High power motor drive converter system and modulation control

• US 5,910,892 A
• Filed: 06/30/1998
• Issued: 06/08/1999
• Est. Priority Date: 10/23/1997
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Lyons, James Patrick, Vlatkovic, Vlatko, Esser, Albert Andreas Maria, Espelage, Paul Martin
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US09/108,041
• Time in Patent Office: 343 Days
• Field of Search: 363/17, 363/41, 363/43, 363/97, 363/98, 363/131, 363/132
• US Class Current: 363/98
• CPC Class Codes: H02M 7/487 Neutral point clamped inverters
• CPC Class Codes: H02M 7/53876 based on synthesising a desired voltage vector via the selection of appropriate fundamental voltage vectors, and corresponding dwelling times

Abstract

A high power motor drive converter includes a three level neutral point clamped (NPC) output power conversion stage including switches; a split series connected DC capacitor bank coupled in parallel with the NPC output power conversion stage; and a controller for selecting switch positions for controlling the NPC output power conversion stage and controlling a neutral voltage balance of the DC capacitor bank by using space vector modulation and predictive charge calculations.

Claims

1. A high power motor drive converter comprising:

a three level neutral point clamped (NPC) output power conversion stage including switches for supplying power to an AC drive motor;

a split series connected DC capacitor bank coupled in parallel with the NPC output power conversion stage;

a controller for selecting switch positions for controlling the NPC output power conversion stage and controlling a neutral voltage balance of the DC capacitor bank by using space vector modulation and predictive charge calculations;

an input power conversion stage coupled in parallel to the capacitor bank.

2. The converter of claim 1 wherein the input power conversion stage comprises a non-regenerative diode rectifier input power conversion stage or a regenerative three level NPC pulse width modulating input power conversion stage.

3. The converter of claim 1 wherein the input power conversion stage comprises a non-regenerative eighteen pulse diode rectifier input power conversion stage and the converter further comprises a dynamic braking circuit coupled in parallel with the capacitor bank.

4. The converter of claim 2 wherein the input power conversion stage comprises the regenerative three level PC pulse width modulating input power conversion stage and wherein neutral points of the NPC pulse width modulating output power conversion stage and the NPC pulse width modulating input power conversion stage are electrically coupled.

5. The converter of claim 2 further including a plurality of snubber circuits, each snubber circuit coupled to a respective one of the switches.

6. The converter of claim 2 further including a neutral-ground reference network tuned to provide camping for reflected wavefronts propagating on the motor cables.

7. The converter of claim 2 wherein the controller is adapted to use the space vector modulation to control a magnitude and a rotation of a reference voltage vector in a complex voltage plane defined by orthogonal axes and phase voltages.

8. The converter of claim 7 wherein the complex voltage plane is divided into twelve thirty degree sectors based on a reference angle of the reference voltage vector with each thirty degree sector being subdivided into three triangular zones based on the reference angle and the magnitude of the reference voltage vector, wherein a total of thirty six triangular zones are present with twelve triangular zones representing reference voltage vectors having magnitudes less than or equal to one half of a maximum magnitude and having a central home vertex and twenty-four triangular zones on an outer perimeter of the twelve triangular zones, the twenty four triangular zones representing reference voltage vectors having magnitudes greater than or equal to one half of the maximum magnitude and having six outer home vertices.

9. The converter of claim 8 wherein the controller is adapted to create a reference voltage vector switching pattern which begins and ends on a selected home vertex of the central and outer home vertices corresponding to a respective position of the reference voltage vector,

the switching pattern proceeding during a gating period from the selected home vertex to corner vertices defining a triangular zone in which the reference voltage vector is present while selecting the relative dwell times at each corner vertex to achieve the desired reference voltage vector over the gating period.

10. The converter of claim 9 wherein the gating period comprises a first gating period and wherein the controller is adapted to create a second gating period with the switching pattern proceeding to the corner vertices in an opposite direction than the first gating period.

11. The converter of claim 9 wherein, if the magnitude of the reference voltage vector is less than one half of the maximum magnitude, the following set of simultaneous linear equations are used to compute the dwell times at the corner vertices:

##EQU4## wherein d=the angle from the reference voltage vector to the closest axis

dtpwm=the gating period time

V*=the reference voltage vector

V_dc =the measured voltage

δ

=an angle of the reference voltage vector with respect to a side of the triangular zone in which the reference voltage vector is present

k03=the per unit dwell time at the home vertex

k1=the per unit dwell time at a first corner vertex

k2=the per unit dwell time at a second corner vertex

t03=the dwell time at the home vertex

t1=the dwell time at the first corner vertex

t2=the dwell time at the second corner vertex.

12. The converter of claim 11 wherein the controller is adapted to, after the completion of a gating period, determine whether to begin a positive or a negative gating sequence by predicting a net charge that would be injected into a neutral point for each alternative sequence as a sum of a product of a phase current and the neutral dwell time for each phase and selecting the gating sequence based on polarities of the predicted net charges to correct for any differences between the reference voltage vector and a measured voltage.

13. The converter of claim 11 wherein, if the magnitude of the reference voltage vector is greater than or equal to one half of the maximum magnitude, then

if the triangular zone has a side adjacent to a side of one of the twelve triangular zones, equations (1-3) of claim 10 are applied with equation (2) being replaced with the following equation:

##EQU5## or, if the triangular zone does not have a side adjacent to a side of one of the twelve triangular zones, equations (1-3) of claim 10 are applied with equation (2) being replaced with the following equation;

##EQU6##

14. The converter of claim 13 wherein the converter is adapted to adjust dwell times of redundant gating states of a home vertex based on the polarity of the predicted neutral change while keeping a sum of the dwell times of the redundant gating states fixed.

15. The converter of claim 9 wherein each of the home vertices has a respective gating state with an assigned polarity weight index and the controller is adapted to respond to transient conditions by choosing a gating state of a new home vertex to minimize the change in the polarity weight index between a present home vertex and the new home vertex.

22. The method of claim 20 wherein, if the magnitude of the reference voltage vector is greater than or equal to one half of the maximum magnitude, then

if the triangular zone has a side adjacent to a side of one of the twelve triangular zones, equations (1-3) of claim 10 are applied with equation (2) being replaced with the following equation:

##EQU8## or, if the triangular zone does not have a side adjacent to a side of one of the twelve triangular zones, equations (1-3) of claim 10 are applied with equation (2) being replaced with the following equation;

##EQU9##

16. A method of controlling a high power motor drive converter including a three level neutral point clamped (NPC) output power conversion stage including switches for supplying power to an AC drive motor, a split series connected DC capacitor bank coupled in parallel with the NPC output power conversion stage, the method comprising:

selecting switch positions for controlling the NPC output power conversion stage and controlling a neutral voltage balance of the DC capacitor bank by using space vector modulation to control a magnitude and a rotation of a reference voltage vector in a complex voltage plane defined by orthogonal axes and phase voltages.

17. The method of claim 16 further including dividing the voltage plane into twelve thirty degree sectors based on a reference angle of the reference voltage vector and subdividing each thirty degree sector into three triangular zones based on the reference angle and the magnitude of the reference voltage vector, wherein a total of thirty six triangular zones are present with twelve triangular zones representing reference voltage vectors having magnitudes less than or equal to one half of a maximum magnitude and having a central home vertex and twenty-four triangular zones on an outer perimeter of the twelve triangular zones, the twenty four triangular zones representing reference voltage vectors having magnitudes greater than or equal to one half of the maximum magnitude and having six outer home vertices.

18. The method of claim 17 further comprising creating a reference voltage vector switching pattern which begins and ends on a selected home vertex of the central and outer home vertices corresponding to a respective position of the reference voltage vector,

the switching pattern proceeding during a gating period from the selected home vertex to corner vertices defining a triangular zone in which the reference voltage vector is present while selecting the relative dwell times at each corner vertex to achieve the desired reference voltage vector over the gating period.

19. The method of claim 18 wherein the gating period comprises a first gating period and further including creating a second gating period with the switching pattern proceeding to the corner vertices in an opposite direction than the first gating period.

20. The method of claim 18 wherein, if the magnitude of the reference voltage vector is less than one half of the maximum magnitude, the following set of simultaneous linear equations are used to compute the dwell times at the corner vertices:

##EQU7## wherein d=the angle from the reference voltage vector to the closest axis

dtpwm=the gating period time

V*=the reference voltage vector

V_dc =the measured voltage

δ

=an angle of the reference voltage vector with respect to a side of the triangular zone in which the reference voltage vector is present

k03=the per unit dwell time at the home vertex

k1=the per unit dwell time at a first corner vertex

k2=the per unit dwell time at a second corner vertex

t03=the dwell time at the home vertex

t1=the dwell time at the first corner vertex

t2=the dwell time at the second corner vertex.

21. The method of claim 20 further including, after the completion of a gating period, determining whether to begin a positive or a negative gating sequence by predicting a net charge that would be injected into a neutral point for each alternative sequence as a sum of a product of a phase current and the neutral dwell time for each phase and selecting the gating sequence based on polarities of the predicted net charges to correct for any differences between the reference voltage vector and a measured voltage.

23. The method of claim 17 wherein each of the home vertices has a respective gating state with an assigned polarity weight index and the controller is adapted to respond to transient conditions by choosing a gating state of a new home vertex to minimize the change in the polarity weight index between a present home vertex and the new home vertex.