EMI reduction circuit for power conversion device, power conversion device, EMI reduction method, and EMI reduction program

Abstract

In a power conversion device in which a pair of PWM signals is input to a differential circuit connected to a load, EMI is reduced while preventing a decrease in the operational accuracy of the load. The EMI reduction circuit includes a spreading code generator that generates a spreading code indicating a first or second logical value in synchronization with a PWM update period, and a modulator that does not modulate a pair of PWM signals when the spreading code is the first value and modulates the pair of PWM signals when the spreading code is the second value. The modulation includes exchanging the values ​​of the pair of PWM signals with each other and inverting the value of each of the pair of PWM signals.

Description

[Technical Field]

[0001] The present disclosure relates to an EMI reduction circuit for a power conversion device, a power conversion device, an EMI reduction method, and an EMI reduction program. [Background technology]

[0002] Patent Document 1 discloses an audio playback device that drives a speaker in response to an audio signal to play back audio. In this device, even if the audio signal contains audible noise, the noise is removed by differentiating two synchronously generated PWM signals in an H-bridge circuit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-61657 Summary of the Invention [Problem to be solved by the invention]

[0004] PWM signals are periodic square waves with steep rises and falls, resulting in a high number of harmonic components. Wiring carrying harmonic currents acts as an antenna, generating electromagnetic interference (EMI). In audio signal playback environments, the wiring between the speaker and the pulse generator (a digital amplifier that generates the PWM signal) tends to be long, making EMI a particularly significant problem. A common EMI countermeasure is to use a low-pass filter to attenuate harmonic components, but this method entails issues such as increased cost, mounting space, and weight due to the additional components. Furthermore, spreading the carrier frequency using spread spectrum generation (SSG) technology can reduce the reproduction of the audio signal from the sound source at the speaker, potentially resulting in a degradation of sound quality. The same problem occurs when an electric motor is used as a load instead of a speaker, potentially reducing the control accuracy of the electric motor.

[0005] An object of the present disclosure is to reduce EMI while preventing a decrease in the operational accuracy of a load in a power conversion device that inputs a pair of PWM signals to a differential circuit connected to a load. [Means for solving the problem]

[0006] In order to solve the above problems, an EMI reduction circuit of a power conversion device according to one embodiment of the present disclosure is a circuit for reducing EMI in a power conversion device that includes a pulse generator that generates a pair of PWM signals and a differential circuit that converts power in accordance with the pair of PWM signals and supplies the power to a load, and includes: a spreading code generator that generates a spreading code indicating a logical value of a first value or a second value in synchronization with a PWM update period; and a modulator that does not modulate the pair of PWM signals when the spreading code is the first value, and modulates the pair of PWM signals when the spreading code is the second value, wherein the modulation includes exchanging the values ​​of the pair of PWM signals with each other and inverting the values ​​of each of the pair of PWM signals. [Effects of the Invention]

[0007] According to the present disclosure, in a power conversion device in which a pair of PWM signals is input to a differential circuit connected to a load, it is possible to reduce EMI while preventing a decrease in the operational accuracy of the load. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram showing the configuration of a power conversion device according to the first embodiment. [Figure 2] FIG. 2 is a circuit diagram showing an H-bridge circuit of the power conversion device of FIG. [Figure 3] Fig. 3(A) is a timing chart showing signals of a power conversion device of a comparative example, and Fig. 3(B) is a timing chart showing signals of the power conversion device of Fig. 1 . [Figure 4]Fig. 4(A) is a diagram showing the frequency spectrum of noise on the transmission line of the power conversion device of the comparative example corresponding to Fig. 3(A). Fig. 4(B) is a diagram showing the frequency spectrum of noise on the transmission line of the power conversion device of Fig. 1. [Figure 5] FIG. 10 is a block diagram showing the configuration of a power conversion device according to a second embodiment. [Figure 6] FIG. 10 is a block diagram showing the configuration of a power conversion device according to a third embodiment. [Figure 7] Fig. 7(A) is a logic circuit diagram of a modulator of the power conversion device of Fig. 6. Fig. 7(B) is a diagram showing a truth table of the logic circuit diagram of Fig. 7(A). [Figure 8] FIG. 10 is a block diagram showing the configuration of a power conversion device according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In all figures describing the embodiments, common components are designated by the same reference numerals, and repeated description will be omitted. Note that the following embodiments do not unduly limit the content of the present disclosure described in the claims. Furthermore, not all components shown in the embodiments are necessarily essential components of the present disclosure. Furthermore, each figure is a schematic diagram and is not necessarily an exact illustration. Furthermore, in the following description, when similar elements are described without distinction, reference numerals (or common reference numerals among reference numerals) may be used, and when similar elements are described with distinction, element identification numbers (or reference numerals) may be used. Furthermore, in the following description, control lines and information lines are indicated as those considered necessary for the description, and do not necessarily represent all control lines and information lines in the product. All components may be interconnected.

[0010] (First embodiment) This embodiment is an example in which the present disclosure is applied to an audio playback device that converts an audio signal into a PWM signal to drive a speaker.

[0011] <Summary> The power conversion device 1 according to this embodiment reduces EMI (electromagnetic interference) caused by the transmission of PWM signals. Specifically, the signal processing device 10 synchronously generates a pair of PWM signals p and m based on an audio signal d from a PCM sound source 2. In the EMI reduction circuit 19, a spreading code generator 12s generates a spreading code s synchronized with the PWM update period, and a modulator 18 performs secondary modulation by inverting and exchanging the logical values ​​of the pair of PWM signals p and m according to the value of the spreading code s. The modulated PWM signals sp and sm are input to an H-bridge circuit 20. The H-bridge circuit 20 differentiates the pair of modulated PWM signals sp and sm and performs switching according to the modulated PWM signals sp and sm to adjust the voltage of the power that drives the speaker 30. The secondary modulation disrupts the periodicity of the PWM signals on the transmission path, reducing noise peaks. Because the secondary modulation is performed by inversion and exchanging, the differential component of the pair of PWM signals is not affected by the secondary modulation, preventing degradation of sound quality.

[0012] <System configuration> FIG. 1 is a block diagram showing the configuration of a power conversion device 1 according to this embodiment. As shown in FIG. 1, the power conversion device 1 constitutes an audio reproduction device that drives a speaker 30 in response to an audio signal d from an audio source 2 to reproduce audio. Generally, the audio signal d is a control signal that commands the operation of the speaker 30, which is a load. The power conversion device 1 adjusts the voltage of load drive power supplied from a power supply to the speaker 30, which is a load, in response to the audio signal d from the audio source 2. Specifically, the power conversion device 1 includes a signal processing device 10 and an H-bridge circuit 20 connected to the output side of the signal processing device 10. The H-bridge circuit 20 is an example of a differential circuit that converts power in response to a pair of PWM signals from the signal processing device 10 and supplies the power to the speaker 30. The H-bridge circuit 20 is adjacent to the signal processing device 10 from the output side. That is, the H-bridge circuit 20 is located immediately downstream of the signal processing device 10. The H-bridge circuit 20 is connected to the speaker 30 via a cable 29, which is a transmission path. In this embodiment, a low-pass filter is omitted from the transmission path between the H-bridge circuit 20 and the speaker 30, but a low-pass filter may be provided.

[0013] The signal processing device 10 is realized by, for example, a microcomputer, which is a general-purpose MCU (Micro Controller Unit). The signal processing device 10 acquires an audio signal d output from a sound source 2, performs secondary modulation to generate a pair of modulated PWM signals (sp, sm), and outputs them to an H-bridge circuit 20. The signal processing device 10 includes a timing generation unit 11, two duty calculators 12p, 12m, two pulse generators 13p, 13m, and an EMI reduction circuit 19.

[0014] The timing generator 11 generates a clock signal that is the basis for the carrier frequency and sampling rate of the PWM signal, and defines the sampling time t. In other words, the timing generator 11 determines the PWM update period.

[0015] The duty calculation units 12p and 12m calculate the duty ratios dp and dm (e.g., dp=50+d(%), dm=50-d(%)) of the pair of PWM signals p and m, respectively, based on the amplitude level (e.g., in the range of -50% to +50%) of the audio signal d at the sampling time t.

[0016] The pulse generators 13p and 13m generate a pair of PWM signals p and m based on a PWM update period determined by the sampling time t. The PWM signals p and m have a duty ratio determined based on the audio signal to the speaker 30. The pulse generator 13p generates a PWM signal p in accordance with the duty ratio dp calculated by the duty calculation unit 13p. The pulse generator 13m generates a PWM signal m in accordance with the duty ratio dm calculated by the duty calculation unit 13m. The pair of PWM signals p and m are Boolean variables that take on a logical value of 0 or 1. The duty calculation units 12p and 12m and the pulse generators 13p and 13m perform primary modulation on the audio signal d.

[0017] The EMI reduction circuit 19 reduces EMI by performing secondary modulation on the pair of PWM signals p and m. The EMI reduction circuit 19 includes a spreading code generator 12s and a modulator 18. The modulator 18 is disposed on the output side of the pulse generators 13p and 13m.

[0018] The spreading code generator 12s generates a spreading code s in synchronization with a PWM update period determined by the sampling time t. The spreading code s is a random number sequence or a pseudo-random number sequence that takes on a logical value of 0 (first value) or 1 (second value). The spreading code generator 12s can use a linear feedback shift register that generates M-sequence random numbers.

[0019] The modulator 18 modulates a pair of PWM signals p and m based on the spreading code s. The modulator 18 does not perform modulation when the spreading code s is 0, and performs modulation when the spreading code s is 1. The modulator 18 has an exchange unit 16, inverters 14m and 14p, and selectors 15p and 15m. The exchange unit 16 exchanges the values ​​of the pair of PWM signals p and m with each other. The inverters 14p and 14m output values ​​(1-m, 1-p) obtained by inverting the values ​​of the PWM signals exchanged by the exchange unit 16. That is, the inverter 14p outputs a value (1-m) obtained by inverting the value of the PWM signal m exchanged by the exchange unit 16, and the inverter 14m outputs a value (1-p) obtained by inverting the value of the PWM signal p exchanged by the exchange unit 16.

[0020] When the spreading code s is 0, the selection units 15p and 15m output the PWM signals from the pulse generators 13p and 13m to the H-bridge circuit 20, and when the spreading code s is 1, the selection units 15p and 15m output the PWM signals that have passed through the exchange unit 16 and the inversion units 14m and 14p to the H-bridge circuit 20. That is, when the spreading code is 0, the modulator 18 does not modulate the pair of PWM signals from the pulse generators 13p and 13m, but modulates the pair of PWM signals from the pulse generators 13p and 13m when the spreading code s is 1. The H-bridge circuit 20 operates based on the modulated PWM signals sp and sm output from the modulator 18. The H-bridge circuit 20 is interposed between the speaker 30 and a power supply for driving the speaker 30.

[0021] Fig. 2 is a circuit diagram showing the H-bridge circuit 20 of the power conversion device 1 of Fig. 1. As shown in Fig. 2, the H-bridge circuit 20 is a circuit in which four switching elements SW1, SW2, SW3, and SW4 are connected in an H configuration. The H-bridge circuit 20 outputs a load drive voltage V(sp-sm) that drives the speaker 30 based on a pair of modulated PWM signals sp and sm input from the signal processing device 10. The speaker 30 vibrates a diaphragm in accordance with the load drive voltage V(sp-sm) to reproduce sound.

[0022] In the circuit on one side of the H-bridge circuit 20, when the PWM signal sp is 1, the switch SW1 is on (closed) and the switch SW2 is off (open), and when the PWM signal sp is 0, the switch SW1 is off (open) and the switch SW2 is on (closed). In the circuit on the other side of the H-bridge circuit 20, when the PWM signal sm is 1, the switch SW3 is on (closed) and the switch SW4 is off (open), and when the PWM signal sm is 0, the switch SW3 is off (open) and the switch SW4 is on (closed). For example, in the circuit in which the PWM signal sp operates the switches SW1 and SW2, an inverting circuit (NOT gate circuit) may be arranged in the portion that operates the switch SW2, and in the circuit in which the PWM signal sm operates the switches SW3 and SW4, an inverting circuit (NOT gate circuit) may be arranged in the portion that operates the switch SW4. A typical H-bridge circuit may include a dead time generation circuit that prevents both switches SW1 and SW2 (or SW3 and SW4) from being turned on simultaneously, in order to prevent the load drive voltage V from being short-circuited to ground (GND) and an overcurrent (through current) from flowing when both switches SW1 and SW2, or both switches SW3 and SW4, are turned on (closed) simultaneously; however, a description of this circuit is omitted from FIG. 2.

[0023] According to the H-bridge circuit 20, the speaker 30 reproduces sound based on the differential component (pm) of the pair of modulated PWM signals sp, sm. In-phase noise components contained in the pair of modulated PWM signals sp, sm are canceled out and not reproduced. Furthermore, in this embodiment, the modulator 18 performs secondary modulation on the pair of PWM signals p, m by inversion and exchange, so that the differential component (sp-sm) of the pair of modulated PWM signals sp, sm after secondary modulation is the same as the differential component (pm) of the pair of PWM signals p, m before secondary modulation, preventing deterioration of sound quality.

[0024] FIG. 3A is a timing chart showing signals of a power conversion device of a comparative example. As shown in FIG. 3A, in the comparative example in which secondary modulation is not applied, the pair of PWM signals p and m are periodic square waves whose duty ratio changes according to the amplitude of the audio signal. The drive voltage applied to both ends of the speaker 30 is the voltage V(pm) across the load that is proportional to the differential component (pm) of the pair of PWM signals p and m. During silent periods, the duty ratios of the pair of PWM signals p and m are both 50%, and the differential component (pm) is zero. During sound output periods, a difference occurs between the duty ratios of the pair of PWM signals p and m, and the differential component (pm) reproduces the audio waveform.

[0025] Here, the radiation component (p+m) of PWM signals p and m is a cause of EMI. The radiation component (p+m) of PWM signals p and m has a periodicity that contains strong harmonic components that are integer multiples of the carrier frequency fs of PWM signals p and m, regardless of whether an audio signal is present. This periodicity causes noise with energy concentrated at specific frequencies.

[0026] FIG. 3B is a timing chart showing signals in the power conversion device 1 of FIG. 1. As shown in FIG. 3B, in the power conversion device 1 according to this embodiment, the spreading code generator 12s generates a random spreading code s (0, 1, 1, 0, . . . ) in synchronization with the PWM period fs. The modulator 18 exchanges and inverts a pair of PWM signals p and m when s = 1 to generate modulated PWM signals sp and sm. The drive voltage across the speaker 30 is proportional to the differential component (sp - sm) between the modulated PWM signals sp and sm. This differential component (sp - sm) is always equal to the differential component (pm) before modulation, regardless of the value of the spreading code s. Therefore, the voltage across the load (sp - sm) in FIG. 3B is the same as the voltage across the load (pm) in FIG. 3A, and the secondary modulation by the modulator 18 does not affect the quality of the sound reproduced from the speaker 30. On the other hand, the periodicity of the radiation component (sp+sm) of the modulated PWM signals sp and sm is disrupted by the influence of the random spreading code s.

[0027] Furthermore, in the case of FIG. 3(B), at the point where the spreading code s changes from 0 to 1 or from 1 to 0, the modulated PWM signal sp and the modulated PWM signal sm become continuous waveforms on the time axis, and no switching occurs in the H-bridge circuit 20. Therefore, compared to the case of FIG. 3(A), the power required for switching in the H-bridge circuit 20, i.e., the switching loss, is reduced.

[0028] Figure 4(A) is a diagram showing the frequency spectrum of noise on the transmission line of a power conversion device of a comparative example corresponding to Figure 3(A). As shown in Figure 4(A), in the simulation results of the comparative example in which secondary modulation is not applied, noise with concentrated energy was generated in the harmonic components that are integer multiples of the carrier frequency fs of the PWM signals p and m. This is the cause of EMI.

[0029] Fig. 4(B) is a diagram showing the frequency spectrum of noise on the transmission path of the power conversion device 1 of Fig. 1. As shown in Fig. 4(B), in the simulation results of the power conversion device 1 of this embodiment, energy in harmonic components that are integer multiples of the carrier frequency fs of the PWM signals p and m is dispersed to nearby frequency bands, and the peak level of the energy is significantly reduced (by 22 dB in the simulation).

[0030] <Summary> According to the configuration described above, secondary modulation using spread code s can disrupt the periodicity of radiation components on the transmission line, effectively reducing EMI. This secondary modulation performs exchange and inversion on a pair of PWM signals, so it does not affect the differential voltage applied to speaker 30 and does not degrade sound quality. In addition, it can eliminate or simplify low-pass filters, which were previously required, providing advantages in terms of cost, size, and weight.

[0031] (Second embodiment) Fig. 5 is a block diagram showing the configuration of a power conversion device 101 according to the second embodiment. As shown in Fig. 5, in the power conversion device 101 according to the second embodiment, "exchange" in the secondary modulation of a pair of PWM signals is performed on the input side of pulse generators 13p and 13m, and "inversion" is performed on the output side of pulse generators 13p and 13m. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0032] The signal processing device 110 of the power conversion device 101 includes an EMI reduction circuit 119. The EMI reduction circuit 119 includes a spreading code generator 12s and a modulator 118.

[0033] The modulator 118 modulates a pair of PWM signals p and m based on the spreading code s. The modulator 118 includes an exchange unit 16, selection units 15p and 15m, and inversion units 14p and 14m. The group of the exchange unit 16 and the selection units 15p and 15m is disposed on the input side of the pulse generators 13p and 13m. Specifically, the group of the exchange unit 16 and the selection units 15p and 15m is disposed between the duty calculators 12p and 12m and the pulse generators 13p and 13m.

[0034] The group of the exchange unit 16 and the selection units 15p and 15m exchanges the values ​​of the signals dp and dm input from the duty calculators 12p and 12m to the pulse generators 13p and 13m, respectively, based on the spreading code s.

[0035] For example, the exchange unit 16 exchanges the values ​​of the signals dp and dm input from the duty calculators 12p and 12m to the pulse generators 13p and 13m, respectively. When the spreading code s is 0, the selection units 15p and 15m input the signals dp and dm from the duty calculators 12p and 12m to the pulse generators 13p and 13m, respectively. When the spreading code s is 0, the selection units 15p and 15m input the signals dp and dm from the duty calculators 12p and 12m to the pulse generators 13p and 13m without exchanging them, and when the spreading code s is 1, the selection units 15p and 15m exchange the values ​​of the signals dp and dm from the duty calculators 12p and 12m with each other and input them to the pulse generators 13p and 13m, respectively.

[0036] The inverters 14p and 14m are arranged on the output side of the pulse generators 13p and 13m. Specifically, the inverters 14p and 14m are arranged between the pulse generators 13p and 13m and the H-bridge circuit 20. The inverters 14p and 14m invert the values ​​of the pair of PWM signals output by the pulse generators 13p and 13m based on the spreading code s. For example, when the spreading code s is 0, the inverters 14p and 14m output the pair of PWM signals from the pulse generators 13p and 13m to the H-bridge circuit 20, and when the spreading code s is 1, the inverters 14p and 14m invert the values ​​of the pair of PWM signals from the pulse generators 13p and 13m and output them to the H-bridge circuit 20.

[0037] In this way, the inversion by the inversion units 14p and 14m is synchronized with the switching by the switching unit 16 and the group of selection units 15p and 15m based on the spreading code s. The modulator 118 does not modulate the pair of PWM signals of the pulse generators 13p and 13m when the spreading code s is 0, but modulates the pair of PWM signals of the pulse generators 13p and 13m by switching and inversion when the spreading code s is 1.

[0038] The above configuration also makes it possible to reduce EMI while preventing deterioration in the quality of the sound reproduced by the speaker 30. Note that the inverters 14p and 14m may be implemented as hardware, while the exchange unit 16 and the selectors 15p and 15m may be implemented as software. In this case, the modulator 118 can be easily implemented in a microcomputer.

[0039] (Third embodiment) Fig. 6 is a block diagram showing the configuration of a power conversion device 201 according to the third embodiment. As shown in Fig. 6, in the power conversion device 201 of the third embodiment, modulators 18p and 18m that perform secondary modulation are arranged outside a signal processing device 210. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0040] The power conversion device 201 includes an EMI reduction circuit 219. The EMI reduction circuit 219 includes a spreading code generator 12s arranged inside a signal processing device 210, and modulators 18p and 18m arranged outside the signal processing device 210. The signal processing device 210 is, for example, a microcomputer 210. The modulators 18p and 18m are arranged on a transmission path between the signal processing device 210 and the H-bridge circuit 20. The modulators 18p and 18m do not perform secondary modulation when the spreading code s is 0, and perform secondary modulation when the spreading code s is 1.

[0041] FIG. 7(A) is a logic circuit diagram of modulators 18p, 18m of power conversion device 201 of FIG. 6. FIG. 7(B) is a diagram showing a truth table of the logic circuit diagram of FIG. 7(A). Note that the circuit diagram of FIG. 7(A) is merely an example, and other embodiments may be used. A deglitch circuit for preventing signal glitches may be added to FIG. 7(A). As shown in FIGS. 6 and 7(A) and 7(B), in modulator 18p that generates modulated PWM signal sp, by inputting PWM signal p to input In0, PWM signal m to input In1, and spreading code s to input In2, modulated PWM signal sp corresponding to sp=(1-s)·p+s·(1-m) can be obtained from output Y. Similarly, modulator 18m that generates modulated PWM signal sm receives PWM signal m at input In0, PWM signal p at input In1, and spreading code s at input In2, and can obtain modulated PWM signal sm equivalent to sm = (1 - s) m + s (1 - p) from output Y. That is, modulators 18p and 18m exchange the values ​​of the pair of PWM signals p and m with each other and invert the values ​​of each of PWM signals p and m.

[0042] According to the above configuration, the spreading code generator 12s is arranged inside the signal processing device 210, while the modulators 18p and 18m can be realized by logic ICs external to the signal processing device 210. Therefore, an EMI reduction function can be easily realized by adding an external logic circuit without making major changes to an existing signal processing device.

[0043] (Fourth embodiment) Fig. 8 is a block diagram showing the configuration of a power conversion device 301 according to a fourth embodiment. As shown in Fig. 5, in the first embodiment, a speaker 30 is used as the load, but in the fourth embodiment, an electric motor 330 is used as the load. Suitable examples of such an electric motor 330 include a brushed motor and a stepping motor. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0044] In the power conversion device 301, what is input to the signal processing device 310 is not an audio signal from a sound source, but a control signal d and a stop signal sz from the motor controller 302. The power conversion device 301 constitutes a motor drive device that drives the electric motor 330 in accordance with the control signal d from the motor controller 302. The power conversion device 301 adjusts the voltage of the load drive power supplied from the power source to the electric motor 330 in accordance with the control signal d from the motor controller 302. The control signal d is a signal that commands the operation of the electric motor 330, which is the load.

[0045] The duty calculation units 12p and 12m of the signal processing device 310 calculate the duty ratios dp and dm (e.g., dp=50+d(%), dm=50-d(%)) of the pair of PWM signals p and m, respectively, based on the amplitude level (e.g., in the range of -50% to +50%) of the control signal d at the sampling time t.

[0046] The positive or negative direction of the control signal d determines the forward or reverse rotation of the electric motor 330, and the amplitude of the control signal d determines the duty ratio of the PWM signals p and m. The PWM signals p and m are generated based on the control signal d for the electric motor 330. This controls the rotation direction and speed of the electric motor 330. The secondary modulation by the EMI reduction circuit 19 functions to reduce EMI when the electric motor 330 is driven in the same way as in the first embodiment.

[0047] An H-bridge circuit device 22 is interposed in the transmission path between the signal processing device 310 and the electric motor 330. The H-bridge circuit device 22 includes an H-bridge circuit 20 and a switching control logic circuit 21 that controls the switches SW1, SW2, SW3, and SW of the H-bridge circuit 20. The switching control logic circuit 21 controls one side of the H-bridge circuit 20 so that, when the PWM signal sp is 1, the switch SW1 is on (closed) and the switch SW2 is off (open), and when the PWM signal sp is 0, the switch SW1 is off (open) and the switch SW2 is on (closed). In the other side of the H-bridge circuit 20, when the PWM signal sm is 1, the switch SW3 is on (closed) and the switch SW4 is off (open), and when the PWM signal sm is 0, the switch SW3 is off (open) and the switch SW4 is on (closed). Note that the switching control logic circuit 21 can also be used for the H-bridge circuit 20 in the configurations of FIGS. 1 and 5 .

[0048] The stop signal sz from the motor controller 302 is input to the switching control logic circuit 21 of the H-bridge circuit device 22, which stops the power supply to the electric motor 330. When the stop signal sz is 1 (stopped state), all four switches sw1 to sw4 of the H-bridge circuit 20 are turned off, regardless of the values ​​of the modulated PWM signals sp and sm. Note that the other configurations are the same as those of the first embodiment, so detailed description will be omitted.

[0049] According to the above configuration, it is possible to reduce EMI without impairing the control accuracy of the electric motor 330, even in various motor drive devices that use PWM signals and H-bridge circuits.

[0050] (Variation) The power conversion device of the present disclosure is not limited to the above-described embodiments. The load to which the power conversion device is applied is not limited to a speaker or an electric motor, and may be any other device that is driven by power converted using a differential circuit controlled by a pair of PWM signals. Furthermore, instead of a switching circuit controlled by digital values ​​using the H-bridge circuit 20 as a differential circuit, an analog circuit such as a class A amplifier, a class B amplifier, a class AB amplifier, or an operational amplifier may be used.

[0051] In the first and fourth embodiments, the exchanging unit 16 is arranged on the input side of the inverters 14p and 14m, but the exchanging unit 16 may also be arranged on the output side of the inverters 14p and 14m. That is, the exchanging unit 16 may be arranged so as to exchange the values ​​(1-p) and (1-m) obtained by inverting the values ​​of the pair of PWM signals 14p and 14m with each other.

[0052] In the second embodiment, the group of exchanging unit 16 and selecting units 15p, 15m is arranged on the input side of pulse generators 13p, 13m, and inverting units 14p, 14m is arranged on the output side of pulse generators 13p, 13m, but this may be reversed. That is, the inverting units 14p, 14m may be arranged on the input side of pulse generators 13p, 13m, and the group of exchanging unit 16 and selecting units 15p, 15m may be arranged on the output side of pulse generators 13p, 13m.

[0053] In the embodiments of Figures 1, 5 and 8, a configuration in which exchange and inversion are performed sequentially on a PWM signal is illustrated, but a configuration in which exchange and inversion are performed together, such as modulators 18p and 18m in Figure 6, may also be adopted.

[0054] The spreading code generator 12s may be configured to prevent the same logical value from being generated consecutively more than a predetermined number of times. For example, the spreading code generator 12s may be configured to count the number of consecutive occurrences of the same logical value, determine whether the number of consecutive occurrences exceeds a predetermined threshold, and change the logical value to be generated if the number of consecutive occurrences exceeds the predetermined threshold. This effectively reduces the peak energy levels of the harmonic components of the PWM signals p and m.

[0055] Furthermore, each functional block in the above-described embodiment may be implemented as a hardware circuit, or may be a processing circuit realized by a processor executing a software program. For example, in the configuration of Fig. 1, all or at least a part of the circuit configuration of the signal processing device 10 may be realized by a processor executing a program. As an example, among the circuit configuration of the signal processing device 10, the timing generator 11 and the pulse generators 13p, 13m may be realized as hardware circuits, and the other components (duty calculators 12p, 12m, spread code generator 12s, and modulator 18) may be realized by a processor executing a program.

[0056] The functions performed by the components described herein may be implemented in circuitry or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), a Central Processing Unit (CPU), an FPGA (Field-Programmable Gate Array), conventional circuitry, and / or combinations thereof, programmed to perform the described functions. A processor includes transistors and other circuits and is considered to be circuitry or processing circuitry. A processor may also be a programmed processor that executes programs stored in memory.

[0057] In this specification, a circuitry, unit, or means is hardware that is programmed to realize or performs the described functions, which may be any hardware disclosed herein or any hardware known to be programmed to realize or perform the described functions.

[0058] If the hardware is a processor considered to be a type of circuitry, the circuitry, means, or unit is a combination of the hardware and software used to configure the hardware and / or processor.

[0059] (Addendum) The matters described in the above embodiments will be supplemented below.

[0060] (Appendix 1) A circuit for reducing EMI in a power conversion device including a pulse generator that generates a pair of PWM signals and a differential circuit that converts power in accordance with the pair of PWM signals and supplies the power to a load, the EMI reduction circuit for the power conversion device including: a spreading code generator that generates a spreading code indicating a logical value of a first value or a second value in synchronization with a PWM update period; and a modulator that does not modulate the pair of PWM signals when the spreading code is the first value and modulates the pair of PWM signals when the spreading code is the second value, wherein the modulation includes exchanging the values ​​of the pair of PWM signals with each other and inverting the value of each of the pair of PWM signals.

[0061] (Appendix 2) 2. The EMI reduction circuit of claim 1, wherein the modulator is disposed on the output side of the pulse generator.

[0062] (Appendix 3) 2. The EMI reduction circuit for a power conversion device according to claim 1, wherein the modulator includes an exchange unit that exchanges values ​​of the pair of PWM signals with each other and an inversion unit that inverts the value of each of the pair of PWM signals, one of the exchange unit or the inversion unit being arranged on the input side of the pulse generator, and the other of the exchange unit or the inversion unit being arranged on the output side of the pulse generator.

[0063] (Appendix 4) 3. The EMI reduction circuit for a power conversion device according to claim 1 or 2, wherein the power conversion device includes a microcomputer including a pulse generator that generates a pair of PWM signals, the differential circuit is disposed between the microcomputer and a load, and the modulator is disposed between the microcomputer and the differential circuit.

[0064] (Appendix 5) 5. The EMI reduction circuit for a power conversion device according to any one of appendixes 1 to 4, wherein the power conversion device does not have a low-pass filter between the differential circuit and the load.

[0065] (Appendix 6) 6. The EMI reduction circuit of a power conversion device according to any one of appendixes 1 to 5, wherein the spreading code generator generates a spreading code using a random number sequence or a pseudo-random number sequence generated in synchronization with a PWM update period.

[0066] (Appendix 7) 7. The EMI reduction circuit of a power conversion device according to any one of appendixes 1 to 6, wherein the PWM signal has a duty ratio determined based on a signal that commands the operation of the load.

[0067] (Appendix 8) 8. The EMI reduction circuit of a power conversion device according to any one of appendices 1 to 7, wherein the load is a speaker, and the PWM signal is a signal generated based on an audio signal for the speaker.

[0068] (Appendix 9) 8. The EMI reduction circuit for a power conversion device according to any one of appendices 1 to 7, wherein the load is an electric motor, and the PWM signal is a signal generated based on a control signal for the electric motor.

[0069] (Appendix 10) A power conversion device comprising: a pulse generator that generates a pair of PWM signals; a differential circuit that converts power in accordance with the pair of PWM signals and supplies the power to a load; a spreading code generator that generates a spreading code indicating a first or second logical value in synchronization with a PWM update period; and a modulator that does not modulate the pair of PWM signals when the spreading code is the first value, and modulates the pair of PWM signals when the spreading code is the second value, wherein the modulation includes exchanging the values ​​of the pair of PWM signals with each other and inverting the value of each of the pair of PWM signals.

[0070] (Appendix 11) A method for reducing EMI in a power conversion device including a pulse generator that generates a pair of PWM signals and a differential circuit that converts power in accordance with the pair of PWM signals and supplies the power to a load, the method comprising: generating a spreading code that indicates a logical value of a first value or a second value in synchronization with a PWM update period; and not modulating the pair of PWM signals when the spreading code is the first value, and modulating the pair of PWM signals when the spreading code is the second value, wherein the modulation includes exchanging the values ​​of the pair of PWM signals with each other and inverting the value of each of the pair of PWM signals.

[0071] (Appendix 12) A program for operating a processor to reduce EMI in a power conversion device including a pulse generator that generates a pair of PWM signals and a differential circuit that converts power in accordance with the pair of PWM signals and supplies the power to a load, the program causing the processor to execute the steps of: generating a spread code indicating a logical value of a first value or a second value in synchronization with a PWM update period; and not modulating the pair of PWM signals when the spread code is the first value, and modulating the pair of PWM signals when the spread code is the second value, wherein the modulation includes exchanging the values ​​of the pair of PWM signals with each other and inverting the value of each of the pair of PWM signals. [Explanation of symbols]

[0072] 1,101,201,301 Power conversion equipment 10,110,210,310 Signal processing device 12s spreading code generator 13p, 13m pulse generator 14p, 14m Reversal section 15p,15m selection section 16 Exchange part 18, 18p, 18m, 118 modulator 19,119,219 EMI reduction circuits 20 H-bridge circuit, differential circuit 30 speakers 330 Electric Motor

Claims

1. A circuit for reducing EMI in a power conversion device including a pulse generator that generates a pair of PWM signals and a differential circuit that converts power in response to the pair of PWM signals and supplies the power to a load, a spreading code generator that generates a spreading code indicating a logical value of the first value or the second value in synchronization with a PWM update period; a modulator that does not modulate the pair of PWM signals when the spreading code has the first value, and modulates the pair of PWM signals when the spreading code has the second value, The EMI reduction circuit of the power conversion device, wherein the modulation includes exchanging values ​​of the pair of PWM signals with each other and inverting values ​​of each of the pair of PWM signals.

2. The EMI reduction circuit for a power conversion device according to claim 1 , wherein the modulator is disposed on the output side of the pulse generator.

3. the modulator includes an exchange unit that exchanges values ​​of the pair of PWM signals with each other, and an inversion unit that inverts the value of each of the pair of PWM signals; 2. The EMI reduction circuit of claim 1, wherein one of the exchange unit or the inversion unit is disposed on the input side of the pulse generator, and the other of the exchange unit or the inversion unit is disposed on the output side of the pulse generator.

4. the power conversion device includes a microcomputer including a pulse generator that generates the pair of PWM signals, the differential circuit being disposed between the microcomputer and the load, The EMI reduction circuit for a power conversion device according to claim 1 , wherein the modulator is disposed between the microcomputer and the differential circuit.

5. 2. The EMI reduction circuit for a power conversion device according to claim 1, wherein the power conversion device does not have a low-pass filter between the differential circuit and the load.

6. 2. The EMI reduction circuit for a power conversion device according to claim 1, wherein the spreading code generator generates the spreading code using a random number sequence or a pseudo-random number sequence generated in synchronization with the PWM update period.

7. 2. The EMI reduction circuit for a power conversion device according to claim 1, wherein the PWM signal has a duty ratio determined based on a signal that commands the operation of the load.

8. 2. The EMI reduction circuit for a power conversion device according to claim 1, wherein the load is a speaker, and the PWM signal is a signal generated based on an audio signal for the speaker.

9. 2. The EMI reduction circuit for a power conversion device according to claim 1, wherein the load is an electric motor, and the PWM signal is a signal generated based on a control signal for the electric motor.

10. a pulse generator for generating a pair of PWM signals; a differential circuit that converts power in response to the pair of PWM signals and supplies the converted power to a load; a spreading code generator that generates a spreading code indicating a logical value of the first value or the second value in synchronization with a PWM update period; a modulator that does not modulate the pair of PWM signals when the spreading code has the first value, and modulates the pair of PWM signals when the spreading code has the second value, The power conversion device, wherein the modulation includes exchanging values ​​of the pair of PWM signals with each other and inverting values ​​of each of the pair of PWM signals.

11. A method for reducing EMI in a power conversion device including a pulse generator that generates a pair of PWM signals and a differential circuit that converts power in response to the pair of PWM signals and supplies the power to a load, comprising: generating a spreading code indicating a logic value of the first value or the second value in synchronization with a PWM update period; not modulating the pair of PWM signals when the spreading code is the first value, and modulating the pair of PWM signals when the spreading code is the second value; The method for reducing EMI in a power conversion device, wherein the modulation includes exchanging values ​​of the pair of PWM signals with each other and inverting values ​​of each of the pair of PWM signals.

12. A program for operating a processor to reduce EMI in a power conversion device including a pulse generator that generates a pair of PWM signals and a differential circuit that converts power in response to the pair of PWM signals and supplies the power to a load, the program comprising: the processor, generating a spreading code indicating a logic value of the first value or the second value in synchronization with a PWM update period; not modulating the pair of PWM signals when the spreading code is the first value, and modulating the pair of PWM signals when the spreading code is the second value; Execute The modulation includes exchanging values ​​of the pair of PWM signals with each other and inverting values ​​of each of the pair of PWM signals.

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