JP3143341B2 - Inverter control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an inverter.

[0002]

2. Description of the Related Art In an electromagnetic cooker, an object to be heated is induction heated by a heating output of an induction heating coil. Therefore, the electromagnetic cooker is provided with an inverter for controlling the heating output of the induction heating coil. This inverter includes an induction heating transistor type in which a series resonance circuit including an induction heating coil and a capacitor connected in series to the induction heating coil is used as a load.
-190082.

FIG. 10 is a schematic diagram of this type of inverter. Between the positive electrode terminal 1a and the negative electrode terminal 1b of the DC power supply 1, a series circuit of a transistor 2 and a transistor 3, which are switching elements, is interposed. Transistor 2
A series circuit of a resonance capacitor 4 and a resonance capacitor 5 is interposed between the collector of the transistor 3 and the emitter of the transistor 3. A connection intermediate point between the resonance capacitors 4 and 5 is connected via an induction heating coil 6 to a connection intermediate point between the emitter of the transistor 2 and the collector of the transistor 3. A flywheel diode 7 having an anode on the emitter side is interposed between the emitter and the collector of the transistor 2, and a flywheel diode 8 having an anode on the emitter side is interposed between the emitter and the collector of the transistor 3.

In this inverter, the transistor 2 and the transistor 3 are alternately turned on and off, and a resonance current flows through the induction heating coil 6. Then, after turning off one transistor 2 (or 3), when a predetermined pause time (dead time) elapses, the other transistor 3 (or 3) is turned off.
(Or 2) is turned on, and the commutation operation is performed so that the transistors 2 and 3 are not simultaneously turned on and the DC power supply 1 is short-circuited.

[0005] The transistors 2 and 3 are turned off before the current of the induction heating coil 6 reaches the zero crossing point t ₀ as shown in FIG. This is because, when the transistor 2 or 3 is turned off after the current of the induction heating coil 6 has passed the zero-crossing time point t ₀ , the resonance current continues to flow through the flywheel diode, and the current of the induction heating coil 6 is reduced as shown in FIG.
changes (b), the zero effective current value is decreased as compared with the case of turning off the transistor 2 or 3 before the cross point t _0, due to the input current of the induction heating coil 6 is reduced.

Normally, this inverter performs control to extend the on-time of the transistor when the input current decreases. However, when the on-time is extended in the state shown in FIG. 11 (b), the input current decreases more and the heating increases. The output cannot be controlled normally. Therefore, it is necessary to surely turn off the transistors 2 and 3 before the current of the induction heating coil 6 reaches the zero crossing point t ₀ .

By the way, the current of the induction heating coil 6 is shown in FIG.
If the transistor 2 is turned off before reaching the zero crossing point as shown in FIG. 12A, the collector voltage of the transistor 3, which is the voltage of the inverter, decreases as shown in FIG. While the transistor 3 is turned on and the transistor 2 is off, the collector voltage of the transistor 2 remains low. Then transistor 3
Is turned off, the collector voltage of the transistor 3 increases. And when the transistors 2 and 3 are turned off,
The phase difference γ of the current of the induction heating coil 6, which is the current of the inverter, from the zero crossing point t ₀ is measured.

When the inverter is started, the operation is started at a high frequency, and thereafter, the operating frequency is gradually lowered with the target of the resonance frequency while comparing the phase of the voltage and current of the inverter. And the measured phase difference γ is
When γ ≦ γ _ad (where γ _ad is the lower limit of the phase difference γ), the operation of lowering the operating frequency is stopped. In this way, the time difference between the zero cross point of the inverter voltage and current is
(Phase difference) is reduced to several μsec to prevent a decrease in the effective current value of the current of the induction heating coil 6.

[0009]

As described above, in the conventional inverter control method, it is necessary to detect the time at which the transistor is turned off and the time at which the current of the induction heating coil crosses zero. It must be detected accurately. However, the inverter has 200
Since a high DC voltage obtained by rectifying the AC voltage of V is supplied, a circuit element capable of withstanding the high voltage is required for the detection unit, and the control circuit of the inverter cannot be configured at low cost. In addition, since it is necessary to detect both the voltage and the current of the inverter, there is a problem that this also increases the cost.

The present invention has been made in view of the above problems, and provides an inverter control method capable of detecting only the current of an inverter and reliably turning off the transistor before the current of the induction heating coil reaches a zero crossing point. With the goal.

[0011]

According to a first aspect of the present invention, there is provided a method of controlling an inverter, which controls a commutation of a switching element which switches a current of a resonance circuit including a coil and a resonance capacitor connected in series with the coil. In the method of controlling an inverter, a current detection unit that detects a current of the coil, a first voltage related to a detection current of the current detection unit,
A voltage generating unit that generates a second voltage with a delayed voltage; and a comparing unit that compares the first voltage and the second voltage, and turns off the switching element according to a comparison result of the comparing unit. It is characterized by the following.

[0012]

[0013]

[0014]

According to the first invention, a first voltage is generated by detecting a current of the coil and a second voltage obtained by delaying the first voltage, and a phase difference between the first voltage and the second voltage is calculated. It corresponds to the period from the time when the switching element is turned off to the time when the current of the coil crosses zero. The first voltage and the second voltage are compared in magnitude, and the switching element is turned off based on the comparison result. Thereby, only the current of the coil is detected, and the switching element can be turned off before the current of the coil reaches the zero crossing point.

[0015]

[0016]

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 1 is a block diagram illustrating a main configuration of an electromagnetic cooker controlled by the inverter control method according to the present invention. The three-phase AC power supply terminals T _U , T _V , T _W are separately connected to the AC input terminals 10a, 10b, 10c of the three-phase rectifier bridge 10. A series circuit of a choke coil 11 and a smoothing capacitor 12 is interposed between the positive DC output terminal 10d and the negative DC output terminal 10e of the three-phase rectifier bridge 10. Smoothing capacitor
12, a series circuit of a transistor 13 and a transistor 14 is connected in parallel. A flywheel diode 15 having an anode connected to the emitter is interposed between the emitter and the collector of the transistor 13.

A flywheel diode 16 having an emitter connected to the anode is interposed between the emitter and the collector of the transistor 14. A series circuit of a resonance capacitor 17 and a resonance capacitor 18 is interposed between the collector of the transistor 13 and the emitter of the transistor 14. A connection midpoint between the resonance capacitors 17 and 18 is connected to a connection midpoint between the emitter of the transistor 13 and the collector of the transistor 14 via an induction heating coil (hereinafter referred to as a heating coil) 19. The output current of the current transformer 20 that detects the current of the heating coil 19 is input to the coil current phase determination circuit 21.

The output from the coil current phase determination circuit 21
The heating coil current phase angle θ and the heating coil current phase
The current phase angle θ + π is obtained by adding the half-period phase angle π to the angle θ.
Another signal is input to the ON-phase limiting circuit 22. On phase system
Switching inversion signal #S output from the limit circuit 22_SWIs
Input to the voltage controlled oscillator 23. Three-phase power terminal T_V (T
_W) To detect the current flowing to the AC input terminal 10b (10c)
The output current of the current transformer 30 (31) depends on the heating output of the heating coil 6.
Heat output signal S to be determined_HIs input to the control signal circuit 24
Is input to Control signal output from control signal circuit 24
S_CIs input to the voltage controlled oscillator 23. Voltage controlled oscillator
Reset signal S output from 23_RIs the ON phase limit
Input to the path 22 and the two-phase splitting circuit 25. Two-phase split circuit 25
Drive signal S output from_D1Is the drive circuit 26 and the on position.
The driving signal S is input to the phase limiting circuit 22 and_D2Is the drive circuit 27
And to the ON-phase limiting circuit 22.

FIG. 2 is a block diagram showing the configurations of the on-phase limiting circuit 22 and the coil current phase determining circuit 21. The reset signal S _R from the voltage controlled oscillator 23 is input to the input terminal B of the one-shot multivibrator 22a. The input terminal A of the one-shot multivibrator 22a is grounded, and the enable terminal CD is connected to the power supply E. A capacitor C ₀ is interposed between the capacitor connection terminal T ₁ and the capacitor connection terminal T ₂ , and a connection point between the capacitor connection terminal T ₂ and the capacitor C ₀ is connected to the power supply E via a resistor R _0.
Connected to The output signal of the output terminal Q is supplied to the reset terminal R of the D flip-flop 22b and the D flip-flop 22c.
Is input to the reset terminal R. D flip-flop 22
The drive signal S _D1 from the two-phase division circuit 25 is input to the input terminal D of
And the inverted output signal of the inverted output terminal #Q is ORed.
The signal is input to one input terminal of the circuit 22d, and the set terminal S is grounded.

At the input terminal D of the D flip-flop 22c
Is the driving signal S from the two-phase dividing circuit 25. _D2Is entered and
The inverted output signal of the inverted output terminal #Q is connected to the other input terminal of the OR circuit 22d.
And the set terminal S is grounded. OR circuit 22d
To switching inversion signal #S _SWIs output. Current transformer
A resistor R is connected between the secondary winding terminals₁And the resistance R₁
Is connected to the base of transistor 21a,
Side terminal is resistor R_TwoAnd a resistor R_ThreeThrough
Connected to DC power supply E.

The collector of the transistor 21a is connected to the power source E, the emitter is connected to the positive input terminal of the comparator 21b +, it is grounded via a resistor R _4. The emitter of the transistor 21a is connected to the comparator 21b via a resistor R.
, And the negative input terminal − is grounded via a capacitor C. An output terminal of the comparator 21b is connected to the power supply E via a resistor R _5, directly to the inverter
Connected to 21c input terminal. The output terminal of the inverter 21c is connected to the clock terminal CK of the D flip-flop 22b and the input terminal of the inverter 21d. The output terminal of the inverter 21d is connected to the clock terminal CK of the D flip-flop 22c.

FIG. 3 shows a voltage controlled oscillator 23 and a two-phase split circuit.
25 is a block diagram illustrating a configuration of the twenty-fifth embodiment. FIG. The control signal S _C from the control signal circuit 24 is input to the positive input terminal of the comparator 23a. The negative input terminal of the comparator 23a - is grounded through a parallel circuit of a transistor 23b and the capacitor C ₁ of the common emitter is connected to the power source E through the resistor R _10. An output terminal of the comparator 23a is connected to one input terminal of the OR circuit 23c, is connected to the power supply E via a resistor R _11. The other input terminal of the OR circuit 23c
, The switching inversion signal #S _SW is input.

The output terminal of the OR circuit 23c is connected to the set terminal S of the SR flip-flop 23d. Output terminal Q of the SR flip-flop 23d via a resistor R ₁₂ transistor 23
Connected to the base of b. Inverted output terminal #Q of the SR flip-flop 23d is connected to an input terminal of the inverter 23e via a resistor R _12, and the input terminal of the inverter 23e resistor R
Connection point between the ₁₂ is grounded through a capacitor C _2. The output terminal of inverter 23e is SR flip-flop 23
d is connected to the reset terminal R.

The inverted output terminal #Q of the SR flip-flop 23d is connected to the clock terminal CK of the D flip-flop 25a,
One input terminal of each of the AND circuits 25b and 25c is connected to the input terminal B of the one-shot multivibrator 22a of the on-phase limiting circuit 22. The output terminal Q of the D flip-flop 25a is connected to the other input terminal of the AND circuit 25b, and the inverted output terminal #Q is connected to the input terminal D of the D flip-flop 25a.
And the other input terminal of the AND circuit 25c. The drive signal S _D1 is output from the output terminal of the AND circuit 25b. The drive signal S _D1 is input to the drive circuit 26 and the on-phase limiting circuit 22. Driving signal S _D2 from the output terminal of the AND circuit 25c is output. The drive signal S _D2 is input to the drive circuit 27 and the on-phase limiting circuit 22.

Next, the control operation of the inverter of the electromagnetic cooker thus configured will be described with reference to FIG. Turn on transistors 13 and 14,
When a current flows through the heating coil 19 with the OFF control, the current transformer 20 detects the current. The output current of the current transformer 20 is the resistance R ₁
Flow, between both terminals of the resistor R ₁ is a voltage corresponding to the output current of the current transformer 20 is obtained. The voltage obtained by adding an offset voltage caused by the resistor R ₂ to the voltage input to the base of the transistor 21a. As a result, the emitter potential of the transistor 21a changes according to the output current of the current transformer 20, like the voltage _VA shown in FIG. The generating a voltage V _B is delayed by the RC filter formed the voltage V _A and a resistor R and a capacitor C.

[0027] Then, the voltage V _A to the positive input terminal of the comparator 21b +, the voltage V _B the negative input terminal - to compares enter into. Thus, the current detected by the current transformer 20, that is, the phase angle θ and the phase angle θ + π of the inverter current are detected.
At the time of the phase angle θ, the output of the comparator 21b becomes L
Level, and the clock terminal CK of the D flip-flop 22b rises to the H level. At this time, if the drive signal S _D1 is still at the H level while the transistor 13 is turned on, the D flip-flop 22b is inverted. Output terminal #Q is L
Level, and the switching inversion signal #S _SW becomes as shown in FIG.
, And the switching inversion signal #S _SW is input to the set terminal S of the RS flip-flop 23d of the voltage controlled oscillator 23.

Then, the inverted output terminal #Q of the RS flip-flop 23d is slightly delayed due to the delay of the circuit operation and is inverted to the L level as shown in FIG. and outputs a signal S _R. AND circuit 25b of the reset signal S _R is biphasic dividing circuit 25, 25c
, The output of the AND circuit 25b is inverted to L level, the drive signal S _D1 becomes L level, and the transistor 13 is turned off before the zero crossing point of the inverter current. Thereafter, the output of the inverter 23e of the voltage controlled oscillator 23 is inverted to the H level after a lapse of a pause (dead time) of a predetermined time (about 1 μs), and the inverted output terminal #Q of the SR flip-flop 23d is again at the H level. And the reset signal S _R becomes H level as shown in FIG. Then, the inverted output terminal #Q of the D flip-flop 25a becomes H level, the H level driving signal _SD2 is output from the AND circuit 25c, and the transistor 14 is turned on.

Also, as shown in FIG. 4C, the phase angle θ + π
Is detected at the point of time when the switching inversion signal #S is
_SW is inverted to L level as shown in FIG. 4 (e), and the drive signal S
_D2 goes low, turning off transistor 14 before the zero crossing of the inverter current.

Further, the inverted output terminal #Q reset signal S _R by rest periods of L level of the SR flip-flop 23d in the voltage controlled oscillator 23, the output terminal Q of the one-shot multivibrator 22a1 of the on phase limiting circuit 22, It becomes H level as shown in FIG. 4 (g) for several μs. Then, during this H-level period, both of the D flip-flops 22b and 22c that have detected that the phase of the drive signal _SD1 has advanced too much are reset. Here, if reset is performed within a period of several μs, when noise occurs near the phase angle θ, θ + π of the output current of the current transformer 20 as the inverter current, the noise is input to the clock terminals CK of the D flip-flops 22b and 22c. The adverse effect of the vibration of the signal can be avoided.

The one-shot multivibrator 22
During the period when the output terminal Q of a is at the H level, the transistor
It is better to make it shorter than 13,14 ON periods. in this way,
Only the current flowing through the heating coil 19 is detected, and based on the detected current waveform, the transistors 13 and 14 can be reliably turned off before the zero crossing point of the current flowing through the heating coil 19.

[0032] In the control method of the inverter described above, by using the resistor R and the voltage V _B generated by a RC filter with capacitor C, a current of the heating coil so as to turn off the transistor before the zero-crossing point since it is, the frequency of the inverter is changed, the amplitude and phase changes of the voltage V _B, the transistor 13 and 14 may vary is the time to turn off. In that case, it can be solved by the following inverter control method.

FIG. 5 is a block diagram showing another configuration of the electromagnetic cooker controlled by the inverter control method according to the present invention. The three-phase AC power supply terminals T _U , T _V , T _W are separately connected to the AC input terminals 10a, 10b, 10c of the three-phase rectifier bridge 10. The positive DC output terminal 10d of the three-phase rectifier bridge 10
A series circuit of a choke coil 11 and a smoothing capacitor 12 is interposed between the negative DC output terminal 10e and the negative DC output terminal 10e. To the smoothing capacitor 12, a series circuit of a transistor 13 and a transistor 14 is connected in parallel. A flywheel diode 15 having an anode connected to the emitter is interposed between the emitter and the collector of the transistor 13.

A flywheel diode 16 having an anode connected to the emitter is interposed between the emitter and the collector of the transistor 14. Flywheel diode
A snubber capacitor C _S1 is connected to 15 in parallel, and a snubber capacitor C _S2 is connected to the flywheel diode 16 in parallel. A series circuit of a resonance capacitor 17 and a resonance capacitor 18 is interposed between the collector of the transistor 13 and the emitter of the transistor 14. A connection intermediate point between the resonance capacitors 17 and 18 is connected to a connection intermediate point between the emitter of the transistor 13 and the collector of the transistor 14 via an induction heating coil (hereinafter referred to as a heating coil) 19. The secondary winding of the current transformer 20 for detecting the current of the heating coil 19 is connected to the positive input terminal + of the comparator 63 and the negative input terminal of the comparator 64.

The negative input terminal of the positive input terminal + and the comparator 64 of the comparator 63 - is grounded through a resistor R _30. An output terminal of the comparator 63, the resistance through the R ₃₁ is connected to the positive input terminal + of the comparator 64, connected point between the positive input terminal of a resistor R ₃₁ and the comparator 64 is grounded through a resistor R _32. Voltage division ratio by the resistors R ₃₁ and R _32, the voltage ir transistor to be compared with the voltage by the current i
It is selected such that the current i corresponding to the current I of the heating coil 19 is sufficient to complete charging / discharging of the snubber capacitors C _S1 and C _S2 during the idle periods of 13,14.

The current level detector 65 is composed of the comparators 63 and 64 and the resistors R ₃₁ and R ₃₂ .
The output terminal of the comparator 64 is connected to the input side of the level conversion circuit 66, and its output side is connected to the input side of the inverter 67,
D circuit 68 is connected to one input terminal. The output side of the inverter 67 is connected to one input terminal of the AND circuit 69. Each output terminal of the AND circuits 68 and 69 is separately connected to one of the OR circuits 70 and the other input terminal, and its output terminal is connected to one input terminal of the AND circuit 71.

An error amplifier 72 to which an output command signal ref from an output command generator (not shown) is input is provided with a current transformer for detecting a current flowing from the three-phase power terminals T _V and T _W to the AC input terminals 10b and 10c. A feedback signal fb corresponding to the current of the heating coil 19, which is the output current of 30, 31, is input. The error signal err output from the error amplifier 72 is input to the voltage controlled oscillator 73, and the switching signal s output from the AND circuit 71 is input to the voltage controlled oscillator 73. The timing signal tm output from the voltage control oscillator 73 is input to the one-shot circuit 74 and the flip-flop 75. The output signal of flip-flop 75 is input to idle time generation circuit 76.

Flip-flop 75 and idle time generating circuit 76
These constitute the drive signal generator 77. The drive signal gu output from the drive signal generation unit 77
The drive signal gl is input to the other input terminals of the D circuit 68 and the other input terminals of the drive circuit 79 and the AND circuit 69. The drive signals gu and gl output by the drive circuits 78 and 79 are transistors 13,1
Entered separately into the base of 4. The judgment valid signal ce output from the one-shot circuit 74 is input to another input terminal of the AND circuit 71. One-shot circuit 74, inverter 67, and AN
The D determination circuits 80, 69, and 71 and the OR circuit 70 constitute a level determination unit 80.

FIG. 6 is a timing chart of signals of various parts, showing a control operation when the electromagnetic cooking device having the above-described configuration operates with a slow current by the inverter control method.
It will be explained together. A three-phase power supply (not shown) is connected to the three-phase rectifier bridge 10 to turn on the transistors 13 and 14 alternately.
When turned off, the direction of the current flowing from the three-phase rectifier bridge 10 to the heating coil 19 is reversed according to the on / off of the transistors 13 and 14. Then, a heating output is obtained from the heating coil 19.

Now, the error amplifier 72 outputs an error signal err based on the output command signal ref and the feedback signal fb, whereby the voltage control oscillator 73 outputs a timing signal tm shown in FIG. The drive signal generator 77 is configured to add a pause time based on the timing signal tm, as shown in FIG.
The drive signals gu and gl shown in (c) are output and input to the drive circuits 78 and 79. Then, the transistors 13 and 14 are driven by the output signals of the drive circuits 78 and 79.

The driving of the transistors 13 and 14 causes a current I to flow through the heating coil 19, which is detected by the current transformer 20.
The output current i of 20 flows through the resistor R _30, the AC voltage generated across the resistor R ₃₀ is changed according to the output current i of the current transformer 20. When the output current i is equal to or higher than the ground potential, the output of the comparator 63 goes high, and when the output current i is equal to or lower than the ground potential, the output goes low, and a voltage synchronized with the output current i is output as shown in FIG. and inputs the voltage resistor R ₃₁ and to generate a divided voltage ir by the R ₃₂ to the positive input terminal of the comparator 64 +. As a result, the comparator 64 outputs the output current i
Compared with the voltage ir, the output voltage l 'of the comparator 64 is at the H level during the period when the voltage due to the current i is smaller than the voltage ir as shown in FIG. This signal l 'is input to the level conversion circuit 66 and converted to a predetermined level, and the output signal l is as shown in FIG.

The output signal 1 is input to the inverter 67, and the inverted signal # 1 shown in FIG. 6 (g) is input to the AND circuit 69. The drive signals gu and gl shown in FIGS. 6B and 6C are input to the AND circuits 68 and 69, and the output signals gu × l of the AND circuits 68 and 69 are established by the establishment of the logic of the AND circuits 68 and 69. , gl × # l
Changes as shown in FIGS. 6 (h) and 6 (i). These output signals gu × l and gl × # 1 are input to the AND circuit 71 via the OR circuit 70, while falling at the rising of the timing signal tm shown in FIG. The judgment valid signal ce shown in FIG. 6 (j) is input to the AND circuit 71. As a result, when the logic of the AND circuit 71 is established, an H level switching signal s is output.

However, the logic of the AND circuit 71 does not hold depending on the signals shown in FIGS. 6 (h), (i) and (j), and the switching signal s is not output as shown in FIG. The transistors 13 and 14 are driven by the timing signal tm, and surely turn off the transistors 13 and 14 before the current flowing through the heating coil 19, that is, the output current i of the current transformer 62 reaches the zero crossing point.

As described above, as shown in FIG. 6D, the output current i of the current transformer 20, which is the current of the heating coil 19, is reduced as shown in FIG.
Since the switching signal s does not rise to the H level when the timing signal tm is delayed from the timing signal tm shown in FIG. 14 ON / OFF switching operation is continued.

Next, the control operation in the case of operating with the inverter current close to the same phase as the timing signal tm will be described with reference to FIG. The timing signal tm, the drive signals gu and gl, and the voltage and voltage ir based on the current i are generated as shown in FIGS. 7 (a), 7 (b), 7 (c) and 7 (d) in the same manner as described above. And the output signal l 'of the comparator 64
As shown in FIG. 7 (e), during the period in which the voltage due to the current i is smaller than the voltage ir, the level becomes H level. This output signal l 'is input to the level conversion circuit 66, and the output signal l
It is converted to a predetermined level as shown in (f). The output signal 1 is inverted by the inverter 67, and the output signal # 1 of the inverter 67 is inverted as shown in FIG.

The output signal gu × 1 of the AND circuit 68 to which the output signal 1 and the drive signal gu shown in FIG. 7B are input is obtained when both the drive signal gu and the output signal 1 are at the H level.
It becomes H level as shown in (h). The output signal gl × # 1 of the AND circuit 68 to which the output signal # 1 and the driving signal gl shown in FIG. 7C are input is shown in FIG. 7 (D) when both the driving signal gl and the output signal # 1 are at the H level. It goes to the H level as shown in i).

These output signals gu × l and gl × # 1 are input to one input terminal of an AND circuit 71 via an OR circuit 70, while rising at the rising of a timing signal tm shown in FIG. The determination valid signal ce shown in FIG. 7 (j) output from the one-shot circuit 74 is input to the other input terminal of the AND circuit 71. As a result, the output signal gu × l or gl ×
A switching signal s shown in FIG. 7 (k), which rises at each rising time of # 1 and falls at the falling time of the determination valid signal ce, is output. Then, the switching signal s is input to the voltage controlled oscillator 73, and the voltage controlled oscillator 73 generates a timing signal tm. That is, regardless of the level of the error signal err, the operating frequency does not further decrease. Therefore, good heating control can be performed without reducing the phase lag of the current flowing through the heating coil 19 further.

FIG. 8 is a block diagram showing another configuration of the electromagnetic cooker controlled by the inverter control method according to the present invention. The output signal of the comparator 63 of the current level detector 65 is input to the level conversion circuit 90. Level conversion circuit 90
Is input to one input terminal of the EXOR circuit 91.
The output signal 1 of the level conversion circuit 66 is input to another input terminal of the EXOR circuit 91. The output signal Id + 1 of the EXOR circuit 91 is input to the clock terminal CK of the RS flip-flop 92.

The input terminal D of the RS flip-flop 92 is connected to the power supply E, and the set terminal S is grounded. The reset terminal R has a timing signal output by the voltage control oscillator 73.
tm is input. The judgment valid signal ce output from the output terminal Q is input to another input terminal of the AND circuit 71. These level conversion circuit 90, EXOR circuit 91 and RS flip-flop
The determination valid signal generator 100 is constituted by 92. The configuration other than the determination valid signal generator 100 is the same as the configuration except for the one-shot circuit 74 in FIG. 5, and the same components are denoted by the same reference numerals.

Next, the control operation of the inverter in this electromagnetic cooker will be described with reference to a timing chart of signals of respective parts in FIG.
It will be explained together. Fig. 9 (a), (b), (c), (d), (e), (f), (g),
(h) Timing signal tm, drive signal gu, drive signal g
l, voltage and voltage ir based on current i, output signal 1, output signal # 1, output signal gr × l, and output signal gl × # 1 are output in the same manner as in FIG. The RS flip-flop 92 in the determination valid signal generator 100 is reset and output from the output terminal Q each time the timing signal tm shown in FIG. The judgment valid signal ce becomes L level.

The output terminal Q is inverted to the H level when the clock terminal CK rises. The clock terminal CK indicates the polarity of the voltage due to the current i shown in FIG. 9 (i). The level-converted signal id shown in FIG. 9 (i)
FIG. 9 is a comparison result of the voltage and the voltage ir due to the current i.
(e) The output signal of the EXOR circuit 91 to which the signal l shown in FIG.
As shown in FIG. 9 (j), the output signal Id + 1 falls when the voltage due to the current i becomes smaller than the voltage ir, and rises when the voltage becomes larger.

That is, the output terminal Q of the RS flip-flop 92
Goes to the H level when the current i exceeds the current ir as shown in FIG. 9 (i). As a result, the judgment valid signal ce becomes
As shown in FIG. 9 (k), the period from when the voltage due to the current i exceeds the voltage ir to when the operation of the transistor is switched is at the H level.

For this reason, when the current of the heating coil 19 is operating in a state close to the same phase as the timing signal tm, the voltage control oscillating unit 73 performs the operation shown in FIG. 9 based on the switching signal s shown in FIG.
The timing signal tm shown in (a) is generated.
Therefore, the operating frequency does not decrease further regardless of the level of the error signal err. Therefore, good heating control can be achieved without further reducing the phase delay of the current flowing through the heating coil 19.

Although not shown, when the inverter operates with a current that is later than the timing signal, the switching signal s does not go to the H level, as described above, so that the voltage based on the level of the error signal err is used. In the generation cycle of the timing signal tm of the control oscillator 73, the transistors 13 and 14 are turned on,
Continue the OFF operation.

In these control operations, the current level of the load is directly detected, and the transistor is turned on and off based on the current level. Therefore, regardless of the operating frequency of the inverter, the current of the load is not more than a predetermined value. In such a case, the operation of the transistor can be reliably switched. Therefore, the snubber capacitor in a charged state is not short-circuited by the transistor, and loss in the transistor can be suppressed to a minimum. In this embodiment, the case where the control method of the inverter is applied to the electromagnetic cooker has been described. However, the present invention can be applied to an inverter other than the electromagnetic cooker, and the same effect can be obtained.

[0056]

As described in detail above, according to the inverter control method of the first invention, only the inverter current is detected and there is no need to detect the high voltage of the inverter.
An inverter control circuit can be realized at low cost.

[0057]

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main configuration of an electromagnetic cooker controlled by an inverter control method according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of an on-phase limiting circuit and a coil current phase determining circuit.

FIG. 3 is a block diagram showing a configuration of a voltage controlled oscillator and a two-phase split circuit.

FIG. 4 is a timing chart of signals of respective parts.

FIG. 5 is a block diagram showing another configuration of the electromagnetic cooker controlled by the inverter control method according to the present invention.

FIG. 6 is a timing chart of signals of respective parts.

FIG. 7 is a timing chart of signals of respective units.

FIG. 8 is a block diagram showing another configuration of the electromagnetic cooker controlled by the inverter control method according to the present invention.

FIG. 9 is a timing chart of signals of each section.

FIG. 10 is a schematic configuration diagram of an inverter.

FIG. 11 is a current waveform diagram of an inverter.

FIG. 12 is an explanatory diagram of timing for turning off a transistor.

[Explanation of symbols]

 13,14 Transistor 17,18 Resonant capacitor 19 Induction heating coil 20 Current transformer 21 Coil current phase discriminating circuit 21b Comparator 22 ON phase limiting circuit 22a One-shot multivibrator 22b, 22c D flip-flop 23 Voltage controlled oscillator 25 Two-phase split circuit R resistance C capacitor

Claims (1)

(57) [Claims] 1. A method for controlling an inverter for controlling commutation of a switching element for switching a current in a resonance circuit including a coil and a resonance capacitor connected in series with the coil, wherein a current detection for detecting a current of the coil And a voltage generation unit that generates a first voltage related to the detection current of the current detection unit and a second voltage obtained by delaying the first voltage, and a comparison that compares the first voltage and the second voltage. A control unit for turning off the switching element according to a comparison result of the comparison unit.