AC motor constant voltage frequency ratio control system and method

Abstract

The invention relates to the technical field of AC motor driving control, and discloses an AC motor constant voltage frequency ratio control system and method, and the system comprises a constant voltage frequency ratio calculation module, an integral operation module, a coordinate transformation module, an energy-saving control module, a compensation module, a space vector modulation module and a three-phase inverter. The coordinate conversion module is used for converting the three-phase current sampling value of the alternating current motor into reactive current and active current under voltage vector orientation; the energy-saving control module is used for calculating an energy-saving voltage increment and an angle oscillation component according to the reactive current and the active current under the voltage vector orientation; and the compensation module is used for compensating the energy-saving voltage increment and an output voltage amplitude reference value to obtain a compensated output voltage amplitude, and compensating the angle oscillation component and a wave emitting angle reference value to obtain a compensated wave emitting angle. According to the invention, the motor instability oscillation phenomenon caused by the energy-saving scheme is effectively prevented.

Description

Technical Field

[0001] This invention relates to the field of AC motor drive control technology, specifically to an AC motor constant voltage-frequency ratio control system and method. Background Technology

[0002] AC motor drive control systems typically employ a constant voltage-frequency ratio (CVFR) control scheme as their foundation. Theoretically, CVFR control is applicable to any type of AC current. For applications with simple operating conditions, such as fans and pumps, CVFR control is relatively simple and easy to implement as it does not depend on motor parameters. Currently, to improve the operating efficiency of CVFR control, most improved schemes select different voltage-frequency ratios in real time based on the motor's operating conditions to optimize system efficiency. However, changing the voltage-frequency ratio under certain operating frequencies can lead to motor instability and significant oscillations, potentially causing damage to system mechanical components. Summary of the Invention

[0003] To address the aforementioned shortcomings in the existing technology, this invention provides a constant voltage-frequency ratio control system and method for AC motors. This system adjusts the motor voltage amplitude by comparing the magnitudes of active and reactive currents in a voltage vector oriented coordinate system, thereby improving system efficiency under light-load operating conditions. Furthermore, to prevent motor instability and oscillation caused by changes in the motor's magnetic field, this scheme also compensates for the wave angle of the constant voltage-frequency ratio control scheme using the angular oscillation component in the current vector angle, effectively preventing motor instability and oscillation caused by the energy-saving scheme itself.

[0004] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: In a first aspect, the present invention proposes a constant voltage-frequency ratio control system for an AC motor, comprising: The constant voltage-frequency ratio calculation module is used to generate reference values ​​for the wave emission angle and the output voltage amplitude based on a given rotational speed. The integral calculation module is used to perform integral calculations on a given rotational speed to generate a reference value for the wave angle. The coordinate transformation module is used to convert the three-phase current sampling values ​​of the AC motor into reactive and active currents under voltage vector orientation. The energy-saving control module is used to calculate the energy-saving voltage increment and angle oscillation component based on the reactive current and active current under voltage vector orientation. The compensation module is used to compensate the energy-saving voltage increment with the output voltage amplitude reference value to obtain the compensated output voltage amplitude, and to compensate the angle oscillation component with the wave transmission angle reference value to obtain the compensated wave transmission angle. The space vector modulation module is used to generate a modulation signal based on the compensated output voltage amplitude and the transmission angle. A three-phase inverter is used to drive an AC motor according to a modulation signal.

[0005] Optionally, the energy-saving control module may calculate the energy-saving voltage increment in the following ways: By comparing the magnitudes of active and reactive currents, the voltage increment is calculated based on the sign function and the absolute value of the current difference, and the energy-saving voltage increment is obtained through integration and limiting.

[0006] Optionally, the sign function is set to 1 when the active current is greater than the reactive current, and -1 otherwise.

[0007] Optionally, the energy-saving control module may calculate the energy-saving voltage increment in the following ways: Using a proportional-integral controller, the voltage increment is calculated by taking the difference between reactive and active current as input and then subjected to limiting processing to obtain the energy-saving voltage increment.

[0008] Optionally, the energy-saving control module also includes a voltage increment limiting module, which limits the calculated energy-saving voltage increment to half of the rated voltage of the AC motor.

[0009] Optionally, the energy-saving control module calculates the angular oscillation component in the following ways: The motor current vector angle is obtained by calculating the arctangent of the ratio of active current iq to reactive current id, and then the angle oscillation component is extracted by a high-pass filter function.

[0010] Optionally, the high-pass filter function may employ a first-order or second-order high-pass digital filter.

[0011] Optionally, the compensation module may compensate for the energy-saving voltage increment with the output voltage amplitude reference value to obtain the compensated output voltage amplitude in the following ways: The compensated output voltage amplitude is obtained by subtracting the energy-saving voltage increment from the reference value of the output voltage amplitude.

[0012] Optionally, the compensation module compensates for the angular oscillation component with the wave transmission angle reference value to obtain the compensated wave transmission angle in the following specific ways: The compensated wave angle is obtained by subtracting the angle oscillation component from the reference value of the wave angle.

[0013] Secondly, this invention proposes a constant voltage-frequency ratio control method for an AC motor, applied to the aforementioned constant voltage-frequency ratio control system for an AC motor, comprising the following steps: Based on the given rotational speed, a reference value for the wave emission angle and a reference value for the output voltage amplitude are generated, and an integral operation is performed on the given rotational speed to generate the reference value for the wave emission angle. The three-phase current sampling values ​​of the AC motor are converted into reactive and active currents under voltage vector orientation. Calculate the energy-saving voltage increment and angle oscillation component based on the reactive current and active current under voltage vector orientation; The output voltage amplitude is obtained by compensating the energy-saving voltage increment with the output voltage amplitude reference value, and the angular oscillation component is obtained by compensating the wave transmission angle with the wave transmission angle reference value. A modulation signal is generated based on the compensated output voltage amplitude and the wave angle. The AC motor is driven to run based on the modulation signal.

[0014] The present invention has the following beneficial effects: This invention adjusts the magnitude of the motor voltage amplitude by comparing the magnitudes of the active and reactive currents in the voltage vector orientation coordinate system, thereby improving the system efficiency under light load operating conditions. At the same time, in order to prevent motor instability and oscillation caused by changes in the motor magnetic field, the angular oscillation component in the current vector angle is used to compensate for the wave angle of the constant voltage-frequency ratio control scheme, thereby effectively preventing the occurrence of motor instability and oscillation caused by the energy-saving scheme itself. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of an AC motor constant voltage-frequency ratio control system according to the present invention; Figure 2 This is an internal schematic diagram of an energy-saving control module; Figure 3 This is another internal schematic diagram of the energy-saving control module; Figure 4 This is a schematic flowchart of a constant voltage-frequency ratio control method for an AC motor according to the present invention. Detailed Implementation

[0016] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0017] like Figure 1 As shown in the figure, an AC motor constant voltage-frequency ratio control system provided in this embodiment of the invention includes: The constant voltage-frequency ratio calculation module is used to generate reference values ​​for the wave emission angle and the output voltage amplitude based on a given rotational speed. The integral calculation module is used to perform integral calculations on a given rotational speed to generate a reference value for the wave angle. The coordinate transformation module is used to convert the three-phase current sampling values ​​of the AC motor into reactive and active currents under voltage vector orientation. The energy-saving control module is used to calculate the energy-saving voltage increment and angle oscillation component based on the reactive current and active current under voltage vector orientation. The compensation module is used to compensate the energy-saving voltage increment with the output voltage amplitude reference value to obtain the compensated output voltage amplitude, and to compensate the angle oscillation component with the wave transmission angle reference value to obtain the compensated wave transmission angle. The space vector modulation module is used to generate a modulation signal based on the compensated output voltage amplitude and the transmission angle. A three-phase inverter is used to drive an AC motor according to a modulation signal.

[0018] Figure 1 In this diagram, VSI represents a three-phase inverter, SVPWM represents a space vector modulation module, M represents an AC motor, 1 / s represents an integral operation module, V / F represents a constant voltage-frequency ratio calculation module, and dq / abc represents a coordinate transformation calculation module. Figure 1 In this context, ω* represents the given rotational speed, θ and V are the wave angle and output voltage amplitude of the constant voltage-frequency ratio control scheme, ia, ib, and ic are the sampled values ​​of the three-phase current of the motor, id and iq are the reactive and active currents under voltage vector orientation, and ΔV and Δθ are the energy-saving voltage increment and angle oscillation component, respectively. Figure 1 As can be seen, this embodiment utilizes an energy-saving control module to perform real-time compensation on the wave angle and output voltage amplitude of the conventional constant voltage frequency ratio control scheme, thereby achieving efficient control of the AC motor.

[0019] In an optional embodiment of the present invention, the energy-saving control module calculates the energy-saving voltage increment in the following manner: By comparing the magnitudes of active and reactive currents, the voltage increment is calculated based on the sign function and the absolute value of the current difference. This calculation is then followed by integration and limiting to obtain the energy-saving voltage increment. The sign function is set to 1 when the active current is greater than the reactive current, and -1 otherwise.

[0020] like Figure 2 As shown, this embodiment determines the direction of the voltage increment by comparing the magnitudes of the active current and reactive current, while the rate of voltage increment can be set manually. Finally, the energy-saving voltage increment is obtained after passing through the voltage increment limiting module. ; ;

[0021] in, a To control the adjustment speed of voltage increment for energy saving, id and iq are the reactive current and active current under voltage vector orientation, respectively.f (id,iq) is the sign function, where |iq-id| represents the absolute value of the difference between the two currents.

[0022] In an optional embodiment of the present invention, the energy-saving control module calculates the energy-saving voltage increment in the following manner: Using a proportional-integral controller, the voltage increment is calculated by taking the difference between reactive and active current as input and then subjected to limiting processing to obtain the energy-saving voltage increment.

[0023] like Figure 3 As shown, this embodiment uses reactive current as the given value and active current as the feedback value. Alternatively, a proportional-integral controller (PI controller) can be used to calculate the incremental value of the output voltage, which can then be obtained through a voltage increment limiting module to achieve the energy-saving voltage increment. ;

[0024] Where kp and ki are the proportional gain and integral gain of the energy-saving PI controller.

[0025] In an optional embodiment of the present invention, the energy-saving control module further includes a voltage increment limiting module for limiting the calculated energy-saving voltage increment to within half of the rated voltage of the AC motor.

[0026] This embodiment is in Figure 2 and Figure 3 The voltage increment limiting module is consistent with the above formula, which limits the voltage increment calculated above to half of the rated voltage of the AC motor. This ensures both stable operation of the AC motor and energy-saving performance of the solution. Let Un be the rated voltage of the AC motor. The voltage increment limiting module then limits the calculated voltage increment to (-Un / 2, 0).

[0027] In an optional embodiment of the present invention, the energy-saving control module calculates the angle oscillation component in the following way: The motor current vector angle is obtained by calculating the arctangent of the ratio of active current iq to reactive current id, and then the angle oscillation component is extracted by a high-pass filter function.

[0028] This embodiment is in Figure 2 and Figure 3 The calculation method for the mid-angle oscillation component is consistent: the motor current vector angle is calculated from the active and reactive currents, and then the angular oscillation component is extracted from the current vector angle using a high-pass filter. The motor current vector angle can be obtained by taking the arctangent of the ratio of active to reactive current. ;

[0029] Here, HPF represents the high-pass filter function, which can be either a first-order or second-order high-pass digital filter. arctan represents the arctangent function.

[0030] In an optional embodiment of the present invention, the specific method by which the compensation module compensates for the energy-saving voltage increment with the output voltage amplitude reference value to obtain the compensated output voltage amplitude includes: The compensated output voltage amplitude is obtained by subtracting the energy-saving voltage increment from the reference value of the output voltage amplitude.

[0031] The compensation module compensates for the angular oscillation component with the wave transmission angle reference value to obtain the compensated wave transmission angle in the following specific ways: The compensated wave angle is obtained by subtracting the angle oscillation component from the reference value of the wave angle.

[0032] In this embodiment, the energy-saving voltage increment after amplitude limiting and the angular oscillation component are used to compensate the output voltage amplitude and the wave angle of constant voltage-frequency ratio control in real time. ; ;

[0033] Where θ* and V* are the reference values ​​for the wave transmission angle and output voltage amplitude of the conventional constant voltage frequency ratio control scheme, respectively, while θ and V are the wave transmission angle and output voltage amplitude of the compensated constant voltage frequency ratio control scheme, respectively. From the above equation, it can be seen that subtracting the angle oscillation component from the reference value of the wave transmission angle of the conventional constant voltage frequency ratio control scheme can achieve real-time compensation for the reference value of the wave transmission angle; similarly, subtracting the energy-saving voltage increment from the reference value of the output voltage amplitude of the conventional constant voltage frequency ratio control scheme can achieve real-time compensation for the reference value of the output voltage amplitude.

[0034] This invention also provides a constant voltage-frequency ratio control method for an AC motor, applied to the aforementioned constant voltage-frequency ratio control system for an AC motor, such as... Figure 4 As shown, it includes the following steps: Based on the given rotational speed, a reference value for the wave emission angle and a reference value for the output voltage amplitude are generated, and an integral operation is performed on the given rotational speed to generate the reference value for the wave emission angle. The three-phase current sampling values ​​of the AC motor are converted into reactive and active currents under voltage vector orientation. Calculate the energy-saving voltage increment and angle oscillation component based on the reactive current and active current under voltage vector orientation; The output voltage amplitude is obtained by compensating the energy-saving voltage increment with the output voltage amplitude reference value, and the angular oscillation component is obtained by compensating the wave transmission angle with the wave transmission angle reference value. A modulation signal is generated based on the compensated output voltage amplitude and the wave angle. The AC motor is driven to run according to the modulation signal.

[0035] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0036] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0037] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0038] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

[0039] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A constant voltage-frequency ratio control system for an AC motor, characterized in that, include: The constant voltage-frequency ratio calculation module is used to generate reference values ​​for the wave emission angle and the output voltage amplitude based on a given rotational speed. The integral calculation module is used to perform integral calculations on a given rotational speed to generate a reference value for the wave angle. The coordinate transformation module is used to convert the three-phase current sampling values ​​of the AC motor into reactive and active currents under voltage vector orientation. The energy-saving control module is used to calculate the energy-saving voltage increment and angle oscillation component based on the reactive current and active current under voltage vector orientation. The compensation module is used to compensate the energy-saving voltage increment with the output voltage amplitude reference value to obtain the compensated output voltage amplitude, and to compensate the angle oscillation component with the wave transmission angle reference value to obtain the compensated wave transmission angle. The space vector modulation module is used to generate a modulation signal based on the compensated output voltage amplitude and the transmission angle. A three-phase inverter is used to drive an AC motor according to a modulation signal.

2. The AC motor constant voltage-frequency ratio control system according to claim 1, characterized in that, The energy-saving control module calculates the energy-saving voltage increment in the following ways: By comparing the magnitudes of active and reactive currents, the voltage increment is calculated based on the sign function and the absolute value of the current difference, and the energy-saving voltage increment is obtained through integration and limiting.

3. The AC motor constant voltage-frequency ratio control system according to claim 2, characterized in that, The sign function is set to 1 when the active current is greater than the reactive current, and -1 otherwise.

4. The AC motor constant voltage-frequency ratio control system according to claim 1, characterized in that, The energy-saving control module calculates the energy-saving voltage increment in the following ways: Using a proportional-integral controller, the voltage increment is calculated by taking the difference between reactive and active current as input and then subjected to limiting processing to obtain the energy-saving voltage increment.

5. A constant voltage-frequency ratio control system for an AC motor according to claim 2 or 4, characterized in that, The energy-saving control module also includes a voltage increment limiting module, which limits the calculated energy-saving voltage increment to half of the rated voltage of the AC motor.

6. The AC motor constant voltage-frequency ratio control system according to claim 1, characterized in that, The energy-saving control module calculates the angle oscillation component in the following ways: The motor current vector angle is obtained by calculating the arctangent of the ratio of active current iq to reactive current id, and then the angle oscillation component is extracted by a high-pass filter function.

7. The AC motor constant voltage-frequency ratio control system according to claim 6, characterized in that, The high-pass filter function uses a first-order or second-order high-pass digital filter.

8. The AC motor constant voltage-frequency ratio control system according to claim 1, characterized in that, The compensation module compensates for the energy-saving voltage increment with the output voltage amplitude reference value to obtain the compensated output voltage amplitude in the following specific ways: The compensated output voltage amplitude is obtained by subtracting the energy-saving voltage increment from the reference value of the output voltage amplitude.

9. The AC motor constant voltage-frequency ratio control system according to claim 1, characterized in that, The compensation module compensates for the angular oscillation component with the wave transmission angle reference value to obtain the compensated wave transmission angle in the following specific ways: The compensated wave angle is obtained by subtracting the angle oscillation component from the reference value of the wave angle.

10. A constant voltage-frequency ratio control method for an AC motor, applied to the constant voltage-frequency ratio control system for an AC motor according to any one of claims 1 to 9, characterized in that, Includes the following steps: Based on the given rotational speed, a reference value for the wave emission angle and a reference value for the output voltage amplitude are generated, and an integral operation is performed on the given rotational speed to generate the reference value for the wave emission angle. The three-phase current sampling values ​​of the AC motor are converted into reactive and active currents under voltage vector orientation. Calculate the energy-saving voltage increment and angle oscillation component based on the reactive current and active current under voltage vector orientation; The output voltage amplitude is obtained by compensating the energy-saving voltage increment with the output voltage amplitude reference value, and the angular oscillation component is obtained by compensating the wave transmission angle with the wave transmission angle reference value. A modulation signal is generated based on the compensated output voltage amplitude and the wave angle. The AC motor is driven to run according to the modulation signal.

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