A method for determining the battery duty cycle for an ac motor type load

Abstract

The application relates to a battery work cycle planning method for an alternating current motor load, and belongs to the technical field of power systems, which comprises the following steps: obtaining operation data of the motor load; according to the working characteristics and starting time of the motor load, the working cycle of the motor load is divided into starting and normal operation conditions, starting active power and starting reactive power are calculated, and rated active power under the normal operation condition is calculated; whether the inverter power factor compensation element meets the anti-rush ripple characteristics of the inverter is calculated according to the starting reactive power; the discharge current of the battery during the starting and normal operation of the motor load is calculated, and then the battery work cycle is planned. The method provided by the application can effectively improve the accuracy of battery capacity selection, ensure that the battery reliably supplies power to the motor load within the specified backup time, and avoid economic waste caused by overlarge battery capacity selection on building space and equipment procurement.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power systems, and particularly relates to a method for formulating a work cycle of a battery for an alternating-current motor load. BACKGROUND

[0002] With the continuous improvement of the reliability of nuclear power station power supply, some important alternating-current motors (electric valves) need to be powered by alternating-current uninterrupted power supplies, and the battery provides backup power supply for a certain time in the working condition of losing all alternating-current power supplies. The alternating-current motor load is different from other computer or monitoring instrument load of a conventional uninterrupted power supply, and has a low power factor and a variable power factor in the starting process. In the past, the battery capacity calculation of the alternating-current uninterrupted power supply system does not fully consider the characteristics of the motor starting condition and the normal condition, and the performance of the alternating-current uninterrupted power supply equipment, or directly calculates the motor starting current and the rated current as the demand of the motor on the battery capacity, or only calculates according to the rated active power of the motor. Since the motor has a low power factor and the starting current is as high as 3-7 times of the rated current, this will have a great influence on the selection of the battery capacity. SUMMARY

[0003] To solve the defects in the prior art, the purpose of the present application is to provide a method for formulating a work cycle of a battery for an alternating-current motor load, which can effectively improve the accuracy of the selection of the battery capacity, ensure that the battery reliably supplies power to the motor load within the specified backup time, and avoid the economic waste caused by the overlarge selection of the battery capacity on the building space and equipment procurement.

[0004] To achieve the above purpose, the technical scheme adopted by the present application is:

[0005] A method for formulating a work cycle of a battery for an alternating-current motor load, comprising the following steps:

[0006] S1, obtaining the operation data of the motor load;

[0007] S2, according to the working characteristics and the starting time of the motor load, dividing the work cycle of the motor load into a starting condition and a normal operation condition, and respectively calculating the starting active power and the starting reactive power of the motor load, and the rated active power of the motor load in the normal operation condition;

[0008] S3, according to the starting reactive power of the motor load, calculating whether the inverter power factor compensation element meets the anti-ripple characteristics of the inverter;

[0009] S4. Calculate the battery discharge current during the starting and normal operation of the motor-type load based on the starting active power, starting time, rated active power, normal operation time, and average voltage value within the battery working cycle, and then determine the battery working cycle.

[0010] Furthermore, in the method for determining the battery duty cycle for AC motor loads as described above, the operating data in step S1 includes motor type, rated voltage, rated power, rated current, rated power factor, starting current, starting power factor, and starting time.

[0011] Furthermore, in the method for determining the battery duty cycle for AC motor loads as described above, the calculation formulas for the starting active power and starting reactive power of the motor load in step S2 are as follows:

[0012]

[0013]

[0014] In the formula:

[0015] P st To start active power; U r Rated voltage; I St This is the starting current; Q is the starting power factor; st To start reactive power.

[0016] Furthermore, regarding the battery duty cycle determination method for AC motor loads as described above, the formula for calculating the rated active power of the motor load under normal operating conditions in step S2 is as follows:

[0017]

[0018] In the formula:

[0019] P r Rated active power; I r Rated current; This is the rated power factor.

[0020] Furthermore, in the battery duty cycle determination method for AC motor type loads as described above, step S3 uses the requirement that the inverter's back-feed ripple voltage is less than 0.5% to verify whether the power factor compensation element inside the inverter meets the reactive power required when the motor starts.

[0021] Furthermore, regarding the battery duty cycle determination method for AC motor-type loads as described above, the formula for calculating the battery discharge current during the start-up of the motor-type load in step S4 is as follows:

[0022]

[0023] In the formula:

[0024] P st is the starting active power;

[0025] η is the inverter efficiency;

[0026] U av is the average voltage during the battery discharge period, which is approximately the average of the initial voltage and the terminal voltage of the battery discharge.

[0027] Further, the battery operation period setting method for the AC motor load as described above, the discharge current calculation formula of the battery when the motor load is normally running in step S4 is:

[0028]

[0029] In the formula: P r is the rated active power.

[0030] The battery operation period setting method for the AC motor load according to the present application has the following significant technical effects:

[0031] The motor load operation period is divided into two sections of starting and normal running, and the starting active power and the rated active power are converted into battery discharge current respectively, which is included in the battery operation period, so that the demand of the AC motor load on the battery capacity is more accurately calculated, and the battery can reliably supply power to the motor load within the specified backup time, while avoiding the economic waste caused by the overlarge battery capacity selection on the building space and equipment procurement. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is the battery operation period setting method for the AC motor load provided in the specific embodiment of the present application;

[0033] Figure 2 is the battery discharge period of a certain squirrel-cage asynchronous motor in the embodiment. DETAILED DESCRIPTION

[0034] The present application will be further described below in combination with specific examples and the accompanying drawings.

[0035] Figure 1 The battery operation period setting method for the AC motor load provided in the specific embodiment of the present application is shown in the flowchart, and the method includes the following steps:

[0036] Step S1, obtaining the operation data of the motor load. The operation data includes motor type, rated voltage, rated power, rated current, rated power factor, starting current, starting power factor, and starting time, etc.

[0037] Step S2, according to the working characteristics and starting time of the motor load, the working cycle of the motor load is divided into starting working condition and normal running working condition, and the active power and reactive power of the motor load in starting working condition and the active power of the motor load in normal running working condition are calculated respectively.

[0038] The calculation formula of the active power and the reactive power of the motor load in starting working condition is respectively:

[0039]

[0040]

[0041] In the formula:

[0042] P st : starting active power; U r : rated voltage; I St : starting current; starting power factor; Q st : starting reactive power.

[0043] The calculation formula of the active power of the motor load in normal running working condition is:

[0044]

[0045] In the formula:

[0046] P r : rated active power; I r : rated current; rated power factor.

[0047] The alternating current motor belongs to inductive load, and the motor needs a certain amount of reactive current to establish the motor magnetic field during starting process, and constantly exchanges energy with the capacitor in the inverter in the voltage alternating period. Only the active current does work, which is finally converted into mechanical energy and heat energy and consumed. In the working condition that the battery supplies power to the alternating current motor through the inverter, the battery only provides active power for the load, so only the active power part of the motor load needs to be considered in the battery capacity calculation.

[0048] Step S3, according to the starting reactive power of the motor load, whether the power factor compensation element of the inverter meets the anti-ripple characteristics of the inverter is calculated.

[0049] The output characteristic of the inverter is usually to output rated power when the rated load power factor is 0.8 (inductive), so for the motor type low power factor load, in addition to selecting the inverter capacity according to the load starting current, whether the power factor compensation element (usually the DC side and AC side filter capacitor) inside the inverter can meet the required reactive power when the motor starts also needs to be considered. If the inverter cannot meet the required reactive power of the load, once the battery provides the reactive power, the feedback current will cause the DC side voltage to rise, which will harm the internal elements of the inverter and cannot meet the requirement that the reverse ripple voltage is less than 0.5% in the inverter design standard. Therefore, the power factor compensation element inside the inverter should be matched with the starting reactive power of the motor.

[0050] Step S4, according to the starting active power of the motor type load, the starting time, the rated active power, the normal operation time and the average voltage value in the battery working cycle, the discharge current of the battery during the starting and normal operation of the motor type load is calculated, and then the battery working cycle is formulated.

[0051] The discharge current calculation formula of the battery during the starting of the motor type load is:

[0052]

[0053] The discharge current calculation formula of the battery during the normal operation of the motor type load is:

[0054]

[0055] In the formula:

[0056] P st is the starting active power;

[0057] P r is the rated active power;

[0058] η is the inverter efficiency;

[0059] U av is the average voltage in the battery discharge cycle, which is approximately the average value of the initial voltage and the termination voltage during the battery discharge.

[0060] The following takes a squirrel-cage asynchronous motor powered by an AC uninterruptible power supply in a nuclear power plant as an embodiment to describe the technical solutions of the present application in detail.

[0061] Step one, obtain the operation data of the motor load

[0062] In this embodiment, the operation data of the squirrel-cage asynchronous motor is specifically:

[0063] Rated voltage U r : ~ 380V

[0064] Rated current I r : 15.5 A

[0065] Rated power P r : 7.5 kW

[0066] Rated power factor 0.74

[0067] Starting current I St : 99 A

[0068] Starting power factor 0.45

[0069] Starting time T1: 5 s

[0070] Total running time T1+T2: 1800 s

[0071] Step two, according to the working characteristics and starting time of the motor, the working cycle of the motor is divided into starting working condition and normal running working condition, and the active power and reactive power of the motor under the starting working condition and the active power of the motor under the normal running working condition are calculated respectively.

[0072] According to the calculation formula provided in step S2 in the above battery working cycle development method for AC motor load, the active power and reactive power of the motor under the starting working condition are respectively:

[0073]

[0074]

[0075] In the formula:

[0076] P st is the starting active power; U r is the rated voltage; I St is the starting current; is the starting power factor; Q st is the starting reactive power.

[0077] In the example, the rated power of the motor is given as 7.5 kW, and the active power of the motor under normal running can also be calculated according to the rated current, rated power factor:

[0078]

[0079] In the formula:

[0080] P r is the rated active power; I r is the rated current; is the rated power factor.

[0081] Step three, calculate the power factor compensation value of inverter according to the reactive power demand when motor starts.

[0082] Since the inductive reactive power required by motor starting is mainly compensated by the filter capacitor inside the inverter, the filter capacitor that the inverter should be equipped with should be at least:

[0083]

[0084] In the formula: Q st is the starting reactive power; U r is the rated voltage; f is the working frequency of the filter capacitor.

[0085] Step four, formulate the battery working cycle according to the motor operation process

[0086] The battery working cycle is divided into two periods according to the motor operation process, the first period T1 is the asynchronous motor starting stage, according to the starting active power of the motor and the average voltage in the battery discharge cycle, the discharge current of the battery in the first period (0-5s) is calculated:

[0087]

[0088] The second period T2 is the normal operation stage of asynchronous motor, according to the rated active power of asynchronous motor and the average voltage in the battery discharge cycle, the discharge current of the battery in the second period (5s-1800s) is calculated:

[0089]

[0090] In the formula:

[0091] η is the efficiency of the inverter, taking 0.87;

[0092] U av is the average voltage in the battery discharge cycle, which can be approximately the average value of the initial voltage and the termination voltage of the battery discharge, for the direct system with rated voltage of 220V, taking 197.6V.

[0093] Finally, the battery discharge cycle as shown in Figure 2 is obtained.

[0094] The method for setting the work cycle of the battery for the alternating current motor load provided by the application divides the motor work cycle into two sections of starting and normal running, and converts the starting active power and the rated active power into the battery discharge current respectively to be counted into the battery work cycle, so as to more accurately calculate the demand of the alternating current motor load on the battery capacity, ensure that the battery reliably supplies power for the motor load within the specified backup time, and avoid the economic waste caused by the overlarge battery capacity selection on the building space and equipment purchase.

[0095] The above embodiments are only examples of the application, and the application can be implemented in other specific ways or other specific forms without departing from the spirit or essential characteristics of the application. Therefore, the described embodiments should be considered illustrative rather than restrictive in any aspect. The scope of the application should be illustrated by the appended claims, and any changes equivalent to the intent and scope of the claims should be included in the scope of the application.

Claims

1. A method for formulating a battery operation cycle for an alternating current motor load, comprising the following steps: S1, obtaining operation data of the motor load, the operation data comprising motor type, rated voltage, rated power, rated current, rated power factor, starting current, starting power factor and starting time; S2, according to the operation characteristics and starting time of the motor load, dividing the operation cycle of the motor load into starting condition and normal operation condition, respectively calculating starting active power and starting reactive power of the motor load, and rated active power of the motor load in normal operation condition; the calculation formulae of the starting active power and the starting reactive power of the motor load are respectively: In the formulae: P st Pstart is the starting active power; U r U is the rated voltage; I st Istart is the starting current; Pstart is the starting active power; Q st Qstart is the starting reactive power; the calculation formula of the rated active power of the motor load in normal operation condition is: In the formula: P r is the rated active power; I r is the rated current; is the rated power factor; S3, according to the starting reactive power of the motor load, checking whether the inverter power factor compensation element meets the anti-ripple characteristics of the inverter, specifically: using the requirement that the anti-ripple voltage of the inverter is less than 0.5% to check whether the power factor compensation element inside the inverter meets the required reactive power when the motor starts; S4, according to the starting active power, starting time, rated active power, normal operation time and average voltage value in the battery operation cycle of the motor load, calculating the discharge current of the battery when the motor load starts and normally operates, and then formulating the battery operation cycle; the calculation formula of the discharge current of the battery when the motor load starts is: In the formula: P st η is the starting active power; η is the inverter efficiency; U av This is the average voltage during the battery discharge cycle, approximately the average of the initial discharge voltage and the discharge termination voltage. the calculation formula of the discharge current of the battery when the motor load normally operates is: In the formula: P r is the rated active power.

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