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Detecting and locating the open-circuit (OC) fault of an insulated-gate bipolar transistor (IGBT) rapidly and accurately is very important to improve the security and reliability of the drive system. However, due to the symmetry of the dual-inverter topology, it is difficult to achieve fault detection for open-end winding permanent magnet synchronous motor (PMSM). Thus, this article proposes a fault diagnosis technology for open-end winding PMSM fed by a dual inverter with a common dc bus. In this method, the faulty phase and the faulty case are identified by the average value of the output of the closed-loop controller, which is used to eliminate the differential-mode current in the system. Then, the faulty phase is isolated by removing the gate signals. Finally, the faulty IGBT is located by restructuring the faulty phase and analyzing the current of the faulty phase. In this method, the OC fault can be detected and the faulty IGBT can be located accurately. Experimental results are shown to validate the proposed detection method. [ABSTRACT FROM AUTHOR]

In this paper, a modified single-carrier and multimodulation sine pulse width modulation (MSCMM-SPWM) is proposed to simplify the implementation of the single-phase asymmetrical neutral-point clamped grid-connected inverter (ANPC-GCI) for the PV generation system application. Furthermore, the expressions of the total switching loss and grid current total harmonic distortion (THD) of ANPC-GCI controlled by the proposed MSCMM-SPWM are derived. Then taking the grid current THD meet the grid-connected standard in the entire operational range as the constraint, an efficiency enhancement scheme for ANPC-GCI based on online adjusting the carrier frequency and the obtained THD expression is proposed. The control configuration of ANPC-GCI, including the proposed MSCMM-SPWM and online efficiency enhancement scheme, is designed. The detailed experimental results verify the correctness and feasibility of the proposed MSCMM-SPWM and the efficiency enhancement scheme. [ABSTRACT FROM AUTHOR]

The multi-inverter-based configuration is usually adopted in the renewable energy source grid-connected generation system (RES-GGS) to obtain a wide operational range and independent output power control of the renewable energy sources (RESs). The complicated configuration inevitably reduces the European efficiency. This paper proposes a multi-topology-mode inverter suitable for RES-GGS, which possesses five equivalent topology modes. When the output voltage and power of the RESs increase gradually, the system transforms its actual topology mode from the complicated ones to the simpler ones to increase the European efficiency. Furthermore, a system-level control strategy that can achieve the independent generation power control of each RES and the grid current closed-loop control is proposed. By online transforming the system among the five topology modes, the characteristics of wide operational range, independent output power control of each RES and high European efficiency are all achieved. The detailed experimental results verify the feasibility and advantages of the proposed multi-topology-mode grid-connected inverter. [ABSTRACT FROM AUTHOR]

This paper proposes a modified cascaded neutral-point-clamped grid-connected inverter (MCNPC-GCI) to achieve a wide operational range and high European efficiency in the photovoltaic generation system. Two bidirectional thyristors are added into the standard single-phase cascaded neutral-point-clamped (NPC) inverter to, respectively, connect the positive and negative poles of the two NPC inverters to achieve the transformation between the cascaded NPC inverter and the equivalent single NPC inverter. The losses and grid current total harmonics distortions of the two topology modes are derived to determine their optimal operational ranges and an approach of online smoothly switching the two topology modes is proposed. Detailed experimental results of the proposed MCNPC-GCI are shown to verify its accuracy and feasibility. [ABSTRACT FROM AUTHOR]

This paper proposes a modified cascaded multilevel grid-connected inverter (MCM-GCI) suitable for photovoltaic grid-connected generation system, which considers wide operation range, low grid current total harmonics distortion (THD), and high European efficiency. In the proposed topology, a bidirectional power switch is added to the standard single-phase cascaded multilevel inverter (CMI) to implement the transformation between CMI mode and H-bridge inverter (HBI) mode. An online topology transformation approach of the MCM-GCI is proposed to guarantee the topology modes transformed safely and smoothly. The proposed MCM-GCI operates in CMI mode when the PV arrays’ output voltage and power are low, and transforms into HBI mode when the PV arrays’ output voltage and power are high. Experimental results of five-level MCM-GCI are represented to validate the feasibility of the proposed topology and it is also compared with other three classic grid-connected inverters to highlight its advantages. Furthermore, more structures based on hybrid CMI, which possess the topology transformation ability, are shown to further improve the generation range and obtain a higher efficiency of the system. [ABSTRACT FROM PUBLISHER]

In this paper, the generation reason and the improved elimination scheme of the current zero-crossing distortion (ZCD) of single-phase grid-connected inverter controlled by unipolar hysteresis current control containing band are investigated in detail. A current ZCD elimination scheme by exchanging the control signal of low-frequency leg of inverter ahead of the zero-crossing points of grid voltage is proposed. The effect of the variation of the amplitude and frequency of tied grid and the filter inductor on the optimal leading exchanging phase angle (LEPA) is analyzed. A single-phase hybrid filter-based enhanced phase-locked loop is proposed to estimate accurately the information of the grid, even under nonideal input conditions. Then, an online filter inductor estimation scheme is proposed to obtain the accurate actual inductor value. The former estimated parameters are used to calculate the exact optimal LEPA online to improve the performance of the current ZCD elimination scheme. Comprehensive experimental results are represented to verify the accuracy and feasibility of the theoretical analysis and the proposed improvement. [ABSTRACT FROM PUBLISHER]

In photovoltaic (PV) grid-connected generation system, the key focus is how to expand the generation range of the PV array and enhance the total efficiency of the system. This paper originally derived expressions of the total loss and grid current total harmonics distortions of cascaded inverter and H-bridge inverter under the conditions of variable output voltage and power of the PV array. It is proved that, compared with the H-bridge inverter, the operation range of the cascaded inverter is wider, whereas the total loss is larger. Furthermore, a novel online variable topology-type grid-connected inverter is proposed. A bidirectional power switch is introduced into the conventional cascaded inverter to connect the negative terminals of the PV arrays. When the output voltages of the PV arrays are lower, the proposed inverter works under cascaded inverter mode to obtain wider generation range. When the output voltages of the PV arrays are higher, the proposed inverter is transformed into equivalent H-bridge inverter mode to reduce the total loss. Thus, wider generation range and higher efficiency are both implemented. Specific demonstration of the proposed inverter based on five-level cascaded inverter is presented. The detailed experimental results verify the accuracy and feasibility of the theoretical analysis and the proposed inverter topology. [ABSTRACT FROM PUBLISHER]

In this paper, a seven-level single-carrier and multi-modulation-wave sinusoidal pulsewidth modulation (SCMM-SPWM) strategy is proposed. In the negative half cycle of the modulation waves (MWs), dc offsets related to the amplitude of the carrier are set on the three MWs, respectively, to apply the same comparison logics of the MWs and carrier during positive and negative half cycles of the MWs. Thus, it is implemented with only one digital signal processor chip without any other attached logical circuit or controller. The reason for generating the zero-crossing voltage pulse disturbance (ZCVPD) in this strategy is analyzed, and the elimination of the ZCVPD is proposed and verified by experimental results. The spectral characters of the conventional multi-MW-based SPWM and the proposed one are originally derived and compared with each other by simulation in detail. The theoretical analysis, simulation, and experimental results indicate that the output characters of the proposed strategy are identical to those of the conventional one; it means that the proposed strategy can replace the conventional one while with the benefit of significantly reducing the cost and bulk of the implemental platform. [ABSTRACT FROM PUBLISHER]

In this paper, a kind of zero-crossing distortion (ZCD) generated in the grid-connected current of a single-phase grid-connected inverter with unipolar hysteresis current control is investigated. By establishing the mathematical model of the grid-connected inverter around the zero-crossing points (ZCPs), the reason for causing the current ZCD is presented. It is ascribed to the slope of the actual current less than that of the reference one around the ZCPs. The expressions of the critical phase angle (the starting point of the current ZCD) and the amplitude of the current distortion corresponding to the parameters of the inverter and connected utility grid are obtained, and the solution for the ZCD based on on-line leading phase angle compensation is proposed. Simulation and experimental results verify the accuracy and feasibility of the theoretical analysis and the proposed solution. [ABSTRACT FROM PUBLISHER]