Intelligent Integration of Renewable Energy Resources Review : Generation and Grid Level Opportunities and Challenges

This paper reviews renewable energy integration with the electrical power grid through the use of advanced solutions at the device and system level, using smart operation with better utilisation of design margins and power flow optimisation with machine learning. This paper first highlights the significance of credible temperature measurements for devices with advanced power flow management, particularly the use of advanced fibre optic sensing technology. The potential to expand renewable energy generation capacity, particularly of existing wind farms, by exploiting thermal design margins is then explored. Dynamic and adaptive optimal power flow models are subsequently reviewed for optimisation of resource utilisation and minimisation of operational risks. This paper suggests that system-level automation of these processes could improve power capacity exploitation and network stability economically and environmentally. Further research is needed to achieve these goals

The effects of parameter errors in field oriented control of induction machines.

Field oriented control is an established technique for rapid control of torque in induction motors. The controller tracks the orientation of the rotor flux, which rotates at synchronous frequency. The component of stator current in phase with this flux (known as the "flux current"), can be used to maintain a constant flux. Under these conditions, torque is directly proportional to the quadrature component of stator current, or "torque current". It has not proved cost-effective to measure either the rotor flux orientation or the motor torque directly. However both can be estimated from a combination of voltages and/or currents and position (or speed). The standard mathematical model uses the resistances and inductances of the motor equivalent circuit. These parameters may vary with temperature, motor operating speed and load. The underlying cause, range and timescale of these variations is examined, along with techniques for tracking the changes on-line. Detailed off-line characterisation results are presented for the test motor, in order to determine how accurately the parameters can be identified in practice. A number of standard torque and flux estimators have been analysed and implemented. Experimental results are presented for a 5.5kW motor drive system. Parameter errors and delays within the controller, which cause an error in the orientation of the stator currents, are shown to affect the motor performance. The motor is incorrectly fluxed, which may reduce its efficiency and peak torque capability in the steady state. In addition, any change in demanded torque is coupled into the flux current, exciting the natural response of the motor. This is characterised by damped oscillations at slip frequency, decaying at a rate determined by the rotor time constant. The implications for closed loop torque and speed control are discussed

The effects of parameter errors in field oriented control of induction machines.

Field oriented control is an established technique for rapid control of torque in induction motors. The controller tracks the orientation of the rotor flux, which rotates at synchronous frequency. The component of stator current in phase with this flux (known as the "flux current"), can be used to maintain a constant flux. Under these conditions, torque is directly proportional to the quadrature component of stator current, or "torque current". It has not proved cost-effective to measure either the rotor flux orientation or the motor torque directly. However both can be estimated from a combination of voltages and/or currents and position (or speed). The standard mathematical model uses the resistances and inductances of the motor equivalent circuit. These parameters may vary with temperature, motor operating speed and load. The underlying cause, range and timescale of these variations is examined, along with techniques for tracking the changes on-line. Detailed off-line characterisation results are presented for the test motor, in order to determine how accurately the parameters can be identified in practice. A number of standard torque and flux estimators have been analysed and implemented. Experimental results are presented for a 5.5kW motor drive system. Parameter errors and delays within the controller, which cause an error in the orientation of the stator currents, are shown to affect the motor performance. The motor is incorrectly fluxed, which may reduce its efficiency and peak torque capability in the steady state. In addition, any change in demanded torque is coupled into the flux current, exciting the natural response of the motor. This is characterised by damped oscillations at slip frequency, decaying at a rate determined by the rotor time constant. The implications for closed loop torque and speed control are discussed

OPEN-CIRCUIT FAULT TOLERANCE OF MULTIPHASE GENERATOR RECTIFIER SYSTEMS

Generator rectifier systems are widely used in transport applications to provide a DC power source. Multiphase generators are attracting interest in the marine and aircraft sectors for medium voltage operation (above 1kV) with fault-tolerant capability. Fault tolerance is enhanced by using a split phase arrangement, where the windings are grouped into submachines, each with its own rectifier that can be interconnected in series or parallel to create the output voltage. This paper uses a 15-phase example, configurable as three 5-phase or five 3-phase submachines, to investigate fault tolerance. The results allow previous work on 12-phase machines to be generalised for any number of phases. In addition, series stacking is shown to maintain DC current whereas parallel stacking maintains the DC voltage. The removal of an entire submachine is shown to be more effective than operating with an unbalanced system due to a single open-circuit coil or diode

Analysis of multiphase induction machines with winding faults

The paper shows how the techniques of generalised harmonic analysis may be used to simulate the steady-state behaviour of a multi-phase cage induction motor with any form of open-circuit or short-circuit fault in the stator winding. The analytical model is verified using a 4-pole machine with a 48-slot stator. Each coil of the stator winding of this machine is brought out to a patch-board that enables the stator to be configured for single-phase, two-phase, three-phase, four-phase, six-phase or twelve-phase excitation. Experimental results are compared with computer predictions for a six-phase machine with both open-circuit and short-circuit faults. © 2005 IEEE