Variable-frequency cooperative starting control method for motor of ship emergency power system

Abstract

The invention relates to a frequency conversion cooperative starting control method for a motor of a ship emergency power system. The method comprises the following steps: step 1, modeling of the ship emergency power system: establishing an optimal configuration model of a ship comprehensive power system based on multiple constraint conditions of operation economy, system operation safety and power distribution rapidity of a diesel generating set; step 2, load starting conditions of the high-power motor: when the number of pole pairs of a motor winding is fixed, the starting torque of the motor can be adjusted by changing the terminal voltage and the power supply frequency; and 3, AFE control is adopted for a rectification part, and V / F control is adopted for an induction motor. The problem that an existing motor starting control method is not suitable for a ship emergency electric power system and cannot meet the requirement of a high power factor is solved, the alternating voltage generated by the AFE can still be kept in a stable state, the frequency conversion control mode is more stable, and the reliability is higher. The method is more suitable for stabilizing the condition of high ship pulse load power change, and the stability of a ship emergency power system is further improved.

Description

Technical Field

[0001] The invention relates to a motor control technology, and in particular to a motor variable frequency coordinated starting control method for a ship emergency power system. Background Art

[0002] With the continuous development of current ship technology, high-power motor loads play an important role in ship emergency power systems. The ship emergency power system is an important facility to ensure that the ship can maintain critical operations in an emergency, and is an important part of the safe operation of the ship. When an accident occurs in the main power grid and it cannot supply power, the emergency power system can automatically provide power for the key equipment, critical equipment and key equipment in the ship that are related to the navigation control of the ship. At this time, the main load is the motor load. Therefore, during the operation of the ship emergency power system, in order to ensure the necessary energy supply of the ship in an emergency, the motor load needs to operate normally in the system to meet the needs of emergency operation.

[0003] When a high-power motor is started and loaded in a ship's emergency power system, it will cause transient voltage reduction, frequency fluctuation, and power fluctuation in the ship's emergency power system, which brings certain challenges to the stable operation of the ship's emergency power system. When a high-power motor is connected to the power grid, the process of accelerating the motor speed from static to rated speed is called the motor's starting process. The most important starting performance of an asynchronous motor is the starting current and starting torque.

[0004] Therefore, how to reduce the starting current and increase the starting torque during the starting process of the motor has always been an important topic that needs to be explored. The three-phase asynchronous motor is a back-EMF load, that is, the back-EMF is used to balance the external voltage. The back-EMF of the motor is zero at the beginning of starting, and the impact current is very large. When the motor capacity is large, the impact current will interfere with the power grid and its load, and even endanger the safe operation of the power grid in serious cases; when the starting current is too large, the motor itself will be impacted by excessive electromagnetic force, and frequent starting will cause the winding to overheat. At the same time, due to the large starting stress, the service life of the load is reduced.

[0005] In the ship emergency power system, the most common method is direct starting, which is to connect the stator winding of the motor directly to the power grid with a knife switch or contactor. The advantage of this method is that the operation and starting equipment are simple, but the disadvantage is that the starting current is very large. The current of the general squirrel cage asynchronous motor direct starting is 4-7 times the rated current, and some motors can even reach 8-12 times, and the starting torque is 1-2 times the rated torque. At the same time, the application of the direct starting method is also limited by the capacity of the power grid. When the capacity of the ship emergency power system is not large, the starting current of this method may cause the power grid voltage to drop significantly, affecting the normal operation of other equipment in the power grid.

[0006] In order to solve the above problems caused by the existing starting method of the ship emergency power system, and the motor can quickly reach the rated speed and work normally, the motor is required to have a sufficiently large starting torque and the starting current should not be too large. In recent years, with the continuous development of power electronics technology, the motor variable frequency starting method has emerged. The motor speed regulation performance indicators achieved by different variable frequency control schemes are different. The commonly used variable frequency schemes are generally divided into open-loop and closed-loop control. Among them, constant voltage-frequency ratio control (V / F) is an open-loop control scheme, and the closed-loop control schemes include slip frequency control, direct torque control, vector control, etc.

[0007] The above studies are mainly aimed at the large motor starting scenario of the land power system, and rarely study the corresponding control strategies for the isolated network of ships. Different from the former, the ship emergency power system should present the characteristics of isolated network and smaller capacity than the main network, so as to reduce the impact on the ship emergency network and ensure safe operation in emergency state. Summary of the invention

[0008] In view of the problem that the current motor starting control method is not suitable for ship emergency power systems and cannot meet the requirements of high power factor, a frequency conversion coordinated starting control method for motors in ship emergency power systems is proposed. In order to ensure the stability and reliability of the ship emergency power system under large motor starting, the present invention proposes a frequency conversion coordinated starting control method in which the rectifier part adopts Active Front End (AFE) control and the induction motor adopts V / F control according to the starting characteristics of large motors. This method comprehensively considers the coordinated process of the AC-DC-AC parts in the frequency conversion process, making the frequency conversion control method more stable and further improving the stability of the ship emergency power system.

[0009] The technical solution of the present invention is:

[0010] A method for controlling the frequency conversion coordinated starting of a motor of a ship emergency power system comprises the following steps:

[0011] Step 1: Modeling of Ship Emergency Power System

[0012] Based on the multi-constraint conditions of diesel generator set operation economy, system operation safety and power distribution rapidity, the ship integrated power system optimization configuration model is established. The speed regulator mathematical model, throttle controller mathematical model, diesel engine mathematical model and induction motor mathematical model are established in turn. Through the analysis of the mathematical models of diesel generator sets and induction motors, the components of the ship emergency power system are established.

[0013] Step 2: High-power motor load starting conditions

[0014] In the ship emergency power system, the power load is supplied by its own generator set, and the power station capacity is small; starting the motor is equivalent to suddenly increasing the load, which will cause an impact on the system and cause an instantaneous drop in voltage; the starting torque is related to the terminal voltage, the number of motor poles and the power supply frequency; when the number of motor winding poles is constant, the starting torque of the motor can be adjusted by changing the terminal voltage and the power supply frequency;

[0015] Step 3: Rectification-inversion coordinated control based on DC voltage

[0016] The rectifier part adopts AFE control, and the induction motor adopts V / F control;

[0017] The AFE inverter adopts a topological structure. In the AFE inverter, the DC voltage is added to the inverter power component after PI adjustment. When the motor state changes suddenly, it will only affect the feedback value in the AFE, and the DC capacitor voltage value will not change, thereby achieving the purpose of improving the dynamic performance of the AFE and reducing the amount of AFE capacitor. The DC voltage is used as the d-axis current reference value after PI adjustment. After the AC side current is adjusted by PI, the reference d-axis and q-axis voltages are modulated by decoupling output SPWM, and the DC voltage is modulated by the inverter.

[0018] The frequency conversion scheme adopts a constant V / F method; speed regulation above the base frequency and speed regulation below the base frequency. When regulating above the base frequency, the voltage is kept constant. At this time, the magnetic flux and frequency are inversely proportional, which is equivalent to the weak magnetic speed-up process of the DC motor; the synchronous speed of the asynchronous motor increases, the electromagnetic torque decreases, and the output power is basically constant. This process can be called constant power speed regulation; within the speed regulation range below the base frequency, the magnetic flux remains unchanged, which belongs to constant torque speed regulation; in the speed regulation process above the base frequency, the magnetic flux decreases as the power supply frequency increases, showing a constant power speed regulation operation characteristic.

[0019] Further, the method specifically includes the following steps:

[0020] Step 1: Modeling of Ship Emergency Power System

[0021] Based on the multi-constraint conditions of diesel generator set operation economy, system operation safety and power distribution rapidity, the ship's integrated power system optimization configuration model is established. The ship's emergency power system includes diesel generator sets, switchboards and induction motors. The switchboard provides power to the diesel generator set, and the power flows from the diesel generator set to the induction motor; the diesel generator set consists of a speed regulator, a throttle controller and a diesel engine. The ship's integrated power system optimization configuration model is established, and the following four mathematical models are established in turn:

[0022] Step 1.1. Establish the mathematical model of the speed regulator

[0023] The speed regulator consists of two parts: a speed sensor and a speed control processor. The speed sensor uses a speed measuring generator to measure a voltage signal proportional to the generator speed. The controller uses a traditional PID control algorithm. Since the measurement link of the speed sensor can be equivalent to a first-order inertia link, the speed control processor uses a PID function to represent it. Therefore, the transfer function G of the speed regulator is 1 (s) can be expressed as:

[0024]

[0025] In the formula, is the first-order inertia function of speed measurement, T 1 is the inertia time constant, s is the Laplace operator of the transfer function; is the PID function of the speed control processor, K p , K I , K D They represent the proportional constant, integral constant and differential constant in PID control respectively;

[0026] The transfer function G of the speed regulator can be obtained by Laplace transforming and rearranging the above formula. 1 (s) is:

[0027]

[0028] In the formula, K 1 , T 2 , T 3 It is the constant obtained after sorting the PID control function;

[0029] Step 1.2. Establish the mathematical model of the throttle controller

[0030] The function of the throttle controller is to execute the oil quantity given instruction output by the speed controller and control the oil quantity through the throttle action; the common throttle controller is composed of a rotating electromagnet, that is, an armature. The rotation of the armature is proportional to the displacement of the sliding sleeve, and its motion increment equation is:

[0031]

[0032] Where l represents the change of armature displacement, i.e. the displacement change of the throttle controller, m is the mass of the armature push rod assembly, D is the damping coefficient, K is s is the return spring stiffness, ΔF m is the electromagnetic force increment, t is the power-on time, and it can be expressed as:

[0033] ΔF m =K i Δi-K l Δl (4)

[0034] Where: K i is the current force gain of the proportional electromagnet, i is the change of electromagnet current, K l is the sum of the displacement force gain and elastic stiffness of the proportional electromagnet; combining equations (3) and (4), and then performing Laplace transformation, we get:

[0035] ms 2 l(s)+Dsl(s)+K s l(s)=K i i(s)-K l l(s) (5)

[0036] In the formula, l(s) and i(s) are the Laplace transformed forms of l and i respectively;

[0037] The transfer function G of the oil quantity controller can be obtained 2 (s):

[0038]

[0039] Simplified to:

[0040]

[0041] In the formula, K 2 , T 4 , T 5 is the constant obtained after sorting;

[0042] Step 1.3. Establishing the mathematical model of diesel engine

[0043] The adjustment characteristics of a diesel engine mainly describe the engine output main mechanical torque T m The relationship between the armature displacement l in the throttle controller; when the throttle controller acts according to the command of the speed regulator, the torque output of the diesel engine will not immediately respond to the action of the throttle actuator due to the lag in the fuel combustion link and the thermal stroke link of the diesel engine itself; when the diesel engine is fixed, the delay time from the action of the throttle actuator to the output torque of the diesel engine is also fixed;

[0044] Since the throttle opening h is related to the diesel engine output torque T m There is a proportional relationship, namely:

[0045] T m =kh (8)

[0046] In the formula, h is the throttle opening, k is the proportional correlation coefficient, which is related to the type of diesel engine selected;

[0047] When the throttle opening changes by Δh under the action of the throttle actuator, the output torque of the diesel engine changes by ΔT m:

[0048] ΔT m =k·Δh (9)

[0049] Assume the delay time of the diesel engine is T d , then after Laplace transform in the complex frequency domain:

[0050]

[0051] Where, ΔT m (s) is ΔT m The form after Laplace transformation;

[0052] Therefore, the transfer function G of the diesel engine is 3 (s) can be expressed as:

[0053]

[0054] The proportion coefficient of each link is K, then:

[0055] K=K 1 K 2 k (12)

[0056] Step 1.4. Establish the mathematical model of induction motor

[0057] For the analysis of the commonly used mathematical model of induction motor, considering the strong coupling, nonlinearity and time-varying nature of the flux differential equation of this group of models, many inconveniences are brought in the actual analysis; on this basis, this group of formulas is converted from the abc coordinate system to the dq0 rotating coordinate system; in the converted equations, the three-phase windings of the stator and rotor have undergone a 3 / 2 transformation, which is equivalent to the two-phase windings in the stationary coordinate system;

[0058] The equation describing the dynamic operation of a three-phase asynchronous motor is shown below as the flux equation:

[0059]

[0060] The above formula is the flux equation in the dq0 coordinate system. In this equation, the flux direction of the rotor of the three-phase motor is along the d-axis direction of the rotating coordinate system. m , L r are the mutual inductance of the two-phase winding and the rotor inductance respectively; ψ rd , rq are the rotor flux on the d-axis and q-axis respectively; i rd 、i sd 、i rq 、i sqThey are the rotor current on the d-axis, the stator current on the d-axis, the rotor current on the q-axis, and the stator current on the q-axis respectively; based on the flux equation, the voltage equation is as follows:

[0061]

[0062] In the formula, u rd 、u sd 、u rq 、u sq are the rotor voltage on the d-axis, the stator voltage on the d-axis, the rotor voltage on the q-axis, and the stator voltage on the q-axis respectively; ω s is the angular velocity of the dq coordinate axis relative to the stator; ω sl is the induction motor slip rate; R s , R r , L s , L r are the resistance and inductance of the stator and rotor of the induction motor respectively; p is the differential operator;

[0063] The torque equation of the induction motor is as follows, in which the magnitude of the torque is directly proportional to the rotor flux on the d-axis and the stator current on the q-axis:

[0064]

[0065] Where, T e is the electromagnetic torque of the induction motor; n p is the pole pair number;

[0066] The above three equations together constitute the mathematical model of the induction motor in the dq0 coordinate system. In this mathematical model, since the amount of coupled data is small, it is convenient for the decoupling control and simulation analysis of the induction motor;

[0067] By analyzing the mathematical models of diesel generator sets and induction motors, the components of the ship's emergency power system were established;

[0068] Step 2: High-power motor load starting conditions

[0069] In the ship's emergency power system, the power load is supplied by its own generator set, and the power station capacity is relatively small; starting the motor is equivalent to suddenly increasing the load, which will cause an impact on the system and cause an instantaneous drop in voltage;

[0070] Starting current I when the induction motor starts st With starting torque T st The formula is as follows:

[0071]

[0072]

[0073] Where: U 1 is the terminal voltage; R 1 is the stator winding resistance; R 2 ′ is the converted rotor winding resistance; X 1σ is the stator winding reactance; X 2 ' σ is the converted rotor winding reactance; Z dx To simplify the results for calculation; n 1 is the synchronous speed of the stator rotating magnetic field; m 1 is the number of stator winding turns;

[0074] It can be seen that the starting torque is not only related to the terminal voltage U 1 It is related to the synchronous speed of the rotating magnetic field in the stator winding, and is inversely proportional to the synchronous speed; the synchronous speed has the following relationship with the power supply frequency and the number of motor poles:

[0075]

[0076] Where: n p is the number of motor pole pairs; f is the power supply voltage frequency; Substituting formula (18) into formula (17), the following formula (19) is obtained:

[0077]

[0078] The starting torque is related to the terminal voltage, the number of motor pole pairs and the power supply frequency. When the number of motor winding pole pairs is constant, the starting torque of the motor can be adjusted by changing the terminal voltage and the power supply frequency.

[0079] Step 3: Rectification-inversion coordinated control based on DC voltage

[0080] In this method, the rectifier part adopts AFE control, and the induction motor adopts V / F control;

[0081] The AFE inverter adopts a topological structure;

[0082] The principle of AFE inverter joint control is: when the system is in a stable state, the DC side power P rec for:

[0083] P rec =e d i d +e q i q (20)

[0084] In the formula, e d 、e q 、i d 、i qare the d-axis and q-axis voltages and currents on the AC grid side respectively; when the DC capacitor voltage is in a balanced state, its stored energy W C , energy change rate P C They are:

[0085]

[0086]

[0087] Where, C is the DC side capacitance; u dc is the DC voltage;

[0088] The inverter output power is:

[0089] P inv =u sd i sd +u sq i sq (twenty three)

[0090] Where P inv is the inverter output power; u sd 、u sq is the d-axis and q-axis stator voltage; i sd 、i sq are the d-axis and q-axis stator currents;

[0091] At any time, the energy flowing into AFE is the sum of the change rate of energy stored in the DC capacitor and the energy consumed by the motor; in the AFE inverter, the DC voltage is added to the inverter power component after PI adjustment. When the motor state changes suddenly, it will only affect the feedback value in AFE, and the DC capacitor voltage value will not change, thereby achieving the purpose of improving the dynamic performance of AFE and reducing the amount of AFE capacitor; the DC voltage is used as the d-axis current reference value after PI adjustment, and the AC side current is adjusted by PI, and the reference d-axis and q-axis voltages are modulated by decoupling output SPWM, and the DC voltage is modulated by the inverter;

[0092] The frequency conversion scheme adopts constant V / F mode;

[0093] According to the principle of electrical machinery, it is easy to know that the stator voltage induced electromotive force E of the asynchronous motor g It can be expressed as follows:

[0094] E g =4.44f 1 N 1 K 1N Φ m (twenty four)

[0095] Where f 1 is the stator voltage frequency, N 1K is the number of internal turns of each phase winding of the stator, 1N is the fundamental wave winding coefficient, Φ m The air gap flux per pole; the speed regulation of asynchronous motor is to maintain the air gap flux per pole Φ m According to formula (24), it is easy to know that as long as E g / f 1 The magnetic flux Φ can be kept constant m unchanged; but in practical applications, E g It is difficult to measure, and when E g When it is large enough, the voltage drop on the stator impedance can be ignored; use the stator input voltage U S To replace E g The problem of difficulty in measuring stator induced electromotive force can be solved by maintaining U S / f 1 The constant approximation controls the magnetic flux to be constant; however, this method has a defect that when the asynchronous motor runs in the low frequency band, the stator induced electromotive force E g Very small, the voltage drop on the stator impedance cannot be ignored; this situation can be solved by properly compensating the stator input voltage U S Improvement, U 0 The voltage raised after compensation; U 1N and f 1N is the fundamental frequency stator voltage and frequency;

[0096] The mathematical expression of the constant V / F working curve is:

[0097]

[0098] In the constant voltage-frequency ratio control process, when the stator voltage of the motor reaches the rated value U 1N If the frequency continues to increase, it will cause the motor insulation to deteriorate and the mechanical characteristics to soften. At this time, the frequency can still continue to rise. Therefore, variable frequency speed regulation actually includes speed regulation above the base frequency and speed regulation below the base frequency. When regulating above the base frequency, the voltage is kept constant. According to the above formula (25), the magnetic flux and frequency are inversely proportional at this time, which is equivalent to the weak magnetic speed increase process of the DC motor. When the synchronous speed of the asynchronous motor increases, the electromagnetic torque decreases, and the output power is basically constant. This process can be called constant power speed regulation. n is the motor speed, Te is the motor electromagnetic torque, and when the frequency f1 is greater than the rated frequency f1N, due to the constant voltage, the electromagnetic torque decreases, and the output power is basically constant.

[0099] Plot the mechanical characteristics of variable frequency speed regulation below the base frequency. It can be seen from the figure that as the frequency decreases, the maximum induced electromagnetic torque of the asynchronous motor will gradually decrease. When the frequency is too low, the stator voltage drop cannot be ignored and the motor's load capacity is limited, so it is necessary to compensate the stator voltage.

[0100] By summarizing the control characteristics below and above the base frequency on one coordinate axis, we can get the variable frequency speed control characteristic diagram of the asynchronous motor: when the speed is adjusted below the base frequency, due to constant power speed regulation, the magnetic flux remains unchanged, and the stator voltage decreases as the frequency decreases; when the speed is adjusted above the base frequency, due to constant power speed regulation, the product of the electromagnetic torque Te and the speed n should remain unchanged, and the magnetic flux decreases as the frequency increases; although the speed of the asynchronous motor is different under different working conditions depending on the load it carries, if the system current remains at the rated value, the torque T of the asynchronous motor e and magnetic flux It has a positive proportional relationship; within the speed regulation range below the base frequency, the magnetic flux remains unchanged, which belongs to constant torque speed regulation; in the speed regulation process above the base frequency, the magnetic flux decreases as the power supply frequency increases, showing a constant power speed regulation operation characteristic.

[0101] Furthermore, it also includes step 4, method verification:

[0102] A model including a diesel generator, an induction motor and the corresponding control system is established in MATLAB / Simulink; the simulation parameters are obtained and simulation is performed. During the simulation, the changing characteristics of the ship emergency power system when the two motors are started and operated using the traditional control scheme and this method are compared, and the simulation results of the uncontrolled start-up and the adaptive collaborative control start-up are compared.

[0103] Furthermore, the diesel generator set in step one consists of three parts: a speed regulator, a throttle controller and a diesel engine: the speed regulator converts the input speed difference signal into a fuel quantity given signal through a built-in speed control algorithm and outputs it to the throttle controller; the throttle actuator controls the throttle action under the drive of the fuel quantity given signal, and the throttle action provides power torque to the diesel engine through the fuel quantity, and the diesel engine outputs power torque to drive the generator to rotate and generate electricity.

[0104] Furthermore, in step three, there are many types of frequency converters, including AC-AC type and AC-DC-AC type. The latter is further divided into current type and voltage type, and their voltage regulation and control methods are also different.

[0105] Furthermore, in step three, the AFE inverter adopts a topological structure consisting of an input inductor, a self-commutated controlled rectifier, a capacitor filter, and a voltage-type PWM inverter. The energy outputs an AC voltage to the rectifier through the left power grid, outputs a DC voltage through the rectifier, and then flows to the motor load through the PWM inverter.

[0106] Furthermore, in step three, the biggest difference between the AFE inverter and the ordinary diode rectifier inverter is that the rectifier part adopts the chopping method; therefore, one of the keys to controlling the AFE inverter is the control of the AFE; currently, the control strategies of the AFE are mainly divided into two categories, namely current control and power control; current control is mainly divided into indirect current control and direct current control, both of which control the current on the AFE AC side, thereby controlling its active power, reactive power and power factor; power control is from the perspective of energy, and under the condition of constant AC voltage, the instantaneous current is indirectly controlled by controlling the instantaneous active power and instantaneous reactive power of the AFE; the main methods of power control are switch table direct power control and fixed switching frequency direct power control.

[0107] Furthermore, in step three, since the open-loop V / F frequency conversion scheme has a simple control algorithm, it only needs to control the output performance of the inverter, is independent of the motor parameters, and does not require the installation of a speed sensor on the motor shaft. It is easy to operate and has strong robustness, and can meet the system's smooth speed regulation requirements within a larger speed regulation range. Therefore, it is suitable for fans and water pumps that do not have high requirements on the dynamic and steady-state characteristics of the motor.

[0108] Furthermore, in step 3, the flux per pole in the motor Φ m It needs to remain unchanged because too small a magnetic flux will lead to insufficient excitation, which will cause the motor torque to decrease and the load cannot be started as required; while too large a magnetic flux will cause magnetic circuit saturation, which may cause the motor to burn out in severe cases.

[0109] The beneficial effects of the present invention are:

[0110] (1) Traditional motor starting control methods are mainly AC-AC type, and their control of motor starting is related to the state of the power system. The proposed method introduces AFE as an effective solution. When the grid side voltage fluctuates, the AC voltage generated by AFE can still ensure a stable state without affecting the control effect.

[0111] (2) The traditional motor starting control method does not take into account the ship emergency power system. The ship emergency power system has high requirements for the load quality factor, and the traditional control method is difficult to meet the requirements. The present invention adopts AFE and V / F variable frequency collaborative starting control method as a method to suppress the large current generated when the motor starts. It has the advantages of fast charging and discharging speed and long service life. It can work for a long time under the state of large current, high power and high energy change frequency, and is more suitable for smoothing the situation of high pulse load power change of ships.

[0112] (3) The high-frequency electromagnetic field of the traditional motor starting control method is relatively large during operation, and certain harmonics will be generated. The proposed variable frequency coordinated starting control method can achieve the effect of reducing harmonics through the AFE inverter, accurately control the DC bus voltage, and significantly reduce the harmonic current generated by the inverter, effectively reducing the harmonics generated under the traditional control method. BRIEF DESCRIPTION OF THE DRAWINGS

[0113] Figure 1 This is a structural diagram of the diesel generator system of the present invention;

[0114] Figure 2 This is a mathematical model diagram of a diesel generator set of the present invention;

[0115] Figure 3 A schematic diagram of coordinate transformation of an induction motor according to the present invention;

[0116] Figure 4 is an equivalent circuit diagram of the induction motor of the present invention;

[0117] Figure 5 AFE inverter topology diagram of the present invention;

[0118] Figure 6 This is a block diagram of the AFE current inner loop feedforward decoupling control of the present invention;

[0119] Figure 7 This is a constant voltage-frequency ratio control characteristic diagram of an asynchronous motor according to the present invention;

[0120] Figure 8 This is a characteristic diagram of the frequency conversion speed regulation machine above the base frequency of the present invention;

[0121] Fig. 9 This is a characteristic diagram of the frequency conversion speed regulation machine below the base frequency of the present invention;

[0122] Fig.10 This is a characteristic diagram of the asynchronous motor variable frequency speed regulation of the present invention;

[0123] Fig.11 This is a voltage waveform diagram of an embodiment of the present invention;

[0124] Fig.12 This is a frequency waveform diagram of an embodiment of the present invention;

[0125] Fig.13 This is a harmonic analysis diagram of an embodiment of the present invention;

[0126] Fig.14 This is a voltage waveform diagram of an embodiment of the present invention;

[0127] Fig.15 This is a frequency waveform diagram of an embodiment of the present invention;

[0128] Fig.16This is a harmonic analysis diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0129] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0130] A variable frequency coordinated starting control method for motors in a ship emergency power system is provided. The proposed control method is applicable to ship emergency power systems for starting high-power motors. The proposed method is a new type of variable frequency coordinated starting control method for motors in a ship emergency power system. In view of the fact that traditional control methods cannot meet the requirements of high power factor, the proposed method can make the rectification part adopt ActiveFront End (AFE) control when the impact current caused by motor starting is too large during the operation of the ship emergency network. The variable frequency coordinated starting control method using V / F control for the induction motor can achieve the requirements of reducing the starting current and having a sufficiently large starting torque. At the same time, it meets the high quality factor of the ship emergency power system and suppresses harmonics, thereby improving the quality of the ship emergency power system.

[0131] A method for variable frequency coordinated starting control of motors in a ship emergency power system is described below.

[0132] Step 1: Modeling of Ship Emergency Power System

[0133] The diesel generator adjusts the speed to within the specified range by changing the amount of circulating fuel injection. The function of the speed governor is to enable the diesel engine to change the amount of fuel injection according to different load changes, thereby automatically adjusting the speed. In order to ensure the stability of the frequency and voltage of the generator, the marine diesel engine for power generation should maintain a constant speed when the load changes. The amount of fuel injection directly affects the output power of the diesel engine. According to the relationship between power, load and speed, we can conclude that when the amount of fuel injection remains unchanged, an increase in load will cause the diesel engine speed to decrease, while a decrease in load will cause the diesel engine speed to increase, which will cause parking and flying operation failures respectively. Therefore, in order to keep the diesel engine running stably at a constant speed when the external load changes, the fuel supply must be adjusted accordingly when the speed changes with the external load, so that its effective power is adapted to the changes in the external load. That is, the diesel engine for power generation must be switched to a speed governor to ensure that the diesel engine can always run stably at the specified speed when the load changes.

[0134] Based on the multi-constraint conditions of diesel generator set operation economy, system operation safety and power distribution rapidity, an optimal configuration model of the ship's integrated power system is established. The ship's emergency power system includes diesel generator sets, switchboards and induction motors. The switchboard provides power to the diesel generator sets, and the power flows from the diesel generator sets to the induction motors.

[0135] like Figure 1 As shown, the diesel generator set consists of three parts: a speed regulator, a throttle controller and a diesel engine. The speed regulator converts the input speed difference signal (the difference between the given rated speed and the actual speed of the diesel generator set measured by the sensor) into a fuel quantity given signal through a built-in speed control algorithm and outputs it to the throttle controller. The throttle actuator controls the throttle action under the drive of the fuel quantity given signal. The throttle action provides power torque to the diesel engine through the fuel quantity. The diesel engine outputs power torque to drive the generator to rotate and generate electricity.

[0136] The ship integrated power system optimization configuration model is established, and the following four mathematical models are established in sequence:

[0137] Step 1.1. Establish the mathematical model of the speed regulator

[0138] The speed regulator consists of two parts: a speed sensor and a speed control processor. The speed sensor uses a speed measuring generator to measure a voltage signal proportional to the generator speed. The controller uses a traditional PID control algorithm. Since the measurement link of the speed sensor can be equivalent to a first-order inertia link, the speed control processor is represented by a PID function. Therefore, the transfer function G of the speed regulator is 1 (s) can be expressed as:

[0139]

[0140] In the formula, is the first-order inertia function of speed measurement, T 1 is the inertia time constant, s is the Laplace operator of the transfer function (s represents the frequency in the Laplace transform domain and is also the independent variable of the transfer function); is the PID function of the speed control processor, K p , K I , K D They represent the proportional constant, integral constant and differential constant in PID control respectively.

[0141] The transfer function G of the speed regulator can be obtained by Laplace transforming and rearranging the above formula. 1 (s) is:

[0142]

[0143] In the formula, K 1, T 2 , T 3 It is the constant obtained after sorting the PID control function.

[0144] Step 1.2. Establish the mathematical model of the throttle controller

[0145] The function of the throttle controller is to execute the oil quantity given instruction output by the speed controller and control the oil quantity through the throttle action. The common throttle controller is composed of a rotating electromagnet (also known as the armature). The rotation of the armature is proportional to the displacement of the sliding sleeve, and its motion increment equation is:

[0146]

[0147] Where l represents the change of armature displacement, i.e. the displacement change of the throttle controller, m is the mass of the armature push rod assembly, D is the damping coefficient, K is s is the return spring stiffness, ΔF m is the electromagnetic force increment, t is the power-on time, and it can be expressed as:

[0148] ΔF m =K i Δi-K l Δl (4)

[0149] Where: K i is the current force gain of the proportional electromagnet, i is the change of electromagnet current, K l is the sum of the displacement force gain and elastic stiffness of the proportional electromagnet. Combining equations (3) and (4), and then performing Laplace transformation, we get:

[0150] ms 2 l(s)+Dsl(s)+K s l(s)=K i i(s)-K l l(s) (5)

[0151] Where l(s) and i(s) are the Laplace transformed forms of l and i respectively.

[0152] The transfer function G of the oil quantity controller can be obtained 2 (s):

[0153]

[0154] Simplified to:

[0155]

[0156] In the formula, K 2 , T 4 , T 5 is the constant obtained after sorting.

[0157] Step 1.3. Establishing the mathematical model of diesel engine

[0158] The adjustment characteristics of a diesel engine mainly describe the engine output main mechanical torque T m The relationship between the armature displacement l in the throttle controller. When the throttle controller acts according to the speed regulator's command, the diesel engine's torque output does not immediately respond to the action of the throttle actuator due to the lag in the diesel engine's own fuel combustion and thermal stroke. When the diesel engine is fixed, the delay time from the action of the throttle actuator to the diesel engine's output torque is also fixed.

[0159] Since the throttle opening h is related to the diesel engine output torque T m There is a proportional relationship, namely:

[0160] T m =kh (8)

[0161] In the formula, h is the throttle opening, and k is the proportional correlation coefficient, which is related to the type of diesel engine selected.

[0162] When the throttle opening changes by Δh under the action of the throttle actuator, the output torque of the diesel engine changes by ΔT m :

[0163] ΔT m =k·Δh (9)

[0164] Assume the delay time of the diesel engine is T d , then after Laplace transform in the complex frequency domain:

[0165]

[0166] Where, ΔT m (s) is ΔT m The form after Laplace transformation.

[0167] Therefore, the transfer function G of the diesel engine is 3 (s) can be expressed as:

[0168]

[0169] The proportion coefficient of each link is K, then:

[0170] K=K 1 K 2 k (12)

[0171] Therefore, the mathematical model of the diesel generator set can be Figure 2 shown.

[0172] Step 1.4. Establish the mathematical model of induction motor

[0173] As a main device unique to the ship emergency power system, the induction motor has a great impact on the transient voltage of the ship emergency power system when it is started. Therefore, it is necessary to establish a mathematical model of the induction motor taking into account electromagnetic transients. This model is sufficient to meet the requirements of the present invention.

[0174] Based on the information [4] that helps to understand this patent (specifically in the last part of the specification), the analysis of the commonly used mathematical model of induction motors takes into account the strong coupling, nonlinearity, time-varying nature of the magnetic flux differential equations, etc. of this group of models, which brings many inconveniences in actual analysis. On this basis, this group of formulas is converted from the abc coordinate system to the dq0 rotating coordinate system. In the converted equations, since the three-phase windings of the stator and rotor have undergone a 3 / 2 transformation, they are equivalent to two-phase windings in a stationary coordinate system. This achieves the reduction of the order of the equations and reduces the coupling relationship between multiple parameters of the induction motor. Decoupling is achieved, and the equations are simplified to make them more practical for the analysis and research of induction motors.

[0175] Figure 3 Figure a in the middle shows the original physical equivalent model of the three-phase asynchronous motor, which can reflect the intuitive working effect between the stator and rotor in the internal structure of the asynchronous motor. Among them, ω is the rotor angular velocity, u a 、u b 、u c are the three-phase voltages of rotor a, b, and c respectively; ω 1 is the stator angular velocity, u A 、u B 、u C are the three-phase voltages of stator A, B, and C, respectively, m is the rotor rotation angle. Figure b shows the model of the asynchronous motor after the coordinate system transformation, which intuitively reflects the working state of each parameter in the dq0 coordinate system. Since the two coordinate axes are perpendicular to each other in the dq0 coordinate system, the complexity caused by the mutual inductance coupling of the parameters between the coordinate axes is eliminated. The equation describing the dynamic operation of the three-phase asynchronous motor is greatly simplified, as shown in the following formula:

[0176]

[0177] The above formula is the flux equation in the dq0 coordinate system. In this equation, the flux direction of the rotor of the three-phase motor is along the d-axis direction of the rotating coordinate system. m , L r are the mutual inductance of the two-phase winding and the rotor inductance respectively; ψ rd , rq are the rotor flux on the d-axis and q-axis respectively; i rd 、i sd 、irq 、i sq They are the rotor current on the d-axis, the stator current on the d-axis, the rotor current on the q-axis, and the stator current on the q-axis respectively; based on the flux equation, the voltage equation is as follows:

[0178]

[0179] In the formula, u rd 、u sd 、u rq 、u sq are the rotor voltage on the d-axis, the stator voltage on the d-axis, the rotor voltage on the q-axis, and the stator voltage on the q-axis respectively; ω s is the angular velocity of the dq coordinate axis relative to the stator; ω sl is the induction motor slip rate; R s , R r , L s , L r are the resistance and inductance of the stator and rotor of the induction motor respectively; p is the differential operator.

[0180] The torque equation of the induction motor is as follows, in which the magnitude of the torque is directly proportional to the rotor flux on the d-axis and the stator current on the q-axis:

[0181]

[0182] Where, T e is the electromagnetic torque of the induction motor; n p is the pole pair number.

[0183] The above three equations together constitute the mathematical model of the induction motor in the dq0 coordinate system. In this mathematical model, since the amount of coupled data is small, it is convenient for the decoupling control and simulation analysis of the induction motor.

[0184] By analyzing the mathematical models of diesel generator sets and induction motors, the components of the ship's emergency power system were established.

[0185] Step 2: High-power motor load starting conditions

[0186] In the ship's emergency power system, the power load is supplied by its own generator set, and the power station capacity is relatively small. Starting the motor is equivalent to suddenly increasing the load, which will cause an impact on the system and cause an instantaneous drop in voltage. The equivalent circuit diagram of the induction motor is as follows: Figure 4 As shown, U 1 is the terminal voltage; R 1 is the stator winding resistance; is the converted rotor winding resistance; X 1σ is the stator winding reactance; X 2 ' σThis is the converted rotor winding reactance; the figure shows the relationship between the terminal voltage of the induction motor and the resistance and reactance of each winding.

[0187] Starting current I when the induction motor starts st With starting torque T st The formula is as follows:

[0188]

[0189]

[0190] Where: U 1 is the terminal voltage; R 1 is the stator winding resistance; R 2 ′ is the converted rotor winding resistance; X 1σ is the stator winding reactance; X 2 ' σ is the converted rotor winding reactance; Z dx To simplify the results for calculation; n 1 is the synchronous speed of the stator rotating magnetic field; m 1 is the number of stator winding turns.

[0191] It can be seen that the starting torque is not only related to the terminal voltage U 1 It is related to the synchronous speed of the rotating magnetic field in the stator winding and is inversely proportional to the synchronous speed. The synchronous speed has the following relationship with the power supply frequency and the number of motor poles:

[0192]

[0193] Where: n p is the number of motor pole pairs; f is the power supply voltage frequency. Substituting formula (18) into formula (17), we get the following formula (19):

[0194]

[0195] The starting torque is related to the terminal voltage, the number of motor pole pairs and the power supply frequency. When the number of motor winding pole pairs is constant, the starting torque of the motor can be adjusted by changing the terminal voltage and the power supply frequency.

[0196] Step 3: Rectification-inversion coordinated control based on DC voltage

[0197] There are many types of frequency converters, including AC-AC type and AC-DC-AC type, the latter of which is further divided into current type and voltage type, and their voltage regulation and control methods are also different. The rectifier part of the present invention adopts AFE control, and the induction motor adopts V / F control.

[0198] AFE inverter adopts Figure 5The topology shown in the figure consists of an input inductor, a self-commutated controlled rectifier, a capacitor filter, and a voltage-type PWM inverter. The energy is output through the left grid as an AC voltage to the rectifier, and then outputs a DC voltage through the rectifier, and then flows to the motor load through the PWM inverter.

[0199] The biggest difference between AFE inverter and ordinary diode rectifier inverter is that the rectifier part adopts chopping mode. Therefore, one of the keys to control AFE inverter is the control of AFE. At present, the control strategies of AFE are mainly divided into two categories, namely current control and power control. Current control is mainly divided into indirect current control and direct current control, both of which control the current on the AC side of AFE, thereby controlling its active power, reactive power and power factor. Power control is based on energy. Under the condition of constant AC voltage, the instantaneous current is indirectly controlled by controlling the instantaneous active power and instantaneous reactive power of AFE. The main methods of power control are switch table direct power control and fixed switching frequency direct power control.

[0200] The principle of AFE inverter joint control is: when the system is in a stable state, the DC side power P rec for:

[0201] P rec =e d i d +e q i q (20)

[0202] In the formula, e d 、e q 、i d 、i q They are the d-axis and q-axis voltage and current on the AC grid side respectively. When the DC capacitor voltage is in a balanced state, its stored energy W C , energy change rate P C They are:

[0203]

[0204]

[0205] Where, C is the DC side capacitance; u dc is a DC voltage.

[0206] The inverter output power is:

[0207] P inv =u sd i sd +u sq i sq (twenty three)

[0208] Where Pinv is the inverter output power; u sd 、u sq is the d-axis and q-axis stator voltage; i sd 、i sq are the d-axis and q-axis stator currents.

[0209] At any time, the energy flowing into AFE is the sum of the change rate of energy stored in the DC capacitor and the energy consumed by the motor. In the AFE inverter, the DC voltage is added to the inverter power component after PI adjustment. When the motor state changes suddenly, it will only affect the feedback value in AFE, and the DC capacitor voltage value will not change, thereby achieving the purpose of improving the dynamic performance of AFE and reducing the amount of AFE capacitor. The AFE active front-end control block diagram is shown in the figure. Figure 6 As shown in the figure, the DC voltage is used as the d-axis current reference value after PI adjustment, and the AC side current is adjusted by PI, and the reference d-axis and q-axis voltages are modulated by decoupling output SPWM, and the DC voltage is modulated by the inverter.

[0210] Since the open-loop V / F frequency conversion scheme has a simple control algorithm, it only needs to control the output performance of the frequency converter, does not rely on the parameters of the motor, does not need to install a speed sensor on the motor shaft, is easy to operate and has strong robustness, and can meet the system's smooth speed regulation requirements within a large speed regulation range. Therefore, it is suitable for fans and water pumps that do not have high requirements on the dynamic and steady-state characteristics of the motor. Combined with the design of the present invention, the frequency conversion scheme adopts a constant V / F method.

[0211] According to the principle of electrical machinery, it is easy to know that the stator voltage induced electromotive force E of the asynchronous motor g It can be expressed as follows:

[0212] E g =4.44f 1 N 1 K 1N Φ m (twenty four)

[0213] Where f 1 is the stator voltage frequency, N 1 K is the number of internal turns of each phase winding of the stator, 1N is the fundamental wave winding coefficient, Φ m is the air gap flux per pole. The flux per pole in the motor Φ m The reason is that too small magnetic flux will lead to insufficient excitation, which will cause the motor torque to decrease and the load cannot be started as required; while too large magnetic flux will cause magnetic circuit saturation, which may cause the motor to burn out in severe cases. m According to formula (24), it is easy to know that as long as E g / f 1The magnetic flux Φ can be kept constant m However, in practical applications, E g It is difficult to measure, and when E g When it is large enough, the voltage drop on the stator impedance can be ignored. S To replace E g This can solve the problem of difficulty in measuring stator induced electromotive force. S / f 1 The constant approximation controls the magnetic flux to be constant. However, this method has a defect that when the asynchronous motor runs in the low frequency band, the stator induced electromotive force E g The voltage drop on the stator impedance cannot be ignored. This situation can be solved by properly compensating the stator input voltage U S improve, Figure 7 This is the constant voltage-frequency ratio control characteristic diagram of the asynchronous motor. Among them, a is the control characteristic after compensation, b is the control characteristic before compensation, U 0 It is the voltage raised after compensation. 1N and f 1N is the fundamental frequency stator voltage and frequency.

[0214] The mathematical expression of the constant V / F working curve is:

[0215]

[0216] In the constant voltage-frequency ratio control process, when the stator voltage of the motor reaches the rated value U 1N If the frequency continues to increase, it will lead to problems such as poor insulation of the motor and softening of mechanical properties. At this time, the frequency can still continue to rise, so variable frequency speed regulation actually includes speed regulation above the base frequency and speed regulation below the base frequency. When regulating above the base frequency, keep the voltage constant. According to the above formula (25), the magnetic flux and frequency are inversely proportional at this time, which is equivalent to the weak magnetic speed increase process of the DC motor. The synchronous speed of the asynchronous motor increases, the electromagnetic torque decreases, and the output power is basically constant. This process can be called constant power speed regulation. Its mechanical characteristics are as follows Figure 8 As shown, n is the motor speed, Te is the motor electromagnetic torque, when the frequency f1 is greater than the rated frequency f1N, due to the constant voltage, the electromagnetic torque decreases, the output power is basically constant, and the curve changes.

[0217] Draw the mechanical characteristics of variable frequency speed regulation below the base frequency as follows Fig. 9 As shown, according to Fig. 9 It can be seen that as the frequency decreases, the maximum induced electromagnetic torque of the asynchronous motor will gradually decrease. When the frequency is too low, the stator voltage drop cannot be ignored and the motor's load capacity is limited, so it is necessary to compensate the stator voltage. Fig. 9 The middle dotted line part is the mechanical characteristic after stator voltage drop compensation. After compensation, the electromagnetic torque increases.

[0218] By summarizing the control characteristics below and above the base frequency on one coordinate axis, the variable frequency speed regulation control characteristics of the asynchronous motor can be obtained as follows: Fig.10 As shown in the figure: when the speed is adjusted below the base frequency, due to constant power speed regulation, the magnetic flux remains unchanged, and the stator voltage decreases as the frequency decreases; when the speed is adjusted above the base frequency, due to constant power speed regulation, the product of the electromagnetic torque Te and the speed n should remain unchanged, and the magnetic flux decreases as the frequency increases. Although the speed of the asynchronous motor is different under different working conditions depending on the load, if the system current remains at the rated value, the torque T of the asynchronous motor e and magnetic flux There is a direct proportional relationship. In the speed regulation range below the base frequency, the magnetic flux remains unchanged, which belongs to constant torque speed regulation; in the speed regulation process above the base frequency, the magnetic flux decreases as the power supply frequency increases, showing a constant power speed regulation operation characteristic.

[0219] Step 4: Method Validation

[0220] A diesel generator, induction motor and corresponding control system model are established in MATLAB / Simulink. The simulation parameters are shown in Table 1.

[0221] Table 1 Simulation parameters

[0222]

[0223] In the simulation process, the present invention uses the traditional control scheme and the proposed control scheme to start the two motors and the changing characteristics of the ship emergency power system. The following is the simulation result.

[0224] Step 4 (a) Uncontrolled start

[0225] The specific process of this working condition is: two motors start at 5s. The corresponding main grid voltage, frequency waveform and harmonic analysis are as follows: Figure 11-13 shown.

[0226] During the startup process, the system's steady-state voltage is 390.014V, the steady-state frequency is 49.63Hz, the maximum voltage drops by 7.69%, the maximum voltage rises by 2.96%, the maximum frequency fluctuation is 0.88%, and the THD is 4.87%. It can be seen that due to the two impact loads at the same time in the system at 5s, the system has less active power margin and worse transient stability, which is reflected in the larger voltage fluctuation amplitude and the longer oscillation process of the frequency waveform during the load switching process.

[0227] Step 4 (ii): Adopting the adaptive cooperative control of the present invention to start

[0228] The specific process of this working condition is: at 4.6s, the two motors start. The corresponding main grid voltage, frequency waveform and harmonic analysis are as follows: Figures 14 to 16 shown.

[0229] During the startup process, the system's steady-state voltage is 390.439V, the steady-state frequency is 49.59Hz, the maximum voltage drop is 1.38%, the maximum voltage drop is 1.21%, the maximum frequency fluctuation is 0.28%, and the THD is 1.34%. It can be seen that after the adaptive coordinated control is adopted, the coordinated fluctuations and harmonics are reduced.

[0230] In order to verify the effectiveness of the control method, the results of using different controls and different start-up times are shown in the following table.

[0231] Table 2 Summary of simulation results of maximum voltage sag under various working conditions (without control)

[0232]

[0233] Table 3 Summary of simulation results of maximum voltage sag under various working conditions (V / F control)

[0234]

[0235] Materials that can help you understand this technology:

[0236] [1] Liu Qingliang, Li Baogang, Xu Quanxiang, et al. Application of AFE technology on scientific research vessels[J]. Shipbuilding Technology, 2016, (05): 9-12.

[0237] [2] Lu Shiping, Chen Ye. Research on the application of AFE variable frequency drive technology on scientific research ships[J]. Ships, 2017, 28(S1): 162-167.

[0238] [3] Zhao Yongjia, Chen Hongyan, Li Yang. V / f control method for stable operation of induction motor in full frequency range[J]. Micromotors, 2022, 55(12): 71-75.

[0239] [4] Zhang Yan, Liao Weiping, Chen Shen, et al. A third-order electromechanical transient model of induction motor in polar coordinate system[J]. Electrical Applications, 2018, 37(05): 28-33.

[0240] References:

[0241] [1] Xu Dan, Zhao Yongjia, Wang Jianlin, et al. A motor control method and circuit for stable operation of AC motor in full frequency range: CN107565863A[P]. 2018.

[0242] [3]Koga K,Ueda R,Sonoda T.Achievement of High Performances forGeneral Purpose Inverter Drive Induction Motor System[C].IndustryApplications Society Meeting,Conference Record of the IEEE,1989:415-425.

[0243] [4]Pongpant J,Po-Ngam S,Konghirun M.The Performance Improvement ofConstant V / f Control of Induction Motor Drive in Low Speed Range[C].IEEERegion 10Conference,2006:1-4.

[0244] [5]Munoz-Garcia A,Lipo T A,Novotny D W.A New Induction Motor V / fControl Method Capable of High-Performance Regulation at Low Speeds[J].IEEETransactions on Industry Applications,1998,34(4):813-821.

[0245] [6]Koga K,Ueda R,Sonoda T.Constitution of V / f Control for Reducingthe Steady State Speed Error to Zero in Induction Motor Drive System[C].Industry Applications Society Meeting.Conference Record of the IEEE,1990:639-646.

[0246] [7] Kazmierkowski MP, Kopcke H JA Simple Control System for CurrentSource Inverter-Fed Induction Motor Drives[J]. IEEE Transactions on IndustryApplications, 1985, 21(3):617-623.

[0247] The above-mentioned embodiment only expresses one implementation mode of the present invention, and its description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A method for controlling the frequency conversion coordinated starting of motors in a ship emergency power system, characterized in that: The following steps are involved: Step 1: Modeling of Ship Emergency Power System Based on the multi-constraint conditions of diesel generator set operation economy, system operation safety and power distribution rapidity, the ship integrated power system optimization configuration model is established. The speed regulator mathematical model, throttle controller mathematical model, diesel engine mathematical model and induction motor mathematical model are established in turn. Through the analysis of the mathematical models of diesel generator sets and induction motors, the components of the ship emergency power system are established. Step 2: High-power motor load starting conditions In the ship emergency power system, the power load is supplied by its own generator set, and the power station capacity is small; starting the motor is equivalent to suddenly increasing the load, which will cause an impact on the system and cause an instantaneous drop in voltage; the starting torque is related to the terminal voltage, the number of motor poles and the power supply frequency; when the number of motor winding poles is constant, the starting torque of the motor can be adjusted by changing the terminal voltage and the power supply frequency; Step 3: Rectification-inversion coordinated control based on DC voltage The rectifier part adopts AFE control, and the induction motor adopts V / F control; The AFE inverter adopts a topological structure. In the AFE inverter, the DC voltage is added to the inverter power component after PI adjustment. When the motor state changes suddenly, it will only affect the feedback value in the AFE, and the DC capacitor voltage value will not change, thereby achieving the purpose of improving the dynamic performance of the AFE and reducing the amount of AFE capacitor. The DC voltage is used as the d-axis current reference value after PI adjustment. After the AC side current is adjusted by PI, the reference d-axis and q-axis voltages are modulated by decoupling output SPWM, and the DC voltage is modulated by the inverter. The frequency conversion scheme adopts a constant V / F method; speed regulation above the base frequency and speed regulation below the base frequency. When regulating above the base frequency, the voltage is kept constant. At this time, the magnetic flux and frequency are inversely proportional, which is equivalent to the weak magnetic speed-up process of the DC motor; the synchronous speed of the asynchronous motor increases, the electromagnetic torque decreases, and the output power is basically constant. This process can be called constant power speed regulation; within the speed regulation range below the base frequency, the magnetic flux remains unchanged, which belongs to constant torque speed regulation; in the speed regulation process above the base frequency, the magnetic flux decreases as the power supply frequency increases, showing a constant power speed regulation operation characteristic.

2. The method for controlling the motor frequency conversion coordinated starting of a ship emergency power system according to claim 1 is characterized in that: The specific steps include: Step 1: Modeling of Ship Emergency Power System Based on the multi-constraint conditions of diesel generator set operation economy, system operation safety and power distribution rapidity, the ship's integrated power system optimization configuration model is established. The ship's emergency power system includes diesel generator sets, switchboards and induction motors. The switchboard provides power to the diesel generator set, and the power flows from the diesel generator set to the induction motor; the diesel generator set consists of a speed regulator, a throttle controller and a diesel engine. The ship's integrated power system optimization configuration model is established, and the following four mathematical models are established in turn: Step 1.

1. Establish the mathematical model of the speed regulator The speed regulator consists of two parts: a speed sensor and a speed control processor. The speed sensor uses a speed measuring generator to measure a voltage signal proportional to the generator speed. The controller uses a traditional PID control algorithm. Since the measurement link of the speed sensor can be equivalent to a first-order inertia link, the speed control processor is represented by a PID function. Therefore, the transfer function G1(s) of the speed regulator can be expressed as: In the formula, is the first-order inertia function of speed measurement, T1 is the inertia time constant, and s is the Laplace operator of the transfer function; is the PID function of the speed control processor, K p , K I , K D They represent the proportional constant, integral constant and differential constant in PID control respectively; The transfer function G1(s) of the speed regulator can be obtained by Laplace transforming and rearranging the above formula: In the formula, K1, T2, and T3 are constants obtained after the PID control function is sorted out; Step 1.

2. Establish the mathematical model of the throttle controller The function of the throttle controller is to execute the oil quantity given instruction output by the speed controller and control the oil quantity through the throttle action; the common throttle controller is composed of a rotating electromagnet, that is, an armature. The rotation of the armature is proportional to the displacement of the sliding sleeve, and its motion increment equation is: Where l represents the change of armature displacement, i.e. the displacement change of the throttle controller, m is the mass of the armature push rod assembly, D is the damping coefficient, K is s is the return spring stiffness, ΔF m is the electromagnetic force increment, t is the power-on time, and it can be expressed as: ΔF m =K i Δi-K l Δl (4) Where: K i is the current force gain of the proportional electromagnet, i is the change of electromagnet current, K l is the sum of the displacement force gain and elastic stiffness of the proportional electromagnet; combining equations (3) and (4), and then performing Laplace transformation, we get: ms 2 l(s)+Dsl(s)+K s l(s)=K i i(s)-K l l(s) (5) In the formula, l(s) and i(s) are the Laplace transformed forms of l and i respectively; The transfer function G2(s) of the oil quantity controller can be obtained: Simplified to: In the formula, K2, T4, and T5 are constants obtained after sorting; Step 1.

3. Establishing the mathematical model of diesel engine The adjustment characteristics of a diesel engine mainly describe the engine output main mechanical torque T m The relationship between the armature displacement l in the throttle controller; when the throttle controller acts according to the command of the speed regulator, the torque output of the diesel engine will not immediately respond to the action of the throttle actuator due to the lag in the fuel combustion link and the thermal stroke link of the diesel engine itself; when the diesel engine is fixed, the delay time from the action of the throttle actuator to the output torque of the diesel engine is also fixed; Since the throttle opening h is related to the diesel engine output torque T m There is a proportional relationship, namely: T m =kh (8) In the formula, h is the throttle opening, k is the proportional correlation coefficient, which is related to the type of diesel engine selected; When the throttle opening changes by Δh under the action of the throttle actuator, the output torque of the diesel engine changes by ΔT m : ΔT m =k·Δh (9) Assume the delay time of the diesel engine is T d , then after Laplace transform in the complex frequency domain: In the formula, ΔT m (s) is ΔT m The form after Laplace transformation; Therefore, the transfer function G3(s) of the diesel engine can be expressed as: The proportion coefficient of each link is K, then: K=K1K2k (12) Step 1.

4. Establish the mathematical model of induction motor For the analysis of the commonly used mathematical model of induction motor, considering the strong coupling, nonlinearity and time-varying nature of the flux differential equation of this group of models, many inconveniences are brought in the actual analysis; on this basis, this group of formulas is converted from the abc coordinate system to the dq0 rotating coordinate system; in the converted equations, the three-phase windings of the stator and rotor have undergone a 3 / 2 transformation, which is equivalent to the two-phase windings in the stationary coordinate system; The equation describing the dynamic operation of a three-phase asynchronous motor is shown below as the flux equation: The above formula is the flux equation in the dq0 coordinate system. In this equation, the flux direction of the rotor of the three-phase motor is along the d-axis direction of the rotating coordinate system. m , L r are the mutual inductance of the two-phase winding and the rotor inductance respectively; ψ rd , rq are the rotor flux on the d-axis and q-axis respectively; i rd 、i sd 、i rq 、i sq They are the rotor current on the d-axis, the stator current on the d-axis, the rotor current on the q-axis, and the stator current on the q-axis respectively; based on the flux equation, the voltage equation is as follows: In the formula, u rd 、u sd 、u rq 、u sq are the rotor voltage on the d-axis, the stator voltage on the d-axis, the rotor voltage on the q-axis, and the stator voltage on the q-axis respectively; ω s is the angular velocity of the dq coordinate axis relative to the stator; ω sl is the induction motor slip rate; R s , R r , L s , L r are the resistance and inductance of the stator and rotor of the induction motor respectively; p is the differential operator; The torque equation of the induction motor is as follows, in which the magnitude of the torque is directly proportional to the rotor flux on the d-axis and the stator current on the q-axis: Where, T e is the electromagnetic torque of the induction motor; n p is the pole pair number; The above three equations together constitute the mathematical model of the induction motor in the dq0 coordinate system. In this mathematical model, since the amount of coupled data is small, it is convenient for the decoupling control and simulation analysis of the induction motor; By analyzing the mathematical models of diesel generator sets and induction motors, the components of the ship's emergency power system were established; Step 2: High-power motor load starting conditions In the ship's emergency power system, the power load is supplied by its own generator set, and the power station capacity is relatively small; starting the motor is equivalent to suddenly increasing the load, which will cause an impact on the system and cause an instantaneous drop in voltage; Starting current I when the induction motor starts st With starting torque T st The formula is as follows: Where: U1 is the terminal voltage; R1 is the stator winding resistance; R2′ is the converted rotor winding resistance; X 1σ is the stator winding reactance; X2′ σ is the converted rotor winding reactance; Z dx To simplify the results for calculation; n1 is the synchronous speed of the stator rotating magnetic field; m1 is the number of turns of the stator winding; It can be seen that the starting torque is not only related to the terminal voltage U1, but also inversely proportional to the synchronous speed of the rotating magnetic field in the stator winding; the synchronous speed has the following relationship with the power supply frequency and the number of motor poles: Where: n p is the number of motor pole pairs; f is the power supply voltage frequency; Substituting formula (18) into formula (17), the following formula (19) is obtained: The starting torque is related to the terminal voltage, the number of motor pole pairs and the power supply frequency. When the number of motor winding pole pairs is constant, the starting torque of the motor can be adjusted by changing the terminal voltage and the power supply frequency. Step 3: Rectification-inversion coordinated control based on DC voltage In this method, the rectifier part adopts AFE control, and the induction motor adopts V / F control; The AFE inverter adopts a topological structure; The principle of AFE inverter joint control is: when the system is in a stable state, the DC side power P rec for: P rec =e d and d +e q and q (20) In the formula, e d 、e q 、i d 、i q are the d-axis and q-axis voltages and currents on the AC grid side respectively; when the DC capacitor voltage is in a balanced state, its stored energy W C , energy change rate P C They are: Where, C is the DC side capacitance; u dc is the DC voltage; The inverter output power is: P inv =in sd and sd +in sq and sq (23) Where P inv is the inverter output power; u sd 、u sq is the d-axis and q-axis stator voltage; i sd 、i sq are the d-axis and q-axis stator currents; At any time, the energy flowing into AFE is the sum of the change rate of energy stored in the DC capacitor and the energy consumed by the motor; in the AFE inverter, the DC voltage is added to the inverter power component after PI adjustment. When the motor state changes suddenly, it will only affect the feedback value in AFE, and the DC capacitor voltage value will not change, thereby achieving the purpose of improving the dynamic performance of AFE and reducing the amount of AFE capacitor; the DC voltage is used as the d-axis current reference value after PI adjustment, and the AC side current is adjusted by PI, and the reference d-axis and q-axis voltages are modulated by decoupling output SPWM, and the DC voltage is modulated by the inverter; The frequency conversion scheme adopts constant V / F mode; According to the principle of electrical machinery, it is easy to know that the stator voltage induced electromotive force E of the asynchronous motor g It can be expressed as follows: E g =4.44f1N1K 1N F m (24) Where f1 is the stator voltage frequency, N1 is the number of inline turns of each phase winding of the stator, K 1N is the fundamental wave winding coefficient, Φ m The air gap flux per pole; the speed regulation of asynchronous motor is to maintain the air gap flux per pole Φ m According to formula (24), it is easy to know that as long as E g / f1 is a constant to maintain the magnetic flux Φ m unchanged; but in practical applications, E g It is difficult to measure, and when E g When it is large enough, the voltage drop on the stator impedance can be ignored; use the stator input voltage U S To replace E g The problem of difficulty in measuring stator induced electromotive force can be solved by maintaining U S / f1 constant approximation controls the magnetic flux to be constant; however, this method has a defect that when the asynchronous motor runs in the low frequency band, the stator induced electromotive force E g Very small, the voltage drop on the stator impedance cannot be ignored; this situation can be solved by properly compensating the stator input voltage U S Improvement, U0 is the voltage raised after compensation; U 1N and f 1N is the fundamental frequency stator voltage and frequency; The mathematical expression of the constant V / F working curve is: In the constant voltage-frequency ratio control process, when the stator voltage of the motor reaches the rated value U 1N If the frequency continues to increase, it will cause the motor insulation to deteriorate and the mechanical characteristics to soften. At this time, the frequency can still continue to rise. Therefore, variable frequency speed regulation actually includes speed regulation above the base frequency and speed regulation below the base frequency. When regulating above the base frequency, the voltage is kept constant. According to the above formula (25), the magnetic flux and frequency are inversely proportional at this time, which is equivalent to the weak magnetic speed increase process of the DC motor. When the synchronous speed of the asynchronous motor increases, the electromagnetic torque decreases, and the output power is basically constant. This process can be called constant power speed regulation. n is the motor speed, Te is the motor electromagnetic torque, and when the frequency f1 is greater than the rated frequency f1N, due to the constant voltage, the electromagnetic torque decreases, and the output power is basically constant. Plot the mechanical characteristics of variable frequency speed regulation below the base frequency. It can be seen from the figure that as the frequency decreases, the maximum induced electromagnetic torque of the asynchronous motor will gradually decrease. When the frequency is too low, the stator voltage drop cannot be ignored and the motor's load capacity is limited, so it is necessary to compensate the stator voltage. By summarizing the control characteristics below and above the base frequency on one coordinate axis, we can get the variable frequency speed control characteristic diagram of the asynchronous motor: when the speed is adjusted below the base frequency, due to constant power speed regulation, the magnetic flux remains unchanged, and the stator voltage decreases as the frequency decreases; when the speed is adjusted above the base frequency, due to constant power speed regulation, the product of the electromagnetic torque Te and the speed n should remain unchanged, and the magnetic flux decreases as the frequency increases; although the speed of the asynchronous motor is different under different working conditions depending on the load it carries, if the system current remains at the rated value, the torque T of the asynchronous motor e and magnetic flux It has a positive proportional relationship; within the speed regulation range below the base frequency, the magnetic flux remains unchanged, which belongs to constant torque speed regulation; in the speed regulation process above the base frequency, the magnetic flux decreases as the power supply frequency increases, showing a constant power speed regulation operation characteristic.

3. The method for controlling the motor frequency conversion coordinated starting of a ship emergency power system according to claim 2 is characterized in that: It also includes step 4, method verification: A model including a diesel generator, an induction motor and the corresponding control system is established in MATLAB / Simulink; the simulation parameters are obtained and simulation is performed. During the simulation, the changing characteristics of the ship emergency power system when the two motors are started and operated using the traditional control scheme and this method are compared, and the simulation results of the uncontrolled start-up and the adaptive collaborative control start-up are compared.

4. The method for controlling the motor frequency conversion coordinated starting of a ship emergency power system according to claim 2, characterized in that: The diesel generator set in step one consists of three parts: a speed regulator, a throttle controller and a diesel engine. The speed regulator converts the input speed difference signal into a fuel quantity given signal through a built-in speed control algorithm and outputs it to the throttle controller. The throttle actuator controls the throttle action under the drive of the fuel quantity given signal. The throttle action provides power torque to the diesel engine through the fuel quantity. The diesel engine outputs power torque to drive the generator to rotate and generate electricity.

5. The method for controlling the motor frequency conversion coordinated starting of a ship emergency power system according to claim 2, characterized in that: In step three, there are many types of inverters, including AC-AC type and AC-DC-AC type. The latter is further divided into current type and voltage type, and their voltage regulation and control methods are also different.

6. The method for controlling the motor frequency conversion coordinated starting of a ship emergency power system according to claim 2, characterized in that: In step three, the AFE inverter adopts a topological structure consisting of an input inductor, a self-commutated controlled rectifier, a capacitor filter, and a voltage-type PWM inverter. The energy outputs the AC voltage to the rectifier through the left power grid, outputs the DC voltage through the rectifier, and then flows to the motor load through the PWM inverter.

7. The method for controlling the motor frequency conversion coordinated starting of a ship emergency power system according to claim 2, characterized in that: In step three, the biggest difference between the AFE inverter and the ordinary diode rectifier inverter is that the rectifier part adopts the chopping method; therefore, one of the keys to controlling the AFE inverter is the control of the AFE; currently, the control strategies of the AFE are mainly divided into two categories, namely current control and power control; current control is mainly divided into indirect current control and direct current control, both of which control the current on the AFE AC side, thereby controlling its active power, reactive power and power factor; power control is from the perspective of energy, and under the condition of constant AC voltage, the instantaneous current is indirectly controlled by controlling the instantaneous active power and instantaneous reactive power of the AFE; the main methods of power control are switch table direct power control and fixed switching frequency direct power control.

8. The method for controlling the motor frequency conversion coordinated starting of a ship emergency power system according to claim 2, characterized in that: In step three, the open-loop V / F frequency conversion scheme has a simple control algorithm. It only needs to control the output performance of the frequency converter, is independent of the motor parameters, and does not require the installation of a speed sensor on the motor shaft. It is easy to operate and has strong robustness. It can meet the system's smooth speed regulation requirements within a larger speed regulation range. Therefore, it is suitable for fans and water pumps that do not have high requirements on the dynamic and steady-state characteristics of the motor.

9. The method for controlling the motor frequency conversion coordinated starting of a ship emergency power system according to claim 2, characterized in that: In step 3, the flux per pole in the motor Φ m It needs to remain unchanged because too small a magnetic flux will lead to insufficient excitation, which will cause the motor torque to decrease and the load cannot be started as required; while too large a magnetic flux will cause magnetic circuit saturation, which may cause the motor to burn out in severe cases.

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