Electric motor and motor control

A system for pumping a liquid comprising:

• an impeller;
• a volute in which the impeller resides;
• a wet rotor-type electric motor configured to drive the impeller, the electric motor comprising a stator, a rotor, a two-pole permanent magnet, and a winding;
• a Hall sensor configured to sense the position of the permanent magnet and generate position data indicative of rotor position;
• a single-phase electric power supply circuit configured to receive an alternating current having a first frequency and provide electric power to the electric motor, wherein the single-phase electric power supply circuit comprises a split rail circuit;
• a motor controller being configured to control the single-phase electric power supply circuit, wherein the motor controller comprises a memory and a processor;
• wherein the memory comprises a look-up table that stores a digital representation of a counter-electromotive force waveform associated with the electric motor, wherein the digital representation comprises a triangle waveform approximation of the counter-electromotive force;
• wherein the processor is configured to execute a motor control software that is configured to (a) receive the position data indicative of rotor position, (b) based on the received position data, electronically commutate the electric motor at a second frequency, wherein the second frequency is less than line frequency and not equal to the first frequency, (c) generate an index into the look-up table based on the received position data by calculating the sum of a waveform angle and an advance angle, (d) retrieve a value stored in the look-up table at the generated index, (e) execute a pulse width modulation routine based on the retrieved value to thereby drive the electric motor with a drive waveform that is substantially similar to the counter-electromotive force waveform, (f) start the electric motor in a predetermined start direction by executing a start-up sequence that comprises (i) driving the motor with an alignment pulse that comprises a single polarity pulse width modulation burst, and (ii) driving the started motor in a ramp-up mode by applying a gradually increasing frequency of pulse width modulation pulses to the winding;
• and
• wherein said rotor position data comprises one of a rising edge and a falling edge, and wherein the waveform angle is 0 degrees for a rising edge and 180 degrees for a falling edge.