Motor drive with VAR compensation

• US 7,800,348 B2
• Filed: 11/21/2007
• Issued: 09/21/2010
• Est. Priority Date: 11/21/2007
• Status: Active Grant

• Current Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Original Assignee: Rockwell Automation Technologies Incorporated (Allen-Bradley Co., Inc.)
• Inventors: Zargari, Navid R.
• Primary Examiner(s): Sterrett; Jeffrey L
• Assistant Examiner(s): Finch, III; Fred E
• Application Number:
  US11/943,671
• Publication Number:
  US 20090128083A1
• Time in Patent Office: 1,035 Days
• Field of Search: 323/207, 363/34, 363/37, 363/96, 363/135
• US Class Current: 323/207
• CPC Class Codes: H02J 3/1892 the arrangements being an integral part of the load, e.g. a motor, or of its control circuit
• CPC Class Codes: H02M 5/4585 having a rectifier with controlled elements

Abstract

Apparatus and methods are disclosed for providing VAR compensation using an AC motor drive, in which an off-line motor drive is configured to prevent power transfer to a motor load output, with a line side converter being operated to control a voltage or current in an intermediate circuit for leading or lagging VAR compensation of an AC power system.

Claims

1. An AC motor drive, comprising:

an input for receiving AC input electrical power from an AC power source;

an output for providing output electrical power to an electric motor load;

an intermediate circuit comprising;

at least one storage element,

a forward current path between the line side converter and the machine side converter,

a return current path between the line side converter and the machine side converter, and

at least one link inductor storage element connected in one of the forward and return current paths of the intermediate circuit;

a line side converter comprising a plurality of switching devices coupled with the input and the intermediate circuit and operative according to a plurality of line side switching control signals to selectively provide power from the input to the intermediate circuit;

a machine side converter comprising a plurality of switching devices coupled with the intermediate circuit and the output and operative according to a plurality of machine side switching control signals to selectively provide power from the intermediate circuit to the output, wherein the machine side converter is a current source inverter; and

a switch control system operatively coupled with the line side and machine side converters to provide the line side converter switching control signals and the machine side switching control signals, the switch control system being operative in a first operating mode to provide the line side and machine side switching control signals to selectively provide power to the electric motor load according to a motor drive control scheme, and the switch control system being operative in a second operating mode to provide the machine side switching control signals to prevent power transfer between the intermediate circuit and the output and to provide the line side switching control signals to selectively couple the input to the intermediate circuit according to a VAR compensation scheme, wherein the switch control system receives a VAR required input, wherein the switch control system provides the line side switching control signals in the second operating mode based at least partially on the VAR required input, and wherein the switch control system provides the machine side switching control signals in the second operating mode to cause the machine side converter to provide a short circuit between the forward and return current paths to prevent power transfer between the intermediate circuit and the output.

2. The motor drive of claim 1, wherein the switch control system comprises a mode select input operative to receive a mode selection signal and wherein the switch control system is operative to selectively generate the switching control signals for motor drive or VAR compensation operation according to the mode selection signal.

3. The motor drive of claim 1, wherein the input comprises:

first and second input current paths between the AC power source and the line side converter; and

at least one line reactor connected in one of the first and second input current paths between the AC power source and the line side converter.

4. The motor drive of claim 3, wherein the input comprises:

first and second input current paths between the AC power source and the line side converter; and

at least one filter capacitor connected between the first and second input current paths between the AC power source and the line side converter.

5. The motor drive of claim 1, wherein the input comprises:

first and second input current paths between the AC power source and the line side converter; and

at least one filter capacitor connected between the first and second input current paths between the AC power source and the line side converter.

6. A power conversion system, comprising:

an input for receiving input electrical power from a power source;

an output for providing output electrical power to a load;

an intermediate circuit comprising at least one storage element, wherein the intermediate circuit comprises;

a forward current path between the line side converter and the machine side converter, a return current path between the line side converter and the machine side converter, and at least one link inductor storage element connected in one of the forward and return current paths of the intermediate circuit;

a line side converter comprising a plurality of switching devices coupled with the input and the intermediate circuit and operative according to a plurality of line side switching control signals to selectively provide power from the input to the intermediate circuit, wherein the machine side converter is a current source inverter;

a machine side converter comprising a plurality of switching devices coupled with the intermediate circuit and the output and operative according to a plurality of machine side switching control signals to selectively provide power from the intermediate circuit to the output; and

a switch control system operatively coupled with the line side and machine side converters to provide the line side converter switching control signals and the machine side switching control signals, the switch control system being operative in a first operating mode to provide the line side and machine side switching control signals to selectively provide power to the load according to a control scheme, and the switch control system being operative in a second operating mode to provide the machine side switching control signals to prevent power transfer between the intermediate circuit and the output and to provide the line side switching control signals to selectively couple the input to the intermediate circuit according to a VAR compensation scheme;

wherein the switch control system provides the machine side switching control signals in the second operating mode to cause the machine side converter to provide a short circuit between the forward and return current paths to prevent power transfer between the intermediate circuit and the output.

7. The power conversion system of claim 6, wherein the switch control system provides the line side switching control signals in the second operating mode to control an amplitude of current circulating through the intermediate circuit.

8. A method of providing VAR compensation in a power system using an AC motor drive having a line side converter connected between a motor drive power input and an intermediate circuit and a machine side converter connected between the intermediate circuit and a motor load output, the method comprising:

operating the line side and machine side converters in a first operating mode to selectively provide power to an electric motor load coupled to the motor load output;

operating the machine side converter in a second operating mode to prevent power transfer between the intermediate circuit and the motor load output by causing the machine side converter to provide a short circuit between forward and return current paths of the intermediate circuit; and

operating the line side converter in the second operating mode to control a current in the intermediate circuit.

9. The method of claim 8, further comprising receiving a VAR required input from an external source, wherein the line side converter is operated to control the current in the intermediate circuit based at least partially on the VAR required input.

10. The method of claim 8, further comprising receiving a VAR required input from an external source, wherein the line side converter is operated to control a current in the intermediate circuit based at least partially on the VAR required input.

11. The method of claim 8, further comprising receiving a mode selection signal, wherein the line side and machine side converters are selectively operated for motor drive or VAR compensation operation according to the mode selection signal.

12. The method of claim 8, further comprising:

receiving a system current feedback signal from an external source; and

generating a VAR required signal in the AC motor drive based at least partially on the system current feedback signal;

wherein the line side converter is operated to control a in the intermediate circuit based at least partially on the VAR required signal.

13. A computer readable media with computer executable instructions for providing VAR compensation in a power system using an AC motor drive having a line side converter connected between a motor drive power input and an intermediate circuit and a machine side converter connected between the intermediate circuit and a motor load output, the computer readable media comprising computer executable instructions for:

operating the line side and machine side converters in a first operating mode to selectively provide power to an electric motor load coupled to the motor load output;

operating the machine side converter in a second operating mode to prevent power transfer between the intermediate circuit and the motor load output by causing the machine side converter to provide a short circuit between forward and return current paths of the intermediate circuit; and

operating the line side converter in the second operating mode to control a current in the intermediate circuit.