System and method for variable DC bus voltage coupled to inverters

A method for controlling a first inverter and a second inverter that are coupled to variable DC voltage bus, in which a plurality of inverter inputs are coupled to a variable direct current (DC) voltage bus and in which a plurality of alternating current inverter outputs are connected to a first variable load and a second variable load, the method comprising:

• measuring an observed voltage level of the variable DC voltage bus for a time interval;
• in the first inverter, determining a first torque command and/or a first speed command comprising a first direct-axis current/voltage command and a first quadrature-axis current/voltage command demanded by real time, transient load conditions on a first electric machine to maintain operation for the time interval based on the first variable load of the first electric machine;
• in the second inverter, determining a second torque command and/or a second speed command comprising a second direct-axis current/voltage command and a second quadrature-axis current/voltage command demanded by real time, transient load conditions on a second electric machine to maintain operation for the time interval based on the second variable load of the second electric machine;
• estimating a minimum required variable DC bus voltage based on the first direct-axis current/voltage command, the first quadrature-axis current/voltage command, the second direct-axis current/voltage command, and the second quadrature-axis current/voltage command for a respective time interval, wherein a reserved component of the variable DC bus voltage is configured to be available to meet the first and second torque commands that are demanded by the real-time transient load conditions on the first electric machine and second electric machine associated with propulsion of a vehicle or driving one or more implements of a vehicle, wherein the estimating of the variable DC bus voltage further comprises estimating the variable DC bus voltage in accordance with the following equation:
• if Vdc_est(EM1)>Vdc_est(EM2), then use Vdc_cmd=Vdc_est(EM1), else Vdc_cmd=VDCThresh,
• where Vdc_est(EM1) is the minimum estimated variable DC bus voltage for the first electric motor;
• where Vdc_est(EM2) is the minimum estimated variable DC bus voltage for the second electric motor,
• where Vdc_cmd is the commanded estimated variable DC bus voltage,
• and VDCThresh is a fixed DC bus voltage threshold;
• and
• providing the estimated minimum required variable DC bus voltage to a voltage regulator to adjust the observed voltage level of the variable DC voltage bus to the estimated minimum required variable DC bus voltage to maintain the operation, as commanded by the current/voltage commands, of the first electric machine under the first variable load and the second electric machine under the second variable load at the time interval.