Signal flow graph modelling of interleaved buck converters

This paper presents a systematic development of unified signal flow graph model for an interleaved buck converter system operating in continuous inductor current mode. From this signal flow graph small, large‐signal and steady‐state models are developed, which are useful to study the converter dynamic and steady‐state behaviour. Converter performance expressions like steady‐state voltage gain, efficiency expressions and other small‐signal characteristic transfer functions are derived. Development of unified signal flow graph is explained for a 3‐cell interleaved converter system. Derivation of large, small‐signal and steady‐state models from the unified signal flow graph is demonstrated by considering a 2‐cell interleaved buck converter system. Large signal model was programmed in TUTSIM simulator, and the large‐signal responses against supply, load disturbances were predicted. Signal flow graph analysis results are validated with PSIM simulations. Further, the mathematical models obtained from the signal flow graph modelling are in agreement with those obtained from the state‐space averaging technique. Copyright © 2003 John Wiley & Sons, Ltd.     

Analysis of Fourth-Order DC–DC Converters: A Flow Graph Approach

The signal flow graph (SFG) nonlinear modeling approach is well known for modeling DC-DC converters and it is a powerful analysis tool for higher order converter systems. Modeling of several specific fourth-order DC-DC converter circuits have been reported using conventional state-space averaging. Particular emphasis has been given, so far, only to arrive at any of the large, small-signal (SS) and steady-state models but not a generalized one. This paper gives the generalized SFG model of the fourth-order DC-DC converter topology that is useful for generating different types of fourth-order DC-DC converter circuits unified models. Further, it is shown that the deduction of large, SS and steady-state models from these unified SFGs is easy and straightforward. All possible fourth-order DC-DC converter circuits from its generalized topology have been identified and an analysis of a few converter circuits is given here for illustration of the proposed modeling method. Large-signal (LS) models are developed for different topology configurations and are programmed in SIMULINK simulator. LS responses against supply and load disturbances are obtained. Experimental observations are provided to validate the proposed modeling method.     

Signal flow graph modelling and analysis of interleaved DC?DC parallel converters

This paper presents a systematic development of a unified signal flow graph model for an interleaved DC–DC parallel converter system operating in continuous current mode. This signal flow graph approach provides a means to translate directly the switching converter to its graphic model, from which the steady-state and dynamic behaviour of the converter can be studied easily. The development of a unified signal flow graph is explained for a three-cell interleaved parallel converter system. Derivation of large-signal, small-signal and steady-state models from a unified signal flow graph is demonstrated by considering a two-cell interleaved converter system operating in complementary activation mode. Converter performance expressions such as steady-state voltage gain, efficiency expressions and small-signal characteristic transfer functions are also derived. A large-signal model was programmed in a TUTSIM simulator, and the large-signal responses against supply and load disturbances were predicted. Signal flow graph analysis results are validated with PSIM simulations. Experimental observations are provided to validate the signal flow graph modelling method. Further, the mathematical models obtained from the signal flow graph modelling are in agreement with those obtained from the state-space averaging technique.     

Modeling of closed-loop voltage-mode controlled interleaved dual boost converter

An extensive small-signal analysis of a voltage-mode controlled interleaved dual boost (IDB) converter operating in continuous current mode based on signal flow graph approach is proposed. Small-signal flow graph is developed, from which open-loop small-signal transfer functions are derived using well known Mason's gain formula. Closed-loop small-signal input-to-output, control-to-output transfer functions are also derived and frequency response characteristics are determined at different duty ratios. Voltage-mode compensator designed using K-factor approach is used for closed-loop operation of IDB converter. Load voltage regulation against supply voltage and load disturbances are demonstrated through experimental results.     

Signal flow graph modeling of two-cell cascade buck converters

This paper presents signal flow graph nonlinear modeling of two-cell cascade buck converters. A systematic procedure for developing the unified flow graph model of the cascade converter is discussed. A simplified procedure is described that can be used to deduce large, small-signal and steady-state models from the unified signal flow graph of the converter. Converter performance expressions, and small-signal and steady-state transfer functions are derived. The large-signal model is developed and programmed into a TUTSIM simulator. Converter large-signal responses are obtained against supply and load disturbances. The validity of the proposed signal flow graph modeling of cascade converters is verified and comparisons are made via PSIM simulator results. A few experimental results are provided to verify the proposed method.     

Small‐signal analysis of interleaved dual boost converter

This paper presents a systematic development of steady‐state, small‐signal models of interleaved dual boost converter operating in a continuous current mode. These models are derived by employing the well‐known signal flow graph method. This signal flow graph approach provides a means to directly translate the switching converter into its equivalent graphic model, from which a complete behaviour of the converter can easily be studied. Steady‐state performance, small‐signal characteristic transfer functions are derived using Mason's gain formula. The bode plots of audiosusceptibility, input impedance, output impedance, and control‐to‐output transfer functions are determined and illustrated using MATLAB for different values of load resistances, duty ratios. Small‐signal frequency responses obtained from the signal flow graph method are validated with PSPICE simulator results. To validate the signal flow graph modelling equations, sample steady‐state experimental results are provided. Copyright © 2001 John Wiley & Sons, Ltd.     

Steady-state and dynamic performance analysis of PV supplied DC motors fed from intermediate power converter

The steady-state and transient performance of PM and series motors coupled to centrifugal pump supplied from Photovoltaic source through intermediate buck-boost converter is analyzed. The effect of duty ratio selection based on maximum power operation of PV source and maximum daily gross mechanical power is investigated on the solar cell array operating point, motor armature voltage, armature current and motor efficiency variation. Studies are carried out by formulating the mathematical models for photovoltaic source, DC motors, power converter and load. Starting torque variation, Torque magnification factors expressions are derived and their variations plotted for the above two cases. Simulation software is developed for the transient and steady-state analysis of PV supplied DC motors for different duty ratios of power converter and solar insolations. Steady-state and transient performance characteristics are presented. The performance of PM DC motor is compared with the series motor operating under identical conditions.     

Neural-network-based maximum-power-point tracking of coupled-inductor interleaved-boost-converter-supplied PV system using fuzzy controller

The photovoltaic (PV) generator exhibits a nonlinear V-I characteristic and its maximum power (MP) point varies with solar insolation. In this paper, a feedforward MP-point tracking scheme is developed for the coupled-inductor interleaved-boost-converter-fed PV system using a fuzzy controller. The proposed converter has lower switch current stress and improved efficiency over the noncoupled converter system. For a given solar insolation, the tracking algorithm changes the duty ratio of the converter such that the solar cell array voltage equals the voltage corresponding to the MP point. This is done by the feedforward loop, which generates an error signal by comparing the instantaneous array voltage and reference voltage corresponding to the MP point. Depending on the error and change of error signals, the fuzzy controller generates a control signal for the pulsewidth-modulation generator which in turn adjusts the duty ratio of the converter. The reference voltage corresponding to the MP point for the feedforward loop is obtained by an offline trained neural network. Experimental data are used for offline training of the neural network, which employs a backpropagation algorithm. The proposed peak power tracking effectiveness is demonstrated through simulation and experimental results. Tracking performance of the proposed controller is also compared with the conventional proportional-plus-integral-controller-based system. These studies reveal that the fuzzy controller results in better tracking performance.     

Analysis and control of a single switch wider step-down gain DC–DC converter for low-voltage applications

This paper presents a point-of-load transformerless DC–DC converter having a wider step-down conversion ratio. In comparison with quadratic/stacked buck converter variants, the presented topology exhibits nonpulsating source current, more effective switch utilization at small voltage gains, and reduced current stress on components. Its comprehensive steady-state analysis is carried out under continuous and discontinuous modes of inductor currents, and design criteria to select L-C components are established. State variable dependency feature in the topology, imposing a reduced fourth-order dynamics, is discussed and subsequently verified from its average model. A fixed frequency sliding mode controller is then designed with a step-by-step evaluation of sliding surface existence, reachability, and stability conditions. The equivalent control law devised in this scheme is duly constituted from source side inductor current dynamics and load voltage error information, so it facilitates simple realization as well as better transient response. Remarkable operational characteristics of the presented converter are studied analytically and demonstrated with experimental observations on a laboratory prototype.     

ANN based peak power tracking for PV supplied DC motors

This paper presents an application of an Artificial Neural Network (ANN) for the identification of the optimal operating point of a PV supplied separately excited dc motor driving two different load torques. A gradient descent algorithm is used to train the ANN controller for the identification of the maximum power point of the Solar Cell Array (SCA) and gross mechanical energy operation of the combined system. The algorithm is developed based on matching of the SCA to the motor load through a buck-boost power converter so that the combined system can operate at the optimum point. The input parameter to the neural network is solar insolation and the output parameter is the converter chopping ratio corresponding to the maximum power output of the SCA or gross mechanical energy output of the combined PV system. The converter chopping ratios at different solar insolations are obtained from the ANN controller for two different load torques and are compared with computed values.