JPH07107785A - Inverter apparatus - Google Patents

Abstract

PURPOSE:To promptly reach a command frequency by a method wherein, when a load current exceeds a limit value and a pulse-width modulated voltage which corresponds to the frequency and the phase of a residual voltage at the restart of the supply of electric power is not output, the progress of a phase is stopped. CONSTITUTION:An apparatus is constituted in such a way that a signal S2 which permits the progress stop of a phase for a pulse-width modulated voltage from a main control circuit 10 is formed, that an AND circuit 17 for the signal S2 and an overcurrent-judgment signal S1 is installed and that the logical product S3 of the overcurrent-judgment signal S1 by the signal S3 is supplied to an integrator 11. Then, when synchronization is turned on from an inverter-output stop state, a voltage- command value V*, a frequency-command value f* and an initial-phase command value theta0 are outputted from the main control circuit 10, the signal S2 which permits the progress stop of the phase for the pulse-width modulated voltage is turned off simultaneously, and the progress of a phase for the integrator 11 is not stopped by the overcurrent-judgment signal S1. As a result, it is possible to prevent an overcurrent at the turning-on of the synchronization from being moved to a regenerative state, and the residual current for an induction motor can be synchronized smoothly with an inverter output voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device used for variable speed operation of an induction motor, and more particularly, when the power supply is restarted at the time of power recovery after a momentary power failure or directly driven by a commercial power source. The present invention relates to an inverter device capable of suppressing overcurrent when switching to driving by the output of the inverter device.

[0002]

2. Description of the Related Art When the drive induction motor is in a free-run state due to a momentary power failure of the power source of the inverter device, the inverter section is stopped, or when the induction motor is switched from operating with commercial power to operating with inverter, When the induction motor is disconnected and the induction motor is in the free running state, the induction motor is restarted by the inverter device. Various methods have been proposed for restarting the induction motor, but here, the synchronous closing method will be described together with the overcurrent suppressing circuit.

FIG. 3 shows a circuit configuration of a conventional inverter device. In the figure, the AC power from the AC power supply 1 is rectified by the rectifier circuit 2 and smoothed by the capacitor 3. The smoothed DC voltage is supplied to the inverter unit 4 including a three-phase bridge circuit formed of switching elements and diodes. The inverter unit 4 is connected to the induction motor 5 as a load and outputs AC power to the induction motor 5.

As the overcurrent suppressing circuit of the inverter device, the circuit disclosed in Japanese Patent Laid-Open No. 4-49866 is used. The current detector 6 detects the load current, and the current detection circuit 7 outputs the absolute value I _m of the current. Comparison circuit 9
Is to compare the limit value I _m set by the current setter 8 with the detected current I _m . The main controller 10 outputs the voltage command value V ^* , the frequency command value f ^*, and the initial phase command θ _o of the inverter device, and the integrator 11 outputs the initial phase command θ.
_The frequency command value f ^* is integrated with _o as the initial value, and the voltage phase command θ ^* is output. The pulse width modulation unit 12 receives the voltage phase command θ ^* and the voltage command value V ^* , and turns on / off the switching elements of the inverter unit 4 signals S _u , S _v , S.
form _w . The reflux state forming circuit 13 is a circuit that turns on the upper half or the lower half of the switching element of the three-phase bridge to convert it into a signal that forms a reflux state. The drive circuit 14 controls ON / OFF of the inverter unit 4 based on the signals S _u ′, S _v ′, and S _w ′ output from the reflux state forming circuit 13.

Next, the operation of the overcurrent suppressing circuit will be described. If the load current increases for some reason during operation of the induction motor 5 and the detected current I _m exceeds the limit value I _o at the voltage phase θ ₁ , for example, the comparison circuit 9 outputs the overcurrent determination signal S ₁ , which is It is supplied to the reflux state forming circuit 13 and the integrator 11. Then, the integrator 11 stops the integrating operation, stops the progress of the voltage phase θ ^* at θ ₁ , and the reflux state forming circuit 13 switches the switching element of the inverter unit 4 to the reflux state, thereby supplying the external power to the induction motor 5. Substantially cut off to suppress increase in current. When the detected current I _m recovers below the limit value I _o , the overcurrent determination signal S ₁
Disappears, the switching element is released from the reflux state, and the integrator 11 restarts the integration of the frequency command value f ^* .

Next, the operation of the synchronization input will be described. The residual voltage detection circuit 15 including a transformer or a photocoupler detects the residual voltage of the induction motor 5 in the free running state, and the synchronous closing control unit 16 detects the residual voltage cycle S.
Propagate ₄ . The synchronization closing control unit 16 calculates the frequency f _* and the synchronization closing phase S ₅ at the time of synchronization input from the cycle of the residual voltage, and transmits it to the main control unit 10.

[0007]

As described above, by the synchronous closing, the induction motor 5 starts to be supplied with electric power that exactly matches the frequency and phase of the induced voltage at that time, and no overcurrent occurs. However, the load fluctuation of the induction motor 5, may not match the frequency and phase due to an error of the output frequency instruction f ^* and the synchronous actuation phase command S ₅ of the synchronous input control unit 16, the magnitude of the output voltage is too large than the residual voltage Then, an overcurrent may flow. At this time, when the detected current I _m in FIG. 3 exceeds the limit value I _o , the inverter unit 4
The switching element is switched to the return state to suppress the increase of the current, and at the same time, the integration of the voltage phase θ ^* is stopped to stop the advance of the phase of the pulse width modulation voltage.

FIG. 4 shows a time chart at this time.
(A) shows the overcurrent discrimination signal S ₁ , (b) shows the voltage phase θ ^* as SINθ ^* , (c) shows the frequency command f ^* , and (d) shows the slip S of the induction motor. is there. During operation at a constant synchronous speed, when the overcurrent determination signal S ¹ is on, the phase θ ^* of the pulse width modulation voltage is stopped from progressing so that the phase of the induced voltage of the induction motor is delayed and the slip S becomes a load and regenerative state. It shows how it becomes. In the regenerative state, not only the arrival at the command frequency is delayed, but also when the power cannot be regenerated, there is a problem that a DC overvoltage state occurs.

The present invention provides an inverter device capable of quickly reaching a command frequency without tripping the induction motor in the free-run state even when an overcurrent is generated when the induction motor in the free-run state is synchronously closed. To aim.

[0010]

In order to achieve the above object, in the present invention, an inverter section in which a switching element for controlling on / off of a DC voltage by pulse width modulation and converting it to an AC has a bridge structure is provided. In the inverter device for supplying alternating current power of the inverter section to the induction motor, the determination means for determining whether the load current supplied to the induction motor exceeds the limit value, and this determination means determines the limit value. When it is determined that it has exceeded, switching element switching means for switching the switching element to bring the bridge into a freewheeling state, and residual voltage detection means for detecting the residual voltage of the induction motor at the time of interruption of power supply to the induction motor. And a control means for restarting the power supply by outputting a pulse width modulation voltage corresponding to the frequency and phase of the residual voltage. When the determination means determines that the limit value has been exceeded and the control means does not output the pulse width modulation voltage corresponding to the frequency and phase of the residual voltage when power supply is restarted, the phase advance of the pulse width modulation voltage And a phase control means for stopping.

[0011]

In the inverter device thus configured, when the power supply from the inverter unit to the induction motor is restarted,
The pulse width modulation voltage corresponding to the frequency and phase of the residual voltage of the induction motor is output from the inverter.However, there is an error in the frequency or phase of the residual voltage and the pulse width modulation voltage, or the magnitude of the pulse width modulation voltage is large. When the load current exceeds the judgment value when it has passed, the phase shift of the pulse width modulation voltage is not stopped, and the switching element having the bridge structure is put into the return state to suppress the overcurrent. However, with respect to the overcurrent in the normal operating state, the phase progression of the pulse width modulation voltage is stopped and the switching element having the bridge structure is brought into the reflux state to suppress the overcurrent.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An inverter device according to an embodiment of the present invention will be described with reference to the drawings. In the figure, the same circuit configuration as that of the conventional inverter device shown in FIG. 3 is denoted by the same reference numeral, and the description thereof will be omitted. The difference between FIG. 3 and FIG. 1 is that the main control circuit 10 is provided with a signal S ₂ for permitting the advance of the phase of the pulse width modulation voltage and the AND circuit of the signal S ₂ and the overcurrent determination signal S 1. 17 is provided, and the logical product S ₃ of the overcurrent determination signal S ₁ and the signal S ₂ is supplied to the integrator 11.

Next, the operation of the inverter device having the above-described structure at the time of synchronizing is described. When the inverter output is stopped and the switch is synchronously turned on, the main control unit 10 outputs the voltage command value V ^* , the frequency command value f ^* , and the initial phase command value θ.
At the same time that the signal _o is output, the signal S ₂ that permits the stop of the phase of the pulse width modulation voltage is turned off, and the overcurrent determination signal S
_{The value 1} prevents the phase of the integrator 11 from advancing.

FIG. 2 shows an example of the synchronization input time chart of this embodiment. Depending on the overcurrent determination signal S ₁ , the voltage phase θ
^It can be seen that the progress of ^* does not stop and the slip of the induction motor does not become negative. (E) and (f) show the signal S ₂ which permits the stop of the phase of the pulse width modulation voltage.
(E) shows the case where the advancement of the phase is stopped from when the synchronization is applied until f ^* increases, and (f) shows the case where the advancement of the phase is prohibited for a predetermined time T from the introduction of the synchronization.

As described above, according to the present embodiment, the switching element of the inverter section is switched to the return state in response to the overcurrent at the time of turning on the synchronization so as to suppress the increase of the current, and the phase of the pulse width modulation rabbit voltage is controlled. Since it is not stopped, it is possible to prevent the transition to the regenerative state, and it is possible to smoothly synchronize the residual voltage of the induction motor and the inverter output voltage.

[0016]

According to the present invention, in response to an overcurrent when the induction motor is turned on synchronously, the switching element having a bridge structure in the inverter section is switched to the return state to suppress the increase in current and to suppress the pulse width modulation voltage. Since the phase is not stopped, it is possible to prevent the loss of synchronization and transition to the regenerative state, and smooth synchronization can be performed. Further, with respect to the overcurrent during acceleration, the switching element of the bridge configuration of the inverter section is switched to the return state to suppress the increase in current, while the phase of the pulse width modulation voltage is stopped from proceeding. Even when the overcurrent suppression state is entered, it is possible to continue the operation by effectively reducing only the current component that contributes to the torque while keeping the magnetic flux inside the induction motor constant.
It is possible to provide an inverter device that can obtain good acceleration performance with a short acceleration time.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an inverter device showing an embodiment of the present invention.

FIG. 2 is a synchronous closing time chart of the inverter device showing the embodiment of the present invention.

FIG. 3 is a circuit configuration diagram of a conventional inverter device.

FIG. 4 is a time chart of synchronization input of the inverter device according to the embodiment of the present invention.

[Explanation of symbols] 1 ... AC power supply, 2 ... Rectifier circuit, 3 ...
Smoothing capacitor, 4 ... Inverter section, 5 ... Induction motor, 6 ... Current detector, 7 ... Current detection circuit,
8 ... Current setting device, 9 ... Comparison circuit, 10 ... Main control unit, 11 ... Integrator, 12 ... Pulse width modulation unit, 13 ... Recirculation state forming circuit, 14 ... Drive circuit,
15 ... Residual voltage detection circuit, 16 ... Synchronous closing control unit, 17
... AND circuit.

Claims (3)

[Claims] 1. An inverter having an inverter unit in which a switching element for controlling ON / OFF of a DC voltage by pulse width modulation and converting it into an AC has a bridge structure, and supplying AC power of the inverter unit to an induction motor. In the device, a determining unit that determines that the load current supplied to the induction motor exceeds a limit value; and when the determining unit determines that the load current exceeds the limit value, the switching element is switched to switch the bridge. A switching element switching means to be in a return state, a residual voltage detecting means for detecting a residual voltage of the induction motor at the time of interruption of power supply to the induction motor, and a pulse width modulation voltage corresponding to a frequency and a phase of the residual voltage. Control means for outputting and restarting the power supply; and the determining means for determining that the limit value has been exceeded, and When the stage does not output the pulse width modulation voltage corresponding to the frequency and phase of the power supply restart time residual voltage, the inverter apparatus characterized in that it comprises a phase control means for stopping the phase progression of the pulse width modulation voltage. 2. The inverter device according to claim 1, wherein the phase control means does not stop the phase advance of the pulse width modulation voltage from when the power supply is restarted until the output frequency is increased or decreased. 3. The inverter device according to claim 1, wherein the phase control means does not stop the phase advance of the pulse width modulation voltage for a predetermined time after the power supply is restarted.