KR101050244B1 - Efficiency Improvement Method of Full Bridge DC / DC Converter for Solar Power Generation - Google Patents

Abstract

The present invention relates to a method for improving efficiency of a full-bridge DC / DC converter for photovoltaic power generation. The present invention relates to a high frequency transformer including a primary coil and a secondary coil wound at a predetermined winding ratio, and a first coil to be connected to the primary coil. The bridge bridge rectifier is connected to the full bridge circuit including a fourth power switch and the secondary coil, and the effective duty is equal to the winding ratio of the high frequency transformer at a voltage at which the solar cell module generates the maximum power. By setting it to be more than stationary, the full-bridge DC / DC converter for photovoltaic power generation, which is designed to optimize the turns ratio of high-frequency transformers, reduces the freewheeling section and increases the effective section powered by it. It relates to an efficiency improvement method.

Full bridge DC / DC converter, high frequency transformer, primary coil, secondary coil, turns ratio, increase powering efficiency, reduce freewheeling,

Description

An Efficiency Improvement of Full Bridge DC / DC Converter for the Photovoltaic System}

1 is a circuit diagram showing a full-bridge DC / DC converter for photovoltaic power generation to which the present invention is applied.

Figure 2 is a waveform diagram showing the output waveform of each part of the present invention.

3 is a view showing a powering mode first cycle operation state of the DC / DC converter of the present invention.

4 is a view showing a second operation state of the freewheeling mode of the DC / DC converter of the present invention.

5 is a view showing a powering mode third cycle operation state of the DC / DC converter of the present invention.

6 is a view showing a powering mode fourth cycle operation state of the DC / DC converter of the present invention.

* Description of the symbols for the main parts of the drawings *

T1: high frequency transformer, L1: primary coil,

L2: secondary coil, S1 ~ S4: power switch,

D1 ~ D4: bridge diode rectifier, C1, C2: condenser,

The present invention relates to a method for improving efficiency of a full-bridge DC / DC converter for photovoltaic power generation. The present invention relates to a high frequency transformer including a primary coil and a secondary coil wound at a predetermined winding ratio, and a first coil to be connected to the primary coil. The bridge bridge rectifier is connected to the full bridge circuit including a fourth power switch and the secondary coil, and the effective duty is equal to the winding ratio of the high frequency transformer at a voltage at which the solar cell module generates the maximum power. By setting it to be more than stationary, the full-bridge DC / DC converter for photovoltaic power generation, which is designed to optimize the turns ratio of high-frequency transformers, reduces the freewheeling section and increases the effective section powered by it. It relates to an efficiency improvement method.

In order to boost the output voltage of the solar cell module that changes according to the external environment in the high frequency link type solar power generation system PCS (Power Conditioning System) to the constant high voltage of DC voltage necessary to convert to commercial power, there must be a DC / DC converter. In addition, a high frequency insulating transformer is required to insulate the solar cell module from a commercial power supply.

A PCS for photovoltaic power generation, consisting of a DC / DC converter and a DC / AC inverter, requires at least 95% efficiency for each DC / DC converter and DC / AC inverter in order for the overall efficiency of the system to be greater than 90%.

Conventional methods for this purpose are to reduce the conduction loss and switching loss of the device in order to increase the efficiency of the DC / DC converter, the first method, the conduction loss reduction method is the device when the device is turned on (ON) The conduction loss is reduced by using a device having a small voltage across both ends, and the second method, a switching loss reduction method, uses a device capable of high-speed switching with low switching loss or a soft switching method.

In order to implement the first method, a method using a device having a small resistance when the power device is connected is mainly used.

In order to implement the second method, a method of using a device having a smaller switching loss for high-speed switching than a general power device in order to reduce the switching loss, and a voltage and current acting on the device at the same time when the power device is turned on or off The method of reducing switching loss by reducing or eliminating is mainly used.

However, conventional methods used to increase the efficiency of DC / DC converters increase the cost of the device and require additional circuitry for soft switching, and in particular, the design of the soft switching is wrong. When the problem was lowered the efficiency was more.

Accordingly, the present invention for solving the above problems is a high-frequency transformer consisting of a primary coil and a secondary coil wound at a predetermined winding ratio, and a full bridge circuit unit consisting of first to fourth power switches to be connected to the primary coil; And a bridge diode rectifier connected to the secondary coil, wherein the winding ratio of the high frequency transformer is set such that the effective duty becomes a predetermined value or more at a voltage at which the solar cell module generates the maximum power. The purpose of this study is to provide a method for improving the efficiency of a full-bridge DC / DC converter for photovoltaic power generation, which reduces the freewheeling period and increases the effective range that is powered.

According to an aspect of the present invention,

According to claim 1,

A high frequency transformer T1 consisting of a primary coil L1 and a secondary coil L2 wound at a predetermined winding ratio, and first to fourth power switches S1 to S4 connected to the primary coil L1. Full bridge circuit portion and bridge diode rectifier (D1 ~ D2) is connected to be connected to the secondary coil (L2), the winding ratio of the coil (L1, L2) of the high frequency transformer (T1) solar cell module It is characterized by setting so that an effective duty becomes more than a reference value in the voltage which generate | occur | produces this maximum power.

According to claim 2,

The coil turns ratio of the transformer (T1) is characterized in that to optimize the generation voltage effective duty to be 75% or more.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings, FIGS. 1 to 6.

1 is a circuit diagram showing a full-bridge DC / DC converter for photovoltaic power generation,

A high frequency transformer T1 consisting of a primary coil L1 and a secondary coil L2 wound at a predetermined winding ratio, and first to fourth power switches S1 to S4 connected to the primary coil L1. The bridge bridge rectifier (D1 ~ D2) is connected to be connected to the full bridge circuit portion and the secondary coil (L2), the LC filter consisting of a coil (L3) and a capacitor (C2) is connected to the rear end have.

Unexplained reference numeral C1 is a capacitor.

The full bridge DC / DC converter configured as described above is used in high frequency link type solar PCS, and it boosts the low variable output DC voltage of the solar cell module to a constant high voltage.

The full bridge DC / DC converter has a phase shift gate drive as shown in FIG. 2 in order to see the effect of soft switching.

The operation modes of the first to fourth switches S1 to S4 are a powering mode for largely passing the effective power to the high frequency transformer T1 and a free-wheeling operation that obscures the flow of current after the powering mode. Mode).

That is, in the powering mode corresponding to the first periods T0 to T1 of FIG. 2, only the first and fourth power switches S1 and S4 are turned on to operate the primary coil of the high frequency transformer T1 as shown in FIG. 3. In the freewheeling mode corresponding to the second periods T1 to T2 of FIG. 2, only the second and fourth power switches S2 and S4 are turned on to power the L1). The current flow after the mode is extinguished. In the powering mode corresponding to the third periods T2 to T3 of FIG. 2, only the second and third power switches S2 and S3 are turned on to operate the high frequency transformer ( Active power is supplied to the primary coil L1 of T1), and in the freewheeling mode corresponding to the fourth periods T3 to T4 of FIG. 2, the third and fourth power switches S3 and S4 as shown in FIG. 6. Only the on-state operation is to extinguish the current flow after the powering mode.

As described above, the reason for supplying the active power to the high frequency transformer T1 by applying the phase shift method in the full bridge converter is to lower the breakdown voltage rating of the device by applying the phase shift method than the general hard switching, and the leakage inductance of the transformer. This is because zero voltage switching can be obtained depending on the value.

However, in this method, unnecessary conduction loss occurs due to an unavoidable mode such as the free wheeling mode after the powering mode section.

That is, the freewheeling mode is to gradually extinguish the current in the coil winding of the high frequency transformer T1 as in the second section T1 to T2 and the fourth section T3 to T4 of FIG. 2. The section is an unnecessary section that generates only a conduction loss through the anti-parallel diodes of the power switches S1 to S4 without transmitting energy to the secondary coil L2 of the transformer.

In order to reduce the loss of the freewheeling mode, the winding ratio of the coils L1 and L2 of the high frequency insulation transformer T1 is optimized to increase the effective duty period which is actually powered, thereby reducing the freewheeling period and reducing the freewheeling period. By reducing the amount of current flowing to the reverse parallel diode and the secondary rectifier diode of the power switch connected to the transformer primary coil (L1) it is possible to reduce the conduction loss.

As described above, the winding ratio of the high frequency transformer (T1) to maximize the effective duty that is powered can be obtained by setting the effective duty to be 75% or more at the voltage at which the solar cell module generates the maximum power. This could be confirmed by experimental data.

For example, if the DC / DC converter's output voltage is 360V and the solar module's maximum power output voltage is 68V, the turns ratio (η) of the transformer can be obtained as shown below.

When the coil turns ratio of the high frequency transformer T is obtained by the above equation, the full bridge DC / DC converter is operated so that the solar cell module can obtain the maximum efficiency, so that the conduction loss in the freewheeling mode is minimized and the power is reduced. The effective duty of the ring mode is maximized to obtain the maximum efficiency.

As described above, the present invention is a full-bridge circuit consisting of a high-frequency transformer consisting of a primary coil and a secondary coil wound at a predetermined winding ratio, and first to fourth power switches to be connected to the primary coil; In the bridge diode rectifier is connected so as to be connected to the car coil, by setting the winding ratio of the high frequency transformer so that the effective duty is a certain value or more at a voltage at which the solar cell module generates the maximum power, to optimize the winding ratio of the high frequency transformer It can be expected to provide an efficiency improvement method of the full-bridge DC / DC converter for photovoltaic power generation, which reduces the freewheeling section and increases the effective section powered by it, so that the maximum generation amount can be obtained.

Claims (2)

In order to reduce the freewheeling period by optimizing the winding ratio, a high frequency transformer consisting of a primary coil and a secondary coil for increasing the effective duty period to be actually powered, and first to fourth powers connected to the primary coil In the bridge bridge rectifier is connected to the full bridge circuit portion consisting of a switch, and the secondary coil, and can reduce the conduction loss by reducing the amount of current flowing to the first to fourth power switch and the diode rectifier, And the coil winding ratio of the high frequency transformer is set such that the effective duty is equal to or greater than a reference value at a voltage at which the solar cell module generates the maximum power. The method of claim 1, The coil winding ratio of the transformer is optimized so that the effective duty of the power generation voltage is 75% or more.

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