JP2851018B2 - Electric car control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an electric vehicle driven by an induction motor.

[0002]

2. Description of the Related Art In order to drive an induction motor with an inverter device that converts direct current into alternating current, it is fundamental to apply a rotating magnetic flux to a rotor of the motor with an AC voltage applied to a stator of the induction motor. FIG. 2 shows a configuration of an inverter device for obtaining a three-phase AC output. 1a to 1f are switching elements such as reverse conducting gate turn-off thyristors,
6 is a control device for issuing a command to switch on or off the switching element, 2 is a filter device usually composed of a reactor and a capacitor, 3 is a DC current collecting device peculiar to an electric vehicle, 5 is an induction motor to be driven, and 4 is a feedback current. The reference numeral 7 denotes a rotation speed detection signal of the induction motor, and 8 denotes a gate signal for commanding conduction or interruption of the switching element.

FIG. 4 is a vector diagram showing the state of the rotating magnetic flux acting on the rotor of the electric motor when the switching elements 1a to 1f are turned on or off by the command signal shown in FIG.

When the induction motor is driven, the state of the rotating magnetic flux is ideally a perfect circle as shown by a broken line in FIG. 4, but in practice it is a polygon as shown by a solid line with an arrow in FIG.
In that case, the length of one side indicates the strength of the magnetic flux, and is approximately proportional to the value obtained by integrating the terminal voltage applied to the stator with time.

In order to change the rotation speed variously with a constant torque, it is general to change the frequency applied to the stator, that is, the basic frequency of the inverter output, while keeping the strength of the magnetic flux constant. At this time, the intensity of the magnetic flux becomes constant by always maintaining the fundamental frequency and the voltage in the same proportional relationship.

A method of controlling the average value of the voltage by operating the time ratio of a simple state of only conduction or interruption in a predetermined relationship is generally called PWM modulation. The inverter device performs a variable voltage variable frequency control by adding a periodic variable element to this voltage operation.

FIG. 5 shows an example of a vector diagram when the fundamental frequency is lowered from the state of the command signal shown in FIG. FIG.
Ideally, the hexagons in FIG. To realize this, switching is performed at a time (corresponding to a circle) corresponding to the midpoint of one side of the hexagon, and the vector growth is temporarily stopped. This can be achieved by making the AC output phase potentials equal.

[0008] As for the switching method for performing the PWM modulation, from the viewpoint of making the shape of the vector diagram close to a perfect circle and from the viewpoint of moving the rotating magnetic flux at a constant speed, the device can decompose the vector as finely as possible and grow the vector. Is frequently set such that the switching is temporarily stopped. The control element that gives this switching pattern is the modulation frequency.

However, there is a certain degree of freedom in setting the switching method. For example, JP-A-2-266869
Japanese Patent Laid-Open Publication No. Hei 3-15204 discloses an improvement in noise generated by switching by changing the modulation frequency or periodically fluctuating the modulation frequency.

[0010]

The vector of the rotating magnetic flux obtained from the three-phase AC output inverter device shown in FIG. 2 has six directions as shown in FIG. Therefore,
When the shape of the vector diagram of the rotating magnetic flux is made close to a perfect circle and the symmetry is ensured, the switching frequency subjected to PWM modulation contains a harmonic component six times the fundamental frequency of the inverter output in principle. The sixth harmonic component appears on the DC side of the inverter device.

Although the six times higher harmonic component is attenuated by the filter device 2 shown in FIG.
Since the signal security equipment laid on the train line is sensitive to a specific frequency in the tens of hertz band, the frequency component of this band of the harmonic wave by the PWM modulation has a serious adverse effect on the signal security equipment (induction obstacle). There is fear.

[0012]

SUMMARY OF THE INVENTION The present invention changes a specific switching pattern to another switching pattern when a harmonic component due to PWM modulation of an inverter device passes through a frequency band related to signal security equipment. It is.

[0013]

FIG. 6 shows an example of the shape of the rotating magnetic flux obtained from the switching pattern for reducing noise. FIG. 6 also shows that switching is performed at the bending points and the circle points of the solid line, similarly to FIG. Also, as in FIG. 5, the switching pattern is repeated so as to make one round of the figure in six different directions, but FIG. 6 shows only one representative side.

FIG. 6 clearly shows a bias in the switching density. Since this density appears six times in one rotation of the vector diagram, the switching frequency, that is, the modulation frequency fluctuates at six times the fundamental frequency of the inverter output. On the other hand, a switching pattern shown in FIG. 7 is prepared to reduce the six-fold higher harmonic component. The switching pattern of FIG. 7 reduces the above-mentioned effects by making the switching density uniform, that is, by making the modulation frequency constant.

Now, the sensitivity frequency of the signal security equipment is 50 Hz.
Assuming that the generation of a six-fold higher harmonic component in a band of ± 5 Hz before and after that is prevented from 7.5 Hz to
The switching pattern of FIG. 7 is selected during the fundamental frequency of 9.2 Hz, and the switching pattern of FIG. 6 is selected outside this band.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in the case of asynchronous PWM modulation in which the modulation frequency can be set independently of the inverter fundamental frequency will be described. FIGS. 6 and 7 show the vector division number (including temporary stop) and the switching timing fixed uniquely, but in the case of asynchronous PWM modulation, substantially the same rotational flux vector shape is obtained. This is a method in which the switching timing is not uniquely fixed on the assumption that the switching is performed. Both the asynchronous PWM modulation and the synchronous PWM modulation in which the modulation frequency is set to an integral multiple of the fundamental frequency have the same effects and harms as the modulation frequency is varied, and the effectiveness of the present invention does not change.

FIG. 1 shows an embodiment of the present invention. All of the components shown in the block diagram of FIG. 1 are to be incorporated in the control device shown in 6 of FIG. In FIG. 1, 61 is PWM.
Modulation device, 62 is a voltage command device, 63 is a fundamental frequency command device, 64 is a low noise switching pattern generator, 6
5 is a low harmonic switching pattern generator, 66 is a switching pattern switching device, and 67 is a frequency band detector.

In response to the induction motor rotation speed signal 7, the basic frequency command device 63 outputs a basic frequency command signal.
In response to this command signal, voltage command device 62 outputs a voltage command such that the strength of the rotating magnetic flux of the induction motor becomes a predetermined value. In a normal state, the switching pattern switching device 66 selects a signal on the side of the low noise switching pattern generating device 64. The PWM modulator creates a gate signal of a switching element from a fundamental frequency command, a voltage command, and a switching pattern signal.

When the frequency of 7.5 Hz to 9.2 Hz described in the section of the operation is instructed as the fundamental frequency, the frequency band detecting device 67 outputs a switching signal to the switching pattern switching device 66. Upon receiving this switching signal, the switching pattern switching device 66 switches the switching pattern signal from the low noise switching pattern signal to the low harmonic switching pattern signal on the low harmonic switching pattern generator 65 side. Therefore, when the fundamental frequency is between 7.5 Hz and 9.2 Hz, the PWM modulator outputs a switching pattern with six times less harmonic components.

The output signal of the switching pattern generator instructs the degree of switching density, that is, the level of the modulation frequency and the range of change. For example,
When the potential of the output signal of the low-noise switching pattern generator 64 is high (10 V), the modulation frequency is high (10 Hz increase of the reference frequency), and when the potential is low (-10 V), the modulation frequency is low (10 Hz decrease of the reference frequency). ), And the potential of this output signal is changed at a frequency six times the fundamental frequency. Specifically, the voltage phases of the fundamental wave are 30 °, 90 °, 150 °, 210 °, and 270.
The modulation frequency is high at 0 °, 330 ° and 0 °, 60 °, 12 °.
The modulation frequency is lowered at 0 °, 180 °, 240 °, and 300 °. The level of the modulation frequency may change continuously or may change stepwise. The low noise effect can be adjusted by changing the height (± 10 Hz) of the modulation frequency. The adjustment of the height is performed by changing the potential level of the output signal of the switching pattern generator. The modulation frequency is changed continuously or stepwise, depending on the shape of the output signal of the switching pattern generator. If the output signal of the switching pattern generator is a DC constant level, the modulation frequency is constant.

The same operation as described above is possible even if the switching pattern is not intended to have a low noise effect, but is intended to have a low loss effect with respect to, for example, harmonics of an induction motor. For example, an embodiment in which the output phase of the output signal of the switching pattern generator is changed according to the relationship between the modulation frequency and the voltage phase of the fundamental wave. Further, the functions shown in FIG. 1 can be easily converted into software so as to be processed by a microprocessor.

[0022]

As described above, it is possible to achieve both low noise driving of the induction motor and prevention of induction failure.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram of a general electric vehicle driving control device.

FIG. 3 is a waveform diagram showing an example of a gate signal of the simplest switching element.

FIG. 4 is a vector diagram of a rotating magnetic flux of the induction motor when switching is performed by the gate signal of FIG. 3;

FIG. 5 is a vector diagram when switching is increased from FIG.

FIG. 6 is a vector diagram based on a low noise switching pattern.

FIG. 7 is a vector diagram based on a low harmonic switching pattern.

[Explanation of symbols]

1a to 1f Switching element 2 Filter device usually composed of a reactor and a capacitor 3 DC current collecting device peculiar to electric vehicle 4 Grounding device for feeding back current 5 Induction motor 6 Control device for issuing a conduction or cutoff command of switching element 7 Induction motor 8 Rotational speed detection signal 8 Gate signal for commanding conduction or interruption of switching element 61 PWM modulator 62 Voltage commander 63 Basic frequency commander 64 Low noise switching pattern generator 65 Low harmonic switching pattern generator 66 Switching pattern switching device 67 Frequency band detection device

Claims (1)

(57) [Claims] An inverter device for converting a direct current into an alternating current is constituted by a switching element having a function of conducting or interrupting at a desired time interval, and a control for PWM-modulating a fundamental frequency of an AC output of the inverter device and a voltage thereof. An electric vehicle control device having a control device, wherein a modulation frequency controlled by the control device periodically fluctuates at least twice or an integral multiple of the number of AC output phases. An electric vehicle control device, wherein when passing through a frequency band relating to equipment, a periodic fluctuation width of the modulation frequency is suppressed.