JP7517168B2 - Fault detection device and fault detection method for three-phase current detection unit - Google Patents

Description

The present invention relates to fault detection in a three-phase current detection unit of a three-phase AC motor driven by an inverter, for example, an in-vehicle motor control.

Figure 2 shows a conventional example of a configuration in which a three-phase AC motor is driven by an inverter. Figure 2 shows the motor control device shown in Figure 1 of Patent Document 1, which detects three-phase currents for motor current control, detects the motor's rotation speed ω for motor rotation speed control, and controls the current flowing to the motor by turning on and off switching elements in the inverter, thereby controlling the motor's rotation speed and torque.

In FIG. 2, 50 is a motor control device, which has an inverter 50a and a control unit 50b. A storage battery 51 is connected to the DC side of the motor control device 50, and a motor 52 (e.g., a PM motor (Permanent Magnet Motor)) is connected to the AC side.

The DC busbar of the inverter 50a is provided with a DC voltage detection sensor 53 for detecting a DC voltage detection value, the U-phase, V-phase, and W-phase of the AC busbar of the inverter 50a are provided with AC current detection sensors 54a, 54b, and 54c for detecting AC current detection values (Iu, Iv, and Iw), and the motor 52 is provided with a magnetic pole position sensor 55 (e.g., a resolver) for detecting the rotation speed detection value (ω) of the motor 52.

The control unit 50b inputs a rotation speed command value from outside the device, a DC voltage detection value from the DC voltage detection sensor 53, an AC current detection value from the AC current detection sensors 54a, 54b, and 54c, and a rotation speed detection value from the magnetic pole position sensor 55.

The control unit 50b outputs the desired voltage command value to a gate drive circuit (not shown) by vector control based on these rotation speed command values and the detection values from various sensors (DC voltage detection sensor 53, AC current detection sensors 54a, 54b, 54c, and magnetic pole position sensor 55).

The gate drive circuit outputs a gate signal based on the input voltage command value to the inverter 50a to control the on/off of a switching element (e.g., an IGBT).

The motor control device 50 controls the motor by converting the DC voltage of the storage battery 51 into a desired AC voltage using an inverter 50a having a switching element and outputting it to the motor 52.

JP 2018-174655 A JP 2013-055796 A JP 2011-050214 A

In the current control unit (50b) of a three-phase AC motor as shown in FIG. 2, in order to detect deviations between the three-phase current detection values and the actual currents due to an abnormality in the current detector, a fault detection method has been implemented that monitors the total sum of the three-phase currents and detects faults.

This fault detection method detects a fault when the sum of the three-phase currents continues to deviate from zero for a certain period of time. However, if the detection gain of only one phase (for example, U phase) is off, as shown in Figure 3, which shows the current waveforms of the three-phase currents Iu, Iv, and Iw and the sum, the sum of the three-phase current detections (shown as "I sum") will be close to zero near the zero crossing of the faulty phase (U phase current Iu), and the time will be reset near the zero crossing where "a fault is detected when the sum continues to deviate from zero for a certain period of time", making fault detection impossible.

Therefore, in order to detect gain deviations with this fault detection method, fault detection must be performed over cumulative time, which poses problems such as the need to raise the threshold to avoid false detection due to current ripple, resulting in reduced accuracy, and the fact that detection is performed over cumulative time, which means it takes a long time from when a fault occurs until it is detected.

In addition, if deviations in current values are detected using effective current values rather than three-phase current values, abnormalities in the current itself can be detected even by the means for fault detection using the accumulated time. However, three-phase current detection values are necessary for control, etc., and it is necessary to check whether there are any abnormalities in the detection values.

The present invention aims to solve the above problems, and its purpose is to provide a fault detection device and a fault detection method for a three-phase current detection section that improves the accuracy of fault detection when there is a deviation in the three-phase current detection gain during motor rotation.

In order to solve the above problem, a fault detection device for a three-phase current detection unit according to claim 1 is provided,
In a current control system that controls a current flowing through a three-phase AC motor driven by an inverter,
a current detection unit that detects a three-phase current flowing through the three-phase AC motor;
a current difference calculation unit that calculates a current difference between each phase of the three-phase current detected by the current detection unit;
a zero-cross detection unit that outputs a zero-cross trigger signal when any of the current differences calculated by the current difference calculation unit becomes zero;
an abnormality determination unit which determines that a gain deviation in current detection has occurred when Tdet<Tref-ΔT or Tdet>Tref+ΔT, based on a reference value Tref, which corresponds to a time interval between zero-cross trigger signals in the case where there is no gain deviation in current detection and is calculated from a rotation speed detection value obtained by detecting the rotation speed of the three-phase AC motor or a motor rotation speed command value, a set margin time ΔT, and a time interval Tdet between zero-cross trigger signals output by the zero-cross detection unit;
The present invention is characterized by comprising:

The fault detection device for a three-phase current detection unit according to claim 2 is the device according to claim 1,
The current detection unit is characterized by having two current sensors that each detect the current of any two of the three phases, and a function of calculating the current of the remaining phase from the detected currents of the two current sensors.

A method for detecting a fault in a three-phase current detection unit according to claim 3,
In a current control system that controls a current flowing through a three-phase AC motor driven by an inverter,
a current detection unit detecting a three-phase current flowing through the three-phase AC motor;
a current difference calculation unit calculating a current difference for each phase of the three-phase current detected by the current detection unit;
a zero-cross detection unit outputting a zero-cross trigger signal at a timing when any of the current differences calculated by the current difference calculation unit becomes zero;
an abnormality determination unit calculating a reference value Tref corresponding to a time interval between zero-cross trigger signals in the case where there is no gain deviation in current detection, from a rotation speed detection value obtained by detecting the rotation speed of the three-phase AC motor or a motor rotation speed command value;
an abnormality determination unit determining that a gain deviation in current detection occurs when Tdet<Tref-ΔT or Tdet>Tref+ΔT based on the calculated reference value Tref, a set margin time ΔT, and a time interval Tdet between zero-cross trigger signals output by the zero-cross detection unit;
The present invention is characterized by comprising:

(1) According to the inventions described in claims 1 to 3, it is possible to detect imbalance in three-phase currents caused by a deviation in the gain of three-phase current detection, improving the accuracy of fault detection when a deviation in the gain of three-phase current detection occurs during motor rotation.

In addition, since the occurrence of a deviation in the gain of the current detection is judged by utilizing the timing at which any of the current differences becomes zero, it is resistant to erroneous detection due to noise and ripples in the detected current at the zero cross timing.
(2) According to the invention described in claim 2, even when current sensors are provided for only two of the three phases, it is possible to determine whether a deviation in the gain of current detection has occurred.

1 is a block diagram of a fault detection device according to an embodiment of the present invention; FIG. 1 is a configuration diagram showing an example of a motor drive configuration using a conventional inverter. FIG. 11 is a current waveform diagram in a conventional method for detecting a fault by monitoring the sum of three-phase currents. FIG. 4 is a current waveform diagram illustrating an embodiment of the present invention when there is no gain deviation of three-phase currents. 5 is a current waveform diagram illustrating an embodiment of the present invention when there is a gain deviation of a U-phase current. FIG. FIG. 11 is a current waveform diagram when an offset deviation occurs in a conventional method for detecting a fault by monitoring the sum value of three-phase currents.

The following describes an embodiment of the present invention with reference to the drawings, but the present invention is not limited to the following embodiment. In this embodiment, in order to detect a deviation in the gain of the current detection during rotation, a fault in the current control system is detected by comparing the crossing point of the three-phase current with the rotation speed.

For example, in the motor drive device of Fig. 2, Fig. 4 shows the three-phase current waveforms when there is no gain misalignment, and Fig. 5 shows the three-phase current waveforms when there is a gain misalignment in the U-phase current. The current waveforms in Figs. 4 and 5 use values derived for one of the three phases (phase V) using the detected values of the other two phases, and the current values of each of the three phases are denoted as Iu, Iw, and Iv (calculated).

During normal operation, the three-phase currents cross over each other every 1/6 of a cycle, as shown at crossing times t1, t2, t3, t4, t5, and t6 in Figure 4. However, if one of the three-phase currents is unbalanced due to a gain shift, the distance between the crossing points will deviate from 1/6 of a cycle, as shown at crossing times t1', t2', t3', t4', t5', and t6' in Figure 5.

Therefore, the three-phase current deviation (Iu-Iv, Iv-Iw, Iw-Iu) is calculated, and the interval between the sign reversal (zero crossing) points (= intersection points of the three-phase currents) of the three-phase current deviation is compared with the 1/6 period derived from the rotation speed.

When 1/6 cycle (the interval between current intersections in Figures 4 and 5) Tdet and the reference value Tref derived from the rotation speed are Tdet<Tref-ΔT or Tdet>Tref+ΔT (ΔT: margin of time), it is determined that a deviation in the current detection gain has occurred, and an alarm is issued or the inverter that controls the motor is shut down due to a fault.

Figure 1 shows a control block for detecting an abnormality according to this embodiment, which is applied to the motor drive device of Figure 2, for example. 101 denotes a current sensor (current detection unit) that is provided on each phase cable connecting the inverter (50a) and the motor (52) and detects the currents Iu, Iw, and Iv of each phase.

The current sensor 101 may be configured to include two current sensors that each detect the current of any two of the three phases, and the current of the remaining phase may be calculated from the currents detected by the two current sensors.

102 is a subtractor (current difference calculation unit) that calculates the current difference (Iu-Iv, Iv-Iw, Iw-Iu) of each phase of the three-phase current detected by the current sensor 101.

103 is a zero-cross detection unit that outputs a zero-cross trigger signal when any of the current differences (Iu-Iv, Iv-Iw, Iw-Iu) calculated by the subtractor 102 becomes zero.

104 is a rotation speed sensor that detects the rotation speed ω of the motor (52).

105 is an abnormality determination unit that has a function of calculating a reference value Tref based on the time interval Tdet between zero-cross trigger signals output from the zero-cross detection unit 103 and the rotation speed detection value ω detected by the rotation speed sensor 104, a function of setting a margin time ΔT, and an abnormality determination function of comparing the time interval Tdet with the reference value Tref and margin time ΔT to determine whether a gain deviation has occurred in the current detection.

The reference value Tref is a value that corresponds to the time interval between zero-cross trigger signals when there is no gain deviation in current detection, and the abnormality determination function has the function of determining that a gain deviation in current detection has occurred when the comparison result is Tdet<Tref-ΔT or Tdet>Tref+ΔT, and generating an alarm (abnormality signal) or shutting down the inverter that controls the motor due to a fault.

The rotation speed detection value ω for deriving the reference value Tref may be replaced with the rotation speed command value input to the inverter.

According to the configuration in Figure 1, when the motor is operating normally, the three-phase currents cross at equal intervals (every 1/6 of a cycle), making it possible to detect imbalances in the three-phase currents due to deviations in the gain of current detection from the deviations in the crossing points of the three-phase currents.

In addition, if one of the three-phase current detections deviates from the actual current due to an offset shift, the sum of the three phases does not become 0 near the zero crossing as shown in Figure 6. This means that it is possible to detect the fault using the conventional fault detection method, which considers the deviation of the sum from 0 for a certain period of time to be a fault.

Therefore, by using this invention in conjunction with the conventional method of monitoring the sum of three-phase currents, it is possible to detect fault conditions in both gain and offset deviations in the current detection value with greater accuracy.

In addition, since an abnormality in the actual current can also be detected by another means for detecting the effective current value, if no abnormality is detected by the other means, it is possible to identify that there is a deviation in the three-phase current gain.

This embodiment can also be applied to a configuration in which there are only two phases of current sensors and the current in the remaining phase is calculated (e.g., a current sensor detects Iu and Iv and calculates Iw = -Iu - Iv).

This embodiment has the following advantages over the conventional fault diagnosis methods described in, for example, Patent Documents 2 and 3:

In other words, in Patent Document 2, fault diagnosis is performed by comparing the currents of the other two phases at the time of the current zero crossing, but in this embodiment, fault diagnosis is performed at the timing of zero crossing detection, and (from the viewpoint of faults in the current detection system) it is also possible to detect a fault by detecting two of the three-phase currents and calculating the value of the remaining phase.

In addition, since the detection timing itself is compared, rather than each detection value of the zero-cross timing, it is also resistant to false detection caused by noise and ripples at the zero-cross timing. Furthermore, from the viewpoint of diagnosing faults in the current detection system, it has the advantage that it can detect current even when only two of the three phases are detected.

In addition, in Patent Document 3, the current value after dq conversion is used, but an abnormality occurs in the current after dq conversion even when there is a failure in the phase (rotation angle) detection. In contrast, in this embodiment, the current value is based on the phase current value that does not use the phase (rotation angle) rather than the current value after dq conversion, so it is not affected by failure in the phase detection unit.

50... Motor control device 50a... Inverter 50b... Control unit 51... Storage battery 52... Motor 53... DC voltage detection sensor 54a to 54c... AC current detection sensors 55... Magnetic pole position sensor 101... Current sensor 102... Subtractor 103... Zero cross detection unit 104... Rotational speed sensor 105... Abnormality determination unit

Claims (3)

In a current control system that controls a current flowing through a three-phase AC motor driven by an inverter,
a current detection unit that detects a three-phase current flowing through the three-phase AC motor;
a current difference calculation unit that calculates a current difference between each phase of the three-phase current detected by the current detection unit;
a zero-cross detection unit that outputs a zero-cross trigger signal when any of the current differences calculated by the current difference calculation unit becomes zero;
an abnormality determination unit which determines that a gain deviation in current detection has occurred when Tdet<Tref-ΔT or Tdet>Tref+ΔT, based on a reference value Tref, which corresponds to a time interval between zero-cross trigger signals in the case where there is no gain deviation in current detection and is calculated from a rotation speed detection value obtained by detecting the rotation speed of the three-phase AC motor or a motor rotation speed command value, a set margin time ΔT, and a time interval Tdet between zero-cross trigger signals output by the zero-cross detection unit;
A fault detection device for a three-phase current detection unit, comprising: The fault detection device for a three-phase current detection unit according to claim 1, characterized in that the current detection unit is provided with two current sensors that each detect the current of any two of the three phases, and a function for calculating the current of the remaining phase from the detected currents of the two current sensors. In a current control system that controls a current flowing through a three-phase AC motor driven by an inverter,
a current detection unit detecting a three-phase current flowing through the three-phase AC motor;
a current difference calculation unit calculating a current difference for each phase of the three-phase current detected by the current detection unit;
a zero-cross detection unit outputting a zero-cross trigger signal at a timing when any of the current differences calculated by the current difference calculation unit becomes zero;
an abnormality determination unit calculating a reference value Tref corresponding to a time interval between zero-cross trigger signals in the case where there is no gain deviation in current detection, from a rotation speed detection value obtained by detecting the rotation speed of the three-phase AC motor or a motor rotation speed command value;
an abnormality determination unit determining that a gain deviation in current detection occurs when Tdet<Tref-ΔT or Tdet>Tref+ΔT based on the calculated reference value Tref, a set margin time ΔT, and a time interval Tdet between zero-cross trigger signals output by the zero-cross detection unit;
A method for detecting a fault in a three-phase current detection unit, comprising:

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