PWM rectifier having de-coupled power factor and output current control loops

• US 6,366,483 B1
• Filed: 07/24/2000
• Issued: 04/02/2002
• Est. Priority Date: 07/24/2000
• Status: Expired due to Term

• Current Assignee: Rockwell Automation Technologies Incorporated (Rockwell Automation, Inc.)
• Original Assignee: Rockwell Automation Technologies Incorporated (Rockwell Automation, Inc.)
• Inventors: Ma, Daming, Wu, Bin, Zargari, Navid R., Rizzo, Steven C.
• Primary Examiner(s): Patel, Rajnikant B.
• Application Number:
  US09/621,847
• Time in Patent Office: 617 Days
• Field of Search: 363/87, 363/89, 363/37, 363/40, 363/41, 363/39, 363/124, 323/282, 323/283, 323/286
• US Class Current: 363/87
• CPC Class Codes: H02M 1/4216 operating from a three-phase input voltage H02M1/4233 takes precedence
• CPC Class Codes: H02M 5/4505 having a rectifier with controlled elements
• 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
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
• CPC Class Codes: Y02P 80/10 Efficient use of energy, e.g. using compressed air or pressurized fluid as energy carrier

Abstract

A PWM rectifier wherein the switching bridge has m input filter capacitors, each connected at a terminal thereof, to the line side of the bridge. These terminals are used to connect an m-phase a.c. power supply (m>=1) having a per phase system inductance to the bridge. A current smoothing inductor is connected to the load side of the bridge and enables a load to be connected thereto. A switching pattern generator controls the switches in the switching bridge based on a reference output current. A first control loop is provided for determining an active portion of the reference output current based on a desired power level of the load and an m-phase voltage at the capacitor terminals. A second control loop is provided for determining a reactive portion of the reference output current based on the m-phase voltage at the capacitor terminals. The reactive portion of the current is selected so as to obtain a desired per phase power factor, such as unity, on the power supply. In this manner the output current and power factor control loops are independent of and not coupled to one another.

Claims

1. A rectifier, comprising:

a switching bridge for converting alternating current into direct current, said bridge having a line side and a load side,

m input filter capacitors, each connected at a terminal thereof to the line side of the bridge, wherein an m-phase a.c. power supply having a per phase system inductance is connectable to the m terminals, m being an integer greater than or equal to one;

the load side having a smoothing inductor, a load being connectable to the smoothing inductor;

a switching pattern generator for controlling switches in the switching bridge based on a reference output current;

a first control loop for determining an active portion of the reference output current based on a desired power level of the load and an m-phase voltage at said terminals; and

a second control loop for determining a reactive portion of the reference output current based on the m-phase voltage at said terminals, the reactive portion being selected so as to obtain a desired per phase power factor on the power supply.

2. The rectifier according to claim 1, wherein m=3 and including a block for transforming the m-phase voltage at said terminals into a two-phase voltage in a rotating reference frame.

3. The rectifier according to claim 2, including a low pass filter connected to the transformation block, whereby the output of the filter provides a fundamental portion of the voltage at said terminals in the rotating reference frame.

4. The rectifier according to claim 3, wherein the active portion of the reference output current is determined as follows:

$i_{p,d}=\frac{P·<br><br>v_{\mathrm{if},d}}{v_{\mathrm{if},d}^2+v_{\mathrm{if},q}^2}$

and $i_{p,q}=\frac{P·<br><br>v_{\mathrm{if},q}}{v_{\mathrm{if},d}^2+v_{\mathrm{if},q}^2}$

where i_p,d, i_p,q are the components of the active portion of the reference output current in the rotating reference frame, P is the desired power of the load, and v_if,d v_if,q are components in the rotating reference frame of fundamental portion of the voltage at said terminals.

5. The rectifier according to claim 4, wherein the reactive portion of the reference output current is determined as follows:

6. The rectifier according to claim 5, including a summer for adding the active and reactive portions of the reference output current.

7. The rectifier according to claim 6, wherein:

the load is an inverter; and

the desired load power is determined as a sum of first and second components, the first component being a calculated power applied to the inverter, and the second component being an output of an error minimizing compensator having as inputs a measured value of the output current and a command output current signal.

8. The rectifier according to claim 7, wherein the calculated power is computed by multiplying an input voltage of the inverter with the measured value of the rectifier output current.

9. An a.c. induction motor drive, comprising:

a rectifier, said rectifier having (a) a switching bridge for converting alternating current into direct current, said bridge having a line side and a load side, (b) m input filter capacitors, each connected at a terminal thereof to the line side of the bridge, wherein an m-phase a.c. power supply having a per phase system inductance is connectable to the m terminals, m being an integer greater than or equal to one, (c) a switching pattern generator for controlling switches in the switching bridge based on a reference output current, (d) a first control loop for determining an active portion of the reference output current based on a desired power level of the load and an m-phase voltage at said terminals, and (e) a second control loop for determining a reactive portion of the reference output current based on the m-phase voltage at said terminals, the reactive portion being selected so as to obtain a desired per phase power factor on the power supply;

a d.c. link choke connected to the load side of the switching bridge; and

a current source inverter connected to the d.c. link choke, the a.c. induction motor being connectable to the current source inverter.

10. The drive according to claim 9, wherein m=3 and including a block for transforming the m-phase voltage at said terminals into a two-phase voltage in a rotating reference frame.

11. The drive according to claim 10, including a low pass filter connected to the transformation block, whereby the output of the filter provides a fundamental portion of the voltage at said terminals in the rotating reference frame.

12. The drive according to claim 11, wherein the active portion of the reference output current is determined as follows:

$i_{p,d}=\frac{P·<br><br>v_{\mathrm{if},d}}{v_{\mathrm{if},d}^2+v_{\mathrm{if},q}^2}$

and $i_{p,q}=\frac{P·<br><br>v_{\mathrm{if},q}}{v_{\mathrm{if},d}^2+v_{\mathrm{if},q}^2}$

where i_p,d, i_p,q are the components of the active portion of the reference output current in the rotating reference frame, P is the desired power of the load, and v_if,d v_if,q are components in the rotating reference frame of fundamental portion of the voltage at said terminals.

13. The drive according to claim 12, wherein the reactive portion of the reference output current is determined as follows:

14. The drive according to claim 13, including a summer for adding the active and reactive portions of the reference output current.

15. The drive according to claim 14, wherein the desired load power is determined as a sum of first and second components, the first component being a calculated power applied to the inverter, and the second component being an output of an error minimizing compensator having as inputs a measured value of the output current and a command output current signal.

16. The drive according to claim 15, wherein the calculated power is computed by multiplying an input voltage of the inverter with the measured value of the rectifier output current.