Motor control device and air conditioner

Abstract

The invention discloses a motor control device and an air conditioner, and the motor control device comprises a position / rotation speed estimation unit which estimates a rotor position and a rotor rotation speed of an AC motor driven by an inverter according to a detection current (iq, id) on a control shaft and a voltage command value (Vd *, Vq *) inputted to the inverter; and a current ripple suppression controller for estimating compensation currents (iqcmp, idcmp) for compensating the current command values (iq *, id *) on the control axis from the detection currents (iq, id) on the control axis and the mechanical angle of the rotor, respectively, so as to reduce position observation errors caused by current control fluctuations. The influence of current pulsation on position observation can be suppressed, and the motor position observation accuracy is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and in particular to a motor control device and an air conditioner. Background Art

[0002] There is known a position sensorless control that estimates the position of the rotor of the AC motor from the current detection value of the inverter and controls the driving of the AC motor based on the estimated position. The AC motor driven by the position sensorless control has excellent environmental resistance and is particularly useful for driving a compressor.

[0003] Most existing air-conditioning systems use sensorless FOC (Field-Oriented Control) technology to control the compressor for frequency modulation and frequency conversion, and most existing air-conditioning compressors are rotary compressors. At present, when the rotary compressor works at a low frequency, the sensorless FOC technology exhibits mechanical pulsation, which leads to fluctuations in current control. As a result, the rotor position estimation error is large, especially when the load fluctuates (for example, at high temperature (such as 59 degrees) and high load, the pressure difference between the compressor exhaust pressure and the suction pressure is large, and there is a suction and exhaust pressure difference in the compressor cavity, resulting in load fluctuations). The load torque fluctuations are superimposed on the mechanical characteristic pulsations, which can easily lead to a larger position observation error and cause a loss of step and shutdown.

[0004] Many existing air-conditioning manufacturers need to add a system pressure relief valve to relieve the compressor exhaust pressure under extreme operating conditions such as high frequency and high load. For example, when the exhaust pressure is greater than about 3.8Mpa, open the system pressure relief valve to release the exhaust pressure, otherwise close the system pressure relief valve to ensure stable operation of the compressor.

[0005] This method requires manual intervention and the addition of an additional system pressure relief valve, and has a low degree of automation and intelligence. Summary of the invention

[0006] In response to the problems pointed out in the background technology, the present application provides a motor control device to obtain dq-axis compensation current for offsetting pulsating torque to reduce the fluctuation of current control, thereby reducing the rotor position estimation error and ensuring stable operation of the unit under low frequency and high load.

[0007] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions: Some embodiments of the present application relate to a motor control device, including: A position / speed estimation unit that estimates the rotor position and rotor speed of the AC motor driven by the inverter based on the detected current (iq, id) on the control shaft and the voltage command value (Vd*, Vq*) input to the inverter; A current pulsation suppression controller is used to infer a compensation current (iqcmp, idcmp) used to compensate for the current command value (iq*, id*) on the control shaft based on the detected current (iq, id) on the control shaft and the mechanical angle of the rotor, so as to reduce the position observation error caused by the current control fluctuation.

[0008] The technical solutions involved in the above embodiments have the following advantages or beneficial effects: When the motor works at low frequency, it exhibits pulsation of mechanical characteristics, resulting in fluctuations in current control. In this way, the rotor position estimation error is large. Therefore, in order to reduce the rotor position estimation error, and considering that the electromagnetic torque of the motor is related to the current (iq, id) on the control shaft, and the current (iq, id) on the control shaft is also related to the shaft error, the control of the electromagnetic torque change caused by mechanical pulsation can be converted into control of the current (iq, id) on the control shaft, and at the same time, the shaft error can also be adjusted to make the shaft error control close to 0, thereby achieving non-position observation of the motor rotor while suppressing pulsation, improving the position observation accuracy, and avoiding the motor losing step and stopping due to the increase in position observation error.

[0009] In some embodiments of the present application, the position / speed inference unit includes: An axis error estimation unit estimates an axis error Δθ between a real axis of an AC motor driven by the inverter and a control axis based on a detection current (iq, id) on the control axis and a voltage command value (Vd*, Vq*) input to the inverter; A phase-locked loop outputs a rotor position and a rotor speed according to the shaft error output by the shaft error inference unit.

[0010] The technical solutions involved in the above embodiments have the following advantages or beneficial effects: The axis error is obtained by using the detection current (iq, id) and voltage command value (Vd*, Vq*) on the control axis, so that the axis error has a great relationship with the detection current (iq, id). Therefore, the effect of controlling the axis error can be achieved by compensating the dq axis current, thereby improving the position observation accuracy.

[0011] The phase-locked loop can lock the axis error to zero and obtain the rotor speed, which is used in the speed loop during the motor vector control process. The rotor position is obtained by integrating the rotor speed. The mechanical angle corresponding to the rotor position can be used to obtain n harmonic pulsating currents, which are used to compensate for the current command values ​​(iq*, id*) and realize the current loop control during the motor vector control process.

[0012] In some embodiments of the present application, the current ripple suppression controller includes: A first compensation unit, which is used to infer a compensation current idcmp for compensating a current command value id* on the control shaft according to a detection current id on the control shaft and a mechanical angle of a rotor; The second compensation unit is used to estimate a compensation current iqcmp for compensating the current command value iq* on the control shaft based on the detection current iq on the control shaft and the mechanical angle of the rotor.

[0013] The technical solutions involved in the above embodiments have the following advantages or beneficial effects: The current command value id* and the current command value iq* on the control axis are compensated respectively to jointly suppress the fluctuation of current control caused by mechanical pulsation and improve the control accuracy of the current loop during the motor vector control process.

[0014] In some embodiments of the present application, the first compensation unit includes: A first current processing unit, configured to transform the detected current id on the control shaft and the mechanical angle into a first current pulsating component represented by a sine wave through Fourier transform processing; A first current conversion unit, which converts the nth harmonic component to be extracted from the first current pulsating component into a DC component in an nth harmonic dq synchronous rotating coordinate system; A first branch and a second branch, which are connected in parallel to the rear end of the first current conversion unit, the first branch is used to control the d-axis DC component of the n-th harmonic in the dq synchronous rotating coordinate axis system to be zero, and the second branch is used to control the q-axis DC component of the n-th harmonic in the dq synchronous rotating coordinate axis system to be zero; The second current processing unit is used to perform inverse transformation into the compensation current idcmp through inverse Fourier transformation according to the current signals output by the first branch and the second branch and the mechanical angle respectively.

[0015] The technical solutions involved in the above embodiments have the following beneficial effects or advantages: Based on the design idea of ​​filtering out the nth multiple of the mechanical frequency, the detection current id on the control shaft is converted from a time domain signal to a frequency domain signal by using Fourier forward transform processing, and the nth harmonic DC component is obtained and controlled to zero. Then, an inverse Fourier transform is performed to convert the frequency domain signal into a time-frequency domain signal, and the compensation current idcmp is obtained, which is then reversely injected into the current command value id* to realize the control of the current id in the current loop during the motor vector control process.

[0016] In some embodiments of the present application, the second compensation unit includes: A third current processing unit is used to transform the detection current iq on the control shaft and the mechanical angle through Fourier transform processing to transform iq into a second current pulsation component represented by a sine wave; A second current conversion unit, which converts the nth harmonic component to be extracted from the second current pulsating component into a DC component in an nth harmonic dq synchronous rotating coordinate system; A third branch and a fourth branch are connected in parallel to the rear end of the second current conversion unit, the third branch is used to control the d-axis DC component of the n-th harmonic in the dq synchronous rotating coordinate axis system to be zero, and the fourth branch is used to control the q-axis DC component of the n-th harmonic in the dq synchronous rotating coordinate axis system to be zero; a fourth current processing unit, configured to perform inverse Fourier transformation processing on the current signals outputted by the third branch and the fourth branch and the mechanical angle, and inversely transform the current signals into the compensation current iqcmp; Here, n is a natural number greater than 1.

[0017] The technical solutions involved in the above embodiments have the following beneficial effects or advantages: Based on the design idea of ​​filtering out the nth multiple of the mechanical frequency, the detection current iq on the control shaft is converted from a time domain signal to a frequency domain signal by using Fourier transform processing, and the nth harmonic DC component is obtained and controlled to zero. Then, an inverse Fourier transform is performed to convert the frequency domain signal into a time-frequency domain signal, and the compensation current iqcmp is obtained, which is then reversely injected into the current command value iq* to realize the control of the current iq in the current loop during the motor vector control process.

[0018] In some embodiments of the present application, the structures of the first branch, the second branch, the third branch and the fourth branch are the same, and the first branch includes: A filter connected to a rear end of the first current conversion unit and configured to filter out other pulsating components except the d-axis DC component; an integral controller receiving a negative value of the d-axis DC component; A limiter is connected to the output end of the integral controller, and the output of the limiter is input to the second current processing unit.

[0019] The technical solutions involved in the above embodiments have the following beneficial effects or advantages: Through the filter, the DC component of the nth harmonic that needs to be extracted is retained, and other pulsating components are filtered out, so that the nth harmonic can be processed separately, so that the DC component can be controlled to 0 after passing through the integral controller and the limiter, and then input into the second current processing unit for frequency domain to time domain conversion, and reversely injected into the current command value id*.

[0020] In some embodiments of the present application, the first compensation unit further includes: A first angle compensation unit, which is used to obtain a mechanical position error corresponding to the nth harmonic, for compensating the mechanical angle; The second current processing unit performs inverse Fourier transformation according to the current signals output by the first branch and the second branch, and the difference between the mechanical angle and the mechanical position error, to inversely transform the current into the compensation current idcmp.

[0021] The technical solutions involved in the above embodiments have the following beneficial effects or advantages: The mechanical angle error also contains the mechanical position error caused by the harmonics of the mechanical speed multiples. Therefore, when performing the inverse Fourier transform, the estimated angle applied to the inverse Fourier transform is compensated, that is, the difference between the mechanical angle and the mechanical position error corresponding to the nth harmonic. The purpose is to remove the pulsating component of the rotor position information containing the nth frequency of the mechanical speed and improve the current ID compensation accuracy.

[0022] In some embodiments of the present application, the second compensation unit further includes: A second angle compensation unit, which is used to obtain a mechanical position error corresponding to the nth harmonic, for compensating the mechanical angle; The second current processing unit performs inverse Fourier transformation according to the current signals output by the third branch and the fourth branch, and the difference between the mechanical angle and the mechanical position error, and inversely transforms them into the compensation current iqcmp.

[0023] The technical solutions involved in the above embodiments have the following beneficial effects or advantages: The mechanical angle error also contains the mechanical position error caused by the harmonics of the mechanical speed multiples. Therefore, when performing the inverse Fourier transform, the estimated angle applied to the inverse Fourier transform is compensated, that is, the difference between the mechanical angle and the mechanical position error corresponding to the nth harmonic. The purpose is to remove the pulsating component of the rotor position information containing the nth frequency of the mechanical speed and improve the current iq compensation accuracy.

[0024] In some embodiments of the present application, an air conditioner is also provided, comprising: The refrigerant circulation loop allows the refrigerant to circulate in the loop consisting of the compressor, condenser, expansion valve and evaporator; The compressor is used to compress the low-temperature and low-pressure refrigerant gas into high-temperature and high-pressure refrigerant gas and discharge it to the condenser; An outdoor heat exchanger and an indoor heat exchanger, one of which works as a condenser and the other works as an evaporator; an inverter for driving an AC motor, wherein the compressor uses the rotational force of the AC motor as a driving source; A motor control device, comprising: A position / speed estimation unit that estimates the rotor position and rotor speed of the AC motor based on the detected current (iq, id) on the control shaft and the voltage command value (Vd*, Vq*) input to the inverter; A current pulsation suppression controller is used to infer a compensation current (iqcmp, idcmp) used to compensate for the current command value (iq*, id*) on the control shaft based on the detected current (iq, id) on the control shaft and the mechanical angle of the rotor, so as to reduce the position observation error caused by the current control fluctuation.

[0025] The technical solutions involved in the above embodiments have the following beneficial effects or advantages: When the compressor works at low frequency, it exhibits pulsation of mechanical characteristics, especially at high temperature (for example, 59 degrees) and high load. The pressure difference between the exhaust pressure and the suction pressure of the compressor is large, and there is a suction and exhaust pressure difference in the compressor cavity. When load fluctuations occur, the load torque fluctuations are superimposed on the mechanical characteristic pulsation, which can easily lead to a larger position observation error and cause a loss of step and shutdown. The motor control device as described above can compensate for the currents iq* and id* on the control shaft, reduce the position observation error caused by the mechanical characteristics of the rotor compressor and load fluctuations, ensure the stable and reliable operation of the air-conditioning unit under high ambient temperature and extreme load conditions, greatly improve the load-carrying capacity of the compressor under low-frequency and high-load conditions, and also expand the applicable scenarios of the air-conditioning unit.

[0026] After reading the specific embodiments of the present invention in conjunction with the accompanying drawings, other features and advantages of the present invention will become more clear. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0028] Figure 1 It is the principle block diagram of the existing air conditioner; Figure 2 A schematic block diagram of the application of the motor control device proposed in this application; Figure 3 A schematic diagram of the actual position and estimated position of the rotor of a motor when the motor control device proposed in the present application performs vector control; Figure 4 It is a detailed block diagram of the existing vector control of the motor; Figure 5 for Figure 4 Internal block diagram of the position / speed inference unit; Figure 6 A detailed block diagram of a motor control device according to the present application performing vector control; Figure 7 for Figure 6 Internal block diagram of the current ripple suppression controller; Figure 8 for Figure 6 Internal frame of the first compensation unit in the current ripple suppression controller Figure 1 ; Fig. 9 for Figure 6 Internal frame of the first compensation unit in the current ripple suppression controller Figure 2 ; Fig.10 for Figure 6 Internal frame of the second compensation unit in the current ripple suppression controller Figure 1 Fig.11 The U-phase current waveform of the compressor before the motor is vector controlled by the motor control device proposed in the present application; Fig.12 The waveform of the U-phase current of the compressor after the motor is vector controlled by the motor control device proposed in the present application; Reference numerals: 10. Motor control device; 101. Speed ​​control unit; 102. Current control unit; 103. Second coordinate converter; 104. First coordinate converter; 105. Position / speed estimation unit; 105A. Axis error estimation unit; 105B. Phase-locked loop; 106. Current pulsation suppression controller; 106A. First compensation unit; 106A1. First current processing unit; 106A2. First current conversion unit; 106A3. First branch; 106A4. First Second branch; 106A5, filter; 106A6, integral controller; 106A7, limiter; 106A8, second current processing unit; 106A9, first angle compensation unit; 106B, first compensation unit; 106B1, third current processing unit; 106B2, second current conversion unit; 106B3, third branch; 106B4, fourth branch; 106B5, fourth current processing unit; 20, inverter; 30, motor; 1a, permanent magnet. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0030] In the description of the present application, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0031] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0032] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0033] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0034] The disclosure below provides many different embodiments or examples to realize different structures of the present invention. In order to simplify the disclosure of the present invention, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention. In addition, the present invention can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplicity and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides various specific examples of processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0035] The compressor in the existing air conditioner adopts position detection without position sensor, and the vector control process of AC motor is adopted in the process of position detection. The AC motor outputs the rotational force used as the driving source of the compressor, that is, the position detection of the AC motor is realized by vector control.

[0036] As follows, the basic working principle of the air conditioner is first described.

[0037] The air conditioner performs the air conditioner's refrigeration cycle by using a compressor, condenser, expansion valve, and evaporator. The refrigeration cycle includes a series of processes involving compression, condensation, expansion, and evaporation to cool or heat the indoor space.

[0038] The low-temperature and low-pressure refrigerant enters the compressor, which compresses it into high-temperature and high-pressure refrigerant gas and discharges the compressed refrigerant gas. The discharged refrigerant gas flows into the condenser. The condenser condenses the compressed refrigerant into a liquid phase, and the heat is released to the surrounding environment through the condensation process.

[0039] The expansion valve expands the high-temperature and high-pressure liquid refrigerant condensed in the condenser into a low-pressure liquid refrigerant. The evaporator evaporates the refrigerant expanded in the expansion valve and returns the low-temperature and low-pressure refrigerant gas to the compressor. The evaporator can achieve a cooling effect by utilizing the latent heat of evaporation of the refrigerant to exchange heat with the material to be cooled. In the entire cycle, the air conditioner can adjust the temperature of the indoor space.

[0040] See also Figure 1 , the outdoor unit of the air conditioner refers to a part of a refrigeration cycle including a compressor and an outdoor heat exchanger, the indoor unit of the air conditioner includes an indoor heat exchanger, and the expansion valve may be provided in the indoor unit or the outdoor unit.

[0041] The indoor heat exchanger and the outdoor heat exchanger function as a condenser or an evaporator. When the indoor heat exchanger functions as a condenser, the air conditioner functions as a heater in a heating mode, and when the indoor heat exchanger functions as an evaporator, the air conditioner functions as a cooler in a cooling mode.

[0042] As follows, a process of performing vector control on the motor 30 using the motor control device 10 is mainly described.

[0043] See also Figure 2 , showing a schematic block diagram of controlling a motor 30 using a motor control device 10, wherein the motor 30 is a three-phase permanent magnet synchronous motor having a device with permanent magnets and a stator with a three-phase armature coil.

[0044] The inverter 20 provides a three-phase AC voltage consisting of a U-phase, a V-phase, and a W-phase to the motor 30 according to a rotor position of the motor 30 .

[0045] The motor control device 10 provides a PWM signal for implementing a required vector control to the inverter 20 circuit according to the detected motor current.

[0046] Figure 3 The analysis model diagram of the motor 30 is shown. UVW represents the fixed coordinate axes of the three phases. 1a is a permanent magnet provided on the rotor of the motor 30. In a rotating coordinate system rotating at the same speed as the rotation speed of the magnetic flux generated by the permanent magnet 1a, the direction of the magnetic flux generated by the permanent magnet 1a is taken as the d-axis, and the rotation axis corresponding to the control of the d-axis is taken as the dc-axis. The phase that is 90 degrees ahead of the d-axis electrical angle is taken as the q-axis, and the phase that is 90 degrees ahead of the dc-axis electrical angle is taken as the dq-axis.

[0047] The rotation coordinate system corresponding to the real axis is a coordinate system that selects the d axis and the q axis as the coordinate axes, and this coordinate axis is called the dq axis. The rotation coordinate system on the control is a coordinate system that selects the dc axis and the dq axis as the coordinate axes, and this coordinate axis is called the dcqc axis.

[0048] In some embodiments of the present application, see Figure 3 , the dcqc axis is the estimated position of the motor, which represents the axis on the control side of the rotating coordinate in general torque control, and is recorded as the control axis; the dq axis is the real position of the motor, which represents the axis on the AC motor side of the rotating coordinate, and is recorded as the real axis.

[0049] The dq axis rotates, and its rotation speed is represented by ωe. The dcqc axis also rotates, and its rotation speed is represented by ω. In the dq axis, the d-axis angle (phase) observed from the fixed axis direction of the armature coil of the U phase is represented by θe. Similarly, in the dcqc axis, the dc-axis angle (phase) observed from the fixed axis direction of the armature coil of the U phase is represented by θ. The angles represented by θ and θe are electrical angles, and are also generally referred to as rotor positions or magnetic pole positions. The rotation speed represented by ω and ωe is the angular velocity in electrical angles.

[0050] The angle difference between the real d-axis position of the rotor (ie, θe) and the estimated dc-axis position (ie, θ) is called the axis error Δθ. The motor control device 10 performs vector control to make θ and θe basically consistent (ie, the control axis error Δθ is zero), complete the coincidence of the control axis and the real axis (ie, the d-axis and the q-axis are consistent with the dc-axis and the qc-axis respectively), and realize the position-free observation of the permanent magnet synchronous motor rotor.

[0051] The voltage command values ​​indicating the target values ​​of the dc-axis voltage and the qc-axis voltage are represented by the dc-axis voltage command value Vd* and the qc-axis voltage command value Vq*, respectively. The current command values ​​indicating the target values ​​of the dc-axis voltage and the qc-axis voltage are represented by the dc-axis current command value id* and the qc-axis current command value iq*, respectively.

[0052] The U-phase component, V-phase component, and W-phase component of the motor voltage are expressed by three-phase voltage command values ​​consisting of a U-phase voltage command value Vu*, a V-phase voltage command value Vv*, and a W-phase voltage command value Vw*.

[0053] See also Figure 4 , describes the principle of motor vector control, adopts speed and current dual closed-loop control, with the speed loop as the outer loop and the current loop as the inner loop.

[0054] First, the working principle of the current loop is explained.

[0055] The U-phase current iu and the V-phase current iv provided by the inverter 20 to the motor are detected by a current detection unit (not shown). And, for the W-phase current iw, it is calculated by the relationship "iw = -iu-iv". iu, iv and iw are respectively the current of the armature coil of the U phase, the current of the armature coil of the V phase and the current of the armature coil of the W phase in the stator of the motor.

[0056] The first coordinate converter 104 can convert the U-phase current iu and the V-phase current iv into the dcqc axis according to the rotor position θ, so as to calculate and output the dc-axis current id and the qc-axis current iq.

[0057] In the vector control of the motor, the first coordinate converter 104 may include Clark transformation and Park transformation, that is, the three-phase currents iu / iv / iw are transformed by Clark transformation to obtain iα and iβ, and then iα and iβ are transformed by Park transformation to obtain iq and id.

[0058] Then, iq and id are used to calculate the q-axis current error value and the d-axis current error value respectively with iq* and id*.

[0059] The q-axis current error value and the d-axis current error value are brought into the current control unit 102 to obtain a dc-axis voltage command value Vd* and a qc-axis voltage command value Vq*.

[0060] In some embodiments of the present application, the current control unit 102 uses current feedback control such as proportional integral control to make the current errors (id*-id) and (iq*-iq) converge to zero.

[0061] The second coordinate converter 103 can convert Vd* and Vq* to fixed coordinate axes of three phases according to Vd* and Vq* and the rotor position θ to calculate and output three-phase voltage command values ​​(Vu*, Vv* and Vw*).

[0062] In some embodiments of the present application, the second coordinate transformer 103 may include an inverse Park transform (ie, an inverse Park transform).

[0063] That is, Vd* and Vq* are subjected to Park inverse transformation to obtain Vα* and Vβ*, and then SVPWM (Space Vector Pulse Width Modulation) operation is performed to obtain a PWM signal. The PWM signal controls the state of the switch tube in the inverter 20 and outputs three-phase voltage command values ​​(Vu*, Vv* and Vw*) to realize the rotation of the drive motor 30.

[0064] Secondly, the working principle of the speed loop is explained.

[0065] Still refer to Figure 4 The rotor speed ω output by the position / speed estimation unit 105 is used, and the speed ω is subtracted from the target speed command value ω*, and then input into the speed control unit (for example, using a PI controller) 101 to adjust the speed to obtain iq*.

[0066] The position / speed estimation unit 105 as described above estimates the rotor position θ and the speed ω by performing proportional integral control using Vd* and Vq* from the current control unit 102 and all or part of iq and id of the first coordinate converter 104, so as to control the axis error Δθ to converge to zero.

[0067] Various methods have been proposed in the past as a method for estimating the rotor position θ and the rotor speed ω. Here, the position / speed estimation unit 105 can adopt any existing method.

[0068] See also Figure 5 , which gives an example of an internal block diagram of the position / rotation speed inference unit 105.

[0069] In some embodiments of the present application, the position / rotation speed inference unit 105 includes an axis error inference unit 105A and a phase-locked loop 105B.

[0070] The axis error estimation unit 105A calculates the axis error Δθ based on Vd*, Vq*, iq, and id, and calculates the axis error Δθ using the following equation (1) shown in Japanese Patent No. 3411878, for example.

[0071] (1) The phase-locked loop 105B can implement PLL (PhaseLocked Loop) control, perform proportional-integral control, lock the shaft error Δθ to zero, obtain the calculated motor speed w, and then integrate the speed ω to calculate the motor rotor position θ.

[0072] When the compressor in the air conditioner works at a low frequency, it exhibits pulsation of mechanical characteristics, especially under high temperature and high load. The pressure difference between the exhaust pressure and the suction pressure of the compressor is large. There is a suction and exhaust pressure difference in the compressor cavity, which will also cause load fluctuations. The load torque fluctuations and the pulsation of mechanical characteristics can easily lead to a larger position observation error and cause a loss of step and shutdown.

[0073] Therefore, in some embodiments of the present application, the motor control device 10, in addition to the parts described above, in order to avoid the pulsation of current control caused by the pulsation as described above, resulting in a larger observed position error, see Figure 6 , a current pulsation suppression controller 106 is introduced to infer a compensation current idcmp for compensating the current command value id* and a compensation current iqcmp for compensating the current command value iq*, so as to eliminate the influence of pulsation on position observation.

[0074] In some embodiments of the present application, see Figure 6 After obtaining the compensation currents idcmp and iqcmp, they are respectively reversely injected into the current command value id* and the current command value iq*, so that the dc-axis current error received by the current control unit 102 changes from id*-id to id*-id-idcmp, and the qc-axis current error received by the current control unit 102 changes from iq*-iq to iq*-iq-iqcmp, so as to eliminate the current pulsation component generated by the torque pulsation in the vector control, reduce the position observation error, and thus improve the motor position observation accuracy.

[0075] As follows, combined Figures 6 to 12 , describes the process of calculating the compensation currents idcmp and iqcmp.

[0076] The electromagnetic torque equation of the motor is: Te=1.5P*iq[Ψf+id*(Ld-Lq)].

[0077] Where, P is the number of motor pole pairs; Ψf is the permanent magnet flux; Ld and Lq are the direct-axis inductance and quadrature-axis inductance respectively; iq is the qc-axis current, and id is the dc-axis current.

[0078] Therefore, for torque pulsation, the electromagnetic torque can be adjusted by adjusting the dcqc axis current feedback value to suppress or balance the fluctuation of load torque.

[0079] Combined with the above formula (1), it can be seen that the axis error Δθ is related to the dcqc axis current id and iq. Therefore, by adjusting iq and id, the influence of the pulsation on the position observation can be adjusted.

[0080] In some embodiments of the present application, based on the design concept of filtering out the harmonics of the mechanical frequency, a compensation current corresponding to the nth harmonic component of the mechanical frequency is obtained.

[0081] It should be noted that the nth harmonic component corresponding to the obtained compensation current should have the largest or relatively large amplitude to eliminate the influence on the current control fluctuation.

[0082] In some embodiments of the present application, the current pulsation suppression controller 106 includes a first compensation unit 106A, which is used to infer a compensation current idcmp used to compensate for the current command value id* on the control shaft based on the detected current id on the control shaft and the mechanical angle θr of the rotor.

[0083] Among them, the mechanical angle θr is equal to the product of the rotor position θ and the number of pole pairs.

[0084] See also Figure 8 and Fig. 9 The first compensation unit 106A includes a first current processing unit 106A1, which is used to convert the time domain signal into a frequency domain signal through Fourier transform processing according to the detection current id and the mechanical angle θr on the control axis, and transform id into a first current pulsation component represented by a sine wave.

[0085] The detection current id as described above may be a sampled value idfb obtained by sampling the current id output by the first coordinate converter 104 , or may be an average value obtained by multiple samplings.

[0086] The detection current id is expanded by Fourier series at an angle θr, and id is transformed into a first current pulsating component represented by a sine wave, including a DC component, a fundamental wave, and an nth harmonic component, wherein n is a natural number greater than 1.

[0087] Each harmonic component in the first current pulsating component is an AC component. In order to realize the control of the n-th harmonic dc axis and dq axis current, a dq synchronous rotating coordinate axis system corresponding to the n-th harmonic is established.

[0088] According to the principle of UVW / dq coordinate transformation, the frequency component with the same rotation direction and speed as the dq axis rotating axis system is a DC component in the dq synchronous rotating coordinate axis system. Therefore, through coordinate transformation, in the nth harmonic dq synchronous rotating coordinate axis system, the nth harmonic component to be extracted is a DC component, and the fundamental wave and other harmonic components are all AC components.

[0089] For example, taking the second harmonic component as an example, in the second harmonic dq synchronous rotating coordinate axis system, the second harmonic component is a DC component, and the fundamental wave and other harmonic components are all AC components.

[0090] Among them, the nth harmonic component of the DC component includes the amplitude of the nth harmonic current on the d-axis and the q-axis in the nth harmonic dq synchronous rotating coordinate axis system, that is, it is branched into two DC components, which will be processed separately as follows.

[0091] The conversion process as described above is performed by the first current conversion unit 106A2.

[0092] For the convenience of description, the extraction of the second harmonic is taken as an example for explanation below.

[0093] After the first current pulsating component is processed into a second harmonic DC component, a fundamental DC component and other harmonic AC components as described above, in order to separately control the two DC components of the second harmonic (denoted as the d-axis DC component and the q-axis DC component), a first branch 106A3 and a second branch 106A4 connected in parallel at the rear end of the first current conversion unit 106A2 are designed.

[0094] The structures of the first branch 106A3 and the second branch 106A4 are the same, and both are used to control the DC component to be zero, that is, the first branch 106A3 is used to control the d-axis DC component to be zero, and the second branch 106A4 is used to control the q-axis DC component to be zero.

[0095] As follows, reference Figure 8 , the structure of the first branch 106A3 is taken as an example for explanation.

[0096] In some embodiments of the present application, the first branch 106A3 includes a filter 106A5 connected to the rear end of the first current conversion unit 106A2 and configured to filter out other harmonic components except the d-axis DC component and to extract the d-axis DC component.

[0097] In some embodiments of the present application, the first branch 106A3 further includes an integral controller 106A6, which receives a negative value of the d-axis DC component and is used to control the d-axis DC component to zero to achieve elimination control.

[0098] In some embodiments of the present application, the first branch 106A3 further includes a limiter 106A7 connected to the output end of the integral controller 106A6 to prevent the integral controller 106A6 from being easily saturated.

[0099] Referring to the description of the first branch 106A3 , the second branch 106A4 is used to control the q-axis DC component to zero, and the only difference from the first branch 106A3 is that the filter in the second branch 106A4 is used to extract the q-axis DC component.

[0100] As mentioned above, the current signal is processed in the frequency domain. If you want to use it in the vector control of the motor, you also need to convert the signal from the frequency domain to the time domain. This part needs to be achieved through inverse Fourier transform.

[0101] In some embodiments of the present application, see Figure 8 The first compensation unit 106A also includes a second current processing unit 106A8, which is used to inversely transform the current signals output by the first branch 106A3 and the second branch 106A4 and the mechanical angle θr into a compensation current idcmp through inverse Fourier transform processing, that is, the signal is converted from the frequency domain to the time domain.

[0102] As mentioned above, see Figure 6 , the compensation current idcmp is negatively fed back to the current control unit 102.

[0103] In some embodiments of the present application, see Fig.10 The second compensation unit 106B has the same structure as the first compensation unit 106A, and the only difference is that the first compensation unit 106A compensates for the current id, while the second compensation unit 106B compensates for the current iq.

[0104] The second compensation unit 106B includes a third current processing unit 106B1 , the structure of which is similar to the first current processing unit 106A1 described above, and is not described in detail herein.

[0105] The second compensation unit 106B includes a second current conversion unit 106B2 , the structure of which is similar to the first current conversion unit 106A2 described above, and is not described in detail herein.

[0106] The second compensation unit 106B includes a third branch 106B3 and a fourth branch 106B4 , and the structures thereof refer to the first branch 106A3 and the second branch 106A4 described above, respectively, and are not described in detail herein.

[0107] The second compensation unit 106B includes a fourth current processing unit 106B5, the structure of which is similar to the second current processing unit 106A8 described above, and is not described in detail here.

[0108] In some embodiments of the present application, it can be seen from the shaft error calculation formula (1) that the actual values ​​of iq and id will affect the estimated value of the rotor position error. Therefore, when performing the inverse Fourier transform, it is necessary to compensate the angle used only for the inverse transform in order to remove the mechanical frequency multiplication pulsation component contained in the rotor position information.

[0109] To achieve angle compensation, see Fig. 9 The first compensation unit 106A also includes a first angle compensation unit 106A9, which can obtain the mechanical position error Δθnω corresponding to the mechanical frequency n (n is a natural number greater than 1) multiplied frequency pulsation component from the rotor position output by the position / speed inference unit 105, which is used to compensate the mechanical angle θr.

[0110] After obtaining the mechanical position error Δθnω, the second current processing unit 106A8 performs inverse Fourier transformation according to the current signals output by the first branch 106A3 and the second branch 106A4 and the difference θdcmp between θr and Δθω, and inversely transforms them into the compensation current idcmp.

[0111] Similarly, the second compensation unit 106B also includes a second angle compensation unit (not shown), which can obtain the mechanical position error Δθnω corresponding to the mechanical frequency n (n is a natural number greater than 1) multiplied frequency pulsation component from the rotor position output by the position / speed inference unit 105, and is used to compensate for the mechanical angle θr.

[0112] After obtaining the mechanical position error Δθnω, the fourth current processing unit 106B5 performs inverse Fourier transformation according to the current signals output by the third branch 106B3 and the fourth branch 106B4 and the difference between θr and Δθω, and inversely transforms them into the compensation current iqcmp.

[0113] In this way, the compensated angle is used to perform an inverse Fourier transform and the current command values ​​id* and iq* are compensated, effectively eliminating the position observation error caused by current fluctuations.

[0114] See also Fig.11 and Fig.12 , Fig.11 The U-phase current waveform of the compressor before the motor 30 is vector controlled by the motor control device 10 proposed in the present application. Fig.12 This is the waveform of the U-phase current of the compressor after the motor 30 is vector controlled by the motor control device 10 proposed in the present application.

[0115] pass Fig.11 and Fig.12It can be seen from the comparison that the motor control device 10 involved in the present application can reduce the pulsation of the compressor current under low frequency and high load, improve the stability of the current control, and thus improve the accuracy of position observation.

[0116] In the description of the above embodiments, specific features, structures, materials or characteristics may be combined in a suitable manner in any one or more embodiments or examples.

[0117] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A motor control device, characterized in that: include: A position / speed estimation unit that estimates the rotor position and rotor speed of the AC motor driven by the inverter based on the detected current (iq, id) on the control shaft and the voltage command value (Vd*, Vq*) input to the inverter; A current pulsation suppression controller is used to infer a compensation current (iqcmp, idcmp) used to compensate for the current command value (iq*, id*) on the control shaft based on the detected current (iq, id) on the control shaft and the mechanical angle of the rotor, so as to reduce the position observation error caused by the current control fluctuation.

2. The motor control device according to claim 1, characterized in that: The position / speed inference unit comprises: An axis error estimation unit estimates an axis error Δθ between a real axis of an AC motor driven by the inverter and a control axis based on a detection current (iq, id) on the control axis and a voltage command value (Vd*, Vq*) input to the inverter; A phase-locked loop outputs a rotor position and a rotor speed according to the shaft error output by the shaft error inference unit.

3. The motor control device according to claim 2, wherein the current ripple suppression controller comprises: A first compensation unit, which is used to infer a compensation current idcmp for compensating a current command value id* on the control shaft according to a detection current id on the control shaft and a mechanical angle of a rotor; The second compensation unit is used to estimate a compensation current iqcmp for compensating the current command value iq* on the control shaft based on the detection current iq on the control shaft and the mechanical angle of the rotor.

4. The motor control device according to claim 3, wherein the first compensation unit comprises: A first current processing unit, configured to transform the detected current id on the control shaft and the mechanical angle into a first current pulsating component represented by a sine wave through Fourier transform processing; A first current conversion unit, which converts the nth harmonic component to be extracted from the first current pulsating component into a DC component in an nth harmonic dq synchronous rotating coordinate system; A first branch and a second branch, which are connected in parallel to the rear end of the first current conversion unit, the first branch is used to control the d-axis DC component of the n-th harmonic in the dq synchronous rotating coordinate axis system to be zero, and the second branch is used to control the q-axis DC component of the n-th harmonic in the dq synchronous rotating coordinate axis system to be zero; A second current processing unit is used for inversely transforming the current signals output by the first branch and the second branch and the mechanical angle into the compensation current idcmp through inverse Fourier transformation; The second compensation unit comprises: A third current processing unit is used to transform the detection current iq on the control shaft and the mechanical angle through Fourier transform processing to transform iq into a second current pulsation component represented by a sine wave; A second current conversion unit, which converts the nth harmonic component to be extracted from the second current pulsating component into a DC component in an nth harmonic dq synchronous rotating coordinate system; A third branch and a fourth branch are connected in parallel to the rear end of the second current conversion unit, the third branch is used to control the d-axis DC component of the n-th harmonic in the dq synchronous rotating coordinate axis system to be zero, and the fourth branch is used to control the q-axis DC component of the n-th harmonic in the dq synchronous rotating coordinate axis system to be zero; a fourth current processing unit, configured to perform inverse Fourier transformation processing on the current signals outputted by the third branch and the fourth branch and the mechanical angle, and inversely transform the current signals into the compensation current iqcmp; Here, n is a natural number greater than 1.

5. The motor control device according to claim 4, characterized in that: The structures of the first branch, the second branch, the third branch and the fourth branch are the same, and the first branch includes: A filter connected to a rear end of the first current conversion unit and configured to filter out other pulsating components except the d-axis DC component; an integral controller receiving a negative value of the d-axis DC component; A limiter is connected to the output end of the integral controller, and the output of the limiter is input to the second current processing unit.

6. The motor control device according to claim 4, characterized in that: The first compensation unit further includes: A first angle compensation unit, which is used to obtain the mechanical position error corresponding to the nth harmonic, for compensating the mechanical angle; The second current processing unit performs inverse Fourier transformation according to the current signals output by the first branch and the second branch, and the difference between the mechanical angle and the mechanical position error, to inversely transform the current into the compensation current idcmp.

7. The motor control device according to claim 4 or 6, characterized in that: The second compensation unit further includes: A second angle compensation unit, which is used to obtain the mechanical position error corresponding to the nth harmonic, for compensating the mechanical angle; The second current processing unit performs inverse Fourier transformation according to the current signals output by the third branch and the fourth branch, and the difference between the mechanical angle and the mechanical position error, and inversely transforms them into the compensation current iqcmp.

8. An air conditioner, characterized in that: include: The refrigerant circulation loop allows the refrigerant to circulate in the loop consisting of the compressor, condenser, expansion valve and evaporator; The compressor is used to compress the low-temperature and low-pressure refrigerant gas into high-temperature and high-pressure refrigerant gas and discharge it to the condenser; An outdoor heat exchanger and an indoor heat exchanger, one of which works as a condenser and the other works as an evaporator; an inverter for driving an AC motor, wherein the compressor uses the rotational force of the AC motor as a driving source; A motor control device, comprising: A position / speed estimation unit that estimates the rotor position and rotor speed of the AC motor based on the detected current (iq, id) on the control shaft and the voltage command value (Vd*, Vq*) input to the inverter; A current pulsation suppression controller is used to infer a compensation current (iqcmp, idcmp) used to compensate for the current command value (iq*, id*) on the control shaft based on the detected current (iq, id) on the control shaft and the mechanical angle of the rotor, so as to reduce the position observation error caused by the current control fluctuation.

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