CN109596923B

CN109596923B - Online detection device and method for bus capacitor of frequency converter and frequency converter

Info

Publication number: CN109596923B
Application number: CN201811579682.0A
Authority: CN
Inventors: 郭志海; 郭威; 陈锦权
Original assignee: Hitachi Elevator China Co Ltd
Current assignee: Hitachi Elevator China Co Ltd
Priority date: 2018-12-24
Filing date: 2018-12-24
Publication date: 2021-07-16
Anticipated expiration: 2038-12-24
Also published as: CN109596923A

Abstract

The application relates to a device and a method for online detection of bus capacitance of a frequency converter and the frequency converter. The frequency converter bus capacitor online detection device comprises a direct-current power supply circuit, a detection capacitor, a detection resistor, a peak value detection circuit and a controller connected with a frequency converter. The direct current power supply circuit can charge a bus capacitor of the frequency converter; the detection capacitor and the detection resistor are connected in series and then connected in parallel at two ends of the bus capacitor; the peak detection circuit is respectively connected with the detection capacitor and the detection resistor, obtains a peak signal of the voltage transient variation of the bus capacitor, and transmits the peak signal to the controller. The controller obtains the internal resistance of the bus capacitor based on the peak signal. The aging condition of the bus capacitor can be judged more accurately through the internal resistance change of the bus capacitor; based on this, the internal resistance of bus capacitor of frequency converter diagnostic milliohm rank for the aging testing is more accurate. Meanwhile, the diagnosis process of on-line detection of the internal resistance can be automatically carried out without manual intervention, and the testing efficiency is improved.

Description

Online detection device and method for bus capacitor of frequency converter and frequency converter

Technical Field

The application relates to the technical field of frequency converters, in particular to a device and a method for online detection of bus capacitance of a frequency converter and the frequency converter.

Background

The bus capacitor of the frequency converter is gradually aged along with time, and the capacity of the capacitor is reduced, the leakage current of the capacitor is increased, and the internal resistance of the capacitor is increased. The final failure of the bus capacitor can cause the shutdown of the frequency converter and even damage other devices, so that the aging condition of the capacitor can be judged by diagnosing the capacitance capacity or leakage current or internal resistance of the bus capacitor, and the capacitor is prevented from being damaged.

In the implementation process, the inventor finds that at least the following problems exist in the conventional technology: the bus capacitor needs to be disassembled when the internal resistance of the capacitor is measured by the bridge to judge the aging condition of the capacitor, and the on-site operation of detection personnel is needed, so that time and labor are wasted.

Disclosure of Invention

On the basis, it is necessary to provide a device and a method for online detection of a bus capacitor of a frequency converter and the frequency converter, aiming at the problems that the detection of the bus capacitor of the frequency converter by the traditional technology requires field operation and wastes time and labor.

In order to achieve the above object, in one aspect, an embodiment of the present application provides an online detection device for a bus capacitor of a frequency converter, including: the device comprises a direct current power supply circuit, a detection capacitor, a detection resistor, a peak value detection circuit and a controller for connecting the frequency converter.

A first electrode of the direct-current power supply circuit is respectively connected with a first end of a bus capacitor of the frequency converter and a first end of the detection capacitor; a second electrode of the direct current power supply circuit is respectively connected with a second end of the bus capacitor and a first end of the detection resistor; the second end of the detection capacitor is respectively connected with the second end of the detection resistor and the first end of the peak detection circuit; the second end of the peak detection circuit is connected with the first end of the detection resistor, and the third end of the peak detection circuit is connected with the controller. The controller is respectively connected with the control end of the direct current power supply circuit, an Insulated Gate Bipolar Transistor (IGBT) module of the frequency converter and a three-phase power switch of the frequency converter.

The peak detection circuit acquires a peak signal of the voltage transient variation of the bus capacitor based on the detection capacitor and the detection resistor and transmits the peak signal to the controller; the controller obtains the internal resistance of the bus capacitor based on the peak signal.

In one embodiment, a DC power circuit includes a DC power source and a charging switch. The first electrode of the direct current power supply is connected with the first end of the bus capacitor and the first end of the detection capacitor through the charging switch respectively, and the second electrode of the direct current power supply is connected with the second end of the bus capacitor and the first end of the detection resistor respectively. The controller is also used for respectively controlling the on-off of the charging switch, the IGBT module and the three-phase power switch.

In one embodiment, the dc power supply circuit further includes a charging resistor.

The first electrode of the direct current power supply is connected with the charging switch through the charging resistor.

Or the second electrode of the direct current power supply is respectively connected with the second end of the bus capacitor and the first end of the detection resistor through the charging resistor.

In one embodiment, the device further comprises an isolation circuit; and the third end of the peak detection circuit is connected with the controller through an isolation circuit.

On the other hand, the embodiment of the application also provides a method for the frequency converter bus capacitor online detection device, which comprises the following steps:

and controlling the IGBT module and the three-phase power switch to be disconnected.

And when the voltage of the bus capacitor is lower than the preset voltage, controlling the direct-current power supply circuit to charge the bus capacitor, and stopping charging of the direct-current power supply circuit when the voltage of the bus capacitor reaches the preset voltage.

And controlling the bridge arm of any phase in the IGBT module to be conducted so as to discharge the bus capacitor through the IGBT module.

And obtaining the internal resistance of the bus capacitor based on the peak signal obtained by the peak detection circuit when the bridge arm is conducted.

In one embodiment, the step of obtaining the internal resistance of the bus capacitor based on the peak signal obtained by the peak detection circuit when the bridge arm is turned on includes:

and obtaining the conduction saturation voltage drop of the IGBT module according to the peak signal.

And processing the conduction saturation voltage drop to obtain the transient current.

And obtaining the internal resistance according to the peak signal and the transient current.

In one embodiment, the step of obtaining the turn-on saturation voltage drop of the IGBT module according to the peak signal includes:

and obtaining the conduction saturation voltage drop by subtracting the preset voltage from the peak value signal.

In one embodiment, the step of processing the turn-on saturation voltage drop to obtain the transient current comprises:

and inquiring in a preset voltage-current relation table to obtain the transient current based on the conduction saturation voltage drop.

Or fitting in a preset IGBT voltage current curve based on the conduction saturation voltage drop to obtain the transient current.

Or obtaining a transient current based on the conduction saturation voltage drop and the relational expression; and the relational expression is obtained by fitting a preset IGBT voltage current curve.

In one embodiment, the step of obtaining the internal resistance according to the peak signal and the transient current includes:

and obtaining the internal resistance based on the ratio of the peak signal to the transient current.

In one embodiment, the frequency converter further comprises a three-phase power switch, a rectifier, a bus capacitor, an IGBT module and the frequency converter bus capacitor online detection device.

The input end of the three-phase power switch is used for connecting a three-phase power supply, and the output end of the three-phase power switch is connected with the input end of the rectifier; the first electrode of the rectifier is respectively connected with the first end of the bus capacitor and the first end of the IGBT module, and the second electrode of the rectifier is respectively connected with the second end of the bus capacitor and the second end of the IGBT module.

One of the above technical solutions has the following advantages and beneficial effects:

the on-line detection device for the bus capacitor of the frequency converter comprises a direct-current power supply circuit, a detection capacitor, a detection resistor, a peak value detection circuit and a controller used for being connected with the frequency converter. The direct current power supply circuit can charge a bus capacitor of the frequency converter; the detection capacitor and the detection resistor are connected in series and then connected in parallel at two ends of the bus capacitor; the peak detection circuit is respectively connected with the detection capacitor and the detection resistor, obtains a peak signal of the voltage transient variation of the bus capacitor, and transmits the peak signal to the controller. The controller obtains the internal resistance of the bus capacitor based on the peak signal. The aging condition of the bus capacitor can be judged more accurately through the internal resistance change of the bus capacitor; based on this, the internal resistance of bus capacitor of frequency converter diagnostic milliohm rank for the aging testing is more accurate. Meanwhile, the diagnosis process of on-line detection of the internal resistance can be automatically carried out without manual intervention, and the testing efficiency is improved.

Drawings

The foregoing and other objects, features and advantages of the application will be apparent from the following more particular description of preferred embodiments of the application, as illustrated in the accompanying drawings. Like reference numerals refer to like parts throughout the drawings, and the drawings are not intended to be drawn to scale in actual dimensions, emphasis instead being placed upon illustrating the subject matter of the present application.

FIG. 1 is a first schematic structural diagram of an on-line detection device for bus capacitance of a frequency converter in one embodiment;

FIG. 2 is a second schematic structural diagram of an on-line detection device for bus capacitance of a frequency converter in one embodiment;

FIG. 3 is a third schematic structural diagram of an on-line detection device for bus capacitance of a frequency converter in one embodiment;

FIG. 4 is a first schematic flow chart diagram of a method for on-line detection of a bus capacitor of a frequency converter in one embodiment;

FIG. 5 is a second schematic flow chart diagram of a method for on-line detection of a bus capacitor of a frequency converter in one embodiment;

FIG. 6 is a third schematic flow chart diagram illustrating a method for on-line detection of bus capacitance of a frequency converter in one embodiment;

FIG. 7 is a first schematic block diagram of a frequency converter in one embodiment;

FIG. 8 is a second schematic block diagram of a frequency converter in one embodiment;

fig. 9 is a schematic flow chart of a method for online detection of internal resistance of a bus capacitor of a frequency converter in one embodiment.

Detailed Description

To facilitate an understanding of the present application, the present application will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present application are shown in the drawings. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

It will be understood that when an element is referred to as being "connected" to another element, it can be directly connected to the other element and be integral therewith, or intervening elements may also be present. The terms "control," "first end," "second end," and the like are used herein for illustrative purposes only.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The frequency converter mainly comprises a rectifying unit (alternating current to direct current), a filtering unit, an inverting unit (direct current to alternating current), a braking unit, a driving unit, a detecting unit, a micro-processing unit and the like. The frequency converter adjusts the voltage and the frequency of an output power supply by switching on and off the internal IGBT module, and provides the required power supply voltage according to the actual requirement of the motor, thereby achieving the purposes of energy conservation and speed regulation. The frequency converter can comprise a three-phase power switch, a bus capacitor and an IGBT module. The three-phase power switch can be used for controlling the connection or disconnection of a three-phase input power supply. The bus capacitor can be used for filtering, and particularly, the output voltage of the rectifying circuit can be smoothed, and the alternating current component can be reduced to the minimum. The IGBT module can be used for converting direct current into alternating current of a driving motor.

The traditional technology obtains the capacitance capacity through the charging and discharging time of the bus capacitor, and then judges the aging condition of the bus capacitor of the frequency converter. In the use process of the frequency converter, along with the aging of the bus capacitor, the change rate of the internal resistance of the capacitor is far larger than that of the capacitance, so that the aging test of the bus capacitor by the traditional technology is not accurate, manual intervention is needed, and the problem of difficult diagnosis of the bus capacitor exists.

To this end, in an embodiment, an on-line detection device for a bus capacitor of a frequency converter is provided, as shown in fig. 1, where fig. 1 is a first schematic structural diagram of the on-line detection device for a bus capacitor of a frequency converter in an embodiment, and includes: the device comprises a direct current power supply circuit, a detection capacitor, a detection resistor, a peak value detection circuit and a controller for connecting the frequency converter.

A first electrode of the direct-current power supply circuit is respectively connected with a first end of a bus capacitor of the frequency converter and a first end of the detection capacitor; a second electrode of the direct current power supply circuit is respectively connected with a second end of the bus capacitor and a first end of the detection resistor; the second end of the detection capacitor is respectively connected with the second end of the detection resistor and the first end of the peak detection circuit; the second end of the peak detection circuit is connected with the first end of the detection resistor, and the third end of the peak detection circuit is connected with the controller. The controller is respectively connected with the control end of the direct-current power supply circuit, the IGBT module of the frequency converter and the three-phase power supply switch of the frequency converter.

Specifically, the direct-current power supply circuit is connected in parallel at two ends of the bus capacitor and can be used for providing standard direct-current voltage when detecting the internal resistance of the bus capacitor. The first end of the detection capacitor is connected with the first end of the bus capacitor, and the second end of the detection capacitor is connected with the second end of the detection resistor; the first end of the detection resistor is connected with the second end of the bus capacitor; namely, the detection capacitor is connected with the detection resistor in series and then is connected with two ends of the bus capacitor in parallel.

The first end of the peak detection circuit is respectively connected with the second end of the detection capacitor and the second end of the detection resistor, the second end of the peak detection circuit is connected with the first end of the detection resistor, and the third end of the peak detection circuit is connected with the controller. That is, the first terminal and the second terminal of the peak detection circuit are connected in parallel with the detection resistor. The controller is respectively connected with the control end of the direct-current power supply circuit, the IGBT module and the three-phase power supply switch.

The detection capacitor and the detection resistor extract the voltage transient variation of the bus capacitor, and the peak detection circuit acquires a peak signal based on the voltage transient variation and transmits the peak signal to the controller. The controller can obtain the internal resistance of the bus capacitance based on the peak signal transmitted by the peak detection circuit.

It should be noted that the IGBT module can be used as a transient load when detecting the internal resistance of the bus capacitor. Specifically, the IGBT module comprises a U-phase bridge arm, a V-phase bridge arm and a W-phase bridge arm. The U-phase bridge arm can comprise a U-phase upper bridge arm and a U-phase lower bridge arm; the V-phase bridge arm can comprise a V-phase upper bridge arm and a V-phase lower bridge arm; the W-phase bridge arm may include a W-phase upper bridge arm and a W-phase lower bridge arm. In one specific example, the U-phase leg includes two IGBTs, the V-phase leg includes two IGBTs, and the W-phase leg includes two IGBTs.

The direct-current power supply circuit can be used for charging the bus capacitor, so that the bus capacitor reaches a preset voltage, and the on-line test of the internal resistance is met. Specifically, the dc power circuit may be powered by a dc power source, a battery, or a three-phase power conversion, and the like, which is not limited herein; alternatively, the dc power circuit may provide 3V (volt), 5V or 10V for the bus capacitor, which is not limited herein.

The detection capacitor and the detection resistor can be used for extracting the voltage transient variation of the bus capacitor, and meanwhile, the detection capacitor and the detection resistor can also be used for isolating the bus voltage. Specifically, the preposed detection capacitor and the detection resistor can isolate the bus voltage in normal operation, and extract the voltage transient variation of the bus capacitor when the internal resistance of the bus capacitor is detected. Alternatively, the detection resistor may be a load with a preset resistance value, and the detection capacitor may be a charge-discharge device with a preset capacitance value.

The peak detection circuit may be used to extract a peak of the input signal, for example, to extract a peak signal of a voltage transient variation of the bus capacitance. Specifically, the peak detection circuit may mainly include a capacitor, a diode, an operational amplifier, and a reset switch, and various embodiments thereof are possible and not limited herein.

The controller can be used for respectively controlling the connection or disconnection of the direct-current power supply circuit, the IGBT module and the three-phase power supply switch; meanwhile, the internal resistance value of the bus capacitor can be obtained according to the fed back peak value signal of the bus capacitor. Specifically, the controller may be implemented by a single chip, a Digital Signal Processing (DSP), a Field Programmable Gate Array (FPGA), or other devices, which is not limited herein.

In the embodiment of the application, the controller can control the frequency converter to stop outputting and cut off the three-phase input power supply; the direct-current power supply circuit can charge a bus capacitor of the frequency converter based on an instruction of the controller; the detection capacitor and the detection resistor are connected in series and then connected in parallel at two ends of the bus capacitor; the peak detection circuit is respectively connected with the detection capacitor and the detection resistor, obtains a peak signal of the voltage transient variation of the bus capacitor and transmits the peak signal to the controller; the controller obtains the internal resistance of the bus capacitor based on the peak signal. The aging condition of the bus capacitor can be judged more accurately through the internal resistance change of the bus capacitor; based on this, the internal resistance of bus capacitor of frequency converter diagnostic milliohm rank for the aging testing is more accurate. Meanwhile, the diagnosis process of online detection of the internal resistance can be automatically carried out without manual intervention or disassembly of the bus capacitor, so that the test efficiency is improved. In addition, the embodiment of the application can be arranged in a frequency converter,

in an embodiment, as shown in fig. 2, fig. 2 is a second schematic structural diagram of an on-line detection device of a bus capacitor of a frequency converter in an embodiment, and a dc power circuit includes a dc power source and a charging switch. The first electrode of the direct current power supply is connected with the first end of the bus capacitor and the first end of the detection capacitor through the charging switch respectively, and the second electrode of the direct current power supply is connected with the second end of the bus capacitor and the first end of the detection resistor respectively. The controller is also used for respectively controlling the on-off of the charging switch, the IGBT module and the three-phase power switch.

Specifically, the dc power supply circuit may include a dc power supply and a charging switch. The direct current power supply is connected with the bus capacitor through the charging switch. The direct current power supply can be used for providing preset voltage for charging the bus capacitor; the charging switch can be used for switching on or switching off the direct current power supply and controlling the charging or stopping the charging of the bus capacitor.

It should be noted that the controller can respectively control the charging switch, the IGBT module, and the three-phase power switch to be turned on or off; specifically, the controller can control the direct-current power supply to charge the bus capacitor based on the charging switch, can control the bridge arm of any phase in the IGBT module to be connected, and can also control the three-phase input power supply to be connected or disconnected based on the three-phase power supply switch. Alternatively, the controller may control the on/off of the charging switch by a relay, a contactor, or a switching tube, which is not specifically limited herein.

The embodiment of the application adopts the direct-current power supply, so that the preset voltage is conveniently provided for the bus capacitor; the preset voltage and the voltage supply of the direct current power supply circuit can be set according to actual requirements. The controller may obtain a preset voltage and/or a charging voltage provided by the dc power circuit.

In one embodiment, as shown in fig. 2, the dc power supply circuit further includes a charging resistor.

Specifically, the direct current power supply circuit further includes a charging resistor; the direct current power supply is connected with the bus capacitor through the charging resistor.

It should be noted that the charging resistor can be used to limit the charging current when the dc power supply is turned on, so as to avoid the damage of the current overload to the frequency converter or the online testing device, and improve the safety.

In an embodiment, as shown in fig. 3, fig. 3 is a third schematic structural diagram of an online detection device of a bus capacitor of a frequency converter in an embodiment, and further includes an isolation circuit; and the third end of the peak detection circuit is connected with the controller through an isolation circuit.

Specifically, the frequency converter bus capacitance online detection device can also comprise an isolation circuit; an isolation circuit is connected between the peak detection circuit and the controller.

It should be noted that the isolation circuit can be used to convert the peak signal into a signal having the same reference ground as the controller, and can isolate the high voltage from the low voltage, thereby improving the safety of the detection device. Specifically, the isolation circuit can realize isolation of high and low voltage and signal conversion based on a linear optical coupler. It should be noted that the specific implementation of the isolation circuit is various and not limited herein.

In an embodiment, a method for detecting a bus capacitor of a frequency converter on line based on the above-mentioned apparatus is provided, as shown in fig. 4, fig. 4 is a first schematic flowchart of a method for detecting a bus capacitor of a frequency converter on line in an embodiment, and includes:

and step S110, controlling the IGBT module and the three-phase power switch to be disconnected.

Specifically, the controller controls the three-phase bridge arm in the IGBT module to be disconnected, stops the output of the frequency converter, and disconnects the three-phase power switch to cut off the three-phase input power. Specifically, the controller may control U, V, W the IGBTs for the three phases to remain in an off state.

And step S120, when the voltage of the bus capacitor is lower than the preset voltage, controlling the direct-current power supply circuit to charge the bus capacitor, and when the voltage of the bus capacitor reaches the preset voltage, stopping charging of the direct-current power supply circuit.

Specifically, when the voltage of the bus capacitor is lower than the preset voltage, the controller switches on the direct-current power supply circuit to charge the bus capacitor, so that the voltage of the bus capacitor reaches the preset voltage. When the bus capacitor is charged to the preset voltage, the controller disconnects the direct current power supply circuit to stop charging.

It should be noted that the preset voltage may be set according to actual requirements, such as 5V, 3V, 10V, and the like, which is not limited herein; meanwhile, the preset voltage can also be the voltage provided by the direct-current power supply circuit. The controller may input the preset voltage in advance, or obtain the preset voltage through the dc power circuit.

And S130, controlling the bridge arm of any phase in the IGBT module to be conducted so as to discharge the bus capacitor through the IGBT module.

Specifically, after the bus capacitor is charged to a preset voltage and the direct-current power supply circuit is disconnected, the controller switches on a bridge arm of any phase in the IGBT module to conduct; the bus capacitor can discharge through the bridge arm conducted in the IGBT module. Specifically, the controller can switch on or off the upper and lower arms of the U-phase, the upper and lower arms of the V-phase, or the upper and lower arms of the W-phase.

And step S140, obtaining the internal resistance of the bus capacitor based on the peak value signal obtained by the peak value detection circuit when the bridge arm is conducted.

Specifically, the peak detection circuit acquires a peak signal of the voltage transient variation of the bus capacitor when the IGBT arm is turned on, and transmits the peak signal to the controller. The controller processes the peak signal to obtain the internal resistance of the bus capacitance.

In the embodiment of the application, the controller can control the output of the frequency converter, the on-off of the frequency converter and the three-phase input power supply and the on-off of any phase in the IGBT module, and can also control the direct-current power supply circuit to charge the bus capacitor and acquire the peak signal of the voltage transient variation of the bus capacitor through the peak detection circuit. Based on this, the controller can on-line measuring the internal resistance of the bus capacitor of converter, the degree of ageing of accurate test bus capacitor to ageing testing process can be by controller automatic operation, avoids the dismantlement of bus capacitor, improves the efficiency and the reliability of test.

In an embodiment, as shown in fig. 5, fig. 5 is a second schematic flowchart of an on-line detection method for a bus capacitor of a frequency converter in an embodiment, where the step of obtaining an internal resistance of the bus capacitor based on a peak signal obtained when a bridge arm is turned on by a peak detection circuit includes:

and step S142, obtaining the conduction saturation voltage drop of the IGBT module according to the peak value signal.

And step S144, processing the conduction saturation voltage drop to obtain the transient current.

And step S148, obtaining the internal resistance according to the peak value signal and the transient current.

Specifically, the controller can process the peak value signal of the voltage transient variation of the bus capacitor when the IGBT is turned on to obtain the turn-on saturation voltage drop of the IGBT module at that time. Further, the controller processes the turn-on saturation voltage drop of the IGBT at the moment, and the transient current at the turn-on moment of the IGBT can be obtained. The controller can process and obtain the internal resistance of the bus capacitor according to the peak value signal of the bus capacitor and the transient current when the IGBT is conducted.

According to the embodiment of the application, the internal resistance of the bus capacitor can be quickly obtained based on the peak signal, the conduction saturation voltage drop and the transient current.

In an embodiment, as shown in fig. 6, fig. 6 is a third schematic flowchart of an on-line detection method for a bus capacitor of a frequency converter in an embodiment, and the step of obtaining a conduction saturation voltage drop of an IGBT module according to a peak signal includes:

step S143, obtaining a conduction saturation voltage drop by subtracting the preset voltage from the peak signal.

Specifically, the turn-on saturation voltage drop of the IGBT module is obtained by subtracting a preset voltage from a peak signal of a bus capacitor when the IGBT is turned on.

It should be noted that the controller may perform a difference between the preset voltage and the peak signal, and determine a result of the difference as the conduction saturation voltage drop, or may optimize a result of the difference by using an optimization coefficient, and determine a result after the optimization as the conduction saturation voltage drop.

and fitting in a preset IGBT voltage and current curve based on the conduction saturation voltage drop to obtain the transient current. Or obtaining a transient current based on the conduction saturation voltage drop and the relational expression; and the relational expression is obtained by fitting a preset IGBT voltage current curve.

Specifically, for the transient current at the turn-on time of the IGBT, the controller may fit in a preset IGBT voltage-current curve to obtain a transient current corresponding to the turn-on saturation voltage drop; meanwhile, the voltage drop of the conduction saturation and the relation can be adopted for processing. The relational expression can be obtained by fitting according to a preset IGBT voltage current curve; specifically, the preset IGBT voltage-current curve may be a relationship curve of the turn-on voltage and the turn-on current of the IGBT data manual; the relational expression can be obtained by fitting according to a relational curve of the breakover voltage and the breakover current of the IGBT data manual.

It should be noted that the controller may store the relational expression, and process the conduction saturation voltage drop based on the relational expression to obtain the transient current. The relation may further include an optimization parameter, which may be used to improve the accuracy of the transient current.

In one embodiment, as shown in fig. 6, the step of processing the turn-on saturation voltage drop to obtain the transient current comprises:

in step S145, the transient current is obtained by looking up in a preset voltage-current relationship table based on the conduction saturation voltage drop.

Specifically, for the transient current at the turn-on time of the IGBT, the controller may further query the current corresponding to the turn-on saturation voltage drop in a preset voltage-current relationship table, and determine the current as the transient current; meanwhile, the controller can also optimize the current, and the optimized result is confirmed as the transient current.

It should be noted that the preset voltage-current relationship table may be a pre-established relationship table of the on-state voltage and the on-state current. Specifically, the accuracy of the on-voltage-to-on-current relationship table may be 0.01V, 0.02V, or 0.05V, which is not limited herein. The controller can set a preset voltage-current relation table with corresponding precision according to actual requirements so as to improve the processing efficiency.

In one embodiment, as shown in fig. 6, the step of obtaining the internal resistance according to the peak signal and the transient current includes:

step S149, the internal resistance is obtained based on the ratio of the peak signal to the transient current.

Specifically, the controller may determine a ratio of the peak signal to the transient current as the internal resistance, or may optimize the ratio using an optimization coefficient, and use the optimized result as the internal resistance. Specifically, the internal resistance of the bus capacitor may be equal to the peak signal of the voltage transient variation of the bus capacitor divided by the transient current when the IGBT is turned on.

In the embodiment of the application, the controller can diagnose the internal resistance of the bus capacitor of the frequency converter at the milliohm level, and the aging condition of the bus capacitor is judged more accurately through the internal resistance change of the bus capacitor; meanwhile, the diagnosis process is automatically carried out, manual intervention is not needed, and the testing efficiency is improved.

It should be understood that, although the steps in the flowcharts of fig. 4 to 6 are shown in order as indicated by the arrows, the steps are not necessarily performed in order as indicated by the arrows. The steps are not performed in the exact order shown and described, and may be performed in other orders, unless explicitly stated otherwise. Moreover, at least some of the steps in fig. 4-6 may include multiple sub-steps or multiple stages that are not necessarily performed at the same time, but may be performed at different times, and the order of performing the sub-steps or stages is not necessarily sequential, but may be performed in turn or alternately with other steps or at least some of the sub-steps or stages of other steps.

In one embodiment, there is provided a frequency converter, as shown in fig. 7, fig. 7 is a first schematic structural diagram of the frequency converter in one embodiment, and includes a three-phase power switch, a rectifier, a bus capacitor, an IGBT module, and the above-mentioned online detection device for bus capacitor of the frequency converter.

Specifically, the frequency converter comprises a three-phase power switch, a rectifier, a bus capacitor and an IGBT module which are sequentially connected; the three-phase power switch is used for being connected with a three-phase input power supply, and the IGBT module is used for being connected with a motor. That is, the rectifier rectifies the input three-phase power and applies the rectified three-phase power to the IGBT module, and the bus capacitor is connected in parallel with the rectifier and the IGBT module, respectively. In addition, the frequency converter is also provided with an on-line detection device for the bus capacitance of the frequency converter, and the on-line detection device can respectively control the on-off of the three-phase power switch and the IGBT module, detect the internal resistance of the bus capacitance on line and carry out aging test on the bus capacitance more accurately.

It should be noted that, the controller of the online detection device may be connected to the gate of each IGBT in the IGBT module, respectively, for controlling the turn-on and turn-off of the IGBT module, and may test the internal resistance of the bus capacitor online, and may also adjust the voltage and frequency of the output power supply, so that the frequency converter provides the required power supply voltage according to the actual needs of the motor. Namely, the on-line detection device for the bus capacitor of the frequency converter can be arranged in the frequency converter and used for controlling the IGBT module to realize frequency conversion, and meanwhile, the aging degree of the bus capacitor can be detected on line. The IGBT topology in the IGBT module may have multiple modes, which is not limited herein.

In an embodiment, as shown in fig. 8, fig. 8 is a second schematic structural diagram of an embodiment of a frequency converter, and an apparatus for online detecting an internal resistance of a bus capacitor of the frequency converter includes: the device comprises a switch K1, an IGBT module, a direct-current low-voltage power supply, a charging resistor Rs, a switch K2, a front detection capacitor Cf, a detection resistor Rf, a peak detection circuit, an isolation circuit and a main controller.

Among them, the switch K1 is a three-phase power switch for connecting/disconnecting a three-phase input power, and specifically, the switch K1 may use a contactor through which a main controller controls the connection/disconnection of the three-phase input power. The IGBT module converts direct current into alternating current of a driving motor and serves as a transient load when detecting internal resistance of a bus capacitor. The direct current low-voltage power supply provides standard direct current voltage when detecting the internal resistance of the bus capacitor. The charging resistor Rs is used to limit the charging current when the dc low-voltage power supply is turned on. The switch K2 is a charging switch for turning on/off the dc low-voltage power supply.

The preposed detection capacitor Cf and the detection resistor Rf isolate the bus voltage in normal operation, and extract the voltage transient variation of the bus capacitor when detecting the internal resistance of the bus capacitor. The peak detection circuit extracts peak signals of transient voltage variations output by the pre-detection capacitor Cf and the detection resistor Rf. The isolation circuit converts the peak signal of the voltage transient variation into a signal having the same reference ground as the main controller.

The main controller controls the on/off of the switches K1, K2 and the IGBT, and calculates the internal resistance value of the bus capacitor according to the fed-back transient variation signal of the bus capacitor voltage.

In an embodiment, based on the frequency converter, an online detection method for internal resistance of a bus capacitor of the frequency converter is provided, as shown in fig. 9, fig. 9 is a schematic flow diagram of the online detection method for internal resistance of the bus capacitor of the frequency converter in an embodiment, and includes the following steps:

a) u, V, W the three-phase IGBTs are all kept in an off state, and the switch K1 is turned off to cut off the three-phase input power supply.

b) And when the voltage of the bus capacitor of the frequency converter is lower than the voltage of the direct-current low-voltage power supply, the switch K2 is switched on, so that the voltage of the bus capacitor reaches the voltage of the direct-current low-voltage power supply.

c) And after the switch K2 is turned off, the IGBTs of the U-phase upper and lower arm, the IGBTs of the V-phase upper and lower arm or the IGBTs of the W-phase upper and lower arm are turned on, so that the bus capacitor is discharged through the IGBTs.

d) And the main controller calculates the conduction saturation voltage drop of the IGBT at the moment according to the voltage transient variation signal of the bus capacitor when the IGBT is conducted. The turn-on saturation voltage drop of the IGBT can be equal to the transient variation of the direct-current low-voltage power voltage minus the bus capacitor voltage when the IGBT is turned on.

e) And the main controller calculates the transient current at the IGBT conduction moment according to the IGBT conduction saturation voltage drop at the moment.

Specifically, the transient current at the turn-on time of the IGBT may be calculated from a relationship curve between the turn-on voltage and the turn-on current of the IGBT.

Or the transient current at the turn-on time of the IGBT can be calculated according to a relational expression of the turn-on voltage and the turn-on current of the IGBT; the relation between the on-state voltage and the on-state current of the IGBT is obtained by fitting according to a relation curve between the on-state voltage and the on-state current of an IGBT data manual.

Or, the transient current at the turn-on time of the IGBT may also be obtained by querying a pre-established relationship table between the turn-on voltage and the turn-on current; wherein, the relation table of the conduction voltage and the conduction current is established with the precision that the conduction voltage is 0.02V.

f) The main controller calculates the internal resistance of the bus capacitor according to the transient variation of the bus capacitor voltage and the transient current at the IGBT turn-on time, and the relation is as follows: the internal resistance of the bus capacitor is equal to the transient variation of the voltage of the bus capacitor divided by the transient current at the turn-on time of the IGBT.

In the embodiment of the application, the frequency converter can diagnose the internal resistance of the milliohm-level bus capacitor, and the aging condition of the bus capacitor is judged more accurately through the internal resistance change of the bus capacitor; meanwhile, the diagnosis process is automatically carried out, manual intervention is not needed, and the testing efficiency is improved.

In one embodiment, a computer-readable storage medium is provided, having a computer program stored thereon, which when executed by a processor, performs the steps of:

In one embodiment, when the processor executes the internal resistance of the bus capacitor based on the peak signal obtained by the peak detection circuit when the bridge arm is turned on, the following steps are also implemented:

In one embodiment, when the computer program is executed by the processor to obtain the turn-on saturation voltage drop of the IGBT module according to the peak signal, the following steps are further implemented:

In one embodiment, the computer program is executed by the processor to process the turn-on saturation voltage drop to obtain the transient current, and further implements the following steps:

In one embodiment, when the computer program is executed by the processor to obtain the internal resistance according to the peak signal and the transient current, the following steps are further implemented:

It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, storage, database, or other medium used in the embodiments provided herein may include non-volatile and/or volatile memory, among others. Non-volatile memory can include read-only memory (ROM), Programmable ROM (PROM), Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), or flash memory. Volatile memory can include Random Access Memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms such as Static RAM (SRAM), Dynamic RAM (DRAM), Synchronous DRAM (SDRAM), Double Data Rate SDRAM (DDRSDRAM), Enhanced SDRAM (ESDRAM), Synchronous Link DRAM (SLDRAM), Rambus Direct RAM (RDRAM), direct bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present application. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present application shall be subject to the appended claims.

Claims

1. The utility model provides a converter bus capacitance on-line measuring device which characterized in that includes: the device comprises a direct-current power supply circuit, a detection capacitor, a detection resistor, a peak value detection circuit and a controller for connecting a frequency converter;

a first electrode of the direct-current power supply circuit is respectively connected with a first end of a bus capacitor of the frequency converter and a first end of the detection capacitor; a second electrode of the direct-current power supply circuit is respectively connected with a second end of the bus capacitor and a first end of the detection resistor; the second end of the detection capacitor is respectively connected with the second end of the detection resistor and the first end of the peak detection circuit; the second end of the peak detection circuit is connected with the first end of the detection resistor, and the third end of the peak detection circuit is connected with the controller;

the controller is respectively connected with the control end of the direct-current power supply circuit, the IGBT module of the frequency converter and the three-phase power switch of the frequency converter;

the peak detection circuit acquires a peak signal of the voltage transient variation of the bus capacitor based on the detection capacitor and the detection resistor, and transmits the peak signal to the controller; the controller obtains the internal resistance of the bus capacitor based on the peak signal; the controller controls the IGBT module and the three-phase power switch to be switched off, controls the direct-current power circuit to charge the bus capacitor when the voltage of the bus capacitor is lower than a preset voltage, and stops charging the direct-current power circuit when the voltage of the bus capacitor reaches the preset voltage; the controller controls the bridge arm of any phase in the IGBT module to be conducted so that the bus capacitor is discharged through the IGBT module, and the internal resistance of the bus capacitor is obtained based on the peak value signal acquired by the peak value detection circuit when the bridge arm is conducted.

2. The on-line detection device for the bus capacitance of the frequency converter according to claim 1, wherein the direct-current power supply circuit comprises a direct-current power supply and a charging switch;

a first electrode of the direct current power supply is respectively connected with a first end of the bus capacitor and a first end of the detection capacitor through the charging switch, and a second electrode of the direct current power supply is respectively connected with a second end of the bus capacitor and a first end of the detection resistor;

the controller is also used for respectively controlling the on-off of the charging switch, the IGBT module and the three-phase power switch.

3. The on-line detection device for the bus capacitance of the frequency converter according to claim 2, wherein the direct current power supply circuit further comprises a charging resistor;

the first electrode of the direct current power supply is connected with the charging switch through the charging resistor; alternatively, the first and second electrodes may be,

and the second electrode of the direct current power supply is respectively connected with the second end of the bus capacitor and the first end of the detection resistor through the charging resistor.

4. The frequency converter bus capacitance online detection device according to any one of claims 1 to 3, characterized by further comprising an isolation circuit;

and the third end of the peak detection circuit is connected with the controller through the isolation circuit.

5. A method for the on-line detection device of the bus capacitance of the frequency converter based on any one of claims 1 to 4 is characterized by comprising the following steps:

controlling the IGBT module and the three-phase power switch to be disconnected;

when the voltage of the bus capacitor is lower than a preset voltage, controlling the direct-current power supply circuit to charge the bus capacitor, and when the voltage of the bus capacitor reaches the preset voltage, stopping charging of the direct-current power supply circuit;

controlling the bridge arm of any phase in the IGBT module to be conducted so as to enable the bus capacitor to discharge through the IGBT module;

and obtaining the internal resistance of the bus capacitor based on the peak value signal obtained by the peak value detection circuit when the bridge arm is switched on.

6. The method according to claim 5, wherein the step of obtaining the internal resistance of the bus capacitor based on the peak signal obtained by the peak detection circuit when the bridge arm is turned on comprises:

obtaining the conduction saturation voltage drop of the IGBT module according to the peak value signal;

processing the conduction saturation voltage drop to obtain transient current;

and obtaining the internal resistance according to the peak value signal and the transient current.

7. The method of claim 6, wherein the step of obtaining the turn-on saturation voltage drop of the IGBT module according to the peak signal comprises:

8. The method of claim 6, wherein processing the turn-on saturation voltage drop to obtain a transient current comprises:

based on the conduction saturation voltage drop, inquiring in a preset voltage-current relation table to obtain the transient current; alternatively, the first and second electrodes may be,

fitting in a preset IGBT voltage current curve based on the conduction saturation voltage drop to obtain the transient current; alternatively, the first and second electrodes may be,

obtaining the transient current based on the conduction saturation voltage drop and a relational expression; and the relational expression is obtained by fitting a preset IGBT voltage current curve.

9. The method according to any one of claims 6 to 8, wherein the step of deriving the internal resistance from the peak signal and the transient current comprises:

10. A frequency converter is characterized by comprising a three-phase power switch, a rectifier, a bus capacitor, an IGBT module and the on-line detection device of the bus capacitor of the frequency converter according to any one of claims 1 to 4; the input end of the three-phase power switch is used for connecting a three-phase power supply, and the output end of the three-phase power switch is connected with the input end of the rectifier; the first electrode of the rectifier is respectively connected with the first end of the bus capacitor and the first end of the IGBT module, and the second electrode of the rectifier is respectively connected with the second end of the bus capacitor and the second end of the IGBT module.