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This paper presents the analysis, design, and implementation of a cost-effective sensorless control technique for a low-cost four-switch, three-phase inverter brushless dc motor drive. The proposed sensorless technique is based on the detection of zero crossing points (ZCPs) of three voltage functions that are derived from the filtered terminal voltages nuao and nubo. Six commutation instants are provided that coincide to ZCPs of voltage functions. Hence, there is no need for any 30deg or 90deg phase delay that is prevalent in conventional sensorless methods. Two low-pass filters are used for elimination of high-frequency noises and calculation of average terminal voltages. Also, a direct phase current control method is used to control the phase currents in the four-switch inverter. An analytical study on position estimation error is discussed, and a correction method for some typical applications is suggested. The performance of the developed sensorless technique is demonstrated by simulation, and then, it is implemented using TMS320LF2407A DSP. Experimental results are provided to confirm the simulations.