Test circuit and method for soft start module in frequency converter

Abstract

A test circuit and a test method of a soft start module in a frequency converter are provided. According to an embodiment of the present disclosure, the test circuit comprises: a series-connected resistor and a contactor; and a current detection device for detecting a current flowing through the resistor, wherein the series-connected resistor and the contactor are connected between two DC bus bars of the frequency converter through bus bar terminals of the frequency converter when testing. The test method comprises: powering off the frequency converter while attracting the contactor in the test circuit; measuring the current flowing through the resistor in the test circuit; and determining whether the soft start module is abnormal based on a comparison of the current with a reference value.

Description

TECHNICAL FIELD

[0001] The present disclosure relates generally to power electronics, and more particularly, to a test circuit and method for a soft start module in a frequency converter. BACKGROUND

[0002] After the frequency converter is assembled, the functions of the circuit on the circuit board and the devices, the inter-board connection and the assembly reliability cannot be guaranteed.

[0003] Generally, the functions of the components, the assembly and the welding reliability are tested at the board level, but the connection reliability after the assembly of multiple boards and the combined functions of multiple links cannot be verified. In many cases, the whole machine function test and verification are directly performed, which cannot comprehensively cover all the hardware performance of the whole machine, and the power-on function test without verification may cause the defective machine to run and be directly damaged.

[0004] It is a difficult problem to use a simple tool to quickly and reliably test a large number of frequency converters on the production line under limited test conditions after the frequency converter is assembled. SUMMARY

[0005] Therefore, the purpose of the present disclosure is at least partially to provide a test circuit and method for a soft start module in a frequency converter to at least partially inhibit or solve the above problems.

[0006] According to a first aspect of the present disclosure, a test circuit for a soft start module in a frequency converter is provided, comprising: a series-connected resistor and contactor; and a current detection device for detecting the current flowing through the resistor, wherein the series-connected resistor and contactor are connected between two DC bus bars of the frequency converter through the bus bar terminals of the frequency converter during testing.

[0007] According to an embodiment of the present disclosure, the test circuit further comprises: a host computer for sending control instructions according to a stored test program, and receiving information and processing; and a master control board for receiving the control instructions of the host computer, and controlling the power supply, power-off and attraction of the contactor of the frequency converter according to the control instructions.

[0008] According to an embodiment of the present disclosure, the test circuit further comprises: a data acquisition card for acquiring the value of the current detected by the current detection device and sending it to the host computer for processing.

[0009] According to an embodiment of the present disclosure, in the test circuit, the current detection device detects the current flowing through the resistor by induction.

[0010] According to another aspect of the present disclosure, a test method of a soft start module in a frequency converter is provided, using the test circuit according to the first aspect of the present disclosure, comprising: powering off the frequency converter while closing a contactor in the test circuit; a current detection device measures the current flowing through a resistor in the test circuit; and based on the comparison of the current and a reference value, determining whether the soft start module is abnormal.

[0011] According to an embodiment of the present disclosure, the current detection device measures the current flowing through the resistor in the test circuit by inductive measurement.

[0012] According to an embodiment of the present disclosure, in the test method, based on the comparison of the current and the reference value, determining whether the soft start module is abnormal comprises: when the current is less than the reference value, determining that the soft start module is abnormal.

[0013] According to an embodiment of the present disclosure, before powering off the frequency converter, the test method further comprises: powering on the frequency converter and waiting for the soft start process to end.

[0014] The test circuit according to the embodiment of the present disclosure can use the filter capacitor inside the frequency converter as an auxiliary circuit after the frequency converter has been assembled, use the external terminals of the frequency converter and the external contactor and resistor, measure the discharge current of the filter capacitor inside the frequency converter, and determine whether the soft start module inside the frequency converter is abnormal by comparing the current with the reference value. Whether the soft start module is abnormal can reflect whether the connection between the related circuit boards (for example, the connection between the control circuit board in the frequency converter and the contactor in the soft start module) is reliable and stable, so that the reliability of the board-to-board connection and assembly before the frequency converter is shipped can be tested, and the test of the frequency converter that has been assembled on the production line can be improved.

[0015] The test circuit according to the present disclosure requires few components, has low cost, and is easy to operate. It can be adapted to various frequency converters by setting different reference values according to different frequency converters. BRIEF DESCRIPTION OF DRAWINGS

[0016] The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of embodiments of the present disclosure taken in conjunction with the accompanying drawings, in which:

[0017] Figure 1 A schematic diagram of a conventional frequency converter is shown;

[0018] Figure 2 A block diagram of a test circuit 200 of a soft start module according to an embodiment of the present disclosure is shown;

[0019] Figure 3A flowchart illustrating a test method 300 according to an embodiment of the present disclosure is shown; and

[0020] Figure 4 A schematic diagram of a test circuit according to another embodiment of the present disclosure is shown.

[0021] Throughout the drawings, same or similar reference numerals can represent same or similar functions throughout the text. DETAILED DESCRIPTION

[0022] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it is to be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present disclosure. Also, in the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concept of the present disclosure.

[0023] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present disclosure. As used herein, the words "a", "an", and "the" are intended to include one or more of the indicated number, unless the context clearly indicates otherwise. Furthermore, the term "including" as used herein is meant to be equivalent to the term "comprising" and is used to indicate that the listed features, steps, operations, and / or components are present, but not excluding the presence or addition of one or more other features, steps, operations, or components.

[0024] All terms used herein, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning that is consistent with the context of the specification, and should not be interpreted in an idealized or overly formal manner.

[0025] Some of the blocks and / or flowcharts in the drawings represent computer program instructions, or programs. These computer program instructions can be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to create means for implementing the functions / operations specified in the block(s) and / or flowchart(s).

[0026] A frequency converter is a power control device that applies variable frequency technology and microelectronic technology to control an AC motor by changing the frequency of the power supply to the motor.

[0027] Figure 1 A schematic diagram of a conventional frequency converter is shown. As shown, a frequency converter 100 generally includes a rectifier circuit 110 configured to convert AC power to DC power, a filter circuit 120 configured to filter the DC power, and an inverter 130 including three-phase branches for converting the DC power to AC power to drive a motor. Figure 1 ​

[0028] The rectifier circuit 110, for example, can use a diode bridge rectifier circuit for converting alternating current to direct current.

[0029] In the direct current rectified by the rectifier circuit, fluctuations are usually contained. In addition, the alternating current generated by the inverter also causes fluctuations in the direct current. In order to suppress the fluctuations, a filter circuit 120 is used. The filter circuit 120 usually uses an inductor or a capacitor to absorb the fluctuating voltage / current. Here, a filter capacitor is used as an example of the filter circuit 120.

[0030] The inverter 130 is used to convert direct current to alternating current of a desired frequency. For example, for three-phase alternating current, six switching devices can usually be used, arranged on three-phase branches respectively, and by turning on and off the switching devices, three-phase alternating current output can be obtained. Insulated Gate Bipolar Transistor (IGBT) is usually used in frequency converters due to its small driving power and low saturation voltage drop. Figure 1 An inverter composed of U, V, W three-phase branches of six IGBTs is shown.

[0031] The frequency converter adjusts the voltage and frequency of the output power source according to the on / off of the switching devices (such as IGBT), so as to provide the required power voltage to the motor according to the actual demand of the motor, so as to achieve the purpose of energy saving and speed regulation. The frequency converter usually also has a soft start module built-in, which is used to slowly raise the voltage of the filter circuit from zero to the rated voltage, avoiding the impact of the inrush current caused by the sudden power-on start of the frequency converter on the filter circuit, the inverter and even the rectifier circuit. For example, Figure 1As shown, the soft start module 140 is connected in series between the DC bus of the frequency converter and the filter circuit 120, and includes a soft start resistor 1402 and an internal contactor 1401 connected in parallel, and the working principle is that, when the frequency converter is powered on, the internal contactor 1401 is in an open state, the current output by the rectifier circuit 110 flows through the soft start resistor 1402 to charge the filter circuit 120 (for example, a filter capacitor), at this time the soft start resistor 1402 functions as a current limiter. When the voltage of the filter capacitor reaches or approaches the normal operating voltage of the DC bus, the control circuit 1403 (that is, the control part of the frequency converter, for example, can be a single-chip microcomputer) will drive the internal contactor 1401 to attract, at this time the internal contactor 1401 bypasses the soft start resistor 1402, so that the filter capacitor is directly connected between the two DC buses, and thus its voltage stabilizes at the bus voltage of the frequency converter. This is the soft start process of the frequency converter. The frequency converter needs to be tested before leaving the factory, and the functions, assembly and welding reliability of some components can be tested at the circuit board level. However, for the connection reliability of multiple circuit boards after assembly, the current technology can only be tested through the basic function test of the whole machine, and cannot be fully covered, for example, whether the connection between the control circuit 1403 and the internal contactor 1401 is stable and reliable cannot be tested through the basic function test of the whole machine. In addition, the existing technology also lacks the ability to test the state of the soft start module, which may cause serious faults. For example, during the soft start process, the current flowing through the soft start resistor 1402 will cause the temperature to rise, and if the temperature rises too high or the internal contactor repeatedly attracts within a short time, it may cause the soft start resistor to be damaged or burned out, posing a safety hazard to the frequency converter. For another example, a fault in the control circuit 1403 may prevent the internal contactor 1401 from entering the attracted state after the soft start process is completed, and thus the output current of the rectifier circuit 110 continuously flows through the soft start resistor 1402, which may also cause the soft start resistor to be damaged or burned out. For another example, if the internal contactor always remains in the attracted state due to a fault, then when the frequency converter is powered off and restarted, the soft start resistor is bypassed due to the attraction of the internal contactor, and the large current in the soft start process will damage the front-end rectifier circuit and the rear-end filter capacitor.

[0032] Therefore, the present application provides a test circuit which can test the link connection reliability and stability of the soft start module in the frequency converter after the frequency converter has been assembled, by using the external terminals of the frequency converter.

[0033] Figure 2 A block diagram of a test circuit 200 of a soft start module according to an embodiment of the present disclosure is shown.

[0034] As Figure 2As shown, the test circuit 200 for the soft start module includes a resistance 210 and an external contactor 220 connected in series between two DC bus lines (positive and negative) of the frequency converter through the bus terminal of the frequency converter. The bus terminal of the frequency converter outputs a DC voltage. The test circuit 200 further includes a current detection device 230 which can detect the current flowing through the resistance 210 in series with the resistance 210 and the external contactor 220 or inductively. Figure 3 A flowchart of the test method 300 according to an embodiment of the present disclosure is shown. The operation of the test circuit according to an embodiment of the present disclosure will be described below in conjunction with Figure 2 and Figure 3 .

[0035] Before the test, in step S305, the frequency converter is powered on to start the soft start process, the soft start module works, the internal contactor 1401 is in an open state, and the current output by the rectifier circuit 110 flows through the soft start resistance 1402 to charge the filter circuit 120. When the voltage of the filter capacitor of the filter circuit 120 reaches or approaches the normal operating voltage of the DC bus, the control circuit 1403 drives the internal contactor 1401 to be attracted, and the soft start process ends.

[0036] Next, the test process is entered. In step S310, the frequency converter is powered off, and at the same time, the external contactor 220 in the test circuit 200 is quickly attracted. At this time, the filter capacitor inside the frequency converter forms a current loop with the test circuit 200 connected through the bus terminal of the frequency converter, and thus the filter capacitor discharges through the external resistance 210. The current flowing through the resistance 210 is measured by the current detection device 230 in the resistance 210. As an example, the current detection device 230 can be a current detector. Figure 2

[0037] If the soft start module works normally, the filter capacitor is discharged through the external resistance 210 at this time. Assuming that the voltage value on the filter capacitor (i.e., the bus voltage of the frequency converter) stabilizes at U after the soft start process ends, and the resistance value of the external resistance is R, if the soft start module works normally, the current will only flow through the external resistance 210 and not through the internal soft start resistance 1402, and thus the current value I = U / R in the loop. U and R are known before the test, so the current I = U / R can be taken as a reference value.

[0038] In step S320, the current actually measured by the current detection device 230 is compared with the reference value, and based on the comparison result, it is determined whether the soft start module is abnormal. Considering the actual situation, a threshold value can be set, and if the difference between the reference value and the actually measured current exceeds the threshold value (i.e., the difference between the two exceeds a certain degree), it is determined that the soft start module is abnormal.

[0039] ​For example, if the connection of the control circuit 1403 with the soft start module is faulty, the control circuit 1403 cannot drive the internal contactor 1401 to attract, at this time, the current will still flow through the soft start resistor 1402 of the soft start module, assuming that the resistance value of the soft start resistor 1402 is R 内 , then the actually measured current I 实际 = U / (R+R 内 ) will be less than the reference value I = U / R, if it is small to a certain extent (for example, the difference between the actually measured current and the reference value exceeds a threshold value), it can be determined that the soft start module is abnormal. That is, by comparing the actually measured current value with the reference value, it can be determined whether the soft start is abnormal, and whether the connection of the circuit board related to the soft start module in the frequency converter is stable and reliable can be tested.

[0040] In other words, after the soft start process of the frequency converter is completed, whether the soft start module works normally can be tested by powering off the frequency converter and measuring the discharge current of the filter capacitor.

[0041] Figure 4 A schematic diagram of a test circuit according to another embodiment of the disclosure is shown.

[0042] As Figure 4 shown, the test circuit 400 includes a host computer 410, a master control board 420, a current detection device 430, an external resistor 440, and a contactor 450. Among them, the external resistor 440 and the contactor 450 are connected in series and connected between the positive and negative bus terminals of the frequency converter. The master control board 420 is connected to the power supply terminals of the frequency converter.

[0043] The host computer 410 can be, for example, a computer, a processor, and pre-stores an automatic test program for testing the soft start module, and realizes the overall control of the soft start module test according to the automatic test program, including sending control instructions to the master control board 420, and receiving and processing related information to determine whether the soft start module is abnormal.

[0044] The master control board 420 is used to control the power supply and power off of the frequency converter and the attraction of the contactor 450 under the control of the host computer 410. The master control board 420 can be, for example, a programmable logic controller (PLC).

[0045] The current detection device 430 is used to detect the current flowing through the external resistor 440. In Figure 4 , the current detection device 430 detects the current in an inductive manner.

[0046] Generally, the host computer 410 first sends a power-on command to the main board 420 according to a pre-stored automatic test program, and the main board 420 controls the power supply of the frequency converter according to the power-on command. After the soft start process of the frequency converter is completed, the host computer 410 sends a power-off command to the main board 420, and the main board 420 powers off the frequency converter according to the power-off command. At the same time, the main board 420 instructs the contactor 450 to attract. The current detection device 430 measures the current flowing through the external resistance 440 connected between the two DC buses of the frequency converter.

[0047] Figure 4 It is also shown that the test circuit can further include a data acquisition card 460 for acquiring the value of the current detected by the current detection device 430 and sending it to the host computer 410 for processing. For example, the host computer 410 compares the detected current value with a reference value and determines whether the soft start module is abnormal according to the comparison result.

[0048] According to the test circuit of the embodiments of the present disclosure, the internal filter capacitor of the frequency converter can be used as an auxiliary circuit after the frequency converter has been assembled, and the external terminals, external contactor and external resistance of the frequency converter can be used to determine whether the internal soft start module of the frequency converter is abnormal by using the current detection device. The test circuit requires few components, has low cost, and is simple to operate, and can be adapted to various frequency converters, and different reference values can be set according to different frequency converters.

[0049] Those skilled in the art can understand that the features described in various embodiments and / or claims of the present disclosure can be combined or / and integrated, even if such combinations or integrations are not explicitly described in the present disclosure. In particular, the features described in various embodiments and / or claims of the present disclosure can be combined and / or integrated in various combinations, without departing from the spirit and teachings of the present disclosure. All such combinations and / or integrations fall within the scope of the present disclosure.

[0050] Although the present disclosure has been shown and described with reference to certain exemplary embodiments thereof, it should be understood by those skilled in the art that various changes in form and details can be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents. Therefore, the scope of the present disclosure should not be limited to the above-described embodiments, but should be determined only by the appended claims, and should be defined by the equivalents of the appended claims.

Claims

1. A circuit for testing a soft-start module in an assembled frequency converter, comprising: A resistor and contactor connected in series, one end of which is connected to the soft starter module in the frequency converter through one bus terminal of the frequency converter, and the other end of which is connected to the soft starter module in the frequency converter through another bus terminal of the frequency converter and a filter module; and Current detection equipment The current detection device is connected in series with the resistor and contactor to detect the current flowing through the resistor; or The current detection device detects the current flowing through the resistor by induction; The contactor engages after the soft-start process of the frequency converter ends and the frequency converter is powered off. The current detection device detects the current flowing through the resistor and determines that the soft-start module in the frequency converter is abnormal when the difference between the current and the reference current value exceeds a threshold. The reference current value is the ratio of the bus voltage of the frequency converter to the resistance.

2. The circuit according to claim 1 further includes: The host computer is used to send control commands according to the stored test program, as well as to receive and process information; as well as The main control board is used to receive control commands from the host computer and control the power supply, power-off of the frequency converter, and the engagement of the contactor according to the control commands.

3. The circuit according to claim 2 further includes: The data acquisition card is used to acquire the current value detected by the current detection device and send it to the host computer for processing.

4. A method for testing a soft-start module in an assembled frequency converter, using the circuit according to any one of claims 1 to 3, comprising: After the soft start process in the frequency converter is completed, the frequency converter is powered off, and the contactor in the circuit is engaged at the same time. The current detection device measures the current flowing through the resistor in the circuit; as well as Based on the comparison between the current and the reference current value, it is determined whether the soft start module is abnormal. If the difference between the current and the reference current value exceeds a threshold, the soft start module is determined to be abnormal. The reference current value is the ratio of the inverter's bus voltage to the resistance in the circuit.

5. The testing method according to claim 4, wherein, The current detection device measures the current flowing through the resistance in the circuit, including: The current detection device measures the current flowing through the resistor by induction.

6. The testing method according to claim 4, wherein, Before powering off the inverter, the following steps are also included: Power the inverter and wait for the soft start process to finish.

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