Phase loss detection method for permanent magnet synchronous motor

Abstract

The invention discloses a permanent magnet synchronous motor open-phase detection method, which is characterized by comprising the following steps of: calculating a three-phase sinusoidal current effective value; according to the three-phase sinusoidal current effective value, judging whether the motor is open-phase or not; if the motor is open-phase, the motor is shut down; wherein in the step of calculating the effective value of the three-phase sinusoidal current, the average value of the sum of squares of the current instantaneous values at the m-1 moment and the sampling value at the m moment are combined, and the sum of squares of the current instantaneous values at the m moment is calculated. According to the invention, through the application of the rapid calculation method of the effective value and the similar average sliding filtering mode, the problems of noise when the current amplitude is small and the instantaneous proportion is too large when the current is small are avoided to a great extent, and the real-time acquisition of the effective value of the current is realized.

Description

Technical Field

[0001] The invention relates to the technical field of sensorless frequency conversion control of permanent magnet synchronous motors, and in particular to a method for detecting phase loss of permanent magnet synchronous motors. Background Art

[0002] In the application of sensorless variable frequency control of permanent magnet synchronous motor, the detection and protection of motor phase loss is often used as a necessary method. Its detection and protection principle can be summarized as follows: during operation, when it is detected that there is no current in a phase line of the motor, it is judged as phase loss. However, in actual application, when the current amplitude is small, a smaller current comparison point is often set. Since the smaller part of the instantaneous value of the current accounts for a larger proportion in the entire cycle at this time, it is easy to trigger the phase loss protection and false protection. At the same time, when the current comparison point is small, the amplitude of the sampling noise may be greater than the set current comparison point, which is easy to miss and affect the accuracy of the protection.

[0003] The existing conventional motor phase loss detection and protection method usually detects in real time whether the three-phase current amplitude is less than the set current comparison point within a set period of time. Although this method has the characteristics of small amount of calculation and simple implementation, when the current amplitude is large, this method can effectively determine whether the motor has a phase loss problem. However, when the current amplitude is small, a smaller current comparison point needs to be set. At this time, the smaller part of the instantaneous current value accounts for a large proportion of the entire cycle, and the sampling noise amplitude may be greater than the set current amplitude. The method of cumulatively judging the current amplitude within a set period of time is easily affected, resulting in misjudgment. It is usually necessary to use a longer judgment time to eliminate the influence of noise and the small instantaneous current value. As a result, it is necessary to perform separate adjustments and phase loss detection for each motor, the protection is not universal, and the program adjustment is difficult. The cumulative judgment over a period of time will cause the protection time to lag, resulting in timeliness problems. Summary of the invention

[0004] In order to solve the universality and timeliness problems of phase loss detection and protection when the signal-to-noise ratio of the current sampling signal is low, and to increase product reliability and system stability, the present invention provides a permanent magnet synchronous motor phase loss detection method, which is characterized by comprising:

[0005] Calculate the effective value of three-phase sinusoidal current;

[0006] Determine whether the motor is missing a phase according to the effective value of the three-phase sinusoidal current;

[0007] If the motor loses a phase, it will stop;

[0008] In the step of calculating the effective value of the three-phase sinusoidal current, the average value of the sum of squares of the instantaneous current values ​​at time m-1 is combined with the sampling value at time m to calculate the sum of squares of the instantaneous current values ​​at time m.

[0009] In one embodiment of the present invention, in the step of calculating the effective value of the three-phase sinusoidal current, when the time used for the current accumulation times is much longer than the current signal cycle, the average value of the square sum after square root is approximately equal to the effective value of the current.

[0010] In another embodiment of the present invention, the step of calculating the effective value of the three-phase sinusoidal current includes:

[0011] Step 1: When sampling instantaneous values ​​N times within the cumulative time width, calculate the square of the instantaneous value of the current at time m;

[0012] Step 2: Calculate the sum of the squares of the instantaneous current values ​​of the latest N-1 points at time m-1, that is, the square of the instantaneous current value from time mN to time m-1;

[0013] Step 3: Calculate the sum of the values ​​in step 1 and step 2 to obtain the sum of squares of the instantaneous values ​​of the N current instantaneous values ​​within the latest accumulated time width at time m;

[0014] Step 4: Repeat steps 2 to 3 to obtain the value of the sum of squares of the currents within the latest N cumulative widths.

[0015] In another embodiment of the present invention, in step 2, the sum of squares of the instantaneous current values ​​of the latest N-1 points at time m-1 is: in It is the sum of squares of the latest N instantaneous current values ​​at time m-1.

[0016] In another embodiment of the present invention, in step 3, in It is the sum of squares of the latest N instantaneous current values ​​at time m.

[0017] In another embodiment of the present invention, at time m, the situation where the motor is out of phase includes:

[0018] When the U phase is missing, there is

[0019] When the V phase is missing, there is

[0020] When the W phase is missing, there is

[0021] In another embodiment of the present invention, when the motor is missing a phase, the current of the corresponding phase line is approximately zero.

[0022] In another embodiment of the present invention, when there is no phase loss in the motor,

[0023] In another embodiment of the present invention, at time m, when the motor is missing a phase, the relationship between the three-phase currents satisfies at least one of the following conditions:

[0024]

[0025] Where mul is the current square sum multiple, and its value is selected to be greater than or equal to 4.

[0026] In another embodiment of the present invention, in step 1, the instantaneous value is sampled N times within the accumulated time width, wherein the time corresponding to the N minimum values ​​needs to be greater than one cycle time of the signal.

[0027] The present invention has the following beneficial effects:

[0028] (1) Detecting and protecting phase loss by calculating effective values ​​can largely avoid the problem of noise when the current amplitude is small and the problem of excessive proportion of small instantaneous current, and solve the problem of conventional algorithms needing to adapt protection currents one by one and false alarms of phase loss.

[0029] (2) The fast calculation method of effective value solves the time-consuming problem caused by the need to use square root and division operations in the traditional effective value calculation process.

[0030] (3) The use of a quasi-average sliding filter method can avoid the problem that the traditional effective value can only output the calculation result once within a period of time, and realize the real-time acquisition of the effective value of the current. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 shows an overall implementation flow chart of an embodiment of the present invention; and

[0032] Figure 2 A flow chart of phase loss detection of a permanent magnet synchronous motor in an embodiment of the present invention is shown. Specific embodiments

[0033] The detailed features and advantages of the present invention are described in detail in the specific embodiments below, and the content is sufficient to enable any person skilled in the art to understand the technical content of the present invention and implement it accordingly, and according to the description, claims and drawings disclosed in this specification, those skilled in the art can easily understand the relevant purposes and advantages of the present invention. Although the description of the present invention will be introduced in conjunction with the preferred embodiment, this does not mean that the features of this invention are limited to this embodiment. On the contrary, the purpose of introducing the invention in conjunction with the embodiment is to cover other options or modifications that may be extended based on the claims of the present invention. In order to provide a deep understanding of the present invention, many specific details will be included in the following description. The present invention can also be implemented without using these details. In addition, in order to avoid confusion or blurring the focus of the present invention, some specific details will be omitted in the description.

[0034] At the same time, the present application uses specific words to describe the embodiments of the present application. For example, "one embodiment", "an embodiment", and / or "some embodiments" refer to a certain feature, structure or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or more in different positions in this specification does not necessarily refer to the same embodiment. In addition, some features, structures or characteristics in one or more embodiments of the present application can be appropriately combined.

[0035] Figure 1 It shows an overall implementation block diagram of an embodiment of the present invention.

[0036] like Figure 1 As shown, the present invention firstly quickly calculates the effective value of the three-phase sinusoidal current signal, thereby greatly reducing the amount of calculation involved in the normal effective value calculation, and then judges the obtained current effective value to detect whether the motor has a phase loss.

[0037] In the stage of quickly calculating the effective value of the three-phase sinusoidal current signal, if the instantaneous three-phase current real-time amplitude is compared with the set current comparison value, when the current signal-to-noise ratio is low, the noise amplitude may be greater than the comparison point. When the instantaneous value of the sinusoidal current signal is small, the part that meets the phase loss judgment condition increases significantly. When a smaller current judgment point is set, misjudgment is very likely to occur.

[0038] Therefore, the present invention avoids the problem by reducing the proportion of the current portion with a smaller instantaneous value in the entire current cycle and increasing the cycle proportion of the portion with a larger instantaneous value.

[0039] For a sinusoidal current signal, its effective value (RMS) is a constant value and is approximately 0.707 times the maximum amplitude. Using the effective value can not only avoid the problem that the current portion with a smaller instantaneous value accounts for a large proportion of the entire current cycle, but also because its value reaches 0.707 times the amplitude, it can maximize the signal-to-noise ratio of the current signal.

[0040] The mathematical calculation formula for the effective value of the sinusoidal current is:

[0041]

[0042] Among them, I RMS is the effective value of the sinusoidal current, I1, I2, I3, I4, ... ... I n-2 ,I n-1 ,I n is the nth sampling value in a current cycle, I m is the amplitude of the current signal.

[0043] However, the above formula (1-1) also has the following problems:

[0044] 1. Square root and division operations consume a lot of computing time, require high computing power, and are disadvantageous to low-computing-power MCUs.

[0045] 2. This method requires accumulation of instantaneous values ​​of a cycle. Different cycles result in different accumulation times within a cycle, which is not conducive to the situation of cycle changes. Moreover, a cycle will only produce one result, which is not conducive to timeliness.

[0046] In view of the above problems, the present invention proposes the following improvement scheme:

[0047] 1. As square root and division operations consume a lot of computing time, the square sum value can be directly used instead of the square root value and the square root average value to save square roots and use multiplication to replace division operations.

[0048] 2. Regarding the problem of different periods, since the current signal is a sinusoidal signal, when the time used for the accumulation number is much longer than the current signal period, the average value of the sum of squares after square root is approximately equal to the effective value of the current, and a longer accumulation time width can be used directly to solve the problem.

[0049] 3. For the case where only one result is produced in one cycle, considering that the effective value changes very slowly relative to the current sampling frequency in actual application, it can be approximately ignored, that is, the effective value at time m is approximately equal to the effective value at time m-1. Based on this, the average value of the sum of squares of the instantaneous current values ​​at time m-1 and the sampling value at time m can be combined to generate the sum of squares of the instantaneous current values ​​at time m. This eliminates the problem that only one result is produced in one cycle.

[0050] In summary, in one embodiment of the present invention, Figure 2 As shown, the quick calculation steps of the effective value of the three-phase sinusoidal current signal are as follows:

[0051] Sample the instantaneous value N times within the cumulative time width, at time m;

[0052] Step 1: Calculate the square of the instantaneous value of the current at time m

[0053] Step 2: Calculate the sum of squares of the instantaneous current values ​​of the latest N-1 points at time m-1 That is, the square of the instantaneous value of the current from moment mN to moment m-1. The calculation method is: in It is the sum of squares of the latest N instantaneous current values ​​at time m-1.

[0054] Step 3: Calculate the sum of the values ​​in step 1 and step 2 to obtain the square sum of the N instantaneous current values ​​within the latest accumulated time width at time m.

[0055] in It is the sum of squares of the latest N instantaneous current values ​​at time m.

[0056] Step 4: Each time an instantaneous value is collected, steps 2 to 3 are repeated to obtain the value of the sum of squares of the currents within the latest N cumulative widths.

[0057] In one embodiment of the present invention, the minimum value of N is limited to the time corresponding to the minimum value being greater than one cycle of the signal. In one embodiment, the signal is a sine-cosine periodic signal, the signal period is 1000Hz (0.001s), the sampling signal sampling frequency is 10K, that is, the sampling interval is 0.0001s, then the number of sampling times for testing one signal period is 0.001 / 0.0001=10. At this time, the minimum value of N should be greater than 10.

[0058] like Figure 2 As shown in the figure, the motor phase loss state detection is performed based on the current characteristics of the motor UVW three-phase when the motor is phase-lost. When the motor is phase-lost, the current of the corresponding phase line is approximately 0. When the motor is not phase-lost, the effective values ​​of the three-phase currents are approximately equal, that is:

[0059] When the U phase is missing, there is

[0060] When the V phase is missing, there is

[0061] When the W phase is missing, there is

[0062] When there is no phase loss, there is

[0063] According to this feature, at time m, after using the three-phase sinusoidal current effective value fast calculation method, when the motor has a phase loss, the relationship between the three-phase currents satisfies at least one of the following conditions:

[0064]

[0065] Among them, mul is the current square sum multiple, and its value should be greater than or equal to 4.

[0066] Therefore, after determining whether the motor is missing a phase, if it is missing a phase, the motor is shut down to achieve the purpose of protecting the motor.

[0067] Thereby achieving the following beneficial effects:

[0068] (1) Detecting and protecting phase loss by calculating effective values ​​can largely avoid the problem of noise when the current amplitude is small and the problem of excessive proportion of small instantaneous current, and solve the problem of conventional algorithms needing to adapt protection currents one by one and false alarms of phase loss.

[0069] (2) The fast calculation method of effective value solves the time-consuming problem caused by the need to use square root and division operations in the traditional effective value calculation process.

[0070] (3) The use of a quasi-average sliding filter method can avoid the problem that the traditional effective value can only output the calculation result once within a period of time, and realize the real-time acquisition of the effective value of the current.

[0071] The terms and expressions used herein are for descriptive purposes only, and the present invention should not be limited to these terms and expressions. The use of these terms and expressions does not mean to exclude any equivalent features of the illustrations and descriptions (or parts thereof), and it should be recognized that various modifications that may exist should also be included in the scope of the claims. Other modifications, variations and substitutions may also exist. Accordingly, the claims should be deemed to cover all such equivalents.

[0072] Similarly, it should be pointed out that although the present invention has been described with reference to the current specific embodiments, ordinary technicians in this technical field should realize that the above embodiments are only used to illustrate the present invention, and various equivalent changes or substitutions may be made without departing from the spirit of the present invention. Therefore, as long as the changes and modifications to the above embodiments are within the scope of the essential spirit of the present invention, they will fall within the scope of the claims of this application.

Claims

1. A method for detecting phase loss in a permanent magnet synchronous motor, characterized in that: include: Calculate the effective value of three-phase sinusoidal current; Determine whether the motor is missing a phase according to the effective value of the three-phase sinusoidal current; If the motor loses a phase, it will stop; In the step of calculating the effective value of the three-phase sinusoidal current, the average value of the sum of squares of the instantaneous current values ​​at time m-1 is combined with the sampling value at time m to calculate the sum of squares of the instantaneous current values ​​at time m.

2. The method for detecting phase loss of a permanent magnet synchronous motor according to claim 1, characterized in that: In the step of calculating the effective value of the three-phase sinusoidal current, when the time used for the current accumulation times is much longer than the current signal cycle, the average value of the square sum after square root is approximately equal to the effective value of the current.

3. The method for detecting phase loss of a permanent magnet synchronous motor according to claim 1, characterized in that: The step of calculating the effective value of the three-phase sinusoidal current comprises: Step 1: When sampling instantaneous values ​​N times within the cumulative time width, calculate the square of the instantaneous value of the current at time m; Step 2: Calculate the sum of the squares of the instantaneous current values ​​of the latest N-1 points at time m-1, that is, the square of the instantaneous current value from time mN to time m-1; Step 3: Calculate the sum of the values ​​in step 1 and step 2 to obtain the sum of squares of the instantaneous values ​​of the N current instantaneous values ​​within the latest accumulated time width at time m; Step 4: Repeat steps 2 to 3 to obtain the value of the sum of squares of the currents within the latest N cumulative widths.

4. The method for detecting phase loss of a permanent magnet synchronous motor according to claim 3, characterized in that: In step 2, the sum of squares of the instantaneous current values ​​of the latest N-1 points at time m-1 is: in It is the sum of squares of the latest N instantaneous current values ​​at time m-1.

5. The method for detecting phase loss of a permanent magnet synchronous motor according to claim 3, characterized in that: In step 3, in It is the sum of squares of the latest N instantaneous current values ​​at time m.

6. The method for detecting phase loss of a permanent magnet synchronous motor according to claim 1, characterized in that: At time m, the motor phase loss situation includes: When the U phase is missing, there is When the V phase is missing, there is When the W phase is missing, there is 7. The method for detecting phase loss of a permanent magnet synchronous motor according to claim 6, characterized in that: When the motor is missing a phase, the current in the corresponding phase line is approximately 0.

8. The method for detecting phase loss of a permanent magnet synchronous motor according to claim 6, characterized in that: At time m, when there is no phase loss in the motor, 9. The method for detecting phase loss of a permanent magnet synchronous motor according to claim 6, characterized in that: At time m, when the motor is missing a phase, the relationship between the three-phase currents satisfies at least one of the following conditions: Where mul is the current square sum multiple, and its value is selected to be greater than or equal to 4.

10. The method for detecting phase loss of a permanent magnet synchronous motor according to claim 1, characterized in that: In step 1, the instantaneous value is sampled N times within the accumulated time width, wherein the time corresponding to the N minimum values ​​needs to be greater than one cycle time of the signal.

Images