Voltage generation with high modulation indices in inverter drives
Circuits, methods, and systems for driving a load are described. An exemplary driving circuit may include a plurality of switching devices and a controller electrically connected to the switching devices. The controller may be configured to receive a reference voltage signal indicating a target voltage for the driving circuit to generate to drive the load. The reference voltage signal may correspond to a reference space vector in a reference frame. The controller may also be configured to determine that the reference space vector falls within a holding region in which the reference voltage signal is subject to over-modulation. The controller may then generate an adjusted reference voltage signal by adjusting the reference space vector to match a predetermined space vector associated with the holding region. In addition, the controller may be configured to provide the adjusted reference voltage signal to the plurality of switching devices to drive the load.
1. A driving circuit for driving a load, comprising:
a plurality of switching devices electrically connected to the load; and
a controller electrically connected to the plurality of switching devices, wherein the controller is configured to:
receive a reference voltage signal indicating a target voltage for the driving circuit to generate to drive the load, the reference voltage signal corresponding to a reference space vector in a reference frame in which a field flux linkage component and a torque component of the reference voltage signal are decoupled to orthogonal directions, wherein the reference space vector represents a combination of the decoupled field flux linkage component and the torque component of the reference voltage signal;
determine that the reference space vector falls within a holding region in which the reference voltage signal is subject to over-modulation;
determine a first holding angle and a second holding angle;
when an angle of the reference voltage is 0 degree and the first holding angle, set an adjusted reference voltage to a first voltage;
when an angle of the reference voltage is between the first holding angle and the second holding angle, vary the adjusted reference voltage linearly with an angle of the adjusted reference voltage being equal to the angle of the reference voltage;
when an angle of the reference voltage is between the second holding angle and 60 degrees, set the adjusted reference voltage to a second voltage; and
provide the adjusted reference voltage signal to the plurality of switching devices to drive the load.
2. The driving circuit of claim 1 , wherein the controller is further configured to:
determine a modulation index based on the reference voltage signal, the modulation index representing a ratio between a magnitude of a fundamental wave of an output voltage generated by the driving circuit resulting from the reference voltage signal and a magnitude of a fundamental wave of a maximum output voltage that can be generated by the driving circuit; and
determine a boundary of the holding region when the modulation index is greater than a predetermined threshold.
3. The driving circuit of claim 1 , wherein:
the plurality of switching devices include six power electronic devices configured to form a three-phase inverter;
a predetermined space vector is selected from six non-zero switching vectors supported by the three-phase inverter, each non-zero switching vector corresponding to a different switching state of the three-phase inverter; and
an angle of the predetermined space vector falls within the holding region.
4. The driving circuit of claim 1 , wherein a magnitude of the reference space vector is greater than 0.606 time of a DC voltage applied to the plurality of switching devices.
5. The driving circuit of claim 2 , wherein the controller is further configured to:
retrieve information of a predetermined holding angle corresponding to the modulation index from a lookup table, the predetermined holding angle indicating the boundary of the holding region.
6. The driving circuit of claim 2 , wherein the controller is further configured to:
calculate a holding angle corresponding to the modulation index, the holding angle indicating the boundary of the holding region.
7. A method for driving a load through a driving circuit including a plurality of switching devices, the method comprising:
receiving a reference voltage signal indicating a target voltage to be generated by the driving circuit to drive the load, the reference voltage signal corresponding to a reference space vector in a reference frame in which a field flux linkage component and a torque component of the reference voltage signal are decoupled to orthogonal directions, wherein the reference space vector represents a combination of the decoupled field flux linkage component and the torque component of the reference voltage signal;
determining that the reference space vector falls within a holding region in which the reference voltage signal is subject to over-modulation;
determining a first holding angle and a second holding angle;
when an angle of the reference voltage signal is smaller than the first holding angle, setting an angle of an adjusted reference angle to 0 degree;
when the angle of the reference voltage is between the first holding angle and the second holding angle, setting the angle of the adjusted reference voltage equal to the angle of the reference voltage;
when the angle of the reference voltage is between the second holding angle and 60 degrees, setting the angle of the adjusted reference voltage to 60 degrees; and
providing the adjusted reference voltage signal to the plurality of switching devices to drive the load.
8. The method of claim 7 , comprising:
determining a modulation index based on the reference voltage signal, the modulation index representing a ratio between a magnitude of a fundamental wave of an output voltage generated by the driving circuit resulting from the reference voltage signal and a magnitude of a fundamental wave of a maximum output voltage that can be generated by the driving circuit; and
determining a boundary of the holding region when the modulation index is greater than a predetermined threshold.
9. The method of claim 7 , wherein:
the plurality of switching devices include six power electronic devices configured to form a three-phase inverter;
a predetermined space vector is selected from six non-zero switching vectors supported by the three-phase inverter, each non-zero switching vector corresponding to a different switching state of the three-phase inverter.
10. The method of claim 7 , wherein a magnitude of the reference space vector is greater than 0.606 time of a DC voltage applied to the plurality of switching devices.
11. The method of claim 8 , comprising:
retrieving information of a predetermined holding angle corresponding to the modulation index from a lookup table, the predetermined holding angle indicating the boundary of the holding region.
12. The method of claim 8 , comprising:
calculating a holding angle corresponding to the modulation index, the holding angle indicating the boundary of the holding region.
13. An electric motor propulsion system of an electric vehicle, the system comprising:
an electric motor configured to output torque for propelling the electric vehicle; and
a motor control system configured to control operations of the electric motor, wherein the motor control system includes a driving circuit including:
a plurality of switching devices electrically connected to the electric motor; and
a controller electrically connected to the plurality of switching devices, wherein the controller is configured to:
receive a reference voltage signal indicating a target voltage for the driving circuit to generate to drive the electric motor, the reference voltage signal corresponding to a reference space vector in a reference frame in which a field flux linkage component and a torque component of the reference voltage signal are decoupled to orthogonal directions, wherein the reference space vector represents a combination of the decoupled field flux linkage component and the torque component of the reference voltage signal;
determine that the reference space vector falls within a holding region in which the reference voltage signal is subject to over-modulation;
determine a first holding angle and a second holding angle;
when an angle of the reference voltage is smaller than the first holding angle, set an angle of an adjusted reference to 0 degree;
when the angle of the reference voltage is between the first holding angle and the second holding angle, set the angle of an adjusted reference voltage equal to an angle of the reference voltage;
when the angle of the reference voltage is between the second holding angle and 60 degrees, set the angle of an adjusted reference voltage to 60 degrees; and
provide the adjusted reference voltage signal to the plurality of switching devices to drive the electric motor.
14. The electric motor propulsion system of claim 13 , wherein the controller is further configured to:
determine a modulation index based on the reference voltage signal, the modulation index representing a ratio between a magnitude of a fundamental wave of an output voltage generated by the driving circuit resulting from the reference voltage signal and a magnitude of a fundamental wave of a maximum output voltage that can be generated by the driving circuit; and
determine a boundary of the over-modulation region when the modulation index is greater than a predetermined threshold.
15. The electric motor propulsion system of claim 13 , wherein:
the plurality of switching devices include six power electronic devices configured to form a three-phase inverter;
a predetermined space vector is selected from six non-zero switching vectors supported by the three-phase inverter, each non-zero switching vector corresponding to a different switching state of the three-phase inverter.
16. The electric motor propulsion system of claim 14 , wherein the controller is further configured to:
retrieve information of a predetermined holding angle corresponding to the modulation index from a lookup table, the predetermined holding angle indicating the boundary of the holding region.
17. The electric motor propulsion system of claim 14 , wherein the controller is further configured to:
calculate a holding angle corresponding to the modulation index, the holding angle indicating the boundary of the holding region.