Pulse offset protection method for detecting short circuits between phases in a driver and driver for performing the method

Abstract

The present invention relates to a pulse offset protection method for detecting an inter-phase short circuit in a driver for controlling a motor, wherein the driver supplies an output voltage to the motor, and wherein the moment for performing the short circuit detection function is selected to minimize interference with the output voltage of the driver. The present invention also relates to a driver for controlling a motor, which driver includes a control section for generating an output signal and an output section connectable to the motor. The driver is arranged to perform the above-mentioned pulse offset protection method.

Description

Technical Field

[0001] The present invention relates to a pulse offset protection method for detecting an inter-phase short circuit in a driver for controlling an electric motor, wherein the driver supplies an output voltage to the electric motor, and wherein the moment for performing the short circuit detection function is selected to minimize the interference with the output voltage of the driver. The present invention also relates to a driver for controlling an electric motor, the driver including a control unit for generating an output signal and an output unit connectable to the electric motor. The driver is provided to perform the above-mentioned pulse offset protection method. Background Art

[0002] Drivers for controlling electric motors may include various monitoring functions for monitoring the driver and / or the electric motor driven by the driver. The present invention relates to a method and an apparatus for allowing the detection of a short circuit in the context of an electric motor driver and a corresponding electric motor.

[0003] In order to detect an inter-phase short circuit in a three-phase electric motor, there must be a voltage difference between the phases. If a short circuit exists, the voltage difference between the two phases will cause the current to increase to a level sufficient to detect the short circuit.

[0004] In the context of current electric motor drivers and corresponding electric motors, it is not necessary to ensure that a short circuit is detected as soon as possible. Therefore, the function of detecting a short circuit can be performed periodically (e.g., in the range of milliseconds). Since the function of detecting a short circuit may cause a change in the output voltage required by the current controller of the electric motor driver, the execution of the short circuit detection may deteriorate the current waveform output by the driver. This may in turn affect the performance of the electric motor and the estimated values of the electric motor (parameters) and generate unwanted noise. Summary of the Invention

[0005] Therefore, an object of the present invention is to optimize the manner of performing the short circuit detection function so that the output voltage of the driver is disturbed as little as possible.

[0006] This object is achieved by the pulse offset protection method according to the present disclosure and the driver according to the present disclosure. According to the pulse offset protection method and the driver, a driver can be provided to perform the method. According to the present invention, there is provided a pulse offset protection method for detecting an inter-phase short circuit in a driver for controlling an electric motor. The driver supplies an output voltage for driving the electric motor. According to the present invention, the moment for performing the short circuit detection function is calculated online. The term "online" herein means the state in which the electric motor driven by the driver is running. Necessary data, calculations, and / or derivations are performed online. This method enables the electric motor to operate at a very low speed.

[0007] The online execution data includes, for example, information corresponding to the frequency at which the short-circuit detection function is desired to be executed, and further includes information corresponding to the frequency of the electric motor. This data is then used in the calculation to determine the moment at which the short-circuit detection function is to be executed.

[0008] To achieve minimal interference with the output voltage of the driver, the short-circuit detection function is executed at the moment when the output voltage of the driver is as far as possible from the active vector of the driver.

[0009] On the one hand, when the output voltage is as far as possible from the active vector, a significant voltage difference between at least two phases will naturally occur. On the other hand, for each active vector, there are two phases with equal voltage waveforms, so short-circuit detection will be difficult. The present invention takes advantage of this situation and executes the short-circuit detection function at the most favorable moment during the operation of the electric motor.

[0010] This pulse offset protection method, especially the short-circuit detection function performed by this pulse offset protection method, can generally be continuously and repeatedly executed during the operation of the electric motor. Through the short-circuit detection method described herein, the present invention can reduce the interference with the generated output voltage.

[0011] Different motor frequencies may generate different frequencies for performing the pulse offset protection function. The data set can be stored in a look-up table or a database and can include the optimal angle at which the pulse offset protection should be executed. For example, if the electric motor operates at 300 RPM or 10 Hz and a pulse offset interval of 4 ms is desired, the pulse offset protection can be executed every 14.4°. The corresponding values can be stored in the look-up table accordingly.

[0012] Similar data sets can be provided for any relevant frequency range. For example, for the frequency range of 10 - 12 Hz, the pulse offset protection can be executed every 14.4°; for the frequency range of 12 - 15 Hz, the pulse offset protection can be executed every 18°; for the frequency range of 15 - 20 Hz, the pulse offset protection can be executed every 24°, etc.

[0013] In another preferred embodiment of the present invention, the short-circuit detection function is executed at a moment determined based on a timer and the moment when the short-circuit detection function was most recently executed. This scheme can set a timer to indicate the moment of executing the pulse offset protection function.

[0014] In a particularly preferred embodiment, the timer is reset each time the short - circuit detection function is executed. If the timer indicates that a new pulse - offset protection should be executed near the active vector, the execution of the pulse - offset protection is delayed or advanced to a given limit value. This can be done by adjusting the value of a counter such that, with the updated timer, the pulse - offset protection is executed at the edge near the active vector. The execution of the short - circuit detection function can be delayed or advanced to maintain a minimum distance between the execution of the short - circuit detection function and the active vector of the driver. The term "distance" herein can represent the time interval or angle between the execution of the short - circuit detection function and the active vector.

[0015] In another preferred embodiment of the present invention, the short - circuit detection function is executed at a moment determined based on the target angle and the angle at which the short - circuit detection function was most recently executed. If the method is being executed for the first time and thus there is no angle at which the short - circuit detection function was most recently or last executed, another value can be used instead. This applies to all embodiments described herein.

[0016] In this embodiment, the angle at which the pulse - offset protection function was last executed can be saved, and the next angle at which a new pulse - offset protection is to be executed can be calculated according to the following formula.

[0017] θ next = ± θ last + ω × PS target

[0018] If the next pulse - offset protection is to be performed near the active vector, the value of θ last can be modified such that the next pulse - offset protection is executed at the edge near the active vector.

[0019] The present invention also relates to a driver for controlling an electric motor, the driver including a control unit for generating an output signal for controlling the electric motor and an output unit that can be connected to the electric motor. The driver is arranged to execute the above - described pulse - offset protection method. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Further details and advantages of the present invention are described with reference to the accompanying drawings. The drawings show:

[0021] Figure 1 : the output voltage of each of the active vectors v1 - v6;

[0022] Figure 2 : the preferred angles of the pulse - offset protection relative to the active vectors v1 - v6; and

[0023] Figure 3 : the timer - dependent pulse - offset protection relative to some of the active vectors. DETAILED DESCRIPTION

[0024] Figure 1 The output voltages of each of the active vectors v1 - v6 are shown. The indicated phases v and w of v1, phases u and v of v2, phases u and w of v3, phases v and w of v4, phases u and v of v5, and phases u and w of v6 all have low voltage differences, making it difficult to detect a short circuit between these phases.

[0025] To detect a short circuit between phases, there needs to be a voltage difference between the phases to raise the current to a level sufficient to detect the short circuit. It is not necessary to ensure that the short circuit is detected as soon as possible. Thus, the function of detecting the short circuit can be performed periodically (e.g., in the millisecond range).

[0026] Since this function changes the output voltage requested by the current controller, performing the short - circuit detection degrades the current waveform, which in turn affects the motor performance, motor estimation, and generates unwanted noise. Therefore, the present invention aims to optimize the moment of performing the short - circuit detection function to interfere with the output voltage as little as possible.

[0027] It is aimed to perform PSP (Pulse Shift Protection) when the output voltage is as far as possible from the active vector, because in this way, a significant voltage difference between the phases will naturally occur. Figure 1 It is shown that for each active vector, there are two phases with equal voltage waveforms. For example, in vector v2 (with a reference output voltage angle of 60°), phases u and v are the same, so short - circuit detection is difficult.

[0028] The present invention describes different ways to select the moment when the short - circuit detection function or pulse shift protection can be performed by the motor drive. In different operating situations of the drive and / or the motor, the motor drive can adopt only one of these ways, or combine two or more of these ways.

[0029] One way to select the moment of performing the short - circuit detection function is based on a table (specifically, a look - up table), where the table can be provided in the memory device of the controller.

[0030] According to the frequency at which the pulse shift protection function is to be performed and according to the motor frequency, the optimal angle at which PSP should be performed can be stored in the look - up table.

[0031] Figure 2 An example is shown where the motor runs at a frequency Freq Motor (e.g., 300 RPM or 10 Hz), and the desired pulse shift interval is 4 ms. As a result, PSP needs to be performed every 14.4° of PSangle. The corresponding formula for determining the angle PSangle takes into account the target angle PS target and is expressed as:

[0032] PSangle = 360 × PS target × Freq Motor

[0033] Similar calculations can be performed for multiple frequency ranges. For example, for the frequency range of 10 - 12 Hz, 14.4° can be used; for the frequency range of 12 - 15 Hz, 18° can be used; for the frequency range of 15 - 20 Hz, 24° can be used, etc.

[0034] However, there are two problems with this method: First, since it is a fixed and static method, if the target period for which the PSP is to be executed needs to be changed, the table has to be recalculated and the corresponding code has to be provided. Another problem with this method is that at low motor speeds, a small change in speed will significantly change the angle at which the PSP is executed. This behavior can lead to an overly large size of the lookup table and corresponding drawbacks such as higher requirements for the drive hardware or problems related to excessive and slow control processing within the drive.

[0035] A method similar to the method using a lookup table is based on calculating the parameters required to control the motor rather than retrieving them from a lookup table. The calculations and derivations that would be used to populate the lookup table are performed online (i.e., while the motor is running). This makes it possible to run the motor at very low speeds, but the calculations required to perform this control can be more expensive and more onerous than other alternatives.

[0036] Another method for implementing this pulse - shift protection method is based on a timer and the moment of the most recent or last execution of the pulse - shift protection method. Refer to Figure 3 to describe this method.

[0037] In this article, a timer is set to indicate the moment of executing the PSP function. The timer is reset at each PSP execution. If the timer indicates that a new PSP should be executed near the active vector, the PSP execution is delayed / advanced to a limit value given by:

[0038] Active vector angle ± PS target × 0.5 ×

[0039] This is done by adjusting the value of a counter so as to use the updated timer to execute the PSP at the edge near the active vector. If the moment is too close to the active vector, as shown in the shaded area near the active vector, the timer is reset so that the next PSP occurs at the boundary of this region.

[0040] Another method is based on the target angle and the angle of the most recent or last execution of the pulse shift protection method. This method saves the angle of the last execution of the PSP and calculates the next angle for the execution of the new PSP according to the following formula:

[0041] θ next = ± θ last + ω × PS target

[0042] If it is determined that the next PSP is to be performed near the active vector, then the value of θ last can be modified so that the next PSP is performed at the edge near the active vector.

[0043] The present invention is not limited to a certain embodiment among the above embodiments, but can be modified in various ways.

[0044] All features and advantages resulting from the claims, the description, and the drawings, including structural details, spatial arrangements, and program steps, are essential to the present invention both individually and in the most diverse combinations.

Claims

1. A pulse offset protection method, the pulse offset protection method being used to detect an interphase short circuit in a driver for controlling a motor, wherein, The driver supplies an output voltage to the motor, and wherein the moment for performing the short-circuit detection function is selected to minimize interference with the output voltage of the driver, characterized in that the short-circuit detection function is performed at the moment calculated online, and wherein the moment calculated online for performing the short-circuit detection function is calculated such that the output voltage of the driver is as far as possible from the active vector of the driver.

2. The pulse offset protection method according to claim 1, wherein The short-circuit detection function is performed at a moment determined based on a timer and the moment of the most recent execution of the short-circuit detection function.

3. The pulse offset protection method according to claim 2, wherein Reset the timer each time the short-circuit detection function is performed.

4. The pulse offset protection method according to claim 3, characterized in that Delay or advance the execution of the short-circuit detection function so as to maintain the minimum distance between the execution of the short-circuit detection function and the active vector of the driver.

5. The pulse offset protection method according to any one of the preceding claims, characterized in that The short-circuit detection function is performed at a moment determined based on a target angle and the angle of the most recent execution of the short-circuit detection function.

6. The pulse offset protection method according to claim 5, characterized in that If the short-circuit detection function is performed near the active vector, modify the value of θnext so as to perform the next short-circuit detection function further away from the active vector.

7. A driver for controlling an electric motor, the driver comprising a control section for generating an output signal and an output section capable of being connected to the electric motor, characterized in that, The driver is set to perform the pulse offset protection method according to any one of claims 1 to 6.

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