JPH04268A - Inverter device - Google Patents

Abstract

PURPOSE:To decrease mechanical vibration and noises by decreasing 4 high-level harmonic components in the output of an inverter device by diffusion of a triangular carrier wave spectrum. CONSTITUTION:The spectral diffusion waveform generation controller 11 of the substantially sinusoidal waveform generation control circuit of an inverter device determines a reference wave frequency and voltage corresponding to a command frequency and indicates them to a sine wave generator 12. At the same time, the spectral diffusion waveform generation controller 11 controls a triangular wave generator 13 to generate a spectrally diffused triangular wave. A waveform comparator 14 compares a sine wave transmitted from the sine wave generator 12 with a spectrally diffused triangular wave, the frequency of which changes every time interval T and which is transmitted from the triangular wave generator 13, and generates a pulse train.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inverter device, and particularly to a sine wave approximation PWM type inverter device used for variable speed drive of electric motors in cooling equipment, industrial equipment, etc.

[Prior Art] As a method of inverter devices used for variable speed drive of induction motors, brushless DC motors, etc., a sine wave approximation P
WM (Pulse Width Modulation) is a transistor bridge, 5 is a sine wave approximation waveform generation control circuit, 6 is a frequency command signal input terminal, and 7 is a transistor in the inverter device.
This is the output end of the bridge 4.

The operation of this inverter device is as follows. An alternating current voltage supplied from an alternating current power source 1 is rectified into direct current by a rectifier bridge 2, and further smoothed by a smoothing capacitor 3 to become a stable direct current voltage. This DC voltage is supplied to the transistor bridge 4. The sine wave approximation waveform generation control circuit 5 generates a pulse train that alternately turns on and off three sets of upper and lower transistors of the transistor bridge 4. As a result, a three-phase AC voltage having a waveform approximating a sine wave is outputted to the output terminal 7 at a frequency applied to the frequency command signal input terminal 6 .

When an induction motor or a brushless DC motor is driven at variable speed by the inverter shown in Fig. 2, the third
As shown in the figure, the ratio of frequency and voltage (inverter output voltage) is often controlled to be constant. This is widely used because it allows electric motors to operate more efficiently. In order to realize such control, the sine wave approximation waveform generation control circuit 5 controls the transistor bridge 4 to
The DC voltage applied to the bridge 4 is pulse width modulated (PW
M) controls the frequency of the output voltage output from the output terminal 7 as a sinusoidal approximate waveform and the voltage ratio to the DC voltage.

In this case, a method called triangular wave comparison PWM as shown in FIG. 4 is generally adopted as PWM. This is done by comparing a square wave and a sine wave as shown in Fig. 4(A) to generate a pulse train shown by the solid line in Fig. 4(B), and performing PWM of the DC voltage with this pulse train. This method controls the output voltage and frequency. in this way,
As shown in Figure 4 (A), by changing the voltage ratio (b/a) and frequency of the reference wave and carrier wave, an approximate sinusoidal waveform as shown by the dotted line in Figure 4 (B) can be obtained. .

FIG. 6 shows details of one phase of the sine wave approximation waveform generation control path 5 in FIG. 2 for realizing the triangular wave comparison PWM method in FIG. , a voltage-variable/frequency-variable sine wave generator 22, and a voltage-fixed/frequency-variable sine wave generator 22.
It is composed of a frequency variable triangular wave generating section 23 and a waveform comparing section 24 that compares a sine wave and a triangular wave.

The waveform generation control unit 21 determines the reference wave frequency and voltage corresponding to the command frequency, and instructs the sine wave generation unit 22 to determine the reference wave frequency and voltage, and at the same time instructs the triangular wave generation unit 23 to determine the carrier wave frequency. Usually, the value of the carrier wave voltage is fixed. The waveform comparison unit 24 compares the voltage of the sine wave output from the sine wave generation unit 9 and the voltage of the triangular wave output from the triangular wave generation unit 23,
A pulse train as shown by the solid line in FIG. 4(B) is generated.

This pulse train is supplied to the transistor bridge 4 shown in FIG. 2, and PWM control is performed.

[Problems to be Solved by the Invention] The conventional inverter device described above only outputs an AC voltage with a waveform approximating a sine wave, and the actually output voltage waveform contains harmonics other than the reference wave. Contains many wave components.

Among the harmonic components, especially those in the low frequency range induce problems such as a decrease in motor efficiency, mechanical vibration, and noise.

FIG. 5(A) shows an example of the voltage spectrum of the output of a conventional inverter device, with the reference wave being 10H2 and the carrier wave being 2.
010 Hz s G irradiation wave to carrier amplitude ratio (4th
The case where b/a) in the figure is set to 0.1 is shown. As shown in the figure, there are many high-level components in the audible frequency range (usually below 10-odd kHz), which is a cause of mechanical vibration and the noise caused by it.

The present invention has been made to solve the above problems, and can reduce as much as possible the high-level harmonic components contained in the output of an inverter device using a sine wave approximation PWM method, thereby alleviating the problems of mechanical vibration and noise. The purpose is to provide an inverter device.

[Means for Solving the Problems] In order to solve the above problems, the present invention uses a triangular wave as a carrier wave and a sine wave as a reference wave, and pulse width modulates a DC voltage with a pulse train obtained by comparing and calculating these waves. This inverter device uses a so-called sinusoidal wave approximation PWM system, which obtains an alternating current voltage with an approximate sinusoidal waveform, and is characterized by having means for changing the carrier wave frequency in a time-series manner within a reference wave period.

[Operation] If the carrier wave frequency is fixed in correspondence with the reference wave frequency (inverter output fundamental wave component) as in a conventional sine wave approximation type inverter device, harmonic components that are integral multiples of the carrier wave frequency will be induced at a high level. be done.

On the other hand, when the carrier wave frequency is changed within the reference wave period as in the present invention, the spectrum of the carrier wave component is spread within a certain band, which causes harmonics that cannot be completely removed in principle. Since the wave components are also spread spectrum, the level of each spectrum of harmonic components is effectively reduced.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a detailed configuration of the -phase component of a sine wave approximation waveform generation control circuit 5 (see FIG. 2) in an inverter device according to an embodiment of the present invention.

The sine wave approximation waveform generation control circuit shown in FIG. The waveform comparator 14 compares the triangular wave and the triangular wave.

The configuration and operation of the inverter device except for this sine wave approximation waveform generation control path 5 are basically as explained in the section of the prior art. That is, in the inverter device shown in FIG. 2, the AC voltage supplied from the AC power supply 1 is rectified by the rectifier 1. The voltage is rectified into direct current by the voltage regulator 2, and further smoothed by the smoothing capacitor 3, resulting in a stable direct current voltage. This DC voltage is supplied to the transistor bridge 4.

The sine wave approximation waveform generation control circuit 5 generates a pulse train that alternately turns on and off three sets of upper and lower transistors of the transistor bridge 4. As a result, a three-phase AC voltage having the frequency given to the frequency command signal input terminal 6 is outputted to the output terminal 7.

As already mentioned, as a method of generating a sine wave approximation waveform by pulse width modulation (PWM), a control method called triangular wave comparison PWM as shown in FIG. Comparison PWM is used.

Next, the sine wave approximation waveform generation control circuit of this embodiment shown in FIG. 1 will be explained. In FIG. 1, a spread spectrum waveform generation control section 11 determines the reference wave frequency and voltage corresponding to the command frequency, and instructs the sine wave generation section 12 to do so. Further, the spread spectrum waveform generation control section 11 simultaneously controls the triangular wave generation section 13 to generate a triangular wave having a spread spectrum according to the following rules.

(2) A frequency fn (n is a slot number) is assigned to each fixed time slot T that is sufficiently short with respect to the reference wave period TR.

■ In each time slot, frequencies fl, f2 . f3. ..., one frequency is selected from among fk, and the frequency of occurrence is made uniform.

From the above, the output P (t) of the triangular wave generator 13 is calculated by the following formula (
1).

P (t) -Σ a U7 (t-nT) S
(2r f n t) n - relaxation (1) a: Amplitude of triangular wave (constant) Ut (t): 1 (0<t≦T)0(t≦0
．． t>T) S(2πfnt): In relation to the triangular wave equation (1) with an amplitude of 11 and a frequency fn, the following equation (2) exists between the reference wave period Tll and the time slot T.

TR=kT (2) In other words, in order to make T sufficiently large relative to T, setting k to a sufficiently large value is a necessary condition for spreading the spectrum evenly and at a low level. Become.

The waveform comparator 14 compares the sine wave output from the sine wave generator 12 and the triangular wave output from the triangular wave generator 13 which has a spread spectrum, that is, the frequency changes at each time interval T, and compares the sine wave output from the sine wave generator 12 with the triangular wave whose frequency changes at every time interval T. A pulse train as shown in B) is generated. This pulse train is supplied to the transistor bridge 4 in FIG. 2, where the DC voltage is switched and pulse width modulated, so that a three-phase AC voltage with a waveform approximating a sine wave is output from the output terminal 7. Ru.

FIG. 5(A) shows the voltage spectrum (relationship between voltage amplitude and frequency) of the output of an inverter device using the conventional sine wave approximation method. In this case, the output frequency of the inverter device (equal to the reference wave frequency) is 10 Hz, the voltage amplitude ratio (b/a in Figure 4) is 0.1, and the carrier wave frequency is fixed at 2.010 Hz. .

On the other hand, FIG. 5(B) shows the voltage spectrum of the output of the inverter device according to the embodiment of the present invention, and the output frequency of the inverter device is 10 Hz and the voltage amplitude ratio is 0.
．． 1 is the same condition as in Fig. 5(A), and the carrier frequency is 1,
10 in 30Hz intervals from 890Hz to 2,160H7
It shows the average voltage spectrum for one cycle when changed to type 81.

In FIG. 5(B), as is clear from the comparison with FIG. 5(A), all the high-level harmonics that were a problem in the past have been compressed to 1/10 or less. Also, although it is not necessarily clear from the diagram, each spectral line is conventionally one, but in the embodiment of the present invention there are 10, which shows the effect of spectrum spreading.In addition, the above-mentioned embodiment In the sine wave approximation waveform generation circuit 5
A normal sequence was generated by comparing a triangular wave as a carrier wave and a sine wave as a reference wave, but the information on the pulse train obtained by performing the comparison calculation in advance is stored in a digital memory etc. and read out. The pulse train may also be generated by

In addition, the present invention can be implemented with various modifications without departing from the scope of the invention.

[Effects of the Invention] As explained above, according to the present invention, sine wave approximation PWM
By changing the carrier wave frequency in the inverter device over time within the reference wave period and spreading the spectrum of the carrier wave (triangular wave), it is possible to reduce the high-level harmonic components contained in the output of the inverter device. , can alleviate mechanical vibration and noise problems.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a sine wave approximation waveform generation control circuit in an embodiment of the present invention, FIG. 2 is a block diagram showing the general configuration of a sine wave approximation PWM inverter device, and FIG. A diagram showing the relationship between the voltage and frequency of an inverter device, FIG. 4 is a diagram for explaining the principle of the sine wave-triangular wave comparison method, and FIG. 5 is a diagram showing the voltage spectrum of the inverter device output according to the conventional technology and the implementation of the present invention. FIG. 6 is a block diagram of a sine wave approximation waveform generation control circuit in a conventional sine wave approximation PWM inverter device. 1... AC power supply, 2... Rectifier bridge, 3... Smoothing capacitor, 4... Transistor bridge, 5
... Sine wave approximation waveform generation control circuit, 6... Frequency command signal input terminal, 7... Transistor bridge output terminal, 11... Spread spectrum waveform generation control section, 12.
... Sine wave generating section, 13... Triangular wave generating section, 14...
・Waveform comparison section. Applicant's agent Patent attorney Takehiko Suzue Figure 4

Claims (1)

[Claims] In an inverter device that uses a triangular wave as a carrier wave and a sine wave as a reference wave, and obtains an AC voltage with a waveform approximating a sine wave by pulse width modulating the DC voltage with a pulse train obtained by comparing these waves, the carrier wave frequency is used as the reference wave. An inverter device characterized by having means for changing time series within a cycle.