System and method for implementing a remedial electrical short
View Patent ↗A vehicle includes a polyphase, permanent magnet synchronous electric machine, DC and AC buses, a battery module, a traction power inverter module (TPIM), and a controller. The controller, which is in communication with the TPIM, executes a method to detect a fault condition, fixes the pulse width modulation (PWM) duty cycles of all phases of the electric machine to 50% such that all phases switch simultaneously, and applies a polyphase OPEN state to the AC bus in response to the detected fault condition. The controller then transitions to a polyphase SHORT state by automatically inserting an adjustable deadtime at each PWM switching transition of the TPIM over a calculated ramp duration, thereby transitioning from an initial deadtime to a minimum deadtime over the calculated ramp duration. The transition reduces peak overshoot of the negative d-axis current of the machine during the fault condition.
1. A system comprising:
a polyphase permanent magnet synchronous electric machine having a negative d-axis current;
a DC bus;
an AC bus;
a DC power supply;
a power inverter module (PIM) that is electrically connected to the DC power supply via the DC bus, and to the electric machine via the AC bus, wherein the PIM includes a set of semiconductor switches that are controlled to convert an AC voltage to a DC voltage, and vice versa; and
a controller in communication with the PIM that is configured to:
detect a fault condition in the system;
determine an initial deadtime;
set pulse width modulation (PWM) duty cycles of all phases of the electric machine to 50% such that all phases switch simultaneously;
apply a polyphase OPEN state to the AC bus in response to the detected fault condition; and
transition to a polyphase SHORT state as a remedial action by automatically inserting an adjustable deadtime at each PWM switching transition of the PIM over a calculated ramp duration, thereby transitioning from the initial deadtime to a minimum deadtime over the calculated ramp duration;
wherein the transition reduces peak overshoot of the negative d-axis current of the electric machine during the detected fault condition.
2. The system of claim 1 , wherein the electric machine is a three-phase AC traction motor, and wherein the polyphase OPEN state and the polyphase SHORT state are a three-phase OPEN and a three-phase SHORT state, respectively.
3. The system of claim 1 , wherein the controller imposes the transition by selectively transmitting a set of command signals to the PIM to implement right-justified or left-justified PWM switching via the semiconductor switches.
4. The system of claim 1 , wherein the controller automatically inserts the adjustable deadtime, at each PWM switching transition of the PIM, to thereby avoid cross-conduction of the semiconductor switches.
5. The system of claim 1 , wherein the controller is configured to compute the transition time as a function of the fundamental electrical period of the electric machine.
6. The system of claim 1 , wherein the controller is configured to:
determine a rotational speed of the electric machine;
receive a DC link voltage from the DC bus;
calculate, via a processor, a back electromotive force (EMF) of the electric machine using the determined speed; and
compute, using the processor, the initial deadtime based upon a ratio of the back EMF to the DC link voltage.
7. The system of claim 1 , wherein the controller enables and phases in deadtime compensation over a computed time to complete a transition from the minimum deadtime to zero volts.
8. The system of claim 1 , wherein the controller is configured to:
determine when a motor speed sensor is faulty or unavailable;
measure a current vector angle of phase currents of the electric machine when the motor speed sensor is faulty or unavailable and current is flowing in the electric machine;
calculate a filtered time derivative of the measured current vector angle; and
estimate a speed of the electric machine using the filtered time derivative.
9. The system of claim 1 , wherein the controller, within one PWM switching period, time-averages brief SHORT and OPEN state segments.
10. A method comprising:
detecting a fault condition in a vehicle having a polyphase permanent magnet synchronous electric machine using a controller, wherein the controller is in communication with a power inverter module (PIM) having a set of semiconductor switches, and wherein the PIM is electrically connected to a DC battery module and to the electric machine;
setting the pulse width modulation (PWM) duty cycles of all phases of the electric machine to 50% such that all phases switch simultaneously;
applying a polyphase OPEN state to an AC bus in response to the detected fault condition;
determining an initial deadtime; and
transitioning over a calculated ramp duration to a polyphase SHORT state as a remedial action by automatically inserting an adjustable deadtime at each PWM switching transition of the TPIM, including transitioning from the initial deadtime to a minimum deadtime over the calculated ramp duration, to thereby reduce peak overshoot of a negative d-axis current of the electric machine during the detected fault condition.
11. The method of claim 10 , further comprising:
setting the initial deadtime to a maximum deadtime value (T d — max ) as a function of the PWM switching period and a minimum pulse width limit of the TPIM.
12. The method of claim 11 , wherein the function is executed by the controller, and is equal to:
T
d
_
max
=
T
SW
2
-
T
min
_
PW
where T SW is the PWM switching period and T min — PW is the minimum pulse width limit of the TPIM.
13. The method of claim 10 , further comprising:
transmitting command signals from the controller to the PIM to implement right-justified or left-justified PWM switching via the semiconductor switches.
14. The method of claim 10 , further comprising:
automatically inserting the adjustable deadtime, at each PWM switching transition of the PIM, to avoid cross-conduction of the semiconductor switches.
15. The method of claim 10 , further comprising:
computing the transition time as a function of the fundamental electrical period of the electric machine.
16. The method of claim 10 , further comprising:
measuring a rotational speed of the electric machine;
receiving a DC link voltage;
calculating a back electromotive force (EMF) of the electric machine using the measured rotational speed; and
computing the initial deadtime using a ratio of the back EMF to the DC link voltage.
17. The method of claim 10 , further comprising:
using deadtime compensation to phase in a transition from the minimum deadtime to zero volts.
18. The method of claim 10 , further comprising:
measuring a current vector angle of the phase currents when a motor speed sensor is faulted and current is flowing in the electric machine;
calculating a filtered time derivative of the measured current vector angle;
estimating a speed of the electric machine using the filtered time derivative;
calculating the back electromotive force (EMF) of the electric machine using the estimated speed; and
computing the initial deadtime using a ratio of the back EMF to the DC link voltage.
19. A vehicle comprising:
an electric traction motor, wherein the electric traction motor is a three-phase, interior permanent magnet synchronous electric machine having a negative d-axis current;
a transmission coupled to the electric traction motor, wherein the transmission receives motor torque from the electric traction motor;
a DC bus;
an AC bus;
a DC power supply;
a traction power inverter module (TPIM) electrically connected to the DC power supply via the DC bus, and to the electric traction motor via the AC bus, wherein the TPIM includes a set of semiconductor switches that are controlled to convert an AC voltage to a DC voltage, and vice versa; and
a controller in communication with the TPIM that is configured to:
detect a fault condition of the vehicle;
set pulse width modulation (PWM) duty cycles of all three phases of the traction motor to 50% such that all three phases switch simultaneously;
apply a three-phase OPEN state to the AC bus in response to the detected fault condition;
determine an initial deadtime; and
transition to a three-phase SHORT state as a remedial action by automatically inserting an adjustable deadtime at each PWM switching transition of the TPIM over a calculated ramp duration, thereby transitioning from the initial deadtime to a minimum deadtime over the calculated ramp duration;
wherein the transition reduces peak overshoot of the negative d-axis current of the traction motor during the fault condition.
20. The vehicle of claim 19 , wherein the transmission includes a gear set having first, second, and third nodes, and wherein:
the electric traction motor is selectively connected to the first node or directly connected to the third node; and
the second node is directly connected to an output member of the transmission.