WO2021147321A1 - Constant air volume induced draft fan - Google Patents

Abstract

Disclosed is a constant air volume induced draft fan comprising a volute (1), a wind wheel (2) and an electric motor (3), wherein the electric motor (3) is installed outside the volute (1) by means of an installation support (4); the electric motor (3) comprises an electric motor body and an electric motor controller; the electric motor body comprises a stator assembly (31), a permanent magnet rotor assembly (32), a rotating shaft (33) and an electric motor shell (34); the wind wheel (2) is installed in the volute (1); the electric motor (3) drives the wind wheel (2) to rotate; the electric motor controller comprises an electric motor operation parameter detection circuit and a microprocessor; and the microprocessor, according to an input target air volume value IN-CFM and a function relational expression P/a ＝ f(n/b) of constant air volume control, enables the induced draft fan to output a constant air volume by controlling the input power and rotating speed, wherein P is the electric motor input power, n is the electric motor rotating speed, a is a power proportionality coefficient, and b is a proportionality coefficient of the rotating speed. By increasing the power proportionality coefficient a and the rotating speed proportionality coefficient b, the induced draft fan can meet the requirements of different working environments.

Description

Constant air volume induced draft fan Technical field:

The invention relates to a constant air volume induced draft fan.

Background technique:

The existing DC induced draft fans are all constant-speed induced draft fans, and the output air volume of the DC induced draft fans is unstable when the static pressure fluctuates greatly.

The applicant applied for an invention patent in 2014. The application number of the patent: CN201410042547.8. Application date: 2014.01.28 Publication (Announcement) No.: CN104807152A. Patent name: A constant air volume control with direct power control of a PM motor Method and its applied HVAC system; this patented constant air volume control method is suitable for low static pressure (0-300Pa), low speed (0-2000RPM), and large air volume (0-1000CFM).

It is not applicable to the occasions of high static pressure, high speed, and small air volume, resulting in a great limitation of the application range. In view of this, the control method must be improved.

In addition, the current induced draft fan is equipped with a motor controller behind the motor, and some electronic components in the motor controller have a high axial height, which results in a larger axial size of the entire induced draft fan, which affects the installation.

Summary of the invention:

The purpose of the present invention is to provide a constant air volume induced draft fan, which solves the technical problem that the application range of constant air volume control is narrow by controlling the motor input power and the motor speed in the prior art.

A further object of the present invention is to provide a constant air volume induced draft fan, which solves the technical problem of the large axial size of the entire induced draft fan in the prior art, which affects the installation.

The purpose of the present invention is achieved through the following technical solutions.

A constant air volume induced draft fan includes a volute, a wind wheel, and a motor. The motor is installed outside the volute through a mounting bracket. The motor includes a motor body and a motor controller. The motor body includes a stator assembly, a permanent magnet rotor assembly, a rotating shaft, and a motor housing. A wind wheel is installed in the volute, and the motor drives the wind wheel to rotate. The motor controller includes a motor operating parameter detection circuit and a microprocessor. The set constant air volume control function P/a=f(n/b), by controlling the input power and speed to make the induced draft fan output a constant air volume, where P is the motor input power, n is the motor speed, and a is the power proportional coefficient , B is the proportional coefficient of speed.

The above-mentioned functional relation P/a=f(n/b) is a polynomial function:

Among them, C ₁ , C ₂ ,..., Cm are coefficients. According to the input target air volume value IN-CFM, a corresponding set of C ₁ , C ₂ ,..., Cm coefficients and power scale coefficients a and The proportional coefficient b of the speed, and the function relation P/a=fx(n/b), x=1, 2, 3,..., the value of the power proportional coefficient a is in the range of 50-100, and the speed proportional coefficient b is The range of 3000-8000.

The motor operating parameter detection circuit includes a bus current detection circuit and a bus voltage detection circuit. The bus current detection circuit and the bus voltage detection circuit detect real-time bus current IDC and real-time bus voltage VDC. Real-time motor input power Pi=IDC×VDC.

The motor operating parameter detection circuit described above includes a phase line current detection circuit and a bus voltage detection circuit. The phase line current detection circuit and the bus voltage detection circuit detect real-time phase current and real-time bus voltage data input to the microprocessor, and the real-time phase current and The real-time bus voltage is converted into the currents Iα, Iβ, voltages Vα, Vβ on the α-β coordinates, and the real-time input power of the motor Pi=3/2 (Iα·Vα+Iβ·Vβ).

The above-mentioned motor controller includes a control box and a control circuit board. The control circuit board is installed inside the control box. The end of the motor housing is equipped with the control box. The opening of the control box faces the end of the motor housing. The width H of the control box is larger than that of the motor housing. The diameter D of the control circuit board should be wide, the edge of the control circuit board is arranged with a longer axial length of the electronic vitality part, and the bottom of the longer axial length of the electronic vitality part extends out of the control box and is located on one side of the motor housing.

The aforementioned electronic element with longer axial length is a capacitive element.

The control box described above has a baffle extending axially, and the baffle shields the outer side of the electronic vitality element with a long axial length.

The above-mentioned baffle is also connected to a cover plate. The cover plate includes a left side plate, a right side plate and a bottom plate. The left side plate, the right side plate, the bottom plate and the baffle enclose the cover body to cover the long axial length electronics. Outside the bottom of the vitality piece.

The bottom of the baffle mentioned above is provided with upper mounting ears protruding outwards, the lower mounting ears protruding outwards from the cover plate, and the upper mounting ears and the lower mounting ears are connected by a first screw.

The above-mentioned motor housing includes a rear end cover, lower lugs extend from both sides of the rear end cover, upper lugs extend from both sides of the control box, and the lower lug and the upper lug are connected by a second screw.

Compared with the prior art, the present invention has the following effects:

1) The constant air volume induced draft fan of the present invention includes a volute, a wind wheel, and a motor. The motor is installed outside the volute through a mounting bracket. The motor includes a motor body and a motor controller. The motor controller includes a motor operating parameter detection circuit. And the microprocessor, characterized in that: the microprocessor obtains the constant air volume control function relation P/a=f(n/b) according to the input target air volume value IN-CFM, where P is the motor input power and n is the motor Rotation speed, a is the power proportional coefficient, b is the proportional coefficient of the speed, by controlling the input power and speed to make the induced draft fan output a constant air volume. By increasing the power ratio coefficient a and speed ratio coefficient b, the operating speed range of the induced draft fan can be 0-8000RPM, the static pressure range is 0-1000Pa, and the small output air volume is 0-300CFM, which is suitable for different working environment requirements.

2) Other advantages of the present invention are described in detail in the embodiments.

Description of the drawings:

Fig. 1 is a perspective view of an induced draft fan according to the first embodiment of the present invention;

Figure 2 is a perspective view from another angle of the induced draft fan in the first embodiment of the present invention;

Figure 3 is an exploded view of the induced draft fan in the first embodiment of the present invention;

Figure 4 is an exploded view of a partial structure of the induced draft fan in the first embodiment of the present invention;

Figure 5 is a top view of the induced draft fan in the first embodiment of the present invention;

Figure 6 is a sectional view taken along line A-A of Figure 5;

Fig. 7 is a perspective view of a motor controller of an induced draft fan according to the first embodiment of the present invention;

Figure 8 is an exploded view of the motor controller of the induced draft fan in the first embodiment of the present invention;

9 is a circuit block diagram of the motor controller of the induced draft fan in the first embodiment of the present invention;

Fig. 10 is a partial circuit diagram corresponding to Fig. 9;

Figure 11 is a control flow chart of the second embodiment of the present invention;

Figure 12 is a cluster of constant air volume fitting curves obtained through experimental measurements in the second embodiment of the present invention;

FIG. 13 is a curve diagram of experimental data fitting curve for direct power control of a constant air volume of a 1/3HP PM motor in the second embodiment of the present invention;

Fig. 14 is a curve diagram of the experimental data fitting curve of using interpolation to solve arbitrary input air volume in the second embodiment of the present invention

15 is a control logic diagram of the constant air volume control method according to the second embodiment of the present invention;

16 is a schematic diagram of a control process of the constant air volume control method according to the second embodiment of the present invention;

FIG. 17 is a schematic diagram of another control process of the constant air volume control method according to the second embodiment of the present invention;

18 is a diagram of test results verified by experiments of the constant air volume control method of the second embodiment of the present invention;

19 is a block diagram of an implementation circuit of the motor controller of the PM motor according to the second embodiment of the present invention;

Figure 20 is a schematic diagram of a traditional vector control of a typical PM motor;

Fig. 21 is a diagram of the relationship between the coordinate systems of a typical vector control of a traditional PM motor;

Figure 22 is a control logic diagram of the constant air volume control method of the second embodiment of the present invention.

Detailed ways:

Hereinafter, the present invention will be further described in detail through specific embodiments in conjunction with the accompanying drawings.

Example one:

As shown in Figures 1 to 8, this embodiment provides a constant air volume induced draft fan, which includes a volute 1, a wind wheel 2, and a motor 3. The motor 3 is installed outside the volute 1 through a mounting bracket 4. The motor 3 includes a motor body And a motor controller. The motor body includes a stator assembly 31, a permanent magnet rotor assembly 32, a rotating shaft 33, and a motor housing 34. A wind wheel 2 is installed in the volute 1, and the motor 3 drives the wind wheel 2 to rotate. The motor controller includes The control box 35 and the control circuit board 36 are installed in the control box 35. The control box 35 is installed at the end of the motor housing 34. The opening 351 of the control box 35 faces the end of the motor housing 34. The width H of the control box 35 is greater than The diameter D of the motor housing 34 should be wide. The edge of the control circuit board 36 is provided with an electronic vitality member 37 with a longer axial length. The bottom of the electronic vitality member 37 with a longer axial length extends out of the control box 35 and is located in the motor housing. 34 on the side. In this way, the height of the motor body and the motor controller combination is reduced, and the space is small, which is suitable for installation of different loads and is more compact.

The aforementioned electronic element 37 with a longer axial length is a capacitive element and has a reasonable layout.

The aforementioned control box shaft 35 has a baffle 352 extending in the direction. The baffle 352 covers the outer side of the electronic vitality element 37 with a longer axial length. The baffle 352 can prevent collision and block the water outside.

The above-mentioned baffle 352 is also connected to a cover plate 38. The cover plate 38 includes a left side plate 381, a right side plate 382 and a bottom plate 383. The left side plate 381, the right side plate 382, the bottom plate 383 and the baffle 352 form a cover. The body cover is outside the bottom of the electronic vitality member 37 with a longer axial length. In this way, the airtightness of the electronic vitality component 37 can be greatly improved, and the electronic vitality component 37 can be effectively protected.

The bottom of the baffle 352 described above is provided with an upper mounting ear 3521 protruding outward, a lower mounting ear 384 protruding from the cover plate 38, and the upper mounting ear 3521 and the lower mounting ear 384 are connected by a first screw 40. The structure is simple, and the installation is convenient.

The above-mentioned motor housing 34 includes a rear end cover 341, lower lugs 3411 extend from both sides of the rear end cover 341, upper lugs 353, lower lugs 3411 and upper lugs 353 extend from both sides of the control box 35. It is connected by the second screw 39, the structure is simple and the installation is convenient.

As shown in Figure 9 and Figure 10, the control circuit board 36 of the motor controller integrates the following circuits: microprocessor, inverter circuit, phase current measurement circuit, bus current detection circuit, bus voltage detection circuit, rectifier circuit, switching power supply and The protection circuit, the phase current measurement circuit detects the phase current of the coil winding in the stator assembly and inputs it to the microprocessor. The microprocessor estimates the real-time speed n and rotor position of the motor based on the phase current of the coil winding. The bus current detection circuit connects the bus The current is input to the microprocessor, and the bus voltage detection circuit inputs the DC bus voltage to the microprocessor. The microprocessor controls the inverter circuit. The inverter circuit controls the power on and off of each phase coil winding of the stator assembly, and the microprocessor controls the motor. Input power control circuit.

Assuming that the PM motor 3 is a 3-phase brushless DC permanent magnet synchronous motor, the rotor position measurement circuit 14 generally uses 3 Hall sensors, and the 3 Hall sensors respectively detect the rotor position in a 360-degree electrical angle cycle, every 120 degrees of rotation. The electrical angle changes the energization of each phase coil winding of the stator assembly 12 once to form a 3-phase 6-step control mode. After the AC INPUT passes through a full-wave rectifier circuit composed of diodes D7, D8, D9, and D10, the DC bus voltage VDC is output at one end of the capacitor C1. The DC bus voltage VDC is related to the input AC voltage. The AC input ( After the voltage of AC INPUT) is determined, the line voltage UP of the 3-phase winding is the PWM chopping output voltage, UP=VDC*w, w is the duty ratio of the PWM signal input by the microprocessor to the inverter circuit, and the line voltage UP is changed The DC bus current IDC can be changed. The inverter circuit is composed of electronic switch tubes Q1, Q2, Q3, Q4, Q5, and Q6. The control terminals of the electronic switch tubes Q1, Q2, Q3, Q4, Q5, and Q6 are respectively output by the microprocessor It is controlled by 6 PWM signals (P1, P2, P3, P4, P5, P6). The inverter circuit is also connected to the resistor R1 to detect the bus current IDC. The bus current detection circuit converts the detected bus current IDC of the resistor R1 and transmits it to microprocessor. The motor input power control is controlled by the electronic switch tube Q7, and a PWM signal output by the microprocessor-namely P0, controls the on-time of the electronic switch tube Q7 to control the motor input power. The protection circuit includes an overcurrent protection circuit, an overvoltage protection circuit, and an overtemperature protection circuit.

Embodiment two:

Specifically shown in Figure 10, Figure 11, the PM motor direct power control constant air volume control method, the PM motor drives the wind wheel, the PM motor has a stator assembly, a permanent magnet rotor assembly and a motor controller, the motor control The device includes a microprocessor, an inverter circuit, a rotor position measurement circuit, a bus current detection circuit, a bus voltage detection circuit, and a motor input power control circuit (not shown in the figure). The rotor position measurement circuit detects the rotor position signal and inputs it to the micro The processor, the microprocessor calculates the real-time speed n of the motor according to the rotor position signal, the bus current detection circuit inputs the bus current to the microprocessor, the bus voltage detection circuit inputs the DC bus voltage to the microprocessor, and the microprocessor controls the reverse The variable circuit, the inverter circuit controls the on and off of each phase coil winding of the stator assembly, and the microprocessor controls the motor input power control circuit, which is characterized in that it includes the following steps:

Step A) Start the motor controller and receive the target air volume value IN-CFM;

Step B) Obtain the corresponding functional relationship P=f _x (n), x=1, 2, 3,..., according to the target air volume value IN-CFM, where n is the speed and P is the input power of the motor;

Step C) Enter the direct power control constant air volume control mode: control the motor or start the motor when the motor speed is zero, so that it reaches a stable operating point (Pt, nt) along the control trajectory of the function P=f(n); Pt nt is a pair of input power and speed on the track satisfying the constant air volume control function P=f(n);

Step D) Maintain direct power control and constant air volume control mode: calculate the real-time input power Pi of the motor according to the motor operating parameters; calculate ΔP=|Pt-Pi|;

Step E) If the power increment value ΔP is less than the set value Pset, keep the current operating point;

Step F) If the power increment value ΔP is greater than or equal to the set value Pset; the power/speed control logic will calculate whether the operating time of the speed loop is reached; if the operating time of the speed loop is not reached, keep the current operating point;

Step G) If the operating time of the speed loop has been reached, enter the speed control loop to adjust the speed according to Δn=|ni-nt|, where ni is the real-time speed, to achieve a new operating point (Pi, ni) on the trajectory, that is, let Pt=Pi, nt=ni, go back to step C.

The above-mentioned function P=f(n) is obtained as follows: first collect raw data, adjust from low static pressure to high static pressure for several target air volumes, and this static pressure must cover the actual static pressure range of the application In the process of adjusting static pressure, keep the motor under constant speed control, and keep the air volume at the target air volume by adjusting the motor speed n and the real-time input power Pi of the motor, and record the steady-state speed n of the motor at this time and the corresponding real-time input of the motor Power Pi. In this way, for a number of target air volumes, a set of speed n and real-time input power Pi of the motor are generated, and then a number of target air volumes are generated by curve fitting. Each target air volume corresponds to a functional relationship P= f _x (n), x=1, 2, 3,...,.

As mentioned above, if the external input target air volume value IN-CFM is not equal to one of the several target air volumes measured above, the function relation formula corresponding to any external input target air volume value IN-CFM can be fitted and calculated by interpolation P=f _x (n), x=1, 2, 3,...,. Realize the constant air volume control of any target air volume in the whole process.

The above-mentioned functional relation P=f(n) is a polynomial function: P=C ₁ +C ₂ ×n+...+C _m ×n ^m-1 , where C ₁ , C ₂ ,..., Cm are Coefficient, n is the motor speed value, each target air volume corresponds to a set of C ₁ , C ₂ ,..., Cm coefficients and stores them. The microprocessor obtains the corresponding value according to the input target air volume value IN-CFM through table lookup or interpolation A set of C ₁ , C ₂ ,..., Cm coefficients, so as to obtain the functional relationship P=f(n).

The functional relation P=f(n) is a second-order function: P=C ₁ +C ₂ ×n+C ₃ ×n ² .

The development and mathematical model establishment of the Direct P Control for Constant Airflow Control Apparatus Method of the present invention is as follows: Generally speaking, in a ventilation system, the fan is driven by a PM motor in a stable The air flow generated by the state of the air. A constant air volume control is achieved by speed and power control under a static pressure condition, see the following relationship: CFM = F(P, speed, pressure), where CFM is air volume, P is power, speed is speed, pressure It is static pressure. When the static pressure changes, use power and speed control to maintain the constant air volume. As the static pressure increases, the power and speed change accordingly. A cluster of constant air volume CFM curves can be tested, as shown in Figure 12. Based on these constant air volume CFM curves, a control model is developed. When the product is controlled to determine the air volume requirements, a constant air volume CFM is provided by controlling the power and speed at a specific static pressure. In Figure 12, the characteristic curve represents the physical characteristics of the constant air volume that maintains the control power and speed. Within the rated power range of all motors, for any type of airflow system air conditioner manufacturer, the power-based test results and speed curve can be It is concluded that a typical quadratic function can be well used to develop modeling as a typical function, P=C ₁ +C ₂ ×n+C ₃ ×n ² , by selecting three on the curve To be fixed points (A, B and C), the data on the corresponding coordinates are (p1, n1), (p2, n2), (p3, n3) to obtain coefficients C1, C2, C3, see the following formula:

pass

and

By solving the equation, m=3.

The process of curve fitting is to select a polynomial to describe the curve, and the coefficient of the polynomial can be obtained by the least square method. In theory, you can use P=C ₁ +C ₂ ×n+C ₃ ×n ² +...+Cm×n ^m-1 , but in fact, choosing the binomial can meet the general needs. The functional relation P=f(n) is a second-order function: P=C ₁ +C ₂ ×n+C ₃ ×n ² , where C ₁ , C ₂ and C ₃ are coefficients, and n is the motor speed value. Any one of the several target air volumes tested corresponds to a set of C ₁ , C ₂ and C ₃ coefficients and stored, and the microprocessor obtains the corresponding set of C _{1 according to the input target air volume value IN-CFM through the look-up table method.} , C ₂ and C ₃ coefficients, to obtain the functional relationship P=f(n). In a certain load, each target air volume corresponds to a set of C ₁ , C ₂ and C ₃ coefficients as shown in Table 1 below:

CFM

C 1

C 2

C 3

150	0.338	-0.151	0.0458
300	0.4423	—0.2113	0.0765
450	. . .	. . .	. . .
600	. . .	. . .	. . .
750	. . .	. . .	. . .
900	. . .	. . .	. . .

Table 1

Figure 13 is the experimental data fitting curve diagram of the direct power control constant air volume of a 1/3HP PM motor in a small pipe HVAC system. For a given target air flow, the system selects some typical air volume CFM as the test point to establish a The database is used for building mathematical models. These typical points include minimum and maximum air volume values, with some intermediate points added. According to product specifications, there are 5 typical air volume CFMs as test points, 150CFM/300CFM/450CFM/600CFM and 750CFM.

Table 2 shows an example of the test data results. The range of the motor speed is from 200 to 1400rpm; the static pressure of the system is from 0 to 1000Pa. Keep the preset constant air volume CCFM output, and obtain a standard per unit value of the motor input power corresponding to Figure 13 to form a database.

Table 2

Using the least square method, each predetermined CFM air volume corresponds to the quadratic function of power and speed, obtained in a standard calculation method: these equations define the power and the speed of any system operating point at a specific static pressure. When inputting the set air volume IN-CFM preset, the motor system defines a corresponding function, and the trajectory of its operating point follows the function definition. Equations (3) to (7) can be expressed as a standard equation, and C ₁ , C ₂ and C ₃ are constants.

That is to say, P=C ₁ +C ₂ ×n+C ₃ ×n ² , the modeling curve of equations (3) to (7) provides the trajectories of 5 selected operating points for several constant air volume CFM requirements, and Power is power, n is the speed.

As shown in Figure 14, if the requested constant air volume IN-CFM is not one of the modeling curves, use an interpolation method to obtain a new characteristic equation to fit the requested constant air volume IN-CFM, for example, when the requested constant air volume IN-CFM is requested The constant air volume IN-CFM=525cfm is required to be received, and the two adjacent curves CFM1-600cfm and CFM2-450cfm can be identified by modeling. Then the two corresponding equations can be used to calculate the new equation for the IN-CFM=525cfm curve. Based on the demanded IN-CFM=525cfm, three selected speeds ω ₁ , ω ₂ , ω ₃ , determine the power value calculated at these speeds, and use the equations corresponding to the two model curves for the dual power points at the selected Speed, linear weighted interpolation can be used to calculate the P value. First, the matrix data is listed as follows.

For a pair of power points (p _1i , p _2i ) corresponding to a selected speed ω, and the selected speeds ω ₁ , ω ₂ , ω ₃ correspond to 3 pairs of power points p _1i , p _2i , linear weighted interpolation can be used to calculate The value of Pi is pi=p _2i +w.(p _1i -p _2i ).

The weight value W is calculated as follows:

Note that CFM2≤IN-CFM≤CFM1, etc. 0≤W≤1. The following matrix equation can be calculated,

In this way, the corresponding IN-CFM=525cfm function P=C ₁ +C ₂ ×n+C ₃ ×n ² can be obtained. To solve this matrix equation, the _{coefficients of C 1} , C ₂ and C ₃ can be calculated. Therefore, any required input air volume IN-CFM can get the power equation. Since this process is initialized by the microprocessor in the motor controller, the single-chip microcomputer, the calculation of power does not need to consume more real-time CPU resources.

The real-time input power Pi of the motor is processed by a digital low-pass filter: the application of filtering technology of an infinite impulse response filter assumes that the input and output are sampled within the sampling period (PWM switching frequency). The sequence representation of power input (P _in1 ,...P _ini …, P _inn ) and the sequence representation of power output (Pout1,...Pouti...,Poutn) correspond to the same time point, and then the low-pass filter can be considered as:

Where T: time constant;

After the above terms, the recurrence relationship is given again. The discrete-time, low-pass filter can be expressed as an exponentially weighted moving average.

p _outi ＝a·p _ini +(1-a)·p _outi-1

in

By definition, the smoothing factor is 0≤α≤1. If α=0.5, then the time constant is equal to the sampling period. If α<<0.5, then the time constant is significantly larger than the sampling interval.

The power filter is controlled by DPC, a≤0.01. So Δt=a T.

The change from one filter output to the next is proportional to the difference between the previous output and input, and this smoothness exponentially decays in proportion to the continuous time system. As expected, as time continues to increase, the discrete-time smoothing factor α decreases, and the sequence of power output (Pout1,...Pouti...,Poutn) reacts slowly, and the sequence of power input represents (P _in1 , …P _ini …, P _inn ) Therefore, the system has higher inertia.

This filtering technique can also be applied to the two signal processing calculations of DC bus voltage and DC bus current.

It can be seen that the Direct Power Control (DPC) uses speed control to achieve power control. The function of the power/speed control logic is to coordinate the power/speed loop time constant to ensure the stability of the system. Control can be achieved by controlling the precise control of the motor, comparing with torque control. Whether it is scalar or vector control, speed control is more effective than torque control, which improves control accuracy.

DPC control is speed control through unique power and fan load speed characteristics. When the motor goes from zero speed to high speed, the power also increases from zero to high speed. The motor speed will rise until it reaches a pair of operating points A (power, speed), which is the static pressure point, as shown in Figure 16. When the static pressure suddenly increases, in the speed control mode, the motor provides more power (or Greater torque) to maintain speed, due to higher static pressure requires a lot of power requirements. The power will suddenly rise to a higher level. When the motor system reaches a new operating point "B" at the same speed, the algorithm will know whether it is at a constant CFM trajectory curve operating point, thereby determining a pair of power/ Speed point "C". But point C is not a stable operating point. Due to high power requirements, go to point "D", repeat, and wait until it converges to a new stable operating point "G", and end.

In implementation, we can reduce power fluctuations when sudden changes are made by using restricted power increment control. It is shown in Figure 17, where the incremental power can be specified as ΔP. As long as the power change exceeds the power increment ΔP, the speed control will perform speed control. In this way, all operating points work in a positive and negative bandwidth corresponding to the constant air volume CFM trajectory curve. The air flow control system in the transition process of static pressure changes is stable.

As shown in Figure 18, the above-mentioned motor direct power control constant air volume control method and algorithm have been tested on our PM motor controller, and all system performance meets the requirements shown in Figure 18.

Figure 15 is the logic block diagram of this algorithm in the PM motor scalar control application. The input power is calculated from the DC bus voltage and current. The power and speed will be limited to the maximum power P _max and the speed n _max .

Calculate the real-time input power value Pi of the motor through the feedback of the DC bus current/voltage, then match the input air volume IN-CFM with the power/speed data to obtain the calculated value Pt of the motor input power, and compare the calculated value Pt of the motor input power with The real-time output power Pi of the motor obtains the power difference ΔP, and the power difference ΔP is limited to avoid excessive power difference ΔP and large adjustment power fluctuations. The power difference ΔP is output through the power/speed control logic for speed loop control, and the PWM inverter performs speed control.

The calculation of the real-time input power Pi of the motor. In Figure 10, scalar control is adopted. The motor operating parameter detection circuit includes a bus current detection circuit and a bus voltage detection circuit. The bus current detection circuit and the bus voltage detection circuit detect the real-time bus current IDC and Real-time bus voltage VDC, real-time motor input power Pi=IDC×VDC.

As shown in Figure 19, assume that the PM motor is a 3-phase brushless DC permanent magnet synchronous motor based on vector control without a rotor position sensor. The phase current detection circuit detects the phase current of the stator winding and then inputs it to the microprocessor. The flow observer calculates the rotor speed n and rotor position based on the phase current and the DC bus voltage. After the AC INPUT passes through a full-wave rectifier circuit composed of diodes D7, D8, D9, and D10, the DC bus voltage Vbus is output at one end of the capacitor C1, and the DC bus voltage Vbus is related to the input AC voltage. Figure 20 is A typical block diagram of vector control.

As shown in Figure 21, it is a typical coordinate system diagram of vector control. Vector control is described in detail in textbooks and patent documents, so there is no need to describe it here. Knowing the target speed of control, vector control can be used to achieve closed-loop control. There are 3 coordinate systems in the figure, one is a fixed Cartesian coordinate system (α-β coordinate), one is the rotor rotation coordinate (d-q axis coordinate system), and the other is the stator flux rotation coordinate system (ds-qs axis coordinate system). In the figure, ω represents the rotor speed, θ is the rotation angle between the d-q axis coordinate system and the α-β coordinate, and δ is the rotation load angle between the d-q axis coordinate system and the ds-qs axis coordinate system. Therefore, the vector current and vector voltage of the d-q axis coordinate system can be converted into the current and voltage of the α-β coordinate system.

In the vector control in Figure 19, the motor operating parameter detection circuit includes a phase current detection circuit and a bus voltage detection circuit. The phase current detection circuit and the bus voltage detection circuit detect the phase current and bus voltage data and input the phase current and bus voltage data to the microprocessor. The real-time bus voltage V _bus is converted into currents Iα, Iβ, voltages Vα, Vβ on the αβ coordinates, and the real-time input power of the motor Pi=3/2 (Iα×Vα+Iβ×Vβ)

As shown in Figure 22, in the sensorless vector control PM motor system, the logical block diagram of the DPC constant air volume control method. The input power is calculated by the vector control. This power is filtered and used for power control. The flux observer estimates the rotor speed and rotor Position, then according to the external input air volume IN-CFM and power/speed data matching, use the function P=f(n) to convert into the corresponding calculated value of motor input power Pt, compare the calculated value of motor input power Pt with the real-time output of the motor For the power Pi, the power difference ΔP is obtained, and the power difference ΔP is limited to avoid excessive power difference ΔP and large fluctuations in the adjustment power. The power difference ΔP is output through the power/speed control logic for speed loop control, and the speed loop control is realized through vector control.

The data of this embodiment is the data obtained when the air volume is 0-1000 CFM, the static pressure is at a low static pressure of 0-300 Pa, and the speed is 0-2000 RPM, which is suitable for constant air volume under this condition.

Embodiment three:

The present invention uses the small constant air volume induced draft fan of the first embodiment. Its output air volume is in the range of 0-300CFM, working in the range of 0-1000Pa, and the rotating speed is in the range of 0-8000RPM. After calculation and comparison, the experimental data of embodiment 1 is very good. Most of the mismatches result in a large constant air volume control error, which cannot meet the customer's requirements, especially when the static pressure is 500Pa-1000Pa and the rotation speed is 4000RPM-8000RPM, the original data error is very large. Therefore, this embodiment provides a new solution on the basis of the second embodiment to expand the requirements of the working environment to which it can adapt.

The calculation model of this embodiment is the same as the calculation model of the second embodiment. The reason for increasing the power proportional coefficient a and speed proportional coefficient b is that when the target constant air volume is not the air volume value in the table, it needs to be calculated by interpolation. The coefficients obtained by the interpolation method are limited. When the speed and power are relatively large, the coefficient calculated by the interpolation method will overflow (the coefficient exceeds 2 ¹⁶ ), and the calculation result cannot be obtained. Therefore, it is necessary to increase the power proportional coefficient a and the speed proportional coefficient b . To obtain the calculation result, both P/a and n/b need to be around 1 (between 0-2). According to the measured speed and power range, the value of the power proportional coefficient a is obtained in the range of 50-100. The scale factor b is in the range of 3000-8000.

table 3

The data in Table 3 will overflow if the coefficients C1, C2, and C3 calculated by the interpolation method in the second embodiment are used (the coefficient exceeds 2 ¹⁶ ), so the current can be implemented only after adjusting the power proportional coefficient a and the rotational speed proportional coefficient b.

This embodiment provides: a constant air volume induced draft fan, including a volute 1, a wind wheel 2, and a motor 3. The motor 3 is installed outside the volute 1 through a mounting bracket 4, the motor 3 includes a motor body and a motor controller, and the motor body includes The stator assembly 31, the permanent magnet rotor assembly 32, the rotating shaft 33, the motor housing 34, the volute 1 is equipped with a wind wheel 2, and the motor 3 drives the wind wheel 2 to rotate. The motor controller includes a motor operating parameter detection circuit and a micro The processor is characterized in that: the microprocessor obtains the function relation P/a=f(n/b) for constant air volume control according to the input target air volume value IN-CFM, where P is the motor input power and n is the motor speed, a is the power proportional coefficient, and b is the proportional coefficient of the speed. By controlling the input power and speed, the induced draft fan can output a constant air volume.

The functional relation P/a=f(n/b) is a polynomial function:

Among them, C ₁ , C ₂ ,..., Cm are coefficients. According to the input target air volume value IN-CFM, a corresponding set of C ₁ , C ₂ ,..., Cm coefficients and power scale coefficients a and The proportional coefficient b of the speed is shown in Table 4 to obtain the functional relationship P/a=f(n/b), the value of the power proportional coefficient a is in the range of 50-100, and the speed proportional coefficient b is 3000-8000 scope.

Air volume CFM	C 1	C 2	C 3	a	b
50	0.238	-0.141	0.0258	64	3320
100	0.1533	-0.193	0.0465	73	4545
150	. . .	. . .	. . .	To	To
200	. . .	. . .	. . .	To	To
250	. . .	. . .	. . .	To	To

300

. . .

. . .

. . .

To

To

Table 4

Claims (10)

1. A constant air volume induced draft fan includes a volute (1), a wind wheel (2), and a motor (3). The motor (3) is installed outside the volute (1) through a mounting bracket (4), and the motor (3) includes a motor The body and the motor controller. The motor body includes a stator assembly (31), a permanent magnet rotor assembly (32), a rotating shaft (33), a motor housing (34), a wind wheel (2) is installed in the volute (1), and the motor ( 3) Drive the wind wheel (2) to rotate, the motor controller includes a motor operating parameter detection circuit and a microprocessor, and is characterized in that the microprocessor is based on the input target air volume value IN-CFM and a preset constant air volume The control function P/a=f(n/b), by controlling the input power and speed to make the induced draft fan output a constant air volume, where P is the motor input power, n is the motor speed, a is the power ratio coefficient, and b is the speed Scale factor.
2. The constant air volume induced draft fan according to claim 1, wherein the function P/a=f(n/b) is a polynomial function:

   

   Among them, C ₁ , C ₂ ,..., C _m are coefficients. According to the input target air volume value IN-CFM, a corresponding set of C ₁ , C ₂ ,..., C _m coefficients and power scale coefficients can be obtained through table lookup or interpolation The proportional coefficient b between a and the speed, so as to obtain the functional relationship P/a=f _x (n/b), x=1, 2, 3,..., the value of the power proportional coefficient a is in the range of 50-100, and the speed ratio The coefficient b is in the range of 3000-8000.
3. The constant air volume induced draft fan according to claim 1, wherein the motor operating parameter detection circuit includes a bus current detection circuit and a bus voltage detection circuit, and the bus current detection circuit and the bus voltage detection circuit detect real-time bus current IDC and real-time bus voltage VDC, real-time motor input power Pi=IDC×VDC.
4. The constant air volume induced draft fan according to claim 1, wherein the motor operating parameter detection circuit includes a phase line current detection circuit and a bus voltage detection circuit, and the phase line current detection circuit and the bus voltage detection circuit detect real-time The phase current and real-time bus voltage data are input to the microprocessor, and the real-time phase current and real-time bus voltage are converted into currents Iα, Iβ, voltage Vα, Vβ on the α-β coordinates, and the real-time input power of the motor Pi=3/2(Iα· Vα+Iβ·Vβ).
5. A constant air volume induced draft fan according to claim 1 or 2 or 3 or 4, characterized in that: the motor controller includes a control box (35) and a control circuit board (36), and a control circuit board (36) Installed inside the control box (35), the end of the motor housing (34) is installed with the control box (35), the opening (351) of the control box (35) faces the end of the motor housing (34), and the width of the control box (35) is H It is wider than the diameter D of the motor housing (34), the edge of the control circuit board (36) is arranged with an electronic element (37) with a longer axial length, and the bottom of the electronic element (37) with a longer axial length It extends out of the control box (35) and is located on one side of the motor housing (34).
6. The constant air volume induced draft fan according to claim 5, characterized in that the electronic element (37) with a longer axial length is a capacitive element.
7. A constant air volume induced draft fan according to claim 6, characterized in that: the control box (35) axially protrudes with a baffle (352), the baffle (352) shields the longer axial length The outer side of the electronic vitality piece (37).
8. A constant air volume induced draft fan according to claim 7, characterized in that: the baffle (352) is also connected with a cover plate (38), and the cover plate (38) includes a left side plate (381) and a right side plate (381). The plate (382) and the bottom plate (383), the left side plate (381), the right side plate (382), the bottom plate (383) and the baffle plate (352) are enclosed to cover the electronic vitality parts ( 37) outside of the bottom.
9. A constant air volume induced draft fan according to claim 8, characterized in that: the bottom of the baffle (352) is provided with upper mounting ears (3521) protruding outwards, and the lower mounting ears are protruding outwards from the cover plate (38). (384), the upper mounting ear (3521) and the lower mounting ear (384) are connected by a first screw (40).
10. A constant air volume induced draft fan according to claim 9, characterized in that: the motor housing (34) includes a rear end cover (341), and lower lugs (3411) protrude from both sides of the rear end cover (341). ), upper lugs (353) protrude from both sides of the control box (35), and the lower lugs (3411) and the upper lugs (353) are connected by a second screw (39).

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