KR101499991B1 - method for sensing fail of a power cable of a motor - Google Patents

Abstract

The present invention relates to a method of detecting a failure of a power cable that transfers driving power to a motor of a hybrid / fuel cell vehicle without a voltage sensor.

A method of detecting a failure of a motor power cable using an output voltage command of an output of a synchronous coordinate system output controller of an inverter is characterized in that the rotation direction is opposite to the rotation direction of the synchronous coordinate system, A first step of defining a rotation coordinate system equal to a rotation speed of the synchronous coordinate system and converting an output voltage command of the synchronous coordinate system output controller into the rotation coordinate system, a second step of converting the result of the first step into a time axis, A third step of filtering the output of the second step with a low-pass filter to extract a DC component, and a fourth step of comparing the DC component with a reference value to determine a failure of the motor power table.

Hybrid, Automobile, Motor, Inverter, Current Control, Normal, Negative

Description

[0001] The present invention relates to a motor power cable fault detection method,

The present invention relates to a method of detecting a failure of a motor power cable, and more particularly, to a method of detecting a failure of a power cable for transmitting driving power to a motor of a hybrid / fuel cell vehicle without a voltage sensor.

In the case of a hybrid vehicle or a fuel cell vehicle, the driving power of the motor is transmitted from the inverter to the motor through a power cable. Therefore, when a problem occurs in the power cable, the motor is not driven smoothly, and ultimately, a stable operation of the vehicle can not be maintained. These power cable failures usually result from non-coupling or poor coupling.

Uncoupled or unconnected power cables cause imbalance in the motor with three phase equilibrium, and the imbalance of these motors causes unbalance of voltage or current applied to the motor.

FIG. 1 is a view showing an unbalanced state of a motor due to U-phase power cable unbonding. If the U phase power cable is not connected, the impedance of the U phase of the motor at the output of the inverter becomes infinite. Therefore, the motor that is viewed from the inverter appears to be unbalanced.

Fig. 2 is a view showing the unbalanced state of the motor due to the U-phase power cable coupling failure. If the U-phase power cable coupling failure occurs, the contact resistance increases and the U-phase impedance seen at the inverter output stage appears to be greater than the V-phase or W-phase impedance. This increased impedance causes imbalance in the motor that the inverter sees.

3 is a diagram showing a three-phase power vector diagram when motor unbalance occurs. If the motor maintains equilibrium, only normal components are observed. However, when unbalance occurs, a reverse phase rotating in the opposite direction to the normal is observed.

When the motor is driven by a constant voltage source (three-phase commercial power), the three-phase imbalance of the motor is observed in the motor current, and if the motor is driven by a constant current source (current controlled inverter) It is observed from the applied voltage, that is, the inverter output voltage.

Since the motor mounted in the hybrid / fuel cell vehicle is driven by the current control inverter, if the motor power cable is unbalanced or unbalanced due to poor coupling, a reverse phase voltage is generated at the inverter output voltage. Conventionally, a voltage sensor is attached to an inverter output voltage, and this reverse phase voltage is monitored to detect a power cable failure.

Figure 4 shows a conventional motor power cable fault detection method. Conventionally, three voltage sensors are used to detect the reverse phase of three phases of the inverter output voltage. Therefore, there is a problem of cost increase due to the mounting of the voltage sensor, and since the inverter output voltage is not a sinusoidal wave but a high-speed pulse width modulation (PWM) waveform, signal processing is further needed to extract a fundamental wave component. There is a problem that separate software logic must be implemented to monitor the error detection.

SUMMARY OF THE INVENTION The present invention has been made in order to meet the above-described needs of the prior art, and an object of the present invention is to provide a motor power cable fault detection method which detects a failure of motor power cable, .

According to another aspect of the present invention, there is provided a method of detecting a failure of a motor power cable using an output voltage command of a synchronous coordinate system output controller of an inverter, A first step of defining a rotation coordinate system which is opposite to the rotation direction and whose rotation speed is the same as the rotation speed of the synchronous coordinate system and which converts the output voltage command of the synchronous coordinate system output controller into the rotation coordinate system; A third step of filtering the output of the second step with a low pass filter to extract a DC component; a third step of comparing the DC component with a reference value to determine a failure of the motor power table; The method comprising the steps of:

As described above, according to the present invention, there is an advantage that the failure of the motor power cable can be detected at an early stage without any additional voltage sensor.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

Before explaining the embodiment of the present invention, the basic principle of the present invention will be described. The inverter controls the motor current to control the output torque of the motor. A typical current control inverter performs synchronous coordinate system vector control. In this current control method, the fundamental wave normal current vector is always observed as a DC component.

Even if the motor is unbalanced due to a fault in the power cable, the inverter tries to maintain the motor's 3-phase current in equilibrium, which results in an imbalance component in the inverter output voltage. The unbalanced component of the inverter output voltage is reflected in the voltage command of the inverter to generate a reverse phase component.

In the synchronous coordinate system, the normal component of the fundamental wave is observed by DC. On the other hand, in the synchronous coordinate system, the component of the antiphase component is observed as a component whose rotational direction is opposite to the rotational direction of the coordinate system and whose rotational speed is the same as the rotational speed of the coordinate system.

When the normal component and the opposite phase component on the synchronous coordinate system are shifted to the time axis, the normal component is DC and the reverse phase component is observed as a harmonic having a frequency component twice the synchronous frequency.

5 (a) is a graph showing the normal component and the opposite-phase component in the synchronous coordinate system, and FIG. 5 (b) is a graph showing the normal component and the opposite-phase component in the time axis.

The present invention proposes a method of detecting a failure of a motor power cable using a frequency difference between normal and reverse phases. The present invention is applied to a current controller of an inverter.

The current controller of the inverter outputs the voltage command to control the motor. If the motor maintains the equilibrium state, the output current is composed only of the normal component. However, if the motor is unbalanced, the reverse current component and the normal component occur in the output current. In the synchronous coordinate system, the steady-state component is DC and the reverse-phase component is observed as a harmonic having twice the frequency of the synchronous frequency component.

In this invention, the rotation frequency is the same as the rotation frequency of the synchronous coordinate system, and the rotation direction is defined as a rotation coordinate system that is opposite to the synchronous coordinate system, and the normal component and the reverse component on the synchronous coordinate system are converted into the rotation coordinate system. Then, when the normal / inverse phase component converted to the rotational coordinate system is transformed to the time axis, the inverse phase component is observed with DC, and the normal phase component is observed as harmonics having twice the synchronous frequency.

Therefore, it is possible to extract a DC component by a low-pass filter, and thereby it is possible to extract a component of a reverse phase component.

6 is a flowchart illustrating a method of detecting a power cable failure of a motor according to the present invention. When the current controller of the synchronous coordinate system is operated (S61), the voltage command generated by the current controller is transmitted to the motor to perform general motor control (S62).

On the other hand, the voltage command generated in the current controller is converted into a rotational coordinate system (S63), converted to a time axis (S64), and filtered by a low-pass filter (S65).

If the extracted opposite phase component is smaller than or equal to the reference value, it is determined that the power cable is normal (S67). If the extracted reverse phase component is smaller than or equal to the reference value, If the extracted antiphase component is larger than the reference value, it is determined that the power table is abnormal (S68).

1 is a view showing an unbalanced state of a motor due to a U-phase power cable non-coupling,

FIG. 2 is a view showing an unbalanced state of the motor in accordance with a U-phase power cable coupling failure;

3 shows a three-phase power vector diagram when motor unbalance occurs,

Figure 4 illustrates a conventional method of detecting a motor power cable failure,

5A is a graph showing a normal component and a reverse component in the synchronous coordinate system, FIG. 5B is a graph showing a normal component and a reverse component in the time axis,

6 is a flowchart illustrating a method of detecting a power cable failure of a motor according to the present invention.

Claims (3)

A method for detecting a failure of a motor power cable using an output voltage command of a synchronous coordinate system output controller of an inverter, A first step of defining a rotation coordinate system in which a rotation direction is opposite to a rotation direction of the synchronous coordinate system and a rotation speed is equal to a rotation speed of the synchronous coordinate system and an output voltage command of the synchronous coordinate system output controller is converted into the rotation coordinate system; A second step of converting the result of the first step into a time base; A third step of filtering the output of the second step with a low-pass filter to extract a DC component, And comparing the DC component with a reference value to determine a failure of the motor power table. delete The method of claim 1, wherein the fourth step determines that the power cable is normal if the DC component is less than or equal to the reference value, and determines that the power table is abnormal if the DC component is greater than the reference value Detection method.

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