GB2608552A

GB2608552A - Direct current networking power system for waterborne vessel, and operation-and power-optimized control method for same

Info

Publication number: GB2608552A
Application number: GB2214606.2A
Authority: GB
Inventors: Wu Yunxiang; Shao Shiyi; Chang Guomei; Wu Zhijiang; Liu Yang; Wang Xiaomei; Tang Wenxian; Chen Yun; Su Shijie; Guo Sheng
Original assignee: Wuxi Silent Electric System Ses Tech Co Ltd
Current assignee: Wuxi Silent Electric System Ses Tech Co Ltd
Priority date: 2020-03-18
Filing date: 2021-02-27
Publication date: 2023-01-04
Also published as: CN111478307B; WO2021185056A1; GB202214606D0; CN111478307A

Abstract

Disclosed is a direct current networking power system for a waterborne vessel, the system comprising a port-side propulsion unit and a starboard-side propulsion unit. The propulsion units include a direct current bus, and the direct current bus is connected to at least two generator-based power supply mechanisms and a waterborne vessel propulsion mechanism. The direct current bus on the port side or the starboard side is provided with a load mechanism. An electronic power switch is provided between direct current buses on the port side and the starboard side. The power system for a waterborne vessel is provided with a means for isolating a portion of a load if the portion is short circuited. If a short circuit occurs at a certain location, the power system is capable of immediately isolating a short circuit source by means of short circuit support, thereby preventing the short circuit at the certain location from paralyzing the entire power system of the waterborne vessel, and improving the safety and redundancy of the system. Further disclosed is an operation- and power-optimized control method for the direct current networking power system for a waterborne vessel. The method improves power allocation accuracy of a power generator unit, and ensures that the power generator unit is running in a most fuel-efficient state.

Description

DC GRID POWER SYSTEM FOR WATERBORNE VESSEL AND

OPERATION-AND POWER-OPTIMIZED CONTROL METHOD FOR

SAME

TECHNICAL FIELD

The present invention relates to a DC grid power system for waterborne vessel, and in particular, to a DC grid power system for a waterborne vessel and an operation-and power-optimized control method for same,

BACKGROUND

A propulsion system for a waterborne vessel is generally composed of a diesel generator, a reducer, and a propulsion motor. The diesel generator drives the propulsion motor through the reducer to propel the waterborne vessel to operate. In this solution, devices are relatively cheap, but there are problems that the shafting takes up a lot of space and the vibration and noise are strong. In addition, when the waterborne vessel load changes greatly, the output power of the diesel generator cannot follow the change quickly, resulting in the defects of poor operating conditions of the diesel generator and high fuel consumption.

In order to save the layout space of the waterborne vessel shafting, increase the response speed, and improve the maneuverability of the electrical drive of the waterborne vessel, an electric propulsion system for an AC grid of a waterborne vessel has been developed. That is, the diesel generator drives the synchronous generator to generate electricity, and the generated constant frequency and constant voltage AC power is used for the AC grid through the AC switchboard. 'The AC voltage after the AC grid passes through the AC-DC-AC frequency converter to drive the propulsion motor of the waterborne vessel to operate. However, the synchronous generator has the characteristics of outputting a constant AC voltage of the same frequency and voltage. When the waterborne vessel load changes, the waterborne vessel can only adapt to the change of load power by cutting off or increasing the synchronous generator This nonlinear switching method may cause the operating diesel generator not to operate at the optimal power efficiency point, and there is a problem of an extremely low fuel usage rate. In addition, the control systems on two sides of the AC switchboard are designed and controlled separately, the integration of the entire system is poor, the device occupies a large space, and the device price is high.

Moreover, with high requirements for the level of the waterborne vessel offshore construction operations, various deck machinery has also tra.nsitioned from the ordinary constant speed operation requirements to the speed regulation requirements. The starting, braking, and speed regulation of waterborne vessel deck machinery all require a separate power supply fix power supply and modulation, which has the problems of complex control devices, a large occupied space, and difficulty in power modulation.

With the development of technology, a DC grid electric propulsion system has been developed. Each diesel generator on the waterborne vessel drives an asynchronous generator, each asynchronous generator is connected to a rectifier thereof, and the rectified DC is connected to the common DC bus. Multi-channel inverters are arranged in parallel on the common DC bus, and each inverter is connected to a propulsion motor or a load of the inverter, which can effectively solve the above problems. However, the following problems still exist in the DC grid electric propulsion system.

When a short circuit occurs in a device in the system, an obvious overcurrent may occur in the DC bus, the inverter, or an AC output terminal. If the faulty device is not selectively removed, the loss of power on the whole waterborne vessel and the loss of controllability of the waterborne vessel may be eventually caused, that is, the loss of propulsion ability, which may seriously lead to collision or fire of the waterborne vessel. According to "Guidelines for Selective Over-current Protection for Power System for Waterborne Vessel", CCS regulations stipulate that the electrical system has the automatic conversion function for the realization of fault selectivity, and except for the case of double sets of important devices powered by different distribution panels, short-circuit protection for all circuits including important device circuits shall be selective protection. In addition, under the premise of satisfying selective protection, the fault circuit should be cut off as soon as possible, thereby reducing the impact on the power system and the risk of fire. After searching the existing literature, it is found that the Chinese Patent Application No. CN201310215544.5 discloses "a network source steady-state voltage regulation optimization method for improving the transient voltage support capacity of the power grid". The method achieves the effect of system voltage regulation through the adjustment of generators and capacitors. For a highly redundant power system for a waterborne vessel, when the load short-circuits, the required support current is excessively large and exceeds the range that can be adjusted by the generators and capacitors, resulting in a series of safety problems of the power system. Therefore, a more stable and safer method is required for the short circuit support of the power system for a waterborne vessel.

In addition, the existing operation-and power-optimized control method for a power system for a waterborne vessel still has the following problems. I. The existing power management system (MIS) does not consider the influence of changes in the marine environment on the load power of the waterborne vessel during the driving of the waterborne vessel, as well as the power consumed by the entire power system, resulting in that the 1?Tvl.S cannot accurately obtain the current total load power of the system, and thus power of die generator set cannot be accurately allocated. In addition, the power management system cannot accurately determine the relationship between the proportion of diesel generator output power and fuel consumption, and cannot ensure that the generator set operates at the optimal economic time, resulting in energy waste.

2. When the DC grid power system for a waterborne vessel fails, such as a short circuit, a generator set fault, and the like, the control system cannot effectively and accurately deft!, mine the source of the fault, and cannot quickly remove the source of the fault or restore the operation of the faulty device, which cannot guarantee the safety and reliability of the operation of the waterborne vessel.

3. The existing DC grid power system cannot effectively cope with the sudden change of load power. When the load power increases sharply, it is necessary to strengthen the output power of the DC bus. The traditional method is to select a generator set with higher power or add a backup generator set, which increases shipbuilding costs. When the load power is reduced, or even the braking energy flows back, the excess electrical energy may lead to reverse power, which vvrill lead to serious consequences such as diesel generator failure and paralysis of the power system for a waterborne vessel. The traditional power system for a waterborne vessel generally handles this part of the energy by adding consumable devices, and there is a problem of energy waste.

When the waterborne vessel runs fast, turns, overtakes, or brakes, the output power of the generator set will suddenly increase or decrease. If the active power distribution of parallel generator sets is seriously unbalanced, when the total load power is relatively large, one generator set is often fully loaded or overloaded, while the other generator is still in a light load state. In this way, the capacity of the unit cannot be fully utilized, and -the efficiency of the entire power station cannot be played, which may cause serious malfunction of the power station. In the patent "active power distribution method for the least system fuel consumption of a plurality of conventional generator sets" (71-201410077794.1), the minimum operating power of diesel generator sets is calculated, and then the most suitable diesel generator sets are obtained through screening, so as to achieve the effect of saving fuel. The paper "Research on the Control Strategy of the Power Generation System of the New Scientific Research Vessel" published in "Ship Engineering" (Issue 2, 2018) by Yang Zhaoyu et al. introduced a power distribution method. Jr the method, power distribution is mainly performed under the electric energy transmission of the AC grid and by changing the frequency of the diesel generator set to change the rotational speed. However, in the method, it is necessary to sample more parameters such as voltage parameters and current parameters related to the power generation of the diesel venerator set, so the control structure is relatively complex, and changing the frequency has high requirements for speed regulation of the motor, so the cost of the diesel generator set is high. Although the method in the patent can effectively save fuel consumption, the system response speed is relatively slow when the load suddenly increases or decreases, and it takes a certain time to achieve the effect of power distribution. The patent "Power Distribution Method for Diesel Generator Sets Based on DC Grid Power Generation System" (201910259541.9) discloses a method for power management of venerator sets in a DC grid and improving power distribution accuracy of generator sets. However, in the case of short-term load changes, it is not economical to start or shut down the generator set, which may increase energy consumption instead.

SUMMARY

The technical problem to be solved by the present invention is to provide a DC grid power system for a waterborne vessel with high safety and high energy utilization In order to solve the above-mentioned technical problems; the technical solution adopted in the present invention is as follows. A direct current (DC) grid power system for a waterborne vessel includes a port-side propulsion unit and a starboard-side propulsion unit. Each of the propulsion units includes a DC bus, the DC bus is connected to at least two generator-based power supply mechanisms and a waterborne vessel propulsion mechanism. The DC bus on the port side or the starboard side is provided with a load mechanism, and an electronic power switch is arranged between the DC buses on the port side and the starboard side. Each of the venerator-based power supply mechanisms includes a diesel generator, the diesel generator is successively connected to a main circuit breaker, a rectifier module, and a fuse through a power supply line, and the power supply line is finally connected to the DC bus. A main voltage sensor is arranged on a wire between the rectifier module and the Ease, and the main voltage sensor is electrically connected to a generator control module.

The load mechanism includes a load inverter module connected to the DC bus through connection wires, fuses are arranged on positive and negative connection wires, a collection point A configured to be connected to a DC voltage sensor configured to detect a voltage value of a DC segment on a load circuit is arranged on the connection wire between the fuses and an input terminal of the load inverter module, an output terminal of the load inverter module is connected to an input terminal of a load circuit breaker of the load circuit, a collection point B' configured to be connected to an alternating current (AC) voltage sensor configured to collect an output AC voltage value after inversion is arranged between the output terminal of the load inverter module and the input terminal of the load circuit breaker, a collection point (7 configured to be connected to an AC current sensor configured to collect an outputted AC current value is arranged on an output terminal of the load circuit breaker, and the DC voltage sensor, the AC voltage sensor, and the AC current sensor are electrically connected to a con trol module; and the load circuit breaker is connected to an AC bus, the AC bus is connected to each electric load module in the power system for a waterborne vessel through a shunt wire, and a branch circuit breaker is arranged on the shunt wire between the electric load module and the AC bus.

As a preferred solution, the waterborne vessel propulsion mechanism includes a propulsion motor, the propulsion motor is connected to the DC bus through an electric line, and an electric circuit breaker, an inverter module, and the fuse are arranged in sequence on the electric line starting from the propulsion motor.

As a preferred solution, the propulsion unit further includes an energy storage mechanism connected to the DC bus, the energy storage mechanism includes an energy storage chopper module connected to the DC bus through two power storage wires, and the energy storage Chopper module is connected to an inductance filter module. A power storage capacitor is arranged between the inductance filter module and one of the power storage wires through a connecting wire, a power storage circuit breaker is arranged on the connecting wire, and the fuse is arra.nged on the power storage wire. A power storage voltage sensor is arranged on and connected to -the power storage wire, and the power storage voltage sensor is connected to an energy storage control module. A DC voltage sensor is arranged on the electric line between the inverter module and the DC bus, and the DC voltage sensor is connected to a motor control module.

As a preferred solution, an AC voltage sensor is arranged on the electric line between the inverter module and the electric circuit breaker, and the AC voltage sensor is connected to the motor control module.

As a preferred solution, an AC current sensor is arranged on the electric line between the propulsion motor and the electric circuit breaker, and the AC current sensor is connected to the motor control module.

As a preferred solution, the propulsion unit further includes a battery-powered mechanism connected to the DC bus, the battery-powered mechanism includes a lithium battery, the lithium battery is connected to the circuit breaker, a battery chopper module, and the fuse in sequence through a cable, and the cable is finally connected to the DC bus.

The beneficial effects of the system are as follows. Since this system includes a port-side propulsion unit and a starboard-side propulsion unit. Each of the propulsion units includes a DC bus, and at least two generator-based power supply mechanisms and a waterborne vessel propulsion mechanism are connected to the DC bus. An electronic power switch is arranged between the DC buses on the port side and the starboard side. When one-side propulsion unit fails, the propulsion unit may be removed from the system through the electronic power switch to ensure that the remaining part can operate normally, thereby improving the safety of the device When a certain location in the power system for a waterborne vessel is short-circuited, the power system can immediately isolate short circuit source through short circuit support, thereby preventing the short circuit at the certain location from paralyzing the entire power system for a waterborne vessel, and improving the safety and redundancy of the system.. Since the power system for a waterborne vessel is huge and complex, this system greatly facilitates fixed-point troubleshooting during the repair of the short-circuit part after the event, thereby saying a lot of time.

The DC grid power system has relatively high stability, reliability, and safety. In the event of a short circuit, the system automatically removes the source of the fault to ensure the stable operation of the entire power system.

Due to the arrangement of an energy storage mechanism, when the motor brakes, the energy storage mechanism stores electrical energy, which can not only avoid reverse power but also solve the problem of energy waste, thereby improving the economy and environmental protection of the power propulsion system for a waterborne vessel. Moreover, with the use of the energy storage mechanism, a diesel generator with a lower power may be selected during the design of the propulsion system to reduce the costs. In addition, power may be supplied to the DC bus by cooperating with the diesel generator during the operation of the waterborne vessel, so that the diesel generator can operate at the optimal fuel consumption point, thereby improving fuel efficiency and reducing operating costs. In addition, the energy storage mechanism can provide short-term power supply for the DC bus when the power system for a waterborne vessel fails so as to realize the fault ride-through of the waterborne vessel.

Since the propulsion unit farther includes a battery-powered mechanism connected to the DC bus, the battery-powered mechanism provides a variety of power sources for the waterborne vessel, so as to ensure the normal operation of the waterborne vessel when the generator fails.

Another technical problem to be solved by the present invention is to provide an operation-and power-optimized control method for a DC grid power system for a waterborne vessel.

In order to solve the above technical problems, the technical solution adopted in the present invention is as follows. The operation-and power-optimized control method for the DC grid power system for a waterborne vessel includes the following steps: step I: turning on a generator set, including: turning on the diesel generator, and detecting, by a speed sensor, a rotational speed of the diesel generator, where if the rotational speed of the diesel generator does not reach 1150-1550 rpm after 1.0-15s, the diesel generators of the electric propulsion system cannot be paralleled, and therefore the system reports an error and sends the error information to a monitoring terminal, so that the maintenance personnel controls the all of the diesel generators to stop through a remote control system and repair the diesel generators; and if the rotational speed of the diesel generator reaches a predetermined value, which indicates that the diesel generator completes the turn-on, the diesel generator starts operating; step 2: precharging the DC bus, including: after the diesel generator operates normally, charging the DC bus through a precharging circuit, monitoring, by the DC voltage sensor, a voltage of the DC bus, and when a voltage of the DC bus reaches 1050-1075 V, closing the main circuit breaker, so that an AC generated by the diesel generator is converted to a DC by the rectifier module to normally supply power to the DC bus; step 3: operating the load, including: upon completion of the precharging of the DC bus, starting to supply power to each load; converting the DC provided by the DC bus to ACs required for the propulsion motor and the daily load respectively through the load inverter module and the inverter module; respectively monitoring, by the two AC voltage sensors, AC-side voltages of the two load inverter modules, to determine whether the required voltage of each load is satisfied, and if the use conditions are satisfied, closing the load circuit breaker and the electric circuit breaker to supply power to the daily load and the propulsion motor; seep 4: inonitorin:u, and adjusting an operating status of the power system, including: power distribution operations on the generator set in the DC grid system, specifically including: step a: setting, by the main controller, parameters for each diesel generator and setting power parameters for each diesel generator set, that is, respectively setting a lower limit and an upper limit Put of an optimal operating load power for an (i = 1, 2, . N) diesel generator, and selecting a first diesel generator set as a default start item; step b: continuously detecting, by the main controller, a total power Pt of the DC grid power system, where when the load operates in the DC bus, the power generation system starts operating, and the first diesel generator set starts operating; reading, by the AC current sensor, an AC 11 generated by the first diesel generator set, detecting, by the voltage sensor, a rectified DC voltage value V, reading, by an AID sampling module, data about 1 and, sending the data to a sub-controller through a bus, calculating, by the sub-controller, an AC voltage Van according to It and Vt, and then calculating, by the sub-controller, a service power P, of the first diesel generator set by using the following formula: P =1hV xI x 0, where 4) is a power factor; causing the generated AC to pass through the rectifier power module, and setting rectification parameters of the rectifier power module to keep the rectified voltage value within V,"" -11"," to ensure P, < step c: calculating, by the main controller, a range of a total optimal operating load power of the diesel generator sets, where since only the first diesel generator set is in the operating state, a lower limit of the total optimal operating load power of the diesel generator sets is P, = P" , and an upper limit of the total optimal operating load power of the diesel generator sets is P =P * step b: successively determining, by the main controller, operating states of all of the diesel generator sets, if an ith diesel generator set is in an operating state, reading, by the AC current sensor of a generator circuit, an AC f, generated by the diesel generator set, detecting, by the voltage sensor, a rectified DC voltage value V,, reading, by an AID sampling module, data about 1-; and V, , sending the data to the sub-controller through the bus, calculating, by the sub-controller, the AC voltage according to 1t and V], and then calculating, by the sub-controller, a service power I", of the diesel generator set by using the following formula: = V731/9 x I x 0 causing the generated AC to pass through the rectifier power module, and setting rectification parameters of the rectifier power module to keep the rectified voltage value within Vim," -ll""" to ensure P, < P < P", ; step e: calculating, by the main controller, the range of the total optimal operating load power of the diesel generator sets by using the following formula: the lower limit of the total optimal operating load power of the diesel generator sets being calculated by: =1 Pil i=1 the upper limit of the total optimal operating load power of the diesel generator sets being calculated by: i =1 step comparing, by the main controller, a total power Pt of the DC bus with the lower limit P, and the upper limit Pu of the total optimal operating load power of the diesel generator sets, where if Pi <13 < P,, , it indicates that a generating power of the each diesel generator is within the optimal operating load power range when a total generating power of the diesel generator sets reaches 13, and step (g) of synchronously controlling voltages of the diesel generators according to a cross-coupling control strategy is performed, where if Pt does not satisfy P1 <13 <13, that is, when Pt >13 or Pt, step (h) of establishing an optimization model and solving an optimal operating sequence of the diesel generator sets is performed; step g: synchronously controlling the voltages of the diesel generators according to the cross-coupling control strategy, including: g-1: calculating, by the main controller, an average voltage " according to the current total power Pt of the DC grid system when 13 <Pt < P" , where 1:" satisfies: 13 <Pt <13, when output voltages of all of the operating diesel generators are all I"; g-2: sending, by the main controller, a voltage regulation command to each sub-controller after In is calculated; g-3: sending, by the sub-controller, a control signal to the AID sampling module after receiving the voltage regulation command from the main controller, and sending, by the AID sampling module, a PWM wave to the rectifier power module after receiving the signal, the PWM wave changing a duty cycle of an IGBT in the rectifier power module to adjust the rectified DC voltage value; g-4: continuously feeding back, by an A/D conversion module on each power generation circuit, the output voltage of the diesel generator to the each sub-controller, and sending, by the sub-controller, the voltage data to the main controller through the bus; g-5: calculating, by the main controller, a difference between 17' and each output voltage after obtaining the voltage data sent by the sub-controller on the power generation circuit, and sending a voltage compensation signal to the each sub-controller according to a voltage difference; g-6: sending, by the sub-controller, a control signal to the AID sampling module after receiving the voltage compensation signal from the main controller, and sending, by the AID sampling module, a PWM wave to the rectifier power module after receiving the signal, the PWM wave changing the duty cycle of the IGBT in the rectifier power module to adjust the rectified DC voltage value; g-7: cyclically performing the operations from step g-4; step h: establishing the optimization model and solving the optimal operating sequence of the diesel generator sets,including: h-1: setting an existing operating generator sequence to W = ,WJ: and a non-operating generator sequence to = 4:S1, where W u 3 = {1; NJ; h-2: calculating J = argmax -1(P1,(s))+P,(s')) if > Pa, that is, finding a diesel generator from the non-operating diesel generators with a largest average optimal operating load power, then performing step h-3, and performing step h-4 if Pt < Pi; h-3: calculating PI (P P,(wi))+ -1 (P,Cs1)+P(sr)), where if Pi<P, W=WL4SJI, S=S4Sj-}, and L = L.1-1, turning on the diesel generator with the largest average optimal operating load power found in step h-2, then performing step h-2, and performing step h-6 until P'>1"; h-4: calculating / = argmax -1 (/)(wi) +P), that is, finding a diesel generator with a (is,/ 2 " largest average optimal operating load power from the operating diesel generators, h-5 calculating P" p(w.)) (p(w') + 11(wl, and if F"> P W=WVW +1, ts 2 2 S=SLAWil, and L = L 1, that is, turning on the diesel generator with the largest average optimal operating load power found in step h-4, then performing step h-4, and performing step h-6 until P" <13, ; h-6: calculating 01 = (/+ ell--1 (/),vvi + PM, , where i = 1, 2" N-L, that s, 2 2 respectively calculating a difference between the average optimal operating load power of any diesel generator in the operating sequence and the average optimal operating load power of any diesel generator Q0n the non-operating sequence, where, = -1 (P(s')+ /),(5')) and 2 " _ _-(if;) novo); 2 " then calculating 1,1 = argmin 1 r -T. v_(1(v,) pi(w,i)± _ where if I = 0, W = S = L L +1 ifJ = 0, w = w s = s u lw, = -if I, .14 0, W =WU{S,}\{W,I, S=SU{W,}\{S,}, L=L the above process is the process of solving the optimal operating sequence of the diesel generators, that is, a maximum value P,"," of P, and a minimum value P of P" that satisfy Pi <P <F are found, so that the lower limit P1 and the upper limit P, of the total optimal operating load power of the diesel generator sets are closest to the total power P, of the DC bus; if I = 0, W = W U (Si}, S =S\{S,}, L = L+1, which indicates that PT= P and P" =P"",",, are satisfied after a diesel generator in a non-operating sequence is turned on without turning off the diesel generator in the operating sequence; if J = 0, W = W \ S = SU {Wi} L=1,-1, which indicates that P, =Pimax and Pt, =Punthi, are satisfied after a diesel generator in an operating sequence is turned off without turning on the diesel generator in the non-operating sequence; and if J 0, W = W U its& tWiji S = SU tWij \ [Si}, L = L, which indicates that P,=Pi"," and Pumax are satisfied after a diesel generator in the non-operating sequence is turned on and a diesel generator in the operating sequence is turned off; and h-7: upon completion of the above steps, that is, the process of solving the optimal operating sequence of the diesel generator sets is completed, periodically detecting, by the main controller, the total power P of the DC bus, if P, changes, performing step 4, and if P, does not change, ending the optimization, and maintaining the existing sequence of the diesel generator sets for operation As a preferred solution, step 4 further includes operations of fault diagnosis and repair; specifically including: when a short circuit occurs in a daily load circuit, and correspondingly a current at the branch circuit breaker instantly rises to a risk value, determining, by an inverter, that the short circuit occurs and immediately reducing the voltage to 0, so that the current at the branch circuit breaker drops to 0; performing; by the inverter, current support for the short circuit and gradually increasing the voltage, so that the current at the branch circuit breaker rises to a set peak value within 0.5s and remains for about 2s, the high current causing the branch circuit breaker to trip and dropping to 0, so as to cut off a short-circuit source to eliminate the fault; and performing; by the inverter, short circuit determination, wherein if the current value is relatively small, the fault is eliminated, and the grid voltage is established within is to recover noimal service of other devices, and if a fault point is not eliminated, automatic stop is enabled after 3s for protection; and when the diesel generator fails, stopping rotation of the propulsion motor, and immediately turning on the power storage capacitor to supply power to the DC bus to ensure the normal operation of the daily load; during the power supply by the power storage capacitor, turning on a standby generator set to supply power and energy to the waterborne vessel, and after the standby generator set is turned on, turning on the propulsion motor if all goes well, so that the waterborne vessel resumes operation, and charging the power storage capacitor through the DC bus for next service, so as to ensure that the daily power supply is not affected during the fault. ;As a preferred solution, step 4 further includes operations of generator power supplement and storage, specifically including: when the operating power required by the waterborne vessel increases to be greater than a rated power of the diesel generator, the voltage value of the DC bus decreases, and the DC voltage sensor detects that the voltage of the DC bus drops, determining, by the main controller, a manner to make up for AP according to a difference AP between the operating power and the rated power of the generator set and an expected overload duration T, when AP is less than a rated output power of the lithium battery, turning on the lithium battery to supply power to the DC bus to make up for AP to ensure the normal operation of the waterborne vessel; and if Al' exceeds the rated output power of the lithium battery and the expected overload duration T is less than 30s, turning on the power storage capacitor to charge the DC bus to make up for Al'; and when the operating power required by the waterborne vessel decreases to be less than the rated power of the diesel generator, and the DC voltage sensor monitors that the voltage of the DC bus restores to the normal state, controlling, by the main controller, the power storage capacitor or the lithium battery to be turned off, so that the DC bus starts charging the power storage capacitor or the lithium battery for next service. ;As a preferred solution, step 4 further includes an operation of storing braking energy, specifically including: presetting parameters in the load circuit, and inputting the parameters into the control module, the set parameters being as follows: a connection point of the main voltage sensor is denoted as a point A, where the point A is configured to collect the DC voltage VT, of the generator-based power supply mechanism, a connection point of the power storage voltage sensor is denoted as a point B, where the point B is configured to collect the voltage ii-put of the DC bus of the energy storage mechanism, a connection point of the DC voltage sensor is denoted as a point C, where the point C is configured to collect the DC voltage V3 of the waterborne vessel propulsion mechanism, a connection point of the AC voltage sensor is denoted as a point D, where the point D is configured to collect the power supply voltage /1,2 of the propulsion motor, and a connection point of the AC current sensor is denoted as a point E, where the point E is configured to collect the power supply current k11 of the propulsion motor; and when the waterborne vessel operates normally and each module operates normally, a DC-side voltage is v and when the waterborne vessel brakes suddenly at a certain moment, after the motor control module in the waterborne vessel propulsion mechanism receives a braking command, controlling, by the motor control module at the waterborne vessel propulsion mechanism, the inverter module to stop inversion, so that the propulsion motor loses power supply and V".., =0, where inertia of propeller rotation drives excess electric energy generated by the rotation of the propulsion motor to be rectified back to the DC grid through the waterborne vessel propulsion mechanism, and at this time, the DC voltage Vic is collected at the point C; and with the inputted excess electr c energy, the voltage DC rated of the entire DC bus rises; when the DC voltage Vikit ed! > Vinate.d is detected by voltage sensors at the points A, B, and C, closing the power storage circuit breaker in the energy storage mechanism, so that the high voltage of the DC bus is depressurized by the energy storage chopper module and charges the power storage capacitor of the energy storage mechanism, and the excess energy is stored; and when the voltage of the DC bus starts to drop and Tx7:td is detected by the voltage sensors at the points A, B, and C, controlling, by the energy storage control module in the energy storage mechanism, the power storage circuit breaker to open, so that the system completes the utilization of the excess energy. ;Beneficial effects of this method are as follows. ;In this method, the impact of changes in the marine environment on the load power of the waterborne vessel and the power consumed by the entire power system are considered, the total load power under the operating state of the system can be accurately obtained in real time, and the relationship between the output power ratio of diesel generators and fuel consumption can be accurately determined by establishing a power distribution optimization model. In this way, the power allocation accuracy of a generator set is improved, and it is ensured that the generator set is running in a most fuel-efficient state, thereby improving the energy efficiency and reducing energy waste and pollution. ;The DC grid power system has high stability, reliability, and safety. In the event of a short circuit (Inverter DC short circuit or daily load short circuit), the system automatically removes the source of the fault to ensure the stable operation of other parts of the power system other than the fault point. When a certain location in the power system for a waterborne vessel is short-circuited, the power system can immediately isolate short circuit source through short circuit support, thereby preventing the short circuit at the certain location from paralyzing the entire power system for a waterborne vessel, and improving the safety and redundancy of the system. Since the power system for a waterborne vessel is huge and complex, this system greatly facilitates fixed-point troubleshooting during the repair of the short-circuit part after the event, thereby saving a lot of time. ;Due to the arrangement of an energy storage mechanism, when the motor brakes, the energy storage mechanism stores electrical energy, which can not only avoid reverse power but also solve the problem of energy waste, thereby improving the economy and environmental protection of the power propulsion system for a waterborne vessel. Moreover, with the use of the energy storage mechanism, a diesel generator with a lower power may be selected during the design of the propulsion system to reduce the costs. In addition, power may be supplied to the DC bus by cooperating with the diesel generator during the operation of the waterborne vessel, so that the diesel generator can operate at the optimal fuel consumption point, thereby improving fuel efficiency and reducing operating costs_ In addition, the energy storage mechanism can provide short-term power supply for -the DC bus when the power system for a waterborne vessel fails, so as to realize the fault ride-through of the waterborne vessel and ensure the normal operation of the waterborne vessel. ;BRIEF DESCRIPTION OF THE DRAWINGS ;FIG I is a schematic structural diagram of Embodiment I of the invention. ;FIG 2 is a schematic structural diagram of Embodiment 2 of the invention. ;FIG 3 is a flowchart of a load short circuit support method. ;In the figure: 101. DC bus, 102. Electronic power switch, 103. DC voltage sensor; 201. Power storage capacitor, 202: Power storage circuit breaker, 203. Inductance filter module, 204: Energy storage chopper module, 205. Fuse, 206. Power storage voltage sensor, 207. Energy storage control module; 301: Lithium battery, 302. Circuit breaker; 303. Chopper module, 304 Fuse, 305. Fuse, 306. Lithium battery voltage sensor., 307. Lithium battery control module; 401. Diesel generator, 402. Main circuit breaker, 403. Rectifier module, 404. Fuse, 405. Main voltage sensor, 406. Generator control module, 407. Generator set monitoring apparatus; 408. AC voltage sensor, 409. AC current sensor, 410. Speed sensor, 411. Sub-controller 411, 412. AiD sampling module; 501. Fuse, 502. Load inverter module, 503. DC voltage sensor, 504. AC voltage sensor, 505. AC current sensor, 506. Control module, 507. Load circuit breaker, 508. AC bus, 509. Branch circuit breaker, 510. Branch circuit breaker, Si]. Branch circuit breaker; 601. Fuse, 602. Inverter module, 603. DC voltage sensor, 604 AC voltage sensor, 605. AC current sensor, 606. Motor control module, 607. Electric circuit breaker, 608. Propulsion motor; 7. Main controller, 8. A/D conversion module. ;DE TAILED DESCRIPTION ;Specific implementations of the present invention are described in detail below with reference to the accompanying drawings. ;Embodiment 1: As shown in FIG 1, a direct current (DC) grid power system for a waterborne vessel is provided, including a port-side propulsion unit and a starboard-side propulsion unit. Each of the propulsion units includes a DC bus 101, and the DC bus 101 is connected to a generator-based power supply mechanism, a waterborne vessel propulsion mechanism, an energy storage mechanism, and a load mechanism, The DC bus -101 on the port side or the starboard side is provided with a DC voltage sensor 103, and the two DC buses 101 are connected by an electronic power switch 102. When one DC bus OF a device connected to the DC bus fails, the electronic power switch 102 is automatically disconnected, and the faulty DC bus is cutoff, to ensure the normal operation of other devices. ;The generator-based power supply mechanism includes a diesel generator 401. The diesel generator 401 is connected to a main circuit breaker 402, a rectifier module 403, and a fuse 404 in sequence through the power supply line, and the cable is finally connected to the DC bus 101. A main voltage sensor 405 is arranged on the wire between the rectifier module 403 and the fuse 404, and the main voltage sensor 405 is electrically connected to a generator control module 406. The diesel generator 401 is provided with a rotational speed sensor 410, and a generator set monitoring apparatus 407 is arranged between the diesel generator 401 and the main circuit breaker 402. The generator set monitoring apparatus 407 includes an AC voltage sensor 408 and an AC current sensor 409 The load mechanism includes a load inverter module 502 connected to the DC bus 101 through connection wires, and fuses 501 are arranged on positive and negative connection wires. A collection point A configured to be connected to a DC voltage sensor 503 configured to detect a voltage value of a DC segment on a load circuit is arranged on the connection wire between the fuses 501 and an input terminal of the loa.d inverter module 502. ;An output terminal of the load inverter module 502 is connected to an input terminal of a load circuit breaker 507 of the load circuit A collection point B' configured to be connected to an alternating current (AC) voltage sensor 504 configured to collect an output AC voltage value after inversion is arranged between the output terminal of the load inverter module 502 and the input terminal of the load circuit breaker 507, A collection point C' configured to be connected to an AC current sensor 505 configured to collect an outputted AC current value is arranged on an output terminal of the load circuit breaker 507, and the DC voltage sensor 503, the AC voltage sensor 504, and the AC current sensor 505 are electrically connected to a control module 506. The load circuit breaker 507 is connected to an AC bus 508, the AC bus 508 is connected to each electric load module in the power system for a waterborne vessel through a shunt wire, and branch circuit breakers 509, 510, and 511 are arranged on the shunt wire between the electric loa.d module and the AC bus 508. ;The waterborne vessel propulsion mechanism includes a propulsion motor 608, the propulsion motor 608 is connected to the DC bus 101 through an electric line, and an electric circuit breaker 607, an inverter module 602, and the fuse 601 are arranged in sequence on the electric line starting from the propulsion motor 608. ;Embodiment 2: As shown in FIG 2, a DC grid power system for a waterborne vessel is provided,: including a port-side propulsion unit and a starboard-side propulsion unit. Each of the propulsion units includes a DC bus 101, and the DC bus 101 is connected to an I\1/2 set of generator-based power supply mechanisms, a waterborne vessel propulsion mechanism, an energy storage mechanism, and a load mechanism. The DC bus 101 on the port side or the starboard side is provided with a DC voltage sensor 103, and the two DC buses 101 are connected by an electronic power switch 102. When one DC bus or a device connected to the DC bus fails, the electronic power switch 102 is automatically disconnected, and the faulty DC bus is cut off, to ensure the normal operation of other devices The generator-based power supply mechanism includes a diesel generator 401. The diesel generator 401 is connected to a main circuit breaker 402, a rectifier module 403, and a fuse 404 in sequence through the power supply line, and the cable is finally connected to the DC bus 101. A main voltage sensor 405 is arranged on the wire between the rectifier module 403 and the fuse 404, and the main voltage sensor 405 is electrically connected to a generator control module 406. The diesel generator 401 is provided with a rotational speed sensor 410, and a generator set monitoring apparatus 407 is arranged between the diesel generator 401 and the main circuit breaker 402. The generator set monitoring apparatus 407 includes an AC voltage sensor 408 and an AC current sensor 409, The load mechanism includes a load inverter module 502 connected to the DC bus 101 through connection wires, and fuses 501 are arranged on positive and negative connection wires. A collection point A' configured to be connected to a DC voltage sensor 503 configured to detect a voltage value of a DC segment on a load circuit is arranged on the connection wire between the fuses 501 and an input terminal of the load inverter module 502. An output terminal of the load inverter module 502 is connected to an input terminal of a load circuit breaker 507 of the load circuit A collection point B' configured to be connected to an alternating current (AC) voltage sensor 504 configured to collect an output AC voltage value after inversion is arranged between the output terminal of the load inverter module 502 and the input terminal of the load circuit breaker 507. A collection point C' configured to be connected to an AC current sensor 505 configured to collect an outputted AC current value is arranged on an output terminal of the load circuit breaker 507, and the DC voltage sensor 503, the AC voltage sensor 504, and the AC current sensor 505 are electrically connected to a control module 506. The load circuit breaker 507 is connected to an AC bus 508, the AC bus 508 is connected to each electric load module in the power system for a waterborne vessel through a shunt wire, and branch circuit breakers 509, 510, and 511 are arranged on the shunt wire between the electric load module and the AC bus 508. ;The waterborne vessel propulsion mechanism includes a propulsion motor 608, the propulsion motor 608 is connected to the DC bus 101 through an electric line, and an electric circuit breaker 607, an inverter module 602, and the fuse 601 are arranged in sequence on the electric line starting from the propulsion motor 608. ;ADC voltage sensor 603 is arranged on the electric line between the inverter module 602 and the DC bus 101 in the waterborne vessel propulsion mechanism, and the DC voltage sensor 603 is connected to a motor control module 606. ;An AC voltage sensor 604 is arranged on the electric line between the inverter module 602 and the electric circuit breaker 607, and the AC voltage sensor 604 is connected to the motor control module 606. ;An AC current sensor 605 is arranged on the electric e between the propulsion motor 608 and the electric circuit breaker 607, and the AC current sensor 605 is connected to the motor control module 606. ;The power system further includes an energy storage mechanism connected to the DC bus 101. The energy storage mechanism includes an energy storage chopper module 204 connected to the DC bus 101 through two power storage wires. The energy storage chopper module 204 is connected to an inductance filter module 203. A power storage capacitor 2W is arranged between the inductance filter module 203 and one of the power storage wires through a connecting wire, a power storage circuit breaker 202 is arranged on the connecting wire, and a fuse 205 is arranged on and connected to the power storage wire. A power storage voltage sensor 206 is arranged on the power storage wire, and the power storage voltage sensor 206 is connected to an energy storage control module 207. ;The power system further includes a battery-powered mechanism connected to the DC bus 101. The battery-powered mechanism includes a lithium battery chopper module 304 connected to the DC bus 1b01 through two power storage wires. The lithium battery chopper module 304 is connected to an inductance filter module 303. A lithium battery 301 is arranged between the inductance filter module 303 and one of the power storage wires through a connecting wire, a lithium battery circuit breaker 302 is arranged on the connecting wire, and a fuse 305 is arranged on and connected to the power storage wire. A lithium battery voltage sensor 306 is arranged on the power storage wire; and the lithium battery voltage sensor 306 is connected to a lithium battery control module 307. ;The operation-and power-optimized control method for a DC grid power system for the waterborne vessel based on Embodiment 2 includes the following steps: step t: turning on a generator set, including: turning on the diesel generator 401, and detecting, by a speed sensor 410, a rotational speed of the diesel generator 401, where if the rotational speed of the diesel generator 401 does not reach 1150-1550 rpm alter 10-15s, the diesel generators 401 of the electric propulsion system cannot be paralleled, and therefore the system reports an error and sends the error information to a monitoring terminal, so that the maintenance personnel controls the all of the diesel generators 401 to stop through a remote control system and repair the diesel generators 401; and if the rotational speed of the diesel generator 401 reaches a predetermined value, which indicates that the diesel generator 401 completes the turn-on, the diesel generator starts operating; step 2: precharging the DC bus including: after the diesel generator 401 operates normally, charging the DC bus 101 through a precharging circuit, monitoring, by the DC voltage sensor 103, a voltage of the DC bus 101, and when a voltage of the DC bus 101 reaches 1050-1075 V. closing the main circuit breaker 402, so that an AC generated by the diesel generator 401 is converted to a DC by (he rectifier module 403 to normally supply power to the DC bus 101; step 3: operating the load, including: upon completion of the precharging of the DC bus 101 starting to supply power to each load; converting the DC provided by the DC bus 101 to ACs required for the propulsion motor 60S and the daily load respectively through the load inverter module 502 and the inverter module 602; respectively monitoring, by the AC voltage sensor 504 and the AC voltage sensor 604, AC-side voltages of the load inverter module 502 and the inverter module 602, to determine whether the required voltage of each load is satisfied, and if the use conditions are satisfied, closing the load circuit breaker 507 and the electric circuit breaker 607 to supply power to the daily load and the propulsion motor 608; step 4: monitoring and adjusting an operating status of the power system, including: power distribution operations on the generator set in the DC grid system, as shown in FIG 3, specifically including: step a: setting, by the main controller 7, parameters for each diesel generator and setting power parameters for each diesel generator set, that is, respectively setting a lower limit Pi, and an upper limit P of an optimal operating load power for an i (i = 1, 2, ..., N) diesel generator, and selecting a first diesel generator set as a default start item; step b: continuously detecting, by the main controller 7, a total power P, of the power system in the DC grid 9, where when the load operates in the DC bus 101, the power generation system starts operating, and the first diesel generator set starts operating; reading, by the AC current sensor 409, an AC T, generated by the first diesel generator set, detecting, by the voltage sensor 405, a rectified DC voltage value V" reading, by an AID sampling module 412, data about I, and V, , sending the data to a sub-controller 411 through a bus, calculating, by the sub-controller 411, an AC voltage VAG, according to I, and Vi, and then calculating, by the sub-controller 411, a service power Pj of the first diesel generator set by using the following formula: p =1fr xi, xØ, where is a power factor; causing the generated AC to pass through the rectifier power module 403, and setting rectification parameters of the rectifier power module 403 to keep the rectified voltage value within V," -Ica,. to ensure P <P, < , where in this embodiment, V., =1050V and V =1100V * step c: calculating, by the main controller 7, a range of a total optimal operating load power of the diesel generator sets, where since only the first diesel generator set is in the operating state, a lower limit of the total optimal operating load power of the diesel generator sets is P, = Pil, and an upper limit of the total optimal operating load power of the diesel generator sets is Pt, = step b: successively determining, by the main controller, operating states of all of the diesel generator sets, if an ith diesel generator set is in an operating state, reading, by the AC current sensor 409 of a generator circuit, an AC T generated by the diesel generator set, detecting, by the voltage sensor 405, a rectified DC voltage value V, , reading, by an AID sampling module 412, data about T and V, , sending the data to the sub-controller 411 through the bus, calculating, by the sub-controller 411, the AC voltage co according to /, and VI, and then calculating, by the sub-controller 411, a service power P of the ith diesel generator set by using the following formula: /1, = x /i x 0 causing the generated AC to pass through the rectifier power module 403, and setting rectification parameters of the rectifier power module 403 to keep the rectified voltage value within V,1, -V""" to ensure Ply < < ; step e: calculating, by the main controller 7, the range of the total optimal operating load power of the diesel generator sets by using the following formula: the lower limit of the total optimal operating load power of the diesel generator sets being calculated by: =EPT the upper limit of the total optimal operating load power of the diesel generator sets being calculated by: step f: comparing, by the main controller 7, a total power P, of the DC bus 101 with the lower limit P, and the upper limit Pi, of the total optimal operating load power of the diesel generator sets, where if P1 <P, < P" , it indicates that a generating power of the each diesel generator is within the optimal operating load power range when a total generating power of the diesel generator sets reaches Pt, and step (g) of synchronously controlling voltages of the diesel generators according to a cross-coupling control strategy is performed, where if P, does not satisfy PT <P,<P that is, when P, >13 or P, < Pr, step (h) of establishing an optimization model and solving an optimal operating sequence of the diesel generator sets is performed; step g: synchronously controlling the voltages of the diesel generators according to the cross-coupling control strategy, including: g-1: calculating, by the main controller 7, an average voltage I' according to the current total power Pt of the DC grid system when P1 <1 <P, , where 1" satisfies: P1 <Pt <I when output voltages of all of the operating diesel generators are all 1-; g-2: sending, by the main controller 7, a voltage regulation command to each sub-controller 411 after I' is calculated; g-3: sending, by the sub-controller 411, a control signal to the AID sampling module 412 after receiving the voltage regulation command from the main controller 7, and sending, by the AID sampling module 412, a PWM wave to the rectifier power module 403 after receiving the signal, the PWNI wave changing a duty cycle of an IGBT in the rectifier power module to adjust the rectified DC voltage value; g-4: continuously feeding back, by an AID conversion module 8 on each power generation circuit, the output voltage of the diesel generator to the each sub-controller 411, and sending, by the sub-controller 411, the voltage data to the main controller 7 through the bus; calculating, by the main controller 7, a difference between I" and each output voltage after obtaining the voltage data sent by the sub-controller 411 on the power generation circuit, and sending, by the main controller 7, a voltage compensation signal to the each sub-controller 411 according to a voltage difference; g-6: sending, by the sub-controller 411, a control signal to the AID sampling module 412 after receiving the voltage compensation signal from the main controller 7, and sending, by the All) sampling module 412, a l'IVVN/1 wave to the rectifier power module 403 after receiving the signal, the PWNI wave changing a duty cycle of an IGBT in the rectifier power module to adjust the rectified DC voltage value; g-7: cyclically performing the operations from step 2-4, step h: establishing the optimization model and solving the optimal operating sequence of the diesel generator sets, including: h-1: setting an existing operating generator sequence to W = and a non-operating generator sequence to S = where W U S = 423, 0_5 0 - 1 (s,) (s)) . h-2: calculating = argmax -(p" f 13, > P," that is, finding a diesel generator ntst.vmf. 2 from the non-operating diesel generators with a largest average optimal operating load power, then performing step h-3, and performing step h-4 if P, <J; h-3: calculating Pt = (1)"(Y"') + )) + 1(Puts ') + Pits ')) , where if P'< , W =Wu S, =, 2 2 S=S\{$-}, and L = L 41, turning on the diesel generator with the largest average optimal operating load power found in step h-2, then performing step h-2, and performing step h-6 until P'>11t; h-4: calculating I = argmax-ywi' +/I(w.)), that is, finding a diesel generator with a rif 2 largest average optimal operating load power from the operating diesel generators, h-5 calculating P" = -1 kw) + p(w.))--1 ( P,, and if P" > Pt, W=W\ {WT}, 2 2 'I S=StAWII, and L.. = -1, that is, turning on the diesel generator with the largest average optimal operating load power found in step h-4, then performing step h-4, and performing step h-6 until P"<11; h-6: calculating 0 = + (P(s') P,(s'i)--1 (P(wi) + P,(wi)),, where = 1, 2, ..., N-L, that is, -2 " 2 " respectively calculating a difference between the average optimal operating load power of any diesel generator in the operating sequence and the average optimal operating load power of any diesel generator in the non-operating sequence where (20,1 = +11(s1)) and _ _1(1)(wit 2 " then calculating = argmin -Wit t_t 2 IjrrjcLOS$A; -L where if I = 0, ifJ = 0, =WUISA, S=S \{S} L =L+1 if I, .14 0, W = W {VV,} S = S 1W,1, = L -1 W = W U ts, \ tw, s s u fs, L=L the above process is the process of solving the optimal operating sequence of the diesel generators, that is, a maximum value Pllita" of P, and a minimum value Punta, of P, that satisfy P, <P <F are found, so that the lower limit P1 and the upper limit P, of the total optimal operating load power of the diesel generator sets are closest to the total power Pt of the DC bus 101; ff I = 0, w = WU {S,}, S =S\ L=L+1, which indicates that P=P and Pu= Pumax are satisfied after a diesel generator in a non-operating sequence is turned on without turning off the diesel generator in the operating sequence; if J = 0, W = W \ {W,} S=SU {W,} L = L -1, which indicates that P, =Pliti." and Pt, =Puma, are satisfied after a diesel generator in an operating sequence is turned off without turning on the diesel generator in the non-operating sequence; and if t 0, W = WU {S,-} \ 8 = AS' U {Wt} \ = /I, , which indicates that and P" =P" are satisfied after a diesel generator in the non-operating sequence is turned on and a diesel generator in the operating sequence is turned off; and h-7: upon completion of the above steps, that is, the process of solving the optimal operating sequence of the diesel generator sets is completed, periodically detecting, by the main controller 7, the total power P of the DC bus 101, if P, changes, performing step 4, and if P, does not change, ending the optimization, and maintaining the existing sequence of the diesel generator sets for operation.

Step 4 further includes operations of fault diagnosis and repair, specifically including the following.

When the two DC buses 101 connected to the port side or the starboard side are in contact and a short circuit occurs, or a DC short circuit occurs in the inverter or the daily load, the electronic power switch 102 connected to the two DC buses 101 will trip within 15-25 is, thereby removing the faulty side from the DC bus of the non-faulty side.

When a DC short circuit occurs in the inverter, the capacitors of all inverters on the faulty side will discharge to the short-circuit point and deliver a current k, the current will flow through the fuse and may cause the fuse to blow. Due to the large capacitance of all non-faulty modules on the faulty side, the long loop, and the impedance of the fuse, the discharge time constant of the entire loop is long. Therefore, the fuse at the short-circuit point is blown due to the I2T accumulation of the current, thus being cut out of the circuit. The fuse of the non-short-circuit point in the faulty side does not reach a pre-arc I2T of the fuse and will not be damaged, so as to realize the selective removal of the fault when the inverter is short-circuited.

When a short circuit occurs in a daily load circuit (the branch circuit breaker 511 corresponding to the fault of the branch is detailed), a current at the branch circuit breaker 511 instantly rises to a risk value, an inverter 502 performs short circuit determination and immediately reduces the voltage to 0, so that the current at the branch circuit breaker 511 drops to 0. The inverter 501 starts to perform current support for the short circuit and gradually increases the voltage, so that the current at the branch circuit breaker 511 rises to a set peak value within 0.5s and remains for about 2s. The high current causes the branch circuit breaker 511 to trip and drops to 0, so as to cut off a short-circuit source to eliminate the fault. Then the inverter 502 performs short circuit determination, where if the current value is relatively small, the fault is eliminated, and the grid voltage is established within Is to recover normal service of other devices, and if a fault point is not eliminated, automatic stop is enabled after 3s for protection.

When the diesel generator 401 fails, rotation of the propulsion motor 608 is stopped, and the power storage capacitor 601 is immediately turned on. to supply power to the DC bus 101 to ensure the normal operation of the daily load; during the power supply by the power storage capacitor 601 (the period generally does not exceed 20s), turning on a standby generator set to supply power and energy to the waterborne vessel, and after the standby generator set is turned on, turning on the propulsion motor 608 if all goes well, so that the waterborne vessel resumes operation, and charging the power storage capacitor 601 through the DC bus 101 for next service, so as to ensure that the daily power supply is not affected during the fault.

Step 4 further includes operations of generator power supplement and storage, and the generator power is supplemented through peak shaving and valley filling, specifically including when the operating power required by the waterborne vessel increases to be greater than a rated power of the diesel generator 401, the voltage value of the DC bus 101 decreases, and the DC voltage sensor 103 detects that the voltage of the DC bus 101 drops, determining, by the main controller 7, a manner to make up for AP according to a difference AP between the operating power and the rated power of the generator set and an expected overload duration T, when AP is less than a rated output power of the lithium battery, turning on the lithium battery 301 to supply power to the DC bus 101 to make up for AP to ensure the normal operation of the waterborne vessel; and if AP exceeds the rated output power of the lithium battery and the expected overload duration T is less than 30s, turning on the power storage capacitor 601 to charge the DC bus 101 to make up for AR; and when the operating power required by the waterborne vessel decreases to be less than the rated power of the diesel generator 401, and the DC voltage sensor 103 monitors that the voltage of the DC bus 101 restores to the normal state, controlling, by the main controller 7, the power storage capacitor 601 or the lithium battery 301 to be turned off, so that the DC bus 101 starts charging the power storage capacitor 601 or the lithium battery 301 for next service.

Step 4 further includes an operation of storing braking energy, specifically including: presetting parameters in the load circuit, and inputting the parameters into the control module, the set parameters being as follows: a connection point of the main voltage sensor 405 is denoted as a point A, where the point A is configured to collect the DC voltage C"21 of the generator-based power supply mechanism, a connection point of the power storage voltage sensor 206 is denoted as a point B, where the point B is configured to collect the voltage fin of the DC bus 101 of the energy storage mechanism, a connection point of the DC voltage sensor 603 is denoted as a point C, where the point C is configured to collect the DC voltage Cc of the waterborne vessel propulsion mechanism, a connection point of the AC voltage sensor 604 is denoted as a point D, where the point D is configured to collect the power supply voltage V412 of the propulsion motor, and a connection point of the AC current sensor 605 is denoted as a point E, where the point E is configured to collect the power supply current /An of the propulsion motor 608; and when the waterborne vessel operates normally and each module operates normally, a DC-side voltage is itirt,T.7.1. t: and when the waterborne vessel brakes suddenly at a certain moment, after the motor control module 606 in the waterborne vessel propulsion mechanism receives a braking command, controlling, by the motor control module 606 at the waterborne vessel propulsion mechanism, the inverter module 602 to stop inversion, so that the propulsion motor 608 loses power supply and kT11,=0, where inertia of propeller rotation drives excess electric energy generated by the rotation of the propulsion motor 608 to be rectified back to the DC grid through the waterborne vessel propulsion mechanism, and at this time, the DC voltage Vnc:, is collected at it r= Ti nc the point C; and with the inputted excess electric energy, the voltage rated of the entire DC bus 101 rises; when the DC voltage I lx:3-47,7c2 Vpc rarai,d is detected by voltage sensors at the points A, B, and C, closing the power storage circuit breaker 202 in the energy storage mechanism, so that the high voltage of the DC bus 101 is depressurized by the energy storage chopper module 204 and charges the power storage capacitor 201 of the energy storage mechanism, and the excess energy is stored; and when the voltage of the DC bus 101 starts to drop and I/pet = -Dr 3 is detected by the voltage sensors at the points A, B, and C, controlling, by the energy storage control module 207 in the energy storage mechanism, the power storage circuit breaker 202 to open, so that the system completes the utilization of the excess energy.

The above embodiments only exemplarily describe the principles and effects of the present invention; and some applied embodiments are not intended to limit the present invention It should be noted that a person of ordinary skill in the art may further make several modifications and improvements without departing from the inventive concept of the present invention, which all fall within the protection scope of the present invention.

Claims

C LA I MSWhat is claimed is: 1. A direct current (DC) grid power system for a waterborne vessel, comprising a port-side propulsion unit and a starboard-side propulsion unit, each of the propulsion units comprises a DC bus, the DC bus is connected to at least two generator-based power supply mechanisms and a waterborne vessel propulsion mechanism, the DC bus on the port side or the starboard side is provided with a load mechanism, an electronic power switch is arranged between the DC buses on the port side and the starboard side, each of the generator-based power supply mechanisms comprises a diesel generator, the diesel generator is successively connected to a main circuit breaker, a rectifier module, and a fuse through a power supply line, the power supply line is finally connected to the DC bus, a main voltage sensor is arranged on a wire between the rectifier module and the fuse, and the main voltage sensor is electrically connected to a generator control module; the load mechanism comprises a load inverter module connected to the DC bus through connection wires, fuses are arranged on positive and negative connection wires, a collection point A' configured to be connected to a DC voltage sensor configured to detect a voltage value of a DC segment on a load circuit is arranged on the connection wire between the fuses and an input terminal of the load inverter module, an output terminal of the load inverter module is connected to an input teiminal of a load circuit breaker of the load circuit, a collection point B' configured to be connected to an alternating current (AC) voltage sensor configured to collect an output AC voltage value after inversion is arranged between the output terminal of the load inverter module and die input terminal of the load circuit breaker, a collection point C' configured to be connected to an AC current sensor configured to collect an outputted AC current value is arranged on an output terminal of the load circuit breaker, and the DC voltage sensor, the AC voltage sensor, and the AC current sensor are electrically connected to a control module: and the load circuit breaker is connected to an AC bus, the AC bus is connected to each electric load module in the power system for a waterborne vessel through a shunt wire, and a branch circuit breaker is arranged on the shunt wire between the electric load module and the AC bus.
2. The DC grid power system for a waterborne vessel according to claim I, wherein the waterborne vessel propulsion mechanism comprises a propulsion motor, the propulsion motor is connected to the DC bus through an electric line, and an electric circuit breaker, an inverter module, and the fuse are arranged in sequence on the electric line starting from the propulsion 2g motor.
3. The DC grid power system for a waterborne vessel according to claim 2, wherein the propulsion unit further comprises an energy storage mechanism connected to the DC bus, the energy storage mechanism comprises an energy storage chopper module connected to the DC bus through two power storage wires, the energy storage chopper module is connected to an inductance filter module, a power storage capacitor is arranged between the inductance filter module and one of the power storage wires through a connecting wire, a power storage circuit breaker is arranged on the connecting wire, and the fuse is arranged on and connected to the power storage wire; a power storage voltage sensor is arranged on the power storage wire, and the power storage voltage sensor is connected to an energy storage control module; and a DC voltage sensor is arranged on the electric line between the inverter module and the DC bus, and the DC voltage sensor is connected to a motor control module.
4. The DC grid power system for a waterborne vessel according to claim 3, wherein an AC voltage sensor is arranged on the electric line between the inverter module and the electric circuit breaker, and the AC voltage sensor is connected to the motor control module.
5, The DC grid power system for a waterborne vessel according to claim 4, wherein an AC current sensor is arranged on the electric line between the propulsion motor and the electric circuit breaker, and the AC current sensor is connected to the motor control module.
6. The DC grid power system for a waterborne vessel according to claim 5, wherein the propulsion unit further comprises a battery-powered mechanism connected to the DC bus, the battery-powered mechanism comprises a lithium battery, the lithium battery is connected to the circuit breaker, a battery chopper module, and the fuse in sequence through a cable; and the cable is finally connected to the DC bus,
7. An operation-and power-optimized control method for the DC grid power system for a waterborne vessel according to claim 6, comprising the following steps: step I: turning on a generator set; comprising: turning on the diesel generator, and detecting; by a speed sensor; a rotational speed of the diesel generator, wherein if the rotational speed of the diesel generator does not reach 1150-1550 rpm after 10-15s, the diesel generators of the electric propulsion system cannot be paralleled, and therefore the system reports an error and sends the error information to a monitoring terminal, so that the maintenance personnel controls the all of the diesel generators to stop through a remote control system and repair the diesel generators; and if the rotational speed of the diesel generator reaches a predetermined value, which indicates that the diesel generator completes the turn-on, the diesel generator starts operating; step 2: precharging the DC bus, comprising: after the diesel generator operates normally, charging the DC bus through a precharging circuit, monitoring, by the DC voltage sensor, a voltage of the DC bus, and when a voltage of the DC bus reaches 1050-1075 V, closing the main circuit breaker, so that an AC generated by the diesel generator is convened to a DC by the rectifier module to normally supply power to the DC bus; step 3: operating the load, comprising: upon completion of the precharging of the DC bus, starting to supply power to each load; converting the DC provided by the DC bus to ACs required for the propulsion motor and the daily load respectively through the load inverter module and the inverter module; respectively monitoring, by the two AC voltage sensors, AC-side voltages of the two load inverter modules, to determine whether the required voltage of each load is satisfied, and if the use conditions are satisfied, closing the load circuit breaker and the electric circuit breaker to supply power to the daily load and the propulsion motor; step 4: monitoring and adjusting an operating status of the power system, comprising: power distribution operations on the generator set in the DC grid system, specifically compri sing step a: setting, by the main controller, parameters for each diesel generator and setting power parameters for each diesel generator set, that is, respectively setting a lower limit P, and an upper limit Pth of an optimal operating load power for an i (i = 1, 2, ..., N) diesel generator, and selecting a first diesel generator set as a default start item; step b: continuously detecting, by the main controller, a total power Pt of the DC grid power system, wherein when the load operates in the DC bus, the power generation system starts operating, and the first diesel generator set starts operating; reading, by the AC current sensor, an AC /, generated by the first diesel generator set, detecting, by the voltage sensor, a rectified DC voltage value Vj, reading, by an AID sampling module, data about I and, sending the data to a sub-controller through a bus, calculating, by the sub-controller, an AC voltage VAcI according to I, and V, , and then calculating, by the sub-controller, a service power P, of the first diesel generator set by using the following formula: P, =x I xØ, wherein * is a power factor; causing the generated AC to pass through the rectifier power module, and setting rectification parameters of the rectifier power module to keep the rectified voltage value El -Vima" to ensure Pi, <13 <1)," ; step c: calculating, by the main controller, a range of a total optimal operating load power of the diesel generator sets, wherein since only the first diesel generator set is in the operating state, a lower limit of the total optimal operating load power of the diesel generator sets is P, = R" and an upper limit of the total optimal operating load power of the diesel generator sets is Pi, =11" ; step d: successively determining, by the main controller, operating states of all of the diesel generator sets, if an ith diesel generator set is in an operating state, reading, by the AC current sensor of a generator circuit, an AC I, generated by the diesel generator set, detecting, by the voltage sensor, a rectified DC voltage value Vi, reading, by an AID sampling module, data about /, and V; , sending the data to the sub-controller through the bus, calculating, by the sub-controller, the AC voltage VACi according to /, and V, , and then calculating, by the sub-controller, a service power Pi of the ith diesel generator set by using the following formula: 1 =JV x /, x 0, wherein 14) is a power factor; causing the generated AC to pass through the rectifier power module, and rectification parameters of the rectifier power module to keep the rectified voltage value 4'""x to ensure P < < IL; step e: calculating, by the main controller, the range of the total optimal operating load power of the diesel generator sets by using the following formula: the lower limit of the total optimal operating load power of the diesel generator sets being calculated by: the upper limit of the total optimal operating load power of the diesel generator sets being calculated by: Pu = Piu i=I step comparing, by the main controller, a total power P, of the DC bus with the lower limit P, and the upper limit P, of the total optimal operating load power of the diesel generator sets, wherein if P1 <13 < Pi, , it indicates that a generating power of the each diesel generator is within the optimal operating load power range when a total generating power of the diesel generator sets reaches Pt, and step (g) of synchronously controlling voltages of the diesel generators according to a cross-coupling control strategy is peiformed, wherein if 1 does not satisfy Pr < P, < P," that is, when P1> P"or P1<P1, step (h.) of establishing an optimization model and solving an optimal operating sequence of the diesel generator sets is performed; step g: synchronously controlling the voltages of the diesel generators according to the cross-coupling control strategy, comprising: g-l: calculating, by the main controller, an average voltage 1" according to the current total power Pt of the DC grid system when Pr <T <P, wherein T" satisfies: Pr < P, < when output voltages of all of the operating diesel generators are all V'; g-2: sending, by the main controller, a voltage regulation command to each sub-controller after V' is calculated; g-3: sending, by the sub-controller, a control signal to the AID sampling module after receiving the voltage regulation command from the main controller, and sending, by the AID sampling module, a PWM wave to the rectifier power module after receiving the signal, the PWM wave changing a duty cycle of an IGHT in the rectifier power module to adjust the rectified DC voltage value; g-4: continuously feeding back, by an AID conversion module on each power generation circuit, the output voltage of the diesel generator to the each sub-controller, and sending, by the sub-controller, the voltage data to the main controller through the bus; g-5: calculating, by the main controller, a difference between V' and each output voltage after obtaining the voltage data sent by the sub-controller on the power generation circuit, and sending a voltage compensation signal to the each sub-controller according to a voltage difference; g-6: sending, by the sub-controller, a control signal to the A/D sampling module after receiving the voltage compensation signal from the main controller, and sending, by the AID sampling module, a PWM wave to the rectifier power module after receiving the signal, the PWM wave changing the duty cycle of the IGBT in the rectifier power module to adjust the rectified DC voltage value; 8-7: cyclically performing, the operations from step 8-4; step h: establishing the optimization model and solving the optimal operating sequence of the diesel generator sets, comprising: h-1: setting an existing operating generator sequence to W.= WO and a non-operating generator sequence to S = wherein W U S = {1,2%,3e*-,141; h-2: calculating = argmax (/3"(s' ) + ) L 2 from the non-operating diesel generators with a largest average optimal operating load power, then performing step h-3, and performing step h-4 if g <P1; h-3 calculating P9 (PI' 91) + Pr'))+ -1 (Ps') + s ')) , wherein if P' < Pt W=Wv{Sj}, S=S4SJI, and L = turning on the diesel generator with the largest average optimal operating load power found in step h-2, then performing step h-2, and performing step h-6 until P' > h-4: calculating I = argmax (P"(w') +p1) that is, finding a diesel generator with a 0-r-ziL:L 2 largest average optimal operating load power from the operating diesel generators; h-5: calculating g" = /-(pw') + 11(wi))--1 Vw') + 1v1)), and if P" >1 2 " S=ScOVII, and L = L -I, that is, turning on the diesel generator with the largest average optimal operating load power found in step h-4, then performing step h-4, and performing step h-6 until Ell< P, , wherein i = 1, 2, N-L, that is, h-6: calculating 0 = (pu(si) plisp)11,, 2 2 respectively calculating a difference between the average optimal operating load power of any diesel generator in the operating sequence and the average optimal operating load power of any diesel generator in the non-operating sequence, wherein 0 = (1),(s')+ P(s')) and (pu(W,) I, then calculating 1,1 = argmin IL I (jAwi + ewl+ _ u wherein if I = 0, W U S S \ = + if 1= 0, if g that s, Ending a diesel generator w=w\fwd, w = w twj s = s U tw, = -1 if I, J 0, w = w u Is, \ -tw, s = s u tw, \ fs, L=L the above process is the process of solving the optimal operating sequence of the diesel generators, that is, a maximum value Pima, of P, and a minimum value Pm., of Pi, that satisfy P1 < P, <F, are found, so that the lower limit Pi and the upper limit Pi, of the total optimal operating load power of the diesel generator sets are closest to the total power P of the DC bus; if I = 0, W = W U {S, ,S' = S \ IS, L = L +1, which indicates that I and P,=P are satisfied after a diesel generator in a non-operating sequence is turned on without turning off the diesel generator in the operating sequence; if J = 0, W = W \ {W,}, S = ,S'U {W1}, L = L -1, which indicates that P,= iln," and P"= P""," are satisfied after a diesel generator in an operating sequence is turned off without turning on the diesel generator in the non-operating sequence; and if J 0, W = W U {S,1\ {W,1, S = SU {W,1 \ {S,1, L = , which indicates that I', = P,""", and Pu -Pumax are satisfied after a diesel generator in the non-operating sequence is turned on and a diesel generator in the operating sequence is turned off; and h-7: upon completion of the above steps, that is, the process of solving the optimal operating sequence of the diesel generator sets is completed, periodically detecting, by the main controller, the total power P, of the DC bus, if P, changes, performing step 4, and if P" does not change, ending the optimization, and maintaining the existing sequence of the diesel generator sets for operation.
8. The operation-and power-optimized control method for the DC grid power system a waterborne vessel according to claim 7, wherein step 4 further comprises operations of fault diagnosis and repair,sped II callv comprising: when a short circuit occurs in a daily load circuit, and correspondingly a current at the branch circuit breaker instantly rises to a risk value, determining, by an inverter, that the short circuit occurs and immediately reducing the voltage to 0, so that the current at the branch circuit breaker drops to 0; performing, by the inverter, current support for the short circuit and gradually increasing the voltage, so that the current at the branch circuit breaker rises to a set peak value within 0.5s and remains for about 2s, the high current causing the branch circuit breaker to trip and dropping to 0, so as to cut off a short-circuit source to eliminate the fault; and performing, by the inverter, short circuit determination, wherein if the current value is relatively small, the fault is eliminated, and the grid voltage is established within Is to recover normal service of other devices, and if a fault point is not eliminated, automatic stop is enabled after 3s for protection; and when the diesel generator fails, stopping rotation of the propulsion motor, and immediately turning on the power storage capacitor to supply power to the DC bus to ensure the normal operation of the daily load; during the power supply by the power storage capacitor, turning on a standby generator set to supply power and energy to the waterborne vessel, and after the standby generator set is turned on, turning on the propulsion motor if all goes well, so that the waterborne vessel resumes operation, and charging the power storage capacitor through the DC bus for next service, so as to ensure that the daily power supply is not affected during the fault.
9. The operation-and power-optimized control method for the DC grid power system for a waterborne vessel according to claim 8, wherein step 4 further comprises operations of generator power supplement and storage, specifically comprising: when the operating power required by the waterborne vessel increases to be greater than a rated power of the diesel generator, the voltage value of the DC bus decreases, and the DC voltage sensor detects that the voltage of the DC bus drops, determining, by the main controller; a manner to make up for AP according to a difference AP between the operating power and the rated power of the generator set and an expected overload duration T, when AP is less than a rated output power of the lithium battery, turning on the lithium battery to supply power to the DC bus to make up for AP to ensure the normal operation of the waterborne vessel; and if AP exceeds the rated output power of the lithium battery and the expected overload duration T is less than 30s, turning on the power storage capacitor to charge the DC bus to make up for AR; and when the operating power required by the waterborne vessel decreases to be less than the rated power of the diesel generator, and the DC voltage sensor monitors that the voltage of the DC bus restores to the normal state, controlling, by the main controller, the power storage capacitor or the lithium battery to be turned off, so that the DC bus starts charging the power storage capacitor or the lithium battery for next service.
10. The operation-and power-optimized control method for the DC grid power system for a waterborne vessel according to claim 9, wherein step 4 farther comprises an operation of braking energy storage, specifically comprising: presetting parameters in the load circuit, and inputting the parameters into the control module, the set parameters being as follows: a connection point of the main voltage sensor is denoted as a point A, wherein the point A is configured to collect the DC voltage F-Dct of the generator-based power supply mechanism, a connection point of the power storage voltage sensor is denoted as a point B, wherein the point B is configured to collect the voltage Er, of the DC bus of the energy storage mechanism, a connection point of the DC voltage sensor is denoted as a point C, wherein the point C is configured to collect the DC voltage of the waterborne vessel propulsion mechanism, a connection point of the AC voltage sensor is denoted as a point D, wherein the point D is configured to collect the power supply voltage V11.2 of the propulsion motor, arid a connection point of the AC current sensor is denoted as a point E, wherein the point E is configured to collect the power supply current of the propulsion motor; and when the waterborne vessel operates normally and each module operates normally, a DC-side voltage is 1; and when the waterborne vessel brakes suddenly at a certain moment, after the motor control module in the waterborne vessel propulsion mechanism receives a braking command, controlling, by the motor control module at the waterborne vessel propulsion mechanism, the inverter module to stop inversion, so that the propulsion motor loses power supply and V4r, =0, wherein inertia of propeller rotation drives excess electric energy generated by the rotation of the propulsion motor to be rectified back to the DC grid through the waterborne vessel propulsion mechanism, and at this time, the DC voltage V, > 11,Jent," dr= TInci-VD.:2 is collected at the point C; and with the inputted excess electric energy, the voltage i* Dr rated of the entire DC bus rises; when the DC voltage > is detected by voltage sensors at the points A, B, and C, closing the power storage circuit breaker in the energy storage mechanism, so that the high voltage of the DC bus is depressurized by the energy storage chopper module and charges the power storage capacitor of the energy storage mechanism, and the excess energy is stored; and when the voltage of the DC bus starts to drop and is detected by the voltage sensors at the points A, B, and C, controlling, by the energy storage control module in the energy storage mechanism, the power storage circuit breaker to open, so that the system completes the utilization of the excess energy.