Three-phase AC motor drive system

Abstract

We will establish a zero-phase correction processing technique that enables the generation of switching signals with arbitrary zero-space vectors. [Solution] In a voltage command value converter 22 that generates a final voltage command value from an initial voltage command value, the zero-phase corrector 22a, which is the main component, is configured using three simple devices: a duty cycle commander 22aa, a general characteristic correction amount calculator 22ab, and a vectorizer 22ac.

Description

Technical Field

[0001] The present invention relates to a technology for generating a three-phase voltage command value useful when driving a three-phase AC motor such as a three-phase synchronous motor or a three-phase induction motor using a power converter (inverter) having a finite bus voltage vdc. In the present invention, the power converter and the inverter are used synonymously. Further, the power converter targeted by the present invention is a power converter that generates a three-phase voltage.

Background Art

[0002] When a three-phase AC motor is energized and driven by a power converter, the main limiting factor for the achievable maximum speed is the bus voltage of the power converter. Fig. 1 schematically shows a three-phase AC motor 1 and a power converter 24 electrically connected thereto. In the figure, the bus voltage vdc of the power converter is schematically shown using a DC power supply symbol. Also, as shown in the figure, the switches of each phase of the u-phase, v-phase, and w-phase are each composed of two upper and lower arms. As a result, there are a total of 3 upper arms and also a total of 3 lower arms.

[0003] Through the switching of the 6 arms, a three-phase voltage is pseudo-generated. The on / off of the two upper and lower arms of each phase is reversely switched in principle, and there are 8 selectable switching patterns. Fig. 2 shows the three-phase voltages generated by the 8 types of switching as 8 basic space vectors vs0' to vs7' on the αβ fixed coordinate system. For the conversion of the three-phase voltage onto the αβ fixed coordinate system, the following phase converter was used (see Non-Patent Document 1).

Equation

[0004] The spatial vector PWM method is a switching signal generation method that offers a high degree of freedom in selecting the zero-space vectors (i.e., the 0th and 7th fundamental space vectors) vs0' and vs7'. However, as a trade-off for this high degree of freedom, the spatial vector PWM method is generally complex.

[0005] The spatial vector PWM method is based on the principle that "when the spatial vector voltage to be generated during the control period Ts is vs', two fundamental spatial vector voltages va' and vb' adjacent to vs' are generated for periods Ta and Tb, respectively, satisfying the following equation."

number

number

number

[0006] As an alternative to the spatial vector PWM method, a switching signal generation method that prioritizes simplicity and reduces complexity is the linear signal comparison PWM method, which generates a switching signal by comparing a voltage command value with a linear carrier (triangular wave, sawtooth wave, etc.). The linear signal comparison PWM method had the problem of "reduced bus voltage utilization," but Yi Jun, Xin Zhong, et al. have achieved a voltage utilization rate equivalent to that of the spatial vector PWM method by limiting the selection of three types of zero space vectors (see Patent Documents 1, 2, and 1).

[0007] The linear-signal comparison PWM method with zero-phase correction processing can be summarized as follows: Zero-phase correction processing When the three-phase signal after positive processing is expressed as vtz*, the zero-phase correction process is described by the following equation (see Non-Patent Document 1).

number

[0008] Regarding the three elements vu*, vv*, and vw* that constitute the initial voltage command value vt* of the three phases, and the three elements vuz*, vvz*, and vwz* that constitute the final voltage command value vtz* of the three phases, the signal definitions are made as follows.

number

[0009] A known first method for determining the zero-phase correction amount is the Yijun method, presented through Patent Document 1. The zero-phase correction amount according to the Yijun method is described as follows (see Non-Patent Document 1).

number

number

[0010] The zero-phase correction amount in equation (7) results in T0=T7=Tc / 2 for the corrected three-phase signal (see Non-Patent Literature 1). On the other hand, the zero-phase correction amount in equation (8a) results in T0=Tc and T7=0 for the corrected three-phase signal, and the zero-phase correction amount in equation (8b) results in T0=0 and T7=Tc for the corrected three-phase signal (see Non-Patent Literature 1). In other words, with the conventional zero-phase correction amount, the only usable zero-space vectors are the three types shown above. When compared with the space vector PWM method, which can use any zero-space vector, it must be said that "the characteristics of the linear-signal comparison PWM method, which has only three applicable zero-space vectors, are extremely limited in the use of zero-space vectors." As a PWM method that further enhances the space vector PWM method, the random space vector PWM method is known. One such method is the random zero-vector distributed space vector PWM method, which allows for the arbitrary and random selection of a combination of two zero-space vectors, vs0' and vs7', in the generation of a PWM switching signal (see Non-Patent Document 2). Conventional linear-signal comparison PWM methods were unable to generate switching signals with arbitrary and random zero-space vectors comparable to those of the random zero-vector distributed space vector PWM method.

[0011] The present invention has been made under the above background, and its object is to establish a zero correction processing technique that enables the generation of switching signals with arbitrary zero space vectors, similar to the space vector PWM method that requires complex calculations, while taking advantage of the simplicity of the linear signal comparison PWM method.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0013]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0014]

Means for Solving the Problems

[0015] To achieve the above objective, the invention of claim 1 includes: an initial voltage command value generation means for generating initial three-phase voltage command values ​​for driving a three-phase AC motor; a voltage command value conversion means for generating a final voltage command value by applying at least zero-phase correction processing to the initial voltage command value; a PWM switching signal generation means for generating a PWM switching signal for a power converter based on a comparison of the final voltage command value and a linear carrier signal; and a power converter that generates a three-phase voltage according to the PWM switching signal and applies the generated three-phase voltage to a three-phase AC motor. A three-phase AC motor drive system having at least the following, where the 0th basic spatial vector voltage corresponding to the state in which all three upper arms of the power converter are turned off is denoted as vs0', the 7th basic spatial vector voltage corresponding to the state in which all three upper arms are turned on is denoted as vs7', the control period is denoted as Ts, the generation period of the 0th basic spatial vector in the control period is denoted as T0, the generation period of the 7th basic spatial vector is denoted as T7, the sum of T0 and T7 is denoted as Tc, and the duty cycles of each generation period are denoted as r0 and r7, respectively, and defined as follows:

number

[0016] The invention of claim 2 is an AC motor drive system according to claim 1, wherein the zero-phase correction process When the three-phase signal after TIFF2026090158000014.tif10164 is represented as vtz*, the phase signals of the u, v, and w phases that constitute the initial voltage command value are represented as vu*, vv*, and vw*, the maximum value of each of the three phase signals is represented as vmax, and the minimum value is represented as vmin, and these can be expressed mathematically as follows,

number

number

number

[0017] The invention of claim 3 is an AC motor drive system according to claim 1 or claim 2, characterized in that the duty cycle, which can take any value, is randomly selected within the range of r7=0 to 1 or r0=0 to 1. [Effects of the Invention]

[0018] The effects of the present invention will now be explained. According to the invention of claim 1, it is possible to add a zero-phase correction process to the voltage command value conversion means that enables the generation of switching signals having arbitrary zero space vectors, similar to the space vector PWM method, while taking advantage of the simplicity of the linear signal comparison PWM method.

[0019] According to the invention of claim 2, it is possible to apply a zero-phase correction process to the voltage command value conversion means, which enables the generation of a switching signal with an arbitrary zero space vector similar to that of the space vector PWM method, while taking advantage of the simplicity of the linear signal comparison PWM method, simply by arbitrarily specifying the duty cycle r7 or r0 in the range of 0 to 1. In other words, it is possible to enhance the effects of the invention of claim 1.

[0020] According to the invention of claim 3, it is possible to add a zero-phase correction process to the voltage command value conversion means that enables the generation of switching signals having arbitrary and random zero-space vectors, similar to the random space vector PWM method, while taking advantage of the simplicity of the linear signal comparison PWM method. In other words, it is possible to enhance the effects of the invention of claim 1 or claim 2. [Brief explanation of the drawing]

[0021] [Figure 1] "A diagram showing the schematic configuration of a three-phase power converter with a busbar voltage vdc connected to a three-phase AC 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 region on a fixed αβ coordinate system." [Figure 3] "A diagram showing the configuration of the AC motor drive system targeted by the present invention." [Figure 4] "A diagram showing one example configuration of a voltage command value converter according to the present invention." [Figure 5] "A diagram showing an example of the response characteristics of the voltage command value converter according to the present invention." [Modes for carrying out the invention]

[0022] Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings. Embodiment Example 1

[0023] Figure 3 shows a schematic configuration of the three-phase AC motor 1, which is the target of the drive, 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 implements the initial voltage command value generation means, and its configuration can be, for example, a configuration that directly generates three-phase voltage command values, or a configuration that constructs a current control system for the AC motor and generates phase voltage command values ​​as its output. The voltage command value converter 22 implements the voltage command value conversion means of the present invention, and the details of this configuration will be described later. The PWM switching signal generator 23 implements the PWM switching signal generation means, and generates a PWM switching signal by comparing the final three-phase voltage command values ​​with linear carriers (triangular wave, sawtooth wave, etc.) in the linear signal comparison PWM method. The PWM switching signal consists of six signals for turning on and off the six arms (see Figure 1) that constitute the power converter 24, and is output to the power converter. The power converter 24 generates a three-phase voltage by switching six arms (see Figure 1) on and off based on six switching signals, and applies the generated three-phase voltage to the AC motor 1 to drive it. As clearly shown in Figure 3, the voltage command value converter 22 and the PWM switching signal generator 23 obtain bus voltage information vdc from the power converter 24 (see Figure 1).

[0024] The present invention relates to a voltage command value converter 22, in particular, among the components of a drive system 2. Figure 4 shows one embodiment of the voltage command value converter 22 based on the inventions of claims 1 and 2. The voltage command value converter 22 in the figure is broadly composed of a zero-phase corrector 22a and a limiter 22b. In the present invention, the zero-phase corrector 22a is essential as a component of the voltage command value converter 22. However, this does not negate the existence of other devices as components of the voltage command value converter 22. To illustrate this fact, in the embodiment example in Figure 4, a limiter with upper and lower limits set to the half-values ​​of the positive and negative bus voltages "±vdc / 2" is shown as a dashed line block to indicate its necessity. 、Since the limiters and other components shown in the dashed block are not the subject of this invention, further explanation will be omitted, and the following will focus on the description of the zero-phase corrector 22a, which is the main focus of this invention.

[0025] The external input signal to the zero-phase corrector 22a is the initial voltage command value vt*. In the example in Figure 4, a three-phase initial voltage command value is assumed. If a two-phase initial voltage command value is received as the input signal, it can be converted to a three-phase initial voltage command value by performing a two-phase to three-phase conversion process. As those skilled in the art will know, the 3x2 matrix for two-phase to three-phase conversion is well known and therefore no further explanation is provided. The zero-phase corrector 22a applies a zero-phase correction process to the initial voltage command value vt* and outputs the three-phase signal after the zero-phase correction process as vtz*.

[0026] The embodiment of the zero-phase corrector 22a shown in Figure 4 is configured based on equations (10) and (11) according to the invention of claim 2. The duty cycle commander 22aa determines the duty cycle r7 of the seventh space vector voltage according to the designer's intent and outputs it to the correction amount calculator 22ab. Equation (11) is incorporated into the correction amount calculator 22ab, and the zero-phase correction amount Δv is determined according to this equation. At this time, the maximum value vmax and minimum value vmin of the elements are determined from the elements of the initial voltage command value vt*. The bus voltage vdc is supplied from the power converter. The determined zero-phase correction amount Δv is output to the vectorizer 22ac. The vectorizer 22ac uses the zero-phase correction amount Δv as the second term on the right-hand side of equation (10a), converts it into a 3 × 1 vector correction amount, and outputs it. The output 3x1 vector correction amount is added to the initial voltage command value vt* according to the right-hand side of equation (10a), and the final voltage command value vtz* is output. The above operation is performed for each control period Ts in which the initial voltage command value vt* is received.

[0027] Experiments were conducted to confirm the intended effects of the present invention based on claims 1 and 2. Several examples of experimental results are shown in Figure 5. The figure shows examples of arbitrarily selectable duty cycles r7, specifically r7 = 0, 0.2, 0.4, 0.6, 0.8, and 1. The meaning of the waveforms is explained using Figure 5(a). The upper three-phase signal shows the initial voltage command values ​​of the u, v, and w phases, which are components of the initial voltage command value vt* (u phase = solid line, v phase = dashed line, w phase = dotted line). In this example, the peak value of the initial voltage command value is assumed to be equal to the half value of the bus voltage vdc / 2. The interrupted single-phase signal is the zero-phase correction amount Δv determined by the correction amount calculator 22ab. The lower three-phase signal shows the final voltage command values ​​of each phase (u-phase = solid line, v-phase = dashed line, w-phase = dotted line), which are components of the final voltage command value vtz* generated by adding the vector correction amounts generated by the vectorizer 22ac (see equation (6d)).

[0028] Figure 5 shows the following: (a) The desired zero-phase correction amount is generated for all specified duty cycles r7. (b) In accordance with the intended zero-phase correction amount, the peak-to-peak value of the final voltage command is without exception reduced to the bus voltage (vdc) or less. (c) In accordance with the intended zero-phase correction amount, and more specifically, in accordance with the magnitude of the duty cycle r7, the maximum and minimum values ​​of the final voltage command value are without exception shifted upward or downward. This characteristic means that "when the final voltage command value is input to a PWM switching signal generator based on the linear signal comparison PWM method, two types of zero-space vectors (the 0th and 7th fundamental space vectors) vs0' and vs7' are generated in accordance with the arbitrarily specified duty cycle." Embodiment Example 2

[0029] Embodiment 1 utilizes equations (10) and (11) in particular from the inventions of claims 1 and 2. Specifically, it utilizes the duty cycle r7 corresponding to the seventh spatial vector. Alternatively, equations (10) and (12) in particular from the inventions of claims 1 and 2 may be used. In other words, the duty cycle r0 corresponding to the zeroth spatial vector may be used. In this case, in the duty cycle commander 22aa in Figure 4, the designer will arbitrarily specify the duty cycle r0. Furthermore, equation (12) will be incorporated into the correction amount calculator 22ab in Figure 4. The zero-phase correction amount Δv generated by the correction amount calculator will be the same according to the relationship presented in equation (4). The experimental results in Figure 5 also show the response when the duty cycle r0 is used (see the respective figure descriptions in Figure 5 for the value of r0). Embodiment 3

[0030] In Embodiment Examples 1 and 2, the selection of the duty cycle in the duty cycle commander 22aa, or the selection rules for this, are assumed to be predetermined by the designer. On the other hand, it is also possible to entrust the selection of the duty cycle in the duty cycle commander 22aa to the duty cycle commander itself. A typical example of this is the random selection of duty cycle r7 or r0. Random automatic selection of duty cycle r7 or r0 can be carried out as follows.

[0031] First, a random number rnd is generated that exhibits a uniform probability density function within the interval 0 to 1. In practice, the random number rnd can be a pseudorandom number, and a known pseudorandom number generator can be used. The number of digits of the random number rnd should be around two decimal places. The generated random number rnd can then be directly selected as the duty cycle r7 or r0, as shown in the following equation.

number

[0032] The random numbers generated randomly by the duty cycle commander itself are treated as duty cycle r7 or r0, and the PWM switching signal generated by comparing these with the final voltage command value and the linear carrier signal becomes a switching signal equivalent to that of the "random zero-vector dispersed space vector PWM method," which is one of the representative random space vector PWM methods. According to the inventions of claims 1 to 3, the same switching signal can be easily generated without using the complicated calculations required for the space vector PWM method. [Industrial applicability]

[0033] This invention is widely suitable for driving three-phase AC motors. [Explanation of Symbols]

[0034] 1 Three-phase AC motor 2 Drive System 21 Initial voltage command value generator 22 Voltage Command Value Converter 22a Zero-phase corrector 22aa Duty Cycle Commander 22ab Correction Amount Calculator 22ac vectorizer 22b Limiter 23 PWM Switching Signal Generator 24 Power Converters

Claims

1. An initial voltage command value generation means for generating three-phase initial voltage command values ​​for driving a three-phase AC motor, A voltage command value conversion means that generates a final voltage command value by applying at least zero-phase correction processing to the initial voltage command value, A PWM switching signal generation means generates a PWM switching signal for a power converter based on a comparison of the final voltage command value and a linear carrier signal, A power converter that generates a three-phase voltage according to a PWM switching signal and applies the generated three-phase voltage to a three-phase AC motor, A three-phase AC motor drive system having at least the following: Let vs0' be the 0th fundamental space vector voltage corresponding to the state in which all three upper arms of the power converter are turned off, and let vs7' be the 7th fundamental space vector voltage corresponding to the state in which all three upper arms are turned on. Let Ts be the control period, and T0 be the period during which the 0th fundamental space vector is generated within the control period. Let T7 be the generation period of the seventh fundamental spatial vector, Tc be the sum of T0 and T7, and let r0 and r7 be the duty cycles of each generation period, respectively. When defined as follows, A three-phase AC motor drive system characterized in that, in the zero-phase correction processing of the voltage command value conversion means, the two duty cycles r0 and r7 can be set to any value within the selection range shown in the above formula for each control cycle.

2. When the three-phase signal after zero-phase correction processing is represented as vtz*, the phase signals of the u-phase, v-phase, and w-phase that constitute the initial voltage command value are represented as vu*, vv*, and vw*, the maximum value of each of the three phase signals is represented as vmax, and the minimum value is represented as vmin, and these are expressed mathematically as follows: Furthermore, when the bus voltage of the power converter is vdc, For each control cycle, According to the following equation, using a duty cycle r7 arbitrarily selected between 0 and 1, Alternatively, according to the following equation using a duty cycle r0 arbitrarily selected between 0 and 1, The three-phase AC motor drive system according to claim 1, characterized in that zero-phase correction processing is performed.

3. The three-phase AC motor drive system according to claim 1 or 2, characterized in that the duty cycle, which can take any value, is randomly selected within the range of r7 = 0 to 1 or r0 = 0 to 1.

Images