JPH04317565A - Dc high-voltage stabilizing power source - Google Patents

Abstract

PURPOSE:To stabilize output voltage by bringing the current phase angle phiat turn off close to the half cycle of a resonation circuit regardless of the magnitude of output power. CONSTITUTION:The output current of a high-voltage rectifying circuit 8 is detected as a voltage value with a current detecting resistor 11, and the output voltage is converted into voltage through the multiplication circuit with reference voltage 13, and the voltage is transmitted as reference voltage to a differential amplifier 17. On the other hand, the input voltage of an inverter circuit 5 is detected with a potential dividing resistor 3 and a detecting resistor 4, and the voltage is transmitted likewise to one end of a differential amplifier 17, and by the comparison with the reference voltage being converted into power and the amplification, the output signal of the differential voltage is transmitted to a phase control circuit 18. This phase adjusting signal is transmitted to a thyristor control rectifying circuit 2, and by the control of the phase angle of a power source, the input voltage of an inverter is changed according to the final output voltage. As a result, this makes it control the stabilization of the voltage at all times in the vicinity of the half cycle pi of the current waveform at turn off.

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to protection of switching elements of a stabilized DC power supply by pulse width control (PWM) of a resonant inverter.

2. Description of the Related Art FIG. 3 is a circuit diagram of a conventional DC stabilization system using a resonant inverter, and FIG. 4 shows voltage and current waveforms of switching elements in the inverter circuit. In FIG. 3, an AC power supply 1 is converted into a DC voltage through a rectifier circuit 19, and the DC voltage is connected to an inverter circuit 5, and a series resonance circuit is created by connecting a resonance capacitor 6 and the leakage reactance of a high-frequency transformer 7 through a switching operation. The high frequency transformer 7 steps up the voltage corresponding to the current carrying width, and the high voltage rectifier circuit 8 applies the DC high voltage to the voltage dividing resistor 9 and the load 12. Voltage control and stabilization are performed by voltage detection. resistance 10
A part of the generated voltage is detected and the differential amplifier 14
, reference voltage 13 to the error amplifier, the output of the difference voltage is transmitted to the pulse width control circuit 15, and the output signal is transmitted to the gate of each switching element of the inverter circuit 5 to control the conduction width of the current. This controls and stabilizes the output voltage. As a result, an output voltage corresponding to the reference voltage 13 can be supplied to the load. In order to control the energization width of the switching element in this way, the phase angle at turn-off is always determined by the output voltage, current value,
In other words, it will change depending on the output power, and depending on the value, it may turn off at the peak value of the LC resonance waveform of the current.In order to prevent reverse voltage at this time and reduce loss when turned off, a snubber circuit is required. is installed to protect the switching elements. However, as shown in FIG. 4, which shows an example of the voltage e and current i waveforms at turn-off, if the phase angle φ turns off near the peak of the switching current, the off-time toff becomes maximum, and during that period The loss is also maximum, and thermal damage may occur.

As mentioned above, the turn-off time may increase depending on the value of the output power, which causes the following problems. (1) When the switching current turns off near its peak value, both the reverse voltage and the loss become large. (2) As a result, the temperature of the element may rise excessively, resulting in destruction. (3) Appropriate protection circuits must be provided to prevent the above.

[Means for Solving the Problems] The present invention, as a means to solve the problems such as loss during turn-off as described above, is designed so that the turn-off current phase angle φ is always half of the resonant circuit, regardless of the magnitude of the output power. This attempts to stabilize the output voltage by feeding back the output power and controlling the input voltage of the inverter so that the period is close to π.

[Operation] By setting the turn-off phase angle to around half the period of the resonant circuit, the switching current value at that time is small as shown in the waveform in Figure 2, and the turn-off time is also short, and the loss generated in the element during that period is also small. Become. This is also related to element cooling, allows for a smaller power supply, and is economically advantageous.

Embodiments An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. In FIG. 1, an input DC voltage for an inverter circuit 5 is generated from an AC power supply 1 via a thyristor-controlled rectifier circuit 2, and a resonance circuit of the inverter circuit 5, a resonance capacitor 6, and a leakage reactance of a high-frequency transformer 7 is formed. , the resonance voltage is stepped up by a high frequency transformer 7, and a high voltage rectifier circuit 8 applies a DC high voltage to a voltage dividing resistor 9 and a load 12. To stabilize the output voltage, a part of the output voltage is detected by a voltage dividing resistor 9 and a voltage detection resistor 10, a reference voltage 13 is transmitted to a differential amplifier 14, and an output signal of the difference voltage is sent to a pulse width control circuit 15. A pulse width signal corresponding to the voltage difference is transmitted to the inverter circuit 5, and its phase angle is controlled to stabilize the voltage. The above is basically the same as the conventional type, but instead of stabilizing only by controlling the phase angle, which is a drawback of the conventional type, the input voltage of the inverter circuit 5 is changed to control the resonant current value. By doing so, the phase angle is kept almost constant, the output voltage is fed back, and its stabilization is always controlled around half the cycle of the resonant current. That is, the output current is detected as a voltage value by the current detection resistor 11, and the output current is detected as a voltage value by the current detection resistor 11.
The output power is converted into a voltage through a multiplier circuit with 3 and the voltage is used as a reference voltage and transmitted to the differential amplifier 17. On the other hand, the input voltage of the inverter circuit is detected by the voltage dividing resistor 3 and the detection resistor 4.
A voltage is detected from the voltage, the voltage is also transmitted to one end of the differential amplifier 17, and the output signal of the difference voltage is transmitted to the phase control circuit 18 through comparison and amplification with the power-converted reference voltage, which adjusts the phase of the output. Thyristor control rectifier circuit 2
By controlling the phase angle of the AC power supply, the inverter input voltage is changed according to the final output power, and the voltage is always stabilized around the half period π of the current waveform at turn-off shown in Figure 2. It is something that makes you As a result, the turn-off time of each switching element is shortened, and both reverse voltage and loss are reduced.

[Effects of the Invention] As described above, by feeding back the output power to the input voltage of the inverter, compared to the conventional resonant inverter system, (1) the loss when the switching elements are turned off is reduced. (2) The current value when the switching element turns off is small, the current does not turn off near the peak value that occurs in the conventional system, and the value of the reverse voltage is also small. (3) Since the inverter input voltage is controlled according to the output, its efficiency is increased overall. (4) Since the switching current is close to a sine wave, the ripple is also improved. (5) Power efficiency is good because the input to the high frequency transformer is always close to a sine wave. These effects are of high industrial and practical value.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram of a DC high voltage stabilized power supply using pulse width control (PWM) of a resonant inverter according to the present invention.

FIG. 2 shows voltage and current waveforms of the switching elements when the inverter is turned off.

[Figure 3] shows the P of a conventional resonant full-bridge inverter.
A circuit configuration diagram of a DC high-voltage stabilized power supply using a WM function.

FIG. 4 shows voltage and current waveforms of one switching element when the inverter is turned off.

[Explanation of symbols]

1………………AC power supply 2………………Thyristor control rectifier circuit 3, 4……
Inverter input voltage division detection resistor 5...Inverter circuit 6...Resonance capacitor 7...High frequency transformer 8...High voltage rectifier circuit 9... ......Voltage dividing resistor 10......Voltage detection resistor 11......Current detection resistor 12...Load 13...Reference voltage 14, 17...Differential amplifier 15... ...Pulse width control circuit 16...Multiplication circuit 18...Phase control circuit 19...Rectifier circuit i...Current waveform of switching element e...
... Voltage waveform of switching element φ, π ...... Phase angle toff ... Turn-off time

Claims (1)

[Claims] Claim 1: In a DC high voltage stabilization circuit using pulse width control of a resonant inverter, its output voltage and current are detected, and a differential amplifier between the detected voltage and a reference voltage applies the difference voltage to the inverter circuit with a pulse width. Feedback is provided through the control circuit to stabilize the output voltage, and at the same time, the voltage with the power equivalent voltage as the reference voltage via the detection current and reference voltage multiplier circuit and the detection voltage of the inverter input voltage are The difference voltage is fed back by the differential amplifier to a rectifier circuit such as a thyristor for generating the inverter input voltage, and the inverter input voltage is automatically adjusted according to the output power.
A DC high-voltage stabilized power supply that always switches the pulse width of the inverter circuit at the optimal phase angle.