JPS5883587A - Power converter - Google Patents

Abstract

PURPOSE:To improve the power factor in wide voltage range by controlling the time width to be opened and closed during the closing time determined by the phase angle by simultaneously setting equally to the phase angle of the switching means having current breaking function. CONSTITUTION:A control delay angle alpha is set to 90 deg., a current flows through a GTOU1 and a thyristor V2 as shown in a loop 1 during the firing period of the GTOU1, and a negative current flows to the power source. At this time the GTOU1 is broken, and the GTOU2 is fired. Then, a load current flows a loop 2 but does not flow through the power source. The output voltage E0 at this time becomes zero. Accordingly, when the time duration is sufficiently shortened, the output voltage E0 and a U-phase current IL can be sufficiently reduced, thereby improving the power factor.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for converting power between alternating current and direct current using a full-wave bridge circuit.

Conventionally, various devices using full-wave bridge circuits have been proposed and put into practical use as devices for obtaining variable DC power from an AC power source or converting DC power into AC power. In addition, single-phase or multi-phase AC is used depending on the application, and those that target multi-phase AC are more technically and equipmentally complex than single-phase AC, but the principles are the same. There are many points. Therefore, in the following explanation, three-phase alternating current will be mainly used as an example, but it will be easy to understand the case of single-phase alternating current from this explanation.

FIG. 1 shows a conventional device for obtaining variable DC voltage from a three-phase AC power supply. In the figure, 3-phase AC power supply E, to U
The three-phase voltages of , V, and W are
It is connected to the AC terminal of a three-phase full-wave thyristor bridge consisting of U2 1 V, l V21WI IW2).

This DC output voltage E. is controlled by controlling the phase of the gate pulse of each thyristor U, -W2, and the resistor RL
, an inductance LL, and a DC voltage EL.

Gate pulse generation phase (thyristor U.

In other words, this is the electrical angle delay from the point when the UW phase voltage switches to positive, and is hereinafter referred to as the control delay angle. ) is α, the DC output voltage E. is expressed as 3V]-E, CO3α... (1) π. The output voltage E when the control delay angle α is 0 and the DC output voltage is maximum, and when the control delay angle α is 90' and the DC output voltage is 0. Waveform, U-phase voltage U and U-phase current I
The relationship between the u waveforms is shown in FIGS. 2(a) and 2(b), respectively. Assuming that the time constant LL/RL of the load impedance is sufficiently longer than the period of the power supply, the DC voltage EL of the load is the output voltage E.

This waveform is shown assuming a slightly lower value. For example, such a condition exists when the armature circuit of a DC motor performs constant current control with a load.

As shown in Figure 2(a), when the output voltage is maximum, U
The center value of the phase current IU matches the center value (maximum value) of the U-phase voltage U, the phase of the fundamental wave component of the U-phase current IU matches the U-phase voltage U, and the power factor is This is the best control system of its kind.

However, as shown in FIG. 2(b), when the output voltage Eo is zero, the center of the U-phase current IU is at the zero point of the U-phase voltage U, and 1. The fundamental wave component of the U-phase current In is 9 from the U-phase voltage U.
With a delay of 0°, we can say that the power factor is zero. Like this 3
The output voltage r by controlling the firing angle of the phase full-wave thyristor bridge. In particular, the method for controlling the output voltage E. It has the disadvantage that the power factor becomes poor in a low range. therefore,
It is desired to improve the power factor in the low output voltage range, reduce the input current, and reduce the capacity of the power supply.

Furthermore, the output voltage EO of the three-phase full-wave bridge circuit includes a ripple component whose fundamental wave is six times the power supply frequency. This ripple component decreases as the output voltage increases, and reaches its maximum when the output voltage is zero, as shown in Figures 2 (a) and (b).
), the output voltage E. When is low, the ripple portion of the output current It becomes large. Therefore, when the load is an armature circuit of a DC motor, noise is generated by the ripple component of the output current Ib, and in particular, the noise caused by the ripple component at a low frequency of about 6 times the power supply frequency becomes a problem.

On the other hand, in order to improve the power factor, a method has recently been proposed in which each of the sirisks shown in FIG. 1 is made into an element having a current interrupting function and is controlled. Elements that have this current interrupting function include gate turn-off thyristors (referred to as GTOs), which interrupt the stain current by passing a pulsed reverse current through the gate, and devices that have a similar function using transistors. ,
Furthermore, there are chopper devices and the like. In this case, each phase voltage U, V, W and DC output voltage E. FIG. 4 shows the waveforms of the U-phase current In and the U-phase current In. In this method, for example, the thyristors U1 to W1 in FIG.
The output voltage Eo is controlled by changing . Therefore, its output voltage E. is pulse-like with a time width P, and the fundamental wave component of the U current Iu is also in phase with the U-phase voltage U, so the power factor can be brought close to 1. Also,
Its output voltage E. contains almost no sixth harmonic component of the power supply, and the output current I1. The ripple component can also be suppressed to a sufficiently small level.

However, in order to continuously control the output voltage E be. Therefore, the output voltage E0 is reduced to 1/10
It is very difficult to control it to a certain extent.

By the way, there are many applications that require control to 1/10 or less of the rated voltage. <For example, in a high-speed elevator driven by a DC motor, the speed is 1/1000 of the rated speed.
It is necessary to control continuously up to the following speeds. In such a case, the above method cannot be applied and the method shown in FIG. 1 has no choice but to be applied.

An object of the present invention is to provide a power conversion device that has a good power factor, can control output voltage over a wide range, and can control output current in both positive and negative directions.

A feature of the present invention is that two sets of full-wave bridge circuits are used, and at least one arm of the full-wave bridge circuits is connected to a controllable switching means having a current interrupting function to convert power between AC and DC. , comprising means for controlling the phase angle of the opening/closing means, and means for controlling a time width for opening and closing the opening/closing means, and controlling the time width to make the output voltage variable and at the same time changing the opening/closing period. As mentioned above, the configuration is such that the phase angle can be controlled and varied. For example, in a range where the output voltage is large, the phase angle, that is, the control delay filter α
The time interval for opening and closing the opening/closing means is controlled by setting 0 to 0, and in a small range of output voltage, the output voltage can be controlled over a wide range by minimizing the time width and then controlling the control delay angle α. Moreover, the power factor is improved over the entire range.

The present invention will be explained below using an illustrative embodiment. In addition, in the example, first of all, GTO is used as a switching means that has a three-phase AC power supply and a single bridge and has a current cutoff function.
A case will be described in which the following is adopted, and a case in which the electric motor is controlled using two sets of primary bridges will be explained. Furthermore, even if a single-phase alternating current or other switching means is used, the operation is almost the same and can be easily understood.

FIG. 4 is a diagram for explaining the present invention in detail. FIG. 4A shows an embodiment of the main circuit, and FIG. 4A shows the output voltage E.

and shows a waveform diagram of the U-phase current In. This waveform diagram shows the output voltage E. is close to zero, that is, the control delay angle α is 90°, and the opening/closing is performed at a frequency of 30 times the power supply frequency with GTOU and time width P. In this way, the control delay angle α
is set to 90', and during the period when G TOU I is firing, oTOUT
A current flows through the thyristor v2, and a load current flows to the power supply. At this time, GTOU is cut off and GTOU is
When V2 is turned on, the load current flows through loop ■ and does not pass through the power supply. Output voltage E at this time. is zero. Therefore, if the time width P is made sufficiently short, the output voltage E. and U-phase current Ir can be made sufficiently small,
The power factor can be much improved compared to the conventional one shown in FIG. 2(b). Also.

By controlling this control delay angle α to 0 and controlling the time width P to the maximum, the output voltage can be controlled over the entire range. Furthermore, as mentioned above, G T OU +
The period in which ignition and GTOV are alternately fired is referred to as 1 period 1, and will be referred to below.

Next, an example of a method of controlling the gate signals of G T OU, . . . G T ow will be described with reference to FIG. In addition, oTOU, ~GTOW.

The firing signals of the thyristors U2-W2 are referred to as GUt-GW2.

GU+ has two modes. Tsumashi.

GU during the period when the load current flows into the power supply (the period when the output voltage is generated) when GTOU is ignited.

GU, GU1 during the period when no load current flows into the power supply (period when the output voltage is zero) are G and U12, and similar suffixes are given to other gate pulses.

Here, the period in which each pulse is generated when the control delay angle is α is shown in FIG. 5(a).

GU should be a signal that generates a positive voltage during the period when G T OUT conducts and is zero during the non-conducting period, and GU2 generates a narrow pulse when firing if the load current is connected. It is fine as long as it is something.

The basic signal that generates such a signal may be one that generates one gate signal for each thyristor in one cycle, like the gate signal of a conventional three-phase full-wave thyristor bridge circuit, and the signal corresponds to each thyristor. G U gate signal
If expressed as +s, it becomes a pulse train as shown in FIG. 5(b). From now on, Ruyou will be known as GU2”G
U23, GV2 ””GVts.

The gate pulses of the thyristors U2°Vt and W2 may be the same as those of the conventional ones.

If this pulse group is passed through a flip-flop circuit, GUl
From the pulse of , to the pulse of GU23, a Rujounahals GU4 is obtained that is ON. These pulses are shown in Figure 5(c).
K Show t. Sarah K G U tt, G V tt
, GW++ is turned ON (pulse at the time of conduction in chopper operation), as shown for period 1 only in FIG. 5(d), let it be P. At this time, the logical expression of the gate pulse to be applied to the GTO can be obtained as follows.

An example of an actual circuit for generating these gate pulses is shown in FIG. The Tr is a Δ-Y transformer, and the neutral point on the secondary side is grounded. P.U.

PV, , PW are phase shifters similar to the conventional ones, and ignition pulses G U +s , G are generated by phase shift signals Sct, respectively.
Generate Uts etc. G U 23, G V ts
, G Wts U GU2 , GV2 , GW respectively
Tekiru used as 2.

Clip these pulses to the flop circuit PU.

In addition to PV, , PW, pulse GU41GV4°GW4 is obtained.

On the other hand, one circuit PP receives a pulse P according to the conduction rate command Sp.
occurs. These signals are passed through the NOT circuit P2 and then sent to the 3-gate NAND circuit P3 so as to satisfy the logical formula (2).
This output is further added to the NAND circuit P4 so as to satisfy equation (3). In this way pulse GU,.

GV heavy and GW electricity can be obtained.

Next, the control method for α and P is that when controlling the positive output voltage, first, the conduction rate of P is kept constant at 0.1, and then α is set to 90.
When changing from 0 to 0, the output voltage increases by 0.

When controlling a negative output voltage, α is set to 90°. Next, when P is changed from 0.1 to 1, in order to obtain the α command sa and the p command Sp from the negative pressure command SL, a function generator having the characteristics as shown in FIG. 7(a) is used as shown in FIG. 7(b). ) just connect as shown.

An example of a circuit for controlling the speed of a DC motor using the circuit system according to the present invention is shown in FIG.

M is the armature of the DC motor, F is its field, and Th is a thyristor amplifier that allows a constant current to flow in one direction.

Further, PC is the gate circuit shown in FIG. 6, and PA is a comparator that compares the output of the DC current transformer CT that detects the armature current with the armature current command S c'. Cc is a switching circuit that determines which side of the three-phase bridge should be given the firing signal when current flows through the armature M. 1. Here, the armature current level and current command are used as the determination conditions. ing.

With such a circuit, the armature current is variably controlled in both positive and negative directions according to the current command Sc.

Also, the speed of the motor is determined by comparing the speed detected by the speed command SL+ and the speed generator PG by a comparator PI, and by controlling the armature current to be positive or negative, the positive or negative torque is controlled. Four-quadrant control is performed to more closely follow the speed command S8.

In this type of control system, in order to eliminate the drawback that when a power outage occurs mainly during a regenerative state, the output voltage of the thyristor circuit becomes zero and the armature current increases rapidly, destroying the thyristor circuit, the armature circuit is usually connected directly. A contactor is inserted, but in a single circuit, Uz, Vt, Wt,
Us -Vs, Ws Since KGTO is adopted, it is possible to cut off the stain root current by giving an off-nogle gate signal to turn off the armature current when it exceeds a certain level, making it a high-speed DC contactor. This eliminates the need for equipment miniaturization and cost reduction.

Furthermore, this embodiment has the advantage that a DC reactor is not required. In other words, the DC reactor is said to have the function of suppressing the rate of change of the sudden increase in armature current during abnormal conditions as described above, and prolonging the cut-off delay time of the DC contact, but the GTO's self-extinguishing function By using this, it is possible to save space and save energy.

Furthermore, this embodiment has the advantage of eliminating the need for a power transformer. In other words, in order to improve the power factor as much as possible, a matching transformer that matches the voltage of the power supply to the rated voltage of the motor is generally installed between the power supply and the AC-DC converter, but GTO can be used instead of a thyristor. In any of the embodiments used in the above, control can be performed in a state where the power factor is always high, so a power transformer is not required, and space and power savings are achieved.

As described above, according to this embodiment, the power factor of three-phase AC power conversion and inverse conversion is improved, the capacity of the power supply can be reduced, and the power factor of the DC contactor and DC reactor can be reduced.

It has great industrial effects, such as eliminating the need for a power transformer.

In addition, in the explanation, Ur + Vt + Wl +
Us, V3. Let w be GTO, but U2゜V2
．． W2, U4-V4, W4 is GTO, Ul,
Vt, Wt, Us, Va, Ws are thyristors Ut, V2, Wt-U4, V4,
It goes without saying that the same effect can be obtained even if a method of opening and closing W4 at a high frequency is adopted.

FIG. 9 shows another embodiment of the present invention. Here, the electric motor drives the counterweight CW and the cage C via the sheep Sh. It is widely known from research that elevators are very often operated at speeds lower than their rated speeds.

In this case, the motor is operated at a considerably lower rated voltage.

According to another embodiment of the present invention, there is an inherent effect that changes in power factor due to differences in operating speed can be kept constant at a substantially high level.

Fig. 10 shows an example of power conversion between single-phase AC and DC. Fig. 10 (a) shows the main circuit between the single-phase AC power supply Eb and the DC load.

GTOR, ~Q T = () S + and thyristor Rt
A bridge circuit consisting of +82 is connected. This G
Output voltage E when only the phase angle α of TORl, GTO81, and thyristor R21S is controlled.

is shown in the same figure (b), and in addition to this phase angle α, GTOR,
.

Output voltage E when the time width P for opening and closing G T OS 1 is controlled. is shown in the same figure (C). This figure shows the case where the control delay angle α is 90° and the output voltage EO is zero. Similarly to the embodiment described above, if the time width P is minimized, the output voltage E is set. It is possible to dramatically improve the power factor when it is set to zero. Similarly, if the delay angle α is controlled from θ to 180° and the time width P is controlled from the maximum to the minimum, control can be achieved over the entire range from forward transformation to inverse transformation.

'In the past, three-phase converters were used for relatively large capacity loads in consideration of the effects of armature current ripple, but
The system shown here has the feature that even though the basic configuration is single-phase, it can exhibit more effects than conventional three-phase converters.

In this manner, the present invention controls not only the phase angle of the opening/closing means having the current interrupting function but also the opening/closing time width during the closing time determined from the phase angle. Therefore, as in the embodiment described above, it is also possible to implement the present invention by connecting a GTO for only one set of phases without connecting a GTO to each phase, and a corresponding effect can be obtained. Can be done. That is, the present invention can be effectively applied to two sets of full-wave bridge circuits in which at least one arm is connected to a switching means having a current interrupting function. Further, the opening/closing means is not limited to the GTO, but any device that can cut off the current may be used.

As described above, according to the present invention, power can be converted with good power factor over a wide voltage range.

[Brief explanation of the drawing]

Figure 1 is the main circuit diagram of a conventional power conversion device, Figures 2 and 3 are conventional power conversion waveform diagrams, Figures 4 to 8 are the main circuit diagram of the conventional power conversion device,
Fig. 4 is an example of the main circuit of a power conversion device and its waveform diagram, Fig. 5 is an explanatory diagram of gate signals, Fig. 6 is a gate circuit diagram, and Fig. 7 is a function generation diagram. FIG. 8 shows a DC motor control circuit, and FIGS. 9 and 10 show a main circuit of a power converter and its waveform diagram for explaining other embodiments of the present invention. E,...3-phase AC power supply, U, V, W...3-phase voltage,
L...Load, GTOU, ~GTOW3...Gate
Turn-off risk, α... Control delay angle, P.
... Opening/closing time width, PU-PW... Phase shifter, F (!
l F p...Function generator, CC...Switching circuit, PI, PA...Comparator, Sh...Sheep, C
W...Counterweight, output n/l E. (()゛ゝ--1'' 3 Figure (η) L (ze) (kyu) (-e) (Continued from page 1 of C 0 Inventor Kiyoya Shima 5 Marunouchi-chome, Chiyoda-ku, Tokyo No. 1 Inside Hitachi, Ltd. 0 Inventor Yoshio Sakai 1070 Ichige, Katsuta City Inside Hitachi, Ltd. Mito Factory Applicant Hitachi Engineering Co., Ltd. 3-2-1 Saiwai-cho, Hitachi City

Claims (1)

[Claims] 1. A controllable switching means having a current interrupting function is connected to at least one arm, and 92 sets of bridged circuits are connected in antiparallel to convert power between AC and DC. , a means for controlling a phase angle of the opening/closing means, a means for controlling a time width for opening/closing the opening/closing means, and a means for opening/closing the opening/closing means for the time width at least during a closing period of the opening/closing means determined by the phase angle. A power conversion device characterized by comprising means for. 2. In claim 1, when the DC terminal voltage of the full-wave bridge circuit is above a predetermined value, the phase angle is kept constant and the time width is controlled; when the voltage is below the predetermined value, the above A power conversion device characterized in that the power conversion device is configured to control the phase angle while keeping the time width constant. 3. Claim 2 is characterized in that the voltage command includes a function generator that varies within the phase angle range, and the time width control means includes a function generator that varies the voltage command within a large range. Power converter. 4. In claim 1, switching means having a current interrupting function is connected to all arms on the positive side or negative side of the full-wave bridge circuit, respectively, and the phase angle control means is connected to each switching means. A power conversion device comprising: and the above-mentioned time width control means; and means for opening and closing the opening/closing means according to both of these means. 5. In claim 4, the opening/closing means is configured to:
A power conversion device comprising means for closing a switching means in a mode of short-circuiting between DC terminals. 6. In claim 1, the two sets of full-wave bridge circuits are three-phase full-wave bridge circuits, and the opening/closing means is configured to open/close at a frequency of six times or more the power supply frequency. 7. In claim 1, the full-wave bridge circuit is a single-phase full-wave bridge circuit, and the opening/closing means operates at a frequency of at least twice the power supply frequency. A power conversion device characterized in that it is configured to open and close. 8. The power conversion device according to claim 1, wherein the full-wave bridge circuit has a DC motor connected between its DC terminals. 9. A power converter according to claim 8, wherein the DC motor drives an elevator having at least two different operation patterns.