JPS646601B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of operating an electric vehicle using a three-phase induction motor as a main motor.

[Conventional technology]

FIG. 3 is a configuration diagram showing a system for driving an electric vehicle by driving a three-phase induction machine using a known variable voltage variable frequency inverter (VVVF inverter).

In Fig. 3, 1 is a pantograph that collects current from the overhead line, current breakers 2 and 3, high-speed breakers 4,
It is connected to a VVVF inverter 7 via a filter reactor 5, a filter capacitor 6, etc.
Here, the VVVF inverter 7 has a constant overhead line voltage, so the voltage and frequency can be controlled.
It is a VVVF inverter. Many types of configurations of this VVVF inverter 7 are already known, so a description thereof will be omitted here, but 7u to 7z have a feedback diode in antiparallel like a reverse conduction thyristor, and use McMurray type auxiliary impulse commutation. Any method that can perform pulse width control (PWM control), such as a method such as the PWM control method, may be used. Output u of VVVF inverter 7,
v, w are generally multiple three-phase squirrel cage induction motors 8
a, 8b, . . . 8n are driven in parallel.

An example of the output waveform of such a VVVF inverter 7 is shown in FIG. 4. FIG. Figure 4 shows the line voltage uv voltage and its on/off ratio (t ₁ /
t ₂ ) gives the average output voltage of the VVVF inverter 7. Generally, it is well known that the on-off ratio and repetition frequency of an induction motor must be approximately proportional to each other.

Further, this will be explained with reference to the block diagram shown in FIG.

In FIG. 5, 31 is a motor torque command for accelerating the vehicle, 32 is a function generator that generates a current command corresponding to the torque, and this output is compared with the current feedback 39 at a subtraction point 33, The deviation value that occurs when the current control amplifier
A voltage command 341 is generated in the ACR 34 so that the voltage becomes zero. On the other hand, it can be said that the torque command 31 and the necessary slip frequency command are almost in a proportional relationship, and the torque command 31 and the necessary slip frequency command are almost proportional to each other. It is added to the speed feedback value 411 at an addition point 43 to cause the voltage controlled oscillator 36 to oscillate. That is,
The oscillator 36 is caused to oscillate at a frequency that is the rotational speed of the three-phase induction machine 40 plus a slip frequency value for generating a desired torque. 37 is a circuit that generates a triangular wave with a constant oscillation width in synchronization with the oscillator 36, and this circuit is normally configured so that a triangular wave with a constant oscillation width is generated regardless of the frequency of the inverter. The explanation will be omitted here.

Here, the normal voltage command 341 is a positive voltage signal with reference to zero, and the constant width triangular wave 371 is also a positive voltage signal with reference to zero. The input of the comparison gate command circuit 35 is turned on when the voltage command 341 is larger than the constant amplitude triangular wave 371.
It is assumed that the connection is made such that it is turned off when the voltage command 341 is smaller than the constant width triangular wave 371.

Now, the voltage command 341 and constant amplitude triangular wave 37
1 is compared in the comparison gate command circuit 35, and the comparison gate command circuit generates a signal waveform for controlling the VVVF inverter 38. This has already been explained using the waveforms in FIG.

By the way, conventionally, in general, the current function generator 32
is usually non-linear as shown in Figure 6, but the cause of this is that the excitation current of the induction motor and the current component contributing to torque form a vector sum, which determines the current, and the current is simply a quantity proportional to the torque. This is because it is not.

[Problem that the invention seeks to solve]

Such a VVVF inverter system is expected to be highly reliable due to the lack of a reversing device, PB converter, etc., and the non-contact system.However, we have taken this a step further by reducing the number of openings and closings as much as possible when the notch goes off during operation. It seems effective to extend the lifespan of
Moreover, when the current interrupters 2, 3, etc. are opened and closed, losses related to charging and discharging of the filter capacitor 6 and control delays are inevitable until the transient phenomenon is completed, resulting in poor controllability.

However, if you only want to solve the above drawbacks, you can just cut off the gate signal of the VVVF inverter while keeping the circuit breakers 2 and 3 closed.
If this is done, abnormal vibrations will occur in the filter capacitor when the overhead line voltage suddenly changes, and when the gate signal of the VVVF inverter is reapplied, the motors 8a to 8n may
There are many problems such as inrush currents occurring because the phase relationship with the VVVF inverter 7 does not match.

[Structure of the invention]

The present invention has been made in view of the above-mentioned points, and its main focus is on the point A (point where the torque is 0) that provides the rated excitation current as shown in Fig. 6 when the electric vehicle is notched off. The current is shifted to point B, where the current value is even smaller, and the main circuit current breaker is not opened except when stopped or when an abnormality occurs.

Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 is a block diagram similar to FIG. 5, showing an example in which means is provided to give a weak excitation current command while the VVVF inverter is energized at the time of notch-off.

In FIG. 1, 44 is an excitation current value command circuit;
Reference numeral 45 denotes a signal switching circuit having a switching function as shown in the figure, which can also employ a low-level priority signal switching device, for example.
Reference numeral 6 denotes a cushion circuit that provides a first-order delay effect when the signal switching circuit 45 operates. In the figure, the same reference numerals as in FIG. 5 indicate the same components.

Here, an excitation current value command circuit 44 and a signal switching circuit 45 are attached to the circuit configuration shown in FIG. It is sent to

In this manner, it is clear that the system shown in FIG. 1 can be effectively used as if the VVVF inverter is notched off and coasts at point B shown in FIG. 6 while energized. Here, B
The excitation current value at the point varies depending on the design of the motor, but approximately 10 to 20% of the rated excitation current is appropriate.

By the way, in such a system, when the vehicle reaches a high-speed operation state, VVVF operation is stopped and switched to constant voltage constant frequency (CVVF) operation, and the overhead wire voltage is often converted to a square wave alternating current and the full voltage is applied.

This means that in the explanation of FIG. 5 as described above, if the vehicle speed increases and the voltage command 341 increases accordingly, the time t ₁ during which the comparison gate command circuit 35 is in the on state increases, and the on-off ratio increases. (t ₁ /t ₂ ) approaches 1. And voltage command 34
If the maximum value of 1 is set to a value larger than the amplitude of the constant amplitude triangular wave 371, the voltage command 3
41 exceeds the amplitude of the constant amplitude triangular wave 371,
The comparison gate command circuit stops its on/off operation and maintains a constant output state, that is, (t ₁ = t ₂ ) in Fig. 4.
CVVF operation can be performed correspondingly.

Furthermore, FIG. 2 shows an example of a notch curve of an electric vehicle, and particularly shows the case of electric power running. That is, from vehicle speed 0 to vehicle speed _V1 , the inverter 7 performs VVVF operation, and the inverter output voltage is proportional to the vehicle speed, as shown in Fig. 4.
Performs PWM control. Between vehicle speed V ₁ and vehicle speed V _nax
Without PWM control (i.e. on-off ratio t ₁ /t ₂
=1) Perform only frequency control with full voltage application. In particular, between 0 and V ₁ is constant torque operation, between V ₁ and _{V 2} is constant output operation, where torque is inversely proportional to speed, and between V ₂ and V _nax
It is generally known that the torque is inversely proportional to the square of the speed in the characteristic acceleration region, and the slip frequency is generally controlled as shown in the figure in accordance with the above operation mode.

V ₁ to perform CVVF operation at such medium and high speeds
Even when operating at speeds between V _nax , the slip frequency is kept at zero when notched off, and
It is extremely advantageous in terms of controllability to switch to PWM control, reduce the on-off ratio (t ₁ /t ₂ ) of the output voltage, perform coasting operation with weak excitation, and always keep the inverter in operation as a VVVF inverter.
Considering the principle of the current control loop explained in FIG.
It is clear that this will result in VVVF operation.

〔Effect of the invention〕

As explained above, according to the present invention, by causing the VVVF inverter to coast while being energized by a weak excitation current at the time of notch-off,
There is no other method that can better respond quickly to unexpected accidents without using much power in terms of energy conservation, and it exhibits extremely superior performance in controlling electric vehicles by reducing the number of times the circuit breakers open and close. We can provide a method to do this.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the main part configuration of an embodiment of the present invention, Fig. 2 is a diagram showing an example of a notch curve of an electric car using a VVVF inverter, and Fig. 3 is a diagram showing an example of a notch curve of an electric car using a VVVF inverter. The configuration diagram shown in Figure 4 is
A diagram showing an example of the output waveform of a VVVF inverter,
FIG. 5 is a known block diagram of a slip frequency control system, and FIG. 6 is a diagram showing the functional relationship between torque command and current. 1... Pantograph, 2, 3... Breaker, 5...
...Filter reactor, 6...Filter capacitor, 7...VVVF inverter, 8a to 8n...
3-phase squirrel cage induction motor, 31...Motor torque command, 32...Function generator, 34...Current control amplifier, 341...Voltage command, 35...Comparison gate command circuit, 36...Voltage control type Oscillator, 38...
VVVF inverter, 40...three-phase induction motor,
41...Frequency voltage converter, 42...Pulse transmitter, 44...Exciting current value command circuit, 45...Signal switching circuit, 46...Cushion circuit.

Claims (1)

[Scope of Claims] 1. An electric vehicle that supplies power to a three-phase induction motor using a variable voltage variable frequency inverter to perform electric power running and regenerative braking, wherein the slip frequency of the variable voltage variable frequency inverter is set to zero when the electric vehicle is notched off. In a device that reduces the torque generated by the motor to zero by throttling the output voltage, it is equipped with a means for generating a weak excitation current command when the zero command for the torque generated by the motor is given, and the main By keeping the circuit breaker closed and passing a weak excitation current, it is possible to reduce the control delay associated with opening and reinserting the main circuit breaker when the circuit breaker is re-notched, and to An electric vehicle driving system that is characterized by reducing the number of openings and closings. 2. In the variable voltage variable frequency inverter, which operates with full voltage application as a constant voltage constant frequency inverter during high-speed power running or regenerative operation of an electric vehicle, voltage control is performed even during high-speed operation when the electric vehicle is off, and the motor excitation current is lower than the rated voltage. An electric vehicle driving system according to claim 1, wherein the value is kept sufficiently low. 3. The electric vehicle operating system according to claim 1, wherein the main circuit circuit breaker is left on except when the vehicle is stopped or there is an abnormality in the circuit.