JPH05244702A - Controller for electric vehicle - Google Patents

Abstract

PURPOSE:To balance voltages of filter capacitors by discharging excessive charges upon occurrence of voltage unbalance between filter capacitors split in series. CONSTITUTION:In case of a three-level inverter wherein filter capacitors 6A, 6B are split in series, one filter capacitor 6A(6B) has a voltage of 0V while the other filter capacitor 6B(6A) has a voltage of 1500V. In this case, a switching element 5B(5A) in an overvoltage control circuit connected in parallel with the filter capacitor 6B(6A) charged with higher voltage is conducted to discharge the filter capacitor 5B(5A). When conduction of the switching element 5B(5A) is interrupted at a point where voltages of the filter capacitors 6A, 6B are balanced, unbalance of voltage can be eliminated. According to the constitution, voltages of split filter capacitors 6A, 6B can be balanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter overvoltage suppressing circuit for controlling an induction motor.

[0002]

2. Description of the Related Art FIG. 3 shows a simple connection of a main circuit of a conventional inverter, which is formed in one phase of an inverter by elements 21 and 22 having a self-arc extinguishing function and free wheel diodes 23 and 24. , V phase, W phase and three phases form an inverter. At the input of the inverter, the filter reactor 3 and the filter capacitor 6 exist as an input filter, and when the voltage of the filter capacitor 6 rises for some reason, the overvoltage suppressing thyristor 5 is fired to the overvoltage suppressing resistor 4 connected in parallel. The discharge current is passed through the switch 2 and the switch 2 is opened to protect the inverter from overvoltage.

Further, as a recent trend of inverters for electric vehicles, as described in the article No. 311 application of transistors to VVVF for vehicle driving at the 27th domestic symposium on cybernetics in railways in 1990, filter capacitors are used. It is in the direction of a three-level inverter divided in series.

Furthermore, the paper No. 9 at the National Conference of Industrial Application Division of the Institute of Electrical Engineers of Japan, 1991, 3kV high voltage GTO for electric vehicles
Three-level inverters are being applied in the field of overhead line voltage as described in the formula VVVF inverter.

However, as seen in the connection of the main circuits in those papers, the overvoltage suppression protection circuit is a circuit similar to that of the conventional two-level inverter. Conventional example
Shown in.

Further, as a three-level inverter, an example in which an overvoltage protection circuit is connected in parallel to respective capacitors connected in series is described in Japanese Patent Application Laid-Open No. 2-262827.

[0007]

In the above-mentioned prior art, the controllability in the case where the control of the three-level inverter is always operating normally and the voltage imbalance of each of the series-divided filter capacitors during abnormal operation occurs. Is not taken into consideration, and in such a case, there is a problem that the circuit must be turned off once.

[0008]

In order to achieve the above object, according to the present invention, an overvoltage suppressing circuit having an on / off function is connected in parallel to each filter capacitor divided in series, and a voltage imbalance occurs between the respective capacitors. In this case, the excess charge is discharged through the overvoltage suppressing circuit so that the voltage is always kept in balance.

[0009]

For example, in the case of a three-level inverter in which the filter capacitor is divided into two in series, it is assumed that the voltage of one filter capacitor is 0V and the voltage of the other filter capacitor is 1500V. In this case, the switching element of the overvoltage suppression circuit connected in parallel with the filter capacitor charged with a high voltage conducts, discharges the voltage of the filter capacitor, and when both filter capacitor voltages are balanced, if the conduction is stopped, the voltage is unbalanced. Is eliminated.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows a general simplified connection of a 3-level inverter. Each phase has two switching elements 12 on the upper arm,
13 and free-wheel diodes 15 and 16, two switching elements 13 and 14 on the lower arm, free-wheel diodes 17 and 18, and clamp diodes 19 and 20 for fixing to the midpoint voltage.
One of the clamp diodes is connected to the midpoint between the two divided filter capacitors 6A and 6B.

The operation of the three-level inverter has been described in detail in a paper of a publicly known example and so the description thereof is omitted here, but the point to be noted is that the voltage of the filter capacitor divided into two is not always balanced. It is a point. That is,
When a protective operation such as overvoltage detection is activated and the inverter is instantaneously gated off, a voltage imbalance occurs in the 2-division capacitor due to the gate stop condition at that time.
In an extreme case, the voltage of the other capacitor may be zero and one capacitor may be charged to the train line voltage. A simple way to avoid this is to connect a balance resistor in parallel with the filter capacitor, but this resistor always causes a drift current to flow, and wasteful power is consumed there, which is a bad idea. Also, it is not a good method to install a device that generates heat unnecessarily.

Therefore, a method of discharging using an overvoltage suppressing resistance can be considered instead of the method of providing a balance resistance. As shown in FIG. 1, the overvoltage suppressing resistor is divided into 4A and 4B, and the switching element having an on / off state for energizing the overvoltage suppressing resistor is also divided into 5A and 5B, each of which constitutes an independent overvoltage suppressing circuit. , Connected to the filter capacitor.

Freewheeling diodes 7A and 7B are connected in parallel to the overvoltage suppressing resistor so that a current is circulated when the switching elements 5A and 5B are turned off.

Next, a control method when the filter capacitor voltage becomes unbalanced will be described below.

The voltages of the filter capacitors divided into two are respectively detected, and when either one of the voltages exceeds a preset value, the switching elements 5A and 5B for suppressing the overvoltage are ignited. There is a control method in which the circuit is once cut off and the main circuit switch 2 is opened to clear the filter capacitor voltage. In this case, since the main circuit switch is once opened and closed, it may not be possible to immediately respond to the operation command.

As a method of avoiding this, a switching element for suppressing an overvoltage is used as a self-arc-extinguishing element having an on / off function, and an element having an overvoltage is repeatedly controlled to be turned on / off at a relatively high frequency and divided into two. Another method is to balance the filter capacitor voltage in a short time. By doing so, it is possible to eliminate the imbalance of the filter capacitor voltage with a minimum loss time, so that a good control method can be provided.

FIG. 2 shows an example of connection of the overvoltage suppressing circuit.
2A is the same as FIG. 1, but if connected as shown in FIG. 2B, the switching elements 5A, 5 for suppressing overvoltage
Since B can be electrically connected, the hardware structure of the semiconductor stack can be summarized neatly. See also FIG.
If connected as shown in (c), overvoltage suppressing resistors 4A, 4B
Can be connected in potential, so that the hardware configuration of the resistor can be well organized. The capacity of the overvoltage suppressing resistor is the same as that of the conventional example shown in FIGS. 3 and 4 when viewed per inverter, and the two overvoltage suppressing switching elements conventionally used in series connection are divided and summarized. However, even if the overvoltage suppressing circuit is divided as shown in FIG. 1, there is almost no minus in terms of hardware configuration.

As the self-arc-extinguishing element, GTO is used as an example, but a power transistor or an IGBT is used.
Similar effects can be obtained by using other self-arc-extinguishing elements. With respect to switching of the elements, not only simple on / off switching but also switching at a cycle of several hundred Hz to several KHz can reduce or omit the overvoltage suppressing resistor.

FIG. 5 shows a voltage detection circuit for the capacitors 6A and 6B. DCPT32A, 32B in parallel with capacitors 6A, 6B
Are respectively connected, and the voltage of each capacitor is detected by this DCPT. Incidentally, 31A, 31
B is a series resistance of DCPT, 41 is a 3-level inverter unit, and 42 is an induction motor driven by a 3-level inverter.

The voltages detected by the DCPTs 32A and 32B are logically processed by the gate controller 43, and gate pulses are applied to the switching elements 5A and 5B having a self-extinguishing function as necessary.

An example of control is shown in FIG. FIG. 6A shows the states of the upper arm filter capacitor voltage ECF1 and the lower arm filter capacitor voltage ECF2.
First, the absolute value E of the difference between the two filter capacitor voltages
_{CF1 to} E _CF2 = V _0, which is within the allowable range. At t = t ₀ , it is assumed that the difference between the two begins to widen due to some factor. It is detected that the difference exceeds the allowable level V ₁ , and in this case the upper arm filter capacitor voltage E
_{Since CF1} is larger, the gate pulse G _P1 is applied to the switching element of the overvoltage suppressing circuit connected in parallel with the upper arm (FIGS. 5B and 5C). The voltage decreases, the voltage of the lower arm increases, and the difference gradually decreases. Difference E _CF1 ~ E _CF2
The gate pulse is stopped at a point where V is below the allowable voltage level V ₂ . By controlling in this way, even if the voltage of the upper arm and the voltage of the lower arm is unbalanced for some reason, it is possible to quickly restore the normal state.

[0022]

According to the present invention, the filter capacitor voltages divided in the three-level inverter can be balanced, so that the optimum design of the device can be achieved, and the effect of downsizing the device and saving energy can be achieved. is there.

[Brief description of drawings]

FIG. 1 is a main circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of another embodiment of the present invention.

FIG. 3 is a main circuit diagram of a conventional example.

FIG. 4 is a main circuit diagram of a conventional example.

FIG. 5 is a circuit diagram showing an embodiment of the present invention.

FIG. 6 is an explanatory diagram of the operation of the embodiment of the present invention.

[Explanation of symbols]

4A, 4B ... Overvoltage suppressing resistor, 5A, 5B ... Overvoltage suppressing switching element, 6A, 6B ... Filter capacitor.

Claims (6)

[Claims] 1. An inverter for an electric vehicle that drives a three-phase induction motor, comprising: a resistor and a switching element for suppressing a voltage rise due to a sudden load reduction during the regenerative braking control. A control device for an electric vehicle, wherein the resistor and the switching element are divided in series. 2. The electric vehicle control device according to claim 1, wherein the electric vehicle inverter is a three-level inverter. 3. The neutral point of the resistor and the switching element which are divided in series according to claim 1,
An electric vehicle controller connected to the neutral point of the filter capacitor of the level inverter. 4. The electric vehicle control device according to claim 1, wherein in the resistor and the switching element divided in series, the switching element is independently controlled. 5. The electric vehicle control device according to claim 1, wherein, in the resistor and the switching element divided in series, an element having a self-extinguishing function is used as the switching element. 6. The electric vehicle control device according to claim 5, wherein two types of gate signals, a collective ON signal and an ON / OFF control signal, are given to the element having an arc extinguishing function.