CN117913771A - Energy management control strategy of multi-electric aircraft power system based on DC-DC FC bidirectional converter - Google Patents
Energy management control strategy of multi-electric aircraft power system based on DC-DC FC bidirectional converter Download PDFInfo
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Abstract
The invention belongs to the technical field of power electronics, and particularly relates to an energy management control strategy of a multi-electric aircraft power system based on a Flying Capacitor (FC) DC-DC bidirectional converter, and a sagging control system is provided for the provided model predictive control strategy. Because the voltage of the direct current bus of the multi-motor aircraft system is 270V, the traditional two-level buck-boost bidirectional converter can cause the voltage ripple to be too large to influence the energy conversion efficiency and stability of the system, therefore, the three-level DC-DC FC bidirectional converter is adopted to complete the regulation of the voltage of the direct current bus, and when the traditional closed-loop control, such as PID control, is applied to a three-level bidirectional DC-DC FC converter device, the system is difficult to track the change of the system quickly and accurately when the system parameters change, and the system has larger impact. The present invention thus employs a model predictive control algorithm because it has a better dynamic response than a linear controller. Meanwhile, considering the health of the battery, the state of charge (state ofcharge, soC) of the battery is also taken into the control variable, so that the SoC of the battery is ensured to be in a safe interval, and the service life of the battery is prolonged.
Description
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to an energy management control strategy of a multi-electric aircraft power system based on a DC-DC FC bidirectional converter, and a sagging control system is provided aiming at the provided model predictive control strategy.
Background
With the development of multiple electric aircraft (More ELECTRIC AIRCRAFT, MEA) technology, a large number of electric loads are integrated in an MEA electric power system, resulting in an increase in grid capacity and complexity. Accordingly, advanced power network architecture is needed to ensure high reliability, stability and efficiency of the MEA, as well as light weight. Integration and development of micro-grid MG in MEA systems is one of the challenges to be solved, since direct current MG is not subject to problems of harmonics, synchronization, reactive power, etc. compared to alternating current/direct current MG. Therefore, the use of direct current MG in the MEA has been a trend.
However, since the dc bus voltage of the multi-electric aircraft system is 270V, the voltage ripple is too large due to the adoption of the conventional two-level buck-boost bidirectional converter, which affects the energy conversion efficiency and stability of the system. Therefore, the three-level DC-DC FC bidirectional converter is adopted to complete the regulation of the DC bus voltage, and when the traditional closed-loop control, such as PID control, is applied to the three-level bidirectional DC-DC FC converter device, the system is difficult to quickly and accurately track the change of the system when the system parameters change, and the system has large impact. Thus, the model predictive control algorithm is employed herein because it has a better dynamic response than a linear controller. Meanwhile, the SoC of the battery is also included in the control variable in consideration of the health of the battery, so that the SoC of the battery is ensured to be within a safe interval, and the service life of the battery is prolonged.
Accordingly, an adaptive energy management control strategy for battery SoC-based EMA systems is presented herein. When all batteries have a high SoC, the dc bus voltage increases. An adaptive power control strategy designed for photovoltaic generators would seamlessly adjust their power output based on the dc bus voltage, leaving a Maximum Power Point Tracking (MPPT) mode. Thus, the battery can avoid overcharge. If the voltage of the direct current bus is reduced, the photovoltaic generator seamlessly returns to the MPPT mode to provide power support; by adjusting the proposed control strategy, the DC bus voltage and the SoC of the battery can be maintained within a safe operating range, and the reliability of the system can be significantly enhanced.
Disclosure of Invention
In view of the problems existing in the background art, the invention aims to provide an energy management control strategy of a multi-electric aircraft power system based on a DC-DC FC bidirectional converter. The specific implementation method of the method is as follows: sampling a battery charge state SoC, a battery voltage V b, a PV module voltage V pv, a dc bus voltage V dc, an FC voltage V fc, a battery current i b, a load current i load and a photovoltaic current i pv through a sampling circuit, sending the battery charge state SoC, the battery voltage V b, the PV module voltage V pv, the dc bus voltage V dc, the FC voltage V fc, the battery current i b, the load current i load and the photovoltaic current i pv into a control module, comparing the battery voltage and the reference voltage at the current moment of a system, the dc bus voltage at the current moment, the DC bus voltage at the PV module voltage and the DC bus voltage and the FC voltage at the steady state through calculation of the control module, judging the working state of the system at the moment and generating the duty ratio of a corresponding switching power supply, and finally generating proper switching signals through a PS-PWM modulator to control each power switch of two converters to quickly enter the steady state, so that the DC bus voltage V dc, the FC voltage V fc and P pv pair dynamic reference values are realizedAnd/>Is fast to follow.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
1. An energy management control strategy (ENERGY MANAGEMENT control strategies, EMS) for a multi-electric aircraft power system based on a DC-DC FC bi-directional converter, characterized by the steps of:
step 1: the topology of the power network architecture and its circuits is determined according to the requirements of the power system of the multi-power aircraft (More ELECTRIC AIRCRAFT, MEA), and the control objectives and operation modes of the power network architecture are determined.
Step 2: according to the proposed multi-electric aircraft network architecture, a control strategy and a target of a DC-DC FC bidirectional converter in an energy storage module are determined. Meanwhile, in order to prolong the service life of the battery and strengthen the safe reliability of the system operation, the direct current bus voltage and the SoC of the energy storage module are designed to be maintained in a safe operation range.
Step 3: according to the proposed multi-electric aircraft network architecture, the control strategy and the target of the Boost converter in the clean energy module are determined. In view of extending the life of the battery, the clean energy module is designed as an adaptive power control strategy that seamlessly adjusts its power output according to the battery SoC.
Finally, the energy storage module and the clean energy module are combined together, so that the power control required by the multi-electric aircraft power system is completed, the power balance in the hybrid power system is maintained seamlessly, and the pressure of the battery is relieved.
2. The energy management control strategy of a multi-electric aircraft power system based on a DC-DC FC bi-directional converter of claim 1, wherein the EMA power network architecture of step 1 is a direct current micro-grid system integrating an energy storage module and a clean energy module. The energy storage module is a storage battery, and the clean energy module is a Photovoltaic (PV) module.
The dc bus voltage of the hybrid system is divided into three operating sections, namely a High Voltage (HV) section, a normal section (NV) and a Low Voltage (LV) section. These parts are respectively associated with units responsible for regulating the dc bus voltage at any time.
3) High pressure section: when (when)When the power system is operating in the high voltage section, which indicates that the dc bus voltage is primarily regulated by the battery, which is in a high state of charge, the photovoltaic module should operate in a Power Limiting (PL) mode.
4) Normal section: when (when)When the power system is operating in the normal section. The photovoltaic modules are operated in MPPT mode to ensure that all available photovoltaic power is fully utilized.
3) Low pressure section: when (when)When the power supply system is operating in the low voltage section. After the photovoltaic module reaches its power generation limit, the energy storage battery module provides the system with surplus power.
Thus, the control targets and the operation modes of the hybrid system are as follows:
5) Photovoltaic module: the primary goal of photovoltaic modules is to provide as much photovoltaic power as is available to meet load demands and battery charging power requirements. When the dc bus voltage is in the high voltage section, which means that the battery is in a high state of charge, the photovoltaic module should limit its output power according to its capacity. Meanwhile, the photovoltaic module should also operate in MPPT mode in time to provide power support for the power system and improve the utilization rate of renewable energy sources. Thus, with the proposed adaptive power control strategy, the photovoltaic module should be able to smoothly switch between MPPT mode and PL mode, thereby improving the power quality.
6) A battery module: the main control objective of the battery is to regulate the dc bus voltage and to meet the load demand and SoC level through coordination with the photovoltaic modules. When the photovoltaic module reaches the transmitting electrode limit, the battery supplies power to the power system. This goal aims to save stored energy to meet the load demand during the photovoltaic power generation valley. Meanwhile, in order to prevent the battery from being overcharged, the battery should be discharged preferentially at the high SoC stage of the battery to avoid charging.
4. The energy management control strategy for a DC-DC FC bi-directional converter-based multi-electric aircraft power system of claim 1, wherein the three-level flying capacitor bi-directional converter of step 2 is implemented by a model predictive control strategy. It can be seen that when the power switches S 3 and S 4 are modulated and the power switches S 1 and S 2 are off, the converter operates in boost mode. The circuit analysis of fig. 1 is performed to obtain a continuous time model of the inductor. The state variable inductor current i L and the flying capacitor voltage v fc of the converter are as follows in the boost mode:
similarly, when power switches S 1 and S 2 are modulated and power switches S 3 and S 4 are turned off, the converter operates in buck mode. For the circuit analysis of fig. 1, the continuous time model of the converter in buck mode is as follows:
Where S 1、S2、S3 and S 4 are the binary switching pulses of the individual power switches. v b and v dc refer to the battery voltage and dc bus voltage, respectively. Comparing the above equations, the simplified continuous-time model equation of the converter can be written as:
Where A and B are the binary pulses of the power switch (A, B ε {0,1 }) and can be written as:
Discretizing this state variable equation using forward Euler method, inductor current for the (k+1) th time step of the converter And flying capacitor voltage/>The predictions were as follows:
where T s is the controller sampling time period, term And/>The battery, the flying capacitor, and the dc bus voltage for the kth time step, respectively.
Inductor current and flying capacitor voltage are control targets in the model. Therefore, an algorithm is formulated to identify the optimal switching pulse of the power switch that achieves the control objective. This is done by formulating a quadratic cost function as follows:
Wherein the method comprises the steps of And/>The reference inductor current and the flying capacitor voltage at time k+1, respectively. The term λ is defined as a weight factor that provides a weight ratio between the inductor current and the flying capacitor voltage when tracking the reference value.
The reference inductor current is derived by applying a power balance on the model (assuming zero converter loss). The inductor current for the kth time step can be written as:
The reference flying capacitor voltage is set to half the reference dc bus voltage and remains fixed throughout operation. The reference flying capacitor voltage is as follows:
4. A converter modulation strategy according to claim 3, wherein the control objective of the DC-DC FC bi-directional converter is to regulate not only the DC bus voltage and the flying capacitor voltage, but also the SoC of the battery in order to extend battery life. Accordingly, the dc bus reference voltage is adjusted herein to account for three states according to different SoC levels, with SoC l and SoC u representing lower and higher SoC levels.
State I: the battery is operated in a high charge state, soCu < SoC <100%, and the battery is discharged preferentially, avoiding charging.
State II: the battery works in a normal state, soCl < SoC < SoCu, and the battery can be safely charged or discharged.
State III: the battery works in a low charge state, soC is 0< SoCl, and the battery should avoid discharging and charge preferentially. Thus, the battery charge and discharge operating conditions depend on the actual SoC level, and the control principle of the battery SoC can be expressed as:
wherein, Is to consider the dynamic reference DC bus voltage of the battery SoC, the range of which is in the normal rangeAn inner part; v dc and δv are the dc bus reference voltage and the adjustable voltage value generated by the SoC recovery program, respectively.
R l and r u are the rise coefficients during the high and low states of the battery, respectively, which can be determined as:
Wherein the method comprises the steps of Is the maximum safe variable range of the DC bus voltage.
At this time, considering an extreme situation, when the battery SoC is in a 100% state, there are:
when the battery SoC is in the 0% state, there are:
It can be seen that even in extreme conditions, the dc bus voltage is still regulated to within the safe range.
The inductor current for the kth time step can be written as:
5. The energy management control strategy of a multi-electric aircraft power system based on a DC-DC FC bi-directional converter according to claim 1, characterized in that the adaptive power control of the proposed photovoltaic module in step 3 is implemented by means of dual loop control of PID. The inner loop is to achieve accurate power tracking. The output voltage and output current of each photovoltaic cell are measured and a modified P & O algorithm is used to track the reference power. The voltage v pv of the PV module can be accurately tracked to a reference value by a proportional-integral (PI) controller G v(s) The outer loop generates the power reference of the inner loop mainly through the adaptive power controller, and the outer loop control scheme can be expressed as follows:
Wherein the method comprises the steps of Is a power reference value, generated by an adaptive power controller; /(I)An output power value which is a maximum power point; v dc is the actual output voltage, equal to the dc bus voltage; m pv is the sag factor of the photovoltaic unit, set as follows:
6. The patent provides an energy management control strategy of a multi-electric aircraft power system based on a DC-DC FC bidirectional converter, which is characterized by comprising a modulation strategy of the DC-DC FC bidirectional converter and a Boost converter in a DC micro-grid system. The DC-DC FC bidirectional converter in the energy storage module generates duty ratios d 1 and d 2 through model predictive control, and the range of the duty ratios d 1 and d 2 is 0<d 1<1、0<d2 <1; the grid electrode of each switching tube of the primary side and the secondary side is connected with the output end of the driving circuit, the two switching tubes of the same converter are alternately conducted, and one end of the inductor L is connected with one section of the IGBT and the output capacitor. The grid electrode of each switching tube is connected with the output end of the driving circuit, and two switching tubes of the same bridge arm cannot be conducted simultaneously. The boost converter of the PV module generates a duty cycle d 3 with a controlled voltage, which ranges from 0<d 3 <1.
The sample/hold circuit is used to detect in real time the cell voltage V b, the PV module voltage V pv, the dc bus voltage V dc, the FC voltage V fc, and the cell current i b, the PV module current i pv. And the sampled value is transmitted to a control module, and the control module is used for adjusting the dc bus voltage v dc, the FC voltage v fc, the power P pv of the battery SoC and the PV module to the reference value through calculation and finally through each switching power supply of the two converters.
Drawings
Fig. 1 is a block diagram of the circuit structure of an MEA power network architecture.
Fig. 2 is a flowchart of a control algorithm of the energy storage battery module in the micro grid.
Fig. 3 is a control strategy block diagram of photovoltaic modules in a microgrid.
Fig. 4 is a flowchart of an MPPT-PL control algorithm proposed by the present invention.
Fig. 5 is a simulated waveform that reaches a steady state time domain in a normal state of the battery.
Fig. 6 is a simulated waveform for achieving a steady state time domain at a low battery state of charge.
Fig. 7 is a simulated waveform for achieving a steady state time domain at a high battery state of charge.
Detailed Description
The present invention will be described in further detail with reference to the embodiments and the accompanying drawings, for the purpose of making the objects, technical solutions and advantages of the present invention more apparent.
Fig. 1 is a circuit block diagram of an MEA power network architecture, which is a direct current micro-grid combining two converters, including a three-level DC-DC FC bi-directional converter, a boost converter, a battery module, a Photovoltaic (PV) module, a load module, and a control circuit, where the three-level DC-DC FC bi-directional converter includes a DC bus voltage v dc, an FC voltage v fc load current i load, 4 switching tubes S 1、S2、S3 and S 4, a direct current bus capacitor C dc, a flying capacitor C fc, and an inductance L b, and the control circuit includes a sample/hold circuit, and a control module. The sample/hold circuit is used for detecting the battery voltage v b, the battery SoC, the DC bus voltage v dc, the FC voltage v fc and the battery current i b in real time, transmitting sampled values to the control module, and controlling the switches of the level DC-DC FC bidirectional converter through the control module.
The bi-directional boost converter includes an output voltage v dc, a PV current i pv, an output capacitance C pv, an inductance L p, and 1 switching tube and diode. The sample/hold circuit is used for detecting the PV voltage v pv, the dc bus voltage v dc and the PV current i pv in real time, transmitting sampled values to the control module, and controlling each power switch of the bidirectional buck-boost converter through the control module.
FIG. 2 is a flow chart of a model predictive control algorithm for energy storage battery modules in a microgrid, which predicts for all binary switching pulse combinations of A and BAnd/>Finally, the best states A (i opt) and B (i opt) are found, thereby minimizing the quadratic cost function over a sample period. Once the optimum state is calculated, the operating mode of the converter, step-up/step-down, is determined based on the sign of the reference inductor current. Furthermore, the respective switching pulses of the individual power switches S 1、S2、S3 and S 4 are calculated as a function of the converter operating mode.
Fig. 3 is a control block diagram of a photovoltaic module in a microgrid. A control block diagram based on droop control as proposed on the equivalent block diagram of boost converter double loop control. Wherein the outer loop mainly generates the power reference of the inner loop through the self-adaptive power controller, the inner loop is a PV voltage loop, and the reference value is accurately tracked through a Proportional Integral (PI) controller G v(s)
Fig. 4 is a flowchart of an improved P & O MPPT-PL control algorithm according to the present invention. Wherein i pv and v pv are the actual output current and voltage of the photovoltaic unit,For the reference power generated by the outer loop, δ is the disturbance step. The improved method has a simpler control algorithm than the existing method and does not require switching between the MPPT mode and the PL mode. Thus, the negative influence on the system can be reduced, and the power quality can be improved.
Fig. 5 is a simulation waveform for achieving a steady state time domain in a normal state of the battery SoC, and parameters of the system are shown in table one. At this time, the battery SoC L<SoC<SoCu is in a normal state, and the dc bus reference voltage is 270V, which is the nominal dc bus voltage. As can be seen from fig. 5 (a), when the PV module is operating in MPPT mode, all power is supplied to the load as much as possible, the battery module assists the PV module to supply power to the load, and at t=0.2 s, the power supplied by the PV module is sufficient to cover the load power, and the PV module supplements the surplus power to the energy storage battery module. While under the influence of illumination, at t=0.2 s, the power provided by the PV module is insufficient to cover the load power, at which time the cells begin to discharge to provide power to the load, and the EMA system reaches power balance. Meanwhile, as can be seen from fig. 5 (b), the dc bus voltage and the flying capacitor voltage accurately track their voltage reference values.
Fig. 6 is a simulated waveform for achieving a steady state time domain at a low battery state of charge. It can be seen that at this point the battery SoC < SoC L, the battery should be charged with priority to avoid discharging. At this time, the PV module works in MPPT mode, and provides all power to the load as much as possible, so as to maintain the power of the load module in a stable available interval. Meanwhile, in order to reduce the pressure of the battery, the reference voltage value of the direct current bus and the power required by the load should be properly reduced. As can be seen from fig. 6 (a), at t=0.2 s, the power provided by the PV module is sufficient to cover the load power, the PV module charges the battery, and the battery SoC begins to rise. As can be seen from fig. 6 (b), the dc bus reference voltage value drops to 265V, the flying capacitor reference voltage value drops to 132.5V, and both the dc bus voltage and the flying capacitor voltage accurately track their voltage reference values.
Fig. 7 is a simulated waveform for achieving a steady state time domain at a high battery state of charge. At this time, the battery SoC > SoC u, the battery should be discharged with priority to avoid charging. At this time, the PV module is operated in PL mode, so that the battery can provide the power required by the load as much as possible, and the power of the load module is maintained in a stable available interval. At the same time, in order to facilitate the amount of battery discharge, the dc bus reference voltage value and the power required by the load should be properly raised. As can be seen from fig. 7 (a), the dc bus voltage value and the load power are both properly improved, the PV module operates in PL mode, the battery is continuously discharged, and the SoC is continuously reduced. As can be seen from fig. 7 (b), the dc bus reference voltage value drops to 280V, the flying capacitor reference voltage value drops to 140V, and both the dc bus voltage and the flying capacitor voltage accurately track their voltage reference values.
While the invention has been described in terms of specific embodiments, any feature disclosed in this specification may be replaced by alternative features serving the equivalent or similar purpose, unless expressly stated otherwise; all of the features disclosed, or all of the steps in a method or process, except for mutually exclusive features and/or steps, may be combined in any manner.
Table one: system parameter map
Claims (6)
1. An energy management control strategy (ENERGY MANAGEMENT control strategies, EMS) for a multi-electric aircraft power system based on a DC-DC FC bi-directional converter, characterized by the steps of:
step 1: the topology of the power network architecture and its circuits is determined according to the requirements of the power system of the multi-power aircraft (More ELECTRIC AIRCRAFT, MEA), and the control objectives and operation modes of the power network architecture are determined.
Step 2: according to the proposed multi-electric aircraft network architecture, a control strategy and a target of a DC-DC FC bidirectional converter in an energy storage module are determined. Meanwhile, in order to prolong the service life of the battery and strengthen the safe reliability of the system operation, the direct current bus voltage and the SoC of the energy storage module are designed to be maintained in a safe operation range.
Step 3: according to the proposed multi-electric aircraft network architecture, the control strategy and the target of the Boost converter in the clean energy module are determined. In view of extending the life of the battery, the clean energy module is designed as an adaptive power control strategy that seamlessly adjusts its power output according to the battery SoC.
Finally, the energy storage module and the clean energy module are combined together, so that the power control required by the multi-electric aircraft power system is completed, the power balance in the hybrid power system is maintained seamlessly, and the pressure of the battery is relieved.
2. The energy management control strategy of a multi-electric aircraft power system based on a DC-DC FC bi-directional converter of claim 1, wherein the EMA power network architecture of step 1 is a direct current micro-grid system integrating an energy storage module and a clean energy module. The energy storage module is a storage battery, and the clean energy module is a Photovoltaic (PV) module.
The dc bus voltage of the hybrid system is divided into three operating sections, namely a High Voltage (HV) section, a normal section (NV) and a Low Voltage (LV) section. These parts are respectively associated with units responsible for regulating the dc bus voltage at any time.
1) High pressure section: when (when)When the power system is operating in the high voltage section, which indicates that the dc bus voltage is primarily regulated by the battery, which is in a high state of charge, the photovoltaic module should operate in a Power Limiting (PL) mode.
2) Normal section: when (when)When the power system is operating in the normal section. The photovoltaic modules are operated in MPPT mode to ensure that all available photovoltaic power is fully utilized.
3) Low pressure section: when (when)When the power supply system is operating in the low voltage section. After the photovoltaic module reaches its power generation limit, the energy storage battery module provides the system with surplus power.
Thus, the control targets and the operation modes of the hybrid system are as follows:
1) Photovoltaic module: the primary goal of photovoltaic modules is to provide as much photovoltaic power as is available to meet load demands and battery charging power requirements. When the dc bus voltage is in the high voltage section, which means that the battery is in a high state of charge, the photovoltaic module should limit its output power according to its capacity. Meanwhile, the photovoltaic module should also operate in MPPT mode in time to provide power support for the power system and improve the utilization rate of renewable energy sources. Thus, with the proposed adaptive power control strategy, the photovoltaic module should be able to smoothly switch between MPPT mode and PL mode, thereby improving the power quality.
2) A battery module: the main control objective of the battery is to regulate the dc bus voltage and to meet the load demand and SoC level through coordination with the photovoltaic modules. When the photovoltaic module reaches the transmitting electrode limit, the battery supplies power to the power system. This goal aims to save stored energy to meet the load demand during the photovoltaic power generation valley. Meanwhile, in order to prevent the battery from being overcharged, the battery should be discharged preferentially at the high SoC stage of the battery to avoid charging.
3. The energy management control strategy for a DC-DC FC bi-directional converter-based multi-electric aircraft power system of claim 1, wherein the three-level flying capacitor bi-directional converter of step 2 is implemented by a model predictive control strategy. It can be seen that when the power switches S 3 and S 4 are modulated and the power switches S 1 and S 2 are off, the converter operates in boost mode. The circuit analysis of fig. 1 is performed to obtain a continuous time model of the inductor. The state variable inductor current i L and the flying capacitor voltage v fc of the converter are as follows in the boost mode:
similarly, when power switches S 1 and S 2 are modulated and power switches S 3 and S 4 are turned off, the converter operates in buck mode. For the circuit analysis of fig. 1, the continuous time model of the converter in buck mode is as follows:
Where S 1、S2、S3 and S 4 are the binary switching pulses of the individual power switches. v b and v dc refer to the battery voltage and dc bus voltage, respectively. Comparing the above equations, the simplified continuous-time model equation of the converter can be written as:
where A and B are the binary pulses of the power switch (A, B ε {0,1 }) and can be written as:
Discretizing this state variable equation using forward Euler method, inductor current for the (k+1) th time step of the converter And flying capacitor voltage/>The predictions were as follows:
Where T s is the controller sampling time period, term And/>The battery, the flying capacitor, and the dc bus voltage for the kth time step, respectively.
Inductor current and flying capacitor voltage are control targets in the model. Therefore, an algorithm is formulated to identify the optimal switching pulse of the power switch that achieves the control objective. This is done by formulating a quadratic cost function as follows:
Wherein the method comprises the steps of And/>The reference inductor current and the flying capacitor voltage at time k+1, respectively. The term λ is defined as a weight factor that provides a weight ratio between the inductor current and the flying capacitor voltage when tracking the reference value.
The reference inductor current is derived by applying a power balance on the model (assuming zero converter loss). The inductor current for the kth time step can be written as:
The reference flying capacitor voltage is set to half the reference dc bus voltage and remains fixed throughout operation. The reference flying capacitor voltage is as follows:
4. A converter modulation strategy according to claim 3, wherein the control objective of the DC-DC FC bi-directional converter is to regulate not only the DC bus voltage and the flying capacitor voltage, but also the SoC of the battery in order to extend battery life. Accordingly, the dc bus reference voltage is adjusted herein to account for three states according to different SoC levels, with SoC l and SoC u representing lower and higher SoC levels.
State I: the battery works in a high charge state, soCu is less than SoC and less than 100%, and the battery is discharged preferentially, so that charging is avoided.
State II: the battery works in a normal state, soCl is smaller than SoC and smaller than SoCu, and the battery can be safely charged or discharged.
State III: the battery works in a low charge state, soC is more than 0 and less than SoCl, and the battery should avoid discharging and charge preferentially. Thus, the battery charge and discharge operating conditions depend on the actual SoC level, and the control principle of the battery SoC can be expressed as:
wherein, Is a dynamic reference DC bus voltage considering the battery SoC, and the range is in the normal range/>An inner part; v dc and δv are the dc bus reference voltage and the adjustable voltage value generated by the SoC recovery program, respectively.
R l and r u are the rise coefficients during the high and low states of the battery, respectively, which can be determined as:
Wherein the method comprises the steps of Is the maximum safe variable range of the DC bus voltage.
At this time, considering an extreme situation, when the battery SoC is in a 100% state, there are:
when the battery SoC is in the 0% state, there are:
It can be seen that even in extreme conditions, the dc bus voltage is still regulated to within the safe range.
The inductor current for the kth time step can be written as:
5. The energy management control strategy of a multi-electric aircraft power system based on a DC-DC FC bi-directional converter according to claim 1, characterized in that the adaptive power control of the proposed photovoltaic module in step 3 is implemented by means of dual loop control of PID. The inner loop is to achieve accurate power tracking. The output voltage and output current of each photovoltaic cell are measured and a modified P & O algorithm is used to track the reference power. The voltage v pv of the PV module can be accurately tracked to a reference value by a proportional-integral (PI) controller G v(s) The outer loop generates the power reference of the inner loop mainly through the adaptive power controller, and the outer loop control scheme can be expressed as follows:
Wherein the method comprises the steps of Is a power reference value, generated by an adaptive power controller; /(I)An output power value which is a maximum power point; v dc is the actual output voltage, equal to the dc bus voltage; m pv is the sag factor of the photovoltaic unit, set as follows:
6. The patent provides an energy management control strategy of a multi-electric aircraft power system based on a DC-DC FC bidirectional converter, which is characterized by comprising a modulation strategy of the DC-DC FC bidirectional converter and a Boost converter in a DC micro-grid system. The DC-DC FC bidirectional converter in the energy storage module generates duty ratios d 1 and d 2 through model predictive control, and the range of the duty ratios d 1 and d 2 is more than 0 and less than 1＜1、0＜d2 and less than 1; the grid electrode of each switching tube of the primary side and the secondary side is connected with the output end of the driving circuit, the two switching tubes of the same converter are alternately conducted, and one end of the inductor L is connected with one section of the IGBT and the output capacitor. The grid electrode of each switching tube is connected with the output end of the driving circuit, and two switching tubes of the same bridge arm cannot be conducted simultaneously. The boost converter of the PV module generates a duty cycle d 3 with a controlled voltage, which ranges from 0 < d 3 < 1.
The sample/hold circuit is used to detect in real time the cell voltage V b, the PV module voltage V pv, the dc bus voltage V dc, the FC voltage V fc, and the cell current i b, the PV module current i pv. And the sampled value is transmitted to a control module, and the control module is used for adjusting the dc bus voltage v dc, the FC voltage v fc, the power P pv of the battery SoC and the PV module to the reference value through calculation and finally through each switching power supply of the two converters.
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