CN105762834A - Photovoltaic inverter intelligent starting control system - Google Patents
Photovoltaic inverter intelligent starting control system Download PDFInfo
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- CN105762834A CN105762834A CN201610141917.2A CN201610141917A CN105762834A CN 105762834 A CN105762834 A CN 105762834A CN 201610141917 A CN201610141917 A CN 201610141917A CN 105762834 A CN105762834 A CN 105762834A
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- 238000001514 detection method Methods 0.000 claims description 4
- 238000001914 filtration Methods 0.000 abstract description 4
- 238000010586 diagram Methods 0.000 description 3
- 238000010248 power generation Methods 0.000 description 2
- 238000004088 simulation Methods 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
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- H02J3/383—
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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
- 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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Abstract
The invention discloses a photovoltaic inverter intelligent starting control system, comprising a boost circuit, an inverter bridge, a grid connected switch and a controller. The output of the boost circuit is in connection with the inverter bridge through a DC bus; the output of the inverter bridge is in connection with the grid connected switch through a filter; the grid connected switch is connected to a power grid system; the controller samples a bus voltage. The system employs the inverter bridge to generate higher harmonics, improves loss of a main switch devices, a filtering inductor and a filtering capacitor, saves a routine starting resistor, and improves self loss of an inverter under no load conditions, thereby realizing testing of the loading capacity of a solar panel, avoiding inverter frequent starting in the morning, guaranteeing the operation life of the grid connected switch, and reducing a failure rate of a photovoltaic inverter system. The method is realized by a digital controller, does not need to be provided with extra hardware, and possesses the characteristics of intelligence, low cost and strong versatility.
Description
Technical Field
The invention relates to the field of photovoltaic inverters, in particular to an intelligent startup control system of a photovoltaic inverter.
Background
The existing photovoltaic inverter is mainly divided into an industrial power station type and a distributed type, and an alternating current contactor and a relay (hereinafter referred to as a grid-connected switch) are respectively used for realizing the separation control with a power grid. These devices belong to mechanical action switches, and have limited service life, generally thousands of times. In order to ensure the service life of the inverter for more than 10 years, the photovoltaic inverter needs to be switched on and off once in the morning and at night, and the service life is halved after more than one operation in other time periods.
In the morning, the sunlight is weak, and although the output voltage of the battery panel is higher than the peak value of the commercial power, the driving power is insufficient. The inverter generally detects a bus voltage connected with the battery panel as a condition of grid-connected operation, and when the voltage is higher than a mains peak value, grid-connected power generation is performed. However, the inverter has minimum operating power (the inverter generates a large amount of harmonics under low power, and therefore minimum starting power is set), and due to the loss of the inverter, the voltage is pulled down due to insufficient driving power of the battery when the inverter is started, so that the inverter exits a grid-connected state. Therefore, frequent start-stop is caused, and the grid-connected switch is continuously operated, so that the service life is shortened.
Due to the problems, before grid-connected operation, the grid-connected switch can be actuated only after the output power of the solar panel is judged to be enough to support the self loss of the inverter and a certain desired amount is left. The following methods are conventionally used:
the first is to connect a starting resistor at the input side of the photovoltaic inverter, and when the output power of the solar panel is enough to support the energy consumption of the resistor and the stable output voltage still exists, the starting resistor is cut off and the grid-connected switch is closed. The circuit consists of a resistor, a relay and other auxiliary devices, the cost is high, and meanwhile, the service life of the self-contained relay is limited.
The second method is to form a hysteresis loop by the startup voltage and the shutdown voltage of the photovoltaic grid-connected inverter. The starting minimum voltage of the photovoltaic grid-connected inverter and the shutdown voltage during operation form a hysteresis loop, so that frequent startup and shutdown are avoided. The essential of the method is to improve the starting voltage point to ensure that the solar panel has enough power output and then starts the solar panel, although a hardware circuit is removed, the power generation is lost at the cost of delaying the starting time, and the size of the hysteresis loop is related to the type and the configured power grade of the panel, so the application range of the method is limited.
And the third method is that after the inverter bridge generates a voltage with the same frequency, phase and amplitude as the power grid, a mode of judging whether the bus voltage is higher than the peak value of the commercial power is used as a starting method. Although the method reduces the frequency of frequent startup, the system loss and the minimum running power during grid connection are not considered, a detection blind area exists, and the problems cannot be completely solved.
Disclosure of Invention
The invention aims to provide an intelligent startup control system of a photovoltaic inverter, which judges the driving capability of a solar cell panel by using the loss of a switching device and a filter device of the inverter, so as to solve the problems in the background technology.
In order to achieve the purpose, the invention provides the following technical scheme:
the intelligent startup control system of the photovoltaic inverter comprises a booster circuit, an inverter bridge, a grid-connected switch and a controller, wherein the booster circuit comprises an inductor L1 and a switch device A consisting of a triode Q1 and a diode D1, the inverter bridge comprises a switch device B consisting of a triode Q2 and a diode D2, the filter comprises an inductor L2, an inductor L3 and a capacitor C1, the inductor L2 is respectively connected with an inductor L3 and a capacitor C1, and the grid-connected switch comprises a switch K1 and a switch K2; the output of the booster circuit is connected with an inverter bridge through a direct current bus, the output of the inverter bridge is connected with a grid-connected switch after passing through a filter, the grid-connected switch is connected to a power grid system, and a controller samples a bus voltage UDC.
The startup method of the intelligent startup control system of the photovoltaic inverter comprises the following steps: the method comprises the steps that the photovoltaic inverter is electrified and enters startup control, startup self-detection is started, for a two-stage photovoltaic inverter with a booster circuit, the booster circuit works firstly, a controller detects whether bus voltage can be maintained at a preset value, and if bus voltage cannot be maintained to be stable, the startup control is quitted; if the bus voltage is maintained at a preset value, the controller of the photovoltaic inverter calculates harmonic reference voltage as a modulation wave, compares the modulation wave with a DSP carrier counter, and generates a high-frequency PWM signal to drive an inverter bridge to work; the controller detects whether the bus voltage can be maintained at a preset value again, if the bus voltage cannot be maintained to be stable, the controller quits the starting control, and if the bus voltage is maintained to be stable and is above the peak value of the commercial power, the controller pulls in a grid-connected switch to enter the grid-connected control.
Compared with the prior art, the invention has the beneficial effects that:
the invention improves the loss of main switching devices, filter inductors and filter capacitors by controlling the inverter bridge to generate higher harmonics, so that the loss is close to the system loss and the minimum operating power of the inverter during grid-connected operation, the conventional starting resistor is saved, the device cost of the photovoltaic inverter is saved, the risk of damage of the starting resistor and a correlator device is reduced, the high-frequency harmonic mode is generated by the photovoltaic inverter, the self loss of the inverter under no load is improved, the load capacity of a solar cell panel is tested, the problem of frequent starting of the inverter in the morning is prevented, the operating life of the grid-connected switch is ensured, and the fault rate of the photovoltaic inverter system is reduced.
Drawings
FIG. 1 is a schematic structural diagram of the present invention.
Fig. 2 is a schematic diagram of the switching loss of the switching device of the present invention.
Fig. 3 is a schematic diagram of the loss of the inductor and the capacitor in the present invention.
FIG. 4 is a simulation graph of harmonic voltage and current at 50 Hz.
FIG. 5 is a simulation graph of harmonic voltage and current at 350 Hz.
FIG. 6 is a schematic flow chart of the present invention.
In the figure: 101-a boost circuit; 102-an inverter bridge; 103-a filter; 104-a grid-connected switch; 105-a controller.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, in an embodiment of the present invention, an intelligent startup control system for a photovoltaic inverter is suitable for a two-stage photovoltaic inverter system and a single-stage photovoltaic inverter system, where the two-stage photovoltaic inverter system is generally a distributed small photovoltaic inverter, and the single-stage photovoltaic inverter system is generally a centralized large photovoltaic inverter.
The intelligent start-up control system of the two-stage photovoltaic inverter comprises a boosting circuit 101, an inverter bridge 102, a grid-connected switch 104 and a controller 105, wherein the boosting circuit 101 comprises an inductor L1 and a switch device A consisting of a triode Q1 and a diode D1, the inverter bridge 102 comprises a switch device B consisting of a triode Q2 and a diode D2, a filter 103 comprises an inductor L2, an inductor L3 and a capacitor C1, the inductor L1 is respectively connected with an inductor L2 and a capacitor C1, and the grid-connected switch 104 comprises a switch K1 and a switch K2; the output of the booster circuit 101 is connected with the inverter bridge 102 through a direct current bus, the output of the inverter bridge 102 is connected with the grid-connected switch 104 after passing through the filter 103, the grid-connected switch 104 is connected to a power grid system, the controller 105 judges whether to pull in the grid-connected switch 104 or not according to the sampled bus voltage UDC to complete start-up control, the inverter bridge 102 and the filter 103 can be a single-phase system or a three-phase system, the controller 105 detects the bus voltage UDC, when the bus voltage UDC exceeds a mains voltage peak value, the booster circuit 101 and the inverter bridge 102 are started to work, and at the moment, the system enters start-up control.
The intelligent start control system of the single-stage photovoltaic inverter does not comprise a booster circuit 101, and the other structures of the intelligent start control system of the single-stage photovoltaic inverter are the same as those of a two-stage photovoltaic inverter system.
The invention discloses a starting control principle and a control method as follows:
the loss of the photovoltaic inverter intelligent start-up control system mainly comprises an inductor L1, a switching device A, a switching device B, an inductor L2, an inductor L3, a capacitor C1, a controller 105 and auxiliary devices. The main losses, except for the controller 105 and other accessory devices, are concentrated in switching device a, switching device B, inductor L1, inductor L2, inductor L3, and capacitor C1.
Referring to fig. 2, the switching loss power of the switching device is calculated as follows:
（1）
（2）
formula (1) Is the switching loss of the switching device, and accounts for the main part, wherein t1-t2 Is the switching starting and stopping time of the switching device, Is the current value, and Us Is the terminal voltage value; the formula (2) is the conduction loss, and accounts for a minor portion, where Rs is the on-resistance of the switching device.
Referring to fig. 3, the power loss calculation formula of the inductor and the capacitor is as follows:
（3）
（4）
equation (3) is the inductor power loss, equation (4) is the capacitor power loss, IL and IC are the current values through the inductor and capacitor, respectively, and Lr and Cr are the on-resistances of the inductor and capacitor, respectively.
Before the grid-connected switch is closed,
thus, the total power loss is:
（5）
from the formula (5), the loss power of the switching device, the inductor and the capacitor is improved by increasing the current I, so that the loss power is close to the loss of the whole machine and the initial operation power. Therefore, the photovoltaic inverter system can be ensured not to exit from the grid-connected state because the bus voltage is pulled low after grid-connected operation.
Physical formulas of capacitor voltage and current:
（6）
as can be seen from the formula (6), the current flowing through the capacitor C1 can be increased by increasing the output voltage frequency of the inverter bridge 102, such as 13/15/17.
Referring to fig. 4-5, fig. 4 shows the filtering current value of 50Hz voltage, and fig. 5 shows the filtering current value of 350Hz voltage, it can be seen that as the number of harmonics increases, the flowing current value also increases proportionally.
Referring to fig. 6, a startup method of an intelligent startup control system of a photovoltaic inverter includes the following steps: the method comprises the steps that the photovoltaic inverter is electrified to enter startup control, startup self-detection is started, for a two-stage photovoltaic inverter with a booster circuit 101, the booster circuit 101 works firstly, a controller 105 detects whether bus voltage can be maintained at a preset value, and if bus voltage cannot be maintained to be stable, the startup control is quitted; if the bus voltage is maintained at the preset value, the controller 105 of the photovoltaic inverter calculates the harmonic voltage as follows:
（7）
wherein,in order to output the peak value of the voltage,is the fundamental voltage frequency.
Since the pv inverter controller 105 is implemented by a digital controller DSP, the discretization process described above is required, and the discretization method is as follows:
（8）
wherein,is the sampling frequency of the DSP and is,is the harmonic frequency;
according to the formulas (7) and (8), the harmonic voltage reference under digitization can be calculated, the voltage is used as a modulation wave and is compared with a DSP carrier counter, and a high-frequency PWM signal is generated to drive the inverter bridge to work. The controller 105 detects whether the bus voltage can be maintained at a preset value again, if the bus voltage cannot be maintained to be stable, the startup control is quitted, if the bus voltage is maintained to be stable and is above the peak value of the mains supply, the fact that the output power of the solar cell panel is enough to support the self loss and the initial operation power of the inverter is shown, the photovoltaic inverter system quits the startup control, the grid-connected switch 104 is pulled in, and the conventional grid-connected control is started.
According to the invention, the inverter bridge 102 is controlled to generate higher harmonics, so that the loss of main switching devices, inductors and capacitors is improved, the loss is close to the system loss and the minimum operating power of the inverter during grid-connected operation, the conventional starting resistor is omitted, the device cost of the photovoltaic inverter is saved, the risk of damage of the starting resistor and the correlator is reduced, the photovoltaic inverter generates high-frequency harmonics, the loss of the inverter under no load is improved, the load capacity of the solar cell panel is tested, the problem of frequent starting of the inverter in the morning is prevented, the operating life of the grid-connected switch 104 is ensured, and the fault rate of the photovoltaic inverter system is reduced.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Claims (2)
1. The intelligent startup control system for the photovoltaic inverter is characterized by comprising a boosting circuit (101), an inverter bridge (102), a grid-connected switch (104) and a controller (105), wherein the boosting circuit (101) comprises an inductor L1 and a switching device A consisting of a triode Q1 and a diode D1, the inverter bridge (102) comprises a switching device B consisting of a triode Q2 and a diode D2, the filter (103) comprises an inductor L2, an inductor L3 and a capacitor C1, the inductor L1 is respectively connected with an inductor L2 and a capacitor C1, and the grid-connected switch (104) comprises a switch K1 and a switch K2; the booster circuit (101) outputsThe output end of the direct current bus is connected with an inverter bridge (102), the output of the inverter bridge (102) is connected with a grid-connected switch (104) after passing through a filter (103), the grid-connected switch (104) is connected to a power grid system, and a controller (105) samples a bus voltage UDC。
2. The startup method of the intelligent startup control system for the photovoltaic inverter according to claim 1, characterized by comprising the following steps: the photovoltaic inverter is electrified and enters startup control, startup self-detection is started, firstly, a booster circuit (101) works, a controller (105) detects whether the bus voltage can be maintained at a preset value, and if the bus voltage cannot be maintained to be stable, the startup control is quitted; if the bus voltage is maintained at a preset value, a controller (105) of the photovoltaic inverter calculates harmonic reference voltage as a modulation wave, compares the modulation wave with a DSP carrier counter, and generates a high-frequency PWM signal to drive an inverter bridge (102) to work; the controller (105) detects whether the bus voltage can be maintained at a preset value again, if the bus voltage cannot be maintained to be stable, the starting control is quitted, and if the bus voltage is maintained to be stable and is above the peak value of the commercial power, the grid-connected switch (104) is pulled in and the grid-connected control is started.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108649897A (en) * | 2018-07-13 | 2018-10-12 | 江苏佳讯纳通能源技术有限公司 | Long-range photovoltaic string formation IV curve detections system based on GPRS and detection method |
| CN109802556A (en) * | 2017-11-17 | 2019-05-24 | 丰郅(上海)新能源科技有限公司 | The starting method of photovoltaic generating system and inverter with photovoltaic DC-to-AC converter |
| CN112087127A (en) * | 2020-07-23 | 2020-12-15 | 传蔚电气(上海)有限公司 | Inverter startup logic method |
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| CN204258620U (en) * | 2014-09-16 | 2015-04-08 | 山东希格斯新能源有限责任公司 | Photovoltaic DC-to-AC converter starts control device |
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| CN109802556A (en) * | 2017-11-17 | 2019-05-24 | 丰郅(上海)新能源科技有限公司 | The starting method of photovoltaic generating system and inverter with photovoltaic DC-to-AC converter |
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| CN112087127A (en) * | 2020-07-23 | 2020-12-15 | 传蔚电气(上海)有限公司 | Inverter startup logic method |
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