CN110912108A - Bus voltage control method for parallel and off-grid smooth switching of direct-current micro-grid - Google Patents

Abstract

The invention discloses a bus voltage control method for smooth switching of grid connection and disconnection of a direct-current micro-grid. The method combines the advantages of peer-to-peer control and centralized control, the difference value between the direct current bus voltage and the reference value is small under grid connection, the virtual admittance hardly works, the energy storage unit works in a current source mode to respond to system power scheduling, and meanwhile bus voltage disturbance can be dynamically and adaptively inhibited; under the fault of the direct-current power grid, the difference value between the direct-current bus voltage and the reference value is increased, and the energy storage unit supports the direct-current bus voltage in a self-adaptive mode through the virtual admittance; after the micro grid finishes island detection and grid-connected switch isolation, the voltage of the direct-current bus can be smoothly recovered to a reference value. The method can effectively realize parallel-grid and off-grid smooth switching of the direct-current micro-grid, particularly under the working condition of unplanned off-grid, has no requirement on rapidity of island detection and grid-connected switch action, is simple and reliable, has low cost, and is easy to design and realize in engineering.

Description

Bus voltage control method for parallel and off-grid smooth switching of direct-current micro-grid

Technical Field

The invention belongs to the field of distributed generation direct current micro-grids in electrical engineering, and particularly relates to a bus voltage control method for smooth switching of parallel and off-grid of a direct current micro-grid.

Background

The direct-current micro-grid containing the energy storage unit can be in grid-connected operation with an external direct-current power grid, participates in system power dispatching, can also be in off-grid operation when the external direct-current power grid fails, independently supplies power for a local load, has high power supply safety and reliability, and has attracted wide attention in recent years.

The peer-to-peer control and the master-slave control are two main bus voltage control methods of a direct-current micro-grid, the energy storage unit is enabled to operate in a voltage source mode no matter in grid connection or grid disconnection based on the peer-to-peer control of current-voltage droop, the switching process of grid connection and grid disconnection does not exist, but the current-voltage droop belongs to voltage difference control, the output power of the energy storage unit can only operate according to a droop curve during grid connection operation, the power dispatching instruction of the power grid cannot be effectively responded, and the direct-current bus voltage can change along with the change of a load during grid disconnection. Although various improved methods based on secondary control are provided in the research review entitled "dc microgrid droop control technology" ("chinese electro-mechanical engineering press", 2018,38(1):72-84.), the complexity of control is increased, and the smooth switching between grid connection and grid disconnection needs to be considered again.

The master-slave control method is characterized in that a direct-current power grid controls direct-current bus voltage during grid connection, the energy storage unit operates in a current source mode and flexibly participates in micro-grid power scheduling, and the energy storage unit operates in an undifferentiated voltage source mode to control the direct-current bus voltage during off-grid, so that power is supplied to a local load, the control is simple, the realization is easy, and the method is widely applied to actual demonstration projects. However, during the transition period between grid connection and grid disconnection, the energy storage unit is switched from a current source mode to a voltage source mode, and during the island detection period, the direct-current bus voltage is uncontrollable, and smooth off-grid switching is important, which becomes the key point of research. For example, the invention patent "a smoothing method and system for controlling and switching bus voltage in and out of grid of direct current microgrid" (publication number: CN106849156A) refers to a smoothing method for controlling and switching bus voltage in and out of grid based on master-slave control, but the direct current bus voltage still changes with the change of load under the scheme.

The above analysis shows that although the existing methods can realize the grid-connected and off-grid smooth switching of the direct current microgrid, the existing methods have respective defects, so that further research needs to be carried out on a bus voltage control method for the grid-connected and off-grid smooth switching of the direct current microgrid.

Disclosure of Invention

The invention provides a bus voltage control method for parallel and off-grid smooth switching of a direct-current micro-grid based on virtual admittance, aiming at the bus voltage control problem of parallel and off-grid smooth switching of the direct-current micro-grid, and combining the advantages of master-slave control and peer-to-peer control. The method combines the advantages of peer-to-peer control and centralized control, the difference value between the direct current bus voltage and the reference value is small under grid connection, the virtual admittance hardly works, the energy storage unit works in a current source mode to respond to system power scheduling, and meanwhile bus voltage disturbance can be dynamically and adaptively inhibited; under the fault of the direct-current power grid, the difference value between the direct-current bus voltage and the reference value is increased, and the energy storage unit supports the direct-current bus voltage in a self-adaptive mode through the virtual admittance; after the micro grid finishes island detection and grid-connected switch isolation, the voltage of the direct-current bus can be smoothly recovered to a reference value. The method can effectively realize parallel-grid and off-grid smooth switching of the direct-current micro-grid, particularly under the working condition of unplanned off-grid, has no requirement on rapidity of island detection and grid-connected switch action, is simple and reliable, has low cost, and is easy to design and realize in engineering.

The object of the invention is thus achieved. The invention provides a bus voltage control method for grid-connected and off-grid smooth switching of a direct-current micro-grid, wherein the direct-current micro-grid related to the control method comprises a direct-current grid V_GThe system comprises a grid-connected switch KB, a direct-current bus, an energy storage unit, a Buck/Boost energy storage DC/DC converter and a load R; DC network V_GThe energy storage unit is connected in parallel to the direct current bus through a grid-connected switch KB, the energy storage unit is connected in parallel to the direct current bus through a Buck/Boost energy storage DC/DC converter, and the load R is connected in parallel to the direct current bus; the Buck/Boost energy storage DC/DC converter comprises an input capacitor C_BatAn inductor L and a switch tube S₁A switch tube S₂And an output capacitor C_Bus(ii) a Will input capacitance C_BatIs marked as node A₁Input capacitance C_BatIs denoted as node A₂Node A₁A₂One end of an inductor L is connected to a node A as an input port of the Buck/Boost energy storage DC/DC converter₁The other end of the inductor L is marked as node A₃Switching tube S₂Is connected to node A₃Upper, switch tube S₂Is connected to node A₂Upper, switch tube S₁Is marked as node A₄Switching tube S₁Is connected to node A₃Upper and output capacitor C_BusIs connected to node A₄Upper and output capacitor C_BusIs connected to node A₂Upper, node A₄A₂The output port of the Buck/Boost energy storage DC/DC converter is used;

the control method is characterized by comprising the following steps:

step 1: sampling the DC bus voltage, denoted as V_BusSampling the voltage of the energy storage unit, denoted as V_BatSampling the current of inductor L, denoted as I_L；

Step 2: given bus voltage reference value V_refGiven a current command value I_refDefine the voltage controller G_VPIDefine the voltage controller G_VPIThe output of (A) is an off-grid current loop reference value I_OLrefSaid voltage controller G_VPIIs a proportional-integral regulator with a transfer function G_VPI(s) is:

wherein k is_vpIs a voltage controller G_VPICoefficient of proportionality, k_viIs a voltage controller G_VPIThe integral coefficient of (a);

and step 3: judging whether a grid-connected switch KB is closed or not, if the grid-connected switch KB is closed, executing the step 3.1 and the step 3.2, and if the grid-connected switch KB is disconnected, executing the step 3.3, the step 3.4 and the step 3.5;

step 3.1: giving a virtual admittance Y, and obtaining a direct current bus voltage V according to the step 1_BusAnd 2, setting a direct current bus voltage reference value V in the step_refAnd the current command value I given in step 2_refAnd calculating to obtain a grid-connected current loop reference value I_GLrefThe calculation formula is as follows:

I_GLref＝I_ref+(V_ref-V_Bus)×Y

step 3.2: the grid-connected current loop reference value I obtained in the step 3.1_GLrefAnd off-grid current loop reference value I_OLrefObtaining a current error signal delta I, delta I ═ I by difference_GLref-I_OLrefExecuting the step 4;

step 3.3: starting the voltage command soft start control in the Nth control period with N being equal to N, wherein N is the cycle number of the voltage command soft start control period, N is 1,2, … N … + ∞, N is an intermediate variable of the cycle number of the control period, and obtaining the initial value V of the voltage command soft start according to the following mode_Bus0：

When N is 1, V_Bus0＝V_Bus

When N ≠ 1, V_Bus0Is not changed

Step 3.4: giving expected voltage command slow start times M, and obtaining voltage command slow start output V in the following mode_Ramp：

When N is less than or equal to M, V_Ramp＝V_Bus0+(V_ref-V_Bus0)×N÷M

When N > M, V_Ramp＝V_ref

Step 3.5: let N be N +1, output V is started slowly with voltage instruction_RampAnd the DC bus voltage V obtained in the step 1_BusObtaining a voltage error signal delta V by difference, wherein the delta V is equal to V_Ramp-V_BusExecuting the step 4;

and 4, step 4: the voltage controller G is obtained as follows_VPIInput Δ E of_rror：

When the grid-connected switch KB is closed, Δ E_rror＝ΔI

When the grid-connected switch KB is turned off, Δ E_rror＝ΔV

And 5: the current loop reference value I is obtained as follows_Lref：

When the grid-connected switch KB is closed, I_Lref＝I_GLref

When the grid-connected switch KB is turned off, I_Lref＝I_OLref

Step 6: the current loop reference value I obtained in the step 5 is compared with_LrefWith the current I of the inductor L obtained in step 1_LObtaining an inductive current error signal delta I by difference_L,ΔI_L＝I_Lref-I_LDefine current loop controller G_IPIDefine current loop controller G_IPIThe output of (a) is an inductance control voltage, denoted as V_LObtaining an inductive current error signal Delta I_LIs a current loop controller G_IPIThe input of, the current loop controller G_IPIIs a proportional-integral regulator with a transfer function G_IPI(s) is:

wherein k is_ipIs a current loop controller G_IPICoefficient of proportionality, k_iiIs a current loop controller G_IPIThe integral coefficient of (a);

and 7: the direct current bus voltage V obtained according to the step 1_BusVoltage V of energy storage unit_BatAnd the inductance control voltage V obtained in the step 6_LThe switching tube S is calculated as follows₁Duty cycle of (d)₁：

d₁＝(V_Bat-V_L)÷V_Bus

The switching tube S is obtained by calculation in the following way₂Duty cycle of (d)₂：

d₂＝1-d₁

Switch tube S₁Duty ratio d of₁And a switching tube S₂Duty ratio d of₂Through a driving and protection circuitSwitching tube S for controlling Buck/Boost energy storage DC/DC converter₁And a switching tube S₂Make-and-break;

and 8: and (5) repeating the steps 1-8, and realizing the bus voltage control of the parallel and off-grid smooth switching of the direct-current micro-grid.

Compared with the prior art, the invention has the advantages that:

1. the parallel-grid and off-grid smooth switching of the direct-current micro-grid is effectively realized, particularly under the unplanned off-grid working condition, extra cost is not required to be added, the requirement on rapidity of island detection is avoided, and the method is flexible and simple and is easy to design and engineer realize;

2. although the energy storage unit works in a current source mode during grid-connected operation, the dynamic disturbance of the direct-current bus voltage can be effectively and adaptively inhibited.

Drawings

Fig. 1 is a schematic diagram of a dc microgrid structure in a bus voltage control method for smooth grid-on and off-grid switching of a dc microgrid according to an embodiment of the present invention.

Fig. 2 is a control block diagram of a bus voltage control method for grid-on and off-grid smooth switching of a dc microgrid in an embodiment of the present invention.

FIG. 3 shows DC bus voltage V obtained by experiment on practical experimental platform according to specific parameters of the present invention and embodiments of the present invention_BusCurrent I of inductor L_LAnd a load current I_OExperimental waveforms of (4).

Detailed Description

Preferred embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

Fig. 1 is a schematic diagram of a dc microgrid structure in a bus voltage control method for smooth grid-on and off-grid switching of a dc microgrid according to an embodiment of the present invention, and it can be understood from fig. 1 that the dc microgrid related to the control method includes a dc power grid V_GThe system comprises a grid-connected switch KB, a direct-current bus, an energy storage unit, a Buck/Boost energy storage DC/DC converter and a load R; DC network V_GThe direct current bus is connected in parallel through a grid-connected switch KB, the energy storage unit is connected in parallel to the direct current bus through a Buck/Boost energy storage DC/DC converter, the load R is connected in parallel to the direct current bus, and the current is definedThe current of the overload is the load current I_OThe direction of flow into the load is positive; the Buck/Boost energy storage DC/DC converter comprises an input capacitor C_BatAn inductor L and a switch tube S₁A switch tube S₂And an output capacitor C_Bus(ii) a Will input capacitance C_BatIs marked as node A₁Input capacitance C_BatIs denoted as node A₂Node A₁A₂One end of an inductor L is connected to a node A as an input port of the Buck/Boost energy storage DC/DC converter₁The other end of the inductor L is marked as node A₃Switching tube S₂Is connected to node A₃Upper, switch tube S₂Is connected to node A₂Upper, switch tube S₁Is marked as node A₄Switching tube S₁Is connected to node A₃Upper and output capacitor C_BusIs connected to node A₄Upper and output capacitor C_BusIs connected to node A₂Upper, node A₄A₂The output port of the Buck/Boost energy storage DC/DC converter is used.

The specific parameters of the embodiment of the invention are as follows: DC network V_GVoltage of 400V, voltage V of the energy storage unit_Bat150V, input capacitance C_BatHas a capacitance value of 110uF, an inductance value of 1mH, and an output capacitor C_BusThe capacity value is 110uF, the resistance value of the load R is 94 omega, the virtual admittance Y is 0.57, and the current instruction value I_refIs 0A, voltage controller G_VPICoefficient of proportionality k_vpIs 1.25, voltage controller G_VPIIntegral coefficient k of_vi1699 Current Loop controller G_IPICoefficient of proportionality k_ipIs 0.6, current loop controller G_IPIIntegral coefficient k of_ii20, a DC bus voltage reference value V_refAt 400V, the expected number of voltage command slow starts M is 3000.

Fig. 2 is a control block diagram of a bus voltage control method for smooth switching of grid connection and disconnection of a dc microgrid in an embodiment of the present invention, and taking a grid-connected state in which an initial grid-connected switch KB is closed as an example, the detailed steps of the control method are as follows:

step 1: sampling the DC bus voltage, denoted as V_BusSampling the voltage of the energy storage unit, denoted as V_BatSampling the current of inductor L, denoted as I_L。

Step 2: given bus voltage reference value V_refGiven a current command value I_refDefine the voltage controller G_VPIDefine the voltage controller G_VPIThe output of (A) is an off-grid current loop reference value I_OLrefSaid voltage controller G_VPIIs a proportional-integral regulator with a transfer function G_VPI(s) is:

wherein k is_vpIs a voltage controller G_VPICoefficient of proportionality, k_viIs a voltage controller G_VPIThe integral coefficient of (2).

In this embodiment: v_ref＝400V，I_ref＝0A，k_vp＝1.25，k_vi＝1699。

And step 3: and (3) judging whether a grid-connected switch KB is closed or not, if the grid-connected switch KB is closed, executing the step 3.1 and the step 3.2, and if the grid-connected switch KB is disconnected, executing the step 3.3, the step 3.4 and the step 3.5.

Step 3.1: giving a virtual admittance Y, and obtaining a direct current bus voltage V according to the step 1_BusAnd 2, setting a direct current bus voltage reference value V in the step_refAnd the current command value I given in step 2_refAnd calculating to obtain a grid-connected current loop reference value I_GLrefThe calculation formula is as follows:

I_GLref＝I_ref+(V_ref-V_Bus)×Y

in this embodiment: y is 0.57.

Step 3.2: the grid-connected current loop reference value I obtained in the step 3.1_GLrefAnd off-grid current loop reference value I_OLrefObtaining a current error signal delta I, delta I ═ I by difference_GLref-I_OLrefAnd step 4 is executed.

Step 3.3: starting the voltage command soft start control in the Nth control period with N being equal to N, wherein N is the cycle number of the voltage command soft start control period, N is 1,2, … N … + ∞, N is an intermediate variable of the cycle number of the control period, and obtaining the initial value V of the voltage command soft start according to the following mode_Bus0：

When N is 1, V_Bus0＝V_Bus

When N ≠ 1, V_Bus0And is not changed.

Step 3.4: giving expected voltage command slow start times M, and obtaining voltage command slow start output V in the following mode_Ramp：

When N is less than or equal to M, V_Ramp＝V_Bus0+(V_ref-V_Bus0)×N÷M

When N > M, V_Ramp＝V_ref

In this embodiment: m is 3000.

Step 3.5: let N be N +1, output V is started slowly with voltage instruction_RampAnd the DC bus voltage V obtained in the step 1_BusObtaining a voltage error signal delta V by difference, wherein the delta V is equal to V_Ramp-V_BusAnd step 4 is executed.

And 4, step 4: the voltage controller G is obtained as follows_VPIInput Δ E of_rror：

When the grid-connected switch KB is closed, Δ E_rror＝ΔI

When the grid-connected switch KB is turned off, Δ E_rror＝ΔV。

And 5: the current loop reference value I is obtained as follows_Lref：

When the grid-connected switch KB is closed, I_Lref＝I_GLref

When the grid-connected switch KB is turned off, I_Lref＝I_OLref。

Step 6: the current loop reference value I obtained in the step 5 is compared with_LrefWith the current I of the inductor L obtained in step 1_LObtaining an inductive current error signal delta I by difference_L,ΔI_L＝I_Lref-I_LController for defining current loopG_IPIDefine current loop controller G_IPIThe output of (a) is an inductance control voltage, denoted as V_LObtaining an inductive current error signal Delta I_LIs a current loop controller G_IPIThe input of, the current loop controller G_IPIIs a proportional-integral regulator with a transfer function G_IPI(s) is:

wherein k is_ipIs a current loop controller G_IPICoefficient of proportionality, k_iiIs a current loop controller G_IPIThe integral coefficient of (2).

In this embodiment: k is a radical of_ip＝0.6，k_ii＝20。

And 7: the direct current bus voltage V obtained according to the step 1_BusVoltage V of energy storage unit_BatAnd the inductance control voltage V obtained in the step 6_LThe switching tube S is calculated as follows₁Duty cycle of (d)₁：

d₁＝(V_Bat-V_L)÷V_Bus

The switching tube S is obtained by calculation in the following way₂Duty cycle of (d)₂：

d₂＝1-d₁

Switch tube S₁Duty ratio d of₁And a switching tube S₂Duty ratio d of₂Switching tube S for controlling Buck/Boost energy storage DC/DC converter through driving and protecting circuit₁And a switching tube S₂Make and break of (2).

And 8: and (5) repeating the steps 1-8, and realizing the bus voltage control of the parallel and off-grid smooth switching of the direct-current micro-grid.

FIG. 3 shows DC bus voltage V obtained by experiment on practical experimental platform according to specific parameters of the present invention and embodiments of the present invention_BusCurrent I of inductor L_LAnd a load current I_OExperimental waveforms of (4). In the figure T₃Before the moment, a grid-connected switch KB is closed, and an energy storage unit works in a current source modeFormula (II) tracking current command value I_ref(given current command value I_refIs 0), T₁At the moment, the load R suddenly changes from no load to 94 omega, and the current I of the inductor L can be seen_LSelf-adaptive output increase in dynamic process to inhibit direct-current bus voltage V_BusIs dropped; t is₂Time direct current power grid V_GFailure to lose the DC bus voltage V_BusSince the island detection and the operation of the grid-connected switch KB take a certain time, the support function of (1) is up to T₃The islanding detection is completed and the grid-connected switch KB is disconnected at the moment, and T can be seen from FIG. 3₂～T₃Current I of inductor L_LSelf-adaptive increasing and removing support direct current bus voltage V_BusWhen the energy storage unit works in a voltage source mode with a voltage difference, although the direct current bus voltage V_BusSlightly dropping, the amplitude of the drop is determined by the preset virtual admittance Y, but the DC bus voltage V_BusIs stable; t is₃～T₄Recovery of DC bus voltage V with smooth duration_BusTo the reference value V of the DC bus voltage_refAnd at the moment, the energy storage unit works in a voltage source mode with no voltage difference to support the direct current bus voltage V_BusAnd finishing the bus voltage control of the parallel and off-grid smooth switching of the direct-current micro-grid. The direct-current bus voltage V in the whole grid-connected and off-grid switching process can be seen_BusThe transition is smooth, and the experimental result proves the feasibility and the effectiveness of the invention.

Claims (1)

1. A bus voltage control method for parallel and off-grid smooth switching of a direct current micro-grid is provided, wherein the direct current micro-grid related to the control method comprises a direct current grid V_GThe system comprises a grid-connected switch KB, a direct-current bus, an energy storage unit, a Buck/Boost energy storage DC/DC converter and a load R; DC network V_GThe energy storage unit is connected in parallel to the direct current bus through a grid-connected switch KB, the energy storage unit is connected in parallel to the direct current bus through a Buck/Boost energy storage DC/DC converter, and the load R is connected in parallel to the direct current bus; the Buck/Boost energy storage DC/DC converter comprises an input capacitor C_BatAn inductor L and a switch tube S₁A switch tube S₂And an output capacitor C_Bus(ii) a Will input capacitance C_BatIs marked as node A₁Input capacitance C_BatIs denoted as node A₂Node A₁A₂One end of an inductor L is connected to a node A as an input port of the Buck/Boost energy storage DC/DC converter₁The other end of the inductor L is marked as node A₃Switching tube S₂Is connected to node A₃Upper, switch tube S₂Is connected to node A₂Upper, switch tube S₁Is marked as node A₄Switching tube S₁Is connected to node A₃Upper and output capacitor C_BusIs connected to node A₄Upper and output capacitor C_BusIs connected to node A₂Upper, node A₄A₂The output port of the Buck/Boost energy storage DC/DC converter is used;

the control method is characterized by comprising the following steps:

step 1: sampling the DC bus voltage, denoted as V_BusSampling the voltage of the energy storage unit, denoted as V_BatSampling the current of inductor L, denoted as I_L；

Step 2: given bus voltage reference value V_refGiven a current command value I_refDefine the voltage controller G_VPIDefine the voltage controller G_VPIThe output of (A) is an off-grid current loop reference value I_OLrefSaid voltage controller G_VPIIs a proportional-integral regulator with a transfer function G_VPI(s) is:

wherein k is_vpIs a voltage controller G_VPICoefficient of proportionality, k_viIs a voltage controller G_VPIThe integral coefficient of (a);

and step 3: judging whether a grid-connected switch KB is closed or not, if the grid-connected switch KB is closed, executing the step 3.1 and the step 3.2, and if the grid-connected switch KB is disconnected, executing the step 3.3, the step 3.4 and the step 3.5;

step 3.1: giving a virtual admittance Y, and obtaining a direct current bus voltage V according to the step 1_BusAnd 2, setting a direct current bus voltage reference value V in the step_refAnd the current command value I given in step 2_refAnd calculating to obtain a grid-connected current loop reference value I_GLrefThe calculation formula is as follows:

I_GLref＝I_ref+(V_ref-V_Bus)×Y

step 3.2: the grid-connected current loop reference value I obtained in the step 3.1_GLrefAnd off-grid current loop reference value I_OLrefObtaining a current error signal delta I, delta I ═ I by difference_GLref-I_OLrefExecuting the step 4;

step 3.3: starting the voltage command soft start control in the Nth control period with N being equal to N, wherein N is the cycle number of the voltage command soft start control period, N is 1,2, … N … + ∞, N is an intermediate variable of the cycle number of the control period, and obtaining the initial value V of the voltage command soft start according to the following mode_Bus0：

When N is 1, V_Bus0＝V_Bus

When N ≠ 1, V_Bus0Is not changed

Step 3.4: giving expected voltage command slow start times M, and obtaining voltage command slow start output V in the following mode_Ramp：

When N is less than or equal to M, V_Ramp＝V_Bus0+(V_ref-V_Bus0)×N÷M

When N > M, V_Ramp＝V_ref

Step 3.5: let N be N +1, output V is started slowly with voltage instruction_RampAnd the DC bus voltage V obtained in the step 1_BusObtaining a voltage error signal delta V by difference, wherein the delta V is equal to V_Ramp-V_BusExecuting the step 4;

and 4, step 4: the voltage controller G is obtained as follows_VPIInput Δ E of_rror：

When the grid-connected switch KB is closed, Δ E_rror＝ΔI

When the grid-connected switch KB is turned off, Δ E_rror＝ΔV

And 5: the current loop reference value I is obtained as follows_Lref：

When the grid-connected switch KB is closed, I_Lref＝I_GLref

When the grid-connected switch KB is turned off, I_Lref＝I_OLref

Step 6: the current loop reference value I obtained in the step 5 is compared with_LrefWith the current I of the inductor L obtained in step 1_LObtaining an inductive current error signal delta I by difference_L,ΔI_L＝I_Lref-I_LDefine current loop controller G_IPIDefine current loop controller G_IPIThe output of (a) is an inductance control voltage, denoted as V_LObtaining an inductive current error signal Delta I_LIs a current loop controller G_IPIThe input of, the current loop controller G_IPIIs a proportional-integral regulator with a transfer function G_IPI(s) is:

wherein k is_ipIs a current loop controller G_IPICoefficient of proportionality, k_iiIs a current loop controller G_IPIThe integral coefficient of (a);

and 7: the direct current bus voltage V obtained according to the step 1_BusVoltage V of energy storage unit_BatAnd the inductance control voltage V obtained in the step 6_LThe switching tube S is calculated as follows₁Duty cycle of (d)₁：

d₁＝(V_Bat-V_L)÷V_Bus

The switching tube S is obtained by calculation in the following way₂Duty cycle of (d)₂：

d₂＝1-d₁

Switch tube S₁Duty ratio d of₁And a switching tube S₂Duty ratio d of₂Switching tube S for controlling Buck/Boost energy storage DC/DC converter through driving and protecting circuit₁And a switching tube S₂Make-and-break;

and 8: and (5) repeating the steps 1-8, and realizing the bus voltage control of the parallel and off-grid smooth switching of the direct-current micro-grid.

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