JPH02248872A - Output voltage detection circuit - Google Patents

Abstract

PURPOSE:To obtain an output voltage detection circuit with limited heating of a resistance by providing a MOSFET in series on the input side of a photocoupler to detect a potential with respect to a bus-line N of a main circuit of phase output voltages of an inverter. CONSTITUTION:In output voltage detection circuits 1, 2 and 3 of an inverter, a negative end of a voltage source 19 is connected to a bus-line N of the inverter, input sectors of a resistance 20 and a photocoupler 18 and a drain end of a MOSFET 17 are connected in series from a positive end thereof and a source end of the MOSFET 17 is connected to the bus N. Moreover, resistances 15 and 16 are connected in series between output terminals U, V and W of the inverter and the bus N and a connection of the resistances 15 and 16 is connected to a gate terminal of the MOSFET 17. Then, resistance values of the resistances 15 and 16 are set so that a voltage at the connection of the resistances 15 and 16 exceeds a threshold voltage of the MOSFET 17 when the output terminals U, V and W are H (high). This enables construction of an output voltage detection circuit with limited heating value by the resistance 20.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a circuit for detecting whether the output voltage of an inverter device is H (a) to a) or L (low).

[Conventional technology]

Fig. 2 is a block diagram of a conventional motor drive PYM inverter. In Fig. 2, six switching elements Ta", Ta-, Tb", Tb-, Tc", Tc are shown.
- by turning on and off the DC voltage Vdc
YM modulation is applied to give the motor a three-phase AC voltage of arbitrary frequency and voltage. At this time, for example, if Ta" and Ta- are turned on at the same time, the DC voltage Vdc is short-circuited and Ta",
Ta'' and Ta- are turned on and off alternately so that they are not turned on at the same time, as this would lead to destruction of Ta-, but in general, it is better to turn off a switching element than to turn it on.
However, during this Ta period, both elements Ta" and Ta- are off, so the motor terminal (U) is in an oven state, i.e. Since the motor terminal voltage becomes uncontrollable, the motor becomes unstable and causes adverse effects such as a large torque ripple Fl.

Therefore, as a conventional method, the potentials of the terminals U, V, and Y with respect to the N bus during the Ta period are detected (detected by a voltage detection circuit (1), etc.), and this detection result and 1'1 are
Compare the M control pattern I (created with the PYM pattern creation circuit (4)), create a pattern that corrects the error that occurred in the Ta period in the Ta correction circuit (5), and apply the resulting pattern to each element. Bass amp + (6) ~ (11
)l is known. This Ta correction circuit improves the adverse effects caused by Ta.

Figure 3 shows a conventional voltage detection circuit ((1) to (3)
) is shown. For example, when motor terminal U is H (high),
A current flows through the resistor R5 to the input side of the two photocoupler, turning on the photocoupler. In the Ta period, Ta', Ta
- Since both are off, depending on the same instantaneous motor current, the reverse diode Ta'' or the reverse diode Ta- turns on.If the motor current is too high, the conventional output voltage detection circuit Since the resistor R1
There were problems such as an increase in power consumption, an increase in loss, a rise in temperature due to heat generation, and a need for a resistor with a large wattage.

For example, if the duty of Ta' and Ta- is 50%,
The power consumption of R, y, is.

Vdc' 1 y, -x- R,2, and in the case of an AC20OY system inverter, V
DC is normally 300V, and the current flowing to the next side of the photocoupler is 20mA.

If the 0 mA current is in the direction shown in FIG. 4-(b), the Ta- reverse direction diode is turned on and the U point becomes Ov.

[Problem to be solved by the invention]

So it's very large. Furthermore, during motor regeneration, Vdc
may rise up to 400V, so 15kQ
2 Normally, when selecting a resistor, the number of watts is about four times the power consumption, so the number of watts for R is 5.3 x 4 = 21.2 per equivalent.
W, which is very large.

One possible way to reduce power consumption is to lower the input current of the photocoupler. However, the Ta period is very short (because of this, the photocoupler is required to have a Goryeo response.

And cheap photocouplers generally have CTR (current transfer ratio)
is near and considering the deterioration of CTR due to aging,
The input current of a photocoupler cannot be lowered unnecessarily.

There is also the problem that lowering the input current makes it less susceptible to noise.

This invention was made to solve the above-mentioned problems, and its purpose is to obtain an output voltage detection circuit that can reduce the power consumption of RI. The output voltage detection circuit according to the invention includes a voltage source whose negative end is connected to the N bus of an inverter, and a resistor, a photocoupler input, and a MOSFET from the positive end of the voltage source.
Connect the drain ends of the MOSFET in series, connect the source end of the MOSFET to the N bus, connect two resistors in series between the inverter output end and the N bus, and connect the two resistors to the connection point. is connected to the gate end of the MOSFET.

[Effect]

Since the output voltage detection circuit according to the present invention is configured as described above, the amount of heat generated is reduced by 2.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a circuit diagram of the present invention.

In the figure, when U is L (low), that is, when element Ta~ is on or the reverse diode of Ta- is on, the MOS
The FET (17) is turned off, the photocoupler (18) is turned off, and the photocoupler output becomes L (1 near). U
When is H (high), that is, whether element Ta" is on or Ta"
When the reverse diode of is on, the resistances R, (15) and R
The voltage at the connection point of 5 (16) is MOS FET (
17) so that the voltage is higher than the VGS threshold voltage.
By selecting the resistance values of (15) and Rs (16), MO
SFET (17) turns on and voltage +1i! A current flows from (19) through the resistor R and (20) to the input side of the photocoupler (18), the photocoupler (18) is turned on, and the photocoupler output becomes H (high).

Since the MOSFET is a magnetic drive type element, it is 9M03F.
It takes almost no current from the main circuit to turn on the ET.

Now, if the VGS threshold voltage mar of MOSFET (17) is 5Y, then V dcmin=
Think of it as if the circuit operates with 100Y.

Vdc
0V, Ta"Ta-'s on/off decorty is 50%, and when motor regenerates, Vdc = 400Y, 10
It becomes 0K 2 .

Also, the loss of the resistor RLl (20) is calculated by setting the voltage of the power supply (19) to +5V and reducing the current flowing to the next side of the photocoupler by 2.
Forward voltage drop at 0mA photo-photocoupler end and MOSFE
Assuming that V++q(On) of T is ignored, W Re =
l 5 x 20mA = OJY Therefore, the total loss for 2 circuits and 1 phase is 0.8 + 0.3 when Vdc = 400V Y = 1. l W This value is 2 compared to W, = 5.31 in the conventional circuit.
It is very small (0%).

Further, in the above circuit, the base power supplies of Ta-, Tb-, and Tc-' of the main circuit can be used as the power supply for each output voltage detection circuit, and the two-circuit configuration can be simplified.

〔Effect of the invention〕

As described above, according to the present invention, since it is configured as shown in FIG. 1, it is possible to obtain an output voltage detection circuit in which the resistance generates less heat.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a conventional inverter device, FIG. 3 is a diagram showing a conventional output voltage detection circuit, and FIGS. ) is Ta
It is a figure explaining the inverter output voltage during a period. In the figure, (1), (2), and (3) are voltage detection circuits, (
4) is a pattern creation circuit, and (5) is a Ta correction circuit. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] In a circuit that detects whether the output voltage of each phase of the inverter is at the potential of the P bus or the potential of the N bus with respect to the N bus voltage of the main circuit, the first Connect the resistor, the input side of the photocoupler, and the drain end of the MOSFET in series from the voltage source and the positive end of the first potential source, and connect the source end of the MOSFET to the negative end of the first voltage source. An output voltage detection circuit further comprising: a voltage dividing circuit connected between the inverter output terminal and the N bus, and a voltage dividing point of the voltage dividing circuit connected to the gate terminal of the MOSFET.