JPH11235089A - Inertial rotation information detecting method and device for ac motor, and motor driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device which can detect the direction during inertial rotation easily. SOLUTION: An induction motor 4 is driven by an inverter circuit 3, and the switches Q2 , Q4 , Q6 of the inverter circuit are turned on simultaneously to detect a rotation direction during subsequent inertial rotation, thus keeping a zero vector control condition. Current is detected by current detectors 6, 7 for peak detection of them. By making phase comparison for them, normal rotation is discriminated from reverse rotation for detection. If a reverse rotation command to the normal rotation occurs with the normal rotating detected, the output frequency and voltage of an inverter at this point are controlled for smooth shift to reverse rotation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving a polyphase AC motor by a polyphase inverter (DC-AC power converter), and a method for detecting rotation information when the AC motor is not driven, that is, during free running. The present invention relates to a device and an AC motor driving method.

[0002]

2. Description of the Related Art Detecting a rotation speed and a rotation direction of a motor in a free running state has significance in setting a condition for restarting the motor. Although the rotation speed and direction in the free running state can be detected by a rotation detector, the provision of the rotation detector not only increases the size of the device but also increases the cost.

The applicant of the present invention has disclosed a method of detecting the inertial rotation speed of an induction motor driven by an inverter without using a rotation detector, as disclosed in Japanese Patent Application No. 7-155218 (Japanese Patent Application Laid-Open No. Hei 8-3).
No. 31894). However, a method for detecting the rotation direction is not proposed here. When the induction motor is rotated only in the forward direction, the detection of the rotation direction is not required. However, when the induction motor is rotated in both the forward direction and the reverse direction, information on the rotation direction during free running (coasting rotation) is required. Is done. Therefore, a first object of the present application is to provide a method and an apparatus capable of easily detecting a rotation direction during coasting rotation.

When an induction motor is driven by an inverter,
When simply switching from the forward rotation drive state to the reverse rotation drive state, not only can the rotation speed and direction not be switched smoothly in a short time, but also the overcurrent protection circuit operates and the motor stops. is there. Therefore, a second object of the present invention is to provide a method capable of smoothly switching the rotation direction.

[0005]

In order to solve the above-mentioned problems and to achieve the above-mentioned first object, according to the present invention, a plurality of series circuits of a first switch and a second switch are connected between a pair of DC power supply terminals. A method of detecting inertial rotation information of the AC motor during a period in which the driving of the polyphase AC motor by the multiphase inverter having the configured configuration is stopped, wherein the first of the plurality of series circuits of the polyphase inverter is And the second switch is simultaneously turned on, and at this time, the input currents of at least the first and second phases of the AC motor are detected, and the input currents of the first phase and the second phase are detected. The present invention relates to a method of detecting inertial rotation information of an AC motor, wherein the information indicating the direction of the inertial rotation of the AC motor is obtained by comparing the phases of the AC current and the input current. It is preferable that the input currents of the first and second phases are converted into binary signals and the phases are compared. In order to execute the method of claim 1, it is desirable to configure a detection device as described in claim 6. According to another aspect of the present invention, a polyphase AC motor is driven by a polyphase inverter having a configuration in which a plurality of series circuits of first and second switches are connected between a pair of DC power supply terminals. A driving method in a second rotation direction opposite to the first rotation direction during a driving stop period after driving the electric motor in the first rotation direction. A first step of detecting a rotation speed and a rotation direction, and an output of the inverter capable of obtaining, after the first step, a rotation speed substantially equal to the rotation speed detected in the first step. A first frequency command value (f1) corresponding to the frequency is prepared, and the first frequency command value (f1)
1) driving the inverter so as to obtain an output frequency corresponding to the output frequency and the output frequency and the output voltage of the inverter such that the ratio V / f between the output frequency f and the output voltage V of the inverter is constant. To obtain a first output voltage value (V1) corresponding to the first frequency command value (f1) in a characteristic diagram showing a relationship between an output frequency and an output voltage for driving the electric motor. A second step of gradually increasing the output voltage of the inverter from zero toward the first output voltage value (V1) so that the output frequency of the inverter becomes equal to the first frequency command value (f1). After the corresponding value and the output voltage of the inverter has reached the first output voltage value (V1),
The output frequency command value of the inverter is gradually reduced from the first frequency command value (f1) toward zero, and the output voltage command value of the inverter is also changed to the first output voltage according to the constant V / f control. A third step of gradually lowering the command value from zero to zero, and setting the output frequency command value of the inverter to have a direction to rotate the motor in the second rotation direction after the third step. A fourth step of gradually changing the output frequency command value toward the output frequency command value and changing the output voltage command value of the inverter in accordance with the constant control of V / f. is there. As described in claim 4, it is desirable that the detection of the rotation direction of the invention of claim 3 is performed by the method of claim 1. It is desirable that the rotation speed be detected based on the detection of the input current of the AC motor during the inertial rotation.

[0006]

According to the first, second, fourth and sixth aspects of the present invention,
Since the direction of the inertial rotation is detected based on the control of the switch of the inverter and the input current of the AC motor, this detection can be performed easily and at low cost. Claim 2
According to the invention, information indicating the rotation direction can be obtained accurately and easily. According to the third, fourth, and fifth aspects of the present invention, a constant V / f state is created during the first rotation direction, and the rotation speed is reduced to zero by the constant V / f control. Is driven by the constant V / f control, so that the rotation direction can be switched smoothly and in a short time. According to the invention of claim 5, both the rotation direction and the rotation speed can be easily detected.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, referring to FIGS. 1 to 9, a method for detecting inertial rotation of an induction motor and a method and a device for driving the same according to embodiments and examples of the present invention will be described. As shown in FIG. 1, a control and driving device for an induction motor includes a three-phase rectifying / smoothing circuit 2 connected to a three-phase AC power supply terminal 1 and a three-phase inverter connected between the pair of DC output terminals 2a and 2b. Circuit 3, a three-phase induction motor 4 as an AC motor connected to the inverter circuit 3, and an inverter control circuit 5
, First and second current detectors 6 and 7, a frequency detection circuit 8, and an inverter operation command device 9.

The inverter circuit 3 is a well-known three-phase bridge type inverter circuit, in which six IGBTs, that is, first to sixth switches Q1 to Q6 comprising insulated gate bipolar transistors are connected in a three-phase bridge. Switch Q
Feedback diodes D1 to D6 are connected in anti-parallel to 1 to Q6. That is, the first and second switches Q1,
A first phase arm comprising a series circuit of Q2;
A second phase arm composed of a series circuit of switches Q3 and Q4, and a third phase arm composed of a series circuit of fifth and sixth switches Q5 and Q6 as an output terminal 2a of a rectifying / smoothing circuit 2 as a DC power supply terminal. 2b, and output lines 3a, 3b, 3c are derived from the midpoint of each phase arm.

The induction motor 4 has primary windings 4a, 4b, 4
A rotor (not shown) is provided in addition to the stator made of C, and a load such as a fan is coupled to the rotor. In this embodiment, the primary windings 4a, 4b, 4c are Y-connected, and the output lines 3a, 3
b, 3c.

The control circuit 5 performs three-phase PWM control on the switches Q1 to Q6 of the inverter circuit 3 and, in a steady state, sets the motor 4 at V / f = predetermined (where V is the inverter output voltage and f is the inverter output frequency). The rotation speed is controlled to a predetermined value according to the conditions, and during the free running (coasting) period, the three lower switches Q2,
Q4 and Q6 are simultaneously turned on, rotation information during the free running period is detected, and start-up control is performed according to the rotation information.

The first and second current detectors 6, 7 are coupled to the output lines 3a, 3c of the inverter circuit 3 and detect the inverter output current, that is, the motor input current. The output lines 6a, 7a of the current detectors 6, 7 are connected to the inverter control circuit 5 and the frequency detection circuit 8, and are used for detecting the rotation direction and the rotation speed during free running.
The outputs of the current detectors 6 and 7 are also used for an overcurrent protection circuit (not shown) for turning off all the switches Q1 to Q6 of the inverter circuit 3 when an overcurrent occurs.

The frequency detection circuit 8 detects the frequency of the current obtained from the current detectors 6 and 7 during free running to obtain rotation speed information of the electric motor 4, and can be called a rotation speed detection circuit. It is. That is, the frequency detection circuit 8 shapes the first and second current detection waveforms into a square wave pulse, and inputs the same into respective counters.
The frequency is detected based on the count output per unit time. The frequency measured here indicates the rotation speed of the electric motor 4. That is, the rotation speed of the motor 4 is Nx, the number of poles is P, and the frequency of the current detected by the current detectors 6 and 7 is f.
Assuming that m, the relational expression of Nx = 120 fm / P holds. Therefore, when the detection frequency fm is multiplied by a constant, the rotation frequency, that is, the rotation speed Nx is obtained. Note that a configuration may be adopted in which a period T seconds of the current detection waveform is detected, and the frequency is obtained by 1 / T. The frequency detecting circuit 8 detects frequencies based on the input currents of the two phases, and sends an average value of the detected frequencies to the inverter control circuit 5 via the output line 8a. Of course 1
The frequency may be detected only by the input current of the phase.

The operation command unit 9 supplies a desired rotation speed (a target rotation speed) of the electric motor 4, that is, a desired frequency command, a normal rotation command and a reverse rotation command of the inverter to the control circuit 5 through lines 9a, 9b and 9c.

FIG. 2 shows the inverter control circuit 5 of FIG. 1 in detail. The inverter control circuit 5 includes a well-known PWM control circuit 11 for controlling the control electrodes of the switches Q1, Q2, Q3, Q4, Q5, and Q6, a frequency command value generation and activation controller 12, a free running detection circuit. 13, a free running control circuit 14 and a rotation direction detection circuit 15. The rotation direction detection circuit 15 includes first and second peak detectors 16 and 17 and a phase comparator 18. It should be noted that many parts of the control circuit 5 are constituted by microcomputers, but are shown in blocks for each function in FIG. 2 for easy understanding.

FIG. 3 shows details of the PWM control circuit 11 of FIG. The inverter control circuit 11 performs a control of V / f = constant and a PWM control known in, for example, JP-A-57-40369. The inverter control circuit 11 includes an output voltage command value generator 21 and a voltage switch 22. A three-phase sine wave generator 23, a triangular wave carrier generator 24,
It comprises three comparators 25, 26, 27 and a gate drive circuit 28. Output frequency command line 12a derived from frequency command value generation and activation controller 12 in FIG.
Converts the frequency command value Fn of the inverter to the voltage command value generator 2
1 and a three-phase sine wave generator 23. The voltage command value generator 21 responds to the frequency command value Fn of the line 12a and generates an output voltage command value Vn according to a condition of Vn / Fn = constant as shown by a characteristic line 29. Three-phase sine wave generator 23
Generates three-phase sinusoidal voltages Vsu, Vsv, and Vsw at the frequency specified by the frequency command value Fn on the line 12a, as shown in FIG. The amplitudes of the voltages Vsu, Vsv, and Vsw are controlled so as to be proportional to the voltage Vn of the voltage command value generator 21 or the voltage Vs of the line 12c. The triangular wave carrier generator 24 includes sine wave voltages Vsu and Vs as shown in FIG.
A triangular wave voltage Vt having a frequency (for example, 20 kHz) sufficiently higher than the frequencies of v and Vsw (for example, 0 to 60 Hz) is generated. The comparators 25, 26 and 27 output sine wave voltages Vsu, Vsv,
Vsw is compared with the triangular wave voltage Vt, and FIG.
(D) The PWM pulse (pulse width modulation pulse) is output. The gate drive circuit 28 includes comparators 25, 26, 27
5 (B), (C) and (D) obtained from FIG. 5 are supplied to the gates (control electrodes) of the first, third and fifth switches Q1, Q3 and Q5, and at the same time, as shown in FIG. C) (D)
The second, fourth and sixth switches Q
2, Q4 and Q6.

The voltage changeover switch 22 has contacts a and b, and is controlled by a signal on an output line 12b of the frequency command value generation and activation controller 12 shown in FIG. 2, and a line 12c is connected to t2 to t3 in FIG. 9D. Ramp voltage obtained during the period, FIG.
The ramp voltage obtained during the period t2 to t3 of 0 (D) is represented by t2 to t2.
sent to the sine wave generator 23 via the contact b only during the period t3,
During the other period, the output of the voltage command value generator 21 is set to the contact a.
Is sent to the sine wave generator 23 via the. In this embodiment, the three-phase sine wave generator 23 comprises a memory and a D / A converter. This memory stores sine wave data of a large number of voltage levels, and sine wave data corresponding to the voltage command value Vn of the voltage command value generator 21 during normal operation and the ramp voltage command value Vs at the time of startup are stored in a line. 9b
At the clock corresponding to the frequency command value Fn of
This is D / A converted, and the voltages Vsu, Vsv,
Vsw. The sine wave generator 23 is connected to the forward rotation command signal line 9b, the reverse rotation command signal line 9c, and the rotation direction information line 12e.
A sine wave is generated at 120-degree intervals in the order of v and Vsw, and a sine wave is generated at 120-degree intervals in the order of Vsw, Vsv, and Vsu during reverse rotation. In this embodiment, as shown in FIG. 5, the gate drive circuit 28 is configured to always apply the PWM pulse to the switches Q1 to Q6 of the respective phases. On the basis of the phase voltage Vsu, the first switch Q1
Control by M pulses, keeping off in the 180-360 degree section, keeping the second switch Q2 off in the 0-180 degree section, performing PWM control in the 180-360 degree section, and setting the third switch Q3 in the 0-180 degree section. Keep off at 120 degree section and 300-360 degree section, PWM control at 120-300 degree section,
The fourth switch Q4 is set in the range of 0 to 120 degrees and 300 to 3
The PWM control is performed in the 60-degree section, the off state is maintained in the 120-300 degree section, and the fifth switch Q5 is turned on in the 0-60 degree section and 2
PWM control is performed in the section of 40 to 360 degrees, kept off in the section of 60 to 240 degrees, and the sixth switch Q6 is kept off in the section of 0 to 60 degrees and 240 to 360 degrees.
PWM control can be performed in the degree section. Further, the time width of the PWM control of the first to sixth switches Q1 to Q6 can be set to 120 degrees. Further, the three-phase sine wave generator 23 is not limited to the above-described embodiment, and can be constituted by, for example, a sine wave generator having a fixed amplitude and a multiplier at the output stage. In this case, a sine wave having a fixed amplitude according to the frequency command is multiplied by the voltage command value to generate a sine wave whose amplitude is controlled.

Frequency command value generation and activation controller 1 shown in FIG.
2 outputs a command value indicating the target frequency f0 given by the line 9a to the line 12a in a steady state, and also starts (transient) during a period t2 to t4 in FIG. 9C.
Frequency command values fs, fa and t2 to t in FIG.
The frequency command values f1, f2, f3 for 5 periods are
The control signal of the switch 22 of FIG. 3 is output on a line 12b, the ramp voltage Vs is output on a line 12c, and the free running control signal is output on a line 12b.
d, and outputs a rotation direction switching signal to a line 12e. That is, when the frequency command value generation and activation controller 12 restarts the normal rotation from the normal rotation coasting state as shown in FIG. T2 in FIG.
The output frequency fs of the inverter at the time of restart during the period from t3 to t3 is determined and sent to the output line 12a.
In the period t3 to t4 in (C), the gradient frequency command value fa for acceleration is transmitted to the line 12a, and after t4 in FIG. 9C, the target frequency command value f0 of the line 9a is changed to the line 12a.
a, and when restarting reverse rotation from normal coasting rotation shown in FIG. 10, the frequency command value f1 corresponding to the detection frequency fm of the line 8a during the period from t2 to t3 in FIG.
Is sent to the line 12a, and t3 to t3 in FIG.
In period t4, the ramp frequency command value f2 for deceleration is applied to line 1
2a, the acceleration gradient frequency command value f3 is sent to the line 12a during the period t4 to t5 in FIG. 10C, and a rotation direction switching signal is output to the line 12e at the time t4 in FIG. is there.

FIG. 4 shows the frequency command value generation and activation controller 12 of FIG. 2 constituted by a microcomputer in detail by analog analogy. The frequency command value generation and activation controller 12 performs first, second, third, fourth, and fifth signal extraction switches 31, 32, 33, 34, 35, a starting frequency generator 36, an OR gate 37, a timer 38, a trigger circuit 39, an RS flip-flop 40, a ramp voltage generator 41, a latch circuit 42, and f / V (frequency / voltage). The converter 43, the forward acceleration frequency generator 44a, the reverse acceleration frequency generator 44b, and the deceleration frequency generator 45
And first, second, and third comparators 46, 47, and 48. 4 will be described in detail later.

In this embodiment, in order to restart the motor 4 smoothly, it is necessary to provide information on the inertial rotation of the motor 4 during the non-driving period of the motor 4, that is, the free-running rotation speed (rotation speed) and the rotation direction. Become. In the present embodiment, the switches Q1 to Q6 of the inverter circuit 3 are controlled to the zero vector state during the inertial rotation, and the output current of the inverter in this state, that is, the input current of the electric motor 4, is detected by the current detectors 6 and 7. The rotation speed and the rotation direction are detected based on the currents Iu and Iw.

First, a method of detecting the rotation speed of the electric motor 4 during the inertial rotation period will be described. The free running detection circuit 13 in FIG. 2 detects that the current of the current detectors 6 and 7 has stopped flowing on the basis of the signal on the line 6a, and outputs a signal indicating that the free running period has started. Give to.

The free running control circuit 14 is based on the output of the free running detection circuit 13 and the signal on the output line 12d of the timer 38 in FIG.
The lower three switches Q2 of the inverter circuit 3 during the period t2
, Q4 and Q6 are simultaneously turned on. The free running control circuit 14
, The switches Q2, Q4, and Q6 can be simultaneously turned on using the PWM control circuit 11.

When the free running control circuit 14 simultaneously turns on all the switches Q2, Q4, Q6 on one side of the inverter circuit 3 during the period from t1 to t2 in FIGS. 9 and 10, a closed circuit as shown in FIG. 6 is formed. You. That is, for the line to which the first current detector 6 is coupled, the first phase winding 4
a-second switch Q2 -fourth diode D4 -second
Closed forward circuit of phase winding 4b, second phase winding 4b-fourth switch Q4-second diode D2-reverse closed circuit of first phase winding 4a, first phase winding 4a-second Switch Q2 −
A forward closed circuit including a sixth diode D6 and a third phase winding 4c, and a reverse closed circuit including a third phase winding 4c, a sixth switch Q6, a second diode D2, and a first phase winding 4a. Is formed. A similar closed circuit is formed in the line to which the second current detector 7 is connected. Here, the output of the first current detector 6 will be described. When the motor 4 is rotating, a voltage is generated in the stator windings 4a to 4c. Therefore, the current detector 6 has a periodicity as illustrated in the period t1 to t2 in FIG. To detect the changing current. The cycle of this current corresponds to the rotation speed of the electric motor 4. Since this current flows while the windings 4a, 4b and 4c are short-circuited by the switches Q2, Q4 and Q6, the current has a relatively large level. The frequency detection circuit 8 of FIG.
The frequency of the current is measured during the period from t1 to t2 in (E) and the period from t1 to t2 in FIG. Since the frequency detected by the frequency detection circuit 8 corresponds to the inertial rotation speed of the electric motor 4, the frequency detection circuit 8 can also be called a rotation speed detection circuit. Note that the frequency detection circuit 8 can also estimate the rotation speed by detecting the inverter output frequency of the electric motor 4 in a normal driving state. The detected frequency fm is sent to the starting frequency generator 36 and the latch circuit 42 in the frequency command value generating and starting controller 12 shown in FIG. This rotation speed detection method has an advantage that the configuration of the detection device is simplified because a rotation type speed sensor is not used. Since the current detectors 6 and 7 are also used as an overcurrent prevention circuit for the inverter circuit 3 and the electric motor 4, the cost does not increase. In this rotation speed detecting method, the switches Q2, Q4, and Q6 on one side of each phase arm of the inverter circuit 3 are simultaneously turned on, and a current based on the free running voltage of the motor 4 is supplied while maintaining this state. Since the frequency of the current is measured, the rotation speed can be detected without the influence of noise based on the ON / OFF of the switches Q1 to Q6. Also, switches Q2, Q4
, Q6 to short-circuit the windings 4a, 4b, 4c and allow current to flow, so that a relatively large current can flow during free running, and the rotational speed can be detected with little influence from disturbance elements such as an AC power line.

The first and second peak detectors 16 and 17 of the rotation direction detection circuit 15 for detecting the rotation direction of the motor 4 during the free running period are provided by the first and second current detectors 6 and 7. It is connected to output lines 6a and 7a.
When the electric motor 4 is coasting in the forward direction (first direction), the detection currents Iu,
Iw flows in the phase relationship shown in FIG. 7A, and when the motor rotates by inertia in the reverse rotation (second direction), the detection currents Iu and Iw of the first and second current detectors 6 and 7 become the same as those in FIG. It flows in the phase relationship shown in FIG. The first and second peak detectors 16 and 17 in FIG. 2 detect the maximum values (positive peaks) of the detection currents Iu and Iw.
FIG. 7 has a detecting means and a minimum value (negative peak) detecting means.
(A) and the sinusoidal detection current Iu shown in FIG.
Iw is shown in FIGS. 7 (B) (C) and 8 (B) (C).
The values are converted into first and second peak detection signals I1 and I2. That is, the period from the positive peak of the detection currents Iu and Iw to the next negative peak (for example, t1 to t3) is low (the first level).
), And the period from the negative peak to the next positive peak (for example, t3 to t5) is high (second level).
(Signals indicating the voltage levels of the signals I1 and I2). In short, the signals I1 and I2 corresponding to the waveforms of the detection currents Iu and Iw shown in FIGS. 7 and 8 formed into a square wave are obtained. Therefore, the signals I1 and I2 may be obtained by shaping the detection currents Iu and Iw into square waves by a zero cross comparator. The phase comparator 18 of FIG. 2 obtains the first and second binary values of FIGS. 7B and 7C or FIGS. 8B and 8C obtained from the first and second peak detectors 16 and 17. Of the peak detection signals I1 and I2 are logically compared. Phase comparator 1
8 detects the direction of rotation of the motor 4, it is not necessary to provide information on the amount of phase difference between the first and second peak detection signals I1 and I2, and as shown in FIG. Rotation direction) state, the current W is determined based on the U-phase detection current Iu.
Whether the detected current Iw of the phase is advanced or the detected current Iw of the W phase is delayed with respect to the detected current Iu of the U phase due to the reverse rotation (second rotation direction) state as shown in FIG. It is only necessary to be able to determine. In this embodiment, FIGS.
During the period from t1 to t2, the switches Q2,
Assuming that Q4 and Q6 are simultaneously turned on to be in the zero vector state, during normal rotation, as shown in FIG.
w advances by 120 degrees, and at the time of reverse rotation, as shown in FIG.
Iw is delayed by 120 degrees with respect to. Therefore, in the present embodiment, the detection of the normal rotation and the reverse rotation based on the first and second peak detection signals I1 and I2 of FIGS. 7B and 7C and FIGS. Alternatively, the second method is used. (1) In the first method, when the first peak detection signal I1 changes from H (high level) to L (low level) (t1, t5, etc.) as shown in FIG. If the signal I2 is L (low level), a signal indicating normal rotation is output from the phase comparator 18, and the first peak detection signal I1 changes from H to L as shown in FIG. t5
When the second peak detection signal I2 is at H, the comparator 18 outputs a signal indicating reverse rotation. (2) In the second method, as shown in FIG. 7, when the first peak detection signal I1 changes from L to H (t3, etc.), the second peak detection signal I2 indicates a normal rotation when it is H. A signal is output from the phase comparator 18 and, when the first peak detection signal I1 changes from L to H as shown in FIG.
When the second peak detection signal I2 is at L, a signal indicating reverse rotation is output from the phase comparator 18. In order to prevent erroneous detection, the first and second peak detection signals I1,
A plurality of phase comparisons are performed in a plurality of periods of I2, and when the same comparison result is obtained in all or a plurality of times or more, the phase comparison unit 18 outputs this as rotation direction information. Of course, if a highly reliable determination can be made by one phase comparison, one phase comparison may be used. The first
And as a variant of the second method, the second peak detection signal I
2, the advance and delay of the first peak detection signal I1 can be determined to detect the rotation direction of the electric motor 4. Further, the phase relationship between the U-phase detection current Iu and the W-phase detection current Iw is determined using a well-known phase comparator used in a PLL circuit or the like that generates an output corresponding to the phase difference between the two,
The state in FIG. 7 may be normal rotation, and the state in FIG. 8 may be reverse rotation. The rotation direction detection signal obtained from the phase comparator 18 shown in FIG. 2 is sent to the deceleration frequency generator 45 in the frequency command value generating and starting controller 12 shown in FIG.

[0024]

[Normal rotation restart method] When the normal rotation drive is stopped at time t0 in FIG. 9 and the motor 4 enters the free running state, the rotation speed N gradually decreases as shown in FIG. 9A. At time t1 during the free running period, as shown in FIG. 9B, when the normal rotation command line 9b changes to a high level indicating the normal rotation command, the normal rotation command is transmitted to the timer 38 via the OR gate 37 in FIG. , And the timer 38 outputs t1 to t2 in FIG.
A pulse indicating a period (Ta) is generated. When a pulse indicating the period of t to t2 is generated from the timer 38, the pulse is sent to the free running control circuit 14 of FIG. 2 via the line 12d. The free running control circuit 14 responds to the fact that the output of the free running detection circuit 13 indicates that the free running period is in the free running period and the line 12d indicates the time period t1 to t2 in FIG. As shown, the switches Q2, Q4, Q6 are simultaneously turned on. As a result, a current flows through the inverter output lines 3a, 3b, and 3c as described above, and the frequency fm indicating the inertial rotation speed is detected by the frequency detection circuit 8 in FIG.
The rotation direction is detected by the rotation direction detection circuit 15 of FIG. The rotation direction detection signal is held by a hold circuit (not shown) until the restart is completed.

When the output pulse of the timer 38 falls from the high level at the time t2 in FIG. 9, the on-control of the switches Q2, Q4, and Q6 by the free running control circuit 14 ends, and at the same time, the trigger circuit 39 in FIG. A signal is generated and flip-flop 40 is triggered. The flip-flop 40 is set during the period from t2 to t3 in FIG. 9, and the switches 31 and 32 are turned on during the period from t2 to t3. The output of the flip-flop 40 is connected to the line 12b.
Is sent to the control terminal of the switch 22 in FIG. 3, and the switch 22 is connected via the contact b to the ramp voltage Vs
To the sine wave generator 23. The ramp voltage generator 41 of FIG.
Generates a ramp voltage Vs in the period from t2 to t3 in FIG. 9D in response to the output of the flip-flop 40. The output of the ramp voltage generator 41 is supplied to the line 12 via the switch 31.
c. The starting frequency generator 36 is connected to the line 9b
9C based on the detected frequency fm of the line 8a in response to the normal rotation command and the output of the flip-flop 40.
The optimum starting frequency fs shown in the period from t3 to t3 is determined and output. It should be noted that the optimum starting frequency fs is
Similarly, the detection frequency fm can be used. This optimum starting frequency fs is sent to the line 12a via the switch 32, and becomes the frequency command value Fn. T2 to t3 in FIG.
In the period Tb, the inverter is driven to generate an output voltage corresponding to the starting voltage Vs shown in FIG. The inverter output frequency during the period from t2 to t3 is maintained at a constant starting frequency fs as shown in FIG.
The rotation speed is also kept substantially constant as shown in FIG.

The time point t 3 in FIG. 9 is determined by the comparator 46. One input terminal of the comparator 46 is connected to the gradient voltage generator 41, and the other input terminal is f / V (frequency
(Voltage) converter 43. f / V converter 43
Converts the output frequency fs of the starting frequency generator 36 into a voltage proportional to this at the time of forward rotation restart, and converts the output frequency f1 of the latch circuit 42 to a voltage proportional thereto at the time of reverse rotation restart. When the output voltage of the f / V converter 43 and the ramp voltage Vs become equal at time t3 in FIG. 9, the output of the comparator 46 is switched, and the flip-flop 40 is reset in response. When the flip-flop 40 is reset, the switches 31 and 32 are turned off, and the ramp voltage Vs
And the supply of the starting frequency fs are stopped. Also,
At time t3, the control of the switch 22 of FIG. 3 by the line 12b is released, and the voltage command generator 21 is connected to the sine wave generator 23 via the contact a of the switch 22.

The forward acceleration frequency generator 44a is connected to the line 9
b, the output of the flip-flop 40 and the starting frequency fs of the starting frequency generator 36 as inputs.
(C) The starting acceleration frequency fa shown in the period Tc from t3 to t4.
Which is sent to the line 12a via the switch 33. That is, the normal rotation acceleration frequency generator 44a sets the gradient voltage Vs to a value corresponding to the starting frequency fs, ie, fs in the V / f constant control, in a state where the normal rotation command is generated.
Starting frequency f in response to the voltage value corresponding to
With s as an initial value, a forward acceleration frequency fa that gradually increases at a predetermined inclination is generated. The forward acceleration frequency fa is sent to the voltage command generator 21 and the sine wave generator 23 shown in FIG. This allows
The rotation speed N of the electric motor 4 smoothly increases toward the target frequency f0 as shown in FIG. Forward acceleration frequency f
The end point t4 of the transmission of a is determined by the comparator 47. The comparator 47 compares the normal rotation acceleration frequency fa with the target frequency f0 of the line 9a, and when they match, controls the switch 33 to be off, and instead controls the switch 35 to be on. As a result, from time t4 in FIG. 9, the target frequency f0 of the line 9a is output as the frequency command value Fn on the line 12a, and the motor 4 rotates at the target rotation speed as shown in FIG. 9A.

[0028]

[Reverse rotation restart method] Next, the reverse rotation restart of FIG. 10 will be described. When the forward drive of the electric motor 4 is stopped at time t0 in FIG. 10, the state shifts to the free running state as in the case of FIG. As shown in FIG. 10 (B), line 9c at time t1
When a reverse rotation command is generated during the period t1 to t2 in FIG.
In the same manner as in the period from t1 to t2 in FIG.
The gate 37, the timer 38, and the free-running control circuit 14 of FIG. 2 operate, and the detection of the frequency fm indicating the rotation speed of the electric motor 4 and the detection of the rotation direction by the rotation direction detection circuit 15 are performed.

In the period from t2 to t3 in FIG. 10, t2 to t3 in FIG.
Similarly to the period t3, the trigger circuit 39, the flip-flop 40, the switches 31, 32, the ramp voltage generation circuit 41, and the switch 22 in FIG. 3 operate. T2 to t3 in FIG.
The difference between the period and the period from t2 to t3 in FIG. 9 is that the starting frequency generator 36 is not operated and the latch circuit 42 is in the operating state. The latch circuit 42 is connected to the set signal of the flip-flop 40 during the period from t2 to t3 in FIG.
Based on the reverse rotation command of c and the detection frequency fm of the line 8a, the detection frequency fm at the time t2 is held and the same control frequency f1 as fm is output. The control frequency f1 is output via the switch 32 to the line 12a as a frequency command in the period from t2 to t3. As a result, the decrease in the rotation speed N of the electric motor 4 shown in FIG. 10A is stopped, and the rotation speed is kept substantially constant during the period from t2 to t3. T2 in FIG. 10 (D)
As shown in the period from t3 to t3, the ramp voltage Vs of the ramp voltage generator 41 gradually rises from zero volts to the voltage V1 similarly to the period from t2 to t3 in FIG. In this embodiment, the slope of the slope voltage Vs is the same between the forward restart of FIG. 9 and the reverse restart of FIG. 10, but the slope voltages Vs having different slopes between FIG. 9 and FIG. Can also be generated. The determination at time t3 in FIG. 10 is the same as the determination at time t3 in FIG. However, in the case of FIG. 10, the f / V converter 43
To the output frequency f1 of the latch circuit 42.

When a signal indicating the time point t3 is generated from the comparator 46 in FIG. 10, the flip-flop 40 is reset, the switches 31 and 32 are turned off, and the ramp voltage generator 41 and the latch circuit 42 are turned off. Further, the switch 22 of FIG. 3 is switched from the contact b to the contact a.
At time t3 in FIG. 10, the deceleration frequency generator 45 operates in synchronization with the reset of the flip-flop 40. The deceleration frequency generator 45 outputs the reverse command of the line 9c and the line 1
The output frequency f1 = fm of the latch circuit 42 is initialized in response to the generation of the signal indicating t3 from the flip-flop 40 when the signal indicating normal rotation during the period t1 to t2 in FIG. As shown in FIG. 10C, a deceleration frequency f2 which gradually decreases at a predetermined gradient as a value is generated. The deceleration frequency f2 generated from the deceleration frequency generator 45 during the period T3 to t4 Tc1 is output to the line 1 via the switch 34.
2a is output as the frequency command value Fn. As a result,
The motor 4 smoothly decelerates by the constant f / V control, and t4
At this point, the rotation speed becomes zero. The time point t4 is determined by the comparator 48. The comparator 48 generates an output indicating that the deceleration frequency f2 has become zero at time t4, controls the switch 34 to be turned off, and controls the reverse rotation acceleration frequency generator 44b to be turned on.

The reversing acceleration frequency generator 44b is provided as shown in FIG.
In FIG. 10 (C), the comparator 48 generates the acceleration frequency f3 during the period T4 to t5, and when the reverse rotation command shown in FIG.
When an output indicating the time point is generated, an acceleration frequency f3 shown in FIG. 10C is generated and transmitted to the line 12a through the switch 33. The output voltage command V0 of the inverter changes in response to the acceleration frequency f3 according to the constant f / V control as shown in FIG. In FIGS. 10 (C) and 10 (D), the frequency and voltage at the time of reverse rotation after t4 are shown on the opposite side from the time of normal rotation. T of the comparator 48
4 The signal indicating the time point, that is, the rotation direction switching control signal is
The signal is supplied to the sine wave generator 23 of FIG. The sine wave generator 23 generates a three-phase sine wave voltage so as to reverse the motor 4 in response to the output of the comparator 48 at time t4 in FIG. 10 during the period when the reverse rotation command is generated on the line 12c. Occur. As a result, the electric motor 4
As shown in (A), the motor rotates in the opposite direction from time t4,
At this point, the frequency reaches the target frequency f0. The detection at the time point t5 in FIG. 10 is performed by the comparator 47 by the coincidence determination between the reverse rotation acceleration frequency f3 and the target frequency f0 in the same manner as the detection at the time point t4 in FIG. The switch 33 is turned off and the switch 35 is turned on by the output of the comparator 47 at the time t5 in FIG. 10, the target frequency f0 of the line 9a is sent out to the line 12a via the switch 35, and the motor 4 outputs the target frequency f0.
Driven by In FIGS. 9 and 10, the target frequency f
After the target rotation speed is obtained by 0, the output frequency of the inverter can be maintained at the target frequency, and the output voltage of the inverter can be reduced to perform high-efficiency operation.

Although switching from normal rotation to reverse rotation has been described with reference to FIG. 10, switching from reverse rotation to normal rotation is performed in the same manner as switching from normal rotation to reverse rotation.

As is clear from the above, the present embodiment has the following advantages. (1) The rotation direction can be easily detected. (2) The rotation speed can be easily detected. (3) Forward rotation restart and reverse rotation restart can be performed easily and smoothly.

[0034]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) The inverter control circuit 5 can be entirely constituted by an analog circuit. (2) The frequency detection circuit 8 is replaced with the peak detection circuit 1 shown in FIG.
It can be configured to count one or both output pulses of 6, 17. (3) Current detectors are provided for all of the three-phase output lines 3a, 3b, and 3c, and the rotation direction can be detected by a combination of two of the three-phase currents. (4) The free running detection circuit 13 can be replaced by a power off detection circuit or a motor stop command circuit. (5) Upper switches Q1, Q3 of the inverter circuit 3
, Q5 are simultaneously turned on to detect the rotation speed and direction during free running. (6) The reverse rotation control can also be performed by switching the order of generation of the control signals applied from the gate drive circuit 28 to the switches Q1 to Q6. (7) The rotation speed can be detected by another means such as a rotation detector.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a control and drive device for an induction motor according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the inverter control circuit of FIG. 1 in detail in principle.

FIG. 3 is a block diagram illustrating a PWM control circuit of FIG. 2 in detail;

FIG. 4 is a block diagram equivalently and in detail illustrating a frequency command value generation and activation controller of FIG. 3;

FIG. 5 is a waveform chart showing a state of each unit in FIG. 3;

FIG. 6 is a circuit diagram showing a circuit at the time of rotation speed and direction detection during free running.

FIG. 7 is a waveform diagram showing a state of each part of the rotation direction detection circuit of FIG. 2 in a normal rotation state.

FIG. 8 is a waveform diagram showing a state of each part of the rotation direction detection circuit of FIG. 2 in a reverse rotation state.

FIG. 9 is a waveform diagram showing a state of each unit in FIG. 1 at the time of normal rotation restart.

FIG. 10 is a waveform chart showing a state of each section in FIG. 1 at the time of reverse rotation restart.

[Explanation of symbols]

 3 Inverter circuit 4 Induction motor 15 Rotation direction detection circuit

Claims (6)

[Claims] 1. The AC motor during a period in which the driving of a polyphase AC motor by a polyphase inverter having a configuration in which a plurality of series circuits of first and second switches are connected between a pair of DC power supply terminals is stopped. And controlling one of the first and second switches of the plurality of series circuits of the multi-phase inverter to be simultaneously on, and at least one of the AC motors at this time. First and second
Detecting the input current of the first phase and comparing the phases of the input current of the first phase and the input current of the second phase to obtain information indicating the direction of coasting rotation of the AC motor. Method for detecting inertial rotation information of an AC motor. 2. A method according to claim 1, wherein a period from a positive peak to a negative peak of the input current of the first and second phases is defined as a first voltage level so as to obtain information on a direction of coasting rotation by comparing the phases. A binary signal having a period from a peak to a positive peak as a second voltage level is formed, and the first signal is formed based on a comparison between the binary signals of the input currents of the first and second phases.
It is determined whether the input current of the second phase is a leading position or a lagging position with respect to the input current of the first phase. When the leading current is the leading phase, the information of the first rotational direction is output. 2. The method for detecting inertial rotation information of an AC motor according to claim 1, wherein information on a second rotation direction opposite to the rotation direction is output. 3. A method of driving a polyphase AC motor by a polyphase inverter having a configuration in which a plurality of series circuits of a first switch and a second switch are connected between a pair of DC power terminals, wherein the motor is a When a drive command in a second rotation direction opposite to the first rotation direction is generated during a drive stop period after driving in the first rotation direction, a rotation speed and a rotation direction in the inertial rotation of the electric motor are detected. And a first frequency command corresponding to an output frequency of the inverter capable of obtaining, after the first step, a rotation speed substantially equal to the rotation speed detected in the first step. A value (f1) is prepared, and the inverter is driven so that an output frequency corresponding to the first frequency command value (f1) is obtained.
In the characteristic diagram showing the relationship between the output frequency and the output voltage for driving the motor by controlling the output frequency and the output voltage of the inverter so that the ratio V / f between the output voltage and the output voltage V becomes constant. The output voltage of the inverter is gradually increased from zero toward the first output voltage value (V1) so that a first output voltage value (V1) corresponding to the first frequency command value (f1) can be obtained. And the output frequency of the inverter becomes the first output voltage value (V1), and the output frequency of the inverter becomes the value corresponding to the first frequency command value (f1). later,
The output frequency command value of the inverter is gradually reduced from the first frequency command value (f1) toward zero, and the output voltage command value of the inverter is also changed to the first output voltage according to the constant V / f control. A third step of gradually lowering the command value from zero toward zero, and setting an output frequency command value of the inverter having a directionality to rotate the motor in the second rotation direction after the third step. The output frequency command value of the inverter is gradually changed toward the output frequency command value and the output voltage command value of the inverter is V / f.
And a fourth step of changing the AC motor in accordance with a constant control. Detecting the rotation direction in the inertial rotation, controlling one of the first and second switches of the plurality of series circuits of the polyphase inverter to be simultaneously turned on; At least first and second AC motors;
Detecting the input current of the first phase and comparing the phase of the input current of the first phase with the input current of the second phase to obtain information indicating the direction of coasting rotation of the AC motor. 3
A method for driving an AC motor using the inverter described in the above. 5. The method according to claim 5, wherein detecting the rotation speed in the inertial rotation includes controlling one of the first and second switches of the plurality of series circuits of the polyphase inverter to be simultaneously turned on. The inverter according to claim 4, wherein the input current of the AC motor is detected, a cycle or a frequency of the detected input current is measured, and the cycle or the frequency is obtained as rotational speed information of the inertial rotation of the AC motor. Driving method of AC motor. 6. The AC motor during a period in which the driving of the polyphase AC motor by the polyphase inverter having a configuration in which a plurality of series circuits of the first and second switches are connected between a pair of DC power supply terminals is stopped. A first and a second current detector for detecting input currents of at least a first and a second phase of the AC motor; and stopping the driving of the AC motor. Control means for simultaneously turning on one of the first and second switches of the plurality of series circuits of the multi-phase inverter, and a period during which the driving of the AC motor is stopped. In which the phases of the input currents of the first and second phases of the AC motor obtained from the first and second current detectors are compared to output information indicating the direction of coasting rotation of the AC motor. An inertia rotation information detection device for an AC motor, comprising: a comparison unit.