V. M. López

Average Inductor Current Sensor for Digitally Controlled Switched-Mode Power Supplies

Current-mode control in digitally controlled switched-mode power supplies typically requires analog-to-digital (A/D) conversion of at least two signals, voltage, and current. The complexity of voltage A/D converters can be reduced using window A/D techniques. In conventional current A/D conversion, however, relatively high resolution is required over a wide range of signals, which results in increased complexity, power consumption, and cost of the controller. This paper proposes a very simple feedback sensor capable of high-resolution average inductor current sensing using two analog comparators and an analog low-pass filter. The approach requires very few external components and employs minimal digital hardware resources. A dynamic model and performance of the average inductor current sensor are experimentally verified on a 12-V input, 19-V output, 50-W boost converter prototype. The applicability of the proposed sensor is demonstrated in a digitally controlled 400-W, 400-V output Boost power factor preregulator.

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 voltage...), 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.

Single ADC Digital PFC Controller Using Precalculated Duty Cycles

Traditional digital power factor correction (PFC) uses three sensors to measure the input and output voltages and the input current. Each sensor, especially the input current one, increases the cost of the system and generates power losses in case of resistive sensors. This paper presents a controller for boost PFC converters. It uses precalculated duty cycles generated offline, and applies them to the switch. In order to control the converter with nonnominal conditions, just one analog-to-digital converter (ADC) is used, which measures the output voltage. Measuring the average and the ripple of the output voltage with this ADC, the controller takes compensation action for changes in the input voltage but also in the load of the converter. The average value is used to control the input voltage changes, while the ripple value is used to control load changes. These two loops present low frequency bandwidth, so the ADC and the whole system can be low cost. Finally, a comparator is used to detect the zero-crossing of the input voltage, so the precalculated values are synchronized with the ac mains. In this way, the converter only uses one ADC and one comparator, both with low bandwidth. Results show that high power factor and normative compliance are reached, even under nonnominal conditions.

Autotuning digital controller for current sensorless power factor corrector stage in continuous conduction mode

A circuit that compensates the volt-seconds error across the inductor in current sensorless digital control for continuous conduction mode power factor correction (PFC) stage is presented. Low cost ad-hoc sigma-delta analog to digital converters (ΣΔ ADCs) are used to sample the PFC input and output voltage. Instead of being measured, the input current is estimated in a digital circuit to be used in the current loop. A nonlinear carrier control is implemented in the digital controller in order to obtain the power factor correction. Drive signal delays cause differences between the digital current and the real current, producing that volt-seconds error. The control algorithm is compensated taking into account the delays. The influence of a wrong compensation is presented. Experimental results show power factor values and harmonic content within the IEC 61000-3-2 Class C standard in different operation conditions. Furthermore, the use of this PFC stage for electronic ballasts to compensate the effect of the utility voltage fluctuation in HID lamps is also verified taking advantage of the digital device capabilities.

Current Phase Surveillance in Resonant Converters for Electric Discharge Applications to Assure Operation in Zero-Voltage-Switching Mode

A digital approach to provide phase surveillance in resonant converters is proposed. The approach provides a mechanism for controllers in resonant inverters to maintain zero-voltage-switching (ZVS) mode operation despite large and abrupt changes in load behavior. Applications are focused on but not limited to generation and control of electrical discharges. The phase surveillance provides effective arc ignition, prevents the eventual arc extinction and assures ZVS in MOSFET turn-on transients. The proposed circuit and control approach makes the converter robust to distorted waveforms associated with either low Q operation, the use of nonlinear soft-saturation core inductors or any other cause that jeopardizes ZVS in high-frequency resonant inverters, including component tolerance, aging, and temperature effects. Two practical circuits are used to demonstrate the phase surveillance operation. A two-phase resonant inverter controlling a welding arc shows how the phase surveillance assures ZVS operation and a single-phase resonant electronic ballast for high-intensity discharge lamps shows how the phase surveillance solves the problem of arc generation. Phase surveillance maintains the frequency dependent characteristics of the resonant inverter, such as the high output impedance that stabilizes the arc beyond the control loop bandwidth, while achieving robust operation for any combination of load, component tolerances, and driver dead times.

Pulsed current source to drive high-brightness LED lamps

This paper presents a resonant converter to drive high-brightness light emitting diode (LED) lamps. The resonant converter operates at constant switching frequency, where the control parameter is the phase displacement ψ between the drive signals of each inverter leg. The proposed driver is able to set different patterns of amplitude and pulsewidth modulation (AM and PWM) of the output current to implement the dimming control of the lamp. This control flexibility arises from the wide bandwidth of the resonant converter ensuring an operation free of instabilities and flicker effects. A 120W prototype intended for street lighting applications has been built to validate the design proposal.

Low THDi front-end stage under non-sinusoidal voltage

A digital controller for Boost front-end stages connected to non-sinusoidal voltage grids is presented in this work. The utility voltage is not pure sinusoidal and presents a typical harmonic distortion (THDv) lower than 5 %, fulfilling the standard limits. Traditional PFC rectifiers achieve a resistor emulator behavior, using the input voltage as reference to control de input current. Critical applications like aircraft systems must comply with very strict harmonic limits impossible to fulfill if the input voltage is distorted. The aim of this work is to present a modification in the nonlinear-carrier (NLC) control to obtain a pure sinusoidal current independently of the input voltage waveshape and therefore introducing some active filtering action in the utility. Experimental results show the agreement with the predicted low current distortion in a Boost CCM front-end stage of 1 kW, connected to a 400 Hz grid.

PCB of a buck converter for laboratory practical classes in power electronics

This paper presents a laboratory PCB (Printed Circuit Board) used in the practical classes of power electronics in the new Degree in Industrial Electronics and Automation taught at the University of Cantabria, where students are trained in the design and measurement of power converters. This laboratory circuit reduces the time spent assembling the circuit and can focus the study on different aspects of the converters. Students place the buck converter to be designed on the developed PCB. This converter is regulated as a voltage source or current source when it is used to supply a LED matrix. The PCB was developed in order to rationalize the students time in the laboratory to achieve their practical objectives. This laboratory circuit is ready for performing measurements of voltage and current on different devices. Furthermore, it is ready for introducing perturbations to measure transfer functions of the converter, so as to design the appropriate regulator.

Frequency control and phase surveillance in resonant electronic ballast

Soft-saturation magnetic cores, traditionally used in low current ripple application, are employed to build the inductor in HF resonant inverters to drive HPS lamps because no oversize is required to accept the over current and voltage during the resonant ignition transient. Soft-saturation core behavior and lamp ignition states are modeled. A frequency control under phase surveillance (FCPS) is proposed during the ignition and steady state operation to assure zero-voltage-switch in the MOSFETs turn-on transients in resonant circuits and high output impedance to stabilize the lighting arc. The result is a reduction in the inductor size along with a reliable converter operation, paving the way for the resonant ballast to increase the switching frequency in high power applications.

Anti-flicker digital PFC controller for HID lamp electronic ballast

HID lamps are sensitive to voltage supply fluctuations producing an effect on human visual perception, known as flicker. The fluctuations are typically caused by the repetitive variation in the power consumed by loads, or by the connection and disconnection of significant loads. New improvements are presented in the power factor correction (PFC) stage for electronic ballasts of high intensity discharge (HID) lamps. A universal low frequency voltage fluctuation detection algorithm is proposed, consistent with the maximum human light flickering perception. A correct actuation on the output voltage loop of a current sensorless digital control for the PFC stage reduces the lamp sensitivity to utility fluctuations. Simulation and experimental results show how lamp flicker is avoided and power factor correction is achieved without measuring the input current.