Observer based monitoring and control of submodules in modular multilevel converter

Patent metadata

Field	Value
Publication number	US-10074988-B2
Application number	US-201415101134-A
Country	US
Kind code	B2
Filing date	Dec 5, 2014
Priority date	Dec 5, 2013
Publication date	Sep 11, 2018
Grant date	Sep 11, 2018

Abstract

This application relates to control methods and apparatus for a voltage source converter comprising a plurality of energy storage devices which can be selectively connected into an arm of the voltage source converter. The apparatus is configured to generate a modelled value of the voltage of an energy storage device of the voltage source converter based on one or more model parameters and the operation of the voltage source converter, receive the modelled value and also a measured value of the voltage of at least one energy storage device, determine an error between the modelled value and the measured value, and generate a model control signal for adapting the model based on said error so that the modelled value substantially corresponds to the measured value. Control circuitry is responsive to said model module and/or said model adaptation module to control operation of the voltage source converter.

First claim

The invention claimed is:

1. A control apparatus for a voltage source converter, the voltage source converter comprising an arm connecting an alternating current terminal to a direct current terminal, the arm comprising a valve and a first reactor, the valve comprising a plurality of sub-modules, a plurality of energy storage devices, and a plurality of switching elements, each of the plurality of sub-modules comprising one of the plurality of energy storage devices and at least one of the plurality of switching elements, the control apparatus comprising:
a valve voltage control configured to control the plurality of switching elements to selectively connect the plurality of energy storage devices into the arm;
a model module configured to generate a modelled value of a voltage of at least one of the plurality of energy storage devices, wherein the modelled value of the voltage of the at least one of the plurality of energy storage devices is based on:
a measured output current of the valve;
the control of the plurality of switching elements by the valve voltage control; and
a capacitance value of at least one of the plurality of energy storage devices; and

wherein the valve voltage control is configured to control the plurality of switching elements based on the modelled value of the voltage of the at least one of the plurality of energy storage devices.

2. The control apparatus of claim 1 , wherein then model module is configured to generate a modelled value of a voltage of at least one of the plurality of energy storage devices by:
scaling the measured output current by the capacitance of the at least one of the plurality of energy storage devices; and
integrating the scaled measured output current.

3. The control apparatus of claim 1 , wherein the model module is configured to:
combine the measured output current with a vector of sub-module switching controls to give a vector representing the currents passing through all of the sub-modules, wherein the vector of sub-module switching controls indicates whether each sub-module is selected or not selected;
integrate the vector representing the currents; and
scale the vector by the capacitance value of at least one of the plurality of energy storage devices.

4. The control apparatus of claim 1 , a model adaptation module configured to:
receive the modelled value of the voltage of the at least one of the plurality of energy storage devices;
receive a measured value of the voltage of the at least one of the plurality of energy storage devices; and
determine an error between the modelled value of the voltage of the at least one of the plurality of energy storage devices and the measured value of the voltage of the at least one of the plurality of energy storage devices.

5. The control apparatus of claim 4 , wherein the model adaptation module is further configured to adapt a model based on the error such that the modelled value of the voltage of the at least one of the plurality of energy storage devices more accurately represents the measured value of the voltage of the at least one of the plurality of energy storage devices.

6. The control apparatus of claim 5 , wherein adapting the model comprises generating a compensation term that is added to the measured output current of the valve.

7. The control apparatus of claim 6 , wherein the compensation term is based on the error that is passed through a proportional-integral controller.

8. The control apparatus of claim 7 , wherein the proportional-integral controller includes a low gain value and a first order filter.

9. The control apparatus of claim 4 , wherein the model adaptation module is further configured to determine a root mean square value of the error and compare the root mean square value of the error to a threshold value.

10. The control apparatus of claim 4 , wherein the model adaptation module is further configured to compare the error to a threshold value.

11. The control apparatus of claim 4 , wherein the model adaptation module is further configured to filter the measured value of the voltage of the at least one of the plurality of energy storage devices.

12. The control apparatus of claim 4 , wherein the valve output current is sampled at a rate that is greater than a rate at which the measured value of the voltage of the at least one of the plurality of energy storage devices is sampled.

13. A voltage source converter, comprising:
a first arm and a second arm, the first arm connecting an alternating current terminal to a positive direct current terminal and the second arm connecting the alternating current terminal to a negative direct current terminal;
the first arm comprising a first valve and a first reactor and the second arm comprising a second valve and a second reactor;
the first valve comprising a plurality of first sub-modules, a plurality of first energy storage devices, and a plurality of first switching elements, each of the plurality of first sub-modules comprising one of the plurality of first energy storage devices and at least one of the plurality of first switching elements;
the second valve comprising a plurality of second sub-modules, a plurality of second energy storage devices, and a plurality of second switching elements, each of the plurality of second sub-modules comprising one of the plurality of second energy storage devices and at least one of the plurality of second switching elements;
a first valve voltage control configured to control the plurality of first switching elements to selectively connect the plurality of first energy storage devices into the first arm;
a second valve voltage control configured to control the plurality of second switching elements to selectively connect the plurality of second energy storage devices into the second arm;
a first model module configured to generate a modelled value of a voltage of at least one of the plurality of first energy storage devices, wherein the modelled value of the voltage of the at least one of the plurality of first energy storage devices is based on:
a measured output current of the first valve;
the control of the plurality of first switching elements by the first valve voltage control; and
a capacitance value of at least one of the plurality of first energy storage devices; and

wherein the first valve voltage control is configured to control the plurality of first switching elements based on the modelled value of the voltage of the at least one of the plurality of first energy storage devices;
a second model module configured to generate a modelled value of a voltage of at least one of the plurality of second energy storage devices, wherein the modelled value of the voltage of the at least one of the plurality of second energy storage devices is based on:
a measured output current of the second valve;
the control of the plurality of second switching elements by the second valve voltage control; and
a capacitance value of at least one of the plurality of second energy storage devices; and

wherein the second valve voltage control is configured to control the plurality of second switching elements based on the modelled value of the voltage of the at least one of the plurality of second energy storage devices.

Assignees

• Alstom Technology Ltd
• Alstom Technology Ltd

Inventors

• Oates Colin

Classifications

• G01R31/64

  Testing of capacitors · CPC title

• G01R31/40

  Testing power supplies (testing photovoltaic devices H02S50/10) · CPC title

• H02M5/458

  using semiconductor devices only · CPC title

• H02M1/32

  Means for protecting converters other than automatic disconnection · CPC title

• H02J3/36 Primary

  Arrangements for transfer of electric power between AC networks via high-voltage DC [HVDC] links; Arrangements for transfer of electric power between generators and networks via HVDC links · CPC title