A coordinated control method for DC networking of photovoltaic power storage propulsion ships based on SoC

Abstract

This invention discloses a battery state-of-charge (SOC) balancing control method based on adaptive adjustment factors, belonging to the field of DC grid operation control technology. The method includes the following steps: utilizing the communication between the local SOC of a battery and its directly adjacent batteries, a consensus algorithm is used to calculate the average value of all batteries; the droop coefficient is multiplied by the current at the output of the DC / DC converter and transmitted to the dual closed-loop control layer; the ideal voltage of the bus output voltage, the difference I, and the power compensation value are summed, and the sum is then subtracted from the droop drop unit and the bus voltage to obtain the difference II; the difference II is controlled by voltage and current to obtain control signal I; control signal I is regulated by pulse width modulation technology to achieve stable output voltage and equalize the SOC of multiple batteries to generate control signal II. This method introduces three SoC balancing adjustment factors to accelerate SoC convergence speed and solve the problem of slow late-stage SoC balancing in traditional methods.

Description

Technical Field

[0001] The present invention belongs to the technical field of DC networking operation control, and relates to a SoC-based DC networking coordination control method for photovoltaic power propulsion ships. Background Art

[0002] With the development of global trade and shipping industry, fossil energy is gradually depleted, and the problem of ship pollution emission is becoming increasingly prominent. Distributed power generation technology for ships, which is mainly based on renewable energy power generation, has received widespread attention. Compared with the ship AC networking mode, the ship DC networking has low cost and no frequency, phase and other problems. It is more suitable for the access of renewable energy and has a broad development prospect. Due to cost, safety and technical considerations, multiple battery energy storage units (BESUs) are usually equipped on electric propulsion ships. BESUs are connected to the DC bus in parallel through converters to provide power for the entire ship. The converter controls the output voltage and suppresses the circulation between BESUs. For example, the recently launched pure electric ships such as "Yara Birkeland" and "Junlv" all use this technology. However, due to differences in production process, storage conditions and use, each BESU will have inconsistent SoC problems. When the SoC is seriously unbalanced, some BESUs will exit operation prematurely, accelerate the discharge speed of the remaining BESUs, and affect the life of the energy storage system and the stability of the ship DC networking. Therefore, the power distribution and SoC balance between BESUs have been widely studied.

[0003] Regarding the coordinated control of solar energy and batteries, the literature [1-3] A coordinated control strategy for a DC microgrid system based on bus voltage stratification is proposed to construct a DC microgrid system structure based on solar power generation. However, when the photovoltaic power fluctuates violently, it will cause large bus voltage fluctuations, seriously affecting the power quality and being unfavorable to the stable operation of the DC microgrid. Summary of the invention

[0004] The above technical problems existing in the prior art are solved by a SoC-based DC networking coordinated control method for photovoltaic power storage propulsion ships, comprising:

[0005] By comparing the photovoltaic power of the photovoltaic unit with the power of the load and the sum of the input and output powers of the battery unit, the working mode of the DC network of the photovoltaic power storage propulsion ship is determined, so that when the photovoltaic power output of the photovoltaic unit is different, the battery unit is controlled to charge or discharge according to the load demand.

[0006] Furthermore, by comparing the photovoltaic power of the photovoltaic unit with the power of the load and the sum of the input and output power of the battery, the warning state of the DC network of the electric storage propulsion ship can also be determined.

[0007] Further: By comparing the photovoltaic power of the photovoltaic unit with the sum of the power of the load and the input and output power of the battery, the working mode of the DC network of the photovoltaic-storage electric propulsion ship is determined, which specifically includes:

[0008] Working mode 1: When the state of charge SoC of the battery < 20%, the photovoltaic output power P V < P L , the photovoltaic unit operates in the MPPT mode, but the output power of the photovoltaic unit and the maximum discharge power of the BESUs are not sufficient to support the power consumed by the marine load, and the ship will stop running;

[0009] Working mode 2: At this time, the state of charge SoC of the battery > 30%, the photovoltaic output power P L -P B1 < P V < P L -0.5P B1 , the photovoltaic unit operates in the MPPT mode, and the battery operates in the discharge mode;

[0010] Working mode 3: When the state of charge of the battery 20% < SoC < 90%, the photovoltaic output power P L < P V < P L +P B2 , the photovoltaic unit operates in the MPPT mode, and the BESUs are charged at a speed less than the maximum charging current I in ;

[0011] Working mode 4: When the state of charge of the battery 20% < SoC < 85%, the photovoltaic output power P Lref +P B2 < P V , P Lref is the rated load power, the photovoltaic unit will operate in constant voltage mode 1, and the BESUs are charged at the maximum charging current I in ;

[0012] Working mode 5: When the state of charge of the battery SoC > 90%, the photovoltaic output power P Lref < P V , at this time, the photovoltaic unit operates in constant voltage mode 2, the photovoltaic unit is responsible for the power consumption of the rated load, and the BESUs operate in the trickle state.

[0013] Further: By comparing the photovoltaic power of the photovoltaic unit with the sum of the power of the load and the input and output power of the battery, the warning state of the DC network of the photovoltaic-storage electric propulsion ship can also be determined, which specifically includes:

[0014] Warning mode 1: When the state of charge of the battery SoC > 20%, P V<P L -P B1 or P L -P B1 <P V <P L -0.5P B1 , when 20% < SoC < 30%, it indicates that the photovoltaic and battery are insufficient to provide the power consumed by the load. Then, unnecessary loads are cut off or some photovoltaic units are turned off to switch the DC network of the electric propulsion ship with energy storage to the normal working mode;

[0015] Early warning mode 2: If 85% < SoC < 90%, P Lref +P B2 <P V , at this time, if the BESUs are charging at the maximum power, increase the load or turn off some photovoltaic units to switch to the stable working mode.

[0016] Furthermore: The battery unit includes n batteries and n battery energy controllers; the batteries are connected to the battery energy controllers; the working process of the battery energy controller is as follows:

[0017] Obtain the output current of n batteries, and obtain the state of charge of each battery based on the ampere-hour integration method;

[0018] Combined with droop control, generate a droop coefficient by averaging all batteries through the state of charge equal current sharing algorithm;

[0019] Multiply the droop coefficient by the current at the output end of the DC / DC converter and send the result to the double closed-loop control layer;

[0020] Obtain the bus voltages on both sides of the load, subtract the ideal voltage value from the bus voltages on both sides of the load to obtain a difference value I for increasing voltage drop compensation to maintain the stability of the bus voltage, and send the obtained difference value I to the double closed-loop control layer;

[0021] Using the obtained droop coefficient and the voltage and current at the output end of the DC / DC converter, through the power compensation algorithm, obtain a power compensation value for eliminating the equal current sharing error caused by the line impedance, and send it to the double closed-loop control layer;

[0022] Sum the ideal voltage of the bus output voltage, the difference value I, and the power compensation value, and then subtract the droop drop unit from the bus voltage to obtain a difference value II;

[0023] The difference value II passes through voltage and current control to obtain a control signal I;

[0024] The control signal I is adjusted through pulse width modulation technology to achieve stable output voltage and generate a control signal II for achieving the state of charge balance of multiple batteries.

[0025] Further: The output voltage of the photovoltaic unit is U pv1 and U pv2 , corresponding to different working modes; U pv1 The expression corresponding to constant voltage mode 1 is as follows:

[0026]

[0027] U pv2 The expression corresponding to constant voltage mode 1 is as follows:

[0028]

[0029] Where: I in is the maximum charging current, R a To adjust the resistance, is the bus voltage rating, It is the power required by important equipment to maintain the operation of the ship.

[0030] Furthermore: It is characterized in that: the droop coefficient R droopi The formula used is:

[0031] The droop coefficient when the battery is discharged is:

[0032]

[0033] The droop factor when the battery is charging:

[0034]

[0035] Where: R droopi Indicates the droop coefficient; K d0 , θ and p are balance adjustment factors, SoC i is the SoC value between BESUs, SoC av is the average value of SoC among BESUs.

[0036] Furthermore: the specific method for eliminating the current sharing error caused by line impedance is as follows:

[0037]

[0038] in: For voltage compensation, Ideal unit output voltage, V i * is the output voltage of the i-th unit, k p and k i is the PI value of the PI controller I. V dci is the ideal output voltage of the converter, V dciis the actual output voltage of the converter, ΔV i is the deviation between the expected value and the output voltage, K' p and K′ i is the PI value of PI controller II.

[0039] Further, the fixed photovoltaic unit operates in MPPT mode or constant voltage mode;

[0040] The process of the MPPT mode is as follows: the voltage and current on both sides of the photovoltaic unit output are collected and the obtained power is sent to the MPPT controller, the obtained value voltage and current are controlled to obtain a control signal III, and the control signal III is modulated by pulse width modulation technology to obtain a control signal IV.

[0041] The process of the constant voltage mode is as follows: the collected voltage on both sides of the photovoltaic unit output is subtracted from the voltage setting value, the difference III is subjected to voltage and current control to obtain a control signal III, and the control signal III is modulated by pulse width modulation technology to obtain a control signal IV.

[0042] A SoC-based DC networking coordination control device for photovoltaic power storage propulsion ships, comprising:

[0043] A bidirectional DC / DC converter unit for modulating voltage and stabilizing bus voltage, wherein the bidirectional DC / DC converter unit is connected to the DC bus;

[0044] A photovoltaic unit that provides the power required by the load and the battery; the photovoltaic unit provides the power required by the load and the battery and is connected to the DC bus through a DC / DC converter unit;

[0045] When the photovoltaic power is insufficient to maintain the load power consumption, the battery unit provides power to the load and plays a role in stabilizing the bus voltage; the battery unit is connected to the DC bus through a DC / DC converter unit;

[0046] A balancing control unit for controlling the shutdown of the DC / DC converter unit to achieve the purpose of controlling the bus voltage. The balancing control unit is connected to the DC / DC converter unit and the DC bus;

[0047] A driving unit amplifies the balancing control unit signal and controls the IGBT to turn off, wherein the driving unit is connected to the DC / DC converter and the balancing control unit.

[0048] The present invention discloses a coordinated control method for direct current networking of a photovoltaic power propulsion ship based on a system-on-chip (SoC). The method proposes a coordinated control strategy for direct current networking of a photovoltaic power propulsion ship taking into account a system-on-chip (SoC). The strategy is divided into five working modes and two early warning modes. While realizing coordinated control of photovoltaic units, it also realizes precise power distribution of battery energy storage units (BESUs) and photovoltaic units, thereby extending the service life of BESUs. The device comprises a bidirectional DC / DC converter unit, a photovoltaic unit, a collection unit and a control unit. The device takes into account the line impedance of each converter unit, thereby improving energy utilization. The device has a simple structure and strong practicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0050] Figure 1 It is the overall control block diagram of the system adopted by the present invention;

[0051] Figure 2 The present invention adopts the division of working modes of photovoltaic-storage coordinated control;

[0052] Figure 3 Conductivity increment method flow chart;

[0053] Figure 4 This is a structural diagram of a DC propulsion ship microgrid adopted by the present invention;

[0054] Figure 5 (a) SoCs of BESUs; (b) PV unit output voltage; (c) DC bus voltage; (d) output current of BESUs. DETAILED DESCRIPTION

[0055] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0056] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0058] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, the numerical expressions and numerical values ​​do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The technology, methods and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be regarded as part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0059] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present invention: the directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.

[0060] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below their position devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0061] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0062] A coordinated control method for DC networking of a photovoltaic power storage propulsion ship based on SoC, comprising:

[0063] The relationship between the photovoltaic power of the photovoltaic unit, the power of the load and the sum of the input and output powers of the battery unit determines the working mode of the DC networking of the photovoltaic power storage propulsion ship, so that when the photovoltaic power output of the photovoltaic unit is different, the battery unit is controlled to charge or discharge according to the load demand.

[0064] By comparing the photovoltaic power of the photovoltaic unit with the power of the load and the sum of the input and output power of the battery, the warning state of the DC networking of the electric storage propulsion ship can also be determined.

[0065] Figure 1 It is the overall control block diagram of the system adopted by the present invention.

[0066] BESUs and PV units are connected in parallel on the busbar via DC / DC converters.

[0067] BESUs adopts a hierarchical control structure, which is divided into primary control layer and secondary control layer.

[0068] The photovoltaic unit adopts MPPT and CVC control mode (constant voltage mode) to meet the power demand of the photovoltaic power storage propulsion ship to the maximum extent and ensure the safe operation of the ship. Based on the photovoltaic unit power output and the SoC of BESUs, the photovoltaic power storage propulsion ship DC microgrid can be divided into five working modes and two warning states.

[0069] Figure 2 The present invention adopts the division of the coordinated control working mode of the photovoltaic energy storage system; according to the photovoltaic output power and the SoC of the BESUs, combined with the maximum discharge power P B1 and the maximum charging power P B2 , five modes of coordinated control of the output power are proposed as follows:

[0070] The battery discharge mode is as follows:

[0071] Working mode 1: When the state of charge SoC of the battery is less than 20%, and the photovoltaic output power P V < P L , the photovoltaic unit operates in the MPPT mode, but the output power of the photovoltaic unit and the maximum discharge power of the BESUs are not sufficient to support the power consumed by the marine load, and the ship will stop running.

[0072] Working mode 2: When the state of charge SoC of the battery is greater than 30%, and the photovoltaic output power P L -P B1 < P V < P L -0.5P B1 , the photovoltaic unit operates in the MPPT mode, and the battery operates in the discharge mode.

[0073] The battery charging mode is as follows:

[0074] Working mode 3: At this time, 20% < SoC < 90%, and the photovoltaic output power P L < P V < P L +P B2 , the photovoltaic unit operates in the MPPT mode, and the BESUs are charged at a speed less than the maximum charging current.

[0075] Working mode 4: At this time, 20% < SoC < 85%, and the photovoltaic output power P Lref +P B2 < P V , P Lref is the rated load power, the photovoltaic unit will operate in the constant voltage mode 1, and the BESUs are charged with the maximum charging current I in ;

[0076] Working mode 5: At this time, SoC > 90%, and the photovoltaic output power P Lref < P V , at this time, the photovoltaic unit operates in the constant voltage mode 2, the photovoltaic unit is responsible for the power consumption of the rated load, and the BESUs operate in the trickle state.

[0077] The two warning modes are as follows, as shown below:

[0078] Warning Mode 1: If at this time SoC > 20% and P V <P L -P B1 or P L -P B1 <P V <P L -0.5P B1 , when 20% < SoC < 30%, it indicates that the photovoltaic and battery are not sufficient to provide the power consumed by the load, and unnecessary loads need to be cut off or some photovoltaic units need to be turned off to switch the system to the normal working mode, where P V (t) is the power generation power of the photovoltaic unit; P B (t) is the charge and discharge power of the battery; P an (t) is the charging power of the shore power; P L (t) is the power consumed by the load; P a (t) is the power consumed by the regulating resistor R a to coordinate the power balance between the photovoltaic unit and the BESUs; t is the unit time. P Lref is the rated load power;

[0079] Warning Mode 2: If 85% < SoC < 90% and P Lref +P B2 <P V , at this time, if the BESUs are charging at the maximum power, loads need to be increased or some photovoltaic units need to be turned off to switch to the stable working mode.

[0080] Figure 3 is the flowchart of the conductance increment method. When the photovoltaic unit works in the MPPT mode, the relative position between the current power point and the maximum power point is determined by setting the critical value flag. When the working point is far from the maximum power point, a large step size is used to approach the maximum power point; when the working point is close to the maximum power point, a small step size is used instead. At the maximum power point, the voltage remains unchanged.

[0081] When the photovoltaic unit works in the constant voltage mode, the output voltage of the photovoltaic unit is U pv1 and U pv2 , corresponding to different working modes respectively. U pv1 and U pv2 take the following values:

[0082]

[0083]

[0084] where: I in is the maximum charging current, R a is the regulating resistor, is the bus voltage rating, It is the power required by the important equipment to maintain the operation of the ship. Formula (1) and formula (2) respectively represent the expressions of constant pressure mode 1 and constant pressure mode 2;

[0085] Furthermore, the battery unit includes n batteries and n battery energy controllers; the batteries and battery energy controllers are connected; the working process of the battery energy controller is as follows:

[0086] Obtain the output current of n batteries, and obtain the state of charge of each battery based on the ampere-hour integration method;

[0087] Combined with droop control, the average value of all batteries is used to generate the droop coefficient through the state of charge current sharing algorithm;

[0088] The product of the droop coefficient and the current at the output of the DC / DC converter is transmitted to the double closed-loop control layer;

[0089] The difference between the collected bus voltage on both sides of the load and the ideal voltage value is calculated to obtain the difference I used to increase the voltage drop compensation to maintain the bus voltage stability, and the obtained difference I is transmitted to the dual closed-loop control layer;

[0090] By using the obtained droop coefficient and the voltage and current at the output end of the DC / DC converter, a power compensation value is obtained through a power compensation algorithm to eliminate the current sharing error caused by the line impedance, and the value is transmitted to the dual closed-loop control layer;

[0091] The ideal voltage of the bus output voltage and the difference I and the power compensation value are summed, and the sum is subtracted from the droop drop unit and the bus voltage to obtain the difference II;

[0092] The difference II is subjected to voltage and current control to obtain a control signal I;

[0093] The control signal I is modulated by pulse width modulation technology to achieve a stable output voltage and a balanced charge state of multiple batteries to generate a control signal II.

[0094] The photovoltaic unit works in MPPT mode or constant voltage mode

[0095] The working process of the MPPT mode is as follows: the voltage and current on both sides of the photovoltaic unit output are collected and the obtained power is sent to the MPPT controller, the obtained value voltage and current are controlled to obtain a control signal III, and the control signal III is modulated by pulse width modulation technology to obtain a control signal IV.

[0096] The working process of the constant voltage mode is as follows: the collected voltage on both sides of the photovoltaic unit output is subtracted from the voltage setting value, and the difference III is subjected to voltage and current control to obtain a control signal III, and the control signal III is modulated by pulse width modulation technology to obtain a control signal IV.

[0097] The state of charge of each battery is obtained by the ampere-hour integration method as follows:

[0098]

[0099] Among them: SoC i (0) and SoC i (t) is the initial SoC value of the i-th energy storage unit and the SoC value at time t, C Ni is the rated capacity of the ith battery, η i is the charging and discharging efficiency of the i-th battery, which is taken as 1 in this application, and i dci is the output current of the converter.

[0100] Two identical DC / DC converters (Converter I and Converter II) are analyzed. The output current value ratio of the DC / DC converter under traditional droop control is:

[0101]

[0102] Where: i dc1 and i dc2 is the ideal output current of converter I and converter II, R1 and R2 are the line impedances of ESUI and ESUII, R droop1 and R droop2 is the droop coefficient of ESUI and ESUII.

[0103] The output voltage of the battery is the same. If the loss of the converter is ignored, the following equation can be obtained:

[0104] P in-i =P out-i =V dci i dci (5)

[0105] Where: P in-i and P out-i is the input and output power of the ith converter, V dci is the output voltage of the ith converter. Combining equations (1) and (3), the ampere-hour integration method can be written as:

[0106]

[0107]

[0108] Combining (2) and (4), we can get formula (5), which shows that SoC balance is related to the converter line impedance and droop coefficient as well as the rated capacity of the battery. Combining SoC with the droop coefficient, an adaptive droop control method based on SoC is proposed to achieve the current balance target. The improved droop coefficient is shown as follows: When the battery is discharged, the droop coefficient R droopi for:

[0109]

[0110] When the battery is charging:

[0111]

[0112]

[0113] In order to reduce bus voltage deviation and line impedance deviation, a secondary bus voltage compensation control is used, including power compensation and voltage compensation control;

[0114] Line impedance compensation It is superimposed on the reference output voltage of each converter to eliminate the current sharing error caused by line impedance. The specific method is as follows:

[0115]

[0116] in: For line impedance compensation, Ideal unit output voltage, V i * is the output voltage of the i-th unit, k p and k i is the PI value of the PI controller I, V dci is the ideal output voltage of the converter, V dci is the actual output voltage of the converter, ΔV i is the deviation between the expected value and the output voltage, K' p and K′ i is the PI value of PI controller II.

[0117]

[0118]

[0119]

[0120] in: is the unit average output voltage, is the nth unit output voltage, I rate-i is the virtual unit output current, ΔV maxis the maximum allowable voltage deviation, P out-i is the output power of the i-th converter. When (12) is satisfied, the influence of different line resistances on SoC balance can be offset, thereby achieving the purpose of accurate power distribution.

[0121] In summary, we can derive a new droop formula:

[0122]

[0123] It effectively solves the problem of droop control and inconsistent line resistance affecting SoC balance, and can achieve accurate current sharing of bus voltage recovery and load current.

[0124] The virtual control unit corresponding to the battery energy controller includes:

[0125] Photovoltaic unit output module: including the maximum power MPPT mode for tracking photovoltaics and the constant voltage mode for tracking the ideal voltage;

[0126] State of charge acquisition module: used to acquire the output current of multiple batteries and obtain the state of charge of each battery based on the ampere-hour integration method;

[0127] Average value acquisition module: used to utilize the communication between the local state of charge of the battery and the state of charge of its directly adjacent batteries, and adopt an improved consistency algorithm to calculate and obtain the average value of all batteries;

[0128] Droop coefficient generation module: Combined with droop control, the average value of all batteries is used to generate the droop coefficient through the state of charge current sharing algorithm;

[0129] Droop drop unit module: used to calculate the product of the droop coefficient and the current at the output end of the DC / DC converter, and transmit the obtained product value to the dual closed-loop control layer;

[0130] Voltage compensation unit module: used to calculate the difference between the collected bus voltage on both sides of the load and the ideal voltage value, obtain the difference I used to increase the voltage drop compensation to maintain the stability of the bus voltage, and transmit the obtained difference I to the dual closed-loop control layer;

[0131] Power compensation unit module: using the droop coefficient and the voltage and current at the output of the DC / DC converter, through the power compensation algorithm, the power compensation value used to eliminate the current sharing error caused by the line impedance is obtained and transmitted to the dual closed-loop control layer;

[0132] Difference calculation module: used to sum the ideal voltage of the bus output voltage, the difference I, and the power compensation value, and then subtract the sum from the product value and the bus voltage to obtain the difference II.

[0133] Dual control module: used to control the difference II through voltage and current to obtain a control signal I;

[0134] Pulse width modulation technology mediation module: used to mediate the control signal I through pulse width modulation technology (PWM) to achieve a stable output voltage and achieve a balanced charge state of multiple batteries to generate a control signal II.

[0135] Figure 4 The structure diagram of the DC propulsion ship microgrid adopted by the present invention; an electric propulsion ship battery SoC balancing device based on an adaptive adjustment factor, comprising:

[0136] A bidirectional DC / DC converter unit for modulating voltage and stabilizing bus voltage, wherein the bidirectional DC / DC converter unit is connected to the DC bus;

[0137] A photovoltaic unit that provides the power required by the load and the battery; the photovoltaic unit provides the power required by the load and the battery and is connected to the DC bus through a DC / DC converter unit;

[0138] When the photovoltaic power is insufficient to maintain the load power consumption, the battery unit provides power to the load and plays a role in stabilizing the bus voltage; the battery unit is connected to the DC bus through a DC / DC converter unit;

[0139] A balancing control unit for controlling the shutdown of the DC / DC converter unit to achieve the purpose of controlling the bus voltage. The balancing control unit is connected to the DC / DC converter unit and the DC bus;

[0140] A driving unit amplifies the signal of the balancing control unit and controls the IGBT to be turned off, wherein the driving unit is connected to the DC / DC converter and the balancing control unit.

[0141] In order to verify the effectiveness of the present invention, simulation verification is carried out using MATLAB / Simulink software. Figure 5 (a) SoCs of BESUs (b) PV unit output voltage (c) DC bus voltage (d) output current of BESUs;

[0142] At t=0-10s, the light intensity is maintained at 80W / m2. At this time, the photovoltaic power storage propulsion ship works in mode 2, and the output power of the photovoltaic unit is 2013W.

[0143] At t=10-15s, the light intensity is increased and maintained at 330W / m2. At this time, the power generated by the photovoltaic unit is 8200W, which just meets the load demand. At this time, BESUs are neither charged nor discharged.

[0144] At t=15-30s, the light intensity is increased and maintained at 550W / m2. At this time, the photovoltaic power storage propulsion ship works in mode three, and the output power of the photovoltaic unit is 14613W.

[0145] At t=30-33.5s, the light intensity is increased and maintained at 950W / m2. At this time, the photovoltaic power storage propulsion ship works in mode 4, and the output power of the photovoltaic unit is 21250W.

[0146] At t=33.5s, the coordinated control system sends out a warning signal. At this time, the load is increased and the power required by the load increases from 8kW to 12kW.

[0147] At t=33.5-38.05s, the light intensity remains unchanged at 950W / m2. Due to the increase in the power required by the load, the solar-storage electric propulsion ship operates in mode four.

[0148] At t=38.05-50s, the light intensity is maintained at 950W / m2. Since the SoC of the BESUs reaches 90%, the solar-storage electric propulsion ship operates in mode five.

[0149] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0150] [1]MI Yang,WU Yanwei,FU Yang,et al.SoC dynamic balancing Strategy for multi-energy storage based on adaptive droop control in DC microgrid[J].PowerSystem Protection and Control, 2017,45(8):37-45..

[0151] [2]HOU Shiying,FANG Yong,SUN Tao,PENG Wenxiong,et al.Application ofHybrid Energy Storage System in Power Balance of Stand-Alone PhotovoltaicPower System[J].Power System Technology,2011,35(5):183..

[0152] [3]ZHENG Lijun,WANG Zipeng,LYU Shixuan,et al.Hierarchical operationcontrol of multi-energy storage in DC microgrid based on state of charge[J].Power System Technology,2021,45(3):1006-1015..

Claims

1. A SoC-based DC networking coordinated control method for photovoltaic power propulsion ships, characterized in that: include: By comparing the photovoltaic power of the photovoltaic unit with the power of the load and the sum of the input and output power of the battery unit, the working mode of the DC network of the photovoltaic power storage propulsion ship is determined, so that when the photovoltaic power output of the photovoltaic unit is different, the battery unit is controlled to charge or discharge according to the demand of the load; The battery unit includes n batteries and n battery energy controllers; the batteries and the battery energy controllers are connected; the working process of the battery energy controller is as follows: Obtain the output current of n batteries, and obtain the state of charge of each battery based on the ampere-hour integration method; Combined with droop control, the average value of all batteries is used to generate the droop coefficient through the state of charge current sharing algorithm; The product of the droop coefficient and the current at the output of the DC / DC converter is transmitted to the double closed-loop control layer; Obtain the bus voltage on both sides of the load, calculate the difference between the bus voltage on both sides of the load and the ideal voltage value, and obtain the difference I used to increase the voltage drop compensation to maintain the bus voltage stability, and transmit the obtained difference I to the dual closed-loop control layer; By using the obtained droop coefficient and the voltage and current at the output end of the DC / DC converter, a power compensation value is obtained through a power compensation algorithm to eliminate the current sharing error caused by the line impedance, and the value is transmitted to the dual closed-loop control layer; The ideal voltage of the bus output voltage and the difference I and the power compensation value are summed, and the sum is subtracted from the droop drop unit and the bus voltage to obtain the difference II; The difference II is subjected to voltage and current control to obtain a control signal I; The control signal I is modulated by pulse width modulation technology to achieve a stable output voltage and a balanced charge state of multiple batteries to generate a control signal II; The droop coefficient The formula used is: The droop coefficient when the battery is discharged is: (8) The droop factor when the battery is charging: (9) in: represents the droop coefficient; , and p is the balance adjustment factor, is the SoC value between BESUs, is the average value of SoC among BESUs.

2. According to the SoC-based DC networking coordinated control method for photovoltaic power propulsion ships according to claim 1, it is characterized by: By comparing the photovoltaic power of the photovoltaic unit with the power of the load and the sum of the input and output power of the battery, the warning state of the DC networking of the electric storage propulsion ship can also be determined.

3. According to the SoC-based DC networking coordinated control method for photovoltaic power propulsion ships according to claim 1, it is characterized by: The working mode of the direct current network of the photovoltaic power storage ship propulsion is determined by comparing the photovoltaic power of the photovoltaic unit with the power of the load and the sum of the input and output power of the battery, which specifically includes: Working mode 1: When the battery state of charge SoC < 20%, the photovoltaic output power P V < P L ,The PV unit works in MPPT mode, but the PV unit output power and the BESUs maximum discharge power are not enough to support the power consumed by the ship load, and the ship will stop operating; Working mode 2: At this time, the battery state of charge SoC>30%, the photovoltaic output power P L - P B1 < P V < P L -0.5 P B1 , the photovoltaic unit works in MPPT mode, and the battery works in discharge mode; Working mode three: When the state of charge of the battery 20% < SoC < 90%, the photovoltaic output power P L < P V < P L + P B2 , the photovoltaic unit operates in the MPPT mode, and the BESUs are charged at a speed less than the maximum charging current I in ; Operating Mode 4: When the state of charge of the battery is 20% < SoC < 85% and the photovoltaic output power P Lref + P B2 < P V , P Lref is the rated load power, the photovoltaic unit will operate in constant voltage mode 1, and the BESUs will charge with the maximum charging current I in ; Working mode 5: When the battery state of charge SoC >90%, the photovoltaic output power P Lref < P V ,At this time, the PV unit works in constant voltage mode 2, the PV unit is responsible for the ,power consumption of the rated load, and the BESUs work in the trickle state.

4. According to the SoC-based DC networking coordinated control method for photovoltaic power propulsion ships according to claim 3, it is characterized by: By comparing the photovoltaic power of the photovoltaic unit with the power of the load and the sum of the input and output power of the battery, the warning state of the DC network of the electric storage propulsion ship can also be determined, which specifically includes: Early warning mode 1: When the state of charge of the battery SoC > 20%, P V < P L - P B1 or P L - P B1 < P V < P L -0.5 P B1 , when 20% < SoC < 30%, it is shown that the photovoltaic and the battery are not sufficient to provide the power consumed by the load, then unnecessary loads are cut off or some photovoltaic units are turned off, so that the DC network for electric propulsion of the ship switches to the normal working mode; Early warning mode 2: If 85% <SoC<90%, P Lref + P B2 < P V ,At this time, if BESUs are charged at maximum power, the load is increased or some PV units are turned off to switch to the stable working mode.

5. According to the SoC-based DC networking coordinated control method for photovoltaic power propulsion ships according to claim 1, it is characterized by: The output voltage of the photovoltaic unit is U pv1 and U pv2， Corresponding to different working modes respectively; U pv1 The expression corresponding to constant voltage mode 1 is as follows: （1） U pv2 The expression corresponding to constant voltage mode 2 is as follows: （2） in: I in is the maximum charging current, R a To adjust the resistance, U * bus is the bus voltage rating, P * load It is the power required by important equipment to maintain the operation of the ship.

6. According to the SoC-based DC networking coordinated control method for photovoltaic power propulsion ships according to claim 1, it is characterized by: The method for eliminating the current sharing error caused by line impedance is as follows: （11） in: For voltage compensation, Ideal unit output voltage, is the output voltage of the ith unit, and is the PI value of the PI controller I, is the ideal output voltage of the converter, is the actual output voltage of the converter, is the deviation between the expected value and the output voltage, and is the PI value of PI controller II.

7. According to a SoC-based photovoltaic storage electric propulsion ship DC networking coordinated control method according to claim 1, the photovoltaic unit operates in MPPT mode or constant voltage mode; The process of the MPPT mode is as follows: the voltage and current on both sides of the photovoltaic unit output are collected and the power is sent to the MPPT controller, the voltage and current are controlled to obtain the control signal III, and the control signal III is modulated by pulse width modulation technology to obtain the control signal IV; The process of the constant voltage mode is as follows: the collected voltage on both sides of the photovoltaic unit output is subtracted from the voltage setting value, the difference III is subjected to voltage and current control to obtain a control signal III, and the control signal III is modulated by pulse width modulation technology to obtain a control signal IV.

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