JP2867452B2 - Frequency tuning circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency tuning circuit used in a power converter for supplying alternating-current power to a resonance circuit.

[Conventional technology]

FIG. 5 shows a conventional frequency tuning circuit of this kind. In the figure, reference numeral 1 denotes a single-phase commercial power supply, and 2 denotes a single-phase inverter, which converts a commercial alternating current into a direct current by a rectifier 2A, and then converts the commercial alternating current into an alternating current of a required frequency by an inverter 2B. 3
Is a reactor, 4 is a condenser, and 5 is a heating coil of an induction heating device (5A is for inductance, and 5B is for resistance). The rectifier 2A of the inverter 2 is a converter composed of a thyristor Thy whose phase is controlled, and its output voltage (average value) is variable. The inverter unit 2B has a bridge connection of four transistors Tr, and a flywheel diode D is connected in anti-parallel to each transistor Tr. 6 is a transistor Tr constituting the inverter unit 2B.
A drive circuit for ON / OFF drive, 7 is a voltage / frequency converter (V /
F converter), and transmits the frequency command F ^* to the driving circuit 6
To send to. Reference numeral 8 denotes a voltage detector for detecting the output voltage Vo of the inverter 2, and the detected voltage is shaped by a comparator 8A. Reference numeral 9 denotes a voltage detector for detecting the voltage Vc across the capacitor 4. The detected voltage is shaped into a rectangular wave by a comparator 9A. 10 is an exclusive OR circuit (hereinafter, exclusive OR circuit)
The output voltage Vo ′ of the comparator 8A and the comparator 9A
Output voltage Vc 'is input. Reference numeral 11 denotes an integrator, and the output Vφ of the exclusive OR 10 (for convenience of explanation, the pulse height is also Vφ
To) and integrates the difference voltage V.phi 'of the bias voltage V _B, and sends the integrated value V _IN to V / F converter 7. 12 is a bias circuit, and sends the bias voltage V _B. The bias voltage V _B is set to be V _B = V.phi / 2.

When the load of the power conversion device is an inductance load such as an induction heating device or an induction melting furnace, it is common to insert a resonance capacitor 4 and operate at a frequency (tuning frequency) fo very close to the resonance frequency. The frequency tuning is performed so that the output frequency f of the inverter 2 becomes the tuning frequency fo.

In the configuration of FIG. 5, when the inverter output frequency f is the tuning frequency fo (FIG. 6 (a)), the voltage Vo 'and the voltage Vc' have a phase difference of 90 [deg.]. Is a signal having a waveform in which the period of the positive period is equal to the period of the level L. Assuming that the output of the integrator 11 (average value per cycle) at this time is V _IN ', the V / F converter 7 outputs the frequency command F ^* = fo while the input is V _IN '.
To send to. If the tuning is deviated, for example, FIG. 6 (b)
As shown in FIG. 6 (c) (example when the tuning frequency is low), the output V of the exclusive OR 10 is high.
Since the period of the level H and the period of the level L of φ become unequal, the output of the integrator 11 fluctuates with respect to V _IN ', and the frequency command F ^* changes in accordance with the fluctuation, and the inverter frequency f Is raised or lowered toward the tuning frequency.

[Problems to be solved by the invention]

In this manner, the frequency tuning is performed. In a usage method in which the inverter 2 is started and its output frequency f is raised from the low frequency region to the tuning frequency to perform frequency tuning, the inverter output frequency f is adjusted to the tuning frequency. fo 1 /
When the voltage Vφ 'rises to the frequency of 3, as shown in FIG. 7, during the period when the voltage Vo' is H or L, it changes from H to L and from L to H, and the average value Becomes zero, the output of the integrator 11 becomes the same as at the time of tuning, the inverter output frequency f is locked at fo / 3, and does not rise to the tuning frequency.

For this reason, conventionally, the output difference between the frequency of Vo ′ and the frequency of Vc ′ is monitored through a frequency / voltage converter, and when the difference is equal to or more than a predetermined value, the output difference is integrated. The lock state is forcibly released by adding to the input of the power converter. However, when the power converter is driven at a high frequency, it is difficult to obtain good accuracy and the frequency / conversion is difficult. There was a problem that a vessel required a considerably expensive thing.

The present invention has been made to solve the above problems,
It is an object of the present invention to provide a frequency tuning circuit that can avoid 1/3 tuning easily and at low cost without using expensive circuit components.

[Means for solving the problem]

To achieve the above object, a first comparator for detecting a phase of an output voltage of a power converter compares a deviation between the output voltage and a first bias voltage with zero potential, and determines a phase of a capacitor voltage. The second comparator for detecting the difference between the output voltage and the second bias voltage is compared with a zero potential, and the two bias voltages are respectively equal to the first bias when the power converter is activated.
And the magnitude of the output of the second comparator as a continuous signal of the polarity in the frequency increasing method.

[Action]

According to the present invention, the inverter output frequency is set to a frequency higher than the tuning frequency from the time of startup, and is reduced toward the tuning frequency when the startup is completed. That is, since the inverter is operated at the tuning frequency and a frequency region higher than the tuning frequency, the inverter does not fall in 1/3 tuning.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

In Figure 1, 21 denotes a bias power source voltage V _1, 22 denotes a bias power source of the voltage V _2. Comparator 8A compares the sum of the voltage V ₀ and the bias voltages V ₁ and the reference potential (0 volt),
Comparator 9A compares the sum of the voltage Vc and the bias voltage V ₂ to the reference potential (0 volt). The maximum output range of the voltage / frequency converter 7 is fo <f when the tuning frequency is fo.
There is _MAX . The bias voltages V ₁ has a larger small voltage value than the value of the output voltage Vo at the inverter startup as shown in FIG. 2 (a), the bias voltage V ₂ also FIG. 2 (b)
As shown in (1), it has a very small voltage value that is larger than the value of the capacitor voltage Vc when the inverter is started. Further, as shown in FIG. 3 (a) and (b), the bias voltage V ₂ is before the bias voltage V ₁ <Vo, is given a value such that V ₂ <Vc. Other configurations are the same as those in FIG. 5, and the same components are denoted by the same reference numerals.

In this configuration, it is assumed that the inverter 2 has been started. During the startup, the inverter output voltage Vo, the capacitor voltage Vc is at the micro-level, the voltage Vo <V _1,
And since it is the voltage Vc <V _2, the input of the comparator 8A and 9A are both the same polarity, the output of the exclusive OR10 becomes an L level, the input is a negative value of the integrator 11, the output is a positive value And V /
The frequency command F ^* sent by the F converter 7 is larger than fo and f
A value close to the _MAX or f _MAX. Activation proceeds, taken in Vc> V ₂ as shown in FIG. 3 (b), the phase of the voltage Vc is to be detected, the output Vo of the comparator 8A and 9A 'and Vc'
Maintaining Since pulse width duty of the portion exceeding bias V ₂ as shown in FIG. 4 is 1/2 or less, without malfunctions output of the integrator 11, a higher frequency command (frequency increase command) . Thereafter, taken Vo> V _1, when the phase of the voltage Vo also begins to be detected, the frequency command F ^* is reduced (the frequency behavior command), the inverter frequency f reaches the fo, the inverter 2 enters the tuning operation .

As described above, in the present embodiment, the inverter peripheral voltage Vo and the capacitor voltage Vc, which are the inputs of the comparators 8A and 9A that detect the phase at the beginning of the start of the inverter 2, use the comparators 8A and 9A , The integrator 11 is configured to integrate a continuous signal, so that the output frequency of the inverter 2 becomes higher than the tuning frequency fo at the beginning of the startup, and when the startup proceeds, the comparators 8A and 9A Since the phase of both voltages starts to be detected and the exclusive OR 10 detects the phase difference between the two voltages, the integrator 11 integrates the alternating signal, and the frequency command F ^* decreases toward the tuning frequency. Then, the operation shifts to tuning operation. Therefore, the inverter 2 is fo ~
is operated in a range of f _MAX, it does not pass through the 1/3 the tuning frequency range, never fall into 1/3-tuned.

In the above embodiment, as the bias voltage V _2, before the bias voltage V ₁ <Vo, but is given a value such that V ₂ <Vc, at the same _{time, V 1 <Vo, V 2} <Vc Of course, it may be made to become.

〔The invention's effect〕

As described above, since the power converter is operated in a frequency range higher than the tuning frequency including the tuning frequency from the start of the operation, the effect of the present invention can be achieved without falling into the 1/3 tuning. Can be obtained simply by applying the detected value of (1) and the detected value of the capacitor voltage to the means for detecting the phase by biasing, so that there is an advantage that the cost can be reduced and the reliability is high as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG.
FIGS. 3 (a) and 3 (b) and FIGS. 3 (a) and 3 (b) are waveform diagrams for explaining a bias voltage in the above embodiment, and FIG. 4 is a diagram showing an example of an exclusive OR input waveform in the above embodiment. ,
FIG. 5 is a circuit diagram showing a conventional frequency tuning circuit, FIGS. 6 (a) to 6 (c) are waveform time charts for explaining the operation of the frequency tuning circuit, and FIG. FIG. 2 ... Inverter as power converter, 2A ... Rectifier, 2B
... Inverter part, 4 ... Resonant capacitor, 5 ... Load, 6 ... Drive circuit, 7 ... V / F converter, 10 ... Exclusive O
R, 11 ... integrator, 21, 22 ... bias power supply.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H02M 7/42-7/98 H05B ⁶ /02-6/06 H05B 6/12

Claims (1)

(57) [Claims] An output of a first and a second comparator for detecting a phase between an output voltage of a power converter for supplying AC power to a resonance circuit and a voltage of a capacitor of the resonance circuit. A logic circuit for transmitting a pulse having a pulse width corresponding to the phase difference between the two voltages, an integrator for integrating the output of the logic circuit, and a voltage / frequency converter receiving the output of the integrator. In a frequency tuning circuit for providing an output of the voltage / frequency converter to the power converter as a frequency command,
The first comparator compares the sum of the output voltage and the first bias voltage with zero potential, and the second comparator compares the sum of the output voltage and the second bias voltage with zero potential. In contrast to the above, the two bias voltages have such magnitudes that the outputs of the first and second comparators at the time of starting the power converter are continuous signals of the polarity in the frequency increasing direction. Frequency tuning circuit.