JPH061989B2 - Control device for transistor inverter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transistor inverter control device that safely performs a protection / restart operation when a momentary power failure occurs in a transistor inverter with a simple configuration.

[Conventional technology]

FIG. 4 is a block diagram showing a conventional control device for a transistor inverter of this type. In FIG. 4, 1 is an AC power supply, 2 is a diode bridge for rectifying the AC power supply 1 to obtain DC, 3, 4 is a reactor and a capacitor for smoothing the direct current obtained by the diode bridge 2, 5 is a transistor inverter for converting the direct current into alternating current, 6 is the load of the inverter 5, and 7 is the magnitude of the direct current circuit voltage. A DC voltage detection circuit that outputs a proportional value, 8 is a low voltage detection circuit for detecting a decrease in the DC circuit voltage, and thus AC power supply voltage, 9 is a DC circuit overvoltage failure detection circuit, and 10 is the energy of the reactor 3 is returned. It is a flywheel thyristor for making it.

Next, the operation of the conventional transistor inverter control device will be described. In the normal operation 3 state, the AC power supply 1 is rectified by the diode bridge 2 and converted into DC, and is smoothed by the reactor 3 and the capacitor 4 to become smooth DC. In a normal operating state, the flywheel thyristor 10 is in a non-firing state, and 3 and 4 act as ordinary LC filters. The smoothed DC is PWM-controlled by the inverter 5 and converted into AC,
It is applied to the load 6.

Next, the operation when an instantaneous power failure occurs will be described with reference to FIG. In FIG. 5, a is a waveform for one phase of the AC power source 1, b is a DC circuit voltage, that is, a terminal voltage waveform of the capacitor 4 in FIG. 4, c is a gate signal waveform of the flywheel thyristor 10, and d. Is an operation command to the inverter 5. At time t ₀ , when a power failure occurs in the AC power supply, the energy to the load 6 is supplied by consuming the electric charge stored in the capacitor 4, so that the capacitor voltage rapidly increases as shown in FIG. 5b. Going down.
At time t ₁ , when the detection level of the low voltage detection circuit 8 is reached, its outputs 8a and 8b change as shown in FIGS. 5c and 5d, the inverter 5 stops operating, and the flywheel thyristor 10 Is fired. When the operation of the inverter is stopped, the energy consumption is very low, so the decay rate of the DC circuit voltage is very low. If there is a short power failure, the DC voltage is kept almost constant during the period from time t ₁ to t ₂ . In time t _2, the the AC power is restored, the DC voltage is as shown by the solid line in FIG. 5 b, to recover and change A → B → C. Here, in the flywheel thyristor 10, the DC circuit voltage originally changes as A → B → C ′ as shown by the broken line in FIG. 5b due to LC vibration due to the reactor 3 and the capacitor 4 at the time of power recovery. Then, an overvoltage is caused, and the DC circuit overvoltage failure detection circuit 9 operates to prevent the malfunction from stopping. That is, the energy of 1/2 L _i ² of the reactor 3 that contributes to the overcharge of the capacitor 4 is returned to the flywheel thyristor 10 from the time point B in FIG. 5B to prevent the overcharge. From a time point t ₂ when the DC circuit voltage starts to recover, a certain confirmation time t _d
At time t ₃ when passed a firing signal 8b points to flywheel thyristor 10 is stopped, the inverter operation command 8a is given again, to return to normal operation.

[Problems to be solved by the invention]

The conventional device is configured as described above, and the flywheel thyristor 10 is required to continue the operation without tripping even at the momentary stop. For this reason, the circuit becomes complicated and large, and the flywheel thyristor gate signal of relatively large power must be maintained even during a power failure, and the control power supply also requires special performance. There was a point.

The present invention has been made to solve the above problems, and enables smooth restarting after an instantaneous power failure without adding special components such as a flywheel and thyristor to the main circuit. An object of the present invention is to obtain a control device for a transistor inverter that can be used.

[Means for solving problems]

The inverter apparatus according to the present invention are those V _CE breakdown voltage of the transistors of the inverter during outage is configured by focusing on higher than V _CE breakdown voltage during operation. Overcharging of the capacitor due to L-C vibration when recovering from an instantaneous power failure is a phenomenon during transistor operation suspension, so it does not specifically prevent overvoltage itself, but it is dealt with by overriding the overvoltage trip and restarting operation. In doing so, it is necessary to confirm that the DC circuit voltage has dropped to a value that is safe enough for the transistor to operate.

[Action]

The detection of the DC circuit voltage for restarting the operation in the present invention is for confirming whether the DC circuit voltage is within the reverse bias safe operating area (ASO) of the transistor.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First
In the figure, 1 to 9 show the same function as the corresponding part of the conventional example of FIG. 4, 11 is a storage circuit such as a flip-flop for storing the signal from the low voltage detection circuit 8, 1
Reference numeral 2 is a safe operation voltage detection circuit for detecting that the DC circuit voltage is lower than the upper limit value for operating the transistor, 13 is a NOT circuit, and 14 is an AND circuit.

Since the operation in the normal state is the same as that of the conventional embodiment shown in FIG. 4, its explanation is omitted.

Next, the operation at the momentary power failure will be described with reference to FIGS. In FIG. 2, a and b are waveforms similar to those in FIGS. 5a and 5b, and c is an output waveform of the memory circuit 11. When the output of the flip-flop 11 is "H", the inverter 5 stops operating and the DC circuit overvoltage failure detection circuit 9 is disabled. When the AC power supply fails at time t ₀ , the low voltage detection circuit 8 operates at time t ₁ as in the case of FIG. 5, and the memory circuit 11 is latched. As a result, the inverter stops operating and the DC circuit overvoltage failure detection circuit 9 is disabled.
At time t _2, the AC power supply by L-C vibrations When resuming is overcharged to a maximum voltage at time t _3. The solid line in FIG. 3 indicates the reverse bias safe operating area (AS) of the transistor.
O), the transistor must be operated inside this curve. Therefore, if the maximum collector current of the transistor in operation is set to I ₁ in the figure, the breakdown voltage V _CE of the transistor in that state becomes V ₁ in the figure, and the breakdown voltage V _CE during rest is V ₂ in the figure. Become. The voltage at time t ₃ in FIG. ₂ exceeds V _{1 in} FIG. 3 but is less than V ₂ in the normal transistor usage method. Therefore, by stopping the operation of the inverter and disabling the DC circuit overvoltage failure detection circuit 9, it is possible to prevent damage to the device and unnecessary failure trips. If the safe operation voltage detection circuit 12 detects that the voltage has dropped to the safe voltage V ₁ or less at time t ₄ due to spontaneous discharge, the memory circuit 11 is reset, the operation of the inverter 5 is restarted, and the direct current circuit is restarted. The overvoltage failure detection circuit 9 becomes operable and returns to the state before the momentary power failure. The condition for resetting the memory circuit 11 includes that the power failure is recovered by the NOT circuit 13 and the AND circuit 14. When operated at the time t ₄ is resumed, the overcharge amount of residual A capacitor is reduced suddenly, the DC circuit voltage b at time t ₅ is returned to the normal voltage.

In the above embodiment, the overvoltage detection circuit 9 is the V ₁
Although it is used as a device for detecting the above level, it becomes completely vulnerable to overvoltage by disabling it. Therefore, the V ₂ level detection in FIG. 3 is always possible for backup. You may use together with the device for. In addition, since the detection levels of the overvoltage detection circuit 9 and the safe operation voltage detection circuit 12 of FIG. 1 are generally the same in principle, it is possible to share some or all of both circuits. .

〔The invention's effect〕

As described above, according to the present invention, the instantaneous power failure restart operation of the inverter can be reliably performed without adding a special component to the main circuit, so that there is an effect that the apparatus can be made compact and inexpensive.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG.
FIG. 4 is a time chart for explaining the operation of FIG. 1, FIG. 3 is a diagram showing a safe operating region of a transistor, FIG. 4 is a block diagram showing a conventional embodiment, and FIG. It is a figure for explanation of operation of a figure. 1 is an AC power supply, 2 is a diode bridge, 3 is a reactor, 4 is a capacitor, 5 is a transistor bridge,
6 is a load, 7 is a DC voltage detection circuit, 8 is a low voltage detection circuit, 9 is a DC voltage overvoltage failure detection circuit, 10 is a flywheel thyristor, 11 is a memory circuit, 12 is a safe operation voltage detection circuit, and 13 is a NOT circuit. , 14 are AND circuits. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A transistor inverter having a transistor inverter for rectifying alternating current by a diode bridge to convert it into direct current, smoothing the direct current by a smoothing circuit composed of a reactor and a capacitor, and then converting it to variable frequency alternating current by a transistor bridge. In the control device, the storage circuit that stops switching of the transistor of the inverter when the AC power supply voltage instantaneously drops and stores that the AC power supply voltage is in the lowered state, and the storage circuit causes the lowered state. A DC circuit overvoltage failure detection circuit in which the operation is stopped when the DC circuit is overvoltage while the fact that something is stored is held, and after the capacitor is overcharged due to LC vibration after the AC power supply voltage is restored. Due to the spontaneous discharge, the above DC circuit voltage becomes a safe value for transistor operation. Control device of a transistor inverter, characterized in that a safe operating voltage detection circuit for solving the memory retention of the memory circuit when lowered.