JPH03226274A - Inverter unit - Google Patents

Abstract

PURPOSE:To increase the carrier frequency of an inverter and to detect abnormal state of the inverter accurately with high speed by providing a first current detecting means for detecting the output current from a converter, a second current detecting means for detecting the discharge current from a capacitor, and means for adding thus detected values. CONSTITUTION:DC output current from a converter 1 is detected through a current detector 4 while the voltage across a capacitor 2 is differentiated through a differentiator 8 to produce an AC discharge current of a capacitor 2. DC output current from the capacitor 1 detected through the current detector 4 is added to the AC discharge current of the capacitor 2 in an adder 9, the sum is then compared with a detected value of DC input current to an inverter 3 and fed to a comparator 5. Since a large surge voltage is prevented, high speed switching operation can be carried out with transistors having low rated voltages.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an inverter device used in a drive control device for a servo motor, a lower speed drive of an induction motor, an uninterruptible power supply (UPS), and the like.

(Prior Art) Figure 7jS5 is a circuit diagram showing an example of a conventional inverter device, in which AC input power is converted to DC power by a converter 1, smoothed by a capacitor 2, and input to an inverter 3. The transistor TR that constitutes
It is converted into AC power by I to TR6 and output. Then, the DC input current of the inverter 3 is detected by the current detector 4, and the detected value is sent to the comparator 5. When the detected value of the DC input current of the inverter 3 is equal to or higher than a predetermined value, the comparator 5 interprets that an abnormality has occurred, and all the transistors TR1 to TR6 are turned off by the transistor drive circuit 6.

In such a configuration, for example, transistors rR1,
If TR2 turns on at the same time due to malfunction, these transistors TRI and TR2 will short-circuit the DC power, causing a large current to flow and causing element destruction, or the above-mentioned current detector 4 etc. may work to cause element destruction. Prevent IF
I can do something.

Note that, as the current detector 4, a 11j flow TL flow detector ([1CCT) using a Hall element or a shunt resistor is used. However, when using a shunt resistor, heat generation of the resistor itself becomes a problem, so in a large capacity inverter device, the
CCT is used.

(Problems to be Solved by the Invention) Since the current detector 4 of the conventional inverter device described above is relatively large in physical size, when it is mounted, the transistor TR of the inverter 3 is used as shown in FIG. The wiring between the capacitor 2 and the capacitor 2 becomes long, and a relatively large inductance occurs in the circuit. The wiring between the transistor TR of the inverter 3 and the capacitor 2 includes a transistor TR.
Since a discontinuous current flows with the switching operation of the transistor TR, a large surge voltage is generated when the transistor TR is switched, especially when it is turned off, due to the influence of the inductance described above, causing breakdown of the breakdown voltage of the transistor TR.

In order to suppress such surge voltage, inverter 3 is usually used.
is provided with a snubber 7. However, if the number of carrier cycles of inverter 3 is high (for example, 20KI+□ or more)
However, the heat generated by the three buffs has become a problem.

Furthermore, when a DCCT is used as the current detector 4, it is inevitable that a certain amount of detection delay will occur, and as a result, a delay will occur between the generation of the short-circuit current and the turning off of transistor B, and this turning off operation will occur. There was a risk that the transistor TR would be destroyed during the delay. Furthermore, when the carrier frequency of the inverter 3 is high, there is a problem in that the iron core of the DCCT generates too much heat. To avoid heat generation in the iron core of DCCT, amorphous metal or the like can be used instead of iron, but amorphous metal or the like has the drawback of being expensive.

The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide an inverter device that can increase the carrier frequency of an inverter and can detect an abnormal state of an inverter quickly and accurately. It is about providing.

(Means for Solving the Problem) The present invention provides a converter that inputs AC power and converts it into DC power, a capacitor that smoothes the DC power,
The present invention relates to an inverter device that converts the smoothed DC power into AC power and outputs the same. , a second current detecting means for detecting the discharge current of the capacitor, and a DC input current of the inverter is determined by adding the detected value by the first current detecting means and the detected value by the second current detecting means. This is achieved by providing an adding means.

(Function) The inverter device of the present invention utilizes the fact that the DC input current of the inverter is a composite value of the output current of the converter and the discharge current of the capacitor. The resulting inductance can be reduced to prevent the generation of large surge voltages, and the DC input current of the inverter can be detected quickly and accurately.

(Embodiment) FIG. 1 is a circuit diagram showing an example of an inverter device of the present invention in correspondence with FIG. 5, and the same components are given the same reference numerals and the explanation will be omitted. In this inverter device, a DC output current of a converter 1 is detected by a current detector 4, a voltage across a capacitor 2 is differentiated by a differentiator 8, and an AC discharge current of the capacitor 2 is obtained. The detected value of the DC output current of 1 and the AC discharge current of the capacitor 2 from the differentiator 8 are added by an adder 9, and the result is sent to the comparator 5 as the detected value of the DC input current of the inverter 3. It has become.

Here, the voltage e across the capacitor 2 is expressed by the following equation (1), where C is the capacitance of the capacitor 2, and the AC discharge current of the capacitor 2 is . As shown:
] The AC discharge current i of the capacitor 2 can be determined.

However, in reality, it is only possible to take into account the influence of the internal inductance of capacitor 2, so the voltage e across capacitor 2 is equal to the resistance of the equal deflection section of capacitor 2, which is
Letting the equivalent internal intance of the capacitor 2 be .degree. C., it is expressed by the following equation (3).

When both sides of the above equation (3) are differentiated, the following equation (4) is obtained. Therefore, the output of the j-number divider 8 includes the components of the second and third terms of the above equation (4). To reduce this component and obtain an accurate AC current of 7M for capacitor 2,
Is it necessary to configure the capacitor 2 with an electrolytic capacitor with a small r and a film capacitor with a small temperature? Also,
Regarding the third term in the above equation (4), the frequency band of the d2i/dt2 component is high and the time is short, so the AC discharge current of the capacitor 2 can be accurately detected by removing this component using an LPF etc. .

FIG. 2 is a perspective view showing a mounting example of the inverter device of the present invention shown in FIG.
Since the current detector 4 is no longer disposed between the transistor Tn and the capacitor 2, the wiring between the transistor Tn and the capacitor 2 becomes shorter, the inductance becomes smaller, and the generation of a large surge voltage can be prevented. In particular, by making the height of the terminal r of the transistor TR and the height of the terminal of the capacitor 2 the same, it becomes possible to connect the transistor Tll and the capacitor 2 with the copper bar 10, which further reduces the inductance. Can be made smaller.

FIG. 3 is a circuit diagram showing another example of the inverter device of the present invention, corresponding to FIG. 1, and the same components are given the same reference numerals and the description thereof will be omitted. This inverter device is provided with a current detector 11 in place of the differentiator 8, and the AC discharge current of the capacitor 2 is detected, and the detected value is sent to the adder 9.
It is now sent to . This current detector 11 can detect the high-frequency alternating current discharge current of the conductor 2, and is a small alternating current detector (A(:C).
T) is used. Since this ACCT is inexpensive and does not use semiconductor elements, it has good responsiveness and can perform current detection with high reliability.

FIG. 4 is a perspective view showing an embodiment of the inverter device of the present invention shown in FIG.
Since only a small ΔCC'rll is passed between R and the capacitor 2, the wiring between the transistor TR and the capacitor 2 is shortened, and the inductance is reduced to prevent the generation of a large surge voltage. I can do it. Furthermore, the effective current (+M) flowing in the wiring between transistor 1 and capacitor 2 is relatively small because there is an upper limit to the allowable current of capacitor 2, so the wiring between transistor TR and capacitor 2 is connected to a twisted wire. Alternatively, it can be a coaxial line, etc., and the inductance can be made extremely small.

(Effects of the Invention) As described above, the inverter device of the present invention can prevent the generation of large nerge voltages, so high-speed switching operation is possible even if transistors with low voltage ratings are used. , the snubber becomes unnecessary or small, and the carrier frequency can be increased. Also,
Since the abnormal state of the inverter can be detected quickly and accurately, destruction of the transistors of the inverter can be reliably prevented.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of an inverter device of the present invention,
FIG. 2 is a perspective view showing an example of its implementation, FIG. 3 is a circuit diagram showing another example of the inverter device of the present invention, FIG. 4 is a perspective view showing an example of its implementation, and FIG. 5 is a conventional inverter device. FIG. 6 is a circuit diagram showing an example of this, and FIG. 6 is a perspective view showing an example of its implementation. 1... Converter, 2... Capacitor, 3... Inverter, 4.11... Current detector, 5... Comparator, 6... Transistor drive circuit, 7... Snubber, 8
...Differentiator, 9...Adder, 10...Copper bar

Claims (1)

[Claims] 1. A converter that receives AC power as input and converts it into DC power, a capacitor that smoothes the DC power, and an inverter that converts the smoothed DC power into AC power and outputs it. An inverter device comprising: a first current detection means for detecting the output current of the converter; a second current detection means for detecting the discharge current of the capacitor; and a detection value by the first current detection means. An inverter device comprising: an addition means for adding the detection value obtained by the second current detection means and the detected value to obtain a DC input current of the inverter. 2. The inverter device according to claim 1, wherein the second current detection means is means for differentiating the terminal voltage of the capacitor.