Motor control device and electric vehicle

Abstract

The invention provides a motor control device which randomly selects a plurality of carrier frequency candidates to disperse harmonic components, suppresses the heat generation of switching elements of an inverter, and expands the dispersion of the harmonic components to suppress electromagnetic noise. A motor control device for controlling an inverter that supplies AC power to an AC motor, the motor control device being characterized by being provided with: a carrier frequency generation unit that selects each of a plurality of carrier frequency candidates at a predetermined ratio on the basis of a random number and outputs the selected carrier frequency candidates as a carrier frequency; a carrier generation unit for generating a carrier on the basis of the selected carrier frequency; and a PWM controller that outputs a PWM signal based on the carrier to an inverter, the predetermined ratio being determined based on frequencies of the plurality of carrier frequency candidates and a predetermined maximum average switching frequency.

Description

Technical Field

[0001] The present invention relates to a motor control device for suppressing electromagnetic noise and harmonics generated by a motor driving inverter and an electric train equipped with the motor control device. Background Art

[0002] As a prior art for suppressing electromagnetic noise and higher harmonics generated in an inverter for driving a motor by dispersing the carrier frequency, there is known a PWM waveform generating device of Patent Document 1. For example, in the abstract of Patent Document 1, it is recorded as a subject that "a PWM waveform generating device is provided, which can suppress particularly harsh carrier sound (applicant: according to paragraph 0009 of the document, etc., which is synonymous with "electromagnetic noise") in a PWM control inverter device mounted on an air conditioner without extremely increasing the carrier frequency, and can equivalently reduce the noise of the air conditioner."

[0003] In addition, claim 5 of the document states that "the PWM waveform generating device according to claim 2 is characterized in that the second carrier frequency switching unit includes: a random order setting unit, which randomly sets the selection order of multiple carrier frequencies of the carrier frequency setting unit; and a fifth carrier frequency switching unit, which selects and switches the carrier frequency from the multiple carrier frequencies of the carrier frequency setting unit at an appropriate timing according to the random selection order set by the random order setting unit."

[0004] Thus, Patent Document 1 proposes a PWM waveform generation method in which one carrier frequency candidate is selected in sequence according to a selection frequency weighted in a random order at a random timing, thereby dispersing harmonic components and reducing electromagnetic noise.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 9-47026 Summary of the invention

[0008] Problems to be solved by the invention

[0009] The switching elements of the inverter are based on the time average value of the carrier frequency f ave However, Patent Document 1 does not mention controlling the average value f aveTherefore, the result of the carrier frequency dispersion in Patent Document 1 is that from the perspective of suppressing the heat generation of the switching element, it is also considered to be inappropriate motor control. In such a case, the possibility of inverter failure due to excessive heating of the switching element cannot be ruled out.

[0010] In addition, as a method of suppressing the heat generation of the switching element under the condition that there are multiple carrier frequency candidates, a method of uniformly lowering the frequency of each carrier frequency candidate is also considered. Figure 1 Since each carrier frequency candidate is set under the constraints shown, it is difficult to uniformly lower the frequency of each carrier frequency candidate. max The upper limit is determined by the processing performance of the motor control device (especially the built-in microcomputer), and the minimum value of the carrier frequency f min The lower limit is determined by the response speed required by the motor control device, so each carrier frequency candidate needs to be set to the minimum value f min To the maximum value f max Therefore, in order to reduce the average value of the carrier frequency f that affects the heat generation of the switching element, ave , at the minimum value of the carrier frequency f min It is effective to concentrate the carrier frequency candidates near , but in this case, the dispersion of the higher harmonic components becomes insufficient and the electromagnetic noise may increase.

[0011] Therefore, an object of the present invention is to provide a motor control device that randomly selects a plurality of carrier frequency candidates to disperse higher harmonic components, thereby suppressing the heat generation of switching elements of an inverter and expanding the dispersion of higher harmonic components to suppress electromagnetic noise.

[0012] Means for solving problems

[0013] A motor control device controls an inverter that supplies AC power to an AC motor, the motor control device comprising: a carrier frequency generating unit that selects each of a plurality of carrier frequency candidates at a predetermined ratio based on a random number and outputs the selected carrier frequency as a carrier frequency; a carrier generating unit that generates a carrier according to the selected carrier frequency; and a PWM controller that outputs a PWM signal based on the carrier to the inverter, and determines the predetermined ratio based on the frequencies of the plurality of carrier frequency candidates and a predetermined maximum average switching frequency.

[0014] Effects of the Invention

[0015] According to the motor control device of the present invention, it is possible to suppress the heat generation of the switching element of the inverter and to expand the dispersion of the harmonic components to suppress electromagnetic noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a graph illustrating the constraints of the carrier frequency.

[0017] Figure 2 This is a functional block diagram showing the overall configuration of the motor drive system according to the first embodiment.

[0018] Figure 3 This is a functional block diagram showing the structure of the carrier frequency generating unit of the first embodiment.

[0019] Figure 4 This is a structural diagram of the driving system of the electric car of Example 2. DETAILED DESCRIPTION

[0020] Hereinafter, embodiments of the motor drive device according to the present invention will be described with reference to the drawings.

[0021] Example 1

[0022] First, use Figure 2 and Figure 3 A motor control device 1 according to a first embodiment of the present invention will be described.

[0023] Figure 2 1 is a functional block diagram showing the overall structure of the motor drive system 100 of the present embodiment. As shown here, the motor drive system 100 includes a motor control device 1, a motor 2, an inverter 3, a DC power supply 4, a DC voltage detector 5, a phase current detector 6, and a magnetic pole position detector 7. Hereinafter, the structure other than the motor control device 1 in the structure of the motor drive system 100 will be sequentially summarized, and then the motor control device 1 will be described in detail.

[0024] The motor 2 is a permanent magnet synchronous motor (PMSM) driven by AC power. In addition, when an AC machine such as a synchronous reluctance motor, a permanent magnet synchronous generator, a winding type synchronous machine, an induction motor, an induction generator, etc. is used instead of the permanent magnet synchronous motor, the effects of the present invention described below can also be obtained.

[0025] The inverter 3 is a power conversion device that converts DC power into AC power according to a gate signal (PWM signal) from the motor control device 1 and supplies the AC power to the motor 2. The inverter 3 uses a plurality of semiconductor switching elements (IGBT, MOSFET, etc.) to convert DC power into AC power, and at this time, the temperature of each semiconductor switching element rises.

[0026] Although not shown in the figure, each semiconductor switching element is provided with a temperature sensor, and the element temperature detected by each temperature sensor is also input to the motor control device 1 .

[0027] The DC power source 4 is a power source that supplies DC power to the inverter 3. The DC power source 4 may be a battery or a power source that outputs DC power obtained by rectifying and smoothing commercial AC power.

[0028] The DC voltage detector 5 is a sensor that detects the output voltage of the DC power supply 4 and outputs the detected output voltage to the motor control device 1 as DC voltage information Vdc.

[0029] The phase current detector 6 is composed of a Hall CT (Current Transformer) and the like, and is a sensor that detects the three-phase currents Iu, Iv, and Iw of the U phase, V phase, and W phase supplied from the inverter 3 to the motor 2, and outputs them as current waveforms Iuc, Ivc, and Iwc to the motor control device 1.

[0030] The magnetic pole position detector 7 is constituted by a resolver or the like, and is a sensor that detects the magnetic pole position of the motor 2 and outputs the magnetic pole position information θ to the motor control device 1 .

[0031] <Details of Motor Control Device 1>

[0032] like Figure 2 As shown, the motor control device 1 of this embodiment includes a frequency calculation unit 11, a coordinate conversion unit 12, a current control unit 13, a coordinate conversion unit 14, a carrier frequency generation unit 15, a carrier generation unit 16, and a PWM controller 17. The following describes each unit in sequence. In addition, specifically, the motor control device 1 is a computer having hardware such as a CPU and other computing devices, a semiconductor memory and other storage devices, and a communication device. Moreover, the above-mentioned functional units are realized by executing a desired program by the computing device, but the following description will appropriately omit such known technologies.

[0033] The frequency calculation unit 11 calculates and outputs the speed information ω1 based on the magnetic pole position information θ detected by the magnetic pole position detector 7. In addition, the calculation here can use a differential calculation, for example.

[0034] The coordinate conversion unit 12 performs coordinate conversion on the current waveforms Iuc, Ivc, and Iwc detected by the phase current detector 6 using the magnetic pole position information θ detected by the magnetic pole position detector 7 , and outputs dq axis current detection values ​​Idc and Iqc.

[0035] The current control unit 13 controls the dq axis current command value Id input from the host device or the like. * , Iq *The appropriate dq axis voltage command value Vd is calculated and outputted so as to match the dq axis current detection values ​​Idc and Iqc input from the coordinate conversion unit 12. * 、Vq * .

[0036] The coordinate conversion unit 14 uses the magnetic pole position information θ detected by the magnetic pole position detector 7 to convert the dq axis voltage command value Vd input from the current control unit 13. * 、Vq * Perform coordinate transformation and output three-phase voltage command value Vu * 、Vv * 、Vw * .

[0037] The carrier frequency generating unit 15 outputs a carrier frequency fc which is effective in suppressing heat and electromagnetic noise generated by the inverter 3. The details of the carrier frequency fc generated here will be described later.

[0038] The carrier wave generating unit 16 generates a carrier wave such as a triangular wave or a sawtooth wave based on the carrier wave frequency fc outputted from the carrier wave frequency generating unit 15 .

[0039] The PWM controller 17 generates a voltage command value Vu according to the three-phase voltage * 、Vv * 、Vw * The duty ratio signal is calculated based on the DC voltage information Vdc, compared with the carrier, and the gate signal (PWM signal) of each phase is output. Then, the switching element of the inverter 3 is PWM-controlled according to the gate signal (PWM signal), so that the motor 2 is rotated at a desired rotation speed corresponding to the instruction from the host device, etc.

[0040] <Details of Carrier Frequency Generator 15>

[0041] Hereinafter, the details of the carrier frequency generating unit 15 which is the gist of the present invention, and the principle and effects of the present invention will be described.

[0042] Figure 3 This is an example of a functional block of the carrier frequency generator 15 of this embodiment. As shown here, the carrier frequency generator 15 includes a first random number generator 15a, a call cycle determiner 15b, a maximum average switching frequency determiner 15c, a selection ratio determiner 15d, and a carrier frequency determiner 15e. Each unit will be described in turn below.

[0043] The first random number generator 15a generates a random number RN1 which is a natural number. The random number RN1 may be any natural number from 1 to 8, for example, or may be a pseudo-random number generated using a mapping reference or a linear congruential method.

[0044] The call cycle determination unit 15b randomly determines the timing (hereinafter referred to as "call cycle") of calling the carrier frequency determination unit 15e described later based on the random number RN1 generated by the first random number generation unit 15a. The call cycle is, for example, a period (n is a natural number) obtained by multiplying the half period (fc / 2) of the current carrier frequency fc by n. If the random number RN1 generated by the first random number generation unit 15a is 3, 3fc / 2 is determined as the call cycle, and if the random number RN1 is 8, 4fc is determined as the call cycle. In addition, in the carrier frequency determination unit 15e described later, it is also allowed to continuously select the same carrier frequency fc as the previous time, so the carrier frequency fc is not always updated synchronously with the call cycle determined by the call cycle determination unit 15b.

[0045] The maximum average switching frequency determination unit 15c is based on the motor speed ω and the motor current I=√(Id 2 +Iq 2 ), element temperature, etc., and determines the maximum value of the average switching frequency in a manner that can suppress the heat generated by the switching element to a level that does not cause a failure of the inverter 3.

[0046] Here, the maximum average switching frequency f is determined as follows ave_max For example, in the region where the motor speed ω is small and the motor current I is large, the temperature rise of the switching element tends to increase. Therefore, the maximum average switching frequency f ave_max Alternatively, if the temperature of the switching element exceeds a predetermined value, the maximum average switching frequency f ave_max Set lower than normal.

[0047] The selection ratio determination unit 15d is based on the maximum average switching frequency f ave_max To determine the selection ratio of each of the prepared multiple carrier frequencies fc. For example, when two types of the first frequency f1 and the second frequency f2 (where f1>f2) are prepared as candidates for the carrier frequency fc, the selection ratio determination unit 15d limits the selection ratio r1 of the first frequency f1, at which the heat generated by the switching element becomes larger, according to Formula 1. In addition, the effect of limiting the selection ratio r1 of the first frequency f1 according to Formula 1 will be described later.

[0048] [Mathematical formula 1]

[0049]

[0050] The carrier frequency determination unit 15e is called when the call cycle determined by the call cycle determination unit 15b is reached, and selects any one of the prepared multiple carrier frequency candidates within the allowable range of the selection ratio determined by the selection ratio determination unit 15d, and outputs it as the carrier frequency fc. In order to realize this function, the carrier frequency determination unit 15e includes a second random number generation unit 15e1 and a frequency selection unit 15e2.

[0051] The second random number generator 15e1 generates a random number RN2 which is a natural number. The random number RN2 may be, for example, any natural number between 1 and 100, or may be a pseudo-random number generated using a mapping reference or a linear congruential method.

[0052] The frequency selection unit 15e2 selects one of the first frequency f1 or the second frequency f2 as the carrier frequency fc based on the random number RN2 generated by the second random number generation unit 15e1 and the selection ratio r1 determined by the selection ratio determination unit 15d. For example, the operation value obtained by dividing the random number RN2 by 100 is compared with the selection ratio r1. If the operation value is less than the selection ratio r1, the first frequency f1 is selected as the carrier frequency fc. If the operation value is greater than the selection ratio r1, the second frequency f2 is selected as the carrier frequency fc. Since the random number RN2 is a random number, by continuing the carrier frequency selection based on this method, the selection ratio of the first frequency f1 gradually approaches the desired selection ratio r1.

[0053] <Effect of Formula 1>

[0054] The average switching frequency f is explained below using Equation 1. ave is the desired maximum average switching frequency f ave_max The following reasons.

[0055] The time for selecting the carrier frequency is proportional to the inverse of the carrier frequency, so equation 2 holds true.

[0056] [Mathematical formula 2]

[0057]

[0058] When equation 2 is solved for the selection ratio r1, equation 3 is obtained.

[0059] [Mathematical formula 3]

[0060]

[0061] Here, if the average switching frequency f ave is the maximum average switching frequency f ave max The following equation 1 is obtained. Therefore, if the selection ratio r1 of the first frequency f1 is determined as in equation 1, the maximum average switching frequency fave_max the following.

[0062] This can prevent the switching element from generating heat greater than an expected value.

[0063] In addition, when the selection ratio is changed, the carrier frequency to be selected does not change, so the carrier frequency itself selected to suppress heat generation is not changed, and only the selection ratio is changed. As a result, there is no need to narrow the selection range of the frequency, so the degree of reduction in the dispersion effect of higher harmonics is small. Therefore, when the average switching frequency is reduced, the dispersion effect of higher harmonics can be improved compared to the countermeasure of uniformly reducing the first frequency f1 and the second frequency f2.

[0064] In this embodiment, a method of limiting the selection ratio r1 by using equation 1 is described, but equation 4 may be used instead of equation 1.

[0065] [Formula 4]

[0066]

[0067] Formula 4 does not consider that the time of outputting the carrier frequency varies according to the frequency, and assumes that the selected carrier frequency does not depend on the frequency and the duration does not change. Since this method makes the calculation simple, even if the difference between the first frequency f1 and the second frequency f2 is small, the result roughly equivalent to that of Formula 1 can be obtained even if the calculation is performed by Formula 4.

[0068] In this embodiment, an example is shown in which the maximum average switching frequency varies according to the speed, current, and temperature of the semiconductor switching elements of the inverter 3 (see Figure 3 The input signal in the first frequency f1 and the second frequency f2 may be used as input signals), but the worst case may be assumed and the maximum average switching frequency may be set to a fixed value. Alternatively, the selection ratio itself may be calculated based on the maximum average switching frequency fixed to the first frequency f1 and the second frequency f2 and set to a fixed value.

[0069] In addition, the present embodiment shows an example in which the calling cycle is random, but even when the calling cycle changes under a predetermined rule, although higher harmonic components may be generated based on the switching of the carrier frequency according to the rule, the same effect can be obtained.

[0070] As described above, according to the motor control device of this embodiment, it is possible to suppress the heat generation of the switching elements of the inverter and to expand the dispersion of the harmonic components to suppress electromagnetic noise.

[0071] <Modification>

[0072] The above shows the case where there are two candidates for the carrier frequency fc, but even if there are three or four candidates, the heat generation in the inverter 3 can be suppressed by considering the selection ratio. The following describes the method of selecting the frequency ratio by taking the case where there are three candidates for the carrier frequency as an example.

[0073] If the selection ratio of the first frequency f1 as a candidate for the carrier frequency fc is set to r1, the selection ratio of the second frequency f2 (where f1>f2) is set to r2, and the selection ratio of the third frequency f3 (where f2>f3) is set to r3 (where r3=1-r1-r2), then the time at which the carrier frequency fc is selected is proportional to the inverse of the carrier frequency, so Equation 5 holds.

[0074] [Formula 5]

[0075]

[0076] When equation 5 is solved for the frequency ratio r1, equation 6 is obtained.

[0077] [Mathematical formula 6]

[0078]

[0079] Based on the above, the selection ratio determination unit 15d limits the selection ratio r1 of the first frequency f1 according to Expression 7. The relationship between Expression 6 and Expression 7 corresponds to the relationship between Expression 3 and Expression 1 when the candidates for the carrier frequency fc are two values.

[0080] [Formula 7]

[0081]

[0082] Here, the selection ratio r2 of the second frequency f2 in the middle of the three frequency candidates is preferably a smaller value if the effect of variance is taken into consideration, so it is fixed to 0.1, for example, and used for the calculation of Formula 7. Alternatively, the selection ratio r2 may be changed according to the conditions by referring to the measurement results of electromagnetic noise. In short, if the selection ratio r1 is limited by Formula 7, the heat generation can be suppressed even when the frequency candidate is 3 values. In addition, when the frequency candidate is 3 values, Formula 8 may be used instead of Formula 7.

[0083] [Mathematical formula 8]

[0084]

[0085] Formula 8 does not consider that the time of outputting the carrier frequency varies according to the frequency, and assumes that the selected carrier frequency does not depend on the frequency and the duration does not change. Since this method makes the calculation simple, when the difference between f1, f2, and f3 is small, even if the calculation is performed through Formula 8, the result roughly equivalent to Formula 7 can be obtained.

[0086] Example 2

[0087] Next, use Figure 4 Embodiment 2 of the present invention will be described. Note that duplicate descriptions of points common to Embodiment 1 will be omitted.

[0088] Figure 4 The structure of the driving system of the electric vehicle according to the second embodiment of the present invention is shown. As shown here, the electric vehicle of this embodiment includes a transmission 21, a differential gear 22, a drive shaft 23, and wheels 24 in addition to the motor control device 1, the motor 2, the inverter 3, and the DC power supply 4 shown in the first embodiment.

[0089] The electric motor 2 is connected to a transmission 21 . The transmission 21 is connected to a drive shaft 23 via a differential gear 22 , and supplies power to wheels 24 .

[0090] Alternatively, the transmission 21 may be omitted and the differential gear 22 may be directly connected, or the electric motor 2 and the inverter 3 may be applied to the front wheels and the rear wheels, respectively.

[0091] Automobiles have strict requirements on motor noise, and since it is an application where the carrier frequency cannot be set low due to the requirement for response, it can be said that this is an application where the effect of the present invention is more significant than other applications. Similarly, railways have strict requirements on motor noise like automobiles, and this is an application where the effect of the present invention is easily demonstrated.

[0092] By applying the present invention, in automobiles and railways, the heat generation of semiconductor switching elements of inverter 3 can be limited to a predetermined level or less, and the harmonic dispersion effect can be obtained by random PWM, thereby improving the riding comfort of drivers and passengers.

[0093] Explanation of symbols

[0094] 100: Motor drive system,

[0095] 1: Motor control device,

[0096] 11: Frequency calculation unit,

[0097] 12: Coordinate transformation unit,

[0098] 13: Current control unit,

[0099] 14: Coordinate transformation unit,

[0100] 15: Carrier frequency generation unit,

[0101] 15a: a first random number generating unit,

[0102] 15b: Calling cycle determination unit,

[0103] 15c: Maximum average switching frequency determination unit,

[0104] 15d: Selection ratio determination unit,

[0105] 15e: Carrier frequency determination unit,

[0106] 15e1: second random number generating unit,

[0107] 15e2: Frequency selection unit,

[0108] 16: Carrier generation unit,

[0109] 17: PWM controller,

[0110] 2: Electric motor,

[0111] 3: Inverter,

[0112] 4: DC power supply,

[0113] 5: DC voltage detector,

[0114] 6: Phase current detector,

[0115] 7: Magnetic pole position detector,

[0116] 21: Transmission,

[0117] 22: Differential gear,

[0118] 23: Drive shaft,

[0119] 24: Wheel.

Claims

1. A motor control device for controlling an inverter for supplying AC power to an AC motor, characterized in that: The motor control device comprises: a carrier frequency generating unit that selects each of a plurality of carrier frequency candidates at a predetermined ratio based on a random number and outputs the selected carrier frequency candidate as a carrier frequency; A carrier wave generating unit, which generates a carrier wave according to the selected carrier wave frequency; as well as a PWM controller that outputs a PWM signal based on the carrier to an inverter, The predetermined ratio is determined based on the frequencies of the plurality of carrier frequency candidates and a predetermined maximum average switching frequency.

2. The motor control device according to claim 1, characterized in that: The carrier frequency generating unit includes an update cycle determining unit that randomly determines the selected update cycle.

3. The motor control device according to claim 1 or 2, characterized in that: The carrier frequency candidate is binary.

4. The motor control device according to claim 3, characterized in that: The predetermined ratio is calculated by the following formula: Where f1 is the first frequency, f2 is the second frequency smaller than f1, r1 is the selection ratio of the first frequency, and f ave_max is the maximum average switching frequency.

5. The motor control device according to claim 1 or 2, characterized in that: The carrier frequency generating unit includes a maximum average switching frequency determining unit that determines the maximum average switching frequency based on a rotation speed or a current value of the AC motor or a device temperature of the inverter.

6. An electric vehicle equipped with an AC motor, an inverter and a motor control device, characterized in that: The AC motor is an electric motor that drives the wheels via a transmission, a differential gear and a drive shaft. The motor control device is the motor control device according to claim 1 or 2.

Images