KR101084639B1 - System for estimating load impedance of induction heating apparatus - Google Patents

Abstract

The present invention relates to a load prediction system for estimating the equivalent inductance and the equivalent resistance which change as the width, thickness, and material of a metal plate, which is a heating object load, change according to the present invention. The present invention is a load prediction system for predicting the impedance of the heating coil and / or the heating element of the induction heating apparatus including an induction coil, a capacitor and a heating coil, the measurement for measuring the voltage or current characteristics of the induction heating apparatus And a load predictor for predicting the impedance of the heating coil and / or the heated object using the measured voltage or current characteristics, wherein the load predictor is configured by using an adaptive estimating algorithm. Disclosed is a load prediction system of an induction heating apparatus, characterized by predicting the impedance of a heating coil and / or the heated object. The load prediction system of the induction heating apparatus as described above detects sudden load fluctuations such as breakage of the metal plate to be heated and prevents the occurrence of overcurrent or equipment failure in the induction heating apparatus by grasping the characteristics of the heating element in advance. And, by predicting the amount of heat of the heating element to provide a function to properly adjust the amount of power input to the induction heating device.

Induction Heater, Load Prediction

Description

Load prediction system of induction heating unit {SYSTEM FOR ESTIMATING LOAD IMPEDANCE OF INDUCTION HEATING APPARATUS}

The present invention relates to a load prediction system for estimating the equivalent inductance and the equivalent resistance which change as the width, thickness, and material of a metal plate, which is a heating object load, change according to the present invention.

Induction Heating is a method of heating a metal object using electromagnetic induction. Induction heating device is composed of a coil wound, and when the high-frequency alternating current is supplied to the coil, induction current is generated on the surface of the metal to be heated by electromagnetic induction. When current flows through the metal to be heated, Joule heat generated by the resistance of the metal increases the temperature of the metal to be heated.

The object to be heated or the metal to be heated may be represented as a load on an electrical circuit connected to the induction heating apparatus, and may be replaced with equivalent inductance and equivalent resistance in the circuit. However, when the width, thickness, material, etc. of the metal to be heated change, the equivalent impedance value converted in the circuit also changes. Accordingly, the amount of heat generated from the metal to be heated is also changed, and the Q factor (Q-factor) of the resonant circuit is changed to change the effective power or reactive power of the resonant circuit. In other words, when the metal to be heated changes, even though the same current flows through the induction heating device, it cannot be heated to the target temperature.In this case, if the voltage applied to the induction heating device is excessively increased, other elements connected to the circuit To the risk of damage. Therefore, there is a need to monitor by directly measuring or predicting the change in the equivalent impedance of the metal to be heated.

In general, in order to monitor the change of the load impedance as described above, the voltage across the induction heater coil and the current flowing through the coil is measured. In practice, however, the equipment for measuring the current of the induction heater coil has a problem that it is difficult to install and very expensive.

In addition, since the technology for predicting the load impedance as described above is not developed, it is difficult to determine whether the heating material can be heated to the target temperature within the limit of the input power of the induction heating apparatus.

The present invention provides a load prediction system of an induction heating apparatus capable of preventing an overcurrent or a failure of a facility by detecting a sudden change in load such as breakage of a metal plate to be heated.

In addition, the present invention provides a load prediction system of an induction heating apparatus that can appropriately adjust the amount of power input to the induction heating apparatus by predicting the heat generation amount of the load.

In addition, the present invention provides a load prediction system of the induction heating apparatus capable of calculating the heating efficiency of the induction heating apparatus.

The present invention is a load prediction system for predicting the impedance of the heating coil and / or the heating element of the induction heating apparatus including an induction coil, a capacitor and a heating coil, the measurement for measuring the voltage or current characteristics of the induction heating apparatus And a load predictor for predicting the impedance of the heating coil and / or the heated object using the measured voltage or current characteristics, wherein the load predictor is configured by using an adaptive estimating algorithm. Disclosed is a load prediction system of an induction heating apparatus, characterized by predicting the impedance of a heating coil and / or the heated object.

In addition, the load prediction system of the induction heating apparatus, the measurement unit discloses the load prediction system of the induction heating apparatus, characterized in that for measuring the input voltage of the induction heating apparatus and the voltage across the capacitor.

In addition, in the load prediction system of the induction heating apparatus, the load prediction unit receives the measured voltage or current characteristics as a digital signal and performs the adaptive estimation algorithm by a digital signal processing method. The load prediction system of a heating apparatus is started.

In addition, in the load prediction system of the induction heating apparatus, the load prediction unit further uses the inductance of the induction coil and the capacitance value of the capacitor, and the adaptive estimation algorithm is an instantaneous cost function of an estimation error. Disclosed is a load prediction system of an induction heating apparatus, characterized by updating an impedance predicted value of the heating coil and / or the heated object according to a gradient update rule for minimizing a function. .

In addition, the load prediction system of the induction heating apparatus discloses the load prediction system of the induction heating apparatus further comprises a display unit for outputting the impedance prediction value of the heating coil and / or the heating target in real time. .

The load prediction system of the present invention can detect an abrupt change in load, such as a break of the metal plate to be heated, and grasp the characteristics of the metal plate to be heated in advance to prevent the occurrence of overcurrent in the induction heating apparatus or the failure of the equipment.

In addition, the load prediction system of the present invention can properly adjust the amount of power input to the induction heating apparatus by predicting the heat generation amount of the load of the induction heating apparatus.

In addition, it is possible to calculate the heating efficiency of the induction heating apparatus by comparing the amount of power input to the induction heating apparatus and the amount of heat generated at the load.

In addition, by calculating the Q-factor of the circuit connected to the induction heating device and the non-heated metal load, it is possible to determine whether the margin resistance of the capacitor used in the circuit is appropriate.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, if it is determined that the detailed description of the related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

The present invention proposes a load prediction system for providing operation information to a device driver by predicting an equivalent impedance change in a load variation situation such as material, width, and thickness of a load material in an induction heating apparatus. According to a preferred embodiment of the present invention, the induction heating apparatus is a so-called LCL resonant induction heating apparatus composed of an inductor and a condenser bank. According to a preferred embodiment of the present invention, without measuring the current (Current Transducer) for measuring the current flowing in the induction heating apparatus (Current Transducer) by measuring the two voltages of the voltage of the inverter exit and the voltage across the capacitor bank Estimate the equivalent impedance of the coil and the load.

1 is a view showing a circuit diagram of an LCL resonant induction heating apparatus and a load prediction system according to a preferred embodiment of the present invention.

로 표시된다.The inverter 110 supplies AC power to the induction heating apparatus. According to a preferred embodiment of the present invention, the inverter 110 may supply AC power transmitted through a power line, or may supply AC power converted from DC power. Throughout this specification, the output voltage across the inverter 110

Is displayed.

로 표시된다.Induction coil 120 is a coil constituting the induction heating device may be generally implemented in the form of a concentric inductor included in the inverter (110). Throughout this specification, the inductance of the induction coil 120

Is displayed.

로, 축전기(130) 양단의 전압은

로 표시된다.The capacitor 130 may be configured as a condenser bank as a device constituting the induction heating device. Throughout this specification, the electric capacity of the capacitor 130 is

As a result, the voltage across the capacitor 130 is

Is displayed.

로 표시된다. 부하저항(160)은 피가열체를 회로의 저항으로 모델링 한 것으로서, 본 명세서 전체 를 통하여 부하저항(160)의 저항값은

로 표시된다. 본 발명의 부하예측 시스템은 인버터(110) 양단의 전압

와 축전기(130) 양단의 전압

를 측정하여, 가열코일(150)의 인덕턴스

과 부하저항(160)의 저항값

을 예측하는 것을 목표로 한다.The heating coil and load equivalent circuit 140 is an electric circuit equivalent model of a coil and a heating object connected for induction heating of the heating object, and includes a heating coil 150 and a load resistor 160. According to a preferred embodiment of the present invention, the heating coil 150 and the load resistor 160 is connected in series with each other, it can be represented by a model connected in parallel across the capacitor 130 again. The heating coil 150 is a coil that wraps around the object to be heated and induces heating of the object to be heated. Throughout the present specification, the inductance of the heating coil 150 is

Is displayed. The load resistor 160 is modeled as the resistance of the circuit to be heated, the resistance value of the load resistor 160 through the entire specification

Is displayed. The load prediction system of the present invention is a voltage across the inverter 110

And voltage across capacitor 130

By measuring the inductance of the heating coil 150

Resistance value of overload resistance 160

Aim to predict.

와 축전기(130) 양단의 전압

를 변환하기 위해 각각 연결될 수 있다. 본 발명의 바람직한 실시예에 따르면, 인버터(110) 양단의 전압

와 축전기(130) 양단의 전압

는 수백 내지 수천 볼트(V)에 해당하는 전압값을 가지므로, 전력변환기(115, 135)는 이를 각각 디지털 신호 처리가 가능한 수 밀리볼트(mV) 내지 수 볼트(V)에 해당하는 전압값으로 N:1 축소 변환할 수 있다.The power transducers 115 and 135 adjust the measured voltage value to a range of voltage values capable of digital signal processing, and the voltage across the inverter 110.

And voltage across capacitor 130

Each can be connected to convert. According to a preferred embodiment of the present invention, the voltage across the inverter 110

And voltage across capacitor 130

Has a voltage value corresponding to hundreds to thousands of volts (V), the power converter 115, 135 is a voltage value corresponding to a few millivolts (mV) to several volts (V) capable of digital signal processing, respectively N: 1 reduction can be converted.

와 축전기(130) 양단의 전압

, 또는 이들 각각을 전력변환한 값들은 모두 아날로그 값이므로, 이를 디지털 신호 처리에 적합하도록 만들기 위해서 A/D 변환기(170)가 사용될 수 있다.The A / D converter 170 converts an analog signal into a digital signal. According to a preferred embodiment of the present invention, the voltage across the inverter 110

And voltage across capacitor 130

Since the power conversion values are all analog values, the A / D converter 170 may be used to make them suitable for digital signal processing.

과 부하저항(160)의 저항값

을 예측한다. 본 발명의 바람직한 실시예에 따르면, 부하예측부(180)는 A/D 변환기(170)를 통하여 디지털 신호로 변환된 값을 입력 받아 디지털 신호처리(Digital Signal Processing) 과정을 거쳐 부하의 임피던스를 예측할 수 있다. 바람직하게는, 부하예측부(180)는 디지털 신호처리 보드(DSP Board) 상에 디지털 신호처리 칩(DSP Chip)을 연결하여 부하예측 알고리즘을 프로그래밍하는 방식으로 구현될 수 있다.The load prediction unit 180 is the inductance of the heating coil 150 in accordance with the load prediction algorithm of the present invention.

Resistance value of overload resistance 160

To predict. According to a preferred embodiment of the present invention, the load prediction unit 180 receives a value converted into a digital signal through the A / D converter 170 to predict the impedance of the load through a digital signal processing (Digital Signal Processing) process Can be. Preferably, the load prediction unit 180 may be implemented by connecting a digital signal processing chip (DSP Chip) on the digital signal processing board (DSP Board) to program the load prediction algorithm.

의 추정값 및 부하저항(160)의 저항값

의 추정값은 물론, 본 발명의 부하예측 알고리즘에 사용되는 각종 파라미터(parameter) 및 오차(error) 값을 그래프 형태로 출력할 수도 있다.The display unit 190 outputs the predicted value through the load prediction unit 180. The display unit 190 includes a monitor, a printer, a speaker, a plotter, a copier, a facsimile, and the like, which output a computer output in a manner such as light, sound, and printing so that a person can recognize through the five senses. . According to a preferred embodiment of the present invention, the inductance of the heating coil 150 through the display unit 190

The estimated value of and the resistance value of the load resistance 160

In addition to the estimated value of, various parameters and error values used in the load prediction algorithm of the present invention may be output in graph form.

Hereinafter, according to a preferred embodiment of the present invention, the load prediction unit 180 describes an algorithm for predicting the equivalent impedance of the load by using a formula.

, 가열코일(150) 및 부하저항(160)에 흐르는 전류를

로 표시하면, 하기 식 1 내지 식 3과 같은 회로 방정식을 얻을 수 있다.In the circuit of Figure 1 the current flowing through the induction coil 120

, Current flowing through the heating coil 150 and the load resistor 160

When expressed by, the circuit equations shown in the following formulas (1) to (3) can be obtained.

[Equation 1]

[Equation 2]

[Equation 3]

When the above formulas 1 to 3 are represented by a determinant, they are expressed as in the following formula 4.

[Equation 4]

,

,

,

,

로 정의된다. 상기 식 4의 양변을 라플라스 변환(Laplace Transform)하고, 인버터(110)의 출력전압

와 축전기(130)의 양단전압

의 입출력 전달함수를 구하면, 하기 식 5와 같이 정리된다.From here

,

,

,

,

Is defined as Laplace transform of both sides of Equation 4, the output voltage of the inverter 110

And the voltage at both ends of the capacitor 130

When the input / output transfer function of is obtained, it is summarized as in Equation 5 below.

[Equation 5]

,

,

,

,

로 정의되는 파라미터(parameter)들이며, 파라미터 벡터(parameter vector)

는

로 정의된다.From here,

,

,

,

,

Parameters defined by the parameter vector

Is

Is defined as

과 부하저항(160)의 저항값

은 하기 식 6과 같이 나타낼 수 있다.From Equation 5, the inductance of the heating coil 150 to be predicted in the present invention

Resistance value of overload resistance 160

Can be expressed as in Equation 6 below.

[Equation 6]

,

,

은 측정을 통해 미리 알 수 있는 축전기(130)의 전기용량

와, 유도코일(120)의 인덕턴스

로부터 직접 도출되는 상수값이므로, 파라미터

및

의 값을 추정함으로써 가열코일(150)의 인덕턴스

과 부하저항(160)의 저항값

을 추정할 수 있게 된다.From here,

The capacitance of the capacitor 130 can be known in advance by measuring

And the inductance of the induction coil 120

Is a constant derived directly from

And

Inductance of the heating coil 150 by estimating the value of

Resistance value of overload resistance 160

Can be estimated.

를 적응 추정 방식(Adaptive Estimation)을 통해 수렴시키는 과정에 대해 설명한다.Parameter vector below

The process of converging through the adaptive estimation method will be described.

Through linear parameterization, an input / output model such as Equation 7 is defined.

[Equation 7]

로 정의되는 출력신호이고,

와 같이 인버터(110)의 출력전압

와 축전기(130)의 양단전압

로 정의되는 입력신호(known signal)이며,

는 시스템이 안정하게(stable) 동작하도록

로 정의되는 3차 필터이다.From here,

Is an output signal defined by

Output voltage of the inverter 110 as shown

And the voltage at both ends of the capacitor 130

Is a known signal defined by

To keep the system stable

Third order filter defined by.

의 추정 모델(Estimation Model)을

와 같이 정의하고, 정상화 추정 에러(Normalized Estimation Error)를

와 같이 정의하면, 순간 비용 함수(Instantaneous Cost Function)는 하기 식 8과 같이 정의된다.

Estimation Model of

And normalized estimation error (Normalized Estimation Error)

When defined as follows, Instantaneous Cost Function is defined as in Equation 8.

[Equation 8]

는 하기 식 9와 같이 갱신(update) 될 수 있다.When the gradient update rule is applied to obtain a parameter vector that minimizes the instantaneous cost function of Equation 8, the estimated value of the parameter vector

May be updated as shown in Equation 9 below.

[Equation 9]

및

의 값과 상기 식 6을 이용하여, 가열코일(150)의 인덕턴스

과 부하저항(160)의 저항값

을 적응 추정 방식(Adative Estimation Algorithm)으로 예측할 수 있게 된다.If the estimated value of the parameter vector converges to a specific value according to the gradient update rule, it is an element of the converged parameter vector.

And

Inductance of the heating coil 150 using the value and Equation 6 above.

Resistance value of overload resistance 160

Can be predicted by the Adaptive Estimation Algorithm.

2 to 4 show the results of verifying the validity of the load prediction system according to a preferred embodiment of the present invention through a computer simulation.

2 illustrates measurement waveforms of the output voltage 210 of the inverter 110 and the voltage 220 of both ends of the capacitor 130. The output voltage 210 of the inverter 110 is represented by a sinusoidal AC voltage, and the voltage 220 at both ends of the capacitor 130 is indicated by reference numerals.

(310),

(320) 및 정상화 추정 에러

(330)의 파형을 도시한 도면이다. 도 3에서 보는 바와 같이, 상기 파라미터

(310),

(320) 및 이에 따른 정상화 추정 에러

(330)의 값은 그라디언트 업데이트 룰이 진행됨에 따라 특 정값으로 수렴된다.3 is a parameter converged using the adaptive estimation algorithm of the present invention.

(310),

320 and normalization estimation error

330 shows waveforms. As shown in Figure 3, the parameter

(310),

(320) and thus normalization estimation error

A value of 330 converges to a specific value as the gradient update rule proceeds.

(410)과 부하저항(160)의 저항값

(420)의 파형을 도시한 도면이다. 역시 도 4에서 보는 바와 같이, 상기 인덕턴스

(410)과 저항값

(420)은 그라디언트 업데이트 룰이 진행됨에 따라 특정값으로 수렴된다. 상기 수렴된 값이 본 발명의 부하 예측 시스템이 추정한 가열코일(150)의 인덕턴스와 부하저항(160)의 저항값이 된다.4 shows the inductance of the heating coil 150 estimated using the adaptive estimation algorithm of the present invention.

410 and the resistance value of the load resistance 160

A waveform of 420 is shown. As shown in Figure 4, the inductance

410 and resistance value

420 converges to a specific value as the gradient update rule proceeds. The converged value becomes the inductance of the heating coil 150 and the resistance of the load resistance 160 estimated by the load prediction system of the present invention.

As mentioned above, the specific contents for the practice of the present invention have been described, but the scope of the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention. It will be self-evident for those who have knowledge. In addition to the gradient update rule used in the parameter update method, various known methods, for example, LMS, RLS, Kalman filter, etc. may be used.

1 is a circuit diagram showing a load prediction system of an induction heating apparatus according to a preferred embodiment of the present invention.

FIG. 2 is a diagram illustrating measurement waveforms of an output voltage of an inverter and voltages of both ends of a capacitor in a load prediction system of an induction heating apparatus according to an exemplary embodiment of the present invention.

3 is a diagram illustrating waveforms of a parameter and normalization estimation error converged using an adaptive estimation algorithm according to an exemplary embodiment of the present invention.

4 illustrates waveforms of resistance values of inductance and load resistance of a heating coil converged using an adaptive estimation algorithm according to an exemplary embodiment of the present invention.

Claims (5)

In an induction heating apparatus including an induction coil, a capacitor and a heating coil, a load prediction system for predicting the impedance of the heating coil, the impedance of the heating object, or the impedance of the heating coil and the heating object, A measuring unit measuring an input voltage of the induction heating device and a voltage across the capacitor; And A load predicting unit for predicting the impedance of the heating coil, the impedance of the heating object, or the impedance of the heating coil and the heating object, using the input voltage of the induction heating device and the voltage across the capacitor, The load prediction unit predicts the impedance of the heating coil, the impedance of the heating object, or the impedance of the heating coil and the heating object by using an adaptive estimation algorithm. Further using the inductance of the induction coil and the capacitance value of the capacitor, The adaptive estimation algorithm according to a gradient update rule for minimizing the instantaneous cost function of the estimation error, the impedance predicted value of the heating coil, the impedance predicted value of the heating object. Or updating the impedance predicted values of the heating coil and the object to be heated. delete The method of claim 1, The load prediction unit receives the input voltage of the induction heating device and the voltage across the capacitor as a digital signal and performs the adaptive estimation algorithm by a digital signal processing method. system. delete The method of claim 1, wherein the load prediction system, And a display unit which outputs an impedance predicted value of the heating coil, an impedance predicted value of the heated object, or an impedance predicted value of the heated coil and the heated object in real time.

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