Steady-State Performance of a Novel Dual-Capacitor Three-Phase Induction Motor in Single-Phase Operation Mode
Single-phase induction motors are powered by a single-phase AC power supply.The air gap field of a single-phase asynchronous motor is an elliptical rotating field that includes a negative sequence rotating field,which causes the motor to produce a braking torque during operation.As a result,the motor's output torque and efficiency are reduced.Generally,applying sinusoidal windings in single-phase motors results in low utilization of the motor stator slot area.Single-phase motors have low efficiency,large size,and high-temperature rise.By connecting appropriate capacitors to the three-phase induction motor windings,the three-phase induction motor can be supplied by a single-phase AC power.This paper proposes a novel windings and capacitors connection method,where the windings of the three-phase induction motor are connected to two capacitors.The connection circuit between capacitors and the three-phase windings for the new single-phase operation motor is given.Then,the phasor diagram about the voltages and the currents is derived.The positive-sequence and negative-sequence equivalent circuits are established.Based on the symmetrical component method,the symmetrical operation condition is analyzed,and the optimal matched capacitors are obtained.Subsequently,the calculation method of motor performance for the new single-phase operation motor in a steady state is investigated.The proposed scheme applies to a standard 550 W three-phase induction motor(Y2-801-4).The influence of the capacitance on motor performance is investigated,and the optimal two capacitances are determined.According to the FEM analysis,currents in three-phase windings are almost balanced,and the distribution of the magnetic field is rational.The air-gap flux density of the new single-phase motor is approximate to the original three-phase induction motor.The performance tests under three-phase and single-phase operation conditions are carried out.The three winding currents during single-phase operation is almost symmetrical,which agrees with the theory.The efficiency,power factor,and maximum torque are 70.2%,1,and 5.8 N·m,respectively.The efficiency is slightly lower than the three-phase motor(71.8%),and the power factor is far higher than the three-phase motor(0.75).The temperature rise of the two operation modes is 72.6 K and 69.8 K,respectively.The temperature rise of the single-phase operation is slightly higher,but it can satisfy the operation requirement.The locked-rotor torque is 1.9 N·m,and the locked-rotor torque ratio is 0.52.The locked-rotor torque is smaller than the three-phase motor and much bigger than the standard single-phase induction motor with an operating capacitor(YY8014,550 W,the locked-rotor torque is 1.3 N·m,locked-rotor torque ratio is 0.35).Compared with the YY8014,the efficiency is increased by 6%,the current is reduced by 15%,and the volume of the effective materials is decreased by 17%.The following conclusions can be drawn.The proposed capacitor connection method is practical.The experiments verify the new scheme and the analysis process.The new single-phase motor's performance is approximate to the original three-phase motor and much better than the common single-phase motor.
Three-phase induction motorsingle-phase operationsymmetrical component methodsteady-state performancesingle-phase induction motor
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