CN114204538A - Direct-current micro-grid interconnection converter and power coordination control method thereof - Google Patents

Direct-current micro-grid interconnection converter and power coordination control method thereof Download PDF

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CN114204538A
CN114204538A CN202111434356.2A CN202111434356A CN114204538A CN 114204538 A CN114204538 A CN 114204538A CN 202111434356 A CN202111434356 A CN 202111434356A CN 114204538 A CN114204538 A CN 114204538A
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power
converter
voltage
control
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CN114204538B (en
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王盼宝
李珅光
任鹏
周洋
王卫
徐殿国
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Industrial Technology Research Institute Of Heilongjiang Province
Harbin Institute of Technology
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Industrial Technology Research Institute Of Heilongjiang Province
Harbin Institute of Technology
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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
    • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H02M3/1582—Buck-boost converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H02M3/1584—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load with a plurality of power processing stages connected in parallel
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H02M3/33584—Bidirectional converters

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention provides a direct current micro-grid interconnected converter and a power coordination control method thereof. Further, a power coordination control method of the interconnected converters is provided, and the control method allows three ports to independently operate so as to realize power flow control between the two direct current micro-grids and the public energy storage. The interconnection converter and the power coordination control method thereof can stabilize the power fluctuation of the system, improve the reliability of the system and reduce the operation cost. The parallel competition control strategy of the common energy storage port enables the transition of the control variable to be smoother, avoids violent transient change or oscillation of the converter, and improves the stability of the control system.

Description

Direct-current micro-grid interconnection converter and power coordination control method thereof
Technical Field
The invention belongs to the technical field of direct-current micro-grids, and particularly relates to a direct-current micro-grid interconnection converter and a power coordination control method thereof.
Background
The micro-grid integrating distributed renewable energy, an energy storage system and various loads has important significance in the aspects of realizing the carbon peak reaching and carbon neutralization targets and solving the environmental and energy problems. Compared with an alternating-current micro-grid, the direct-current micro-grid has the advantages of simplicity in control, low loss, high power quality and the like. The single direct current micro-grid mainly obtains energy from photovoltaic and wind energy, but the power of the photovoltaic and wind power generation system is influenced by weather conditions and has intermittency and volatility. After the direct-current micro-grids are interconnected, redundant power in one micro-grid can be transferred to the other micro-grid, and vice versa. Load is shared with the adjacent direct current micro-grid, so that the influence of renewable energy power change caused by weather change is reduced, and the stability of the system is improved. Meanwhile, the interconnection of the micro-grids can reduce the requirement of a single micro-grid on energy storage and reduce the operation cost.
The existing direct current micro-grid interconnection converter can be divided into a parallel connection type and a series connection type, wherein the parallel connection type can be divided into an isolation type and a non-isolation type. The non-isolated converter is small in size, high in power density and simple to control, but has no electric isolation and is only suitable for interconnection of two micro-grids with approximate voltage levels. The isolated converter is beneficial to isolating faults and improving the power supply reliability, but the rated power and the transmission power of the converter are the same, and the cost is high. Therefore, the researchers propose a series-connection type direct-current micro-grid interconnection converter, and the voltage is adjusted by injecting the voltage into the connecting line of the two direct-current micro-grids in series, so that the power flow is convenient to control, and the loss is low.
The direct current micro-grid interconnection converter generally adopts a two-port or multi-port bidirectional DC-DC converter, and the control strategies can be divided into three types, namely phase shift angle control, duty ratio control and phase shift angle plus duty ratio control. The duty ratio control mode is simple, but the bidirectional flow of energy cannot be realized. The phase shift angle control can realize bidirectional flow of energy, is still applicable to the condition that the primary and secondary voltage difference of the transformer is large, but has less control freedom. The phase shift angle and duty ratio control increase one degree of freedom, improve the input voltage regulation range and reduce the circulation current between the ports. Therefore, the interleaved parallel three-port converter in the combined converter provided by the invention adopts phase shift angle plus duty ratio control.
Disclosure of Invention
The invention provides a direct-current micro-grid interconnected converter and a power coordination control method thereof, aiming at solving the problems in the prior art. The direct-current microgrid interconnection converter provided by the invention is a series-type converter, the voltage stress of an output port of the converter is low, the operation loss is small, and the cost is effectively reduced.
The invention is realized by the following technical scheme, and provides a direct current micro-grid interconnection converter which is formed by cascading a staggered parallel full-bridge three-port converter and a full-bridge DC-DC converter; the interconnection converter is provided with three ports, the primary side input of the three-port converter is a port 1, the secondary side integrated staggered parallel Buck-boost is a port 3, and the output of the full-bridge DC-DC converter is a port 2; the port 1 is connected with the microgrid 1 in parallel, the port 2 is connected with the two microgrid connecting lines in series, and the port 3 is connected with the public energy storage; the port 2 is connected in series between the two direct current micro-grids to inject dynamic adjustable voltage to realize power transmission between the two direct current micro-grids.
Further, the working modes of the three ports of the direct-current microgrid interconnection converter are specifically as follows:
(1) port 1: the input of the primary side of the three-port converter forms a port 1, the port 1 is connected with a direct current bus of the microgrid 1 in parallel, and the voltage of a port 2' is always kept at a constant value through the phase shift control of the primary side and the secondary side of the three-port converter; the third port of the three-port converter is a port 2';
(2) port 2: the output port of the full-bridge DC-DC converter is connected with the connecting lines of the two DC micro-grids in series to form a port 2 of the interconnected converter, and the main function of the port 2 is to generate a voltage difference required by power transmission in a line connecting the DC bus 1 and the DC bus 2;
(3) port 3: a port 3 of the interconnection converter is formed by a secondary side integrated bidirectional Buck-Boost topological circuit, and the public energy storage can exchange power with a port 1 of the interconnection converter through the port 3; when the local energy storage of the two direct current micro-grids and the power transmission between the micro-grids are not enough to process redundant power, the public energy storage can be charged through the interconnection converter, and similarly, when the two direct current micro-grids have insufficient power, the public energy storage is discharged to support the bus voltage of the two direct current micro-grids.
The invention provides a power coordination control method of a direct current micro-grid interconnected converter, which is characterized in that ports of the control method are relatively independent, and the ports of the converter are allowed to operate independently, so that the power flow control of a direct current micro-grid interconnected system is realized, and the control method comprises three control loops of three-port converter constant voltage output control, port 2 series voltage control and port 3 common energy storage port control; and the available net power generated by the local control strategy of the single direct-current microgrid is used as the reference input of the power coordination control of the direct-current microgrid interconnection converter.
Furthermore, the three-port converter in the interconnected converter adopts primary side phase shift angle control and secondary side duty ratio control, the primary side controls the voltage of the port 2' to be constant through the phase shift angle phi, and the secondary side controls the voltage of the port to be constant through changing the switching tube S5～S8Duty cycle D1To control the charge and discharge power of the common energy stored at the port 3.
Furthermore, a constant voltage output control loop of the three-port converter adopts voltage and current double closed loop control, and the control aims to keep the voltage of the port 2' constant and serve as the input voltage of the full-bridge DC-DC converter to maintain the power required by the normal work of the full-bridge DC-DC converter; the deviation of the reference value of the voltage of the port 2' compared with the actual value is sent to a PI controller to generate the reference value of the current control loop
Figure BDA0003381090630000021
Thereafter, the reference value is compared
Figure BDA0003381090630000022
After comparing with the actual value of the input current of the port 1, the deviation is sent to a PI controller to generate a required control quantity phase shift angle phi, and the output voltage of the port 2' can be kept constant under various working conditions of the operation of the full-bridge DC-DC converter.
Further, the common energy storage of the port 3 of the interconnected converter is used for realizing input and output power control and voltage-limiting and current-limiting charging control; adopting a parallel competition mechanism, introducing a minimum selector and selecting a minimum duty ratio D1Secondary switch tube S as three-port converter5～S8The minimum selector consists of a power controller BPR, a voltage controller BVR, a current controller BCR and a minimum contention logic.
Further, when the SoC state of the common energy storage does not exceed the upper limit and the current and the voltage of the SoC state are lower than the set limit values, the output of the BVR and BCR controllers is in positive saturation, and the duty ratio D of the BVR_BVRAnd duty cycle D of BCR_BCRAt maximum, the BPR controller controls port 3 according to a given power reference signal P1+P2The charge and discharge power of the public energy storage is controlled so as to absorb or compensate the power difference of the two direct current micro-grids; when the common energy storage is about to be fully charged, the BVR controller automatically exits the saturation state, at which time D_BVRDuty cycle D to be less than BPR_BPRThe BVR controls the take-over port 3, and the public energy storage stops charging; when the charging current of the public energy storage reaches the upper limit value, the BCR controller exits the saturation state, the public energy storage enters a constant-current charging mode, and the damage of the public energy storage, namely P, caused by overcurrent charging is avoided1Available net power, P, for the microgrid 12Is the net power available from the microgrid 2.
Further, the BPR controller passes the net power available P to both DC microgrid1And P2Summing to obtain its power control reference signal
Figure BDA0003381090630000031
According to power reference signal
Figure BDA0003381090630000032
Carrying out charge-discharge control on the public stored energy; when P is present1+P2>When 0, the micro-grid has redundant power, and the public energy storage is charged; when P is present1+P2<At 0, the micro-grid has insufficient power, and the public stored energy is discharged.
Further, a current reference signal can be generated using equation (1)
Figure BDA0003381090630000033
With the actual current IBThe compared deviation is sent to a PI controller to generate a secondary duty ratio D1And is further used for producing a switching tube S5-S8The on pulse of (1);
Figure BDA0003381090630000034
wherein, VBIs the actual voltage;
available net power P of the microgrid 11The power absorbed or compensated by the public energy storage system is the reference power P of the transmission power between the two DC micro-gridst *，Pt *And the actual power PtAfter comparison, the deviation signal is transmitted to a PI controller GpIs a voltage controller GvcProviding a reference; voltage reference
Figure BDA0003381090630000035
Generated by the formula (2):
Vs *＝(Pt *-Pt)Gp (2)
reference power P according to power flow requirementst *Can have both positive and negative polarities if Pt *Is positive, indicating that the direction of power flow is from microgrid 1 to microgrid 2,
Figure BDA0003381090630000036
is also positive; if Pt *Negative, there is a power flow from the microgrid 2 to the microgrid 1,
Figure BDA0003381090630000037
is negative.
Furthermore, the full-bridge DC-DC converter is used for generating positive and negative adjustable voltages to realize the required series voltage regulation and comprises a power controller and a voltage controller, the controllers aim at regulating the output voltage of the port 2 of the interconnected converter to enable the output voltage to have the required amplitude and polarity, a droop control strategy is added into a full-bridge DC-DC control loop, after droop control is added, a virtual resistor R is equivalently connected in series with the equivalent resistor of the transmission line, and the control accuracy is improved under the condition of not increasing energy loss; then the actual output voltage V of port 2sAnd
Figure BDA0003381090630000041
comparing, inputting the compared deviation to a voltage type PI controller, and outputting a control signal VcTo generate a switching tube S9-S12To control the voltage transmission between two dc grids, I2Is the microgrid 2 current.
The invention provides a direct-current micro-grid interconnection converter which is formed by cascading a staggered parallel three-port converter and a full-bridge DC-DC converter and can realize low-loss operation and public energy storage access of the direct-current micro-grid interconnection converter. Further, a power coordination control method of the interconnected converters is provided, and the control method allows three ports to independently operate so as to realize power flow control between the two direct current micro-grids and the public energy storage. The interconnection converter and the power coordination control method thereof can stabilize the power fluctuation of the system, improve the reliability of the system and reduce the operation cost. The parallel competition control strategy of the common energy storage port enables the transition of the control variable to be smoother, avoids violent transient change or oscillation of the converter, and improves the stability of the control system.
Drawings
Fig. 1 is a structural diagram of a dc microgrid interconnection converter according to the present invention.
Fig. 2 is a connection diagram of interconnection transformers and a microgrid.
FIG. 3 is a block diagram of a coordinated control method for interconnected converter power.
Fig. 4 is a waveform diagram of mode 1 to mode 4 dynamic response experiments.
Fig. 5 is a waveform diagram of the mode 5 to mode 8 dynamic response experiment.
Fig. 6 is a waveform diagram of the dynamic response experiment in mode 9 and mode 10.
Fig. 7 is a waveform diagram of an experiment of the charging upper limit voltage of the storage battery.
Fig. 8 is a waveform diagram of an experiment for the maximum charging current of the storage battery.
Fig. 9 is a block diagram of a coordinated control method for the overall power of the interconnection converter and the microgrid.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
With reference to fig. 1 to 9, the present invention provides a DC microgrid interconnection converter, which is formed by cascading a cross parallel full-bridge three-port converter and a full-bridge DC-DC converter; the interconnection converter is provided with three ports, the primary side input of the three-port converter is a port 1, the secondary side integrated staggered parallel Buck-boost is a port 3, and the output of the full-bridge DC-DC converter is a port 2; the port 1 is connected with the microgrid 1 in parallel, the port 2 is connected with the two microgrid connecting lines in series, and the port 3 is connected with the public energy storage; the port 2 is connected in series between the two direct current micro-grids to inject dynamic adjustable voltage to realize power transmission between the two direct current micro-grids. The connection relationship between the dc microgrid interconnection converter and the two dc microgrids is shown in fig. 2. Wherein, PG1、PB1、PL1、PG2、PB2And PL2Representing the total generated power, the local stored energy power and the load power of the dc microgrid 1 and the dc microgrid 2, respectively. PbThe charging and discharging power for public energy storage. The dc microgrid inter-grid power transfer depends only on the tie line resistance and the voltage difference across the tie line, the main function of the port 2 being to generate the required voltage difference in the line connecting the dc bus 1 and the dc bus 2. If the injected series voltage is positive, power flows from the microgrid 1 to the microgrid 2, and if the voltage is negative, the power flows in the opposite direction.
The working modes of three ports of the direct-current micro-grid interconnection converter are as follows:
(1) port 1: the input of the primary side of the three-port converter forms a port 1, the port 1 is connected with a direct current bus of the microgrid 1 in parallel, and the voltage of a port 2' is always kept at a constant value through the phase shift control of the primary side and the secondary side of the three-port converter; the third port of the three-port converter is a port 2';
(2) port 2: the output port of the full-bridge DC-DC converter is connected with the connecting lines of the two DC micro-grids in series to form a port 2 of the interconnected converter, and the main function of the port 2 is to generate a voltage difference required by power transmission in a line connecting the DC bus 1 and the DC bus 2;
(3) port 3: a port 3 of the interconnection converter is formed by a secondary side integrated bidirectional Buck-Boost topological circuit, and the public energy storage can exchange power with a port 1 of the interconnection converter through the port 3; when the local energy storage of the two direct current micro-grids and the power transmission between the micro-grids are not enough to process redundant power, the public energy storage can be charged through the interconnection converter, and similarly, when the two direct current micro-grids have insufficient power, the public energy storage is discharged to support the bus voltage of the two direct current micro-grids.
The invention provides a power coordination control method of a direct current micro-grid interconnected converter, which is characterized in that ports of the control method are relatively independent, and the ports of the converter are allowed to operate independently, so that the power flow control of a direct current micro-grid interconnected system is realized, and the control method comprises three steps of constant voltage output control of a three-port converter, serial voltage control of a port 2 and common energy storage port control of a port 3A control loop; available net power P generated by local control strategy of single direct current micro-grid1And P2And the two net powers are used as reference inputs of the power coordination control of the direct-current micro-grid interconnection converter.
The three-port converter in the interconnected converter adopts primary side phase shift angle control and secondary side duty ratio control, the primary side controls the voltage constancy of the port 2' through the phase shift angle phi, and the secondary side controls the switching tube S through changing5～S8Duty cycle D1To control the charge and discharge power of the common energy stored at the port 3.
The constant voltage output control loop of the three-port converter adopts voltage and current double closed loop control, and the control aims to keep the voltage of a port 2' constant and serve as the input voltage of the full-bridge DC-DC converter so as to maintain the power required by the normal work of the full-bridge DC-DC converter; the deviation of the reference value of the voltage of the port 2' compared with the actual value is sent to a PI controller to generate the reference value of the current control loop
Figure BDA0003381090630000051
Thereafter, the reference value is compared
Figure BDA0003381090630000052
After comparing with the actual value of the input current of the port 1, the deviation is sent to the PI controller to generate a required control quantity phase shift angle phi, the control strategy has good load regulation rate, and the output voltage of the port 2' can be kept constant under various working conditions of the operation of the full-bridge DC-DC converter.
The public energy storage of the port 3 of the interconnected converter is used for realizing input and output power control and voltage-limiting current-limiting charging control; adopting a parallel competition mechanism, introducing a minimum selector and selecting a minimum duty ratio D1Secondary switch tube S as three-port converter5～S8The minimum selector is composed of a Power controller (BPR), a Voltage controller (BVR), a Current controller (BCR) and a minimum contention logic. Two traditional controls of parallel competition control strategy, state detection and mode switchingCompared with a control strategy, the control strategy has great advantages, can realize smooth transition of control variables during state switching, avoids transient sudden change or converter oscillation, and improves the stability of the system.
When the SoC state of the common energy storage does not exceed the upper limit and the current and the voltage of the SoC state are lower than the set limit values, the output of the BVR and BCR controllers is in positive saturation, and the duty ratio D of the BVR_BVRAnd duty cycle D of BCR_BCRAt maximum, the BPR controller controls port 3 according to a given power reference signal P1+P2The charge and discharge power of the public energy storage is controlled so as to absorb or compensate the power difference of the two direct current micro-grids; when the common energy storage is about to be fully charged, the BVR controller automatically exits the saturation state, at which time D_BVRDuty cycle D to be less than BPR_BPRThe BVR controls the take-over port 3, and the public energy storage stops charging; when the charging current of the public energy storage reaches the upper limit value, the BCR controller exits the saturation state, the public energy storage enters a constant-current charging mode, and the damage of the public energy storage, namely P, caused by overcurrent charging is avoided1Available net power, P, for the microgrid 12Is the net power available from the microgrid 2.
BPR controller through available net power P to two DC micro-grids1And P2Summing to obtain its power control reference signal
Figure BDA0003381090630000061
According to power reference signal
Figure BDA0003381090630000062
Carrying out charge-discharge control on the public stored energy; when P is present1+P2>When 0, the micro-grid has redundant power, and the public energy storage is charged; when P is present1+P2<At 0, the micro-grid has insufficient power, and the public stored energy is discharged.
The current reference signal can be generated by using the formula (1)
Figure BDA0003381090630000063
With the actual current IBThe compared deviation is sent to a PI controller to generate a secondary side duty ratioD1And is further used for producing a switching tube S5-S8The on pulse of (1);
Figure BDA0003381090630000064
wherein, VBIs the actual voltage;
available net power P of the microgrid 11The power absorbed or compensated by the public energy storage system is the reference power P of the transmission power between the two DC micro-gridst *，Pt *And the actual power Pt(Pt＝V4I2) After comparison, the deviation signal is transmitted to a PI controller GpIs a voltage controller GvcProviding a reference; voltage reference
Figure BDA0003381090630000065
Generated by the formula (2):
Vs *＝(Pt *-Pt)Gp (2)
reference power P according to power flow requirementst *Can have both positive and negative polarities if Pt *Is positive, indicating that the direction of power flow is from microgrid 1 to microgrid 2,
Figure BDA0003381090630000066
is also positive; if Pt *Negative, there is a power flow from the microgrid 2 to the microgrid 1,
Figure BDA0003381090630000071
is negative.
The full-bridge DC-DC converter for generating positive and negative adjustable voltages to achieve the required series voltage regulation consists of a power controller and a voltage controller, the purpose of these controllers is to adjust the output voltage of the interconnected converter port 2 to have the required amplitude and polarity, since the transmission line has a small equivalent resistance in practice, in order to increase the control accuracyA droop control strategy is added into the full-bridge DC-DC control loop, after droop control is added, a virtual resistor R is equivalently connected in series with the equivalent resistor of the transmission line, and the control accuracy is improved under the condition that energy loss is not increased; then the actual output voltage V of port 2sAnd
Figure BDA0003381090630000072
comparing, inputting the compared deviation to a voltage type PI controller, and outputting a control signal VcTo generate a switching tube S9-S12To control the voltage transmission between two dc grids, I2Is the microgrid 2 current.
In order to verify the effect of the invention, the power coordination control strategy effect of the direct current micro-grid interconnected converter is verified through experiments. The experimental parameters were as follows: two-DC micro-grid bus voltage V1＝V2400V, common energy storage rated voltage Vb24V, converter port 2' voltage VlkThe primary power inductance is 5 muh and the secondary power inductance is 120 muh, 48V.
Table 1 shows experimental result power data of different modes during the operation of the public energy storage, fig. 4 is a system dynamic response experimental waveform of modes 1 to 4, in mode 1, the remaining power of the microgrid 1 is smaller than the insufficient power of the microgrid 2, in order to meet the load power requirement of the microgrid 2, the public energy storage is discharged with a power of 100W, and a series voltage V is injected between two direct current microgridssTo control the power transfer between two microgrid's, the output voltage V of port 2lkAlways kept at a constant 48V, not affected by power transmission. In mode 2, the demanded power of the microgrid 2 is suddenly reduced by 200W, as can be seen from the figure, the transmission power PtPositive, the amplitude is reduced to 300W. The public energy storage works in a charging state to improve the utilization rate of renewable energy sources and the corresponding series voltage VsAnd also decreases.
TABLE 1 Power data of Experimental results in different modes
Figure BDA0003381090630000073
Mode 3 is the opposite of the case of mode 2, with excess power on microgrid 2 and insufficient power on microgrid 1, but the excess net power on microgrid 2 is not sufficient to meet the required net power on microgrid 1. At the moment, the public energy storage provides 100W of power, so that load shedding of the microgrid 1 is avoided, the stability of the system is improved, and the corresponding series voltage VsThe polarity is also changed.
Fig. 5 shows the dynamic response experimental waveforms of the modes 5 to 8, at this time, only a single dc microgrid has residual power and insufficient power, the power demand of the other microgrid is balanced, the modes 5 and 6 are for transmitting energy between the microgrid 2 and the public energy storage, and the modes 7 and 8 are for transmitting energy between the microgrid 1 and the public energy storage, which verifies that the proposed control strategy has good dynamic response when the single microgrid and the public energy storage perform energy transmission.
Fig. 6 shows the experimental waveforms of the mode 9 and mode 10 dynamic responses, when the microgrid 1 and the microgrid 2 have surplus or insufficient power at the same time, and the power demand balance of the whole interconnected system is maintained by means of the charging or discharging of the common energy storage. Similarly, in all modes of operation, PtAnd PbTrack its reference power command Pt *And
Figure BDA0003381090630000081
corresponding series injection voltage VsBy varying its magnitude and polarity to deliver the required power, the DC link voltage VlkAlways kept constant at 48V.
Fig. 7 shows the experimental waveforms when the battery reaches the upper charge limit voltage, and it can be seen that the battery is initially charged with a current of 2A, when the battery is nearly fully charged, its terminal voltage reaches the upper limit voltage, the BVR controller begins to exit saturation, D _ BVR gradually decreases, when D _ BVR < D _ BPR, the BVR controller wins the parallel contention, the constant voltage controller takes over the control of port 3, and the battery stops charging.
Fig. 8 shows an experimental waveform when the storage battery reaches the maximum charging current, the maximum charging current of the storage battery is set to 4A, when the charging reference power of the storage battery becomes large, so that the charging current of the storage battery reaches the set upper limit value, the BCR controller starts to exit saturation, D _ BCR gradually decreases, when D _ BCR < D _ BPR, the BCR controller wins in parallel competition, the constant current controller takes over the control of the port 3, and the charging current of the storage battery is maintained at the upper limit value, so as to prevent the storage battery from being overcharged.
Fig. 9 shows a block diagram of the interconnection converter and microgrid overall power coordination control method of the present invention, which mainly includes a dc microgrid interconnection converter topology and its power coordination control strategy. The direct-current micro-grid interconnection converter is formed by cascading a staggered parallel three-port converter and a full-bridge DC-DC converter, the converter is provided with three ports, the port 1 is connected with the micro-grid 1 in parallel, the port 2 is connected with two micro-grid connecting lines in series, and the port 3 is connected with a public energy storage. The port 2 is connected in series between the two direct current micro-grids to inject dynamic adjustable voltage to realize power transmission between the two direct current micro-grids. The power coordination control strategy of the interconnection converter allows three ports to independently operate so as to realize power flow control between the two direct current micro-grids and public energy storage, wherein the port 1 and the port 2 'adopt phase shift control to realize constant voltage output of the port 2', and the port 3 adopts a parallel competition control strategy to select duty ratio control quantity thereof, so that constant power control and voltage limiting/current limiting charging control can be realized. The full-bridge DC-DC converter adopts droop-based power voltage double closed-loop control to output dynamic adjustable voltage.
The dc microgrid interconnection converter and the power coordination control method thereof proposed by the present invention are described in detail above, and specific examples are applied herein to illustrate the principle and the implementation manner of the present invention, and the description of the above embodiments is only used to help understanding the method of the present invention and the core idea thereof; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.

Claims (10)

1. A direct current micro-grid interconnection converter is characterized in that the interconnection converter is formed by cascading a staggered parallel full-bridge three-port converter and a full-bridge DC-DC converter; the interconnection converter is provided with three ports, the primary side input of the three-port converter is a port 1, the secondary side integrated staggered parallel Buck-boost is a port 3, and the output of the full-bridge DC-DC converter is a port 2; the port 1 is connected with the microgrid 1 in parallel, the port 2 is connected with the two microgrid connecting lines in series, and the port 3 is connected with the public energy storage; the port 2 is connected in series between the two direct current micro-grids to inject dynamic adjustable voltage to realize power transmission between the two direct current micro-grids.
2. The interconnection converter according to claim 1, wherein the three ports of the dc microgrid interconnection converter have the following operation modes:
(1) port 1: the input of the primary side of the three-port converter forms a port 1, the port 1 is connected with a direct current bus of the microgrid 1 in parallel, and the voltage of a port 2' is always kept at a constant value through the phase shift control of the primary side and the secondary side of the three-port converter; the third port of the three-port converter is a port 2';
(2) port 2: the output port of the full-bridge DC-DC converter is connected with the connecting lines of the two DC micro-grids in series to form a port 2 of the interconnected converter, and the main function of the port 2 is to generate a voltage difference required by power transmission in a line connecting the DC bus 1 and the DC bus 2;
(3) port 3: a port 3 of the interconnection converter is formed by a secondary side integrated bidirectional Buck-Boost topological circuit, and the public energy storage can exchange power with a port 1 of the interconnection converter through the port 3; when the local energy storage of the two direct current micro-grids and the power transmission between the micro-grids are not enough to process redundant power, the public energy storage can be charged through the interconnection converter, and similarly, when the two direct current micro-grids have insufficient power, the public energy storage is discharged to support the bus voltage of the two direct current micro-grids.
3. The power coordination control method of the direct current microgrid interconnection converter, as claimed in claim 1, is characterized in that ports of the control method are relatively independent, and the ports of the converter are allowed to operate independently, so that power flow control of a direct current microgrid interconnection system is realized, and the control method comprises three control loops of three-port converter constant voltage output control, port 2 series voltage control and port 3 common energy storage port control; and the available net power generated by the local control strategy of the single direct-current microgrid is used as the reference input of the power coordination control of the direct-current microgrid interconnection converter.
4. A method according to claim 3, characterized in that the three-port converter of the interconnected converters is controlled by a phase shift angle on the primary side, which controls the voltage at port 2' to be constant by means of a phase shift angle Φ, and by a duty cycle on the secondary side, which controls the switching tube S by means of a change5～S8Duty cycle D1To control the charge and discharge power of the common energy stored at the port 3.
5. The method of claim 3, wherein the constant voltage output control loop of the three-port converter adopts a voltage-current double closed loop control, and the purpose of the control is to make the port 2' keep the voltage constant, as the input voltage of the full-bridge DC-DC converter, and maintain the power required by the normal operation of the full-bridge DC-DC converter; the deviation of the reference value of the voltage of the port 2' compared with the actual value is sent to a PI controller to generate the reference value of the current control loop
Figure FDA0003381090620000011
Thereafter, the reference value is compared
Figure FDA0003381090620000012
After comparing with the actual value of the input current of the port 1, the deviation is sent to a PI controller to generate a required control quantity phase shift angle phi, and the output voltage of the port 2' can be kept constant under various working conditions of the operation of the full-bridge DC-DC converter.
6. Method according to claim 3, characterized in that the common energy storage of the interconnected converter ports 3 is used for input and output power control and voltage limiting and current limitingControlling charging; adopting a parallel competition mechanism, introducing a minimum selector and selecting a minimum duty ratio D1Secondary switch tube S as three-port converter5～S8The minimum selector consists of a power controller BPR, a voltage controller BVR, a current controller BCR and a minimum contention logic.
7. The method of claim 6, wherein when the SoC state of the common energy storage does not exceed an upper limit and the current and voltage thereof are below set limit values, the output of the BVR and BCR controller is in positive saturation and the duty cycle D of the BVR is_BVRAnd duty cycle D of BCR_BCRAt maximum, the BPR controller controls port 3 according to a given power reference signal P1+P2The charge and discharge power of the public energy storage is controlled so as to absorb or compensate the power difference of the two direct current micro-grids; when the common energy storage is about to be fully charged, the BVR controller automatically exits the saturation state, at which time D_BVRDuty cycle D to be less than BPR_BPRThe BVR controls the take-over port 3, and the public energy storage stops charging; when the charging current of the public energy storage reaches the upper limit value, the BCR controller exits the saturation state, the public energy storage enters a constant-current charging mode, and the damage of the public energy storage, namely P, caused by overcurrent charging is avoided1Available net power, P, for the microgrid 12Is the net power available from the microgrid 2.
8. The method of claim 7, wherein the BPR controller passes the net power available P to both dc micro grids1And P2Summing to obtain its power control reference signal
Figure FDA0003381090620000021
According to power reference signal
Figure FDA0003381090620000022
Carrying out charge-discharge control on the public stored energy; when P is present1+P2>When 0, the micro-grid has redundant power, and the public energy storage is charged; when P is present1+P2<At 0, the micro-grid has insufficient power, and the public stored energy is discharged.
9. The method of claim 8, wherein the current reference signal is generated using equation (1)
Figure FDA0003381090620000023
With the actual current IBThe compared deviation is sent to a PI controller to generate a secondary duty ratio D1And is further used for producing a switching tube S5-S8The on pulse of (1);
Figure FDA0003381090620000024
wherein, VBIs the actual voltage;
available net power P of the microgrid 11The power absorbed or compensated by the public energy storage system is the reference power P of the transmission power between the two DC micro-gridst *，Pt *And the actual power PtAfter comparison, the deviation signal is transmitted to a PI controller GpIs a voltage controller GvcProviding a reference; voltage reference Vs *Generated by the formula (2):
Vs *＝(Pt *-Pt)Gp (2)
reference power P according to power flow requirementst *Can have both positive and negative polarities if Pt *Is positive, indicating that the direction of power flow is from microgrid 1 to microgrid 2, Vs *Is also positive; if Pt *Negative, there is a power flow, V, from the microgrid 2 to the microgrid 1s *Is negative.
10. The method of claim 9, wherein a full bridge DC-DC converter is used to generate positive and negative adjustable voltages,the droop control circuit is composed of a power controller and a voltage controller, the controllers aim to adjust the output voltage of a port 2 of an interconnection converter to enable the output voltage to have the required amplitude and polarity, a droop control strategy is added in a full-bridge DC-DC control loop, after the droop control is added, a virtual resistor R is equivalently connected in series with an equivalent resistor of a transmission line, and the control accuracy is improved under the condition that the energy loss is not increased; then the actual output voltage V of port 2sAnd
Figure FDA0003381090620000031
comparing, inputting the compared deviation to a voltage type PI controller, and outputting a control signal VcTo generate a switching tube S9-S12To control the voltage transmission between two dc grids, I2Is the microgrid 2 current.
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