A method and device for protecting an electric motor
By configuring current transformers in the three phases of the motor and outputting two signals for overcurrent and phase loss detection, the problem of slow response of existing motor protectors is solved, achieving faster fault identification and higher safety.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANPING JIANYANG DISTRICT PORT AN ELECTRONIC TECH CO LTD
- Filing Date
- 2026-01-21
- Publication Date
- 2026-05-26
Smart Images
Figure CN122092151A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of motor protector technology, specifically to a motor protection method and protector. Background Technology
[0002] Motor protectors are used to monitor the operating status of motors in real time. They promptly execute alarms or power cut-off actions to prevent motor damage in the event of electrical and mechanical faults such as overload, phase loss, locked rotor, and short circuit. Overload, locked rotor, and short circuit are directly manifested as overcurrent; therefore, motor protectors typically identify these faults through overcurrent detection circuits.
[0003] Existing motor protectors monitor the current in a specific phase of the motor using a dedicated current transformer. When an overcurrent occurs, the protector outputs an overcurrent signal, prompting the downstream controller to perform control measures such as stopping the motor. However, because overcurrent detection is only available in one phase, it cannot respond promptly if other phases experience overcurrent first. Furthermore, this separate current transformer makes the protector's structure bulky. Summary of the Invention
[0004] One of the objectives of this invention is to provide a motor protection method that aims to improve the problem of slow response of existing motor protectors during overcurrent detection.
[0005] To achieve the above objectives, the present invention adopts the following technical solution:
[0006] A method for protecting an electric motor, comprising:
[0007] Current transformers are configured on each of the three phases of the motor, and each current transformer outputs at least two mutual inductance current signals. The first mutual inductance current signal is input into the overcurrent detection circuit for overcurrent detection. The second mutual inductance current signal is input into the phase loss detection circuit for phase loss detection. The operating state of the motor is controlled based on the detection results of the overcurrent detection and phase loss detection.
[0008] Furthermore, when the overcurrent detection result is an overcurrent signal, the overcurrent signal is fed back to the phase loss detection circuit to block the phase loss detection circuit, so that the overcurrent signal is output before the phase loss signal.
[0009] Furthermore, in the phase loss detection circuit, three comparators are configured to detect the three phases respectively. The output terminal of the first comparator is connected to the input terminal of the second comparator, and the output terminal of the second comparator is connected to the input terminal of the third comparator.
[0010] The second objective of this invention is to provide a motor protector that improves the problem of slow response of existing motor protectors during overcurrent detection.
[0011] To achieve the above objectives, the present invention adopts the following technical solution:
[0012] A motor protector for implementing the aforementioned motor protection method includes: three current transformers, respectively configured on the three phases of the motor, to generate mutual inductance current and output at least two mutual inductance current signals; an overcurrent detection circuit connected to the current transformers, which sequentially rectifies a first mutual inductance current signal, converts it into a first voltage signal, inputs it to a first comparator, compares it with a first reference voltage, and generates an overcurrent detection result; a phase loss detection circuit connected to the current transformers, which sequentially rectifies a second mutual inductance current signal, converts it into a second voltage signal, inputs it to a second comparator, compares it with a second reference voltage, and generates a phase loss detection result; and a controller that controls the operating state of the motor based on the overcurrent detection result and the phase loss detection result.
[0013] Furthermore, the three current transformers include transformer R1, transformer R8, and transformer R11, with the first terminal of each transformer grounded; the overcurrent detection circuit includes diodes D2, D4, and D6, a switching resistor R13, an overcurrent reference, and a comparator U1C. The overcurrent reference is connected to the first input terminal of the comparator U1C. The second terminal of transformer R1, diode D2, and switching resistor R13 are connected in series to the second input terminal of the comparator U1C. The second terminal of transformer R8, diode D4, and switching resistor R13 are connected in series to the second input terminal of the comparator U1C. The second terminal of transformer R11, diode D6, and switching resistor R13 are connected in series to the second input terminal of the comparator U1C.
[0014] Furthermore, the overcurrent detection circuit also includes a capacitor C12, one end of which is grounded and the other end is connected to the second input terminal of the comparator U1C.
[0015] Furthermore, the phase loss detection circuit includes diodes D1, D3, and D5, switching resistors R2, R9, and R12, comparators U1A, U1D, and U1B, and a phase loss reference. The second terminal of transformer R1, diode D1, and switching resistor R2 are connected to the first input terminal of comparator U1A. The second terminal of transformer R8, diode D3, and switching resistor R9 are connected to the first input terminal of comparator U1D. The second terminal of transformer R11, diode D5, and switching resistor R12 are connected to the first input terminal of comparator U1B. The phase loss reference is connected to the second input terminals of comparators U1A, U1D, and U1B, respectively.
[0016] Furthermore, the output of comparator U1A is connected to the first input of comparator U1D, and the output of comparator U1D is connected to the first input of comparator U1B.
[0017] Furthermore, it also includes a feedback circuit, which includes diode D7, diode D9, resistors R5, R7, and R10, transistor Q1, and capacitor C7. Diode D7 is connected in reverse parallel across resistor R13. Resistor R10 is connected to ground and the second terminal of diode D7. Resistor R7 is connected to the second terminal of diode D7 and the base of transistor Q1. Capacitor C7 is connected to the base of transistor Q1 and ground. Resistor R5 is connected to the collector of transistor Q1 and the power supply. Diode D9 is connected to the collector of transistor Q1 and the first terminal of resistor R2.
[0018] Furthermore, the overcurrent reference includes an adjustable resistor W1 and a capacitor C11. The first end of the adjustable resistor W1 is grounded, the second end is connected to the power supply, and the adjustment end is connected to the first input end of U1C. The capacitor C11 is connected in parallel with the second end of the adjustable resistor W1 and the adjustment end.
[0019] By adopting the above technical solution, the present invention has the following advantages compared with the prior art:
[0020] 1. The present invention reuses the current transformer of the phase loss detection circuit, so that the current transformer of each phase outputs two mutual inductance current signals, one for phase loss detection and the other for overcurrent detection. In this way, without increasing the number of components, the response speed of overcurrent detection is improved, and the safety is enhanced.
[0021] 2. Overcurrent can easily cause component burnout, and its harm is greater than that of phase loss. This invention gives overcurrent detection a higher priority. When an overcurrent signal is detected, the overcurrent signal is fed back to the phase loss detection circuit to block the phase loss detection circuit, so that the overcurrent signal takes precedence over the phase loss signal output, thereby improving safety.
[0022] 3. This invention uses a phase loss detection circuit to identify cascaded comparators with three-phase phase loss. That is, the output signal of the front comparator is input to the input terminal of the rear comparator, so that when the level of the front comparator changes, the level of the rear comparator will also change, which enhances the reliability of the logic OR function and reduces the risk of missed detection. Attached Figure Description
[0023] Figure 1 This is a schematic diagram of the motor protection method of the present invention;
[0024] Figure 2 This is a schematic diagram of the overcurrent response process of the present invention;
[0025] Figure 3 This is a schematic diagram of the comparator cascade for phase loss detection in this invention;
[0026] Figure 4 This is a topology diagram of the core circuit of the motor protector of the present invention;
[0027] Figure 5This is a schematic diagram of a specific embodiment of the motor protector of the present invention.
[0028] Explanation of reference numerals in the attached figures:
[0029] Current transformer R1, current transformer R8, current transformer R11;
[0030] Diodes D1, D2, D3, D4, D5, D6, D7, D8, and D9;
[0031] Conversion resistors R2, R9, R13, and R12;
[0032] Comparator U1A, comparator U1B, comparator U1C, comparator U1D;
[0033] Adjustable resistors W1, R3, R4, R5, R7, R8, R10, R15, and R16;
[0034] Capacitors C1, C2, C3, C4, C7, C8, C9, C10, C11, C12, and C14. Detailed Implementation
[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0036] Additionally, it should be noted that the terms "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" are all based on the orientation or positional relationship shown in the accompanying drawings. They are merely for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element of the present invention must have a specific orientation. Therefore, they should not be construed as limitations on the present invention.
[0037] When an element is referred to as being "fixed to," "set on," or "contained on" another element, it can be directly on or indirectly on that other element. When an element is referred to as being "connected to," it can be directly connected to or indirectly connected to that other element.
[0038] Unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances. Example 1
[0039] Please refer to Figure 1 As shown, this invention discloses a method for protecting an electric motor, which includes:
[0040] Current transformers are configured on each of the three phases of the motor, and each current transformer outputs at least two mutual inductance current signals.
[0041] The first mutual inductance current signal is input into the overcurrent detection circuit for overcurrent detection;
[0042] The second mutual inductance current signal is input into the phase loss detection circuit for phase loss detection;
[0043] The operating status of the motor is controlled based on the detection results of overcurrent detection and phase loss detection.
[0044] That is, the present invention splits the output signal of the current transformer used for detecting phase loss in each phase into two paths. One path is still used for phase loss detection, and the other path is used for overcurrent detection. In this way, without adding components, it can immediately respond and output an overcurrent signal when any phase is overcurrent, so that the back-end controller can adjust the motor state in time (such as shutting down the motor), thus improving safety.
[0045] Please refer to Figure 2 As shown, in a preferred embodiment, when the overcurrent detection result is an overcurrent signal, the present invention feeds back the overcurrent signal to the phase loss detection circuit to block the phase loss detection circuit, so that the overcurrent signal is output before the phase loss signal.
[0046] Specifically, it can use NPN transistors for overcurrent signal feedback. The core component of the phase loss detection circuit is a voltage comparator, whose input needs to receive three-phase voltage sampling signals and compare them with a reference voltage to determine whether a phase is missing. The NPN transistor, through its on / off state, directly feeds the overcurrent signal back to the comparator input, thereby changing the validity of the phase loss detection circuit's output signal by altering the level, thus prioritizing overcurrent fault handling and improving safety. For example, assuming the comparator in the phase loss detection circuit requires a high-level signal to trigger phase loss protection, in this case, because the comparator's input is forcibly pulled low, the comparator output directly flips to the unprotected state. Even if the phase loss detection circuit samples a phase loss signal, the comparator cannot recognize it, and the phase loss protection function is completely blocked, ensuring that overcurrent protection is executed first.
[0047] Please refer to Figure 3 As shown, in a preferred embodiment, the present invention configures three comparators for detecting the three phases in the phase loss detection circuit. The output terminal of the first comparator is connected to the input terminal of the second comparator, and the output terminal of the second comparator is connected to the input terminal of the third comparator.
[0048] In this way, the output signal of the front phase comparator will be input to the input terminal of the rear phase comparator, so that when the level of the front phase comparator changes, the level of the rear phase comparator will also change, which enhances the reliability of the logic OR function, reduces the risk of missed detection, and ensures that if any phase is lost, the output signal can be promptly sent to the back-end controller. Example 2
[0049] Please refer to Figure 4 As shown, the present invention also discloses a motor protector for implementing the motor protection method described in Embodiment 1, which includes a current transformer, an overcurrent detection circuit, a phase loss detection circuit, and a controller.
[0050] The system includes three current transformers, each configured on one of the three phases of the motor to generate mutual inductance current. Each current transformer outputs at least two mutual inductance current signals. Connecting the overcurrent detection circuit to the current transformers rectifies the first mutual inductance current signal, converts it into a first voltage signal, and inputs it to a first comparator for comparison with a first reference voltage to generate an overcurrent detection result. Connecting the phase loss detection circuit to the current transformers sequentially rectifies the second mutual inductance current signal, converts it into a second voltage signal, and inputs it to a second comparator for comparison with a second reference voltage to generate a phase loss detection result. Finally, the controller adjusts the motor's operating state based on the overcurrent and phase loss detection results.
[0051] Please refer to Figure 4As shown, in a preferred embodiment, the present invention further includes a feedback circuit. The input terminal of the feedback circuit is connected to the output terminal of the overcurrent detection circuit, and the output terminal of the feedback circuit is connected to the input terminal of the phase loss detection circuit. Thus, when the detection result of the overcurrent detection is an overcurrent signal, the overcurrent signal is fed back to the phase loss detection circuit to change the signal of the phase loss detection circuit, block the phase loss detection circuit, and make the overcurrent signal take precedence over the phase loss signal in the output.
[0052] Please refer to Figure 3 As shown, in a preferred embodiment, the present invention configures three comparators in the phase loss detection circuit to detect the three phases respectively. The output terminal of the first comparator is connected to the input terminal of the second comparator, and the output terminal of the second comparator is connected to the input terminal of the third comparator. This ensures that the output signal of the preceding phase comparator is input to the input terminal of the following phase comparator, thereby changing the level of the following phase comparator when the level of the preceding phase comparator changes. This enhances the reliability of the logic OR function and reduces the risk of missed detections.
[0053] like Figure 5 As shown, a specific implementation example of the present invention is given. For ease of understanding, in polarized electronic components, such as diodes, the first and second terminals are set according to the direction of current flow, i.e., the current flows from the first terminal to the second terminal.
[0054] The circuit includes three current transformers: R1, R8, and R11, with the first terminal of each transformer grounded. The overcurrent detection circuit comprises diodes D2, D4, and D6, a switching resistor R13, an overcurrent reference, and a comparator U1C. The overcurrent reference is connected to the first input terminal of comparator U1C. The second terminal of transformer R1, diode D2, and switching resistor R13 are connected in series to the second input terminal of comparator U1C. Similarly, the second terminal of transformer R8, diode D4, and switching resistor R13 are connected in series to the second input terminal of comparator U1C. Finally, the second terminal of transformer R11, diode D6, and switching resistor R13 are connected in series to the second input terminal of comparator U1C.
[0055] Thus, through the rectification of diodes D2, D4, and D6, and the conversion of switching resistor R13, the first mutual inductance current signal is transformed into a first voltage signal, which is then input into comparator U1C and compared with the first reference voltage to determine whether there is an overcurrent.
[0056] The first reference voltage is generated by an overcurrent reference, which includes an adjustable resistor W1 and a capacitor C11. The first terminal of the adjustable resistor W1 is grounded, the second terminal is connected to a 12V power supply, and the adjustment terminal is connected to the first input terminal of U1C. The capacitor C11 is connected in parallel with the second terminal of the adjustable resistor W1 and the adjustment terminal. Thus, the first reference voltage can be adjusted by adjusting the adjustment terminal of the adjustable resistor W1.
[0057] The first terminal of capacitor C14 is connected to the first terminal of the switching resistor R13, and the second terminal is grounded; the first terminal of capacitor C12 is connected to the second input terminal of comparator U1C, and the second terminal is grounded; thus, the first mutual inductance current signal and the first voltage signal are filtered.
[0058] The phase loss detection circuit includes diodes D1, D3, and D5, switching resistors R2, R9, and R12, comparator U1A, comparator U1D, comparator U1B, and a phase loss reference.
[0059] The second terminal of current transformer R1, diode D1, and switching resistor R2 are connected to the first input terminal of comparator U1A; the second terminal of current transformer R8, diode D3, and switching resistor R9 are connected to the first input terminal of comparator U1D; the second terminal of current transformer R11, diode D5, and switching resistor R12 are connected to the first input terminal of comparator U1B; and the phase loss reference is connected to the second input terminals of comparators U1A, U1D, and U1B respectively.
[0060] Thus, through the rectification of diodes D1, D3, and D5, and the conversion of resistors R2, R9, and R11, the second mutual inductance current signal is transformed into a second voltage signal. This signal is then input into comparators U1A, U1D, and U1B respectively and compared with the second reference voltage to determine whether a phase is missing.
[0061] The output of comparator U1A is connected to the first input of comparator U1D, the output of comparator U1D is connected to the first input of comparator U1B, and the output of U1B is connected to the controller at the back end (not shown in the figure).
[0062] The phase loss reference includes resistor R4, diode D8, and capacitor C9. The first terminal of resistor R4 is connected to a 12V power supply, and the second terminal is input to the inverting inputs of comparators U1A, U1D, and U1B, respectively. The first terminals of diode D8 and capacitor C9 are both grounded, and their second terminals are connected in parallel with the second terminal of resistor R4.
[0063] Thus, the second standard voltage is set by resistor R4, and clamped to the forward voltage drop of diode D8 (in one specific embodiment of this application, a 4148 type diode, approximately 0.7V) by grounding the diode. In this case, diode D8 acts as a voltage regulator, preventing the output reference voltage from being affected by small fluctuations in the power supply. The reference voltage node is susceptible to high-frequency interference from power supply coupling and device thermal noise. The capacitive reactance of capacitor C9 decreases with increasing frequency, allowing high-frequency noise signals to be directly short-circuited to ground, resulting in a smoother output reference voltage and preventing noise-induced false triggering of the voltage comparator. Simultaneously, capacitor C9 can compensate for voltage changes through charging and discharging, maintaining the stability of the reference node voltage.
[0064] Resistor R3 and capacitor C1, resistor R15 and capacitor C2, and resistor R16 and capacitor C3 form three sets of RC filter circuits. One end is grounded, and the other end is connected to the second terminal of diode D1, the second terminal of diode D3, and the second terminal of diode D5, respectively, to filter the signal.
[0065] The first terminals of capacitors C4, C8, and C10 are connected to the first terminals of comparators U1A, U1D, and U1B, respectively, and the second terminals are grounded to filter the signal.
[0066] The feedback circuit includes diodes D7 and D9, resistors R5, R7, and R10, transistor Q1, and capacitor C7. Diode D7 is connected in reverse parallel across resistor R13. Resistor R10 is connected to ground and the second terminal of diode D7. Resistor R7 is connected to the second terminal of diode D7 and the base of transistor Q1. Capacitor C7 is connected to the base of transistor Q1 and ground. Resistor R5 is connected to the collector of transistor Q1 and the power supply. Diode D9 is connected to the collector of transistor Q1 and the first terminal of resistor R2.
[0067] Thus, when an excessive current reaches the second input terminal of comparator U1C, an overcurrent signal is generated. Simultaneously, a signal is output to the base of transistor Q1 through the reverse-biased diode D7. After the transistor is turned on, because the emitter is grounded, the collector potential is clamped to near ground potential (low level). The diode D9 connected in series with the collector is turned on, and the low-level signal is transmitted to the first terminal of the phase loss detection comparator through diode D9. At this time, the comparator needs a high-level signal to trigger the controller's phase loss protection. Since the input terminal of comparator U1A is forcibly pulled low, the output terminal of comparator U1A directly flips to the unprotected state. Even if the phase loss detection circuit samples the phase loss signal, the comparator cannot recognize it, and the phase loss protection function is completely blocked, ensuring that the overcurrent protection is executed first.
[0068] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A method for protecting an electric motor, characterized in that, include: Current transformers are configured on each of the three phases of the motor, and each current transformer outputs at least two mutual inductance current signals. The first mutual inductance current signal is input into the overcurrent detection circuit for overcurrent detection; The second mutual inductance current signal is input into the phase loss detection circuit for phase loss detection; The operating status of the motor is controlled based on the detection results of overcurrent detection and phase loss detection.
2. The motor protection method as described in claim 1, characterized in that: When the overcurrent detection result is an overcurrent signal, the overcurrent signal is fed back to the phase loss detection circuit to block the phase loss detection circuit, so that the overcurrent signal is output before the phase loss signal.
3. The motor protection method as described in claim 1, characterized in that: In the phase loss detection circuit, three comparators are configured to detect the three phases respectively. The output of the first comparator is connected to the input of the second comparator, and the output of the second comparator is connected to the input of the third comparator.
4. A motor protector for implementing the motor protection method as described in claim 1, characterized in that, include: Three current transformers are respectively configured on the three phases of the motor to generate mutual inductance current and output at least two mutual inductance current signals; The overcurrent detection circuit is connected to the current transformer. It sequentially rectifies the first current transformer signal, converts it into a first voltage signal, inputs it to the first comparator, compares it with the first reference voltage, and generates an overcurrent detection result. The phase loss detection circuit is connected to the current transformer. It sequentially rectifies the second current transformer signal, converts it into a second voltage signal, and inputs it to the second comparator to compare it with the second reference voltage, thereby generating the phase loss detection result. The controller controls the motor's operating status based on the overcurrent detection results and phase loss detection results.
5. The motor protector as described in claim 4, characterized in that: The three current transformers include transformer R1, transformer R8 and transformer R11, and the first terminal of each transformer is grounded. The overcurrent detection circuit includes diodes D2, D4, and D6, a switching resistor R13, an overcurrent reference, and a comparator U1C. The overcurrent reference is connected to the first input terminal of the comparator U1C. The second terminal of the current transformer R1, diode D2, and switching resistor R13 are connected in series to the second input terminal of the comparator U1C. The second terminal of the current transformer R8, diode D4, and switching resistor R13 are connected in series to the second input terminal of the comparator U1C. The second terminal of the current transformer R11, diode D6, and switching resistor R13 are connected in series to the second input terminal of the comparator U1C.
6. The motor protector as described in claim 5, characterized in that: The overcurrent detection circuit also includes a capacitor C12, one end of which is grounded and the other end is connected to the second input terminal of the comparator U1C.
7. The motor protector as described in claim 5, characterized in that: The phase loss detection circuit includes diodes D1, D3, and D5, switching resistors R2, R9, and R12, comparators U1A, U1D, and U1B, and a phase loss reference. The second terminal of transformer R1, diode D1, and switching resistor R2 are connected to the first input terminal of comparator U1A. The second terminal of transformer R8, diode D3, and switching resistor R9 are connected to the first input terminal of comparator U1D. The second terminal of transformer R11, diode D5, and switching resistor R12 are connected to the first input terminal of comparator U1B. The phase loss reference is connected to the second input terminals of comparators U1A, U1D, and U1B, respectively.
8. The motor protector as described in claim 7, characterized in that: The output of comparator U1A is connected to the first input of comparator U1D, and the output of comparator U1D is connected to the first input of comparator U1B.
9. The motor protector as described in claim 7, characterized in that: It also includes a feedback circuit, which includes diode D7, diode D9, resistors R5, R7, and R10, transistor Q1, and capacitor C7. Diode D7 is connected in reverse parallel across resistor R13. Resistor R10 is connected to ground and the second terminal of diode D7. Resistor R7 is connected to the second terminal of diode D7 and the base of transistor Q1. Capacitor C7 is connected to the base of transistor Q1 and ground. Resistor R5 is connected to the collector of transistor Q1 and the power supply. Diode D9 is connected to the collector of transistor Q1 and the first terminal of resistor R2.
10. The motor protector as described in claim 5, characterized in that: The overcurrent reference includes an adjustable resistor W1 and a capacitor C11. The first end of the adjustable resistor W1 is grounded, the second end is connected to the power supply, and the adjustment end is connected to the first input end of U1C. The capacitor C11 is connected in parallel with the second end of the adjustable resistor W1 and the adjustment end.