CN105591400B - A kind of fast robust single electric current feedback of LCL type gird-connected inverter - Google Patents
A kind of fast robust single electric current feedback of LCL type gird-connected inverter Download PDFInfo
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- H02J3/383—
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/002—Flicker reduction, e.g. compensation of flicker introduced by non-linear load
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- H—ELECTRICITY
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Abstract
The invention discloses a kind of fast robust single electric current feedback of LCL type gird-connected inverter, by introducing single electric current feedback control, with reference to the fast robust PWM method of proposition, realizes grid-connected inverters control.The invention only needs to sample grid-connected current, without extra sensor, reduces hardware cost, improves system reliability.The fast robust PWM control methods of the present invention, in the case where not introducing duty-cycle limit, completely eliminate grid-connected current outer shroud and active damping inner ring one claps the computation delay of hysteresis, the positive and negative boundary frequency for realizing equivalent damping resistance is higher than the essential requirement of LCL resonant frequency scopes of design, and the sampling of this method 0.5 times of switch periods of permission and duty cycle calculate the time, improve the overall robustness and dynamic property of gird-connected inverter.
Description
Technical Field
The invention relates to the field of PWM (pulse-width modulation) inversion control and new energy thereof, in particular to a fast robust single current feedback control method of an LCL (lower control limit) type grid-connected inverter.
Background
The grid-connected inverter is used as a core device for connecting distributed energy sources and a public power grid, and plays a vital role in a distributed power generation system. The output filter adopts an LCL type filter, can effectively inhibit high-frequency harmonic waves output by the inverter, reduces the volume and the quality of the filter, and has important application value in engineering. However, the LCL filter is a low-damping third-order system, which has a resonance problem, and is easy to cause instability of the grid-connected inverter, and there are a lot of literature to discuss and solve the resonance problem of the LCL type grid-connected inverter, and the method mainly includes a passive damping method of a capacitor branch series resistor, and based on an active damping method such as capacitor current feedback, capacitor voltage feedback, multi-state variable combination feedback or grid-connected current feedback, the methods can suppress the LCL resonance spike, but compared with the passive damping method, the active damping method has flexible and variable implementation modes, does not need additional power consumption, and has advantages in engineering application. The grid-connected current feedback active damping method only needs a grid-connected current sensor, so that the hardware cost is reduced, and the reliability of the system is improved. The GFCAD control method based on the high-pass filter is widely researched and applied due to the fact that the GFCAD control method is simple to implement and does not introduce noise interference, but the influence of delay of a control system on the strategy is not researched and analyzed.
The grid-connected inverter has inherent control delay under digital control, has large influence on the active damping effect, and can change the size and the positive and negative directions of the equivalent virtual damping resistance. The characteristic of the virtual resistor at the resonant frequency of the LCL is crucial and directly relates to the working performance of the inverter. The fundamental reason of the robustness problem caused by the impedance of the power grid is that the equivalent damping resistance of the active damping method is equal to 0 in the design range of the LCL resonant frequency, and the characteristic is generated by the control delay of the system. Wherein: 1) The neural network estimator, the fuzzy controller, the adaptive error correction controller and other methods adopted by the prediction current control technology are relatively complex, and the implementation on grid-connected power generation engineering is difficult. 2) The method of instant sampling, multiple sampling and the like adopted by the sampling mode is modified, and the time interval between the sampling moment and the duty ratio updating moment is shortened, so that the calculation delay is reduced. But the full range change of the duty ratio from 0 to 1 cannot be realized due to the limitation of sampling delay; meanwhile, the normal work of the control system is influenced by easily introducing switching ripples and high-frequency switching noises by modifying a sampling mode. 3) The real-time operation method of the bipolar mode and the double sampling mode adopted by the modified pulse width modulation mode can not only completely eliminate the control delay of one-beat lag, but also is not limited by the duty ratio, but also requires the sampling delay and the time of the duty ratio calculation to be not higher than 0.25 time of the switching period, thereby increasing the application difficulty in engineering.
Disclosure of Invention
The invention aims to solve the technical problems that aiming at the defects of the prior art, the stability influence of control delay on a grid-connected inverter system is analyzed, a rapid robust single current feedback control method of an LCL type grid-connected inverter is provided, the problems that the grid-connected inverter can have inherent control delay under digital control and can change the size and the positive and negative directions of equivalent virtual damping resistance are solved, the calculation delay of one-beat lag of a grid-connected current outer ring and an active damping inner ring is completely eliminated, the sampling and duty ratio calculation time of 0.5 time of a switching period is allowed, and the problem that an additional sensor is needed or a single current feedback parameter is not easy to select in the conventional LCL type grid-connected inverter is solved.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a fast robust single current feedback control method of an LCL type grid-connected inverter comprises the following steps:
1) At the initial point of each sampling period, the A/D sampling circuit of the LCL type grid-connected inverter samples the grid voltage u g Grid-connected current i g Voltage u of filter capacitor c And inverter circuit direct-current side capacitor voltage U of LCL type grid-connected inverter dc Respectively sampling, and sending the sampling data to a control module of the LCL type grid-connected inverter for processing;
2) Grid-connected current i g Control signal u is obtained through grid-connected current feedback active damping module based on high-pass filter 1 (ii) a Grid-connected current feedback active damping module G based on high-pass filter v (s) watchThe expression is as follows:wherein, ω is d 、K d Cut-off angular frequency and gain of the high-pass filter, respectively, s = j ω, j is the imaginary unit symbol;
3) Grid-connected current i g With given grid-connected current command signal i ref Differencing to obtain a signal e i ；
4) Signal e i Obtaining a control signal u through a grid-connected current quasi-resonant controller 2 (ii) a The expression of the grid-connected current quasi-resonant controller G(s) is as follows:
wherein, K p And K r Proportionality factor and resonance gain, omega, respectively, of a quasi-resonant PR controller r Is the cut-off frequency; omega 0 Is the fundamental angular frequency;
5) Control signal u 1 And a control signal u 2 Obtaining LCL type grid-connected inverter control signal u by difference d ；
6) LCL type grid-connected inverter control signal u d And carrier u tri Obtaining the duty ratio d of the LCL type grid-connected inverter by a fast robust PWM modulation method; the duty ratio d controls the on and off of a switching tube of an inverter circuit through a drive protection circuit of the LCL type grid-connected inverter; the fast robust PWM modulation method is realized by two stages: 1) In the initial stage of start-up operation, i.e. from 0 to kT s At the moment, PWM modulation is adopted, and a modulation signal d (i-1) of a previous switching period is loaded at the wave trough of a carrier; 2) Second phase of operation of the LCL grid-connected inverter, i.e. kT s And loading the duty ratio signals twice, wherein the loading positions are respectively positioned at the wave trough and the wave crest of the carrier, and the duty ratio D is loaded at the wave trough of the carrier 1 (k + i) loading the duty ratio D (k + i) at the peak of the carrier wave, and satisfying D 1 (k + i) = D (k + i-1), and performs AD sampling and PWM modulation signal calculation preferentially at 0.5T s Front-end duty cycle meterC, T s Is a switching cycle.
In the step 6), for the k + i switching period (i =2,3,4 \8230;), the duty ratios D are loaded at the respective carrier wave troughs 1 (k + i), the duty cycle D (k + i) is loaded at the carrier peak, and satisfies:
D 1 (k+i)＝D(k+i-1)；
D(k+i)＝2[d(k+i)-0.5D 1 (k+i)]；
in the above formula, D 1 (k + i) is the duty ratio loaded at the wave trough of the carrier in the k + i switching period, wherein i is more than or equal to 2, D (k + i-1) is the duty ratio loaded at the wave crest of the carrier in the k + i switching period, D (k + i) is the duty ratio loaded at the wave crest of the carrier in the k + i switching period, D (k + i) is the duty ratio of the k + i switching period, and since D (k + i) is more than or equal to 0 and less than or equal to 1, the duty ratio D (k + i) of the k + i switching period should satisfy the following conditions:
0.5D(k+i-1)≤d(k+i)≤0.5+0.5D(k+i-1)
it can be seen that D (k + i) is limited to a certain extent by D (k + i-1) loaded at the peak of the previous switching period, and the duty ratio thereof cannot be changed from 0 to 1. In order to eliminate the limitation of D (k + i) on D (k + i) by D (k + i-1), D is reset at the valley of the carrier wave 1 (k + i) to decouple D (k + i-1) from D (k + i).
Duty cycle D with loading at the trough 1 (k + i) there are the following three cases:
wherein D (k + i-1) is the duty ratio loaded at the peak of the carrier wave in the k + i-1 th switching cycle, D 1 (k + i) is the duty ratio d (k + i-1) loaded at the wave trough of the carrier in the k + i th switching period, and delta d is the duty ratio of the k + i-1 th switching period opt Is the duty cycle offset.
The grid-connected inverter adopts a bipolar PWM mode, the modulation wave of the grid-connected inverter is a sine wave and has the same frequency and phase with the voltage of a power grid, when d =0.5, the actual modulation signal is equal to 0, when d >0.5, the modulation wave is in the positive half cycle, and when d <0.5, the modulation wave is in the negative half cycle.
When the modulation wave is in the positive half period, setting D 1 (k + i-1) =1, and the duty ratio range at this time is:
0.5≤d(k+i)≤1；
when the modulation wave is in the negative half cycle, set D 1 (k + i-1) =0, and the duty ratio ranges in this case:
0≤d(k+i)≤0.5；
because the modulated wave and the voltage waveform of the power grid are in the same frequency and phase, the grid-connected current waveform is suddenly changed at a certain time, and only the size, but not the direction, of the grid-connected current waveform is changed, so the value range of the duty ratio d (k + i) is as follows:
0≤d(k+i)≤1；
therefore, when the inverter operates dynamically, the limitation of duty ratio is not introduced, and the dynamic performance of the system is greatly improved.
Compared with the prior art, the invention has the following beneficial effects: aiming at the problems that the equivalent impedance of the active damping method is coupled with the impedance of a power grid due to the inherent control delay under digital control, the system cannot run stably due to wide-range change of the impedance of the power grid and the robustness of the grid-connected inverter to the impedance of the power grid is poor, the invention adopts a rapid robust single current feedback strategy, adopts a single current feedback control method and a rapid robust PWM control method, reduces the number of sensors and improves the stability of the system by introducing single current feedback control, completely eliminates the calculation delay of one-beat lag of a grid-connected current outer ring and an active damping inner ring by a PWM control method under the condition of not introducing duty ratio limitation, and meets the requirement that the positive and negative boundary frequency of the equivalent damping resistor is higher than the LCL resonant frequency design range, thereby greatly improving the robustness and dynamic performance of the grid-connected inverter. The fast robust single current feedback method increases system damping, inhibits resonance peak of the LCL filter, provides an optimized parameter selection method, reduces a single current feedback coefficient to a single variable, solves the problem that the traditional LCL type grid-connected inverter needs an additional sensor or introduces a single current feedback parameter which is not easy to select, completely eliminates calculation delay of one-beat delay of a grid-connected current outer ring and an active damping inner ring, allows sampling of 0.5 time of a switching period and duty ratio calculation time, and improves system reliability and dynamic property.
Drawings
Fig. 1 is a control structure diagram of an LCL grid-connected inverter according to an embodiment of the present invention;
fig. 2 is a block diagram of a fast robust single current feedback control of the LCL type grid-connected inverter according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a fast robust PWM control design scheme of an LCL-type grid-connected inverter according to an embodiment of the present invention;
FIG. 4 is a flow chart of a fast robust PWM control method according to an embodiment of the present invention;
FIG. 5 shows a grid voltage u according to an embodiment of the present invention s Measuring current i through network g Simulating a waveform;
FIG. 6 shows an embodiment R of the present invention g (ω) a frequency characteristic diagram;
FIG. 7 shows an embodiment ω of the present invention d And R g (ω) a plot of the relationship between the demarcation frequencies;
FIG. 8 is a schematic diagram of the stability margin of the method of the present invention.
Detailed Description
As shown in fig. 1, the single-phase photovoltaic LCL type grid-connected inverter includes a boost circuit, an inverter circuit, an LCL filter circuit, an a/D sampling circuit, a controller DSP2812, and a driving protection circuit, and the photovoltaic array, the boost chopper circuit, the inverter circuit, the LCL filter circuit, and the power grid are connected in sequence; the output voltage of the photovoltaic array is U pv The output current of the photovoltaic array is I pv (ii) a The input end of the A/D sampling circuit is connected with the LCL filter circuit; the voltage boosting circuit is composed of a capacitor C pv Inductor L 0 Diode VD 0 Insulated Gate Bipolar Transistor (IGBT) Q 0 Composition in which an inductance L flows 0 Has a current of I L0 (ii) a The inverter circuit is an inverter direct current side capacitor C dc And an Insulated Gate Bipolar Transistor (IGBT) S 1 、S 2 、S 3 And S 4 Forming; the controller DSP2812 is connected with the input end of the drive protection circuit and the output end of the A/D sampling circuit; the LCL filter circuit is composed of an inductor L 1 Inductor L 2 And a capacitor C, R 1 And R 2 Are respectively a filter inductance L 1 And L 2 The parasitic resistance of (1); the driving protection circuit drives the inverter circuit. The inverter circuit is connected with the LCL filter circuit, the DSP controller is respectively connected with the A/D sampling circuit and the drive protection circuit, and the drive protection circuit is connected with the switch tube of the rectification circuit. The output of the driving protection circuit controls the on-off of a switch tube in the inverter circuit. Inductor L 1 And an inductance L 2 And the capacitor C of the single-phase photovoltaic grid-connected inverter forms a filter circuit of the single-phase photovoltaic grid-connected inverter, is used for filtering higher harmonics of grid-connected current, and has a remarkable attenuation effect. i.e. i L For flowing through the inductance L 1 Current of (Z) g Is the impedance of the grid, U dc For the DC-side capacitor voltage, i, of the inverter circuit g For grid-connected current, u g Is the grid voltage.
The invention discloses a rapid robust single current feedback control method of an LCL type grid-connected inverter, which comprises the following steps:
1) At the initial point of each sampling period, the A/D sampling circuit of the LCL type grid-connected inverter samples the grid voltage u g Grid-connected current i g Voltage u of filter capacitor c And inverter circuit DC side capacitor voltage U dc Respectively sampling, and sending the sampling data to a control module for processing;
2) Grid-connected current i g The control signal u is obtained by Grid-Current-Feedback-Active Damping (GFCAD) module processing based on a high-pass filter 1 Grid-connected current command signal i ref And a grid-connected current i g Differencing to obtain a signal e i ，e i Obtaining a control signal u through a quadrature proportional-resonant (QPR) controller 2 Control signal u 1 And a control signal u 2 The difference value of (d) is obtained as an inverter control signal u d ；
Wherein G is v (s) is an expression of a Grid-Current-Feed-back-Active Damping (GFCAD) controller based on a high-pass filter:
in the formula, omega d 、K d The cut-off angular frequency and the gain of the high-pass filter, respectively.
G(s) is an expression of a grid-connected current quasi-resonant (QPR) controller:
in the formula, K p And K r Proportionality coefficient and resonance gain, omega, respectively, of a quasi-resonant PR controller r Is the cut-off frequency; omega 0 The frequency is the fundamental wave angular frequency, and the adaptability to slight fluctuation of the power grid frequency can be improved.
4) Inverter control signal u d Obtaining the equivalent duty ratio d of the inverter by a rapid robust PWM modulation method, wherein the rapid robust PWM control modulation method is realized in two stages, namely 1) in the initial stage (0 to kT) of starting operation s ) The traditional PWM modulation is adopted, and a modulation signal d (i-1) of one switching period is loaded at the wave trough of a carrier, wherein i is more than or equal to 2. 2) Inverter operating second phase (kT) s Later), loading duty ratio signals twice, wherein the loading positions are respectively positioned at the wave trough and the wave crest of the carrier, and loading duty ratios D at the wave trough of the carrier 1 (k + i) loading the duty ratio D (k + i) at the peak of the carrier wave, and satisfying D 1 (k + i) = D (k + i-1), and the AD sampling and PWM modulation signal calculation are preferentially performed in the program, at 0.5T s Complete duty cycle calculation before, T s Is a switching cycle;
5) And performing bipolar modulation on the SPWM modulated wave and the triangular carrier to obtain a duty ratio signal of the switching tube of the inverter circuit, and controlling the switching-on and switching-off of the switching tube of the inverter circuit through a drive protection circuit of the LCL type grid-connected inverter.
Fig. 2 is a block diagram of the fast robust single current feedback control of the LCL type grid-connected inverter of the invention.
The single current feedback is introduced, the parasitic resistance of the filter is ignored, and the inverter outputs the voltage u inv Current i to network side g The closed loop transfer function of (a) is:
in the formula, omega res For the resonance angular frequency of the LCL type filter:
grid-connected current i g Obtaining a control signal u through a Grid-current-Feedback-Active Damping (GFCAD) controller based on a high-pass filter 1 Of grid-connected current command signal i ref And a grid-connected current i g Difference e of i Obtaining a control signal u through a quadrature resonance controller (QPR) 2 Control signal u 1 And a control signal u 2 Differencing to obtain inverter control signal u d D, inverter control signal u d The equivalent duty ratio d of the inverter is obtained by a fast robust PWM modulation method, the fast robust PWM control only has 0.5 switching period delay, the problem that the traditional PWM control only has 1.5 switching period delay is solved, the dynamic speed of a grid-connected current tracking command signal is improved, and the resonance of a damping inner ring is favorably inhibited. And (3) performing fast robust PWM control, wherein the control delay of the inverter is reduced to:
equivalent to the inductance L 2 An impedance in series with the network impedance of：
Z g (w) may be expressed as a resistance R g And a reactance X g Are connected in series:
Z g (ω)＝R g (ω)+jX g (ω)
resistance R g And reactance X g The expressions are respectively:
wherein:
can be drawn according to the above formula g (ω) the frequency characteristic is shown in FIG. 6, it is clear that R g (omega) a demarcation frequency greater than 0.5f s Outside the designed interval of the resonant frequency; and no matter omega d How to vary, R g The frequency of the boundary of (omega) is not lower than 0.5f s As in fig. 7. Therefore, the possibility that the boundary frequency of the equivalent resistance under digital control crosses the actual resonant frequency is fundamentally eliminated by adopting the rapid robust PWM control method, and the stability of the system is improved. As shown in fig. 8, with the fast robust PWM control method, the resonance conjugate pole is moved in the unit circle as a whole, compared to the conventional PWM modulation strategy. In this case, L is only required g The inverter at the position of =0 has better stability margin, the system can stably operate, and the inverter has good robustness to the impedance of the power grid.
Fig. 3 is a schematic diagram of a fast robust PWM control design scheme of the LCL type grid-connected inverter.
U in the figure d (k) For the kth switching cycle inverter DC side voltage u d (k + 1) is the DC side voltage of the inverter in the (k + 1) th switching period, u d (k + 2) is the DC side voltage of the inverter in the k +2 switching period, D (k-1) is the duty cycle of the k-1 switching period, D (k) is the duty cycle of the k switching period, D (k + 1) is the duty cycle of the k +1 switching period, D (k + 2) is the duty cycle of the k +2 switching period, D (k + 1) is the duty cycle loaded at the carrier wave crest of the k +1 switching period, D (k + 2) is the duty cycle loaded at the carrier wave crest of the k +2 switching period 1 (k + 2) is the duty cycle loaded at the k +2 switching cycle carrier trough, D 1 (k + 3) is the duty cycle loaded at the k +3 switching cycle carrier trough, T s Is a switching cycle.
Take the k +1 th switching cycle as an example:
1)t 1 time of day, pulse width of T s d (k), where d (k) is the duty cycle of the kth switching cycle, such that, of k +1 switching cycles, 0.5 times the switching cycle has a pulse width of 0.5T s d(k)。
2)t 2 Time of day, inverter control signal u d Equal to the carrier signal u at that time tri The switch is turned off.
3)t 3 At that time, the (k + 1) th switching cycle duty cycle d (k + 1) is calculated.
4)t 4 At the moment, the pulse width is updated again, and the pulse width of the (k + 1) th switching period is T s D (k + 1) and a duty cycle D (k + 1) with a pulse width T for satisfying the (k + 1) th switching period s d (k + 1), the pulse width of the next half of the switching period should be adjusted to T s d(k+1)-0.5T s D (k), the duty ratio D (k + 1) is set to 2 times D (k + 1) -0.5T considering that the carrier wave in PWM modulation is a symmetrical triangular wave s d(k)。
5)t 5 At that time, the switch is turned on.
Fig. 4 is a flow chart of a fast robust PWM control implementation technique. The fast robust PWM control method provided by the invention can be realized based on the DSP 2812. The general timer of the DSP is in a continuous increasing/decreasing mode to obtain symmetrical carriers of corresponding frequencies, and the duty ratio is obtained by comparing matching events. When the modulation method is in the second stage, the duty ratio is loaded twice in one carrier period, and the comparison register can be reset repeatedlyThe duty cycles D are loaded at the underflow interrupt (carrier wave trough) and the periodic interrupt (carrier wave crest) respectively 1 And (k + i-1) and D (k + i), acquiring the time of duty ratio D =0.5 by zero-crossing capture, and obtaining the switching period of switching from the negative half wave to the positive half wave of the modulation wave. Because the modulated wave and the voltage of the power grid are in the same frequency and phase, the modulated wave respectively occupies 0.5N switching cycles in positive and negative half-waves, wherein N is the carrier number of the power grid cycle, and the value of the carrier number is f s /f 0 ，f 0 Frequency, f, of fundamental wave of the mains voltage s Is the system switching frequency. Therefore, the 0.5N switching cycles are switching cycles in which the modulation wave is switched from the positive half cycle to the negative half cycle. Considering that the duty ratio D is close to 0.5 in the range of 0.05N switching cycles at the switching position of the positive half wave and the negative half wave of the modulation wave, even if the inverter suddenly changes from no load to full load, the duty ratio D can meet the condition that D (k + i-1) is more than or equal to 0.5D (k + i-1) and less than or equal to 0.5D (k + i-1). Therefore, in order to facilitate smooth switching of the positive half period and the negative half period of the modulation wave, the duty ratio D is loaded in the range of 0.05N switching periods at the switching position of the positive half wave and the negative half wave of the modulation wave 1 (k + i) wherein D 1 (k + i) = D (k + i-1); the duty ratio D is within the range of 0.05N-0.55N switching periods of the modulation wave 1 (k + i) equals 1; the duty ratio D (k + i) is equal to 0 in the modulation wave range from 0.6N to 0.95N switching periods.
FIG. 5 shows the grid-connected current i g And the network voltage u g The simulated waveform of (2). And a system simulation model is established by Matlab/Simulink. By using a fast robust PWM control method, the boundary frequency of the equivalent damping resistor is out of the design interval of the resonant frequency, the influence of the control delay on the stability and the damping effect of the system is counteracted, and a disturbance signal 19800rad/s is introduced near the resonant frequency, whereinFor a grid-connected current instruction value, a rapid robust PWM control strategy is adopted, the grid-connected current can well track the instruction current, the grid-connected current and the grid-side voltage have the same frequency and phase, the grid-connected current does not oscillate, and the system has good steady-state performance and robustness to the power grid impedance.
Claims (2)
1. A fast robust single current feedback control method of an LCL type grid-connected inverter is characterized by comprising the following steps:
1) At the initial point of each sampling period, the A/D sampling circuit of the LCL type grid-connected inverter samples the grid voltage u g Grid-connected current i g Voltage u of filter capacitor c Inverter circuit DC side capacitor voltage U of LCL type grid-connected inverter dc Respectively sampling, and sending the sampling data to a control module of the LCL type grid-connected inverter for processing;
2) Grid-connected current i g Grid-connected current feedback active damping module G based on high-pass filter v (s) obtaining a control signal u 1 (ii) a Grid-connected current feedback active damping module G based on high-pass filter v The expression of(s) is:wherein, ω is d 、K d Cut-off angular frequency and gain of the high-pass filter, respectively, s = j ω, j being the imaginary unit symbol;
3) Grid-connected current i g With given grid-connected current command signal i ref Differencing to obtain a signal e i ；
4) Signal e i Obtaining a control signal u through a grid-connected current quasi-resonant controller G(s) 2 (ii) a The expression of the grid-connected current quasi-resonant controller G(s) is as follows:
wherein, K p And K r Proportional coefficient and resonance gain, ω, of the grid-connected current quasi-resonant controller G(s), respectively r Is the cut-off frequency; omega 0 Is the fundamental angular frequency;
5) Control signal u 1 And a control signal u 2 Obtaining LCL type grid-connected inverter control signal u by difference d ；
6) LCL type grid-connected inverter control signal u d And carrier u tri Obtaining the duty ratio d of the LCL type grid-connected inverter by a fast robust PWM modulation method; the duty ratio d controls the on and off of a switching tube of an inverter circuit through a drive protection circuit of the LCL type grid-connected inverter; the fast robust PWM method is realized by two stages: 1) In the initial stage of start-up operation, i.e. from 0 to kT s At the moment, PWM modulation is adopted, and the duty ratio d (i-1) of the last switching period is loaded at the wave trough of the carrier; 2) In the second stage of the operation of the LCL type grid-connected inverter, duty ratio signals are loaded twice in one switching period, the loading positions are respectively positioned at the wave troughs and the wave crests of the carrier, and the duty ratios D are loaded at the wave troughs of the carrier 1 (k + i) loading the duty ratio D (k + i) at the peak of the carrier wave, and satisfying D 1 (k + i) = D (k + i-1), and performs AD sampling and PWM modulation signal calculation preferentially at 0.5T s Complete duty cycle calculation before, T s Is a switching cycle; wherein D 1 (k + i) is the duty ratio loaded at the wave trough of the carrier in the k + i switching period, wherein i is more than or equal to 2; d (k + i) is the duty cycle loaded at the k + i th switching cycle carrier wave peak; d (k-i) is the duty cycle of the kth-i switching period; d (k + i-1) is the duty cycle loaded at the k + i-1 th switching cycle carrier peak.
2. The fast robust single current feedback control method of the LCL type grid-connected inverter according to claim 1, wherein in step 6), the duty ratio calculation formulas of the (k + 1) th switching period and the (k + i) th switching period are respectively:
in the formula: d (k) is the duty cycle of the kth switching period, d (k + 1) is the duty cycle of the kth switching period, d (k + i) is the duty cycle of the kth switching period, wherein i is more than or equal to 2, D 1 (k + i-1) is the carrier wave trough in the k + i-1 th switching periodThe loaded duty ratio is adopted, and D (k + 1) is the duty ratio loaded at the carrier wave crest in the (k + 1) th switching period; d (k + i) is the duty cycle of the carrier peak loading at the k + i-th switching cycle.
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| CN107181421A (en) * | 2017-06-09 | 2017-09-19 | 金陵科技学院 | It is a kind of to reduce the control method that digital control delay influences on LCL type combining inverter |
| CN108321842B (en) * | 2018-02-28 | 2021-05-25 | 西安理工大学 | Active damping optimization method for grid-connected current control of L-type grid-connected inverter |
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| CN111245004B (en) * | 2018-11-28 | 2023-06-16 | 哈尔滨工业大学 | Composite robust control method of high-frequency SiC photovoltaic grid-connected inverter under weak current network |
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