JPS60106392A - Inverter - Google Patents

Abstract

PURPOSE:To always effectively set synchronization of an induction motor by accurately predicting the synchronizing timing from the frequency of the induced voltage of an induction motor. CONSTITUTION:After a power source is instantaneously interrupted, a controller 4 is reset, and the main switching element of a main circuit 1 remains OFF. When the power source is recovered and a phase signal P is input, a frequency measuring circuit 5 starts predicting the frequency. The controller 4 accurately measures the period J continuously by the measuring circuit 5, thereby calculating so as to generate a correction signal C when the predicted calculation of the frequency is obtained. Thus, the signal (e) of the frequency in response to the rotating speed signal (d) and the rotating speed signal (d) are corrected by the signal C, a control signal (g) corresponding to the output of the frequency is generated, and supplied to the main circuit 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an inverter for supplying power to an AC motor such as an induction motor, and particularly for use when restarting power supply after a momentary power outage, or during commercial operation. The present invention relates to an inverter having a function necessary for synchronization when switching from direct drive by a power source to drive by an inverter output.

[Background of the invention]

For example, one method of controlling the speed of an AC motor such as an induction motor is to change the frequency and voltage of the supplied power.
This method provides speed control that is close to ideal,
For this reason, inverters have come to be widely used for controlling induction motors (hereinafter referred to as IM) and the like.

By the way, one of the functions necessary for such an IM drive inverter is a synchronization function.

This function is a control system that drives the IM directly from the commercial power supply during momentary power outages or when speed control of the IM is not required, and drives the IM via the inverter only when speed control is required. When switching the IM from commercial power to inverter output in the system, the IM is
This is a necessary function to switch 1M to the inverter output almost continuously without stopping (and to avoid overcurrent due to out of phase at this time).
This is generally called synchronization because while M is rotating due to inertia, the phase of the output voltage of the inverter is synchronized with the induced voltage in advance and connection is made.

The conventional method of synchronizing inverters has been to use a PLL (phase locked loop) control circuit, which rotates due to inertia after the power is cut off, as shown in Figure 1. A signal p representing the phase is detected from the induced voltage υ of the IM, and a signal 0 representing the output frequency and phase of the inverter is obtained by a PLL control circuit using this phase signal P as a reference signal, and the phase difference between the signal P and 00 is When the represented correction signal C becomes sufficiently small, an inverter output is generated to start supplying power to the IM.

However, this conventional synchronization method cannot provide sufficient responsiveness to the PLL control circuit used therein, and as a result, the load torque of the IM is relatively large, and due to the inertia' after the power is cut off. If the rotational speed of the IM decreases quite rapidly, the phase control by the PLL control circuit cannot keep up with the decrease in the rotational speed of the IM, and the phase lock state may not be obtained because the capture range is exceeded. However, there was a drawback that synchronization could not be performed reliably.

[Purpose of the invention]

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to
To easily provide an engine which can always and reliably perform synchronization regardless of the load torque state of the engine.

[Summary of the invention]

In order to achieve this object, the present invention detects the frequency at that point from the induced voltage of the IM prior to synchronization, then predicts the frequency of the induced voltage of the IM at a predetermined timing thereafter, and Embodiments of the Invention The inverter according to the present invention will be explained in detail below with reference to illustrated embodiments. explain.

FIG. 2 shows an embodiment of the present invention. In the figure, 1 is the main circuit of the inverter, 2 is the voltage detector, 3 is the phase detection circuit, and 4 is the main circuit of the inverter.
5 is a main control circuit, 5 is a frequency measurement circuit, 6 and 8 are amplifier circuits, 7 is a VCO (voltage controlled oscillation circuit), 9 is a speed control circuit, and 10 is a speed setter.

The main circuit 1 performs a switching operation in response to a control signal D supplied from the main control circuit 4, and functions to supply the IM with power having a voltage and frequency independent of the voltage and frequency of the power supplied from the commercial power source.

The voltage detector 2 serves to detect the voltage appearing at the output terminal of the main circuit 1, and therefore the signal υ obtained at its output represents the induced voltage of the IM.

The phase detection circuit 3 detects the zero crossing point of the signal υ which changes almost sinusoidally, and detects a signal P representing the phase of the signal V.
It functions to generate.

The main control circuit 4 includes a microcomputer, etc., and performs various signal processing necessary for controlling the operation of the inverter, including generation of a control signal DA for the main circuit 1.

The frequency measuring circuit 5 processes the phase signal p to calculate the frequency of the signal V, and further calculates the frequency of the signal V at the synchronization timing after a predetermined time from the time when this frequency is detected from the frequency to a predetermined value. It works to predict and calculate according to a function.

Note that this circuit 5 does not need to be provided as an independent circuit, and may be provided as a function as part of the processing by the microcomputer of the main control circuit 4.

The amplifier circuit 6 is for amplifying the frequency correction signal C.

The VCO 7 functions to generate a signal e having a frequency corresponding to the rotational speed signal d inputted via the amplifier circuit 8.

The amplifier circuit 8 is for amplifying the rotational speed signal d.

The speed control circuit 9 functions to generate a speed setting signal in response to a signal input by the speed setter 10.

Next, the operation of this embodiment will be explained.

In normal operating conditions, a rotational speed signal d and a frequency signal e are connected to the main control circuit 4 by a speed setting signal outputted by the speed control circuit 9 according to the rotational speed set by the speed setting device 10. As a result, the main control circuit 4 supplies a predetermined control signal 1 to the main circuit IK, and three-phase power having a frequency and voltage corresponding to the set rotation speed is supplied from the main circuit 1 to the IM. There is.

However, if a power outage occurs in the commercial power supply,
The generation of the control signal q from the main control circuit 4 is stopped, the main switching element in the main circuit 1 remains off, and the power supply to the IM is also turned off.

On the other hand, even after this power outage occurs, the IM continues to rotate due to the rotational inertia of itself and the load, and three-phase induced voltages are generated in its armature windings.

Therefore, if the power outage that occurred at that time was a so-called instantaneous power outage, in which the power was restored in a relatively short time, the IM would still be rotating when the power was restored, and the induced voltage would still be present. in a state.

Therefore, as soon as the control function of the inverter returns to an operable state after a momentary power interruption, the phase detection circuit 3 generates the phase signal P based on the voltage signal V from the voltage detector 2.

On the other hand, at this time, the control circuit 4- is reset due to the power outage, and the control signal y is not generated. Therefore, even after the power is restored, the main switching element of the main circuit 1 is still turned off at this time. It remains as it is.

Therefore, if the time point when the power is restored after the instantaneous power interruption is designated as "to", the voltage signal V changes from this time point "to" onward as the rotational speed of the IM decreases, as shown in FIG. Then, as shown in FIG. 3, the phase detection circuit 3 generates a phase signal P at the zero-crossing point of the voltage signal V from minus to plus after time 5K, as shown in FIG. 3, and inputs this to the frequency measurement circuit 5.

The frequency measurement circuit 5 starts a frequency prediction calculation operation when the power is restored and the phase signal P is inputted.

First, after time to, the phase signal P appears sequentially at time t. y tl + t2... old... binding, and the time between them is τ1. τ2...and,
The frequency of the voltage signal V at these times is f
,,f2...song...-. Furthermore, it is assumed that the decrease in rotational speed during inertial rotation of the IM shows a linear change.

Then, the frequency f of the voltage signal υ at this time becomes as shown in FIG. Note that in FIG. 4, fo is the value of the frequency f at time to, and therefore the following equation holds true.

j2ht+fo・Song・(1) However, k is a constant.

On the other hand, the data given to the frequency measuring circuit 5 are the time points io, 11, 12, etc., when the phase signal P appears, and what is immediately apparent from this is the time between these times, that is, the period τ1 (time to and tl interval).

τ2 (interval between time points t1 and t2)... Since the reciprocal of the period is the frequency, if we look at the frequency f of the voltage signal V, as is clear from FIG. will be obtained. In other words,
If the interval between time 1n-2 and tn-1 is τn-1, the reciprocal of this 1/τn-1 is neither the frequency at time t knee 2 nor the frequency at time tn-1, 9 intermediate points tn 2+7L between these times tn-2 and tn-1
The frequency at 1 is fn-2n-1, and similarly 1/τ
The frequency represented by U becomes the frequency fn-1,n at time tn,-1,Y intermediate between time tn-1 and trL.

Therefore, from these relationships and equation (1), it is possible to predict the frequency jrL at time tU, which is expressed by the following equation.

1 1 2 fn=te-r ”r0r ・・・・・・ (3) 3n-
1nn-1 Therefore, in the control circuit 4, the frequency measurement circuit 5 continuously obtains an accurate measurement of the period τ, and from this, the calculation of equation (3) is performed to obtain a predicted calculation of the frequency f. at the time
A correction signal C is generated at trL 1, which corrects the signals e and d, and a control signal 1 corresponding to the output of frequency frL is generated.
is generated and supplied to the main circuit 1.

Therefore, the switching element of the main circuit 1 at this time t
It begins to be triggered at time t (1), which is slightly delayed from n.

Therefore, power that accurately matches the frequency and phase of the next induced voltage begins to be applied to the IM, and synchronization can be performed without causing an overcurrent.

According to this embodiment, if the voltage signal V can be completely detected over two cycles, it is possible to calculate the data at time trLK, and the predicted frequency at this time depends on the inertial characteristics of the IM including the load torque. Since the values correspond to each other, calculations can be made with sufficient accuracy in any case, and accurate synchronization can be performed at all times.

By the way, above we have explained the synchronization input when the power is momentarily cut off, but this embodiment operates in the same way even when the IM is switched from commercial power supply to inverter drive, and always performs accurate synchronization. In other words, in this case, first disconnect the commercial power from the IM that is operating on commercial power, and then immediately connect the IM to the output terminal of main circuit 1 in Figure 2. It is sufficient to set the time to time t in FIGS. 3 and 4 and control the inverter in exactly the same manner as described above.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to accurately predict the frequency of the induced voltage of the IM at the synchronization start timing from the frequency of the induced voltage of the IM immediately before the synchronization start timing, thereby making it possible to perform synchronization. Therefore, it is possible to eliminate the drawbacks of the prior art and easily provide an inverter that can always be reliably synchronized.

[Brief explanation of drawings]

FIG. 1 is a timing chart explaining the synchronization operation in a conventional inverter, FIG. 2 is a block diagram showing an embodiment of the inverter according to the present invention, FIG. 3 is a timing chart explaining the operation, and FIG. 4 FIG. 2 is an explanatory diagram of frequency prediction operation in the present invention. 1... Inverter main circuit, 2... Voltage detector, 3... Phase detection circuit, 4...
・Main control circuit, 5... Frequency measurement circuit, 6...
...Amplification circuit, 7...Voltage controlled oscillation circuit,
8...Amplification circuit, 9...Speed control circuit, 10...Speed setter. Fig. 1 Ki-inlay fimin 7 pa Fig. 3 J ↑ @j Yumi-pu-in taimishi 7゛ Fig. 4

Claims (1)

[Scope of Claims] 1. In an inverter equipped with a synchronization function for an AC motor, means for detecting the frequency of the induced voltage of the motor within a predetermined period until the timing at which the synchronization should be applied is reached; and a means for predicting and calculating the frequency of the induced voltage at the synchronization timing based on the frequency determined, and the output frequency of the inverter is controlled by the predicted frequency to perform synchronization. An inverter characterized by: 2. The inverter according to claim 1, wherein the frequency prediction by the means for predicting and calculating the frequency of the induced voltage is performed by linear approximation.