This paper proposes a new family of multilevel inverter topology that is able to generate seven voltage levels by utilizing one or two floating capacitors and ten power switches. This novel boost switched-capacitor 7-level inverter (BSC7LI) possesses voltage boosting capability with an achievable maximum voltage level 1.5 times the input direct current (dc) voltage. The generation of higher output voltage does not incur high-voltage stress on any power switch in this topology, as the peak inverse voltages of all power switches do not exceed the input source voltage. In addition, capacitor voltage balancing is not essential since the floating capacitors are effectively balanced during the charging and discharging processes. Furthermore, the proposed topology eliminates the need for multiple isolated dc sources, and a single dc source is sufficient in both its single-phase and three-phase topologies. The operating principle and steady-state analysis of the proposed topology are elaborated. Experimental results from a single-phase prototype are then presented to verify the validity of the proposed topology.

Pumped storage power plant has gained a high level of attention in recent years, mainly because of its ability to act as a large-scale energy storage option and to improve power system flexibility. Doubly fed asynchronous machine with the partially rated power electronic converter is adopted in pumped storage plants to provide variable speed operation and improve energy efficiency. This paper summarizes the power converter topologies in large rated variable speed pumped storage plant (VSPSP), also covers the suitability of each converter topology, modulation techniques, and parallel converter schemes. Also, it presents operational issues of the parallel converter system in VSPSP such as the shutdown of the plant due to insufficient converter redundancy and lack of fault-tolerant control schemes, a power outage due to the inadequacy of converter protection system, and unbalanced power sharing due to circulating current. Furthermore, the reliable mitigating/additional techniques are discussed for future research. It concludes that the refinement of these aforementioned issues will provide continuous operation of the plant.

Doubly fed induction machine (DFIM) is increasingly being preferred in sites where there is large variation in water head (e.g., Tehri hydropower complex in India having water head variation from 130 to 230 m), as it offers high dynamic stability and better energy efficiency at part loads. Smooth starting, unity power factor, and better rotor current profile are the reasons; back-to-back voltage source converters are used in rotor side of the machine. Speed and power factor of DFIM are controlled through power converters in accordance with surplus power available in grid and water head of dam. This paper presents dynamic behavior of a 250 MW DFIM hydro-generating unit, to be commissioned in 1000 MW Tehri pumped storage plant, operating in pumping mode. Further, the performance of pumping operation of DFIM is assessed under power converter and control circuit failures. Persevere ability of the machine is analyzed based on performance measures: Speed, current, reactive power consumption. From the analysis, energy storage loss of about 66.61 MU/year is estimated in a 1000 MW plant due to the inadequate power and control redundancy. A 2.2 kW DFIM is experimented at laboratory level to support the simulation.

Traditionally voltage control in the distribution power system (DPS) is performed through voltage regulating devices (VRDs), including on-load tap changers (OLTCs), step voltage regulators (SVRs), and switched capacitor banks (SCBs). The recent IEEE 1547:2018 from March 2018 requires inverter fed distributed energy resources (DERs) to contribute reactive power to support the grid voltage. To accommodate VAR from DERs, well-organized control algorithm is required to use in this mode to avoid grid oscillations and unintended switching operations of VRDs. This paper presents two voltage control strategies (i) static voltage control considering voltage-reactive power mode (IEEE 1547:2018), (ii) dynamic and extensive voltage control with maximum utilization of DER capacity and system stability. Further, effective time-graded control is implemented between VRDs and DER units to reduce the simultaneous and negative operation. The proposed voltage control strategies are tested in a realistic 140-bus southern California distribution power system through extensive time-domain simulation studies. The results show that voltage quality in a distribution system is effectively achieved through the proposed voltage control strategies with a significant reduction in the number of switching operations of VRDs. In addition, proposed voltage control strategies increase the reliability and security of the DPS during unexpected failures.

Doubly fed Induction machine (DFIM) is increasingly being preferred in large rated variable speed pumped storage power plants (PSPP) since it provides better energy efficiency due to optimization of pump/turbine efficiency. Increased efficiency results from the flexibility of operating speed at different hydraulic heads. In doubly fed configuration partial rated power converters feed the rotor circuit. Parallel connected back-to-back voltage source converter (VSC) on rotor side is responsible for starting, braking (dynamic/regenerative) and speed (real power) control of the unit. This paper presents the smooth starting and regenerative braking, and assesses performance under power converter and sensor faults of a 250 MW DFIM pump turbine unit to be commissioned in Tehri PSPP, India. Survivability of the unit during faults is analyzed based on: (i) current, (ii) speed, (iii) dc link voltage. Further, this paper investigates fault tolerant operation of 250 MW DFIM unit at open circuit fault in converters. A 2.2 kW DFIM is tested in the laboratory to corroborate the simulation.

Penetration of distributed energy resources (DERs) such as wind, solar units are rapidly increasing in distribution power system (DPS). In view of power grid reliability and efficiency, cyber and physical secure of these units are highly important since it can directly impact power system operations. This paper investigates the dynamic behavior of power distribution during cyber, physical strikes on reactive power control in DER units. Various fault scenarios including modifications in voltage-reactive power curve pattern such as slope of the curve, dead band; and changes in capacitive or/and inductive reactive power delivery to the power grid are presented. Further, fault scenarios are investigated with the presence of dynamic VAR (volt-ampere reactive) compensation (DVC) units in the system. A southern California 140-bus distribution power system is selected as a test system and faults are analyzed in both Matlab/Simulink and ETAP simulation platforms. The results evidence that the modifications in reactive power control values at DER units significantly affects the voltage quality/security of the system and change the number of switching actions of voltage regulators (VRs). In contrast, DPS connected with DVCs improves voltage quality and reduces the number of switching actions of VRs, also voltage quality/security is maintained during faults.