WO2019075879A1 - Running mode conversion method for alternating-current/direct-current hybrid microgrid - Google Patents
Running mode conversion method for alternating-current/direct-current hybrid microgrid Download PDFInfo
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- WO2019075879A1 WO2019075879A1 PCT/CN2017/115203 CN2017115203W WO2019075879A1 WO 2019075879 A1 WO2019075879 A1 WO 2019075879A1 CN 2017115203 W CN2017115203 W CN 2017115203W WO 2019075879 A1 WO2019075879 A1 WO 2019075879A1
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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
- H02J4/00—Circuit arrangements for mains or distribution networks not specified as ac or dc
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- the invention belongs to the field of power system micro-grid, and relates to an AC-DC hybrid micro-grid operation mode conversion method.
- the Micro Grid With the increasing energy crisis, the Micro Grid (MG) has developed rapidly. Since the microgrid contains multiple types of distributed power generators (DGs), energy storage devices, and coordination controllers in different states, the power source, energy management, and power quality requirements of the MG are different from those of the large power grid.
- grid energy management system has functions different from the power grid, it needs to develop according to MG and MG constituent unit of the operating characteristics of a reasonable run strategy to ensure economic and reliable operation of microgrids]. Therefore, it is of great significance to study the operation mode and conversion mode of the microgrid.
- the Chinese Journal of Electrical Engineering establishes a general model for the microgrid for cogeneration of cold and heat, considering the electricity A series of constraints and flue gas and steam constraints optimize system operation.
- Power System Automation proposes an energy management strategy for hybrid energy storage devices, respectively for supercapacitors with high power density and The battery with high energy density is controlled, and the pre-control strategy of the terminal voltage of SC is introduced.
- the simulation platform is used to simulate and verify the above control method strategy.
- the power automation equipment has established an optimization model that takes into account the diesel generator set and the demand side load, and accurately estimates the operation and maintenance cost of the energy storage device in the microgrid by the rain flow counting method, according to the short-term load forecasting and Ultra-short-term load forecasting technology to develop and adjust the energy management strategies of the day and day, so that the units in the micro-grid are in optimal operation.
- the object of the present invention is to provide an AC/DC hybrid microgrid operation mode conversion method in order to solve the above problems.
- the AC/DC hybrid microgrid comprises an AC microgrid and a DC microgrid, wherein the AC microgrid and the DC microgrid are connected by an AC/DC interconnect converter PCS,
- the AC microgrid includes an AC bus, a PV array PV, an energy storage device, and an AC side load, wherein the PV array, the energy storage device, and the load are connected to the AC bus; the AC microgrid is switched to the grid through the PCC. Mode or off-grid mode of operation;
- the AC-DC interconnect converter PCS When the PCC is closed, the AC-DC interconnect converter PCS operates in a constant voltage control mode, and the AC-side grid-connected operation mode includes a first AC operation mode.
- the AC/DC interconnect converter PCS When the PCC is disconnected, the AC/DC interconnect converter PCS is switched to the PQ control mode, and the AC side off-network operation mode includes a second AC operation mode, a second two AC operation mode, and a second three AC operation mode;
- the first alternating current operation mode is that all the photovoltaic arrays PV are operated in the MPPT mode, the energy storage device is standby or charged and discharged, and the AC side load is all put into use;
- the second alternating current operation mode is that the energy storage device operates in the V/f mode, and all the photovoltaic array PVs are operated in the MPPT mode, and the AC side loads are all put into use;
- the second two alternating current operation mode is that the energy storage device operates in the V/f mode, and part of the photovoltaic array PV is cut off, and the remaining photovoltaic array PVs are operated in the MPPT mode, maintaining the frequency and voltage of the alternating microgrid, and the AC side loads are all put into use;
- the second three AC operation mode is that the energy storage device first outputs the maximum power, and the AC/DC interconnection converter PCS increases the power input to the AC microgrid or cuts off part of the AC side load until the energy storage device recovers V. /f control mode, all PV array PVs are operated in MPPT mode;
- the AC microgrid When the PCC is closed, the AC microgrid operates in a first AC mode of operation
- the AC microgrid When the PCC is disconnected, the AC microgrid is switched from the first alternating current operating mode to the second alternating current operating mode;
- the AC microgrid switches from the second alternating current operating mode to the second alternating current operating mode
- the AC microgrid switches from the second AC mode to the second AC mode;
- P PV is the power output of the PV array PV
- P PCS is the power of the AC/DC interconnect converter PCS flowing into the AC side of the microgrid
- P bch-max is the maximum charging power of the energy storage device
- P bdi-max is the storage The maximum discharge power can be installed
- P load is the power consumed by the AC side load
- the DC microgrid includes a DC bus, a second PV array PV, a second energy storage device, and a DC side load, and the second PV array PV, the second energy storage device, and the DC side load are connected to the DC bus;
- the operating mode of the DC microgrid includes a first DC operating mode
- the operating mode of the DC microgrid includes a second direct current operation mode, a second two-DC operation mode, and a second three-DC operation mode;
- the first DC operating mode is to maintain the DC bus voltage at the first voltage by using the AC/DC interconnect converter PCS, all the second PV array PVs are operated in the MPPT mode, and the second energy storage device performs charging and discharging control, the DC side The load is fully put into use;
- the second direct current operation mode is to maintain the DC bus voltage at the second voltage by using the second energy storage device, all the second photovoltaic array PVs are operated in the MPPT mode, and the AC/DC interconnection converter PCS performs charging and discharging control, and the DC The side loads are all put into use;
- the second two-DC operation mode is that the second energy storage device operates in a maximum power charging or full charge standby state, and a part of the second photovoltaic array PV is cut off, and the remaining second photovoltaic array PVs are operated in the MPPT mode, so that the second energy storage device Operate in constant voltage control mode to maintain DC bus voltage, DC side load is fully put into use;
- the second three-DC operation mode is to cut off part of the DC side load so that the discharge power of the second energy storage device is less than The maximum discharge power until the second energy storage device operates in the constant voltage mode, and all the second photovoltaic array PVs operate in the MPPT mode;
- P PV2 is the output power of the DC side photovoltaic power of the micro grid
- P PCS2 is the power of the DC bus input to the AC/DC interconnect converter PCS
- P bch-max2 is the maximum charging power allowed by the second energy storage device
- P load2 For the power of the DC side load
- P bdi-max2 is the maximum discharge power of the second energy storage device.
- the energy storage device comprises a battery and a super capacitor.
- the energy storage device on the AC side also includes a super capacitor, which can fully utilize the characteristics of fast charging and discharging of the super capacitor.
- the first voltage is 400V.
- the second voltage is 400V.
- the second energy storage device performs constant power charging and discharging control.
- the AC/DC hybrid microgrid operating module conversion method of the present invention adopts an AC/DC hybrid microgrid with high flexibility and strong regenerative energy absorption capability, and proposes that the microgrid AC side and the microgrid DC side are different.
- the operation mode and the conversion conditions and the conversion mode in the state can realize seamless switching between the operation modes, and provide technical support for the safe and stable operation of the AC-DC hybrid microgrid.
- FIG. 1 is a schematic structural view of an AC-DC microgrid
- Figure 3 is a control mode of the second alternating current operation mode
- Figure 4 is a control mode of the second two alternating current operation modes
- Figure 5 is a control mode of the second three alternating current operation modes
- FIG. 6 is a schematic diagram of conversion of an AC side AC side operation mode
- Figure 7 is a control mode of the first DC operating mode
- Figure 8 is a control mode of the second continuous flow operation mode
- Figure 9 is a control mode of the second two-DC operation mode
- Figure 10 is a control mode of the second three-DC operation mode
- FIG. 11 is a schematic diagram of conversion of a DC side operating mode of a microgrid
- Figure 12 is the relationship between the PCC and the operating state of the interconnected PCS
- Figure 13 is a first DC operating mode simulation voltage curve
- Figure 14 is a second constant current operation mode simulation voltage curve
- Figure 15 is a voltage curve of the DC bus of the grid-connected off-grid
- Figure 16 is an unplanned off-grid AC bus voltage on the AC side of the microgrid
- Figure 17 shows the frequency of the unplanned off-grid AC bus on the AC side of the microgrid
- Figure 18 is a hierarchical control structure of a microgrid
- Figure 19 shows the basic control timing of the seamless switching operation mode of the microgrid
- Figure 20 is a schematic diagram of the main power mode switching.
- the AC side and the DC side of the AC/DC hybrid microgrid of the present invention both include a PV array PV, an energy storage device, and a load, wherein the AC side energy storage device includes a battery and a super capacitor, and the AC bus passes through
- the common connection point is connected to the distribution network, and the DC side and the AC side are connected by an AC/DC converter that enables bidirectional flow of energy.
- Priority is given to some DC-type DGs and loads connected to the DC bus.
- a part of the PV array is also incorporated on the AC bus, and part of the AC load is directly Connect to the AC bus.
- the microgrid constructed by the invention has high flexibility and strong regenerative energy absorption capacity.
- the power output of the PV array is:
- f PV is the power derating factor of the photovoltaic system, which represents the ratio of the actual output power of the photovoltaic system to the output power under the rated conditions, which is used to account for the surface contamination of the photovoltaic panel, the covering of rain and snow, and the aging of the photovoltaic panel itself.
- the battery model adopts the Kinetic Battery Model (KiBaM) model, and assumes that the battery port voltage is constant, and the charge and discharge current of the battery in each time step is constant, regardless of the influence of environmental conditions.
- KiBaM Kinetic Battery Model
- the total energy stored by the battery pack at any time is equal to the sum of available energy and binding energy, ie:
- W 1 is available energy
- W 2 is bound energy
- the available energy of the battery pack after charging and discharging can be calculated:
- W 1,0 is the available energy of the battery pack at the initial time (kW ⁇ h); W 1,end is the available energy of the battery pack at the end time (kW ⁇ h); W 0 is the total energy of the battery pack at the initial time (kW ⁇ h); P is the battery pack discharge (positive) or charge (negative) power (kW), does not include charge and discharge loss; ⁇ t is the time interval (in the algorithm, ie time step, h); c is the battery capacity The ratio represents the ratio of available energy to total energy in the fully charged state of the battery; k is the battery rate constant (h -1 ), indicating the conversion rate of available energy and bound energy.
- W 2,end is the binding energy (kW ⁇ h) of the battery pack at the end time.
- the available energy W 1 at any time satisfies the relationship: 0 ⁇ W 1 ⁇ cW max , where W max represents the maximum storable energy (kW ⁇ h) of the battery.
- W max represents the maximum storable energy (kW ⁇ h) of the battery.
- the maximum charging current and speed constraint of the battery should also be taken into account in the maximum charging power constraint, and the corresponding maximum charging power (kW) is obtained as follows:
- N bat is the total number of battery strings connected in parallel;
- I max is the maximum charging current of the battery (A);
- U N is the rated voltage (V) of the battery;
- ⁇ c is the maximum charging rate of the battery (A / (Ah)).
- the final battery charging and discharging power is limited to:
- ⁇ bat,c is the battery charging efficiency
- ⁇ bat,d is the battery discharge efficiency
- the model can use the following expression:
- P con AC represents the AC side power (kW) of the converter, positive in the inverter, negative in the rectification, the same below;
- P con DC represents the sum of the DC side power of the converter (kW).
- ⁇ inv and ⁇ rec represent the efficiency of converter inversion and rectification;
- R inv and R rec represent the maximum active power (kW) of the converter inverter and rectification, which is numerically equal to its rated capacity.
- a bidirectional converter model can represent either a bidirectional converter model or a unidirectional rectifier or inverter.
- a unidirectional inverter model can be expressed as follows:
- the load in the microgrid is roughly divided into two categories: important load and participation in the demand side management load.
- the important load needs to ensure uninterrupted power supply;
- the participating demand side management load is divided into three categories: interruptible load, translatable load and elastic load (also known as controllable load).
- the invention regards the participation demand side management load as all interruptible load, the interruptible load as the non-important load, and the micro grid dispatcher has the interruption right of such load.
- the AC side of the microgrid switches its grid-connected or off-grid operation mode through the PCC.
- the present invention divides the grid connection of the micro-grid on the AC side into two main modes.
- the first AC operation mode the PV array operates in the MPPT mode, and the energy storage standby or charging and discharging with a certain strategy, as shown in FIG. 2 .
- the second AC operation mode the difference between the output power of the photovoltaic power P PV and the power P PCS of the interconnection PCS flowing into the micro-grid AC side and the power consumption of the load P load is the maximum charging power P bch-max and maximum of the energy storage.
- the energy storage is operated in the V/f mode, and the photovoltaic array operates in the MPPT mode, as shown in FIG. 3 .
- the second two-AC operation mode the sum of the output power P PV of the photovoltaic and the power P PCS of the interconnection PCS flowing into the AC side of the micro-grid is greater than the power of the load P load and the maximum charging power of the energy storage at this time (P bch-max or 0)
- P bch-max or 0 the maximum charging power of the energy storage at this time
- some PV arrays are cut off, other PVs are still running in MPPT mode, and the energy storage is operated in V/f control mode to maintain the frequency and voltage of the AC side of the microgrid.
- the specific control method is shown in Figure 4.
- the DC side is divided into two main modes according to the control mode of the interconnected PCS.
- the first DC operating mode using the interconnected PCS to maintain the DC bus voltage at 400V, the PV array operates in MPPT mode, and the stored energy is charged and discharged according to a given command, as shown in Figure 7.
- the second all-current operation mode using the energy storage to maintain the DC bus voltage at 400V, the PV array operates in the MPPT mode, and the interconnected PCS performs charging and discharging control according to a given command, and the control mode is as shown in FIG.
- the second two-DC operation mode if the output power P PV2 of the DC side of the micro-grid and the power-P PCS2 of the interconnected PCS input DC bus are greater than the maximum charging power allowed by the energy storage at this time (P bch-max2 or 0) ) and the load power P load2 , the voltage will rise, the mode is changed from the second direct current operation mode to the second two-DC operation mode, and the energy storage operation is in the maximum power charging or full charge standby state, and the cutting is performed.
- the control mode is shown in Figure 9; as the load increases or the PV output decreases, when the PV output is less than the load, the gradual input is removed. The photovoltaics are restored to the second continuous flow mode of operation.
- the second three-DC operation mode if the output power P PV2 of the photovoltaic side on the DC side of the micro-grid, the maximum discharge power P bdi-max2 at the time of energy storage and the power-P PCS2 of the interconnected PCS flowing into the DC bus are less than the power of the load P Load2 , at this time the voltage will drop, from the second direct current operation mode to the second three-current operation mode, in order to make the energy storage still operate in the constant pressure mode, the load is cut off according to the load level so that the discharge power of the stored energy is less than its maximum Discharge power. When the stored energy is switched from the discharge to the charged state, the load is gradually input until the second continuous flow operation mode is restored.
- the PCC has two operating modes, closed and disconnected, which can be switched to each other; the interconnected PCS has three operating modes of constant voltage control, standby and PQ control, and the three switches between each other.
- the PCC and the operating mode of the interconnected PCS There is a certain relationship between the PCC and the operating mode of the interconnected PCS.
- the interconnected PCS can run in any mode, but mainly operates in the constant voltage mode; when the PCC is disconnected, the interconnected PCS can only run in the PQ control and standby. Mode, not in constant voltage control mode, and mainly in PQ control mode.
- the invention performs simulation verification by taking the micro grid as the example of the grid connection state.
- microgrid operation mode is divided according to the grid connection or not, it is only necessary to simulate the parallel/off-grid handover of the microgrid. The simulation first needs to start the microgrid.
- the first DC operating mode the DC bus is charged by the interconnected PCS, the voltage is maintained at 400V, and then the PV array and the load operating in the MPPT mode are respectively connected, and the DC side energy storage is charged and discharged according to the given command.
- the process is simulated by the model built in Simulink.
- the curve of the DC bus during the simulation is shown in Fig. 13.
- the DC bus When the interconnected PCS is started at 0.05s, the DC bus is charged. During the charging process, the maximum voltage reaches 475V, and the voltage tends to be stable after 0.2s. In the 0.45s, 0.7s and 0.8s respectively, the 19.4kW, 6.2kW and 5.58kW PV arrays are connected, and the voltage fluctuations are all within 5%; in the 0.9s, 1.1s and 1.2s, respectively, 20kW, 5.1kW and 4.9kW are incorporated. Load, voltage fluctuations are also within 5%.
- interconnecting the PCS to charge the DC bus is a soft-start process that does not create a large overvoltage on the DC side.
- the photovoltaic inverter also has a starting process, and the power gradually becomes larger and there is no impact. This simulation is to simulate the overvoltage level of the microgrid under the most extreme conditions.
- the second direct current operation mode (self-starting): the DC side is mainly energy storage, the energy storage charges the DC bus, and then the constant voltage control is performed, and the PV array and the load operating in the MPPT mode are respectively accessed in a certain order.
- the interconnected PCS performs charge and discharge control according to the given command.
- the simulated voltage waveform is shown in Figure 14.
- the DC bus is charged by the energy storage device, and then merged into 5kW load and 5kW PV at 0.4s and 0.8s respectively.
- the DC side has a small energy storage capacity, it can still be maintained under such large power fluctuations.
- the DC bus voltage fluctuates within 10%.
- the AC side of the microgrid can also be self-started and activated by an external circuit, which is not studied by the present invention.
- Planned off-network means that the system obtains state switching instructions in advance, and systematically adjusts the relationship between distributed generation and output of each energy storage unit and controllable load, while ensuring power supply to important loads in the system.
- Unplanned off-network is the control process when the grid fails or is disconnected.
- the interconnected PCS operates in the constant voltage control mode.
- the process of connecting the DC side of the microgrid to the grid is complicated, and the voltage stability is The influence is relatively large, which is the main research object of the DC side of the micro-grid connected to the network.
- the main switching process of the grid-connected network is as follows: the protection device detects the voltage amplitude and frequency anomaly of the AC side of the micro-grid, sends a disconnection command to the grid-connected switch, and sends a mode switching command to the interconnected PCS by the switch position feedback signal, interconnecting the PCS.
- the DC side energy storage interface of the microgrid communicates with the dry contact signal.
- the operation mode is switched from the constant voltage control mode to the standby or constant power control mode, and the energy storage DC converter is switched from the charging and discharging modes to
- the constant voltage mode controls the DC bus voltage
- the grid switch controls the disconnection. The three cooperate to complete the seamless switching of the system from the grid to the off-grid.
- Figure 15 shows the variation of the DC bus voltage when simulating the process of grid-connected off-grid in Simulink.
- the interconnected PCS is disconnected due to AC side fault or other reasons.
- the coordinating controller detects that the PCS is disconnected and sends a switching operation mode command to the energy storage converter.
- the energy storage converter is charged by constant power.
- the discharge control mode is switched to the constant voltage mode to maintain the DC bus voltage. In this process, due to the power imbalance, the voltage rises briefly to 404V, and the regulation effect of the energy storage rapidly decreases.
- the DC-connected DC-connected network process has the same effect on the DC side of the micro-grid as the DC-side input load, and will not be discussed here.
- the coordination controller sends instructions to the interconnected PCS.
- the interconnected PCS After the interconnected PCS receives the signal, it communicates with the DC side energy storage converter using dry contacts, and the grid converter operates. Switching from the standby or constant power control mode to the constant voltage control mode, after the DC side energy storage converter receives the interlock signal, it switches from the voltage regulation mode to the constant power charge/discharge or standby mode, and the three cooperate to complete the system off-grid. Seamless switching of the web.
- the switching of the AC side of the micro-grid from the grid-connected to the off-grid state can also be divided into two types: planned off-network and unplanned off-network.
- the PCC communicates with the AC side energy storage and the interconnected PCS signals, the energy storage is converted from the constant power control mode to the V/F control mode, and the interconnected PCS is converted by the constant voltage mode. It is a constant power control or standby mode, and its power is locked to the power of the interconnected PCS at the moment of switching. If the stored energy is discharged at the maximum discharge power or the maximum charging power is still unable to maintain the voltage and frequency of the AC side of the microgrid, the power of the interconnected PCS can be adjusted to an appropriate value to achieve the purpose of maintaining the stability of the AC side of the microgrid.
- the voltage of the AC busbar during unplanned off-grid is shown in Figure 16, and the frequency is shown in Figure 17.
- the coordination controller issues a synchronous closing command to the PCC, and the PCC performs the synchronous closing.
- the energy storage is converted from the V/f control to the PQ control, and the micro-grid AC side completes the off-grid-to-network connection process.
- the invention also discloses a microgrid control structure, and the three-layer control structure adopted by the microgrid is as shown in FIG. 18.
- the DG or energy storage device can often operate in a variety of control modes depending on the condition of the microgrid, including maximum power point tracking (MPPT) control, constant voltage control, constant voltage/constant frequency (V/f) control, and the like.
- MPPT maximum power point tracking
- V/f constant voltage/constant frequency
- the distribution network ensures that the voltage and frequency of the AC side of the microgrid are stable, and the DG is often output with maximum power; the DC side of the microgrid adopts the master-slave control mode, and the AC side or energy storage of the microgrid is used as the main power source to maintain DC bus voltage.
- a certain DG in the AC side of the microgrid ensures voltage and frequency stability.
- the energy storage device adopts V/f control to ensure that the voltage and frequency are at specified values, and other DGs use constant power control (PQ control) and output at maximum power; the energy storage device on the DC side of the microgrid adopts constant voltage control as the main power source.
- Other distributed DGs are output at maximum power.
- the energy storage device needs to be able to compensate for the power difference caused by the load change. Therefore, the energy storage must be able to accurately control the output within its allowable charge and discharge power range, and quickly compensate the power difference.
- the second layer is the coordinated control layer, which functions to reduce the negative impact of the distribution network due to DG output and load changes when the microgrid is in the grid-connected state.
- the microgrid can be integrated into the distribution as a stable and controllable load. Network, through the micro-grid coordination controller to coordinate control of each unit to achieve tie line power control; when the micro-grid is in the off-grid state, through the master-slave control to ensure that the voltage and frequency are within the specified range, the main power supply compensates for the DG output or The difference in power generated by load changes.
- This layer control can also implement the switching function between the MG modes. In order to reduce the impact of this function on the operating parameters of the microgrid, it is necessary to have functions such as MG fault detection and synchronous detection, and coordinate switching between control modes.
- the master-slave control mode is adopted.
- the control timing is shown in Figure 19.
- the main control mode of each DG in the MG is switched. When the control mode of the main power source is switched, the output power fluctuation should be as small as possible.
- Figure 20 shows the control structure used in this paper.
- the PQ control and V/f control of the main power supply use the same current inner loop. When the switching control method is used, only the voltage outer loop is switched. In this process, in order to minimize the impact generated when the control mode is switched, the control logic and algorithm need to be applied reasonably.
- This layer mainly realizes the energy management function of the microgrid, and optimizes the operation of the microgrid through corresponding optimization algorithms:
- the microgrid When the microgrid is in the off-grid state, adjusting the information of each distributed DG output power reference value, the microgrid can be in the most economical operation state.
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Abstract
A running mode conversion method for an alternating-current/direct-current hybrid microgrid. The used alternating-current/direct-current hybrid microgrid has high flexibility and has high renewable energy absorption ability, running modes, conversion conditions and conversion modes of a microgrid alternating-current side and a microgrid direct-current side in different states are provided with regard to a switching mode of the alternating-current/direct-current hybrid microgrid in different running states, seamless switching among running modes can be achieved, and a technical support is provided for safe and stable running of the alternating-current/direct-current hybrid microgrid.
Description
本发明属于电力系统微电网领域,涉及一种交直流混合微电网运行模式转换方法。The invention belongs to the field of power system micro-grid, and relates to an AC-DC hybrid micro-grid operation mode conversion method.
随着能源危机的日益严重,微电网(Micro Grid,MG)得以迅速发展。由于微电网内部含有多种类别并处在不同状态的分布式电源(Distributed Generator,DG)、储能装置以及协调控制器,MG的电能来源,能量管理以及电能质量要求都与大电网不同,微电网的能量管理装置所具有的功能也不同于大电网,其需根据MG的组成单元以及MG的运行特点来制定出合理的运行策略,保证微电网的经济可靠运行]。因此,研究微电网的运行模式以及转换方式具有重要的意义。With the increasing energy crisis, the Micro Grid (MG) has developed rapidly. Since the microgrid contains multiple types of distributed power generators (DGs), energy storage devices, and coordination controllers in different states, the power source, energy management, and power quality requirements of the MG are different from those of the large power grid. grid energy management system has functions different from the power grid, it needs to develop according to MG and MG constituent unit of the operating characteristics of a reasonable run strategy to ensure economic and reliable operation of microgrids]. Therefore, it is of great significance to study the operation mode and conversion mode of the microgrid.
今年来,微电网能量管理系统成为研究热点之一,也有诸多研究成果。文献:王成山,武震,李鹏.微电网关键技术研究[J].电工技术学报,2014,29(2):1-12.,研究岛屿上离网MG系统的经济优化问题,结合储能装置的约束条件,建立综合考虑了各种运行维护和环境成本的优化模型。文献:田泼.交直流混合微电网建模与变流器控制技术研究[D].济南:山东大学,2014.中的EMS有维持微电网内部电压频率稳定和优化微电网内各DG的输出两种功能。文献王成山,洪博文,郭力,等.冷热电联供微电网优化调度通用建模方法[J].中国电机工程学报中针对冷热电联供的微电网建立通用模型,考虑电的一系列约束条件和烟气以及蒸汽的约束条件,优化系统运行。文献王成山,洪博文,郭力.不同场景下的光蓄微电网调度策略[J].电网技术研究微电网在不同状态下的模型与各种约束条件,设计了两种微电网优化运行策略,一种是计及储能装置在运行过程中的折旧费用来优化计算,另一种是不计及储能装置在运行过程中的折旧费用来优化计算,得到两种不同的优化运行方法。文献洪博文,郭力,王成山,等.微电网多目标动态优化调度模型与方法[J].电力自动化设备建立了计及环境目标与经济目标两种目标的优化调度模型,综合考虑环境成本与微电网运行成本,采用遗传算法对其进行计算,得到其优化调度方案。文献张野,郭力,贾宏杰,等.基于平滑控制的混合储能系统能量管理方法[J].电力系统自动化提出了针对混合储能装置的能量管理策略,分别对功率密度高的超级电容与能量密度大的蓄电池进行控制,介绍SC的端电压预先控制策略,并采用仿真平台对以上控制方法策略进行仿真验证。文献郝雨辰,窦晓波,吴在军,等.微电网分层分布式能量优
化管理[J].电力自动化设备建立了计及柴油发电机组和需求侧负荷的优化模型,并通过雨流计数法来精确得出微电网中储能装置的运维成本,根据短期负荷预测与超短期负荷预测技术来制定并调整日前与日内能量管理策略,使微电网中各单元处于最优运行状态。This year, the microgrid energy management system has become one of the research hotspots, and there are many research results. LIANG Chengshan,WU Zhen,LI Peng.Study on key technologies of microgrid[J].Transactions of China Electrotechnical Society, 2014,29(2):1-12. To study the economic optimization problem of off-grid MG system on island, combined with energy storage The constraints of the device establish an optimization model that takes into account various operational and environmental costs. Literature: Tian Po. Research on AC/DC hybrid microgrid modeling and converter control technology [D]. Jinan: Shandong University, 2014. EMS maintains the stability of the internal voltage and frequency of the microgrid and optimizes the output of each DG in the microgrid. Two features. Literature Wang Chengshan, Hong Bowen, Guo Li, et al.General Modeling Method for Micro-grid Optimization Scheduling of Cooling, Heating and Power Supply[J].The Chinese Journal of Electrical Engineering establishes a general model for the microgrid for cogeneration of cold and heat, considering the electricity A series of constraints and flue gas and steam constraints optimize system operation. Literature Wang Chengshan, Hong Bowen, Guo Li. Scheduling strategy of optical storage microgrid in different scenarios[J].Power grid technology research Microgrid model and various constraints in different states, design two microgrid optimization operation strategies One is to calculate the depreciation expense of the energy storage device during operation to optimize the calculation, and the other is to optimize the calculation without considering the depreciation expense of the energy storage device during operation, and obtain two different optimized operation methods. LI Hongwen, GUO Li, WANG Chengshan, et al. Multi-objective dynamic optimization scheduling model and method for microgrid[J]. Power automation equipment has established an optimal scheduling model that takes into account both environmental and economic objectives, taking into account environmental costs. Compared with the operating cost of the microgrid, the genetic algorithm is used to calculate and obtain the optimal scheduling scheme. Literature Zhang Ye, Guo Li, Jia Hongjie, et al. Energy management method for hybrid energy storage system based on smoothing control[J]. Power System Automation proposes an energy management strategy for hybrid energy storage devices, respectively for supercapacitors with high power density and The battery with high energy density is controlled, and the pre-control strategy of the terminal voltage of SC is introduced. The simulation platform is used to simulate and verify the above control method strategy. Literature Hao Yuchen, Dou Xiaobo, Wu Zaijun, et al. Microgrid hierarchical distributed energy optimization
Management [J]. The power automation equipment has established an optimization model that takes into account the diesel generator set and the demand side load, and accurately estimates the operation and maintenance cost of the energy storage device in the microgrid by the rain flow counting method, according to the short-term load forecasting and Ultra-short-term load forecasting technology to develop and adjust the energy management strategies of the day and day, so that the units in the micro-grid are in optimal operation.
针对已有研究对象均为交流微电网或直流微电网,对交直流混合微电网这类新型微电网的运行模式的研究较少。For the existing research objects are AC microgrid or DC microgrid, there are few studies on the operation mode of the new microgrid such as AC/DC hybrid microgrid.
因此,需要一种交直流混合微电网运行模式转换方法。Therefore, there is a need for an AC/DC hybrid microgrid operating mode conversion method.
发明内容Summary of the invention
本发明的目的就在于为了解决上述问题,提供一种交直流混合微电网运行模式转换方法。The object of the present invention is to provide an AC/DC hybrid microgrid operation mode conversion method in order to solve the above problems.
本发明通过以下技术方案来实现上述目的:The present invention achieves the above objects by the following technical solutions:
一种交直流混合微电网运行模块转换方法,所述交直流混合微电网包括交流微电网和直流微电网,所述交流微电网和直流微电网通过交直流互联换流器PCS连接,An AC/DC hybrid microgrid operation module conversion method, the AC/DC hybrid microgrid comprises an AC microgrid and a DC microgrid, wherein the AC microgrid and the DC microgrid are connected by an AC/DC interconnect converter PCS,
所述交流微电网包括交流母线、光伏阵列PV、储能装置和交流侧负荷,所述光伏阵列、储能装置和负荷均连接所述交流母线;所述交流微电网通过PCC切换其并网运行模式或离网运行模式;The AC microgrid includes an AC bus, a PV array PV, an energy storage device, and an AC side load, wherein the PV array, the energy storage device, and the load are connected to the AC bus; the AC microgrid is switched to the grid through the PCC. Mode or off-grid mode of operation;
当PCC闭合时,交直流互联换流器PCS运行于恒压控制模式,所述交流侧并网运行模式包括第一交流运行模式,When the PCC is closed, the AC-DC interconnect converter PCS operates in a constant voltage control mode, and the AC-side grid-connected operation mode includes a first AC operation mode.
当PCC断开时,交直流互联换流器PCS切换至PQ控制模式,所述交流侧离网运行模式包括第二一交流运行模式、第二二交流运行模式和第二三交流运行模式;When the PCC is disconnected, the AC/DC interconnect converter PCS is switched to the PQ control mode, and the AC side off-network operation mode includes a second AC operation mode, a second two AC operation mode, and a second three AC operation mode;
所述第一交流运行模式为全部光伏阵列PV均以MPPT模式运行,储能装置待机或充放电,交流侧负荷全部投入使用;The first alternating current operation mode is that all the photovoltaic arrays PV are operated in the MPPT mode, the energy storage device is standby or charged and discharged, and the AC side load is all put into use;
所述第二一交流运行模式为储能装置以V/f模式运行,全部光伏阵列PV均以MPPT模式运行,交流侧负荷全部投入使用;The second alternating current operation mode is that the energy storage device operates in the V/f mode, and all the photovoltaic array PVs are operated in the MPPT mode, and the AC side loads are all put into use;
所述第二二交流运行模式为储能装置以V/f模式运行,切除部分光伏阵列PV,其余光伏阵列PV以MPPT模式运行,维持交流微电网的频率和电压,交流侧负荷全部投入使用;The second two alternating current operation mode is that the energy storage device operates in the V/f mode, and part of the photovoltaic array PV is cut off, and the remaining photovoltaic array PVs are operated in the MPPT mode, maintaining the frequency and voltage of the alternating microgrid, and the AC side loads are all put into use;
所述第二三交流运行模式为储能装置先以最大功率输出,所述交直流互联换流器PCS增加向交流微电网输入的电能或切除部分所述交流侧负荷,直至储能装置恢复V/f控制模式,全部光伏阵列PV均以MPPT模式运行;
The second three AC operation mode is that the energy storage device first outputs the maximum power, and the AC/DC interconnection converter PCS increases the power input to the AC microgrid or cuts off part of the AC side load until the energy storage device recovers V. /f control mode, all PV array PVs are operated in MPPT mode;
当PCC闭合时,所述交流微电网以第一交流运行模式运行;When the PCC is closed, the AC microgrid operates in a first AC mode of operation;
当PCC断开时,所述交流微电网从第一交流运行模式切换至第二一交流运行模式;When the PCC is disconnected, the AC microgrid is switched from the first alternating current operating mode to the second alternating current operating mode;
当PPV+PPCS-Pbch-max>=Pload时,所述交流微电网从第二一交流运行模式切换至第二二交流运行模式;When P PV +P PCS -P bch-max >=P load , the AC microgrid switches from the second AC operating mode to the second AC operating mode;
当PPV+PPCS-Pbch-max<Pload时,所述交流微电网从第二二交流运行模式切换至第二一交流运行模式;When the P PV +P PCS -P bch-max <P load , the AC microgrid switches from the second alternating current operating mode to the second alternating current operating mode;
当PPV+PPCS+Pbdi-max<Pload时,所述交流微电网从第二一交流运行模式切换至第二三交流运行模式;When the P PV +P PCS +P bdi-max <P load , the AC microgrid switches from the second AC mode to the second AC mode;
当PPV+PPCS+Pbdi-max>Pload时,所述交流微电网从第二三交流运行模式切换至第二一交流运行模式;When P PV +P PCS +P bdi-max >P load , the AC microgrid switches from the second three AC operation mode to the second AC operation mode;
式中,PPV为光伏阵列PV输出的功率,PPCS为交直流互联换流器PCS流入微电网交流侧的功率,Pbch-max为储能装置的最大充电功率,Pbdi-max为储能装置最大的放电功率,Pload为交流侧负荷消耗的功率;Where, P PV is the power output of the PV array PV, P PCS is the power of the AC/DC interconnect converter PCS flowing into the AC side of the microgrid, P bch-max is the maximum charging power of the energy storage device, and P bdi-max is the storage The maximum discharge power can be installed, and P load is the power consumed by the AC side load;
所述直流微电网包括直流母线、第二光伏阵列PV、第二储能装置和直流侧负荷,所述第二光伏阵列PV、第二储能装置和直流侧负荷均连接所述直流母线;The DC microgrid includes a DC bus, a second PV array PV, a second energy storage device, and a DC side load, and the second PV array PV, the second energy storage device, and the DC side load are connected to the DC bus;
当PCC闭合且交直流互联换流器PCS采用恒压控制模式时,所述直流微电网的运行模式包括第一直流运行模式;When the PCC is closed and the AC/DC interconnect converter PCS adopts a constant voltage control mode, the operating mode of the DC microgrid includes a first DC operating mode;
当交直流互联换流器PCS采用PQ控制模式或待机时,所述直流微电网的运行模式包括第二一直流运行模式、第二二直流运行模式和第二三直流运行模式;When the AC/DC interconnect converter PCS adopts the PQ control mode or standby, the operating mode of the DC microgrid includes a second direct current operation mode, a second two-DC operation mode, and a second three-DC operation mode;
所述第一直流运行模式为利用交直流互联换流器PCS维持直流母线电压在第一电压,全部第二光伏阵列PV均以MPPT模式运行,第二储能装置进行充放电控制,直流侧负荷全部投入使用;The first DC operating mode is to maintain the DC bus voltage at the first voltage by using the AC/DC interconnect converter PCS, all the second PV array PVs are operated in the MPPT mode, and the second energy storage device performs charging and discharging control, the DC side The load is fully put into use;
所述第二一直流运行模式为利用第二储能装置维持直流母线电压在第二电压,全部第二光伏阵列PV均以MPPT模式运行,交直流互联换流器PCS进行充放电控制,直流侧负荷全部投入使用;The second direct current operation mode is to maintain the DC bus voltage at the second voltage by using the second energy storage device, all the second photovoltaic array PVs are operated in the MPPT mode, and the AC/DC interconnection converter PCS performs charging and discharging control, and the DC The side loads are all put into use;
所述第二二直流运行模式为第二储能装置运行于最大功率充电或满充待机状态,切除部分第二光伏阵列PV,其余第二光伏阵列PV以MPPT模式运行,使第二储能装置运行于恒压控制模式以维持直流母线电压,直流侧负荷全部投入使用;The second two-DC operation mode is that the second energy storage device operates in a maximum power charging or full charge standby state, and a part of the second photovoltaic array PV is cut off, and the remaining second photovoltaic array PVs are operated in the MPPT mode, so that the second energy storage device Operate in constant voltage control mode to maintain DC bus voltage, DC side load is fully put into use;
所述第二三直流运行模式为切除部分直流侧负荷使第二储能装置的放电功率小于其
最大放电功率直至第二储能装置运行于恒压模式,全部第二光伏阵列PV均以MPPT模式运行;The second three-DC operation mode is to cut off part of the DC side load so that the discharge power of the second energy storage device is less than
The maximum discharge power until the second energy storage device operates in the constant voltage mode, and all the second photovoltaic array PVs operate in the MPPT mode;
当PPV2-PPCS2-Pbch-max2>=Pload2时从第二一直流运行模式切换至第二二直流运行模式; Switching from the second all-current operation mode to the second two-DC operation mode when P PV2 -P PCS2- P bch-max2 >=P load2 ;
当PPV2-PPCS2-Pbch-max2<Pload2时从第二二直流运行模式切换至第二一直流运行模式; Switching from the second two-DC operation mode to the second constant-current operation mode when P PV2 -P PCS2- P bch-max2 <P load2 ;
当PPV2-PPCS2+Pbdi-max2<Pload2时从第二一直流运行模式切换至第二三直流运行模式; Switching from the second all-current operation mode to the second three-DC operation mode when P PV2 -P PCS2+ P bdi-max2 <P load2 ;
当PPV2-PPCS2+Pbdi-max2>Pload2时从第二三直流运行模式切换至第二一直流运行模式; Switching from the second three-DC operation mode to the second constant-current operation mode when P PV2 -P PCS2+ P bdi-max2 >P load2 ;
式中,PPV2为微电网直流侧光伏的输出功率,PPCS2为交直流互联换流器PCS输入直流母线的功率,Pbch-max2为第二储能装置允许的最大的充电功率,Pload2为直流侧负荷的功率,Pbdi-max2为第二储能装置的最大的放电功率。Where, P PV2 is the output power of the DC side photovoltaic power of the micro grid, P PCS2 is the power of the DC bus input to the AC/DC interconnect converter PCS, and P bch-max2 is the maximum charging power allowed by the second energy storage device, P load2 For the power of the DC side load, P bdi-max2 is the maximum discharge power of the second energy storage device.
更进一步的,所述储能装置包括蓄电池和超级电容。交流侧的储能装置还包括超级电容,可以充分发挥超级电容充放电速度快的特性。Further, the energy storage device comprises a battery and a super capacitor. The energy storage device on the AC side also includes a super capacitor, which can fully utilize the characteristics of fast charging and discharging of the super capacitor.
更进一步的,所述第一电压为400V。Further, the first voltage is 400V.
更进一步的,所述第二电压为400V。Further, the second voltage is 400V.
更进一步的,所述第一直流运行模式中第二储能装置进行定功率充放电控制。Further, in the first DC operating mode, the second energy storage device performs constant power charging and discharging control.
有益效果:本发明的交直流混合微电网运行模块转换方法采用的交直流混合微电网灵活性较高且具有较强的可再生能源吸收能力,提出了微电网交流侧和微电网直流侧在不同状态下的运行模式以及转换条件以及转换方式,可实现运行模式之间的无缝切换,为交直流混合微电网的安全稳定运行提供技术支撑。Advantageous Effects: The AC/DC hybrid microgrid operating module conversion method of the present invention adopts an AC/DC hybrid microgrid with high flexibility and strong regenerative energy absorption capability, and proposes that the microgrid AC side and the microgrid DC side are different. The operation mode and the conversion conditions and the conversion mode in the state can realize seamless switching between the operation modes, and provide technical support for the safe and stable operation of the AC-DC hybrid microgrid.
图1为交直流微电网的结构示意图;1 is a schematic structural view of an AC-DC microgrid;
图2为第一交流运行模式的控制方式;2 is a control mode of the first alternating current operation mode;
图3为第二一交流运行模式的控制方式;Figure 3 is a control mode of the second alternating current operation mode;
图4为第二二交流运行模式的控制方式;Figure 4 is a control mode of the second two alternating current operation modes;
图5为第二三交流运行模式的控制方式;Figure 5 is a control mode of the second three alternating current operation modes;
图6为微电网交流侧运行模式的转换示意图;6 is a schematic diagram of conversion of an AC side AC side operation mode;
图7为第一直流运行模式的控制方式;Figure 7 is a control mode of the first DC operating mode;
图8为第二一直流运行模式的控制方式;Figure 8 is a control mode of the second continuous flow operation mode;
图9为第二二直流运行模式的控制方式;Figure 9 is a control mode of the second two-DC operation mode;
图10为第二三直流运行模式的控制方式;
Figure 10 is a control mode of the second three-DC operation mode;
图11为微电网直流侧运行模式的转换示意图;11 is a schematic diagram of conversion of a DC side operating mode of a microgrid;
图12为PCC与互联PCS运行状态间的关系;Figure 12 is the relationship between the PCC and the operating state of the interconnected PCS;
图13为第一直流运行模式仿真电压曲线;Figure 13 is a first DC operating mode simulation voltage curve;
图14为第二一直流运行模式仿真电压曲线;Figure 14 is a second constant current operation mode simulation voltage curve;
图15为并网转离网直流母线电压变化曲线;Figure 15 is a voltage curve of the DC bus of the grid-connected off-grid;
图16为微电网交流侧非计划离网交流母线电压;Figure 16 is an unplanned off-grid AC bus voltage on the AC side of the microgrid;
图17为微电网交流侧非计划离网交流母线频率;Figure 17 shows the frequency of the unplanned off-grid AC bus on the AC side of the microgrid;
图18为微电网分层控制结构;Figure 18 is a hierarchical control structure of a microgrid;
图19为微电网无缝切换运行模式基本控制时序;Figure 19 shows the basic control timing of the seamless switching operation mode of the microgrid;
图20为主电源模式切换示意图。Figure 20 is a schematic diagram of the main power mode switching.
下面将结合本发明实施例中的附图,对本发明实施例中的技术方案进行清楚、完整地描述,显然,所描述的实施例仅仅是本发明一部分实施例,而不是全部的实施例。基于本发明中的实施例,本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例,都属于本发明保护的范围。The technical solutions in the embodiments of the present invention are clearly and completely described in the following with reference to the accompanying drawings in the embodiments of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, but not all embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention.
请参阅图1所示,本发明的交直流混合微电网的交流侧和直流侧均包含光伏阵列PV、储能装置和负荷,其中,交流侧的储能装置包括蓄电池和超级电容,交流母线通过公共连接点与配电网连接,直流侧与交流侧则通过一个可实现能量双向流动的AC/DC变流器连接。优先将一些直流形式的DG和负荷接入直流母线,同时,为了保证MG的直流侧与交流侧在特殊状况下能够分别独立运行,在交流母线上也并入了一部分PV阵列,部分交流负荷直接接入交流母线。本发明构建的微电网灵活性较高且具有较强的可再生能源吸收能力。Referring to FIG. 1 , the AC side and the DC side of the AC/DC hybrid microgrid of the present invention both include a PV array PV, an energy storage device, and a load, wherein the AC side energy storage device includes a battery and a super capacitor, and the AC bus passes through The common connection point is connected to the distribution network, and the DC side and the AC side are connected by an AC/DC converter that enables bidirectional flow of energy. Priority is given to some DC-type DGs and loads connected to the DC bus. At the same time, in order to ensure that the DC side and the AC side of the MG can operate independently under special conditions, a part of the PV array is also incorporated on the AC bus, and part of the AC load is directly Connect to the AC bus. The microgrid constructed by the invention has high flexibility and strong regenerative energy absorption capacity.
交直流混合微电网系统模型:AC/DC hybrid microgrid system model:
(1)光伏发电系统模型(1) Photovoltaic power generation system model
光伏阵列的功率输出为:The power output of the PV array is:
式中:fPV为光伏系统的功率降额因数,表示光伏系统实际输出功率与额定条件下
输出功率的比值,用于计及由于光伏板表面污渍和雨雪的遮盖以及光伏板自身老化等引起的损耗,一般取0.9;YPV为光伏阵列容量,kW;IT为实际光照度,kW/m2;IS为标准测试条件下的光照度,一般取1kW/m2;αp为功率温度系数,%/℃;Tcell为当前光伏电池的表面温度,℃,可根据当前环境温度进行估算;Tcell,STC为标准测试条件下的光伏电池温度,一般取25℃。Where: f PV is the power derating factor of the photovoltaic system, which represents the ratio of the actual output power of the photovoltaic system to the output power under the rated conditions, which is used to account for the surface contamination of the photovoltaic panel, the covering of rain and snow, and the aging of the photovoltaic panel itself. The loss is generally 0.9; Y PV is the PV array capacity, kW; I T is the actual illuminance, kW / m 2 ; I S is the illuminance under the standard test conditions, generally 1kW / m 2 ; α p is the temperature coefficient of power , % / ° C; T cell is the surface temperature of the current photovoltaic cell, ° C, can be estimated according to the current ambient temperature; T cell, STC is the temperature of the photovoltaic cell under standard test conditions, generally taken 25 ° C.
(2)蓄电池模型(2) Battery model
蓄电池模型采用Kinetic Battery Model(简称KiBaM)模型,同时假定电池端口电压恒定、各时步内电池的充放电电流恒定,不考虑环境条件的影响。The battery model adopts the Kinetic Battery Model (KiBaM) model, and assumes that the battery port voltage is constant, and the charge and discharge current of the battery in each time step is constant, regardless of the influence of environmental conditions.
电池组在任意时刻储存的总能量等于可用能量与束缚能量之和,即:The total energy stored by the battery pack at any time is equal to the sum of available energy and binding energy, ie:
W=W1+W2 (2)W=W 1 +W 2 (2)
其中,W1为可用能量;W2为束缚能量。Where W 1 is available energy; W 2 is bound energy.
依据电池组实际充放电功率,可计算出充放电后电池组的可用能量:According to the actual charge and discharge power of the battery pack, the available energy of the battery pack after charging and discharging can be calculated:
其中,W1,0为初始时刻电池组的可用能量(kW·h);W1,end为终止时刻电池组可用能量(kW·h);W0为初始时刻电池组的总能量(kW·h);P为电池组放电(为正)或充电(为负)功率(kW),不包含充放电损耗;Δt为时间间隔(在算法中亦即时间步长,h);c为电池容量比例,表示蓄电池满充状态下可用能量和总能量的比值;k为电池速率常数(h-1),表示可用能量与束缚能量的转化速率。Where W 1,0 is the available energy of the battery pack at the initial time (kW·h); W 1,end is the available energy of the battery pack at the end time (kW·h); W 0 is the total energy of the battery pack at the initial time (kW· h); P is the battery pack discharge (positive) or charge (negative) power (kW), does not include charge and discharge loss; Δt is the time interval (in the algorithm, ie time step, h); c is the battery capacity The ratio represents the ratio of available energy to total energy in the fully charged state of the battery; k is the battery rate constant (h -1 ), indicating the conversion rate of available energy and bound energy.
结合式(2)和式(3),同时考虑到总能量减少量等于放电量PΔt,可得到充放电后电池组的束缚能量:Combining equations (2) and (3), taking into account that the total energy reduction is equal to the discharge amount PΔt, the binding energy of the battery pack after charging and discharging can be obtained:
W2,end=W0-PΔt-W1,end (4)W 2,end =W 0 -PΔt-W 1,end (4)
其中,W2,end为终止时刻电池组的束缚能量(kW·h)。Where W 2,end is the binding energy (kW·h) of the battery pack at the end time.
任意时刻可用能量W1满足关系式:0≤W1≤cWmax,其中Wmax表示蓄电池最大可存储能量(kW·h)。结合时间步长终止时刻可用能量W1,end计算式(3),可以得到蓄电池KiBaM模型单步最大允许充电功率和最大充放电功率[9],分别为:The available energy W 1 at any time satisfies the relationship: 0 ≤ W 1 ≤ cW max , where W max represents the maximum storable energy (kW·h) of the battery. Combining the energy step W at the end of the time step and calculating the equation (3), the single-step maximum allowable charging power and the maximum charging and discharging power of the battery KiBaM model can be obtained [9] , respectively:
为防蓄电池的过充、过放,最大充电功率约束中还应计及蓄电池的最大充电电流和速率约束,得到对应的最大充电功率(kW)分别为:In order to prevent overcharging and overdischarging of the battery, the maximum charging current and speed constraint of the battery should also be taken into account in the maximum charging power constraint, and the corresponding maximum charging power (kW) is obtained as follows:
其中,Nbat为电池串并联总数;Imax为电池的最大充电电流(A);UN为电池的额定电压(V);αc为电池的最大充电速率(A/(Ah))。Where N bat is the total number of battery strings connected in parallel; I max is the maximum charging current of the battery (A); U N is the rated voltage (V) of the battery; α c is the maximum charging rate of the battery (A / (Ah)).
结合KiBaM模型中对蓄电池充放电功率的限制,并计及充放电损耗,得到最终的蓄电池充放电功率限制为:Combined with the limitation of the charging and discharging power of the battery in the KiBaM model, and taking into account the charge and discharge loss, the final battery charging and discharging power is limited to:
-Pbat,cmax≤Pbat≤Pbat,dmax (9)-P bat,cmax ≤P bat ≤P bat,dmax (9)
Pbat,dmax=ηbat,dPbat,cmax,kbm (11)P bat,dmax =η bat,d P bat,cmax,kbm (11)
其中,ηbat,c为电池充电效率;ηbat,d为电池放电效率。Where η bat,c is the battery charging efficiency; η bat,d is the battery discharge efficiency.
(3)变流器模型(3) Converter model
由于光蓄并网发电系统中同时包含直流母线和交流母线,需要变流器进行整流或逆变,其模型可以使用下面的表达式:Since the optical storage grid-connected power generation system includes both the DC bus and the AC bus, the converter needs to be rectified or inverted. The model can use the following expression:
式中:Pcon,AC表示变流器交流侧功率(kW),逆变时为正,整流时为负,下同;Pcon,DC表示变流器直流侧功率之和(kW)。ηinv和ηrec表示变流器逆变和整流的效率;Rinv和Rrec表示变流器逆变和整流的最大有功功率(kW),数值上等于其额定容量。Where: P con, AC represents the AC side power (kW) of the converter, positive in the inverter, negative in the rectification, the same below; P con, DC represents the sum of the DC side power of the converter (kW). η inv and η rec represent the efficiency of converter inversion and rectification; R inv and R rec represent the maximum active power (kW) of the converter inverter and rectification, which is numerically equal to its rated capacity.
上式既可以表示双向变流器模型,也可以表示单向的整流器或逆变器,如单向的逆变器模型可以表示如下:
The above formula can represent either a bidirectional converter model or a unidirectional rectifier or inverter. For example, a unidirectional inverter model can be expressed as follows:
(4)负荷建模(4) Load modeling
微电网内负荷大致分为两类:重要负荷和参与需求侧管理负荷。重要负荷需保证不间断供电;参与需求侧管理负荷又分为三类:可中断负荷、可平移负荷与弹性负荷(又称为可控类负荷)。本发明将参与需求侧管理负荷全部视为可中断负荷,可中断负荷为非重要负荷,微电网调度者拥有此类负荷的中断权。The load in the microgrid is roughly divided into two categories: important load and participation in the demand side management load. The important load needs to ensure uninterrupted power supply; the participating demand side management load is divided into three categories: interruptible load, translatable load and elastic load (also known as controllable load). The invention regards the participation demand side management load as all interruptible load, the interruptible load as the non-important load, and the micro grid dispatcher has the interruption right of such load.
交流侧运行模式AC side operation mode
微电网交流侧通过PCC切换其并网或离网运行模式,本发明将微电网交流侧并网与否分为两种主要模式。The AC side of the microgrid switches its grid-connected or off-grid operation mode through the PCC. The present invention divides the grid connection of the micro-grid on the AC side into two main modes.
(1)交流侧并网(1) Connected to the AC side
第一交流运行模式:光伏阵列以MPPT模式运行,储能待机或以一定的策略充放电,如图2所示。The first AC operation mode: the PV array operates in the MPPT mode, and the energy storage standby or charging and discharging with a certain strategy, as shown in FIG. 2 .
(2)交流侧离网(2) AC side off the network
PCC断开的同时,互联PCS由恒压模式切换至PQ控制模式。While the PCC is disconnected, the interconnected PCS is switched from the constant voltage mode to the PQ control mode.
第二一交流运行模式:光伏的输出功率PPV与互联PCS流入微电网交流侧的功率PPCS之和与负荷消耗的功率Pload的差值处于储能的最大充电功率Pbch-max与最大放电功率Pbdi-max之间,此时储能以V/f模式运行,光伏阵列以MPPT模式运行,如图3所示。The second AC operation mode: the difference between the output power of the photovoltaic power P PV and the power P PCS of the interconnection PCS flowing into the micro-grid AC side and the power consumption of the load P load is the maximum charging power P bch-max and maximum of the energy storage. Between the discharge power P bdi-max , the energy storage is operated in the V/f mode, and the photovoltaic array operates in the MPPT mode, as shown in FIG. 3 .
第二二交流运行模式:光伏的输出功率PPV与互联PCS流入微电网交流侧的功率PPCS之和大于负荷的功率Pload与储能此时的最大充电功率(Pbch-max或0)之和时,切除部分光伏阵列,其他光伏仍运行于MPPT模式,储能运行于V/f控制模式,维持微电网交流侧的频率和电压。具体控制方式如图4所示。The second two-AC operation mode: the sum of the output power P PV of the photovoltaic and the power P PCS of the interconnection PCS flowing into the AC side of the micro-grid is greater than the power of the load P load and the maximum charging power of the energy storage at this time (P bch-max or 0) In the sum, some PV arrays are cut off, other PVs are still running in MPPT mode, and the energy storage is operated in V/f control mode to maintain the frequency and voltage of the AC side of the microgrid. The specific control method is shown in Figure 4.
运行第二三交流运行模式:光伏输出的功率PPV、互联PCS流入微电网交流侧的功率PPCS与储能最大的放电功率Pbdi-max之和小于负荷的功率,此时储能以最大功率输出,系统仍存在功率缺额,能量管理系统此时会增大互联PCS向交流侧输入的电能(互联PCS运行于恒功率控制时)或对交流侧负荷按级切除(互联PCS处于待机状态时),使储能恢复V/f控制模式。具体控制方式如图5所示。Run the second three AC operation mode: the power of PV output P PV , the power P PCS of the interconnected PCS flowing into the AC side of the microgrid and the maximum discharge power P bdi-max of the energy storage are less than the power of the load, and the energy storage is maximum at this time. Power output, the system still has power shortage, the energy management system will increase the energy input from the interconnected PCS to the AC side (when the interconnected PCS is running in constant power control) or the AC side load is cut off (the interconnected PCS is in the standby state) ), so that the energy storage restores the V/f control mode. The specific control method is shown in Figure 5.
以上各模式间的关系如图6所示。The relationship between the above modes is shown in Fig. 6.
各模式间的转换条件如表1所示:
The transition conditions between modes are shown in Table 1:
表1 微电网交流侧运行模式转换条件Table 1 Micro-grid AC side operating mode transition conditions
直流侧运行模式:DC side operation mode:
与微电网交流侧类似,直流侧根据互联PCS的控制模式分为两种主要模式。Similar to the AC side of the microgrid, the DC side is divided into two main modes according to the control mode of the interconnected PCS.
(1)互联PCS恒压控制模式时(交流侧并网)(1) When interconnecting PCS constant voltage control mode (connected to the AC side)
第一直流运行模式:利用互联PCS维持直流母线电压在400V,PV阵列以MPPT模式运行,储能按给定的指令进行充放电控制,如图7所示。The first DC operating mode: using the interconnected PCS to maintain the DC bus voltage at 400V, the PV array operates in MPPT mode, and the stored energy is charged and discharged according to a given command, as shown in Figure 7.
(2)互联PCS采用PQ控制模式或待机时(交流侧并网转离网时,若互联PCS为稳压模式,在转换瞬间应切换为PQ模式)(2) When the interconnected PCS adopts the PQ control mode or standby mode (when the AC side is connected to the network and disconnected from the network, if the interconnected PCS is in the voltage regulation mode, it should be switched to the PQ mode at the moment of conversion)
第二一直流运行模式:利用储能维持直流母线电压在400V,PV阵列以MPPT模式运行,互联PCS按给定的指令进行充放电控制,控制方式如图8所示。The second all-current operation mode: using the energy storage to maintain the DC bus voltage at 400V, the PV array operates in the MPPT mode, and the interconnected PCS performs charging and discharging control according to a given command, and the control mode is as shown in FIG.
第二二直流运行模式:若在微电网直流侧光伏的输出功率PPV2与互联PCS输入直流母线的功率-PPCS2之和大于储能此时允许的最大的充电功率(Pbch-max2或0)与负荷的功率Pload2之和,此时电压将抬升,模式由第二一直流运行模式转为第二二直流运行模式,此时储能运行于最大功率充电或满充待机状态,切除部分光伏,使储能仍运行于恒压控制模式以维持直流母线电压,控制方式如图9所示;随着负荷的增加或光伏出力的减小,
当光伏出力小于负荷时,逐步投入被切除的光伏,直至恢复至第二一直流运行模式。The second two-DC operation mode: if the output power P PV2 of the DC side of the micro-grid and the power-P PCS2 of the interconnected PCS input DC bus are greater than the maximum charging power allowed by the energy storage at this time (P bch-max2 or 0) ) and the load power P load2 , the voltage will rise, the mode is changed from the second direct current operation mode to the second two-DC operation mode, and the energy storage operation is in the maximum power charging or full charge standby state, and the cutting is performed. Part of the photovoltaic, so that the energy storage is still running in the constant voltage control mode to maintain the DC bus voltage, the control mode is shown in Figure 9; as the load increases or the PV output decreases, when the PV output is less than the load, the gradual input is removed. The photovoltaics are restored to the second continuous flow mode of operation.
第二三直流运行模式:若在微电网直流侧光伏的输出功率PPV2、储能此时最大的放电功率Pbdi-max2与互联PCS流入直流母线的功率-PPCS2之和小于负荷的功率Pload2,此时电压将下降,由第二一直流运行模式转为第二三直流运行模式,为使储能仍运行于恒压模式,按负荷等级切除负荷使储能的放电功率小于其最大放电功率。当储能由放电转为充电状态时,逐级投入负荷,直至恢复至第二一直流运行模式。The second three-DC operation mode: if the output power P PV2 of the photovoltaic side on the DC side of the micro-grid, the maximum discharge power P bdi-max2 at the time of energy storage and the power-P PCS2 of the interconnected PCS flowing into the DC bus are less than the power of the load P Load2 , at this time the voltage will drop, from the second direct current operation mode to the second three-current operation mode, in order to make the energy storage still operate in the constant pressure mode, the load is cut off according to the load level so that the discharge power of the stored energy is less than its maximum Discharge power. When the stored energy is switched from the discharge to the charged state, the load is gradually input until the second continuous flow operation mode is restored.
微电网直流侧各运行模式之间的关系如图11所示,微电网直流侧各模式间的切换条件如表2所示。The relationship between the operating modes of the DC side of the microgrid is shown in Figure 11, and the switching conditions between the modes on the DC side of the microgrid are shown in Table 2.
表2 微电网直流侧运行模式转换条件Table 2 DC grid DC operating mode transition conditions
由于微电网交流侧和直流侧的运行模式是分别提出的,两者之间存在一定的交互关系,主要为PCC和互联PCS运行状态之间的关系,如图12所示。Since the operation modes of the AC side and the DC side of the microgrid are separately proposed, there is a certain interaction relationship between the two, mainly the relationship between the operating state of the PCC and the interconnected PCS, as shown in FIG.
其中,PCC存在闭合和断开两种运行模式,可相互切换;互联PCS存在恒压控制、待机和PQ控制三种运行模式,三者之间相互切换。PCC和互联PCS的运行模式之间存在一定联系,当PCC闭合时,互联PCS可运行于任意模式,但主要运行于恒压模式;当PCC断开时,互联PCS只可运行于PQ控制和待机模式,不可运行于恒压控制模式,且主要运行于PQ控制模式。Among them, the PCC has two operating modes, closed and disconnected, which can be switched to each other; the interconnected PCS has three operating modes of constant voltage control, standby and PQ control, and the three switches between each other. There is a certain relationship between the PCC and the operating mode of the interconnected PCS. When the PCC is closed, the interconnected PCS can run in any mode, but mainly operates in the constant voltage mode; when the PCC is disconnected, the interconnected PCS can only run in the PQ control and standby. Mode, not in constant voltage control mode, and mainly in PQ control mode.
运行模式切换仿真验证
Operation mode switching simulation verification
本发明以微电网在并网状态为例进行仿真验证。The invention performs simulation verification by taking the micro grid as the example of the grid connection state.
由于微电网运行模式是根据并网与否来划分的,因此仅对微电网的并/离网切换进行仿真即可。仿真首先需要将微电网启动。Since the microgrid operation mode is divided according to the grid connection or not, it is only necessary to simulate the parallel/off-grid handover of the microgrid. The simulation first needs to start the microgrid.
(1)微电网直流侧启动(1) Microgrid DC side start
第一直流运行模式:利用互联PCS给直流母线充电,维持其电压在400V,然后分别接入以MPPT模式运行的PV阵列和负荷,直流侧储能按给定的指令进行充放电控制。The first DC operating mode: the DC bus is charged by the interconnected PCS, the voltage is maintained at 400V, and then the PV array and the load operating in the MPPT mode are respectively connected, and the DC side energy storage is charged and discharged according to the given command.
通过在Simulink中搭建的模型对此过程进行仿真,仿真过程中直流母线的曲线如图13所示。The process is simulated by the model built in Simulink. The curve of the DC bus during the simulation is shown in Fig. 13.
在0.05s时启动互联PCS,给直流母线充电,充电过程中,电压最大值达到475V,在0.2s后电压趋于稳定。在0.45s、0.7s和0.8s分别接入19.4kW、6.2kW和5.58kW光伏阵列,电压波动均在5%以内;在0.9s、1.1s和1.2s分别并入20kW、5.1kW和4.9kW负荷,电压波动也在5%以内。When the interconnected PCS is started at 0.05s, the DC bus is charged. During the charging process, the maximum voltage reaches 475V, and the voltage tends to be stable after 0.2s. In the 0.45s, 0.7s and 0.8s respectively, the 19.4kW, 6.2kW and 5.58kW PV arrays are connected, and the voltage fluctuations are all within 5%; in the 0.9s, 1.1s and 1.2s, respectively, 20kW, 5.1kW and 4.9kW are incorporated. Load, voltage fluctuations are also within 5%.
实际上,互联PCS对直流母线充电是一个软启动过程,并不会在直流侧形成很大的过电压。而光伏逆变器也有一个启动过程,功率逐渐变大,不会有冲击。本次仿真是在模拟最极端条件下微电网的过电压水平。In fact, interconnecting the PCS to charge the DC bus is a soft-start process that does not create a large overvoltage on the DC side. The photovoltaic inverter also has a starting process, and the power gradually becomes larger and there is no impact. This simulation is to simulate the overvoltage level of the microgrid under the most extreme conditions.
第二一直流运行模式(自启动):直流侧以储能为主,储能对直流母线进行充电,然后进行恒压控制,按照一定的顺序分别接入以MPPT模式运行的PV阵列和负载,互联PCS按给定的指令进行充放电控制。仿真电压波形如图14所示。The second direct current operation mode (self-starting): the DC side is mainly energy storage, the energy storage charges the DC bus, and then the constant voltage control is performed, and the PV array and the load operating in the MPPT mode are respectively accessed in a certain order. The interconnected PCS performs charge and discharge control according to the given command. The simulated voltage waveform is shown in Figure 14.
图14中,直流母线用储能装置充电,后在0.4s和0.8s分别并入5kW负载和5kW光伏,虽然直流侧的储能容量较小,但在如此大的功率波动下,仍能维持直流母线电压的波动在10%以内。In Figure 14, the DC bus is charged by the energy storage device, and then merged into 5kW load and 5kW PV at 0.4s and 0.8s respectively. Although the DC side has a small energy storage capacity, it can still be maintained under such large power fluctuations. The DC bus voltage fluctuates within 10%.
微电网交流侧也可实现自启动与通过外部电路启动,本发明不再对其进行研究。The AC side of the microgrid can also be self-started and activated by an external circuit, which is not studied by the present invention.
(2)微电网直流侧并/离网切换(2) DC side DC/DC switching
当微电网直流侧由并网状态向离网状态切换时可分为计划性脱网和非计划性脱网两种情况。When the DC side of the microgrid is switched from the grid-connected state to the off-grid state, it can be divided into two cases: planned off-network and unplanned off-net.
计划性脱网,是指系统预先得到状态切换指令,有计划地调节分布式发电和各储能单元出力以及可控负荷之间的关系,同时保证对系统内重要负荷的供电。Planned off-network means that the system obtains state switching instructions in advance, and systematically adjusts the relationship between distributed generation and output of each energy storage unit and controllable load, while ensuring power supply to important loads in the system.
非计划性脱网是当电网故障或断开时的控制过程。微电网交流侧与大电网并网时,互联PCS运行于恒压控制模式,此时微电网直流侧并网转离网过程复杂,对电压稳定性
影响较大,是微电网直流侧并网转离网的主要研究对象。并网转离网主要的切换过程如下:保护装置检测到微电网交流侧电压幅值与频率异常,给并网点开关发断开指令,由开关位置反馈信号给互联PCS发模式切换指令,互联PCS和微电网直流侧储能接口通过干接点信号互通,互联PCS接到开关位置信号后运行模式由恒压控制模式切换为待机或恒功率控制模式,储能直流变换器由充、放电模式切换为恒压模式,控制直流母线电压,同时并网点开关控制自身断开,三者配合完成系统并网到离网的无缝切换。图15为Simulink中对并网转离网过程进行仿真时直流母线电压的变化曲线。Unplanned off-network is the control process when the grid fails or is disconnected. When the AC side of the microgrid is connected to the large grid, the interconnected PCS operates in the constant voltage control mode. At this time, the process of connecting the DC side of the microgrid to the grid is complicated, and the voltage stability is
The influence is relatively large, which is the main research object of the DC side of the micro-grid connected to the network. The main switching process of the grid-connected network is as follows: the protection device detects the voltage amplitude and frequency anomaly of the AC side of the micro-grid, sends a disconnection command to the grid-connected switch, and sends a mode switching command to the interconnected PCS by the switch position feedback signal, interconnecting the PCS. The DC side energy storage interface of the microgrid communicates with the dry contact signal. After the interconnected PCS receives the switch position signal, the operation mode is switched from the constant voltage control mode to the standby or constant power control mode, and the energy storage DC converter is switched from the charging and discharging modes to The constant voltage mode controls the DC bus voltage, and the grid switch controls the disconnection. The three cooperate to complete the seamless switching of the system from the grid to the off-grid. Figure 15 shows the variation of the DC bus voltage when simulating the process of grid-connected off-grid in Simulink.
图15中,1.5s时由于交流侧故障或其他原因,互联PCS断开,协调控制器检测到PCS断开后向储能变流器发转换运行模式指令,储能变流器由恒功率充放电控制模式切换到恒压模式以维持直流母线电压,此过程中,由于功率的不平衡,电压短暂上升至404V后,由于储能的稳压作用迅速下降。In Figure 15, at 1.5 s, the interconnected PCS is disconnected due to AC side fault or other reasons. The coordinating controller detects that the PCS is disconnected and sends a switching operation mode command to the energy storage converter. The energy storage converter is charged by constant power. The discharge control mode is switched to the constant voltage mode to maintain the DC bus voltage. In this process, due to the power imbalance, the voltage rises briefly to 404V, and the regulation effect of the energy storage rapidly decreases.
交流侧与大电网并网且互联PCS运行于恒功率控制模式时,微电网直流侧并网转离网过程对微电网直流侧的影响与向直流侧投入负荷一样,在此不再讨论。When the AC side is connected to the large grid and the interconnected PCS is operating in the constant power control mode, the DC-connected DC-connected network process has the same effect on the DC side of the micro-grid as the DC-side input load, and will not be discussed here.
当电网恢复,交流侧与大电网并网后,协调控制器给互联PCS下发指令,互联PCS接收到信号后,和直流侧储能变换器利用干接点进行互通,并网变流器运行模式由待机或恒功率控制模式切换为恒压控制模式,直流侧储能变换器接到互锁信号后,由稳压模式切换为恒功率充放电或待机模式,三者配合完成系统离网到并网的无缝切换。When the grid is restored and the AC side is connected to the grid, the coordination controller sends instructions to the interconnected PCS. After the interconnected PCS receives the signal, it communicates with the DC side energy storage converter using dry contacts, and the grid converter operates. Switching from the standby or constant power control mode to the constant voltage control mode, after the DC side energy storage converter receives the interlock signal, it switches from the voltage regulation mode to the constant power charge/discharge or standby mode, and the three cooperate to complete the system off-grid. Seamless switching of the web.
(3)微电网交流侧并/离网切换(3) Micro-grid AC side/off-network switching
1)并网转离网过程1) Grid-connected network process
微电网交流侧由并网向离网状态切换同样可分为计划性脱网与非计划性脱网两种类型。The switching of the AC side of the micro-grid from the grid-connected to the off-grid state can also be divided into two types: planned off-network and unplanned off-network.
非计划性脱网过程,大电网故障或PCC断开时,PCC与交流侧储能以及互联PCS信号互通,储能由恒功率控制模式转换为V/F控制模式,互联PCS由恒压模式转换为恒功率控制或待机模式,且锁定其功率为切换瞬间通过互联PCS的功率。若此时储能以最大放电功率放电或最大充电功率充电仍无法维持微电网交流侧的电压和频率,可调节互联PCS的功率至适当值,达到维持微电网交流侧稳定的目的。Unplanned off-network process, when the large power grid fails or the PCC is disconnected, the PCC communicates with the AC side energy storage and the interconnected PCS signals, the energy storage is converted from the constant power control mode to the V/F control mode, and the interconnected PCS is converted by the constant voltage mode. It is a constant power control or standby mode, and its power is locked to the power of the interconnected PCS at the moment of switching. If the stored energy is discharged at the maximum discharge power or the maximum charging power is still unable to maintain the voltage and frequency of the AC side of the microgrid, the power of the interconnected PCS can be adjusted to an appropriate value to achieve the purpose of maintaining the stability of the AC side of the microgrid.
非计划性脱网时交流母线的电压如图16所示,频率如图17所示。The voltage of the AC busbar during unplanned off-grid is shown in Figure 16, and the frequency is shown in Figure 17.
在0.5秒时,断开PCC并将储能由PQ控制模式转变为V/f控制模式,由图16与17知,此时电压出现了一定的抖动,但很快就恢复正常,母线频率基本不变。
At 0.5 seconds, the PCC is disconnected and the energy storage is switched from the PQ control mode to the V/f control mode. It is known from Figures 16 and 17, that the voltage appears to have a certain jitter, but it quickly returns to normal, and the bus frequency is basically constant.
2)离网转并网过程2) Off-net to grid connection process
当大电网恢复稳定后,协调控制器对PCC发出同期合闸命令,PCC进行同期合闸,储能由V/f控制转换为PQ控制,微电网交流侧完成离网转并网过程。When the large power grid resumes stability, the coordination controller issues a synchronous closing command to the PCC, and the PCC performs the synchronous closing. The energy storage is converted from the V/f control to the PQ control, and the micro-grid AC side completes the off-grid-to-network connection process.
本发明还公开了微电网控制结构,微电网采用的三层控制结构如图18所示。The invention also discloses a microgrid control structure, and the three-layer control structure adopted by the microgrid is as shown in FIG. 18.
(1)第一层控制(1) First layer control
DG或储能装置根据微电网的状况常可运行于多种控制模式,包括最大功率点跟踪(MPPT)控制,恒压控制,恒压/恒频(V/f)控制等。The DG or energy storage device can often operate in a variety of control modes depending on the condition of the microgrid, including maximum power point tracking (MPPT) control, constant voltage control, constant voltage/constant frequency (V/f) control, and the like.
微电网并网时,配电网保证微电网交流侧的电压和频率稳定,DG常以最大功率输出;微电网直流侧采用主从控制模式,由微电网交流侧或储能作为主电源,维持直流母线电压。When the microgrid is connected to the grid, the distribution network ensures that the voltage and frequency of the AC side of the microgrid are stable, and the DG is often output with maximum power; the DC side of the microgrid adopts the master-slave control mode, and the AC side or energy storage of the microgrid is used as the main power source to maintain DC bus voltage.
微电网离网运行时,由微电网交流侧内某个DG来保证电压和频率稳定。通常由储能装置采取V/f控制保证电压和频率在规定值,其它DG均采用恒功率控制(PQ控制)并以最大功率输出;微电网直流侧的储能设备作为主电源采取恒压控制,其他分布式DG均以最大功率输出。储能装置需要能够补偿负荷变化所产生的功率差额,因此储能必须能够在其容许充放电功率范围内准确的控制输出,快速补偿功率差额。When the microgrid is operating off-grid, a certain DG in the AC side of the microgrid ensures voltage and frequency stability. Usually, the energy storage device adopts V/f control to ensure that the voltage and frequency are at specified values, and other DGs use constant power control (PQ control) and output at maximum power; the energy storage device on the DC side of the microgrid adopts constant voltage control as the main power source. Other distributed DGs are output at maximum power. The energy storage device needs to be able to compensate for the power difference caused by the load change. Therefore, the energy storage must be able to accurately control the output within its allowable charge and discharge power range, and quickly compensate the power difference.
(2)第二层控制(2) Layer 2 control
第二层为协调控制层,其作用是在微电网处于并网状态时减小配电网因DG输出和负荷变化而产生负面影响,微电网能够当作稳定、可控的负荷并入配电网,通过微电网协调控制器对各单元的协调控制来实现联络线功率控制;在微电网处于离网状态时,通过主从控制保证电压和频率处在规定范围内,主电源补偿DG输出或负荷变化所产生的功率差额。The second layer is the coordinated control layer, which functions to reduce the negative impact of the distribution network due to DG output and load changes when the microgrid is in the grid-connected state. The microgrid can be integrated into the distribution as a stable and controllable load. Network, through the micro-grid coordination controller to coordinate control of each unit to achieve tie line power control; when the micro-grid is in the off-grid state, through the master-slave control to ensure that the voltage and frequency are within the specified range, the main power supply compensates for the DG output or The difference in power generated by load changes.
该层控制还可以实现MG各模式之间的切换功能。为了减小该功能对微电网运行指标的影响,还需具备MG故障检测,同步检测等功能,并可以协调控制模式间的切换。本文采用主从控制模式,其控制时序如图19所示,主要切换MG内各DG的控制方式,其中切换主电源的控制方式时,其输出功率波动应尽可能小。图20为本文采用的控制结构,主电源的PQ控制和V/f控制采用同一电流内环,切换控制方法时只对电压外环进行切换。在此过程中,为了最大程度减小控制方式切换时产生的冲击,还需合理应用控制逻辑和算法。This layer control can also implement the switching function between the MG modes. In order to reduce the impact of this function on the operating parameters of the microgrid, it is necessary to have functions such as MG fault detection and synchronous detection, and coordinate switching between control modes. In this paper, the master-slave control mode is adopted. The control timing is shown in Figure 19. The main control mode of each DG in the MG is switched. When the control mode of the main power source is switched, the output power fluctuation should be as small as possible. Figure 20 shows the control structure used in this paper. The PQ control and V/f control of the main power supply use the same current inner loop. When the switching control method is used, only the voltage outer loop is switched. In this process, in order to minimize the impact generated when the control mode is switched, the control logic and algorithm need to be applied reasonably.
(3)第三层控制
(3) Layer 3 control
该层主要实现微电网的能量管理功能,通过相应的优化算法优化微电网的运行:This layer mainly realizes the energy management function of the microgrid, and optimizes the operation of the microgrid through corresponding optimization algorithms:
1)微电网处于并网状态时,计算出微电网与配电网之间联络线的最优功率值(作为微电网第二层控制目标参考值);1) When the microgrid is in the grid-connected state, calculate the optimal power value of the tie line between the microgrid and the distribution network (as the reference value of the second-layer control target of the micro-grid);
2)微电网处于离网状态时,调节各分布式DG输出功率参考值等信息,便可使微电网处于最经济运行状态。
2) When the microgrid is in the off-grid state, adjusting the information of each distributed DG output power reference value, the microgrid can be in the most economical operation state.
Claims (8)
- 一种交直流混合微电网运行模块转换方法,其特征在于,所述交直流混合微电网包括交流微电网和直流微电网,所述交流微电网和直流微电网通过交直流互联换流器PCS连接,An AC/DC hybrid microgrid operation module conversion method, characterized in that the AC/DC hybrid microgrid comprises an AC microgrid and a DC microgrid, and the AC microgrid and the DC microgrid are connected by an AC/DC interconnect converter PCS ,所述交流微电网包括交流母线、光伏阵列PV、储能装置和交流侧负荷,所述光伏阵列、储能装置和负荷均连接所述交流母线;所述交流微电网通过PCC切换其并网运行模式或离网运行模式;The AC microgrid includes an AC bus, a PV array PV, an energy storage device, and an AC side load, wherein the PV array, the energy storage device, and the load are connected to the AC bus; the AC microgrid is switched to the grid through the PCC. Mode or off-grid mode of operation;当PCC闭合时,交直流互联换流器PCS运行于恒压控制模式,所述交流侧并网运行模式包括第一交流运行模式,When the PCC is closed, the AC-DC interconnect converter PCS operates in a constant voltage control mode, and the AC-side grid-connected operation mode includes a first AC operation mode.当PCC断开时,交直流互联换流器PCS切换至PQ控制模式,所述交流侧离网运行模式包括第二一交流运行模式、第二二交流运行模式和第二三交流运行模式;When the PCC is disconnected, the AC/DC interconnect converter PCS is switched to the PQ control mode, and the AC side off-network operation mode includes a second AC operation mode, a second two AC operation mode, and a second three AC operation mode;所述第一交流运行模式为全部光伏阵列PV均以MPPT模式运行,储能装置待机或充放电,交流侧负荷全部投入使用;The first alternating current operation mode is that all the photovoltaic arrays PV are operated in the MPPT mode, the energy storage device is standby or charged and discharged, and the AC side load is all put into use;所述第二一交流运行模式为储能装置以V/f模式运行,全部光伏阵列PV均以MPPT模式运行,交流侧负荷全部投入使用;The second alternating current operation mode is that the energy storage device operates in the V/f mode, and all the photovoltaic array PVs are operated in the MPPT mode, and the AC side loads are all put into use;所述第二二交流运行模式为储能装置以V/f模式运行,切除部分光伏阵列PV,其余光伏阵列PV以MPPT模式运行,维持交流微电网的频率和电压,交流侧负荷全部投入使用;The second two alternating current operation mode is that the energy storage device operates in the V/f mode, and part of the photovoltaic array PV is cut off, and the remaining photovoltaic array PVs are operated in the MPPT mode, maintaining the frequency and voltage of the alternating microgrid, and the AC side loads are all put into use;所述第二三交流运行模式为储能装置先以最大功率输出,所述交直流互联换流器PCS增加向交流微电网输入的电能或切除部分所述交流侧负荷,直至储能装置恢复V/f控制模式,全部光伏阵列PV均以MPPT模式运行;The second three AC operation mode is that the energy storage device first outputs the maximum power, and the AC/DC interconnection converter PCS increases the power input to the AC microgrid or cuts off part of the AC side load until the energy storage device recovers V. /f control mode, all PV array PVs are operated in MPPT mode;当PCC闭合时,所述交流微电网以第一交流运行模式运行;When the PCC is closed, the AC microgrid operates in a first AC mode of operation;当PCC断开时,所述交流微电网从第一交流运行模式切换至第二一交流运行模式;When the PCC is disconnected, the AC microgrid is switched from the first alternating current operating mode to the second alternating current operating mode;当PPV+PPCS-Pbch-max>=Pload时,所述交流微电网从第二一交流运行模式切换至第二二交流运行模式;When P PV +P PCS -P bch-max >=P load , the AC microgrid switches from the second AC operating mode to the second AC operating mode;当PPV+PPCS-Pbch-max<Pload时,所述交流微电网从第二二交流运行模式切换至第二一交流运行模式;When the P PV +P PCS -P bch-max <P load , the AC microgrid switches from the second alternating current operating mode to the second alternating current operating mode;当PPV+PPCS+Pbdi-max<Pload时,所述交流微电网从第二一交流运行模式切换至第二三交流运行模式;When the P PV +P PCS +P bdi-max <P load , the AC microgrid switches from the second AC mode to the second AC mode;当PPV+PPCS+Pbdi-max>Pload时,所述交流微电网从第二三交流运行模式切换至第二一交流 运行模式;When P PV +P PCS +P bdi-max >P load , the AC microgrid switches from the second three AC operation mode to the second AC operation mode;式中,PPV为光伏阵列PV输出的功率,PPCS为交直流互联换流器PCS流入微电网交流侧的功率,Pbch-max为储能装置的最大充电功率,Pbdi-max为储能装置最大的放电功率,Pload为交流侧负荷消耗的功率;Where, P PV is the power output of the PV array PV, P PCS is the power of the AC/DC interconnect converter PCS flowing into the AC side of the microgrid, P bch-max is the maximum charging power of the energy storage device, and P bdi-max is the storage The maximum discharge power can be installed, and P load is the power consumed by the AC side load;所述直流微电网包括直流母线、第二光伏阵列PV、第二储能装置和直流侧负荷,所述第二光伏阵列PV、第二储能装置和直流侧负荷均连接所述直流母线;The DC microgrid includes a DC bus, a second PV array PV, a second energy storage device, and a DC side load, and the second PV array PV, the second energy storage device, and the DC side load are connected to the DC bus;当PCC闭合且交直流互联换流器PCS采用恒压控制模式时,所述直流微电网的运行模式包括第一直流运行模式;When the PCC is closed and the AC/DC interconnect converter PCS adopts a constant voltage control mode, the operating mode of the DC microgrid includes a first DC operating mode;当交直流互联换流器PCS采用PQ控制模式或待机时,所述直流微电网的运行模式包括第二一直流运行模式、第二二直流运行模式和第二三直流运行模式;When the AC/DC interconnect converter PCS adopts the PQ control mode or standby, the operating mode of the DC microgrid includes a second direct current operation mode, a second two-DC operation mode, and a second three-DC operation mode;所述第一直流运行模式为利用交直流互联换流器PCS维持直流母线电压在第一电压,全部第二光伏阵列PV均以MPPT模式运行,第二储能装置进行充放电控制,直流侧负荷全部投入使用;The first DC operating mode is to maintain the DC bus voltage at the first voltage by using the AC/DC interconnect converter PCS, all the second PV array PVs are operated in the MPPT mode, and the second energy storage device performs charging and discharging control, the DC side The load is fully put into use;所述第二一直流运行模式为利用第二储能装置维持直流母线电压在第二电压,全部第二光伏阵列PV均以MPPT模式运行,交直流互联换流器PCS进行充放电控制,直流侧负荷全部投入使用;The second direct current operation mode is to maintain the DC bus voltage at the second voltage by using the second energy storage device, all the second photovoltaic array PVs are operated in the MPPT mode, and the AC/DC interconnection converter PCS performs charging and discharging control, and the DC The side loads are all put into use;所述第二二直流运行模式为第二储能装置运行于最大功率充电或满充待机状态,切除部分第二光伏阵列PV,其余第二光伏阵列PV以MPPT模式运行,使第二储能装置运行于恒压控制模式以维持直流母线电压,直流侧负荷全部投入使用;The second two-DC operation mode is that the second energy storage device operates in a maximum power charging or full charge standby state, and a part of the second photovoltaic array PV is cut off, and the remaining second photovoltaic array PVs are operated in the MPPT mode, so that the second energy storage device Operate in constant voltage control mode to maintain DC bus voltage, DC side load is fully put into use;所述第二三直流运行模式为切除部分直流侧负荷使第二储能装置的放电功率小于其最大放电功率直至第二储能装置运行于恒压模式,全部第二光伏阵列PV均以MPPT模式运行;The second three-DC operation mode is to cut off part of the DC side load so that the discharge power of the second energy storage device is less than its maximum discharge power until the second energy storage device operates in the constant voltage mode, and all the second PV array PVs are in the MPPT mode. run;当PPV2-PPCS2-Pbch-max2>=Pload2时从第二一直流运行模式切换至第二二直流运行模式; Switching from the second all-current operation mode to the second two-DC operation mode when P PV2 -P PCS2- P bch-max2 >=P load2 ;当PPV2-PPCS2-Pbch-max2<Pload2时从第二二直流运行模式切换至第二一直流运行模式; Switching from the second two-DC operation mode to the second constant-current operation mode when P PV2 -P PCS2- P bch-max2 <P load2 ;当PPV2-PPCS2+Pbdi-max2<Pload2时从第二一直流运行模式切换至第二三直流运行模式; Switching from the second all-current operation mode to the second three-DC operation mode when P PV2 -P PCS2+ P bdi-max2 <P load2 ;当PPV2-PPCS2+Pbdi-max2>Pload2时从第二三直流运行模式切换至第二一直流运行模式; Switching from the second three-DC operation mode to the second constant-current operation mode when P PV2 -P PCS2+ P bdi-max2 >P load2 ;式中,PPV2为微电网直流侧光伏的输出功率,PPCS2为交直流互联换流器PCS输入直流母线的功率,Pbch-max2为第二储能装置允许的最大的充电功率,Pload2为直流侧负荷的功率,Pbdi-max2为第二储能装置的最大的放电功率。 Where, P PV2 is the output power of the DC side photovoltaic power of the micro grid, P PCS2 is the power of the DC bus input to the AC/DC interconnect converter PCS, and P bch-max2 is the maximum charging power allowed by the second energy storage device, P load2 For the power of the DC side load, P bdi-max2 is the maximum discharge power of the second energy storage device.
- 如权利要求1所述的交直流混合微电网运行模块转换方法,其特征在于,所述储能装置包括蓄电池和超级电容。The AC/DC hybrid microgrid operation module conversion method according to claim 1, wherein the energy storage device comprises a battery and a super capacitor.
- 如权利要求1所述的交直流混合微电网运行模块转换方法,其特征在于,所述第一电压为400V。The AC/DC hybrid microgrid operation module conversion method according to claim 1, wherein the first voltage is 400V.
- 如权利要求1所述的交直流混合微电网运行模块转换方法,其特征在于,所述第二电压为400V。The AC/DC hybrid microgrid operation module conversion method according to claim 1, wherein the second voltage is 400V.
- 如权利要求1所述的交直流混合微电网运行模块转换方法,其特征在于,所述第一直流运行模式中第二储能装置进行定功率充放电控制。The AC/DC hybrid microgrid operation module conversion method according to claim 1, wherein the second energy storage device performs constant power charge and discharge control in the first DC operation mode.
- 如权利要求1所述的交直流混合微电网运行模块转换方法,其特征在于,The AC/DC hybrid microgrid operation module conversion method according to claim 1, wherein所述光伏阵列PV和第二光伏阵列PV均通过下式表示:Both the photovoltaic array PV and the second photovoltaic array PV are represented by the following formula:式中,PPV为光伏阵列的输出功率,fPV为光伏系统的功率降额因数,表示光伏系统实际输出功率与额定条件下输出功率的比值;YPV为光伏阵列容量;IT为实际光照度;IS为标准测试条件下的光照度;αp为功率温度系数;Tcell为当前光伏电池的表面温度;Tcell,STC为标准测试条件下的光伏电池温度。Where, P PV is the output power of the photovoltaic array, f PV is the power derating factor of the photovoltaic system, indicating the ratio of the actual output power of the photovoltaic system to the output power under the rated condition; Y PV is the PV array capacity; I T is the actual illumination ; I S is the illuminance under standard test conditions; α p is the temperature coefficient of power; T cell is the surface temperature of the current photovoltaic cell; T cell, STC is the temperature of the photovoltaic cell under standard test conditions.
- 如权利要求1所述的交直流混合微电网运行模块转换方法,其特征在于,所述储能装置包括蓄电池,所述蓄电池的充放电功率限制为:The AC/DC hybrid microgrid operation module conversion method according to claim 1, wherein the energy storage device comprises a battery, and the charge and discharge power of the battery is limited to:-Pbat,cmax≤Pbat≤Pbat,dmax -P bat,cmax ≤P bat ≤P bat,dmaxPbat,dmax=ηbat,dPbat,cmax,kbm P bat,dmax =η bat,d P bat,cmax,kbm其中,ηbat,c为电池充电效率;ηbat,d为电池放电效率,Pbat,cmax,kbm为蓄电池单步最大允许充电功率Pbat,dmax,kbm为蓄电池单步最大充放电功率,Pbat,cmax,mcc为计及蓄电池的最大充电电流约束的最大充电功率,Pbat,cmax,mcr为计及蓄电池的最大充电速率约束的最大充电功率,Where η bat,c is the charging efficiency of the battery; η bat,d is the discharge efficiency of the battery, P bat,cmax,kbm is the maximum allowable charging power of the battery single step P bat, dmax,kbm is the maximum charging and discharging power of the battery single step, P Bat,cmax,mcc are the maximum charging powers that take into account the maximum charging current of the battery. P bat,cmax,mcr are the maximum charging powers that are limited by the maximum charging rate of the battery.其中,Nbat为电池串并联总数;Imax为电池的最大充电电流;UN为电池的额定电压;αc为电池的最大充电速率,W为蓄电池在任意时刻储存的总能量,其等于可用能量与束缚能量之和,即:W=W1+W2,其中,W1为可用能量;W2为束缚能量;充放电后电池组的可用能量通过下式表示:Where N bat is the total number of battery strings connected in parallel; I max is the maximum charging current of the battery; U N is the rated voltage of the battery; α c is the maximum charging rate of the battery, and W is the total energy stored by the battery at any time, which is equal to the available The sum of energy and binding energy, namely: W = W 1 + W 2 , where W 1 is the available energy; W 2 is the binding energy; the available energy of the battery after charging and discharging is represented by the following formula:其中,W1,0为初始时刻电池组的可用能量;W1,end为终止时刻电池组可用能量;W0为初始时刻电池组的总能量;P为电池组放电或充电功率;Δt为时间间隔;c为电池容量比例,表示蓄电池满充状态下可用能量和总能量的比值;k为电池速率常数;Where W 1,0 is the available energy of the battery at the initial time; W 1,end is the energy available to the battery at the end time; W 0 is the total energy of the battery at the initial time; P is the discharge or charging power of the battery; Δt is the time Interval; c is the ratio of battery capacity, indicating the ratio of available energy to total energy in the fully charged state of the battery; k is the battery rate constant;充放电后电池组的束缚能量:The binding energy of the battery pack after charging and discharging:W2,end=W0-PΔt-W1,end W 2,end =W 0 -PΔt-W 1,end其中,W2,end为终止时刻电池组的束缚能量;Where W 2,end is the binding energy of the battery pack at the end time;任意时刻可用能量W1满足下式:0≤W1≤cWmax,其中,Wmax表示蓄电池最大可存储能量。The available energy W 1 at any time satisfies the following formula: 0 ≤ W 1 ≤ cW max , where W max represents the maximum storable energy of the battery.
- 如权利要求1所述的交直流混合微电网运行模块转换方法,其特征在于,The AC/DC hybrid microgrid operation module conversion method according to claim 1, wherein所述交直流互联换流器PCS通过下式表示:The AC-DC interconnect converter PCS is represented by the following formula:式中:Pcon,AC表示变流器交流侧功率,逆变时为正,整流时为负;Pcon,DC分别表示变流器直流侧功率之和,ηinv和ηrec分别表示变流器逆变和整流的效率;Rinv和Rrec分别表示变流器逆变和整流的最大有功功率。 Where: P con, AC represents the AC side power of the converter, positive in the inverter, negative in the rectification; P con, DC respectively represent the sum of the DC side power of the converter, η inv and η rec respectively represent the current Inverter and rectification efficiency; R inv and R rec represent the maximum active power of the converter inverter and rectification, respectively.
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