CN110798123A - Variable frequency driving system and method for improving common mode interference - Google Patents
Variable frequency driving system and method for improving common mode interference Download PDFInfo
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- CN110798123A CN110798123A CN201810866328.XA CN201810866328A CN110798123A CN 110798123 A CN110798123 A CN 110798123A CN 201810866328 A CN201810866328 A CN 201810866328A CN 110798123 A CN110798123 A CN 110798123A
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- power switch
- variable frequency
- mode interference
- improving
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
- H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
- H02P27/06—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
- H02M1/123—Suppression of common mode voltage or current
Abstract
The invention provides a variable frequency driving system and method for improving common-mode interference, which comprises the following steps: the power converter converts input alternating current into direct current bus voltage; the inverter is connected to the output end of the power converter and converts the direct-current bus voltage into output alternating current; the motor is connected with the output end of the inverter, and the shell of the motor is connected with the ground inside the variable-frequency driving system and is driven by the output alternating current to operate; and the radiator is fixed on the power semiconductor devices of the power converter and the inverter in an insulating way. The radiator is connected with a fixed potential, first displacement current generated on a drain electrode of a first power switch tube in the power converter flows through the first loop, and second displacement current generated on a collector electrode of each power switch tube in the inverter respectively flows through the corresponding second loop, so that common mode interference is improved. The invention can reduce the system volume, simplify the wiring and reduce the cost.
Description
Technical Field
The invention relates to the field of frequency conversion, in particular to a frequency conversion driving system and method for improving common-mode interference.
Background
The variable frequency driving system realizes speed regulation by changing the power supply frequency of the motor, thereby regulating the load, reducing power consumption, reducing loss and prolonging the service life of equipment. As shown in fig. 1, the inverter drive system 1 includes a power converter 11, an inverter 12, a motor 13, and heat sinks T1 and T2, wherein the power converter 11 converts an input ac power into a dc bus voltage, and the inverter 12 converts the dc bus voltage into a dc bus voltage, so as to drive a winding of the motor 13 to operate. Under the test condition, whether the common-mode interference is within the standard or not is tested through the fixed impedance of the line impedance stabilizing network 14; in an actual operating environment, the line impedance stabilization network 14 is not present.
The conducted common-mode Electromagnetic Interference (EMI) in the variable frequency drive system mainly includes the conducted common-mode EMI of the power converter and the conducted common-mode EMI of the inverter circuit.
The source of common mode electromagnetic interference conducted by the power converter is mainly caused by the fact that an electric node with a potential which changes sharply with time in a circuit generates displacement current in a distributed capacitance of the electric node to the ground and flows through a ground loop. In general, the drain of a metal-oxide semiconductor field effect transistor (MOSFET) Q11 in the power converter 11 is fixed to an external heat sink T1 through a heat dissipation metal layer of its package by an insulating spacer, and thus, the drain of the metal-oxide semiconductor field effect transistor Q11 has a distributed capacitance Cj1 to the heat sink T1, and the heat sink T1 has a distributed capacitance Ct1 to ground. The potential of the node n1 connected to the drain of the mosfet Q11 is changed drastically with the on/off state of the mosfet Q11, i.e., du/dt of the node n1 is large. Therefore, du/dt of the node n1 generates a large displacement current icm1 on the distributed capacitances Cj1 and Ct1, and the displacement current icm1 flows into a ground loop through a ground line to form common mode interference.
Similarly, the drains of the Insulated Gate bipolar transistors Q21-Q26 in the inverter circuit 12 are fixed to the external heat sink T2 through the heat dissipation metal layer of the package casing thereof by the insulating spacer, so that the drains of the Insulated Gate bipolar transistors Q21-Q26 have a large distributed capacitance Cj31, Cj32, Cj33 to the heat sink T2, and the heat sink T2 has a distributed capacitance Ct2 to the ground; the potentials of the nodes n21, n22 and n23 are changed violently with the change of the on-off states of the insulated gate bipolar transistors Q21-Q26 in the inverter circuit 12, namely du/dt of the three nodes is large; accordingly, the du/dt of the nodes n21, n22 and n23 generates a large displacement current icm2 in the distributed capacitances Cj31, Cj32, Cj33 and Ct2, respectively, and the three displacement currents icm2 are combined and then flow into a ground circuit through a ground line, so that common mode interference is formed. Furthermore, since the motor 13 casing is grounded, considering that the nodes n21, n22, and n23 of the inverter circuit 12, which are connected to the three-phase output end of the motor coil, have one large distributed capacitor Cj21, Cj22, and Cj23 for the motor casing, respectively, while the du/dt of the nodes n21, n22, and n23 is large as described above, the du/dt of the nodes n21, n22, and n23 generates a large displacement current icm3 on the distributed capacitors Cj21, Cj22, and Cj23 for the motor coil to the motor casing, respectively, and the three displacement currents icm3 are combined and then flow into a ground loop through the ground line of the motor casing, thereby forming common mode interference.
As shown in fig. 2, the prior art generally improves the power converter conducted common mode electromagnetic interference by providing a multi-stage common mode filter 15 at the input end of the ac power supply; the disadvantage is that the multi-stage common mode filter 15 has a large volume and needs to occupy a large position when being arranged on the circuit board, so that the size of the circuit board needs to be correspondingly increased; in addition, the introduction of the multi-stage common mode filter 15 also increases the cost of the system. The prior art also improves the inverter circuit conducted common mode electromagnetic interference by arranging a three-phase common mode filter 16 between the output end of the inverter circuit 12 and the input end of the motor 13; if the sitting type three-phase common mode filter is used, the volume is large, and a large space position is occupied; if the three-phase common mode filter is formed by winding the three-phase power line of the motor on the common mode magnetic core, the three-phase common mode filter needs to be manually wound by a person, and an insulating protective sleeve is arranged outside the three-phase common mode filter, so that the production cost is increased.
Therefore, how to improve the common mode interference of the variable frequency driving system without increasing the system volume and reducing the cost of manpower and material resources has become one of the problems to be solved by those skilled in the art.
Disclosure of Invention
In view of the above drawbacks of the prior art, an object of the present invention is to provide a variable frequency driving system and a method for improving common mode interference, which are used to solve the problems of large size, high cost, and the like when the variable frequency driving system improves common mode interference in the prior art.
To achieve the above and other related objects, the present invention provides a variable frequency drive system for improving common mode interference, which at least includes:
the power converter is used for converting input alternating current into direct current bus voltage;
the inverter is connected to the output end of the power converter and used for converting the direct current bus voltage into output alternating current;
the shell of the motor is connected with the ground inside the variable frequency driving system for improving the common-mode interference and is driven by the output alternating current to operate;
and the radiators are fixed on the power semiconductor devices of the power converter and the inverter in an insulating manner, and are connected with a fixed potential.
Preferably, the fixed potential is a positive electrode, a negative electrode or a voltage dividing node of the dc bus voltage.
Preferably, the negative electrode of the dc bus voltage is connected to the ground inside the variable frequency drive system for improving the common mode interference through the first capacitor.
More preferably, the capacitance value of the first capacitor is 1 nF-30 nF.
Preferably, a first inductor is connected in series between an internal ground and an external ground of the variable frequency drive system for improving common mode interference.
Preferably, the power converter comprises a boost circuit, a buck circuit or a buck-boost circuit.
Preferably, the power converter comprises a rectifying unit, a second inductor, a first power switch tube, a first diode and an output capacitor; the input end of the rectifying unit is respectively connected with the live wire and the zero wire of the input alternating current; one end of the second inductor is connected with the anode of the output end of the rectifying unit, and the other end of the second inductor is connected with the first end of the first power switch tube; the second end of the first power switch tube is connected with the negative electrode of the output end of the rectifying unit, and the third end of the first power switch tube is connected with a first control signal; the anode of the first diode is connected with the drain electrode of the first power switch tube, and the cathode of the first diode is connected with the cathode of the output end of the rectifying unit through the output capacitor.
Preferably, the inverter includes six power switching tubes, wherein the second power switching tube and the third power switching tube are connected in series between a positive electrode and a negative electrode of the dc bus voltage, the fourth power switching tube and the fifth power switching tube are connected in series between the positive electrode and the negative electrode of the dc bus voltage, the sixth power switching tube and the seventh power switching tube are connected in series between the positive electrode and the negative electrode of the dc bus voltage, and each power switching tube is connected to a control signal.
Preferably, the input end of the power converter is further connected with a first common-mode filter, and the first common-mode filter is single-stage or multi-stage.
Preferably, the input end of the motor is further connected with a second common mode filter.
More preferably, the variable frequency drive system for improving common mode interference includes two radiators fixed to the power semiconductor devices of the power converter and the inverter, respectively, and each radiator is connected to a fixed potential.
To achieve the above and other related objects, the present invention provides a method for improving common-mode interference of a variable frequency drive system, which at least includes:
the method comprises the steps that radiators which are fixed on power semiconductor devices of a power converter and an inverter in an insulating mode are connected with fixed potentials to form a first loop and a second loop, first displacement currents generated on distributed capacitors between power switch tubes in the power converter and the radiators flow through the first loop, second displacement currents generated on distributed capacitors between the power switch tubes connected with a negative pole of a direct-current bus voltage output by the power converter and the radiators in the inverter respectively flow through the corresponding second loops, and therefore common-mode interference is improved.
Preferably, a first capacitor is connected between the negative pole of the dc bus voltage and a ground inside the variable frequency drive system to form a third loop, and third displacement currents generated on distributed capacitors between each power switch tube connected to the negative pole of the dc bus voltage and each motor winding and the motor housing in the inverter respectively flow through the corresponding third loop, thereby improving common mode interference.
More preferably, a first inductance is used to suppress a third displacement current on a ground line inside the variable frequency drive system.
As described above, the variable frequency driving system and method for improving common mode interference of the present invention have the following advantages:
the frequency conversion driving system and the frequency conversion driving method for improving the common-mode interference effectively shield the common-mode noise source coupled from the radiator to the ground in the power converter and the inverter by only wiring the fixed potential of the radiator under the condition of not increasing any external circuit and device, thereby improving the common-mode electromagnetic interference generated by taking each power switching tube in the power converter and the inverter as a source. Furthermore, the input end of the alternating current power supply can be provided with no common mode filter, or the number of stages of the common mode filter can be reduced, so that the production cost is greatly reduced; the number of the common mode filter stages arranged at the input end of the alternating current power supply can be the same as that of the common mode filter stages in the prior art, so that the suppression effect of common mode interference is better improved.
According to the variable frequency driving system and the variable frequency driving method for improving the common-mode interference, the large capacitor is connected between the negative electrode of the direct current bus and the ground in series, and the common-mode noise source coupled from the motor coil to the motor shell in the inverter circuit is effectively shielded, so that the common-mode electromagnetic interference generated by using each power switch tube as a source in the inverter is further improved. Furthermore, the input end of the motor power supply can be not provided with a three-phase common mode filter, and compared with the three-phase common mode filter, the serially connected large capacitor has smaller volume, simple wiring and convenient operation, and can simultaneously reduce the device cost and the labor cost; the input end of the motor can also be provided with a three-phase common mode filter, so that the suppression effect of common mode interference is better improved.
Drawings
Fig. 1 is a schematic structural diagram of a variable frequency drive system in the prior art.
Fig. 2 is a schematic structural diagram of a variable frequency driving system for improving common mode interference in the prior art.
Fig. 3 is a schematic structural diagram of a variable frequency driving system for improving common mode interference according to the present invention.
Fig. 4 is a schematic structural diagram of a variable frequency drive system for improving common mode interference according to the present invention.
Description of the element reference numerals
1 variable frequency driving system
11 power converter
12 inverter
13 electric machine
14 line impedance stabilizing network
15 multistage common mode filter
16 three-phase common mode filter
2 frequency conversion driving system for improving common mode interference
21 power converter
211 rectifying unit
22 inverter
23 electric machine
24 line impedance stabilizing network
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Please refer to fig. 3 and 4. It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the components related to the present invention are only shown in the drawings rather than drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.
Example one
As shown in fig. 3, the present embodiment provides a variable frequency driving system 2 and a method for improving common-mode interference, where the variable frequency driving system 2 for improving common-mode interference includes:
the power converter 21, the inverter 22, the motor 23, the first capacitor Cy, the first inductor L1, and the radiator T.
As shown in fig. 3, the power converter 21 is connected to an input ac power for converting the input ac power into a dc bus voltage.
Specifically, the power converter includes a boost circuit, a buck circuit or a buck-boost circuit, and different power converter structures may be set as needed, which is not limited to this embodiment. As shown in fig. 3, in the present embodiment, the power converter includes one of a rectifying unit 211 and a voltage boost circuit, wherein the voltage boost circuit includes a second inductor L2, a first power switch Q11, a first diode D1, and an output capacitor C2.
More specifically, the input end of the rectifying unit 211 is connected to the live line L and the zero line N of the input alternating current, the rectifying unit 211 includes four diodes and a filter capacitor C1, the four diodes form a rectifier bridge structure, the filter capacitor C1 is connected between the output ends of the rectifier bridge, the upper plate of the filter capacitor C1 is a node N4, and the lower plate is a node N5. One end of the second inductor L2 is connected to the positive electrode of the output end of the rectifying unit 211, and the other end is connected to the drain d of the first power switch Q11. The source of the first power switch Q11 is connected to the negative electrode of the output end of the rectifying unit 211, the gate is connected to a first control signal, and the first control signal controls the on and off of the first power switch Q11, so as to control the magnitude of the dc bus voltage output by the power converter 21, in this embodiment, the first power switch Q11 is a metal-oxide semiconductor field effect transistor; in practical applications, the type of the first power switch Q11 may be set as required, including but not limited to an insulated gate bipolar transistor, where the collector of the first power switch Q11 is connected to the second inductor L2, the emitter of the first power switch Q11 is connected to the negative terminal of the output terminal of the rectifying unit 211, and the gate of the first power switch Q11 is connected to the first control signal; the drain of the first power switch Q11 is a node n1, and the source thereof is a node n 3. The anode of the first diode D1 is connected to the drain of the first power switch Q11, and the cathode of the first diode D1 is connected to the cathode of the output terminal of the rectifying unit 211 via the output capacitor C2. The upper plate of the output capacitor C2 is used as the positive pole DC-BUS + (node n6) of the DC BUS voltage, and the lower plate of the output capacitor C2 is used as the negative pole DC-BUS- (node n7) of the DC BUS voltage. The first diode D1 is used to prevent the output capacitor C2 from discharging to the negative DC-BUS-of the DC BUS voltage.
It should be noted that, in this embodiment, the output capacitor C2 is a capacitor, and in actual use, the output capacitor C2 may be a series, parallel, or series-parallel connection of a plurality of capacitors, which is not limited to this embodiment.
As shown in fig. 3, the inverter 22 is connected to the output end of the power converter 21, and is configured to convert the dc bus voltage into an output ac power.
Specifically, the structure of the inverter 22 may be any one selected as needed, and is not limited to this embodiment. As shown in fig. 3, in the present embodiment, the inverter 22 includes six power switching tubes to form a three-phase inverter bridge, wherein a second power switching tube Q21 and a third power switching tube Q22 are connected in series between the positive DC-BUS + of the DC BUS voltage and the negative DC-BUS-of the DC BUS voltage (the collector of the second power switching tube Q21 is connected to the positive DC-BUS + of the DC BUS voltage, and the emitter of the second power switching tube Q21 is connected to the collector of the third power switching tube Q22, the emitter of the third power switching tube Q22 is connected to the negative DC-BUS-of the DC BUS voltage), and a connection point between the second power switching tube Q21 and the third power switching tube Q22 is a node n 21; a fourth power switch Q23 and a fifth power switch Q24 are connected in series between the positive DC-BUS + of the DC BUS voltage and the negative DC-BUS-of the DC BUS voltage (connection ports are the same as those of the second power switch Q21 and the third power switch Q22, which are not described herein again), and a connection point of the fourth power switch Q23 and the fifth power switch Q24 is a node n 22; a sixth power switch Q25 and a seventh power switch Q26 are connected in series between the positive DC-BUS + of the DC BUS voltage and the negative DC-BUS-of the DC BUS voltage (connection ports are the same as those of the second power switch Q21 and the third power switch Q22, which are not described herein again), and a connection point of the sixth power switch Q25 and the seventh power switch Q26 is a node n 23; each power switch tube in the inverter 22 is connected to a control signal. In this embodiment, each power switch in the inverter 22 is an insulated gate bipolar transistor, and the type of each power switch can be set as required in actual use. The three-phase output end of the inverter circuit 22 is connected with the three-phase input end of the motor 23.
As shown in fig. 3, the motor 23 is connected to the output end of the inverter 22, and the casing of the motor 23 is connected to the ground inside the variable frequency drive system 2 for improving common mode interference, and is driven by the output ac power to operate.
Specifically, the motor 23 is a three-phase motor, and when output alternating current is supplied to three-phase stator windings (each having an electrical angle of 120 degrees), a rotating magnetic field is generated, and the rotating magnetic field cuts the rotor winding, so that an induced current is generated in the rotor winding.
It should be noted that, in actual use, the motor 23 may be a single-phase motor, and the structure of the inverter 2 is modified adaptively, which is not described herein again.
As shown in fig. 3, the heat sink T is fixed to the power semiconductor devices in the power converter 21 and the inverter 22 by insulating spacers, so as to dissipate heat from the first power switch Q11 in the power converter 21, the first diode D1, and the power switch transistors (Q21 to Q26) in the inverter 22. In this embodiment, the power semiconductor device includes a first power switch Q11-a seventh power switch Q26 and the first diode D1, and the heat sink T is attached to the heat sink metal casing of each power switch and the first diode D1 through an insulating spacer.
Specifically, the metal casing of the heat sink T is connected to a fixed potential, where the fixed potential is an anode DC-BUS + of the DC BUS voltage, a cathode DC-BUS + of the DC BUS voltage, or a voltage dividing node of the DC BUS voltage (when the output capacitor C2 is a series, parallel, or series-parallel connection of a plurality of capacitors, any connecting node of each capacitor is a fixed point), and the fixed potential can also be obtained by adding a voltage dividing circuit to divide the DC BUS voltage. In this embodiment, the metal casing of the heat sink T is connected to the negative DC-BUS-of the DC BUS voltage.
More specifically, the first diode D1 has a large distributed capacitance to the heat sink T, and since the node n6 is connected to the positive DC-BUS + of the DC BUS voltage, which is stable during normal operation of the circuit, the potential at the node n6 is also stable, and thus the influence of the distributed capacitance of the first diode D1 on the common mode interference is negligible. The drain d of the first power switch Q11 has a large distributed capacitance Cj1 to the heat sink T, and the heat sink T has a distributed capacitance Ct to the ground inside the variable frequency drive system 2 for improving common mode interference; when the first power switch Q11 is switched, node n1 has a large du/dt, and distributed capacitances Cj1 and Ct are major factors affecting common mode interference. The large du/dt at node n1 produces a large first displacement current icm1 across the distributed capacitances Cj1 and Ct. At this time, since the heat sink T is connected to a fixed potential (negative DC-BUS-of the DC BUS voltage), the first power switch Q11, the distributed capacitance Cj1 between the drain of the first power switch Q11 and the heat sink T, and the heat sink T form a first loop; the first displacement current icm1 flows through the first loop without flowing into the ground loop through the distributed capacitance Ct and ground, thereby improving power converter conduction common mode electromagnetic interference.
More specifically, as the node n6 is stable, the collector of the second power switch Q21, the fourth power switch Q23 and the sixth power switch Q25 have negligible influence on the common mode interference due to the distributed capacitance of the heat sink T. The collectors of the third power switch Q22, the fifth power switch Q24, and the seventh power switch Q26 have large distributed capacitances Cj31, Cj32, Cj33 to the heat sink T, respectively, and nodes n21, n22, and n23 have large du/dt during switching operation; the large du/dt at nodes n21, n22, n23 generates large second displacement currents icm2 on distributed capacitances Cj31, Cj32, Cj33, respectively. At this time, since the heat sink T is connected to a fixed potential (the negative DC-BUS of the DC BUS voltage), the third power switch Q22, the fifth power switch Q24, the seventh power switch Q26, the distributed capacitors Cj31, Cj32, Cj33 corresponding thereto, and the heat sink T form a corresponding second loop, that is, the second loop includes three loops, where one loop is the third power switch Q22, the distributed capacitor Cj31 between the third power switch Q22 and the heat sink T, and a loop formed by the heat sink T, and the other two loops correspond to corresponding power switch tubes, and specific paths are not repeated herein. The second displacement current icm2 generated on each distributed capacitor Cj31, Cj32 and Cj33 flows through each corresponding second loop, and does not flow into the ground loop through the distributed capacitor Ct and the ground line, so that the common-mode electromagnetic interference conducted by the inverter is improved.
In this case, the first power switch Q11 of the power converter 21, the first diode D1, and the power switches (Q21 to Q26) of the inverter 22 need to be prepared on the same plane.
As shown in fig. 3, the negative DC-BUS-of the DC BUS voltage is connected to the ground inside the variable frequency drive system 2 for improving common mode interference through the first capacitor Cy.
Specifically, the capacitance value of the first capacitance Cy is set to 1nF to 30nF, and further, the capacitance value of the first capacitance Cy is preferably 5nF, 10nF, 15nF, or 20 nF.
More specifically, large distributed capacitances Cj21, Cj22, Cj23 exist between the three-phase windings in the motor 23 and the housing of the motor 23, respectively, and du/dt of the nodes n21, n22, n23 also generate large third displacement currents icm3 on the distributed capacitances Cj21, Cj22, Cj23 of the coils of the motor 23 to the housing of the motor 23, respectively. At this time, since the first capacitor Cy is connected in series between the negative DC-BUS-of the DC BUS voltage and the ground inside the variable frequency drive system 2 for improving the common mode interference, the third power switch Q22, the fifth power switch Q24, the seventh power switch Q26, the distributed capacitors Cj21, Cj22, Cj23 corresponding to the seventh power switch Q26, and the first capacitor Cy form a corresponding third loop, that is, the third loop includes three loops, one loop is formed by the distributed capacitors Cj21 and the first capacitor Cy between the winding of the motor 23 and the motor 23, which are connected to the third power switch Q22 and the third power switch Q22, and the other two loops correspond to the corresponding power switches, and specific paths are not repeated herein. Third displacement currents icm3 generated on the distributed capacitors Cj21, Cj22 and Cj23 flow through the corresponding third loops, so that common-mode electromagnetic interference conducted by the inverter is improved.
As shown in fig. 3, the first inductor L1 is connected in series between the ground inside the variable frequency drive system 2 for improving common mode interference and the external ground PE.
Specifically, a small part of the third displacement current icm3 may flow into the ground inside the variable frequency drive system 2 for improving common mode interference, and the first inductor L1 suppresses the smaller part of the third displacement current icm3 flowing into the ground loop through the ground line. Since the frequency of the switch in the inverter 22 is high, the third displacement current icm3 is a high-frequency current, and the high-frequency current icm3 is difficult to pass by utilizing the characteristic that the inductance is higher as the frequency of the inductor is higher, so that the effect of suppressing the third displacement current icm3 is achieved, and the common-mode electromagnetic interference conducted by the inverter circuit is improved.
In a test state, the input ac power is connected to the ground outside the variable frequency drive system for improving the common-mode interference through the Line Impedance stabilizing network (LSN) 24, and whether the common-mode interference is within a standard is tested through the fixed Impedance of the Line Impedance stabilizing network 24; in an actual operating environment, the line impedance stabilization network 24 is not present.
It should be noted that, the present embodiment further includes a first common mode filter (not shown) connected to the input end of the power converter 21, where the first common mode filter is single-stage or multi-stage and can be set according to the requirement of the common mode interference rejection effect. The present embodiment further includes a second common mode filter (not shown) connected to the input end of the motor 23, in the present embodiment, the second common mode filter is a three-phase common mode filter, and the type of the second common mode filter can be set according to the type of the motor 23.
Example two
As shown in fig. 4, the present embodiment provides a variable frequency driving system and a method for improving common mode interference, which is different from the first embodiment in that the variable frequency driving system for improving common mode interference includes two radiators, and each radiator is connected to the positive DC-BUS + of the DC BUS voltage.
Specifically, as shown in fig. 4, the present embodiment includes a first heat sink T1 and a second heat sink T2, the first heat sink T1 is fixed to the power semiconductor devices (the first power switch Q11 and the first diode D1) of the power converter 21 through an insulating gasket to achieve the function of dissipating heat for the first power switch Q11 and the first diode D1 in the power converter 21; the second heat sink T2 is fixed to each of the power semiconductor devices (the second power switch Q21 to the seventh power switch Q26) of the inverter 22 by an insulating spacer, so as to perform a function of dissipating heat from each of the power switch transistors (Q21 to Q26) in the inverter 22. The metal housings of the first and second heat sinks T1 and T2 are both connected to the positive DC-BUS + of the DC BUS voltage.
In practical applications, the first heat sink T1 and the second heat sink T2 may be connected to different fixed potentials, which is not limited to the embodiment.
More specifically, the first loop is a loop formed by the first power switch Q11, the distributed capacitor Cj1 between the drain of the first power switch Q11 and the first heat sink T1, the first heat sink T1 and the output capacitor C2. The second loop is a corresponding loop formed by the third power switch Q22, the fifth power switch Q24, the seventh power switch Q26 and their corresponding distributed capacitors Cj31, Cj32, Cj33, the second heat sink T2 and the output capacitor C2.
Other structures and methods of the variable frequency driving system for improving common mode interference of the present embodiment are the same as those of the first embodiment, and are not described herein.
It should be noted that, according to the different selection of the fixed potential, the paths through which the loops flow are different, and those skilled in the art can directly obtain the paths of the loops according to the connection nodes of the fixed potential.
It should be noted that the present invention may further include three or more than three heat sinks respectively fixed on the first power switch Q11, the first diode D1, the second power switch Q21 to the seventh power switch Q26 in an insulating manner, wherein a plurality of power semiconductor devices share the same heat sink, or each power semiconductor device corresponds to one heat sink respectively, and the heat sinks may be set as required, which is not described herein again.
Because the invention processes the fixed potential wiring of the radiator, the common mode noise source coupled from the radiator to the ground in the power converter circuit is effectively shielded, thereby improving the common mode electromagnetic interference conducted by the power converter and the common mode electromagnetic interference conducted by the inverter; a large capacitor is connected between the negative electrode of the direct current bus voltage and the ground in series, so that a common-mode noise source coupled from a motor coil to a motor shell in an inverter circuit is effectively shielded, and the common-mode electromagnetic interference conducted by the inverter circuit is improved. Therefore, the invention can be provided with no common mode filter or a common mode filter with lower level number according to the requirement, greatly reduces the production cost on the premise of effectively inhibiting the common mode interference, or is provided with a multi-level common mode filter (with the same level number as the prior art), thereby further improving the inhibition effect of the common mode interference. In addition, the motor power input end of the invention can be not provided with a three-phase common mode filter, compared with the three-phase common mode filter, the serially connected large capacitor has smaller volume, simple wiring and convenient operation, and can further reduce the device cost and the labor cost on the premise of effectively inhibiting the common mode interference, or the three-phase common mode filter is arranged, thereby further improving the inhibiting effect of the common mode interference.
In summary, the present invention discloses a variable frequency driving system and method for improving common mode interference, including: the power converter is used for converting input alternating current into direct current bus voltage; the inverter is connected to the output end of the power converter and used for converting the direct current bus voltage into output alternating current; the shell of the motor is connected with the ground inside the variable frequency driving system for improving the common-mode interference and is driven by the output alternating current to operate; and the radiators are fixed on the power semiconductor devices of the power converter and the inverter in an insulating manner, and are connected with a fixed potential. Connecting a radiator which is fixed on a power semiconductor device of a power converter and an inverter in an insulating manner with a fixed potential to form a first loop and a second loop, wherein a first displacement current generated on a drain electrode of a power switch tube in the power converter flows through the first loop, a second displacement current generated on a collector electrode of each power switch tube, of which an emitter electrode is connected with a negative electrode of a direct-current bus voltage output by the power converter, in the inverter respectively flows through the corresponding second loops, and the first displacement current and the second displacement current do not enter a ground loop, so that common-mode interference is improved. The invention can reduce the system volume, simplify the wiring and reduce the cost. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (14)
1. A variable frequency drive system for improving common mode interference, the variable frequency drive system for improving common mode interference comprising:
the power converter is used for converting input alternating current into direct current bus voltage;
the inverter is connected to the output end of the power converter and used for converting the direct current bus voltage into output alternating current;
the shell of the motor is connected with the ground inside the variable frequency driving system for improving the common-mode interference and is driven by the output alternating current to operate;
and the radiators are fixed on the power semiconductor devices of the power converter and the inverter in an insulating manner, and are connected with a fixed potential.
2. The variable frequency drive system for improving common-mode interference of claim 1, wherein: the fixed potential is the positive pole, the negative pole or a voltage dividing node of the direct current bus voltage.
3. The variable frequency drive system for improving common-mode interference of claim 1, wherein: and the negative electrode of the direct-current bus voltage is connected with the ground in the variable-frequency driving system for improving the common-mode interference after passing through the first capacitor.
4. A variable frequency drive system for improving common mode interference according to claim 3, wherein: the capacitance value of the first capacitor is 1 nF-30 nF.
5. The variable frequency drive system for improving common-mode interference of claim 1, wherein: a first inductor is connected in series between the internal ground and the external ground of the variable frequency drive system for improving the common mode interference.
6. The variable frequency drive system for improving common-mode interference of claim 1, wherein: the power converter comprises a boost circuit, a buck circuit or a buck-boost circuit.
7. The variable frequency drive system for improving common-mode interference of claim 1, wherein: the power converter comprises a rectifying unit, a second inductor, a first power switch tube, a first diode and an output capacitor; the input end of the rectifying unit is respectively connected with the live wire and the zero wire of the input alternating current; one end of the second inductor is connected with the anode of the output end of the rectifying unit, and the other end of the second inductor is connected with the first end of the first power switch tube; the second end of the first power switch tube is connected with the negative electrode of the output end of the rectifying unit, and the third end of the first power switch tube is connected with a first control signal; the anode of the first diode is connected with the drain electrode of the first power switch tube, and the cathode of the first diode is connected with the cathode of the output end of the rectifying unit through the output capacitor.
8. The variable frequency drive system for improving common-mode interference of claim 1, wherein: the inverter comprises six power switch tubes, wherein a second power switch tube and a third power switch tube are connected in series between the positive pole and the negative pole of the direct-current bus voltage, a fourth power switch tube and a fifth power switch tube are connected in series between the positive pole and the negative pole of the direct-current bus voltage, a sixth power switch tube and a seventh power switch tube are connected in series between the positive pole and the negative pole of the direct-current bus voltage, and each power switch tube is connected with a control signal.
9. The variable frequency drive system for improving common-mode interference of claim 1, wherein: the input end of the power converter is also connected with a first common mode filter, and the first common mode filter is single-stage or multi-stage.
10. The variable frequency drive system for improving common-mode interference of claim 1, wherein: and the input end of the motor is also connected with a second common mode filter.
11. A variable frequency drive system for improving common mode interference according to any one of claims 1 to 10, wherein: the variable frequency driving system for improving the common mode interference comprises two radiators which are respectively fixed on the power semiconductor devices of the power converter and the inverter, and each radiator is connected with a fixed potential.
12. A method for improving common mode interference of a variable frequency drive system is characterized by at least comprising the following steps:
the method comprises the steps that radiators which are fixed on power semiconductor devices of a power converter and an inverter in an insulating mode are connected with fixed electric potentials to form a first loop and a second loop, first displacement currents generated on distributed capacitors between power switch tubes in the power converter and the radiators flow through the first loop, and second displacement currents generated on distributed capacitors between the power switch tubes connected with the negative pole of direct-current bus voltage output by the power converter in the inverter and the radiators respectively flow through the corresponding second loops.
13. The method of improving common-mode interference in a variable frequency drive system of claim 12, wherein: and third displacement currents generated on power switch tubes connected with the negative electrode of the direct-current bus voltage in the inverter and distributed capacitors between motor windings and a motor shell respectively flow through the corresponding third loops.
14. A method of improving common-mode interference in a variable frequency drive system according to claim 12 or 13, wherein: and adopting a first inductor to restrain a third displacement current on a ground wire in the variable-frequency driving system.
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| CN201810866328.XA CN110798123A (en) | 2018-08-01 | 2018-08-01 | Variable frequency driving system and method for improving common mode interference |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111628660A (en) * | 2020-06-05 | 2020-09-04 | 浙江鲲悟科技有限公司 | Compressor variable frequency speed regulating system and control method of direct current bus voltage |
| CN111628659A (en) * | 2020-06-05 | 2020-09-04 | 浙江鲲悟科技有限公司 | Compressor variable frequency speed regulating system and control method of direct current bus voltage |
| WO2023044848A1 (en) * | 2021-09-26 | 2023-03-30 | 宁德时代新能源科技股份有限公司 | Switching circuit and power supply device |
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2018
- 2018-08-01 CN CN201810866328.XA patent/CN110798123A/en active Pending
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111628660A (en) * | 2020-06-05 | 2020-09-04 | 浙江鲲悟科技有限公司 | Compressor variable frequency speed regulating system and control method of direct current bus voltage |
| CN111628659A (en) * | 2020-06-05 | 2020-09-04 | 浙江鲲悟科技有限公司 | Compressor variable frequency speed regulating system and control method of direct current bus voltage |
| CN111628660B (en) * | 2020-06-05 | 2021-08-27 | 浙江鲲悟科技有限公司 | Compressor variable frequency speed regulating system and control method of direct current bus voltage |
| WO2021244669A1 (en) * | 2020-06-05 | 2021-12-09 | 浙江鲲悟科技有限公司 | Compressor variable-frequency speed adjusting system and control method for direct-current bus voltage |
| WO2023044848A1 (en) * | 2021-09-26 | 2023-03-30 | 宁德时代新能源科技股份有限公司 | Switching circuit and power supply device |
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