A variable frequency motor maximum operating frequency control method

Abstract

The application discloses a variable-frequency motor maximum operation frequency control method, which controls the operation frequency of the motor according to the position in a voltage vector diagram and a modulation depth coefficient K r When K r is in the range of K r1 <K r ≤K r2 , the operation frequency is prohibited from rising; when K r >K r2 is met, the operation frequency can only decrease; and only when K r ≤K r1 is met, the operation frequency is allowed to rise. The application can greatly utilize the limit value of the bus voltage when the motor operation frequency is high, the load is heavy or the bus voltage is low, improve the maximum rotating speed of the compressor, control the rotating speed of the motor in real time, stably control the operation of the motor and avoid the phenomenon of forcedly improving the rotating speed of the motor to cause fault shutdown.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, and in particular to a method for controlling the maximum operating frequency of a variable frequency motor. Background Technology

[0002] With the rapid development of power electronics technology and new semiconductor devices, AC speed control technology has been continuously improved and refined. The increasingly sophisticated frequency converters, with their excellent output waveforms and superior performance-price ratio, are widely used in AC motors. For example, large and medium-sized roller motors used in steel mills for rolling mills, traction motors for railways and urban rail transit, elevator motors, crane motors for container lifting equipment, motors for water pumps and fans, compressors, and motors for household appliances have all adopted AC variable frequency speed control motors with good results. Traditional variable frequency motors operate at a frequency controlled according to the speed command value given by the host computer. When the bus voltage is low or the motor load is heavy and a higher operating speed is required, the control voltage vector may exceed the vertices of the voltage vector hexagon and become unadjustable, leading to unstable motor operation and subsequent fault shutdown. Summary of the Invention

[0003] The purpose of this invention is to provide a method for controlling the maximum operating frequency of a variable frequency motor in order to solve the above-mentioned problems. This invention automatically adjusts the motor operating frequency according to the position of the control voltage vector in the voltage vector hexagon, thereby achieving the goal of stable motor operation.

[0004] The present invention achieves the above objectives through the following technical solutions:

[0005] A method for controlling the maximum operating frequency of a variable frequency motor, based on the modulation depth coefficient K r The position in the voltage vector diagram controls the motor's operating frequency when K... r In K r1 <K r ≤K r2 Within the specified range, the operating frequency is prohibited from increasing; when K is satisfied... r >K r2 When K is at that time, the operating frequency can only be reduced; only when K r ≤K r1 Only when the operating frequency is increased is it allowed to rise, among which

[0006] Furthermore, the specific method of the present invention includes the following steps:

[0007] Step 1: Detect the bus voltage and calculate the modulation depth coefficient K. r ;

[0008] in,

[0009] Step 2, when K r ≤K r1 At that time, control command value f1 * Follow the frequency command value f given by the host computer r During operation, the actual operating frequency f1 of the motor follows f1. * Changes; where K r1 To adjust the depth factor by 1;

[0010] Step 3, when K r1 ≤K r ≤K r2 At that time, if the motor frequency command value f1 * Satisfy f r >f1 * If the motor frequency command value f1 is set to f1, then increasing the motor operating frequency is prohibited. * Satisfy f r <f1 * Then the motor frequency command value f1 * Follow f r Decrease; where K r2 To adjust the depth factor by 2;

[0011] Step 4, when K r >K r2 At this time, regardless of the actual operating frequency f1 of the motor, the command value f1 for reducing the motor frequency is reduced. * until K r1 ≤K r ≤K r2 Under certain conditions, the motor frequency command value f1 * Stop the descent, or satisfy K r ≤K r1 Under certain conditions, the motor frequency command value f1 * Only then can it rise again, among which

[0012] The beneficial effects of this invention are as follows:

[0013] This invention can maximize the utilization of the maximum value of the bus voltage when the motor operates at a high frequency, under heavy load, or when the bus voltage is low, thereby increasing the maximum speed of the compressor, controlling the motor speed in real time, and stabilizing the motor operation, thus avoiding the phenomenon of fault reporting and shutdown caused by forcibly increasing the motor speed. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the voltage vector of the present invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0017] In any embodiment, such as Figure 1 As shown, a method for controlling the maximum operating frequency of a variable frequency motor according to the present invention includes:

[0018] The control board bus voltage V is obtained through AD conversion. EDC Calculate the voltage vector V r , or

[0019] Where V d * This is the d-axis voltage command value, V. q * This is the q-axis voltage command value, V. α * This is the α-axis voltage command value, V β * It is the β-axis voltage command value; then obtain the modulation ratio K. r , in,

[0020] When K r ≤K r1 At that time, control command value f1 * Follow the frequency command value f given by the host computer r During operation, the actual operating frequency f1 of the motor follows f1. * change;

[0021] When K r1 ≤K r ≤K r2 At that time, if the motor frequency command value f1 * Satisfy fr >f1 * If the motor frequency command value f1 is set to f1, then increasing the motor operating frequency is prohibited. * Satisfy f r <f1 * Then the motor frequency command value f1 * Follow f r decline;

[0022] When K r >K r2 At this time, regardless of the actual operating frequency f1 of the motor, the command value f1 for reducing the motor frequency is reduced. * until K r1 ≤K r ≤K r2 Under certain conditions, the motor frequency command value f1 * Stop the descent, or satisfy K r ≤K r1 Under certain conditions, the motor frequency command value f1 * Only then can it rise again (when f) r >f1 * (time), among which

[0023] In one specific embodiment, such as Figure 1 As shown, a method for controlling the maximum operating frequency of a variable frequency motor according to the present invention includes:

[0024] Voltage vectors U1(100), U2(110), U3(010), U4(011), U5(001), and U6(101) form a regular hexagon. U7(111) and U0(000) are zero vectors located at the center of the hexagon. S1 is the incircle of the regular hexagon, and its intersection point A with vector U1(100) is... S4 is the circumcircle of a regular hexagon, and the intersection point B with vector U1(100) is... When vector V r When it is within S1, at this time The motor is in linear regulation (i.e., the motor operating frequency is according to V). r (The size is adjusted linearly according to the ratio), when vector V r Between S1 and S4, at this time The motor is under over-modulation regulation (i.e., the motor operating frequency is according to V). r (The size is adjusted non-proportionally and non-linearly), K r ≤K r1 In reality, it is a vector V. r K is located inside circle S2. r1 <K r ≤K r2 In reality, it is a vector V. rK is between S2 and S3. r >K r2 It is between S3 and S4.

[0025] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. Furthermore, various different embodiments of the present invention can also be arbitrarily combined, as long as they do not violate the spirit of the present invention, they should also be considered as the content disclosed in the present invention.

Claims

1. A method of controlling the maximum operating frequency of a variable frequency motor, characterized by, The control panel bus voltage V is obtained by AD conversion EDC , the voltage vector V r , or where V d * is a d-axis voltage command value, V q * is a q-axis voltage command value, V α * is an a-axis voltage command value, V β * is a β-axis voltage command value; the modulation ratio K is obtained again r , where, When K r ≤K r1 At that time, the motor frequency command value f1 * Follow the frequency command value f given by the host computer r During operation, the actual operating frequency f1 of the motor follows f1. * Changes; where K r1 To adjust the depth factor by 1; When K r1 ≤ K r ≤ K r2 , if the motor frequency command value f1 * satisfies f r > f1 * , the motor operating frequency is prohibited from rising, and if the motor frequency command value f1 * satisfies f r < f1 * , the motor frequency command value f1 * follows f r downward; wherein K r2 is an adjustment depth coefficient 2; When K r >K r2 , the motor frequency command value f1 * is reduced regardless of the actual motor frequency f1 r1 , until the condition K r ≤ K r2 is satisfied, the motor frequency command value f1 * stops decreasing, or the condition K r ≤ K r1 is satisfied and when f r > f1 * , the motor frequency command value f1 * can again increase, where Wherein, voltage vector U1(100), U2(110), U3(010), U4(011), U5(001), U6(101) constitute a regular hexagon, U7(111), U0(000) is zero vector, in the center point of the regular hexagon; S1 is the inscribed circle of the regular hexagon, and the intersection point A of vector U1(100) S4 is the circumscribed circle of the regular hexagon, and the intersection point B of vector U1(100) When the vector V r is within S1, at this time The motor is in linear regulation, that is, the motor operating frequency is proportional to V r , and the size is linearly regulated in proportion, when the vector V r is between S1 and S4, at this time The motor is in overmodulation regulation, that is, the motor operating frequency is proportional to V r , and the size is regulated in non-proportional non-linear, K r ≤K r1 The actual vector V r is inside the S2 circle, K r1 <K r ≤K r2 The actual vector V r is between S2 and S3, K r >K r2 is between S3 and S4.

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