Control device of a rotating machine

Abstract

A control device (1) of a rotating machine includes a voltage application unit (3) that generates three-phase voltages to be applied to a rotating machine (2); and a control unit (4) that controls a voltage generation operation of the voltage application unit (3) in a first pulse width modulation mode or a second pulse width modulation mode, wherein the first pulse width modulation mode is a pulse width modulation method in which a carrier wave frequency is asynchronous with a frequency of a voltage command, wherein the second pulse width modulation mode is a pulse width modulation method in which a carrier wave frequency is synchronous with the frequency of the voltage command.Based on a first carrier wave used in generating a signal that controls the voltage application unit in the first pulse width modulation mode, a second carrier wave used in generating a signal that controls the voltage application unit in the second pulse width modulation mode, and an output voltage phase command that commands a phase of each of the voltages to be output to the rotating machine, the control unit (4) selects one of the first pulse width modulation mode and the second pulse width modulation mode as a pulse width modulation method to be used for controlling the voltage generation operation.

Description

Area

[0001] The present disclosure relates to a rotating machine control device that controls a rotating machine. General state of the art

[0002] To operate an AC motor, which is a type of rotating machine (hereinafter referred to as the rotating machine), at variable speeds, the power supplied to the rotating machine must be converted into a desired voltage and frequency. An inverter device is used for power conversion. A typical inverter device consists of a main circuit that uses semiconductor switching elements and a control device that controls the semiconductor switching elements. The inverter device achieves the desired frequency and voltage by on-off control of the semiconductor switching elements. Pulse-width modulation (PWM) control is often used as a method for switching the semiconductor switching elements.

[0003] Pulses used in PWM control are generated by comparing a voltage command to be applied to the rotating machine (hereinafter referred to as the voltage command) with a carrier wave used for pulse generation. The carrier wave to be used is, for example, a triangular wave. As the carrier wave frequency increases, output pulses contain fewer harmonics, resulting in reduced harmonic losses when applied to the rotating machine.

[0004] However, as the carrier wave frequency increases, the semiconductor switching elements are switched more frequently, resulting in heat generation associated with increased switching losses. Therefore, an upper limit for the carrier wave frequency is determined from the perspective of thermal design.

[0005] If the carrier wave frequency is fixed regardless of the rotating machine speed, the switching frequency increases as the rotating machine speed increases, resulting in unacceptable heat generation. Accordingly, control is performed such that the carrier wave frequency is fixed when the rotating machine speed is lower and is changed synchronously with the voltage command frequency when the rotating machine speed is higher. A PWM method in which a carrier wave frequency is not synchronized with the voltage command frequency is called an asynchronous PWM mode, while a PWM method in which a carrier wave frequency is synchronized with the voltage command frequency is called a synchronous PWM mode (the asynchronous PWM mode and the synchronous PWM mode may be simply referred to as asynchronous PWM and synchronous PWM hereinafter).For synchronous PWM, there is a method that adopts multiple carrier wave frequencies to change a number of pulses included in one cycle of the voltage command.

[0006] Switching between PWM methods (referred to as PWM modes in this document) without any consideration causes oscillations in the current flowing through the rotating machine (referred to as current oscillations in this document). When current oscillations occur, the current flowing through the rotating machine, i.e., the machine current, may deviate from the allowable current of each semiconductor switching element, potentially causing breakage of the switching elements. Furthermore, depending on the frequency of the current oscillations, there is a possibility of violating current harmonic regulations, in which case the installation of an additional filter circuit may be required. Furthermore, mechanical vibrations and noise in the rotating machine can become problematic if the rotating machine's torque oscillates proportionally to current oscillations.

[0007] Various measures have been taken to address such current oscillations occurring during switching between PWM modes. For example, Patent Literature 1 discloses a technique for switching between a variable voltage operation method using pulse width modulation and a single-pulse control method near a phase angle where the centers of primary magnetic flux trajectories deviate the least in a stationary reference frame of the rotating machine. List of citationsPatent literature

[0008] Patent Literature 1: Japanese Patent No. 2911734 Brief description of the inventionProblem to be solved by the invention

[0009] However, the technique described in Patent Literature 1, which causes switching between PWM modes in a predetermined phase, has a problem in that the technique cannot be applied to switching between the asynchronous PWM that operates without synchronization with the voltage phase and the synchronous PWM that operates in synchronization with the voltage phase.

[0010] The present disclosure has been made in view of the foregoing, and an object of the present disclosure is to obtain a control device of a rotating machine capable of limiting current oscillations when the PWM mode used to control the generation operation of voltage to be applied to a rotating machine is switched between the asynchronous PWM and the synchronous PWM. Ways to solve the problem

[0011] In order to solve the above-described problem and achieve the object, a control device of a rotating machine according to the present disclosure includes: a voltage application unit for generating three-phase voltages to be applied to a rotating machine; and a control unit for controlling a voltage generation operation of the voltage application unit in a first pulse width modulation mode or a second pulse width modulation mode, wherein the first pulse width modulation mode is a pulse width modulation method in which a carrier wave frequency is asynchronous with a frequency of a voltage command, wherein the second pulse width modulation mode is a pulse width modulation method in which a carrier wave frequency is synchronous with a frequency of a voltage command.Based on a first carrier wave used in generating a signal that controls the voltage application unit in the first pulse width modulation mode, a second carrier wave used in generating a signal that controls the voltage application unit in the second pulse width modulation mode, and an output voltage phase command that commands a phase of each of the voltages to be output to the rotating machine, the control unit selects one of the first pulse width modulation mode and the second pulse width modulation mode as a pulse width modulation method to be used for controlling the voltage generation operation. Effect of the invention

[0012] The rotating machine control device according to the present disclosure has the effect of limiting current oscillations when the PWM mode used to control the generation operation of the voltage to be applied to the rotating machine is switched between the asynchronous PWM and the synchronous PWM. Short description of the drawings Fig. 1 is a diagram illustrating an exemplary configuration of a control device of a rotating machine according to a first embodiment. Fig. 2 is a diagram illustrating an exemplary configuration of a timer generator included in the rotating machine control device according to the first embodiment. Fig. 3 is a diagram illustrating an exemplary configuration of a voltage application unit included in the rotating machine control device according to the first embodiment. Fig. 4 is a diagram illustrating an example of a storage unit that stores comparison values used by the timer generator according to the first embodiment in a process of generating a timer signal. Fig. 5 is a diagram illustrating another example of the storage unit that stores the comparison values used by the timer generator according to the first embodiment in the process of generating the timer signal. Fig. 6 is a diagram illustrating an exemplary configuration of a timer generator included in a control device of a rotating machine according to a second embodiment. Fig. 7 is a diagram illustrating an example of a storage unit that stores comparison values and a delayed phase that the timer generator according to the second embodiment uses in a process of generating a timer signal. Fig. 8 is a diagram illustrating another example of the storage unit that stores the comparison values and the delayed phase that the timer generator according to the second embodiment uses in the process of generating the timer signal. Fig. 9 is a diagram showing a variation of the Fig. 7 illustrated storage unit. Fig. 10 is a diagram showing a variation of the Fig. 8 illustrated storage unit. Fig. Figure 11 is a diagram illustrating a first example of current oscillations occurring during switching between PWM modes. Fig. Figure 12 is a diagram illustrating a second example of current oscillations occurring during switching between PWM modes. Fig. 13 is a diagram illustrating examples of carrier waves each used in two synchronous PWM modes between which switching is performed. Fig. Figure 14 is a diagram illustrating a magnetic flux evaluation function generated by synchronous carrier waves #1 and #2 generated in Fig. 13 are illustrated. Fig. 15 is a diagram illustrating examples of carrier waves used in two PWM modes, respectively, when switching from an asynchronous one of the PWM modes to a synchronous one is performed. Fig. Figure 16 is a diagram illustrating a magnetic flux evaluation function generated by the asynchronous and synchronous carrier waves generated in Fig. 15 are illustrated. Description of embodiments

[0013] With reference to the drawings, a detailed description of the control devices of a rotating machine according to embodiments of the present disclosure is provided hereinafter in this specification. First embodiment.

[0014] Before explaining details of a control device of a rotating machine according to the present embodiment, a description will first be provided of current oscillations that become problematic during switching between PWM modes.

[0015] Fig. 11 is a diagram illustrating a first example of current oscillations occurring during switching between PWM modes, particularly the example of current oscillations occurring when a conventional rotating machine control device, which is a comparative example, switches between the PWM modes. Fig. Figure 11 illustrates currents expressed in a rotating reference frame (by dq transformation) based on a magnetic pole position of a rotating machine after a three-phase to two-phase transformation of three-phase alternating currents of the rotating machine. The current oscillations that occur during switching between PWM modes can be extracted by passing the d-axis and q-axis machine currents through a bandpass filter (BPF) centered around a voltage command frequency. A first row from the top in Fig. Figure 11 illustrates the d-axis current, namely the d-axis machine current, and a second row illustrates oscillations of the d-axis current (the d-axis current after passing through the BPF). A third row illustrates the q-axis current, namely the q-axis machine current, and a fourth row illustrates oscillations of the q-axis current (the q-axis current after passing through the BPF). A dotted vertical center line indicates a time of switching between PWM modes.

[0016] A description is provided of a factor that may contribute to the occurrence of the Fig. 11. If the rotating machine to be controlled is an interior permanent magnet synchronous motor (IPMSM), voltage equations in the rotating reference frame are represented by formula (1). Formula 1: {vd=Rid(t)+dφddt−ωφqvq=Riq(t)+dφqdt+ωφd [φd=φm+Ldid(t)φq=Lqiq(t)]

[0017] In formula (1) v d and v q voltages applied to the d-axis and q-axis of the IPMSM, respectively, and i d and i q represent currents flowing along the d-axis and q-axis of the IPMSM, respectively. L d and L q represent the inductance of the d-axis and the q-axis of the IPMSM and φ d and φ q represent the magnetic flux of the d-axis and q-axis of the IPMSM, respectively. φm represents the magnetic flux, R represents the winding resistance, and ω represents the angular frequency of a fundamental voltage applied to the IPMSM. d / dt represents a differentiation operation. i d and i q are time functions. Time is represented by t.

[0018] Formula (1) is assumed to represent the voltage equations in a transient state immediately after switching between PWM modes, while formula (2) below represents the voltage equations in a steady state. Voltage equations for differences are represented by formula (3) below. Formula 2: {vd=Rid'(t)+dφd'dt−ωφq'vq=Riq'(t)+dφq'dt+ωφd' [φd'=φm+Ldid'(t)φq'=Lqiq'(t)] Formula 3: {0=RΔid(t)+dΔφddt−ωΔφq0=RΔiq(t)+dΔφqdt+ωΔφq [Δφd=φd−φd'Δφq=φq−φq']

[0019] In formulas (2) and (3), the currents of the d-axis and q-axis in the steady state are given by i d ' and i q ' and the magnetic fluxes of the d-axis and q-axis in the stationary state are given by φ d ' and φ q'. In formula (3), each term expressing a difference between formula (1) and formula (2) is denoted by Δ, where the differences of the currents of the d-axis and q-axis are denoted by Δi d and Δi q and the differences of the magnetic fluxes of the d-axis and q-axis are given by Δφ d and Δφ q It is assumed that the voltages applied to the IPMSM remain unchanged between the transient state and the steady state; therefore, the difference of each voltage between formulas (1) and (2) is 0. i d ' and i q ' in formula (2) and Δi d and Δi q in formula (3) are also time functions.

[0020] Using the Laplace transform to solve formula (3) for the currents as time functions, formula (4) can be derived. In formula (4), e is Napier's constant, which is used to represent an exponential function. Formula 4: Δid(t)=e−R(Ld+Lq)2LdLqt⋅1LdΔφd2+Δφq2⋅sin(ωt+θ)Δiq(t)= e−R(Ld+Lq)2LdLqt⋅1LqΔφd2+Δφq2⋅cos(ωt+θ)θ=tan−1(ΔφdΔφq) Δφd=φd−φd' Δφq=φq−φq'

[0021] According to formula (4), the currents Δi d and Δi q during switching between the PWM modes sine and cosine waves proportional to the differences in the magnetic fluxes of the motor, Δφ d and Δφ q , along the axes before and after switching. In combination with exponential terms, the currents Δi d and Δi qto damped oscillations. Furthermore, the d-axis and q-axis currents are inversely proportional to the d-axis and q-axis inductances of the motor L d and L q Among the variables included in formula (4), only the differences in the magnetic fluxes of the motor, Δφ d and Δφ q , can be manipulated by a controller without modifying the motor. Therefore, current oscillations can be limited when switching between PWM modes to compensate for the differences Δφ d and Δφ q of the motor's magnetic fluxes. The frequency of the current oscillations is the angular frequency ω of an inverter and the phase of the current oscillations is determined by performing an arctangent operation on the differences Δφ d and Δφ q the magnetic fluxes of the motor.

[0022] This article describes a method for calculating motor fluxes. The flux linkages (motor fluxes) φ u , φ v and φ w of the u-, v- and w-phases can be calculated from the phase voltages v u , v v and v w of the three phases, the phase currents i u , i v and i w of the three phases and the winding resistance R. Equations for calculating the motor fluxes are represented by formula (5). Formula 5: φu=∫vu−Riudtφv=∫vv−Rivdtφw=∫vw−Riwdt

[0023] If the speed of the rotating machine is greater than or equal to an average speed, the second term on each right-hand side of formula (5) is smaller than the first term on each right-hand side and can therefore be ignored. Therefore, the calculation of motor fluxes only needs to use integrals of the phase voltages. Since voltages applied from the inverter to the motor are each the product of a corresponding PWM pulse applied to a gate of a semiconductor switching element in the inverter and half the supply voltage, the integral of the voltage for each phase of the motor and an integral of the corresponding PWM pulses applied to the gate have similar waveforms. Therefore, quantities equivalent to the motor fluxes can be calculated from the PWM pulses applied to the inverter.

[0024] To express the motor fluxes in the rotating reference frame, a three-phase to two-phase transformation is performed, which is shown in formula (6) below. Furthermore, a transformation of the rotating reference frame based on the magnetic pole position θ m of the engine as shown in formula (7). Formula 6: [φαφβ]=23[1−12−12032−32][φuφvφw] Formula 7: [φαφβ]=[cosθmsinθm−sinθmcosθm][φαφβ]

[0025] According to the above formula (4), reducing the differences Δφ d and Δφ q of the motor's magnetic fluxes before and after switching between PWM modes limit the current oscillations during switching between PWM modes. The term for the differences in the motor's magnetic fluxes in formula (4) is defined as a weighting function of the magnetic flux E f defined as shown in formula (8) below. Formula 8: Ef=Δφd2+Δφq2

[0026] Fig. Figure 12 illustrates motor currents during switching between PWM modes when the magnetic flux evaluation function E f is reduced. Fig. Figure 12 is a diagram illustrating the second example of current oscillations during switching between PWM modes. As shown in Fig. Figure 11 shows a first row from the top illustrating the d-axis current, a second row illustrating oscillations of the d-axis current (the d-axis current after passing the BPF), a third row illustrating the q-axis current, and a fourth row illustrating oscillations of the q-axis current (the q-axis current after passing the BPF). A dotted vertical center line indicates a time of switching between the PWM modes. The Fig. The current oscillations illustrated in Figure 12 correspond to an example of current oscillations resulting from the application of the first embodiment. As shown in Fig. 12, reducing the evaluation function of the magnetic flux E f , which is defined by formula (8), current oscillations during switching between PWM modes compared to the Fig. 11 illustrated case.

[0027] Next, a description of properties of a magnetic flux evaluation function associated with switching between synchronous PWM modes and a magnetic flux evaluation function associated with switching from an asynchronous PWM mode to a synchronous PWM mode is provided.

[0028] Fig. Figure 13 is a diagram illustrating examples of carrier waves used in each of the two synchronous PWM modes between which switching is performed. The carrier waves are referred to as synchronous carrier waves #1 and #2. Fig. 14 is a representation showing the Fig. 13 illustrated evaluation function of the magnetic flux E fss generated by the synchronous carrier waves #1 and #2.

[0029] In synchronous PWM, a carrier wave is synchronized with a phase of the u-phase voltage (hereinafter referred to simply as the voltage phase); therefore, the voltage applied to the IPMSM is synchronized with the voltage phase, and the motor flux, expressed by the integral of the voltage applied to the IPMSM, is also synchronized with the voltage phase. Since the motor flux is synchronized with the voltage phase before and after switching between PWM modes, the evaluation function of the magnetic flux E is fss consequently synchronized with the voltage phase, as in Fig. 14. The evaluation function of the magnetic flux E fss , which is associated with switching between the synchronous PWM modes, each of which has the Fig. 13, has a waveform that repeats every 60 degrees, as shown in Fig. 14. Therefore, to switch between the synchronous PWM, a phase in which the evaluation function of the magnetic flux E fss is minimized, can be easily pre-calculated from a relationship between the respective carrier waves of the synchronous PWM.

[0030] Fig. Figure 15 is a diagram illustrating examples of carrier waves used in the two PWM modes (asynchronous PWM and synchronous PWM) when switching from asynchronous PWM to synchronous PWM. The carrier wave used in asynchronous PWM refers to an asynchronous carrier wave, and the carrier wave used in synchronous PWM refers to a synchronous carrier wave. Fig. 16 is a diagram showing the evaluation function of the magnetic flux E fas generated by the asynchronous and synchronous carrier wave, which in Fig. 15 are illustrated.

[0031] In an asynchronous PWM, a carrier wave (which corresponds to the Fig. 15) is not synchronized with the voltage phase; therefore, the voltage applied to the IPMSM is not synchronized with the voltage phase, and the motor flux, which is expressed by the integral of the voltage applied to the IPMSM, is also not synchronized with the voltage phase. Therefore, the evaluation function of the magnetic flux E fasnot synchronized with the voltage phase when calculated based on the motor flux obtained when the IPMSM is controlled in synchronous PWM and the motor flux obtained when the IPMSM is controlled in asynchronous PWM. Furthermore, no waveform repeating every 60 degrees, as observed when switching between synchronous PWM modes, is observed. Since the carrier wave of the asynchronous PWM is not synchronized with the voltage phase, the magnetic flux evaluation function E changes. fas its shape over a cycle of the voltage phase depends on a phase of the carrier wave of the asynchronous PWM. Therefore, to switch from the asynchronous PWM mode to the synchronous PWM mode, it is necessary to identify a phase at which the magnetic flux evaluation function E fasis minimized. Since a difference in magnetic flux remains the same even when switching from the synchronous PWM mode to the asynchronous PWM mode, identifying a phase at which the magnetic flux evaluation function is minimized is not possible. In other words, for switching between the asynchronous PWM and the synchronous PWM, identifying the phase at which the magnetic flux evaluation function is minimized is not possible.

[0032] Next, a description will be provided of the control device of a rotating machine according to the first embodiment. Fig. 1 is a diagram illustrating an exemplary configuration of the rotating machine control device 1 according to the first embodiment.

[0033] The control device 1 of a rotating machine includes a voltage application unit 3 and a control unit 4. The voltage application unit 3 is connected to a rotating machine 2 and generates three-phase voltages V u , V v and V w to be applied to the rotating machine 2. The control unit 4 is connected to the voltage application unit 3 and generates PWM pulses V ug , V vg and V wg as PWM signals to control the voltage generation operation of the voltage application unit 3 in a first PWM mode or a second PWM mode. In the present embodiment, the first PWM mode is described as an asynchronous PWM, and the second PWM mode is described as a synchronous PWM.

[0034] The control unit 4 includes a timing generator 5, a PWM mode selector 6, a modulation wave generator 7, a carrier wave selector 8 and a PWM pulse generator 9.

[0035] First carrier waves cr u1 , cr v1 and cr w1 , second carrier waves cr u2 , cr v2 and cr w2 , and an output voltage phase command θ are input to the timer generator 5. The output voltage phase command θ outputs a command value for one phase of each of the three-phase voltages V u , V v and V w to be output from the voltage application unit 3 to the rotating machine 2. The timer generator 5 determines, based on the first carrier wave cr u1 , cr v1 or cr w1 , the second carrier wave cr u2 , cr v2 or cr w2and the output voltage phase command θ, whether or not a timing is appropriate for switching between the PWM modes. After determining that the timing is appropriate for switching between the PWM modes, the timer generator 5 generates a timer signal Tr indicating that the timing is appropriate for switching between the PWM modes.

[0036] A fundamental frequency F INV the voltage output from the voltage application unit 3, the voltage commands V u *, V v * and V w * used to control the rotating machine 2 and the timer signal Tr output from the timer generator 5 are input to the PWM mode selector 6. The PWM mode selector 6 generates a PWM mode selection signal P Modus based on the fundamental frequency F INV , the voltage commands V u *, V v * and V w * and the timer signal Tr.

[0037] The voltage commands V u *, V v * and V w *, the output voltage phase command θ and the PWM mode selection signal P Modus are input to the modulation wave generator 7. The modulation wave generator 7 generates modulation waves v u *, v v * and v w * based on the voltage commands V u *, V v * and V w *, the output voltage phase command θ and the PWM mode selection signal P Modus .

[0038] The first carrier waves cr u1 , cr v1 and cr w1 , the second carrier waves cr u2 , cr v2 and cr w2 and the PWM mode selection signal P Modus are input to the carrier wave selector 8. Based on the PWM mode selection signal P Modus the carrier wave selector 8 selects the first carrier waves cr u1 , cr v1 and cr w1 or the second carrier waves cr u2 , cr v2and cr w2 to be used as the carrier waves cr u , cr v and cr w to be issued.

[0039] The modulation waves v u *, v v * and v w * and the carrier waves cr u , cr v and cr w are input into the PWM pulse generator 9. Based on the modulation waves v u *, v v * and v w * and the carrier waves cr u , cr v and cr w the PWM pulse generator 9 generates the PWM pulses V ug , V vg and V wg which serve as the PWM signals for controlling the voltage application unit 3. In the following description, PWM pulses generated by the PWM pulse generator 9 when operating in the asynchronous PWM may be referred to as the asynchronous PWM pulses, and PWM pulses generated by the PWM pulse generator 9 when operating in the synchronous PWM may be referred to as the synchronous PWM pulses.

[0040] The PWM Pulse V ug , V vg and V wg generated by the PWM pulse generator 9 are input to the voltage application unit 3. Based on the PWM pulses V ug , V vg and V wg the voltage application unit 3 generates the three-phase voltages V u , V v and V w which are to be applied to the rotating machine 2.

[0041] The rotating machine 2 is driven by the three-phase voltages V u , V v and V w driven by the voltage output from the voltage application unit 3. The rotating machine 2 may be the aforementioned IPMSM, an induction motor (IM), or a synchronous reluctance motor (SynRM).

[0042] The first carrier waves cr u1 , cr v1 and cr w1input to the timing generator 5 and the carrier wave selector 8 are the carrier waves corresponding to the first PWM mode and are asynchronous carrier waves that are not synchronized with the output voltage phase command θ. The second carrier waves cr u2 , cr v2 and cr w2 are the carrier waves corresponding to the second PWM mode and are synchronous carrier waves synchronized with the output voltage phase command θ. The first carrier waves cr u1 , cr v1 and cr w1 can be carrier waves that are in phase or carrier waves that are out of phase among the three phases. Likewise, the second carrier waves can be u2 , cr v2 and cr w2 Carrier waves can be in-phase or carrier waves that are out of phase among the three phases. The first carrier waves cr u1 , cr v1 and cr w1 and the second carrier waves cru2 , cr v2 and cr w2 are unitless signals and their respective values change between -1 and +1.

[0043] Fig. 2 is a diagram illustrating an exemplary configuration of the timer 5 included in the rotating machine control device 1 according to the first embodiment.

[0044] The timer generator 5 includes a first determining means 50, a second determining means 51, operators 52 to 54 and a logical operator 55 of conjunction.

[0045] The first carrier wave cr u1 and a calculated result cr st1 , which is a precalculated sign for the slope of the first carrier wave cr u1 and stored in a memory are input into the first determining device 50. The calculated result cr st1, which is stored in the memory, is a comparison value. The first determining means 50 compares a sign for a slope of the input first carrier wave cr u1 with the comparison value cr st1 . The first determining means 50 outputs a value indicating true when both match, and outputs a value indicating false when both do not match. Specifically, the first determining means 50 outputs "1" when the sign of the slope of the first carrier wave cr u1 and the comparison value cr st1 match, and “0” if the sign of the slope of the first carrier wave cr u1 and the comparison value cr st1 do not match.

[0046] The second carrier wave cr u2 and a calculated result cr st2 , which is a precalculated sign for the slope of the second carrier wave cr u2and stored in the memory are input into the second determining means 51. The calculated result cr st2 , which is stored in the memory, is a comparison value. The second determining means 51 compares a sign for a slope of the input second carrier wave cr u2 with the comparison value cr st2 . The second determining means 51 outputs a value indicating true when both match, and outputs a value indicating false when both do not match. Specifically, the second determining means 51 outputs "1" when the sign of the slope of the second carrier wave cr u2 and the comparison value cr st2 match, and “0” if the sign of the slope of the second carrier wave cr u2 and the comparison value cr st2 do not match.

[0047] The first carrier wave cr u1 and a result cr nt1of pre-calculating the first carrier wave cr u1 , which is stored in the memory, are input into the operator 52. The calculated result cr nt1 , which is stored in the memory, is a comparison value. The operator 52 calculates an instantaneous carrier wave value difference Δcr1 between an instantaneous value of the input first carrier wave cr u1 and the comparison value cr nt1. The operator 52 outputs a value indicating true when the instantaneous carrier wave value difference Δcr1 is 0 or within an acceptable deviation range, and outputs a value indicating false when the instantaneous carrier wave value difference Δcr1 is not within the acceptable deviation range. Specifically, the operator 52 outputs "1" as the value indicating true when the instantaneous carrier wave value difference Δcr1 is less than a predetermined threshold, and outputs "0" as the value indicating false when the instantaneous carrier wave value difference Δcr1 is greater than or equal to the threshold.

[0048] The second carrier wave cr u2 and a result cr nt2 of pre-calculating the second carrier wave cr u2 , which is stored in the memory, are entered into the operator 53. The calculated result cr nt2, which is stored in the memory, is a comparison value. The operator 53 calculates an instantaneous carrier wave value difference Δcr2 between an instantaneous value of the input second carrier wave cr u2 and the comparison value cr nt2 . The operator 53 outputs a value indicating true when the instantaneous carrier wave value difference Δcr2 is 0 or within an acceptable deviation range, and outputs a value indicating false when the instantaneous carrier wave value difference Δcr2 is not within the acceptable deviation range. Specifically, the operator 53 outputs "1" as the value indicating true when the instantaneous carrier wave value difference Δcr2 is less than a predetermined threshold, and outputs "0" as the value indicating false when the instantaneous carrier wave value difference Δcr2 is greater than or equal to the threshold.

[0049] The output voltage phase command θ and a result θ tthe pre-calculation of the output voltage phase command θ, which is stored in the memory, are input into the operator 54. The calculated result θ t , which is stored in the memory, is a comparison value. The operator 54 calculates a phase difference Δθ between the input output voltage phase command θ and the comparison value θ t . The operator 54 outputs a value indicating true when the phase difference Δθ is 0 or within an acceptable deviation range, and outputs a value indicating false when the phase difference Δθ is not within the acceptable deviation range. Specifically, the operator 54 outputs "1" as the value indicating true when the phase difference Δθ is less than a predetermined threshold, and outputs "0" as the value indicating false when the phase difference Δθ is greater than or equal to the threshold.

[0050] The signals outputted from the first determiner 50, the second determiner 51, and the operators 52 to 54 are respectively input to the conjunction logical operator 55. The conjunction logical operator 55 outputs a value indicating true as the timer signal Tr when each input signal is the value indicating true, that is, "1," and outputs a value indicating false as the timer signal Tr when the input signals include any values indicating false. Specifically, the conjunction logical operator 55 outputs "1" as the timer signal Tr when each input signal is the value indicating true, and outputs "0" as the timer signal Tr when the input signals include any values indicating false.

[0051] The above-mentioned pre-calculated comparison values, namely cr st1 , cr st2 , cr nt1 , cr nt2 and θ tmay be stored in the timer generator 5 or in an external storage means.

[0052] In the example described in the present embodiment, the timing generator 5 determines based on the first and second carrier waves cr u1 and cr u2 for the u-phase and the output voltage phase command θ, whether the timing for switching between the PWM modes is appropriate or not, and changes the state of the timer signal Tr upon determining that the timing for switching between the PWM modes is appropriate. However, the timer generator 5 may determine the timing for switching between the PWM modes based on the first and second carrier waves for the v-phase and the output voltage phase command θ, or based on the first and second carrier waves for the w-phase and the output voltage phase command θ.

[0053] Based on the fundamental frequency F INVthe voltage output from the voltage application unit 3 and the voltage commands V u *, V v *, and V w * used to control the rotating machine 2, the PWM mode selector 6 generates the PWM mode selection signal P Modus which selects the first PWM mode or the second PWM mode, and outputs the PWM mode selection signal P Modus to the modulation wave generator 7 and the carrier wave selector 8. The PWM mode selector 6 switches a value of the PWM mode selection signal P Modus at a time when the timer signal Tr input from the timer generator 5 logically reverses from false to true.

[0054] The modulation waves v u *, v v * and v w* generated by the modulation wave generator 7 are three-phase sine waves for the u-phase, the v-phase, and the w-phase, respectively. A phase difference of 120 degrees is maintained between the modulation waves v u *, v v * and v w * The amplitudes of the modulation waves v u *, v v * and v w * are determined by the voltage commands V u *, V v * and V w * which are input to the modulation wave generator 7. Each of the voltage commands V u *, V v * and V w * has a size from 0 to 4 / π, where a maximum amplitude of a fundamental wave obtained from the Fourier series expansion of a square wave is 4 / π.

[0055] Each of the modulation waves v u *, v v * and v w* may include a superimposed third harmonic having a frequency three times that of the modulation wave in order to improve a utilization rate of the voltage output from the voltage application unit 3. When the magnitudes of the voltage commands V u *, V v * and V w *, with which the rotating machine 2 is driven, each exceed 1, gains can be multiplied to obtain relationships between fundamental voltages, which are calculated from the Fourier series expansion of the voltages v u , v v and v w applied to the rotating machine 2 and the corresponding voltage commands V u *, V v * and V w* are determined. The above-mentioned third harmonics and correction gains may differ between modulation waves corresponding to the asynchronous PWM pulses and modulation waves corresponding to the synchronous PWM pulses. For this reason, the modulation wave generator 7 switches between the modulation waves corresponding to the asynchronous PWM pulses and the modulation waves corresponding to the synchronous PWM pulses based on the PWM mode selection signal P Modus in order to be the modulation waves v u *, v v * and v w * to be issued.

[0056] Based on the PWM mode selection signal P Modus the carrier wave selector 8 selects the first carrier waves cr u1 , cr v1 and cr w1 , which correspond to the asynchronous PWM pulses, or the second carrier waves cr u2 , cr v2 and cr w2corresponding to the synchronous PWM pulses to serve as the carrier waves cr u , cr v and cr w to be issued.

[0057] The PWM pulse generator 9 compares sizes of the modulation waves v u *, v v * and v w * input from the modulation wave generator 7 and the carrier waves cr u , cr v and cr w , which are input from the carrier wave selector 8, separately for the u-phase, the v-phase and the w-phase. For the u-phase, the PWM pulse v ug , which is output to the voltage application unit 3, is true, that is, “1”, when the modulation wave v u * larger than the carrier wave cr u is, and false, that is “0”, if the modulation wave v u * less than or equal to the carrier wave cr uSimilarly, for the v-phase and the w-phase, sizes of the modulation and carrier waves are compared for each phase, and a value (“1” or “0”) based on a comparison result is set as the PWM pulse v vg or V wg output to the voltage application unit 3.

[0058] The voltage application unit 3 has, for example, a Fig. 3 illustrated configuration. Fig. 3 is a diagram illustrating the exemplary configuration of the voltage application unit 3 included in the rotating machine control device 1 according to the first embodiment, and particularly illustrating the exemplary circuit configuration when the voltage application unit 3 is a three-phase PWM inverter.

[0059] The voltage application unit 3 includes a leg 30A to which a semiconductor element UP of an upper arm and a semiconductor element UN of a lower arm are connected in series, a leg 30B to which a semiconductor element VP of an upper arm and a semiconductor element VN of a lower arm are connected in series, and a leg 30C to which a semiconductor element WP of an upper arm and a semiconductor element WN of a lower arm are connected in series.

[0060] The legs 30A to 30C are connected in parallel, and a bus voltage is applied to the legs 30A to 30C through the DC buses 35a and 35b. The voltage application unit 3 converts DC power supplied to the legs 30A to 30C from a power source 36 through the DC buses 35a and 35b into AC power and supplies the converted AC power to the rotating machine 2, thereby driving the rotating machine 2.

[0061] In Fig. 3, the semiconductor elements UP, UN, VP, VN, WP, and WN are exemplified by metal-oxide-semiconductor field-effect transistors (MOSFETs). The semiconductor element UP includes a transistor 30a and a diode 30b connected in antiparallel to the transistor 30a. The other semiconductor elements UN, VP, VN, WP, and WN have the same configuration as the semiconductor element UP. The term "antiparallel" means that the anode side of the diode 30b is connected to the first terminal corresponding to a source of the MOSFET, while a cathode side of the diode 30b is connected to a second terminal corresponding to a drain of the MOSFET.

[0062] The semiconductor elements UP, UN, VP, VN, WP and WN to be used can, for example, be insulated gate bipolar transistors (IGBTs) instead of MOSFETs.

[0063] A connection point 32 between the semiconductor element UP of the upper arm and the semiconductor element UN of the lower arm of the leg 30A is connected to a first phase (for example, the u-phase) of the rotating machine 2. A connection point 33 between the semiconductor element VP of the upper arm and the semiconductor element VN of the lower arm of the leg 30B is connected to a second phase (for example, the v-phase) of the rotating machine 2. A connection point 34 between the semiconductor element WP of the upper arm and the semiconductor element WN of the lower arm of the leg 30C is connected to a third phase (for example, the w-phase) of the rotating machine 2. The connection points 32, 33, and 34 of the voltage application unit 3 represent AC terminals.

[0064] Here, a description is provided of voltage vectors output by the voltage application unit 3. The voltage application unit 3 is, as mentioned above, the three-phase PWM inverter serving as a power conversion unit that generates the desired voltage by performing PWM control on the DC power having the voltage V DC supplied from the power source 36 through the DC buses 35a and 35b. The three-phase PWM inverter has two vertically arranged semiconductor switching elements for each phase, and the upper and lower semiconductor switching elements function such that one of the semiconductor switching elements is in an ON state. Therefore, the three-phase PWM inverter has two to the power of three (eight) possible switching states.

[0065] Next, a description of the above-mentioned pre-calculated comparison values cr st1 , cr st2 , cr nt1, cr nt2 and θ t , which in the Fig. 2 illustrated timer generator 5.

[0066] For example, if the asynchronous and synchronous carrier waves adopted for switching between the PWM modes during the operation of the rotating machine 2 are in the Fig. 15 illustrated relationship, the Fig. 16 illustrated evaluation function of the magnetic flux E fasprecalculated outside the control device 1 of a rotating machine. This precalculation is performed by integrating three-phase asynchronous PWM pulses obtained by comparing the magnitudes of the modulation waves corresponding to the asynchronous PWM and the asynchronous carrier waves, and three-phase synchronous PWM pulses obtained by comparing the magnitudes of the modulation waves corresponding to the synchronous PWM and the synchronous carrier waves, and then performing calculations described in the above formulas (6), (7), and (8).

[0067] As first described in the present embodiment, the phase at which the signal on a vertical axis in Fig. 16 shown evaluation function of the magnetic flux E fas reaches a minimum value, a phase that minimizes the amplitude of current oscillations. In Fig. 16, the voltage phase of the U-phase at 223 degrees is the phase that minimizes the amplitudes of the current oscillations. Therefore, by extracting and using a sign of the slope and an instantaneous value of each of the asynchronous and synchronous carrier waves at the 223-degree voltage phase of the u-phase from Fig. 15 the current oscillations during switching between the PWM modes are limited even without calculating the motor fluxes during the operation of the rotating machine 2. In other words, the signs of the slopes and the instantaneous values of the asynchronous and synchronous carrier waves corresponding to the time when the evaluation function of the magnetic flux E fas reaches its minimum and can be identified by the relationship between the asynchronous and synchronous carrier waves, precalculated and used as the above-mentioned comparison values cr st1 , cr st2 , cr nt1 and cr nt2used. Furthermore, the voltage phase of the u-phase, in which the evaluation function of the magnetic flux E fas reaches its minimum when the above-mentioned reference value θ t As described, the comparison values cr st1 , cr st2 , cr nt1 , cr nt2 and θ t which are required when the timer generator 5 generates the timer signal Tr, are precalculated.

[0068] Since the three-phase PWM pulses are generated by comparing the modulation waves v u *, v v * and v w * with the carrier waves cr u , cr v and cr ware generated, their respective mean values over a cycle may not be equal to 0, unlike a sine wave. The fact that integrating the three-phase PWM pulses with their respective mean values over a cycle does not equal 0 results in the integrals diverging positively or negatively, depending on the signs of the mean values of the three-phase PWM pulses over a cycle. Accordingly, the integrals of the three-phase PWM pulses can be calculated after subtracting the mean value of the PWM pulses corresponding to each phase over a cycle from the three-phase PWM pulses.

[0069] As in Fig. 4, the above comparative values cr st1 , cr st2 , cr nt1 , cr nt2 and θ t stored in a storage unit 58 and are output from the storage unit 58 when the timer generator 5 generates the timer signal Tr. Fig. 4 is a diagram illustrating the storage unit 58 given as an example for storing the comparison values used by the timer generator 5 according to the first embodiment in a process of generating the timer signal Tr. The storage unit 58 may be provided inside or outside the timer generator 5.

[0070] The above comparative values cr st1 , cr st2 , cr nt1 , cr nt2 and θ t can be fixed values or variables stored in a table that are outputs that change depending on input conditions. Fig. 5 illustrates an exemplary configuration of a memory unit 58 in which the comparison values cr st1 , cr st2 , cr nt1 , cr nt2 and θ t the variables are. Fig. Fig. 5 is a diagram illustrating the storage unit 58, which is given as another example for storing the comparison values used by the timer generator 5 according to the first embodiment in the process of generating the timer signal Tr. The storage unit 58 shown in Fig. 5 as the other example is illustrated, contains a table 59. In the Fig. 5 illustrates Table 59, an asynchronous carrier wave frequency F AS within one cycle of the output voltage phase command θ, a synchronous carrier wave frequency F SY within one cycle of the output voltage phase command θ and the voltage commands V u *, V v * and V w * is entered and a linear search is performed to find the pre-calculated and stored comparison values cr st1 , cr st2 , cr nt1 , cr nt2 and θ t to spend.

[0071] As described above, the rotating machine control device 1 according to the present embodiment is configured to appropriately use one of the two PWM modes, namely the asynchronous PWM and the synchronous PWM, to control the rotating machine 2. The rotating machine control device 1 includes the timer generator 5, which detects the timing for switching to the PWM mode to be used, thereby limiting current oscillations, and generates the signal indicating this timing. The timer generator 5 detects the timing for switching between the PWM modes based on the first carrier wave used for PWM pulse generation in the asynchronous PWM, the second carrier wave used for PWM pulse generation in the synchronous PWM, and the output voltage phase command.The timing generator 5 then changes the output timing signal to the state indicating that the timing is appropriate for switching between the PWM modes. Specifically, the timing generator 5 detects cr based on the first carrier wave. u1 , the second carrier wave cr u2 , the output voltage phase command θ and the precalculated comparison values cr st1 , cr st2 , cr nt1 , cr nt2 and θ t the time at which the relationship between the first carrier wave cr u1 , cr v1 or cr w1 and the second carrier wave cr u2 , cr v2 or cr w2is established, causes a difference between the integral of the asynchronous PWM pulses and the integral of the synchronous PWM pulses to become smaller than a predetermined value. The timer generator 5 then changes the output state of the timer signal. The control unit 4 of the rotating machine control device 1 switches the PWM mode used to control the rotating machine 2 when the state of the timer signal output from the timer generator 5 changes. In this way, the PWM mode can be switched at the time when the difference between the magnetic flux of the rotating machine 2 in the asynchronous PWM and the magnetic flux of the rotating machine 2 in the synchronous PWM becomes smaller, resulting in limited current oscillations during switching between the PWM modes. Second embodiment.

[0072] Next, a description will be given of a second embodiment. For convenience, a rotating machine control device according to the second embodiment will be referred to as the rotating machine control device 1a to distinguish it from the rotating machine control device 1 according to the first embodiment. The rotating machine control device 1a according to the present embodiment includes a Fig. 6 illustrated timer generator 5a instead of the timer generator 5 (see Fig. 1 and Fig. 2) included in the rotating machine control device 1 according to the first embodiment. Components other than the timer generator 5a are the same as those in the first embodiment and will therefore not be described. Fig. 6 is a diagram illustrating an exemplary configuration of the timer generator 5a included in the rotating machine control device 1a according to the second embodiment.

[0073] The timing generator 5a includes operators 52 to 54, a logical conjunction operator 55a, a phase hold means 56, and an operator 57. The operators 52 to 54 are the same as the operators 52 to 54 of the timing generator 5 according to the first embodiment and will therefore not be described. In the present embodiment, θ t1 as a result of calculating the output voltage phase command θ into the operator 54.

[0074] The signals outputted from the operators 52 to 54, respectively, are input to the conjunction logical operator 55a. The conjunction logical operator 55a outputs a value indicating true as a timer signal Tr' when each input signal is a value indicating true, that is, "1," and outputs a value indicating false as the timer signal Tr' when the input signals include any values indicating false. Specifically, the conjunction logical operator 55a outputs "1" as the timer signal Tr' when each input signal is the value indicating true, and outputs "0" as the timer signal Tr' when the input signals include any values indicating false.

[0075] The timer signal Tr' output from the conjunction logical operator 55a and the output voltage phase command θ are input to the phase hold device 56. The phase hold device 56 stores a phase of the output voltage phase command θ at a time point when the timer signal Tr' changes from false to true, and outputs the stored phase as a reference phase θ b This means that the phase hold device 56 continues to use the value of the output voltage phase command θ corresponding to the time at which the timing signal Tr' has changed from false to true as the reference phase θ b issues.

[0076] The reference phase θ b , which is output by the phase holding device 56, and a precalculated delayed phase θ t2, which is stored in the memory, are input to the operator 57. The operator 57 calculates a phase difference between the input reference phase θ b and the input delayed phase θ t2 . The operator 57 outputs a value indicating true as the timer signal Tr when the calculated phase difference is 0 or within an acceptable deviation range, and outputs a value indicating false as the timer signal Tr when the calculated phase difference is not within the acceptable deviation range. Specifically, the operator 57 outputs "1" as the timer signal Tr when the calculated phase difference is less than a predetermined threshold, and outputs "0" as the timer signal Tr when the calculated phase difference is greater than or equal to the threshold.

[0077] The timer generator 5a according to the second embodiment shown in Fig. 6, uses the specific phase at which the asynchronous and synchronous carrier waves reach their peak value at -1 or +1 (a maximum or minimum value), respectively, as the reference phase θ b and outputs the timing signal Tr at a phase that is a fixed amount relative to the reference phase θ b is delayed.

[0078] The operators 52 and 53 respectively detect peak values of the carrier waves cr u1 and cr u2 Since each carrier wave has a slope of 0 at its peak, there is no need to determine the sign of the slope. Therefore, the precalculated comparison value cr nt1 for the first carrier wave cr u1 and the precalculated comparison value cr nt2 for the second carrier wave cr u2 set to -1 or +1. The precalculated comparison value θ t1for the output voltage phase command θ is set to a phase at which the synchronous carrier wave reaches its peak value. For example, in the Fig. 15 and used above, since the asynchronous and synchronous carrier waves each reach -1 at 150 degrees, the reference phase θ b be set to 150 degrees.

[0079] A description of the pre-calculated delayed phase θ t2 It is considered that the first carrier wave cr u1 and the second carrier wave cr u2 which are input into the timer generator 5a, which in the example from Fig. 15 are the asynchronous and synchronous carrier waves, respectively. In this case, the asynchronous and synchronous carrier waves generate the magnetic flux weighting function E fas , which in Fig. 16 is illustrated. In Fig. 16 is the phase at which the evaluation function of the magnetic flux E fas reaches its minimum, 223 degrees. Therefore, when the reference phase θ b is set to 150 degrees, the delayed phase θ t2 is set to 223 degrees. The timer generator 5a outputs the timer signal Tr based on this setting, and the PWM mode selector 6 switches the PWM mode at a timing in accordance with this timer signal Tr. Consequently, current oscillations are limited during switching between the PWM modes.

[0080] As in Fig. 7 illustrates, the precalculated comparison values cr nt1 , cr nt2 and θ t1 and the precalculated delayed phase θ t2 in Fig. 6 are stored in a storage unit 60 and are output from the storage unit 60 when the timer generator 5a generates the timer signal Tr. Fig. 7 is a diagram illustrating the storage unit 60 given as an example for storing the comparison values and the delayed phase that the timer generator 5a according to the second embodiment uses in a process of generating the timer signal Tr. The storage unit 60 may be provided inside or outside the timer generator 5a.

[0081] The above comparative values cr nt1 , cr nt2 and θ t1 and the delayed phase θ t2 can be fixed values or can be variables stored in a table that are outputs that change depending on the input conditions. Fig. Figure 8 illustrates an exemplary configuration of a memory unit 60 in which the comparison values cr nt1 , cr nt2 and θ t1 and the delayed phase θ t2 the variables are. Fig. Fig. 8 is a diagram illustrating the storage unit 60 provided as another example for storing the comparison values and the delayed phase used by the timing generator 5a according to the second embodiment in the process of generating the timing signal Tr. The storage unit 60 shown in Fig. 8 as the other example is illustrated, contains a table 61. In the Fig. 8 illustrated Table 61 are the asynchronous carrier wave frequency F AS within one cycle of the output voltage phase command θ, the synchronous carrier wave frequency F SY within one cycle of the output voltage phase command θ and the voltage commands V u *, V v * and V w * Inputs and a linear search is performed to find the pre-calculated and stored comparison values cr nt1 , cr nt2 and θ t1 and the precalculated and stored delayed phase θ t2to spend.

[0082] The storage unit 60 can be as in Fig. 9 or Fig. 10 illustrated configuration. Fig. 9 is a diagram showing a variation of the Fig. 7 illustrated storage unit 60. Fig. 10 is a diagram showing a variation of the Fig. 8 illustrated storage unit 60.

[0083] The Fig. 9 and 10 respectively differs in that the information stored in the storage unit 60 is partly different from the information shown in the Fig. 7 and 8, respectively, and that the operators 62 and 63 are included after the storage unit 60. While the Fig. 7 and 8, respectively, as mentioned above, the comparison values cr nt1 , cr nt2 and θ t1and the delayed phase θ t2 stores, stores the Fig. 9 and 10, the storage unit 60 illustrates the comparison values cr nt1 , cr nt2 and θ t1 and the delayed phase θ t2 '. In other words, the Fig. 9 and 10, respectively, the memory unit 60 illustrates the delayed phase θ t2 ' instead of the delayed phase θ t2 , which in the Fig. 7 or 8 is stored in the memory unit 60 illustrated.

[0084] In the configuration that is used in each of the Fig. 9 and Fig. 10, the operator 62 calculates a phase difference Δθ between the output voltage phase command θ and the comparison value θ t1 , which is stored in the storage unit 60. Furthermore, the operator 63 adds the phase difference Δθ output from the operator 62 to the delayed phase θ t2', which is stored in the storage unit 60, and outputs a result of this addition operation as a corrected delayed phase θ t2 If the phase difference Δθ is not 0, the reference phase θ b misaligned with the peak value of the synchronous carrier wave, so that the phase at which the magnetic flux evaluation function E fas reaches the minimum value, is also misaligned. For this reason, operator 63 adds the phase difference Δθ to the delayed phase θ t2 ' to determine the delayed phase θ t2 ', whereby the corrected delayed phase θ t2 is obtained.

[0085] The rotating machine control device 1a to which the timer 5a described in the present embodiment is applied can switch the PWM mode at the same timing as the rotating machine control device 1 according to the first embodiment and can limit current oscillations during switching between the PWM modes.

[0086] The above configurations illustrated in the embodiments are illustrative; they may be combined with other well-known techniques, and some may be omitted or modified without departing from the essence. The embodiments may be combined with each other. List of reference symbols

[0087] 1 rotating machine control device; 2 rotating machine; 3 voltage application unit; 4 control unit; 5, 5a timing generator; 6 PWM mode selector; 7 modulation wave generator; 8 carrier wave selector; 9 PWM pulse generator; 30A, 30B, 30C legs; 30a transistor; 30b diode; 32, 33, 34 connection point; 35a, 35b DC bus; 36 power source; 50 first determining means; 51 second determining means; 52, 53, 54, 57, 62, 63 operator; 55, 55a logical operator of conjunction; 56 phase holding means; 58, 60 storage unit; 59, 61 table. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2911734

[0008]

Claims

A control device of a rotating machine, comprising: a voltage application unit for generating three-phase voltages to be applied to a rotating machine; and a control unit for controlling a voltage generation operation of the voltage application unit in a first pulse width modulation mode or a second pulse width modulation mode, wherein the first pulse width modulation mode is a pulse width modulation method in which a carrier wave frequency is asynchronous with a frequency of a voltage command, wherein the second pulse width modulation mode is a pulse width modulation method in which a carrier wave frequency is synchronous with a frequency of a voltage command, wherein, based on a first carrier wave used in generating a signal that controls the voltage application unit in the first pulse width modulation mode, a second carrier wave used in generating a signal,that controls the voltage application unit in the second pulse width modulation mode, and an output voltage phase command that commands a phase of each of the voltages to be output to the rotating machine, the control unit selects one of the first pulse width modulation mode and the second pulse width modulation mode as a pulse width modulation method to be used to control the voltage generation operation. A rotating machine control device according to claim 1, wherein, when switching a pulse width modulation method used to control the voltage generation operation, the control unit detects, based on the first carrier wave, the second carrier wave, and the output voltage phase command, a timing at which a difference between a flux linkage of the rotating machine during control of the voltage generation operation in the first pulse width modulation mode and a flux linkage of the rotating machine during control of the voltage generation operation in the second pulse width modulation mode is minimized, and uses the detected timing as a timing for switching the pulse width modulation method. A rotating machine control device according to claim 1 or 2, wherein the control unit includes: a timer generator for determining a timing for switching a pulse width modulation method used for controlling the voltage generation operation based on the first carrier wave, the second carrier wave, and the output voltage phase command; and a pulse width modulation mode selector for selecting one of the first pulse width modulation mode and the second pulse width modulation mode as a pulse width modulation method to be used for controlling the voltage generation operation when the timer generator determines that the timing for switching the pulse width modulation method is appropriate. A rotating machine control device according to claim 3, comprising a storage unit for storing a sign of a slope of the first carrier wave, a sign of a slope of the second carrier wave, a current value of the first carrier wave, a current value of the second carrier wave, and a phase of a voltage to be output to the rotating machine, which correspond to the time when a difference between a flux linkage of the rotating machine during control of the voltage generation operation in the first pulse width modulation mode and a flux linkage of the rotating machine during control of the voltage generation operation in the second pulse width modulation mode is minimized, wherein the timer generator determines that the time is appropriate for switching the pulse width modulation method,when a sign of a slope of the first carrier wave and a sign of a slope of the second carrier wave match a sign of a slope of a first carrier wave and a sign of a slope of a second carrier wave, respectively, stored in the storage unit, wherein a difference between a current value of the first carrier wave and a current value of a first carrier wave stored in the storage unit and a difference between a current value of the second carrier wave and a current value of the second carrier wave stored in the storage unit is each smaller than a predetermined threshold, and a difference between a value of the output voltage phase command and a phase of a voltage to be output to the rotating machine stored in the storage unit is smaller than a predetermined threshold. A rotating machine control device according to claim 4, wherein the storage unit includes: a table into which a frequency of the first carrier wave, a frequency of the second carrier wave, and the voltage command are input, and in which a linear search is performed to output a sign of a slope of the first carrier wave, a sign of a slope of the second carrier wave, an instantaneous value of the first carrier wave, an instantaneous value of the second carrier wave, and a phase of a voltage to be output to the rotating machine, which are stored. A rotating machine control device according to claim 3, comprising a storage unit for storing a current value of the first carrier wave, a current value of the second carrier wave, and a phase of a voltage to be output to the rotating machine, which correspond to the time when a difference between a flux linkage of the rotating machine during control of the voltage generation operation in the first pulse width modulation mode and a flux linkage of the rotating machine during control of the voltage generation operation in the second pulse width modulation mode is minimized, and a delayed phase derived from a relationship between the first carrier wave and the second carrier wave, wherein at a time when a difference between a current value of the first carrier wave and a current value of a first carrier wave stored in the storage unit,and a difference between a current value of the second carrier wave and a current value of the second carrier wave stored in the storage unit is each smaller than a predetermined threshold, and a difference between a value of the output voltage phase command and a phase of a voltage to be output to the rotating machine stored in the storage unit is smaller than a predetermined threshold, the timer generator uses a value of the output voltage phase command as a reference phase, and the timer generator determines that the timing for switching the pulse width modulation method is appropriate when a difference between the reference phase and a delayed phase stored in the storage unit is smaller than a predetermined threshold. A rotating machine control device according to claim 6, wherein the storage unit includes: a table into which a frequency of the first carrier wave, a frequency of the second carrier wave, and the voltage command are input, and in which a linear search is performed to output an instantaneous value of the first carrier wave, an instantaneous value of the second carrier wave, a phase of a voltage to be output to the rotating machine, and the delayed phase, which are stored. A rotating machine control device according to claim 6 or 7, wherein a phase difference between a value of the output voltage phase command and a phase of a voltage to be output to the rotating machine output from the storage unit is calculated, the calculated phase difference is added to the delayed phase output from the storage unit to correct the delayed phase, and the timer generator determines the timing for switching using the corrected delayed phase.

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