Proposed Modulation Algorithm Research Articles

Segment Reduction-Based Space Vector Pulse Width Modulation for a Three-Phase F-Type Multilevel Inverter with Reduced Harmonics and Switching States

An improved segment reduction-based space vector pulse width modulation (SVPWM) for an F-type three-level inverter (FT2LI) is presented in this article. The proposed SVPWM algorithm decreases the additional switching state transition of each triangle with the application of an improved nine- and three-segment reduction switching strategy. The main feature of the segment reduction technique is that it eliminates second-order harmonics in the inverter output side with good total harmonic distortion (THD), low switching losses, and minimum filter requirements when compared with carrier-based PWM (CBPWM) techniques such as multi-carrier sine PWM (MC-SPWM), sixty-degree PWM (60° PWM), and switching frequency optimal PWM (SFO PWM). The proposed modulation algorithm for FT2LI is implemented on the MATLAB/Simulink platform. The performance of the proposed segment reduction-based SVPWM algorithm is tested experimentally on an FT2LI at various amplitude and frequency modulation indices, and the experimental results are verified with the simulation results. Additionally, a comparative analysis carried out to study the relationship between the segment reduction-based SVPWM and CBPWM techniques inferred that the suggested segment reduction-based SVPWM algorithms can optimize high-order harmonic distributions and have a minimum computational burden.

A Hybrid Switching Modulation of Isolated Bidirectional DC-DC Converter for Energy Storage System in DC Microgrid

Isolated bi-direction DC-DC converters are widely used for energy storage systems (ESS) of DC microgrids. Particularly, a current-fed isolated bi-directional DC-DC converter (CF-IBDC) receives much attention due to its merits such as the naturally attenuated current ripple on the battery side. However, high efficiency cannot be obtained at the light and heavy load conditions under the conventional control methods. In this paper, a hybrid switching modulation is proposed to improve the power conversion efficiency of the CF-IBDC under light and heavy load conditions. The duty cycle of the secondary sides and the phase shift angle are independently controlled according to the amount of the transferred power. The control strategy is based on the optimization of zero-voltage switching (ZVS) conditions and the minimization of the circulating current in the power converter. Using the proposed control algorithm, the ZVS capability can be obtained under the entire load condition, and the circulating current can be minimized under the single phase-shift modulation (SPSM). Experimental results with a 1-kW laboratory prototype CF-IBDC validate the effectiveness of the proposed modulation algorithm.

Modulation Technique for a $3 \times 5$ Matrix Converter Achieving a Maximum Input Reactive Power Range Based on Load Information

In this article, a load information-based modulation algorithm is proposed for a three-input five-output matrix converter (3 ×5 MC) to achieve a maximum input reactive power, whose superiority can be illustrated visually through a 2-D modulation graph. This article first derives the modulation matrix and its inherent constraints in the framework of duty-cycle calculation. After that, a constrained optimization problem for maximizing the reactive power is formulated; with the aforementioned constraints mapped to the 2-D modulation graph, the solution can be obtained without a substantial computational burden. The main contribution of this article is the adoption of a 2-D modulation graph to solve the constrained optimization problem for maximizing the input reactive power of a 3 ×5 MC, which presents a new viewpoint by employing load information in modulation constraints. Finally, experiment results are presented for assessing the performance of the proposed modulation algorithm.

Research on an Improved Three-Level SVPWM Modulation Algorithm Based on ID-NPC Topology

The conventional three-level SVPWM (Space Vector Pulse Width Modulation) algorithm is a basic modulation algorithm, which can be performed easily due to clear modulation ideas. Considering different criteria for sectors, however, the basic vector action time is calculated repeatedly, the selection of vector action sequence is cumbersome, and the algorithm execution time is extended as a result of processing by the digital processing chip. In order to better adapt to the PMSM (Permanent Magnet Synchronous Motor) control requirements of the ID-NPC (Improved Diodes Neutral Point Clamped) topology for converter control objects, the sector judgment part, time effect part and vector synthesis part are optimized according to the principles of saving hardware resources and shortening the execution cycle. The vector synthesis optimization algorithm of 2 × amplitude substitution and the vector synthesis algorithm of 1/2 × amplitude substitution are both proposed. Finally, the ID-NPC topology is used to verify the proposed modulation algorithm.

A Multizero-Sequence Component Injection Algorithm for a Five-Level Flying Capacitor Rectifier Under Unbalanced DC-Link Voltages

In this article, the mechanism of current distortions for a five-level flying capacitor rectifier under unbalanced dc-link voltages is analyzed in detail. A multizero-sequence component injection algorithm based on phase-shifted pulsewidth modulation is proposed. In specific, the proposed modulation algorithm divides the fundamental period into clamping and continuous intervals. Considering the inherent topological constraint that the terminal voltage is related to the polarity of the phase current, clamping compensation component is added to three-phase reference signals for clamping one-phase reference signal to zero in order to mitigate current distortions near the zero-crossing points during the clamping interval. Each flying capacitor voltage is regulated by adjusting two switching modulation waves with independent compensation component injection to avoid affecting the average terminal voltage. To improve the quality of dual dc voltages, optimized compensation component is simultaneously injected to three-phase modulation waves for minimizing the ripple component of the average neutral-point current during the continuous interval. In addition, the allowable ranges of both unbalanced voltage degree and unbalanced power degree are theoretically deduced. Finally, simulations and experiments are conducted to verify the effectiveness of the proposed algorithm.

Active Modulation Strategy for Capacitor Voltage Balancing of Three-Level Neutral-Point-Clamped Converters in High-Speed Drives

In this article, the equivalent relationship between the nearest-three-virtual space vector and carrier-based pulsewidth-modulation scheme is established based on space vector coordinate for a three-level neutral-point-clamped (3L-NPC) converter. Moreover, to solve the neutral-point voltage imbalance problem of the studied 3L-NPC converter-fed high-speed drives, an active modulation strategy with the generalized bias-offset injection technique is proposed. Meanwhile, the excessive computational burden is significantly overcome by the fast calculation approach. The effectiveness of the proposed modulation algorithm is validated through both simulation and experimental results obtained from a 45 kW, 32 kr/min aircraft electric starter/generator prototype system.

Improving the harmonic composition of output voltage in multilevel inverters under an optimum mode of amplitude modulation

One of the most important parameters of multilevel inverters is the sinusoidal output voltage . There are many different modulation algorithms, which make it possible to obtain different indicators of the sinusoidal output voltage and different content of the higher harmonics. This paper reports a universal modulation algorithm, which makes it possible to obtain the shape of the output voltage of a multilevel inverter at any number of stages, optimized for the content of the higher harmonics, namely a minimum of the coefficient of harmonic distortions. The proposed algorithm enables obtaining the lowest possible THD for any level voltage. The advantage of the proposed algorithm compared to similar optimization algorithms is ensuring smaller harmonic distortions, as well as its relative simplicity. The reported algorithm is based on the amplitude modulation of the sine signal with a 25 % modulation relative to the highest discreteness. The analytical expressions have been given that make it possible to determine the time (angle) of enabling each level of the output voltage to form a minimum of the root mean square value of higher harmonics. To confirm the optimum analytic point, the MATLAB/Simulink programming environment was employed to design a series of multi-level voltage inverters, which form the five-, seven-, nine-, and eleven-level shapes of output voltage. The current study has shown that the optimum points for all shapes of multilevel voltages are achieved at the same coefficient of amplitude modulation. It has been demonstrated that the proposed modulation algorithm could also be used to control the amplitude and frequency of the output voltage in a multilevel inverter. The paper gives a control characteristic of the output voltage of a multilevel inverter at the pulse amplitude modulation

Studying a voltage stabilization algorithm in the cells of a modular six­level inverter

Multi-level autonomous voltage converters are increasingly used in industry, specifically: in wind and solar energy generation, high-voltage substations, in industrial and traction electric drives. In comparison with two-level inverters, multilevel inverters have a series of significant advantages, specifically, greater output power, greater efficiency value, smaller content of higher harmonics at loading and in a power grid. Reducing the content of higher harmonics in the output current of a multilevel inverter directly decreases additional losses at loading and improves the overall value of efficiency.Our study of a six-level modular inverter has shown that the algorithm of a spatial-vector modulation causes a disbalance in voltage on the capacitors of cells. In this case, voltage in half the cells tends to zero while in the other half of the cells it increases two-fold, which leads to a significant distortion of the output voltage. This paper gives reasons for this instability, as well as presents the improved spatial-vector modulation algorithm of the multilevel converter, which makes it possible to stabilize voltage in cells.We have proposed an algorithm of voltage stabilization on the cells of a modular multilevel inverter. The voltage stabilization is achieved by a hysteresis regulation with an alternating transition of the spatial-vector pulse-width modulation and inverse vector control system under condition that the voltage deviation on the cell is above or below the predefined permissible level.The MATLAB 2017b software was used to conduct simulation of the six-level voltage inverter, which confirmed effectiveness of the proposed modulation algorithm

Research into energy characteristics of single-phase active four-quadrant rectifiers with the improved hysteresis modulation

The traction electric drives for electric rolling stock of alternating current employ the diode and thyristor rectifiers that predetermine a series of shortcomings. These include the significant emission of reactive power and higher harmonics of currents to the contact network, as well as the impossibility of implementing electricity recuperation to the contact network. In this regard, it is promising to use single-phase four-quadrant active rectifiers with a correction of power coefficient. The advantage of these converters is ensuring a power coefficient close to unity, the implementation of the sinusoidal input current, as well as the possibility of implementing electricity recuperation to the power network. In the systems of control over active rectifiers quite common are the control systems with hysteresis modulation. However, hysteresis modulation predetermines the need to implement high and variable frequency for switching power keys, which negatively affects power losses in a transducer. Therefore, a control system with improved hysteresis modulation has been proposed. Due to the improved algorithm for switching power keys the proposed improved hysteresis control system makes it possible to reduce the number of switching power switches. That decreases the dynamic losses of power in an active rectifier, which makes it possible to improve the efficiency of electric rolling stock in general. The simulation modeling conducted in the MATLAB 2017b software has confirmed effectiveness of the proposed modulation algorithm. In addition, during implementation of the proposed commutation algorithm there is an improvement in the harmonic composition of input current. The reduction in the amplitudes of higher harmonics of input current has been confirmed, as well as the improvement in the resultant coefficient of harmonic distortions

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.

Opposite Vector Based Phase Shift Carrier Space Vector Pulse Width Modulation for Extending the Voltage Balance Region in Single-Phase 3LNPC Cascaded Rectifier

A phase shift carrier space vector pulse width modulation scheme based on an opposite vector voltage balancing strategy is proposed to extend the balance region of dc-link capacitor voltages for a single-phase three-level neutral point clamped cascaded rectifier (3LNPC-CR). The internal-module and mutual-module 3LNPC-CR balancing strategies are simultaneously applied to improve the voltage balancing capacity when the dc loads are unbalanced. The voltage balance boundaries of three space vector pulse width modulations using the traditional strategy, the zero vector strategy, and the opposite vector strategy are compared. The analysis results indicate that the proposed modulation algorithm maintained balanced voltages for all modules even if one load of the module was removed. Meanwhile, the equalization of the neutral point voltage for the single-phase 3LNPC-CR was also achieved. Finally, the voltage balancing capacity and rectifier performance of the proposed strategy was verified by simulations and experiments.

Optimal Modulation Algorithm for Hybrid Clamped Three-Level Inverter

The principle of a three phase hybrid clamped three-level inverter was presented. Taking sixty-four switch states into consideration, the operational states of hybrid clamped three-level inverter and different current circuits in different switch states were detailed derived. Optimal modulation algorithm was proposed based on the neutral small vectors by different combination, which can realize the automatic balancing of the neutral-point voltage with few switching cycles and did not need to measure the voltage of the clamped capacitors. The proposed modulation algorithm was also capable of restraining the turn-off over-voltage of the power switching devices effectively. Simulation results were given to verify the feasibility and correctness. Experimental results obtained by DSP-based implementation of the controller on 1 MW prototype show good performance in terms of DC-bus voltages regulation (small neutral point potential function and low DC ripple coefficient) and good sinusoidal current.

An isolated/non-isolated novel multilevel inverter configuration for a dual three-phase symmetrical/asymmetrical star-winding converter

This article is devoted to the development of a novel isolated/non-isolated multilevel inverter configuration for a dual three-phase star-winding converter. The proposed topology fits the (low-voltage/high-current) applications of medium-power, AC tractions and More-Electric Aircraft (MEA) propulsion systems. The power circuit module consists of voltage source inverters (VSIs) with isolated/non-isolated DC supply. Further, each single phase of the VSI is introduced with one bi-directional switching device (MOSFET/IGBT) and two capacitors with linked neutral points. Also, an original modified single-carrier five-level modulation (MSCFM) algorithm is developed in this article that easy to implement in real digital processors. The proposed modulation algorithm generates 5-level output voltages at each terminal of the VSI as equivalent to standard multilevel inverters. The observed results are presented by numerical modeling of the complete AC converter system with (Matlab/PLECS) simulation software. The investigation confirms that the results are in good agreement with the developed theoretical background and the proposed multilevel inverter is applicable to asymmetrical and symmetrical dual three-phase star-winding converter configurations.

Modulation Strategy for Multiphase Neutral-Point-Clamped Converters

This paper presents a novel modulation strategy for n -phase neutral-point-clamped (NPC) converters. The proposed modulation strategy is able to control and completely remove the low-frequency neutral-point (NP) voltage oscillations for any operation point and load types. Even when unbalanced and/or nonlinear loads are considered, the NP voltage remains under total control. Consequently, the strategy is very attractive for n -phase active filters. In addition, it enables the use of low-capacity film capacitors in NPC converters. The proposed modulation takes the carrier-based modulation strategy as a basis. It is formulated following a generalized approach that makes it expandable to n -phase NPC converters. In addition, the NP voltage is controlled directly using a closed-loop algorithm that does not rely on the use of the linear control regulators or the additional compensators used in other modulation algorithms. Therefore, no tuning of parameters is required and it performs optimally for any operating conditions and kind of loads, including unbalanced and nonlinear loads. Although the high-frequency harmonic content of the output voltages may increase, the weighted total harmonic distortion generated by the proposed strategy is similar to that of a standard sinusoidal pulse width modulated strategy. The proposed modulation algorithm has been tested in a four-leg NPC converter prototype performing as a three- and four-phase system and operating with balanced and unbalanced loads.

Generalised switching scheme for a space vector pulse‐width modulation‐basedN‐level inverter with reduced switching frequency and harmonics

This study presents a generalised online switching scheme for a space vector pulse-width modulation (SVPWM)-based multilevel inverter of any voltage level. The proposed SVPWM algorithm implements a generalised three-(similar to five) and seven-segment switching scheme using the three most desired switching states and one suitable redundant state for each triangle. In addition, a novel three-segment and seven-segment switching scheme has been proposed, which eliminates extra switching commutations and hence minimises the switching frequency of the devices while reducing harmonics. The proposed modulation algorithm using the generalised expressions is implemented online. The performance of the proposed novel algorithm for N-level inverter is tested experimentally on a five-level cascaded inverter at various fundamental frequencies and the experimental results are verified with the simulation results.

Performance evaluation of a simple and general space vector pulse‐width modulation‐based M ‐level inverter including over‐modulation operation

This study presents a simple and a generalised space vector pulse-width modulation scheme for a neutral point clamped multi-level inverter as well as cascaded inverter of any level. This modulation algorithm implements the online generation of desired switching states and their sequences through generalised expressions without any predetermined stored data in a memory look-up table. The proposed algorithm also incorporates the concept of reference vector and on-time modification combined during the over-modulation region for any level of inverter. Performance of the proposed modulation algorithm is tested experimentally through a digital signal processor-based controller for a five-level cascaded inverter with very low execution time that does not depend much on the level of inverter. The simulation waveform and the harmonic analysis of the voltage at different modulation index are presented and these are verified with the experimental results.