A fuel cell and lithium battery system for an unmanned aerial vehicle and a control method thereof

Abstract

A fuel cell and lithium battery system and control method for an unmanned aerial vehicle, including a hydrogen-oxygen fuel cell, a lithium battery, MOSFET switch tubes Q<subgt;1< / subgt>, MOSFET switch tubes Q<subgt;2< / subgt>, MOSFET switch tubes Q<subgt;3< / subgt>, a voltage control circuit, a hydrogen-oxygen fuel cell voltage detection unit, a lithium battery voltage detection unit, and a load; by controlling the conduction and cutoff of the MOSEFT switch tubes, and by the voltage difference between the hydrogen-oxygen fuel cell and the lithium battery to achieve the state transformation of the voltage control circuit, the step-down, direct, and step-up outputs of the hydrogen-oxygen fuel cell are completed, enabling the unmanned aerial vehicle to work in the best state, improving the service life of the hydrogen-oxygen fuel cell and the lithium battery, and improving the working efficiency of the entire system.

Description

Technical Field

[0001] The present invention belongs to the technical field of UAV power supplies, and particularly relates to a fuel cell and a lithium battery system for UAVs and a control method therefor. Background Art

[0002] In recent years, with the rapid development and wide application of hydrogen-oxygen fuel cell technology, composite energy UAVs have developed rapidly. Although the addition of hydrogen-oxygen fuel cells has improved the endurance time of UAVs, in the composite power system, the hydrogen-oxygen fuel cell takes a long time to reach the optimal working point and has a soft output characteristic and cannot provide a very strong energy output. Therefore, the starting performance is poor. To ensure the performance of the UAV and provide sufficient power during the start-up and acceleration of the UAV, a lithium battery is required to intervene as an auxiliary energy source to provide additional power, prevent the hydrogen-oxygen fuel cell from being over-discharged, recover braking energy while meeting the motor power demand, and enhance the energy utilization rate of the UAV.

[0003] There are four conventional topologies for hydrogen-oxygen fuel cells and lithium batteries, namely, direct parallel connection of hydrogen-oxygen fuel cells and lithium batteries, parallel connection of a lithium battery after adding a DC / DC converter to the output terminal of the hydrogen-oxygen fuel cell, parallel connection of a hydrogen-oxygen fuel cell after adding a DC / DC converter to the output terminal of the lithium battery, and parallel connection after adding DC / DC converters to the output terminals of both the hydrogen-oxygen fuel cell and the lithium battery. The most commonly used structure (the article Real-time energy management for fuel cell electric vehicle using speed prediction-based model predictive control considering performance degradation published in Applied Energy) is to add a DC / DC boost converter to the output terminal of the hydrogen-oxygen fuel cell and then connect it in parallel with the lithium battery for power supply. However, this structure cannot correspond to the polarization characteristics of the fuel cell, greatly reducing the energy utilization rate of the system and increasing the control difficulty of a single boost converter. Summary of the Invention

[0004] To overcome the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a fuel cell and a lithium battery system for UAVs and a control method therefor. By controlling the conduction and cut-off of the MOSEFT switch tube and realizing the state transformation of the voltage control circuit through the voltage difference between the hydrogen-oxygen fuel cell and the lithium battery, step-down, direct, and boost output of the hydrogen-oxygen fuel cell are completed, enabling the UAV to work in the best state, extending the service life of the hydrogen-oxygen fuel cell and the lithium battery, and improving the working efficiency of the entire system.

[0005] To achieve the above purpose, the technical solution provided by the present invention is:

[0006] A fuel cell and lithium battery system for an unmanned aerial vehicle, comprising a hydrogen-oxygen fuel cell, a lithium battery, MOSFET switching tubes Q1, MOSFET switching tubes Q2, MOSFET switching tubes Q3, a voltage control circuit, a hydrogen-oxygen fuel cell voltage detection unit, a lithium battery voltage detection unit, and a load; the positive electrode of the hydrogen-oxygen fuel cell is connected to the input end of inductor L1 and the drain of MOSFET switching tube Q3, and the negative electrode is connected to the source of MOSFET switching tube Q1, the negative electrode of filter capacitor C1, the negative electrode of the lithium battery, and the negative electrode of the load; the output end of inductor L1 is connected to the source of MOSFET switching tube Q3, the input end of inductor L2, the positive electrode of diode D4, and the drain of MOSFET switching tube Q1; the output end of inductor L2 is connected to the positive electrode of the load; the negative electrode of diode D4 is connected to the input end of the voltage control circuit and the positive electrode of filter capacitor C1, and the output end of the voltage control circuit is connected to the source of MOSFET switching tube Q2 and the positive electrode of the load; the drain of MOSFET switching tube Q2 is connected to the positive electrode of the lithium battery, and filter capacitor C2 is connected in parallel across the load; freewheeling diodes D1, D2, and D3 are respectively connected in parallel across MOSFET switching tubes Q1, Q2, and Q3; a voltage detection unit V is connected in parallel across the hydrogen-oxygen fuel cell and the lithium battery;

[0007] The inductor L1, MOSFET switching tube Q1, and diode D4 constitute a high-power boost circuit;

[0008] The inductor L2 is a small inductor with a size smaller than L1, and together with the freewheeling diode D1 of MOSFET switching tube Q1 and MOSFET switching tube Q3, it constitutes a low-power buck circuit.

[0009] The fuel cell and lithium battery composite power supply system for an unmanned aerial vehicle with an integrated buck-boost and direct parallel structure selects a buck, boost, or direct parallel output mode according to the voltage-current output characteristic curve of the hydrogen-oxygen fuel cell. The inductor L2 is a small inductor with a size smaller than L1, and it quickly adjusts the buck output of the hydrogen-oxygen fuel cell when the hydrogen fuel cell starts. The mode is switched through MOSFET switching tubes and a voltage control circuit to ensure that the hydrogen-oxygen fuel cell operates in a high-efficiency range.

[0010] The voltage control circuit includes a high-low level conversion circuit, a MOSEFT switching tube, and a general subtraction circuit; the hydrogen-oxygen fuel cell voltage V measured by the voltage detection unit i1 and the lithium battery voltage V i2It is input into a general subtraction circuit, and the voltage difference between the lithium battery voltage and the hydrogen-oxygen fuel cell voltage is obtained as the input signal of the high-low level conversion circuit. When the input signal voltage is less than the voltage of diode D6, pins 8 and 7 of optocoupler TLP250 are not conducting, and pins 6 and 5 are conducting. Since pin 5 is equivalent to ground, pin 6 is also equivalent to ground at this time, T1 is at zero potential, and S1-source is reverse-biased by zener diode D5. At this time, a low-level signal is input to the MOSEFT switch tube, and the switch is turned off, and the hydrogen-oxygen fuel cell is in a step-down output mode;

[0011] When the input signal voltage is greater than the voltage of diode D6, pins 8 and 7 of optocoupler TLP250 are conducting, pins 6 and 5 are not conducting, the potential of pin 7 is equal to the potential of pin 8, pins 7 and 6 are connected, the potential of T1 is 15V, and S1-source is reverse-biased by zener diode D5. At this time, a high-level signal is input to the MOSEFT switch tube, and the switch is turned on, and the hydrogen-oxygen fuel cell is in a direct or boost output mode.

[0012] The described control method for a fuel cell and lithium battery system for an unmanned aerial vehicle includes:

[0013] 1) Output scheme:

[0014] Step 1: When the system starts, the voltage of the hydrogen-oxygen fuel cell is higher than the voltage of the lithium battery, the voltage control circuit is turned off, MOSEFT switch tubes Q1 are turned off, Q2 is turned on, and Q3 conducts and turns off at high frequency. At this time, the system works in the step-down output mode of the hydrogen-oxygen fuel cell and is connected in parallel with the lithium battery to supply energy to the load;

[0015] Step 2: When the voltage of the hydrogen-oxygen fuel cell is less than or equal to the voltage of the lithium battery, the voltage control circuit is turned on, MOSEFT switch tube Q1 is turned off, and Q2 and Q3 are turned on. At this time, the system works in the direct output mode of the hydrogen-oxygen fuel cell and is connected in parallel with the lithium battery to supply energy to the load;

[0016] Step 3: When the system runs for a period of time and the voltage of the hydrogen-oxygen fuel cell drops to a set level, the voltage control circuit is turned on, MOSEFT switch tube Q3 is turned off, Q2 is turned on, and Q1 conducts and turns off at high frequency. At this time, the system works in the boost output mode of the hydrogen-oxygen fuel cell and is connected in parallel with the lithium battery to supply energy to the load;

[0017] Step 4: When the lithium battery needs to be charged due to insufficient power, at this time, MOSEFT switch tube Q2 is turned off, and the hydrogen-oxygen fuel cell charges the lithium battery through diode D2.

[0018] 2) Energy feeding scheme: When recovering braking energy, the voltage control circuit is turned off, MOSEFT switch tubes Q2 and Q3 are turned off, and the braking energy is absorbed by the lithium battery through diode D2.

[0019] Compared with the prior art, the beneficial effects produced by the present invention are as follows:

[0020] The fuel cell and lithium battery system for drones of the present invention can control the conduction and cut-off of the MOSFET switch tube, and achieve the state transformation of the voltage control circuit through the voltage difference between the hydrogen-oxygen fuel cell and the lithium battery, complete the step-down, direct, and step-up output of the hydrogen-oxygen fuel cell, enable the drone to work in the best state, improve the service life of the hydrogen-oxygen fuel cell and the lithium battery, and improve the working efficiency of the entire system. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is the overall structure diagram of the switchable mode composite power supply system in the embodiment of the present invention.

[0022] Figure 2 It is the schematic diagram of the step-up and step-down output of the circuit corresponding to the polarization curve of the hydrogen-oxygen fuel cell.

[0023] Figure 3 It is the structure diagram of the voltage control circuit.

[0024] Figure 4 It is the switch tube state and power flow path diagram of the step-down parallel lithium battery output mode of the hydrogen-oxygen fuel cell.

[0025] Figure 5 It is the switch tube state and power flow path diagram of the direct parallel lithium battery output mode of the hydrogen-oxygen fuel cell.

[0026] Figure 6 It is the switch tube state and power flow path diagram of the step-up parallel lithium battery output mode of the hydrogen-oxygen fuel cell.

[0027] Figure 7 It is the switch tube state and power flow path diagram of the step-up output of the hydrogen-oxygen fuel cell and the lithium battery charging mode at the same time.

[0028] Figure 8 It is the switch tube state and power flow path diagram of the lithium battery separate recovery mode. DETAILED DESCRIPTION OF THE INVENTION

[0029] The technical solution of the present invention will be further described below in conjunction with specific embodiments. The embodiments are used to illustrate the present invention and do not limit the scope of the present invention. The switch tube can be replaced by switches with the same function, and the capacity and voltage adjustment range of the hydrogen-oxygen fuel cell and the lithium battery can be selected according to the actual situation.

[0030] Such as Figure 1As shown, a fuel cell and lithium battery system for an unmanned aerial vehicle includes a hydrogen-oxygen fuel cell, a lithium battery, an inductor L1, an inductor L2, a filter capacitor C1, a filter capacitor C2, a MOSFET switch Q1, a MOSFET switch Q2, a MOSFET switch Q3, a diode D1, a diode D2, a diode D3, a diode D4, a voltage control circuit, a hydrogen-oxygen fuel cell voltage detection unit, a lithium battery voltage detection unit, and a load. The positive electrode of the hydrogen-oxygen fuel cell is connected to the input end of the inductor L1 and the drain of the MOSFET switch Q3, and the negative electrode is connected to the source of the MOSFET switch Q1, the negative electrode of the filter capacitor C1, the negative electrode of the lithium battery, and the negative electrode of the load. The output end of the inductor L1 is connected to the source of the MOSFET switch Q3, the input end of the inductor L2, the positive electrode of the diode D4, and the drain of the MOSFET switch Q1. The output end of the inductor L2 is connected to the positive electrode of the load. The negative electrode of the diode D4 is connected to the input end of the voltage control circuit and the positive electrode of the filter capacitor C1, and the output end of the voltage control circuit is connected to the source of the MOSFET switch Q2 and the positive electrode of the load. The drain of the MOSFET switch Q2 is connected to the positive electrode of the lithium battery, and the filter capacitor C2 is connected in parallel across the load. Freewheeling diodes D1, D2, and D3 are respectively connected in parallel across the MOSFET switches Q1, Q2, and Q3. A voltage detection unit V is connected in parallel across the hydrogen-oxygen fuel cell and the lithium battery.

[0031] The inductor L1, the MOSFET switch Q1, and the diode D4 form a high-power boost circuit.

[0032] The inductor L2 is a small inductor with a size smaller than that of L1, and together with the freewheeling diode D1 of the MOSFET switch Q1 and the MOSFET switch Q3, it forms a low-power buck circuit.

[0033] The fuel cell and lithium battery composite power supply system for an unmanned aerial vehicle with an integrated buck-boost and direct parallel structure selects a buck, boost, or direct parallel output mode according to the voltage-current output characteristic curve of the hydrogen-oxygen fuel cell, as Figure 2 shown, where the inductor L2 is a small inductor with a size smaller than that of L1, which can quickly adjust the buck output of the hydrogen-oxygen fuel cell during the startup of the hydrogen fuel cell, improving the efficiency of the buck conversion circuit. The mode is switched through the MOSFET switch and the voltage control circuit to ensure that the hydrogen-oxygen fuel cell operates in a high-efficiency range.

[0034] The voltage control circuit is as Figure 3 shown, and includes a high-low level conversion circuit, a MOSEFT switch, and a general subtraction circuit; it compares the hydrogen-oxygen fuel cell voltage V i1 measured by the voltage detection unit with the lithium battery voltage V i2It is input into a general subtraction circuit, and the voltage difference between the lithium battery voltage and the hydrogen-oxygen fuel cell voltage is obtained as the input signal of the high-low level conversion circuit. When the input signal voltage is less than the voltage of diode D6 (0.3V, approximately 0), pins 8 and 7 of optocoupler TLP250 are not conducting, and pins 6 and 5 are conducting. Since pin 5 is equivalent to ground, pin 6 is also equivalent to ground at this time. T1 is at zero potential, and S1-source has a potential of 3.5V because zener diode D5 (3.5V) is reverse-biased. So, T1 and S1-source are 0 - 3.5V = -3.5V. At this time, a low-level signal is input to the MOSEFT switch tube, and the switch is turned off, and the hydrogen-oxygen fuel cell is in the buck output mode;

[0035] When the input signal voltage is greater than the voltage of diode D6 (0.3V, approximately 0), pins 8 and 7 of optocoupler TLP250 are conducting, and pins 6 and 5 are not conducting. The potential of pin 7 is equal to the potential of pin 8, and pins 7 and 6 are connected. The potential of T1 is 15V, and S1-source has a potential of 3.5V because zener diode D5 (3.5V) is reverse-biased. So, T1 and S1-source are 15 - 3.5V = 11.5V. At this time, a high-level signal is input to the MOSEFT switch tube, and the switch is turned on, and the hydrogen-oxygen fuel cell is in the direct or boost output mode.

[0036] The described control method for a fuel cell and lithium battery system for an unmanned aerial vehicle selects different output schemes according to different operating conditions, including:

[0037] 1) Output scheme:

[0038] Step 1: When the system starts, the voltage of the hydrogen-oxygen fuel cell is higher than that of the lithium battery. The voltage control circuit is turned off, MOSEFT switch tubes Q1 are turned off, Q2 is turned on, and Q3 conducts and turns off at a high frequency. The inductor L2 of the buck circuit is a small inductor with a size smaller than L1 and does not share the same inductor with the boost circuit, improving the working efficiency of the high buck circuit. At this time, the system operates in the hydrogen-oxygen fuel cell buck output mode and is connected in parallel with the lithium battery to supply energy to the load, as Figure 4 shown;

[0039] Step 2: The voltage detection unit is used to detect the magnitudes of the hydrogen-oxygen fuel cell voltage and the lithium battery voltage. When the hydrogen-oxygen fuel cell voltage is less than or equal to the lithium battery voltage, the voltage control circuit is turned on, MOSEFT switch tube Q1 is turned off, and Q2 and Q3 are turned on. At this time, the system operates in the hydrogen-oxygen fuel cell direct output mode and is connected in parallel with the lithium battery to supply energy to the load, as Figure 5 shown;

[0040] Step 3: When the system runs for a period of time and the voltage of the hydrogen-oxygen fuel cell drops to a certain level, the voltage control circuit conducts, the MOSEFT switch Q3 turns off, Q2 turns on, and Q1 conducts and turns off at a high frequency. At this time, the system operates in the boost output mode of the hydrogen-oxygen fuel cell and is connected in parallel with the lithium battery to supply energy to the load, as Figure 6 shown;

[0041] Step 4: When the lithium battery needs to be charged due to insufficient power, the MOSEFT switch Q2 turns off at this time, and the hydrogen-oxygen fuel cell charges the lithium battery through the diode D2, as Figure 7 shown.

[0042] 2) Energy feeding scheme: When recovering braking energy, the voltage control circuit turns off, the MOSEFT switches Q2 and Q3 turn off, and the braking energy is absorbed by the lithium battery through the diode D2, as Figure 8 shown.

Claims

1. A fuel cell and lithium battery system for an unmanned aerial vehicle, characterized in that: It includes a hydrogen-oxygen fuel cell, a lithium battery, MOSFET switches Q1, Q2, Q3, a voltage control circuit, a hydrogen-oxygen fuel cell voltage detection unit, a lithium battery voltage detection unit, and a load; the positive electrode of the hydrogen-oxygen fuel cell is connected to the input end of inductor L1 and the drain of MOSFET switch Q3, and the negative electrode is connected to the source of MOSFET switch Q1, the negative electrode of filter capacitor C1, the negative electrode of the lithium battery, and the negative electrode of the load; the output end of inductor L1 is connected to the source of MOSFET switch Q3, the input end of inductor L2, the positive electrode of diode D4, and the drain of MOSFET switch Q1; the output end of inductor L2 is connected to the positive electrode of the load; the negative electrode of diode D4 is connected to the input end of the voltage control circuit and the positive electrode of filter capacitor C1, and the output end of the voltage control circuit is connected to the source of MOSFET switch Q2 and the positive electrode of the load; the drain of MOSFET switch Q2 is connected to the positive electrode of the lithium battery, and filter capacitor C2 is connected in parallel across the load; freewheeling diodes D1, D2, and D3 are respectively connected in parallel across MOSFET switches Q1, Q2, and Q3; a voltage detection unit V is connected in parallel across the hydrogen-oxygen fuel cell and the lithium battery; The inductor L1, MOSFET switch Q1, and diode D4 form a high-power boost circuit; The inductor L2 is a small inductor with a size smaller than L1, and together with the freewheeling diode D1 of MOSFET switch Q1 and MOSFET switch Q3, it forms a low-power buck circuit.

2. The system according to claim 1, wherein: According to the voltage-current output characteristic curve of the hydrogen-oxygen fuel cell, a buck, boost, or direct parallel output mode is selected. Among them, the inductor L2 is a small inductor with a size smaller than L1, and it quickly adjusts the buck output of the hydrogen-oxygen fuel cell when the hydrogen fuel cell starts. The mode is switched through MOSFET switches and the voltage control circuit to ensure that the hydrogen-oxygen fuel cell operates in a high-efficiency range.

3. The system according to claim 1, wherein: The voltage control circuit includes a high-low level conversion circuit, a MOSEFT switch, and a general subtraction circuit; the high-low level conversion circuit includes an optocoupler TLP250 and a Zener diode D5; pin 6 of the optocoupler TLP250 is connected to the gate of MOSEFT switch Q4, and the potential state T1 output by pin 6 is used to control MOSEFT switch Q4; pin 8 of the optocoupler TLP250 is connected to the cathode of the Zener diode D5 and the source of MOSEFT switch Q4 after passing through a resistor R2, and the potential state S1-Source here and T1 jointly control the turn-off and turn-on of MOSEFT switch Q4; The voltage V of the hydrogen-oxygen fuel cell measured by the voltage detection unit i1 and the voltage V of the lithium battery i2 are input into a general subtraction circuit to obtain the voltage difference between the lithium battery voltage minus the hydrogen-oxygen fuel cell voltage as the input signal of the high-low level conversion circuit. When the input signal voltage is less than the voltage of diode D6, pins 8 and 7 of optocoupler TLP250 are not conducting, and pins 6 and 5 are conducting. Since pin 5 is equivalent to ground, pin 6 is also equivalent to ground at this time, T1 is at zero potential, and S1-source is reverse-biased by zener diode D5. At this time, a low-level signal is input to the MOSEFT switch tube, and the switch is turned off, and the hydrogen-oxygen fuel cell is in the buck output mode; When the input signal voltage is greater than the voltage of diode D6, pins 8 and 7 of optocoupler TLP250 conduct, while pins 6 and 5 do not conduct. The potential of pin 7 is equal to that of pin 8, and pins 7 and 6 are connected. The potential of T1 is 15V. Since zener diode D5 is reverse-biased, a high-level signal is input to the MOSEFT switch tube at this time, and the switch conducts, and the hydrogen-oxygen fuel cell operates in a direct or boost output mode.

4. The control method of the system according to claim 1, characterized in that, Including: 1) Output scheme: Step 1: When the system starts, the voltage of the hydrogen-oxygen fuel cell is higher than that of the lithium battery. The voltage control circuit is turned off, MOSEFT switch tubes Q1 is turned off, Q2 conducts, and Q3 conducts and turns off at a high frequency. At this time, the system operates in the buck output mode of the hydrogen-oxygen fuel cell and is connected in parallel with the lithium battery to supply energy to the load. Step 2: When the voltage of the hydrogen-oxygen fuel cell is less than or equal to the voltage of the lithium battery, the voltage control circuit conducts, MOSEFT switch tube Q1 is turned off, and Q2 and Q3 conduct. At this time, the system operates in the direct output mode of the hydrogen-oxygen fuel cell and is connected in parallel with the lithium battery to supply energy to the load. Step 3: When the system runs for a period of time and the voltage of the hydrogen-oxygen fuel cell drops to a set level, the voltage control circuit conducts, MOSEFT switch tube Q3 is turned off, Q2 conducts, and Q1 conducts and turns off at a high frequency. At this time, the system operates in the boost output mode of the hydrogen-oxygen fuel cell and is connected in parallel with the lithium battery to supply energy to the load. Step 4: When the lithium battery needs to be charged due to insufficient power, MOSEFT switch tube Q2 is turned off at this time, and the hydrogen-oxygen fuel cell charges the lithium battery through diode D2. 2) Energy feeding scheme: When recovering braking energy, the voltage control circuit is turned off, MOSEFT switch tubes Q2 and Q3 are turned off, and the braking energy is absorbed by the lithium battery through diode D2.

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