Power factor controller for active converter

• US 5,808,880 A
• Filed: 08/30/1996
• Issued: 09/15/1998
• Est. Priority Date: 08/30/1996
• Status: Expired due to Term

• Current Assignee: Otis Elevator Company (Otis Worldwide Corp.)
• Original Assignee: Otis Elevator Company (Otis Worldwide Corp.)
• Inventors: Marvin, Daryl J.
• Primary Examiner(s): Berhane, Adolf
• Assistant Examiner(s): JARDIEU, DEREK
• Application Number:
  US08/701,914
• Time in Patent Office: 746 Days
• Field of Search: 363/35, 363/37, 363/51, 323/207, 323/208, 323/209, 323/210, 323/211, 318/376, 318/801, 318/802, 318/803, 318/804
• US Class Current: 363/37
• CPC Class Codes: B66B 1/302 for energy saving
• CPC Class Codes: B66B 1/304 with starting torque control
• CPC Class Codes: H02M 1/4233 using a bridge converter comprising active switches

Abstract

A method and apparatus for controlling a regenerative drive having line and load converters connected by a DC link, the load converter for connection to an AC machine, and the line converter for connection to an AC source/sink by means of line reactors, the drive for causing real power to flow in the line reactors to control the DC link voltage at a selected DC voltage and for determining when a commanded line converter voltage exceeds a selected maximum line converter voltage for also causing reactive power to flow in the line reactors to reduce the line converter voltage required to control the real power flow.

Claims

1. A method of controlling a regenerative drive having line and load converters connected by a direct current (DC) link, the load converter for connection to an alternating current (AC) machine and the line converter for connection to an AC source/sink by means of line reactors, comprising the steps of:

controlling real power flow in the line reactors for controlling a voltage of said DC link at a selected magnitude; and

summing a line converter AC voltage command signal and a selected maximum line converter AC voltage signal for providing a control signal having a magnitude indicative of a difference between said line converter AC voltage command signal and said maximum line converter AC voltage signal; and

causing, in response to said control signal, reactive power to flow in the line reactors to reduce the line controller AC voltage required to control the real power flow.

2. A method of controlling a line converter (24) of a regenerative drive controlled by a line converter control for providing line converter phase voltage command signals for controlling said line converter by means of pulse width modulation, said line converter for connection by means of line reactors to an AC source/sink (26), comprising the steps of:

summing (92) a commanded DC link (28) voltage (94) and an actual DC link voltage (96) for providing a real current command signal (86) having a magnitude indicative of a difference between said commanded DC link voltage and said actual DC link voltage;

summing (84) said real current command signal (86) and an actual real current signal (82a), for providing a real voltage command signal (108) having a magnitude indicative of a difference between said real current command signal and said actual real current signal;

summing (72) a maximum line converter voltage (74) and a commanded line converter voltage (70), for providing an error signal (76a) having a magnitude indicative of a difference between said maximum line converter voltage and said commanded line converter voltage;

integrating said error signal without any proportional gain for providing a reactive current command signal (58);

summing (78) said reactive current command signal (58) and an actual reactive current signal (80), for providing a reactive voltage command signal (106) having a magnitude indicative of a difference between said reactive current command signal and said actual reactive current signal;

squaring said real voltage command signal (108), squaring said reactive voltage command signal (106), and summing said squared reactive voltage command signal and said squared real voltage command signal, for providing the commanded line converter voltage (70); and

processing (110) said real voltage command signal (108) and said reactive voltage command signal (106), for providing said line converter phase voltage command signals (114).

3. A regenerative drive for connection to an alternating current (AC) machine (12), and for connection to plural line inductors (L_a, L_b, L_c) connected to an AC source/sink (26), said plural line inductors for conducting AC, said regenerative drive comprising:

a line converter (24), responsive to line AC from the plural line inductors, for providing direct current (DC) to a DC link (28) having a capacitor (33) thereacross;

a load converter (30), responsive to DC from the DC link, for converting the DC from the DC link to motoring AC and for providing said motoring AC to the AC machine in a motoring mode and responsive to regenerative AC from the AC machine in a regenerative mode, for converting said regenerative AC to DC for providing DC to the DC link, wherein said line converter is responsive to DC from the DC link with said AC machine in said regenerative mode, for converting said DC to AC and providing said AC for conduction via the plural line inductors to the AC source/sink; and

a line converter control (36), responsive to a plurality of input signals for providing a plurality of output signals for controlling said line converter for controlling said AC conducted on said plural line inductors, characterized in that an integral control loop is used to control a reactive part of said AC conducted on said plural line inductors to reduce a line converter voltage required to control a real part of said AC conducted on said plural line inductors, without any proportional gain in said control loop.

4. Method of controlling a line converter of a regenerative drive for connection by means of line reactors to an alternating current (AC) source/sink having a line voltage that fluctuates about a nominal value in a tolerance band, comprising the steps of:

determining that a commanded or sensed line converter AC voltage exceeds a level due to said line voltage rising above said nominal value in said tolerance band, and thereafter

causing reactive current to flow, as well as real current, in the line reactors to reduce a line converter AC voltage required to control the real current.

5. Apparatus for controlling a line converter of a regenerative drive for connection by means of line reactors to an alternating current (AC) source/sink having a line voltage that fluctuates about a nominal value in a tolerance band, comprising:

means for determining that a commanded or sensed line converter AC voltage exceeds a level due to said line voltage rising above said nominal value in said tolerance band; and

means for causing reactive current to flow, as well as real current, in the line reactors to reduce a line converter AC voltage required to control the real current.