Method to control a frequency converter

• US 7,525,824 B2
• Filed: 03/29/2006
• Issued: 04/28/2009
• Est. Priority Date: 03/30/2005
• Status: Expired due to Fees

• Current Assignee: General Electric Technology GmbH (GE Aerospace)
• Original Assignee: Alstom Technology Ltd. (Alstom SA)
• Inventors: Veenstra, Martin
• Primary Examiner(s): HAN, YOUNGHUIE JESSICA
• Application Number:
  US11/391,919
• Publication Number:
  US 20060268587A1
• Time in Patent Office: 1,126 Days
• Field of Search: 322/20, 322/22, 322/25, 322/28, 322/37, 363/37, 363/76, 363/89, 363/127, 363/97, 290/44
• US Class Current: 363/37
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers
• CPC Class Codes: H02M 5/4505 having a rectifier with controlled elements

Abstract

A method for the control of a static frequency converter, in which an alternating voltage provided by a generator with a first frequency is first rectified in a switched rectifier, and in which the DC-voltage thus present in an intermediate circuit is inverted to an alternating voltage with a grid frequency by means of a switched inverter. The generator is provided with an excitation coil and with means for controlling the power made available to the grid by means of controlling the strength of the excitation field provided by the excitation coil and, if need be, also of the phase relationship between the voltage of the frequency converter and the generator voltage and the grid voltage, respectively. The generator side alternating voltage of the rectifier is controlled to a frequency which is substantially constant in accordance with the first frequency and the inverter is controlled on the basis of the measured value of the DC-voltage in the intermediate circuit.

Claims

1. A method for controlling a static frequency converter, the method comprising:

generating a first alternating voltage having a first frequency using a generator having at least one excitation coil;

rectifying the first frequency using a switched rectifier so as to provide direct voltage in an intermediate circuit;

converting the direct voltage in the intermediate circuit into a grid alternating voltage having a grid frequency using a switched inverter;

regulating at least a strength of an excitation field generated by the at least one excitation coil using a regulator so as to control power fed into the grid;

wherein control of the frequency converter in the rectifier is performed in such a manner that the frequency of the alternating voltage of the rectifier on a generator side is regulated to an essentially constant value of the first frequency, and

wherein control in the inverter is performed based on a measured value of the direct voltage in the intermediate circuit.

2. The method as recited in claim 1, wherein the regulator further regulates a phase relation between the frequency converter voltage and the generator voltage and regulates the grid voltage.

3. The method as recited in claim 1, wherein the direct voltage in the intermediate circuit is used as a regulating parameter over at least one capacitance in the intermediate circuit.

4. The method as recited in claim 1, wherein the control in the inverter is performed in such a way that a frequency (ω

_i,) of the inverter on the grid side is regulated according to the following function

ω

_i=ω

_n+Δ

ω

wherein the function Δ

ω

is expressed by

Δ

ω

K_P(u_C−

u*_C),

wherein K_p stands for a specified, proportional control gain, and u*_c stands for a reference value of the capacitance voltage that is selected as a function of the desired reactive power.

5. The method as recited in claim 4, wherein the capacitance voltage is selected dynamically.

6. The method as recited in claim 4, wherein the function Δ

ω

, additionally taking into consideration the damping, is employed with a predefined differential control gain K_D for purposes of the control in the inverter, according to the formula;

$\mathrm{\Delta <br><br>}<br><br><br><br>{\mathrm{\omega <br><br>}}^{\mathrm{\prime <br><br>}}<br><br>\stackrel{\mathrm{\Delta <br><br>}}{=}<br><br>K_P<br><br>\left(u_C-u_C^{*}\right)+K_D<br><br>\frac{d<br><br>}{d<br><br>t}<br><br>\left(u_C-u_C^{*}\right)=\mathrm{\Delta <br><br>}<br><br><br><br>\mathrm{\omega <br><br>}+\frac{K_D}{K_P}<br><br>\frac{d<br><br>\mathrm{\Delta <br><br>\omega <br><br>}}{d<br><br>t}.$

9. The method as recited in claim 1, wherein the frequency converter is a three-stage converter, wherein the direct voltage in the intermediate circuit is ascertained as the mean value of the voltages present over the two capacitances between a (+) level and a (0) level as well as between the (0) level and a (−

) level.

10. The method as recited in claim 1, wherein at least one of the controlled rectifier and the controlled inverter are operated in fundamental-frequency clocking.

11. The method as recited in claim 1, wherein the static frequency converter includes thyristors.

12. The method as recited in claim 11, wherein the thyristors include at least one of GTOs, IGBTs, MOSFETs and ICGTs.

13. The method as recited in claim 1, wherein a central control unit is provided which uses a measurement of at least one of the voltage and the current upstream and/or downstream from the static frequency converter to make an adaptation of the amplitude of the alternating voltage fed into the grid by appropriately actuating the regulator.

14. The device as recited in claim 1, wherein the controlled rectifier is a three-level rectifier and the controlled inverter is a three-level inverter and are both operated in fundamental-frequency clocking.

7. The method as recited in 1, wherein the strength of the excitation field generated by the at least one excitation coil and its phase relation is set by means of an excitation voltage (U_f) that is controlled as a function of the generator voltage(U_g), the generator frequency(ω

_g), the active power of the generator (P_g) and the reactive power (Q_g) of the generator.

8. The method as recited in claim 7, wherein the excitation voltage(U_f) is regulated according to the following formula:

U_f=R_fI_f+U′

_f.

15. A power generating device comprising:

a generator having at least one regulatable excitation coil;

a static frequency converter including at least one controlled rectifier in fundamental-frequency clocking, at least one controlled inverter in fundamental-frequency clocking, an intermediate circuit, and at least one control unit configured to regulate the rectifier and the inverter; and

a device configured to measure values of a direct voltage and disposed in the intermediate circuit, wherein the values are used for control of the inverter.

16. The device as recited in claim 15, further comprising a regulator configured to regulate at least one of an amplitude and a phase relation of the excitation voltage for the regulatable excitation coil, and configured to adapt the strength or phase relation of the excitation field to requirements of the grid.