JPS586094A - Brake control system for inverter - Google Patents

Abstract

PURPOSE:To simplify the structure of an inverter and to increase the lifetime of the inverter by effectively and rapidly decelerating an AC motor to be controlled to the rotating speed less than a resonance point when the output from an inverter main circuit is stopped. CONSTITUTION:When an overcurrent flows in a line, the base signals of all transistors Tr11-Tr32 are interrupted upon reception of a signal from a current detector 11 which detects the overcurrent, the transistors Tr11, Tr22 are then fired. Then the transistors Tr21, Tr32 are then fired after the prescribed period of time is elapsed, the transistors Tr31, Tr12 are then fired after the prescribed period of time is further elapsed, these operations are then repeated, thereby forming always a DC brake circuit of an AC motor 8. In this manner, the motor 8 is rapidly decelerated to the rotating speed less than the resonance point.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a braking control system for an inverter that electrically brakes an AC motor that is composed of switching elements and the like and is driven by an inverter device.

When controlling the rotational speed of an AC motor, variable voltage,
Inverter devices are commonly used as variable frequency power sources, and when an abnormality such as an overcurrent occurs during line control operation, it is possible to immediately stop the output and protect the inverter device. It is done.

Fig. 1 (a), (b) Ka, when the inertia moment of the AC motor, especially its rotor, or the inertia moment of the connected load is very large, and the operation of the AC motor is controlled by an inverter device at time t. The corresponding rotational speed characteristics and the vibration characteristics of the rotating system including the AC motor corresponding to the time t are shown, respectively. Figure 1 - Curve (1) shows the state of operation at a constant frequency;
is a circle indicating the state when the rotational speed rises.

Now, at time t1, the inverter current increases and exceeds the maximum rating of the switching elements due to a sudden load increase or an arm short circuit in the inverter main circuit configured by the switching elements. In this case, the protection circuit within the inverter operates immediately, and the ON signal to the switching element is interrupted. If such a cut-off state continues, the AC motor will rotate by inertia as shown in the curved line without receiving power from the inverter, and at this time, because the moment of inertia of the rotating system is large as described above, , the rotational speed slowly decreases over a very long period of time. In general, many rotating bodies resonate at a predetermined rotational speed; for example, in Fig. 1←), rotational speed N1. If N2 has a resonance point, the vibration component becomes significantly large at the point corresponding to the rotational speed N+, N2, as shown in FIG. 2(b) K. However, if the moment of inertia of the rotating system is large and its rotational speed slowly decreases over a very long period of time, the time required to pass through the resonance point becomes long, and the rotating system including the AC motor and load There is even a risk that the device may be exposed to vibration for a long period of time, leading to its destruction. Therefore, when power supply from the inverter device to the AC motor is stopped in the event of an abnormality such as an overcurrent, it is necessary to apply braking to the rotating system to quickly reduce the rotational speed to a rotational speed below the resonance point.

FIG. 2 discloses a variable speed drive system including a typical three-phase inverter device and an AC motor that have been conventionally provided. In this case, transistors are used as switching elements in the inverter main circuit 1, and each arm 1rI-jv ? jw 2
transistors Tr++ and Tr12. Trz+
and °rrz2. Tr3+ and Trs2 form a husband and wife structure, and transistors Tr11 and Tr12 . TrH and Tru
, U and V for each interconnection point of Trs+ and Tr52.

The W-phase output terminals are To, Tv, and Tw.

Further, power is supplied to this inverter main circuit 1 from a DC power supply 5 having a smoothing capacitor 2, and a transistor T
By switching r u to Trs2, for example, through 180 degrees, the output terminals Tσ, Tv.

Outputs three-phase AC to the TV. On the other hand, between the smoothing capacitor 2 and the inverter main circuit 1, there is a switch S1 on the positive potential side. A series circuit of a burnout prevention fuse 4, a switch S2, and a series circuit of a current detector 5 are connected to the negative potential side, and a smoothing capacitor 2 and each phase output terminal Tt
A switch S1 . S2, STI, Sv, Sv,
So, Sv.

Sv is connected as shown. In this case, switch S1
and Sl, 82 and 82, STI and Sv, Sv and S
v.

Sv and 3v have a so-called conjugate relationship in which when one is on, the other is off. In addition, D11 to D52 are Fufihoi μ
It is a diode.

FIG. 5 shows an example of the operation of the variable speed drive system configured as described above, in particular, turning on the transistors Tr11 to Trsz.

This is a time chart showing the OFF operation based on the fin current detected by the current detector 5 and the inverted signal BE. That is, the transistors Tr11 to Tl-212 are switched in a 180-degree conduction method, and the fin current flow detected by the current detector 5 is the same as that of each transistor Tr11 to Tr1.
When the current value is less than the maximum rated current value ICo of No. 2, switching of the transistors Tr11 to Trsz continues, and a low-level inverted signal BE is output. Then, at time t1, the AC motor 6 breaks down, the load suddenly increases,
When an overcurrent exceeding the maximum rated current value CO flows through the fins due to an arm short-circuit in the inverter main circuit 1, etc., the on-signal to the transistors Tr+s to Trn is cut off, the inversion signal BE is inverted, and this inversion timing is utilized. The switches S1. and S1. Sl...
... are mutually inverted. Then, from the positive terminal of the DC power supply 5 to the switch S1. A DC current flows through the two windings of the AC motor 6 via Sv, Sv, and S2, applying DC braking, and the AC motor 6 is quickly decelerated to a rotational speed below the resonance point.

However, in the variable speed drive system shown in Figure 2,
Switch S1. Since a large number of mechanical contacts such as Sl are used, the circuit configuration is complicated and the service life is likely to be shortened due to damage to the contacts. Also, switch S1.
Since Sl and the like require a large current capacity in order to intermittent direct current, it is difficult to implement in a high-output inverter device, and even if it could be implemented, it would be uneconomical.

The present invention has been made in view of the above circumstances, and its purpose is to reliably and quickly decelerate a controlled AC motor to a rotational speed below the resonance point when the output from the inverter main circuit is stopped. It is an object of the present invention to provide a braking control method for an inverter that can simplify the structure and prolong the life of the inverter.

An embodiment of the present invention will be described below with reference to FIGS. 4 to 8.

In Fig. 4, 7 is the inverter main circuit, which uses transistors as switching elements, and each arm 7o, 7v, 7v of the three-phase bridge is connected to two transistors Tr11, Tru, Tr2, and T.
rsz, Trst and Trsz and one quick-acting fuse F1. F2 and Fi, each consisting of a fast-acting fuse F1 and a transistor TrH, F2 and Tru,
Each interconnection point of Fl and Trsz is used as each phase output terminal Tυ, Tv, Tv of U, V, W phase, and these output terminals Tυ, Tv, Tv are connected to each winding terminal TJ/, of three-phase AC motor 8. ■/ and W/ are connected. Further, power is supplied to this inverter main circuit 7 from a DC power supply 10 having a smoothing capacitor 9, and transistors 'rrN~
By switching T1-52 by energizing, for example, 180 degrees, three-phase alternating current is output to the output terminals T+y, Tv, and TV. In this case, the transistor Trtt
, Trtt, and Trst correspond to the first switching elements, and the F functions Tru, Tru, T
ru corresponds to the second switching element. and,
A current detector 11 is interposed between the negative potential side of the smoothing capacitor 9 and the inverter main circuit 7, and flywheel diodes D11 to Dtz are interposed between the collector and emitter of each transistor Tr11 to Tr2. be done.

FIG. 5 shows an example of the operation of the variable speed drive system having the configuration shown in FIG.
The on/off operation of r11 to Tru is detected by the current detector 11, and the inversion signal B is inverted to low V/1/ when the current detector 11 detects an overcurrent.
This is a time chart Y shown together with E. Now, at time t1, if the fin current exceeds the maximum rated current value CO of each transistor Tr11 to Trsz due to a failure of the AC motor 8, a sudden increase in load, an arm short circuit of the inverter main circuit 7, etc. Detect this with nine current detectors 1
1, each transistor Tr u to Trs
The base signal of z is cut off, and the inverter main circuit 7
AC output from the output terminals To, Tma, and Tv is stopped. However, if the moment of inertia of the load including the rotor of the AC motor 8 is large, it is necessary to quickly reduce the rotation speed of the AC motor 8 to a rotation speed below the resonance point of its rotating system, as described above. . In this case, if the base signal to each transistor Tr11 to Tru is temporarily interrupted and the transistors Trll and Trot are turned on, the positive terminal of the DC power supply 10 → the transistor Tr1
t → 2nd winding of AC motor 8 → transistor 'I'r*t
→ A DC braking circuit is formed between the terminals of the DC current $110, and the AC motor 8 quickly passes through the resonance point rotation speed. However, if an arm short circuit occurs in the arm 70 of the inverter main circuit 7 and an overcurrent flows and the base signals of each transistor Tru to Trsx are interrupted, then the Overcurrent is more important than time! If the time for exceeding the maximum rated current value ICO of Tr1t to Tru is earlier, the transistors Tr11. Both or one of Tr12 may be destroyed. When such a situation occurs, the above-mentioned braking control method is insufficient, so the following braking control method is used. In addition, in the following, U-phase arm 7
0 was targeted, but the same applies to the other arms 7ma and 7v.

(1) Trv+ is normal, Tru2 is destroyed (collector-emitter short circuit)... As shown in Figure 6, which shows the same content as Figure 5, at time t1
After the base signal is cut off at
When rn and Tr2z are fired, an arm short circuit occurs again in the U-phase pool 7σ and an overcurrent flows in the line, so the base signals of all F transistors Tr11 to Trst are cut off again. After this, F Funjista Trzt,
Trst is fired and the transistors Trz1.
Nine DC braking circuits are formed through the two windings of the AC motor 8.

(II)) Physister Tr11. Both transistors Trlz are destroyed (collector-emitter short circuit)...As shown in FIG. 7, which shows the same content as FIG. When Trtz is destroyed, Arm 7
Short-circuit current flows through U, resulting in rapid breakage X' F 1
Fuse-cut. Therefore, the transistor Tr+1°Trtz
Although a DC braking circuit is not formed even if transistors Trz1. When Trs2g is fired, the transistor Tr21y Trsze crosses fJfF
.

A DC braking circuit is formed via the two windings of the electric motor 8.

(II)) Fungistor Tr11 is destroyed (base cannot be controlled or collector-emitter is open), transistor Tru is in any state... In this case, fast-acting fuse F1 remains as is, and the above (
Similarly to case 11), transistor Tr21. True
2) DC system @IC! ll tract is formed.

(IV)) The transistor Tr++ is destroyed (the collector
Short distance between emitters M), ) transistor Tr B is normal.
In this case, as shown in FIG. 5, the base signal is cut off at time t1, and then the transistor Tru.

'rr When a firing command is issued to H, the transistor Tr
A DC braking circuit similar to that described above is formed regardless of the destruction of u.

To summarize the above, when an overcurrent flows through the fins,
After receiving a signal from the current detector 11 that detected this, the base signals of all the transistors Tru to Trs2 are cut off, and then the transistor Tru is turned off.

Tr22 is ignited, and after a certain period of time has passed, F
Transistor Trz+ and Tru2 are turned on, and when a certain period of time has elapsed, transistor Trs+ is turned on.

By repeating the operation of igniting 'I'r1z, a DC braking circuit for the AC motor 8 is always formed, so that the AC motor 8 quickly reaches a rotational speed below the resonance point. The speed will be reduced to

FIG. 8 shows an example of a circuit for realizing the stop modes (1) to (1v) described above. In FIG. 8, 12 is the output terminal of the base block signal BO,
This pace block signal BO is output when the current detector 11 detects an overcurrent.

Reference numeral 16 denotes a group of output terminals for a base signal that instructs the firing timing of transistors Tr11 to Tr32, and each output terminal 1
The output from 5 is applied to one input terminal of each group of AND circuits 14. 15 is a flip-flop which receives the pace block signal BO and inverts to a low level signal output state;
The output is given to each other input terminal of the group of AND circuits 14, so that the current detector 11 is over 1! When the current is detected, a low level signal is input to the other input terminal of the AND circuit 14 group, and a total of seven signals from the output terminal 15 are sent to the AND circuit 1.
It is no longer possible to pass through the fourth group, and the base signal is cut off. 16 is a ternary counter that counts up every time it receives the pace block signal BO, and 17 is O that receives each output from this counter 16 and the AND circuit 14 group.
R circuit group, its output terminal is transistor 'rr1
1~Tr! It corresponds to each base of 2. In such a configuration, when an overcurrent flows through the fin and the pace block signal Ba is output, all transistors Tr11 to Tr5
The base signal for counter 2 is cut off and the counter 1
6 output terminal 01 is "1j, other output terminals Q2, Q
s becomes rOJ, and an O braking circuit is formed. At this time, when transistor destruction occurs in the state (1) above, overcurrent flows again and the pace block signal Bo is output, so the counter 16 counts up and "1" is output only from its output terminal 02. As a result, transistors Tr2t and Tru are turned on, thereby forming a DC braking circuit. When the pace block signal BO is further outputted at M4, the counter 16 outputs "1" only from the output terminal OS, and the transistors Trrs, T! A DC braking circuit is formed through ``12.'' 18 starts a timer operation when receiving the pace block signal Bo, and clears the counter 16 to the initial state when the timer operation ends. A timer is used, and the timer operation time is set corresponding to the time required for DC braking.

As is clear from the above description, according to the present invention, when the output from the inverter main circuit is stopped, the controlled AC motor can be reliably and quickly decelerated to a rotational speed below the resonance point, and It is possible to provide a braking control method for an inverter that can eliminate the need for mechanical contacts, simplify the structure, and extend its life.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the rotational speed characteristics and vibration characteristics of an AC motor, Fig. 2 is a wiring diagram showing a variable speed drive system for an AC motor originally provided, and Fig. 3 is a time chart showing the operation of the system. It is. Figures 4 to 8 relate to one embodiment of the present invention, in which Figure 4 is a wiring diagram showing a variable speed drive system for an AC motor, and Figures 5 to 7 show the operation of the various components of the system. FIG. 8 is a block diagram showing the main circuit configuration. In the figure, 7 is the inverter main circuit, 70.7 m, 7v is the arm, and 8 is AC 1! Motivation, Trll, Trz+, T
ril is a transistor (first switching element), T
r12゜Tr2z, Tril is the transistor (second
The switching elements ), Fl, F2, and Fs are fast-acting fuses. Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1. An AC motor is driven by an inverter main circuit having a plurality of sets of arms each having a first switching element, a second switching element, and a fast-acting fuse connected in series;
In the event of an abnormality such as overcurrent, all switching elements are turned off, and then the first switch between the two sets of arms is turned off. A braking control method for an inverter, characterized in that a group of switching elements in the above combination are sequentially switched on to form a DC braking circuit for a front AC motor by a combination of second switching elements.