JPS58107090A - Protecting system of voltage type inverter for driving induction motor - Google Patents

Abstract

PURPOSE:To avoid a shock to a torque transmission system, and to improve comfortableness on driving by preventing the working of an arm short-circuit function when an overvoltage protecting function works. CONSTITUTION:An overvoltage detector 13 is operated when the terminal voltage of a filter capacitor (FC) 3 detected by means of a voltage detector 10 exceeds predetermined voltage, a thyristor 9 is supplied with gate signals while a contact 7 is opened, and a relay 15 is furnished with operating currents and the contact 16 is opened. An arm short-circuit detector 14 is operated when the terminal voltage of the FC3 detected by means of the voltage detector 10 reaches predetermined value or less, a gate controlling section 12 is supplied with control signals through the contact 16 of the relay 15, and all GTO's 4-1-4-6 are turned ON.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection method for a voltage source inverter for driving an induction motor, which reduces torque fluctuation when a protection operation is performed.

Induction motor (hereinafter referred to as IM) 1-1 Since the starting torque is generally small and it is difficult to obtain a wide speed control range, DC motors have traditionally been used exclusively as index motors for vehicles.

However, in recent years, by driving the IM' using a voltage source inverter fed from a DC power source, the IM has been used as an index motor for vehicles that require large torque at startup and also require speed control over a wide range. The characteristics of IM, such as low cost and easy maintenance, have been taken advantage of and it has become widely adopted. Ta.

The voltage source inverter used here is supplied with power from a constant voltage DC power source and converts it into square wave AC power, and is generally provided with a low-pass filter consisting of a reactor and a capacitor between it and the DC power source.

An example of such a voltage-type inverter circuit for driving an IM is shown in Figure 1. This inverter is a GTO thyristor (gate turn-off thyristor), which has been significantly improved in recent years as a semiconductor switch element. In Fig. 1, 1 is a DC power supply, 2 is a filter reactor (called FL), 3Fi filter capacitor (called FC), and 4-1 to 4-6 are GTOs. Thyristors (abbreviated as GTO), s-i to 5-6 are freewheel diodes, and 6 is a three-phase IM.

The GTOs 4-1 to 4-6 are turned on and off by gate signals supplied from a gate control section (not shown), and function to supply three-phase square wave alternating current to the winding of the IM 6 to generate torque.

Therefore, if the on-off tubes of each GTO 4-1 to 4-6 are controlled at a predetermined timing using the gate signal from the gate control section, it is possible to change the voltage in the frequency of the three-phase AC supplied to the IM. This can be achieved by controlling the starting torque and rotation speed of the tube.

At this time, if harmonics due to the on/off of GTOs 4-1 to 4-6 flow through the DC power supply IK, a large induction disturbance will occur. Therefore, the Ronokusu filter t consisting of FL2 and Fe3
It is installed between the inverter and the DC power supply 1 to prevent harmonics from flowing into the DC power supply 1. By the way, in the drive circuit of such a voltage type IM according to The terminal voltage of FC3 may rise abnormally due to voltage fluctuations in 1 or abnormalities in control operation.Therefore, some kind of line maintenance circuit is required to protect FCa and GTO4-1 to GTO4-6 from such voltage rises. For this purpose, the terminal voltage of FC3 is constantly monitored, and when the voltage exceeds a predetermined value, a resistor with a relatively low resistance value is inserted in parallel with Ktj FC3 to discharge the charge of FC3. The commonly used method is to do so.

In addition, in such an inverter device, CCTO4-1 to CCTO4-6 may be ignited incorrectly due to noise mixed into the control circuit system.
If 4-2 and 4-2 were turned on at the same time, it would short-circuit the DC side of the inverter, causing an excessive surge current to flow from FC3 and causing a sound that could destroy the GTO. For this reason, K also needs some kind of protection circuit. Therefore, when simultaneous conduction of the upper and lower arms is detected, K turns on the other remaining GTOs of the inverter. This causes FC3 to turn on. Generally, a method is adopted in which all the GTOKs of the inverter are shunted to reduce the surge current per GTO, and for this purpose, detection of simultaneous conduction of the upper and lower arms 4, constant monitoring of the terminal voltage of FC3, It is customary to start this process from K when this voltage becomes below a predetermined value. Note that, as is well known, in such an inverter device, a unit portion including a switch element inserted between a DC side and an AC side is called a t-arm.

FIG. 2 shows an example of an IM drive voltage source inverter equipped with two types of wire maintenance circuits.

In FIG. 2, 7 is a contact of an electromagnetic contactor, 8 is a resistor, 9 is a thyristor, 10t:l voltage detector, 11 is an overvoltage and arm short circuit detector, 12 is a gate control section, Other details are the same as in Figure 1.

The voltage detector 10 constantly and continuously monitors the terminal voltage of the FC3 (which is the same as the input DC voltage of the inverter), and when it exceeds a first predetermined value, sends an overvoltage signal to the first and second overvoltage signals.
Function 1 to generate a short circuit signal when the value of 1! is below a predetermined value. love.

The detector 11 inputs the signal from the voltage detector 1O, supplies a gate signal to the thyristor 9 when an overvoltage signal is supplied, opens the contact 7 at the same time, and controls when a short circuit signal is input. It operates to supply a signal to the gate control section 12 and open the contact 7.

The gate control unit 12 generates a gate signal for controlling the starting torque and rotational speed of the IM 41, and also generates a gate signal for the detection a+11.
When a control signal is input from GTO4-1 to GTO4-4
It functions to give an on signal to all gates of -6.

Therefore, if for some reason the terminal voltage of FCa exceeds the above-mentioned first predetermined value while three-phase AC is being supplied to IM6 from the inverter and it is operating, an overvoltage signal is output from the voltage detector lO, and this As a result, the resistor 8 is connected in parallel to FCa, so that the charge of FCa is discharged through this resistor 8 with a relatively small time constant, causing its terminal voltage to suddenly change. Therefore, damage caused by overvoltage being applied to FCa and GTO4-1 to GTO1 is prevented. Note that since the contact 7 is also opened at this time, there is no possibility that the direct current from the direct current power supply 1 will flow into the resistor 8.

In addition, if a short circuit occurs in either the upper or lower arms of GTO4-1-4-6, the terminal voltage of J)FCa will suddenly decrease and become below the second predetermined value mentioned above. A short circuit signal is output from the voltage detector 10, and as a result,
GTO4-1 to GTO4-6 are all turned on, and the discharge current of FCa is divided and distributed to all arms.
4-6 Prevent damage. At this time, K is also at contact 7.
Since it is opened, there is no risk of short-circuiting the DC power supply 1.

Note that, as is clear from the above explanation, the resistance value of the resistor 8 is set to a relatively low value according to the capacitance of FCa, and
Needless to say, it is necessary to ensure that the discharge time constant of a is sufficiently small.

Therefore, according to the device shown in this In2 diagram, FCa and GTO
There is no risk that the tubes 4-1 to 4-6 will be damaged during operation, and sufficient reliability can be maintained when the tubes are used under relatively harsh operating conditions such as in a vehicle.

However, when the conventional device shown in FIG. 2 is applied to drive a vehicle, a large and sudden change occurs in the IM torque when the protective function is activated.
This has disadvantages in that the stress on the torque transmission system becomes excessive, causing damage, and the riding comfort tends to deteriorate due to sudden changes in vehicle speed. That is, in the conventional example shown in FIG. 2, when the terminal voltage of FCa becomes excessive and exceeds the first predetermined value, resistor 8 is connected in parallel with FCa, causing the terminal voltage of LFCa to drop rapidly. Therefore, the voltage at this time is
When the value becomes less than a predetermined value, the gate controller 1 is
A control signal is sent to GTO 2, and all GTOs 4-1 to 4-6 are turned on.

When the overvoltage protection 1 function is activated, the arm short-circuit protection function, which does not normally need to be activated, also activates. I'm going to go there. If all the GTOs 4-1 to 4-6 become conductive while IM6 is rotating, the terminals of IM6 are shorted, and the I
A large transient current flows through M6, causing a sudden change in torque.

However, power running e-regeneration [frequently repeated 9
When returning a vehicle, there is a large fluctuation in the voltage on the DC power supply side during driving and regeneration, and there are many chances for the overvoltage protection function to activate. Therefore, in the conventional example described above, the arm Since the short-circuit protection function also operates, the above-mentioned drawback occurs.

Here, in the conventional example shown in Fig. 2, the results of the simulation of torque changes when all the GTOs 4-1 to 4-6 are made conductive while the IM 6 is rotating are shown in Fig. 3.

In the diagram IIjL3, (a) represents the armature current of each phase, (b) represents the armature current of each phase, and (e) represents the time t.

Although a method has been described above in which all GTOs are turned on when an arm short-circuit is detected, an arm short-circuit protection circuit is also known in which the GTO is fixed at 1 when an arm short-circuit is detected. In this method, even if the other GTOs are turned on immediately after an arm short circuit is detected, there is a delay in response, so we cannot expect much of a shunting effect. It is used when there is no overcurrent, or when the overcurrent capacity of the GTO element used is sufficiently large and there is no problem of damage, and when you want to prevent excess overcurrent from flowing to other GTOKs. However, the simulation result in this case is as shown in FIG.

In this M4E, as in the jI3 diagram, (a) is the torque of IM6, (b) to) is its armature current, and (e) is time.

Therefore, as is clear from these Figures 3 and 4,
It can be seen that in the conventional example described above, large torque fluctuations occur in either case.

An object of the present invention is to eliminate the drawbacks of the prior art described above and to prevent torque fluctuations when the overvoltage protection function is activated.
The present invention provides a protection method for a voltage source inverter for driving an L7tIM.

In order to achieve this target sound, the present invention has an At feature that prevents the arm short-circuit function from operating when the overcurrent protection function is operating.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the drawings will be described as an example of a protector case of a voltage source inverter for IM drive according to the present invention.

Figure 5 shows an embodiment of the present invention, in which 13 is an overvoltage detector;
The 4Fi arm short-circuit detection circuit, 15 is a relay, and 16 is its normally closed contact, and the rest is the same as the conventional example shown in FIG.

The overvoltage detector 13 detects F detected by the voltage detector 10.
It is activated when the terminal voltage of e2 exceeds the first predetermined voltage level, and supplies a gate signal to the thyristor 9 and contacts 7.
In addition, relay 15 is supplied with operating current and its contacts 16 are opened.

The arm short circuit detector 14 detects f#- with the voltage detector 10.
It operates when the terminal voltage of Fe2 falls below a predetermined value of Relay 2, and the gate control unit 12 is activated via the contact 16 of the relay 15.
and all GT04-1 to 4-6t-
It functions to turn on or fix the gate pipes of GTO4-1 to 4-6.

Therefore, for some reason, for example, when the electric car is in regenerative operation, the absorption of power by the VC of another electric car is interrupted, and the terminal voltage of Fe2 becomes excessive.This causes the thyristor 9 to turn on. Assume that the overvoltage protection function is activated.

Then, the terminal voltage of J) Fe2 suddenly decreases, and as a result, the arm short circuit detector 14 responds and generates a control signal to the gate control section 12. Therefore, the operation up to this point is the same as the conventional example shown in Fig. 2, and if this continues, all of GTO4-1 to GTO4-6 will be turned on, or their gates will be fixed, resulting in a large and rapid IM6K. However, in this embodiment, as mentioned above, one relay 15 is provided, and when the overvoltage detector 13 operates, the relay 15 also operates and opens its contacts 16. ing. Therefore, even if the overvoltage detector 13 operates and the overvoltage protection function by the parallel circuit of the resistor 8 is activated, there is no risk of excessive fluctuation noise in the torque of the IM6, and no large shock is caused to the torque transmission system. This prevents damage that may result in damage or worsen ride comfort.

Then, when an arm short-circuit accident occurs and the terminal voltage of Fe2 drops below the second predetermined value, the overvoltage detector 13 does not respond due to this, and the relay 15 remains inoperative. Therefore, the control signal from the arm short-circuit detector 14 is directly supplied to the gate control unit 12 via the normally closed contact 16t, and there is no possibility that the operation of the arm short-circuit protection function will be disturbed, ensuring reliable maintenance at all times. In the embodiment shown in Fig. 5, the relay 15 is used, but an electronic switch circuit or the like may be used instead, and the point is to detect overvoltage. When the overvoltage protection function is activated by the operation of the arm short circuit detector 13, the present invention can be implemented by any circuit or element that can inhibit the operation of the arm short circuit protection function by the arm short circuit detector 14. M+ is possible.

As explained above, according to the present invention, the torque fluctuation of the IM when the overvoltage protection function is activated can be sufficiently suppressed with a simple configuration.
Even when an IM't- driven by a voltage source inverter is used as an index motor of a vehicle such as an electric car, there is no risk of shock and damage to the torque transmission system or deterioration of riding comfort, and IMO It is possible to provide a protection system for an IM drive voltage source inverter that is useful for constructing low-cost vehicles by making full use of the characteristics.

[Brief explanation of the drawing]

Figure 1 is the 3rd diagram of a voltage source inverter for driving an induction motor. Figure 4 Figure 5

Claims (1)

[Claims] 1. An induction motor drive having a filter consisting of a reactor and a capacitor on the DC input side, and having an arm short-circuit protection function and an overvoltage protection function by connecting a low resistance element between the terminals of the capacitor. In the voltage type inverter for use, a means for monitoring the operation of the overvoltage protection function is provided, and when the overvoltage protection function is activated, a trap is configured to prohibit the operation of the arm short circuit protection function. Protection method for voltage source inverters used to drive motors. 2. Scope of the 411'F request In item 1, the arm short circuit protection function is configured to be performed by means of detecting the occurrence of an arm short circuit and bringing all remaining arms of the inverter into a conductive state when the arm short circuit occurs. What we did f: Maintenance formula of voltage source inverter for driving induction motor with % image. 3. Scope of claims '#g1 In the above-mentioned arm short-circuit protection function, when the occurrence of an arm short-circuit is detected, the control state mt of the remaining arm of the inverter is controlled to be fixed as it is. configured to be carried out
A protection method for voltage source inverters used to drive induction motors.