A method for controlling the rotational speed of a ship's waterjet propulsion system

Abstract

This invention provides a method for controlling the rotational speed of a ship's waterjet propulsion system, comprising: Step 1: calculating the shortest loading time of the waterjet propulsion system based on the prime mover's loading capacity; Step 2: calculating the rotational speed increment limit for the next control cycle based on the rotational speed command of the current control cycle; Step 3: taking the smaller of the rotational speed increment limit and the rotational speed increment of the original control cycle to generate the rotational speed command for the next control cycle. This method solves the problem of mismatch between the acceleration command curve and the prime mover's loading capacity for ships with high maneuverability requirements; it only adjusts the command and does not involve the internal rotational speed closed-loop control logic of the prime mover (in mechanical propulsion) or the propulsion motor (in electric propulsion), facilitating remote control system implementation; it does not affect the normal acceleration and deceleration process controlled according to the pre-set rotational speed command curve, and only takes effect when the prime mover's loading rate is too high.

Description

Technical Field

[0001] This invention relates to the field of ship waterjet propulsion system technology, and in particular to a method for controlling the rotational speed of a ship waterjet propulsion system. Background Technology

[0002] For ship waterjet propulsion systems, the power of the jet pump mainly depends on the speed of the jet pump. Changes in ship speed have little impact on the power of the jet pump, which is approximately a single-valued function of the speed. Therefore, even during emergency acceleration, the prime mover of the ship's waterjet propulsion system is less likely to experience the load limitation problem that propeller propulsion systems often face, which reduces the difficulty of speed control in the control system.

[0003] However, for high-powered prime movers such as diesel engines and gas turbines, including mechanical propulsion (directly driving the injection pump) and electric propulsion (used as a generator prime mover, with the motor driving the injection pump), manufacturers generally impose limits on the prime mover loading rate. Since the injection pump power is approximately the cube of the rotational speed, if the injection pump speed increases linearly, the prime mover loading rate will increase with the increase in injection pump speed. Unless a very low injection pump speed acceleration rate is set, the later acceleration phase can easily exceed the prime mover's loading capacity, affecting the prime mover's safety and service life. For some ships with high maneuverability requirements, to fully utilize the prime mover's capabilities, a steeper injection pump acceleration curve is set, such as a segmented acceleration curve, completing the acceleration process close to the prime mover's maximum loading capacity to achieve the ship's maneuverability indicators during acceleration. Setting up a segmented acceleration curve requires model simulation or actual ship testing, and the process is cumbersome. The more segments, the greater the testing difficulty, further increasing the complexity of the control system application. Summary of the Invention

[0004] In view of the above-mentioned problems existing in the prior art, the present invention provides a speed control method for a ship waterjet propulsion system, which does not rely on a segmented acceleration curve, can automatically meet the loading capacity limit of the prime mover, and can automatically limit the acceleration rate according to the speed command so that the loading rate of the prime mover does not exceed the limit during the acceleration process, thus ensuring the maneuverability and safety of the acceleration process.

[0005] This invention provides a method for controlling the rotational speed of a ship's waterjet propulsion system, comprising:

[0006] Step 1: Calculate the shortest loading time for the waterjet propulsion system based on the prime mover's loading capacity;

[0007] Step 2: Calculate the speed increment limit for the next control cycle based on the speed command for the current control cycle;

[0008] Step 3: Take the smaller of the speed increment limit and the speed increment of the original control cycle to generate the speed command for the next control cycle.

[0009] In some embodiments of the present invention, the prime mover includes an electric propulsion generator set and a mechanical propulsion prime mover.

[0010] In some embodiments of the present invention, in step one, the method includes:

[0011] The conversion from the shortest loading time of the prime mover to the shortest loading time of the propulsion system is based on the maximum continuous operating load rate of the ship's waterjet propulsion system.

[0012] In some embodiments of the present invention, step one specifically includes:

[0013] Let Tacc_min0 be the shortest time for the prime mover to reach rated power from no load, in seconds. Assuming the load rate of the prime mover under maximum continuous operating conditions of the ship's waterjet propulsion system is k1, then the shortest loading time for the ship's waterjet propulsion system is:

[0014] Tacc_min=k1*k2*Tacc_min0

[0015] Where k2 is the safety factor, and k2 > 1.

[0016] In some embodiments of the present invention, step two specifically includes:

[0017] Let the maximum continuous operating speed command of the ship's waterjet propulsion system be n_mcr, the speed command period be ΔT, and the speed command for the current control period be n0. Then, the calculation method for the speed increment limit of the next control period is as follows:

[0018] △n_max=n_mcr 3 *△T / (3*Tacc_min*n0 2 );

[0019] Calculate the speed increment limit for the next control cycle.

[0020] In some embodiments of the present invention, step three specifically includes:

[0021] Assuming the setpoint for the speed increment in the next control cycle of the control system is originally Δn0, which can be obtained from the pre-set acceleration curve, the speed increment is limited by the speed increment limit Δn_max, that is, the smaller of Δn0 and Δn_max is taken:

[0022] △n=min(△n_max,△n0)

[0023] The speed command for the next control cycle is:

[0024] n1 = n0 + △n.

[0025] Compared with the prior art, the beneficial effects of the speed control method for the ship waterjet propulsion system provided in this embodiment of the invention are as follows: it solves the problem of mismatch between the acceleration command curve of ships with high maneuverability requirements and the loading capacity of the prime mover; it only adjusts the command and does not involve the internal speed closed-loop control logic of the prime mover (for mechanical propulsion) or the propulsion motor (for electric propulsion), which is convenient for remote control system implementation; it does not affect the normal acceleration and deceleration process controlled according to the preset speed command curve, and only plays a role when the loading rate of the prime mover is too fast. Attached Figure Description

[0026] Figure 1 A flowchart of a speed control method for a ship waterjet propulsion system provided in an embodiment of the present invention;

[0027] Figure 2 The propulsion power-speed matching relationship of a waterjet propulsion ship in the speed control method of the ship waterjet propulsion system provided in the embodiment of the present invention;

[0028] Figure 3 The diagram of the propulsion diesel engine speed during the acceleration process of a waterjet propulsion ship in the speed control method of the ship waterjet propulsion system provided in the embodiment of the present invention is the result when the method is not used.

[0029] Figure 4 The diagram shows the power output of a diesel engine during the acceleration process of a waterjet-propelled ship in the speed control method of the ship's waterjet propulsion system provided in the embodiment of the present invention, and the result when the method is not used.

[0030] Figure 5 The diagram shows the engine speed of a propulsion diesel engine during the acceleration process of a waterjet-propelled ship, as provided in the speed control method for a ship's waterjet propulsion system according to an embodiment of the present invention, and the result when using this method.

[0031] Figure 6 The diagram shows the power output of a diesel engine during the acceleration process of a waterjet propulsion ship, as provided in the speed control method for a waterjet propulsion system according to an embodiment of the present invention, and the result when using this method. Detailed Implementation

[0032] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Various embodiments and features of this application are described herein with reference to the accompanying drawings.

[0034] These and other features of this application will become apparent from the following description of preferred forms of embodiments given as non-limiting examples, with reference to the accompanying drawings.

[0035] It should also be understood that although this application has been described with reference to some specific examples, those skilled in the art can certainly implement many other equivalent forms of this application, which have the features described in the claims and are therefore all within the scope of protection defined herein.

[0036] The above and other aspects, features and advantages of this application will become more apparent when taken in conjunction with the accompanying drawings and in view of the following detailed description.

[0037] Specific embodiments of this application are described below with reference to the accompanying drawings; however, it should be understood that the claimed embodiments are merely examples of this application, which can be implemented in various ways. Well-known and / or repeated functions and structures are not described in detail to ascertain the true intent based on the user's historical operations, and to avoid unnecessary or redundant details that would obscure this application. Therefore, the specific structural and functional details claimed herein are not intended to be limiting, but merely serve as the basis and representative basis for the claims to teach those skilled in the art to use this application in various ways with substantially any suitable detailed structure.

[0038] This specification may use the phrases “in one embodiment,” “in another embodiment,” “in yet another embodiment,” or “in other embodiments,” all of which may refer to one or more of the same or different embodiments according to this application.

[0039] This invention provides a method for controlling the rotational speed of a ship's waterjet propulsion system, such as... Figures 1 to 6 As shown, the speed control method includes:

[0040] Step 1: Calculate the shortest loading time for the waterjet propulsion system based on the prime mover's loading capacity;

[0041] Step 2: Calculate the speed increment limit for the next control cycle based on the speed command for the current control cycle;

[0042] Step 3: Take the smaller of the speed increment limit and the speed increment of the original control cycle to generate the speed command for the next control cycle.

[0043] In this embodiment, the prime mover includes an electric propulsion generator set and a mechanical propulsion prime mover.

[0044] In this embodiment, in step one, the method includes:

[0045] The conversion from the shortest loading time of the prime mover to the shortest loading time of the propulsion system is achieved based on the maximum continuous load rate (MCR) of the ship's waterjet propulsion system.

[0046] The method specifically includes: Let the shortest loading time of the prime mover from no load to rated power be Tacc_min0, in seconds. Assume the load rate of the prime mover under the maximum continuous operating condition of the ship's waterjet propulsion system is k1. Then the shortest loading time of the ship's waterjet propulsion system is:

[0047] Tacc_min=k1*k2*Tacc_min0

[0048] Where k2 is the safety factor, k2 > 1; where the rotational speed n_mcr is the actual set value of the rotational speed command in the MCR state of the propulsion system, which is not necessarily the rated value of the prime mover (for mechanical propulsion) or the propulsion motor (for electric propulsion).

[0049] In this embodiment, step two specifically includes:

[0050] Let the maximum continuous operating speed command of the ship's waterjet propulsion system be n_mcr, the speed command period be ΔT, and the speed command for the current control period be n0. Then, the calculation method for the speed increment limit of the next control period is as follows:

[0051] △n_max=n_mcr 3 *△T / (3*Tacc_min*n0 2 );

[0052] Calculate the speed increment limit for the next control cycle, and the calculation formula for the speed increment limit is based on the relationship between propulsion power and the cube of speed.

[0053] In this embodiment, step three specifically includes:

[0054] Assuming the setpoint for the speed increment in the next control cycle of the control system is originally Δn0, which can be obtained from the pre-set acceleration curve, the speed increment is limited by the speed increment limit Δn_max, that is, the smaller of Δn0 and Δn_max is taken:

[0055] △n=min(△n_max,△n0)

[0056] The speed command for the next control cycle is:

[0057] n1 = n0 + △n.

[0058] To facilitate understanding of the above technical solutions, specific examples are provided below:

[0059] A certain waterjet propulsion vessel uses a diesel engine as its main engine, which drives the jet pump via a gearbox and shaft system. This type of diesel engine has a maximum speed of 1150 rpm, and the engine is set to operate at 1100 rpm under MCR conditions, corresponding to a load factor of approximately 0.89 and an idle speed of 400 rpm. The propulsion power (main engine power) and speed have an approximate cubic relationship, see [reference needed]. Figure 2 .

[0060] The diesel engine features built-in closed-loop speed control and accepts speed commands from the remote control system. The shortest loading time for the diesel engine from no-load to rated load is 55 seconds. The acceleration process from no-load to MCR condition is as follows: Figure 3 , Figure 4 As shown. Figure 3 The "original acceleration command" is a pre-set acceleration curve with an acceleration rate of 15 rpm per second. The acceleration process begins at the 10th second, and the actual rotational speed of the host accelerates uniformly following the command without overloading. However, the power curve becomes increasingly steep, and the loading rate exceeds the equipment requirements. Therefore, the control method of this invention is used to limit the acceleration rate.

[0061] According to the method of this invention, Tacc_min0 = 55, k1 = 0.89, k1 * Tacc_min0 = 49, and considering the safety factor k2, Tacc_min = 60 can be taken.

[0062] n_mcr = 1100 (rpm), remote control system command cycle ΔT = 0.05 (s).

[0063] Based on the current control cycle speed command n0, using the calculation formula:

[0064] △n_max=n_mcr 3 *△T / (3*Tacc_min*n0 2 )

[0065] We can obtain △n_max = 1100 3 *0.05 / (3*60*n0) 2 ).

[0066] △n0=15*△T=0.75

[0067] The actual speed command increment Δn = min(Δn_max, Δn0).

[0068] This leads to the speed command n1 = n0 + Δn for the next control cycle.

[0069] The acceleration process from empty to MCR operating condition as described above is as follows: Figure 5 , Figure 6 As shown. The acceleration process begins at the 10th second. Figure 5The “original acceleration command” is a pre-set acceleration curve with an increment of 15 rpm per second. After limiting the speed increment for each command cycle using the method of this invention, the speed command sent to the host is the red dotted line in the figure (“speed command of this method”).

[0070] from Figure 6 As can be seen, the host power loading is relatively slow in the first 30 seconds. The "speed command of this method" overlaps with the "original acceleration command," meaning the "original acceleration command" is not restricted, and the system still executes according to the "original acceleration command." After 30 seconds, the loading rate reaches the limit value, and the system limits the speed command increment, executing according to the "speed command of this method." The host power changes smoothly, with essentially linear loading, until the acceleration process is completed.

[0071] As can be seen from the above technical solutions, the speed control method for a ship waterjet propulsion system provided in the above embodiments of the present invention solves the problem of mismatch between the acceleration command curve and the loading capacity of the prime mover for ships with high maneuverability requirements; it only adjusts the command and does not involve the internal speed closed-loop control logic of the prime mover (for mechanical propulsion) or the propulsion motor (for electric propulsion), which is convenient for remote control system implementation; it does not affect the normal acceleration and deceleration process controlled according to the preset speed command curve, and only plays a role when the prime mover loading rate is too fast.

[0072] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. The scope of protection of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its spirit and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A method for controlling the rotational speed of a ship's waterjet propulsion system, characterized in that, include: Step 1: Calculate the shortest loading time for the waterjet propulsion system based on the prime mover's loading capacity; Step 2: Calculate the speed increment limit for the next control cycle based on the speed command for the current control cycle; Step 3: Take the smaller of the speed increment limit and the speed increment of the original control cycle, and generate the speed command for the next control cycle; In step one, the method specifically includes: Let Tacc_min0 be the shortest time for the prime mover to be loaded from no load to rated power, in seconds. If the load factor of the prime mover under the maximum continuous operating condition of the ship's waterjet propulsion system is k1, then the shortest loading time of the ship's waterjet propulsion system is: Tacc_min=k1*k2*Tacc_min0 Where k2 is the safety factor, k2>1; In step two, the method specifically includes: Let the maximum continuous operating speed command of the ship's waterjet propulsion system be n_mcr, the speed command period be ΔT, and the speed command for the current control period be n0. Then, the calculation method for the speed increment limit for the next control period is as follows: △n_max= n_mcr 3 *△T / (3*Tacc_min*n0 2 ): Calculate the speed increment limit for the next control cycle.

2. The method for controlling the rotational speed of a ship's waterjet propulsion system according to claim 1, characterized in that, The prime mover includes electric propulsion generator sets and mechanical propulsion prime movers.

3. The method for controlling the rotational speed of a ship's waterjet propulsion system according to claim 1, characterized in that, In step one, the method includes: The conversion from the shortest loading time of the prime mover to the shortest loading time of the propulsion system is based on the maximum continuous operating load rate of the ship's waterjet propulsion system.

4. The method for controlling the rotational speed of a ship's waterjet propulsion system according to claim 3, characterized in that, In step three, the method specifically includes: Assuming the setpoint for the speed increment in the next control cycle of the control system is originally Δn0, which can be obtained from the pre-set acceleration curve, the speed increment is limited by the speed increment limit Δn_max, that is, the smaller of Δn0 and Δn_max is taken: △n = min(△n_max, △n0) The speed command for the next control cycle is: n1 = n0 + △n.

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