CN110611326A - Droop control method and system of grid-connected inverter - Google Patents
Droop control method and system of grid-connected inverter Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
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Abstract
A droop control method and system for a grid-connected inverter comprise the following steps: bringing the obtained grid voltage, current, frequency information and angular frequency of the inverter into a pre-constructed virtual synchronous generator rotation model to obtain a phase angle value; bringing the phase angle value and the obtained voltage amplitude value into a three-phase voltage synthesis model to obtain a three-phase voltage reference value; the three-phase voltage reference value and the PWM generator are used for generating PWM waves, and the inverter is controlled based on the PWM waves, so that the grid-connected inverter adopting power droop control and current droop control has damping and inertia characteristics, the stability of the voltage and the frequency of a power grid is improved, the safe and stable operation of the power grid system is maintained, the survival capability of new energy is improved, and the economic and social benefits of a new technology are revealed.
Description
The technical field is as follows:
the invention relates to the field of power distribution networks, in particular to a droop control method and system for a grid-connected inverter.
Background art:
the vigorous development of clean energy is one of the effective ways to relieve the energy crisis and environmental deterioration in the world. With the rapid development of distributed power generation units in power systems, which take clean energy as a main form, the permeability of clean energy in power grid systems is also rapidly increasing. When the grid system is disturbed by a large scale at the load side, the grid system is easily unstable due to the lack of sufficient energy to balance the disturbance in a short time. Meanwhile, the distributed energy technology is an important development direction of the future world energy technology, and has the characteristics of high energy utilization efficiency, small negative environmental influence, high energy supply reliability and good economic benefit. The distributed energy is an energy development mode which can best embody multiple advantages of energy conservation, emission reduction, safety, flexibility and the like, and promotes the popularization and application of a distributed energy system. Therefore, the excellent distributed energy industry enterprises in China increasingly attach importance to the research on the industry market, particularly the deep research on the trend change of the development environment and the demand of the company.
The research of distributed power generation starts late, and with the promotion of energy strategic adjustment, certain planning, implementation policies and fund subsidy policies related to renewable energy sources are developed successively, so that the method is used for the research of distributed power generation and promotes the rapid development of the distributed power generation.
Power electronic devices represented by new energy grid-connected inverters and controllable load rectifiers are rapidly connected into a power grid. Due to the fact that a small-inertia, quick and high-frequency power electronic system is connected to a large-inertia, low-speed and power-frequency power system, a large number of adaptability problems such as no participation in power grid adjustment, no support for power grid fault recovery, difficult control, frequent plugging and unplugging, and low robustness in a dynamic and steady state process are generated, the grid-connected inverter cannot make corresponding response under the conditions of power grid voltage and frequency abnormity, and the power grid frequency and voltage stability are low.
The invention content is as follows:
in order to solve the above-mentioned defects in the prior art, the invention provides a droop control method and system for a grid-connected inverter.
The technical scheme provided by the invention is as follows:
a droop control method for a grid-connected inverter, the method comprising:
acquiring the grid voltage, current, frequency information, voltage amplitude and angular frequency of an inverter;
bringing the power grid voltage, current, frequency information and angular frequency into a pre-constructed virtual synchronous generator rotation model to obtain a phase angle value;
the phase angle value and the voltage amplitude value are brought into a three-phase voltage synthesis model to obtain a three-phase voltage reference value;
and generating PWM waves based on the three-phase voltage reference values and a PWM generator, and controlling an inverter based on the PWM waves.
Preferably, the constructing of the virtual synchronous generator rotation model includes:
based on the grid voltage, current and frequency information of the inverter, a control algorithm of the synchronous generator is adopted to obtain a virtual potential and a mechanical torque;
constructing a rotor motion equation based on the mechanical torque, the angular frequency and the rotational inertia and the damping coefficient of the synchronous generator, and constructing a stator electrical equation based on the virtual potential;
and constructing a virtual synchronous generator rotation model based on the rotor motion equation and the stator electrical equation.
Preferably, the equation of motion of the rotor is as follows:
in the formula, theta is a phase angle value; t ismMechanical torque for synchronous generators；TeIs the electromagnetic torque of the synchronous generator; t isDDamping torque for the synchronous generator; j is the rotational inertia of the synchronous generator; dPThe damping coefficient of the synchronous generator; omega is the mechanical and electrical angular frequency of the synchronous generator; omegaoIs the grid angular frequency of the synchronous generator; prefA virtual mechanical power command value output for the inverter; peVirtual electromagnetic power output for the inverter.
Preferably, the stator electrical equation is as follows:
in the formula, L is the synchronous inductance of the synchronous generator; e is a virtual potential; r is a stator resistor; i is an output current; u is the inverter terminal voltage.
Preferably, the obtaining of the angular frequency and the voltage amplitude comprises:
acquiring output current or active power and reactive power of the inverter based on the abnormal conditions of the grid voltage and frequency of the inverter;
when the acquired data are active power and reactive power of the inverter, calculating by adopting a power droop control algorithm based on the active power and the reactive power to obtain angular frequency and voltage amplitude;
when the acquired data is the output current of the inverter, the output current is decomposed into active current and reactive current, and calculation is performed by adopting a current droop control algorithm based on the active current and the reactive current to obtain angular frequency and voltage amplitude.
Preferably, the current droop control algorithm is calculated as follows:
in the formula: omega*Is the rated angular frequency; u shape*Is the voltage amplitude;is an active current command value;is a reactive current instruction value; a is an active current frequency droop coefficient; and b is a reactive current and voltage droop coefficient.
Preferably, the power droop control algorithm is calculated as follows:
in the formula: f is a rated frequency; u shapeoIs the amplitude; poIs an active power command value; qoIs a reactive power instruction value; m and n are sag coefficients.
A droop control system for a grid-tied inverter, the system comprising:
an acquisition module: the method comprises the steps of obtaining the grid voltage, current, frequency information, voltage amplitude and angular frequency of an inverter;
the model module is used for bringing the power grid voltage, current, frequency information and angular frequency into a pre-constructed virtual synchronous generator rotation model to obtain a phase angle value;
a synthesis module: the phase angle value and the voltage amplitude value are brought into a three-phase voltage synthesis model to obtain a three-phase voltage reference value;
a control module: for generating PWM waves based on the three-phase voltage reference values and a PWM generator, and controlling an inverter based on the PWM waves
Preferably, the model module includes: an obtaining unit, a building unit and a model unit;
the obtaining unit is used for obtaining a virtual potential and a mechanical torque by adopting a control algorithm of the synchronous generator based on the grid voltage, current and frequency information of the inverter;
the construction unit is used for constructing a rotor motion equation based on the mechanical torque, the angular frequency and the rotational inertia and the damping coefficient of the synchronous generator and constructing a stator electrical equation based on the virtual potential;
and the model unit is used for constructing a virtual synchronous generator rotation model based on the rotor motion equation and the stator electrical equation.
Preferably, the obtaining module includes: an acquisition module;
the acquisition module is used for acquiring the output current or active power and reactive power of the inverter based on the abnormal conditions of the grid voltage and frequency of the inverter;
when the acquired data are active power and reactive power of the inverter, calculating by adopting a power droop control algorithm based on the active power and the reactive power to obtain angular frequency and voltage amplitude;
when the acquired data is the output current of the inverter, the output current is decomposed into active current and reactive current, and calculation is performed by adopting a current droop control algorithm based on the active current and the reactive current to obtain angular frequency and voltage amplitude.
Compared with the prior art, the invention has the following beneficial effects:
1. the technical scheme provided by the invention comprises the following steps: acquiring the grid voltage, current, frequency information, voltage amplitude and angular frequency of an inverter; bringing the power grid voltage, current, frequency information and angular frequency into a pre-constructed virtual synchronous generator rotation model to obtain a phase angle value; the phase angle value and the voltage amplitude value are brought into a three-phase voltage synthesis model to obtain a three-phase voltage reference value; the inverter is controlled based on the PWM waves generated by the three-phase voltage reference value and the PWM generator, the inverter reacts under the condition of abnormal grid voltage and frequency, the stability of the grid voltage and frequency is improved, the recovery of grid faults is realized, the control is simple, the plugging and unplugging times are reduced, the interference of external disturbance is resisted in a limited way, and the maximized distributed inverter power supply is connected to the grid to bring huge benefits to users, a grid and the society.
2. According to the technical scheme provided by the invention, droop control and virtual synchronous generator control strategies are combined, two droop control methods for enabling the grid-connected inverter to have damping and inertia are provided, power droop control and current droop control are respectively improved, the damping and inertia of the virtual synchronous generator are applied to the droop control, the grid-connected inverter adopting the power droop control and the current droop control has damping and inertia characteristics, the power droop control and the current droop control strategies are adopted, the safe and stable operation of a power grid system is further maintained, and the survival capacity of new energy is improved.
Description of the drawings:
FIG. 1 is a flow chart of steps implemented by the inverter droop control method of the present invention;
FIG. 2 is a general block diagram of the current droop control with damping and inertia of the present invention;
FIG. 3 is a block diagram of the current droop control of the present invention;
FIG. 4 is a general block diagram of the power droop control with damping and inertia of the present invention
FIG. 5 is a block diagram of the power droop control of the present invention;
FIG. 6 is a main circuit of a three-phase voltage source inverter according to the present invention;
FIG. 7 is a block diagram of a virtual synchronous generator control algorithm of the present invention;
fig. 8 is a virtual synchronous generator mechanical rotation module of the present invention.
The specific implementation mode is as follows:
for a better understanding of the present invention, reference is made to the following description taken in conjunction with the accompanying drawings and examples.
Example 1
In order to improve the survival ability of new energy, guarantee the stability of a power grid and show economic and social benefits of a new technology, the invention provides two droop control methods which enable a grid-connected inverter to have damping and inertia, the two droop control methods are respectively improved aiming at power droop control and current droop control, the damping and the inertia of a virtual synchronous generator are applied to the droop control methods, the grid-connected inverter adopting the power droop control and the current droop control has damping and inertia characteristics, the stability of the voltage and the frequency of the power grid is improved, and the safe and stable operation of a power grid system is further maintained.
The specific implementation steps shown in fig. 1 are as follows:
the method comprises the following steps: acquiring the grid voltage, current, frequency information, voltage amplitude and angular frequency of an inverter;
step two: bringing the power grid voltage, current, frequency information and angular frequency into a pre-constructed virtual synchronous generator rotation model to obtain a phase angle value;
step three: bringing the phase angle value and the obtained voltage amplitude value into a three-phase voltage synthesis model to obtain a three-phase voltage reference value;
step four: and generating PWM waves based on the three-phase voltage reference values and a PWM generator, and controlling an inverter based on the PWM waves.
The control strategy provided by the invention comprises a current or power droop controller, a virtual generator mechanical rotation algorithm and a three-phase voltage synthesis module. The active current I output by the power grid is obtained by acquiring the output current of the inverter and calculatingpAnd a reactive current IqAnd serves as an input to the current droop. The command values for the reference voltage E and the frequency ω are generated by a current droop control algorithm. The frequency omega is used as the input quantity of a mechanical rotation algorithm of the virtual synchronous generator controller, and the voltage E is directly sent to the three-phase voltage synthesis module. The phase angle theta is generated under the action of the virtual synchronous generator controller. Finally, three-phase reference voltage E is obtained through three-phase voltage synthesis calculationabc。
Wherein, the first step: obtaining grid voltage, current, frequency information, voltage amplitude and angular frequency of an inverter, comprising:
acquiring the grid voltage, current and frequency information of the inverter;
the voltage amplitude and the angular frequency can be obtained by adopting a power droop control strategy with damping and inertia or a current droop control strategy with damping and inertia, and the calculation steps are as follows:
(1) a current droop control strategy with damping and inertia is employed, generally block diagram, as shown in fig. 2:
1: for collecting grid-connected invertersOutputting current I, and decomposing to obtain active current IdAnd a reactive current IqAnd takes its value as an input for current droop control.
2: and after the calculation is carried out by using a current droop control algorithm, outputting a reference voltage amplitude E and an angular frequency omega. The output angular frequency omega is used as the input quantity of a mechanical rotation module of the virtual synchronous generator, and the reference voltage amplitude E is used as the input quantity of a three-phase voltage synthesis module;
a block diagram of current droop control in inductive conditions based on line equivalent impedance, as illustrated in fig. 3. As can be seen from the figure, the current droop control can be expressed as:
in the formula: omega*、U*、Respectively a rated angular frequency, an amplitude value, an active current instruction value and a reactive current instruction value; a. and b is an active current frequency droop coefficient and a reactive current voltage droop coefficient respectively.
The droop coefficients a and b directly affect the dynamic response of the system, but the system eventually settles.
The inverter adopts a virtual synchronous generator control strategy, a mechanical rotation module is introduced behind a current droop controller, and the control method is mainly used for simulating the characteristic as much as possible, so that the inverter has damping and inertia characteristics, the anti-interference capability is improved, the droop external characteristic is realized, the control of a synchronizer is realized, the inverter is closer to the dynamic and static characteristics of a synchronous generator, and the aim of maintaining the safe and stable operation of a power grid is fulfilled. The present invention applies this feature to the droop control algorithm and also to achieve this.
(2) A power droop control strategy with damping and inertia is employed, overall block diagram, as shown in fig. 4:
1: collecting active power P and reactive power Q output by a grid-connected inverter, and sending the values to a power droop control module;
2: and after the calculation is carried out by utilizing a power droop control algorithm, outputting a reference voltage amplitude E and an angular frequency omega. The output angular frequency omega is used as the input quantity of a mechanical rotation module of the virtual synchronous generator, and the reference voltage amplitude E is used as the input quantity of a three-phase voltage synthesis module;
a power droop control block diagram, as shown in fig. 5. As can be seen, the droop control can be expressed as:
in the formula: f. ofo、Uo、Po、QoRespectively a rated frequency, an amplitude value, an active power instruction value and a reactive power instruction value; m and n are droop coefficients.
Step two: bringing the grid voltage, current, frequency information and angular frequency into a pre-constructed virtual synchronous generator rotation model to obtain a phase angle value, comprising:
as shown in fig. 6, the main circuit structure of the three-phase voltage grid-connected inverter is a distributed power supply whose dc side is mainly clean energy, and a dc source is directly used instead of the distributed power supply for simplifying the analysis. Q1～Q6R, L, C are inductance parasitic resistance, filter inductance and filter capacitance of the inverter respectively. Through measures such as synchronous control, electric energy finally flows into a power grid through a public coupling point.
A control algorithm block diagram of the virtual synchronous generator is shown in FIG. 7. As can be seen from the control block diagram, the virtual potential E output by the virtual synchronous generator reactive power regulation part can be represented as:
E＝ΔEQ+Eo+ΔEU＝k(Qref-Q)+Eo+kv(Uref-U)
in the formula,. DELTA.EQ、Eo、ΔEURespectively a reactive power regulating value, a virtual synchronous generator no-load electromotive force and a generator end voltage regulating value; k is a radical ofQ、kvRespectively a reactive power regulation coefficient and a voltage regulation coefficient; qrefQ is respectively a reference reactive power and an instantaneous reactive power value output by the inverter terminal; u shaperefAnd U is a reference value and an output value of the voltage at the end of the inverter respectively.
Since the reactive output and the generator-side voltage of the synchronous generator are realized by adjusting excitation, the reactive adjusting module of the virtual synchronous power generation algorithm is also mainly used for simulating the process, namely, the voltage and the reactive power output by the inverter are adjusted through the virtual electric potential E.
Mechanical torque T of active power regulating partmCan be expressed as:
in the formula, ToAnd Δ T are a mechanical torque command value and a frequency deviation feedback command value, respectively. The active power regulation principle is used for simulating the regulation process of the output active power of the traditional synchronous generator.
The rotor motion equation simulates the characteristics of the rotor motion of a synchronous generator and is expressed as:
in the formula, Tm、TeAnd TDMechanical, electromagnetic and damping torques of the synchronous generator, respectively; J. d is the rotational inertia and the damping coefficient of the synchronous generator respectively; omega, omegaoThe mechanical angular frequency and the grid angular frequency of the synchronous generator (where the number of pole pairs of the synchronous generator is 1, ω is both the mechanical angular frequency and the electrical angular frequency of the synchronous generator). The rotational inertia J and the damping coefficient D enable the virtual synchronous generator to have the inertia of the synchronous generator and damp and attenuate unbalanced power in the working process.
The stator electrical part can be represented as:
in the formula, L, E, u, i and R are respectively synchronous inductance, potential, terminal voltage, output current and stator resistance of the synchronous generator.
As shown in FIG. 8, the module contains a damping coefficient DPAnd an inertia coefficient J.
Wherein the virtual mechanical power P output by the inverterrefThe instruction values are:
Pref＝E*·Id
virtual electromagnetic power P output by invertereComprises the following steps:
Pref＝eaia+ebib+ecic
in the formula: e.g. of the typejAnd ij(j is a, b, c) are three-phase voltage and current output by the inverter respectively; peVirtual electromagnetic power output for the inverter.
From the analysis, the mechanical part and the electrical part of the virtual synchronous generator are mainly simulated by a rotor motion equation and a stator electrical equation, and active frequency modulation and reactive voltage regulation are carried out according to a control algorithm by acquiring information of voltage, current and frequency of a power grid.
Step three: bringing the phase angle value and the obtained voltage amplitude value into a three-phase voltage synthesis model to obtain a three-phase voltage reference value;
calculating by using a mechanical rotation equation of the virtual synchronous machine, and sending a calculation result phase angle theta to the three-phase voltage synthesis module;
the three-phase voltage synthesis module outputs three-phase reference voltage E through calculation based on the phase angle theta and the reference voltage amplitude Eabc；
Step four: and generating PWM waves based on the three-phase voltage reference values and a PWM generator, and controlling an inverter based on the PWM waves.
And sending the generated three-phase reference voltage into a PWM generator to generate PWM waves to control the inverter.
Damped and inertial power droop control strategies: a mechanical rotation module of the virtual synchronous generator is added in the power droop control, so that the grid-connected inverter adopting the power droop control has damping and inertia, has the excellent characteristics of the power droop control and the virtual synchronous machine control, and enhances the stability of the frequency and the voltage of a power grid.
Current droop control strategy with damping and inertia: a mechanical rotation module of the virtual synchronous generator is added in the current droop control, so that the grid-connected inverter adopting the current droop control has damping and inertia, has the excellent characteristics of the current droop control and the virtual synchronous machine control, and enhances the stability of the frequency and the voltage of a power grid.
According to the method provided by the invention, the mechanical rotation module of the virtual synchronous machine is added in the power droop control and the current droop control respectively, so that the grid-connected inverter has the excellent characteristics of droop control, damping and inertia, and the stability of safe operation of a power grid is enhanced.
Example 2
Based on the same concept, the invention also provides a droop control system with damping and inertia for the grid-connected inverter, and the system comprises:
a droop control system for a grid-tied inverter, the system comprising:
an acquisition module: the method comprises the steps of obtaining the grid voltage, current, frequency information, voltage amplitude and angular frequency of an inverter;
the model module is used for bringing the power grid voltage, current, frequency information and angular frequency into a pre-constructed virtual synchronous generator rotation model to obtain a phase angle value;
a synthesis module: the phase angle value and the voltage amplitude value are brought into a three-phase voltage synthesis model to obtain a three-phase voltage reference value;
a control module: for generating PWM waves based on the three-phase voltage reference values and a PWM generator, and controlling an inverter based on the PWM waves
The model module comprises: an obtaining unit, a building unit and a model unit;
the obtaining unit is used for obtaining a virtual potential and a mechanical torque by adopting a control algorithm of the synchronous generator based on the grid voltage, current and frequency information of the inverter;
the construction unit is used for constructing a rotor motion equation based on the mechanical torque, the angular frequency and the rotational inertia and the damping coefficient of the synchronous generator and constructing a stator electrical equation based on the virtual potential;
and the model unit is used for constructing a virtual synchronous generator rotation model based on the rotor motion equation and the stator electrical equation.
The acquisition module includes: an acquisition module;
the acquisition module is used for acquiring the output current or active power and reactive power of the inverter based on the abnormal conditions of the grid voltage and frequency of the inverter;
when the acquired data are active power and reactive power of the inverter, calculating by adopting a power droop control algorithm based on the active power and the reactive power to obtain angular frequency and voltage amplitude;
when the acquired data is the output current of the inverter, the output current is decomposed into active current and reactive current, and calculation is performed by adopting a current droop control algorithm based on the active current and the reactive current to obtain angular frequency and voltage amplitude.
Abbreviations and key term definitions in the figures of the present invention:
the mechanical part of VSC controller is: a mechanical part based on high-voltage direct-current control of voltage source commutation;
current is the Current (Current or power);
drooper is drooped (current or power).
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and block diagrams of methods, systems, and computer program products according to embodiments of the application. It will be understood that each flow and block of the flow diagrams and block diagrams, and combinations of flows and blocks in the flow diagrams and block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and block diagram block or blocks.
The present invention is not limited to the above embodiments, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are included in the scope of the claims of the present invention which are filed as the application.
Claims (10)
1. A droop control method of a grid-connected inverter is characterized by comprising the following steps:
acquiring the grid voltage, current, frequency information, voltage amplitude and angular frequency of an inverter;
bringing the power grid voltage, current, frequency information and angular frequency into a pre-constructed virtual synchronous generator rotation model to obtain a phase angle value;
the phase angle value and the voltage amplitude value are brought into a three-phase voltage synthesis model to obtain a three-phase voltage reference value;
and generating PWM waves based on the three-phase voltage reference values and a PWM generator, and controlling an inverter based on the PWM waves.
2. The method of claim 1, wherein the constructing of the virtual synchronous generator rotation model comprises:
based on the grid voltage, current and frequency information of the inverter, a control algorithm of the synchronous generator is adopted to obtain a virtual potential and a mechanical torque;
constructing a rotor motion equation based on the mechanical torque, the angular frequency and the rotational inertia and the damping coefficient of the synchronous generator, and constructing a stator electrical equation based on the virtual potential;
and constructing a virtual synchronous generator rotation model based on the rotor motion equation and the stator electrical equation.
3. The method of claim 2, wherein the rotor equation of motion is as follows:
in the formula, theta is a phase angle value; t ismMechanical torque of the synchronous generator; t iseIs the electromagnetic torque of the synchronous generator; t isDDamping torque for the synchronous generator; j is the rotational inertia of the synchronous generator; dPThe damping coefficient of the synchronous generator; omega is the mechanical and electrical angular frequency of the synchronous generator; omegaoIs the grid angular frequency of the synchronous generator; prefA virtual mechanical power command value output for the inverter; peVirtual electromagnetic power output for the inverter.
4. The method of claim 2, wherein the stator electrical equation is as follows:
in the formula, L is the synchronous inductance of the synchronous generator; e is a virtual potential; r is a stator resistor; i is an output current; u is the inverter terminal voltage.
5. The method of claim 1, wherein the obtaining of the angular frequency and the voltage amplitude comprises:
acquiring output current or active power and reactive power of the inverter based on the abnormal conditions of the grid voltage and frequency of the inverter;
when the acquired data are active power and reactive power of the inverter, calculating by adopting a power droop control algorithm based on the active power and the reactive power to obtain angular frequency and voltage amplitude;
when the acquired data is the output current of the inverter, the output current is decomposed into active current and reactive current, and calculation is performed by adopting a current droop control algorithm based on the active current and the reactive current to obtain angular frequency and voltage amplitude.
6. The droop control method of a grid-connected inverter according to claim 5, wherein the current droop control algorithm is calculated as follows:
in the formula: omega*Is the rated angular frequency; u shape*Is the voltage amplitude;is an active current command value;is a reactive current instruction value; a is an active current frequency droop coefficient; and b is a reactive current and voltage droop coefficient.
7. The droop control method of a grid-connected inverter according to claim 5, wherein the power droop control algorithm is calculated as follows:
in the formula: f is a rated frequency; u shapeoIs the amplitude; poIs an active power command value; qoIs a reactive power instruction value; m and n are sag coefficients.
8. A droop control system for a grid-tied inverter, the system comprising:
an acquisition module: the method comprises the steps of obtaining the grid voltage, current, frequency information, voltage amplitude and angular frequency of an inverter;
the model module is used for bringing the power grid voltage, current, frequency information and angular frequency into a pre-constructed virtual synchronous generator rotation model to obtain a phase angle value;
a synthesis module: the phase angle value and the voltage amplitude value are brought into a three-phase voltage synthesis model to obtain a three-phase voltage reference value;
a control module: and the inverter is used for generating PWM waves based on the three-phase voltage reference values and the PWM generator and controlling the inverter based on the PWM waves.
9. The system of claim 8, wherein the model module comprises: an obtaining unit, a building unit and a model unit;
the obtaining unit is used for obtaining a virtual potential and a mechanical torque by adopting a control algorithm of the synchronous generator based on the grid voltage, current and frequency information of the inverter;
the construction unit is used for constructing a rotor motion equation based on the mechanical torque, the angular frequency and the rotational inertia and the damping coefficient of the synchronous generator and constructing a stator electrical equation based on the virtual potential;
and the model unit is used for constructing a virtual synchronous generator rotation model based on the rotor motion equation and the stator electrical equation.
10. The system of claim 8, wherein the acquisition module comprises: an acquisition module;
the acquisition module is used for acquiring the output current or active power and reactive power of the inverter based on the abnormal conditions of the grid voltage and frequency of the inverter;
when the acquired data are active power and reactive power of the inverter, calculating by adopting a power droop control algorithm based on the active power and the reactive power to obtain angular frequency and voltage amplitude;
when the acquired data is the output current of the inverter, the output current is decomposed into active current and reactive current, and calculation is performed by adopting a current droop control algorithm based on the active current and the reactive current to obtain angular frequency and voltage amplitude.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN112104001A (en) * | 2020-10-12 | 2020-12-18 | 四川科陆新能电气有限公司 | Power supply droop coefficient optimization control method |
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