CN113572169A - Optimization design of harmonic-free detection active power filter of power supply circuit for radar - Google Patents
Optimization design of harmonic-free detection active power filter of power supply circuit for radar Download PDFInfo
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Abstract
The invention provides an optimized design of a power supply circuit harmonic-free detection active power filter for a radar, which mainly adopts the following steps: according to the power of the direct current side and the alternating current side of the system, comparing the fluctuation power of the main ripple waves with the instantaneous power of the direct current side, and designing a direct current side split capacitor decoupling circuit; introducing closed-loop control, reducing the 6-frequency multiplication fluctuation amount to 3-frequency multiplication through 3-frequency multiplication orthogonal transformation by using the voltage fluctuation amount at the direct current side, and selecting frequency by using a PR (pulse resonance) controller to extract 3-frequency multiplication components as an inductive current instruction value; filtering the command signal through a sliding window average filter, filtering out residual harmonic waves, and simultaneously keeping a direct current component; and a phase lead link is connected in series behind the sliding window average filter for phase compensation, so that an ideal power grid current waveform is obtained. According to the invention, the split capacitor decoupling circuit is introduced at the direct current side, so that the direct current side capacitor and the main voltage ripple are reduced. In addition, residual harmonic waves are eliminated through sliding window average filtering with a phase lead compensation link, compensation precision is further improved, and power grid output waveforms are improved.
Description
Technical Field
The invention relates to the field of power grid harmonic analysis, in particular to an optimized design of a power supply circuit harmonic-free detection active power filter for a radar.
Background
With the development of modern power electronic technology, a large number of nonlinear loads such as power electronic devices are put into industrial production and daily life of people, and the quality of electric energy of a power grid is increasingly serious while the living standard and the living quality of people are improved. An Active Power Filter (APF) is a power electronic device for dynamically inhibiting harmonic waves and compensating reactive power, is flexible in harmonic wave compensation and high in response speed, is an important means for effectively controlling harmonic waves, and is widely concerned in the field of harmonic wave control.
At present, the control mode of the traditional active power filter can be equivalent to composite control consisting of current feedforward and no harmonic detection. Compared with the traditional active power filter, the harmonic-free detection active power filter has the advantages that the detection links of load current and compensation current are omitted, detection and calculation of the harmonic and reactive current of the load are not needed, errors and delay caused by the harmonic detection link are avoided, system control is simplified, and system cost is saved. The grid current reference is given entirely by the voltage controller output, and its dynamic performance and compensation accuracy depend on the performance of the voltage controller.
However, in the power supply circuit system for the radar, the load types are multiple, the nonlinearity is serious, the working modes are multiple, and larger harmonic current is generated, so that the voltage waveform of the power grid is seriously deformed, and the normal operation of other equipment in the power grid system is influenced. By adopting the harmonic-free detection APF, although the current and the voltage waveform on the power grid side are corrected to a certain degree, the following defects still exist:
1. the direct current side voltage fluctuation is large during low capacitance, the voltage of a power supply circuit is distorted, the normal operation of electrical equipment is influenced, extra power transmission loss is generated, the operation efficiency of the system is reduced, and the working cost of the system is increased.
2. The residual harmonics of the dc side voltage cause electromagnetic interference to communication equipment in the vicinity of the device.
Disclosure of Invention
The purpose of the invention is as follows: in order to overcome the technical defects, the invention provides an optimized design of a harmonic-free detection active power filter of a power supply circuit for a radar.
The technical scheme is as follows: in order to achieve the technical effects, the technical scheme provided by the invention is as follows: the optimization design of the harmonic-free detection active power filter of the power supply circuit for the radar is characterized by comprising the following steps of:
step 1: according to the power of the direct current side and the alternating current side of the system, comparing the main ripple wave power with the instantaneous power of the direct current side, and designing a split capacitor decoupling circuit of the direct current side;
step 2: introducing closed-loop control, converting the 6 frequency multiplication fluctuation quantity in the voltage into 3 frequency multiplication through 3 frequency multiplication orthogonal alternating conversion by the voltage fluctuation quantity on the direct current side, and extracting the 3 frequency multiplication component in the error signal as an instruction value i of the inductive current through frequency selection of a PR controllerf *；
And step 3: filtering the command signal through a sliding window average filter, filtering residual harmonic components in the direct current side voltage, and simultaneously keeping direct current components in the direct current side voltage;
and 4, step 4: and a phase lead link is connected in series behind the sliding window average filter for phase compensation, so that an ideal power grid current waveform is obtained.
Furthermore, the direct current side split capacitor decoupling circuit filters high-frequency components by adopting a power decoupling circuit, and increases V compared with the conventional active power filter APF7、V8One half bridge arm, with two identical film capacitors C on the DC side1、C2The series connection replaces the original electrolytic capacitor, and the midpoint of the capacitor and the midpoint of the half-bridge pass through a filter inductor LfAre connected. Control switch tube V7、V8Make the capacitor C1、C2The voltage is superposed with 3 times frequency voltage components on the basis of half of the voltage of the direct current side capacitor, and the 3 times frequency voltage components on the two capacitors have equal amplitude and opposite phases. If split capacitance C1And C2The capacitance values are equal, the voltage of the split capacitor can be controlled, the fluctuation of the frequency doubling power at the DC side 6 tracks the fluctuation component of the frequency doubling power at the AC side 6, and C1And C2Voltage fluctuation onEqual amplitude and opposite phase of the components, C1And C2The voltage fluctuation of the direct current side is mutually offset, and the six-time frequency power fluctuation suppression of the direct current side can be realized.
Furthermore, the closed-loop control is introduced, the power decoupling circuit of the digital controller is adopted for control, the fluctuation quantity of the direct-current side voltage is obtained by the actually measured voltage value and the instruction value of the direct-current side, the 6-frequency multiplication fluctuation quantity in the voltage is subjected to frequency reduction to 3-frequency multiplication through 3-frequency multiplication orthogonal alternating conversion, the 3-frequency multiplication component in the error signal is extracted through frequency selection of the PR controller and serves as the instruction value i of the inductive currentf *The inductance current adopts a proportional controller kpfi。
The DC voltage fluctuation amount not only contains 6 frequency multiplication fluctuation, but also contains 6n frequency multiplication components such as 12 and 18, and is converted into 9 frequency multiplication and 15 frequency multiplication components through 3 frequency multiplication orthogonal transformation. The PR controller extracts these components as a command value i of the inductor currentf *. At the moment, the inductive current contains 9 frequency multiplication components and 15 frequency multiplication components, and the frequency multiplication capacitor voltage vc1、vc2The action will generate power fluctuation with 6, 12 and 18 times frequency, and the power is transmitted through the current controller kpfiThe current components of 9 frequency doubling and 15 frequency doubling can be tracked to offset the 12 and 18 frequency doubling power fluctuation on the alternating current side, so that the effect of power decoupling is achieved.
Further, the frequency response function expression of the sliding window average filter in the s domain and the z domain by introducing the sliding window average filter (MAF) in an APF voltage control loop is as follows
Wherein T isωWindow size of MAF, N ═ Tω/TsIs the number of samples within a window time.
If the window size T of MAF is setωSet as fundamental period T of the gridThen MAF theoretically can filter out all harmonic components in the signal and leave the dc component in the signal intact, thereby further improving the compensation accuracy.
Furthermore, a phase advance link is connected in series behind the sliding window average filter, the MAF is approximated by adopting a second-order Pade to obtain a MAF transfer function, a system phase advance link is designed, parameters of the controller are designed by using undetermined coefficients, and finally, different parameter design criteria of the corresponding control system are given.
Has the advantages that: compared with the prior art, the invention has the following advantages:
1. the invention aims at a power supply circuit non-harmonic detection active power filter for radar, and introduces a split capacitor decoupling circuit at the APF direct current side. The main voltage ripples of 6, 12 and 18 times of voltage fluctuation of the direct current side are eliminated through power decoupling control, and the direct current side capacitance and the direct current side voltage fluctuation are reduced.
2. The direct-current voltage outer ring of the system is controlled by adopting a PI controller, residual harmonic components are eliminated by adding MAF with a phase lead compensation link, the compensation precision is further improved, the output waveform of a power grid is improved, and the optimal design of the power supply circuit harmonic-free detection active power filter for the radar is realized.
Drawings
FIG. 1 is a flow chart of an optimized design of a harmonic-free detection active power filter of a power supply circuit for radar of the present invention;
FIG. 2 is a schematic diagram of a three-phase active power filter of the present invention;
FIG. 3 is a schematic diagram of an active power filter based on DC split capacitor power decoupling according to the present invention;
FIG. 4 is a control block diagram of a power decoupling circuit based on a split capacitor according to the present invention;
FIG. 5 is a block diagram of the DC voltage control of the present invention with MAF added;
FIG. 6 is a block diagram of the DC side voltage control with the MAF and phase advance elements added according to the present invention;
FIG. 7 shows the DC side current when the DC split capacitor decoupling circuit and the multi-PR controller are addedVoltage and its FFT analysis (a) direct current side voltage Vdc(b) Before power decoupling, voltage FFT (c) at the direct current side after power decoupling;
fig. 8 shows the grid current and its FFT analysis when a dc split capacitor decoupling circuit and a 3-frequency multiplication PR controller are added to the present invention (a) the grid current (b) the grid current before power decoupling (thd) (c) the grid current FFT after power decoupling;
FIG. 9 shows the grid current command value amplitude i under different filtering conditions according to the present inventions *Is *And | FFT analysis.
Detailed Description
The invention will be further described with reference to the accompanying drawings and specific embodiments. It is to be understood that the present invention may be embodied in various forms, and that there is no intention to limit the invention to the specific embodiments illustrated, but on the contrary, the intention is to cover some exemplary and non-limiting embodiments shown in the attached drawings and described below.
It is to be understood that the features listed above for the different embodiments may be combined with each other to form further embodiments within the scope of the invention, where technically feasible. Furthermore, the particular examples and embodiments of the invention described are non-limiting, and various modifications may be made in the structure, steps, and sequence set forth above without departing from the scope of the invention.
As shown in fig. 1, the optimal design flow chart of the harmonic-free detection active power filter of the power supply circuit for radar of the present invention includes the following steps:
step 1: according to the power of the direct current side and the alternating current side of the system, comparing the main ripple wave power with the instantaneous power of the direct current side, and designing a split capacitor decoupling circuit of the direct current side;
step 2: introducing closed-loop control, converting the 6 frequency multiplication fluctuation quantity in the voltage into 3 frequency multiplication through 3 frequency multiplication orthogonal alternating conversion by the voltage fluctuation quantity on the direct current side, and extracting the 3 frequency multiplication component in the error signal as an instruction value i of the inductive current through frequency selection of a PR controllerf *；
And step 3: filtering the command signal through a sliding window average filter, filtering residual harmonic components in the direct current side voltage, and simultaneously keeping direct current components in the direct current side voltage;
and 4, step 4: and a phase lead link is connected in series behind the sliding window average filter for phase compensation, so that an ideal power grid current waveform is obtained.
Example (b):
fig. 2 shows a three-phase active power filter system of a power supply circuit for radar according to the present embodiment, including: a direct current power supply, a three-phase inverter circuit, an APF circuit, a load and the like. If the network voltage is not distorted, the network voltage ua、ub、ucAPF compensating current ica、icb、iccCan be expressed as
Where k represents the harmonic order, ω represents the fundamental angular velocity, and θ represents the initial phase angle of the current.
The instantaneous power p at the AC side can be obtained according to the voltage and the current of the active power filtercAs follows, the instantaneous power component of the filter inductance can be neglected, since the filter inductance is generally small.
From the above equation, it can be seen that the system has 6n times frequency power fluctuation, and the power fluctuation quantity is proportional to the sum of the harmonic current amplitudes of 6n-1 and 6n + 1. Neglecting the switching tube loss, the ac side power fluctuation is directly transferred to the dc side and causes the fluctuation of the dc side capacitor voltage. Following a specific expression for deriving the DC-side voltage ripple, the instantaneous DC-side capacitor power can be expressed as
Decomposition of the DC-side voltage into a DC component VdcAnd ripple component Δ vdcCan be brought into the above formula
Due to ripple component Δ vdcMuch smaller than the direct current component vdcFurther obtain
From the above formula, it can be known that the dc-side capacitor voltage has a ripple with a frequency of 6n times, and the ripple amplitude is related to the dc-side capacitor capacitance value and the capacitor voltage. From the equation, it can be seen that the voltage fluctuation amplitude decreases with the increase of the harmonic frequency when the load harmonic amplitude is constant, and thus the dc-side capacitor voltage mainly has six-fold frequency fluctuation of the fundamental wave.
In order to reduce the influence of voltage fluctuation on the direct current side of the system, the direct current side split capacitor decoupling circuit is adopted for suppressing the voltage fluctuation, the direct current side split capacitor decoupling circuit is simple to control, and the capacitance value of the direct current side capacitor can be obviously reduced. A schematic diagram of an active power filter using a dc split capacitive power decoupling circuit is shown in fig. 3. Increase in V compared to the APF before7、V8One half bridge arm, with two identical film capacitors C on the DC side1、C2The series connection replaces the original electrolytic capacitor, and the midpoint of the capacitor and the midpoint of the half-bridge pass through a filter inductor LfAre connected.
From the foregoing analysis, it is known that the dc-side voltage ripple is mainly 6 frequency-doubled ripple, and the ripple power thereof is:
DC side split capacitor C1、C2The active power filter mainly plays a role in supporting the operating voltage of the active power filter and inhibiting voltage fluctuation on the direct current side. Thus the switching tube V can be controlled7、V8Make the capacitor C1、C2The voltage is half V of the voltage of the capacitor on the direct current sidedcAnd 3 frequency voltage components are superposed on the basis of/2, and the 3 frequency multiplication voltage components on the two capacitors have equal amplitudes and opposite phases. The voltage v on the split capacitor at this timec1、vc2Can be expressed as:
in the formula Vc3Amplitude of voltage fluctuation multiplied by 3, thetac3Is the initial phase angle of the alternating voltage component.
At this time, the capacitor C1And C2Current of
Filter inductance i known from KCLfThe inductor current above is:
if(t)＝ic2(t)-ic1(t)
＝-3ωVc3(C1+C2)sin(3ωt+θc3)
the instantaneous power p on the dc sidefIs composed of
If split capacitance C1And C2Capacity equal C1＝C2＝CfThe instantaneous value of the DC side power can be rewritten as
The power of the DC side is equal to that of the AC side, and ripple wave power p corresponding to 6 frequency multiplication wave is comparedcmainAnd instantaneous power p on the DC sidefThe amplitude and phase of the resulting split capacitor are
The voltage of the split capacitor can be controlled to make the frequency doubling power fluctuation of the DC side 6 track the frequency doubling power fluctuation component of the AC side 6, and C1And C2The voltage fluctuation components on are equal in amplitude and opposite in phase, C1And C2The voltage fluctuation of the direct current side is mutually offset, and the six-time frequency power fluctuation suppression of the direct current side can be realized.
Neglecting the filter inductance LfPower, simplified form of the above
In the formula PcmainTo cause 6 times frequency power fluctuation component of the DC voltage ripple.
Then there is
Due to split capacitanceAmplitude of pressure fluctuation VcCan not be greater than VdcA/2, then
When the direct current side voltage is 800V and the APF capacity is 15kVA, CfAbout 1000 muF.
For the conventional APF, if the DC side allows the voltage fluctuation quantity DeltaVdcWhen 2%, the DC electrolytic capacitor C has
The decoupling of the split capacitors on the DC side can greatly reduce the capacitance value of the capacitors on the DC side, and the two split capacitors are connected in series, the equivalent capacitance value is C of each capacitor f1/2, the dynamic response speed of the system can be improved.
Because the split capacitor method power decoupling can be realized by directly controlling the voltage value of the direct current split capacitor, the reference value is obtained by calculation, the control belongs to open loop control, and the accuracy of the control is influenced by the accuracy of system parameters. The invention improves the decoupling precision of the system by introducing closed-loop control, and FIG. 4 is a control block diagram of a power decoupling circuit based on a split capacitor, wherein G isfi(s) and Gfv(s) is the transfer function of the filter inductance and the split capacitance. The fluctuation quantity of the DC side voltage is obtained from the actual measurement voltage value and the instruction value of the DC side, 6 frequency multiplication fluctuation quantity in the voltage is subjected to frequency reduction to 3 frequency multiplication through 3 frequency multiplication orthogonal alternating conversion, and the frequency multiplication is subjected to PR controller GcfvSelecting frequency to extract 3 frequency multiplication components in the error signal as the instruction value i of the inductive currentf *The inductance current adopts a proportional controller kpfi。
The DC voltage fluctuation amount not only contains 6 frequency multiplication fluctuation, but also contains 6n frequency multiplication components such as 12 and 18, and is converted into 9 frequency multiplication and 15 frequency multiplication components through 3 frequency multiplication orthogonal transformation. Can be in the controller GcfvThe middle-added 9-frequency multiplication PR controller and the 15-frequency multiplication PR controller extract the components as a command value i of the inductive currentf *. At the moment, the inductive current contains 9 frequency multiplication components and 15 frequency multiplication components, and the frequency multiplication capacitor voltage vc1、vc2The action will generate power fluctuation with 6, 12 and 18 times frequency, and the power is transmitted through the current controller kpfiThe current components of 9 frequency doubling and 15 frequency doubling can be tracked to offset the 12 and 18 frequency doubling power fluctuation on the alternating current side, so that the effect of power decoupling is achieved.
Considering that the direct current side 6, 12, 18 double frequency fluctuation can be suppressed by the split capacitance decoupling circuit, it is difficult to suppress higher order frequency harmonics by decoupling. The invention further improves the compensation precision by introducing a sliding window average filter into the APF voltage control loop to filter the instruction signal.
The sliding window average filter is an infinite impulse response filter, and has a transfer function in the s-domain and a transfer function in the z-domain as follows
Further get the frequency response function of MAF in s and z domains:
from the above formula, it can be seen that MAF can completely retain the DC component in the signal, and the filtering angular frequency is n/TωThe harmonic component of (a). If the window size T of MAF is setωSet to the fundamental period T of the grid, MAF can theoretically filter out all harmonic components in the signal, so the dc side voltage residual ripple can be filtered out by adding MAF in the dc voltage control loop. Control block diagram after MAF addition as shown in FIG. 5Wherein G isPI(s) is a transfer function of the direct current side voltage controller; gc(s) is a current inner loop transfer function; gpAnd(s) is a transfer function of the controlled object of the voltage loop. Adding sliding window size T in DC voltage control loopωThe MAF (time-varying direct current) with the value T can filter out residual harmonic components in the voltage of the direct current side, and simultaneously keep the direct current components in the voltage, so that the accuracy of a grid current reference value is ensured.
In addition, because the MAF has inherent time delay, a phase lead link is connected behind the MAF in series for phase compensation, and the dynamic response speed of the system is ensured. A dc side voltage control block diagram with MAF and phase advance elements added is shown in fig. 6. To facilitate the design of the voltage controller parameters, the MAF is approximated using a second order Pade, and the MAF transfer function is approximated as follows.
The phase advance link of the system is designed, and the phase advance link can be defined as follows
The above formula can be divided into three parts, the first part (1+ tau)1s+τ2s2) With MAFpadeImplementing zero-pole cancellation, τ1And τ2Is a primary term and a secondary term coefficient; the second part k is a gain coefficient; the rest is that a second-order low-pass filter is added to facilitate the implementation of the lead link. Let the coefficients of the first and second terms in the lead link be tau1And τ2Are each tau1＝T ω2 and τ2＝Tω 29 and MAFpade(s) zero-pole cancellation is realized, so that the design of the controller is simplified, and the open-loop transfer function of the control system can be obtained as
Closed loop transfer function of
The closed-loop transfer function is a typical third-order system, and the undetermined coefficient can be used for designing the parameters of the controller, and as shown in the following, a term s + omega is provided in a denominatorpConvenient reduction of rank is
The correspondence between the coefficients is thus obtained:
get omegap＝10ωnThe pole ωpCan be ignored, thereby
Where ξ is the damping coefficient of the system, ωnIs the natural oscillation frequency. Ensuring better dynamic process, and taking xi to be 1/V2 when the system overshoot is smaller when the voltage changes, wherein the control bandwidth omega isbAnd natural angular frequency omeganHas a relationship of ωn≈1.554ωb. By the design criteria of the control system, the outer loop control bandwidth of the control system is generally less than 1/10 of the inner loop control bandwidth, the inner loop control bandwidth of the active power filter is generally 2000Hz, and therefore the voltage outer loop control bandwidth is less than 200 Hz. Taking the bandwidth omega of the voltage control loop to ensure the response speed of the systembAt 400 pi, the controller parameters are designed as follows.
τ1＝Tω/2＝0.01
τ2＝Tω 2/9＝1.76×10-4
ωf＝7.12ωb
ξf＝1.309
k＝10/(21Kdc)
By combining the theoretical analysis, the main ripple components of 6, 12 and 18 times of direct current side voltage fluctuation can be eliminated through the control of the split capacitor decoupling circuit, residual harmonic components are eliminated by adding MAF with a phase lead compensation link, the direct current side capacitor voltage fluctuation is suppressed while the direct current side capacitor is reduced, and the optimization design of the power supply circuit for the radar for harmonic-free detection active power filter is further realized.
The specific parameters are substituted into the following steps, and the technical effect of the invention is further verified through simulation analysis.
A power supply circuit harmonic-free detection APF circuit model for radar based on direct current side split capacitance power decoupling and with MAF + PI direct current side voltage control is built in an MTLAB/Simulink environment. The current control adopts a multi-PR controller, and the nonlinear load is a three-phase rectifying load. The main parameters are as follows: the voltage E of the power grid line is 380V, the voltage frequency f is 50Hz, the direct current side capacitor C is 4900uF, and the direct current side split capacitor C1＝1000uF,C21000Uf, APF output inductor L4 mH, filter inductor L on the dc sidef1.5mH, sampling frequency fs＝20kHz。
In order to verify the effectiveness of the direct-current side split capacitor decoupling circuit, the direct-current side split capacitor decoupling circuit adopts a multi-PR controller to control an inductive current iLThe time-direct-current side voltage and the FFT analysis thereof are shown in fig. 7, and the direct-current side split capacitance decoupling control is applied when t is 0.1 s. From the spectrum analysis of the DC side voltage, the DC side voltage VdcThe 6 and 12 frequency multiplication fluctuation is greatly inhibited, and the 18 frequency multiplication fluctuation is also inhibited to a certain extent. Grid current i at this timesThe waveform and its FFT analysis are shown in fig. 8, where the grid-side current distortion is low, and the harmonics in the grid are suppressed to a large extent.
In addition, in order to verify the effectiveness of the MAF filtering method provided by the invention, the amplitude | i of the grid current instruction value is outputs *I, and the power grid current instruction value amplitude I added with the sliding window average filter and the sliding window average filter with the phase correction links *The comparison curve for | is shown in fig. 9. It can be seen from the figure that the amplitude harmonic of the grid current command value subjected to MAF filtering is completely filtered, but has a certain phase delay with the grid current command value. The MAF phase delay after phase correction is reduced.
Therefore, the optimal design of the harmonic-free detection active power filter of the power supply circuit for the radar can effectively reduce the voltage fluctuation of the direct current side in low capacitance, further improve the compensation precision of the active power filter and further improve the output characteristic of the system.
Claims (5)
1. An optimized design of a harmonic-free detection active power filter of a power supply circuit for a radar is characterized by comprising the following steps:
step 1: according to the power of the direct current side and the alternating current side of the system, comparing the main ripple wave power with the instantaneous power of the direct current side, and designing a split capacitor decoupling circuit of the direct current side;
step 2: introducing closed-loop control, converting the 6 frequency multiplication fluctuation quantity in the voltage into 3 frequency multiplication through 3 frequency multiplication orthogonal alternating conversion by the voltage fluctuation quantity on the direct current side, and extracting the 3 frequency multiplication component in the error signal as an instruction value i of the inductive current through frequency selection of a PR controllerf *；
And step 3: filtering the command signal through a sliding window average filter, filtering residual harmonic components in the direct current side voltage, and simultaneously keeping direct current components in the direct current side voltage;
and 4, step 4: and a phase lead link is connected in series behind the sliding window average filter for phase compensation, so that an ideal power grid current waveform is obtained.
2. The design of the direct current side split capacitive decoupling circuit of claim 1, wherein the power decoupling circuit is adopted to filter high frequency components, and V is increased compared with the APF of the traditional active power filter7、V8One half bridge arm, DC sideUsing two identical thin-film capacitors C1、C2The series connection replaces the original electrolytic capacitor, and the midpoint of the capacitor and the midpoint of the half-bridge pass through a filter inductor LfAre connected. Control switch tube V7、V8Make the capacitor C1、C2The voltage is superposed with 3 times frequency voltage components on the basis of half of the voltage of the direct current side capacitor, and the 3 times frequency voltage components on the two capacitors have equal amplitude and opposite phases. If split capacitance C1And C2The capacitance values are equal, the voltage of the split capacitor can be controlled, the fluctuation of the frequency doubling power at the DC side 6 tracks the fluctuation component of the frequency doubling power at the AC side 6, and C1And C2The voltage fluctuation components on are equal in amplitude and opposite in phase, C1And C2The voltage fluctuation of the direct current side is mutually offset, and the six-time frequency power fluctuation suppression of the direct current side can be realized.
3. The lead-in closed-loop control according to claim 1, wherein a power decoupling circuit of a digital controller is adopted for control, the fluctuation amount of the voltage on the direct current side is obtained by actually measuring the voltage value and the instruction value on the direct current side, 6 frequency multiplication fluctuation amount in the voltage is subjected to frequency reduction to 3 frequency multiplication through 3 frequency multiplication orthogonal alternating conversion, 3 frequency multiplication component in the error signal is extracted through frequency selection of a PR controller and is used as the instruction value i of the inductive currentf *The inductance current adopts a proportional controller kpfi。
The DC voltage fluctuation amount not only contains 6 frequency multiplication fluctuation, but also contains 6n frequency multiplication components such as 12 and 18, and is converted into 9 frequency multiplication and 15 frequency multiplication components through 3 frequency multiplication orthogonal transformation. The PR controller extracts these components as a command value i of the inductor currentf *. At the moment, the inductive current contains 9 frequency multiplication components and 15 frequency multiplication components, and the frequency multiplication capacitor voltage vc1、vc2The effect of the current controller k can generate power fluctuation of 6, 12 and 18 frequency multiplicationpfiThe current components of 9 frequency doubling and 15 frequency doubling can be tracked to offset the 12 and 18 frequency doubling power fluctuation on the alternating current side, so that the effect of power decoupling is achieved.
4. The sliding window averaging filter of claim 1, wherein the frequency response function in the s-domain and z-domain is expressed as follows by introducing a sliding window averaging filter (MAF) in the APF voltage control loop
Wherein T isωWindow size of MAF, N ═ Tω/TsIs the number of samples within a window time.
If the window size T of MAF is setωAnd setting the fundamental wave period T of the power grid, the MAF can theoretically filter all harmonic components in the signal and completely reserve direct-current components in the signal, so that the compensation precision is further improved.
5. The method as claimed in claim 1, wherein a second order Pade is used to approximate the MAF to obtain the MAF transfer function, the phase advance element of the system is designed, the undetermined coefficient is used to design the controller parameters, and finally, different parameter design criteria of the corresponding control system are given.
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| CN106374491A (en) * | 2016-09-22 | 2017-02-01 | 北京机械设备研究所 | Direct current capacitive voltage control method for active power filter |
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