JPH11162624A - Inverter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control the temperature of a pan correctly and easily by providing a high linearity relation between a power instruction and an output power by a simple circuit structure. SOLUTION: This inverter device makes a pan 19 generate heat by means of electromagnetic induction heating by virtue of a high frequency magnetic field which is generated by supplying power to a magnetic field generation coil 12 at switching period of the on-time Ton obtained based on a power instruction Pr, and generating the high frequency magnetic field corresponding to the output power of the magnetic field generation coil 12. This device has an on-time determination circuit 40 to obtain the on-time Ton so as to make the output power shown by the power instruction Pr coincide with the output power of the magnetic field generation coil 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device for generating heat from a conductive object such as a pot by electromagnetic induction heating using a high-frequency magnetic field.

[0002]

2. Description of the Related Art In electromagnetic induction heating, a conductor is present in a high-frequency magnetic field, and the conductor itself generates heat due to eddy current loss in the conductor. In recent years, attention has been paid to the characteristics of electromagnetic induction heating, in which a heating element is efficiently heated without using a fire, and for example, electromagnetic induction heating has been widely used as a heat source for cooking utensils such as rice cookers, stoves, and hot plates. It is getting.

[0003] The electromagnetic induction heating device represented by the above-mentioned cooking utensil is provided with an inverter device for converting power supplied at home or business frequency into high frequency power to generate a high frequency magnetic field. As shown in FIG. 5, a conventional inverter device includes a rectifying unit 52 for rectifying AC power input from an AC power supply 51, and a resonance type device for generating a high-frequency magnetic field based on the rectified power supplied from the rectifying unit 52. And the power supply to the magnetic field generator 53 is turned on / off.
A drive circuit 55 having a switch section 54 for switching off, a measuring circuit 56 for measuring the voltages of the magnetic field generating section 53 and the switch section 54, and the switch section 54 being turned on at an arbitrary ON time switching cycle. / OFF control circuit 57 and power command Pr multiplied by a proportional coefficient
An ON time determination circuit 61 for obtaining the N time Ton is provided.

When the power command Pr is input from the operator or the temperature controller to the ON time determination circuit 61, the inverter device configured as described above multiplies the ON time Ton by multiplying the ON time Ton by a predetermined proportional coefficient value. After the calculation in the ON time determination circuit 61, the ON time Ton is output to the control circuit 57, and the switching element (Q) 59 is turned ON / OFF in the switching cycle of the ON time Ton. As a result, electric power corresponding to the ON time of the switching element (Q) 59 is supplied to the magnetic field generator 53, and the magnetic field generator 53 forms a high-frequency magnetic field corresponding to the output power. It will generate heat.

[0005]

However, in the configuration in which the pot 58 is heated by the ON time Ton obtained by multiplying the power command Pr by the proportional coefficient value as in the above-described conventional technique, the temperature of the heat generated by the pot 58 can be accurately determined. There is a problem that it is difficult to control.

That is, the switching element (Q) 59 is turned on.
Since the ON time Ton for determining the time Ton is obtained by multiplying the power command Pr by the proportional coefficient value, the power command Pr
Is proportional to On the other hand, FIG.
As shown in (b), the switching element (Q) 59 is
When in the N state, the coil 6 provided in the magnetic field generation unit 53
Since the current I _l1 flowing through 0 increases with the passage of time, the power (output power) supplied to the magnetic field generation unit 53
Is not proportional to the ON time Ton of the switching element (Q) 59.

Therefore, conventionally, the ON time Ton is determined by the power command Pr having a high linearity relationship with the ON time Ton.
The output power is controlled so that the output power has a low linearity with respect to the output power. Often deviates from the optimal value. Thus, for example, when the temperature of the heat generated in the pot 58 is measured and feedback control is performed by the temperature controller, the temperature controller frequently changes the power command Pr, so that the temperature control performance is reduced.

In view of this, it is conceivable to perform feedback control to obtain the increase or decrease of the ON time Ton based on the output power instead of the heat generation temperature.
A circuit that measures a voltage and a current that fluctuates at a switching frequency of up to 30 kHz is required, which complicates the circuit configuration and makes it difficult to determine a control gain when performing feedback control of output power.

Therefore, according to the present invention, the heat generation temperature of the pot 58 can be accurately and easily controlled by providing a high linearity relationship between the power command Pr and the output power with a simple circuit configuration. It is intended to provide an inverter device.

[0010]

In order to solve the above-mentioned problems, an invention according to claim 1 is an invention which determines an ON-state obtained based on a power command.
An inverter device for supplying power to the magnetic field generating coil at a switching cycle of time, generating a high-frequency magnetic field corresponding to the output power of the magnetic field generating coil, and heating the object to be heated by electromagnetic induction heating by the high-frequency magnetic field; An on-time determining means for determining the on-time so that the output power indicated by the command matches the output power of the magnetic field generating coil is provided. According to the above configuration, since the ON time is determined so that the output power indicated by the power command and the output power of the magnetic field generating coil match, the power command and the output power have a highly linear relationship. . Therefore, for example, when a temperature controller is connected to the object to be heated, the optimal output power for the heat generation of the object to be heated indicated by the power command from the temperature controller is output from the magnetic field generating coil. It is possible to perform feedback control based on high accuracy. Thus, unlike the case of performing feedback control while measuring the output power of the magnetic field generating coil, it is not necessary to provide a complicated measurement circuit corresponding to a high-frequency switching cycle in the ON time determination means. The heat generation temperature of the object can be controlled accurately and easily.

According to a second aspect of the present invention, in the inverter device according to the first aspect, the ON-time determining means calculates the theoretical output power of the magnetic field generating coil so as to calculate the theoretical output power of the magnetic field generating coil. It has a power calculation formula having the supply time as a variable, and obtains a supply time when the theoretical output power calculated from the power calculation formula matches the output power indicated by the power command as an ON time. I have. According to the above configuration, since the ON time is obtained based on the power calculation formula, it is possible to easily and quickly respond to various specifications and specification changes of the inverter device.

According to a third aspect of the present invention, in the inverter device according to the first aspect, the ON-time determining means matches the output power indicated by the power command with the output power of the magnetic field generating coil. Preset power command and ON
There is a data table with time, and an ON time corresponding to a power command is obtained from the data table. According to the above configuration, the ON time is obtained based on the data table of the power command and the ON time.
Even if the data processing ability of the time determining means is low, the ON time can be sufficiently obtained. Therefore, for example, a CPU with low processing capability can be used, so that an inverter device can be obtained at low cost.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. As shown in FIG. 1, the inverter device according to the present embodiment includes a one-stone-type drive circuit 1 that generates a high-frequency magnetic field so as to heat a pot 19 (an object to be heated) made of a conductor by electromagnetic induction heating. A measuring circuit 2 for measuring an operation state (current or voltage) of each part in the circuit 1,
Based on the operation state obtained from the measurement circuit 2, the control circuit 3 controls the drive circuit 1 so that the pan 19 generates heat to a desired heating temperature, and outputs the ON time Ton used for controlling the control circuit 3. And an ON time determination circuit 40 that performs the operation.

The drive circuit 1 has a rectifier 5, a magnetic field generator 6, and a switch 7. The rectifying unit 5 has a rectifier 8 composed of a diode bridge connected to the AC power supply 4 having a commercial frequency, and a smoothing circuit 11 composed of a smoothing coil 9 and a smoothing capacitor 10. Thus, the rectifier 5 functions as an inverter power supply by performing full-wave rectification of the AC power input from the AC power supply 4 by the rectifier 8 and removing ripple components in the rectified power by the smoothing circuit 11.

The output side of the rectifier 5 is connected to a magnetic field generator 6.
It is connected to the. The magnetic field generating unit 6 is parallel to the magnetic field generating coil 12 so that the magnetic field generating coil 12 generates a high-frequency magnetic field with the output power corresponding to the power supplied from the rectifying unit 5 and the magnetic field generating coil 12 performs LC parallel resonance. And a resonance capacitor 13 connected thereto. A switching unit 7 including a switching element (Q) 14 and a diode 15 is provided at a stage subsequent to the magnetic field generation unit 6, and the switching unit 7 turns on / off the switching element (Q) 14.
The power supply to the magnetic field generating coil 12 is turned on / off, thereby setting the amount of power supplied to the magnetic field generating coil 12 per switching cycle.

The driving circuit 1 is connected to a measuring circuit 2. The measurement circuit 2 has a plurality of differential amplifiers (not shown). These differential amplifiers are connected to both ends of the resonance capacitor 13 and the switching element (Q) 14, respectively, and detect the coil voltage V _L1 and the SW element voltage V _SW and output them to the control circuit 3. ing. The control circuit 3 monitors the operation state of the drive circuit 1 based on the coil voltage V _L1 and the SW element voltage V _SW from the measurement circuit 2 and, when the ON time Ton is input, The switching element (Q) 14 is turned on / off by outputting a SW element driving signal at a switching cycle of the ON time indicated by the ON time Ton.

The control circuit 3 is connected to an ON time determination circuit 40 for determining the ON time Ton so that the output power indicated by the power command Pr matches the output power of the magnetic field generating coil 12. The ON time determination circuit 40
I / O unit 41 for inputting / outputting time Ton and power command Pr
And a memory unit 4 storing an ON time calculation routine to be described later.
2 and a CPU 43 that executes an ON time calculation routine
And a data bus 44 for interconnecting the units 41, 42, 43. Then, the ON time determination circuit 40
When the power command Pr is input from the operator or the temperature controller, the power command Pr is executed by executing the ON time calculation routine.
And outputs a signal in response to the determination of the ON time Ton.

The operation of the inverter device having the above configuration will be described. Drive circuit 1 is 100 Hz from AC power supply 4
When the AC power is supplied at a frequency of 120 Hz, the AC power is full-wave rectified to twice the frequency in the rectifier 8 in the drive circuit 1, and the ripple component in the rectified power is removed in the smoothing circuit 11. Is used as an inverter power supply.

Next, the measuring circuit 2, the control circuit 3, and the ON
When power is supplied from a constant power supply device (not shown) to the time determination circuit 40, the measurement circuit 2 detects the coil voltage V _L1 and the SW element voltage V _SW of the drive circuit 1 and outputs them to the control circuit 3. . Further, the ON time determination circuit 40 obtains an ON time Ton for linearizing the externally input power command Pr and the output power of the magnetic field generating coil 12, and outputs the ON time Ton to the control circuit 3.

That is, the ON time determination circuit 40 executes the ON time calculation routine shown in FIG. 2 when the power is turned on, and takes in the power command Pr input from the operator or the temperature controller. Then, the power command Pr is set as a reference value so as to perform the initial setting of the calculation start, and the repetition variable i, the total current value S, and the total time T are set to “0” (S1).

Next, in order to calculate the theoretical output power P indicating the output power of the magnetic field generating coil 12 from the power calculation equation (12), the theoretical output power P is used for calculating the current value I _L1 [i] in the equation (12). Initial value x of the state variable x [i]

[0] is set, and the calculation step width ΔT is set (S2). At this time, the calculation step width ΔT is set to a value that is sufficiently small with respect to the switching frequency f (about 20 to 30 kHz) in order to increase the accuracy of the calculation.
It is preferable to set about / 100. (12)
The method of introducing the equation and the state variable x [i] will be described later.

Next, after adding "1" to the repetition variable i (S3), the state variable x corresponding to the repetition variable i is added.
[I] is replaced by the state equation (x [i] ← Aon ^* ) of equation (10) ^.
X [i]) (S4). The matrix exponential function A
on ^* = exp (Aon · ΔT) may be calculated in advance offline. Then, the calculated state variable x
A current value I _L1 [i] is obtained based on [i], and a total current value S
And the calculation step width ΔT is added to the total time T (S5).

Thereafter, by dividing the integrated value of the voltage E across the smoothing capacitor 10 serving as the inverter power supply and the total current value S by the total time T, the theoretical output power P (= E ×
(S / T) (S6). Then, the theoretical output power P is compared with the power command Pr (S7). If the power command Pr is less than the theoretical output power P (S7, yes), the above-mentioned S3 is determined.
And re-execute, add "1" to the repetition variable i, and execute S4 to S6 to obtain a new theoretical output power P. When S3 to S6 are repeated and the power command Pr matches the theoretical output power P (S7, no), the repetition variable i and the calculation step width Δ
ON time Ton (= i · ΔT) by integrating T
Is calculated (S8), and the content of the command signal is changed to the ON time Ton (S9).

When the ON time Ton is obtained as described above, the ON time Ton is output from the ON time determination circuit 40 to the control circuit 3 as a command signal as shown in FIG. The circuit 3 turns on / off the switching element (Q) 14 in the switching cycle of the ON time Ton.
F. When the switching element (Q) 14 is turned on / off, power is supplied from the inverter power supply to the magnetic field generating coil 12, and the magnetic field generating coil 1 is turned on.
When the high-frequency magnetic field corresponding to the output power is generated from 2, the pot 19 made of a conductive material is heated by electromagnetic induction and generates heat at a temperature proportional to the output power.

Thus, since the heating temperature of the pot 19 and the output power of the magnetic field generating coil 12 are in a proportional relationship, and the output power of the magnetic field generating coil 12 and the power command Pr are in a proportional relationship, for example, When the temperature is feedback-controlled by the temperature controller, the power command Pr generated based on the measured value of the heat generation temperature is determined by the optimum output power in the pan 1
In order to make 9 generate heat, the heat generation temperature of the pan 19 is accurately controlled.

Next, it is used in the ON time calculation routine of FIG.
(12) and the method of deriving the state variable x [i]
explain about. First, the voltage in the drive circuit 1 of FIG.
・ To find the theoretical formula of current, as shown in FIG.
The generating coil 12 and the pan 19 are modeled. Note that R_Two
And L _TwoCalculates the resistance and inductance of the pot 19
Respectively, L₁Is the inductance of the magnetic field generating coil 12.
Shows a closet. Thereby, the magnetic field generating coil 12
The circuit equation in the analysis model of
You.

[0027]

(Equation 1)

Here, a new state variable φ ₁ = L ₁ I _L1
When deformed using the phi ₂ = MI _L2,

[0029]

(Equation 2)

Where τ = L ₂ / R ₂ , k = M / (L ₁ L
₂ ) ^1/2 . τ is a load time constant on the secondary side, and k has a meaning of a coupling coefficient. By transforming equation (2),

[0031]

(Equation 3)

[0032]

(Equation 4)

Further, by substituting equation (4) into the first equation of equation (2) and transforming it,

[0034]

(Equation 5)

Is obtained. Here, since the condition differs depending on whether the switching element (Q) 14 is ON / OFF,
Summarize each case separately. First, when the switching element (Q) 14 is ON, the following equation is established.

[0036]

(Equation 6)

The switching element (Q) 14 is OF
At the time of F, the following equation is established.

[0038]

(Equation 7)

[0039] (4), (5), (6) and (4), (5), collectively (7), the take heart state variable and [I _L1 φ ₂ V _L1] ^T , The following state equations (8) and (9) are obtained.

[0040]

(Equation 8)

[0041]

(Equation 9)

Expressions (8) and (9) are expressed as follows: Q: ON x ^* (t) = A _on · x (t) Q: OFF x ^* (t) = A _off · x (t) . Where x (t) = [I _L1 φ ₂ V _L1 ] ^T
It is. By using the above theoretical formula, the current / voltage and output power of the switching element (Q) 14 during the operation of the inverter device can be calculated. Specifically, assuming that the calculation cycle is ΔT, the value of the state variable is O
In period N,

[0043]

(Equation 10)

It can be calculated by the discrete equation of state. Here, exp (A _on ΔT) is a matrix exponential function. Similarly, in the OFF period,

[0045]

[Equation 11]

It can be calculated by the following discrete state equation. Next, in the inverter device shown in FIG. 1, a case where the voltage across the smoothing capacitor 10 is set to a constant value E by an LC filter is considered. When the switching element (Q) 14 of the inverter device is switching in the quasi-E class operation mode, the output power p
Becomes equal to the input power. Since the input current in the OFF period is 0 and the input current in the ON period is equal to the current flowing through the magnetic field generating coil 12, the theoretical output power P is

[0047]

(Equation 12)

Can be expressed by the following power calculation formula. Then, I _L1 [i] in the equation (12) is a state equation x [i].
Can be obtained by calculating x [i] according to equation (8). In matrix form, I _L1
[I] = [100] x. Here, the OFF period Tof
f is the magnetic field generating coil 12 and the resonance capacitor 13
Is determined, it can be regarded as a fixed value. Therefore, assuming that the power command is Pr, the repetition variable i is increased at the timing of the calculation step ΔT, and the equation (12) is calculated. As shown in FIG. 4, i becomes P [n] = Pr.
ON time T by calculating n × ΔT when = n
on (= nΔT) can be obtained.

When calculating the equations (8) and (9), (L ₁ , τ, k) is required as a parameter. These parameters are used in designing the inverter as follows. Can be determined. First, the magnetic field generating coil 12 and the resonance capacitor 13 are temporarily set, and the inverter device is operated. The drive frequency of the inverter device is set to twice the LC resonance frequency in order to set ON time = OFF time. Next, in the ON period, the gradient is obtained in a period in which the coil current can be regarded as a substantially constant gradient. This slope, since the E / L _1, can be obtained inductance L ₁ of the magnetic field generating coil 12. Thereafter, the coil current and current waveform are measured while changing τ and k in the equations (8) and (9), so that τ and k at which the frequency and voltage peaks of the theoretical waveform and the actual measured waveform match are determined. Ask.

As described above, since (L ₁ , τ, k) is obtained, it becomes possible to calculate the current / voltage and output voltage of the switching element (Q) 14 by the equations (8) and (9). In the actual design, readjusting the C ₁ or the like based on the specifications of the peak and the switching frequency of the voltage-current.

In the present embodiment, the theoretical output power P is obtained by executing the ON time calculation routine shown in FIG. 2 and calculating the equation (12). However, the present invention is not limited to this. That is, theoretical output powers P corresponding to various power commands Pr are obtained in advance from equation (12), and the relationship between these theoretical output powers P and power commands Pr is stored in the memory unit 4 in FIG.
2 is stored as a data table. Then, when the power command Pr from the operator or the temperature controller is taken in,
The ON time Ton corresponding to the power command Pr may be extracted from the data table and output to the control circuit 3 as a command signal. According to this configuration, since it is not necessary to calculate the theoretical output power P, it is possible to employ the CPU unit 43 having a low processing capacity, so that the cost of parts can be reduced.

[0052]

According to the first aspect of the present invention, power is supplied to a magnetic field generating coil at a switching period of an ON time obtained based on a power command, and a high-frequency magnetic field corresponding to output power of the magnetic field generating coil is generated. In an inverter device for heating an object to be heated by electromagnetic induction heating by the high-frequency magnetic field, an ON time determining means for determining the ON time so that output power indicated by the power command matches output power of the magnetic field generating coil. It is a configuration that it has. According to the above configuration, since the ON time is determined so that the output power indicated by the power command and the output power of the magnetic field generating coil match, the power command and the output power have a highly linear relationship. . Therefore, for example, when a temperature controller is connected to the object to be heated, the optimal output power for the heat generation of the object to be heated indicated by the power command from the temperature controller is output from the magnetic field generating coil. It is possible to perform feedback control based on high accuracy. Thus, unlike the case of performing feedback control while measuring the output power of the magnetic field generating coil, it is not necessary to provide a complicated measurement circuit corresponding to a high-frequency switching cycle in the ON time determination means. There is an effect that the heat generation temperature of the object can be controlled accurately and easily.

According to a second aspect of the present invention, in the inverter device according to the first aspect, the ON time determining means calculates the theoretical output power of the magnetic field generating coil so that the power to the magnetic field generating coil is calculated. A power calculation formula having the supply time as a variable is provided, and the supply time when the theoretical output power calculated from the power calculation formula matches the output power indicated by the power command is obtained as the ON time. According to the above configuration, since the ON time is obtained based on the power calculation formula, it is possible to easily and quickly respond to various specifications and specification changes of the inverter device.

According to a third aspect of the present invention, in the inverter device according to the first aspect, the on-time determining means matches the output power indicated by the power command with the output power of the magnetic field generating coil. Preset power command and ON
It has a data table with time, and the ON time corresponding to the power command is obtained from the data table. According to the above configuration, the ON time is obtained based on the data table of the power command and the ON time, so that the ON time can be sufficiently obtained even if the data processing capability of the ON time determining means is low. Therefore, for example, a CPU having a low processing capacity can be used, so that an inverter device can be obtained at low cost.

[Brief description of the drawings]

FIG. 1 is a block diagram of an inverter device.

FIG. 2 is a flowchart of an ON time calculation routine.

FIG. 3 is a circuit diagram modeling a magnetic field generating coil and a pan.

FIG. 4 is an explanatory diagram showing a process of calculating an ON time in a power calculation formula.

FIG. 5 is a block diagram of a conventional inverter device.

FIGS. 6A and 6B are explanatory diagrams showing operation waveforms of respective units, where FIG. 6A is an explanatory diagram when the ON time Ton is short, and FIG. 6B is an explanatory diagram when the ON time Ton is long.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 drive circuit 2 measurement circuit 3 control circuit 4 AC power supply 5 rectifier 6 magnetic field generator 7 switch 8 rectifier 9 smoothing coil 10 smoothing capacitor 11 smoothing circuit 12 magnetic field generating coil 13 resonance capacitor 14 switching element (Q) 15 Diode 19 Pot 40 ON time determination circuit 41 I / O unit 42 Memory unit 43 CPU unit

Claims (3)

[Claims] An electric power is supplied to a magnetic field generating coil at a switching cycle of an ON time obtained based on a power command, a high frequency magnetic field corresponding to an output power of the magnetic field generating coil is generated, and electromagnetic induction heating is performed by the high frequency magnetic field. An inverter device that generates heat by heating the object to be heated, characterized in that the inverter device has an ON time determining means for determining the ON time so that the output power indicated by the power command matches the output power of the magnetic field generating coil. And an inverter device. 2. The on-time determining means calculates a theoretical output power of the magnetic field generating coil,
It has a power calculation formula having the power supply time to the magnetic field generating coil as a variable, the supply time when the theoretical output power calculated from the power calculation formula matches the output power indicated by the power command. O
2. The inverter device according to claim 1, wherein the value is obtained as N hours. 3. The on-time determining means has a data table of an on-time and a power command set in advance so that the output power indicated by the power command matches the output power of the magnetic field generating coil. The inverter device according to claim 1, wherein an ON time corresponding to a power command is obtained from the data table.