An Interior Permanent Magnet machine system comprising: an IPM machine having a nominal operating direct current (dc) bus voltage; an inverter switching circuit adapted to convert the voltage of a dc bus to a terminal voltage applied at terminals of the IPC machine; and a controller connected to a sensing circuit adapted to detect an operating dc bus voltage of the dc bus, the controller adapted to control the IPM machine based on the nominal operating dc bus voltage and the detected operating dc bus voltage, wherein the controller is connected to a sensor adapted to detect an operating rotor shaft speed of the IPM machine, the controller is configured to determine a ratio of the detected operating dc bus voltage to the detected operating rotor shaft speed and to generate a set of direct axis and quadrature axis current commands to control an output torque of the IPM machine based upon the determined ratio; wherein the controller is configured to adjust the determined ratio by multiplying a compensation coefficient with the determined ratio; the adjusted ratio representing a variation of parameters of the IPM machine at different rotor shaft speeds and the controller includes a first processing unit configured to detect the operating dc bus voltage and three phase currents of the IPM machine, a second processing unit configured to detect an angular rotor shaft position of the IPM machine and an operating rotor shaft speed of the IPM machine, and a calculation unit configured to determine the ratio of the detected operating dc bus voltage to the detected operating rotor shaft speed, the set of direct-axis and quadrature-axis current commands being based on the determined ratio, characterized in that the compensation coefficient depends on the dc bus voltage and the rotor shaft speed and that the controller includes two three-dimensional lookup tables configured to determine the set of direct-axis and quadrature-axis current commands based on the determined ratio. an IPM machine having a nominal operating direct current (dc) bus voltage; an inverter switching circuit adapted to convert the voltage of a dc bus to a terminal voltage applied at terminals of the IPC machine; and a controller connected to a sensing circuit adapted to detect an operating dc bus voltage of the dc bus, the controller adapted to control the IPM machine based on the nominal operating dc bus voltage and the detected operating dc bus voltage, wherein the controller is connected to a sensor adapted to detect an operating rotor shaft speed of the IPM machine, the controller is configured to determine a ratio of the detected operating dc bus voltage to the detected operating rotor shaft speed and to generate a set of direct axis and quadrature axis current commands to control an output torque of the IPM machine based upon the determined ratio; wherein the controller is configured to adjust the determined ratio by multiplying a compensation coefficient with the determined ratio; the adjusted ratio representing a variation of parameters of the IPM machine at different rotor shaft speeds and the controller includes a first processing unit configured to detect the operating dc bus voltage and three phase currents of the IPM machine, a second processing unit configured to detect an angular rotor shaft position of the IPM machine and an operating rotor shaft speed of the IPM machine, and a calculation unit configured to determine the ratio of the detected operating dc bus voltage to the detected operating rotor shaft speed, the set of direct-axis and quadrature-axis current commands being based on the determined ratio, characterized in that the compensation coefficient depends on the dc bus voltage and the rotor shaft speed and that the controller includes two three-dimensional lookup tables configured to determine the set of direct-axis and quadrature-axis current commands based on the determined ratio.