A constant air volume induced draft fan

Abstract

The present invention discloses a constant air volume induced draft fan, which comprises 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 inside 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 microprocessor makes the induced draft fan output a constant air volume by controlling the input power and speed according to the input target air volume value IN-CFM and the functional relationship formula P / a = f(n / b) of constant air volume control, where P is the input power of the motor, n is the motor speed, a is the power proportionality coefficient, and b is the proportionality coefficient of the speed. It can make the operating speed range of the induced draft fan be 0 - 8000 RPM, the static pressure range be 0 - 1000 Pa, and the small output air volume be 0 - 300 CFM, which is applicable to different ranges.

Description

Technical Field:

[0001] The present invention relates to a constant air volume induced draft fan. Background Art:

[0002] Existing DC induced draft fans are all constant speed induced draft fans. When the static pressure fluctuates greatly, the air volume output by the DC induced draft fan is unstable.

[0003] The applicant applied for a patent for invention in 2014. The application number of this patent is: CN201410042547.8, the application date is: 2014.01.28, the publication (announcement) number is: CN104807152A, and the patent name is: A constant air volume control method for direct power control of an open PM motor and its applied HVAC system; this constant air volume control method of this patent is applicable to low static pressure (0 - 300 Pa), low speed (0 - 2000 RPM), and large air volume (0 - 1000 CFM).

[0004] It is not applicable to occasions with high static pressure, high speed, and small air volume, resulting in a large limitation in the application range. In view of this, it is necessary to improve this control method.

[0005] In addition, for the current induced draft fan, a motor controller is installed behind the motor. Some of the axial heights of the electronic components in the motor controller are relatively high, resulting in a relatively large axial dimension of the entire induced draft fan, which affects the installation. Summary of the Invention:

[0006] The purpose of the present invention is to provide a constant air volume induced draft fan to solve the technical problem of relatively narrow application range of constant air volume control by controlling the input power and motor speed in the prior art.

[0007] A further purpose of the present invention is to provide a constant air volume induced draft fan to solve the technical problem that the axial dimension of the entire induced draft fan is relatively large and affects the installation in the prior art.

[0008] The purpose of the present invention is achieved through the following technical solutions.

[0009] 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 inside the volute, and the motor drives the wind wheel to rotate. The motor controller includes a motor operation parameter detection circuit and a microprocessor. It is characterized in that: the microprocessor makes the induced draft fan output a constant air volume by controlling the input power and speed according to the input target air volume value IN - CFM and the pre - set function of constant air volume control P / a = f(n / b), where P is the motor input power, n is the motor speed, a is the power proportionality coefficient, and b is the proportionality coefficient of the speed.

[0010] The above function relation P / a = f(n / b) is a polynomial function:

[0011]

[0012] Where C1, C2, …, Cm are coefficients. According to the input target air volume value IN-CFM, a corresponding set of coefficients C1, C2, …, Cm, power ratio coefficient a, and rotational speed ratio coefficient b are obtained through the look-up table method or interpolation method, so as to obtain the function relation P / a = fx(n / b), x = 1, 2, 3, … The value range of the power ratio coefficient a is 50 - 100, and the value range of the rotational speed ratio coefficient b is 3000 - 8000.

[0013] The above-mentioned 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 the real-time bus voltage VDC. The real-time input power of the motor Pi = IDC × VDC.

[0014] The above-mentioned 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 real-time phase current and the real-time bus voltage data and input them into the microprocessor. The real-time phase current and the real-time bus voltage are converted into currents Iα, Iβ, voltages Vα, Vβ on the α-β coordinate. The real-time input power of the motor Pi = 3 / 2(Iα·Vα + Iβ·Vβ).

[0015] 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 control box is installed at the tail of the motor housing. The opening of the control box faces the tail of the motor housing. The width H of the control box is wider than the diameter D of the motor housing. Electronic components with a longer axial length are arranged at the edge of the control circuit board. The bottom of the electronic components with a longer axial length extends out of the control box and is located on one side of the motor housing.

[0016] The above-mentioned electronic components with a longer axial length are capacitor components.

[0017] The above-mentioned control box axially extends a baffle, and the baffle blocks the outside of the electronic components with a longer axial length.

[0018] A cover plate is also connected to the above-mentioned baffle. 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 a cover body to cover the outside of the bottom of the electronic components with a longer axial length.

[0019] The bottom of the above-mentioned baffle protrudes outward to form an upper mounting ear, and the cover plate protrudes outward to form a lower mounting ear. The upper mounting ear and the lower mounting ear are connected by a first screw.

[0020] The motor housing described above includes a rear end cover. Lower lugs extend from both sides of the rear end cover, and upper lugs extend from both sides of the control box. The lower lugs and the upper lugs are connected by second screws.

[0021] Compared with the prior art, the present invention has the following effects:

[0022] 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 a microprocessor. It is characterized in that: the microprocessor obtains the functional relationship formula 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, n is the motor speed, a is the power proportionality coefficient, and b is the speed proportionality coefficient. By controlling the input power and speed, the induced draft fan outputs a constant air volume. By increasing the power proportionality coefficient a and the speed proportionality coefficient b, the operating speed range of the induced draft fan can be 0 - 8000 RPM, the static pressure range can be 0 - 1000 Pa, and the small output air volume can be 0 - 300 CFM, which is suitable for different working environment requirements.

[0023] 2) Other advantages of the present invention are described in detail in the embodiments. Description of the drawings:

[0024] Figure 1 is a perspective view of the induced draft fan of Embodiment 1 of the present invention from one angle;

[0025] Figure 2 is a perspective view of the induced draft fan of Embodiment 1 of the present invention from another angle;

[0026] Figure 3 is an exploded view of the induced draft fan of Embodiment 1 of the present invention from one angle;

[0027] Figure 4 is a partial structure exploded view of the induced draft fan of Embodiment 1 of the present invention;

[0028] Figure 5 is a top view of the induced draft fan of Embodiment 1 of the present invention;

[0029] Figure 6 is this Figure 5 A - A cross-sectional view;

[0030] Figure 7 is a perspective view of the motor controller of the induced draft fan of Embodiment 1 of the present invention;

[0031] Figure 8 is an exploded view of the motor controller of the induced draft fan of Embodiment 1 of the present invention;

[0032] Figure 9It is the circuit block diagram of the motor controller of the induced draft fan in the first embodiment of the present invention;

[0033] Figure 10 is Figure 9 the corresponding partial circuit diagram;

[0034] Figure 11 It is the control flow chart in the second embodiment of the present invention;

[0035] Figure 12 It is a cluster of constant air volume fitting curves obtained through experiments in the second embodiment of the present invention;

[0036] Figure 13 It is the experimental data fitting curve graph of the direct power control of the 1 / 3HP PM motor with constant air volume in the second embodiment of the present invention;

[0037] Figure 14 It is the experimental data fitting curve graph of solving the experimental data of any input air volume by using the interpolation method in the second embodiment of the present invention

[0038] Figure 15 It is the control logic diagram of the constant air volume control method in the second embodiment of the present invention;

[0039] Figure 16 It is a schematic diagram of a control process of the constant air volume control method in the second embodiment of the present invention;

[0040] Figure 17 It is another schematic diagram of a control process of the constant air volume control method in the second embodiment of the present invention;

[0041] Figure 18 It is the test result graph verified through experiments of the constant air volume control method in the second embodiment of the present invention;

[0042] Figure 19 It is an implementation circuit block diagram of the motor controller of the PM motor in the second embodiment of the present invention;

[0043] Figure 20 It is the schematic diagram of the vector control of a typical traditional PM motor;

[0044] Figure 21 It is the relationship diagram of each coordinate system of the vector control of a typical traditional PM motor;

[0045] Figure 22 It is the control logic diagram of the constant air volume control method in the second embodiment of the present invention. Specific implementation method:

[0046] The present invention will be further described in detail below through specific embodiments in combination with the accompanying drawings.

[0047] Embodiment 1:

[0048] As Figures 1 to 8 shown, 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 inside the volute 1, and the motor 3 drives the wind wheel 2 to rotate. The motor controller includes a control box 35 and a control circuit board 36. The control circuit board 36 is installed inside the control box 35. The control box 35 is installed at the tail of the motor housing 34. The opening 351 of the control box 35 faces the tail of the motor housing 34. The width H of the control box 35 is wider than the diameter D of the motor housing 34. Electronic components 37 with a relatively long axial length are arranged at the edge of the control circuit board 36. The bottom of the electronic components 37 with a relatively long axial length extends out of the control box 35 and is located on one side of the motor housing 34. This reduces the height of the combination of the motor body and the motor controller, occupies less space, is suitable for installation with different loads, and the structure is more compact.

[0049] The above-mentioned electronic components 37 with a relatively long axial length are capacitor components, and the layout is reasonable.

[0050] The above-mentioned control box 35 axially extends a baffle 352. The baffle 352 shields the outside of the electronic components 37 with a relatively long axial length. The baffle 352 can prevent collision and block the water outside.

[0051] A cover plate 38 is further connected to the above-mentioned baffle 352. 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 enclose a cover body to cover the outside of the bottom of the electronic components 37 with a relatively long axial length. This can greatly improve the tightness of the electronic components 37 and effectively protect the electronic components 37.

[0052] The bottom of the above-mentioned baffle 352 protrudes outward to form an upper mounting ear 3521, and the cover plate 38 protrudes outward to form a lower mounting ear 384. 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.

[0053] 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 extend from both sides of the control box 35. The lower lugs 3411 and the upper lugs 353 are connected by a second screw 39. The structure is simple and the installation is convenient.

[0054] As Figure 9 、 Figure 10As shown, the control circuit board 36 of the motor controller integrates the following circuits: a microprocessor, an inverter circuit, a phase current measurement circuit, a bus current detection circuit, a bus voltage detection circuit, a rectifier circuit, a switching power supply, and a protection circuit. The phase current measurement circuit detects the phase current of the coil windings 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 windings. The bus current detection circuit inputs the bus current to the microprocessor, and the bus voltage detection circuit inputs the DC bus voltage to the microprocessor. The microprocessor controls the inverter circuit, and the inverter circuit controls the on / off of each phase coil winding of the stator assembly. The microprocessor controls the motor input power control circuit.

[0055] Assume that the PM motor 3 is a three-phase brushless DC permanent magnet synchronous motor. The rotor position measurement circuit 14 generally uses three Hall sensors. The three Hall sensors respectively detect the rotor position in a 360-degree electrical angle cycle. Each time it rotates 120 degrees electrical angle, the power-on of each phase coil winding of the stator assembly 12 is changed, forming a three-phase six-step control mode. After the AC input (AC INPUT) passes through the 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. After the voltage of the AC input (AC INPUT) is determined, the line voltage UP of the three-phase winding is the PWM chopping output voltage, UP = VDC * w, where w is the duty cycle of the PWM signal input by the microprocessor to the inverter circuit. Changing the line voltage UP can change the DC bus current IDC. The inverter circuit is composed of electronic switching tubes Q1, Q2, Q3, Q4, Q5, and Q6. The control ends of the electronic switching tubes Q1, Q2, Q3, Q4, Q5, and Q6 are respectively controlled by six PWM signals (P1, P2, P3, P4, P5, P6) output by the microprocessor. The inverter circuit is also connected to a resistor R1 for detecting the bus current IDC. The bus current detection circuit converts the detected bus current IDC of the resistor R1 and transmits it to the microprocessor. The motor input power control is controlled by the electronic switching tube Q7. One PWM signal output by the microprocessor, that is, P0, controls the conduction time of the electronic switching 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.

[0056] Embodiment 2:

[0057] Specifically, see Figure 10 、 Figure 11As shown, the constant air volume control method for direct power control of a PM motor. The PM motor drives a wind wheel. The PM motor has a stator assembly, a permanent magnet rotor assembly, and a motor controller. The motor controller 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 microprocessor. 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. The microprocessor controls the inverter circuit, and the inverter circuit controls the on / off of each phase coil winding of the stator assembly. The microprocessor controls the motor input power control circuit. It is characterized by the following steps:

[0058] Step A) Start the motor controller and receive the target air volume value IN-CFM;

[0059] Step B) Obtain the corresponding functional relationship P = f x (n), x = 1, 2, 3,..., where n is the speed and P is the input power of the motor;

[0060] 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, and make it reach a stable working point (Pt, nt) along the control trajectory of the function P = f(n); Pt, nt is a pair of input power and speed located on the trajectory that satisfies the constant air volume control function P = f(n);

[0061] Step D) Maintain the direct power control constant air volume control mode: Calculate the real-time input power Pi of the motor according to the motor operation parameters; Calculate ΔP = |Pt - Pi|;

[0062] Step E) If the power increment value ΔP is less than the set value Pset, maintain the existing working point;

[0063] 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 operation time of the speed loop has reached; If the operation time of the speed loop has not reached, maintain the existing working point;

[0064] Step G) If the operation time of the speed loop has reached, enter the speed control loop to adjust the speed according to Δn = |ni - nt|, ni is the real-time speed, and achieve a new working point (Pi, ni) on the trajectory, that is, make Pt = Pi, nt = ni, and return to step C.

[0065] The above-mentioned function P = f(n) is obtained as follows: First, collect the original data. For several target air volumes, adjust from low static pressure to high static pressure, and this static pressure should cover the actual static pressure range of the application. During the process of adjusting the static pressure, keep the motor under constant speed control, and by adjusting the motor speed n and the real-time input power Pi of the motor, maintain the air volume at the target air volume, and record the steady-state speed n of the motor and the corresponding real-time input power Pi of the motor at this time. In this way, for several target air volumes, a set of speed n and real-time input power Pi of the motor are generated. Then, through the method of curve fitting, a function relation P = f x (n), where x = 1, 2, 3, …,

[0066] If the above-mentioned externally input target air volume value IN-CFM is not equal to any one of the several measured target air volumes, the function relation P = f x (n) corresponding to any externally input target air volume value IN-CFM can be calculated by interpolation and fitting, where x = 1, 2, 3, …,. The constant air volume control for any target air volume throughout the process is achieved.

[0067] The above-mentioned function relation P = f(n) is a polynomial function: P = C1 + C2×n +... + C m ×n m-1 , where C1, C2, …, Cm are coefficients, n is the motor speed value, a set of C1, C2, …, Cm coefficients corresponding to each target air volume are stored, and the microprocessor obtains the corresponding set of C1, C2, …, Cm coefficients through the look-up table method or interpolation method according to the input target air volume value IN-CFM, so as to obtain the function relation P = f(n).

[0068] The above-mentioned function relation P = f(n) is a second-order function: P = C1 + C2×n + C3×n 2 .

[0069] The development and mathematical model establishment of the direct power control constant air volume control method (Direct P Control for Constant Airflow Control Apparatus Method) of the present invention is as follows: Generally speaking, in a ventilation system, the fan driven by a PM motor generates air flow in a stable state. A constant air volume control is achieved by speed and power control under a static pressure condition, as shown in the following relationship: CFM = F (P, speed, pressure), where CFM is air volume, P is power, speed is speed, and pressure is static pressure. When the static pressure changes, the constant air volume is maintained by power and speed control. As the static pressure increases, the power and speed change accordingly. A cluster of constant air volume CFM curves can be tested, such as Figure 12 Based on these constant CFM curves, a control model is developed that, when the product control determines the air volume requirement, provides a constant CFM by controlling power and speed at a specific static pressure. Figure 12 In the figure, the characteristic curve represents the physical characteristics of maintaining constant air volume by controlling power and speed. Within the rated power range of all motors, for air conditioning manufacturers of any type of airflow system design, based on the test results of power and speed curves, it can be concluded that a typical quadratic function can be well used for developing modeling. As a typical function, P = C1 + C2 × n + C3 × n 2 By selecting three undetermined points (A, B and C) on the curve, the corresponding coordinate data are (p1, n1), (p2, n2), (p3, n3) to obtain the coefficients C1, C2, C3, as shown in the following formula:

[0070] pass and By solving the equation, m=3.

[0071] The process of curve fitting is to select a polynomial to describe the curve. The coefficients of the polynomial can be obtained by the least squares method. In theory, P = C1 + C2 × n + C3 × n 2 +...+Cm×n m-1 In fact, choosing binomial can meet general needs. The functional relationship P = f(n) is a second-order function: P = C1 + C2 × n + C3 × n 2, where C1, C2, and C3 are coefficients, n is the motor speed value. For any one of the several target air volumes tested, a corresponding set of C1, C2, and C3 coefficients is stored. The microprocessor obtains the corresponding set of C1, C2, and C3 coefficients through a look-up table method based on the input target air volume value IN-CFM, thereby obtaining the functional relationship P = f(n). For each target air volume in a certain load, the corresponding set of C1, C2, and C3 coefficients is shown in Table 1 below:

[0072] CFM <![CDATA[C1]]> <![CDATA[C2]]> <![CDATA[C3]]> 150 0.338 —0.151 0.0458 300 0.4423 —0.2113 0.0765 450 。。。 。。。 。。。 600 。。。 。。。 。。。 750 。。。 。。。 。。。 900 。。。 。。。 。。。

[0073] Table 1

[0074] Figure 13 is the experimental data fitting curve graph of the direct power control constant air volume of a 1 / 3HP PM motor in a small duct HVAC system. For a given target air flow, the system selects some typical air volume CFM as test points to establish a database for establishing a mathematical model. These typical points include the minimum and maximum air volume values, and some additional intermediate points according to the product specifications. There are 5 typical air volume CFM as test points, which are 150CFM / 300CFM / 450CFM / 600CFM, and 750CFM respectively.

[0075] Table 2 shows an example of the test data results. The range of the motor speed is from 200 to 1400 rpm; the static pressure of the system is from 0 to 1000 Pa. Keeping the preset constant air volume CCFM output, a corresponding Figure 13 per-unit value of the motor input power is obtained to form a database.

[0076]

[0077]

[0078] Table 2

[0079] Using the least squares method, each predetermined CFM air volume corresponds to a quadratic function of power and speed, which is obtained by a standard calculation method: These equations define the power and the speed at the operating point of any system at a specific static pressure. When the input set air volume IN-CFM is preset, the motor system defines a corresponding function, and the locus of its operating point follows the function definition. Equations (3) to (7) can be expressed as a standard equation, where C1, C2, and C3 are constants.

[0080]

[0081]

[0082]

[0083]

[0084]

[0085] That is, P = C1 + C2×n + C3×n is obtained 2 , the modeling curves of equations (3) to (7) provide the locus of 5 selected operating points for several constant air volume CFM requirements. Power is the power and n is the rotational speed.

[0086] Such as Figure 14 shown, if the requested constant air volume IN - CFM requirement is not one of the modeling curves, an interpolation method is used 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 = 525 cfm requirement is received, the adjacent two curve CFM1 - 600 cfm and CFM2 - 450 cfm modeling can be identified. Then the two corresponding equations can be used to calculate the new equation of the curve with IN - CFM = 525 cfm. Based on the demand of IN - CFM = 525 cfm, three selected speeds ω1, ω2, ω3, the power values calculated at these speeds are determined. Using the equations corresponding to the two model curves for the double power points at the selected speeds, linear weighted interpolation can be used to calculate the P value. First

[0087] List the matrix data as follows.

[0088]

[0089] For a pair of power points (p 1i , p 2i ) corresponding to a selected speed ω, the selected speeds ω1, ω2, ω3 correspond to 3 pairs of power points p 1i , p 2i , linear weighted interpolation can be used to calculate the Pi value as

[0090] pi = p 2i + w.(p 1i - p 2i ).

[0091] The weight value W is calculated as follows:

[0092] Note that CFM2 ≤ IN - CFM ≤ CFM1, and 0 ≤ W ≤ 1. The following matrix equation can be calculated,

[0093]

[0094] So the function P = C1 + C2×n + C3×n corresponding to IN - CFM = 525 cfm 2can be obtained. Solving this matrix equation allows the calculation of the coefficients C1, C2, and C3. Therefore, a power equation can be obtained for any required input air volume IN-CFM. Since this process is initialized by the microprocessor - single-chip microcomputer in the motor controller, the calculation of power does not consume a large amount of real-time CPU resources.

[0095] The real-time input power Pi of the motor is processed using a digital low-pass filter: the application of the filtering technique of an infinite impulse response filter assumes that the input and output samples are within the sampling period (PWM switching frequency). The sequence representation of the power input (P in1 , … P ini …, P inn ) and the sequence of the power output (Pout1, … Pouti …, Poutn) are used to represent corresponding to the same time point. Then, the low-pass filter can be considered as:

[0096] where T: time constant;

[0097] After the above terms, the recurrence relation is re-given. For discrete time, the low-pass filter can be expressed as an exponentially weighted moving average.

[0098] p outi = a · p ini + (1 - a) · p outi-1

[0099] where

[0100]

[0101] By definition, the smoothing factor 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 greater than the sampling interval.

[0102]

[0103] For power filtering in DPC control, a ≤ 0.01. So Δt = aT.

[0104] The change from one filter output to the next is proportional to the difference between the previous output and the input. This proportion of exponentially decaying smoothness is in a continuous-time system. As expected, as time increases continuously, the discrete-time smoothing factor α decreases, and the sequence representing the power output (Pout1, … Pouti …, Poutn) responds more slowly to the sequence representing the power input (P in1 , … P ini …, P inn ) Therefore, the system has higher inertia.

[0105] This filtering technology can also be applied to the two signal processing calculations of DC bus voltage and DC bus current.

[0106] It can be seen that this direct power control DPC (Direct Power Control) 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. The control can be achieved by controlling the precise control of the motor and torque control. Whether in scalar or vector control, speed control is more effective than torque control and improves control accuracy.

[0107] DPC control is a speed control based on the unique power and fan load speed characteristics. As the motor speed increases from zero to high speed, the power also increases from zero to high speed. The motor speed will increase until it reaches a pair of operating points A (power, speed), which are static pressure points, such as Figure 16 As shown, when the static pressure suddenly increases, in speed control mode, the motor provides more power (or more torque) to maintain speed, because the higher static pressure requires a large power requirement. The power will suddenly rise to a higher level, and when the motor system reaches a new operating point "B" at the same speed, the algorithm will know that this is not an operating point in the constant CFM trajectory curve, and thus determine a pair of power / speed points "C". But point C is not a stable operating point due to the high power requirement, and then go to point "D", repeatedly, and so on, converging to a new stable operating point "G", ending.

[0108] In implementation, we can reduce the power fluctuation during sudden changes by using limited power increment control. It is shown in Figure 17 In this case, the incremental power can be specified as ΔP. As long as the power change exceeds the power increment ΔP, the speed control will be in speed control. In this way, all operating points operate in a positive and negative bandwidth corresponding to the constant air volume CFM trajectory curve. The air flow control system is stable during the static pressure change transition process.

[0109] like Figure 18 As shown, the above motor direct power control constant air volume control method and algorithm have been tested on our PM motor controller, and all system performances meet the following requirements: Figure 18 Requirements shown.

[0110] Figure 15 This is the logic block diagram of the algorithm applied to PM motor scalar control. The input power is obtained by calculating the DC bus voltage and current. The power and speed will be limited to the maximum power P max , and speed n max Within.

[0111] Calculate the real-time input power value Pi of the motor through the DC bus current / voltage with feedback. Then, based on the matching of the external input air volume IN-CFM with the power / speed data, obtain the calculated value Pt of the motor input power. Compare the calculated value Pt of the motor input power with the real-time output power Pi of the motor to obtain the power difference ΔP. The power difference ΔP is limited to avoid excessive power difference ΔP and regulate large power fluctuations. The power difference ΔP is output through the power / speed control logic for speed loop control, and the PWM frequency converter performs speed control.

[0112] Calculation of the real-time input power Pi of the motor Figure 10 In this case, 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 the real-time bus voltage VDC. The real-time input power Pi of the motor = IDC × VDC.

[0113] As Figure 19 Shown in the figure, assume that the PM motor is a three-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 flux observer in the microprocessor calculates the rotor speed n and the rotor position based on the phase current and the DC bus voltage. After the AC input (ACINPUT) passes through the 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. The DC bus voltage Vbus is related to the input AC voltage. Figure 20 It is a typical block diagram of vector control.

[0114] As Figure 21 Described above, 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, closed-loop control can be achieved using vector control. There are three coordinate systems in the figure, one is a fixed Cartesian coordinate system (α-β coordinate), one is the rotor rotating coordinate system (d-q axis coordinate system), and one is the stator flux rotating 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 in the d-q axis coordinate system can be converted into the current and voltage in the α-β coordinate system.

[0115] In Figure 19 In the vector control, 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 them to the microprocessor. The real-time phase current and the real-time bus voltage V busand convert them into currents Iα, Iβ, voltages Vα, Vβ in the αβ coordinate system. The real-time input power Pi of the motor is 3 / 2(Iα×Vα + Iβ×Vβ).

[0116] As Figure 22 shown, in a sensorless vector control PM motor system, the logic block diagram of the DPC constant air volume control method. The input power is calculated by vector control. This power is used for power control after filtering. The flux observer estimates the rotor speed and rotor position. Then, according to the matching of the externally input air volume IN-CFM and the power / speed data, the calculated value Pt of the corresponding motor input power is converted using the function P = f(n). The calculated value Pt of the motor input power is compared with the real-time output power Pi of the motor to obtain the power difference ΔP. The power difference ΔP is limited to avoid excessive power difference ΔP and regulate large power fluctuations. The power difference ΔP is output through the power / speed control logic for speed loop control, and the speed loop control is achieved through vector control.

[0117] The data of this embodiment are the data obtained under the conditions of air volume 0 - 1000 CFM, static pressure 0 - 300 Pa at low static pressure, and speed 0 - 2000 RPM, which are suitable for constant air volume under these conditions.

[0118] Embodiment 3:

[0119] The present invention uses the small constant air volume induced draft fan of Embodiment 1, whose output air volume ranges from 0 to 300 CFM, operates at 0 - 1000 Pa, and the speed ranges from 0 to 8000 RPM. After calculation and comparison, a large part of the experimental data in Embodiment 1 do not match, resulting in a large constant air volume control error and unable to meet the customer's requirements. Especially in the working state of static pressure 500 Pa - 1000 Pa and speed 4000 RPM - 8000 RPM, the original data error is very large. Therefore, based on Embodiment 2, this embodiment provides a new solution to expand the requirements for its applicable working environment.

[0120] The calculation model of this embodiment is the same as that of Embodiment 2. The reason for adding the power ratio coefficient a and the speed ratio coefficient b is that when the target constant air volume is not the air volume value in the table, interpolation method needs to be used for calculation, and the coefficients obtained by the interpolation method are limited. When the speed and power are relatively large, the coefficients calculated by the interpolation method will overflow (the coefficient exceeds 2 16 ), and no calculation result can be obtained. Therefore, it is necessary to add the power ratio coefficient a and the speed ratio coefficient b. To obtain the calculation result, it is required that both P / a and n / b are around 1 (between 0 and 2). According to the measured speed and power ranges, the value range of the power ratio coefficient a is 50 - 100, and the value range of the speed ratio coefficient b is 3000 - 8000.

[0121]

[0122]

[0123] Table 3

[0124] If the coefficients C1, C2, and C3 calculated by the interpolation method of Example 2 are used for the data in Table 3, they will overflow (the coefficients exceed 2 16 ), so it can only be implemented by adjusting the power ratio coefficient a and the speed ratio coefficient b.

[0125] 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. 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 inside the volute 1, and the motor 3 drives 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 obtains the functional relationship 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, n is the motor speed, a is the power ratio coefficient, and b is the speed ratio coefficient. The induced draft fan outputs a constant air volume by controlling the input power and speed.

[0126] The functional relationship P / a = f(n / b) is a polynomial function:

[0127]

[0128] Where C1, C2,..., Cm are coefficients, and a corresponding set of C1, C2,..., Cm coefficients, the power ratio coefficient a, and the speed ratio coefficient b are obtained by the look-up table method or the interpolation method according to the input target air volume value IN-CFM, as shown in Table 4, so as to obtain the functional relationship P / a = f(n / b). The value range of the power ratio coefficient a is 50 - 100, and the value range of the speed ratio coefficient b is 3000 - 8000.

[0129]

[0130]

[0131] Table 4

Claims

1. A constant air volume induced draft fan, comprising 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 inside the volute (1), and the motor (3) drives 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 makes the induced draft fan output a constant air volume by controlling the input power and rotational speed according to the input target air volume value IN-CFM and the pre-set function of constant air volume control P / a = f(n / b), where P is the motor input power, n is the motor rotational speed, a is the power proportionality coefficient, and b is the rotational speed proportionality coefficient; the function P / a = f(n / b) is a polynomial function: Where C1, C2, …, Cm are coefficients, and a set of corresponding C1, C2, …, Cm coefficients, power ratio coefficient a, and rotational speed ratio coefficient b are obtained by means of a look-up table method or an interpolation method according to the input target air volume value IN-CFM, so as to obtain the functional relationship P / a = f x (n / b), where x = 1, 2, 3, …, the value range of the power ratio coefficient a is 50 - 100, and the value range of the rotational speed ratio coefficient b is 3000 - 8000.

2. 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. The bus current detection circuit and the bus voltage detection circuit detect the real-time bus current IDC and the real-time bus voltage VDC, and the real-time motor input power Pi = IDC × VDC.

3. The constant air volume induced draft fan according to claim 2, characterized in that: 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 real-time phase current and real-time bus voltage data and input them into the microprocessor. The real-time phase current and real-time bus voltage are converted into currents Iα, Iβ, voltages Vα, Vβ on the α-β coordinate, and the real-time motor input power Pi = 3 / 2(Iα·Vα + Iβ·Vβ).

4. A constant air volume induced draft fan according to claim 1 or 2 or 3, characterized in that: The motor controller includes a control box (35) and a control circuit board (36). The control circuit board (36) is installed inside the control box (35). The control box (35) is installed at the tail of the motor housing (34). The opening (351) of the control box (35) faces the tail of the motor housing (34). The width H of the control box (35) is wider than the diameter D of the motor housing (34). Electronic components (37) with a longer axial length are arranged at the edge of the control circuit board (36). The bottom of the electronic components (37) with a longer axial length extends out of the control box (35) and is located on one side of the motor housing (34).

5. The constant air volume induced draft fan according to claim 4, wherein: The electronic components (37) with a longer axial length are capacitor components.

6. The constant air volume induced draft fan according to claim 5, wherein: The control box (35) axially extends a baffle (352), and the baffle (352) shields the outside of the electronic components (37) with a longer axial length.

7. The constant air volume induced draft fan according to claim 6, characterized in that: A cover plate (38) is also connected to the baffle (352). 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) enclose a cover body to cover the outside of the bottom of the electronic components (37) with a longer axial length.

8. The constant air volume induced draft fan according to claim 7, characterized in that: The bottom of the baffle (352) protrudes outwards to form an upper mounting ear (3521), and the cover plate (38) protrudes outwards to form a lower mounting ear (384). The upper mounting ear (3521) and the lower mounting ear (384) are connected by a first screw (40).

9. The constant air volume induced draft fan according to claim 8, characterized in that: The motor housing (34) includes a rear end cover (341). 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). The lower lugs (3411) and the upper lugs (353) are connected by a second screw (39).

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