Output Phase Voltage Research Articles

M3D‐DPWM strategy for three‐phase four‐leg inverter with higher harmonic suppression capability

AbstractThree‐phase four‐leg inverters are widely used in power systems due to their inherent ability to handle unbalanced loads. However, with conventional 3D space vector pulse width modulation (3D‐SVPWM), high harmonics of large amplitude exist in the output voltage around the switching frequency and its integer multiples leading to noise in the load motor and limiting the application range of the inverter system. The passband amplification of conventional sinusoidal filters and their cutoff frequency vary with the load, so it is particularly important to investigate the regulation strategy with harmonic suppression. In this study, an improved 3D discontinuous pulse width modulation (M3D‐DPWM) strategy is proposed based on 3D‐SVPWM. By reducing the conventional 3D‐SVPWM switching segments and changing the vector synthesis sequence of the last half switching cycle, the output phase voltage period is reduced to half of the original one, which achieves the purpose of suppressing the output voltage at the switching frequency and its odd multiple high harmonics without changing the fundamental characteristics and adding additional circuits. In contrast, the conventional 3D‐SVPWM switching frequency is increased to 20 kHz to achieve similar performance. Finally, the effectiveness of the proposed strategy is verified by simulation and experiment.

Experimental Investigation of Modified Level Shift PWM with Capacitor Voltage Balancing on Single Phase Modular Multilevel Converter

Modular Multilevel Converters (MMCs) are a prominent voltage source converter topology that is rapidly gaining popularity in medium/high power/voltage applications, including high-voltage DC transmission systems and electric vehicle systems. However, MMC has the critical issue of unbalanced submodule capacitor voltages and circulating current. The MMC distributes DC-link energy evenly among its submodule capacitors, rather than storing it in a large capacitor like conventional voltage source converters. In MMC, the submodule floating capacitors interface the DC input voltage and AC output voltage. Therefore, capacitor voltages must be balanced. The existing capacitor voltage control struggles to handle many gate pulses at medium and high voltages. An effective control scheme is needed to solve the issues mentioned earlier. This paper presents a performance analysis of a 1-Φ MMC using a modified level shift PWM technique based on Universal Control Modulation Scheme (UCMS) and a sorting-based capacitor voltage balancing algorithm. MATLAB/Simulink software implements the proposed control method for a 1-Φ , seven-level MMC. The outcomes of the simulation demonstration reveal that phase disposition PWM offers less harmonic distortion of output phase voltage than the other level shift PWM techniques, such as phase disposition PWM and alternate phase disposition PWM. The simulation results also demonstrate the effective use of the sorting-based capacitor balancing algorithm to regulate the voltages of the submodule capacitors. Finally, the real-time GUI tool validates the simulation results using an experimental prototype of 1-Φ MMC with the dSPACE MicroLabBox 1202.

Multicarrier PWM techniques for three phase modular multilevel converter application in MRI systems

This research paper presents about the performance analysis of three phase modular multilevel converter with level shifted (phase disposition pulse width modulation) and phase shifted pulse width modulation (PWM) method. This research not only discusses the significance of different modulation procedures in the context of modular multilevel converters but also carefully evaluates each of their unique performance characteristics. This research is based on the fundamental creation of pulses and patterns that can only be acquired by comparing sinusoidal reference signals with triangular carrier signal. Both levels shifted (phase disposition) and phase shifted PWM procedures are used to calculate the phase output voltage of a converter at 2N+1 level. The output waveform is crucially shaped by these modulation techniques, which also ensure effective energy conversion and lower harmonic content. On the basis of the output voltage waveform's quality, the comparative research is conducted and simulated results were presented.

Analysis and design of an efficient three‐phase voltage source inverter with performance optimization

SummaryThe paper designs a novel efficient three‐phase voltage source inverter with performance optimization. When auxiliary circuits connected in parallel with every bridge arm are involved in working process of the designed inverter, main switches will realize zero‐voltage switching in the wide load range, which is beneficial for further decline of the loss of main switches. Furthermore, the optimized duty cycle of the gate drive signal of auxiliary switches is used to restrict circuiting current loss. Besides, when the designed inverter works in a dead zone, the resonance will occur in the auxiliary circuits to cause the output phase voltage to vary from zero or the DC supply voltage to the DC supply voltage or zero as soon as possible, which is beneficial for further decline of the output phase voltage error and the suppression of dead effect. The paper provides relevant analysis on each working status within a switching period along with design requirements. By analyzing test waveforms, it affirms that main switches realize zero‐voltage switching. The efficiency of the designed inverter reaches 98.8% at rating condition. The experiment affirms that the designed inverter has an edge over another two inverters for comparison in performance optimization.

An improved nested 3-phase 5-level MLI design with optimized output voltage and total harmonic distortion

Multilevel Inverters (MLIs) have advanced progressively and demonstrated enormous capacity in power electronics. To provide a 5-level voltage output with a 3-phase full-bridge arrangement and an additional bi-directional switch, a dc voltage input was split by two capacitors. This setup has two issues namely the output voltage limiting the magnitude of the input supply voltage and the voltage disparity between the isolating capacitors. This study suggests an improved nested 3-phase 5-level MLI design with a voltage level and total harmonic distortion (THD) that are both optimized. The suggested arrangement has the features of a lower proportion of passive elements and separated DC sources as it is constructed with a cascade linking of nested two-level cells (NTCs). The suggested unit cell was found to produce a 9-level output voltage (line) by producing a 5-level output voltage (phase) with a peak value that is double the level of the input voltage. The output voltage increasing the capacity of the suggested circuit is its prominent advantage, and the efficacy of the suggested design is 95% and validated by the simulated resultsKeywords: Multilevel Inverters (MLIs), Total harmonic distortion (THD), Voltage level.

Wavelet-based rapid identification of IGBT switch breakdown in voltage source converter

The power electronic converters have drawn a lot of attention from investigators in recent years. Modern power electronics converters rely heavily on insulated gate bipolar transistors (IGBT). Conventional distribution systems may be made more reliable, stable, and secure by using a microgrid (MG). An acceptable, enticing, and useful option for power distribution networks is inverter-based MGs. This article describes a method for identifying the IGBT switch breakdown failure (IBDF) in a 3-phase, 3-level Voltage Source Converter (VSC) linked to the photovoltaic (PV) grid. The VSC's output phase voltage was subjected to an analysis based on the Discrete Wavelet Transform (DWT) methodology. Kurtosis, skewness, and root-mean-square (RMS) values of the wavelet coefficients of the output phase voltage harmonic spectra of the VSC are all factored in during studies. For the detection of IBDF, comparative learning has been used to identify the specific parameter that is most suitable. Moreover, the comparative analysis and unique contribution of this investigation have been demonstrated.

Comparative Study of IGBT and SiC MOSFET Three-Phase Inverter: Impact of Parasitic Capacitance on the Output Voltage Distortion

This study investigates the nonlinearities in three-phase inverters for SiC-based systems and compares their performance to IGBT-based systems. An analytical model of inverter voltage distortion is developed, which accounts not only for dead time (td), switching delay time, switching frequency (fs), and voltage drops of power devices, but also for output parasitic capacitance (Cout). Experimental tests validate the model, which provides a more accurate estimate of the inverter’s output phase voltage distortion. The power device characteristics are obtained from datasheets, while Cout is determined through experimentation. Three-phase inverters with varying switching frequencies, fundamental frequencies, and dead-time values are used in simulations and experiments to determine the influence of nonlinearity on phase voltage deviation and current distortion. The results show that, due to SiC devices’ faster switching time, the phase voltage deviation and phase current distortion are lower in SiC-based inverters than in IGBT-based ones for high-frequency applications, as the dead time can be reduced.

A decentralized control strategy for single‐phase cascaded photovoltaic inverters with MPPT ability

AbstractCascaded inverters can improve efficiency and reduce cost, so it is widely used in photovoltaic (PV) grid connected power generation system. However, aging or partial shielding of PV panels will lead to their different maximum power points (MPP). This paper proposes a decentralized control strategy for grid‐connected cascaded PV inverters without any communication, which is capable of integrating PV inverters of different capacities connected in series into the grid, and enable them to achieve maximum power point tracking (MPPT) independently. Compared with the traditional centralized control method relying on real‐time communication, the proposed scheme has advantages of improved reliability and decreased costs. The overall system stability is analysed, and the stability condition is derived as well. The Hardware‐In‐the‐Loop test results show that all the inverters in the cascaded system have their output frequency and voltage phase synchronized autonomously, and achieve MPPT independently even in the presence of variation of light condition. Thus, the feasibility of the proposed method is verified.

Thermal Energy Harvesting in a Composite Beam Using Piezoelectric, One-Way and Two-Way Shape Memory Alloys

Shape memory alloys (SMA) exhibit the shape memory effect (SME), allowing the alloy which is upon a cyclic thermal loading to return to its original shape after heating beyond the transformation temperature. Two-way SMAs deform during heating and cooling and are suitable for thermal energy harvesting applications. Also, piezoelectric materials (PM) can convert mechanical strain into electrical voltage or current. In this work, a thermal energy harvesting structure is introduced and analyzed. The structure is a composite cantilever beam, comprising two layers, i.e., one-way or two-way SMA and PM. The beam is subjected to different fluctuating temperature ranges, and then we obtain results about energy harvesting performance such as phase transformation strain and output voltage. After developing the nonlinear constitutive equations for one-way and two-way SMEs, the effect of pre-strain and two types of SMAs, i.e., one-way and two-way SMAs are compared with each other under a particular thermal loading. Moreover, the effect of the SMA thickness layer on the output voltage and power has been investigated. Regarding the results, we conclude that for larger pre-strains and maximum temperature of the cycle, greater piezoelectric power is induced. But for a small pre-strain (0.2%), no phase transformation and no output power are observed. Furthermore, it is concluded that in a thermal loading by using two-way SMAs, an electrical potential can be derived without any pre-strain, and increasing the thickness of SMA can rise output power remarkably.

A Three-Phase Dual-Output T-Type Three-Level Converter

A novel three-phase dual-output T-type three-level converter (DO-T-TLC) topology is proposed in this article. The proposed topology has the dc-link and two sets of three-phase ac voltage output terminals. The topology of DO-T-TLC is introduced. Then, the operating principle of multiplexing switches and the available switching states of converter are analyzed, including current path, output phase voltage level, and blocking voltage of different switching states. The phase disposition pulsewidth modulation scheme with dc offsets is discussed in detail, and the key problems of the modulation scheme under both the common frequency and different frequency operation modes, such as voltage level selection, displacement angle constraint, and modulation index range, are studied. For the imbalance of two series capacitors in the dc-link, the mechanism is first revealed, and then a dc-link capacitor voltage balance method to control the average neutral point current is proposed. When DO-T-TLC is used in different operation modes, the ability and effect of this method to balance capacitor voltages are summarized. A low-power three-phase prototype is built, and the experimental results are given to verify the feasibility of the proposed topology and the effectiveness of the modulation scheme to control the voltage balance.

Harmonic Voltage Amplitude Calculation and Fundamental Amplitude Correction Based on Synchronized SVPWM of Two-level VSI under Low Switching Frequency

The switching frequency of two-level VSI is usually limited to a very low level for high-power drives to minimize the switching losses. For the synchronized SVPWM under low switching frequency, there will be a relative deviation of fundamental amplitude between the output voltage and the reference voltage. To solve this problem, in this paper, a method to calculate the amplitude of output phase voltage harmonics under synchronized SVPWM is proposed, and an online fundamental amplitude correction method is proposed based on this calculation result.

Three-Phase Hybrid Converter With Simultaneous DC and AC Outputs

A novel topology of three-phase hybrid converter (TP-HC) which can supply simultaneously both DC and AC loads is presented. This topology is obtained by adding three switches to T-type three-level inverter. Consequently, this converter can achieve one group of DC/DC power transformation and another three-phase three-level AC voltage outputs with adjustable amplitude. The topology and operation modes of the proposed hybrid converter are introduced. Then the working principle and the available switching states of converter are analyzed, including current path, output phase voltage level and blocking voltage of different switching states. The characteristics of three typical hybrid converters are compared. A strategy combining time-sharing modulation and virtual space vector modulation (VSVPWM) is adopted to realize simultaneous DC and AC outputs of the converter. Then the capacitance voltage balance of the DC link is realized. In order to simplify the modulation strategy, a carrier based on pulse width modulation (CBPWM)strategy is proposed. Then, boost ratio of this converter is analyzed in detail. Finally, the feasibility of the proposed topology and the effectiveness of modulation strategy are verified by simulation and experiment.

Development of Converter Output Voltage Phase-Shift Keying Methods as Applied to a Seven-Phase Motor

Phase-shift keying (modulation) of the output voltage of a three-phase converter connected to a symmetrical three-phase winding is one of the stages of the motor vector control technology. This process has well been studied and lies in a practical application field. One of the supposed lines in the development of modern electric traction systems is to construct an electric drive based on a multiphase motor (with the number of phases more than three). In implementing a multiphase motor vector control technology, new opportunities appear, in particular, a new phase-shift keying method. The article considers the voltage phase-shift keying process as applied to a seven-phase winding with the aim to develop seven-phase converter control algorithms implementing the output voltage phase-shift keying, which is possible due to the features of a seven-phase symmetrical motor winding. In the study, the vector analysis techniques and Fourier series expansion methods were used. Experimental studies confirming the obtained theoretical results have been carried out. The scientific novelty of the work lies in that a new converter phase output voltage phase-shift keying method as applied to a seven-phase symmetrical winding and a new converter control algorithm implementing this method have been proposed. The results can be useful in implementing the vector control of a multiphase motor.

Coordinate Compression Strategy of Resistance and Reactance for MHz-Range Inverter System

This article proposes a coordinate impedance compression strategy for high frequency inverter systems. Based on a two parallel inverter structure, the strategy adopts two methodologies: 1) a passive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> network to adjust the current and voltage seen by each inverter module, and 2) an active modulation of the inverter input voltage and output voltage phase to adjust the load current distribution. For the proposed strategy, the resistance and reactance can be compressed coordinately, which can help the inverter to operate in high efficiency load range. The Half-Bridge Class D inverter is taken as an example to be analyzed. A 10-MHz prototype is built and the experimental results verify the correctness and feasibility of the proposed strategy.

Seamless Transition for Parallel Inverters With Novel Self-Adaptive Hybrid Controller and Presynchronization Unit

This article proposes a seamless transition strategy between grid-connected (GC) and stand-alone (SA) states for a microgrid (MG) consisting of parallel inverters. Most inverters in MG operate with novel self-adaptive hybrid controllers, and one inverter near the point of common coupling (PCC) acts as presynchronization (PS) unit. When islanding happens, the inverters based on self-adaptive hybrid control can inherently transfer from grid current control in the GC state to droop control in the SA state, critical islanding detection is needless. When the grid restores, the PS unit can regulate its reactive power to influence the output voltage phase of other inverters in MG and realize the PS of MG and grid. The main advantages are concluded into three points. First, seamless transition of parallel inverters is realized without reconfiguration of control structure, and power-sharing among parallel inverters is achieved without communication lines. Second, unlike droop control, the self-adaptive hybrid control can regulate the grid current of the inverter accurately when the grid fluctuates or is distorted. Third, the PS unit can save the complexity and cost of remote communication for PS. The effectiveness of the proposed seamless transition strategy is verified by simulation and experiment results.

A Novel Pre-Synchronization Control Method Based on Open-Loop Phase Detection for the Maritime VSC-HVDC System

Maritime island grids based on renewable energy are being rapidly developed, which poses a new challenge to the traditional pre-synchronization process of grid connection. Aiming at the problems of impulse current out of limit and long steady-state regulation time, a novel pre-synchronization control method is provided based on open-loop phase detection, which is realized by replacing the frequency detection method of the difference judgment part. The open-loop detection model of voltage phase and amplitude based on the synchronous rotating coordinate system is established first. Then the voltage phase is linearized to control the output frequency and finally reduces the voltage deviation through the compensation of virtual power to achieve the effect of a smooth grid connection. The novel pre-synchronization method has a fast response speed and no regulator effect, which can synchronize the actual values of output voltage amplitude, phase, and frequency. Simulation results verify the excellent performance of the proposed method in island stable operation and grid connection under disturbance.

A Hypothesis Method for T-Type Three-Level Inverters Open-Circuit Fault Diagnosis Based on Output Phase Voltage Model

The open-circuit (OC) faults for T-type three-level inverters often share similar distorted output features, which are usually distinguished by adopting invasive methods. The purpose of this article is to locate the OC fault by rebuilding the established phase voltage model according to the hypothesis method. Based on the vector decomposition principle and voltage-second balancing theory, the output phase voltage model is established considering neutral point voltage unbalance and time-offset injection. The hypothetical phase voltage vector and residual for fault reasoning can be obtained by inputting the suspected OC faults positions to the model. The hierarchical fault diagnosis scheme involves two steps. First, the group-level fault can be located according to voltage residual vector amplitude and angle. Considering the impact of parameter error, dead time, and delay time, an adaptive residual vector amplitude threshold is designed. Next, the device-level fault can be located by building two suspected phase voltage models to approximate the real system. Furthermore, the fault location rules under zero-crossing (ZC) and non-ZC conditions are summarized. Especially, the proposed hypothesis method has correctness verification ability to avoid misdiagnosis. Experimental results show the robustness and effectiveness of the proposed low coupling fault diagnosis method.

Three-phase Active Tracking AC-AC Voltage Regulator based on Buck Converter with an Efficient Hybrid Control Technique

This study proposes a switch-mode three-phase active tracking AC-AC voltage regulator based on the buck converter. The regulator topology incorporates a moderate number of components with less complexity and high efficiency. An efficient hybrid control technique, based on a closed-loop PID controller that is supported with a new designed feedforward controller, is proposed for the regulator control different to the similar studies in the literature. The hybrid control technique augments the response of active tracking of the reference output phase voltages to achieve an improved quality close to sine-wave output phase voltages for either the input AC phase voltages that are ideal pure sine-wave or include various harmonics. The regulator topology has a modular structure for independent control of each output phase. So, the regulator can help to achieve close to sine-wave output phase voltages to supply a balanced/unbalanced wye-connected three-phase load or independent single-phase loads. The presented three-phase regulator and the control technique are tested with simulation and experimental studies. The laboratory set-up of the regulator is designed for 2.2 kW output power, 0-300 Vp input phase voltages (50 Hz), and 0-200 Vp output phase voltages. The results demonstrated that the proposed switch-mode three-phase buck-type active tracking voltage regulator can provide the desired AC phase voltages with less than 5% THD (total harmonic distortion) and low harmonics for different operating conditions.

Line-Frequency-Isolation Flexible AC-Link Converter Based on Direct AC-AC Choppers

Line-Frequency-Isolation Flexible AC-Link Converter based on direct AC-AC choppers (FACL) is a novel AC-AC power conversion device expected to realize voltage compensation and power flow control. Compared with traditional voltage source inverter (VSI)-based devices, FACL has no DC-link capacitors that lead to high equipment failure rate. First, this paper systematically introduces FACL. The power conversion principle of FACL is analyzed, and the output comparison between the unipolar and bipolar FACL is presented. Then a high-performance bipolar FACL is proposed. It eliminates the shortcomings of the existing FACL topologies, such as bidirectional switches, undesirable phase shift, and restricted output range. Additionally, for facilitating the control of FACLs, a variant of the conventional dq reference frame called DQ-ABC synchronous rotating reference frame (DSRRF) is adopted. DSRRF provides a platform for the flexible operation in the form of DC between two three-phase voltages, which is beneficial to FACL control. On the basis of DSRRF, the closed-loop control strategy of FACLs is designed so that the decoupling control and closed-loop control of the output voltage amplitude and phase can be achieved conveniently. Finally, the open-loop and closed-loop experimental tests are carried out based on a 1 kW experimental prototype to verify the theoretical analysis.

Boost Converter Based 3-phase AC-AC Active Tracking Voltage Regulator Controlled by a Robust Hybrid Control Method

In this study, a switch-mode three-phase active tracking AC-AC voltage regulator based on the boost converter is proposed with a moderate number of active and passive elements used in the topology. A robust hybrid control, where a novel designed feedforward controller supports the closed-loop PID controller, is proposed for the control of the regulator apart from similar studies in the literature. Active tracking response of the reference output phase voltages is augmented by the proposed hybrid control method. Thus nearly close to sine-wave output phase voltages can be obtained, whether the input AC phase voltages are ideal pure sine or not. Also, the modular structure of the regulator topology enables independent control for each output phase. Thus, the supply of balanced/unbalanced wye-connected three-phase loads or independent single-phase loads with nearly close to ideal sine wave voltages can be achieved by the modularity of the regulator. Both experimental and simulation test studies are performed for the proposed regulator system. A laboratory set-up for the regulator is designed for 0-200 Vp input phase voltages (50 Hz), and 0-300 Vp output phase voltages, and 1.8 kW output power. The achieved results for both simulation and experimental tests verify the proposed switch-mode boost-type regulator’s ability to provide output phase voltages nearly close to sine wave with total harmonic distortion (THD) values under 5%.