Controlling a voltage source converter in a DC system
View Patent ↗A first voltage source converter and converter station including such a first voltage source converter, as well as a method and computer program product for controlling the first voltage source converter are disclosed. The first voltage source converter has a DC side for connection to a DC system, has an AC side for connection to an AC system and is interconnected with an AC side of a second voltage source converter, which has a DC side connected to the DC system. The first voltage source converter includes a number of converter valve pairs, each being connected to a corresponding AC phase of the AC system and a control unit controlling the converter valves to generate at least one AC waveform and to reduce oscillations between the converters.
1. A first voltage source converter having a direct current (DC) side for connection to a DC system and having an alternating current (AC) side for connection to an AC system and for interconnection with an AC side of a second voltage source converter, said second voltage source converter having a DC side connected to the DC system and the first voltage source converter comprising:
a number of converter valve pairs, each pair being connected to a corresponding AC phase of the AC system; and
a control unit operative to control the converter valve pairs to generate at least one voltage waveform and the control unit when reducing oscillations is configured to create a virtual resistance around a resonance frequency formed between the first voltage source converter and the second voltage source converter,
wherein the control unit when forming the virtual resistance is operative to multiply a phase current with a proportional gain for obtaining an oscillations damping control signal, reducing oscillations between the first voltage source converter and the second voltage source converter by combining the oscillations damping control signal with a converter reference voltage.
2. The first voltage source converter according to claim 1 , wherein the control unit is further configured to process the phase current so that a main power frequency component is excluded from the multiplication.
3. The first voltage source converter according to claim 2 , wherein the processing comprises high pass filtering the phase current.
4. The first voltage source converter according to claim 3 , wherein a cut-off frequency of the high pass filtering is in a range of 1-70 Hz.
5. The first voltage source converter according to claim 4 , wherein the control unit is further operative to combine the oscillations damping control signal with the converter reference voltage in order to obtain a valve control signal.
6. The first voltage source converter according to claim 3 , wherein the control unit is further operative to combine the oscillations damping control signal with the converter reference voltage in order to obtain a valve control signal.
7. The first voltage source converter according to claim 2 , wherein the control unit is further operative to combine the oscillations damping control signal with the converter reference voltage in order to obtain a valve control signal.
8. The first voltage source converter according to claim 1 , wherein the control unit is further operative to combine the oscillations damping control signal with the converter reference voltage in order to obtain a valve control signal.
9. The first voltage source converter according to claim 8 , wherein the control unit is operative to combine the oscillations damping control signal with the converter reference voltage in a dq frame.
10. The first voltage source converter according to claim 8 , wherein the control unit is operative to combine the oscillations damping control signal with the converter reference voltage in a static frame.
11. The first voltage source converter according to claim 1 , wherein the first voltage source converter is configured to operate in a different control mode than current feedback control.
12. The first voltage source converter according to claim 1 , wherein the first voltage source converter is configured to operate in a voltage and frequency or in a voltage and phase control mode.
13. A converter station comprising the first voltage source converter according to claim 1 .
14. The converter station according to claim 13 , further comprising the second voltage source converter.
15. A method of controlling a first voltage source converter having a direct current (DC) side connected to a DC system, having an alternating current (AC) side connected to an AC system and being interconnected with an AC side of a second voltage source converter, said second voltage source converter having a DC side connected to the DC system and said first voltage source converter comprising a number of converter valve pairs, each pair being connected to a corresponding AC phase of the AC system, the method being performed in a control unit of the first voltage source converter and comprising:
controlling the converter valve pairs to generate at least one voltage waveform;
creating a virtual resistance around a resonance frequency formed between the first voltage source converter and the second voltage source converter, forming of the virtual resistance by multiplying a phase current with a proportional gain for obtaining an oscillations damping control signal; and
reducing oscillations between the first voltage source converter and the second voltage source converter by combining the oscillations damping control signal with a converter reference voltage.
16. The method according to claim 15 , wherein the forming of the virtual resistance further comprises processing the phase current so that a main power frequency component is excluded from the multiplication.
17. The method according to claim 16 , wherein the processing comprises high pass filtering the phase current.
18. The method according to claim 15 , further comprising combining the oscillations damping control signal with the converter reference voltage in order to obtain a valve control signal.
19. The method according to claim 18 , wherein the oscillations damping control signal is combined with the converter reference voltage in a dq frame.
20. A computer program product for controlling a first voltage source converter having a direct current (DC) side connected to a DC system, having an alternating current (AC) side connected to an AC system and being interconnected with an AC side of a second voltage source converter, said second voltage source converter having a DC side connected to the DC system and said first voltage source converter comprising a number of converter valve pairs, each pair being connected to a corresponding AC phase of the AC system, the computer program product comprising a non-transitory data carrier with computer program code configured to cause a control unit of the first voltage source converter to:
control the converter valve pairs to generate at least one voltage waveform; and
create a virtual resistance around a resonance frequency formed between the first voltage source converter and the second voltage source converter, forming of the virtual resistance by multiplying a phase current with a proportional gain for obtaining an oscillations damping control signal, reducing oscillations between the first voltage source converter and the second voltage source converter by combining the oscillations damping control signal with a converter reference voltage.