Frequency converter direct current capacitor configuration method considering phase jump voltage sag

Abstract

The invention provides a frequency converter direct current capacitor configuration method considering phase jump voltage sag, and relates to the field of frequency converters and electric energy quality. The method comprises the following steps: measuring a voltage sag instantaneous value of phase jump, and calculating a power grid characteristic voltage based on the voltage sag instantaneous value; calculating the DC average voltage of the voltage sag down-converter based on the power grid characteristic voltage; configuring a frequency converter DC capacitor based on the DC average voltage of the frequency converter under the voltage sag; wherein the frequency converter is connected to the generator through the induction motor. According to the method, the voltage sag tolerance duration of the frequency converter can be prolonged, and the voltage sag tolerance capability of the frequency converter is improved, so that the frequency converter can safely and stably pass through the voltage sag stage, and frequency converter jump stop and industrial production halt are avoided.

Description

Technical Field

[0001] The invention relates to the field of frequency converter and power quality, and in particular to a method for configuring direct current capacitors of frequency converters taking into account phase jump voltage sag. Background Art

[0002] With the increase in the number of modern industrial users and the improvement of production requirements, more high-efficiency and highly integrated production equipment are used in the industrial production process. Among them, frequency converters are common equipment for realizing intelligent manufacturing and efficient production, but frequency converters are extremely sensitive to power quality problems such as voltage sags. When voltage sags occur, frequency converters are prone to equipment tripping due to the action of protection devices, and even cause the entire production line to stop production, causing serious economic losses and safety issues to industrial production.

[0003] The configuration strategy of DC capacitors of traditional inverters usually only ensures the safe and stable operation of the inverter under normal working conditions, ignoring the impact of voltage sag amplitude and phase jump in new power systems on the operation of the inverter, that is, the tolerance of the inverter. Therefore, the voltage tolerance of the inverter configured with DC capacitors in the traditional way is poor, that is, the ability of the inverter to cross the voltage sag fault is limited, the safety is low, and it is easy to trip and cause industrial production to stop. Summary of the invention

[0004] In order to solve the above-mentioned technical problems existing in the prior art, prolong the tolerance time of the inverter, and improve the tolerance capacity of the inverter, so that the inverter can maintain a safe state during the voltage sag stage, avoid inverter tripping and industrial shutdown, the present invention provides a method for configuring the DC capacitor of the inverter taking into account the phase jump voltage sag.

[0005] Specifically, the inverter DC capacitor configuration method taking into account the phase jump voltage sag includes the following steps:

[0006] Step S1: measuring the instantaneous value of voltage sag including phase jump, and calculating the grid characteristic voltage based on the instantaneous value of voltage sag;

[0007] Step S2: Calculating the average DC voltage of the inverter during voltage sag based on the characteristic voltage of the power grid;

[0008] Step S3: configuring the DC capacitor of the inverter based on the DC average voltage of the inverter under the voltage sag;

[0009] Therein, the frequency converter is connected to the generator via the induction motor.

[0010] Preferably, the DC average voltage is the DC average voltage V that takes into account the single-phase phase jump voltage temporary drop. dc ,

[0011]

[0012] Where, E is the unit voltage of the power grid, V is the characteristic voltage of the power grid calculated based on the instantaneous value of the voltage sag under the single-phase phase jump voltage sag, k1 is the first intermediate calculation quantity, and φ is the phase jump;

[0013] The DC capacitance is the DC capacitance C that takes into account the single-phase phase jump voltage drop dc ,

[0014]

[0015] Where, T N is the electromagnetic torque rating of the induction motor, ω N is the rated speed of the generator, ω sag The voltage temporarily drops the generator speed, t sag is the duration of voltage sag, and J is the moment of inertia.

[0016] Preferably, the instantaneous value of the voltage sag is the voltage U of the phase A under the single-phase phase jump voltage sag. a ;

[0017]

[0018] Where ω is the angular frequency of the grid voltage and t is the time.

[0019] Preferably, the instantaneous value of the voltage sag is the voltage U of the phase b under the single-phase phase jump voltage sag. b ;

[0020]

[0021] Preferably, the instantaneous value of the voltage sag is the c-phase voltage U under the single-phase phase jump voltage sag c ;

[0022]

[0023] Preferably, the DC average voltage is the DC average voltage V′ taking into account the temporary drop of the two-phase phase jump voltage dc ,

[0024]

[0025] Wherein, k2 is the second intermediate calculation quantity, V' is the grid characteristic voltage calculated based on the instantaneous value of the voltage sag under the two-phase phase jump voltage sag;

[0026] The DC capacitance is the DC capacitance C′ under the voltage drop caused by the two-phase phase jump dc ,

[0027]

[0028] Preferably, the instantaneous value of the voltage sag is the voltage U′ of the phase b under the voltage sag of the two-phase phase jump. b ;

[0029]

[0030] Preferably, the instantaneous value of the voltage sag is the voltage U′ of the phase C under the voltage sag of the two-phase phase jump. c ;

[0031]

[0032] Preferably, the DC average voltage is the DC average voltage V″ taking into account the temporary drop of the three-phase phase jump voltage dc ,

[0033]

[0034] Wherein, V” is the grid characteristic voltage calculated based on the instantaneous value of voltage sag under the three-phase phase jump voltage sag;

[0035] The DC capacitance value is the DC capacitance C″ that takes into account the temporary drop in the three-phase phase jump voltage dc ,

[0036]

[0037] Preferably, the instantaneous value of the voltage sag is the voltage U″ of phase A under the voltage sag of the three-phase phase jump. a ;

[0038]

[0039] Preferably, the instantaneous value of the voltage sag is the voltage U″ of the phase b under the voltage sag of the three-phase phase jump. b ;

[0040]

[0041] Preferably, the instantaneous value of the voltage sag is the voltage U″ of the phase C under the voltage sag of the three-phase phase jump. c ;

[0042]

[0043] The inverter DC capacitor configuration method provided by the present invention can extend the inverter's tolerance time and improve the inverter's voltage sag tolerance, so that the inverter can safely and stably pass through the voltage sag stage, avoiding inverter tripping and industrial shutdown. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Schematic diagram of voltage sag caused by single-phase phase jump.

[0045] Figure 2 This is the effect of single-phase phase jump voltage sag on the inverter DC voltage.

[0046] Figure 3 Schematic diagram of voltage sag caused by two-phase phase jump.

[0047] Figure 4 This is the effect of the two-phase phase jump voltage sag on the inverter DC voltage.

[0048] Figure 5 Schematic diagram of voltage sag caused by three-phase phase jump.

[0049] Figure 6 It is the result of the inverter DC capacitor configuration for the single-phase phase jump voltage drop.

[0050] Figure 7 The result of the inverter DC capacitor configuration is a two-phase phase jump voltage drop. DETAILED DESCRIPTION

[0051] Hereinafter, the technical solution provided by the present invention will be further elaborated in detail with reference to the accompanying drawings.

[0052] Under the same voltage sag amplitude, the size of the inverter DC capacitor can determine the inverter's tolerance time under voltage sag. At the same time, the phase jump characteristics of the voltage sag can affect the inverter's tolerance time. Therefore, through theoretical analysis of the instantaneous voltage of the voltage sag with single-phase, two-phase and three-phase phase jumps, the inverter DC average voltage under three types of voltage sag is established, and finally the configuration strategy of the inverter DC capacitor with three types of phase jump voltage sag is determined based on the inverter DC average voltage. By taking into account the inverter DC capacitor configuration strategy of the voltage sag with phase jump, the inverter's tolerance time is extended and the inverter's tolerance capacity is improved, so that the inverter can safely and stably pass through the voltage sag stage, avoiding inverter tripping and industrial shutdown.

[0053] Specifically, the configuration method includes:

[0054] Step S1: Determine the relationship between the inverter DC capacitor and the voltage sag tolerance time;

[0055] Step S2: Determine the instantaneous value expression of the voltage sag taking into account the single-phase phase jump, and calculate the DC average voltage of the inverter under the voltage sag taking into account the single-phase phase jump;

[0056] Step S3: determining an instantaneous value expression of a voltage sag taking into account a two-phase phase jump, and calculating a DC average voltage of the inverter under the voltage sag taking into account a two-phase phase jump;

[0057] Step S4: determining an instantaneous value expression of a voltage sag taking into account a three-phase phase jump, and calculating a DC average voltage of the inverter under the voltage sag taking into account a three-phase phase jump;

[0058] Step S5: Calculate the inverter DC capacitor configuration taking into account the phase jump voltage sag.

[0059] The step S1 comprises the following sub-steps:

[0060] Step S11: Calculation of inverter tolerance time:

[0061]

[0062] In the formula, C is the DC capacitance of the inverter, p is the load power of the inverter, V o is the average DC voltage under normal working conditions, V min It is the DC voltage under voltage sag;

[0063] Step S12: The inverter tolerance time is positively correlated with the inverter DC capacitance, and the tolerance time is improved as the configured capacitance increases.

[0064] The step S2 comprises the following sub-steps:

[0065] Step S21: The voltage drop of the single-phase phase jump is as follows: Figure 1 shown.

[0066] The instantaneous value of voltage sag taking into account single-phase phase jump is:

[0067]

[0068] Where U a , U b , U c is the instantaneous value of the three-phase voltage of a, b, and c, E is the unit voltage of the power grid, V is the characteristic voltage of the power grid, t is the time, φ is the phase jump, and ω is the angular frequency;

[0069] The instantaneous value of the voltage drop of any phase taking into account the single-phase phase jump is measured, and the grid characteristic voltage V is calculated from the above expression.

[0070]

[0071] Then the corresponding DC average voltage is calculated based on the grid characteristic voltage V.

[0072] Step S22: Taking into account the voltage drop caused by the single-phase phase jump, the average DC voltage V dc for:

[0073]

[0074]

[0075] Take the impact of single-phase phase jump voltage drop on the inverter DC voltage as an example. Figure 2 shown.

[0076] The DC average voltage is affected by the phase jump and the amplitude of the sag. In the shallow sag area, the phase jump angle has a greater impact on the DC voltage. For example, the voltage U after the voltage sag sag is 0.9pu. With the change of phase jump angle, the DC voltage decreases from 2.24pu to 1.72pu. The DC voltage is maximum when φ is around -20°. In the deep sag area, the influence of phase jump becomes smaller, and the influence of sag amplitude gradually increases. sag When the sag amplitude is reduced to U sag is 0.4pu, and the voltage is stable at 1.48pu to 1.27pu. sag It is 0p.u., and the DC voltage is stable around 0.93pu.

[0077] The step S3 comprises the following sub-steps:

[0078] Step S31: The voltage drop of the two-phase phase jump is as follows: Figure 3 shown.

[0079] The instantaneous value of the voltage sag taking into account the two-phase phase jump is:

[0080] U a = Esinωt;

[0081]

[0082] The instantaneous value of the voltage drop of any phase taking into account the phase jump of the two phases is measured, and the characteristic voltage V of the power grid is calculated by the above expression.

[0083]

[0084] Then the corresponding DC average voltage is calculated based on the grid characteristic voltage V.

[0085] Step S32: Taking into account the voltage drop caused by the two-phase phase jump, the average DC voltage V of the inverter is reduced. dc for:

[0086]

[0087] Take the impact of two-phase phase jump voltage drop on the inverter DC voltage as an example. Figure 4 shown.

[0088] Under the two-phase phase jump voltage sag, the impact of the phase jump is significantly greater than that of the single-phase phase jump voltage sag. The DC voltage range is 1.98pu-0p.u., and when the phase jump φ is -45°, the DC voltage is the largest under the same sag amplitude. When the sag amplitude is 0p.u., the DC voltage is as low as 0 and does not change with the change of the phase jump angle. Under a certain sag amplitude, as the phase jump angle increases, the DC voltage also decreases. From the above analysis, it can be seen that the two-phase phase jump voltage sag has a greater impact on the DC voltage, and the DC average voltage can still maintain a high level under the single-phase phase jump voltage sag.

[0089] The step S4 comprises the following sub-steps:

[0090] Step S41: The voltage drop of the three-phase phase jump is as follows: Figure 5 shown.

[0091] The instantaneous value of voltage sag taking into account the three-phase phase jump is:

[0092] U a =Vsin(ωt+φ);

[0093]

[0094] The instantaneous value of the voltage drop of any phase taking into account the three-phase phase jump is measured, and the grid characteristic voltage V is calculated from the above expression.

[0095]

[0096]

[0097] Then the corresponding DC average voltage is calculated based on the grid characteristic voltage V.

[0098] Step S42: Taking into account the voltage drop caused by the three-phase phase jump, the average DC voltage of the inverter is:

[0099]

[0100] The step S5 comprises the following sub-steps:

[0101] Step S51: When the terminal voltage is U, the capacity is C dc The energy stored in the DC capacitor is E C for:

[0102]

[0103] Step S52: In addition to the mechanical power output by the inverter, the energy E required for the induction motor rotor to rotate k for:

[0104]

[0105] Where J is the moment of inertia, ω r is the generator speed.

[0106] Step S53: The purpose of optimizing the configuration of the DC capacitor is to consider that in the case of voltage sag, the DC capacitor discharges to meet the inverter output energy W p consumption to ensure that the speed, torque, etc. remain stable.

[0107]

[0108] Where, t sag-st is the voltage sag start time, t sag-ed is the end time of voltage sag, P N is the rated power, P sag is the power after voltage sag, T sag is the electromagnetic torque after voltage sag, ω sag is the generator speed after the voltage drops temporarily.

[0109] Step S54: The purpose of optimizing the configuration of the DC capacitor is to consider the energy W required for the DC capacitor to discharge to maintain the rotation of the induction motor rotor in the case of voltage sag. E , to ensure that the speed, torque, etc. remain stable,

[0110]

[0111] In the formula, E k-N The energy required for the rotor of the induction motor to rotate at rated operation, E k-sag is the energy required for the induction motor rotor to rotate after the voltage drops, ω N is the rated operating speed of the generator.

[0112] Step S55: When the voltage drops temporarily, the induction motor will run stably at a certain speed, and the electromagnetic torque of the induction motor will be balanced, that is, T sag =T N At the same time, further considering the phase jump effect of voltage sag, substituting the DC average voltage of the above three types of inverters taking into account the phase jump voltage sag into the above formula, the calculation formula for the DC capacitor size taking into account the phase jump can be obtained as follows:

[0113]

[0114] Take the DC capacitor configuration result considering the single-phase phase jump voltage sag as an example. Figure 6 As shown:

[0115] The sag amplitude has a greater impact on the optimal configuration of capacitor capacity. When the sag amplitude is 0p.u., taking into account the impact of the phase jump, the capacitor capacity required is 0.045F, which is equivalent to an increase of 3mF of capacitor capacity per kilowatt of the inverter to achieve voltage sag crossing. As the sag amplitude gradually increases, the capacitor capacity decreases rapidly. Under the same sag amplitude, similar to the change law of the DC average voltage, when the phase jump changes to -10°, the capacitor capacity required to be configured is the lowest.

[0116] Take the DC capacitor configuration result considering the two-phase phase jump voltage sag as an example, Figure 7 shown.

[0117] The capacitance required for two-phase phase jump voltage sag increases rapidly compared to that required for single-phase phase jump voltage sag. Considering that the voltage sag amplitude is mostly above 0.74pu, the capacitance required for the sag interval with a sag amplitude above 0.74pu is shown. It can be further seen that under two-phase phase jump voltage sag, the phase jump has a greater impact within this sag amplitude range. When the sag amplitude is 0.74pu and the phase jump is 45°, the capacitance that needs to be optimized is 2.45F, which is a relatively large capacitance value.

[0118] By comparison, it can be concluded that the capacitor capacity required for single-phase phase jump voltage sag is smaller than that required for two-phase phase jump voltage sag. At the same time, since most voltage sags are single-phase phase jump voltage sags, optimizing the configuration of the inverter DC capacitor for single-phase phase jump voltage sags can enable the inverter to cross such voltage sags.

[0119] In summary, it can be seen that the inverter DC capacitor configuration method provided by the present invention can improve the inverter's tolerance time and the inverter's voltage sag tolerance, so that the inverter can safely and stably pass through the voltage sag stage and avoid inverter tripping and industrial shutdown.

Claims

1. A method for configuring a DC capacitor of a frequency converter taking into account a phase jump voltage sag, characterized in that: The following steps are involved: Step S1: measuring the instantaneous value of voltage sag including phase jump, and calculating the grid characteristic voltage based on the instantaneous value of voltage sag; Step S2: Calculating the average DC voltage of the inverter during voltage sag based on the characteristic voltage of the power grid; Step S3: configuring the DC capacitor of the inverter based on the DC average voltage of the inverter under the voltage sag; Therein, the frequency converter is connected to the generator via the induction motor.

2. The inverter DC capacitor configuration method taking into account phase jump voltage sag as claimed in claim 1, characterized in that: The DC average voltage is the DC average voltage V when the single-phase phase jump voltage drops. dc , Where, E is the unit voltage of the power grid, V is the characteristic voltage of the power grid calculated based on the instantaneous value of the voltage sag under the single-phase phase jump voltage sag, k1 is the first intermediate calculation quantity, and φ is the phase jump; The DC capacitance is the DC capacitance C that takes into account the single-phase phase jump voltage drop dc , Where, T N is the electromagnetic torque rating of the induction motor, ω N is the rated speed of the generator, ω sag The voltage temporarily drops the generator speed, t sag is the duration of voltage sag, and J is the moment of inertia.

3. The inverter DC capacitor configuration method taking into account phase jump voltage sag as claimed in claim 2, characterized in that: The instantaneous value of voltage sag is the voltage U of phase A under the voltage sag of single-phase phase jump. a ; Where ω is the angular frequency of the grid voltage and t is the time.

4. The inverter DC capacitor configuration method taking into account phase jump voltage sag as claimed in claim 2, characterized in that: The instantaneous value of voltage sag is the voltage U of phase b under the voltage sag of single-phase phase jump. b ; 5. The inverter DC capacitor configuration method taking into account phase jump voltage sag as claimed in claim 2, characterized in that: The instantaneous value of voltage sag is the voltage U of phase C under the voltage sag of single-phase phase jump. c ; 6. The inverter DC capacitor configuration method taking into account phase jump voltage sag as claimed in claim 1, characterized in that: The DC average voltage is the DC average voltage V after the two-phase phase jump voltage drops. d ' c , Wherein, k2 is the second intermediate calculation quantity, V' is the grid characteristic voltage calculated based on the instantaneous value of the voltage sag under the two-phase phase jump voltage sag; The DC capacitance is the DC capacitance C' under the voltage drop caused by the two-phase phase jump dc , 7. The inverter DC capacitor configuration method taking into account phase jump voltage sag as claimed in claim 6, characterized in that: The instantaneous value of voltage sag is the voltage U of phase b under the voltage sag of two-phase phase jump. b '; 8. The method for configuring the DC capacitor of the frequency converter taking into account the phase jump voltage sag as claimed in claim 6, characterized in that: The instantaneous value of voltage sag is the voltage U of phase C under the voltage sag of two-phase phase jump. c '; 9. The inverter DC capacitor configuration method taking into account phase jump voltage sag as claimed in claim 1, characterized in that: The DC average voltage is the DC average voltage V after the three-phase phase jump voltage drops. d ” c , Wherein, V” is the grid characteristic voltage calculated based on the instantaneous value of voltage sag under the three-phase phase jump voltage sag; The DC capacitance value is the DC capacitance C that takes into account the temporary drop in the three-phase phase jump voltage. d ” c , 10. The inverter DC capacitor configuration method taking into account phase jump voltage sag as claimed in any one of claim 9, characterized in that: The instantaneous value of voltage sag is the voltage U' of phase A under the voltage sag of three-phase phase jump. a '; 11. The inverter DC capacitor configuration method taking into account phase jump voltage sag as claimed in claim 9, characterized in that: The instantaneous value of voltage sag is the voltage U of phase b under the voltage sag of three-phase phase jump. b ”; 12. The inverter DC capacitor configuration method taking into account phase jump voltage sag as claimed in claim 9, characterized in that: The instantaneous value of voltage sag is the voltage U of phase C under the voltage sag of three-phase phase jump. c ”;

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