Control Of Power Converters Research Articles

A Jitter Amplification Phenomenon in Multisampled Digital Control of Power Converters

This article investigates a nonlinear phenomenon related to multisampling control of power converters. The nonlinearity, manifested as increased gain regions in static modulator transcharacteristic, is caused by the discontinuity of the modulating waveform and can result in increased jittering of the duty cycle. This article proposes a statistical model for predicting the jittering impact on the duty-cycle variance, analytic derivations for the jittering conditions, and an antijittering algorithm. A numerically obtained static modulator transcharacteristic is given to illustrate the increased gain regions. Verifications, performed on a multisampled digitally controlled buck converter, show a good match between the theoretical analysis, simulation, and experimental results. This article is accompanied by videos demonstrating the jitter amplification and the algorithm operation.

Observer-Based Sliding-Mode Control for Grid-Connected Power Converters Under Unbalanced Grid Conditions

This article proposes a novel robust control strategy for three-phase power converters operated under unbalanced grid conditions. A consolidated control objective is obtained in the stationary <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\alpha \beta$</tex-math></inline-formula> frame, which can be flexibly adjusted according to the degree of oscillation in the active and reactive powers and the balance of the three-phase current. Based on the dynamics of the converter and control objective, a control scheme in a cascaded framework is presented, in which an adaptive observer is applied to estimate the positive and negative sequences of the grid voltage. In the current tracking loop, a super-twisting algorithm current controller coupled with a super-twisting differentiator is implemented to track the current references, featuring rapid dynamics, and improved robustness. Additionally, in the voltage regulation loop, an effective composite controller is developed to regulate the dc-link voltage, where a super-twisting observer is used to estimate the load disturbance, thereby improving the performance of the converter. The experimental results are provided to confirm the effectiveness and superiority of the proposed control strategy.

Optimal Control With Maximum Cost Performance Measure

Optimal control of discrete-time systems with a less common performance measure is investigated, in which the cost function to be minimized is the maximum, instead of the sum, of a cost per stage over the control time. Three control scenarios are studied under a finite-horizon, a discounted infinite-horizon, and an undiscounted infinite-horizon performance measure. For each case, the Bellman equation is derived by direct use of dynamic programming, and the necessary and sufficient conditions for an optimal control are established around this equation. A motivating example on optimal control of dc-dc buck power converters is presented.

A Unified Approach for the Control of Power Electronics Converters. Part I—Stabilization and Regulation

This work deals with the control of power electronics converters. In that context, the majority of the problems of interest can be translated into two main problems: stabilization control problems and tracking control problems. Numerous methods exist in the literature to propose solutions which are based on several ways of handling them in a more appropriate context: linear, nonlinear, switching, and hybrid control, to cite the most important. In recent years, a considerable effort has been made to derive control design methods taking into account the specificities and properties of the complex behavior of these systems, going beyond the numerous techniques based on approximated models or focused on the specific converter topology under study and, in that way, making a step towards a desirable genericity level. It is the objective of this work to go a step further trying to tackle the control of power converters in a unified way. The idea is to avoid, as much as possible, the use of approximations and exploit all the mathematical properties of the associated switched models. Writing them in a specific way, it is possible to deal with a lot of problems of interest whose solutions are based on assumptions which are the expressions of some kind of practical feasibility, and then closely related to the existence of solutions to the studied problems. In some cases, the resulting controls have an inevitable complexity level which reflects one of the problems under study. For such situations, the implementation issues are important and are not discussed in details in this paper. The proposed methods are illustrated by numerical simulations conducted with the help of PSIM software. This research work is decomposed into two parts, the first one focused on stabilization problems is developed in this paper. The other one concerning the tracking problems will be developed in a future paper.

Multivariable Deadbeat Control of Power Electronics Converters with Fast Dynamic Response and Fixed Switching Frequency

Power converters have turned into a critical and every-day solution for electric power systems. In fact, the incorporation of renewable energies has led towards the constant improvement of power converter topologies and their controls. In this context, over the last 10 years, model predictive control (MPC) is positioned as one the most studied and promising alternatives for power converter control. In voltage source inverters (VSI), MPC has only been applied in the inner current control loop, accelerating and improving its dynamic response, but as mentioned, has been limited only to the current control loop. The fastest of the MPC techniques is the Deadbeat (DB) control, and in this paper, it is proposed to employ DB control on the entire system, therefore accelerating the time response not only for the current loops, but also for voltage loops. At the same time, this avoids overshoots and overpower in order to protect the power converter, leading to the fastest dynamic response according to VSI capabilities. For renewable energies, fast-dynamics entails fast maximum power tracking and therefore, maximizes energy harvesting, or in other words, reduces the losses due to the control dynamics. Thus, this paper gives a clear procedure and key points for designing a DB control for all the variables based on a mathematical model, which is corroborated by simulations and the experimental results.

Very Low Sampling Frequency Model Predictive Control for Power Converters in the Medium and High-Power Range Applications

Several control strategies have been proposed with the aim to get a desired behavior in the power converter variables. The most employed control techniques are linear control, nonlinear control based on linear and nonlinear feedback, and predictive control. The controllers associated with linear and nonlinear algorithms usually have a fixed switching frequency, featuring a defined spectrum given by the pulse width modulation (PWM) or space vector modulation (SVM) time period. On the other hand, finite set model predictive control (FS-MPC) is known to present a variable switching frequency that results too high for high power applications, increasing losses, reducing the switches lifetime and, therefore, limiting its application. This paper proposes a predictive control approach using a very low sampling frequency, allowing the use of predictive control in high power applications. The proposed method is straightforward to understand, is simple to implement, and can be computed with off-the-shelf digital systems. The main advantage of the proposed control algorithm comes from the combination of the model predictive control and the SVM technique, drawing the principal benefits of both methods. The provided experimental results are satisfactory, displaying the nature of space vector-based schemes but at the same time the fast response as expected in predictive control.

A Fast Convergent Homotopy Perturbation Method for Solving Selective Harmonics Elimination PWM Problem in Multi Level Inverter

Pulse width modulation (PWM) control for power converters have been vastly investigated and used in many industrial application. For medium voltage and high power applications, low switching frequency PWM techniques are preferred over high switching frequency-based PWM techniques. The preprogrammed low switching frequency-based PWM technique known as selective harmonics elimination (SHE) gives the better quality waveform at a lower switching frequency. The main difficulty in applying SHE PWM is in solving of non-linear transcendental equations for obtaining switching angles. Several methods have been proposed for computation of switching angles that include numerical techniques, optimization techniques, and algebraic techniques. However, the computation of switching angles is still a challenging task in the application of SHE PWM. In this paper, a novel fast convergent homotopy perturbation method (HPM) is proposed to compute switching angles for a multilevel inverter at a faster rate. The solutions obtained by the proposed technique is as accurate as obtained by the algebraic methods with no dependency on the initial guess. The proposed technique can compute the higher number of switching angles with multiple solutions in some modulation index range. A prototype is developed and the computed switching angles have been verified using field-programmable gate arrays (FPGA) controller to validate the results for practical applications.

Applying Synchronous Condenser for Damping Provision in Converter-dominated Power System

The dynamic characteristics of converter-dominated systems are governed by controlling power converters and the interactions between converter systems and conventional alternators. Frequency oscillations can appear under dynamic operation conditions caused by the phase-locked loop dynamics and interactions among the converter control systems. The oscillations may be poorly damped, which can result in reduced power generation, longer settling time, or disconnections of sensitive components. It is foreseeable that damping services will be critical for power grid stabilization in the future with high penetration of renewable generation. In this work, synchronous condensers (SCs) are evaluated and applied to provide damping services to the power grid under post-event conditions. An innovative supplementary controller for the automatic voltage regulator of SCs is proposed to improve the frequency stabilization in a converter-dominated system after disturbances. Using local and remote measurements, SCs are able to modulate the reactive power output and hence, the terminal bus voltage, which further impacts the power flow in the system; therefore, damping can be provided to the frequency oscillations. The control is implemented on an industrial-level hardware platform, and the performance is verified by the hardware-in-the-loop simulation.

Active Thermal Control for Modular Power Converters in Multi-Phase Permanent Magnet Synchronous Motor Drive System

Modular winding structure has been employed in the Permanent Magnet Synchronous Motors (PMSMs) to increase the reliability and reduce the torque ripple. Nevertheless, the reliability of the motor system depends on the lifetime of the power semiconductor devices. Since the thermal cycles, which can generate the mechanical stress between the different material layers in power devices, are the key factors to influence the lifetime of power devices, in this paper, an Active Thermal Control (ATC) for modular power converters in PMSM drive is proposed to extend the system lifetime. The power routing method is employed to balance the power in a quadruple modular winding PMSM system. The Rainflow Counting Algorithm is used to calculate the thermal cycles with a load mission profile, and estimate the lifetime of the power converters. The proposed method is validated by both simulation and experiments.

Evaluation of Fuzzy Membership Function Effects for Maximum Power Point Tracking Technique of Photovoltaic System

The photovoltaic generation system (PGS) is considered a potential renewable energy harvesting system. However, the low conversion efficiency of PGS and maximum power point tracking (MPPT) technique are the main challenges that must be solved. In addition, the switching frequency of the converters employed also affects the MPPT system performance. A high gain voltage DC-DC converter is proposed to replace conventional power converter and fuzzy logic controller (FLC) is applied in the MPPT for optimizing solar energy harvesting system. Nevertheless, evaluation of suitable fuzzy membership function is needed for optimal MPPT technique of photovoltaic system. In this paper, FLC of MPPT for photovoltaic application system was built using various membership functions in MATLAB/Simulink environment. The switching frequency of the high gain voltage DC-DC converter is varied to test the robustness of the performance of each FLC membership function. The results showed that the FLC-based MPPT technique for high gain voltage DC-DC converter with GBell membership function type has the capability to track the maximum power point (MPP) accurately and to achieve optimum power conversion. Furthermore, GBell membership showed having stable and consistent performance at various switching frequencies.

A Novel Simplified Implementation of Finite-Set Model Predictive Control for Power Converters

This article presents a novel simplified method to implement the finite set - model predictive control technique for photovoltaic generation systems connected to the ac network. This method maintains the advantages of the conventional finite set - model predictive control, such as fast response, simple implementation, and easy understanding; but it also eliminates the use of a cost function and hence the weighting factors, instead, it finds the optimal operating state directly from the model and the discrete number of valid states of the converter. Although the proposed algorithm does not compute a cost function, it is able to select the inverter state that minimizes the tracking error by using a hexagonal convergence region. The main advantage of this technique is to reduce the computational cost in 43% of the algorithm that selects the best state, presenting a simple and complete algorithm without compromising the predictive control performance. The proposed algorithm properly operates under various conditions such as changes in the network frequency and changes in the system parameters.

Module-Based Laboratory Course for the Industry Sponsored “Research and Design Master Program” in Power Electronics

The main purpose of this paper is to present a developed modular laboratory course for the industry sponsored “Research and Design Master Program” in power electronics. The objective of this modular laboratory course is for students to (i) Appreciate the theory of power converter with the aid of the state-of-art simulation tools, (ii) Derive the converter model and design the controller, (iii) Understand the magnetic components, (iv) Comprehend the closed-loop control of power converter, and confirm the modeling and controller design, (v) Realize the power converters by PCB layout, magnetic components implementation and debug. Therefore, this modular laboratory course is expected to bring the industry sponsored “Research and Design Master Program” students both systematic learning and hands-on experience. This module-based laboratory course is designed mainly by considering the application of magnetic components to power converters. The designed course modules include (i) Forward converter module for inductor and transformer with center-tapped winding, (ii) Flyback converter module for transformer with air-gap acting as inductor and transformer, (iii) Push-pull converter module for transformer with center-tapped winding and (iv) Half or Full-bridge converter module for driver transformer. The controller design for each module with closed-loop control is included. The designed laboratory course has been given for years and some assessment results will be illustrated. The feedback from the students indicates that this designed modular course receives excellent acknowledgment for providing practical training and covering the wide range of magnetic components as well as controller design in power converter learning.

One-Step-Prediction Discrete Observer Based Frequency-Locked-Loop Technique for Three-Phase System

In grid-tied power converters, the grid parameters such as the frequency, phase angle of the fundamental component, and the harmonics are essential to the control of power converters, the fast and accurate estimation of the grid parameters is a challenge especially for high-order harmonics. This paper proposes a one-step-prediction (OSP) discrete observer (OSPDO) to observe the fundamental and harmonic sequence components of the grid voltage. Based on the proposed OSPDO, a frequency locked loop (FLL) is designed. The proposed OSPDO-FLL has a good robustness to sampling frequency on dynamic response and high precision for frequency estimation. The proposed algorithm can estimate up to maximum 50th harmonic with a low sampling frequency thanks to the robust properties. Finally, the good characteristics of the proposed synchronization algorithm are verified by simulations and laboratory experiments.

Sensorless Control of DC Microgrid Based on Artificial Intelligence

Nowadays, DC microgrids are preferred in the field of renewable energy. The autonomous DC microgrids aim to provide smooth power flow from renewables to loads. While satisfying certain load profiles and sustaining the power as the desired level, the control of power converters is considerable. To ascend the resilience of DC microgrids, battery storage systems (BSSs) are also used as a backup unit for supplying uninterrupted power. The main task of BSSs is to compensate for the lack of power when the load is higher than supplied power or store the surplus of power in case that the load demand is less than the extracted power. In other words, by draining and storing the power, BSSs help to increase the flexibility of the system and keep the main DC bus voltage within acceptable bounds. This study introduces artificial intelligence (AI)-based method to diminish the number of implemented sensors and control power converters without reducing efficiency. In this paper, artificial neural networks (ANNs) as a subset of AI are exploited. Diminishing the number of sensors in the control layer makes the system more reliable. To validate the effectiveness of the proposed system, phases of ANNs' simulations are performed in MATLAB/Simulink.

Grid dynamics shaping using flexible controlled power converters

An idea towards stabilizing a grid with numerous distributed generators (DGs) and renewable energy sources (RESs) is to compensate system inertia, damping characteristic, and weak dynamics, virtually. This may be established by a primary power source (e.g., DG or energy storage) together with a flexible controlled power electronics converter. This setup will then operate to emulate desirable dynamics, by flexible shaping of its output active and reactive powers. This approach provides a promising solution to improve power grid stability and performance in the presence of high penetration of DGs/RESs. In this paper, the general idea of the flexible controlled power converter (CPC) is explained and its significant role in enhancing the renewable integrated power grids is emphasized.

One-Cycle Zero-Integral-Error Current Control for Shunt Active Power Filters

Current control has, for decades, been one of the more challenging research fields in the development of power converters. Simple and robust nonlinear methods like hysteresis or sigma-delta controllers have been commonly used, while sophisticated linear controllers based on classical control theory have been developed for PWM-based converters. The one-cycle current control technique is a nonlinear technique based on cycle-by-cycle calculation of the ON time of the converter switches for the next switching period. This kind of controller requires accurate measurement of voltages and currents in order achieve a precise current tracking. These techniques have been frequently used in the control of power converters generating low-frequency currents, where the reference varies slowly compared with the switching frequency. Its application is not so common in active power filter current controllers due to the fast variation of the references that demands not only accurate measurements but also high-speed computing. This paper proposes a novel one-cycle digital current controller based on the minimization of the integral error of the current. Its application in a three-leg four-wire shunt active power filter is presented, including a stability analysis considering the switching pattern selection. Furthermore, simulated and experimental results are presented to validate the proposed controller.

Improved Variable DC Approach to Minimize Drivetrain Losses in Fuel Cell Marine Power Systems

This article proposes a novel approach for operating hybrid fuel cell and battery power systems in marine vessels. The target of the approach is to reduce energy losses in drivetrain devices. In the proposed approach, the dc bus voltage of the hybrid power system is adjusted according to fuel cell operating points, which enables operation in freewheel mode, and thus significantly reducing power conversion losses. Feasibility of the proposed approach is verified using a real-time hardware-in-loop simulation setup consisting of prevalidated virtual models and real industrial power converter controllers. The results presented in the work illustrate that the variable dc approach enables significant improvements in drivetrain efficiencies, and thus providing significant savings for vessel operators. Additionally, variable dc approach is shown to eliminate high-frequency current ripple at the fuel cell terminals, which can further improve the efficiency and the lifetime of the fuel cells.

Non-linear control over a continuous current to continuous current power converter using exact linearization

Taking as a starting point the exact feedback linearization to transform a non-linear system into a linear one through coordinate transformation and state-space feedback based on its non-linear model, we have presented in this document the modelling, analysis and non-linear control of a boost-type power converter, with the objective of comparing the results with a proportional, integral and derivative controller. This technique was then applied on a power converter from continuous current to continuous current and the dynamics were analyzed zero to verify the validity of the controller, which was simulated in the Simulink-Matlab software. Finally, the simulation results showed that the system with the exact linearization controller is not only free of excess, but also improves the stability in the output voltage.

Bang-Bang control over a direct current to direct current converter

The following document presents an optimal control technique to control power converters direct current to direct current using the Bang-Bang control technique, for example a Buck power reducing converter will be shown, Subsequently and using an approach based on the principle of the maximum of Pontryagin, an optimized switched control technique (bang-bang) is designed and implemented that allows to obtain a performance comparable to the on-off action in terms of dynamic characteristics. Additional tests allow quantifying the optimality of the proposed technique and verifying the performance of the controlled system in energy terms, showing that an optimal switched control has, in addition to the minimization of the functional cost (minimum error energy), a lower incidence in the generation of high frequency switching noise, compared to conventional technique. As one of the most important aspects highlighted in the results corresponds to the simplicity of design and the high efficiency of the Bang-Bang controllers, making the output voltage practically no ripples.

Lyapunov based adaptive controller for power converters used in hybrid energy storage systems

Depleting fossil fuels, natural gas resources, escalating oil prices, and global warming issues have made fuel cell (FC) based electric vehicles (EVs), a vital replacement to its conventional counterpart. Modeling of such a system contains power-conditioning circuitry, which exhibits nonlinear nature. In this paper, a model for hybrid electric vehicle is proposed with FC as primary source, whereas ultra-capacitor (UC) and battery are secondary sources. All the sources are linked with a direct current (DC) bus comprising of DC-DC converters. The study of the system is done mathematically and simulations are performed on MATLAB/Simulink. The dynamic model based on Lyapunov based adaptive control technique with model uncertainties designed to accomplish the following objectives. Firstly, the perfect regulation of DC bus voltage having minimum steady-state error under the load variations. Secondly, current of battery and UC precisely followed quickly under their relating reference values. Finally, asymptotically stability of the closed loop system. Proposed controller performances are analyzed using MATLAB/Simulink and comparative analysis is done with the sliding mode controller (SMC) and proportional integral derivative (PID) controller, which demonstrates the closed-loop stability of the proposed controller. Moreover, all control objectives are achieved efficiently.