Patent ID: 8729846

Claim:
A motor drive system comprising: an inverter that supplies power to a three-phase motor by supplying alternating current to three phases of the three-phase motor, the inverter including at least three upper arms and at least three lower arms, each of the at least three upper arms and each of the at least three lower arms including a switching element and a freewheeling diode that are connected in parallel; and a control unit that performs control of the switching elements included in the inverter by switching between a first control, a second control, and a third control, wherein the first control puts the switching elements in a non-conduction state and thereby causes the inverter to stop the supply of alternating current to the three phases, the second control causes the switching elements to repeatedly switch between a conduction state and the non-conduction state and thereby causes the inverter to perform the supply of alternating current to the three phases, and the third control places and maintains a switching element of an upper arm, among the at least three upper arms, and a switching element of a lower arm, among the at least three lower arms, in the conduction state from commencement of the third control until commencement of the supply of alternating current to the three phases, the switching element of the upper arm corresponding to a phase, among the three phases, through which alternating current is to flow in a first direction entering the three-phase motor upon commencement of the supply of alternating current to the three phases, the switching element of the lower arm corresponding to a phase, among the three phases, through which alternating current is to flow in a second direction exiting the three-phase motor upon commencement of the supply of alternating current to the three phases, the control unit controls the switching elements included in the inverter by performing an intermittent control of (i) repeatedly performing a set of controls that includes the first control, the third control, and the second control performed in the stated order, and (ii) ensuring that, in every repetition of the set of controls, an average of a torque output by the three-phase motor during the period equals a demanded torque, and in every repetition of the set of controls, the control unit switches from the first control to the third control, and then to the second control, thereby causing the inverter to stop the supply of alternating current to the three phases and then to commence the supply of alternating current to the three phases.