Motor drive control method, motor variable frequency drive controller and air conditioner

Abstract

The invention provides a motor drive control method, a motor variable frequency drive controller and an air conditioner, and relates to the technical field of motor drive control, the method comprises the steps that the current operation demand voltage of a motor is obtained, and the demand voltage is in positive correlation with the current operation frequency of the motor; determining a target voltage of power factor correction according to the required voltage and a preset correction coefficient; the target voltage is greater than the required voltage; and under the condition that the power factor correction starting condition is met, controlling power factor correction starting and controlling the power factor correction module to operate according to the target voltage. According to the embodiment of the invention, the target voltage of the PFC is controlled to change along with the change of the required voltage of the motor, so that the temperature rise speed and the fault rate of the IGBT and the capacitor are reduced under the condition that the hardware cost is not increased, and the stability of PFC voltage control is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of motor drive control, and more particularly, to a motor drive control method, a motor variable-frequency drive controller, and an air conditioner. Background Art

[0002] A motor FOC (Field-Oriented Control) variable-frequency drive controller generally includes several parts: a rectifier bridge and a filtering device, a PFC (Power Factor Correction) boost circuit, and an IPM (Intelligent Power Module). The output of the drive controller is connected to the motor body.

[0003] The variable-frequency drive controller mainly performs the following processes: input rectification, power factor correction, and inversion. Specifically, it receives external commands (such as speed regulation, start-stop signals), processes them through operations, and outputs control signals to the PFC circuit and the inverter circuit; at the same time, it can monitor parameters such as voltage and current, and when an abnormality occurs (such as overvoltage, overcurrent), it can quickly take protective measures.

[0004] The control of PFC in traditional motor drive controllers is as follows: 1. When the detected AC current > the PFC turn-on threshold current, the PFC is turned on, and the PFC target voltage is a fixed value (for example, 380V); 2. When the detected AC current < the PFC turn-off threshold current, the PFC is turned off.

[0005] The above control method is simple and effective, but there are the following problems:

[0006] 1. Once the PFC is turned on, the PFC target voltage is the maximum value, but a high voltage is not required when the motor runs at a low speed; 2. When the bus voltage is kept at the maximum value for a long time, the load on the IGBT (Insulate-Gate Bipolar Transistor) and electrolytic capacitors is increased, thereby increasing the temperature of the IGBT and capacitors; 3. When the IGBT and capacitors are in a high-temperature state, their service life is easily reduced, resulting in controller damage. Summary of the Invention

[0007] To solve the above problems, an embodiment of the present invention provides a motor drive control method, including: obtaining the required voltage of the motor during current operation, where the required voltage is positively correlated with the current operation frequency of the motor; determining the target voltage of power factor correction according to the required voltage and a preset correction coefficient; the target voltage is greater than the required voltage; when the power factor correction turn-on condition is satisfied, control the power factor correction to turn on and control the operation of the power factor correction module according to the target voltage.

[0008] The motor drive control method provided by the embodiment of the present invention changes the target voltage of the PFC according to the change of the motor demand voltage, which reduces the temperature rise speed and failure rate of the IGBT and capacitor without increasing the hardware cost, and improves the stability of the PFC voltage control.

[0009] Optionally, the target voltage is greater than the minimum operating voltage of the power factor correction module and less than the maximum withstand voltage of the capacitor in the power factor correction module.

[0010] In the embodiment of the present invention, a range limit is imposed on the above target voltage to prevent exceeding the adjustment range during power factor correction.

[0011] Optionally, the calculation method of the demand voltage is as follows:

[0012] When the motor is running, the following equation exists:

[0013]

[0014] Among them, U motor is the total voltage required for motor operation; R s is the motor coil resistance; i is the motor coil current; L is the motor coil inductance; is the derivative of the motor coil current with respect to time; E ext is the motor back electromotive force;

[0015] When the motor is in steady-state operation, E ext can represent the voltage required for the current motor operation, as follows

[0016]

[0017] Among them, ω e is the motor speed, is the motor magnetic flux; omitting the resistance voltage division R s *i, the induced electromotive force After that, the motor demand voltage U motor is directly related to the motor operating frequency as follows:

[0018]

[0019] Optionally, the calculation method of the target voltage is as follows:

[0020] U PFC = U motor *Rate

[0021] Among them, Rate is a correction factor greater than one.

[0022] In the embodiments of the present invention, a specific calculation method for the required voltage is provided, and the target voltage for controlling the PFC changes with the motor required voltage.

[0023] Optionally, the method further includes determining whether the following conditions are met: detecting that the PFC current > the PFC turn-on current; detecting that the motor frequency > the PFC turn-on frequency; detecting that the AC current peak value > the PFC turn-on peak current; if any of the above conditions is met, it is determined that the power factor correction turn-on condition is satisfied.

[0024] In the embodiments of the present invention, a power factor correction turn-on condition is provided, and if any one is satisfied, the PFC is turned on.

[0025] Optionally, the method further includes a voltage loop control optimization step, and the voltage loop control optimization step includes: sampling the current bus voltage U1; sampling the bus voltage U2 again after a preset time; calculating U2 - U1, and summing the calculation result with the original input of the PI controller to obtain the Sum value; inputting the Sum value into the PI controller to obtain the voltage loop output, and controlling the power factor correction module according to the output.

[0026] In the embodiments of the present invention, the voltage loop control of the PFC is optimized to ensure that the actual voltage can follow the target voltage and improve the stability of the bus voltage control.

[0027] Optionally, the method further includes a motor control optimization step, and the motor control optimization step includes voltage distribution in the following manner:

[0028] If then directly output U d and U q ;

[0029] If then directly output U d , let

[0030] where U d is the voltage of the d-axis of the motor, U q is the voltage of the q-axis of the motor, and U dc is the current bus voltage.

[0031] In the embodiments of the present invention, the voltage distribution method after the decoupling of the dq axes in the motor control is optimized, which can effectively improve the limit frequency of the motor and the adaptability of the motor to voltage changes.

[0032] Optionally, the method further includes determining whether the following conditions are met: detecting that the PFC current < the PFC turn-off current; detecting that the motor frequency ≤ the PFC turn-on frequency; if any of the above conditions is met, the power factor correction is controlled to turn off.

[0033] In the embodiments of the present invention, power factor correction turn-on conditions are provided, and if any one of them is satisfied, the PFC is turned off.

[0034] Embodiments of the present invention provide a motor variable-frequency drive controller for implementing the motor drive control method described in any one of the above.

[0035] Embodiments of the present invention provide an air conditioner including the above motor variable-frequency drive controller.

[0036] The motor variable-frequency drive controller and the air conditioner provided in the embodiments of the present invention can achieve the same technical effects as the above motor drive control method. Description of the Drawings

[0037] Figure 1 It is a schematic flowchart of a motor drive control method provided in an embodiment of the present invention;

[0038] Figure 2 It is a comparison diagram between traditional PFC target voltage control and PFC PAM target voltage control in an embodiment of the present invention;

[0039] Figure 3 It is a schematic diagram of the principle of voltage loop control optimization in an embodiment of the present invention;

[0040] Figure 4 It is a schematic diagram of motor FOC control in an embodiment of the present invention. Detailed Embodiments

[0041] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention will be given with reference to the accompanying drawings.

[0042] In the embodiments of the present invention, the target voltage of the PFC is controlled to change with the motor demand voltage, so that when the operation of the IGBT and the capacitor meets the requirements of the motor operation, their working loads are reduced as much as possible, and the device life is extended.

[0043] Figure 1 A schematic flowchart of a motor drive control method in an embodiment of the present invention is shown. The method is applied to a motor variable-frequency controller and includes the following steps:

[0044] S102, obtaining the demand voltage of the motor currently in operation.

[0045] When the motor runs at a low speed, high voltage is not required. At this time, the power factor correction module does not need to maintain a fixed high-voltage output, but can adopt a dynamic voltage output that changes with the demand voltage of the motor. Through the analysis of the voltage required for the operation of the motor, it is determined that its demand voltage is positively correlated with the current operating frequency of the motor during steady-state operation.

[0046] S104. Determine the target voltage for power factor correction based on the above-mentioned required voltage and the preset correction factor; this target voltage is greater than the required voltage.

[0047] In this embodiment, a correction factor is preset, for example, a positive number greater than one. Multiply the required voltage by this preset correction factor to obtain the target voltage for power factor correction. To ensure that the PFC output voltage can meet the requirements for motor operation, there needs to be a certain margin between the target voltage and the required voltage, and the value of the target voltage is greater than the required voltage.

[0048] To prevent exceeding the adjustment range during power factor correction, in this embodiment, a range limit is also imposed on the above-mentioned target voltage. Specifically, the above-mentioned target voltage is greater than the minimum operating voltage of the power factor correction module and less than the maximum withstand voltage of the capacitor in the power factor correction module. For example, this minimum operating voltage is the AC voltage multiplied by 1.414, and the maximum withstand voltage of this capacitor can be 400V or 450V.

[0049] S106. When the power factor correction enabling condition is met, then control the power factor correction to start and control the operation of the power factor correction module according to the above-mentioned target voltage.

[0050] Exemplarily, it can be determined whether the following conditions are met:

[0051] Detect that the PFC current > PFC start current;

[0052] Detect that the motor frequency > PFC start frequency;

[0053] Detect that the AC current peak value > PFC start peak current;

[0054] If any of the above conditions is met, it is determined that the power factor correction enabling condition is met.

[0055] When the power factor correction enabling condition is met, then control the power factor correction to start, and control the operation of the power factor correction module according to the above-mentioned target voltage.

[0056] Exemplarily, the above method further includes determining whether the PFC shutdown condition is met, as follows:

[0057] Detect that the PFC current < PFC shutdown current;

[0058] Detect that the motor frequency ≤ PFC start frequency;

[0059] If any of the above conditions is met, then control the power factor correction to shut down.

[0060] The motor drive control method provided by the embodiment of the present invention changes the target voltage of the PFC according to the change of the motor demand voltage, reduces the temperature rise speed and failure rate of the IGBT and capacitors without increasing the hardware cost, and improves the stability of the PFC voltage control.

[0061] In this embodiment, the motor drive control method using PFC PAM (Pulse Amplitude Modulation) is taken as an example for illustration.

[0062] The following equation exists when the motor is running:

[0063]

[0064] Where U motor is the total voltage required for motor operation; R s is the motor coil resistance; i is the motor coil current; L is the motor coil inductance; is the derivative of the motor coil current with respect to time; E ext is the motor back electromotive force;

[0065] Therefore, U motor is composed of three parts: the resistor voltage division R s *i, the induced electromotive force the motional electromotive force E ext (back electromotive force)

[0066] When the motor is in steady-state operation, the back electromotive force E ext accounts for more than 90%. Therefore, E ext can represent the voltage required for the current motor operation. Where

[0067]

[0068] ω e represents the motor speed, represents the motor magnetic flux, which is an inherent property of the motor and is a fixed value; therefore, the resistor voltage division R s *i and the induced electromotive force are omitted, and the motor demand voltage U motor is directly related to the motor operating frequency. As follows:

[0069]

[0070] The PFC target voltage calculation method (PAM control) is as follows:

[0071] The PFC target voltage is determined by the motor demand voltage and is calculated in the following manner.

[0072] U PFC = Umotor *Rate

[0073] Where Rate is the correction coefficient to ensure a certain margin for the PFC target voltage.

[0074] After calculating according to the above formula, it is also necessary to limit the range of U PFC to prevent U PFC from exceeding the adjustment range.

[0075] Specifically, U PFC needs to be within the range of [AC voltage * 1.414, maximum withstand voltage of the capacitor] to meet the PFC minimum operating voltage and ensure the reliability of the capacitor operation.

[0076] Figure 2 The figure shows a comparison diagram of the traditional PFC target voltage control and the PFC PAM target voltage control in this embodiment. The left figure is a schematic diagram of the traditional PFC target voltage control, and the right figure is a schematic diagram of the PFC PAM target voltage control in this embodiment.

[0077] In the left figure, the target voltage when PFC is off is 0, and the target voltage when PFC is on is a fixed value. In the right figure, the target voltage when PFC is off is 0, the lowest target voltage when PFC is on is AC voltage * 1.414, and the target voltage increases with the increase of the motor frequency until the target voltage increases to the maximum voltage.

[0078] This embodiment also provides an experimental method for the value of the above coefficient Rate. The experimental process for confirming the coefficient Rate is as follows:

[0079] Step 1: Set the initial coefficient Rate_Temp;

[0080] Step 2: Under the standard operating conditions of the motor, adjust the operating frequency from the lowest frequency to the highest frequency;

[0081] Step 3: Record the monitoring data (the current operating frequency of the motor, the motor required voltage, the current bus voltage);

[0082] Step 4: Observe the monitoring data. Before reaching the PFC maximum target voltage, if the current bus voltage > (motor required voltage + 20V). Then it is considered that the Rate coefficient meets the requirements, and take Rate = Rate_Temp * 1.1. If the current bus voltage is too small or too large, then adjust Rate_Temp up / down accordingly, and re-execute Step 2 until the appropriate Rate parameter is obtained.

[0083] During the experiment, the voltage margin (bus voltage - motor required voltage) can be viewed in real time. The motor required voltage increases with the increase of the motor operating frequency. During this process, keep the above voltage margin at an appropriate value (such as 20V).

[0084] In addition, since the above control process causes the PFC target voltage to change frequently, in order to ensure that the actual voltage can follow the target voltage, the voltage loop control of the PFC can be optimized, and the voltage output control in the motor control can also be optimized. Based on this, the voltage loop control optimization is also provided in this embodiment as follows:

[0085] Step 1: Sample the current bus voltage U1.

[0086] Step 2: Sample the bus voltage U2 again after a preset duration. This preset duration can be 0.2 ms;

[0087] Step 3: Calculate U2 - U1, and sum the calculation result with the original input of the PI (proportional integral controller) controller to obtain the Sum value. By comparing the DC bus voltages collected successively, the voltage drop value can be obtained, and this drop value is also used as one of the inputs of the PI controller, and is input into the PI controller together with the target voltage and the bus voltage collected again.

[0088] Step 4: Input the above Sum value into the PI controller to obtain the voltage loop output, and control the power factor correction module according to the output.

[0089] Figure 3 The schematic diagram of the voltage loop control optimization in this embodiment is shown. As Figure 3 shown, the difference between the bus voltage 2 ms ago and the current voltage is used as one of the inputs of the PI controller, and the PI controller outputs the proportional gain (Kp) and the integral gain (Ki) to the current loop.

[0090] The above improvement measures are beneficial to the stability of the PFC in controlling the bus voltage under the conditions of input voltage drop and frequent change of the target voltage. In the case of target voltage fluctuation, it is ensured that the actual bus voltage has good followability.

[0091] The motor control optimization is also provided in this embodiment, and the voltage distribution is carried out in the following manner:

[0092] If then directly output U d and U q ;

[0093] If then directly output U d , let

[0094] where U d is the voltage of the d-axis of the motor, and U q is the voltage of the q-axis of the motor, Udc is the current bus voltage.

[0095] Figure 4 shows the schematic diagram of the motor FOC control in this embodiment. As Figure 4 shown,

[0096] the quadrature-axis current quantity U is calculated through a proportional-integral controller q , and then the direct-axis voltage quantity U is calculated through another proportional-integral controller d . In this embodiment, "dq voltage distribution" is added, and the voltage control quantities u α and u β in the rotating coordinate system are obtained through the inverse Park transformation, and then the control quantities are modulated onto the three-phase inverter through the SVPWM (Space Vector Pulse Width Modulation) algorithm, thereby controlling the rotation of the motor.

[0097] The three-phase current values are sampled, and the current values i α and i β in the two-phase rotating coordinate system are obtained through the Clark transformation, and then the current values i d and i q in the two-phase stationary coordinate system are obtained through the Park transformation.

[0098] The optimization point of the above control improvement for the motor in this embodiment lies in optimizing the voltage distribution method after dq-axis decoupling in the motor control. On the premise of ensuring the stable output of the d-axis voltage, the remaining voltage is distributed to the q-axis, which can effectively improve the limit frequency of the motor and the adaptability of the motor to voltage changes.

[0099] In the embodiment of the present invention, without additional hardware costs, the temperature rise and failure rate of IGBTs and capacitors are reduced, and the stability of PFC voltage control is improved; the stability of motor FOC control is improved.

[0100] The embodiment of the present invention provides a motor variable-frequency drive controller for implementing the above motor drive control method.

[0101] The embodiment of the present invention provides an air conditioner including the above motor variable-frequency drive controller.

[0102] The motor variable-frequency drive controller and the air conditioner provided by the embodiment of the present invention can achieve the same technical effects as the above motor drive control method.

[0103] An embodiment of the present invention provides a computer-readable storage medium. The computer-readable storage medium stores a computer program. When the computer program is read and run by a processor, it implements the method provided in the above embodiment and can achieve the same technical effects. To avoid repetition, it will not be elaborated here. Among them, the computer-readable storage medium includes, for example, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disc, etc.

[0104] Of course, those skilled in the art can understand that all or part of the processes in implementing the method of the above embodiment can be completed by a computer program instructing a control device. The program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the above method embodiments. Among them, the storage medium can be a memory, a magnetic disk, an optical disc, etc.

[0105] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be subject to the scope defined by the claims.

[0106] Finally, it should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the element.

[0107] The various embodiments in this specification are described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other.

[0108] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be subject to the scope defined by the claims.

Claims

1. A motor drive control method, characterized in that: include: Obtaining a current required voltage of the motor, wherein the required voltage is positively correlated with a current operating frequency of the motor; Determining a target voltage for power factor correction according to the required voltage and a preset correction factor; The target voltage is greater than the required voltage; When the power factor correction start-up condition is met, the power factor correction is controlled to be turned on and the power factor correction module is controlled to operate according to the target voltage.

2. The method according to claim 1, characterized in that The target voltage is greater than a minimum operating voltage of the power factor correction module and less than a maximum withstand voltage of a capacitor in the power factor correction module.

3. The method according to claim 1, characterized in that The required voltage is calculated as follows: When the motor is running, the following equation exists: Among them, U motor The total voltage required for motor operation; R s is the motor coil resistance; i is the motor coil current; L is the motor coil inductance; is the time derivative of the motor coil current; E ext is the motor back electromotive force; When the motor is in steady state operation, E ext Can represent the voltage required for the current motor operation, as follows Among them, ω e is the motor speed, is the motor flux; the resistor voltage divider R is omitted s *i. Induced electromotive force After that, the motor requires voltage U motor Directly related to the motor operating frequency is as follows:

4. The method according to claim 3, characterized in that The target voltage is calculated as follows: U PFC =U motor *Rate Here, Rate is a correction factor greater than one.

5. The method according to claim 1, characterized in that The method further includes determining whether the following conditions are met: It is detected that the PFC current is greater than the PFC on current; The motor frequency is detected to be greater than the PFC start-up frequency; It is detected that the AC current peak value is greater than the PFC start-up peak current; If any of the above conditions is met, it is determined that the power factor correction start condition is met.

6. The method according to claim 1, characterized in that The method further comprises a voltage loop control optimization step, wherein the voltage loop control optimization step comprises: Sample the current bus voltage U1; After a preset time, the bus voltage U2 is sampled again; Calculate U2-U1, and sum the calculation result with the original input of the PI controller to get the Sum value; The Sum value is input into the PI controller to obtain a voltage loop output, and the power factor correction module is controlled according to the output.

7. The method according to claim 1, characterized in that The method further comprises a motor control optimization step, wherein the motor control optimization step comprises performing voltage distribution as follows: if Then directly output U d with U q ; if Then directly output U d ,make Among them, U d is the voltage of the motor d axis, U q is the voltage of the motor q axis, U dc is the current bus voltage.

8. The method according to claim 1, characterized in that The method further includes determining whether the following conditions are met: It is detected that the PFC current is less than the PFC shutdown current; The motor frequency is detected to be ≤ PFC start-up frequency; If any of the above conditions is met, the power factor correction is controlled to be turned off.

9. A motor variable frequency drive controller, characterized in that: Used to execute the motor drive control method described in any one of claims 1-8.

10. An air conditioner, characterized in that: Including the motor variable frequency drive controller as described in claim 9.

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