Patent ID: 8639405
Filing Date: 2014-01-28
Classification: B60L,B60W,H02P,Y02T

Abstract:
1. An electric motor drive system for an electric vehicle provided with an alternating-current electric motor for generating vehicle driving force, comprising: a direct-current power supply; a converter structured so as to output a second direct-current voltage that is equal to or higher than a first direct-current voltage from the direct-current power supply to a direct-current power supply line by variably controlling the first direct-current voltage according to a voltage command value; an inverter that is structured so as to perform power conversion between direct-current power in the direct-current power supply line and alternating-current power that drives the alternating-current electric motor, by a plurality of switching elements such that the alternating-current electric motor operates according to an operating command; a control mode selecting unit that controls the inverter according to one of two modes, one mode being a first control mode that is applied when a modulation factor of the power conversion, which is expressed by the ratio of a fundamental wave component of the amplitude of a line voltage of the alternating-current electric motor to the second direct-current voltage, is equal to or less than a predetermined value, and the other mode being a second control mode for controlling the alternating-current electric motor with a modulation factor that is higher than that of the first control mode; and a voltage command value setting unit that sets the voltage command value for the converter, wherein the voltage command value setting unit includes i) a required torque response determining unit that determines the degree of torque response required of the alternating-current electric motor, according to the state of the electric vehicle, ii) a first setting unit that sets the voltage command value within a range of the second direct-current voltage where the first control mode is able to be applied, according to the operating state of the alternating-current electric motor when it is determined that the required torque response is higher than a predetermined level, and iii) a second setting unit that sets the voltage command value such that the second control mode is able to be applied, according to the operating state of the alternating-current electric motor when it is determined that the required torque response is not higher than the predetermined level.