Research On Variable Frequency Control Of Single Phase Induction Machines

Due to its simple structure, strong durable and low cost, single-phase induction machines have been widely applied in low-power industrial applications, home appliances.and so on.Traditional control strategies of single-phase induction machines,including variable voltage control, pole changing control and V/F control, have some disadvantages such as poor dynamic performance, low efficiency, small speed range.With the growing concer about world energy crisis,low-cost operation and the efficient use of energy, new approach is needed for applications in which it is required an improvement of the overall performance of a single-phase drive system.Vector Control and Direct Torque Control technologies, which provide excellent performance and high power-factor control to guarantee the efficient use of energy, are the most popular control strategies in variable-frequency, variable-speed AC machine drive system.However, the two control strategies applied in single-phase induction motor drive system are still in reasearch.What the paper studied is how the two control strategies could be applied in single-phase induction motor drive system:(1) Different converter topologies which could be used to supply the single-phase induction machines will be studied.After compared, the basic drive configuration being applied in this paper is proposed.The converter employed consists of a single-phase rectifier in series with a two-phase three-leg inverter.(2) Universal,the single-phase induction motor studied here is asymmetry.So the approach presented can be applied to any single-phase machine that has two windings.Based on the coordinate transformation from the stationary reference frame to the reference frame aligned along with the rotor-flux vector, flux and torque can be controlled by flux component and torque component of stator current.Simulative is conducted through Matlab and simulation results are presented to demonstrate the main characteristics of the proposed drive system.lt can be demonstrated that vector control system has perfect dynamic performance, fast response and wide speed range.But,calculations associated with vector control are far more demanding,and performance of vector control is also affected by rotor parameters variation.(3) Direct torque control (DTC) technology is a new strategy of AC drive systems. The selected voltage vector could affect both the touque and stator flux.By this way,the command stator flux and torque magnitudes are compared with the respective estimated values,and the errors are processed through hysteresis-band controllers.Simulative is conducted.The results show DTC strategy has fast response, less calculation,simple implementation and good robustness. But it has some disadvantages such as variable switching frequency,torque distortions, and low-speed stator calculation problem.Simulations would also be carried out in order to compare the advantages and disadvantages between rotor-flux-oriented vector control scheme and direct torque control scheme.