CN111245004B - Composite robust control method of high-frequency SiC photovoltaic grid-connected inverter under weak current network - Google Patents
Composite robust control method of high-frequency SiC photovoltaic grid-connected inverter under weak current network Download PDFInfo
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H02J3/01—Arrangements for reducing harmonics or ripples
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- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
- H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
- H02M7/53875—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output
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- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/40—Arrangements for reducing harmonics
Abstract
The invention relates to a composite robust control method of a high-frequency SiC photovoltaic grid-connected inverter under a weak current network. Calculating to obtain a reference value of the current loop by designing LCL filter parameters; the power density of the high-frequency SiC photovoltaic grid-connected inverter is increased, grid-connected current is fed back, and an active damping feedback function H is designed ad (s) determining an open loop transfer function G of the high frequency SiC photovoltaic grid-connected inverter open (s); the feedforward function of the power grid voltage is improved, a first-order low-pass filter is configured, and a new power grid voltage transfer function G is obtained v (s) suppressing each subharmonic by using an odd number of repetition quasi PR current controller to obtain a modulated wave u αβ * The SVPWM module obtains a switch driving signal for driving the SiC switch tube. According to the invention, an additional sensor is not needed, and a second-order differential link and a proportional link are adopted to jointly realize the feedforward of the power grid voltage so as to eliminate the influence of weak power grid impedance on the stability of the high-frequency inverter.
Description
Technical Field
The invention relates to the technical field of control of high-frequency SiC photovoltaic grid-connected inverters, in particular to a composite robust control method of a high-frequency SiC photovoltaic grid-connected inverter under a weak current network.
Background
With the increase of the grid-connected power of the distributed power supply and the wide distribution of the position of the connected power grid, the end or local area of the power grid shows weak power grid characteristics of low short-circuit capacity and high power grid impedance, the power grid impedance can change the loop gain of an inverter control system, and the system is possibly unstable; and grid voltage background harmonic waves can lead to grid-connected current distortion. Therefore, when designing the photovoltaic grid-connected inverter, the working state of a normal power grid is considered, and meanwhile, the inverter can be ensured to run stably and reliably in a more complex weak power grid system.
With the development of the global energy internet, the performance requirements on power electronic equipment are higher and higher, and semiconductor power electronic devices manufactured by silicon carbide (SiC) which is a third-generation semiconductor material are paid more attention to and researched by the superior performances of high frequency, high temperature resistance and the like. The high-frequency photovoltaic inverter based on the SiC power device can be provided with a smaller output filter, so that the size and weight of a passive device are reduced, and the power density of the inverter is improved; however, when the inverter with high frequency and small filter is connected to a weak power network with high impedance, serious stability problems are easy to occur. Aiming at the stability problem of the interaction effect of the inverter based on the Si MOSFET/IGBT and the weak current network, the stability problem is usually solved by adopting a power network impedance measurement technology or a robust controller design at present, but the stability analysis of the SiC MOSFET grid-connected inverter with higher frequency is lacking. In addition, in terms of suppressing resonance of the LCL filter and improving grid-connected current quality, the control loop generally adopts a capacitive current feedback method requiring an additional sensor.
Disclosure of Invention
The invention provides a composite robust control method of a high-frequency SiC photovoltaic grid-connected inverter, which aims to solve the stability problem caused by unmatched impedance of the high-frequency SiC photovoltaic inverter and a high power grid under a weak power grid, and provides the following technical scheme:
a composite robust control method of a high-frequency SiC photovoltaic grid-connected inverter under a weak current network comprises the following steps:
step one: according to the power grade, switching frequency and current ripple requirement parameters of the high-frequency SiC photovoltaic grid-connected inverter, designing and outputting parameters of an LCL filter;
step two: collecting output voltage u of high-frequency SiC photovoltaic grid-connected inverter a 、u b And u c Collecting output current i of high-frequency SiC photovoltaic grid-connected inverter a 、i b And i c Output voltage u of high-frequency SiC photovoltaic grid-connected inverter acquired by Clarke transformation a 、u b 、u c And output current i a 、i b 、i c Conversion to two-phase stationary coordinate system alpha beta, according to definition of instantaneous power and active power reference value P * And reactive power reference value Q * Calculating the reference value i of the current loop α * And i β * ；
Step three: the power density of the high-frequency SiC photovoltaic grid-connected inverter is increased, grid-connected current is selected to be fed back, and an active damping feedback function H is designed according to an active damping mechanism ad (s) determining a stability constraint of the active damping inner loop according to a us criterion;
step four: consider the grid impedance L g According to an active damping feedback function H ad (s) combining full bridge gain k PWM Filter side inductance L 1 Filter capacitor C and power grid side inductance L 2 Feedforward voltage function G f (s) and current controller G c (s) determining an open loop transfer function G of the high frequency SiC photovoltaic grid-connected inverter open (s)；
Step five: according to the open loop transfer function G of the high-frequency SiC photovoltaic grid-connected inverter obtained in the step four open (s) improving the feedforward function of the power grid voltage, and configuring a first-order low-pass filter to obtain a new power grid voltage transfer function G v (s)；
Step six: the current controller adopts an odd repeated quasi PR controller, the odd repeated quasi PR controller is utilized to carry out fast zero-difference tracking on the fundamental wave signal, and the odd repeated controller is utilized to inhibit each harmonic wave;
step seven: will collect i α 、i β Respectively with reference current value i α * And i β * After 0 comparison, the modulated wave u is obtained by combining the quasi PR current controller with the power grid voltage feedforward and the power grid current feedback control αβ * And obtaining a switch driving signal through the SVPWM module for driving the SiC switching tube.
Preferably, the parameters of the output LCL filter are designed by:
L 2 ＝rL 1 (2)
wherein U is dc Is the direct-current side voltage, i rmax For maximum allowable current ripple value, f s For switching frequency, r is the ratio of the network side inductance to the inverter side inductance, P is the rated power of the inverter, lambda is the ratio of reactive power to total power, E n Is the effective value of the phase voltage of the three-phase power grid, f is the fundamental frequency of the power grid, L 1 Is the inductance of the filter side, C is the filter capacitance, L 2 Is the filter net side inductance.
Preferably, the second step specifically includes:
the first step: output voltage u of high-frequency SiC photovoltaic grid-connected inverter acquired by Clarke transformation a 、u b 、u c And output current i a 、i b 、i c Converting into a two-phase stationary coordinate system alpha beta to obtain a two-phase stationary voltage u α 、u β Two-phase quiescent current i α 、i β ；
And a second step of: with PQ outer loop control, according to the definition of instantaneous power and the reference value P of active power * And reactive power reference value Q * Calculating to obtain a reference value i of the current loop α * And i β * The reference value i of the current loop is calculated by the following formula α * And i β * ：
Wherein u is α 、u β Is a two-phase rest voltage, i α 、i β For two-phase stationary current i α * And i β * Is the reference value of the current loop, P * For the active power reference value, Q * Is a reactive power reference value.
Preferably, the third step specifically comprises:
the first step: designing an active damping feedback function H according to an active damping mechanism ad (s) expressed by the following formula:
wherein H is ad (s) a feedback function in the form of a high pass filter, k ad For high pass filter gain omega h Is the turning frequency, k of the high-pass filter PWM And s is Laplacian, which is the full bridge gain of the inverter.
And a second step of: the active damping inner loop stability constraint is expressed by:
preferably, the open loop transfer function G of the high frequency SiC photovoltaic grid-connected inverter is determined by open (s)：
Wherein, gopen(s) is an open loop transfer function of the high-frequency SiC photovoltaic grid-connected inverter, A=L 1 (L 2 +L g )C，B＝L 1 (L 2 +L g )Cω h ，D＝L 1 +L 2 +L g -k PWM L g G f (s)，E＝(L 1 +L 2 +L g )ω h -k PWM k ad -k PWM L g ω h G f (s), lg is the grid impedance, gc(s) is the current controller, and Gf(s) is the feed-forward voltage function.
Preferably, the fifth step specifically comprises:
the first step: according to the open loop transfer function G of the high-frequency SiC photovoltaic grid-connected inverter obtained in the step four open (s) improving the grid voltage feedforward function to the sum of a second order differential form and a proportional form;
and a second step of: a first-order low-pass filter is configured, and a new power grid voltage transfer function G is obtained through the following expression v (s)：
Wherein G is v (s) is a new grid voltage transfer function, τ is a low pass filter time constant.
Preferably, the repetitive quasi-PR controller is expressed by:
wherein G is QPR (s) is a repetitive quasi-PR controller function, k pi ，k ri The ratio and resonance coefficient, ω, of the current loop quasi PR control, respectively c For cut-off frequency omega r Is the resonant frequency.
Preferably, the odd number of repetition controller is expressed by:
wherein G is RC (s) is an odd number of repeated controller functions, T is the sampling time, Q(s) is the integral attenuation coefficient less than 1, C(s) is the compensation function designed for the control object, k rc To repeat the controller gain.
The invention has the following beneficial effects:
1. and an active damping method of grid-connected current feedback is adopted to inhibit the resonance peak of the output LCL filter. Compared with the traditional capacitive current feedback active damping method, the method does not need an additional sensor, and fully plays the advantage of high power density of the high-frequency SiC photovoltaic grid-connected inverter.
2. On the basis of a grid-connected current feedback active damping method, the stability problem of the traditional proportional voltage feedforward control under the weak current grid is considered, and a second-order differential link and a proportional link are adopted to jointly realize the grid voltage feedforward so as to completely eliminate the influence of weak current grid impedance on the stability of the high-frequency inverter.
3. In consideration of the problems of power grid background voltage harmonic waves and harmonic waves in a current reference command, current fundamental waves and the harmonic waves are controlled independently, and the problem of output current distortion caused by the power grid background harmonic waves and the command reference harmonic waves is solved by adopting a current controller based on repeated quasi PR of an odd number internal model.
Drawings
Fig. 1 is a topological structure diagram of a three-phase grid-connected inverter based on SiC power devices.
Fig. 2 is a block diagram of the overall control of a composite robust control method for a high frequency SiC photovoltaic grid-connected inverter.
FIG. 3 is a block diagram of an additional grid voltage feedforward grid-tie current active damping control architecture.
Fig. 4 is an odd number of repetitions of the quasi-PR current controller.
FIG. 5 is a simulation contrast diagram of a low-frequency Si, high-frequency SiC inverter with a grid impedance of 0, FIG. 5 (a) is a grid impedance L g Grid-connected current waveform of Si inverter at 0, FIG. 5 (b) is grid impedance L g And a grid-connected current waveform diagram of the SiC inverter when the current is 0.
FIG. 6 is a simulation contrast diagram of a low-frequency Si and high-frequency SiC inverter with a grid impedance of 2mH, FIG. 6 (a) is a grid impedance L g Grid-connected current waveform of Si inverter at 2mH, FIG. 6 (b) is grid impedance L g And a grid-connected current waveform diagram of the SiC inverter at 2 mH.
FIG. 7 is a simulated comparison graph of a conventional control method and a composite robust control method under the condition of a power grid with a power grid impedance of 2mH, and FIG. 7 (a) is a grid-connected current waveform graph of a Si inverter adopting the conventional control method under the condition of a weak power grid with a power grid impedance of 2mH and a switching frequency of 10 kHz; FIG. 7 (b) is a graph of a grid-connected current waveform of a SiC inverter employing a conventional control method at a weak grid impedance of 2mH and a switching frequency of 50 kHz; fig. 7 (c) is a graph of a grid-connected current waveform of a SiC inverter employing a hybrid robust control method at a weak grid impedance of 2mH and a switching frequency of 50 kHz.
FIG. 8 is an open loop transfer function characteristic of a conventional control method and a complex robust control method under different grid impedances, FIG. 8 (a) is a graph showing the impedance L at a weak grid g Traditional power grid voltage proportion feedforward control strategy at 2mH and composite robust control proposed hereinFig. 8 (b) is an open-loop transfer function characteristic diagram of the composite robust control strategy for different grid impedances.
Detailed Description
The present invention will be described in detail with reference to specific examples.
First embodiment:
according to the topology structure diagram of the three-phase grid-connected inverter based on the SiC power device shown in FIG. 1, the topology structure diagram mainly comprises a DC side voltage U dc Switching devices SiC MOSFET, L 1 、L 2 LCL filter composed of C and L g U is the equivalent impedance of the line g For a three-phase ac grid, PCC is the point of common coupling.
In order to solve the stability problem caused by the unmatched impedance of the high-frequency SiC photovoltaic inverter and the high power grid under the weak power grid, a composite robust control method of the high-frequency SiC photovoltaic inverter is provided, as shown in fig. 2: the method mainly comprises PQ outer loop control, active damping control, fundamental wave and harmonic wave control and improved power grid voltage feedforward control.
Step one: according to the power grade, switching frequency and current ripple requirement parameters of the high-frequency SiC photovoltaic grid-connected inverter, designing and outputting parameters of an LCL filter;
step two: collecting output voltage u of high-frequency SiC photovoltaic grid-connected inverter a 、u b And u c Collecting output current i of high-frequency SiC photovoltaic grid-connected inverter a 、i b And i c Output voltage u of high-frequency SiC photovoltaic grid-connected inverter acquired by Clarke transformation a 、u b 、u c And output current i a 、i b 、i c Conversion to two-phase stationary coordinate system alpha beta, according to definition of instantaneous power and active power reference value P * And reactive power reference value Q * Calculating the reference value i of the current loop α * And i β * ；
Step three: to increase the power density of the high-frequency SiC photovoltaic grid-connected inverter, the grid-connected current is selected to be fed back, and an active damping feedback function H is designed according to an active damping mechanism ad (s) determining a stability constraint of the active damping inner loop according to a us criterion;
step four: consider the grid impedance L g According to an active damping feedback function H ad (s) combining full bridge gain k PWM Filter side inductance L 1 Filter capacitor C and power grid side inductance L 2 Feedforward voltage function G f (s) and current controller G c (s) determining an open loop transfer function G of the high frequency SiC photovoltaic grid-connected inverter open (s)；
Step five: according to the open loop transfer function G of the high-frequency SiC photovoltaic grid-connected inverter obtained in the step four open (s) improving the feedforward function of the power grid voltage, and configuring a first-order low-pass filter to obtain a new power grid voltage transfer function G v (s)；
Step six: the current controller adopts an odd repeated quasi-PR controller, the quasi-PR controller is used for carrying out fast zero-difference tracking on fundamental wave signals, and the odd repeated controller is used for inhibiting all subharmonics;
step seven: will collect i α 、i β Respectively and reference current value i α * 、i β * After 0 comparison, combining the quasi PR current controller with the grid voltage feedforward and the grid current feedback control to obtain a modulation wave u αβ * And obtaining a switch driving signal through the SVPWM module for driving the SiC switching tube.
The parameters of the LCL filter are reasonably designed, and the specific formula is as follows:
L 2 ＝rL 1 (2)
wherein U is dc Is the direct-current side voltage, i rmax To allow electricityMaximum fluctuation value of flow, f s For switching frequency, r is the ratio of the network side inductance to the inverter side inductance, P is the rated power of the inverter, lambda is the ratio of reactive power to total power, E n Is the effective value of the phase voltage of the three-phase power grid, f is the fundamental frequency of the power grid, L 1 Is the inductance of the filter side, C is the filter capacitance, L 2 Is the filter net side inductance.
The overall control block diagram of the system is shown in fig. 2. The method mainly comprises PQ outer loop control, active damping control, fundamental wave and harmonic wave control and improved power grid voltage feedforward control. The inverter output voltage u is sampled first a 、u b 、u c Output current i a 、i b 、i c Output voltage u of high-frequency SiC photovoltaic grid-connected inverter acquired by Clarke transformation a 、u b 、u c And output current i a 、i b 、i c Converting into a two-phase stationary coordinate system alpha beta to obtain a two-phase stationary voltage u α 、u β Two-phase quiescent current i α 、i β 。
With PQ outer loop control, according to the definition of instantaneous power and the reference value P of active power * And reactive power reference value Q * Calculating to obtain a reference value i of the current loop α * 、i β * The specific formula is as follows:
wherein u is α 、u β Is a two-phase rest voltage, i α 、i β For two-phase stationary current i α * And i β * Is the reference value of the current loop, P * For the active power reference value, Q * Is a reactive power reference value.
Based on the traditional PQ control and the power grid voltage feedforward control, the LCL filter resonance peak is suppressed for realizing active damping, meanwhile, no additional sensor is added, the inverter power density is improved, the grid-connected current is selected to be fed back, and the mechanism of active damping is combinedDesigning a feedback function H in the form of a high-pass filter ad (s) as shown in formula (5):
wherein H is ad (s) a feedback function in the form of a high pass filter, k ad For high pass filter gain omega h Is the turning frequency, k of the high-pass filter PWM And s is Laplacian, which is the full bridge gain of the inverter.
According to the Lawster criterion, the stability constraint condition of the active damping inner ring under the scheme can be obtained, as shown in a formula (6):
in combination with the grid-connected current active damping control block diagram of the additional grid voltage feedforward shown in fig. 3, the grid impedance L is considered g According to an active damping feedback function H ad (s) and combine full bridge gain k PWM Filter side inductance L 1 Filter capacitor C and net side inductance L 2 Voltage feedforward function G f (s) and a current controller G c (s) obtaining an open loop transfer function G of the grid-connected inverter open (s) as shown in formula (7):
wherein, gopen(s) is an open loop transfer function of the high-frequency SiC photovoltaic grid-connected inverter, A=L 1 (L 2 +L g )C，B＝L 1 (L 2 +L g )Cω h ，D＝L 1 +L 2 +L g -k PWM L g G f (s)，E＝(L 1 +L 2 +L g )ω h -k PWM k ad -k PWM L g ω h G f (s), lg is the grid impedance, gc(s) is the current controller, and Gf(s) is the feed-forward voltage function.
In order to eliminate the influence of grid impedance on the grid-connected inverter, on the basis of an active damping method of single grid-connected current feedback, from the perspective of a system open loop transfer function shown in a formula (7), the stability problem generated under a weak grid by traditional proportional voltage feedforward is considered, and the grid voltage feedforward function is improved to be the sum of a second order differential form and a proportional form, so that L in the system open loop transfer function is completely eliminated g A component; meanwhile, in order to avoid the noise problem possibly caused by the differential term in the feedforward function, a first-order low-pass filter is configured for the feedforward function to obtain a new power grid voltage transfer function G v (s) as shown in formula (8):
wherein G is v (s) is a new grid voltage transfer function, τ is a low pass filter time constant.
Further, in order to solve the problem of inverter output current distortion possibly caused by weak current network background harmonic, an odd number repeated quasi-PR controller shown in fig. 4 is adopted, and the quasi-PR controller is utilized to realize fast zero-difference tracking of fundamental wave signals, so that good dynamic performance of the system is ensured; because only odd-order harmonic exists in the three-phase power grid, the suppression of each odd-order harmonic is realized by using a repeated controller based on an odd-order internal model, and the good steady-state performance of the system is ensured. The expression of the quasi PR controller is shown as (9)
Wherein, kpi, kri are the ratio and resonance coefficient of the current loop PR control, ωc is the cut-off frequency, ωr is the resonance frequency, respectively.
The expression of the repetitive controller is shown as the formula (10)
Wherein G is RC (s) repeating the controller functionT is the sampling time, Q(s) is the integral attenuation coefficient less than 1, C(s) is the compensation function designed for the control object, k rc To repeat the controller gain.
Will collect i α 、i β Respectively and reference current value i α * 、i β * And after 0 comparison, the modulation wave u is obtained through repeating the quasi PR current controller and combining with the power grid voltage feedforward and the power grid current feedback control αβ * And then a switch driving signal is obtained through the SVPWM module and is used for driving the SiC switching tube.
Specific embodiment II:
in order to further describe the correctness and feasibility of the method of the invention in detail, the method of the invention is verified by simulation by combining the specific example. The simulation parameters in this example are: DC voltage U dc The power grid rated voltage effective value is 110V, and the power class of the inverter is 1.5kW. Si inverter operating frequency selects 10kHz, LCL filter parameter is designed as L 1 ＝5mH，L 2 =1.25 mh, c=4.7 μf, siC inverter operating frequency is selected to 50khz, lcl filter parameters are designed to L 1 ＝1mH，L 2 ＝0.2mH，C＝4.7μF。
To verify that the stability of the high frequency SiC inverter is more susceptible to weak grid impedance, the low grid impedance L for the Si inverter and the SiC inverter, respectively g Simulations were performed at 0 and 2mH, respectively. Fig. 5 (a) and 5 (b) are respectively at the grid impedance L g When the voltage is 0, the grid-connected current waveforms of the Si inverter and the SiC inverter are shown in FIG. 6 (a) and FIG. 6 (b) respectively at the grid impedance L g And a grid-connected current waveform diagram of the Si inverter and the SiC inverter when the current is 2 mH.
As can be seen from fig. 5 (a) and 5 (b), when there is no grid impedance, the waveform quality of the grid-connected current of the Si inverter or the SiC inverter is high, and the inverter can operate stably; as can be seen from fig. 6 (a) and 6 (b), when the grid impedance is 2mH, the grid-connected current waveform of the Si inverter is still stable, and the grid-connected current stability of the SiC inverter is rapidly deteriorated, proving the grid impedance L g And filter net side impedance L 2 Is not matched with the matching process of (a)At higher levels, the stability of the system is more susceptible to impact.
FIG. 7 (a) is a waveform diagram of a grid-connected current of a Si inverter adopting a conventional control method under the conditions that the impedance of a weak current network is 2mH and the switching frequency is 10kHz, and it can be seen that the waveform quality of the grid-connected current is good at this time, and the inverter stably operates; FIG. 7 (b) is a graph of a grid-connected current waveform of a SiC inverter adopting a conventional control method under the conditions of weak grid impedance of 2mH and switching frequency of 50kHz, wherein the grid-connected current waveform is severely distorted, and the stability of the inverter is greatly affected; fig. 7 (c) is a graph of a grid-connected current waveform of a SiC inverter employing a composite robust control method at a weak grid impedance of 2mH and a switching frequency of 50kHz, the current waveform is restored to normal and the inverter is stably operated.
Further, the effectiveness of the composite robust control method is illustrated from the aspect of system stability.
FIG. 8 (a) shows the impedance L at weak current network g Fig. 8 (b) is an open-loop transfer function characteristic diagram of a conventional grid voltage ratio feedforward control strategy and a composite robust control strategy proposed herein at 2mH, and fig. 8 (b) is an open-loop transfer function characteristic diagram of a composite robust control strategy at different grid impedances.
As can be seen from fig. 8 (a), when the grid impedance is 2mH, the phase margin of the system under the conventional grid voltage ratio feedforward control is-5 °, and the system is unstable; and under the control of composite robustness, the phase margin of the system is 63 degrees, and the system runs stably. From fig. 8 (b), it can be seen that the open loop transfer function of the system under the composite robust control will not change with the power grid impedance, i.e. the phase margin of the system will not be affected by the power grid impedance, and the system can operate stably.
And an active damping method of grid-connected current feedback is adopted to inhibit the resonance peak of the output LCL filter. Compared with the traditional capacitive current feedback active damping method, the method does not need an additional sensor, and fully plays the advantage of high power density of the high-frequency SiC photovoltaic grid-connected inverter.
On the basis of a grid-connected current feedback active damping method, the stability problem of the traditional proportional voltage feedforward control under the weak current grid is considered, and a second-order differential link and a proportional link are adopted to jointly realize the grid voltage feedforward so as to completely eliminate the influence of weak current grid impedance on the stability of the high-frequency inverter.
In consideration of the problems of power grid background voltage harmonic waves and harmonic waves in a current reference command, current fundamental waves and the harmonic waves are controlled independently, and the problem of output current distortion caused by the power grid background harmonic waves and the command reference harmonic waves is solved by adopting a current controller based on repeated quasi PR of an odd number internal model.
The above-mentioned preferred implementation manner of the composite robust control method of the high-frequency SiC photovoltaic grid-connected inverter under the weak current network is not limited to the above-mentioned embodiments, and all technical solutions under thought belong to the protection scope of the present invention. It should be noted that modifications and variations can be made by those skilled in the art without departing from the principles of the present invention, which is also considered to be within the scope of the present invention.
Claims (8)
1. A composite robust control method of a high-frequency SiC photovoltaic grid-connected inverter under a weak current network is characterized by comprising the following steps: the method comprises the following steps:
step one: according to the power grade, switching frequency and current ripple requirement parameters of the high-frequency SiC photovoltaic grid-connected inverter, designing and outputting parameters of an LCL filter;
step two: collecting output voltage u of high-frequency SiC photovoltaic grid-connected inverter a 、u b And u c Collecting output current i of high-frequency SiC photovoltaic grid-connected inverter a 、i b And i c Output voltage u of high-frequency SiC photovoltaic grid-connected inverter acquired by Clarke transformation a 、u b 、u c And output current i a 、i b 、i c Conversion to two-phase stationary coordinate system alpha beta, according to definition of instantaneous power and active power reference value P * And reactive power reference value Q * Calculating the reference value i of the current loop α * And i β * ；
Step three: increasing power density of high-frequency SiC photovoltaic grid-connected inverterThe degree, the grid-connected current is selected to be fed back, and an active damping feedback function H is designed according to an active damping mechanism ad (s) determining a stability constraint of the active damping inner loop according to a us criterion;
step four: consider the grid impedance L g According to an active damping feedback function H ad (s) combining full bridge gain k PWM Filter side inductance L 1 Filter capacitor C and power grid side inductance L 2 Feedforward voltage function G f (s) and current controller G c (s) determining an open loop transfer function G of the high frequency SiC photovoltaic grid-connected inverter open (s)；
Step five: according to the open loop transfer function G of the high-frequency SiC photovoltaic grid-connected inverter obtained in the step four open (s) improving the feedforward function of the power grid voltage, and configuring a first-order low-pass filter to obtain a new power grid voltage transfer function G v (s)；
Step six: the current controller adopts an odd repeated quasi-PR controller, the quasi-PR controller is used for carrying out fast zero-difference tracking on fundamental wave signals, and the odd repeated controller is used for inhibiting all subharmonics;
step seven: the two-phase stationary current i to be collected α 、i β Respectively with reference current value i α * And i β * After 0 comparison, combining the quasi PR controller with the grid voltage feedforward and the grid current feedback control to obtain a modulation wave u αβ * And obtaining a switch driving signal through the SVPWM module for driving the SiC switching tube.
2. The composite robust control method of the high-frequency SiC photovoltaic grid-connected inverter under the weak current network, which is disclosed in claim 1, is characterized in that: parameters of the output LCL filter are designed by:
L 2 ＝rL 1 (2)
wherein U is dc Is the direct-current side voltage, i rmax For maximum allowable current ripple value, f s For switching frequency, r is the ratio of the network side inductance to the inverter side inductance, P is the rated power of the inverter, lambda is the ratio of reactive power to total power, E n Is the effective value of the phase voltage of the three-phase power grid, f is the fundamental frequency of the power grid, L 1 Is the inductance of the filter side, C is the filter capacitance, L 2 Is the filter net side inductance.
3. The composite robust control method of the high-frequency SiC photovoltaic grid-connected inverter under the weak current network, which is disclosed in claim 1, is characterized in that: the second step is specifically as follows:
the first step: output voltage u of high-frequency SiC photovoltaic grid-connected inverter acquired by Clarke transformation a 、u b 、u c And output current i a 、i b 、i c Converting into a two-phase stationary coordinate system alpha beta to obtain a two-phase stationary voltage u α 、u β Two-phase quiescent current i α 、i β ；
And a second step of: with PQ outer loop control, according to the definition of instantaneous power and the reference value P of active power * And reactive power reference value Q * Calculating to obtain a reference value i of the current loop α * And i β * The reference value i of the current loop is calculated by the following formula α * And i β * ：
Wherein u is α 、u β Is a two-phase rest voltage, i α 、i β For two-phase stationary current i α * And i β * Is the reference value of the current loop, P * For the active power reference value, Q * Is a reactive power reference value.
4. The composite robust control method of the high-frequency SiC photovoltaic grid-connected inverter under the weak current network, which is disclosed in claim 1, is characterized in that: the third step is specifically as follows:
the first step: designing an active damping feedback function H according to an active damping mechanism ad (s) expressed by the following formula:
wherein H is ad (s) a feedback function in the form of a high pass filter, k ad For high pass filter gain omega h Is the turning frequency, k of the high-pass filter PWM The full-bridge gain of the inverter is obtained, and s is Laplacian;
and a second step of: the active damping inner loop stability constraint is expressed by:
l in formula (6) 1 Representing the filter side inductance, L 2 Representing the grid side inductance.
5. The composite robust control method of the high-frequency SiC photovoltaic grid-connected inverter under the weak current network, which is disclosed in claim 1, is characterized in that: determining an open loop transfer function G of a high frequency SiC photovoltaic grid-connected inverter by open (s)：
Wherein G is open (s) is an open loop transfer function of the high frequency SiC photovoltaic grid-connected inverter, a=l 1 (L 2 +L g )C，B＝L 1 (L 2 +L g )Cω h ，D＝L 1 +L 2 +L g -k PWM L g G f (s)，E＝(L 1 +L 2 +L g )ω h -k PWM k ad -k PWM L g ω h G f (s), lg is the impedance of the power grid, G c (s) is a current controller, G f (s) is a feed-forward voltage function; l in formula (7) 1 Representing the filter side inductance, L 2 Represents the inductance of the power grid side, C represents the filter capacitance, and k PWM Representing the inverter full bridge gain.
6. The composite robust control method of the high-frequency SiC photovoltaic grid-connected inverter under the weak current network, which is disclosed in claim 1, is characterized in that: the fifth step is specifically as follows:
the first step: according to the open loop transfer function G of the high-frequency SiC photovoltaic grid-connected inverter obtained in the step four open (s) improving the grid voltage feedforward function to the sum of a second order differential form and a proportional form;
and a second step of: a first-order low-pass filter is configured, and a new power grid voltage transfer function G is obtained through the following expression v (s)：
Wherein G is v (s) is a new grid voltage transfer function, τ is a low pass filter time constant; l in formula (8) 1 Represents the inductance of the filter side, C represents the filter capacitance, k PWM Representing the inverter full bridge gain.
7. The composite robust control method of the high-frequency SiC photovoltaic grid-connected inverter under the weak current network, which is disclosed in claim 1, is characterized in that: the repetitive quasi-PR controller is expressed by the following formula:
wherein G is QPR (s) is a repeating quasi-PR controller function，k pi ，k ri The ratio and resonance coefficient, ω, of the current loop quasi PR control, respectively c For cut-off frequency omega r Is the resonant frequency.
8. The method for composite robust control of the high-frequency SiC photovoltaic grid-connected inverter under the weak current network, which is disclosed by claim 7, is characterized in that: the controller is expressed by the following expression according to the odd number of repetitions:
wherein G is RC (s) is an odd number of repeated controller functions, T is the sampling time, Q(s) is the integral attenuation coefficient less than 1, C(s) is the compensation function designed for the control object, k rc To repeat the controller gain.
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| CN113258615B (en) * | 2021-06-08 | 2021-10-08 | 西南石油大学 | Grid-connected inverter frequency self-adaptive control method, device, equipment and storage medium |
| CN113595430B (en) * | 2021-08-05 | 2022-12-20 | 上海交通大学 | Three-loop controller of LCL type grid-connected inverter and parameter design method thereof |
| CN113517720B (en) * | 2021-09-10 | 2022-02-11 | 四川大学 | Fractional phase compensation control method and device for LCL grid-connected inverter under weak grid |
| CN113839421A (en) * | 2021-11-16 | 2021-12-24 | 四川大学 | Stability combination control method for LCL type grid-connected inverter under weak grid |
| CN114884125A (en) * | 2022-05-23 | 2022-08-09 | 中赟国际工程有限公司 | High-stability control method for LCL type grid-connected inverter system under weak power grid |
| CN115207968B (en) * | 2022-06-22 | 2024-05-03 | 湖南工业大学 | Method for improving stability margin of photovoltaic grid-connected inverter under weak current network |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106712099A (en) * | 2017-02-27 | 2017-05-24 | 重庆大学 | Multi-parallel photovoltaic grid-connected inverter design method |
| TWI599134B (en) * | 2016-06-21 | 2017-09-11 | Synchronization method for two separate areas in independent microgrid | |
| CN108429281A (en) * | 2018-03-15 | 2018-08-21 | 上海电力学院 | A kind of LCL type gird-connected inverter parallel virtual impedance adjustment |
| CN108448583A (en) * | 2018-05-02 | 2018-08-24 | 燕山大学 | A kind of modified adjuster applied to light current gird-connected inverter off the net |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103545838B (en) * | 2013-09-17 | 2015-11-25 | 南京航空航天大学 | A kind of combining inverter mixing damping adaptive control method be applicable under light current net access conditions |
| CN105591400B (en) * | 2016-01-15 | 2018-04-17 | 湖南大学 | A kind of fast robust single electric current feedback of LCL type gird-connected inverter |
| CN105915094B (en) * | 2016-04-22 | 2018-08-31 | 哈尔滨工业大学 | LCL type control method of grid-connected inverter based on power network current single-sensor |
-
2018
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| TWI599134B (en) * | 2016-06-21 | 2017-09-11 | Synchronization method for two separate areas in independent microgrid | |
| CN106712099A (en) * | 2017-02-27 | 2017-05-24 | 重庆大学 | Multi-parallel photovoltaic grid-connected inverter design method |
| CN108429281A (en) * | 2018-03-15 | 2018-08-21 | 上海电力学院 | A kind of LCL type gird-connected inverter parallel virtual impedance adjustment |
| CN108448583A (en) * | 2018-05-02 | 2018-08-24 | 燕山大学 | A kind of modified adjuster applied to light current gird-connected inverter off the net |
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