# Online Efficiency Optimization and Speed Sensorless Control of Single-Phase Induction Motors
## 7 Conclusions  
In this paper, a novel single-phase inverter-based drive has been proposed to provide us with speed control and optimum efficiency for SPIMs. Since SPIMs are a low rating and rather inexpensive kind of motor, being affordable and mechanical sensor-free were introduced as the major issues to be addressed. To realize closed loop speed control without using mechanical sensors, a new speed estimation technique has been addressed. This method is developed based on the fact that STCR is dependent on the slip and operating frequency. Accordingly, the slip is estimated based on the known operating frequency and measured value of STCR using a NN. The estimated slip is then used to obtain the rotor speed, which is fed to the speed controller which determines the reference frequency. To minimize the motor losses, the voltage magnitude is adjusted based on an online efficiency optimization method. In this method, the optimum operating voltage is indirectly calculated by using a PI controller which attempts to realize the optimum SCTR. The advantage of this strategy is that unlike optimal voltage, the optimum SCTR is independent of the load but only depends on the frequency and motor parameters. The optimum SCTR is first calculated based on the operating frequency from a lookup table (offline) and then updated using gradient decent algorithm (online). The foremost advantage of the proposed online optimization method comparing to the preceding methods is its independency upon motor parameters. The proposed control strategy has been verified by simulation results. The simulation results show that the proposed control scheme provides a considerable enhancement in term of energy efficiency while realizing speed regulation. Although the  
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