JPH0214319Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an improvement of a dynamic braking device for a voltage source inverter that obtains a dynamic braking force when driving a load using a voltage source inverter that provides a DC output through a rectifier or the like and obtains an AC output from an inverter circuit. .

When driving a load with a voltage source inverter (hereinafter simply referred to as an inverter), for example, the regenerated energy of an induction motor cannot be returned to the power source because the regenerated energy is obtained as a DC output via a rectifier rather than an AC power input. Therefore, the voltage of the output of the DC stage is increased by the regenerated energy, resulting in an overvoltage state, which may cause damage to the switching elements of the inverter. To prevent this, the inverter is usually protected by using overvoltage tripping means. Also,
In this type of inverter, a method is generally adopted in which a dynamic brake circuit is inserted between the positive and negative terminals of the DC stage output to obtain braking force by consuming the regenerated energy. There are various methods for realizing such a dynamic brake circuit, but since the voltage rise time of the DC stage output is fast, many of them use a method of turning the brake resistor on and off using a semiconductor switch.

However, in such a dynamic brake device, it is necessary to select a DC voltage level that requires braking operation at a safe operating point by considering conditions such as power supply fluctuations and load fluctuations. The value cannot be made so high due to various conditions such as protection cooperation, and the difference between the dynamic brake operating point and the overvoltage trip value is small and there is little margin. Thus, when selecting the dynamic brake operating point, it is necessary to carefully examine the power fluctuation rate, the stability and delay of various operations, and other main circuit constants.

1 and 2 are a connection diagram showing a conventional example and an explanatory diagram showing the relationship between its operating point and DC stage voltage.

That is, in the apparatus shown in FIG. 1, a three-phase AC power source 1 is converted into DC by a converter circuit 2 and is supplied via a filter circuit 3, and the output of this filter circuit 3 becomes the DC stage output. Further, the DC stage voltage V _DC is applied to the induction motor 5 through the inverter circuit 4, and variable voltage/variable frequency control is performed by a control circuit (not shown), so that the induction motor 5 is driven by the inverter. Furthermore, as illustrated, a dynamic brake circuit consisting of a semiconductor switch 6 and a resistor 7 is inserted to control the amount of dynamic brake. Note that the semiconductor switch 6 is assumed to be a transistor to simplify the explanation.

Here, 8 is a dynamic brake control circuit. In other words, the dynamic brake control circuit 8
is transformer 811 and diode bridge 812
± power is supplied from the and capacitors 813 and 814, and the operating point can be adjusted by the variable resistor 815 from the input of the DC stage voltage V _DC ,
When the voltage at the output point of variable resistor 815 rises above the voltage of Zener diode 816, current flows through resistor 817 to the base emitter of transistor 818. Here, 819 is a resistor. Therefore, when transistor 818 operates, base amplifier 820 drives semiconductor switch 6. Here, by applying a reverse bias to the semiconductor switch 6 by a negative power supply when the transistor 818 is not in operation, the braking current, that is, the current flowing through the resistor 7 is operated to be cut off.

In addition, Figure 2 shows the AC voltage of the three-phase commercial power supply on the horizontal axis and the DC voltage of the DC stage output on the vertical axis, showing the operating line of the dynamic brake circuit with respect to the input power supply voltage, and W ₁ is the DC voltage. The characteristic line W ₂ of the stage voltage V _DC is an operating line showing the transition of the operating point of the dynamic brake circuit. As described above, it is clear that it is necessary to select the operating point of the dynamic brake device with particular consideration to power supply fluctuations. In other words, if the operating point is too low, the semiconductor switch 6 will remain in constant operation when the power supply voltage rises, resulting in wasted energy being consumed by the resistor 7. Conversely, if the operating point is too high, the withstand voltage of the switching elements etc. will be increased. There must be.

FIGS. 3 and 4 are connection diagrams showing another conventional example and explanatory diagrams showing the relationship between the operating point and the DC stage voltage. That is, in the circuit shown in FIGS. 3 and 4, the dynamic brake control circuit 8' has a resistor 821 as exemplified in addition to the circuit shown in FIG. It is connected through a resistor 821 to have a function of compensating for power supply fluctuations at the operating point. Therefore, the operating line shown in FIG.
The difference from FIG _{. 2 is that the operating point changes in proportion to the power supply voltage, as shown in W 2} '.

As shown in Figures 1 and 2, the circuits shown in Figures 1 and 2 do not have a power supply fluctuation compensation circuit and are set to values that do not operate when the power supply voltage is high even in the rated power supply state. As the DC stage voltage V _DC is increased excessively during the operation delay time, the margin with the operating point of the overvoltage tripping means is lost, and the margin is reduced by the resistance value of resistor 7 and the capacitance of the DC stage capacitor. It has drawbacks of varying degrees.

Furthermore, the devices shown in Figures 3 and 4 have their operating points variably shifted due to power fluctuations, eliminating the drawbacks shown in Figures 1 and 2, but the DC stage There is a drawback that the maximum brake torque also decreases as the voltage V _DC decreases.

The present invention has been developed in order to eliminate the above-mentioned problems.The dynamic brake operating point is made to vary according to power supply fluctuations, and is maintained at a constant position especially below the rated power supply voltage. The present invention provides a dynamic brake device using a voltage source inverter that has a margin between the two and can avoid a decrease in brake torque when the power supply decreases. The present invention will be explained in detail below with reference to the drawings.

5 and 6 show the apparatus shown in FIG.
1 is a connection diagram of an embodiment of the present invention similar to the device shown in the figure, and an explanatory diagram showing the relationship between its operating point and DC stage voltage, where 8'' is a dynamic brake control circuit and W ₂ '' is an operating line. Figures 1 to 4 in the diagram
The same reference numerals as in the figure indicate parts having the same function.

That is, the dynamic brake control circuit 8'' shown in FIG. 5 has a resistor 82 in the dynamic brake control circuit 8' shown in FIG.
1 is further provided with a Zener diode 822 in series with the illustrated polarity direction, and can act to obtain the operating line W ₂ '' shown in FIG. 6. Except for such changes. The other parts are the same as those in FIGS. 3 and 4, so their explanation will be omitted. Note that the Zener diode 8
22 is assumed to have its Zener voltage selected so as to be approximately equal to the value of the negative voltage when the power supply is rated.

In other words, the dynamic brake control circuit 8'' is
Below the voltage of the Zener diode 822, the series circuit of the resistor 821 and the Zener diode 822 becomes non-conductive, so power supply voltage compensation is not performed and the operating point becomes constant, and when the voltage exceeds that voltage, dynamic brake control is activated. It has the same effect as circuit 8'. Therefore, as shown in FIG. 6, it is clear that the operating point of the operating line W ₂ '' becomes constant from near the rated voltage.
is shown as being composed of components such as transistors and Zener diodes, but it may also be constructed using operational amplifiers, ICs, etc.
It is also easier to replace other components with circuits that perform the same operations.

As explained above, according to the present invention, it is possible to provide a device that effectively compensates the dynamic brake operating point, has a sufficient margin, and can avoid a decrease in brake torque.

[Brief explanation of the drawing]

Figures 1 and 2 are connection diagrams showing a conventional example and explanatory diagrams showing the relationship between its operating point and DC stage voltage. Figures 3 and 4 are connection diagrams showing another conventional example and their operating points. An explanatory diagram showing the relationship between the DC stage voltage, and FIGS. 5 and 6 are connection diagrams showing an example similar to the device shown in FIG. 1 and the device shown in FIG. 3 according to the present invention, and an explanation showing the relationship between the operating point and the DC stage voltage. It is a diagram. 2...Converter circuit, 3...Filter circuit,
4...Inverter circuit, 6...Semiconductor switch,
7...Resistor, 8,8',8''...Dynamic brake control circuit, _W1 ...Characteristic line of DC stage voltage V _DC , _W2 , _W2 ', _W2 ''...Dynamic brake circuit line of motion.

Claims (1)

[Scope of utility model registration request] Equipped with a semiconductor type dynamic brake circuit consisting of a resistor and a semiconductor switch in series between the positive and negative terminals of a DC stage of a voltage type inverter that receives AC power, provides DC output via a rectifier, etc., and receives AC output from the inverter circuit. In a dynamic brake device for a voltage source inverter that controls the semiconductor switch using the output of a comparator that detects a voltage rise in the output of a DC stage, the operating point of the comparator is provided with a power fluctuation compensation function that operates proportionally to fluctuations in the power supply. and a reference value generation means in which the power supply fluctuation compensation function is disabled, and the power supply fluctuation compensation function is activated at a power supply voltage equal to or higher than the reference value of the reference value generation means, and at a power supply voltage less than the reference value. 1. A dynamic brake device for a voltage source inverter, characterized in that the compensation function is disabled and the comparator is operated at a constant operating point.