CN101944841B - Inversion control digital filter - Google Patents
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Abstract
The invention discloses a kind of inversion control digital filters, carry out digital low-pass filtering by the control amount em exported to PI controller, the high fdrequency component in control amount em are filtered out, so that the feedforward amount of control amount e ' m and network voltage
Synthesis total control amount Em, the pulse width modulating signal generation circuit being added generate duty ratio K according to the total control amount Em of synthesis and are free of high dither with the pulse width modulating signal PWM wave that the total control amount Em of synthesis changes, finally, the grid-connected current of the on-off time ratio output of power switch tube is also free of high fdrequency component in pulse width modulating signal PWM control inversion bridge circuit, to reduce the wave distortion of grid-connected current, make electricity generation system stable operation.
Description
Technical field
The invention belongs to inversion grid connection electricity generation system technical field, more specifically, relate to a kind of inversion control digital filter.
Background technology
Photovoltaic inversion electricity generation system is paid close attention to by the many countries in the whole world at present, and photovoltaic DC-to-AC converter has also obtained very big development as the key component of photovoltaic inversion grid connection electricity generation system.Generally, as shown in Figure 1, photovoltaic inversion grid connection electricity generation system all is made up of solar panel array 1, photovoltaic DC-to-AC converter 2.Wherein, photovoltaic DC-to-AC converter 2 comprises MPPT maximum power point tracking (MPPT) module 201, bus circuit 202, inverter bridge circuit 203 and control circuit 204 parts, function exactly with conversion of solar energy be electric energy and with energy delivery to electrical network 3.
Fig. 1 is the basic block diagram of photovoltaic inversion grid connection electricity generation system.The function of solar panel array 1 is an electric energy with conversion of solar energy exactly; MPPT maximum power point tracking (MPPT) module 201 directly links to each other with solar panel array 1; To regulate the operating state of solar panel, solar panel is operated on the maximum power point.Bus circuit 202 links to each other with solar panel array 1 through the booster circuit on the MPPT maximum power point tracking module 201; System begins to carry out power transfer when its busbar voltage is elevated to the value of appointment, and the power delivery that solar panel is transformed is to inverter bridge circuit 203.Inverter bridge circuit 203 is responsible for converting the direct current that bus circuit 202 transmits into alternating current (normally 50Hz civil power).Control circuit 204 is keys of whole photovoltaic inversion grid connection electricity generation system steady operation, and the realization of maximal power tracing, the balance of busbar voltage are controlled quietly, the tracking Control of inverter bridge circuital current all will rely on control circuit 204 to carry out computing and scheduling.
To the tracking Control purpose of inverter bridge circuital current is in order to make grid-connected current and line voltage with homophase frequently, and guarantees that its wave distortion is within prescribed limit.
To the inverter bridge circuital current; Be in the grid-connected current tracking Control course of work; If the pulse width modulating signal PWM to power switch pipe on-off time ratio in the control inverter bridge circuit handles imperfection; Pulse width modulating signal PWM contains high dither, can cause grid-connected current problems such as wave distortion, electricity generation system instability to occur.
Summary of the invention
The object of the invention is to overcome the deficiency of prior art, proposes a kind of inversion control digital filter, is used for leaching the unwanted high dither of pulse width modulating signal PWM, has reduced the wave distortion of grid-connected current, has guaranteed the stability of electricity generation system.
For realizing the foregoing invention purpose, inversion control digital filter of the present invention is characterized in that, described inversion control digital filter is a wave digital lowpass filter, and its input is connected with the PI controller output end, is used for the PI controller according to current error
The controlled quentity controlled variable e that produces
mCarry out digital low-pass filtering, with controlled quentity controlled variable e
mIn high fdrequency component filter out the controlled quentity controlled variable e ' after the high fdrequency component filtering of output
mFeedforward amount with line voltage
Carry out addition, synthetic master control amount E
mOutput to pulse width modulating signal and produce circuit; Pulse width modulating signal produces circuit according to synthetic master control amount E
m, produce duty ratio K with synthetic master control amount E
mThe pulse width modulating signal PWM that changes goes to control the on-off time ratio of power switch pipe in the inverter bridge circuit, must export grid-connected current and line voltage with the frequency homophase;
Described current error
Be that current detection circuit is to grid-connected current I
NetSample, the sampling period is T, obtains M current sampling data in the grid-connected current primitive period L
Wherein, M=L/T, m=0,1,2 ..., M-1, current sampling data
0 phase point of corresponding grid-connected current first-harmonic, then in comparator, the current sampling data of each phase place
Expectation electric current with corresponding phase
Compare, obtain:
Detect certain some current sampling data of grid-connected current first-harmonic when current detection circuit
Expectation electric current less than corresponding phase
The time, the output current error
For just, the PI controller produces positive controlled quentity controlled variable e
m, then, in the inversion control digital filter, to controlled quentity controlled variable e
mCarry out digital low-pass filtering, with controlled quentity controlled variable e
mIn high fdrequency component filter out, again with the feedforward amount of line voltage
Carry out addition, synthetic master control amount E
mIncrease, like this, the duty ratio K of this pulse width modulating signal PWM increases, the grid-connected current of this point
Increase, until with the expectation electric current of corresponding phase
Equate; Vice versa, and like this, M point in the grid-connected current primitive period L all carries out identical control, makes output grid-connected current and line voltage with the frequency homophase, reaches the current peak of expectation simultaneously.
Goal of the invention of the present invention is achieved in that
Inversion control digital filter of the present invention is through the controlled quentity controlled variable e to the output of PI controller
mCarry out digital low-pass filtering, with controlled quentity controlled variable e
mIn high fdrequency component filter out, make controlled quentity controlled variable e '
mFeedforward amount with line voltage
Carry out the synthetic master control amount E of addition
m, pulse width modulating signal produces circuit according to synthetic master control amount E
mProduce duty ratio K with synthetic master control amount E
mThe pulse width modulating signal PWM ripple that changes does not contain high dither; Finally; In the pulse width modulating signal PWM control inverter bridge circuit power switch pipe switching time specific output grid-connected current do not contain high fdrequency component yet; Thereby reduced the wave distortion of grid-connected current, made electricity generation system stable operation.
Description of drawings
The basic block diagram of Fig. 1 photovoltaic inversion grid connection electricity generation system;
Fig. 2 is the theory diagram of a kind of embodiment of inversion control digital filter of the present invention;
Fig. 3 is the Bode diagram of simulation low-pass filter;
Fig. 4 is the oscillogram that does not add the preceding controlled quentity controlled variable of inversion control digital filter;
Fig. 5 is the oscillogram of controlled quentity controlled variable behind the adding inversion control digital filter;
Fig. 6 postpones the control sketch map.
Embodiment
Describe below in conjunction with the accompanying drawing specific embodiments of the invention, so that those skilled in the art understands the present invention better.What need point out especially is that in the following description, when perhaps the detailed description of known function and design can desalinate main contents of the present invention, these were described in here and will be left in the basket.
Embodiment
Fig. 2 is a kind of embodiment theory diagram of grid-connected current control device that adopts inversion control filter of the present invention.
As shown in Figure 2, in the present embodiment, wave digital lowpass filter 2046 of the present invention, its input is connected with PI controller 2043 outputs, is used for PI controller 2043 according to current error
The controlled quentity controlled variable e that produces
mCarry out digital low-pass filtering, with controlled quentity controlled variable e
mIn high fdrequency component filter out the controlled quentity controlled variable e ' after the high fdrequency component filtering of output
mFeedforward amount with line voltage
Carry out addition, synthetic master control amount E
mOutput to pulse width modulating signal and produce circuit 2045; Pulse width modulating signal produces circuit 2045 according to synthetic master control amount E
m, produce duty ratio K with synthetic master control amount E
mThe pulse width modulating signal PWM that changes goes to control the on-off time ratio of power switch pipe in the inverter bridge circuit 203, must export grid-connected current I
NetWith line voltage frequency homophase together.
As shown in Figure 2, described current error
Be 2041 couples of grid-connected current I of current detection circuit
NetSample, the sampling period is T, obtains M current sampling data in the grid-connected current primitive period L
Wherein, M=L/T, m=0,1,2 ..., M-1, current sampling data
0 phase point of corresponding grid-connected current first-harmonic, then in comparator 2042, the current sampling data of each phase place
Expectation electric current with corresponding phase
Compare, obtain:
In the present embodiment; As shown in Figure 2; Current detection circuit 2041, comparator 2042, PI controller 2043, add circuit 2044, pulse width modulating signal produce circuit 2045 and wave digital lowpass filter 2046 is formed photovoltaic DC-to-AC converter grid-connected current control device; Be used for tracking Control, make grid-connected current and line voltage with the frequency homophase to inverter bridge circuit 203 electric currents.
The amplitude of grid-connected current is by the decision of the difference of equivalent output voltage of power switch pipe (IGBT) and line voltage, can control its equivalent output voltage through the time of power switch closed and disconnected.Because the control frequency of power switch is far above the frequency of grid-connected current, in the control procedure of integral body, the action of each data sampling, computing and power switch all is incoherent, so controller also is independently to the control of grid-connected current on each phase place.Therefore, inverter grid-connected current control device is to grid-connected current I
NetControl, to have eliminated the influence between the out of phase point, make control more accurate, the output waveform better effects if.
As shown in Figure 2, master control amount E
mIt is feedforward amount at line voltage
The basis on the output controlled quentity controlled variable e of the less PI controller of stack
mObtain, wherein the feedforward amount of line voltage
Account for the major part of master control amount, because line voltage is more stable sine wave, so the feedforward amount of line voltage
Be according to stable sinusoidal variations.And the output controlled quentity controlled variable e of PI controller
mBe according to current error
Calculate, the input of PI controller is the sampled value of power network current
With the expectation current value
Poor, the current sample frequency is higher than the frequency of line voltage far away, is 18KHz in the present embodiment.Can know that by nyquist sampling theorem the sampled signal itself that obtains may contain very high-frequency harmonic wave; Simultaneously because the characteristic of the inductance that is incorporated into the power networks can make the control point produce certain delay; And also there is certain fluctuation in sampled point itself; All these reasons all can exert an influence to sampled result, make the output controlled quentity controlled variable e of PI controller
mThough little but unstable, the ripple in the controlled quentity controlled variable is mainly caused by it.Output controlled quentity controlled variable e when the PI controller
mOn when containing the ripple of high frequency, serious distortion will appear in the grid-connected current waveform of output.To the problems referred to above, the present invention has designed 2046 pairs of output of wave digital lowpass filter controlled quentity controlled variable e
mCarry out LPF, filtering controlled quentity controlled variable e
mIn the high fdrequency component that comprises.As shown in Figure 2, the H in the grid-connected current control device (s) link is exactly the digital filter 2046 of the present invention's design, and the design focal point of this wave digital lowpass filter 2046 is confirming of bandpass flatness, suppressed frequency band attenuation rate, cut-off frequency and digital filter exponent number.
In the present embodiment, the selection of the cut-off frequency of inversion control digital filter of the present invention will be considered from two aspects.At first, in inverter, output current will pass through the LC simulation low-pass filter and carry out filtering before being incorporated into the power networks, and the Bode diagram of its simulation low-pass filter is as shown in Figure 3.The 3dB cut-off frequency computing formula of simulation low-pass filter is:
According to the inductance of forming simulation low-pass filter and the cut-off frequency f that electric capacity can calculate simulation low-pass filter
cFor guaranteeing the integrality of simulation low-pass filter filtering output current frequency, the cut-off frequency of inversion control digital filter should be greater than the cut-off frequency of simulation low-pass filter.In addition, the cut-off frequency of the inversion control digital filter amount of being controlled e also
mThe qualification of peak frequency, detect the waveform of output current through experiment, can see as controlled quentity controlled variable e '
mFrequency within limits the time, the grid-connected current waveform ripple content of output is very little, the grid-connected current waveform be basically and line voltage with the standard sine wave of homophase frequently.As time goes on; The frequency part that control signal exceeds this qualification constantly increases, and presents wild effect, and is accompanied by output waveform and serious distortion occurs; So can set this frequency as the cut-off frequency of confirming the inversion control digital filter, the unwanted high fdrequency component of filtering.In the present embodiment, according to above restriction about the digital filter cut-off frequency, the cut-off frequency of confirming inversion control digital filter of the present invention is 2 times of the cut-off frequency of the simulation low-pass filter that the inversion control output current carried out LPF.In this enforcement, the cut-off frequency f of simulation low-pass filter
cBe 1.5kHz, the band connection frequency of inversion control digital filter is greater than 1.5kHz, and this band connection frequency is 3kHz in a kind of 5000w photovoltaic DC-to-AC converter design.
Among the present invention; Inversion control digital filter requirement passband can be smooth as far as possible; Slowly decay to the cut-off frequency point then; Mainly by the exponent number decision of the type of filter and filter, the exponent number of its median filter and suppressed frequency band width and bandpass flatness have certain relation in the design of the attenuation rate of filter suppressed frequency band: when generally exponent number reduces passband decay less, the suppressed frequency band broad; When exponent number increased, suppressed frequency band narrowed down, but the fluctuation of meeting can increase in the passband.Inversion control digital filter resistance of the present invention design frequently focuses on and improves the passage flatness, because the object of filtering, i.e. controlled quentity controlled variable e
mIt is the control signal that contains high-frequency signal; Itself contains certain high fdrequency component; Design of Filter need guarantee that useful control signal can farthest be kept, thus passband in ripple should be controlled in the 0.001dB, promptly the variable quantity of passband inner control signal be no more than ± 0.12 ‰.Controlled quentity controlled variable e
mAccount for master control amount E
mRatio less, the cumulant of each integral operation is also corresponding less, and digital system self contains quantization error, the precision of controlled quentity controlled variable is limited, to controlled quentity controlled variable e
mHigh fdrequency component carry out small amount of attenuation and can both play the effect of stablizing controlled quentity controlled variable.Therefore, the cut-off frequency of median filter of the present invention need not ask too high with decay.Cut-off frequency can be according to controlled quentity controlled variable e
mIn the spectrum width decision of unstable high fdrequency component; The decay of cut-off frequency then requires to be not less than at least 0.04dB.
In the present embodiment; Bandpass flatness and suppressed frequency band have carried out certain constraint to the selection of inversion control digital filter exponent number, in addition, because the inversion control digital filter itself has the effect of delay; For the inversion control digital filter, the time T of delay
dCorresponding sampling points is counted P
dWith the relational expression of the exponent number k of filter be:
P
d＝(k-1)/2
Because there is the delay of N sampled point in the PI controller, can not surpass the delay of controlling unit the time of delay of inversion control digital filter, power switch pipe controlled the time T that therefore postpones otherwise can't obtain effective impulse bandwidth modulation signals PWM
dCorresponding sampling points is counted P
dCannot be greater than PI controller delay sampling points N; The grid-connected current control device needs certain calculating treatmenting time T in addition
c, its corresponding sampling points is counted P
cSo the exponent number k of inversion control digital filter will choose appropriate value, to satisfy condition:
P
d+P
c＜N
To guarantee controlled quentity controlled variable e
mStill have time enough to control through after the filtering.
Through above analysis, the cut-off frequency of inversion control digital filter, exponent number and filter type all will carry out suitable choosing just can design desirable wave digital lowpass filter.Inversion control digital filter of the present invention designs according to above-mentioned requirements; This filter is selected 5 rank linear phase filters in the 5000w inversion control; Band connection frequency is 3kHz; Cut-off frequency is 7kHz, uses the Frequent Filters design software to design the concrete parameter that obtains a inversion control filter, and its performance reaches ripple less than 0.001dB; The decay of cut-off frequency point is greater than 0.04dB.
Fig. 4 is the oscillogram that does not add the preceding controlled quentity controlled variable of inversion control digital filter.
Controlled quentity controlled variable e before not adding digital filter
mWaveform as shown in Figure 4, controlled quentity controlled variable e wherein
mRipple mainly cause by current PI D control output; And ripple can increase gradually; In the control of reality, can produce serious influence; If do not carry out suitable processing, the grid-connected current waveform of output will have bigger ripple, and might cause whole system to report an error and quit work.
Fig. 5 is the oscillogram of controlled quentity controlled variable behind the adding inversion control digital filter.
Controlled quentity controlled variable e ' behind the adding digital filter
mWaveform as shown in Figure 5, controlled quentity controlled variable e '
mHigh frequency ripple by filtering, waveform become level and smooth, grid-connected current control device more stable work like this, the inverter output current wave is respond well.So the digital filter of the present invention's design is reasonably, and has obtained good effect.
As shown in Figure 2, in the process of photovoltaic DC-to-AC converter work, because control system itself is from grid-connected current I
NetSample data are handled; Producing pulse width modulating signal PWM again controls power switch pipe and needs the regular hour; And also have delay on the inductance that is incorporated into the power networks, so can not in the same cycle, accomplish to sampling, computing and the control of some phase point electric currents.To this problem, as shown in Figure 2 in the present embodiment, adopted the method that postpones control: on the basis of general PI control principle, PI controller 2043 is improved, in PI controller 2043, added delayer Z behind the integrator
-N, delayer Z
-NExport one the road and feed back to input; Current sampling data
Process and the expectation electric current of joining corresponding phase
Compare the output current error
2043 pairs of current errors of PI controller then
Do PI control computing, wherein, integration amount postpones N sampled point in delayer, like this, and the controlled quentity controlled variable e of PI controller 2043 outputs
mProlong N sampled point, as the control of the corresponding phase point grid-connected current of following one-period.Kp among Fig. 2 and Ki represent the ratio and the integral parameter of PI controller respectively.
Fig. 6 postpones the control sketch map.
Postpone as shown in Figure 6 the adding in integral element, offset the controlled quentity controlled variable hysteresis that various time delays cause, and reduced owing to the corresponding system mistake that makes mistakes and cause with working control point of sampled point.Among Fig. 2, being a primitive period L between working control point and the sampled point, is the delay that system control itself produces between working control point and the control point.Relevant with the control lag n of each primitive period sampling number M and system itself for choosing of delay sampling points N, the unit of n is a sampled point number, and the grid-connected current primitive period is L, and the sampling period is T, then:
Definite formula of delay sampling points N is:
N＝M-n
Under big inertia environment, export controlled quentity controlled variable in advance and in actual output point sampling, can farthest reduce the problem that lose at sampling and control point.In addition, the proportional component proportion is very small in controlled quentity controlled variable, does not therefore need specially to add to postpone to control.
The present invention is applied in the 5000w solar energy inversion system, can obtain wave distortion THD less than 2% output current, and the cycle of current first harmonics is 0.02s in this system, and the cycle of sampling is 55.5 μ s, and the delay n of control has selected 4, so the size of N is 356.
In the present embodiment, the PI controller is about 356 sampled points time of delay, and so long delay can design sufficiently high exponent number; But realize considering based on the software of digital filter simultaneously; The high more complexity that then realizes of exponent number is high more, and resource that the computing of dsp chip needs and time are just many more, so; In the present embodiment, it is more suitable that inversion control digital filter exponent number is controlled at five rank (k=5).
Although above the illustrative embodiment of the present invention is described; So that the technical staff of present technique neck understands the present invention, but should be clear, the invention is not restricted to the scope of embodiment; To those skilled in the art; As long as various variations appended claim limit and the spirit and scope of the present invention confirmed in, these variations are conspicuous, all utilize innovation and creation that the present invention conceives all at the row of protection.
Claims (2)
1. an inversion control digital filter is characterized in that, described inversion control digital filter is a wave digital lowpass filter, and its input is connected with the PI controller output end, is used for the PI controller according to current error
The controlled quentity controlled variable e that produces
mCarry out digital low-pass filtering, with controlled quentity controlled variable e
mIn high fdrequency component filter out the controlled quentity controlled variable e ' after the high fdrequency component filtering of output
mFeedforward amount with line voltage
Carry out addition, synthetic master control amount E
mOutput to pulse width modulating signal and produce circuit; Pulse width modulating signal produces circuit according to synthetic master control amount E
m, produce duty ratio K with synthetic master control amount E
mThe pulse width modulating signal PWM that changes goes to control the on-off time ratio of power switch pipe in the inverter bridge circuit, and output grid-connected current and line voltage are with the frequency homophase;
Described current error
Be that current detection circuit is to grid-connected current I
NetSample, the sampling period is T, obtains M current sampling data in the grid-connected current primitive period L
Wherein, M=L/T, m=0,1,2 ..., M-1, current sampling data
0 phase point of corresponding grid-connected current first-harmonic, then in comparator, the current sampling data of each phase place
Expectation electric current with corresponding phase
Compare, obtain:
I
PeakBe the expectation current peak.
2. inversion control digital filter according to claim 1 is characterized in that, the cut-off frequency of described inversion control digital filter is for carrying out 2 times of cut-off frequency of the simulation low-pass filter of LPF to the inverter output current;
The time T that the inversion control digital filter postpones
dCorresponding sampling points is counted P
dWith the relational expression of the exponent number k of filter be:
P
d＝(k-1)/2
The calculating treatmenting time T of grid-connected current control device
c, its corresponding sampling points is counted P
c, the exponent number k of inversion control digital filter satisfies condition:
P
d+P
c＜N
The sampling number that N postpones for the PI controller.
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| CN107222101B (en) * | 2017-05-16 | 2019-09-10 | 西安交通大学 | A kind of integrated converter circuit for light energy collection |
| CN108282077B (en) * | 2017-12-23 | 2020-05-22 | 浙江正泰电器股份有限公司 | Self-adaptive PI (proportional integral) adjusting method |
| CN108448613B (en) * | 2018-03-29 | 2019-06-21 | 东南大学 | A kind of Current Sensorless type grid current control method suitable for gird-connected inverter |
| CN111355450B (en) * | 2020-04-03 | 2023-07-14 | 青海省第三地质勘查院 | Quasi-sinusoidal pseudo-random signal generation device and generation method thereof |
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| EP1768266A2 (en) * | 2005-09-26 | 2007-03-28 | Samsung Electronics Co., Ltd. | Radio frequency signal receiver for controlling bias current and method for controlling bias current |
| CN201402983Y (en) * | 2009-04-14 | 2010-02-10 | 福建省宏远科技有限公司 | Digitalized dynamic intelligent reactive-load compensating gear |
| CN101714763A (en) * | 2009-09-03 | 2010-05-26 | 周德佳 | High-efficiency stable multifunctional single-stage photovoltaic single-phase grid-connected control method |
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| EP0757432A2 (en) * | 1995-08-04 | 1997-02-05 | The Boeing Company | Starting of synchronous machine without rotor position of speed measurement |
| EP1768266A2 (en) * | 2005-09-26 | 2007-03-28 | Samsung Electronics Co., Ltd. | Radio frequency signal receiver for controlling bias current and method for controlling bias current |
| CN201402983Y (en) * | 2009-04-14 | 2010-02-10 | 福建省宏远科技有限公司 | Digitalized dynamic intelligent reactive-load compensating gear |
| CN101714763A (en) * | 2009-09-03 | 2010-05-26 | 周德佳 | High-efficiency stable multifunctional single-stage photovoltaic single-phase grid-connected control method |
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