JPS6082065A - Power converter - Google Patents

Abstract

PURPOSE:To improve the controlling responsiveness with a simple structure by outputting a current reference signal in response to the compared result of the detected value of a load current with a reference value. CONSTITUTION:An output signal compared and amplified in a current controller 37 from current feedback signal obtained through a transformer 38 and a rectifier 39 with a current reference 34 is used directly as a current reference signal for controlling a rectifier 11. In other words, the output of the controller 37 is compared with the output of a rectifier 26, and the output is applied through a current controller 27 to a phase controller 29, compared with the AC input voltage phase obtained through a transformer 28 to generate a firing pulse.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is directed to an AC output power conversion device that exhibits low impedance characteristics when viewed from the load side, such as a voltage source inverter, and in particular uses a reactor or an electromagnetic device as the load. The present invention relates to a power conversion device suitable for driving a load, such as a stirring device, whose stain flow is mainly determined by the amount of magnetic flux.

[Technical background of the invention]

Voltage source inverters or cycloconverters are generally used as variable frequency/variable voltage power converters to drive loads with strong inductance, such as reactors and electromagnetic stirring devices, whose currents do not change suddenly. .

FIG. 1 shows a block diagram of a conventionally used voltage source inverter as an example of such a power conversion device. A rectifier circuit 11 converts alternating current into variable voltage direct current, and smoothes the direct current voltage through a smoothing circuit consisting of a direct current reactor 12 and a filter capacitor 13. Furthermore, the inverter circuit 14 reversely converts the signal into alternating current having a desired frequency, and supplies power to, for example, an electromagnetic stirring device 15 serving as a load. A control circuit for controlling the rectifier circuit 11 and the inverter circuit 14 is constructed as follows.

a voltage reference given by voltage frequency reference 21;
The output AC voltage is insulated via the transformer n, and the voltage feedback signal, which is further converted to DC via the rectifier circuit 23, is compared and amplified in the voltage control circuit U, and becomes a current reference. This current reference and the input or current are isolated via the transformer 5,
Furthermore, the current feedback signal converted to direct current through the rectifier circuit A is compared and amplified in the current control circuit τ, and serves as a phase reference.

Furthermore, this phase reference is compared with the AC input voltage phase obtained via the transformer 28''f in the phase control circuit 9, and a firing pulse is given to the thyristor forming the rectifier circuit 11.

On the other hand, the frequency reference IB given by the voltage/frequency reference 21 gives ignition/extinguishing pulses to the GTO (gate turn-on resistor) constituting the inverter circuit 14 via the oscillation circuit I, so that the output has a desired frequency. Generate alternating current.

;A2 figure is based on this control circuit 32! 2 is a diagram illustrating internal synthesis of a rectifier circuit 11 and an inverter circuit 14, which are the main circuit configurations of a power conversion device that is driven in two ways. FIG. Rectifier circuit 11
Although details of the operation of the inverter circuit 14 and how to apply control pulses are omitted, for example,
1-9890 describes its operation in detail.

[Problems with background technology]

The electromagnetic stirring device 15 used as a load of the power conversion device described above has a function of applying a magnetic flux to the material passing through the device and stirring the material by changing the magnetic flux. Such loads have strong inductance, and the average value of the load current does not change rapidly, on the order of tens of milliseconds, but it is not possible to directly control the load current in order to precisely control the amount of magnetic flux. It becomes necessary.

FIGS. 3 and 4 are block diagrams showing an example of a conventional control circuit. In the example shown in FIG. 3, a function generating circuit 36 is used which inputs a current reference and a frequency reference and generates a current voltage command value of 6 V from a pre-measured load impedance. The disadvantage of this circuit is that it is not directly controlled and therefore has poor accuracy.

In the example shown in FIG. 4, a four-current control circuit 37 is provided outside the control circuit 32, and the output current feedback signal obtained between the transformers and the rectifier circuit 39 is compared and amplified with the current base.
The purpose is to obtain a voltage reference ey. However, this circuit has three loops to control the pulses of the rectifier circuit 11, making it complicated, and since there is voltage control in the middle, the control response usually has to be quite slow, on the order of several seconds. there were.

Furthermore, when using a cycloconverter, the current in each phase can be directly controlled, resulting in highly accurate control; however, it requires a large amount of reactive power in the power supply, and the main circuit configuration is complex, requiring a large number of cycloconverters. Further, the control circuit is complicated, and as the frequency increases, harmonic current increases.

[Purpose of the invention]

The purpose of this invention is to drive a load that originally has low internal impedance, such as a voltage source, and the load connected to it has strong inductance and the average value of its current does not change rapidly. Another object of the present invention is to provide a power conversion device that has a simple control configuration and can provide a system-desirable control response on the order of several gigantic milliseconds.

[Summary of the invention]

In order to achieve the above object, the present invention supplies a variable voltage DC current that is controlled in response to a deviation signal between a current reference signal and a current feedback signal to an inverter circuit via a smoothing circuit, thereby preventing rapid current fluctuations. In a power conversion device that connects and drives a load with no electric current flowing through the inverter circuit, the power conversion device includes means for detecting an amount of electricity corresponding to the magnitude of the current flowing through the load, and a means for detecting an amount of electricity corresponding to the magnitude of the current flowing through the load, and a means for detecting an amount of electricity corresponding to the magnitude of the current flowing through the load, and a means for detecting an amount of electricity corresponding to the magnitude of the current flowing through the load, and a means for detecting an amount of electricity corresponding to the magnitude of the current flowing through the load, and a current control circuit for comparing and amplifying the reference amount,
Using the output of the current control circuit as the current reference signal is 4'! It is a sign.

[Embodiments of the invention]

FIG. 5 is a block diagram showing one embodiment of the present invention.

In the following drawings, the same components as those shown in FIGS. 1 to 4 are denoted by the same reference numerals, and their explanations will be omitted.

The circuit configuration shown in FIG. 5 differs from that shown in FIGS. 1 and 4 in that the voltage reference e, the voltage control circuit u1, the transformer 2,
2 and the rectifier circuit 23 are omitted, and the transformer 3 is replaced with the α flow reference.
8 and the rectifier circuit 39 are compared and amplified in the current control circuit 37, and the output signal is used as a current reference signal for directly controlling the rectifier circuit 11.

The operation of the current control circuit 37 in this control configuration includes the function of the voltage limiting circuit 37 in FIG. This is because the electromagnetic stirring device 15 can be regarded as almost a passive load, so its phase voltage V, phase current ■1, inductance L1, and resistance R are v if the operating frequency is f, = (R+jx2πtxL)IL ・+ −−−−＋・
It is expressed by a simple relational expression (1). Therefore, if the change in the operating frequency f is much slower than the change in 'Kameryuko', then (R + j .

From this, the circuit shown in Fig. 5 does not provide exactly the same characteristics as those using a major loop for voltage control, but since this configuration directly controls the output current,
This has the advantage that the control accuracy is high regarding the current or the magnetic flux in the electromagnetic stirring device 15 of the load.

FIG. 6 is a block diagram showing another embodiment of the invention. In addition to the configuration shown in FIG. 5, this embodiment has the configuration shown in FIG.
Maximum voltage reference 4 detected via and set to a predetermined value
A voltage limiting circuit 43 is provided for reducing the current command value given to the current control circuit n in accordance with the amount of deviation when the detected value exceeds the set value. The voltage limiting circuit 43 can use, for example, a subtracter configured with an operational amplifier, and by changing its gain, the amount by which the current command value is reduced can be adjusted.

In the circuit of FIG. 6, if the detected value of the output voltage exceeds the maximum voltage reference 42, the DC voltage will also exceed the maximum voltage because the output voltage and the voltage of the smoothing circuit are in a proportional relationship.
It becomes necessary to limit this. Therefore, by reducing the current command value given to the current control circuit n in accordance with the amount of deviation exceeded, the lightning flowing into the smoothing circuit is suppressed and a limit is placed so that the voltage does not rise any further. I can do it.

The amount of this reduction is determined by the above-mentioned gain, and it goes without saying that the larger the gain, the smaller the amount that exceeds the maximum voltage reference 42 can be suppressed.

With this configuration, while maintaining the same effect as described in the first embodiment shown in FIG. 5 during normal operation, it is possible to maintain safety during operation when a voltage exceeding the maximum voltage is required This has the effect that operation can be continued within a predetermined voltage value of the device.

FIG. 7 is a block diagram showing still another embodiment of the invention. The difference from the embodiment shown in FIG. 6 is that a voltage control circuit 44 compares the detected value of the output voltage obtained via a transformer 40 and a rectifier circuit 41 with a maximum voltage reference 42 set to a predetermined value. This output signal and the output signal of the current control circuit 37 are input to determine whether or not the voltage is in a limited state, and the switch 45 is controlled to switch one of the output signals as the current command value of the current control circuit. The point is that a logic 46 is provided to do this.

A specific circuit example of the logic 46 is shown in FIG. The input voltages e and e are compared by the operational amplifiers 461 and 462, and a logic signal of '1' is given to the logic 463 if eA>ga, and '0' if eA (aB).

When the logic signal is "10", the a contact of the switch 45 is connected, and when the logic signal is "1", the b contact of the switch 45 is connected.
It is configured to make a contact.

Therefore, the lower of the input voltage e or θ3 can be obtained as the output voltage e. This output voltage e
is given as a current reference signal for the current control circuit 17 in FIG.

As described above, in the embodiment shown in FIG. 7, when the detected value of the output voltage exceeds the maximum voltage reference 42, the voltage control circuit operates to lower the output voltage. If this output voltage required by the voltage control circuit is used as the current reference signal of the current control circuit 27, this value will be lower than the output voltage of the current control circuit 37, so the output voltage will be set to a value that matches the maximum reference voltage. It will be controlled. In this way, the embodiment shown in Fig. 7 has the same effect as the embodiment shown in Fig. 5, in which the current control is a major loop during normal operation, but it is not suitable for operations where a voltage exceeding the maximum voltage is required. This has the effect of allowing the power converter to continue operating by making the most of its capacity while limiting the voltage to its maximum voltage.

〔Effect of the invention〕

As described above in detail based on the embodiments, this invention uses current control instead of voltage control in the major loop of the control circuit that controls the rectifier circuit, so the control configuration is simple and system-friendly. This has the advantage of being able to stably obtain control responses of several hundred milliseconds, which is often required for.

In addition, since current control directly controls the load current, the electromagnetic stirring device serving as the load has highly accurate magnetic flux control characteristics. In addition, a voltage limiting circuit is provided to feed back the output voltage and have a voltage limiting function, so that when operation is required above the maximum voltage of the device, the device can continue to operate safely within a specified range. I can do it.

Furthermore, by changing the above-mentioned voltage limiting circuit to a voltage control circuit, 'e) Lll (- reference 11! It has the advantage of being possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a general circuit configuration of a conventional power conversion device, and FIG. 2 is a circuit diagram showing detailed circuit examples of a rectifier circuit and an inverter circuit, which are the main circuits of the power conversion device.
3 and 4 are circuit diagrams showing examples of conventional control circuits, FIGS. 5, 6, and 7 are block diagrams showing embodiments of the present invention, respectively, and FIG. 8 is a circuit diagram showing an example of a conventional control circuit. FIG. 2 is a circuit diagram showing a detailed configuration of logic used in the example. 11... Rectifier circuit, 13... Filter capacitor,
14... Inverter circuit, 15... Electromagnetic stirring device (
Load), 22, 28, 40...Transformer, ah? 2
G, 39, 41...distorted wave circuit, u, 44...
Voltage control circuit, 25, 38...Transformer, 27, 3
7...Current control circuit, 32...Control circuit, Ah...
Current-i5 standard, 42... Maximum voltage reference, 43... Voltage limiting circuit, 45... Switch, 46... Logic. Applicant's agent Kiyoshi Inomata 51 Figure b 3 Kunimo 4 ■ 55 Mouth color 6 Shuno 7 Figure δ 58 Figure

Claims (1)

[Claims] 1. A variable voltage DC current controlled in response to a deviation signal between a current reference signal and a current feedback signal is supplied to an inverter circuit via a smoothing circuit, and rapid current fluctuations are not caused. In a power conversion device for driving a load connected to the inverter circuit, the power conversion device includes means for detecting an amount of electricity corresponding to the magnitude of a current flowing through the load, and a means for detecting an amount of electricity corresponding to a magnitude of a current flowing through the load, and a means for detecting an amount of electricity corresponding to a magnitude of a current flowing through the load, and a means for detecting an amount of electricity corresponding to a magnitude of a current flowing through the load, and a means for detecting an amount of electricity corresponding to a magnitude of a current flowing through the load, and a means for detecting an amount of electricity corresponding to a magnitude of a current flowing through the load, and a means for detecting an amount of electricity corresponding to a magnitude of a current flowing through the load, and a combination of the detected amount of electricity and a preset current reference amount. 1. A military sword conversion device comprising: a current control circuit for comparing and amplifying a current control circuit, and using an output of the current control circuit as the current reference signal. 2. A patent characterized in that when the amount of electricity corresponding to the output voltage of the inverter circuit exceeds a predetermined value, the output of the current control circuit is reduced in accordance with the amount of deviation and used as the current reference signal. A power conversion device according to claim 1. 3. When the amount of electricity corresponding to the output voltage of the inverter circuit exceeds a preset maximum voltage reference, the amount of deviation is used as the current reference signal instead of the output of the current control circuit. A power conversion device according to claim 1.