At present, commercial variable speed drives require a shaft mounted speed sensor to operate accurately at zero and low speeds. The operation of the drive at zero and low speeds deteriorates significantly if no speed sensor is used. A new technique for sensorless control of variable speed ac motor drives has been researched in EPSRC Grant EP/D069017/1. The technique provides accurate control of motor speed, position and load, even at zero and very low speeds, without the need for a shaft mounted speed sensor.The aim of the work described in this proposal is to demonstrate that this new technique is flexible and robust enough to enhance and upgrade the performance of commercial variable speed ac motor drives, . The specific objective is to ensure that the technique can be applied to a wide range of different ac motors (from different motor manufacturers) and that the inverter can setup its control parameters automatically if appropriate. This plug and play , high performance sensorless control will allow the inverter to be used for a variety of new applications and for a wide range of power ratings. Before potential licensees are willing to invest in the technology, it is crucial to demonstrate that it can be used in plug and play mode with any ac motor. The technical work package within this Follow-on fund will deliver this proof thereby making successful commercialisation possible.

A sensorless electric motor drive is the popular term for drives which do not use shaft mounted speed or position sensors. Sensorless operation is highly desirable for reasons of cost, simplicity and system integrity. However, it is well known that there are serious problems with sensorless motor drive control at zero and low speeds and this has been one of the main research topics in this field for many years. The conventional method for sensorless control, used in commercial products, is to estimate the machine flux and speed using a mathematical model of the motor. Below 1 to 2% base speed however, position and speed estimation using such a model deteriorates and speed and torque control is lost. There has been a recent impetus for zero speed sensorless drives for more-electric aircraft and vehicular applications. For the former, there is a requirement for direct electromechanical (EM) actuation of critical actuators in which locking of the mechanical transmission is not permissible. In the vehicular field direct EM drives will be required for the main drive train, and for power steering, active suspension and braking actuation. One approach to the solution of the zero speed problem, which does not require a machine model, has been to exploit the natural asymmetries or saliencies in AC machines. These saliencies are cause by magnetic flux saturation and the geometry of the construction of the motor itself. Flux or rotor position can then be tracked by processing the current response to a test voltage signal injection overlaid on the supplied motor voltage. These signal injection methods are now quite well understood, but do contribute to increased accoustic noise, reduced efficiency, the requirement for additional sensors, and an increase in bearing wear and electrical stress within the machine windings.The current proposal aims to overcome the above disadvantages by developing methodologies by which:1) No signal injection is required, the method being integrated with the fundamental voltage applied to the drive via the power converter. This eliminates the problems of extra noise, losses, bearing wear and electrical stresses.2) The requirements for sensors is substantially reduced (depending on the application). For bespoke applications (e.g. aerospace, automotive), the aim will be for one current sensor and one low cost di/dt sensor. For industrial standard drives the target aim is to use only the existing line current sensors. These aims are quite challenging. Mathematical feasibility of a non-signal injection method has been shown at Nottingham and the technique is currently subject to patent at the University. Practical investigation is now possible owing to advances in high-accuracy timing and sampling available in low-cost digital control systems.

Power Electronic Converters are key elements in many safety-critical, high-reliability, electrical systems working in uncertain and harsh environments. Examples include aerospace power supplies and servo converters, marine propulsion and traction drives, and offshore renewable energy generator systems. The traditional approaches to achieve high converter reliability are to de-rate the semiconductor devices and to include redundancy in the system configuration. These approaches can increase the Mean Time Between Failures of converters but will not prevent a catastrophic failure from happening. The aim of this research is to develop a new approach of monitoring the converter device degradation over a period of time and provide the ability to predict failures before they happen. The research will address the challenges of carrying out and understanding the results of key measurements in order to derive information about the internal state of the semiconductor devices in real-time operating conditions. The mechanisms leading to the aging and failure of the devices will be investigated, and a relationship between the device condition and its terminal characteristics established. Condition monitoring techniques will be based on converter terminal electrical signals, which are interpreted together with information about the thermal and load conditions of the converter system. Experiment, and computer modelling and simulation in the thermal, low frequency and high frequency electrical domains will be carried out to develop the condition monitoring techniques. The results will be valuable to device manufacturers, manufacturers of power electronic converters, and to the end users of such systems, particularly in critical applications.

Power Electronic Converters are key elements in many safety-critical, high-reliability, electrical systems working in uncertain and harsh environments. Examples include aerospace power supplies and servo converters, marine propulsion and traction drives, and offshore renewable energy generator systems. The traditional approaches to achieve high converter reliability are to de-rate the semiconductor devices and to include redundancy in the system configuration. These approaches can increase the Mean Time Between Failures of converters but will not prevent a catastrophic failure from happening. The aim of this research is to develop a new approach of monitoring the converter device degradation over a period of time and provide the ability to predict failures before they happen. The research will address the challenges of carrying out and understanding the results of key measurements in order to derive information about the internal state of the semiconductor devices in real-time operating conditions. The mechanisms leading to the aging and failure of the devices will be investigated, and a relationship between the device condition and its terminal characteristics established. Condition monitoring techniques will be based on converter terminal electrical signals, which are interpreted together with information about the thermal and load conditions of the converter system. Experiment, and computer modelling and simulation in the thermal, low frequency and high frequency electrical domains will be carried out to develop the condition monitoring techniques. The results will be valuable to device manufacturers, manufacturers of power electronic converters, and to the end users of such systems, particularly in critical applications.

Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.