JPS6216073A - Power converter - Google Patents

Abstract

PURPOSE:To conduct control by detecting currents for a power converter precisely by adding a detecting current integrating circuit and a switching circuit clearing the integrating value of the detecting current integrating circuit while synchronizing with the operating frequency of an inverter section to a current detecting circuit. CONSTITUTION:DC voltage from input terminals 1, 2 is lead out of output terminals 5, 6 through an inverter section 3 and a rectifying smoothing circuit 4. A current detecting circuit 9 detects the input currents of the inverter section 3, and transmits an output from the inverter section 3 over a control section 8 through a comparator 11. The control section 8 drives the inverter section 3 through a driving circuit 10. In the current detecting circuit 9, a resistor 9C and a capacitor 9D constitute a detecting current integrating circuit, and a switch 9E also functioning as a transistor synchronizes the integrating value of the capacitor 9D with the operating frequency of the inverter section 3 and clears it.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power conversion device equipped with an inverter section that intermittently generates a waveform 'a current having a slope portion in which the t current value increases with the passage of time. .

[Prior art] First, an example of a conventional power conversion device will be explained with reference to FIG. It is converted into AC voltage by inverter part B,
The AC voltage 7 is converted into a smoothed DC voltage by a rectifying and smoothing circuit 4. This DC voltage is applied to a load (not shown) through the output terminal 5 and 6, and is also detected by the output voltage detection circuit 7, and the output voltage detection signal is
! The current flowing through the switching semiconductor element 6B of the 0 i/verter section 6, which is applied to the 0 input/verter section 6, is detected by the current detection circuit 9 consisting of a current transformer 9A, a rectifier 9B, and a resistor 9C.

The voltage across the resistor 9C is input to the comparator 11 as a current detection signal and compared with the reference voltage of the reference power supply 120. When the current detection signal exceeds the reference voltage t, the comparator 11 sends a signal to the control circuit 8. The control circuit 8 gives a signal to the drive circuit to turn off the switching semiconductor element 3]1n.

To explain the current detection in more detail here, with the switching operation of the switching semiconductor element 6B of the inverter section 6, the DC component Idc proportional to the output current and the current value change over time as shown in Figure 6(A). A current having a waveform totally synthesized with the rising slope portion Sa (hereinafter referred to as upper right 9) is generated in the primary winding of the power conversion transformer. This upward slope Sa occurs because the excitation current of the power conversion transformer of the converter section 6A and the current of the smoothing choke of the rectifier and smoothing circuit 4 increase with time. Here, current transformer 9A
If a core with a large cross-sectional area is used, the current transformer 9
The current obtained on the secondary side of A is a detection current having a waveform having a slope Sb at the upper right corner 9 as shown by the solid line in FIG. The detected flow m at the slope part sb'6g is applied to both ends of the resistor 9C at the slope part Scf in the upper right corner as shown in the same figure (C).
generates a current detection signal with a The comparison circuit 11 compares this current detection signal with the reference voltage of the reference source 12, and when the current detection signal exceeds the reference voltage, sends an off signal to the switching semiconductor element 3B. If it is up, the DC component i
As long as dc is small, it will not reach the reference voltage, but as the DC component increases, the right end of the slope part Sc of the current detection signal will reach the reference voltage first, and as the DC component increases further, the switching The pulse width of the current flowing through the semiconductor device is gradually narrowed down. That is,
Pulse width control can be performed continuously according to the magnitude of the DC component dc, and the output voltage-current characteristic exhibits a constant current drooping characteristic as shown in Fig. 6 (g). The constant current drooping characteristic is an important characteristic when charging a storage battery, and allows charging with a constant current even when the voltage of the storage battery is lowered.

[Problem that the invention seeks to solve]

However, there is a strong demand for power converters to be smaller and lighter due to the use of hybrid ICs for power supplies, and to meet this demand, it is also necessary to downsize current transformers. When a current transformer is completely downsized, that is, when its core is made sufficiently small, the excitation xi flowing through the current transformer naturally increases. When the slope of increase in this exciting current exceeds the slope Sa of the current on the primary side of current transformer 9A shown in Figure 6 (A), the 'WL current detected on the secondary side of the current transformer is As shown by the chain line in CB), the waveform has a flat top or a sloped portion where the current value decreases over time (hereinafter referred to as lower right C). When the transmission ratio is greatly reduced in this way, it is practically impossible to detect all the current flowing through the switching semiconductor element 't' and use the current detection signal as a control element.

In other words, when the current detection signal has a waveform with the slope shown in the lower right corner, if the current detection signal exceeds the reference voltage,
Since the rising portion always reaches the reference voltage first, the pulse width is rapidly narrowed down, making continuous pulse width control impossible. The output voltage-current characteristics at this time are shown in Figure 6 (F
), it becomes unstable and discontinuous, rapidly going back and forth between the drooping starting point and an arbitrary point that depicts the figure-7 characteristic. This characteristic is a problem when charging the lI battery, and during parallel operation, unstable control (turbulence) and discontinuous control occur at the starting point of drooping of any one device, which also becomes a problem.

[Means to solve all problems]

A detection current integrator circuit for compensating for a reduction in transmission ratio caused by the excitation current flowing through the f-current device, a switch for clearing the integrated value of the detection current integrator circuit in synchronization with the operating frequency of the inverter section, and a Lami current detection circuit. Add to.

[For production]

Even if the detected current obtained on the secondary side by sufficiently miniaturizing the current transformer is a flat waveform at the top or an intermittent waveform with a slope of υ in the lower right, the total integral of the detected current The voltage across the detection current integration circuit is used as the current detection signal, and the integrated value is cleared in synchronization with the operating frequency of the inverter, so a 1iI current detection signal' with a waveform having a slope of υ in the upper right corner is obtained. I can do it.

〔Example〕

An embodiment of a power conversion device according to the present invention will be described with reference to FIG. The same symbols as those in FIG. 4 described above indicate equivalent parts and metals.

In the current detection circuit 9, a resistor 9C and a capacitor 9D constitute the entire detection circuit, and a switch 9E such as a transistor periodically clears the integrated value of the capacitor 9D.

The current transformer 9A is miniaturized to the extent that even if the slope of the detected current on the secondary side is upward to the right, the slope is very gentle, flat, or downward to the right.

The detected current obtained on the secondary side of current transformer 9A is shown in Figure 6 CB.
), the detected current is rectified by the rectifier 9B, and the detected current is rectified by the resistor 9.
It flows through Ct- to the capacitor 9D and fully charges it.

During this period, of course, the switch 9E remains open. Therefore, the voltage across the detection circuit 1iL is the sum of the voltage drop across the resistor 9C and the charging voltage across the capacitor 9D.

The voltage on both sides of the resistor 9C is the current flowing through it as shown in Figure 6 (
Since the waveform has a downward slope to the right as shown by the dashed line in B), it becomes a waveform that radiates seven times from the lower right corner 9 as shown by the dashed line in C and C) of the same figure, and the photoelectric wave of Conde/Su91). The pressure has a waveform with an upward slope to the right as shown in (L) in the same figure. Therefore, if the charging time fixed deposit of the detection current integration circuit is selected so that the sum of these voltages has a predetermined #A slope rising to the right, a current detection signal having a #4 slope rising to the upper right can be obtained.

Preferably, the time constant is selected so that the slope f+ of the current on the primary side of the current transformer 9A is equal to the slope of the current detection signal.

If the upward slope to the right of the current detection signal obtained in this way exceeds the reference voltage of the reference power supply 120, the comparator 11#
The i signal is output to the total control circuit 8. Based on this signal, the control circuit 8 applies a drive signal to the switch 9E, which completely closes the switch 9E and releases the charge from the converter 9D. It is sufficient that this integral value is cleared before one accent of the next cycle passes, and the switch 9E must be open at the time when the current of the next cycle passes.

Next, another embodiment of the present invention will be explained with reference to FIG. In this figure, the same symbols as those in FIG. 1 indicate equivalent members.

#JL current galvanometer output circuit 9, first current transformer 9 A' corresponds to the upper current flowing on the secondary side of the inverter section B
- current is obtained, and the inverter section 6 is connected to its output terminal 13.14.
This is to provide necessary control power such as reverse bias energy or drive energy for the switching conductor element. The second current transformer 9A is the first current transformer 9
The secondary 11111 k current of A' is detected, and the detected current is passed through the diode 9 B % Resistor 9 for voltage division
F.

and flows to capacitor 9D via resistor 90t.

In this embodiment, since the reduction in the transmission ratio of both current transformers 9A' and 9A is superimposed, the charging time constant t of capacitor 9D
The present invention works particularly effectively by selecting -=. The operation of this circuit is the same as that in FIG. 1, so a description thereof will be omitted.

In the above embodiments, we will discuss the case where the detected current on the secondary side of the current transformer slopes downward to the right.Even if the detected current has a waveform with an upward slope to the right, the slope is quite gentle. In this case, a comparator with very high precision is required, and the operation becomes unstable and inaccurate due to noise, etc., so the present invention is also very effective in such cases5. [Effects of the Invention] As described above, according to the present invention, even if the current transformer is downsized and the transmission ratio between its primary and secondary components is significantly reduced, the reduction in the transmission ratio can be reduced simply by adding all the small electronic components. Since distortion in the waveform of the current detection signal caused by this can be sufficiently compensated for, the overall device can be downsized, and the power conversion device can be accurately controlled using the detected current.

[Brief explanation of the drawing]

1 and 2 are diagrams showing different embodiments of the power conversion device according to the present invention, FIG. 6 is a diagram showing waveforms for explaining the power conversion device w/Lt, and FIG. 4 is a diagram showing a conventional power conversion device. FIG. 3 is a diagram showing the equipment. 1.2...DC input terminal 6...Inverter section 4
... Rectifier smoothing circuit 5.6 ... Output terminal 7.
... Voltage detection circuit 8... Control circuit 9... Outlet output circuit 10... Drive circuit 11... Comparator Nippon Telegraph and Telephone Corporation (D) -→Shichiryoku Denshi

Claims (1)

[Claims] an inverter section that intermittently generates a waveform current having a slope that increases over time; a current detection circuit that includes at least a current transformer that detects the current; and a current detection signal of the current that exceeds a set level. In a power conversion device equipped with a control circuit having at least a function of controlling the output of the inverter section, the current detection circuit compensates for a reduction in the transmission ratio caused by the exciting current flowing through the current transformer. and a switch for clearing the integrated value of the detection current integration circuit in synchronization with the operating frequency of the inverter section, and using the voltage across the detection current integration circuit as the current detection signal. A power conversion device characterized by: