Electric valve drive circuit and superheat controller

Abstract

To accurately control an electric valve.SOLUTION: An electronic expansion valve drive circuit 8 includes: FETs Q1 to Q4 that turn coils L1 to L4 of an electronic expansion valve 24 on or off based on an excitation signal; a current detection circuit 82 that detects a current flowing through the coils L1 to L4; a triangular wave generation unit 83 that outputs a control signal for controlling the FETs Q1 to Q4 so as to limit a current that flows through the coils L1 to L4 and whose measurement value is detected in a predetermined range based on a measurement value detected by the current detection circuit 82; and a comparison circuit 84. Further, a delay circuit 86 is provided between the comparison circuit 84 and the FETs Q1 to Q4 to delay the control signal.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a drive circuit for an electrically operated valve such as an electronic expansion valve used in a superheat controller or the like. [Background technology]

[0002] Conventionally, refrigeration devices using an electronic expansion valve have been known. This type of refrigeration device calculates the difference (degree of superheat) between the temperature on the outlet side of an evaporator and the temperature on the inlet side of the evaporator in a refrigeration cycle system of the refrigeration device, and controls the opening degree of the electronic expansion valve by, for example, PID control according to the deviation between the measured value of the degree of superheat and a set value (target value) of the degree of superheat (see, for example, Patent Document 1).

[0003] A stepping motor is used in the motor-operated valves such as the electronic expansion valves described above to perform precise opening and closing control. A constant current chopper drive circuit is known as a drive circuit for the stepping motor (step motor) (see, for example, Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4672001 [Patent Document 2] Japanese Utility Model Application Publication No. 60-25400 [Patent Document 3] Japanese Patent Application Publication No. 4-21398 Summary of the Invention [Problem to be solved by the invention]

[0005] In the circuits described in Patent Documents 2 and 3, when the coil of the step motor is switched ON or OFF, the voltage in the circuit may become temporarily unstable, which may cause the circuit to malfunction and prevent precise opening and closing control of the motor-operated valve.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to control a motor-operated valve with high accuracy. [Means for solving the problem]

[0007] The invention made to solve the above problem is characterized by comprising a control unit that outputs an excitation signal for an electric valve, a switching element that switches a coil of the electric valve ON or OFF based on the excitation signal, a current detection unit that detects a current flowing through the coil, a current limiting unit that outputs a control signal to control the switching element so as to limit the current flowing through the coil to a predetermined range based on the current value detected by the current detection unit, and at least one of a first delay circuit that is provided between the current detection unit and the current limiting unit and delays the current value, or a second delay circuit that is provided between the current limiting unit and the switching element and delays the control signal. Effect of the Invention

[0008] According to the present invention, the first delay circuit or the second delay circuit can be used to perform control while avoiding an unstable period when switching the switching element ON or OFF. [Brief description of the drawings]

[0009] [Figure 1] 1 is a diagram showing an example of a refrigeration device using an electronic expansion valve as a motor-operated valve according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic configuration diagram of a controller shown in FIG. [Diagram 3] 3 is a circuit diagram of the electronic expansion valve driving circuit shown in FIG. 2. [Figure 4] 3 is a timing chart of the operation of the electronic expansion valve driving circuit shown in FIG. 2. [Diagram 5] 3 is a modified example of the electronic expansion valve driving circuit shown in FIG. 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A superheat controller and a motor-operated valve control circuit according to one embodiment of the present invention will be described below. Fig. 1 is a diagram showing an example of a refrigeration device using an electronic expansion valve as the motor-operated valve according to this embodiment.

[0011] 1, the cooling device includes an evaporator 21 installed in a freezer 20, a compressor and a condenser in a refrigerator 22, a liquid supply solenoid valve 23, and an electronic expansion valve 24 connected in a ring shape by piping to configure a well-known refrigeration cycle. The electronic expansion valve 24 has, for example, a two-phase unipolar stepping motor, and is driven by an electronic expansion valve drive circuit included in the controller 1.

[0012] In Figure 1, reference numeral 25 denotes an evaporator outlet temperature sensor that measures the temperature on the outlet side of the evaporator 21, reference numeral 26 denotes an evaporator inlet temperature sensor that measures the temperature on the inlet side of the evaporator 21, and reference numeral 27 denotes an inside temperature sensor that measures the temperature inside the freezer 20, and the measurement signals from these sensors are input to the controller 1.

[0013] The controller 1 has a control unit such as a microcomputer, an electronic expansion valve drive circuit, a memory, a display unit, an operation unit, etc., and calculates the difference (degree of superheat) between the evaporator outlet temperature measured by the evaporator outlet temperature sensor 25 and the evaporator inlet temperature measured by the evaporator inlet temperature sensor 26, and outputs an operation signal to the electronic expansion valve 24 to control the opening degree of the electronic expansion valve 24 by PID control according to the deviation between the measured value of the superheat and a set value (target value) of the superheat. That is, the controller 1 functions as a superheat controller according to this embodiment.

[0014] Fig. 2 shows a schematic configuration diagram of the controller 1 shown in Fig. 1. As shown in Fig. 1, the controller 1 includes a power supply 2, a temperature input 1_3, a temperature input 2_4, a temperature input 3_5, a pressure input 6, a control microcomputer 7, and an electronic expansion valve drive circuit 8. Of the configuration shown in Fig. 2, the control microcomputer 7 and the electronic expansion valve drive circuit 8 constitute the motor-operated valve drive circuit according to this embodiment.

[0015] The power supply 2 is supplied with an external power supply (system power supply) such as a commercial power supply, and after converting it into, for example, a DC voltage, supplies it to the control microcomputer 7, the electronic expansion valve drive circuit 8, etc. The temperature input 1_3 is an interface to which an evaporator outlet temperature sensor 25 is connected. The temperature input 2_4 is an interface to which an evaporator inlet temperature sensor 26 is connected. The temperature input 3_5 is an interface to which an in-cabinet temperature sensor 27 is connected. The pressure input 6 is an interface to which a pressure sensor that detects the evaporation pressure on the outlet side of the evaporator 21 is connected.

[0016] The control microcomputer 7 is responsible for the overall control of the controller 1. The control microcomputer 7 generates an excitation signal (operation signal) for controlling the opening degree of the electronic expansion valve 24 based on the data detected by each of the above-mentioned sensors, and outputs the excitation signal to the electronic expansion valve drive circuit 8. As the excitation method, a well-known method such as a 1-2 phase excitation method can be used.

[0017] The electronic expansion valve driving circuit 8 includes a driving circuit 81, a current detection circuit 82, a triangular wave generating unit 83, a comparison circuit 84, and a logic circuit 85.

[0018] The drive circuit 81 has a plurality of switching elements that switch ON / OFF of a plurality of coils (see FIG. 3) in the electronic expansion valve 24, and drives the electronic expansion valve 24. The current detection circuit 82 detects the current flowing through a coil that is switched ON among the plurality of coils. The triangular wave generation unit 83 generates a triangular wave as a reference waveform to be compared with the current value detected by the current detection circuit 82 in a comparison circuit 84 described later. Note that, although a triangular wave is described as the reference waveform in this embodiment, a sawtooth wave, a sine wave, or the like may also be used.

[0019] The comparison circuit 84 compares the triangular wave generated by the triangular wave generation unit 83 with the current value detected by the current detection circuit 82. The logic circuit 85 calculates the logical product (AND) of the output of the comparison circuit 84 and the excitation signal.

[0020] 3 shows a circuit diagram of the electronic expansion valve drive circuit 8. The drive circuit 81 includes field effect transistors (FETs) Q1-Q4 and diodes D1-D4. The drain of the FET Q1 is connected to the coil L1 of the electronic expansion valve 24 and the anode of the diode D1, the source is connected to a resistor R6 of the current detection circuit 82, and the gate is connected to a resistor R23 of the delay circuit 86, which will be described later. The drain of the FET Q2 is connected to the coil L2 of the electronic expansion valve 24 and the anode of the diode D2, the source is connected to the resistor R6 of the current detection circuit 82, and the gate is connected to a resistor R24 ​​of the delay circuit 86, which will be described later.

[0021] The drain of the FET Q3 is connected to the coil L3 of the electronic expansion valve 24 and the anode of the diode D3, the source is connected to the resistor R1 of the current detection circuit 82, and the gate is connected to the resistor R25 of the delay circuit 86. The drain of the FET Q4 is connected to the coil L4 of the electronic expansion valve 24 and the anode of the diode D4, the source is connected to the resistor R1 of the current detection circuit 82, and the gate is connected to the resistor R26 of the delay circuit 86.

[0022] The anode of diode D1 is connected to the drain of FET Q1, and the cathode is connected to power supply 2. The anode of diode D2 is connected to the drain of FET Q2, and the cathode is connected to power supply 2. The anode of diode D3 is connected to the drain of FET Q3, and the cathode is connected to power supply 2. The anode of diode D4 is connected to the drain of FET Q4, and the cathode is connected to power supply 2.

[0023] The current detection circuit 82 includes resistors R1-R10, capacitors C1 and C2, and operational amplifiers A1 and A2. Here, in the current detection circuit 82, a circuit including resistors R1-R5, capacitor C1, and operational amplifier A1 detects currents corresponding to coils L3 and L4 (B phase and B bar phase) of the electronic expansion valve 24. And a circuit including resistors R6-R10, capacitor C2, and operational amplifier A2 detects currents corresponding to coils L1 and L2 (A phase and A bar phase) of the electronic expansion valve 24.

[0024] Resistor R1 is a current detection resistor that detects the current flowing through coils L3 and L4 as a voltage value. Resistor R6 is a current detection resistor that detects the current flowing through coils L1 and L2 as a voltage value. Moreover, operational amplifier A1 amplifies and outputs the voltage value (measured value) detected by resistor R1. Moreover, operational amplifier A2 amplifies and outputs the voltage value (measured value) detected by resistor R6. These operational amplifiers A1 and A2 are provided at the output terminal of the current detection circuit 82, and amplify and offset the change in the measured value in accordance with the triangular wave, thereby reducing the effects of noise, etc., and ensuring stable operation.

[0025] The triangular wave generating section 83 includes resistors R15 to R18, a capacitor C3, and an operational amplifier A5. The triangular wave generating section 83 configures a well-known integrating circuit using these elements, and outputs a triangular wave.

[0026] The comparison circuit 84 includes resistors R11 to R14 and operational amplifiers A3 and A4. Here, in the comparison circuit 84, a circuit including resistors R11 and R12 and an operational amplifier A3 compares the measurement value detected by the current detection resistor R1 with the triangular wave output from the triangular wave generating unit 83. Then, a circuit including resistors R13 and R14 and an operational amplifier A4 compares the measurement value detected by the current detection resistor R6 with the triangular wave output from the triangular wave generating unit 83. In other words, the operational amplifiers A3 and A4 function as comparators.

[0027] The logic circuit 85 includes resistors R19 to R22 and FETs Q5 to Q8. The logic circuit 85 is a circuit including resistor R19 and FET Q5, which calculates the logical product of the excitation signal (A-phase) output from the control microcomputer 7 and the output of the operational amplifier A4 constituting the comparison circuit 84. Also, a circuit including resistor R20 and FET Q6 calculates the logical product of the excitation signal (A-phase) output from the control microcomputer 7 and the output of the operational amplifier A4 constituting the comparison circuit 84. Also, a circuit including resistor R21 and FET Q7 calculates the logical product of the excitation signal (B-phase) output from the control microcomputer 7 and the output of the operational amplifier A3 constituting the comparison circuit 84. Also, a circuit including resistor R22 and FET Q8 calculates the logical product of the excitation signal (B-phase) output from the control microcomputer 7 and the output of the operational amplifier A3 constituting the comparison circuit 84.

[0028] The electronic expansion valve drive circuit 8 further includes a delay circuit 86. The delay circuit 86 is provided between the logic circuit 85 and the drive circuit 81. The delay circuit 86 includes resistors R23 to R26 and capacitors C4 to C7. The resistor R23 is provided between the resistor R19 of the logic circuit 85 and the FET Q1 of the drive circuit 81. The resistor R24 ​​is provided between the resistor R20 of the logic circuit 85 and the FET Q2 of the drive circuit 81. The resistor R25 is provided between the resistor R21 of the logic circuit 85 and the FET Q3 of the drive circuit 81. The resistor R26 is provided between the resistor R22 of the logic circuit 85 and the FET Q4 of the drive circuit 81.

[0029] The capacitor C4 is provided between the resistor R23 and the FET Q1 and the ground. The capacitor C5 is provided between the resistor R24 ​​and the FET Q2 and the ground. The capacitor C6 is provided between the resistor R25 and the FET Q3 and the ground. The capacitor C7 is provided between the resistor R26 and the FET Q4 and the ground.

[0030] When the coils L1 to L4 are turned ON or OFF by the FETs Q1 to Q4, the ground potential and the like in the electronic expansion valve drive circuit 8 becomes unstable, which may result in noise generation and malfunction of the comparison circuit 84. Therefore, in order to prevent the drive circuit 81 from operating due to a signal during the unstable period, the output of the logic circuit 85 is delayed by the delay circuit 86 and input to the drive circuit 81. This delay circuit 86 is a circuit formed of a resistor and a capacitor that makes the switching of the control signal, which is the output of the logic circuit 85, gentler, thereby slowing down the waveform and delaying it.

[0031] 3, FETs Q1 to Q4 are each turned ON or OFF based on an excitation signal generated based on the calculation result in the control microcomputer 7. When the FETs Q1 to Q4 are turned ON, a current flows through the coils L1 to L4 of the electronic expansion valve 24. That is, the FETs Q1 to Q4 function as switching elements that switch the coils of the electronic expansion valve 24 (motorized valve) ON or OFF.

[0032] For example, the current flowing through coil L4 is detected as a voltage value by current detection resistor R1, and the detected voltage value (measured value) is amplified by operational amplifier A1 and then input to the non-inverting input terminal of operational amplifier (comparator) A3 of comparison circuit 84. Meanwhile, a triangular wave generated by triangular wave generating unit 83 is input to the inverting input terminal of comparator A3. When the measured value becomes higher than the level of the triangular wave, the output of comparator A3 becomes low level. When the output of comparator A3 becomes low level, the output of logic circuit 85 becomes low level by logical AND operation, and after a predetermined delay time in delay circuit 86, FET Q4 turns OFF. Then, when the measured value becomes lower than the level of the triangular wave, the output of comparator A3 becomes high level and FET Q4 turns ON.

[0033] That is, the current detection circuit 82 functions as a current detection unit that detects the current flowing through the coil of each phase. Also, the comparison circuit 84 functions as a current limiting unit that outputs a control signal to control the FETs Q1 to Q4 (switching elements) based on the current value detected by the current detection circuit 82 (current detection unit) so as to limit the current flowing through the coil whose current value was detected to a predetermined range.

[0034] Here, the operation of the comparison circuit 84 according to this embodiment will be described with reference to Fig. 4. Fig. 4 is a timing chart showing a triangular wave W and a measured value Vc. ON and OFF at the bottom of Fig. 4 indicate ON and OFF of FETs Q1 to Q4.

[0035] The triangular wave W is generated by the triangular wave generating unit 83, and is a triangular waveform that repeatedly increases and decreases at a constant rate of increase and decrease between a predetermined minimum potential and maximum potential. When the measured value Vc is equal to or greater than the maximum potential, the duty of the control signal output by the comparison circuit 84 (comparators A3 and A4) is 0% (always OFF), and when the measured value Vc is equal to or less than the minimum potential, the duty of the control signal is 100% (always ON). When the measured value Vc is lower than the triangular wave W, the control signal output by the comparison circuit 84 is at a high level, and when the measured value Vc is higher than the triangular wave W, the control signal is at a low level. Therefore, when the measured value Vc is between the minimum potential and maximum potential of the triangular wave W, the duty becomes smaller (the ON period becomes shorter) as the measured value Vc approaches the maximum potential, and the duty becomes larger (the ON period becomes longer) as the measured value Vc approaches the minimum potential.

[0036] The maximum value of the measured value shown in FIG. 4 is a voltage corresponding to the maximum value of the current that can be supplied from the power source 2. In this embodiment, when the maximum potential of the triangular wave W is exceeded, the duty becomes 0%, so that the current of the maximum value of the measured value shown in FIG. 4 does not flow through the coil L4, etc. In other words, when the maximum value of the measured value exceeds the maximum potential of the triangular wave W, the duty becomes 0% before the measured value reaches the maximum value. When the maximum value of the measured value is equal to the maximum potential of the triangular wave W, the measured value becomes the maximum value and the duty becomes 0%. When the maximum value of the measured value is less than the maximum potential of the triangular wave W, the duty does not become 0% even when the measured value becomes the maximum value, but becomes greater than 0%. The relative relationship between the maximum value of the measured value and the maximum potential of the triangular wave W may be any of the above cases.

[0037] The minimum value of the measured value shown in FIG. 4 is a voltage corresponding to the minimum value of the current detected by the current detection resistors R1 and R6. This minimum value of the measured value is usually a voltage value indicating 0A. If the minimum value of the measured value exceeds the minimum potential of the triangular wave W, the duty will be less than 100% even if the measured value is the minimum value. If the minimum value of the measured value is equal to the minimum potential of the triangular wave W, the duty will be 100% when the measured value is the minimum value. If the minimum value of the measured value is less than the minimum potential of the triangular wave W, the duty will be 100% up to the minimum potential even if the measured value exceeds the minimum value. The relative relationship between the minimum value of the measured value and the minimum potential of the triangular wave W may be in any of the above cases. In other words, the amplitude of the triangular wave W is appropriately determined according to the range of the current to be passed through the coil and the relationship between the maximum and minimum values ​​of the measured value described above.

[0038] That is, the comparison circuit 84 functions as a current limiting section that controls the FETs Q1 to Q4 (switching elements) based on the current value detected by the current detection circuit 82 so as to limit the current flowing through the coil to a predetermined range.

[0039] According to this embodiment, the control microcomputer 7 outputs an excitation signal for the electronic expansion valve 24. The electronic expansion valve drive circuit 8 includes FETs Q1-Q4 for switching the coils L1-L4 of the electronic expansion valve 24 ON or OFF based on the excitation signal, a current detection circuit 82 for detecting the current flowing through the coils L1-L4, and a comparison circuit 84 for outputting a control signal for controlling the FETs Q1-Q4 based on the measured value detected by the current detection circuit 82 so as to limit the current flowing through the coils L1-L4 whose measured value has been detected to a predetermined range. The electronic expansion valve drive circuit 8 further includes a delay circuit 86 that is provided between the comparison circuit 84 and the FETs Q1-Q4 and delays the control signal.

[0040] By configuring the electronic expansion valve drive circuit 8 as described above, the delay circuit 86 allows the comparison circuit 84 to control the FETs Q1 to Q4 while avoiding the unstable time period immediately after the coils L1 to L4 change to ON or OFF. In addition, the comparison circuit 84 can prevent currents more than necessary from flowing through the coils L1 to L4.

[0041] Also, operational amplifiers A3 and A4 are provided for comparing the triangular wave generated by the triangular wave generating unit 83 with the current value detected by the current detecting circuit 82, and the control signal for controlling the FETs Q1 to Q4 is a signal based on the output signal of the operational amplifiers A3 and A4 (logical AND with the excitation signal). In this way, the comparator circuit 84 can operate to limit the current, and it is possible to prevent a current more than necessary from flowing through the coils L1 to L4.

[0042] In addition, because a triangular wave is used as the reference waveform, it is possible to limit the current in proportion to the current flowing through the coil L1, etc. Therefore, the strength of the limit can be adjusted to match the current flowing through the coil, etc., and driving can be continued.

[0043] In addition, the current detection circuit 82 has operational amplifiers A1 and A2 at its output terminals, so that the voltage value detected by the current detection resistors R1 and R6 can be amplified or offset, thereby reducing the influence of noise and the like in the comparison circuit 84, making it possible to perform stable judgments that are less susceptible to malfunction. This makes it possible to use inexpensive resistors for the current detection resistors R1 and R6.

[0044] In the circuit shown in FIG. 3, the delay circuit 86 is provided between the logic circuit 85 and the drive circuit 81, but it may be provided between the current detection circuit 82 and the comparison circuit 84.

[0045] Fig. 5 shows an example in which a delay circuit is provided between the current detection circuit 82 and the comparison circuit 84. In Fig. 5, the delay circuit 86 is deleted. Instead, delay circuits 87a and 87b are added. The delay circuit 87b includes resistors R27 and R28 connected in series between the current detection resistor R1 and the operational amplifier A1, and a capacitor C8 connected in parallel with the current detection resistor R1. The delay circuit 87a includes resistors R29 and R30 connected in series between the current detection resistor R6 and the operational amplifier A2, and a capacitor C9 connected in parallel with the current detection resistor R6.

[0046] That is, the delay circuits 87a and 87b shift and delay the timing of the comparison judgment with the triangular wave in the comparison circuit 84. Therefore, the comparison judgment of the comparison circuit 84 is made based on the measurement value after the stable period, regardless of the measurement value of the current detection resistors R1 and R6 during the unstable period described above. The delay circuits 87a and 87b may be provided in the subsequent stage of the operational amplifiers A1 and A2. In short, it is only necessary to delay the input side (measurement value) of the comparison circuit 84. In the case of FIG. 5, it is possible to operate the comparison circuit 84 while avoiding the unstable period.

[0047] Moreover, both the delay circuits 86 and 87a and 87b may be provided, which can further reduce the influence of noise.

[0048] The present invention is not limited to the above-described embodiment. In other words, a person skilled in the art can implement various modifications according to conventional knowledge without departing from the gist of the present invention. As long as the motor-operated valve drive circuit and superheat controller of the present invention are included in the scope of the present invention, even if the modifications are made, they will of course be included in the scope of the present invention. [Explanation of symbols]

[0049] 1 Controller (superheat controller) 24 Electronic expansion valve (motorized valve) 7 Control microcomputer (control unit, motorized valve drive circuit) 8 Electronic expansion valve drive circuit (motorized valve drive circuit) 81 Drive circuit 82 Current detection circuit 83 Triangular wave generator 84 Comparison circuit (current limiter) 85 Logic Circuits 86 Delay circuit (second delay circuit) 87a Delay circuit (first delay circuit) 87b Delay circuit (first delay circuit) A1, A2 Op-amp (amplifier circuit) A3, A4 Op-amp (comparator) L1~L4 coils Q1~Q4 FET (switching element)

Claims

1. A control unit that outputs an excitation signal for the motor-operated valve; a switching element that switches a coil of the motor-operated valve between ON and OFF based on the excitation signal; A current detection unit that detects a current flowing through the coil; a current limiting unit that outputs a control signal for controlling the switching element so as to limit the current flowing through the coil to a predetermined range based on the current value detected by the current detection unit; At least one of a first delay circuit provided between the current detection unit and the current limiting unit to delay the current value, and a second delay circuit provided between the current limiting unit and the switching element to delay the control signal; An electric valve drive circuit comprising:

2. the current limiting unit includes a comparator that compares a reference waveform with the current value, 2. The motor-operated valve drive circuit according to claim 1, wherein the control signal is based on an output signal of the comparator.

3. 3. The motor-operated valve drive circuit according to claim 2, wherein the reference waveform is a triangular wave.

4. 2. The motor-operated valve drive circuit according to claim 1, wherein the current detection section has an amplifier circuit at an output terminal.

5. A superheat controller comprising the motor-operated valve drive circuit according to any one of claims 1 to 5.

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