Universal Digital Controller for Boost CCM Power Factor Correction Stages Based on Current Rebuilding Concept

Continuous conduction mode power factor correction (PFC) without input current measurement is a step forward with respect to previously proposed PFC digital controllers. Inductor volt-second (vsL) measurement in each switching period enables digital estimation of the input current; however, an accurate compensation of the small errors in the measured vsL is required for the estimation to match the actual current. Otherwise, they are accumulated every switching period over the half-line cycle, leading to an appreciable current distortion. A vsL estimation method is proposed, measuring the input (vg) and output voltage (vo). Discontinuous conduction mode (DCM) occurs near input line zero crossings and is detected by measuring the drain-to-source MOSFET voltage vds. Parasitic elements cause a small difference between the estimated voltage across the inductor based on input and output voltage measurements and the actual one, which must be taken into account to estimate the input current in the proposed sensorless PFC digital controller. This paper analyzes the current estimation error caused by errors in the ON-time estimation, voltage measurements, and the parasitic elements. A new digital feedback control with high resolution is also proposed. It cancels the difference between DCM operation time of the real input current, (TDCMg) and the estimated DCM time (TDCMreb). Therefore, the current estimation is calibrated using digital signals during operation in DCM. A fast feedforward coarse time error compensation is carried out with the measured delay of the drive signal, and a fine compensation is achieved with a feedback loop that matches the estimated and real DCM time. The digital controller can be used in universal applications due to the ability of the DCM time feedback loop to autotune based on the operation conditions (power level, input voltage, output v- ltage...), which improves the operation range in comparison with previous solutions. Experimental results are shown for a 1-kW boost PFC converter over a wide power and voltage range

Performance analysis of 1ϕ T/4 PLLs with secondary control path in current sensorless bridgeless PFCs

New power factor correction (PFC) stages such as bridgeless converters and the associated current shaping techniques require grid synchronization to ensure unity Displacement Power Factor (DPF). Sensorless line current rebuilding algorithms also need synchronization with the line voltage to compensate at least for part of the current estimation error. The application of a secondary control path to reach faster and more robustly the proper operation point previously applied in single/three-phase PLLs in grid connected converters is here proposed for the current sensorless bridgeless PFCs. This work analyzes the performance of three single-phase T/4 PLL structures, first without secondary control path, and later with feedforward and feedback secondary control paths, both in simulation and experimentally, and evaluates their applicability to current sensorless digitally controlled single phase bridgeless PFCs based on the current rebuilding technique.This work has been supported by the Spanish Ministry of Economy and Competitiveness under grant TEC2014-52316-R ECOTREND Estimation and Optimal Control for Energy Conversion with Digital Devices

High-resolution error compensation in continuous conduction mode power factor correction stage without current sensor

Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. V. M. López-Martín, F. J. Azcondo, and Á. de Castro, "High-resolution error compensation in continuous conduction mode power factor correction stage without current sensor", in 2012 15th International Power Electronics and Motion Control Conference (EPE/PEMC), Novi Sad (Serbia), 2012.Continuous conduction mode power factor correction (PFC) without input current measurement is a step forward with respect to previously proposed PFC digital controllers. Inductance volt-second (vsL) measurement in each switching period enables the estimation of input current, but an accurate compensation of the small errors in the measured vsL is required. Otherwise, they are accumulated over a half-cycle line, leading to an appreciable current distortion. A vsL estimation is proposed, measuring the input (vin) and the the output voltage (vo). Discontinuous conduction mode (DCM) occurs near input line zero crossings, and is also detected by measuring MOSFET vds. This article analyzes the current estimation error caused by errors in the on-time estimation and voltage measurements, and proposes the minimization of vsL errors by cancelling the difference between estimated DCM (TDCMinereb) and real DCM (TDCMin) times with a signal (vdig), generated in the digital device. Therefore, the current estimation is calibrated using digital signals during the operation in DCM. Feedfoward coarse time error compensation is carried out with the measured delay of the drive signal, and then a fine compensation is achieved with a feedback loop that adjusts vdig. Experimental results are shown for a 1 kW boost PFC converter.This work was supported in part by the Spanish Ministry of Science TEC - FEDER 2011-2361

Digital control of a multi-channel boundary-conduction-mode boost converter for power-factor-correction applications

This thesis focuses on the design of digital control schemes for multi-channel boundary-conduction-mode (BCM) boost converters. Multi-channel BCM boost converters are commonly used for the front-end power-factor-corrected (PFC) stage of isolated ac-dc power supplies due to the advantages of being low cost and having high efficiency for a universal line-voltage input. Single-channel and two-channel BCM boost converters using analog control ICs have been commonly used in industry. However, the use of multi-channel BCM boost converters with more than two-channels has been limited as there are no analog control integrated circuits (IC) existing on the market with the ability to control BCM boost converters with more than two channels. Digital microcontrollers are an enabling technology, which can be used to implement a control scheme for a multi-channel BCM boost converter with any number of boost-converter channels. Moreover, digital microcontrollers have the added benefit of reducing the power supply’s overall system cost. For example, in an ac-dc medical power supply, there is typically a dedicated analog control IC for the PFC stage, a dedicated analog control IC for a dcdc isolated stage, and a low-power microcontroller used for safety and house-keeping functions, such as reducing standby power, detecting line-fault conditions, providing external communications, etc. The total system cost is reduced by replacing these three chips with a single microcontroller, which provides all the same functions. This requires the development of digital control algorithms which enable the microcontroller to match the performance of the analog control IC for the PFC stage. These functions include providing a well-regulated output voltage, ensuring the input current has high power quality, and permitting interleaving between the different boost-converter channels. It is difficult to have a well-regulated output voltage for two reasons. Firstly, the controller must provide fast output-voltage dynamics over the universal line-voltage range from 85 Vrms to 265 Vrms. Secondly, the output voltage of PFC rectifiers contains a 2nd harmonic ripple which can be fed into the control loop and distort the line current. In this work, an adaptive notch filter which works over a range of line frequencies, is designed to attenuate the feedback of the 2nd harmonic ripple. The notch filter allows the voltage compensator to be designed at a higher bandwidth, thus ensuring fast output-voltage regulation. Moreover, an adaptive voltage-compensator gain is used to guarantee fast output-voltage regulation at all line voltages. BCM boost converters have a variable switching frequency. Hence, a phase-shift control scheme is used to allow interleaving between the different boost-converter channels. It is important that the phase-shift control scheme requires minimal microcontroller computational resources. This allows a low-cost microcontroller to be used. In this work, a novel phase-shift control scheme is proposed. The phase-shift control algorithm is executed at a fixed frequency much lower than the maximum switching frequency of the converter. This reduces the computational requirements of the algorithm. It is important that the PFC controller provides low input-current distortion. BCM boost PFC rectifiers suffer from a zero-crossing distortion of the line current. Feedforward control is commonly adopted in to overcome this problem, however most digital feedforward control schemes require complicated design procedures or are computationally expensive. In this work, a novel feedforward algorithm is proposed which has a simple design procedure, low computational requirements and provides high power factor. In applications which are not cost sensitive, it can be more preferable to use a more powerful microcontroller and more computationally expensive algorithms. Hence, a digital average-current-mode-control (ACMC) scheme is proposed to regulate the input current of BCM boost converter. The algorithm allows for an even greater improvement in power quality of the input line current compared to feedforward control, but comes at the cost of a more complex controller implementation. The design, implementation and performance of the proposed digital control algorithms have been experimentally verified. Experimental results for the different control schemes are demonstrated on a 2-channel 600 W and a 3-channel 1 kW BCM PFC rectifier

Digital Control Techniques for Single-Phase Power Factor Correction Rectifiers

Tightening governmental regulations and industry standards for input current harmonics and input power factor correction (PFC) of common electronic devices such as servers, computers and televisions continues to increase the need for high-performance, low-cost power factor correction controllers. In response to this need, digital non-linear carrier (DNLC) PFC control has been developed and is presented in this thesis. DNLC PFC control offers many unique advantages over existing PFC control techniques in terms of design simplicity, low harmonic current shaping over a wide load range including CCM and DCM operation and a reliable, inexpensive digital implementation based on low-resolution analog-to-digital converters (A/D\u27s) and digital pulse width modulator (DPWM). Implementation of the controller requires no microcontroller or digital signal processor (DSP) programming, and is well suited for a simple, low-cost integrated-circuit realization. DNLC PFC control is derived and analyzed for single-phase universal input PFC boost rectifiers. Further analysis of the operation of digitally controlled PFC rectifiers leads to the development of voltage loop compensator design constraints that avoid limit-cycling of the voltage loop. It is demonstrated that voltage loop limit-cycling is unavoidable when using traditional PFC control techniques un- der certain output loading conditions. However, it is also shown that voltage loop limit-cycling is avoidable under the same operating conditions when a DNLC PFC controller is implemented. Additionally, a unique output voltage sensing A/D is also developed that improves the PFC voltage loop transient response to load transients when paired with the DNLC PFC controller. Experimental results are shown for a 300W universal input boost PFC rectifier

Methods for improving stability and power quality in networks with high levels of power electronics

Advanced power electronics are essential to the development of fully active electric power systems. There are, however, potential problems that can arise when high levels of power-electronic systems are distributed throughout a network. Most importantly, power electronics can degrade the quality of the power that is delivered by utility companies; furthermore, they can cause instabilities that lead to complete failures. New "smart" power systems are highly dynamic, meaning that a regulated converter thought to be stable under ideal conditions could easily become unstable for reasons well outside of the designer's control. This thesis addresses the issue of improving power quality in networks with high levels of power electronics. The core concept presented here is an effective on-line approach for the estimation of network impedance, a time-varying quantity that plays a key role in reducing power quality. Real-time information about the network impedance at the Point of Common Coupling (PCC) can produce more stable power converters and pave the way for new measurement techniques that help to monitor power quality. This thesis also examines the application of network impedance measurements for producing model-based adaptive controllers that allow power-electronic systems to remain stable when connected to "non-stiff" networks. This work can be applied in any system that is heavily dependent on power electronics, including terrestrial "Smart Grids," all-electric ships, aircraft, and spacecraft

Auto-tuning of Digitally Controlled Single-Phase Low Harmonic Rectifiers and Inverters

Effective power transfer has been one of the main issues in power electronics. In particular, low-harmonic alternating current (AC) shaping is required by various regulations at the interface between AC power grid and direct current (DC) loads or sources,. In order to meet rapidly evolving efficiency standards and environmental concerns, intelligent AC current shaping strategies are required. In the power converter stage, however, inherent uncertainties caused by passive component tolerances and changes in operating conditions may impair the control loop stability, while mis-detection of operating modes over wide load range aggravates the situation further. This thesis introduces an auto-tuning technique in digitally controlled single-phase AC-DC rectifiers and DC-AC inverters. The approach is capable of precise on-line estimation of the power stage passive component values. The control loop compensator parameters are modified adaptively to maintain the nominal stability margins and control loop bandwidth based on the estimated component values. Furthermore, accurate continuous conduction mode (CCM) and discontinuous conduction mode (DCM) boundary detection is achieved as a result of the tuning process, without the need for additional circuitry. Implementation of the tuning approach is relatively simple. The proposed tuning approach is verified on experimental AC-DC and DC-AC prototypes