Power conversion device and sound quality improvement method

Abstract

A power conversion device (10) comprising an inverter (1) for controlling driving of a rotary electric machine (20) by PWM control for switching between a plurality of modes is provided with a sound signal output device (3) whereby a sound signal is output before and / or after the switching of the PWM mode on the basis of at least one of PWM control information before switching of the PWM mode and PWM control information after switching of the PWM mode, and the sound signal output from the sound signal output device (3) is superimposed on the sound of the rotary electric machine (20).

Description

Power conversion device and sound quality improvement method

[0001] This disclosure relates to a power conversion device and a method for improving sound quality.

[0002] Pulse Width Modulation (PWM) inverters, which convert a square wave signal into a pseudo-sine wave signal using PWM, are widely used as power conversion devices to operate various equipment such as rotating electric machines (motors). In PWM control, the square wave signal is switched as a pulse signal, and the number of pulse signals is controlled by the carrier frequency, which is the reciprocal of the period. The carrier frequency is determined mainly to satisfy the requirements of minimizing heat and losses and ensuring the stability of equipment control, and therefore switches intermittently. Because this switching causes torque pulsation, noise, etc., technologies have been developed to suppress these. For example, Patent Document 1 describes an inverter that supplies power to a motor, in which the voltage and phase at the output of the inverter are determined based on the motor's rotation frequency and the torque command for motor drive, and the number of pulses during one electrical cycle of the motor is generated under conditions that reduce the switching frequency of the inverter and the distortion rate of the motor current, thereby suppressing motor losses due to harmonics. It also describes how the effects of pulse number switching can be reduced by switching the number of pulses at a timing when the three-phase switching state of the inverter does not change. Patent Document 2 describes a PWM inverter device that has multiple synchronous PWM modes with different pulse counts for the same output frequency, and by switching and selecting one of these modes over time, even if the output frequency is the same, different pulse counts in the synchronous PWM modes generate harmonic components of different frequencies, thereby preventing a constant frequency harmonic voltage from being continuously applied to the AC motor and reducing the generation of magnetic noise and mechanical vibration.

[0003] JP2013-187933A JP10-201246A

[0004] However, when the PWM mode is controlled in accordance with the motor rotation speed, torque command, etc. to intermittently switch the number of pulses, etc., the generated sound is also switched discontinuously, so it is difficult to completely eliminate beat noise and the like generated at the time of switching. In addition, when the carrier frequency of the inverter is intermittently switched while the motor is rotating, the generated noise order, tone color, etc. change instantaneously, which poses a problem of causing unpleasant auditory sensation or a sense of discomfort.

[0005] The present disclosure has been made to solve the above-mentioned problems, and an object of the present disclosure is to provide a power conversion device capable of improving auditory sensation. Another object of the present disclosure is to provide a sound quality improvement method.

[0006] A power conversion device according to the present disclosure is a power conversion device including an inverter that drives and controls a rotating electrical machine by PWM control that switches between a plurality of modes, the power conversion device comprising: a sound signal output device that outputs a sound signal based on at least one of PWM control information before mode switching and PWM control information after mode switching in at least one of before and after mode switching.

[0007] A sound quality improvement method according to the present disclosure is a sound quality improvement method for improving sound quality of sound generated from a rotating electrical machine that is driven and controlled by PWM control that switches between a plurality of modes, the method comprising: outputting a sound signal based on at least one of PWM control information before mode switching and PWM control information after mode switching in at least one of before and after mode switching, and superimposing the sound signal on sound generated from the rotating electrical machine to improve sound quality.

[0008] According to the present disclosure, in at least one of before and after mode switching by PWM control, a sound signal is output based on at least one of PWM control information before mode switching and PWM control information after mode switching, and the sound signal is superimposed on sound generated from the motor, so that the sound quality of unpleasant noise and sound that causes a sense of discomfort can be improved.

[0009] This is a block diagram showing the schematic configuration of a power converter according to Embodiment 1. This is an explanatory diagram showing an example of an audio signal output from a power converter according to Embodiment 1. This is an explanatory diagram showing an example of an audio signal output from a power converter according to Embodiment 1. This is an explanatory diagram showing an example of a motor sound caused by PWM control according to Embodiment 1. This is an explanatory diagram showing an example of an audio signal output from a power converter according to Embodiment 1. This is an explanatory diagram showing an example of an audio signal superimposed on a motor sound caused by PWM control according to Embodiment 1. This is an explanatory diagram showing an example of an audio signal output from a power converter according to Embodiment 1. This is an explanatory diagram showing an example of an audio signal output from a power converter according to Embodiment 1. This is an explanatory diagram showing an example of an audio signal output from a power converter according to Embodiment 1. This is an explanatory diagram showing an example of an audio signal output from a power converter according to Embodiment 1. This is an explanatory diagram showing an example of an audio signal output from a power converter according to Embodiment 1. This is an explanatory diagram showing an example of an audio signal output from a power converter according to Embodiment 1. This is an explanatory diagram showing an example of an audio signal output map stored in the power converter according to Embodiment 1. This is an explanatory diagram showing an example of mounting the power converter according to Embodiment 2 on a vehicle. This is a diagram showing the schematic configuration of the power conversion device according to Embodiment 3. This is a flowchart showing the processing steps of the sound quality improvement method according to Embodiment 4. This is a schematic block diagram showing an example of a processing circuit that realizes each function of the power conversion device according to Embodiment 4.

[0010] Embodiments will be described with reference to the drawings. Here, the same parts and corresponding components are denoted by the same reference numerals, and their detailed descriptions are omitted.

[0011] Embodiment 1. Figure 1 is a block diagram showing the schematic configuration of a power converter 10 according to Embodiment 1. The power converter 10 includes an inverter 1 that drives a motor 20 by PWM control that switches between multiple modes. It also includes a sound signal output device 3 that outputs a sound signal based on at least one of the PWM control information before the mode switch and the PWM control information after the mode switch, at least one of the two states. For example, based on the rotation speed command, torque command, etc. of the motor 20, the PWM signal controller 2 determines the mode, pulse count, etc., and the inverter 1 drives the motor 20 by converting power based on the determined mode, pulse count, etc. The sound signal output device 3 acquires PWM control information before and after the mode switch, including the mode switch information performed by the PWM signal controller 2, and generates a sound signal based on this, or selects the appropriate sound signal from a plurality of stored sound signals. For example, the sound signal output device 3 shown in Figure 1 acquires PWM control information such as mode, pulse count, carrier frequency fc, motor speed 20 rotation speed, and torque from the PWM signal controller 2 using the control information acquisition unit 31. The sound signal control unit 32 causes the sound signal generation unit 33 to calculate the sound signal to be output from the acquired PWM control information, or selects a sound signal from the sound signal storage unit 34, controls the timing of outputting the sound signal, and commands the sound signal output unit 35 to output. The sound signal output unit 35 transmits the sound signal to the speaker 30 or the like based on the command from the sound signal control unit 32. The timbre of the sound signal is, for example, a simulated motor sound. If sound signals are linked to multiple modes and stored, it is not necessary to perform calculations each time, which can improve processing speed.

[0012] Inverter 1 controls the motor drive current by supplying, for example, DC power between the positive and negative buses of the inverter and controlling the switching. The switching elements constituting inverter 1 are controlled on and off by a PWM signal from PWM signal controller 2. If the fundamental frequency of the sine modulated wave by PWM control, i.e., the fundamental frequency of the AC that drives motor 20, is f, then for example, if motor 20 has an 8-pole, 48-slot configuration, then 4 waves (4f) are required for one rotation, so the rotational speed of motor 20 is proportional to the fundamental frequency f. The carrier frequency fc is the number of pulses β × the fundamental frequency f, and in synchronous mode, the number of pulses β is constant, so the rotational speed and the carrier frequency fc are proportional. In synchronous PWM control, the carrier frequency fc is increased in proportion to the motor rotational speed to generate a modulated wave based on the motor rotational speed command. At this time, a distortion current is generated due to the energy difference between the energy reflected from the load such as motor 20 and the output of inverter 1. For example, the distortion current is generated in the vicinity of the carrier frequency fc (mainly fc ± 2f, 2fc ± f). Furthermore, when third-harmonic injection modulation is performed by adding a third-harmonic component to the fundamental frequency f in order to improve the voltage utilization rate of the DC power supply, distortion currents are generated not only in the aforementioned components but also in fc±4f. In synchronous PWM control, electromagnetic noise is generated at (β-3)×f, (β-1)×f, (β+1)×f, and (β+3)×f. The noises that are particularly unpleasant are (β-3)×f and (β+3)×f. On the other hand, in asynchronous PWM control, for example, a modulated wave is generated based on a motor rotation speed command while the carrier frequency fc is kept constant. In this case as well, distortion currents are generated near the carrier frequency fc (mainly fc±2f, 2fc±f). In asynchronous PWM control, when the carrier frequency is ψHz, sound is generated at ψ-3f, ψ-1f, ψ+1f, and ψ+3f. The noises that are particularly unpleasant are ψ-3f and ψ+3f. Therefore, sound quality is improved by superimposing sound signals at the frequencies in which these unpleasant noises occur.

[0013] Specific examples of sound signal output will be explained. Here, f is the fundamental frequency of the AC current used to drive the motor 20, and for example, 9f represents the 9th component of the fundamental frequency f. The number of pulses in one cycle of the fundamental frequency, determined by PWM control, is expressed as the pulse count, with the unit P. Figure 2 shows an example of sound signal output when the control mode of inverter 1 switches from asynchronous 5kHz → synchronous 15P → synchronous 12P → asynchronous 10kHz. The 9f component of the motor sound, represented by the dashed line, is particularly noisy in the case of synchronous 12P. Therefore, the sound signal shown by the solid line is output before synchronous 12P control and after synchronous 12P switches to asynchronous 10kHz. The sound signal is superimposed on the motor sound, smoothing the overall sound, thus improving the sound quality of sounds that cause unpleasant noise or discomfort. Figure 3 shows an example of sound signal output when the control mode of inverter 1 switches from asynchronous 5kHz → synchronous 15P → synchronous 12P → synchronous 9P. In the 12f component, the motor sound, represented by the dashed line, exhibits a prominent noise level during synchronous 15P and synchronous 9P operation. Therefore, the sound signal, shown by the solid line, is output before synchronous 15P control, after synchronous 15P switches to synchronous 12P, and until it switches to synchronous 9P. Similarly, the sound signal is superimposed on the motor sound, smoothing the overall sound and improving the quality of sounds that cause unpleasant noise or discomfort. In this case, the 9f component also generates noise in the same way as described above, so it is preferable to output a sound signal for it as well.

[0014] Figures 4, 5, and 6 show the sound characteristics when the motor 20 is accelerated from 0 rpm to 13,000 rpm while switching the control mode of the inverter 1 between asynchronous 5 kHz, synchronous 15P, synchronous 12P, and asynchronous 10 kHz. The thick dashed line in Figure 4 is an example of motor noise caused by PWM control. When the control mode is asynchronous 5 kHz, the noise is prominent in the 5 kHz + 3f and 5 kHz - 3f components; when the control mode is synchronous 15P, it is prominent in the 12f, 14f, 16f, and 18f components; when the control mode is synchronous 12P, it is prominent in the 9f, 11f, 13f, and 15f components; and when the control mode is asynchronous 10 kHz, it is prominent in the 10 kHz + 3f and 10 kHz - 3f components. In other words, it can be seen that the sound changes discontinuously each time the control mode is switched. Figure 5 shows an example of an audio signal superimposed on the motor noise with a thick solid line, and Figure 6 shows an example where the audio signal (thick solid line) is superimposed on the motor noise (thick dashed line). It can be seen that the overall sound is smoothed by superimposing an audio signal on the motor sound. In Figure 6, the overall sound becomes cos(K+F) + cos(K-F), which is obtained by expanding a continuous cosK × cosF, and unpleasant noises can be improved. Here, K is the order component of the current distortion, and F is the fundamental wave component (1f).

[0015] This section describes an example of calculating an audio signal that simulates motor noise. For example, when inverter 1 has a carrier frequency fc and drives a three-phase motor 20 with AC at a fundamental frequency f, the harmonic components of the voltage applied to the stator are fc±0f, fc±2f, fc±4f, fc±6f, fc±8f, ..., 2fc±f, 2fc±3f, 2fc±5f, 2fc±7f, 2fc±9f, ... Of these, the fc±0f, fc±6f, 2fc±3f, and 2fc±9f components are ignored because their phase voltages are in phase with UVW. Also, since the influence decreases as you move away from fc and 2fc, only the nearby fc±2f, fc±4f, 2fc±f, and 2fc±5f components are considered. Furthermore, if the control update period for the current command value of inverter 1 is equal to the switching period, which is the reciprocal of the carrier frequency fc, that is, if the control is updated for each triangular wave of the carrier wave, then voltage harmonic components fc±1f and 2fc±2f are generated. The spatial distribution of the stator magnetomotive force generated by the 1f fundamental wave component and these harmonic components is equal to the number of pole pairs of the motor. For example, in an 8-pole, 48-slot distributed winding motor, there are four waves per turn (spatial mode 4th order component) and their harmonic components (spatial mode 8th, 12th, ...th order components). The stator magnetomotive force, organized as (spatial order, time order) considering only the aforementioned spatial mode 4th order component, is shown in Table 1. Here, a negative spatial order is a backward wave in the opposite direction to the rotor rotation direction, and a positive spatial order is a forward wave in the same direction.

[0016]

[0017] Table 2 is obtained by organizing the spatial and temporal orders that constitute the magnetic flux density from this stator magnetomotive force.

[0018]

[0019] And, K and F in Table 2, and the following equation (1)

[0020]

[0021] This allows for the calculation of the electromagnetic excitation force, i.e., the sound signal, for each spatial mode shown in Table 3. The calculation of the sound signal is not limited to this method.

[0022]

[0023] In other words, the sound signal outputter 3 can suppress sudden changes in noise by outputting a sound signal at times other than the mode in which noise exceeding the noise threshold is generated by PWM control, thereby improving sounds that cause discomfort or unease. The noise threshold can be set appropriately, but for example, it can be set to about 50-55 dB near the motor and about 20-25 dB inside the vehicle 40. It is preferable to consider human auditory characteristics such as A-weighting (weighting of frequencies within the range that humans can hear) when setting the noise threshold. Here, it is acceptable if a part of the sound signal is superimposed in the mode in which noise exceeding the noise threshold is generated by PWM control, as long as it does not result in sounds that cause discomfort or unease. The sound signal outputter 3 can suppress sudden changes in noise by outputting a sound signal at times other than the mode in which noise exceeding the noise threshold is generated by PWM control, thereby improving sounds that cause discomfort or unease.

[0024] Furthermore, the noise from the motor 20 includes sounds other than those caused by the intermittently switching PWM control during the motor's rotation. These sounds are even multiples of the fundamental frequency f of the AC current driving the motor 20, and when they overlap with the sounds caused by the PWM control, the abrupt changes in sound are small. Therefore, the sound signal may only be output when the sound signal to be output is an odd multiple of the fundamental frequency f and is not synchronized. This simplifies the sound signal output control and suppresses the increase in volume. For example, as shown in Figure 7, the sound signal outputter 3 outputs a sound signal when the sound signal to be output is an odd multiple of the fundamental frequency f of the motor 20, and does not output a sound signal when it is an even multiple. The sound signal may also be set to a level below the sound threshold. By outputting the sound signal only in the parts where the noise changes drastically due to the motor, abrupt changes in noise can be suppressed, and the increase in volume added by the sound signal can be further suppressed. It is preferable to reproduce the order components of the sound that change when passing through the switching rotation speed or torque using a speaker 30 or the like, as this makes the sound sound continuous.

[0025] As shown in Figure 8, the sound signal output at timings other than the mode in which noise exceeding the noise threshold occurs due to PWM control may be gradually increased before noise exceeding the noise threshold occurs and gradually decreased afterward. For example, if the rotation speed command for the motor 20 is received, the control mode is determined by the PWM signal controller 2, and transmitted to the sound signal output 3 before communicating with the inverter 1, the signal can be gradually increased before noise exceeding the noise threshold occurs. Alternatively, the signal may be gradually decreased only after noise exceeding the noise threshold occurs. If the operating mode is predetermined, the sound signal should be output at the appropriate timing. As shown in Figure 9, the sound signal output at timings other than the mode in which noise exceeding the noise threshold occurs due to PWM control may be gradually increased only before noise exceeding the noise threshold occurs. A mixture of cases where the signal is gradually increased before noise exceeding the noise threshold occurs and gradually decreased afterward, and cases where the signal is gradually increased only before noise exceeding the noise threshold occurs, may be used. The sound signal output device 3 can prevent an increase in the total volume by gradually increasing the sound signal before noise exceeding the noise threshold occurs, and gradually decreasing the sound signal after noise exceeding the noise threshold occurs, thereby reducing the volume of the sound signal as it moves away from the rotational speed at which noise occurs.

[0026] As shown in Figure 10, the audio signal below the output threshold may be continuously output regardless of whether the PWM control mode has been switched. For example, the audio signal may be output even in the noisy 9f component synchronous 12P. For example, by gradually increasing the audio signal from the low-noise synchronous 15P, stopping the increase in the audio signal at the noisy synchronous 12P, and gradually decreasing the audio signal at the low-noise asynchronous 10kHz, it is possible to prevent a timing discrepancy in the switching. As shown in Figure 11, for example, the audio signal may be gradually increased in the 12f component synchronous 15P and synchronous 9P before switching, and the audio signal may be output even in synchronous 15P and synchronous 9P. In other words, if the audio signal outputter 3 gradually increases the audio signal from the low-noise mode to the high-noise mode, stops or decreases the increase in the high-noise mode and outputs the audio signal, and gradually decreases the audio signal in the low-noise mode, a seamless audio signal is created, and sounds that cause unpleasant noise or discomfort can be improved. The output is not limited to the mode shown in Figures 8 to 11, where the sound signal is gradually increased and then gradually decreased. In other modes, the sound signal may be gradually increased from a low-noise mode to a high-noise mode, and a continuous sound signal below the output threshold may be output. The output threshold can be set appropriately, and should be a sound signal at a volume that does not cause unpleasant or unnatural noise. In other words, when the sound signal outputter 3 is in a mode where noise above the noise threshold is generated, it can stop or decrease the increase of the sound signal and output a sound signal, thereby creating a seamless sound signal.

[0027] Let f be the fundamental frequency of the motor 20 and β be the number of pulses in one period of the fundamental wave. We will now explain an example of determining the sound signal by considering the sound components in the case of the number of pulses β in synchronous mode. For example, the spatial order and temporal order are calculated using the following equations (2) to (5).

[0028]

[0029] Here, r is a natural number determined by the number of pole slots in a synchronous motor, and is approximately the greatest common divisor. For example, for a motor 20 with 8 poles and 48 slots distributed winding, r = 8, and for a motor with 20 poles and 24 slots concentrated winding, r = 4. Generally, noise tends to be more noticeable in the spatial 0th order than in the spatial rth order, so it is best to output only the spatial 0th order, i.e., (β±3) × f, sound signals. Figure 12 shows an example where β = 12, and sound signals are output at timings other than those where noise above the noise threshold occurs in the 9f and 15f components, and sound signals are not output in the 11f and 13f components. This reduces the overall volume due to the sound signals and saves processing in the sound signal control unit 32 within the sound signal output unit 3, as well as the storage capacity of the sound signal storage unit 34.

[0030] Figure 13 shows the characteristics when switching between three-phase and two-phase modulation at a pulse count of 12P for the 9f component. Even when switching from two-phase to three-phase, and from synchronous to asynchronous, the noise does not change abruptly because the sound generation frequency does not change if the carrier frequency fc remains the same. Therefore, the sound signal output device 3 may output sound only when the carrier frequency fc changes during mode switching. This simplifies the control by the sound signal control unit 32 and suppresses an increase in volume.

[0031] Preferably, the sound signal storage unit 34 stores sound signals, for example, those represented by multiples of the fundamental frequency f, as a sound signal database based on PWM control. For example, as shown in Figure 14, the timing of outputting sound signals in the sound signal map of each component based on the PWM control mode is stored. For example, in the 6f sound signal map, sound signals are output at asynchronous, synchronous 15P, synchronous 6P, and synchronous 1P, indicated by the diagonal lines, and no sound signals are output at synchronous 9P and synchronous 3P. In the 9f sound signal map, sound signals are output at asynchronous, synchronous 15P, synchronous 9P, synchronous 3P, and synchronous 1P, indicated by the diagonal lines, and no sound signals are output at synchronous 6P. For example, sound signal output maps for each order component are stored. By storing sound signal output maps for each order according to the control mode, noise caused by motor sounds can be appropriately masked. If there is hysteresis in the PWM control mode map, hysteresis may also be provided in the output sound signals. For example, the frequency of the sound signal output when switching from the first mode to the second mode may be changed to make it different from the frequency of the sound signal output when switching from the second mode to the first mode. In other words, the sound signal output device 3 can produce seamless playback sound by changing the sound signal output when switching from the first mode to the second mode and the sound signal output when switching from the second mode to the first mode.

[0032] If the sound signal output by the sound signal outputter 3 is used as a simulated motor sound, it will sound natural. For example, the sound signal outputter 3 only needs to generate or select a sound signal of an order component that occurs at the rotational speed of the motor 20 before or after switching modes. If the carrier frequency of the asynchronous mode is ψ and the fundamental frequency proportional to the rotational speed of the motor 20 is f, the sound signal outputter 3 only needs to generate or select a sound signal of at least one of the frequencies ψ+3f and ψ-3f before the mode switches to the asynchronous mode, or at the timing when the mode switches from the asynchronous mode to another mode. If the fundamental frequency proportional to the rotational speed of the motor 20 is f and the number of pulses in one period of the fundamental wave is β, the sound signal outputter only needs to generate or select a sound signal of at least one of the frequencies f×(β+3) and f×(β-3) before the mode switches to the synchronous mode, or at the timing when the mode switches from the synchronous mode to another mode. To address the noise caused by intermittently switching PWM control during the rotation of the motor 20, if a speaker 30 or the like reproduces an audio signal with an order component that changes when passing through the switching rotation speed or torque, the sound can be heard continuously without any sense of incongruity even when superimposed on the motor noise, thereby improving the sound quality of sounds that cause unpleasant noise or discomfort.

[0033] Thus, the power converter 10 is a power converter equipped with an inverter that drives and controls the motor 20 by PWM control that switches between multiple modes, and is equipped with a sound signal output device that outputs a sound signal based on at least one of the PWM control information before the mode switching and the PWM control information after the mode switching, at least one of the two states, thereby improving the sound quality of unpleasant noises and sounds that cause discomfort generated from the motor 20.

[0034] Furthermore, since the noise generated from the motor 20 can be predicted at the timing of switching from at least one of the following modes—asynchronous mode operating at a predetermined carrier frequency, synchronous mode operating with a specific number of pulses, two-phase modulation, and three-phase modulation—it can be smoothed by outputting an audio signal. In addition, by acquiring PWM control information and outputting an audio signal generated based on the PWM control information, or selected from a stored audio signal database, at the timing based on the PWM control information, the noise generated from the motor 20 can be masked. By using the mode, number of pulses, and carrier frequency fc of the PWM control, as well as at least one of the rotational speed and torque of the motor 20, the noise generated from the motor 20 can be predicted. Furthermore, by outputting an audio signal at timings other than the mode in which noise is generated, fluctuations in the noise generated from the motor 20 can be masked.

[0035] Furthermore, by outputting a sound signal when the sound signal to be output is an odd multiple of the fundamental frequency f of the motor 20, and not outputting a sound signal or setting the sound signal below the sound threshold when it is an even multiple, the increase in additional volume can be suppressed. In addition, by performing at least one of the following processes: gradually increasing the sound signal towards a mode in which noise above the noise threshold occurs, and gradually decreasing the sound signal after a mode in which noise above the noise threshold occurs, the sound signal output can be made seamless while preventing an increase in the total volume. By stopping or decreasing the increase of the sound signal and outputting the sound signal during a mode in which noise above the noise threshold occurs, the sound signal output can be made seamless. Also, if the fundamental frequency of the motor 20 is f and the number of pulses in one period of the fundamental wave is β, by outputting a sound signal at (β±3)×f and not outputting a sound signal or setting the sound signal below the output sound threshold at (β±1)×f, it is possible to improve sounds that are heard continuously and cause unpleasant noise or discomfort. Furthermore, by outputting an audio signal only when the carrier frequency fc of inverter 1 changes during mode switching, the control by the audio signal control unit 32 can be simplified, and an increase in volume can be suppressed.

[0036] Furthermore, by changing the sound signal output when switching from the first mode to the second mode and the sound signal output when switching from the second mode to the first mode, seamless playback sound can be achieved. In addition, by generating or selecting sound signals of order components that occur according to the rotation speed of the motor 20 before or after switching modes, the sound can be heard continuously without any sense of incongruity even when superimposed on the motor sound, and the sound quality of sounds that cause unpleasant noises or sense of incongruity can be improved. Moreover, if the carrier frequency of the asynchronous mode is ψ and the fundamental wave frequency of the motor 20 is f, the sound signal outputter can generate or select sound signals of at least one of the frequencies ψ+3f and ψ-3f before switching to the asynchronous mode, or at the timing when switching from the asynchronous mode to another mode, so that the sound can be heard continuously without any sense of incongruity even when superimposed on the motor sound, and unpleasant noises or sense of incongruity can be improved. Furthermore, if the fundamental frequency of the motor 20 is f and the number of pulses in one period of the fundamental wave is β, the sound signal output device generates or selects sound signals of at least one of the frequencies f × (β + 3) and f × (β - 3) before the mode switches to the synchronous mode, or at the timing when the mode switches from the synchronous mode to another mode. This allows the sound to be heard continuously without any sense of incongruity even when superimposed on the motor sound, and improves the sound quality of sounds that cause unpleasant noises or discomfort.

[0037] While it is generally sufficient to consider only the fundamental frequency of the modulated wave based on the rotational speed command of the motor 20, harmonics may also be considered in the calculation. Furthermore, when determining the number of pulses, etc., based on the output torque of the motor 20, the torque may be used as PWM control information to determine the timing of outputting the sound signal.

[0038] Embodiment 2. Figure 15 is an explanatory diagram showing an example of mounting the power converter 10 according to Embodiment 2 on a vehicle 40. In the power converter 10 according to Embodiment 2, the inverter 1 is mounted in the engine room of the vehicle 40, for example, where the motor 20 is installed, and the sound signal is reproduced from a speaker 30 in the vehicle interior where the passengers 41 are seated. The other configurations are the same as in Embodiment 1. The speaker 30 is installed, for example, near the driver's seat and the rear seats. The sound signal output by the sound signal outputter 3 of the power converter 10 is a signal for generating sound from the speaker 30. In this way, by reproducing the sound signal from a speaker 30 attached to the vehicle 40 driven by the motor 20, there is no need to provide a separate speaker 30. Furthermore, unpleasant noises and sounds that cause discomfort generated from the motor 20 can be improved, and the ride comfort can be improved. Note that the vehicle 40 may be a passenger car, a railway car, or the like. Furthermore, it is also effective to install the speakers at sites where, for example, a motor 20 for a generator is used, rather than the motor 20 mounted on the vehicle 40. In this case, the speakers 30 should be installed near the generator, near the workers, etc. This can suppress discomfort and unease among workers.

[0039] Embodiment 3. Figure 16 is a schematic diagram of the power converter 10 according to Embodiment 3. The power converter 10 according to Embodiment 3 includes at least one of a PWM-controlled boost circuit 12 and a buck circuit as a voltage conversion circuit for converting DC voltage, and the voltage conversion circuit also serves as an audio signal output device 3. The other configurations are the same as in Embodiment 1 or Embodiment 2. In Figure 16, the drive control device 42, which receives a drive command for the motor 20, issues commands such as a rotation speed command and a torque command to the PWM control unit 13 of the power converter 10. The power converter 10 includes an inverter 11 that drives the motor 20 by PWM control that switches between multiple modes. A boost circuit (DC / DC converter) 12 is provided at the input of the inverter 11, for example. By making the switching frequency of the PWM-controlled boost circuit 12 variable and adjusting this frequency to produce an audio signal, it can be radiated as sound by the magnetostriction and electromagnetic force of the reactor 14, or it can be used to assist the audio signal reproduced by the speaker 30. By using the boost circuit 12 as the sound signal control unit 32 and sound signal output unit 35, and the reactor 14 as the speaker 30, it is not necessary to provide a separate speaker 30. For example, when installed in a vehicle 40, the voltage is boosted according to the driving state of the vehicle 40, but a step-down circuit may also be used.

[0040] Embodiment 4. Figure 17 is a flowchart showing the processing steps of the sound quality improvement method according to Embodiment 4. The sound quality improvement method according to Embodiment 4 is a sound quality improvement method that improves the sound quality of sound generated from a motor 20 driven by PWM control that switches between multiple modes, and improves the sound quality by outputting an audio signal based on at least one of the PWM control information before the mode switching and the PWM control information after the mode switching, and superimposing it on the sound generated from the rotating electric machine. For example, as shown in Figure 17, the PWM control mode, number of pulses, etc. are determined based on the rotation speed command, torque command, etc. of the motor 20 (step S101). Then, PWM control information before and after the mode switching, including the PWM control mode switching information, is acquired (step S102). Then, an audio signal is generated based on the PWM control information, or the corresponding audio signal is selected from the stored audio signals (step S103). Then, power conversion is performed based on the determined mode, number of pulses, etc., to drive the motor 20 (step S104). Then, an audio signal is output and superimposed on the sound generated by the motor 20 (step S105).

[0041] The devices and data exchange methods constituting the power converter 10 are not limited to the examples described above, but the power converter 10 is provided with a communication interface 903, a processor 901, and a memory 902, for example, as shown in Figure 18. For example, a CPU (Central Processing Unit) is used for the processor 901. The memory 902 sends and receives data with the processor 901 and stores the data. Motor 20 rotation speed commands, torque commands, etc. are acquired via the communication interface 903. Each process, such as calculation of control mode and pulse count by the PWM signal controller 2, control by the sound signal control unit 32, and sound signal generation by the sound signal generation unit 33, is executed by the processor 901. Sound signal output maps, calculation formulas, etc. are stored in the memory 902.

[0042] The processor 901 and the memory 902 may be shared for use as a single unit, or a plurality of the processor 901 and the memory 902 may be provided. Further, the processor 901 may be provided with logic circuits using, for example, ASIC (Application Specific Integrated Circuit), IC (Integrated Circuit), DSP (Digital Signal Processor), FPGA (Field Programmable Gate Array), etc., and various signal processing circuits. By providing a plurality of processors 901 of the same type or different types, each process may be shared and executed by a plurality of arithmetic processing units.

[0043] The plurality of memories 902 include, for example, a RAM (Random Access Memory) configured to enable reading and writing of data from the processor 901, a ROM (Read Only Memory) configured to enable reading of data from the processor 901, and the like.

[0044] Each function of the power conversion device 10 is realized by the processor 901 executing software or a program stored in the memory 902 and cooperating with hardware. The set data may be stored in the memory 902 as part of the software or program, or may be input by a user. A non-transitory recording medium 905 having the sound quality improvement program 904 recorded thereon may be distributed and installed in the power conversion device 10 (the memory 902).

[0045] As described above, at least one of before and after switching of the PWM control mode, a sound signal is output based on at least one of PWM control information before mode switching and PWM control information after mode switching, and is superimposed on a sound generated from the motor 20, whereby unpleasant sounds and sounds that cause a sense of discomfort can be improved.

[0046] While this disclosure describes various exemplary embodiments, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but are applicable individually or in various combinations to the embodiments. Therefore, countless variations not illustrated are conceivable within the scope of the art disclosed herein. These include, for example, modifying, adding, or omitting at least one component, or even extracting at least one component and combining it with components from other embodiments.

[0047] 1, 11 Inverter, 2 PWM signal controller, 3 Sound signal outputter, 10 Power converter, 12 Boost circuit, 13 PWM control unit, 14 Reactor, 20 Motor, 30 Speaker, 31 Control information acquisition unit, 32 Sound signal control unit, 33 Sound signal generation unit, 34 Sound signal storage unit, 35 Sound signal output unit, 40 Vehicle, 41 Passenger, 42 Drive control device

Claims

1. A power converter equipped with an inverter that drives and controls a rotating electric machine by PWM control that switches between multiple modes, the power converter further equipped with an audio signal outputter that outputs an audio signal based on at least one of the PWM control information before the mode switching and the PWM control information after the mode switching, at least one of the two of the two.

2. The power converter according to claim 1, wherein the switching of the multiple modes is a switching from at least one of asynchronous mode operating at a predetermined carrier frequency, synchronous mode operating with a specific number of pulses, two-phase modulation, and three-phase modulation.

3. The power conversion device according to claim 1 or 2, wherein the sound signal output device acquires the PWM control information and outputs the sound signal generated or selected from a sound signal database stored based on the PWM control information at a timing based on the PWM control information.

4. The power converter according to any one of claims 1 to 3, wherein the PWM control information is at least one of the mode, number of pulses, and carrier frequency of the PWM control, and the rotational speed and torque of the rotating electric machine.

5. The power conversion device according to any one of claims 1 to 4, wherein the sound signal outputter outputs the sound signal at a timing other than the mode in which noise exceeding the noise threshold occurs based on the PWM control information.

6. The power conversion device according to any one of claims 1 to 5, wherein the sound signal output device performs at least one of the following processes: gradually increasing the sound signal toward the mode in which noise above a noise threshold occurs, and gradually decreasing the sound signal after the mode in which noise above a noise threshold occurs.

7. The power conversion device according to any one of claims 1 to 6, wherein the sound signal outputter stops or reduces the increase of the sound signal and outputs the sound signal during the mode in which noise above a noise threshold occurs.

8. The power conversion device according to any one of claims 1 to 7, wherein the sound signal outputter outputs the sound signal when the sound signal to be output is an odd multiple of the fundamental frequency of the AC that drives the rotating electric machine, and does not output the sound signal or reduces the sound signal to a sound threshold when it is an even multiple.

9. The power conversion device according to any one of claims 1 to 7, wherein the sound signal outputter outputs the sound signal when the sound signal to be output is (β±3)×f, given that the fundamental frequency of the AC driving the rotating electric machine is f and the number of pulses in one period of the fundamental wave is β, and does not output the sound signal or reduces the sound signal to less than the output sound threshold when the sound signal to be output is (β±1)×f.

10. The power conversion device according to any one of claims 1 to 7, wherein the sound signal outputter outputs the sound signal only when the carrier frequency of the inverter changes during the mode switching.

11. The power converter according to any one of claims 1 to 7, wherein the sound signal outputter outputs a modified sound signal when the mode is switched from the first mode to the second mode, and a modified sound signal when the mode is switched from the second mode to the first mode.

12. The power conversion device according to any one of claims 1 to 7, wherein the sound signal output device generates or selects the sound signal of an order component that is generated according to the rotational speed of the rotating electric machine before or after switching the mode.

13. The power converter according to any one of claims 1 to 7, wherein, when the carrier frequency in asynchronous mode is ψ and the fundamental frequency of the AC driving the rotating electric machine is f, the sound signal output device generates or selects the sound signal with a frequency of at least one of ψ+3f and ψ-3f before the mode switches to asynchronous mode or at the timing of switching from asynchronous mode to another mode.

14. The power converter according to any one of claims 1 to 7, wherein, when the fundamental frequency of the AC that drives the rotating electric machine is f and the number of pulses in one period of the fundamental wave is β, the sound signal output device generates or selects at least one of the sound signals f × (β + 3) and f × (β - 3) before the mode switches to the synchronous mode, or at the timing when the mode switches from the synchronous mode to another mode.

15. The power conversion device according to any one of claims 1 to 14, wherein the sound signal is a signal for generating sound from a speaker.

16. The power conversion device according to claim 15, wherein the inverter is mounted on a vehicle and the sound signal is reproduced from a speaker inside the vehicle.

17. A power conversion device according to any one of claims 1 to 16, comprising at least one of a PWM-controlled boost circuit and a buck circuit as a voltage conversion circuit for converting a DC voltage, wherein the voltage conversion circuit also serves as the sound signal output device.

18. A sound quality improvement method for improving the sound quality of a sound generated from a rotating electric machine driven by PWM control that switches between multiple modes, wherein, at least one of the PWM control information before the mode switching and the PWM control information after the mode switching is output based on the sound signal, and the sound quality is improved by superimposing the sound signal on the sound generated from the rotating electric machine.

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