JPS637168A - Power unit for inverter - Google Patents

Abstract

PURPOSE:To improve a load efficiency by controlling a DC output voltage on the basis of an output frequency set value or a load state to set a PWM (pulse-width modulation) waveform having high basic wave content as an output voltage of an inverter. CONSTITUTION:When an AC input voltage is rectified to a DC voltage by a diode bridge 1, the DC voltage is detected by resistors 8, 9 in a detector 5, and input to a differential amplifier 10. An output frequency set value is input through a D/A converter 11 to the amplifier 10. An AC input voltage waveform is collected by a transformer 4, multiplied by the output signal of the detector 5 by a multiplier 6, and then input to a differential amplifier 7. The amplifier 7 compares the output from the multiplier 6 with the terminal voltage of a resistor 15, and applies a control signal through an inverting amplifier 14 to a transistor 2. Thus, the ON/OFF operation of the transistor 2 is controlled to obtain a stable DC output voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an inverter power supply device, and more particularly to a device that improves the method of converting alternating current to direct current.

(Prior Art) Conventionally, as a method for obtaining a DC voltage that serves as the M source of the inverter output in an inverter power supply device, for example, a rectifier circuit using a diode bridge as shown in FIG. 4 or a voltage doubler rectifier circuit as shown in FIG. 5 has been used. However, these circuits have a problem in that the DC output voltage 0 changes in proportion to the fluctuation of the AC input voltage Vi.

Therefore, as shown in FIG. 6, a high power factor power supply circuit has been used that follows and controls the waveform of the input voltage ■i to obtain a stable DC output voltage Vo.

That is, the DC voltage Vo is detected by the resistors 61 and 62, and compared with the reference voltage VSt set by the Zener diode 63 by the differential amplifier 64.

Further, the input voltage waveform detected by the transformer 65 is multiplied by the output signal of the differential amplifier 64 in a multiplier circuit 66, and this is compared with the DC voltage rectified by the diode bridge 67 in the differential amplifier 68. . Then, the output signal of the differential amplifier 68 controls the transistor 69 to stabilize the DC output voltage 0.

In this way, it has become possible to obtain a stable DC output voltage Vo even if the AC input voltage vi fluctuates.

(Problem to be solved by the invention) However, since the circuit shown in FIG. It is necessary to reduce the pulse width of the PWM (pulse width modulation) signal for output voltage control, and as a result, the efficiency of the motor etc. driven by this inverter output may deteriorate, or the chopper noise caused by PWM may increase. There was a problem in that leakage current increased.

Thus, an object of the present invention is to provide an inverter power supply device that solves the problems of the prior art described above, and can improve motor efficiency at low frequency and low voltage output, reduce chopper noise, and reduce leakage current. There is a particular thing.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the inverter power supply device of the present invention converts an AC input voltage into a DC voltage, inputs an output frequency setting value, and converts the AC input voltage into a DC voltage. In an inverter power supply device that converts a voltage into an inverter output having a frequency of this set value and supplies this to a load, the effective value of the AC input voltage is calculated based on the output frequency set value or the load current flowing through the load. It is equipped with a control section that changes the value within a range of approximately σ times or more.

(Function) By providing the control unit as described above, it is possible to operate with a lower DC voltage when the output frequency setting value is low or when the load current is small, which allows the fundamental wave content to be high. It is possible to set a PWM waveform with a large pulse width.

(Example) Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a configuration diagram of an inverter power supply device according to an embodiment of the present invention. A transistor 2 for output current control is connected in parallel to the output side of a diode bridge 1 for full-wave rectification of an AC input voltage Vi, and a control 11 section 3, which is a feature of the present invention, is connected to the gate of this transistor 2. ing.

This control unit 3 has a transformer 4 which inputs an AC input voltage 1.
, a detection section 5 that detects the DC output voltage ■0, a multiplication circuit 6 that multiplies the input voltage waveform captured by the transformer 4 by the output signal S1 of the detection section 5, and the output signal of this multiplication circuit 6 and a diode bridge. It consists of a differential amplifier 7 that takes the difference from the output signal of 1 and amplifies it to output a control signal S2, and an inverting amplifier 14 that inverts the control signal S2.

Further, within the detection section 5, a differential amplifier 10 is provided which takes the difference between the DC output voltage Vo detected by the resistors 8 and 9 and a reference voltage, amplifies the difference, and outputs the difference as an output signal S1. The reference voltage side of this difference e amplifier 10 has D/
The output frequency setting value f is inputted through the A converter 11, and is also inputted to the Zener diode 13 through the diode 12.
and a power supply Vcc are connected.

Next, the operation of this embodiment will be described.

First, when the AC input voltage ■i is rectified into a DC voltage ■0 by the diode bridge 1, this DC voltage Vo is detected by the resistors 8 and 9 in the detection section 5, and the differential amplifier 1
It is input to 0. - side, output frequency setting value f G, t
The D/A converter 11 converts it into an analog voltage proportional to the frequency, and the differential amplifier 10 uses it as a reference voltage yst.
is input. Then, in the differential amplifier 10, the difference between the DC voltage vO and the reference voltage ■st is taken and amplified to become an output signal S1.

Further, the AC input voltage waveform is captured by the transformer 4, multiplied by the output signal S1 of the detection unit 5 by the multiplier circuit 6, and then inputted to the differential amplifier 7.

A voltage corresponding to the voltage drop across the resistor 15 due to the negative output current of the diode bridge 1 is input to the negative input terminal of the differential amplifier 7 . As a result, the differential amplifier 7 outputs a control signal S2 of "1" when the output from the multiplier circuit 6 is larger than the negative input from the resistor 15, and outputs a control signal S2 of "O11" in the opposite case. . Then, this control signal S2 is inputted to the negative input terminal of the inverting amplifier 14 and inverted, and then
It is input to the gate of transistor 2. Thereby, the on/off of the transistor 2 is controlled, and a stable DC output voltage vO is obtained.

Therefore, when the output frequency setting value f is low, the reference voltage VSt input to the differential amplifier 10 becomes small, so that the DC voltage 0 detected by the resistors 8 and 9 becomes the reference voltage VSt.
A signal S1 that controls the on/off of the transistor 2 so as to lower the DC voltage vO from the differential amplifier 1o
is output.

As a result, the DC voltage Vo is stabilized at a low value.

Furthermore, when the reference voltage VSt becomes too low and the DC voltage ■0 becomes smaller than the instantaneous value of the AC input voltage ■i, even though the transistor 2 is controlled by the output signal S2 of the differential amplifier 7, the The capacitor at the output end is charged, causing the DC output voltage VO to
I will not be able to do anything.

Therefore, in such a case, the Zener diode 13 supplies a voltage approximately σ times the effective value of the AC input voltage 1 to the differential amplifier 10 via the diode 12, and this voltage becomes the reference voltage Vst. It is configured.

In addition, as shown in Figure 2 as a PWM pattern,
By setting the voltage in the high frequency section with a DC output voltage of 0 and writing a pattern that takes into account motor efficiency, noise, etc., and writing the same voltage setting pattern using conventional PWM in the low frequency section, operation at all frequencies is possible. It becomes possible.

Further, if the motor voltage is set so that the lowest operating frequency is the lowest value of the DC output voltage vO, it is possible to perform pulse amplitude modification JA (PAM) at all frequencies.

Further, in the above embodiment, the output frequency setting value f was D/A converted to the reference voltage VSt, but as shown in FIG. It may be converted into a voltage by the setting circuit 33 and used as the reference voltage yst.

[Effects of the Invention] As explained above, according to the present invention, the following excellent effects are exhibited.

(1) By controlling the DC output voltage based on the output frequency setting value or load condition, it is no longer necessary to set the output voltage value using the pulse width, and a PWM waveform with a high fundamental wave content can be set as the inverter output voltage. Therefore, load efficiency is improved.

(2) During low frequency operation, the DC output voltage decreases, so the current ripple also decreases, which reduces motor chopper noise and leakage current.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an inverter power supply device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing an example of PWM pattern setting, FIG. 3 is a partial configuration diagram of another embodiment, and FIGS. FIG. 6 is a configuration diagram showing a conventional example. In the figure, 3 is a control section, 5 is a detection section, 11 is a D/A converter,
12 is a diode, and 13 is a Zener diode. Agent Patent Attorney Nori Chika Ken Shu
Yukio Yuyama Figure 1 Solid-liquid @cf Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] In an inverter power supply device that converts an AC input voltage into a DC voltage, inputs an output frequency setting value, converts the DC voltage into an inverter output having a frequency of this setting value, and supplies this to a load. An inverter power supply device comprising: a control unit that changes the AC input voltage in a range of approximately √2 times or more of the effective value of the AC input voltage based on an output frequency setting value or a load current flowing through the load.