Electric vehicle hybrid energy storage system based on wide-gain DC / DC converter

Abstract

The invention discloses an electric vehicle hybrid energy storage system based on a wide-gain DC / DC converter, and belongs to the technical field of power electronics. The hybrid energy storage system comprises a thin-film capacitor FC, a power battery module, a wide-gain DC / DC converter module, a DC / DC converter module, an inverter module and a driving motor. The wide-gain DC / DC converter module adopts a novel wide-gain DC / DC converter based on an intermediate capacitor, and is composed of an improved Buck / Boost module 1, an improved Buck-Boost module 2, an intermediate capacitor C and a high-voltage side DC bus capacitor CH. Through mutual cooperation of the modules, the voltage gain of the wide-gain DC / DC converter module is widened, and the braking energy utilization efficiency of the thin-film capacitor is improved. According to the wide-gain DC / DC converter module provided by the invention, the number of passive devices is remarkably reduced, the cost of the converter is reduced, and the energy conversion efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of power electronics, and in particular to an electric vehicle hybrid energy storage system based on a wide-gain DC / DC converter. Background Art

[0002] Electric vehicles have many advantages such as low noise, simple structure, easy maintenance, and high energy conversion efficiency, and have become an emerging force in the rapid development of the automobile market. However, the long charging time, short life, and poor endurance of power battery modules have restricted the further promotion of electric vehicles. In addition, the start, stop, acceleration, and deceleration of electric vehicles will cause high-frequency power fluctuations in the power battery module. Not only will the energy consumption of electric vehicles increase, but the cruising range will also decrease significantly. Frequent charging and discharging with large currents will also reduce the life and reliability of the battery.

[0003] The hybrid energy storage system combines the advantages of high energy density of power battery modules and high power density of supercapacitors SC, which can reduce damage to battery packs and improve the transient performance of electric vehicles. It is an effective measure to solve the above problems before the fundamental breakthrough of power battery module technology. However, the voltage of supercapacitor monomers is low, and multiple stages must be connected in series to match the high-voltage DC bus of electric vehicles, which increases the equivalent series resistance and reduces the efficiency of the hybrid energy storage system. In addition, the maximum operating temperature of supercapacitors is only 70°C, which is not suitable for electric vehicles with harsh working environments. The rated voltage of film capacitors FC can reach 1200V and the rated temperature is 120°C, which effectively avoids the shortcomings of supercapacitors used in hybrid energy storage systems. In addition, the power density of film capacitors FC is 50-100 times that of supercapacitors, which can significantly improve the power performance of electric vehicles. However, due to the constraints of cost and volume, the capacitance of film capacitors FC used in hybrid energy storage systems is only a few hundredths of that of supercapacitors. In order to effectively utilize the braking energy of electric vehicles, the characteristic of film capacitors that they can withstand large pulsating currents can be fully utilized, and the energy density and power density of film capacitors can be increased by expanding the working voltage range of film capacitors. Therefore, the wide-gain DC / DC converter module connecting the film capacitor FC and the high-voltage side DC bus becomes a key component of the thin-film hybrid energy storage system.

[0004] Researchers have proposed a variety of wide-gain DC / DC converter module structures. The four-switch Buck / Boost bidirectional converter has a simple structure and is easy to control, but its voltage gain range is limited and cannot meet the working requirements of the film capacitor hybrid energy storage system. Although the voltage gain of the converter can be improved by introducing a coupled inductor, the inherent leakage inductance problem not only increases the turn-off peak voltage of the power device, but also reduces the working efficiency of the electric vehicle hybrid energy storage system. The Z-source and quasi-Z-source structures can not only obtain high voltage gain, but also improve the reliability of the converter, but the voltage stress of the power device of this type of wide-gain DC / DC converter module is high. The multi-level DC / DC converter module can solve the problem of high voltage stress of power devices, but it has the disadvantages of a significant increase in the number of power devices and complex control strategies. The switch capacitor module has a simple structure and is easy to control. The DC / DC converter module built on it can easily achieve voltage gain expansion. However, the low-voltage side and high-voltage side ground of the converter need to be connected through a power switch, and the periodic level changes caused by the on-off of the power device will cause serious electromagnetic interference. Although bidirectional DC / DC based on switched inductor structure can solve the problem of common power switch for low-voltage side and high-voltage side, the inductor parameter accuracy requirements in this structure are strict, which can easily cause large current spikes, increase the control difficulty and reduce the reliability of the converter.

[0005] The above analysis shows that although the existing DC / DC converter modules can achieve high gain requirements, there are still various problems in using them in the film capacitor hybrid energy storage system of electric vehicles. In order to efficiently utilize the braking energy of electric vehicles and further improve the mileage and driving experience of electric vehicles, it is urgent to develop a bidirectional DC / DC converter with simple structure, high efficiency, high power density and wide voltage gain that meets the requirements of the film capacitor hybrid energy storage system. Summary of the invention

[0006] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art. The present invention provides an electric vehicle hybrid energy storage system based on a wide-gain DC / DC converter, which adopts a new wide-gain DC / DC converter based on an intermediate capacitor. By improving the Buck / Boost module 1, the Buck-Boost module 2 and the intermediate capacitor C to simplify the structure of the wide-gain DC / DC converter module, the step-up and step-down gain range is widened, and the efficiency and power density of the converter are improved.

[0007] An electric vehicle hybrid energy storage system based on a wide-gain DC / DC converter comprises a film capacitor FC, a power battery module, a wide-gain DC / DC converter module, a DC / DC converter module, an inverter module and a drive motor;

[0008] The wide-gain DC / DC converter module adopts a novel wide-gain DC / DC converter based on an intermediate capacitor, and the novel wide-gain DC / DC converter based on an intermediate capacitor is composed of an improved Buck / Boost module 1, an improved Buck-Boost module 2, an intermediate capacitor C and a high-voltage side DC bus capacitor C. H Composition: the input side of the wide gain DC / DC converter module is the low voltage side of the wide gain DC / DC converter module, the output side of the wide gain DC / DC converter module is the high voltage side of the wide gain DC / DC converter module, and the low voltage side and the high voltage side are absolutely grounded.

[0009] Furthermore, the power battery module and the film capacitor FC are respectively used as the input of the DC / DC converter module and the wide gain DC / DC converter module, and are connected in parallel to the high voltage side DC bus capacitor C after the output of the DC / DC converter module and the wide gain DC / DC converter module. H The DC bus of the wide gain DC / DC converter module is connected in parallel to the DC bus capacitor C on the high voltage side of the wide gain DC / DC converter module. H When the electric vehicle is working in a deceleration or braking state, the wide gain DC / DC converter module reduces the braking energy on the high-voltage DC bus side and stores it in the film capacitor FC; when the electric vehicle is working in a climbing or acceleration state, the wide gain DC / DC converter module boosts the energy of the film capacitor FC and sends it to the high-voltage side DC bus capacitor C H , connected in parallel with the power battery module to power the drive motor.

[0010] Furthermore, the improved Buck / Boost module 1 is composed of a first inductor L1, a first switch tube S1 and a second switch tube S2; one end of the first inductor L1 and the drain of the third switch tube S3 are simultaneously connected to the positive electrode of the film capacitor FC; the other end of the first inductor L1 is connected to the drain of the first switch tube S1 and the source of the second switch tube S2; the drain of the second switch tube S2 is connected to the high-voltage side DC bus capacitor C H The positive pole of the DC bus is connected.

[0011] Furthermore, the improved Buck-Boost module 2 is composed of a second inductor L2, a third switch tube S3 and a fourth switch tube S4. One end of the first inductor L1 and the drain of the third switch tube S3 are simultaneously connected to the positive electrode of the film capacitor FC; one end of the second inductor L2, the positive electrode of the intermediate capacitor C, and the high-voltage side DC bus capacitor C HThe source of the third switch tube S3 is connected to the drain of the fourth switch tube S4 and the other end of the second inductor L2; the source of the fourth switch tube S4 is connected to the source of the first switch tube S1 and the negative electrode of the intermediate capacitor C.

[0012] Furthermore, when the electric vehicle brakes or decelerates, the vehicle state control signal K output is -1, and the braking energy generated by the drive motor makes the DC bus capacitor voltage U H Increase, detect the film capacitor voltage U FC and the state of charge SOC of the power battery module; when the film capacitor voltage U FC Lower than the set upper limit U * FC1 When the wide gain DC / DC converter module is controlled to work in the buck mode, the DC bus capacitor voltage U H Release energy to the film capacitor FC until the film capacitor voltage U FC Higher than the set upper limit U * FC1 ; When the film capacitor voltage U FC Exceeding the set upper limit value U * FC1 When the wide gain DC / DC converter module is controlled to achieve the DC bus capacitor voltage U H , stop releasing energy to the film capacitor FC, and instead release energy to the power battery module until the state of charge SOC of the power battery module reaches the set value SOC of the power battery module * S ; In the process of controlling the wide gain DC / DC converter module to work in the buck mode, the wide gain DC / DC converter module controls the release of energy according to the set value of the high-voltage side DC bus voltage to avoid the DC bus undervoltage operation; when the state of charge SOC of the power battery module and the film capacitor voltage U FC When both reach the set value, the braking energy is consumed by the energy consumption resistor to avoid the DC bus voltage U H Too high may damage the converter.

[0013] Furthermore, when the electric vehicle is climbing or accelerating, the vehicle state control signal K is output as 1, and the DC bus capacitor voltage U H Drop, detect the film capacitor voltage U FC The state of charge SOC of the power battery module; when the film capacitor voltage U FC Higher than the minimum allowable operating voltage U * FC2 When the wide gain DC / DC converter module is controlled to work in the boost mode, the wide gain DC / DC converter module realizes the film capacitor FC combined with the power battery module to the high voltage side DC bus capacitor C HRelease energy; When the wide gain DC / DC converter module is operated in the boost mode, the energy value released by the film capacitor FC should satisfy the DC bus capacitor voltage U H Stable until the film capacitor voltage U FC Lower than the minimum allowable operating voltage U * FC2 Stop; when the film capacitor voltage U FC Lower than the minimum allowable operating voltage U * FC2 When the power is turned on, the energy required by the drive motor is only provided by the power battery module.

[0014] Furthermore, the method for implementing the bidirectional control strategy of the converter is: sampling by a sensor to obtain the DC bus capacitor voltage U H , film capacitor voltage U FC And the low voltage side current i FC , to achieve the normal operation of the converter and ensure the high efficiency and stability of the hybrid energy storage system; the specific methods are as follows:

[0015] Step S1, calculating the power flow control signal K, the proposed converter switches between boost and buck modes;

[0016] Step S2: DC bus capacitor voltage U H With reference voltage U ref To control the target, the voltage controller is used to generate a reference current I ref ;

[0017] Step S3: The current controller uses the reference current i in the current loop ref To control the feedback current i FC , the result is output to the PWM generator to generate the gate signals S1~S4 of the power switch.

[0018] Furthermore, in the buck mode, the wide-gain DC / DC converter module alternately operates in state one and state two; when the wide-gain DC / DC converter module operates in state one, part of the energy on the high-voltage side is transmitted to the first inductor L1, and the remaining energy flows to the low-voltage side film capacitor FC, and the energy of the second inductor L2 in the improved Buck-Boost module 2 is completely provided by the intermediate energy storage capacitor C; when the wide-gain DC / DC converter module operates in state two, the first inductor L1 transmits energy to the intermediate capacitor C and the low-voltage side film capacitor FC respectively, and the second inductor L2 transmits energy to the low-voltage side film capacitor FC; when the wide-gain DC / DC converter module operates in state two, the voltage across the film capacitor FC is equal to the voltage across the second inductor L2, which is much smaller than the high-voltage side DC bus voltage, thereby achieving the purpose of wide-range voltage reduction.

[0019] Furthermore, in the boost mode, the wide-gain DC / DC converter module alternately operates in state three and state four; when the wide-gain DC / DC converter module operates in state three, the low-voltage side film capacitor FC and the intermediate capacitor C simultaneously transmit energy to the first inductor L1, and at the same time, the low-voltage side film capacitor FC transmits energy to the second inductor L2, and the current flowing through the second inductor L2 increases; when the wide-gain DC / DC converter module operates in state four, the second inductor L2 transmits energy to the intermediate capacitor C, and the first inductor L1 and the low-voltage side film capacitor FC simultaneously transmit energy to the high-voltage side DC bus, thereby achieving the purpose of wide-range boosting.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The wide-gain DC / DC converter module proposed in the present invention has a maximum voltage gain of 21 and a minimum voltage gain of 0.047 when the duty cycle is 0.2-0.8, which effectively broadens the operating voltage range of the film capacitor and significantly improves the power density of the wide-gain DC / DC converter module.

[0022] 2. Compared with wide-gain DC / DC converter modules with the same gain capability, the wide-gain DC / DC converter module proposed by the present invention has significantly reduced numbers of power switches and passive components, thereby reducing costs while having higher power density and lower costs.

[0023] 3. The bidirectional DC / DC conversion circuit proposed in the present invention has its input ground and output ground directly connected, which effectively avoids the electromagnetic interference problem caused by the separation of the high and low voltage sides of the existing high-gain and wide-gain DC / DC converter modules, and further improves the reliability of the circuit.

[0024] 4. The wide-gain DC / DC converter module proposed in the present invention effectively reduces the voltage stress of the intermediate capacitor and improves the DC / DC conversion reliability and working efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Attached Figure 1 It is a schematic diagram of the hybrid energy storage system for electric vehicles of the present invention.

[0026] Attached Figure 2 It is a circuit diagram of the wide gain DC / DC converter module in the present invention.

[0027] Attached Figure 3 Schematic diagram of driving signals of each power switch tube in buck mode in the present invention.

[0028] Attached Figure 4 FIG. 1 is a schematic diagram of power flow in the buck mode of the present invention.

[0029] Attached Figure 5It is a schematic diagram of power flow in state 2 of the buck mode in the present invention.

[0030] Attached Figure 6 Schematic diagram of the driving signal of each power switch tube in the boost mode of the present invention.

[0031] Attached Figure 7 It is a schematic diagram of three power flows in the boost mode of the present invention.

[0032] Attached Figure 8 It is a schematic diagram of four power flows in the boost mode of the present invention.

[0033] Attached Fig. 9 It is a schematic diagram of the bidirectional control method of the converter in the present invention. DETAILED DESCRIPTION

[0034] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings, and the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Combination Figure 1 The present invention provides an electric vehicle hybrid energy storage system based on a wide-gain DC / DC converter, characterized in that it includes a film capacitor FC, a power battery module, a wide-gain DC / DC converter module, a DC / DC converter module, an inverter module and a drive motor. The power battery module and the film capacitor FC are respectively used as the input of the DC / DC converter module and the wide-gain DC / DC converter module, and are connected in parallel to the high-voltage side DC bus capacitor C after the output of the DC / DC converter module and the wide-gain DC / DC converter module. H The DC bus then provides electrical energy to the drive motor through the inverter module.

[0036] Combination Figure 2 The wide-gain DC / DC converter module adopts a novel wide-gain DC / DC converter based on an intermediate capacitor. The novel wide-gain DC / DC converter based on an intermediate capacitor is composed of an improved Buck / Boost module 1, an improved Buck-Boost module 2, an intermediate capacitor C and a high-voltage side DC bus capacitor C. HThe input side of the wide-gain DC / DC converter module is the low-voltage side of the wide-gain DC / DC converter module, and the output side of the wide-gain DC / DC converter module is the high-voltage side of the wide-gain DC / DC converter module, and the low-voltage side and the high-voltage side are absolutely grounded; the improved Buck / Boost module 1 is composed of a first inductor L1, a first switch tube S1 and a second switch tube S2; the improved Buck-Boost module 2 is composed of a second inductor L2, a third switch tube S3 and a fourth switch tube S4; one end of the first inductor L1 and the drain of the third switch tube S3 are simultaneously connected to the positive electrode of the film capacitor FC; the other end of the first inductor L1 is connected to the drain of the first switch tube S1 and the source of the second switch tube S2; the drain of the second switch tube S2 is connected to the high-voltage side DC bus capacitor C H The positive electrode of the second inductor L2, the positive electrode of the intermediate capacitor C, and the positive electrode of the DC bus capacitor C H The source of the third switch tube S3 is connected to the drain of the fourth switch tube S4 and the other end of the second inductor L2; the source of the fourth switch tube S4 is connected to the source of the first switch tube S1 and the negative electrode of the intermediate capacitor C.

[0037] Furthermore, the working principle of the electric vehicle hybrid energy storage system based on a wide gain DC / DC converter described in the present invention is as follows:

[0038] According to the driving conditions of the electric vehicle, the new wide-gain DC / DC converter module described in the present invention works in two corresponding modes: boost and buck. The buck mode corresponds to the deceleration or braking state of the electric vehicle. The braking energy is transmitted to the DC bus of the hybrid energy storage system through the inverter module, and is further bucked and fed back to the film capacitor FC through the wide-gain DC / DC converter module described in the present invention; the boost mode corresponds to the climbing or acceleration state of the electric vehicle. The energy stored in the film capacitor FC in the buck mode is boosted by the converter, and then transmitted to the DC bus in conjunction with the power battery module for use by the drive motor. The above working mode can effectively avoid high current charging and discharging of the power battery module, and effectively improve the utilization rate of braking energy and the dynamic performance of the electric vehicle while improving the reliability and safety of the power battery module.

[0039] In buck mode, the power switch control signal is as follows: Figure 3 As shown: the first switch tube S1 and the third switch tube S3 are always turned off, the second switch tube S2 and the fourth switch tube S4 work in the chopping state, and the control signals are consistent. The wide gain DC / DC converter module buck mode working state is as follows Figure 4 and Figure 5 shown.

[0040] Figure 4Buck mode state 1: the first switch tube S1 and the third switch tube S3 are both turned off, and the second switch tube S2 and the fourth switch tube S4 are both turned on. The braking energy of the drive motor absorbed by the high-voltage DC bus side is stored in the first inductor L1 and the low-voltage side film capacitor FC through the second switch tube S2, and the current of the first inductor L1 increases and the voltage of the film capacitor FC increases. At the same time, the intermediate capacitor C transfers energy to the second inductor L2 through the fourth switch tube S4, and the current of the second inductor L2 increases.

[0041] Figure 5 Buck mode state 2: the first switch tube S1, the second switch tube S2, the third switch tube S3 and the fourth switch tube S4 are all turned off. The second inductor L2 transfers energy to the low-voltage side film capacitor FC through the anti-parallel diode of the third switch tube S3, and the first inductor L1 transfers energy to the low-voltage side film capacitor FC and the intermediate capacitor C through the anti-parallel diode of the first switch tube S1.

[0042] In the above two buck modes, the voltage of the film capacitor FC and the energy distribution of the intermediate capacitor C are achieved by controlling the duty cycle of the second switch tube S2 and the fourth switch tube S4, further expanding the voltage variation range of the film capacitor FC and effectively expanding the voltage gain of the new wide-gain DC / DC converter module described in the present invention.

[0043] In boost mode, the power switch control signal is as follows: Figure 6 As shown: the first switch tube S1 and the third switch tube S3 work in the chopping state and have the same control signal, and the second switch tube S2 and the fourth switch tube S4 are always turned off. The working state of the wide gain DC / DC converter module in the boost mode is as follows Figure 7 and Figure 8 shown.

[0044] Figure 7 It is the boost mode state 1: the first switch tube S1 and the third switch tube S3 are both turned on, and the second switch tube S3 and the fourth switch tube S4 are both turned off. The low-voltage side film capacitor FC releases energy to the second inductor L2 through the third switch tube S3, and the current of the second inductor L2 increases; the middle capacitor C is connected in series with the low-voltage side film capacitor FC to release energy to the first inductor L1 through the first switch tube S1, and the current of the first inductor L1 increases. In this mode, the first inductor L1 stores the energy of the film capacitor FC and the middle capacitor C, and the energy density is greatly improved.

[0045] Figure 8It is the boost mode state 2: the first switch tube S1, the second switch tube S2, the third switch tube S3 and the fourth switch tube S4 are all turned off. The second inductor L2 transfers energy to the intermediate capacitor C through the anti-parallel diode of the fourth switch tube S4, and the voltage of the intermediate capacitor C rises, preparing for mode 1. The low-voltage side film capacitor FC and the first inductor L1 are connected in series to transfer energy to the high-voltage DC bus through the anti-parallel diode of the second switch tube S2, and the voltage gain of the new wide-gain DC / DC converter module described in the present invention is effectively expanded by increasing the energy density of the first inductor L1 in mode 1.

[0046] Furthermore, the voltage stress analysis of the novel wide-gain DC / DC converter module described in the present invention is as follows:

[0047] The novel wide gain DC / DC converter module of the present invention significantly reduces the voltage stress of the capacitor: Figure 4 The buck mode power flow path shown is written as the inductor voltage and capacitor voltage relationship equations:

[0048]

[0049] right Figure 5 The buck mode shown lists the relationship between the inductor voltage and the capacitor voltage as follows:

[0050]

[0051] According to the volt-second balance principle, the voltage of the intermediate capacitor C and the step-down gain are solved as follows:

[0052]

[0053] The above formula shows that the voltage stress of the intermediate capacitor C of the bidirectional wide gain DC / DC converter in the buck mode is up to 1 / 3U H , is always less than the high-voltage DC bus voltage. The voltage stress of the intermediate capacitor C in the boost mode is the same. Therefore, the novel wide-gain DC / DC converter module of the present invention significantly reduces the capacitor voltage stress and improves the reliability of the converter.

[0054] Furthermore, the novel wide gain DC / DC converter module of the present invention is controlled in working mode as follows:

[0055] Table 1 Converter system control logic table

[0056]

[0057] According to the driving conditions of the electric vehicle, the novel wide gain DC / DC converter module of the present invention works in two modes: buck and boost. The table lists the working modes of the novel wide gain DC / DC converter module according to the working voltage U of the low voltage side film capacitor. FC , low voltage side working current i FC , High-voltage side DC bus capacitor voltage U H And control of parameters related to the state of charge (SOC) of the power battery module.

[0058] When the electric vehicle brakes or decelerates, the vehicle state control signal K output is -1, and the drive motor generates braking energy so that the DC bus capacitor voltage U H Increase, the energy distribution controller according to the film capacitor voltage U FC The novel wide gain DC / DC converter module of the present invention operates in the buck mode. FC Less than the set upper limit value U * FC1 When the converter of the present invention is controlled to realize the DC bus capacitor voltage U H Release energy to the film capacitor FC until it exceeds the set upper limit. When the film capacitor FC energy exceeds the set value, the energy distribution controller controls the DC bus capacitor voltage U H The power battery module then releases energy until it reaches the set value SOC of the power battery module. * S When the state of charge SOC of the power battery module and the film capacitor voltage U FC The braking energy is consumed by the energy-consuming resistor to avoid the DC bus voltage U H Too high will cause the converter to be damaged. The above work effectively avoids the problem of high current charging of the power battery module and improves the utilization rate of braking energy. At the same time, the energy distribution controller controls the release of energy according to the set value of the high-voltage side DC bus voltage to avoid undervoltage operation of the DC bus.

[0059] When the electric vehicle is climbing or accelerating, the vehicle state control signal K output is 1, and the DC bus capacitor voltage U H The energy distribution controller detects the film capacitor voltage U FC According to the state of charge SOC of the power battery module, the energy distribution controller controls the new wide gain DC / DC converter module to work in boost mode. FC Greater than or equal to the minimum allowable working voltage U * FC2 When the novel wide gain DC / DC converter module of the present invention is controlled to realize the film capacitor FC and the power battery module to jointly supply the high voltage side DC bus capacitor CH Release energy. In this process, the energy released by the film capacitor FC should be controlled to meet the DC bus capacitor voltage U H Stable until the film capacitor voltage U FC Lower than the minimum allowable operating voltage U * FC2 Stop. When the film capacitor voltage U FC When the current is lower than the set value, the energy of the electric vehicle is only provided by the power battery module. The above work can effectively solve the problem of high current discharge of the power battery module and improve the dynamic performance of the electric vehicle.

[0060] Furthermore, the novel wide-gain DC / DC converter module control method of the present invention is as follows:

[0061] Fig. 9 The novel wide gain DC / DC converter module control method is described, and its control target is to achieve the DC bus voltage U H At the same time, the film capacitor voltage U is controlled according to the working state of the electric vehicle. FC Changes can effectively improve the utilization rate of braking energy of electric vehicles.

[0062] The specific idea is: when K = 1, the converter works in boost mode, with U ref-boost is the DC bus capacitor voltage U H The reference voltage is obtained by the voltage controller, and the low-voltage side reference current average value of the novel wide-gain DC / DC converter module of the present invention is further combined with the gain coefficient U H / u FC Multiply to generate reference current i ref-boost The current controller is based on i ref-boost The PWM generator generates S1~S4 control signals to realize the hybrid energy storage system to supply energy to the drive motor.

[0063] When K = -1, the converter works in buck mode. ref-buck is the DC bus capacitor voltage U H The reference voltage is obtained by the voltage controller, and the low-voltage side reference current average value of the novel wide-gain DC / DC converter module of the present invention is further combined with the gain coefficient U FC / u H Multiply to generate reference current i ref-buck The current controller is based on i ref-buck The PWM generator generates S1-S4 control signals to realize the film capacitor FC to store the braking energy of the electric vehicle.

[0064] The novel wide-gain DC / DC converter module proposed in the present invention has the following outstanding advantages: fewer components, simple structure and control, wide voltage gain can be achieved at a relatively low cost, and the utilization rate and reliability of electric vehicle braking energy can be improved at the same time; the low-voltage side and the high-voltage side of the converter are absolutely common grounded, avoiding high-frequency electromagnetic interference caused by the potential difference, and improving the efficiency and reliability of the converter; the capacitor voltage stress in the converter is low, and the maximum is only 1 / 3 of the high-voltage DC bus voltage, which improves the reliability of the converter. Therefore, the novel wide-gain DC / DC converter module proposed in the present invention can be used in electric vehicle hybrid energy storage systems to effectively improve the utilization rate of braking energy and the reliability of the system, and can significantly improve the mileage of electric vehicles under the existing power battery module technology conditions.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electric vehicle hybrid energy storage system based on a wide gain DC / DC converter, characterized in that: Including film capacitor FC, power battery module, wide gain DC / DC converter module, DC / DC converter module, inverter module and drive motor; The wide-gain DC / DC converter module adopts a novel wide-gain DC / DC converter based on an intermediate capacitor, and the novel wide-gain DC / DC converter based on an intermediate capacitor is composed of an improved Buck / Boost module 1, an improved Buck-Boost module 2, an intermediate capacitor C and a high-voltage side DC bus capacitor C. H Composition: the input side of the wide gain DC / DC converter module is the low voltage side of the wide gain DC / DC converter module, the output side of the wide gain DC / DC converter module is the high voltage side of the wide gain DC / DC converter module, and the low voltage side and the high voltage side are absolutely grounded.

2. The electric vehicle hybrid energy storage system based on a wide gain DC / DC converter according to claim 1, characterized in that: The power battery module and the film capacitor FC are respectively used as the input of the DC / DC converter module and the wide gain DC / DC converter module, and are connected in parallel to the high voltage side DC bus capacitor C after the output of the DC / DC converter module and the wide gain DC / DC converter module. H The DC bus of the wide gain DC / DC converter module is connected in parallel to the DC bus capacitor C on the high voltage side of the wide gain DC / DC converter module. H When the electric vehicle is working in a deceleration or braking state, the wide gain DC / DC converter module reduces the braking energy on the high-voltage DC bus side and stores it in the film capacitor FC; when the electric vehicle is working in a climbing or acceleration state, the wide gain DC / DC converter module boosts the energy of the film capacitor FC and sends it to the high-voltage side DC bus capacitor C H , connected in parallel with the power battery module to power the drive motor.

3. The electric vehicle hybrid energy storage system based on a wide gain DC / DC converter according to claim 1, characterized in that: The improved Buck / Boost module 1 is composed of a first inductor L1, a first switch tube S1 and a second switch tube S2; one end of the first inductor L1 and the drain of the third switch tube S3 are simultaneously connected to the positive electrode of the film capacitor FC; the other end of the first inductor L1 is connected to the drain of the first switch tube S1 and the source of the second switch tube S2; The drain of the second switch tube S2 is connected to the high-voltage side DC bus capacitor C H The positive pole of the DC bus is connected.

4. The electric vehicle hybrid energy storage system based on a wide gain DC / DC converter according to claim 1, characterized in that: The improved Buck-Boost module 2 is composed of a second inductor L2, a third switch tube S3 and a fourth switch tube S4; one end of the first inductor L1 and the drain of the third switch tube S3 are simultaneously connected to the positive electrode of the film capacitor FC; one end of the second inductor L2, the positive electrode of the intermediate capacitor C, and the high-voltage side DC bus capacitor C H The source of the third switch tube S3 is connected to the drain of the fourth switch tube S4 and the other end of the second inductor L2; the source of the fourth switch tube S4 is connected to the source of the first switch tube S1 and the negative electrode of the intermediate capacitor C.

5. The electric vehicle hybrid energy storage system based on a wide gain DC / DC converter according to claim 1, characterized in that: When the electric vehicle brakes or decelerates, the vehicle state control signal K output is -1, and the braking energy generated by the drive motor makes the DC bus capacitor voltage U H Increase, detect the film capacitor voltage U FC and the state of charge SOC of the power battery module; when the film capacitor voltage U FC Lower than the set upper limit U * FC1 When the wide gain DC / DC converter module is controlled to work in the buck mode, the DC bus capacitor voltage U H Release energy to the film capacitor FC until the film capacitor voltage U FC Higher than the set upper limit U * FC1 ; When the film capacitor voltage U FC Exceeding the set upper limit value U * FC1 When the wide gain DC / DC converter module is controlled to achieve the DC bus capacitor voltage U H , stop releasing energy to the film capacitor FC, and instead release energy to the power battery module until the state of charge SOC of the power battery module reaches the set value SOC of the power battery module * S ; In the process of controlling the wide gain DC / DC converter module to work in the buck mode, the wide gain DC / DC converter module controls the release of energy according to the set value of the high-voltage side DC bus voltage to avoid the DC bus undervoltage operation; when the state of charge SOC of the power battery module and the film capacitor voltage U FC When both reach the set value, the braking energy is consumed by the energy consumption resistor to avoid the DC bus voltage U H Too high may damage the converter.

6. The electric vehicle hybrid energy storage system based on a wide gain DC / DC converter according to claim 1, characterized in that: When the electric vehicle is climbing or accelerating, the vehicle state control signal K output is 1, and the DC bus capacitor voltage U H Drop, detect the film capacitor voltage U FC The state of charge SOC of the power battery module; when the film capacitor voltage U FC Higher than the minimum allowable operating voltage U * FC2 When the wide gain DC / DC converter module is controlled to work in the boost mode, the wide gain DC / DC converter module realizes the film capacitor FC combined with the power battery module to the high voltage side DC bus capacitor C H Release energy; When the wide gain DC / DC converter module is controlled to work in the boost mode, the energy value released by the film capacitor FC should satisfy the DC bus capacitor voltage U H Stable until the film capacitor voltage U FC Lower than the minimum allowable operating voltage U * FC2 Stop; when the film capacitor voltage U FC Lower than the minimum allowable operating voltage U * FC2 When the power is turned on, the energy required by the drive motor is only provided by the power battery module.

7. The electric vehicle hybrid energy storage system based on a wide gain DC / DC converter according to claim 1, characterized in that: The method for realizing the bidirectional control of the converter is: sampling by a sensor to obtain the DC bus capacitor voltage U H , film capacitor voltage U FC And the low voltage side current i FC , to achieve the normal operation of the converter and ensure the high efficiency and stability of the hybrid energy storage system; the specific methods are as follows: Step S1, calculating the power flow control signal K, the proposed converter switches between boost and buck modes; Step S2: DC bus capacitor voltage U H With reference voltage U ref To control the target, the voltage controller is used to generate a reference current I ref ; Step S3: The current controller uses the reference current i in the current loop ref To control the feedback current i FC , the result is output to the PWM generator to generate the gate signals S1~S4 of the power switch.

8. The electric vehicle hybrid energy storage system based on a wide gain DC / DC converter according to claim 5, characterized in that: In the buck mode, the wide-gain DC / DC converter module alternately operates in state one and state two; when the wide-gain DC / DC converter module operates in state one, part of the energy on the high-voltage side is transmitted to the first inductor L1, and the remaining energy flows to the low-voltage side film capacitor FC, and the energy of the second inductor L2 in the improved Buck-Boost module 2 is completely provided by the intermediate energy storage capacitor C; when the wide-gain DC / DC converter module operates in state two, the first inductor L1 transmits energy to the intermediate capacitor C and the low-voltage side film capacitor FC respectively, and the second inductor L2 transmits energy to the low-voltage side film capacitor FC; when the wide-gain DC / DC converter module operates in state two, the voltage across the film capacitor FC is equal to the voltage across the second inductor L2, which is much smaller than the high-voltage side DC bus voltage, thereby achieving the purpose of wide-range voltage reduction.

9. The electric vehicle hybrid energy storage system based on a wide gain DC / DC converter according to claim 6, characterized in that: In the boost mode, the wide-gain DC / DC converter module alternately operates in state three and state four; when the wide-gain DC / DC converter module operates in state three, the low-voltage side film capacitor FC and the intermediate capacitor C simultaneously transmit energy to the first inductor L1, and at the same time, the low-voltage side film capacitor FC transmits energy to the second inductor L2, and the current flowing through the second inductor L2 increases; when the wide-gain DC / DC converter module operates in state four, the second inductor L2 transmits energy to the intermediate capacitor C, and the first inductor L1 and the low-voltage side film capacitor FC simultaneously transmit energy to the high-voltage side DC bus, thereby achieving the purpose of wide-range boosting.

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