JPH07181207A - Method of measuring instantaneous value of multi-phase ac voltage - Google Patents

Abstract

PURPOSE:To enable application for the control of an AC electric equipment by determining an instantaneous value of a fundamental wave of a multi-phase AC voltage while detecting an instantaneous value of the maximum value of the multi-phase AC voltage. CONSTITUTION:When a multi-phase AC voltage 1 is synthesized by a vector synthesization 3, a rotary vector is obtained. An instantaneous value 10 of the maximum value can be obtained by an amplitude calculation 4 from the vector. On the other hand, when the multi-phase AC voltage contains a harmonic voltage, the instantaneous value 10 of the maximum value is obtained by in- phase conversion 5 of the harmonic voltage. Moreover, the instantaneous value 11 of the fundamental wave can be obtained by the removal 6 of the harmonic voltage. In addition, when the multi-phase AC voltage contains an unbalanced or harmonic voltage, the instantaneous value 10 of the maximum value can be obtained by a rotary coordinate conversion 7 and the estimation 8 of the maximum value.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the control of alternating voltages, such as balanced or unbalanced polyphase voltages and those voltages in which the voltages include harmonic voltages, such as power active filters, and the amplitude of the alternating voltage. The present invention relates to a method for detecting the maximum value of a polyphase AC voltage and the instantaneous value of a fundamental wave required for control.

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Laid-Open No. 1-311286, a method of measuring an instantaneous value of a maximum value of a sine wave AC voltage is converted into a DC voltage by a rectifier and a value after an arbitrary time from a point of zero crossing is measured. A method of calculating the instantaneous value of the maximum value by measuring, and further, JP-A-3-39659 and JP-A-3-2525.
No. 60, JP-A-3-39661, etc., a method of calculating the instantaneous value of the maximum value from the data of three points of the measured AC voltage at arbitrary fixed intervals has been adopted. However, in the power active filter and the amplitude control of the AC voltage, control using the maximum value of the AC voltage and the instantaneous value of the fundamental wave is required, and most of the AC voltage handled includes harmonic voltage. Therefore, the above-mentioned measurement method assuming that the measured AC voltage is a sine wave causes an error due to the harmonic voltage.

[0003]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to develop a method for measuring the instantaneous value of the maximum value of a polyphase AC voltage including a balanced or unbalanced polyphase AC voltage and a harmonic voltage. An object of the present invention is to improve a control method of an AC electric device by providing a system capable of outputting an instantaneous value of a fundamental wave of a polyphase AC voltage.

[0004]

The method for measuring the maximum value of the polyphase AC voltage and the instantaneous value of the fundamental wave according to the present invention is as shown in FIG. 1, in which the A / D converter 2 is used for each phase of the polyphase AC voltage 1. Are converted into digital quantities by, and converted into rotation vectors by vector synthesis 3. This conversion method is shown using the three-phase voltage of FIG. 2 as an example. Now, by shifting the voltage of each phase of the three-phase voltage by 120 ° and obtaining the composite vector of the three of the a-phase voltage 12, the b-phase voltage 13, and the c-phase voltage 14, the rotation speed is 15 at the angular velocity. The rotation vector has a magnitude that matches the instantaneous value 10 of the maximum value of the three-phase voltage. Instantaneous value Vm of this maximum value
(T) is the voltage of each phase Va (t), Vb
Assuming a sine wave of (t) and Vc (t),

[Equation 1]

[Equation 2] You can ask for it. The expression (1) corresponds to the vector synthesis 3 of the polyphase AC voltage shown in FIG. 1, and the expression (2) corresponds to the amplitude calculation 4, and the instantaneous value 10 of the maximum value of the polyphase AC voltage is used.
Is obtained as the output of this. However, if the three-phase AC voltage contains a harmonic voltage or the polyphase AC voltage is an unbalanced three-phase voltage, the magnitude of the output vector of the amplitude calculation 4 and the angular velocity 15 change, and the first (1 ) And the value obtained by the equation (2) and the instantaneous maximum value of the actual three-phase AC voltage do not match. In order to correct this, the error due to the harmonic voltage is corrected by one of the following two methods shown in FIG.

The first method is to make all the harmonic voltages included in the three-phase AC voltage have the same phase and the same amplitude in the in-phase 5 of the harmonic voltage.

[Equation 3] Can be expressed as The fundamental wave voltages Ea (t), E on the right side of the equation (3) are
b (t), Ec (t) and the harmonic voltage Vh (t) are in the form of sum, and the term of the harmonic voltage is

[Equation 4] Then, the expression (3) becomes equal to the expression (1). Therefore, when the harmonic voltage of the same phase and the same amplitude is included, the instantaneous value of the maximum value of the multi-phase AC voltage can be accurately calculated by the equations (1) and (2). Utilizing this property,
For example, the voltage Va (t) of the a-phase of the three-phase AC voltage is used as a reference, and the voltages Vb (t) and Vc (t) of the remaining phases have the same phase and the same amplitude Vb '(t as the harmonic voltage of the a-phase. ), V
By injecting the correction voltage 9 so that it becomes c ′ (t), it is possible to obtain an accurate instantaneous value of the maximum value of the polyphase AC voltage. Furthermore, by utilizing the fact that the harmonic voltage of each phase is in phase and the sum of the fundamental wave voltage becomes zero,

[Equation 5] As described above, the total sum of the three-phase AC voltages Va (t), Vb ′ (t), and Vc ′ (t) including the harmonic voltage of the same phase and the same amplitude is 3ε, and this value is obtained by the harmonic voltage removal 6. Subtracting from the voltage of each phase,

[Equation 6] And the instantaneous values of the fundamental wave voltage Ea (t), Eb (t),
Ec (t) can be obtained, and its output can be taken out as the instantaneous value 11 of the fundamental wave.

A second method for eliminating the influence of the harmonic voltage contained in the polyphase AC voltage and the error due to the unbalanced voltage is shown in FIG.
The stationary vector X'by the rotational coordinate transformation 7 shown in
(T), Y '(t),

[Equation 7] Ask in. The maximum instantaneous value of the polyphase AC voltage can be obtained from this static vector. In this method, the static vector 17 of the multi-phase AC voltage including the harmonic voltage is t1 when the time when the static vector is subtracted from Xo and Yo of the origin 16 in FIG.
And the both ends of the stationary vector 18 at time t2 are connected, a perpendicular line is drawn at the midpoint, and the coordinates of the intersection with the reference axis 19 determined by the sampling time are obtained. If the coordinates of this are X and Y, the instantaneous value 10 of the maximum value of the polyphase AC voltage is

[Equation 8] Required by.

The method of obtaining the maximum value 10 and the fundamental wave instantaneous value 11 has been described so far, but a method of applying these methods to the control method of the power active filter will be described below. When the load current 22 in FIG. 4 includes a flicker current or a harmonic current, this becomes the power supply current 21 and flows into the distribution line, causing various problems. Therefore, it is necessary to operate the power supply current 21 to approach the fundamental wave current. In this method, the commercial power supply 20 and the load current 22 shown in FIG.
Commercial power supply voltage Ve (t) and load current Io (t)

[Equation 9] And the target value Ie of the power supply current is obtained by the method of obtaining the maximum value instantaneous value 10 and the fundamental wave instantaneous value 11 in FIG.
(T)

[Equation 10] Get by. Here, E (t) is an instantaneous value of the fundamental wave, which is a value obtained by the method according to the present invention. Io (t) is measured from the output voltage of the current sensor. When the target value Ie (t) of the power supply current obtained by the equation (10) and the equation (9) are combined,

[Equation 11] To get This current is an expression that gives the control current of the inverter. By supplying this current to the inverter as the control current 26, the power supply current 21 can be controlled to a sine wave current. Here, the value of K in the equation (10) is

[Equation 12] Given in. When Io (t) of this value changes abruptly, it is necessary to average it in accordance with the change period so that the time variation does not increase.

[0008]

According to the present invention, the method for measuring the instantaneous value of the maximum value of the polyphase AC voltage having a small content of the percentage harmonic voltage is shown in FIG.
By generating a rotation vector from the multi-phase AC voltage 1 by vector composition 3 and obtaining the amplitude thereof by the amplitude calculation 4, the instantaneous value of the maximum value of the multi-phase AC voltage can be obtained by a simple calculation. On the other hand, there are two types of methods for measuring multi-phase AC voltage with many harmonic voltages, and the first method is to make the maximum value and the instantaneous value of the fundamental wave accurate by making the harmonic voltages in phase. . In the second method, when the polyphase AC voltage includes an unbalanced or harmonic voltage, the instantaneous value of the maximum value of the polyphase AC voltage is calculated from the intersection with the reference axis by using two static vectors at different times. Can be accurately and quickly requested.
Further, by applying the above-mentioned measuring method of the maximum value and the instantaneous value of the fundamental wave to the control of the AC electric equipment, an effective control system can be constructed.

[0009]

FIG. 1 is a schematic diagram of a method for measuring an instantaneous value of a polyphase AC voltage according to the present invention. A method for obtaining the maximum instantaneous value of the polyphase AC voltage by three kinds of methods and one kind of polyphase AC It shows how to find the instantaneous value of the fundamental wave of voltage.

First, the first method for obtaining the maximum value of the maximum value of the polyphase AC voltage is a method suitable when the unbalanced voltage or the harmonic voltage contained in the polyphase AC voltage is small. That is, in order to obtain the maximum instantaneous value of the polyphase AC voltage by this method, the voltage of each phase of the polyphase AC voltage 1 is
After the digital value is converted by the / D converter 2, the vector composition 3 is calculated by the equation (1), and the maximum instantaneous value 10 is obtained by using the equation (2) of the amplitude calculation 4.

The second and third methods are methods for accurately obtaining the maximum value and the instantaneous value of the fundamental wave when the polyphase AC voltage includes an unbalanced voltage or a harmonic voltage. This is because the operation up to the vector composition 3 is the same as that of the first method, but of these, the second method is the first phase (arbitrary phase) of the multi-phase AC voltage 1 due to the in-phase 5 of the harmonic voltage. However, if the correction voltage 9 is added to the harmonic voltage included in all phases other than the first phase) to make the harmonic voltage in phase and with the same amplitude as that of the first phase, ) And the principle shown in the equation (4), the instantaneous value 10 of the maximum value of the multi-phase AC voltage 1 can be accurately obtained. Here, the method of applying the correction voltage 9 is the average value of the instantaneous values 10 of the maximum values obtained in the amplitude calculation 4, or
The maximum value instantaneous value 10 which is the output of the maximum value estimation 8 is used, and all the phases other than the first phase are adjusted so that the maximum value instantaneous value obtained by the equation (3) becomes the closest value to this value. Correct the voltage 9
It is obtained by the method of adjusting in.

Next, the third method is, among the outputs of the rotational coordinate conversion 7 shown in FIG. 3, two vectors having different measurement times, the stationary vector 17 at t1 and the stationary vector 18 at t2.
Both vectors are written from the origin 16 Xo and Yo, the ends of both vectors are connected by a straight line, a perpendicular line is drawn at the midpoint of the straight line, and the intersection point of this line and the reference axis 19 is obtained, and the maximum is obtained. The instantaneous value 10 of the value is obtained by the equation (8). Here, the reference axis is determined by using the average value of the static vector obtained by the rotational coordinate transformation 7.

The above has described the embodiment concerning the method of obtaining the three types of maximum instantaneous values. Next, the embodiment of the method of obtaining the instantaneous value of the fundamental wave of the polyphase AC voltage will be described. Figure 1
In, the sum of the multi-phase AC voltages obtained by the in-phase 5 of the harmonic voltage can be expressed by the equation (5). That is, since the sum of the fundamental waves in the second line of the equation (5) becomes zero, the first line of the equation (5) is calculated from the sum of the multi-phase AC voltages including the harmonic voltages of the same phase and the same amplitude. To obtain ε. This value is a multi-phase AC voltage Va in which the harmonic voltages are in-phase as shown in equation (6).
The instantaneous value 11 of the fundamental wave can be obtained by subtracting from the values of (t), Vb '(t), and Vc' (t).

The experimental results obtained by using the above-described method for measuring the maximum value of the polyphase AC voltage and the instantaneous value of the fundamental wave for measuring the commercial three-phase voltage are shown below. The measured three-phase voltage is three-phase 200
The commercial voltage of V, and the harmonic voltage contained in it is a
Phase 5th harmonic voltage 1.5%, 7th that 1.2%, b
The fifth harmonic voltage of the phase is 2.0%, that of the seventh is 0.9%,
The 5th harmonic voltage of phase c is 2.1% and that of the 7th is 1.4%
In addition to these, higher harmonic voltage is included, but it is omitted because it is within the maximum measurement error range. The content of the third harmonic voltage was in the order of negligibility with respect to the fifth harmonic voltage and the seventh harmonic voltage because the transformer was Δ-connected. Furthermore, the unbalanced component of the fundamental wave voltage was of a magnitude that did not affect the maximum measured value. FIG. 5 shows the waveform of each phase of this commercial three-phase AC voltage. The result of calculating the instantaneous value 10 of the maximum value of this voltage by the formulas (1) and (2) is shown in FIG.
Is the uppermost curve of. As shown in the figure, the 6th harmonic component generated by the 5th harmonic voltage and the 6th harmonic component by the 7th harmonic voltage are the largest, and the measured value shows an error of about ± 2.6%. It has occurred. Similarly, the characteristic shown in the middle part of FIG. 6 is the characteristic of the instantaneous value of the maximum value obtained by using the equations (1), (7) and (8). This result shows that there is impulse noise around ± 2%, but if averaged, it is ±
The error is within 0.6%. The characteristic shown at the bottom of FIG. 6 is the characteristic of the instantaneous value of the maximum value obtained by using the in-phase of the harmonic voltage, and it is possible to obtain a highly accurate result of ± 0.28%. The measurement example of the maximum instantaneous value has been described above, and FIG. 7 shows the instantaneous value 11 of the fundamental wave of the three-phase AC voltage of FIG. 5 using the equation (6). This waveform also has an error within ± 0.8%, and a highly accurate fundamental wave voltage waveform can be obtained.

Next, an embodiment of the control of the power active filter using the above-described method of measuring the maximum value of the polyphase AC voltage and the instantaneous value of the fundamental wave will be described. The load current of a power active filter is a rapidly changing current including flicker current and harmonic current. Therefore, the load current Io (t) and the commercial power supply voltage Ve (t) shown in FIG. 4 are detected by the voltage and current detection 25, the fundamental wave is extracted with respect to the voltage, and the current is averaged at an appropriate cycle. This cycle is determined in consideration of the capacity of the inverter circuit 24. As a result, the target value Ie (t) of the power supply current is obtained by the expression (10), and by using this current as the target value to control the inverter by the expression (11), a smooth power supply current can flow. Like

[0016]

As described above, according to the present invention, when the voltages of all the phases of the multi-phase AC voltage are sampled at the same time and the values are vector-synthesized, the magnitude is the maximum of the multi-phase AC voltage. It is possible to instantly find the maximum value of the polyphase AC voltage by utilizing the fact that the value becomes the value. In addition, even when the polyphase AC voltage is unbalanced or contains a harmonic voltage, the maximum value can be accurately and instantaneously obtained.
The instantaneous value of the fundamental wave voltage can be obtained by removing the harmonic voltage from the polyphase AC voltage. Therefore, a high-quality control system can be constructed by using this method for controlling AC electric equipment.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a method for measuring the maximum value of a polyphase AC voltage and the instantaneous value of a fundamental wave according to the present invention.

FIG. 2 is a diagram showing a method of performing vector synthesis according to the present invention using a three-phase AC voltage.

FIG. 3 is a diagram showing a method for estimating the maximum value of a polyphase AC voltage using two static vectors according to the present invention.

FIG. 4 is a diagram showing a method for controlling a power active filter to which the method for measuring the maximum value of a polyphase AC voltage and the instantaneous value of a fundamental wave according to the present invention is applied.

FIG. 5: Waveform of commercial three-phase voltage

FIG. 6 is the instantaneous value of the maximum voltage value of FIG. 5 obtained using the method of the invention.

FIG. 7: Instantaneous value of the fundamental wave of the voltage of FIG. 5 obtained using the method of the invention

[Explanation of symbols]

1 Measured multi-phase AC voltage 2 A / D converter 3 Composite calculation of vector using equation (1) 4 Amplitude calculation of vector using equation (2) 5 Equations (3) and (4) Calculation of in-phase and same-amplitude harmonic voltage using formula and formula (5) 6 Calculation of instantaneous value of fundamental wave using formula (6) 7 By rotational coordinate conversion using formula (7) Static vector 8 Estimate calculation of maximum value by Fig. 3 and Eq. (8) 9 Voltage applied to make harmonic voltage in-phase and amplitude 10 Output instantaneous value of maximum 11 Output instantaneous value of fundamental wave 12 a-phase voltage of three-phase voltage 13 b-phase voltage of three-phase voltage 14 c-phase voltage of three-phase voltage 15 angular frequency of three-phase voltage 16 origin of vector 17 time still at time t1 vector 18 time still at time t2 Vector 19 X '(t) and Y'of the equation (7) from the origin 16
Axis passing through the average value of (t) 20 Commercial power supply 21 Current flowing from commercial power supply 22 Load current 23 Load 24 Inverter for controlling power supply current 25 Maximum value of fundamental wave voltage and load current using the method of the present invention Circuit for detecting instantaneous value of 26 Inverter control current obtained by the method of the present invention

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[Procedure amendment]

[Submission date] March 22, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Title of invention

[Correction method] Change

[Correction content]

Title: Method for measuring instantaneous value of multi-phase AC voltage

Claims (4)

[Claims] 1. A method for obtaining an instantaneous value of a maximum value of a polyphase AC voltage from a magnitude of a combined value of instantaneous vectors of respective phases,
When the multi-phase AC voltage is a balanced multi-phase AC voltage, the magnitude of the combined value of the instantaneous vectors is obtained from the magnitude of the instantaneous voltage of each phase, and the maximum instantaneous value of the multi-phase AC voltage is obtained. Measuring method of the instantaneous value of the maximum value of the multi-phase AC voltage. 2. A method for obtaining the maximum value of a polyphase AC voltage and the instantaneous value of a fundamental wave from the magnitude of the combined value of the instantaneous vectors of each phase, wherein the polyphase AC voltage includes a harmonic voltage, Obtain an instantaneous value of the maximum value of the polyphase AC voltage from the magnitude of the instantaneous voltage of each phase by applying an arbitrary voltage from the outside and making all the harmonic voltages contained in the polyphase AC voltage have the same phase and the same amplitude. At the same time, the sum of each phase voltage is multiplied by the number of phases of the harmonic voltage, and the value obtained by dividing this value by the number of phases is subtracted from each phase voltage to obtain the instantaneous value of the fundamental wave of the multi-phase AC voltage. A method for measuring the maximum value of the polyphase AC voltage and the instantaneous value of the fundamental wave, which is characterized by obtaining the values. 3. A method for obtaining the maximum instantaneous value of a multi-phase AC voltage from the magnitude of the combined value of the instantaneous vectors of each phase,
When the polyphase AC voltage includes an unbalanced polyphase AC voltage or a harmonic voltage, a combined value of the instantaneous vectors is obtained from the magnitude of the instantaneous voltage of each phase, and the vector is defined as the angular frequency of the polyphase AC voltage. The instantaneous value of the maximum value of the multi-phase AC voltage is obtained from the estimated vector obtained from the intersection of the perpendicular line emerging from the center between the tips of the two instantaneous vectors with different measurement times converted to the coordinates rotating at the same speed. A method for measuring the instantaneous value of the maximum value of a polyphase AC voltage, which is characterized by the following. 4. A method for controlling a power active filter to which the measuring method of the present invention is applied, wherein the measuring method of the present invention detects the instantaneous value of the fundamental wave of the polyphase AC voltage and the load current Convert to multi-phase AC voltage with a sensor,
A control method for a power active filter, characterized in that control is performed so that a polyphase AC current having an arbitrary phase angle and amplitude flows as a power supply current with respect to the instantaneous value of the fundamental wave of the polyphase AC voltage. .