JPH0750961B2 - Overvoltage protection device for electric vehicle inverter - Google Patents

Description

The present invention relates to a thyristor which constitutes an overvoltage protection device at an inverter input end when an electric vehicle equipped with an induction motor controlled by an inverter is in regenerative braking. The present invention relates to an overvoltage protection device for an electric vehicle inverter that extinguishes arcs.

[Conventional technology]

In recent years, an induction motor is used as an electric motor for driving an electric vehicle, and a means for controlling the induction motor by a variable voltage frequency inverter (hereinafter, simply referred to as an inverter) is often adopted. The inverter is ON / OFF controlled at a predetermined frequency during power running of the electric vehicle, and the induction motor is driven at a frequency lower than this, while it is turned on at a frequency lower than the frequency of the induction motor during regenerative braking operation of the electric vehicle. Controlled off. Such on / off control is performed by the pulse output from the pulse width modulation means. Hereinafter, the circuit of such an electric vehicle will be described with reference to the drawings.

FIG. 4 is a block diagram of a conventional induction motor control circuit. In the figure, 1 is an overhead wire, 2 is a pantograph of an electric car, 3 is an induction motor of an electric car, 4 is a line breaker, and 5L and 5C are smoothing reactors and smoothing capacitors. Reference numeral 6 is an inverter, which is composed of six parallel circuits of a GTO thyristor (gate turn-off thyristor) 6G and a diode 6D, and supplies the induction motor 3 with three-phase alternating current. Numeral 7 is a pulse width modulation means, which applies pulse width modulated pulses to each GT.
The inverter 6 is turned on / off by applying it to the O thyristor 6G. Reference numeral 8 is a protection circuit connected between the input terminals of the inverter 6, and is composed of a series circuit of a resistor 8R, a switch 8SW, and a thyristor 8S.

9 is a sensor that detects the number of revolutions of the induction motor 3 and outputs the frequency f _r , and 10 is a desired slip frequency of the induction motor 3.
A slip frequency generator that outputs f _sp , and 11 is an adder / subtractor that adds and subtracts the frequency _fr and the slip frequency f _sp . Adder / subtractor 1
1 adds both when the electric car is in the power running mode,
Both are subtracted when in regenerative braking mode. Reference numeral 12 is V / f for keeping the induction motor voltage (corresponding to the modulation voltage of the pulse width modulation means 7) with respect to the frequency f _INV (frequency of the carrier wave of the pulse width modulation means 7) output from the adder / subtractor 11 in a constant relationship.
It is a generator. The excitation magnetic flux of the induction motor 3 is made constant by the output signal Vm of the V / f generator 12.

Reference numeral 13 is a DC transformer connected to both ends of the smoothing capacitor 5C and detects the voltage of the smoothing capacitor 5C. Reference numeral 14 denotes an overvoltage detector, which includes a reference voltage source 14B and a comparator 14C that compares the reference voltage source 14B with the output voltage of the DC transformer 13. When the output voltage of the DC transformer 13 is higher than the voltage of the reference voltage source 14B, the overvoltage detector 14 issues an OFF command to the line breaker 4, an ignition command to the thyristor 8S, and an OFF command to the switch 8SW. , A control stop command is output to the pulse width modulation means 7, respectively. In addition,
The overvoltage detector 14 operates only in the regenerative braking mode of the electric vehicle, and does not operate in the power running mode.

Now, when the electric vehicle shifts from the power running mode to the regenerative braking mode, the induction motor 3 becomes a generator and outputs its electric energy to the overhead wire 1 via the diode 6D of the inverter 6. This output electrical energy is either received by another running electric vehicle or absorbed at a substation. However, there is no other electric vehicle running, and
If the substation does not have the above-mentioned electric energy absorbing equipment or if it is out of order, the input terminal voltage of the inverter 6 rises, which may eventually destroy the GTO thyristor 6G of the inverter 6.

In order to prevent such a situation from occurring, the DC transformer 13 detects the input terminal voltage of the inverter 6, and this is the reference voltage source.
When the reference voltage of 14B is exceeded, the overvoltage detector 14 outputs a command signal, ignites the thyristor 8S and causes a current to flow through the resistor 8R to absorb the electric energy. At the same time, disconnector 4
GTO thyristor 6G by opening the pulse width modulation means 7
Stop the gate control of. The switch 8SW will be described later. As a result, the GTO thyristor 6G is protected, and thereafter, the electric vehicle is braked by mechanical braking such as air braking.

On the other hand, the thyristor 8S should naturally extinguish the arc because the current output from the induction motor 3 is attenuated. However, since the induction motor 3 has residual magnetism, even if the control of the inverter 6 is stopped, the induction motor 3 continues to generate electric power for a while, and a current continues to flow in the thyristor 8S during this time. The thyristor 8S is not extinguished if the holding current is higher than. If the operation is switched to the power running mode before the thyristor 8S is extinguished, the overhead line 1
The current flowing from the resistor 8R flows through the resistor 8R and the thyristor 8S, and this large current may burn the resistor 8R.

In order to prevent such burnout of resistor 8R, switch 8S
W is provided. That is, by the output signal of the overvoltage detector 14, the switch 8S is slightly delayed after ignition of the thyristor 8S.
When W is turned off, the thyristor 8S can be surely extinguished, and the risk of the resistor 8R being burnt out can be eliminated.

[Problems to be Solved by the Invention]

By the way, since the switch 8SW is inserted into the main circuit of the induction motor 3, it has a drawback that it has to have a high breakdown voltage structure and is extremely expensive.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide an overvoltage protection device for an electric vehicle inverter that can surely extinguish a thyristor without using an expensive switch.

[Means for Solving the Problems]

In order to achieve the above object, the present invention provides an induction motor for driving an electric vehicle, an inverter for controlling the induction motor, a modulation means for controlling the inverter, and a smoothing device connected between input terminals of the inverter. Capacitor, a series circuit of a resistor and a thyristor connected in parallel to the smoothing capacitor, and ignition of the thyristor when the voltage between the input terminals of the inverter exceeds a predetermined value during regenerative braking of the electric vehicle. A command and an overvoltage detector that outputs a control stop command of the inverter, in which the inverter is output when there is an output from the overvoltage detector,
It is characterized in that control means is provided for controlling the current flowing through the thyristor to a control state in which it is attenuated to an arc extinguishing current of the thyristor or less and outputting the control stop command after a predetermined time.

[Work]

During the regenerative braking operation, when the voltage between the input terminals of the inverter exceeds a predetermined voltage, the modulation means controls the inverter so that the current flowing through the thyristor is attenuated to the extinction current of the thyristor or less. As a result, the installation of expensive switches can be omitted.

〔Example〕

 Hereinafter, the present invention will be described based on the illustrated embodiments.

FIG. 1 is a block diagram of an overvoltage protection device for an electric vehicle inverter according to a first embodiment of the present invention. In the figure, the same parts as those shown in FIG. Reference numeral 8'denotes a protection circuit of this embodiment, which is formed by only the resistor 8R and the thyristor 8S, excluding the switch 8SW of the conventional device. A timer 17 delays the output signal of the overvoltage detector 14 by a predetermined time and outputs the delayed signal. Reference numeral 18 denotes an output voltage reducer, which is composed of, for example, a function generator. This output voltage reducer 18 outputs a numerical value "1" when the output of the overvoltage detector 14 is at a low level, and changes when the overvoltage is detected by the overvoltage detector 14 and its output changes to a high level. The numerical value output from the point of time is gradually reduced as shown in the figure. 19 is a multiplier, which outputs the output value of the output voltage decelerator 18 to V /
The output Vm of the f generator 12 is multiplied to obtain a new value Vm '.

Next, the operation of this embodiment will be described. During normal regenerative braking, the voltage across the terminals of the inverter 6 does not become an overvoltage, the output of the overvoltage detector 14 is at a low level, and the output of the output voltage reducer 18 is a numerical value "1". Therefore, Vm '= Vm, and the inverter 6 is controlled by the pulse width modulation means 7 in the same manner as the conventional one.

During such normal regenerative braking, when the voltage across the terminals of the inverter 6 becomes overvoltage and the output of the overvoltage detector 14 becomes high level due to the reason described above, the thyristor 8S fires and the electrical energy is absorbed by the resistor 8R. And output voltage taper
The output value of 18 decreases from 1.0. Therefore, the output Vm of the V / f generator 12 is multiplied by a value which is 1.0 or less in the multiplier 19 and is gradually reduced, and the value Vm 'is also gradually reduced. As a result, the modulation rate in the pulse width modulation means 7 decreases, and the gate of the GTO thyristor 6G of the inverter 6 is narrowed accordingly. As a result, the induced voltage of the induction motor 3 is forcibly reduced by the inverter 6. In conventional equipment, when an overvoltage occurs, the GTO
Since the control is immediately stopped without narrowing the gate of the thyristor 6G, the induced voltage of the induction motor 3 does not immediately disappear, but gradually decreases over a certain period of time, and the induced voltage remains during this period. Thyristor due to residual magnetic field
It is probable that a large current flowed to 8S, making arc extinguishing difficult. However, in this embodiment, since the control of narrowing the gate of the GTO thyristor 6G is executed for a predetermined time after the overvoltage is generated, the induced voltage is also forcedly reduced accordingly, and eventually the thyristor 8S The flowing current can be suppressed to a value much lower than the holding current. This ensures that the thyristor 8S can be naturally extinguished. On the other hand, the control stop command output from the overvoltage detector 14 to the pulse width modulation means 7 is delayed by the timer 17 for a predetermined time so that the diaphragm control as described above is performed reliably. In any case, the GT of the inverter 6
The O-thyristor 6G is finally turned off.

The characteristic of the output voltage declining device 7 does not necessarily have to perform the linear decrease as shown in the figure, and may have any characteristic as long as the numerical value is decreased.

As described above, in this embodiment, the predetermined time from the occurrence of the overvoltage,
Since the gate of the GTO thyristor of the inverter is controlled to be narrowed and the induced voltage of the induction motor is forcibly attenuated, the thyristor of the protection circuit can be surely extinguished.

FIG. 2 is a block diagram of an overvoltage protection device for an electric vehicle inverter according to a second embodiment of the present invention. In the figure, the same parts as those shown in FIG. Reference numeral 21 is a timer for delaying the control stop command output from the overvoltage detector 14 to the pulse width modulation means 7 by a predetermined time. Reference numeral 22 denotes an operation mode switch, which is composed of, for example, a function generator. The operation mode switch 22 outputs a predetermined positive slip frequency when the output of the overvoltage detector 14 is at a low level, but when the overvoltage is detected and goes to a high level, its output value f _s ′ becomes It gradually decreases until it reaches a certain negative value. 23 is a slip frequency generator 10
Is a minimum value selector that selects the smaller output by comparing the output f _sp of the output f _sp with the output f _s ′ of the operation mode switch 22.

Now, when the voltage between the input terminals of the inverter 6 becomes an overvoltage and the output of the overvoltage detector 14 becomes high level during regenerative braking, the thyristor 8S fires and the resistor 8R absorbs electrical energy. On the other hand, the output f _s ′ of the operation mode switch 22 decreases and finally becomes a negative value. Minimum value selector 23 outputs
Since f _s ′ is negative and smaller than the value f _sp , that value is selected and input to the adder / subtractor 11 as the slip frequency f _s .
In this case, since the operation mode is the regenerative braking mode, the adder / subtractor 11 is in the subtraction state. However, since the value f _s output from the minimum value selector 23 is a negative value as described above, the operation in the adder / subtractor 11 is addition, that is, (f _r + | f _s |). Therefore, the frequency of the inverter 6 becomes higher than the frequency of the induction motor 3, and the operation mode becomes the power running mode. Eventually, the operation mode switch 22 outputs a negative value, so that the operation mode is switched from the regenerative braking mode to the power running mode.

When the operation mode is switched to the power running mode, the induction motor 3 is in a state in which it reversely absorbs the electric energy output in the regenerative braking mode up to that point. Therefore,
The current flowing through the thyristor 8S decays rapidly and
8S can be surely extinguished. The control stop command output from the overvoltage detector 14 is delayed by the timer 21 so that the switching from the regenerative braking mode to the power running mode can be performed without trouble, and after the operation mode is switched to the power running mode. It is input to the pulse width modulation means 7, and the gate of the GTO thyristor of the inverter 6 is turned off only at this point.

When the operation mode is switched from the regenerative braking mode to the power running mode, if the interrupter 4 is reclosed for some reason, the induction motor 3 is driven when it should be braked. If the thyristor 8S is not yet extinguished, the resistor 8R may be burned out. In order to prevent this, it is desirable to provide means for prohibiting reclosing of the line breaker 4 until the control stop command is output from the timer 21. As this means, a combination of a logic circuit and a relay that turns off the interrupter 4 on condition that the output of the overvoltage detector 14 is at a high level and the output of the timer 21 is at a low level is used. To be

Thus, in this embodiment, the operation mode switch is provided,
When the overvoltage occurs, the operation mode is switched from the regenerative braking mode to the power running mode, so that the thyristor of the protection circuit can be surely extinguished.

In the description of each of the above embodiments, the function generator, the timer,
Although the circuit using the minimum value selector, the multiplier and the like has been described as an example, these functions can also be implemented by program processing by a microcomputer.

〔The invention's effect〕

As described above, in the present invention, when an overvoltage occurs during regenerative braking, the inverter is controlled so as to attenuate the current flowing in the thyristor of the protection circuit, and then the inverter is stopped for control, so that an expensive switch is used. It is possible to reliably extinguish the thyristor of the protection circuit without using.

[Brief description of drawings]

1 and 2 are block diagrams of an electric vehicle inverter overvoltage protection device according to first and second embodiments of the present invention, and FIG. 3 is a block diagram of a conventional electric vehicle inverter overvoltage protection device. is there. 1 ... overhead line, 3 ... induction motor, 6 ... inverter, 7
...... Pulse width modulation means, 8 '... Protection circuit, 8R ... Resistor, 8S ... Thyristor, 13 ... DC transformer, 14 ... Overvoltage detector, 17,21 ... Timer, 18 ... Output Voltage reducer, 2
2 …… Operation mode selector, 23 …… Minimum value selector

Claims (3)

[Claims] 1. An induction motor for driving an electric vehicle, an inverter for controlling the induction motor, a modulation means for controlling the inverter, a smoothing capacitor connected between input terminals of the inverter, and a smoothing capacitor for smoothing the smoothing. A series circuit of a resistor and a thyristor connected in parallel with a capacitor, and when the voltage between the input terminals of the inverter exceeds a predetermined value during regenerative braking of the electric vehicle, a firing command of the thyristor and control stop of the inverter With an overvoltage detector that outputs a command, when the output from this overvoltage detector, the inverter is controlled to a control state in which the current flowing through the thyristor is attenuated to the arc extinction current of the thyristor or less. And a control means for outputting the control stop command after a certain period of time is provided. Protection device. 2. The control means according to claim 1, wherein the control means delays the output of the control stop signal for a predetermined period, and the modulation rate of the modulating means is narrowed to the delay period by the delay means. An overvoltage protection device for an electric vehicle inverter, comprising: a throttle means. 3. The control means according to claim 1, wherein the control means delays the output of the control stop signal by a predetermined period, and the regenerative operation mode is the power running mode within the delay period by the delay means. An overvoltage protection device for an electric vehicle inverter, comprising: