A direct current micro-grid control method and system and a ship power system

Abstract

The present application relates to the technical field of direct current micro-grid, and particularly relates to a direct current micro-grid control method, system and ship power system. The direct current micro-grid control method comprises a direct current micro-grid construction step, a voltage compensation droop control step, a virtual direct current motor control step and an output current PI control step. The method can effectively solve the phenomenon of DC bus voltage rise and drop in the steady state process of the load by introducing the voltage compensation droop control step, and can reduce voltage fluctuation in the transient state by introducing the virtual direct current motor control, can better suppress voltage and power fluctuation, effectively cope with load power fluctuation and mutation in different working conditions, and greatly improve the safety and stability of the direct current micro-grid system.

Description

Technical Field

[0001] This invention relates to the field of DC microgrid technology, and in particular to a DC microgrid control method, system, and ship power system. Background Technology

[0002] Energy conservation and emission reduction are of significant research value to the shipping industry, as they can reduce ship operating costs and bring social and environmental benefits. With the development of new energy technologies and industrial control technologies for ships, hybrid-powered ships have been widely adopted. In particular, with the increasing sophistication of high-voltage direct current (HVDC) technology, shipboard DC microgrids are more suitable for the flexible integration of various distributed energy sources compared to shipboard AC microgrids, reducing losses and costs while improving power generation and distribution efficiency. Therefore, the application of DC microgrids based on hybrid energy storage in shipboard power systems has become a major research focus for scholars both domestically and internationally. However, research has found that due to the inherent characteristics of ships, especially tugboats, frequent fluctuations and abrupt changes in load power during long-term operations lead to large fluctuations in DC bus voltage, causing significant damage to the power grid. Therefore, further research into methods to suppress DC bus voltage and power fluctuations on ships is crucial.

[0003] Currently, existing patents and literature have proposed solutions to improve the DC bus voltage fluctuation problem caused by load power fluctuations and sudden changes, but at least the following problems still exist: transient voltage fluctuations are aggravated when the load changes, voltage rise and voltage drop problems are easily caused when the load changes, the system response time is slow, and the transient process time is long. Summary of the Invention

[0004] To address at least one deficiency of existing DC microgrids, in a first aspect, the present invention provides a DC microgrid control method, comprising the following steps:

[0005] The DC microgrid construction steps include: the DC microgrid includes at least one generator set, at least one energy storage battery pack, a DC bus, and a load, wherein the generator set and the energy storage battery pack are electrically connected to the load through the DC bus;

[0006] Voltage compensation droop control steps; Constructing the actual voltage value U of the DC bus output. dc Reference voltage value of DC bus The droop control function and the voltage bias value ΔU of the DC bus. dc The voltage compensation equation; using the input current I0 of the DC bus as the input signal, the reference voltage value is adjusted based on the droop control function. Droop control is performed using the voltage bias value ΔU of the DC bus. dc As an input signal, the reference voltage value of the DC bus is based on the voltage compensation equation. Perform voltage compensation and output the reference voltage value. Power reference value P after voltage-compensated droop control ref So that the actual output voltage of the DC bus is equal to the reference voltage value.

[0007] Virtual DC motor control steps: Establish a virtual DC motor model, and based on the virtual DC motor model, adjust the power reference value P in the voltage compensation droop control step. ref Calculations are performed to obtain the current setpoint I. ref ;

[0008] Output current PI control steps; for the given current value I ref The conversion is performed to obtain the output current I of the energy storage battery pack. 1ref And control signals are generated through PI control.

[0009] In one embodiment, the generator set includes a diesel generator, a three-winding transformer, and two sets of six-pulse diodes; the three-winding transformer includes an input winding and two output windings, the input winding is electrically connected to the diesel generator, and each of the two output windings is electrically connected to a six-pulse diode and then connected in parallel to the DC bus.

[0010] In one embodiment, the voltage compensation amount of the DC bus is set to μU. dc The voltage bias value ΔU dc The function is The droop control function is:

[0011] ΔU dc =i oi (r i +R i )-μU dc ;

[0012] In the formula, i oi Let r be the no-load output current of the i-th energy storage battery pack. i R is the virtual resistance of the i-th energy storage battery pack. i is the line impedance of the i-th energy storage battery pack; μ is the voltage compensation coefficient.

[0013] In one embodiment, the voltage compensation equation is:

[0014] ΔU dc (t)=ΔU dc ·e -ρt ;

[0015] In the formula, ρ is the convergence coefficient, and ρ > 0.

[0016] In one embodiment, in the voltage compensation droop control step, the voltage bias value ΔU dc After calculation using the voltage compensation equation, the reference voltage value is compared. The values ​​are added together, and then subtracted from the parameters calculated by the droop control function of the input current I0 to obtain the voltage reference data after droop control and voltage compensation. The voltage reference data is compared with the actual voltage value U. dc Subtracting the values ​​and passing them through a PI controller yields current reference data, which is then multiplied by the voltage reference data to obtain the power reference value P. ref .

[0017] In one embodiment, establishing the virtual DC motor model in the virtual DC motor control step includes:

[0018] The mechanical equations of the virtual DC motor are established as follows:

[0019]

[0020] Δω=ω-ω0;

[0021] In the formula, H is the inertial time constant of the virtual DC motor, and T m T represents the mechanical torque of the virtual DC motor. e Let ω be the electromagnetic torque of the virtual DC motor, D be the damping coefficient of the virtual DC motor, ω be the mechanical angular velocity of the virtual DC motor, and ω0 be the rated mechanical angular velocity of the virtual DC motor.

[0022] The electromotive force equation for the armature circuit of the virtual DC motor is established as follows:

[0023] E = U + IR a ;

[0024] In the formula, E is the armature electromotive force of the virtual DC motor, U is the terminal voltage of the virtual DC motor, I is the armature current of the virtual DC motor, and R is the armature current of the virtual DC motor. a This is the equivalent resistance of the armature circuit;

[0025] Electromagnetic power P and electromagnetic torque T of a virtual DC motor e The formula is:

[0026] P = EI;

[0027] T e =P / ω.

[0028] In one embodiment, during the virtual DC motor control step, the power reference value P ref The mechanical torque T is obtained by dividing by the rated mechanical angular velocity ω0. mThe current setpoint I is then obtained through calculations based on the virtual DC motor mechanical equation and the virtual DC motor armature circuit electromotive force equation. ref .

[0029] In one embodiment, the current given value I ref The conversion is performed to obtain the output current I of the energy storage battery pack. 1ref The conversion formula is:

[0030]

[0031] In the formula, U1 is the actual output voltage of the energy storage battery pack.

[0032] Secondly, the present invention also provides a DC microgrid control system, comprising:

[0033] A DC microgrid construction module; the DC microgrid includes at least one generator set, at least one energy storage battery pack, a DC bus and a load, wherein the generator set and the energy storage battery pack are electrically connected to the load through the DC bus;

[0034] Voltage compensation droop control module; constructs the actual voltage value U of the DC bus output. dc Reference voltage value of DC bus The droop control function and the voltage bias value ΔU of the DC bus. dc The voltage compensation equation; using the input current I0 of the DC bus as the input signal, the reference voltage value is adjusted based on the droop control function. Droop control is performed using the voltage bias value ΔU of the DC bus. dc As an input signal, the reference voltage value of the DC bus is based on the voltage compensation equation. Perform voltage compensation and output the reference voltage value. Power reference value P after voltage-compensated droop control ref So that the actual output voltage of the DC bus is equal to the reference voltage value.

[0035] Virtual DC motor control module; establishes a virtual DC motor model, and based on the virtual DC motor model, adjusts the power reference value P in the voltage compensation droop control step. ref Calculations are performed to obtain the current setpoint I. ref ;

[0036] Output current PI control module; for the current setpoint I ref The conversion is performed to obtain the output current I of the energy storage battery pack. 1ref And control signals are generated through PI control.

[0037] Thirdly, the present invention also provides a ship power system, including a DC microgrid control method as described in any embodiment of the first aspect above, or a DC microgrid control system as described in the second aspect above.

[0038] Based on the above, compared with the prior art, the DC microgrid control method provided by the embodiments of the first aspect of the present invention can effectively solve the problem of voltage rise and fall of DC bus voltage during steady state by introducing a voltage compensation droop control step. By introducing virtual DC motor control to reduce voltage fluctuations during transients, it can better suppress voltage and power fluctuations, effectively cope with load power fluctuations and sudden changes under different operating conditions, and greatly improve the safety and stability of DC microgrid system.

[0039] Other features and beneficial effects of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other beneficial effects of the invention can be realized and obtained by means of the structures particularly pointed out in the description, claims and drawings. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Unless otherwise specified, the positional relationships shown in the drawings in the following description are based on the direction in which the components are drawn in the figure.

[0041] Figure 1 A flowchart illustrating the steps of a DC microgrid control method according to an embodiment of the present invention;

[0042] Figure 2 This is a schematic diagram of the structure of a DC microgrid system in one embodiment of the present invention;

[0043] Figure 3 This is a circuit connection diagram of a generator set according to an embodiment of the present invention;

[0044] Figure 4 Equivalent circuit diagram for droop control;

[0045] Figure 5 This is a curve showing the drooping characteristic.

[0046] Figure 6 This is a control block diagram of the voltage compensation droop control step in one embodiment of the present invention;

[0047] Figure 7This is a control block diagram of the virtual DC motor control steps in one embodiment of the present invention;

[0048] Figure 8 This is a control block diagram of the output current PI control steps in one embodiment of the present invention;

[0049] Figure 9 The output voltage curve of the DC bus during operation of a DC microgrid without the control method described in the embodiments of the present invention;

[0050] Figure 10 The output voltage curve of the DC bus during operation of a DC microgrid incorporating the control method described in this embodiment of the invention;

[0051] Figure 11 This is an output power curve of a generator set without the control method described in the embodiments of the present invention;

[0052] Figure 12 The output power curve of the generator set incorporating the control method described in the embodiments of the present invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The technical features designed in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0054] In the description of this invention, it should be noted that all terms used in this invention (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains, and should not be construed as limiting the invention; it should be further understood that the terms used in this invention should be understood to have the same meaning as those in the context of this specification and in the relevant field, and should not be understood in an idealized or overly formal sense, except as expressly defined in this invention.

[0055] Firstly, please refer to Figure 1 An embodiment of the present invention provides a DC microgrid control method, the DC microgrid control method comprising at least the following steps:

[0056] S10, DC microgrid construction steps; the DC microgrid includes at least one generator set, at least one energy storage battery pack, a DC bus and a load, wherein the generator set and the energy storage battery pack are electrically connected to the load through the DC bus.

[0057] In practical implementation, the DC microgrid in this embodiment collects the energy from the generator set and energy storage battery pack onto the DC bus, and then supplies it to the load via an inverter. Preferably, the generator set can use a diesel generator as its power source, and the energy storage battery pack can use lithium batteries and supercapacitors as its power source.

[0058] For example, regarding green tugboat power systems, please refer to [link / reference]. Figure 2 The system can adopt a hybrid power system, with the power source consisting of 3 generator sets and 2 energy storage battery packs. The propulsion system includes three electric motors and propellers. The DC microgrid of the green tugboat power system uses a DC bus to collect the energy from the generator sets and energy storage battery packs to the DC bus, and then supplies the propulsion system and other ship loads through an inverter.

[0059] In an alternative implementation, such as Figure 3 As shown, the generator set includes a diesel generator, a three-winding transformer, and two sets of six-pulse diodes; the three-winding transformer includes an input winding and two output windings, the input winding is electrically connected to the diesel generator, and each of the two output windings is electrically connected to a six-pulse diode and then connected in parallel to the DC bus.

[0060] In this embodiment, a twelve-pulse diode consisting of two sets of six-pulse diodes is used for rectification. Its droop characteristic allows the generator set's output power to be maintained within the economic power range during steady state, thereby improving voltage fluctuations caused by frequent and sudden changes in load power. Furthermore, compared to traditional rectification methods, using a three-winding transformer and twelve-pulse diode rectification for grid connection effectively reduces high-order harmonics and improves grid voltage quality.

[0061] by Figure 3 Taking the generator set shown as an example, its rectifier input-output relationship is as follows:

[0062]

[0063] In the formula, V dc V is the DC side voltage of the generator set's rectifier; m The peak value of the output voltage of a three-winding transformer; ω e L is the rated electrical angular velocity of the generator set; L is the equivalent inductance on the rectifier input side of the generator set; I dc This refers to the rectifier output current of the generator set.

[0064] Because the generator set uses uncontrolled rectification, the output voltage on the rectified side decreases as the load power increases. In other words, the generator set's output power and the rectified output voltage have a drooping relationship. Taking the green tugboat power system as an example, the generator set has a rated output power of 1400kW. Tests showed that when connected to loads of 700kW (50% of the generator set's rated power), 1050kW (75% of the generator set's rated power), and 1400kW (100% of the generator set's rated power), the output voltage of the green tugboat power system remained stable at 1000V only when connected to a 1050kW load. That is, by adjusting the green tugboat power system and stabilizing its output voltage at 1000V, the generator set can output economical power in steady state.

[0065] To ensure that the generator set outputs economical power in steady state and to suppress voltage fluctuations, one embodiment of the present invention further includes the following steps:

[0066] S20, Voltage Compensation Droop Control Step; Constructing the actual voltage value U of the DC bus output. dc Reference voltage value of DC bus The droop control function and the voltage bias value ΔU of the DC bus. dc The voltage compensation equation; using the input current I0 of the DC bus as the input signal, the reference voltage value is adjusted based on the droop control function. Droop control is performed using the voltage bias value ΔU of the DC bus. dc As an input signal, the reference voltage value of the DC bus is based on the voltage compensation equation. Perform voltage compensation and output the reference voltage value. Power reference value P after voltage-compensated droop control ref So that the actual output voltage of the DC bus is equal to the reference voltage value.

[0067] In practical implementation, the main function of the voltage compensation droop control step is to compensate for the voltage rise or drop caused by load changes, without affecting the original DC bus output current, so that the system output voltage remains constant. Therefore, in this embodiment, the equivalent circuit for droop control of the system is first established. Specifically, it can be established according to the constructed DC microgrid. In this embodiment of the invention, the DC microgrid includes a generator set and an energy storage battery pack as power sources to supply power to the load. Therefore, the established equivalent circuit for droop control also consists of a voltage source U. o1 Voltage source U o2Each of these components is connected in series with its virtual resistors r1 and r2, as well as with line impedances R1 and R2, and then connected in parallel to supply power to the equivalent common load, as detailed below. Figure 4 The diagram shown is the equivalent circuit diagram for droop control.

[0068] according to Figure 4 The equivalent circuit diagram can be used to derive:

[0069] U dc =U oi -i oi (r i +R i );

[0070] In the formula, U oi Let i be the no-load output voltage of the i-th energy storage battery pack; i oi Let r be the no-load output current of the i-th energy storage battery pack. i R is the virtual resistance of the i-th energy storage battery pack. i Let be the line impedance of the i-th energy storage battery pack.

[0071] Based on the above formula, we can draw the following: Figure 5 The droop characteristic curve shown in the figure, i load V is the output current value of the DC bus. dc This is the output voltage value of the DC bus. L is the rated voltage of the DC bus, and L is the droop curve of the original system. * The droop curve after compensation.

[0072] from Figure 5 As can be seen from this, due to the droop characteristic, the output voltage value V of the DC bus... dc Voltage rating below DC bus At that time, the voltage deviation of the DC bus is ΔU dc To eliminate the DC bus voltage deviation without affecting the original DC bus output current, the droop characteristic curve L can be shifted upwards to obtain a new droop characteristic curve L. * Observe the new droop characteristic curve L * It can be observed that without changing the original DC bus output current, the DC bus output voltage reaches the rated voltage value. Let the DC bus voltage compensation be μU. dc And there are The compensated droop characteristic curve relationship function is then obtained as follows: Due to the voltage bias value ΔU dc The function is Therefore, the droop control function is:

[0073] ΔU dc =ioi (r i +R i )-μU dc ;

[0074] In the formula, i oi Let r be the no-load output current of the i-th energy storage battery pack. i R is the virtual resistance of the i-th energy storage battery pack. i is the line impedance of the i-th energy storage battery pack; μ is the voltage compensation coefficient.

[0075] Differentiating both sides of the above droop control function, and ensuring the time derivative of the current term is 0 to avoid affecting the original DC bus output current, we obtain: To compensate for voltage deviation, the voltage compensation amount of the DC bus must meet the following requirement: μU dc =∫(ρΔU dc Combining the above formulas, we can obtain the voltage compensation equation: ΔU / dt; dc (t)=ΔU dc ·e -ρt In the formula, ρ is the convergence coefficient, and ρ > 0.

[0076] Since the convergence coefficient ρ is greater than 0, the DC bus voltage deviation can converge to 0 within a certain time. The convergence time is related to the selection of the convergence coefficient ρ. In this voltage compensation control, only the DC bus output voltage value is changed, and the derivative of the current is 0, which ensures that the DC bus output current value remains unchanged.

[0077] Therefore, as Figure 6 As shown, in the voltage compensation droop control step, the voltage bias value ΔU dc After calculation using the voltage compensation equation, the reference voltage value is compared. The values ​​are added together, and then subtracted from the parameters calculated by the droop control function of the input current I0 to obtain the voltage reference data after droop control and voltage compensation. The voltage reference data is compared with the actual voltage value U. dc Subtracting the values ​​and passing them through a PI controller yields current reference data, which is then multiplied by the voltage reference data to obtain the power reference value P. ref .

[0078] S30, Virtual DC Motor Control Step: Establish a virtual DC motor model, and based on the virtual DC motor model, adjust the power reference value P in the voltage compensation droop control step. ref Calculations are performed to obtain the current setpoint I. ref .

[0079] In specific implementation, establishing the virtual DC motor model includes:

[0080] The mechanical equations of the virtual DC motor are established as follows: Δω=ω-ω0; where H is the inertial time constant of the virtual DC motor, and T m T represents the mechanical torque of the virtual DC motor. e Let H be the electromagnetic torque of the virtual DC motor, D be the damping coefficient of the virtual DC motor, ω be the mechanical angular velocity of the virtual DC motor, and ω0 be the rated mechanical angular velocity of the virtual DC motor. The inertial time constant H and the damping coefficient D are typically selected based on the dynamic response time of the connected energy storage unit and the system load, and are not limited here. For example, in this embodiment, the preferred energy storage battery pack is a combination of a lithium battery pack and a supercapacitor. The dynamic response time of the lithium battery pack is typically in the second range, and the dynamic response time of the supercapacitor is typically in the millisecond range. Considering the frequent fluctuations and sudden changes in load power, the values ​​of the inertial time constant H and the damping coefficient D in the lithium battery pack control strategy can be 2 and 20, respectively, while the values ​​of the inertial time constant H and the damping coefficient D in the supercapacitor control strategy can be 0.25 and 5, respectively.

[0081] The electromotive force equation for the armature circuit of the virtual DC motor is: E = U + IR a In the formula, E is the armature electromotive force of the virtual DC motor, E = C T Φω, C T Φ is selected based on the parameters of the actual generator set, for example, it can be 5.1; U is the terminal voltage of the virtual DC motor, I is the armature current of the virtual DC motor, and R... a Let P be the equivalent resistance of the armature circuit; then the electromagnetic power P and electromagnetic torque T of the virtual DC motor are... e The formula is: P = EI; T e =P / ω.

[0082] Therefore, as Figure 7 As shown, in the virtual DC motor control steps, the power reference value P ref The mechanical torque T is obtained by dividing by the rated mechanical angular velocity ω0. m The current setpoint I is then obtained through calculations based on the virtual DC motor mechanical equation and the virtual DC motor armature circuit electromotive force equation. ref .

[0083] S40, Output current PI control step; The current setpoint I... ref The conversion is performed to obtain the output current I of the energy storage battery pack. 1ref And control signals are generated through PI control.

[0084] In specific implementation, such as Figure 8As shown, the main function of the output current PI control step is to control the input DC bus current setpoint I. ref The conversion is performed, and then the PWM control of the current loop PI regulator and PWM generator outputs a control signal, which is then transmitted to control devices such as IGBTs to adjust system parameters. The DC bus output current setpoint I... ref In the conversion section, since the current loop in traditional voltage-current dual-loop PI control tracks the output current of the energy storage battery pack, a conversion is required. Assuming the bidirectional DC-DC converter has a transmission efficiency of 100%, the output power at the energy storage battery pack end and the DC bus end is equal. That is, for the current setpoint I... ref The conversion is performed to obtain the output current I of the energy storage battery pack. 1ref The conversion formula is: In the formula, U1 is the actual output voltage of the energy storage battery pack.

[0085] In summary, to verify the control effect of the present invention, this embodiment takes the construction of a green tugboat power system model as an example, such as... Figure 2 As shown, the power system includes three generator sets, two sets of energy storage battery banks, a DC bus, four propulsion systems, and ship loads. The generator sets and energy storage battery banks supply power to the propulsion systems and ship loads via the DC bus. The control method of this embodiment is incorporated into the simulation, with the operating conditions switching every 10 seconds. The operating conditions change sequentially as follows: berthing, port entry / exit, economic navigation, towing, berthing, towing, economic navigation, port entry / exit, and berthing again, for a total of 90 seconds. The power required for berthing is 63.5 kW, for port entry / exit 1499.3 kW, for economic navigation 2482.8 kW, and for towing 4076.7 kW. In berthing, only the two sets of energy storage battery banks provide power. In port entry / exit and economic navigation, the two generators and two sets of energy storage battery banks share the power supply, and all three propulsion systems operate simultaneously. In towing operation, three generator sets and two energy storage battery sets share the power supply, and four propulsion systems work simultaneously.

[0086] In the aforementioned green tugboat power system, the DC bus output voltage without the DC microgrid control method described in this embodiment of the invention is detected, specifically as follows: Figure 9 As shown, the DC bus output voltage of the DC microgrid control method described in this embodiment of the invention is detected, specifically as follows: Figure 10As shown in the figure, the steady-state value of the DC bus voltage after incorporating the control method of this embodiment remains at the rated voltage of 1000V; the DC bus voltage without incorporating the control method of this embodiment exhibits a transient voltage valley of 954V when switching from berthing to towing conditions. After incorporating the control method of this embodiment, the transient voltage valley is 985V, and the transient voltage fluctuation optimization rate reaches 67%; the DC bus voltage without incorporating the control method of this embodiment exhibits a transient voltage peak of 1015V when switching from economic navigation conditions to port entry / exit conditions. After incorporating the control method of this embodiment, the transient voltage peak is 1004V, and the transient voltage fluctuation optimization rate reaches 73%. Therefore, the DC microgrid control method provided by this embodiment effectively solves the voltage rise and voltage drop problem caused by voltage compensation droop control.

[0087] In the aforementioned green tugboat power system, the output power of the generator set that has not incorporated the DC microgrid control method described in this embodiment of the invention is detected as follows: Figure 11 As shown, the output power of the generator set incorporating the DC microgrid control method described in this embodiment of the invention is detected as follows: Figure 12 As shown in the figure, before the control method described in this embodiment of the invention was implemented, the peak transient output power of each generator set reached 1430kW, indicating a short-term overload. After implementing the control method described in this embodiment of the invention, the peak transient output power of each generator set was 1280kW, and no overload occurred throughout the entire process. The figure also shows that because the steady-state output voltage of the DC bus remained at the rated voltage of 1000V, the generator set of the green tugboat, after incorporating the energy storage battery pack, stably outputs the economical power value in steady state, reaching 75% (1050kW) of the generator set's rated power.

[0088] As can be seen from the above, after incorporating the DC microgrid control method provided in the embodiments of the present invention, the generator set maintains economic power output during the steady-state process of the green tugboat, and the DC bus voltage outputs a stable rated voltage of 1000V. During the transient process, the generator set and the energy storage battery pack do not experience overload. It can be seen that the voltage and power fluctuations can be effectively suppressed, and the DC bus voltage fluctuation is less than or equal to 1.5%, which can better cope with the load power fluctuations and sudden changes under different working conditions of the tugboat.

[0089] Secondly, the present invention also provides a DC microgrid control system, comprising:

[0090] A DC microgrid construction module; the DC microgrid includes at least one generator set, at least one energy storage battery pack, a DC bus and a load, wherein the generator set and the energy storage battery pack are electrically connected to the load through the DC bus;

[0091] Voltage compensation droop control module; constructs the actual voltage value U of the DC bus output. dc Reference voltage value of DC bus The droop control function and the voltage bias value ΔU of the DC bus. dc The voltage compensation equation; using the input current I0 of the DC bus as the input signal, the reference voltage value is adjusted based on the droop control function. Droop control is performed using the voltage bias value ΔU of the DC bus. dc As an input signal, the reference voltage value of the DC bus is based on the voltage compensation equation. Perform voltage compensation and output the reference voltage value. Power reference value P after voltage-compensated droop control ref So that the actual output voltage of the DC bus is equal to the reference voltage value.

[0092] Virtual DC motor control module; establishes a virtual DC motor model, and based on the virtual DC motor model, adjusts the power reference value P in the voltage compensation droop control step. ref Calculations are performed to obtain the current setpoint I. ref ;

[0093] Output current PI control module; for the current setpoint I ref The conversion is performed to obtain the output current I of the energy storage battery pack. 1ref And control signals are generated through PI control.

[0094] This DC microgrid control system not only effectively solves the voltage rise and fall phenomenon of the DC bus during steady-state processes and reduces voltage fluctuations during transients, but also effectively improves voltage fluctuations caused by frequent and sudden changes in load power. This ensures that the entire DC microgrid system is free from overload, improves power system stability and response efficiency, and guarantees microgrid safety. The specific functions, roles, and methods of each module can be found in the above-described method embodiments, and will not be repeated here.

[0095] Thirdly, the present invention also provides a ship power system, including a DC microgrid control method as described in any of the embodiments of the first aspect above, or a DC microgrid control system as described in the embodiments of the second aspect above.

[0096] This system can also effectively handle load power fluctuations and sudden changes under different operating conditions. The specific functions, roles, and steps of the method or system can be found in the embodiments of the first and second aspects described above, and will not be repeated here.

[0097] In summary, the DC microgrid control method, system, and ship power system provided by this invention solve the voltage rise and fall problems caused by traditional droop control in hybrid energy storage by utilizing voltage compensation droop control steps. Furthermore, the invention improves the voltage fluctuation problem caused by introducing voltage compensation by utilizing virtual DC motor control steps. Simultaneously, this invention, in conjunction with the generator set's use of a three-winding transformer and twelve-pulse diode rectification, leverages the output droop characteristics to stabilize the generator's output power at the economic power point. This mitigates voltage fluctuations caused by frequent and sudden changes in load power, ensuring the entire DC microgrid system is free from overload, improving power system stability and response efficiency, guaranteeing microgrid safety, and achieving the goals of oil-electric energy integration and high-efficiency energy saving and emission reduction.

[0098] Furthermore, those skilled in the art should understand that although many problems exist in the prior art, each embodiment or technical solution of the present invention can be improved in only one or a few aspects, without necessarily solving all the technical problems listed in the prior art or the background art simultaneously. Those skilled in the art should understand that any content not mentioned in a claim should not be construed as a limitation on that claim.

[0099] Although this document frequently uses terms such as DC microgrid, voltage compensation, droop control, and virtual DC motor, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of the invention; interpreting them as any additional limitation would contradict the spirit of the invention. The terms "first," "second," etc. (if present) in the specification, claims, and accompanying drawings of the embodiments of the invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions 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.

Claims

1. A DC microgrid control method, characterized in that, Includes the following steps: The DC microgrid construction steps include: the DC microgrid includes at least one generator set, at least one energy storage battery pack, a DC bus, and a load, wherein the generator set and the energy storage battery pack are electrically connected to the load through the DC bus; Voltage droop control steps; Constructing the actual voltage value output from the DC bus. Reference voltage value of DC bus The droop control function and the voltage bias value of the DC bus. The voltage compensation equation; with the input current of the DC bus. As an input signal, the reference voltage value is based on the droop control function. Perform droop control based on the voltage bias value of the DC bus. As an input signal, the reference voltage value of the DC bus is based on the voltage compensation equation. Perform voltage compensation and output the reference voltage value. Power reference value after voltage compensation droop control So that the actual output voltage of the DC bus is equal to the reference voltage value. The voltage compensation equation is as follows: ； In the formula, Let be the convergence coefficient, and ; Virtual DC motor control steps: Establish a virtual DC motor model, and based on the virtual DC motor model, adjust the power reference value in the voltage compensation droop control step. Calculations are performed to obtain the current setpoint. ; Output current PI control steps; For the given current value The conversion is performed to obtain the output current of the energy storage battery pack. And control signals are generated through PI control.

2. The DC microgrid control method according to claim 1, characterized in that: The generator set includes a diesel generator, a three-winding transformer, and two sets of six-pulse diodes. The three-winding transformer includes an input winding and two output windings. The input winding is electrically connected to the diesel generator, and each of the two output windings is electrically connected to a six-pulse diode and then connected in parallel to the DC bus.

3. The DC microgrid control method according to claim 1, characterized in that: Let the voltage compensation amount of the DC bus be... The voltage bias value The function is The droop control function is: ； In the formula, For the first The no-load output current of each energy storage battery pack For the first The virtual resistance of an energy storage battery pack For the first Line impedance of the energy storage battery pack; This is the voltage compensation coefficient.

4. The DC microgrid control method according to claim 1, characterized in that: In the voltage compensation droop control step, the voltage bias value After calculation using the voltage compensation equation, the reference voltage value is compared. Add them together, and then add them to the input current. The voltage reference data after droop control and voltage compensation is obtained by subtracting the parameters calculated by the droop control function. This voltage reference data is then compared with the actual voltage value. Subtracting the values ​​and passing them through a PI controller yields a current reference value, which is then multiplied by the voltage reference value to obtain a power reference value. .

5. The DC microgrid control method according to claim 1, characterized in that, In the virtual DC motor control step, establishing the virtual DC motor model includes: The mechanical equations of the virtual DC motor are established as follows: ； ； In the formula, The inertial time constant of the virtual DC motor. This represents the mechanical torque of a virtual DC motor. The electromagnetic torque of the virtual DC motor. This represents the damping coefficient of the virtual DC motor. The mechanical angular velocity of the virtual DC motor. This represents the rated mechanical angular velocity of the virtual DC motor. The electromotive force equation for the armature circuit of the virtual DC motor is established as follows: ； In the formula, This represents the armature electromotive force of a virtual DC motor. This refers to the terminal voltage of the virtual DC motor. For the armature current of the virtual DC motor, This is the equivalent resistance of the armature circuit; Electromagnetic power of a virtual DC motor and electromagnetic torque The formula is: ； 。 6. The DC microgrid control method according to claim 5, characterized in that: In the virtual DC motor control steps, the power reference value By comparing with the rated mechanical angular velocity Divide to obtain the mechanical torque The current setpoint is then obtained through calculations based on the virtual DC motor mechanical equation and the virtual DC motor armature circuit electromotive force equation. .

7. The DC microgrid control method according to claim 1, characterized in that, For the given current value The conversion is performed to obtain the output current of the energy storage battery pack. The conversion formula is: ； In the formula, This is the actual output voltage value of the energy storage battery pack.

8. A DC microgrid control system, characterized in that, include: A DC microgrid construction module; the DC microgrid includes at least one generator set, at least one energy storage battery pack, a DC bus and a load, wherein the generator set and the energy storage battery pack are electrically connected to the load through the DC bus; Voltage compensation droop control module; constructs the actual voltage value output from the DC bus. Reference voltage value of DC bus The droop control function and the voltage bias value of the DC bus. The voltage compensation equation; with the input current of the DC bus. As an input signal, the reference voltage value is based on the droop control function. Perform droop control based on the voltage bias value of the DC bus. As an input signal, the reference voltage value of the DC bus is based on the voltage compensation equation. Perform voltage compensation and output the reference voltage value. Power reference value after voltage compensation droop control So that the actual output voltage of the DC bus is equal to the reference voltage value. The voltage compensation equation is as follows: ； In the formula, Let be the convergence coefficient, and ; Virtual DC motor control module; establishes a virtual DC motor model, and based on the virtual DC motor model, adjusts the power reference value in the voltage compensation droop control step. Calculations are performed to obtain the current setpoint. ; Output current PI control module; for the given current value The conversion is performed to obtain the output current of the energy storage battery pack. And control signals are generated through PI control.

9. A ship electrical system, characterized in that: This includes using the DC microgrid control method as described in any one of claims 1-7, or the DC microgrid control system as described in claim 8.

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