CN112421676B - Microgrid grid-connected and off-grid smooth switching current and voltage phase compensation method - Google Patents

Microgrid grid-connected and off-grid smooth switching current and voltage phase compensation method Download PDF

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CN112421676B
CN112421676B CN202011242108.3A CN202011242108A CN112421676B CN 112421676 B CN112421676 B CN 112421676B CN 202011242108 A CN202011242108 A CN 202011242108A CN 112421676 B CN112421676 B CN 112421676B
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grid
current
microgrid
control
voltage
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CN112421676A (en
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冯仰敏
杨沛豪
赵勇
李立勋
李万镒
常洋涛
邬冯值
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Xian Thermal Power Research Institute Co Ltd
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Xian Thermal Power Research Institute Co Ltd
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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
    • 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
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • 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
    • H02J3/388—Islanding, i.e. disconnection of local power supply from the network
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]

Abstract

The invention discloses a microgrid grid-connected and off-grid smooth switching current and voltage phase compensation method, which comprises the following steps of: introducing a phase compensation controller of the virtual synchronous machine stepper into a control system to obtain a phase angle expression after compensation; a feedforward decoupling control algorithm is adopted to eliminate a current coupling term between the d-axis component and the q-axis component to obtain an input expression; obtaining a current outer loop control equation with a voltage compensation term; obtaining a voltage inner loop control equation with a current compensation phase; obtaining a microgrid grid-connected to off-grid switching control system with compensation control; obtaining an input reference value expression; obtaining a voltage outer ring control equation with a current compensation phase; obtaining a current inner loop control equation with a voltage compensation phase; and obtaining a microgrid off-grid to grid-connected switching control system with compensation control. The invention adds a corresponding current compensation link and a voltage compensation link, and ensures that the reference current value and the voltage value are unchanged before and after the switching of the micro-grid.

Description

Microgrid grid-connected and off-grid smooth switching current and voltage phase compensation method
Technical Field
The invention relates to a microgrid grid-connected and off-grid smooth switching current-voltage phase compensation method, in particular to a method for compensating current, voltage and phase when a microgrid is switched from grid-connected operation to off-grid operation and from off-grid operation to grid-connected operation respectively.
Background
With the continuous increase of the capacity of the power grid, the structure of the regional power grid is complicated, and in order to improve the support for the power generation of renewable energy sources and realize the large-scale application of the renewable energy sources, the micro-grid needs to be developed vigorously. Under normal conditions, the micro-grid and the large power grid are in grid-connected operation, when the large power grid fails or the power quality does not meet the load requirement, the micro-grid needs to be quickly and actively disconnected from the large power grid, and the micro-grid is transited to an island mode, so that uninterrupted power supply of important loads of the system is guaranteed. And when the large power grid is recovered to be normal, the micro grid is reconnected with the large power grid, and the grid connection mode is recovered.
Grid-connected operation and off-grid operation are two stable operation states of the microgrid, and the switching between the two states may cause problems of transient voltage fluctuation, frequency fluctuation, current impact and the like, and even affect the normal operation of the load in severe cases. Therefore, to ensure safe and stable operation of the microgrid, the above-mentioned problems must be eliminated.
Disclosure of Invention
The invention aims to provide a microgrid grid-connected and off-grid smooth switching current-voltage phase compensation method, which is characterized in that when a microgrid is switched from grid-connected operation to off-grid operation and from off-grid operation to grid-connected operation, corresponding current compensation links and voltage compensation links are added, so that the reference current value and the voltage value before and after switching of the microgrid are unchanged, and a phase compensation link based on a virtual synchronizer is further introduced, so that the phase compensation in the switching process is realized.
The invention is realized by adopting the following technical scheme:
a microgrid grid-connected and off-grid smooth switching current and voltage phase compensation method comprises the following steps:
1) According to the principle that the reference angular speed of the d axis before the micro grid is switched is consistent with the rotation angular speed of the d axis after the micro grid is switched, introducing a phase compensation controller of the virtual synchronous machine stepper into a control system to obtain a phase angle expression after compensation;
2) In the microgrid converter control system, a feedforward decoupling control algorithm is adopted to eliminate a current coupling term between d-axis components and q-axis components to obtain an input expression;
3) When the microgrid is controlled to be switched from grid-connected control to off-grid control, on the basis of the input expression of the microgrid converter control system in the step 2), stable values of output voltages of d and q shafts of a PI controller based on a microgrid grid-connected mode are introduced to serve as voltage compensation items, and a current outer ring control equation with the voltage compensation items is obtained;
4) When the micro-grid is converted from grid-connected control to off-grid control, current compensation is added into closed-loop voltage inner-loop control to obtain a voltage inner-loop control equation with a current compensation phase;
5) According to the compensation phase angle expression obtained in the step 1), the current outer ring control equation in the step 3) and the voltage inner ring control equation in the step 4), obtaining a microgrid grid-connected to off-grid switching control system with compensation control;
6) When the microgrid is converted from off-grid control to grid-connected control, the inner ring is changed into current closed-loop control to obtain an input reference value expression;
7) Introducing the microgrid current inner ring input reference value expression in the step 6) into voltage outer ring control to obtain a voltage outer ring control equation with a current compensation phase;
8) When the microgrid is converted from off-grid control to grid-connected control, voltage compensation is added into closed-loop current inner-loop control to obtain a current inner-loop control equation with a voltage compensation phase;
9) And obtaining a microgrid off-grid to grid-connected switching control system with compensation control according to the compensation phase angle expression obtained in the step 1), the voltage outer ring control equation in the step 7) and the current inner ring control equation in the step 8).
The further improvement of the invention is that the specific implementation method of the step 1) comprises the following steps: according to the principle that the reference angular speed of the d axis before the micro grid is switched is consistent with the rotation angular speed of the d axis after the micro grid is switched, introducing a phase compensation controller of the virtual synchronous machine stepper into a control system to obtain a phase angle expression after compensation: theta u ＝θ+∫ω vsg dt; wherein: omega vsg Is the angular frequency of the virtual synchronous machine; θ is the initial phase.
The further improvement of the invention is that the specific implementation method of the step 2) comprises the following steps: in the microgrid converter control system, a feedforward decoupling control algorithm is adopted to eliminate a current coupling term between d-axis and q-axis components, and an input expression is obtained:
Figure BDA0002768761400000031
wherein: u. u d * 、u q * D-axis and q-axis voltage reference values under a dq synchronous rotation coordinate system at the AC side of the microgrid converter; u. of d 、u q The current values of d-axis and q-axis voltages under a dq synchronous rotation coordinate system at the AC side of the microgrid converter are obtained; omega is the voltage angular frequency of the AC side of the microgrid converter; l is d 、L q Inductances of d and q axes, respectively; i.e. i d 、i q Current values of d-axis current and q-axis current under a dq synchronous rotation coordinate system at the AC side of the microgrid converter are obtained; k is a radical of p As a proportional phase of the control system, proportionally reflecting a deviation signal of the system; k is a radical of i As an integral phase of the control system, integral operation is carried out on the deviation signal to eliminate the deviation; i all right angle d * 、i q * And d and q axis current reference values of the microgrid converter on an alternating current side dq synchronous rotating coordinate system.
The further improvement of the invention is that the specific implementation method of the step 3) is as follows: when the microgrid is switched from grid-connected control to off-grid control, on the basis of the input expression of the microgrid converter control system in the step 2), stable values of output voltages of d and q axes of a PI controller based on a microgrid grid-connected mode are introduced to serve as voltage compensation items, and a current outer ring control equation with the voltage compensation items is obtained:
Figure BDA0002768761400000032
wherein: u. of dpq 、u qpq And outputting voltage steady-state values for d and q axes of the PI controller in the microgrid grid-connected mode.
The further improvement of the invention is that the specific implementation method of the step 4) comprises the following steps: when the micro-grid is converted from grid-connected control to off-grid control, current compensation is added into closed-loop voltage inner-loop control, and a voltage inner-loop control equation with a current compensation phase is obtained:
Figure BDA0002768761400000033
wherein: i.e. i dpq 、i qpq And outputting current steady-state values for d and q axes of the PI controller in the microgrid grid-connected mode.
The further improvement of the invention is that the specific implementation method of the step 5) comprises the following steps: according to the compensation phase angle expression obtained in the step 1), the current outer ring control equation in the step 3) and the voltage inner ring control equation in the step 4), the microgrid grid-connected to off-grid switching control system with compensation control is obtained, and through current and voltage compensation and phase compensation control, the reference current value and the voltage value before and after microgrid grid-connected and off-grid smooth switching are not changed, the original system power is not changed, and smooth transition in the system switching process is guaranteed.
The further improvement of the invention is that the specific implementation method of the step 6) is as follows: when the off-grid control of the microgrid is converted into grid-connected control, the inner ring is changed into current closed-loop control, and an input reference value expression is obtained:
Figure BDA0002768761400000041
wherein: i.e. i dvf 、i qvf And outputting current steady-state values for d and q axes of the PI controller in the off-grid mode of the microgrid.
The further improvement of the invention is that the specific implementation method of the step 7) comprises the following steps: introducing the microgrid current inner ring input reference value expression in the step 6) into voltage outer ring control to obtain a voltage outer ring control equation with a current compensation phase:
Figure BDA0002768761400000042
wherein:
Figure BDA0002768761400000043
synchronous rotating coordinate system for alternating current side dq of microgrid converterAnd d and q axes are compensated current reference values.
The further improvement of the invention is that the specific implementation method of the step 8) is as follows: when the microgrid is converted from off-grid control to grid-connected control, voltage compensation is added to closed-loop current inner-loop control, and a current inner-loop control equation with a voltage compensation phase is obtained:
Figure BDA0002768761400000044
wherein:
Figure BDA0002768761400000045
compensated voltage reference values of d and q axes of a dq synchronous rotation coordinate system on the AC side of the microgrid converter; adding corresponding current compensation amount in a closed-loop voltage control link; u. of dvf 、u qvf And outputting voltage steady-state values for d and q axes of the PI controller in the off-grid mode of the microgrid.
Compared with the prior art, the invention has at least the following beneficial technical effects:
1. the method adopts a phase compensation technology based on the virtual synchronous machine, and improves the stability of the microgrid in the switching process.
2. According to the invention, when the microgrid is switched from a grid-connected mode to an off-grid mode, the output value of the PI controller in the grid-connected mode is introduced, so that seamless connection and smooth transition of the operation mode can be realized, and stable voltage support is provided for the system.
3. In order to ensure that the reference voltage value keeps stable transition in the switching process, the invention adds current compensation into closed-loop voltage control to ensure the stability of the voltage control.
4. When the microgrid is switched from off-grid control to grid-connected control, a corresponding current compensation link and a corresponding voltage compensation link are added, so that the reference current value and the voltage value before and after the microgrid is switched are not changed.
Drawings
Fig. 1 is a phase mapping diagram in a microgrid switching operation;
fig. 2 is a schematic diagram of the control of switching the microgrid from grid connection to off-grid connection;
fig. 3 is a schematic diagram of control over switching of off-grid to grid-connection of a microgrid;
fig. 4 is a microgrid simulation model;
FIG. 5 is a simulation waveform of the voltage and current of the AC bus controlled by the uncompensated switching when the microgrid is switched from grid-connected to off-grid model;
FIG. 6 is a compensation switching control alternating current bus voltage and current simulation waveform when the microgrid is switched from grid-connected to off-grid model;
FIG. 7 is a simulation waveform of the voltage and current of an alternating-current bus controlled by uncompensated switching when a microgrid is switched from an off-grid mode to a grid-connected mode;
fig. 8 is a simulation waveform of the voltage and the current of the alternating-current bus controlled by compensation switching when the microgrid is switched from an off-grid mode to a grid-connected mode.
Detailed Description
The technical scheme of the invention is further described in detail through the attached drawings.
As shown in fig. 1, a microgrid includes a large number of power electronic devices, and a weak grid connection condition may exist, so that the stability of the microgrid is difficult to guarantee. The invention provides a phase compensation technology based on a virtual synchronous machine, and improves the stability of the microgrid.
When the microgrid switches and operates, asynchronous conditions may occur in phases before and after switching, and sudden changes of angle positions occur before and after switching, so that voltage phases are increased and decreased to a certain extent, the switching is unsuccessful, the microgrid grid-connected control is converted into an off-grid control process, coordinate equivalent transformation needs to be carried out, a reference vector of grid voltage is on a d axis, and in the microgrid off-grid control process, the direction of a rotation vector of the d axis needs to be referred. Therefore, the reference vector orientation of the d-axis needs to be controlled during the conversion process, i.e. the reference angular velocity of the d-axis before switching is consistent with the d-axis rotation angular velocity after switching.
The invention designs a phase compensation controller with a virtual synchronous machine, namely, when a system is switched and controlled, the phase angle of the voltage vector of a power grid at the previous moment is memorized and is used as a phase angle compensation value after switching. The phase angle after switching is expressed as:
θ u ＝θ+∫ω vsg dt (1)
in formula (1): omega vsg Is the angular frequency of the virtual synchronous machine; θ is the initial phase.
As shown in fig. 2, the present invention adopts a feedforward decoupling control algorithm to eliminate the current coupling term between the d-axis component and the q-axis component, and the input quantities are:
Figure BDA0002768761400000061
in the formula (2), u d * 、u q * D-axis and q-axis voltage reference values under a dq synchronous rotation coordinate system at the AC side of the microgrid converter; u. u d 、u q The current values of d-axis and q-axis voltages under a dq synchronous rotation coordinate system at the AC side of the microgrid converter are obtained; omega is the voltage angular frequency of the AC side of the microgrid converter; l is d 、L q D and q axes of inductance; i.e. i d 、i q Current values of d-axis and q-axis currents under a dq synchronous rotation coordinate system at the AC side of the microgrid converter; k is a radical of p As a proportional phase of the control system, a deviation signal of the system can be proportionally reflected; k is a radical of i As the integral phase of the control system, the integral operation can be carried out on the deviation signal to eliminate the deviation; i.e. i d * 、i q * And d and q axis current reference values of the microgrid converter on an alternating current side dq synchronous rotating coordinate system.
When the microgrid is connected to the grid and is controlled to be disconnected from the grid, usually the PI controller is in a stable state before control is changed, and after the control is changed, the output value of the current loop is changed from 0 to a stable state, but transition time is needed. Meanwhile, the PI control has inertia and cannot be stopped immediately, so that voltage can fluctuate momentarily in the switching process of the system, and the fluctuation can cause voltage or phase mutation, thereby influencing the stability of the whole system. In order to prevent the influence caused by inner ring PI control in the system switching process, when the grid-connected mode is switched to the off-grid mode, the output value of the PI controller in the grid-connected mode is introduced, so that seamless connection smooth transition is realized, and stable voltage support is provided for the system. The voltage of the off-grid controller can be compensated to the initial voltage value of the grid-connected controller as a compensation value, and the corresponding voltage compensation term algorithm is as follows:
Figure BDA0002768761400000071
in formula (3): u. of dpq 、u qpq And outputting voltage steady-state values for d and q axes of the PI controller in the microgrid grid-connected mode.
In the microgrid grid-connected to off-grid control, the current PI control outer loop input may be suddenly changed, in order to ensure that the reference voltage keeps stable transition in the switching process, the current compensation is added into the closed-loop voltage inner loop control, namely:
Figure BDA0002768761400000072
in formula (4): i.e. i dpq 、i qpq And outputting current steady-state values for d and q axes of the PI controller in the microgrid grid-connected mode.
As shown in fig. 3, when the microgrid off-grid control is switched to the grid-connected control, the control variable of the inner loop is current, and the reference value is:
Figure BDA0002768761400000073
in formula (5): i all right angle dvf 、i qvf And outputting current steady-state values for d and q axes of the PI controller in the microgrid off-grid mode.
In order to ensure the stability of the constant dc voltage control without changing the output power of the system, the active power and the reactive power are set to 0, and equation (5) can be simplified as follows:
Figure BDA0002768761400000074
similar to the conversion from grid-connected to off-grid of the microgrid, when the microgrid is changed from grid-connected control to off-grid control, a corresponding current compensation link is added in the voltage outer loop control:
Figure BDA0002768761400000075
in formula (7):
Figure BDA0002768761400000076
and compensating current reference values of d and q axes under a synchronous rotating coordinate system of the dq at the AC side of the microgrid converter.
Adding a corresponding voltage compensation link in the current inner loop control:
Figure BDA0002768761400000081
in formula (8):
Figure BDA0002768761400000082
and compensating voltage reference values of d and q axes under a dq synchronous rotation coordinate system on the AC side of the microgrid converter. Adding corresponding current compensation quantity in a closed-loop voltage control link; u. of dvf 、u qvf And outputting voltage steady-state values for d and q axes of the PI controller in the microgrid off-grid mode.
Through the current and voltage compensation and the phase compensation control, the reference current value and the voltage value before and after the switching of the microgrid can be ensured to be unchanged, the power of an original system can not be changed, and the smooth transition in the switching process of the system is ensured.
As shown in fig. 4, in order to verify the effectiveness of the grid-connected and off-grid smooth switching current-voltage phase compensation method provided by the present invention. And (4) building a micro-grid simulation model containing two distributed power supply points as shown in the figure under Matlab/Simulink. Distributed power supply point 1 and distributed power supply point 2 alternating-current side voltage U ac And =0.4kV, is connected with a double-winding split transformer with the capacity of 1000kVA, and is connected to a power grid after being boosted to 6.8 kV. The RLC filtering parameters of the two transmission lines are the same, namely: l is a radical of an alcohol f1 ＝L f2 ＝4.7mH、R f1 ＝R f2 ＝5Ω、C f1 ＝C f2 =490 μ F; the line impedance of the two transmission lines is R 01 ＝0.6+j0.15Ω、R 02 ＝0.3+j0.15Ω。
As shown in fig. 5, when the microgrid is switched from a grid-connected operation state to an off-grid operation state, the microgrid converter keeps the ac bus voltage constant. Before a compensation control strategy is not implemented, the bus current generates obvious sudden change in the transition period and the phase cannot be quickly tracked, so that the switching process is easy to fail.
As shown in fig. 6, when the microgrid is switched from the grid-connected operation state to the off-grid operation state, the microgrid converter always keeps the voltage of the alternating-current bus constant after the compensation control strategy is implemented. The microgrid converter output current can quickly respond to state change and a phase offset phenomenon is not found.
As shown in fig. 7, when the microgrid is switched from an off-grid state to a grid-connected state, the microgrid converter can also keep the ac bus voltage constant without implementing a compensation control strategy. But during state switching, the bus current produces significant abrupt changes and cannot track the phase in real time.
As shown in fig. 8, when the microgrid is switched from an off-grid state to a grid-connected state, after applying the compensation control strategy, the microgrid converter always keeps the voltage of the alternating-current bus constant, the current quickly responds, and the phase offset phenomenon is not found. In the process of switching the microgrid from an off-grid mode to a grid-connected mode, the sudden change of the output current can be reduced by implementing a compensation control strategy, the same voltage and current phases are kept, and the smooth transition of the switching process is facilitated.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, changes and equivalent structural changes made to the above embodiment according to the technical spirit of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims (9)

1. A microgrid grid-connected and off-grid smooth switching current and voltage phase compensation method is characterized by comprising the following steps:
1) According to the principle that the reference angular speed of the d axis before the microgrid is switched is consistent with the d axis rotation angular speed after the microgrid is switched, introducing a phase compensation controller of the virtual synchronous machine into a control system to obtain a phase angle expression after compensation;
2) In the microgrid converter control system, a feedforward decoupling control algorithm is adopted to eliminate a current coupling term between d-axis components and q-axis components to obtain an input expression;
3) When the microgrid is controlled to be switched from grid-connected control to off-grid control, on the basis of the input expression of the microgrid converter control system in the step 2), stable values of output voltages of d and q shafts of a PI controller based on a microgrid grid-connected mode are introduced to serve as voltage compensation items, and a current outer ring control equation with the voltage compensation items is obtained;
4) When the micro-grid is converted from grid-connected control to off-grid control, current compensation is added to closed-loop voltage inner-loop control to obtain a voltage inner-loop control equation with a current compensation phase;
5) Obtaining a microgrid grid-connected to off-grid switching control system with compensation control according to the compensation phase angle expression obtained in the step 1), the current outer ring control equation in the step 3) and the voltage inner ring control equation in the step 4);
6) When the microgrid is converted from off-grid control to grid-connected control, the inner ring is changed into current closed-loop control to obtain an input reference value expression;
7) Introducing the microgrid current inner ring input reference value expression in the step 6) into voltage outer ring control to obtain a voltage outer ring control equation with a current compensation phase;
8) When the microgrid is converted from off-grid control to grid-connected control, voltage compensation is added into closed-loop current inner-loop control to obtain a current inner-loop control equation with a voltage compensation phase;
9) And obtaining a microgrid off-grid to grid-connected switching control system with compensation control according to the compensation phase angle expression obtained in the step 1), the voltage outer ring control equation in the step 7) and the current inner ring control equation in the step 8).
2. The microgrid grid-connected and off-grid smooth switching current and voltage phase compensation method according to claim 1, characterized in that the specific implementation method of the step 1) is as follows: according to the principle that the reference angular speed of the d axis before the micro-grid is switched is consistent with the rotation angular speed of the d axis after the micro-grid is switched, a virtual synchronous machine phase compensation controller is introduced into a control systemObtaining a compensated phase angle expression: theta u ＝θ+∫ω vsg dt; wherein: omega vsg Is the angular frequency of the virtual synchronous machine; θ is the initial phase.
3. The microgrid grid-connected and off-grid smooth switching current and voltage phase compensation method according to claim 2, characterized in that the specific implementation method of the step 2) is as follows: in the microgrid converter control system, a feedforward decoupling control algorithm is adopted to eliminate a current coupling term between d-axis components and q-axis components, and an input expression is obtained:
Figure FDA0002768761390000021
wherein: u. u d * 、u q * D-axis and q-axis voltage reference values under a dq synchronous rotation coordinate system at the AC side of the microgrid converter; u. of d 、u q The current values of d-axis and q-axis voltages under a dq synchronous rotation coordinate system at the AC side of the microgrid converter are obtained; omega is the voltage angular frequency of the AC side of the microgrid converter; l is d 、L q Inductances of d and q axes, respectively; i.e. i d 、i q Current values of d-axis current and q-axis current under a dq synchronous rotation coordinate system at the AC side of the microgrid converter are obtained; k is a radical of p As a proportional phase of the control system, proportionally reflecting a deviation signal of the system; k is a radical of formula i As the integral phase of the control system, carrying out integral operation on the deviation signal to eliminate the deviation; i all right angle d * 、i q * And d and q axis current reference values of the microgrid converter on an alternating current side dq synchronous rotating coordinate system.
4. The microgrid grid-connected and off-grid smooth switching current and voltage phase compensation method according to claim 3, characterized in that the specific implementation method of the step 3) is as follows: when the microgrid is switched from grid-connected control to off-grid control, on the basis of the input expression of the microgrid converter control system in the step 2), stable values of output voltages of d and q axes of a PI controller based on a microgrid grid-connected mode are introduced to serve as voltage compensation items, and a current outer ring control equation with the voltage compensation items is obtained:
Figure FDA0002768761390000022
wherein: u. of dpq 、u qpq And outputting voltage steady-state values for d and q axes of the PI controller in the microgrid grid-connected mode.
5. The microgrid grid-connected and off-grid smooth switching current and voltage phase compensation method according to claim 4, characterized in that the specific implementation method of the step 4) is as follows: when the micro-grid is converted from grid-connected control to off-grid control, current compensation is added to closed-loop voltage inner-loop control, and a voltage inner-loop control equation with a current compensation phase is obtained:
Figure FDA0002768761390000031
wherein: i all right angle dpq 、i qpq And outputting current steady-state values for d and q axes of the PI controller in the microgrid grid-connected mode.
6. The microgrid grid-connected and off-grid smooth switching current and voltage phase compensation method according to claim 5, characterized in that the specific implementation method of the step 5) is as follows: according to the compensation phase angle expression obtained in the step 1), the current outer ring control equation in the step 3) and the voltage inner ring control equation in the step 4), the microgrid grid-connected to off-grid switching control system with compensation control is obtained, and through current and voltage compensation and phase compensation control, the reference current value and the voltage value before and after microgrid grid-connected and off-grid smooth switching are not changed, the original system power is not changed, and smooth transition in the system switching process is guaranteed.
7. The microgrid grid-connected and off-grid smooth switching current and voltage phase compensation method according to claim 6, characterized in that the specific implementation method of step 6) is as follows: when the microgrid is converted from off-grid control to grid-connected control, the inner ring is changed into current closed-loop control, and an input reference value expression is obtained:
Figure FDA0002768761390000032
wherein: i.e. i dvf 、i qvf And outputting current steady-state values for d and q axes of the PI controller in the off-grid mode of the microgrid.
8. The microgrid grid-connected and off-grid smooth switching current and voltage phase compensation method according to claim 7, characterized in that the specific implementation method of the step 7) is as follows: introducing the micro-grid current inner ring input reference value expression in the step 6) into voltage outer ring control to obtain a voltage outer ring control equation with a current compensation phase:
Figure FDA0002768761390000033
wherein: i.e. i df * 、i qf * And compensating current reference values of d and q axes under a dq synchronous rotation coordinate system on the AC side of the microgrid converter.
9. The microgrid grid-connected and off-grid smooth switching current and voltage phase compensation method according to claim 8, characterized in that the specific implementation method of the step 8) is as follows: when the microgrid is converted from off-grid control to grid-connected control, voltage compensation is added into closed-loop current inner-loop control, and a current inner-loop control equation with a voltage compensation phase is obtained:
Figure FDA0002768761390000041
wherein: u. of df * 、u qf * Compensating voltage reference values of d and q axes under a dq synchronous rotation coordinate system at the AC side of the microgrid converter; adding corresponding current compensation amount in a closed-loop voltage control link; u. of dvf 、u qvf And outputting voltage steady-state values for d and q axes of the PI controller in the microgrid off-grid mode.
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