JPS5872378A - Pulse width modulation type inverter - Google Patents

Abstract

PURPOSE:To perform smooth switching in a pulse width modulation type inverter by deciding the switching point from an open loop operation to a closed loop operation in response to the amplifier output signal level of a voltage control system and the output voltage command signal level of a function generator. CONSTITUTION:The amplitude relationship between the signal amplified from an error voltage of a voltage detection signal inputted from a rectifier 5 from the voltage command signal inputted from an A/D converter 8 under the open loop voltage control is monitored by a coincidence detector 23. When the coincidence of the both signals is detected by the detector 23, a contact S1 is opened based on the detection signal, a contact S2 is closed, thereby switching the prescribed voltage control from the open loop to the closed loop operation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable pulse width lil type inverter device, and particularly when picking up a load motor group during inertial operation, it is preferable to use closed-loop AVR operation rather than open-loose AVR operation (voltage control). The purpose of the present invention is to provide an inverter device that allows smooth switching and smooth transition to steady state control.

For example, when any one of the load motors in a group of load motors that was operated at variable speed using a variable pulse width TSM inverter device causes a ground fault and is cut off at a selected speed, and the remaining healthy motor is picked up by restarting the inverter. Furthermore, if the AC input power supply of the inverter device experiences a momentary power outage for some reason, and when the power is restored, the inverter device is restarted to pick up the load motors that are rotating due to inertia. is to control the output voltage of the inverter by controlling the DC output voltage of the forward converter,
Immediately after picking up a load motor group, the voltage control system is operated in a closed loop on the inverter side, and the output voltage V and output frequency F of the inverter are gradually increased with a predetermined relationship ratio, until a predetermined steady state is reached. However, in the case of a pulse width modulation type inverter, the inverter's output voltage is controlled by either adjusting the amplitude value of the triangular wave signal of the carrier wave, or Furthermore, since the peak value t-M of the sine wave signal of the sine wave generation circuit that generates the same frequency as the inverter output frequency is adjusted, and the pulse width of the inverter output voltage is controlled by hopping, after picking up the load motor group, It is not possible to immediately operate the voltage control system in a closed loop. Therefore, after picking up a load motor group, the circuit including the voltage control amplifier of the voltage control system is temporarily disconnected, and the output voltage of the inverter is controlled in a so-called open loop to gradually increase the voltage. . Problems that arise during such operation include, for example, when switching AVR operation from open loop to closed loop, there is a timing problem at the time of switching, such as at what point the signal is detected and the switch is made, and furthermore, when the AVR operation is switched from open loop to closed loop. The problem of starting time is how to shorten the time required for switching, and how to switch smoothly without causing any shock to the load motor. There are still many unresolved problems in control methods.

The present invention was invented in view of this point, and in particular, one of the operational features of the present application is that the switching point is set at the point in time when the output of the function generator and the output of the voltage control amplifier match. This will be described in detail below based on examples.

The figure shows a specific circuit configuration diagram of this embodiment. In the same embodiment, IV represents a target pulse width modulation type inverter device, and its main circuit configuration is well known, so it is omitted. 1 is an AC speed breaker for opening and closing the output bus of the inverter and the load side bus, and 21 to 2n are load motor groups 6.
1 to 6n are electromagnetic contactors for opening and closing, 4 is a voltage detection transformer for extracting the output voltage of the inverter during normal operation and the motor induced voltage when picking up the load motor, and 5 is a voltage detection transformer for extracting the motor induced voltage when picking up the load motor. 6 is a waveform shaping circuit for converting the AC input voltage into a rectangular wave, and 7 is a signal "1" input from the waveform shaping circuit. 8 is a setting circuit that measures the time between 0 and 0 signals, detects the frequency, picks it up, and sets the later inverter output frequency. 8 converts the input pulse train digital signal to a DC level voltage signal. D/A for
In the conversion circuit, 9 is a comparison circuit that compares the voltage detection signal and the voltage command signal, 10 is a voltage control amplifier for once amplifying the error voltage, and 11 is a DC level voltage signal that amplifies the error voltage. The first converts the pulse train into a digital signal.
12 is a second conversion circuit that converts a DC level voltage signal into a pulse train digital signal;
is a pulse width control device, which includes an oscillator 14 that oscillates a predetermined pulse signal based on a frequency command signal set by a frequency setting circuit 7, and a triangular wave signal of a carrier wave by integrating the pulse signal from this oscillator 14. A triangular wave signal generating circuit 15 that generates a triangular wave signal generating circuit 15, a sine wave signal generating circuit 17 that generates a three-phase sine wave signal having the same frequency as the output frequency of the inverter based on a pulse signal from an oscillator, and an input signal that digitizes the error voltage. and an amplitude adjustment circuit 16 for determining the modulation degree of the triangular wave signal based on the input signal obtained by digitizing the DC level voltage signal and adjusting the amplitude value of the triangular wave signal, and an amplitude adjustment circuit 16 for adjusting the amplitude value of the triangular wave signal based on the determined modulation degree. A modulation circuit 18 that modulates a triangular wave signal, a comparison circuit 19 that combines the modulated triangular wave signal and a three-phase sine wave signal, and a Each of the circuits includes a gate circuit 20 that obtains a signal with a predetermined pulse width as a gate signal, and a gate amplification circuit 21 that amplifies the gate signal. Reference numeral 22 denotes a function generating circuit, and this circuit has a characteristic such that, for example, the voltage command signal increases with a square S characteristic (root characteristic) over time, and is generated in advance so that it is input when the motor is picked up. It is defined as Memaehara. 23 is a coincidence detection circuit, and this circuit is for monitoring the amount of coincidence between the signal level derived from the maximum value deriving circuit described later and the output signal level of the voltage control amplifier. S at the first contact that closes in later open loop operation.

4. A second contact that closes during steady mode operation or when the motor picks up and then shifts to the steady mode later. This is the second contact that closes during operation. Although the example shows a case where a contact is applied, in practical terms, a non-contact type is used. An electronic switch is applied.

To describe the operation of this embodiment configured as above, during steady operation, if any one of the load motor groups 6, to 6n suffers a ground fault or the like for some reason, the variable pulse width type After immediately stopping the inverter device IV and disconnecting the accident machine, the inverter is restarted, and after performing predetermined phasing using a well-known method, the AC breaker 1 is turned on and the load motor group of the healthy machine is restarted. If the power is picked up, or even if the commercial frequency power supply is momentarily interrupted and the specified phase is adjusted while only the frequency control system of the inverter is being utilized, the AC speed cutter (1) is turned on and the load motor group of the healthy machine is switched on. In this case, in this practical example, first, the first contact S is opened and the second contact S2 is closed, and the induced voltage detection signal on the load side is taken in from the voltage detection transformer 4. Based on this, this detection signal is converted into a rectangular wave signal by the waveform shaping circuit 6 to obtain a "1" level signal and a "0" level signal, and the time of these two signals is set at a frequency of 7. The frequency of the induced voltage on the load side is measured by a circuit, and the frequency for restarting the inverter is set based on this frequency detection signal. The frequency command signal set in this way is transmitted to the D/A conversion circuit 8.
Convert it to a DC level voltage signal to obtain a voltage command signal, and compare this voltage command signal with the voltage detection signal led from the rectifier circuit 5 in a comparison circuit 9 to generate an error voltage. This error voltage is once amplified by the voltage control amplifier 10 and the contact 8. The amplified error voltage is led to the first conversion circuit 11 through the pulse train, and the amplified error voltage is converted into a pulse train digital signal and applied to the amplitude value adjustment circuit 16. In parallel with this operation, a signal obtained by converting the voltage detection signal obtained by the rectifier circuit 5 into a pulse train digital signal by the second conversion circuit 12 and a frequency setting circuit 7
The oscillation circuit 14 is operated based on the frequency signal of the pulse train set in , and the triangular wave signal of the carrier wave obtained by performing a predetermined integration operation on this oscillation pulse signal group in the triangular wave generating circuit 15 has the amplitude value of 16. Since the amplitude value adjustment circuit 16 determines the degree of modulation of the triangular wave signal of the carrier wave based on each input digital signal, the amplitude value adjustment circuit 16 determines the degree of modulation of the triangular wave signal of the carrier wave based on each input digital signal. Modulate the signal. The triangular wave signal modulated in this manner is matched with the 93-phase sine wave signal generated by the sine wave generating circuit 17 based on the input oscillation pulse signal in the comparator circuit 19, and the combined two A gate signal of an arbitrary width is obtained by the gate circuit 20 based on the intersection of the signals, and this gate signal is once amplified by the amplifier circuit 21 and supplied to the pulse width variable 114i type inverter IV. The output frequency and output voltage are controlled according to the electromotive voltage-frequency of the load motor rotating with inertia.

The inverter is restarted based on the predetermined operation described above, the output frequency and output voltage of the inverter are increased, and a well-known method is used based on the zero point detection signal of the induced voltage on the load motor side. When it is detected that the inverter and the load motor are synchronized by performing the specified phase matching, the AC breaker 1 is turned on based on this detection signal to pick up the load motor group of the healthy machine, and at the same time The contact S2, which has been closed until then, is opened and the other contact S1 is closed, thereby switching the voltage control system, which was operating in a closed loop at the time of predetermined phase matching, to an open loop. When the voltage control system is switched to open loop in this way, the induced voltage detection signal on the load side derived from the rectifier circuit 5 is input to the maximum value derivation circuit of Ds and Dt, and the input voltage is input by this maximum value derivation circuit. The voltage detection signal generated by the function generation circuit 22 is matched with the voltage signal of a predetermined mode generated by the function generation circuit 22, and the larger signal is outputted to the first A/D conversion circuit 11 through the contact St. Here, regarding the characteristics of the output voltage signal of the function generation circuit 22, for example, the mutual relationship between the motor induced voltage at the time of pickup and the output frequency is that the voltage is lower than the frequency, so in order to correct this relationship, time changes are made. Since the voltage has a characteristic that the voltage increases according to the square root characteristic, the function is generated immediately when the load motor is picked up (the voltage signal of the predetermined mode generated in the circuit 22 passes through the path from the contact S1 to the A/D conversion circuit 11). It is guided to the amplitude value adjustment circuit 16. Therefore, in the amplitude value adjustment circuit 16, the triangular wave generation circuit 15 and 9
The degree of modulation of the triangular wave signal of the carrier wave to be guided is sequentially determined based on the voltage signal input from the function generating circuit 22, and the triangular wave signal is modulated according to the determined modulation variation, and the triangular wave signal and the triangular wave signal are Comparison circuit 1 compares the intersection point with the phase sine wave signal
9, and a gate signal of the desired pulse width is obtained by the gate circuit 20. By controlling the firing of the elements of the inverse converter based on the gate signal group obtained in this way, the pulse width of the inverter's output voltage is sequentially controlled by chopping, and the output voltage is changed to the voltage of the function generator circuit. Raise as instructed. A signal obtained by amplifying the error voltage between the voltage command signal inputted from the A/D conversion circuit 8 and the voltage detection signal inputted from the rectification circuit 5 under the open-loop voltage control as described above, and the function generation circuit 22 25 coincidence detection circuits monitor the magnitude relationship with the voltage signal derived from the voltage signal.

The output voltage of the inverter rapidly increases and the load motor group is further accelerated, and the 25 detection circuit detects that the voltage command signal in the predetermined pattern mode and the induced voltage detection signal on the load motor side match in level. When detected, the contact S1 is opened and the other contact S2 is closed based on this detection signal.
1 Switch the predetermined voltage control from open loop to closed loop operation. After switching to closed-loop operation in this way,
Based on the output signal of the voltage control amplifier 10, the amplitude value adjustment circuit 16 determines the degree of variation of the triangular wave signal, and shifts to a steady mode in which predetermined chopping control is performed. The pulse width control described above is performed by adjusting the amplitude value of the triangular wave signal of the carrier wave, but for example, the pulse width control is performed by adjusting the amplitude value of the triangular wave signal of the carrier wave. A predetermined pulse width control may be performed by adjusting the output signal of the voltage control amplifier or the output signal of the function generation circuit.

As described in 1-1 above, in the present invention, the transition point at which open-loop voltage control is switched to closed-loop operation after picking up a load motor is determined based on the amplifier output signal level of the voltage control system and the output voltage command of the function generator circuit. Since it is designed to switch on the condition that the signal levels match, it has various effects as shown below.

■ It is possible to shift to the steady mode simply by monitoring the output of the function generator circuit and the output of the voltage control amplifier, so the shift can be made smoothly without causing any shock to the inverter control system or the load side. I can do it.

■ After the load motor group is picked up, the output voltage is increased compared to the output frequency to accelerate the motor, and the specified voltage control is performed in an open loop, so the control system maintains stability without any hunting. Moreover, the start-up time to the steady operation mode can be shortened.■ The switching point from open-loop operation to closed-loop operation is determined based on the output of the function generation circuit and the output of the amplifier. 1. It is possible to simplify the circuit configuration and provide a very economical inverter device.

[Brief explanation of the drawing]

The figure is a diagram of a specific circuit structure FM of a pulse width modulation type inverter device showing an embodiment according to the present invention. 6 is a waveform shaping circuit, 7 is a frequency setting circuit, 8 is a D/A conversion circuit, 10 is a voltage control amplifier, 11-12 D/A
a conversion circuit, a 15-piece pulse width control device f, 14 an oscillation circuit, 15 a triangular wave signal generation circuit, 16 an amplitude value adjustment circuit,
17 is a sine wave signal generation circuit, 18 is a modulation circuit, 9-1
9 is a comparison circuit, 20 is a gate circuit, 21-digit gate amplifier circuit, 22 is a function generation circuit, and 2!1 is a coincidence detection circuit.

Claims (1)

[Claims] During the transition period from when the load motor group is picked up to a predetermined speed, the circuit including the voltage control amplifier is disconnected and the predetermined voltage is controlled in an open loop. Although the specified voltage control is performed in a closed loop, when the specified voltage is controlled in an open loop, the amplitude value of the carrier wave signal or the sine wave signal is calculated based on the voltage command output from the function generation circuit. A predetermined pulse width control is performed by setting the peak value of is monitored by the coincidence detection circuit, and based on the signal detected by the blind tube in which the levels of both signals match in the scattering output circuit, the voltage control is switched from open-loose voltage control to closed-loop voltage control, and during closed-loop voltage control, A pulse width modulation type inverter, characterized in that a predetermined pulse width control is performed by adjusting the amplitude value of a carrier wave signal or the peak value of a sine wave signal using the output signal of a voltage control amplifier. Device.