Tomonobo Senjyu

Wind velocity and position sensorless operation for PMSG wind generator

In order to perform an efficient operation of a wind generation system, it is necessary to drive a windmill at an optimal rotor speed. For that purpose, a rotor position and wind velocity sensor become indispensable. However, these equipments are required to remove from wind generation system due to cost reduction and reliability enhancement. In this paper, wind velocity and position sensorless operating method of wind generation system using the full-order observer is proposed.

Transient stability analysis of induction generator using torque-time characteristic

Transient stability assessment of wind power generator is one of main issues in power system security and operation. The transient stability for the wind power generator is determined by its corresponding critical clearing time (CCT). Conventionally, determination of the induction generator CCT involves a large number of trial and error methods that requires repetitive runs of related time domain simulation. In this paper, we present transient stability analysis technique for induction generator used in wind power generating system at three-phase fault conditions. The proposed method saves time in consuming the repetitive runs of related time domain simulation. The validity of the developed technique is confirmed by the results obtained from trial and error method using Matlab/Simulink.

Supersession of large penetration photovoltaic power transients using storage batteries

This paper treats the impact of output fluctuations caused by cloud transients on the distribution power systems fed by large photovoltaic (PV) system by considering PHEVs to be main component of future smart grids. The PHEVs charging station is seen as bulk storage battery which acts as controllable loads and interacts with intermittent PV power generation. A control strategy for the PHEVs battery is developed in which the PV generation scheduled power is prepared based on clear sky assumption. In normal state, the storage batteries are set in charging mode. The results simulate the impact of 50% PV penetration on a 33-node radial distribution feeder during 24 hour period. PV generation plants were connected at buses 18 and 33 which display weakest voltages. The simulations are carried out for clear sky, full cloudy sky and cloud transient with different models of the PV interface inverter. The results show that the generating reactive power by PV inverter enhances the feeder voltage profiles. However, during cloud transient, application of PHEVs storage systems is required to alleviate the feeder voltage flicker. PHEVs charging stations were connected at the same buses of PV generation plants. The developed controllers can be integrated with charging station smart meter and can be extended for real time billing schemes in both charging and discharging modes.

Coordinated charging of plug-in hybrid electric vehicle for voltage profile enhancement of distribution systems

Because of increasing in the number of plug-in hybrid electric vehicles (PHEV) is expected in the next years, so it will have impact on the power system performance, stability, voltage profile and system loses. Consequently, it is necessary to study the strategy and control methods of the PHEV charging strategies. In this paper, a new technique is used for charging the batteries of PHEVs in real time. The objective of the developed control strategy is to keep the system voltage in secure operation irrespective of the number of vehicles and their place along the distribution feeder. The strategy adopts the steady state voltage profile of the system that is easy to compute using the smart-grid load flow program implemented in the distribution management systems. The developed control method uses fuzzy logic controller. The developed strategy uses real-time Network voltage and the PHEV state of charge as the main inputs of the fuzzy controller. Based on the controller output, the bi-directional converters of each PHEVs converter decide the desired level of charging. This ensures secure operation of distribution systems during charging whatever the number of connected PHEVs to the grid. Besides, the control strategy decides the level of charging for each PHEV according to its state of charge. The Newton-Raphson method is used as the continuous power-flow solver in the distributed management system for network voltage calculation. Lithium-Ion battery is used for each PHEV is used to test out the developed control strategy.

High efficiency drive for micro-turbine generator based on current phase and revolving speed optimization

This paper presents a high efficiency drive strategy for the micro-turbine generator (MTG) in which the permanent magnet synchronous generator (PMSG) is employed. The PMSG operates with maximum efficiency by optimizing the decomposition of the dq-xes armature currents in the synchronous reference frame. In addition, in order to effectively use the turbine output power, compressor optimizing the revolving speed of the PMSG minimizes input power. Simulation results confirm the validity of the proposed method.

Voltage stability assessment of photovoltaic energy systems with voltage control capabilities

This paper studies the impact of large-scale PV generation, up to 50% penetration level, on distribution system voltage regulation and voltage stability. The system voltage profiles are computed using power-flow calculations with load variation of a 24-hour time scale. The voltage stability is examined at different times of the day using a developed continuation power-flow method with demand as continuation parameter and up to the maximum loading conditions. The load-flow analysis implemented for both voltage regulation and voltage stability analysis is performed by using the forward/backward sweep method. The secant predictor technique is developed for predicting the node voltages which are then corrected using the load flow solver. Three models of the PV interface inverter are implemented in this study with full set of data representing environmental conditions. The voltage profiles are regulated using the PV interface inverters which support reactive power at unavailability of sun light. The available inverter capacity is utilized for regulating the system node voltages. The most possible scenarios of system voltage collapse are investigated at different times of the day. The developed methods and models are used to assess the performance of a 33-bus radial distribution feeder with high level of PV penetration. The results show that the PV interface inverters have to be designed to operate for reactive power support in order to improve voltage profile, secure power systems operation, and increase the lifetime of the online tap changing transformers.

Load balancing of active distribution systems with high Photovoltaic power penetration

This paper treats the problem of voltage control and balancing of the unbalanced three-phase loads in distribution systems with Distributed Generators (DG) and tap change transformers. The DGs considered in this paper are supposed to be Photovoltaic (PV) generators, due to the growing demand of renewable energies. Unbalanced three-phase loads operation can have undesirable effects on the distribution system components, beside making the voltage control more difficult. For that reason, the proposed method aims to balance the unbalanced three-phase loads and control the voltage using the available reactive power generated from the DG through the inverters interfaced with PV modules. The Newton Raphson method is used solve the unbalanced three phase power flow equations of the distribution system, while the three phase elements models are considered. Twenty-four-hour data are used to simulate a 14-bus distribution system with unbalanced three-phase loads in 7 nodes to verify the effectiveness of the method. The simulation results show that the node voltages are balanced and kept within the statutory range.

Real time voltage control of unbalanced distribution systems with photovoltaic generation

This paper presents a real time operation of tap changing transformers and converters interfaced with distributed generators (DGs) in unbalanced three-phase distribution systems. The unbalanced three-phase power flow equations are solved using Newton Raphson method, and the three phase elements models are considered. Since the renewable energies are attracting worldwide attention, the DGs considered here are supposed based on photovoltaic (PV) generators. However, the large amount of distributed generation causes voltage deviation beyond a statutory range in distribution systems. The method proposed in this paper control the voltage through the inverters interfaced with PV modules, using an optimized day-ahead schedule of reactive power resources, which include PV inverters and online transformers. The reactive power outputs of PV inverters are determined according to the locally measured voltage. The voltage droop characteristics are determined by fuzzy controllers. A 24-hour data are used to simulate real time and assess the effectiveness of the proposed voltage control strategy of unbalanced distribution systems. The simulation results show that the voltage fluctuations due to photovoltaic generation are minimized to be within the desired range.

Position control of ultrasonic motors using two-control inputs H/sub /spl infin// controller

The ultrasonic motor has nonlinearity characteristics, which varies with driving conditions associated the variations of temperature and applied load torque of USM. The nonlinearity characteristics for actuators are problem in accurate position control. To improve the control performance of the ultrasonic motor, we apply two-control inputs H/sub /spl infin// controller for position control of the USM. Applying an H/sub /spl infin// methodology we derive a stabilizing controller to meet design objectives and robust stability and performance against such variations. Using two-control inputs improve the position tracking ability of USM. The validity of the proposed method is confirmed by experimental results.