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.

This project develops new sensing technology for use in power electronic systems, helping the UK to better compete with global leaders in power electronics. Power electronics is a key electrification technology: it is needed in electric vehicles, renewable energy generation, our electricity grid, and anywhere where the flow of power needs to be accurately dosed. This dosing is carried out by rapidly switching currents on and off to create the desired average. This technology reduces our carbon footprint and contributes nearly £50bn per year to the UK economy and supports 82,000 skilled jobs in over 400 UK-based companies (2016 data). The power electronics industry is undergoing significant change, as ultra-fast transistors made from silicon carbide (SiC) or gallium nitride (GaN) have recently emerged, to replace silicon transistors. These new transistors switch 10x faster, which results in 75% less energy being lost in power converters, and enables converters to be shrunk to less than half their previous size. This makes it much easier to build them into other systems, e.g. electric vehicles, resulting in lighter cars with more space for batteries. This project is about helping to maximise the potential of the new transistors. Many companies are struggling to adopt them, because whilst the very fast switching provides the benefits of improved efficiency and radically smaller system size, it also creates problems with electromagnetic interference, and device and system reliability. The transistors switch current on or off so fast (in less than ten nanoseconds, the time it takes light to travel 3 meters), that engineers cannot accurately measure how the voltages and currents change during this time, even with their best equipment, which means it is difficult to fix problems such as interference. Because of this, even the leading companies are slowing down these new transistors, and losing some of their efficiency potential. Our project develops small, low-cost sensors, that make these nanosecond-scale changes visible. They will allow engineers to see exactly how the transistors are switching, helping them develop better, smaller, lighter, and more reliable power electronics. They will allow computer-controlled SiC and GaN power converters to sense when they are creating too much electromagnetic noise, and reduce this by switching more intelligently. It will allow power circuits to detect external short circuits and isolate these before they damage the power converter. We are also developing sensors that provide engineers, or control systems, directly with information that they need (e.g. device temperature), rather than having to infer this indirectly from volts and amps, making the measurements faster and more efficient. The sensors work by detecting electric or magnetic fields via coils, conductive plates, or antennas. The received signal is fed into a chip inside the sensor that computes the required parameter. These new SiC and GaN transistors have made small field sensors on circuit boards viable for the first time, because as signal speeds increase, the wavelengths of these signals become shorter (cm-scale), meaning that their fields can be picked up with millimetre-size coils or antennas. In order to ensure that we develop what industry needs, we are working with 12 partners across automotive, renewable energy, semiconductors, commercial R&D organisations with deep sector experience, and we are accepting new collaborators on request. Our project provides partners and other UK companies and universities with sample sensors. Their feedback, and discussions with partners helps us prioritise our research, and ensures that we are using our research funds to solve the most important problems. We are providing workshops to help keep engineers up-to-date with advanced measurement techniques, and keeping our results online (publications and a dedicated website) for companies to use as desired.