JP4488409B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device that can restart an induction motor without using a speed detector.

  When an induction motor that is rotating without being driven by an inverter is restarted by the inverter, the frequency, phase, and amplitude of the supplied inverter output voltage are set to the rotation frequency, residual voltage phase, and amplitude of the induction motor that is in a free rotation state. It is necessary to match. If there is a difference in the phase and amplitude of the voltage, an excessive current flows through the inverter, and if there is a difference in the frequency, an impact torque is applied to the electric motor, or an excessive regenerative current flows from the electric motor to the inverter.

  Conventionally, as a method of calculating the rotation frequency, voltage phase, and amplitude of an electric motor, there is a method of detecting the rotation frequency, residual voltage phase from the residual induced voltage of the electric motor. Since the induction motor generates an AC voltage having a rotation frequency by rotating the magnetic flux remaining in the iron core even when the power is cut off, the rotation speed can be detected by using this residual voltage (see, for example, Patent Document 1). ).

In addition, a method has been proposed in which after the residual voltage disappears, the number of rotations of the motor is estimated by adjusting the primary frequency so that the torque current flowing with respect to the applied voltage becomes zero. (
For example, see Patent Document 2. ).
JP-A-8-331892 (page 4-5, FIG. 1) JP 2002-369597 A (page 3-4, FIG. 1)

  However, in the method disclosed in Patent Document 1, since the residual voltage of the induction motor disappears in a very short time, the time when the power supply to the inverter is cut off is long, or the induction motor is rotated by another device. Could not be applied.

  Further, in the method disclosed in Patent Document 2, after estimating the number of revolutions of the motor during free run, the frequency of the inverter is fixed to a frequency corresponding to the estimated number of revolutions, and the voltage is returned to normal operation. Yes. In this way, since the frequency and voltage are restored separately, it takes time to restart, and when the motor speed changes after fixing the frequency, it is not possible to cope with this, and overcurrent There was a risk that regenerative current would flow. In addition, although the torque current of the induction motor is controlled to 0, the actual power conversion device and the induction motor have an electrical and mechanical loss, and the rotor magnetic flux position at the time of starting is unknown. The detection itself is difficult and the error of speed estimation becomes large.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a power converter capable of preventing overcurrent and regenerative overvoltage and restarting an induction motor in a short time without shock.

  To achieve the above object, a power converter according to the present invention converts an AC input into an AC output of variable frequency and variable voltage to drive an induction motor, and controls the output of the power converter. The control unit includes a current detection unit that detects an input current of the induction motor, and the control unit adjusts a ratio between the frequency and the output voltage, and a frequency adjustment unit that adjusts a frequency reference signal to be supplied to the AC motor. V / f ratio adjusting means, a voltage control means for calculating a voltage command by a product of the frequency obtained from the frequency adjusting means and the V / f ratio, and controlling the terminal voltage of the AC motor, and the current detecting means Means for calculating an effective current having the same phase as the voltage command from the detected current, and when starting or restarting the induction motor, the frequency in the V / f ratio adjusting means is a predetermined initial value. The wave number and V / f ratio are set to a predetermined initial V / f ratio. When the effective current is within a predetermined power running threshold range from a predetermined regeneration threshold value, the V / f ratio is increased by a predetermined V / f ratio increasing method. When the effective current is less than or equal to a predetermined regeneration threshold or greater than or equal to the power running threshold, the V / f ratio is maintained, and a predetermined frequency adjustment method is used from the difference between the effective current and the predetermined regeneration threshold or power running threshold. The output frequency is adjusted, and when the V / f ratio reaches a predetermined value, the frequency adjustment is finished, and then the frequency and voltage are controlled according to the frequency reference signal given from the adjusted frequency, It is characterized by shifting to the operation mode.

  According to the present invention, it is possible to provide a power conversion device that can prevent overcurrent and regenerative overvoltage and restart the induction motor in a short time without shock regardless of whether the induction motor is stopped or rotating.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram of a power conversion apparatus according to Embodiment 1 of the present invention.

  The power converter 2 supplied with the three-phase AC voltage from the AC power source 1 converts this AC into a three-phase AC voltage having an arbitrary frequency / voltage amplitude based on the voltage command given from the controller 3, and the AC Electric power is supplied to the induction motor 4.

  Hereinafter, the internal configuration of the controller 3 will be described. The controller 3 has two operation modes, a normal mode and a startup mode. First, the configuration corresponding to the operation in the normal mode will be described.

  In the normal mode, the motor frequency reference fset provided from the frequency setter 5 is set to have an appropriate acceleration / deceleration rate by the rate unit 6A, and the internal frequency reference f * is obtained as an output thereof. The internal frequency reference f * is multiplied by the V / f ratio Φset set by the V / f ratio setting unit 7 by the multiplier 8 to obtain a voltage reference V *. On the other hand, the integrator 8A integrates the internal frequency reference f * to obtain the phase angle θ, and the voltage reference Vu, Vv and Vw of each phase is calculated by the amplitude phase three-phase converter 10A from the voltage reference V * and the phase angle θ. These are given to the power converter 2.

  Next, a configuration corresponding to the operation in the start mode will be described. In the start-up mode, the instantaneous currents Iu, Iv, and Iw detected by the current detectors 9u, 9v, and 9w are converted into the same phase as the instantaneous values Vu, Vv, and Vw of each phase voltage reference by the current conversion circuit 10B. The effective current Ir and the reactive current Ii delayed by 90 ° from the voltage are obtained by calculation. A frequency conversion amount obtained by integrating the difference amount between the effective current Ir and the power running current set value Irp set by the power running current setter 11A by the integrator 8B, and the frequency initial value set by the frequency initial value offset circuit 15 The frequency correction amount fc is calculated by adding the value fos. During the start-up mode, the output of the rate device 6A is replaced with the frequency correction amount fc by the changeover switch 14A, and this is set as the internal frequency reference f *.

  On the other hand, when the start mode is started, the rate device 6B sets the initial value of the rate output Φ ^ to 0, selects this signal by the changeover switch 14B, and starts operation at the V / f ratio Φ * = 0. After the start of operation, the comparator 12 compares the effective current Ir detected by the current conversion circuit 10B, the regenerative current set value Irn set by the regenerative current setter 11B, and the powering current set value Irp set by the powering current setter 11A. If the effective current Ir is between the regenerative current set value Irn and the power running current set value Irp, the value of the rate output Φ ^ is increased by the rate device 6B at a predetermined rate. Further, when the detected effective current Ir is smaller than the regenerative current set value Irn and larger than the power running current set value Irp, the value of the rate output Φ ^ is held. Here, the rate unit 6B is set to a rate setting that increases the rate output Φ ^ in a time corresponding to the secondary time constant of the motor, for example.

  When the value of the rate output Φ ^ coincides with Φset set by the V / f ratio setter 7, the start mode end determination circuit 13 ends the start mode and switches the switches 14A and 14B to the normal mode side. By this switching, the frequency reference fc at the end of the start-up mode shifts to the normal mode in which the rate follows the frequency reference fset given by the frequency setting unit 5.

  The operation in the configuration described above will be described below.

  FIG. 2 is an operation time chart when the initial frequency fos of the frequency initial value offset circuit 15 is set to the maximum usable frequency of the induction motor 4 and restarted at t = 0. In the operation time chart of FIG. 2, time transitions of the internal frequency reference f *, the V / f ratio Φ *, the voltage reference V *, the effective current Ir, and the motor torque T of the AC motor 4 are shown.

  First, in the region 1 shown in FIG. 2, the V / f ratio Φ * is increased at a predetermined rate until the effective current Ir reaches the powering current set value Irp as described above. At the same time, the adjustment of the internal frequency reference f * is started so that the effective current Ir matches the powering current set value Irp.

  When the effective current Ir coincides with the power running current set value Irp, the process shifts to the region 2. After the effective current Ir exceeds the power running current set value Irp, only the adjustment of the internal frequency reference f * is performed while maintaining the V / f ratio Φ *. I do.

  When the internal frequency reference f * and the rotation frequency of the induction motor 4 approach each other due to the above frequency adjustment, the region shifts to the region 3, and the effective current Ir decreases and is controlled to the power running current set value Irp, while the V / f ratio is changed. Increase to a predetermined value.

  When the V / f ratio reaches a predetermined rated value, the process proceeds to region 4 and the start mode end determination circuit 13 operates to switch to the normal operation mode. In the region 4, the rate operation follows the frequency command fset for the induction motor set by the frequency setting unit 5.

  In this way, by setting the maximum use frequency of the induction motor 4 as the initial frequency fos, the primary frequency given to the induction motor 4 becomes higher than the rotation frequency and always restarts in a power running state. Thereby, even when the power converter 2 does not have a power regeneration capability, the rotating motor can be restarted stably. Moreover, since it restarts, supplying electric power to the induction motor 4, it is effective when it is desired to suppress the speed reduction as much as possible.

  FIG. 3 is an operation time chart when the induction motor 4 is stopped and restarted under the same conditions as in FIG. The operation time chart of FIG. 3 shows time transitions of the internal frequency reference f *, the V / f ratio Φ *, the voltage reference V *, and the effective current Ir. Even when the induction motor 4 is stopped, an effective current Ir proportional to the difference between the primary frequency and the rotation frequency (slip frequency) flows, so that it can be restarted by performing the same control as in FIG. .

  However, in this case, the internal frequency reference f * is adjusted from the maximum value to 0 even though the induction motor is stopped, and then the V / f ratio is increased at a constant rate and then the normal mode is entered. Accelerates, so it takes longer to complete the restart.

  FIG. 4 is an operation time chart when the initial frequency fos of the frequency initial value offset circuit 15 is set to 0 and restarted at t = 0. In the operation time chart of FIG. 4, time transitions of the internal frequency reference f *, the V / f ratio Φ *, the voltage reference V *, and the effective current Ir are shown.

  In FIG. 4, in the region 1, the regeneration mode is set, and the V / f ratio is increased at a predetermined rate until the effective current Ir reaches the regeneration current set value Irn. At the same time, the adjustment of the internal frequency reference f * is started so that the effective current Ir matches the regenerative current set value Irn.

  When the effective current Ir coincides with the regenerative current set value Irn, the process proceeds to the region 2, and after the effective current falls below the regenerative current set Irn, only the adjustment of the internal frequency reference f * is performed while maintaining the V / f ratio.

  When the internal frequency reference f * and the rotation frequency of the induction motor 4 approach each other due to the frequency adjustment, the process shifts to the region 3, and the effective current Ir increases and is controlled to the regenerative current set value Irn, while the V / f ratio is changed. Increase to a predetermined value.

  When the V / f ratio reaches a predetermined rated value, the process proceeds to region 4 and the start mode end determination circuit 13 operates to switch to the normal operation mode. In the region 4, the rate operation follows the frequency command fset for the induction motor set by the frequency setting unit 5.

  FIG. 5 is an operation time chart when the induction motor 4 is stopped and restarted under the same conditions as in FIG. The operation time chart of FIG. 5 also shows time transitions of the internal frequency reference f *, the V / f ratio Φ *, the voltage reference V *, and the effective current Ir.

  In this case, since there is no difference (slip frequency) between the primary frequency applied to the induction motor 4 and the rotation frequency of the induction motor 4 after the start of the power converter 2, no effective current Ir is generated. Therefore, in the case of FIG. 5, the operation time chart from the region 3 in FIG. 4 is obtained. In this way, when the induction motor 4 is restarted from the stopped state when the initial frequency fos is 0, the time for adjusting the internal frequency reference f * corresponding to the region 2 is unnecessary compared with the case of FIG. It becomes possible to start with.

  However, when the induction motor 4 is restarted during rotation as shown in FIG. 4, it is necessary to flow a regenerative current. Therefore, when the power converter 2 does not have a regenerative capability, there is a possibility that a DC overvoltage is generated. Therefore, for a power converter that does not have regenerative capability, after setting the initial frequency fos to 0, if the active current Ir is detected on the positive side, it is determined to be in a stopped state and is started as it is. If it is detected on the negative side, the start-up time can be shortened by immediately resetting the initial frequency fos to the maximum use frequency of the induction motor 4.

  The V / f ratio rate unit 6B in the startup mode increases at a predetermined rate, but a method of automatically adjusting the rate gradient as described below is also conceivable.

The reactive current Ii is generated in an amount proportional to the differentiation of V / f ratio = Φ as shown in the following equation (1). Here, Lm represents the excitation inductance of the induction motor 4, L2 represents the inductance of the rotor of the induction motor 4, and R2 represents the resistance of the rotor of the induction motor 4.
Ii = Φ / Lm + L2 / (Lm × R2) × dΦ / dt (1)
Therefore, if the rate increase rate of the V / f ratio is increased so that the reactive current Ii does not become excessive according to the equation (1), it is possible to shift to the normal operation mode in a short time without flowing a large current.

  According to the present invention, the control is basically started with the V / f ratio at start-up being 0, that is, V = 0 at any frequency f. The induction motor 4 can be smoothly restarted by the power converter 2 without generating a large current. Further, by adjusting the internal frequency reference f *, that is, the output frequency of the power converter 2 while controlling the effective current Ir within a predetermined range, the effective power is reduced and no shock is applied to the induction motor 4. By adjusting the output frequency while increasing the V / f ratio so as to be a predetermined amount during normal operation, it is possible to shift to the normal operation state in the shortest time. This is effective regardless of whether the induction motor 4 is rotating or stopped. Conversely, if the power running current set value Irp, that is, the threshold of the effective current Ir is set high, the induction motor 4 can be restarted while applying desired power and torque, so that the reduction in the speed of the induction motor 4 can be suppressed. It becomes possible.

  FIG. 6 is a circuit configuration diagram of the power conversion device according to the second embodiment of the present invention. About each part of this Example 2, the same part as each part of the power converter device which concerns on Example 1 of FIG. 1 is shown with the same code | symbol, and the description is abbreviate | omitted. The second embodiment differs from the first embodiment in that instead of the current conversion circuit 10B, the power running current setter 11A, and the regenerative current setter 11B, the instantaneous power calculation circuit 16, the power running power setter 17A, and the regenerative power setter 17B. This is the point.

  The instantaneous power calculation circuit 16 calculates the instantaneous active power P by calculation from the instantaneous currents Iu, Iv and Iw detected by the current detectors 9u, 9v and 9w and the phase voltage references Vu, Vv and Vw. A frequency conversion amount obtained by integrating the difference amount between the instantaneous active power P and the power running power set value Pp set by the power running power setter 16A by the integrator 8B, and the frequency initial value set by the frequency initial value offset circuit 15 The frequency correction amount fc is calculated by adding the value fos. During the start-up mode, the changeover switch 14A replaces the output of the rate device 6A with this frequency correction amount fc, and this is used as the internal frequency reference f *, as in the first embodiment.

  Similarly to the case of the first embodiment, when the start mode is started, the rate device 6B sets the initial value of the rate output Φ ^ to 0, selects this signal by the changeover switch 14B, and the V / f ratio Φ * = Start at 0. After the start of operation, the instantaneous active power P detected by the instantaneous power calculation circuit 16 is compared with the regenerative power set value Pn set by the regenerative power setter 17B and the power running power set value Pp set by the power running power setter 17A. When the instantaneous active power P is between the regenerative power set value Pn and the power running power set value Pp, the value of the rate output Φ ^ is increased by the rate unit 6B at a predetermined rate. When the detected instantaneous active power P is smaller than the regenerative power set value Pn and larger than the power running power set value Pp, the value of the rate output Φ ^ is held.

Note that the instantaneous power calculation circuit 15 obtains the instantaneous active power P by the following equation (2) under the condition that the output of the power converter 2 is three-phase balanced.
P = Vu × Iu + Vv × Iv + Vw × Iw (2)
By controlling the instantaneous effective power P to the minimum, it is possible to restart with a minimum shock applied to the induction motor 4 as in the case of the first embodiment.

  A power converter according to Embodiment 3 of the present invention will be described with reference to FIGS. FIG. 7 is a circuit configuration diagram of the power conversion device according to the third embodiment of the present invention. About each part of this Example 3, the same part as each part of the power converter device which concerns on Example 1 of FIG. 1 is shown with the same code | symbol, and the description is abbreviate | omitted. The third embodiment is different from the first embodiment in that the current conversion circuit 10B, the power running current setting device 11A, the regenerative current setting device 11B, the current detectors 9u, 9v, and 9w are replaced with a direct current voltage detector 18 and a direct current. The voltage setting device 19 is provided.

  FIG. 8 is an internal configuration diagram illustrating an example of the power converter 2 according to the third embodiment of the present invention. As shown in FIG. 8, the third embodiment is directed to a configuration in which a non-regenerative DC power supply circuit 20 such as a diode converter is connected to an inverter circuit 22 via a smoothing capacitor 21 as the power converter 2.

  In FIG. 7, the calculation of the frequency correction amount fc in the startup mode is obtained as follows. That is, using the DC voltage Vdc detected by the DC voltage detector 18 and the DC voltage setting value Vset set by the DC voltage setting device 19, a frequency conversion amount obtained by integrating the difference between the two by the integrator 8B and the frequency initial value The frequency correction amount fc is obtained by adding fos. In the case of the third embodiment, the frequency initial value fos of the frequency initial value offset circuit 15 is set to zero.

  Thus, when the initial frequency value fos of the initial frequency offset circuit 15 is 0, the rotational frequency of the induction motor is always higher than the primary frequency, and the rotational energy of the induction motor 4 flows into the power converter 2. At this time, as shown in FIG. 8, if the power converter 2 does not have a regeneration function, energy is stored in the smoothing capacitor 21 and the DC voltage across the smoothing capacitor 21 rises. This DC voltage rise is detected by the DC voltage detector 18 and the excess from the DC voltage level setter 19 is integrated to correct the frequency correction amount fc, thereby suppressing the DC overvoltage and suppressing the internal frequency reference f *. Can be quickly adjusted to the rotational frequency of the induction motor 4.

  As described above, even when the DC voltage of the power converter 2 is used for the control at the time of restart, the shock applied to the induction motor 4 can be minimized and restarted as in the case of the first embodiment.

  In FIG. 8, an example of a two-level conversion circuit is shown. However, if the DC power supply circuit does not have a regenerative function even in a three-level configuration or a configuration in which a single-phase inverter is connected in multiple stars, An effect is obtained.

  FIG. 9 is a circuit configuration diagram of the power conversion device according to the fourth embodiment of the present invention. About each part of this Example 4, the same part as each part of the power converter device which concerns on Example 1 of FIG. 1 is shown with the same code | symbol, and the description is abbreviate | omitted. The fourth embodiment is different from the first embodiment in that output voltage detectors 23u, 23v, and 23w that detect the output voltage of the power converter 2, and a voltage amplitude V_f and a frequency f_f at the time of restart are calculated by receiving this output. A PLL (Phase Locked Loop) circuit 24 is provided, and an initial value of the magnetic flux rate unit 6B in the start mode is set to a value obtained by dividing the voltage amplitude V_f calculated by the PLL circuit 24 by the frequency f_f. The calculated frequency f_f is replaced with the frequency initial value fos of the frequency initial value offset circuit 15.

  FIG. 10 is an operation time chart of the fourth embodiment. The operation time chart of FIG. 10 shows time transitions of the internal frequency reference f *, the V / f ratio Φ *, the voltage reference V *, and the effective current Ir.

  As shown in FIG. 10, the internal frequency reference f * at the time of restart coincides with the frequency f_f calculated by the PLL circuit 24, that is, the rotational frequency of the induction motor 4, and the voltage reference V * at the time of restart is the PLL circuit. 24 coincides with the voltage amplitude V_f calculated in 24. Accordingly, the adjustment of the region 3 is performed directly from the time of activation, and it is possible to reach the V / F ratio in the normal mode in a short time.

  Even when the residual voltage of the induction motor 4 is detected using the output voltage detection circuits 23u, 23v and 23w and the rotation frequency of the induction motor 4 is obtained, if the V / f ratio is output at the rated value from the beginning, The rush current to the induction motor is generated from the voltage difference. According to this method, the V / f ratio at the time of restart is set to the detected voltage / frequency ratio, so the rush current at the time of restart is set. Does not occur.

  When the induction motor 4 is rotated by a mechanical load or the like and its rotation frequency is known in advance, or when the induction motor 4 is restored after a power failure, the rotation frequency of the induction motor 4 can be detected or estimated by some means. In this case, by setting the frequency as an initial value at the time of restarting, the time for the region 1 and the region 2 can be greatly shortened.

  As described above, according to the power conversion device of the fourth embodiment of the present invention, the shock applied to the induction motor can be minimized and restarted in a shorter time as in the case of the first embodiment. Become.

  In the above description, the description has been made centering on the case of restarting. However, it goes without saying that the power conversion device according to the present invention is not necessarily limited to restarting but can also be applied during normal startup. .

The circuit block diagram of the power converter device which concerns on Example 1 of this invention. The operation | movement time chart when starting by making the frequency initial value into the maximum in Example 1 of this invention. FIG. 5 is an operation time chart when the frequency initial value is maximized and the engine is started from a rotational speed of 0 in Embodiment 1 of the present invention. FIG. FIG. 5 is an operation time chart when starting with the frequency initial value set to 0 in Embodiment 1 of the present invention. FIG. FIG. 3 is an operation time chart when the initial frequency is set to 0 and the engine is started from a rotational speed of 0 in Embodiment 1 of the present invention. The circuit block diagram of the power converter device which concerns on Example 2 of this invention. The circuit block diagram of the power converter device which concerns on Example 3 of this invention. The circuit block diagram of the power converter of the power converter device which concerns on Example 3 of this invention. The circuit block diagram of the power converter device which concerns on Example 4 of this invention. The operation | movement time chart of the power converter device which concerns on Example 4 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 AC power supply 2 Power converter 3 Controller 4 Induction motor 5 Frequency setting device 6A, 6B Rate device 7 V / f ratio setting device 8A, 8B Integrator 9u, 9v, 9w Current detector 10A Amplitude phase three phase converter 10B Current conversion circuit 11A Power running current setter 11B Regenerative current setter 12 Comparator 13 Start mode end determination circuit 14A, 14B Switch 15 Frequency initial value offset circuit 16 Instantaneous power calculation circuit 17A Power running power setter 17B Regenerative power setter 18 DC Voltage detector 19 DC voltage setting device 20 DC power supply circuit 21 Smoothing capacitor 22 Inverter circuits 23u, 23v, 23w Voltage detector 24 PLL circuit

Claims (10)

A power converter that drives an induction motor by converting AC input into AC output of variable frequency and variable voltage;
A control unit for controlling the output of the power converter;
A current detecting means for detecting an input current of the induction motor;
The controller is
A frequency adjusting means for adjusting a frequency reference signal to be given to the AC motor;
A V / f ratio adjusting means for adjusting a ratio between the frequency and the output voltage;
A voltage control means for calculating a voltage command by a product of the frequency obtained from the frequency adjusting means and a V / f ratio, and controlling a terminal voltage of the induction motor;
Means for calculating an effective current in phase with the voltage command from the current detected by the current detection means;
When starting or restarting the induction motor,
The frequency in the V / f ratio adjusting means is a predetermined initial frequency, the V / f ratio is a predetermined initial V / f ratio,
When the effective current is within a range from a predetermined regeneration threshold to a predetermined powering threshold, the V / f ratio is increased by a predetermined V / f ratio increasing method,
When the effective current is less than or equal to a predetermined regeneration threshold or greater than or equal to the power running threshold, the V / f ratio is maintained, and the output frequency is adjusted by a predetermined frequency adjustment method from the difference between the effective current and the predetermined regeneration threshold or power running threshold. Adjust
The frequency adjustment is terminated when the V / f ratio reaches a predetermined value, and then the frequency and voltage are controlled in accordance with the frequency reference signal given from the adjusted frequency to shift to the normal operation mode. The power converter characterized by this. A power converter that drives an induction motor by converting AC input into AC output of variable frequency and variable voltage;
A control unit for controlling the output of the power converter;
A current detecting means for detecting an input current of the induction motor;
The controller is
A frequency adjusting means for adjusting a frequency reference signal to be given to the AC motor;
A V / f ratio adjusting means for adjusting a ratio between the frequency and the output voltage;
A voltage control means for calculating a voltage command by a product of the frequency obtained from the frequency adjusting means and a V / f ratio, and controlling a terminal voltage of the induction motor;
Means for calculating instantaneous active power from the current detected by the current detection means and the voltage command;
When starting or restarting the induction motor,
The frequency in the V / f ratio adjusting means is a predetermined initial frequency, the V / f ratio is a predetermined initial V / f ratio,
When the instantaneous active power is within a predetermined power running threshold range from a predetermined regeneration threshold, the V / f ratio is increased by a predetermined V / f ratio increasing method,
When the instantaneous active power is less than or equal to a predetermined regeneration threshold or greater than or equal to a power running threshold, the V / f ratio is maintained and output by a predetermined frequency adjustment method from the difference between the instantaneous active power and the predetermined regeneration threshold or power running threshold. Adjust the frequency,
The frequency adjustment is terminated when the V / f ratio reaches a predetermined value, and then the frequency and voltage are controlled according to the frequency reference signal given from the adjusted frequency to shift to the normal operation mode. The power converter characterized by having made it. A non-regenerative type power converter that converts an AC input into an AC output of variable frequency and variable voltage and drives an induction motor;
A control unit for controlling the output of the power converter;
DC voltage detection means for detecting the DC voltage of the power converter,
The controller is
A frequency adjusting means for adjusting a frequency reference signal to be given to the AC motor;
A V / f ratio adjusting means for adjusting a ratio between the frequency and the output voltage;
Voltage control means for calculating a voltage command by the product of the frequency obtained from the frequency adjusting means and the V / f ratio, and for controlling the terminal voltage of the induction motor;
When starting or restarting the induction motor,
The frequency in the V / f ratio adjusting means is a predetermined initial frequency, the V / f ratio is a predetermined initial V / f ratio,
When the detected value by the DC voltage detecting means is within a predetermined DC voltage set value, the V / f ratio is increased by a predetermined V / f ratio increasing method,
When the detected value by the DC voltage detecting means is equal to or greater than a predetermined DC voltage set value, the V / f ratio is maintained and a predetermined value is determined from the difference between the detected value by the DC voltage detecting means and the predetermined DC voltage set value. Adjust the output frequency with the frequency adjustment method of
The frequency adjustment is terminated when the V / f ratio reaches a predetermined value, and then the frequency and voltage are controlled according to the frequency reference signal given from the adjusted frequency to shift to the normal operation mode. The power converter characterized by having made it.   The power converter according to any one of claims 1 to 3, wherein the initial V / f ratio is set to zero.   In the frequency adjustment method, an amount proportional to a difference between the active current or instantaneous active power and the predetermined regeneration threshold or powering threshold is integrated and an amount converted into a frequency is added to the initial frequency for adjustment. The power converter according to claim 1 or 2, wherein The initial frequency is 0,
The power converter according to claim 3, wherein an amount obtained by integrating an amount proportional to the frequency and converted into a frequency is added to the initial frequency for adjustment.   The power converter according to claim 1, wherein the initial frequency is a maximum usable frequency of the induction motor. The initial frequency is 0,
The electric power according to claim 1 or 2, wherein when the active current or instantaneous active power at the time of starting or restarting is negative, the initial frequency is replaced with an operating maximum frequency operation of the induction motor. Conversion device.   The power conversion apparatus according to claim 1, wherein the V / f ratio increasing method increases the rate of V / f ratio increase in inverse proportion to the reactive current. Furthermore, it has voltage detection means for detecting the frequency of the alternating voltage of the induction motor and its voltage amplitude,
The initial frequency is a frequency detected by the voltage detection means,
4. The power converter according to claim 1, wherein the initial V / f ratio is a ratio of a voltage amplitude and a frequency detected by the voltage detection unit. 5.

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