JP6662277B2 - Inverter control device - Google Patents

Description

  The present invention relates to an inverter control device, and more particularly to a pulse width modulation (PWM) type inverter control device.

  As disclosed in Japanese Patent Application Laid-Open No. 9-47026 (Patent Document 1), a pulse width modulation type inverter control device is known. In Patent Literature 1, when the inverter device is controlled by the pulse width modulation method, the carrier frequency is controlled so as to be appropriately switched at a time interval shorter than one cycle of the output from the inverter.

JP-A-9-47026

  If the carrier frequency is switched at a time interval shorter than one cycle of the output of the inverter as in Patent Document 1, the symmetry of the output waveform in one cycle is lost, and the load connected to the output side of the inverter is affected. there is a possibility. In addition, when a high output frequency is set, the carrier frequency is frequently switched in a time shorter than one cycle of the output waveform, and there is a problem that a load is placed on the arithmetic processing of the control system.

  SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and provides an inverter control device that can reduce the influence on a load and can reduce the load on the arithmetic processing of the inverter control system. Aim.

  To achieve the above object, an inverter control device according to the present invention is configured as follows.

  An inverter control device according to the present invention generates a pulse width modulation (PWM) signal based on a magnitude comparison between an inverter output command value and a carrier signal, and controls the inverter by this. The inverter converts DC to AC according to the PWM signal. The inverter output command value indicates a target voltage waveform (sine wave) to be output by the inverter due to a periodic change. The carrier signal represents a triangular wave corresponding to the carrier frequency by a periodic change.

  The inverter control device includes a phase information calculator, a carrier frequency selector, and a carrier generator.

  The phase information calculation unit predicts a carrier frequency change timing at which the inverter output command value becomes 0 every n (n is a natural number) cycles from a timing at which the inverter output command value becomes 0 every 1/2 cycle.

  The carrier frequency selection unit randomly selects one from a plurality of predetermined carrier frequencies every n periods.

  The carrier generation unit changes the carrier frequency to one selected by the carrier frequency selection unit at a carrier frequency change timing, and generates a carrier signal according to the changed carrier frequency. Preferably, the carrier waveform is continuous before and after the carrier frequency change timing, and switching is performed so that the sign of the slope of the waveform does not change.

  According to the present invention, since the carrier frequency is randomly switched at regular intervals of the output command value of the inverter, the symmetry of one cycle of the output waveform can be ensured, so that the effect on the load can be reduced and The load on the arithmetic processing of the control system can be reduced. In addition, the peak frequency band of noise and mechanical vibration is dispersed, so that noise and mechanical vibration caused by the carrier frequency can be prevented from being concentrated in a specific frequency band.

FIG. 1 is a schematic configuration diagram for describing an inverter system configuration according to a first embodiment of the present invention. FIG. 9 is a diagram for describing an example of predicting a carrier frequency change timing. FIG. 7 is a diagram for describing a change in a carrier waveform before and after a carrier frequency change timing. 5 is a flowchart of a control routine executed by the inverter control device according to the first embodiment of the present invention. It is a figure for explaining dispersion of a peak frequency band of noise and mechanical vibration. FIG. 3 is a conceptual diagram illustrating a hardware configuration example of a processing circuit included in the inverter control device according to the first embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Elements common to the drawings are denoted by the same reference numerals, and redundant description will be omitted.

Embodiment 1 FIG.
<Inverter system configuration>
FIG. 1 is a schematic configuration diagram for describing an inverter system configuration according to Embodiment 1 of the present invention. The inverter system shown in FIG. 1 includes a DC power supply 1, an inverter main circuit 2, a filter 3, a load 4, and an inverter control device 5. Here, the inverter main circuit 2 will be described as a single-phase inverter.

  The inverter main circuit 2 converts DC supplied from the DC power supply 1 into AC and outputs the AC to the filter 3 in accordance with a pulse width modulation (PWM) signal output from the inverter control device 5.

  As an output control method of the inverter, there is PWM control for varying a pulse width. Since the inverter operates by switching, the pulse waveform to be output has a constant amplitude and the pulse width must be controlled. By the PWM control, the magnitude of the output voltage or current can be controlled by controlling the duty of the pulse. Further, the output waveform can be approximated to a sine wave by the PWM control.

In a triangular wave-sine wave method widely used as PWM control, a pulse is generated by comparing the magnitude of a high-frequency triangular wave with that of a sine wave. In this method, a triangular wave is used as a carrier, and a sine wave is used as a target voltage waveform to be output by an inverter. The target voltage waveform to be outputted by the inverter a sine wave _{e s = E s sinω s t} . In this case, e _s is an inverter output command value, the inverter output command value at the angular frequency omega _s is a sine wave voltage of amplitude E _s. On the other hand, the carrier represented by the triangular wave has a higher frequency than the sine wave representing the target voltage waveform to be output by the inverter.

  The inverter main circuit 2 converts the DC voltage into an AC voltage approximating a target voltage waveform by turning on / off the switching circuit at a high speed according to the PWM signal.

<Inverter control device>
The inverter control device 5 is a control device for driving an inverter, and includes a command value generation unit 6, a phase information calculation unit 7, a carrier frequency selection unit 8, a carrier generation unit 9, and a PWM generation unit 10.

  The command value generator 6 calculates a sine wave which is a target voltage waveform to be output by the inverter main circuit 2 according to the voltage reference input to the inverter control device 5 and converts the target voltage at each time into an inverter output command value. To the phase information calculation unit 7 and the PWM generation unit 10. As described above, the inverter output command value changes periodically.

  The phase information calculation unit 7 predicts a carrier frequency change timing at which the inverter output command value becomes 0 every n (n is a natural number) cycles from a timing at which the inverter output command value becomes 0 every 1/2 cycle. The phase information (zero cross point) indicating the carrier frequency change timing is output to the carrier frequency selection unit 8 and the carrier generation unit 9.

  FIG. 2 is a diagram for explaining an example of predicting a carrier frequency change timing. FIG. 2 shows an example in which the carrier frequency is changed every cycle (n = 1) of the inverter output command value. The inverter output command value becomes 0 every 1/2 cycle. Therefore, the timing B (the carrier frequency change timing), which is the zero cross point one cycle later, can be predicted from the timing A, which is the zero cross point at the half cycle. The phase information calculation unit 7 outputs the phase information indicating the predicted timing B to the carrier frequency selection unit 8 and the carrier generation unit 9.

  When the phase information is input, the carrier frequency selection unit 8 randomly selects one from a plurality of predetermined carrier frequencies every n periods. Preferably, these carrier frequencies are set to integer multiples of the frequency of the target output waveform.

  In the example shown in FIG. 2, different carrier frequencies (f1, f2, f3) are selected for each cycle of the inverter output command value. The selected carrier frequency is output to carrier generation section 9.

  The carrier generator 9 generates a carrier signal used for pulse width modulation. The carrier generation unit 9 changes the carrier frequency to one selected by the carrier frequency selection unit 8 at the carrier frequency change timing, and generates a carrier signal according to the changed carrier frequency.

  In the example shown in FIG. 2, the carrier frequency is changed randomly at every cycle of the inverter output command value. At timing B, the carrier frequency is changed from f1 to f2 and at timing C from f2 to f3.

  At this time, before and after the carrier frequency change timing, the carrier waveform is continuous, and the polarity of the waveform is switched so as not to change.

  FIG. 3 is a diagram for describing a change in the carrier waveform before and after the carrier frequency change timing. 2, the carrier frequency is changed from f1 to f2 at timing B (zero-cross point after one cycle of the inverter output control value). Before and after the timing B at which the carrier frequency is changed, the two carrier waveforms continue at the same phase, and the carrier frequency is switched without changing the sign of the waveform.

  The PWM generation unit 10 performs a pulse width modulation signal (PWM) based on a magnitude comparison between an inverter output command value representing a target voltage waveform to be output by the inverter due to a periodic change and a carrier signal output from the carrier generation unit 9. Signal). The PWM signal is output to inverter main circuit 2.

<Flow chart>
FIG. 4 is a flowchart of a control routine executed by the inverter control device 5 to realize the above-described operation. This control routine is repeatedly executed for each control cycle.

  In the routine shown in FIG. 4, first, in step S100, the inverter control device 5 receives a voltage reference.

  In step S110, the command value generator 6 calculates a sine wave, which is a target voltage waveform to be output by the inverter main circuit 2, from the voltage reference, and outputs the target voltage at each time as an inverter output command value.

  In step S120, the phase information calculation unit 7 determines whether or not the sequentially input inverter output command value is zero or near zero. When the determination condition is satisfied, the process proceeds to the processing in step S130. If the determination condition is not satisfied, the process returns to step S110 to continue the processing.

  In step S130, the phase information calculation unit 7 predicts a carrier frequency change timing at which the inverter output command value becomes 0 every n cycles from a timing at which the inverter output command value becomes 0 every 1/2 cycle. Specifically, when the successively input inverter output command value is 0 or near 0, it is determined that the time is a timing of becoming 0 every 1/2 cycle. The timing for changing the carrier frequency n cycles after the timing is calculated.

  In step S140, the carrier frequency selection unit 8 randomly selects one from a plurality of predetermined carrier frequencies.

  In step S150, the carrier generator 9 determines whether the current time is the carrier frequency change timing calculated in S130. If the determination condition is satisfied, the process proceeds to step S160. If the determination condition is not satisfied, the determination process of step S150 is performed again.

  In step S160, at the carrier frequency change timing, the carrier generator 9 changes the carrier frequency to the carrier frequency selected in step S140, and generates a carrier signal according to the changed carrier frequency.

  In step S170, the PWM generator 10 generates a pulse width modulation signal based on a comparison between the inverter output command value and the set carrier signal. The generated pulse width modulation signal is output to inverter main circuit 2.

  By repeating this series of controls, the carrier frequency can be changed randomly at regular intervals of the inverter output command value. Note that the initial carrier frequency at the time of starting the inverter is set separately.

  As described above, according to the inverter control device according to the present embodiment, the symmetry of one cycle of the output waveform can be ensured by randomly switching the carrier frequency every fixed cycle of the output command value of the inverter. The effect on the load can be reduced, and the load on the arithmetic processing of the control system of the inverter can be reduced.

  In addition, as shown in FIG. 5, the peak frequency band of noise and mechanical vibration is dispersed, so that noise and mechanical vibration caused by the carrier frequency can be prevented from being concentrated in a specific frequency band.

<Modification>
By the way, in the system of the first embodiment described above, the inverter main circuit 2 is described as a single-phase inverter, but may be a three-phase inverter.

<Example of hardware configuration>
FIG. 6 is a conceptual diagram illustrating a hardware configuration example of a processing circuit included in the inverter control device 5. Each part in the inverter control device 5 shows a part of a function, and each function is realized by a processing circuit. For example, the processing circuit includes at least one processor 91 and at least one memory 92. For example, the processing circuit includes at least one dedicated hardware 93.

  When the processing circuit includes the processor 91 and the memory 92, each function is realized by software, firmware, or a combination of software and firmware. At least one of software and firmware is described as a program. At least one of software and firmware is stored in the memory 92. The processor 91 realizes each function by reading and executing the program stored in the memory 92. The processor 91 is also called a CPU (Central Processing Unit), a central processing unit, a processing unit, an arithmetic unit, a microprocessor, a microcomputer, and a DSP. For example, the memory 92 is a nonvolatile or volatile semiconductor memory such as a RAM, a ROM, a flash memory, an EPROM, an EEPROM, or the like, a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, a DVD, or the like.

  When the processing circuit includes the dedicated hardware 93, the processing circuit is, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a combination thereof. For example, each function is realized by a processing circuit. For example, each function is realized by a processing circuit collectively.

  Further, a part of each function may be realized by dedicated hardware 93, and the other part may be realized by software or firmware.

  As described above, the processing circuit realizes each function by the hardware 93, software, firmware, or a combination thereof.

Reference Signs List 1 DC power supply 2 Inverter main circuit 3 Filter 4 Load 5 Inverter controller 6 Command value generator 7 Phase information calculator 8 Carrier frequency selector 9 Carrier generator 10 PWM generator 91 Processor 92 Memory 93 Hardware A, B, C Zero-cross point timing

Claims (1)

An inverter control device that controls the inverter by a pulse width modulation signal generated based on a magnitude comparison between an inverter output command value and a carrier signal representing a target voltage waveform to be output by the inverter due to a periodic change,
A phase information calculating unit for predicting a carrier frequency change timing at which the inverter output command value becomes 0 every n (n is a natural number) cycles from a timing at which the inverter output command value becomes 0 every 1/2 cycle;
A carrier frequency selection unit that randomly selects one from a plurality of predetermined carrier frequencies for each of the n cycles;
In the carrier frequency change timing, a carrier generation unit that changes a carrier frequency to one selected by the carrier frequency selection unit and generates the carrier signal according to the changed carrier frequency ,
Before and after the carrier frequency change timing, the carrier waveform is continuous, and the sign of the slope of the waveform does not change,
An inverter control device characterized by the above-mentioned.

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