Variable Switching Research Articles

Variable Switching Frequency Scheme Minimizing Inductor Saturation Margin for Totem-Pole Rectifier Based on Frequency-Domain Ripple Analysis

Powdered iron core (PIC) inductors demand a considerable design margin to avoid magnetic saturation, limiting the converters’ power density. This article formulates a frequency-domain method to assess the saturation’s influence on the current ripple, and proposes an optimal variable switching frequency scheme to offset the harmonics growth. A Totem-Pole rectifier prototype is built to estimate this scheme. Its harmonics distortion is reduced by 0.69% without causing instability or extra power loss. Thus, deeper saturation is allowed for PIC inductors and the saturation margin is narrowed, shrinking inductor’s volume by 2/3 to reach a higher power density.

Hybrid-Mode Adaptive Zero-Voltage Switching for Single-Phase DC–AC Conversion With Paralleled SiC MOSFETs

State-of-the-art soft-switching modulations such as critical conduction mode and triangular current mode increase the conduction loss of power semiconductors and require variable switching frequencies; thus, these soft-switching methods are seldom used in high-power dc–ac conversion. To achieve soft-switching while maintaining low root mean square currents, this article proposes a hybrid quadrilateral and continuous current mode (HQCCM) modulation for general high-frequency single-phase dc–ac conversion based on paralleled silicon carbide metal oxide semiconductor field-effect transistors. The proposed HQCCM adaptively operates in soft-switching quadrilateral current mode or hard-switching continuous conduction mode in one ac line cycle depending on the instantaneous ac load current. Thus, high efficiencies can be achieved over the full power range. This HQCCM modulation features adaptive soft-switching, constant switching frequency, and compatibility to line filter and is applicable for high-power applications. A 4.4-kW single-phase dc–ac inverter is developed and tested to verify the advantages of the HQCCM. This article is accompanied by a video demonstrating the effectiveness of the proposed HQCCM in varying load scenarios.

Improvement of Model Predictive Based Maximum Power Point Tracking Using Direct Control Predictive Power Point Tracking Algorithm

In this paper, a Direct Control Predictive Power Point Tracking Algorithm has been proposed to improve the performance of the Maximum Power Point Tracking (MPPT) algorithm based on the Model Predictive (MP). This work has generally been divided into two types of MPPT based on MP. The first is the Model Predictive Variable Switching Frequency (MP-VSF) Model, and the second is the Model Predictive Fixed Switching Frequency (MP-FSF) Model. MP-VSF focuses on replacing the conventional Proportional Integral (PI) controller with Finite Set-Model Predictive Control (FS-MPC), but the tracking algorithm still utilizes the Perturb and Observe (P&O) algorithm. Meanwhile, MP-FSF replaces P&O with a simple PV predictive model called the Digital Observer (DO). DO leads in speed tracking and algorithm design because it no longer uses increment or decrement steps such as P&O to achieve MPP. The proposed improvement is to reconstruct DO by adding FS-MPC in one unit. This makes it possible to produce an optimal control signal that can be used without additional modulation to create a duty ratio like conventional DO. To determine the performance of the proposed algorithm, this work validates it with two scenarios, where the first scenario is in constant weather and the second is with dynamic weather. Both techniques were tested using the Single Board Hardware in The Loop approach. The proposed algorithm efficiency and tracking speed performance are also compared to MP-VSF, MP-FSF, and P&O. Moreover, an evaluation was also carried out to determine the computational time of each studied MPPT.

Command filtered dual backstepping variable structure robust switching control of uncertain nonlinear system

Command filtered dual backstepping variable structure robust switching control of uncertain nonlinear system

Real-Time Validation of a Novel IAOA Technique-Based Offset Hysteresis Band Current Controller for Grid-Tied Photovoltaic System

Renewable energy sources have power quality and stability issues despite having vast benefits when integrated with the utility grid. High currents and voltages are introduced during the disconnection or injection from or into the power system. Due to excessive inverter switching frequencies, distorted voltage waveforms and high distortions in the output current may be observed. Hence, advancing intelligent and robust optimization techniques along with advanced controllers is the need of the hour. Therefore, this article presents an improved arithmetic optimization algorithm and an offset hysteresis band current controller. Conventional hysteresis band current controllers (CHCCs) offer substantial advantages such as fast dynamic response, over-current, and robustness in response to impedance variations, but they suffer from variable switching frequency. The offset hysteresis band current controller utilizes the zero-crossing time of the current error for calculating the lower/upper hysteresis bands after the measurement of half of the error current period. The duty cycle and hysteresis bands are considered as design variables and are optimally designed by minimizing the current error and the switching frequency. It is observed that the proposed controller yields a minimum average switching frequency of 2.33 kHz and minimum average switching losses of 9.07 W in comparison to other suggested controllers. Results are validated using MATLAB/Simulink environment followed by real-time simulator OPAL-RT 4510.

A switched system approach for the direct solution of singular optimal control problems

Optimal control problems where the control variable appears linearly in the formulation lead to singular control arcs that introduce analytical and numerical complications during the solution process. In this work, the switching behavior (switching between singular and nonsingular control arcs) is exploited to solve singular optimal control problems using a direct method. The problem is reformulated as a switched system optimal control problem where each control arc defines a different subsystem, i.e., lower and upper limits and a singular arc. The switching between control arcs is handled using binary functions that depend on time. The switched system is embedded into a larger family by relaxing the binary functions to avoid integer variables. The variable switching times at which the control switches between arcs are mapped to fixed points in a new time domain using a time-scaling transformation. A direct transcription method along with control parametrization is applied to transform the embedded problem into a nonlinear programming formulation that contains few variables and constraints. A penalty term is introduced to obtain binary solutions for the optimal selection of control arcs. The proposed reformulation avoids the use of mesh refinement techniques and continuation methods, and allows to solve challenging problems in very short CPU times with high accuracy.

Hysteresis Based Quasi Fixed Frequency Current Control of Single Phase Full Bridge Grid Integrated Voltage Source Inverter

The traditional Fixed Band Hysteresis Current Control (FB-HCC) though being widely used for the current control of grid integrated voltage source inverter (GI-VSI), has the drawback of variable switching frequency. To overcome this drawback, Complex Programmable Logic Device (CPLD) based switching scheme is proposed in this paper. The proposed method calls for a single reference wave and the control concept is to terminate the rising and falling inductor current (iL) either by the comparator or by the CPLD, based on the nature of its slope. Termination of the iL with steeper slope by the comparator ensures lower current ripple, whereas the CPLD ensures constant switching frequency (fsw). However, the iL obtained with the proposed logic has a DC offset, which is corrected by modifying the reference. The basic concept, switching logic, and reference correction are thoroughly detailed. MATLAB/Simulink results are included to verify the proposed concept. The constant frequency operation of the proposed method is also validated in a 2 kW, 230 V, 50 Hz GI-VSI prototype.

Modified Fast Terminal Sliding Mode Control for DC-DC Buck Power Converter with Switching Frequency Regulation

In this paper, a modified fast terminal sliding mode control (FTSMC) with a fixed switching frequency is proposed for regulating the output voltage of the DC-DC buck converters. The design steps of the proposed FTSMC such as the selection of sliding surface, switching control strategy, existence, robustness, and stability analysis are presented in detail. To overcome the variable switching frequency in FTSMC, a frequency control loop is designed. Moreover, the proposed FTSMC with fixed switching frequency can be implemented by using only one voltage sensor. Hence, the proposed control method not only offers a fast dynamic response and fixed switching frequency but also simplifies the controller design in practical implementation. The effectiveness of the proposed control methods has been investigated by experimental studies. The results reveal that the proposed methods exhibit a good performance under both steady-state and dynamic transients caused by the variations in load resistance, input voltage, and reference voltage. Moreover, the proposed method is compared with four existing methods.

An Advanced Shunt Active Power Filter (SAPF) for Non-ideal Grid Using Predictive DPC

The usage of power electronic converters and other non-linear devices is very common in this modern era because of their flexibility in control. However, they inject harmonics into the power system. To deal with the problem, the use of filters has become almost inevitable. Active power filters controlled by direct power control (DPC) have overtaken this responsibility from the passive filters because of their numerous advantages. To deal with the real-world power system grid which is far from the idealized character of being balanced and sinusoidal, the proposed method uses the extended pq theory integrated with the dual second-order generalized integrator (D-SOGI) for the correct estimation of the all-important instantaneous powers. In contrast, the conventional pq theory is used in the existing works, which doesn’t hold in a non-ideal grid. In addition to that, here, for the selection of the switching vector, an advanced and more accurate predictive DPC method which is specifically designed to operate in a non-ideal grid, replaces the static look-up tables used in the previous works. Further, to make the filter designing easier, the proposed method focuses on constant switching frequency operation eliminating the problems arising from variable switching frequency used in literature. The proposed technique is tested in MATLAB/Simulink environment and the real-time system to validate its feasibility.

Distributed Competition of Multi-Robot Coordination Under Variable and Switching Topologies

This paper investigates a distributed competition behavior in multi-robot coordination under variable communication topology and switching one. In terms of multi-robot competition-based coordination, a winner-take-all (WTA) strategy is leveraged to address this issue with inevitable environmental barriers incorporated. Moreover, an innovative control theory stimulated gradient neural network (CTSGNN) algorithm is proposed to realize the WTA with prominent robustness and convergence over the traditional ones. Besides, to adapt to diversified local communication modes among multi-robot systems, fast variable and low switching topologies are constructed to establish two dynamic consensus estimators, accompanied by the proposed distributed control schemes. Traditional algorithms are introduced and served as a contrast. Afterward, the global convergence of the proposed algorithm in dealing with multi-robot competitive coordination, the universality of the application scenario, as well as the weaknesses of traditional methods are substantiated theoretically. The effectiveness and superiority of the proposed CTSGNN algorithm and the resultant distributed control schemes by integrating consensus estimators are further sustained via simulations. Note to Practitioners—The motivation of this paper is the coordination operation of multi-robot systems, but it is also applicable to other fields adopting multi-agent systems. Most of the existing researches on multi-robot coordination only exploit their collaborative behavior, which usually leads to the system redundancy and overflow of control costs. To this end, an innovative control algorithm is proposed for this competitive coordination and remains to be perfect in terms of stability and accuracy. Then, this paper establishes new distributed control schemes for multi-robot systems to compete for optimal dynamic task allocation. In this sense, under the premise of ensuring a successful task execution, only a few individuals with strong abilities and advantages are assigned. It is promising to maximize resource utilization, increase efficiency, and be extended to multi-objective scenarios. Note that the design of this scheme takes into account the environmental constraints and physical constraints of the robot itself. Theoretical analysis and preliminary simulation experiments prove the high efficiency of the control scheme. In ongoing research, the competitive coordination tasks of the mobile robot systems and communication delays or fault in control scheme design are explored to expand the operation scope and system extensibility.

Optimal Sector-Based Sequential Model Predictive Control for Current Source Rectifier

Conventional model predictive control (MPC) methods for current source rectifier (CSR) use either a PI controller or weight factor-based methods, which require time-consuming tuning methods to develop an efficient controller. Moreover, the limitations on the bandwidth requirements of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LC$ </tex-math></inline-formula> filter cause resonances and grid current distortions if a variable switching frequency-based predictive control is used. So, a new fixed switching frequency-based MPC algorithm has been developed to control the load and source current simultaneously, thereby facilitating the weight factor less operation and applying a predefined space vector sequence. Unlike the conventional single cost function methods applied to CSR, the proposed method uses separate cost function for each control variable. Simultaneously, to provide fixed frequency operation, duty ratio-based modulation of grid current control has been applied. A virtual impedance-based active damping has been embedded into the supply current control to suppress the oscillations caused by the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LC$ </tex-math></inline-formula> filter and grid current harmonics. Simulation and experimental results have been supported to validate the improvements in terms of supply current total harmonic distortion (THD), steady state, and transient switching performance.

High-Voltage Power Supply for High Repetitive Rate Marx Generator with Quasi-Resonant Zero-Current Switching Transistor Control Algorithm

Due to having a number of advantages, Marx generators are still the most widely used devices for generating high-voltage pulses in many fields of science and technology. To ensure their proper operation, especially when the generation of many frequent, highly repetitive pulses is required, a highly efficient high-voltage power supply is needed. The paper describes a specially developed power supply (input voltage 48 V DC, output voltage up to 50 kV) based on the conventional Full Bridge topology with two high-frequency high-voltage transformers and a 6-stage voltage multiplier. In order to avoid many problems caused by low coupling between primary and secondary windings of the transformers and the large parasitic capacitances of the secondary windings, a special quasi-resonant zero-current switching transistor control algorithm with variable switching frequency (dependent on output load) was developed. In the described method, the energy is supplied to the transformer in short pulses, when a pair of diagonal transistors of the full-bridge converter were turned on. Then, the freewheeling state is maintained until all of the energy stored in the leakage inductance of the transformer has been transferred to the secondary side, which means that the current in the primary windings drops to zero. This approach reduces energy losses, electromagnetic disturbances and prevents current distortion in primary winding.

Constant switching frequency‐based delta‐sigma modulation of single‐phase AC–AC zeta converter

SummaryDirect pulse width modulated (PWM) AC–AC converters, derived from their DC–DC counterparts, serve as promising media for AC–AC power conversion because they offer benefits, such as single‐stage power conversion, absence of bulky DC links, and small footprint. In this study, a single‐phase ( ) AC–AC zeta converter was analyzed under buck, boost, and buck‐boost operations. Delta‐sigma modulation (DSM) technique, known for its simple logic implementation, excellent reference‐tracking property, robust control, and fast transient response, was employed for the load voltage control of a AC–AC zeta converter. However, the conventional DSM technique relies on a fixed hysteresis band (FHB) for restricting the integrated (sigma) error (delta) between the reference and estimated control voltages within a narrow band, which causes the converter to operate at a variable switching frequency (VSF). Although VSF enhances the converter performance with low total harmonic distortion (THD) and high degree of flexibility over waveform quality, it poses serious implications such as higher switching losses, putting more strain on thermal management of switches. This paper presents a constant switching frequency‐based DSM technique based on an adaptive hysteresis band (AHB) for a AC–AC zeta converter. The converter is controlled using FHB‐DSM and AHB‐DSM techniques, and a comparison is drawn between the two in terms of various performance indices. In this comparison, FHB‐DSM serves as a benchmark and an optimum switching frequency based on AHB‐DSM technique is determined, which exhibits low switching losses while maintaining the same THD limits, dynamic response, and waveform quality as that of FHB‐DSM technique. The proposed strategy was validated by simulation studies in MATLAB/SIMULINK software. Furthermore, a real‐time simulator, OPAL‐RT (OP4510), was used to validate the study with real‐time implementation.

Newton trust-region methods with primary variable switching for simulating high temperature multiphase porous media flow

Coupling multiphase flow with energy transport due to high temperature heat sources introduces significant new challenges since boiling and condensation processes can lead to dry-out conditions with subsequent re-wetting. The transition between two-phase and single-phase behavior can require changes to the primary dependent variables adding discontinuities as well as extending constitutive nonlinear relations to extreme physical conditions. Practical simulations of large-scale engineered domains lead to Jacobian systems with a very large number of unknowns that must be solved efficiently using iterative methods in parallel on high-performance computers. Performance assessment of potential nuclear repositories, carbon sequestration sites and geothermal reservoirs can require numerous Monte-Carlo simulations to explore uncertainty in material properties, boundary conditions, and failure scenarios. Due to the numerical challenges, standard NR iteration may not converge over the range of required simulations and require more sophisticated optimization method like trust-region.We use the open-source simulator PFLOTRAN for the important practical problem of the safety assessment of future nuclear waste repositories in the U.S. DOE geologic disposal safety assessment Framework. The simulator applies the PETSc parallel framework and a backward Euler, finite volume discretization. We demonstrate failure of the conventional NR method and the success of trust-region modifications to Newton’s method for a series of test problems of increasing complexity. Trust-region methods essentially modify the Newton step size and direction under some circumstances where the standard NR iteration can cause the solution to diverge or oscillate. We show how the Newton Trust-Region method can be adapted for Primary Variable Switching (PVS) when the multiphase state changes due to boiling or condensation. The simulations with high-temperature heat sources which led to extreme nonlinear processes with many state changes in the domain did not converge with NR, but they do complete successfully with the trust-region methods modified for PVS. This implementation effectively decreased weeks of simulation time needing manual adjustments to complete a simulation down to a day. Furthermore, we show the strong scalability of the methods on a single node and multiple nodes in an HPC cluster.

Performance enhancement of DCMLI fed DTC-PMSM drive in electric vehicle

This paper focus on the simulation and hardware analysis of a diode clamped multilevel inverter (DCMLI) fed direct torque control (DTC) permanent magnet synchronous motor (PMSM) drive in electric vehicle (EV) application. DTC-PMSM drive is more used for torque and speed control. The existing DTC PMSM drive consists of torque and flux hysteresis comparators and suffers from variable switching frequency and torque ripples. These problems can be solved by using carrier-based space vector modulation (CBSVM) about torque and flux. In this proposed approach a DCMLI fed 4 poles, 0.5 HP DTC PMSM drive system is designed and simulated using carrier-based CBSVM. Simulation and experimental implementation are carried out in MATLAB environment and AVR Microcontroller respectively. The simulated performances are studied in steady-state and transient conditions for varying load, speed, and torque. The results of the DTC-PMSM drive system using CBSVM show that the proposed method can effectively reduce the torque ripple and maintain a constant speed and also improved driving performance of drive for electric vehicle applications.

A New Model Predictive Current Controller for Grid-Connected Converters in Unbalanced Grids

Distributed energy resources are often connected to low-voltage distribution networks where the grid voltages may be unbalanced. This leads to an unwanted ripple in the output active power at twice the fundamental grid frequency. In this article, a new model predictive current controller is proposed for unbalanced grids. The variable switching frequency of existing model predictive controllers is fixed and the power quality is improved. A Kalman filter estimator is used to extract the positive and negative sequence components. A new calculation time compensation technique is proposed, which offers superior accuracy to existing approaches. A grid voltage discretization compensation strategy is outlined, and its effectiveness is demonstrated. Finally, the system stability is verified theoretically. Simulation and laboratory results are included to prove the robustness of the proposed controller and support the theoretical analysis.

On several numerical strategies to solve Richards’ equation in heterogeneous media with finite volumes

We propose several numerical approaches building on upstream mobility two-point flux approximation finite volumes to solve Richards’ equation in domains made of several rock-types. Our study encompasses four different schemes corresponding to different ways to approximate the nonlinear transmission condition systems arising at the interface between different rocks consisting in the continuity of the pressure and the fluxes, as well as different resolution strategies based on Newton’s method with variable switch. We benchmark the robustness and accuracy of the different methods on filling and drainage test cases with standard nonlinearities of Brooks-Corey and van Genuchten-Mualem type, as well as with challenging steep nonlinearities.

Positive recurrence of a solution of an SDE with variable switching intensities

Positive recurrence of a d-dimensional diffusion with an additive Wiener process, with switching and with one recurrent and one transient regimes and variable switching intensities is established under suitable conditions. The approach is based on embedded Markov chains.

ZVS-Interleaved Synchronous Buck DC–DC Converter With a Coupled Inductor by Varying Switching Frequency and Deadtime

This article proposes a fully digital variable switching frequency and deadtime control method for a synchronous rectifier buck dc–dc converter with an inverse coupled inductor. It does not need auxiliary circuits, zero-crossing detection (ZCD), or high-bandwidth sensors. Even in facing the polyline shape of the current in inductors due to the coupling effect, zero-voltage switching (ZVS) can be achieved with the proposed varying switching frequency control to make the turn <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> current be constant. Based on ZVS achievement of the power switches, the deadtime is variable to reduce the conduction loss over body diodes further. The modes and resonant process are analyzed in detail. A 1-kW experimental prototype was built to verify the effectiveness of the proposed control method. The peak efficiency is over 99% in the experimental test.

Digital Regulation of Wireless Power Transfer Systems Using an Embedded Lock-In Amplifier

High-performance operation of inductive wireless power transfer (WPT) systems requires judicious tuning of the inverter connected to the transmission hardware for high-performance operation and reliability. In many applications, disturbances to both the coupling condition and the secondary-side load reshape the system dynamics, motivating the design of closed-loop regulation and impedance detection techniques. Although several analog methods have been presented, they require multiple additional components and are dependent upon fixed component values and operating frequency. In this article, a novel digital approach is presented for use in series–series compensated WPT systems. The proposed system extracts both the phase and the magnitude of the primary current in real time. Through closed-loop regulation, zero-voltage switching is sustained without additional compensation components, while the output current is controlled. By utilizing a digital framework, no additional analog components are required, improving system reliability and cost. The state identification method is self-tuning, providing robust suppression of switching noise even with a variable switching frequency. A computationally efficient construction ensures a fast converging measurement and enables high-frequency operation. Analysis, simulations, and experimental results are included to comprehensively verify these characteristics.