R. M. Nelms

Posicast-based digital control of the buck converter

The analysis, design, and microcontroller-based implementation of a digital controller using a Posicast element are presented for the buck converter. Posicast is a feedforward compensator that eliminates overshoot in system response, but the traditional approach is sensitive to variations in natural frequency. The new method described here reduces the undesirable sensitivity by using Posicast within a feedback loop. Compared to classical proportional-integral-derivative (PID) control, the new control results in lower noise in the control signal because the controller has a lower gain at high frequency. Furthermore, the authors experiments indicate that the new controller is less sensitive to the inherent time delay associated with a digital controller for a dc-dc converter. The authors present a straightforward method to design controller parameters from the small-signal averaged model of the converter dynamics. Experimental results for a PID-controlled converter and Posicast-type controller are also compared.

Digital control of a boost converter using Posicast

Analysis, design, simulation and DSP-based implementation of a digital controller using a Posicast element are presented for the boost converter. Different from the classical Posicast approach, the proposed control method here reduces undesirable sensitivity greatly by using Posicast within a feedback loop. Furthermore, unfavorable effects on system stability caused by the RHP zero and parasitic elements in the boost converters dynamics can be ignored in the design of controller because of its narrow open-loop bandwidth. Transient and frequency responses are presented. The performance of a Posicast-based controller for a boost converter has been investigated through simulation and verified by experiment. The sensitivity of the system dynamical response to variations in controller parameters was examined. The effect of load resistance variation was also tested.

Fuzzy logic average current-mode control for DC/DC converters using an inexpensive 8-bit microcontroller

Described in This work is the design and implementation of a microcontroller-based fuzzy logic average current-mode control (ACMC) for DC/DC converters. A fuzzy logic ACMC boost converter operating in the continuous conduction mode has been designed using a PIC16C782 microcontroller. Design procedures and implementation issues are discussed. No complex algorithm is required to estimate the controlled current because of the on-board peripherals of the microcontroller. By using lookup tables and other techniques, the fuzzy logic algorithm is implemented on the microcontroller successfully. Experimental results are presented, and encouragingly demonstrate the performance that a fuzzy logic ACMC DC-DC converter can achieve.

High voltage capacitor charging power supplies for repetitive rate loads

Three techniques for charging power capacitors to voltages in the range of 2-40 kV are examined and compared. The first technique, which uses a high-voltage DC power supply with a charging resistor, is shown to have a maximum efficiency of 50%. This requires that both the high-voltage DC power supply and the charging resistor have increased power ratings. As a result, this concept is utilized only in applications where the charge rate is low, i.e. 2000 J/s. The second method, resonance charging, is more efficient than the first but requires high-voltage components. Latchup of the high-voltage switches is possible, and the power rating of this technique can be high. Neither the first nor the second technique can compensate for capacitor leakage. The third technique, which utilizes a high-frequency power converter, applies power electronics technology to capacitor charging applications. The advantages are improved efficiencies through the implementation of zero current or zero voltage switching techniques, improved voltage regulation, and utilization of semiconductor devices as the switching elements. This technique allows for the compensation of capacitor leakage.<<ETX>>

An output feedback sliding mode speed regulator for DC drives

Synthesis of the switching surface equation in a variable structure speed controller is accomplished by using a phase lead type compensator. In addition, the switching control is designed using only the sign of the switching surface function and an estimate of the maximum value of the equivalent sliding control. As a result, the proposed variable structure controller relies only upon output feedback. The problem of control chattering is addressed by substituting a saturation function for the switching control. The practical significance of the work is demonstrated by designing a robust speed regulator for a DC drive, without direct acceleration measurement or the use of a state estimator. Results from a control experiment complement the discussion. >

Experimental evaluation of a fuzzy controller using a parallel integrator structure for DC-DC converters

This paper presents the design, implementation and experimental evaluations of a fuzzy controller using a linear integrator for buck and boost converters. The fuzzy controllers are designed based on expert knowledge of the converters and simulated experimental results. The fuzzy controller for the boost converter uses two different fuzzy controller configurations during transient and steady state to achieve fast and stable response, while there is only one fuzzy controller configuration used for the buck converter. The fuzzy controllers were implemented on a TI TMS320F2812 DSP. Experimental results for both the buck and the boost converter are shown to verify that the fuzzy controllers are capable of providing fast response and good rejection to disturbances.

A comparison of resonant inverter topologies for HPS lamp ballasts

The utility of resonant inverter topologies in electronic ballasts for high-pressure sodium (HPS) lamps is examined. The three basic types of resonant inverters, series-loaded, parallel-loaded, and series-parallel-loaded, are compared for their applicability in electronic ballasts. A parallel-loaded resonant (PLR) inverter operating at a constant switching frequency is selected because of the high voltage gains possible. As a result, it is not necessary to use a transformer to provide enough voltage to start the HPS lamp from a low-voltage DC source such as that obtained from rectification of 120 V AC source. A PLR inverter was designed based on this analysis. A computer simulation of this design verified inverter operation when driving an HPS lamp. A laboratory prototype was then constructed and found to operate satisfactorily.<<ETX>>

200/spl deg/C operation of a 500 W DC-DC converter utilizing power MOSFETs

This paper presents results from the operation of the power stage of a 500 W DC-DC converter at an ambient temperature of 200/spl deg/C. This converter is designed to provide an output voltage of 42 V DC from a 28 V DC input. It utilizes an H-bridge configuration composed of 8 International Rectifier Power MOSFETs (parallel connections of 2 MOSFETs) and 4 Motorola diodes to convert the DC input voltage to high frequency square wave which can then be stepped up with a transformer. The transformer output voltage is then rectified and filtered to produce the DC output voltage. A phase-shifted PWM switching scheme is utilized to control the MOSFETs in the H-bridge. This scheme allows zero-voltage turn-on of the MOSFETs to improve the efficiency. The efficiency of this converter when operated on the laboratory bench was measured to be 89%. The H-bridge and transformer were then placed in an oven and operated over an ambient temperature range of 20-200/spl deg/C. The efficiency varied from 86% to 85.4% over this temperature range. The long feedthroughs for oven operation caused the efficiency to decrease from 89% to 86.1%.<<ETX>>

Using a Debye polarization cell to predict double-layer capacitor performance

Double-layer capacitors (DLCs) are relatively complex devices. Different models have been proposed for DLCs. Presented in this paper is an evaluation of the Debye Polarization cell as a model for a double-layer capacitor. The elements in this circuit model can be related to the chemical reactions which occur inside the DLC. Circuit element values are found from AC impedance measurements for a DLC and a computer program which utilizes a nonlinear least squares fitting technique. Variations in circuit element values with DC bias level and manufacturing have been investigated. The performance of the Debye polarization cell in slow discharge and pulse load applications has been compared to actual circuit measurements and to simulated results using a classical equivalent circuit.