Jesus Leyva-Ramos

Repetitive-Based Controller for a UPS Inverter to Compensate Unbalance and Harmonic Distortion

This paper discusses a repetitive-based controller for an uninterruptible power supply (UPS) inverter. It is shown that a bank of resonant filters, used as a refinement term for harmonic compensation in earlier works, is equivalent to a repetitive scheme with a particular structure. The latter is implemented using a simple feedback array with a delay line, thus making the implementation relatively easy. More precisely, the repetitive scheme takes a negative feedback structure plus a feedforward path whenever the odd harmonics are considered for compensation only. The repetitive scheme, equivalent to the bank of resonant filters, acts as a refinement term to reject the harmonic distortion caused by the unbalanced and distorted load current, and thus, allowing the UPS inverter to deliver an almost pure sinusoidal balanced voltage. Experimental results in a 1.5 KVA three-phase inverter are included to show the performance of the proposed controller

An Adaptive Control for UPS to Compensate Unbalance and Harmonic Distortion Using a Combined Capacitor/Load Current Sensing

This paper investigates the control of an uninterruptible power supply (UPS) using a combined measurement of capacitor and load currents in the same current sensor arrangement. The purpose of this combined measurement is, on one hand, to reach a similar performance as that obtained in the inductor current controller with load current feedforward and, on the other hand, to easily obtain an estimate of the inductor current for overcurrent protection capability. Based on this combined current measurement, a voltage controller based on resonant harmonic filters is investigated in order to compensate for unbalance and harmonic distortion on the load. Adaptation is included to cope with uncertainties in the system parameters. It is shown that after transformations the proposed controller gets a simple and practical form that includes a bank of resonant filters, which is in agreement with the internal model principle and corresponds to similar approaches proposed recently. The controller is based on a frequency-domain description of the periodic disturbances, which include both symmetric components, namely, the negative and positive sequence. Experimental results on the output stage of a three-phase three-wire UPS are presented to assess the performance of the proposed algorithm

A Negative Feedback Repetitive Control Scheme for Harmonic Compensation

In this letter, a different feedback structure of the repetitive control that apparently is more appropriate for applications in power electronics is proposed. Moreover, a simple analog-circuit implementation is proposed which is suitable for high-frequency power electronics applications, where digital control is unpractical due to cost and performance of available DSPs and microcontrollers

Analog Circuits to Implement Repetitive Controllers With Feedforward for Harmonic Compensation

A feedforward modification for both positive- and negative-feedback schemes of repetitive control is described. It was shown that repetitive controllers can be a useful tool for tracking of periodic reference signals and compensation of periodic disturbances, in other words, for harmonic compensation. It was shown that the feedforward modification considerably improves the frequency response and performance, providing higher gains with enhanced selectivity. Simple analog circuits are presented to implement both positive- and negative-feedback repetitive schemes. A description of the circuits and their corresponding experimental frequency responses are also given

A design criteria for the current gain in current-programmed regulators

The design of the inner loop for current-programmed regulators is discussed in this paper. The effect that current gain has on the quality factor Q of the LC filter is shown. A methodology is derived to reduce this value that, in most cases, can be very high. A high quality factor can produce drastic changes with undesirable effects on regulator stability. A low quality factor will produce two real poles with a consequent reduction in the current response. After the proper selection of the current gain is done, the design procedure for the proportional integral controller of the outer loop can be continued. The design-oriented analysis is applicable to the three basic switch-mode pulsewidth modulation converters, i.e. buck, boost and buck-boost. At the end, the procedure is applied to a 280 W boost regulator that shows the simplicity of this approach.

A controller for a boost converter with harmonic reduction

An adaptive controller for the compensation of output voltage ripple due to harmonic distortion in the input voltage is proposed for a pulse width modulated (PWM) boost converter. Following the Lyapunov approach, we designed an adaptive law to cope with uncertainties in the disturbance signals and parameters. Complexity of the proposed controller is reduced by rotations which transform the adaptive terms into a sum of resonant filters tuned at the frequencies of the harmonics under compensation, and operating on the output voltage error. To facilitate the implementation, we have tried to preserve the structure of the proposed controller as close as possible to the conventional one, which includes a voltage outer loop (basically a proportional plus integral (PI) control on the output voltage error) and an inner control loop (basically a proportional control plus a feedforward term). In the proposed controller, the bank of resonant filters appears as a refinement term added to the inner control loop. Indeed, they insert notches in the audio-susceptibility curve, which are tuned at the harmonics under compensation. Thus, in addition to the benefits of a conventional feedforward PWM control, the bank of resonant filters are able to cancel selected harmonics. Experimental results on a boost converter board, using a poorly regulated voltage source, are presented to assess the performance of our approach.

Robust stability analysis for current-programmed regulators

Uncertainty models for the three basic switch-mode converters: buck, boost, and buck-boost are given in this paper. The resulting models are represented by linear fractional transformations with structured dynamic uncertainties. Uncertainties are assumed for the load resistance R=R/sub O/(1+/spl delta//sub R/), inductance L=L/sub O/(1+/spl delta//sub L/), and capacitance C=C/sub O/(1+/spl delta//sub C/). The interest in these models is clearly motivated by the need to have models for switch-mode DC-DC converters that are compatible with robust control analysis, which require a model structure consisting of a nominal model and a norm-bounded modeling uncertainty. Therefore, robust stability analysis can be realized using standard /spl mu/-tools. At the end of the paper, an illustrative example is given which shows the simplicity of the procedure.

Analog circuits to implement repetitive controllers for tracking and disturbance rejection of periodic signals

In this paper, simple analog circuits to implement a repetitive control scheme are discussed. The repetitive control has shown to be a useful tool for tracking of periodic reference signals and for compensation of periodic disturbances. The main advantages of the proposed circuitry are: 1) no digital conversion required; 2) easy tuning to the corresponding frequency; and 3) cost effectiveness. A description of the circuits and corresponding experimental frequency responses are given.

Current-Mode Control for a Quadratic Boost Converter with a Single Switch

In this paper, a methodology for controller design of a quadratic boost converter is given using average current- mode control. It is shown that the transfer function of the first inductor current-to-duty ratio is minimum phase; thus, this inductor current is selected for feedback purposes. For the inner loop, a current gain and a high gain compensator are selected where the corresponding sintonization procedure is given. For the outer loop, a conventional Pi-controller is designed. The design-oriented analytic results allow the designer to easily pinpoint the control circuit parameters that optimize the converters performance. At the end, experimental results are given for a 49 W switching regulator where step changes between 10% to full load are shown.

Modeling and Control of a Cascaded Boost Converter with a Single Switch

In this paper, a controller design methodology is given for a cascaded boost converter with a single switch using current-mode control. Nonlinear and linear models are presented, the later exhibits fourth-order characteristic dynamics with right-half side zeros. The proposed control scheme is based on sensing the current of the switch and using it for feedback purposes. When the current loop is introduced, the fourth-order dynamics of the converter is changed to a dominant first-order, which simplifies substantially the controller design of the outer loop. For this loop, a conventional controller is designed. The design-oriented analytic results allow the designer to easily pinpoint the control circuit parameters that optimize the converters performance. At the end, experimental results are given for a 23 W current-mode regulator