D.C. FROM A.C. – CONTROLLED RECTIFICATION The vast majority of drives of all types draw their power from constant voltage 50 or 60 Hz mains, and in nearly all mains converters the first stage consists of a rectifier which converts the a.c. to a crude form of d.c. Where a constant-voltage (i.e. unvarying average) ‘d.c.’ […]
Electronic Converters for Motor Drives In this article we look at examples of the power converter circuits which are used with motor drives, providing either d.c. or a.c. outputs, and working from either a d.c. (battery) supply, or from the conventional a.c. mains. The treatment is not intended to be exhaustive, but should serve to
Control Arrangements for Inverter Fed Drives For speed control manufacturers offer options ranging in sophistication from a basic open-loop scheme which is adequate when precise speed holding is not essential, through closed-loop schemes with tacho or encoder feedback, up to vector control schemes which are necessary when optimum dynamic performance is called for. The variety
Inverter Fed Induction Motor Drives Induction motor can only run efficiently at low slips, i.e. close to the synchronous speed of the rotating field. The best method of speed control must therefore provide for continuous smooth variation of the synchronous speed, which in turn calls for variation of the supply frequency. This is achieved using
Speed Control of Induction Motor To operate efficiently an induction motor must run with a small slip. It follows that any efficient method of speed control must be based on varying the synchronous speed of the field, rather than the slip. The two factors that determine the speed of the field, are the supply frequency
Generating and Braking of Induction Motor Having explored the torque–speed curve for the normal motoring region, where the speed lies between zero and just below synchronous, we must ask what happens if the speed is above the synchronous speed, or is negative. A typical torque–speed curve for a cage motor covering the full range of
Influence of Rotor Parameters on Torque Speed Curves We know that the rotor resistance and reactance influence the shape of the torque–speed curve. The designer can vary both of these parameters, and we will explore the pros and cons of the various alternatives. To limit the mathematics the discussion will be mainly qualitative, but it
Influence of Rotor Parameters on Torque Speed Curves Read More »
Stable Operating Regions of Induction Motor In addition to having sufficient torque to start the load it is obviously necessary for the motor to bring the load up to full speed. To predict how the speed will rise after switching on we need the torque–speed curves of the motor and the load, and the total
Starting Methods of Induction Motors Our everyday domestic experience is likely to lead us to believe that there is nothing more to starting a motor than closing a switch, and indeed for most low-power machines (say up to a few kW ) – of whatever type – that is indeed the case. By simply connecting
Process of Motor Selection The process of motor selection often highlights difficulties in three areas. Firstly, there is a good deal of overlap between the major types of motor and drive. This makes it impossible to lay down a set of hard and fast rules to guide the user straight to the best solution for