CN112671282B - AC/DC excitation natural switching method in three-stage synchronous motor starting process - Google Patents
AC/DC excitation natural switching method in three-stage synchronous motor starting process Download PDFInfo
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Abstract
The invention discloses a three-stage synchronous motor starting process alternating current-direct current excitation natural switching method, which is characterized in that at the beginning of starting, a three-phase alternating current with constant amplitude is injected into a three-phase excitation winding at the stator side of a main exciter, the phase sequence of the three-phase alternating current is controlled to generate a rotating excitation magnetic field opposite to the starting direction of the three-stage synchronous motor, the frequency difference between the rotating excitation magnetic field and the rotating speed of the main exciter is controlled to be constant in combination with the rotating speed of the motor in the starting process, so that the armature winding at the rotor side of the main exciter generates constant output voltage which does not change along with the rotating speed in a three-phase alternating current excitation mode, the frequency of the three-phase alternating current excitation of the main exciter is reduced along with the rising of the rotating speed of the motor, when the frequency is reduced to 0, the three-phase excitation control mode at the moment is kept, the main exciter is naturally switched into direct current excitation, torque fluctuation cannot occur in the alternating current excitation and direct current excitation in the whole starting process of the three-stage synchronous motor, and the control mode is not required to be changed in the alternating current excitation and direct current excitation process.
Description
Technical Field
The invention relates to an alternating current-direct current excitation natural switching method in a starting process of a three-stage synchronous motor, and belongs to the technical field of motor control.
Background
In the great trend that multi-electric aircraft and all-electric aircraft become the development directions of advanced aircraft in the future, the variable-frequency alternating-current power supply is increasingly paid attention to. Compared with other types of aircraft alternating current main power supplies, the variable frequency alternating current power supply has the following characteristics: (1) the reliability is high, and constant installation and a power electronic conversion device are eliminated; (2) the efficiency is high, and the volume and the weight are small; (3) the starting power generation is easy to realize; (4) the single machine capacity is larger. At present, an advanced aircraft A380 of an air passenger company selects a variable-frequency alternating-current power supply as a main motor of a variable-frequency alternating-current power supply system, four channels of the whole aircraft supply power, the total capacity reaches 600kVA, and a B787 aircraft adopts a high-power variable-frequency alternating-current starting power generation system with the total capacity reaching 1000 kVA.
The three-stage brushless synchronous motor is widely applied to a variable frequency alternating current power supply system as an aero-generator, and the most advanced civil aircraft B787 variable frequency alternating current power supply system at present uses the three-stage synchronous motor as a starting generator, so that the starting and power generation integration is realized. The three-stage synchronous motor consists of a permanent magnet auxiliary exciter, a main exciter, a rotary rectifier and a main generator. In the power generation mode, the auxiliary exciter provides direct current excitation for the main exciter through the generator control unit, the armature winding induction potential of the main exciter provides power for the excitation winding of the main generator through the rotary rectifier, the rotor is driven by the aeroengine to rotate, induction potential is generated in the stator winding of the main generator, and electric energy is output to power various electric loads on the aircraft. In the start mode, the main generator is operated in an electric state, requiring a start from rest. Because the exciter is in a static state, induced potential cannot be generated on the armature winding of the exciter, exciting current cannot be provided for the main generator, and the main generator is difficult to excite and cannot start from a static state. Therefore, in order to realize the starting and running functions of the three-stage synchronous motor, three-phase alternating current is required to be fed into the stator winding of the main exciter, and the generated rotating magnetic field generates induction potential at the armature winding of the exciter, and the induction potential is rectified by the rotating rectifier to provide excitation for the main generator.
As the motor speed increases, the three-phase ac excitation effect of the main exciter gradually decreases. Therefore, the main exciter can start the motor from rest in a three-phase alternating-current excitation mode within a rotating speed range, and when the rotating speed of the motor reaches a certain value, the three-phase alternating-current excitation can not meet the starting requirement, and the main exciter needs to be switched to a direct-current excitation mode to ensure that the main generator continues to operate. When the AC/DC excitation switching is performed, the excitation effect before and after the switching is required to be the same, and the induced voltage phase of the rotor is also required to be the same, namely the magnitude and the direction of a magnetic field generated by the stator current of the main exciter are required to be the same before and after the switching, otherwise, the AC/DC excitation switching has a transition process, and smooth switching cannot be realized. Therefore, the AC/DC excitation smooth switching method in the starting process of the three-stage synchronous motor has great research significance.
Disclosure of Invention
The invention aims to: the invention aims to solve the problems in the prior art, and provides a three-stage synchronous motor starting process alternating current-direct current excitation natural switching method, wherein a three-phase alternating current excitation is adopted by a main exciter of the three-stage synchronous motor at the initial starting stage, the alternating current excitation effect is weakened along with the rising of the rotating speed, and the three-stage synchronous motor is smoothly switched into direct current excitation through a natural switching method after reaching a certain rotating speed.
The technical scheme is as follows: in order to achieve the above purpose, the invention adopts the following technical scheme:
a natural switching method of AC/DC excitation in the starting process of a three-stage synchronous motor comprises three-phase AC excitation control, three-phase DC excitation control and natural switching control of AC/DC excitation, wherein the three-phase AC excitation control is adopted at the beginning of the starting process, and the AC/DC excitation switching is carried out through a natural switching method after the rotating speed of the motor is increased, so that the three-phase DC excitation control is switched.
The three-phase alternating current excitation control comprises the following steps:
the three-phase bridge inverter of the main exciter is controlled by adopting an inverter space vector modulation mode, so that the dq-axis current is kept constant. The inverter space vector modulation control module enables the rotation direction of the space vector to be opposite to the rotation direction of the motor, and controls the frequency difference between the rotation frequency of the exciting voltage vector and the rotation speed frequency of the motor to be kept constant, so that the rotor cuts a magnetic field at a constant speed, a constant amplitude voltage is induced on the rotor side, and a constant exciting current is provided for the exciting winding of the main generator after the rotor passes through the rotary rectifier, so that the stability of starting torque is ensured.
Calculating the angular frequency of the three-phase alternating current excitation control of the main exciter according to the detected starting rotating speed of the three-stage synchronous motor and combining the pole pair number of the main exciter and the excitation power output requirement:
wherein omega ref For a given slip angular frequency, n r The starting speed of the three-stage synchronous motor is p is the pole pair number of the main exciter. The main exciter excitation inverter is controlled according to the method, so that the rotation speed difference between the main exciter excitation magnetic potential and the rotation speed of the three-stage synchronous motor is kept constant, the output voltage of the main exciter rotor is constant, the main motor is provided with constant excitation current after the main exciter rotor passes through the rotary rectifier, the output starting torque is ensured to be stable in the starting process, and the angular frequency of the three-phase alternating current excitation control of the main exciter is continuously reduced along with the increase of the starting rotation speed.
The AC/DC excitation natural switching is specifically as follows:
as the rotation speed increases, the difference between the given angular frequency and the rotor angular frequency is smaller and smaller, the value is compared with zero, and when the excitation angular frequency value is larger than zero, the excitation angular frequency value is taken as the angular frequency omega of the inverter vector diff . Under the control method, the alternating current/direct current excitation switching moment is the angular frequency omega of the space vector diff And when the voltage is reduced to 0, latching the switching tube conduction mode of the excitation control converter at the moment, controlling the voltage of the three-phase winding of the main exciter stator to be a constant value, and automatically switching to a direct current excitation mode. When the angular frequency of the space vector is kept to be 0 during switching, the position angle theta of the main exciter output current space vector is kept unchanged after passing through the integrator, and the exciting current space vector stops rotating. In this way, the three-phase exciting current output by the inverter is stable and unchanged, and torque pulsation generated by exciting switching is eliminated.
The three-phase direct current excitation control is specifically as follows:
and the three-phase bridge inverter of the main exciter is controlled by adopting an inverter space vector modulation mode. And entering a direct-current excitation stage, always keeping the space vector angular frequency to be 0, and keeping the current space vector position angle theta unchanged, so that the conduction mode of the switching tube is unchanged, and the direction and the magnitude of the excitation magnetic field before and after switching are unchanged. Under this scheme, the control mode of direct current excitation and alternating current excitation is basically unchanged.
Compared with the prior art, the invention has the following beneficial effects:
1. the alternating current excitation scheme provided by the invention ensures that the excitation voltage of the main generator is constant in the starting process, ensures that the direction and the size of the excitation magnetic field of the exciter are unchanged before and after alternating current and direct current excitation are switched, and provides constant excitation current for the excitation winding of the main generator, thereby enabling the main generator to output constant torque.
2. The AC/DC excitation switching scheme provided by the invention does not need to determine an excitation switching point according to the motor rotation speed in the starting process.
3. The AC/DC excitation natural switching method provided by the invention has the advantages that the modulation mode of the main exciter three-phase inverter is not changed in the excitation switching process, the control modes of the AC excitation and the DC excitation before and after switching are basically unchanged, and the implementation is easy.
Drawings
FIG. 1 is a schematic diagram of a three-stage synchronous motor to which the present invention is applied;
FIG. 2 is a block diagram of the natural switching control of AC/DC excitation in the starting process of the three-stage synchronous motor of the invention;
FIG. 3 is a waveform diagram of a simulation of the stator current of a main exciter of a three-stage synchronous motor according to the present invention;
FIG. 4 is a waveform diagram of a simulation of the current of a main exciter rotor of a three-stage synchronous motor according to the present invention;
FIG. 5 is a waveform diagram of simulation of exciting winding current of a primary generator of a three-stage synchronous motor according to the present invention;
FIG. 6 is a waveform diagram of a simulation of motor output torque during the starting process of the three-stage synchronous motor of the present invention;
Detailed Description
The invention will now be described in detail with reference to the accompanying drawings and specific examples.
The schematic structure of the three-stage synchronous motor suitable for the invention is shown in fig. 1, wherein a main generator, a rotary rectifier, a main exciter and a permanent magnet auxiliary exciter are coaxially connected. When the three-stage synchronous motor is in a zero-speed or low-speed state at the initial stage of starting, three-phase alternating current excitation is adopted for starting. When the rotation speed rises to reach a natural switching point, the main exciter is switched from three-phase alternating current excitation to three-phase direct current excitation.
As shown in the ac/dc excitation natural switching control block diagram of the three-stage synchronous motor starting process of fig. 2, the permanent magnet auxiliary exciter part is omitted because the permanent magnet auxiliary exciter does not participate in the starting process. The three-stage synchronous motor AC/DC excitation switching starting comprises the following three stages:
(1) Three-phase alternating current excitation control stage
When the three-stage synchronous motor starts from a static state, the main exciter adopts three-phase alternating current excitation, the measured current of the three-phase winding of the stator of the main exciter is compared with the given current under the dq axis after Clarke transformation and Park transformation in FIG. 2, and u is obtained after PI control d And u is equal to q So that the given current under the dq axis of the main exciter stator remains constant. According to u d And u is equal to q And outputting PWM signals by adopting an inverter space vector modulation mode. The inverter space vector modulation control module reverses a rotational direction of the space vector to a rotational direction of the motor. Defining the rotating speed direction of the motor as a positive direction, calculating the rotating speed of the motor according to the position of the motor rotor detected by the position sensor, wherein the angular frequency of the three-phase alternating current excitation control of the main exciter is as follows:
wherein omega ref For a given slip angular frequency, n r For rotor speed, p is the pole pair number. Therefore, the frequency difference between the rotation frequency of the exciting voltage vector and the rotation speed frequency of the motor can be kept constant, so that the rotor cuts a magnetic field at a constant speed, the exciting current of the main generator in the alternating-current exciting stage is ensured to be stable, and the output starting torque is ensured to be stable. Frequency matchingRate omega diff And (3) carrying out integral calculation to obtain the angle theta of the voltage space vector to be output, and inputting the angle theta into an inverter space vector modulation module so that the controller generates a corresponding voltage space vector.
(2) AC/DC excitation switching stage
During starting, the exciting frequency gradually decreases with the increase of the motor rotation speed, and when the exciting frequency decreases to 0, namely the frequency omega of the voltage vector rotation output by the inverter diff When reaching 0, omega is maintained diff When 0 is unchanged, the current space vector position angle theta is kept unchanged after passing through the integrator, and the exciting current space vector stops rotating. And (3) latching a switching tube conduction mode of the excitation control converter at the moment, controlling the voltage of the three-phase winding of the stator of the main exciter to be a constant value, and naturally switching alternating current excitation into direct current excitation. The modulation mode of the main exciter three-phase inverter is not changed in the excitation switching process, and the AC/DC excitation control mode is basically unchanged.
(3) DC excitation control stage
As the motor speed increases, the angular frequency omega of the three-phase alternating current excitation control of the main exciter is always maintained after the motor is switched to direct current excitation diff And when the current space vector position angle theta is zero, the current space vector position angle theta is unchanged after the current space vector position angle theta passes through the integrator, the conduction mode of the inverter switching tube is unchanged, and the three-phase inverter still adopts an alternating current excitation phase inverter space vector modulation mode.
In order to verify the effectiveness of the method, matlab/Simulink simulation is conducted on the three-stage synchronous motor in the embodiment and the corresponding working conditions. The working conditions are as follows: reference frequency omega ref =20pi rad/s, given the main exciter stator current i d *＝0,i q *＝20A。
Fig. 3 is a waveform of a stator current of a main exciter during starting by MATLAB simulation, in which the amplitude of the exciting current of the main exciter is controlled to be constant, the exciting frequency of the exciter is reduced to zero at 0.53s, and ac excitation is naturally switched to dc excitation.
Fig. 4 is a simulation waveform of rotor current of the main exciter, fig. 5 is a waveform of exciting winding current of the main generator, rotor current does not suddenly change during switching of ac/dc excitation, exciting winding current of the main generator is stable, rising after current switching is caused by rising of motor speed after switching to dc excitation, and rising of induced voltage of the rotor is small compared with rising of induced voltage although impedance is also increased, so that current is rising. As the rotational speed continues to rise, the main generator current slowly rises, eventually tending to be constant. Fig. 6 is a waveform of output torque of the motor during starting, and motor torque is not suddenly changed at the time of ac/dc excitation switching. Is a smooth handoff. Simulation results show that the AC/DC excitation natural switching control method in the starting process of the three-stage synchronous motor can realize smooth switching of AC/DC excitation and avoid torque pulsation.
The foregoing description of the preferred embodiments of the present invention is merely for illustrating the technical idea of the present invention and is not intended to limit the scope of the present invention, so that those skilled in the art should not be able to make any equivalent substitutions and modifications within the spirit and principle of the present invention.
Claims (3)
1. The natural switching method of AC/DC excitation in the starting process of the three-stage synchronous motor is characterized in that: at the beginning of the starting process, the main exciter adopts three-phase alternating current excitation control, a stator three-phase excitation winding of the main exciter is injected with three-phase alternating current to generate a rotary excitation magnetic field which is opposite to the direction of the three-stage synchronous motor, and the three-phase alternating current is induced in a rotor armature winding of the main exciter and is rectified by a rotary rectifier to provide constant excitation current for an excitation winding of the main generator; as the rotating speed of the three-stage synchronous motor increases, after the angular frequency of the three-phase alternating-current excitation control is reduced to 0, the main exciter is switched from the three-phase alternating-current excitation to the three-phase direct-current excitation control, so that the natural switching of the alternating-current and direct-current excitation control of the three-stage synchronous motor is realized, the excitation current of the main generator in the starting process is kept constant, and the torque control requirement of the three-stage synchronous motor in the starting process is met;
in the three-phase ac excitation control mode, the angular frequency of the three-phase ac excitation control of the main exciter gradually decreases as the rotational speed of the three-stage synchronous motor increases, and when the angular frequency of the three-phase ac excitation control of the main exciter decreases to 0, the switching tube conduction mode of the excitation control converter at that time is latched, the stator three-phase excitation winding voltage of the main exciter is controlled to be a constant value, and after the rotor armature winding of the main exciter induces three-phase ac power, excitation is provided to the excitation winding of the main generator through the rotary rectifier, and the three-phase dc excitation control mode is automatically switched.
2. The natural switching method of alternating current and direct current excitation in the starting process of the three-stage synchronous motor as claimed in claim 1, wherein the method comprises the following steps: calculating the angular frequency of the three-phase alternating current excitation control of the main exciter according to the detected starting rotating speed of the three-stage synchronous motor and combining the pole pair number of the main exciter and the excitation power output requirement:
wherein omega diff Angular frequency, omega of the control of the three-phase ac excitation of the main exciter ref For a given slip angular frequency, n r The starting rotating speed of the three-stage synchronous motor is p is the pole pair number of the main exciter;
the main exciter excitation inverter is controlled according to the method, so that the rotation speed difference between the main exciter excitation magnetic potential and the rotation speed of the three-stage synchronous motor is kept constant, the output voltage of the main exciter rotor is constant, the main motor is provided with constant excitation current after the main exciter rotor passes through the rotary rectifier, the output starting torque is ensured to be stable in the starting process, and the angular frequency of the three-phase alternating current excitation control of the main exciter is continuously reduced along with the increase of the starting rotation speed.
3. The natural switching method of alternating current and direct current excitation in the starting process of the three-stage synchronous motor as claimed in claim 1, wherein the method comprises the following steps: comparing the angular frequency omega of the three-phase AC excitation control of the main exciter in the AC excitation control mode diff And 0, when ω diff When the weight is greater than 0, omega is taken out dif As the primary exciter controlled three-phase inverter inputThe angular frequency of the output voltage space vector modulation; at the natural switching point of AC/DC excitation control of the three-stage synchronous motor, namely omega diff When the voltage space vector of the three-phase inverter is 0, the angular frequency of the voltage space vector of the three-phase inverter is 0, an integrator is adopted to keep the phase angle theta of the output current of the three-phase alternating-current excitation control unchanged, so that the output excitation magnetic potential of the main exciter stops rotating, and the output excitation magnetic potential is equivalent to the direct-current excitation magnetic potential, the space position angle and the amplitude of the excitation magnetic potential of the main exciter at a natural switching point are kept unchanged before and after switching, and the constant output control of the main exciter in the alternating-current and direct-current excitation switching process is realized by combining the constant control of the amplitude of the three-phase excitation current.
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| 基于两相励磁机的多级式无刷同步起动/发电系统起动阶段关键技术研究;焦宁飞;《中国博士学位论文全文数据库》;20190115;第13-17、35-42页 * |
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