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Space vector modulation (SVM) is a mature modulation scheme, which is widely used for voltage source inverters. In this article, a flexible online SVM scheme is proposed for a cascaded H-bridge multilevel inverter (CHMI) under short-circuit and open-circuit switch as well as cell failure conditions. The proposed scheme directly calculates all the active redundant switching states and the dwelling duty cycles of the three space vectors enclosing the reference vector for a CHMI such that balanced line-to-line voltages and currents under failure conditions are generated. Accordingly, the resultant switching sequences are determined to meet any specific requirement, e.g., even-order harmonics elimination and minimization of switching losses. Furthermore, in order to reduce voltage stress on the semiconductors under short- and open-circuit switch conditions, an equal power distribution criterion is introduced. The proposed SVM scheme is fast and independent of the number of levels. Experimental results are presented to demonstrate performance and effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Expansion of the DC distribution networks in the future power system has raised concerns over their stability assessment. To assess stability of the expanded DC distribution networks, the conventional zone aggregation method requires access to not only the nodes connected to the converters but also some other nodes within the DC passive network. However, access to the nodes within the DC passive network is not always feasible as some parts of the DC network may be buried or encapsulated. To address this issue, this paper proposes a new zone aggregation method for impedance-based stability assessment of the expanded DC-distribution networks. Compared with the conventional method, the main advantages of the proposed method are as follow: i) it only utilizes the impedance/admittance information of the nodes connected to the converters. Moreover, all the impedances/admittances can be measured directly without knowing the internal structure and/or parameters; ii) it can assess stability of expanded distribution networks with minimum number of nodes. Performance and effectiveness of the proposed method are evaluated and validated by simulation studies on a 10-bus DC distribution network and a modified IEEE 37-bus system in the Matlab/Simulink software environment. [ABSTRACT FROM AUTHOR]

The increasing power/load demand is becoming a new concern for the grid operators as it can potentially overload transmission lines. Among advantages of a multi-terminal dc (MTDC) grid, its high controlability makes it a promising asset for ac line overload alleviation. This paper proposes a model predictive control based strategy, which regularly updates the power setpoints of the MTDC converter stations and ac generators to alleviate ac line overloads. To compute and update the power setpoints, necessary measurements are received by the controller within regular time intervals. The proposed controller ensures that subsequent to any ac line overload, changing the power setpoints of the MTDC converter station does not cause any operation violation in the MTDC grid. Furthermore, it ensures that the ac voltage limits and voltage stability criteria are met to avoid voltage instability. Performance and effectiveness of the proposed controller are evaluated by simulation studies on two systems, i.e., the 39-bus New England system integrated with a 5-bus MTDC system and the IEEE 118-bus system connected to a 6-bus MTDC system. Simulation results confirm that the MTDC grid can play a major role in controlling active powers of most of the ac transmission lines. [ABSTRACT FROM AUTHOR]

Today, energy crises attracted many researchers’ attention to renewable energy technologies especially photovoltaic (PV) systems. The main challenge of PV systems is unpredictable nature of solar power generation. To overcome this challenge, a storage system is integrated which reduces demand reliance on electricity grid and uses excess energy that solar panels produce. As investment cost of the storage system is considerable, finding an optimal technology, size, and configuration are crucial. In this paper, the optimal battery system is excluded from existing PV plant installing in a commercial building located in Mashhad/Iran. Here, the sizing procedure is based on a financial evaluation which considers the damage costs due to outages that the commercial building is experiencing during the PV system life spam. To compare results, the battery size is also determined by stochastic methods, e.g. Monte-Carlo simulation method. The simulation results confirm the advantages of the proposed approach compare with classic ones. [ABSTRACT FROM AUTHOR]

Growing concerns with the harmonic oscillation phenomenon of multiterminal DC (MTDC) systems calls for appropriate harmonic stability analysis methods. However, the conventional ac or dc admittance-based stability assessment methods cannot effectively protect trade secret and user privacy, distinguish different system instability root causes, and put forward corresponding instability mitigation methods. To address the aforementioned issues, this article first establishes a hybrid ac/dc admittance-based stability assessment model for a MTDC system. Then, by introducing the determinant-based General Nyquist Criterion (GNC), the system stability is assessed and three types of instability root causes, including the ac side, the dc side, and the coupling interaction between the ac and dc sides are identified. Regarding the instability caused by the ac side, the dominant interlinking converter is directly identified, in which the instability can be mitigated by reshaping its q-axis admittance. In contrast, for the instability caused by the latter two root causes, the most influential interlinking converter is recognized by an additional sensitivity analysis. The instability is then mitigated by reshaping the dc-side equivalent admittance of the most influential interlinking converter. Compared with the conventional methods, the proposed method offers advantages as follows: 1) trade secret and user privacy is effectively protected, 2) different system instability root causes can be effectively distinguished, and 3) instabilities caused by diverse root causes can be mitigated by corresponding methods. Finally, the proposed method is verified by simulations in the MATLAB/Simulink environment. [ABSTRACT FROM AUTHOR]

The cascaded H-bridge multilevel converter (CHMC) is a promising topology for medium- and high-voltage applications, as it features modularity and scalability. In this letter, a simplified space vector modulation (SVM)-based reconfiguration strategy is proposed to enable fault-tolerant operation of a CHMC. Assuming that the faulty power cells are bypassed, the proposed strategy decomposes the asymmetric CHMC into two parts, i.e., healthy part with healthy modules and unhealthy part with faulty modules. Consequently, the basic reference vector (BRV) and the remainder reference vector (RRV) are generated from the reference vector (RV) to achieve balanced line-to-line voltages and currents with optimized harmonic performance. The proposed strategy can be easily implemented online. Performance and effectiveness of the proposed strategy is verified by experimental results. [ABSTRACT FROM AUTHOR]