CN115276499A - A method and system for estimating the rotational speed of a permanent magnet synchronous fan motor for natural rotation - Google Patents

Abstract

The invention discloses a speed estimation method and system for natural rotation of a permanent magnet synchronous fan motor, comprising the following steps: judging whether the motor is in natural rotation; Generate a space vector current; in the last PWM cycle of the input zero-voltage vector, select a sampling time point t _n-1 , perform the angle acquisition step, and obtain the first angle; in the current PWM cycle of the input zero-voltage vector, select Set a sampling time point t _n , perform the angle acquisition step, and obtain the second angle; obtain the instantaneous angular velocity of the rotor according to the rate of change of the first and second angles; obtain the average angular velocity of natural rotation after the instantaneous angular velocity is subjected to digital low-pass filtering; It is judged whether the permanent magnet synchronous fan motor adopts braking according to the average angular velocity. The invention solves the technical problems that the existing estimation method greatly increases the amount of code, occupies more storage space and has larger errors.

Description

Method and system for estimating the rotational speed of a permanent magnet synchronous fan motor in natural rotation

technical field

The invention relates to the technical field of frequency conversion fans for air conditioners, in particular to a method and system for estimating the rotational speed of a permanent magnet synchronous fan motor in natural rotation.

Background technique

In recent years, due to the widespread adoption of frequency conversion technology, motor technology has entered an important period of change. Moreover, out of consideration of energy crisis and environmental protection, new requirements are put forward for the motor. Now, the development of high-efficiency motors is not limited to the simple pursuit of small and light weight in the traditional sense, but is regarded as a global issue. At present, permanent magnet synchronous motors using high-performance permanent magnets have been widely used because of their advantages of high efficiency and wide adjustable speed range. Especially in the air-conditioning and HVAC fields of large electricity consumers, more and more outdoor fans of air-conditioning equipment use AC permanent magnet synchronous motors to replace traditional asynchronous motors.

However, the permanent magnet synchronous motor has the following characteristics. When the controller encounters a strong wind in the state of no output, the permanent magnet synchronous motor will run at high speed and be in the power generation state, so that when it is restarted, it is prone to start failure or overcurrent protection. . Therefore, it is necessary to detect the initial speed of the permanent magnet synchronous motor to determine whether it is necessary to maintain the headwind state, whether it is necessary to brake, and if it is necessary to brake, what method of braking is required, etc.

For the detection of the initial rotational speed of the permanent magnet synchronous motor, there are mainly two processing methods at present. One is not to do detection, no matter what the reverse speed is, it will adopt compulsory braking, this kind of processing method can not use natural wind energy, and even cause a large overcurrent to cause unit protection; the other is to use a more complex The basic principle of the algorithm is to use the mathematical model of the permanent magnet synchronous motor and conduct online estimation based on the automatic control technology. However, this method is different from the algorithm in normal operation. It is equivalent to a program that requires two sets of complex algorithms, resulting in The amount of code is greatly increased and takes up more storage space. Moreover, the algorithm needs to increase the space voltage vector, which has a braking effect on the actual speed, resulting in a large calculation error.

Contents of the invention

In order to overcome the deficiencies of the prior art, the present invention provides a speed estimation method and system for the natural rotation of a permanent magnet synchronous fan motor, which solves the problem that the existing speed estimation method greatly increases the amount of code, takes up a lot of storage space and has a large error In order to achieve the purpose of being less affected by braking, estimating the actual speed with high accuracy and reducing the storage space of the control chip.

In order to solve the above problems, the technical scheme adopted in the present invention is as follows:

A method for estimating the speed of natural rotation of a permanent magnet synchronous fan motor, comprising the following steps:

Judging whether the permanent magnet synchronous fan motor in the current state is a natural rotation, if so, after inputting the zero voltage vector to the three-phase stator winding of the permanent magnet synchronous fan motor under natural rotation, prompting the three-phase stator winding to produce a space vector current;

In the last PWM cycle of inputting the zero voltage vector, a sampling time point t _n-1 is selected, and an angle acquisition step is performed to obtain the first angle;

In the current PWM cycle of the input zero voltage vector, select a sampling time point t _n , execute the angle acquisition step, and obtain the second angle;

Obtaining the instantaneous angular velocity of the rotor during natural rotation according to the rate of change between the first angle and the second angle;

After the instantaneous angular velocity is digitally low-pass filtered, the average angular velocity of natural rotation is obtained;

judging whether the permanent magnet synchronous fan motor adopts braking according to the average angular velocity;

Wherein, the permanent magnet synchronous fan motor includes a three-phase stator winding and a rotor, and the rotor rotates naturally when it is downwind, headwind or shut down, and the angle acquisition step includes: collecting the three-phase current of the three-phase stator winding; According to the three-phase current, the projection of the space vector current generated by the three-phase stator winding on the two-phase stationary coordinate axis is obtained; according to the projection on the two-phase stationary coordinate axis, the space vector current and the two-phase The angle between the stationary axes, that is, the angle of rotation.

As a preferred embodiment of the present invention, when obtaining the projection of the space vector current on the two-phase stationary coordinate axis, it includes: using the three-phase current to directly obtain the projection of the space vector current I _s on the α-axis of the two-phase stationary coordinate system The projection i _β of i _α and β axes is shown in Equation 1 and Equation 2:

i _α =i _u (Formula 1);

Among them, i _u is the U-phase current sampling value, and i _α is the component on the α-axis in the two-phase stationary coordinate system;

Among them, _iv and i _w are the sampling values of V and W phase currents, and i _β is the component on the β axis in the two-phase stationary coordinate system.

As a preferred embodiment of the present invention, when obtaining the first angle and the second angle, it includes: assuming that the angle between the space vector current I _s and the α axis is θ _s , then the projection i _α and projection i _β and the relationship between the space vector current I _s as shown in formula 3 and formula 4:

i _α =I _s cosθ _s (Formula 3);

i _β =I _s sinθ _s (Formula 4);

The θ _s is obtained through the formula 3 and the formula 4, as shown in the formula 5:

Wherein, the first angle and the second angle are respectively the angles θ _s1 and θ _s2 between the space vector current I _s and the α-axis at the time point t _n-1 and the time point t _n .

As a preferred embodiment of the present invention, when obtaining the average angular velocity of the rotor under natural rotation, it includes: obtaining the time change value dt through the time point t _n-1 and time point t _n , and obtaining the time change value dt through the first angle θ _S1 and the second angle θ _S2 to obtain the angle change value dθ _s , as shown in formula 6 and formula 7:

dt= _tn -tn _-1 (Formula 6);

_dθs = _θs2 - _θs1 (Equation 7);

The instantaneous angular velocity of the rotor is obtained through the dt and _dθs , as shown in formula 8:

即为估算转子的平均角速度。Then Wr is digitally low-pass filtered to get

That is to estimate the average angular velocity of the rotor.

As a preferred embodiment of the present invention, when inputting a zero-voltage vector to the three-phase stator winding, it includes: starting a three-phase full-bridge inverter to input a zero-voltage vector to the three-phase stator winding;

Wherein, the three-phase full-bridge inverter includes a first bridge arm, a second bridge arm and a third bridge arm, and when outputting a zero voltage vector, the first bridge arm, the second bridge arm and the third bridge arm The duty cycle is equal.

大于0为顺风，小于0为逆风。As a preferred embodiment of the present invention, when it is judged that the permanent magnet synchronous fan motor in the current state is naturally rotating, it is judged to be naturally rotating with the wind or against the wind, and the judging condition is: stipulate the direction along the phase sequence U, V, W is positive, then

Greater than 0 is tailwind, less than 0 is headwind.

As a preferred embodiment of the present invention, when judging whether the permanent magnet synchronous fan motor in the current state is in natural rotation, if not, then there is no need to perform the angle acquisition step, and it is judged that the permanent magnet synchronous fan motor is at rest or inching state, there is no need to start upwind or headwind.

As a preferred embodiment of the present invention, when judging whether to apply braking, it includes:

时，需要采取制动；when

, braking is required;

时，不需要采取制动，可以直接启动；when

, no need to apply brakes, it can be started directly;

Wherein, Wr_set0 and Wr_set1 are set braking speeds, the value range of Wr_set0 is 0≤Wr_set0≤90rpm, and the value range of Wr_set1 is Wr_set1≤-90rpm.

As a preferred embodiment of the present invention, when judging whether to apply braking, it also includes:

时，不需要制动，把计算的旋转角度、电流值置为闭环程序的初始化值，直接切换到闭环程序运行到设定转速；when

When the brake is not needed, set the calculated rotation angle and current value as the initialization value of the closed-loop program, and directly switch to the closed-loop program to run to the set speed;

时，进行逆风减速运行，把计算的旋转角度、电流值置为闭环程序的初始化值，直接切换到闭环程序运行，设定转速为0，然后再正常启动至设定转速；when

, carry out headwind deceleration operation, set the calculated rotation angle and current value as the initialization value of the closed-loop program, directly switch to the closed-loop program operation, set the speed to 0, and then start normally to the set speed;

时，判断为强逆风，处理方式有两种：第一种停止三相全桥逆变器PWM输出，利用强逆风给机组自然散热；第二种进行逆风减速运行，把计算的旋转角度、电流值置为闭环程序的初始化值，直接切换到闭环程序运行，设定转速为0，然后再正常启动至设定转速；when

When it is judged to be a strong headwind, there are two ways to deal with it: the first one stops the PWM output of the three-phase full-bridge inverter, and uses the strong headwind to naturally dissipate heat for the unit; Set the value as the initialization value of the closed-loop program, switch directly to the closed-loop program operation, set the speed to 0, and then start normally to the set speed;

时，给定静止磁场使所述永磁同步风扇电机强制静止；when

, a given static magnetic field makes the permanent magnet synchronous fan motor compulsorily stationary;

Wherein, the value range of Wr_set2 is Wr_set3<Wr_set2≤-120rpm; the value range of Wr_set3 is Wr_set3≤-420rpm.

A speed estimation system for natural rotation of a permanent magnet synchronous fan motor, comprising:

Rotation judging unit: used to judge whether the permanent magnet synchronous fan motor in the current state is in natural rotation, if so, after inputting the zero voltage vector to the three-phase stator winding of the permanent magnet synchronous fan motor under natural rotation, the three-phase stator winding is prompted to generate a space vector current;

Angle acquisition unit: used to select a sampling time point t _n-1 in the last PWM period of the input zero voltage vector, and perform the angle acquisition step to obtain the first angle; in the current PWM period of the input zero voltage vector, Select a sampling time point t _n , execute the angle acquisition step to obtain the second angle;

Angular velocity calculation unit: used to obtain the instantaneous angular velocity of the rotor during natural rotation according to the rate of change between the first angle and the second angle; the average angular velocity of natural rotation is obtained after the instantaneous angular velocity is digitally low-pass filtered ;

An angular velocity judging unit: used to judge whether the permanent magnet synchronous fan motor adopts braking according to the average angular velocity;

Wherein, the permanent magnet synchronous fan motor includes a three-phase stator winding and a rotor, and the rotor rotates naturally when it is downwind, headwind or shut down, and the angle acquisition step includes: collecting the three-phase current of the three-phase stator winding; According to the three-phase current, the projection of the space vector current generated by the three-phase stator winding on the two-phase stationary coordinate axis is obtained; according to the projection on the two-phase stationary coordinate axis, the space vector current and the two-phase The angle between the stationary axes, that is, the angle of rotation.

Compared with the prior art, the beneficial effects of the present invention are:

(1) The present invention does not depend on motor parameters, and does not need to consider whether the rotor is a surface-mounted or built-in structure, and the calculation is simple and the result is reliable;

(2) The present invention can greatly reduce the amount of program codes, reduce the storage space and even the cost of the control chip, and is especially suitable for special chips for motor control with small storage space and limited resources.

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

Description of drawings

Fig. 1 - is the step diagram of the speed estimation method of the natural rotation of the permanent magnet synchronous fan motor of the embodiment of the present invention;

Figure 2 - is a schematic diagram of angular velocity estimation according to an embodiment of the present invention;

Fig. 3 is a schematic structural diagram of a three-phase full-bridge inverter according to an embodiment of the present invention.

Detailed ways

The speed estimation method of the natural rotation of the permanent magnet synchronous fan motor provided by the present invention, as shown in Figure 1, comprises the following steps:

Step S1: Determine whether the permanent magnet synchronous fan motor in the current state is in natural rotation, and if so, after inputting the zero voltage vector to the three-phase stator winding of the permanent magnet synchronous fan motor in natural rotation, the three-phase stator winding is prompted to generate a space vector current;

Step S2: Select a sampling time point t _n-1 in the last PWM period in which the zero-voltage vector is input, and perform an angle acquisition step to obtain the first angle;

Step S3: In the current PWM period in which the zero-voltage vector is input, a sampling time point t _n is selected, and an angle acquisition step is performed to obtain a second angle;

Step S4: Obtain the instantaneous angular velocity of the rotor during natural rotation according to the rate of change between the first angle and the second angle;

Step S5: After the instantaneous angular velocity is digitally low-pass filtered, the average angular velocity of natural rotation is obtained;

Step S6: judging whether the permanent magnet synchronous fan motor adopts braking according to the average angular velocity;

Among them, the permanent magnet synchronous fan motor includes a three-phase stator winding and a rotor. The rotor rotates naturally when it is downwind, headwind or shut down. The angle acquisition step includes: collecting the three-phase current of the three-phase stator winding; obtaining the three-phase stator winding according to the three-phase current. The projection of the space vector current generated by the winding on the two-phase stationary coordinate axis; according to the projection on the two-phase stationary coordinate axis, the angle between the space vector current and the two-phase stationary coordinate axis is obtained, that is, the rotation angle.

Further, the zero voltage vector referred to in the present invention is defined as the upper bridge switch tubes of the three-phase inverter full bridge are turned on at the same time, and the lower bridge switch tubes are turned off at the same time, or the upper bridge switch tubes are turned off at the same time, and the lower bridge switch tubes are simultaneously turned off. conduction.

AC Permanent Magnet Synchronous Motor (PMSM) is a general term for motors that replace the mechanical rectification of DC motor brushes and commutators with semiconductor rectification. Mounted on the rotor side, it becomes a so-called rotary rotor type structure. Since the PMSM replaces the mechanical rectification function with the semiconductor rectification function, the permanent magnet is installed on the rotor, and the armature coil is installed on the stator, thereby forming a rotating magnetic field structure. It can also be understood that the structure of the stator side of the traditional three-phase asynchronous motor remains unchanged, while the armature coil winding is replaced by a permanent magnet device on the rotor side, and a semiconductor rectifier device is added, which is commonly referred to as a frequency converter. PMSM is inseparable from the frequency converter, and a single PMSM cannot be started and operated by itself.

Fans using PMSM motors are also called DC fans. Due to their low noise, low energy consumption, and wide speed range, they are widely used in household inverter air conditioners, and in commercial air conditioners, such as unit machines, hot air blowers, and hot water fans. It is also very commonly used in machines and multi-lines. The function of the fan motor of the air-conditioning equipment is to properly dissipate heat from the heat exchanger and ensure that the air conditioner operates at its best. If the best working condition can be ensured, there is no specific requirement on the direction of fan rotation. Therefore, if the natural wind can be used to dissipate heat in strong winds, it can further save electricity. If the best working condition of the air conditioner cannot be ensured, it needs to start against strong wind Set speed to tailwind. Therefore, by using the estimation method of the present invention, the rotational speed of the rotor under natural rotation can be estimated, thereby judging whether the air conditioner is in an optimal working state.

In the above step S3, as shown in Figure 2, when obtaining the projection of the space vector current on the two-phase stationary coordinate axis, it includes: using the three-phase current to directly obtain the space vector current I _s on the α-axis of the two-phase stationary coordinate system The projection i _α of and the projection i _β of the β axis are specifically shown in Equation 1 and Equation 2:

i _α =i _u (Formula 1);

Among them, i _u is the U-phase current sampling value, and i _α is the component on the α-axis in the two-phase stationary coordinate system;

Among them, _iv and i _w are the sampling values of V and W phase currents, and i _β is the component on the β axis in the two-phase stationary coordinate system.

In the above step S3, as shown in Figure 2, when obtaining the first angle and the second angle, it includes: assuming that the angle between the space vector current I _s and the α axis is θ _s , then the projection i _α and projection i _β are related to the space The relationship between the vector current I _s is shown in Equation 3 and Equation 4:

i _α =I _s cosθ _s (Formula 3);

i _β =I _s sinθ _s (Formula 4);

Calculate θ _s by using Equation 3 and Equation 4, as shown in Equation 5:

Wherein, the first angle and the second angle are the angles θ _s1 and θ _s2 between the space vector current I _s and the α-axis at time point t _n-1 and time point t _n respectively.

In the above steps S4 and S5, as shown in Figure 2, when obtaining the average angular velocity of the rotor under natural rotation, it includes: obtaining the time change value dt through the time point t _n-1 and the time point t _n , and obtaining the time change value dt through the first angle θ _S1 and the second angle θ _S2 obtain the angle change value dθ _s , as shown in Formula 6 and Formula 7:

dt= _tn -tn _-1 (Formula 6);

_dθs = _θs2 - _θs1 (Equation 7);

The instantaneous angular velocity of the rotor is obtained by dt and dθ _s , as shown in Equation 8:

即为估算转子的平均角速度。Then Wr is digitally low-pass filtered to get

That is to estimate the average angular velocity of the rotor.

From the foregoing, it can be seen that the PMSM motor is another structural form of DC motor, and the analysis and control methods are equivalent to DC motors based on the double-reaction theory of the motor, and the dq-axis mathematical model based on the rotating coordinate system is established. The voltage equation is as follows:

V _d ＝R _s I _d +sL _d I _d -ω _r L _q I _q

V _q ＝R _s I _q +sL _q I _q +ω _r L _d I _d +ω _r K _e

Among them, V _d and V _q are the motor terminal voltage in the dq coordinate system, I _d and I _q are the motor current in the dq coordinate system, ω _r is the rotational angular velocity of the rotor, and K _e is the counter electromotive force constant.

If the rotational angular velocity of the rotor is calculated by the above voltage equation, the three-phase current I _a , I _b , I _c in the stationary coordinate system must be transformed into the current I _d , I _q in the rotating coordinate system, because it is impossible to know The angle θ _e between the d-axis of the rotating coordinate system and the a-axis of the stationary coordinate system cannot obtain accurate I _d and I _q . Although it is possible to build a state observer and calculate it through a suitable control link, it is obvious that this method has a large amount of calculation and must inject a voltage of a non-zero vector. The existence of a voltage of a non-zero vector will inhibit the natural speed, making the calculated result The deviation is large.

The method provided by the invention is to estimate the angular velocity ω _r from the voltage equation in the equivalent two-phase static α, β coordinate system. This method theoretically eliminates the influence of external factors such as rotor structure and motor parameters, and does not need to establish a mathematical model based on a rotating coordinate system for any motor, does not depend on motor parameters, and the calculation method is simple and reliable.

In the above step S1, when inputting a zero-voltage vector to the three-phase stator winding, it includes: starting the three-phase full-bridge inverter to input the zero-voltage vector to the three-phase stator winding;

Wherein, the three-phase full-bridge inverter includes a first bridge arm, a second bridge arm and a third bridge arm, and when outputting a zero voltage vector, the duty cycle of the first bridge arm, the second bridge arm and the third bridge arm equal.

The present invention uses a three-phase full-bridge inverter to input zero-voltage vectors to the three-phase stator windings of the motor to obtain phase currents in the state of zero-voltage vectors, so as to minimize the impact on the actual speed, and the method of outputting zero-voltage vectors is given The duty cycle of each of the three bridge arms is equal, and the detection time can be set according to the actual situation.

大于0为顺风，小于0为逆风。In the above step S1, when it is judged that the permanent magnet synchronous fan motor in the current state is rotating naturally, it is judged to be naturally rotating with the wind or against the wind, and the judgment condition is: it is stipulated that the direction along the phase sequence U, V, W is positive ,but

Greater than 0 is tailwind, less than 0 is headwind.

In the above-mentioned step S1, when judging whether the permanent magnet synchronous fan motor in the current state is a natural rotation, if not, then there is no need to perform the angle acquisition step, and it is judged that the permanent magnet synchronous fan motor is in a static or inching state, and there is no need to perform smooth, Headwind starts.

In the above step S6, when judging whether to apply braking, it includes:

时，需要采取制动；when

, braking is required;

时，不需要采取制动，可以直接启动；when

, no need to apply brakes, it can be started directly;

Wherein, Wr_set0 and Wr_set1 are set braking speeds, the value range of Wr_set0 is 0≤Wr_set0≤90rpm, and the value range of Wr_set1 is Wr_set1≤-90rpm.

Further, when judging whether to apply braking, it also includes:

时，不需要制动，把计算的旋转角度、电流值置为闭环程序的初始化值，直接切换到闭环程序运行到设定转速；when

When the brake is not needed, set the calculated rotation angle and current value as the initialization value of the closed-loop program, and directly switch to the closed-loop program to run to the set speed;

时，进行逆风减速运行，把计算的旋转角度、电流值置为闭环程序的初始化值，直接切换到闭环程序运行，设定转速为0，然后再正常启动至设定转速；when

, carry out headwind deceleration operation, set the calculated rotation angle and current value as the initialization value of the closed-loop program, directly switch to the closed-loop program operation, set the speed to 0, and then start normally to the set speed;

时，判断为强逆风，处理方式有两种：第一种停止三相全桥逆变器PWM输出，利用强逆风给机组自然散热；第二种进行逆风减速运行，把计算的旋转角度、电流值置为闭环程序的初始化值，直接切换到闭环程序运行，设定转速为0，然后再正常启动至设定转速；when

When it is judged to be a strong headwind, there are two ways to deal with it: the first one stops the PWM output of the three-phase full-bridge inverter, and uses the strong headwind to naturally dissipate heat for the unit; Set the value as the initialization value of the closed-loop program, switch directly to the closed-loop program operation, set the speed to 0, and then start normally to the set speed;

时，给定静止磁场使所述永磁同步风扇电机强制静止；when

, a given static magnetic field makes the permanent magnet synchronous fan motor compulsorily stationary;

Wherein, the value range of Wr_set2 is Wr_set3<Wr_set2≤-120rpm; the value range of Wr_set3 is Wr_set3≤-420rpm.

The speed estimation system for the natural rotation of the permanent magnet synchronous fan motor provided by the present invention includes:

Rotation judging unit: used to judge whether the permanent magnet synchronous fan motor in the current state is in natural rotation. If so, after inputting the zero voltage vector to the three-phase stator winding of the permanent magnet synchronous fan motor under natural rotation, the three-phase stator winding is prompted to generate space vector current;

Angle acquisition unit: used to select a sampling time point t _n-1 in the last PWM period of the input zero voltage vector, and perform the angle acquisition step to obtain the first angle; in the current PWM period of the input zero voltage vector, Select a sampling time point t _n , execute the angle acquisition step to obtain the second angle;

Angular velocity calculation unit: used to obtain the instantaneous angular velocity of the rotor during natural rotation according to the rate of change between the first angle and the second angle; after the instantaneous angular velocity is digitally low-pass filtered, the average angular velocity of natural rotation is obtained;

Angular velocity judging unit: used to judge whether the permanent magnet synchronous fan motor adopts braking according to the average angular velocity;

Among them, the permanent magnet synchronous fan motor includes a three-phase stator winding and a rotor. The rotor rotates naturally when it is downwind, headwind or shut down. The angle acquisition step includes: collecting the three-phase current of the three-phase stator winding; obtaining the three-phase stator winding according to the three-phase current. The projection of the space vector current generated by the winding on the two-phase stationary coordinate axis; according to the projection on the two-phase stationary coordinate axis, the angle between the space vector current and the two-phase stationary coordinate axis is obtained, that is, the rotation angle.

When the air conditioner is stopped, driven by the natural wind, the fan rotates. At this time, the inverter has no output. Since there is no speed or position sensor, it is theoretically impossible to detect the rotation speed. The present invention adopts the field-oriented control method without position sensor, and the hardware topology adopts a voltage-type three-phase full-bridge inverter, as shown in Fig. In order to detect the headwind speed, the space vector current generated by the motor must flow through the precision resistance of the three-phase full-bridge inverter. The invention calculates the rotating speed by inputting the zero-voltage vector to the three-phase stator winding of the motor and using the induced current generated by the induced voltage of the stator winding.

Compared with the prior art, the beneficial effects of the present invention are:

(1) The present invention does not depend on motor parameters, and does not need to consider whether the rotor is a surface-mounted or built-in structure, and the calculation is simple and the result is reliable;

(2) The present invention can greatly reduce the amount of program codes, reduce the storage space and even the cost of the control chip, and is especially suitable for special chips for motor control with small storage space and limited resources.

The above-mentioned embodiment is only a preferred embodiment of the present invention, and cannot be used to limit the protection scope of the present invention. Any insubstantial changes and substitutions made by those skilled in the art on the basis of the present invention belong to the scope of the present invention. Scope of protection claimed.

Claims (10)

1. A method for estimating the rotational speed of the natural rotation of a permanent magnet synchronous fan motor, characterized in that, comprising the following steps: Judging whether the permanent magnet synchronous fan motor in the current state is a natural rotation, if so, after inputting the zero voltage vector to the three-phase stator winding of the permanent magnet synchronous fan motor under natural rotation, prompting the three-phase stator winding to produce a space vector current; In the last PWM cycle of inputting the zero voltage vector, a sampling time point t _n-1 is selected, and an angle acquisition step is performed to obtain the first angle; In the current PWM cycle of the input zero voltage vector, select a sampling time point t _n , execute the angle acquisition step, and obtain the second angle; Obtaining the instantaneous angular velocity of the rotor during natural rotation according to the rate of change between the first angle and the second angle; After the instantaneous angular velocity is digitally low-pass filtered, the average angular velocity of natural rotation is obtained; judging whether the permanent magnet synchronous fan motor adopts braking according to the average angular velocity; Wherein, the permanent magnet synchronous fan motor includes a three-phase stator winding and a rotor, and the rotor rotates naturally when it is downwind, headwind or shut down, and the angle acquisition step includes: collecting the three-phase current of the three-phase stator winding; According to the three-phase current, the projection of the space vector current generated by the three-phase stator winding on the two-phase stationary coordinate axis is obtained; according to the projection on the two-phase stationary coordinate axis, the space vector current and the two-phase The angle between the stationary axes, that is, the angle of rotation. 2. The method for estimating the speed of natural rotation of a permanent magnet synchronous fan motor according to claim 1, wherein, when obtaining the projection of the space vector current on the two-phase stationary coordinate axes, it comprises: using the three-phase current to directly Calculate the projection i _α of the space vector current I _s on the α-axis of the two-phase stationary coordinate system and the projection i _β of the β-axis, as shown in formula 1 and formula 2: i _α =i _u (Formula 1); Among them, i _u is the U-phase current sampling value, and i _α is the component on the α-axis in the two-phase stationary coordinate system;

Among them, _iv and i _w are the sampling values of V and W phase currents, and i _β is the component on the β axis in the two-phase stationary coordinate system. 3. The method for estimating the rotational speed of the permanent magnet synchronous fan motor according to claim 2, wherein, when obtaining the first angle and the second angle, it includes: assuming that the space vector current I _s and the α The angle of the axis is θ _s , then the relationship between the projection i _α and projection i _β and the space vector current I _s is shown in formula 3 and formula 4: i _α =I _s cosθ _s (Formula 3); i _β =I _s sinθ _s (Formula 4); The θ _s is obtained through the formula 3 and the formula 4, as shown in the formula 5:

Wherein, the first angle and the second angle are respectively the angles θ _s1 and θ _s2 between the space vector current I _s and the α-axis at the time point t _n-1 and the time point t _n . 4. The method for estimating the rotational speed of the permanent magnet synchronous fan motor in natural rotation according to claim 3, wherein, when obtaining the average angular velocity of the rotor under natural rotation, it includes: passing through the time point t _n-1 and time The time change value dt is obtained at point t _n , and the angle change value dθ _s is obtained through the first angle θ _S1 and the second angle θ _S2 , as shown in formula 6 and formula 7: dt= _tn -tn _-1 (Formula 6); _dθs = _θs2 - _θs1 (Equation 7); The instantaneous angular velocity of the rotor is obtained through the dt and _dθs , as shown in formula 8:

Then Wr is digitally low-pass filtered to get

That is to estimate the average angular velocity of the rotor. 5. The method for estimating the speed of natural rotation of the permanent magnet synchronous fan motor according to claim 1, wherein, when a zero voltage vector is input to the three-phase stator winding, it comprises: starting a three-phase full-bridge inverter inputting a zero-voltage vector to the three-phase stator winding; Wherein, the three-phase full-bridge inverter includes a first bridge arm, a second bridge arm and a third bridge arm, and when outputting a zero voltage vector, the first bridge arm, the second bridge arm and the third bridge arm The duty cycle is equal. 6. The method for estimating the rotational speed of a permanent magnet synchronous fan motor against wind and natural rotation according to claim 1, wherein when it is judged that the current state of the permanent magnet synchronous fan motor is natural rotation, it is judged to be natural rotation along the wind or natural rotation against the wind Rotation, the judgment condition is: stipulate that the direction along the phase sequence U, V, W is positive, then

Greater than 0 is tailwind, less than 0 is headwind. 7. The speed estimation method of the natural rotation of the permanent magnet synchronous fan motor according to claim 1, characterized in that, when judging whether the permanent magnet synchronous fan motor in the current state is a natural rotation, if not, then there is no need to implement the angle Obtaining step, and judging that the permanent magnet synchronous fan motor is in a static or inching state, and does not need to be started in a forward or reverse direction. 8. The method for estimating the speed of natural rotation of a permanent magnet synchronous fan motor according to claim 1, characterized in that, when judging whether to apply braking, it includes: when

, braking is required; when

, no need to apply brakes, it can be started directly; Wherein, Wr_set0 and Wr_set1 are set braking speeds, the value range of Wr_set0 is 0≤Wr_set0≤90rpm, and the value range of Wr_set1 is Wr_set1≤-90rpm. 9. The method for estimating the speed of natural rotation of the permanent magnet synchronous fan motor according to claim 8, characterized in that, when judging whether to apply braking, it also includes: when

When the brake is not needed, set the calculated rotation angle and current value as the initialization value of the closed-loop program, and directly switch to the closed-loop program to run to the set speed; when

, carry out headwind deceleration operation, set the calculated rotation angle and current value as the initialization value of the closed-loop program, directly switch to the closed-loop program operation, set the speed to 0, and then start normally to the set speed; when

When it is judged to be a strong headwind, there are two ways to deal with it: the first one stops the PWM output of the three-phase full-bridge inverter, and uses the strong headwind to naturally dissipate heat for the unit; Set the value as the initialization value of the closed-loop program, switch directly to the closed-loop program operation, set the speed to 0, and then start normally to the set speed; when

, a given static magnetic field makes the permanent magnet synchronous fan motor compulsorily stationary; Wherein, the value range of Wr_set2 is Wr_set3<Wr_set2≤-120rpm; the value range of Wr_set3 is Wr_set3≤-420rpm. 10. A speed estimation system for natural rotation of a permanent magnet synchronous fan motor, characterized in that it includes: Rotation judging unit: used to judge whether the permanent magnet synchronous fan motor in the current state is in natural rotation, if so, after inputting the zero voltage vector to the three-phase stator winding of the permanent magnet synchronous fan motor under natural rotation, the three-phase stator winding is prompted to generate a space vector current; Angle acquisition unit: used to select a sampling time point t _n-1 in the last PWM period of the input zero voltage vector, and perform the angle acquisition step to obtain the first angle; in the current PWM period of the input zero voltage vector, Select a sampling time point t _n , execute the angle acquisition step to obtain the second angle; Angular velocity calculation unit: used to obtain the instantaneous angular velocity of the rotor during natural rotation according to the rate of change between the first angle and the second angle; the average angular velocity of natural rotation is obtained after the instantaneous angular velocity is digitally low-pass filtered ; An angular velocity judging unit: used to judge whether the permanent magnet synchronous fan motor adopts braking according to the average angular velocity; Wherein, the permanent magnet synchronous fan motor includes a three-phase stator winding and a rotor, and the rotor rotates naturally when it is downwind, headwind or shut down, and the angle acquisition step includes: collecting the three-phase current of the three-phase stator winding; According to the three-phase current, the projection of the space vector current generated by the three-phase stator winding on the two-phase stationary coordinate axis is obtained; according to the projection on the two-phase stationary coordinate axis, the space vector current and the two-phase The angle between the stationary axes, that is, the angle of rotation.

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