JPH0379953B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulse width modulation type inverter device, and in particular, when picking up a group of load motors during inertial operation, switching from open-loop AVR operation (voltage control) to closed-loop AVR operation is particularly important. The purpose of this invention is to provide an inverter device that can smoothly shift to steady state control.

If any one of the load motors operating at variable speed with a pulse width modulation type inverter experiences a ground fault and is selectively cut off, the remaining healthy machine restarts the inverter to pick it up, or even if the inverter If the AC input power supply of the 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 rotating due to inertia, if the voltage source inverter or current source inverter is used, Since the output voltage of the inverter is controlled by controlling the DC output voltage of the converter, the voltage control system is operated in a closed loop on the inverter side immediately after picking up the load motor group, and the inverter output voltage V and The output frequency F can be gradually increased with a predetermined relationship ratio, and the transition can be made to a predetermined steady state operation.On the other hand, with a pulse width modulation type inverter, it is possible to control the output voltage of the inverter. As is well known, adjust the amplitude value of the triangular wave signal of the carrier wave, or
Furthermore, since the pulse width of the inverter output voltage is controlled by chopping by adjusting the peak value of the sine wave signal of the sine wave generator circuit that generates the same frequency as the inverter output frequency, it is possible to control the pulse width of the inverter output voltage immediately after picking up the load motor group. It is not possible to 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 during such operation include, for example, when switching AVR operation from open loop to closed loop, the timing of the switch, such as what signal is detected and switched at what point, and the time required to switch to steady operation. Control methods for pulse width modulation type inverter devices are still unclear, such as how to shorten the start-up time and how to smoothly switch over the load motor without causing any shock. There are a lot of problems to solve.

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 root function generator and the output of the voltage control amplifier match. A detailed explanation will be given 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 breaker for opening and closing the output bus of the inverter and the load side bus; 2 ₁ to 2 _o are electromagnetic contactors for opening and closing the load motor group 3 ₁ to 3 _o ; and 4 is for opening and closing the load motor group 3 1 to 3 o; 5 is a voltage detection transformer for extracting the motor induced voltage when the output voltage of the inverter is picked up by the load motor; 5 is a rectifier circuit for rectifying the AC voltage taken out from the transformer to obtain a desired voltage signal; 6 7 is a waveform shaping circuit for converting the AC input voltage into a rectangular wave. 7 is a waveform shaping circuit that measures the time between a "1" signal and a "0" signal input from the waveform shaping circuit to detect the frequency. A frequency setting circuit that sets the inverter output frequency after being picked up; 8 is an F/V conversion circuit that converts the input pulse train digital signal into a DC level voltage signal; 9 is a voltage detection signal and voltage command signal 10 is a voltage control amplifier for once amplifying the error voltage, and 11 is a first A/D conversion for converting the DC level voltage signal obtained by amplifying the error voltage into a pulse train digital signal. In the circuit, 12 is a second A/D conversion circuit that converts a DC level voltage signal into a pulse train digital signal, and 13 is a pulse width control device, which controls the frequency command signal set by the frequency setting circuit 7. an oscillator 14 that oscillates a predetermined pulse signal based on the oscillator 14; a triangular wave signal generation circuit 15 that integrates the pulse signal from the oscillator 14 and generates a triangular wave signal as a carrier wave;
A sine wave signal generation circuit 17 generates a three-phase sine wave signal of the same frequency as the output frequency of the inverter based on a pulse signal from an oscillator, an input signal obtained by digitizing the error voltage, and a DC level voltage signal. an amplitude adjustment circuit 16 for determining the modulation degree of the triangular wave signal based on the converted input signal and adjusting the amplitude value of the triangular wave signal; and a modulation circuit 18 for modulating the triangular wave signal based on the determined modulation degree. and a comparison circuit 19 that combines the modulated triangular wave signal and the three-phase sine wave signal, and a gate signal that obtains a signal with a predetermined pulse width based on the intersection of the triangular wave signal and the sine wave signal obtained by the comparison circuit 19. A gate circuit 20 and a gate amplification circuit 21 each amplify the gate signal. Reference numeral 22 denotes a root function generation circuit, which has a characteristic such that, for example, the voltage command signal increases with a square root characteristic (root characteristic) over time, and is generated in advance so that it is input when the motor is picked up. It has been stipulated in advance. 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. S2 is the first contact that closes during open-loop operation, and _S2 is the second contact that closes during steady-state mode or during closed-loop operation until the transition to steady mode after the motor is picked up. As shown, a non-contact electronic switch is practically applied.

To describe the operation of this embodiment configured as described above, during steady operation, any one of the load motors ₃₁ to _3o may suffer a ground fault or the like for some reason, and the pulse width modulation type Immediately stop the inverter IV, disconnect the faulty machine, restart the inverter, perform predetermined phasing using a well-known method, and then close the AC circuit breaker 1 to group the load motors of the healthy machine. If the commercial frequency power supply is momentarily cut off and the specified phase alignment is performed while only the frequency control system of the inverter is utilized, AC breaker 1 is turned on and the load motor group of the healthy machine is switched on. In this embodiment, first, the induced voltage detection signal on the load side, which is taken in from the voltage detection transformer 4 with the first contact S ₁ open and the second contact S ₂ closed, is 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. Detect the frequency of the induced voltage on the load side by measuring it in the circuit,
Based on this frequency detection signal, the frequency for restarting the inverter is set. The frequency command signal thus set is converted into a DC level voltage signal by the F/V conversion circuit 8 to obtain a voltage command signal, and this voltage command signal and the voltage detection signal derived from the rectifier circuit 5 are 9, and if an error voltage is generated, this error voltage is once amplified by the voltage control amplifier 10 and sent to the first A/D conversion circuit ₁₁ through the contact S2.
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, the voltage detection signal obtained by the rectifier circuit 5 is converted into a pulse train digital signal by the second A/D conversion circuit 12, and the frequency signal of the pulse train set by the frequency setting circuit 7 is used. Oscillation circuit 1
4, and the oscillation pulse signal group is subjected to a predetermined integration operation using 15 triangular wave generating circuits.The triangular wave signal of the carrier wave obtained by performing a predetermined integration operation on this oscillation pulse signal group is input to each of the 16 amplitude value adjustment circuits, so that the amplitude The value adjustment circuit 16 determines the degree of modulation of the triangular wave signal of the carrier wave based on each input digital signal, and the 18 modulation circuits modulate the triangular wave signal according to the determined degree of modulation. The triangular wave signal modulated in this manner and the three-phase sine wave signal generated by the sine wave generation circuit 17 based on the input oscillation pulse signal are combined in the comparator circuit 19, and both signals are combined. 20 gate circuits obtain a gate signal of an arbitrary width based on the intersection of The frequency and output voltage are controlled according to the induced voltage-frequency of a load motor rotating with inertia.

Based on the above-mentioned predetermined operation, restart the inverter, increase the inverter's output frequency and output voltage, and use a well-known method 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 Open the contact S ₂ which is closed until the end and close the other contact S ₁ ,
The voltage control system that was operating in a closed loop at the time of predetermined phase matching is switched 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 D ₁ −D ₂ , and the voltage detection signal inputted by this maximum value derivation circuit and the root function generation circuit 22 are The generated voltage signals of the predetermined mode are matched, and the larger signal is outputted to the first A/D conversion circuit 11 through the contact _S1 . Here, regarding the characteristics of the output voltage signal of the root function generation circuit 22, for example, the correlation between the motor induced voltage at the time of pickup and the output frequency is that the voltage is lower than the frequency. Since the voltage has a characteristic that increases according to the square root characteristic with respect to the current, the voltage signal of the predetermined mode generated in the root function generation circuit 22 is immediately transferred from the contact S ₁ to the A/D conversion circuit 11 when the load motor is picked up. The signal is guided to the amplitude value adjustment circuit 16 through the path. Therefore, in the amplitude value adjustment circuit 16, the degree of modulation of the triangular wave signal of the carrier wave derived from the triangular wave generating circuit 15 is determined by the root function generating circuit 22.
The triangular wave signal is modulated according to the determined modulation degree, and the intersection point between the triangular wave signal and the three-phase sine wave signal is determined by the comparator circuit 19. , a gate signal with a desired pulse width is obtained by 20 gate circuits. By controlling the firing of the elements of the inverter based on the gate signal group obtained in this way, the pulse width of the inverter's output voltage is sequentially stepped and controlled to generate a root function of the output voltage. Increase the voltage according to the circuit voltage command. A signal obtained by amplifying the error voltage between the voltage command signal inputted from the F/V conversion circuit 8 and the voltage detection signal inputted from the rectification circuit 5 under open-loop voltage control as described above, and the root function generation circuit The magnitude relationship with the voltage signal derived from 22 is monitored by a coincidence detection circuit 23. The output voltage of the inverter rapidly increases and the load motor group is further accelerated, and the detection circuit 23 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, and the predetermined voltage control is switched from open loop to closed loop operation. After switching to closed-loop operation in this way, the degree of modulation of the triangular wave signal is determined by the amplitude value adjustment circuit 16 based on the output signal of the voltage control amplifier 10, and a transition is made to a steady mode in which a predetermined chopping control is performed. be. 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 and further the output signal of the root function generation circuit.

As described 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 by the amplifier output signal level of the voltage control system and the output voltage command signal of the root function generation circuit. Since the switching is performed on the condition that the levels match, various effects can be achieved as shown below.

Since it is possible to shift to the steady mode simply by monitoring the output of the root function generation circuit and the output of the voltage control amplifier, the shift can be made smoothly without giving 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 starting time to the steady operation mode can be shortened.

Since the switching point from open-loop operation to closed-loop operation is determined simply by the output of the root function generation circuit and the output of the amplifier, the circuit configuration can be simplified and an extremely economical inverter device can be provided. be able to.

[Brief explanation of drawings]

The figure is a specific circuit configuration diagram 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 an F/V conversion circuit, 10 is a voltage control amplifier, 11-
12 is a D/A conversion circuit, 13 is a pulse width control device, 14 is an oscillation circuit, 15 is a triangular wave signal generation circuit, 16 is an amplitude value adjustment circuit, 17 is a sine wave signal generation circuit, 18 is a modulation circuit, 9-19 is a comparison circuit,
20 is a gate circuit, 21 is a gate amplifier circuit, 22
2 is a root function generation circuit, and 23 is a coincidence detection circuit.

Claims (1)

[Claims] 1. A rectifier circuit that rectifies a detection signal output from a voltage detection transformer that detects induced voltage during inertial operation of a load motor group driven by a pulse width modulation type inverter, and a rectifier that rectifies the output signal of the voltage detection transformer. A waveform shaping circuit that converts the output signal into a DC wave, a frequency setting circuit that sets the inverter output frequency using the output signal of the waveform shaping circuit, and an F/V conversion circuit that converts the output signal of the frequency setting circuit into a DC level voltage signal. , a voltage control amplifier that compares the output signal of this F/V conversion circuit and an output signal of the rectifier circuit and amplifies this difference voltage, and digitally converts the output signal of this voltage control amplifier via a second switch. a first A/D conversion circuit that converts the DC signal of the rectifier circuit into a digital signal; a second A/D conversion circuit that converts the DC signal of the rectifier circuit into a digital signal; The output signal of the A/D conversion circuit No. 1 and the output signal output from the frequency setting circuit are input to a pulse width control device, and the output signal of the pulse width control device is used to control the pulse width modulation type inverter device. In a pulse width modulation type inverter device that controls a gate circuit to pick up a group of load motors in inertial operation and restart operation, the output level and route of an output signal from a rectifier circuit are determined at the time of picking up a group of load motors. The output signal of the maximum value deriving circuit composed of a first diode and a second diode that outputs a signal whose level is higher than the output level of the output signal of the function generating circuit is sent to the first switch via the first switch. A coincidence detection circuit that outputs the signal to an A/D conversion circuit, and also inputs the output signal of the maximum value deriving circuit and the output signal of the voltage control amplifier, and monitors the signal levels of both, determines that the signal levels of the two coincide. When this is detected, the output signal from the maximum value deriving circuit is switched between the first switch and the second switch from the state where the output signal is outputted to the first A/D conversion circuit via the first switch. and a coincidence detection circuit that controls the output signal of the voltage control amplifier to be output to the first A/D conversion circuit via a second switch. .