Multilevel Space Vector Modulation Research Articles

DTC Based on Five-level SVM with Balancing Strategy of Sensorless DSSM

This paper presents a direct torque control based on multilevel space vector modulation of a double star synchronous machine operating without speed sensor. Each star of the machine is supplied by a five-level diodeclamped inverter. This topology of multilevel inverters represents one of the most interesting solutions to increase voltage and power levels and to achieve high quality voltage waveforms. However, a very important issue in using diode-clamped inverters is the ability to guarantee the stability of the DC-link capacitor voltages. To overcome this problem the multilevel space vector modulation equipped by a balancing strategy is proposed to suppress the unbalance of DC-link capacitor voltages. For achieving high performances control of the multiphase drive, the proposed control method needs accurate information about rotor position and rotor speed. To this end, they are estimated by using Luenberger observer.

A Generic Multi-Level SVM Scheme Based on Two-Level SVM for n-Level Converters

Multi-level converters are widely used in various industrial applications. Among various space vector modulation (SVM) schemes, the multi-level SVM scheme based on two-level space vector pulse width modulation (SVPWM) is recognised as a simplified multi-level SVM scheme, which can reduce the computation complexity. However, this scheme is still complicated when the number of the voltage levels is large. This paper proposes a modified SVM scheme that can further simplify the multi-level SVM scheme based on two-level SVPWM. The proposed SVM scheme can directly determine the two-level hexagon where the reference voltage vector is located by calculating a simple formula. The whole modulation process can be completed by only three steps. Meanwhile, the proposed method is generic for any n-level converter without adding much calculation, which greatly simplifies the modulation process. Experimental results have been provided, which verify the effectiveness and generality of the proposed SVM scheme for two types of multi-level converters.

Virtual Flux Predictive Direct Power Control of Five-level T-type Multi-terminal VSC-HVDC System

This paper proposes a Virtual Flux Predictive Direct Power Control (PDPC) for a five-level T-type multi-terminal Voltage Source Converter High Voltage Direct Current (VSC-HVDC) transmission system. The proposed PDPC scheme is based on the computation of the average voltage vector using a virtual flux predictive control algorithm, which allows the cancellation of active and reactive power tracking errors at each sampling period. The active and reactive power can be estimated based on the virtual flux vector that makes AC line voltage sensors not necessary. A constant converter switching frequency is achieved by employing a multilevel space vector modulation, which ensures the balance of the DC capacitor voltages of the five-level t-type converters as well. Simulation results validate the efficiency of the proposed control law, and they are compared with those given by a traditional direct power control. These results exhibit excellent transient responses during range of operating conditions.

MULTI-LEVEL SVM FOR SIX-PHASE MULTI-LEVEL INVERTERS TO DRIVE DUAL STATOR INDUCTION MACHINE

This article proposes a new six-phase multi-level space vector modulation (SVM) method to control a six-phase induction machine (SPIM) driven by a multi-level separate direct current (DC) source (SDCS) inverter.

Simultaneous DC Current Balance and CMV Reduction for Parallel CSC System With Interleaved Carrier-Based SPWM

Parallel current source converter (CSC) has attracted increasing attention due to the potential advantages to increase the system power capacity, reliability, and output quality. Compared with multilevel space vector modulation (SVM) and selective harmonic elimination, carrier-based sinusoidal pulsewidth modulation (SPWM) enjoys inherent scalability and modularity, which is very easy to be implemented in N-CSC parallel system by interleaving the carriers. The dc current balance and common-mode voltage (CMV) are the main concerns in parallel CSC system and most of the research was focused on SVM. However, dc current balance and CMV reduction methods with interleaved SPWM were not well addressed. In this article, we mainly investigate three different interleaved SPWM methods, namely, bi-tri logic SPWM, six-step direct PWM, and direct duty-ratio PWM (DDPWM). The comparison results show that the proposed interleaved DDPWM can balance the dc current and suppress CMV simultaneously, which can improve the output quality and reduce load-side CMV stress effectively. The validity and effectiveness of the proposed methods are verified on a parallel CSC system with shared dc-link by simulation and experimental results.

Multicarrier-Based PWM Strategies With Complete Voltage Balance Control for NNPC Inverters

Compared with multilevel space vector modulation, level-shifted multicarrier sinusoidal pulsewidth modulation (SPWM) for nested neutral point-clamped (NNPC) inverters requires much less calculations and implementation efforts, but the existing conventional SPWM cannot suppress the severe flying-capacitor (FC) voltage ripples under low output-frequency conditions. In order to solve this problem, a multicarrier-based PWM strategy with complete voltage balance control (VBC) capacity is proposed in this paper. For NNPC inverters operating under low output-frequency conditions, two preprocessing steps, the zero-sequence injection and the modulation-signal rearrangement, are proposed before the comparisons between level-shifted carriers and modulating signals. These preprocessing steps make the average currents flowing through FCs zero, which is beneficial to greatly reduce the FC voltage ripples under low output-frequency conditions. Together with additional VBC, the proposed modulation can assure the FC voltages balanced under the entire output-frequency conditions. Principles and implementation processes of proposed modulation techniques and VBC methodsare elaborated in detail and compared with conventional modulation methods. Both simulation results from a 5-MVA system and experimental results based on a 5-kVA platform are presented to verify the effectiveness.

Research on a Multi-level Space Vector Modulation Strategy in Non-orthogonal Three-dimensional Coordinate Systems

Research on a Multi-level Space Vector Modulation Strategy in Non-orthogonal Three-dimensional Coordinate Systems

Simplified Space Vector Modulation Techniques for Multilevel Inverters

This paper presents simplified techniques for the space vector modulation (SVM) of any n -level multilevel inverter. Three techniques have been presented to simplify the identification of the nearest three vectors to the reference vector. The first two techniques are based on resolving the multilevel inverter space vector diagram into appropriate two-level hexagons. This results in simplification of the multilevel SVM problem into a two-level SVM problem. The third technique is an algorithm-based technique which makes use of a 60°-spaced gh coordinate system to perform the SVM of a multilevel inverter. Switching sequence design for all the three techniques is presented with the aim of minimization of the device switching frequency. Simulation and experimental results have been provided to verify the feasibility of the proposed techniques. Simulation results are provided for up to 21-level cascaded H-bridge (CHB) inverters, while the experimental verification is done on a five-level laboratory prototype. Although only the CHB inverter is considered in this study, the proposed techniques are perfectly general and can be applied to all types of multilevel inverters, and are extendable to any number of levels.

Virtual flux direct power control of the three-level NPC shunt active power filter based on backstepping control

In this paper, a novel control strategy of multilevel shunt active power filter is presented. The idea behind the proposed control scheme is to combine the backstepping control and direct power control with virtual flux concept into one controller able to improve the performance of active power filter. The choice of the multilevel topology leads to a clear enhancement in the compensation of the polluting load harmonics. To take full benefit of this choice, the task of balancing voltages of dc-link capacitors is assigned to the multilevel space vector modulation with balancing ability. For this reasons, the adopted multilevel active power filer is proposed to reduce harmonic currents flowing into the power system and to draw a nearly sinusoidal current with unity power factor. Complete simulation of the resultant active filtering system validates the efficiency of the proposed backstepping control law. Compared to the traditional control, the used of backstepping control allows to exhibit excellent transient response during large load variations.

A Modified Space Vector Modulation Method for Fault-Tolerant Operation of Multilevel Converters

This paper proposes a new fault-tolerant strategy for the purpose of revamping the performance of three-phase multilevel (ML) converters with faulty switches. The proposed fault-tolerant strategy is based on an adaptation of the modified space vector modulation (SVM) technique to the fundamental phase-shift compensation method. The proposed fault-tolerant strategy generates balanced line-to-line voltages with increased voltage levels in the faulty condition. In this paper, first a brief background about cascaded H-bridge (CHB) ML converters and SVM technique is provided. Then the proposed fault-tolerant strategy and the modified SVM technique are presented. Finally, several experimental results are provided to validate operation of the proposed strategy.

An Effective Control Method for Three-Phase Quasi-Z-Source Cascaded Multilevel Inverter Based Grid-Tie Photovoltaic Power System

The quasi-Z-source cascaded multilevel inverter (qZS-CMI) presented many advantages over conventional CMI when applied in photovoltaic (PV) power systems. For example, qZS-CMI provides the balanced dc-link voltage and voltage boost ability, saves one-third modules, etc. However, current research studies only disclosed control of single-phase qZS-CMI-based PV power systems, and there was no literature related to control of three-phase qZS-CMI-based PV power systems. In this paper, for the first time, three-phase qZS-CMI's control is proposed and demonstrated for application to PV power systems. The models of PV-panel-fed qZS H-bridge module and qZS-CMI-based PV power system are built to accurately design control algorithms for each module and the whole system. The proposed control method includes the distributed maximum power point tracking for each module, dc-link peak voltage balance control for all modules, and grid-tie control for the whole system; moreover, a new multilevel space vector modulation method is proposed for the three-phase qZS-CMI. Simulation and experimental results on a test bench with a three-phase seven-level qZS-CMI-based PV power system verify the proposed control and modulation methods.

An Effective Control Method for Quasi-Z-Source Cascade Multilevel Inverter-Based Grid-Tie Single-Phase Photovoltaic Power System

An effective control method, including system-level control and pulsewidth modulation for quasi-Z-source cascade multilevel inverter (qZS-CMI) based grid-tie photovoltaic (PV) power system is proposed. The system-level control achieves the grid-tie current injection, independent maximum power point tracking (MPPT) for separate PV panels, and dc-link voltage balance for all quasi-Z-source H-bridge inverter (qZS-HBI) modules. The complete design process is disclosed. A multilevel space vector modulation (SVM) for the single-phase qZS-CMI is proposed to fulfill the synthetization of the step-like voltage waveforms. Simulation and experiment based on a seven-level prototype are carried out to validate the proposed methods.

A simple multi-level space vector modulation algorithm for five-phase open-end winding drives

Three-phase open-end winding variable speed drives with dual-inverter supply have been extensively investigated for various applications, including series hybrid powertrains and propulsion motors. The topology is simple to realise while offering a higher number of switching states without the need for capacitor balancing algorithms, when compared to standard multi-level converters. There are very few works which consider the use of multi-phase machines in such topologies. One of the reasons for this is that inclusion of a multi-phase machine leads to exponential increase in the number of possible switching states and so the design of a suitable space vector modulator (SVM) represents a considerable challenge. This paper considers a five-phase open-end winding drive and proposes a relatively simple SVM algorithm, based on the already well understood five-phase two-level drive SVM method. The proposed modulation technique has the advantage of being straightforward to implement and, like its two-level counterpart, is able to generate output voltages with minimum low-order harmonic content. The method generates up to seventeen-level output phase voltage and therefore offers superior harmonic performance when compared to the two-level five-phase topology. The developed scheme is verified via simulation including the dynamic performance of the five-phase machine operating under V/f control and experimentally using a passive load.

Evaluation of a Multilevel Cascaded-Type Dynamic Voltage Restorer Employing Discontinuous Space Vector Modulation

In this paper, the application of a cascaded multilevel inverter as a dynamic voltage restorer (DVR) is investigated. Two discontinuous multilevel space vector modulation (SVM) techniques are implemented for DVR control and are shown to reduce inverter switching losses while maintaining virtually the same harmonic performance as the conventional multilevel SVM at a high number of levels. This paper also presents a mathematical relationship for computing the distortion at the point of common coupling (PCC) as a function of the distortion of the DVR. This enables the selection of the number of levels required for a certain application. An extended sag duration support compared to the two-level DVR is another advantage of the DVR with a cascaded multilevel inverter. The common-mode voltage (CMV) at the PCC has been evaluated for the three SVM techniques (the conventional multilevel SVM and the two discontinuous SVM), presenting a lower CMV for the second discontinuous SVM. A design example is presented for an 11-kV 5-MVA DVR multilevel cascaded inverter for up to 17 levels, employing the conventional multilevel SVM and the two discontinuous SVM techniques.

Conventional Space-Vector Modulation Techniques Versus the Single-Phase Modulator for Multilevel Converters

Space-vector modulation (SVM) is a well-suited technique to be applied to multilevel converters and is an important research focus in the last 25 years. Recently, a single-phase multilevel modulator has been introduced, showing its conceptual simplicity and its very low computational cost. In this paper, some of the most conventional multilevel SVM techniques have been chosen to compare their results with those obtained with single-phase multilevel modulators. The obtained results demonstrate that the single-phase multilevel modulators applied to each phase are equivalent with the chosen well-known multilevel SVM techniques. In this way, single-phase multilevel modulators can be applied to a converter with any number of levels and phases, avoiding the use of conceptually and mathematically complex SVM strategies. Analytical calculations and experimental results are shown, validating the proposed concepts.

Mapped hybrid spaced vector modulation for multilevel cascaded-type voltage source inverters

A new multilevel space vector modulation (SVM) technique, termed mapped hybrid SVM, is presented. The SVM technique enables the use of three-level SVM with multilevel inverters without introducing any carrier level modulation or phase shifts. The proposed technique is theoretically analysed for five-, seven- and nine-level inverters and then generalised for the m-level inverter, validated by simulation using Matlab/Simulink and confirmed practically for a five-level, shunt, active power filter.

Systematic analytical-based generalised algorithm for multilevel space vector modulation with a fixed execution time

A generalised algorithm is proposed for multilevel space vector modulation (SVM), which is applicable to any number of levels. The algorithm is based on numerical analysis and gives a fixed execution time when implemented in a digital signal processor, irrespective of the number of levels. In addition, the algorithm procedures eliminate the difficulty in determining the reference vector location, the on-time calculations and switching state selection. A visualisation of the multilevel SVM analysis is detailed, without using any representative technique. The redundant paths can be readily utilised for capacitor balancing. The proposed algorithm caters for over modulation and minimum pulse, and is validated by Matlab/Simulink simulations and practical implementation. A 6 kW three-level active power filter is implemented practically using the proposed algorithm. It is shown that the algorithm is readily codable and time efficient.

Mapped phase-shifted space vector modulation for multi-level voltage-source inverters

A new multi-level space vector modulation (SVM) technique, termed mapped phase-shifted SVM, is proposed. The SVM technique enables the use of two-level SVM with multi-level inverters without introducing any carrier level modulation or phase shifts. The proposed technique is theoretically analysed for three-, five- and seven-level inverters and then generalised for the m-level inverter, validated by simulation using Matlab/Simulink, and confirmed practically for a five-level, shunt, active power filter.

Generalised direct positioning approach for multilevel space vector modulation: theory and DSP–implementation

In three-phase DC/AC multilevel converters, the space vector modulation is the preferred pulse width modulation (PWM) technique. A particular area relative to the space vector modulation (SVM) analysis for multilevel converter is focused and a direct positioning approach for finding the location of the reference vector among available triangles within the SVM diagram is proposed. The developed procedure is then generalised for an n-level converter by proposing a (n−1)2×1 complex matrix that locates the exact place at the end of the reference vector. To verify the proposed method, the whole modulation process was implemented with DSP for three- and four-level converters. To prove the effectiveness of the proposed method in higher-level cases, it was also applied to five- and six-level SVMs. Experimental results validate the direct positioning approach to be an accurate and reliable technique for digital implementation purposes, reducing the total modulation time as well as saving it for complex control techniques needed in industrial applications of SVM.