CN103630748B - A kind of device and method measured for micro-grid harmonic impedance - Google Patents

A kind of device and method measured for micro-grid harmonic impedance Download PDF

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CN103630748B
CN103630748B CN201310562344.7A CN201310562344A CN103630748B CN 103630748 B CN103630748 B CN 103630748B CN 201310562344 A CN201310562344 A CN 201310562344A CN 103630748 B CN103630748 B CN 103630748B
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harmonic
circuit
voltage
signal
micro
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CN103630748A (en
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卓放
师洪涛
侯李祥
岳小龙
杨祯
张东
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西安交通大学
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Abstract

The invention discloses a kind of device and method measured for micro-grid harmonic impedance, device comprises harmonic current source injection device, harmonic voltage and Harmonic currents detection device, data collector, host computer; Harmonic current source injection device is used for electrical network harmonic electric current; Harmonic voltage and harmonic current detection circuit, for detecting micro power network before and after harmonic current injection, the harmonic voltage size in network and harmonic current size; Data collector, samples for the signal detected harmonic voltage and harmonic current detection circuit, and data is fed through host computer; Host computer, calculating harmonic voltage and harmonic current variable quantity for carrying out process to the signal of sampling, calculating the harmonic impedance of micro power network each several part.Harmonic current injection device of the present invention to injecting all controllable harmonic current of amplitude, frequency, phase place, waveform in electrical network, thus can improve the precision of network harmonic impedance measurement.

Description

A kind of device and method measured for micro-grid harmonic impedance

[technical field]

The present invention relates to micro power network field, particularly a kind of device and method measured for micro-grid harmonic impedance.

[background technology]

Micro power network contains multiple distributed power source, and distributed power source is accessed in micro power network by converters mostly.Reciprocation between converters and the reciprocation between converters and electrical network can reduce the stability of micro power network system greatly.Therefore, the stability of system must be considered in the design and working of micro power network.And the stability of system and the harmonic impedance parameter of system have close relationship, stability analyze of method to system adopting harmonic impedance parameter identification is current study hotspot, and therefore the Measurement accuracy of micro-grid harmonic impedance just seems particularly important.

The main method that current system impedance is measured has switched capacitor method, thyristor branch road switching method and harmonic current injection etc.Switched capacitor method is reduced investment outlay, but the harmonic wave that this method produces is uncontrollable, fractional harmonic electric current may be caused to lack, and amplitude is too small, and radio-frequency component decay is very large; Thyristor branch road switching method can control the size of harmonic electric current, but accurately can not control the harmonic frequency of injected system, and signal HFS lacks; Two kinds of above-mentioned methods all can not the harmonic impedance of Measurement accuracy micro power network.

Harmonic current injection then utilizes harmonic current source to inject a controlled harmonic current directly to system, thus can obtain comparatively accurately, system harmonic impedance that frequency spectrum is complete.

Traditional harmonic current source generally adopts the mode of PWM, is both regulated the characteristic of harmonic electric current by the break-make of gauge tap pipe.But the method is subject to the impact of switching tube switching frequency, the harmonic current of injection is generally at below 1KHz.In some specifically research, harmonic impedance as three-phase alternating current system needs the harmonic impedance matrix of measuring system under dq coordinate system, now in measuring, often need to inject one by multiple signal madulation sophisticated signal together to system, now PWM often can not meet the demands.

Therefore how to inject a high frequency in electrical network and the harmonic current signal that can also control easily such as its phase place, amplitude, waveform, how the network after harmonic is carried out to the detection of harmonic voltage, harmonic current, the how harmonic impedance of computational grid each several part, and for the stability analysis etc. of system, be the key issue of research.

[summary of the invention]

The object of the present invention is to provide a kind of device and method measured for micro-grid harmonic impedance, all controlled harmonic current of phase place, frequency, amplitude, waveform can be injected to electrical network, with the harmonic impedance of Measurement accuracy micro power network more accurately.

To achieve these goals, the present invention adopts following technical scheme:

For the device that micro-grid harmonic impedance is measured, comprise harmonic current source injection device, harmonic voltage and Harmonic currents detection device, data collector, host computer;

Harmonic current source injection device comprises testing circuit, signal generating circuit, amplifying circuit and interface circuit; Testing circuit, for detection of grid voltage signal and after filtering after input signal circuit for generating; Signal generating circuit comprises DSP, D/A converting circuit and FPGA; The output terminal of the input end connection detection circuit of DSP, the voltage signal of DSP to input carries out the phase-locked phase information obtaining voltage signal, then harmonic voltage waveform, harmonic voltage frequency, harmonic voltage amplitude and harmonic voltage waveform phase difference is synthesized with the phase information of voltage signal, generate harmonic voltage signal and export to FPGA; FPGA exports amplifying circuit to after harmonic voltage signal being exported to D/A converting circuit conversion; Amplifying circuit comprises amplitude amplifying circuit and power amplification circuit; The amplitude of harmonic voltage signal that amplitude amplifying circuit logarithmic mode change-over circuit exports exports power amplification circuit to after amplifying; Power amplification circuit exports to interface circuit to after the power amplification of the harmonic voltage signal of input; Interface circuit, the harmonic voltage signal for being exported by power amplification circuit converts harmonic current signal injection to in electrical network;

Harmonic voltage and harmonic current detection circuit, for detecting micro power network before and after harmonic current injection, the harmonic voltage size in network and harmonic current size;

Data collector, samples for the signal detected harmonic voltage and harmonic current detection circuit, and data is fed through host computer;

Host computer, calculating harmonic voltage and harmonic current variable quantity for carrying out process to the signal of sampling, calculating the harmonic impedance of micro power network each several part.

The present invention further improves and is: described testing circuit comprises voltage hall sensor and sample circuit, voltage hall sensor is used for the single-phase or ployphase voltages signal of detection of grid, and the voltage signal that sample circuit is used for voltage hall sensor detects carries out filtering.

The present invention further improves and is: FPGA is for judging that the harmonic voltage signal inputted is whether within default value limited field.

The present invention further improves and is: described signal generating circuit also comprises signal conditioning circuit, is transferred to FPGA carries out protection judgement after the harmonic current signal that the harmonic voltage signal that the temperature signal of the power amplification circuit of collection, power amplification circuit export by described signal conditioning circuit, interface circuit export carries out filtering by DSP.

The present invention further improves and is: described DSP is DSP2812.

For the method that micro-grid harmonic impedance is measured, comprise the following steps: adopt and be used for the device that micro-grid harmonic impedance measures and inject twice separate harmonic current to micro power network; Detect micro power network before and after twice harmonic current injection by harmonic voltage and Harmonic currents detection device, the harmonic voltage size in network and harmonic current size are also uploaded to host computer by data collecting card; Before and after twice harmonic current injection that host computer is uploaded according to data collecting card, the harmonic voltage size in network and harmonic current size calculate the harmonic impedance of micro power network each several part.

The present invention further improves and is: before and after twice harmonic current injection, and the two groups of harmonic voltages produced in network and current disturbing signal are respectively with

Harmonic impedance matrix in micro power network dq coordinate system is:

Z d d ( jω h ) Z d q ( jω h ) Z q d ( jω h ) Z q q ( jω h ) = v ^ d 1 ( ω h ) v ^ d 2 ( ω h ) v ^ q 1 ( ω h ) v ^ q 2 ( ω h ) i ^ d 1 ( ω h ) i ^ d 2 ( ω h ) i ^ q 1 ( ω h ) i ^ q 2 ( ω h ) -1

Wherein v ^ d q 1 = v ^ d 1 v ^ q 1 T , v ^ d q 2 = v ^ d 2 v ^ q 2 T , i ^ d q 1 = i ^ d 1 i ^ q 1 T , i ^ d q 2 = i ^ d 2 i ^ q 2 T ; ω hfor the frequency of current disturbing.

Relative to prior art, the present invention has following beneficial effect: harmonic current injection device of the present invention to injecting all controllable harmonic current of amplitude, frequency, phase place, waveform in electrical network, thus can improve the precision of network harmonic impedance measurement; Apparatus of the present invention control simple and reliable, and precision is high, and cost is low, to be applicable in low voltage electric network that harmonic impedance is measured, the engineer applied occasion such as design of filter and stability analysis.The inventive method injects independently twice phase place, amplitude, all controllable harmonic current of frequency by harmonic current injection device to electrical network, and adopt the harmonic current of each several part and the harmonic voltage of correspondence thereof in wide band voltage, current Hall sensor Sampling network, after data collector sampling, be fed through the calculating carrying out harmonic impedance in host computer; The inventive method is simple, accuracy is high.

[accompanying drawing explanation]

Fig. 1 micro power network structural representation;

The structured flowchart that Fig. 2 (a) is apparatus of the present invention; The hardware schematic diagram that Fig. 2 (b) is signal generating circuit;

Fig. 3 (a) is the hardware-initiated process flow diagram of signal generating circuit; The process flow diagram that Fig. 3 (b) occurs for harmonic signal;

Fig. 4 is harmonic impedance calculation flow chart;

Fig. 5 is the three-phase alternating current system schematic of equivalence;

Fig. 6 is three-phase alternating current system small-signal model schematic diagram;

Fig. 7 (a) is inverter output impedance self-impedance measurement result schematic diagram; Fig. 7 (b) is inverter output impedance transimpedance measurement result schematic diagram;

Fig. 8 (a) is load harmonic impedance self-impedance measurement result schematic diagram; Fig. 8 (b) is load harmonic impedance transimpedance measurement result schematic diagram;

Fig. 9 is stability analysis result schematic diagram.

[embodiment]

As shown in Figure 1, the multiple distributed power source such as photovoltaic generating system, wind power system of having guaranteed replacement in micro power network, in order to the harmonic impedance of measuring system, a kind of device for micro-grid harmonic impedance measurement proposed in the present invention as shown in Figure 2.

Refer to shown in Fig. 2 (a) to 3 (b), a kind of device measured for micro-grid harmonic impedance of the present invention, comprises harmonic current source injection device, harmonic voltage and Harmonic currents detection device, data collector, host computer.

Harmonic current source injection device is made up of testing circuit, signal generating circuit, amplifying circuit, interface circuit.The core of signal generating circuit is DSP2812 control circuit, and it is by the line voltage of sampling, can be controlled the phase place of output signal, meanwhile, can also be controlled the key element such as amplitude, frequency outputed signal by programming easily by soft phase-locked method.The synthetic schemes of soft phase-locked and harmonic signal is as shown in Fig. 3 (a) He Fig. 3 (b).

Testing circuit is made up of voltage hall sensor and sample circuit, and voltage hall sensor is used for three-phase voltage signal Ua, Ub, Uc of detection of grid; Voltage hall sensor connects sample circuit, electrical network three-phase voltage signal Ua, Ub, Uc that voltage hall sensor detects in real time deliver in signal generating circuit after the analog to digital conversion and conditioning (filtering) of over-sampling circuit, are used for calculating amplitude, the phase place of line voltage.

The hardware of signal generating circuit is take DSP2812 as the control circuit of core, and it also comprises signal conditioning circuit, D/A converting circuit, power module and FPGA.

The input end of DSP2812 receives the three-phase voltage signal U of the micro power network gathered a, U b, U c, DSP2812 is to the three-phase voltage signal U of input a, U b, U ccarry out software phlase locking and obtain three-phase voltage signal U a, U b, U cphase information, then by the instruction of harmonic voltage waveform, harmonic voltage frequency instruction, the instruction of harmonic voltage amplitude and the instruction and three-phase voltage signal U of harmonic voltage waveform phase difference a, U b, U cphase information synthesize, the harmonic voltage signal generating phase place, frequency, amplitude, waveform controlled exports to FPGA; FPGA is for judging whether the harmonic voltage signal inputted (prevents from damaging follow-up modulate circuit, power amplifier and interface circuit), if by this harmonic voltage signal U within limited field within limited field pamplifying circuit is exported to after exporting D/A converting circuit conversion to.

Amplifying circuit comprises amplitude amplifying circuit and power amplification circuit, adopts the mode of Linear Amplifer, by harmonic voltage signal U pcarry out amplitude amplification and power amplification, in order to make the signal after amplification undistorted, amplifying circuit has the bandwidth of 1MHz, and wherein harmonic distortion is less than 0.01, and signal to noise ratio (S/N ratio) is greater than 95dB, fully meets the requirement of amplification.The harmonic voltage signal U that amplitude amplifying circuit exports DSP pamplitude amplify after export power amplification circuit to; Power amplification circuit is to the harmonic voltage signal U of input pinterface circuit is exported to after the power amplification of `.

Harmonic current injection interface circuit, primarily of voltage-current converter circuit composition, by the harmonic voltage signal U that prime power amplification circuit exports p`` converts harmonic current signal i to pbe injected in electrical network.

Adopt DSP control circuit and power amplification circuit to produce the method for harmonic signal, avoid the restriction of conventional P WM method breaker in middle pipe switching frequency, more required harmonic signals can be produced.

Signal generating circuit also comprises signal conditioning circuit, and the input end of signal conditioning circuit connects temperature signal, the harmonic voltage signal U of power amplification circuit p``, harmonic current signal i p, and be transferred to FPGA by DSP after filtering is carried out to these signals and judge, judge that whether these signals are abnormal, send corresponding alarm signal if abnormal.

Harmonic voltage and harmonic current detection circuit are made up of Hall element, detect micro power network before and after harmonic current injection, the harmonic voltage size in network and harmonic current size.

Data collector, adopts high-speed data acquisition card, samples, and data are fed through host computer to the signal that Hall element detects.

The signal of host computer to sampling processes, and calculates harmonic voltage and harmonic current variable quantity, calculates the harmonic impedance of micro power network each several part.

The measuring method flow process of system harmonic impedance parameter:

In three-phase alternating current system, for three-phase symmetrical system, its dq coordinate system medium frequency is ω hcurrent disturbing and its corresponding voltage disturbance between relation can be designated as:

v ^ d ( jω h ) v ^ q ( jω h ) = Z d d ( jω h ) Z d q ( jω h ) Z q d ( jω h ) Z q q ( jω h ) i ^ d ( jω h ) i ^ q ( jω h )

For two groups of separate voltage and current disturbing signals with then have:

v ^ d 1 ( ω h ) v ^ d 2 ( ω h ) v ^ q 1 ( ω h ) v ^ q 2 ( ω h ) = Z d d ( jω h ) Z d q ( jω h ) Z q d ( jω h ) Z q q ( jω h ) i ^ d 1 ( ω h ) i ^ d 2 ( ω h ) i ^ q 1 ( ω h ) i ^ q 2 ( ω h )

Wherein v ^ d q 1 = v ^ d 1 v ^ q 1 T , v ^ d q 2 = v ^ d 2 v ^ q 2 T , i ^ d q 1 = i ^ d 1 i ^ q 1 T , i ^ d q 2 = i ^ d 2 i ^ q 2 T .

Thus the harmonic impedance matrix that can obtain in dq coordinate system is now:

Z d d ( jω h ) Z d q ( jω h ) Z q d ( jω h ) Z q q ( jω h ) = v ^ d 1 ( ω h ) v ^ d 2 ( ω h ) v ^ q 1 ( ω h ) v ^ q 2 ( ω h ) i ^ d 1 ( ω h ) i ^ d 2 ( ω h ) i ^ q 1 ( ω h ) i ^ q 2 ( ω h ) - 1

As can be seen from the above equation, in order to obtain the harmonic impedance of system at a certain Frequency point, needing to inject at this frequency place twice separate harmonic current, namely must ensure that the square formation that two groups of current disturbing signals form is nonsingular matrix.

To the flow process of system harmonic electric current and data collection and analysis as shown in Figure 4.

As can be seen from Figure 4, the separate harmonic current of two groups of injection needs to carry out dq conversion and fft analysis respectively, then substitutes in impedance matrix and solves impedance parameter.

The stability analysis of micro power network system:

By the power module in micro power network integrally, integrally, then system can be equivalent to a three-phase alternating current system as shown in Figure 5 to loading section, if mains side be input as u s, its voltage gain transport function is G s, the output of load-side is u o, voltage gain transport function is G l.

In synchronous rotating frame, modeling is carried out to this three-phase alternating current system, its small-signal model can be obtained as shown in Figure 6, wherein for the small-signal disturbance of power input voltage, with be respectively busbar voltage and load output voltage to the response of this small-signal disturbance.Z s(s) and Y ls () is respectively mains side equivalent output impedance matrix and load-side equivalent inpnt admittance matrix.

Load output voltage response can be obtained by Fig. 6 to be shown below with the transport function relation between power input voltage disturbance:

u ^ o d q = G L d q ( s ) ( I + Z s ( s ) Y L ( s ) ) - 1 G s d q ( s ) u ^ s d q

Due to voltage gain transport function G sdq(s) and G ldqs generally there is not RHP limit in (), therefore the stability of system depends on back rate matrix L (s)=Z s(s) Y l(s).

L ( s ) = L d d ( s ) L d q ( s ) L q d ( s ) L q q ( s ) = Z s d d ( s ) Z s d q ( s ) Z s q d ( s ) Z s q q ( s ) Y L d d ( s ) Y L d q ( s ) Y L q d ( s ) Y L q q ( s )

When power subsystem and load subsystem independent operating are stablized, i.e. mains side equivalent output impedance matrix Z s(s) and load-side equivalent inpnt admittance matrix Y lwhen () does not all exist RHP limit s, two of L (s) characteristic locuses are limited in the stability that can ensure system in s planar unit circle.The eigenwert of matrix when point on characteristic locus represents a certain frequency, therefore, when all eigenwerts of L (s) are all within unit circle, AC system is stablized.

i(jω)|<1-∞<ω<∞,i=1,2

Adopt above impedance measurement method, to the harmonic impedance measurement result of system as shown in Fig. 7 ~ Fig. 8, wherein comparatively smooth curve is theoretical value, and another curve is experimental measurements.Wherein Fig. 7 (a) output impedance self-impedance Z under dq coordinate system that is source inventer in micro power network ddmeasurement result, Fig. 7 (b) is inverter output impedance transimpedance Z dqmeasurement result.Fig. 8 (a) load self-impedance Z ddmeasurement result, as can be seen from the figure, measured value and the theoretical value of harmonic impedance are consistent, demonstrate the validity of measurement mechanism.Host computer to the result of system stability analysis as shown in Figure 9, as can be seen from the figure return the eigenvalue of rate matrix all within unit circle, now stablize by system.

The present invention gives a kind of device and method measured for micro-grid harmonic impedance, and built experiment porch and verify, as can be seen from experimental waveform, harmonic current injection device to injecting all controllable harmonic current of amplitude, frequency, phase place, waveform in electrical network, can meet above requirement; The present invention can measure each several part harmonic impedance of micro power network accurately, and can analyze the stability of system accurately.Compared to other scheme, it controls reliable, and precision is high, and cost is low, is applicable to the engineer applied occasions such as the impedance measurement of low pressure micro power network and stability analysis.

Claims (6)

1., for the device that micro-grid harmonic impedance is measured, it is characterized in that, comprise harmonic current source injection device, harmonic voltage and Harmonic currents detection device, data collector, host computer;
Harmonic current source injection device comprises testing circuit, signal generating circuit, amplifying circuit and interface circuit; Testing circuit, for detection of grid voltage signal and after filtering after input signal circuit for generating; Signal generating circuit comprises DSP, D/A converting circuit and FPGA; The output terminal of the input end connection detection circuit of DSP, the voltage signal of DSP to input carries out the phase-locked phase information obtaining voltage signal, then harmonic voltage waveform, harmonic voltage frequency, harmonic voltage amplitude and harmonic voltage waveform phase difference is synthesized with the phase information of voltage signal, generate harmonic voltage signal and export to FPGA; FPGA exports amplifying circuit to after harmonic voltage signal being exported to D/A converting circuit conversion; Amplifying circuit comprises amplitude amplifying circuit and power amplification circuit; The amplitude of harmonic voltage signal that amplitude amplifying circuit logarithmic mode change-over circuit exports exports power amplification circuit to after amplifying; Power amplification circuit exports to interface circuit to after the power amplification of the harmonic voltage signal of input; Interface circuit, the harmonic voltage signal for being exported by power amplification circuit converts harmonic current signal injection to in electrical network;
Harmonic voltage and Harmonic currents detection device, for detecting micro power network before and after harmonic current injection, the harmonic voltage size in network and harmonic current size;
Data collector, samples for the signal detected harmonic voltage and Harmonic currents detection device, and data is fed through host computer;
Host computer, calculating harmonic voltage and harmonic current variable quantity for carrying out process to the signal of sampling, calculating the harmonic impedance of micro power network each several part.
2. a kind of device measured for micro-grid harmonic impedance according to claim 1, it is characterized in that, described testing circuit comprises voltage hall sensor and sample circuit, voltage hall sensor is used for the single-phase or ployphase voltages signal of detection of grid, and the voltage signal that sample circuit is used for voltage hall sensor detects carries out filtering.
3. a kind of device measured for micro-grid harmonic impedance according to claim 1, is characterized in that, FPGA is for judging that the harmonic voltage signal inputted is whether within default value limited field.
4. a kind of device measured for micro-grid harmonic impedance according to claim 1; it is characterized in that; described signal generating circuit also comprises signal conditioning circuit, is transferred to FPGA carries out protection judgement after the harmonic current signal that the harmonic voltage signal that the temperature signal of the power amplification circuit of collection, power amplification circuit export by described signal conditioning circuit, interface circuit export carries out filtering by DSP.
5. a kind of device measured for micro-grid harmonic impedance according to claim 1, it is characterized in that, described DSP is DSP2812.
6. the method measured for micro-grid harmonic impedance, it is characterized in that, comprise the following steps: adopt the device measured for micro-grid harmonic impedance according to any one of claim 1 to 5 to inject twice separate harmonic current to micro power network; Detect micro power network before and after twice harmonic current injection by harmonic voltage and Harmonic currents detection device, the harmonic voltage size in network and harmonic current size are also uploaded to host computer by data collector; Before and after twice harmonic current injection that host computer is uploaded according to data collector, the harmonic voltage size in network and harmonic current size calculate the harmonic impedance of micro power network each several part.
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