KR20130128941A - Method and apparatus for determining reactor saturation - Google Patents

Abstract

There are many uses of reactors in the industry, and saturation judgments for various input frequencies are not well-formed when using such reactors. In the present invention, in order to formally determine whether the reactor is saturated, the current flowing through the reactor is detected, and the magnitude of the harmonic components included in the current is compared with the current fundamental wave component through a Fourier transform to determine whether the reactor is saturated.

Description

Method and apparatus for determining reactor saturation

The present invention relates to a method and apparatus for determining whether a reactor is saturated, and more particularly, to set a saturation judgment value for determining a saturation point of a reactor and to compare it with a harmonic component of a current flowing through the reactor. The present invention relates to a method and an apparatus for determining whether the device is in the normal operating area or not.

Industrial reactors have a variety of uses, most commonly in the inverter system plays a role in suppressing harmonic components generated by the characteristics of the rectifier. The reactor may have an AC reactor installed at the front of the inverter input and a DC reactor installed at the inverter DC link stage.

When AC reactor is used on the primary side of inverter, it is effectively used for harmonic suppression and power factor improvement of input voltage, and when used on secondary side of inverter, it plays a role of noise reduction and harmonic suppression.

In addition, in a system in which a direct start between a power supply and a motor is started without using an inverter, a series reactor is inserted between an AC power supply and a motor to lower the motor voltage by the reactor's voltage drop, thereby limiting the starting current. This can prevent damage to the motor which may occur.

However, despite these various uses, industrial reactors all have unique saturation points, and detailed data on such saturation points are not provided to reactor users. If the reactor is used at the saturation point, not only can the system degrade, but also the reactor heats up, resulting in reactor damage.

It is an object of the present invention to provide a method and apparatus for effectively determining the saturation region of an industrial reactor at various frequencies.

According to an embodiment of the present invention, the method includes: setting a saturation judgment value for determining whether the reactor is saturated; Detecting a current flowing through the reactor by a control device; Performing a Fourier transform by the controller using the detected current as an input; And determining, by the controller, that the reactor is saturated when the ratio of the harmonic component of the current calculated through the Fourier transform is greater than the saturation determination value, wherein the saturation determination value is the current. A method for determining whether a reactor is saturated is set based on a fundamental wave component.

Preferably, when it is determined that the reactor is saturated, the control device is characterized in that the command to reduce the value of at least one of the reference voltage and the reference current to the power converter connected to the reactor.

Preferably, the saturation determination value is set based on the current fundamental wave component, and the saturation determination value is set as a percentage based on the rms value for the current fundamental wave component.

Preferably, the step of determining that the reactor is saturated is characterized in that the reactor is saturated if the ratio of the fundamental wave of the third harmonic component of the harmonic components of the current is larger than the saturation determination value. .

Preferably, the step of determining that the reactor is saturated is characterized in that the reactor is saturated when the ratio of the total harmonic distortion (THD) of the current to the fundamental wave is greater than the saturation determination value.

Preferably, the control device is characterized in that for detecting the voltage applied to the reactor and the frequency of the input power source to calculate the inductance of the reactor.

According to one embodiment of the present invention, a saturation determination value setting unit for setting a saturation determination value for determining whether the reactor is saturated; A current detector for detecting a current flowing in the reactor; And performing a Fourier transform using the detected current as an input, and determining that the reactor is saturated when the ratio of the harmonic component of the current calculated through the Fourier transform is greater than the saturation determination value. It includes, but the saturation determination value is provided based on the current fundamental wave component is provided with a control device for determining whether the reactor saturation.

Through the method and apparatus for calculating the saturation point database of the reactor according to the present invention, it is possible to effectively calculate the saturation point of the industrial reactor to effectively grasp the deterioration potential of the reactor and the stable operating region of the reactor, and the user can effectively determine the reactor. It is possible to use.

1A and 1B show an example of a BH curve showing magnetic properties of a general magnetic body.
2 illustrates a current pattern in a saturation region according to an embodiment of the present invention.
Figure 3 shows a block diagram of the entire system according to an embodiment of the present invention.
4 is a block diagram illustrating in more detail the control device of FIG. 3 in accordance with an embodiment of the present invention.
5 is a flowchart for performing saturation determination of the reactor according to an embodiment of the present invention.
6 is a saturation current graph graphing the current of the saturation point at various frequencies according to an embodiment of the present invention.

Hereinafter, an apparatus and a method according to the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. The following terms are defined in consideration of the functions of the present invention, and they may vary depending on the intentions or customs of the client, the operator, the user, and the like. Therefore, the definition should be based on the contents throughout this specification.

Like reference numerals in the drawings denote like elements.

1 shows an example of a B-H curve showing magnetic properties of a general magnetic body.

As shown in FIG. 1A, the horizontal axis of the B-H curve is a curve drawn by taking the intensity H [A / m] of the magnetic field and the vertical axis the magnetic flux density B [T]. The B-H curve reflects the magnetic properties of the magnetic body, and the B-H curve is used for the magnetic circuit design. The shape of the B-H curve differs depending on the material of the magnetic material. In FIG. 1A, region 100 is a linear region representing a normal operating region of the magnetic body, and region 110 represents a nonlinear region in which the magnetic body is saturated.

When the nonlinear region 110 is crossed on the B-H curve, the slope di / dt of the current rapidly changes (raises) and causes heat generation of the reactor and instability of the power conversion system. Such operation in the saturation region causes a phenomenon such as a step out of the motor in the reactor, and the reactor loses its function as a reactor.

As shown in FIG. 1B, the B-H curve in ferromagnetic material such as iron alternates between H and +, so that a hysteresis loop is drawn.

If the magnetic material is in a saturated state and continuously flowing current, the magnetic material may deteriorate and degrade performance. In a system employing such a reactor, proper performance, for example, proper filtering performance may not be expected. Therefore, it is important for the user who operates the power converter to properly understand the saturation point of the reactor to be employed.

When a user purchases a reactor, information about a saturation point is usually included, but such information is limited. In general, only B-H information about 60 Hz is usually provided and there is no even this. Therefore, there is a limit in knowing the B-H characteristic and saturation point in various frequency bands. Unfortunately, the reactor saturation point is not even accurate for the reactor manufacturer. Reactor manufacturers and companies that apply / use such reactors may test the saturation point at the initial development of the reactor, but it is rare to test the saturation point in mass production. Reactor performance may change significantly when the specifications selected at the time of initial development are changed by the iron core or the magnetic material supplier, and the present invention for determining the saturation point may also help in detecting such defective products.

Therefore, even a manufacturer who purchases and uses a reactor does not know the B-H aspect of the reactor and sells and uses it.

Recently, the power grid has been advanced since Korea's major blackout, and the use of inverters for energy saving is increasing due to the reduction of greenhouse gases and environmental problems. This increase in harmonics will weaken the grid's immunity, so the government is looking for ways to limit harmonics.

As countermeasures, active and passive harmonic filters have been considered. To verify these filters, a power supply is required to supply the frequency of the harmonic content. Power supply for harmonic components such as 180Hz, 240Hz, 300Hz, 360Hz, which are multiples of commercial power 60Hz, can be provided through an inverter, a kind of power converter.

As we saw earlier, frequencies in the 100-500 Hz range are possible with inverters, but in this case it is not easy to find out where the saturation point is when using the reactor in the higher frequencies. Therefore, if you have a variety of saturation point table for each high frequency band, the user can clearly identify the operating area of the reactor, and the entire power system can be stably operated while the reactor is operating normally. It can be a big help.

2 illustrates a current pattern in a saturation region according to an embodiment of the present invention.

In the pattern graph, 200 shows a current waveform representing the operation in the linear region (normal region) of the reactor. As can be seen from 200, in the linear region of the reactor, the current waveform shows a state where the fundamental wave is maximized and there are almost no harmonic components.

In contrast, 210 and 220 represent current waveforms entering the saturation region (nonlinear region) of the reactor. In the case of 220, the voltage applied to the reactor is greater than 210, so that the rms value of the current is larger, and it is understood that the time t1 entering the saturation region is faster than the time t2 entering the saturation region 210. have.

As can be seen in Fig. 2, when the saturation point is reached, current distortion starts to occur, such as 210 or 220. The most characteristic of the current variation reaching the saturation is that the distortion component that looks like the third harmonic component for the fundamental wave is It can be seen that the most influential ingredients. That is, since the distortion of the current intensifies at the peak value of the fundamental wave, it can be determined that the saturation point is mainly reached when the third harmonic component increases.

Therefore, since the voltage and current applied to the reactor in the power conversion system are usually monitored, the control device that determines the saturation by measuring the third harmonic component in the monitoring process of determining the waveform of the current determines whether the saturation is performed. Can be.

Figure 3 shows a block diagram of the entire system according to an embodiment of the present invention.

The entire system for determining the saturation has a form in which a control device 300 according to an embodiment of the present invention is added to a general power conversion system.

The power conversion system, once represented by the inverter 330, receives power from the three-phase power source 310. 3 is only one embodiment, it is apparent to those skilled in the art that it can be applied to a single phase rather than three phases.

The three-phase power is filtered through the reactor 320 and supplied to the inverter. The inverter 330 system is shown in a simple block diagram, but again, PWM switching and DC link and DC link voltages, which accumulate and filter the power semiconductor switch elements, such as six iGBTs and GTOs, which rectify three-phase currents, and the rectified DC outputs. In the same way, the inverter stage for supplying the variable frequency and the variable voltage can be easily configured by those skilled in the art.

The inverter output may be stepped down by the step-down transformer 340 as needed. Step-down transformer 340 may or may not be necessary depending on the system. Inverter 330 output is now supplied to reactor 350. The 350 reactor is a load reactor.

What we want to know is whether the load reactor 350 is saturated, and when the current is saturated at a certain frequency and voltage. The control unit 360 detects and receives a current of the reactor stage. Current detection usually uses a current detector (CT). The voltage applied to the reactor stage is also detected and received as an input of the control unit 360. The control device 300 for saturation determination according to the present invention may include a control unit 360, a PLC 370 for giving a voltage and current command value, and a UI 380 for allowing a user to set the saturation determination value. .

The control unit 360 may be a device having a processor and a simple input / output device (ADC, etc.). If the control unit 360 detects the current value, it performs Fourier transform (FFT) on the current value to calculate and measure the magnitude of the third harmonic component. In this case, the third harmonic component may be calculated in the form of a comparison value with respect to the detected current fundamental wave component. As shown in FIG. 2, since the third harmonic component takes the form of a large current while the current value increases rapidly, it may be determined that the third harmonic component has entered the reactor saturation region when the third harmonic component increases to some extent. The user may give a margin for entering the reactor saturation in advance through the UI 380 such as a touch screen. That is, for example, the user may preset to recognize that the third harmonic component has completely entered the saturation region when it reaches 5% of the current fundamental wave component.

If the 3rd harmonic component in the system is 3% of the fundamental wave, the fixed value may be set in the saturation region of the reactor, but the noise may be severe depending on the environment in which the power conversion system is driven. Since it may not be, it would be desirable to give the user the option to set the margin width large or small according to the surrounding driving environment.

More specifically, when the initial saturation judgment margin is set too small, the system may incorrectly enter the saturation region due to noise even though the reactor 350 does not actually enter the saturation region. Therefore, it is desirable to set the saturation determination value with a certain margin in advance so that it can be determined that the reactor has entered the saturation region certainly.

As a result of Fourier transforming the detected current by the control unit 360, if the third harmonic component exceeds the saturation determination value 5% set for the fundamental wave, the control device determines that the reactor has entered the saturation region, and the saturation determination Based on this, the PLC 370 applies the setpoint Vref / iref to lower the voltage and / or current to the inverter 330 for reactor protection and stable operation of the system.

In response to the lowered voltage and / or current commands, the inverter 330 applies a low output to the reactor 350 so that the system can operate in a stable region (linear region of the reactor). If the stable operation continues to some extent, the PLC 370 continues the operation until the voltage command / current command is increased and again does not enter the saturation region (non-linear region of the reactor). When the voltage command and the current command are raised or lowered according to the saturation judgment, it is desirable to consider the noise and set the voltage command / current command to be applied along the hysteresis curve so that the system does not repeat the command value high and low too often.

When saturation judgment is made, it is convenient to compare the rms values of the third harmonic components based on the root mean square (rms) values of the detected current fundamental components. According to the user's selection, the third harmonic component and the current fundamental component may be compared, or the total harmonic distortion (THD) value reflecting the total harmonic components may be compared with the current fundamental component to determine whether to enter the saturation region.

The control unit 360 may also calculate the inductance value of the reactor. Knowing the detected current and voltage,

You can find the value of L (inductance) by Where w represents the input frequency (w = 2πf).

4 is a block diagram illustrating in more detail the control device of FIG. 3 in accordance with an embodiment of the present invention.

In more detail, the control device 300 of FIG. 3 includes a current detector 301, a voltage detector 303, a processor 365, an inductance calculator 305, a voltage current commander 375, and a UI 380. It can be configured as. In FIG. 3, the control unit 360 may be understood as a unit including a processor 365 and an inductance calculator 305.

Here, the current detector 301 and the voltage detector 303 are optional units that can be separately placed outside, and the voltage current command unit 375 may also be separately configured as a device such as the PLC 370 as described above with reference to FIG. 3. have. Similarly, the UI 380 may be configured as an optional device that can be connected to the control device by separately configuring the control device 300 in the form of a touch screen.

The processor 365 performs a Fourier transform on the current detected by the current detector 301, and compares the current detected by the UI 380 with the saturation determination value input through the UI 380, as described above. The voltage current command unit 375 applies a voltage and current command to a power converter such as the inverter 330 according to the determination result of the saturation of the process.

The inductance calculator calculates an inductance value based on the current, voltage, and frequency of the system input from the current detector 301 and the voltage detector 303. The processor 365 may perform the same function of calculating the inductance calculator 305 and calculating the inductance value.

5 is a flowchart for performing saturation determination of the reactor according to an embodiment of the present invention.

First, in S510, the saturation determination value for determining whether the reactor is saturated is set in advance through a device such as a user interface (UI). The control device detects a current flowing in the reactor (S520). The controller determines that the reactor is saturated when the ratio of the harmonic component of the current calculated through the Fourier transform (S530) of the detected current is greater than the saturation determination value (S540).

Optionally, the controller may be changed to reduce reference voltage (voltage command value) and reference current (current command value) applied to a power converter such as an inverter to prevent deterioration of the reactor and to stably operate the system.

In the system of FIG. 3 introduced above, the inverter 330 system can determine the saturation point of the reactor 350 under various conditions according to the variable voltage and the variable frequency setting change, and thus, the constant condition (constant frequency and constant voltage). You can create a saturation point table under

That is, through the operation of the inverter, the reactor 350 is saturated at 50A at 300V and 120Hz, and data such as saturated at 40A at 300V and 240Hz can be collected.

In addition to the saturation point table (database) described above, a saturation current graph can be generated.

6 is a saturation current graph graphing the current of the saturation point at various frequencies according to an embodiment of the present invention.

Referring to the saturation current graph, the user can easily predict whether the operation is possible in the stable region or the abnormal region operation beyond the saturation point by comparing the current value near the operation to be used. In FIG. 6, it can be seen that when the current has an i * value, stable system driving can be performed without entering the saturation region in the entire frequency region.

In addition, the apparatus and system according to the present invention can be embodied as computer readable codes on a computer readable recording medium. A computer-readable recording medium includes all kinds of recording apparatuses in which data that can be read by a computer system is stored. The computer-readable recording medium may include a storage medium such as a magnetic storage medium (eg, a ROM, a floppy disk, a hard disk, etc.) and an optical reading medium (eg, a CD-ROM, a DVD, etc.). The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

Embodiments have been disclosed through the drawings and the specification. Although specific terms have been used herein, they are used only for the purpose of describing the present invention and are not used to limit the meaning or the scope of the present invention described in the claims. Therefore, those skilled in the art will implement that various modifications and equivalent other embodiments are possible from this. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

300; Control device
310; 3-phase power
330; inverter
350; Reactor
360; The control unit
370; PLC
380; UI
301; Current detector
303; Voltage detector
305; Inductance calculator
365; Processor
375; Voltage and current command
385; UI

Claims (13)

Setting a saturation judgment value for determining whether the reactor is saturated;
Detecting a current flowing through the reactor by a control device;
Performing a Fourier transform by the controller using the detected current as an input; And
Determining, by the controller, that the reactor is saturated when the ratio of the harmonic component of the current to the fundamental wave calculated through the Fourier transform is greater than the saturation determination value,
And the saturation determination value is set based on the current fundamental wave component. The reactor according to claim 1, wherein when it is determined that the reactor is saturated, the control device instructs the power converter connected to the reactor to reduce the value of at least one of a reference voltage and a reference current. Method to determine whether the saturation of. The method of claim 1, wherein the setting of the saturation determination value based on the current fundamental wave component sets the saturation determination value as a percentage based on the rms value of the current fundamental wave component. Method for judging. The method of claim 1, wherein the determining that the reactor is saturated comprises determining that the reactor is saturated when the ratio of the third harmonic component to the fundamental wave of the current harmonic component is greater than the saturation determination value. Method for determining whether the reactor is saturated. The method of claim 1, wherein the determining that the reactor is saturated comprises determining that the reactor is saturated when the ratio of the current to the fundamental wave of total harmonic distortion (THD) is greater than the saturation determination value. Method for determining whether the reactor is saturated. The method of claim 1, wherein the controller detects a voltage applied to the reactor and calculates an inductance of the reactor by detecting a frequency of an input power source. The method of claim 1, wherein the current is a three-phase current. A saturation determination value setting unit for setting a saturation determination value for determining whether the reactor is saturated;
A current detector for detecting a current flowing in the reactor; And
Performing a Fourier transform using the detected current as an input, and determining that the reactor is saturated if the ratio of the harmonic component of the current calculated through the Fourier transform is greater than the saturation determination value. Including,
And the saturation determination value is set based on the current fundamental wave component as a reference. 10. The method of claim 8, wherein when it is determined that the reactor is saturated, the control device includes a voltage current command unit for instructing the power converter connected to the reactor to reduce at least one of a reference voltage and a reference current. Control device for determining whether the reactor is saturated, characterized in that. 10. The reactor according to claim 8, wherein the saturation determination value is set based on the current fundamental wave component, and the saturation determination value is set as a percentage based on the rms value of the current fundamental wave component. Control device for judging. The method of claim 8, wherein the determining that the reactor is saturated comprises determining that the reactor is saturated when the ratio of the third harmonic component to the fundamental wave of the current component is greater than the saturation determination value. Control device for determining whether the reactor is saturated. 9. The method of claim 8, wherein the determining that the reactor is saturated comprises determining that the reactor is saturated when the ratio of the total harmonic distortion (THD) of the current to the fundamental wave is greater than the saturation determination value. Control device for determining whether the reactor is saturated. The control apparatus of claim 8, further comprising an inductance calculator configured to detect a voltage applied to the reactor, detect a frequency of an input power source, and calculate an inductance of the reactor.

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