JP2910192B2 - Inverter for induction heating - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an inverter for induction heating, and more particularly, to an inverter for induction heating, which is used for an electromagnetic cooker or the like so that it can be used for both single-phase AC and three-phase AC input. The present invention relates to an induction heating inverter in which control circuit constants are automatically switched.

(Prior Art) FIGS. 3 (a) and 4 (a) show a rectifier circuit used for an induction heating inverter, and FIG. 3 (a).
Fig. 4 (a) shows a case where a three-phase AC power supply 51A is used as a power supply, and Fig. 4 (a) shows a case where a single-phase AC power supply 51B is used.
In these figures, 52A and 52B are three-phase and single-phase diode bridges, respectively, and 53 is a small-capacity smoothing capacitor such as a film capacitor.

In each of the above rectifier circuits, each diode bridge 51A,
The magnitude of the AC voltage input to 52B (effective value, peak value Vp)
When the average values 3Vp / π and 2Vp / π of the output DC voltages v ₁ and v ₂ shown in FIGS. 3 (b) and 4 (b) are compared, single-phase / three-phase = (2Vp / π) / (3Vp / π) = 2/3. That is, in order to supply the same power to the load, it is necessary to give a current of at least 3/2 times with a single-phase input as compared with a three-phase input. However, according to this, a component having a large current capacity is required, and there is a disadvantage that the cost is increased and the device is enlarged, which is not an advantageous measure.

In view of this point, conventionally, the power is generally derated with the same current capacity. In this case, however, the rated output differs between a single phase and a three phase in one device. For example, in an electromagnetic cooker using an inverter for induction heating, a power controller is used in the control circuit, and when the maximum output differs between single-phase and three-phase, it is necessary to change circuit constants around the power controller. . For this reason, conventionally, circuit constants are switched by switching a manual switch or changing a connection of a jumper wire.

(Problem to be Solved by the Invention) The above-described conventional technology has the following problems.

When the number of input phases is different, switching of circuit constants has been performed manually, so that there is a high possibility that forgetting to switch the manual switch or erroneous connection of jumper wires will occur.

Inverters for induction heating have a large adverse effect on equipment due to moisture, oil, dust, dust and the like in kitchens and factories. Therefore, the life and reliability of the manual switch, which is a mechanical switch, are significantly reduced.

The present invention has been made in order to solve the above problems, and an object thereof is to automatically switch a circuit constant according to the number of input phases without switching a manual switch or changing a connection of a jumper wire. An object of the present invention is to provide an inverter for induction heating which is made possible.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a rectifier circuit capable of rectifying both single-phase and three-phase AC voltages and converting the same into a DC voltage, Connected to perform high-frequency switching and convert the DC voltage into an AC voltage. In the induction heating inverter, the number of phases of the input voltage of the rectifier circuit is either single-phase or three-phase by comparing the output DC voltage of the rectifier circuit with a reference voltage in the control circuit of the induction heater inverter. A phase number discriminating means for discriminating whether or not there is an input phase number discriminating signal, and a circuit constant for electronically switching a power command value to a power controller of the inverter unit based on the input phase number discriminating signal. Number switching means, and multiplication means for calculating the input power of the inverter section from the input current of the rectifier circuit and the output DC voltage. Input to the power controller.

(Operation) According to the present invention, the instantaneous value or average value of the output DC voltage of the rectifier circuit is detected, so that the input phase number determining means determines whether the input is a single-phase input or a three-phase input and inputs the signal. The phase number discrimination signal is output. This discrimination signal is turned on / off by an electronic switch such as an analog switch constituting the circuit constant switching means.
The circuit constant is automatically switched by being applied as an OFF signal and switching the input power command value of the inverter unit.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. First
FIG. 1 shows a circuit configuration of an electromagnetic cooker using an induction heating inverter according to this embodiment. In the figure, a, b,
c is an AC input terminal, 2 is a diode bridge acting as a three-phase full-wave rectifier circuit or a single-phase full-wave rectifier circuit, 3 is a small-capacity smoothing capacitor such as a film capacitor, 4 is an inverter unit for high-frequency switching, and 5 is The resonance capacitor 6 is a heating coil, and these constitute a main circuit of the inverter for induction heating. Note that the capacitor 3 not only smoothes the output voltage of the diode bridge 2 but also functions as a noise absorber for preventing switching noise of the inverter unit 4 from being fed back to the AC input side.

On the other hand, the control circuit includes a current transformer 1 connected to the AC input terminals a and c, a current detected by the current transformer 1 (input current to the induction heating inverter) id, and a power voltage of the inverter unit 4.
A multiplier 8 by which Vd is multiplied and an input power P which is an output of the multiplier 8
Are a power controller 12, a power commander 16, a reference voltage generator 17, a voltage detector 13 to which the reference voltage and the input voltage Vd are input, and an output thereof. An analog switch 15 switched by an input phase number discrimination signal, resistors 10 and 11 connected in parallel to which a power command value P ^* from a power command unit 16 is applied, and a current transformer 18 for detecting an output current of the inverter unit 4 And an inverter drive circuit 14 that receives the detected current and the output of the power regulator 12 as inputs and outputs an on / off control signal for the switching element of the inverter 4.

The inverter drive circuit 14 includes an adder 14A, a current amplifier 14B, a pulse generator 14C, and an amplifier 14D.

Next, the operation of the electromagnetic cooker will be briefly described with reference to FIG. First, a single-phase or three-phase AC voltage is applied to the AC input terminals a, b or a, b, c. This AC input is rectified by the diode bridge 2 and smoothed by the smoothing capacitor 3 to become DC (pulsating current). This DC voltage is converted into a high frequency voltage by the inverter unit 4,
The voltage is applied to the resonance capacitor 5 and the heating coil 6. As a result, magnetic flux is generated from the heating coil 6, electromagnetic energy is given to the pan 7, and the pan 7 is heated.

The power adjustment at this time is performed by adjusting the input voltage Vd to the inverter unit 4.
And the force current id are converted by the multiplier 8 into the input power P,
The input power P and the power command value P ^* of the power command unit 16 are added in a current manner via resistors 9 and 10, respectively.
It becomes 12 inputs. And the output of this power controller 12 is
It is added to an inverter drive circuit 14 including an adder 14A, a current regulator 14B, a pulse generator 14C, and an amplifier 14D. The drive circuit 14 outputs an on / off control signal for a switching element of the inverter unit 4.

Here, the maximum output differs depending on whether the AC input is single-phase or three-phase, as described above.
Needs to be changed. In this embodiment, the input resistance of the power command value P ^* to the power controller 12 is set by closing the analog switch 15 and connecting the resistors 10 and 11 in parallel or by opening the analog switch 15 and inserting only the resistor 10. Depending on this, the constant is changed.

At this time, switching of the analog switch 15 is performed by an output from the voltage detector 13. That is, the input voltage Vd of the inverter unit 4 is detected by the voltage detector 13 as its instantaneous value or average value, and as shown in FIG. 3 (b) and FIG. The instantaneous or average values of v ₁ and v ₂ ) in FIGS. 3 (b) and 4 (b) are single-phase,
Varies by three phases. For this reason, the voltage detector 13 discriminates between single phase and three phase based on the magnitude of the voltage Vd, outputs an input phase number discrimination signal, and switches the analog switch 15.

2 (a) and 2 (b) show specific examples of the voltage detector 13. FIG. 2 (a) shows a comparator 19 which compares the instantaneous value of the voltage Vd with a reference voltage to determine the number of input phase signals. FIG. 2B is a circuit for comparing the average value of the voltage Vd obtained via the filter 20 with a reference voltage and outputting an input phase number discrimination signal. The configuration of the voltage detector 13 may be other than these.

Further, in the above-described embodiment, the case where a small-capacity smoothing capacitor is provided has been described. However, the present invention is also applicable to an induction heating inverter having no such capacitor.

(Effects of the Invention) As described above, according to the present invention, it is possible to automatically switch the circuit constants required when the number of input phases is different. There is no risk of connection error or the like, and the operation reliability of the induction heating inverter can be improved.

Further, compared to the case where a mechanical switch such as a manual switch is used as in the related art, the life and reliability of the switch can be empirically doubled even in a poor installation environment.

Further, if the input voltage of the inverter section is detected as an instantaneous value, there is an effect that it can be applied to an open phase detection circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an electromagnetic cooker showing one embodiment of the present invention, FIGS. 2 (a) and 2 (b) show specific examples of a voltage detector, and FIGS. 3 and 4 are conventional. 3 (a) is an explanatory diagram of a three-phase full-wave rectifier circuit, FIG. 3 (b) is a waveform diagram of its output voltage, and FIG. 4 (a) is a single-phase full-wave rectifier circuit. FIG. 2B is an explanatory diagram of the wave rectifier circuit, and FIG. 2B is a waveform diagram of the output voltage. 1,18 Current transformer 2, Diode bridge 3 Smoothing capacitor 4, Inverter unit 5 Resonant capacitor 6, Heating coil 7 Pot, 8 Multiplier 9-11 ... Resistance, 12 ... Power regulator 13 ... Voltage detector, 14 ... Inverter drive circuit 15 ... Analog switch, 16 ... Power commander 17 ... Reference voltage generator, 19 ... Comparator 20 ... filter

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H02M 7/00-7/98 H05B 6/12 H05B 6/06

Claims (1)

(57) [Claims] 1. A rectifier circuit capable of rectifying both single-phase and three-phase AC voltages and converting them into a DC voltage, connected to the DC side of the rectifier circuit to perform high-frequency switching, and convert the DC voltage to an AC voltage. An inverter unit for converting, wherein the average value of the DC voltage after rectifying the single-phase AC voltage and the three-phase AC voltage having the same effective value by the rectifier circuit is different, wherein the control of the induction heating inverter is performed. A circuit that determines whether the number of phases of the input voltage of the rectifier circuit is single-phase or three-phase by comparing the output DC voltage of the rectifier circuit with a reference voltage and outputs an input phase number determination signal. Number discriminating means, circuit constant switching means for electronically switching a power command value for the power regulator of the inverter unit according to the input phase number discriminating signal, input current and output DC voltage of the rectifier circuit Multiplying means for calculating the input power of the inverter unit from
An inverter for induction heating, wherein an output of the multiplying means and the power command value are added in a current manner and input to the power regulator.