Synchronous motor drive system

Abstract

To solve a problem in which, when a three-phase synchronous motor is rotated at high speed with a power converter having a limited bus voltage, an initial voltage command value corresponding to a voltage that the power converter cannot generate may be generated, and such the initial voltage command value must be continuously and effectively converted to a final voltage command value corresponding to the voltage that can be generated by the power converter with a light operation load.SOLUTION: In the present invention, a final voltage command value converter 22 is constituted by a zero phase corrector 22a, an amplifier 22b, and a limiter 22c.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a technology for generating three-phase voltage command values ​​that is useful when a three-phase synchronous motor, such as a three-phase permanent magnet synchronous motor or a three-phase synchronous reluctance motor, is rotated at high speed using a power converter (inverter) with a limited bus voltage. Note that in this invention, the terms power converter and inverter are used synonymously. The power converter that is the subject of this invention is a power converter that generates a three-phase voltage. [Background technology]

[0002] When a three-phase synchronous motor is energized and driven by a power converter, the main limiting factor for the maximum achievable speed is the bus voltage of the power converter. Figure 1 shows a schematic diagram of a three-phase synchronous motor 1 and a power converter 24 electrically connected to it. In the figure, the bus voltage VDC of the power converter is shown schematically using a DC power supply symbol. When the three-phase voltages that can be generated by the power converter are converted into two-phase voltages and expressed as an area on a two-axis orthogonal αβ fixed coordinate system, they form a hexagonal shape, and their maximum value is governed by the bus voltage of the power converter.

[0003] For example, if three-phase voltages are expressed as a 3x1 vector as follows:

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[0004] Figure 2 shows the region of three-phase voltages that can be generated by a power converter with a bus voltage vdc, plotted on an αβ fixed coordinate system after converting the three-phase voltages to two-phase voltages using the simplest three-phase to two-phase converter of equation (2a). The inside of the hexagon in the figure indicates the region of voltages that can be generated by a power converter with a bus voltage vdc. In this example, which uses the three-phase to two-phase converter of equation (2a), the distance from the center of the hexagon (the origin of the αβ fixed coordinate system) to the corner of the hexagon is equal to the bus voltage vdc. In order for the power converter to generate a voltage equivalent to the final voltage command value used to generate the PWM switching signal, the final voltage command value must be located inside the hexagon, including its edges. As is clear from the above explanation, the "hexagon" in the present invention means a "hexagon that indicates a voltage generating region," but hereinafter it will be simply referred to as a hexagon.

[0005] In particular, smooth driving is possible when a synchronous motor is driven by a voltage generated based on a final voltage command value that belongs to the inscribed circle of a hexagon (including the edge of the inscribed circle). The voltage that belongs to the inscribed circle is used when driving at speeds below the rated speed. In this invention, the area inside the inscribed circle (including the edge of the inscribed circle) is called the linear region, and the area outside the inscribed circle (excluding the edge of the inscribed circle) is called the nonlinear region.

[0006] When aiming for high-speed rotation exceeding the rated speed, it often happens that the initially generated initial voltage command value lies outside the inscribed circle or even outside the hexagon. The final voltage command value used to generate the PWM switching signal must lie within the hexagon. In particular, an initial voltage command value outside the hexagon must be converted into a final voltage command value that corresponds to one point on the side of the hexagon (see Figure 2).

[0007] Numerous methods have already been reported for converting an initial voltage command value belonging to a nonlinear region into a single point within a hexagon (see Non-Patent Document 1, Patent Documents 1 and 2). These include the phase invariant method, which ensures phase invariance before and after conversion for an initial voltage command value as a 2 × 1 vector; the minimum norm error method, which minimizes the error (error in norm evaluation) before and after conversion; and the norm invariant method, which ensures norm invariance before and after conversion on the condition that the initial current command value exists within the circumscribed circle of the hexagon (see Non-Patent Document 1). Other methods include a method in which the final voltage command value is determined according to different rules for three regions: within the inscribed circle, between the inscribed circle and the hexagon, and outside the hexagon, and then switched discontinuously (see Patent Document 1), and a method in which processing is completed as a two-phase signal on a two-axis Cartesian coordinate system without any processing as a three-phase signal (Non-Patent Document 1 and Patent Document 2).

[0008] These methods generally have one of the following problems: (a) They are complicated; (b) They cannot be applied when the initial current command value is outside the circumscribing circle of the hexagon; (c) They require discontinuous switching of the final voltage command value depending on whether the initial voltage command value belongs to one of three regions: inside the inscribing circle, between the inscribing circle and the hexagon, or outside the hexagon; and (d) They do not have the characteristic that the final voltage command value converges continuously to a six-step driving pulse signal as the initial voltage command value increases, although this characteristic is desirable. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Jun Ishida: "Drive control device and drive control method for AC motors", Published Patent Application No. 2008-11682 (June 30, 2006) [Patent Document 2] Hiroki Otani: "Rotating Electric Machine Control System", Published Patent Application No. 2012-95485 (2010-10-28) [Non-patent literature]

[0010] [Non-Patent Document 1] X. Guo, M. He, and Y. Yang: “Over modulation strategy of power converters: A review,” IEEE Access, Vol. 2018, pp. 69528-69544 (2018) Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been made in light of the above background, and its purpose is to provide a synchronous motor drive system equipped with a final voltage command value generation function that has the following characteristics: (a) It is simple and easy to implement. (b) It can be applied even when the initial current command value is outside the circumscribing circle of a hexagon. (c) Regardless of whether the initial voltage command value belongs to any of the three regions: inside the inscribing circle, between the inscribing circle and the hexagon, or outside the hexagon, the final voltage command value is continuously generated by a single generation method. (d) As the initial voltage command value increases, the final voltage command value continuously converges to a six-step drive pulse signal. [Means for solving the problem]

[0012] In order to achieve the above object, the invention of claim 1 provides a synchronous motor drive system having at least initial voltage command value generating means for generating an initial voltage command value for driving a three-phase synchronous motor, voltage command value converting means for converting the initial voltage command value to a final voltage command value that can correspond to a voltage that can be generated by a three-phase power converter when the initial voltage command value is excessive, PWM switching signal generating means for generating a PWM switching signal for the three-phase power converter based on the final voltage command value, and a power converter for generating three-phase voltages in accordance with the PWM switching signals and applying the generated three-phase voltages to the three-phase synchronous motor, wherein the voltage command value converting means performs zero-phase correction processing on the initial voltage command value or three-phase signals obtained by processing the initial voltage command value. and limiter means for performing nonlinear limiting processing with a lower limit of "-vdc / 2" and an upper limit of "+vdc / 2" independently on each phase signal (u-phase signal, v-phase signal, w-phase signal) of the three-phase signal generated by performing both the zero-phase correction processing and the amplification processing, where vdc is the bus voltage of the power converter, to generate a final voltage command value.

[0013] The invention of claim 2 is the synchronous motor drive system of claim 1, wherein the three-phase signal to be subjected to zero-phase correction processing is expressed as vt*, and the u-phase, v-phase, and w-phase signals constituting the three-phase signal are respectively expressed as vu*, When expressed as TIFF0007627411000003.tif9166, the following formula is used:

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[0014] The effects of the present invention will now be described. As will be described in detail in the following embodiment, the voltage command value conversion means according to claim 1 of the present invention is composed of only three simple means: zero-phase correction means, amplification means, and limiter means, and is therefore very simple and easy to implement. It can handle any of the three cases where the initial voltage command value falls within the inscribed circle, between the inscribed circle and the hexagon, or outside the hexagon, as will be described in detail in the following embodiment. In this case, there is no need to change the generation rule for the final voltage command value. Since the generation rule is not changed, the final voltage command value also changes continuously for the initial voltage command value whose magnitude changes continuously. As can be seen from the fact that the voltage command value conversion means includes amplification means that multiplies the initial voltage command value by a positive gain exceeding 1, this voltage command value conversion means can be easily applied even when the initial current command value is outside the circumscribed circle of the hexagon. Moreover, as will be described in detail in the following embodiment, the final voltage command value continuously converges to a six-step driving pulse signal as the initial current command value increases. As described above, according to the present invention as defined in claim 1, it is possible to obtain the effect of simultaneously solving many of the problems that conventional voltage command value conversion means have.

[0015] Next, we will explain the effects of the invention of claim 2. Several zero-phase correction methods are known, related to improving the voltage utilization rate of initial voltage command values ​​in the linear domain. The invention of claim 2 is a new extension of the zero-phase correction method developed for initial voltage command values ​​in the linear domain to the nonlinear domain, including outside the inscribed circle and outside the hexagon. This zero-phase correction method has the effect of converging the corrected three-phase signals toward the central zero amplitude point. The limiter means configured with the zero-phase correction means performs nonlinear limiting processing with a lower limit of "-vdc / 2" and an upper limit of "+vdc / 2." The limiter means performs limiting processing symmetrically based on the central zero amplitude point. As is already clear from the above, the zero-phase correction means of the invention of claim 2 has similar characteristics to the limiter means configured simultaneously, and the two means are highly compatible. As a result, the invention of claim 2 achieves the effect of generating a highly symmetric final voltage command value. Ultimately, it also achieves the effect of enhancing the effect of claim 1. [Brief explanation of the drawings]

[0016] [Figure 1] "Diagram showing the schematic configuration of a three-phase power converter with a bus voltage VDC connected to a three-phase synchronous motor" [Figure 2] "A diagram showing the voltages that can be generated by a three-phase power converter with a bus voltage Vdc as a hexagonal area on an αβ fixed coordinate system, along with the inscribed and circumscribed circles." [Figure 3] "A diagram showing the configuration of a synchronous motor drive system to which the present invention is applied" [Figure 4] "A diagram showing one example of the configuration of a voltage command converter according to the present invention" [Figure 5] "Graphs showing three examples of gain characteristics of an amplifier according to the present invention" [Figure 6] "Graph showing the characteristics of the limiter according to the present invention" [Figure 7] "A diagram showing one example of the configuration of a voltage command converter according to the present invention" DETAILED DESCRIPTION OF THE INVENTION

[0017] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0018] FIG. 3 shows a schematic configuration of a three-phase synchronous motor 1 to be driven and its drive system 2. The drive system 2 is broadly composed of an initial voltage command value generator 21, a voltage command value converter 22, a PWM switching signal generator 23, and a power converter 24. The initial voltage command value generator 21 realizes an initial voltage command value generating means, and this configuration may be configured, for example, to directly generate three-phase voltage command values ​​or to construct a current control system for the synchronous motor and generate phase voltage command values ​​as its output. The voltage command value converter 22 realizes a voltage command value converting means of the present invention, and details of this configuration will be described later. The PWM switching signal generator 23 realizes a PWM switching signal generating means, and uses a triangular wave comparison PWM, space vector PWM, or the like to generate six switching signals for turning on and off six inverter elements (see FIG. 1) that constitute the power converter 24 from the three-phase final voltage command values. The power converter 24 turns on and off six inverter elements (see FIG. 1) based on six switching signals to generate a three-phase voltage, and applies the generated three-phase voltage to the synchronous motor 1 to drive it.

[0019] The present invention relates particularly to the voltage command value converter 22 among the components of the drive system 2. An embodiment based on the inventions of claims 1 and 2 is shown in Fig. 4. The voltage command value converter 22 in the figure is composed of, from the left, a zero-phase corrector 22a, an amplifier 22b, and a limiter 22c.

[0020] The input signal to the zero-phase corrector 22a is the initial voltage command value vt*. The example in FIG. 4 assumes a three-phase initial voltage command value. When a two-phase initial voltage command value is received as an input signal, it can be converted into a three-phase initial voltage command value through two-phase to three-phase conversion processing. The two-phase to three-phase conversion processing is performed by multiplying the transpose of the 2×3 matrix (see equation (2)) used in the three-phase to two-phase conversion by a required scalar coefficient. Since the 3×2 matrix for two-phase to three-phase conversion is well known to those skilled in the art, further explanation will be omitted. The zero-phase corrector 22a performs zero-phase correction processing on the initial voltage command value vt* and outputs the three-phase signal after the zero-phase correction processing as vtz*. The zero-phase correction processing can be performed using equation (3) based on the invention of claim 2.

[0021] If the gain of the amplifier 22b is g, the amplifier 22b multiplies the three-phase signal vtz* after the zero-phase correction process, which is the input signal, by the gain g and outputs the result as vtzg*. That is, the amplifier 22b performs the process of the following equation.

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[0022] In equation (4b), rin corresponds to the radius of the inscribed circle of the hexagon in Figure 2. The inscribed circle radius rin corresponding to the three-phase to two-phase transformation in equations (2a), (2b), and (2c) is given by the following equations:

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[0023] Figure 5 shows three examples of the characteristics of the gain g versus the evaluation norm value. In the figure, rcr means the radius of the circumscribing circle of the hexagon (see Figure 2). The circumscribing circle radius rcr corresponding to the three-phase to two-phase transformations in equations (2a), (2b), and (2c) is given by the following equations:

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[0024] FIG. 5(a) shows an example in which a nonlinear monotonically increasing characteristic is adopted as the gain characteristic for an evaluation norm value that exceeds the inscribed circle radius. FIG. 5(b) is a simplified version of FIG. 5(a), showing an example in which a monotonically increasing characteristic expressed by a linear line is adopted as the gain characteristic for an evaluation norm value that exceeds the inscribed circle radius. FIG. 5(c) is a further simplified version of FIG. 5(b), showing an example in which a constant value exceeding 1 is effectively adopted as the gain characteristic for an evaluation norm value that exceeds the inscribed circle radius. The amplifier of the present invention can be given various characteristics other than the three examples above. Although this is a unique example, it is also possible to give a sufficiently large value equivalent to infinity as the gain for an evaluation norm value that is equal to or greater than the circumscribed circle radius.

[0025] As can be clearly seen from Figure 5, the gain can be applied from the case where the evaluation norm value is equal to or less than the radius of the inscribed circle, i.e., when the initial voltage command value belongs to the linear region, to the case where the evaluation norm value exceeds the radius of the inscribed circle and even exceeds the radius of the circumscribed circle, i.e., when the initial voltage command value belongs to the nonlinear region. The gain is continuous with respect to the evaluation norm value, and there is no sudden change in the gain. The example in Figure 5 also illustrates this characteristic of the gain.

[0026] The input signal to limiter 22c is a three-phase signal generated by both zero-phase correction processing and amplification processing. In the embodiment shown in FIG. 4, this three-phase signal is the output signal vtzg* of amplifier 22b. Limiter 22c performs limiter processing independently on each phase signal (u-phase signal, v-phase signal, w-phase signal) of the input three-phase signal vtzg*, and outputs the processed signal as the final voltage command value vt*. If the u-phase signal constituting the input three-phase signal vtzg* is vuzg* and this limiter-processed signal is vu*, the limiter processing in the invention of claim 1 can be strictly expressed by the following equation:

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[0027] A second embodiment of the voltage command value converter 22 based on the inventions of claims 1 and 2 is shown in Fig. 7. The voltage command value converter 22 in Fig. 7 is similar to the first embodiment in Fig. 4 in that it is composed of three devices: a zero-phase corrector 22a, an amplifier 22b, and a limiter 22c. The difference between the two embodiments lies in the order in which the three devices are configured. In the configuration example in Fig. 7, the three devices are configured in the order of amplifier 22b, zero-phase corrector 22a, and limiter 22c.

[0028] The amplifier 22b in this embodiment receives an initial voltage command value vt* as input, multiplies it by a gain g, and outputs the result as vtg*. The gain characteristics at this time are the same as those in the first embodiment described with reference to FIG. 5. The calculation of the norm evaluation value for specifying a specific value of the gain is also the same as that in the first embodiment (see equations (2), (5), and (6)). This gain processing can be rephrased as "amplification processing in which the magnitude of the initial voltage command value before the zero-phase correction processing is evaluated as a vector norm, and the initial voltage command value before the zero-phase correction processing is multiplied by a positive gain exceeding 1 according to the evaluation norm value."

[0029] The initial voltage command value in the example of Figure 7 may be either a two-phase signal or a three-phase signal. Receiving a two-phase initial voltage command value as an input signal is convenient for calculating the evaluation norm value. Two-phase to three-phase conversion processing must be performed immediately before or after gain processing, and the output signal must be a three-phase signal.

[0030] The zero-phase corrector 22a receives the output vtg* from the amplifier 22b as an input, performs zero-phase correction processing, and outputs the processed signal as vtzg*. The zero-phase correction processing in this case can be the same as that in the first embodiment. Specifically, processing can be performed in accordance with the principle shown in equation (3) based on the invention of claim 2.

[0031] The input signal to the limiter 22c is a three-phase signal generated by both zero-phase correction processing and amplification processing. In the embodiment shown in FIG. 7, this is the output signal vtzg* of the zero-phase corrector 22a. The limiter processing in this embodiment is the same as the limiter processing in the first embodiment, so further explanation will be omitted. Embodiment 3

[0032] In the first and second embodiments, the specific method of zero-phase phase correction processing is based on the method of the invention defined in claim 2. When the three-phase signal to be subjected to zero-phase phase correction processing is expressed as in the following equation (8b), and the amplitude V and frequency ω in this equation are known, the amount of correction may be determined as in equation (8c), and the correction processing may be performed as in equation (8a).

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[0033] The present invention is suitable for driving a three-phase synchronous motor that aims for high speed rotation exceeding the rated speed. [Explanation of symbols]

[0034] 1 Three-phase synchronous motor 2. Drive system 21 Initial voltage command generator 22 Voltage command value converter 22a Zero phase corrector 22b Amplifier 22c Limiter 23 PWM switching signal generator 24 Power Converter

Claims

1. an initial voltage command value generating means for generating an initial voltage command value for driving a three-phase synchronous motor; and a voltage command value converting means for converting the initial voltage command value into a final voltage command value included in the range of three-phase voltages that can be generated by a three-phase power converter having a finite bus voltage when the initial voltage command value indicates a value that exceeds the range of three-phase voltages that can be generated by the three-phase power converter. a PWM switching signal generating means for generating a PWM switching signal for the three-phase power converter based on a final voltage command value; a power converter that generates a three-phase voltage in accordance with a PWM switching signal and applies the generated three-phase voltage to a three-phase synchronous motor; A synchronous motor drive system having at least The voltage command value conversion means a zero-phase correction means for performing a zero-phase correction process on an initial voltage command value or a three-phase signal obtained by processing the initial voltage command value; an amplifying means for evaluating a magnitude of the three-phase signal after the zero-phase correction process or the initial voltage command value before the zero-phase correction process as a vector norm, and amplifying the three-phase signal after the zero-phase correction process or the initial voltage command value before the zero-phase correction process, which has an evaluation norm value belonging to a nonlinear region, by a positive gain exceeding 1; limiter means for performing nonlinear limiter processing independently on each phase signal (u-phase signal, v-phase signal, w-phase signal) of a three-phase signal generated by performing both zero-phase correction processing and amplification processing, with a lower limit value of "-vdc / 2" and an upper limit value of "+vdc / 2", when a bus voltage of the power converter is vdc, to generate a final voltage command value; A synchronous motor drive system comprising:

2. The three-phase signal to be subjected to zero-phase correction processing is expressed as vt*, and the u-phase, v-phase, and w-phase that constitute the three-phase signal are When a three-phase signal is expressed as vtz*, the following equation is used:

2. The synchronous motor drive system according to claim 1, wherein said zero-phase correction means is configured according to the above formula or a relationship mathematically equivalent to said formula.

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