JPS63148873A - Inverter device - Google Patents

Abstract

PURPOSE:To prevent an inverter transformer against DC deviation of magnetic field, by providing a detecting means composed of a saturable reactor to detect DC current flowing to the primary side of the inverter transformer and a resistance. CONSTITUTION:An inverter device using GTO's (gate turnoff thyristers) 2GU-2GY as switching element is composed of GTO's, gate circuits 2U-2Y, and an inverter transformer 3. It feeds the current to a load 4 and is equipped with a gate control circuit 10. On this occasion, a series splicer of a saturable reactor 21 and a resistance 22 is used instead of a shunt as a means to detect DC current, with which the current is inputted into the gate control circuit 10 through an isolating amplifier 23. Thus, even if there is a difference in the product of voltage-time whether by the positive or negative output of the inverter, the current can be detected which is sure to give DC deviation of magnetic field to the inverter transformer by the abovementioned detecting means 21-22.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention relates to an inverter device that converts direct current to alternating current,
In particular, the present invention relates to an inverter device that can prevent DC bias in a transformer on the inverter output side.

(Prior Art) FIG. 4 shows an example of a conventional inverter device using a gate turn-off thyristor (hereinafter referred to as GTO) as a switching element. In Fig. 4, 1 is a DC power supply;
2GU~2GY are GTO12DLI~2DY are feedback diodes, 2U~2Y are each GTo 2G
A gate circuit that amplifies and gives a gate signal to U~2GY,
3 is the inverter transformer, 4 is the load, 10 is 0 2G
This is a gate control circuit that provides a predetermined gate signal to the gate circuits 2U to 2Y of U to 2GX. 20 is a shunt that detects the inverter output current, and 23 is an isolation amplifier.

FIG. 5 is a time chart for explaining the operation of the 46th inverter device. In Fig. 5, 2GU-V~
2GY-V represents the voltage waveform between the anode and cathode of GTO2GU to 2GY, respectively. vl represents the inverter output voltage waveform. The shaded area in Figure 5 is G.
Only TO2U represents the voltage deficit especially in the case of slow turn-on. Since the voltage peak value on the positive side and negative side of the inverter output is equal to the voltage value of the DC power supply, each GTO
If there is a difference in the switching time, a difference occurs in the voltage-time product between the positive side and the negative side of the inverter output, as shown in FIG. As a result, in the case shown in FIG. 4, a direct current (2) flows through the primary winding of the inverter transformer 3 in the direction shown in FIG. 4, causing the inverter transformer 3 to be biased by direct current.

Therefore, in the past, a shunt 3 was installed on the primary side of the inverter transformer 3.
is provided, the DC current is detected, the detected voltage of the shunt 3 is isolated and amplified by the isolation amplifier 23, and the gate control circuit 1o is
The detection signal is used to control the voltage-time product of the positive output and negative output of the inverter to be equal, thereby preventing DC bias in the inverter transformer 3.

(Problems to be Solved by the Invention) Generally, when a direct current flows through the windings of a transformer, the iron core of the transformer experiences direct current bias. The saturation magnetic flux of the transformer core is determined by the product of its magnetic flux density and its cross-sectional area, and when the transformer core receives DC bias magnetization, the magnetic flux due to the DC current and the magnetic flux due to the AC voltage overlap in the core, so The greater the direct current flowing through the windings, the more likely the iron core will become saturated.

Therefore, in order to make the iron core less likely to saturate, the cross-sectional area of the iron core is increased to lower the magnetic flux density, but when using the same iron core material, the lower the magnetic flux density is, the larger the transformer becomes.

On the other hand, it is known that in a normal transformer, the core becomes saturated when a direct current of several percent of the rated current flows through the windings. Therefore, in order to prevent the inverter transformer 3 from becoming saturated in FIG. need to be controlled. For example, if the rated secondary output voltage of the shunt 20 is 50 mV and the DC current that saturates the inverter transformer 3 is 2% of the rated current, the secondary output voltage of the shunt 3 is 5Q IVX
0002-1 11V. When an inverter device becomes high-voltage and crowded, the strength of the magnetic and electric fields generated inside the device increases. Therefore, it is difficult to accurately detect the DC current flowing to the primary side of the inverter transformer 3, and it is difficult to properly perform control to prevent DC bias magnetization.

Therefore, in the conventional method shown in FIG. 4, a coaxial cable is used as the wire between the shunt 20 and the isolated amplifier 23, and the coaxial cable is further shielded by being housed in a conduit. , when the shielding treatment is applied,
Assembling workability deteriorates and costs increase. Furthermore, as described above, the detection voltage of the shunt 20 is so small that even the shielding process is insufficient and erroneous detection cannot be avoided.

The present invention has been made to eliminate the above-mentioned drawbacks, and includes a detection means that can reliably detect the DC current flowing to the primary side of the inverter transformer without erroneously detecting it, and prevents DC bias in the inverter transformer. The purpose is to provide an inverter device that is possible.

[Structure of the invention] (Means and effects for solving the problems) In the present invention,
In order to achieve the above object, a detection means consisting of a resistor and a saturable reactor that saturates with a small amount of direct current are connected in series between the inverter transformer and the inverter, and detects the main switching elements constituting the inverter. When a difference occurs in the voltage-time product between the positive output and the negative output of the inverter due to a difference in each switching time, etc., a direct current generated due to the difference in the voltage-time product flows through the detection means,
The polarity and magnitude of the current are detected by the resistor constituting the detection means, the voltage across the resistor is input to the output voltage control system of the inverter, and the voltage-time product of the positive output and negative output of the inverter is varied. The voltage-time product of the positive output and negative output of the inverter transformer should be equal.
By preventing direct current from flowing to the next side, biased direct current magnetization of the inverter transformer is prevented.

(Example) FIG. 1 is a diagram showing an embodiment of the present invention.

In FIG. 1, the names and operating functions of the parts designated by the same reference numerals as in FIG. 4 are the same, and their explanations will be omitted. The difference between FIG. 1 and FIG. 4 is that in FIG. 1, a circuit in which a saturable reactor 21 and a resistor 22 are connected in series is provided as a means for detecting direct current, instead of the shunt 20 in FIG. 4. It is in.

In FIG. 1, 21 is a saturable reactor that saturates with a small amount of direct current, and 22 is a resistor that converts the current flowing through the saturable reactor 21 into a voltage.

FIG. 2 shows the B-H characteristics of the saturable reactor 21, where B represents the magnetic flux density and H represents the strength of the magnetic field. B-H in Figure 2
As is clear from the figure, the characteristic is a so-called rectangular hysteresis characteristic, in which the iron core of the saturable reactor 21 is easily saturated when a DC current flows through the saturable reactor 21 (as H in FIG. 2 increases). shall be taken as a thing. Reference numeral 10 denotes a known gate control circuit which has the same function as that explained in the example of the prior art, and will be described in detail below. In other words, 10 is an inverter output voltage control circuit, which controls O of GTO2GU to 2GY.
It has a function that allows the voltage width (pulse width) of the positive output and negative output of the inverter to be individually controlled by controlling the FF timing, and furthermore, when the external signal e shown in FIG. Depending on the polarity, one has the function of widening the voltage width of the positive output and the negative output, and the other has the function of narrowing it.

Now, suppose that a difference occurs in the switching times of GTO2tJ to GTO2Y, and the voltage-time product of the inverter output is larger on the negative side than on the positive side. In this case, saturable reactor 2
1 has the characteristic of being saturated with a small amount of current, so it is saturated before the inverter transformer 3 is saturated, and the saturable reactor 21
A current 1 flows in the direction shown in FIG.

As a result, a voltage proportional to the current I shown in FIG. 1 is generated across the detection resistor 22, and this voltage is applied to the gate control circuit 10 through the isolation amplifier 23 as the external signal e. The external control signal e is given to an error amplifier (not shown) in the gate control circuit, and due to the function of the error amplifier,
The voltage width of the positive output of the inverter is widened, and the voltage width of the negative output is narrowed. The movement of the voltage width continues until the voltage-time products of the positive output and the negative output become equal. As a result, the first
The current I shown in the figure almost no longer flows, and the inverter transformer 3 is no longer subjected to direct current bias.

Conversely, if the voltage-time product of the inverter output is larger on the positive side than on the negative side, the direction of the DC current flowing to the primary side of the inverter transformer 3 is opposite to the current ■ shown in Figure 1. As a result, the voltage width of the positive output of the inverter is narrowed, and the voltage width of the negative output is widened, and as described above, by the operation of the error amplifier, the voltage-time products of the positive output and the negative output are controlled to be equal. The inverter transformer 3 is no longer subjected to direct current bias.

On the other hand, the inverter output voltage is 1, the saturable reactor 2 is
The saturable reactor 21 is represented by saturation, where the resistance value of the winding is R1 and the resistance value of the detection resistor 22 is R2. Therefore, if R2 is selected to an appropriate value, the saturable reactor 21
It is possible to select an arbitrary voltage as the voltage (2) across the detection resistor 22 when the voltage is saturated. That is, for example, the voltage v2
It is also possible to select tens of volts, which is more than 10,000 times higher than the 1 mV detection voltage of the conventional shunt 20, making it possible to extremely minimize the effects of magnetic and electric fields inside the device. .

Although the above description has been made assuming that the detection means includes one resistor, a plurality of resistors may be provided as shown in FIG. 3, and any one of the resistors may be used as the voltage detection means. It goes without saying that the configuration, main switching elements, and number of phases of the inverter to which the present invention is applied are not limited to those shown in FIG.

[Effects of the Invention] As explained above, according to the present invention, even if a difference in voltage-time product occurs between the positive output and the negative output of the inverter due to the difference in switching time of the main switching elements constituting the inverter, etc. Also, the detection means consisting of a saturable reactor and a resistor makes it possible to reliably detect the current that causes DC bias without being affected by the magnetic field or electric field inside the device, and it is possible to detect the DC bias in the inverter transformer. It can be prevented. Furthermore, since there is no need to use coaxial cables or conduits as in the past, assembly work becomes easier and costs are reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing 8-)-1 characteristics of the saturable reactor 21 used in the present invention, and FIG. 3 is a diagram showing another detection method of the present invention. FIG. 4 is a circuit diagram of an inverter device using the conventional detection means, and FIG. 5 is a time chart for explaining the operation of the inverter device of FIG. 4. 1...DC N source, 2 G U ~2 G Y-G T
0. 2DU~2DY...Diode, 2U~2Y...Gate circuit, 3...Inverter transformer, 4...Load,
DESCRIPTION OF SYMBOLS 10...Gate control circuit, 21...Saturable reactor, 22.22a, 22b...Resistor, 23...Isolation amplifier. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 4 Figure 5

Claims (1)

[Claims] In an inverter device having a transformer between an inverter and a load and having a function of individually varying the voltage-time products of positive output and negative output voltages of the inverter, a resistance and a resistance are connected between the primary lines of the transformer. A detecting means for detecting a direct current component is provided by connecting saturable reactors in series, and when a direct current component occurs in the output voltage of the inverter, the polarity and magnitude of the direct current component are determined by a resistor included in the detecting means. The detected voltage is input to the output voltage control system of the inverter as a correction amount, and the voltage widths of the positive output and negative output voltages of the inverter are varied so that one widens and the other narrows, thereby adjusting the positive output of the inverter. An inverter device characterized in that the inverter device is controlled so that the voltage-time product of the negative output voltage and the negative output voltage are equal.