Virtual vector model predictive control method for six-phase permanent magnet propulsion motor of ship

Abstract

The invention discloses a virtual vector model predictive control method for a six-phase permanent magnet propulsion motor of a ship, and aims to solve the limitation of traditional finite set model predictive control on current harmonic suppression and harmonic plane copper loss. Based on the multi-degree-of-freedom structural characteristics of a six-phase permanent magnet synchronous motor, through vector space decoupling transformation, a control space is divided into an alpha-beta controllable subspace and an x-y controllable subspace, the characteristics of reverse distribution and mutual superposition and cancellation of voltage vectors of the x-y subspace are fully utilized, and a virtual voltage vector synthesis strategy is designed in combination with a volt-second balance principle. Therefore, the distribution of voltage vectors is optimized, and the harmonic current in the x-y space is eliminated. By introducing a current delay compensation technology, the method effectively reduces the current harmonic distortion rate and x-y harmonic plane copper loss under the condition of ship propeller load operation, greatly improves the steady-state control performance of the system, and provides a theoretical basis and practical support for the optimization design of ship propulsion six-phase permanent magnet synchronous motor control.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and in particular, to a model predictive control method for a ship six-phase permanent magnet propulsion motor based on virtual voltage vector synthesis. Background Art

[0002] With the continuous improvement of the global requirements for high efficiency, environmental protection and sustainable development, the ship industry is undergoing a transformation towards high reliability, electrification, intelligence and greenness. In this context, as the core power device of a ship, the technical level of the electric propulsion system directly affects the overall performance, energy consumption and environmental impact of the ship. Therefore, how to improve the efficiency and reliability of the electric propulsion system has become the focus of research.

[0003] Due to its high efficiency, high-power drive, strong fault tolerance and high control freedom, the six-phase permanent magnet synchronous motor (PMSM) has gradually become an important research object in ship electric propulsion systems. Compared with traditional three-phase motors, six-phase motors have stronger redundancy capabilities and can continue to operate stably when partial faults occur, thus significantly improving the reliability and safety of the system. This characteristic gives six-phase motors important advantages in the maneuverability and mobility of ships.

[0004] However, the multi-phase characteristics of six-phase motors also pose new challenges to the control system. Currently, motor drive control systems need to have excellent dynamic response capabilities and steady-state control performance to ensure stable power output and low energy loss of the motor under various operating conditions. The traditional model predictive current control (MPC) has become an effective means of optimizing current loop control due to its simplicity and ease of implementation, but its application in multi-phase motor control still has certain limitations.

[0005] In addition, current harmonics may be generated during the operation of six-phase motors, especially the harmonic components in the x-y plane, which will have a negative impact on the performance and efficiency of the motor. Therefore, how to effectively suppress current harmonics and improve the control performance of six-phase motors has become an important technical problem to be solved urgently. A reasonable control optimization strategy can not only improve the performance of six-phase motors, but also expand their application potential in complex ship operating conditions. Summary of the Invention

[0006] To address the above problems, this paper proposes a model predictive control method for a ship's six-phase permanent magnet propulsion motor based on virtual voltage vector synthesis. First, this method uses vector space decoupling coordinate transformation to extract the stator currents of the two control subspaces from the space model of the six-phase permanent magnet synchronous motor. Based on the characteristics that the fundamental wave components in the x-y subspace do not participate in the motor energy conversion, and that the outermost and the second outermost voltage vectors in the same direction in the α-β subspace are in opposite directions and can cancel each other out after being mapped to the x-y subspace, this method expands the predictive basic vectors on the basis of the traditional model predictive current control based on 13 large vectors, and synthesizes the target virtual voltage vector.

[0007] Through this optimization strategy, better control of the ship propulsion six-phase permanent magnet synchronous motor with a propeller load is achieved. This method effectively suppresses the harmonic distortion in the control current, significantly improves the steady-state performance of the motor control system, and enhances the overall stability and efficiency of the system.

[0008] The technical means adopted in the present invention are as follows:

[0009] The present invention provides a model predictive control method for a ship's six-phase permanent magnet propulsion motor based on virtual voltage vector synthesis, including:

[0010] S1: Establish a mathematical model of a six-phase permanent magnet synchronous motor based on the vector space decoupling method, construct a simulation model of the six-phase permanent magnet synchronous motor, and perform reduced-order decoupling processing on the simulation model of the six-phase permanent magnet synchronous motor through rotational coordinate transformation;

[0011] S2: Conduct vector space decoupling analysis on the mathematical model of the six-phase permanent magnet synchronous motor, extract the voltage vector distribution characteristics of the two effective control subspaces of α-β and x-y, and preselect the basic vector information;

[0012] S3: With the goal of eliminating the harmonic current in the x-y subspace, perform virtual voltage vector synthesis on the preselected basic voltage vector information, calculate the duty cycle of each basic voltage vector, reasonably allocate the action time ratio of the basic voltage vectors, and determine the finally synthesized virtual voltage vector;

[0013] S4: Establish a current prediction model for the six-phase permanent magnet synchronous motor, use the current prediction delay compensation method to compensate and correct the real-time sampled current signal to obtain the current compensation value, input the compensated current value into the current prediction model of the six-phase permanent magnet synchronous motor, and use the synthesized virtual voltage vector to perform predictive control on the compensated current;

[0014] S5: Design the predictive current optimization cost function. Through the optimization calculation of the predicted current value, obtain the corresponding optimal six-way switch signals, and input the optimal six-way switch signals into two three-phase two-level inverters, so as to perform predictive control on the synthetic virtual voltage vector model of the six-phase permanent magnet synchronous motor;

[0015] S6: Based on the load characteristics of the actual ship propeller, establish a ship propeller load mathematical model with the motor speed as the input and the load torque as the output, which is used to simulate the dynamic characteristics of the propeller load, and perform a propeller load loading simulation analysis on the six-phase permanent magnet synchronous motor.

[0016] Further, when synthesizing the virtual voltage vector from the preselected basic voltage vector information: Let the two vectors in the same direction in the α-β subspace be v 53 and v 36 , within a single period, the action ratio of v 53 is T n , the action ratio of v 36 is T m , T is the sampling period, V dc is the DC bus voltage. From the relationship that the sum of the actions of the two vectors in the harmonic x-y subspace is equal to zero, the following relationship can be obtained:

[0017]

[0018] Substitute the amplitudes of each voltage vector in the harmonic x-y subspace and solve for the values of T n and T m :

[0019]

[0020] Further, the six-phase permanent magnet synchronous motor current prediction model is:

[0021]

[0022] Among them, the expression of the current compensation value at the k + 1 moment is:

[0023]

[0024] In the above formula, u dopt , u qopt are the d-axis and q-axis components of the optimal voltage vector selected at the previous moment; i d (k), i d (k + 1) and i q (k), i q (k + 1) are the sampled values of the stator current components on the d-axis and q-axis at the corresponding k and k + 1 moments respectively; R s is the stator resistance; L d and Lq are the d-axis and q-axis stator inductances; ω r is the rotor angular velocity; ψ f is the permanent magnet flux linkage, and T s is the sampling period.

[0025] Furthermore, the performance indexes of the d-q axis currents in the α-β subspace are:

[0026]

[0027] where: g represents the cost function value, d ref , q ref respectively represent the reference values of the stator current components on the d-axis and q-axis, i d (k + 2), i q (k + 2) represents the predicted current value at the k + 1 moment.

[0028] Furthermore, the thrust and torque of the mathematical model of the ship propeller load are expressed as:

[0029]

[0030] In the formula, ρ is the seawater density, D is the propeller diameter, v p is the forward speed of the propeller in seawater, n is the propeller speed, K P ′ and K T ′ are the thrust coefficient and torque coefficient of the propeller respectively, and P and T p represent the thrust and torque of the mathematical model of the ship propeller load.

[0031] Define the ratio of the distance advanced by the propeller in one revolution to the diameter as the advance ratio of the propeller. The expression of the advance ratio in a bounded form is:

[0032]

[0033] where J' represents the advance ratio of the propeller, v p is the forward speed of the propeller in seawater, n is the propeller speed, and D is the propeller diameter.

[0034] Based on the vector space decoupling technology, the present invention establishes an accurate mathematical model of a six-phase permanent magnet synchronous motor for ship propulsion and constructs a simulation model of its motor body. Through the rotation coordinate transformation, the order reduction and decoupling of the model are realized, further simplifying the complexity of the control system, while retaining the integrity of the dynamic characteristics of the motor, providing a theoretical basis and a simulation verification platform for the development of an efficient control strategy.

[0035] On this basis, the present invention conducts a vector space decoupling analysis on the six-phase permanent magnet synchronous motor model, and extracts the voltage vector distribution characteristics of two effective control subspaces, namely α-β and x-y. According to these characteristics, the basic voltage vectors are preselected. The goal is to eliminate the harmonic current in the x-y subspace. By synthesizing virtual voltage vectors from the preselected basic voltage vectors, the suppression of harmonic current is achieved. By calculating the duty cycle of each basic voltage vector and reasonably allocating the proportion of its action time, the synthesized virtual voltage vector is finally determined.

[0036] In order to further improve the control accuracy, after establishing the current prediction model, the present invention introduces the current delay compensation technology. By compensating and correcting the real-time sampled current signal, the compensated current value is input into the current prediction control model. Through the synthesized virtual voltage vector, the compensated current is predicted and controlled. At the same time, an optimized cost function is designed to realize the optimized calculation of the predicted current value, so as to obtain the optimal six-way switch signals, and input them into two three-phase two-level inverters. Finally, the synthesized virtual voltage vector model predictive control of the six-phase permanent magnet synchronous motor is realized.

[0037] Finally, based on the load characteristics of the actual ship propeller, the present method establishes a motor load mathematical model with the motor speed as the input and the load torque as the output, and builds its simulation model to simulate the dynamic characteristics of the propeller load. Through the load loading simulation analysis, the application effect of this control strategy in the ship propulsion six-phase permanent magnet synchronous motor is verified. Brief Description of the Drawings

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0039] Figure 1 It is the control block diagram of a ship six-phase permanent magnet propulsion motor model predictive control method based on virtual voltage vector synthesis provided by the present invention;

[0040] Figure 2 It is the drive topology structure diagram of a six-phase permanent magnet synchronous motor provided by the present invention;

[0041] Figure 3 It is the space voltage vector distribution diagram of a six-phase permanent magnet synchronous motor provided by the present invention;

[0042] Figure 4 It is the structure diagram of a ship propeller load mathematical model provided by the present invention;

[0043] Figure 5 The waveform diagram of the motor feedback rotational speed and the propeller load torque provided by the present invention;

[0044] Figure 6 The phase current waveform diagram of the control method provided by the present invention and the traditional model predictive control method;

[0045] Figure 7 The x-y harmonic plane current waveform diagram of the control method provided by the present invention and the traditional model predictive control method;

[0046] Figure 8 The motor electromagnetic torque waveform diagram of the control method provided by the present invention and the traditional model predictive control method;

[0047] Figure 9 The schematic diagram of the Fourier harmonic analysis of the motor phase current of the control method provided by the present invention and the traditional model predictive control method. Detailed implementation manners

[0048] In order to enable those skilled in the art of the present technology to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0049] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those clearly listed steps or units, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or devices.

[0050] Combined with Figures 1 to 4 , Figure 1 The control block diagram of a model predictive control method for a ship six-phase permanent magnet propulsion motor based on virtual voltage vector synthesis provided by the present invention; Figure 2 A drive topology structure diagram of a six-phase permanent magnet synchronous motor provided by the present invention; Figure 3 A spatial voltage vector distribution diagram of a six-phase permanent magnet synchronous motor provided by the present invention; Figure 4 A mathematical model structure diagram of a ship propeller load provided by the present invention; to illustrate a specific embodiment of a model predictive control method for a ship six-phase permanent magnet propulsion motor based on virtual voltage vector synthesis provided by the present invention, including:

[0051] S1: Based on the vector space decoupling technology, establish the mathematical model of the six-phase permanent magnet synchronous motor and construct the simulation model of its motor body. On this basis, realize the reduced-order decoupling of the model through rotational coordinate transformation, further simplify the control complexity, and at the same time retain the integrity of the motor dynamic characteristics, providing a theoretical support and simulation verification platform for the development of efficient control strategies;

[0052] S2: Through the vector space decoupling analysis of the mathematical model of the six-phase permanent magnet synchronous motor, extract the voltage vector distribution characteristics of the two effective control subspaces of α-β and x-y, and accordingly conduct the basic vector preselection;

[0053] S3: Aiming at eliminating the harmonic current in the x-y subspace, synthesize the virtual voltage vector for the preselected basic voltage vectors, calculate the duty cycle of each basic voltage vector, reasonably allocate the proportion of its action time, and determine the finally synthesized virtual voltage vector;

[0054] S4: Establish the current prediction model of the six-phase permanent magnet synchronous motor, use the current prediction delay compensation method to compensate and correct the real-time sampled current signal to obtain the current compensation value, input the compensated current value into the current prediction model of the six-phase permanent magnet synchronous motor, and use the synthesized virtual voltage vector to perform predictive control on the compensated current;

[0055] S5: Design the predictive current optimization cost function, obtain the corresponding optimal six-way switch signals through the optimization calculation of the current prediction value, and input them into two three-phase two-level inverters, so as to realize the predictive control of the synthesized virtual voltage vector model of the six-phase permanent magnet synchronous motor;

[0056] S6: Based on the load characteristics of the actual ship propeller, establish the load mathematical model of the ship propeller with the motor speed as the input and the load torque as the output, used to simulate the dynamic characteristics of the propeller load, and conduct the load loading simulation analysis on the six-phase permanent magnet synchronous motor.

[0057] Specifically, Figure 1 The overall control steps are as follows:

[0058] (1) Sample the phase current, rotor position and speed at time k, perform VSD and Park transformations on the phase current, and obtain the current i of each subspace at time k d,q,x,y ;

[0059] (2) Using the concept of virtual voltage vector, within a single cycle, form a synthesized voltage vector by synthesizing multiple basic voltage vectors, making its component in the x-y subspace zero, thereby effectively reducing the harmonic current;

[0060] (3) Calculate the current value i at time k + 1 based on the optimal voltage vector compensation at the previous moment d,q(k+1); Obtain the q-axis current reference value i through the speed loop q_ref ;

[0061] (4) Establish a current prediction model and calculate the predicted current value i at time k+2 corresponding to the candidate voltage vector using the current compensation value at time k+1 d,q(k+2) , and substitute them into the cost function respectively. Input the voltage vector when the cost function takes the minimum value into the inverter.

[0062] S1: Decouple and model the Y-shaped phase-shifted 30° six-phase permanent magnet synchronous motor. Based on the amplitude invariant constraint, the VSD transformation matrix is expressed as:

[0063]

[0064] The relationship between the decoupled plane voltage and the six-phase voltage is:

[0065] [v α v β v x v y v o1 v o2 T =T αβ [v a v b v c v d v e v f T

[0066] Using the first two rows in the T αβ formula, map the fundamental components and harmonics of the 12n±1 (n = 1, 2, 3 ···) order to the α-β subspace that controls energy conversion. The middle two rows in Equation (1.1) map the harmonics of the 6n±1 order (n = 1, 3, 5 ···) to the x-y subspace, and no electromagnetic torque will be generated, but it will cause additional power loss. The last two rows in Equation (1.1) represent the zero-sequence harmonic components, and their harmonics are of the 3n order (n = 1, 3, 5 ···). Since the neutral points of the two sets of three-phase windings in the motor structure are independently connected to each other, the zero-sequence plane current will not flow and the value is zero, so it is not used as a control plane.

[0067] Perform the Park transformation on the machine variables in the α-β plane to obtain the synchronous rotating coordinate system model:

[0068]

[0069] [v d v q T =T dq [v α ​​​v β T

[0070] Using this method, the actual models of the motor in the synchronous rotating coordinate system and the x-y subspace can be obtained as follows:

[0071]

[0072] The electromagnetic torque equation of the six-phase permanent magnet synchronous motor is:

[0073] T e = 3p n i q [i d (L d -L q ) + ψ f

[0074] The motion equation of the six-phase permanent magnet synchronous motor is:

[0075]

[0076] In the above formula, v d and v q are the stator voltage components on the d-axis and q-axis; i d and i q are the components of the stator current on the d-axis and q-axis respectively; R is the stator resistance; L d and L q are the d-axis and q-axis stator inductances respectively; ω r is the rotor angular velocity; P is the time derivative operator; ψ f is the permanent magnet flux linkage; v x and v y are the stator voltage components in the x-y subspace; i x and i y are the stator current components in the x-y subspace; L ls is the leakage self-inductance.

[0077] Build its motor simulation model in the Matlab / Simulink environment based on the above-mentioned six-phase permanent magnet synchronous motor mathematical model.

[0078] Furthermore, S2: The six-phase permanent magnet synchronous motor usually uses two sets of three-phase two-level voltage source inverters with a common bus to drive. Specifically, as Figure 2 shown, since the upper and lower switching devices of each inverter bridge arm work in a complementary conduction state, each bridge arm can present two different working states. Therefore, the total number of permutations and combinations of the switching states of the entire inverter is 2 6 ​​There are 64 possible states, thus forming 64 different space voltage vectors. However, not all of these voltage vectors are valid. After excluding redundant vectors and zero vectors, only 48 effective voltage vectors remain. These effective voltage vectors are generated during the operation of the motor through control strategies (such as space vector modulation) and directly participate in the torque control and speed regulation of the motor. The selection of effective voltage vectors ensures that the motor can operate efficiently and provide precise control.

[0079] Mark the voltage vectors generated by the inverter as follows:

[0080] v = [S A S B S C S D S E S F T

[0081] Where S i (i = A, B, C, D, E, F) represents the switching state of each bridge arm, and S i = 1 means the upper bridge arm switching device is on and the lower bridge arm switching device is off; S i = 0 means the upper bridge arm switching device is off and the lower bridge arm switching device is on; Mark the serial number of the voltage vector using the octal counting method for the switching state. The correspondence between the switching state and the voltage vector can be expressed as:

[0082] [S] = {S a , S b , S c , S d , S e , S f}

[0083] For example, "100100" represents v 36 , and the 64 space voltage vectors are arranged correspondingly in the α-β subspace and the x-y subspace according to the magnitude of the amplitude, specifically as Figure 3 shown.

[0084] ​Furthermore, in step S3: in a six-phase permanent magnet synchronous motor drive system, only the control variables in the α-β subspace directly participate in the electromechanical energy conversion, while the control variables in the x-y subspace mainly generate losses. The voltage vectors generated by each inverter will simultaneously map in both the α-β subspace and the x-y subspace. According to the formula of harmonic current, even a small voltage vector may cause an increase in harmonic current after passing through the low harmonic inductor, thus affecting the performance of the system. Therefore, using the concept of virtual voltage vectors, within a single period, by synthesizing multiple basic voltage vectors, a synthesized voltage vector is formed such that its component in the x-y subspace is zero, thereby effectively reducing the harmonic current. This idea is based on the distribution characteristics of space voltage vectors: in a six-phase motor, the α-β subspace is located in the outermost and the second outermost layers in the same direction. After the voltage vectors are mapped to the x-y subspace, their directions are opposite. Using this characteristic, by calculating the action time of each sub-voltage vector, a virtual voltage vector can be synthesized so that its component in the x-y subspace is zero, thereby effectively reducing the harmonic current in the system.

[0085] The specific steps of virtual vector synthesis are as follows: First, taking two vectors v 53 and v 36 in the same direction in the α-β subspace as an example, denote the action ratio of v 53 within a single period as T n , and the action ratio of v 36 as T m . Then, T is the sampling period. According to the basic idea of synthesizing the virtual voltage vector, the relationship between the two vectors in the harmonic x-y subspace is as follows:

[0086]

[0087] Substituting the amplitudes of each voltage vector in the harmonic x-y subspace, the values of T n and T m can be solved:

[0088]

[0089] Correspondence table of the action time of voltage vectors v 53 and v 36 with the switching states:

[0090] In some alternative embodiments, referring to Table 1, it is as follows:

[0091] Table 1. Correspondence table of the action time of voltage vectors v53 and v36 with the switching states

[0092]

[0093] The remaining virtual voltage vectors are synthesized in turn according to this method, and all synthesized virtual voltage vector data tables can be obtained by calculating through the sub-vector action time formula:

[0094] In some alternative embodiments, referring to Table 2, as follows:

[0095] Table 2. Synthesized Virtual Voltage Vector Data Table

[0096]

[0097]

[0098] Furthermore, S4: The current prediction delay compensation technology established and introduced in the step of the six-phase permanent magnet synchronous motor current prediction model is as follows:

[0099] The prediction model of the motor usually uses the form of a discretized state equation, and generally the forward Euler equation shown below is used for discretization:

[0100]

[0101] In the formula, T s is the control period; x is the motor state quantity, such as current, voltage, electromagnetic torque, stator flux linkage, etc.; k + 1 and k are the (k + 1)-th and k-th sampling periods respectively.

[0102] Combined with the voltage equation of the motor, the discrete state equation of the motor can be obtained by discretization as:

[0103]

[0104] In model predictive current control, due to the existence of links such as sampling, calculation, pulse optimization, and configuration in the actual digital control system, the optimal voltage vector calculated in each control period cannot act on the inverter immediately, but can only be realized in the next period. This phenomenon is usually referred to as the "one-beat delay" problem. To solve this problem, a two-step method is often adopted. Specifically, first, the variable value at the current moment (k + 1) is compensated to correct the deviation caused by sampling and calculation delays. Then, based on the compensated variable value at the (k + 1) moment, the variable value at the next moment (k + 2) is predicted. By this method, the influence of delay on the control performance can be effectively reduced, the real-time response ability and accuracy of the system can be improved, and thus the effect of current control can be optimized.

[0105] The calculation expression of the current compensation value at the (k + 1) moment in the model predictive control method of the ship six-phase permanent magnet propulsion motor based on virtual voltage vector synthesis is:

[0106]

[0107] The current prediction model is as follows:

[0108]

[0109] where u dopt and u qopt are the d-axis and q-axis components of the optimal voltage vector selected at the previous moment.

[0110] Furthermore, S5: The cost function for optimizing the predicted current designed in the above steps is:

[0111] To simplify the cost function, the virtual voltage vector has been used to effectively suppress the generation of harmonic currents. Therefore, the harmonic terms no longer need to be included in the cost function, thus avoiding the complexity of adjusting the weight coefficients. Based on this, the specific form of the cost function can be further optimized, focusing on the d-q axis predicted current cost function in the α-β subspace, and the specific form is:

[0112]

[0113] Furthermore, S6: The mathematical model of the ship propeller load in the above steps is as follows:

[0114] To apply the propeller load to the motor, a mathematical model of the ship propeller load needs to be established. According to the research on the hydrodynamic performance of the propeller, the thrust and torque of the ship propeller can be expressed as:

[0115]

[0116] where ρ is the seawater density, generally taken as 1025 kg / m 3 ; D is the propeller diameter; v p is the forward speed of the propeller in seawater; n is the propeller speed; K P ′ and K T ′ are the thrust coefficient and torque coefficient of the propeller respectively, and both are functions of the advance ratio.

[0117] The ratio of the distance advanced by the propeller in one revolution to the diameter is called the advance ratio of the propeller. The bounded form of the advance ratio is adopted, and its expression is:

[0118]

[0119] To obtain the functional relationship between the thrust coefficient K P ′, the torque coefficient K T ′ and the advance ratio J′, the fitting formula of the Chebyshev polynomial is adopted, and the polynomial coefficients are the coefficients with a pitch ratio of 0.9. When the propeller rotates, it will cause additional resistance to the hull, and the influence caused by this resistance increment can be represented by the thrust deduction coefficient t′. Then the effective thrust P e generated by the propeller is:

[0120]

[0121] When a ship sails in water, the water around the hull will be affected by the ship, resulting in a water flow that flows along with the ship. This phenomenon is called wake. The wake will cause the advance speed of the propeller. The wake will cause the advance speed v p and the ship speed v s to be different. The relationship between the two is as follows:

[0122] v p =(1 - ω′)v s

[0123] In the formula, ω′ is the wake fraction coefficient.

[0124] The total resistance received by the ship is:

[0125]

[0126] In the formula, r is the resistance coefficient.

[0127] The motion equation of the ship-engine-propeller system can be expressed as:

[0128]

[0129] In the formula, m is the hull mass; Δm is the mass of the attached water, generally taking 5% - 15% of the hull mass;

[0130] In some alternative embodiments, referring to Table 3, as follows:

[0131] Table 3. Parameters related to the ship and the propeller

[0132]

[0133] According to the above formula, a ship propeller load model is established, and its block diagram is as Figure 4 shown. The parameters related to the ship and the propeller in the mathematical model are listed in Table 3. Since actual ship data is used, the calculated propeller load is relatively large. To ensure that the load does not exceed the load range of the test motor, a coefficient needs to be multiplied on the basis of the calculated value to ensure the normal operation of the motor system.

[0134] In the simulation test, the motor given speeds are divided into three levels: 200 r / min, 500 r / min, and the rated speed of 750 r / min, simulating the staged starting conditions of the ship. The motor given speed and the propeller load torque waveforms are as Figure 5 shown.

[0135] A simulation test is carried out using the model predictive control method of a ship six-phase permanent magnet propulsion motor based on virtual voltage vector synthesis and the traditional 13 large vector model predictive control method, and the test duration is set to 1 second. The simulation object is a 3-pole six-phase permanent magnet synchronous motor with a rated speed of 750 r / min and a DC bus voltage of 537 V. The feedback speed of the motor and the output torque of the propeller load have step changes at 0.3 s and 0.7 s, and the specific waveforms are as shown in Figure 5 shown.

[0136] Figures 5 to 9 The comparative test results of the model predictive control method of the ship six-phase permanent magnet propulsion motor based on virtual voltage vector synthesis of the present invention and the traditional model predictive current control method are shown. Specifically, they include:

[0137] Figure 5 are the waveforms of the motor feedback speed and the propeller load torque; Figure 5 (a) is the waveform diagram of the motor feedback speed, Figure 5 (b) is the waveform diagram of the propeller load torque.

[0138] Figure 6 is the phase current waveform diagram of the control method provided by the present invention and the traditional model predictive control method; Figure 6 (a) is the phase current waveform under the traditional model predictive current control method, Figure 6 (b) is the phase current waveform under the control method described in the present invention.

[0139] Figure 7 is the x-y harmonic plane current waveform diagram of the control method provided by the present invention and the traditional model predictive control method; Figure 7 (a) is the x-y axis current waveform under the traditional model predictive current control method, Figure 7 (b) is the x-y axis current waveform under the control method described in the present invention.

[0140] Figure 8 is the motor electromagnetic torque waveform diagram of the control method provided by the present invention and the traditional model predictive control method; Figure 8 (a) is the motor electromagnetic torque waveform under the traditional model predictive current control method, Figure 8 (b) is the motor electromagnetic torque waveform under the control method described in the present invention.

[0141] Figure 9 is the schematic diagram of the Fourier harmonic analysis of the motor phase current of the control method provided by the present invention and the traditional model predictive control method; Figure 9 (a) is the total harmonic analysis of the phase current under the traditional model predictive current control method, Figure 9 (b) is the total harmonic analysis of the phase current under the control method described in the present invention.

[0142] It can be seen from the simulation results that the motor has a good operating state under the model predictive control method of the ship six-phase permanent magnet propulsion motor based on the virtual voltage vector synthesis. In particular, the maximum amplitude of the harmonic plane x-y axis current of the motor is suppressed to about 0.2 A; and the current harmonic of the motor under the rated speed and rated current conditions is only 2.57% through the Fourier harmonic analysis; which proves the feasibility and effectiveness of the model predictive control method of the ship six-phase permanent magnet propulsion motor based on the virtual voltage vector synthesis provided by the present invention.

[0143] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A model predictive control method for a six-phase permanent magnet propulsion motor of a ship based on virtual voltage vector synthesis, characterized in that: include: S1: Based on the vector space decoupling method, a mathematical model of a six-phase permanent magnet synchronous motor is established, and a simulation model of the six-phase permanent magnet synchronous motor is constructed, and a reduced-order decoupling process is performed on the simulation model of the six-phase permanent magnet synchronous motor through a rotating coordinate transformation; S2: Perform vector space decoupling analysis on the mathematical model of the six-phase permanent magnet synchronous motor, extract the voltage vector distribution characteristics of the two effective control subspaces α-β and xy, and pre-select basic vector information; S3: with the goal of eliminating the harmonic current in the xy subspace, synthesize the virtual voltage vector for the pre-selected basic voltage vector information, calculate the duty cycle of each basic voltage vector, reasonably allocate the action time ratio of the basic voltage vector, and determine the final synthesized virtual voltage vector; S4: Establish a current prediction model for a six-phase permanent magnet synchronous motor, use a current prediction delay compensation method to compensate and correct the real-time sampled current signal to obtain a current compensation value, input the compensated current value into the current prediction model for the six-phase permanent magnet synchronous motor, and use a synthetic virtual voltage vector to predict and control the compensated current; S5: Design a predicted current optimization cost function, optimize and calculate the current prediction value, obtain the corresponding optimal six-way switch signals, and input the optimal six-way switch signals into two three-phase two-level inverters, so as to predict and control the synthetic virtual voltage vector model of the six-phase permanent magnet synchronous motor; S6: Based on the load characteristics of actual ship propellers, a mathematical model of ship propeller load is established with motor speed as input and load torque as output to simulate the dynamic characteristics of propeller load, and propeller load loading simulation analysis of the six-phase permanent magnet synchronous motor is performed.

2. The model predictive control method for a six-phase permanent magnet propulsion motor of a ship based on virtual voltage vector synthesis according to claim 1 is characterized in that: When performing virtual voltage vector synthesis on the pre-selected basic voltage vector information: let the two vectors in the same direction in the α-β subspace be v 53 and v 36 , within a single cycle v 53 The action ratio is T n , v 36 The action ratio is T m , T is the sampling period, V dc is the DC bus voltage. The sum of the two vectors in the harmonic xy subspace is equal to zero, and the following relationship can be obtained: Substituting the amplitude of each voltage vector in the harmonic xy subspace, we can get T n and T m Values:

3. The model predictive control method for a six-phase permanent magnet propulsion motor of a ship based on virtual voltage vector synthesis according to claim 1 is characterized in that: The current prediction model of the six-phase permanent magnet synchronous motor is: The current compensation value expression at time k+1 is: In the above formula, u dopt 、u qopt The d and q axis components of the optimal voltage vector selected at the last moment; i d (k),i d (k+1) and i q (k), i q (k+1) are the sampling values ​​of the stator current components on the d-axis and q-axis at the corresponding time k and k+1 respectively; R s is the stator resistance; L d and L q are the stator inductances of the d-axis and q-axis respectively; ω r is the rotor angular velocity; ψ f is the permanent magnet flux, T s is the sampling period.

4. The model predictive control method for a six-phase permanent magnet propulsion motor of a ship based on virtual voltage vector synthesis according to claim 1 is characterized in that: The cost function of the dq-axis predicted current in the α-β subspace is: Among them: g represents the cost function value, d ref ,q ref Represent the reference values ​​of the stator current components on the d-axis and q-axis, i d (k+2), i q (k+2) represents the predicted current value at time k+1.

5. The model predictive control method for a six-phase permanent magnet propulsion motor of a ship based on virtual voltage vector synthesis according to claim 1 is characterized in that: The thrust and torque of the ship propeller load mathematical model are expressed as: Where ρ is the density of seawater, D is the propeller diameter, and v p is the propeller forward speed in seawater, n is the propeller speed, K P ′ and K T ′ are the thrust coefficient and torque coefficient of the propeller, P and T p Represent the thrust and torque of the mathematical model of ship propeller load; The ratio of the distance traveled by the propeller in one rotation to its diameter is defined as the propeller advance ratio. The advance ratio expression in bounded form is: Where J' represents the propeller speed ratio, v p is the forward speed of the propeller in seawater, n is the propeller speed, and D is the propeller diameter.

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