Sensorless Control of Electromagnetic Actuators

Research focus

The aim of this research project is to improve the dynamics of the control of electromagnetic actuators while keeping the total system cost low by eliminating the need for a position sensor.


Brief description

Electromagnetic actuators or sometimes called solenoid actuators can be seen everywhere in the industry where mechanical switching of valves is required. For example, plants that require switching of fluid or gas use for power generation, or fuel and exhaust valves in internal combustion engines.

So far these actuators are either controller mechanically, with springs and camshaft in cars, or electrically with on/off function. The drawback of mechanical control is the loss of freedom on the control cycle since the camshaft is coupled to the main engine. The drawback of on/off control is the mechanical wear that generates due to high speed impact velocities the actuator experiences when closed or opened.

The aim of this project is to design a feedback control system for the actuator so that high dynamics can be maintained without increasing mechanical wear and at the same time gain freedom on the control cycle. This is possible if a position sensor is installed on the actuator. However, position sensors add cost and complexity to the system. Thus removing the sensor would bring a lot of cost and simplicity benefits.

Sensorless control has been applied on rotating electrical machines for more than two decades. It can be split to two categories: model based estimation and saliency based estimation. Model based estimation uses a mathematical model of the plant to estimate the parameters, mainly the back e.m.f. and thus the speed. This method works for high enough speeds however will fail at low speeds since the back e.m.f is directly related to the speed.

The other method aims at exploiting the nonlinearities of the machine; mainly the change of inductance with position. Due to magnetic reasons the inductance is not totally constant over the stroke or rotation of the machine. If this inductance can be estimated from voltage and current measurements only, the position of the mover or rotor can be estimated as well.