Space Vector Approach Research Articles

Hybrid Modulation Strategy for Asymmetrical Cascaded Multilevel Converters Under Normal and Fault Conditions

This paper proposes a hybrid modulation strategy for asymmetrical cascaded multilevel converters operating under normal and faulty conditions on power cells. The proposed algorithm explores the advantages of both space vector (SV) and carrier-based modulation approaches. An SV is used for higher voltage cells to properly choose their voltage vectors in a way such as to avoid converter saturation, particularly under fault conditions. A generic algorithm to identify the domains of higher voltage vectors in which a reference lies, without the need for separation lines, is proposed. Then, to simplify the implementation of the algorithm, carrier-based modulation is employed for lower voltage cells, which switch with pulsewidth modulation. This suppresses the need for defining multiple switching sequences for different operational conditions, and it avoids converter saturation as much as possible, particularly under fault conditions on power cells. Simulation and experimental results for normal and faulty operational conditions are given, validating the theoretical analysis and demonstrating the good performance of the proposed hybrid modulation approach.

A Simple Generalized PWM Algorithm for Three Phase Voltage Source Inverter Fed AC Drives

This paper presents a simple Generalized Pulse Width Modulation (GPWM) algorithm for Three Phase Voltage Source Inverter fed AC Drives. The conventional space vector approach requires angle and sector estimation for the calculation of gating times of the inverter and hence increases the complexity of the PWM algorithm. However, the proposed algorithm uses the concept of imaginary switching times to calculate the gating times. These imaginary switching times can be evaluated by using the instantaneous phase voltages only. To generate various PWM algorithms, generalized expression for the offset time is derived. In the derived offset expression, by varying a constant (k0) value from zero to one, various Discontinuous PWM (DPWM) algorithms can be generated along with the Space Vector PWM (SVPWM) algorithm. Thus, the proposed GPWM algorithm gives all the possible modulators for 3-phase, two-level inverters. To validate the proposed PWM algorithms, numerical simulation and experimental studies have been carried out and the results have been presented.

Three-Phase-to-Three-Phase AC/AC DC-Link Five-Leg Converters Based on Three- and Two-Level Legs

The five-leg back-to-back converter shares a leg between the grid and load sides. In the conventional five-leg converter, all legs are of same type, i.e., either two- or three-level legs. This paper presents topologies of five-leg converters based on the combination of two- and three-level legs. The proposed configurations permit one to obtain intermediary characteristics between the five-leg converter with all three-level legs and that with all two-level legs. The choice of the number of two- and three-level legs and how combine them are shown in order to obtain some characteristics of the grid- and load-side converter voltages. The modeling of the system and the pulsewidth-modulation strategy based on carrier-based and space-vector approaches is presented. Analysis of the total harmonic distortion and power switches losses are also addressed to characterize the configurations. Experimental and simulated results show the system feasibility.

Generalized Scalar PWM Algorithm for VSI Fed Induction Motor Drives with Reduced Complexity

This paper presents a simple and novel generalized pulse width modulation (GPWM) algorithm for voltage source inverter fed induction motor drives. The classical space vector approach requires angle and sector information for the calculation of switching times, which increases the complexity of the PWM algorithm. Hence, to reduce the complexity, the proposed GPWM algorithm generates the modulating signals by using the instantaneous phase voltages only. In the proposed algorithm, a unique zero sequence signal is added to the instantaneous phase voltages in order to generate the modulating waveforms. By varying a constant in the zero sequence signal from 0 to 1, various PWM algorithms such as space vector PWM (SVPWM) and discontinuous PWM (DPWM) algorithms are generated. Moreover, a simple overmodulation algorithm is also presented in this paper. Thus, the proposed GPWM algorithm generates all possible PWM algorithms in the entire modulation region. To validate the proposed algorithm, several simulation and experimental results are presented and compared. The results show the best agreement with the published work.

Space vector‐based three‐level discontinuous pulse‐width modulation algorithm

Discontinuous pulse-width modulation (PWM) techniques result in reduced power loss in voltage source inverters. This study presents the space vector approach to the three-level discontinuous PWM technique. The switching sequences for four basic types of discontinuous PWM and the implementation are presented. An improved discontinuous PWM algorithm is presented for low modulation index region. All these algorithms are verified experimentally and the results are presented. The performance of discontinuous PWM algorithms is compared with that of conventional space vector-based PWM algorithms.

Reactive Power Compensation for Unbalanced Fluctuating Loads by Using Two-Dimensional Instantaneous Space Vector Approach

To improve the power quality and efficiency on feeding unbalanced loads, this paper proposes a scheme of instantaneous current compensation that can modify the power factor and balance the three-phase currents simultaneously. The method of instantaneous space vectors can compensate the reactive power effectively, but the problems of unbalanced load currents remains. This paper suggests a method that can mitigate the unbalanced load currents by setting the active power as a constant for each cycle. Field measurement data were analyzed. Simulation results confirmed the feasibility of correcting the power factor and balancing load currents simultaneously using the proposed method.

Space Vector PWM Technique for a Three-to-Five-Phase Matrix Converter

Variable-speed multiphase (more than three phases) drive systems are seen as serious contenders to the existing three-phase drives due to their distinct advantages. Supply to the multiphase drives is invariably given from a voltage source inverter. However, this paper proposes an alternative solution for supplying multiphase drive system using a direct ac-ac converter called a matrix converter. This paper proposes the pulsewidth modulation (PWM) algorithm for the matrix converter topology with three-phase grid input and five-phase variable-voltage and variable-frequency output. The PWM control technique developed and presented in this paper is based on space vector approach. This paper presents the complete space vector model of the three-to-five-phase matrix converter topology. The space vector model yield 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> total switching combinations which reduce to 243 states considering the imposed constraints, out of which 240 are active and 3 are zero vectors. However, for space vector PWM (SVPWM) implementation, only 90 active and 3 zero vectors can be used. The SVPWM algorithm is presented in this paper. The viability of the proposed solution is proved using analytical, simulation, and experimental approaches.

Four-Leg-Based Fault-Tolerant Matrix Converter Schemes Based on Switching Function and Space Vector Methods

A four-leg-based fault-tolerant matrix converter topology is proposed, along with switching function and space vector approaches for modulation schemes, to improve the reliability of matrix converter drives. The four-leg-based fault-tolerant structure utilizes an additional redundant phase module. Based on the reconfigured hardware topology, fault-tolerant modulation strategies with both switching function and space vector approaches are developed to provide the matrix converter drives with continuous and disturbance-free operation. Pulsewidth-modulated algorithms with closed-form expressions, based on a switching function matrix, are presented to synthesize redefined output waveforms with reconfigured converter structures. Furthermore, a space-vector-based scheme using the indirect equivalent circuit with the fictitious dc link is also developed for the fault-tolerant topology after failures. Experimental results show the feasibility of the proposed four-leg-based fault-remedial approach, along with the developed modulation techniques.

Simple and Novel Hybrid Random PWM Algorithm for DTC-Induction Motor Drive for Reduced Acoustical Noise

A simple and novel hybrid random PWM algorithm for direct torque controlled induction motor drive for reduced acoustical noise and harmonic distortion is presented in this paper to reduce the complexity of the classical space vector approach. The proposed algorithm is developed by using the imaginary switching times, which does not require angle and sector information. In order to get the randomization effect, the proposed algorithm uses discontinuous pulsewidth modulation maximum (DPWMMAX) algorithm in conjunction with the space vector pulsewidth modulation (SVPWM) algorithm. The harmonic analysis of the two switching sequences is carried out and by comparing each other in each sampling time interval, the proposed algorithm selects a suitable switching sequence. In the proposed algorithm by changing the factor  , the switching sequences of SVPWM and DPWMMAX algorithms are generated. The proposed PWM algorithm uses 0127 and 721 sequences when  value takes 0.5 and 0 respectively. As the zero state time is varied randomly according to the operating sequence, randomization effect will occur, which results in reduced dominating harmonics and hence gives reduced acoustical noise. To validate the proposed PWM algorithm, the numerical simulation studies have been carried out and results are presented and compared. The simulation results confirm the effectiveness of the proposed algorithm.

Comparative Analysis of Discontinuous and Continuous PWM Techniques in VSI-Fed Five-Phase Induction Motor

This paper reports on flux harmonic distortion factor and current ripple analysis for various discontinuous pulse-width-modulation (PWM) techniques, which are applicable in conjunction with five-phase two-level inverter-fed induction motors. The analysis is based on the application of the complex space vector approach. The results are compared throughout with the corresponding continuous PWM techniques. Different space vector PWM and carrier-based PWM methods are encompassed by the analysis. This paper is supported by extensive simulation results. Verification of theoretical findings is provided through experimental measurements on a five-phase induction motor.

Switching Ripple Characteristics of Space Vector PWM Schemes for Five-Phase Two-Level Voltage Source Inverters—Part 1: Flux Harmonic Distortion Factors

Multiphase variable-speed drives supplied from two-level voltage source inverters (VSIs) are, at present, contenders for numerous industrial applications. Various pulsewidth modulation (PWM) methods for multiphase VSIs, aimed at sinusoidal output voltage generation, have been developed using both carrier-based and space-vector approaches. An increased number of voltage space vectors, available for the synthesis of the output voltage, offer greater flexibility for the PWM scheme development, compared to the three-phase case. This paper presents comprehensive analytical analysis and comparison of switching ripple characteristics of two continuous space vector PWM (SVPWM) methods for a five-phase two-level VSI. Considered SVPWM schemes select a different set of four active space vectors per switching period in order to generate sinusoidal output voltages. This paper also presents the evaluation of the flux harmonic distortion factors of the SVPWM techniques. Correlation with corresponding current ripple and total harmonic distortion is established in Part 2 of this paper, where theoretical considerations are verified by simulations and through experimental investigation on a five-phase VSI-fed induction motor drive.

Analysis of Stability Limitations of a VSC-HVDC Link Using Power-Synchronization Control

In this paper, the stability limitations are analyzed for a voltage-source converter (VSC) based high-voltage direct-current (HVDC) link using power-synchronization control for two feasible operation modes: alternating-voltage control and reactive-power control. As a comparison, the analysis has been done by the phasor approach and the space-vector approach. While the phasor approach is straightforward to apply and gives intuitive analytical results, the space-vector approach reflects more dynamic insights of the system. This is achieved by using a unified dynamic modeling of both the ac system and the VSC by means of a new introduced modeling approach Jacobian transfer matrices. This approach shows that non-minimum-phase phenomena due to competing effects between alternating voltages and currents following phase-angle changes impose a fundamental limitation on the achievable bandwidth of the VSC-HVDC link. At moderate voltage levels, a VSC-HVDC link operating in alternating-voltage control mode is able to achieve higher bandwidth than in reactive-power control mode since the right-half plane (RHP) zero is located further from the origin in the former mode.

Analysis of Output Current Ripple rms in Multiphase Drives Using Space Vector Approach

Multiphase variable-speed drives, supplied from two-level voltage source inverters (VSIs), are nowadays considered for various industrial applications. Although numerous pulsewidth modulation (PWM) schemes for multiphase VSIs, aimed at sinusoidal output voltage generation, have been developed, no detailed analysis of the impact of these modulation schemes on the output current ripple has ever been reported. This paper presents a comprehensive analytical analysis and comparison of the output current ripple caused by the application of three different continuous PWM schemes, using a five-phase VSI as an example. Main properties of sinusoidal PWM, fifth harmonic injection PWM, and space vector PWM are elaborated and analyzed using the harmonic flux concept. Space vector theory is applied in the analysis. As a result, harmonic distortion factors are obtained for each PWM scheme. Theoretical considerations are verified by simulations and experimental investigation using a custom-designed five-phase VSI-fed induction motor drive.

Discussion on Instantaneous $p$–$q$ Strategiesfor Control of Active Filters

Active filters (AFs) compensate harmonic currents demanded by non linear or time variants loads, with the aim to draw sinusoidal currents from the source. Different control strategies for AF have been proposed: among them, p-q theory is the most popular. However, the p-q strategy presents some drawbacks. As already reported in the literature, unexpected harmonic frequencies are generated in the source current as a consequence of such a control strategy. The aim of this paper is to provide, by means of the space vector approach to the p-q theory, analytical expressions that allow to determine the order and the amplitude of the harmonic components in the source current as function of load current or voltage harmonic distortion. By means of these expressions the limits and drawbacks of p-q strategies are quantified and a tool able to quantitatively predict the results of such a control is provided. Simulation results presented in the literature are interpreted according to the proposed expressions; moreover, further simulations are carried out in order to analyze some relevant cases not considered in previous works.

Advanced bus-clamping PWM techniques based on space vector approach

Conventional space vector pulsewidth modulation (CSVPWM) employs conventional switching sequence, which divides the zero vector time equally between the two zero states in every subcycle. Existing bus-clamping PWM (BCPWM) techniques employ clamping sequences, which use only one zero state in a subcycle. This paper deals with a special type of switching sequences, termed here as “double-switching clamping sequences,” which use only one zero state and apply an active vector twice in a subcycle. The present work brings out a class of bus-clamping PWM techniques, which employ such sequences. It is shown analytically as well as experimentally that the proposed BCPWM techniques result in reduced harmonic distortion in the line currents over CSVPWM as well as existing BCPWM techniques at high modulation indices for a given average switching frequency of FSW. At high modulation indices, the dominant harmonic components in the line voltages are around 2 FSW with the proposed BCPWM techniques, while the dominant components are around FSW and 1.5 FSW, respectively, with CSVPWM and existing BCPWM techniques. The proposed techniques also reduce the inverter switching losses at high power factors over CSVPWM and existing BCPWM techniques.

A novel synchronism method for thyristor power converters using the space vector approach

Phase-controlled operation of thyristor power rectifiers requires instantaneous phase information of the fundamental component of the grid voltage in order to generate the proper gating sequence. In many high-power, high-precision applications, such as driving the bending magnets of large particle accelerators, the power converters are fed from a local grid, which produces significant frequency variations and large voltage notches superimposed to the sinusoidal AC voltage due to the commutation interval. These strong disturbances impose some difficulties in measuring the phase of the mains, affecting the precision of the converter. In this paper, we present a new method to generate a fast and precise synchronism signal based on the concept of space vectors. The proposed method allows to track line frequency changes within one cycle of the mains in spite of the large voltage notches produced by the commutation overlap angle. Simulation and experimental results are provided.

Evaluation of Modulation Schemes for Three-Phase to Three-Phase Matrix Converters

This paper presents a method for evaluating different modulation schemes employed with three-phase to three-phase matrix converters. The evaluation method addresses three important modulator characteristics: the output waveform quality, the input waveform quality and the switching losses associated with the modulation schemes. The method is used to evaluate four different modulation strategies, all based on the direct space-vector modulation approach. Further, regarding the switching losses, the paper proposes a new space-vector approach by which the switching losses can be reduced by 15%-35%, depending on the output load angle. This new modulation approach is applicable whenever the output voltage reference is below half the input voltage and the output voltage quality is then superior to that of the conventional space vector modulation scheme. The functionality of the new modulation scheme is validated by both simulations and experimental results and compared to waveforms obtained by using exiting space vector modulation schemes. The output voltage of the proposed scheme turns out to be comparable to the best of the conventional schemes while the input current is more distorted.

Extension of operation of space vector PWM strategies with low switching frequencies using different overmodulation algorithms

This paper investigates the operation of four space vector-based synchronized pulse-width modulation (PWM) strategies in the overmodulation zone using three different overmodulation algorithms. It is shown that the symmetries in the PWM waveforms generated can be preserved in the overmodulation zone also. With any given overmodulation algorithm, the voltage control characteristics (i.e., fundamental voltage versus control variable) are found to vary with PWM strategy, pulse number and type of clamping. The inverse of the appropriate voltage control curve is used during premodulation to maintain the modulator gain constant. The differences in the nature of the voltage control characteristics with the different overmodulation algorithms are brought out. These characteristics are compared and contrasted against those at high switching frequencies. The harmonic distortion in the different cases is evaluated and compared. It is shown that the bus clamping strategies perform better than the conventional strategy with any given overmodulation algorithm employed. These strategies, which exploit the flexibilities in the space vector approach, are useful in high power drives on account of their superior waveform quality at low switching frequencies and high DC bus utilization.

Two novel synchronized bus-clamping PWM strategies based on space vector approach for high power drives

Two synchronized bus-clamping pulse width modulation (PWM) strategies based on the space vector approach are proposed for high-power induction motor drives. The two strategies together can produce PWM waveforms with any odd pulse number, preserving the waveform symmetries. The proposed strategies operate upto the six-step mode, maintaining the proportionality between the reference magnitude and the fundamental voltage generated throughout. These two strategies lead to lesser harmonic distortion as well as lesser peak current over the conventional space vector strategy (CSVS) in the high speed ranges of constant V/F drives. The reduction in the harmonic distortion over CSVS subject to a given maximum switching frequency (F/sub SW(MAX)/) of the inverter is demonstrated theoretically as well as experimentally for F/sub SW(MAX)/=750 Hz and 450 Hz, both with and without overmodulation. The best reduction in the distortion is as high as 30% to 50% in the different cases considered. Further, these two PWM strategies are also useful in reducing the switching frequency of the inverter over sine-triangle PWM and CSVS subject to an upper limit on the harmonic distortion.

Synchronised PWM strategies based on space vector approach. Part 1: Principles of waveform generation

The authors deal with space-vector-based generation of synchronised three-phase PWM waveforms with three-phase, half-wave and quarter-wave symmetries. The necessary and sufficient conditions for synchronisation and the waveform symmetries are brought out in terms of the inverter states. These conditions are applied to the conventional and modified forms of space vector modulation to generate synchronised PWM waveforms with all the symmetries. Further, the necessary conditions governing the numbers of switchings of the different phases in any given sector to maintain the symmetries are identified. These rules are used to develop two new clamping strategies, namely the asymmetric zero-changing strategy and the boundary sampling strategy, which exploit the flexible features of space vector methods like double-switching of a phase and clamping of two phases in a sampling period. Typical waveforms corresponding to the different strategies are presented along with their theoretical and experimental spectra. The performance assessment of these strategies and their application to drives are dealt with in Part 2.