JP2001298957A - Power supply and starting method for the power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the overshoot of load voltage when staring a power supply which includes an alternating-current power circuit, a pulse number control circuit that pulse-number-modulation-controls the AC power circuit, and a reactor that comprises a resonance circuit together with the capacitive component of a load supplied with power from the AC power circuit. SOLUTION: At t1 when a certain time has passed after the issuance of an operation command from the pulse number control circuit, the voltage Vs of an AC voltage source is reduced to a predetermined value. At t2 when a certain time has thereafter passed, the voltage is returned to the original value. This operation allows the overshoot of load voltage VL to be reduced to an insignificant amount, so that the risk of damage to a load due to overvoltage can be circumvented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device and a method of starting the power supply device, and more particularly to a resonance type in which a specified power is supplied to a load by a combination of an inverter and a resonance circuit using an induction heater, a discharge tube and the like as a load. The present invention relates to an inverter device and a method of starting the same.

[0002]

2. Description of the Related Art FIG. 8 shows a circuit configuration of a conventional system. As shown in FIG. 1, the conventional circuit includes an AC voltage source 1 using an inverter or the like, a reactor 2, a capacitive load 3, and a pulse density control control circuit 4. . The capacitive load 3 includes, for example, a resistance component R,
It is assumed that a parallel circuit is formed with the capacitance component C. At this time, a resonance circuit is formed by the capacitance component C of the reactor 2 and the capacitive load 3. Therefore, a voltage higher than that of the voltage source 1 can be applied to the load by the LC resonance phenomenon.

In such a configuration, setting lower than the resonance frequency of the resonance circuit the frequency of the AC voltage source, as shown in FIG. 9 is an operation waveform, the power supply current to the power supply voltage V _s I _s is the lag phase. Furthermore the load voltage V _L becomes delayed phase with respect to the power source current I _s, the value is greater than the power supply voltage V _s. Value of the supply voltage V _s, by selecting the frequency of the voltage source, the resonant frequency to an appropriate value, it is possible to set the load voltage V _L and the load power to a suitable value.

When a discharge tube or the like is used as a load, it may be desirable to keep the peak value of the load voltage _VL constant in order to perform stable operation. That is, the discharge tube is in one of a discharge state and a non-discharge state, and there is no intermediate state. Therefore, to control the load power in such a case, the so-called pulse density modulation (pulse density modulation) is used.
A control method called density modulation (PDM) is used. The pulse density modulation control scheme is in operation while the constant load voltage V _L supply voltage V _s and the operating frequency is constant, frequently repeated the operation in accordance with given power command stops and, operating in a predetermined time This is a method of controlling the average power by controlling the duty ratio between the period and the stop period. That is, as shown in FIG. 10, when it is desired to set the average power to P2 for an inverter whose power becomes P1 during continuous operation, the PDM signal is given as an inverter operation / stop command, thereby providing a voltage source. 1
It is only necessary to frequently repeat the operation and stop of. In one cycle of this PDM signal, even if the inverter output power is not composed of equally-spaced pulses, the average power P2 can be obtained if the number of pulses per cycle is constant, that is, if the pulse density is constant. You can. in this way,
The average power can be set to a desired value by controlling the inverter to alternately repeat the operation state and the stop state. Note that the figure shows the inverter output voltage,
The waveforms of the inverter output current and the inverter instantaneous power are also shown.

[0005]

In the above-mentioned conventional circuit, a so-called overshoot may occur in which the peak value of the load voltage _VL at the time of startup becomes larger than that in the steady state. FIG. 11A shows an example of the waveform. This overshoot occurs according to the following principle.

[0006] Now, the power supply voltage V _s is started at the zero-cross timing. Wherein the initial current of the power supply current I _s, the initial voltage of the load voltage V _L are both zero.
On the other hand, in the steady state shown in FIG. 9, the current I _s at the instant of the power supply voltage V _s zero crossing -I _s0, the load voltage V _L has an instantaneous value that becomes -V _L0. Accordingly, the circuit of the startup can be regarded as the circuit in a steady state, the initial current I _s0 shown in Figure 12, the superposition of the circuit indicating the transient state of the initial voltage V _L0. Load voltage V _L
The steady term V _L1 and the transient term V _L2 are as shown in FIG. The frequency of the stationary term V _L1 is the power supply frequency, and the frequency of the transient term V _L2 is the resonance frequency. Since the stationary term _VL1 and the transient term _VL2 have different frequencies,
There are a case where both waveforms are added and a case where they cancel each other. If both peaks or their vicinity overlap at a certain timing, the amplitude of the load voltage _VL increases and overshoot occurs. This overlap occurs many times,
Since the transient term V _L2 is an attenuated waveform, usually only the first overlap is a problem.

[0007] Due to this overshoot, a voltage higher than the originally intended voltage is applied to the load.
Overvoltage may damage the load. In order to prevent overshoot, it is common to use a so-called soft start in which the power supply voltage is gradually raised from a low value. However, when using pulse density modulation, there is a disadvantage that one operation period ends before soft start ends depending on conditions, and a desired output cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide a power supply apparatus and a method of starting the power supply apparatus, which can effectively suppress overshoot at the time of startup. That is.

[0009]

A power supply according to the present invention comprises an AC power supply circuit, a pulse density control circuit for performing pulse density modulation control of the AC power supply circuit, and a capacitive component of a load to which power is supplied by the AC power supply circuit. A reactor constituting a resonance circuit together with the reactor, wherein a second time after a predetermined time elapses from a first time after a predetermined period elapses from a time when the AC power circuit is started during a time when the AC power circuit is started. A voltage control circuit for reducing a voltage value applied to the load before time is included. Also,
The voltage control circuit may control the first time and the second time so that a peak value of a voltage applied to the load is minimized.
And the voltage value to be lowered is determined.

A method of starting a power supply device according to the present invention includes an AC power supply circuit, a pulse density control circuit for performing pulse density modulation control of the AC power supply circuit, and a resonance circuit together with a capacitive component of a load to which power is supplied by the AC power supply circuit. A power supply device including a reactor, wherein a voltage value applied to the load at a first time after a predetermined period elapses from a time when the AC power supply circuit is started during the time when the AC power supply circuit is started is changed. Setting a first voltage value to be lower, and setting a second voltage value higher than the first voltage value at a second time after a lapse of a predetermined time from the first time. Features. Further, the first time, the second time, and the first voltage value are determined so that a peak value of a voltage applied to the load is minimized.

In short, in a circuit in which a so-called resonance circuit comprising a series circuit of a reactor and a capacitor is connected to an AC voltage source, the second voltage lower than the first specified voltage after the voltage source is started at the first specified voltage. The voltage is temporarily reduced to the specified voltage, and then the third voltage is higher than the second specified voltage.
, The overshoot of the load voltage described above can be suppressed. In this case, since the timing at which the overshoot occurs can be easily predicted from the power supply frequency and the resonance frequency according to the above-described principle, the power supply voltage is narrowed in accordance with the timing at which the overshoot occurs, and the rise of the voltage is suppressed.

[0012]

Next, an embodiment of the present invention will be described with reference to the drawings. In the drawings referred to in the following description, the same parts as those in the other drawings are denoted by the same reference numerals. FIG. 1 is a block diagram showing an embodiment of a power supply device according to the present invention. In this figure, the present device differs from the conventional device in that a voltage control circuit 5 is added. When the inverter configuration is adopted, the voltage source 1
As shown in FIG. 2, a triangular wave generating circuit 11 for generating a triangular wave 110 and a comparing circuit 12 for comparing the triangular wave 110 with a voltage command 50 from the voltage control circuit 5
A pulse distribution circuit 13 that generates a switching pulse 130 in accordance with a comparison output 120 of the comparison circuit 12,
And a switching circuit configured to control the polarity of an inverter output voltage 140 to be applied to a load.

The voltage control circuit 5 includes a pulse density control circuit 4
After a predetermined time from the issuance of the operation command, the voltage level of the voltage command 50 is reduced to a predetermined value at a time t1, and the voltage level is returned to the original value again at a time t2 after a predetermined time has elapsed. FIG. 3 is a waveform chart showing the operation of each unit in FIG. As shown in the figure, the voltage command 50 is set at a time t after a predetermined time has elapsed from the operation start time t0.
At 1, the voltage level decreases, and further returns to the original voltage level at time t <b> 2 after a lapse of a predetermined time.

In this example, between time t1 and t2,
80% voltage level V with respect to normal voltage level V _{100
Shall be} reduced to ₈₀ . Thereby, the triangular wave 11
The pulse width of the comparison output 120, which is the result of comparison with 0, becomes narrow during the period from time t1 to t2. The comparison output 120 is input to the pulse distribution circuit 13, and a switching pulse 130 is output. The switching pulse 130 turns on and off each of the switching elements constituting the switching circuit 14, whereby the operation as an inverter is performed. At this time, inverter output voltage 140 changes from time t1 to time t.
Up to 2, the pulse width becomes narrow.

That is, as shown in FIG. 4A, the switches S1 and S4 are turned on, and the switches S2 and S3 are turned on.
Is turned off, and the switches S1 and S4 are turned off and the switches S2 and S3 are turned on as shown in FIG.
By controlling the on / off timing of steps S4 to S4, a known inverter operation can be obtained. This state (a) or (b) indicates that the waveform of the inverter output voltage 140 in FIG.
E "or" -E ".

On the other hand, during the period when the waveform of the inverter output voltage 140 in FIG.
4 is in the state of FIG. 4 (c) or (d). That is, in the state of FIG. 4C or 4D, when viewed from the load side, both terminals of the inverter output are short-circuited.
Thus, a period of 0 V is created. As shown in FIG. 3, the waveform of the load voltage when the voltage command 50 is changed so as to decrease is shown in FIG. As shown in the figure, lower the voltage V _s of the AC voltage source 1 at a predetermined time after t1 from the operation command is issued from the pulse density control circuit 4 to a predetermined value, it has elapsed further predetermined time At t2, the voltage is returned to the original value again. By the operation as described above, as shown in the figure, the overshoot of the load voltage _VL can be reduced to a level that does not cause a problem, so that the risk of damage due to the overvoltage of the load can be avoided.

In the case where an inverter is used as the AC voltage source 1, such voltage control can be realized by the above-described pulse width control or the like. If the voltage source is not an inverter,
If it is a variable voltage source such as a generator or linear amplifier,
The voltage setting may be controlled on / off according to the output of the voltage control circuit 5. By the way, the times t1 and t2 and the voltage level value are set in advance. However, when the frequency of the AC voltage source 1 is changed, the frequency is switched to an optimum value accordingly. 6 and 7 show simulation results by the present inventor. In these figures, the peak value of the AC power supply voltage is 1000 V, the frequency is 1400 Hz, and the inductance of the reactor is 1
00 μH, load capacitance 100 μF, load resistance value 20 Ω, peak load voltage at steady state 435
It is assumed that the voltage is 0V. Then, the inventor changes the voltage drop starting point in 0.5 steps between 0.5 and 2.0 cycles, and sets the voltage drop time width to 0.5 between 1.0 and 2.5 cycles. When the amplitude ratio of the power supply voltage is changed at intervals of 0.2 between 0.8 (voltage level is reduced by 20%) and 0.2 (voltage level is reduced by 80%), the voltage peak value is obtained. In contrast, how the times t1 and t2 and the voltage amplitude ratio are changed to reduce the overshoot value is shown. The value of the overshoot is smaller as the value is closer to 1.000.

As a result of performing the simulation as described above, the overshoot is 1.002 in the case of the symbol “☆” shown in FIG. In this case, time t1 is 1.071 m from the start of activation.
s, time t2 is 2.143 ms from the start of activation,
The voltage level is reduced by 0.4, that is, 60%. By the above-described operation, as shown in FIG. 5, the overshoot of the load voltage can be reduced to a level that does not cause a problem, so that the risk of damage due to the overvoltage of the load can be avoided.

Incidentally, the voltage level before time t1 and the voltage level after time t2 do not necessarily have to match. According to the analysis result of the simulation by the inventor, the time t2 and the lowered voltage level are considered to have a large effect on the overshoot. Therefore, after the voltage level reduction period, if the voltage level is raised to a higher level, Even if it does not return to the original voltage level, it seems that there is no effect on suppressing the overshoot itself.

In this case, the final voltage value (the voltage value after the start-up is completed) is determined by the power supplied to the load and cannot be changed. If the voltage is raised to the final voltage value without returning to the above voltage level, the overshoot itself can be suppressed. The power supply device described above includes an AC power supply circuit,
A power supply device including a pulse density control circuit for performing pulse density modulation control of the AC power supply circuit, and a reactor constituting a resonance circuit together with a capacitive component of a load supplied with power by the AC power supply circuit. Setting a voltage value applied to the load to a lower first voltage value at a first time after a lapse of a predetermined period from the activation time, and a second voltage after a lapse of a predetermined time from the first time. At a time of the second voltage value is set to a second voltage value higher than the first voltage value. The first time, the second time, and the first voltage value are determined so that the peak value of the voltage applied to the load is minimized.

[0021]

As described above, according to the present invention, at the time of starting transition of the AC power supply circuit, the voltage value applied to the load at the first time after the elapse of a predetermined period from the starting point is reduced. By setting the voltage value and setting the voltage value to a second voltage value higher than the first voltage value at a second time after a lapse of a predetermined time, overshoot of the load voltage at the time of starting the power supply device is effectively suppressed. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a power supply device according to the present invention.

FIG. 2 is a block diagram showing a configuration example of a voltage source in FIG.

FIG. 3 is a diagram illustrating the operation of each unit in FIG. 2;

FIG. 4 is a diagram illustrating a control state of a switching circuit in FIG. 2;

FIG. 5 is a waveform diagram showing a load voltage when the power supply device of FIG. 1 is activated.

6 is a diagram showing simulation results of times t1 and t2 in FIG. 3 and a voltage level to be reduced.

FIG. 7 is a diagram showing simulation results of times t1 and t2 in FIG. 3 and a voltage level to be reduced;
It is a continuation part of FIG.

FIG. 8 is a block diagram showing a configuration of a conventional power supply device.

FIG. 9 is a waveform chart showing the operation of the circuit of FIG.

FIG. 10 is a waveform chart showing an operation of a general pulse density modulation control method.

11A is a waveform diagram of a load voltage at which an overshoot occurs, and FIG. 11B is a waveform diagram showing a steady term and a transient term of the load voltage.

12 is a diagram illustrating an operation of the circuit of FIG. 8 in a transient state.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC voltage source 2 Reactor 3 Load 4 Pulse density control circuit 5 Voltage control circuit

Claims (4)

[Claims] 1. A power supply including an AC power supply circuit, a pulse density control circuit for performing pulse density modulation control of the AC power supply circuit, and a reactor forming a resonance circuit together with a capacitive component of a load supplied with power by the AC power supply circuit. A voltage value to be applied to the load during a transition of activation of the AC power supply circuit from a first time after a lapse of a predetermined period from a start time to a second time after a lapse of a predetermined time from the activation time. A power supply device, comprising: a voltage control circuit that reduces the power consumption. 2. The voltage control circuit according to claim 1, wherein the first time, the second time, and the voltage value to be reduced are determined so that a peak value of a voltage applied to the load is minimized. The power supply device according to claim 1, wherein: 3. A power supply including an AC power supply circuit, a pulse density control circuit for performing pulse density modulation control of the AC power supply circuit, and a reactor constituting a resonance circuit together with a capacitive component of a load supplied with power by the AC power supply circuit. A method of activating a device, wherein a voltage value applied to the load is set to a lower first voltage value at a first time after a lapse of a predetermined period from a time of activation of the AC power supply circuit during a transition of activation of the AC power supply circuit. Starting the power supply device at a second time higher than the first voltage at a second time after a lapse of a predetermined time from the first time. . 4. The method according to claim 1, wherein the first time, the second time, and the first voltage value are determined such that a peak value of a voltage applied to the load is minimized. A method for activating a power supply device according to claim 3.