JP7627411B2 - Synchronous motor drive system - Google Patents

Description

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 the present invention, the terms power converter and inverter are used interchangeably. The power converter that is the subject of the present invention is a power converter that generates a three-phase voltage.

When a three-phase synchronous motor is energized and driven by a power converter, the main limiting factor of 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 thereto. In the figure, the bus voltage vdc of the power converter is shown using a DC power supply symbol. When the three-phase voltage that can be generated by the power converter is converted into a two-phase voltage and expressed as a region on a two-axis orthogonal αβ fixed coordinate system, it forms a hexagonal shape, and its maximum value is governed by the bus voltage of the power converter.

２×３行列として記述される三相二相変換器を、（１）式の３×１ベクトルの左側から作用させれば、変換後の二相電圧として２×１ベクトルを得ることができる。代表的な三相二相変換器は、次の３種である。

３種の三相二相変換器は、互いに一定係数による比例関係にあり、三相二相変換器により変換生成された二相電圧もこの一定係数による比例関係を維持する。For example, if three-phase voltages are expressed as a 3x1 vector as follows:

If a three-phase to two-phase converter described as a 2 × 3 matrix is applied to the left of the 3 × 1 vector in equation (1), a 2 × 1 vector can be obtained as the two-phase voltage after conversion. There are three typical types of three-phase to two-phase converters:

The three types of three-phase to two-phase converters are in a proportional relationship with each other by a fixed coefficient, and the two-phase voltages converted and generated by the three-phase to two-phase converters also maintain this proportional relationship by the fixed coefficient.

FIG. 2 shows the region of three-phase voltages that can be generated by a power converter having a bus voltage vdc, which is drawn on an αβ fixed coordinate system after converting the three-phase voltages into two-phase voltages using the simplest three-phase to two-phase converter of the formula (2a). The inside of the hexagon in the figure shows the region of voltages that can be generated by a power converter having a bus voltage vdc. In this example using the three-phase to two-phase converter of the formula (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 to make the power converter generate a voltage equivalent to the final voltage command value used to generate a PWM switching signal, the final voltage command value must be inside the hexagon, including its sides.
As is clear from the above explanation, the "hexagon" of the present invention means a "hexagon that indicates a region where voltage can be generated", and will be simply referred to as a hexagon hereinafter.

In particular, 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), smooth driving is possible. The voltage that belongs to the inscribed circle is used when driving at a speed below the rated speed. In the present invention, the area inside the inscribed circle (including the edge of the inscribed circle) is called the linear area, and the area outside the inscribed circle (excluding the edge of the inscribed circle) is called the nonlinear area.

When aiming for high-speed rotation exceeding the rated speed, it often happens that the initially generated initial voltage command value is outside the inscribed circle or even outside the hexagon. The final voltage command value used to generate the PWM switching signal needs to be inside the hexagon. In particular, the initial voltage command value outside the hexagon needs to be converted to a final voltage command value corresponding to one point on the side of the hexagon (see FIG. 2).

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

These methods generally have any 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 continuously converges to a six-step driving pulse signal as the initial voltage command value increases, although this characteristic is desirable.

Jun Ishida: "Drive control device and drive control method for AC motor", published patent application 2008-11682 (June 30, 2006) Hiroki Otani: "Rotary Electric Machine Control System", Published Patent Application, JP2012-95485 (2010-10-28)

X. Guo, M. He, and Y. Yang: “Over modulation strategy of power converters: A review,” IEEE Access, Vol. 2018, pp. 69528-69544 (2018)

The present invention has been made under the above circumstances, and an object of the present invention is to provide a synchronous motor drive system equipped with a final voltage command value generating function having 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) The final voltage command value is continuously generated by a single generation method 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; and (d) As the initial voltage command value increases, the final voltage command value continuously converges to a six-step driving pulse signal.

In order to achieve the above object, the present invention 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 into a final voltage command value corresponding 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 a three-phase signal obtained by processing the initial voltage command value. the magnitude of the three-phase signal after the zero-phase correction processing or the initial voltage command value before the zero-phase correction processing as a vector norm, and amplifying the three-phase signal after the zero-phase correction processing or the initial voltage command value before the zero-phase correction processing by multiplying the three-phase signal after the zero-phase correction processing or the initial voltage command value before the zero-phase correction processing by a positive gain exceeding 1 within at least a certain range of the evaluation norm value in accordance with the evaluation norm value; and limiter means for performing nonlinear limiter processing with a lower limit value of "-vdc/2" and an upper limit value of "+vdc/2" independently on each phase signal (u-phase signal, v-phase signal, w-phase signal) of the three-phase signal generated by applying 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.

と表現するとき、次式

あるいは本式と数学的に等価な関係に従い、該ゼロ相補正手段を構成したことを特徴とする。The invention of claim 2 provides a synchronous motor drive system according to 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:

Alternatively, the zero phase correction means is configured in accordance with a relationship that is mathematically equivalent to this formula.

The effects of the present invention will be described. As will be described in detail in the embodiment example below, the voltage command value conversion means according to the present invention of claim 1 is composed of only three simple means, namely, a zero-phase correction means, an amplification means, and a limiter means, and is very simple and easy to implement. It can be adapted to any of the three areas of the initial voltage command value, that is, inside the inscribed circle, between the inscribed circle and the hexagon, and outside the hexagon, as will be described in detail in the embodiment example below. In this case, it is not necessary to change the generation rule of 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 understood from the fact that the voltage command value conversion means has an amplification means that performs an amplification process by multiplying the initial voltage command value by a positive gain exceeding 1, the voltage command value conversion means can be applied without difficulty even when the initial current command value exists outside the circumscribed circle of the hexagon. Moreover, as will be described in detail in the embodiment example below, a characteristic is obtained in which 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 first aspect of the present invention, it is possible to obtain an effect that many of the problems that the conventional voltage command value conversion means had can be simultaneously solved.

Next, the effect of the invention of claim 2 will be explained. There are several known methods of zero-phase correction in relation to the improvement of the voltage utilization rate of the initial voltage command value belonging to the linear region. The invention of claim 2 is a new extension of the zero-phase correction method developed for the initial voltage command value belonging to the linear region to the nonlinear region including the outside of the inscribed circle and the outside of the hexagon. This zero-phase correction method has the effect of concentrating the corrected three-phase signal to the center amplitude zero point. The limiter means configured together with the zero-phase correction means performs nonlinear limiter processing with a lower limit value of "-vdc/2" and an upper limit value of "+vdc/2". The limiter means performs limiter processing targeting the center amplitude zero point as a reference. As already clear from the above, the zero-phase correction means of the invention of claim 2 has the same characteristics as the limiter means configured simultaneously, and the two means are very compatible with each other. As a result, according to the invention of claim 2, the effect of being able to generate a final voltage command value with high symmetry can be obtained. In addition, the effect of being able to enhance the effect of claim 1 can also be obtained.

"A diagram showing the schematic configuration of a three-phase power converter having a bus voltage VDC connected to a three-phase synchronous motor" "A diagram showing the voltages that can be generated by a three-phase power converter with a bus voltage VDC as a hexagonal region on an αβ fixed coordinate system, along with the inscribed and circumscribed circles." "A diagram showing the configuration of a synchronous motor drive system to which the present invention is applied" "A diagram showing one configuration example of a voltage command converter according to the present invention" "A diagram showing three examples of the gain characteristics of an amplifier according to the present invention" "A diagram showing the characteristics of the limiter according to the present invention" "A diagram showing an example of the configuration of a voltage command converter according to the present invention"

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

Example 1

3 shows a schematic configuration of a three-phase synchronous motor 1 to be driven and a 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 is an implementation of an initial voltage command value generating means, and as a configuration thereof, for example, there is a configuration in which a three-phase voltage command value is directly generated, and there is also a configuration in which a current control system for the synchronous motor is constructed and a phase voltage command value is generated as an output. The voltage command value converter 22 is an implementation of a voltage command value converting means of the present invention, and the details of this configuration will be described later. The PWM switching signal generator 23 is an implementation of a PWM switching signal generating means, and uses a triangular wave comparison PWM, a space vector PWM, or the like to generate six switching signals for turning on and off six inverter elements (see FIG. 1) constituting the power converter 24 from the three-phase final voltage command value. 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.

The present invention relates in particular to the voltage command value converter 22 among the components of the drive system 2. An embodiment based on the invention according to 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.

The input signal to the zero-phase corrector 22a is the initial voltage command value vt*. In the example of FIG. 4, a three-phase initial voltage command value is assumed. When a two-phase initial voltage command value is received as an input signal, it is sufficient to convert it into a three-phase initial voltage command value by performing two-phase to three-phase conversion processing. The two-phase to three-phase conversion processing is a multiplication of a transposed matrix of a 2×3 matrix (see formula (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 is 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*. For the zero-phase correction processing, formula (3) based on the invention of claim 2 may be utilized.

（４）式は、「ゼロ相補正処理後の三相信号あるいはゼロ相補正処理前の初期電圧指令値の大きさをベクトルノルムとして評価し、評価ノルム値に応じ、ゼロ相補正処理後の三相信号に対して、１を超える正のゲインを乗じ増幅処理する」様子を、数式で表記したものとなっている。（４ｂ）式におけるｒｉｎは、図２の六角形内接円の半径に該当する。（４ｂ）式が示すように、評価ノルム値が内接円半径の以下となる場合には、換言するならば初期電圧指令値が線形領域に帰属する場合には、ゲインｇは１となり、増幅器は何らの増幅処理をすることなく、入力信号を無処理のまま出力する。増幅器が所期の働きを行うのは、評価ノルム値が内接円半径を超える場合に、換言するならば初期電圧指令値が非線形領域に帰属する場合に、限られている。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 to output vtzg*. That is, the amplifier 22b performs the process of the following equation.

Equation (4) expresses in mathematical terms the manner in which "the magnitude of the three-phase signal after the zero-phase correction process or the initial voltage command value before the zero-phase correction process is evaluated as a vector norm, and the three-phase signal after the zero-phase correction process is multiplied by a positive gain exceeding 1 according to the evaluation norm value, and is amplified." In equation (4b), rin corresponds to the radius of the inscribed circle of the hexagon in FIG. 2. As shown in equation (4b), when the evaluation norm value is equal to or less than the inscribed circle radius, in other words, when the initial voltage command value belongs to a linear region, the gain g becomes 1, and the amplifier does not perform any amplification process and outputs the input signal without processing it. The amplifier performs the expected function only when the evaluation norm value exceeds the inscribed circle radius, in other words, when the initial voltage command value belongs to a nonlinear region.

上式が明記しているように、六角形内接円の半径ｒｉｎは、母線電圧ｖｄｃが変動する場合には、母線電圧変動に応じ変化することになる。当然のことながら、（４ｂ）式のベクトルノルムは、利用の（２ａ）、（２ｂ）、（２ｃ）式に対応した形で、評価されねばならない。この点に注意すれば、ベクトルノルムは、三相の状態あるいは二相の状態のいずれでも評価可能である。（２）式の三相二相変換を前提とする場合、ゼロ相成分の有無は、評価ノルム値に影響を与えない。（４ｂ）式は、この点を数式で明記している。In equation (4b), r in corresponds to the radius of the inscribed circle of the hexagon in Fig. 2. The inscribed circle radius r in the three-phase to two-phase transformations of equations (2a), (2b), and (2c) are expressed by the following equations, respectively.

As the above formula clearly states, the radius rin of the hexagonal inscribed circle changes in response to the bus voltage fluctuation when the bus voltage vdc fluctuates. Naturally, the vector norm of formula (4b) must be evaluated in a form corresponding to the used formulas (2a), (2b), and (2c). If this point is taken into consideration, the vector norm can be evaluated in either a three-phase state or a two-phase state. When the three-phase to two-phase transformation of formula (2) is assumed, the presence or absence of a zero-phase component does not affect the evaluated norm value. Formula (4b) clearly states this point mathematically.

上式が明記しているように、六角形外接円の半径ｒｃｒは、母線電圧ｖｄｃが変動する場合には、母線電圧変動に応じ変化することになる。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 of equations (2a), (2b), and (2c) is expressed by the following equations.

As the above formula clearly indicates, when the bus voltage vdc fluctuates, the radius rcr of the circumscribing circle of the hexagon changes in response to the bus voltage fluctuation.

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

As can be clearly seen from Fig. 5, the gain is applicable from the case where the evaluation norm value is equal to or smaller than the radius of the inscribed circle, i.e., 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., 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 jump change in the gain. The example of Fig. 5 also illustrates this characteristic of the gain.

（７）式のリミッタ特性は、図６のように描画することもできる。（７）式および図６のｖｄｃは、電力変換器の母線電圧である（図１参照）。ｖ相信号、ｗ相信号に対しても、同様のリミッタ処理が独立に実施される。The input signal to the limiter 22c is a three-phase signal generated by performing 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 the amplifier 22b. The 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 v-t*. If the u-phase signal constituting the input three-phase signal vtzg* is vuzg* and this limiter-processed signal is v-u*, the limiter processing in the invention of claim 1 is strictly expressed by the following equation.

The limiter characteristic of equation (7) can also be plotted as shown in Fig. 6. In equation (7) and Fig. 6, vdc is the bus voltage of the power converter (see Fig. 1). Similar limiter processing is performed independently for the v-phase signal and the w-phase signal.

Example 2

A second embodiment of the voltage command value converter 22 based on the invention 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 is 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 the amplifier 22b, the zero-phase corrector 22a, and the limiter 22c.

The amplifier 22b in this embodiment receives an initial voltage command value vt* as an 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 process can be rephrased as "an amplification process in which the magnitude of the initial voltage command value before the zero-phase correction process is evaluated as a vector norm, and the initial voltage command value before the zero-phase correction process is multiplied by a positive gain exceeding 1 according to the evaluation norm value."

The initial voltage command value in the example of Fig. 7 may be either a two-phase signal or a three-phase signal. When a two-phase initial voltage command value is received as an input signal, it is convenient for calculating the evaluation norm value. It is necessary to perform two-phase to three-phase conversion processing immediately before or after gain processing, and to make the output signal a three-phase signal.

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, the processing can be performed according to the principle shown in formula (3) based on the invention of claim 2.

The input signal to the limiter 22c is a three-phase signal generated by performing both the zero-phase correction process and the amplification process. In the embodiment of Fig. 7, it is the output signal vtzg* of the zero-phase corrector 22a. The limiter process in this embodiment is the same as the limiter process in the first embodiment, so further explanation is omitted.

Example 3

なお、請求項１の発明は、上記以外のゼロ相補正処理の使用を妨げるものではないことを指摘しておく。In the first and second embodiments, the specific method of the zero-phase correction process uses the method according to the invention of claim 2. When the three-phase signal to be subjected to the zero-phase correction process is expressed as in the following formula (8b) and the amplitude V and frequency ω in the formula are known, the amount of correction may be determined as in formula (8c) and the correction process may be performed as in formula (8a).

It should be noted that the invention of claim 1 does not preclude the use of zero-phase correction processes other than those described above.

The present invention is suitable for driving a three-phase synchronous motor that is intended to rotate at high speeds exceeding the rated speed.

REFERENCE SIGNS LIST 1 Three-phase synchronous motor 2 Drive system 21 Initial voltage command value generator 22 Voltage command value converter 22a Zero-phase corrector 22b Amplifier 22c Limiter 23 PWM switching signal generator 24 Power converter

Claims (2)

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: 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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