JPS624735B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a power supply control device using an electric valve.
In particular, it relates to a device for controlling the firing phase of an electric valve.

For example, when power is supplied to a lagging power factor load such as a welding machine from an alternating current power source, a configuration as shown in FIG. 1 is adopted to control the power supply current by ignition control of an electric valve. This supplies the output of an AC power supply 1 to a resistor 3 and an inductance 4, which are loads, via an electric valve 2. The electric valve 2 is controlled by:
This is done by applying a power synchronization signal taken out from the power supply by the transformer 5 to the phase control circuit 6, and this phase control circuit 6 giving the gate signal V _G to the electric valve 2.

The phase control circuit 6 adjusts the charging current of the capacitor 9 by adjusting the variable resistors 7 and 8, and each time the charging voltage of the capacitor 9 reaches a predetermined value, the unijunction transistor 10 is turned on to control the secondary voltage of the transformer 11. The pulse appearing on the side is used as the gate signal _VG . in this case,
The variable resistor 7 is used to limit the firing phase of the electric valve 2 so that it does not advance beyond the load power factor angle when the variable resistor 8 is short-circuited.
After setting , the load current is adjusted by the variable resistor 8.

However, the device of FIG. 1 has a problem when the load power factor is close to 0, that is, when there is almost only inductance. This will be explained with reference to FIGS. 2a and 2b. In FIG. 2A, the ignition phase of igniting the electric valve 2 at time t ₁ and thereafter obtaining the full ignition output voltage V _O is shown as V _G . As is clear from this illustrated waveform, since a transient DC component flows, a fully fired output waveform cannot be obtained unless the firing phase is changed every cycle. In addition, FIG. 5b shows a waveform when ignition is delayed from the power factor angle of the load. In this case, since the transient DC component attenuates within half a cycle, it is sufficient to fire in the same phase in order to obtain a symmetrical output voltage. That is, if ignition is performed at a phase that is ahead of the load power factor angle, control becomes discontinuous due to transients, and there is a range in which control becomes impossible.

Therefore, conventionally, in order to prevent the phase from advancing beyond the load power factor angle even if the set value of the variable resistor 8 for current setting in FIG. 1 changes, the variable resistor 8 is
It is necessary to adjust the limit value of the ignition phase angle. When there are multiple loads such as a welding machine load, or when the load power factor changes, conventionally the firing phase is limited to a phase that is delayed from the load power factor and the output voltage is reduced. are doing.

However, this method has the disadvantage that the range in which the output voltage can be controlled is narrowed and the utilization rate of the device is poor.

SUMMARY OF THE INVENTION An object of the present invention is to provide a control device that can perform continuous control even when the load power factor changes, and that can utilize the output voltage up to the full ignition output.

An embodiment of the present invention will be described below with reference to FIGS. 3 to 5.

FIG. 3 is a waveform diagram for explaining the principle of the present invention. Now, the ignition phase is fixed for one cycle of the power supply voltage, and the phase is changed every cycle, and the ignition phase of the previous and last time is set as θ ₁ , and the time during which the electric valve is off is t ₁ shall be. When the load power factor Cosφ≈0, α=θ ₁ −1/2t ₁ (1) holds true, where α is the phase angle for full firing in the next cycle. The meaning of this equation is that when Cosφ≒0, if the firing phase angle is advanced by 1/2t ₁ , the angle at which the electric valve turns off will also be delayed by 1/2t ₁ , which means that the time the electric valve is turned off will be delayed by 1/2t 1. If the phase is advanced by 1/2, the electric valve will be fully fired without turning off.

With such control, if cosφ>0, full firing will not be reached in one cycle, but it will approach full firing in several cycles.

Moreover, α=θ ₁ −1/2Kt ₁ (K>1) (2) Here, if K is a function of Cosφ, the total firing will be approached more quickly.

According to equation (1), the limit value (α _L ) of the ignition phase angle in the next cycle is (θ ₁ −1/2t ₁ ), and the load current control phase (α control) is (θ ₁ −△α ₁ ). If 1/2t ₁ >Δα ₁ , the firing phase angle becomes θ ₁ −Δα ₁ =θ ₂ .

The α limit of the next cycle becomes (θ ₂ −1/2t ₂ ), the α control becomes (θ ₂ −△α ₂ ), and (Δα ₂
>1/2t ₂ ), phase limit control is performed so that the firing phase becomes (θ ₂ −1/2t ₂ ).

It has been found that by such control, it is possible to control to a point close to full ignition in about 3 cycles, regardless of the load power factor. As an extreme example, if we consider the case of Cosφ = 1, if firing is started at α = 90°, then α = 45° in the first cycle, α = 225° in the second cycle,
Since α≒11° in the third cycle, the output in the third cycle is more than 95% of the total firing output.

FIG. 4 shows an embodiment of the present invention, in which the same reference numerals as in FIG. 1 indicate the same elements. In this device, a voltage detector 21 detects the voltage across the electric valve 2.
The phase of the output power supply voltage is detected by the transformer 5. Then, input each detection output to the phase detection circuit 22,
The power supply phase V _AC and the control residual angle phase are respectively V
It is applied as _{an SCR} to the logic circuit 23 to obtain logic signals a, b, c, and d.

These logic signals are input as current signals to integrators 31 and 41 via resistor R, and integrator 31 calculates the limit value α _L of the ignition phase angle, and integrator 41 calculates the point of the next half cycle. Keep the arc phase. Also, the comparators 32 and 42 convert the firing phase angle limit value α _L and the firing phase into logic levels, respectively, and convert the phase control signal α and the α _L
The AND circuit is given to the AND circuit 33, and the output of this AND circuit is sent to the electric valve 2 via the pulse amplifier 34.
Give to the gate.

On the other hand, the firing phase of the previous half cycle is memorized by the integrator 41, and the output V ₃ of this integrator 41
is compared by a comparator 22 and converted into a logic level, which is connected to one of the electric valves 2 via a pulse amplifier 43.

On the other hand, the load current value is detected by the current transformer 35,
The output of the effective value converter 36 and the output of the current setter 37 are compared, and the output is passed through the amplifier 38 to the phase control circuit 39.
outputs a phase control signal output α.

FIG. 5 is a waveform diagram showing the operation of the above embodiment. As shown in FIG. 5, a logic signal V _AC is generated from the power supply voltage V, and the voltage across the electric valve is detected by a voltage detector 21 to generate a logic signal V _SCR . Create signals a, b, c, and d from these two types of signals, and apply a constant voltage +V ₁ to the integrator 31 through a resistor.
It is applied and integrated via _R1 and only when contact a is operating. On the other hand, only when the constant voltage -V ₁ is passed through the resistor R/2 and contact b is operating, the integrator 4
1 and integrate.

Then, the output V ₂ of the integrator 31 is converted by the comparator 32 into a logic level α _L. This signal α _L
This means that the calculation of equation (1) described above has been performed. That is, R of each input resistance is selected to be R/2 so that the rate of change of V ₂ is twice as high when contact a is on as when contact b is on. Therefore, it becomes possible to calculate 1/2t ₁ in equation (1), and since the calculation of 1/2t ₁ starts from the time (θ ₁ - t ₁ ) in Figure 3, the phase limit after the calculation is completed is This means that α _L =θ ₁ −t ₁ +1/2 t ₁ =θ ₁ −1/2t ₁ has been found. That is, unless the phase advances beyond this limit value α _L , the ignition phase will not advance beyond the power factor angle.

When the phase control signal α controlled by the phase control circuit 39 advances beyond time _T5 , the AND circuit 3
3, the electric valve control signal V _G1 is limited to α _L as shown in the figure.

On the other hand, the integrator 41 stores the phase at which the contact C is closed, calculates this phase after the contact d closes, converts it into a logic signal by the comparator 22, and sends the phase control signal V via the pulse amplifier 24. Output _G2 . Next, at time _T8 , the same operation as the previous time is repeated to calculate and control α _L.

According to this method, control is performed with the same phase during one cycle, and phase limit control is performed such that the phase is advanced in the next cycle by 1/2 of the time that the electric valve is off for each cycle.

Instead of α = θ ₁ -1/2t ₁ in the above example, α = θ ₁ -1/nt ₁ according to the load power factor angle, and n2, when the power factor angle is 90°, n = 2, power factor angle When 0, n
It is also possible to control n as a function of φ so that φ=1. Further, in FIG. 4, the alpha phase limit control is calculated in analog, but the same effect can of course be obtained even if it is configured digitally. Furthermore, the same effect can be obtained by performing similar calculations using a computer and performing software processing such as limiting the phase advance angle for each cycle to 1/2t ₁ or 1/nt ₁ .

As described above, the present invention does not require any adjustment even when the load power factor changes, and since the present invention automatically controls the entire output to be applied to the load, the device capacity can be fully utilized. In particular, in the case of a welding machine that frequently switches loads, it can be used stably and with high efficiency. Further, according to the present invention, since no DC component flows, there is no risk of DC bias magnetization even if a transformer is connected to the load.

[Brief explanation of the drawing]

Fig. 1 is a wiring diagram showing the configuration of a power supply control device using a conventional electric valve, Fig. 2 is an explanatory diagram showing the necessity of ignition phase restriction in the same device, and Fig. 3 is an explanatory diagram of the principle of the present invention. , FIG. 4 is a block diagram showing one implementation side of the present invention, and FIG. 5 is an explanatory diagram of the operation of the embodiment of FIG. 4. 1...Power supply, 2...Electric valve, 3, 4...Load,
5...Transformer, 6...Phase control circuit.

Claims (1)

[Scope of Claims] 1. A device for controlling AC power supplied from an AC power source to a load via an electric valve, comprising means for detecting the voltage of the power source and a turn-off period of the electric valve; means for calculating _a point-side phase angle limit value α _L for firing the electric valve at a particular cycle of voltage of; A power supply control device using an electric valve, characterized in that it is equipped with an AND gate that takes a final firing phase angle given from two values. α _L = θ ₁ − (1/n) t ₁ where θ ₁ and t ₁ are the firing phase angle and turn-off period of the electric valve in series of cycles of the particular cycle, and n is less than or equal to 2. Positive integer.