JPH0520962B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention provides braking control for electric vehicles driven by controlling the speed of an induction motor (hereinafter referred to as IM) with a variable voltage/variable frequency inverter (hereinafter simply referred to as inverter). Regarding equipment.

When controlling IM with an inverter to drive an electric vehicle, the inverter's output frequency, or IM
The rotational field frequency of IM is f _INV , the rotational frequency of IM is f _R ,
If the slip frequency is f _S , then during power running f _INV = f _R + f _S ...(1) During regeneration, f _INV = f _R - f _S ...(2) At the same time, constant slip frequency control is performed and the inverter output Magnitude of voltage V and output frequency
The output power V is controlled so that the ratio V/f _INV to f _INV is constant, and the output torque T of IM is constant.

Figure 1 shows the equivalent circuit of the IM viewed from the primary side.
In Figure 1, V〓 is the inverter output voltage or IM input voltage, I〓 _M is the IM input current, I〓 _R is the IM rotor current, I〓 _S is the exciting current, r ₁ is the stator winding resistance, x ₁ is stator winding reactance, r ₂ is rotor winding reactance, x ₂ is excitation reactance, S is slip and f _S
and f _INV can be expressed as f _S /f _INV .

The relationship between the output torque T of the IM and the voltage, current, and frequency of each part can be expressed by the following equations (3) to (6) within a small range of the slip frequency _fS .

T=K ₁・｜V｜/f _INV・｜I〓 _R …(3) I〓 _M ＝I〓 _R +I〓 _S …(4) ｜I〓 _S ｜≒K ₂ ｜V｜/f _INV …( 5) Ф〓＝K ₃ I〓 _S …(6) However, Ф〓: rotating field flux, K ₁ to _{K 3} : constant, |
V〓|=V.

Further, a vector diagram of voltages and currents at each part in FIG. 1 is shown in FIG. 2. As can be seen from FIG. 1, equation (5) can be derived because the stator winding resistance r ₁ is negligibly small. When V/f _INV is held constant, I〓 _S becomes a constant current whose magnitude is shown by equation (5) and lags V〓 by 90°. Therefore, from equation (4), |I〓 _R | = |I〓 _M −I〓 _S | …(7) Therefore, if |I〓 _M | is controlled to be constant, |I〓 _R | becomes constant. , V/f _INV are constant, so the output torque T can be constant from equation (3). To summarize the above,
V/f _INV is constant, and f _S is adjusted so that I〓 _M | is constant.
A constant torque control method that corrects this is generally used as an inverter control method for electric vehicles.

FIG. 3 shows an example of the circuit configuration of the inverter and IM. In the figure, 1 is a DC power supply, 2 is a disconnector,
3 is a filter reactor, 4 is a filter capacitor, 5 is an inverter, 6 is an IM, 7 is a rotational frequency sensor for detecting the rotational frequency f _R of this IM6, 8 is for detecting the input current I〓 _M of IM
ACCT, 9 determines the inverter output voltage V〓 and the output frequency f _INV based on f _R and I〓 _M so that the output torque T becomes the command value T ^* , and controls the controllable rectifying element such as the thyristor of the inverter 5 This is an inverter control circuit that provides the ignition signal.

An example of this inverter control circuit 9 is shown in detail in FIG.

In the figure, 10 is a current pattern circuit that determines the current pattern I _P from the torque command value T ^* , 11 is a slip frequency pattern circuit that determines the slip frequency pattern f _SP from the current pattern I _P , and 12 is the current pattern
A comparison amplification circuit compares and amplifies I _P and the magnitude of the IM input current I _M |I〓 _M |, and 13 adds the slip frequency pattern f _SP and the output △f _S of the comparison amplification circuit 12. 14 is an adder/subtractor that adds and subtracts the IM rotation frequency f _R and the slip frequency f _S for power running and regeneration to determine the _inverter output frequency f _INV ; 15 is an adder/subtractor that determines the V/f constant characteristic. ¹⁶ is _{f INV}
This is a modulation circuit that generates a firing signal for the controllable rectifying element of the inverter 5 from V ^{* and V*} .

Now, in regenerative braking, the power supply voltage of the inverter 5 may become an overvoltage due to reasons such as the absence of a regenerative load. An overvoltage may affect the inverter 5 and IM6 and cause dielectric breakdown. Therefore, normally, the inverter 5 must be stopped by opening the breaker 2.

This invention has been made for the case of IM single drive shown in Fig. 3 and the case of IM parallel drive (not shown), and is a braking system for electric vehicles that promptly lowers the power supply voltage when the inverter power supply voltage becomes overvoltage. The purpose is to provide a control device.

FIG. 5 shows an inverter control circuit 9A which is an embodiment of the present invention.

In the figure, 17 is a deviation calculation circuit between the power supply voltage and the overvoltage set value, and when the power supply voltage _VE exceeds the above set value, the current pattern circuit 10' calculates the deviation from the current pattern I _P1 obtained from the torque command value T ^* . The output I _V of 17 is subtracted by a subtracter 18 to reduce the current pattern I _P =I _P1 -I _V. As a result, the slip frequency f _S decreases, the rotor current I _R decreases from the following equation (8), and the IM input current |I _M 〓| can decrease from the equation (4).

｜I〓 _R ｜=K ₄・｜Ф〓｜・f _S …(8) However, K ₄ is a constant.

By reducing the IM input current | _I〓M |, the power supply voltage V _E can be lowered, and the inverter 5 and IM6 can be protected. In other words,
Even if an overvoltage occurs, the inverter 5 can be operated without opening the shield breaker 2 shown in FIG. 3, and highly efficient regeneration characteristics can be obtained.

The target value for reducing this current pattern, that is, the target value for the amount of decrease in the current pattern I _p is ultimately
Up to the excitation current of IM6. this is,
This is to prevent the torque T from becoming negative if the current pattern is reduced by more than the excitation current, and no regenerative torque is generated, thereby preventing the regenerative brake from working and reducing the regenerative efficiency.

Furthermore, when a plurality of IMs are connected in parallel, the narrowing target value may be set to a value _IS1 corresponding to the sum of the excitation currents of the IMs connected in parallel.

FIG. 6 shows a current pattern narrowing method. When the power supply voltage V _E exceeds the set value at time t ₁ , the deviation calculation circuit 17 operates and begins to reduce the current pattern I _P to the final reduction value I _S or I _S1 . At time _t1 , the power supply voltage V _E falls below the set value, returning the current pattern to the original control target.

As described above, according to the present invention, it is possible to fully utilize the regenerative braking of IM, and it is possible to obtain highly efficient regenerative characteristics.

[Brief explanation of the drawing]

Figure 1 is an equivalent circuit diagram of IM, Figure 2 is a voltage/current vector diagram of each part in Figure 1, Figure 3 is a diagram showing an example of the circuit configuration of an inverter and IM, and Figure 4 is a diagram of a conventional inverter. FIG. 5 is a block diagram showing a control circuit, FIG. 5 is a block diagram showing an inverter control circuit embodying the present invention, and FIG. 6 is a current pattern squeeze diagram in the present invention. 5 is an inverter, 6 is an induction motor, 9A is an inverter control circuit, 10' is a current pattern circuit, 1
1 is a slip frequency pattern circuit, 17 is a deviation calculation circuit, and 18 is a subtracter. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A braking control device for an electric vehicle having an inverter control circuit 9A, wherein the electric vehicle performs power running and regenerative braking by an induction motor 6 and an inverter 5 controlled by the inverter control circuit 9A. The inverter control circuit 9A combines voltage/frequency inverter control and slip frequency control. It outputs a control signal to the inverter 5 for controlling the torque of the induction motor 6, and includes a current pattern circuit 10', a deviation calculation circuit 17, and a subtracter 18.
and a slip frequency pattern circuit 11, the current pattern circuit 10' receives a torque command (T) and generates a current pattern that is a control command value, and the deviation calculation circuit 17 generates a current pattern that is a control command value. The detected value of the power supply side voltage of inverter 5 (VE)
is input, and when VE exceeds this set value during braking, the deviation is K ₂ / (1 + T _1S ) and output. The slip frequency pattern circuit 11 generates an output (IP) by subtracting the output of the arithmetic circuit 17.
A braking control device for electric vehicles that inputs the output of and generates a slip frequency pattern that is a control command value.