Buck Converter Operating Research Articles

A Hybrid Converter System for High-Performance Large Induction Motor Drives

A hybrid converter system employing a combination of a load-commutated inverter (LCI), a dc-dc buck converter, and a voltage-source inverter (VSI) is proposed for the large induction motor drives. The VSI ensures the safe commutation of the LCI with active commutation angle control over all speed regions. By replacing capacitor banks and a forced dc-commutation circuit, this system can eliminate all drawbacks related to these circuits in the conventional LCI-based induction motor drives. Sinusoidal motor current and voltage waveforms are achieved with the VSI providing the reactive and harmonic power to the motor, resulting in high-performance drives. The buck converter enables both the VSI and the LCI to be fed from the single-diode rectifier. As a result, the dc-link inductor size can be reduced and the LCI is operated without the controlled rectifier. In addition, faster dynamic response can be obtained through the VSI and the buck converter operation. Finally, the buck converter performs the dc-link current control to ensure minimum VSI rating. The feasibility of the proposed hybrid circuit for the high-power drive systems is verified by computer simulation for a 500-hp induction motor. Experimental results are also included for a 1-hp induction motor laboratory setup controlled by the proposed hybrid system.

A comparative study of carrier-frequency modulation techniques for conducted EMI suppression in PWM converters

A rigorous mathematical analysis and a comparative study of carrier-frequency modulation (CFM) techniques for the conducted electromagnetic interference (EMI) suppression in pulsewidth-modulated converters is presented. CFM techniques dither the switching period with a small amplitude variation around the nominal value, so that the harmonic power is redistributed over the spectrum of concern. Two types of dithering signals, including the periodic and random signals, are investigated in this paper. The operational characteristics as well as the input and output power spectra of the converters with the two modulating signals are compared. In particular, their characteristics in the low- and high-frequency harmonic power redistribution will be depicted. It is shown that random CFM (RCFM) gives a more effective way to disperse the harmonics around the switching frequency than the periodic CFM (PCFM) with the same frequency deviation. However, RCFM introduces higher low-frequency harmonics than the PCFM at the converter output. Furthermore, effects of the resolution filter bandwidth in the electromagnetic compatibility analyzer on conducted EMI measurement is discussed. The validity of the analyses is confirmed experimentally by using a dc/dc buck converter operating in continuous conduction mode.

Input filter interactions in peak-current-mode-controlled buck converter operating in CICM

Peak-current-mode (PCM) control is a widely used method to control switched-mode converters. Most often an input filter is necessary to meet electromagnetic interference requirements. The input filter can cause instability and degradation of input and output dynamics if not properly designed. The input filter design from the output dynamics viewpoint has been addressed in numerous papers, resulting in well-agreed results in the case of direct duty-ratio control. The same methods and criteria have also been applied to PCM control, but the results have turned out to be conflicting. This paper shows that the adverse effect of the input filter on the output performance of a peak-current-controlled buck converter in continuous inductor-current mode is insignificant. The input performance is, however, significantly affected, necessitating the use of proper damping. It is also shown that the instability is caused solely by the instability of the input filter under negative incremental resistance. The methods used are unified in nature, but the results obtained in this study cannot be generalized to be valid for types of converters other than a buck converter.

Theoretical and experimental investigation of the fast- and slow-scale instabilities of a DC-DC converter

We use an exact formulation based on nonlinear maps to investigate both the fast-scale and slow-scale instabilities of a voltage-mode buck converter operating in the continuous conduction mode and its interaction with a filter. Comparing the results of the exact model with those of the averaged model shows the shortcomings of the latter in predicting fast-scale instabilities. We show the impact of parasitics on the onset of chaos using a high-frequency model. The experimentally validated theoretical results of this paper provide an improved understanding of the dynamics of the converter beyond the linear regime and this may lead to less conservative control design and newer applications.

High power factor rectifier based on buck converter operating in discontinuous capacitor voltage mode

The buck converter with LC input filter operating in discontinuous capacitor voltage mode has inherent power factor correction properties and continuous input current. The paper presents a detailed analysis of the converter operating in this mode, leading to design criteria. Finally, experimental results for a 48 V/sub dc//100 W converter are presented.

Use of a priori information in the identification of global nonlinear models-a case study using a buck converter

This paper investigates some issues related to grey-box identification. In particular it is discussed how a priori information about the system static nonlinearity can be incorporated into the model. Also, it is shown that in some applications involving nonlinear systems, there must be a tradeoff between the accuracy of the estimated model static nonlinearity and the quality of forecasts. These concepts are applied in the identification of a real DC-DC buck converter operating in continuous mode. Improvement in model global stability was achieved by using simple a priori information that takes into account the steady-state voltage relation of the converter. Models that are valid over a wide operating range are included. Such models are compact and can be estimated directly from data obtained from the converter.

A comparative investigation on the use of random modulation schemes for DC/DC converters

A comparative investigation on the use of random modulation schemes for DC/DC power converters is presented. The modulation schemes under consideration include randomized pulse position modulation, randomized pulsewidth modulation (PWM) and randomized carrier-frequency modulation with fixed and variable duty cycle. The paper emphasizes the suitability and applicability of each scheme in DC/DC power converters. Issues addressed include the effectiveness of randomness level on spreading the dominating frequencies that normally exist in constant-frequency PWM schemes, and the low-frequency power spectral density (PSD) of each scheme. The validity of the analyses is confirmed experimentally by using a DC/DC buck converter operating in the continuous conduction mode. The PSD of the output under each scheme is presented and compared.

Novel zero-voltage-transition PWM multiphase converters

Novel zero-voltage-transition (ZVT) pulse-width-modulation (PWM) multiphase converters are presented. To construct a ZVT multiphase converter in a conventional way, it is necessary to add the auxiliary circuits with as many number of phases. In the proposed converter, only one auxiliary circuit provides the zero-voltage switching (ZVS) for main switches and diodes of all phases. So, the new converters are cost effective and attractive for high-performance and high power-density conversion applications. Operation, features, and characteristics of the two-phase buck converter are illustrated and verified on a 4-kW 100-kHz insulated gate bipolar transistor (IGBT)-based (a MOSFET for the auxiliary switch) experimental circuit.

Analysis of switching regulators by phase portrait technique

The phase portrait technique is used to analyze transient and steady-state operation of switching regulators. The regulator model and analysis procedure are established, treatment of circuit nonlinearities, its time varying nature and feedback configuration is included. The proposed technique is applied to the analysis of buck converter operation. The benefits of analysis are discussed in view of understanding the switching regulator operation.

A fast time-domain algorithm for the simulation of switching power converters

An efficient algorithm for the simulation of switched-mode power converters is developed. A Chebyshev series expansion is used to effectively solve the differential equations describing the system in each topology. The power of the new simulation technique lies both in the simple, but accurate, polynomial approximation for the state transition matrices and in the ability to explicitly obtain the instants at which the switching of the circuit topology takes place. The simulation technique is illustrated with reference to a simple Buck converter operating at a constant frequency. The derivation of the new algorithm is presented and its performance is analyzed. The case of a rapidly varying input forcing function is analyzed. Examples illustrating the generality and the computational efficiency of the algorithm are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Discrete Time Domain Modelling and Analysis of DC-DC Converters with Continuous and Discontinuous Inductor Current

Using discrete time state variable representation, a generalized computer-aided modelling and analysis of DC-DC converters is presented. The methodology provides exact modelling and is applicable to all types of power stages and duty-cycle control, including continuous and discontinuous inductor current operation. Converter stability, transient behavior and audio susceptibility can be analytically evaluated and predicted. The generalized theory of the proposed approach to converter modelling and analysis is presented first, followed by a demonstrative example applying the theory to a constant frequency buck converter operating in continuous and discontinuous inductor current mode-Excellent agreement with laboratory test data has been observed.