Optimal Switching Sequence Research Articles

Reducing Harmonics Distortion in Five-Phase VSI Using Space-Vector-Based Optimal Hybrid PWM

Compared with three-phase motors, multiphase motors offer several advantages such as higher efficiency, lower torque pulsation, and higher fault tolerance. To exploit these advantages, a multiphase modulator with low current harmonics is essential. However, the switching sequence of conventional space-vector pulse width modulation (SVPWM) is not optimal because of high stator flux ripple, which is proportional to line current harmonics. In this study, all possible switching sequences for a given switching number and carrier frequency were explored. On the basis of stator harmonic current analysis, the optimal switching sequence was selected for different modulation indices and reference angles. Then the optimal spacial distribution of each sequence to minimize root-mean-square harmonic current was derived, yielding optimal hybrid pulse width modulation (OHPWM). Similar to SVPWM, the proposed OHPWM produces an equivalent phase voltage to a reference in average means. By employing different switching sequences, the proposed method can reduce the total current harmonics distortion. Both simulations and experiments confirmed the correctness of the theoretical derivation of the proposed modulator.

Cascaded Common Nodal Point Multi-level Inverter Topology

Recent trends in the multi-level inverter (MLI) technology demand reduced number of switches, driver circuits, isolated DC sources, peak inverse voltage (PIV), appreciable number of voltage level, and lower total harmonic distortion. This paper presents an improved cascaded MLI configuration. Each module comprises ten switches, two isolated DC sources, and two capacitors; it can generate a maximum of 9-level output voltage waveform. Optimized switching sequence is developed that ensures minimum switching transitions and is implemented through single-carrier pulse width modulation for the control of the proposed topology. The classical cascaded H-bridge inverter and some recently developed MLI configurations were compared with the proposed inverter circuit. Results show that the proposed inverter configuration generates high number of output voltage levels with reduced number of power switches and PIV. It also has a lower per-unit power loss profile. Unit capacitor voltage balancing scheme is developed, which ensures proper control of the unit step voltage level in each of the cascaded modules, at extreme loading condition. For two cascaded inverter modules, simulation and experimental verifications are carried out on the proposed inverter for an R–L load. Simulation results of the output voltage waveforms and its harmonic spectrum are in conformity with experimental results.

Model Predictive Control for Single-Phase NPC Converters Based on Optimal Switching Sequences

In this paper, a model predictive control (MPC) based on optimal switching sequences (OSSs) for a single-phase grid-connected full-bridge neutral-point-clampled (NPC) power converter is presented. The predictive control algorithm is formulated in terms of OSSs, which was originally proposed to govern three-phase power converters. In this paper, the OSS concept is extended to control single-phase power converters. The proposed MPC algorithm belongs to the continuous control set MPC and is able to provide fixed switching frequency while handling system constraints. The proposed algorithm has been experimentally tested in an NPC power converter prototype. Experimental results show the desired fixed switching behavior in the steady-state condition and the intrinsic fast dynamic provided by MPC during transients. Furthermore, the test outcomes demonstrate the robustness of the proposed controller under large system parameter deviations.

An overheating‐tolerant space vector modulation algorithm for multilevel inverters

As promising and suitable candidates for high‐power applications, multilevel inverters have become one of the most promising solutions in various applications. However, power switching devices are highly subjected to thermal overheating, which leads to shortened lifetime and reduced reliability. Thermal overheating may result from the degradation of power switching devices due to continuous overloading and power cycling. In addition, degradation and faults in the cooling system of power switching devices may cause thermal stresses as well. A new overheating‐tolerant space vector modulation algorithm is proposed in this paper to alleviate thermal stresses from overheated power switching device. The proposed algorithm relies on using the redundancy property between switching states in multilevel inverters to continuously evaluate a cost function of the junction temperature of the overheated device for all possible switching sequence sets and then selects the optimal switching sequence. In addition, the proposed algorithm preserves the DC‐link capacitor voltage without reduction in the output current of the inverter. The proposed algorithm is general, which can be applied to n‐level inverters. Both simulation and experimental results reveal the efficient performance of the proposed algorithm using a three‐level T‐type inverter as a case study. Accordingly, the lifetime and reliability of the inverter are enhanced considerably using the proposed algorithm. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Predictive Optimal Switching Sequence Direct Power Control for Grid-Connected Power Converters

Grid-connected power converters play a key role in several applications such as the integration of renewable energy sources and motor drives. For this reason, the development of high performance control strategies for this particular class of power converters has increasingly attracted the interest of both academic and industry researchers. This paper presents the predictive optimal switching sequence (OSS) direct power control (DPC) (OSS-DPC) algorithm for grid-connected converters. The OSS-DPC method belongs to the predictive-DPC family and provides the desired power references by calculating globally OSSs. To address computational and implementation issues, an efficient control algorithm, named reduced OSS-DPC, is introduced. The implementation of the proposed control strategy in a standard DSP is evaluated on a two-level power converter prototype working as a STATCOM. Experimental results show the algorithm's potential to provide high performance during both transient and steady states.

A New Switching Pattern for Multilevel Inverter Based on Selective Harmonic Elimination Using Genetic Algorithm

Abstract – In this paper, a new switching pattern is presented for multilevel inverters. With changing off-angel of each switch, the on time interval of all switches will approximately be equal and then the lifetime of inverter will increase, also using this method can reduce electrical stress on switches in higher levels of inverter. Switching angels as for desired modulation index are calculated using genetic algorithm whereas selective harmonics are controlled within the allowable range. The computed angels are simulated in Matlab/Simulink for respective circuits to validate the results. Keywords : Multilevel Inverter, Harmonic Elimination, THD, Genetic Algorithm 1. Introduction providing lower levels of voltage,. Also some switches are The main concepts of multilevel inverters, introduced about 3 decades ago [1-2], entails performing power conversion in multiple voltage steps to obtain improved power quality, lower switching losses, better electromagnetic compatibility, higher voltage capability, eliminating the harmonics from the output voltage, and minimizing the THD [3]. Several topologies for multilevel inverter have been proposed over these years, the most popular ones are the diode-clamped [4-5], flying capacitor [6-7] and the cascaded H -bridge [8-11] structures. Theoretically, multilevel inverters can synthesize an infinite output-voltage level. By increasing the number of levels in the inverter, the output voltage has more step generation, a staircase waveform, which has a reduced harmonic distortion [12]. However, a large number of levels increase the number of switching devices, diodes, and other passive elements. Cascade H-Bridge multilevel inverter is common structure used in construction of multilevel inverter. In this structure several H-bridge single phase inverter is connected series and provide the desired voltage level. One of the essential problems in these inverters is failing of switches during inverter’s operation time which leads to a failure in a whole inverter. This failure is due to two reasons: One or more switches in bridges providing lower levels of voltage are defective due to longer operation time rather than other switches, these switches are in bridges defective because of working on higher switching frequency rather than other switches, these switches are in bridges providing higher levels of voltage,. Also switching loss at the second group switches is higher than other switches, it reduces the efficiency of the circuit.In this work to overcome these problems a new switching method is proposed. In this method on time of all switches in all bridges of Multilevel inverter is approximately equal. This method is quite similar to common multilevel inverter however there is the difference in each switch’s offangle.There have been many attempts at finding an optimal switching sequence for both voltage, and current. The most common method is either pulse width modulation (PWM) or space vector modulation (SVM). While attempts at PWM and SVM have success, it is hard to claim that any have found the absolute best switching sequence solution [13-15].This problem leads to non-linear equations and direct solution of non-linear equations can lead to discontinuity at certain modulation indices. The prevalent methods to solve this problem utilize intelligent methods. In this paper GA is used to solve this problem. The optimal switching angles are generated, selective harmonic are eliminated and consequently THD of output voltage is minimized. To validate the results, the computed switching angles are used in simulated circuit [12].

Capacitor Voltage Balancing of Three-Phase Neutral-Point-Clamped Rectifier Using Modified Reference Vector

This paper presents a control strategy using optimized switching sequences which results in capacitor voltage balancing of a three-phase neutral-point-clamped rectifier. In front end rectifiers, magnitude and lag angle of reference current vector (w.r.t supply voltage vector) varies depending upon amount of reactive power compensation and load current. Accordingly, the effectiveness of small and medium vectors (using SVPWM) for same switching state varies in each sector and its regions. This observation along with detailed analysis of current pattern for both the capacitors and their effect on neutral point voltage forms the basis of the proposed approach, which is to modify the reference vector for changing the number of sampling periods within each sector and its regions. The rectifier exhibits excellent performance in terms of other critical parameters like unity input power factor, low input current THD, minimum possible switching losses, reduced-rippled, and well-regulated dc-bus voltage, particularly, the capacitor voltage balancing. The proposed control algorithm is tested through exhaustive simulations and validated through experimental results obtained from a laboratory prototype of the rectifier.

Polarimetric mode of full polarization interferometric radiometer

全极化综合孔径辐射计（Full Polarization Interferometric Radiometer，FPIR）是一套高分辨率、轻量化、低功耗的X波段一维综合孔径微波辐射计.分析了FPIR的极化理论，推导出FPIR的极化可视度函数.为了获取全极化信息，FPIR系统采用两种不同的天线阵列设计方案.对于每种稀疏天线阵列，设计了最优极化切换序列.设计的最优极化序列不仅使灵敏度的损失达到最小，还使得水平极化、垂直极化和交叉极化亮温的灵敏度达到相同水平.

Individual Driver Modeling via Optimal Selection of Steering Primitives

A shared lane keeping assistance system supports the driver in the steering task. In contrast to an autonomous system, the shared system works in parallel with the driver by applying an additional torque on the steering wheel. This means the system and the driver perform the steering task in cooperation. As the driver is still part of the control loop a driver model is required to predict the steering behavior of the actual driver. In this paper we introduce a new lateral steering model which is suited to characterize individual drivers. This model describes, in contrast to other models, the neuromuscular system, limbs and its control for a specific driver by using a set of dynamic primitives (so called movemes). These movemes build a gray-box model for the neuromuscular system. The steering wheel angle is the predicted output of the moveme model. In order to generate a steering angle trajectory suited for the desired maneuver, the steering model switches between these movemes. Therefore, the central component of the driver model is a framework which determines the optimal switching sequence of the movemes. For this task an optimal control strategy is introduced. The approach is validated using a simulation of an ISO-double lane change with movemes which were identified from a set of real driver trajectories. The results show that the steering trajectories of the driver model highly correspond with the recorded driver trajectories.

Vector-Quantized Space-Vector-Based Spread Spectrum Modulation Scheme for Multilevel Inverters Using the Principle of Oversampling ADC

A generalized space-vector-based spread spectrum modulation scheme for multilevel inverters is proposed in this paper. The proposed scheme uses the principle of sigma-delta modulation as applied to analog-to-digital converters (ADCs), based on the view that a multilevel converter could be interpreted as an oversampling ADC. The principle of vector quantization is utilized for quantizing the instantaneous reference voltage space vector in the proposed space-vector-based sigma-delta converter. The switching vectors of the inverter are naturally selected without sector identification, ensuring optimum switching sequence under all conditions including the overmodulation region. As the sigma-delta converter results in a randomly varying switching frequency, the proposed scheme has spread spectrum characteristics. To avoid fractional arithmetic, a 60° coordinate system is used to represent the space vector in this paper. The proposed scheme can be used for any general n -level inverter, and experimental results are presented for four-, five-, and six-level inverters, driving a 2-hp three-phase induction motor in an open-end winding configuration. The experimental results of the proposed scheme are compared with the space-vector pulsewidth modulation (PWM) scheme and random PWM scheme.

Optimal Control of Digital Hydraulic Drives using Mixed-Integer Quadratic Programming

Abstract Control of dynamical systems gets considerably harder with an increasing number of control variables. Especially when the control variables are restricted to integer values, the solution is of combinatorial complexity. An example of such systems are Digital Hydraulic Drives, where several cylinders contribute to the output torque independently. In this work we present an optimal control approach for torque control of Digital Hydraulic Drives using Mixed-Integer Quadratic Programming in a Model Predictive Control framework. The nonlinear behavior and discrete valued inputs resulting from the use of on-off valves, are accommodated in the control model using a Mixed Logical Dynamical System representation. With the presented approach, optimal switching sequences for the electrical valves are computed that produce the desired torque trajectory with fast tracking and minimal ripple, while keeping switching events at a minimum and respecting physical system constraints.

A Three-Phase Delta Switch Rectifier for Use in Modern Aircraft

In the course of the More Electric Aircraft program frequently active three-phase rectifiers in the power range of several kilowatts are required. It is shown that the three-phase -switch rectifier (comprising three -connected bidirectional switches) is well suited for this application. The system is analyzed using space vector calculus and a novel PWM current controller modulation concept is presented, where all three phases are controlled simultaneously; the analysis shows that the proposed concept yields optimal switching sequences. Analytical relationships for calculating the power components average and rms current ratings are derived to facilitate the rectifier design. A laboratory prototype with an output power of 5 kW is built and measurements taken from this prototype confirm the operation of the proposed current controller. Finally, initial EMI-measurements of the system are also presented.

Simple multilevel inverter-based induction motor drive scheme using sigma–delta converter with space-vector quantiser

In this study, sigma–delta (ΣΔ) modulation-based random pulse width modulations (PWM) scheme with vector quantisation for three-level inverter is proposed. In the proposed scheme, the instantaneous reference space vector is mapped to an equivalent two-level inverter and the proposed space-vector-based ΣΔ modulation is applied on this mapped reference space vector. The scheme uses the principle of vector quantisation for quantising the mapped reference space vector in the ΣΔ modulator. The switching signals are generated directly from the amplitude of the three-phase reference signal without using lookup table and complex arithmetic calculations. The resultant vectors of the two-level inverter can be easily translated to the actual switching vectors, and this proposed method of working on the mapped reference space vector makes the proposed scheme suitable for any general n-level inverter. The switching vectors of the inverter are naturally selected ensuring optimum switching sequence under all conditions including the over-modulation region. The proposed scheme is implemented for three-level inverter driving a two-horse power (HP) three-phase induction motor. The performance of the proposed scheme is compared with space-vector PWM scheme and random PWM schemes with different modulation indices and experimental results are presented.

Complete Fast Analytical Solution of the Optimal Odd Single-Phase Multilevel Problem

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, we focus on the computation of optimal switching angles for general multilevel (ML) odd symmetry waveforms. We show that this problem is similar to (but more general than) the optimal pulsewidth modulation (PWM) problem, which is an established method of generating PWM waveforms with low baseband distortion. We introduce a new general modulation strategy for ML inverters, which takes an analytic form and is very fast, with a complexity of only <formula formulatype="inline"><tex Notation="TeX">${\cal O}(n\log^{2}n)$</tex></formula> arithmetic operations, where <formula formulatype="inline"><tex Notation="TeX">$n$</tex></formula> is the number of controlled harmonics. This algorithm is based on a transformation of appropriate trigonometric equations for each controlled harmonics to a polynomial system of equations that is further transformed to a special system of composite sum of powers. The solution of this system is carried out by a modification of the Newton's identity via Padé approximation, formal orthogonal polynomials (FOPs) theory, and properties of symmetric polynomials. Finally, the optimal switching sequence is obtained by computing zeros of two FOP polynomials in one variable or, alternatively, by a special recurrence formula and eigenvalues computation. </para>

A GRAPH THEORY-BASED DISTRIBUTION FEEDER RECONFIGURATION FOR SERVICE RESTORATION

An electric power distribution network (PDN) carries electricity from the transmission system and delivers it to consumers at load centres through a number of power lines (branches). Switching ON and OFF of these power lines makes the power to flow in PDN. The PDN can undergo outages, which may be forced or scheduled outage. During outages, the supply of power is either partially or completely isolated from PDN to the load centres. This deficit of power supply has to be minimum in PDN. To achieve this goal, proper switching of power lines in PDN is required. This paper describes the implementation of two different graph theory-based methodologies for electric PDN. One algorithm is based on Heuristic search method, which obtains the best solution in the viewpoint of minimizing the number of switching operations and another approach applies Dijkstra's algorithm, which finds an optimal switching sequence by considering the reliability of the entire PDN even during varying load conditions. The proposed two methods are tested and evaluated on a IEEE 16 bus distribution system whose results are presented systematically.

Voltage-Profile Estimation and Control of a Distribution Feeder

Monitoring the voltage profile of a distribution feeder can improve the reliability and quality of the distribution power system. However, economic constraints limit widespread deployment of monitoring equipment. This paper presents a method to estimate the voltage profile of a radial distribution feeder with limited number of monitoring points. Using the voltage-profile estimation, load-forecasting information, and bus-impedance matrix, this paper also describes a technique to find an optimal capacitor-bank switching sequence that minimizes the number of switching changes along the feeder for a 24-h period.

Continuous-Time Digital Controller for High-Frequency DC-DC Converters

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper introduces a voltage mode digital controller for low-power high-frequency dc-dc switch-mode power supplies (SMPS) that has fast transient response, approaching physical limitations of a given power stage. In steady state, the controller operates as a conventional pulsewidth modulation regulator and during transients it utilizes a novel fast voltage recovery mechanism, based on real-time processing of the output voltage in digital domain. This continuous-time digital signal processing mechanism is implemented with a very simple processor consisting of a set of asynchronous comparators, delay cells, and combinatorial logic. To eliminate the need for current measurement and calculate the optimal switching sequence of the power stage transistors, the processor performs a capacitor charge balance algorithm, which is based on the detection of the output voltage peak/valley point. The effectiveness of the controller is demonstrated on an experimental 5 W, 5 V to 1.8 V, 400 kHz buck converter. The converter recovers from load transients through a single on-off action of the power switch, virtually reaching the shortest possible time, limited by the values of the power stage filter components only. </para>

Solving The Optimal PWM Problem for Odd Symmetry Waveforms

Optimal pulse width modulation (PWM) problem is an established method of generating PWM waveforms with low baseband distortion. In this paper we focused on computation of optimal switching angles of a PWM waveform for generating general odd symmetric waveforms with applications in control. We introduce an exact and fast algorithm with the complexity of only O(n2) arithmetic operations. This algorithm is based on transformation of appropriate trigonometric equations for each harmonics to a polynomial system of equations that is transferred to a special system of power sums. The solution of this system is carried out by modification of Newton's identity via Padé approximation and orthogonal polynomials theory and property of symmetric polynomials. Finally, the optimal switching sequence is obtained by computing the zeros of two orthogonal polynomials in one variable.

Optimal Control of Continuous-Time Switched Affine Systems

This paper deals with optimal control of switched piecewise affine autonomous systems, where the objective is to minimize a performance index over an infinite time horizon. We assume that the switching sequence has a finite length, and that the decision variables are the switching instants and the sequence of operating modes. We present two different approaches for solving such an optimal control problem. The first approach iterates between a procedure that finds an optimal switching sequence of modes, and a procedure that finds the optimal switching instants. The second approach is inspired by dynamic programming and identifies the regions of the state space where an optimal mode switch should occur, therefore providing a state feedback control law.

Control of underactuated robot manipulators using switching computed torque method: GA based approach

A new concept for controlling of underactuated robot manipulators is presented by using switching computed torque method. One fundamental feature of the present approach is to use the partly stable controllers (PSCs) in order to fulfill the ultimate control objective. Dynamic model of an underactuated robot system is directly analyzed to synthesize partly stable, computed torque controllers without performing rigorous linearizations or any other deformation methods to the original nonlinear system. Here, we use genetic algorithms (GAs) to employ the optimum control action for a given time frame with the available set of elemental controllers, depending on which links or state variables are controlled, i.e. the selection of optimum switching sequence of the control actions. Two underactuated robot manipulators are taken into consideration so as to illustrate the design procedure. Simulation results show the effectiveness of the proposed method. This basic concept has led authors to explore a vast research area on controlling underactuated manipulators.