Motor control device for grain dryer

Abstract

The utility model discloses a motor control device for a grain dryer. The motor control device comprises a full-bridge rectification circuit; the full-bridge rectification circuit is electrically connected with the signal amplification circuit; the voltage signal amplified by the signal amplification circuit is input into the protection circuit; according to the utility model, a traditional thermal relay is replaced, the current protection circuit is integrated on the PCB, different protection circuit schemes can be flexibly selected according to the cost or the installation area space, the size of a control system is reduced, the working current is monitored in real time through the current transformer, accurate control of the motor is realized, and overload and overheating conditions are avoided.

Description

Technical Field

[0001] The utility model belongs to the technical field of safety protection circuits, in particular to a motor control device for a grain dryer. Background Art

[0002] Traditional grain dryers often use thermal relays as output protection components for electronic controls. These relays utilize the thermal effect of induced current. When the dryer current exceeds a set value, the internal bimetallic strip bends due to heat, triggering the contact to open, cutting off power and protecting the dryer.

[0003] However, using thermal relays solely for grain dryer motor control output protection has certain limitations. It fails to provide other important protection features, such as overcurrent protection. In the complex operating environment of a grain dryer, a single overload protection feature may not be sufficient to fully protect the motor from various faults. Utility Model Content

[0004] The utility model aims to solve at least one of the technical problems in the prior art. To this end, the utility model proposes a motor control device for a grain dryer.

[0005] To achieve the above-mentioned object, according to an embodiment of the first aspect of the present utility model, a motor control device for a grain dryer is provided, comprising: a full-bridge rectifier circuit;

[0006] The full-bridge rectifier circuit is electrically connected to the signal amplifying circuit;

[0007] The voltage signal amplified by the signal amplifying circuit is input into the protection circuit.

[0008] Further: the signal amplification circuit includes an operational amplifier U1.1;

[0009] The operational amplifier U1.1 outputs an amplified voltage signal.

[0010] Furthermore: the protection circuit includes two types: one is a protection circuit composed of an overcurrent protection circuit and an overload protection circuit in parallel; the other is a protection circuit composed of an analog-to-digital converter U11 and a single-chip microcomputer U12.

[0011] Furthermore: the full-bridge rectifier circuit is composed of six diodes forming a rectifier bridge and electrically connected to three current transformers;

[0012] The turns ratio of the current transformer is set to 1:2000;

[0013] The rectifier bridge converts the three-phase AC signal passing through the current transformer into a DC signal. After rectification, the rectifier bridge converts the current into a voltage signal through a resistor R1. At the same time, a capacitor C1 is connected in parallel with the resistor R1 to smooth the output voltage, ensuring that the subsequent circuit can receive a stable DC voltage signal.

[0014] The DC voltage signal output by the full-bridge rectifier circuit is input to the positive input terminal of the operational amplifier U1.

[0015] Furthermore: one end of the negative input terminal of the operational amplifier U1.1 is grounded via a resistor R3, and the other end is connected to the output terminal via a resistor R4 to form negative feedback;

[0016] The ratio of resistor R3 to resistor R4 determines the amplification factor of the output voltage of the operational amplifier;

[0017] In order to prevent the operational amplifier from oscillating, a capacitor C2 is connected in parallel with the resistor R4;

[0018] The output of the operational amplifier is connected to a resistor R5 and then to ground through a capacitor C3;

[0019] The purpose is to form an RC heavy circuit for delay filtering to further improve the stability of the output voltage.

[0020] Furthermore: the overcurrent protection circuit includes: a voltage comparator U3.1;

[0021] The positive input terminal of the voltage comparator U3.1 is connected to the reference voltage output by the precision reference voltage source U2 and the output terminal of the operational amplifier through two resistors R6 and R7, respectively, forming a positive feedback structure and constituting a Schmitt trigger;

[0022] When the signal amplified by the signal amplifying circuit exceeds the upper threshold of the Schmitt trigger, the overcurrent protection signal is triggered.

[0023] Further: the overload protection circuit includes: an integration circuit;

[0024] The integration circuit is composed of an operational amplifier U5.1, an integration capacitor C4, an integration resistor R8, and a bias resistor R9. The purpose of providing a bias resistor R9 is to prevent voltage saturation.

[0025] The inverting input of the operational amplifier U5.1 is connected to a precision reference voltage source U4 through an integrating resistor R8. At the same time, an integrating capacitor C4 is connected across the inverting input and output terminals, and a bias resistor R9 is connected in parallel with the integrating capacitor C4.

[0026] The non-inverting input terminal of the operational amplifier U5.1 is connected to the voltage signal amplified by the operational amplifier U1.1 through the resistor R10. When the voltage signal amplified by the operational amplifier U1.1 exceeds the set threshold and lasts for a specified time, the voltage on the integrating capacitor C4 will gradually rise.

[0027] The output of the integrating circuit is connected to a Schmitt trigger consisting of a voltage comparator U6.1;

[0028] When the voltage on the integrating capacitor C4 rises to the upper threshold of the Schmitt trigger, the overload protection signal is triggered.

[0029] Furthermore: the AINO port of the analog-to-digital converter U11 receives the voltage signal amplified by the operational amplifier U1.1;

[0030] The VDD port of the analog-to-digital converter U11 outputs a digital signal converted from an analog voltage signal to the VCC port of the microcontroller U12.

[0031] Furthermore: the single chip microcomputer U12 has a built-in integrator algorithm;

[0032] The integrator algorithm includes an overcurrent protection algorithm, which specifically compares the current collected by the current collection sensor with a preset threshold;

[0033] The integrator algorithm also includes an overvoltage protection algorithm. The overload protection algorithm specifically accumulates and calculates the current collected by the current acquisition sensor, calculates the cumulative effect of the current over time, that is, the thermal stress state of the equipment, and starts accumulating when the current exceeds a preset threshold. When the accumulated value exceeds the specified range of the equipment, it indicates that the equipment is in an overload state.

[0034] The beneficial effects of the utility model are:

[0035] 1. Space saving: Instead of traditional thermal relays, the current protection circuit is integrated on the PCB. Different protection circuit solutions can be flexibly selected according to cost or installation area space, reducing the size of the control system.

[0036] 2. Precise control: The current transformer monitors the working current in real time to achieve precise control of the motor and avoid overload and overheating. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0038] Figure 1 It is a structural diagram of the utility model;

[0039] Figure 2This is the full-bridge rectifier circuit diagram of the utility model;

[0040] Figure 3 This is a signal amplifying circuit diagram of the iron remover of the present utility model;

[0041] Figure 4 This is the overcurrent protection circuit diagram of the utility model;

[0042] Figure 5 This is the overload protection circuit diagram of the utility model;

[0043] Figure 6 This is a protection circuit diagram composed of the analog-to-digital converter U11 and the single-chip microcomputer U12 of the utility model;

[0044] Figure 7 This is a structural diagram of a specific embodiment of the present invention;

[0045] Figure 8 This is a structural diagram of the second specific embodiment of the present utility model. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0047] like Figure 1 As shown, a structural diagram of a motor control device for a grain dryer includes: a full-bridge rectifier circuit; a signal amplifying circuit electrically connected to the full-bridge rectifier circuit; and a voltage signal amplified by the signal amplifying circuit input into a protection circuit.

[0048] Specifically:

[0049] The signal amplification circuit includes an operational amplifier U1.1; the operational amplifier U1.1 outputs the amplified voltage signal; the protection circuit includes two types: one is a protection circuit composed of an overcurrent protection circuit and an overload protection circuit in parallel; the other is a protection circuit composed of an analog-to-digital converter U11 and a single-chip microcomputer U12.

[0050] The acquisition circuit collects the current internal voltage / current of the grain dryer to the Figure 2The full-bridge rectifier circuit shown in FIG. 1 is composed of six diodes D1 to D6 forming a rectifier bridge electrically connected to three current transformers L1 to L3. The turns ratio of the current transformers L1 to L3 is set to 1:2000. The rectifier bridge converts the three-phase AC power signal passing through the current transformers L1 to L3 into a DC power signal. After rectification, the rectifier bridge converts the current into a voltage signal through a resistor R1. A capacitor C1 is connected in parallel with the resistor R1 to smooth the output voltage.

[0051] The DC voltage signal output by the full-bridge rectifier circuit is input to Figure 3 The positive input terminal of the operational amplifier U1.1 in the signal amplification circuit shown in the figure, in the signal amplification circuit, one end of the negative input terminal of the operational amplifier U1.1 is grounded through a resistor R3, and the other end is connected to the output terminal through a resistor R4 to form negative feedback; the ratio of resistor R3 to resistor R4 determines the amplification factor of the output voltage of the operational amplifier; in order to prevent the operational amplifier from oscillating, a capacitor C2 is also connected in parallel to the resistor R4; the output terminal of the operational amplifier is connected to a resistor R5 and then to the ground through a capacitor C3, forming an RC heavy circuit for delay filtering to further improve the stability of the output voltage.

[0052] See also Figure 4 、 Figure 5 and Figure 7 , which is an overcurrent protection circuit, an overload protection circuit and the structure of embodiment 1 in a protection circuit of a specific embodiment of the utility model;

[0053] The voltage signal amplified by the signal amplifying circuit is input into the protection circuit. The protection circuit of this embodiment includes an overcurrent protection circuit and an overload protection circuit.

[0054] The amplified voltage signal is input to Figure 4 The negative input terminal of voltage comparator U3.1 in the overcurrent protection circuit shown; the positive input terminal of voltage comparator U3.1 is connected to the reference voltage output of precision reference voltage source U2 and the output terminal of the operational amplifier through two resistors R6 and R7, respectively, forming a positive feedback structure, forming a Schmitt trigger. This structure can avoid oscillation near the threshold value, thereby preventing false operation; when the amplified signal exceeds the upper threshold of the Schmitt trigger, the overcurrent protection signal is triggered.

[0055] The amplified voltage signal is also input into Figure 5In the integration circuit of the overload protection circuit shown, the output of the integration circuit is connected to a Schmitt trigger composed of a voltage comparator U6.1; this integration circuit is composed of an operational amplifier U5.1, an integration capacitor C4, an integration resistor R8 and a bias resistor R9 (to prevent saturation); the inverting input terminal of the operational amplifier is connected to a precision reference voltage source U4 through the integration resistor R8, and the integration capacitor C4 is connected between the inverting input terminal and the output terminal of the operational amplifier U5.1; the non-inverting input terminal of the operational amplifier U5.1 is connected to the voltage signal amplified by the operational amplifier U1 through the resistor R10; that is, when the input signal (here is the current signal amplified by the signal amplification circuit) exceeds the set threshold and lasts for the set time, the voltage on the integration capacitor C4 will gradually rise, and when the upper threshold of the Schmitt trigger is triggered, the overload protection signal is triggered.

[0056] See also Figure 6 and Figure 8 , is a protection circuit diagram composed of an analog-to-digital converter U11 and a single-chip microcomputer U12 in another specific embodiment of the present invention and the structure of the second embodiment;

[0057] The single-chip computer U12 reads the current data transmitted by the analog-to-digital converter U11 in real time and compares it with the preset maximum current value of the grain dryer electronic control system; if it detects that the current value at any moment exceeds the threshold, the single-chip computer U12 will immediately trigger the overcurrent protection signal;

[0058] Microcontroller U12 has a built-in integrator algorithm. This algorithm integrates the current values ​​(expressed as voltage) continuously input by analog-to-digital converter U11 to accumulate the current's effect over time, thereby reflecting the device's load. When the voltage value (representing the current) read by microcontroller U12 exceeds a set starting threshold, indicating that the device is beginning to experience a heavy load, the integrator program begins positive integration. Over time, the integral value gradually accumulates. Once the integral value reaches the preset overload protection threshold, microcontroller U12 immediately triggers the overload protection signal.

[0059] The above embodiments are only used to illustrate the technical method of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical method of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical method of the present invention.

Claims

1. A motor control device for a grain dryer, characterized in that: include: Full-bridge rectifier circuit; The full-bridge rectifier circuit is electrically connected to the signal amplifying circuit; The voltage signal amplified by the signal amplifying circuit is input into the protection circuit; The full-bridge rectifier circuit is composed of six diodes forming a rectifier bridge and three current transformers electrically connected; The turns ratio of the current transformer is set to 1:2000; The rectifier bridge converts the three-phase AC signal passing through the current transformer into a DC signal; after rectification, the rectifier bridge converts the current into a voltage signal through a resistor R1, and a capacitor C1 is connected in parallel with the resistor R1 to smooth the output voltage; The DC voltage signal output by the full-bridge rectifier circuit is input to the positive input terminal of the operational amplifier U1.

1.

2. A motor control device for a grain dryer according to claim 1, characterized in that: The signal amplification circuit includes an operational amplifier U1.1; The operational amplifier U1.1 outputs an amplified voltage signal.

3. The motor control device for a grain dryer according to claim 1, characterized in that: The protection circuits include two types: one is a protection circuit composed of an overcurrent protection circuit and an overload protection circuit in parallel; the other is a protection circuit composed of an analog-to-digital converter U11 and a single-chip microcomputer U12.

4. The motor control device for a grain dryer according to claim 2, characterized in that: One end of the negative input terminal of the operational amplifier U1.1 is grounded via a resistor R3, and the other end is connected to the output terminal via a resistor R4 to form negative feedback; The ratio of resistor R3 to resistor R4 determines the amplification factor of the output voltage of the operational amplifier; In order to prevent the operational amplifier from oscillating, a capacitor C2 is connected in parallel with the resistor R4; The output of the operational amplifier is connected to a resistor R5 and then to ground through a capacitor C3.

5. The motor control device for a grain dryer according to claim 3, characterized in that: The overcurrent protection circuit includes: a voltage comparator U3.1; The positive input terminal of the voltage comparator U3.1 is connected to the reference voltage output by the precision reference voltage source U2 and the output terminal of the operational amplifier through two resistors R6 and R7, respectively, forming a positive feedback structure and constituting a Schmitt trigger; When the signal amplified by the signal amplifying circuit exceeds the upper threshold of the Schmitt trigger, the overcurrent protection signal is triggered.

6. The motor control device for a grain dryer according to claim 3, characterized in that: The overload protection circuit includes: an integration circuit; The integration circuit is composed of an operational amplifier U5.1, an integrating capacitor C4, an integrating resistor R8 and a bias resistor R9; The inverting input of the operational amplifier U5.1 is connected to a precision reference voltage source U4 through an integrating resistor R8. At the same time, an integrating capacitor C4 is connected across the inverting input and output terminals, and a bias resistor R9 is connected in parallel with the integrating capacitor C4. The non-inverting input terminal of the operational amplifier U5.1 is connected to the voltage signal amplified by the operational amplifier U1.1 through the resistor R10. When the voltage signal amplified by the operational amplifier U1.1 exceeds the set threshold and lasts for a specified time, the voltage on the integrating capacitor C4 will gradually rise. The output of the integrating circuit is connected to a Schmitt trigger consisting of a voltage comparator U6.1; When the voltage on the integrating capacitor C4 rises to the upper threshold of the Schmitt trigger, the overload protection signal is triggered.

7. The motor control device for a grain dryer according to claim 3, characterized in that: The AINO port of the analog-to-digital converter U11 receives the voltage signal amplified by the operational amplifier U1.1; The VDD port of the analog-to-digital converter U11 outputs a digital signal converted from an analog voltage signal to the VCC port of the microcontroller U12.

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