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Grid voltage transients and, in particular, grid voltage swells pose control challenges for static compensators (StatComs). This article presents an efficient control strategy for changing the dc value of capacitor voltages, which is especially useful for operating a low-capacitance StatCom (LC-StatCom) under grid voltage swells. In the proposed strategy, the capacitor voltages are changed as a function of the grid voltage magnitude in each phase. This article details all the required control stages for implementing this control strategy. The effectiveness of this strategy to deal with grid voltage swells is compared with other strategies both in conventional StatComs and LC-StatComs using a simulated 36-MVA 11-level cascaded H-bridge converter in MATLAB Simulink. The comparison is based on current transient performance and an analytical model of switching losses. Finally, the feasibility of this strategy is confirmed by experiments on a 1 kVA prototype. [ABSTRACT FROM AUTHOR]

The cascaded H-bridge (CHB) low-capacitance static compensator (LC-StatCom) has a limited inductive region compared to a conventional StatCom, both in balanced and unbalanced conditions, due to the inherent large oscillations on the capacitor voltages. This article presents a detailed analysis of the viable operating region in these converters that takes into account the inherent large oscillations. The analysis facilitates sizing of the dc-link capacitors to ensure that the StatCom is able to inject a given range of positive- and negative-sequence current. Though the analysis is generic and applicable to the CHB StatComs with relatively large capacitance values, it is more relevant in the LC-StatComs. In addition, the article derives reference steady-state signals that can be used as feedforward terms in LC-StatCom control loops to enhance the control performance. The article presents simulation and experimental results, in balanced and unbalanced conditions to corroborate the proposed analysis. [ABSTRACT FROM AUTHOR]

This article presents a constrained model predictive control (MPC) strategy for a three-phase low-capacitance static compensator (LC-StatCom) with delta configuration. The controller consists of an outer loop that provides dynamic references for the active grid current component and the circulating current; whereas, the inner predictive loop minimizes the quadratic error of state variables subject to operating limit conditions, thus providing optimal control signals that produce a fast response while guaranteeing the prescribed safe operating limit conditions. The article also proposes an enhanced discrete-time model, which uses intersample values, that improves the accuracy of the model predictions when the sampling rate is not high enough to assume constant state variables. As a result, it facilitates the implementation of MPC on less powerful processors compared to the conventional modeling. The proposed control is especially suited for the LC-StatComs since it incorporates analytical computation of desired steady-state trajectories, which takes into account the induced oscillation on the capacitor voltages that are inherent to the LC-StatComs. The proposed approach has been verified by simulation and experimentally with a laboratory prototype. [ABSTRACT FROM AUTHOR]

A low-capacitance static compensator (LC-StatCom) based on a cascaded H-bridge (CHB) multilevel converter can be an efficient and low-cost solution for reactive power compensation in power grids. However, the reduced capacitance, and, therefore, faster capacitor voltage dynamics, makes it challenging to control it. Classical cascade control schemes, in which the bandwidths associated with the inner current loop and the outer capacitor voltage loop need to be separated enough, are the most reported approaches. Nevertheless, for the LC-StatCom case, the voltage loop can be almost as fast as that one of the current loop. For this reason, this article proposes a control approach that does not separate voltage and current dynamics. Concretely, we propose a multi-input linear time-variant control law, based on incremental passivity theory for CHB multilevel converters. The proposed control guarantees stability despite saturation in the control signal. In addition, it provides capacitor voltage balance without the need to use a specific balancing stage. This article, first, reviews the average model of the converter and, then, analyses the steady-state dynamic behavior to determine the desired and coherent reference signals. Then, it applies an incremental passivity control approach to drive the LC-StatCom state variables to the desired references. After introducing the proposed control law, experimental results on a seven-level 1-kVA CHB LC-StatCom are shown to demonstrate its excellent performance in steady state and transients. [ABSTRACT FROM AUTHOR]

A consistent framework for robust linear quadratic regulators (LQRs) control of power converters is presented. Systems with conventional LQR controllers present good stability properties and are optimal with respect to a certain performance index. However, LQR control does not assure robust stability when the system is highly uncertain. In this paper, a convex model of converter dynamics is obtained taking into account uncertainty of parameters. In addition, the LQR control for switching converters is reviewed. In order to apply the LQR control in the uncertain converter case, we propose to optimize the performance index by using linear matrix inequalities (LMIs). As a consequence, a new robust control method for dc-dc converters is derived. This LMI-LQR control is compared with classical LQR control when designing a boost regulator. Performance of both cases is discussed for load and line perturbations, working at nominal and nonnominal conditions. Finally, the correctness of the proposed approach is verified with experimental prototypes. [ABSTRACT FROM AUTHOR]

A design method using quantitative feedback theory (QFT) for robust control of PWM DC-DC converters is developed. Parametric and nonparametric uncertainty can be described accurately with this technique. Besides, with the proposed method, the controller can consider both continuous and discontinuous conduction mode models (CCM and DCM respectively). Considering these sources of uncertainty results in a robust controller insensitive to parametric variations and also to different plant cases due to different conduction modes. A power converter satisfying a well-known industry standard is presented as a design example, in order to demonstrate that, with the proposed procedure, the performance of the regulated system can be tightly specified not only in terms of frequency requirements, but also in terms of time-domain characteristics, like overshoot and establishment time. The synthesised robust controller has been verified with experimental data from a power converter prototype, achieving satisfactory results. [ABSTRACT FROM AUTHOR]

Studies the quasi-periodic route to chaos both numerically and experimentally in a dc-dc boost switching regulator. Block diagram of the pulse-width modulation voltage controlled dc-dc boost converter; Possible waveforms of a dc-dc boost converter; Subcritical character of Neimark-Sacker bifurcation, hysteresis and coexisting attractors.

Focuses on a study which presented a method based on a circuit-oriented approach for large signal stability analysis of the boost regulator. Review of equivalent circuit of a boost converter; Linear control laws for large-signal stability; Control implementation for large signal stability.

Investigates the use of neural networks (NN's) for identification and control of power converters. Analysis of approximation by means of NN's of nonlinear control techniques suitable for large-signal operation; What simulation results in a pulsewidth-modulated (PWM) boost converter under large-signal operation illustrates; Directions for future work.

In this paper, second-order sliding-mode (SOSM) control approach is applied to synchronous buck dc–dc converters. The proposed SOSM controller can stabilize synchronous buck dc–dc converters using a simple digital state-machine structure, without requiring current sensing or an integral term in the control loop. The SOSM controller results in fast step-load and start-up transient responses, and is robust against parameter uncertainties. Fast transients and current limitation during start up can be accomplished by adjusting one controller parameter. Furthermore, a hysteresis method is introduced to control the switching frequency. The proposed approach is verified by experimental results on a 1.25-V 10-A prototype. [ABSTRACT FROM PUBLISHER]

This article presents a discontinuous modulation (DM) strategy for static compensators (StatComs) based on a cascaded H-bridge (CHB) converter with a star configuration. The proposed DM strategy considers the capacitor voltage oscillations at twice the fundamental frequency and the effect of zero-sequence voltage injection on the capacitor voltages. Considering these effects is especially important in CHB-StatComs with large capacitor voltage ripples (low-capacitance StatComs), where the assumption of a constant dc-link voltage, which is the basis of conventional DM strategies, does not apply. This article also describes a coherent set of steady-state waveforms for CHB-StatComs under DM. In addition to the well-known benefit of reducing the switching losses, the proposed DM also reduces the dc-link capacitors size and extends the operating range. The viability of the proposed DM strategy is verified experimentally on a small-scale prototype. In addition, simulation results are obtained using a real-scale system to study feasibility of the DM under unbalanced conditions. [ABSTRACT FROM AUTHOR]

A new digital robust control law for dc-dc converters is analyzed and implemented in this paper. The robust control QFT technique, which has been successfully used with analog implementations, has been adapted to the digital domain. Concretely, this paper considers the design of a power conditioning unit, which must take into account the uncertainty of the converter, as the conduction mode, the load, the input voltage or the storage elements while assuring that the specifications of a well-known standard are met. The robust control has been implemented by means of a digital device. The sampling frequency is a critical parameter for this kind of system which exhibits fast dynamics. The paper shows a procedure to analyze the minimum sampling frequency of the regulation loop. The procedure consists of transforming an standard analog QFT design to a digital controller by means of an accurate transformation from the s to z domain. After this transformation, we assure the robust stability of the converter by means of the Kharitonov theorem. This approach allows the designer to avoid iterations while finding an appropriate sampling frequency. The experimental prototype has been implemented by means of a FPGA device where the sampling frequency is 100 kHz for a buck power stage with a switching frequency of 200 kHz. The experimental results that are in good agreement with theoretical derivations. [ABSTRACT FROM AUTHOR]

This paper presents two different robust controllers for boost converters with two stages in a cascade. The first robust controller is monovariable; that is, the duty-cycle is the same for the two switches. The monovanable controller ensures that some prescribed constraints on pole placement and control effort are met, and optimizes the load disturbance rejection, while takes into account the uncertainty in certain parameters. The first controller is then compared with a multivariable robust controller; that is, with independent duty cycles in each switch. The multivariable controller takes into account the same uncertainty, constraints and optimization function. The comparison shows that the multivariable controller performs better at the expense of a slightly more complex implementation; that is, the multivanable controller provides a better rejection of the load disturbance. The paper also describes simulations and experimental results that are in perfect agreement with theoretical derivations. [ABSTRACT FROM AUTHOR]

This paper deals with the modeling and the robust controller synthesis for nonlinear dc–dc converters. In the first part of this paper, a model for the bilinear dynamics is presented. Such nonlinear dynamics can be included in a convex polytope such that the trajectories of the converter out of the equilibrium are assured to remain inside a guaranteed region of stability despite of the bilinear term. Such a description of the dynamic response of the converter is employed, in the second part of this paper, to propose synthesis algorithms that can guarantee, a priori, the stability and performance requirements of the design. The resulting region of stability can take into account not only the bilinear terms but also the saturation of the control input, which is a topic of major importance in high-performance dc–dc converters. The aim of this paper is to contribute with a robust control framework which allows the designers to deal with the common requirements of regulated dc–dc converters. The correctness of the results has been verified both with numerical simulations and experimental measurements from dc–dc converter prototypes. [ABSTRACT FROM PUBLISHER]

The paper adapts the Newton-like Extremum-Seeking Control technique to extract the maximum power from photovoltaic panels. This technique uses the gradient and Hessian of the panel characteristic in order to approximate the operating point to its optimum. The paper describes in detail the gradient and Hessian estimations carried out by means of sinusoidal dithering signals. Furthermore, we compare the proposed technique with the common Extremum Seeking Control that only uses the gradient. The comparison is done by means of PSIM simulations and it shows the different transient behaviors and the faster response of the Newton-like Extremum-Seeking Control solution. [ABSTRACT FROM AUTHOR]

In this paper, the problem of paralleling dc-dc switching converters is solved by means of power gyrators. The key element of the parallel connection is a buck converter with input filter acting as a power gyrator of type G with controlled output current, i.e., with its dc output current being proportional to its dc input voltage, electromagnetic interference minimization, current distribution among converters, stability, and voltage regulation are ensured by this approach. It is shown that a voltage regulator based on the parallel operation of power gyrators with democratic current sharing is always stable regardless of the number of connected modules. Experimental results of a dc-dc voltage regulator based on the parallel connection of three power gyrators with democratic current sharing are in perfect agreement with the theoretical predictions. [ABSTRACT FROM AUTHOR]