Standard subway permanent magnet traction converter control method

Abstract

The invention discloses a standard subway permanent magnet traction converter control method, which belongs to the technical field of subway permanent magnet traction converter control, and comprises the following steps of: 1, controlling the maximum torque current ratio; step 2, field weakening control; step 3, carrying out SVPWM synchronous modulation; step 4, re-throwing at a belt speed; 5, single-current closed-loop control is carried out; compared with synchronous motor control in the industrial field, the control method can be suitable for a high-voltage system, and synchronous motor control under the low switching frequency is achieved. The switching mode of square wave control is optimized, so that the synchronous motor control system realizes maximum torque current ratio control in a full-speed domain range, and the efficiency of the control system is improved. SVPWM synchronous modulation is realized, the switching frequency of a high-speed area is reduced, the traction efficiency is improved, and compared with a control mode of entering a square wave by using an overmodulation mode, current harmonics are reduced. The belt speed restarting in the full-speed domain range is realized, and the influence of the back electromotive force of the permanent magnet synchronous motor in the high-speed region is overcome.

Description

Technical Field

[0001] The invention belongs to the technical field of rail transportation, and in particular relates to a control method for a standard subway permanent magnet traction converter. Background Art

[0002] With the development of rare earth permanent magnet materials with high magnetic energy product and strong coercivity, permanent magnet motors have gradually entered everyone's field of vision. In particular, the development and application of neodymium iron boron materials have effectively reduced the cost of rare earth materials, allowing rare earth permanent magnet motors to be used on a large scale in industrial and civilian fields. Permanent magnet traction motors are currently a hot topic in the technical research of rail transit traction systems.

[0003] Compared with asynchronous motors, permanent magnet synchronous motors have higher efficiency and higher power density. Tests show that the efficiency of permanent magnet synchronous motors can reach 97%, while the efficiency of asynchronous motors is up to 92%. Under the policy background of energy conservation and emission reduction, permanent magnet traction systems can make positive contributions to energy conservation and emission reduction in rail transit. According to reports, the energy saving effect of using permanent magnet synchronous traction systems is about 10%.

[0004] Compared with the asynchronous motor of the same level, the volume and mass of the permanent magnet synchronous motor can be reduced by 20-30%, so the power density is significantly improved. The significant improvement in the efficiency of the permanent magnet synchronous motor means that its own heat generation is reduced. Especially for the rotor, the rotor heat generation of the permanent magnet synchronous motor is low, which is conducive to the fully enclosed design of the motor. The fully enclosed motor design not only eliminates the maintenance work of regular disassembly and cleaning of the motor interior, but also significantly reduces noise.

[0005] At present, the three most widely used control strategies for permanent magnet synchronous motors are: constant voltage-frequency ratio (V / f) control, direct torque control (DTC) and vector control (VC). The basic principle of constant voltage-frequency ratio control is to keep the ratio of voltage to angular frequency constant at base speed. This control method is open-loop speed control. Its advantages are that the control circuit is relatively simple, easy to implement, and no speed sensor is required. Its disadvantages are poor dynamic performance, and when the load is suddenly added or unloaded, the motor is prone to loss of step, which leads to the system being unable to operate stably. Therefore, this control method is basically not used in situations where high performance is required.

[0006] As early as 1985, Professor M. Depenbrock of Ruhr University in Germany proposed the theory of direct torque control. Subsequently, on this basis, a similar control scheme was also proposed by Japanese scholar LTakshashi, which later gradually developed into the current direct torque control strategy. Its basic principle is to select a suitable voltage vector according to the deviation of the stator flux and the electromagnetic torque according to the current position, reduce the deviation between the two, and thus realize torque control. The advantages of direct torque control are simple principles and relatively fast torque response; the disadvantages are that its performance is relatively poor at low speeds, and when the speed regulation range is limited, the torque pulsation generated cannot be avoided. In 1996, Professor Hu Yuwen of Nanjing University of Aeronautics and Astronautics and the University of New South Wales in Australia successfully cooperated to apply the direct torque control theory to permanent magnet motors, and successfully extended the strategy to the weak magnetic constant power range.

[0007] In 1971, F. Blaschke, an engineer from SIEMENS in Germany, proposed the concept of vector control, which is also called field oriented control (FOC). The basic principle of field oriented control is to control the excitation current and torque current of the motor separately. First, the stator current is detected by signal acquisition method, and the stator is decomposed into two parts: one part is the electric excitation current, which is used to generate a magnetic field; the other part is the torque current, which is used to generate torque. By controlling these two currents, it is equivalent to controlling the stator current. In this way, the synchronous motor can achieve the same effect as the DC motor in terms of control. The advantages of vector control are wide speed regulation range and good dynamic and static performance, and the disadvantage is that the whole system is relatively complex. The increasing development of power electronics technology and microprocessing technology has laid the foundation for the realization of vector control. The vector control of the built-in permanent magnet synchronous motor requires coordinated control of the AC and DC axis currents, making full use of the permanent magnet torque and reluctance torque of the motor to improve the torque response of the motor. Through the development of forty years, vector control has become more and more perfect in technology and more and more successful in application. In permanent magnet synchronous motor control systems, vector control has the characteristics of a wider speed regulation range, smooth output torque, and stronger overload capacity. Therefore, vector control is the preferred solution for high-performance motor drive systems. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a control method for a standard subway permanent magnet traction converter in view of the shortcomings of the background technology; a vector control method is adopted to achieve optimal control in the constant torque area and the weak magnetic area.

[0009] The present invention adopts the following technical solutions to solve the above technical problems:

[0010] A standard subway permanent magnet traction converter control method specifically comprises the following steps:

[0011] Step 1, maximum torque current ratio control;

[0012] Step 2, magnetic field weakening control;

[0013] Step 3, SVPWM synchronous modulation;

[0014] Step 4, re-cast with speed;

[0015] Step 5: Single current closed-loop control.

[0016] As a further preferred solution of a control method for a standard subway permanent magnet traction converter of the present invention, the step 1 of maximum torque current ratio control specifically comprises the following steps:

[0017] If there is no explanation for the variables in the formula, their meanings are as follows:

[0018] Step 1.1, let γ be the phase angle between the current space vector and the d-axis position; get

[0019] i d =i s *cosγ

[0020] i q =i s *sinγ Formula 1.1

[0021] Among them, i d is the peak current of the motor d axis; i q is the peak current of the motor q axis; i s is the peak value of the motor current;

[0022] Then the electromagnetic torque formula is written as:

[0023]

[0024] Among them, T em is the motor torque; P n is the number of motor pole pairs; φ f is the motor flux;

[0025] The relationship between the unit current electromagnetic torque and the current phase angle is obtained:

[0026]

[0027] Among them, L d is the motor d-axis inductance; L q is the motor q-axis inductance;

[0028] When the current amplitude remains constant, the electromagnetic torque takes the maximum value Then we get:

[0029] (L d —L q )i s cos2γ+φ f cosγ=0 Formula 1.4

[0030] (L d —L q )i s (2cos 2 γ-1)+φ f cosγ=0 formula 1.5

[0031] By solving formula 1.4 and formula 1.5, we can get the value of γ when the torque reaches the maximum value:

[0032]

[0033] According to formula 1.6 and formula 1.1, we can get

[0034]

[0035] According to formula 1.7 and formula 1.8, the current vector of the synchronous motor base speed region is obtained, and the vector satisfies the maximum torque current ratio;

[0036] When the motor runs at a speed exceeding the base speed, the voltage drop on the stator resistance is small and can be ignored. At this time, the voltage equation can be simplified to:

[0037]

[0038] Among them, w s is the motor angular frequency, electrical frequency; u d is the motor d-axis voltage; u q is the motor q-axis voltage;

[0039] During the operation of the motor, the motor operating voltage is limited by the rated voltage or the maximum output voltage of the inverter, and the current is limited by the maximum allowable current of the motor;

[0040]

[0041] In order to fully utilize the inverter capacity and fully utilize the DC bus voltage, the inverter motor system generally adopts the maximum motor minimum inverter matching solution; Substituting formula 1.9 into formula 2.0, we can get:

[0042]

[0043] Among them, u smax is the maximum value of the motor phase voltage amplitude; i smax is the maximum value of the motor current amplitude;

[0044] It can be seen from formula 2.1 that the current limit curve of the motor is a circle with the current amplitude as the radius and the center at the origin; while the voltage limit curve is an ellipse; below the base speed, the motor runs according to the current trajectory determined by formula 1.6, and above the base speed, the motor runs according to the current trajectory determined by formula 2.1.

[0045] As a further preferred solution of a standard subway permanent magnet traction converter control method of the present invention, the step 3SVPWM synchronous modulation specifically comprises the following steps:

[0046] Space vector PWM is based on the volt-second balance principle. In each sampling period, the required reference voltage vector is generated by the linear combination of the two effective voltage vectors and the zero vector in the sector where the voltage vector is located. According to the volt-second balance principle, the action time of the non-zero vector and the zero vector is determined, as shown in formula 2.2.

[0047]

[0048] Among them, T X is the action time of vector 1; T2 is the action time of vector 2; T Y is the zero vector action time;

[0049] The modulation ratio M in the formula is V [\] / (2V 5^ / π), where M is the SVPWM output modulation degree; the denominator is the fundamental amplitude of the square wave; Ts is the switching period; α is the angle of the vector in the stationary coordinate system;

[0050] In each sampling period, the difference in zero voltage vectors causes the basic differences in various space vector PWM strategies. Various basic PWM strategies are obtained by permuting and combining zero voltage vectors and effective voltage vectors. Taking sector I as an example, the four possible voltage vectors are 0, 1, 2, and 7. If two zero voltage vectors are placed on both sides of two effective voltage vectors, a switch state switching sequence of 0127 or 7210 can be obtained, corresponding to the traditional space vector strategy CSVS. If only one of the zero voltage vectors is used, a switching sequence of 012, 210, or 721, 127 is obtained, corresponding to the basic bus clamping strategy BBCS and the basic bus clamping strategy BBCS II. If a sampling point of the sector is set at the starting boundary of the sector, a switching sequence of 010 and 101 is obtained, and the other sampling points are the same as BBCS, then the boundary sampling strategy BSS and the boundary sampling strategy SS II are obtained.

[0051] As a further preferred solution of a standard subway permanent magnet traction converter control method of the present invention, the step 4 of belt speed re-investment specifically comprises the following steps:

[0052] After the vehicle enters the power-free zone, the system controls the contactor between the inverter and the motor to be disconnected. Before entering the power-on zone again, the system controls the contactor to be closed. At this time, the motor current is zero, and the q-axis voltage is established according to formula 1.9; the d-axis voltage is established according to the relationship between the current angular velocity and the rated angular velocity:

[0053]

[0054] Among them, w s is the electrical angular frequency of the motor converted from the current vehicle speed, w s_rate The electrical angular frequency at the rated speed of the motor

[0055] After entering the energized area, before controlling the closing contactor, press u d As the phase adjustment amount, u q As the back-EMF tracking quantity, the inverter output voltage vector is first controlled and then the contactor is closed.

[0056] As a further preferred solution of a standard subway permanent magnet traction converter control method of the present invention, the single current closed-loop control in step 5 specifically comprises the following steps:

[0057] Define δ as the angle between the motor voltage vector and the positive direction of the d-axis, then the d and q axis voltages are expressed as:

[0058]

[0059] The relationship between torque and voltage phase angle is derived as:

[0060]

[0061] For a limited speed system, the voltage phase angle ranges in traction and braking conditions are (π / 2, π) and (0, π / 2), respectively. Under no-load conditions, δ is π / 2. For an infinite speed system, the effective range of the voltage phase angle is not (0, π). The output torque is controlled by controlling the voltage phase angle.

[0062] When based on voltage phase angle control, the relationship between d, q axis current and voltage phase angle δ is:

[0063]

[0064] It can be seen from formula 2.6 that in the traction or braking state, both id and iq have a monotonic relationship with δ, and it is considered to use id or iq current regulator to adjust the phase angle; it can be seen from formula (2.6) that when only considering the single state of traction or braking, the direct-axis voltage or quadrature-axis voltage under the square wave condition has a monotonic relationship with the voltage phase angle; as long as the direct-axis voltage or quadrature-axis voltage is determined, the voltage phase angle will also be uniquely determined; and the voltage phase angle has a monotonic relationship with the motor torque, and the direct-axis voltage or quadrature-axis voltage also has a monotonic relationship with the torque; the voltage phase angle is indirectly adjusted by adjusting the direct-axis voltage or quadrature-axis voltage; when a single d-axis current closed-loop control is adopted, the monotonic relationship between the torque and the voltage phase angle under the traction and braking conditions is different, and needs to be processed separately, while when a single q-axis current closed-loop control is adopted, the monotonic relationship between the torque and the voltage phase angle under the traction and braking conditions is consistent, and does not need to be processed separately; the single q-axis current regulation method is adopted;

[0065] The switching between the single q-axis current loop and the dual current loop is to switch into the single current loop when the inverter output voltage is greater than a certain voltage switching point and the motor speed is greater than a certain speed switching point, and to exit the single current loop otherwise. A certain hysteresis loop area is set for the voltage switching point and speed switching point for entering and exiting; the voltage switching point is selected according to the voltage limit of the current operating condition; the speed switching point is selected according to the speed when the voltage circular curve is completely in the left half of the dq-axis plane under the rated voltage.

[0066] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0067] The present invention provides a control method for a standard subway permanent magnet traction inverter. Compared with the synchronous motor control in the industrial field, this control method can be applied to high-voltage systems to achieve synchronous motor control at low switching frequencies. The switching mode of square wave control is optimized, so that the synchronous motor control system can achieve maximum torque-to-current ratio control within the full speed range, thereby improving the efficiency of the control system. SVPWM synchronous modulation is achieved, the switching frequency in the high-speed area is reduced, the traction efficiency is improved, and the current harmonics are reduced compared to the control mode of using overmodulation to enter the square wave. Belt speed re-investment within the full speed range is achieved, overcoming the influence of the back electromotive force of the permanent magnet synchronous motor in the high-speed area. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 is the voltage and current limiting curve of the synchronous motor of the present invention;

[0069] Figure 2 This is a block diagram of voltage feedback weak magnetic control of the present invention;

[0070] Figure 3 It is the segmented synchronous modulation strategy of the present invention;

[0071] Figure 4 This is a schematic diagram of the digital implementation principle of 11-frequency division synchronous modulation of the present invention;

[0072] Figure 5 It is a flow chart of belt speed re-throw control of the present invention;

[0073] Figure 6 is the relationship between the torque and the voltage phase angle of the present invention;

[0074] Figure 7 This is the dual current closed loop and single current closed loop switching and control flow chart of the present invention

[0075] Figure 8 It is a principle block diagram of the standard subway permanent magnet traction converter of the present invention.

[0076] Fig. 9 It is a control principle block diagram of the present invention. DETAILED DESCRIPTION

[0077] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings:

[0078] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. The present invention is described in detail below based on the drawings and preferred embodiments, and the purpose and effect of the present invention will become clearer. It should be understood that the specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0079] like Figures 1 to 9 As shown, a standard subway permanent magnet traction converter control method specifically comprises the following steps;

[0080] Step 1, maximum torque current ratio control;

[0081] Step 2, magnetic field weakening control;

[0082] Step 3, SVPWM synchronous modulation;

[0083] Step 4, re-cast with speed;

[0084] Step 5: Single current closed-loop control.

[0085] In one embodiment, the present invention includes the following.

[0086] Maximum torque current ratio control:

[0087] When the permanent magnet synchronous motor works below the base speed, the MTPA control strategy is implemented on the motor to reduce system losses. The MTPA control strategy can minimize the stator current vector amplitude under the given torque of the motor, greatly improving the torque conversion rate. This control algorithm can reduce the copper loss of the motor, reduce the loss of the rectifier and inverter, improve the voltage utilization, and make the torque of the permanent magnet synchronous motor reach the maximum value when it works below the base speed.

[0088] Let γ be the phase angle between the current space vector and the d-axis position.

[0089] i d =i s *cosγ

[0090] i q =i s *sinγ Formula 1.1

[0091] Among them, i d is the peak current of the motor d axis; i q is the peak current of the motor q axis; i s is the peak value of the motor current;

[0092] Then the electromagnetic torque formula can be written as:

[0093]

[0094] Among them, T em is the motor torque; P n is the number of motor pole pairs; φ f is the motor flux;

[0095] The relationship between the unit current electromagnetic torque and the current phase angle is obtained as follows:

[0096]

[0097] Among them, L d is the motor d-axis inductance; L q is the motor q-axis inductance;

[0098] When the current amplitude remains constant, the electromagnetic torque takes the maximum value Then we get:

[0099]

[0100] By solving formula 1.4 and formula 1.5, we can get the value of γ when the torque reaches the maximum value:

[0101]

[0102] According to formula 1.6 and formula 1.1, we can get

[0103]

[0104] According to formula 1.7 and formula 1.8, the current vector of the synchronous motor base speed zone can be obtained, which satisfies the maximum torque current ratio.

[0105] When the motor runs at a speed exceeding the base speed, the voltage drop on the stator resistance is small and can be ignored. At this time, the voltage equation can be simplified to:

[0106]

[0107] Among them, w / is the motor angular frequency, electrical frequency; u5 is the motor d-axis voltage; u6 is the motor q-axis voltage;

[0108] During motor operation, the motor operating voltage is limited by the rated voltage or the maximum output voltage of the inverter, and the current is limited by the maximum allowable current of the motor.

[0109]

[0110] In order to fully utilize the inverter's capabilities and fully utilize the DC bus voltage, the inverter-motor system generally adopts the maximum motor minimum inverter matching solution. Substituting formula 1.9 into formula 2.0 yields:

[0111]

[0112] Among them, u / ％VW is the maximum value of the motor phase voltage amplitude; i / ％VW is the maximum value of the motor current amplitude;

[0113] From formula 2.1, we can find that the current limit curve of the motor is a circle with the current amplitude as the radius and the center at the origin. The voltage limit curve is an ellipse. Figure 1 As shown. Below the base speed, the motor runs according to the current trajectory determined by formula 1.6, and above the base speed, the motor runs according to the current trajectory determined by formula 2.1. The maximum torque-to-current ratio can be achieved in the full speed range, improving the motor efficiency.

[0114] Field weakening control

[0115] The weak magnetic field operation current trajectory determined by formula 2.1 requires solving a univariate quartic equation, which needs to be solved by Newton's iteration method. It cannot be calculated in real time in DSP, so it will be calculated in advance and saved as a two-dimensional table. When the program is running, the current operation trajectory is obtained by looking up the table. The weak magnetic field control implemented by this method will cause the system to be unable to enter weak magnetic field when the speed changes rapidly, causing the converter to overcurrent. Therefore, voltage feedback weak magnetic field needs to be introduced in the weak magnetic field area. The voltage feedback weak magnetic field block diagram is as follows Figure 2shown.

[0116] SVPWM synchronous modulation

[0117] The pulse width modulation (PWM) technology of the inverter is one of the most widely used modulation methods. At present, PWM modulation technology is widely used in AC traction drive systems. PWM modulation technology can ensure that the output voltage and current waveforms of the inverter are close to sine, so that the magnetic flux of the load motor is also close to sine. There are many modulation methods based on the PWM principle, such as third harmonic injection method, space vector modulation (SVPWM), random pulse width modulation, etc. In the field of low switching frequency applications, the most commonly used ones are Figure 3 The segmented modulation PWM strategy shown.

[0118] Space vector PWM is based on the volt-second balance principle. In each sampling period, the required reference voltage vector is generated by the linear combination of the two effective voltage vectors and the zero vector in the sector where the voltage vector is located. According to the volt-second balance principle, the action time of the non-zero vector and the zero vector is determined. As shown in formula 2.2.

[0119]

[0120] Among them, T X is the action time of vector 1; T2 is the action time of vector 2; T Y is the zero vector action time;

[0121] The modulation ratio M in the formula is V [\] / (2V 5^ / π), where M is the SVPWM output modulation degree; the denominator is the fundamental amplitude of the square wave; Ts is the switching period; α is the angle of the vector in the stationary coordinate system;

[0122] In each sampling period, the difference in zero voltage vectors causes the basic difference in various space vector PWM strategies. By permuting and combining zero voltage vectors and effective voltage vectors, various basic PWM strategies can be obtained. Taking sector I as an example, the four possible voltage vectors are 0, 1, 2, and 7. If two zero voltage vectors are placed on both sides of two effective voltage vectors, the switch state switching sequence can be obtained: 0127 or 7210, corresponding to the conventional space vector strategy (CSVS); if only one of the zero voltage vectors is used, the switching sequence can be obtained: 012, 210, or 721, 127,

[0123] Corresponding to the basic bus clamping strategy (BBCS) and the basic bus clamping strategy II (BBCS II); if a sampling point of the sector is set at the starting boundary of the sector, a switching sequence can also be obtained: 010 and 101, and the other sampling points are the same as BBCS, then the boundary sampling strategy (BSS) and the boundary sampling strategy II (BSS II) can be obtained.

[0124] This software uses CSVS to achieve 3-way division, BBCS II strategy to achieve 5-way division, and BBCS I to achieve 11-way division and 7-way division.

[0125] Figure 4 For the BBCS I with 11-division 30-degree clamping, the distribution of the switching angle in the range of 0 to 180 degrees shows that there are 15 sampling points in the first half of the fundamental cycle. At the first sampling point S1, both phases A and B are single-sided rising edges, and phase C is clamped to the negative bus, so the initial levels of phases A, B, and C are all low. The opening time of phase A is 100, the opening time of phase B is 100, and the switch of phase C does not operate. The same applies to other sampling points. The BBCS I modulation strategy with 11-division 300-degree clamping has a total of 30 sampling points in one fundamental cycle, which means that 30 carrier interruptions are required. Compared with the traditional 11-division synchronous modulation, the phase delay caused by modulation will be greatly reduced, so this is also a major advantage of using the basic vector clamping modulation strategy.

[0126] Speed ​​re-cast

[0127] The driving route of rail transit vehicles is divided into powered areas and non-powered areas. When the vehicle passes through the non-powered area, the power will be cut off, and the inverter will no longer output voltage to drive the permanent magnet synchronous motor; when entering the powered area again, it is necessary to restart the inverter output when the vehicle speed is not 0, and it is necessary to avoid triggering overcurrent, overvoltage and other fault protection, so as to achieve the vehicle's re-traction / braking control. After the vehicle enters the non-powered area, the system controls the contactor between the inverter and the motor to disconnect. Before controlling the contactor to close after entering the powered area again, the motor current is zero at this time, and the q-axis voltage is established according to formula 1.9 (w s is the electrical angular frequency of the motor converted from the current vehicle speed, w s_rate is the electrical angular frequency at the rated speed of the motor), and the d-axis voltage is established according to the relationship between the current angular velocity and the rated angular velocity:

[0128]

[0129] Among them, w s is the electrical angular frequency of the motor converted from the current vehicle speed, w s_rateIt is the electrical angular frequency at the rated speed of the motor.

[0130] After entering the energized area, before controlling the closing contactor, press u d As the phase adjustment amount, u q As the back-EMF tracking quantity, the inverter output voltage vector is first used to control the contactor to close. This control method can effectively reduce the current and voltage impact generated after closing the contactor within the full speed range of the vehicle. The control flow chart of speed re-throw is as follows Figure 5 Show.

[0131] Single current closed loop control

[0132] In square wave conditions, due to the fixed voltage amplitude, the traditional dual current loop vector control will conflict with each other and is difficult to apply. At this time, the voltage control degree of freedom is 1, and the only variable that can be adjusted is the voltage phase angle. Therefore, the voltage phase angle method has received widespread attention. The principle of the voltage phase angle method will be introduced below.

[0133] Define δ as the angle between the motor voltage vector and the positive direction of the d-axis, then the d and q axis voltages can be expressed as:

[0134]

[0135] The relationship between torque and voltage phase angle can be derived as:

[0136]

[0137] For a limited speed system, the voltage phase angle ranges in traction and braking conditions are (π / 2, π) and (0, π / 2), respectively. Under no-load conditions, δ is π / 2. For an infinite speed system, the effective range of the voltage phase angle is not (0, π), and further analysis is required in conjunction with the second weak magnetic zone. This system only analyzes limited speed systems. It is difficult to intuitively see the monotonic relationship between torque and voltage phase angle from formula 2.5. Plot the torque and phase angle relationship curves and their derivative relationship curves at different speeds, as shown in the figure. Figure 6 shown. Figure 6 The relationship curves of torque and voltage phase angle change and their derivative relationship curves are drawn in the figure for rated speed and rated speed. Figure 6 It can be seen that the derivative of the torque with respect to the voltage phase angle is greater than 0 at any speed. Therefore, the torque Te and the voltage phase angle are monotonically increasing. By controlling the voltage phase angle, the output torque can be controlled.

[0138] When based on voltage phase angle control, the relationship between d, q axis current and voltage phase angle δ is:

[0139]

[0140] It can be seen from formula 2.6 that in the traction or braking state, both id and iq have a monotonic relationship with δ, so it is possible to consider using id or iq current regulator to adjust the phase angle. In addition, it can be seen from formula (2.6) that when only considering the single state of traction or braking, the direct-axis voltage or quadrature-axis voltage under the square wave condition has a monotonic relationship with the voltage phase angle. Therefore, as long as the direct-axis voltage or quadrature-axis voltage is determined, the voltage phase angle will also be uniquely determined. The voltage phase angle has a monotonic relationship with the motor torque, so the direct-axis voltage or quadrature-axis voltage also has a monotonic relationship with the torque. That is, the voltage phase angle can also be indirectly adjusted by adjusting the direct-axis voltage or quadrature-axis voltage. When a single d-axis current closed-loop control is used, the monotonic relationship between the torque and the voltage phase angle is different in the traction and braking conditions, and needs to be processed separately. When a single q-axis current closed-loop control is used, the monotonic relationship between the torque and the voltage phase angle under the traction and braking conditions is consistent, and does not need to be processed separately. Therefore, the software adopts the method of single q-axis current regulation.

[0141] The switching between the single q-axis current loop and the dual current loop, the software switches to the single current loop when the inverter output voltage is greater than a certain voltage switching point and the motor speed is greater than a certain speed switching point, and exits the single current loop otherwise. A certain hysteresis area is set for the voltage switching point and speed switching point for entering and exiting. This method can avoid losing the maximum torque-to-current ratio characteristic due to premature switching into the single current loop, and can also avoid frequent switching between the two current control modes. The voltage switching point is selected according to the voltage limit of the current operating condition; the speed switching point is selected according to the speed when the voltage circular curve is completely in the left half of the dq-axis plane under the rated voltage. The switching and control process of the dual current closed loop and the single current closed loop is as follows: Figure 7 Show..

[0142] Those skilled in the art can understand that the above are only preferred examples of the invention and are not intended to limit the invention. Although the invention is described in detail with reference to the above examples, those skilled in the art can still modify the technical solutions recorded in the above examples or replace some of the technical features with equivalents. Any modification, equivalent replacement, etc. made within the spirit and principle of the invention should be included in the protection scope of the invention. All technical features in this embodiment can be freely combined according to actual needs.

[0143] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A standard subway permanent magnet traction converter control method, characterized in that: The specific steps include: Step 1, maximum torque current ratio control; Step 2, magnetic field weakening control; Step 3, SVPWM synchronous modulation; Step 4, re-cast with speed; Step 5: Single current closed-loop control.

2. A standard subway permanent magnet traction converter control method according to claim 1, characterized in that: The step 1 of maximum torque current ratio control specifically comprises the following steps: If there is no explanation for the variables in the formula, their meanings are as follows: Step 1.1, let γ be the phase angle between the current space vector and the d-axis position; get i d =i s *cosγ i q = i s * sinγ Equation 1.1 Among them, i d is the peak current of the motor d axis; i q is the peak current of the motor q axis; i s is the peak value of the motor current; Then the electromagnetic torque formula is written as: Among them, T em is the motor torque; P n is the number of motor pole pairs; φ f is the motor flux; The relationship between the unit current electromagnetic torque and the current phase angle is obtained: Among them, L d is the motor d-axis inductance; L q is the motor q-axis inductance; When the current amplitude remains constant, the electromagnetic torque takes the maximum value Then we get: (L d -L q )i s cos(2γ + φ) f cosγ = 0 Equation 1.4 (L d -L q )i s (2cos 2 γ - 1)+φ f cosγ = 0 Equation 1.5 By solving formula 1.4 and formula 1.5, we can get the value of γ when the torque reaches the maximum value: According to formula 1.6 and formula 1.1, we can get According to formula 1.7 and formula 1.8, the current vector of the synchronous motor base speed region is obtained, and the vector satisfies the maximum torque current ratio; When the motor runs at a speed exceeding the base speed, the voltage drop on the stator resistance is small and can be ignored. At this time, the voltage equation can be simplified to: Among them, w s is the motor angular frequency, electrical frequency; u d is the motor d-axis voltage; u q is the motor q-axis voltage; During the operation of the motor, the motor operating voltage is limited by the rated voltage or the maximum output voltage of the inverter, and the current is limited by the maximum allowable current of the motor; In order to fully utilize the inverter's capabilities and fully utilize the DC bus voltage, the inverter-motor system generally adopts the maximum motor minimum inverter matching solution; Substituting formula 1.9 into formula 2.0, we get: Among them, u smax is the maximum value of the motor phase voltage amplitude; i smax is the maximum value of the motor current amplitude; It can be seen from formula 2.1 that the current limit curve of the motor is a circle with the current amplitude as the radius and the center at the origin; while the voltage limit curve is an ellipse; below the base speed, the motor runs according to the current trajectory determined by formula 1.6, and above the base speed, the motor runs according to the current trajectory determined by formula 2.

1.

3. A standard subway permanent magnet traction converter control method according to claim 1, characterized in that: The step 3SVPWM synchronous modulation specifically comprises the following steps: Space vector PWM is based on the volt-second balance principle. In each sampling period, the required reference voltage vector is generated by the linear combination of the two effective voltage vectors and the zero vector in the sector where the voltage vector is located. According to the volt-second balance principle, the action time of the non-zero vector and the zero vector is determined. As shown in formula 2.2; Where T1 is the action time of vector 1; T2 is the action time of vector 2; T Z is the zero vector action time; The modulation ratio M in the formula is V REF / (2V dc / π), where M is the SVPWM output modulation degree; the denominator is the fundamental amplitude of the square wave; Ts is the switching period; and α is the angle of the vector in the stationary coordinate system. In each sampling period, the difference in zero voltage vectors causes the basic differences in various space vector PWM strategies. Various basic PWM strategies are obtained by permuting and combining zero voltage vectors and effective voltage vectors. Taking sector I as an example, the four possible voltage vectors are 0, 1, 2, and 7. If two zero voltage vectors are placed on both sides of two effective voltage vectors, a switch state switching sequence of 0127 or 7210 can be obtained, corresponding to the traditional space vector strategy CSVS. If only one of the zero voltage vectors is used, a switching sequence of 012, 210, or 721, 127 is obtained, corresponding to the basic bus clamping strategy BBCS and the basic bus clamping strategy BBCS II. If a sampling point of the sector is set at the starting boundary of the sector, a switching sequence of 010 and 101 is obtained, and the other sampling points are the same as BBCS, then the boundary sampling strategy BSS and the boundary sampling strategy SS II are obtained.

4. A standard subway permanent magnet traction converter control method according to claim 1, characterized in that: The step 4 of re-casting with speed specifically comprises the following steps: After the vehicle enters the power-free zone, the system controls the contactor between the inverter and the motor to be disconnected. Before entering the power-on zone again, the system controls the contactor to be closed. At this time, the motor current is zero, and the q-axis voltage is established according to formula 1.9; the d-axis voltage is established according to the relationship between the current angular velocity and the rated angular velocity: Among them, w s is the electrical angular frequency of the motor converted from the current vehicle speed, w s_rate The electrical angular frequency at the rated speed of the motor After entering the energized area, before controlling the closing contactor, press u d As the phase adjustment amount, u q As the back-EMF tracking quantity, the inverter output voltage vector is first controlled and then the contactor is closed.

5. A standard subway permanent magnet traction converter control method according to claim 1, characterized in that: The step 5 single current closed-loop control specifically comprises the following steps: Define δ as the angle between the motor voltage vector and the positive direction of the d-axis, then the d and q axis voltages are expressed as: The relationship between torque and voltage phase angle is derived as: For a limited speed system, the voltage phase angle ranges in traction and braking conditions are (π / 2, π) and (0, π / 2), respectively. Under no-load conditions, δ is π / 2. For an infinite speed system, the effective range of the voltage phase angle is not (0, π). The output torque is controlled by controlling the voltage phase angle. When based on voltage phase angle control, the relationship between d, q axis current and voltage phase angle δ is: From formula 2.6, it can be seen that in the traction or braking state, both id and iq have a monotonic relationship with δ, and it is considered to use id or iq current regulator to adjust the phase angle; It can be seen from formula (2.6) that when only a single state of traction or braking is considered, the direct-axis voltage or quadrature-axis voltage under square wave conditions has a monotonic relationship with the voltage phase angle; as long as the direct-axis voltage or quadrature-axis voltage is determined, the voltage phase angle will also be uniquely determined; and the voltage phase angle has a monotonic relationship with the motor torque, and the direct-axis voltage or quadrature-axis voltage also has a monotonic relationship with the torque; the voltage phase angle is indirectly adjusted by adjusting the direct-axis voltage or quadrature-axis voltage; when a single d-axis current closed-loop control is used, the monotonic relationship between the torque and the voltage phase angle is different in the traction and braking conditions, and needs to be processed separately, while when a single q-axis current closed-loop control is used, the monotonic relationship between the torque and the voltage phase angle in the traction and braking conditions is consistent, and does not need to be processed separately; the single q-axis current regulation method is used; The switching between the single q-axis current loop and the dual current loop is to switch into the single current loop when the inverter output voltage is greater than a certain voltage switching point and the motor speed is greater than a certain speed switching point, and to exit the single current loop otherwise. A certain hysteresis loop area is set for the voltage switching point and speed switching point for entering and exiting; the voltage switching point is selected according to the voltage limit of the current operating condition; the speed switching point is selected according to the speed when the voltage circular curve is completely in the left half of the dq-axis plane under the rated voltage.

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