JP3029037B2 - Converter control method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a converter for converting an AC voltage into a DC voltage by rectifying and smoothing the AC voltage and converting the input current waveform into a waveform similar to the input voltage waveform.

[Conventional technology]

8 and 9 are diagrams for explaining a conventional converter control method. FIG. 8 is a circuit diagram, and FIG. 9 is an operation waveform diagram.

In FIG. 8, the AC voltage is full-wave rectified by the full-wave rectifier circuit 2 via the high-frequency filter 1, and the switching elements 4 and 5 of the chopper circuit 3 are switched at a frequency sufficiently higher than the frequency of the AC voltage. Chopper circuit 3
To obtain a DC voltage at the output.

The operation of the chopper circuit 3 shown in FIG. 8 will be described with reference to the operation waveform diagram shown in FIG. First, when the switching elements 4 and 5 are simultaneously turned on, energy is accumulated in the choke coil 6 and the current I ₁ (shown in FIG. 9 (b)) flowing through the choke coil 6 and the current I ₁ flowing through the switching elements 4 and 5
₂ (shown in FIG. 9 (c)) is that if the inductance of the choke coil 6 is L and the voltage full-wave rectified by the full-wave rectifier circuit 2 is E (shown in FIG. 9 (a)), E / L Rise with the slope of. Next, turn off the switching elements 4 and 5 at the same time, the energy accumulated in the choke coil 6, a rectifying diode 7, the current I ₁ flowing through the current (choke coil 6 via the flywheel diode 8 9 Figure (b)
To the current I ₃ flowing through the rectifying diode 7 Figure 9 (d)
) Flows, and charges a large-capacity smoothing capacitor 9 to obtain a DC output voltage _Eo from the capacitor 9. The current I ₁ flowing through the choke coil 6 is detected by the current transformer 10 and the current detection value obtained by extracting the low-frequency component, the deviation between the output voltage E _o and the reference voltage E _ref detected and amplified by the error amplifier 11 The difference between the proportional value of the full-wave rectified waveform of the AC voltage and the voltage detection value obtained by calculating with a voltage-controlled gain amplifier (hereinafter referred to as VCA) 12 is amplified by an operational amplifier 13 and its output is minimized. The drive of the switching elements 4 and 5 is controlled by the pulse width control circuit 14 as described above.

By controlling in this manner, the current waveform (shown in FIG. 9 (b)) of the choke coil 6 is made similar to the full-wave rectified voltage waveform (shown in FIG. 9 (a)), and harmonics of the input current are obtained. The components are reduced.

[Problems to be solved by the invention]

However, in such a control method, since the current waveform of the choke coil is similar to the full-wave rectified voltage waveform, harmonics can be reduced as compared with the capacitor input type rectifier circuit, but the input current waveform is different from the input voltage waveform. It is no longer similar. Because, to make the input current waveform similar to the input voltage waveform, the duty ratio of the switching element must be constant regardless of the voltage phase. However, as in this example, the current of the choke coil is changed to a sine wave. Then, the duty ratio of the switching element must be controlled by the voltage phase. As a result, there is a disadvantage that the input power factor is deteriorated. In addition, VCA has a problem that it is expensive and requires offset adjustment. Furthermore, a special current transformer is required to measure DC current.

[Means for solving the problem]

In order to eliminate the above-mentioned drawbacks, the present invention provides a full-wave rectifier circuit for obtaining a full-wave rectified voltage by full-wave rectifying an AC voltage, and a conversion frequency connected to an output of the full-wave rectifier circuit and sufficiently higher than the AC voltage. , Two switching elements that are simultaneously turned on and off, a choke coil sandwiched between the switching elements, two diodes connected to both ends of the choke coil, and a smoothing capacitor. A method of controlling a converter that stores energy in the choke coil when turned on, discharges energy to the smoothing capacitor through the two diodes when turned off, and supplies power to a load from both ends of the capacitor. The current is reset every switching, and the driving of the switching element is set to a fixed frequency, and the output voltage A control method of a converter, characterized in that the on-time is controlled in accordance with the operation, a full-wave rectifier circuit for obtaining a full-wave rectified voltage by full-wave rectification of an AC voltage, and a primary output to the full-wave rectifier circuit. A transformer having a winding connected thereto, a switching element connected between a primary winding of the transformer and an output of the full-wave rectifier circuit, the ON / OFF control of which is performed at a conversion frequency sufficiently higher than the AC voltage; A series circuit of a diode connected to a secondary winding and a smoothing capacitor, wherein energy is stored in the primary winding of the transformer when the switching element is on, and the energy is stored in the secondary winding of the transformer when the switching element is off. In a converter control method for supplying energy to a load from both ends of the capacitor by discharging energy to the smoothing capacitor through the capacitor, the current of the primary winding of the transformer is switched. Is reset for each etching, in which the driving of the switching element and a fixed frequency, to provide a converter control method, characterized by controlling the on-time in accordance with a variation in the output voltage.

[Action]

According to such a converter control method, the input current waveform can be made similar to the input voltage waveform, and the input power factor can be improved as if a resistor were connected to the input terminal.

〔Example〕

1 and 2 are diagrams for explaining an embodiment of the present invention. FIG. 1 is a circuit diagram, and FIG. 2 is an operation waveform diagram.

In FIG. 1, an AC voltage is connected to an input terminal of a full-wave rectifier circuit 2 via a high-frequency filter 1, and a switching element 4, a choke coil 6, and a switching element 5 are connected between DC output terminals of the full-wave rectifier circuit 2. Connected in series. Then, a series circuit of a rectifying diode 7 and a smoothing capacitor 9 is connected in parallel with the switching element 5, and a connection point between the switching element 4 and the choke coil 6 and a connecting point between the switching element 5 and the smoothing capacitor 9 are connected. The flywheel diode 8 is connected in the direction of conduction when the switching elements 4 and 5 are off, and an output is taken out between terminals of the smoothing capacitor 9. Then, the stabilization control of the output voltage, the output voltage E _o dividing by resistors 16 and 17 min in the error amplifier circuit 15, an error between the reference voltage E _ref amplified by the error amplifier 11, a pulse with a pulse width control circuit 14 After conversion to width, drive circuits 18, 19
By turning on and off the switching elements 4 and 5.

Next, the operation will be described. Assuming that the voltage value at an arbitrary phase of the full-wave rectified voltage is E, the current I ₂ flowing when the switching elements 4 and 5 are simultaneously turned on is I ₂ = Et / L, where the inductance value of the choke coil 6 is L. if it is on-time t is reset current of the choke coil is connected to each switching constant, connecting the peak value of the current I ₂ line second
As shown in FIG. 2B, the waveform of the full-wave rectified voltage shown in FIG.

When the switching elements 4 and 5 are driven at a switching frequency sufficiently higher than the frequency of the AC voltage, and the current of the choke coil 6 is reset at each switching, the output current of the full-wave rectifier circuit 2 changes at each switching.
The series of average values of the current I ₂ flowing through 5. The average value _{Iav for} each switching is T for the switching period and T for the on-time.
If on Since ET _on / L is similar to the full-wave rectified voltage waveform as described above, if Ton / T is kept constant, the output current of the full-wave rectifier circuit will be similar to the full-wave rectified voltage waveform, Therefore, the input current waveform is similar to the input voltage waveform.

Since all the current flowing to the input flows to the output, the voltage of the smoothing capacitor 9 fluctuates at the fundamental frequency of the full-wave rectified voltage E. If the output voltage stabilization control has a gain with respect to the fundamental frequency of the full-wave rectified voltage E, the off time of the switching element will be controlled to reduce the fluctuation of this frequency component, and T _on / T changes and the input current waveform does not resemble the voltage waveform. Therefore, the error amplifier circuit shown in FIG.
The AC current of 15 is sufficiently reduced by the capacitor 20 and the resistor 21 so as not to respond to the fundamental frequency of the full-wave rectified voltage E, and to be able to perform stabilization control only for DC so that the input current waveform Has a similar shape to the voltage waveform.

FIG. 3 is a diagram for explaining another embodiment of the present invention, in which a band-pass filter 22 is inserted in the output voltage detecting section of the circuit of FIG. The signal is input to the error amplifier 11 after being removed, and the response to load fluctuation and input fluctuation is improved.

FIG. 4 is a diagram for explaining another embodiment of the present invention, wherein a high-speed response converter circuit is provided at the output of the circuit of FIG.
23 connected. In the embodiment shown in FIG. 1, the response is slow. Also in the embodiment shown in FIG. 3, when there is a voltage pulsation of the fundamental frequency component of the full-wave rectified voltage and the load is hindered, or when input / output insulation is required, high-speed operation is required. In addition, the control is performed so that the input and output are insulated, and power with high voltage accuracy can be supplied to the load. This converter circuit 23
Is well known, and the description of the operation is omitted. Also,
Although this embodiment shows a forward converter,
Similar effects can be obtained with any circuit configuration such as a flyback converter.

FIG. 5 is a diagram for explaining another embodiment of the present invention, in which a flyback type circuit is used instead of the chopper circuit of FIG. 1, and the input and output need to be insulated. Used for etc.

In FIG. 5, an AC voltage is connected to an input terminal of a full-wave rectifier circuit 2 via a high-frequency filter 1, and a primary winding N1 of a transformer 24 and a switching element are connected between the DC output terminals of the full-wave rectifier circuit 2. 4 are connected. Then, a series circuit of the rectifying diode 7 and the smoothing capacitor 9 is connected to the secondary winding N2 of the transformer 24, and an output is taken out between terminals of the smoothing capacitor 9. The output voltage stabilization control is performed by dividing the output voltage _Eo by the resistors 16 and 17 in the error amplifier circuit 15, amplifying the error from the reference voltage _Eref by the error amplifier 11, and isolating the error by the photocoupler 25. After the pulse width is transmitted to the pulse width control circuit 14 and converted into a pulse width, the pulse width is sent to the drive circuit 18 to drive the switching element 4 on and off. In this embodiment, the operation is almost the same as that described in the embodiment of FIG. 1, and the same effect can be obtained.

FIG. 6 is a view for explaining another embodiment of the present invention. A band-pass filter 22 is inserted in the output voltage detecting section of the circuit of FIG. The signal is input to the error amplifier 11 after being removed, and the response to load fluctuation and input fluctuation is improved.

FIG. 7 is a diagram for explaining another embodiment of the present invention. A high-speed response chopper circuit 26 is connected to the output of the circuit of FIG.
Are connected. In the embodiment shown in FIG. 5, the response is slow, and also in the embodiment shown in FIG. It is configured so that accurate power can be supplied. This chopper circuit
26 is well known, and the description of the operation is omitted.

〔The invention's effect〕

As described above, the present invention does not use a special circuit for a current detection current transformer for current waveform control or a circuit that does not require a VCA. It can be made similar, as if a resistor was connected to the input terminal, and the input power factor could be improved.

[Brief description of the drawings]

FIGS. 1 and 2 are diagrams for explaining an embodiment of the present invention, FIGS. 3 to 7 are diagrams for explaining an embodiment of the present invention, and FIGS. 8 and 9 respectively. Is a diagram for explaining a conventional example. DESCRIPTION OF SYMBOLS 1 ... Filter for high frequency, 2 ... Full-wave rectifier circuit 3 ... Chopper circuit 4,5 ... Switching element 6 ... Choke coil, 7 ... Rectifier diode 8 ... Diode for flywheel 9 ... Smoothing Capacitor, 10 Current transformer 11 Error amplifier 12, VCA 13 Differential amplifier 14, Pulse width control circuit 15 Error amplifier circuit 16, 17, Resistor 18, 19 Drive circuit, 20: Capacitor 21: Resistor, 22: Band-pass filter 23: High-speed response converter circuit 24: Transformer, 25: Photocoupler 26: High-speed response chopper circuit

Claims (3)

(57) [Claims] 1. A full-wave rectifier circuit for obtaining a full-wave rectified voltage by full-wave rectification of an AC voltage, and is connected to an output of the full-wave rectifier circuit, and is simultaneously turned on and off at a conversion frequency sufficiently higher than the AC voltage. A switching element, a choke coil sandwiched between the switching elements, two diodes connected to both ends of the choke coil, and a smoothing capacitor. When the switching element is turned on, energy is supplied to the choke coil. And controlling the converter to release energy to the smoothing capacitor through the two diodes when the power is off and to supply power from both ends of the capacitor to a load. It is released when the element is off and reset at each switching, and after the reset, the switch is turned off. A driving frequency of the switching element is set to a fixed frequency so as to turn on the switching element, and an on-time is controlled according to a change in output voltage. 2. A full-wave rectifier circuit for obtaining a full-wave rectified voltage by full-wave rectifying an AC voltage, a transformer having a primary winding connected to an output of the full-wave rectifier circuit, and a primary winding of the transformer. A switching element connected between the line and the output of the full-wave rectifier circuit and controlled to be turned on and off at a conversion frequency sufficiently higher than the AC voltage; and a series of a diode and a smoothing capacitor connected to the secondary winding of the transformer. A circuit for storing energy in the primary winding of the transformer when the switching element is turned on, and discharging energy from the secondary winding of the transformer to the smoothing capacitor via the diode when the switching element is turned off. A method for controlling a converter for supplying power from both ends of a transformer to a load, comprising: releasing energy stored in a primary winding of the transformer when the switching element is off; A method for controlling a converter, comprising resetting each switching and turning on the switching element at a fixed frequency so as to turn on the switching element after the reset, and controlling the on-time in accordance with a change in output voltage. 3. The converter control method according to claim 1, wherein the on-time of the switching element does not respond to a fundamental frequency of the full-wave rectified voltage.