JPS6053555B2 - Regenerative braking method and device for induction motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for regenerative braking of an induction motor driven by a variable voltage frequency inverter (hereinafter a VVVF inverter is simply referred to as an inverter) used in a vehicle, for example.

Recently, with the practical use of large-capacity inverters using thyristors, the slip frequency of induction motors can be controlled by controlling the output voltage and output frequency of the inverter.
Systems for driving vehicles are being put into practical use.

Based on the speed-torque characteristic of the induction motor, frequency control is performed by setting the slip frequency to positive during power running acceleration and negative slip frequency during regenerative braking deceleration. Based on the concept of a vehicle drive system using a conventional DC series-wound motor, the braking car speed characteristics of an induction motor for driving a vehicle are as shown in FIG. That is, in FIG. 1, the region <1> is a constant current control region that controls the output voltage as well as changes in speed so that the output current of the inverter remains constant. In the region <■>, the inverter output voltage V is maximum,
It remains constant with respect to speed changes, and voltage control is not possible. In this case, it is a constant voltage (induction motor applied voltage) and a constant frequency control region. The full frequency control range when driving an induction motor for a vehicle is as small as a few percent, and in this case, the approximate equation is:

Here, T: Braking torque, V: IM voltage (inverter output voltage), f1: Inverter frequency, Fs: Suberi frequency, I: ■ Current (inverter output current), KT, K! ;
Each represents a constant. According to equation (3), if the induction motor current 1 is controlled to be constant and the slip frequency Fs is constant, constant braking torque operation becomes possible. Also, (1
), if the voltage applied to the induction motor is controlled to be constant and the smoothing frequency Fs is constant, the torque is inversely proportional to the frequency f1 of the inverter, that is, the square of the speed. In order to realize the control method described above, there is a conventional system constructed as shown in FIG.

That is, the inverter 1 drives the induction motor 2. The comparator 4 compares the current reference 1p and the induction motor current detected by the current transformer 3, and the deviation signal ΔI
is input to the phase shifter 5 and determines the magnitude of the output voltage of the inverter 1. Also, use the current reference 1p. The signal is input to a Veri frequency pattern generator 6, and its output is passed through a polarity inverter 7 to determine the Veri frequency Fs. The rotational speed of the induction motor 2 is detected by a pulse generator 8, and the obtained rotational frequency F, and the Veri frequency Fs are added together by an adder 9.
As F, -Fs, the input of the frequency control circuit 10 that controls the frequency of the inverter 1, that is, the inverter frequency f
Decide on 1. The voltage of the VVVF inverter as above,
Frequency control enables regenerative braking of induction motors. By the way, in the region <.■> in FIG. 1, that is, during high-speed regeneration, the braking torque T decreases in inverse proportion to the square of the speed, so the regeneration efficiency decreases. Furthermore, in order to compensate for this, it is necessary to increase the power of the vehicle's air brake, for example, which increases wear on the brake shoe. This invention aims at expanding the constant torque regeneration area during regenerative braking in a system controlled by an induction motor ■■■F inverter.
The purpose of the present invention is to provide a regenerative braking method and device for an induction motor that improves regenerative efficiency.

The present invention will be explained below with reference to the drawings, but first the regenerative braking device of the present invention will be explained with reference to FIG. 3. The basic configuration of the regenerative braking device/device for this generation is similar to that shown in FIG. 2 described above, and differs only in the following points. That is, the current reference h and the inverter frequency f1 are input to the current correction pattern generator 11 to find the product of both, and this is corrected via the maximum current limiter 12 and becomes the current reference 1P.
Get 1. The current reference 1p and IPl are compared by the high priority circuit 13, and the larger one of them becomes the final current reference 1P2. Further, this final current reference 1P2 and the inverter output current (induction motor current) detected by the current transformer 3 are compared by a comparator 4, and this deviation signal ΔI is sent to a frequency correction pattern generator 14. Input the frequency ΔFs to be corrected. Further, the maximum frequency Fs obtained by inputting the current reference 1p to the maximum frequency pulse generator 6 and the maximum frequency ΔFs to be corrected are added by an adder 15, and the maximum frequency limiter 16 After passing through the polarity inverter 7, the final full frequency FSL
get. The operation of the device of the invention constructed as described above will be described below.

The current reference 1p and the inverter frequency f1 are input to the current correction pattern generator 11, the product of both is determined, and this value is corrected via the current maximum value limiter 12 to obtain the current reference 1P1. As a result, constant torque operation is realized in a region where the output voltage V is constant at the maximum, that is, where voltage control is not possible. To explain this point here, from the above-mentioned equations (1) and (2), the following equation approximately holds true for the torque T.

As a result, the current I for making the torque T constant becomes as shown in the following equation.

However, K: constant The current reference 1p of equation (5) corresponds to the output current 1 in the constant torque region I> in FIG.

This makes it possible to achieve constant torque operation in areas where voltage control is not possible. On the other hand, the above-mentioned corrected current reference 1,1 is
FIG. 44 shows the inverter frequency f1.

Ip(Max) is the maximum limiter value. Furthermore, as the corrected current reference and the predetermined current reference, the higher priority circuit 13 selects the larger value of Ipl or Ip, so the final current reference IP2 is determined as shown in FIG. Become. Then, the output current of the inverter 1 detected by the current reference P2 and the current transformer 3 is compared in the comparator 4, and this deviation signal ΔI is input to the frequency correction pattern generator 14, and the output current as shown in FIG. The corrected frequency ΔFs is obtained, and the deviation Δ11 is the point at which the output voltage of the inverter 1 becomes maximum. In addition, a predetermined current reference is input to the frequency pattern generator 6, and the frequency Fs determined here is obtained.
and the full frequency ΔFs to be corrected are added in an adder 15, and the final full frequency FSl is obtained via the maximum full frequency value 16 and the polarity inverter 7, which is the seventh full frequency FSl.
As shown in the figure, the signal is applied to the frequency control circuit 10. F
s(Max) is the maximum limiter value. This results in
The region in which the output voltage of inverter 1 is constant at maximum and voltage control is not possible.
Induction motor) follows the current reference IP2 so that the final frequency FSl is . Since it is corrected, the output current becomes 0 and the inverter frequency f1, and constant torque operation becomes possible from equation (4). Therefore, the control range can be expanded until the constant torque region during regenerative braking reaches the maximum limiter value F, (Max). Figure 8 is VV
It shows the speed-torque characteristic during regenerative braking of the induction motor by VF inverter 1, where T is the braking torque, and ■
is the output voltage and I is the output current.

In FIG. 8, the area marked (*) is a constant torque/operation area based on conventional constant current and constant frequency control. ku■〉
Is it possible to use the current reference corrected by this invention in the region of ? This is a constant torque operating region where full frequency control is performed. In the area of ku■〉, the smooth frequency is the maximum limiter value,
At a constant voltage (IM applied voltage), torque is in a region inversely proportional to the square of speed. It goes without saying that in a region where the rotational speed of the induction motor decreases and voltage control is possible, constant current and constant frequency control is performed as before.

In the above-mentioned embodiments, the induction motor is used for driving a vehicle, but this is not limited to it, and it can be used for an elevator or anything else. According to this invention, in a device that performs regenerative braking of an induction motor using a VF inverter that can control the output voltage and output frequency, constant torque braking is performed even when the output voltage of the inverter is at its maximum and voltage control is not possible. This makes it possible to increase regeneration efficiency and suppress supplementary air braking force in high-speed ranges, making it possible to provide a regenerative braking method and device for an induction motor that reduces wear on brake shoes.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of the braking car speed characteristics of a typical induction motor, Fig. 2 is a control block diagram showing an example of a conventional basic regenerative braking device, and Fig. 3 is a diagram showing an example of the present invention. A control block diagram showing an embodiment of a regenerative braking device according to 1, 1, 4, 5, 6 and 7 shows a corrected current reference and current control to explain the operation of the same embodiment. The final current reference, complete frequency correction pattern and
FIG. 8 is a diagram showing the final full frequency for performing full frequency control, and FIG. 8 is a diagram showing the braking car speed characteristic of the induction motor of the same embodiment. 1... Variable voltage variable frequency inverter (VVVF inverter), 2... Induction motor, 3... Current transformer, 4...
... Comparator, 5... Phase shifter, 6... Full frequency pattern generator, 7... Polarity inverter, 8... Pulse generator, 9... Adder, 10...・Frequency control circuit, 1
DESCRIPTION OF SYMBOLS 1... Current correction pattern generator, 12... Maximum current value limiter, 13... High priority circuit, 14... Full frequency correction pattern generator, 15... Adder, 16
...Maximum frequency limiter.

Claims (1)

[Claims] 1. When performing regenerative braking of an induction motor using an inverter that can control the output voltage and output frequency, in a speed range where the output voltage of the inverter is below the maximum value, a certain given current command and inverter output The output voltage of the inverter is controlled by the deviation value from the current, and in the speed range exceeding the maximum output voltage of the inverter, the given current command is corrected in proportion to the speed, and the corrected current command and the above Correcting the slip frequency with a deviation value from the output current of the inverter, and changing the slip frequency so that the output current of the inverter follows the corrected current command,
A regenerative braking method for an induction motor, characterized by compensating for a decrease in braking force. 2. A variable voltage variable frequency inverter connected to the winding of the induction motor, a current correction pattern generator that receives the inverter's current reference and inverter frequency and calculates a corrected current reference from the product of both, and this current correction pattern. The corrected current reference of the generator is connected to a high-order priority circuit which receives the current reference through a current maximum value limiter and outputs only the larger of the current references to obtain the final current reference of the inverter; A phase shifter receives a deviation signal between the final current reference of the priority circuit and the output current of the inverter and determines the phase of the inverter, and a phase shifter receives the deviation signal of the current and determines the slip frequency to be corrected accordingly. a slip frequency correction pattern generator to obtain the current reference; a slip frequency pattern generator to which the current reference is input and determine a slip frequency according to the current reference; and the outputs of this slip frequency pattern generator and the slip frequency correction pattern generator are added. Regeneration of an induction motor, comprising an adder and a frequency control circuit that controls the frequency of the inverter with a sum signal of the output of the adder obtained through the maximum slip frequency limit and the rotational frequency of the induction motor. Braking device.