Redundant Vectors Research Articles

Improved DSVPWM strategy for transformerless three-level grid-connected inverter

Aiming at the leakage current problem in the transformerless three-level grid-connected inverter, an equivalent model of the common-mode circuit is established, and the analysis shows that in addition to the common-mode voltage, the fluctuation of the neutral point voltage is also an important reason for the leakage current. Therefore, an improved DSVPWM strategy is proposed, which introduces a non-basic vector in the same sector as the synthesized reference vector. This not only makes up for the shortcomings of the traditional DSVPWM strategy that cannot balance the neutral point voltage due to the lack of redundant vectors, but also retains the advantage of halving the common-mode voltage amplitude in the traditional strategy, because this introduced vector is the basis vector for other sectors. In order to prevent the total vector action durations from overflowing and reasonably allocate the duration of each vector action, a corresponding neutral point voltage balance algorithm is designed, so that the neutral point voltage is effectively controlled, and the leakage current is greatly attenuated. Simulation results verify the effectiveness of the proposed improved modulation strategy.

Single-Switch Open-Circuit Diagnosis Method Based on Average Voltage Vector for Three-Level T-Type Inverter

Fault-tolerant control strategy plays a significant role in improving the reliability of three-level T-type inverter where fault diagnosis method is the key and a research hotspot. Load power factor variation and modulation index regulation have great effect on conventional load current based diagnosis methods. Therefore, this article proposes a novel voltage vector based method for single-switch open-circuit fault diagnosis in three-level T-type inverter. Average output voltage vector calculated by voltages between dc-link neutral-point and bridge output terminals is taken as the eigenvector in the procedure and failed switch can be located by three diagnosis variables including angle of eigenvector, normalized modulus of eigenvector, and neutral-point potential. These variables will be some certain values under circuit fault, which are defined as eigenvalues. The vector trajectory prediction technology is utilized for threshold setting, by which the diagnosis is suitable for different power factors and different modulation indices. The strategy of redundant vector replacement is applied to realize fault-tolerant operation and verifying the proposed scheme. Simulations and experiments are carried out to illustrate the superiorities of the proposal.

Interrupt-Free Operation of Dual-Motor Four-Wheel Drive Electric Vehicle Under Inverter Failure

This article presents a new open-end winding induction motor (OEWIM)-based dual-motor differential four-wheel drive (D4WD) for the electric vehicle (EV). Constant speed operation through cruise control is achieved using direct torque control (DTC) algorithm. The redundant vectors are used in the switching vector selection of the DTC algorithm to achieve balanced battery currents. Fault-tolerant operation (FTO) of the drive is demonstrated, where the EV will work with full torque even if one of the inverters in rear motor drive or front motor drive or both fail. The dynamic model of the proposed drive is presented. The proposed drive and FTO are verified through simulation as per the FTP-75 driving cycle. An experimental prototype of the proposed drive is developed, and the abovementioned algorithms are verified experimentally as per the FTP-75 and HFET driving cycles. Both the simulation and experimental results are presented, and these results agree with the theoretical observations. Stable operation of EV for the entire test cycle under normal operation, as well as inverter fault conditions, is demonstrated.

DC‐link capacitor voltage balance strategy of independent double three‐phase common bus five‐level NPC/H‐bridge inverter based on finite control set

This study aims at the DC-link capacitor voltage imbalance problem of independent double three-phase common bus five-level neutral point-clamped/H-bridge inverter, which is applied to an electromagnetic launch system under instant high-power and high-current conditions. First, the traditional method of voltage balance strategy based on redundant vectors is described, and the key factors leading to the DC-link capacitor voltage fluctuation is analysed in detail. Second, the objective function is constructed to predict the variation trend of DC-link capacitance voltage difference. Third, an optimised voltage balance strategy is proposed. At first, the optimised strategy calculates the variation trends of the voltage difference for all three-phase switch vector combinations. Then, the results make up a voltage balance finite control set. At last, compare the results in the set to select the vector combination corresponding to the minimum variation for output. Finally, tested by the semi-physical real-time simulation platform, and the proposed optimised voltage balance strategy is verified effective for improving DC-link capacitor voltage imbalance and inhibiting the voltage difference fluctuation.

Binary Outer Product Expansion of Convolutional Kernels

Convolutional neural networks (CNNs) have found great success in many artificial intelligence applications. At the heart of a CNN is the operation of convolution between multi-channel data and learned kernels. It is usually implemented as a floating-point large matrix multiplication, a major bottleneck of computational speed and memory usage. In this paper, we propose a binary outer product expansion (BOPE) method to represent a kernel matrix or tensor as a weighted sum of the outer products between binary vectors of values +1 or −1. This allows for network compression and simplified computation at the same time. Our theoretical analysis shows such a decomposition converges to the original matrix given a sufficient number of binary vectors. We present computational methods to estimate outer product weights using either optimized or random binary base vectors. Significant data compression can be achieved for a highly redundant matrix, since weights and binary vectors require less storage than array elements. In addition, most floating-point multiplication in matrix convolution can be replaced by addition and binary XOR, lessening computation and memory requirements. We propose a compact convolutional layer in which highly redundant convolutional kernels are projected onto binary vectors, and represented as a weighted sum of outer products. It is shown that the number of weights in AlexNet, VGG−19 and ResNet-50 can be reduced 3.45, 6.87 and 2.95 times respectively with less than a 1% loss in the top-1 and top-5 classification accuracy on ImageNet, and MobileNetV2 can be reduced 2.31 times with a 2% loss. Compared to the standard CNN, this compact convolutional network has fewer trainable weights, is better regularized, and is easier to train from fewer training samples. Therefore, it is particularly suited for devices with limited computation, memory, and battery power.

Fault Tolerant Control of Five-Level Inverter Based on Redundancy Space Vector Optimization and Topology Reconfigruation

Compared with two-level and three-level inverters, five-level inverters have more redundant space vectors to implement flexible control strategy. A fault tolerance method for open circuit fault of power tube in Neutral Point Clamped (NPC) five level inverter is proposed. The open circuit fault of inverter is divided into type I and type II in this paper. Redundant space vector optimization and topological reconfiguration fault tolerance strategies are used for type I and type II failures, respectively. The basic vector of the synthetic reference vector $\text{U}_{\mathrm {ref}}$ is reoptimize according to the redundant vector, and get a new control strategy after the decision. This method enables the inverter to achieve fault-tolerant operation without modifying hardware or adding bridge arms. The output performance of the inverter after fault is guaranteed and the cost of fault tolerance is greatly reduced. The feasibility and effectiveness of the proposed fault-tolerant method are verified through experiments.

A Fast Multilevel SVPWM Method Based on the Imaginary Coordinate With Direct Control of Redundant Vectors or Zero Sequence Components

This paper for the first time comprehensively presents a multilevel space vector pulse width modulation (SVPWM) method based on the imaginary coordinate system. This method is probably one of the most efficient methods in fast multilevel SVPWMs. It avoids trigonometric operation, look-up tables and only requires simple logic judgement and arithmetic calculation. A distinct advantage of this method over other coordinate-transformation-based methods is that it does not need to transform from the imaginary coordinate system back to the a-b-c (or α-β) coordinate in order to select the redundant vectors using look-up tables. The redundant vectors or zero-sequence components are directly worked out in the proposed method, e.g., for balancing dc-link capacitor voltages, which avoids identifying the starting vector, vector rotation direction (clockwise or anti-clockwise), vector sequence, etc. as used in conventional methods. This paper entails each step to implement this SVPWM method, which can be replicated for multilevel converters with any number of voltage levels. The presented method has been used and validated by various converters, including a three-level and a five-level neutral-point-clamped converter. The archive value of this paper is that it demonstrates a milestone of fast multilevel SVPWM based on coordinate transformation.

Unified SVPWM Algorithm and Optimization for Single-Phase Three-Level NPC Converters

The high-order harmonics caused by the modulation strategy can deteriorate power quality. The harmonic characteristics of the carrier-based pulsewidth modulation are relatively fixed and difficult to optimize, while space vector pulsewidth modulation (SVPWM) has more flexibility. The unified SVPWM design method for single-phase three-level neutral-point clamped (NPC) converters is fully presented in this article. Based on the proposed unified SVPWM method, two existing traditional vector sequences are designed first, and then several advanced multisegment SVPWM algorithms are proposed. According to the particularity of the three-level NPC topology, two hybrid SVPWM algorithms are proposed to optimize harmonic performance. Moreover, the high-order harmonic characteristics and the number of switching actions are analyzed in detail for all SVPWM algorithm modes. In addition, these SVPWM algorithms are associated and unified by introducing weight coefficients of the redundant vectors. Simulation and experimental results verify the feasibility and effectiveness of the proposed SVPWM algorithms, which show that the proposed methods can optimize high-order harmonic distribution and reduce the line current harmonics.

Data‐driven control for combustion process of circulating fluidised bed boiler

Owing to the advantages of burning low-quality coal (coal slime and coal gangue), furnace desulfurisation, low N O x emission and deep load adjustment, the circulating fluidised bed (CFB) combustion technology becomes one of the few fossil fuel utilisation technologies funded continuously by the Chinese government. However, compared with the pulverised coal boiler, the combustion process of CFB boiler is more complicated because of the larger time delay, significant uncertainty and more coupled variables. In this study, a data-driven proportional–integral-derivative (DD-PID) control strategy is presented for the combustion control of CFB boiler to improve the operating performance under full operating conditions. By analysing the running mechanism of combustion process, an inverse decoupler is introduced to transfer the combustion object to the generalised controlled object, which has relatively independent input–output relationship. After that, a normative procedure of DD-PID, including PID-parameter database establishment, information-vector neighbourhood selection, active PID-parameter determination, database update, and redundant vector deletion, is given. Finally, a series of case study, including numerical tests applied to the proposed combustion model and application test employed on 330 MW CFB simulation platform proves the feasibility of DD-PID control strategy.

Integrated Control of Five-Level Diode-Clamped Rectifiers

This paper presents an approach for dealing with the control of five-level, diode-clamped rectifiers. The control of such converters is challenging, as voltage balancing among capacitors is not a trivial task. Some of the existing approaches that cope with this problem use specific modifications of one of the traditional modulation techniques, such as using redundant vectors in space vector modulation (SVM). The main feature of the proposed technique is that part of the modulation is considered in the system equations and, in this way, the voltage balance can be solved designing a specific controller for this problem. As a result, several levels are used within a switching period. Furthermore, it is shown that the proposed approach hardly affects the control of active and reactive powers and total dc-link voltage in such a way that the well-known direct power control can be applied. As a consequence, the resultant modulation stage is simpler than other techniques based on, e.g., SVM. The effectiveness and good performance of the system under the proposed control approach are validated by both simulation and experimental results.

A 5-Level Inverter Scheme Using Single DC Link With Reduced Number of Floating Capacitors and Switches for Open-End IM Drives

This paper presents a 5-level inverter topology for open-end induction motor drives by using a single dc source. The open stator windings of the drive are supplied with a 3-level flying capacitor inverter from one end and capacitor-fed 2-level inverter from another end. The voltage ratio of the dc link to the capacitor in 2-level inverter is maintained at 4:1 ratio to generate five-level voltage output. The capacitor in 2-level inverter is balanced by the switching redundant vector combinations from both the inverters while the floating capacitors in the 3-level inverter are balanced by using redundant switching states. The proposed topology gives 5-level operation with less number of floating capacitors and power semiconductor switches compared to other existing topologies. Also, the balancing of the capacitors is independent of load power factor and modulation index. Further, the generalization of the proposed dual inverter scheme for any n -level inverter is also included in this paper. The experimental results and required analysis are also presented to validate the inverter scheme.

Model Predictive Virtual-Flux Control of Three-Phase Vienna Rectifier Without Voltage Sensors

In this paper, a finite-control-set model predictive virtual-flux control (FCS-MPVFC) for a three-phase Vienna rectifier is developed and implemented to achieve voltage sensorless control, which is very robust to distorted grid-side voltage operation. Firstly, by investigating the relationship between virtual-fluxes aroused from grid-side voltages and line voltages in $d$ - $q$ frame, the control object is directly associated with virtual-flux tracking error minimization. Secondly, the reference line virtual-flux is calculated based on the controllability of active/reactive power associated with the delay compensation and load angle. Thirdly, to enhance the steady-state performance, switching sequence rather than single switching vector is utilized during one sampling period. Furthermore, a redundant vector pre-selection is adopted to balance the neutral-point voltage. The proposed strategy is compared with the traditional finite-control-set model predictive current control (FCS-MPCC) method. Both simulated and experimental results verify the effectiveness of the proposed control algorithm.

Research on Multidomain Fault Diagnosis of Large Wind Turbines under Complex Environment

Under the complicated environment of large wind turbines, the vibration signal of a wind turbine has the characteristics of coupling and nonlinearity. The traditional feature extraction method for the signal is hard to accurately extract fault information, and there is a serious problem of information redundancy in fault diagnosis. Therefore, this paper proposed a multidomain feature fault diagnosis method based on complex empirical mode decomposition (CEMD) and random forest theory (RF). Firstly, this paper proposes a novel method of complex empirical mode decomposition by using the correlation information between two-dimensional signals and utilizing the idea of ensemble empirical mode decomposition (EEMD) by adding white noise to suppress the problem mode mixing in empirical mode decomposition (EMD). Secondly, the collected vibration signals are decomposed into IMFs by CEMD. Then, calculate 11 time domain characteristic parameters and 13 frequency domain characteristic parameters of the vibration signal, and calculate the energy and energy entropy of each IMF components. Make all the characteristic parameters as the multidomain feature vectors of wind turbines. Finally, the redundant feature vectors are eliminated by the importance of each feature vector which has been calculated, and the feature vectors selected are input to the random forest classifier to achieve the fault diagnosis of large wind turbines. Simulation and experimental results show that this method can effectively extract the fault feature of the signal and achieve the fault diagnosis of wind turbines, which has a higher accuracy of fault diagnosis than the traditional classification methods.

Functional survivability analysis of structurally complex technical systems

Aim. The paper analyzes the functional survivability of structurally complex technical systems. This approach is the evolution of the structural survivability paradigm, when the system/element failure criterion is binary. The paper shows that given a wide variety of probabilistic scenarios of adverse effects (AE) on a system, an invariant model kernel is identified that is responsible for the interpretation of functional redundancy. The aim is to identify the proportion of retained operable states within the acceptable computational time, when the fixed number u of elements is disabled as the result of AE. In this case the analysis of survival law is conducted at the confluence of functional redundancy analysis and probabilistic AE models of arbitrarily wide variety. Methods . A technical system is considered a controllable cybernetic system equipped with specialized survival facilities (SF). System survivability analysis uses logic and probabilistic methods, as well as the results of the combinatorial theory of random allocation. It is assumed that: a) AE are localized and single (one effect affects exactly one element); b) each of the system’s elements has a binary logic (operability – failure) and zero resilience, i.e. destruction after one effect is guaranteed. Subsequently this assumption is generalized for the case of r-fold AE and L-resilient element. Results. The paper reconstructs a number of variants of the destruction law and survivability functions of technical systems. It is identified that those distributions are based on prime and generalized Morgan numbers, as well as Stirling numbers of the second kind that can be recovered using the simplest recurrence formulas. While the assumptions of the mathematical model are generalized for the case of nr-fold AE and L-resilient elements, the generalized Morgan numbers involved in the estimation of the destruction law are identified using the random allocation theory by means of n-fold differentiation of the generating polynomial. In this case it does not appear to be possible to establish a recursive relation between the generalized Morgan numbers. It is shown that under homogeneous assumptions regarding the survivability model (equally resilient system elements, equally probable AEs) in the correlation kernel for the system survivability function, regardless of the destruction law, is the functional redundancy vector F(u, e ), where u is the number of affected elements, e is the system’s limiting efficiency criterion, below which its functional failure is diagnosed, F(u, e ) is the number of system states operable in terms of e under u failures (destructions) of its elements. Conclusions. Point models of survivability are an excellent tool of express analysis of structurally complex systems and tentative estimation of survivability functions. The most simple assumptions of structural survivability can be generalized in cases when the system’s operability logic is not binary, yet is associated with the level of system operation efficiency. In this case we must speak of functional survivability. The PNP computational complexity of the survivability evaluation problem does not allow solving it by means of a simple enumeration of the system states and AE variants. Ways must be found of avoiding simple enumeration, e.g. by using conversion of the system operability function and its decomposition by means of generalized logical and probabilistic methods.

Nearest and Non-Nearest Three Vector Modulations of NPCI Using Two-Level Space Vector Diagram—A Novel Approach

Space vector modulation (SVM) is a widely used method for multilevel inverters. Most of the SVM methods are nearest three vector (N3V) based schemes. Therefore, several researchers have proposed advanced implementation algorithms with reduced complexity for N3V methods. However, topologies like neutral point (NP) clamped inverter (NPCI) require some distinctive methods (called as non-N3V methods) to balance NP voltage for high modulation index and low power factor operations. Currently, the existing non-N3V methods exercise highly complex algorithms for duty ratio calculation and subtriangle identification. This paper presents a new approach, suitable for both N3V and non-N3V methods, with reduced implementation complexity. The proposed algorithm is based on an equivalent two-level space vector diagram and does not require any trigonometry, coordinate transformation, or volt-second balance solution. Unlike other carrier-based methods, it can change the switching sequence as well as the duration of redundant vectors. Moreover, the proposed approach does not require extra steps for implementing hybrid modulation and it can also be extended to multilevel topologies. One N3V, two non-N3V, and hybrid methods are developed using the proposed modulation algorithm, and are compared in detail. Simulation and experimentation on a three-level NPCI verify the validity of the proposed algorithm.

Finite-Set Model-Predictive Control Strategies for a 3L-NPC Inverter Operating With Fixed Switching Frequency

In this paper, finite-set model-predictive control (FS-MPC) methodologies for a grid-connected three-level neutral-point-clamped converter are investigated. The proposed control strategies produce fixed switching frequency, maintaining all the advantages of predictive control such as fast dynamic response, inclusion of nonlinearities and restrictions, and multivariable control using a single control loop. The first of the proposed FS-MPC strategies is based on a multiobjective cost function, designed to regulate both the inverter currents and the balancing of the dc-link capacitor voltages. The second FS-MPC strategy is derived from the first one, and it is based on a cost function that regulates only the grid current, with the balancing of the capacitor voltages being realized by controlling the duty cycles of the redundant vectors. The proposed control systems are experimentally validated using a 5-kW prototype. The experimental results show a good performance for both strategies, in steady-state and transient response, with a total harmonic distortion lower than 2% for the currents supplied to the grid.

A Modulation Technique for Neutral Point Voltage Control of the Three-Level Neutral-Point-Clamped Converter

The neutral-point voltage-balancing control is a critical issue of a neutral-point-clamped converter. The conventional control strategy is to inject the specific zero-sequence voltage to regulate the redundant vector, but it is unacceptable to the three-phase four-wire system. This paper provides a neutral-point voltage-balancing control by the dipolar modulation, and the control freedom of the zero-sequence voltage is flexible. Therefore, the proposed method is suitable for both three-phase three-wire and three-phase four-wire systems. Besides, the proposed method improves the control dynamic in a reactive power system. The proposed neutral-point voltage-balancing control is verified by the mathematical analysis and experimental results. The control dynamic, power loss estimation, and the output current performance are analyzed in this paper.

N-D SVPWM With DC Voltage Balancing and Vector Smooth Transition Algorithm for a Cascaded Multilevel Converter

Direct current voltages unbalance of respective power cells is an inherent and critical problem in a cascaded multilevel converter, which is widely used in the solid-state transformer. In this paper, an n -dimension space vector pulse width modulation is presented to address this issue in a three-level H-bridge-based cascaded multilevel converter. This algorithm utilizes the redundant switching pairs of the inner cell and the redundant vectors of mutual cells to balance capacitors’ and cells’ voltages. Meanwhile, a smooth vector transition strategy is included in this algorithm to avoid the level-skip phenomenon. The calculation processes are analyzed in one-cell, two-cells, and three-cells modes, respectively. It is simple, calculable, and flexible to extend in n -cells mode. Finally, the voltage balancing capacity of the inner cell and mutual cells with smooth level transition are verified by simulations and experiments not only at startup but also with unbalanced loads.

Naive Bayes Bearing Fault Diagnosis Based on Enhanced Independence of Data.

The bearing is the key component of rotating machinery, and its performance directly determines the reliability and safety of the system. Data-based bearing fault diagnosis has become a research hotspot. Naive Bayes (NB), which is based on independent presumption, is widely used in fault diagnosis. However, the bearing data are not completely independent, which reduces the performance of NB algorithms. In order to solve this problem, we propose a NB bearing fault diagnosis method based on enhanced independence of data. The method deals with data vector from two aspects: the attribute feature and the sample dimension. After processing, the classification limitation of NB is reduced by the independence hypothesis. First, we extract the statistical characteristics of the original signal of the bearings effectively. Then, the Decision Tree algorithm is used to select the important features of the time domain signal, and the low correlation features is selected. Next, the Selective Support Vector Machine (SSVM) is used to prune the dimension data and remove redundant vectors. Finally, we use NB to diagnose the fault with the low correlation data. The experimental results show that the independent enhancement of data is effective for bearing fault diagnosis.

Stability Study of Output Voltages of Two-Stage PV System Based Three Levels Inverter

This paper presents an algorithm of regulation of AC voltage of photovoltaic conversion system composed by PV generator-boost converter-three phases three levels inverter for stand-alone application without introduced any system to regulate the fluctuation of the DC bus. The maximum power point tracking based on the “perturb & observe” (P&O) approach as a control strategy of a boost DC-DC converter is applied. In order to get the best AC voltage waveform, the simplified space vector pulse width modulation technique is used in this paper. To maintain the two capacitors voltages of DC bus equal, the redundant vectors of space vector diagram of three levels inverter are used. Without any system to regulate the fluctuation of the DC bus and to get a stable output inverter voltage, authors in this paper propose a proportional regulator of inverter modulation index. A theoretical analysis with a complete simulation of the system with different profiles of irradiance is presented to prove the excellent performance of the proposed technique.