JP2008099475A - Power conversion device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide power conversion device and method with which a noise spectrum in a desired frequency band can be made flat. <P>SOLUTION: In an inverter system 1, a controller 10 having an arithmetic unit which digitally controls the opening and closing operations of a switching element that converts the input power into a desired form is provided with a carrier frequency generating part 9, which discretely as well as periodically subjects the frequency fc of a carrier signal output to comparators 8a, 8b and 8c generating control signals for opening/closing the switching element, to time change. The carrier frequency generating part 9 selects values fc11 and fc12 of the carrier frequency fc so that the frequency m11×fc11 of the m11-th higher harmonics of value fc11 of the carrier frequency fc and frequency m12×fc12 of the m12-th higher harmonics for the other value fc12 of the carrier frequency fc do not overlap, at a frequency lower than the clock frequency F of the arithmetic unit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power conversion device and a power conversion method used for a motor mounted on a vehicle.

Conventionally, four switches are configured in an H-bridge shape, and by opening and closing those switches, the current that achieves the desired motor rotational force by PWM control of the magnitude and direction of the current applied to the motor from the DC power supply A drive stepping motor control device is known. This stepping motor control device periodically changes the carrier frequency in PWM control to a sine wave shape in order to reduce the EMI noise spectrum generated by opening and closing the four switches. Thereby, in the EMI noise spectrum, EMI noise can be diffused in a wide frequency band, and the peak level of the EMI noise spectrum is reduced. In this way, it is possible to suppress radio reception and obstacles to other electronic devices.
JP-A-7-99795

  However, since the above stepping motor control device periodically changes the carrier frequency into a sine wave by digital control, there is a problem that the carrier frequency can take only discrete values. When the value of the carrier frequency becomes discrete, the frequency of the m-th harmonic (m: integer) of the value of the carrier frequency and the mq-order harmonic of other values of the carrier frequency (mq: integer, q: 1, 2, .., and the frequency of r) are superimposed. When the frequency of the mth harmonic and the frequency of the mq harmonic are superimposed, a spectral component having a high noise level with respect to the frequency of the mth harmonic and a spectral component having a high noise level with respect to the frequency of the mq harmonic. Are superimposed on each other, a spectrum component having a higher noise level is formed at the superimposed frequency, and the noise spectrum cannot be flattened.

  The present invention has been made in view of these problems, and an object thereof is to provide a power conversion device and a power conversion method capable of flattening a noise spectrum in a desired frequency band.

  To achieve the above object, in the power conversion device according to the present invention, the frequency of the carrier wave output for generating the control signal for opening and closing the opening / closing means for converting the input power into a desired form is digitally controlled. The carrier frequency changing means for changing time discretely and periodically includes the m-th harmonic (m: integer) frequency in the carrier frequency value and the mq-order harmonic (mq) in other values of the carrier frequency. : Integer, q: 1, 2,..., R) are selected such that each value of the frequency of the carrier wave is selected so as not to overlap within a desired frequency band.

  According to the present invention, the frequency of the m-th harmonic in the value of the carrier frequency and the frequency of the mq-order harmonic in the other values of the carrier frequency are not superimposed in the desired frequency band. The noise spectrum can be flattened.

  As an example of a power converter according to the present invention, an inverter system including an inverter that supplies sinusoidal AC power to a motor by PWM-modulating the output of a DC power supply will be described. Hereinafter, inverter systems according to first to fourth embodiments of the present invention will be described with reference to FIGS. 1 to 7.

(First embodiment)
A power conversion device 1 according to a first embodiment of the present invention and a power conversion method used for the power conversion device 1 will be described with reference to FIGS. 1 to 5.

(Configuration of power converter)
Hereinafter, the configuration and operation of the inverter system 1 will be described with reference to FIG. FIG. 1 is a diagram showing a configuration of an inverter system 1 according to a first embodiment of the present invention. As shown in FIG. 1, an inverter system 1 that is a power converter 1 includes a PWM inverter 2, a three-phase brushless DC motor (hereinafter referred to as a motor) 3, and a current detection unit 4 that includes current sensors 4 a, 4 b, and 4 c. , A control device 10 that is a control means incorporating an arithmetic device (hereinafter referred to as a CPU), a battery B, and a capacitor C are provided as main components. Further, the control device 10 includes a current command generator 5, PID controllers 6a, 6b, and 6c, a carrier signal generator 7 that is a carrier wave output means, comparators 8a, 8b, and 8c that are control signal generators, and a carrier frequency change. A carrier frequency generation unit 9 as means is provided as a main component. The PWM inverter 2 selects the positive or negative polarity of the DC power source composed of the battery B and the capacitor C according to the control of the comparators 8a, 8b, and 8c, and selects the selected electrodes for the U phase, V phase, and W phase of the motor 3, respectively. There are six switching elements Tu +, Tu−, Tv +, Tv−, Tw +, Tw− connected to the electrodes, and these switching elements are constituted by semiconductor elements such as IGBT (Insulated Gate Bipolar Transistor). Yes.

  The current sensors 4a, 4b, and 4c detect U-phase, V-phase, and W-phase current values supplied from the PWM inverter 2 to the motor 3, respectively. The current command generator 5 includes current sensors 4a, 4b, A sinusoidal current command value is generated so that the detected current value 4c is converted into a sinusoidal alternating current. The PID controllers 6a, 6b, and 6c detect the current detection values of the current sensors 4a, 4b, and 4c so that the current detection values of the current sensors 4a, 4b, and 4c follow the current command values generated by the current command generator 5. Is PID controlled.

  The carrier frequency generation unit 9 changes the frequency (hereinafter referred to as carrier frequency) fc (see FIG. 2 described later) of the carrier signal generated by the carrier signal generation unit 7. Then, the carrier signal generation unit 7 outputs a triangular wave carrier signal having the carrier frequency fc to the comparators 8a, 8b, and 8c.

  The comparators 8a, 8b, and 8c compare the magnitude relationship between the output values of the PID controllers 6a, 6b, and 6c and the triangular wave carrier signal, and the switching elements Tu + and Tu− of the PWM inverter 2 according to the magnitude relationship. , Tv +, Tv−, Tw +, Tw−, a signal for controlling on / off is input to the PWM inverter 2. The operation of the comparator 8a will be described in detail by taking the control of the U-phase switching elements Tu + and Tu− as an example. When the output value of the PID controller 6a is larger than the triangular wave carrier signal, When a positive voltage is applied to the U phase of the motor 3 by controlling Tu + and Tu− to be on and off, respectively, conversely, when the output value 6a of the PID controller is smaller than the triangular wave carrier signal , Tu + and Tu− are controlled to be in an off state and an on state, respectively, so that a negative voltage is applied to the U phase of the motor 3.

(Time change of carrier frequency)
Here, the time change of the carrier frequency fc according to the first embodiment of the present invention will be described. FIG. 2 is a diagram illustrating a sine wave-like time change of the carrier frequency fc in digital control. Note that FIG. 2 shows one cycle of a sine wave-like time change of the carrier frequency fc (hereinafter referred to as one modulation cycle).

  Here, in general, the EMI noise generated by opening and closing of the switching element has a spectral component having a high noise level with respect to the frequency m × fc of the m-th harmonic (m: integer) of the predetermined frequency fc of the carrier signal. is doing. Therefore, by changing the carrier frequency fc with time, the spectral component having a high noise level generated at the m-order harmonic frequency m × fc of the predetermined carrier frequency fc is changed to a frequency band (time change of the carrier frequency fc). For example, the EMI noise spectrum is flattened and the peak level is reduced by spreading in the frequency band (for example, m × fc1 to m × fcN in FIG. 2) of m-order harmonics of fc1 to fcN in FIG. . However, as the time change of the carrier frequency fc in the digital control, only discrete values of fc1,..., FcN can be used as shown in FIG. Further, even if the carrier frequency fc is changed with time, the average value of the number of times of switching / time does not change. Therefore, the frequency m × fc1,..., M of the m-th harmonic of the frequency band fc1,. The total noise level generated in xfcN, that is, the total energy of EMI noise does not change. Therefore, the energy of the EMI noise is not sufficiently diffused in the frequency band m × fc1 to m × fcN of the m-th harmonic, and the m-th harmonic of the discrete value fc1 ·· fcN of the carrier frequency fc. , That is, m × fc1,..., M × fcN. Therefore, the noise level with respect to the m-th harmonic frequency m × fc1,..., M × fcN of the discrete values fc1,..., FcN of the carrier frequency fc is predetermined when the carrier frequency fc is not changed over time. The noise level generated at the m-th harmonic frequency m × fc of the carrier frequency fc is equal to a level obtained by dispersing discrete values.

  In addition, when the carrier frequency fc is changed with a discrete value over time, the m-th harmonic frequency (for example, m1 × fc1) of a certain value (for example, fc1) of the carrier frequency fc and other carrier frequencies fc The frequency (eg, m2 × fc2,..., MN × fcN) of the mq order harmonic (mq: integer, q: 1, 2,..., R) of the value (eg, fc2,..., FcN) There are also cases where they overlap. When the m-order harmonic frequency (for example, m1 × fc1) and the mq-order harmonic frequency (for example, m2 × fc2,..., MN × fcN) are superimposed, the m-order harmonic frequency ( For example, a spectral component having a high noise level with respect to m1 × fc1) and a spectral component having a high noise level with respect to the frequency of the mq-order harmonics (for example, m2 × fc2,..., MN × fcN) are superimposed and further increased. Since a spectral component having a noise level is formed, the noise spectrum cannot be flattened. Therefore, in the first embodiment of the present invention, as will be described later, when the carrier frequency fc is changed with time by the discrete values fc11, fc12, and fc13, the m11th order of the discrete value fc11 (see FIG. 5). The harmonic frequency m11 × fc11, the m12th harmonic frequency m12 × fc12 of another value fc12 (see FIG. 5), and the m13th harmonic frequency m13 × fc13 of another value fc13 (see FIG. 5). The values fc11, fc12, and fc13 are selected so that they are not superimposed at a frequency lower than the clock frequency F (see FIG. 3) of the CPU built in the control device 10.

(Relationship between carrier frequency and clock frequency)
Here, the relationship between the carrier frequency fc and the clock frequency F will be described. It is known that the cycle of the carrier signal (hereinafter referred to as carrier cycle) Tc is an integral multiple of the CPU clock cycle Δt. Note that the reciprocal of the carrier period Tc is the carrier frequency fc. Similarly, the reciprocal of the clock period Δt is the clock frequency F. Further, in the digital control, as shown in FIG. 2, since only a discrete value can be used for the time change of the carrier frequency fc, only a discrete value can be used for the carrier cycle Tc as well. Therefore, the discrete value Tci (i = 1, 2,..., N) of the carrier period Tc is obtained by using the clock period Δt,
Tc1 = K1 × Δt
Tc2 = K2 × Δt
Tc3 = K3 × Δt
・
・
・
TcN-1 = KN-1 * [Delta] t
TcN = KN × Δt
Can be expressed as Here, Ki is an integer value. From this, the discrete value fci of the carrier frequency fc is the reciprocal of the carrier period Tci,
fci = 1 / Tci = 1 / (Ki × Δt)
= (1 / Ki) × (1 / Δt)
= (1 / Ki) x F
Can be expressed as From the above relational expression, the value obtained by multiplying the discrete value fci of the carrier frequency fc by Ki, that is, the frequency Ki × Fci of the Ki-order harmonic is always equal to the clock frequency F of the CPU. This means that no matter what value each discrete value fci of the carrier frequency fc is selected, the noise level of the Ki-order harmonic frequency Ki × fci = F at each discrete value fci of the carrier frequency fc It shows that high spectral components are necessarily superimposed at the clock frequency F. Note that the CPU clock frequency F is uniquely determined by the CPU performance, and it is not realistic to change it to an arbitrary value. Further, depending on the selection of the discrete value fci of the carrier frequency fc, a spectral component having a high noise level with respect to the mq-order harmonic frequency mq × fci at each discrete value fci is superimposed at a frequency lower than the clock frequency F. In some cases.

More specifically, for example, it is desired to superimpose a spectral component having a high noise level with respect to the frequency mq × fci of the mq-order harmonic at each discrete value fci of the carrier frequency fc in the AM band (531 kHz to 1602 kHz). If not, it is necessary to first select the CPU so that the clock frequency F is outside the AM band. Furthermore, even if a CPU whose clock frequency F is outside the AM band, for example, 2 MHz (Δt = 500 nsec) is selected, three values of the discrete values fc1, fc2 and fc3 of the carrier frequency fc are obtained.
fc1 = 18.52 kHz = 1 / (500 nsec × 108) = 1 / (Δt × K1)
fc2 = 20.00 kHz = 1 / (500 nsec × 100) = 1 / (Δt × K2)
fc3 = 21.74 kHz = 1 / (500 nsec × 92) = 1 / (Δt × K3)
The discrete values fc1, fc2 and fc3 are
fc1 = 1 / (500 nsec × 4 × 27) = 1 / (2 μsec × m1)
fc2 = 1 / (500 nsec × 4 × 25) = 1 / (2 μsec × m 2)
fc3 = 1 / (500 nsec × 4 × 23) = 1 / (2 μsec × m3)
It can be expressed as. That is, as in the case where a CPU having a clock period of 2 μsec and a clock frequency of ½ μsec = 500 kHz is selected, a spectral component having a high noise level with respect to a frequency 27 × fc1 of m1 = 27th harmonic at a discrete value fc1, discrete A spectral component having a high noise level with respect to a frequency 25 × fc2 of m2 = 25th harmonic at a low value fc2 and a spectral component having a high noise level with respect to a frequency 23 × fc3 of m3 = 23rd harmonic at a discrete value fc3 are 500 kHz. Superimpose at an integer multiple of. Therefore, the above spectral components are superimposed at frequencies of 500 kHz, 1000 kHz, and 1500 kHz that are lower than the clock frequency F = 2 MHz. Therefore, a spectral component having a higher noise level is formed at a frequency that is an integral multiple of the above frequency of 500 kHz.

  FIG. 3 is a theoretical explanatory diagram of an EMI noise spectrum formed when the carrier frequency fc is changed. FIG. 3A shows a discrete value when the carrier frequency fc is discretely changed with time at fc1 = 18.52 kHz, fc2 = 20.00 kHz, and fc3 = 21.74 kHz in the specific example described above. The noise spectrum generated only by fc1 is shown. 3B shows a noise spectrum generated only by the discrete value fc2 in the above case, FIG. 3C shows a noise spectrum generated only by the discrete value fc3, and FIG. The EMI noise spectrum generated by the discrete values fc1, fc2 and fc3 is shown. In the specific example described above, since the clock frequency F = 2 MHz, as described above, K1 = 108, K2 = 100, and K3 = 92. M represents the greatest common divisor of fc1, fc2, and fc3. Therefore, in the above case, M = 4.

  From this, as shown in FIG. 3 (d), when the carrier frequency fc is changed over time with discrete values fc1, fc2 and fc3, (K1 / M) = m1 = 27th order harmonic at the discrete value fc1 Spectral component with high noise level for wave frequency 27 × fc1, (K2 / M) = m2 = 25th harmonic frequency at discrete value fc2 Spectral component with high noise level and discrete value fc3 (K3 / M) = m3 = A spectral component having a high noise level is superimposed at a frequency F / M = 500 kHz lower than the clock frequency F with respect to the frequency 23 × fc3 of the 23rd-order harmonic in FIG. It can be seen that is formed. From this, each of the above spectral components is superimposed at a frequency that is an integral multiple of the frequency F / M = 500 kHz, and a spectral component having a higher noise level is formed. On the other hand, at frequencies other than a frequency that is an integral multiple of frequency F / M = 500 kHz, the above-described spectral components are not superimposed, and spectral components having a higher noise level are not formed. As described above, the clock frequency F = Ki × fci. The relationship between ki and mq is mq = ki / M.

  FIG. 4 is a diagram showing waveforms obtained by actually measuring EMI noise spectra at discrete values fc1, fc2, and fc3 of the carrier frequency fc shown in FIG. In FIG. 4, the noise spectrum (thin line) generated when the carrier frequency fc is constant as shown in FIG. 3, the noise spectrum (thin line) generated when fc2 is constant, and the fc3 constant. And a noise spectrum (thick line) when the carrier frequency fc is changed over time at fc1, fc2 and fc3. From FIG. 4, when the carrier frequency fc is constant fc1, a spectral component having a high noise level appears at the clock frequency F / M = 500 kHz. Similarly, when the carrier frequency fc is constant fc2, a spectral component with a high noise level appears at 500 kHz. Even when the carrier frequency fc is constant fc3, a spectral component having a high noise level appears at 500 kHz. Therefore, even if the carrier frequency fc is changed with time by fc1, fc2, and fc3, the noise level at 500 kHz is not sufficiently reduced as shown in FIG. Here, when the carrier frequency fc is changed with time at fc1, fc2 and fc3, the noise level for the frequency m1 × fc1 of the m1st harmonic generated when fc1 is constant, and when fc2 is constant It becomes a value close to the average value of the noise level for the frequency m2 × fc2 of the m2 order harmonic generated at the frequency m3 × fc3 of the m3 order harmonic generated when the frequency fc3 is constant.

  Therefore, in the first embodiment, as shown in FIG. 5, when the carrier frequency fc is changed with time by the discrete values fc11, fc12, and fc13, the frequency m11 of the m11th harmonic of the discrete value fc11. × fc11, m12 harmonic frequency m12 × fc12 of other value fc12 and m13 harmonic frequency m13 × fc13 of other value fc13 are more than the clock frequency F of the CPU built in control device 10 Each value fc11, fc12, and fc13 is selected so as not to overlap at a low frequency. Hereinafter, a method of selecting each value fc11, fc12, and fc13 will be specifically described.

(Selection method of discrete value of carrier frequency)
FIG. 5 is a diagram showing waveforms obtained by actually measuring EMI noise spectra at discrete values fc11, fc12, and fc13 according to the first embodiment. In the first embodiment, similarly to the above, for the CPU having the clock frequency F = 2 MHz and the clock period Δt = 500 nsec, the discrete values fc11, fc12, and fc13 of the carrier frequency fc are set to fc11 = 18.69 kHz = 1 / ( 500nsec × 107)
fc12 = 20.00kHz = 1 / (500nsec × 100)
fc13 = 21.98 kHz = 1 / (500 nsec × 91)
The discrete values fc11, fc12 and fc13 are
fc11 = 1 / (Δt × 107 (prime number)) = 1 / (Δt × K11)
fc12 = 1 / (Δt × 4 × 25) = 1 / (Δt × K12)
fc13 = 1 / (Δt × 7 × 13) = 1 / (Δt × K13)
It can be expressed as. Here, the integer values K11 = 107, K12 = 4 × 25 and K3 = 7 × 13, and the greatest common divisor M is 1. That is, m11 = K11 = 107, m12 = K12 = 100, m13 = K13 = 91. Thus, in the first embodiment, the discrete values fc11, fc12, and fc13 of the carrier frequency fc are the products of the integer values K11, K12, and K13, each having the greatest common divisor M of 1, and the clock period Δt. The reciprocal of is selected. From this, when the carrier frequency fc is changed with time by the discrete values fc11, fc12 and fc13, the spectral component having a high noise level with respect to the frequency 107 × fc11 = F of m11 = K11 = 107th harmonic in the discrete value fc11 M12 = K12 = 100th harmonic frequency at discrete value fc12 = 100 × fc12 = F spectral component having a high noise level with respect to F and m13 = K13 = 91st harmonic frequency at discrete value fc13 91 × fc13 = It can be seen that a spectral component having a high noise level with respect to F is superimposed only at an integer multiple of the clock frequency F.

  In FIG. 5, when the carrier frequency fc is constant when the discrete value fc11 is constant, the noise spectrum (thin line) generated when the fc12 is constant, and when fc13 is constant. 2 shows a noise spectrum (thin line) generated when the carrier frequency fc is changed with time at fc11, fc12, and fc13. From FIG. 5, when the carrier frequency fc is constant fc11, a spectral component having a high noise level appears at 500 kHz. However, when the carrier frequency fc is constant at fc12, the frequency at which a spectral component having a high noise level appears is not 500 kHz. Similarly, when the carrier frequency fc is constant at fc13, the frequency at which a spectral component having a high noise level appears is not 500 kHz. Therefore, when the carrier frequency fc is changed with time by fc1, fc2, and fc3, as shown in FIG. 5, the spectral components having a high noise level with respect to the harmonic frequencies of fc11, fc12, and fc13 are spread to different frequencies, The noise spectrum is flattened. Therefore, the noise level can be reduced.

  As described above, in the first embodiment, the discrete values fc11, fc12 and the carrier frequency fc are set to the reciprocal of the product of the integer values K11, K12 and K13 having the greatest common divisor M of 1 and the CPU clock period Δt. Since fc13 is selected, the frequency m11 × fc11 of the m11th harmonic in fc11, the frequency m12 × fc12 of the m12th harmonic in fc12, and the frequency m13 × fc13 of the m13th harmonic in fc13 are the clock frequencies. Since there is no superposition at a frequency lower than F, the spectral component having a high noise level with respect to the frequency m11 × fc11 of the m11th harmonic at the discrete value fc11, and the frequency m12 of the m12th harmonic at the discrete value fc12. A spectral component with a high noise level for xfc12 and discrete Since the spectral component having a high noise level with respect to the frequency m13 × fc13 of the m13th harmonic in fc13 is not superimposed at a frequency lower than the clock frequency F, the formation of the spectral component having a higher noise level is suppressed, so that the clock frequency F The noise spectrum in the lower frequency band can be flattened.

(Second Embodiment)
Next, the power conversion device and the power conversion method used in the power conversion device according to the second embodiment will be described with reference to FIG. 6 focusing on differences from the power conversion device 1 and the power conversion method according to the first embodiment. I will explain. Moreover, about 2nd Embodiment, the same number is attached | subjected to the structure similar to 1st Embodiment, and description is abbreviate | omitted. In addition, the structure of the power converter device of 2nd Embodiment is as substantially the same as the power converter device 1 of 1st Embodiment. The second embodiment differs from the first embodiment only in the method of selecting discrete values fc21,..., Fc2N of the carrier frequency fc.

In the second embodiment, fc21,..., Fc2N are used as discrete values of the carrier frequency fc. Each value fc21,..., Fc2N is assumed to be a clock cycle Δt = 500 nsec.
fc21 = 17.70 kHz = 1 / (Δt × 113) = 1 / (Δt × K21)
fc22 = 19.80 kHz = 1 / (Δt × 101) = 1 / (Δt × K22)
・
・
・
fc2N = 22.47 kHz = 1 / (Δt × 89) = 1 / (Δt × K2N)
Is selected. Here, K21 = 113, K22 = 101,..., K2N = 89 are prime numbers. That is, the greatest common divisor M of each integer value K21,..., K2N is 1. Thus, by selecting the discrete values fc21,..., Fc2N of the carrier frequency fc, the same effects as in the first embodiment can be obtained in the second embodiment.

  FIG. 6 is a flowchart for realizing the time change of the carrier frequency fc in the discrete values fc21,..., Fc2N according to the second embodiment. FIG. 6A automatically calculates the discrete values fc21,..., Fc2N of the carrier frequency fc in the second embodiment, and uses the discrete values fc21,. The flow of the control process which implement | achieves the time change of fc is shown, FIG.6 (b) has shown the prime number map used for Fig.6 (a). Here, the prime number map includes an array in which integer values K1,..., K2N used for control processing for calculating discrete values fc21,..., Fc2N of the carrier frequency fc in the second embodiment are arranged. It is a database. In the database, the integer values K1,..., K2N of the above array are stored in advance corresponding to the array element numbers fc (0) to fc (N-1) indicating the order of time change of the carrier frequency fc. Yes.

  As shown in FIG. 6 (a), the control process for realizing the temporal change of the carrier frequency fc at the discrete values fc21,..., Fc2N of the carrier frequency fc of the second embodiment is as follows. The count value j is set to 0. Thereby, the integer value K21 of the array element number fc (0) is set as the value of the integer value k (step S1). Next, a discrete value fc21 is calculated using the integer value k (step S2). PWM calculation processing is executed using the discrete value fc21 (step S3). Thereafter, the count value j is incremented by 1 (step S4). Next, it is determined whether or not the count value j exceeds the number of discrete values of the carrier frequency fc, that is, the number N of prime map arrays (step S5). If the count value j does not exceed the number N (No in step S5), the integer value corresponding to the array number fc (j) is read from the prime map shown in FIG. 6B as the value of the integer value k. (Step S6). Thereafter, the process returns to the control process in step S2, and a discrete value is calculated using an integer value corresponding to the array element number fc (j). Thereafter, the control process of steps S2 to S6 is repeatedly executed. Thereby, discrete values fc21,..., Fc2N of the carrier frequency fc are calculated based on the integer value K2N corresponding to the array element number fc (N−1) from the integer value K21 corresponding to the array element number fc (0). Is done. On the other hand, when the count value j exceeds the number N of the prime map arrays in the control process of step S5 (Yes in step S5), the process returns to the control process of step S1 and the count value j is set to zero. Thereby, the integer value K21 of the array element number fc (0) is set as the value of the integer value k (step S1). In this way, the discrete values fc21,..., Fc2N of the carrier frequency fc can be easily and automatically calculated from the integer values K21,..., K2N arranged in the prime number map.

(Third embodiment)
Next, a power conversion device and a power conversion method used in the power conversion device according to the third embodiment will be described with reference to FIG. 7 focusing on differences from the power conversion device 1 and the power conversion method according to the first embodiment. I will explain. Moreover, about 3rd Embodiment, the same number is attached | subjected to the structure similar to 1st Embodiment, and description is abbreviate | omitted. In addition, the structure of the power converter device of 3rd Embodiment is as substantially the same as the power converter device 1 of 1st Embodiment. The third embodiment differs from the first embodiment only in the selection method of the discrete values fc31, fc32 and fc33 of the carrier frequency fc.

FIG. 7 is a diagram illustrating an EMI noise spectrum at discrete values fc31, fc32, and fc33 according to the third embodiment. As shown in FIG. 7, in the third embodiment, the noise spectrum in the entire frequency range lower than the clock frequency F = 5 MHz is not flattened, but the noise spectrum is flattened only in a desired frequency band of 2 to 3 MHz. . Here, since the discrete values fc31, fc32, and fc33 of the carrier frequency fc of the third embodiment are the clock period Δt = 200 nsec,
fc31 = 15.02 kHz = 1 / (Δt × 333) = 1 / (Δt × 3 × 111)
fc32 = 19.84 kHz = 1 / (Δt × 252) = 1 / (Δt × 3 × 84)
fc33 = 24.88 kHz = 1 / (Δt × 201) = 1 / (Δt × 3 × 67)
Is selected. That is, the discrete values fc31, fc32, and fc33 are
fc31 = 1 / (Δt × K31) = 1 / (Δt × M × m31)
fc32 = 1 / (Δt × K32) = 1 / (Δt × M × m32)
fc33 = 1 / (Δt × K33) = 1 / (Δt × M × m33)
It can be expressed as. From the above, the greatest common divisor M of the integer values K31, K32, and K33 is 3. From this, the frequencies of the mq-order harmonics of fc31, fc32, and fc33 are superimposed at a frequency that is an integral multiple of the frequency F / M = 5 MHz / 3 = 1.667 MHz, which is lower than the clock frequency F = 5 MHz. That is, in the frequency range lower than the clock frequency F, a spectrum component having a high noise level with respect to the frequency m31 × fc31 (= 1.667 MHz) of the m31st harmonic and a spectrum having a high noise level with respect to the frequency m32 × fc32 of the m32th harmonic. A component and a spectral component having a high noise level with respect to the frequency m33 × fc33 of the m33th harmonic are superimposed. Further, a spectral component having a high noise level for the frequency 2 × m31 × fc31 (= 3.333 MHz) of the 2 × m31 harmonic and a spectral component having a high noise level for the frequency 2 × m32 × fc32 of the 2 × m32 harmonic. And a spectral component having a high noise level with respect to the frequency 2 × m33 × fc33 of the 2 × m33 order harmonic are superimposed. However, the frequencies 1.667 MHz and 3.333 MHz on which the frequencies of the mq harmonics of fc31, fc32, and fc33 are superimposed are not included in the desired frequency band of 2 to 3 MHz in the third embodiment. Similar to the embodiment, the noise spectrum in a desired frequency band of 2 to 3 MHz can be flattened. In such a case, there is no problem even if the frequencies of the mq-order harmonics of fc31, fc32, and fc33 are superimposed at a frequency that is an integer multiple of the frequency F / M lower than the clock frequency F.

(Fourth embodiment)
Next, a power conversion device and a power conversion method used in the power conversion device according to the fourth embodiment will be described focusing on differences from the power conversion device 1 and the power conversion method according to the first embodiment. In the fourth embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In addition, the structure of the power converter device of 4th Embodiment is as substantially the same as the power converter device 1 of 1st Embodiment. The fourth embodiment differs from the first embodiment only in the selection method of the discrete values fc41,..., Fc4N of the carrier frequency fc.

In the fourth embodiment, the range of discrete values fc41,..., Fc4N of the carrier frequency fc is defined as 15 kHz or more and 25 kHz or less at the clock frequency F = 2 MHz and the clock period Δt = 500 nsec. In this case, the discrete values fc41,..., Fc4N need to be selected in the range of the maximum value fcmax = 25 kHz and the minimum value fcmin = 15 kHz. Therefore, the maximum value fcmax and the minimum value fcmin are
fcmax = 15.00 kHz = 1 / (Δt × 133.3)
= (1 / b) × (1 / Δt) = (1 / 133.3) × (1 / Δt)
fcmin = 25.00 kHz = 1 / (Δt × 80)
= (1 / a) × (1 / Δt) = (1/80) × (1 / Δt)
It can be expressed as. From this point, it is necessary to select each integer value Ki within a range of 80 to 133.3. Therefore, in the fourth embodiment, the discrete values fc41,..., Fc4N are calculated from the integer value Ki selected so that the greatest common divisor M is 1 in the range of 80 to 133.3. ing. From this, also in 4th Embodiment, the effect similar to 1st Embodiment is acquirable. Furthermore, even when the range of discrete values fc41,..., Fc4N of the carrier frequency fc is limited, the discrete values fc41,..., Fc4N can be easily selected.

  The embodiment described above is an example of the implementation of the present invention, and the scope of the present invention is not limited thereto, and other various embodiments are within the scope described in the claims. It is applicable to. For example, in the first to fourth embodiments, the inverter system 1 including the PWM inverter 2 that supplies a sinusoidal AC current to the motor 3 by PWM-modulating the output of the DC power source has been described as an example. However, the present invention is not limited to the above, and the same effect can be obtained when applied to other systems that change the form of power by switching. For example, a configuration in which a motor is driven with an H-bridge configuration shown in the prior art, a CPU 12 that outputs a carrier signal with a variable carrier frequency based on a signal from a command value input 11 shown in FIG. The present invention can also be applied to a configuration including a drive circuit 13 that outputs a switching signal for controlling opening / closing of the switch 15 to the single switch 15 and a load 14 to which a voltage is applied from the voltage source + V by the opening / closing operation of the single switch 15.

  In the first and third embodiments, three values have been explained as discrete values of the carrier frequency fc. However, the present invention is not particularly limited to this, as in the second and fourth embodiments. In addition, the present invention can be applied to a carrier frequency fc having a plurality of discrete values.

  In the first to fourth embodiments, a discrete value of the carrier frequency fc that changes with time in a sinusoidal manner within one modulation period is selected so that the mq-order harmonic frequency of the value does not overlap. However, the time change of the carrier frequency fc is not limited to a sine wave shape. For example, the triangular wave shape shown in FIG. 9, the sawtooth wave shape shown in FIG. 10, the rectangular wave shape shown in FIG. 11, and the periodic wave shape shown in FIG. And can be applied to various waveforms.

  Further, in the fourth embodiment, in the frequency band lower than the clock frequency F, the frequency of mq-order harmonics of discrete values fc41,..., Fc4N is not superimposed, as in the first embodiment. Discrete values fc41,..., Fc4N are calculated from the integer value Ki where the greatest common divisor M is 1. However, the present invention is not particularly limited to this, as shown in the second embodiment. A prime number map may be used. Further, as shown in the third embodiment, each value is selected so that the frequency of the mq-order harmonics of discrete values fc41,..., Fc4N is not superimposed in a desired frequency band. Also good.

The figure which shows the structure of the inverter system used as the 1st Embodiment of this invention. The figure which shows the sine wave-like time change of the carrier frequency in digital control Theoretical illustration of the EMI noise spectrum formed when the carrier frequency is changed The figure which shows the waveform which measured the EMI noise spectrum in each discrete value of the carrier frequency shown in FIG. The figure which shows the waveform which measured the EMI noise spectrum in the discrete value which concerns on 1st Embodiment. The flowchart which implement | achieves the time change of the carrier frequency in the discrete value which concerns on 2nd Embodiment. The figure which shows the EMI noise spectrum in the discrete value which concerns on 3rd Embodiment. Diagram showing load drive configuration with a single switch The figure which shows the time change of the triangular wave shape of the carrier frequency in digital control The figure which shows the sawtooth time change of the carrier frequency in digital control The figure which shows the time change of the rectangular wave shape of the carrier frequency in digital control The figure which shows the time change of the periodic waveform of the carrier frequency in digital control

Explanation of symbols

1 Inverter system that is a power converter, 2 PWM inverter,
3 Three-phase brushless DC motor, 4 current detector,
4a, 4b, 4c current sensor, 5 current command generator,
6a, 6b, 6c PID control unit,
7 Carrier signal generation unit which is carrier wave output means,
8a, 8b, 8c Comparator as control signal generating means,
9 Carrier frequency generation unit as carrier frequency changing means,
10 Control device which is control means,
11 command value input, 12 CPU, 13 drive circuit, 14 load,
15 switches,
B battery, C capacitor, fc, carrier frequency, GND ground,
Tu +, Tu−, Tv +, Tv−, Tw +, Tw− switching elements that are opening and closing means,
+ V voltage source,

Claims (5)

An electric power conversion device comprising an opening / closing means for converting input power into a desired form, and a control means for digitally controlling the opening / closing operation of the opening / closing means,
The control means includes a control signal generating means for generating a control signal for opening and closing the opening and closing means,
Carrier wave output means for outputting a carrier wave to the control signal generating means;
Carrier frequency changing means for changing the frequency of the carrier wave discretely and periodically with time,
The carrier frequency changing means includes the frequency of the m-th harmonic (m: integer) in the frequency value of the carrier and the mq-order harmonic (mq: integer, q: 1, 2) in other values of the carrier frequency. ,..., R) frequency values of the carrier wave are selected so as not to overlap in a desired frequency band.   2. The power conversion device according to claim 1, wherein each value of the frequency of the carrier wave is a reciprocal of a product of each integer value having a greatest common divisor of 1 and a clock cycle of the control means.   The power conversion apparatus according to claim 2, wherein each integer value is a prime number. When the maximum value of the carrier frequency is fcmax, the minimum value is fcmin, the clock period of the control means is Δt, and arbitrary integer values are a and b, the maximum value and the minimum value are:
fcmin = (1 / a) × (1 / Δt)
fcmax = (1 / b) × (1 / Δt)
Calculated from
4. The power conversion according to claim 1, wherein each value of the frequency of the carrier wave is a reciprocal of a product of an integer value within the range of the integer values a and b and the clock period. 5. apparatus. Convert the power input by the switching means to the desired form,
A power conversion method for digitally controlling an opening / closing operation of the opening / closing means by a control means,
The control signal generating means of the control means generates a control signal for opening and closing the opening and closing means,
The carrier wave output means of the control means outputs a carrier wave to the control signal generation means,
The carrier frequency changing means of the control means changes the frequency of the carrier wave discretely and periodically, and the frequency of the m-th harmonic (m: integer) in the value of the carrier wave frequency, and the frequency of the carrier wave Select each value of the carrier frequency so that the frequency of mq order harmonics (mq: integer, q: 1, 2,..., R) at other values does not overlap within the desired frequency band. A power conversion method characterized by:

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