Energy management and coordinated control method of photovoltaic direct-current microgrid

Abstract

The application discloses an energy management and coordinated control method of a photovoltaic direct-current microgrid, and relates to the technical field of microgrid control systems. The photovoltaic direct-current microgrid comprises a microgrid control system, a direct-current bus, a distributed photovoltaic power generation unit connected to the direct-current bus, an energy storage unit, and a load unit; the direct-current bus is connected to an alternating-current power grid through a grid-connected AC / DC conversion module; the microgrid control system collects output voltage and output current of the distributed photovoltaic power generation unit and a state of charge of the energy storage unit, divides the output voltage of the distributed photovoltaic power generation unit into different levels, controls the operation state of the photovoltaic direct-current microgrid according to the corresponding mode of the level and the state of charge of the energy storage unit, and keeps the power balance among the distributed photovoltaic power generation unit, the energy storage unit and the load unit in different modes. The application can effectively reduce the charging and discharging times of the energy storage unit, prolong the service life of the energy storage system, and improve the energy utilization efficiency of the photovoltaic direct-current microgrid system.

Description

Technical Field

[0001] This invention relates to the field of DC microgrid technology, and more specifically to a method for energy management and coordinated control of a photovoltaic DC microgrid. Background Technology

[0002] The output of photovoltaic (PV) power generation systems is affected by solar irradiance and numerous weather factors, resulting in randomness and volatility in power output. Large-scale PV grid connection can impact the grid, affecting its reliability and stability. Constructing DC microgrids with PV power generation as the main component, and utilizing energy storage units within the microgrid to smooth or manage power output fluctuations, has become a crucial development direction for PV grid-connected technology. Microgrids integrate distributed power sources, energy storage devices, and loads into controllable, independent units. They can work collaboratively with the main grid and also possess the ability to operate autonomously off-grid, making them an important way to improve the stability and grid connection capability of distributed PV power generation systems.

[0003] In a photovoltaic (PV) DC microgrid system, PV power generation units are the primary power supply units, while energy storage units are used to mitigate power fluctuations. Due to the spatiotemporal instability of solar energy resources, PV power output exhibits intermittent and polygonal characteristics. Furthermore, PV systems typically operate in MPPT (Multi-Level Photovoltaic) mode and therefore lack the ability to regulate output power. These factors combined lead to large-scale fluctuations in bus voltage and power imbalances within the DC microgrid, thus reducing system stability. In addition, to ensure stable power supply to the load in a PV DC microgrid, the capacity of energy storage units needs to increase as the proportion of PV power increases. However, energy storage units have higher investment costs and shorter lifespans than PV units. Therefore, how to manage and coordinate the energy of a PV DC microgrid, enabling PV power generation units to regulate their output power to partially fulfill the functions of energy storage units or reduce energy storage capacity and extend its lifespan, is one of the key issues that needs to be addressed in DC microgrids. Summary of the Invention

[0004] In view of the problems and defects pointed out in the background art, the present invention aims to provide an energy management and coordinated control method for photovoltaic DC microgrids, so as to reduce the capacity configuration of energy storage units in photovoltaic DC microgrids and extend their service life.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for energy management and coordinated control of a photovoltaic DC microgrid, wherein the photovoltaic DC microgrid includes a microgrid control system, a DC bus, and distributed photovoltaic power generation units, energy storage units, and load units connected to the DC bus. The DC bus is connected to the AC grid through a grid-connected AC / DC conversion module. The microgrid control system collects the output voltage and output current of the distributed photovoltaic power generation units and the state of charge of the energy storage units, and classifies the collected output voltage of the distributed photovoltaic power generation units into levels. Based on the level and combined with the state of charge of the energy storage units, the system adopts corresponding modes to control the operation of the photovoltaic DC microgrid. The power of the distributed photovoltaic power generation units, energy storage units, and load units remains balanced under different modes.

[0006] Preferably, the method for controlling the operating status of the photovoltaic DC microgrid by adopting a corresponding mode based on its hierarchical level and the state of charge of the energy storage unit is as follows: when ,and In this mode, the photovoltaic DC microgrid is in grid-connected status, while distributed photovoltaic power generation units and energy storage units are in standby mode. The power of the load units is obtained from the AC grid, and the DC bus voltage is maintained by the external grid. The power balance equation in this mode is: ; when ,and In this mode, a load control mode is adopted. Under this mode, the photovoltaic DC microgrid is in an off-grid state, the distributed photovoltaic power generation units are in standby mode, the energy storage units discharge through adaptive droop control, and the DC bus voltage is controlled by the energy storage units. The power balance equation in this mode is: ; when ,and In this mode, the energy storage control mode is adopted. Under this mode, the photovoltaic DC microgrid is in an off-grid state, the distributed photovoltaic power generation units use MPPT control, the energy storage units discharge through adaptive droop control, and the DC bus voltage is controlled by the energy storage units. The power balance equation in this mode is: ; when At this time, a photovoltaic power generation control mode is adopted. In this mode, the photovoltaic DC microgrid is in an off-grid state, and the distributed photovoltaic power generation unit adopts constant voltage control to continuously supply power to the load and energy storage unit and ensure the power supply to the load. The energy storage unit selects charging or standby mode according to the state of charge: when When the energy storage unit is charged, When the energy storage unit is in standby mode, the DC bus voltage is maintained by the distributed photovoltaic power generation unit; the power balance equation in this mode is: ; in, The output voltage of the distributed photovoltaic power generation unit is collected. To collect the state of charge of the energy storage unit, This is the first critical voltage value. This is the second critical voltage value, and ; This refers to the minimum critical state of charge of the energy storage unit. This represents the maximum critical state of charge of the energy storage unit. The power consumed by the load unit. The power supplied by the AC power grid to the load. This refers to the discharge power of the energy storage unit. This refers to the output power of the distributed photovoltaic power generation unit.

[0007] Preferably, the microgrid control system for critical values , , , The selection is based on the following formula: ; in, The rated output voltage of the photovoltaic power generation unit. This refers to the output current of the distributed photovoltaic power generation unit. This represents the line impedance.

[0008] Compared with the prior art, the present invention has the following advantages: This invention provides an energy management and coordinated control method for a photovoltaic DC microgrid based on the output voltage of distributed photovoltaic (PV) power generation units and the load status of energy storage units. The method switches the control mode of the PV DC microgrid according to the output voltage of the distributed PV power generation units and the load status of the energy storage units, while maintaining power balance among the distributed PV power generation units, energy storage units, and load units. This invention can effectively reduce the number of charge-discharge cycles of energy storage units, extend the lifespan of energy storage systems, and improve the energy utilization efficiency of the PV DC microgrid system. Attached Figure Description

[0009] Figure 1 The photovoltaic DC microgrid structure provided by this invention; Figure 2 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0011] Figure 1The photovoltaic DC microgrid structure provided by this invention, such as Figure 1 As shown, the photovoltaic DC microgrid provided by this invention includes a DC bus, a microgrid control system, multiple distributed photovoltaic power generation units, multiple energy storage units, and multiple load units. The distributed photovoltaic power generation units are connected to the DC bus via unidirectional DC / DC converters, the energy storage units are connected to the DC bus via bidirectional DC / DC converters, and the multiple load units are connected to the DC bus via unidirectional DC / DC converters or unidirectional AC / DC inverters. The DC bus is connected to the AC grid via bidirectional AC / DC inverters. All unidirectional DC / DC converters, bidirectional DC / DC converters, unidirectional AC / DC inverters, and bidirectional AC / DC converter modules are controlled by the microgrid control system.

[0012] The microgrid control system sets two critical voltage values ​​to divide the output voltage of the distributed photovoltaic power generation unit into three voltage levels. This is the first critical voltage value. This is the second critical voltage value, and At the same time, two critical values ​​are set for the state of charge of the energy storage unit. This refers to the minimum critical state of charge of the energy storage unit. This represents the maximum critical state of charge of the energy storage unit. In this embodiment, the microgrid control system addresses four critical values. , , , The selection is determined based on the following formula: ; in, The rated output voltage of the photovoltaic power generation unit. This refers to the output current of the distributed photovoltaic power generation unit. This represents the line impedance.

[0013] Figure 2 This is a schematic diagram of the method flow of the present invention, such as... Figure 2 As shown, firstly, the microgrid control system collects the output voltage and output current of the distributed photovoltaic power generation units and the state of charge of the energy storage units. It then divides the collected output voltage of the distributed photovoltaic power generation units into levels and controls the operation of the photovoltaic DC microgrid according to the level and the state of charge of the energy storage units. The power among the distributed photovoltaic power generation units, energy storage units and load units remains balanced under different modes.

[0014] The specific switching conditions and control methods for each mode are as follows: when ,and In this mode, the microgrid control system keeps the photovoltaic DC microgrid in grid-connected mode, while the distributed photovoltaic power generation units and energy storage units are in standby mode. The load units obtain power from the AC grid, and the DC bus voltage is maintained by the AC grid. The power balance equation in this mode is: .

[0015] when ,and In this mode, a load control mode is adopted. Under this mode, the microgrid control system keeps the photovoltaic DC microgrid in an off-grid state, the distributed photovoltaic power generation units are in standby mode, the energy storage units discharge through adaptive droop control, and the DC bus voltage is controlled by the energy storage units. The power balance equation in this mode is: .

[0016] when ,and In this mode, an energy storage control mode is adopted. Under this mode, the microgrid control system keeps the photovoltaic DC microgrid in an off-grid state. Distributed photovoltaic power generation units use MPPT control, and the energy storage unit discharges through adaptive droop control. This smooths the output power of the distributed photovoltaic power generation units and compensates for the power shortage of the load units. The load units are in normal operating condition, and the DC bus voltage is controlled by the energy storage unit. The power balance equation in this mode is: .

[0017] when At this time, a photovoltaic power generation control mode is adopted. In this mode, the microgrid control system controls the photovoltaic DC microgrid to be in an off-grid state. The distributed photovoltaic power generation unit adopts constant voltage control to continuously supply power to the load and energy storage unit and ensure the power supply to the load. The energy storage unit selects charging or standby mode according to the state of charge. When the energy storage unit is charged, When the energy storage unit is in standby mode and the load unit is in normal operation, the DC bus voltage is maintained by the distributed photovoltaic power generation unit; the power balance equation in this mode is: .

[0018] Parameter definition: where, This refers to the output voltage of the distributed photovoltaic power generation unit. The state of charge of the energy storage unit. This is the first critical voltage value. This is the second critical voltage value, and ; This refers to the minimum critical state of charge of the energy storage unit. This represents the maximum critical state of charge of the energy storage unit. The power consumed by the load unit. The power supplied by the external power grid to the load. This refers to the discharge power of the energy storage unit. This refers to the output power of the distributed photovoltaic power generation unit.

[0019] This invention proposes an energy management and coordinated control method for a photovoltaic (PV) DC microgrid. Based on the output voltage of the PV power generation unit and the state of charge (SOC) of the energy storage unit, and since the output voltage and power of the PV power generation unit are proportional to solar irradiance, the method manages and coordinates the energy of the PV DC microgrid based on the power output characteristics of the PV power generation unit. Under high irradiance conditions, when the PV power generation unit outputs high power, it employs constant voltage control to output power, and the bus voltage is controlled by the PV power generation unit. Under moderate irradiance conditions, when the PV power generation unit outputs low power, it uses MPPT control to ensure maximum power output, while the energy storage unit smooths out the PV power output; both work together to control the DC bus voltage. Under low irradiance conditions, when the PV power generation unit has no output power, it is in standby mode, and the energy storage unit outputs power to ensure microgrid operation and control the DC bus voltage. This invention effectively reduces the number of charge / discharge cycles of the energy storage unit, extends the lifespan of the energy storage system, and improves the energy utilization efficiency of the PV DC microgrid system.

[0020] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for energy management and coordinated control of a photovoltaic DC microgrid, characterized in that, The photovoltaic DC microgrid includes a microgrid control system, a DC bus, and distributed photovoltaic power generation units, energy storage units, and load units connected to the DC bus. The DC bus is connected to the AC grid through a grid-connected AC / DC conversion module. The microgrid control system collects the output voltage and current of the distributed photovoltaic power generation units and the state of charge of the energy storage units. It then classifies the collected output voltages of the distributed photovoltaic power generation units into levels and controls the operation of the photovoltaic DC microgrid according to the level and the state of charge of the energy storage units. The power of the distributed photovoltaic power generation units, energy storage units, and load units remains balanced under different modes.

2. The energy management and coordinated control method for photovoltaic DC microgrids according to claim 1, characterized in that, The method for controlling the operation status of photovoltaic DC microgrids by adopting corresponding modes based on their hierarchical level and the state of charge of energy storage units is as follows: when ,and In this mode, the photovoltaic DC microgrid is in grid-connected status, while distributed photovoltaic power generation units and energy storage units are in standby mode. The power of the load units is obtained from the AC grid, and the DC bus voltage is maintained by the external grid. The power balance equation in this mode is: ; when ,and In this mode, a load control mode is adopted. Under this mode, the photovoltaic DC microgrid is in an off-grid state, the distributed photovoltaic power generation units are in standby mode, the energy storage units discharge through adaptive droop control, and the DC bus voltage is controlled by the energy storage units. The power balance equation in this mode is: ; when ,and In this mode, the energy storage control mode is adopted. Under this mode, the photovoltaic DC microgrid is in an off-grid state, the distributed photovoltaic power generation units use MPPT control, the energy storage units discharge through adaptive droop control, and the DC bus voltage is controlled by the energy storage units. The power balance equation in this mode is: ; when At this time, a photovoltaic power generation control mode is adopted. In this mode, the photovoltaic DC microgrid is in an off-grid state, and the distributed photovoltaic power generation unit adopts constant voltage control to continuously supply power to the load and energy storage unit and ensure the power supply to the load. The energy storage unit selects charging or standby mode according to the state of charge: when When the energy storage unit is charged, When the energy storage unit is in standby mode, the DC bus voltage is maintained by the distributed photovoltaic power generation unit; the power balance equation in this mode is: ; in, The output voltage of the distributed photovoltaic power generation unit is collected. To collect the state of charge of the energy storage unit, This is the first critical voltage value. This is the second critical voltage value, and ; This refers to the minimum critical state of charge of the energy storage unit. This represents the maximum critical state of charge of the energy storage unit. The power consumed by the load unit. The power supplied by the AC power grid to the load. This refers to the discharge power of the energy storage unit. This refers to the output power of the distributed photovoltaic power generation unit.

3. The energy management and coordinated control method for photovoltaic DC microgrids according to claim 2, characterized in that, The microgrid control system for critical values , , , The selection is based on the following formula: ； in, This refers to the rated output voltage of the photovoltaic power generation unit. This refers to the output current of the distributed photovoltaic power generation unit. This represents the line impedance.

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