JPH0132721B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a control device for an electric vehicle, and particularly to a control device for an electric vehicle suitable for improving adhesive performance. Generally, in electric vehicles, constant torque control is performed to maintain a constant acceleration in order to improve riding comfort. As a general method of constant torque control using an induction motor, in electric vehicles, the slip frequency s
and the motor current I is controlled to be constant, and as a result, the ratio V ₁ / _FINV between the fundamental wave voltage V ₁ of the inverter output and the inverter frequency _INV is kept constant. That is, a control method as shown in FIG. 1 is used. In the figure, 1 is a DC overhead wire, and 2 is a pantograph, which in the case of AC feeding corresponds to a DC coupling circuit after rectification. 3 and 4 are a filter reactor and a filter capacitor, respectively, which have the purpose of smoothing. 5 is a variable voltage input DC voltage.
It is a high frequency pulse width modulated variable voltage variable frequency inverter that converts into an alternating voltage of variable frequency. The output voltage of the inverter 5 is supplied to induction motors 6a and 6b. 7 is a pulse generator provided to detect the rotation frequency _M of the induction motor 6a.
Reference numeral 8 denotes an adder/subtracter that adds and subtracts the rotational frequency _M and a constant slip frequency _S to calculate the output frequency _INV of the inverter 5. Constant slip frequency control is performed as _INV = _M + _S during power running and _INV = _M - _S during regeneration. 9 is a current detector that detects the motor current I; 10 is a comparison amplifier that compares the detected motor current I and a constant current reference value I _p and amplifies the difference; This is the modulation degree PMF that indicates the degree of modulation of the output variable voltage. Reference numeral 11 denotes a phase shifter which determines the operation of the inverter 5 by inputting the output frequency _INV of the inverter, which is the output of the adder/subtractor 8, and the modulation degree, which is the output of the comparator amplifier 10. Figure 2 shows the phase shifter 11.
An example of the detailed functions of is shown below. In FIG. 2, 21 is a carrier wave and 22 is a modulated wave. Here, the ratio of the peak value of the modulated wave 22 to the peak value of the carrier wave 21 is referred to as modulation degree PMF. That is, if the peak value of the carrier wave 21 is 1, the peak value of the modulated wave 22 is as shown in FIG.
Becomes a PMF. Also, the output frequency _INV of adder/subtractor 8
is the frequency of the modulated wave 22. In FIG. 2, reference numeral 23 is a U-phase modulation signal that compares the carrier wave 21 and the modulated wave 22, and is set to "0" when the carrier wave 21 is larger, and set to "1" when the carrier wave 21 is larger. 24 is a V-phase modulation signal that is delayed by 1/3 period from the U-phase modulation signal 23 when one period of the modulation wave 22 is assumed. Although not shown in FIG. 2, the V phase modulation signal 24
A W-phase modulation signal 25 is generated with a delay of 1/3 period. The three-phase modulated signals 23, 24, and 25 are used as controllable element firing signals in the detailed diagram of the inverter 5 shown in FIG. In FIG. 3, 27 and 28 are U-phase controllable elements such as thyristors, 29 and 30 are V-phase controllable elements, and 31 and 32 are W-phase controllable elements. When the U phase modulation signal 23 is “1”, the upper U
Let "0" be the firing signal of the phase controllable element 27, and let "0" be the firing signal of the lower U-phase controllable element 28. Other V,
The same applies to the W phase. At this time, a pulse-like alternating voltage as shown in FIG. 26 is generated between the UV phase output lines in FIG. 3. Although not shown in the diagram, 2
An alternating voltage with a phase shift of 6 and 1/3 cycles is generated. FIG. 4 shows a case where the modulation depth PMF is larger than that in FIG. 2. As can be seen from Figure 4, the degree of modulation
When the PMF is increased, the pulse width of the alternating voltage between the output lines of each phase becomes thicker, and the voltage becomes larger.
As described above, by changing the modulation degree PMF and adjusting the magnitude of the output voltage, constant current control can be performed and a constant slip frequency can be achieved. In such a control method, the induction motor 6b
When the induction motor 6b starts idling, the output frequency of the inverter 5 does not increase, so the slip frequency of the idling induction motor 6b decreases, and as a result, the current decreases. In this case, since constant current control is performed, the output voltage increases. Therefore, the current in the other induction motor 6a that is not idling becomes large, sometimes inducing idling. SUMMARY OF THE INVENTION An object of the present invention is to provide a control device for an electric vehicle that prevents a healthy induction motor from inducing idling due to the influence of an idling induction motor. An embodiment of the present invention will be described below with reference to the drawings. FIG. 5 shows an embodiment of the invention. This embodiment differs from the conventional one shown in FIG. 1 in that a limiter circuit 12 is provided. The limiter circuit 12 has a function of not directly converting the output of the comparator amplifier 10 into the modulation degree PMF, but rather limiting it so that it does not exceed the maximum value of the modulation degree corresponding to the inverter frequency. An example of the maximum modulation depth value corresponding to the inverter frequency is shown in FIG. In FIG. 6, ₀ is the rated frequency of the induction motors 6a and 6b, and the dashed line is a frequency proportional straight line 31 that becomes "1" when the inverter frequency _INV is ₀ , and the control margin △ The straight line to which the PMF is added and whose maximum value is saturated at "1" is defined as the maximum value of the modulation degree corresponding to the inverter frequency. Therefore, according to this embodiment, the induction motor 6
Even if idling occurs in motor b and the current in the induction motor 6b decreases, the value of the modulation degree PMF does not increase beyond the value corresponding to the inverter frequency, so the inverter output voltage does not increase and the torque of the induction motor 6a decreases. It does not increase and cause idling. Another embodiment of the invention is shown in FIG. This embodiment differs from the embodiment illustrated in FIG.
The point is that this is applicable to the case where the inverter input voltage is not constant. In the figure, 13 is a voltage detector that detects the inverter input voltage. 14 is a divider that divides the output _INV of the adder/subtractor 8 by the output E of the voltage detector 13. In other words, the frequency proportional line when the rated input voltage E ₀ is 31 in Figure 8, and the frequency at the point when the input voltage E ₁ is lower than the rated value _{is 1.}
shall be. Also, since the aforementioned V ₁ / _INV is constant at the modulation depth of "1", (however,

[Formula] is the proportional coefficient at maximum output). Therefore, the slope _1/1 of the frequency proportional line 32 is _1/1 = E ₀ / ₀ × 1/E ₁ . Furthermore, a straight line 32' representing the maximum value of modulation degree corresponding to the frequency proportional straight line 32 can be expressed by an equation. PMFmax=k ₀ × _INV /E ₁ +△PMF... (However, k ₀ = E ₀ / ₀ : Constant) Similarly, if the input voltage E ₂ is higher than the rating, _{set 1} to
₂ with E ₁ replaced by E ₂ . That is,
The maximum modulation degree PMFmax for the input voltage E is determined by performing the calculation expressed by the formula. PMFmax= _k0 × _INV /E+ΔPMF (where _k0 = _E0 / ₀ : constant) The divider 14 performs the above division and multiplies by the constant _k0 . Therefore, according to this embodiment,
Even when the input voltage fluctuates, the relationship between the modulation depth and output voltage can be corrected, and the inverter frequency _INV
The increase in the modulation degree can be limited by the optimum modulation degree maximum value PMFmax corresponding to the induction motor 6b.
Even if the current decreases due to idling, the inverter output voltage will not rise above the value corresponding to the inverter frequency _INV . As explained above, according to the present invention, since the torque of the non-slip induction motor is not increased, it is possible to prevent the induction of slipping.

[Brief explanation of drawings]

Fig. 1 is a circuit connection block diagram showing a conventional control device, Figs. 2 and 4 are explanatory diagrams showing a modulation method, Fig. 3 is a connection diagram showing an inverter configuration, and Fig. 5 is an example of the present invention. A circuit connection block diagram showing an embodiment, FIG. 6 is a characteristic diagram for explaining the function of the limiter circuit in FIG. 5, FIG. 7 is a circuit connection block diagram showing another embodiment of the present invention, and FIG. This figure is a characteristic diagram for explaining the function of the divider in FIG. 7. Note that the same reference numerals in the figures indicate the same or corresponding parts. 5: Inverter, 6a, 6b: Induction motor, 7: Pulse generator, 8: Adder/subtractor, 9: Current detector, 10: Comparison amplifier, 11: Phase shifter, 1
2: limiter circuit, 13: voltage detector, 14: divider.

Claims (1)

[Claims] 1. In an electric vehicle equipped with a variable voltage variable frequency inverter connected to a power supply with a rated voltage E and a plurality of induction motors driven by the torque to be generated by the output voltage of this inverter, the output current of the inverter is set to a command value. a first means for controlling the degree of modulation, which is a modulation rate of the output voltage of the inverter, so that the slip frequency determined from the torque to be generated and the rotation frequency of the induction motor during power running of the electric vehicle; a second signal that controls the output frequency of the inverter using a signal obtained by subtracting the slip frequency from the rotational frequency during regeneration;
a third means for suppressing the degree of modulation so that it does not exceed a value of a frequency proportional line such that the degree of modulation is 1 when the output frequency of the inverter is , and a fourth means for detecting a power supply voltage. When the power supply voltage changes from the rated voltage E, the inverter output frequency is divided by the changed power supply voltage, and the modulation degree is suppressed from becoming larger than the value obtained by multiplying E/f. Characteristic electric vehicle control device.