JPH0782044B2 - Power converter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a power converter used for measuring a power flow in a power system when performing management operation of power as energy.

[Conventional technology]

As is well known, in managing and operating electric power as energy, it is indispensable to measure the power flow of the electric power system. Various methods have been conventionally used as methods for measuring the power flow in such a power system.

However, most of the conventional power converters perform a calculation process by deriving a voltage proportional to power (reactive power) from the voltage and current detected as an analog quantity.

FIG. 4 is a block diagram showing an example of the configuration of a conventional power converter. In the figure, 1 is the voltage connected to the secondary side of a voltage transformer (hereinafter referred to as PT) for measuring system voltage. Input converter, 2 is a current input transformer connected to the secondary side of a measuring converter (hereinafter referred to as CT) that measures the current of the system, and 3 is the voltage and current of each transformer 1, 2. The electric power of the Hall element etc.
Voltage conversion circuit (hereinafter referred to as W / V conversion circuit), 4 is a sample hold amplifier (hereinafter referred to as SHA), 5 is a voltage / frequency conversion circuit with filter (hereinafter referred to as V / F conversion circuit with filter), and 6 is It is a microprocessor (hereinafter referred to as MPU).

Next, the operation will be described.

The detected values output from the voltage input transformer 1 and the current input transformer 2 are given to the W / V conversion circuit 3 and converted into a DC voltage signal according to the magnitude of each detected value, and the SHA4 is used. After being held, it is applied to the V / F conversion circuit 5 with a filter at an appropriate timing. Since the DC voltage signal is applied to the filter-equipped V / F conversion circuit 5 via SHA4 in this manner, the voltage signal having a frequency proportional to the DC voltage signal is supplied from the filter-equipped V / F conversion circuit 5. When the voltage signal is given to the MPU 6, the MPU 6 performs arithmetic processing to obtain a desired digital output.

[Problems to be solved by the invention]

The conventional power converter has a configuration in which analog type electronic circuit devices are used for various devices including the W / V conversion circuit 3 which forms the converter, but is replaced with a digital type. Since it is easy to understand the performance of various devices and is relatively easy to operate, since the W / V conversion circuit 3 described above is provided with an element with a small output signal order such as a Hall element, It is necessary to amplify the signal output from the W / V conversion circuit 3 or wave the mixed noise, and there is a limit to the improvement of accuracy and stability. Moreover, although the V / F conversion circuit 5 with a filter has simple timing control, when it is used in a place where the power flow changes drastically like an electric power system, the input voltage to the V / F conversion circuit 5 with a filter changes. There is a problem in that the power measurement function cannot be fully exerted because it may be severe and not necessarily advantageous in response.

The present invention has been made to solve the above problems, and it can withstand practical use even in a location where power flow changes drastically, such as a power system, and is high-speed and accurate for measuring, controlling, and protecting the power system. , To obtain a power converter that is widely applicable to monitoring.

[Means for solving problems]

The power converter according to the present invention is provided with voltage deriving means for deriving the primary combined voltage from the voltage and current of the power system, and the output obtained by adding the voltage to the output of the voltage deriving means is sampled at predetermined intervals to perform digital processing. However, a microprocessor for inputting the digitally processed output is provided, and zero crossing detection means for issuing an interrupt input to the microprocessor when the instantaneous value of the primary coupling voltage becomes zero is provided by the microprocessor. It is provided with a lookup table for digitizing and storing the contents to be calculated.

[Work]

A power converter according to the present invention derives a primary coupling voltage from a voltage and a current of a power system, samples an output obtained by adding the voltage of the power system to the primary coupling voltage at an appropriate time interval, and digitally converts the output. Enter in the set. At the same time, the primary coupling voltage is input to the zero-crossing detector, the zero-crossing detector detects the time when the zero crossing occurs, and the output is generated as an interrupt input to the microprocessor, so that the phase difference between multiple vectors is detected. measure. Then, the reactive power and the active power are detected from the phase difference and the digitally processed voltage.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First
FIG. 2 is a block diagram showing the construction of an embodiment of the present invention, second.
The figure shows the flow chart of the configuration shown in FIG. 1, and FIG. 3 shows the voltage e of the power system and the voltage e + applied to the two resistors.
It is a graph which shows the phase relationship between ki and e-ki, and in FIG. 1, the same code | symbol is attached | subjected to the same and equivalent component as FIG. 4, and the description is abbreviate | omitted. However, the voltage input transformer 1 is different in that two secondary windings are provided. In the figure, 3-P and 3-N are resistors for obtaining the voltages e _P and e _N , and e _P ≡e + ki is connected to the resistor 3-P and resistor 3-
We derive e _N ≡ e-ki for _N. SHA4 holds and stores the instantaneous values of e, e _P , and e _N for a predetermined period. 51 is the above e, e _P , e _N
It is a multiplexer (hereinafter referred to as MPX) for sequentially applying voltage to the next stage while switching three kinds of voltage.
Is an analog / digital converter (hereinafter referred to as an A / D converter) that converts the instantaneous values of the voltages e, e _P , and e _N switched and applied by the MPX51 into a digital signal. 7 is MPU6
This is a lookup table for digitizing a part of the contents to be arithmetically processed in advance. 8-p, 8-n are the above e _P , e _N
It is a zero crossing detector (hereinafter referred to as ZCD) that outputs when the instantaneous value of becomes zero. ZCD8-p and ZCD8-n are adapted to receive the primary coupling voltages e _P and e _N , respectively, as inputs.

The voltage input transformer 1, current input transformer 2, resistors 3-N, 3-P, SHA4, MPX51, A / D converter 52, MPU6 and ROM7 are all used as general-purpose products. The operation and performance are publicly known.

Next, the operation will be described.

First, the principle of this operation will be described with reference to FIG. Introduce the voltage and current of the power system and calculate the instantaneous value
Let e, i be the vector e + ki, e, e−ki in FIG.
As a positive constant is _{k, e P = e + ki} = Esinωt + kIsin (ωt +) ≡A P sin (ωt + θ P) Is.

If m≡tan (θ _P + θ _N ) is set as the amount of m, then θ _P and θ _N can be taken to be positive.

If we choose an appropriate value of k so that E ² >> k ² I ² , Therefore, the ineffective force Q is Also, the effective force is Becomes

As described above, the reactive power Q generated by the two quantities e and i is the phase difference θ between the two vectors e + ki, e−ki and e.
_It can be detected by measuring _P , θ _N , and the active power P is also deduced from this relationship.

Those shown the above relationship is Figure 3, curve I e = Esinωt ............... curve I Similarly curves II, III are _{e P = A P sin (ωt} + θ P) ...... curve II e _N = A _N sin (ωt−θ _N ) ... Representing curve III, respectively.

The point P1 on the time axis is the zero crossing time of the voltage e _P , the point N1 is the zero crossing time of the voltage e _N , and the point 0 is the zero crossing time of the voltage e.
Represents the angle θ ₁ , and the interval 0 → N1 represents the angle θ ₂ .

These three quantities, e _P , e _N , e, are sine waves, so P1, N1,0
When the angular frequency changes by π, the second zero crossing time is reached, and this point is expressed as P ₂ , N ₂ , and π, and N _{1 to} P ₂ : π−θ _P −θ _N P _{2 to} N ₂ : θ _P + θ _N.

That is, θ _P + θ _N can be found by measuring the interval between the zero crossing points of the two voltages e _P and e _N , which corresponds to m.

From the above, if the three quantities e, e + ki (≡e _P ), e−ki (≡ e _N ) are measured and the magnitude is measured for e and the phase difference is measured for e _P , e _N , EIsin Therefore, it can be seen that reactive power and active power such as EIcos can be detected.

Therefore, in this embodiment, first, the voltage e, i to be measured is converted into a voltage input transformer 1 and a current input transformer 2.
After inputting, the primary coupling voltage e _p , e _n is derived by the resistors 3-p, 3-n, and the voltage e is added to this to obtain three types of voltage e,
SHA4, MPX51, and A / D converter 52 sample e _P and e _N at appropriate time intervals, A / D-convert them, and input them to MPU6. At the same time, the primary coupling voltages e _P , e _N are monitored by the ZCD8-P, 8-N which detects the time when the zero point has passed, and when the zero point has passed, an interrupt input is generated to the MPU6.

The operation will be described in more detail with reference to the flow chart of FIG.

First, after clearing the table, it is confirmed in steps 101 to 105 whether or not there is an abnormality in the input interface or the like, especially whether or not the ZCD8-p, 8-n normally operates. After that, in steps 106 to 109, e, e + ki, e
Read three voltage values of -ki. Then, in step 110, it is monitored whether the value of the voltage e _p is within the dead band ε set to be slightly lower than the sensitivity of ZCD8-p.
If it is determined that the value of the voltage e _p is not within the dead band ε, the process proceeds to step 116. If it is determined that the value of the voltage e _p is within the dead band ε, the process proceeds to step 111 and it is determined whether or not the ZCD8-p has operated. If the ZCD8-p is not operating, the process returns to step 107 via steps 122 and 123. When the ZCD8-p operates, the counter 112 in the MPU6 is operated by the step 112.
Is started and the counter 2 is returned by step 113. Then, at step 114, ZCD8
If −n is operated, it is judged whether or not the counter 1 operates, and the counter 1 counts the time corresponding to θ _P + θ _N to calculate θ (1), and if not operated, the step 1 is performed via steps 122 and 123.
Return to 07. Further, in step 116, the value of the voltage e _n is ZCD
Monitor whether it is within the dead band ε, which is set slightly lower than the sensitivity of 8-n. When the value of the voltage e _n in the dead zone width ε is determined not to entering a port, it will return to step 107 via step 122 and 123. Also, the dead band width ε
When the value of the voltage e _n is determined that entering a port in, the process proceeds to step 117, which determines whether ZCD8-n is activated. If the ZCD8-n is not operating, step 12
You will return to step 107 via 2,123. Also ZC
When the D8-n operates, the counter 2 in the MPU 6 is activated by the step 118 and the counter 1 is restored by the step 119. After that, in step 120, it is judged whether or not the ZCD8-p operates, and if it operates, the counter 2 counts the time corresponding to θ _n to calculate θ (2), and if it does not operate, the steps 122 and 123 are executed. Return to step 107 via.

Or more e, e _p, the phase angle measurement in .omega.t = 0 around in a change in e _n can collect one data corresponding to the end θ _{P +} θ _N. Let these be θ (1) and θ (2).

Then the operation in the first half cycle is entered. Similar to the phase measurement of θ _P + θ _N near the 0 point, along the flow from step 107 to step 123, first, e, e _p (≡e + k
After i) and e _n (≡e−ki) are read, the levels of e _p and e _n are monitored and the operation of ZCD8-p is waited. Counter 1
After the operation of, the counter 2 is activated and when the angular frequency exceeds π, it waits for the ZCD8-n to operate. If the time interval from the operation of the counter 1 to the operation of the counter 2 is calculated, the phase angle corresponding to θ _P + θ _N can be measured.

By the above, the phase angle measurement near ωt = π is finished and θ _p ,
One kind of data corresponding to θ _n can be collected. This is θ
(3) and θ (4).

Θ (1), θ (2), θ obtained in this way
(3) and θ (4) should be θ (1) + θ (2) = θ (3) + θ (4) if the system and measurement are normal (steps 124 and 125). If θ (1)
If the value of .about..theta. (4) is not normal, the operation proceeds to step 131.
If it is normal, the process proceeds to step 126. In step 126, the value of e is obtained by sampling an instantaneous value and obtaining an appropriate number of data, so the sample value is integrated to obtain the average value.
Then, θ (1) to θ obtained in step 126
A value corresponding to θ _p + θ _n was obtained from (4), and this value was used in the principle section.

Obtain tan (θ _P + θ _N ) = m by referring to a table.

From these, use the value of E Is also obtained by referring to the table (step 128).

In general, the values of E and θ do not fluctuate significantly as long as the system is healthy, so the number of rows in the prepared table may be smaller than the general table, and the number of bits in the read-only memory that constitutes the lookup table LUT is It can be achieved practically enough.

Furthermore, Is used to obtain the value on the right side by a table-up method (step 129).

As a result, Icos is obtained, and thus EIcos is obtained using the above table (step 130).

As described above, one set of active / reactive power data for half cycles was obtained by observing changes in e and i during half cycles.

By repeating this, one set of data is obtained every half cycle, and these are integrated and averaged to obtain the average power and integrated power.

If θ (1) and θ (2) are not appropriate, remeasurement is performed and the same routine is executed from step 131 at another read timing. Using this data, θ (1),
The calculation of θ (2) is the same as described above.

In addition to the above-described embodiment, various modifications can be considered for power conversion. It goes without saying that the gist of these is included in the present invention to the extent that they do not conflict with the technical idea of the present invention.

〔The invention's effect〕

As described above, according to the present invention, the magnitude of the voltage e having a narrow fluctuation range is measured using the sample hold amplifier and the multiplexer, and the output is obtained when the instantaneous values of the voltages e _P and e _N become zero. Phase angle measurement is performed using a zero crossing detector that emits, and the results and the look-up table are used to perform arithmetic processing such as trigonometric functions, squares, squares, and products. It is not easily affected by noise, etc., stable measurement is possible, and there is an effect that high-speed calculation can be performed without using special multiplication parts. By increasing the capacity of the lookup table, the calculation accuracy is easy. The effect is that it can be controlled.

[Brief description of drawings]

FIG. 1 is a block diagram showing a power converter according to an embodiment of the present invention, FIG. 2 is a flow chart having the configuration shown in FIG. 1, and FIG. 3 is applied to a voltage e of a power system and two resistors. Graph diagram showing the phase relationship between the voltage e + ki, e-ki,
FIG. 4 is a block diagram showing a conventional power converter. 3-p and 3-n are resistors, 4 is a sample hold amplifier, 51
Is a multiplexer, 52 is an analog / digital converter, 6 is a microprocessor, 7 is a lookup table, and 8-p and 8-n are zero crossing detectors. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A power converter for introducing voltage and current of a power system and detecting active power and reactive power generated from these voltage and current, and a voltage deriving means for deriving a primary combined voltage from the voltage and current. A sample-hold circuit for sampling and holding the primary coupling voltage and the voltage of the power system derived by the voltage deriving means, digital processing means for digitally processing while sequentially switching the outputs from the sample-hold circuit, and the digital processing A microprocessor to which the output is sent, a zero crossing detecting means for issuing an interrupt input to the microprocessor when the instantaneous value of the primary coupling voltage of the voltage deriving means becomes zero, and the contents to be calculated by the microprocessor are digitized. And a look-up table for storing the data stored by the zero crossing detection means. The electric power characterized in that the active power and the reactive power are detected by referring to the phase difference between the temporary coupling voltages and the magnitude of the voltage of the power system measured by the lookup table. converter.