JPH0322866A - Pwm control device for inverter - Google Patents

Abstract

PURPOSE:To realize low-loss, efficient and low-noise PWM control of an inverter by a method wherein the title device is provided with a PWM control means, switching a chopper circuit with a switching frequency which is two times of the switching frequency of an inverter bridge. CONSTITUTION:The PWM(pulse width modulation) of an inverter unit is driven through a PWM control circuit 28 by a PWM signal obtained by comparing the output V23 of a triangular wave generator 23 and the voltage -V23 of the reverse phase of the output V23 with the output of an amplifier 27. In this case, a chopper unit is switched through a PWM control circuit 24 by the PWM signal or an output 30, obtained by passing the triangular wave output V23 through a frequency doubler 30, as a carrier. Accordingly, the output frequency component and a differential frequency component become 2f, which is frequency component except an audible frequency even when the frequency (f) is selected so as to be a comparatively low frequency, whereby the PWM control of the inverter may become low-noise.

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) The present invention is a CVCF suitable for offices that require quietness.
This invention relates to a PWM control device for an inverter such as the above.

(Prior art) Conventional UPS (UNITERRLIPTIBL)
The configuration of the E PowerSOURCE is shown in FIG. 5 and will be explained.

From the commercial power supply 1 through the reactor 2 and current detector 3, the I
G B T (Insulated gate B
ipolartranstor) 4. 5
A chopper circuit consisting of diodes 6 and 67 controls the input current from the commercial power supply in a sinusoidal or waveform manner, smoothes the DC voltage with a capacitor 8, and charges the battery 9 in a floating manner.

DC voltage I G B T lO. 11. PWM (pulse
It is converted into alternating current by width modulation control and applied to the primary side of the transformer 16, and the harmonics caused by the PWM control are absorbed by the secondary side capacitor l7. The output voltage of the transformer 1B is detected by a transformer 818 and controlled so that the output voltage is constant.

DC voltage Vc detected by voltage detector 20 and voltage reference VR
Compare and use amplifier 2l as a current reference! Current detected by current detector 3 by outputting R! The current is controlled by the amplifier 22, and compared with the output of the triangular wave generator 23, the PWM control circuit 24 outputs a PWM signal to the drive circuit 25.
The voltage of the capacitor 8 is controlled to be constant while converting the input current of the commercial current 1 into a sine wave by controlling the IGBTs 4 and 5 via PWM.

The inverter output voltage is controlled by comparing the AC voltage reference generated by the voltage reference circuit 2G and the inverter output detected by the transformer l8, amplified by the amplifier 27, and comparing it with the triangular wave V23. By P
The drive circuit 29 drives the IGBT of the inverter bridge l4 using the WM signal, and controls the output of the transformer WIG to be constant by PWM control.

(Problem to be solved by the invention) Recently, UPS and cv CF (ConstVnt V
ol stageConstantF”requenC
Y) Electric power sources are increasingly being used as power sources for office machines, and flat power sources are also often installed in offices, and low-noise power sources are now required. .

In the conventional configuration shown in FIG. 5, since the switching elements are controlled by PWM, magnetostrictive noise based on the switching frequency is generated from the reactor 2 and the transformer 16.

In order to prevent this magnetostrictive sound from being heard, the carrier frequency (triangular wave frequency) of conventional PWM was set to 15 to 20 KII.
This was prevented by setting the audible frequency above Z.

However, MOSFET is an element that can perform PWM control at such high frequencies and has low switching loss, but MOS
The on-resistance of FETs is high, and the use of high-voltage, large-current devices has been abandoned for economic reasons. Recently, IGBTs have tended to be adopted as high-voltage, large-current devices in this range, but IGBTs have large switching losses due to till current, and PWM control at 15 to 20 KHZ or higher reduces converter efficiency. there were.

Therefore, the control circuit shown in FIG. 6 has been adopted as a conventional method for reducing noise without reducing efficiency.

That is, the chipper circuit performs PWML control using the frequency of the first triangular wave generator 23a, and the inverter circuit performs PWM control using the frequency of the second triangular wave generator 23b, thereby slightly lowering the frequency of the second triangular wave generator. Through control, a balance between efficiency and noise was achieved.

As shown in FIG. 7, the PWM of the inverter bridge is determined by comparing the triangular wave V23 and V23, which is in opposite phase to V23, with the output V27 of the intensifier 27 to obtain a PWM waveform. BTIO is PWM controlled by A signal, and IGBT13 is PWM controlled by B signal.
When the WM control is performed, the waveform applied to the converter l6 becomes a waveform with a frequency twice the carrier frequency, as shown in C.

However, in the circuit shown in Figure 6, a frequency component twice the frequency of the first triangular wave and the second triangular wave is generated, so the difference between these two becomes the beat, and the beat frequency is audible to the ear. It has been difficult to achieve both sound and high efficiency in the past.

The purpose of the present invention is to improve the shortcomings of the conventional method, reduce the switching frequency as much as possible and improve the efficiency.
The present invention also provides a PWM control device for an inverter that does not generate switching frequency components in the audible frequency range.

[Structure of the Invention] (Means for Solving the Problems) The inverter bridge uses a PWM method that compares the carrier frequency with its inverse T-channel to obtain an output with a frequency twice the switching frequency. By performing PWM control at twice the frequency synchronized with the carrier frequency, all frequency components, including these beat frequency components, are made to be more than twice the carrier frequency.

(Function) Inverter bridge output is twice the carrier frequency!!
Since the chipper circuit also has components that are an integral multiple of twice the carrier frequency, these beat frequencies also have components that are more than twice the carrier frequency.

(Example) An embodiment of the present invention is shown in FIG. 1 and will be described.

Components that are the same as those in FIG. 5 are designated by the same numbers, and explanations thereof will be omitted. In FIG. 1, the main circuit portion is omitted and only the control circuit is shown.

The PWM of the inverter section is the PWM$IIgIJ circuit 28
The chopper section is driven by a PWM signal that compares the output V23 of the triangular wave generator 23, the VTr with the opposite phase of V21, and the output of the amplifier 27, and the chopper section performs PWM control using the output V30 of the triangular wave V23 passed through the double frequency circuit 30 as a carrier. The circuit 24 switches it as a PWM signal.

As explained in FIG. 7, when the frequency of the triangular wave V23 is f, the inverter bridge output is 2nf (n=1.2
...) has a component of components. On the other hand, the chopper part is V30 (
2 [') as the carrier frequency to PW 1, the output has a frequency component of n 2f (n-1.2...), so the beat of these two is 2nf (n=o, 1...
), so the lowest frequency is an integral multiple of 2f. For this reason, if f is selected as IOKIIZ, it will not contain any high frequency components below 20KIIZ, and therefore will not contain any audible frequency components.

As explained above, according to this embodiment, the inverter section is PWM-controlled with a carrier frequency of frequency f, and the chipper section is PWM-controlled with a carrier frequency of 2f, so that the output frequency component and the difference Jim wave number component become 2f. Even if f is selected to be a relatively low frequency (.), it becomes a frequency component outside the audible frequency, so it is possible to provide PWM control with low noise, low switching loss, and high efficiency.

In addition, as shown in Fig. 2, the actuator 2 from the single-phase power supply
is converted into direct current by a diode bridge 60 via
The present invention can be applied in exactly the same way even when a boost chopper circuit consisting of an IGBT 4 and a diode 6 is configured.

Further, as shown in FIG. 3, the direct current Ifi. B1 can be applied in the same way even when a step-down voltage converter circuit consisting of an IGBT 4, a diode 6, and a reactor 62 is configured.

In addition, as shown in Fig. 4, the actuator 2 from the three-phase power supply,
It can be similarly applied to the case where a step-up chopper circuit consisting of diode bridges 60, i (; BT4 and diodes 6) is used to supply a load to the transformer 67 from an inverter bridge 134, 65, 68 by an inverter. Of course.

Note that there is also a method of using a double wave rectifier circuit or a D/A converter as the modulation frequency doubling circuit.

Furthermore, it goes without saying that the above explanation can also be applied to the case where PWM control is performed digitally.

[Effects of the Invention] According to the present invention, the inverter section is PWM-controlled with a carrier frequency of frequency f, and the harmonic component of the inverter output section is reduced to 2f.
The chopper section has a carrier frequency of 2f and P
Through WM control, by making the harmonic components at each output part an integer multiple of 2f, these beat frequencies are also an integer multiple of 2f, and by making 2f higher than the audible frequency, f is lowered. Therefore, it is possible to provide PWM control of an inverter with low loss, high efficiency, and low noise.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention, and FIGS. 2, 3, and 4 show other embodiments of the present invention. 5 and 6 are block diagrams of conventional PWM inverters, and FIG. 7 is a diagram explaining the operation of the conventional PWM inverter. 1... Commercial power supply 3... Power supply detector 6, 7... Diode 9... Battery 10, 11, 12. 13...iGBTl4...
・Inverter bridge 16...Transformer 18...Transformer 20...Voltage detection wire 23...Triangular wave generator 25...Drive same path 27...Switch 29...Drive same path 2...Reactor 4. 5...I GBT 8...Capacitor 17...Capacitor 19...Voltage leveling 21.22...1 width evaporator 24...PWM circuit 26...Voltage leveling circuit 28...・PWM circuit 30...double circuit

Claims (1)

[Claims] It is equipped with a chopper circuit that obtains a DC voltage through PWM control of the input current, and an inverter bridge that further performs PWM control on the DC voltage and converts it into an AC voltage, and the voltage waveform of the AC voltage due to the PWM control is set at the switching frequency of the inverter bridge. PWM in which the switching frequency of the chopper circuit is set to twice the switching frequency of the inverter bridge,
PWM of an inverter characterized by providing a control means
Control device.