TWI773372B - Micro grid system and pre-synchronization estimation method - Google Patents

Abstract

A micro grid system is provided for being connected with a power grid system, and includes: a master sub-system, a slave sub-system and a controller for controlling the master sub-system and the slave sub-system to execute a grid connection mode or an island mode. Before the island mode is switched into the grid connection mode, the controller executes a pre-synchronization estimation procedure to determine whether the grid connection mode can be executed by a phase difference between the micro grid system and the power grid system.

Description

Microgrid system and pre-synchronization judgment method

The present disclosure relates to a microgrid system and a control method thereof, in particular to a microgrid system with switchable operation modes and a pre-synchronization judgment method thereof.

Microgrid systems are new microgrids composed of distributed power sources and adjacent loads that can be used in conjunction with utility power systems. In the case of the normal power supply of the mains system, the microgrid system can be connected with the mains system to operate together. This mode is called grid-connected mode. When the mains system does not supply power normally, such as when the mains system fails or the power quality does not meet the demand, the microgrid system can disconnect from the mains and operate independently. This mode is called the islanding mode.

However, there is currently a lack of a good control mechanism that can perform the transition from the islanded operation mode to the grid-connected mode at an appropriate time, for example, when switching from the islanded operation mode to the grid-connected mode (for example, the utility power system is restored from a fault condition to the grid-connected mode). When it is normal), the voltage phase angle of the microgrid system and the mains system may be out of sync. At this time, if the grid-connected mode is executed immediately, there will be problems.

Therefore, a microgrid system and a pre-synchronization judgment method are needed to improve the above problems.

The present disclosure provides a microgrid system for connecting with a mains system, comprising: a main subsystem, a subordinate subsystem, and a microgrid controller, which controls the operation of the main subsystem and the subordinate subsystem to execute a grid-connected mode or The islanding operation mode, in which, when preparing to switch from the islanding operation mode to the grid-connected mode, the microgrid controller executes a pre-synchronization judgment program to determine whether to execute the grid-connected mode according to the phase difference between the microgrid system and the mains system.

The present disclosure further provides a pre-synchronization determination method for use in a microgrid system, wherein the microgrid system is used for connecting with the mains system, and includes a main subsystem, a slave subsystem and a microgrid controller, and the microgrid controller is configured by Control the operation of the main subsystem and the subordinate subsystems to execute the grid-connected mode or the islanding operation mode, wherein the method includes the steps: the microgrid controller prepares to switch from the islanding operation mode to the grid-connected mode; the microgrid controller is based on the microgrid system. Obtain the angle command from the microgrid frequency command or the angular frequency value in the island operation mode; the microgrid controller compares the angle command with the phase angle of the mains system; and the microgrid controller determines based on the comparison result of the angle command and the phase angle of the mains system Whether to switch to grid-connected mode.

Other novel features of the present disclosure will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

1: Microgrid system

2: Mains system

3: Static toggle switch

4: Microgrid Controller

5: Main Subsystems

6: Slave subsystem

7: Control circuit

71: Power calculation and lock loop module

72: Proportional integral calculation module

73: abc/dq coordinate axis conversion module

74: dq/abc coordinate axis conversion module

75: Sine wave pulse width modulation module

76a~76d: Mode switch

77: Pre-sync prediction module

77a: Pre-sync trigger program switch

78: Angular frequency calculation module

79: Integrator

8: Control circuit

81: Power calculation and lock loop module

82a~82d: Proportional integral calculation module

83: dq/abc coordinate axis conversion module

84a~84c: Proportional controller

85: Sine wave pulse width modulation module

S61~S65: Steps

FIG. 1 is a schematic diagram of a microgrid system according to an embodiment of the present disclosure.

FIG. 2 is a schematic diagram of the operation of the microgrid controller of the microgrid system according to an embodiment of the present disclosure.

FIG. 3 is a schematic diagram of a detailed structure of a microgrid system according to an embodiment of the present disclosure.

FIG. 4 is a circuit diagram of a control circuit of a main subsystem of a microgrid system according to an embodiment of the present disclosure.

FIG. 5 is a control circuit diagram of a slave subsystem of a microgrid system according to an embodiment of the present disclosure.

FIG. 6 is a flow chart of the steps of a pre-synchronization determination method according to an embodiment of the present disclosure.

When read in conjunction with the accompanying drawings, the following embodiments are used to clearly demonstrate the above and other technical contents, features and/or effects of the present disclosure. Through the description of the specific embodiments, people will further understand the technical means and effects adopted by the present disclosure to achieve the above-mentioned purposes. In addition, since the contents disclosed in the present disclosure should be easily understood and implemented by those skilled in the art, all equivalent replacements or modifications without departing from the concepts of the present disclosure should be included in the claims.

It should be noted that, herein, unless otherwise specified, "a" element is not limited to a single element, but may also refer to one or more of the element.

In addition, ordinal numbers such as "first" or "second" in the specification and claims are merely to describe the claimed elements, and do not represent or imply that the claimed elements have any order of ordinal numbers, and are not the claimed elements and Another claimed sequence between elements or steps of a method of manufacture. These ordinal numbers are used only to distinguish one request element with a particular name from another request element with the same name.

Furthermore, in the specification and claims, for example, the word "adjacent" is used to describe being adjacent to each other, and does not necessarily mean that they are in contact with each other.

In addition, descriptions such as "when..." or "when..." in the present disclosure represent aspects such as "now, before, or after", and are not limited to simultaneous occurrences, which are described here first. In the present disclosure, descriptions such as "arranged on" and the like refer to the corresponding positional relationship between two elements, and do not limit whether there is contact between the two elements, unless otherwise specified, which is described in advance. Furthermore, when the disclosure describes multiple effects, if the word "or" is used between the effects, it means that the effects can exist independently, but it does not exclude that multiple effects can exist simultaneously.

In addition, words such as "connected" or "coupled" in the description and claims refer not only to direct connection with another element, but also to indirect connection or electrical connection with another element. In addition, the electrical connection includes a direct connection, an indirect connection, or an aspect in which the two components communicate with each other by radio signals.

Furthermore, in the specification and claims, the terms "about", "approximately", "substantially" and "substantially" generally mean that the difference between a value and a given value is within 10% of the given value, or Within 5%, or within 3%, or within 2%, or within 1%, or within the range of 0.5%. The quantity given here is an approximate quantity, that is, "about", "approximately", "approximately", "approximately", "approximately", "approximately", "approximately", "approximately", "approximately", "approximately", "substantially" and "substantially" may still be implied without the specific description of "about", "approximately", "substantially", "substantially" The meaning of "substantially" and "substantially". Furthermore, the terms "range is from the first value to the second value", "range is between the first value and the second value" means that the range includes the first value, the second value and other values in between.

In addition, each element may be implemented as a single circuit or an integrated circuit in a suitable manner, and may include one or more active elements, such as transistors or logic gates, or one or more passive elements, such as resistors, capacitors , or inductance, but not limited thereto. The elements may be connected to each other in a suitable manner, eg, using one or more lines to form a series or parallel connection with the input signal and the output signal, respectively. In addition, each element may allow input and output signals to enter and exit sequentially or in parallel. The above configurations are all determined according to the actual application.

In addition, in this document, terms such as "system", "equipment", "device", "module", or "unit" refer to an electronic component or a digital circuit composed of a plurality of electronic components, an analog circuits, or other broader circuits, and they do not necessarily have a hierarchical or hierarchical relationship unless otherwise specified.

In addition, the technical features of different embodiments disclosed in the present disclosure may be combined to form another embodiment.

FIG. 1 is a schematic diagram of a microgrid system 1 according to an embodiment of the present disclosure. As shown in FIG. 1 , the microgrid system 1 can be used to connect with a mains system 2 , wherein the microgrid system 1 can be electrically connected to the mains system 2 through at least one static switch 3 . The microgrid system 1 may include a microgrid controller 4 , a master subsystem 5 and at least one slave subsystem 6 . The microgrid controller 4 can control the operation of the main subsystem 5 and the subordinate subsystems 6, so that the microgrid system 1 can execute a grid-connected mode or an island operation mode. The grid-connected mode can be implemented when the utility power system 2 is normally powered, and the island operation mode can be implemented when the utility power system 2 is not powered normally, such as when the power supply is stopped or the power supply quality is poor, but not limited thereto.

When the grid-connected mode is executed, the microgrid controller 4 can control the static switch 3 to be turned on, so that the microgrid system 1 and the mains system 2 are connected. At this time, the microgrid system 1 and the mains system 2 can operate together to supply power.

When the island operation mode is executed, the microgrid controller 4 can control the static switch 3 to be disconnected, so that the connection between the microgrid system 1 and the mains system 2 is interrupted. At this time, the microgrid system 1 can operate independently to supply power.

In some cases, for example, when the mains system 2 recovers from abnormal power supply to normal power supply, the microgrid system 1 will switch from the island operation mode to the grid-connected mode. The operation of grid-connected mode may cause problems when not synchronized (eg the voltage phase angle of the power supply is different). One of the features of the present invention is that it can solve this problem.

FIG. 2 is a schematic diagram of the operation of the microgrid controller 4 of the microgrid system 1 according to an embodiment of the present invention, and please refer to FIG. 1 at the same time. As shown in FIG. 2 , when the microgrid system 1 is ready to switch from the island operation mode to the grid-connected mode, the microgrid system 1 can execute a pre-synchronization judgment method, that is, the microgrid controller 4 can execute a pre-synchronization judgment procedure, In order to determine whether to switch to the grid-connected mode according to the phase difference between the micro-grid system 1 and the mains system 2 . Thereby, it can be ensured that the operation of the grid-connected mode can be performed normally.

Next, the detailed structure of the microgrid system 1 will be described. FIG. 3 is a schematic diagram of a detailed structure of the microgrid system 1 according to an embodiment of the present invention, and please refer to FIG. 1 and FIG. 2 at the same time.

As shown in FIG. 3 , the main subsystem 5 and the slave subsystem 6 can pass through the static switch 3 and the mains system 2 respectively. The microgrid controller 4 can be electrically connected to the main subsystem 5 through a control circuit 7 , and the main subsystem 5 is controlled by the control circuit 7 . The microgrid controller 4 can be electrically connected to the slave subsystem 6 through another control circuit 8 , and controls the slave subsystem 6 through the other control circuit 8 . The microgrid controller 4 can also be electrically connected to the static switch 3 to control the conduction of the static switch 3 .

In one embodiment, the microgrid system 1 may be composed of various distributed power sources combined with power electronic converters, but is not limited thereto. In one embodiment, the main subsystem 5 may be, for example, an energy storage system, but is not limited thereto. In one embodiment, the slave subsystem 6 may be, for example, a solar photovoltaic system, but is not limited thereto.

In one embodiment, in the grid-connected mode, both the master subsystem 5 and the slave subsystem 6 can execute a real power and imaginary power control mode. In one embodiment, in the islanding mode, the master subsystem 5 can execute a voltage and frequency control mode, and the slave subsystem 6 can execute a real power and imaginary power control mode.

Next, the control methods of the master subsystem 5 and the slave subsystem 6 will be described in detail.

Parts of the main subsystem 5 will be described first. FIG. 4 is a circuit diagram of the control circuit 7 of the main subsystem 5 of the microgrid system 1 according to an embodiment of the present invention, and please refer to FIGS. 1 to 3 at the same time.

As shown in FIG. 4 , the control circuit 7 may include a power calculation and phase lock loop (power calculation and phase lock loop, power calculation and PLL) module 71, a plurality of proportional integral (PI) modules 72a~ 72d, an abc/dq coordinate axis conversion module 73, a dq/abc coordinate axis conversion module 74, a sinusoidal pulse width modulation (SPWM) module 75, a plurality of mode switching switches 76a~76d and a pre-synchronization estimation module 77, wherein the pre-synchronization estimation module 77 is electrically connected with a pre-synchronization trigger switch 77a. In one embodiment, the above modules and switches can be implemented by electronic circuits, but not limited thereto. Furthermore, the main subsystem 5 is a three-phase grid system.

The connection between the control circuit 7 and the main subsystem 5 may refer to the example in FIG. 4 , but is not limited thereto.

First, the operation of the control circuit 7 in the grid-connected mode will be described.

In one embodiment, when the main subsystem 5 executes the grid-connected mode, the static switch 3 is turned on, and the mains system 2 and the main subsystem 5 operate simultaneously. At this time, the power calculation and phase-locked loop module 71 can measure the system terminal voltages Va, Vb, Vc of _the main subsystem 5 through _a voltage sensor, and obtain the output _{currents isa ,} i of the main subsystem 5 _sb , isc , then the power calculation and phase-locked loop module 71 _can calculate the real power _Ps of the main subsystem ₅ according to the system terminal voltages Va , _Vb , Vc and the output _{currents isa} , _isb , _isc , the virtual power Q _s , the microgrid frequency f and the microgrid line-to-line voltage peak V _ab,peak and the voltage phase angle θ _e .

In one embodiment, the microgrid controller 4 can control the mode switching switches 76a, 76b to switch to the grid-connected mode (Mode I), so _that a comparison result of the real power command P ^* _s and the real power Ps (for example, the difference, but not limited thereto) is input to the proportional-integral calculation module _72a , and a comparison result of the imaginary power command Q ^* _s and the imaginary power Qs (such as the difference between the two, but not limited thereto) is input to the proportional-integral calculation module 72b, and the proportional-integral calculation module 72a can output a q-axis control current command i ^* _sq after performing proportional-integral calculation, and the proportional-integral calculation module 72b can output another d-axis control current command i after performing proportional-integral calculation ^* _sd .

In one embodiment, the microgrid controller 4 can control the mode switch 76c to switch to the grid-connected mode (Mode I), so that the abc/dq coordinate axis conversion module 73 outputs currents _isa and isb _according to the voltage phase angle _θe . , i _sc are converted from three-phase to q-axis current i _sq and d-axis current is _sd . Afterwards, the comparison result of the q-axis control current command i ^* _sq and the q-axis current i _sq (such as the difference between the two, but not limited thereto) can be input to the proportional-integral calculation module 72c for proportional-integral calculation, while the d-axis control _The comparison result of the current command i ^* _sd and the d-axis current isd (eg, the difference between the two, but not limited thereto) can be input to the proportional-integral calculation module 72d for proportional-integral calculation.

In one embodiment, the microgrid controller 4 can control the mode switch 76d to switch to the grid-connected mode (Mode I), and the calculation results of the proportional-integral calculation module 72c and the proportional-integral calculation module 72d can be input to dq/abc The coordinate axis conversion module 74 is used for coordinate conversion to form three-phase control signals u _cona , u _conb , and u _conc . In one embodiment, the three-phase control signals u _cona , u _conb , and u _conc can be modulated by the sine wave pulse width modulation module 75 and output to the main subsystem 5 , thereby achieving the actual operation of the main subsystem 5 . Power and virtual power control.

In this way, the real power and imaginary power control modes performed by the main subsystem 5 in the grid-connected mode can be understood.

Next, the operation of the control circuit 7 in the island operation mode will be described.

In one embodiment, when the main subsystem 5 executes the island operation mode, the static switch 3 is turned off, so the main subsystem 5 is responsible for maintaining the supply voltage and frequency of the microgrid system 1 .

In one embodiment, the microgrid controller 4 can provide (eg, the administrator can set through the microgrid controller 4) a microgrid line-to-line voltage peak command V ^* _ab,peak and a microgrid frequency command f ^* . In addition, the microgrid controller 4 can switch the mode switching switches 76a to 76d to the island operation mode (Mode II).

In one embodiment, the comparison result between the microgrid line-to-line voltage peak command V ^* _ab,peak and the microgrid line-to-line voltage peak value V _ab,peak (such as the difference between the two, but not limited to this) can be calculated by proportional integration. The group 72a performs proportional and integral calculations to form the q-axis control current command i ^* _sq . In addition, the comparison result of the microgrid frequency command f ^* and the microgrid frequency f (for example, the difference between the two, but not limited to this) can be calculated by the proportional integral calculation module 72b, thereby forming the d-axis control current command i ^* _sd . In addition, the microgrid frequency command f ^* can be calculated by an angular frequency calculation module 78 and an integrator 79 to form a voltage phase angle command θ ^* _e .

In one embodiment, the abc/dq coordinate axis conversion module 73 converts the output currents _isa , isb , isc from three _- phase into the q-axis current i _sq and the d-axis current _isd , _according to the voltage phase angle command θ ^* _e , The comparison result of the q-axis control current command i ^* _sq and the q-axis current i _sq (such as the difference between the two, but not limited to this) can be calculated by the proportional-integral calculation module 72c, and the d-axis control current command i ^* The comparison result of the _sd and the d-axis current i _sd (for example, the difference between the two, but not limited thereto) can be calculated by the proportional-integral calculation module 72d.

In one embodiment, the calculation results of the proportional-integral calculation module 72c and the proportional-integral calculation module 72d can be input to the dq/abc coordinate axis conversion module 74 for coordinate conversion, thereby forming the three-phase control signals u _cona , u _conb , u _conc . In one embodiment, the three-phase control signals u _cona , u _conb , and u _conc can be modulated by the sine wave PWM module 75 and output to the main subsystem 5 , thereby achieving the voltage of the main subsystem 5 and frequency control.

In this way, the voltage and frequency control modes performed by the main subsystem 5 in the islanding mode can be understood.

Next, the operation of the control circuit 8 in the grid-connected mode and the island operation mode will be described. FIG. 5 is a circuit diagram of the control circuit 8 of the slave subsystem 6 of the microgrid system 1 according to an embodiment of the present invention, and please refer to FIGS. 1 to 4 at the same time.

In one embodiment, when the slave subsystem 6 executes the grid-connected mode and the islanding mode, both execute the real power and imaginary power control modes, and both use constant power control.

As shown in FIG. 5, the control circuit 8 may include a power calculation and phase-locked loop (power calculation and PLL) module 81, a plurality of proportional integral calculation (PI) modules 82a-82b, and a dq/abc coordinate axis conversion module. 83. A plurality of proportional (P) controllers 84 a ˜ 84 c and a sine wave pulse width modulation (SPWM) module 85 . In one embodiment, the above modules and switches can be implemented by electronic circuits, but not limited thereto. Furthermore, the slave subsystem 6 is a three-phase grid system.

The connection between the control circuit 8 and the slave subsystem 6 may refer to the example of FIG. 5 , but is not limited thereto.

In one embodiment, when the slave subsystem 6 executes the grid-connected mode or the island operation mode, the power calculation and phase-locked loop module 81 can measure the system terminal voltages Va and V of the slave subsystem 6 through _a voltage sensor. _b , V _c , and obtain the output currents isu , isv , _isw of the slave _subsystem 6 , and then the power calculation and phase-locked loop module 81 can be based on the system terminal voltages Va , _{Vb ,} Vc _and the output current _{i su} , _isv and isw _calculate the real power P _p , the imaginary power Q _p and the voltage phase angle θ _e of the slave subsystem 6 .

In one embodiment, a comparison result _of the real power command P ^* _p and the real power Pp (such as the difference between the two, but not limited to this) can be input to the proportional integral calculation module 82a for proportional integral calculation, and its The calculation result can be input to the dq/abc coordinate axis conversion module 83 . In addition, a comparison result of the _imaginary power command Q ^* _p and the imaginary power Qp (such as the difference between the two, but not limited to this) can be input to the proportional-integral calculation module 82b for proportional-integral calculation, and the calculation result can also be Input to the dq/abc coordinate axis conversion module 83.

In one embodiment, the dq/abc coordinate axis conversion module 83 can convert the calculation results of the proportional-integral calculation module 82a and the proportional-integral calculation module 82b into three-phase control current commands i ^* _su , i according to the voltage phase angle θ _e . ^* _sv , i ^* _sw .

In one embodiment _, the comparison results of the three-phase control current commands i ^* _su , i ^* _sv , i ^* _sw and the output _currents isu , _issv , isw (for example, the difference between the two, but not limited thereto) can be respectively The proportion is adjusted through the proportional controllers 84a-84c, thereby forming the three-phase control signals u _conu , u _conv , and u _conw . In one embodiment, the three-phase control signals u _conu , u _conv , and u _conw can be modulated by the sine wave pulse width modulation module 85 and output to the slave subsystem 6 , thereby achieving the determination of the slave subsystem 6 . Power Control.

Thereby, the real power and imaginary power control modes of the slave subsystem 6 can be understood.

Next, the details of the pre-synchronization determination method will be described. FIG. 6 is a flowchart of steps of a pre-synchronization determination method (ie, a pre-synchronization determination procedure executed by the microgrid controller 4 ) according to an embodiment of the present disclosure, and please refer to FIGS. 1 to 5 at the same time.

As shown in FIG. 6 , first step S61 is executed, and the microgrid controller 4 determines whether the commercial power system 2 has resumed normal power supply.

If not, the microgrid controller 4 keeps the microgrid system 1 in the island operation mode, and does not turn on the pre-synchronization trigger switch 77a, so the pre-synchronization prediction module 77 is not activated.

If yes, then step S62 is executed, and the microgrid controller 4 turns on the pre-synchronization triggering program switch 77a to activate the pre-synchronization prediction module 77, wherein the pre-synchronization prediction module 77 can obtain the voltage phase angle command of the microgrid system 1 θ ^* _e and the voltage phase angle θ _g of the mains system 2 .

After that, step S63 is executed, the microgrid controller 4 controls the pre-synchronization prediction module 77 to compare the voltage phase angle command θ ^* _e with the mains voltage phase angle θg, and judges that the voltage phase angle command θ ^* _e is in phase with the mains voltage _. Whether the difference between the angles θ _g is less than a predetermined value.

When the difference between the voltage phase angle command θ ^* _e and the mains voltage phase angle _θg is less than the preset value, it means that the power supply of the microgrid system 1 and the mains system 2 are synchronized. At this time, step S64 is executed, and the microgrid controller 4. The microgrid system 1 can be switched from the island operation mode to the grid-connected mode.

On the contrary, when the difference between the voltage phase angle command θ ^* _e and the mains voltage phase angle _θg is greater than or equal to the preset value, it means that the power supply of the microgrid system 1 and the mains system 2 is not synchronized, and step S65 is executed at this time. , the microgrid controller 4 can execute a corner frequency compensation program to update the voltage phase angle command θ ^* _e . After that, steps S63 to S65 are re-executed until the difference between the voltage phase angle command θ ^* _e of the microgrid system 1 and the mains voltage phase angle _θg is smaller than the preset value. Thereby, the pre-synchronization determination method can be completed.

Regarding step S62, in one embodiment, the voltage phase angle command θ ^* _e can be formed by calculating the microgrid frequency command f ^* through the angular frequency calculation module 78 and the integrator 79, but is not limited thereto.

預設值

5度)，且不限於此。在一實施例中，預設值可介於0.5至2.5度之間(亦即0.5度

預設值

2.5度)，且不限於此。在一實施例中，預設值可介於0.5至1.5度之間(亦即0.5度

預設值

1.5度)，且不限於此。在一實施例中，預設值可介於0.5至1度之間(亦即0.5度

預設值

1度)，且不限於此。在一實施例中，預設值可為1度，且不限於此。 Regarding step S63, in one embodiment, the microgrid controller 4 can control the pre-synchronization prediction module 77 to calculate the difference between the voltage phase angle command θ ^* _e and the mains voltage phase angle _θg , and determine the voltage phase angle Whether the absolute value of the difference between the command θ ^* _e and the mains voltage phase angle _θg is less than the preset value. In one embodiment, the default value may be between 0.5 and 5 degrees (ie, 0.5 degrees

default value

5 degrees), and not limited thereto. In one embodiment, the default value may be between 0.5 and 2.5 degrees (ie, 0.5 degrees

default value

2.5 degrees), and not limited thereto. In one embodiment, the default value may be between 0.5 and 1.5 degrees (ie, 0.5 degrees

default value

1.5 degrees), and not limited thereto. In one embodiment, the default value may be between 0.5 and 1 degree (ie, 0.5 degree

default value

1 degree), and not limited thereto. In one embodiment, the default value may be 1 degree, but is not limited thereto.

Regarding step S65, in one embodiment, under the angular frequency compensation procedure, the microgrid controller 4 can control the pre-synchronization prediction module 77 to add an additional angular frequency to the current angular frequency value ω of the microgrid frequency command f ^* value to obtain an updated angular frequency value, and then update the voltage phase angle command θ ^* _e through integration. In one embodiment, the additional angular frequency value can be represented by the following equation: ΔW _d ( N +1 )=Δ W _d ( N )+T; where Δ W _d ( N +1) is the additional angular frequency value, Δ W _d ( N ) is the current angular frequency value, T is the adjustment angular frequency parameter, N is the execution times of the angular frequency compensation program, and is an integer greater than 1 (for example, if the current execution is N times, the next execution is N +1 and so on). In one embodiment, the adjustment parameter frequency (T) may be 0.01 rad/s, but is not limited thereto.

In this way, the pre-synchronization judgment between the micro-grid system 1 and the mains system 2 can be completed, and the micro-grid system 1 can be adjusted in real time, so that the micro-grid system 1 and the mains system 2 can complete the pre-synchronization.

Thereby, the present invention provides an improved microgrid system 1 and a pre-synchronization determination method, which can solve the problems of the prior art.

The features of the various embodiments of the present invention can be arbitrarily mixed and matched as long as they do not violate the spirit of the invention or conflict with each other.

The above-mentioned embodiments are only examples for convenience of description, and the scope of the claims claimed in the present invention should be based on the scope of the patent application, rather than being limited to the above-mentioned embodiments.

1: Microgrid system

2: Mains system

3: Static toggle switch

4: Microgrid Controller

5: Main Subsystems

6: Slave subsystem

Claims (7)

A micro-grid system for connecting with a mains system, comprising: a main subsystem; at least one sub-system; and a micro-grid controller to control the operation of the main sub-system and the sub-system to execute a combination of grid mode or an islanding operation mode; wherein, when preparing to switch from the islanding operation mode to the grid-connected mode, the microgrid controller further executes a pre-synchronization judgment procedure to determine the phase between the microgrid system and the mains system according to the The difference determines whether to switch to the grid-connected mode; wherein in the grid-connected mode, the main subsystem and the at least one subordinate subsystem execute a real power and imaginary power control mode, and in the island operation mode, the main subsystem executes a voltage and frequency control mode, the at least one slave subsystem executes a real power and imaginary power control mode; wherein in the pre-synchronization determination procedure, the microgrid controller places the microgrid system in a state of the islanding operation mode The angle command is compared with a voltage phase angle of the mains system, wherein the angle command is obtained according to a current angular frequency value of a microgrid frequency command of the microgrid system in the island operation mode. The microgrid system according to claim 1, wherein when the absolute value of the difference between the angle command of the microgrid system and the phase angle of the mains voltage is less than a preset value, the microgrid controller executes the parallel grid mode; when the absolute value of the difference between the angle command of the microgrid system and the mains voltage phase angle is greater than or equal to the preset value, the microgrid controller continues to execute a corner frequency compensation program to update the angle command until the absolute value of the difference between the angle command of the microgrid system and the mains voltage phase angle is less than the preset value. The microgrid system of claim 2, wherein under the angular frequency compensation procedure, the microgrid controller adds an additional angular frequency value to the current angular frequency value of the microgrid frequency command to obtain an updated angular frequency frequency value to update the angle command. The microgrid system of claim 3, wherein the additional angular frequency value is presented as: Δ W _d ( N +1 )=Δ W _d ( N )+T; wherein Δ W _d ( N +1) is the additional angular Frequency value, △ W _d ( N ) is the current angular frequency value, T is the adjusted angular frequency parameter, N is the number of times the angular frequency compensation program is executed, and is an integer greater than 1. A pre-synchronization judgment method is used in a micro-grid system, wherein the micro-grid system is used for connecting with a commercial power system, and includes a main subsystem, at least one slave subsystem and a micro-grid controller, and the micro-grid system The controller controls the operation of the main subsystem and the slave subsystem to execute a grid-connected mode or an islanding operation mode, wherein the method includes the step of: the microgrid controller prepares to switch from the islanding operation mode to the paralleling operation mode grid mode; the microgrid controller obtains an angle command according to a microgrid frequency command or a corner frequency value of the microgrid system in the island operation mode; the microgrid controller compares the angle command with a mains power of the mains system voltage phase angle; and the microgrid controller determines whether to switch to the grid-connected mode according to the angle command and the comparison result of the mains voltage phase angle of the mains system. The method of claim 5, wherein when the absolute value of the difference between the angle command and the mains voltage phase angle is less than a preset value, the microgrid controller executes the grid-connected mode, and otherwise, continues to perform An angle frequency compensation program is used to update the angle command until the absolute value of the difference between the angle command and the phase angle is smaller than the preset value. The method of claim 6, wherein under the angular frequency compensation procedure, the microgrid controller adds an additional angular frequency value to a current angular frequency value of the microgrid frequency command to obtain an updated angular frequency value , which in turn updates the angle command.

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