Control circuit for DC network to maintain zero net change in energy level

• US 9,209,693 B2
• Filed: 11/07/2011
• Issued: 12/08/2015
• Est. Priority Date: 11/07/2011
• Status: Active Grant

• Current Assignee: Alstom Technology Ltd. (Alstom SA)
• Original Assignee: Alstom Technology Ltd. (Alstom SA)
• Inventors: Davidson, Colin Charnock, Trainer, David Reginald, Okaeme, Nnamdi
• Primary Examiner(s): Pham, Emily P
• Application Number:
  US14/356,882
• Publication Number:
  US 20150028826A1
• Time in Patent Office: 1,492 Days
• US Class Current: 1/1
• CPC Class Codes: H02H 7/268 for dc systems
• CPC Class Codes: H02J 3/36 Arrangements for transfer of electric power between ac networks via a high-tension dc link
• CPC Class Codes: H02M 1/08 Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• CPC Class Codes: H02M 7/4835 comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
• CPC Class Codes: Y02E 60/60 Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Abstract

There is a control circuit comprising first and second DC terminals for connection to a DC network, the first and second DC terminals having a plurality of modules and at least one energy conversion element connected in series therebetween to define a current transmission path, the plurality of modules defining a chain-link converter, each module including at least one energy storage device, the or each energy storage device being selectively removable from the current transmission path to cause a current waveform to flow from the DC network through the current transmission path and the or each energy conversion element and thereby remove energy from the DC network, the or each energy storage device being selectively removable from the current transmission path to modulate the current waveform to maintain a zero net change in energy level of the chain-link converter.

Claims

1. A control circuit comprising first and second DC terminals for connection to a DC network, the first and second DC terminals having a plurality of modules and at least one energy conversion element connected in series therebetween to define a current transmission path, the plurality of modules defining a chain-link converter, each module including at least one energy storage device, the at least one energy storage device being selectively removable from the current transmission path to cause a current waveform to flow from the DC network through the current transmission path and the at least one energy conversion element and thereby remove energy from the DC network, the at least one energy storage device being selectively removable from the current transmission path to modulate the current waveform to maintain a zero net change in energy level of the chain-link converter, each module further including:

a) two pairs of switching elements connected in parallel with the at least one energy storage device in a full-bridge arrangement to define a 4-quadrant bipolar module that can provide zero, positive or negative voltage and can conduct current in two directions, or

b) first and second sets of series-connected current flow control elements, each set of current flow control elements including a switching element to selectively direct current through the or each energy storage device and a passive current check element to limit current flow through the module to a single direction, the first and second sets of series-connected current flow control elements and the or each energy storage device being arranged in a full-bridge arrangement to define a 2-quadrant bipolar rationalized module that can provide zero, positive or negative voltage while conducting current in a single direction.

2. A control circuit according to claim 1, wherein at least one switching element is or includes a semiconductor device.

3. A control circuit according to claim 2, wherein the or each semiconductor device is an insulated gate bipolar transistor, a gate turn-off thyristor, a field effect transistor, an injection enhanced gate transistor or an integrated gate commutated thyristor.

4. A control circuit according to claim 2 wherein at least one switching element further includes an anti-parallel diode connected in parallel with the or each corresponding semiconductor device.

5. A control circuit according to claim 1 wherein the or each energy conversion element is or includes a resistor.

6. A control circuit according to claim 1 wherein the or each energy storage device is or includes a capacitor, a battery, or a fuel cell.

7. A control circuit according to claim 1 including a plurality of energy conversion elements connected in series with the plurality of modules.

8. A control circuit according to claim 7 wherein the energy conversion elements and the modules are arranged to define an alternating sequence of energy conversion elements and modules.

9. A control circuit according to claim 7 further including a third terminal connected in series between the first and second DC terminals, the third terminal being for connection to ground, the plurality of modules including first and second sets of modules, the first set of modules being connected in series with at least one energy conversion element between the first DC terminal and the third terminal, the second set of modules being connected in series with at least one other energy conversion element between the second DC terminal and the third terminal.

10. A control circuit according to claim 1 further including a controller to selectively remove each energy storage device from the current transmission path.

11. A control circuit according to claim 1 wherein the current waveform includes one or more current waveform components.

12. A control circuit according to claim 11 wherein the or each current waveform component is selected from a group including a half-sinusoidal current waveform component, a trapezoidal current waveform component, and higher order harmonic current waveform components.

13. A control circuit according to claim 11 wherein the current waveform is modulated to add or remove one or more current waveform components.

14. A control circuit according to claim 1 wherein the current waveform is modulated to include a plurality of current pulses and add a time delay between consecutive current pulses.

15. A control circuit according to claim 14 wherein the durations of each current pulse and the time delay are equal.

16. A control circuit according to claim 1 wherein the voltage rating of the chain-link converter is set to exceed the voltage of the DC network.

17. A control circuit according to claim 1 wherein the or each energy storage device is selectively removable from the current transmission path to charge one or more other energy storage devices.