Reactive energy compensator and associated method for balancing half-bus voltages

• US 8,912,767 B2
• Filed: 01/08/2013
• Issued: 12/16/2014
• Est. Priority Date: 01/09/2012
• Status: Active Grant

• Current Assignee: GE Energy Power Conversion Technology Limited (GE Vernova, Inc.)
• Original Assignee: GE Energy Power Conversion Technology Limited (GE Vernova, Inc.)
• Inventors: Morati, Mathieu, Urbain, Matthieu, Girod, Daniel
• Primary Examiner(s): Laxton, Gary L
• Assistant Examiner(s): Sprenger, Kevin H
• Application Number:
  US13/736,416
• Publication Number:
  US 20130176757A1
• Time in Patent Office: 707 Days
• Field of Search: 323/205, 323207-209, 363 39- 41, 363/71, 307/105
• US Class Current: 323/207
• CPC Class Codes: H02J 3/1842 wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
• CPC Class Codes: H02J 3/1857 wherein such bridge converter is a multilevel converter
• CPC Class Codes: H02M 7/487 Neutral point clamped inverters
• CPC Class Codes: H02M 7/537 using semiconductor devices only, e.g. single switched pulse inverters
• CPC Class Codes: Y02E 40/20 Active power filtering [APF]

Abstract

A reactive energy compensator that can be electrically connected to an AC electrical network, including at least one input direct voltage bus, at least one voltage inverter including switches and first and second capacitors having first and second voltages at their terminals, control means for the switches, including computation means capable of generating a target control current, means for combining the target control current and the output current from the inverter, means for transmitting a control signal capable of driving the switches, and correction means for the control signals of the switches, the correction means being capable of adding a balancing current to the target control current, the balancing current being able to correct the target control current so as to reduce the difference between the values of the first and second voltages, the target control current being increased for an even harmonic of the network frequency.

Claims

1. A reactive energy compensator capable of being electrically connected to an AC electrical network having M phase(s) and having a network frequency, M being greater than or equal to 1, the compensator comprising M phase(s) and including:

at least one input direct voltage bus capable of supplying reactive energy;

at least one voltage inverter connected to the direct voltage bus and capable of converting a direct input current into an alternating output current, the or each inverter comprising two input terminals, M output terminal(s) and M switching branches, each output terminal corresponding to a phase, each switching branch including controllable electronic switches, the or each inverter also comprising a first capacitor having a first voltage at its terminals and a second capacitor having a second voltage at its terminals, the two capacitors being connected serially between the two input terminals of the inverter; and

control means for the electronic switches of the or each inverter, comprising computation means capable of generating a target control current from a current to be compensated, means for combining the target control current and the output current from the inverter to supply a differential current, means for transmitting a control signal capable of driving the switches from the differential current to shape the output current, and correction means, from the first and second voltages, for the control signals of the switches, the correction means being capable of reducing the difference between the value of the first voltage and that of the second voltage,

wherein the correction means are able to add a balancing current to the target control current, the balancing current being able to correct the target control current so as to reduce the difference between the values of the first and second voltages, the target control current being increased for an even harmonic of the network frequency.

2. The reactive energy compensator according to claim 1, wherein the correction means can determine a value of the balancing current, the balancing current being a periodic frequency signal equal to a non-zero even multiple of the network frequency.

3. The reactive energy compensator according to claim 2, wherein the balancing current is a sinusoidal frequency signal equal to a non-zero even multiple of the network frequency.

4. The reactive energy compensator according to claim 2, wherein the amplitude of the balancing current is proportional to the difference between the current value of the first voltage and the current value of the second voltage.

5. The reactive energy compensator according to claim 1, wherein each electronic switch is a two-way switch, and comprises a transistor and a diode connected in anti-parallel.

6. The reactive energy compensator according to claim 5, wherein the transistor is an insulated gate bipolar transistor.

7. The reactive energy compensator according to claim 1, wherein the balancing current is a periodic frequency signal equal to twice the network frequency.

8. A method for balancing half-bus voltages in a reactive energy compensator according to any one of the preceding claims, including the following steps:

calculating control signals for the electronic switches of the or each inverter of the reactive energy compensator;

correcting the control signals, so as to reduce the difference between the value of the first voltage and that of the second voltage; and

applying modified control signals to said electronic switches,

wherein the step for correcting the control signals comprises a step for adding, using the correction means of the compensator, a balancing current to the target control current, the balancing current being able to correct the target control current in order to reduce the difference between the values of the first and second voltages, the target control current being increased for an even harmonic of the network frequency.

9. The method according to claim 8, wherein the step for correcting the control signals comprises a prior step for determining, using the correction means of the compensator, a value of the balancing current, the balancing current being a periodic frequency signal equal to a non-zero even multiple of the network frequency.

10. The method according to claim 9, wherein during the step for determining a value of the balancing current, the amplitude of the balancing current is considered to be proportional to the difference between the current value of the first voltage and the current value of the second voltage.