JP2982612B2 - PQ calculation correction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a voltage and a current of a power system to be measured for active power and reactive power with a voltage transformer and a current transformer, and measures the measured secondary voltage of the voltage transformer and the current transformer. The present invention relates to a PQ calculation correction method for calculating active power and reactive power in a power system to be measured from an output voltage and a measured secondary output current.

[0002]

2. Description of the Related Art To measure active power and reactive power, it is necessary to detect voltage and current from a power system to be measured. In general, a device for measuring the active power and the reactive power of a power system includes a voltage transformer in order to set an input signal (a signal corresponding to a voltage and a current of the power system) to a level that can be read by an arithmetic circuit in the device. And current transformers are mostly used.

[0003]

However, due to the characteristics of these voltage transformers and current transformers, various errors occur when data is taken into the arithmetic circuit, and the measurement accuracy of the active power and the reactive power decreases. In other words, the secondary outputs of the voltage transformer and the current transformer include offset, gain error and phase error, and are effective from the measured secondary output voltage of the voltage transformer and the measured secondary output current of the current transformer. When the power and the reactive power are calculated, the active power and the reactive power include an offset, a gain error, and an error due to a phase error due to the characteristics of the voltage transformer and the current transformer. It could not be calculated.

An object of the present invention is to provide a PQ operation correction method capable of accurately calculating active power and reactive power by minimizing an error caused by characteristics of a voltage transformer and a current transformer.

[0005]

According to the PQ operation correction method of the present invention, first, a secondary output voltage of a voltage transformer and a secondary output current of a current transformer are sampled to measure a measured secondary output voltage and a measured secondary output voltage. , The voltage gain error and the current gain error of the secondary output current are calculated, and the phase error of the phase difference between the measured secondary output voltage and the measured secondary output current is calculated. Next, the secondary output voltage of the voltage transformer and the secondary output current of the current transformer are sampled to obtain a measured secondary output voltage and a measured secondary output current.
Next, the measured active power and the measured reactive power are calculated from the measured secondary output voltage and the measured secondary output current.
Next, a correction operation is performed on the actually measured active power and reactive power based on the voltage gain error, the current gain error, and the phase error to calculate true active power and true reactive power. Next, true active power and true reactive power are output.

[0006]

According to the configuration of the present invention, the voltage gain error, the current gain error, and the phase error caused by the characteristics of the voltage transformer and the current transformer are calculated in advance, and the measured active power in the power system to be measured is calculated. Corrects the voltage and current offsets, voltage gain errors, current gain errors, and phase errors due to the characteristics of the voltage and current transformers and the true active power and true reactive power for the measured reactive power. Is calculated, the error caused by the characteristics of the voltage transformer and the current transformer can be minimized, and the active power and the reactive power can be accurately calculated.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, this PQ calculation correction method firstly uses a secondary output voltage and a current transformer of a voltage transformer for detecting a voltage and a current of a power system to be measured for active power and reactive power, respectively. Each of the secondary output currents is sampled to calculate the voltage gain error and the current gain error of the actually measured secondary output voltage and the actually measured secondary output current, respectively, and to calculate between the actually measured secondary output voltage and the actually measured secondary output current. The phase error of the phase difference is calculated and stored in the error table of the memory (error calculation routine of step S1).

Next, the data of the secondary output voltage of the voltage transformer and the data of the secondary output current of the current transformer are sampled by a fixed number to obtain the actually measured secondary output voltage and the actually measured secondary output current (step S2). Next, the measured active power and the measured reactive power are calculated from the measured secondary output voltage and the measured secondary output current (step S3).

Next, it is determined whether or not the voltage gain error, the current gain error, and the phase error are to be calculated again (step S4). If they are not to be calculated again, then a table is obtained for the measured active power and the measured reactive power. Correction calculation is performed based on the above voltage gain error, current gain error, and phase error to obtain true active power and true reactive power (step S5). When calculating again, the same processing as step S1 is performed (error calculation routine of step S6), and then step S5 is executed.

Finally, true active power and true reactive power
Is output (step S7), and the process returns to step S2. here
Now, the specifics of the error calculation routine in steps S1 and S6
The basic contents will be described with reference to FIG. First, voltage change from outside
Enter a known reference value for the transformer and the current transformer.
You. At this time, the voltage transformer of the voltage transformer and the current transformer
Ratio k_PAnd current transformation ratio k _CAlso input (step
U1).

Next, the measured secondary output voltage and the measured secondary output current are taken in from the voltage transformer and the current transformer by sampling (step U2). Then, the secondary output voltage and the secondary output current measured from the voltage transformer and current transformer, since each voltage transformation ratio k _P times and current transformation ratio k _C a value obtained by multiplying the input value (reference value) The above errors (voltage and current offset, voltage and current gain error, phase error) are obtained (step U
3).

Next, a voltage and current offset, a voltage and current gain error, and a phase error are written into an error table in the memory (step U4). FIG.
FIG. 2 shows a block diagram of a PQ calculation device that performs a Q calculation correction method. Note that this PQ calculation device shows a block diagram of a circuit that calculates active power and reactive power of a three-phase power system. In FIG. 3, 1 to 3 are a, b, and c, respectively.
Is a current input terminal for inputting the three-phase currents ia, ib, and ic. 4 to 6 are three-phase voltages va of a, b, and c, respectively.
, Vb, vc. 7-9
Are low pass filters (LP
F). Reference numerals 10 to 12 denote low-pass filters (LPFs) that pass only the fundamental wave components of the three-phase voltages va, vb, and vc of a, b, and c, respectively. Reference numeral 13 denotes a multiplexer (MPX) for selectively outputting the outputs of the low-pass filters 7 to 12. Reference numeral 14 denotes a sample and hold circuit (SH) for the output of the multiplexer 13. Reference numeral 15 denotes an analog / digital converter (A / D). Reference numeral 16 denotes an input / output circuit (I / O). Reference numeral 17 denotes a CPU for performing various arithmetic processing. A ROM 18 stores programs and the like. 1
Reference numeral 9 denotes a RAM provided with an error table and the like. 20
Is a two-port RAM. Reference numeral 21 denotes a selection switch for performing various setting operations such as designating recalculation of an error.

FIG. 4 is a schematic diagram for obtaining a voltage gain error and a current gain error, wherein 31 is a voltage source, 32 is a current source, 33 is a voltmeter, 34 is an ammeter, and 35 is a voltage transformer (PT). , 36 are current transformers (CT), and 37 is a PQ operation circuit. FIG. 5 is a schematic diagram for obtaining a phase error. 41 is a voltage source, 42 is a resistor, 43 is a voltmeter,
Is an ammeter, 45 is a voltage transformer, 46 is a current transformer, 47
Is a PQ operation circuit.

FIG. 6 is a waveform diagram showing a state of sampling the secondary output voltage v and the secondary output current i when a phase error is obtained. Sampling is performed at a period that is an integer fraction (for example, 1/16) of the period of the fundamental wave and is performed for N periods (for example, 12 periods) of the fundamental wave. Hereinafter, a procedure for calculating each error and calculating the true active power and the true reactive power from the measured active power and the measured reactive power will be described using mathematical expressions (corresponding to the flowcharts of FIGS. 1 and 2).

First, the calculation of the error of the voltage transformer and the current transformer will be described (corresponding to the flowchart of FIG. 2). First, calculation of the voltage offset and the current offset of the voltage transformer and the current transformer, and the calculation of the voltage gain error and the current gain error will be described. In the following description, for the sake of simplicity, it is assumed that the voltage transformer ratio of the voltage transformer and the current transformer ratio of the current transformer are respectively 1.

The voltage transformer and the current transformer have reference values v,
When i is input, the corresponding output values v 'and i' are expressed by (Equation 1) and (Equation 2), respectively. Here, v ₀ is a voltage offset, i ₀ is a current offset, ε _v is a voltage gain error, and ε _i is a current gain error.

[0017]

(Equation 1)

[0018]

(Equation 2)

Therefore, when 0 is input as each of the reference values v and i, a voltage offset v ₀ and a current offset i ₀ are obtained. Next, a known reference value v, i is input, and the output that appears at that time is based on v ′, i ′ and the voltage offset v ₀ and current offset i ₀ obtained earlier.
Voltage gain error epsilon _v and current gain error epsilon _i is obtained.

The calculation of the above error is performed according to the schematic diagram of FIG. Next, the calculation of the phase error will be described. In-phase reference value v for voltage and current transformers
When (= sinωt) and i (= sinωt) are input, the output values v ′ and i ′ corresponding thereto are expressed by (Equation 3) and (Equation 4), respectively. Here, εθ is a phase error.

[0021]

(Equation 3)

[0022]

(Equation 4)

From the (Equation 3) and (Equation 4), when the actually measured active power P 'is obtained, it becomes as shown in (Equation 5).

[0024]

(Equation 5)

Next, from the equation (Equation 4) in which the phase is shifted by π / 2 and (Equation 3), the actually measured reactive power Q ′ is obtained.
(Equation 6)

[0026]

(Equation 6)

Therefore, the measured active power P 'and the measured active power P'
Reactive power Q 'and voltage offset v found earlier₀, Current
Huset i₀, Voltage gain error ε_vAnd current gain error
Difference ε _i, The phase error εθ is obtained by (Equation 7).

[0028]

(Equation 7)

The above phase error εθ is performed according to the schematic diagram of FIG. Note that each of the offsets and errors is a fixed period that is an integer fraction of one cycle of the rated frequency of the power system to be measured. For example, sampling is performed during a period that is an integral multiple of the rated frequency of the power system to be measured. It is obtained by an operation based on the data strings of the outputs of the obtained voltage transformer and current transformer. The state of the above sampling is shown in FIG.

When the active power and the reactive power of the three-phase power system are measured by the two-power meter method or the three-power meter method, each of the above-described calculations and sampling is performed for each of the voltage transformer and the current transformer. Voltage and current offsets, voltage and current gain errors, and phase errors for all voltage and current transformers are determined and stored in an error table in the memory.

The algorithm for obtaining the voltage and current offsets, the voltage and current gain errors, and the phase errors has been described above. Next, an algorithm for calculating true active power and true reactive power from the voltage and current offset, the voltage and current gain error, the phase error, and the measured active power and the measured reactive power obtained by sampling will be described.

When the voltage of the power system and the instantaneous value of the voltage are taken in by sampling, the data including the error (actually measured voltage v ', actually measured current i') is expressed by the following equation (8).
It is expressed as (Equation 9). Where V is the voltage amplitude, I
Is the current amplitude, and θ is the phase difference between the voltage v ′ and the current i ′.

[0033]

(Equation 8)

[0034]

(Equation 9)

Here, the error components ε _v , ε _i ,
v ₀ and i ₀ are within ± 1% of the base value, and εθ is ±
It shall be within 1 °. From Equations (8) and (9), assuming that the measured active power is P 'and the reactive power is Q', the measured active power P 'and the measured reactive power Q' are (Equation 1)
0) and (Equation 11).

[0036]

(Equation 10)

[0037]

[Equation 11]

On the other hand, the true active power including no error is P,
Similarly, assuming that the true reactive power that does not include an error is Q, the true active power P and the true active power Q are respectively (Equation 1)
2), (Expression 13).

[0039]

(Equation 12)

[0040]

(Equation 13)

Here, dividing both sides of (Equation 10) and (Equation 11) by (Equation 12) and (Equation 13) respectively yields (Equation 14) and (Equation 15).

[0042]

[Equation 14]

[0043]

(Equation 15)

Here, -1 ° <εθ <1 °, and cosε
θ ≒ 1, sinεθ ≒ εθ (rad), and v ₀ · i
_{If 0} 00, the true active power P and the true reactive power Q
Is as shown in (Equation 16) and (Equation 17).

[0045]

(Equation 16)

[0046]

[Equation 17]

Further, here, tan θ = Q / P ≒ Q ′ /
Assuming that P ', the true active power P and the true reactive power Q are as shown in (Equation 18) and (Equation 19).

[0048]

(Equation 18)

[0049]

[Equation 19]

Therefore, the actually measured voltage v 'and the actually measured current i' are sampled, and the actually measured active power P 'and the actually measured reactive power Q' are obtained from the waveform data. _{From v} , the current gain error ε _i , and the phase error εθ, the true active power P and the true reactive power Q can be obtained with high accuracy by (Equation 18) and (Equation 19). Note that the actually measured voltage v 'and the actually measured current i'
The procedure for obtaining the actually measured active power P 'and the actually measured reactive power Q' from the waveform data is well known in the art, and the detailed description is omitted, but the procedure for obtaining the actually measured voltage v 'and the actually measured current i' is omitted. If the amplitude and phase difference are known,
It can be calculated by performing the arithmetic processing as in 2) and (Equation 13).

The active power P and the reactive power Q are determined by the two-power meter method or the three-power meter method as described above.
The sampling of the voltage v 'and the current i' is performed at a fixed period equal to an integral number (for example, 1/16) of one period of the rated frequency of the power system, for example, at the time of detection of each error. This is performed for a period, and various calculations are performed based on the obtained sampling data.

As described above, when the correction calculation is performed, the gain adjustment operation which has been performed conventionally is not required at all, and the measurement operation of the active power and the reactive power is simplified and can be performed with high accuracy. It becomes possible.

[0053]

According to the PQ calculation correction method of the present invention,
The voltage gain error, the current gain error, and the phase error due to the characteristics of the voltage transformer and the current transformer are calculated in advance, and the voltage transformer and the reactive power are measured with respect to the measured active power and reactive power in the power system to be measured. Since the true active power and the reactive power are calculated by correcting the voltage gain error, the current gain error, and the phase error caused by the characteristics of the current transformer, the error caused by the characteristics of the voltage transformer and the current transformer is minimized. It is possible to calculate the active power and the reactive power accurately and accurately, and it is not necessary to perform a complicated gain adjustment operation, so that the measuring operation of the active power and the reactive power is simplified.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a procedure of a PQ calculation correction method according to an embodiment of the present invention.

FIG. 2 is a specific flowchart of a main part of FIG. 1;

FIG. 3 is a block diagram illustrating a PQ calculation device that realizes a PQ calculation correction method.

FIG. 4 is a schematic diagram of a PQ calculation device when calculating a voltage offset, a current offset, a voltage gain error, and a current gain error.

FIG. 5 is a schematic diagram of a PQ calculation device when obtaining a phase error.

FIG. 6 is a waveform diagram showing a state of sampling.

[Explanation of symbols]

 7-12 Low Pass Filter 13 Multiplexer 14 Sample Hold Circuit 15 Analog / Digital Converter 16 Input / Output Circuit 17 CPU 18 ROM 19 RAM 20 2-Port RAM

Claims (1)

(57) [Claims] 1. A secondary output voltage of a voltage transformer and a secondary output current of a current transformer are sampled to calculate a voltage gain error and a current gain error of a measured secondary output voltage and a measured secondary output current, respectively. A first step of calculating a phase error of a phase difference between an actually measured secondary output voltage and an actually measured secondary output current; and a secondary output voltage of the voltage transformer and a secondary output current of the current transformer. A second step of sampling the measured secondary output voltage and the measured secondary output current, and measuring the measured secondary output voltage and the measured secondary output current from the measured secondary output voltage and the measured secondary output current. A third step of calculating the active power and the measured reactive power; and a step of calculating the active power and the measured reactive power obtained in the third step in the first step. A fourth step of performing a correction operation based on the voltage gain error, the current gain error, and the phase error to calculate a true active power and a true reactive power; and A fifth step of outputting active power and true reactive power.