In this paper, angular modulation index (AMI) implemented through a modified space vector modulation for the dual voltage source inverters (VSI) is proposed with the primarily aiming to reduce ...switching losses. The desired voltage across the load is synthesized by applying appropriate phase-angle displacement between space vector references. The proposed approach avoids the use of a dc/dc boost converter (which imposes loss and weight/price penalty to duplicate the dc-link voltage) and results to be particularly suitable for electrical/hybrid vehicle applications. Namely, the application of saving energy to keep driving has been identified as major concern. Hence, this work focuses on the strategy to enhance efficiency. The principles of the proposed controlling method and switching loss, which is reduced at least by 50%, are theoretically evaluated. This paper proposes a pioneering mathematical approach to correctly determine total harmonic distortion (THD) value of the voltage/current for the dual-VSI structure. Furthermore, simulation and experimental results prove that the proposed method insures benefits in terms of common-mode voltage, THD of the voltage, and switching loss reduction. The dual-VSI prototype supplying 1.5-kW induction motor is assembled in the laboratory to experimentally evaluate performance of the proposed method. Also, the simulation results carried out through MATLAB/Simulink environment are given to confirm performance of this easy-to-implement and high-efficient method.
This paper introduces a PWM scheme for both common mode voltage elimination and zero-sequence circulating current suppression. Our approach began with analyzing the relationship among basic vectors, ...common mode voltage elimination, and zero-sequence circulating current suppression to select optimal vectors that support both objectives. Following this, we arranged these selected vectors strategically to achieve simultaneous common mode voltage elimination and zero-sequence circulating current suppression, resulting in six optimal vector sequences for each 60° sector. Considering the redundancy of the proposed vector sequences, each 60° sector is subdivided into four subsectors for optimal performance, each employing its optimal vector sequences. Additionally, we implemented a carrier-based modulation scheme to simplify the implementation of the proposed vector sequences. The vertical and horizontal comparisons with the existing common mode voltage elimination method and other representative zero-sequence circulating current suppression modulation schemes reveal that our method attains both common mode voltage elimination and zero-sequence circulating current suppression, outperforming existing methods. Experimental results further confirm the effectiveness of our proposed approach.
Transformerless grid-connected inverters (TLI) feature high efficiency, low cost, low volume, and weight due to using neither line-frequency transformers nor high-frequency transformers. Therefore, ...TLIs have been extensively investigated in the academic community and popularly installed in distributed photovoltaic grid-connected systems during the past decade. This article analyzes and summarizes the state of the art of TLI techniques, three rules of maintaining constant common-mode voltage (CMV) of TLIs at switching frequency have been concluded from a generic CMV analysis model at the beginning. Second, suppression methods of leakage current (LC) and dc current injection (DCCI), so-called two key challenges for first-generation TLIs, have been classified and discussed in detail, respectively. Finally, future trends and some challenges of TLIs based on wide bandgap devices named second-generation TLIs have been presented in this article.
In photovoltaic (PV) applications, a transformer is often used to provide galvanic isolation and voltage ratio transformations between input and output. However, these conventional iron- and ...copper-based transformers increase the weight/size and cost of the inverter while reducing the efficiency and power density. It is therefore desirable to avoid using transformers in the inverter. However, additional care must be taken to avoid safety hazards such as ground fault currents and leakage currents, e.g., via the parasitic capacitor between the PV panel and ground. Consequently, the grid connected transformerless PV inverters must comply with strict safety standards such as IEEE 1547.1, VDE0126-1-1, EN 50106, IEC61727, and AS/NZS 5033. Various transformerless inverters have been proposed recently to eliminate the leakage current using different techniques such as decoupling the dc from the ac side and/or clamping the common mode (CM) voltage (CMV) during the freewheeling period, or using common ground configurations. The permutations and combinations of various decoupling techniques with integrated voltage buck-boost for maximum power point tracking (MPPT) allow numerous new topologies and configurations which are often confusing and difficult to follow when seeking to select the right topology. Therefore, to present a clear picture on the development of transformerless inverters for the next-generation grid-connected PV systems, this paper aims to comprehensively review and classify various transformerless inverters with detailed analytical comparisons. To reinforce the findings and comparisons as well as to give more insight on the CM characteristics and leakage current, computer simulations of major transformerless inverter topologies have been performed in PLECS software. Moreover, the cost and size are analyzed properly and summarized in a table. Finally, efficiency and thermal analysis are provided with a general summary as well as a technology roadmap.
In this article, a common-mode voltage reduction pulsewidth modulation (CMV-R PWM) for three-level neutral point clamped inverter based on the simplification of the three-level space-vector diagram ...into that of a two-level inverter is studied. By replacing the switching sequence of two-level space-vector PWM with that of CMV-R PWM, the common-mode voltage of the proposed method can be restricted to one-sixth of the dc-link voltage. With the new switching sequences, the neutral-point voltage control by calculating an optimized injected zero-sequence voltage is introduced. Simulation and comparative analysis is given to illustrate the features of the proposed method. The effectiveness and correctness of the proposed method is verified by experiment.
This paper briefly reviews the common-mode voltage (CMV) and neutral point (NP) voltage for neutral point clamped three-level inverter (NPC TLI). Then, the space vector pulsewidth modulation (SVPWM) ...and traditional virtual SVPWM (VSVPWM) are discussed in terms of these two issues, revealing the drawbacks in reducing CMV or eliminating NP voltage oscillation. A novel virtual space vector modulation, named as RCMV_VSVPWM, is proposed in this paper to reduce CMV and eliminate NP voltage oscillation for NPC TLI. By selecting vectors with lower CMVs, a set of novel virtual voltage vectors are generated. The highlight of the method is zero average NP current in one control cycle and lower CMV. Furthermore, the active NP voltage control suitable for RCMV_VSVPWM is presented and evaluated. The corresponding experimental results are given, which are well-consistent with theoretical analysis.
In this paper, we propose model predictive control methods to reduce the common-mode voltage of three-phase voltage source inverters (VSIs). In the reduced common-mode voltage-model predictive ...control (RCMV-MPC) methods proposed in this paper, only nonzero voltage vectors are utilized to reduce the common-mode voltage as well as to control the load currents. In addition, two nonzero voltage vectors are selected from the cost function at every sampling period, instead of using only one optimal vector during one sampling period. The two selected nonzero vectors are distributed in one sampling period in such a way as to minimize the error between the measured load current and the reference. Without utilizing the zero vectors, the common-mode voltage controlled by the proposed RCMV-MPC algorithms can be restricted within ±Vdc/6. Furthermore, application of the two nonzero vectors with optimal time sharing between them can yield satisfactory load current ripple performance without using the zero vectors. Thus, the proposed RCMV-MPC methods can reduce the common-mode voltage as well as control the load currents with fast transient response and satisfactory load current ripple performance compared with the conventional model predictive control method. Simulation and experimental results are included to verify the effectiveness of the proposed RCMV-MPC methods.
The zero-sequence loop inherently exists in the structure of the three-phase open-end winding permanent-magnet synchronous machine (OW-PMSM) system with common dc bus, which provides the circulating ...path for zero-sequence current (ZSC) and consequently causes the torque ripple and extra system loss. Besides, the common-mode voltage (CMV), which can cause many negative effects, such as the bearing current and the failure of motor bearing, is another concern in the driving system. However, the simultaneous suppression of ZSC and the CMV control of the devices is investigated mainly in the application of the induction machine system and the multiphase OW-PMSM system, whereas it is ignored in the application of the three-phase OW-PMSM system, in which the suppression of ZSC is more complex considering the effect of flux linkage harmonic components. On this basis, this article proposes a strategy that can not only suppress the ZSC, but also eliminate the ripple of CMV in the three-phase OW-PMSM system. In the proposed method, the suppression of ZSC is achieved by synchronously adjusting the duration time of each phase within every control cycle based on the reference voltage of zero-sequence control loop, which can simplify the conventional rearrangement-based scheme. Furthermore, the duration time of each phase is distributed into each switch device of the two inverters, with the principle of eliminating the ripple of CMV. Consequently, both the suppression of ZSC and the CMV control can be achieved easily. Furthermore, the influence of dead time on the CMV control is analyzed, indicating that the CMV control is irrelevant with the dead time. Moreover, the effective modulation range of the proposed technique is analyzed. Finally, the experimental validation is conducted on a three-phase OW-PMSM system with common dc bus.
A novel direct torque control (DTC) using rotating sector switching table is proposed for a matrix converter (MC) fed permanent magnet synchronous motor (PMSM) system in order to minimise common-mode ...voltage of the system, exploiting MC rotating vector's advantage of generating zero common-mode voltage. To overcome the difficulty that the angle between adjacent rotating vectors varies according to the phase of input voltage, the rotating vectors are classified into two groups, and each group of vectors have identical rotating direction and fixed angle between adjacent vectors. Rotating sectors of the vector plane are then established, and concise switching table is put forward for the MC-DTC. Experiments are carried out on a 1.6 kW prototype. The results demonstrate considerable common-mode voltage reduction and adequate dynamic performance of the proposed MC-DTC.
Three-level inverter has an outstanding performance and is more advantageous in the switching vector selection than two-level inverter. In particular, the neutral-point voltage unbalance and ...common-mode voltage (CMV) reduction of three-level inverter should be carefully regulated for the appropriate operation, both of which, however, are mutually coupled resulting that the conventional space vector modulation (SVM) scheme cannot deal with them properly. To overcome this limitation, this paper proposes an improved space vector modulation (ISVM) technique to reduce the CMV and neutral-point voltage imbalance simultaneously. The generating mechanism of neutral-point voltage oscillation is derived. Based on the analysis, the proposed ISVM method adopts four voltage vectors (large, medium, small, and zero vectors) with adjusted dwell times to eliminate the ac unbalance of the neutral-point voltage. Considering the occurrence of neutral-point voltage disturbances, the dc neutral-point unbalance voltage is controlled by selecting the P-type or N-type small vector and adjusting the dwell times of small vectors for neutral-point voltage recovery. In addition, a novel switching sequence arrangement method with the minimal number of switches transition in one switching cycles and between switching cycles is proposed to reduce the total switching loss. Theoretical analysis and verification results show that the proposed ISVM scheme can reduce the magnitude of CMV to half of value using the conventional SVM, and an accurate control of ac and dc unbalanced neutral-point voltage can be obtained.
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