TW202418739A - Symmetrical high voltage gain dc converter - Google Patents

Abstract

This invention relates to symmetrical high voltage gain DC converter, which is suitable for the conversion of renewable energy, especially for solar panel or fuel cell applications by using a symmetrical structure, active switching coupling inductor, coupling inductor boosting technology, and other technologies that is composed of input parallel and output series structure in order to enhance the voltage gain, and the two switches are driven by interleaved signals in 180° [one-half of a switching cycle] to achieve high boost, high efficiency and high power applications, and to increase the practical efficiency characteristics in its overall implementation.

Description

Symmetrical High Voltage Gain DC Converter

The present invention relates to a symmetrical high voltage gain DC converter, and more particularly to a symmetrical high voltage gain DC converter suitable for power conversion of renewable energy, especially solar panels or fuel cells. The symmetrical high voltage gain DC converter uses a symmetrical structure, active switching coupled inductors, coupled inductor boosting technology, and is composed of a parallel input and series output structure to increase voltage gain. Two switches are driven by an interlaced signal with a working phase of 180° [half of a switching cycle] to achieve high boost, high efficiency and high power applications, and to enhance the practical performance characteristics in its overall implementation and use.

As global warming worsens, the global climate change is becoming more serious. Countries around the world have begun to actively examine this serious problem. Therefore, starting from December 1997, 38 countries and the European Union signed the "Kyoto Protocol" in Japan. In the middle, the 21st United Nations Climate Change Conference [COP 21] held in Paris, France in 2015 passed the historic "Paris Agreement". The 195 participating countries unanimously agreed to control greenhouse gas emissions and industrialization to keep global warming within 2 degrees Celsius by 2100 and strive to control it within 1.5 degrees. Then, the 24th United Nations Climate Change Conference [COP 21] held in Poland in 2018 24], all of which continue to ensure that the international standards and carbon reduction targets of various countries are met. With the improvement of solar and wind power generation technology and the gradual reduction of costs, the development of renewable energy power generation technology and high-efficiency power conversion technology is an inevitable trend in future technological development. In this way, excessive use of fossil energy can be avoided to reduce carbon dioxide emissions.

In terms of renewable energy or green energy, common ones include solar energy, tidal energy, wind energy, hydropower, biomass energy, geothermal energy and fuel cells. Among these renewable energy sources, the technology of solar energy and fuel cell power generation systems is most commonly applied and discussed in distributed DC power generation systems. Renewable energy distributed power generation systems include solar modules, fuel cell modules, high step-up DC-DC converters, inverters, DC-DC power converters and loads or power grids. In terms of solar power generation systems, solar arrays convert light energy into electrical energy, and each solar array can be composed of several solar modules connected in series or in parallel. However, too many solar arrays connected in series will cause lattice mismatch, or the shading effect cannot be avoided, thus limiting the output voltage of the solar array, which is usually less than 50V. Therefore, the system needs a symmetrical high-voltage gain DC converter to import a high DC bus voltage of 400V as a high DC input voltage for the subsequent DC-AC inverter. The inverter then outputs power to the AC load [such as a motor] or is connected in parallel with the mains. Therefore, the symmetrical high-voltage gain DC converter plays a very important role in distributed power generation systems.

In distributed power generation systems, solar power generation and fuel cells are one of the most important renewable energy sources. However, in home applications, for the safety and reliability of the environment, the output side of renewable energy is generally low DC voltage, usually less than 40V _dc . In order to meet the needs of subsequent grid-connected power generation or connection to a DC microgrid, a step-up converter is used to increase the low voltage to a high-voltage DC bus, usually by about 10 times, to generate the high DC voltage required by the inverter [DC-AC Inverter]. For a power system that uses renewable energy, for example: for a single-phase AC 220V grid system, this high-voltage DC bus is usually 380V~400V, which is convenient for the load application of the DC-AC back-end inverter or the use of parallel power.

Today, the inventor has taken this into consideration and, based on his rich experience in design development and actual manufacturing in the relevant industry for many years, has conducted further research and improvement on the existing structure and defects, and provided a symmetrical high-voltage gain DC converter in order to achieve the purpose of better practical value.

The main purpose of the present invention is to provide a symmetrical high voltage gain DC converter, which is mainly suitable for power conversion of renewable energy, especially for the application of solar panels or fuel cells. It uses a symmetrical structure, active switching coupled inductors, coupled inductor boost technology and multiple technologies, and is composed of a parallel input and series output structure to enhance the voltage gain. The two switches are driven by an interlaced signal with a working phase of 180° [half of a switching cycle] to achieve high boost, high efficiency and high power applications, and the overall implementation and use of the converter has increased practical performance characteristics.

In order to make the technical content, purpose of the invention and the effects achieved by the present invention more complete and clear, they are described in detail below, and please refer to the disclosed drawings and figure numbers:

First, please refer to the first figure of the circuit diagram of the present invention. The converter (1) of the present invention mainly operates at the input voltage The positive electrode is connected to the first capacitor The first end and the second switch The first end and the primary side of the first coupled inductor The first end of the first capacitor The second end is connected to the second capacitor The first terminal and the third capacitor The second terminal and the fourth capacitor The first end of the second switch The second end is connected to the secondary side of the second coupled inductor The second end of the fifth diode Negative pole and sixth diode The positive electrode of the first coupled inductor is A first magnetizing inductance is formed , the primary side of the coupled inductor The second end is connected to the first diode The negative electrode and the second diode The negative electrode of the first diode The positive pole is connected to the secondary side of the first coupled inductor The first end of the first coupled inductor is The second end is connected to the third diode The negative electrode of the second diode The positive electrode and the first switch The first end of the third diode The positive electrode is connected to the third capacitor The first end and load The first end of the first switch The second end of the second capacitor The second end and the primary side of the second coupled inductor The first end of the The negative pole of the second coupled inductor is A second magnetizing inductance is formed , the primary side of the second coupled inductor The second end is connected to a fourth diode The positive electrode and the fifth diode The positive electrode of the fourth second electrode The negative pole is connected to the secondary side of the second coupled inductor The first end of the sixth diode The negative electrode is connected to the fourth capacitor The second end and the load The second end.

When the converter (1) is in steady state, according to the ON/OFF state of each switch, the converter (1) can be divided into four linear operation stages within a switching cycle. In order to achieve a high voltage boost, the conduction ratio is greater than 0.5, and the first switch and the second switch The phase difference is half of the switching cycle. To simplify the analysis, the following assumptions are made:

1. All power semiconductor components [switches and diodes] are ideal, that is, the forward voltage drop is zero.

2. Each capacitor value is large enough, so the capacitor voltage can be regarded as a constant voltage.

3. The turns ratio of the coupled inductors is equal. ]; and the magnetizing inductance is much larger than the leakage inductance, so the leakage inductance can be ignored.

4. The magnetizing inductance current of the coupled inductor operates in continuous conduction mode [Continuous Conduction Mode, CCM].

5. All inductors and capacitors in the circuit are ideal components and have no parasitic impedance.

6. The converter (1) has reached a stable state.

In a switching cycle Please refer to the timing diagram of the second figure of the present invention for the timing and waveform of the power converter:

Phase I ]: Please refer to the third figure for the equivalent linear circuit diagram of the first stage of the present invention. This stage starts at , the first switch and the second switch The first diode is in the ON state. , the third diode , the fourth diode , the sixth diode The first magnetizing inductance is turned off due to the reverse bias. , the second magnetizing inductance All across the input voltage , then the inductor current , With fixed slope and From the energy point of view, in this stage, the input voltage charges the primary side of the magnetizing inductance to store energy. When the second switch When the state changes from ON to OFF, the converter (1) enters the second stage.

Phase II ]: Please refer to the fourth figure for the equivalent linear circuit diagram of the second stage of the present invention. This stage starts at , the second switch has been switched from ON to OFF, the first switch Keep it ON. Due to the inductor current Continuous, so that the fourth diode , the sixth diode The first diode turns ON. , the third diode , the fifth diode The current is cut off due to the reverse bias. Still with slope Linear rise, current Slope Linear decrease. When the second switch When the state changes from OFF to ON, the converter (1) enters the third stage.

The third stage ］: Please refer to the fifth figure for the equivalent linear circuit diagram of the third stage of the present invention. This stage starts at , the action is the same as the first stage, the first switch and the second switch are both in the ON state, the first diode , the third diode , the fourth diode , the sixth diode All of them are OFF due to the reverse bias. At this time, the first magnetizing inductance , the second magnetizing inductance All across the input voltage , then the inductor current , With fixed slope and From the energy point of view, in this stage, the input voltage charges the primary side of the magnetizing inductance to store energy. When the first switch When the state changes from ON to OFF, the converter (1) enters the fourth stage.

The fourth stage ]: Please refer to the sixth figure for the equivalent linear circuit diagram of the fourth stage of the present invention. This stage starts at , the first switch has been switched from ON to OFF, the second switch Keep it ON. Due to the inductor current The first diode is continuous. , the third diode The second diode turns ON. , the fourth diode , the sixth diode The current is cut off due to the reverse bias. Still with slope Linear rise, current Slope Linear decrease. When the first switch When the state changes from OFF to ON, the converter (1) enters the next switching cycle.

According to the operating principle of the converter (1), the steady-state characteristics of the converter (1) are derived. In order to simplify the analysis, the leakage inductance and the extremely short transient phase are ignored. All capacitor values are large enough so that the capacitor voltage can be regarded as a constant within a switching cycle.

The first magnetizing inductance is derived below. The first magnetizing inductance voltage that satisfies the volt-second balance theorem , and find the voltage conversion ratio Since the circuit is a symmetrical structure, the second magnetizing inductance The second magnetizing inductance voltage Corresponding voltage conversion ratio The first switch can be mainly divided into the first stage, the second stage and the third stage. When conducting, the total time is , circuit analysis shows that the first magnetizing inductance voltage , the voltage relationship is:

,and (1)

In the fourth stage, the first switch No conduction, time is , circuit analysis shows that the first magnetizing inductance voltage , the voltage relationship is:

in (2)

According to the volt-second balance theorem, it can be deduced that the converter (1) right The voltage gain is:

(3)

Because of the symmetrical structure, the second magnetizing inductance The second magnetizing inductance voltage , to obtain right The voltage gain is:

(4)

Finally, the voltage gain of the converter (1) is:

(5)

From the above equation, we can see that the voltage gain of the converter (1) has two design degrees of freedom: the coupled inductor turns ratio and conduction ratio The converter (1) can achieve a high boost ratio by properly designing the turns ratio of the coupled inductor so that it does not need to operate at an extremely large conduction ratio. and conduction ratio The voltage gain curve of the invention [please refer to the seventh figure of the voltage gain, conduction ratio and coupled inductor turns ratio curve of the present invention] clearly shows that when the conduction ratio , When , the voltage gain is 10.4 times; when , , the voltage gain is 15 times.

From the second stage and the fourth stage of the operation principle of the converter (1), the second switch can be obtained respectively. and the first switch Voltage stress:

, (6)

On the other hand, the voltage stress of the diode can be obtained from the second stage:

, (7)

(8)

Similarly, the voltage stress of the diode can be obtained from the fourth stage:

, (9)

(10)

Since the voltage stress of the power switch and diode of the traditional boost converter is the output voltage , and the switch voltage stress of the converter (1) is significantly lower than the output voltage , so a MOSFET with a low rated withstand voltage and a lower on-resistance can be used, which can reduce the switching loss. On the other hand, the voltage stress of the diode of the converter (1) is also much lower than the output voltage. , diodes with lower voltage stress can use power diodes with lower forward conduction voltage drop, which can reduce conduction loss.

In addition, based on the circuit action analysis results, Is-Spice software was used for preliminary simulation [please refer to the eighth figure for the simulation circuit diagram of the present invention], the converter (1) specifications: input voltage 40V, output voltage 400V, maximum output power 1000W, switching frequency 50kHz, coupled inductor turns ratio , verifying the characteristics of the converter (1); the following uses simulation waveforms to verify and explain the characteristics of the converter (1):

1. Verify high voltage gain stability characteristics:

Please also refer to Figure 9 for the switch drive signal of this invention. , , Input voltage and output voltage As shown in the simulation waveform, the converter (1) high voltage gain stability characteristics are verified. At 1000W, , , the simulation results show that: the same as the analysis, the converter (1) does not have to operate at a very large conduction ratio and has a high voltage gain ratio.

2. Verify the power switch low voltage stress:

Please also refer to Figure 10 for the switch drive signal of this invention. , and switch cross-voltage signal , As shown in the simulation waveform, the first switch or the second switch When OFF, the cross voltage and Both are about 220V, which is much lower than the output voltage of 400V, which is consistent with the analysis results. Compared with the traditional boost converter whose switch voltage stress is the output voltage, the converter (1) has the advantage of low switch voltage stress.

3. Verify that the converter (1) operates in CCM:

Please also refer to Figure 11 for the magnetizing inductance voltage of this invention. , and magnetizing inductance current , As shown in the simulation waveform, when the full load is 1000W, the average value of the magnetizing inductance voltage is zero, and the current , The minimum values are all greater than zero, and it is obvious that the converter (1) operates in continuous conduction mode.

4. Verify the voltage stress of each diode:

Please also refer to the 12th figure of the invention of the diode , , The voltage simulation waveform diagram and the diode of the present invention in Figure 13 , , As shown in the voltage simulation waveform, due to the symmetry of the circuit, the two groups correspond to each other. and The voltage stress of the diode is about 40V. and The voltage stress of the diode is about 90V. and The voltage stress of the diodes is about 220V, which is much lower than the output voltage. This verifies that the diodes have the advantage of low voltage stress, which is better than the traditional boost converter whose diode voltage stress is the output voltage, which is consistent with the analysis results.

5. Verify the voltage of each capacitor:

Please also refer to Figure 14 for the capacitor invented , , , As shown in the voltage simulation waveform, the capacitor voltage and About 20V, and About 200V is consistent with the analytical derivation results.

From the above description of the use and implementation of the present invention, it can be seen that compared with the existing technical means, the present invention mainly has the following advantages:

1. The parallel input structure of the converter reduces the component current stress. The two switches adopt staggered operation to reduce the input current ripple. The symmetrical topology design and the introduction of coupled inductor technology make the converter have low conduction ratio and high voltage gain characteristics, which greatly reduces the switch conduction ratio, avoids the possibility of gain reduction caused by parasitic resistance, and can reduce conduction loss and improve efficiency.

2. The two design conditions of conduction ratio and coupled inductor turns ratio greatly improve the design freedom.

3. The switch voltage stress is greatly reduced compared to the traditional boost converter, so a low-rated voltage MOSFET with a smaller RDS(on) can be selected to reduce losses and improve efficiency.

4. The converter operates in an interleaved manner, so it has a ripple cancellation characteristic, which can reduce the size of the filter components and improve the power density.

However, the aforementioned embodiments or drawings do not limit the product structure or usage of the present invention. Any appropriate changes or modifications by a person having ordinary knowledge in the relevant technical field should be deemed to be within the patent scope of the present invention.

In summary, the embodiments of the present invention can achieve the expected effects, and the specific structure disclosed therein has not been seen in similar products, nor has it been disclosed before the application. It fully complies with the provisions and requirements of the Patent Law. Therefore, an application for an invention patent is filed in accordance with the law, and we sincerely request your review and grant of the patent. We would be grateful for your kindness.

1: Converter

:Input voltage

:First Capacitor

: Second capacitor

:Third capacitor

:Fourth capacitor

:First switch

: Second switch

: Primary side of the first coupled inductor

: Secondary side of the first coupled inductor

:First magnetizing inductance

: Second coupled inductor primary side

: Secondary side of the second coupled inductor

: Second magnetizing inductance

:First Diode

:Second diode

:Third Diode

:The fourth second pole

:Fifth Diode

:Sixth Diode

:Load

Figure 1: Circuit diagram of the present invention

Figure 2: Timing diagram of the present invention

Figure 3: Equivalent linear circuit diagram of the first stage of the present invention

Figure 4: Equivalent linear circuit diagram of the second stage of the present invention

Figure 5: Equivalent linear circuit diagram of the third stage of the present invention

Figure 6: Equivalent linear circuit diagram of the fourth stage of the present invention

Figure 7: Voltage gain vs. conduction ratio vs. coupled inductor turns ratio of the present invention

Figure 8: Schematic diagram of the analog circuit of the present invention

Figure 9: Switch driving signal of the present invention , , Input voltage and output voltage The simulated waveform of

Figure 10: Switch driving signal of the present invention , and switch cross-voltage signal , The simulated waveform of

Figure 11: Magnetizing inductance voltage of the present invention , and magnetizing inductance current , The simulated waveform of

Figure 12: Diode of the present invention , , Voltage simulation waveform of

Figure 13: Diode of the present invention , , Voltage simulation waveform of

Figure 14: Capacitor of the present invention , , , Voltage simulation waveform of

1: Converter

V _in : Input voltage

C ₁ : First capacitor

C ₂ : Second capacitor

C ₃ : The third capacitor

C ₄ : Fourth capacitor

S ₁ : First switch

S ₂ : Second switch

Np1 : _primary side of the first coupled inductor

N _{s 1} : Secondary side of the first coupled inductor

L _{m 1} : First magnetizing inductance

Np2 : _primary side of the second coupled inductor

N _{s 2} : Secondary side of the second coupled inductor

L _{m 2} : Second magnetizing inductance

D ₁ : First diode

D ₂ : Second diode

D ₃ : The third diode

D ₄ : Fourth diode

D ₅ : Fifth diode

D ₆ : Sixth diode

R _o : Load

Claims (4)

A symmetrical high voltage gain DC converter, which mainly connects the first end of the first capacitor, the first end of the second switch and the first end of the primary side of the first coupled inductor to the positive pole of the input voltage of the converter, the second end of the first capacitor is connected to the first end of the second capacitor, the second end of the third capacitor and the first end of the fourth capacitor, the second end of the second switch is connected to the second end of the secondary side of the second coupled inductor, the negative pole of the fifth diode and the positive pole of the sixth diode, the second end of the primary side of the coupled inductor is connected to the negative pole of the first diode and the negative pole of the second diode, the positive pole of the first diode is connected to the first end of the secondary side of the first coupled inductor, the positive pole of the first diode is connected to the positive pole of the sixth diode, and the negative pole of the fifth diode is connected to the negative pole of the fifth diode. The second end of the secondary side of a coupled inductor is connected to the negative electrode of a third diode, the positive electrode of the second diode and the first end of a first switch, the positive electrode of the third diode is connected to the first end of the third capacitor and the first end of a load, the second end of the first switch, the second end of the second capacitor and the first end of the primary side of the second coupled inductor are connected to the negative electrode of the input voltage, the second end of the primary side of the second coupled inductor is connected to the positive electrode of a fourth diode and the positive electrode of a fifth diode, the negative electrode of the fourth diode is connected to the first end of the secondary side of the second coupled inductor, and the negative electrode of the sixth diode is connected to the second end of the fourth capacitor and the second end of the load. A symmetrical high voltage gain DC converter as described in claim 1, wherein the converter has a first magnetizing inductance formed on the primary side of the first coupled inductor. A symmetrical high voltage gain DC converter as described in claim 1, wherein the converter has a second magnetizing inductance formed on the primary side of the second coupled inductor. The symmetrical high voltage gain DC converter as claimed in claim 1, wherein the voltage gain of the converter is , where D is the conduction ratio.

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