CN108347161B - Frequency converter soft start circuit and frequency converter comprising same - Google Patents

Frequency converter soft start circuit and frequency converter comprising same Download PDF

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Publication number
CN108347161B
CN108347161B CN201710062781.0A CN201710062781A CN108347161B CN 108347161 B CN108347161 B CN 108347161B CN 201710062781 A CN201710062781 A CN 201710062781A CN 108347161 B CN108347161 B CN 108347161B
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contactor
frequency converter
coupled
coil
soft start
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CN108347161A (en
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戴训江
李涛涛
王建渊
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Bosch Rexroth Xian Electric Drives and Controls Co Ltd
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Bosch Rexroth Xian Electric Drives and Controls Co Ltd
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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
    • H02M1/36—Means for starting or stopping converters
    • 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
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
    • H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
    • H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
    • H02M5/453—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M5/458—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)
  • Inverter Devices (AREA)

Abstract

The present invention relates to power electronics technologies, and in particular, to a soft start circuit for a frequency converter and a frequency converter including the same. The soft start circuit (130) of the frequency converter according to one aspect of the invention comprises a microcontroller (131), a soft start resistor (132), a direct current contactor (133), a flyback switching power supply (135) and a direct current contactor driver (134) coupled between a coil of the direct current contactor (133) and the ground, wherein a switching unit (1351) of the flyback switching power supply (135) comprises a first metal oxide field effect transistor (M1) and a second metal oxide field effect transistor (M2) which are coupled in series between a primary side of the transformer (T1) and the ground and have substantially synchronous switching states.

Description

Frequency converter soft start circuit and frequency converter comprising same
Technical Field
The present invention relates to power electronics technologies, and in particular, to a soft start circuit for a frequency converter and a frequency converter including the same.
Background
The frequency converter is a power control device which applies a frequency conversion technology and controls an alternating current motor by changing the working frequency of the motor. The frequency converter mainly comprises a rectifying and filtering unit, an inversion unit, a driving unit, a control unit and the like. The frequency converter supplies required voltage and frequency to the motor by controlling the on and off of an internal Insulated Gate Bipolar Transistor (IGBT).
The frequency converter typically has a built-in soft start circuit coupled between the rectifying unit and the inverting unit of the frequency converter to limit inrush current into the dc link capacitor at start-up. The soft start circuit generally comprises a soft start resistor and a direct current contactor which are connected in parallel, and the working principle of the soft start circuit is that when a frequency converter is started, the direct current contactor is in an off state, the output current of a rectifying unit charges a direct current link capacitor through the soft start resistor, and the soft start resistor plays a role in limiting current; when the voltage of the direct current link capacitor reaches or approaches the normal working voltage of the direct current bus, the driving circuit drives the direct current contactor to enter a contact closing state, and at the moment, the direct current contactor contact is connected with the direct current bus and the direct current capacitor, so that the continuity of power supply of the direct current link capacitor is maintained.
The prior art soft start circuit generally utilizes a flyback switching power supply to supply power. The working principle of the switching power supply is that when the switching element is in a conducting state, current passes through the primary winding of the transformer, energy is stored in the coil, and at the moment, because the polarity of the primary winding is opposite to that of the secondary winding, the energy is not transmitted to a load; when the switching element is in the off state, the primary winding of the transformer will generate a reverse potential and the load will have a current flowing. In the flyback switching power supply, it is generally necessary to use a high-voltage-resistant metal oxide field effect transistor (MOSFET) as a switching element, which greatly increases the cost. In addition, in order to provide various dc voltages, the flyback switching power supply of the prior art often employs a transformer with multiple windings, which reduces the reliability and short circuit tolerance of the transformer.
In addition, the prior art soft start circuits lack the ability to monitor the condition of the dc contactor, which can cause serious faults. For example, in the soft start process, the current flowing through the soft start resistor may generate a temperature rise, and if the temperature rise is too large or the soft start resistor is repeatedly started in a short time, the resistor may be damaged or burned, which brings a potential safety hazard to the subsequent starting of the frequency converter. As another example, a failure of the driving circuit or the control unit will make the dc contactor fail to enter the contact closing state after the soft start process is ended, and thus the output current of the rectifying unit continuously flows through the soft start resistor, which is fatal to the resistor. Furthermore, if the relay contacts are permanently stuck together due to wear, arcing or the relay is still in a closed state when the frequency converter is powered down and restarted, the soft start resistor will be bypassed and the large current during starting will damage the front-end rectifying unit and the back-end dc link capacitor.
Disclosure of Invention
The invention aims to provide a frequency converter soft start circuit which has the advantages of low implementation cost, diagnosis protection function and the like.
The frequency converter soft start circuit according to one aspect of the invention comprises:
a microcontroller;
a soft start resistor coupled between a rectifying unit of the frequency converter and the dc charging capacitor;
the contact of the direct current contactor is respectively coupled with the rectifying unit of the frequency converter and the direct current charging capacitor;
a flyback switching power supply, comprising:
the primary winding of the transformer obtains electricity from a direct current bus of the frequency converter, and the secondary winding of the transformer is coupled with a coil of the direct current contactor;
a switching unit coupled between the primary winding of the transformer and ground to control on and off between the primary winding of the transformer and ground;
a DC contactor driver coupled between a coil of the DC contactor and ground, configured to close or open contacts of the DC contactor under control of the microcontroller,
wherein the switching unit comprises a first metal oxide field effect transistor and a second metal oxide field effect transistor coupled in series between the primary of the transformer and ground and having substantially synchronized switching states.
Another object of the present invention is to provide a frequency converter having advantages of low implementation cost and high reliability.
A frequency converter according to an aspect of the invention comprises:
a rectifying unit;
an inverter unit; and
the frequency converter soft start circuit is coupled between the rectifying unit and the inverter unit.
Drawings
The above and/or other aspects and advantages of the present invention will become more apparent and more readily appreciated from the following description of the various aspects, taken in conjunction with the accompanying drawings, in which like or similar elements are designated with like reference numerals, and which:
fig. 1 is a schematic diagram of a frequency converter according to an embodiment of the invention.
Fig. 2 is a winding diagram of a typical unipolar double-coil type dc contactor.
Fig. 3 is a schematic circuit diagram of a flyback switching power supply applicable to the frequency converter shown in fig. 1.
Fig. 4 is a circuit schematic of an exemplary contact condition monitoring unit that may be applied to the frequency converter shown in fig. 1.
Fig. 5 is a graph of an output signal waveform of the contact state monitoring unit shown in fig. 4 during a normal soft start.
Fig. 6 is a schematic circuit diagram of a dc contactor driver that can be applied to the frequency converter shown in fig. 1.
Fig. 7 shows a characteristic curve of the coil current flowing through the dc contactor during the start-up of the frequency converter.
Fig. 8 is a schematic diagram of a frequency converter according to another embodiment of the present invention.
Detailed Description
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. The embodiments described above are intended to be illustrative of the full and complete disclosure of this invention, and thus, to provide a more complete and accurate understanding of the scope of the invention.
Words such as "comprising" and "comprises" mean that, in addition to having elements or steps which are directly and unequivocally stated in the description and the claims, the solution of the invention does not exclude other elements or steps which are not directly or unequivocally stated.
Terms such as "first" and "second" do not denote an order of the elements in time, space, size, etc., but rather are used to distinguish one element from another.
Embodiments of the present invention are described below in detail with the aid of the attached drawings.
Fig. 1 is a schematic diagram of a frequency converter according to an embodiment of the invention. The inverter 10 shown in fig. 1 includes a rectifying unit 110, an inverter unit 120, and an inverter soft start circuit 130, wherein the rectifying unit 110 rectifies and converts alternating current (e.g., three-phase alternating current shown in fig. 1) supplied by an alternating current power supply to obtain pulsating direct current, and the inverter unit 120 controls the internal Insulated Gate Bipolar Transistors (IGBTs) to be turned on and off to provide a required voltage and frequency for the motor M. The frequency converter soft start circuit is further described below.
Referring to fig. 1, the inverter soft start circuit 130 is coupled between the rectification unit 110 and the inverter unit 120, and includes a microcontroller 131, a soft start resistor 132, a dc contactor 133, a dc contactor driver 134, and a flyback switching power supply 135. Optionally, the frequency converter soft start circuit 130 further includes a contact state monitoring unit 136.
When the inverter 10 is started, the output current of the rectifying unit 110 charges the dc link capacitors C1, C2. The dc contactor 133 should be placed in an open state at this time so that the charging current flows through the soft-start resistor 132 into the capacitors C1, C2, thereby preventing the latter from being damaged by the current surge. When the voltage of the DC link capacitors C1, C2 reaches or approaches the normal operating voltage of the DC BUS, the DC contactor driver 134 energizes the coil of the DC contactor 133 under the control of the microcontroller 131, the generated electromagnetic force closes the contacts, and the output current of the rectifying unit 110 flows to the DC BUS (identified by DC + BUS and DC-BUS in fig. 1) and the DC link capacitors C1, C2 via the DC contactor 133, thereby maintaining the continuity of the DC link capacitor power supply.
Referring to fig. 1, the relay 133 includes a contact switch K connected in parallel with the soft start resistor 132, and a coil L having both ends coupled to the flyback switching power supply 135 and the dc contactor driver 134, respectively. Further, a reverse diode D1 is connected in parallel across the coil L to suppress a transient voltage caused when the relay driver is turned off. The dc contactor driver 134 includes a switching device such as a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) or a transistor, which will be described in detail below.
In the present embodiment, the dc contactor 133 may be a single-pole double-coil type dc contactor having a winding form as shown in fig. 2, or a single-coil type dc contactor.
In the soft start circuit 130 shown in fig. 1, the flyback switching power supply 135 receives power from the dc bus on one hand, and supplies power to the dc contactor 133 and the like on the other hand.
Fig. 3 is a schematic circuit diagram of a flyback switching power supply applicable to the frequency converter shown in fig. 1. The flyback switching power supply 135 shown in fig. 3 includes a transformer T1, a switching unit 1351, a filter circuit 1352, and a snubber circuit 1353.
Referring to fig. 3, the primary winding of transformer T1 takes power from the DC BUS DC + BUS and the secondary winding is coupled to the coil of DC contactor 133 to provide DC voltage to the latter. The switching unit 1351 comprises a first MOSFET M1, a second MOSFET M2, and a first PWM signal generator U1, wherein the first MOSFET M1 and the second MOSFET M2 are coupled in series between the primary winding of the transformer T1 and the ground or DC BUS DC-BUS. The gate of the first MOSFET M1 is connected to the DC BUS DC + BUS via resistors R3 and R4 and to ground via resistor R4 and reverse biased zener Z1, the source is connected to the gate via reverse biased zener Z2, the drain is connected to the primary winding of transformer T1 and to the source via capacitor C3. The gate of the second MOSFET M2 is connected to the first pulse width modulated signal generator U1 through a resistor R5, the drain is connected to the source of the first MOSFET M1, and the source is connected to ground through a resistor R6. In addition, the voltage signal across the resistor R6 is fed back to the first pwm signal generator U1 so that the latter can adjust its output signal based on the voltage between the source of the second MOSFET M2 and ground, thereby controlling the storage and release of energy in the primary winding of the transformer T1.
In the present embodiment, the switching states of the first MOSFET M1 and the second MOSFET M2 are changed substantially in synchronization. Specifically, when the second MOSFET M2 is turned on, since the source of the first MOSFET M1 is coupled to ground through the second MOSFET M2, so that the voltage applied between the source and the gate of the first MOSFET M1 by the zener Z2 is greater than the gate threshold voltage of the first MOSFET M1, the first MOSFET M1 rapidly enters a conductive state, and the current of the dc bus flows through the primary winding of the transformer T1 and the first and second MOSFETs M1 and M2; when the second MOSFET M2 is turned off, the current of the dc bus flows through the primary winding of the transformer T1 and the capacitor C3 between the drain and the source of the first MOSFET M1, causing the voltage between the drain and the source of the first MOSFET M1 to increase rapidly, thereby raising the source potential, and when the source potential reaches a certain magnitude, the voltage between the gate and the source of the first MOSFET M1 will be made smaller than the gate threshold voltage, thereby causing the first MOSFET M1 to enter an off state.
In the embodiment shown in FIG. 3, a filter circuit 1352 is coupled between the DC BUS DC + BUS and the DC-BUS to filter the current drawn from the DC BUS. The snubber circuit 1353 is coupled across the primary winding of the transformer T1 and suppresses a reverse overvoltage generated across the primary winding of the transformer T1 when the second MOSFET M2 is turned off, thereby preventing the first and second MOSFETs from being damaged by breakdown.
Compared with the flyback switching power supply in the prior art, the present embodiment can effectively reduce the drain-source withstand voltage capability of a single element by using two MOSFETs connected in series as switching elements, thereby reducing the cost. In the flyback switching power supply shown in fig. 3, the input is directly taken from the dc bus, and the dc voltage adapted to the dc contactor 133 is directly generated in the secondary winding of the transformer after conversion, thereby preventing the surge current from being applied when the dc contactor is started.
It is to be noted that although the present embodiment shows an N-channel type field effect transistor, a P-channel type field effect transistor is also applicable.
Fig. 4 is a circuit schematic of an exemplary contact condition monitoring unit that may be applied to the frequency converter shown in fig. 1. As shown in fig. 4, the contact state monitoring unit 136 includes a signal amplification circuit 136A and an optical coupling circuit 136B. The signal amplification circuit 136A includes an operational amplifier a1 and a peripheral circuit constituted by resistors R7-R13 and capacitors C5-C7, a non-inverting input terminal and an inverting input terminal of the operational amplifier a1 are coupled to two contacts of the dc contactor 133, respectively, and an output terminal thereof is coupled to the photo-coupling circuit 136B. The optocoupler circuit 136B includes a light emitting diode D2 and a phototransistor Q1, wherein the anode of the light emitting diode D2 is connected to the output of the operational amplifier a1 via a resistor R12, and the collector of the phototransistor Q1 is connected to the microcontroller 131 via a resistor R13.
FIG. 5 is a graph of the output signal waveform of the contact state monitoring unit shown in FIG. 4 during normal soft start, wherein the uppermost graph shows the variation of the current flowing through the soft start resistor, and the horizontal axis of the graph is time t and the vertical axis is the current intensity I; the curve diagram below shows the change situation of the voltage on the direct current bus, wherein the horizontal axis in the diagram is time t, and the vertical axis in the diagram is voltage V; then, a graph which is immediately below the graph shows a signal output waveform of the contact state detection unit in the soft start period, wherein the horizontal axis in the graph is time t, and the vertical axis in the graph is signal amplitude A; the bottom graph shows the timing of the closing of the dc contactor contacts.
In case the soft start of the frequency converter is normal, the rectifying unit 110 charges the dc link capacitor through the soft start resistor 132. Since the charging time is short and the contacts of the dc contactor 133 are connected in parallel with the soft start resistor 132, a single pulse signal will be generated at the output of the operational amplifier a1 after a sufficiently large dc bus voltage is developed during soft start. Under the driving of the pulse signal, the led D2 will generate a corresponding optical pulse signal, which is amplified by the phototransistor Q1 to form a signal waveform as shown in fig. 5 and output to the microcontroller 131. The microcontroller 131 may thus make a determination that the current soft start is normal and maintain the contacts of the dc contactor 133 in the open state until a preset time (e.g., time t2 in fig. 5) is reached.
If the microcontroller 131 fails (e.g., the signal port coupled to the dc contactor driver 134 of fig. 1 is latched in a low state due to an interference signal) or because the switching elements (e.g., the drive transistors and fets) in the dc contactor driver 134 fail, the contacts of the dc contactor 133 will not close after the soft start process. In this case, the dc bus current continuously flows through the soft-start resistor 132. Since the current flowing through is a continuous pulse, a continuous pulse detection signal will also be generated at the output of the operational amplifier a1 of the contact state monitoring unit 136, which is amplified by the opto-coupling circuit 136B and output to the microcontroller 131, which can thus make a decision that the dc contactor 133 is not closed, generate a fault alarm indication and stop the operation of the frequency converter 10 directly or via another control unit. In particular, the frequency converter may be deactivated by stopping the power supply of the grid to the frequency converter 10 or by switching off the inverter unit 120.
The soft start resistor 132 will be bypassed during soft start if the dc contactor contacts stick together permanently due to wear, arcing, or remain in a closed state when the inverter is restarted at power down. At this time, no pulse signal is output at the output terminal of the operational amplifier a1 of the contact state monitoring unit 136, so that the port P1 of the microcontroller 131 connected to the contact state monitoring unit 136 is always in a low level state, and the microcontroller 131 can thereby make a judgment that the contacts of the dc contactor 133 are always in a closed state, generate a malfunction alarm indication, and stop the operation of the frequency converter 10 directly or through other control units. In particular, the frequency converter may be deactivated by stopping the power supply of the grid to the frequency converter 10 or by switching off the inverter unit 120.
Fig. 6 is a schematic circuit diagram of a dc contactor driver that can be applied to the frequency converter shown in fig. 1. The dc contactor driver 134 shown in fig. 6 includes a third MOSFET M3 and a second PWM signal generator U2. Referring to fig. 6, the third MOSFET M3 has a drain connected to the coil L2 of the dc contactor 133, a source connected to the ground through a resistor R14, and a gate connected to the second PWM signal generator U2 through a resistor R15. The voltage signal across resistor R14, which is effectively reflective of the magnitude of the current flowing through coil L2 in dc contactor 133, is amplified by operational amplifier a2 and sent to microcontroller 131. In this embodiment, the microcontroller 131 adjusts the output signal of the second PWM signal generator U2 based on the voltage signal across the resistor R14 in the following manner: if the current of the coil of the dc contactor, which is represented by the voltage signal flowing through the resistor R14, is greater than the preset holding current, the coil current is returned to the holding current by adjusting the signal output by the second PWM signal generator U2 (e.g., adjusting the duty ratio of the signal), and if the coil current exceeds a preset safety threshold (which is greater than the holding current), the second PWM signal generator U2 stops outputting the signal.
Fig. 7 shows a characteristic curve of the coil current flowing through the dc contactor during the start-up of the frequency converter, with time t on the horizontal axis and current intensity I on the vertical axis. As shown in FIG. 7, at the beginning of the coil energization, the coil current increases rapidly and reaches the first peak IpeakThen rapidly falls to a certain amplitude delta I, and then begins to increase until the surge peak current ImaxThereby forming a valley I after the first peakvalley. Corresponding to the characteristic curve, at the coil current from the first peak IpeakDown to the bottom of the valley IvalleyThe armature moves downward and the valley of the coil current corresponds to the position where the armature is fully dropped (i.e., the position where the contacts are fully closed). The contact position of the dc contactor can be detected using the characteristics shown in fig. 7.
Fig. 8 is a schematic diagram of a frequency converter according to another embodiment of the present invention. The frequency converter 10 shown in fig. 8 includes a rectifying unit 110, an inverter unit 120, and a frequency converter soft start circuit 130, wherein the frequency converter soft start circuit 130 is coupled between the rectifying unit 110 and the inverter unit 120. Compared with the embodiment shown in fig. 1, the frequency converter soft start circuit 130 of the present embodiment includes a dc contactor coil current measuring circuit 137 and a dc contactor contact position detecting circuit 138 in addition to a microcontroller 131, a soft start resistor 132, a dc contactor 133, a dc contactor driver 134, a flyback switching power supply 135 and a contact state monitoring unit 136. The operation principle and the circuit structure of the dc contactor driver 134, the flyback switching power supply 135 and the contact state monitoring unit 136 have been described above with reference to fig. 1 to 6, and thus, the detailed description thereof is omitted.
The dc contactor driver 134 of this embodiment also includes a shunt resistor R14 between the source of the third MOSFET M3 and ground, as in the embodiment described with reference to fig. 1-6, so that the dc contactor coil current measurement circuit 137 is capable of measuring the current flowing through the coil of the dc contactor 133 by connecting across the shunt resistor R14. The measurement signal of the dc contactor coil current measurement circuit 137 is sent to the microcontroller 131 so that the microcontroller 131 can adjust the output signal of the second PWM signal generator in the manner described above.
On the other hand, the measurement signal is also output to the dc contactor contact position detection circuit 138 for detecting the contact position of the dc contactor 133. Specifically, the dc contactor contact position detection circuit 138 may determine whether the contacts of the dc contactor 133 are fully closed in the following manner: if the falling amplitude of the current of the coil of the dc contactor, which is represented by the voltage signal flowing through the resistor R14, after reaching the first peak value during the start of the inverter is greater than the preset threshold value, it is judged that the contact of the dc contactor 133 is fully closed, and otherwise, it is judged that the contact closing operation of the dc contactor 133 is failed. As shown in fig. 8, the dc contactor contact position detection circuit 138 is coupled to the microcontroller 131 in addition to the dc contactor coil current measurement circuit 137 to output the detection result of the contact position to the microcontroller 131. Accordingly, when the microcontroller 131 receives a detection result indicating that the contacts are not completely closed from the dc contactor contact position detection circuit 138, the frequency converter 10 may be stopped directly or through another control unit. In particular, the frequency converter may be deactivated by stopping the power supply of the grid to the frequency converter 10 or by switching off the inverter unit 120.
While certain aspects of the present invention have been shown and discussed, those skilled in the art will appreciate that: changes may be made in the above aspects without departing from the principles and spirit of the invention, the scope of which is, therefore, defined in the appended claims and their equivalents.

Claims (8)

1. A frequency converter soft start circuit (130), comprising:
a microcontroller (131);
a soft-start resistor (132) coupled between the rectifying unit (110) and the dc charging capacitor (C1, C2) of the frequency converter (10);
a direct current contactor (133) whose contacts are coupled with a rectifying unit (110) and a direct current charging capacitor (C1, C2) of the inverter (10), respectively;
a flyback switching power supply (135) comprising:
a transformer (T1) having a primary winding for taking power from a direct current BUS (DC + BUS) of the frequency converter and a secondary winding coupled to a coil of the direct current contactor (133);
a switch unit (1351) coupled between the primary winding of the transformer (T1) and ground to control conduction and disconnection between the primary winding of the transformer (T1) and ground;
a DC contactor driver (134) coupled between a coil of the DC contactor (133) and ground, configured to close or open contacts of the DC contactor (133) under control of the microcontroller (131),
characterized in that the switching unit (1351) comprises a first metal oxide field effect transistor (M1) and a second metal oxide field effect transistor (M2) coupled in series between the primary of the transformer (T1) and ground and having substantially synchronized switching states,
wherein the DC contactor driver (134) comprises a second pulse width modulation signal generator (U2) and a third metal oxide field effect transistor (M3), the third metal oxide field effect transistor (M3) is coupled between the coil of the DC contactor (133) and ground, the second pulse width modulation signal generator (U2) is coupled with the gate of a third metal oxide field effect transistor (M3), the microcontroller (131) controls the DC contactor driver (134) in the following manner:
returning the current of the coil to a preset holding current by adjusting a signal output from a second pulse width modulation signal generator (U2) if the current flowing through the coil of the DC contactor (133) is greater than the holding current, stopping the second pulse width modulation signal generator (U2) from outputting the signal if the current flowing through the coil of the DC contactor (133) is greater than a preset safety threshold, wherein the safety threshold is greater than the holding current,
wherein, further comprising:
a dc contactor coil current measurement circuit (137) configured to be connected across a shunt resistor (R14) between the source of the third mosfet (M3) and ground to measure the current flowing through the coil of the dc contactor (133); and
a DC contactor contact position detection circuit (138) coupled to the DC contactor coil current measurement circuit (137) and the microcontroller (131) and configured to determine whether the contacts of the DC contactor (133) are fully closed and output the determination to the microcontroller (131) in the following manner:
if the current flowing into the coil of the DC contactor (133) reaches a first peak value (I) during the start-up of the frequency converter (10)peak) And if the later falling amplitude (delta I) is larger than a preset threshold value, judging that the contact of the direct current contactor (133) is completely closed, otherwise, judging that the contact closing operation of the direct current contactor (133) breaks down.
2. The frequency converter soft start circuit (130) as claimed in claim 1, wherein the switching unit (1351) further comprises a first pulse width modulated signal generator (U1), the gate of the first mosfet (M1) is coupled with the DC BUS (DC + BUS) and with the source via a zener diode (Z2), the drain thereof is coupled with the source via a capacitor (C3), the gate of the second mosfet (M2) is coupled with the first pulse width modulated signal generator (U1), the drain is coupled with the source of the first mosfet (M1), and the source is coupled with ground, the output signal of the first pulse width modulated signal generator (U1) is adjusted based on the voltage between the source of the second mosfet (M2) and ground.
3. The frequency converter soft start circuit (130) as claimed in claim 1, wherein the current flowing through the coil of the dc contactor (133) is measured with a shunt resistor (R14) provided between the source of the third mosfet (M3) and ground.
4. The frequency converter soft start circuit (130) as claimed in claim 1, further comprising a contact state monitoring unit (136) coupled with the microcontroller (131) and configured to generate a corresponding monitoring signal according to a voltage at a contact of the dc contactor (133), the monitoring signal indicating whether the contact is in a normal state or an abnormal state and a fault type when in the abnormal state.
5. The frequency converter soft start circuit (130) as claimed in claim 4, wherein the contact state monitoring unit (136) comprises an operational amplifier (A1), a non-inverting input terminal and an inverting input terminal of the operational amplifier (A1) are respectively coupled to different contacts of the DC contactor (133), the monitoring signal is a signal output at an output terminal of the operational amplifier (A1), and a pulse number and amplitude of the signal indicate whether the contacts are in a normal state or an abnormal state and a fault type when in the abnormal state.
6. The frequency converter soft start circuit (130) as claimed in any one of claims 1 to 5, wherein the DC contactor (133) is a single pole double coil type DC contactor.
7. The frequency converter soft start circuit (130) of any one of claims 1 to 5, wherein the DC contactor (133) is a single coil type DC contactor.
8. A frequency converter (10), comprising:
a rectifying unit (110);
an inverter unit (120); and
a frequency converter soft start circuit (130) as claimed in any one of claims 1 to 7 coupled between the rectification unit (110) and an inverter unit (120).
CN201710062781.0A 2017-01-25 2017-01-25 Frequency converter soft start circuit and frequency converter comprising same Active CN108347161B (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102751854A (en) * 2011-04-18 2012-10-24 英飞特电子（杭州）股份有限公司 Circuit of switching elements
CN203056956U (en) * 2012-12-24 2013-07-10 浙江倍得福电器有限公司 Soft start circuit of switch power source
CN203377777U (en) * 2013-08-09 2014-01-01 广东易事特电源股份有限公司 A soft start circuit of an auxiliary power supply
CN103746570A (en) * 2013-12-31 2014-04-23 华为技术有限公司 Rectifier and electric power equipment
CN105591365A (en) * 2016-02-25 2016-05-18 珠海格力节能环保制冷技术研究中心有限公司 Frequency converter main circuit relay failure protection method

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102751854A (en) * 2011-04-18 2012-10-24 英飞特电子（杭州）股份有限公司 Circuit of switching elements
CN203056956U (en) * 2012-12-24 2013-07-10 浙江倍得福电器有限公司 Soft start circuit of switch power source
CN203377777U (en) * 2013-08-09 2014-01-01 广东易事特电源股份有限公司 A soft start circuit of an auxiliary power supply
CN103746570A (en) * 2013-12-31 2014-04-23 华为技术有限公司 Rectifier and electric power equipment
CN105591365A (en) * 2016-02-25 2016-05-18 珠海格力节能环保制冷技术研究中心有限公司 Frequency converter main circuit relay failure protection method

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