CN110932234A - Common-mode current control device, motor and common-mode current control method thereof - Google Patents
Common-mode current control device, motor and common-mode current control method thereof Download PDFInfo
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- CN110932234A CN110932234A CN201911052456.1A CN201911052456A CN110932234A CN 110932234 A CN110932234 A CN 110932234A CN 201911052456 A CN201911052456 A CN 201911052456A CN 110932234 A CN110932234 A CN 110932234A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/08—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
- G01R19/16566—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533
- G01R19/16571—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533 comparing AC or DC current with one threshold, e.g. load current, over-current, surge current or fault current
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/20—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for electronic equipment
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Abstract
本发明公开了一种共模电流控制装置、电机及其共模电流控制方法，该装置包括：检测单元和控制单元；其中，所述检测单元，用于检测电机的共模电流；所述控制单元，用于确定检测到的共模电流是否大于设定电流、或确定在设定时长内检测到的共模电流的上升速率是否高于设定速率；若检测到的共模电流大于设定电流、或在设定时长内检测到的共模电流的上升速率高于设定速率，则触发预设的保护机制，以实现对电机和电机控制器的保护。本发明的方案，可以解决使用空开或保险管对电机的对地电流进行保护的方式存在成本高的问题，达到降低成本的效果。
The invention discloses a common mode current control device, a motor and a common mode current control method thereof. The device comprises: a detection unit and a control unit; wherein, the detection unit is used to detect the common mode current of the motor; the control The unit is used to determine whether the detected common mode current is greater than the set current, or whether the rising rate of the detected common mode current within the set time period is higher than the set rate; if the detected common mode current is greater than the set current If the rising rate of the current, or the common mode current detected within the set time period is higher than the set rate, a preset protection mechanism is triggered to protect the motor and the motor controller. The solution of the present invention can solve the problem of high cost in the way of using an air circuit breaker or a fuse to protect the ground current of the motor, and achieve the effect of reducing the cost.
Description
Technical Field
The invention belongs to the technical field of motors, and particularly relates to a common-mode current control device, a motor and a common-mode current control method thereof, in particular to a short-circuit protection device for a variable-frequency motor, a motor and a common-mode current control method thereof, such as a short-circuit protection device for a variable-frequency compressor, a compressor and a common-mode current control method thereof.
Background
At present, variable frequency motors are applied to more and more occasions, for example, the air conditioning industry is gradually changing the frequency.
The variable frequency motor can be divided into two parts, one part is a variable frequency controller, namely a frequency converter; the other part is a motor. The variable frequency motor is driven by a frequency converter, and if overlarge current to a floor drain or short circuit to the ground occurs, serious consequences of electrification of a shell and damage of the frequency converter are easily caused.
Because the short-circuit current of the motor to the ground does not flow through the frequency converter, the current common protection scheme for the short-circuit to the ground uses an air switch (namely an air circuit breaker, which is a kind of circuit breaker) or a protective tube to protect the short-circuit of the motor to the ground, but the cost is high.
The above is only for the purpose of assisting understanding of the technical aspects of the present invention, and does not represent an admission that the above is prior art.
Disclosure of Invention
The present invention is directed to provide a common mode current control device, a motor and a common mode current control method thereof, which solve the problem of high cost in the method of protecting the ground current of the motor by using an air switch or a fuse, and achieve the effect of reducing the cost.
The present invention provides a common mode current control device, comprising: a detection unit and a control unit; the detection unit is used for detecting the common-mode current of the motor; the control unit is used for determining whether the detected common mode current is larger than a set current or determining whether the rising rate of the detected common mode current in a set time length is higher than the set rate; if the detected common mode current is larger than the set current or the rising rate of the detected common mode current in the set time is higher than the set rate, a preset protection mechanism is triggered to realize the protection of the motor and the motor controller.
Optionally, the detection unit includes: the device comprises a magnetic field generation module, a magnetic induction module and a voltage acquisition module; the magnetic field generation module is used for generating a magnetic field based on the common-mode current of the motor; the magnetic induction module is used for carrying out magnetic coupling with a magnetic field generated based on the common-mode current to generate magnetic induction electromotive force; the voltage acquisition module is used for sampling magnetic induction electromotive force generated by magnetic coupling to obtain a voltage signal generated based on the common-mode current so as to realize detection of the common-mode current of the motor; and transmitting the obtained voltage signal to the control module.
Optionally, the magnetic field generation module comprises: a common mode inductor; the common mode inductor is connected in series with an input line of a three-phase power supply of the motor; the magnetic induction module comprises: an induction coil; the induction coil is wound on an inductance magnetic core of the common-mode inductor; the voltage sampling module comprises: sampling a resistor; the sampling resistor and the induction coil form a loop.
Optionally, the common mode inductor is formed by winding an input line of a three-phase power supply of the motor on the inductor core in the same phase; the common mode inductor is a three-phase conjugate inductor.
Optionally, the common mode inductor and the induction coil are co-wound on an inductor core of the common mode inductor.
Optionally, the controlling unit triggers a preset protection mechanism, including: and triggering a preset protection signal to enable the motor controller to cut off a power supply of the motor according to the protection signal and stop supplying power to the motor.
Optionally, wherein the control unit includes: an MCU of the motor controller; and/or, a motor controller comprising: a motor frequency converter; and/or, the power supply of the motor comprises: a variable frequency power supply of the motor.
In accordance with another aspect of the present invention, there is provided a motor including: the common mode current control device described above.
In another aspect, the present invention provides a method for controlling a common mode current of a motor, including: detecting a common mode current of the motor; determining whether the detected common mode current is larger than a set current or whether the rising rate of the detected common mode current in a set time period is higher than a set rate; if the detected common mode current is larger than the set current or the rising rate of the detected common mode current in the set time is higher than the set rate, a preset protection mechanism is triggered to realize the protection of the motor and the motor controller.
Optionally, detecting a common mode current of the motor comprises: generating a magnetic field based on a common mode current of the motor; magnetically coupling with a magnetic field generated based on the common mode current to generate a magnetic induced electromotive force; and sampling the magnetic induction electromotive force generated by magnetic coupling to obtain a voltage signal generated based on the common-mode current so as to realize the detection of the common-mode current of the motor.
Optionally, triggering a preset protection mechanism includes: and triggering a preset protection signal to enable the motor controller to cut off a power supply of the motor according to the protection signal and stop supplying power to the motor.
According to the scheme of the invention, the common mode current on the three-phase input line of the motor (such as a compressor) is detected, when the common mode current is too large or rises too fast, protection is triggered, and power supply to the motor (such as the compressor) is stopped, so that the damage of the frequency converter and the electrification of the shell caused by the damage can be avoided, and the safety is ensured.
Furthermore, according to the scheme of the invention, the magnitude of the ground current of the motor (such as a compressor) is judged by detecting the magnitude of the common-mode current of the motor (such as the compressor), so that the problem of ground short circuit protection of the motor (such as the compressor) can be solved, the ground short circuit protection of the motor (such as the compressor) can be quickly responded, and the safety is good.
Furthermore, according to the scheme of the invention, the leakage current of the motor (such as a compressor) to the ground is detected on line, so that the electric shock accident caused by the electrification of the shell due to overlarge leakage current is avoided, the cost of the ground short circuit protection scheme is reduced, and the safety is good.
Therefore, according to the scheme of the invention, the common mode current on the three-phase input line of the motor (such as a compressor) is detected, when the common mode current is too large or rises too fast, protection is triggered, power supply for the motor (such as the compressor) is stopped, the motor (such as the compressor) and the frequency converter are protected, the problem of high cost in a mode of protecting the ground current of the motor by using an air switch or a protective tube is solved, and the effect of reducing the cost is achieved.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
FIG. 1 is a schematic structural diagram of a common mode current control device according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the current paths of the common mode current (e.g., short circuit to ground and earth leakage) and the differential mode current of an embodiment of the motor (e.g., compressor) of the present invention;
FIG. 3 is a schematic structural diagram of a common mode current control device of an embodiment of a motor (e.g., a compressor) according to the present invention;
fig. 4 is a schematic structural diagram of a common mode current control device of another embodiment of an electric machine (e.g., a compressor) of the present invention, and particularly, an expanded structural diagram of the common mode inductor and the induction coil in fig. 3;
FIG. 5 is a flowchart illustrating a common mode current control method according to an embodiment of the present invention;
FIG. 6 is a flowchart illustrating an embodiment of triggering a predetermined protection mechanism in the method of the present invention.
The reference numbers in the embodiments of the present invention are as follows, in combination with the accompanying drawings:
1-common mode inductance; 2-an induction coil; 3-sampling a resistor; 4-air conditioner frequency converter; 102-a detection unit; 104-control unit.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the specific embodiments of the present invention and the accompanying drawings. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
According to an embodiment of the present invention, there is provided a common mode current control apparatus. Referring to fig. 1, a schematic diagram of an embodiment of the apparatus of the present invention is shown. The common mode current control apparatus may include: a detection unit 102 and a control unit 104.
In an alternative example, the detecting unit 102 may be used to detect a common mode current of a motor (e.g., a compressor).
Optionally, the detecting unit 102 may include: the device comprises a magnetic field generation module, a magnetic induction module and a voltage acquisition module.
In particular, the magnetic field generation module may be configured to generate a magnetic field based on a common mode current of a motor (e.g., a compressor).
Specifically, the magnetic induction module may be configured to magnetically couple with a magnetic field generated based on the common-mode current to generate a magnetic induction electromotive force.
Specifically, the voltage acquisition module may be configured to sample a magnetic induction electromotive force generated by magnetic coupling to obtain a voltage signal generated based on the common-mode current, so as to implement detection of the common-mode current of a motor (e.g., a compressor); and transmitting the obtained voltage signal to the control module.
For example: the common mode inductor is used for detecting the common mode current on the three-phase input line of the motor (such as a compressor), when the common mode current is too large or rises too fast, protection is triggered, power supply to the motor (such as the compressor) is stopped, and the motor (such as the compressor) and the frequency converter are protected.
Therefore, the magnetic field is generated based on the common-mode current of the motor (such as a compressor), and is further coupled with the magnetic field to generate the magnetic induction electromotive force, the magnetic induction electromotive force is sampled to obtain the voltage signal generated by the common-mode current, the sampling of the common-mode current of the motor (such as the compressor) is realized, the structure is simple, the cost is low, and the sampling result is accurate.
More optionally, the magnetic field generation module may include: a common mode inductor 1. The common mode inductor 1 is connected in series with an input line of a three-phase power supply of a motor (such as a compressor). For example: referring to the example shown in fig. 3, the number of the common mode inductors 1 is three, and the three common mode inductors 1 are respectively connected in series to three input lines of a three-phase power supply.
More optionally, the magnetic induction module may include: an induction coil 2. And the induction coil 2 is wound on an inductance core of the common mode inductor 1. Therefore, the ground protection can be realized by mainly adopting a common-mode inductor (such as the common-mode inductor 1) and an induction coil (such as the induction coil 2), and the cost is greatly reduced.
More optionally, the voltage sampling module may include: the resistor 3 is sampled. The sampling resistor 3 forms a loop with the induction coil 2, and samples and obtains the voltage signal by inducing the voltage signal generated on the induction coil 2 by induced current generated by induced electromotive force.
For example: the common-mode inductor 1, the induction coil 2, the sampling resistor 3 and the voltage sampling module can be arranged for realizing the short-circuit protection of the air-conditioning frequency converter 4. For example: the common mode inductor 1 is connected in series with a three-phase input line of a motor (such as a compressor). And the induction coil 2 is wound on an inductance core of the common mode inductor 1. A sampling resistor 3, which induces a current in the induction coil 2 to generate a sampling voltage thereon. And the air conditioner frequency converter 4 of the air conditioner frequency conversion stops supplying power to the motor (such as a compressor) after receiving the protection turn-off signal.
Therefore, a magnetic field is generated by the common-mode inductor based on the common-mode current of the motor (such as a compressor), the magnetic coupling is carried out between the magnetic field and the induction coil to generate the induced electromotive force, the current generated on the induced electromotive force is sampled by the sampling resistor, and then a voltage signal generated based on the common-mode current is obtained, so that the detection of the common-mode current of the motor is realized, and the structure is simple and the cost is low.
More optionally, the common mode inductor 1 is formed by winding an input line of a three-phase power supply of a motor (such as a compressor) on an inductor core in the same phase. The common mode inductor 1 is a three-phase conjugate inductor.
For example: as shown in fig. 4, three-phase input lines of a motor (such as a compressor) are wound on a magnetic core in the same phase to form a three-phase conjugate common mode inductor 1, the load current of the motor (such as a compressor) belongs to differential mode current, a current loop is composed of three motors (such as compressors), the current flowing into and out of the three lines is equal at every moment, differential mode magnetic fields induced in the magnetic core are mutually counteracted, it can be considered that the magnetic field in the magnetic core has no differential mode component, therefore, no induced current exists on the induction coil 2, no potential difference is generated at two ends of a sampling resistor, and it can be considered that the motor (such as a compressor) works normally.
Therefore, the three-phase conjugate inductor is formed by winding the input line of the three-phase power supply of the motor (such as a compressor) on the inductance core in the same phase, and is used as the common mode inductor for generating a magnetic field based on the common mode current of the motor (such as the compressor), so that hardware equipment is not required to be additionally added, and the cost is greatly reduced.
More optionally, the common mode inductor 1 and the induction coil 2 are co-wound on an inductor core of the common mode inductor (1).
For example: as shown in fig. 4, the common mode inductor 1 and the induction coil 2 are wound on the inductor core of the common mode inductor 1, the magnetic field generated by the common mode inductor 1 is coupled on the induction coil 2, and the induction coil 2 forms electromotive force which is sampled by the sampling resistor and sent to the MCU for processing.
Therefore, the common-mode inductor and the induction coil share the magnetic core, so that the structure is simplified, the cost is saved, and the generation of a magnetic field based on common-mode current and the coupling reliability of the magnetic field and the induction coil can be guaranteed.
In an alternative example, the control unit 104 may be configured to determine whether the detected common mode current is greater than the set current, or determine whether a rising rate of the detected common mode current is higher than the set rate within a set time period; if the detected common mode current is larger than the set current or the rising rate of the detected common mode current is higher than the set rate within the set time, the protection of the floor drain current and/or the ground short circuit current of the motor (such as a compressor) is determined to be needed, and a preset protection mechanism is triggered to realize the protection of the motor and the motor controller.
For example: the motor (such as a compressor) to ground current (namely leakage current and short-circuit current of the motor (such as the compressor) to ground) belongs to common mode current, the load current on the motor (such as the compressor) belongs to differential mode current, and the magnitude of the motor (such as the compressor) to ground current can be judged by detecting the magnitude of the common mode current of the motor (such as the compressor). Therefore, the problem of ground short circuit protection of the motor (such as a compressor) can be solved in a novel ground short circuit detection mode, the ground short circuit protection of the motor (such as the compressor) can be responded quickly, and the frequency converter damage and the shell electrification caused by the ground short circuit protection can be avoided. In addition, the leakage current of the motor (such as a compressor) to the ground can be detected on line, electric shock accidents caused by electrification of the shell due to overlarge leakage current are avoided, and the cost of a ground short-circuit protection scheme is reduced.
Therefore, under the condition that the common-mode current of the motor (such as a compressor) is determined to be larger than the set current or the rising rate of the common-mode current of the motor (such as the compressor) in the set time period is determined to be higher than the set rate, the ground current protection of the motor (such as the compressor) is determined to be needed so as to trigger a preset protection mechanism, the protection of the motor (such as the compressor) and a motor (such as the compressor) controller is realized, the protection reliability is good, and the cost is low.
Optionally, the triggering of the preset protection mechanism by the control unit 104 may include: and triggering a preset protection signal to enable the motor (such as a compressor) controller to cut off a power supply of the motor (such as the compressor) according to the protection signal and stop supplying power to the motor (such as the compressor).
For example: as shown in fig. 4, since the ground leakage current and the short-circuit current of the motor (such as a compressor) are different from the load current, and the loop passes through the ground wire of the motor (such as a compressor) to the casing, the magnetic fields generated in the common mode inductor 1 are superposed in the same direction, and the common mode magnetic field is generated in the magnetic core. When the leakage current of a motor (such as a compressor) is increased or a short circuit to the ground occurs, the common mode magnetic field in the magnetic core magnetic field is continuously strengthened, the common mode magnetic field induces current on the induction coil 2, the current flows through the sampling resistor 3 to generate voltage drop and is detected, when the current reaches a protection threshold value, a protection signal is triggered and sent to the frequency converter, and the variable frequency power supply of the motor (such as the compressor) is cut off.
Therefore, the ground current protection of the motor (such as a compressor) is realized by cutting off the power supply of the motor (such as the compressor), and the protection mode is reliable and safe.
In the above embodiments, the setting manner of the control unit 104, the motor (e.g., compressor) controller, and the power supply of the motor (e.g., compressor) may include any one or any several of the following situations.
The first setting scenario: the control unit 104 may include: the MCU of the motor (e.g., compressor) controller may be a controller provided independently of the motor (e.g., compressor).
For example: the main current components of the three live wires of the motor (such as a compressor) are differential mode currents, the phasor sum is zero, so the three live wires are wound on a common mode inductor, the generated magnetic fields are mutually counteracted, and finally, the presented magnetic fields are generated by the common mode currents on the common mode inductor, namely the earth leakage currents and the earth short-circuit currents of the motor (such as the compressor), so the common mode inductor is used for detecting the earth leakage currents and the earth short-circuit currents of the motor (such as the compressor). And the magnetic field that the common mode current produced couples with induction coil 2, and induction coil 2 produces the electromotive force and is sampled by sampling resistance 3, forms the voltage signal and sends converter MCU to handle.
Therefore, the MCU of the motor controller is used as the control unit 104, the control unit 104 does not need to be additionally arranged, and the motor controller is simple in structure and low in cost.
The second setting scenario: a motor controller may include: and a motor frequency converter.
Therefore, the safety and reliability of the working of the motor (such as a compressor) frequency converter can be ensured by protecting the motor (such as a compressor) frequency converter.
The third setting scenario: the power supply of the motor may include: a variable frequency power supply of the motor.
Therefore, by cutting off the variable frequency power supply of the motor, the safety of ground current protection of the motor (such as a compressor) and the motor (such as a compressor) frequency converter can be ensured, and the reliability of power supply of the variable frequency power supply of the motor (such as the compressor) can also be ensured.
Through a large number of tests, the technical scheme of the invention detects the common mode current on the three-phase input line of the motor (such as a compressor), when the common mode current is too large or rises too fast, the protection is triggered, and the power supply to the motor (such as the compressor) is stopped, so that the damage of the frequency converter and the electrification of the shell caused by the damage can be avoided, and the safety is ensured.
According to an embodiment of the present invention, there is also provided a motor, such as a compressor, corresponding to the common mode current control apparatus. The motor (e.g., compressor) may include: the common mode current control device described above.
In an alternative embodiment, the invention provides a short-circuit protection device for an inverter motor (such as a compressor), which solves the problem of short-circuit protection of the motor (such as the compressor) to the ground in a novel form of short-circuit detection to the ground, and can quickly respond to the short-circuit protection of the motor (such as the compressor) to the ground, thereby avoiding the damage of an inverter and the electrification of a shell. In addition, the leakage current of the motor (such as a compressor) to the ground can be detected on line, electric shock accidents caused by electrification of the shell due to overlarge leakage current are avoided, and the cost of a ground short-circuit protection scheme is reduced.
Specifically, the current to ground of the motor (e.g., a compressor) (i.e., the leakage current and the short-circuit current to ground of the motor (e.g., a compressor)) belongs to a common-mode current, the load current on the motor (e.g., a compressor) belongs to a differential-mode current, and the current to ground of the motor (e.g., a compressor) can be determined by detecting the magnitude of the common-mode current of the motor (e.g., a compressor).
Optionally, the invention provides a novel ground current detection mode, which detects a common mode current on a three-phase input line of a motor (such as a compressor) through a common mode inductor, and when the common mode current is too large or rises too fast, triggers protection, stops supplying power to the motor (such as the compressor), and protects the motor (such as the compressor) and a frequency converter.
In an alternative embodiment, reference may be made to the examples shown in fig. 3 and 4 to illustrate specific implementation procedures of the scheme of the present invention.
Fig. 3 may show an exemplary structure of a short-circuit protection device for an inverter motor, such as a compressor.
As shown in fig. 3, the short-circuit protection device for an inverter motor (e.g., a compressor) of the present invention may be provided with a common mode inductor 1, an induction coil 2, a sampling resistor 3, and a voltage sampling module, so as to implement short-circuit protection for an air conditioner inverter 4.
The common mode inductor 1 is connected in series with a three-phase input line of a motor (such as a compressor). And the induction coil 2 is wound on an inductance core of the common mode inductor 1. A sampling resistor 3, which induces a current in the induction coil 2 to generate a sampling voltage thereon. And the air conditioner frequency converter 4 of the air conditioner frequency conversion stops supplying power to the motor (such as a compressor) after receiving the protection turn-off signal.
Specifically, the main current components of the three live wires of the motor (such as a compressor) are differential mode currents, the phasor sum is zero, so the three live wires are wound on a common mode inductor, the generated magnetic fields are mutually counteracted, and finally, the presented magnetic field is generated by the common mode current on the common mode inductor, namely the earth leakage current and the earth short-circuit current of the motor (such as a compressor), so the common mode inductor is used for detecting the earth leakage current and the earth short-circuit current of the motor (such as a compressor). And the magnetic field that the common mode current produced couples with induction coil 2, and induction coil 2 produces the electromotive force and is sampled by sampling resistance 3, forms the voltage signal and sends converter MCU to handle.
Fig. 4 may show an exemplary implementation diagram of a common mode inductor and an induction coil, which is an exemplary diagram of an expanded view of the common mode inductor and the induction coil in fig. 3.
As shown in fig. 4, the common mode inductor 1 and the induction coil 2 are wound on the inductor core of the common mode inductor 1, the magnetic field generated by the common mode inductor 1 is coupled on the induction coil 2, and the induction coil 2 forms electromotive force which is sampled by the sampling resistor and sent to the MCU for processing.
Fig. 2 may show current paths for common mode currents and differential mode currents of a motor (e.g., a compressor). The common mode current and the differential mode current of the motor (such as a compressor) will be specifically described with reference to fig. 2.
As shown in fig. 2, the common mode current refers to the current flowing through the ground line in the current path, and is generally the interference current, the pair current of the deviceGround leakage current and short-circuit to ground current. This common mode current flows in the same direction through the three phase lines and finally through the ground, which means that: i iscL1+IcL2+IcL3+IPE＝0。IcL1For common mode current flowing through phase line L1, IcL2For common mode current flowing through phase line L2, IcL3For common mode current flowing through phase line L3, IPEIs the current flowing through ground.
The magnetic field generated by the common mode inductance:
the magnetic field generated for the common mode current flowing through phase line L1,
the magnetic field generated for the common mode current flowing through phase line L2,
the magnetic field generated for the common mode current flowing through phase line L3,
a magnetic field generated by a current flowing through the ground.
As shown in fig. 2, the definition of the differential mode current is different from the common mode current, and the current path of the differential mode current is three-phase lines, and does not pass through the ground line, and it always flows in from one of the three-phase lines and flows out from the other two lines, which means that: i isdL1+IdL2+IdL3＝0。IdL1For differential mode current flowing through phase line L1, IdL2For differential mode current flowing through phase line L2, IdL3Is a differential mode current flowing through phase line L3.
The magnetic field generated by the differential mode current:
the magnetic field generated for the differential mode current flowing through phase line L1,
the magnetic field generated for the differential mode current flowing through phase line L2,
a magnetic field generated for the differential mode current flowing through phase line L3.
That is, if the sum of the phasors of the differential mode currents in the three live wires is 0, and the three live wires are wound around the magnetic core in the same phase, the generated magnetic fields cancel each other out. The current when the load is working is the differential mode current.
As shown in fig. 4, three-phase input lines of a motor (such as a compressor) are wound on a magnetic core in the same phase to form a three-phase conjugate common mode inductor 1, the load current of the motor (such as a compressor) belongs to differential mode current, a current loop is composed of three motors (such as compressors), the currents flowing into and out of the three lines are equal at every moment, differential mode magnetic fields induced in the magnetic core are mutually counteracted, it can be considered that the magnetic field in the magnetic core has no differential mode component, therefore, no induced current exists on the induction coil 2, no potential difference is generated at two ends of the sampling resistor, and it can be considered that the motor (such as a compressor) works normally.
Because the current of the motor (such as a compressor) to the earth leakage and the short circuit current are different from the load current, the loop of the motor (such as the compressor) passes through the ground wire of the motor (such as the compressor) to the shell, the magnetic fields generated in the common mode inductor 1 are superposed in the same direction, and the common mode magnetic field is generated in the magnetic core. When the leakage current of a motor (such as a compressor) is increased or short circuit to the ground occurs, the common mode magnetic field in the magnetic core magnetic field is continuously strengthened, current can be induced on the induction coil 2, the current flows through the sampling resistor 3 to generate voltage drop and is detected, when the current reaches a protection threshold value, a protection signal is triggered and sent to the frequency converter, and the variable frequency power supply of the motor is cut off.
It can be seen that, in general, the ground protection circuit uses an air switch or three safety tubes connected in series to the input terminals of three live wires or power lines of a motor (such as a compressor), which is costly, requires manual intervention, and cannot be automatically protected and restored. According to the scheme of the invention, the ground protection can be realized by mainly adopting a common-mode inductor (such as the common-mode inductor 1) and an induction coil (such as the induction coil 2), so that the cost is greatly reduced.
Since the processes and functions implemented by the motor (e.g., compressor) of the present embodiment substantially correspond to the embodiments, principles and examples of the apparatus shown in fig. 1, reference may be made to the related descriptions in the foregoing embodiments without specific details in the description of the present embodiment, and further description thereof is omitted.
Through a large number of tests, the technical scheme of the invention judges the magnitude of the ground current of the motor (such as a compressor) by detecting the magnitude of the common-mode current of the motor (such as the compressor), can solve the problem of ground short-circuit protection of the motor (such as the compressor), can quickly respond to the ground short-circuit protection of the motor (such as the compressor), and has good safety.
According to an embodiment of the present invention, there is also provided a method for controlling a common mode current of a motor (e.g., a compressor) corresponding to the motor (e.g., the compressor), as shown in fig. 5, which is a schematic flow chart of an embodiment of the method of the present invention. The common mode current control method of the motor (such as a compressor) can comprise the following steps: step S110 to step S130.
At step S110, a common mode current of a motor (e.g., a compressor) is detected.
Optionally, with reference to a schematic flow chart of an embodiment of triggering the preset protection mechanism in the method of the present invention shown in fig. 6, a specific process of triggering the preset protection mechanism in step S110 is further described, which may include: step S210 to step S230.
Step S210, a magnetic field is generated based on a common mode current of a motor (e.g., a compressor).
Step S220 is to magnetically couple with a magnetic field generated based on the common mode current to generate a magnetic induced electromotive force.
Step S230, sampling the magnetic induction electromotive force generated by the magnetic coupling to obtain a voltage signal generated based on the common mode current, so as to detect the common mode current of the motor (e.g., a compressor).
For example: the common mode inductor is used for detecting the common mode current on the three-phase input line of the motor (such as a compressor), when the common mode current is too large or rises too fast, protection is triggered, power supply to the motor (such as the compressor) is stopped, and the motor (such as the compressor) and the frequency converter are protected.
Therefore, the magnetic field is generated based on the common-mode current of the motor (such as a compressor), and is further coupled with the magnetic field to generate the magnetic induction electromotive force, the magnetic induction electromotive force is sampled to obtain the voltage signal generated by the common-mode current, the sampling of the common-mode current of the motor (such as the compressor) is realized, the structure is simple, the cost is low, and the sampling result is accurate.
At step S120, it is determined whether the detected common mode current is greater than the set current or whether a rising rate of the detected common mode current is higher than the set rate for a set period of time.
At step S130, if the detected common mode current is greater than the set current, or the rising rate of the detected common mode current is higher than the set rate within the set time period, it is determined that the protection of the motor (such as a compressor) against the earth leakage current and/or the earth short-circuit current is required, and a preset protection mechanism is triggered to implement the protection of the motor (such as a compressor) and the motor (such as a compressor) controller.
For example: the motor (such as a compressor) to ground current (namely leakage current and short-circuit current of the motor (such as the compressor) to ground) belongs to common mode current, the load current on the motor (such as the compressor) belongs to differential mode current, and the magnitude of the motor (such as the compressor) to ground current can be judged by detecting the magnitude of the common mode current of the motor (such as the compressor). Therefore, the problem of ground short circuit protection of the motor (such as a compressor) can be solved in a novel ground short circuit detection mode, the ground short circuit protection of the motor (such as the compressor) can be responded quickly, and the frequency converter damage and the shell electrification caused by the ground short circuit protection can be avoided. In addition, the leakage current of the motor (such as a compressor) to the ground can be detected on line, electric shock accidents caused by electrification of the shell due to overlarge leakage current are avoided, and the cost of a ground short-circuit protection scheme is reduced.
Therefore, under the condition that the common-mode current of the motor (such as a compressor) is determined to be larger than the set current or the rising rate of the common-mode current of the motor (such as the compressor) in the set time period is determined to be higher than the set rate, the ground current protection of the motor (such as the compressor) is determined to be needed so as to trigger a preset protection mechanism, the protection of the motor (such as the compressor) and a motor (such as the compressor) controller is realized, the protection reliability is good, and the cost is low.
Optionally, the triggering of the preset protection mechanism in step S130 may include: and triggering a preset protection signal to enable the motor (such as a compressor) controller to cut off a power supply of the motor (such as the compressor) according to the protection signal and stop supplying power to the motor (such as the compressor).
For example: as shown in fig. 4, since the ground leakage current and the short-circuit current of the motor (such as a compressor) are different from the load current, and the loop passes through the ground wire of the motor (such as a compressor) to the casing, the magnetic fields generated in the common mode inductor 1 are superposed in the same direction, and the common mode magnetic field is generated in the magnetic core. When the leakage current of a motor (such as a compressor) is increased or a short circuit to the ground occurs, the common mode magnetic field in the magnetic core magnetic field is continuously strengthened, the common mode magnetic field induces current on the induction coil 2, the current flows through the sampling resistor 3 to generate voltage drop and is detected, when the current reaches a protection threshold value, a protection signal is triggered and sent to the frequency converter, and the variable frequency power supply of the motor (such as the compressor) is cut off.
Therefore, the ground current protection of the motor (such as a compressor) is realized by cutting off the power supply of the motor (such as the compressor), and the protection mode is reliable and safe.
Since the processes and functions implemented by the method of this embodiment substantially correspond to the embodiments, principles and examples of the motor (such as a compressor) shown in fig. 2 to fig. 4, the description of this embodiment is not detailed, and reference may be made to the related descriptions in the foregoing embodiments, which are not repeated herein.
Through a large number of tests, the technical scheme of the embodiment is adopted, the leakage current of the motor (such as a compressor) to the ground is detected on line, electric shock accidents caused by electrification of the shell due to overlarge leakage current are avoided, the cost of the ground short-circuit protection scheme is reduced, and the safety is good.
In summary, it is readily understood by those skilled in the art that the advantageous modes described above can be freely combined and superimposed without conflict.
The above description is only an example of the present invention, and is not intended to limit the present invention, and it is obvious to those skilled in the art that various modifications and variations can be made in the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims (11)
1. A common mode current control device, comprising: a detection unit and a control unit; wherein,
the detection unit is used for detecting the common-mode current of the motor;
the control unit is used for determining whether the detected common mode current is larger than a set current or determining whether the rising rate of the detected common mode current in a set time length is higher than the set rate;
if the detected common mode current is larger than the set current or the rising rate of the detected common mode current in the set time is higher than the set rate, a preset protection mechanism is triggered to realize the protection of the motor and the motor controller.
2. The apparatus of claim 1, wherein the detection unit comprises: the device comprises a magnetic field generation module, a magnetic induction module and a voltage acquisition module; wherein,
the magnetic field generation module is used for generating a magnetic field based on the common-mode current of the motor;
the magnetic induction module is used for carrying out magnetic coupling with a magnetic field generated based on the common-mode current to generate magnetic induction electromotive force;
the voltage acquisition module is used for sampling magnetic induction electromotive force generated by magnetic coupling to obtain a voltage signal generated based on the common-mode current so as to realize detection of the common-mode current of the motor; and transmitting the obtained voltage signal to the control module.
3. The apparatus of claim 2, wherein the magnetic field generation module comprises: a common mode inductor (1); the common mode inductor (1) is connected in series with an input line of a three-phase power supply of the motor;
the magnetic induction module comprises: an induction coil (2); the induction coil (2) is wound on an inductance magnetic core of the common mode inductor (1);
the voltage sampling module comprises: a sampling resistor (3); the sampling resistor (3) and the induction coil (2) form a loop.
4. A device according to claim 3, characterized in that said common mode inductance (1) is formed by the input line of the three-phase power supply of the motor wound in phase on the inductor core; the common mode inductor (1) is a three-phase conjugate inductor.
5. A device according to claim 3, characterized in that the common-mode inductor (1) and the induction coil (2) are co-wound on an inductor core of the common-mode inductor (1).
6. The apparatus according to one of claims 1 to 5, wherein the control unit triggers a preset protection mechanism comprising:
and triggering a preset protection signal to enable the motor controller to cut off a power supply of the motor according to the protection signal and stop supplying power to the motor.
7. The apparatus according to one of claims 1 to 5, wherein,
the control unit includes: an MCU of the motor controller;
and/or the presence of a gas in the gas,
a motor controller comprising: a motor frequency converter;
and/or the presence of a gas in the gas,
a power supply for an electric motor comprising: a variable frequency power supply of the motor.
8. An electric machine, comprising: a common mode current control device as claimed in any one of claims 1 to 7.
9. A common mode current control method of an electric motor according to claim 8, comprising:
detecting a common mode current of the motor;
determining whether the detected common mode current is larger than a set current or whether the rising rate of the detected common mode current in a set time period is higher than a set rate;
if the detected common mode current is larger than the set current or the rising rate of the detected common mode current in the set time is higher than the set rate, a preset protection mechanism is triggered to realize the protection of the motor and the motor controller.
10. The method of claim 9, wherein detecting a common mode current of the motor comprises:
generating a magnetic field based on a common mode current of the motor;
magnetically coupling with a magnetic field generated based on the common mode current to generate a magnetic induced electromotive force;
and sampling the magnetic induction electromotive force generated by magnetic coupling to obtain a voltage signal generated based on the common-mode current so as to realize the detection of the common-mode current of the motor.
11. The method according to claim 9 or 10, wherein triggering a predetermined protection mechanism comprises:
and triggering a preset protection signal to enable the motor controller to cut off a power supply of the motor according to the protection signal and stop supplying power to the motor.
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