CN107765099B - Broadband testing device and method for measuring impedance of grounding body - Google Patents
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Abstract
The invention discloses a broadband testing device for measuring impedance of a grounding body, which comprises an excitation source based on analog PI regulation; the excitation source based on the analog PI regulation comprises an AC/DC converter, a DC/AC converter, a PI regulator, an SPWM and a comparator; the input end of the AC/DC converter is the input end of an excitation source based on analog PI regulation; the output end of the AC/DC converter is connected with the input end of the DC/AC converter, and the output end of the DC/AC converter is used as the output end of the excitation source based on the analog PI regulation; the output end of the DC/AC converter is connected with the first input end of the comparator, the output end of the given circuit is connected with the second input end of the comparator, the output end of the comparator is connected with the input end of the PI regulator, and the output end of the PI regulator is connected with the control end of the AC/DC converter; the input end of the DSP-based controller is connected with the output end of the DC/AC converter, and the two output ends of the DSP-based controller are respectively connected with the given circuit and the input end of the SPWM; the output end of the SPWM is connected with the control end of the DC/AC converter. The output frequency band of the invention is wider at 20 Hz-30 kHz.
Description
Technical Field
The invention relates to the field of grounding impedance measurement, in particular to a broadband testing device and a broadband testing method for measuring grounding body impedance.
Background
The grounding net is laid underground and is in close contact with soil, and oxygen, acidic solution, stray current, microorganisms and the like in the soil have certain erosion effect on the grounding net. The soil characteristics and components of different regions are different, and the corrosion capacity of the soil to a grounding grid is different. Therefore, monitoring and sensing the operation state of the grounding grid and timely maintaining the grounding grid are very important for ensuring the reliable operation of electrical equipment and the safety of power supply and utilization. And the impedance characteristic of the grounding grid becomes the only means for representing and sensing the operating state of the grounding grid. Because a large amount of power frequency electromagnetic interference exists in a grounding grid measuring field, and the transmission distances of the tested signal lines are far away from each other and interfere greatly, the testing instrument is required to have output current as large as possible, namely, the power of the whole testing instrument is ensured to be large enough so as to ensure the anti-interference capability of the whole testing process.
With the continuous development of test and measurement technology, the ground impedance test method and the ground impedance tester are continuously developed and improved. Hand-operated resistance meters, pincerlike resistance meters, variable-frequency high-power impedance test systems and the like appear in sequence. The frequency conversion high-power impedance test system is tested according to a pilot frequency method, and the test current is required to be 3-20A, and the frequency is required to be 40-60 Hz. The anti-interference capability of the test process is ensured by adopting the test current as large as possible, the measurement frequency which is easy to operate and is as close to the power frequency as possible is used, the detection of the measurement result is convenient, and the test result is very close to the power frequency condition.
However, with the intensive research on the aspects of ground grid fault diagnosis, ground grid corrosion rate prediction, ground material characteristic test and the like, people are urgently required to understand the medium-frequency and high-frequency characteristics of the ground grid more deeply. Meanwhile, through the intensive research in the aspect, the unified standard in the aspects of the construction of the grounding grid and the measurement of the grounding impedance in IEEE/GB is gradually revised. The main test objective is to test the characteristics of the grounded screen at mid frequency, i.e. around 1kHz, and at high frequency around 30 kHz. However, under the requirement of such test frequency, the test is generally completed by means of signal amplification, and the test equipment has large volume, small output power and poor interference resistance.
Disclosure of Invention
The invention aims to provide a broadband testing device and a broadband testing method for measuring the impedance of a grounding body, so as to overcome the problem that the frequency range of the existing variable frequency testing equipment is narrow. The invention designs a portable, intelligent, broadband and high-power grounding impedance test device by introducing a frequency conversion technology, improves the output power of the whole test system on the premise of not excessively increasing the volume and the weight as much as possible while widening the test frequency, and designs a matched impedance measurement part for the test device, so that the test device becomes a complete grounding device broadband comprehensive test system.
In order to achieve the purpose, the invention adopts the following technical scheme:
a broadband testing device for measuring the impedance of a grounding body is characterized by comprising an excitation source based on analog PI regulation and a DSP-based controller;
the excitation source based on the analog PI regulation comprises an AC/DC converter, a DC/AC converter, a PI regulator, an SPWM and a comparator; the input end of the AC/DC converter is the input end of an excitation source based on analog PI regulation; the output end of the AC/DC converter is connected with the input end of the DC/AC converter, and the output end of the DC/AC converter is used as the output end of the excitation source based on the analog PI regulation; the output end of the DC/AC converter is connected with the first input end of the comparator, the output end of the given circuit is connected with the second input end of the comparator, the output end of the comparator is connected with the input end of the PI regulator, and the output end of the PI regulator is connected with the control end of the AC/DC converter;
the input end of the DSP-based controller is connected with the output end of the DC/AC converter, and the two output ends of the DSP-based controller are respectively connected with the input end of the given circuit and the input end of the SPWM; the output end of the SPWM is connected with the control end of the DC/AC converter.
Furthermore, in the excitation source based on analog PI regulation, an input AC/DC converter converts alternating current into direct current to provide bus voltage for a DC/AC converter, and then the direct current is converted by the DC/AC converter to generate a sine wave power supply with adjustable frequency and amplitude; a given signal of an excitation source is generated by a DSP-based controller, compared with an output voltage signal of a DC/AC converter in a comparator, and an error signal is sent to an analog PI regulator to form a voltage control loop.
Furthermore, the AC/DC converter is used as a DC source and a front stage of the AC source to provide bus voltage for the DC/AC converter; wherein, the output switching of AC and DC is completed by adopting a group of change-over switches; the output end of the AC/DC converter is connected with a first switch contact, and the output end of the DC/AC converter is connected with a second switch contact; the fixed end of the change-over switch is connected with the first input end of the comparator, and the movable end of the change-over switch can be selectively connected with the first switch contact or the second switch contact and is used for switching the output of the AC and the DC.
Further, the controller based on the DSP controls the DA converter to generate a controllable excitation source given signal, and an error signal generated after the comparison with a feedback signal of the output voltage of the DC/AC converter controls the bus voltage provided by the AC/DC part through the PI regulator; meanwhile, the controller based on the DSP generates a broadband SPWM synchronous modulation waveform to control the frequency of the alternating current output by the DC/AC converter, and completes measurement of voltage and current signals of an impedance measurement point together with a peripheral sampling signal processing circuit, and calculates an impedance value.
Furthermore, the system also comprises a human-computer interaction system based on ARM; the ARM-based human-computer interaction system is connected with the DSP-based controller; the ARM-based human-computer interaction system is used for receiving a user configuration instruction through an external key, displaying the current measurement configuration condition and the impedance measurement result through an LCD display, and monitoring the state of the whole system through the ARM and a communication channel of the DSP.
Furthermore, the AC/DC converter and the DC/AC converter are connected in a two-stage structure through an LC buffer circuit.
Further, the output end of the DC/AC converter is provided with selectable capacitors C1 and C2, and the frequency range of the alternating current output by the excitation source based on the analog PI regulation can be 20 Hz-30 kHz by switching C1 and C2.
A broadband test method for measuring impedance of a grounded body, comprising: the output end of the excitation source for simulating PI regulation is connected with a grounding body to be tested to provide excitation voltage; the sampling circuit collects voltage and current signals at two ends of the grounding body and converts the voltage and current signals into 0-3V voltage signals to be sent to an AD (analog-to-digital) circuit in the DSP-based controller for processing, and then the DSP-based controller calculates digital quantities of the voltage and the current obtained through AD conversion to obtain an impedance value of the grounding body.
According to the design requirements of the broadband comprehensive test system of the grounding device, the overall design framework of the system is determined. The device mainly comprises three parts: the system comprises an excitation source based on analog PI regulation, a DSP-based controller and an ARM-based human-computer interaction system.
The excitation source main circuit of the broadband comprehensive test system of the grounding device is divided into a two-stage structure, input AC/DC converts alternating current into direct current to provide bus voltage for a DC/AC part, and then the sine wave power supply with adjustable frequency and amplitude is generated through DC/AC conversion. A given signal of an excitation source is generated through the DSP, the given signal is compared with an output voltage signal, and an error signal is sent to the analog PI regulator to form a voltage control loop.
The AC-DC converter is used as a DC source and a front stage of the AC source and provides bus voltage for the DC-AC part. Wherein, the output switching of AC and DC is completed by a group of switches.
The DSP-based controller mainly has the following functions: the DA converter is controlled to generate a controllable excitation source given signal, a broadband SPWM synchronous modulation waveform is generated, measurement of voltage and current signals of an impedance measurement point is completed together with a peripheral sampling signal processing circuit, an impedance value is calculated, and meanwhile the DA converter is responsible for receiving an instruction signal given by an ARM and achieving state monitoring of the whole excitation source.
The ARM-based human-computer interaction system is mainly used for receiving a user configuration instruction through an external key, displaying a current measurement configuration condition and an impedance measurement result through an LCD (liquid crystal display), and monitoring the state of the whole system through the ARM and a communication channel of a DSP (digital signal processor).
Compared with the prior art, the invention has the following beneficial effects:
1. on the basis of analyzing the existing high-frequency measurement system and the inverter power supply, the invention provides the structure of the existing broadband grounding impedance measurement system, and the main power part of the system adopts a two-stage structure of AC-DC and DC-AC.
2. The broadband output is a key part of the invention, and is mainly finished by means of SPWM + resonance except that a high-performance MOSFET is adopted to push the switching frequency to 300kHz (two groups of filter parameters of low frequency and high frequency are designed, and the low frequency filtering and the high frequency resonance are realized by switching a filter capacitor).
3. In the signal conditioning process, isolation sampling, instrument amplification, precise rectification and programmable gain control circuits are respectively used for processing signals to achieve the precision required by the system, and the automatic selection of the measuring range is realized.
4. A design method and a program architecture of an LCD interface circuit of a man-machine interaction system based on ARM are provided, and a flow for realizing measurement and management is provided.
Drawings
FIG. 1 is a block diagram of a broadband testing device for measuring impedance of a grounding body according to the present invention;
FIG. 2 is a system block diagram of an excitation source;
FIG. 3 is a schematic diagram of an output filter capacitor switching circuit;
FIG. 4 is a system block diagram of a DSP-based controller;
fig. 5 is a schematic diagram of a hardware structure of the human-computer interaction system.
Detailed Description
Referring to fig. 1, the broadband testing device for measuring the impedance of the grounding body according to the present invention includes an excitation source based on analog PI regulation, a DSP-based controller (DSP broadband SPWM and signal processing system), and an ARM-based human-computer interaction system.
The excitation source based on the analog PI regulation comprises an AC/DC converter, a DC/AC converter, a PI regulator, an SPWM and a comparator; the input end of the AC/DC converter is the input end of an excitation source based on analog PI regulation; the output end of the AC/DC converter is connected with the input end of the DC/AC converter, and the output end of the DC/AC converter is used as the output end of the excitation source based on the analog PI regulation; the output end of the DC/AC converter is connected with the first input end of the comparator, the output end of the given circuit is connected with the second input end of the comparator, the output end of the comparator is connected with the input end of the PI regulator, and the output end of the PI regulator is connected with the control end of the AC/DC converter. The analog output quantity of the given circuit is used as reference voltage to be compared with the sampling value of the output voltage, and the comparison result is fed back to the PI regulator, so that the closed-loop control of the output voltage is realized.
The input end of the DSP-based controller is connected with the output end of the DC/AC converter, and the two output ends of the DSP-based controller are respectively connected with the input end of the given circuit and the input end of the SPWM; the output end of the SPWM is connected with the control end of the DC/AC converter.
And the ARM-based human-computer interaction system is connected with the DSP-based controller.
The excitation source main circuit based on analog PI regulation is divided into two-stage structures, an input AC/DC converter converts alternating current into direct current to provide bus voltage for a DC/AC converter, and the direct current is converted by the DC/AC converter to generate a sine wave power supply with adjustable frequency and amplitude. A given voltage signal of an excitation source is generated by a DSP-based controller, compared with an output voltage signal of a DC/AC converter in a comparator, and an error signal is sent to an analog PI regulator to form a voltage control loop.
The AC/DC converter is used as a DC source and a front stage of the AC source and provides bus voltage for the DC/AC converter. Wherein the output switching of AC and DC is done with a set of switches (as shown in fig. 2). The output end of the AC/DC converter is connected with a first switch contact, and the output end of the DC/AC converter is connected with a second switch contact; the fixed end of the change-over switch is connected with the first input end of the comparator, and the movable end of the change-over switch can be selectively connected with the first switch contact or the second switch contact and is used for switching the output of the AC and the DC.
The DSP-based controller mainly has the following functions: controlling a DA converter to generate a controllable excitation source given signal, and controlling a bus voltage provided by an AC/DC part through a PI regulator by an error signal generated after the error signal is compared with a DC/AC converter output voltage feedback signal; meanwhile, the controller based on the DSP generates a broadband SPWM synchronous modulation waveform to control the frequency of the alternating current output by the DC/AC converter, the frequency and the peripheral sampling signal processing circuit complete the measurement of voltage and current signals of an impedance measurement point, the impedance value is calculated, and meanwhile, the controller is responsible for receiving an instruction signal given by the ARM and realizing state monitoring on the whole excitation source. During testing, the output voltage and frequency of an excitation source simulating PI regulation are monitored to be set values within an adjustable range through closed-loop control of a PI regulator and SPWM; connecting the output end of an excitation source for simulating PI regulation with a grounding body to be tested to provide excitation voltage; the sampling circuit collects voltage and current signals at two ends of the grounding body and converts the voltage and current signals into 0-3V voltage signals to be sent to an AD (analog-to-digital) circuit in the DSP-based controller for processing, and then the DSP-based controller calculates digital quantities of the voltage and the current obtained through AD conversion to obtain an impedance value of the grounding body.
The ARM-based human-computer interaction system is mainly used for receiving a user configuration instruction through an external key, displaying a current measurement configuration condition and an impedance measurement result through an LCD (liquid crystal display), and monitoring the state of the whole system through the ARM and a communication channel of a DSP (digital signal processor).
In the system, a controller based on DSP is the control core of the whole system; and the ARM-based human-computer interaction system manages a human-computer interaction interface, is responsible for providing measurement information for the DSP and receiving a measurement result returned by the DSP.
The system structure of the excitation source of the invention is shown in figure 2, and consists of two-stage structures of an AC/DC converter and a DC/AC converter, which are connected through an LC buffer circuit, and the system has AC/DC output capability through a change-over switch at an output end.
Because the frequency band of the output of the invention is wider, and the frequency range of the output alternating current is 20 Hz-30 kHz, the invention designs two groups of filter parameters: selectable capacitors C1 and C2 are arranged at the output end of the DC/AC converter, and the output waveform quality in a wide frequency range can be ensured by switching C1 and C2, so that the frequency range of the output alternating current is 20 Hz-30 kHz; as shown in fig. 3.
The system block diagram of the DSP-based controller is determined according to the design requirements of the overall scheme, as shown in fig. 4. The whole system takes a DSP as a controller and is divided into 5 blocks according to the functions of the DSP. The device comprises a waveform modulation part controlled by EPWM, a signal conditioning circuit controlled by SPI1 and sent to A/D for analog-digital conversion, a capacitance switching circuit and an AC/DC logic control circuit controlled by GPIO, a given circuit of an excitation source consisting of a D/A converter controlled by SPI2 and a communication interface controlled by SCI and ARM. The TMS320F28035 of TI company is selected as a main control device on the premise of comprehensively considering system requirements.
The hardware structure of the man-machine interaction system is designed according to the overall scheme requirement, and is shown in figure 5. Wherein main control unit has selected the ARM chip STM32F103 of ST for use, display device has selected the 5.7 cun OCM320240-3 LCD of Jinpeng company for use, can realize ARM and LCD's data instruction exchange through FSMC (nimble static memory controller) interface, the pilot lamp that GPIO mouth controlled is used for indicating system's running state, the button is used for under the operating condition of difference, the realization is to the input of user's instruction, the inside USART of ARM is accomplished through with DSP's communication.
Claims (8)
1. A broadband testing device for measuring the impedance of a grounding body is characterized by comprising an excitation source based on analog PI regulation and a DSP-based controller;
the excitation source based on the analog PI regulation comprises an AC/DC converter, a DC/AC converter, a PI regulator, an SPWM wave driving circuit and a comparator; the input end of the AC/DC converter is the input end of an excitation source based on analog PI regulation; the output end of the AC/DC converter is connected with the input end of the DC/AC converter, and the output end of the DC/AC converter is used as the output end of the excitation source based on the analog PI regulation; the output end of the DC/AC converter is connected with the first input end of the comparator, the output end of the given circuit is connected with the second input end of the comparator, the output end of the comparator is connected with the input end of the PI regulator, and the output end of the PI regulator is connected with the control end of the AC/DC converter;
the input end of the DSP-based controller is connected with the output end of the DC/AC converter, and the two output ends of the DSP-based controller are respectively connected with the input end of the given circuit and the input end of the SPWM wave driving circuit; the output end of the SPWM wave driving circuit is connected with the control end of the DC/AC converter.
2. The broadband test device for measuring the impedance of the grounding body according to claim 1, wherein in the excitation source based on the analog PI regulation, an AC/DC converter converts input alternating current into direct current to provide bus voltage for a DC/AC converter, and then the direct current is converted by the DC/AC converter to generate a sine wave power supply with adjustable frequency and amplitude; a given signal of an excitation source is generated by a DSP-based controller, compared with an output voltage signal of a DC/AC converter in a comparator, and an error signal is sent to an analog PI regulator to form a voltage control loop.
3. The broadband test device for measuring the impedance of the grounding body according to claim 1, wherein the AC/DC converter is used as a direct current source and provides bus voltage for the DC/AC converter; wherein, the switching between the AC output and the DC output is completed by a group of change-over switches; the output end of the AC/DC converter is connected with a first switch contact, and the output end of the DC/AC converter is connected with a second switch contact; the fixed end of the change-over switch is connected with the first input end of the comparator, and the moving end of the change-over switch can be selectively connected with the first switch contact or the second switch contact and is used for switching the alternating current output and the direct current output.
4. The broadband test device for measuring the impedance of the grounding body as claimed in claim 1, wherein the DSP-based controller controls the given circuit to generate a controllable excitation source given signal, and an error signal generated after the comparison with the DC/AC converter output voltage feedback signal controls the bus voltage provided by the AC/DC converter through a PI regulator; meanwhile, the controller based on the DSP generates a broadband SPWM synchronous modulation waveform to control the frequency of the alternating current output by the DC/AC converter, and completes measurement of voltage and current signals of an impedance measurement point together with a peripheral sampling signal processing circuit, and calculates an impedance value.
5. The broadband test device for measuring the impedance of the grounding body according to claim 1, further comprising an ARM-based human-computer interaction system; the ARM-based human-computer interaction system is connected with the DSP-based controller; the ARM-based human-computer interaction system is used for receiving a user configuration instruction through an external key, displaying the current measurement configuration condition and the impedance measurement result through an LCD display, and monitoring the state of the whole system through the ARM and a communication channel of the DSP.
6. The broadband test device for measuring the impedance of the grounding body as recited in claim 1, wherein the AC/DC converter and the DC/AC converter are connected in a two-stage structure by an LC snubber circuit.
7. The broadband test device for measuring the impedance of the grounding body as claimed in claim 1, wherein the output end of the DC/AC converter is provided with selectable capacitors C1 and C2, and the frequency range of the alternating current output by the excitation source based on the analog PI regulation can be 20 Hz-30 kHz by switching C1 and C2.
8. A broadband test method for measuring impedance of a ground body, which is based on the broadband test apparatus for measuring impedance of a ground body of any one of claims 1 to 7, comprising: the output end of the excitation source for simulating PI regulation is connected with a grounding body to be tested to provide excitation voltage; the sampling circuit collects voltage and current signals at two ends of the grounding body and converts the voltage and current signals into 0-3V voltage signals to be sent to an AD (analog-to-digital) circuit in the DSP-based controller for processing, and then the DSP-based controller calculates digital quantities of the voltage and the current obtained through AD conversion to obtain an impedance value of the grounding body.
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| CN109283396A (en) * | 2018-10-29 | 2019-01-29 | 国网陕西省电力公司电力科学研究院 | Ground resistance measurement method and system, the pincers resistance instrument for quantifying noiseproof feature |
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| CN103176050A (en) * | 2011-12-20 | 2013-06-26 | 西安胜利仪器有限责任公司 | Design method of novel ground resistance tester |
| CN103336177B (en) * | 2013-06-07 | 2015-10-28 | 国家电网公司 | The method of testing of a kind of grounded screen resistance to earth and ground capacitance |
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