Somnath Maity

Analysis and Modeling of an FFHC-Controlled DC–DC Buck Converter Suitable for Wide Range of Operating Conditions

To achieve the best optimized performance in terms of stability and dynamic behavior of power electronic converters, it is necessary to use a more advanced control technique and accurate mathematical model. This paper proposes a fixed-frequency hysteretic current (FFHC) controller that uses both sliding-mode control (SMC) technique and fixed-frequency current controller with a hysteresis band to achieve all properties of the variable structure controller. However, realizing such fixed-frequency sliding-mode controller using small-signal-averaged (SSA) model of the power converters and Utkins equivalent control technique may not be valid for all conditions. We show that it can be applicable only when the fast-scale dynamics of the converter system is stable, which can be achieved successfully by analyzing the stability of the FFHC-controlled buck converter using Filippov method and Floquet theory. The regions of stability are then presented to show the domains of existence of nominal period-1 and higher periodic orbits in 2-D parameter space. We also demonstrate how to derive the equivalent control law from the modified tristate converter topology to design the controller. Finally, the experimental results are presented to validate the effectiveness of this hybrid FFHC controller.

Modeling and Analysis of a Fast and Robust Module-Integrated Analog Photovoltaic MPP Tracker

Analog circuitry-based photovoltaic (PV) maximum power point (MPP) tracking (MPPT) technique is attractive due to its low cost and capability of easy integration with normal dc-dc switching converters. However, realization of classical digital MPPT algorithms using analog circuitries is a challenging task. It necessarily requires to store the information of module voltage/current and power in order to find the desired MPP. While at the same time, improper design of digital MPPT controllers may cause poor tracking performances or limit cycle oscillations to manifest, which are generally seen as being undesirable. This paper proposes a fast and robust analog PV MPP tracker without imposing any external control or perturbation. The fast dynamic performances with absolute robustness are ensured here by integrating the concepts of Utkins equivalent sliding mode control law and fast-scale stability analysis of actual switched converter systems. Moreover, the superiority of the proposed MPP tracker (in terms of high-tracking performances) over classical ones, and its impact in series-connected converters configuration are analytically demonstrated through the procedure developed in this paper. Finally, the analytical results have been validated by means of simulations and experiments.

Dynamics and Stability Issues of a Discretized Sliding-Mode Controlled DC-DC Buck Converter Governed by Fixed-Event-Time Switching

This paper finds and investigates the application of fixed-event-time based discretized sliding mode (DSM) controller in dc-dc buck converter, to achieve fast transient response and high robustness under wide parameters variation. We show that how these can be achieved by integrating the concept of Utkins equivalent control law and discontinuous border-collision bifurcation (DBCB) theory developed for 2-D discontinuous piecewise smooth (PWS) maps. Moreover, based on derived 2-D discontinuous maps of DSM-controlled converter, we investigate its inherent steady-state dynamical properties or bifurcation behaviors under different parameters variation. Numerically as well as experimentally obtained bifurcation diagrams are then presented to show the domains of existence of different oscillatory modes and their sequence of occurrence. Such phenomena are not only useful to study the robustness of the system but may also facilitates to design the input filter with fast transient response. The performance of DSM controller is experimentally verified and compared with hysteresis and classical peak current-mode controller.

CCM/GM Relative Skip Energy Control and Bidirectional Dynamic Slope Compensation in a Single-Inductor Multiple-Output DC–DC Converter for Wearable Device Power Solution

Compact size wearable devices require multiple supplies with relative large loading difference, which causes serious cross regulation, large ripple, and oscillation in single-inductor multiple-output (SIMO) DC-DC converter. Thus, a continuous conduction mode/green mode (CCM/GM) relative skip energy control (RSEC) in SIMO is proposed for wearable device power solution. Different from the conventional absolute skip method, the RSEC eliminates unnecessary skip-induced voltage ripple and cross regulation with well regulation performance over wide load and voltage ranges. Optimization between efficiency and voltage ripple achieves low noise supply and reduced switching loss. In addition, smooth transition between CCM and GM provides high power and longer usage time in wearable devices. Furthermore, bidirectional dynamic slope compensation conquers subharmonic oscillation and avoids invalid pulses in the energy delivery operation of current-mode SIMO DC-DC converters. The test chip fabricated in the 0.18 μm CMOS process occupies 2.24 mm2 active area. Maximum output ripple, overshoot/undershoot, and cross regulation are kept below 40 mV, 27 mV, and 0.0432 mV/mA, respectively.

A fixed frequency dual-mode DC-DC buck converter with fast-transient response and high efficiency over a wide load range

Maintaining high efficiency and achieving fast dynamic response over wide load condition are extremely important in most modern power management applications, and also for various typical load demands. In this paper, we present the design of a fixed frequency hysteretic current (FFHC) controlled dual-mode tri-state dc-dc step-down (Buck) switching regulators/converters for wide load variation. Depending on the load requirements, it can adaptively switch between two operating modes-pseudo-continuous continuous mode (PCCM) to discontinuous conduction mode (DCM) and adjust the switching frequency of operation accordingly. Moreover, based on simplified discretized model or map, we also show that under certain conditions the proposed dual-mode tri-converter is not only useful for achieving the fast dynamic responses under wide load range, but also improve the power conversion efficiency, especially, at light load condition.

PI controller design for indirect vector controlled induction motor: A decoupling approach

Decoupling of the stator currents is important for smoother torque response of indirect vector controlled induction motors. Typically, feedforward decoupling is used to take care of current coupling that requires exact knowledge of motor parameters, additional circuitry and signal processing. In this paper, a method is proposed to design the regulating proportional-integral gains that minimize coupling without any requirement of the additional decoupler. The variation of the coupling terms for change in load torque is considered as the performance measure. An iterative linear matrix inequality based H∞ control design approach is used to obtain the controller gains. A comparison between the feedforward and the proposed decoupling schemes is presented through simulation and experimental results. The results show that the proposed scheme is simple yet effective even without additional block or burden on signal processing.

Modeling and control of a battery connected standalone photovoltaic system

This paper presents modeling and control of a standalone photovoltaic (PV) system in which a battery is used as a backup source for power management between the source and the load. Lead-acid battery is commonly used in high power PV applications due to its low cost and availability in large size. The modeling of PV system and lead-acid battery by using the corresponding equivalent circuits are discussed here. Three independent control loops are proposed to control the standalone PV system; MPPT control loop for extracting maximum power from PV module under different solar irradiation, battery control loop for bidirectional power flow between battery and dc-link through buck-boost converter to keep the input dc voltage constant, and inverter control loop for maintaining good voltage regulation and achieving fast dynamic response under sudden load fluctuations. The stability of the above control loops are verified by using Bode diagram. Finally the proposed method is applied to 2 kW, 110 V, 50 Hz, two-stage single-phase standalone PV system. The simulation and the experimental results are presented to validate the theoretical analysis, effectiveness and feasibility of the proposed control strategy.

Modeling and control of grid-connected DC/AC converters for single-phase micro-inverter application

This paper presents modeling and control for a single-phase grid-connected two-stage micro-inverter system. An average signal model has been developed for a single-phase bridge inverter. The proposed controller has three cascaded control loops. The inner current loop consists of a variable frequency hysteric current mode control which regulates output filter inductor current thereby improved system response. The small signal modeling of the proposed control method is discussed. Again, as the dc-link capacitor plays a crucial role in two-stage micro inverter applications, a DC-link voltage controller is employed in outer control loop to keep the bus voltage constant. The grid current loop regulates the injected current to the grid at a reduced THD level. The stability of the above control loops are also verified by using Bode-diagram. Finally the proposed method is then applied to 500 Watts, 110V, 50Hz, two- stage single-phase grid-connected Photo-voltaic (PV) system. The simulation and the experimental results are presented to validate the theoretical analysis, effectiveness and feasibility of the proposed control strategy.

An Efficient PV Power Optimizer With Reduced EMI Effects: Map-Based Analysis and Design Technique

The aim of this paper is to develop a one-dimensional (1-D) discrete-time model or map that will ensure reliable and safe chaotic operation of a modular photovoltaic (PV) power optimizer (PO) system. Based on this 1-D map, we perform the detailed bifurcation analysis and discuss a preliminary design guideline to operate the system into a desired chaotic regime, i.e., just after the golden mean. We show that operating POs in chaotic regime cannot only yield broader power spectrum with reduced spectral peak at the switching frequency harmonics of the system, but also exhibits faster tracking responses with overall conversion efficiency

Fixed-frequency sliding mode control for power quality improvement of a grid-connected inverter

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