JP7205176B2 - motor drive system - Google Patents

Description

TECHNICAL FIELD The present invention relates to a motor drive system for driving an AC motor using an inverter, and more particularly to a technique for suppressing an excessive increase in the DC intermediate voltage and output current of the inverter.

FIG. 8 is a schematic configuration diagram of a system that drives a permanent magnet synchronous motor (PMSM) with an inverter. In the figure, 10 is a DC power supply, 20 is a circuit breaker, 30 is a smoothing capacitor, 40 is a bridge circuit of semiconductor switching elements Q _u , Q _v , Q _w , Q _x , Q _y , Q _z such as IGBTs and MOSFETs. 100 is an AC motor such as PMSM (hereinafter also simply referred to as a motor).

In the drive system described above, when circuit breaker 20 is opened during regenerative operation of motor 100, regenerative energy is accumulated in smoothing capacitor 30 and the voltage across the capacitor (DC intermediate voltage) rises, resulting in overvoltage. At this time, if an overvoltage trip is performed by shutting off all phases of the switching elements by the protection operation of the inverter 40, the residual energy due to the current flowing through the stator winding of the motor 100 is released through the freewheeling diode in the inverter 40. It flows into the smoothing capacitor 30 . As a result, the voltage of the smoothing capacitor 30 will exceed the overvoltage level and further increase, causing damage to the switching element.
Such a problem is particularly conspicuous when a small-capacity smoothing capacitor 30 is used in order to reduce the size of the device, such as an in-vehicle inverter.

As a conventional countermeasure for the above problem, when an overvoltage state of the DC intermediate voltage of the inverter 40 is detected, all the switching elements of the upper arm or the lower arm of the inverter 40 are turned on to short-circuit the stator windings of the motor 100. By blocking the flow of energy from the motor 100 to the smoothing capacitor 30 via the inverter 40 (referred to as a three-phase short circuit or a three-phase winding short circuit), an increase in the DC intermediate voltage is prevented.
In FIG. 9, for example, all phase switching elements Q _x , Q _y , and Q _z of the lower arm of the inverter 40 are turned on at the same time to prevent the current in the direction indicated by the broken line from flowing into the smoothing capacitor 30 . It shows how to avoid an increase in the intermediate voltage.

As described above, the three-phase short-circuit is effective as a countermeasure against overvoltage of the inverter 40 .
However, for example, in a permanent magnet synchronous motor drive system, if a three-phase short circuit is simply performed when the DC intermediate voltage of the inverter becomes overvoltage, the transient current of each phase will be The component is greatly biased to the positive side or the negative side, and there is a risk that the switching element will be destroyed by the resulting overcurrent.

For this reason, in the electric vehicle control device described in Patent Document 1, prior to the three-phase short-circuit processing, pre-processing as shown in FIG. 10 is executed.
For example, when the transient current flowing in the U-phase of the inverter 40 is the maximum, the switching elements Q _u , Q _y , and Q _z are turned on for the time T ₁ as preprocessing, equivalently as shown in FIG. ), _a pulse voltage having a width of T1 (voltage generated by the power stored in the smoothing capacitor 30) is applied to the U phase, and this pulse voltage cancels the transient current flowing in the U phase to prevent overcurrent.

FIG. 10(b) is a flow chart of the pre-processing described above. _First , the voltage of the smoothing capacitor 30 is taken in and the time T1 is calculated (steps S1 and S2). This time T1 is calculated using the final current value based on the voltage of the smoothing capacitor 30, the attenuation time constant of the U- _phase transient current at the time of three-phase short circuit, the amplitude of the steady current, and the like.
Next, the command for applying the pulse voltage of FIG. 10(a) is calculated as the short-circuit voltage command (S3), and when the predetermined timing comes (S4 YES), according to the short-circuit voltage command, _over time T1 The operation of turning on the switching elements _Qu , _{Qy, and Qz and} turning off the other switching elements is executed as "preceding on/off control" (S5). After the time T1 has passed (S6 YES), the switching elements _Qu are turned off and _Qx is turned on, thereby turning on the _switching elements _Qx , _Qy , and _Qz of all phases of the lower arm. This is to shift to phase short-circuit processing (S7).

As another prior art, there is a permanent magnet synchronous motor that performs an intermittent short-circuit operation that alternately repeats opening and short-circuiting during the period from the opening operation of the switching elements of the upper arm or the lower arm to the three-phase short-circuiting operation. A drive is described in US Pat. FIG. 11 is a timing chart showing the operation of this prior art.
According to this prior art, an intermittent short _- circuit operation period T2 is provided before shifting to a complete three-phase short-circuit operation, and control is performed to gradually lengthen the duty of the short _- circuit period during this period T2. It suppresses the overcurrent that occurs when the operation immediately shifts to the three-phase short-circuit operation.

On the other hand, three-phase short-circuit control in an AC motor is also known as a so-called short-circuit brake. However, it is disclosed that the braking force is suppressed by performing two-phase short-circuit control.
Further, in Patent Document 4, as a short-circuit brake similarly applied to a three-phase brushless motor, the switching elements of the upper arm of the inverter are turned on in all phases, and the switching elements of the lower arm are turned on for three phases, two phases, or one phase. A technique is disclosed in which a desired braking force is secured while avoiding unnecessary charging of a capacitor by regenerated power without generating back electromotive force by only turning on the brake.

Japanese Patent No. 3394436 (paragraphs [0038] to [0043], FIGS. 1, 2, etc.) Japanese Patent No. 5398815 (paragraph [0016], FIGS. 1, 7, etc.) JP 2013-243824 A (paragraphs [0065] to [0104], FIGS. 3 to 5, etc.) Japanese Patent Application Laid-Open No. 7-184391 (paragraphs [0012] to [0018], FIGS. 4 to 6, etc.)

In the conventional techniques described in Patent Documents 1 and 2, it is possible to suppress overvoltage and overcurrent by performing preceding on/off control and intermittent short-circuit operation prior to three-phase short-circuiting. Immediately after the start, a transient overcurrent flows between the inverter and the motor, which may cause damage to the switching elements and wiring, demagnetization of the motor, and the like.
Here, FIG. 12 shows the DC intermediate voltage E _dc , the phase currents I _u , I _v , and I _w when the three-phase short circuit starts at time t ₁ , and each phase switching element Q _x in the lower arm of the inverter. FIG. 4 is a waveform diagram showing the behavior of _Qy and _Qz ; All the switching elements of the upper arm are turned off.
According to FIG. ₁₂ , by simultaneously turning on the switching elements _{Qx, Qy, and Qz at time} t1, it is possible to suppress the rise of the DC intermediate voltage _Edc , while the _phase current is reduced immediately after time t1. It can be seen that the value is transiently increased.

Generally, when stopping the three-phase short-circuiting process, the switching elements of the lower arm or the upper arm that have been turned on until then are turned off to turn off the switching elements of the upper and lower arms of all phases. However, according to this, the following problems arise.
FIG. 13 is a waveform diagram showing an operation when a three-phase short circuit is started and then stopped. When the three-phase short circuit is stopped by simultaneously turning off the _switching elements _Qx , _Qy , and _Qz at time t2 after starting the _three -phase short circuit at time t1, the current flowing through the switching elements at that time goes disappears, and this current becomes a current that charges the smoothing capacitor 30 via the freewheeling diode. As a result, the DC intermediate voltage _Edc exceeds the overvoltage level immediately after _time t2, causing the smoothing capacitor 30 to exceed the breakdown voltage.

As described above, Patent Documents 1 to 4 do not disclose any techniques for avoiding the overcurrent that occurs immediately after the start of the three-phase short circuit and the overvoltage that occurs immediately after the all-phase cutoff that stops the three-phase short circuit. not
Therefore, the problem to be solved by the present invention is to provide a motor drive system that protects the components of the device by avoiding the occurrence of overcurrent immediately after the start of the three-phase short circuit and overvoltage at the time of stopping the three-phase short circuit processing. That's what it is.

In order to solve the above-mentioned problems, the invention according to claim 1 has a smoothing capacitor connected in parallel to a DC power supply, and a DC input terminal of an inverter formed by bridge-connecting a plurality of switching elements to both ends of the smoothing capacitor. In a motor drive system comprising a controller in which the AC output terminals of the inverter are connected to the stator windings of the AC motor and which generates drive pulses for turning on and off the switching elements,
The control device is
overvoltage detection means for detecting an overvoltage of the voltage across the smoothing capacitor;
polarity determination means for determining the polarity of the phase current output from the inverter;
a process of turning off all the switching elements of the inverter when an overvoltage is detected by the overvoltage detecting means, a process of turning on the lower arm switching elements of the phase whose polarity of the phase current detected by the polarity determining means is negative, and the remaining a control means for sequentially executing a process of turning on the lower arm switching elements of the phases to turn on the lower arm switching elements of all phases to short-circuit the stator windings;
characterized by having

In the invention according to claim 2, a DC input terminal of an inverter formed by bridge-connecting a plurality of switching elements is connected to both ends of a smoothing capacitor connected in parallel to a DC power supply, and an AC output terminal of the inverter is connected In a motor drive system comprising a control device connected to a stator winding of an AC motor and generating a drive pulse for turning on and off the switching element,
The control device is
overvoltage detection means for detecting an overvoltage of the voltage across the smoothing capacitor;
polarity determination means for determining the polarity of the phase current output from the inverter;
A process of turning off all the switching elements of the inverter when the overvoltage detection means detects an overvoltage, a process of turning on the upper arm switching element of the phase in which the polarity of the phase current detected by the polarity determination means is positive, and the remaining a control means for sequentially executing a process of turning on the upper arm switching elements of the phases to turn on the upper arm switching elements of all the phases to short-circuit the stator windings;
characterized by having

In the invention according to claim 3, a DC input terminal of an inverter formed by bridge-connecting a plurality of switching elements is connected to both ends of a smoothing capacitor connected in parallel to a DC power supply, and an AC output terminal of the inverter is connected In a motor drive system comprising a control device connected to a stator winding of an AC motor and generating a drive pulse for turning on and off the switching element,
The control device is
overvoltage detection means for detecting an overvoltage of the voltage across the smoothing capacitor;
polarity determination means for determining the polarity of the phase current output from the inverter;
a process of turning off all switching elements of the inverter when an overvoltage is detected by the overvoltage detecting means; a process of turning on the lower arm switching elements of all phases of the inverter to short-circuit the stator winding; and the polarity determining means. turning off the lower arm switching elements of the phases in which the polarity of the phase current detected is positive, and turning off the lower arm switching elements of the remaining phases to turn off the lower arm switching elements of all the phases and fix the a control means for sequentially executing a process of stopping the short-circuiting of the child windings;
characterized by having

In the invention according to claim 4, a DC input terminal of an inverter formed by bridge-connecting a plurality of switching elements is connected to both ends of a smoothing capacitor connected in parallel to a DC power supply, and an AC output terminal of the inverter is connected In a motor drive system comprising a control device connected to a stator winding of an AC motor and generating a drive pulse for turning on and off the switching element,
The control device is
overvoltage detection means for detecting an overvoltage of the voltage across the smoothing capacitor;
polarity determination means for determining the polarity of the phase current output from the inverter;
a process of turning off all switching elements of the inverter when an overvoltage is detected by the overvoltage detecting means; a process of turning on upper arm switching elements of all phases of the inverter to short-circuit the stator winding; and the polarity determining means. turning off the upper arm switching elements of the phases in which the polarity of the phase current detected is negative; a control means for sequentially executing a process of stopping the short-circuiting of the child windings;
characterized by having

The invention according to claim 5 is the motor drive system according to claim 1,
The control means is
For the inverter that short-circuits the stator winding by turning on the lower arm switching elements of all phases,
A process of turning off the lower arm switching elements of the phases in which the polarity of the phase current detected by the polarity discriminating means is positive, and turning off the lower arm switching elements of the remaining phases to turn off the lower arm switching elements of all phases. and stopping the short-circuiting of the stator windings.

The invention according to claim 6 is the motor drive system according to claim 2,
The control means is
For the inverter that short-circuits the stator winding by turning on the upper arm switching elements of all phases,
A process of turning off the upper arm switching elements of the phases in which the polarity of the phase current detected by the polarity discriminating means is negative, and turning off the upper arm switching elements of the remaining phases to turn off the upper arm switching elements of all phases. and stopping the short-circuiting of the stator windings.

The invention according to claim 7 is the motor drive system according to any one of claims 1 to 6,
The control means generates the drive pulse by performing speed control or torque control using one or more input information of the voltage across the smoothing capacitor, the phase current, and the rotational speed of the AC motor. Characterized by

According to the present invention, in the case of three-phase short-circuiting of the stator windings of an AC motor when the DC intermediate voltage of the inverter becomes overvoltage, the occurrence of overcurrent at the start of short-circuit processing and overvoltage at the time of stopping short-circuiting can be prevented. can be prevented. As a result, it is possible to more reliably perform the protective operation of the switching elements, smoothing capacitors, and the like that constitute the inverter.

1 is a schematic configuration diagram of a motor drive system according to an embodiment of the present invention; FIG. FIG. 2 is a block diagram showing the main part of the control device in FIG. 1; FIG. FIG. 4 is a circuit diagram of an inverter showing operation during short-circuit processing according to the embodiment of the present invention; FIG. 4 is a waveform diagram of voltage and current of each part during short-circuit processing according to the embodiment of the present invention, and an operation explanatory diagram of the switching element; FIG. 4 is a waveform diagram of voltage and current of each part during short-circuit processing according to the embodiment of the present invention, and an operation explanatory diagram of the switching element; FIG. 4 is a circuit diagram of the inverter according to the embodiment of the present invention, showing the operation when the three-phase short circuit is stopped; FIG. 4 is a waveform diagram of voltage and current at each part from the start of a short circuit to a stop according to the embodiment of the present invention, and an operation explanatory diagram of a switching element; 1 is a schematic configuration diagram showing a drive system of a permanent magnet synchronous motor; FIG. It is a circuit diagram of an inverter showing an example of three-phase short-circuit processing. FIG. 10A is an equivalent circuit diagram (FIG. 10A) and a flow chart (FIG. 10B) showing the operation of the conventional technology described in Patent Document 1; 4 is a timing chart showing the operation of the conventional technology described in Patent Document 2; FIG. 10 is a waveform diagram showing an operation immediately after the start of a three-phase short circuit in the prior art; FIG. 10 is a waveform diagram showing the operation from the start of a three-phase short circuit to after it stops in the prior art;

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a motor drive system according to an embodiment of the present invention, and the same parts as those in FIG. 8 are denoted by the same reference numerals.

In FIG. 1, the DC power supply 10 includes a battery, a boost chopper and a DC/DC converter for DC-DC conversion, a PWM converter and a diode rectifier for AC-DC conversion, and the like. Also, the circuit breaker 20 is composed of a DC relay, a semiconductor switching element, a fuse, or the like.
A series circuit of a discharge resistor and a semiconductor switching element (not shown) is connected in parallel to the smoothing capacitor 30 connected across the series circuit of the DC power supply 10 and the circuit breaker 20 .
The semiconductor switching elements _Qu , _Qv , _Qw , _Qx , _Qy , and _Qz of the inverter 40 whose DC input terminal is connected to the smoothing capacitor 30 include IGBTs as well as MOSFETs, power transistors, and the like. The motor 100 that can be used and is driven by this inverter 40 includes a permanent magnet synchronous motor (PMSM) as shown, an induction motor (IM), a reluctance motor, and the like.

The smoothing capacitor 30 is provided with a voltage detector 50 for detecting the voltage (direct current intermediate voltage) E _dc across the smoothing capacitor 30, and the output side of each phase of the inverter 40 detects phase currents _Iu , _Iv and _Iw . A current detector 60 is provided to detect.
Further, the motor 100 is provided with a sensor 110 that detects the angular velocity ω (or angle θ) of the rotor. Note that the sensor 110 is not necessary when the motor 10 is driven by so-called sensorless control.

A control device 70 that controls the inverter 40 is supplied with a speed command or a torque command from a host system, and also receives voltage detection values E _dc and phase current detection values I _u and I _v 1 , I _w , and the speed detection value ω(θ) are input. Control device 70 turns switching elements Q _u , Q _v , Q _w , Q _x , Q _y , and Q _z of inverter 40 on and off by driving pulses generated based on these detected values, and drives motor 100 at a predetermined level. Operates to run under speed or output torque.

Next, the configuration of the main parts of the control device 70 will be described with reference to FIG.
The control device 70 includes a voltage command calculation section 73 comprising calculation means such as a CPU. The voltage command calculator 73 uses one or more pieces of information among the voltage detection value E _dc , the phase current detection values I _u , I _v , and I _w , and the speed detection value ω(θ) to calculate the speed given from the host. Speed control is performed so that the rotation speed of the motor 100 matches the command, or torque control is performed so that the output torque of the motor 100 matches the torque command, and the output voltage command V ^* of the inverter 40 is calculated. Then, for example, the switching elements Q _u , Q _v , Q _w , Q _x , Q _y , Q _z of the inverter 40 are turned on and off by the operation of the PWM circuit 74 that compares the output voltage command V ^* with the carrier. to generate a drive pulse for Here, speed control or torque control may be configured so as to be changeable according to a command or parameter from a host.

The controller 70 is also provided with an overvoltage detection circuit 71 that outputs an overvoltage detection signal when the DC intermediate voltage _Edc exceeds the overvoltage threshold. The above overvoltage threshold is a value set in advance so that the DC intermediate voltage _Edc does not exceed the breakdown voltage of the smoothing capacitor 30 and the switching elements, and is generated by dividing the control power supply voltage with resistors. The voltage command calculation unit 73 to which the overvoltage detection signal is input turns off drive pulses for all the switching elements of the inverter 40 for a certain period of time via the PWM circuit 74 .

Further, the control device 70 is provided with a polarity determination circuit 72 that compares the phase current detection values _Iu , _Iv , and _Iw with current threshold values to determine the polarity of each phase current. Here, the polarity of the phase current is defined as positive in the direction from the inverter 40 to the motor 100, for example, as shown in FIG. A polarity discrimination signal generated by the polarity discrimination circuit 72 is input to the voltage command calculation section 73 .

Next, the operation of this embodiment will be described.
First, according to FIGS. 3 to 5, the operation of turning on the off-state switching elements of the lower arm or upper arm of inverter 40 in order to short-circuit the three phases of the stator windings of motor 100 will be described.

The polarity discrimination circuit 72 uses different current threshold values for short-circuiting the stator winding of the motor 100 when turning on the lower arm switching element of the inverter 40 and when turning on the upper arm switching element. to determine the polarity of the phase current.
As an example, a case will be described in which short-circuit processing is performed by turning on the lower arm switching element while all switching elements are turned off when an overvoltage of the DC intermediate voltage _Edc is detected.

When the phase current detection value falls below a current threshold value that is a positive value of zero or more, the polarity determination circuit 72 determines the polarity of the phase current to be negative, and outputs a polarity determination signal to the voltage command calculation unit 73 . The above current threshold has a predetermined offset on the positive side in order to prevent misjudgment when the phase current is near zero or when there is a gap between the overvoltage detection timing and the current detection timing. It is desirable to set the value
The voltage command calculation unit 73 recognizes from the polarity discrimination signal that the polarity of a certain phase current is negative, and generates an output voltage command V ^* for turning on the switching element of the lower arm of the phase. to generate drive pulses.

FIG. 3 is a circuit diagram of the inverter 40 showing the operation during short-circuit processing described above. In FIGS. 3(a) and 3(b), x marks indicate switching elements in the off state, and solid line and dashed line o marks indicate switching elements that are turned on.
Since the polarity of the _V -phase current Iv is negative in FIG. 3A, the polarity discrimination circuit 72 first turns on the switching element _Qy of the lower arm based on the polarity discrimination signal of the _V -phase current Iv. Operate. As for the U-phase and W-phase, in which the polarity of the current is positive, current flows through the _free wheel diodes of the switching elements Q _x and Q _z as indicated by the arrows in FIG. The momentary operation does not change even if _Qz is not turned on.

FIG. 4 is a waveform diagram of the DC intermediate voltage E _dc and each phase current when only the switching element Q _y is turned on at time t _1a , and an explanatory diagram of the operation of the switching element. Comparing this FIG. 4 with FIG. 12 in which all the switching elements Q _x , Q _y , Q _z of the lower arm are turned on at the same time, the effect of suppressing the DC intermediate voltage _Edc is almost the same, but immediately after time t _1a 12 is smaller than that in FIG.
Further, when there are two phases in which the polarity of the current is negative, by turning on the switching elements of the two phases, the current immediately after turning on can be suppressed.

However, as is clear from _FIG . 4, in the steady state after a certain period of time has elapsed from time t1a, the current gradually increases as in the case of a one-phase or two-phase short-circuit failure.
Therefore, when a predetermined time has passed since the V-phase switching element _Qy was turned on, the remaining two-phase switching elements _Qx and _Qz of the lower arm are turned on, thereby turning on all the switching elements Q of the lower arm. _{x 1} , Q _y , and Q _z are turned on to shift to a three-phase short circuit state. Here, it is assumed that the predetermined time is a value proportional to the rotation speed of the motor 100 . FIG. 3(b) shows the states of the lower arm switching elements _Qx , _Qy , and _Qz at this time.

In FIG. 5, as described above, the switching element _{Qy is turned on at time t1a, and the remaining two phase switching elements Qx and Qz are turned on} at time _t1b after a predetermined time has elapsed to shift to the three-phase short-circuit state. FIG. 3 is a waveform diagram of a DC intermediate voltage E _dc and each phase current, and an explanatory diagram of the operation of the switching element in the case of FIG.
Comparing FIG. 5 with _FIG . 4, after time _t1a , the rise in the DC intermediate voltage _Edc is suppressed in the same manner as in FIG. is decreasing.

When the current of one phase is zero (the current of the other two phases is at its maximum value), if the switching elements of the remaining two phases are turned on, the next maximum current value will be Since it is possible to secure a long time until the arrival of the current, the attenuation of the current during that time is increased, and the overcurrent can be further reduced.
Further, when the polarity of the two-phase current is negative at the timing when the overvoltage of the DC intermediate voltage _Edc is detected, the two-phase lower arm switching element is turned on. The magnitude is an intermediate value between when all three-phase lower-arm switching elements are turned on and when only one-phase switching element is turned on.

The above description is for the case where the lower arm switching element of the inverter 40 is turned on to perform the three-phase short-circuit processing.
On the other hand, when the upper arm switching element of the inverter 40 is turned on to perform the three-phase short-circuit processing, the polarity determination circuit 72 detects the current threshold when the phase current detection value exceeds the current threshold set to a negative value of zero or less. Determine the polarity of the phase current as positive. Then, the upper arm switching element of the relevant phase is first turned on, and after a predetermined time proportional to the rotational speed of the motor, the upper arm switching elements of the remaining two phases are turned on, thereby transitioning to the three-phase short circuit state. The above current threshold has a predetermined offset on the negative side in order to prevent misjudgment when the phase current is near zero or when there is a gap between the overvoltage detection timing and the current detection timing. It is desirable to set the value

Next, according to FIGS. 6 and 7, the operation for turning off the switching elements in the lower arm or the upper arm of the inverter 40 in the ON state in order to stop the three-phase short-circuit processing will be described.

In this case, the polarity determination circuit 72 uses different current thresholds when stopping the three-phase short-circuit processing by turning off the lower arm switching element of the inverter 40 and when turning off the upper arm switching element. Determine the polarity of the phase currents.
As an example, in a state in which all the upper arm switching elements are turned off and all the lower arm switching elements are turned on to perform the three-phase short-circuiting process, turning off the lower arm switching elements stops the three-phase short-circuiting process. A case of doing so will be explained.

The polarity discrimination circuit 72 determines that the polarity of the phase current is positive when the phase current detection value exceeds a current threshold value that is a positive value of zero or more, and outputs a polarity discrimination signal to the voltage command calculation section 73 . In order to prevent misjudgments such as when the phase current is near zero, when the current changes during dead time, or when there is a gap between the overvoltage detection timing and the current detection timing, the above current threshold is It is desirable to set the value with a predetermined offset on the positive side.
The voltage command calculation unit 73 recognizes from the polarity discrimination signal that the polarity of a certain phase current is positive, generates an output voltage command V ^* for turning off the switching element of the lower arm of the phase, and the PWM circuit 74 to generate drive pulses.

FIG. 6 is a circuit diagram of the inverter 40 showing the operation when the short-circuiting process is stopped. In FIGS. 6A and 6B, ◯ marks indicate switching elements that are in the ON state, and solid line and broken line X marks indicate switching elements that are turned OFF.
Since the polarities of the _V -phase current _Iv and _W -phase current _Iw are positive in FIG. , the switching elements Q _y and Q _z of are first turned off.
FIG. 6(b) shows how the switching element _{Qx of the lower arm, which had been in the ON state only until then, is turned off after a predetermined time has passed since the switching elements Qy and Qz were turned} off. there is As a result, all switching elements are turned off, and the three-phase short-circuiting process is completely stopped.

FIG. 7 shows a state in which all the switching elements _Qx , _Qy , and _Qz of the lower arm are turned on at time t1 to short _- circuit the three phases, and at time t2, the switching elements are switched as shown in _FIG . 6(a). DC intermediate voltage E _dc when Q _y and Q _z are first turned off, and then at time t ₃ the remaining switching elements Q _x are turned off as shown in FIG. FIG. 4 is an explanatory diagram of operation of each switching element;
Observing the phase currents in FIG. 7, since the polarities of the _{V -} phase current Iv and _W -phase current Iw are positive at time t2, the switching elements _{Qy and Qz are} turned off at this time, and the polarity is negative U It can be seen that the switching element _Qx is turned off at time _t3 when the phase current _Iu becomes zero.
Further, even if the _three -phase short circuit is completely stopped at time t3 in FIG. 7 _, the DC intermediate voltage _Edc does not rise. Intermediate voltage _Edc has risen well above the overvoltage level. Therefore, the superiority of the method of turning off the switching elements step by step as in this embodiment is obvious.

The above description is for the case where the lower arm switching element of the inverter 40 is turned off to stop the three-phase short-circuit processing.
On the other hand, when the upper arm switching element of the inverter 40 is turned off to stop the three-phase short-circuit processing, the polarity determination circuit 72 sets the phase current detection value to a current threshold set to a negative value of zero or less. If it falls below, the polarity of the phase current is determined to be negative. Then, the upper arm switching element of the relevant phase is first turned off, and after a predetermined time proportional to the rotational speed of the motor, the upper arm switching elements of the remaining phases are turned off, thereby completely stopping the three-phase short-circuiting process.
In order to prevent misjudgments such as when the phase current is near zero, when the current changes during dead time, or when there is a gap between the overvoltage detection timing and the current detection timing, the above current threshold is It is desirable to set the value with a predetermined offset on the negative side.

As described above, according to this embodiment, when the three phases of the stator windings of the motor 100 are short-circuited when the DC intermediate voltage _Edc of the inverter 40 becomes an overvoltage, the overvoltage at the start of the short-circuiting process is reduced. It is possible to prevent the occurrence of overvoltage when the current or the short circuit is stopped, and it is possible to more reliably perform the protective operation of the switching element, the smoothing capacitor, and the like.

10: DC power supply 20: Circuit breaker 30: Smoothing capacitor 40: Inverter 50: Voltage detector 60: Current detector 70: Control device 71: Overvoltage detection circuit 72: Polarity discrimination circuit 73: Voltage command calculation unit 74: PWM circuit 100 : AC motor 110 : Sensors Q _u , Q _v , Q _w , Q _x , Q _y , Q _z : Semiconductor switching elements

Claims (7)

A smoothing capacitor connected in parallel to a DC power source is connected to both ends of the smoothing capacitor, and the DC input terminals of an inverter formed by bridge-connecting a plurality of switching elements are connected, and the AC output terminals of the inverter are connected to the stator windings of the AC motor. In a motor drive system comprising a control device connected to and generating a drive pulse for turning on and off the switching element,
The control device is
overvoltage detection means for detecting an overvoltage of the voltage across the smoothing capacitor;
polarity determination means for determining the polarity of the phase current output from the inverter;
a process of turning off all the switching elements of the inverter when an overvoltage is detected by the overvoltage detecting means, a process of turning on the lower arm switching elements of the phase whose polarity of the phase current detected by the polarity determining means is negative, and the remaining a control means for sequentially executing a process of turning on the lower arm switching elements of the phases to turn on the lower arm switching elements of all phases to short-circuit the stator windings;
A motor drive system comprising: A smoothing capacitor connected in parallel to a DC power source is connected to both ends of the smoothing capacitor, and the DC input terminals of an inverter formed by bridge-connecting a plurality of switching elements are connected, and the AC output terminals of the inverter are connected to the stator windings of the AC motor. In a motor drive system comprising a control device connected to and generating a drive pulse for turning on and off the switching element,
The control device is
overvoltage detection means for detecting an overvoltage of the voltage across the smoothing capacitor;
polarity determination means for determining the polarity of the phase current output from the inverter;
A process of turning off all the switching elements of the inverter when the overvoltage detection means detects an overvoltage, a process of turning on the upper arm switching element of the phase in which the polarity of the phase current detected by the polarity determination means is positive, and the remaining a control means for sequentially executing a process of turning on the upper arm switching elements of the phases to turn on the upper arm switching elements of all the phases to short-circuit the stator windings;
A motor drive system comprising: A smoothing capacitor connected in parallel to a DC power source is connected to both ends of the smoothing capacitor, and the DC input terminals of an inverter formed by bridge-connecting a plurality of switching elements are connected, and the AC output terminals of the inverter are connected to the stator windings of the AC motor. In a motor drive system comprising a control device connected to and generating a drive pulse for turning on and off the switching element,
The control device is
overvoltage detection means for detecting an overvoltage of the voltage across the smoothing capacitor;
polarity determination means for determining the polarity of the phase current output from the inverter;
a process of turning off all switching elements of the inverter when an overvoltage is detected by the overvoltage detecting means; a process of turning on the lower arm switching elements of all phases of the inverter to short-circuit the stator winding; and the polarity determining means. turning off the lower arm switching elements of the phases in which the polarity of the phase current detected is positive, and turning off the lower arm switching elements of the remaining phases to turn off the lower arm switching elements of all the phases and fix the a control means for sequentially executing a process of stopping the short-circuiting of the child windings;
A motor drive system comprising: A smoothing capacitor connected in parallel to a DC power source is connected to both ends of the smoothing capacitor, and the DC input terminals of an inverter formed by bridge-connecting a plurality of switching elements are connected, and the AC output terminals of the inverter are connected to the stator windings of the AC motor. In a motor drive system comprising a control device connected to and generating a drive pulse for turning on and off the switching element,
The control device is
overvoltage detection means for detecting an overvoltage of the voltage across the smoothing capacitor;
polarity determination means for determining the polarity of the phase current output from the inverter;
a process of turning off all switching elements of the inverter when an overvoltage is detected by the overvoltage detecting means; a process of turning on upper arm switching elements of all phases of the inverter to short-circuit the stator winding; and the polarity determining means. turning off the upper arm switching elements of the phases in which the polarity of the phase current detected is negative; a control means for sequentially executing a process of stopping the short-circuiting of the child windings;
A motor drive system comprising: In the motor drive system according to claim 1,
The control means is
For the inverter that short-circuits the stator winding by turning on the lower arm switching elements of all phases,
A process of turning off the lower arm switching elements of the phases in which the polarity of the phase current detected by the polarity discriminating means is positive, and turning off the lower arm switching elements of the remaining phases to turn off the lower arm switching elements of all phases. and stopping the short-circuiting of the stator windings. In the motor drive system according to claim 2,
The control means is
For the inverter that short-circuits the stator winding by turning on the upper arm switching elements of all phases,
A process of turning off the upper arm switching elements of the phases in which the polarity of the phase current detected by the polarity discriminating means is negative, and turning off the upper arm switching elements of the remaining phases to turn off the upper arm switching elements of all phases. and stopping the short-circuiting of the stator windings. In the motor drive system according to any one of claims 1 to 6,
The control means is
A motor drive characterized in that the drive pulse is generated by performing speed control or torque control using one or more input information among the voltage across the smoothing capacitor, the phase current, and the rotation speed of the AC motor. system.

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