Carrier-based Modulation Technique Research Articles

Duty-Ratio-Based Direct Torque Control With Enhanced Harmonic Current Suppression for Dual-Three-Phase Permanent Magnet Motor

This article proposes a new duty-ratio-based direct torque control (DR-DTC) with enhanced harmonic current suppression for a dual-three-phase permanent magnet (DTP-PM) motor. First, a new virtual voltage vector construction method based on the carrier-based modulation technique is proposed. Twelve virtual voltage vectors with null average voltage values in two harmonic subspaces are constructed. The sequences of the constructed virtual voltages can be calculated directly in the natural coordinate system. In addition, the whole sequences are standard symmetrical, which can be easily generated by a digital controller. After that, an online harmonic current compensation method is investigated. Additional controllers compensate for the harmonic currents induced by the back electromotive force and nonlinear factors. Since the virtual voltage vectors have null average voltage values in two harmonic subspaces and the online harmonic current compensation method is designed, the proposed DR-DTC can be introduced to the DTP-PM motor with a single neutral point and two neural points. With the proposed strategy, the capability of harmonic current suppression can be significantly improved, and the processes of virtual voltage construction can be simplified. In addition, the advantages of the conventional DR-DTC can be inherited. Finally, experiments are carried out to validate the feasibility of the proposed strategy.

Harmonics Minimization in PUC Type Solar Multilevel Converter with Multicarrier Switching Schemes

This paper presents the power quality investigation of a seven-level three-phase packed U-cell (PUC) converter with multicarrier switching schemes. This system is grid-connected, and each phase has two solar PV arrays of different voltages. Various modulation schemes are available for switching the multilevel converter, and level-shifted multicarrier pulse width modulation is widely used for easy implementation. A new modified carrier-based modulation technique is introduced for solar PV array fed PUC inverter. The main aim is to reduce the harmonic content in the seven-level output voltage. It also increases the magnitude of the fundamental component of the converter voltage. The comparison of the presented technique shows its advantages over other existing modulation schemes. Closed-loop control is implemented with the inclusion of a modified switching scheme for switching the three-phase PUC converter. The proportional resonant controller provides excellent dynamic performance to feed the power into the grid. Modeling and simulation of the system are done in MATLAB/Simulink. Furthermore, obtained simulation results verify the effectivity of the switching scheme towards minimizing total harmonic distortion. The overall system is validated in the real-time simulator for steady-state and dynamic environmental conditions.

Analysis of Harmonic Distortion Reduction through Modular Multi-Level Inverter using Nearest Level Modulation (NLM) Control Strategy

The research paper presents the control strategy to reduce THD (Total Harmonic Distortions) losses by the implementation of the Nearest Level Modulation control technique in a Modular Multilevel Converter. Modular Multilevel Converter is found one of the leading technologies in Power Electronics & Control, its applications are very common in HVDC systems, FACTS (Flexible Alternating-current Transmission system), Variable frequency drives and Electric vehicles as well. The power quality of MMC is better and has lesser THD in comparison to conventional converters like 2-level converters with carrier-based modulation techniques. The MMC has been designed with high scalability and has high voltage and power capacity. Sub-module is an integral part of MMC which is built up as an identical and controllable part of it. This converter is also called a controllable voltage source (VSC). Researchers aim to come up with a detailed review of control methods and necessary operations applied to MMC-based systems for HVDC, particularly focusing to control the total harmonic distortions. Power converters use many modulation techniques, but the existing techniques contribute to a great part in switching losses. MMC up to 49 levels, by implementing the Nearest Level Modulation (NLM) technique, is robust and has less complexity for the systems like MMC-HVDC, and the levels control the total harmonic distortions. In this research paper, the reduction of THD by increasing the voltage levels in MMC is comprehensively evaluated. The simulation results in MATLAB/Simulink are used to examine and confirm the proposed control strategy for stable operation of MMC for HVDC application.

A Comprehensive Modulation Strategy for the Neutral-Point Clamped Wind Power Converter Thermal Management During Low-Voltage Ride Through

The temperature fluctuations in the semiconductor devices within neutral-point clamped (NPC) wind power converter during low-voltage ride-through operation would reduce the lifetime cycle of the converter and jeopardize the reliability of the wind power system. In this article, a thermal management strategy based on carrier-based modulation techniques, i.e., zero-sequence and dipolar injections, is proposed to address this issue. The temperature fluctuations in semiconductor devices among three phases can be reduced and balanced. Besides, the neutral-point voltage balancing can be guaranteed. Simulation and experimental results are presented to verify the feasibility and effectiveness of the proposed technique. Its influences on the converter total power loss and output current harmonics are discussed as well.

Prediction of DC-Link Voltage Switching Ripple in Three-Phase Four-Leg PWM Inverters

This paper presents a thorough prediction of DC-link voltage switching ripples in the three-phase four-leg inverters operating in balanced and unbalanced working conditions. The unbalanced modes examined here employ the highest degree of AC current imbalance while still preserving three-phase operation. This behavior can be found in many grid-connected or standalone grid-forming three-phase converters that supply “heavy” single-phase loads, comprising a recent trend in smart-grid, smart electric vehicle (EV)-charging applications. In this sense, for instance, the smart EV chargers might be employed in conditions when different power is drawn/injected from/to the grid, providing power conditioning services to the latter. The analysis of three-phase four-leg inverters is then extended to single-phase operations typical of home-charging or vehicle-to-home (V2H) applications. Their performances in terms of DC-link voltage switching ripple are demonstrated. Two of the most common carrier-based PWM modulation techniques are employed to drive the three-phase inverter—namely, sinusoidal PWM and centered PWM (carrier-based analogy of the space vector modulation). The derived mathematical expressions of peak-to-peak and RMS values of DC-link voltage switching ripple for balanced and unbalanced conditions are handy for designing the associated DC-link capacitor and estimating the overall efficiency of the converter. Extensive numerical simulations and experimental tests have been performed to validate the presented analytical developments.

Analysis of Cascaded Multilevel Inverter with a Reduced Number of Switches for Reduction of Total Harmonic Distortion

Multilevel inverters (MLI) are aligned with lower harmonics and less commutation losses, which offer high power capacity. MLI is one of the best widespread converters due to its ability to eliminate the harmonic distortion without dropping the converter power output. The cascaded MLI is utilized for a reduced number of switches. In this topology, the switching angles at fundamental frequency are attained by solving the selective harmonic eliminations using sine cosine algorithm. This attains the desired output voltage with the elimination of certain lower order harmonics. In this paper, the analysis of seven-level cascaded MLI is presented with the scheme of carrier-based modulation techniques i.e. Phase-Disposition (PD), Phase-Opposition Disposition (POD) and Alternative Phase-Opposition Disposition (APOD). The Artificial intelligence (AI) is carried out for PD technique. These techniques are capable of defining the required switching angles to eliminate the preferred values of harmonics. The harmonic contents of output voltage in carrier-based modulation are observed with the indices, such as the modulation index with frequency modulation index and amplitude modulation index. The simulation results are obtained for seven-level inverter using MATLAB/SIMULINK. The hardware implementation is carried out using Main Power Management IC TPS65217C Beagle Bone Black Board for seven-level open loop control to justify the achievement of the suggested topology.

Modulation Methods for 3L-NPC Converter Power Loss Management in STATCOM Application

The uneven power loss distribution among the semiconductor devices is one critical issue of the three-level neutral-point clamped converter. Besides, different operating conditions will result in different loss distribution profiles. The case with low power factor and high modulation usage, which is common in the static synchronous compensator (STATCOM) application, has not been paid much attention to in the literature. In this paper, the power loss distribution under this condition is discussed. And a novel carrier-based modulation technique is proposed to balance the power loss distribution and reduce the power loss in the most stressed device. In addition, an active neutral-point (NP) voltage balancing control strategy is also proposed based on the proposed modulation scheme. Simulation and laboratory results are presented to verify the performances of the proposed modulation technique in power loss redistribution and NP voltage control. Its influence on the output current harmonic performance is also evaluated.

Investigation on Extending the DC Bus Utilization of a Single-Source Five-Level Inverter With Single Capacitor-Fed H-Bridge Per Phase

Enhancement of dc bus voltage utilization for a five-level inverter with single dc source and capacitor-fed H-bridge (CHB) units is investigated in this paper. A carrier-based modulation technique is used for boosting the dc bus utilization, which is established by providing detailed mathematical analysis. The five-level inverter used here is realized by cascading a CHB unit to each phase of a three-level neutral point clamped inverter. The increase in dc bus voltage utilization owes to the pole voltage redundancies offered by CHB units. The floating capacitors of H-bridge units are balanced within a quarter fundamental cycle using the switching state redundancies of pole voltage levels. The aforementioned modulation technique allows the inverter to enhance the dc bus utilization from 0.577 $\text{V}_{\text{dc}}$ to 0.63 $\text{V}_{\text{dc}}$ under unity power factor. This enhancement is obtained in the linear modulation range without increasing the dc bus voltage, and thus, the inverter can operate without the presence of low-order harmonics in its phase voltages. The strength of this paper lies in its detailed mathematical analysis for finding out the limiting modulation index and power factor condition in the light of floating capacitor voltage balancing issue. Simulation as well as experimental verification of the modulation scheme is carried out on an induction motor drive under various operating conditions. It is shown that this carrier-based modulation technique is suitable for any single source inverter topology with one CHB unit per phase.

Leakage Current Suppression of Three-Phase Flying Capacitor PV Inverter With New Carrier Modulation and Logic Function

Flying capacitor photovoltaic (PV) inverters have been widely discussed in the literature. However, the relevant leakage current issues have not received much attention. In this paper, the modulation techniques for a transformerless three-phase flying capacitor PV inverter are investigated for the leakage current suppression. First, the theoretical analysis of the system common mode model and leakage current is presented. Second, three kinds of conventional carrier-based modulation techniques are evaluated, and results indicate that they fail to effectively suppress the leakage current. Third, a new carrier modulation and logic function is presented. It is able to maintain the constant common mode voltage, and consequently, the leakage current can be significantly reduced. Finally, the experimental tests are conducted on a transformerless three-phase flying capacitor PV inverter to verify the effectiveness of the proposed method.

Modulation With Sinusoidal Third-Harmonic Injection for Active Split DC-Bus Four-Leg Inverters

Three-phase four-leg inverters are commonly employed to supply unbalanced loads avoiding the use of a transformer. A suitable output filter is necessary to improve the harmonic content of the output voltage and current waveforms. To this aim, different kind of filters, presenting both symmetrical and asymmetrical phase-to-phase and phase-to-neutral behavior, can be used. The paper discusses and analyzes the effects of different carrier-based modulation techniques, based on the independent control of the fourth leg from that of the other phases, with reference to the different filter topologies. The comparison, performed through extensive simulations and experimental tests, have demonstrated that in case of the asymmetrical filter utilization, such as the active split dc-bus (also known as split-link ), the conventional continuous and discontinuous space-vector modulations produce a significant harmonic content in the output voltages even at no-load condition. Moreover, the analysis is extended considering the interaction between the modulation strategy and load characteristics as linear, nonlinear, balanced and unbalanced loads. The problem is discussed in detail and a specific design procedure for the active split dc-bus is presented.

Grid-connected inverter using fused converters

This paper proposes a new modified sinusoidal pulse width modulation (MSPWM) triggering technique for a SEPIC converter. To demonstrate this, a transformer less multistage DC-DC converter interconnected with many renewable energy is considered, which is finally fed to the grid system. The multistage DC-DC converter utilises a fused CUK-SEPIC converter and a SEPIC converter. The fused CUK-SEPIC converter provides the required voltage from a number of renewable sources and the SEPIC converter does the job of DC rectification. A new modified carrier based modulation technique is applied in the SEPIC converter. This is the claim of the paper. The proposed modulation technique avoids the usage of the bulky transformers in real time. Further in the present study, the usage of the multistage DC-DC converter is justified as the voltage produced by all the renewable energy sources put together is less, which necessitates a multistage boost.

Random PWM Technique for Dual-Inverter-Fed Vector-Controlled Induction Motor Drive

From the analysis of harmonic spectrum of conventional PWM techniques, it is observed that a high amount of energy is concentrated around the harmonics of switching frequencies as side bands resulting in acoustic noise, vibration and electromagnetic interference. These effects can be mitigated by spreading the spectrum and reducing the magnitude of harmonics around switching frequencies. This can be achieved by introducing the randomness in control signals. In this paper a simplified and more generalized carrier-based random pulse width modulation (RPWM) technique is presented for asymmetrical dual-inverter-fed vector-controlled induction motor drive. In the proposed RPWM technique a zero sequence signal is added to the commended reference signal to obtain the required modulating signal. The randomness is introduced in generating the zero-sequence signal. To validate the proposed RPWM technique, simulation and experimental studies are carried out and the results are presented.

Space Vecor Modulated Three Level NeutralPoint Clamped Inverter Using A Single ZSource Network

The Neutral Point Clamped (NPC) three-level inverter with Z-source network is a relatively recent converter topology that exhibits both voltage-buck and voltage-boost capability. This concept can be applied to all acto- ac, dc-to-dc, ac-to-dc, and dc-to-ac power conversion whether two-level or multilevel. However, multilevel inverters offer many benefits for higher power applications. Existing publications have shown the control of a Z-source flying capacitor inverter using the carrier-based modulation technique. This paper presents the control of a neutral point clamped three-level inverter with Z-source network using the space vector modulation technique. This gives a number of benefits in both implementation and harmonic performance which enables the operation of the Z-source arrangement to be optimized and implemented digitally without introducing any extra commutations.

Editorial: IEEE Transactions on Power Electronics, February 2015

A single-phase, single-stage current source inverter-based photovoltaic system for grid connection is proposed. The system utilizes transformer-less single-stage conversion for tracking the maximum power point and interfacing the photovoltaic array to the grid. The maximum power point is maintained with a fuzzy logic controller. A proportional-resonant controller is used to control the current injected into the grid. To improve the power quality and system efficiency, a double-tuned parallel resonant circuit is proposed to attenuate the second- and fourth- order harmonics at the inverter dc side. A modified carrierbased modulation technique for the current source inverter is proposed to magnetize the dc-link inductor by shorting one of the bridge converter legs after every active switching cycle. Simulation and practical results validate and confirm the dynamic performance and power quality of the proposed system.

Real Time Implementation of Multi Carrier Based PWM Techniques for Single Phase Nine Level Trinary Source CMLI Using dSPACE

Multi carrier based Pulse Width Modulation techniques have been implemented for switching of prototype of single phase trinary source cascaded multilevel inverter in which 9- level output voltage can be achieved with fewest components. Different species of Carrier Overlapping Pulse Width Modulation (COPWM-A, COPWM-B and COPWM –C) strategies along with trapezoidal reference are used. The gating pulses are generated using dSPACE dS1103 Real Time Interface (RTI) hardware and control desk with MATLAB- SIMULINK environment. It is observed that COPWM-A provides relatively lower THD. Relatively higher RMS output voltage for modulation index ma=0.8 to 1 is obtained with COPWM – B. The performance indices used are Total Harmonic Distortion (THD), Root Mean Square (RMS) output voltage, Crest Factor (CF),Form Factor (FF) and Distortion Factor (DF).

Space-Vector-Modulated Three-Level Inverters With a Single Z-Source Network

The Z-source inverter is a relatively recent converter topology that exhibits both voltage-buck and voltage-boost capability. The Z-source concept can be applied to all dc-to-ac, ac-to-dc, ac-to-ac, and dc-to-dc power conversion whether two-level or multilevel. However, multilevel converters offer many benefits for higher power applications. Previous publications have shown the control of a Z-source neutral point clamped inverter using the carrier-based modulation technique. This paper presents the control of a Z-source neutral point clamped inverter using the space vector modulation technique. This gives a number of benefits, both in terms of implementation and harmonic performance. The adopted approach enables the operation of the Z-source arrangement to be optimized and implemented digitally without introducing any extra commutations. The proposed techniques are demonstrated both in simulation and through experimental results from a prototype converter.

Single-Phase Single-Stage Transformer less Grid-Connected PV System

In this paper, a single-phase, single-stage current source inverter-based photovoltaic system for grid connection is proposed. The system utilizes transformer-less single-stage conversion for tracking the maximum power point and interfacing the photovoltaic arrays to the grid. The maximum power point is maintained with a fuzzy logic controller. A proportional-resonant controller is used to control the current injected into the grid. To improve the power quality and system efficiency, a double-tuned parallel resonant circuit is proposed to attenuate the second- and fourth- order harmonics at the inverter dc side. A modified carrier-based modulation technique for the current source inverter is proposed to magnetize the dc-link inductor by shorting one of the bridge converter legs after every active switching cycle. Simulation and practical results validate and confirm the dynamic performance and power quality of the proposed system.

Performance Evaluation of Real Time Implementation of New Hybrid PWM Strategies for Single Phase Seven Level Asymmetrical Inverter

Carrier Based Pulse Width Modulation (CBPWM) techniques have been used widely for switching of multilevel inverters due to simplicity and reduced computational requirements than the Space Vector Modulation (SVM). New hybrid carrier based PWM strategies have been implemented for a prototype of single phase seven level asymmetrical inverter in this work. Two inverter bridge circuits are used to achieve seven level output voltage. Phase Disposition (PD), Phase Opposition Disposition (POD), Alternate Phase Opposition Disposition (APOD) and Carrier Overlapping (CO) PWM strategies are used with triangular carriers above zero axis and rectified sine carriers below zero axis along with stepped reference. The triggering pulses are generated using the dSPACE dS1103/Real Time Interface (RTI) hardware and front end tool control desk with MATLAB-SIMULINK environment. The performance indices used are Total Harmonic Distortion (THD), Form factor (FF), Distortion Factor (DF), Root Mean Square (RMS) output voltage. It is observed that COPWM provides relatively better DC bus utilization and relatively lesser harmonic distortion for modulation index ma=0.7-1

FPGA Realization of Trapezoidal PWM for Generalized Frequency Converter

Combining concept of cyclo-converter and cyclo-inverter, a generalized frequency converter has been developed where undesirable harmonic components are minimized using nonsinusoidal carrier-based PWM, which is a trapezoidal pulsewidth modulation technique. The study begins by establishing a model of frequency converter to obtain the firing sequence for cyclo-converter and cyclo-inverter mode of operation. The converter is simulated using the well-known software Matlab and simulations results are presented for a single-phase ac supply. It has been found that, for cyclo-inverter operation, the minimum total harmonic distortion in the output voltage is found to be 4.8%, while during cyclo-converter operation it is only 2%. Simulation results are validated with the experimental results. A prototype of frequency converter is developed where a field-programmable gate array is used to generate the PWM trigger signal through Xilinx 9.2i. The results are also compared with other existing carrier-based modulation techniques.

Multicarrier PWM With DC-Link Ripple Feedforward Compensation for Multilevel Inverters

Like most power converter topologies, multilevel inverters are controlled with modulation techniques that are conceptually based on nonlinear waveform synthesis assuming constant dc-link voltages. However, real applications have load and supply dependent dc-links that usually present important low frequency ripple, which is also modulated and transmitted to the load, generating undesirable low frequency voltage and current distortion. This paper introduces a simple but effective dc-link ripple feedforward strategy into traditional carrier-based modulation techniques. The dc-link ripples are measured and used to modify the carriers or the reference directly in the modulation stage. Simulation and experimental results show the accuracy of the proposed method, eliminating low order harmonics in the load current.