CN110247429B - Analysis method for voltage feedforward control photovoltaic power generation considering coupling - Google Patents
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Abstract
An analysis method for controlling photovoltaic power generation by considering coupled voltage feedforward can solve the technical problem that the stable and safe operation of a power grid is directly influenced by the coupling resonance of the parallel grid connection of a plurality of inverters for photovoltaic power generation. The method comprises the following steps: s1, establishing an equivalent model of the photovoltaic power generation system; s2, carrying out analysis of the photovoltaic power generation system grid-connected control based on voltage feedforward control considering coupling; s3, establishing a grid-connected photovoltaic power generation model equivalent model considering coupled voltage feedforward control based on the photovoltaic power generation system equivalent model of S1 and by combining the analysis result of S2; and S4, establishing a photovoltaic power generation double-inverter parallel grid-connected equivalent model based on the grid-connected photovoltaic power generation model equivalent model of S3. The method calculates the coupling between the inverter and the inverter, between the inverter and the parallel inverter, and between the inverter and the power grid during grid connection, corrects the original model parameters in proportion, and compared with other models, the model has more comprehensive consideration factors, thereby improving the effectiveness of the model.
Description
Technical Field
The invention relates to the technical field of parallel connection and grid connection of inverters of a power system, in particular to an analysis method for voltage feedforward control photovoltaic power generation considering coupling.
Background
The large-scale use of power generation equipment of renewable energy sources (such as photovoltaic, fan and the like) and the integration of the power generation equipment into a power grid bring new challenges to the stable operation of a power system, and the stable and safe operation of the power grid is directly influenced by the coupling resonance of the parallel connection and the grid connection of a plurality of photovoltaic power generation inverters. The mutual inductance phenomenon in the inverter is complex, different models exist under different installation modes, and different application occasions exist, but the existing multi-inverter parallel grid-connected model is not completely suitable for the grid-connected stability analysis of a large-scale photovoltaic power station.
In the current research results, the research on the parallel grid-connected coupling resonance of the multi-inverter is divided into two aspects of a control strategy and a simulation of a model, the control strategy for inhibiting the coupling resonance mainly comprises a double-closed-loop active damping control strategy, inverter side current single closed-loop control, split capacitance method single current closed-loop control and the like, but the control methods do not consider the influence of the voltage quality of a power grid on the current of the power grid, and the mutual inductance inside the inverter is not considered.
Disclosure of Invention
The analysis method for controlling photovoltaic power generation by considering coupled voltage feedforward can solve the technical problem that the stable and safe operation of a power grid is directly influenced by the coupling resonance of the parallel grid connection of multiple inverters for photovoltaic power generation.
In order to achieve the purpose, the invention adopts the following technical scheme:
an analytical method for controlling photovoltaic power generation in consideration of coupled voltage feedforward, comprising the steps of:
s1, establishing an equivalent model of the photovoltaic power generation system;
s2, carrying out analysis of the photovoltaic power generation system grid-connected control based on voltage feedforward control considering coupling;
s3, establishing a grid-connected photovoltaic power generation model equivalent model considering coupled voltage feedforward control based on the photovoltaic power generation system equivalent model of S1 and by combining the analysis result of S2;
and S4, establishing a photovoltaic power generation double-inverter parallel grid-connected equivalent model based on the grid-connected photovoltaic power generation model equivalent model of S3.
Further, the step S1 is to establish an equivalent model of the photovoltaic power generation system;
the method specifically comprises the following steps:
s1.1, drawing an equivalent model of a photovoltaic power generation system, comprising: the photovoltaic cell module, the inverter and a control system thereof and the LCL type filter are arranged on the power grid;
s1.2, the inverter and the control system thereof comprise an inverter side current feedback control system closed loop transfer function considering coupling between internal inductances of the photovoltaic power generation system, and the closed loop transfer function is as follows:
the parameter expression in the formula (1) is as follows:
i2 1for a single inverter grid-connected current, KpAnd KiProportional coefficient and integral coefficient of PI controller, H is current feedback coefficient, irefTo command the system with current uiFor the inverter-side output voltage i1For the inverter-side output current ucFor filtering the capacitor voltage i2Is L2Branch current ugFor the mains voltage, icFor filtering the capacitor current, L1、L2Is a filter inductance, M12Is L1And L2The mutual inductance of (2).
Further, the S2 develops an analysis of the photovoltaic power generation system grid-connected control based on the voltage feedforward control considering the coupling; the method specifically comprises the following steps:
s2.1, writing back a route equation and a node equation according to the grid-connected model column of the photovoltaic power generation system:
in formula (3), M2gIs L2Equivalent inductance L of power gridgMutual inductance coefficient between;
s2.2, considering the coupling relation between internal inductors of the inverter and between the inverter and a power grid, and performing column writing
Closed loop transfer function of the grid-connected control system for photovoltaic power generation:
i2(s)＝K2iref(s)-Y2ug(s) (4)
the parameter expression in the formula (4) is as follows:
s2.3, as can be seen from the formula (4), the inverter grid-connected current i adopts the traditional current feedback control scheme2Under the influence of the voltage of the power grid, in order to reduce the influence of the voltage of the power grid on the grid-connected current of the photovoltaic power generation, a voltage feedforward control strategy considering coupling is adopted, the grid voltage feedforward control is added before PWM control, and the obtained grid-connected current is as follows:
i2(s)＝K2iref(s)-Y3ug(s) (6)
the parameters in formula (6) are as follows:
further, the S3 establishes a grid-connected photovoltaic power generation model equivalent model considering the coupled voltage feedforward control based on the photovoltaic power generation system equivalent model of S1 and by combining the analysis result of S2;
the method specifically comprises the following steps:
s3.1, the equivalent circuit of the grid-connected photovoltaic power generation model comprises an inverter equivalent current source, circuit equivalent impedance and power grid equivalent impedance, and output impedance Z controlled by inverter voltage feedforward is introduced into a photovoltaic power generation system controlled by power grid voltage feedforward0The connection point of the photovoltaic power generation system and the power grid is called a public connection point (PCC point);
s3.2, in the single established grid-connected photovoltaic power generation model adopting voltage feedforward control, firstly, a voltage source u is applied by using a circuit superposition principlegShort-circuit, counting current source irefInfluence on grid-connected current:
then the current source irefOpen circuit, calculate voltage source ugInfluence on grid-connected current:
and combining the formula (8) and the formula (9) to obtain an output value of the power grid current:
in the formula z0Is an inverter-side equivalent impedance, zgIs the equivalent impedance of the grid, z1Impedance introduced for voltage feed-forward control, igFor grid current (grid-connected current), irefCommanding a current for the control system;
s3.3, known
Comparing equation (6) and equation (10) yields:
will K2、Y3Is calculated in place of the formula (12):
further, the S4 establishes a photovoltaic power generation double-inverter parallel grid-connected equivalent model based on the grid-connected photovoltaic power generation model equivalent model of S3;
the method specifically comprises the following steps:
s4.1, when a plurality of inverters are connected into a power grid in parallel, due to the fact that the coupling condition inside the system is more complex, coupling exists between internal inductors of a single inverter and the power grid, the coupling can also be mutually coupled with internal inductors of other inverters connected in parallel, the influence of the coupling on an equivalent model is reflected as the change of the impedance of the power grid, a method for correcting a control coefficient is adopted in a calculation formula, and when n inverters are connected into the power grid in parallel, an expression of grid-connected current of the n inverters can be obtained:
i2_mfor m inverter grid-connected current, Gm,iCoupling factor for i inverter to m inverter, Gm,gCoupling factors of the power grid to the mth inverter;
s4.2, calculating parameters in the S4.1 in a double-inverter parallel grid-connected model according to a proportion, taking a first inverter as an example:
in the formula i2_1Is the grid-connected current of the first parallel inverter iref，1And iref，2Respectively, command currents of two inverters, Y3_1And Y3_2Respectively representing the equivalent impedances, Z, of two invertersgFor the equivalent impedance of the grid, K2_1And K2_2The equivalent current source coefficients of the two inverters are respectively;
s4.3, in the photovoltaic power generation system, the adopted inverter has the same filter parameters and control algorithm, namely:
s4.4, calculating i according to the above2_1By recalculating i2_2And, obtaining:
s4.5, combined type (15-17), calculating i 2:
s4.6, obtaining a photovoltaic power generation double-inverter parallel grid-connected equivalent model according to the formula (18); wherein the parameters are as follows:
according to the technical scheme, the analysis method for voltage feedforward control photovoltaic power generation considering coupling is an analysis method for coupling between parallel inverters considering mutual inductance between the inverters and a power grid and power grid impedance influence, and can provide an accurate equivalent model comprehensively considering influence factors for parallel connection and grid connection of the multiple inverters, so that the inverter grid connection model is suitable for safe and stable operation of a large-scale parallel-series power grid.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention combines mutual inductance and voltage feedforward control, provides a photovoltaic power generation control strategy considering coupling voltage feedforward control, and changes the situation that the consideration factor is incomplete under the traditional voltage feedforward control condition and the mutual inductance inside the inverter cannot be accurately reflected, so that the control strategy is more reasonable, and the change of the state quantity can be directly reflected more accurately and efficiently.
2. The invention provides a single-inverter photovoltaic power station equivalent model considering coupled voltage feedforward control, and the equivalent model is provided by partially weakening the influence of the power grid voltage on the power grid current under the condition of ensuring the effectiveness through the control of a current source parallel output impedance equivalent inverter and the influence introduced by the other output impedance equivalent voltage feedforward control.
3. The invention provides a photovoltaic power generation double-inverter parallel grid-connected equivalent model considering coupled voltage feedforward control, which is used for calculating the coupling between an inverter and the model, between the inverter and a parallel inverter and between the inverter and a power grid during grid connection and correcting the original model parameters in proportion.
Drawings
FIG. 1 is a schematic diagram of the process steps of the present invention;
FIG. 2 is a photovoltaic power generation equivalent model of the present invention;
FIG. 3 is an inverter side current feedback control scheme of the present invention;
FIG. 4 is a partially coupled inverter-side current feedback control scheme contemplated by the present invention;
FIG. 5 is a grid-connected model of a photovoltaic power generation stack according to the present invention;
FIG. 6 is an inverter side current feedback control scheme of the present invention that contemplates full coupling;
FIG. 7 is a voltage feed forward control scheme of the present invention that contemplates full coupling;
FIG. 8 is a single photovoltaic power generation model equivalent model of the present invention considering fully coupled voltage feed-forward control;
FIG. 9 is a dual inverter parallel grid-connected model of the present invention;
FIG. 10 is a photovoltaic power generation double-inverter parallel grid-connected equivalent model.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention.
As shown in fig. 1, in the present embodiment, an analysis method for controlling photovoltaic power generation by considering coupled voltage feedforward includes the following steps:
s1, establishing an equivalent model of the photovoltaic power generation system;
s2, carrying out analysis of the photovoltaic power generation system grid-connected control based on voltage feedforward control considering coupling;
s3, establishing a grid-connected photovoltaic power generation model equivalent model considering coupled voltage feedforward control based on the photovoltaic power generation system equivalent model of S1 and by combining the analysis result of S2;
and S4, establishing a photovoltaic power generation double-inverter parallel grid-connected equivalent model based on the grid-connected photovoltaic power generation model equivalent model of S3.
The following detailed description is made with reference to the accompanying drawings:
s1, establishing an equivalent model of the photovoltaic power generation system;
s1.1, the photovoltaic power generation system equivalent model comprises: photovoltaic cell subassembly, inverter and control system, LCL type wave filter thereof. The inverter control system adopts a traditional inverter side current feedback control scheme based on a PI controller. As shown in fig. 2 and 3.
S1.2, considering the closed loop transfer function of the inverter side current feedback control system coupled between the internal inductances of the photovoltaic power generation system, the closed loop transfer function is as follows: as shown in fig. 4
The parameters in formula (1) are calculated as follows:
i2 1for a single inverter grid-connected current, KpAnd KiProportional and integral parameters of the current regulator, H is the current feedback coefficient, irefTo command the system with current uiFor the inverter-side output voltage i1For the inverter-side output current ucFor filtering the capacitor voltage i2Is L2Branch current ugFor the mains voltage, icFor filtering the capacitor current, L1、L2Is the filter inductance, M12Is L1And L2The mutual inductance coefficient of (a);
s2, carrying out analysis of the photovoltaic power generation system grid-connected control strategy based on voltage feedforward control considering coupling;
s2.1, writing back a route equation and a node equation according to the grid-connected model column of the photovoltaic power generation system: as shown in fig. 5
In formula (3), M2gIs L2Equivalent inductance L of power gridgMutual inductance coefficient between;
s2.2, considering coupling relations among internal inductances of the inverters and between the inverters and a power grid, and writing a closed loop transfer function of the photovoltaic power generation grid-connected control system: as shown in fig. 6
i2(s)＝K2iref(s)-Y2ug(s) (4)
The parameters in formula (4) are set as follows:
s2.3, as can be seen from the formula (4), the inverter grid-connected current i adopts the traditional current feedback control scheme2Under the influence of the voltage of the power grid, in order to reduce the influence of the voltage of the power grid on the grid-connected current of the photovoltaic power generation, the voltage feedforward control considering coupling is adopted, a grid voltage feedforward control loop is added before PWM control, and the grid-connected current at the moment is obtained as follows: as shown in fig. 7
i2(s)＝K2iref(s)-Y3ug(s) (6)
The parameters in the formula are as follows:
s3, establishing a grid-connected photovoltaic power generation model equivalent model considering coupled voltage feedforward control;
s3.1, an equivalent circuit of a grid-connected photovoltaic power generation model generally comprises an inverter equivalent current source, circuit equivalent impedance and power grid equivalent impedance, and in a photovoltaic power generation system adopting power grid voltage feedforward control, output impedance Z of inverter voltage feedforward control is introduced0A PCC node is arranged at the grid connection position of the inverter side and the grid side in the graph; as shown in fig. 8
S3.2, in the single established grid-connected photovoltaic power generation model adopting voltage control feedforward control, firstly, applying a circuit superposition principle to a voltage source ugConsider as a short circuit, calculate the current source irefInfluence on grid-connected current:
then the current source irefConsider as an open circuit, calculate the voltage source ugInfluence on grid-connected current:
and combining the formula (8) and the formula (9) to obtain an output value of the power grid current:
in the formula z0Is an inverter-side equivalent impedance, zgIs the equivalent impedance of the grid, z1Impedance introduced for voltage feed-forward control, igFor grid current (grid-connected current), irefCommanding a current for the control system;
s3.3, known
Comparing equation (6) and equation (10) yields:
will K2、Y3Is calculated in place of the formula (12):
s4, connecting the photovoltaic power generation double inverters in parallel and connecting a grid with an equivalent model;
s4.1, when a plurality of inverters are connected into a power grid in parallel, the coupling condition inside the system is more complex, and not only the internal inductances of a single inverter and the power grid are coupled, but also the internal inductances of the single inverter and the power grid are coupled with each other, and the internal inductances of the inverters are also coupled with other parallel-connected inverter internal inductance elements, as shown in fig. 9. The influence of coupling on the equivalent model is reflected as the change of the power grid impedance, a method for correcting a control coefficient is adopted in the calculation formula, and an expression of grid-connected current of n inverters can be obtained when the n inverters are connected in parallel and connected in a grid mode:
i2_ m is the grid-connected current of the mth inverter, Gm, i is the coupling factor of the ith inverter to the mth inverter, and Gm, g is the coupling factor of the power grid to the mth inverter;
s4.2, calculating parameters in the S4.1 in a double-inverter parallel grid-connected model according to a proportion, taking a first inverter as an example:
where i2_1 is the grid-connected current of the first parallel inverter, iref，1And iref，2The command current of the first inverter and the command current of the second inverter are respectively, Y3_1 and Y3_2 respectively represent the equivalent impedance of the first inverter and the equivalent impedance of the second inverter, Zg is the equivalent impedance of a power grid, and K2_1 and K2_2 are the equivalent current source coefficient of the first inverter and the equivalent current source coefficient of the second inverter respectively;
s4.3, inverters of the same manufacturer and the same model are adopted in the photovoltaic power generation system, and filter parameters and control algorithms are the same, namely:
s4.4, calculating i according to the above2_1By recalculating i2_2And, obtaining:
s4.5, combining and standing (15-17), and calculating i2：
And S4.6, obtaining a photovoltaic power generation double-inverter parallel grid-connected equivalent model according to the formula (18). Wherein the parameters are as follows: as shown in fig. 10
To sum up, the analysis method for controlling photovoltaic power generation by considering the voltage feedforward of the coupling in the embodiment of the invention is an equivalent model for controlling a photovoltaic power generation double-inverter parallel system by considering the voltage feedforward of the coupling, considers the influence of the coupling on the stability of a power grid when a single-machine model and the double-inverter parallel grid-connection are connected, weakens the influence of the voltage of the power grid on the current of the power grid by adopting the voltage feedforward control, adds mutual inductance parameters in an inverter and between the inverter and the power grid in a control strategy, improves the accuracy and the effectiveness of a single-inverter model, and equates the influence of mutual coupling between the inverters on the system into the influence on an impedance and a current source when the double-inverter parallel grid-connection model is established, so that the model is more accurate, and lays a foundation for the parallel grid-connection.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (4)
1. An analysis method for controlling photovoltaic power generation by considering coupled voltage feedforward is characterized in that: the method comprises the following steps:
s1, establishing an equivalent model of the photovoltaic power generation system;
s2, carrying out analysis of the photovoltaic power generation system grid-connected control based on voltage feedforward control considering coupling;
s3, establishing a grid-connected photovoltaic power generation model equivalent model considering coupled voltage feedforward control based on the photovoltaic power generation system equivalent model of S1 and by combining the analysis result of S2;
s4, establishing a photovoltaic power generation double-inverter parallel grid-connected equivalent model based on the grid-connected photovoltaic power generation model equivalent model of S3;
the S1 building a photovoltaic power generation system equivalent model;
the method specifically comprises the following steps:
s1.1, drawing an equivalent model of a photovoltaic power generation system, comprising: the photovoltaic cell module, the inverter and a control system thereof and the LCL type filter are arranged on the power grid;
s1.2, the inverter and the control system thereof comprise an inverter side current feedback control system closed loop transfer function considering coupling between internal inductances of the photovoltaic power generation system, and the closed loop transfer function is as follows:
the parameter expression in the formula (1) is as follows:
i2 1for a single inverter grid-connected current, KpAnd KiProportional coefficient and integral coefficient of PI controller, H is current feedback coefficient, irefTo command the system with current uiFor the inverter-side output voltage i1For the inverter-side output current ucFor filtering the capacitor voltage i2Is L2Branch current ugFor the mains voltage, icFor filtering the capacitor current, L1、L2Is a filter inductance, M12Is L1And L2The mutual inductance of (2).
2. The coupled voltage feedforward controlled photovoltaic power generation-considered analysis method according to claim 1, wherein: the S2 carries out analysis of the photovoltaic power generation system grid-connected control based on the voltage feedforward control considering coupling; the method specifically comprises the following steps:
s2.1, writing back a route equation and a node equation according to the grid-connected model column of the photovoltaic power generation system:
in formula (3), M2gIs L2Equivalent inductance L of power gridgMutual inductance coefficient between;
s2.2, considering coupling relations among internal inductances of the inverters and between the inverters and a power grid, and writing a closed loop transfer function of the photovoltaic power generation grid-connected control system:
i2(s)＝K2iref(s)-Y2ug(s) (4)
the parameter expression in the formula (4) is as follows:
s2.3, as can be seen from the formula (4), the inverter grid-connected current i adopts the traditional current feedback control scheme2Under the influence of the voltage of the power grid, in order to reduce the influence of the voltage of the power grid on the grid-connected current of the photovoltaic power generation, a voltage feedforward control strategy considering coupling is adopted, the grid voltage feedforward control is added before PWM control, and the obtained grid-connected current is as follows:
i2(s)＝K2iref(s)-Y3ug(s) (6)
the parameters in formula (6) are as follows:
3. the coupled voltage feedforward controlled photovoltaic power generation-considered analysis method according to claim 2, characterized in that: the S3 is based on the photovoltaic power generation system equivalent model of S1 and combined with the analysis result of S2, and a grid-connected photovoltaic power generation model equivalent model considering coupled voltage feedforward control is established;
the method specifically comprises the following steps:
s3.1, the equivalent circuit of the grid-connected photovoltaic power generation model comprises an inverter equivalent current source, circuit equivalent impedance and power grid equivalent impedance, and output impedance Z controlled by inverter voltage feedforward is introduced into a photovoltaic power generation system controlled by power grid voltage feedforward0The connection point of the photovoltaic power generation system and the power grid is called a public connection point (PCC point);
s3.2, in the single established grid-connected photovoltaic power generation model adopting voltage feedforward control, firstly, a voltage source u is applied by using a circuit superposition principlegShort-circuit, counting current source irefInfluence on grid-connected current:
then the current source irefOpen circuit, calculate voltage source ugInfluence on grid-connected current:
and combining the formula (8) and the formula (9) to obtain an output value of the power grid current:
in the formula z0Is an inverter-side equivalent impedance, zgIs the equivalent impedance of the grid, z1Impedance introduced for voltage feed-forward control, igFor grid currents, in particular grid-connected currents, irefCommanding a current for the control system;
s3.3, known
Comparing equation (6) and equation (10) yields:
will K2、Y3Is calculated in place of the formula (12):
4. the coupled voltage feedforward controlled photovoltaic power generation-considered analysis method according to claim 3, wherein: the S4 establishes a photovoltaic power generation double-inverter parallel grid-connected equivalent model based on the grid-connected photovoltaic power generation model equivalent model of S3;
the method specifically comprises the following steps:
s4.1, when a plurality of inverters are connected into a power grid in parallel, due to the fact that the coupling condition inside the system is more complex, coupling exists between internal inductors of a single inverter and the power grid, the coupling can also be mutually coupled with internal inductors of other inverters connected in parallel, the influence of the coupling on an equivalent model is reflected as the change of the impedance of the power grid, a method for correcting a control coefficient is adopted in a calculation formula, and when n inverters are connected into the power grid in parallel, an expression of grid-connected current of the n inverters can be obtained:
i2_mfor m inverter grid-connected current, Gm,iCoupling factor for i inverter to m inverter, Gm,gCoupling factors of the power grid to the mth inverter;
s4.2, calculating parameters in the S4.1 in a double-inverter parallel grid-connected model according to a proportion, taking a first inverter as an example:
in the formula i2_1Is the grid-connected current of the first parallel inverter iref，1And iref，2Respectively, command currents of two inverters, Y3_1And Y3_2Respectively representing two inversionsEquivalent impedance of the device, ZgFor the equivalent impedance of the grid, K2_1And K2_2The equivalent current source coefficients of the two inverters are respectively;
s4.3, in the photovoltaic power generation system, the adopted inverter has the same filter parameters and control algorithm, namely:
s4.4, calculating i according to the above2_1By recalculating i2_2And, obtaining:
s4.5, combined type (15-17), calculating i 2:
s4.6, obtaining a photovoltaic power generation double-inverter parallel grid-connected equivalent model according to the formula (18); wherein the parameters are as follows:
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