A multi-control strategy for coordinated optimization control of microgrid energy

Abstract

The present invention discloses a multi-control strategy for coordinated optimization control of microgrid energy, including: the microgrid is provided with two sets of energy storage devices; a microgrid control strategy is set to optimize the control of the microgrid through the microgrid control strategy; the microgrid control strategy includes: the microgrid control strategy 1 is to discharge the first energy storage device during the peak period of the electricity price through the objective function and charge the first energy storage device during the valley period of the electricity price; Min(πTPSC - πTPSD), where πT represents the dynamic electricity price; PSC represents the energy storage charging power; PSD represents the energy storage discharging power; the microgrid control strategy 2 is to purchase electricity from the grid through the objective function when the first energy storage device is operating; Min(πTPUtility), where PUtility represents the electric energy purchased from the grid; the present invention focuses on the coordinated optimization of the power grid, wind power and energy storage, improves the elasticity of the power system, can promote the integration of renewable energy, and saves the transmission cost of the multi-control strategy for coordinated optimization of microgrid energy.

Description

Technical Field

[0001] The present invention relates to the technical field of microgrid control, and in particular to a multi-control strategy microgrid energy coordination and optimization control method. Background Art

[0002] The concept of microgrid can promote enterprises and users to reasonably utilize renewable energy, reduce environmental pollution, save the operation cost of the power grid, and also save the electricity bills of users, bringing considerable economic and environmental benefits to society. Different from the traditional large power grid, the microgrid has the following advantages: (1) When a variety of distributed power sources are connected to the power grid, it can promote the operation and regulation of the distribution network itself; (2) It can effectively reduce the reserve capacity in the microgrid; (3) It can provide cooling, heating and electrical energy to the load, greatly improving the energy utilization rate; (4) It provides reliable support for power supply to loads in remote areas; (5) It provides side voltage support for the load and improves the power quality; (6) When a fault occurs in the large power grid, the microgrid can continuously provide electrical energy for important loads, improving the reliability of power quality; (7) It improves the optimized utilization rate of distributed energy and effectively reduces environmental pollution. There are various types of renewable energy in the microgrid multi-energy system, such as wind energy, light energy, tidal energy, etc. Developing the microgrid multi-energy system can promote the development of smart grid and the rational utilization of energy structure.

[0003] The research on microgrid optimization and control technology can ensure the safe and stable operation of the microgrid. There are many types and different specifications of distributed power sources connected in the microgrid, which will have a great impact on the safe operation of the microgrid. This requires reasonable configuration of the power sources. In addition, there are uncontrollable devices such as photovoltaic cells and wind turbines, as well as schedulable devices such as micro gas turbines, fuel cells, and energy storage devices in the distributed energy of the microgrid. How to reasonably arrange the power output of the power sources is the key to ensuring the safe and economic operation of the microgrid. When the microgrid is operating in parallel, there is also a two-way energy interaction with the large power grid. Under the electricity market, the integrated energy microgrid needs to adjust the power generation plan of its own equipment according to different electricity market incentives to achieve an optimized operation control strategy.

[0004] A microgrid is a small power system that includes various forms of energy and can optimize the energy in a partial area to ensure the balance of output power. The traditional large power grid has the functions of power generation, power transmission, and power distribution, and the functions of the microgrid are similar. In recent years, with the continuous increase in the installed capacity of wind power, wind power generation is of great help in reducing power outages due to grid failures and improving the power supply reliability of renewable power sources. Most of the current energy management control strategies are to utilize wind resources as locally as possible to achieve local supply and demand in the system; some regions adopt as much renewable energy as possible, such as large-scale photovoltaic power generation, wind power generation, etc.; some adopt intelligent power consumption technologies to reduce the proportion of energy storage; and some consider both the profit control strategy of demand response and the profit control strategy of contract energy management. Summary of the Invention

[0005] The present invention provides a multi-control strategy microgrid energy coordination and optimization control method, which focuses on the collaborative optimization of the power grid, wind power, and energy storage, improves the elasticity of the power system, and can promote the integration of renewable energy and save transmission costs for the multi-control strategy microgrid energy coordination and optimization.

[0006] A multi-control strategy microgrid energy coordination and optimization control method includes the following steps:

[0007] 1) The microgrid is provided with two sets of energy storage devices;

[0008] 2) Set the microgrid control strategy, and optimize the control of the microgrid through the microgrid control strategy;

[0009] The microgrid control strategy includes:

[0010] The microgrid control strategy 1 is to discharge the first energy storage device during the peak period of electricity price through the objective function formula (1), and charge the first energy storage device during the valley period of electricity price;

[0011] Min(π T P SC -π T P SD ) (1)

[0012] Among them, π T represents the dynamic electricity price; P SC represents the charging power of the first energy storage device; P SD represents the discharging power of the first energy storage device;

[0013] The microgrid control strategy 2 is to purchase electricity from the power grid through the objective function formula (2) when the first energy storage device is operating;

[0014] Min(π T P Utility ) (8)

[0015] Among them, P Utility represents the electric energy purchased from the power grid;

[0016] The two sets of energy storage devices mentioned above include:

[0017] The first energy storage device, which is coupled with the wind turbine. The first energy storage device supplies power to the microgrid during normal operation and provides power to the microgrid during shutdown;

[0018] The second energy storage device, which is used as an emergency energy storage device. The electric energy stored in the second energy storage device is only used as an emergency resource to supply power to critical loads in the microgrid system, and the stored electric energy is not allowed to be sold back to the power grid.

[0019] The microgrid control strategy mentioned above also includes:

[0020] The microgrid control strategy 3 is to supply power to disaster-prone areas by pre-planning the electric energy of the second energy storage device according to the objective function formula (15), and to control the directional power supply of the second energy storage device after an emergency occurs;

[0021] Among them, π T represents the dynamic electricity price; I represents the number of energy storage stations in normal operation; E s represents the capacity (kWh) of the first energy storage device; E S,max represents the maximum capacity (kWh) of the first energy storage device; P SC represents the charging power of the first energy storage; P SD represents the discharging power of the first energy storage; k 1 represents the storage state of the second energy storage device; E ES represents the capacity (kWh) of the second energy storage device; E ES,max represents the maximum capacity (kWh) of the second energy storage device; P ESC Input rate (kW) of the second energy storage device; P ESD Output power (kW) of the second energy storage device.

[0022] The microgrid control strategy mentioned above also includes:

[0023] The microgrid control strategy 4 is that the fully charged first energy storage device and the second energy storage device are used as emergency resources to supply power to critical loads in the system during a power outage.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] The present invention establishes an accurate load prediction model and an electricity price pricing mechanism based on the actual operation conditions. The above two points are the basis for the coordinated control of the present invention. According to the actual operation, four different working modes are established, which can cover the complete usage scenarios; and a coordinated optimization control model applicable to the four different scenarios is established. During actual operation, the operation mode that conforms to the current scenario is automatically selected from the four operation modes to achieve the optimal energy coordinated control. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a flow chart of a coordinated optimization algorithm for a multi-control strategy microgrid;

[0027] Figure 2 Simulation results of the energy coordinated optimization control strategy for a multi-mode microgrid, where, a is the bus voltage, b is the source-load power, c is the current of the energy storage device, and d is the exchanged power of the grid-connected converter. DETAILED DESCRIPTION OF THE INVENTION

[0028] As Figure 1 shown, first, by statistically analyzing the historical data, the law of load change is found to establish a load prediction model; secondly, by combining the peak and off-peak electricity pricing, hourly pricing is created for the four different working modes; according to the specific scenario, different operation modes are automatically selected to achieve the optimal energy coordinated control. A multi-control strategy microgrid energy coordinated optimization control strategy includes:

[0029] (1) The microgrid is provided with two sets of energy storage devices: Energy storage 1: An energy storage device coupled with a wind turbine, which supplies power to the grid during normal operation and provides power during shutdown. By default, this energy storage device is always in operation; Second energy storage device: The electric energy stored in this energy storage device is only used as an emergency resource to supply power to the critical loads in the system, and the stored electric energy is not allowed to be sold back to the grid.

[0030] (2) Four microgrid control strategies are set, and the four control strategies basically cover all usage scenarios, and different optimization goals are achieved in different scenarios.

[0031] (3) Control strategy 1: During the peak period of electricity price, the first energy storage device discharges, and during the valley period of electricity price, the first energy storage device charges to make a profit through the price difference; its objective function is: Min(π T P SC -π T P SD )

[0032] (4) Control strategy 2: During the peak period of electricity consumption, the power generated by the microgrid itself cannot meet the usage of the microgrid, and electricity needs to be purchased from the grid; its objective function is: Min(π T P Utility )

[0033] (5) Control Strategy 3: By pre-planning which disaster-prone areas the electrical energy stored in the energy storage is supplied to, after an emergency occurs, the energy storage can be controlled to supply power in a more rapid manner; its objective function is:

[0034] (6) Control Strategy 4: The fully charged energy storage device is used as an emergency resource during a large-scale power outage to supply power to critical loads in the system.

[0035] Example 1

[0036] Assume that advance scheduling is carried out at a granularity of one hour per day. We propose a scheduling model that includes four operation control strategies, which can cover the complete usage scenarios, and an optimal scheduling model is established respectively.

[0037] Control Strategy 1 and Control Strategy 2 can utilize the energy storage to make a profit.

[0038] 1) Control Strategy 1 operates during the normal operation of the power grid and can freely charge and discharge. The objective function can minimize the restoration cost (Restoration cost: the difference between the price of battery charging and discharging at a higher electricity price).

[0039] The objective function is expressed as in Equation (1):

[0040] Min(π T P SC -π T P SD ) (1)

[0041] Where, π T represents the dynamic electricity price ($ / kWh); P SC represents the charging power of the first energy storage device (kW); P SD represents the discharging power of the first energy storage device (kW);

[0042] The maximum value of the charging of the first energy storage device is represented by the constraint in Equation (2):

[0043] ηP SC =E S,max (2)

[0044] Where, η represents the storage efficiency of the first energy storage device; E S,max represents the maximum capacity of the first energy storage device (kWh);

[0045] The charge-discharge balance is represented by Equation (3):

[0046] ηP SC -ηP SD =0 (3)

[0047] The constraint of the charging power is expressed as in Equation (4):

[0048] 0 ≤ P SC ≤ P S,max (4)

[0049] where P S,max represents the maximum input / output power (kW) of the first energy storage device;

[0050] The constraint of the discharging power of the first energy storage device is expressed as in Equation (5):

[0051] 0 ≤ P SD ≤ P S,max (5)

[0052] The capacity of the first energy storage device at time 0 is 0, as shown in Equation (6):

[0053] E s (t = 0) = 0 (6)

[0054] The capacity of the first energy storage device at time T (when the energy storage is discharged completely) is 0, as shown in Equation (7):

[0055] E s (t = T) = 0 (7)

[0056] where E s represents the capacity (kWh) of the first energy storage device;

[0057] 2) Control strategy 2 operates in a scenario where power needs to be purchased from the grid, minimizing the power purchase cost while meeting the demand.

[0058] The objective function is expressed as in Equation (8):

[0059] Min(π T P Utility ) (8)

[0060] where P Utility represents the electrical energy purchased from the grid (kW);

[0061] The balance among the electrical energy purchased from the grid, the charging / discharging of the first energy storage device, and the electrical energy demanded by the load is expressed as in Equation (9):

[0062] P Utility - P SC + P SD - P Demand = 0 (9)

[0063] where P Demand represents the power required by the load (kW);

[0064] The charge / discharge balance of the first energy storage device operating normally is expressed as in Equation (10):

[0065] (ηI)P SC -(I / n)P SD =0 (10)

[0066] Wherein, I represents the number of energy storage stations operating normally; n represents the number of energy storage stations;

[0067] The constraint of the charging power is expressed as in Equation (11):

[0068] 0≤P SC ≤P S,max (11)

[0069] Wherein, P S,max represents the maximum input / output power (kW) of the first energy storage device;

[0070] The constraint of the discharging power is expressed as in Equation (12):

[0071] 0≤P SD ≤P S,max (12)

[0072] The capacity of the first energy storage device at time 0 is 0, as shown in Equation (13):

[0073] E s (t=0)=0 (13)

[0074] The capacity of the first energy storage device at time T (when the energy storage is discharged completely) is 0, as shown in Equation (14):

[0075] E s (t=T)=0 (14)

[0076] Users can choose the charging state (SOC) of the energy storage at the end of a day. If no choice is made, the results of Control Strategy 1 and Control Strategy 2 are the same. Under these two control strategies, the energy storage system coupled with the wind turbine system can operate independently, and the energy can be fed back to the power grid during peak electricity price periods to achieve maximum benefits.

[0077] 3) Control Strategy 3: The energy storage supplies power in a targeted manner during natural disasters. There are two solutions for the excess production of renewable energy. One is to consume it through flexible loads, and the other is to store electrical energy in energy storage facilities. Pre-plan which disaster-prone areas the electrical energy stored in the energy storage devices will supply power to. After an emergency occurs, control can be carried out more quickly, and the stored electrical energy can be redistributed according to demand to reduce overload and stabilize the system.

[0078] To minimize the electricity cost within the microgrid, the objective function is as shown in Equation (15):

[0079]

[0080] Among them, π T represents the dynamic electricity price; I represents the number of energy storage stations operating normally; E s represents the capacity (kWh) of the first energy storage device; E S,max represents the maximum capacity (kWh) of the first energy storage device; P SC represents the charging power of the first energy storage; P SD represents the discharging power of the first energy storage; k 1 represents the storage state of the second energy storage device; E ES represents the capacity (kWh) of the second energy storage device; E ES,max represents the maximum capacity (kWh) of the second energy storage device; P ESC Input rate (kW) of the second energy storage device; P ESD Output power (kW) of the second energy storage device.

[0081] Constraints for purchasing electric energy from the power grid, wind turbine power generation, charging / discharging of the first energy storage device, charging / discharging of the second energy storage device, and load demand balance are as shown in (16):

[0082] P Utility +(k 2 I)P Wind -P SC +P SD +(k 1 I)(-P ESC +P ESD )-P Demand =0 (16)

[0083] Among them, P Wind wind power (kW); P ESC Input rate (kW) of the second energy storage device; P ESD Output power (kW) of the second energy storage device; k 2 represents the operating state of the wind power system.

[0084] When the storage state is 1, the constraint for charge-discharge balance of the second energy storage device is as shown in (17):

[0085] (η E I)P ESC -(I / η E )P ESD =0→if(k 1 =1) (17)

[0086] Among them, η E efficiency of the second energy storage device;

[0087] Constraints for the input of the second energy storage device at different times are shown in Equation (18):

[0088]

[0089] The constraint of the charging power is expressed as follows:

[0090] 0 ≤ P SC ≤ P S,max (19)

[0091] where P S,max represents the maximum input / output power of the energy storage (kW);

[0092] The constraint of the discharging power is expressed as in Equation (20):

[0093] 0 ≤ P SD ≤ P S,max (20)

[0094] The constraint of the output of the second energy storage device is expressed as in Equation (21):

[0095] 0 ≤ P ESD ≤ P ES,max (21)

[0096] where P ES,max represents the maximum input power of the second energy storage device (kW);

[0097] The constraint of the capacity of the first energy storage device is expressed as in Equation (22):

[0098] 0 ≤ E S ≤ E S,max (22)

[0099] where E S,max represents the maximum capacity of the first energy storage device (kWh);

[0100] The constraint of the capacity of the second energy storage device is expressed as in Equation (23):

[0101] 0 ≤ E ES ≤ E ES,max (23)

[0102] where E ES represents the capacity of the second energy storage device (kWh);

[0103] 4) Control strategy 4: Operate during power outages. In the event of a typhoon or other natural disaster weather, if a large-scale power outage occurs, disconnect the load from the system; the fully charged arbitrage storage is used as an emergency resource to supply power to critical loads in the system.

[0104] Test case 1

[0105] The simulation conditions are as follows: the rated voltage of the DC bus is 380V, and each voltage difference of 10V is a voltage level; the maximum power of the two groups of photovoltaic cells are 30kW and 40kW respectively, and the corresponding droop coefficients are 0.12 and 0.09; the rated power of the wind power generation unit is 50kW, and the rated wind speed is 10m / s; the rated power of the two groups of energy storage devices is 10Kw, the upper and lower limits of SOC are 90% and 10%, the virtual resistance R0 is 0.8, the power exponent n of the regulation factor is 10; the virtual capacitance corresponding to the super capacitor is 0.7587.

[0106] Set the initial wind speed to 9.5m / s, the load to 100kW, the SOC of battery pack 1 to 48%, the SOC of the second battery pack to 50%, connect a 10KW load after 5s, and increase the wind speed to 10m / s at 15s. The simulation results are as Figure 2 shown.

[0107] Figure 2 follows: from 0 to 10.724s, the energy storage device unit operates under control strategy 3, and the charging power of SOC energy storage 1 is relatively large; from 10.724 to 15s, the energy storage device unit operates under control strategy 1(2). At this time, the increase in light intensity leads to an increase in the photovoltaic output power, and the surplus power of the system cannot be completely consumed, resulting in an increase in the DC bus voltage, but it is not higher than 390V; from 15 to 20s, the increase in wind speed at this time leads to an increase in the output power of the wind power generation unit, and the surplus power of the system continues to increase. The DC bus voltage is higher than 390V, and the surplus power is incorporated into the AC grid with a unity power factor, and the bus voltage is stabilized at 392V, achieving benefits.

[0108] Through simulation, the effectiveness of the multi-mode microgrid energy coordination and optimization control strategy of the present invention has been fully verified.

Claims

1. A multi-control strategy for coordinated optimization control of microgrid energy, characterized in that, it includes: The microgrid is equipped with two sets of energy storage devices, and the two sets of energy storage devices include: The first energy storage device, which is coupled with the wind turbine. The first energy storage device supplies power to the microgrid during normal operation and provides power to the microgrid during downtime. The second energy storage device, which is used as an emergency energy storage device. The electric energy stored in the second energy storage device is only used as an emergency resource to supply power to critical loads in the microgrid system, and the stored electric energy is not allowed to be sold back to the grid. Set the microgrid control strategy to optimize the control of the microgrid through the microgrid control strategy; The microgrid control strategy includes: Microgrid control strategy 1 is to discharge the first energy storage device during the peak period of electricity price through the objective function formula (1) and charge the first energy storage device during the valley period of electricity price; (1) Among them, represents the dynamic electricity price; represents the first energy storage charging power; represents the first energy storage discharging power; Microgrid control strategy 2 is to purchase electricity from the grid through the objective function formula (2) when the first energy storage device is operating; (8) Among them, represents the electric energy purchased from the power grid; Microgrid control strategy 3 is to supply power to disaster-prone areas by pre-planning the electric energy of the second energy storage device according to the objective function formula (15), and control the second energy storage device to supply power directionally after an emergency occurs; (15)； Among them, represents the dynamic electricity price; represents the number of energy storage stations operating normally; represents the capacity of the first energy storage device; represents the maximum capacity of the first energy storage device; represents the first energy storage charging power; represents the first energy storage discharge power; represents the storage state of the second energy storage device; represents the capacity of the second energy storage device; represents the maximum capacity of the second energy storage device; Input rate of the second energy storage device; Output power of the second energy storage device; Microgrid control strategy 4 is that the fully charged first energy storage device and the second energy storage device are used as emergency resources to supply power to critical loads in the system during a power outage.

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