CN114204538B - 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 PDFInfo
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- CN114204538B CN114204538B CN202111434356.2A CN202111434356A CN114204538B CN 114204538 B CN114204538 B CN 114204538B CN 202111434356 A CN202111434356 A CN 202111434356A CN 114204538 B CN114204538 B CN 114204538B
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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
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- 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
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- 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
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- 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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- Supply And Distribution Of Alternating Current (AREA)
- Dc-Dc Converters (AREA)
Abstract
The invention provides a direct-current micro-grid interconnection converter and a power coordination control method thereof. Further, a power coordination control method of the interconnected converters is provided, which allows the three ports to operate independently to realize the 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 public energy storage port enables the transition of the control variable to be smoother, avoids severe transient change or oscillation of the converter, and improves the stability of the control system.
Description
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 the distributed renewable energy source, the energy storage system and various loads has important significance in achieving the carbon peak, the carbon neutralization target and solving the environmental and energy problems. Compared with an alternating-current micro-grid, the direct-current micro-grid has the advantages of simple control, low loss, high electric energy quality and the like. The single direct current micro-grid mainly acquires energy from photovoltaic and wind energy, but the power of a photovoltaic and wind power generation system is affected by weather conditions, and has intermittence and volatility. And after interconnecting the dc micro-grids, excess power in one micro-grid may be transferred to the other micro-grid and vice versa. By sharing the load with the adjacent direct current micro-grid, the influence of the renewable energy power change caused by weather change is reduced, and the stability of the system is improved. Meanwhile, the micro-grid interconnection can reduce the energy storage requirement of a single micro-grid, and the operation cost is reduced.
The existing direct current micro-grid interconnection converter can be divided into a parallel type converter and a series type converter, wherein the parallel type converter can be divided into an isolated type converter and a non-isolated type converter. The non-isolated converter has small volume, high power density and simple control, but is not electrically isolated and is only suitable for interconnection of two micro-grids with close voltage levels. The isolated converter is favorable for isolating faults and improving the power supply reliability, but the rated power of the converter is the same as the transmission power, and the cost is high. Therefore, a learner proposes a series-connection type direct-current micro-grid interconnection converter, and the voltage is adjusted by injecting the voltage into the connecting wires of the two direct-current micro-grids in series, so that the control of the power flow is convenient, 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 strategy can be divided into three types, namely phase-shift angle control, duty cycle control and phase-shift angle plus duty cycle control. The duty cycle control is simple, but cannot achieve bi-directional flow of energy. The phase shift angle control can realize the bidirectional flow of energy, is still applicable to the condition of larger voltage difference between the primary side and the secondary side of the transformer, but has less control freedom. The phase shift angle and duty ratio control increases one degree of control freedom, improves the input voltage adjusting range, and reduces the circulation between ports. Therefore, the staggered parallel three-port converter in the parallel converter provided by the invention adopts phase shift angle plus duty ratio control.
Disclosure of Invention
The invention provides a direct-current micro-grid interconnection converter and a power coordination control method thereof, which aim to solve the problems in the prior art. The direct-current micro-grid interconnection converter provided by the invention is a series-connection converter, the voltage stress of an output port is low, the operation loss is small, and the cost is effectively reduced.
The invention is realized by the following technical scheme, the invention 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 interconnected converter is provided with three ports, the primary side input of the three-port converter is port 1, the secondary side integrated staggered parallel Buck-boost is port 3, and the output of the full-bridge DC-DC converter is port 2; the port 1 is connected with the micro-grid 1 in parallel, the port 2 is connected with the connecting wires of the two micro-grids in series, and the port 3 is connected with public energy storage; the port 2 is used for injecting dynamic adjustable voltage in series between the two direct current micro-grids to realize power transmission between the two direct current micro-grids.
Further, the working modes of the three ports of the direct current micro-grid interconnection converter are specifically as follows:
(1) Port 1: the input of the primary side of the three-port converter forms a port 1, and is connected with a direct current bus of the micro-grid 1 in parallel, and the voltage of the 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 port 2';
(2) Port 2: the output port of the full-bridge DC-DC converter is connected in series with the connecting wires of the two DC micro-grids to form a port 2 of the interconnection 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: the port 3 of the interconnection converter is formed by a secondary side integrated bidirectional Buck-Boost topology circuit, and through the port 3, the public energy storage can exchange power with the port 1 of the interconnection converter; when the local energy storage of the two direct current micro-grids and the power transmission between the micro-grids are insufficient to process redundant power, the public energy storage can be charged through the interconnection converter, and when the two direct current micro-grids have insufficient power, the public energy storage discharges 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 interconnection converter, which is characterized in that all ports of the control method are relatively independent, and the ports of the converter are allowed to independently operate, so that the power flow control of the direct current micro-grid interconnection system is realized; the available net power generated by the local control strategy of the single direct-current micro-grid is used as a reference input for the power coordination control of the interconnection converter of the direct-current micro-grid.
Further, three-port converters in the interconnected converters employ primary side phase shift angle control, secondary side duty cycle control, primary side control port 2' voltage constant by phase shift angle Φ, and secondary side control by changing switching tube S 5 ～S 8 Duty cycle D 1 To control the charge and discharge power of the common stored energy of the ports 3.
Further, the constant voltage output control loop of the three-port converter adopts voltage-current double closed-loop control, and the purpose of the control is to keep the voltage of the port 2' constant, and the constant voltage output control loop is used as the input voltage of the full-bridge DC-DC converter to maintain the power required by the normal operation of the full-bridge DC-DC converter; after the deviation of the reference value of the port 2' voltage compared with the actual value is sent to a PI controller, the reference value of the current control loop is generatedAfter that, the reference value ∈>After comparing with the actual value of the input current of the port 1, the deviation is sent into 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 full-bridge DC-DC converter.
Further, the public energy storage of the interconnection converter port 3 is used for realizing input and output power control and voltage-limiting and current-limiting charging control; adopting parallel competition mechanism, introducing minimum selector, selecting minimum duty ratio D 1 Secondary side switching tube S as three-port converter 5 ～S 8 The minimum selector is composed of a power controller BPR, a voltage controller BVR, a current controller BCR and minimum contention logic.
Further, the methodWhen the state of the public energy storage SoC does not exceed the upper limit and the current and voltage thereof are lower than the set limit values, the outputs of the BVR and the BCR controller are saturated positively, the duty ratio D of the BVR _BVR And duty cycle D of BCR _BCR At maximum, the BPR controller controls port 3 according to a given power reference signal P 1 +P 2 To control the charge and discharge power of the public energy storage, so as to absorb or compensate the power difference of the two DC micro-grids; when the public energy storage is about to be fully charged, the BVR controller automatically exits the saturation state, at this time, D _BVR Duty cycle D to be smaller than BPR _BPR BVR control takes over control of port 3 and common stored energy stops charging; when the charging current of the public energy storage reaches the upper limit value, the BCR controller exits from a saturated state, the public energy storage enters into a constant-current charging mode, and damage of the public energy storage caused by over-current charging is avoided, P 1 To the net power available to the microgrid 1, P 2 Which is the net power available to the microgrid 2.
Further, the BPR controller uses the net power P available to both dc micro-grids 1 And P 2 Summing to obtain its power control reference signalAccording to the power reference signal->Charging and discharging control is carried out on public energy storage; when P 1 +P 2 >When 0, the micro-grid has redundant power, and public energy storage is charged; when P 1 +P 2 <And 0, the micro-grid has insufficient power, and public energy storage discharges.
Further, a current reference signal can be generated using equation (1)And the actual current I B The compared deviation is sent into a PI controller to generate a secondary side duty ratio D 1 And is further used for producing a switching tube S 5 -S 8 Is set to be a conduction pulse of (a);
wherein V is B Is the actual voltage;
the net power P available from the micro grid 1 1 Adding the power absorbed or compensated by the public energy storage system to obtain reference power P which is the transmission power between two direct current micro-grids t * ，P t * And the actual power P t After comparison, the deviation signal is transmitted to the PI controller G p Is a voltage controller G vc Providing a reference; voltage referenceGenerated by formula (2):
V s * ＝(P t * -P t )G p (2)
reference power P according to power flow requirements t * May have both positive and negative polarities, if P t * Is positive, indicating that the direction of power flow is from the micro grid 1 to the micro grid 2,the polarity of (2) is also positive; if P t * Negative, then there is a power flow from the micro-grid 2 to the micro-grid 1, +.>The polarity of (2) is negative.
Further, the full-bridge DC-DC converter is configured to generate positive and negative adjustable voltages to achieve a desired series voltage adjustment, and is composed of a power controller and a voltage controller, wherein the purpose of the controllers is to adjust the output voltage of the interconnection converter port 2 to have a desired amplitude and polarity, a droop control strategy is added in the full-bridge DC-DC control loop, after droop control is added, a virtual resistor R is connected in series with an equivalent resistor of a transmission line, and the control accuracy is increased without increasing energy loss; the actual output voltage V of port 2 is then applied s And (3) withComparing, inputting the compared deviation into a voltage type PI controller, and outputting a control signal V c To generate a switching tube S 9 -S 12 To control the voltage transmission between two DC micro-grids, I 2 Is 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, which allows the three ports to operate independently to realize the 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 public energy storage port enables the transition of the control variable to be smoother, avoids severe transient change or oscillation of the converter, and improves the stability of the control system.
Drawings
Fig. 1 is a block diagram of a dc micro grid interconnection converter according to the present invention.
Fig. 2 is a diagram of the interconnection of the converter to the microgrid.
Fig. 3 is a block diagram of an interconnection inverter power coordination control method.
Fig. 4 is a waveform diagram of a mode 1 to mode 4 dynamic response experiment.
Fig. 5 is a waveform diagram of a dynamic response experiment of modes 5 to 8.
Fig. 6 is a waveform diagram of mode 9 and mode 10 dynamic response experiments.
Fig. 7 is a waveform diagram of the upper limit voltage test for battery charge.
Fig. 8 is a waveform diagram of an experiment for achieving maximum charging current of the storage battery.
Fig. 9 is a block diagram of an overall power coordination control method for an interconnected converter and a micro-grid.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 1-9, the invention 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 interconnected converter is provided with three ports, the primary side input of the three-port converter is port 1, the secondary side integrated staggered parallel Buck-boost is port 3, and the output of the full-bridge DC-DC converter is port 2; the port 1 is connected with the micro-grid 1 in parallel, the port 2 is connected with the connecting wires of the two micro-grids in series, and the port 3 is connected with public energy storage; the port 2 is used for injecting dynamic adjustable voltage in series between the two direct current micro-grids to realize power transmission between the two direct current micro-grids. The connection relationship between the direct-current micro-grid interconnection converter and the two direct-current micro-grids is shown in fig. 2. Wherein P is G1 、P B1 、P L1 、P G2 、P B2 And P L2 Representing the total generated power, the local stored energy power and the load power of the direct current micro-grid 1 and the direct current micro-grid 2 respectively. P (P) b Charge and discharge power for the public energy storage. The main function of the port 2 is to create the required voltage difference in the lines connecting the dc bus 1 and the dc bus 2, depending only on the tie resistance and the voltage difference across the tie. If the injected series voltage is positive, power flows from the micro grid 1 to the micro grid 2, and if the voltage is negative, the power flows in the opposite direction.
The working modes of the three ports of the direct current micro-grid interconnection converter are specifically as follows:
(1) Port 1: the input of the primary side of the three-port converter forms a port 1, and is connected with a direct current bus of the micro-grid 1 in parallel, and the voltage of the 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 port 2';
(2) Port 2: the output port of the full-bridge DC-DC converter is connected in series with the connecting wires of the two DC micro-grids to form a port 2 of the interconnection 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: the port 3 of the interconnection converter is formed by a secondary side integrated bidirectional Buck-Boost topology circuit, and through the port 3, the public energy storage can exchange power with the port 1 of the interconnection converter; when the local energy storage of the two direct current micro-grids and the power transmission between the micro-grids are insufficient to process redundant power, the public energy storage can be charged through the interconnection converter, and when the two direct current micro-grids have insufficient power, the public energy storage discharges 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 interconnection converter, which is characterized in that all ports of the control method are relatively independent, and the ports of the converter are allowed to independently operate, so that the power flow control of the direct current micro-grid interconnection system is realized; available net power P generated by single direct current micro-grid local control strategy 1 And P 2 The two net powers are used as reference inputs for power coordination control of the direct current micro-grid interconnection converter.
Three-port converters in the interconnected converters employ primary side phase shift angle control, secondary side duty cycle control, primary side controlling the voltage of port 2' constant by phase shift angle Φ, and secondary side controlling the switching tube S by changing the switching tube S 5 ～S 8 Duty cycle D 1 To control the charge and discharge power of the common stored energy of the ports 3.
The constant voltage output control loop of the three-port converter adopts voltage-current double closed-loop control, and the purpose of the control is to keep the voltage of the port 2' constant, and the constant voltage output control loop is used as the input voltage of the full-bridge DC-DC converter to maintain the power required by the normal operation of the full-bridge DC-DC converter; the deviation of the reference value and the actual value of the port 2' voltage is sent to aAfter the PI controller is used, a reference value of a current control loop is generatedAfter that, the reference value ∈>After comparing with the actual value of the input current of the port 1, the deviation is sent into a PI controller to generate a required control quantity phase shift angle phi, the control strategy has good load adjustment rate, and the output voltage of the port 2' can be kept constant under various working conditions of the full-bridge DC-DC converter.
The public energy storage of the interconnected converter port 3 is used for realizing input and output power control and voltage-limiting and current-limiting charging control; adopting parallel competition mechanism, introducing minimum selector, selecting minimum duty ratio D 1 Secondary side switching tube S as three-port converter 5 ～S 8 The minimum selector is composed of a power controller (Battery Power Regulator, BPR), a voltage controller (Battery Voltage Regulator, BVR), a current controller (Battery Current Regulator, BCR) and minimum contention logic. Compared with two traditional control strategies of state detection and mode switching, the parallel competition control strategy has great advantages, and can enable the control variable to realize smooth transition during state switching, avoid transient abrupt change or converter oscillation and improve the stability of the system.
When the state of the public energy storage SoC does not exceed the upper limit and the current and the voltage thereof are lower than the set limit values, the outputs of the BVR and the BCR controller are saturated positively, and the duty ratio D of the BVR _BVR And duty cycle D of BCR _BCR At maximum, the BPR controller controls port 3 according to a given power reference signal P 1 +P 2 To control the charge and discharge power of the public energy storage, so as to absorb or compensate the power difference of the two DC micro-grids; when the public energy storage is about to be fully charged, the BVR controller automatically exits the saturation state, at this time, D _BVR Duty cycle D to be smaller than BPR _BPR BVR control takes over control of port 3 and common stored energy stops charging; when the charging current of the public energy storage reaches the upper limitWhen the value is reached, the BCR controller exits from the saturation state, the public energy storage enters into a constant-current charging mode, the damage of the public energy storage caused by overcurrent charging is avoided, and P 1 To the net power available to the microgrid 1, P 2 Which is the net power available to the microgrid 2.
BPR controller through available net power P to two DC micro-grids 1 And P 2 Summing to obtain its power control reference signalAccording to the power reference signal->Charging and discharging control is carried out on public energy storage; when P 1 +P 2 >When 0, the micro-grid has redundant power, and public energy storage is charged; when P 1 +P 2 <And 0, the micro-grid has insufficient power, and public energy storage discharges.
The current reference signal can be generated by using (1)And the actual current I B The compared deviation is sent into a PI controller to generate a secondary side duty ratio D 1 And is further used for producing a switching tube S 5 -S 8 Is set to be a conduction pulse of (a);
wherein V is B Is the actual voltage;
the net power P available from the micro grid 1 1 Adding the power absorbed or compensated by the public energy storage system to obtain reference power P which is the transmission power between two direct current micro-grids t * ，P t * And the actual power P t (P t ＝V 4 I 2 ) After comparison, the deviation signal is transmitted to the PI controller G p Is a voltage controller G vc Providing a reference; voltage referenceGenerated by formula (2):
V s * ＝(P t * -P t )G p (2)
reference power P according to power flow requirements t * May have both positive and negative polarities, if P t * Is positive, indicating that the direction of power flow is from the micro grid 1 to the micro grid 2,the polarity of (2) is also positive; if P t * Negative, then there is a power flow from the micro-grid 2 to the micro-grid 1, +.>The polarity of (2) is negative.
The full-bridge DC-DC converter is used for generating positive and negative adjustable voltages to realize the required series voltage regulation, and consists of a power controller and a voltage controller, wherein the controllers aim to adjust the output voltage of the interconnection converter port 2 to have the required amplitude and polarity; the actual output voltage V of port 2 is then applied s And (3) withComparing, inputting the compared deviation into a voltage type PI controller, and outputting a control signal V c To generate a switching tube S 9 -S 12 To control the voltage transmission between two DC micro-grids, I 2 Is the microgrid 2 current.
In order to verify the effect of the invention, experimental verification is carried out on the effect of the power coordination control strategy of the direct current micro-grid interconnection converter.The experimental parameters were as follows: busbar voltage V of two direct-current micro-grid 1 ＝V 2 =400V, common energy storage rated voltage V b =24v, converter port 2' voltage V lk =48v, primary power inductance of 5 μh, secondary power inductance of 120 μh.
Table 1 shows experimental result power data of different modes of public energy storage operation, FIG. 4 is a waveform of system dynamic response experiment of modes 1-4, in mode 1, the residual power of micro-grid 1 is smaller than the insufficient power of micro-grid 2, in order to meet the load power requirement of micro-grid 2, public energy storage is discharged at 100W power, and series voltage V is injected between two DC micro-grids s To control the power transfer between two micro-grids, the output voltage V of the port 2 lk Always kept at a constant 48V, unaffected by the power transfer. In mode 2, the demanded power of the micro grid 2 is suddenly reduced by 200W, and as can be seen from the figure, the transmission power P t Positive, 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 V s And also decreases.
Table 1 experimental results power data in different modes
Mode 3 is the reverse of the case of mode 2, where microgrid 2 has excess power and microgrid 1 has insufficient power, but the excess net power of microgrid 2 is insufficient to meet the required net power of microgrid 1. The public energy storage provides 100W of power at the moment, thereby avoiding the load shedding of the micro-grid 1, improving the stability of the system and corresponding series voltage V s The polarity is also changed.
Fig. 5 shows the dynamic response experimental waveforms of modes 5 to 8, at this time, only a single direct current micro-grid has residual and insufficient power, the power requirement of another micro-grid is balanced, modes 5 and 6 are used for transmitting energy between the micro-grid 2 and the public energy storage, modes 7 and 8 are used for transmitting energy between the micro-grid 1 and the public energy storage, and the proposed control strategy is verified to have good dynamic response when the single micro-grid and the public energy storage are used for transmitting energy.
Fig. 6 shows the mode 9 and mode 10 dynamic response experimental waveforms when both the micro grid 1 and the micro grid 2 have residual or insufficient power, relying on the charge or discharge of the common stored energy to maintain the balance of power demands of the entire interconnected system. Similarly, in all modes of operation, P t And P b Tracking its reference power command P t * Andcorresponding series injection voltage V s By varying its magnitude and polarity to transmit the required power, the dc link voltage V lk Always kept constant at 48V.
Fig. 7 shows the experimental waveform of the battery reaching the upper charge limit voltage, it can be seen that the battery is initially charged at a current of 2A, the terminal voltage reaches the upper limit voltage when the battery is near full, the BVR controller starts to exit saturation, the d_bvr gradually decreases, the BVR controller wins in parallel competition when the d_bvr < d_bpr, and the constant voltage controller takes over control of port 3, and the battery stops charging.
Fig. 8 shows an experimental waveform when the battery reaches the maximum charge current, the maximum charge current of the battery is set to 4A, when the charge reference power of the battery becomes large, so that the charge current of the 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 charge current of the battery is maintained at the upper limit value so as to avoid overcharge of the battery.
The block diagram of the whole power coordination control method of the interconnected converter and the micro-grid is shown in fig. 9, and mainly comprises a topological structure of the interconnected converter of the direct-current micro-grid and a power coordination control strategy thereof. The direct-current micro-grid interconnection converter is formed by cascading an interleaved parallel three-port converter and a full-bridge DC-DC converter, the converter is provided with three ports, a port 1 is connected with a micro-grid 1 in parallel, a port 2 is connected with connecting wires of the two micro-grids in series, and a port 3 is connected with public energy storage. The port 2 is used for injecting dynamic adjustable voltage in series between the two direct current micro-grids 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 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 parallel competition control strategy to select the duty ratio control quantity, so that fixed power control and voltage/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 foregoing describes in detail a dc micro-grid interconnection converter and a power coordination control method thereof, and specific examples are applied to illustrate the principles and embodiments of the present invention, and the description of the foregoing examples is only for helping to understand the method and core idea of the present invention; meanwhile, as those skilled in the art will have variations in the specific embodiments and application scope in accordance with the ideas of the present invention, the present description should not be construed as limiting the present invention in view of the above.
Claims (10)
1. The direct-current micro-grid interconnection converter is characterized by being formed by cascading a staggered parallel full-bridge three-port converter and a full-bridge DC-DC converter; the interconnected converter is provided with three ports, the primary side input of the three-port converter is port 1, the secondary side integrated staggered parallel Buck-boost is port 3, and the output of the full-bridge DC-DC converter is port 2; the port 1 is connected with the micro-grid 1 in parallel, the port 2 is connected with the connecting wires of the two micro-grids in series, and the port 3 is connected with public energy storage; the port 2 is used for injecting dynamic adjustable voltage in series between the two direct current micro-grids to realize power transmission between the two direct current micro-grids.
2. The interconnected converter of claim 1, wherein the three ports of the dc micro-grid interconnected converter operate in a mode that:
(1) Port 1: the input of the primary side of the three-port converter forms a port 1, and is connected with a direct current bus of the micro-grid 1 in parallel, and the voltage of the 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 port 2';
(2) Port 2: the output port of the full-bridge DC-DC converter is connected in series with the connecting wires of the two DC micro-grids to form a port 2 of the interconnection 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: the port 3 of the interconnection converter is formed by a secondary side integrated bidirectional Buck-Boost topology circuit, and through the port 3, the public energy storage can exchange power with the port 1 of the interconnection converter; when the local energy storage of the two direct current micro-grids and the power transmission between the micro-grids are insufficient to process redundant power, the public energy storage can be charged through the interconnection converter, and when the two direct current micro-grids have insufficient power, the public energy storage discharges to support the bus voltage of the two direct current micro-grids.
3. The power coordination control method of the direct current micro grid interconnection converter according to claim 2, wherein the control method is characterized in that ports are relatively independent, the independent operation of the ports of the converter is allowed, so that the power flow control of the direct current micro grid interconnection system is realized, and the control method comprises three control loops, namely constant voltage output control of the three-port converter, serial voltage control of the port 2 and common energy storage port control of the port 3; the available net power generated by the local control strategy of the single direct-current micro-grid is used as a reference input for the power coordination control of the interconnection converter of the direct-current micro-grid.
4. A method according to claim 3, characterized in that the three-port converter in the interconnected converter employs primary side phase shifting angle control, secondary side duty cycle control, the primary side controlling the voltage of port 2' constant by shifting the phase angle Φ, and the secondary side controlling the switching tube S in the three-port converter by changing the switching tube S 5 ～S 8 Duty cycle D 1 To control the charge and discharge power of the common stored energy of the ports 3.
5. A method according to claim 3, characterized in that the constant voltage output control loop of the three-port converter employs a voltage-current double closed-loop control, the purpose of which is to keep the port 2' voltage constant, as the input voltage of the full-bridge DC-DC converter, to maintain the power required for the full-bridge DC-DC converter to operate normally; after the deviation of the reference value of the port 2' voltage compared with the actual value is sent to a PI controller, the reference value of the current control loop is generatedAfter that, the reference value ∈>After comparing with the actual value of the input current of the port 1, the deviation is sent into 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 full-bridge DC-DC converter.
6. A method according to claim 3, wherein the common energy storage of the interconnected converter ports 3 is used for input-output power control and voltage-limiting and current-limiting charge control; adopting parallel competition mechanism, introducing minimum selector, selecting minimum duty ratio D 1 Secondary side switching tube S as three-port converter 5 ～S 8 The minimum selector is composed of a power controller BPR, a voltage controller BVR, a current controller BCR and minimum contention logic.
7. The method of claim 6, wherein when the state of the common stored energy SoC does not exceed an upper limit and the current and voltage are below the set limit, the BVR and BCR controller outputs are saturated positively and the BVR duty cycle D _BVR And duty cycle D of BCR _BCR At maximum, the BPR controller controls port 3 according to a given power reference signal P 1 +P 2 To control the charge and discharge power of the public energy storage to absorb or supplementCompensating the power difference of the two direct current micro-grids; when the public energy storage is about to be fully charged, the BVR controller automatically exits the saturation state, at this time, D _BVR Duty cycle D to be smaller than BPR _BPR BVR control takes over control of port 3 and common stored energy stops charging; when the charging current of the public energy storage reaches the upper limit value, the BCR controller exits from a saturated state, the public energy storage enters into a constant-current charging mode, and damage of the public energy storage caused by over-current charging is avoided, P 1 To the net power available to the microgrid 1, P 2 Which is the net power available to the microgrid 2.
8. The method of claim 7, wherein the BPR controller uses the net power P available to both dc micro-grids 1 And P 2 Summing to obtain its power control reference signalAccording to the power reference signal->Charging and discharging control is carried out on public energy storage; when P 1 +P 2 >When 0, the micro-grid has redundant power, and public energy storage is charged; when P 1 +P 2 <And 0, the micro-grid has insufficient power, and public energy storage discharges.
9. The method of claim 8, wherein the current reference signal is generated using equation (1)And the actual current I B The compared deviation is sent into a PI controller to generate a secondary side duty ratio D 1 And is further used for producing a switching tube S 5 -S 8 Is set to be a conduction pulse of (a);
wherein V is B Is the actual voltage;
the net power P available from the micro grid 1 1 Adding the power absorbed or compensated by the public energy storage system to obtain the reference power of the transmission power between the two direct current micro-gridsAnd the actual power P t After comparison, the deviation signal is transmitted to the PI controller G p Is a voltage controller G vc Providing a reference; voltage reference->Generated by formula (2):
reference power according to power flow requirementsCan have both positive and negative polarities, if +.>Is positive, indicating that the direction of power flow is from micro-grid 1 to micro-grid 2,/->The polarity of (2) is also positive; if->Negative, then there is a power flow from the micro-grid 2 to the micro-grid 1, +.>The polarity of (2) is negative.
10. According to claimThe method of 9, wherein the full-bridge DC-DC converter is configured to generate positive and negative adjustable voltages to achieve a desired series voltage adjustment, and the full-bridge DC-DC converter is composed of a power controller and a voltage controller, wherein the purpose of the controllers is to adjust the output voltage of the port 2 of the interconnection converter to have a desired amplitude and polarity, a droop control strategy is added into the full-bridge DC-DC control loop, and after droop control is added, a virtual resistor R is serially connected to an equivalent resistor of a transmission line, so that the control accuracy is improved without increasing energy loss; the actual output voltage V of port 2 is then applied s And (3) withComparing, inputting the compared deviation into a voltage type PI controller, and outputting a control signal V c To generate a switching tube S in a full-bridge DC-DC converter 9 -S 12 To control the voltage transmission between two DC micro-grids, I 2 Is the microgrid 2 current.
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| CN109274271A (en) * | 2018-10-16 | 2019-01-25 | 哈尔滨工业大学 | Three Port Translation device of twin-stage isolated DC and its hybrid energy-storing control method |
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