applied to a boost channel.

Investigation on Operating Characteristics in Three Level Full Bridge AC–DC Converter using Different Control Strategies for Telecom

This paper presents the improvement of operating characteristics of three level full bridge ac–dc converter by proposing four different closed loop control techniques for telecom applications. Comparisons between different controllers have been considered to evaluate the power quality parameters with fast dynamic response under various operating conditions. Simulations have been done with Matlab/Simulink with four different voltage and current controllers, namely; PID with hysteresis current controller, Fuzzy Logic with hysteresis current controller (FL-HCC), Hysteresis Modulation based Sliding Mode Controller (HM-SMC) and Genetic Algorithm based Average Current Control (GA-ACC). Comparative analysis has been carried out with power factor, total harmonic distortion (THD) for various loading conditions upto 300 W. Based on the comparative analysis, GA-ACC technique provides better power quality parameters with improved dynamic response than the other three controllers. GA-ACC technique improved the power factor to 0.9911 and source current THD of 5.11% for converter. Also, voltage ripple and efficiency of the converter were calculated and tabulated under a wide range of load variations. Simulated results of the converter with GA-ACC have been validated with the experimental results.

Digital Average-Ripple-Based Control Techniques for Switching Converters With Fast Transient Performance

Digital average-ripple-based (AR) control techniques, which are categorized in digital average inductor current (DAIC) control, digital average voltage (DAV) control, and digital average voltage/digital average inductor current (DAV/DAIC) control, for buck-type converters, are investigated and analyzed in this article, and digital average voltage/digital average capacitor current (DAV/DACC) control is subsequently proposed. Among them, the proposed DAV/DACC control using dual-edge modulation exhibits fast transient performance and has high output-regulation accuracy even without a digital compensator. The control laws of digital AR controls with dual-edge modulation are derived and their stabilities are investigated by sampled-data modeling. It is concluded that the stability of the digital AR controls for the buck-type converter is better than that of peak-ripple-based (PR) controls and valley-ripple-based (VR) controls, where the stability of DAV/DACC control and DAV/DAIC control can be further enhanced by adjusting current-feedback ratio. The quasi digital average voltage (QDAV) control is further proposed to provide fast transient performance for the boost-type converter. A series of relevant simulations and experiments are given to verify the theoretical analysis.

Analysis and design of novel non-isolated quadratic boost DC-DC converter

This column elucidates analysis and design of novel single switch non-isolated quadratic boost converter. The operating principle is discussed both in CCM and DCM mode. Analysis includes closed loop average current mode control. The proposed converter exhibits stable operation under input voltage and load change. Linear control theory is applied for the loop compensator design. The suitability of the proposed scheme is well visualised and validated through simulation results procured using PSIM 9.1.1 and experimental results obtained from a practical 75 watt converter. The converter is designed for 75 watts with 89%-90% measured efficiency, where voltage and current ripple is 2% of output voltage and 1% of rated inductor current, respectively.

Small Signal Analysis and Control of Snubberless Naturally-Clamped Soft-Switching Current-Fed Push-Pull DC/DC Converter

This article presents detailed small-signal modeling and closed-loop control design for transient performance evaluation of a high-frequency snubberless isolated current-fed push-pull dc-dc converter. The topology attains the natural commutation of semiconductor devices through zero current switching. The state-space averaging technique is employed to derive the transfer functions. A two-loop average current controller is designed and implemented on a digital signal processor to evaluate and demonstrate the transient performance of the converters. A complete procedure for a closed-loop control design is illustrated. Simulation results using PSIM 11.1.64 with the designed controller are shown to validate the stability of the system. Experimental results demonstrated satisfactory transient performance at various load conditions of the converter and validated the derived model and the control design.

Control of a charging station for electric vehicles

A weighted average current control applied to a three-phase inductor-capacitor-inductor grid-connected battery charger for electric vehicles is presented in this paper. The proposed controller is based on a combination of the partial currents of the system (inverter and grid currents), which are feedback into the control loop. Therefore, by using this approach a reduction of the system order is achieved. The proposed controller allows a bidirectional control of the converter currents, thus allowing both, a controlled charge of the battery and the injection of the current with low distortion in the grid. Further, the implemented controller does not needs to measure the inverter currents. The control strategy is validated with simulation results.

Realising ZVS and ZCS in a continuous conduction boost converter with boundary mode control

Boost regulators working in the continuous conduction mode (CCM) are very popular in switch-mode power conversion. This configuration is widely adapted for power factor correction (PFC) in switch mode AC to DC converters. For lower power levels of up to 200 watts, boundary conduction mode (BCM) PFC is adapted, and for power requirements beyond about 200 W, CCM boost with average current control scheme is favoured. A novel technique is proposed in this paper to achieve complete soft-switching viz. Zero voltage switching and zero current switching for the main boost switch in CCM mode. The uniqueness of the scheme lies in not adding any auxiliary MOSFET switch and/or control algorithm. All the switching elements exhibit soft-switching, thus improving efficiency and reducing the EMI considerably. Most of the reported techniques for soft switching in CCM boost utilise additional active switches. A working model is fabricated to demonstrate and validate the scheme. The test results and the waveforms are presented and analysed. An 800 watts PFC converter exhibiting complete soft switching is built using the proposed technique and is evaluated for its performance.

Improvement of Power Quality in an Adaptive Boost PFC Converter with Generation of PWM Control Signal by Cascading Power Factor and Chaos Controller Circuits

This work discusses about a digital controller system for reduced effect of chaos and improved power factor of a 1-phase AC-DC converter system. It is shown that, the proposed controller technique is able to suppress the chaos at variable load condition of a boost power factor correction (BPFC) converter. Furthermore, a systematic methodology based on bifurcation diagram from tuning the controller is proposed. To achieve improved power quality in BPFC converter, combination of average and peak inductor current mode control methods are performed. In the MATLAB/SIMULINK environment, simulation circuit for the BPFC converter with average current control method is developed to improve power factor. Further, to reduce the effect of chaos produced in converter, peak inductor current mode with delayed feedback control method is adopted. At an output power of 650 W operating at 130K Hz switching frequency, this converter provides Total Harmonic Distortion (THDi) reduction of 20% and improved Power Factor (PF) of input current compared to other conventional converter. For real time operation of the system, rapid prototyping test is carried out using DAQ (Data acquisition) board NI 6351. The delayed feedback control has a better performance than any other methods proposed earlier.

Online Estimation of ESR for DC-Link Capacitor of Boost PFC Converter Using Wavelet Transform Based Time–Frequency Analysis Method

Aluminum electrolytic capacitor (AEC) is one of the most age-affected components in ac–dc conversion, and its equivalent series resistance ( ESR ) is an important index for reflecting the healthy condition of AEC. In AEC-used boost power factor correction (PFC) converters, ESR of AEC causes a small jump in the switching ripple of output voltage at switching moments, especially at turn- off moments. This small jump is hardly observed at line-frequency scale, either using time-domain analysis or frequency-domain analysis. However using time–frequency analysis this jump is very prominent due to its singularity. In this article, an online ESR estimation method of AEC is proposed by using the wavelet transform (WT) based time–frequency analysis. The relationship between ESR and the jump amount of output voltage at turn- off moments is analyzed first, and then the ESR calculation model is derived using WT with the wavelet basis of the first derivative of Gaussian function. An appropriate sampling interval for the output voltage and the inductor current is determined. Besides, the online ESR estimation scheme is implemented including the hardware and software designs. Furthermore, a prototype of boost PFC converter with 220 V ac input and 360 V dc output is built, where an average current mode control chip UC3854 is used. Four factors are discussed for estimation accuracy in the experiment, and the estimated results are consistent with the results measured by LCR meter with a relative error less than 10%.

Comparative study on predictive dead-beat peak current, valley current and average current control algorithms for phase-shifted full-bridge DC/DC converters

Three types of digital predictive dead-beat current control algorithms (PDB-CCAs) for phase-shifted full-bridge DC–DC converters with peak current, valley current and average current are presented. The PDB-CCAs are derived directly from the switching characteristics and topological structures of the converters. The proposed algorithms can predict the inductor current in the next switching period by sampling the input voltage, output voltage and inductor current in the current switching period. To ensure the stability of the inductor current, the PDB-CCAs result in a greatly improved transient performance, since the inductor current tracks the reference in one switching period or less when a reference perturbation or current perturbation occurs. In addition, although the procedure for deriving the control algorithms is complex, they can be easily implemented by a digital controller after reasonable simplification. Finally, simulation and experimental results are obtained and they agree with the theoretical results, which demonstrate the validity of the proposed PDB-CCAs.