CN118801457A - Low voltage ride-through overcurrent suppression method and system for grid-type voltage management device - Google Patents
Low voltage ride-through overcurrent suppression method and system for grid-type voltage management device Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for AC mains or AC distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for AC mains or AC distribution networks
- H02J3/12—Circuit arrangements for AC mains or AC distribution networks for adjusting voltage in AC networks by changing a characteristic of the network load
- H02J3/16—Circuit arrangements for AC mains or AC distribution networks for adjusting voltage in AC networks by changing a characteristic of the network load by adjustment of reactive power
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
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Abstract
本发明属于变流器控制技术领域，公开了一种构网型电压治理装置低电压穿越过电流抑制方法及系统，锁相环对电网电压进行锁相，输出变换角度θ，d轴与电网电压矢量重合；q轴为垂直与电压矢量方向，通过给定iq_ref由PI调节器调节q轴电压的输出改变无功电流大小，控制注入电网无功功率；d轴与电网电压矢量重合，在d轴方向控制电压大小的方向对有功分量进行控制；dq/abc的旋转角度由有功下垂模块、基础频率模块以及锁相环模块构成；电网幅值计算模块用于计算电网电压。本发明使逆变器同时具备电压源与电流源特性，从而具备良好的构网与并网功能。由于d轴的电压环的控制，当出现非计划性离网时同样可以保持稳定的电压输出。
The present invention belongs to the technical field of converter control, and discloses a method and system for suppressing low voltage ride-through overcurrent of a grid-type voltage management device. A phase-locked loop phase-locks the grid voltage, outputs a transformation angle θ, and the d-axis coincides with the grid voltage vector; the q-axis is perpendicular to the voltage vector direction, and the output of the q-axis voltage is adjusted by a PI regulator by giving iq_ref to change the reactive current magnitude, and control the reactive power injected into the grid; the d-axis coincides with the grid voltage vector, and the active component is controlled in the direction of the voltage magnitude in the d-axis direction; the rotation angle of dq/abc is composed of an active droop module, a basic frequency module, and a phase-locked loop module; and a grid amplitude calculation module is used to calculate the grid voltage. The present invention enables the inverter to have both voltage source and current source characteristics, thereby having good grid-building and grid-connected functions. Due to the control of the voltage loop of the d-axis, a stable voltage output can also be maintained when unplanned off-grid occurs.
Description
Technical Field
The invention belongs to the technical field of converter control, and particularly relates to a low-voltage passing-over current suppression method and system for a grid-structured voltage treatment device.
Background
With the continuous increase of the generating capacity ratio of the photovoltaic power generation in a power system, the continuous progress and development of the photovoltaic industry technology, particularly the high-speed increase of the distributed photovoltaic power generation, brings great attention to the control technology innovation of the solar photovoltaic power generation system. The photovoltaic power generation system presents high nonlinear characteristics due to the characteristics of the photovoltaic array, so that great difficulty is brought to stability analysis and controller design of the power system; on the other hand, the random and intermittent characteristics of the solar irradiation resource also bring great challenges to the stable control of the power grid of the transformer area, such as frequent voltage fluctuation, thereby causing the burning of power equipment, the scrapping of produced products and even serious power grid accidents. With further improvement of the photovoltaic permeability, the continuous access of the high-density photovoltaic power supply brings many new requirements to the photovoltaic control system for the problems of on-site absorption balance of the photovoltaic power, stable support of the power grid and the like.
In order to fully consume the mass distributed sources and achieve the maximum utilization of the distributed sources, scholars propose to improve the power supply scheme of the distribution transformer area by utilizing a network-structured static var generator. On the basis of fully researching and researching the out-of-limit voltage faults of the distribution transformer area, a network-structured static reactive generator with reasonable capacity is configured at a key node, and the power supply quality of the network-structured distribution transformer area is improved by utilizing the active supporting and networking capability of the network-structured inverter on the voltage frequency and combining the impedance characteristics of the middle and tail ends of the distribution network.
The network-structured control strategy is derived from the simulation of dynamic characteristics of the synchronous motor, so that the network-structured converter and the network-structured converter have different operation characteristics. The grid-connected converter can be approximately regarded as a controlled current source with high parallel impedance, and the output power is indirectly controlled or voltage regulation is realized by controlling the output current; while a grid-formed converter can be seen as a controlled voltage source with a low series impedance, the output power being controlled by the control port voltage. In the aspect of a response mode to power grid disturbance, the follow-up grid converter shows a current source characteristic, and when the grid-connected point voltage is disturbed, before the phase-locked loop can lock the phase correctly, the follow-up grid converter tends to keep the amplitude and phase angle of the output current unchanged, but the abrupt change of the output voltage is inevitably caused, so that the voltage stability is not maintained; the grid-structured converter shows voltage source characteristics, and when the voltage of the grid-connected point is disturbed, the internal potential tends to be kept unchanged, so that the voltage stability is maintained. The network-structured converter can realize self-synchronization by imitating a power balance synchronization mechanism of a synchronous machine and discarding a detection link. Correspondingly, the grid-structured converter also avoids the strong interaction between the converter and a weak power grid caused by a phase-locked loop to a certain extent, and is easier to keep stable under the weak power grid.
Disclosure of Invention
Aiming at the problems existing in the prior art, the invention provides a method and a system for suppressing low-voltage crossing current of a network-structured voltage treatment device.
The invention is realized in such a way that a low voltage passing-over current suppression method of a network-structured voltage management device comprises the following steps:
S1: the phase-locked loop performs phase locking on the power grid voltage, outputs a transformation angle theta, and the d axis coincides with the power grid voltage vector;
S2: the q-axis is vertical to the vector direction of the voltage, the output of the q-axis voltage is regulated by a PI regulator through giving iq_ref to change the reactive current, and the reactive power of the injected power grid is controlled;
S3: the d axis coincides with the power grid voltage vector, and the active component is controlled in the direction of controlling the voltage in the d axis direction;
s4: the rotation angle of dq/abc is formed by active droop module, basic frequency module and phase-locked loop module;
S5: when the converter is connected with the grid, the phase-locked loop module is in a working state, and at the moment, the electric angle output by the active droop module is clamped;
s6: when the converter leaves the network, the phase-locked loop is cut off, and the sagging module normally works the converter to have common sagging characteristics;
S7: the power grid amplitude calculation module is used for calculating power grid voltage and ensuring that output voltage is close to the power grid voltage as much as possible.
Further, the angle θ of the power grid in S1 is given by a phase-locked loop, and is input to the coordinate transformation module as a transformation angle. When the system is in an off-grid state phase-locked loop, the system is deactivated, and the transformation angle is determined by the integral of the sum of the base frequency and the frequency increment of the active droop output.
Further, in the step S2, when the reactive current is set, the limitation of the maximum current of the converter and the current output active current should be satisfied, as shown in the formula 1:
further, the S3 output d-axis voltage, such that the system has a voltage source characteristic, the control of which may be selected from open loop or closed loop control.
Further, v q is a component generated by controlling the reactive current i q, and the relationship between them is shown in formula 2:
v q＝iq. Omega. L (2)
In the formula 2, ω is the angular speed of the power grid, L is the inductance between the inverter and the power grid, and as can be seen from the formula 2, v q is still far smaller than the voltage of the power grid even under the condition of large reactive current, so that the addition of the q-axis current loop does not affect the voltage source characteristic of the system.
Further, the active droop module and the fundamental frequency in the step S4 can work in real time, and omega e is the angular speed of the power grid when the power grid normal phase-locked loop works; when the phase-locked loop breaks the output angular frequency to be the sum of the basic frequency omega basic and the active droop module omega drop; wherein the fundamental frequency ω basic is a constant 2pi·f, and f is the fundamental frequency.
The invention also provides a low-voltage ride through overcurrent suppression system of the network-structured voltage management device, which comprises the following components:
a phase-locked loop module: the device is used for phase locking of the power grid voltage, outputting a transformation angle and enabling a d axis to coincide with a power grid voltage vector;
Reactive current control module: the output of the q-axis voltage is regulated through a PI regulator based on the q-axis direction, and the reactive current is changed, so that the reactive power injected into a power grid is controlled;
active current control module: controlling the voltage in the d-axis direction, thereby controlling the active component;
dq/abc coordinate transformation module: the rotation angle is determined by the active droop module, the basic frequency module and the phase-locked loop module;
the power grid amplitude calculation module: for the calculation of the voltage of the power grid, ensuring that the output voltage is as close to the grid voltage as possible.
Further, the phase-locked loop module is in a working state when the system is connected with the grid, and outputs an electric angle to clamp the output of the active droop module; when the system is off-grid, the phase-locked loop module is out of operation, and the transformation angle is determined by the integral of the sum of the basic frequency and the frequency increment output by the active droop module.
Further, when the reactive current control module sets reactive current, the limitation of the maximum current of the converter and the current output active current needs to be met.
Further, the active droop module and the basic frequency module can work in real time under the grid-connected state and the off-grid state of the system, wherein the basic frequency is a constant reference frequency; when the power grid works normally, the phase-locked loop module outputs the angular speed of the power grid, and when the phase-locked loop module is disconnected, the output angular frequency is the sum of the basic frequency and the active droop module.
In combination with the technical scheme and the technical problems to be solved, the technical scheme to be protected has the following advantages and positive effects:
Firstly, the inverter has the characteristics of a voltage source and a current source through the control strategy designed by the invention, so that the inverter has good networking and grid-connected functions. Active power and reactive power fed into the power grid are controlled through a d axis and a q axis respectively under the grid connection condition, and the current loop action of the q axis can control the current of the power grid stably even if the power grid drops greatly. Meanwhile, due to the control of the d-axis voltage ring, stable voltage output can be kept when the unplanned off-grid occurs.
Secondly, the invention solves the problem of inaccurate phase locking of the power grid voltage in the prior art by introducing the phase-locked loop module and the dq/abc coordinate conversion module. The phase-locked loop module can carry out accurate phase locking on the power grid voltage, and ensure that the d-axis coincides with the power grid voltage vector, thereby realizing more efficient active and reactive power control. The phase-locking technology not only improves the response speed of the system, but also enhances the adaptability of the voltage management device in complex power grid environments.
And secondly, an advanced reactive current control algorithm is adopted, the output of the q-axis voltage is regulated through the PI regulator, the magnitude of reactive current is changed, and the accurate control of the reactive power injected into the power grid is realized. The algorithm fully considers the maximum current limit and the current output active current condition of the converter in design, ensures that the system can stably operate in various operation states, and further avoids the problem of unstable reactive power control common in the traditional method.
In addition, the active droop control module and the basic frequency module solve the problem of frequency control under off-grid state by dynamically adjusting the output frequency of the converter. When the system is in a grid-connected state, the electric angle output by the active droop module is clamped by the phase-locked loop module; when the system is off-grid, the phase-locked loop module is taken out of operation, and the conversion angle is determined by the integral of the sum of the base frequency and the frequency increment of the active droop output. The design ensures that the system can stably operate in grid-connected and off-grid states and has excellent frequency response characteristics.
Finally, the invention also achieves significant technical advances in grid amplitude calculation and control. The output voltage can be as close as possible to the power grid voltage through accurate calculation of the power grid amplitude calculation module, so that the output voltage quality of the voltage management device is improved. By combining the d-axis voltage output of open loop or closed loop control, the invention ensures that the system has good voltage source characteristics, and can maintain the stability and reliability of the system voltage even under the condition of large reactive current. The series of technical innovations make the invention significantly advanced in voltage management and low voltage cross-over current suppression.
Thirdly, the prior art has larger hysteresis and instability in the aspects of grid voltage phase locking and control, and particularly, the instability of a system is easily caused in the switching process of grid connection and grid disconnection of the converter. According to the invention, the phase-locked loop module is added with a power grid voltage phase-locking function, and the output conversion angle is overlapped with the d-axis voltage vector, so that the rapid phase locking and stable control of the power grid voltage are realized. The technical scheme solves the problem of phase locking lag of the power grid voltage in the prior art, and improves the response speed and stability of the system.
In the prior art, the reactive power control is unstable due to the influence of the voltage fluctuation of a power grid and the limitation of the output current of a converter in the control of reactive current and active components. The invention adjusts the q-axis voltage output through the PI regulator to change the magnitude of reactive current, thereby controlling the reactive power injected into the power grid; meanwhile, the voltage is controlled in the d-axis direction by superposition of the d-axis and the power grid voltage vector, so that the accurate control of the active component is realized. According to the scheme, on the premise of ensuring the maximum current of the converter and the limitation of the current output active current, the stable control of reactive current and active components is realized.
In the prior art, in the switching process between grid-connected and off-grid states of the converter, unstable electrical angle output is easy to occur, and the operation of the system is influenced. According to the invention, through clamping the electric angle output by the active droop module when the converter is connected with the grid and cutting off the phase-locked loop when the converter is disconnected from the grid, the droop module can work normally, the converter is ensured to have the common droop characteristic, the stability and the stability of the system in switching between the grid-connected state and the off-grid state are ensured, and the problem of unstable switching in the prior art is solved.
In the aspect of power grid amplitude calculation and output voltage matching, accurate calculation and rapid voltage matching are difficult to achieve in the prior art, and the fluctuation of the output voltage of the system is large. According to the invention, the power grid voltage is accurately calculated through the power grid amplitude calculation module, so that the output voltage is ensured to be as close to the power grid voltage as possible; meanwhile, the active droop module and the basic frequency module work in real time, so that the stability of the output angular frequency of the system in different working states is guaranteed, and the problem of inaccurate voltage matching in the prior art is solved. The scheme remarkably improves the voltage source characteristic and the operation stability of the system.
Fourth, the invention adopts the phase-locked loop (PLL) to carry out phase locking on the power grid voltage, outputs a transformation angle, ensures that the d-axis coincides with the power grid voltage vector, and obviously improves the response speed of the system to the power grid voltage change by optimizing the parameters of the phase-locked loop. In the prior art, the grid voltage phase lock has hysteresis, so that the system is slow in response and unstable. According to the invention, the grid angle is accurately calculated and is input to the coordinate transformation module as the transformation angle, so that the system can keep stable phase locking of voltage during grid connection and grid disconnection, the problem of phase locking hysteresis is solved, and the real-time performance and stability of the system are improved.
The voltage output of the q-axis is regulated by the PI regulator to control the magnitude of reactive current, and the active component is controlled by adopting a method that the d-axis coincides with the voltage vector of the power grid. In the traditional technology, reactive power and active power control are often unstable due to the limitation of power grid voltage fluctuation and converter output current. The invention considers the limitation of the maximum current and the current output active current of the converter in design, realizes the stable control of reactive current and active component by calculating through a mathematical model (as shown in formula 1), and solves the problem of unstable power control in the prior art.
When the converter is connected with the grid, the invention clamps the electric angle output by the active droop module to ensure that the phase-locked loop module is in a working state; when the converter is off-grid, the phase-locked loop is cut off, so that the droop module works normally. The design realizes the stable switching of the converter between the grid-connected state and the off-grid state by combining the active droop control and the phase-locked loop algorithm, and solves the problem of unstable electrical angle output in the switching process in the traditional technology. The droop control and the real-time switching mechanism of the phase-locked loop ensure the stable operation of the system in different states, and the reliability of the system is obviously improved.
Through the power grid amplitude calculation module, the power grid voltage can be accurately calculated, and the output voltage is ensured to be as close to the power grid voltage as possible. Meanwhile, the active sagging module and the basic frequency module are combined to work in real time, so that the accurate control of the angular speed of the power grid is realized. And outputting the angular speed of the power grid when the phase-locked loop works, and outputting the angular frequency of the sum of the basic frequency and the frequency increment of the active droop module when the phase-locked loop is disconnected. Through the design of the mathematical model (as shown in the formula 2), the invention solves the problem of inaccurate power grid voltage matching in the prior art, and improves the voltage source characteristic and the stability of the system, thereby realizing remarkable technical progress.
Drawings
FIG. 1 is a flow chart of a method for suppressing low voltage crossing current of a network voltage treatment device according to an embodiment of the present invention;
fig. 2 is a control block diagram of a grid-tied inverter provided by an embodiment of the present invention;
FIG. 3 is a graph showing the relationship between a rotational coordinate system and grid voltage according to an embodiment of the present invention;
FIG. 4 is a schematic illustration of a grid voltage dip provided by an embodiment of the invention
FIG. 5 is an illustration of an unintended offline provided by an embodiment of the present invention;
FIG. 6 is a reactive current regulation process provided by an embodiment of the present invention;
FIG. 7 is a simulation model provided by an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Embodiment one: application of household photovoltaic grid-connected power generation system
The household photovoltaic grid-connected power generation system needs to realize stable voltage control and reactive power compensation under different power grid states so as to improve the power quality and the system stability. The existing photovoltaic grid-connected inverter is easy to generate overcurrent during low-voltage ride through, and the safe operation of the system is affected.
1. System configuration:
The grid-structured voltage management device is connected with a household photovoltaic grid-connected inverter to form a photovoltaic grid-connected power generation system.
The photovoltaic array is connected with the direct current side of the inverter through the DC/DC converter, and the alternating current side of the inverter is connected with the power grid.
2. Low voltage ride through and over current suppression:
in the grid-connected state, the system performs phase locking on the grid voltage through a phase-locked loop (PLL), and outputs a transformation angle so that the d-axis coincides with the grid voltage vector (step S1).
During low voltage ride through, the system adjusts q-axis voltage output through the PI regulator, changes reactive current magnitude, controls reactive power injected into the power grid (step S2), controls voltage magnitude in the d-axis direction, and controls active components (step S3).
The rotation angle of dq/abc is composed of an active droop module, a fundamental frequency module, and a phase-locked loop module (step S4).
When the converter is connected with the grid, the phase-locked loop module is in a working state, the electric angle output by the active droop module is clamped (step S5), the phase-locked loop is cut off when the converter is disconnected from the grid, and the droop module works normally (step S6).
The power grid amplitude calculation module is used for calculating power grid voltage and ensuring that the output voltage is as close to the power grid voltage as possible (step S7).
The effect is as follows:
through the low-voltage crossing current inhibition method, the photovoltaic grid-connected inverter can effectively inhibit overcurrent during low-voltage crossing, and safe operation of a system is ensured.
The stability and the electric energy quality of the power grid voltage are improved, and a reliable photovoltaic power generation solution is provided for household users.
Embodiment two: application in industrial wind power generation system
In an industrial wind power generation system, stable voltage control and reactive power compensation of a wind power generator set are required to be realized under different power grid states, so that the quality of power output and the stability of the system are ensured. The wind generating set is easy to have the problem of unstable voltage during grid connection and off-grid state switching.
1. System configuration:
The net-structured voltage management device is connected with an industrial wind generating set to form a wind power generation system.
The wind driven generator is connected to a power grid through a converter, and the voltage management device is integrated in a control system of the converter.
2. Grid voltage control and reactive compensation:
in the grid-connected state, the system performs phase locking on the grid voltage through a phase-locked loop, and outputs a transformation angle to enable the d-axis to coincide with the grid voltage vector (step S1).
During operation, the system adjusts q-axis voltage output through the PI regulator, changes reactive current magnitude, controls reactive power injected into the power grid (step S2), controls voltage magnitude in the d-axis direction, and controls active components (step S3).
The rotation angle of dq/abc is composed of an active droop module, a fundamental frequency module, and a phase-locked loop module (step S4).
When the converter is connected with the grid, the phase-locked loop module is in a working state, the electric angle output by the active droop module is clamped (step S5), the phase-locked loop is cut off when the converter is disconnected from the grid, and the droop module works normally (step S6).
The power grid amplitude calculation module is used for calculating power grid voltage and ensuring that the output voltage is as close to the power grid voltage as possible (step S7).
The effect is as follows:
Through the voltage management device, the wind generating set can realize stable control of voltage and reactive power compensation during grid connection and off-grid state switching.
The stability and the electric energy quality of the power grid voltage are improved, the reliable operation of the wind power generation system under different working states is ensured, and a high-efficiency stable wind power generation solution is provided for industrial users.
The embodiment of the invention provides a low-voltage passing-over current inhibition method of a network-structured voltage management device, which comprises the following steps:
S1: the phase-locked loop performs phase locking on the power grid voltage, outputs a transformation angle theta, and the d axis coincides with the power grid voltage vector, and the relation is shown in figure 3;
S2: the q-axis is vertical to the vector direction of the voltage, the output of the q-axis voltage is regulated by a PI regulator through giving iq_ref to change the reactive current, and the reactive power of the injected power grid is controlled;
S3: the d axis coincides with the power grid voltage vector, and the active component is controlled in the direction of controlling the voltage in the d axis direction;
s4: the rotation angle of dq/abc is formed by active droop module, basic frequency module and phase-locked loop module;
S5: when the converter is connected with the grid, the phase-locked loop module is in a working state, and at the moment, the electric angle output by the active droop module is clamped;
s6: when the converter leaves the network, the phase-locked loop is cut off, and the sagging module normally works the converter to have common sagging characteristics;
S7: the power grid amplitude calculation module is used for calculating power grid voltage and ensuring that output voltage is close to the power grid voltage as much as possible.
The control strategy in fig. 3 is expressed in a two-phase rotating coordinate system, wherein the d-axis coincides with the grid voltage, which corresponds to the active component, and the q-axis is the reactive component. The control strategy generally aims at directing a power grid voltage vector in a grid-connected state, respectively and independently controlling q-axis (reactive) current and d-axis voltage, and respectively controlling the active and reactive of a system through d-axis voltage setting and q-axis current setting. The system has two working modes of grid connection and off-grid, wherein active and reactive control can be realized in the grid connection mode.
Further, the angle θ of the power grid in S1 is given by a phase-locked loop, and is input to the coordinate transformation module as a transformation angle. When the system is in an off-grid state phase-locked loop, the system is deactivated, and the transformation angle is determined by the integral of the sum of the base frequency and the frequency increment of the active droop output.
Further, in the step S2, when the reactive current is set, the limitation of the maximum current of the converter and the current output active current should be satisfied, as shown in the formula 1
Further, the S3 output d-axis voltage, such that the system has a voltage source characteristic, the control of which may be selected from open loop or closed loop control.
Further, v q is a component generated by controlling the reactive current i q, and the relationship between them is shown in formula 2:
v q＝iq. Omega. L (2)
In the formula 2, ω is the angular speed of the power grid, L is the inductance between the inverter and the power grid, and as can be seen from the formula 2, v q is still far smaller than the voltage of the power grid even under the condition of large reactive current, so that the addition of the q-axis current loop does not affect the voltage source characteristic of the system.
Further, the active droop module and the fundamental frequency in the step S4 can work in real time, and omega e is the angular speed of the power grid when the power grid normal phase-locked loop works; when the phase-locked loop breaks the output angular frequency to be the sum of the basic frequency omega basic and the active droop module omega drop; wherein the fundamental frequency ω basic is a constant 2pi·f, and f is the fundamental frequency.
The present invention will be specifically described with reference to fig. 7, which shows a main circuit of a three-phase grid-connected system.
Fig. 4 shows the inverter in a grid-connected state, and waveforms in fig. 4 are the output voltage of the inverter filter and the grid-connected current, respectively. Setting the initial grid voltage to be 1P.U., dropping the grid voltage from 1P.U. to 0.5P.U. within 0.60.7s, it can be seen from FIG. 4 that the grid-connected current remains stable under the condition that the grid voltage drops greatly, and the characteristic close to the current source grid-connected inverter is reflected. Fig. 5 shows an unplanned off-grid condition of the inverter. The inverter is initially in a grid-connected state, and is separated from the power grid at 0.50.6s, so that the output voltage of the inverter is still stable after the grid separation, and the inverter has good voltage source characteristics. Fig. 6 shows a power regulation process in the grid-connected inverter state, which indicates that the system has good power regulation capability.
It should be noted that the embodiments of the present invention can be realized in hardware, software, or a combination of software and hardware. The hardware portion may be implemented using dedicated logic; the software portions may be stored in a memory and executed by a suitable instruction execution system, such as a microprocessor or special purpose design hardware. Those of ordinary skill in the art will appreciate that the apparatus and methods described above may be implemented using computer executable instructions and/or embodied in processor control code, such as provided on a carrier medium such as a disk, CD, or dvd rom, a programmable memory such as read only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The device of the present invention and its modules may be implemented by hardware circuitry, such as very large scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., as well as software executed by various types of processors, or by a combination of the above hardware circuitry and software, such as firmware.
The foregoing is merely illustrative of specific embodiments of the present invention, and the scope of the invention is not limited thereto, but any modifications, equivalents, improvements and alternatives falling within the spirit and principles of the present invention will be apparent to those skilled in the art within the scope of the present invention.
Claims (10)
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