CN109866643B - Light storage and charging direct-current micro-grid control method - Google Patents
Light storage and charging direct-current micro-grid control method Download PDFInfo
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/7072—Electromobility specific charging systems or methods for batteries, ultracapacitors, supercapacitors or double-layer capacitors
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T90/00—Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02T90/10—Technologies relating to charging of electric vehicles
- Y02T90/12—Electric charging stations
Abstract
The invention provides a light storage and charging direct-current micro-grid control method, and belongs to the field of direct-current micro-grid control. Firstly, judging the voltage of a direct current bus, and selecting a control mode in which a direct current microgrid is positioned; in the mode 1, the photovoltaic battery adopts a maximum power tracking output mode, the energy storage battery adopts a constant voltage mode to control the bus voltage, and the electric automobile adopts a super fast charging/fast charging mode; in the mode 2, the photovoltaic battery adopts a constant voltage mode to control the bus voltage, the energy storage battery adopts a current-limiting charging mode, and the electric vehicle charging adopts a super fast charging/fast charging mode; in the mode 3, the photovoltaic battery adopts a maximum power tracking output mode, the energy storage battery adopts a current-limiting constant voltage mode to control the bus voltage, and the electric automobile adopts a slow charging mode for charging; in the mode 4, the states of the photovoltaic cell and the energy storage cell are the same as those in the mode 3, and the electric vehicle adopts a blocking mode for charging. The invention can control the bus voltage under various situations and ensure the stable operation of the light storage and charging direct current micro-grid.
Description
Technical Field
The invention belongs to the field of direct-current microgrid control, and particularly relates to a light storage and charging direct-current microgrid control method.
Background
In 2030, the sales volume of new energy automobiles in China reaches 40% -50% of the total sales volume of automobiles in China, meanwhile, the remaining volume of the new energy automobiles reaches 8 million-1 hundred million vehicles, and the energy of the batteries of the 8 million-1 hundred million electric automobiles reaches about 50 hundred million degrees of electricity, so that the large-scale high-power charging of the electric automobiles inevitably brings huge impact on a power grid, influences the peak-valley balance of the power grid, and threatens the stable operation of the power grid. As a novel distributed power distribution organization form and an energy structure, the micro-grid can relieve the influence of large-scale electric automobile charging on a large power grid, adapts to the characteristics of randomness and dispersity of electric automobile charging, and is an important solution and development trend for electric automobile charging infrastructure construction between cities.
The proportion of non-fossil energy power generation in China in 2030 is up to 50%, the total amount of non-fossil energy installed newly added in China in 2018 is up to 7000 ten thousand kilowatts, but the problems of energy loss, electric energy quality and the like caused by the fact that large-scale distributed renewable energy is connected to a power grid can be solved by the technology of the renewable energy micro-power grid, so that the renewable energy micro-power grid with the synergistic interaction function is developed for charging electric automobiles, and the renewable energy micro-power grid is not only a development intersection point of electrified transportation and low-carbon energy in China, but also a common solution for the problems of large-scale electric automobile charging and large-scale renewable energy grid connection.
Compared with an alternating-current microgrid, the direct-current microgrid mainly has the following advantages in three aspects: in the aspect of efficiency of the micro-grid system, the photovoltaic cell, the energy storage cell and the electric vehicle are all direct-current charging and discharging equipment, and compared with an alternating-current network, the direct-current micro-grid system can reduce energy loss caused by power electronic equipment in the process of electric energy conversion, improve the energy utilization rate and reduce equipment investment; in the aspect of reliable operation of the microgrid, compared with an alternating-current microgrid, the direct-current microgrid is more convenient to realize the problem of simultaneous grid connection of a plurality of distributed power supplies, the problem of synchronization of frequency and phase among all power supplies does not need to be considered, and the stable and reliable operation of the system can be ensured only by controlling the voltage of the direct-current microgrid; in the aspect of the electric energy quality of the microgrid, because the direct-current microgrid does not have factors such as reactive power, harmonic waves and the like which influence the electric energy quality, the direct-current microgrid is more suitable for coping with the application scenes of renewable energy power generation with high volatility and intermittence and sensitive load sudden change, and can provide electric energy supply with higher quality. Therefore, the direct-current microgrid is more suitable for serving as a solution of a light storage and charging system for charging electric vehicles.
In order to cope with complex and changeable working conditions in the microgrid system, ensure the coordinated and stable operation among all parts in the microgrid system and the reliable electric energy supply to loads in the microgrid, the direct-current microgrid system needs to make a corresponding reasonable and effective control strategy, maintain the energy balance between the stability of the bus voltage of the direct-current microgrid and the power supply load and ensure the smooth switching among different modes. Therefore, the control technology of the direct-current microgrid is an important technology in a direct-current microgrid system and is a basic guarantee for stable operation of the direct-current microgrid. At present, the number of patents in the field of direct-current micro-grid control is small, and particularly, the number of patents in the field of direct-current micro-grid control for charging electric vehicles is more limited. Patent 201611073301.2 adopts a self-adaptive droop control method, and through a local distributed algorithm, the average voltage of the whole network is iteratively evaluated, and a target virtual resistor meeting the requirements of current sharing and voltage regulation is dynamically searched.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a method for controlling a light storage and charging direct-current micro-grid. The invention is oriented to the electric vehicle charging station for large-scale electric vehicle super quick charging, the specific reference voltage is set in different modes, the operation is simpler and more reliable, the set parameters of the controller do not need to be changed in real time, the invention is suitable for the existing controller products, and the stable operation of the light storage and charging direct current micro-grid can be maintained under all the scenes.
The invention provides a method for controlling a light storage and charging direct current micro-grid, which is characterized by comprising the following steps of:
1) judging the voltage of the direct current bus, and selecting a control mode of the direct current microgrid:
if the voltage of the direct current bus is more than 600V and less than 700V, entering the control mode 1 of the step 2);
if the voltage of the direct current bus is larger than or equal to 700V, entering a control mode 2 of the step 3);
if the voltage of the direct current bus is larger than 550V and smaller than or equal to 600V, entering a control mode 3 of the step 4);
if the voltage of the direct current bus is less than or equal to 550V, entering a control mode 4 of the step 5);
2) in the control mode 1, the bus reference voltage is 650V, the photovoltaic cell adopts a maximum power tracking output mode, the energy storage cell adopts a constant voltage mode to control the bus voltage, and the electric automobile adopts a super fast charge or fast charge mode;
the method comprises the following steps that a photovoltaic cell adopts a Maximum Power Point Tracking (MPPT) mode, a photovoltaic cell DC/DC controller collects output voltage and current signals of the photovoltaic cell, the output reference voltage of the photovoltaic cell is obtained through calculation of a MPPT algorithm, the difference value between the obtained output reference voltage of the photovoltaic cell and the actual output voltage of the photovoltaic cell is transmitted to a first PI controller in the photovoltaic cell DC/DC controller, the output reference current of the photovoltaic cell is obtained through calculation, the difference value between the output reference current of the photovoltaic cell and the actual output current of the photovoltaic cell is transmitted to a second PI controller in the photovoltaic cell DC/DC controller, and finally the difference value is used as the input of a Pulse Width Modulation (PWM) wave of the photovoltaic cell DC/DC through a photovoltaic cell current limiting link, so that the photovoltaic cell is controlled to output in the MPPT mode;
the energy storage battery adopts a constant voltage mode to control the bus voltage, the energy storage battery DC/DC controller collects the bus voltage, the difference value between the collected bus voltage and the bus voltage reference value is transmitted to a first PI controller in the energy storage battery DC/DC controller, the output reference current of the energy storage battery is obtained through calculation, the difference value between the output reference current of the energy storage battery and the actual output current of the energy storage battery is transmitted to a second PI controller in the energy storage battery DC/DC controller, and finally the difference value is used as the input of the PWM wave of the energy storage battery DC/DC through an energy storage battery current limiting link, so that the energy storage battery is controlled to output and control the bus voltage by adopting the constant voltage mode;
3) in the control mode 2, the bus reference voltage is 700V, the bus voltage is controlled by the photovoltaic battery in a constant voltage mode, the energy storage battery is in a current-limiting charging mode, and the electric vehicle is charged in a super fast charging or fast charging mode;
the method comprises the following steps that a photovoltaic cell controls bus voltage in a constant voltage mode, a photovoltaic cell DC/DC controller collects the bus voltage, the difference value between the collected bus voltage and a bus voltage reference value is transmitted to a first PI controller in the photovoltaic cell DC/DC controller, output reference current of the photovoltaic cell is obtained through calculation, the difference value between the output reference current of the photovoltaic cell and actual output current of the photovoltaic cell is transmitted to a second PI controller in the photovoltaic cell DC/DC controller, and finally a photovoltaic cell current limiting link is used as input of PWM waves of the photovoltaic cell DC/DC, so that the photovoltaic cell is controlled to output and control the bus voltage in the constant voltage mode;
the energy storage battery adopts a current-limiting charging mode, the energy storage battery DC/DC controller collects the SOC of the energy storage battery estimated by a battery management system of the energy storage battery, the charging reference current of the energy storage battery is calculated through a one-dimensional function between the charging reference current of the energy storage battery and the SOC of the energy storage battery, the difference value between the charging reference current of the energy storage battery and the actual charging current of the energy storage battery is transmitted to a second PI controller of the energy storage battery DC/DC controller, and then the current-limiting link of the energy storage battery is used as the input of a PWM wave of the DC/DC of the energy storage battery, so that the energy storage battery is controlled to adopt the;
4) in the control mode 3, the bus reference voltage is 600V, the photovoltaic battery adopts a maximum power tracking output mode, the energy storage battery adopts a current-limiting constant voltage mode to control the bus voltage, and the electric vehicle adopts a slow charging mode for charging;
the photovoltaic battery adopts a Maximum Power Point Tracking (MPPT) mode, the energy storage battery adopts a current-limiting constant voltage mode to control bus voltage, the energy storage battery outputs reference current by utilizing the difference value of the bus voltage and a bus voltage reference value and then through calculation of a first proportional-integral (PI) controller of the energy storage battery, then the energy storage battery outputs reference current by utilizing one-dimensional function calculation between the energy storage battery output reference current and the SOC of the energy storage battery, the minimum value of the two output reference current values is selected, the difference value of the minimum value and the actual output current of the energy storage battery is transmitted to a second PI controller in the DC/DC controller of the energy storage battery, and then the difference value is used as the input of a Pulse Width Modulation (PWM) wave of the DC/DC of the energy storage battery through a current-limiting link of;
5) in the control mode 4, the bus reference voltage is 550V, the photovoltaic battery adopts a maximum power tracking output mode, the energy storage battery adopts a current-limiting constant voltage mode to control the bus voltage, and the electric vehicle adopts a blocking mode for charging;
the working mode of the photovoltaic battery and the working mode of the energy storage battery are the same as the control mode 3, the electric automobile adopts a blocking mode in charging, the DC/DC controller of the charging pile collects bus voltage, when the bus voltage is reduced to 550V, the charging reference current of the electric automobile is converted into 0A from the slow charging reference current, and the charging load of the electric automobile is blocked, so that the bus voltage is prevented from further reducing.
The invention has the characteristics and beneficial effects that:
the invention can meet the quick charging requirement of the electric automobile under all conditions, can also maintain the stable operation of the direct-current microgrid system, does not need a central controller based on the bus voltage signal switching control mode, meets the working condition of plug and play, improves the reliability and robustness of the system, ensures the stable and reliable operation of the optical storage charging direct-current microgrid, and can also meet the control precision and capability requirements of the DC/DC controller in the current market.
The method for controlling the light storage and charging direct-current micro-grid is mainly applied to an electric vehicle charging station and can also be applied to other scenes of the light storage and charging direct-current micro-grid.
Drawings
FIG. 1 is a schematic representation of four modes in the process of the present invention.
Fig. 2 is a schematic diagram of a control strategy of the method of the present invention in the scenario of mode 1.
Fig. 3 is a schematic diagram of a control strategy of the method of the present invention in the scenario of mode 2.
Fig. 4 is a schematic diagram of a control strategy of the method of the present invention in the scenario of mode 3. (ii) a
Fig. 5 is a schematic diagram of a control strategy of the method of the present invention in the scenario of mode 4.
FIG. 6 is a diagram of simulation results for a transition from mode 1 to mode 2 in an embodiment of the present invention.
FIG. 7 is a graph of simulation results for a transition from mode 1 to mode 3 in an embodiment of the present invention.
FIG. 8 is a graph of simulation results for a transition from mode 3 to mode 4 in an embodiment of the present invention.
Detailed Description
The invention provides a method for controlling a light storage and charging direct current microgrid, and the method is further described in detail with reference to the accompanying drawings and specific embodiments. It should be understood that the specific examples described herein are for purposes of illustration only and are not intended to limit the invention.
The invention provides a method for controlling a light storage and charging direct current micro-grid, which comprises the following steps:
1) judging the voltage of the direct current bus, and selecting a control mode of the direct current microgrid:
if the voltage of the direct current bus is more than 600V and less than 700V, entering the control mode 1 of the step 2);
if the voltage of the direct current bus is larger than or equal to 700V, entering a control mode 2 of the step 3);
if the voltage of the direct current bus is larger than 550V and smaller than or equal to 600V, entering a control mode 3 of the step 4);
and if the direct current bus voltage is less than or equal to 550V, entering the control mode 4 of the step 5).
As shown in fig. 1, the present invention switches control modes based on a dc bus voltage signal, and Ubus is the dc bus voltage signal; the control modes of the invention comprise four modes of a mode 1, a mode 2, a mode 3 and a mode 4; in the control mode 1, the bus reference voltage is 650V, the photovoltaic cell adopts a maximum power tracking output mode, the energy storage cell adopts a constant voltage mode to control the bus voltage, and the electric automobile adopts a super fast charging/fast charging mode; in the control mode 2, the bus reference voltage is 700V, the bus voltage is controlled by the photovoltaic battery in a constant voltage mode, the energy storage battery is in a current-limiting charging mode, and the electric vehicle is charged in a super fast charging/fast charging mode; in the control mode 3, the bus reference voltage is 600V, the photovoltaic battery adopts a maximum power tracking output mode, the energy storage battery adopts a current-limiting constant voltage mode to control the bus voltage, and the electric vehicle adopts a slow charging mode for charging; in the control mode 4, the bus reference voltage is 550V, the photovoltaic cell adopts a maximum power tracking output mode, the energy storage cell adopts a current-limiting constant voltage mode to control the bus voltage, and the electric vehicle adopts a blocking mode for charging; the super quick charging mode, the quick charging mode and the slow charging mode are determined according to the charging power of the charging pile of the light storage charging system, no fixed charging power value exists, the charging power of the super quick charging mode is larger than 120kW, the quick charging mode is larger than 60kW, the slow charging mode is lower than 30kW, and the charging power of the blocking mode is 0 kW.
2) As shown in fig. 2, in a control mode 1 of the present invention, a Maximum Power Point Tracking (MPPT) mode is adopted by a photovoltaic cell, a DC/DC (direct current to direct current power converter) controller of the photovoltaic cell collects output voltage and current signals of the photovoltaic cell, an output reference voltage of the photovoltaic cell is calculated by a built-in MPPT algorithm (maximum power point tracking output algorithm), the MPPT algorithm adopted in this example is a variable step size disturbance observation method, a difference value between the output reference voltage of the photovoltaic cell obtained by the disturbance observation method and an actual output voltage of the photovoltaic cell is transmitted to a first PI controller built in the DC/DC controller of the photovoltaic cell, an output reference current of the photovoltaic cell is calculated, and a difference value between the output reference current of the photovoltaic cell and the actual output current of the photovoltaic cell is transmitted to a second PI controller in the DC/DC controller of the photovoltaic cell, the proportional coefficient and the integral coefficient of the first PI controller and the second PI controller are respectively 1 and 50 (the first PI controller is a voltage control link, and the second PI controller is a current control link). And finally, a current limiting link is used as the input of a PWM (pulse width modulation) wave of the DC/DC of the photovoltaic cell (the input of the PWM wave is a number between 0 and 1, and the current limiting link limits the input between 0 and 1), so that the photovoltaic cell is controlled to output in an MPPT mode. In the mode 1 of the invention, an energy storage battery (light storage and charge comprises a photovoltaic battery and an energy storage battery, the energy storage battery and the photovoltaic battery belong to a light storage and charge system together) adopts a constant voltage mode to control bus voltage, an energy storage battery DC/DC controller collects the bus voltage, transmits the difference value between the collected bus voltage and a bus voltage reference value to a first PI controller arranged in the energy storage battery DC/DC controller, calculates to obtain an output reference current of the energy storage battery, and transmits the difference value between the output reference current of the energy storage battery and the actual output current of the energy storage battery to a second PI controller arranged in the energy storage battery DC/DC controller, and the proportional coefficient and the integral coefficient of the first PI controller and the second PI controller are respectively 1 and 50 (the first PI controller is a voltage control link, and the second PI controller is a current control link). And finally, a current limiting link is used as the input of the PWM wave of the DC/DC of the energy storage battery, so that the energy storage battery is controlled to output the voltage of the control bus in a constant voltage mode.
The charging process of the electric vehicle comprises a pre-charging process and a formal charging process, when a charging interface of the electric vehicle is connected with a charging pile, a charging pile controller firstly acquires data of the voltage of a battery of the electric vehicle and the voltage of a DC/DC capacitor of the charging pile and starts to pre-charge the DC/DC capacitor of the charging pile, a pre-charging flow of the charging pile is controlled through a PI control link built in the charging pile DC/DC, the pre-charging flow is set to be 1A, when the difference value of the voltage of the DC/DC capacitor of the charging pile and the voltage of the battery of the electric vehicle is less than a set voltage threshold value, the voltage threshold value is set to be 2V, a pre-charging switch closes a pre-charging circuit and is disconnected, the charging pile starts to charge the electric vehicle with the set current, and in the formal charging process, the charging current of the electric automobile is gradually increased at a certain specific speed (0A/s-100A/s) from 0A until the maximum allowable charging current is reached, after the charging current reaches the maximum value, the electric automobile starts to be continuously charged at the maximum power until the voltage of the battery of the electric automobile reaches a preset upper limit, and the charging process is finished. The maximum charge current of the super fast charge is 288A in the example, the current increase rate is 72A/s, the maximum charge current of the fast charge is 96A, and the current increase rate is 24A/s.
3) As shown in fig. 3, in the control mode 2 of the present invention, the photovoltaic cell controls the bus voltage in a constant voltage mode, the bus voltage reference value is 700V, the photovoltaic cell DC/DC controller collects the bus voltage, and transmits a difference between the collected bus voltage and the bus voltage reference value to a first PI controller built in the photovoltaic cell DC/DC controller, calculates an output reference current of the photovoltaic cell, and transmits a difference between the output reference current of the photovoltaic cell and an actual output current of the photovoltaic cell to a second PI controller in the photovoltaic cell DC/DC controller, and a proportionality coefficient and an integral coefficient of the second PI controller are 1 and 50, respectively. And finally, the current limiting link is used as the input of the PWM wave of the DC/DC of the photovoltaic cell (the input of the PWM wave is a number between 0 and 1, and the current limiting link limits the input between 0 and 1), so that the photovoltaic cell is controlled to output and control the bus voltage in a constant voltage mode. In the control mode 2 of the invention, the energy storage battery adopts a current-limiting charging mode, the DC/DC controller of the energy storage battery collects the SOC (state of charge) of the energy storage battery estimated by a Battery Management System (BMS) of the energy storage battery, the charging reference current of the energy storage battery is obtained by calculating a table look-up function, which is a one-dimensional function between the charging reference current of the energy storage battery and the SOC of the energy storage battery, which is set manually, in this example, when the SOC of the energy storage battery is lower than 70%, the charging reference current of the energy storage battery is the maximum allowable charging current, in this example 410A, when the SOC of the energy storage battery reaches 70%, the charging current of the energy storage battery is limited, when the SOC of the energy storage battery reaches 90%, the energy storage battery is blocked to be charged, in the SOC interval of 70% -90%, the charging reference current of the energy storage battery is linearly reduced along with the SOC until the charging reference current is reduced to 0A. And transmitting the difference value between the obtained charging reference current of the energy storage battery and the actual charging current of the energy storage battery to a second PI controller of the DC/DC controller of the energy storage battery, wherein the proportional coefficient and the integral coefficient of the PI controller are respectively 1 and 50. And then a current-limiting link is used as the input of the PWM wave of the DC/DC of the energy storage battery, so that the energy storage battery is controlled to adopt a current-limiting charging mode.
4) As shown in fig. 4, in the control mode 3 of the present invention, the photovoltaic cell adopts a Maximum Power Point Tracking (MPPT) mode, the energy storage cell adopts a current-limiting constant voltage mode to control the bus voltage, the output reference current of the energy storage cell is the minimum value between the output reference current value of the energy storage cell calculated by the difference between the bus voltage and the reference value of the bus voltage through the first PI controller and the output reference current of the energy storage cell obtained from the SOC of the energy storage cell through a look-up function, which is a one-dimensional function between the output reference current of the energy storage cell and the SOC of the energy storage cell set manually, in this example, when the SOC of the energy storage cell is higher than 40%, the output reference current of the energy storage cell is the maximum allowable output reference current, which is 410A in this example, when the SOC of the energy storage cell is lower than 40%, the discharge current of the energy storage cell starts to be limited, and when the SOC of the, in the SOC interval of 40% -20%, the output reference current of the energy storage battery is linearly reduced until the output reference current is reduced to 0A. And transmitting the difference value between the minimum value and the actual output current of the energy storage battery to a second PI controller in the DC/DC controller of the energy storage battery, wherein the proportional coefficient and the integral coefficient of the PI controller are respectively 1 and 50, and then the proportional coefficient and the integral coefficient are used as the input of PWM waves of the DC/DC controller of the energy storage battery through a current limiting link, so that the energy storage battery is controlled to adopt a current-limiting constant voltage mode to control the bus voltage. In the control mode 3 of the invention, the electric automobile is charged in a slow charging mode, the charging pile DC/DC acquires bus voltage, when the bus voltage is reduced to 600V, the charging reference current of the electric automobile is converted into a slow charging reference current from a super fast charging reference current, in the example, the slow charging reference current is 32A, and then the input of the PWM wave of the DC/DC is obtained through a PI control link and a current limiting link, so that the electric automobile is controlled to be charged in the slow charging mode.
5) As shown in fig. 5, in the control mode 4 of the present invention, the operating modes of the photovoltaic cell and the energy storage cell are the same as the control mode 3, the electric vehicle is charged in the blocking mode, the charging pile DC/DC collects the bus voltage, when the bus voltage is reduced to 550V, the charging reference current of the electric vehicle is converted from the slow charging reference current to 0A, and the charging load of the electric vehicle is blocked, so as to prevent the bus voltage from further reducing.
In order to verify the effectiveness of the control method, simulation analysis of the control method is carried out on the basis of a Matlab/Simulink platform, and parameters related to a simulation model are parameters in an example.
Fig. 6 is a diagram illustrating simulation results of the dc microgrid switching from mode 1 to mode 2, and it can be found from the simulation results, when the maximum charging current of the energy storage battery cannot meet the maximum power output of the photovoltaic battery, the bus voltage can be increased due to the unbalanced power at the two sides of the micro-grid source charge, from 650V to 700V in a period of 2s, when the bus voltage reaches 700V, the system enters a control mode of a mode 2, the photovoltaic cell is converted from the MPPT mode to a constant voltage mode to control the bus voltage, the coordination between the photovoltaic cell and the power of the energy storage cell can be realized by increasing the current to reduce the input power of the photovoltaic cell, and the simulation result shows that under the control strategy of the mode 2, the bus voltage can be stabilized to be about 700V by the control strategy designed by the invention, and the stable operation of the microgrid system under the high-voltage output situation can be maintained.
Fig. 7 is a diagram showing a simulation result of a system changing from mode 1 to mode 3, and it can be seen from the simulation result that when the output power of the energy storage battery meets the charging load requirement, the system can meet the requirement of super fast charging of the electric vehicle, but when the maximum output power of the energy storage battery cannot meet the charging requirement, the bus voltage will suddenly drop from 650V to 600V within 0.2s, when the bus voltage reaches 600V, the system will enter the control mode of mode 3, the electric vehicle charging mode will change from super fast charging to slow charging, so as to ensure the power balance in the microgrid system, and the bus voltage is stabilized at 600V to prevent the bus voltage from continuously dropping, and a sudden change will occur in the bus voltage and the output current of the energy storage battery at the moment of power switching, but the change range is within the range that the bus and the components can bear. In the mode 3, through the coordination control of charging the energy storage battery and the electric automobile at the same time, the system can realize the smooth transition from super fast charging to slow charging of the electric automobile and the stable operation of the system.
The simulation result of the system in fig. 8 is a graph of the simulation result of the transition from mode 3 to mode 4, and it can be seen from the simulation result that when the SOC of the energy storage battery continues to decrease, which results in that the outputtable power is not enough to maintain the demand of slow charging of the system, the bus voltage will decrease from 600V to 550V within 3s, and when the bus voltage decreases to 550V, the system will cut off the charging load of all electric vehicles, and avoid further discharging of the energy storage battery and the continuous decrease of the bus voltage.
Claims (1)
1. A light storage and charging direct current micro-grid control method is characterized by comprising the following steps:
1) judging the voltage of the direct current bus, and selecting a control mode of the direct current microgrid:
if the voltage of the direct current bus is more than 600V and less than 700V, entering the control mode 1 of the step 2);
if the voltage of the direct current bus is larger than or equal to 700V, entering a control mode 2 of the step 3);
if the voltage of the direct current bus is larger than 550V and smaller than or equal to 600V, entering a control mode 3 of the step 4);
if the voltage of the direct current bus is less than or equal to 550V, entering a control mode 4 of the step 5);
2) in the control mode 1, the bus reference voltage is 650V, the photovoltaic cell adopts a maximum power tracking output mode, and the energy storage cell adopts a constant voltage mode to control the bus voltage;
the method comprises the following steps that a photovoltaic cell adopts a Maximum Power Point Tracking (MPPT) mode, a photovoltaic cell DC/DC controller collects output voltage and current signals of the photovoltaic cell, the output reference voltage of the photovoltaic cell is obtained through calculation of a MPPT algorithm, the difference value between the obtained output reference voltage of the photovoltaic cell and the actual output voltage of the photovoltaic cell is transmitted to a first PI controller in the photovoltaic cell DC/DC controller, the output reference current of the photovoltaic cell is obtained through calculation, the difference value between the output reference current of the photovoltaic cell and the actual output current of the photovoltaic cell is transmitted to a second PI controller in the photovoltaic cell DC/DC controller, and finally the difference value is used as the input of a Pulse Width Modulation (PWM) wave of the photovoltaic cell DC/DC through a photovoltaic cell current limiting link, so that the photovoltaic cell is controlled to output in the MPPT mode;
the energy storage battery adopts a constant voltage mode to control the bus voltage, the energy storage battery DC/DC controller collects the bus voltage, the difference value between the collected bus voltage and the bus voltage reference value is transmitted to a first PI controller in the energy storage battery DC/DC controller, the output reference current of the energy storage battery is obtained through calculation, the difference value between the output reference current of the energy storage battery and the actual output current of the energy storage battery is transmitted to a second PI controller in the energy storage battery DC/DC controller, and finally the difference value is used as the input of the PWM wave of the energy storage battery DC/DC through an energy storage battery current limiting link, so that the energy storage battery is controlled to output and control the bus voltage by adopting the constant voltage mode;
3) in the control mode 2, the bus reference voltage is 700V, the photovoltaic battery adopts a constant voltage mode to control the bus voltage, and the energy storage battery adopts a current-limiting charging mode;
the method comprises the following steps that a photovoltaic cell controls bus voltage in a constant voltage mode, a photovoltaic cell DC/DC controller collects the bus voltage, the difference value between the collected bus voltage and a bus voltage reference value is transmitted to a first PI controller in the photovoltaic cell DC/DC controller, output reference current of the photovoltaic cell is obtained through calculation, the difference value between the output reference current of the photovoltaic cell and actual output current of the photovoltaic cell is transmitted to a second PI controller in the photovoltaic cell DC/DC controller, and finally a photovoltaic cell current limiting link is used as input of PWM waves of the photovoltaic cell DC/DC, so that the photovoltaic cell is controlled to output and control the bus voltage in the constant voltage mode;
the energy storage battery adopts a current-limiting charging mode, the energy storage battery DC/DC controller collects the SOC of the energy storage battery estimated by a battery management system of the energy storage battery, the charging reference current of the energy storage battery is calculated through a one-dimensional function between the charging reference current of the energy storage battery and the SOC of the energy storage battery, the difference value between the charging reference current of the energy storage battery and the actual charging current of the energy storage battery is transmitted to a second PI controller of the energy storage battery DC/DC controller, and then the current-limiting link of the energy storage battery is used as the input of a PWM wave of the DC/DC of the energy storage battery, so that the energy storage battery is controlled to adopt the;
4) in the control mode 3, the bus reference voltage is 600V, the photovoltaic cell adopts a maximum power tracking output mode, and the energy storage cell adopts a current-limiting constant voltage mode to control the bus voltage;
the photovoltaic battery adopts a Maximum Power Point Tracking (MPPT) mode, the energy storage battery adopts a current-limiting constant voltage mode to control bus voltage, the energy storage battery outputs reference current by utilizing the difference value of the bus voltage and a bus voltage reference value and then through calculation of a first proportional-integral (PI) controller of the energy storage battery, then the energy storage battery outputs reference current by utilizing one-dimensional function calculation between the energy storage battery output reference current and the SOC of the energy storage battery, the minimum value of the two output reference current values is selected, the difference value of the minimum value and the actual output current of the energy storage battery is transmitted to a second PI controller in the DC/DC controller of the energy storage battery, and then the difference value is used as the input of a Pulse Width Modulation (PWM) wave of the DC/DC of the energy storage battery through a current-limiting link of;
5) in the control mode 4, the bus reference voltage is 550V, the photovoltaic battery adopts a maximum power tracking output mode, the energy storage battery adopts a current-limiting constant voltage mode to control the bus voltage, and the electric vehicle adopts a blocking mode for charging;
the working mode of the photovoltaic battery and the working mode of the energy storage battery are the same as the control mode 3, the electric automobile adopts a blocking mode in charging, the DC/DC controller of the charging pile collects bus voltage, when the bus voltage is reduced to 550V, the charging reference current of the electric automobile is converted into 0A, and the charging load of the electric automobile is blocked, so that the bus voltage is prevented from further reducing.
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