CN115166348A - Charging pile electric energy metering and calibrating method - Google Patents
Charging pile electric energy metering and calibrating method Download PDFInfo
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- CN115166348A CN115166348A CN202210648134.9A CN202210648134A CN115166348A CN 115166348 A CN115166348 A CN 115166348A CN 202210648134 A CN202210648134 A CN 202210648134A CN 115166348 A CN115166348 A CN 115166348A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R22/00—Arrangements for measuring time integral of electric power or current, e.g. electricity meters
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R35/00—Testing or calibrating of apparatus covered by the other groups of this subclass
- G01R35/04—Testing or calibrating of apparatus covered by the other groups of this subclass of instruments for measuring time integral of power or current
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/70—Energy storage systems for electromobility, e.g. batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/7072—Electromobility specific charging systems or methods for batteries, ultracapacitors, supercapacitors or double-layer capacitors
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T90/00—Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02T90/10—Technologies relating to charging of electric vehicles
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Abstract
The invention discloses a method for measuring and calibrating electric energy of a charging pile, which comprises the following steps: s1, collecting voltage, current and temperature of a charging pile in a charging process; s2, calculating phase angle difference of average active power P, voltage and current
And a single grid voltage period T; s3, calibrating charging power; calculating a calibration coefficient k = standard instrument measurement value/charging pile calculation electric energy; setting two-dimensional array k [ i ]][t](ii) a S4, calculating electric energy; current actual power
The electric energy output from the gun head in a single power grid period is WT = P'. T, the electric energy in each power grid voltage period T is accumulated to obtain total electric energy, and then the electric energy is obtained
Description
Technical Field
The invention relates to the technical field of electric vehicle charging, in particular to a method for measuring and calibrating electric energy of a charging pile.
Background
With the development of new energy vehicles, infrastructure construction and charging pile intelligent charging technology are also in rapid development. In 2020, new energy charging piles are incorporated into new capital construction ranks, and public charging piles (hereinafter, referred to as public piles) are extremely increasing in a short period of time. Due to the fact that the charging gun is of a special structure, the electric energy metering device is generally difficult to place at the gun end and is placed in the controller, large current flows from the controller to the gun end of the charging pile and needs to pass through the crimping terminal (crimping resistance exists), a gun line (line loss exists), and line loss generated by different currents can be different. Meanwhile, the sensors (voltage sensor and current sensor) in the controller are also influenced by the ambient temperature, so that the temperature factor and the charging environment are caused, and various nonlinear relations exist in the temperature rise in the charging process. (line loss, crimp resistance, temperature in the charging environment, temperature rise during charging), it is difficult to correct by an algorithm. Even if compensation could be made with the feedback circuit, higher cost and additional circuitry would be added. Meanwhile, due to rapid development of power electronic technology, various power electronic devices are increasingly widely applied to power systems, industries, transportation and families, and harmonic waves in a power grid are increased due to nonlinear loads, so that voltage and current waveforms are distorted, the frequency is changed, and the stability of data collected by a controller is seriously interfered. In order to meet the requirements of customers and the challenges of detection mechanisms, a method which can respond to temperature influences and line loss caused by different currents in real time, can be used in severe power grid environments and other factors and can calculate the electric quantity of the gun head is urgently needed.
Disclosure of Invention
Aiming at the defects and shortcomings of the prior art, the method for measuring and calibrating the electric energy of the charging pile is provided, and the calibration coefficient k under any temperature and any current is calculated in real time, so that the calibration coefficient is more accurate.
In order to achieve the above object, the present invention provides the following technical solutions.
A method for measuring and calibrating electric energy of a charging pile is characterized by comprising the following steps: the method comprises the following steps:
s1, collecting voltage, current and temperature of a charging pile in a charging process;
s2, calculating the average active power P passing through the charging pile through the voltage and the current, and calculating the phase angle difference of the voltage and the current
Time intervals T1 and T2 of two rising edges and two falling edges are respectively calculated by capturing the rising edge and the falling edge of the power grid frequency, and a single power grid voltage period T is obtained through T1 and T2;
s3, calibrating charging power; the method specifically comprises the following steps:
s31, measuring and collecting an electric energy value of the gun head of the charging gun through a standard instrument;
s32, calculating the electric energy value in the charging pile according to the average active power P,
calculating a calibration coefficient k = standard instrument measurement value/charging pile calculation electric energy;
s33, setting a two-dimensional array k [ i ] [ t ], adjusting different environment temperatures, recording calibration coefficients k at different temperatures and different currents, obtaining the calibration coefficient k at each specific environment and current, and recording the calibration coefficient k in the two-dimensional array;
s34, carrying out bilinear interpolation on the calibration coefficient k, so that the current calibration coefficient required can be calculated in real time under each continuous current value and temperature value of the charging pile;
s4, calculating electric energy; the electric energy W is the integral of the average power of the gun head to time, and the electric energy in each frequency power grid voltage period T is accumulated; current practicePower of
The electric energy output from the gun head in a single power grid period is WT = P'. T, the electric energy in each power grid voltage period T is accumulated to obtain total electric energy, and then the electric energy is obtained
W is the actual electric energy through filling the electric pile rifle head promptly.
The beneficial effects of the invention are as follows: according to the method, the calculated frequency is participated in the calculation of the acquisition frequency of the current and the voltage, so that the current and the voltage are periodically sampled in a single period, and the influence of non-whole period sampling on a phase angle is avoided; meanwhile, the phase angle is calculated, so that the calculated amount is smaller, the operation speed is higher, meanwhile, only the information at the required frequency point is analyzed through the extraction of the frequency spectrum, the influence of noise and each subharmonic is effectively inhibited, and the influence of current and temperature (temperature rise and environment comprehensive temperature) on the collection of voltage and current in the charging process is solved through calibrating the secondary array; and carrying out bilinear interpolation on the calibration coefficient, and calculating the calibration coefficient k at any temperature and any current in real time, so that the calibration coefficient is more accurate.
As an improvement of the present invention, in step S2, each grid voltage period T is averaged to obtain the most recent consecutive n grid period values T, which are taken as the grid period effective value T.
As an improvement of the present invention, in step S2, the calculation method of the single grid voltage period T is:
if Tmin is not less than t1 and not more than Tmax and Tmin is not less than t2 and not more than Tmax, a single period t = (t 1+ t 2)/2; if t1 is not more than Tmin, or t1 is not less than Tmax, t = t2; if t2 is less than or equal to Tmin or t2 is more than or equal to Tmax, t = t1; if t1 is less than or equal to Tmin or t1 is more than or equal to Tmax, and if t2 is less than or equal to Tmin or t2 is more than or equal to Tmax, t =20ms;
as a modification of the present invention, the step S2 specifically includes the following steps:
s21, collecting and calculating the power grid frequency; collecting actual instantaneous voltage corresponding to any collecting point;
s22, collecting and calculating voltage and current of a power grid;
s23, calculating a phase angle difference
Carrying out Fourier transform on U (n) to obtain a frequency domain sequence U (k);
and S24, calculating the average active power P.
In step S22, the grid voltage is stepped down by a voltage transformer and a current transformer and is transmitted to a voltage and current detection module, voltage and current data are collected, effective voltage and current at a collection point are calculated by root mean square, and apparent power is calculated according to the voltage and current.
As a modification of the present invention, in step S22, the following steps are specifically included:
s221, setting a sampling period and sampling points, setting the sampling period of a counting period of a timer to be T/N, and collecting voltage ADC (analog to digital converter) data during interruption of the timer, wherein the number of the collecting points in each power grid period is N;
s222, collecting and calculating a voltage effective value U; biasing, by a circuit, a voltage of a power supply; sequentially putting the data u (n) acquired each time into a cache; after N data are recorded, returning to the starting position of the cache, and updating cache data, wherein N =0,1,2, 8230, N-1;
u(n)＝|ADn-X|*U1/2X*q1；
wherein u (n) is the actual instantaneous voltage corresponding to any acquisition point, q1 is the transformation ratio of the voltage transformer, ADn is the voltage sampling AD sampling value, and X is the AD sampling number corresponding to the bias voltage;
the voltage of a single cycle
U1 is voltage acquisition reference voltage, X is AD sampling number corresponding to the bias current, U1 is voltage acquisition reference voltage, q1 is transformation ratio of the voltage transformer, and N is the number of sampling points in each period;
s223, collecting and calculating a current effective value I, and biasing the current of the power supply through a circuit; sequentially putting the data I (n) acquired each time into a cache; after N data are recorded, returning to the starting position of the cache, and updating the cache data, wherein N =0,1,2 \8230; 8230; N-1;
I(n)＝|ADn-X|*I1/2X*q2；
wherein I (n) is the actual instantaneous current corresponding to any acquisition point, q2 is the current transformer transformation ratio, ADn is the current sampling AD sampling value, and X is the AD sampling number corresponding to the bias current;
the current of a single cycle
Wherein ADn is a current sampling AD sampling value, X is the AD sampling number corresponding to the bias current,
and acquiring reference current for the current, wherein q2 is the transformation ratio of the current transformer, and N is the number of sampling points in each period.
As a modification of the present invention, in step S23, the specific calculation steps are:
DFT is carried out on U (n) to obtain a frequency domain sequence U (k);
wherein k =0,1,2, \8230;, N-1, N is the set sampling point number, ua, ub are the real part and imaginary part of k-th-order component of voltage frequency domain, respectively, wherein
DFT is carried out on the I (n) to obtain a frequency domain sequence I (k);
ia. Ib is a real part and an imaginary part of the k-time component of the voltage frequency domain respectively;
when k =1, the voltage current complex number of the fundamental wave calculates the angular difference
In step S24, the average power
As a modification of the present invention, the specific steps in S34 include:
s341, firstly, finding the interval where the current and the temperature in the calibrated k [ i ] [ t ] exist in an array according to the current i and the temperature t, and respectively defining variables i1, i2, t1 and t2 to respectively represent the current i and the temperature t;
s342, calculating a first dimension; under the current i1, taking t as a variable, carrying out a first interpolation operation between t1 and t2, and obtaining k [ i1] [ t ] = k [ i1] [ t1] - [ (k [ i1] [ t1] -k [ i1] [ t2 ])/(t 1-t 2) ] (t 1-t 2) from y = [ y1- (y 1-y 2)/(x 1-x 2) ] (x 1-x),
wherein k [ i1] [ t ] is a value calibration value calculated by calibrating the coefficient at the current i1 and the temperature t, k [ i2] [ t ] = k [ i2] [ t1] - [ (k [ i2] [ t1] -k [ i2] [ t2 ])/(t 1-t 2) ] (t 1-t),
wherein k [ i2] [ t ] is a value calibration value calculated by a calibration coefficient at the current i2 and the temperature t;
s343, second dimension calculation, under the current temperature t, using i as variable, carrying out second interpolation operation between i1 and i2 to obtain k [ i ] [ t ] = k [ i1] [ t ] - [ (k [ i1] [ t ] -k [ i2] [ t ])/(i 1-i 2) ] (i 1-i),
wherein k [ i ] [ t ] is a value calibration value calculated by a calibration coefficient at the current i and the temperature t;
s344, calculating to obtain k [ i ] [ t ];
k[i1][t]＝k[i1][t1]-[(k[i1][t1]-k[i1][t2])/(t1-t2)]*(t1-t)；
k[i2][t]＝k[i2][t1]-[(k[i2][t1]-k[i2][t2])/(t1-t2)]*(t1-t)；
k[i][t]＝k[i1][t]-[(k[i1][t]-k[i2][t])/(i1-i2)]*(i1-i)。
a charging pile uses the method for measuring and calibrating the electric energy of the charging pile.
Detailed Description
A method for measuring and calibrating electric energy of a charging pile comprises the following steps:
s1, electrifying a charging pile, and authorizing normal charging; the charging pile acquires voltage, current and temperature (including ambient temperature and comprehensive temperature in the charging process) in the charging process in real time through a voltage transformer, a current transformer and a temperature sensing resistor;
s2, calculating the average active power P passing through the charging pile controller through the voltage and the current, and calculating the phase angle difference of the voltage and the current
The method comprises the following specific steps:
s21, collecting and calculating the power grid frequency; collecting actual instantaneous voltage corresponding to any collecting point;
s211, receiving a rising edge and a falling edge of the power grid frequency sampling GPIO by the single-chip microcomputer MCU through one PWM input capturing voltage and current detection module, respectively calculating time intervals T1 and T2 of the two rising edges and the two falling edges, and obtaining a single power grid voltage and power grid voltage period T through T1 and T2; if Tmin is not less than t1 and not more than Tmax and Tmin is not less than t2 and not more than Tmax, a single period t = (t 1+ t 2)/2; if t1 is not more than Tmin, or t1 is not less than Tmax, t = t2; if t2 is less than or equal to Tmin or t2 is more than or equal to Tmax, t = t1; if t1 is not less than Tmin or t1 is not less than Tmax, and if t2 is not less than Tmin or t2 is not less than Tmax, then t =20ms, in the embodiment, tmin is 18182us and Tmax is 22222us, and by setting t1 and t2, frequency sampling errors caused by slope interference or other abnormalities of the power grid are avoided.
S212, taking an average of the obtained latest n consecutive grid period values T of each grid voltage period T as a grid period effective value T, in this embodiment, n is 5, and averaging is performed through the latest 5 period values, so that linear change of frequency is ensured, and time-frequency fundamental frequency sampling distortion caused by harmonic is filtered. Meanwhile, the period of each calculation is used as the acquisition period of the next frequency, the frequency is dynamically adjusted, and software synchronization is realized.
S22, collecting and calculating voltage and current of a power grid; the power grid voltage is reduced through the voltage transformer and the current transformer and is transmitted to the voltage and current detection module, N sampling points are arranged in each power grid voltage period T, each acquisition period is T/N, the single chip microcomputer MCU acquires voltage and current data through the calculated T/N as the acquisition period, the number N of the sampling points in the embodiment is 128, namely 128 sampling points are acquired in the power grid voltage period T, and effective voltage and current of the 128 acquisition points are calculated through root mean square. Apparent power was calculated from the voltage and current. The active power of multiple harmonics is greatly reserved, the calculation load pressure brought by DFT is avoided, and the calculation precision can be met.
The method specifically comprises the following steps:
s221, setting a sampling period and sampling points, setting the sampling period of a counting period of a timer to be T/N, and collecting voltage ADC data during timer interruption, wherein the number of the sampling points in each power grid period is N;
s222, collecting and calculating a voltage effective value U; 1/2 voltage division is carried out on the power supply voltage through a circuit, namely, the voltage of the power supply is biased; the device is used for collecting alternating current voltage; the single chip microcomputer MCU samples through 12-bit AD, and sequentially puts data u (n) acquired each time into a cache; after N data are recorded, returning to the starting position of the cache, and updating the cache data, wherein N =0,1,2 \8230; 8230; N-1;
u(n)＝|ADn-X|*U1/2X*q1；
wherein u (n) is the actual instantaneous voltage corresponding to any acquisition point, q1 is the voltage transformer transformation ratio, ADn is the voltage sampling AD sampling value, X is the AD sampling number corresponding to the bias voltage, and 2X is the precision of AD sampling;
the voltage of a single cycle
Wherein, U1 is a voltage acquisition reference voltage, N is the number of acquisition points, and N =128;
s223, collecting and calculating a current effective value I, and biasing the current of the power supply through a circuit; sequentially putting the data I (n) acquired each time into a cache; after N data are recorded, returning to the starting position of the cache, and updating cache data, wherein N =0,1,2, 8230, N-1;
I(n)＝|ADn-X|*I1/2X*q2；
wherein I (n) is the actual instantaneous current corresponding to any acquisition point, q2 is the current transformer transformation ratio, ADn is the current sampling AD sampling value, A is the AD sampling number corresponding to the bias current, X is the AD sampling number corresponding to the bias current, and 2X is the precision of AD sampling;
the current of a single cycle
ADn is a current sampling AD sampling value, A is the AD sampling number corresponding to the bias current,
for current collection reference current, q2 is the transformation ratio of the current transformer, N is the number of collection points, and N =128.
S23, calculating the phase angle difference
Carrying out Fourier transform on U (n) to obtain a frequency domain sequence U (k);
the specific calculation steps are as follows:
DFT is carried out on U (n) to obtain a frequency domain sequence U (k);
wherein k =0,1,2, \8230;, N-1, N is the number of sampling points set, ua, ub are the real and imaginary parts of the k-th sub-component of the voltage frequency domain, respectively, wherein
DFT is carried out on the I (n) to obtain a frequency domain sequence I (k);
ia. Ib is a real part and an imaginary part of the k-time component of the voltage frequency domain respectively;
when k =1, the voltage current complex number of the fundamental wave calculates the angular difference
Through Discrete Fourier Transform (DFT), the continuous variable time domain signal is transformed into a discrete signal which is beneficial to a single chip microcomputer MCU to calculate a frequency domain signal, phase angle calculation is carried out, so that the calculated amount is smaller, the operation speed is higher, and meanwhile, through extraction of frequency spectrum, only information at a required frequency point is analyzed, and the influence of noise and each subharmonic is effectively inhibited.
S24, calculating the average active power P; the average apparent power is calculated once at every N current and voltage sampling points, and the average power in a single period
The influence of different motorcycle types OBC and other related circuits on the charging efficiency of the power grid is solved by the access of the phase angle.
S3, calibrating charging power; the method specifically comprises the following steps:
s31, measuring and collecting an electric energy value of the gun head of the charging gun through a standard instrument;
s32, calculating the electric energy value in the charging pile according to the average active power P,
calculating a calibration coefficient k = standard instrument measurement value/charging pile calculation electric energy;
s33, adjusting different environment temperatures, recording calibration coefficients k at different temperatures and at different currents, obtaining the calibration coefficient k at each specific environment and at each current, and recording the calibration coefficients k into a two-dimensional array; setting the two-dimensional array k [ i ] [ t ] with temperature and current,
{
{k11,k12,k13},
{k21,k22,k23}，
……
{k71,k72,k73},
{k81,k82,k83},
}
in the formula, the k arrays have 8 rows, namely 8 arrays, which represent 8 current division points and represent currents of 7A,10A,12A,14A,26A,20A, 26A and 32A. Each array contained 3 elements, representing 3 temperature cut points, representing temperatures (ambient) at-30 deg.C (integrated temperature of-7 deg.C), 25 deg.C (integrated temperature of 53 deg.C), and 50 deg.C (integrated temperature of 85 deg.C). K11 indicates the calibration value of the charging pile at the temperature of minus 7 ℃ when the current of the charging pile is 32A; k12 indicates the calibration value of 53 ℃ at 32A for charging pile current, \8230 \ 8230;, 7A for k83 bit current, and 85 ℃ for ambient temperature. The product was uncapped and placed in an ambient temperature cabinet. Different ambient temperatures are adjusted, and when the current is not applied at different temperatures, the proportion of the calculated value of the charging pile to the measured value is recorded as k. Thus, all parameters are recorded and calculated, and a calibration coefficient k in each specific environment and current is obtained and recorded into an array;
s34, carrying out bilinear interpolation on the calibration coefficient k, and carrying out real-time calculation on the calibration coefficient by using a two-dimensional interpolation method in order to further perfect k differences at different temperature points and at different currents, namely carrying out interpolation operation on 2 dimensions of current and temperature simultaneously, so that the charging pile can calculate the currently required calibration coefficient in real time at each continuous current value and temperature value; the method comprises the following specific steps:
s341, finding the calibrated interval of the current and the temperature in the k [ i ] [ t ] from the current i and the temperature t to the array, and respectively defining variables i1, i2, t1 and t2 to respectively represent the current i and the temperature t;
s342, calculating a first dimension; under the current i1, taking t as a variable, carrying out a first interpolation operation between t1 and t2, and obtaining k [ i1] [ t ] = k [ i1] [ t1] - [ (k [ i1] [ t1] -k [ i1] [ t2 ])/(t 1-t 2) ] (t 1-t 2) from y = [ y1- (y 1-y 2)/(x 1-x 2) ] (x 1-x),
wherein k [ i1] [ t ] is a value calibration value calculated by a calibration coefficient at a current i1 and a temperature t, k [ i2] [ t ] = k [ i2] [ t1] - [ (k [ i2] [ t1] -k [ i2] [ t2 ])/(t 1-t 2) ] (t 1-t),
wherein k [ i2] [ t ] is a value calibration value calculated by calibrating the coefficient at the current i2 and the temperature t;
s343, second dimension calculation is carried out, i is taken as a variable at the current temperature t, and second interpolation operation is carried out between i1 and i2 to obtain
k[i][t]＝k[i1][t]-[(k[i1][t]-k[i2][t])/(i1-i2)]*(i1-i)，
Wherein k [ i ] [ t ] is a value calibration value calculated by a calibration coefficient at the current i and the temperature t;
s344, calculating to obtain k [ i ] [ t ];
k[i1][t]＝k[i1][t1]-[(k[i1][t1]-k[i1][t2])/(t1-t2)]*(t1-t)；
k[i2][t]＝k[i2][t1]-[(k[i2][t1]-k[i2][t2])/(t1-t2)]*(t1-t)；
k[i][t]＝k[i1][t]-[(k[i1][t]-k[i2][t])/(i1-i2)]*(i1-i)。
s4, calculating electric energy; the electric energy W is the integral of the average power of the gun head to time, and the electric energy in each frequency power grid voltage period T is accumulated; current actual power
The electric energy output from the gun head in a single power grid period is WT = P'. T, the electric energy in each power grid voltage period T is accumulated to obtain total electric energy, and then the electric energy is obtained
W is the actual electric energy through filling the electric pile rifle head promptly.
The invention is based on the fact that the charging pile multiplexes the collected data of other functions (over-current, over-voltage and over-temperature) under the condition of not depending on an electric energy chip; the frequency acquisition uses double triggering and a double acquisition mechanism, so that frequency sampling errors caused by slope interference or other abnormalities are avoided; the frequency calculation adopts an averaging method, so that the influence of harmonic waves on the change of the frequency is reduced; the dynamic adjustment of the frequency realizes software synchronization and reduces the frequency spectrum leakage and barrier effect caused by asynchronous sampling; the calculated frequency is participated in the calculation of the acquisition frequency of the current and the voltage, so that the current and the voltage are periodically sampled in a single period, and the influence of non-whole period sampling on a phase angle is avoided; through Discrete Fourier Transform (DFT), the continuous variable time domain signal is transformed into a discrete signal which is beneficial to a single chip microcomputer MCU to calculate a frequency domain signal, phase angle calculation is carried out, so that the calculated amount is smaller, the operation speed is higher, and meanwhile, through extraction of a frequency spectrum, only information at a required frequency point is analyzed, and the influence of noise and each subharmonic is effectively inhibited; the secondary array is used for calibration, so that the influence of current and temperature (temperature rise and environment comprehensive temperature) on the acquisition of voltage and current in the charging process is avoided; and carrying out bilinear interpolation on the calibration coefficient, and calculating the calibration coefficient k at any temperature and any current in real time, so that the calibration coefficient is more accurate.
The invention also discloses a charging pile and a method for measuring and calibrating the electric energy of the charging pile.
The above description is only a preferred embodiment of the present invention, and all equivalent changes or modifications of the structure, characteristics and principles described in the present invention are included in the scope of the present invention.
Claims (8)
1. A method for measuring and calibrating electric energy of a charging pile is characterized by comprising the following steps: the method comprises the following steps:
s1, collecting voltage, current and temperature of a charging pile in a charging process;
s2, calculating the average active power P passing through the charging pile through the voltage and the current, and calculating the phase angle difference of the voltage and the current
Time intervals T1 and T2 of two rising edges and two falling edges are respectively calculated by capturing the rising edge and the falling edge of the power grid frequency, and a single power grid voltage period T is obtained through T1 and T2;
s3, calibrating charging power; the method specifically comprises the following steps:
s31, measuring and collecting an electric energy value of the gun head of the charging gun through a standard instrument;
s32, calculating an electric energy value inside the charging pile according to the average active power P;
calculating a calibration coefficient k = standard instrument measurement value/charging pile calculation electric energy;
s33, setting a two-dimensional array k [ i ] [ t ], adjusting different environment temperatures, recording calibration coefficients k at different temperatures and different currents, obtaining the calibration coefficient k at each specific environment and current, and recording the calibration coefficient k in the two-dimensional array;
s34, carrying out bilinear interpolation on the calibration coefficient k, so that the current calibration coefficient required can be calculated in real time under each continuous current value and temperature value of the charging pile;
s4, calculating electric energy; the electric energy W is the integral of the average power of the gun head to time, and the electric energy in each frequency power grid voltage period T is accumulated; current actual power
The electric energy output from the gun head in a single power grid period is WT = P'. T, the electric energy in each period T is accumulated to obtain the total electric energy, and then the electric energy is obtained
W is the actual electric energy through filling the electric pile rifle head promptly.
2. The charging pile electric energy metering and calibrating method according to claim 1, wherein the charging pile electric energy metering and calibrating method comprises the following steps: in step S2, each grid voltage period T averages the obtained latest n consecutive grid period values T to obtain a grid period effective value T.
3. The charging pile electric energy metering and calibrating method according to claim 1, wherein the charging pile electric energy metering and calibrating method comprises the following steps: in step S2, the method for calculating the single grid voltage period T is:
if Tmin is not less than T1 and not more than Tmax and Tmin is not less than T2 and not more than Tmax, a single power grid voltage period T = (T1 + T2)/2; if t1 is not more than Tmin, or t1 is not less than Tmax, t = t2; if t2 is less than or equal to Tmin or t2 is more than or equal to Tmax, t = t1; if t1 is not less than Tmin or t1 is not less than Tmax, and if t2 is not less than Tmin or t2 is not less than Tmax, t =20ms.
4. The method for measuring and calibrating the electric energy of the charging pile according to claim 1, characterized by comprising the following steps: the step S2 specifically includes the following steps:
s21, collecting and calculating the frequency of the power grid; collecting actual instantaneous voltage corresponding to any collecting point;
s22, collecting and calculating voltage and current of a power grid;
s23, calculating the phase angle difference
Carrying out Fourier transform on U (n) to obtain a frequency domain sequence U (k);
and S24, calculating the average active power P.
5. The method for measuring and calibrating the electric energy of the charging pile according to claim 4, characterized by comprising the following steps: in step S22, the grid voltage is stepped down by the voltage transformer and the current transformer and transmitted to the voltage and current detection module, the voltage and current data is collected, the effective voltage and current at the collection point are calculated by the root mean square, and the apparent power is calculated according to the voltage and current.
6. The charging pile electric energy metering and calibrating method according to claim 5, wherein the charging pile electric energy metering and calibrating method comprises the following steps: in step S22, the method specifically includes the following steps:
s221, setting a sampling period and sampling points, setting the sampling period of a counting period of a timer to be T/N, and collecting voltage ADC data during timer interruption, wherein the number of the sampling points in each power grid period is N;
s222, collecting and calculating a voltage effective value U; biasing, by a circuit, a voltage of a power supply; sequentially putting the data u (n) acquired each time into a cache; after N data are recorded, returning to the starting position of the cache, and updating cache data, wherein N =0,1,2, 8230, N-1;
u(n)＝|ADn-X|*U1/2X*q1；
wherein u (n) is the actual instantaneous voltage corresponding to any acquisition point, q1 is the transformation ratio of the voltage transformer, ADn is the voltage sampling AD sampling value, and X is the AD sampling number corresponding to the bias voltage;
the voltage of a single cycle
U1 is voltage acquisition reference voltage, X is AD sampling number corresponding to the bias current, U1 is voltage acquisition reference voltage, q1 is transformation ratio of the voltage transformer, and N is the number of sampling points in each period;
s223, collecting and calculating a current effective value I, and biasing the current of the power supply through a circuit; sequentially putting the data I (n) acquired each time into a cache; after N data are recorded, returning to the starting position of the cache, and updating the cache data, wherein N =0,1,2 \8230; 8230; N-1;
I(n)＝|ADn-X|*I1/2X*q2；
wherein I (n) is the actual instantaneous current corresponding to any acquisition point, q2 is the current transformer transformation ratio, ADn is the current sampling AD sampling value, and X is the AD sampling number corresponding to the bias current;
the current of a single cycle
Wherein ADn is a current sampling AD sampling value, X is the AD sampling number corresponding to the bias current,
and acquiring reference current for current, wherein q2 is the transformation ratio of the current transformer, and N is the number of sampling points in each period.
7. The method for measuring and calibrating the electric energy of the charging pile according to claim 6, characterized by comprising the following steps: in step S23, the specific calculation steps are:
DFT is carried out on U (n) to obtain a frequency domain sequence U (k);
wherein k =0,1,2, \8230;, N-1, N is the set sampling point number, ua and Ub are respectively the real part and the imaginary part of the k-th component of the voltage frequency domain, wherein
DFT is carried out on the I (n) to obtain a frequency domain sequence I (k);
ia. Ib is a real part and an imaginary part of the k-time component of the voltage frequency domain respectively;
when k =1, the voltage current complex of the fundamental wave calculates the angular difference
In step S24, the average power
8. The method for measuring and calibrating the electric energy of the charging pile according to claim 1, characterized by comprising the following steps: the specific steps in S34 include:
s341, firstly, finding the interval where the current and the temperature in the calibrated k [ i ] [ t ] exist in an array according to the current i and the temperature t, and respectively defining variables i1, i2, t1 and t2 to respectively represent the current i and the temperature t;
s342, calculating a first dimension; under the current i1, taking t as a variable, carrying out a first interpolation operation between t1 and t2, wherein y = [ y1- (y 1-y 2)/(x 1-x 2) ] (x 1-x);
obtaining k [ i1] [ t ] = k [ i1] [ t1] - [ (k [ i1] [ t1] -k [ i1] [ t2 ])/(t 1-t 2) ] (t 1-t), wherein k [ i1] [ t ] is a value calibration value calculated by a calibration coefficient at the current i1 and the temperature t, and k [ i2] [ t ] = k [ i2] [ t1] - [ (k [ i2] [ t1] -k [ i2] [ t2 ])/(t 1-t 2) ] (t 1-t), wherein k [ i2] [ t ] is a value calibration value calculated by a calibration coefficient at the current i2 and the temperature t;
s343, second dimension calculation is carried out, i is taken as a variable at the current temperature t, and second interpolation operation is carried out between i1 and i2 to obtain
k[i][t]＝k[i1][t]-[(k[i1][t]-k[i2][t])/(i1-i2)]*(i1-i)，
Wherein k [ i ] [ t ] is a value calibration value calculated by a calibration coefficient at the current i and the temperature t;
s344, calculating to obtain k [ i ] [ t ];
k[i1][t]＝k[i1][t1]-[(k[i1][t1]-k[i1][t2])/(t1-t2)]*(t1-t)；
k[i2][t]＝k[i2][t1]-[(k[i2][t1]-k[i2][t2])/(t1-t2)]*(t1-t)；
k[i][t]＝k[i1][t]-[(k[i1][t]-k[i2][t])/(i1-i2)]*(i1-i)。
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