Pulse width modulation device for converting direct voltage into a three-phase alternating voltage

• US 5,831,843 A
• Filed: 09/26/1997
• Issued: 11/03/1998
• Est. Priority Date: 03/24/1997
• Status: Expired due to Fees

• Current Assignee: Asea Brown Boveri AB (ABB Limited)
• Original Assignee: Asea Brown Boveri AB (ABB Limited)
• Inventors: Lindberg, Anders, P.ang.lsson, Rolf
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): HAN, YOUNGHUIE JESSICA
• Application Number:
  US08/939,009
• Time in Patent Office: 403 Days
• Field of Search: 363/35, 363/36, 363/37, 363/40, 363/41, 363/43, 363/95, 363/97, 363/98, 363/131, 363/132
• US Class Current: 363/41
• CPC Class Codes: H02M 1/12 Arrangements for reducing harmonics from ac input or output
• CPC Class Codes: H02M 7/5395 by pulse-width modulation

Abstract

A device for converting direct voltage into a three phase alternating voltage having a two level converter connected to a direct voltage network and to an alternating voltage network. A control apparatus for performing pulse width modulation determines the pulse width modulation pattern for each phase by comparing a triangular wave for each phase with a reference alternating voltage. The triangular wave is inverted an even number of times during a fundamental oscillation of the reference alternating voltage and the time position of the inversions of each triangular wave is always such that two triangular waves are half a period displaced with respect to the third.

Claims

1. An apparatus for converting direct voltage into three phase alternating voltage comprising:

first, second and third two level converters connected between a source of direct voltage and to a respective phase of a source of three phase alternating voltage having a plurality of electronic switches;

means for controlling each of said electronic switches in response to a specific modulation pattern for each phase; and

means for generating each of said specific modulation patterns comprising;

(a) means for generating first, second and third reference alternating frequency signals which have a frequency which is a multiple of a frequency of said source of alternating voltage, and which are displaced in phase with respect to each other;

(b) a triangular wave generator for generating first, second, and third triangular waves of the same frequency which is a multiple of the frequency of said first, second and third reference alternating frequency signals;

(c) means for inverting each triangular wave an even number of times during a cycle of a respective first, second and third reference alternating frequency signals so that two of the triangular waves are inverted one half a period from a third of said triangular waves;

(d) means for comparing each of said triangular waves with a respective of said first, second and third reference alternating frequency signal to determine the amplitude difference between said triangular waves and a respective reference alternating signal; and

(e) means for generating first second, and third pulse patterns of negative and positive pulses which represent the time each triangular wave is greater and smaller than a respective reference alternating signal.

2. The apparatus according to claim 1 wherein said means for inverting inverts said triangular waves at substantially constant time intervals.

3. The apparatus according to claim 1 wherein said triangular waves are inverted so that the inversions of said first triangular wave occur at a constant time interval from the inversions of said second triangular wave.

4. The apparatus according to claim 1 wherein said triangular waves are inverted when the direction of voltage increase or decrease of a respective reference alternating voltage changes.

5. The apparatus according to claim 1 wherein said triangular waves are inverted at least two times during a cycle of a respective reference alternating voltage.

6. The apparatus according to claim 1 wherein a respective triangular wave is inverted when the reference alternating voltages for the remaining triangular waves substantially intersect each other.

7. The apparatus according to claim 1 wherein said triangular waves are inverted when the direction of voltage increase or decrease of said triangular waves changes.

8. The apparatus according to claim 1 wherein said alternating reference voltages have a frequency which is at least ten times the frequency of said three phase alternating voltage.

9. The apparatus according to claim 1 wherein said triangular waves have an amplitude which is half the amplitude of the direct voltage.