CN109245086B - Photovoltaic direct current system and low voltage ride through control method thereof - Google Patents
Photovoltaic direct current system and low voltage ride through control method thereof Download PDFInfo
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Abstract
The invention provides a photovoltaic direct current system and a low voltage ride through control method thereof, when the voltage of a direct current bus falls, the voltage of the direct current bus and the ride through power of a DC/DC converter are firstly obtained, then according to the ride through power, a voltage value corresponding to the photovoltaic module when the output power of the photovoltaic module is the ride through power is searched on a maximum power tracking curve of the photovoltaic module, the voltage value is taken as the ride through voltage of the corresponding photovoltaic module, and finally the photovoltaic module is controlled to output the ride through power and the ride through voltage. According to the technical scheme provided by the invention, when the voltage of the direct current bus falls off, the original photovoltaic direct current system is not required to be changed, the current of the grid-connected side of the DC/DC converter can be kept unchanged only by controlling the output of the photovoltaic assembly according to the power of the grid-connected side of the DC/DC converter, and the direct current bus cannot impact the DC/DC converter, so that the problem of grid disconnection of the photovoltaic DC/DC converter is solved.
Description
Technical Field
The invention belongs to the technical field of photovoltaic power generation, and particularly relates to a photovoltaic direct current system and a low voltage ride through control method thereof.
Background
With the increasing consumption of traditional energy sources and the increasing severity of environmental problems, people are looking for new energy sources capable of replacing traditional energy sources, and therefore, the new energy sources are more and more valued as clean and pollution-free renewable energy sources such as wind energy and solar energy.
The solar power generation is a technology for converting solar energy into electric energy by utilizing the photovoltaic effect of a photovoltaic module, and the solar power generation equipment mainly comprises the photovoltaic module, a controller and an inverter/converter, wherein the photovoltaic module comprises a solar panel which is packaged and protected after being connected in series, so that a large-area solar module can be formed, and the solar power generation equipment is formed by matching with components such as a power controller and the like.
Mppt (maximum Power Point tracking), namely, maximum Power tracking, detects the generated voltage of the photovoltaic module in real time by using a maximum Power tracking controller, and controls the voltage value and the current value to maximize the output Power of the photovoltaic module.
The principle of the photovoltaic direct-current grid-connected system is shown in fig. 1, and each photovoltaic module is connected with a direct-current bus through a corresponding DC/DC converter. When a direct current bus of the photovoltaic direct current grid-connected system has voltage drop, the stable operation of the system is influenced. The voltage drop of the direct current bus refers to the phenomenon that the voltage amplitude of the direct current bus suddenly deviates from the normal working range at a certain moment, but the voltage amplitude is restored to the normal level after a short period of time. When the voltage of the direct current bus falls, impact is generated on a DC/DC converter which connects the photovoltaic component to the direct current bus, so that output current of the DC/DC converter fluctuates and even overcurrent occurs, the corresponding photovoltaic DC/DC converter is disconnected, the permeability of distributed power generation is reduced, and the photovoltaic DC/DC converter can be burnt seriously. At present, a method for solving the problem of grid disconnection of the photovoltaic DC/DC converter caused by voltage drop of a direct-current bus in the direct-current grid-connected system is not provided.
Disclosure of Invention
The invention aims to provide a photovoltaic direct current system and a low voltage ride through control method thereof, which are used for solving the problem of grid disconnection of a photovoltaic DC/DC converter caused by voltage drop of a direct current bus in a photovoltaic direct current grid-connected system.
In order to achieve the purpose, the technical scheme provided by the invention is as follows:
a low voltage ride through control method of a photovoltaic direct current system comprises the following steps:
(1) acquiring the direct-current bus voltage and the power of the grid-connected side of the DC/DC converter after the voltage drop occurs, and taking the power as ride-through power;
(2) searching a corresponding voltage value when the output power of the photovoltaic module is the ride through power on a maximum power tracking curve of the photovoltaic module, and taking the voltage value as the ride through voltage of the corresponding photovoltaic module;
(3) and controlling the photovoltaic module to output the cross-over voltage and the cross-over power until the voltage of the direct current bus is recovered to be normal.
Further, the ride through voltage is searched within a set range of a maximum power tracking curve of the photovoltaic module.
Further, judging whether the power corresponding to the lower voltage limit value in the maximum power tracking curve of the photovoltaic module is smaller than the power corresponding to the upper voltage limit value; if the value is less than the preset value, the following processing is carried out:
judging whether the voltage of the direct current bus is larger than a voltage value corresponding to the maximum power in the maximum power tracking curve of the photovoltaic module; if the maximum power value is larger than the maximum power value, searching for a ride-through voltage between the voltage lower limit value of the maximum power tracking curve of the photovoltaic module and the voltage value corresponding to the maximum power; and if the voltage value is not larger than the maximum power tracking curve, searching for a ride-through voltage between the voltage lower limit value of the maximum power tracking curve of the photovoltaic module and the voltage value of the direct current bus.
Further, judging whether the power corresponding to the voltage lower limit value of the maximum power tracking curve of the photovoltaic module is larger than the power corresponding to the voltage upper limit value of the maximum power tracking curve of the photovoltaic module; if the value is larger than the preset value, the following processing is carried out:
judging whether the voltage of the direct current bus is larger than a voltage value corresponding to the maximum power in the maximum power tracking curve of the photovoltaic module; if the voltage value is not larger than the maximum power tracking curve, searching through voltage between the voltage lower limit value of the maximum power tracking curve of the photovoltaic module and the voltage value of the direct-current bus; if the value is larger than the preset value, the following processing is carried out:
judging whether the voltage of the direct current bus is larger than a set voltage value or not; if the maximum power value is not larger than the preset maximum power value, searching for a ride-through voltage between the lower voltage limit value of the maximum power tracking curve of the photovoltaic module and the voltage value corresponding to the maximum power of the photovoltaic module; if the maximum power value is larger than the preset maximum power value, searching through voltage between a voltage value corresponding to the maximum power in the maximum power tracking curve of the photovoltaic assembly and a voltage value of the direct-current bus;
in the maximum power tracking curve of the photovoltaic module, when the voltage output by the photovoltaic module is a set value, the corresponding power is equal to the power corresponding to the lower limit value of the voltage.
Further, after the voltage drops, the power of the grid-connected side of the DC/DC converter after the voltage drops is calculated according to the current of the grid-connected side of the DC/DC converter before the voltage drops and the voltage of the direct current bus after the voltage drops.
A photovoltaic direct current system comprises photovoltaic modules, wherein the photovoltaic modules are connected with a direct current bus through corresponding DC/DC converters; the photovoltaic module is also provided with a maximum power tracking controller;
the maximum power tracking controller is used for acquiring the voltage of the direct current bus and the power of the grid-connected side of the DC/DC converter after the voltage drop occurs to the direct current bus, and taking the power as ride-through power;
searching a corresponding voltage value when the output power of the photovoltaic module is the ride through power on a maximum power tracking curve of the photovoltaic module, and taking the voltage value as the ride through voltage of the corresponding photovoltaic module;
and controlling the photovoltaic module to output the cross-over voltage and the cross-over power until the voltage of the direct current bus is recovered to be normal.
Further, the ride through voltage is searched within a set range of a maximum power tracking curve of the photovoltaic module.
Further, judging whether the power corresponding to the lower voltage limit value in the maximum power tracking curve of the photovoltaic module is smaller than the power corresponding to the upper voltage limit value; if the value is less than the preset value, the following processing is carried out:
judging whether the voltage of the direct current bus is larger than a voltage value corresponding to the maximum power in the maximum power tracking curve of the photovoltaic module; if the maximum power value is larger than the maximum power value, searching for a ride-through voltage between the voltage lower limit value of the maximum power tracking curve of the photovoltaic module and the voltage value corresponding to the maximum power; and if the voltage value is not larger than the maximum power tracking curve, searching for a ride-through voltage between the voltage lower limit value of the maximum power tracking curve of the photovoltaic module and the voltage value of the direct current bus.
Further, judging whether the power corresponding to the voltage lower limit value of the maximum power tracking curve of the photovoltaic module is larger than the power corresponding to the voltage upper limit value of the maximum power tracking curve of the photovoltaic module; if the value is larger than the preset value, the following processing is carried out:
judging whether the voltage of the direct current bus is larger than a voltage value corresponding to the maximum power in the maximum power tracking curve of the photovoltaic module; if the voltage value is not larger than the maximum power tracking curve, searching through voltage between the voltage lower limit value of the maximum power tracking curve of the photovoltaic module and the voltage value of the direct-current bus; if the value is larger than the preset value, the following processing is carried out:
judging whether the voltage of the direct current bus is larger than a set voltage value or not; if the maximum power value is not larger than the preset maximum power value, searching for a ride-through voltage between the lower voltage limit value of the maximum power tracking curve of the photovoltaic module and the voltage value corresponding to the maximum power of the photovoltaic module; if the maximum power value is larger than the preset maximum power value, searching through voltage between a voltage value corresponding to the maximum power in the maximum power tracking curve of the photovoltaic assembly and a voltage value of the direct-current bus;
in the maximum power tracking curve of the photovoltaic module, when the voltage output by the photovoltaic module is a set value, the corresponding power is equal to the power corresponding to the lower limit value of the voltage.
Further, after the voltage drops, the power of the grid-connected side of the DC/DC converter after the voltage drops is calculated according to the current of the grid-connected side of the DC/DC converter before the voltage drops and the voltage of the direct current bus after the voltage drops.
The invention has the beneficial effects that: according to the technical scheme provided by the invention, when the voltage of the direct current bus falls off, the original photovoltaic direct current system is not required to be changed, the current of the grid-connected side of the DC/DC converter can be kept unchanged only by controlling the output of the photovoltaic assembly according to the power of the grid-connected side of the DC/DC converter, and the direct current bus cannot impact the DC/DC converter, so that the problem of grid disconnection of the photovoltaic DC/DC converter is solved.
The crossing voltage of the photovoltaic module can be quickly searched on the maximum power tracking curve of the photovoltaic module by setting the search range of the crossing power.
Drawings
FIG. 1 is a schematic structural diagram of a photovoltaic DC system in a system embodiment;
FIG. 2 is a diagram illustrating a relationship between an output voltage, an output power, and a DC bus voltage of a photovoltaic module under a first operating condition in an embodiment of a system;
FIG. 3 is a diagram illustrating a relationship between photovoltaic module output voltage, output power, and DC bus voltage under a second operating condition in an embodiment of the system;
FIG. 4 is a control flow diagram of a DC/DC converter in a first operating mode in an embodiment of the system;
FIG. 5 is a flow chart illustrating control of the DC/DC converter in a second operating mode in an embodiment of the system;
FIG. 6 is a diagram illustrating simulation results of the low voltage ride through method in the system embodiment.
Detailed Description
The invention aims to provide a photovoltaic direct current system and a low voltage ride through control method thereof, which are used for solving the problem of grid disconnection of a photovoltaic module caused by voltage drop of a direct current bus in a direct current grid-connected system.
In order to achieve the purpose, the technical scheme provided by the invention is as follows:
a low voltage ride through control method of a photovoltaic direct current system comprises the following steps:
(1) acquiring the direct-current bus voltage and the power of the grid-connected side of the DC/DC converter after the voltage drop occurs, and taking the power as ride-through power;
(2) searching a corresponding voltage value when the output power of the photovoltaic module is the ride through power on a maximum power tracking curve of the photovoltaic module, and taking the voltage value as the ride through voltage of the corresponding photovoltaic module;
(3) and controlling the photovoltaic module to output the cross-over voltage and the cross-over power until the voltage of the direct current bus is recovered to be normal.
The following further describes embodiments of the present invention with reference to the drawings.
The embodiment of the system is as follows:
the embodiment provides a photovoltaic direct current system, a topological structure of which is shown in fig. 1, photovoltaic modules PV are connected to a direct current bus through corresponding DC/DC converters, the photovoltaic modules PV are used for generating power, that is, solar energy is converted into electric energy, because voltage generated during power generation of the photovoltaic modules cannot be directly input into the direct current bus, the corresponding DC/DC converters are arranged on a line connecting the photovoltaic modules PV with the direct current bus, and each photovoltaic module is provided with a corresponding maximum power tracking controller in order to ensure efficiency of photovoltaic power generation.
When the voltage of the direct current bus falls, the maximum power tracking controller is needed to regulate the output voltage and the output power of the photovoltaic module, so that the photovoltaic module is not disconnected from the network, and the electric energy can be transmitted to the direct current bus by the maximum power which can be output currently, and the specific control method comprises the following steps:
the method comprises the following steps: when the voltage of the direct current bus falls, acquiring the current of the grid-connected side of the DC/DC converter before the voltage falls and the voltage of the direct current bus after the voltage falls, wherein the voltage of the direct current bus is the voltage of the grid-connected side of the DC/DC converter;
step two: calculating the power of the grid-connected side of the DC/DC converter according to the current of the grid-connected side of the DC/DC converter before voltage drop and the voltage of the grid-connected side of the DC/DC converter after the voltage drop, and taking the power as ride-through power;
step three: searching a corresponding voltage value when the output power of the photovoltaic module is the ride through power on a maximum power tracking curve of the photovoltaic module, and taking the voltage value as the ride through voltage of the corresponding photovoltaic module;
step four: and controlling the photovoltaic module to input the ride-through voltage and the ride-through power to the corresponding DC/DC converter until the voltage of the direct current bus is recovered to be normal.
Because the maximum power tracking curves of the photovoltaic modules under different working conditions are also different, the methods for searching the ride-through voltage for the photovoltaic modules under different working conditions in the third step are also different, and the specific steps are as follows:
(1) judging the working condition of the photovoltaic module; when the power corresponding to the lower voltage limit value in the maximum power tracking curve of the photovoltaic module is smaller than the power corresponding to the upper voltage limit value, as shown in fig. 2, the photovoltaic module belongs to a first working condition; when the power corresponding to the lower limit value of the voltage in the maximum power tracking curve of the photovoltaic module is greater than the power corresponding to the upper limit value of the voltage, as shown in fig. 3, the photovoltaic module belongs to a second working condition;
for the photovoltaic module under the first working condition, the process flow of the method for searching for the ride-through voltage is shown in fig. 4:
when the voltage drops, if the voltage of the direct current bus is smaller than a voltage value Umppt corresponding to a maximum power Pmppt in a maximum power tracking curve of the photovoltaic module, that is, in an area between a and B in the maximum power tracking curve shown in fig. 2, for example, the voltage value of the direct current bus is U1; searching for a ride-through voltage in a range between A and U1 shown in FIG. 2, namely searching for the ride-through voltage in a voltage range between a lower voltage limit Umin and a voltage U1 of a maximum power tracking curve, wherein the corresponding power of the ride-through voltage in the maximum power tracking curve is the ride-through power;
if the voltage of the direct current bus is greater than the voltage value Umppt corresponding to the maximum power Pmppt in the maximum power tracking curve of the photovoltaic module, that is, in the region between B and D shown in fig. 2, if the voltage value of the direct current bus is U2, if the cross voltage is searched in the range between B and U2, if the cross voltage is not searched, the cross voltage is also searched in the region between a and B, therefore, in this embodiment, the cross voltage is directly searched in the region between a and B, that is, in the voltage range between the lower voltage limit value Umin of the maximum power tracking curve and the voltage value Umppt corresponding to the maximum power Pmppt, and the corresponding power of the cross voltage in the maximum power tracking curve is the cross power;
when the voltage of the direct current bus is greater than the upper voltage value limit Umax of the maximum power tracking curve of the photovoltaic module, such as the voltage U3 shown in fig. 2, the manner of searching the ride-through voltage at this time is the same as the manner of searching when the direct current voltage is U2.
For the photovoltaic module under the second working condition, the process flow of the method for searching for the ride-through voltage is shown in fig. 5:
when the voltage drops, if the voltage of the direct current bus is smaller than a voltage value Umppt corresponding to a maximum power Pmppt in a maximum power tracking curve of the photovoltaic module, that is, in an area between a and B in the maximum power tracking curve shown in fig. 3, for example, the voltage value of the direct current bus is U1; searching for a ride-through voltage in a range between A and U1 shown in FIG. 3, namely searching for the ride-through voltage in a voltage range between a lower voltage limit Umin and a voltage U1 of a maximum power tracking curve, wherein the corresponding power of the ride-through voltage in the maximum power tracking curve is the ride-through power;
if the voltage of the direct current bus is greater than a voltage value Umppt corresponding to the maximum power Pmpt in the maximum power tracking curve of the photovoltaic module, judging whether the electricity of the direct current bus is less than the voltage Us, if so, the voltage of the direct current bus is in a region between B and C shown in the figure 3, and if so, the voltage value of the direct current bus is U2; if the crossing voltage is searched in the range between B and U2, when the crossing voltage cannot be searched, the crossing voltage is searched in the region between A and B, therefore, in the embodiment, the crossing voltage is directly searched in the region between A and B, namely, in the voltage range between the lower voltage limit value Umin of the maximum power tracking curve and the voltage value Umppt corresponding to the maximum power Pmppt, and the power corresponding to the crossing voltage in the maximum power tracking curve is the crossing power;
in a maximum power tracking curve of the photovoltaic module, the power Pc corresponding to the voltage Us is the same as the power Pa corresponding to the voltage lower limit value Umin;
if the voltage of the direct current bus is greater than the voltage Us, that is, the voltage of the direct current bus is in a region between C and D as shown in fig. 3, for example, the voltage value of the direct current bus is U3, then a through voltage is searched between B and U3, that is, a through voltage is searched in a voltage range between a voltage value Umppt corresponding to the maximum power tracking curve maximum power Pmppt and a voltage value U3, and the power corresponding to the through voltage in the maximum power tracking curve is the through power;
when the voltage of the direct current bus is greater than the upper voltage value limit Umax of the maximum power tracking curve of the photovoltaic module, such as the voltage U4 shown in fig. 3, the manner of searching the ride-through voltage at this time is the same as the manner of searching when the direct current voltage is U3.
The effect of performing the low voltage ride through according to the above method is shown in fig. 6, where the dc bus voltage before the drop is 700V, the maximum power point voltage of the PV module is about 410V, the output current is about 23.5A, and the dc bus voltage drops to 450V at 0.15 s. According to the low-voltage ride-through method, the photovoltaic DC/DC converter quickly reduces the power of the PV assembly to ride-through power, then performs power tracking on the basis of the voltage (about 320V) corresponding to the ride-through power and keeps the output current (power) unchanged, so that the ride-through and fall-through time of the system is ensured, the voltage of the direct-current bus is recovered to a normal value at the moment of 0.3s, and the photovoltaic DC/DC converter recovers maximum power tracking to enable the output power of the photovoltaic DC/DC converter to reach the level before voltage drop.
The method comprises the following steps:
the present embodiment provides a low voltage ride through control method of a photovoltaic dc system, which is the same as the low voltage ride through control method of the photovoltaic dc system in the above system embodiments, and has been described in detail previously, and will not be described herein.
Claims (6)
1. A low voltage ride through control method of a photovoltaic direct current system is characterized by comprising the following steps:
(1) acquiring the direct-current bus voltage and the power of the grid-connected side of the DC/DC converter after the voltage drop occurs, and taking the power as ride-through power;
(2) searching a corresponding voltage value when the output power of the photovoltaic module is the ride through power in a set range on a maximum power tracking curve of the photovoltaic module, and taking the voltage value as the ride through voltage of the corresponding photovoltaic module;
comparing and judging the power corresponding to the lower voltage limit value and the power corresponding to the upper voltage limit value in the maximum power tracking curve of the photovoltaic module;
if the power corresponding to the lower voltage limit value in the maximum power tracking curve of the photovoltaic module is smaller than the power corresponding to the upper voltage limit value, the following processing is carried out: judging whether the voltage of the direct current bus is larger than a voltage value corresponding to the maximum power in the maximum power tracking curve of the photovoltaic module; if the maximum power value is larger than the maximum power value, searching for a ride-through voltage between a voltage value corresponding to the maximum power of the maximum power tracking curve of the photovoltaic assembly and a voltage value of the direct-current bus, and if the voltage value is not searched, searching for the ride-through voltage between a voltage lower limit value of the maximum power tracking curve of the photovoltaic assembly and the voltage value corresponding to the maximum power; if the voltage value is not larger than the maximum power tracking curve, searching through voltage between the voltage lower limit value of the maximum power tracking curve of the photovoltaic module and the voltage value of the direct-current bus;
(3) and controlling the photovoltaic module to output the cross-over voltage and the cross-over power until the voltage of the direct current bus is recovered to be normal.
2. The method according to claim 1, wherein after comparing and determining the power corresponding to the lower voltage limit and the power corresponding to the upper voltage limit in the maximum power tracking curve of the photovoltaic module, if the power corresponding to the lower voltage limit of the maximum power tracking curve of the photovoltaic module is greater than the power corresponding to the upper voltage limit, the following steps are performed:
judging whether the voltage of the direct current bus is larger than a voltage value corresponding to the maximum power in the maximum power tracking curve of the photovoltaic module; if the voltage value is not larger than the maximum power tracking curve, searching through voltage between the voltage lower limit value of the maximum power tracking curve of the photovoltaic module and the voltage value of the direct-current bus; if the value is larger than the preset value, the following processing is carried out:
judging whether the voltage of the direct current bus is larger than a set voltage value or not; if the maximum power value is not larger than the preset maximum power value, searching for a ride-through voltage between the lower voltage limit value of the maximum power tracking curve of the photovoltaic module and the voltage value corresponding to the maximum power of the photovoltaic module; if the maximum power value is larger than the preset maximum power value, searching through voltage between a voltage value corresponding to the maximum power in the maximum power tracking curve of the photovoltaic assembly and a voltage value of the direct-current bus;
in the maximum power tracking curve of the photovoltaic module, when the voltage output by the photovoltaic module is a set value, the corresponding power is equal to the power corresponding to the lower limit value of the voltage.
3. The method according to claim 1, wherein after a voltage drop occurs, the power of the grid-connected side of the DC/DC converter after the voltage drop is calculated according to the current of the grid-connected side of the DC/DC converter before the voltage drop occurs and the voltage of the DC bus after the voltage drop occurs.
4. A photovoltaic direct current system comprises photovoltaic modules, wherein the photovoltaic modules are connected with a direct current bus through corresponding DC/DC converters; the photovoltaic module is also provided with a maximum power tracking controller;
the maximum power tracking controller is used for acquiring the voltage of the direct current bus and the power of the grid-connected side of the DC/DC converter after the voltage drop of the direct current bus occurs and taking the power as ride-through power;
searching a corresponding voltage value when the output power of the photovoltaic module is the ride through power in a set range on a maximum power tracking curve of the photovoltaic module, and taking the voltage value as the ride through voltage of the corresponding photovoltaic module; comparing and judging the power corresponding to the lower voltage limit value and the power corresponding to the upper voltage limit value in the maximum power tracking curve of the photovoltaic module;
if the power corresponding to the lower voltage limit value in the maximum power tracking curve of the photovoltaic module is smaller than the power corresponding to the upper voltage limit value, the following processing is carried out: judging whether the voltage of the direct current bus is larger than a voltage value corresponding to the maximum power in the maximum power tracking curve of the photovoltaic module; if the maximum power value is larger than the maximum power value, searching for a ride-through voltage between a voltage value corresponding to the maximum power of the maximum power tracking curve of the photovoltaic assembly and a voltage value of the direct-current bus, and if the voltage value is not searched, searching for the ride-through voltage between a voltage lower limit value of the maximum power tracking curve of the photovoltaic assembly and the voltage value corresponding to the maximum power; if the voltage value is not larger than the maximum power tracking curve, searching through voltage between the voltage lower limit value of the maximum power tracking curve of the photovoltaic module and the voltage value of the direct-current bus;
and controlling the photovoltaic module to output the cross-over voltage and the cross-over power until the voltage of the direct current bus is recovered to be normal.
5. The photovoltaic direct current system according to claim 4, wherein after comparing and judging the power corresponding to the lower voltage limit value and the power corresponding to the upper voltage limit value in the maximum power tracking curve of the photovoltaic module, if the power corresponding to the lower voltage limit value of the maximum power tracking curve of the photovoltaic module is greater than the power corresponding to the upper voltage limit value, the following processing is performed:
judging whether the voltage of the direct current bus is larger than a voltage value corresponding to the maximum power in the maximum power tracking curve of the photovoltaic module; if the voltage value is not larger than the maximum power tracking curve, searching through voltage between the voltage lower limit value of the maximum power tracking curve of the photovoltaic module and the voltage value of the direct-current bus; if the value is larger than the preset value, the following processing is carried out: judging whether the voltage of the direct current bus is larger than a set voltage value or not; if the maximum power value is not larger than the preset maximum power value, searching for a ride-through voltage between the lower voltage limit value of the maximum power tracking curve of the photovoltaic module and the voltage value corresponding to the maximum power of the photovoltaic module; if the maximum power value is larger than the preset maximum power value, searching through voltage between a voltage value corresponding to the maximum power in the maximum power tracking curve of the photovoltaic assembly and a voltage value of the direct-current bus;
in the maximum power tracking curve of the photovoltaic module, when the voltage output by the photovoltaic module is a set value, the corresponding power is equal to the power corresponding to the lower limit value of the voltage.
6. The photovoltaic direct current system according to claim 4, wherein after the voltage drop occurs, the power of the grid-connected side of the DC/DC converter after the voltage drop is calculated according to the current of the grid-connected side of the DC/DC converter before the voltage drop occurs and the voltage of the direct current bus after the voltage drop occurs.
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| CN102170142A (en) * | 2011-04-22 | 2011-08-31 | 河海大学 | Low-voltage ride-through method for photovoltaic inverter |
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| CN104269878A (en) * | 2014-07-29 | 2015-01-07 | 西安交通大学 | Low-voltage ride through control method for grid-connected photovoltaic power generation system capable of providing reactive support |
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