Space Vector Plane Research Articles

A Virtual Vector Based DTC Scheme With Enhanced Resolution for Dual Inverter Fed Five-Phase IM Drives

A virtual voltage vector based direct torque control (DTC) scheme with enhanced resolution for five-phase induction motor (IM) drives with open-end stator windings, fed by two inverters, is proposed in this article. In the proposed scheme, the voltage space vector plane is divided into 20 sectors, by using 40 virtual voltage vectors produced as resultants of the virtual voltage vectors of the individual inverters thereby substantially increasing the sector resolution compared to the 10-sector based conventional five-phase DTC schemes. This DTC scheme incorporates a five-level hysteresis comparator for torque control and the required voltage vectors of different magnitudes are produced by appropriately combining the vectors of the two inverters. The increased sector resolution along with five-level hysteresis torque controller facilitates finer flux and torque control. As the effective common mode voltage in the motor windings is made zero in every switching period, both inverters can be connected to a common dc supply without causing circulation of zero sequence current. The proposed scheme is validated by performing experiment on a five-phase IM drive.

Dead-Time Compensation in Active NPC Three-Level Inverters Considering Current Ripple

Existence of dead time that makes the ultimate terminal voltage being inconsistent with the modulation voltage, is recognized as the main reason for leading output voltage distortion, as well as the corresponding low-frequency current harmonics through the filter inductance in inverters. The distortion becomes particularly severe in high power-density high efficiency applications where the wide bandgap semiconductors are gradually being adopted, providing higher switching frequency with small junction capacitance. In order to explain this phenomenon, the mechanism of three-phase current distortion in the vicinity of phase current zero-crossing point is thoroughly studied by vector analysis in the space-vector (SV) plane. The relevant factors that lead to the degradation of current quality are also summarized. Improved compensation strategy has been proposed to ameliorate the current distortion. Compared with the conventional method, an additional item for current ripple compensation is introduced, the value of which is obtained by the deadbeat predictive method. This simple scheme avoids the compensation error caused by current ripple and significantly reduces the current total harmonic distortion (THD) value under the case of small inductance. Furthermore, neutral-point (NP) potential balance control is also considered in conjunction with the scheme. Simulations and experiments are carried out in an active NP clamped (ANPC) inverter platform, which demonstrates the validity of theoretical analysis and the proposed method.

Clamping Modulation Technique for Balancing Power Losses of Dual Inverter With Isolated DC Bus

This paper proposes a clamping modulation technique to reduce and balance power losses in a dual inverter with an isolated DC bus. To drive an open-end winding permanent magnet synchronous motor (OEW-PMSM), dual inverter consisting of six legs has twelve switching actions, twice as many as a two-level voltage source inverter (VSI) per switching period. However, many switching actions cause power losses in switching devices, reducing the efficiency of the system. In this paper, a four-leg clamping modulation technique is presented to reduce the switching actions by analyzing the relationship between two reference voltage vectors of primary and secondary inverters on a space vector plane. To clamp four of the six legs overall, the switching states are determined by combining active and zero vectors during the switching period. The selected vector combinations differ according to 18 sectors divided by the magnitude and angle of the reference voltage vector. The zero vectors required for 18 sectors are then distributed to balance the power losses in upper and lower switching devices of each leg. This technique is implemented with carrier-based pulse width modulation (PWM) by calculating each three-phase reference voltage from two reference voltage vectors composed of the vector combinations. Balancing of the power loss between the upper and lower switching devices is achieved by adding offset voltages corresponding to the zero vector of each sector. The validity of the proposed technique is verified experimentally.

Performance of Reduced-DC-Source-Based Three-Phase High-Resolution Multilevel Inverter With Optimal Asymmetry

Asymmetrical cascaded bridge multilevel converters use voltage sources of different magnitudes to generate a higher number of levels. However, the availability of sources of different ratings feeding the bridges is a limitation. This article overcomes such a limitation by utilizing the concept of capacitor voltage balancing using the level doubling network (LDN) principle in the space-vector plane. With the use of optimal asymmetry, the presented topology can generate 43 levels at the output line voltage by using only 12 switches per phase. Hence, the most notable attribute of the presented topology is that it does not require isolated auxiliary power supplies to develop such a high-resolution output voltage. LDNs in this topology are self-balanced, and the auxiliary full-bridges require a closed-loop controller to balance their dc bus capacitor voltage. To validate the proposed concept, MATLAB simulations and experimental results are presented in this article.

A Mixed SVPWM Technique for Three-Phase Current Reconstruction With Single DC Negative Rail Current Sensor

The single current sensor operation (SCSO) has attracted widespread attention in the motor drive system because of its ability to reduce cost and volume. However, when the SCSO is used with the conventional space vector puleswidth modulation (SVPWM) technique, the current reconstruction unobservable area in the sector boundary and low modulation area will degrade the accuracy of sampling data. In this article, a mixed SVPWM (MSVPWM) control scheme is proposed to eliminate the unobservable area. With the proposed scheme, the zero vectors (<inline-formula><tex-math notation="LaTeX">${{{\bm V}}_{{\rm {0}}}}$</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">${{{\bm V}}_{{\rm {7}}}}$</tex-math></inline-formula>) are replaced by the complementary effective vectors to achieve the same effect in the sector boundary and low modulation area, and the SVPWM is applied to the remaining space vector plane. These inserted effective vectors make the current observation window time prolonged to ensure that the dc-link current data can be accurately acquired in the entire space vector plane. Hence, the high-quality reconstruction of the phase current can be realized with less impact on the output of current ripples and reconstruction errors. Moreover, the relationship between the rotation speed and the increase in switching losses under different switching frequencies is quantitatively analyzed. The effectiveness of the MSVPWM reconstruction algorithm was verified by experimental results obtained from a permanent-magnet synchronous servo motor.

Hybrid Switching of Four-Voltage-Vector Model-Free Predictive Current Control for Four-Switch Three-Phase Inverter-Fed SynRM Drive Systems

Conventional model-based predictive current control (MBPCC) suffers from common drawbacks of high reliance on system model parameters and the use of a single input voltage vector that result in large pulsating current ripples and prediction errors. In the case of a four-switch three-phase inverter (FSTPI) topology, the implementation of the predictive controller is exacerbated due to limited numbers of candidate voltage vectors. This paper presents an integrated model-free predictive current control with a hybrid switching mechanism to solve the problem. The proposed method introduces the combined switching mechanism of input voltage vectors with fixed and variable modulations by increasing the number of switching voltage vectors. The four basic voltage vectors generated in the four-switch three-phase inverter create twenty-four new synthesized voltage vectors through fourfold linear expansions of the space vector plane. The switching durations of input voltage vectors are determined by calculating their optimal duty ratios. As a result, the proposed method improved the prediction accuracy by increasing the iteration calculations of current differences every sampling period. The proposed method, known as the hybrid switching of four-voltage-vector model-free predictive current control (HS-4VV-MFPCC), is practically tested <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">via</i> simulation and experimental works to evaluate its effectiveness and performance improvement.

Modeling and control strategy analysis of a hydraulic energy-storage wave energy conversion system

Worldwide increasing energy demands promote development of environment-friendly energy sources. As consequences, ocean wave is exploited as an ideal energy source to mitigate greenhouse gas emissions. In this paper, a hydraulic energy-storage wave energy conversion system is constructed, and a mathematical model of main components is built for analysis. Control strategies of generator-side and grid-side are defined for the system, where a Vienna rectifier is applied to converter of generator-side. A two-level space vector plane simplified modulation method for Vienna rectifier is designed for the three-level system and a modulation algorithm is detailed, which has lower complexity compared with traditional three-level space vector pulse width modulation (SVPWM) algorithm. An improved adjusting factor method is proposed to solve the potential imbalance of neutral point caused by uneven charging to the upper and lower capacitors in the three-level structure, which optimizes sector division and inhibits the neutral-point potential offset and fluctuation effectively. Using Matlab/Simulink, the intermittent and continuous power conversion modes of the system under different wave conditions are simulated. The results indicate stable operation of the system, feasible topology scheme, modulation algorithm and control strategy, and effective suppression of AC-side harmonics.

Robust dichotomy solution-based model predictive control for the grid-connected inverters with disturbance observer

This paper proposes a robust dichotomy-based model predictive control (DS-MPC) with a fixed switching frequency for the grid-connected inverter (GCI). The proposed fast dichotomy algorithm can select and deduce the optimal voltage vector dynamically through the space vector plane. Therefore, the proposed DS-MPC strategy could ensure dynamic performance and steady-state performance as well. Also, the current control robustness can be improved through DS-MPC with disturbance observer (DO) based on the extended Kalman filter (EKF). The novelty of this control is that the current control with fast dynamic response can be realized in the weak grid, even if the grid voltages are greatly distorted. Simulation and hardware experiments on the weak grid validate the effectiveness of the proposed DS-MPC with the EKF observer approach.

Novel fuzzy direct torque control based on constructed functional transformed grey model

To reduce the ripple of the magnetic flux and torque of motors and the reduce the hysteresis in motor speed control, an improved grey model predictive fuzzy direct torque control (DTC) method based on function transformation is proposed. First, a function transformation is used to transform the sampled sequences to nonnegative values. This overcomes the disadvantages caused by fluctuant and random sampling of the motor torque and stator flux linkage. Second, an equal dimensional new information model is used to keep the dimensions unchanged, which reduces the time to predict the motor parameters through the model. Moreover, the voltage space vector plane is divided into six sectors, which simplifies the fuzzy control system rules. Simulation results show that the proposed fuzzy direct torque control based on the improved grey model method reduces the influence of hysteresis on the control system, decreases the motor flux chain and torque ripple, improves the response speed of the torque and rotational speed, reduces overshoot, achieves good effects in terms of anti-interference capability and dynamic response, and improves the real-time performance and accuracy of the fuzzy control system.

A Novel SVPWM Scheme for Field-Oriented Vector-Controlled PMSM Drive System Fed by Cascaded H-Bridge Inverter

In the motor drive system fed by multilevel inverter, the problems such as the complexity of reference voltage synthesis, high common mode voltage (CMV), and high switching loss are usually the obstacles to the practical application. In order to reduce the computational complexity and improve the performance of permanent magnet synchronous motor (PMSM), a novel space vector pulsewidth modulation scheme, which is practical and independent of level number is proposed for PMSM vector control. First, the space vector plane is redivided, and the coordinates of the nearest three vectors and their duty cycles can be obtained directly by determining the location of reference vector, which simplifies the calculation and does not need any iterative algorithm. Then, the optimal switching state and switching sequence are selected online so as to ensure the minimum switching loss under the premise of minimum CMV. This article provides an original method and new idea for motor drive system fed by multilevel inverter. Finally, the practicability and validity of the proposed method are verified by simulation and experiment.

A Dual Two-Vector-Based Model Predictive Flux Control With Field-Weakening Operation for OW-PMSM Drives

This article proposes a dual two-vector-based model predictive flux control (DTV-MPFC) strategy for open winding permanent magnet synchronous motor drives with two isolated voltage source inverters (VSIs). In the MPFC strategy, the reference stator flux vector can be compensated to realize field-weakening (FW) operation by controlling the value of the cost function. However, the accuracy of the cost function based FW strategy is limited when the tracking error of the stator flux vector exists. In this article, a DTV-MPFC strategy is proposed to synthesize the reference flux increment vector precisely and the FW operation boundary is kept within the linear modulation region to enhance the FW operation performance. Each inverter applies two vectors during the control period and the switching frequency of the VSIs is minimized with the proposed strategy. When the dc-link voltages of the VSIs are unequal, the number of candidate flux increment vectors and the distribution of the space vector plane are different. A generalized vector selection and duration calculation scheme is proposed to realize the DTV-MPFC strategy in this case. Experimental studies are carried out to verify the validity and effectiveness of the proposed strategy.

Space‐vector‐based hybrid PWM for reduced line current ripple and common mode voltage in paralleled interleaved three‐phase two‐level converter

This paper proposes a hybrid space vector modulation (HBSVM) to reduce line current ripple while maintaining the optimal common mode voltage and zero sequence circulating current peak. The analysis reveals that the vector errors can be reduced by an equivalent basic vector with an adjustable length, which is synthesised by two basic vectors of the same vector angle. Then, a variable k is defined to denote the distribution of the two basic vectors. In addition, due to the implementation of k , a special vectors timing sequence is proposed. With the proposed generalised sequence, this paper investigates the current ripple over the switching period. Furthermore, we derive a map of the optimal distribution factor k opt to minimise the current ripple. Each 30° sector is divided into three subsectors; each applies k opt to minimise the current ripple. With the proposed two variables ( p and q ), a simple flowchart for k opt selection in the whole space vector plane is developed. The proposed HBSVM uses the optimal distribution k opt according to the position of the reference voltage, achieving the minimised line current ripple. The proposed HBSVM achieves the best line current quality while maintaining the optimal ZSCC and CMV peak, as validated by experiments.

Selective finite‐states model predictive control of grid interfaced three‐level neutral point clamped photovoltaic inverter for inherent capacitor voltage balancing

A selective finite states model predictive control is proposed for a grid interfaced three-level neutral point clamped solar photovoltaic inverter. The proposed control approach eliminates the weighting factor selection for dc-link capacitor voltage balancing and reduces the computational burden for real-time implementation. The switching states required for the prediction and objective function optimisation are selected based on the position of reference voltage vector in the space vector plane, inverter current directions and the charge status of the dc-link capacitors. As a result, the selection of optimal switching state is fast, easy to implement and eliminates the selection of weighting factor for capacitor voltage balancing. The feasibility of the proposed control approach is verified through simulation and laboratory-scale experimentation. The results confirm that the proposed method attains the inherent dc-link capacitor voltage balance and also retains the dynamic and steady-state current tracking in comparison with the classical finite control-set model predictive control.

Hybrid exploration state for the simplified finite control set‐model predictive control with a deadbeat solution for reducing the current ripple in permanent magnet synchronous motor

This research tends to provide a novel exploration state for finite control set-model predictive control. The aim of this study is to reduce the line current ripple at a given average switching frequency. The proposed method with hybrid exploration state divides the space vector plane into two regions. Each conventional exploration state is applied to a region, which would result in a lower root mean square current ripple. The above-mentioned procedure is based on the calculation of the stator flux ripple in the stationary reference frame during the sampling time. Consequently, a simple expression based on the magnitude and the phase angle of the reference voltage vector will be obtained, which can be employed as a measure for the current ripple. The superior performance of the proposed method over the conventional exploration state methods is verified by the theoretical results and the experimental tests.

Modified SVPWM Algorithm for 3-level Inverter Fed DTC Induction Motor Drive

In this paper, a modified space vector pulse width modulation (MSVPWM) algorithm is developed for 3-level inverter fed direct torque controlled induction motor drive (DTC-IMD). MSVPWM algorithm simplifies conventional space vector pulse width modulation (CSVPWM) algorithm for multilevel inverter(MLI), whose complexity lies in sector/subsector/sub-subsector identification; which will commensurate with number of levels. In the proposed algorithm sectors are identified as in two level inverter and subsectors/sub-subsectors are identified by shifting the original reference vector to sector 1 (S1). This is valid due to the fact that a three level space vector plane is a composition of six two level space planes, and are symmetrical with reference to six pivot states. Switching state/sequence selection is also very important while dealing with SVPWM strategy for MLI. In the proposed algorithm out of 27 available switching states apt switching state is selected based on sector and subsector number, such that voltage ripple is considerably less. To validate the proposed algorithm, it is tested on a three level neutral point clamped (NPC) inverter fed DTC-IMD. The performance of the MSVPWM algorithm is analyzed by comparing no load stator current ripple of the three level DTC-IMD with two level DTC-IMD. Significant reduction in steady state torque and flux ripple is observed. Hence, reduced acoustic noise is a distinctive facet of the proposed method.

A Voltage Space Vector Diagram Formed by Six Concentric Dodecagons for Induction Motor Drives

A new voltage space vector diagram consisting of six concentric dodecagons is proposed in this paper. The space vector diagram is developed for an open-end induction motor drive fed from two three-level neutral point clamped (NPC) inverters with asymmetric isolated dc voltage sources. As already reported in literature, a dodecagonal space vector diagram is advantageous over a hexagonal one, since the 6n ± 1 (n = odd) harmonics are absent in the phase voltage and the linear modulation range is extended. The present work further improves the existing dodecagonal space vector diagrams by dividing the space vector plane into six concentric dodecagons, while retaining the aforementioned advantages. A high-resolution pulsewidth modulation strategy is developed in this paper, which compared to existing schemes, reduces the harmonic content of the motor phase voltage without resorting to higher switching frequency. A comparative study of output voltage quality produced by the proposed topology and a five-level inverter shows substantial improvement in the present work. At the same time, the present topology does not require any special design of the inverter and uses two popular three-level NPC inverters. Experimental verification on a laboratory prototype indicates the possible application of this concept for high power drives.

A Pulsewidth Modulated Control of Induction Motor Drive Using Multilevel 12-Sided Polygonal Voltage Space Vectors

In this paper, a novel 12-sided polygonal space vector structure is proposed for an induction motor drive. The space vector pattern presented in this paper consists of two 12-sided concentric polygons with the outer polygon having a radius double the inner one. As compared to previously reported 12-sided polygonal space vector structures, this paper subdivides the space vector plane into smaller sized triangles. This helps in reducing the switching frequency of the inverters without deteriorating the output voltage quality. It also reduces the device ratings and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dt</i> stress on the devices to half. At the same time, other benefits obtained from the existing 12-sided space vector structure, such as increased linear modulation range and complete elimination of 5th and 7th order harmonics in the phase voltage, are also retained in this paper. The space vector structure is realized by feeding an open-end induction motor with two conventional three-level neutral point clamped (NPC) inverters with asymmetric isolated DC link voltage sources. The neutral point voltage fluctuations in the three-level NPC inverters are eliminated by utilizing the switching state multiplicities for a space vector point. The pulsewidth modulation timings are calculated using sampled reference waveform amplitudes and are explained in detail in this paper. Experimental verification on a laboratory prototype shows that this configuration may be considered suitable for high power drives.