Electric propulsion power limiting method based on power station load rate

Abstract

The technical scheme of the invention discloses an electric propulsion power limiting method based on a power station load rate. According to the method, the power station load rate supplied by the propulsion frequency converter is calculated in real time, different propulsion power limiting strategies are adopted according to different power station load rates, and three power limiting modes of load rate overrun, rapid power limiting and emergency power limiting are adopted. Through three power limiting modes, the advantages of the electric propulsion system are played to the maximum extent on the premise of ensuring the safety of the electric power system, and the method is suitable for electric propulsion systems with different voltage grades, different electric systems, different generator set numbers and different power station numbers.

Description

Technical Field

[0001] The present invention relates to a power propulsion power limit method based on the power station load rate, and belongs to the field of ship electric propulsion systems. Background Technique

[0002] Compared with ships adopting conventional propulsion types, ships adopting electric propulsion types have many advantages such as comprehensive regulation and control of platform electric energy and propulsion electric energy, flexible equipment arrangement, and being suitable for high-power load installation on ships.

[0003] When an electric propulsion ship sails at high speed, its power station is usually in a high-load state. When the load rate of the power station reaches the set value for adding a unit in the power station monitoring system, the crew can be prompted to put into a standby unit or reduce the propulsion power to avoid power station overload. If a unit in the network fails and shuts down at this time, the power borne by this unit suddenly adds to the remaining units, and the remaining units are very likely to be overloaded and shut down, resulting in a power outage of the whole ship. Therefore, it is necessary to formulate a propulsion power limit strategy according to the current working conditions of the power station to ensure the safe and stable operation of the electric propulsion system.

[0004] Patent CN 105226706 B proposes a propulsion power adaptive control method. This method is based on the power limit value (available power value) of the propulsion frequency converter. By sending the power limit value to the propulsion frequency converter, the output power of the propulsion frequency converter is controlled not to exceed the available power. When it is monitored that the load rate of the unit reaches 95%, the power limit value of the propulsion frequency converter is reduced to reduce the propulsion power until the load rate of the unit is reduced to the relatively safe level of 85%. When a generator set fails and shuts down emergently, according to the number of failed units, the power limit value of the propulsion frequency converter is classified to ensure the safe operation of the remaining generator sets. This method has relatively high requirements for the setting of the power limit value of the propulsion frequency converter. In addition, the power limit strategy when a unit fails and shuts down has poor applicability. If the number of units in the power station network is large and the load rate of the power station is low before the failure, there is no need to limit the power of the propulsion frequency converter; if the power station is powered by large-capacity units and small-capacity units in the network, when a large-capacity unit fails and shuts down, in order to ensure the safe operation of the small units, it may be necessary to quickly cut off the propulsion load. When a small-capacity unit fails and shuts down, it may not be necessary to cut off the propulsion load.

[0005] The paper "Application of Power Limitation Control Strategy of Electric Propulsion System in a Real Ship Project" (DOI: 10.16443 / j.cnki.31-1420.2015.04.005) proposed a power limitation strategy for floating cranes. This scheme is divided into "dynamic power limitation" and "rapid power limitation". "Rapid power limitation" is based on abnormal tripping faults of generator sets. This strategy is applicable to power stations with a small number of units. When one unit trips due to a fault, it is very likely to cause the remaining unit to be overloaded. However, it is not applicable to power stations with a large number of units or when large-capacity and small-capacity units are interconnected. A single unit fault does not necessarily cause the overload of the remaining units.

[0006] The paper "Application of Power Limitation Strategy in Ship DC Power Station" (DOI: 10.13632 / j.meee.2023.10.018) proposed a power limitation strategy for ship DC power stations, which uses the instantaneous value and change rate of the DC bus voltage combined with the unit load rate to achieve load power limitation. This method is applicable to ships with a DC network form and is not applicable to ships with an AC power system. Summary of the Invention

[0007] The technical problem to be solved by the present invention is that when an electric propulsion ship sails at high speed, its power station is usually in a high-load state. When the load rate of the power station reaches the set value for adding a unit in the power station monitoring system, the crew can be prompted to put into standby units or reduce the propulsion power to avoid power station overload. If a unit in the on-line units fails and shuts down at this time, the power borne by this unit suddenly adds to the remaining units, and the remaining units are very likely to be overloaded and shut down, resulting in a power failure of the whole ship. Therefore, it is necessary to formulate a propulsion power limitation strategy according to the current working conditions of the power station to ensure the safe and stable operation of the electric propulsion system.

[0008] To solve the above technical problems, the technical solution of the present invention is to disclose a power limitation method for electric propulsion based on the load rate of the power station, which is characterized by including the following steps:

[0009] First step, calculate the load rate q of the power supply station where the propulsion frequency converter is located in real time, and send the load rate q to the propulsion frequency converter;

[0010] Second step, the propulsion frequency converter judges whether the load rate satisfies q < q1. If it is satisfied, the external speed increase / power increase or speed decrease / power decrease instruction is normally executed, where q1 is a preset threshold one;

[0011] Step 3: The propulsion frequency converter determines whether the load factor satisfies q1 ≤ q < q2, where q2 is the preset threshold value 2. If it is satisfied, enter the "load factor overlimit" mode. The propulsion frequency converter slowly executes the external speed increase / power increase instruction. According to engineering experience, the rate of increase in the speed / power of the propulsion frequency converter can be reduced to 1 / 5 of the normal rate or other multiples to avoid overloading the on-grid generating units due to too fast loading of the propulsion load. The propulsion frequency converter normally executes the speed decrease / power decrease instruction;

[0012] Step 4: The propulsion frequency converter determines whether the load factor satisfies q2 ≤ q < q3, where q3 is the preset threshold value 3. If it is satisfied, no longer execute the external speed increase / power increase instruction; the propulsion frequency converter normally executes the speed decrease / power decrease instruction;

[0013] Step 5: The propulsion frequency converter determines whether the load factor satisfies q3 ≤ q < q4, where q4 is the ratio of the long-time protection setting value of the generator to the rated current value of the generator. If it is satisfied, the propulsion frequency converter controls the speed of the propulsion motor to decrease by a certain speed value. After the speed decrease is completed, then determine the next action according to the current power station load factor; the propulsion frequency converter normally executes the speed decrease / power decrease instruction;

[0014] Step 6: The propulsion frequency converter determines whether the load factor satisfies q4 ≤ q < q5, where q5 is the ratio of the short-time protection setting value of the generator to the rated current value of the generator. If it is satisfied, the power limit controller enters the fast power limit mode according to this state at the same time, sends a "fast power limit" control signal to the propulsion frequency converter, the propulsion frequency converter cuts off the outer loop of power / speed control, and only retains the inner loop control of the excitation current. The propulsion frequency converter does not stop;

[0015] Step 7: The propulsion frequency converter determines whether the load factor satisfies q ≥ q5. If it is satisfied, the power limit controller enters the emergency power limit mode according to this state at the same time, sends an "emergency power limit" control signal to the propulsion frequency converter, the propulsion frequency converter directly blocks the pulse signal of its internal power device, the propulsion frequency converter stops emergently, and after a delay period, the propulsion frequency converter starts with speed, and the speed target value is the follow-up speed of the propeller.

[0016] Preferably, in the first step, the load factor q is calculated by the following formula:

[0017] q = ∑Pi 输出 / P 电站

[0018] In the formula, Pi 输出 is the output power of the i-th generating unit sharing the grid with the propulsion frequency converter, and P 电站 is the total capacity of the power station where the propulsion frequency converter is located.

[0019] Preferably, if the grid-connected generating units are AC generating units, then Pi 输出= 1.732 * ki * Ui * Ii * wherein, is the power factor of the AC power grid;

[0020] If the grid-connected generating set is a DC generating set, then Pi 输出 = ki * Ui * Ii;

[0021] In the formula, ki is the opening and closing state of the circuit breaker of the i-th generating set connected to the propulsion frequency converter periodically and real-time collected by the power limit controller, Ui is the voltage value at the outlet end of the i-th generating set connected to the propulsion frequency converter periodically and real-time collected by the power limit controller, and Ii is the current value at the outlet end of the i-th generating set connected to the propulsion frequency converter periodically and real-time collected by the power limit controller.

[0022] Preferably, the total capacity P 电站 is calculated by the following formula:

[0023] P 电站 = ∑ki × Pi 额定

[0024] In the formula, Pi 额定 is the rated power of the i-th generating set, and ki is the opening and closing state of the circuit breaker of the i-th generating set connected to the propulsion frequency converter periodically and real-time collected by the power limit controller.

[0025] Preferably, the first threshold q1 is usually taken as 85% according to engineering experience, the second threshold q2 can be taken as 90% according to engineering experience, and the third threshold q3 can be taken as 95% according to engineering experience.

[0026] Preferably, for the AC system, the ratio q4 can be taken as 115% and the ratio q5 can be taken as 250% according to engineering experience; for the DC system, the ratio q4 can be taken as 120% and the ratio q5 can be taken as 150% according to engineering experience.

[0027] Preferably, the power limit controller has a digital input interface, an analog input interface, a digital output interface, an analog output interface, and has the ability of logical operation.

[0028] Preferably, the generating set includes but is not limited to diesel generating sets, gas turbine generating sets, steam turbine generating sets, and can be medium-voltage AC, medium-voltage rectification, low-voltage AC or low-voltage rectification generating sets.

[0029] Preferably, the propulsion frequency converter is a voltage source type propulsion frequency converter.

[0030] Preferably, the control method of the propulsion frequency converter adopts the field-oriented vector control method of speed / power outer loop + current inner loop.

[0031] The present invention calculates the load rate of the power station powered by the propulsion frequency converter in real time, and adopts different propulsion power limit strategies according to different power station load rates, which are divided into three power limit modes: "load rate exceeding limit", "rapid power limit", and "emergency power limit". Through the three power limit modes, the advantages of the electric propulsion system are maximally exerted on the premise of ensuring the safety of the power system, and it is applicable to electric propulsion systems with different voltage levels, power systems, numbers of generator sets, and numbers of power stations.

[0032] Compared with the prior art solutions, the present invention has the following beneficial effects:

[0033] The present invention is not limited by the voltage level, power system, number of generator sets, and number of power stations of the power system, and is applicable to most electric propulsion ships, with strong applicability and versatility.

[0034] For the high-load working conditions of the electric propulsion system, the present invention sends a 4-20 mA analog signal of "load rate exceeding limit" to the propulsion frequency converter through the power limit controller, refines the working strategy of the propulsion frequency converter under different load rates, exerts the energy unified regulation ability of the electric propulsion system, and ensures the normal operation of the propulsion load. In the event of a sudden generator set shutdown failure, the power limit controller sends digital control signals of "rapid power limit" and "emergency power limit" to the propulsion frequency converter, which can quickly limit the propulsion power, prevent the entire ship from losing power due to the overload of the remaining generator sets, and effectively ensure the safe and stable operation of the electric propulsion system. Description of the Drawings

[0035] Figure 1 It is the network architecture diagram of the electric propulsion system according to an embodiment of the present invention;

[0036] Figure 2 It is the power limit flow chart according to an embodiment of the present invention. Detailed Embodiments

[0037] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0038] Such as Figure 1As shown in the figure, in the embodiment of the present invention, the power system includes two power stations. The generator sets supply power to the propulsion load and other loads through main switchboard 1 and main switchboard 2. G1 to G6 are generator sets, QF1 to QF4 are bus coupler breakers, ACB1 to ACB6 are generator set breakers, CB1 to CB4 are load breakers, CS1 to CS4 are cross-connect breakers, F1 and F2 are propulsion frequency converters, and M1 and M2 are propulsion motors. Ethernet optical fiber communication is adopted between power limit controller 1 and power limit controller 2.

[0039] The data sent by the power limit controller to the propulsion frequency converter is the "load rate exceeding limit" state, which is the load rate of the power supply station where the propulsion frequency converter is located, and is an analog quantity of 4 - 20 mA; the data sent by the power limit controller to the propulsion frequency converter is the "fast power limit" state, which is a digital quantity; the data sent by the power limit controller to the propulsion frequency converter is the "emergency power limit" state, which is a digital quantity.

[0040] Combined with Figure 2 , based on the above power system, a power propulsion power limit method based on the power station load rate disclosed in the embodiment of the present invention specifically includes the following steps:

[0041] Step 1: Power limit controller 1 and power limit controller 2 identify the grid topology, and respectively collect the opening and closing states ki, the outlet voltage value Ui, and the outlet current value Ii of the generator set breakers shared by propulsion frequency converters F1 and F2 in real time at a timing period of 1 ms, and perform filtering processing.

[0042] Step 2: The power limit controller calculates the total capacity P of the power supply station where the propulsion frequency converter is located, 电站 = ∑ki × Pi 额定 , where Pi 额定 is the rated power of the i-th generator set. The power limit controller calculates the output power of the generator sets sharing the network with the propulsion frequency converter: If the generator sets sharing the network are AC generator sets, then where is the power factor of the AC power grid; if the generator sets sharing the network are DC generator sets, then Pi 输出 = ki * Ui * Ii.

[0043] Step 3: Power limit controller 1 and power limit controller 2 calculate the load rate q of the power supply stations where propulsion frequency converters F1 and F2 are located in real time, q = ∑Pi 输出 / P 电站 , and send the power station load rate q to the propulsion frequency converter.

[0044] Step 4: The propulsion frequency converter determines whether the load rate satisfies q < q1 (q1 is the power generation unit addition point of the power station, and usually takes the value of 85% according to engineering experience). If it is satisfied, the external speed increase / power increase or speed decrease / power decrease instruction is normally executed.

[0045] Step 5: The propulsion frequency converter determines whether the load rate satisfies q1 ≤ q < q2 (q2 can take the value of 90% according to engineering experience). If it is satisfied, it enters the "load rate overlimit" mode, and the propulsion frequency converter slowly executes the external speed increase / power increase instruction. According to engineering experience, the rising rate of the speed / power of the propulsion frequency converter can be reduced to 1 / 5 of the normal rate or other multiples to avoid overloading the on-grid generating units due to too fast loading of the propulsion load; the propulsion frequency converter normally executes the speed decrease / speed decrease / power decrease instruction.

[0046] Step 6: The propulsion frequency converter determines whether the load rate satisfies q2 ≤ q < q3 (q3 can take the value of 95% according to engineering experience). If it is satisfied, the external speed increase / power increase instruction is no longer executed; the propulsion frequency converter normally executes the speed decrease / power decrease instruction.

[0047] Step 7: The propulsion frequency converter determines whether the load rate satisfies q3 ≤ q < q4 (q4 is the ratio of the long-time protection setting value of the generator to the rated current value of the generator. For the AC system, it can take the value of 115% according to engineering experience, and for the DC system, it can take the value of 120% according to engineering experience). If it is satisfied, the propulsion frequency converter controls the speed of the propulsion motor to decrease by a certain speed value, which can take the value of 5 revolutions according to engineering experience. After the speed decrease is completed, the next action is judged according to the current load rate of the power station; the propulsion frequency converter normally executes the speed decrease / power decrease instruction.

[0048] Step 8: The propulsion frequency converter determines whether the load rate satisfies q4 ≤ q < q5 (q5 is the ratio of the short-time protection setting value of the generator to the rated current value of the generator. For the AC system, it can take the value of 250% according to engineering experience, and for the DC system, it can take the value of 150% according to engineering experience). If it is satisfied, the power limit controller enters the fast power limit mode according to this state at the same time, sends a "fast power limit" control signal to the propulsion frequency converter, the propulsion frequency converter cuts off the outer loop of power / speed control, and only retains the inner loop control of the excitation current. The propulsion frequency converter does not stop.

[0049] Step 9: The propulsion frequency converter determines whether the load rate satisfies q ≥ q5. If it is satisfied, the power limit controller enters the emergency power limit mode according to this state at the same time, sends an "emergency power limit" control signal to the propulsion frequency converter, the propulsion frequency converter directly blocks the pulse signal of its internal power device, the propulsion frequency converter shuts down emergently, and after a delay period, the propulsion frequency converter starts with speed, and the speed target value is the follow-up speed of the propeller. The delay time can take the value of 10 s according to engineering experience.

[0050] In the above-mentioned power propulsion power limitation method based on the power station load rate, a preferred implementation is that its power limitation controller has interfaces such as digital input, analog input, digital output, and analog output, and has the ability of logical operation.

[0051] In the above-mentioned power propulsion power limitation method based on the power station load rate, a preferred implementation is that its generator set includes but is not limited to diesel generator sets, gas turbine generator sets, and steam turbine generator sets, and can be a medium-voltage AC, medium-voltage rectification, low-voltage AC, or low-voltage rectification generator set.

[0052] In the above-mentioned power propulsion power limitation method based on the power station load rate, a preferred implementation is that its propulsion frequency converter is a voltage-source type propulsion frequency converter. It can be a medium-voltage or low-voltage propulsion frequency converter. Its control method adopts the field-oriented vector control method of speed / power outer loop + current inner loop.

Claims

1. A power limit method for electric propulsion based on the power station load rate, characterized in that It includes the following steps: First step: Calculate the load rate q of the power supply station where the propulsion frequency converter is located in real time, and send the load rate q to the propulsion frequency converter; Second step: The propulsion frequency converter determines whether the load rate satisfies q < q1. If it is satisfied, it normally executes the external speed increase / power increase or speed decrease / power decrease command, where q1 is a preset threshold one; Third step: The propulsion frequency converter determines whether the load rate satisfies q1 ≤ q < q2, where q2 is a preset threshold two. If it is satisfied, it enters the "load rate overlimit" mode. The propulsion frequency converter slowly executes the external speed increase / power increase command. According to engineering experience, the rising rate of the speed / power of the propulsion frequency converter can be reduced to 1 / 5 of the normal rate or other multiples to avoid overloading the on-grid generating units due to too fast loading of the propulsion load; the propulsion frequency converter normally executes the speed decrease / speed decrease / power decrease command; Fourth step: The propulsion frequency converter determines whether the load rate satisfies q2 ≤ q < q3, where q3 is a preset threshold three. If it is satisfied, it no longer executes the external speed increase / power increase command; the propulsion frequency converter normally executes the speed decrease / power decrease command; Fifth step: The propulsion frequency converter determines whether the load rate satisfies q3 ≤ q < q4, where q4 is the ratio of the long-time protection setting value of the generator to the rated current value of the generator. If it is satisfied, the propulsion frequency converter controls the speed of the propulsion motor to decrease by a certain speed value. After the speed decrease is completed, it then determines the next action according to the current power station load rate; The propulsion frequency converter normally executes the speed decrease / power decrease command; Sixth step: The propulsion frequency converter determines whether the load rate satisfies q4 ≤ q < q5, where q5 is the ratio of the short-time protection setting value of the generator to the rated current value of the generator. If it is satisfied, the power limit controller enters the fast power limit mode according to this state at the same time, sends a "fast power limit" control signal to the propulsion frequency converter, the propulsion frequency converter cuts off the power / speed control outer loop, and only retains the excitation current inner loop control. The propulsion frequency converter does not stop; Seventh step: The propulsion frequency converter determines whether the load rate satisfies q ≥ q5. If it is satisfied, the power limit controller enters the emergency power limit mode according to this state at the same time, sends an "emergency power limit" control signal to the propulsion frequency converter, the propulsion frequency converter directly blocks the pulse signal of its internal power device, the propulsion frequency converter stops emergently, and after a delay period, the propulsion frequency converter starts with speed, and the speed target value is the follow-up speed of the propeller.

2. The power limit method for electric propulsion based on the power station load factor according to claim 1, characterized in that In the first step, the load rate q is calculated by the following formula: q = ∑Pi 输出 / P 电站 where Pi 输出 is the output power of the i-th generating unit sharing the network with the propulsion frequency converter, and P 电站 is the total capacity of the power station where the propulsion frequency converter is located.

3. The power limit method for electric propulsion based on the power station load rate according to claim 2, characterized in that, If the co-networked generating set is an AC generating set, then where is the power factor of the AC power grid; If the co-networked generator set is a DC generator set, then Pi 输出 = ki * Ui * Ii; In the formula, ki is the closing and opening state of the circuit breaker of the i-th generating unit sharing the grid with the propulsion frequency converter periodically and real-time collected by the power limit controller, Ui is the voltage value at the outlet end of the i-th generating unit sharing the grid with the propulsion frequency converter periodically and real-time collected by the power limit controller, and Ii is the current value at the outlet end of the i-th generating unit sharing the grid with the propulsion frequency converter periodically and real-time collected by the power limit controller.

4. The power limit method for electric propulsion based on the power station load rate according to claim 2, wherein, Total capacity P 电站 Calculated using the following formula: P 电站 = ∑ki × Pi 额定 wherein, Pi 额定 is the rated power of the i-th generating unit, and ki is the closing and opening state of the circuit breaker of the i-th generating set connected to the propulsion frequency converter collected by the power limit controller in real time periodically.

5. The power limitation method for electric propulsion based on the power station load rate according to claim 2, characterized in that, The threshold one q1 usually takes a value of 85% according to engineering experience, the threshold two q2 can take a value of 90% according to engineering experience, and the threshold three q3 can take a value of 95% according to engineering experience.

6. The power limitation method for electric propulsion based on the power station load factor according to claim 2, characterized in that, For an AC system, according to engineering experience, the ratio q4 can take a value of 115% and the ratio q5 can take a value of 250%; for a DC system, according to engineering experience, the ratio q4 can take a value of 120% and the ratio q5 can take a value of 150%.

7. The power limitation method for electric propulsion based on the power station load factor according to claim 1, characterized in that, The power limit controller has digital input interfaces, analog input interfaces, digital output interfaces, and analog output interfaces, and has the ability of logical operation.

8. The power limit method for electric propulsion based on the power station load rate according to claim 1, wherein The generator set includes but is not limited to diesel generator sets, gas turbine generator sets, and steam turbine generator sets, and can be a medium-voltage AC, medium-voltage rectifier, low-voltage AC or low-voltage rectifier generator set.

9. A power limit method for electric propulsion based on the power station load factor according to claim 1, characterized in that The propulsion frequency converter is a voltage-source type propulsion frequency converter.

10. A power limit method for electric propulsion based on the power station load rate according to claim 9, characterized in that The control method of the propulsion frequency converter adopts the field-oriented vector control method of speed / power outer loop + current inner loop.

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