CN110824272A - Island detection method and island detection system - Google Patents
Island detection method and island detection system Download PDFInfo
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Abstract
The invention provides an island detection method, which is characterized in that the directional error of the voltage phase angle of a power grid is superposed on a reactive current instruction as disturbance quantity positive feedback so as to adjust the reactive power output of a grid-connected inverter, when a power grid contactor is disconnected and an island effect occurs, the frequency deviation of the voltage of a grid-connected point causes the generation of the directional angle error, further, the reactive current instruction performs positive feedback adjustment, the frequency deviation degree of the voltage of the grid-connected point is increased, and finally, a threshold value is exceeded, a detection system is triggered to perform passive protection, and the machine is stopped successfully. The island detection method and the island detection system eliminate the island detection blind zone, have simple control and can quickly and accurately detect the inverter island; meanwhile, the quality of electric energy is not influenced during grid-connected operation.
Description
Technical Field
The invention relates to the technical field of grid-connected power generation, in particular to an island detection method and an island detection system.
Background
As an energy exchange device between renewable energy and a power grid, a grid-connected inverter has been widely applied to new energy power generation systems including wind power generation, photovoltaic power generation, wave power generation, and the like. The distributed power generation system generally comprises a new energy power generation device, a local load and a power distribution network, and the load is supplied with power by a grid-connected inverter and a power grid together.
When the grid is disconnected with the inverter due to faults or circuit cutting and the like, the grid-connected inverter is connected with the load, the grid-connected point loses the support of voltage and frequency, the amplitude and the frequency of the grid-connected point voltage are determined by the characteristics of the local load and the output power of the inverter, and at the moment, an island effect can occur, so that the system cannot be automatically stopped. When the islanding effect occurs, the grid-connected point voltage is not in a rated state, which may deteriorate the operation performance of the user equipment, and more importantly, the islanding effect may cause the line which should be shut down to still operate in a live-line manner, which brings potential danger to operation and maintenance personnel and users of the power system. Therefore, the island detection and anti-island operation technology in the field of grid-connected inverter off/grid-connected operation control has obvious significance for guaranteeing the safe operation of the grid-connected inverter.
Currently, practical island detection methods can be classified into passive island detection and active island detection according to detection mechanisms. The passive island detection method generally monitors the amplitude and frequency of the voltage of a grid-connected point in real time, and when the amplitude or frequency exceeds the limit, a grid-connected inverter triggers protection and stops the grid-connected inverter when the grid-connected point is disconnected. But only triggered when the voltage amplitude or frequency exceeds a threshold, so this scheme has a relatively distinct Detection dead Zone (NDZ) when the islanding occurs. The active island detection is that a small amount of active current is injected into a power grid, so that the frequency of the voltage of a grid-connected point of an inverter forms a phenomenon of continuous upward adjustment or downward adjustment when the inverter is disconnected from the power grid, the frequency exceeds a threshold value, and the passive island detection is triggered. However, in the active detection method, disturbance needs to be injected into active power at a steady state, which deteriorates power quality. Meanwhile, for the resistance-capacitance load, a larger detection blind area exists in the scheme.
Disclosure of Invention
In view of the above disadvantages of the prior art, an object of the present invention is to provide an island detection method and an island detection system, which are used to solve the problems in the prior art that an island detection blind area is large and the quality of the output power of the inverter is affected by the injection disturbance.
In order to achieve the purpose, the invention adopts the following scheme:
an island detection method comprising the steps of: collecting voltage signals of a grid connection point, and acquiring an angle orientation error value of the voltage signals; carrying out proportional differential adjustment on the angle orientation error value to obtain the disturbance quantity of a reactive power instruction of the grid-connected inverter; superposing the disturbance quantity of the reactive power instruction on a reactive current instruction of the grid-connected inverter so as to control the reactive power output of the grid-connected inverter; detecting various parameters of the grid-connected point voltage in real time, comparing the parameters with a preset threshold range, and judging that an island is generated if any one of the parameters exceeds the threshold range.
In an embodiment of the present invention, after the voltage signal of the grid-connected point is collected, a step of performing Park transformation on the collected voltage signal of the grid-connected point is further included, and the Park transformation is used to transform the collected three-phase voltage of the grid-connected point into a synchronous rotating coordinate system.
In an embodiment of the present invention, the superimposing the disturbance amount of the reactive power command on the grid-connected inverter reactive current command to control the grid-connected inverter reactive power output includes: comparing the reactive current output by the grid-connected inverter with the reactive current instruction superimposed with the disturbance quantity to obtain a first difference value; comparing the active current output by the grid-connected inverter with the active current instruction to obtain a second difference value; carrying out proportional integral adjustment on the first difference value and the second difference value, and outputting a voltage modulation instruction under a synchronous rotating coordinate system; performing Park inverse transformation on the voltage modulation command under the synchronous rotation coordinate system to convert the voltage modulation command into a three-phase voltage modulation command; and performing pulse width modulation on the three-phase voltage modulation command to obtain a switch control signal of the grid-connected inverter so as to control the reactive power output of the grid-connected inverter.
In an embodiment of the present invention, the pulse width modulation of the three-phase voltage modulation command includes performing sinusoidal pulse width modulation or space vector pulse width modulation on the three-phase voltage modulation command.
In an embodiment of the present invention, the detecting of each parameter of the grid-connected point voltage in real time includes detecting an amplitude and a frequency of the grid-connected point voltage in real time.
In an embodiment of the present invention, after it is determined that the islanding is generated, the method further includes a step of controlling the grid-connected inverter to stop inverting.
The invention also designs an island detection system, which comprises: the sampling module is used for sampling voltage signals and current signals of grid-connected points; the phase-locked loop is used for performing phase locking on the voltage signal of the grid-connected point and outputting an angle orientation error value of the voltage of the grid-connected point; the proportional differential regulator is used for carrying out proportional differential regulation on the angle orientation error value to obtain the disturbance quantity of the reactive power instruction of the grid-connected inverter; the adder is used for superposing the disturbance quantity of the reactive power instruction on a reactive current instruction of the grid-connected inverter; the reactive power control module is used for controlling the reactive power output of the grid-connected inverter according to the reactive current instruction superposed with the disturbance quantity; and the comparison and judgment module is used for detecting various parameters of the grid-connected point voltage, comparing the various parameters with a preset threshold range and judging whether an island is generated.
In an embodiment of the present invention, the island detection system further includes a Park transformation module, and the Park transformation module is configured to transform the three-phase voltage of the grid-connected point into a synchronous rotating coordinate system.
In an embodiment of the present invention, the reactive power control module includes: the first comparator is used for comparing the reactive current output by the grid-connected inverter with the reactive current command superimposed with the disturbance quantity to obtain a first difference value; the second comparator is used for comparing the active current output by the grid-connected inverter with the active current instruction to obtain a second difference value; the proportional integral regulator is used for performing proportional integral regulation on the first difference value and the second difference value and outputting a voltage modulation instruction under a synchronous rotation coordinate system; the Park inverse transformation module is used for carrying out Park inverse transformation on the voltage modulation command under the synchronous rotating coordinate system and transforming the voltage modulation command into a three-phase voltage modulation command; and the modulation module is used for carrying out pulse width modulation on the three-phase voltage modulation command to obtain a switch control signal of the grid-connected inverter so as to control the reactive power output of the grid-connected inverter.
In an embodiment of the present invention, the modulation module is a sine pulse width modulator or a space vector pulse width modulator.
In an embodiment of the present invention, the island detection system further includes an execution module, and the execution module is configured to control the grid-connected inverter to stop when the comparison and judgment module judges that an island is generated.
As described above, according to the island detection method and the island detection system disclosed by the invention, the directional error of the grid voltage phase angle is superposed on the reactive current instruction as the disturbance quantity positive feedback, so that the reactive power output of the grid-connected inverter is controlled. During normal grid-connected operation, grid-connected voltage is clamped by the voltage of a power grid, so that small positive feedback disturbance cannot influence the normal operation of a system; when the power grid contactor is disconnected and an island effect occurs, the frequency deviation of the voltage of the grid-connected point can cause the generation of an orientation angle error, a reactive current instruction is further adjusted in a positive feedback mode, the frequency deviation degree of the voltage of the grid-connected point is increased, a threshold value is finally exceeded, the detection system is triggered to perform passive protection, and the power grid is shut down successfully.
The island detection method eliminates the island detection blind zone, is simple to control, and can quickly and accurately detect the inverter island; compared with the existing active disturbance scheme, the scheme has the advantage of good steady-state power quality; the grid-connected inverter can be applied to distributed energy units such as wind power generation, solar power generation, fuel cells and the like, and is wide in application range, including being applied to a unidirectional distributed grid-connected power generation system and a three-phase distributed grid-connected power generation system.
Drawings
Fig. 1 is a topology structure diagram of a grid-connected inverter with a local load.
Fig. 2 is a waveform diagram of a grid-connected point voltage and a grid-connected inverter output current before and after a passive island detection in the prior art is successful.
Fig. 3 is a waveform diagram of a grid-connected point voltage and a grid-connected inverter output current before and after a passive island detection failure in the prior art.
Fig. 4 is a flowchart of an island detection method according to an embodiment of the invention.
Fig. 5 is a waveform diagram of the grid-connected point voltage and the grid-connected inverter output current after the islanding is detected by the method of the present invention.
Fig. 6 is a waveform diagram of the grid-connected point voltage frequency after the islanding is detected by the method of the present invention.
Fig. 7 is an island detection system and a control block diagram thereof according to the present invention.
Description of the element reference numerals
1 phase-locked loop
2-ratio differential regulator
3 adder
4 reactive power control module
41 first comparator
42 second comparator
43 proportional-integral regulator
44 Park inverse transformation module
45 modulation module
5 Park conversion module
S1-S4 Steps 1-4
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict.
It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention, and although the drawings only show the components related to the present invention and are not drawn according to the number, shape and size of the components in the actual implementation, the type, quantity and proportion of the components in the actual implementation can be changed freely, and the layout of the components can be more complicated.
Example 1
The invention provides an island detection method which is suitable for a grid-connected inverter adopting grid voltage orientation, wherein the grid-connected inverter is provided with a local load, and the local load can be any combination of a pure resistive load, an inductive load and a capacitive load.
Referring to fig. 1, a grid-connected inverter topology with a local load (RLC), where point a is a grid-connected point, and a power equation thereof can be described as:
Pload+jQload＝(Pinv+ΔP)+j(Qinv+ΔQ)
wherein, PloadActive power consumed for local loads, QloadReactive power consumed for local loads, PinvActive power, Q, for output of the grid-connected inverterinvWhen the current flowing into the power grid from the local load of the grid-connected point is not zero, namely the grid-connected inverter has power exchange with the power grid and the local load, the requirements are met: i Δ P + j Δ Q | > 0.
At this point, when the grid contactor S1 is open, the grid inverter will still be supplying power to the local load before the grid inverter has not blocked the pulse. Considering that the power on the local load versus the grid-connected point voltage/frequency relationship satisfies the following relationship whether or not the grid contactor S1 is open:
then, the following conclusions can be drawn:
the above formula shows that when the output power of the grid-connected inverter is not matched with the rated power of the local load, the power grid disconnection contactor can cause at least one of the voltage amplitude and the frequency of the grid-connected point to be obviously changed, at the moment, the island detection can be completed only by observing the voltage vector of the grid-connected point in real time in the grid-connected inverter, and the grid-connected inverter can also automatically disconnect from the grid. As shown in fig. 2, when the grid-connected inverter output power does not match the local load rated power, the waveform of the grid-connected point voltage and the waveform of the grid-connected inverter output current after the grid contactor is turned off are given.
However, when the current of the grid-connected point to the grid is close to zero, namely Δ P + j Δ Q ≈ 0, the output power of the grid-connected inverter and the rated power of the local load are in a power balance state or a state close to a balance state, namely, the current flowing to the grid through the grid-connected point is very small, at this time, the contactor S1 is disconnected, the system formed by the grid-connected inverter and the local load can still keep a state before grid disconnection, at this time, the grid-connected inverter control system cannot automatically judge the grid disconnection state, so that the grid-connected inverter cannot automatically stop, namely, an island effect is generated. Fig. 3 shows the waveform of the grid-connected point voltage under the islanding effect and the waveform of the output current of the grid-connected inverter.
Aiming at the situation that an island cannot be accurately detected in the state that the output power of the grid-connected inverter and the rated power of the local load are balanced, the invention discloses an island detection method which can quickly and accurately detect the island phenomenon, has no detection blind area and does not influence the power quality, and please refer to fig. 4, wherein the detection method specifically comprises the following steps:
s1, collecting voltage signals of the grid-connected point, and acquiring an angle orientation error value of the voltage signals;
s2, carrying out Proportional differential control (PD) on the angle orientation error value to obtain the disturbance quantity of the reactive power instruction of the grid-connected inverter;
s3, superposing the disturbance quantity of the reactive power instruction on the reactive current instruction of the grid-connected inverter to control the reactive power output of the grid-connected inverter;
s4, detecting each parameter of the grid-connected point voltage in real time, comparing the parameters with a preset threshold range, and judging that an island is generated if any one of the parameters exceeds the threshold range.
Because the disturbance quantity of the reactive power instruction is superposed on the reactive current instruction of the grid-connected inverter, a smaller positive feedback is superposed on a current loop equivalently. During normal grid-connected operation, grid-connected voltage is clamped by the voltage of a power grid, so that the normal operation of the system cannot be influenced by small positive feedback disturbance. When the power grid contactor is disconnected and an island effect occurs, because the power grid voltage cannot be clamped, the frequency of the grid-connected point voltage and the rated frequency can have small deviation, so that the deviation of the actual angle and the directional angle is caused, the deviation is used as the disturbance quantity of reactive power and is superposed on the reactive current after proportional differential control to form a reactive current positive feedback loop, and at the moment, the frequency of the grid-connected point voltage meets the following relation:
further, it is found that:
wherein f is0、f1The grid fundamental frequency and the grid connection point frequency H of the power grid contactor without island detection after disconnection are respectivelyD(s) is a proportional-derivative equivalent transfer function, H ═ HD(s)/s, s being a complex variable in the Laplace transform, Δ VqAs a measure of the directional error of the mains voltage, C0For constants only related to system state and system parameters, it can be seen that the grid-connected point frequency after introducing positive feedback can be significantly shifted as long as the controller parameters are adjusted such that k ≈ 1. In particular, when the system is in a grid-connected state, f is satisfiedg＝f0＝f1The introduction of positive feedback does not have any effect on the system frequency.
The amplitude and the frequency of the grid-connected point voltage need to be detected in real time and compared with a preset threshold range, and if the voltage peak value of the voltage signal of the grid-connected point exceeds the preset voltage range or the frequency of the voltage signal of the grid-connected point exceeds the preset frequency range, an island is judged to be generated. At this time, the grid-connected inverter is controlled to stop inverting and disconnect the grid-connected inverter from the local load.
It should be noted that the island detection method of the present invention is implemented based on a synchronous rotating coordinate system, and further includes a step of performing Park conversion on the three-phase voltage and the three-phase current after the three-phase voltage and the three-phase current of the grid-connected point are collected, and the step is used for converting the three-phase voltage and the three-phase current into the synchronous rotating coordinate system.
As an example, controlling the reactive power output of the grid-connected inverter specifically includes the following steps:
firstly, comparing the reactive current output by the grid-connected inverter with a reactive current instruction superposed with a disturbance amount to obtain a first difference value, and outputting a reactive voltage modulation instruction after performing Proportional Integral Control (PI) on the first difference value; meanwhile, the active current output by the grid-connected inverter is compared with the active current instruction to obtain a second difference value, and the active voltage modulation instruction is output after the second difference value is subjected to proportional-integral control.
And carrying out Park inverse transformation on the reactive voltage modulation command and the active voltage modulation command, and converting the voltage modulation command under the synchronous rotation coordinate system into a three-phase voltage modulation command.
And finally, performing pulse width modulation on the reactive voltage modulation command and the active voltage modulation command to obtain a switch control signal of the grid-connected inverter so as to control the reactive power output of the grid-connected inverter. The Pulse Width Modulation may include Sine Pulse Width Modulation (SPWM) or Space Vector Pulse Width Modulation (SVPWM).
Fig. 5 is a waveform diagram of the voltage of the grid-connected point and the inverter output current after islanding is detected according to the method of the present invention. Fig. 6 is a waveform diagram of the grid-connected point voltage frequency after islanding is detected according to the method of the present invention. The island detection method can quickly and effectively detect the island state and complete the shutdown of the grid-connected inverter.
Example 2
Referring to fig. 7, the present application further discloses an island detection system, which includes: a sampling module (not shown) for sampling three-phase voltage and three-phase current signals of a grid-connected point; a phase-locked loop 1 for comparing the three-phase voltage signal U of the grid-connected pointa、Ub、UcPerforming phase locking, and outputting an angle orientation error value err _ q of the grid-connected point voltage; the proportional differential regulator 2 is used for carrying out proportional differential regulation on the angle orientation error value err _ q to obtain a disturbance quantity delta Vq of a reactive power instruction of the grid-connected inverter; the adder 3 is used for adding the disturbance quantity delta Vq of the reactive power instruction to a grid-connected inverter reactive current instruction Iq _ ref; the reactive power control module 4 is used for controlling the reactive power output of the grid-connected inverter according to the reactive current instruction Iq' _ ref superposed with the disturbance quantity; and a comparison and judgment module (not shown) for detecting each parameter of the grid-connected point voltage, and comparing each parameter with a preset threshold range to judge whether an island is generated.
The island detection system further comprises a Park conversion module 5, wherein the Park conversion module 5 is used for converting the three-phase voltage U of a grid-connected pointa、Ub、UcAnd three-phase current Ia、Ib、IcConverting the voltage into a synchronous rotating coordinate system to obtain an active voltage UdReactive voltage UqActive current IdAnd a reactive current Iq。
As an example, the reactive power control module 4 comprises: a first comparator 41 for comparing the reactive current I outputted from the grid-connected inverterqComparing the reactive current command Iq' _ ref superposed with the disturbance quantity to obtain a first difference value delta Iq; a second comparator 42 for comparing the active current I outputted from the grid-connected inverterdComparing the active current command Id _ ref to obtain a second difference value delta Id; a proportional-integral regulator 43 for proportional-integral regulating the first difference value Δ Iq and the second difference value Δ Id and outputting a voltage modulation command u* dAnd u* q(ii) a Inverse Park transform module 44 for scaling proportional integralVoltage modulation command u in synchronous rotation coordinate system output by the device 43* dAnd u* qConverted into three-phase voltage modulation command u* a、u* bAnd u* c(ii) a A modulation module 45 for modulating the three-phase voltage modulation command u output by the Park inverse transformation module 44* a、u* bAnd u* cAnd performing pulse width modulation, and obtaining a switch control signal of the grid-connected inverter to control the reactive power output of the grid-connected inverter. The modulation module 45 is, as an example, a sinusoidal pulse width modulator or a space vector pulse width modulator. It should be noted that the phase-locked loop output further includes a grid-connected point voltage phase angle θ and an angular velocity ω, and the phase angle θ is used in the Park transformation calculation and the Park inverse transformation calculation.
As an example, the island detection system further includes an execution module (not shown), and in the case that the comparison and judgment module judges the island effect, the execution module is used for blocking the grid-connected inverter pulse signal and controlling the grid-connected inverter to stop.
In summary, the island detection method and the island detection system disclosed by the invention superimpose the directional error of the grid voltage phase angle as the disturbance quantity positive feedback on the reactive current instruction, thereby controlling the reactive power output of the grid-connected inverter. During normal grid-connected operation, grid-connected voltage is clamped by the voltage of a power grid, so that small positive feedback disturbance cannot influence the normal operation of a system; when the power grid contactor is disconnected and an island effect occurs, the frequency deviation of the voltage of the grid-connected point can cause the generation of an orientation angle error, a reactive current instruction is further adjusted in a positive feedback mode, the frequency deviation degree of the voltage of the grid-connected point is increased, a threshold value is finally exceeded, the detection system is triggered to perform passive protection, and the power grid is shut down successfully.
The island detection method eliminates the island detection blind zone, is simple to control, and can quickly and accurately detect the inverter island; compared with the existing active disturbance scheme, the scheme has the advantage of good steady-state power quality; the grid-connected inverter can be applied to distributed energy units such as wind power generation, solar power generation, fuel cells and the like, and is wide in application range, including being applied to a unidirectional distributed grid-connected power generation system and a three-phase distributed grid-connected power generation system. Therefore, the present invention effectively overcomes the disadvantages of the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (11)
1. An island detection method, comprising the steps of:
collecting voltage signals of a grid connection point, and acquiring an angle orientation error value of the voltage signals;
carrying out proportional differential adjustment on the angle orientation error value to obtain the disturbance quantity of a reactive power instruction of the grid-connected inverter;
superposing the disturbance quantity of the reactive power instruction on a reactive current instruction of the grid-connected inverter so as to control the reactive power output of the grid-connected inverter;
detecting various parameters of the grid-connected point voltage in real time, comparing the parameters with a preset threshold range, and judging that an island is generated if any one of the parameters exceeds the threshold range.
2. The islanding detection method according to claim 1, further comprising a step of performing Park transformation on the acquired voltage signal of the grid-connected point after the voltage signal of the grid-connected point is acquired, wherein the Park transformation is used for transforming the three-phase voltage of the acquired grid-connected point into a synchronous rotating coordinate system.
3. The islanding detection method according to claim 2, wherein the step of superimposing the disturbance amount of the reactive power command on the grid-connected inverter reactive current command to control the grid-connected inverter reactive power output comprises the steps of:
comparing the reactive current output by the grid-connected inverter with the reactive current instruction superimposed with the disturbance quantity to obtain a first difference value; comparing the active current output by the grid-connected inverter with the active current instruction to obtain a second difference value;
carrying out proportional integral adjustment on the first difference value and the second difference value, and outputting a voltage modulation instruction under a synchronous rotating coordinate system;
performing Park inverse transformation on the voltage modulation command under the synchronous rotation coordinate system to obtain a three-phase voltage modulation command;
and performing pulse width modulation on the three-phase voltage modulation command to obtain a switch control signal of the grid-connected inverter so as to control the reactive power output of the grid-connected inverter.
4. The islanding detection method of claim 3, wherein the pulse width modulating the three-phase voltage modulation command comprises sinusoidal pulse width modulating or space vector pulse width modulating the three-phase voltage modulation command.
5. The islanding detection method of claim 1, wherein the real-time detection of the parameters of the grid-connected point voltage comprises real-time detection of the amplitude and frequency of the grid-connected point voltage.
6. The islanding detection method according to claim 1, further comprising a step of controlling a grid-connected inverter to stop inversion after it is determined that an islanding has occurred.
7. An islanding detection system, the system comprising:
the sampling module is used for sampling voltage and current signals of a grid-connected point;
the phase-locked loop is used for performing phase locking on the voltage signal of the grid-connected point and outputting a deviation value of an actual angle and an orientation angle of the grid-connected point voltage;
the proportional differential regulator is used for carrying out proportional differential regulation on the angle orientation difference value to obtain the disturbance quantity of the reactive power instruction of the grid-connected inverter;
the adder is used for superposing the disturbance quantity of the reactive power instruction on a reactive current instruction of the grid-connected inverter;
the reactive power control module is used for controlling the reactive power output of the grid-connected inverter according to the reactive current instruction superposed with the disturbance quantity;
and the comparison and judgment module is used for detecting various parameters of the grid-connected point voltage, comparing the various parameters with a preset threshold range and judging whether an island is generated.
8. The islanding detection system of claim 7, further comprising a Park transformation module for transforming three-phase voltages of grid-connected points into a synchronous rotating coordinate system.
9. The islanding detection system of claim 8, wherein the reactive power control module comprises:
the first comparator is used for comparing the reactive current output by the grid-connected inverter with the reactive current command superimposed with the disturbance quantity to obtain a first difference value;
the second comparator is used for comparing the active current output by the grid-connected inverter with the active current instruction to obtain a second difference value;
the proportional integral regulator is used for performing proportional integral regulation on the first difference value and the second difference value and outputting a voltage modulation instruction under a synchronous rotation coordinate system;
the Park inverse transformation module is used for carrying out Park inverse transformation on the voltage modulation command under the synchronous rotating coordinate system and transforming the voltage modulation command into a three-phase voltage modulation command;
and the modulation module is used for carrying out pulse width modulation on the three-phase voltage modulation command to obtain a switch control signal of the grid-connected inverter so as to control the reactive power output of the grid-connected inverter.
10. The islanding detection system of claim 9, wherein the modulation module is a sinusoidal pulse width modulator or a space vector pulse width modulator.
11. The island detection system according to claim 7, further comprising an execution module, wherein the execution module is configured to control the grid-connected inverter to stop when the comparison and judgment module judges that an island is generated.
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| CN111541271A (en) * | 2020-05-13 | 2020-08-14 | 广东电网有限责任公司韶关供电局 | Method and system for identifying island operation and grid-connected operation of small hydropower station |
| CN111756066A (en) * | 2020-07-06 | 2020-10-09 | 上海交通大学 | Operation control and island detection method and system for photovoltaic direct current converter |
| CN113364038A (en) * | 2021-06-25 | 2021-09-07 | 山东理工大学 | Inverter frequency control-based multi-distributed power supply island detection method |
| CN113759184A (en) * | 2020-06-03 | 2021-12-07 | 台达电子企业管理（上海）有限公司 | Island detection method and device of inverter |
| CN115483709A (en) * | 2022-10-17 | 2022-12-16 | 北京索英电气技术有限公司 | Island detection method and device of energy grid-connected system |
| US11936310B2 (en) | 2020-06-03 | 2024-03-19 | Delta Electronics (Shanghai) Co., Ltd | Control method and device for three-phase AC system |
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