JPH03128698A - Voltage type inverter - Google Patents

Abstract

PURPOSE:To prevent a voltage rise by connecting the parallel circuit of a DC contactor and a current-limiting resistor between a power rectifier and a power inverter and opening a contact by a voltage controller when the excess of the input currents and input voltage of the power inverter is detected. CONSTITUTION:The parallel circuit of a DC contactor 2 and current-limiting resistors 4, 21 is mounted between a power rectifier 1 and a power inverter 5. The input currents of the power inverter 5 are detected by a CT 22 and a DC current detector 23 and input to a voltage controller 24 while the input voltage of the power inverter 5 is detected 9 and input to the voltage controller 24. When a stationary state is brought after starting and the contactor 2 is closed, the contactor 2 is opened by the controller 24 and voltage is lowered by the resistor 21 when DC currents are brought to 5% of rating or a regenerative state is brought, a transistor switch 7 is turned ON, and DC voltage is lowered to 90% of rating. Accordingly, a voltage rise at the time of low load or the time of regeneration is prevented simply, thus obviating the breakdown of a circuit element.

Description

[Detailed description of the invention] [Industrial application field]

This invention includes a forward converter made of diodes and an automatic inverse converter made of transistors, and performs pulse width modulation control (PWM control) on the inverse converter to obtain a variable voltage frequency at the output. This relates to voltage type inverters.

[Prior Art] FIG. 3 shows, for example, an inverter application manual P. 199, September 1980, September 1980, published by Denki Shoin, is a constituent country that shows the conventional voltage type inverter. In the figure, l is a diode converter as a forward converter, 2 is a DC contactor, 3 is a large-capacity electrolytic capacitor for smoothing, 4 is a current-limiting resistor that charges the large-capacity electrolytic capacitor 3 when the inverter is started, and 5 is a transistor. 6 is a motor as an output, 7 is a transistor switch as a voltage control switch, 8 is a discharge resistor, 9 is a DC voltage detector, and 10 is a DC voltage control device. Next, the operation will be explained. First, a diode converter 1 converts alternating current into a constant voltage direct current, which is smoothed by a large-capacity electrolytic capacitor 3, and an inverter 5 inverts this direct current into alternating current with the voltage and frequency required by the motor 6. . This waveform processing is realized by pulse width modulation control of the inverse converter 5, but this control circuit is omitted in the figure. Since this voltage type inverter has a large-capacity electrolytic capacitor 3 in the DC circuit, the inrush current is limited by opening the DC contactor 2 at startup and charging the large-capacity electrolytic capacitor 3 through the current-limiting resistor 4. I'm there. Further, the DC voltage detector 9 monitors the DC voltage across the large-capacity electrolytic capacitor 3, and when this DC voltage exceeds a predetermined voltage value Vo and increases by ΔV, as shown in FIG. 4(b), This phenomenon is determined by the DC voltage detector 9 to indicate that power is being regenerated. That is, when the electric motor 6 is driven by the energy on the load side at a frequency exceeding the rotational speed at the frequency driven by the inverter 5, the electric motor 6 acts as a generator, so as shown in FIG. 4(a), The direct current Io changes to a negative current and regenerates power to the power source. When this DC voltage exceeds a predetermined value, the detection signal is transmitted to the DC voltage control device 10, and the DC voltage control device 10 controls the transistor switch 7 on/off to control the large capacity electrolytic capacitor 3.
The electric charge is consumed through the discharge resistor 8, and the DC voltage is controlled to be kept below a certain value. [Problems to be Solved by the Invention] Since the conventional voltage type inverter is configured as described above, during power regeneration operation, the DC voltage is
The voltage increased by as much as 15%, and there were problems such as the need to use inverter elements with high breakdown voltage, which made them expensive. This invention was made to solve the above-mentioned problems.During light load electric operation or power regeneration operation, the DC contactor is opened and power is supplied through the resistor, thereby increasing the DC voltage to the rated value. To obtain a voltage type inverter that makes it possible to use inverter elements with low withstand voltage by keeping the DC voltage 10 to 15% lower in advance and controlling transistor switches so that the DC voltage does not exceed the rated value even during power regeneration operation. purpose.

[Means to solve the problem]

The voltage type inverter according to the present invention detects the DC voltage on the input side of the inverter with a DC voltage detector, detects the DC current flowing through the inverter with the DC current detection means, and inputs it into the voltage controller. The voltage controller outputs a control signal for the voltage control switch and an off signal for the DC contactor during power regeneration to suppress a rise in DC voltage.

[For use]

The voltage controller in this invention detects and captures the DC voltage and DC current of the voltage type inverter using a DC voltage detector and DC current detection means, and activates the voltage control switch when the DC current becomes less than a predetermined value during power regeneration operation. Controlled to discharge DC voltage. Further, the DC contactor is switched from on to off to control the DC voltage of the inverter to a value lower than the rated value.

【Example】

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, the same parts as in FIG. 3 are shown with the same reference numerals. 21 is a resistor that supplies power during light load electric operation or power regeneration operation, and 22 is a DCCT for DC current detection ( 23 is a DC current detector, and 24 is a voltage controller that controls the DC voltage according to the load. Next, the operation will be explained. The basic operation is the same as the conventional example, so the explanation will be omitted. First, a DC current is detected by the DCCT 22 and converted into a predetermined signal waveform via a DC current detector 23. When this DC current is below a certain value (for example, 5% of the rating), the voltage controller 24 generates an output signal,
The DC contactor 2 is opened and power is supplied with a voltage drop through the resistor 21. At the same time, the transistor switch 7 is turned ON to control the DC voltage to a value lower than the rated value (for example, 90% of the rated value). In this case, it can be seen that the resistor 21 only needs to consume 0.5% of the power of the rated load, so it can be small. By controlling in this way, the transistor switch 7
Even in consideration of DC voltage ripples caused by response delays, etc., it is possible to maintain the DC voltage below the rated value even in the power regeneration state. In the case of the conventional method, when power regeneration operation starts as mentioned above, the DC voltage changes from the rated voltage Vo to ΔV (usually 10 to 15
%) increases (see Figure 4). On the other hand, in the case of this invention, as shown in FIG.
When the DC current becomes less than a certain value Δ■, it is converted to DCCT2.
2, and the DC voltage is detected by the DC voltage detector 9 and inputted to the voltage controller 24, and the rated voltage Vo
Since control is performed to set the value ΔV1 to a lower value, the DC voltage including the ripple voltage will not exceed the rated value even during power regeneration operation. In addition, in the above embodiment, an example using a DC contactor was described, but as long as the on/off can be controlled,
It may also be a semiconductor switch. In addition, an example was explained in which a resistor 21 was newly provided for power supply during light load electric operation and power regeneration operation.
The current limiting resistor 4 may be made larger and used in common with the current limiting resistor 4. Furthermore, although an example in which transistors are used as the inverter 5 and the voltage control switch 7 has been described, GT○
Other automatic switches such as a gate turn-off switch may also be used.

【Effect of the invention】

As described above, according to the present invention, in addition to the conventional DC voltage control by detecting the DC voltage, a DCCT is provided to detect the DC current, the DC current is waveform-processed by the DC current detector, and the voltage controller Since the voltage control switch is controlled by inputting the input voltage to the voltage control switch, the voltage control switch can meet the specifications with a low withstand voltage element, and since a low-priced device is sufficient, the device can be constructed at a low cost. be.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a voltage type inverter according to an embodiment of the present invention, Fig. 2 is a DC voltage and current characteristic diagram showing the effects of this invention, and Fig. 3 is a block diagram of a conventional voltage type inverter. , FIG. 4 is a conventional DC voltage and current characteristic diagram. In the figure, 1 is a forward converter (diode converter),
2 is a DC contactor, 3 is a large-capacity electrolytic capacitor, 4 is a current limiting resistor, 5 is an inverter, 7. is the voltage control switch (
9 is a DC voltage detector, 21 is a resistor, 22 is a DCCT, 23 is a DC current detector (22,
23 is a direct current detection means>, and 24 is a voltage controller. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A large-capacity electrolytic capacitor is provided between the forward converter and the inverse converter, and a DC contactor and a current limiting resistor are connected in parallel and provided on the output side of the forward converter in order to control the rush current of the large-capacity electrolytic capacitor. , and is provided with a DC voltage detector that detects the DC voltage across the large-capacity electrolytic capacitor during power regeneration operation, and has a voltage control switch that maintains the DC voltage at a constant level. a DC current detection means for detecting a DC current; a voltage controller that takes in the output signals of the DC current detection means and the DC voltage detector, turns on a voltage control switch, and outputs a control signal to open a DC contactor; A voltage type inverter comprising a resistor connected in parallel with the DC contactor.