Method in frequency converter provided with voltage intermediate circuit, and frequency converter

1. A method in a frequency converter provided with a voltage intermediate circuit in connection with interference in a network to be supplied, the frequency converter comprising a network converter part and an inverter part and a DC intermediate circuit between them, the method comprising

controlling the intermediate circuit voltage at the beginning of network interference by limiting the torque on the inverter side,

detecting interference in the network voltage,

setting a torque reference to a predetermined value in response to the network interference,

detecting network voltage recovery, and

controlling the torque reference to a normal value in response to the network voltage recovery.

2. A method according to claim 1 , wherein the network interference is detected as an increase in the DC intermediate circuit voltage or from measurements carried out by the network converter.

3. A method according to claim 1 , wherein the network interference is detected in the output of the network converter part.

4. A method according to claim 1 , wherein the detecting of the network interference comprises a step where information on the interference is transmitted to the control unit of the frequency converter.

5. A method according to claim 1 , wherein the setting of the torque reference to a predetermined value comprises a step where the torque of the inverter part is controlled to a predetermined value.

6. A method according to claim 1 , wherein the predetermined value of the torque reference is zero or another computed value.

7. A method according to claim 1 , wherein the network voltage recovery is detected in the output of the network converter part.

8. A method according to claim 1 , wherein the detecting of the network voltage recovery comprises a step where information on the network voltage recovery is transmitted to the control unit.

9. A method according to claim 1 , wherein the controlling of torque reference to a normal value comprises a step where the torque reference is controlled to the normal value using a ramp.

10. A frequency converter provided with a voltage intermediate circuit and comprising a network inverter part and an inverter part and a DC intermediate circuit between them, the frequency converter comprising

means for controlling the DC intermediate circuit voltage,

means for detecting interference in the network voltage,

means responsive to the network voltage interference for setting a torque reference to a predetermined value,

means for controlling the torque of the inverter part and limiting the current of the network converter,

means for noticing network voltage recovery, and

means responsive to the network voltage recovery for controlling the torque reference to a normal value.

11. A method according to claim 2 , wherein the detecting of the network interference comprises a step where information on the interference is transmitted to the control unit of the frequency converter.

12. A method according to claim 3 , wherein the detecting of the network interference comprises a step where information on the interference is transmitted to the control unit of the frequency converter.

13. A method according to claim 5 , wherein the predetermined value of the torque reference is zero or another computed value.

14. A method according to claim 7 , wherein the detecting of the network voltage recovery comprises a step where information on the network voltage recovery is transmitted to the control unit.