JP4216748B2 - Electromagnetic cooker - Google Patents

Description

  The present invention relates to an electromagnetic cooker that performs cooking using an electromagnetic induction action.

  In an electromagnetic cooker, generally, AC of a commercial power source is rectified by a rectifier circuit, and the current rectified by the rectifier circuit is converted into a high-frequency current having a frequency according to heating conditions by an inverter and supplied to a heating coil. Yes. When the heating coil is supplied with a high-frequency current, an alternating magnetic field corresponding to the supplied high-frequency current is generated in the heating coil, and the alternating current is generated in an object to be heated such as an iron pan disposed on the heating coil. An eddy current corresponding to the magnetic field is generated, and the object to be heated is heated by the Joule heat of the eddy current.

  For efficient heating, a capacitor that constitutes a resonance circuit together with the heating coil is inserted in the inverter. Further, for example, the power consumption of the electromagnetic cooker is compared with a target value that can be adjusted according to the set temperature so that proper heating according to the temperature adjustment is possible, and the target value is supported according to the difference. Feedback (feedback control) is used to control the operating frequency of the inverter in order to maintain constant power. This feedback control enables stable heating.

  However, if the pan is removed from the heating coil during the heat treatment, or if the pan is moved greatly, or if the pan on the heating coil is replaced with a pan of a different material, the current flowing through the resonance circuit, i.e., the current flowing through the heating coil, is increased. It increases rapidly or the phase of the current advances greatly compared to the phase of the voltage. Under such circumstances, an excessive current flows through the inverter, which may cause damage to the inverter.

  For this reason, it has been proposed to detect an abnormal state by detecting the current flowing through the heating coil or detecting the advance of the phase of this current and comparing the detection result with each allowable value (for example, patents). See references 1 and 2.)

  When such an abnormality due to excessive current or phase advance is detected, the operating frequency of the inverter can be adjusted by feedback control according to the detected parameter, and an overcurrent can be prevented from flowing through the inverter.

In this case, for example, when an abnormality is detected using a constant power control system that controls the operating frequency of the inverter based on power consumption, that is, input power to the electromagnetic cooker, as the main control system, an abnormality is detected from the main control system. It is desirable to control the inverter operating frequency by switching to an auxiliary control system such as a current control system or a phase control system using the current or phase difference as a parameter.
JP-A-4-269488 JP-A-11-121159

  However, the time constant set in each control system stabilizes the control system without being affected by the pulsating current remaining in the direct current output from the rectifier circuit, thereby appropriately changing the operating frequency of the inverter. Therefore, it is set to a relatively large value. Therefore, even if an abnormality is detected by the current or phase detection means, it is necessary to elapse time corresponding to the time constant before the substantial switching of the control system occurs.

  Therefore, in order to more reliably protect the inverter from the overcurrent without impairing the stabilization of the control system, it has been desired to realize a quick control system switching with a relatively simple circuit configuration. .

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electromagnetic cooker that can quickly switch a control system with a relatively simple circuit configuration and can reliably protect an inverter from an overcurrent.

  The present invention basically includes an inverter driven by a driver circuit to supply a high-frequency current corresponding to the operating frequency to the heating coil, and a control for controlling the operation of the driver circuit to control the operating frequency of the inverter. A power control system for controlling an operating frequency of the inverter so as to maintain a value set so that power consumption of the electromagnetic cooker can be adjusted. An auxiliary control system for controlling the operating frequency of the inverter so that a current flowing through the heating coil or a phase difference between the current and the voltage does not exceed an allowable value, and both control systems are output from both control systems. And a selection circuit unit that selects an operation frequency signal corresponding to the output voltage of the selected one of the control systems, and selects the operation frequency signal according to the level relationship between the voltages.

  Between the output terminals of the both control systems to the selection circuit unit, the voltage at the output terminal of either one of the control systems is set in order to speed up switching from the power control system to the auxiliary control system. When the sum of the voltage at the output end of the other control system and a predetermined value is exceeded, current from the output end of the one control system toward the output end of the other control system is allowed and the both controls A rectifying element circuit section for holding the output terminal voltage difference of the system at the predetermined value is provided.

  In the electromagnetic cooker according to the present invention, switching between the power control system, which is the main control system, and the auxiliary control system is performed by the selection circuit unit, and the selection control unit depends on the level of the voltage between the output terminals of both control systems. Made. In a steady operation state under constant power supply by control of the main control system, for example, the output terminal voltage of the power control system is set to be higher than the output terminal voltage of the auxiliary system control system, and the rectifier element circuit The unit holds the voltage between the output terminals of both control systems at a predetermined voltage difference.

  In this case, an increase in the voltage at the output terminal of the power control system indicates that the deviation from the target value becomes large. An increase in the voltage at the output terminal of the auxiliary control system indicates that the deviation from the allowable value becomes large. Therefore, in a steady state where no abnormality is detected, the voltage at the output end of the auxiliary control system is maintained at a higher voltage value than the voltage at the output end of the power control system.

  In a steady state where no abnormality is detected unless a rectifying element circuit section is provided between the output terminal of the power control system and the output terminal of the auxiliary control system, the voltage at the output terminal of the auxiliary control system is the power control. It is kept at a very high voltage value compared with the voltage at the output end of the system.

  However, in the electromagnetic cooker according to the present invention, since the rectifying element circuit unit is provided, the output terminal voltage difference between both control systems does not become such a large value, and the voltage difference between both output terminals. Is held at a small predetermined value. The voltage difference between the two terminals is maintained at a relatively small predetermined value regardless of the fluctuation of the other output end pressure.

  At this time, for example, when a large abnormal current flows through the heating coil, the output voltage of the auxiliary control system is directed to a value smaller than the output voltage value of the power control system, for example, as described above, in order to suppress the abnormal current. Decrease.

  The degree of this decrease is set relatively moderately according to the time constant set in the auxiliary control system in order to stabilize the control system. However, according to the present invention, as described above, the voltage difference between the output terminals of the two control systems is maintained at a predetermined small voltage difference by the rectifying element circuit unit, and thus is set by the rectifying element circuit unit. As a result of the voltage drop to the predetermined potential difference, the relationship between the output voltage value of the main control system and the output voltage value of the auxiliary control system is reversed early, which allows quick switching from the main control system to the auxiliary control system. Made.

  Therefore, the switching between the power control system and the auxiliary control system can be speeded up with a relatively simple configuration without impairing the stable operation of each control system.

  The power control system obtains a difference between the target value and the detected value by the first detecting means for detecting the input power that is the power consumption of the electromagnetic cooking device, and returns a signal corresponding to the difference to the input side. The first feedback amplifier circuit unit operating with a time constant can be configured as a main element. The auxiliary control system obtains a difference between the detected value and the maximum allowable value for the detected value detected by the second detecting means for detecting the current flowing through the heating coil or the phase difference between the current and the voltage, and the detected value. A second feedback amplifier circuit section that operates with a predetermined time constant to feed back a signal corresponding to the difference to the input side can be configured as a main element.

  As the selection circuit unit, a selection circuit unit that selects the control system having the low output terminal voltage out of the two control systems can be adopted. In this case, as the rectifying element circuit unit, from the output terminal of the auxiliary control system Rectifying element circuit having a rectifying element that allows a current toward the output terminal of a power control system and that generates a predetermined voltage difference between both terminals regardless of increase or decrease in applied voltage between the terminals of the rectifying element Part can be adopted.

  As the second detection means, both a current detection means for detecting a current flowing through the heating coil and a phase detection means for detecting a phase difference between the current flowing through the heating coil and its voltage can be used in combination. In this case, the auxiliary control system obtains a difference between the maximum allowable current value for the heating coil and the detected value detected by the current detecting means, and returns a signal corresponding to the difference to the input side with a predetermined time constant. A current control system having an operating feedback amplification circuit unit, and a difference between a maximum allowable advance phase difference for the phase difference and a phase difference detected by the phase detection means, and a signal corresponding to the difference is input to the input side A phase control system having a feedback amplifier circuit section that operates with a predetermined time constant for feedback. The selection circuit unit may be a selection circuit unit that selects an output voltage of the feedback amplification circuit unit having the smallest output among the feedback amplification circuit units. Further, the rectifying element circuit section is phase-controlled between the output terminal of the feedback amplifier circuit section of the power control system and the output terminal of the feedback amplifier circuit section of the current control system and the output terminal of the feedback amplifier circuit section of the power control system. Each can be provided between the output terminal of the feedback amplifier circuit section of the system.

  The rectifying element of the rectifying element circuit unit can be configured by a diode that generates a potential difference based on a junction barrier energy difference between the anode and the cathode when a forward current flows.

  The present invention is applied to switching of various first and second control systems having different parameters instead of switching between the main control system and the auxiliary control system in which the power control system is the main control system. Can do.

  According to the present invention, the voltage difference of the predetermined potential difference set by the rectifying element circuit unit is only given between the output terminal of the auxiliary control system and the output terminal of the power control system. For example, when a large abnormal current flows in the heating coil or a current having a large phase advance angle with respect to the voltage flows in the heating coil, the output terminal voltage of the auxiliary control system drops, for example, to suppress this abnormal current. Regardless of the time constant set to stabilize the system, the output voltage value of the main control system and the output voltage value of the auxiliary control system are reversed at an early stage, and this shifts the main control system to the auxiliary control system. The switching is made quickly.

  Therefore, it is possible to quickly switch between the power control system and the auxiliary control system with a relatively simple configuration without impairing the stable operation of each control system, thereby reliably protecting the inverter from damage due to excessive current. Can do.

  Further, according to the present invention, the first and second control systems having different parameters can be quickly switched with a relatively simple configuration without impairing the stable operation of each control system. Can be reliably protected from damage due to excessive current.

  The features of the present invention will be described in detail below with reference to the illustrated embodiments.

<Example 1>
FIG. 1 shows a main part of an electromagnetic cooker 10 according to the present invention. Prior to the description along FIG. 1, the electromagnetic cooker 10 will be described along FIG.

  As shown in FIG. 2, the electromagnetic cooker 10 according to the present invention is obtained by a rectifier circuit 12 that receives an input of electric power from a commercial power supply 11, rectifies the alternating current and converts it into a direct current, and the rectifier circuit. An inverter 13 that converts a direct current into a high-frequency current having a desired frequency, a heating coil 14 that receives supply of the high-frequency current from the inverter, and a control circuit 15 that controls the operation of the inverter 13 are provided.

  The heating coil 14 is connected in series to the capacitor 16 of the inverter 13 and forms a resonance circuit together with the capacitor. The control circuit 15 controls the operating frequency signal supplied from the driver circuit 17 to the inverter 13. The inverter 13 operates to supply a high-frequency current having a frequency corresponding to the operating frequency signal supplied from the driver circuit 17 to the heating coil 14.

  When a high-frequency current having this operating frequency is supplied to the heating coil 14 via the capacitor 16 of the resonance circuit, the heating coil 14 generates an alternating magnetic field corresponding to the high-frequency current, and induction of this alternating magnetic field generated by the heating coil 14. Due to the action, an eddy current is generated in, for example, an iron pan (not shown) on the heating coil 14, and the pan is heated by the Joule heat of the eddy current.

  When the frequency of the high-frequency current supplied to the heating coil 14 decreases, the amount of power supplied to the heating coil 14 increases, so that the heating temperature by the heating coil 14 increases. Further, when the frequency of the high-frequency current to the heating coil 14 is increased, the amount of power supplied to the heating coil 14 is reduced, so that the heating temperature by the heating coil 14 is decreased. Therefore, the heating temperature and the operating state of the electromagnetic cooking device 10 can be controlled by controlling the operating frequency signal supplied from the control circuit 15 to the driver circuit 17.

  For this control, a power detection means 18, a phase detection means 19 and a current detection means 20 are provided, and a rectifying element circuit section 30 is provided as shown in FIG.

  In the example shown in FIG. 1, the power detection unit 18 uses a multiplier that integrates an input current and an input voltage to the rectifier circuit 12 (see FIG. 2). The power detection means 18 detects the power input from the commercial power supply 11 to the rectifier circuit 12, that is, the power consumption of the electromagnetic cooker 10, and outputs the detected power value signal to the power control system feedback amplification circuit unit 15 a of the control circuit 15. .

  In the example shown in FIG. 1, the phase detection unit 19 is configured to calculate the voltage of the supply current from the operating frequency signal from the driver circuit 17 that determines the voltage period of the supply power to the heating coil 14 and the supply current to the heating coil 14. Find the phase advance angle for. The phase detection means 19 detects the phase difference with respect to the voltage of the current supplied to the heating coil 14, and outputs the detected phase difference signal to the phase control system feedback amplification circuit unit 15b.

  In the example shown in FIG. 1, the current detection unit 20 uses a rectifier circuit that obtains the average value of the current value flowing through the heating coil 14. The current detection means 20 detects the current supplied to the heating coil 14 and outputs the detected current value signal to the current control system feedback amplification circuit unit 15 c of the control circuit 15.

  The control circuit 15 is provided with a selection circuit unit 15d (see FIG. 2) that selectively outputs control signals output from the control system feedback amplification circuit units 15a to 15c to the driver circuit 17.

  As shown in FIG. 1, the control system feedback amplifier circuit sections 15a to 15c of the control circuit 15 are connected to the differential amplifiers 21a to 21c, the output terminals 31a to 31c of the differential amplifiers 21a to 21c, and their inverting input terminals. And connected time constant setting circuits 22a to 22c. Resistors 23a-23c are connected in parallel with the respective time constant setting circuits 22a-22c. Each of the time constant setting circuits 22a to 22c is configured by an RC series circuit in the illustrated example. The non-inverting input terminals of the differential amplifiers 21a to 21c are grounded through resistors 24a to 24c.

  The output signal of the power detection means 18 is input to the inverting input terminal of the differential amplifier 21a of the power control system feedback amplifier circuit unit 15a through the resistor 25a. The input power set value corresponding to the set temperature is input to the non-inverting input terminal of the differential amplifier 21a through the resistor 26a as an adjustable target value.

  The differential amplifier 21a outputs the difference between the input power set value corresponding to the set temperature and the input power value output from the power detection means 18 to the differential amplifier 21a. Then, since the voltage is fed back to the inverting input terminal of the differential amplifier 21a, the voltage at the output terminal 31a operates so as to approach the input power setting value that is the target value. Since the voltage of the output terminal 31a is output to the output terminal 32a of the power control system feedback amplification circuit unit 15a, the power control system feedback amplification circuit unit 15a has an input whose detected voltage value by the power detection means 18 is a target value. A negative feedback amplifier circuit that operates so as to approach the power set value is configured.

  The amplification factor of the differential amplifier 21a of the power control system feedback amplifier circuit unit 15a is determined by the resistors 23a, 24a, 25a, and 26a. Further, since the pulsation remains in the electric power detected by the electric power detection means 18 after rectification by the rectifier circuit 12, in order to prevent the power control system feedback amplification circuit unit 15a from becoming unstable due to the residual pulsation, a time constant is used. The time constant of the setting circuit 22a is set to a sufficiently large value so as to eliminate the influence of this residual pulsation.

  The power control by the power control system feedback amplifier circuit unit 15a is used as the main control system. In a normal use state, the output voltage of the differential amplifier 21a, that is, the voltage of the output terminal 32a of the power control system feedback amplifier circuit unit 15a is For example, it is set so that stable constant power control can be performed at 4V.

  The output signal from the phase detector 19 is input to the inverting input terminal of the differential amplifier 21b of the phase control system feedback amplifier circuit unit 15b via the resistor 25b. Further, since a set value corresponding to an allowable advance phase difference is input as a target value to the non-inverting input terminal of the differential amplifier 21b via the resistor 26b, the voltage at the output terminal 31b is the target value. It operates to approach a certain phase difference setting value. Since the voltage of the output terminal 31b is output to the output terminal 32b of the phase control system feedback amplification circuit unit 15b, the phase control system feedback amplification circuit unit 15b has the phase difference detected by the phase detection means 19 as a target value. A negative feedback amplifier circuit that operates to approach the allowable set value is configured. The time constant set by the time constant setting circuit 22b is the same as that in the power control system feedback amplifier circuit unit 15a.

  However, in order to make the phase control system feedback amplifier circuit unit 15b function as an auxiliary control system of the power control system feedback amplifier circuit unit 15a, a predetermined phase obtained during normal operation under the control of the power control system feedback amplifier circuit unit 15a is used. In advance, the output terminal voltage of the differential amplifier 21b is set to maintain, for example, 12 V, which is the maximum drive voltage of the differential amplifier. Accordingly, when a large phase advance exceeding the predetermined phase angle is detected by the phase detection means 19, the phase advance operates so as to approach the target set value.

  In the current control feedback amplifier circuit section 15c, the output signal from the current detection means 20 is input to the inverting input terminal of the differential amplifier 21c through the resistor 25c. A set value corresponding to an allowable output current value to the heating coil 14 is input as a target value to the non-inverting input terminal of the differential amplifier 21c via the resistor 26c.

  Therefore, the current control feedback amplifier circuit unit 15c basically constitutes a negative feedback amplifier circuit that operates so that the current value detected by the current detection means 20 approaches the allowable set value that is the target value. The time constant set by the time constant setting circuit 22c is the same as that in the power control system feedback amplifier circuit unit 15a.

  However, unlike the phase control system feedback amplifier circuit unit 15b, the rectifying element circuit unit 30 is not connected between the output terminal 32c of the current control system feedback amplifier circuit unit 15c and the output terminal 32a of the power control system feedback amplifier circuit unit 15a. A rectifying element 30a is connected.

  The rectifying element 30a is made of a diode such as a Schottky diode or a high-speed diode, and has a cathode connected to the output terminal 32a of the power control feedback feedback circuit 15a and an anode of the current control feedback feedback circuit 15c. It is connected to the output terminal 32c. When a forward voltage is applied between the anode and the cathode of the diode, a predetermined potential difference corresponding to the junction barrier energy difference is generated between the anode and the cathode. When the diode is a Schottky diode, this potential difference is about 0.5V, and when the diode is a high-speed diode, it is about 0.9V.

  Since both the output terminals 32a and 32c are connected by such a diode so that the cathode side becomes the output terminal 32a and the anode side becomes the output terminal 32c, the potential of the output terminal 32c on the anode side becomes the cathode side. When the potential becomes higher than the predetermined potential difference caused by the barrier energy difference described above than the potential of the output terminal 32a, current flows from the output terminal 32c of the current control system feedback amplifier circuit unit 15c toward the output terminal 32a of the power control system feedback amplifier circuit unit 15a. Flows. This current flow is such that the voltage at the output terminal 31c of the differential amplifier 21c of the current control feedback amplifier circuit unit 15c is higher than the voltage at the output terminal 32a of the power control feedback feedback circuit unit 15a. Try to hold on. In order to compensate for this voltage drop, a voltage compensating resistor 33c is inserted in the differential amplifier 21c between the output end 32c and the amplifier body. Therefore, when the output terminal 32c of the current control system feedback amplifier circuit unit 15c is higher than the sum of the voltage at the output terminal 32a of the power control system feedback amplifier circuit unit 15a and the potential difference defined by the rectifier element 30a, the output The voltage at the output end 32c decreases so that the voltage at the end 32c is the sum of the voltage at the output end 32a and the potential difference defined by the rectifying element 30a.

  Similarly to the phase control system feedback amplifier circuit unit 15b, the current control system feedback amplifier circuit unit 15c has a power control system feedback amplifier circuit unit 15a that functions as an auxiliary control system for the power control system feedback amplifier circuit unit 15a. At a predetermined current value detected by the current detection means 20 during normal operation under control, the voltage value of the output terminal 32c is set to be higher than the voltage of the output terminal 32a of the power control feedback feedback circuit section 15a. Has been. As described above, the voltage compensation resistor 33c and the rectifying element 30a are provided in association with the current control feedback amplifier circuit unit 15c.

  Therefore, at a predetermined current value detected by the current detection means 20 during normal operation under the control of the power control system feedback amplifier circuit unit 15a, the voltage at the output terminal 32c of the current control system feedback amplifier circuit unit 15c is It retains a value higher than the voltage at the output terminal 32a of the system feedback amplifier circuit unit 15a by the predetermined voltage value defined by the rectifier 30a. In addition, during normal operation under the control of the power control system feedback amplifier circuit unit 15a, the voltage at the output terminal 32c of the current control system feedback amplifier circuit unit 15c is biased by the rectifying element 30a, thereby causing a power control system feedback amplifier circuit. Since the voltage of the output terminal 32c follows the change of the voltage value of the output terminal 32a with a difference of the predetermined voltage value from the voltage of the output terminal 32a of the unit 15a, the voltage of the output terminal 32c is the power control system feedback amplification. In accordance with the fluctuation of the output terminal 32a of the circuit unit 15a, the voltage fluctuates integrally while maintaining a voltage value higher than the voltage of the output terminal 32a by the predetermined voltage.

  Further, when the current detection unit 20 detects a large current value exceeding a predetermined current value, the current detection unit 20 operates to reduce the voltage of the output terminal 32c so that the current value approaches the target set value. By this control operation, the voltage of the output terminal 32c of the current control system feedback amplifier circuit unit 15c is more than the sum of the voltage value defined by the rectifying element 30a and the voltage value of the output terminal 32a of the power control system feedback amplifier circuit unit 15a. When the voltage drops, a reverse voltage acts on the rectifying element 30a. Therefore, the output terminal 32c of the current control feedback amplifier circuit unit 15c is held at a voltage lower than the voltage value of the output terminal 32a, and this low voltage is output. It is output to the end 32c.

  Output terminals 32a to 32c of the feedback amplifier circuit units 15a to 15c are connected to the selection circuit unit 15d. In the illustrated example, the selection circuit unit 15d is configured by a well-known diode OR circuit having three diodes 27a to 27c. The cathodes of the diodes 27a to 27c are connected to the output terminals 32a to 32c of the control system feedback amplification circuit units 15a to 15c, respectively. The anodes of the diodes 27a to 27c are connected to a voltage dividing point 28a of the voltage circuit 28 that defines a minimum frequency for an operating frequency corresponding to the maximum power so as to regulate the maximum power. When a voltage lower than the voltage at the voltage dividing point 28a acts on the cathode side of the diodes 27a to 27c, the voltage at the voltage dividing point 28a becomes equal to the lowest cathode voltage among the cathode voltages of the diodes 27a to 27c. Therefore, the lowest voltage value among the cathode voltages of the diodes 27a to 27c, that is, the voltages of the output terminals 32a to 32c of the feedback amplification circuit units 15a to 15c connected to the cathodes is output to the voltage dividing point 28a. Is done.

  Therefore, the selection circuit unit 15d selectively selects any one of the feedback amplification circuit units 15a, 15b, or 15c indicating the lowest output voltage among the outputs of the feedback amplification circuit units 15a to 15c, and the voltage dividing point 28a. Connect to.

  The voltage signal output to the voltage dividing point 28 a is converted into a drive frequency signal by a converter 29 that converts the voltage into a drive frequency signal and input to the driver circuit 17. The converter 29 exhibits an output characteristic having an inversely proportional relationship between the input voltage and the frequency indicated by the frequency signal. Therefore, when the voltage at the voltage dividing point 28a increases, the frequency of the drive frequency signal input to the driver circuit 17 decreases.

  From this, when the voltage at the voltage dividing point 28a increases, the drive frequency of the inverter 13 decreases, and as a result, the power supplied to the heating coil 14 increases. On the other hand, when the voltage at the voltage dividing point 28a falls, the drive frequency of the inverter 13 rises, the power supplied to the heating coil 14 falls, and as a result, the load on the inverter 13 is reduced.

  Therefore, in the normal operation state of the electromagnetic cooker 10, as described above, the output voltage of the power control system feedback amplifier circuit unit 15a is the auxiliary control system, the phase control system feedback amplifier circuit unit 15b and the current control system feedback amplifier circuit. Since the voltage is set lower (for example, 4V) than the voltages of the output terminals 32b and 32c of the unit 15c, the negative feedback control of the power control system feedback amplification circuit unit 15a functions. For this reason, when the power consumption increases from the target value, the drive frequency to the inverter 13 is increased by the control action of the power control system feedback amplification circuit unit 15a. On the contrary, if the power consumption is to be lowered from the target value, the drive frequency to the inverter 13 is reduced by the power control feedback amplifier circuit 15a.

  By the proper feedback control with a predetermined time constant by the main control system including the power control system feedback amplifier circuit unit 15a, the electromagnetic cooker 10 performs constant power control substantially along the power set value.

  Further, for example, when the phase detection unit 19 of the phase control system detects an abnormal advance angle with respect to the phase of the current to the heating coil 14, and the detection signal is input to the inverting input terminal of the differential amplifier 21b, the differential amplifier 21b Output voltage, ie, the voltage at the output terminal 32b of the phase control system feedback amplifier circuit unit 15b, in accordance with the time constant set by the time constant circuit 22b, the target value input to the non-inverting input terminal of the differential amplifier, It descends toward the target value indicating the allowable phase advance value. On the other hand, in such an abnormal advance detection state, the output voltage of the differential amplifier 21a of the power control system feedback amplifier circuit unit 15a that is the main control system, that is, the voltage of the output terminal 32a of the power control system feedback amplifier circuit unit 15a is To rise. As a result, when inversion occurs in the magnitude relationship between the voltage values of the output terminals 32a and 32b of both control system feedback amplification circuit sections 15a and 15b, a switching operation of the selection circuit section 15d occurs.

  The timing of this switching operation will be described along the graph of FIG. 3 conceptually. The horizontal axis of the graph shown in FIG. 3 is the time axis, and the vertical axis indicates the voltage value.

Characteristic line 34a is a output voltage of the differential amplifier 21a of the power control system feedback amplifier circuit section 15a is output 32a voltage when the abnormal power exceeding the allowable advance at time t ₀ is supplied to the heating coil 14 Indicates a change in value. An appropriate control operation is maintained by the input power control until the time t _{0 when the} abnormality occurs, and accordingly, the output voltage of the output terminal 32a of the power control feedback amplifier circuit unit 15a is, for example, in the vicinity of an output voltage value of about 4V. Is retained. However, if an abnormality occurs at time t ₀ , the input voltage to the differential amplifier 21 a abnormally rises due to the abnormal advance angle exceeding the allowable advance angle, so that the output terminal 32 a of the power control system feedback amplifier circuit unit 15 a The voltage rises toward the maximum drive voltage value, for example, 12V.

On the other hand, a characteristic line 34b represents the change in the voltage value of the output terminal 32b of the output voltage, that the phase control system feedback amplifier circuit portion 15b of the differential amplifier 21b when the abnormal advance is detected at time t _0. Until the time t ₀ when this abnormality occurs and is detected, the output voltage value of the differential amplifier 21b, that is, the voltage at the output terminal 32b of the phase control feedback amplifier circuit unit 15b is the maximum drive voltage, for example, about 12V. Although it is held at the output voltage value, as described above, when the abnormal advance angle detection signal is input to the differential amplifier 21b, it drops toward the control level voltage along the time constant characteristic of the time constant setting circuit 22b.

At this time, as shown in FIG. 3, after the elapsed time at time t ₂ both characteristic lines 34a and 34b intersect but, until time t ₂ which intersects the time t ₀ when abnormality occurs, the first control system power The power control system by the control system feedback amplifier circuit unit 15a, that is, the main control system is switched to the auxiliary control system which is a phase control system by the phase control system feedback amplifier circuit unit 15b. After this switching, power supply to the heating coil 14 is appropriately performed under the control of the phase control system feedback amplification circuit unit 15b.

In contrast, for example, when the abnormal current that at time t ₀ exceeds the allowable current is supplied to the heating coil 14, as in the case of abnormal advance that the has occurred, until the time t ₀ is the difference between the power control system The output of the dynamic amplifier 21a is held in the vicinity of an output voltage value of about 4V, for example. Further, when an abnormality occurs at time t ₀ , the input voltage to the differential amplifier 21a abnormally increases due to the abnormal current exceeding the allowable current. Therefore, the power control system feedback amplification that is the output voltage of the differential amplifier 21a. As shown by the characteristic line 34a, the voltage at the output end 32a of the circuit unit 15a increases toward the maximum drive voltage value, for example, 12V.

  At this time, the voltage value of the output terminal 32c, which is the output voltage value of the differential amplifier 21c of the current control system feedback amplifier circuit unit 15c which is the auxiliary control system, is the time constant setting circuit 22c due to the abnormal current exceeding the allowable current. It drops toward the control level voltage along the constant characteristic. That is, the voltage value of the output terminal 32b of the phase control system feedback amplifier circuit unit 15b also drops along the same time constant characteristic as the characteristic line 34b shown in FIG.

  However, as described above, due to the bias action of the rectifying element circuit unit 30 inserted between the current control system feedback amplifier circuit unit 15c and the selection circuit unit 15d, the output terminal 32c of the current control system feedback amplifier circuit unit 15c The voltage is given a negative bias so as to be higher than the predetermined voltage V1 defined by the rectifying element 30a than the output end 32a of the power control feedback amplifier circuit unit 15a. As shown in the graph, it changes below the characteristic line 34b along the characteristic line 34c parallel thereto.

As a result, since both characteristic lines 34a and 34c intersect at time t ₁ earlier than time t ₂ from abnormality detection time t ₀ , the rectifying element circuit is detected from the power control system (15a) after the abnormality is detected. Compared with the switching to the phase control system (15b) in which the unit 30 is not provided, the switching to the current control feedback amplifier circuit unit 15c is performed earlier.

  Therefore, according to the electromagnetic cooker 10 of the first embodiment, the abnormal advance angle from the power control system (15a) to the phase control system (15b) is obtained by adding the rectifying element circuit unit 30 that does not require a power supply circuit. Compared with the switching by the detection of the current, the switching to the current control system (15c) by the detection of the abnormal current can be performed quickly. Therefore, the current control from the power control system (15a) can be performed with a relatively simple circuit configuration. It is possible to reliably prevent an excessive current from being supplied to the heating coil 14 at the time of switching to the system (15c).

<Example 2>
In the control circuit 15 provided in the electromagnetic cooker 10 of the second embodiment shown in FIG. 4, the rectifying element circuit unit 30 is replaced between the current control system feedback amplification circuit unit 15c and the power control system feedback amplification circuit unit 15a. The current control system feedback amplifier circuit unit 15c and the phase control system feedback amplifier circuit unit 15b are provided.

  That is, in the second embodiment of FIG. 4, the cathode of the rectifying element 30b made of the same diode as described above is connected to the output terminal 32a ′ of the power control system feedback amplifier circuit unit 15a, and its anode is the phase control system feedback amplifier circuit. It is connected to the output terminal 32b of the part 15b.

  Further, a voltage compensation resistor 33b similar to that described above is inserted between the output terminal 31b of the differential amplifier 21b of the phase control system feedback amplifier circuit section 15b and the differential amplifier body.

  The rectifying element circuit unit 30 including the rectifying element 30b and the voltage compensating resistor 33b has a voltage difference between the output terminal 32b of the phase control feedback amplifier circuit unit 15b and a predetermined potential difference corresponding to the junction barrier energy difference of the rectifying element 30b. When the voltage of the output terminal 32b becomes higher than the sum of the voltage of the output terminal 32a 'of the power control feedback amplifier circuit section 15a, the voltage of the output terminal 32b is the sum of the voltage of the output terminal 32a' and the potential difference defined by the rectifying element 30b. The voltage at the output end 32b is dropped so that

  Therefore, according to the second embodiment shown in FIG. 4, the abnormal advance angle to the phase control system (15b) is compared with that at the time of switching from the power control system (15a) to the current control system (15c) by detecting the abnormal current. Since switching by detection can be performed quickly, supply of excessive current to the heating coil 14 at the time of switching from the power control system (15a) to the phase control system (15b) can be reliably prevented. Thereby, supply of an excessive current to the heating coil 14 at the time of switching from the power control system (15a) to the phase control system (15b) can be reliably prevented.

<Example 3>
In the third embodiment shown in FIG. 5, the rectifying element circuit unit 30 is provided between the current control system feedback amplifier circuit unit 15c and the power control system feedback amplifier circuit unit 15a, and between the current control system feedback amplifier circuit unit 15c and the phase control system feedback. It is provided on both sides of the amplifier circuit unit 15b.

  As shown in FIG. 5, the cathode of the rectifying element 30a made of the same diode as described above is connected to the output terminal 32a of the power control system feedback amplifier circuit unit 15a, and its anode is the output of the current control system feedback amplifier circuit unit 15c. It is connected to the terminal 32c. Further, the cathode of the rectifying element 30b is connected to the output terminal 32a 'of the power control system feedback amplification circuit unit 15a, and the anode thereof is connected to the output terminal 32b of the phase control system feedback amplification circuit unit 15b.

  Between the output terminal 31c of the differential amplifier 21c of the current control feedback amplifier circuit section 15c and the differential amplifier body and the output terminal 31b of the differential amplifier 21b of the phase control feedback amplifier circuit section 15b and the differential amplifier body Between the two, voltage compensation resistors 33b and 33c similar to those described above are inserted.

  According to the electromagnetic cooker 10 shown in the third embodiment, at the time of switching by detecting an abnormal advance angle from the power control system (15a) to the phase control system (15b) and from the power control system (15a) to the current control system (15c). In any of the switching operations by detecting an abnormal current, the power control system (15a) that is the first control system is switched to the phase control system (15b) or the current control system (15c) that is the second control system. Since switching can be performed quickly, an excessive current to the heating coil 14 at the time of switching from the power control system (15a) to the phase control system (15b) and the current control system (15c) with a relatively simple circuit configuration. Can be reliably prevented.

  In each of the above-described embodiments, the example in which the selection circuit unit 15d selects the lowest voltage has been described. Instead, a constant power supply circuit, a constant voltage of the constant power supply circuit, and an output of each feedback amplifier circuit section 15a, 15b, 15c are provided between the feedback amplifier circuit sections 15a, 15b, 15c and the selection circuit section 15d. An arithmetic circuit unit that obtains a difference from the voltages of the terminals 32a to 32c is inserted, and a control system that outputs the highest voltage among the differential outputs of the arithmetic circuit unit can be selected by the selection circuit unit.

  Moreover, although the example which employ | adopted the electric power control system as the main control system and employ | adopted the phase control system or the electric current control system as the auxiliary | assistant control system was shown, this invention is not limited to this, Various control parameters of the electromagnetic cooker 10 are shown. It can be applied to control system switching by

It is an electric circuit diagram which shows the principal part of Example 1 of the electromagnetic cooker which concerns on this invention. It is a block diagram which shows roughly the electric circuit of the electromagnetic cooker which concerns on this invention. It is a graph which shows the switching timing of the control system of Example 1 which concerns on this invention. It is drawing similar to FIG. 1 which shows Example 2 of the electromagnetic cooker which concerns on this invention. It is drawing similar to FIG. 1 which shows Example 3 of the electromagnetic cooker which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electromagnetic cooker 13 Inverter 14 Heating coil 15 Control circuit 15a Power control system feedback amplification circuit part (main control system, 1st control system)
15b Phase control system feedback amplifier circuit (auxiliary control system, second control system)
15c Current control feedback amplifier circuit (auxiliary control system, second control system)
15d selection circuit unit 17 driver circuit 18 power detection means (first detection means)
19 Phase detection means (second detection means)
20 Current detection means (second detection means)
30 (30a, 33b, 33c) Rectifier element circuit part 30a Rectifier element (diode)
33b, 33c Voltage compensation resistor

Claims (5)

An electromagnetic cooker comprising an inverter driven by a driver circuit to supply a high-frequency current corresponding to an operating frequency to a heating coil, and a control circuit for controlling the operation of the driver circuit to control the operating frequency of the inverter. And
The control circuit includes: a power control system for controlling an operating frequency of the inverter to maintain a power consumption of the electromagnetic cooker set to be adjustable; a current flowing through the heating coil or the current and the current Auxiliary control system for controlling the operating frequency of the inverter so that the phase difference from the voltage does not exceed the allowable value, and the two control systems are selected according to the level relationship between the output voltages of the two control systems, and selected And a selection circuit unit that outputs an operating frequency signal corresponding to the output voltage of the one control system to the driver circuit,
Between the output terminals of the both control systems to the selection circuit unit, the voltage at the output terminal of either one of the control systems is set in order to speed up switching from the power control system to the auxiliary control system. When the sum of the voltage at the output end of the other control system and a predetermined value is exceeded, current from the output end of the one control system toward the output end of the other control system is allowed and the both controls An electromagnetic cooker comprising a rectifying element circuit section for holding the output terminal voltage difference of the system at the predetermined value. Furthermore, the first detection means for detecting the power consumption, and a second detection means for detecting a current flowing through the heating coil or a phase difference between the current and the voltage,
The power control system obtains a difference between a target value and a value detected by the first detection means, and operates with a predetermined time constant so as to feed back a signal corresponding to the difference to the input side. The auxiliary control system obtains a difference between the maximum allowable value for the detection value detected by the second detection means and the detection value, and feeds back a signal corresponding to the difference to the input side. A second feedback amplifier circuit section operating with a predetermined time constant as much as possible,
The selection circuit unit selects the control system having a low output terminal voltage from the two control systems,
The rectifying element circuit unit is a rectifying element that allows current to flow from the output terminal of the auxiliary control system to the output terminal of the power control system, depending on the value of the voltage applied between the terminals of the rectifying element. The electromagnetic cooker according to claim 1, further comprising a rectifying element that generates a predetermined voltage difference between both terminals. The second detection means has a current detection means for detecting a current flowing through the heating coil, and a phase detection means for detecting a phase difference between the current flowing through the heating coil and its voltage,
The auxiliary control system obtains a difference between a maximum allowable current value for the heating coil and a detection value detected by the current detection means, and uses a predetermined time constant to feed back a signal corresponding to the difference to the input side. A difference between a current control system having an operating feedback amplifier circuit section, a maximum allowable advance phase difference with respect to the phase difference and a phase difference detected by the phase detection means, and a signal corresponding to the difference on the input side It is composed of a phase control system having a feedback amplification circuit section that operates with a predetermined time constant for feedback.
The selection circuit unit selects an output voltage of the feedback amplification circuit unit having the lowest output voltage among the feedback amplification circuit units,
Between the output terminal of the feedback amplifier circuit unit of the power control system and the output terminal of the feedback amplifier circuit unit of the current control system and the output terminal of the feedback amplifier circuit unit of the power control system and the phase control The electromagnetic cooker according to claim 2, wherein the rectifier element circuit unit is provided between an output terminal of the feedback amplification circuit unit of the system.   The electromagnetic cooker according to claim 2, wherein the rectifying element is a diode that generates a potential difference based on a junction barrier energy difference between an anode and a cathode when a forward current flows. An electromagnetic cooker comprising an inverter driven by a driver circuit to supply a high-frequency current corresponding to an operating frequency to a heating coil, and a control circuit for controlling the operation of the driver circuit to control the operating frequency of the inverter. And
The control circuit includes a first control system for controlling the operating frequency of the inverter based on a first parameter, and a second control for controlling the operating frequency of the inverter based on a second parameter. And a selection circuit unit that selects both control systems according to a level relationship between the output voltages of the two control systems and outputs an operating frequency signal corresponding to the output voltage of one of the selected control systems to the inverter And
Between the output terminals of the two control systems to the selection circuit unit, the voltage at the output terminal of one of the control systems is the voltage of the other control system in order to speed up switching between the two control systems. When the sum of the voltage of the output terminal and a predetermined value is exceeded, the current from the output terminal of the one control system to the output terminal of the other control system is allowed, and the output terminal voltage of the both control systems An electromagnetic cooker, characterized in that a rectifying element circuit unit for holding the difference at the predetermined value is provided.

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