JP2005285103A - Control circuit and power control apparatus having the control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve detection accuracy of a load current enabling use of detection of a transformer, by causing an AC current to flow to the transformer at all times. <P>SOLUTION: Provided is a control circuit 20, which performs ON/OFF control of a switching section 3 connected between an AC power supply 5 and a heater 4, wherein the control circuit 20 performs control to allow the present turning on of the switch section 3, when it is determined that an AC power supply 5 waveform (i.e., AC waveform) polarity at a previous turning on at the switching section 3 is not the same as an AC waveform polarity at the present turning on; and wherein the control circuit 20 performs control to inhibit the present turning on of the switching section 3, when it is determined that the polarities are the same. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control circuit that performs on / off control of a switch unit connected between an AC power supply and a load, and a power control apparatus using the control circuit. In particular, this power control apparatus includes a load current detection unit that detects a load current using a current transformer to control the power supplied to the load.

  The detection of load current supplied to the load from the AC power supply is easy because it is easily insulated from the AC power supply, has a wide current detection range, and is suitable for large current detection. CT) is widely used in general.

  On the other hand, in a temperature control system such as a heater, a power control device that controls the power applied to the heater by connecting a switch unit between the AC power source and the heater and turning the switch unit on and off on a time basis. There is. Such a power control device includes, for example, a cycle control method in which the voltage of the AC power supply is zero-crossed and the switch section is turned on / off every half cycle of the AC power supply, or the switch section by controlling the phase angle of the AC power supply. There is a phase control system that controls on / off of the signal (see Patent Document 1).

  In the above power control device, a current transformer is used to detect disconnection of the heater. When the current value detected by the current transformer is less than a preset value, it is determined that the heater is disconnected. Many are equipped with a function to output a disconnection alarm. A current transformer is made by winding a detection winding around a toroidal core. By passing a conductor through which a current is to be measured through the current transformer, an induced electromotive force is generated between the current flowing through the conductor and the detection winding. Is detected, and the magnitude of this induced electromotive force is detected to detect an alternating current. The ratio between the alternating current to be measured and the alternating current output from the current transformer is determined by the turn ratio (current transformation ratio) of the detection winding.

However, since the current transformer detects the current using the induced electromotive force between the two coils as described above, it can only detect the alternating current in principle. Therefore, when an AC current flows through the heater, for example, when an ON / OFF control with a sufficiently long interval between ON and OFF is performed, the heater current can be detected with high accuracy, but the heater is turned ON / OFF every half cycle of AC. Depending on the application, the alternating current may flow in the same direction. In this case, the heater current is a current in which ripple is superimposed on the direct current, so the electromotive force induced in the coil of the current transformer is the change in current. Only a minute (in this case, ripple), which is smaller than the original detection current determined by the current to be detected and the current transformation ratio, and the detection accuracy is extremely lowered.
JP 2001-265446 A

  The present invention makes it possible to accurately detect the disconnection of a load such as a heater, even when a current transformer is used for turning on and off every half cycle of alternating current, and to improve the detection speed and the accuracy thereof. It is a problem to be solved to enable control with high accuracy and high responsiveness in a power control apparatus using the same.

  The control circuit according to the first aspect of the present invention is a control circuit for controlling on / off of a switch unit connected between an AC power supply and a load, and the AC power source waveform (AC The polarity of the waveform) and the polarity of the AC waveform when this is on are the same. If it is determined that they are not the same, control is performed to allow the switch to be turned on this time, and it is determined that they are the same. In some cases, control is performed to prohibit the switch unit from being turned on this time. Preferably, for the permission and prohibition processing, a polarity detection unit that detects the polarity of the AC waveform, and a storage unit that stores the polarity of the AC waveform when the switch unit is turned on from the detection output of the polarity detection unit And the polarity of the alternating current waveform when the switch is previously turned on and the polarity of the alternating current waveform when the switch is turned on are the same, and the alternating current when the switch is turned on this time is determined. When it is determined that the polarity of the waveform is not the same as the polarity of the alternating current waveform at the time of previous ON, the signal processing unit that allows the switch unit to be turned on this time and prohibits the switch unit from being turned on this time when it is determined to be the same With.

  According to the first aspect of the present invention, in the power control in which the power from the AC power source is applied to the load, for example, the heater by the on / off control of the switch unit, when the disconnection of the heater is detected by the current transformer, The detector can accurately detect the load current also by ON / OFF control of the switch section. That is, the current transformer is configured by winding a detection winding around a toroidal core. Therefore, when a current transformer is incorporated in the wiring between the heater and the AC power supply, if the previous half cycle of AC current and the current half cycle have the same polarity, the AC current to be detected is the actual load current. It becomes smaller and the detection accuracy is extremely lowered. On the other hand, in the present invention, since the previous half cycle of the alternating current and the current half cycle have different polarities, the current is alternating current, and the alternating current to be detected corresponds to the actual load current, Detection accuracy is greatly improved.

  Specifically, according to the present invention, the correlation (current transformation ratio) between the current transformer output and the actual load current is stabilized, the current detection accuracy is improved, and the first half cycle after the load AC power supply is turned on. Can be detected, and the responsiveness such as detection of disconnection of a load such as a heater, overcurrent detection, etc. is remarkably improved, and further, current using a current transformer in high-accuracy cycle control in JP-A-2001-265446 It is possible to achieve an effect such that detection is possible.

  As a preferable aspect of the control circuit, a load current detection unit that detects a load current from a current transformer output is provided, and the signal processing unit detects whether or not the load is disconnected based on the output of the load current detection unit. When the polarity of the alternating current waveform when the switch unit is turned on is indefinite, the output of the load current detection unit is invalidated. As a result, the same polarity may be continuous when the power control device is turned on, or when the load AC power supply fails, but in this case, the detected current is not used for disconnection detection processing. In addition, it is possible to avoid erroneous detection of the presence or absence of disconnection of the load.

  The control circuit according to the second aspect of the present invention is a control circuit that controls on / off of a switch unit connected between an AC power source and a load, and the switch unit until the switch unit is turned on from any previous time point. It is determined whether or not the odd / even number of the polarity change of alternating current coincides with the odd / even number of the polarity change at the time of turning on this time. When the determination is made, control is performed to prohibit the switch unit from being turned on this time. Preferably, for the processing of the allowance and prohibition, the count detection unit that counts the number of alternating polarity changes until the switch unit is turned on from an arbitrary time point, and stores the odd / even number of the polarity change number, The odd number / even number of the polarity change number at the previous ON time of the switch unit is obtained from the count detection unit, and it is determined whether the odd number / even number of the polarity change number at the previous ON time matches the odd number / even number of the polarity change number at the current ON time. A signal processing unit that permits the switch unit to be turned on this time when it is determined not to match, and prohibits the switch unit from being turned on this time when it is determined to match.

  According to the second aspect of the present invention, in the power control in which the power from the AC power source is applied to the load, for example, the heater by the on / off control of the switch unit, when the heater breakage is detected by the current transformer, The detector can accurately detect the load current also by ON / OFF control of the switch section. That is, the current transformer is configured by winding a detection winding around a toroidal core. Therefore, when a current transformer is incorporated in the wiring between the heater and the AC power supply, the AC current to be detected becomes smaller than the actual load current if the odd-even half cycle of the AC current matches, and the detection accuracy becomes extremely high. descend. On the other hand, in the present invention, since the odd / even of the half cycle at the previous ON time of the alternating current is different from the half cycle at the current ON time, the current is an alternating current, and the alternating current to be detected corresponds to the actual load current. As a result, the detection accuracy is greatly improved.

  As a preferable aspect of the control circuit, a load current detection unit using a current transformer is provided, and the signal processing unit detects the disconnection of the load based on the output of the load current detection unit, and When the odd / even number of alternating current polarity changes counted from the time is indefinite, the output of the load current detector is invalidated. As a result, the same polarity may be continuous when the power control device is turned on, or when the load AC power supply fails, but in this case, the detected current is not used for disconnection detection processing. In addition, it is possible to avoid erroneous detection of the presence or absence of disconnection of the load.

  The power control device according to the present invention outputs an output power command value for each predetermined cycle of a half cycle or more of the AC power supply according to the input power command value, and is connected between the AC power supply and the load. Is a power control device that controls on / off control according to the output power command value to control power supply to the load, and accumulates an error between the output power command value and the input power command value. The addition unit that adds the input power command value and the output error accumulation value accumulated by the output error accumulation unit, and the addition value added by the addition unit and the threshold value are compared. Comprises 100% output power command value and 0% output power command value when less than the threshold, and the first or second control circuit of the present invention. is there.

  According to the present invention, it is possible to provide a control circuit capable of using the current detected by the current transformer by always passing an alternating current through the current transformer, and in a power control apparatus using the control circuit, The supply of power to the load can be controlled with high accuracy and high responsiveness.

  Hereinafter, a power control device including a control circuit according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a temperature control system including the power control apparatus. This temperature control system includes a temperature controller 1, a power control device 2, a switch unit 3 including SSR and others, a heater 4 as a load, an AC power supply 5, a current transformer 6, and a temperature sensor 7. It is composed of The switch unit 3 is connected between the heater 4 and the AC power source 5. The heater 4 is disposed inside a heating furnace (not shown), and the temperature sensor 7 detects the temperature inside the heating furnace and outputs the detection output to the temperature controller 1. The current transformer 6 is attached to a wiring (conductive wire) for forming a closed circuit by the switch unit 3, the heater 4, and the AC power source 5, and detects a heater current that is a load current flowing through the conductive wire. Yes.

  In the above temperature control system, the power control apparatus 2 includes the sample / hold unit 2A that holds the input power command value Xin from the temperature controller 1 for half a cycle, and the input power command value X (n) after the sample / hold. Output error calculation unit 2B that calculates an output error E (n) between the actual output value Yout (n) and an output error accumulation unit 2C that accumulates the output error E (n) obtained by the output error calculation unit 2B; , An addition unit (correction unit) 2D that adds the input power command value X (n) and the output error cumulative value Σ (n−1), an addition output value Y (n) of the addition unit 2D, and a threshold value as a reference value And a comparison unit 2E that outputs 100% or 0% output power command value Yout (n) according to the comparison result. The comparison unit 2E outputs a 100% or 0% output power command value Yout (n).

  The power control device 2 also detects the polarity of the waveform of the AC power supply 5 (AC waveform), and the polarity of the AC waveform detected by the polarity detection unit 2F when at least the switch unit 3 is turned on. Performs signal processing such as a storage unit 2G that stores the polarity of the AC waveform, a current detection unit 2H that detects the heater current from the output of the current transformer 6, and a heater disconnection that is detected from the detection output of the current detection unit 2H. At the same time, it is determined whether or not the polarity of the previous AC waveform stored in the storage unit 2G matches the polarity of the AC waveform when the switch unit 3 is currently turned on from the polarity detection unit 2F. When it is determined that the polarity of the AC waveform at the time is not the same as the polarity of the AC waveform at the time of previous ON, the switch unit 3 is allowed to be turned on this time, and when it is determined that it is the same, the switch unit 3 is prohibited from being turned on this time. Signal processor 2 Provided with a door. The signal processing unit 2I also disables the output of the current detection unit 2H when the AC waveform when the switch unit 3 was previously turned on is indefinite. The power control apparatus 2 includes a control unit 2J that controls the above-described units. Each of these parts can be constituted by a microcomputer. For example, the microcomputer includes a CPU that controls the entire CPU, a program memory that stores a program that executes the operation of the CPU, a work memory that provides a work area for the CPU, a bus that interconnects these, and the like However, each unit described above can be functionally configured by the microcomputer. Of course, the present invention is not limited to the software configuration of the microcomputer, and may be a hardware configuration. For example, the polarity detection unit 2F that detects the waveform of the AC power supply 5 may be a well-known one. When the AC power supply 5 is connected to the non-inverting input unit and the inverting input unit of the comparator and the polarity of the AC power supply is positive, A light-emitting bidirectional thyristor that is configured with a comparator that outputs a pulse and stops outputting the pulse when negative, or is connected in parallel to an AC power supply, and a light-receiving transistor that responds to the optical output of the bidirectional thyristor And when the polarity of the AC power supply is positive from the collector of the light receiving transistor, a pulse is output, and when it is negative, the pulse output is stopped.

  When it is determined by the polarity detection unit 2F, storage unit 2G, signal processing unit 2I, and control unit 2J that the polarity of the AC waveform at the previous ON time and the polarity of the AC waveform at the current ON time are different in the switch unit 3 Constitutes a control circuit 20 that performs control to allow the switch unit 3 to be turned on this time, and when it is determined that the switch unit 3 is the same, prohibits the switch unit 3 from being turned on this time. The control unit 2J has a function of causing each unit to execute the flowcharts shown in FIGS. 2 and 3. However, the control unit 2J has a function of executing the flowcharts shown in FIGS. 2J is not necessarily essential for the control circuit 20.

  In addition, regarding the storage content of the storage unit 2G, the storage content may be updated by the signal processing unit 2I, or the storage content may be updated by the storage unit 2G itself. For example, when the storage unit 2G stores the detection output (first polarity) of the polarity of the AC waveform of the half cycle when the switch unit 3 is currently turned on from the polarity detection unit 2F, the storage unit 2G receives the next half cycle from the polarity detection unit 2F. An AC waveform polarity detection output (second polarity) is input. When the first polarity already stored in the storage unit 2G is used as the previous polarity, the signal processing unit 2I updates the storage in the storage unit 2G from the first polarity to the next second polarity, and the second polarity Make the polarity available as the previous polarity. Alternatively, the storage unit 2G updates the polarity data in response to the use of the polarity of the signal processing unit 2I. The signal processing unit 2I may input the current polarity data directly from the polarity detection unit 2F. The polarity of the AC waveform stored in the storage unit 2G is stored in a flag format. That is, the previous polarity is the previous polarity flag A. When the flag is +1 (positive), the power supply polarity at the previous half cycle output is positive, and when the flag is -1 (negative), the power supply polarity at the previous half cycle output is negative. When the flag is “0”, there is no previous output or indefinite. The current polarity is the current polarity flag B. When the flag is +1 (positive), the power polarity at the current half cycle output is positive, and when the flag is -1 (negative), the power polarity at the current half cycle output is negative. When the flag is “0”, there is no current output or it is indefinite.

  The control circuit 20 performs the following flag update control with respect to the setting of the polarity flags A and B stored in the storage unit 2G. That is, the polarity flag is set to 0 as an initial value. As (Condition 1), when the polarity flag = 0, the switch unit 3 is allowed to be turned on this time, and when the power supply polarity at the time of the current on is positive, the polarity flag is set to +1, and the power supply at the time of the current on When the polarity is negative, the polarity flag is set to -1. (Condition 2) When the polarity flag is +1 and the polarity of the power supply at this time is negative, the current power on is permitted, and 2 is subtracted from the polarity flag to set the polarity flag to −1. When the polarity is positive, this time on is prohibited. (Condition 3) When the polarity flag is -1 and the power supply polarity at this time is on, the current on is permitted, and 2 is added to the polarity flag to set the polarity flag to +1. If is negative, turn on is prohibited this time. A current detection error is output when the polarity flag is other than -1, 0, +1.

  The operation of the temperature control system having the above configuration will be described with reference to FIGS. FIG. 2 is a basic flowchart of the system, and FIG. 3 is a detailed flowchart of the output permission determination subroutine of FIG. In starting the operation, the control unit 2J including the CPU first performs an initial process (step ST1). As the initial process, the threshold value S of the comparison unit 2E is set (step ST2), the variable n of the register 2J built-in register is cleared (step ST3), and the parameter initial value is set. Σ (n) is cleared (0%), the previous polarity flag A is set to 0 (zero) (step ST4), and the like.

  Subsequent to the initial process, the variable n of the control unit 2J built-in register is incremented by 1 (n ← n + 1) (step ST5). Then, the input power command value X (n) is taken into the adder 2D from the temperature controller 1 via the sample hold circuit 2A. (Step ST6). As described above, the heater 4 is housed in a heating furnace, and an object to be heated to be heated by the heater 4 is disposed inside the heating furnace. And the temperature regulator 1 controls the drive amount of the heater 4 from the output of the temperature sensor 7 in order to heat a to-be-heated object appropriately, and adjusts the temperature in a heating furnace. Therefore, the temperature controller 1 obtains the input power command value Xin from the output of the temperature sensor 7 and outputs it to the power adjustment device 2. The adder 2D simultaneously receives the output error accumulation Σ (n−1) from the output error accumulator 2C to the previous time. The adding unit 2D adds the current input command value X (n) and the previous output error accumulation Σ (n−1), and outputs the added value to the comparing unit 2E as a corrected output value Y (n). (Step ST7).

  Next, an output threshold value determination process is performed (ST8). In this output threshold value determination process, the comparison unit 2E compares the corrected output value Y (n) with the threshold value S (50%) and determines whether the corrected output value Y (n) exceeds the threshold value S (50%). . Subsequently, it is determined whether or not an output power command has been issued (ST9). If the corrected output value Y (n) is equal to or greater than the threshold value S (50%), the output power command value Yout (n) is determined to be 100 [%] (in this case, the output power command is present). When (n) is smaller than the threshold value S (50%), the output power command value Yout (n) is determined as 0 [%] (in this case, there is no output power command). The threshold value S is an example and may be changed as appropriate.

  If it is determined in ST9 that “output power command is present”, output permission / inhibition is determined (ST10). The determination of whether to permit output follows the flowchart (described later) in FIG. On the other hand, if it is determined that “no output power command”, the deviation between the current input power command value X (n) and the actually output output power command value Yout (n), that is, the output error E (n) ← X (n) −Yout (n) is calculated by the calculation unit 2B (step ST11), and the output error accumulation unit 2C adds the current output error E ( n) is added, and the output error accumulation is updated from Σ (n−1) to Σ (n) (step ST12). After the above half cycle processing, the process returns to step ST5, the variable n is incremented by 1, and the next half cycle processing is executed. The processing from step ST5 to step ST12 is repeated over the control cycle, and when entering the next control cycle, the variables n and Σ (n) are updated again and the same processing is repeated.

  The above cycle control is proposed in Japanese Patent Application Laid-Open Nos. 2001-265446, 2002-325428, etc., and detailed description based on specific numerical values is referred to the same publication and the like, and the description is omitted in this specification. To do.

  Next, the output permission determination step ST10 will be described with reference to FIG.

  In step SUB1, it is determined whether or not the previous polarity flag A is zero. When it is determined that the previous polarity flag A is 0, the process proceeds to step SUB5 to step SUB8. When it is determined that the previous polarity flag A is not 0, the process proceeds to step SUB2. In step SUB2, it is determined whether or not the previous polarity flag A is +1 (positive). When it is determined that the previous polarity flag A is +1 (positive), the process proceeds to step SUB10 to step SUB13. When it is determined that the previous polarity flag A is not +1 (positive), the process proceeds to step SUB3. In step SUB3, it is determined whether or not the previous polarity flag A is -1 (negative). When it is determined that the previous polarity flag A is -1 (negative), the process proceeds to step SUB14 to step SUB17. When it is determined that the previous polarity flag A is not -1 (negative), the process proceeds to step SUB4 and the output of the current transformer CT is captured.

  First, regarding step SUB5 to step SUB8 when it is determined in step SUB1 that the previous polarity flag A is 0, it is first determined in step SUB5 whether or not the current polarity flag B is +1 (positive). If it is determined in step SUB5 that the current polarity flag B is not +1 (positive), the previous polarity flag A is set to -1 (negative) in step SUB6, and if it is determined that the current polarity flag B is +1 (positive), step In SUB7, the previous polarity flag A is set to +1 (positive). In both step SUB6 and step SUB7, in the next step SUB8, output of the output power command value Yout (n) from the comparison unit 2e to the switch unit 3 is permitted. However, since the previous polarity flag A is 0 in step SUB1 and whether the previous polarity flag A is +1 (positive) or -1 (negative) is undefined, in steps SUB5 to SUB7, the previous polarity flag A and the current polarity flag B Therefore, in step SUB9, the output of the current transformer CT is not captured. Then, in preparation for the next polarity determination, the current polarity flag B is set to −1 (negative) and +1 (positive) as the previous polarity flag A in steps SUB6 and SUB7, respectively.

  If it is determined in step SUB2 that the previous polarity flag A is +1 (positive), the process proceeds to step SUB10 to step SUB13. In step SUB10, it is determined whether or not the current polarity flag B is +1 (positive). If it is determined that the current polarity flag B is not +1 (positive), the process proceeds to step SUB11, the previous polarity flag A is updated to -1 (negative), and then, in step SUB12, the output power command value Yout ( n) The output to the switch unit 3 is allowed. This is because the previous polarity flag A and the current polarity flag B are different. When it is determined that the current polarity flag B is +1 (positive), the polarity is the same as the polarity of the previous polarity flag A, so that the output power command value Yout (n) from the comparison unit 2E is switched to the switch unit 3 in step SUB13. Prohibit output. At this time, the output power command value Yout (n) is 0%. This is because the previous polarity flag A and the current polarity flag B are the same.

  If it is determined in step SUB3 that the previous polarity flag A is -1 (negative), it is determined in step SUB14 whether the current polarity flag B is -1 (negative). If it is determined in step SUB14 that the current polarity flag B is not -1 (negative), the previous polarity flag A is updated to +1 (positive) in step SUB15, and then the output power command value Yout (from the comparison unit 2E in step SUB16). n) The output to the switch unit 3 is allowed. This is because the previous polarity flag A and the current polarity flag B are different. If it is determined in step SUB14 that the current polarity flag B is -1 (negative), output of the output power command value Yout (n) from the comparison unit 2E to the switch unit 3 is prohibited in step SUB17. This is because the previous polarity flag A and the current polarity flag B are the same. In the above steps SUB12, SUB13, SUB16, and SUB17, the current transformer CT output is captured in step SUB4.

  As described above, when there is an output command in step ST9 of the flowchart of FIG. 2, the above-described output permission / rejection determination is performed based on the flowchart of FIG. 3 which is a detailed flowchart of step ST10. When the output is permitted, the previous polarity flag A and the current polarity flag B are different. Next, the case where the output to the switch unit 3 is allowed only when the previous polarity flag A and the current polarity flag B are different as in the present invention, and the previous polarity flag A and the current polarity flag B as in the prior art are Differences in the output of the current transformer 6 in the case where the output to the switch unit 3 is allowed even in the same case will be described with reference to FIGS.

  FIG. 4 shows a conventional example when the input command value X (n) (control amount) is 25%, and FIG. 5 shows the present embodiment when the input command value X (n) (control amount) is 25%. 4 (a) and 5 (a) both show the actual heater current (load current) waveform (filled portion), and FIGS. 4 (b) and 5 (b) both show the output waveform of the current transformer 6. FIG. Indicates. However, the broken line as a whole indicates the AC waveform of the AC power supply 5, and the shaded portion indicates the heater current and the output waveform of the current transformer 6. As apparent from FIGS. 4 and 5, the output of the current transformer 6 is conventionally low in level with respect to the actual heater current, and is output even during a period in which no current actually flows. On the other hand, in the present embodiment, the output of the current transformer 6 corresponds to the actual heater current, and there is no output of the current transformer 6 during the period when the heater current is not flowing. This indicates that the output of the current transformer 6 in the present embodiment corresponds to the actual heater current.

  FIG. 6 shows a conventional example when the input command value X (n) (control amount) is 50%, and FIG. 7 shows the present embodiment when the input command value X (n) (control amount) is 50%. 6 (a) and 7 (a) both show actual heater current waveforms (filled portions), and FIGS. 6 (b) and 7 (b) both show output waveforms of the current transformer 6. FIG. However, the broken line as a whole indicates the AC waveform of the AC power supply 5, and the shaded portion indicates the heater current and the output waveform of the current transformer 6. As apparent from FIGS. 6 and 7, the output of the current transformer 6 is conventionally lower in level than the actual heater current and is output even during a period in which no current actually flows. On the other hand, in the present embodiment, the output of the current transformer 6 corresponds to the actual heater current, and there is no output of the current transformer 6 during the period when the heater current is not flowing. This indicates that the output of the current transformer 6 in the present embodiment corresponds to the actual heater current.

  In addition, for the control amounts other than the above, for example, 4.3%, 7.7%, 14%, 33%, etc., the present inventors indicate that the output of the current transformer 6 corresponds to the actual heater current and is negative. It has been confirmed that it does not occur on the half cycle side.

  From the above, in this embodiment, the switch unit 3 is turned on based on the input command value X (n) with respect to the closed circuit in which the switch unit 3 is connected between the heater 4 and the AC power supply 5. In the power control device 2 that performs off-control, the output of the current transformer 6 is taken into the current detection unit 2H, and the disconnection detection of the heater is performed by the signal processing unit 2I based on the detection output of the current detection unit 2H. Can be done accurately.

(Other forms)
With reference to FIG. 8, another embodiment of the present invention will be described. 8, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and description of the same reference numerals will be omitted. In this embodiment, in the control circuit 20 of FIG. 1, instead of the polarity detection unit 2F and the storage unit 2G, a zero-cross detection unit 2K and a count detection unit 2L are provided, and the processing contents of the signal processing unit 2I are correspondingly changed. Characterized by changes. The zero-cross detection unit 2K detects a zero-cross of the voltage of the AC power supply 5, and the count detection unit 2L uses the zero-cross detection of the zero-cross detection unit 2K to exchange AC until the switch unit 3 is turned on from an arbitrary time point. The number of polarity changes is counted, and the odd / even of the number of polarity changes is stored. Then, the signal processing unit 2I performs signal processing such as detecting a heater disconnection from the detection output of the current detection unit 2H, and the odd number (polarity change number) of the previous polarity change number of the switch unit 3 from the count detection unit 2L. Is an odd number or an odd number) and the odd number / even number of the current polarity change number, and when the previous and current number of polarity change numbers do not match, the switch part 3 is allowed to be turned on this time, and when it matches, it is prohibited. It is like that.

  In this embodiment, the zero-cross detection unit 2K, the count detection unit 2L, and the signal processing unit 2I, from an arbitrary point in time, the odd number of the alternating polarity change number when the switch unit 3 was turned on last time, and the current polarity change number The control circuit 20 is configured to perform control to allow the switch unit 3 to be turned on this time when it does not coincide with the odd-even number, and to perform control to prohibit the switch unit 3 from being turned on when it matches.

  This control circuit 20 also performs the following flag update control with respect to the setting of the polarity flags A and B stored in the count detector 2L. That is, the polarity flag is set to 0 as an initial value. As (Condition 1), when the polarity flag = 0, the switch unit 3 is allowed to be turned on this time, and when the odd number of the power supply polarity change number at the time of the current turn on is an odd number, the polarity flag is set to +1. The polarity flag is set to -1 when the odd / even number of the power supply polarity change number at the time of turning on is an even number. (Condition 2) When the polarity flag is +1 and the odd / even number of the power supply polarity change number at this time is an even number, this time is turned on, and 2 is subtracted from the polarity flag to set the polarity flag to -1. Further, when the power supply polarity at this time is an odd number, this time is prohibited. (Condition 3) When the polarity flag is -1 and the odd / even number of the power supply polarity change number at this time is odd, the current flag is turned on and 2 is added to the polarity flag to set the polarity flag to +1. Further, when the power supply polarity at this time is an even number, this time on is prohibited. A current detection error is output when the polarity flag is other than -1, 0, +1.

  The operation will be described with reference to the flowchart of FIG. However, in the above embodiment, the previous polarity flag A and the current polarity flag B have the half cycle polarity of the AC power supply when the switch unit 3 is turned on. In this embodiment, the previous polarity flag A is an arbitrary value of the switch unit 3. With respect to the odd / even number of the polarity change from the time point to the previous ON time, it is set to +1 (positive) when the odd number is an odd number, and is set to −1 (negative) when the number is even. The current polarity flag B is +1 (positive) when the odd / even number is odd, and is −1 (negative) when the odd number is even, with respect to the odd / even number of the polarity change from the arbitrary time point of the switch unit 3 to the current on state. According to such a definition, the flowchart of FIG. 3 based on the odd / even number of polarity changes is the same as described above, and the details thereof are omitted. Briefly, in steps SUB6 and SUB7, the previous polarity flag A is 0 and is indefinite, but the output is allowed, but the output of the current transformer 6 is not captured. In step SUB11, since the previous polarity flag A is +1 (positive) and the current polarity flag B is -1 (negative), output is permitted in step SUB12, and in step SUB13, the previous polarity flag A is +1 (positive). However, since the current polarity flag B is also +1 (positive), output is prohibited. Further, in step SUB15, since the previous polarity flag A is -1 (negative) and the current polarity flag B is +1 (positive), output is permitted in step SUB16, and in step SUB17, the previous polarity flag A is -1 ( Negative), but since the current polarity flag B is also -1 (negative), output is prohibited.

  Even in this embodiment, the signal processing unit 2I disables the output of the current detection unit 2H when the switch unit 3 is turned on last time and the odd / even number of the AC polarity change number counted from the arbitrary timing is indefinite. It is supposed to be.

  From the above, in the present embodiment as well, in the same manner as in the above embodiment, the switch unit 3 is connected to the input command value X with respect to the closed circuit in which the switch unit 3 is connected between the heater 4 and the AC power source 5. In the power control device 2 that performs on / off control based on (n), the output of the current transformer 6 is taken into the current detection unit 2H, and the signal processing unit 2I detects disconnection based on the detection output of the current detection unit 2H. By doing so, the heater disconnection process can be accurately performed.

It is a schematic block diagram of the temperature control system which concerns on the best form of this invention. It is a flowchart with which it uses for operation | movement description of the form of FIG. It is a detailed flowchart of step ST10 of FIG. It is a figure where it uses for description of the effect with the past and this invention. It is a figure where it uses for description of the effect with the past and this invention. It is a figure where it uses for description of the effect with the past and this invention. It is a figure where it uses for description of the effect with the past and this invention. It is a schematic block diagram of the temperature control system which concerns on the other form of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Temperature controller 2 Power control device 3 Switch part 4 Heater 5 AC power supply 6 Current transformer 7 Temperature sensor 2A Sample hold part 2F Polarity detection part 2G Memory | storage part 2I Signal processing part

Claims (7)

  A control circuit for controlling on / off of a switch unit connected between an AC power source and a load, wherein the polarity of the waveform of the AC power source (AC waveform) at the previous ON time and the current ON state in the switch unit is It is determined whether or not the polarity of the AC waveform is the same. When it is determined that the polarity is not the same, control is performed to allow the switch section to be turned on this time. When it is determined that the polarity is the same, the switch section is turned on this time. A control circuit characterized by performing prohibition control. A polarity detector for detecting the polarity of the AC waveform;
A storage unit that stores the polarity of the AC waveform when the switch unit is turned on from the detection output of the polarity detection unit;
It is determined whether the polarity of the alternating current waveform at the time of previous on in the switch unit stored in the storage unit is the same as the polarity of the alternating current waveform at the time of current on. When it is determined that the polarity is not the same as the polarity of the alternating current waveform at the time of previous ON, the switch unit is allowed to be turned on this time, and when it is determined to be the same, the signal processing unit that prohibits the switch unit from being turned on this time,
The control circuit according to claim 1, further comprising: It has a load current detector that detects load current from the current transformer output,
The signal processing unit detects the disconnection of the load based on the output of the load current detection unit, and when the polarity of the AC waveform when the switch unit was previously turned on is indefinite, the load current detection unit The control circuit according to claim 2, wherein the output is invalidated.   This is a control circuit for controlling on / off of a switch unit connected between an AC power source and a load, and in this switch unit, the odd number and the present of the number of AC polarity changes from the previous arbitrary point in time It is determined whether or not the odd number of the number of polarity changes at the time of ON matches, and when it is determined that they do not match, control is performed to allow the switch unit to be turned ON this time. A control circuit characterized by performing control for prohibiting ON. A zero cross detector for detecting a zero cross of the voltage of the AC power supply;
A count detection unit that counts the number of polarity changes of alternating current until the switch unit is turned on from an arbitrary time point using the zero-cross detection obtained by the zero-cross detection unit, and stores the odd / even number of the polarity change number,
The odd number / even number of the polarity change number at the previous ON time of the switch unit is obtained from the count detection unit, and it is determined whether the odd number / even number of the polarity change number at the previous ON time matches the odd number / even number of the polarity change number at the current ON time. When it is determined that they do not match, a signal processing unit that allows the switch unit to be turned on this time, and when it is determined to match, a signal processing unit that prohibits the switch unit from being turned on this time,
The control circuit according to claim 4, further comprising: It has a load current detector that detects load current from the current transformer output,
The signal processing unit detects the presence or absence of disconnection of the load based on the output of the load current detection unit, and the odd-even number of the number of polarity changes when the switch unit was previously turned on counted from the arbitrary time point is indefinite. 6. The control circuit according to claim 5, wherein the output of the load current detection unit is invalidated. According to the input power command value, the output power command value is output every predetermined cycle of the AC power supply more than a half cycle, and the switch unit connected between the AC power supply and the load is set to the output power command value. A power control device that controls power supply to the load by performing on / off control in response,
An output error accumulating unit for accumulating an error between the output power command value and the input power command value;
An adding unit for adding the input power command value and the output error accumulated value accumulated by the output error accumulating unit;
The addition value added by the adding unit is compared with a threshold value. When the addition value is equal to or greater than the threshold value in this comparison, the output power command value is output as 100%. A comparator to output;
A control circuit according to any one of claims 1 to 6;
A power control apparatus comprising:

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