CN103269157A - Bi-Directional Dual-Input SEPIC DC Converter and Its Power Distribution Method - Google Patents

Abstract

The invention discloses a bidirectional double-input SEPIC direct-current converter and a power distribution method thereof, wherein the bidirectional double-input SEPIC direct-current converter comprises a first SEPIC pulse current source unit, a second SEPIC pulse current source unit and an output filter circuit; the first SEPIC pulse current source unit comprises a first input direct current voltage source A and a first power switch tube M₁A second power switch tube M₃A first inductor L₁A second inductor L₃And a first capacitor C₁(ii) a The second SEPIC pulse current source unit comprises a second input direct current voltage source B and a third power switch tube M₂The fourth power switch tube M₄A third inductor L₂A fourth inductor L₄And a second capacitor C₂(ii) a The first SEPIC pulse current source unit and the second SEPIC pulse current source unit are connected in parallel; the output filter circuit comprises an output filter capacitor C. The power distribution method comprises the steps of carrying out power distribution and load feedback power control on two input direct current voltage sources. The present invention has: the circuit has the characteristics of complex structure, capability of realizing voltage boosting and reducing, large output voltage regulation range, capability of realizing energy feedback, small loss, high circuit efficiency, small ripple in output voltage waveform, no need of an isolation transformer, parallel connection of two current sources, capability of being used in large-current occasions and the like.

Description

Bi-Directional Dual-Input SEPIC DC Converter and Its Power Distribution Method

technical field

The invention relates to the field of power electronic converters, in particular to a bidirectional double-input SEPIC DC converter and a power distribution method thereof.

Background technique

With the increasingly prominent environmental protection issues, people pay more and more attention to the development and utilization of renewable energy. Renewable energy has the characteristics of cheap, reliable, clean and pollution-free, and abundant energy, so renewable energy power generation has shown a good market prospect. At present, the most widely used renewable energy power generation forms include photovoltaic power generation, fuel cell power supply, wind power generation, hydropower generation, geothermal power generation, etc., but these power generation forms have the characteristics of unstable power supply, discontinuity, and changes with climate conditions. , so a distributed power supply system using multiple energy sources for joint power supply is required.

In the traditional new energy joint power supply system, each energy form usually requires a DC/DC converter to convert various energy sources into DC output, and connect them in parallel to the common DC bus to supply DC loads, but its structure is relatively complicated. And the cost is higher. In order to simplify the circuit structure and reduce system cost, multiple single-input DC converters can be replaced by a multiple-input DC converter (Multiple-Input Converter, MIC). MIC allows a variety of energy inputs, and the nature, amplitude and characteristics of the input sources can be the same or very different. Multiple input sources can supply power to the load separately or simultaneously, thus improving the stability and flexibility of the system and realizing energy Optimal utilization and reduced system cost.

Contents of the invention

In order to overcome the above-mentioned problems in the prior art, the object of the present invention is to provide a topology structure and a control method that are relatively simple and can realize automatic distribution and utilization of energy.

In order to solve the above-mentioned technical problems, the present invention is achieved through the following technical solutions:

A bidirectional dual-input SEPIC DC converter, comprising a first SEPIC pulse current source unit, a second SEPIC pulse current source unit and an output filter circuit;

The first SEPIC pulse current source unit includes a first input DC voltage source A, a first power switch tube M ₁ , a second power switch tube M ₃ , a first inductor L ₁ , a second inductor L ₃ and a first capacitor C ₁ , the positive pole of the first input DC voltage source A is connected to one end of the first inductor L ₁ , the other end of the first inductor L ₁ is connected to the drain of the first power switch tube M ₁ and one end of the first capacitor C ₁ , the other end of the first capacitor _C1 is connected to the source of the second power switch tube _M3 and one end of the second inductor _L3 , and the other end of the second inductor _L3 is connected to the negative electrode of the first input DC voltage source A, the second A source connection of the power switch tube _M1 ;

The second SEPIC pulse current source unit includes a second input DC voltage source B, a third power switch M ₂ , a fourth power switch M ₄ , a third inductance L ₂ , a fourth inductance L ₄ and a second capacitor C ₂ , the anode of the second input DC voltage source B is connected to one end of the third inductance L ₂ , the other end of the third inductance L ₂ is connected to the drain of the third power switch tube M ₂ and one end of the second capacitor C ₂ , the other end of the second capacitor _C2 is connected to the source of the fourth power switch tube _M4 and one end of the fourth inductance _L4 , and the other end of the fourth inductance _L4 is connected to the negative electrode of the second input DC voltage source B, the first end of the fourth inductance L4 The source electrodes of the three power switch tubes _M2 are connected;

The first SEPIC pulse current source unit and the second SEPIC pulse current source unit are connected in parallel;

The output filter circuit includes an output filter capacitor C, wherein one end of the output filter capacitor C is respectively connected to the drain of the second power switch tube _M3 in the first SEPIC pulse current source unit, and the drain electrode of the second SEPIC pulse current source unit. The drain of the fourth power switch tube _M4 is connected to one end of the load R, and the other end of the output filter capacitor C is respectively connected to the second inductor L3 in the first SEPIC pulse current source unit and the second inductor _L3 in the second SEPIC pulse current source unit. Four inductors L ₄ and the other end of the load R are connected.

The object of the present invention also is to provide a kind of bidirectional double-input SEPIC DC converter power distribution method, and it comprises following content:

The first input DC voltage source A is a photovoltaic cell, and the second input DC voltage source B is a storage battery. Power distribution and load feedback power control are performed on the two input DC voltage sources. The first input DC voltage source A is input with maximum power, and maintains the maximum power input through the maximum power tracking algorithm, and the second input DC voltage source B is used as a power buffer unit, and automatically distributes energy through a regulator with reverse output: When the power demanded by the load is greater than the power provided by the first input DC voltage source A, the second input DC voltage source B discharges; when the load demanded power is less than the power provided by the first input DC voltage source A, the second input DC voltage source B Charging; when the load demand power is greater than the input power of the first input DC voltage source A, the output of the regulator is a positive value, which is converted into the duty cycle of the third power switch tube _M2 to control the discharge power of the second input DC voltage source B ; When the load demand power is less than the input power of the first input DC voltage source A, the load voltage rises, and the regulator output is a negative value, which is converted into the duty cycle of the fourth power switch tube _M4 to control the second input DC voltage source The charging power of B keeps the load voltage stable.

Due to the adoption of the above technical solution, compared with the prior art, the bidirectional double-input SEPIC DC converter and its power distribution method provided by the present invention have the following beneficial effects:

Although the circuit structure of the present invention is relatively complicated, it has the following characteristics: it can realize step-down and step-down, the adjustment range of the output voltage is large, it can realize energy feedback, the loss is small, the efficiency of the circuit is high, the ripple in the output voltage waveform is small, and no isolation is required. Transformer; parallel connection of two current sources can be used in high current occasions; two-way energy input can make full use of new energy, and can transfer energy in both directions to achieve optimal energy utilization; easy to realize modularization and easy to expand applications.

Compared with the dual-input SEPIC circuit, the present invention can realize energy feedback. Due to the addition of bidirectional function on the basis of the original dual input, when the load requires more power, the two input sources supply power to the load at the same time, which is the same as the traditional dual input SEPIC circuit. When the load requires less power, the new The electric energy generated by the energy source is greater than the energy required by the load. Through proper control, the reverse flow of energy is realized, and the excess energy is stored in the battery. When the electric energy generated by the new energy source is insufficient, the battery is discharged again to maintain the stability of the output voltage. This leads to an optimal distribution of energy.

Description of drawings

Fig. 1 is the electric schematic diagram of bidirectional double-input SEPIC DC converter of the present invention;

Fig. 2 is a structural block diagram of the control system of the present invention;

Fig. 3 to Fig. 10 are the equivalent circuits of the bidirectional dual-input SEPIC DC converter of the present invention in different switching modes;

Fig. 11 is a schematic waveform diagram of simultaneous power supply of A and B in the present invention;

Fig. 12 is a schematic waveform diagram of A's independent power supply in the present invention;

Fig. 13 is the principle waveform diagram of B independent power supply among the present invention;

Fig. 14 is the schematic waveform diagram of A power supply, B energy storage, and C energy consumption in the present invention;

Fig. 15 is a principle waveform diagram of A power supply, B energy storage, and C feedback energy in the present invention;

Fig. 16 is the simulation waveform of the present invention;

Fig. 17 is the electrical schematic diagram of the present invention in the solar car motor system.

Meanings of symbols in the above drawings: V ₁ and V ₂ are the input voltages of the first input DC voltage source A and the second input DC voltage source B respectively; M ₁ , M ₂ , M ₃ , and M ₄ are the first and second input voltages respectively. 3. The second and fourth power switch tubes; D ₁ , D ₂ , D ₃ , and D ₄ are respectively the body diodes of the first, third, second, and fourth power switch tubes; L ₁ , L ₂ , L ₃ , L ₄ is the first, third, second, and fourth inductors; C ₁ , C ₂ are the first and second capacitors; C is the output filter capacitor; R is the load; V _M1 , V _M2 , V _M3 , V _M4 is the driving voltage of the first, third, second and fourth power switch tubes; i _L1 and i _L2 are the input inductor current, i is the load current, and I is the average value of the load current; V _O is the output voltage; t, t ₀ to t ₄ are time.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment the present invention is described in further detail:

As shown in Figure 1, a bidirectional dual-input SEPIC DC converter includes a first SEPIC pulse current source unit, a second SEPIC pulse current source unit and an output filter circuit;

The first SEPIC pulse current source unit includes a first input DC voltage source A (hereinafter referred to as power supply A), a first power switch M ₁ , a second power switch M ₃ , a first inductor L ₁ , a second inductor L ₃ and the first capacitor C ₁ , the positive pole of the power supply A is connected to one end of the first inductor L ₁ , the other end of the first inductor L ₁ is connected to the drain of the first power switch tube M ₁ , and one end of the first capacitor C ₁ The other end of the first capacitor _C1 is connected to the source of the second power switch tube _M3 and one end of the second inductor _L3 , and the other end of the second inductor _L3 is connected to the negative pole of the power supply A and the first power switch tube The source connection of _M1 ;

The second SEPIC pulse current source unit includes a second input DC voltage source B (hereinafter referred to as power supply B), a third power switch tube M ₂ , a fourth power switch tube M ₄ , a third inductor L ₂ , and a fourth inductor L ₄ and the second capacitor C ₂ , the positive pole of the power supply B is connected to one end of the third inductor L ₂ , the other end of the third inductor L ₂ is connected to the drain of the third power switch tube M ₂ , and one end of the second capacitor C ₂ The other end of the second capacitor _C2 is connected to the source of the fourth power switch tube _M4 and one end of the fourth inductance _L4 , and the other end of the fourth inductance _L4 is connected to the negative pole of the power supply B and the third power switch tube The source connection of _M2 ;

The first SEPIC pulse current source unit and the second SEPIC pulse current source unit are connected in parallel;

The output filter circuit includes an output filter capacitor C, wherein one end of the output filter capacitor C is respectively connected to the drain of the second power switch tube _M3 in the first SEPIC pulse current source unit, and the drain electrode of the second SEPIC pulse current source unit. The drain of the fourth power switch tube _M4 is connected to one end of the load R, and the other end of the output filter capacitor C is respectively connected to the second inductor L3 in the first SEPIC pulse current source unit and the second inductor _L3 in the second SEPIC pulse current source unit. Four inductors L ₄ and the other end of the load R are connected.

As shown in Figure 2, according to the structural block diagram of the control system of the present invention, in the bidirectional double-input SEPIC DC converter, the master-slave control mode is selected to distribute the input power of two input DC voltage sources, and the power supply A selects solar cells as the main power supply equipment, The power supply B selects the storage battery as the backup energy supply equipment, which meets the requirements of the priority utilization of energy in the renewable energy supply system. At the same time, adjust the input current reference value of the power supply A to achieve the maximum power output of the solar cell, that is, to achieve maximum power point tracking (Maximum Power Point Tracking, MPPT). Power supply B automatically distributes energy through a regulator with reverse output (such as a PI regulator): when the load demand power is greater than the input power of power supply A, the regulator output is a positive value, which is converted into the power of the third power switch tube _M2 The duty cycle controls the discharge power of the power supply B; when the load demand power is less than the input power of the power supply A, the load voltage rises, and the output of the regulator is a negative value, which is converted into the duty cycle of the fourth power switch tube _M4 to control the power supply The charging power of B keeps the load voltage stable.

The working principle of the converter of the present invention will be specifically analyzed below with reference to FIGS. 3 to 10 . Before the analysis, make the following assumptions: ①All switching tubes are ideal devices, regardless of switching time and conduction voltage drop; ②All inductors and capacitors are ideal devices.

According to the switching states of the power switch tubes M ₁ ~ M ₄ , the converter can be divided into the following eight working modes:

1. Switch mode I:

As shown in Figure 3, M ₁ and M ₂ are turned on, M ₃ and M ₄ are turned off, the inductors L ₁ and L ₂ draw energy from the power supply V ₁ and V ₂ respectively, the inductor current i _L1 and i _L2 increase, and the current The paths are V ₁ -L ₁ -M ₁ and V ₂ -L ₂ -M ₂ respectively; capacitor C ₁ discharges to L ₃ , capacitor C ₂ discharges to L ₄ , and the current paths are C ₁ -M ₁ -L ₃ and C ₂ -M ₂ -L ₄ ; the load current is provided by the discharge of capacitor C.

2. Switch Mode II:

As shown in Figure 4, M ₁ is turned on, M ₂ , M ₃ and M ₄ are turned off, the inductor L ₁ draws energy from the power supply V ₁ , the inductor current i _L1 increases, and the current path is V ₁ -L ₁ -M ₁ ; Capacitor C ₁ discharges to L ₃ , and the current path is C ₁ -M ₁ -L ₃ ; the load current is provided by the discharge of capacitor C.

3. Switch Mode III:

As shown in Figure 5, M ₂ is turned on, M ₁ , M ₃ and M ₄ are turned off, the inductor L ₂ draws energy from the power supply V ₂ , the inductor current i _L2 increases, and the current path is V ₂ -L ₂ -M ₂ ; Capacitor C ₂ discharges to L ₄ , the current path is C ₂ -M ₂ -L ₄ ; the load current is provided by the discharge of capacitor C.

4. Switch mode IV:

As shown in Figure 6, M ₁ , M ₂ , M ₃ and M ₄ are turned off, D ₃ and D ₄ are turned on, the inductor L ₁ will pass through the capacitor C ₁ , diode D ₃ , capacitor C and load R, and the inductor L ₂ will continue to flow through capacitor C ₂ , diode D ₄ , capacitor C and load R, the inductor current i _L1 and i _L2 will decrease, and the current paths are V ₁ -L ₁ -C ₁ -D ₃ -C and V ₂ -L ₂ -C ₂ -D ₄ -C. At the same time, the inductance _L3 passes through the diode _D3 and the capacitor C, the load R completes the freewheeling, the inductance _L4 passes through the diode _D4 and the capacitor C, the load R completes the freewheeling, and the current paths are _L3 - _D3 -C and _L4 respectively -D ₄ -C.

5. Switch mode V:

As shown in Figure 7, M ₁ , M ₂ , M ₃ and M ₄ are turned off, D ₃ is turned on, the inductor L ₁ will continue to flow through the capacitor C ₁ , the diode D ₃ , the capacitor C and the load R, and the inductor current i _L1 decreases, the current path is V ₁ -L ₁ -C ₁ -D ₃ -C. At the same time, L ₃ passes through the diode D ₃ and the capacitor C, and the load R completes freewheeling, and the current path is L ₃ -D ₃ -C.

6. Switch Modal VI:

As shown in Figure 8, M ₁ , M ₂ , M ₃ and M ₄ are turned off, D ₄ is turned on, the inductor L ₂ will continue to flow through the capacitor C ₂ , the diode D ₄ , the capacitor C and the load R, and the inductor current i _L2 decreases, the current path is V ₂ -L ₂ -C ₂ -D ₄ -C. At the same time, L ₄ passes through diode D ₄ and capacitor C, and the load R completes freewheeling, and the current path is L ₄ -D ₄ -C.

7. Switch mode VII:

As shown in Figure 9, M ₄ is turned on, M ₁ , M ₂ and M ₃ are turned off, the load unit charges V ₂ through C ₂ and L ₂ , the inductor current i _L2 increases in reverse, and the current path is CM ₄ -C ₂ -L ₂ -V ₂ . At the same time, the inductor L ₄ draws energy from the load unit, and the current path is CM ₄ -L ₄ .

8. Switch Mode VIII:

As shown in Figure 10, M ₁ , M ₂ , M ₃ and M ₄ are turned off, D ₂ is turned on, L ₂ continues to flow through D ₂ to charge V ₂ , the inductor current i _L2 decreases in reverse, and the current path is L ₂ -V ₂ -D ₂ . At the same time, the inductor L ₄ completes freewheeling through the diode D ₂ and the capacitor C ₂ , and the current path is L ₄ -D ₂ -C ₂ .

From the above analysis, it can be seen that with the power source A (solar battery) and power source B (battery) as two input voltage sources, according to the energy transfer in the circuit, there are 5 working modes for the bidirectional dual-input SEPIC DC converter:

1. The power supply A and the power supply B supply power at the same time, and the working sequence of the circuit is I and IV modes. The principle waveform of the converter is shown in Figure 11, and the input inductor current i _L1 and i _L2 are always greater than zero;

2. The power supply A is powered separately, and the working sequence of the circuit is II and V modes. The principle waveform of the converter is shown in Figure 12, and the input inductor current i _L1 is always greater than zero;

3. The power supply B is powered separately, and the working sequence of the circuit is III and VI modes. The principle waveform of the converter is shown in Figure 13, and the input inductor current i _L2 is always greater than zero;

4. Power source A supplies power, power source B stores energy, and power source C consumes energy. The working sequence of the circuit is II, V, VII, and VIII modes. The principle waveform of the converter is shown in Figure 14. The input inductor current i _L2 crosses zero, but the load current The mean I is greater than zero;

5. Power source A supplies power, power source B stores energy, and power source C feeds back. The working sequence of the circuit is II, V, VII, and VIII modes. The principle waveform of the converter is shown in Figure 15. The input inductor current i _L2 crosses zero, but the load current is average The value I is less than zero.

As shown in Figure 16: where (a) is the load switching signal, (b) is the waveform of the output voltage V _O , and (c) is the waveform of the load current i. First, the two input power supplies supply power at the same time. After stabilization, part of the load is cut off, so that the input power of power supply A is greater than the load power, and automatically switches to the energy feedback working mode. According to the different working modes, it can be divided into two working stages:

Phase 1: Two input power supplies supply power to the load at the same time, where the maximum power tracking is performed on power supply A, so that power supply A is input at the maximum power. The input power of power supply B is controlled through a voltage regulator so that it can provide insufficient power. It can be seen from (b) that the output voltage is stable at 50V, and from (c) it can be seen that the load current i is always greater than zero.

Stage 2: Cut off part of the load, resulting in transient power imbalance. Power supply A works at the maximum power point through the maximum power tracking algorithm and keeps it constant. Since the output voltage is greater than the given value, the output of the voltage loop regulator decreases and becomes is a negative value, the power supply B switches to the energy storage mode to balance the input power and load consumption power. It can be seen from (b) that the output voltage is stabilized at 50V after adjustment. It can be seen from (c) that the load current i has a positive part and a negative part, indicating that energy feedback can be performed and energy distribution can be realized automatically.

In the above working process, it also includes the working mode in which the two input power supplies supply power to the load independently and the load side feeds back energy, which will not be described in detail here. The feasibility and correctness of the topology and power distribution method proposed by the present invention are proved by simulation.

The following is an example of the application of this topology in a solar car:

Fig. 17 is the electrical principle diagram of this invention in the solar car motor system, and its specific implementation steps are as follows:

1. The solar cell and the storage battery supply power to the motor system at the same time. When the car is started or heavy-loaded, the required power is relatively large. According to the power distribution method proposed by the present invention, the maximum power of the solar cell is tracked, and _M1 is controlled to be on and off, so that The solar battery supplies power to the motor system with the maximum power, and then controls the _M2 on and off, so that the battery can provide insufficient power, so that the solar energy can be fully utilized, and the instantaneous power can be increased compared with a single power supply.

2. The solar battery supplies power alone. When the battery fails or the solar battery just meets the needs of the motor system, the solar battery supplies power alone. At this time, by controlling the on-off of _M1 , the power balance is maintained to ensure the normal operation of the motor system.

3. The battery supplies power alone. In cloudy days or when the solar battery fails, the storage battery supplies power alone. The on-off of _M2 is controlled by the voltage regulator to stabilize the output voltage and meet the requirements of the motor system.

4. Solar battery power supply, battery energy storage, and motor system energy consumption. When the light is strong and the power emitted by the solar cell is greater than the power required by the motor system, the on-off of _M4 is controlled to store the excess power of the solar energy in the battery to avoid energy waste and make full use of light energy.

5. Solar battery power supply, battery energy storage, motor system feedback energy. When the car is braking or going downhill, the motor system works in the regenerative braking state, converting mechanical energy into electrical energy and feeding it back to the input side. In this case, the energy emitted by the solar battery and the energy fed back by the motor system must be stored in the In the storage battery, through maximum power tracking, control the on-off of M ₁ to make the solar cell output at the maximum power, control the on-off of M ₄ , store energy in the battery, and avoid energy waste.

Claims (2)

1. A bidirectional double-input SEPIC DC converter is characterized in that: comprise the first SEPIC pulse current source unit, the second SEPIC pulse current source unit and output filter circuit; The first SEPIC pulse current source unit includes a first input DC voltage source A, a first power switch tube M ₁ , a second power switch tube M ₃ , a first inductor L ₁ , a second inductor L ₃ and a first capacitor C ₁ , the positive pole of the first input DC voltage source A is connected to one end of the first inductor L ₁ , the other end of the first inductor L ₁ is connected to the drain of the first power switch tube M ₁ and one end of the first capacitor C ₁ , the other end of the first capacitor _C1 is connected to the source of the second power switch tube _M3 and one end of the second inductor _L3 , and the other end of the second inductor _L3 is connected to the negative electrode of the first input DC voltage source A, the second A source connection of the power switch tube _M1 ; The second SEPIC pulse current source unit includes a second input DC voltage source B, a third power switch M ₂ , a fourth power switch M ₄ , a third inductance L ₂ , a fourth inductance L ₄ and a second capacitor C ₂ , the anode of the second input DC voltage source B is connected to one end of the third inductance L ₂ , the other end of the third inductance L ₂ is connected to the drain of the third power switch tube M ₂ and one end of the second capacitor C ₂ , the other end of the second capacitor _C2 is connected to the source of the fourth power switch tube _M4 and one end of the fourth inductance _L4 , and the other end of the fourth inductance _L4 is connected to the negative electrode of the second input DC voltage source B, the first end of the fourth inductance L4 The source electrodes of the three power switch tubes _M2 are connected; The first SEPIC pulse current source unit and the second SEPIC pulse current source unit are connected in parallel; The output filter circuit includes an output filter capacitor C, wherein one end of the output filter capacitor C is respectively connected to the drain of the second power switch tube _M3 in the first SEPIC pulse current source unit, and the drain electrode of the second SEPIC pulse current source unit. The drain of the fourth power switch tube _M4 is connected to one end of the load R, and the other end of the output filter capacitor C is respectively connected to the second inductor L3 in the first SEPIC pulse current source unit and the second inductor _L3 in the second SEPIC pulse current source unit. Four inductors L ₄ and the other end of the load R are connected. 2. a kind of power distribution method of bidirectional double-input SEPIC DC converter, is characterized in that: It includes the following: The first input DC voltage source A is a photovoltaic cell, and the second input DC voltage source B is a storage battery. Power distribution and load feedback power control are performed on the two input DC voltage sources. The first input DC voltage source A is input with maximum power, and maintains the maximum power input through the maximum power tracking algorithm, and the second input DC voltage source B is used as a power buffer unit, and automatically distributes energy through a regulator with reverse output: When the power demanded by the load is greater than the power provided by the first input DC voltage source A, the second input DC voltage source B discharges; when the load demanded power is less than the power provided by the first input DC voltage source A, the second input DC voltage source B Charging; when the load demand power is greater than the input power of the first input DC voltage source A, the output of the regulator is a positive value, which is converted into the duty cycle of the third power switch tube _M2 to control the discharge power of the second input DC voltage source B ; When the load demand power is less than the input power of the first input DC voltage source A, the load voltage rises, and the regulator output is a negative value, which is converted into the duty cycle of the fourth power switch tube _M4 to control the second input DC voltage source The charging power of B keeps the load voltage stable.

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