JPH063992B2 - Power converter - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a power conversion device having a smoothing circuit including a capacitor and a voltage type inverter connected to the smoothing circuit.

[Technical background of the invention]

FIG. 1 is a block diagram showing a general configuration of a conventional power conversion device. A rectifier circuit 11 converts alternating current into variable voltage direct current, and a smoothing circuit composed of a direct current reactor 12 and a filter capacitor 13 smoothes this direct current voltage. Further, the inverter circuit 14 reversely converts the alternating current having a desired frequency into an alternating current and supplies power to the electromagnetic stirring device 15 serving as a load. The load is not limited to the electromagnetic stirrer 15, and any load such as a reactor or an AC load such as an AC motor can be used.

The control circuits of the rectifier circuit 11 and the inverter circuit 14 are configured as follows. The voltage reference from the voltage / frequency reference 21 and the voltage feedback signal obtained by insulating the output voltage of the inverter circuit 14 through the transformer 22 and converting it to direct current through the rectifier circuit 23 are compared and amplified in the voltage control circuit 24 to obtain the current. It becomes a standard. In addition, this current reference and the input AC current
The current feedback signal, which has been insulated via the rectifier circuit 26 and converted to direct current through the rectifier circuit 26, is compared and amplified in the current control circuit 27 to serve as a phase reference. This phase reference and the AC input voltage phase obtained via the transformer 28 are compared by the phase control circuit 29, and given to the thyristor constituting the rectifier circuit 11 as information for controlling the firing angle of the firing pulse. On the other hand, the frequency reference from the voltage frequency reference 21 is given to the GTO (gate turn-on element) forming the inverter circuit 14 as an ignition pulse and an ignition pulse via the oscillation circuit 30, and the desired frequency output from the inverter circuit 14 is supplied. You can get an exchange.

FIG. 2 shows a rectifier circuit 11 and an inverter circuit which are main circuits of a power converter driven by such a control circuit.
It shows 14 configurations. The description of the operation of the rectifier circuit 11 and the inverter circuit 14 and the method of giving the control pulse is omitted, but the details of the operation are described in, for example, Japanese Patent Publication No. 51-9890.

[Problems of background technology]

When the voltage-type inverter 14 having the above-mentioned smoothing circuit is driven, the reactive power exchanged with the load causes a current to flow through the filter capacitor 13 of the smoothing circuit through the GTO and the diode which form the inverter circuit 14.

FIG. 3 is a diagram for explaining the voltage fluctuation of the filter capacitor due to the reactive power component current. FIG. 3 (a) shows the waveforms of the output three-phase alternating currents i _u , i _v , and i _w of the inverter circuit 14. FIG. 3 (b) shows the charging / discharging current i _c from the filter capacitor 13 that supplies this current. If the polarity of the discharging current is positive, the shaded negative polarity portion becomes the charging current. The average value of both currents becomes zero. Thus, the three-phase alternating currents i _u , i _v , i _w and the charging / discharging current i _c are shown in FIG.
The reason for the relationship shown in (a) and (b) is that the active power supplied to the load directly flows into the inverter circuit 14 via the rectifier circuit 11 and the DC reactor 12, and this amount is generally This is because, in such operation, the DC value can be regarded as a substantially constant value, and therefore the filter capacitor 13 adjusts the remaining reactive power. The voltage fluctuation of the filter capacitor 13 is determined by the charge / discharge current value i _c and the capacity of the filter capacitor 13.
For example, as shown in FIG. 3 (c), when the DC voltage Ec is high, the fluctuation e _c becomes relatively small, and there is no problem even if the control is performed with a constant load under a general load. This is a problem when the DC voltage is low or when the output AC frequency is low and the amount of reactive power exchanged in one cycle is large. That is, as shown in FIG. 3 (d), there is a state in which the relative variation e _c becomes large and the voltage value falls to zero.

Even in such an operating state, the voltage control circuit and the current control circuit generally perform average value control, and therefore they are related to the control response, but normally operate without any problem. However, since the output voltage waveform is a fragmented voltage waveform as shown in Fig. 3 (d), the harmonic current increases or decreases according to the waveform at that time, so the performance or thermal May be adversely affected.

Originally, when the relative fluctuation e _{c of the} output voltage is small, the line voltage is a rectangular wave with a phase difference of 120 °, and the harmonic component is the 5th, 7th, 11th, 13th ... , 14%, 9%, 7% ... It should be the included waveform. This harmonic component changes due to the variation e _c of the output voltage. As a countermeasure against this, conventionally, the filter capacitor 13 has been largely selected according to the characteristics at low frequencies. However, in the voltage type inverter, the external shape and the cost of the filter capacitor 13 occupy a large proportion of the entire device, so that the cost is increased and the size is increased.

Also, as another means, a means for speeding up the response of the voltage control circuit 24 shown in FIG. 1 has been taken so as to reduce the fluctuation of the filter capacitor voltage, but in order to stabilize the overall system, its control is controlled. There was a limit to the response.

[Object of the Invention]

An object of the present invention is to provide a power conversion device that does not adversely affect a load by adding a control circuit whose structure is not so complicated and causing no interruption of the smoothing circuit voltage even at a low frequency.

[Outline of Invention]

According to the present invention, in order to achieve the above object, a smoothing circuit including a capacitor, and a rectifying circuit that supplies a direct current of a variable voltage controlled in response to a deviation signal between a current reference signal and a current feedback signal to the smoothing circuit. In the power conversion device comprising an inverter circuit connected to the smoothing circuit and performing switching from direct current to alternating current, a detection circuit for detecting an amount of electricity corresponding to the magnitude of the charging / discharging current flowing in the capacitor, A means for adding the output electric quantity of the detection circuit to the current reference signal is provided to suppress the voltage fluctuation of the capacitor due to the reactive power.

Example of Invention

Embodiments of the present invention will be described below in detail. The same parts as those shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

FIG. 4 is a block diagram showing the first embodiment of the present invention. The difference from the conventional configuration shown in FIG. 1 is that the terminal voltage of the filter capacitor 13 is detected through a transformer 32, this signal is differentiated by a differentiating circuit 33, and then the current of the rectifying circuit 11 is controlled. The point that means for adding to the current reference value of 27 is provided. The differentiating circuit 33 can be easily realized by using an operational amplifier, a capacitor and a resistor. That is, it can be realized by configuring the input impedance of the operational amplifier with a series circuit of a capacitor and a resistor and configuring the impedance that gives a gain by the resistor.

In the circuit of FIG. 4, if the terminal voltage of the filter capacitor 13 is V _c and the charge / discharge current is i _c , Therefore, the signal proportional to the charge / discharge current i _c of the filter capacitor 13 can be obtained by differentiating the detected voltage of the filter capacitor 13. By adding this signal to the output of the voltage control circuit 24 so that the current flowing out from the rectifier circuit 11 increases,
The active power component current and the reactive power component current can be supplied at the same time. Since compensation is performed without intervention of voltage control in this way, voltage fluctuation of the filter capacitor 13 can be reduced without delay in control. Therefore, even if the load is driven by a low-frequency AC, the output voltage distortion is small, and a power exchange device that does not adversely affect the performance and heat of the load can be realized.

FIG. 5 is a block diagram showing another embodiment of the present invention. In this embodiment, the DC current at the DC output end of the smoothing circuit is detected via the transformer 35, and the filter circuit is detected from this signal.
The DC component is removed by 36 and added to the current reference value of the current control circuit 27. The filter circuit 36 is, for example, as shown in FIG.
It can be realized by connecting 2, 364, 365 and resistors 363, 366 so as to form a bypass filter. In the second embodiment, the charging / discharging current i _c of the filter capacitor 13 is
Is detected as the sum of the active power component current and the reactive power component current, and the active power component current is removed as a direct current amount to obtain the charging / discharging current i _c of the filter capacitor 13 which is the reactive power component current. Similar to the first embodiment, this signal is added to the control circuit so that the current flowing out from the rectifying circuit 11 is compensated in the forward direction, so that the same operation and effect can be obtained.

The present invention can be applied not only to a main circuit of a general power conversion circuit as shown in FIG. 2 but also to a power conversion device having a rectifier circuit 111 capable of regenerating power to an AC power supply as shown in FIG. It can be applied, and in this case, the effect becomes more remarkable. This is because when the active power component current is smaller than the peak value of the reactive power component current, a certain period of one cycle becomes the regenerative current. Therefore, if this regenerative current is returned to the power supply side, the voltage fluctuation of the filter capacitor 13 can be further suppressed.

The present invention can also be applied to a power conversion device having a bidirectional chopper circuit 112 as shown in FIG. If the DC power supply 10 is used instead of the AC power supply to supply power to the capacitor 13 via the bidirectional chopper circuit 62, the same operation as the operation of the circuit shown in FIG. 7 is performed.

〔The invention's effect〕

As described in detail based on the above embodiments, in a power conversion device having a smoothing circuit including a capacitor, the amount of electricity corresponding to the magnitude of the charge / discharge current of this capacitor is detected, and this amount of electricity is used as a current reference value. By performing compensation control as the correction value of, the fluctuation of the voltage of the filter capacitor due to the reactive power can be suppressed to a small level even during operation at low frequency, so that the adverse effect on the load due to the distortion of the output voltage waveform can be prevented. . Further, since the voltage fluctuation at the low frequency is small, the capacity itself of the filter capacitor can be reduced, and the cost and the outer shape can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a conventional power conversion device,
FIG. 2 is a circuit diagram showing a typical configuration example of a rectifier circuit and an inverter circuit of a power conversion device, FIG. 3 is a waveform diagram for explaining a voltage fluctuation of a filter capacitor due to a reactive power component current, FIG. 4 and FIG. Is a block diagram showing an embodiment of the present invention, FIG. 6 is a circuit diagram showing an example of a filter circuit used in the embodiment of FIG. 5, and FIGS. 7 and 8 are power converters to which the present invention can be applied. It is a figure which shows the other example of a main circuit structure. 11 ... Rectifier circuit, 13 ... Filter capacitor, 14 ... Inverter circuit, 22, 28 ... Transformer, 23, 26 ... Rectifier circuit, 24 ... Voltage control circuit, 27 ... Current control circuit, 29 ... Phase control circuit, 32 ...
Transformer, 33 ... Differentiation circuit, 35 ... Current transformer, 36 ... Filter circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Bibliography 1987-139290 (JP, U)

Claims (3)

[Claims] 1. A smoothing circuit including a capacitor, a rectifying circuit for supplying a DC current of a variable voltage controlled in response to a deviation signal between a current reference signal and a current feedback signal to the smoothing circuit, and the smoothing circuit. In a power converter comprising an inverter circuit that is connected and exchanges direct current to alternating current,
A detection circuit for detecting the amount of electricity corresponding to the magnitude of the charging / discharging current flowing through the capacitor, and means for adding the output amount of electricity of the detection circuit to the current reference signal are provided, and the voltage of the capacitor due to the reactive power is provided. A power conversion device characterized in that fluctuations are suppressed. 2. The detection circuit according to claim 1, wherein the detection circuit comprises means for detecting a terminal voltage of the capacitor and a differentiating circuit for differentiating the detected terminal voltage. Power converter. 3. The detection circuit comprises a means for detecting the direct current of a variable voltage, and a filter circuit for removing the direct current component in the detected direct current and outputting only the variable component. The power conversion device according to claim 1.