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A novel single-stage doubly grounded transformerless inverter configuration which can buck-boost the output voltage is proposed in this paper. In this transformerless inverter configuration grid neutral is directly connected to PV panel negative rail which suppresses/eliminates the PV leakage currents. In addition, the tracking of maximum power point is possible for wide variation of weather conditions due to buck-boost voltage capability of inverter. Moreover, the proposed inverter topology has symmetrical operation in both half cycles hence injects negligible DC offset current in to the grid. Here the symmetrical operation of inverter is achieved due to one inductor is used for both half cycles of the grid. The proposed topology is realized using five switches, two of which work at 50 Hz and remaining three switches at high frequency which reduces overall semiconductor losses. Further, the proposed inverter topology is controlled through a newly developed modulation technique and possible working modes are analyzed and described thoroughly. For performance validation, the experimental analysis of grid connected proposed inverter is performed on a 1 kVA system and results show that proposed inverter feeds power in to the grid with lesser THD while achieving greater efficiency. [ABSTRACT FROM AUTHOR]

Both the local and concurrent commutation failures (LCF and CCF) are concerned threats to the secure operation of multi-infeed LCC-HVDC (MIDC) systems, which will be largely impacted by the voltage stability. However, this impact has not been clearly revealed yet by earlier works due to the lack of the related analytical evaluation method. Thus in this paper, the analytical evaluation method related to the LCF and CCF with the voltage stability in MIDC systems is firstly proposed considering the complicated inter-inverter interactions. This is realized by deriving the analytical expressions of the LCF and CCF immunity indices (LCFII and CCFII) as the functions of the voltage stability factor (VSF) based on the system quasi-steady-state model. Moreover, the proposed method is used to clearly evaluate the impact of the voltage stability on the LCF and CCF by comprehensively conducting the parametric dependence analysis of the LCFII, CCFII, and VSF versus various system parameters and operation variables. The analysis results indicate that in some certain situations, increasing the voltage stability of MIDC systems however imposes an unexpected negative impact on the LCF and CCF. Finally, the simulation results of the PSCAD/EMTDC program based on a tri-infeed LCC-HVDC system validate the theoretical developments. [ABSTRACT FROM AUTHOR]

This paper proposes a new three-phase to five-phase transformer, with a 30-pulse AC–DC converter for power quality improvement in vector-controlled induction motor drive. Here, three isolated transformers (T1, T2, and T3) are used and each transformer is designed to convert three-phase AC-supply into five-phase AC supply, to achieve ten-pulse AC–DC conversion. A unique configuration and angle among these three transformers is designed in such a way that the resultant input current of this transformer shows 30 pulses in it. A hybrid multilevel inverter is proposed in this paper, which is cascading a three-level neutral point clamped inverter with a two-level voltage source inverter to drive an induction motor (IM). A modified level shifted carrier-based sinusoidal pulsewidth modulation and a 3rd harmonic injection techniques are utilized to modify the modulating signal, to enhance the fundamental magnitude, and to reduce the harmonics than traditional technique. The responses of proposed medium voltage induction motor drive (MVIMD) are evaluated by simulating in MATLAB-Simulink. The proposed MVIMD performance is then verified using a scaled down laboratory prototype under various operating conditions such as steady state, starting, load perturbation, speed control, field weakening, varying load conditions, and over a wide speed range of IM. [ABSTRACT FROM AUTHOR]

This paper presents a new series capacitor based frequency scan method to assess the subsynchronous resonance risk including induction generator effect (IGE) and subsynchronous control interaction (SSCI). Most existing frequency scan methods are generator based and calculate the impedance as viewed from the neural bus of the study generator. In this paper, the generator-based frequency scan method is discovered to be inadequate or inapplicable to deal with a cluster of inverter-based generation resources under some circumstances. The proposed method scans the impedance as viewed from the series capacitor to assess the IGE/SSCI risk. With nearby inverter-based generation resources modeled by their frequency-dependent impedances, the proposed method is capable of assessing the IGE/SSCI risk for a cluster of inverter-based generation resources. The electromagnetic transient simulation was conducted to validate the proposed method. The proposed method also successfully demonstrates the nonlinear impact of the number of in-service units on the SSCI performance for a cluster of inverter-based generators. [ABSTRACT FROM AUTHOR]

Unlike the short circuit faults, the breakage fault does not offer distinctive characteristics compared with normal operation transients in DC distribution system and the fault information is difficult to be analyzed, which bring great challenges to breakage protection. In this case, this paper introduces a fault characteristic analysis method for breakage faults and proposes a novel breakage protection scheme based on ratio of positive and negative fault currents for DC distribution network. By establishing the fault circuit equations, the breakage fault features are analyzed for protection. Meanwhile, the ratio of current summation over their subtraction is used to further amplify fault characteristics, which overcomes the reliability problem of conventional breakage protection. A six-terminal flexible DC distribution network is built in PSCAD/EMTDC to verify the proposed protection method. Simulation results show that the protection is robust to the measurement noise and can identify an internal breakage fault and realize the broken pole selection rapidly. [ABSTRACT FROM AUTHOR]

In this paper, a static synchronous compensator (STATCOM) is proposed in which a new modular structure with conventional three-phase voltage source inverters is used to multilevel operation. The inverters are connected to a transformer in an open-end winding configuration and with three independent DC links. In this structure, the inverters will be connected in a cascade configuration. Besides the multilevel operation, the system is also characterized by low required blocking voltages for switch ratings, since the proposed STATCOM can apply the double of the DC capacitor voltage to the transformer windings. The development of the control system for the proposed topology is also presented. The operation of the proposed topology and the performance of the developed control system will be tested through several simulation and experimental tests. [ABSTRACT FROM AUTHOR]

The adverse impacts of commutation failure (CF) of a line-commutated converter (LCC)-based high-voltage direct current (HVdc) system on the connected ac system are becoming more serious for high-power ratings, for example, the development of ultra-HVdc systems. Aiming to solve the problem of CF particularly for higher power/current LCC HVdc systems, this paper proposes a new method, which utilizes a thyristor-based controllable capacitor (TBCC), to eliminate CFs. The topology of the proposed TBCC LCC HVdc and its operating principles are presented. Then, mathematical analysis is carried out for the selection of component parameters. To validate the performance of the proposed method, modified LCC-HVdc and capacitor-commutated converter (CCC)-based HVdc systems based on the modified CIGRE HVdc system are modeled in a real-time digital simulator. Simulation studies for zero impedance single-phase and three-phase faults are carried out, and comparisons are made with both LCC-HVdc and CCC-HVdc systems. Furthermore, voltage and current stress of the TBCC are investigated and power-loss calculations are presented. The results show that the proposed method is able to achieve CF elimination under the most serious faults while the increase of power losses due to the TBCC is small. [ABSTRACT FROM AUTHOR]