Energy management method for DC power supply system of electric propulsion ship

Abstract

The present invention relates to an energy management method for a DC power supply system of an electric propulsion ship. A diesel generator set is connected to a DC bus through a diode rectifier, and a lithium-ion battery pack is connected to the DC bus through a DC converter, forming a DC power supply system. The DC power supply system is equipped with an energy management system for scheduling and managing the DC power supply system. The energy management system has three power supply modes: pure battery mode, pure diesel-electric mode, and hybrid power mode. The DC power supply system adopts a diode rectifier solution, which greatly reduces the cost of the system; the diesel generator set cooperates with the battery pack to improve the system operation efficiency; the energy management system controls the output voltage phase angle of the diesel generator set to realize a virtual multi-pulse rectification form, effectively reducing the voltage ripple of the DC power supply system. The multi-strategy mode switching function and real-time energy management strategy effectively solve the problem of energy scheduling and distribution strategy of diesel generator sets and battery packs.

Description

Technical Field

[0001] The present invention relates to a new energy ship direct current power supply technology, and in particular to an energy management method for a direct current power supply system of an electric propulsion ship. Background Art

[0002] Hybrid ships have the advantages of long cruising time, high operating efficiency of diesel generators, and flexible operation modes of the entire ship. In the global environment of energy conservation and emission reduction, they have been favored by many users. At present, diesel generators plus controlled rectifiers are generally used to achieve DC networking. The price of controlled rectifiers in large-scale DC networking accounts for a relatively high proportion of the cost of the entire DC power supply system, which hinders the development of DC networking.

[0003] In order to solve the problem of high price of controlled rectifiers in DC networking, a solution of using diode rectification instead of controlled rectifiers was proposed. However, the output DC ripple of the diode uncontrolled rectifier is large, which will affect the efficiency of the propulsion motor and increase the harmonic content of the daily inverter output.

[0004] Currently, there are few cases of using uncontrolled rectifiers as DC networking, and even fewer cases of using uncontrolled rectifiers plus battery packs to coordinate DC networking, because this solution has the characteristics of complex control logic and high control response requirements of the energy management system. Summary of the invention

[0005] Aiming at the problems of large output ripple and complex control logic of the uncontrolled rectifier networking scheme used in the current DC power supply system of electric propulsion ships, an energy management method for the DC power supply system of electric propulsion ships was proposed.

[0006] The technical solution of the present invention is: an energy management method for a DC power supply system of an electric propulsion ship, wherein a diesel generator set is connected to a DC bus through a diode rectifier, and a lithium-ion battery pack is connected to the DC bus through a DC converter, forming an electric propulsion ship DC power supply system; the DC power supply system of the electric propulsion ship is equipped with an energy management system for dispatching and managing the DC power supply system, the energy management system collects the output voltage, frequency and phase angle of each diesel generator set, and controls the output voltage and speed of the diesel generator through real-time Ethernet; the energy management system controls the output voltage and current of the DC converter through real-time Ethernet; the energy management system is provided with three power supply modes: pure battery mode, pure diesel-electric mode, and hybrid power mode; in pure electric mode, the battery pack transmits electric energy to the DC distribution board bus through a DC converter, and the energy management system controls the two DC converters to balance power through voltage and power droop modes;

[0007] In pure diesel-electric mode, only the diesel generator sets supply power to the DC bus through the diode rectifier, and the energy management system controls the voltage and power droop mode of each diesel generator set for power balancing;

[0008] In hybrid mode, the diesel generator set and the battery pack simultaneously supply power to the DC bus, and the energy management system dispatches and manages the power distribution of the diesel generator set and the battery pack.

[0009] Furthermore, the electric propulsion ship DC power supply system includes n diesel generator sets connected to the DC bus through diode rectification, n is greater than 2, and the energy management system controls the speed of the diesel generator sets, controls the frequency of the voltage emitted by each diesel generator set to be consistent, and the voltage phase angle differs by 2π / n.

[0010] Furthermore, when only one diesel generator set is supplying power to the grid, the DC converter sets the maximum and minimum output voltage limits so that the battery pack absorbs or releases energy from the DC bus and controls the ripple value of the DC bus.

[0011] Furthermore, the energy management system controls the diesel generator set to accelerate and decelerate through real-time Ethernet to adjust the output voltage phase angle of the diesel generator set, as follows:

[0012] When the energy management system's given phase angle ω1 is greater than the actual generator set output phase angle ω2, the energy management system controls the unit controller to accelerate through the real-time Ethernet. The acceleration signal is a switch pulse signal. The given pulse width T is determined by the energy management system's given phase angle ω1 and the actual generator set output phase angle ω2. T1 is the pulse period; on the contrary, when ω1 is less than ω2, the energy management system controls the unit controller to slow down through real-time Ethernet.

[0013] Furthermore, the DC power supply system of the electric propulsion ship is in hybrid power mode. The energy management system collects the total power of the main propulsion and daily load, that is, the current real-time total power of the load P1. The rated power of a single diesel generator set currently on the grid is recorded as P 1N , the current rated power of the grid-connected battery group P 2N , the number of diesel generator sets currently on the grid is n;

[0014] When P1>a%P 1N When the energy management system controls the DC converter output power P1-a%P 1N ;

[0015] When P1>a%P 1N And P1<a%P 1N +b%P 2N When the current continues for more than the set time c, an additional diesel generator set is added to the DC grid, and the DC converter stops outputting power.

[0016] When P1>a%P 1N +b%P2N When a diesel generator set is added to the DC grid, the DC converter stops outputting power;

[0017] When P1<a%P 1N (n-1) / n and the duration exceeds the set time d, the energy management system controls to reduce one diesel generator set to connect to the grid for power supply;

[0018] When the battery pack SOC is lower than the minimum power setting value e%, and P1<a%P 1N ,The energy management system controls the DC converter to charge the battery, charging power = a%P 1N -P1; When the battery pack SOC is greater than the maximum power setting value f%, the energy management system controls the DC converter to stop charging the battery.

[0019] The beneficial effects of the present invention are as follows: the energy management method of the DC power supply system of the electric propulsion ship of the present invention adopts a diode rectifier, which can greatly reduce the cost of the system; the configuration of the battery pack can improve the operating efficiency of the diesel generator set; the output voltage, frequency and phase angle of the diesel generator set are controlled by the energy management system to achieve virtual 12 pulses, 18 pulses or 24 pulses, which can effectively reduce the ripple of the DC power supply system. The configuration of the multi-strategy mode switching function and the real-time energy management strategy effectively solves the problem of energy scheduling and allocation strategy of the diesel generator set and the battery pack. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of a DC power supply system for an electric propulsion ship according to the present invention;

[0021] Figure 2 This is a schematic diagram of the architecture of the diesel generator and battery pack connected to the DC power grid of the present invention;

[0022] Figures 3A to 3D It is a schematic diagram of the rectified voltage ripple of virtual 6 pulses, 12 pulses, 18 pulses and 24 pulses of the present invention;

[0023] Figure 4 The output voltage and power droop characteristic curve of the DC converter of the present invention;

[0024] Figure 5 This is a schematic diagram of ripple control when a diesel generator set is powered. DETAILED DESCRIPTION

[0025] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0026] like Figure 1 The figure shows a schematic diagram of a DC power supply system for an electric propulsion ship according to an embodiment of the present invention. The DC power supply system for an electric propulsion ship includes 4 sets of 1000kWh diesel generator sets, 2 sets of 500kWh battery packs, 1 set of 930VDC DC distribution board, 1 set of 400VAC AC distribution board, 2 sets of 1500kW propulsion motors and 1 set of energy management system; the DC distribution board includes 4 sets of 1000kW diode uncontrolled rectifiers connected between the diesel generator sets and the DC bus, 2 sets of 500kW DC converters connected between the battery pack and the DC bus, 2 sets of 500kW daily inverters connected between the DC bus and the AC distribution board, and 2 sets of 1500kW propulsion inverters connected between the DC bus and the propulsion motor, wherein the daily inverter is one for use and one for standby.

[0027] Figure 2 The figure shows a schematic diagram of the architecture of diesel generator and battery pack connected to the DC grid. The diesel generator set is connected to the DC bus through a filter and a diode rectifier; the battery pack is connected to the DC bus through a DC filter and a DC converter.

[0028] The DC power supply system of electric propulsion ships is divided into pure electric mode, pure diesel-electric mode and hybrid power mode.

[0029] In pure electric mode, the battery pack transmits electrical energy to the DC distribution board bus through the DC converter, and the energy management system controls the two DC converters to balance power through voltage and power droop modes.

[0030] In pure diesel-electric mode, only the diesel generator sets supply power to the DC bus through the diode rectifier, and the energy management system controls the voltage and power droop mode of each diesel generator set for power balancing.

[0031] In hybrid mode, the diesel generator set and the battery pack simultaneously supply power to the DC bus, and the energy management system dispatches and manages the power distribution of the diesel generator set and the battery pack.

[0032] The electric propulsion ship can reversely supply power to the DC bus through the daily inverter to charge the battery pack. It can also charge the battery pack by connecting to the DC bus through a DC charging pile.

[0033] 1. Specific implementation of energy management system

[0034] The energy management system uses a redundant programmable controller as the main controller, and uses real-time Ethernet Profinet to interact with the diesel generator controller, DC converter, propulsion inverter and daily inverter for data. It is equipped with a CAN module for communication between the battery pack BMS and the DC charging pile, the communication protocol J1939, a network port module for communication with the ship's integrated control system, and an Ethernet module for communication with the touch screen.

[0035] The main contents of communication between the energy management system and the diesel generator set controller are: 1) Control data include: unit start, unit stop, unit given frequency, unit given voltage, unit acceleration, unit deceleration; 2) Status data include: unit voltage actual frequency, unit voltage phase, unit output voltage, unit output power, unit fault word, unit ready, unit running, unit alarm, unit fault.

[0036] The main contents of communication between the energy management system and DC converter, propulsion inverter and daily inverter are: 1) Control data includes: module start, module stop, bus control mode, charge and discharge mode; 2) Status data includes: module DC voltage, module output voltage, module frequency, module power, module current, module voltage, module temperature, module fault word, module ready, module operation, module alarm, module fault.

[0037] 2. Implementation of frequency and phase control of diesel generator sets

[0038] By adjusting the voltage phase angle of the diesel generator set, a virtual multi-pulse rectification form is formed, such as Figures 3A to 3D The figure shows the schematic diagram of the rectifier voltage ripple of virtual 6 pulses (one generator set), 12 pulses (two generator sets), 18 pulses (three generator sets) and 24 pulses (four generator sets). The more pulses there are, the smaller the ripple voltage is, which can effectively reduce the voltage ripple of the DC bus, reduce the efficiency of the propulsion inverter reduced by voltage ripple, and reduce the harmonic content of the output voltage of the daily inverter.

[0039] When two diesel generator sets are connected to the DC bus through a diode rectifier, the energy management system controls the first diesel generator set connected to the DC grid to be given a phase angle of 0 degrees, and the second diesel generator set connected to the DC grid to be given a phase angle of 180 degrees.

[0040] When three diesel generator sets are connected to the DC bus through diode rectification, the energy management system controls the first diesel generator set connected to the DC grid to be given a phase angle of 0 degrees, the second diesel generator set connected to the DC grid to be given a phase angle of 120 degrees, and the third diesel generator set connected to the DC grid to be given a phase angle of 240 degrees.

[0041] When four diesel generator sets are connected to the DC bus through diode rectification, the energy management system controls the first diesel generator set connected to the DC grid to be given a phase angle of 0 degrees, the second diesel generator set connected to the DC grid to be given a phase angle of 90 degrees, the third diesel generator set connected to the DC grid to be given a phase angle of 180 degrees, and the fourth diesel generator set connected to the DC grid to be given a phase angle of 270 degrees.

[0042] The energy management system controls the diesel generator set to accelerate and decelerate through real-time Ethernet to adjust the output voltage phase angle of the diesel generator set.

[0043] Where T is the given pulse width, T1 is the pulse period, T1 is 4 seconds, ω1 is the phase angle given by the energy management system, and ω2 is the actual generator set output phase angle. The maximum value of T is limited to 3 seconds.

[0044] When the given phase angle ω1 is greater than the actual generator set output phase angle ω2, the energy management system controls the unit controller to accelerate through the real-time Ethernet. The acceleration signal is a switch pulse signal, and the given pulse width is determined by the difference between the given phase angle and the actual phase angle (i.e., Formula 1). On the contrary, when ω1 is less than ω2, the energy management system controls the unit controller to decelerate through the real-time Ethernet.

[0045] When the diesel generator set is connected to the DC grid, it usually takes about 30 seconds to adjust the actual phase angle to the given phase angle. During normal operation, the phase angle is fine-tuned, and generally one to two pulse cycles can complete the adjustment.

[0046] 3. Implementation of voltage control of diesel generator sets

[0047] The rated output voltage of the diesel generator set in this project is 690VAC. When the power of the diesel generator set is 0kW, the DC bus voltage = 1.35*690 = 930VDC. The energy management system controls the energy output of the diesel engine by adjusting the generator output voltage. When the DC bus reaches 900VDC, the diesel generator set outputs a rated power of 1000kW. The energy management system controls the unit output voltage and power droop curve, which can achieve power balance between each diesel generator set.

[0048] 4. Implementation of DC converter output power balance control

[0049] The rated voltage of the battery pack in this project is 800VDC. In pure electric mode, after the DC converter is boosted, when the DC bus voltage reaches 930VDC, the power of the DC converter is 0. Figure 4 The output voltage and power droop characteristic curve of the DC converter is shown in Figure 1. When the DC bus voltage is 900VDC, the output power is 500kW. The energy management system controls the output voltage and power droop curve of the DC converter to achieve power balance between each battery pack.

[0050] 5. Implementation of ripple control when one diesel generator set is on the grid

[0051] like Figure 5As shown in the figure, when a diesel generator set and a battery system are connected to the grid, the voltage ripple on the DC bus is large. The DC converter between the battery pack and the DC bus sets the upper voltage control curve and the lower voltage control curve according to the DC bus voltage requirements. When the bus voltage is higher than the upper voltage control curve, the DC converter absorbs energy to charge the battery; when the bus voltage is lower than the lower voltage control curve, the DC converter releases energy to the DC bus through the battery pack; thereby offsetting the up and down ripples on the DC bus.

[0052] 6. Implementation of management and control of adding and reducing machines in DC power supply system

[0053] The DC power supply system is in hybrid mode. The energy management system collects the total power of the main propulsion and daily load, that is, the current real-time total power of the load P1. The rated power of a single diesel generator set currently on the grid is recorded as P 1N , the current rated power of the grid-connected battery group P 2N , the current number of diesel generator sets on the grid is n.

[0054] Control logic of adding two machines in the network:

[0055] The diesel generator set additional machine setting value a=85, if two generator sets are connected to the grid, P 1N =2000kW, P 2N =1000kW;

[0056] If the current load P1 = 1900kW, that is, P1>a%P 1N =1700kW, the energy management system controls the DC converter (i.e., the battery pack) to output power P1-a%P 1N =200kW, one diesel generator set bears 1700kW.

[0057] The battery pack enters the setting value b = 80, the time setting value c = 30, if P1> a%P 1N =1700kW and P1 <a%P 1N +b%P 2N = 2500kW for more than c = 30 minutes, an additional diesel generator set is added to the DC grid, and the DC converter stops outputting power.

[0058] If P1>a%P 1N +b%P 2N =2500kW, add a diesel generator set to the DC grid, and the DC converter will stop outputting power. After the diesel engine provides power, the battery pack will stop providing power, avoiding frequent start and stop of the diesel engine.

[0059] Two machines in the network and less machine control logic:

[0060] The diesel generator set reduction time setting value d=10, if P1 <a%P 1N (n-1) / n=850kW, when the duration exceeds d=10 minutes, the energy management system controls to reduce one diesel generator set to be connected to the grid for power supply;

[0061] Battery charging control logic:

[0062] Assume that two generators are on the grid, and the current load is P1 = 1500kW, when the battery pack SOC is lower than the minimum power setting value e% = 30%, and P1 <a%P 1N =1700kW, the energy management system controls the DC converter to charge the battery, charging power = a%P 1N -P1=200kW; when the battery pack SOC is greater than the maximum power setting value f%=90%, the energy management system controls the DC converter to stop charging the battery.

[0063] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. An energy management method for a DC power supply system of an electric propulsion ship, characterized in that: The diesel generator set is connected to the DC bus through a diode rectifier, and the lithium-ion battery pack is connected to the DC bus through a DC converter, forming a DC power supply system for electric propulsion ships; the DC power supply system for electric propulsion ships is equipped with an energy management system for dispatching and managing the DC power supply system. The energy management system collects the output voltage, frequency and phase angle of each diesel generator set, and controls the output voltage and speed of the diesel generator through real-time Ethernet; the energy management system controls the output voltage and current of the DC converter through real-time Ethernet; The energy management system has three power supply modes: pure battery mode, pure diesel-electric mode, and hybrid power mode; In pure electric mode, the battery pack transmits electric energy to the DC distribution board bus through the DC converter, and the energy management system controls the two DC converters to balance power through voltage and power droop mode; In pure diesel-electric mode, only the diesel generator sets supply power to the DC bus through the diode rectifier, and the energy management system controls the voltage and power droop mode of each diesel generator set for power balancing; In hybrid mode, the diesel generator set and the battery pack simultaneously supply power to the DC bus, and the energy management system dispatches and manages the power distribution of the diesel generator set and the battery pack; The electric propulsion ship DC power supply system includes n diesel generator sets connected to the DC bus through diode rectification, n is greater than or equal to 2, and the energy management system controls the speed of the diesel generator sets, controls the frequency of the voltages emitted by the diesel generator sets to be consistent, and the voltage phase angles differ by 2π / n; The energy management system controls the diesel generator set to accelerate and decelerate through real-time Ethernet to adjust the output voltage phase angle of the diesel generator set, as follows: When the energy management system's given phase angle ω1 is greater than the actual generator set output phase angle ω2, the energy management system controls the unit controller to accelerate through the real-time Ethernet. The acceleration signal is a switch pulse signal. The given pulse width T is determined by the energy management system's given phase angle ω1 and the actual generator set output phase angle ω2. T1 is the pulse period; on the contrary, when ω1 is less than ω2, the energy management system controls the unit controller to slow down through real-time Ethernet.

2. The energy management method of the DC power supply system of an electric propulsion ship according to claim 1, characterized in that: When only one diesel generator set is supplying power to the grid, the DC converter sets the maximum and minimum output voltage limits so that the battery pack absorbs or releases energy from the DC bus and controls the ripple value of the DC bus.

Images