JPH08317638A - Power conversion apparatus - Google Patents

Abstract

PURPOSE: To obtain a power conversion apparatus by which a switching loss can be reduced by a method wherein a current waveform from switching element is resonated via a capacitor for a high-frequency component filter, the capacitance of the capacitor is changed and a smooth waveform is formed. CONSTITUTION: A circuit has a function to control a current by a mean-value comparison system in such a way that a power-supply current is synchronized with the waveform of a commercial power-supply voltage. A DC source whose power has been converted by an electrolytic capacitor 13 is converted into an alternating current by four switching elements 23 to 26 constituting a full bridge. An output is input to a rectifier diode 20 via a transformer 15 so as to be converted into a DC voltage. Then, a film capacitor 16 is connected in parallel with the output of the recitifier diode 20 and a surge voltage is supplied. The switching loss of the switching elements 23 to 26 can be reduced by utilizing a resonance phenomenon generated at this time. In addition, the output of the capacitor 16 can reduce the pulsation of a current flowing to a load 17 when the capacitance of the inductance of a DC reactor 14 is made large. Consequently, a switching loss can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an effective power converter in a battery charger for an uninterruptible power supply and an electric vehicle.

[0002]

2. Description of the Related Art As shown in Japanese Unexamined Patent Publication No. 6-78535, first, a rectifier circuit composed of diodes is input to convert power to a DC source. The power is converted to a high-frequency pseudo AC power source using a switching element and input to a downsized high-frequency transformer. By using this transformer, the voltage can be converted to a voltage set arbitrarily according to the turns ratio, and electrical insulation from the commercial power source can be achieved to improve safety. The output of this transformer is a circuit that controls the amount of output power by using a diode, a choke coil, and a switching element, and performs DC conversion again.

FIG. 1 shows an example of a full-bridge type DC-DC converter circuit 102. In the two-arm configuration, the outputs of four stone switching elements are connected to the primary winding of a transformer for the purpose of insulation and voltage adjustment. . By alternately turning on and off the switching of these four stones by the principle of plowing, it is converted into a rectangular wave AC voltage and input to the transformer. At this time, the switching frequency is made constant and the output voltage is changed by changing the ON time width. Had control.

[0004]

However, since the output voltage waveform of the switching element is a rectangular wave whose on-time and off-time are clear, the output current waveform is accompanied by a sharp change,
There has been a problem that the switching loss increases and the reliability of the device decreases.

Radio noise (radio interference) occurs due to the switching operation. By controlling ON / OFF of the switching element, the voltage or current waveform is accompanied by a sharp change. Therefore, there are many noise components of the switching frequency component. Therefore, the receiving device or the like is adversely affected. To prevent this, it is general to connect a capacitor and a resistor in series for one diode element. However, since the loss is large, the cooling device becomes large, and the generated noise is large, which causes the filter circuit to become large.

Further, in the method of stabilizing the output, it is necessary to change the switching frequency while keeping the on-time width of switching constant. Further, as in Japanese Patent Laid-Open No. 6-78535, there is a method of controlling the output voltage to be constant by using a switching element and a reactor in the output front stage.
However, the current flowing through the load pulsates, and the filter for removing the high frequency ripple of the current becomes large, which causes a problem that the reactor is large.

The commonly used commercial power input circuit is
Since it is composed of diodes, the power factor is poor and the power supply utilization rate is poor. If the power factor is bad, sufficient power cannot be sent with the limited power supply equipment. Therefore, there are problems that the breaker is cut off, the fuse is blown, and sufficient electric power cannot be sent to the load. Also, since the input source is an AC voltage, it is difficult to convert it to a stable DC source. When the commercial power supply input current is a sine wave and the phase difference with the input voltage waveform is small, the input power becomes V · Isin2ωt and pulsates. Therefore, the voltage across the electrolytic capacitor fluctuates, and the current flowing into the load pulsates. To reduce this pulsation, a large amount of electrolytic capacitor capacity is required. Therefore, there arises a problem that the volume increases.

[0008]

Means for Solving the Problems Full Bridge DC-D
In order to suppress the loss and noise generated from the switching element and the rectifying diode of the C converter circuit, the output of the rectifying diode is temporarily passed through a high frequency component filter capacitor to resonate the current waveform flowing from the switching element. By changing the capacitance of the capacitor, the resonance frequency changes and a smooth current waveform is produced without abrupt changes.

In order to control the magnitude of the load power output from the full-bridge type DC-DC converter circuit, when the power factor control unit performs switching control so that the input current of the commercial power source becomes a sine wave, the sine wave waveform It controls the magnitude of the effective value of.

In order to stabilize the output, the capacity of the electrolytic capacitor may be increased. The volume increases with the use of many electrolytic capacitors, but if that becomes a problem, input power of the commercial power supply can be obtained by adding the sine wave of the fundamental wave component or the third harmonic of the fundamental wave. Will be suppressed to some extent, and the capacitance of the electrolytic capacitor can be reduced.

In order to reduce the influence of noise on other devices, it is better to reduce the noise level protruding at a certain frequency component. The frequency component is a switching frequency component, and it is better not to fix the frequency. Moreover, since the output voltage is not controlled, it is not necessary to fix it.
Therefore, the switching frequency is ± 2Hz of the normal frequency.
The values are randomly changed within the range.

[0012]

As a result, the switching element of the full-bridge type DC-DC converter circuit can be turned on at the current zero point or turned off at the portion where the current value is low, thereby reducing the overlapping portion of the voltage and the current during switching. Thus, the loss can be reduced and the generated noise can be reduced. Moreover, since the surge voltage is suppressed to some extent in the output voltage waveform of the switching element, the surge absorbing circuit that is normally inserted between the switching elements has a circuit configuration that does not require the insertion of a resistor and has a small loss. Also,
The number of parts is small. The full-bridge DC-DC converter section does not require special control, and thus has a small and inexpensive circuit configuration.

The maximum noise level of the harmonic component can be lowered by changing the switching frequency of the switching element of the full-bridge type DC-DC converter circuit at random, instead of fixing it. By dispersing the frequency band in which noise is generated, the maximum value of noise can be suppressed, and thus the constant of the noise countermeasure filter circuit can be reduced.

[0014]

EXAMPLE FIG. 1 shows an example of the present invention. A single-phase commercial power source is used as an input source 11, and diodes 18, 19 and flywheel diodes 27, 28, a switching element 21,
The circuit constituted by 22 has the function of controlling the current by the average value comparison method so that the power supply current is synchronized with the commercial power supply voltage waveform. This time, diode 1 composed of two in series
Switching element 2 composed of 8 and 19 in series
By adopting the step-up type two-stone series system of 1 and 22, loss reduction and cost reduction were achieved. For the large capacity type, it is advisable to adopt the full bridge method as shown in FIG. Switching is a PWM method, and in the circuit of FIG.
When 2 is turned on, a short-circuit current flows in the path of reactor 12 → diode 19 → commercial power supply 11. Then, the commercial power supply voltage and the voltage value of the electromotive force generated by the reactor 12 become higher than the terminal voltage of the electrolytic capacitor 13, so that energy flows to the load side. It suffices to keep the voltage between the electrolytic capacitors constant regardless of the load 17, but when the power factor is 1, the energy supplied to the capacitors is the value obtained by multiplying the voltage: V · sinωt and the current: I · sinωt. It is pulsating greatly. The current flowing into the electrolytic capacitor 13 is shown as I _ACDC in FIG. Due to the pulsation of the current I _ACDC , the output current Ib of FIG. 4 flowing into the load 17 fluctuates. In order to prevent this, the electrostatic capacity of the electrolytic capacitor 13 is increased to increase the energy storage capacity, and the electric power flowing into the load 17 is brought close to a constant value. However, increasing the capacity of the electrolytic capacitor increases the volume of the device. In order to prevent the volume from increasing as much as possible, it is effective to use a command value for commercial power input that suppresses the vicinity of the maximum value of the sine wave as a countermeasure. That is, the value obtained by adding the third harmonic to the sine waveform V _AC is added. In this case, as a matter of course, the harmonic component (third harmonic) increases in the input current waveform I _AC shown in FIG. It is better to set the input current so that the legally regulated value is not exceeded. The method of controlling to the input current I _AC is as follows. The power factor controller 30 calculates (subtracts and integrates) the detected current and the command value, and then compares the triangular wave with PW.
Generate an M signal. Input current I _AC So-called output current Ib
To change the magnitude of, the magnitude of the effective value of the command value is controlled. Therefore, the energy flowing to the load 17 can be controlled by changing the magnitude of the effective value of this command value.

The direct current source converted into electric power by the electrolytic capacitor 13 is composed of four switching elements 2 in a full bridge configuration.
At 3 to 26, the voltage is converted into the simulated AC wave V _BR shown in FIG. By performing AC conversion and passing through the transformer 15, the winding ratio can be changed to an arbitrary voltage, and the load side and the commercial power source can be electrically insulated. Next, the output of this transformer is input to the rectifying diode 20 and converted into a DC voltage. At this time, the voltage waveform between the diode 1 element is applied with a surge voltage higher than the average applied voltage and may exceed the allowable voltage value of the element. Further, since the output voltage / current waveform of the rectifying diode 20 is steep, it becomes a source of noise such as radio interference. Therefore, the film capacitor 16 is connected in parallel to the output of the rectifying diode 20 to suppress the surge voltage. The circuit is simple, and since no resistor is provided, the loss is small and the problem of heat generation does not occur. Moreover, due to the influence thereof, a resonance phenomenon like the current waveform I _BR shown in FIG. 3 occurs due to the capacitance of the capacitor 16, the wiring inductance and the leakage inductance of the transformer 15. By utilizing this resonance phenomenon, the switching loss of the switching elements 23 to 26 having the full bridge structure can be reduced. When the switching element is on-switched, the current is zero current switching, and when the switching element is off-switched, the current does not reach zero current, but the value is lower than the average current value.

The output of the capacitor 16 is connected to the load 17 via the DC reactor 14. If the capacitance of the inductance of the DC reactor 14 is large, the load 17
The pulsation of the current Ib shown in FIG.

Full-bridge type DC-DC converter unit 1
The switching elements 23 to 26 of No. 02 generate noise such as radio interference due to switching. In order to suppress noise as much as possible, there is a method of randomly changing the switching frequency in the DC / DC converter controller 31. This can be easily done by using a microcomputer with an integrated timer unit. This microcomputer is P shown in FIG.
It is possible to generate the triangular wave-shaped numerical values necessary for generating the WM signal. In order to generate this numerical value, first the sum of products operation is performed, and if the numerical value exceeds a certain upper limit value, then this value is subtracted. If the value from the subtraction falls below a certain lower limit value, the product-sum operation described above is performed again. By changing the upper limit value and the lower limit value at random as shown in FIG. 5, it is possible to change the frequency of the triangular wave Car, that is, the switching frequency. The range of changing the frequency shall be within ± 2Hz of the reference value. In this system, the flow rate, that is, the output power, does not change even if the flow rate control by frequency control is performed. Power factor control switching circuit 101
Is a control of a power factor of 1, and serves to make the output voltage (electrolytic capacitor voltage) of a power factor of 1 constant if the load supply power is constant. If an attempt is made to reduce the flow rate of electric power to the load side to suppress it, energy will be accumulated in the electrolytic capacitor and the terminal voltage will rise. The current that flows during the on-time of the switching element rises accordingly, and even if the frequency is changed, the power supplied to the load is unlikely to change. Therefore, this frequency random change method can be used.

[0018]

As a result, the loss and heat generation are small, the reliability is improved and the efficiency is improved, the switching frequency can be further increased, and the transformer and the filter for removing high frequency noise can be downsized. The device has a simple circuit configuration and can be used as an inexpensive and lightweight battery charger.

[Brief description of drawings]

FIG. 1 is a main circuit diagram.

FIG. 2 is a current waveform diagram in which a commercial power supply voltage and a third harmonic component are added.

FIG. 3 is a current waveform diagram that resonates with a simulated AC voltage waveform.

FIG. 4 is an input current waveform and an output current waveform diagram of an electrolytic capacitor.

FIG. 5 is an explanatory diagram of a variable switching frequency generation principle.

[Explanation of symbols]

11 ... Commercial power supply, 12 ... AC reactor, 13 ... Electrolytic capacitor, 14 ... DC reactor, 15 ... Transformer, 16
... film capacitor, 17 ... load, 18, 19 ... input diode, 20 ... rectifying diode, 21, 22 ... power factor improving switching element, 23-26 ... DC / DC converter switching element, 27, 28 ... flywheel Diode, 30 ... Power factor controller, 31 ...
DC / DC converter controller, 101 ... Power factor control switching circuit, 102 ... DC / DC converter circuit, 103 ... DC conversion circuit.

Claims (4)

[Claims] 1. A direct current source is converted into alternating current by using a switching element, and this alternating current source can be converted to direct current again by passing a current through a transformer and through a circuit composed of a rectifying diode, a capacitor and an inductor. In the circuit
The power conversion device, wherein the switching element for AC conversion has a constant switching frequency and a constant ON time width, and a capacitor is provided in parallel with the output end of the rectifying diode. 2. A third component for the fundamental wave component of the commercial power frequency.
The commercial power supply current is input using a switching element so as to form a waveform with harmonic components added, and is converted to a DC source using an electrolytic capacitor.The obtained DC source is converted into a rectangular wave voltage using a switching element. Convert it through a transformer,
A power conversion device characterized by performing DC conversion again using a circuit composed of a rectifying diode, a capacitor, and an inductor. 3. A third component for the fundamental wave component of the commercial power frequency.
A commercial power supply current is input using a switching element so that the waveform will be the sum of harmonic sine waves, and it is converted to a DC source using an electrolytic capacitor.The obtained DC source is a rectangular wave voltage using a switching element. In the circuit that performs AC to AC conversion and then DC conversion again using a circuit composed of a rectifying diode, a capacitor and an inductor via a transformer, the switching element that performs AC conversion to obtain a rectangular wave voltage has a constant switching frequency. And a constant on-time width, and a capacitor is provided in parallel with the output end of the circuit of the rectifying diode. 4. A circuit in which a direct current source is converted into alternating current by using a switching element, and this alternating current source can be converted to direct current again by energizing a circuit composed of a rectifying diode, a capacitor and an inductor through a transformer. In the switching element for AC conversion, the switching frequency is periodically changed and the ratio of ON time to OFF time is made constant, and a capacitor is provided in parallel with the output end of the rectifying diode. Power conversion device.