JPH05184182A - Inverter controller - Google Patents

Abstract

PURPOSE:To perform high-efficiency operation at low load by reducing the carrier frequency, according to car velocity and load, and calm the noise at high load by raising carrier frequency, in the controller of an inverter for an electric rolling stock. CONSTITUTION:An induction motor 15 is driven by performing voltage type PWM control with an inverter 12 through an input filter 19 from a battery 18. A microcomputer 1 operates a speed command value by the revolution N of a motor, and further operates a vector, and outputs three-phase current command value, and ACRs 4, 5, and 6 outputs sine wave voltage command values by the deviation from the actual current value of the motor 15. So, PWMs 9, 10, and 11 generate control signals, comparing the output value of a triangular wave oscillator OSC3 with a sine wave voltage command value, and turns on or turns off IGBT through a gate driver 20. What is more, a logic circuit 2 judges the difference of load condition by a motor current 10 and motor revolution N, and changes the cycle of OSC3, and performs optimum operation from both aspects of efficiency and noise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter for an electric vehicle, which has a function capable of efficiently traveling especially at light load,
Further, the present invention relates to an inverter control device capable of reducing noise even under high load.

[0002]

2. Description of the Related Art In an electric vehicle driven by an inverter, the merits of the original brazing of an AC motor have been utilized by the development of power electronics, and there is a tendency to shift from DC to AC.

As the control of the inverter, vector control is generally used, and the excitation current is generally constant.
For general industrial use, these considerations were sufficient because torque characteristics are more important than efficiency.

In the case of an electric vehicle, the acceleration characteristic is important, but the efficiency in a steady operation state is also important. As a solution to both of these, as shown in Japanese Examined Patent Publication No. 2-58875, there is one relating to good fan characteristics of both efficiency and acceleration by adjusting voltage depending on load conditions.

However, the loss of the power element itself is about 3 to 6 times different between the DC chopper and the inverter.
There was a problem that the power element loss of the inverter was large, and further study was necessary to improve the actual efficiency.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly efficient inverter that lowers the carrier frequency of the inverter and reduces switching loss according to the operating conditions.

Another object of the present invention is to provide an inverter which uses current information as a load condition and performs a high efficiency operation at a light load.

Another object is that the load is 10 KH when the load is high.
An object of the present invention is to provide an inverter characterized in that noise is reduced by raising the carrier frequency to z or higher.

[0009]

Means for Solving the Problems As a main circuit element constituting an inverter, a high speed switching element such as an IGBT or FET capable of driving an electric car is used, and a switching frequency is raised to 10 KHz or higher to reduce noise. We decided to reduce the carrier frequency, reduce the switching loss, and reduce the loss of the AC machine and the inverter according to the vehicle speed and the load so that the efficiency is improved in the light load traveling that discusses one charging mileage.

A voltage-responsive triangular wave oscillator is used as the carrier frequency varying means, and a microcomputer is used as the input condition determining circuit.

[0011]

The carrier frequency varying means changes the switching frequency of the PWM inverter to change the IGBT frequency.
It works to reduce switching loss and improve efficiency. Also, depending on the load condition and the vehicle speed determination means, it operates at high efficiency at light load, the switching frequency is within the flexible frequency, and the sound is heard but the current also decreases, so that it does not increase noise, while at the time of high load, Switching frequency is over 10KHz, current waveform is 20K
It has the function of reducing noise to Hz.

As an alternative, if the means for varying the carrier frequency is not a comparison between a triangular wave and a sine wave, but a PWM is directly created by a microcomputer at an unequal pitch, the same effect can be obtained.

[0013]

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

First, the main circuit is composed of the main battery 18
Further, the input motor 19 is passed through, the voltage-type PWM control is performed by the inverter 12, and the induction motor 15 is rotated. The induction motor 15 drives the traveling load 8 through the gear 7. It usually runs on the road with tires.

Next, for the control circuit, in the microcomputer 1, a speed command is calculated by the accelerator, brake, and motor rotation speed N, and further vector calculation is performed, and a three-phase current command i is calculated.
_u *, i _v *, and outputs the i _w *. Since a current corresponding to this is flown, the ACR 4, 5, 6 may differ depending on the deviation from the actual current of the motor.
Through the sine wave voltage commands v _u *, v _v *, v _w *.

In the voltage type PWM inverter, the voltage is chopped and applied so that the average effective voltage becomes the same as a sine wave. The chopping at this time is the output of the OSC, which is a triangular wave oscillator, and the sine wave voltage. Some v _u *, v _v *,
By comparing with v _w *, a signal is generated from PWM 9, 10, and 11, and the IGBT is turned on and off through the gate driver 20.

At this time, the chopping frequency is called the carrier frequency, and is 2 in the cycle of the basic frequency.
It is usually done so that the time is 0 or more. The carrier frequency of 10 KHz to 20 KHz is quiet with respect to sound, but it is a negative factor in terms of efficiency. This time, the logic circuit 2 that optimally selects the cycle of the OSC 3 according to the load condition and the rotation speed condition is provided.

FIG. 2 is a diagram showing load points of an electric vehicle.

At the time of acceleration, the vehicle speed v ₁ passes through the maximum torque T _3, and at the maximum speed, the vehicle speed v ₂ and the torque are T ₂ . Further, when traveling on a flat road with a light load, the vehicle is operated at v ₁ and T ₁ .

The logic circuit 2 in FIG. 1 discriminates such a difference in load points from the motor current I and the motor speed N, and changes the cycle of the OSC as shown in FIG.
We try to operate optimally from both sides of noise.

In FIG. 3, comparing the points (T ₁ v ₁ ) and (T ₂ , v ₂ ) in terms of torque and rotation speed, the sinusoidal voltage signal v _u
The higher the frequency, the higher the frequency. On the other hand, the carrier frequency O
As for the SC output, under the condition that the ripple current is small and the waveform is close to a sine wave in the vector controllable range, (T ₁ v ₁ ) can lower the OSC frequency.
As shown in, the switching loss can be reduced and the efficiency can be improved.

In addition, comparing the point (T ₁ v ₁ ) and the point (T ₃ , v ₁ ) in FIG. 3, as shown in FIG. At the load point of (T ₃ , v ₁ ), the carrier was set to about 10 KHz.

FIG. 6 is a block diagram showing the vector control in FIG.

With respect to the accelerator opening and the brake stroke, the acceleration command 21 and the deceleration command 22 give an acceleration command and a deceleration command, respectively, and then a speed command is calculated. A speed control calculation is performed based on a deviation between the speed command and the motor rotation speed N to calculate a torque command τ *. Further, the weak-excitation calculating unit 25 calculates the magnetic flux command φ * in order to control the magnitude of the magnetic flux according to the motor speed. While calculating the excitation current command I _M based on the magnetic flux command phi *, induction motor in consideration of the circuit time constant of, performs a first-order delay calculation by the excitation current calculation unit 27 calculates the excitation current command I _M There is. Since the torque τ of the induction motor is proportional to the value obtained by multiplying the exciting current and the torque current orthogonal thereto, the torque current calculating unit 2
In 6, the torque current command I _t is obtained by dividing the torque command τ by the exciting current command I _M. The vector sum of the orthogonal torque current command I _t and the exciting current I _M is 1
Since it becomes the next current command, I ₁ * is the current command calculation unit 28,
The torque angle command ψ * is calculated by the torque angle calculation unit 29.

Further, the slip velocity calculation unit 31 calculates the slip velocity command ω _s of the induction motor from the torque command τ * and the magnetic flux command φ *. Since the slip velocity command ω _s ′ is proportional to the torque command τ * and inversely proportional to the square of the magnetic flux command φ *, the slip velocity command calculator 31 performs this calculation. The rotation speed command ω ₁ * of the exciting current is obtained by adding the sliding speed ω _s ′ to the motor speed ω, and the integrator 32 integrates the rotation speed to obtain the phase of the exciting current command I _M , that is, , The excitation current phase command θ ₀ is obtained. As a result, the phase command θ * is obtained from ψ * + θ ₀ . The current command I ₁ * and the phase command θ * obtained by the above method are the primary current command vectors when viewed from the stationary coordinate system. These were shifted by 120 ° 3-phase current command i _u *, i _v *, to convert the i _w * is 3-phase conversion circuit 3
It is 0.

[0026]

The effect of the present invention is that it is possible to improve the light load efficiency during one-charge running while reducing the noise peculiar to an electric vehicle during acceleration.

[Brief description of drawings]

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

FIG. 2 is a diagram showing load points of an electric vehicle.

FIG. 3 is a diagram showing an optimal operating state in terms of efficiency and noise by changing the OSC cycle.

FIG. 4 is a diagram showing that the carrier is set to about 10 KHz at the load point of (T ₃ , v ₁ ) in order to make it about the same as other driving ranges in terms of noise.

FIG. 5 is a diagram showing that switching loss is reduced.

6 is a block diagram showing the vector control of FIG. 1. FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Microcomputer, 2 ... Logic circuit, 3 ... Variable triangular wave oscillator, 12 ... Inverter main circuit, 15 ... AC machine, 16 ... Rotation sensor (encoder).

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Ryozo Masaki 4026, Kuji-machi, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi Ltd. Inside the Narashino factory of Hitachi, Ltd.

Claims (4)

[Claims] 1. A voltage-type PWM inverter for an electric vehicle, comprising a first circuit for calculating a speed or torque command of an AC machine in accordance with an accelerator opening, and in accordance with an output of the first circuit, A second circuit for controlling the speed or torque of the electric motor, a comparator for comparing the sine wave output of the second circuit and the output of the triangular wave generating circuit, and an inverter main circuit driven by the output of the comparator are provided. An inverter control device, comprising: a carrier frequency of the triangular wave generation circuit, which is changed according to a vehicle speed or a rotation speed of an AC machine and a load condition. 2. The inverter controller according to claim 1, wherein a motor current value is used as a method for detecting a load condition. 3. The inverter control device according to claim 1, wherein the carrier frequency of the triangular wave generation circuit is increased as the speed or load increases. 4. The carrier frequency of the triangular wave generating circuit according to claim 1, wherein a minimum value and a maximum value are set, and a load,
An inverter control device characterized in that it changes according to the vehicle speed.