CN104113052A - Method for protecting active power filter (APF) - Google Patents
Method for protecting active power filter (APF) Download PDFInfo
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- CN104113052A CN104113052A CN201410305638.6A CN201410305638A CN104113052A CN 104113052 A CN104113052 A CN 104113052A CN 201410305638 A CN201410305638 A CN 201410305638A CN 104113052 A CN104113052 A CN 104113052A
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E40/20—Active power filtering [APF]
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Abstract
The invention discloses a method for protecting an active power filter (APF). In the method for protecting the APF provided by the invention, by current limiting of instruction current, compensating current actually output by the APF is limited within a reasonable range, thereby preventing the instruction current from being too large, causing APF overcurrent and damaging the APF. In the method in the invention, proportional current limiting and switch-off current limiting are performed on the instruction current in sequence, and dual protection is realized through two times of current limiting, thereby improving reliability of a system, better protecting the APF, and prolonging service life.
Description
Technical field
The invention belongs to electric and electronic technical field, be specifically related to a kind of guard method of Active Power Filter-APF.
Background technology
Being widely used in when advancing industrial productivity development and electric automatization level to improve of the growing maturation of power electronic technology and Electric Power Automation Equipment, also caused serious harmonic pollution in electric power net problem, Active Power Filter-APF (APF) arises at the historic moment.
Active Power Filter-APF (APF) is by comprising main circuit (current transformer), drive circuit and control system.Its compensation process is for first passing through voltage transformer (PT), current transformer (CT) obtains the current signal of system voltage and nonlinear load, control system is processed the voltage and current signal obtaining, calculate instruction current corresponding to each harmonic that needs compensation, again according to this instruction current, generate for driving the driving pulse of current transformer, the break-make of switching device (power device) in control main circuit real-time, output actual needs offset current, in this offset current and load current, need the each harmonic of compensation to offset, finally obtain the power network current of the sine of expectation, thereby improved the quality of power supply of electrical network.
As a mains by harmonics and idle dynamic compensating device, APF not only needs have good stable state compensation performance and dynamic responding speed, most importantly will guarantee reliable and stable operation.The prerequisite of APF stable operation is the rated capacity that its compensation capacity can not surpass self, because power cell is very responsive to instantaneous overcurrent and overvoltage in its current transformer, overcurrent in short-term and overvoltage also may cause the damage of switching tube, so will avoid crossing of APF to hold operation as far as possible.
The situation that under normal circumstances, may cause APF to cross appearance operation has two kinds: the nonlinear load of (1) access utility network is uprushed; (2) load of access utility network is short-circuited or the fault such as open circuit, and the system asymmetrical component of causing is uprushed.If both of these case causes APF to cross, hold operation, its basic reason is that uprushing of load current harmonic component causes uprushing of instruction current.So limit the operation of cross holding of APF, most critical be will limit instruction current within self-compensation situation range of capacity.
The people such as Yang Zhenyu are being entitled as parallel connection type active electric filter current limliting compensation policy research (Electric Power Automation Equipment .2006,26 (3): 21-25) in a literary composition, propose a kind of software Current limited Control strategy, only reference current is processed, control and realize simply, and obtained good current limitation effect.But it exists the problem of a most critical not yet to solve: instruction current maximum value i
refmaxwith the maximum compensation current i that allows of system
maxdefinition.Traditional current limliting and proportional limit Flow Policy of blocking is for instruction current maximum value i
refmaxdefinition be exactly the absolute value of instruction current peak value, and the maximum compensation current i that allows of system
maxaccording to power system capacity, be defined as a fixing value.
In fact, for one, can compensate 0～2.5kHz with the APF system of interior any subharmonic, instruction current maximum value i
refmaxmust not simply be defined as the absolute value of instruction current peak value.The peak value when effective value of instruction current reaches system rated capacity except will consider to compensate full frequency band harmonic wave time, the peak value when effective value of instruction current reaches system rated capacity in the time of also will considering to compensate low order or single harmonic component.Conventionally the rated capacity of APF is that the specified harmonic current effective value that can compensate with every phase defines.In conjunction with actual conditions, when APF need to compensate full frequency band harmonic wave, if the offset current effective value of system reaches rated value, now the peak value of instruction current often only compensates low order or single harmonic component than APF system and the instruction current peak value of offset current effective value while reaching rated value is much higher.So, if simply by instruction current maximum i
refmaxbe defined as peak value, may occur so two kinds of situations below:
(1) if the peak value of instruction current is defined as the maximum offset current peak value i that allows of system when while compensating full frequency band harmonic wave by APF, effective value reaches rated value
peak, so when APF compensation low order or single harmonic component, even if the effective value of offset current has surpassed rated value, the maximum that does not reach default due to the peak value of instruction current now allows offset current peak value i
peak, instruction current can continue to increase, until peak value reaches the i of setting
peak, and now the effective value of instruction current considerably beyond specified effective value, thereby cause APF overcurrent.
(2) if the peak value of instruction current is defined as the maximum offset current peak value i that allows of system when while compensating low order or single harmonic component by APF, effective value reaches rated value
peak(being maximum permissible current), so when APF compensation full frequency band harmonic wave, because the peak value when instruction current reaches the i of setting
peaktime, the effective value of instruction current does not also reach system rated value far away, thereby causes APF utilance not high.
Meanwhile, obtain the selective harmonic compensation that is used for the instruction current effective value of ratio current limliting link and realizes APF and need to adopt a kind of effective harmonic detecting method.The congruent people of tree specifies subharmonic current to control (Proceedings of the CSEE .2010 (03): 55-62) propose a kind of selective harmonic Current Detection Algorithm based on synchronously rotating reference frame conversion being entitled as under many synchronous rotating frames, but the method need to be passed through multiple rotary coordinate transform, amount of calculation is large, and need to design a low pass or band pass filter, the accuracy of detection of harmonic component depends on the design of filter, and the improper meeting of parameter designing of filter directly affects accuracy of detection.
In addition, can cause the fluctuation of APF DC voltage during large capacity nonlinear load sudden change, if overvoltage appears in DC side, the switching device that is connected in parallel on dc-link capacitance two ends likely causes because of transient high-voltage breakdown damaging.
Summary of the invention
For the deficiencies in the prior art, the invention provides a kind of guard method of Active Power Filter-APF.
The guard method of Active Power Filter-APF of the present invention, comprises the steps:
(1) extract the each harmonic component that needs compensation in load current, and the each harmonic component stack of extraction is obtained to instruction current;
(2) according to the specified offset current effective value of Active Power Filter-APF with need the higher harmonics number of times of compensation to set successively first threshold and Second Threshold;
(3) using first threshold as maximum permissible current, described instruction current is carried out to ratio current limliting, obtain the first instruction current;
(4) Second Threshold is blocked to current limliting as blocking peak current to the first described instruction current, obtain the second instruction current;
(5) according to the second instruction current, generate for driving the driving pulse of Active Power Filter-APF current transformer, make current transformer export corresponding offset current.
In the guard method of the Active Power Filter-APF that the present invention proposes by instruction current is carried out to current limliting, make the offset current restriction of the actual output of Active Power Filter-APF in the reasonable scope, prevent because the excessive APF of the causing overcurrent of instruction current (offset current that refers to actual output surpasses the maximum permissible value that switching device can bear) damages Active Power Filter-APF, and in the present invention, instruction current is carried out successively ratio current limliting and blocks current limliting, by twice current limliting, realize duplicate protection, improved the reliability of system, can better protect Active Power Filter-APF, increase the service life.
Carrying out ratio current limliting and blocking before current limliting processes, the compensation frequency preset proportion current limliting of first setting according to user and block the relevant parameter of current limliting.According to actual conditions, set relevant parameter like this, use single parameter comparison with all fixing under any operating mode in prior art, more flexible, in the situation that APF only compensates low-order harmonic, can further improve the fan-out capability of APF, improved the utilization ratio of APF, even in the situation that full frequency band compensates, within also effectively offset current being limited in to specified fan-out capability scope.The ratio current limliting of this kind of parameter adjustable type and block current-limiting method and contribute to realize that APF fan-out capability under different operating modes maximizes and the unification of high reliability.
As preferably, described step (1) extracts based on sliding window iteration DFT algorithm the each harmonic component that needs compensation.
Based on sliding window iteration DFT algorithm, overcome the defect that in the harmonic current detection based on synchronous rotating frame, coordinate transform is complicated, parameter designing is difficult, and by cancelling cycle average filter, the sliding window DFT of tradition algorithm is improved, greatly reduced taking program space resource, realize single or the stack of any subharmonic and extracted, there is very high precision.
The detailed process of extracting nth harmonic classification based on sliding window iteration DFT algorithm is as follows:
Sliding window of a initialization, the length of described sliding window is the sum of a sampled point in the primitive period, is designated as N, supposes that the data of sliding window sampling are stored in the array X[N that a size is N] in, in initial condition downslide window, the value of all elements is 0, i.e. X[0]～X[N-1]=0;
B gathers a new data x (k τ), and (x (k τ) is the sampled data in a certain moment, wherein k represents current sampled point numbering, and the span of k is 0～N-1, and τ is sampling time interval), the sliding window of renewal sampled data corresponding to this sampled point before the primitive period;
C. calculate and need the nth harmonic of extraction in the phase place of current sampling point, be specially:
One-period is 2 π, and N sampled point of one-period sampling, therefore the phase difference between each sampled point is
the phase place of supposing first sample point in the present invention is 0, and the phase place of k sample point is exactly
owing to being nth harmonic, the phase place of k sample point nth harmonic is
D. the numbering k that the judges current sampling point k=N-1 that whether satisfies condition, N is the sum of a sampled point in the primitive period:
If meet, order:
The real part A of the nth harmonic component that current sampling point place is calculated for harmonic component instantaneous value
nwith imaginary part B
nbe respectively: A
n=a
n, B
n=b
n;
The nth harmonic component instantaneous value x of current sampling point place
n(k) be:
x
n(k)＝a
ncos(2πnk/N)+b
nsin(2πnk/N)，
Wherein,
a
n＝a
n+x(kτ)*cos(2πnk/N)，
b
n＝b
n+x(kτ)*sin(2πnk/N)。
Otherwise, order:
Current sampling point place is for the real part A of the instantaneous value of the nth harmonic component that calculates
nwith imaginary part B
nbe respectively: A
n=A'
n, B
n=B'
n, A' wherein
nand B'
nbe respectively the real part A of a primitive period nth harmonic component
nwith imaginary part B
n, calculate harmonic component real part and the imaginary part used at current sampling point place and do not upgrade, continue along the value of using a cycle;
Further, according to real part A
nwith imaginary part B
nobtain the instantaneous value x of current sampling point place nth harmonic component
n(k) be:
x
n(k)＝A
ncos(2πnk/N)+B
nsin(2πnk/N)，
E. after sampling number k adds 1, return and continue execution step b, until finish during k=N.
Described step (2) is calculated first threshold i according to following formula
max:
i
max＝K
i*i
p，
Wherein, i
pfor specified offset current effective value;
The first proportionality coefficient is K
i:
Wherein, h is for needing the higher harmonics number of times of compensation.
Described step (2) is calculated Second Threshold i according to following formula
peak:
i
peak＝K
p*i
max，
Wherein, i
maxfor first threshold;
K
pbe the second proportionality coefficient:
Wherein, h is for needing the higher harmonics number of times of compensation.
The higher harmonics number of times of compensation is set the first proportionality coefficient and the second proportionality coefficient makes APF operational efficiency maximize principle as required, guarantee APF stable operation safely and reliably under various different operating modes, the utilization ratio that can realize again the switching device (power cell) of current transformer reaches the highest.Specifically choose process as follows: first by the Simulink copying of Matlab, build the relevant APF model of emulation, according to the harmonic number of the needs compensation of setting and the harmonic current waveform characteristic under corresponding compensation harmonic number of times (being mainly the relation of harmonic current effective value and harmonic wave current peak) initialization, these two proportionality coefficients (i.e. the first proportionality coefficient and the second proportionality coefficient are set, also comprise frequency range how to divide with each frequency range in the initial value of ratio coefficient value choose), according to the APF model of emulation true peak electric current under the effect of initialization proportionality coefficient value, whether surpass maximum offset current peak value and the actual offset current effective value of allowing and whether surpass the maximum offset current effective value that allows, if do not surpass, can suitably strengthen proportionality coefficient and carry out again compliance test result, otherwise, if surpass, suitably reduce to carry out compliance test result.Through repeatedly obtaining two optimum proportionality coefficients after feedback regulation and checking, gradient type set point provided by the invention can be used as preferably.
Described step (3) process is as follows:
(3-1) effective value of computations electric current, and the business who obtains divided by effective value and the greater in first threshold of instruction current by first threshold is as ratio orificing factor;
(3-2) according to formula:
i'
ref＝k*i
ref
Calculate the first instruction current i'
ref, i
reffor instruction current, k is ratio orificing factor.
The effective value i of instruction fetch electric current
rmswith first threshold i
maxin the greater, be designated as i
max, then use first threshold i
maxdivided by this greater i
maxthe business who obtains is as ratio orificing factor k, i.e. k=i
max/ i
mAX.When the effective value of instruction current is greater than first threshold constantly, i
mAX=i
rmsnow ratio orificing factor k is less than 1, and then the first instruction current i' obtaining
refbe less than instruction current i
ref(former instruction current), plays the effect of current limliting.When the effective value of instruction current is less than first threshold, i
mAX=i
max, now ratio efficiency factor k is 1, and then the first instruction current obtaining equals instruction current, is equivalent to the instruction current former state originally calculating to export.
Basis in the present invention:
The effective value i of computations electric current
rms, N is sampling number in a primitive period sum, h represents compensation harmonic number of times for the highest compensation harmonic number of times, n.
In described step (4) according to formula:
The first instruction current is blocked to current limliting.
Using the output of ratio current limliting link as the input of blocking current limliting link, thereby form the dual current limliting of blocking current limliting after first ratio current limliting, after blocking current limliting, can obtain the second instruction current i "
ref, this second instruction current is for generation of driving the driving pulse of current transformer, by blocking current limliting, the amplitude of the first instruction current is limited to [i
peak, i
peak] between, further prevent that offset current is excessive.
The DC voltage (being the voltage at dc-link capacitance two ends) that described guard method also comprises real-time detection Active Power Filter-APF, carries out hardware lockout current limliting according to DC voltage to Active Power Filter-APF, and detailed process is as follows:
(S1) detect in real time the DC voltage of Active Power Filter-APF;
(S2) DC voltage detecting is nursed one's health in the voltage range of setting and obtained corresponding Equivalent DC side voltage;
(S3) Equivalent DC side voltage conditioning being obtained and the 3rd threshold value compare, and proceed as follows according to comparative result:
If be more than or equal to the 3rd threshold value, block the driving pulse of current transformer in Active Power Filter-APF, until lift a blockade during Equivalent DC side voltage drop to the four threshold value, make the corresponding offset current of current transformer output;
Otherwise, inoperation.
Because load changing is easy to occur the situation of DC side overvoltage, in order to regulate DC voltage, make it return to normal level, controller can be in original first-harmonic real component that superpose in detecting according to load harmonic current the instruction current draw, two component one stacks, likely surpass the maximum offset current permissible value of APF, thereby cause APF overcurrent, but this kind of overcurrent condition can effectively limit by instruction current limliting provided by the invention.But when the fluctuation of load; due to the variation of instruction current and follow the tracks of and conventionally can have certain time-delay; so superpose in dependence instruction current, a first-harmonic real component completes the control of DC voltage; need certain time delay; when also having little time to regulate, very possible instruction current just due to DC side overvoltage, caused APF to damage.In the present invention, pass through to detect in real time DC voltage, when DC side overvoltage being detected, directly block the driving pulse of power model in APF, prevent that overvoltage from causing the damage of switching device, simultaneously DC side is because the afterflow effect of diode also can decline gradually, thereby completes the adjusting of DC voltage, can effectively eliminate time delay, real-time, impact electric current has good inhibitory action, and controls flexibly, realizes simple.
The principle of hardware lockout current limliting is as follows: when the equivalent voltage value of DC voltage instantaneous value surpasses maximum set value (the 3rd threshold value), driving pulse is forced to drag down (driving pulse that blocks current transformer in Active Power Filter-APF), block current transformer just at the switching device (power cell) of conducting, make circuit enter afterflow state, the afterflow effect of the diode by switching device two ends reduces DC voltage gradually, when the equivalent voltage value of DC voltage instantaneous value drops to minimum set point (the 4th threshold value), driving pulse reopens, power cell recovers normal work, and then play the effect of protecting Active Power Filter-APF under DC side overpressure situation.
Because the DC voltage collecting under APF normal operation is generally higher voltage (about 700 ± 50V left and right), cannot directly relatively protect, for ease of realizing, in the present invention, the DC voltage of the Active Power Filter-APF collecting is nursed one's health in the voltage range of setting and obtained corresponding Equivalent DC side voltage; Then utilize Equivalent DC side voltage to complete comparison to determine whether carrying out hardware lockout current limliting.In the present invention, according to practical application request, set suitable equivalence conditioning no-load voltage ratio K
t, K generally
tspan be 0.004～0.006.Utilize the equivalence conditioning no-load voltage ratio K setting
taccording to following formula by the DC voltage V detecting
dcconditioning obtains Equivalent DC side voltage V ' in the voltage range of setting
dc:
V′
dc＝K
T*V
dc。
In fact, if technical conditions allow, can not nurse one's health yet, directly with the DC voltage collecting, carry out follow-up comparison.
The 3rd described threshold value V
1according to formula:
V
1＝K
T*(V
dcp+ΔV
h)
Calculate, wherein, V
dcprepresent DC voltage rated value, Δ V
hthe overvoltage allowance that represents DC side overvoltage protection, K
trepresent equivalence conditioning no-load voltage ratio.
The 4th described threshold value V
2according to formula:
V
2＝K
T*(V
dcp-ΔV
l)
Calculate V
dcprepresent DC voltage rated value, Δ V
lrepresent the under-voltage allowance that DC side overvoltage protection is removed, K
trepresent equivalence conditioning no-load voltage ratio.
The under-voltage allowance that the overvoltage allowance of DC side overvoltage protection and DC side overvoltage protection are removed choose the sensitivity that can directly have influence on protection, the principle of choosing will be considered the reliability of protection on the one hand, therefore value can not be too large, otherwise susceptibility is too low; That can not get on the other hand is too little, otherwise likely misoperation can occur, and affects APF operating efficiency.As preferably, the overvoltage allowance Δ V of DC side overvoltage protection
hdesirable 50～100V, the under-voltage allowance Δ V that DC side overvoltage protection is removed
ldesirable 100～150V.
Compared with prior art, there is following advantage in the present invention:
(1) combine ratio current limliting and block current limliting advantage separately, adopt the duplicate protection that blocks current limliting after first ratio current limliting to guarantee the reliability of PWM driving pulse.
(2) Current wave-shape characteristic while having considered APF compensation full frequency band harmonic wave and only having compensated low order or single harmonic component, according to the flexible preset proportion current limliting of practical situations and the threshold value of blocking current limliting, can effectively limit the size of instruction current, and then play the metering function to the offset current of APF output, can guarantee again the utilization ratio of APF under all kinds of operating modes.
(3) when instruction current being carried out successively to ratio current limliting and blocking current limliting; according to the DC voltage of APF, carry out the guard method based on hardware lockout; effectively eliminated to utilize in instruction current and superposeed and when a first-harmonic real component regulates DC voltage, have the defect of certain time-delay; can promptly protect the switching device of current transformer; to prevent DC side, cross crushing switching device; impact load changing has good inhibitory action, and controls flexibly, realizes simple.
(4) use a kind of improved sliding window iteration DFT algorithm to overcome the defect that harmonic current detection coordinate transform is complicated, parameter designing is difficult based on synchronous rotating frame, and by cancelling cycle average filter, the sliding window DFT of tradition algorithm is improved, greatly reduced taking program space resource, realize single or the stack of any subharmonic and extracted, there is very high precision.
Accompanying drawing explanation
The flow chart of the guard method of the Active Power Filter-APF of Fig. 1 the present embodiment;
Fig. 2 is the reference voltage circuit of the present embodiment;
Fig. 3 is the hysteresis comparator circuit of the present embodiment;
Fig. 4 is the SAPF system configuration schematic diagram of the present embodiment;
Fig. 5 is the SAPF of the present embodiment full frequency band stable state compensation waveform under rated condition;
Fig. 6 is the stable state compensation waveform that the SAPF of the present embodiment carries out current limliting compensation;
Fig. 7 is the dynamic compensation waveform that the SAPF of the present embodiment carries out current limliting compensation.
Embodiment
Below in conjunction with accompanying drawing and instantiation, the present invention is further illustrated.
The guard method of the Active Power Filter-APF of the present embodiment, as shown in Figure 1, comprises the steps:
(1) extract the each harmonic component that needs compensation in load current, and the each harmonic component stack of extraction is obtained to instruction current;
In the present embodiment, based on sliding window iteration DFT algorithm, extract the each harmonic component that needs compensation, the detailed process of extracting nth harmonic classification based on sliding window iteration DFT algorithm is as follows:
Sliding window of a initialization, the length of sliding window is the sum of a sampled point in the primitive period, be designated as N (N=200 in the present embodiment), the data of supposing sliding window sampling are stored in the array X[N that a size is N] in, in initial condition downslide window, the value of all elements is 0, i.e. X[0]～X[N-1]=0;
B gathers a new data x (k τ), and k represents a numbering that the current sampling point in the primitive period is corresponding, and τ is sampling time interval (for the 1/N primitive period doubly), the sliding window of renewal sampled data corresponding to this sampled point before the primitive period;
C. calculate and need the nth harmonic of extraction in the phase place of current sampling point, be specially:
One-period is 2 π, and N point of one-period sampling, therefore the phase difference between each sampled point is
the phase place of supposing first sample point in the present invention is 0, and the phase place of k sample point is exactly
owing to being nth harmonic, so the phase place of k sample point nth harmonic is
D. the numbering k that the judges current sampling point k=N-1 that whether satisfies condition, N is the sum of a sampled point in the primitive period:
If meet, order:
The real part A of the nth harmonic component that current sampling point place is calculated for harmonic component instantaneous value
nwith imaginary part B
nbe respectively: A
n=a
n, B
n=b
n;
Current sampling point place nth harmonic component instantaneous value is:
x
n(k)＝a
ncos(2πnk/N)+b
nsin(2πnk/N)，
Wherein,
a
n＝a
n+x(kτ)*cos(2πnk/N)，
b
n＝b
n+x(kτ)*sin(2πnk/N)，
Otherwise, order:
The real part A of the nth harmonic component that current sampling point place is calculated for harmonic component instantaneous value
nwith imaginary part B
nbe respectively: A
n=A'
n, B
n=B'
n, A' wherein
nand B'
nbe respectively the real part A of a primitive period nth harmonic component
nwith imaginary part B
n, calculate harmonic component real part and the imaginary part used at current sampling point place and do not upgrade, continue along the value of using a cycle;
The instantaneous value of current sampling point place nth harmonic component is:
x
n(k)＝A
ncos(2πnk/N)+B
nsin(2πnk/N)，
E. after sampling number k adds 1, return and continue execution step b, until finish during k=N.
Each circulation finishes, and can obtain current sampling point place nth harmonic component (being the instantaneous value of nth harmonic component), and corresponding A
nand B
n.
(2) according to the specified offset current effective value of Active Power Filter-APF with need the higher harmonics number of times of compensation to set successively first threshold and Second Threshold;
According to following formula, calculate first threshold i
max:
i
max＝K
i*i
p，
Wherein, i
pfor specified offset current effective value;
K
ibe the first proportionality coefficient:
Wherein, h is for needing the higher harmonics number of times of compensation.
According to following formula, calculate Second Threshold i
peak:
i
peak＝K
p*i
max，
Wherein, i
maxfor first threshold;
K
pbe the second proportionality coefficient:
Wherein, h is for needing the higher harmonics harmonic number of compensation.
(3) using first threshold as maximum permissible current, instruction current is carried out to ratio current limliting, obtain the first instruction current;
(3-1) basis:
The effective value i of computations electric current
rms, N is sampling number in a primitive period sum, and h is for needing the higher harmonics harmonic number of compensation, and n represents the harmonic wave harmonic number (only compensate odd number inferior, n gets odd number) of needs compensation;
And the business who obtains divided by effective value and the greater in first threshold of instruction current by first threshold is as ratio orificing factor;
(3-2) according to formula:
i'
ref＝k*i
ref
Calculate the first instruction current i'
ref, i
reffor instruction current, k is ratio orificing factor.
(4) usining Second Threshold blocks current limliting as blocking peak current to the first instruction current, obtains the second instruction current; Specific as follows according to formula:
The first instruction current is blocked to current limliting, using the output of ratio current limliting link as the input of blocking current limliting link, thereby form the dual current limliting of blocking current limliting after first ratio current limliting, after blocking current limliting, can obtain the second instruction current i "
ref, this i "
refbe final reference instruction electric current, by blocking current limliting, the amplitude of the first instruction current be limited to [i
peak, i
peak] between, further prevent that offset current is excessive.
(5) according to the second instruction current, generate for driving the driving pulse of the current transformer of Active Power Filter-APF, make current transformer export corresponding offset current.
The DC voltage (voltages at dc-link capacitance two ends) that the guard method of the present embodiment also comprises real-time detection Active Power Filter-APF, carries out hardware lockout current limliting according to DC voltage to Active Power Filter-APF, and detailed process is as follows:
(S1) DC voltage of Real-time Collection Active Power Filter-APF;
(S2) DC voltage detecting is nursed one's health in the voltage range of setting and obtained corresponding Equivalent DC side voltage, specific as follows:
In the present embodiment, the DC voltage detecting is nursed one's health below 5V, is set equivalence conditioning no-load voltage ratio KT=0.00517, according to following formula by the DC voltage V detecting
dcconditioning obtains Equivalent DC side voltage V ' in the voltage range of setting
dc:
V′
dc＝K
T*V
dc。
(S3) DC side equivalent voltage conditioning being obtained and the 3rd threshold value compare, and proceed as follows according to comparative result:
If be more than or equal to the 3rd threshold value, block the driving pulse of current transformer in Active Power Filter-APF, until lift a blockade during Equivalent DC side voltage drop to the four threshold value, and then complete the adjusting to the offset current of current transformer output;
Otherwise, inoperation.
In the present embodiment, DC voltage rated value is 750V, the overvoltage allowance Δ V of DC side overvoltage protection
dcget 100V, the under-voltage allowance Δ that DC side overvoltage protection is removed ' V
dcget 150V, the DC side overvoltage protection value on historical facts or anecdotes border is 850V, and overvoltage protection releasing value is 600V.
According to formula:
V
1＝K
T*(V
dcp+ΔV
h)
Calculate the 3rd threshold value V
1, wherein, V
dcprepresent DC voltage rated value, Δ V
hthe overvoltage allowance that represents DC side overvoltage protection, K
trepresent equivalence conditioning no-load voltage ratio, obtain the 3rd threshold value V
1=4.4V.
According to formula:
V
2＝K
T*(V
dcp-ΔV
l)
Calculate the 4th threshold value V
2, V
dcprepresent DC voltage rated value, Δ Vl represents the under-voltage allowance that DC side overvoltage protection is removed, K
trepresent equivalence conditioning no-load voltage ratio, obtain the 4th threshold value V
1=3.1V.
Hardware lockout current limliting completes based on following system, and this system comprises voltage modulate circuit, reference voltage circuit, hysteresis comparator circuit, Drive Protecting Circuit, wherein:
Voltage modulate circuit, for nursing one's health the DC voltage collecting output equivalent DC voltage in the voltage range of setting;
Reference voltage circuit, for generating corresponding reference voltage according to setting voltage scope;
Hysteresis comparator circuit, take reference voltage and Equivalent DC side voltage is input, the corresponding threshold value of exporting corresponding level signal and hysteresis comparator circuit is respectively the 3rd threshold value and the 4th threshold value, is respectively 4.4V and 3.1V;
Drive Protecting Circuit, receives the output of hysteresis comparator circuit, and when the output level of hysteresis comparator circuit is high level, output drives guard signal, and this driving guard signal is for blocking the driving pulse of APF current transformer.
Reference voltage circuit as shown in Figure 2, comprise voltage stabilizing didoe U1, the first pin 1 of voltage stabilizing didoe U1 is connected with power supply DVCC by current-limiting resistance R1, the second pin 2 ground connection GND of voltage stabilizing didoe U1, between the first pin 1 and the second pin 2, be connected with shunt capacitance C3, the 3rd pin 3 of voltage stabilizing didoe U1 is connected with the first pin by the first divider resistance R2, by the second divider resistance R3, be connected with the second pin, for realizing stable output reference voltage, power supply DVCC is by the first filter capacitor C1 and the second filter capacitor C2 ground connection DGND in parallel.
This reference voltage circuit is usingd the first pin of voltage stabilizing didoe U1 as the reference voltage V of output output equivalent DC voltage
ref, the reference voltage V of output
refsize depend on and the reference voltage of R2, R3 and voltage stabilizing didoe meet following relation:
In formula, V
treference voltage for voltage-stabiliser tube used.
Can be by regulating relevant parameter to obtain different reference voltages according to the voltage range of setting.
In the present embodiment, in reference voltage circuit, voltage stabilizing didoe U1 is TL431 type, reference voltage is 2.5V, the present embodiment R2=1.2k Ω, R3=3k Ω, all the other parameters are selected to set according to routine, are respectively C1=0.1uF, C2=0.01uF, C3=1nF, R1=120 Ω, the reference voltage of corresponding output is:
Fig. 3 is hysteresis comparator circuit, comprises comparator U2, Equivalent DC side voltage V
dcby resistance R 4, be connected to the positive input 5 (V+) of comparator U2, reference voltage V
refby resistance R 5, be connected to the reverse input end 6 (V-) of comparator U2.Positive input 5 is also by capacitor C 4 ground connection DGND; strobe; the output 7 of comparator U2 is connected to power supply DVCC (5V) by resistance R 7; on plaing, draw effect; and between positive input and output, be connected with feedback resistance R6, the output of comparator is connected to next stage Drive Protecting Circuit.
The voltage range of setting in the present embodiment is below 5V, corresponding the 3rd threshold value V
1with the 4th threshold value V
2be respectively 4.4V and 3.1V, the parameter in hysteresis comparator circuit need to be rationally set, set principle as follows:
Wherein, V
pHand V
pLbe respectively the low and high level of stagnant loop circuit output voltage.
V in hysteresis comparator circuit in the present embodiment
pH=0V, V
pL=5V, sets R4=6.2k Ω accordingly, R6=24k Ω.All the other parameters are selected to set according to routine, as follows respectively:
C4＝1nF，R5＝5.1kΩ，R7＝39kΩ。
Under normal circumstances, the Equivalent DC side voltage of input between 3.1V～4.4V, now output level signal V
pfor 0V.When the Equivalent DC side voltage of inputting is more than or equal to 4.4V (the 4th threshold value V
2) time, the level signal V of output
pfor high level, until Equivalent DC side voltage is less than or equal to 3.1V (the 3rd threshold value V
1) time, the level signal V of output
pagain be low level.
In order further to verify, carried out corresponding experimental verification by beneficial effect of the present invention on a 14kVA three-phase four-wire system SAPF model machine of building, prototyping system structure as shown in Figure 4.In figure, u
sa, u
sb, u
scfor electrical network three-phase phase voltage, i
sa, i
sb, i
sc, i
sNbe respectively electrical network three-phase phase current and current in middle wire, L
ga, L
gb, L
gcfor each phase leakage inductance of electrical network, i
la, i
lb, i
lc, i
lNbe respectively load three-phase phase current and current in middle wire, i
ca, i
cb, i
cc, i
cNbe respectively compensation three-phase phase current and current in middle wire.Nonlinear load adopts three-phase not control the load of rectifier bridge band resistance sense, L
c, L
s, R
dand C
fform AC output filter, the switching harmonics in filtering output current and unwanted high fdrequency component.The major parameter of three-phase four-wire system SAPF prototyping system is as shown in table 1.
Table 1
| Symbol | Parameter declaration | Numerical value |
| u s | Electrical network phase voltage | 220V |
| f s | Mains frequency | 50Hz |
| V dc | DC voltage | 750V |
| C dc | DC side total capacitance | 11.75mF |
| f sm | Sample frequency | 10kHz |
| f sw | Switching frequency | 10kHz |
Fig. 5 is the full frequency band stable state compensation waveform of this 14kVA three-phase four-wire system SAPF model machine under rated full load condition, I in figure
l, I
c, I
sbe respectively load current, offset current and current on line side.Specified offset current effective value i
p=20A.Can find out, under nominal working conditions, compound current-limiting method based on instruction current current limliting is inoperative, instruction current value is detected load harmonic current value, it is sinusoidal wave that grid side current waveform after compensation is, total harmonic distortion THD (Total Harmonic Distortion)=3.6%, illustrates that this model machine has good harmonic compensation ability.
Fig. 6 is the Steady Experimental result of carrying out current limliting compensation on this model machine, I in figure
l, I
c, I
sbe respectively load current, offset current and current on line side.Setting load harmonic current effective value is 60A, and the selective harmonic compensation frequency is 3,5,7,11 times.The higher harmonics number of times h=11 that needs compensation, maximum offset current effective value (the being first threshold) i that in corresponding instruction current current limliting, define system allows
max=30A, peak value (being Second Threshold) i
peak=69A.As seen from the figure, although harmonic current effective value to be compensated is 3 times of the specified compensation ability of this model machine in load current, considerably beyond its compensation range, the effective value of system balance electric current is limited in i all the time
max, the situation that there will not be serious overcurrent to move.In addition, utilize wavestar to carry out spectrum analysis to offset current, known its effective value is 29.4A, approaches very much first threshold i
max=30A, error, in 2%, has very high control precision.Also can find out simultaneously, the conventional method of getting all the time rated value than the maximum offset current effective value of define system, under the prerequisite that guarantees SAPF safe and reliable operation, many output has compensated the harmonic current that approaches 10A, and the situation lower device utilization ratio of compensation low-order harmonic has improved 50%.
Fig. 7 is the dynamic experiment result of carrying out current limliting compensation on this model machine, I in figure
l, I
c, I
sbe respectively load current, offset current and current on line side.Set zero load-40A harmonic load and dynamically switch, the compensation frequency of SAPF is still 3,5,7,11 times.Can find out, during shock load, although load harmonic current to be compensated is considerably beyond the compensation ability of this SAPF, but the actual offset current effective value of model machine output has well been limited in 30A, the situation that does not occur load changing moment offset current to exceed system maximum permissible value and SAPF overcurrent is moved, illustrates that when load is dynamically switched, this current limliting strategy also can have good control effect.
The above; be only the specific embodiment of the present invention, but protection scope of the present invention is not limited to this, is anyly familiar with those skilled in the art in the technical scope that the present invention discloses; the variation that can expect easily or replacement, within all should being encompassed in protection scope of the present invention.
Claims (8)
1. a guard method for Active Power Filter-APF, is characterized in that, comprises the steps:
(1) extract the each harmonic component that needs compensation in load current, and the each harmonic component stack of extraction is obtained to instruction current;
(2) according to the specified offset current effective value of Active Power Filter-APF with need the higher harmonics number of times of compensation to set successively first threshold and Second Threshold;
(3) using first threshold as maximum permissible current, described instruction current is carried out to ratio current limliting, obtain the first instruction current;
(4) Second Threshold is blocked to current limliting as blocking peak current to the first described instruction current, obtain the second instruction current;
(5) according to the second instruction current, generate for driving the driving pulse of Active Power Filter-APF current transformer, make current transformer export corresponding offset current.
2. the guard method of Active Power Filter-APF as claimed in claim 1, is characterized in that, described step (1) extracts based on sliding window iteration DFT algorithm the each harmonic component that needs compensation.
3. the guard method of Active Power Filter-APF as claimed in claim 1, is characterized in that, described step (2) is calculated first threshold i according to following formula
max:
i
max＝K
i*i
p，
Wherein, i
pfor specified offset current effective value;
K
ibe the first proportionality coefficient:
Wherein, h is for needing the higher harmonics number of times of compensation.
4. the guard method of Active Power Filter-APF as claimed in claim 1, is characterized in that, described step (2) is calculated Second Threshold i according to following formula
peak:
i
peak＝K
p*i
max，
Wherein, i
maxfor first threshold;
K
pbe the second proportionality coefficient:
Wherein, h is for needing the higher harmonics number of times of compensation.
5. the guard method of Active Power Filter-APF as claimed in claim 1, is characterized in that, described step (3) process is as follows:
(3-1) effective value of computations electric current, and the business who obtains divided by effective value and the greater in first threshold of instruction current by first threshold is as ratio orificing factor;
(3-2) according to formula:
i'
ref＝k*i
ref
Calculate the first instruction current i'
ref, i
reffor instruction current, k is ratio orificing factor.
6. the guard method of Active Power Filter-APF as claimed in claim 1; it is characterized in that; described guard method also comprises the DC voltage of real-time detection Active Power Filter-APF, according to DC voltage, Active Power Filter-APF is carried out to hardware lockout current limliting, and detailed process is as follows:
(S1) detect in real time the DC voltage of Active Power Filter-APF;
(S2) DC voltage detecting is nursed one's health in the voltage range of setting and obtained corresponding Equivalent DC side voltage;
(S3) Equivalent DC side voltage conditioning being obtained and the 3rd threshold value compare, and proceed as follows according to comparative result:
If be more than or equal to the 3rd threshold value, block the driving pulse of current transformer in Active Power Filter-APF, until lift a blockade during Equivalent DC side voltage drop to the four threshold value, make current transformer export corresponding offset current;
Otherwise, inoperation.
7. the guard method of Active Power Filter-APF as claimed in claim 6, is characterized in that, the 3rd described threshold value V
1according to formula:
V
1＝K
T*(V
dcp+ΔV
h)
Calculate V
dcprepresent DC voltage rated value, Δ V
hthe overvoltage allowance that represents DC side overvoltage protection, K
trepresent equivalence conditioning no-load voltage ratio.
8. the guard method of Active Power Filter-APF as claimed in claim 7, is characterized in that, the 4th described threshold value V
2according to formula:
V
2＝K
T*(V
dcp-ΔV
l)
Calculate V
dcprepresent DC voltage rated value, Δ V
lrepresent the under-voltage allowance that DC side overvoltage protection is removed, K
trepresent equivalence conditioning no-load voltage ratio.
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| CN104749435A (en) * | 2015-04-01 | 2015-07-01 | 四川厚天科技股份有限公司 | DFT harmonic detection method without accumulated error sliding window |
| CN105048466A (en) * | 2015-09-10 | 2015-11-11 | 苏州市欧米伽智能控制技术有限公司 | Compound control method for parallel hybrid active power filters |
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| CN106684874A (en) * | 2017-03-15 | 2017-05-17 | 河南理工大学 | Active power filter specific harmonic optimizing and compensating method |
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