Method for controlling inverters

• US 7,859,871 B2
• Filed: 07/17/2007
• Issued: 12/28/2010
• Est. Priority Date: 09/04/2006
• Status: Active Grant

• Current Assignee: Fronius International GmbH (G&K Privatstiftung)
• Original Assignee: Fronius International GmbH (G&K Privatstiftung)
• Inventors: Angerer, Christian, Heigl, Hannes, Kreuzer, Harald
• Primary Examiner(s): Vu; Bao Q
• Assistant Examiner(s): Tran; Nguyen
• Application Number:
  US12/310,291
• Publication Number:
  US 20090251933A1
• Time in Patent Office: 1,260 Days
• Field of Search: 363/40, 363/55, 363/71, 363/72, 363/95, 363/109, 363/120
• US Class Current: 363/71
• 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 7/493 the static converters being arranged for operation in parallel

Abstract

The invention relates to a method for controlling the voltage and power of several HF inverters (2), connected in parallel at the output, of an electrically isolated inverter assembly as well as for distributing the load to these HF inverters (2) each consisting of at least one DC-DC converter (3), one intermediate circuit (4) and one DC-AC converter (5), with a command variable (U_i′) being formed for each HF inverter (2) so as to preset a nominal value for control of an intermediate-circuit voltage (U_ZKi) at the intermediate circuit (4) of the HF inverter (2). The load of each HF inverter (2) is determined by a control unit (13) by measuring the current or power required, an internal resistance of the HF inverter (2) is simulated via which internal resistance a virtual voltage drop (U_VR) is caused which depends on the load determined and is used for controlling the voltage (U_ZKi) of the intermediate circuit (4) so as to produce a purposive change in the output voltage of each HF inverter (2).

Claims

1. A method for controlling the voltage and power of several HF inverters (2), connected in parallel at the output, of an electrically isolated inverter assembly as well as for distributing the load to these HF inverters (2) each consisting of at least one DC-DC converter (3), one intermediate circuit (4) and one DC-AC converter (5), with a command variable (U_i′

) being formed for each HF inverter (2) so as to preset a nominal value for control of an intermediate-circuit voltage (U_ZKi) at the intermediate circuit (4) of the HF inverter (2), wherein the load of each HF inverter (2) is determined by a control unit (13) at the input of each HF inverter (2) by measuring the input power (P_i), that a virtual internal resistance of each HF inverter (2) is simulated by each control unit (13), via which internal resistance a virtual voltage drop (U_VR) is caused which depends on the load determined, which virtual voltage decrease (U_VR) is used for controlling the voltage (U_ZKi) of the intermediate circuit (4) so as to produce a purposive change in the output voltage of each HF inverter (2).

2. The method according to claim 1, wherein a reduction variable is calculated based on the internal resistance of each HF inverter (2) simulated by the control unit (13).

3. The method according to claim 2, wherein the reduction variable is calculated from the product of the input voltage (P_i) and a matching factor (K_i).

4. The method according to claim 3, wherein the matching factor (K_i) is assigned to the type of the HF inverter (2) used, and that a correspondingly specific matching factor (K_i) is loaded from a memory of the control unit (13) for calculating the reduction variable.

5. The method according to claim 2, wherein a command variable (U_i′

) for presetting the nominal value of the intermediate-circuit voltage (U_ZKi) is detected for each HF inverter (2) as a function of the reduction variable.

6. The method according to claim 5, wherein the command variable (U_i′

) is calculated from the difference between a reference voltage (U<sub>i—

ref</sub>) and the reduction variable.

7. The method according to claim 2, wherein real variables, in particular direct-current variables, are used for the simulated resistance and/or reduction variable.

8. The method according to claim 5, wherein the command variable (U_i′

) for presetting the nominal value of the intermediate-circuit voltage (U_ZKi) is reduced when the load of the HF inverter (2) increases at the output (8) and is increased when the load of the inverter (2) decreases at the output (8).

9. The method according to claim 1, wherein a voltage controller (19) and at least one current controller (20), e.g. one PI controller each, arranged downstream thereof are used for controlling the intermediate-circuit voltage (U_ZKi), wherein a further command variable (I_i′

) is preset by the voltage controller (19) for control of the nominal current supplied to the intermediate circuit (4) by the current controller (20) so that the intermediate-circuit voltage (U_ZKi) will be set via the nominal current supplied to the intermediate circuit (4).

10. The method according to claim 1, wherein a choke current (I_ZKi) is measured for controlling the intermediate-circuit voltage U_ZKi and is supplied to the intermediate circuit (4).

11. The method according to claim 9, wherein the intermediate-circuit voltage (U_ZKi) and optionally the choke current (I_ZKi) are fed back to the voltage controller (19) and optionally to the current controller (20) for creating a control deviation.

12. The method according to claim 1, wherein at least when the parallel operation is started, the HF inverters (2) are synchronized via a line (23) by means of a signal and/or pulse.

13. The method according to claim 12, wherein furthermore time-uncritical data, e.g. error or diagnosis signals, performance parameters, state variables, and the like, are transferred via the line (23).