Method for determination of the risk to disturbance-free operation of a frequency converter

• US 7,622,886 B2
• Filed: 06/21/2005
• Issued: 11/24/2009
• Est. Priority Date: 06/24/2004
• Status: Expired due to Fees

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Schierling, Hubert
• Primary Examiner(s): Leykin; Rita
• Application Number:
  US11/570,841
• Publication Number:
  US 20080272727A1
• Time in Patent Office: 1,617 Days
• Field of Search: 318/807, 307/125, 307/126, 307/129, 307/130, 307/131, 700/294, 700/293, 700/297
• US Class Current: 318/807
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 5/458 using semiconductor devices only

Abstract

The invention relates to a method for determining the chance of a disturbance-free operation of a frequency converter (2) connected to a feeding network (18). According to the invention, during the operation of said frequency converter (2), an intermediate circuit voltage (U_ZK) is continuously measured and a network-side intermediate circuit current (i_ZKmains) is continuously determined; these measuring quantities are compared with pre-determined operating values of the frequency converter (2), and quantities which are higher or lower than said values are respectively stored; and the frequency (H_ij) of said higher and lower measuring quantities is determined and converted into a characteristic number for the quality of the feeding network (18). As said characteristic number decreases, the chance of a disturbance-free operation of the frequency converter (2) increases. In this way, a frequency converter (2) is able to detect the risk of appliance disturbance or failure as a result of network disturbances before the operation is interrupted.

Claims

1. A method for determining a risk to a disturbance-free operation of a frequency converter connected to a mains power supply, comprising the steps of:

during operation of the frequency converter, continuously measuring an intermediate-circuit voltage and a mains-side intermediate-circuit current;

comparing the measured intermediate-circuit voltage and measured mains-side intermediate-circuit current with preset operating values of the intermediate-circuit voltage and the mains-side intermediate-circuit current for the frequency converter;

recording overshoots and undershoots of the measured intermediate-circuit voltage and measured mains-side intermediate-circuit current determined in the comparison;

computing a frequency with which the overshoots and undershoots occur; and

converting the computed frequency to a characteristic quality factor of the mains power supply.

2. The method of claim 1, further comprising subdividing a range of values where any one of the measured intermediate-circuit voltage and the measured mains-side intermediate-circuit current is above or below the preset operating values into a plurality of sections.

3. The method of claim 2, further comprising assigning a weighting factor to each of the plurality of sections.

4. The method of claim 1, further comprising generating a warning message if the characteristic quality factor is smaller than a predetermined quality factor of the mains power supply.

5. The method of claim 1, wherein the mains-side intermediate-circuit current is computed from a measured intermediate circuit voltage and a measured motor-side intermediate circuit current according to the following equation:

i_ZKmains=C_Zk·

dU_ZK/dt+i_Zkmotor

wherein

i_ZKmains is the mains-side intermediate-circuit current,

i_ZKmotor is the motor-side intermediate-circuit current,

C_zk is the intermediate-circuit capacitance, and

dU_zK/dt is the rate of change of the intermediate circuit voltage.

6. The method of claim 5, wherein the motor-side intermediate-circuit current is measured.

7. The method of claim 5, wherein the motor-side intermediate-circuit current is determined as a function of the measured intermediate-circuit voltage and a computed motor power according to the following equation:

i_ZKmotor=P_motor/U_ZK

wherein

i_ZKmotor is the motor-side intermediate-circuit current,

U_ZK is the intermediate circuit voltage, and

P_motor is the computed motor power.

8. The method of claim 7, wherein the motor power is computed from measured motor currents and preset motor voltages according to the following equation:

P_motor=u₁·

i₁+u₂·

i₂+u₃·

i₃

wherein

U₁, u₂, and u₃ are the preset motor voltages,

i₁, i₂, and i₃ are the measured motor currents, and

P_motor is the computed motor power.

9. A method for determining a risk to a disturbance-free operation of a frequency converter connected to a mains power supply, comprising the steps of:

during operation of the frequency converter, continuously measuring an intermediate-circuit voltage and a mains-side intermediate-circuit current;

applying a non-linear weighting factor to the measured intermediate-circuit voltage and mains-side intermediate-circuit current;

integrating the non-linearly weighted intermediate-circuit voltage and mains-side intermediate-circuit current; and

adding the integrated, non-linearly weighted intermediate-circuit voltage and the integrated, non-linearly weighted mains-side intermediate-circuit current to produce a characteristic quality factor of the mains power supply.

10. The method of claim 9, further comprising generating a warning message if the characteristic quality factor is smaller than a predetermined quality factor of the mains power supply.

11. The method of claim 9, wherein the mains-side intermediate-circuit current is computed from a measured intermediate circuit voltage and a measured motor-side intermediate circuit current according to the following equation:

i_ZKmains=C_zk·

dU_ZK/dt+i_Zkmotor

wherein

i_ZKmains is the mains-side intermediate-circuit current,

i_ZKmotor is the motor-side intermediate-circuit current,

C_zk is the intermediate-circuit capacitance, and

dU_zK/dt is the rate of change of the intermediate circuit voltage.

12. The method of claim 11, wherein the motor-side intermediate-circuit current is measured.

13. The method of claim 11, wherein the motor-side intermediate-circuit current is determined as a function of the measured intermediate-circuit voltage and a computed motor power according to the following equation:

i_ZKmotor=P_motor/U_ZK

wherein

i_ZKmotor is the motor-side intermediate-circuit current,

U_ZK is the intermediate circuit voltage, and

P_motor is the computed motor power.

14. The method of claim 13, wherein the motor power is computed from measured motor currents and preset motor voltages according to the following equation:

P_motor=u₁·

i₁+u₂·

i₂+u₃·

i₃

wherein

u₁, u₂, and u₃ are the preset motor voltages,

i₁, i₂, and i₃ are the measured motor currents, and

P_motor is the computed motor power.