Smooth transition control between overmodulation and six step pulse width modulation
AssigneeBorgWarner Inc.
InventorsYang Sun, Caleb Secrest
Life of this patent
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Abstract
A method is provided for producing a smooth transition between overmodulation and six-step operation of a SVPWM-controlled 3-phase electric machine. In one aspect, the method predicts the PWM sample for which the control voltage vector will cross the middle of each SVPWM hexagon sector. Then, based on the current voltage angle and duty cycle, as well as on an estimated future voltage angle and duty cycle, an average duty cycle is calculated and inserted. In addition, a PWM carrier waveform is selected to ensure the PWM pulses applied to each period result in continuous switching states.
Claims20
A controller for controlling a voltage source inverter (VSI) electrically operatively connected between a DC voltage source and a multi-phase AC electric machine, the VSI including a plurality of selectively controllable switches that are activatable and de-activatable according to a space vector pulse width modulated (SVPWM) duty cycle with a rotating control voltage within an inverter voltage limit hexagon defining six sectors, the controller comprising a computing device and software, the computing device and software configured and operable to perform the following steps:
- calculating a normal duty cycle for each phase of the AC electric machine;
- determining the modulation index (MI) and comparing the MI to a predetermined threshold value MI_threshold;
- if MI is less than or equal to MI_threshold, control one or more of the plurality of switches according to the normal duty cycle;
- and
- if MI is greater than MI_threshold;
- calculating a modified duty cycle based on an average ideal control voltage over a full PWM cycle;
- and then
- controlling the one or more of the plurality of switches according to the modified duty cycle.
A controller for controlling a voltage source inverter (VSI) electrically operatively connected between a DC voltage source and a multi-phase AC electric machine as control voltage demand for the electric machine increases, the VSI including a plurality of selectively controllable switches that are activatable and de-activatable according to a space vector pulse width modulated (SVPWM) duty cycle with a rotating control voltage within an inverter voltage limit hexagon defining six sectors, the controller comprising a computing device and software, the computing device and software configured and operable to perform the following steps:
- calculating a modulation index (MI) as a function of the increasing control voltage;
- determining when the MI enters the over-modulation (OVM) region;
- when the MI is in the OVM-I region, calculating a normal duty cycle for each phase of the AC electric machine and then controlling the one or more of the plurality of switches according to the normal duty cycle;
- and
- when the MI enters an OVM-II region, calculating a modified duty cycle based on an average ideal control voltage over a full PWM cycle and then controlling the one or more of the plurality of switches according to the modified duty cycle.
A method for controlling a voltage source inverter (VSI) electrically operatively connected between a DC voltage source and a multi-phase AC electric machine, the VSI including a plurality of selectively controllable switches that are activatable and de-activatable according to a space vector pulse width modulated (SVPWM) duty cycle with a rotating control voltage vector within an inverter voltage limit hexagon defining six sectors, the method comprising:
- calculating a normal duty cycle for each phase of the AC electric machine;
- determining the modulation index (MI) and comparing the MI to a predetermined threshold value MI_threshold;
- if MI is less than or equal to MI_threshold, control one or more of the plurality of switches according to the normal duty cycle;
- and
- if MI is greater than MI_threshold;
- calculating a modified duty cycle based on an average ideal control voltage over a full PWM cycle;
- and then
- controlling the one or more of the plurality of switches according to the modified duty cycle.
Dependencies are inferred from the claim text.