CN117375465B

CN117375465B - Busbar boosting control method for neutral point power supply permanent magnet synchronous motor

Info

Publication number: CN117375465B
Application number: CN202311324857.4A
Authority: CN
Inventors: 王大方; 李琪; 郭鹏; 金毅; 张昱瑾; 许彭斌; 方淇; 廖前洋
Original assignee: Weihai Tianda Automobile Technology Co ltd; Harbin Institute of Technology Weihai
Current assignee: Weihai Tianda Automobile Technology Co ltd; Harbin Institute of Technology Weihai
Priority date: 2023-10-13
Filing date: 2023-10-13
Publication date: 2024-06-11
Anticipated expiration: 2043-10-13
Also published as: CN117375465A

Abstract

The application provides a neutral point power supply permanent magnet synchronous motor bus boosting control method, which comprises the following steps: establishing an equivalent system model of the permanent magnet synchronous motor under a neutral point power supply topological structure, wherein the equivalent system model comprises an equivalent Boost circuit and an inverter; determining a driving-boosting control strategy and a bus voltage dynamic regulation strategy for the inverter based on the equivalent system model; and performing driving-boosting control on the inverter by using the driving-boosting control strategy, and performing dynamic adjustment on the DC bus voltage of the inverter by using the bus voltage dynamic adjustment strategy. The control method provided by the application provides a detailed and feasible driving-boosting control scheme aiming at the neutral point power supply topological structure, and combines the actual working condition of the motor to dynamically adjust the bus voltage, so that the system loss can be effectively reduced on the basis of ensuring the stable operation of the motor.

Description

Busbar boosting control method for neutral point power supply permanent magnet synchronous motor

Technical Field

The application belongs to the technical field of motor control, and further relates to a permanent magnet synchronous motor control technology, in particular to a neutral point power supply permanent magnet synchronous motor bus boosting control method.

Background

In order to effectively shorten the charging time and relieve the mileage focus of a user, at present, vehicle enterprises at home and abroad have all started to lay out an 800V high-voltage platform of an electric vehicle, wherein, the power supply is led out from a neutral point of a motor, which is a novel topological structure provided for the application of the high-voltage platform of the electric vehicle, and the structure connects a power supply between the neutral point of a three-phase permanent magnet synchronous motor and a negative electrode of a direct current bus, and utilizes the neutral point to supply power, so that an inverter and a motor winding can be multiplexed to realize the boosting function, and the capability of improving and regulating the voltage of the direct current bus can be realized under the condition of not increasing components and parts, which is equivalent to saving a real DC/DC converter. For example, in practical application, a 400V power battery can be adopted, a neutral point power supply structure is utilized to boost to 800V bus voltage, a 400V matching is still adopted for the high-voltage accessory, a local 800V framework is formed, the advantages of high power and high efficiency of the 800V electric drive system can be fully exerted, and meanwhile, the matching cost of the high-voltage accessory is saved; in addition, bus voltage can be regulated in real time by utilizing the equivalent DC/DC converter function, so that the loss of a power switch is reduced, the voltage utilization rate is improved, and the cost and the volume of the system are reduced.

The technical problems faced in applying the neutral point power supply topology structure to the field of electric automobiles include the following aspects: firstly, a topological structure of neutral point power supply needs to give consideration to drive control of a motor and boost control of an equivalent DC/DC converter in the control process, but a detailed and feasible control scheme is not proposed at present; secondly, the neutral point power supply topological structure is used for boosting, the problem of limited boosting range exists, and for the problem, a mechanism for simultaneously utilizing two neutral point motors or adding a small-sized boosting converter is adopted for improvement, but the application range of the structure is limited, and meanwhile, the boosting converter is added, so that the advantages of the basic structure in terms of cost and volume are reduced, and the practicability of the current stage is smaller; in addition, higher bus voltages may cause higher power switching losses in the inverter, especially under light load conditions, which may be more pronounced for high voltage platforms.

Disclosure of Invention

The application aims to provide a neutral point power supply permanent magnet synchronous motor bus boosting control method for solving the problems in the prior art.

The application provides a neutral point power supply permanent magnet synchronous motor bus boosting control method, which comprises the following steps:

S100, establishing an equivalent system model of the permanent magnet synchronous motor under a neutral point power supply topological structure, wherein the equivalent system model comprises an equivalent Boost circuit and an inverter;

s200, determining a driving-boosting control strategy and a bus voltage dynamic regulation strategy for an inverter based on the equivalent system model;

S300, performing driving-boosting control on the inverter by using the driving-boosting control strategy, and dynamically adjusting the DC bus voltage of the inverter by using the bus voltage dynamic adjustment strategy.

Further, the equivalent Boost circuit boosts the power supply voltage to the DC bus voltage of the inverter through an equivalent inductor and an equivalent power switch; the direct-current bus voltage is converted into three-phase voltage of the permanent magnet synchronous motor through an inverter; the neutral point of the three phase line of the permanent magnet synchronous motor is led out, and a power supply is connected between the neutral point and the negative electrode of the direct current bus.

Further, the equivalent system model is built by the following steps:

S110, regarding the inverter as an ideal inverter, ignoring the voltage drop and dead time of a switching tube, and obtaining a voltage expression of a neutral point power supply topological structure under a A, B, C three-phase static coordinate system as shown in the following formula:

Wherein u _AO、u_BO、u_CO is the three-phase terminal voltage output by the inverter, u _AN、u_BN、u_CN is the three-phase voltage of the motor, alpha _A、α_B、α_C is the duty ratio of the three-phase upper switch of the inverter, u _dc is the direct current bus voltage of the inverter, and u _in is the power supply voltage;

s120, performing dq0 axis rotation transformation on the voltage expression under the A, B, C three-phase static coordinate system to obtain the voltage expression of the neutral point power supply topological structure under the dq0 axis coordinate system, wherein the voltage expression is shown in the following formula:

Wherein u _dO、u_qO、u_0O is the equivalent terminal voltage output by the inverter under the dq0 axis coordinate system, u _d、u_q、u₀ is the d axis, q axis and 0 axis voltages of the motor under the dq0 axis coordinate system, alpha _d、α_q、α₀ is the equivalent duty ratio of the inverter under the dq0 axis coordinate system, and the equivalent system of the neutral point power supply topological structure after the dq0 axis rotation transformation meets the following formula;

Wherein i ₀ is the 0-axis current in the dq 0-axis coordinate system;

s130, substituting a motor voltage equation into a voltage expression of the neutral point power supply topological structure in the dq0 axis coordinate system to obtain an equivalent system model of the neutral point power supply topological structure shown in the following formula:

wherein i _d、i_q is the d-axis current and q-axis current in the dq 0-axis coordinate system, ω _e、R_s is the rotor electric angular velocity and stator resistance of the motor, L _d、L_q、L₀ is the d-axis component, q-axis component and 0-axis component of the inductance of the motor, and ψ _f is the permanent magnet flux linkage.

Preferably, the drive-boost control strategy includes a drive control strategy and a boost control strategy for an inverter; the driving control strategy is executed by a driving controller based on an internal model decoupling control mode; the boost control strategy is performed by a current-voltage dual closed loop controller.

Further, d-axis proportional gain K _{p_d}, d-axis integral gain K _{i_d}, q-axis proportional gain K _{p_q}, q-axis integral gain K _{i_q} of the drive controller are determined by:

Where α is the drive controller coefficient.

Further, the inner loop of the dual closed loop controller is a current controller, and the proportional gain K _{p_i} and the integral gain K _{i_i} are:

Wherein T ₀ is the inner loop closed loop time constant;

The control outer loop of the double closed loop controller is a voltage controller, and the proportional gain K _{p_v} and the integral gain K _{i_v} of the voltage controller are determined based on the design index of the equivalent system.

Further, the design index is the expected crossing frequency f _c and the phase angle margin PM of the equivalent system, and the proportional gain K _{p_v} and the integral gain K _{i_v} of the voltage controller are determined by:

In a first step, a transfer function G _iv(s) of i _N to u _dc is established as shown in the following formula:

S is complex variable of Law transformation, i _N is inductance current at neutral point, C is capacitance value of DC bus capacitor;

second, an open loop transfer function G ₂(s) of the equivalent system is established as shown in the following formula:

Wherein, H ₁(s)＝T₀ s+1, which is the transfer function of the voltage controller;

Third, determining the expected crossing frequency f _c and the phase angle margin PM of the equivalent system, and solving the equation set shown in the following formula to determine K _{p_v}、K_{i_v}:

Further, the bus voltage dynamic adjustment strategy is determined based on the following steps:

S210, acquiring the relation between u _dc and u _in under a steady-state working condition based on the equivalent system model:

s220, changing a voltage equation under a neutral point power supply topological structure into the following formula:

α_ku_dc＝u_kN+u_in，

Wherein k=a, B, C, α _k is the duty ratio of the upper switch of each phase of the inverter, u _kN is the phase voltage of each phase of the permanent magnet synchronous motor;

s230, determining constraint conditions of phase voltage of the permanent magnet synchronous motor under the steady-state working condition as shown in the following formula based on the relationship between u _dc and u _in under the steady-state working condition in the value range of alpha _k:

S240, determining the following bus voltage dynamic regulation strategy based on the constraint conditions:

When the permanent magnet synchronous motor works under the heavy load working condition, alpha ₀ =0.5 is kept so as to keep the voltage of the direct current bus of the inverter at 2u _in,

When the permanent magnet synchronous motor works under the light load working condition, alpha ₀ is adjusted according to the actual working condition, so that the direct current bus voltage of the inverter is dynamically adjusted within the range of [ u _in,2u_in ].

Further, the adjusting α ₀ according to the actual working condition specifically includes:

determining the extra copper loss P _col of the permanent magnet synchronous motor under the neutral point power supply topological structure based on the following steps:

the switching loss P _sw1 of a power device of the permanent magnet synchronous motor under the neutral point power supply topological structure is determined based on the following steps:

wherein, I ₁、U_dc1 is the load current and the DC bus voltage of the switching tube under the neutral point power supply topological structure, and t _on、t_off、f、C_oss is the on time, the off time, the switching frequency and the parasitic output capacitance of the switching tube;

the real-time value of alpha ₀ is determined based on the additional copper loss P _col and the switching loss P _sw of the permanent magnet synchronous motor under real-time working conditions.

Further, the driving-boosting control strategy is used for driving-boosting control of the inverter, specifically, driving control and boosting control are performed on the DC bus of the inverter based on the following steps:

Wherein, Is the target value of the DC bus voltage of the inverter,/>Target voltages for dq-axis drive control of inverter DC bus are respectively,/>And K is a calibration coefficient for the target voltage for performing 0-axis boost control on the DC bus of the inverter.

According to the busbar boosting control method for the neutral point power supply permanent magnet synchronous motor, provided by the embodiment of the application, the equivalent model is built based on the characteristics of the neutral point power supply topological structure, a detailed and feasible driving-boosting control strategy is built through analysis of the equivalent model, and the voltage of the motor can be effectively boosted by utilizing the topological structure led out by the neutral point on the basis of not increasing a boosting device; meanwhile, the boosting characteristic aiming at the neutral point power supply topological structure is established as a busbar boosting dynamic regulation strategy, and the boosting amplitude is reasonably regulated according to the actual working condition of the motor, so that the optimal improvement of the motor efficiency under each working condition is realized.

Drawings

Fig. 1 is a flowchart of a method for controlling boosting of a busbar of a permanent magnet synchronous motor for neutral point power supply according to an embodiment of the present application;

FIG. 2 is an architecture diagram of an equivalent system model of a neutral point power topology in accordance with an embodiment of the present application;

FIG. 3 is a schematic diagram of system drive-boost control of a permanent magnet synchronous motor according to an embodiment of the present application;

Fig. 4 is a phase voltage output waveform when α ₀ =0.5 according to an embodiment of the present application;

FIG. 5 is a phase voltage output waveform at 0.5< alpha ₀ +.1 according to an embodiment of the present application;

FIG. 6 is a phase voltage output waveform at 0.ltoreq.alpha ₀ <0.5 according to an embodiment of the present application;

FIG. 7 is a functional block diagram of a bus voltage dynamic adjustment algorithm according to an embodiment of the present application;

FIG. 8 is a boost control experimental image of a motor under steady state conditions according to example 1 of the present application;

FIG. 9 is an experimental image of dynamic adjustment of bus voltage according to example 1 of the present application;

FIG. 10 is a comparison of total loss of the system according to example 1 of the present application;

fig. 11 is a system total loss reduction ratio according to embodiment 1 of the present application.

Detailed Description

The present application will be further described below based on preferred embodiments with reference to the accompanying drawings.

The terminology used in the description presented herein is for the purpose of describing embodiments of the application and is not intended to be limiting of the application. It should also be noted that unless explicitly stated or limited otherwise, the terms "disposed," "connected," and "connected" should be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; the two components can be connected mechanically, directly or indirectly through an intermediate medium, and can be communicated internally. The specific meaning of the above terms in the present application will be specifically understood by those skilled in the art.

As described in the background art, when the permanent magnet synchronous motor is powered by adopting the neutral point power supply topology structure, the neutral point of the three-phase permanent magnet synchronous motor with the star-shaped windings is led out, a power supply is connected between the neutral point of the motor and the negative electrode of the direct current bus, and the neutral point is used for power supply so as to multiplex the inverter and the windings of the motor to realize driving and boosting. Therefore, the control of the motor system adopting the neutral point power supply topological structure for power supply simultaneously comprises motor driving control and boosting control, and in addition, the boosting range is required to be adjusted according to the actual working condition so as to avoid that the bus voltage after boosting exceeds the stable control range.

To solve the above-mentioned problems, the present application provides a control method for boosting a busbar of a permanent magnet synchronous motor with power supplied by a neutral point, and fig. 1 shows a flowchart of the control method in some embodiments, and as shown in fig. 1, the method includes the following steps:

The following describes steps S100 to S300 in detail with reference to the drawings and the specific embodiments.

< Modeling of equivalent System model under neutral Point Power topology >.

In order to realize the control of the motor system adopting the neutral point power supply mode, firstly, an equivalent system model of the synchronous motor under the neutral point power supply topological structure is established through a step S100, and in some specific embodiments, the modeling process of the equivalent system comprises the following steps:

Wherein u _AO、u_BO、u_CO is the three-phase terminal voltage output by the inverter, u _AN、u_BN、u_CN is the three-phase voltage of the motor, alpha _A、α_B、α_C is the duty ratio of the three-phase upper switch of the inverter, u _dc is the direct current bus voltage of the inverter, and u _in is the power supply voltage.

Wherein i ₀ is the 0-axis current in the dq 0-axis coordinate system;

< Analysis of equivalent System model >

After an equivalent system model under the neutral point power supply topological structure is established through the formula (4), the composition of the equivalent system model is further analyzed to determine what control strategy needs to be adopted for the motor.

First, as is clear from the expression (4), the d and q axis models critical to the motor driving control in the equivalent system model are not changed, so that the motor can still be driven by the conventional vector control method.

Next, the 0-axis portion in the equivalent system model was analyzed, and as shown in equation (4), the zero-axis voltage component of the system is as follows:

according to kirchhoff's current law, at neutral point N there is:

i_A+i_B+i_C+i_N＝0 (6)，

substituting the formula (6) into the formula (3) to obtain:

substituting the formula (7) into the formula (5) to obtain:

When the system is operating at steady state, the pressure drop across R _s and L ₀ can be ignored, and the following can be obtained:

Namely: the zero-axis component of the system is an equivalent Boost converter, and as can be seen from the formula (3) and the formula (9), alpha ₀ is the average duty ratio of the three-phase upper switch of the inverter A, B, C, and alpha ₀ is more than or equal to 0 and less than or equal to 1, so that u _dc≥u_in can be obtained, namely, the input voltage u _in of the system is boosted to the direct-current bus voltage u _dc,α₀ through the equivalent Boost converter, namely, the Boost duty ratio of the equivalent Boost converter, and the real-time Boost control of the direct-current bus voltage u _dc of the inverter can be realized through the closed-loop control of alpha ₀.

Based on the analysis of the equivalent system model, a topological diagram of the equivalent system model under the neutral point power supply topological structure shown in fig. 2 can be established, the left side in fig. 2 is a zero axis component, namely an equivalent Boost circuit, the power supply voltage u _in is boosted to an equivalent direct current bus voltage u _dc through an equivalent inductor L ₀/3 and an equivalent power switch S ₀, and then the inverter supplies power to the permanent magnet synchronous motor, so that the driving of the permanent magnet synchronous motor is realized.

In addition, under the neutral point power supply topological structure, the power supply voltage u _in is converted into the phase voltage of the permanent magnet synchronous motor by the inverter after being boosted, so that whether the boosted phase voltage meets the stable operation condition or not is also required to be considered, in addition, although the boosting drive can exert the advantages of high power and high efficiency when the motor is in a heavy load working condition, the motor does not need such high bus voltage when in a light load working condition, the higher bus voltage can cause higher power switching loss of the inverter, and the switching loss under the light load is more prominent for a high-voltage platform, so that the boosting amplitude is reasonably adjusted according to the actual working condition of the motor.

From the above analysis, in order to well control the permanent magnet synchronous motor using the neutral point for power supply, a driving-boosting control strategy for driving-boosting control of the inverter and a bus voltage dynamic adjustment strategy for dynamically adjusting the dc bus voltage of the inverter should be determined, respectively.

In the embodiment of the present application, the control strategy is obtained through step S200, and then the control strategy is executed through step S300 to realize the control of the permanent magnet synchronous motor.

The generation and execution steps of each control strategy are described in detail below.

< Determination of drive-boost control strategy >

The determination process of the drive-Boost control strategy, i.e., the process of designing a PI controller that enables the permanent magnet synchronous motor to track the command voltage in real time, is performed in step S200 in the embodiment of the present application, fig. 3 shows a schematic diagram of drive-Boost control of the permanent magnet synchronous motor employing a neutral point power supply structure in some preferred embodiments, as analyzed above, in which the dq-axis model for the motor drive control section is the same as that of the conventional three-phase permanent magnet synchronous motor, while the 0-axis model of Boost control is the same as that of the conventional Boost converter, and the two are decoupled from each other, and can be independently controlled,

Therefore, in the driving control part, a vector control method of a motor under a traditional structure can be adopted, a driving controller is adopted to execute a driving control strategy, and a control mode of internal mold decoupling is adopted to optimize the control effect, so that command voltage u _d*、u_q of the dq axis is obtained; in the Boost control part, a Boost circuit design method can be adopted, and a voltage-current double-closed-loop controller is adopted to execute a Boost control strategy, so that the command voltage u ₀ of the 0 axis is obtained. After u _d*,u_q*,u₀ is obtained, the three-phase command voltage u _A、u*_B、u*_C is obtained through coordinate transformation, and PWM signals are generated by comparing the three-phase command voltage with carrier signals, so that command integration of drive control and boost control is realized, and boost control is realized at the same time of drive control.

In some specific embodiments, the driving controller, the boost controller, and the driving-boost control strategy implemented by the driving controller and the boost controller may be implemented into a DSP or other device for operation by an executable program, and the implementation manner of the control strategy is known to those skilled in the art and will not be described herein.

A. and determining control parameters of the driving controller.

As shown in fig. 3, in the embodiment of the present application, as described above, the driving controller may use a PI controller to respectively drive and control the d axis and the q axis in a control manner of internal mold decoupling, so that the internal mold decoupling has relatively low requirements on the motor model, and has better robustness, and meanwhile, the parameter setting work of the PI controller can be greatly simplified based on the internal mold control.

In some specific embodiments, the parameters of the driving controller include d-axis proportional gain K _{p_d}, d-axis integral gain K _{i_d}, q-axis proportional gain K _{p_q}, and q-axis integral gain K _{i_q}, and the parameter values thereof may be determined by the following formula:

Where α is the drive controller coefficient.

B. and determining control parameters of the boost controller.

As shown in fig. 3, in the embodiment of the present application, the boost controller adopts a voltage-current dual closed-loop controller, and an inner loop of the dual closed-loop controller is a current controller, so as to control an inner loop of the inductor current; the outer ring is a voltage controller, the capacitor voltage is used as a control outer ring, and both the voltage controller and the control outer ring adopt the form of a PI controller. The error between the command voltage u× _dc and the actual voltage u _dc is controlled by a current controller to obtain a command value i× _N of neutral line current, i.e. inductance current, and the command value i× ₀,i*₀ of 0-axis current and the error value of the actual 0-axis current i ₀ are transformed by coordinates to obtain a command value u× ₀,u*₀ of 0-axis voltage by a voltage controller, i.e. the command voltage for boost control.

In the embodiment of the application, the proportional gain K _{p_i} and the integral gain K _{i_i} of the current controller can be determined by giving the current loop closed-loop time constant T ₀:

In an embodiment of the present application, the proportional gain K _{p_v} and the integral gain K _{i_v} of the voltage controller may be determined based on the design index of the equivalent system by:

Firstly, according to a small signal model analysis method of a general Boost conversion circuit, a transfer function G _iv(s) from i _N to u _dc shown in the following formula is obtained:

Next, an open loop transfer function G ₂(s) of the equivalent system shown by the following formula is established:

Then, determining design metrics for the equivalent system, which in some preferred embodiments include the expected crossover frequency f _c and the phase angle margin PM for the equivalent system;

Finally, the equations shown in the following are combined and solved to determine K _{p_v}、K_{i_v}:

< execution of drive-boost strategy >

In the embodiment of the present application, the control of the permanent magnet synchronous motor is performed through step S300, specifically, as shown in fig. 3, the driving-boosting control of the permanent magnet synchronous motor is performed, that is, the required command bus voltage is designed according to the current working condition of the permanent magnet synchronous motor, and then the driving-boosting strategy is performed through the driving controller and the boosting controller, so that the dc bus voltage of the inverter can track the command bus voltage in real time.

According to the formula (7), to determine the dc bus voltage u _dc, the dq0 axis equivalent terminal voltage u _dO、u_qO、u_0O output by the current inverter needs to be determined, and then the dq0 axis voltage u _d、u_q、u₀ corresponding to the current working condition of the permanent magnet synchronous motor needs to be obtained. Because the actual dq0 axis voltage is inconvenient to directly acquire in the actual motor control process, the actual voltage is replaced by the target dq0 axis voltage for calculation.

According to the vector synthesis principle, the dq axis voltage component is synthesized into the bus voltage required by drive control, and according to coordinate transformation, the bus voltage required by the current working condition of the system is obtained after the 0 axis voltage component is superimposed on the bus voltage required by drive, and then the target value of the bus voltage can be expressed as:

Wherein, For the bus voltage target value required by the current operation condition of the system,/>And respectively obtaining the dq0 axis target terminal voltage corresponding to the current operation condition.

According to the drive-boost control algorithm, the target voltage u ^* _d、u^* _q required by dq-axis drive control and the target voltage u ^* ₀ required by 0-axis boost control under the current working condition of the permanent magnet synchronous motor can be obtained, so that the following steps are obtained:

Substituting the formula (16) into the formula (15) can obtain:

(17) Where u ^* _d、u^* _q is a control signal output by the driving controller, and there is a certain disturbance in the actual driving condition of the motor, and these disturbances are further amplified in equation (17), so in some preferred embodiments, a Low-pass filter (Low-PASS FILTER, LPF) may be used to filter the bus voltage required for driving control, and the output result after filtering is further calculated to obtain the target value of the command bus voltage, where the cut-off frequency of the Low-pass filter may be designed according to the fundamental frequency of the system.

In practical application, in order to meet the voltage requirements under transient conditions such as abrupt torque change and other specific conditions in the motor driving process, a certain margin needs to be left on the basis of the target value of the dc bus voltage, so in some preferred embodiments, the target value of the dc bus voltage is determined by the following formula:

The calibration coefficient which is set for ensuring that the voltage of the direct current bus meets the allowance can be selected according to actual requirements and K is more than or equal to 1.

< Determination and execution of bus Voltage dynamic Regulation strategy >

According to analysis of an equivalent system model, the power supply voltage u _in can be boosted under the neutral point power supply topological structure, so that the following factors are required to be considered in the actual operation process: 1) The phase voltage after boosting meets the stable operation condition to avoid that the voltage boosting is too high to cause the stable control, 2) the motor does not need higher bus voltage under specific working conditions (for example, the motor runs under light load working conditions), and if the higher bus voltage is maintained, the higher power switching loss of the inverter is caused. Obviously, the target bus voltage value is designed according to the actual working condition of the motor and automatically adjusted to the ideal bus voltage, so that the loss of the power switch is reduced, the efficiency of the electric drive system is improved, and the driving range of the automobile is further improved.

For this reason, in the embodiment of the present application, step S200 further determines a bus voltage dynamic adjustment strategy in addition to the above-described driving-boosting control strategy, and dynamically adjusts the dc bus voltage of the inverter through step S300.

In an embodiment of the application, the bus voltage dynamic regulation strategy is determined by:

Because alpha ₀ is more than or equal to 0 and less than or equal to 1, the bus voltage can be theoretically boosted from the power voltage u _in to infinity, but in practical application, the inverter is required to output the voltage required by the stable operation of the motor while boosting; on the other hand, increasing the bus voltage to an unnecessary level results in higher switching losses of the power device. It is therefore necessary to determine the appropriate voltage regulation range by means of model analysis.

α_ku_dc＝u_kN+u_in (20)，

Where k=a, B, C, α _k is the duty cycle of the upper switch of each phase of the inverter, and u _kN is the phase voltage of each phase of the permanent magnet synchronous motor.

Further obtainable by formula (20):

Since 0.ltoreq.alpha _k.ltoreq.1, the following applies:

Further transformation can obtain that when the step-up ratio is alpha ₀, the motor phase voltage range which can be output by the system meets the following conditions:

-α₀u_dc≤u_kN≤(1-α₀)u_dc (23)，

Considering the relationship between u _dc and u _in under the steady-state condition shown in the formula (9), the constraint condition of the permanent magnet synchronous motor phase voltage under the steady-state condition shown in the following formula is finally determined in step S230:

Analyzing the motor phase voltage which can be output by the system based on (24):

in the first case, if α ₀ =0.5, i.e. u _dc＝2u_in:

-u_in≤u_kN≤u_in (25)，

at this time, the motor phase voltage u _kN which can be output by the system is a symmetrical sine wave with the amplitude smaller than or equal to u _in, as shown in fig. 4, that is, the motor can stably run within the range of the phase voltage + -u _in.

In the second case, if 0.5 < alpha ₀.ltoreq.1, i.e. u _in≤u_dc＜2u_in:

Due to Then/>The output of u _kN at this time is shown in fig. 5 according to equation (24).

Since the motor phase voltage u _kN is required to be a symmetrical sine wave, stable output can be achieved only when u _kN is within the range of ± (1- α ₀)/α₀·u_in), and when the amplitude of u _kN is greater than (1- α ₀)/α₀·u_in), output can be achieved in the negative half cycle, but an overmodulation phenomenon occurs near the peak of the positive half cycle, at which time stable control of the motor is not possible.

According to the designed bus voltage dynamic regulation algorithm, the bus voltage required by the current working condition of the motor is (1-alpha ₀)/α₀·u_in, and the amplitude cannot exceed u _in), so that stable voltage output of a positive half cycle and a negative half cycle can be realized.

In the third case, if 0.ltoreq.α ₀ < 0.5, i.e. u _dc＞2u_in:

Due to Then/>The output of u _kN at this time is shown in fig. 6 according to equation (24).

Since the motor phase voltage u _kN is required to be a symmetrical sine wave, stable output can be realized only when u _kN is within the range of + -u _in, when the amplitude of u _kN is larger than u _in, output can be realized in a positive half cycle, an overmodulation phenomenon can occur near the peak value of a negative half cycle, and stable control of the motor cannot be performed. Therefore, in the process of dynamically adjusting the bus voltage, when the voltage boosting instruction of the system, namely the bus voltage required by the current working condition of the motor, exceeds twice u _in, stable control cannot be performed, and at the moment, the higher bus voltage also brings more power device loss, so that the boosting range is not taken in practical application.

Through the above analysis, the following bus voltage dynamic adjustment strategy is finally determined in step 240 based on the constraint condition shown in equation (24):

In some preferred embodiments of the present application, the adjustment of α ₀ according to the actual condition may be performed based on loss analysis during the drive-boost control of the motor, specifically:

firstly, determining the extra copper loss P _col of the permanent magnet synchronous motor under a neutral point power supply topological structure based on the following steps:

And secondly, determining the switching loss P _sw1 of the power device of the permanent magnet synchronous motor under the neutral point power supply topological structure.

Because the switching process of the power device is complex, the accurate loss modeling of the power device is complex, and parameters in the switching process of the power device are usually measured by matching with an experimental platform such as double pulses in the actual use process. In order to simplify the analysis process, in the embodiment of the application, a loss formula after linearizing the switching process is adopted, and the switching loss of a single switching tube can be expressed as:

Wherein, I _D、V_D is the load current and DC bus voltage of the switching tube, and t _on、t_off、f、C_oss is the on time, off time, switching frequency and parasitic output capacitance of the switching tube.

Considering the number of switching tubes in the system, the switching loss P _sw1 of the power device under the neutral point power supply topology structure can be expressed as:

I ₁、U_dc1 is the load current and the DC bus voltage of the switching tube under the neutral point power supply topological structure respectively.

Finally, an objective optimization function can be established by adopting the extra copper loss P _col and the switching loss P _sw1 as parameters, and the real-time value of alpha ₀ is determined by taking the system loss optimization as an objective, so that a strategy for dynamically adjusting the bus voltage under the light load working condition is obtained.

After the bus voltage dynamic regulation strategy is obtained through the steps, the method can be combined with the driving-boosting control strategy in the step S300, and the target value of the DC bus voltage of the inverter is regulated in real time according to the actual working condition, so that the efficiency of an electric driving system is improved, the system loss is reduced, and the driving range of an automobile is further improved. Fig. 7 shows a schematic diagram of an implementation of bus voltage dynamic regulation and drive-boost for a permanent magnet synchronous motor according to an embodiment of the application.

Example 1.

In the embodiment, a 2kW motor is built by adopting a neutral point power supply topological structure and a conventional power supply structure to carry out experiments on a towing platform, wherein the motor is controlled by adopting the neutral point power supply permanent magnet synchronous motor bus boosting control method provided by the application.

The motor pair-towing bench used for experiments mainly comprises a load motor, a driving motor, a cast iron bottom plate, a torque sensor and a coupler. The driving motor is an open winding double three-phase permanent magnet synchronous motor, only one group of three-phase windings is used, and three wiring ends at one end of the windings are connected together and can be led out as a neutral point. In the opposite dragging experiment, a driving motor adopts a torque control mode, and a load motor adopts a rotating speed control mode. The parameters of the driving motor obtained by calibration are shown in table 1:

Table 1 drive motor parameter table

Parameters (parameters)	Sign symbol	Numerical value	Unit (B)
				Polar logarithm	p₀	5	-
Stator resistor	R_s	0.328	Ω
				D-axis inductor	L_d	1.13	mH
Q-axis inductor	L_q	1.13	mH
				0-Axis inductor	L₀	0.75	mH
Permanent magnet flux linkage	ψ_f	0.0825	Wb
				Rated voltage	U_AC	220	V
Rated power	P_N	2000	W
				Rated torque	T_N	9.55	N·m
Rated rotational speed	n_N	2000	r/min

The controller parameters are shown in table 2:

Table 2 controller parameter table

Parameters (parameters)	Sign symbol	Numerical value	Unit (B)
				Switching frequency	f_s	10	kHz
Control period	T_s	100	μs
				Bus capacitor	C	500	μF

FIG. 8 shows a boost control experimental image of a motor under a steady-state working condition, wherein the motor load rotating speed is 100r/min, the bus voltage is set to be 120V, the electromagnetic torque is 3 N.m, and as can be seen from the figure, the bus voltage can be kept to be stably boosted under the steady-state working condition of the motor, and the bus voltage is subject to fluctuation of +/-5V and belongs to an acceptable fluctuation range; meanwhile, the electromagnetic torque can be stably output, the torque is +/-0.2N.m fluctuation, the fluctuation is small, the dq axis current can be accurately tracked, the simulation waveform in fig. 9 is verified, and the effectiveness of a designed boost control algorithm under a steady-state working condition is proved.

As shown in fig. 9, which is an experimental image of dynamic adjustment of the bus voltage, the motor torque was set to 2n·m at the beginning, the motor was accelerated to 500r/min from 2.5 seconds to 2.6 seconds, and after the motor was held for 6.8 seconds, the motor was decelerated back to 200r/min from 6.8 seconds to 6.9 seconds, during which the motor torque was kept constant at 2n·m. Before 0.03 seconds, the command bus voltage is about 82V, when the motor is accelerated for 2.5 to 2.6 seconds, the command bus voltage is gradually increased from 82V to about 97V, and when the motor is decelerated for 6.8 to 6.9 seconds, the command bus voltage is reduced to 82V; after that, the motor command torque is raised from 2 N.m to 5 N.m for 16.5 seconds and then adjusted back to 2 N.m, and the motor rotation speed is kept unchanged at 200r/min during 13.2 seconds, and it can be seen that the command bus voltage is also raised slightly from 82V to 84V when the torque is raised for 13.2 seconds, the actual bus voltage is lowered slightly from about 3V and then raised to the command bus voltage, and the motor rotation speed is adjusted back to 82V when the torque is lowered for 13.2 seconds. In the whole process, the actual bus voltage well tracks the command bus voltage, and the motor can ensure stable torque output.

For comparison with a conventional power supply structure, in this embodiment, a motor is built by using the conventional power supply structure to perform an experiment on the towing platform, and a conventional control method is used to control the towing platform.

In the experiment, the bus voltage under the traditional power supply structure is 120V, the power supply voltage under the neutral point power supply structure is 60V, the bus voltage is dynamically regulated in a boosting way, the load rotating speed is regulated between 20r/min and 500r/min, and the command torque is regulated between 1 N.m and 10 N.m. In order to further compare the effect of dynamic adjustment of the bus voltage on reducing the system loss, the power supply voltage is set to be 60V, the bus voltage is fixedly boosted to be 120V, the total system loss under each working condition point is recorded through experiments, and compared with the standard structure and the total system loss of dynamic adjustment of the bus voltage, loss images are shown in fig. 10, and the corresponding loss reduction ratio is shown in fig. 11 for example.

As can be seen from fig. 10 and 11, in the power interval of 2.09W to 523.56W, the total loss of the system after the bus voltage is dynamically regulated under the neutral point power supply structure is lower than that of the standard power supply structure, and the effect of reducing the loss is more obvious when the system power is smaller, and the loss is reduced to 69.09% under the working conditions of 20r/min and 1n·m; with the gradual rise of the motor power, the loss of the dynamic adjustment busbar voltage of the neutral point power supply mechanism gradually approaches the standard power supply mechanism, and the proportion of loss reduction is smaller and smaller.

In addition, as can be seen from fig. 10 and 11, after the system power gradually rises, the total loss of the system with the fixed twice boost voltage exceeds the standard power supply structure, which is caused by the increased copper loss of the neutral line, and the total loss of the system is the lowest under the same working condition by reducing the switching loss of the power device, and under the working condition of 500r/min and 10n·m, the designed dynamic regulating bus voltage algorithm reduces the loss of the system to 6.64% compared with the standard power supply structure, and the fixed twice bus voltage is increased by 14.98% compared with the standard power supply structure, which further verifies that the adoption of the bus voltage dynamic regulating algorithm under the neutral point power supply structure can reduce the loss of the electric drive system, improve the system efficiency and have practical application value.

While the foregoing is directed to embodiments of the present application, other and further embodiments of the application may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. The busbar boosting control method for the neutral point power supply permanent magnet synchronous motor is characterized by comprising the following steps of:

s300, performing driving-boosting control on the inverter by using the driving-boosting control strategy, and dynamically adjusting the DC bus voltage of the inverter by using the bus voltage dynamic adjustment strategy;

the equivalent Boost circuit boosts the power supply voltage to the DC bus voltage of the inverter through an equivalent inductor and an equivalent power switch;

the direct-current bus voltage is converted into three-phase voltage of the permanent magnet synchronous motor through an inverter;

the neutral point of the three phase line of the permanent magnet synchronous motor is led out, and a power supply is connected between the neutral point and the negative electrode of the direct current bus;

the equivalent system model is established by the following steps:

Wherein i ₀ is 0-axis current under dq 0-axis coordinate system, and i _A、i_B、i_C is A, B, C three-phase current respectively;

Wherein i _d、i_q is d-axis current and q-axis current in dq 0-axis coordinate system respectively, ω _e、R_s is rotor electric angular velocity and stator resistance of the motor respectively, L _d、L_q、L₀ is d-axis component, q-axis component and 0-axis component of inductance of the motor respectively, and ψ _f is permanent magnet flux linkage;

the drive-boost control strategy comprises a drive control strategy and a boost control strategy for the inverter;

The driving control strategy is executed by a driving controller based on an internal model decoupling control mode;

the boost control strategy is executed by a current-voltage double closed loop controller;

The d-axis proportional gain K _{p_d}, the d-axis integral gain K _{i_d}, the q-axis proportional gain K _{p_q} and the q-axis integral gain K _{i_q} of the driving controller are determined by the following formulas:

Wherein α is a drive controller coefficient;

The inner loop of the double closed loop controller is a current controller, and the proportional gain K _{p_i} and the integral gain K _{i_i} are as follows:

Wherein T ₀ is the inner loop closed loop time constant;

The control outer loop of the double closed loop controller is a voltage controller, and the proportional gain K _{p_v} and the integral gain K _{i_v} of the voltage controller are determined based on the design index of the equivalent system;

The design indexes are the expected crossing frequency f _c and the phase angle margin PM of the equivalent system, and the proportional gain K _{p_v} and the integral gain K _{i_v} of the voltage controller are determined by the following steps:

Wherein s is complex variable of Law transformation, i _N is inductance current at neutral point, C is capacitance value of DC bus capacitor, R _e is equivalent load resistance value of permanent magnet synchronous motor;

the bus voltage dynamic regulation strategy is determined based on the following steps:

α_ku_dc＝u_kN+u_in，

When the permanent magnet synchronous motor works under a light load working condition, alpha ₀ is adjusted according to the actual working condition, so that the direct current bus voltage of the inverter is dynamically adjusted within the range of [ u _in,2u_in ];

The alpha ₀ is adjusted according to the actual working condition, and specifically:

2. The method for controlling the boost of a bus of a neutral point powered permanent magnet synchronous motor according to claim 1, wherein the driving-boost control strategy is used for driving-boost control of an inverter, specifically for driving control and boost control of a dc bus of the inverter based on the following formula: