Method and apparatus for compensating for device dynamics and voltage drop in inverter based control systems

• US 6,469,916 B1
• Filed: 10/01/2001
• Issued: 10/22/2002
• Est. Priority Date: 10/01/2001
• Status: Expired due to Term

• Current Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Original Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Inventors: Kerkman, Russel J., Leggate, David
• Primary Examiner(s): Vu, Bao Q.
• Application Number:
  US09/968,072
• Time in Patent Office: 386 Days
• Field of Search: 363/98, 363/41, 363/95, 363/134, 363/132, 318/811, 318/619
• US Class Current: 363/41
• CPC Class Codes: H02M 7/53873 with digital control

Abstract

A method for mitigating current distortion on inverter supply lines that supply a load with power from a PWM inverter, the inverter including a switch and diode bridge constructed using devices that are characterized by losses that cause current distortion, the invert, lines and load together characterized by inductive and capacitive dynamics that also cause line current distortions, the method including identifying both a device drop error due to device operating characteristics and a system related dynamics error due to interaction of system components and using those errors along with a more conventional dead time compensation scheme to modify modulating waveforms used in PWM comparison by a controller.

Claims

1. An apparatus for mitigating distortion at the output terminals of a multi-phase inverter drive system linked via supply lines to a load wherein the system includes an inverter and an inverter controller, the inverter including a plurality of switches that link positive and negative DC buses to the lines at output terminals, the controller receiving modulating signals and carrier signals and comparing the modulating signals and the carrier signals to generate firing pulses to control the switches, the inverter characterized by device drop losses and the system, load and lines characterized by device dynamics losses that cause terminal current distortion, device errors including both device drop and device dynamics losses, the apparatus comprising, for each phase:

a device compensator receiving system phase current signals and, based on the received current signals, generating a device error compensation signal; and

a summer receiving the phase modulating signal and the device error compensation signal and mathematically combining the modulating signal and error signal to generate a compensated modulating signal, the summer providing the compensated modulating signal to the controller for comparison to the carrier signal.

2. The apparatus of claim 1 further including, for each phase, a dead time compensator that generates a dead time compensation error signal se that is provided to the summer, the summer, mathematically combining the dead time compensation signal, the modulating signal and the device error signal for the phase to generate the compensated modulating signals.

3. The apparatus of claim 2 wherein the device compensator includes both a device drop compensator and a device dynamics compensator and the device error signal includes both a device drop error and a device dynamics error signal, the summer, for each phase, mathematically combining each of the modulating signal, the device drop error signal, the device dynamics error signal and the dead time compensation error signal to generate the compensated modulating signals.

4. The apparatus of claim 3 wherein the controller generates a duty cycle count for each phase and the device drop compensator receives the cycle count and generates a device drop error signal as a function of both the current signals and the cycle count.

5. The apparatus of claim 4 wherein the device dynamics compensator receives the cycle count and generates the device dynamics error signal as a function of both the current signals and the cycle count.

6. The apparatus of claim 4 further including a temperature module that determines the temperature of the inverter devices and provides a temperature signal to the device drop compensator, the device drop compensator generating the device drop error signal as a function of the temperature signal, the current signal and the cycle count.

7. The apparatus of claim 1 wherein the current signals are phase current command signals.

8. The apparatus of claim 1 further including current sensors linked to each of the supply lines and wherein the current signals are feedback signals indicating the line currents supplied to the load.

9. The apparatus of claim 1 wherein the device compensator includes a device drop compensator, for each phase, the controller generates a duty cycle count indicating the percent T_α

/T_s of a carrier cycle T_s during which the phase is linked to the positive DC rail, the inverter includes a switch and inverse parallel diode bridge and the device drop error signal V_dde determined by solving the following equations, where i>

0;

10. The apparatus of claim 9 further including a temperature module that determines the temperature of the inverter devices and provides a temperature signal to the device drop compensator, the V_igbt and V_diode values determined by solving the following equations:

11. The apparatus of claim 1 wherein the device compensator includes a device dynamics compensator and wherein the dynamics compensator determines the dynamics error signal by solving the following equations:

where;

I_thresh>

i_u>

0;

12. The apparatus of claim 11 wherein the dynamics error signal is identified by solving the following equations:

13. The apparatus of claim 11 wherein, when i_u>

0 the summer subtracts the device dynamic error from the modulating signal and where i_u<

0 the summer adds the device dynamic error to the modulating signal.

14. The apparatus of claim 11 wherein the controller generates a carrier count that counts back and forth between a minimum number and a maximum number and wherein the dynamics compensator determines the dynamics error signal by solving the following equations, where the carrier count is counting up:

15. The apparatus of claim 11 wherein the K value is determined during a commissioning procedure wherein two different DC values are used to drive the system, resulting currents are compared to expected currents and first and second gain values are generated that cause the resulting currents to essentially equal the expected currents, the K value being the average of the first and second gain values.

17. The method of claim 15 further including the steps of, for each phase, generating a dead time compensation signal as a function of the phase current and wherein the step of mathematically combining includes combining the dead time compensation signal, the modulating signal and the device error signal to generate the compensated modulating signals.

18. The method of claim 17 wherein the step of generating the device error signal includes the steps of generating both a device drop error signal and a device dynamics error signal and wherein the step of mathematically combining includes the step of mathematically combining each of the modulating signal, the device drop error signal, the device dynamics error signal and the dead time compensation error signal to generate the compensated modulating signals.

19. The method of claim 18 wherein the controller generates a duty cycle count for each phase and the step of generating a device compensation signal includes generating a device drop error signal as a function of both the current signals and the cycle count.

20. The method of claim 19 wherein the step of generating the device dynamics error signal includes generating the device dynamics compensation signal as a function of both the current signals and the cycle count.

21. The method of claim 19 further including the steps of determining the temperature of the inverter devices and providing a temperature signal and wherein the step of generating the device drop error signal includes generating the device drop error signal as a function of the temperature signal, the current signal and the cycle count.

16. A method for mitigating distortion at the output terminals of a multi-phase inverter drive system linked via supply lines to a load wherein the system includes an inverter and an inverter controller, the inverter including a plurality of switches that link positive and negative DC buses to the lines at output terminals, the controller receiving modulating signals and carrier signals and comparing the modulating signals and the carrier signals to generate firing pulses to control the switches, the inverter characterized by device drop losses and the system, load and lines characterized by device dynamics losses that cause terminal current distortion, device errors including both device drop and device dynamics losses, the method comprising the steps of, for each phase:

generating a device error compensation signal as a function of system phase current signals;

mathematically combining the modulating signal and error signal to generate a compensated modulating signal; and

providing the compensated modulating signal to the controller for comparison to the carrier signal.

22. The method of claim 16 further including the step of determining the supply line currents and providing the line currents as the phase currents.

23. The method of claim 16 wherein the device compensator includes a device drop compensator, for each phase, the controller generates a duty cycle count indicating the percent T_α

/T_s of a carrier cycle T_s during which the phase is linked to the positive DC rail, the inverter includes a switch and inverse parallel diode bridge and the step of determining the device drop error signal value is determined by solving the following equations, where i>

0;

24. The method of claim 23 further including the step of determining the temperature of the inverter devices and identifying the V_igbt and V_diode values by solving the following equations:

25. The method of claim 16 wherein the step of generating a device error compensation signal includes generating device a device dynamics error signal by solving the following equations:

26. The apparatus of claim 25 wherein the dynamics error signal is identified by solving the following equations:

27. The apparatus of claim 26 wherein, when i_u>

0 the step of mathematically combining includes subtracting the device dynamic error from the modulating signal and where i_u<

0 the step of mathematically combining includes adding the device dynamic error to the modulating signal.

28. The apparatus of claim 26 wherein the controller generates a carrier count that counts back and forth between a minimum number and a maximum number and wherein the step of determining the dynamics error signal includes solving the following equations, where the carrier count is counting up: