CN116995731A - Energy-storage-free grid-structured photovoltaic unit control method based on improved constant voltage method - Google Patents
Energy-storage-free grid-structured photovoltaic unit control method based on improved constant voltage method Download PDFInfo
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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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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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
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
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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
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
- H02J3/241—The oscillation concerning frequency
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
- H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
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Abstract
The invention provides a control method of a non-energy-storage type grid-structured photovoltaic unit based on an improved constant voltage method, which comprises the following steps: the method comprises the steps that firstly, an improved constant voltage-based method is adopted to enable a system to work at a maximum power point, wherein the improved constant voltage-based method adopts a reserved voltage mode to reserve power indirectly so as to ensure the upper limit and the lower limit of power regulation, and MPPT (maximum power point tracking) can be continuously carried out; adopting an algorithm for preventing the voltage breakdown of the direct current bus to directly control the direct current voltage when the photovoltaic is overloaded so as to inhibit the voltage breakdown of the direct current; and thirdly, performing power adjustment by adopting an active power adjustment active support algorithm of the energy-storage-free networking photovoltaic unit and a phase angle self-generation control strategy. The control algorithm and the device system provided by the invention can realize the networking performance of the photovoltaic power supply, construct a novel power system with 100% new energy, and stabilize the frequency and the voltage of the supporting system.
Description
Technical Field
The invention relates to the field of net-structured functions of photovoltaic power stations, in particular to a control method of a net-structured photovoltaic unit without energy storage based on an improved constant voltage method.
Background
With the continuous improvement of the installation ratio of new energy, the problem of safety and stability of the power grid is more serious. The power grid in China is led by the synchronous generator, and gradually turns into the new energy power electronic control leading. However, in an alternating current power grid where a synchronous generator power supply and a new energy source generate electricity simultaneously, synchronization is still a necessary condition for the power grid to stably operate. Therefore, in order to ensure the development of larger-scale new energy sources in China and the safe and stable operation demands of the power grid, the new energy sources also need to have the capacity of supporting the inertia, frequency and voltage of the power grid, especially the capacity of constructing a power system, and ensure the stable operation of the high-proportion new energy power system together with a conventional power supply.
In order to realize active support of photovoltaic and control of frequency and voltage support, the functions are usually realized by adopting a light and storage combined mode. The inertia and primary frequency modulation functions are realized by additionally installing energy storage on the photovoltaic direct-current bus, the photovoltaic unit still adopts MPPT control, and the energy storage and the photovoltaic are coordinated to control and optimize the energy utilization efficiency and meet the network function requirements of self-generation phase angle voltage and the like. However, the method has certain defects when being applied to engineering practice: for the existing photovoltaic power station, because the construction of the primary side is completed, when energy storage is added to a direct current bus, the problems of difficult construction and uncooled occupied area exist, and meanwhile, an inverter power device such as an IGBT (insulated gate bipolar transistor) cannot adapt to the instantaneous current of a photovoltaic and energy storage unit after the energy storage is added, so that the actual transformation is difficult to carry out; on the other hand, because of the development of a novel power system, a photovoltaic power supply needs to realize a grid-formation control function and has primary frequency modulation and inertia functions, and control for frequency disturbance, inertia response and the like, which needs to provide additional power support instantaneously, is different from a wind photovoltaic power supply, because no mechanical part exists, inertia response primary frequency modulation and the like cannot be realized in a manner of releasing rotor kinetic energy, power must be reserved for responding to active support, and the adoption of a reserved power control manner can lead to failure of a common MPPT algorithm such as a common conductivity micro-increment method, a power disturbance method and the like, a maximum power tracking point of the system under weather change cannot be found, and the system is easy to stop during long-term stable operation, and a large amount of power is reserved for controlling the grid-formation unit so as to cause electric discarding. Thus, conventional VSG control adds an energy storage device on the primary side.
Meanwhile, the existing Virtual Synchronization (VSG) control still commonly adopts phase-locked loop (PLL) control, phase angle voltage cannot be generated automatically, and an actual main power supply is difficult to support a power system to stably operate. If the self-generated voltage and phase angle are adopted as the main power supply, the direct current bus voltage is required to be quite stable, and the unit can spontaneously respond to ms-level disturbance of the power angle and the voltage. Therefore, for the adoption of the net-structured photovoltaic unit without energy storage, how to ensure the stability of the voltage of the direct current bus to ensure that the direct current bus runs at a proper working point is a key.
Disclosure of Invention
In view of the above, the invention provides a control method of a non-energy-storage type network-structured photovoltaic unit based on an improved constant voltage method, introduces a direct current bus voltage collapse prevention algorithm, combines a conventional rotor motion equation in a virtual synchronous power generation technology, provides a network-structured photovoltaic unit control strategy capable of realizing engineering application and landing, realizes accurate non-energy-storage type network-structured photovoltaic unit power reservation, and is applied to an engineering site to realize a network-structured photovoltaic belt whole station system.
The energy-storage-free grid-formation photovoltaic unit control method based on the improved constant voltage method is characterized by comprising the following steps of:
the method comprises the steps that firstly, an improved constant voltage-based method is adopted to enable a system to work at a maximum power point, wherein the improved constant voltage-based method adopts a reserved voltage mode to reserve power indirectly so as to ensure the upper limit and the lower limit of power regulation, and MPPT (maximum power point tracking) can be continuously carried out;
adopting an algorithm for preventing the voltage breakdown of the direct current bus to directly control the direct current voltage when the photovoltaic is overloaded so as to inhibit the voltage breakdown of the direct current;
and thirdly, performing power adjustment by adopting an active power adjustment active support algorithm of the energy-storage-free networking photovoltaic unit and a phase angle self-generation control strategy.
Further, the reserved power in the first step is 10% -15%.
Further, the photovoltaic grid-formation in step one operates on the right half plane of the MPPT curve when regulated by a modified constant voltage-based method. .
Furthermore, the second step adopts an algorithm for preventing the voltage breakdown of the direct current bus to directly control the direct current voltage when the photovoltaic is overloaded so as to realize the suppression of the direct current voltage breakdown, and the specific implementation steps are as follows:
UP lim ＝k pUdc (U dc -U dc_min )+k iUdc ∫(U dc -U dc_min )dt (2)
wherein DeltaP lim For additional active power reference value not greater than zero, U dc_min Is not more than
Minimum DC voltage of left half plane, k pUdc 、k iUdc The direct current voltage controller is respectively a proportion coefficient and an integral coefficient of the direct current voltage controller, wherein a proportion term is used for improving the response speed of the controller, an integral term is used for eliminating steady-state errors, and an integral term adopts internal limiting to avoid saturation of the controller.
Further, the controller is a PI controller with upper amplitude limit of 0, and the reference input signal is U dc_min The output signal is the active power increment delta P 0 ；U dc_min The instruction is U calculated by MPPT of constant voltage method dc_min Representing the lowest voltage that the photovoltaic power supply is allowed to run at steady state; when (when)U dc Higher than U dc_min When the output of the controller is 0, the photovoltaic power supply works in a sagging characteristic area; when the load increases and exceeds the MPPT power of the photovoltaic power supply, the direct current capacitor is continuously discharged, once U dc Below U dc_min The controller reduces active power, transfers redundant power at the alternating current side to other micro power sources to enable U to be dc Finally stabilize at U dc_min 。
Furthermore, the step three adopts an active power regulation active support algorithm of the non-energy-storage type grid-structured photovoltaic unit and a phase angle self-generation control strategy to carry out power regulation, and the specific implementation steps are as follows:
wherein omega is the output angular frequency amplitude command of the converter, theta is the output phase of the converter, omega 0 The output angular frequency of the converter is that J is virtual inertia, P is the average active power output by the converter, and delta P lim For additional active power reference value not greater than zero, P pv And the integrated value is obtained after MPPT, reserved power and frequency modulation power.
Further, P pv The expression of (2) is:
wherein m is w For active-frequency control droop coefficient, P mpp For maximum active power calculated by MPPT curve of constant voltage method, P N And k is a reserved power percentage, and f is grid-connected point frequency.
Compared with the prior art, the invention has the following beneficial effects:
(1) The MPPT control algorithm for improving the constant voltage method provided by the invention realizes maximum power tracking under the reserved power, effectively solves the problem that the conventional MPPT algorithm such as a common conductivity micro-increment method, a power disturbance method and the like cannot find the maximum power tracking point of a system under weather change, ensures that a grid-structured photovoltaic energy tube stably operates for a long time to avoid shutdown, and reduces the proportion of reserved power controlled by a grid-structured unit;
(2) The invention provides a direct current bus voltage collapse prevention algorithm, which realizes that a photovoltaic unit always operates on the left half plane of an MPPT curve, and further solves the core problem of stable control of the voltage of the photovoltaic direct current bus without an energy storage network;
(3) The control strategy of the energy-storage-free networking photovoltaic unit is provided by combining a traditional virtual synchronous rotor motion equation and a primary frequency/voltage regulation algorithm, a phase-locked loop is omitted, and the self-generation of the phase angle of the photovoltaic unit is realized, and ms-level inertial response and primary frequency/voltage regulation characteristics are realized. The invention can realize the net construction performance of the whole photovoltaic station, construct a novel power system with 100% new energy, and stabilize the frequency and voltage of the supporting system.
Drawings
Fig. 1 is a schematic diagram of MPPT setpoint for constant voltage method;
FIG. 2 is a schematic diagram of a photovoltaic power DC bus voltage stability analysis;
FIG. 3 is a flowchart of an algorithm for preventing DC bus voltage breakdown in accordance with an embodiment of the present invention;
FIG. 4 is a schematic diagram of a phase angle self-generating control strategy of a non-energy-storage type grid-structured photovoltaic unit according to an embodiment of the invention;
FIG. 5 is a schematic diagram of an overall control strategy of a non-energy-storage type grid-built photovoltaic unit according to an embodiment of the present invention;
FIG. 6 is a semi-physical simulation verification schematic diagram of a non-energy-storage type networking photovoltaic unit according to an embodiment of the invention;
FIG. 7 is a schematic diagram of a primary part model structure of a non-energy-storage type net-structured photovoltaic unit;
FIG. 8 is a dynamic response curve of frequency under unexpected load changes;
fig. 9 is an MPPT reserved power curve of a non-energy-storage type grid-structured photovoltaic unit according to an embodiment of the present invention;
FIG. 10 is a graph showing the results of a loop power test with multiple machines connected in parallel;
FIG. 11 is a schematic diagram of a phase angle waveform of a photovoltaic self-generated voltage of a disconnected main network under the balance of load and station output;
fig. 12 is a plot of the primary frequency modulation dynamic performance test frequency down-disturb 49.80Hz (photovoltaic output pn=30mw);
fig. 13 is a plot of primary frequency modulation dynamic performance test frequency up-conversion 50.20Hz (photovoltaic output pn=30mw);
fig. 14 is a schematic diagram of a reactive power conditioning curve of a power plant.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The embodiment of the invention provides a control method of a non-energy-storage type network-structured photovoltaic unit based on an improved constant voltage method, which comprises the following steps of:
the method comprises the steps of firstly, adopting an improved constant voltage-based method to enable a system to work at a maximum power point, wherein the improved constant voltage-based method indirectly reserves power in a reserved voltage mode so as to ensure the upper limit and the lower limit of power adjustment, and continuously carrying out MPPT point tracking. The embodiment of the invention realizes maximum power tracking under the reserved power, effectively solves the problem that the common MPPT algorithm such as a common conductivity micro-increment method, a power disturbance method and the like cannot find the maximum power tracking point of the system under the weather change, ensures that the grid-structured photovoltaic energy tube stably operates for a long time to avoid shutdown, and reduces the proportion of the reserved power controlled by the grid-structured machine set.
The constant voltage method (Constant Voltage Tracking, CVT) is an MPPT control algorithm that is simple to control and easy to implement. The main principle is as follows (as shown in fig. 1): when the temperature T is fixed, the position of the MPPT is shifted when the illumination intensity curve S is changed, but the shifted MPPT is positioned on the same vertical line with the original position, if the illumination intensity S is continuously changed, the position of the MPPT is changedAgain, the changed position is still on the same vertical line with the position of the previous MPPT, so, by utilizing the characteristic of MPPT, we can determine the voltage U corresponding to the position of the vertical line MPPT To control the output voltage to maintain the battery output at U MPPT At this point, the system can be operated at the maximum power point. The effect of temperature was ignored in this algorithmic test. In practical applications, regardless of temperature effects, generally, the U of a photovoltaic cell oc ＝KU MPPT U in oc Is open circuit voltage, U MPPT For maximum power point DC bus voltage, K is a proportionality coefficient (generally between 1.2 and 1.28), and U oc Is required to be smaller than the maximum open circuit voltage U ocmax The above procedure can be expressed by the formula (1):
because the photovoltaic control strategy without energy storage is adopted, in order to ensure that the photovoltaic power supply outputs inertia and has primary frequency modulation capability, power reserve is needed, a certain efficiency gap exists in the aspect of maximum power tracking (10-15% less power generation efficiency) compared with a common conductivity micro-increment method and a power disturbance method by a constant voltage method, but the photovoltaic control strategy without energy storage is advantageous in network construction control, because the photovoltaic control strategy without energy storage can stably operate only by reserving more than 20% -30% of power, and particularly MPPT point tracking cannot be realized after the conductivity micro-increment method and the power disturbance method, and long-term stable operation cannot be realized after large illumination fluctuation. The constant voltage method adopts a mode of reserving voltage to reserve power indirectly, is beneficial to better ensuring the upper limit and the lower limit of power adjustment due to poor efficiency in the aspect of maximum power tracking in the early stage, can continuously track MPPT points, and is relatively suitable for the running environment of the network-structured unit.
On the other hand, the photovoltaic grid-formation regulation must run on the right half plane of the MPPT curve, and the analysis process is as follows:
the photovoltaic array P-V curve is shown in FIG. 2, when the DC bus voltage U dc When the voltage is smaller than MPPT point voltageOutput power P of photovoltaic array pv Along with U dc Is increased by an increase in (a); when U is dc When the voltage is larger than the MPPT point voltage, the output power P pv Along with U dc And decreases with increasing numbers. When the load power is P load When U dc May correspond to point a or point a' in fig. 2.
When U is dc At point a, if the load increases by Δp, the photovoltaic power supply will be required to provide excess power to match the load due to the constant voltage and frequency. The dc capacitor thus provides excess power in the form of a discharge which will result in U dc And (3) lowering. U according to P-V characteristics of a photovoltaic array dc Will be P pv And (3) increasing. Therefore, U after the load increases by ΔP dc Will transition from point A to point B, at which point P pv Is P load +Δp. When U is dc At point a, if the load decreases by Δp, the photovoltaic array will similarly charge the capacitor, thereby causing U dc Lifting, U dc Is raised so that P pv And (3) reducing. Thus, U when the load decreases by ΔP dc Will transition from point A to point C, at which point P pv Is P load -ΔP。
It can be seen that U dc Stable at operating point a. In addition, U dc The photovoltaic power supply also has the characteristic similar to a generator in the operating range, and when the load is increased or decreased, the direct-current voltage can be automatically discharged or charged, so that the system is automatically transited to a new balance point, the stability of the alternating-current output voltage and the frequency is always maintained, and no additional control is needed in the whole regulating process. This characteristic makes photovoltaic power sources well suited for application in micro-grids using voltage source control. When U is dc At point a', the opposite is true. If the load increases by delta P, the DC capacitor will discharge, U according to the P-V characteristics of the photovoltaic array dc Will further reduce P pv Thus, unbalance of output power and load power of the photovoltaic array is aggravated, and finally, the phenomenon of voltage collapse of the direct current bus is caused.
And secondly, adopting an algorithm for preventing the voltage breakdown of the direct current bus to directly control the direct current voltage when the photovoltaic is overloaded, so as to realize the suppression of the direct current voltage breakdown.
According to the previous analysis, the photovoltaic power supply will cause the direct current voltage to cross the MPPT point to enter an unstable area when overload occurs, thereby causing the voltage collapse of the direct current bus. It is therefore necessary to study the overload suppression strategy of photovoltaic power sources. Conventional P max The controller can suppress overload of the micro power supply with constant direct-current side voltage, but is not suitable for application in a photovoltaic inverter. Under the influence of illumination change, the MPPT power of the photovoltaic power supply can change, and the maximum power P is difficult to adjust in time max For the actual MPPT power, if P max A power greater than MPPT will cause a breakdown in dc voltage. If the direct voltage can be directly controlled when the photovoltaic is overloaded, the direct voltage breakdown is expected to be restrained. Therefore, the embodiment of the invention introduces an algorithm for preventing the voltage breakdown of the direct current bus, as shown in fig. 3, and the specific implementation steps are as follows:
UP lim ＝k pUdc (U dc -U dc_min )+k iUdc ∫(U dc -U dc_min )dt (2)
wherein DeltaP lim For additional active power reference value not greater than zero, U dc_min To be not more than the minimum DC voltage of the left half plane, k pUdc 、k iUdc The direct current voltage controller is respectively a proportion coefficient and an integral coefficient of the direct current voltage controller, wherein a proportion term is used for improving the response speed of the controller, an integral term is used for eliminating steady-state errors, and an integral term adopts internal limiting to avoid saturation of the controller.
The controller is a PI controller with upper amplitude limit of 0, and the reference input signal is U dc_min The output signal is the active power increment delta P 0 。U dc_min The instruction is U calculated by MPPT of constant voltage method dc_min Representing the lowest voltage that the photovoltaic power supply is allowed to run at steady state. When U is dc Higher than U dc_min When the controller output is 0, the photovoltaic power source works in the sagging characteristic area. When the load increases and exceeds the MPPT power of the photovoltaic power supply, the direct current capacitor is continuously discharged, once U dc Below U dc_min The controller will quickly reduce the active power, will exchange the sideExcess power is transferred to other micro power supplies to make U dc Finally stabilize at U dc_min 。
And thirdly, performing power adjustment by adopting an active power adjustment active support algorithm of the energy-storage-free networking photovoltaic unit and a phase angle self-generation control strategy.
Because the photovoltaic and the energy storage have certain identity in the voltage source characteristic, the embodiment of the invention combines the traditional virtual synchronization method and considers the power regulation reservation, and proposes an active regulation active supporting algorithm and a phase angle self-generation control strategy of the energy-storage-free networking photovoltaic unit, as shown in fig. 4:
the specific implementation process can be expressed by the following formula:
wherein omega is the output angular frequency amplitude command of the converter, theta is the output phase of the converter, omega 0 The output angular frequency of the converter is that J is virtual inertia, P is the average active power output by the converter, and delta P lim For additional active power reference value not greater than zero, P pv For the integrated value after MPPT, reserved power and frequency modulation power, the expression is:
wherein m is w For active-frequency control droop coefficient, P mpp For maximum active power calculated by MPPT curve of constant voltage method, P N For rated power of the photovoltaic power supply, k is the reserved power percentage and is generally 10% -15%, and f is the grid-connected point frequency.
The invention considers the power regulation algorithm and combines the traditional voltage source control algorithm, namely: the voltage-reactive droop control, the virtual impedance algorithm and the voltage-current double-loop control strategy are adopted, and the algorithm for preventing the voltage collapse of the direct-current bus is provided in the step two of the invention, and the whole control block diagram is shown in figure 5.
In the overall control strategy described above, the reactive-voltage sag can be expressed as:
E＝n Q (Q ref -Q)+E N (5)
wherein n is Q Is the reactive-voltage sag coefficient, Q and Q ref Respectively the reactive power of the grid-connected point and the reactive power reference value E N And E is the actual grid-connected point voltage value. The dual loop control strategy and the active technique method in the control block diagram are consistent with the algorithms of other conventional inverters, and the invention is not repeated herein.
In order to verify the effectiveness of the algorithm, the invention carries out multi-dimensional and multi-layer verification work based on a semi-physical simulation platform and an actual engineering site, and the method comprises the following steps:
the test platform mainly comprises a semi-physical simulation controller and an RTLAB simulation model, wherein a real hardware board of a solar power supply device SG500MX-V6 to be modified on site of the semi-physical simulation controller is used as a controller, and voltage source control related software codes of the invention are carried, as shown in figure 6. The RTLAB simulation model is mainly a primary part of a photovoltaic unit and mainly comprises a photovoltaic panel, a three-phase bridge type IGBT device and a filter circuit, as shown in fig. 7.
The analog timer is set to 5s. Initially the local load is pl=400 kW and ql=20 kVar; load increases to pl=420 kW and ql=25 kvar at 1s, 2s restoring the initial value; load was reduced to pl=380 kW and ql=10kvar at 3s and the initial value was restored at 4 s; figures 8-10 show a comparison of the virtual control method with a conventional droop control strategy on the frequency dynamic response curve under sudden load changes.
The results show that the controllers all have good energy storage-like regulation performance. As shown in fig. 8, the system state does not lose stability during both power disturbances and transients. The active power can be flexibly controlled, the reaction time is less than 5ms, the control accuracy is high, the circulation influence cannot occur (figure 10), and the reserved power of the photovoltaic power supply at the MPPT point achieves the ideal effect (figure 9).
And (3) field test simulation verification:
case two gives an example item to verify the validity of the networking control strategy. The mixed renewable energy power station consisting of wind energy and solar energy is positioned in the middle of Hubei province in China. The rated photovoltaic power generation capacity of the station is about 50MW. In view of economy and construction, 60% of photovoltaic units are upgraded to the same voltage source grid controllers as the present invention, and the results of the field tests are shown in fig. 11-13.
The effectiveness of the self-generated phase angle voltage of the photovoltaic station is shown in fig. 11, the PV active power response of the secondary winding of the current transformer under the condition of multiple frequency interference is shown in fig. 12 and 13, and the effectiveness and the correctness of the algorithm in the actual engineering project are verified. Fig. 14 and table 1 show the flexible controllability of the grid-structured photovoltaic unit in reactive voltage regulation. The above results effectively demonstrate the advantages of the technology of the present invention between photovoltaic grids.
Table 1 reactive power regulation capability test for power station
The embodiment of the invention provides a grid-formed photovoltaic unit control method based on a constant voltage method, which adopts a conventional MPPT algorithm such as a conventional conductivity micro-increment method, a power disturbance method and the like to replace a constant voltage method considering voltage collapse of a direct current bus, so that the accurate energy-free grid-formed photovoltaic unit power reservation is realized, and meanwhile, an improved photovoltaic grid-formed voltage outer ring control method is introduced and applied to an engineering site, so that a grid-formed photovoltaic belt whole-station system is realized. The photovoltaic power station network-structured function requirement can be met, and the application scene of the photovoltaic power station in a novel power system is effectively improved.
The foregoing is merely illustrative embodiments of the present invention, and the present invention is not limited thereto, and any changes or substitutions that may be easily contemplated by those skilled in the art within the scope of the present invention should be included in the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.
Claims (7)
1. The energy-storage-free grid-formation photovoltaic unit control method based on the improved constant voltage method is characterized by comprising the following steps of:
the method comprises the steps that firstly, an improved constant voltage-based method is adopted to enable a system to work at a maximum power point, wherein the improved constant voltage-based method adopts a reserved voltage mode to reserve power indirectly so as to ensure the upper limit and the lower limit of power regulation, and MPPT (maximum power point tracking) can be continuously carried out;
adopting an algorithm for preventing the voltage breakdown of the direct current bus to directly control the direct current voltage when the photovoltaic is overloaded so as to inhibit the voltage breakdown of the direct current;
and thirdly, performing power adjustment by adopting an active power adjustment active support algorithm of the energy-storage-free networking photovoltaic unit and a phase angle self-generation control strategy.
2. The method for controlling the non-energy-storage type network-structured photovoltaic unit based on the improved constant voltage method as claimed in claim 1, wherein the method comprises the following steps: the reserved power in the first step is 10% -15%.
3. The method for controlling the non-energy-storage type network-structured photovoltaic unit based on the improved constant voltage method as claimed in claim 1, wherein the method comprises the following steps: in the first step, the photovoltaic net structure operates on the right half plane of the MPPT curve when adjusted by adopting a modified constant voltage method.
4. The method for controlling the non-energy-storage type network-structured photovoltaic unit based on the improved constant voltage method as claimed in claim 1, wherein the method comprises the following steps: the second step adopts an algorithm for preventing the voltage collapse of the direct current bus to directly control the direct current voltage when the photovoltaic is overloaded so as to realize the inhibition of the direct current voltage collapse, and the specific implementation steps are as follows:
ΔP lim ＝k pUdc (U dc -U dc_min )+k iUdc ∫(U dc -U dc_min )dt (2)
wherein DeltaP lim For additional active power reference value not greater than zero, U dc_min To be not more than the minimum DC voltage of the left half plane, k pUdc 、k iUdc The direct current voltage controller is respectively a proportion coefficient and an integral coefficient of the direct current voltage controller, wherein a proportion term is used for improving the response speed of the controller, an integral term is used for eliminating steady-state errors, and an integral term adopts internal limiting to avoid saturation of the controller.
5. The method for controlling the non-energy-storage type network-structured photovoltaic unit based on the improved constant voltage method as claimed in claim 4, wherein the method comprises the following steps: the controller is a PI controller with upper amplitude limit of 0, and the reference input signal is U dc_min The output signal is the active power increment delta P 0 ；U dc_min The instruction is U calculated by MPPT of constant voltage method dc_min Representing the lowest voltage that the photovoltaic power supply is allowed to run at steady state; when U is dc Higher than U dc_min When the output of the controller is 0, the photovoltaic power supply works in a sagging characteristic area; when the load increases and exceeds the MPPT power of the photovoltaic power supply, the direct current capacitor is continuously discharged, once U dc Below U dc_min The controller reduces active power, transfers redundant power at the alternating current side to other micro power sources to enable U to be dc Finally stabilize at U dc_min 。
6. The method for controlling the non-energy-storage type network-structured photovoltaic unit based on the improved constant voltage method as claimed in claim 1, wherein the method comprises the following steps: the third step adopts an active power regulation active support algorithm of the energy-storage-free networking photovoltaic unit and a phase angle self-generation control strategy to carry out power regulation, and the specific implementation steps are as follows:
wherein omega is the output angular frequency amplitude command of the converter, theta is the output phase of the converter, omega 0 The output angular frequency of the converter is that J is virtual inertia, P is the average active power output by the converter, and delta P lim For additional active power reference value not greater than zero, P pv And the integrated value is obtained after MPPT, reserved power and frequency modulation power.
7. The method for controlling the non-energy-storage type network-structured photovoltaic unit based on the improved constant voltage method as claimed in claim 6, wherein the method comprises the following steps: p (P) pv The expression of (2) is:
wherein m is w For active-frequency control droop coefficient, P mpp For maximum active power calculated by MPPT curve of constant voltage method, P N And k is a reserved power percentage, and f is grid-connected point frequency.
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