JP2527911B2 - PWM converter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a pulse width modulation (PWM) converter device for converting alternating current into direct current.

[0002]

2. Description of the Related Art FIG. 6 is a main circuit configuration diagram showing a conventional PWM type converter in which a power source current I _s is a sine wave and a power factor is 1, where 1 is an AC power source, 2 is a system impedance, 3 is a load, 5 is a ripple suppression filter capacitor, 6 is a ripple suppression filter reactor, 8 is a power converter composed of a self-extinguishing type switching element and an anti-parallel connection circuit 7 of a diode, and 11 is a load Is a side DC capacitor, and 12 is component parts 5, 6, 8 and 11
1 shows a PWM type converter configured by.

The power converter 8 includes a DC voltage V _dc of the load side DC capacitor 11 and a load side DC voltage command value V _{dc (} not shown).
Comparing with ^* , the self-extinguishing type switching element is turned on / off as the DC voltage is charged / discharged and the power supply current I _s is a sine wave and the power factor is 1.

The ripple suppression filter reactor 6 and the ripple suppression filter capacitor 5 suppress ripples associated with switching with respect to the AC power supply 1.

[0005]

In the conventional PWM converter 12, the self-extinguishing type switching element of the power converter 8 is turned on / off as the power supply current I _s becomes a sine wave and the power factor becomes 1.

Therefore, since the self-extinguishing type switching element performs high-speed switching in the state where the DC voltage V _dc of the load side DC capacitor 11 is applied and the power supply current I _s flows, the self-extinguishing type switching element is The duty of operation became heavy and it became an expensive PWM converter.
As described above, the present invention is intended to provide a PWM converter, which has a conventionally expensive power factor = 1 and does not introduce a ripple into an AC power supply, at a low cost.

[0007]

Therefore, in the present invention, a thyristor bridge is used for controlling the load side DC voltage V _dc , and a sine wave of the power supply current I _s is provided on the AC power supply side of the thyristor bridge. , A power converter connected in series.

That is, a PWM converter installed in series between an AC power supply and a DC load, wherein the ripple suppression filter is connected in series to the AC power supply, and the AC power supply of the ripple suppression filter. A power converter composed of a self-extinguishing type switching element and a diode connected in series on the opposite side, a power converter DC capacitor connected to the DC side of the power converter, and the power converter A thyristor bridge connected in series to the opposite side of the ripple suppression filter, a load side DC capacitor connected to the DC side of the thyristor bridge, and a control device for controlling the power converter and the thyristor bridge, The control device detects a power supply current and detects a harmonic component thereof, and a harmonic voltage command by multiplying the harmonic current component by a gain K. And a means for outputting a gate signal of the self-extinguishing switching element of the power converter by comparing the triangular wave carrier signal by adding the fundamental wave reactive voltage command value and the harmonic voltage command value. A means for detecting the direct current voltage of the load side direct current capacitor and controlling the ignition of the thyristor bridge by the difference from the direct current voltage command value.

[0009]

The operation of the PWM converter according to the present invention is shown in FIG.
The voltage-current vector diagram of

In FIG. 5, V _s is the AC power supply voltage, and V _q
Reactive voltage, V _t is the terminal voltage applied to the thyristor bridge power converter occurs, each represent a fundamental wave vector of I _s supply current.

When the DC voltage of the load side DC capacitor is controlled by the thyristor bridge, the power supply current I _s lags behind the AC terminal voltage V _t of the thyristor bridge. Therefore, the power converter converts the AC terminal voltage V _t to the thyristor bridge into the AC power supply voltage V _t by the fundamental reactive voltage V _{q in} advance.
_If it is advanced from _s , the power supply current I _s can be maintained at a power factor of 1.

Further, to detect a high frequency component of the power source current I _s, so that the power supply current I _s does not contain high frequency components by generating a harmonic component in the power converter, a high frequency component of the power source current I _s Can be suppressed.

[0013]

Embodiments of the PWM converter according to the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of a main circuit configuration of a PWM converter of the present invention, FIG. 2 is a block diagram of a control device of the PWM converter of the present invention, and FIG. FIG. 3 is a waveform diagram showing a waveform example when a power converter configured by a switching element and a diode in the PWM converter is short-circuited or turned on and off.

In FIG. 1, 1 is a three-phase AC power supply, 2 is system impedance, 3 is a load, 5 is a ripple suppression filter capacitor, 6 is a ripple suppression filter reactor, and 8 is a self-extinguishing type switching element. A power converter configured by an anti-parallel connection circuit 7 with a diode, 9 is a power converter capacitor, 10 is a thyristor bridge, 11 is a load side DC capacitor, and 4 surrounded by a chain line is a PWM converter. Yes, component 5,
6, 8, 10, and 11, which are shown in FIGS.
The same symbols are used for the same elements as.

Since FIG. 1 shows a single-line connection diagram, the case where the AC power supply 1 is a single phase is specifically shown in FIG. That is, the current I _S that flows from the single-phase AC power supply 1 through the system inductance 2 and the filter capacitor 5 and the filter reactor 6 becomes the current I _L through the single-phase power converter 8 connected in series, and becomes the thyristor. Supplied to bridge 10. In this case, the current I _L is the same as the current I _S as shown in FIG. 3, but the combined voltage V _C of the single-phase power converter 8 and the ripple suppression filter has a waveform as shown in FIG. The single-phase power converter 8 constitutes a bridge by the anti-parallel switching circuit 6 and an anti-parallel connection circuit 6 of a diode. This configuration is the same in the case of the power converter 8 shown in FIG. A power converter capacitor 9 is connected to the DC side. In this case, the thyristor bridge 10 is, of course, also configured by a thyristor bridge connection as shown in the drawing, and the DC voltage V _dc is supplied to the load 3 via the load side DC capacitor 11 on the DC side.

A concrete example of the case where the AC power source 1 has three phases is as shown in FIG. In the case of three phases, the single-phase power converter 8 in the case of the single phase may be inserted in each phase, but as shown in the figure, the transformer 29 is used to reduce the number of elements and the price. And the three-phase power converter 8 is connected in series. That is, the three-phase AC power supply 1 passes through the system impedance 2,
It is connected to the primary side of the transformer 29 for each phase via the filter capacitor 5 and the filter reactor 6, and is connected to the thyristor bridge 10 via this transformer primary side. The three-phase power converter 8 is constructed by connecting the self-extinguishing type switching element and the anti-parallel connection circuit 6 of the diode by the Gretz connection. This structure is the same as in the case of the power converter 8 shown in FIG. The three-phase AC input terminals are respectively connected to the secondary side of the transformer 29 which is Y-connected, and the power converter capacitor 9 is connected to the DC side. The thyristor bridge 10 is also composed of a thyristor's Gretz connection, and the DC voltage V _dc is supplied to the load 3 via the load side DC capacitor 11 on the DC side. Even in this configuration, the power supply current I _S and the thyristor bridge input current I _L are the same, but the voltage across the primary side of the transformer and the combined voltage V _C of the ripple suppression filter have a waveform as shown in FIG. .

In FIG. 2, reference numeral 21 is a power supply current harmonic component detection circuit, 22 is a K multiplication circuit, 23 is an adder, 24 is a triangular wave generation circuit, 25 is a comparison circuit, 26 is a subtractor, and 27 is a proportional integration circuit. , 28 are firing angle determination circuits.

The PWM converter 4 according to the present invention detects the power source current I _s , detects the power source current harmonic component I _sh by the power source current harmonic component detection circuit 21, and outputs it to the K-multiplier circuit 22. The K-multiplier circuit 22 inputs the power supply current harmonic component I _sh , multiplies the gain by K, and adds the harmonic voltage command signal V _h to the adder 23.
Output to. The adder 23 inputs and adds the harmonic voltage command signal V _h and the fundamental wave reactive voltage command V _q ^* corresponding to the fundamental wave reactive voltage component described in FIG. 5, and outputs the voltage command V _c ^* to the comparison circuit 25. To do. The comparison circuit 25 inputs the voltage command V _c ^* and the harmonic triangular wave signal S output from the triangular wave generation circuit 24, compares the magnitudes, and outputs the gate signal V _GC of the switching element of the power converter 8.

That is, the harmonic voltage command signal V _h suppresses the harmonic component of the power supply current I _s , and the fundamental reactive voltage command V _q ^* determines the terminal voltage V _t of the thyristor bridge 10 as shown in FIG. To be done.

Further, according to FIGS. 3 and 4, the power supply current I _S
The sine wave conversion of will be described. Figure 3 is a power converter 8 of the PWM converter 4 of Figure 1, a short circuit at time T ₀ before the time T ₀ later when allowed operation, the load current I
_It shows _L , the power supply current I _S , and the combined voltage V _C of the applied voltage of the power converter and the ripple suppression filter. FIG. 4 shows a single-phase equivalent circuit diagram including the PWM converter 4 and the load 3. Here, V _S is the three-phase AC power supply voltage, V _C is the applied voltage of the power converter and the combined voltage of the ripple suppression filter, V _L is the voltage of the thyristor bridge, and they are in series with the system impedance L _S. And the power supply current I _S flows. The power converter 8 connected between the system power supply and the non-linear load, that is, the thyristor bridge, has a load current I _L flowing through the thyristor bridge 10 (in this case, the load current I _L is the same as the power supply current I _S ). It may be controlled so that it becomes a wave.

That is, the power converter 8 outputs the power source current harmonic component I _sh

## EQU1 ## If control is performed so that I _sh = 0 (1),

V _c = V _s −V _L (2) and the power converter 8 is represented by the equation (2) and generates the voltage V _c as shown in FIG. The component I _sh can be zero.

At this time, since the power converter 8 only needs to generate the harmonic voltage shown by V _c in FIG. 3, the voltage is about 1/4 of the power supply voltage V _s , and the load kVA is conventionally used. It is possible to reduce the capacity of the power converter 8 required to the same extent to about 1/4.

Further, the DC voltage V _dc of the load side DC capacitor 11 of the thyristor bridge 10 is detected and subtracted from the DC voltage command value V _dc ^* applied to the subtractor 26, and the output is proportional to the proportional integrator circuit. Send to 27. The firing angle determination circuit 28 receives the DC voltage deviation signal ΔV _dc input from the proportional integration circuit 27,
The firing angle of the thyristor bridge 10 is determined, and the gate signal V _Gl is output to the thyristor used in the thyristor bridge.

[0025]

As is apparent from the above description, according to the present invention, in the PWM converter installed in series between the AC power supply and the DC load, the DC voltage control is performed by the thyristor bridge 10, and the power supply current is controlled. By suppressing the harmonics of the power converter 8 by the power converter 8, the capacity of the power converter 8 which has conventionally required the capacity of the load kVA is equal to the capacity of the load kVA of 1
It becomes possible to set about / 4. Control of DC voltage requiring a large-capacity switching element is performed by a thyristor bridge 10 that can be used for normal commercial frequencies and that is composed of a thyristor without self-extinguishing ability,
The power converter 8 that requires an expensive self-arc-extinguishing switching element is a very economical system because it is configured with a small-capacity self-arc-extinguishing switching element for power factor improvement and harmonic elimination. Can be configured.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a main circuit configuration of a PWM converter of the present invention.

FIG. 2 is a block diagram of a PWM converter control device according to the present invention, in which (a) is a power converter control device;
(B) shows a control device of the thyristor bridge.

FIG. 3 is a waveform diagram showing an example of waveforms depending on on / off of a power converter configured by a switching element and a diode in the PWM converter of the present invention.

FIG. 4 shows a single-phase equivalent circuit diagram including the PWM converter of the present invention and a load.

FIG. 5 is a voltage-current vector diagram for explaining the operation of the PWM converter according to the present invention.

FIG. 6 is a main circuit configuration diagram showing a conventional PWM converter.

FIG. 7 is a main circuit configuration diagram showing a specific example when the PWM converter of the present invention is used for a single-phase AC power supply.

FIG. 8 is a main circuit configuration diagram showing a specific example when the PWM converter of the present invention is used for a three-phase AC power supply.

[Explanation of symbols]

1 AC power supply 2 system impedance 3 load 4 PWM converter 5 capacitor for ripple suppression filter 6 reactor for ripple suppression filter 7 anti-parallel connection circuit of switching element and diode 8 composed of self-extinguishing type switching element and diode Power converter 9 Power converter capacitor 10 Thyristor bridge 11 Load side DC capacitor 12 PWM converter 21 Power supply current harmonic component detection circuit 22 K multiplication circuit 23 Adder 24 Triangle wave generation circuit 25 Comparison circuit 26 Subtractor 27 Proportional integration circuit 28 Firing angle determination circuit 29 Transformer I _L Load current I _s Power supply current I _sh Power supply current Harmonic component L _s System impedance S Harmonic triangular wave signal V _c Power converter voltage V _c ^* Voltage command V _dc Load side DC capacitor Sui the DC voltage V _dc ^* load DC voltage command value V _GC power converter Gate signal V _h harmonic voltage instruction signals V _L thyristor bridge fundamental reactive voltage V _q ^* fundamental reactive voltage command voltage V _q power converter for generating a thyristor used for the gate signal V _Gl thyristor bridge quenching device V _s Three-phase AC power supply voltage V _t Thyristor bridge terminal voltage ΔV _dc DC voltage deviation signal

Claims (1)

(57) [Claims] 1. A PWM converter installed in series between an AC power supply and a DC load, the ripple suppression filter being connected in series to the AC power supply, and the AC power supply of the ripple suppression filter. A power converter composed of a self-extinguishing type switching element and a diode connected in series on the opposite side, a power converter DC capacitor connected to the DC side of the power converter, and the power converter A thyristor bridge connected in series to the opposite side of the ripple suppression filter, a load side DC capacitor connected to the DC side of the thyristor bridge, and a control device for controlling the power converter and the thyristor bridge,
The control device detects a power supply current and detects a harmonic component thereof, a means for multiplying the harmonic current component by a gain K to output a harmonic voltage command value, a fundamental reactive voltage command value, and A means for outputting the gate signal of the self-extinguishing type switching element of the power converter by adding the harmonic voltage command value and comparing with the triangular wave carrier signal, and detecting the DC voltage of the load side DC capacitor Means for controlling ignition of the thyristor bridge according to a difference from a voltage command value.