CN109532518B - A composite power supply including two unidirectional DC converters and its control method - Google Patents

Abstract

A composite power supply including two unidirectional DC converters and a control method thereof, comprising: a battery pack, a switch, a power diode integrated box, a motor inverter, a unidirectional Buck-Boost converter, a super capacitor and a unidirectional Buck converter The method is as follows: the composite power supply determines the high and low level states of the four digital control interfaces of the two unidirectional DC converters according to the operating state of the electric vehicle and the supercapacitor voltage, thereby controlling the working modes of the two unidirectional DC converters. The beneficial effects of the present invention are: the composite power supply structure and the working mode and control method of the DC converter of the present invention can avoid frequent and disorderly charging and discharging of the battery pack, and when the braking energy is sufficient, the super capacitor can perform constant current on the battery pack. Charging effectively protects the safety of the battery, prolongs the service life of the battery, and avoids the time delay problem caused by the bidirectional DC converter during the alternating current and reverse operation, and improves the stability and reliability of the composite power system.

Description

A composite power supply including two unidirectional DC converters and its control method

technical field

The invention belongs to the field of on-board power supplies of electric vehicles, in particular to a composite power supply comprising two unidirectional direct current converters and a control method thereof.

Background technique

With the gradual promotion of electric vehicles, the problem of battery pack life shortening due to frequent charging and discharging has become prominent. In addition, car manufacturers and research institutions all over the world are further studying the overall improvement and optimization of the performance of electric vehicle components and the performance of the whole vehicle, and the on-board power supply is one of the most critical components to improve the performance of electric vehicles. Due to the impossibility of breakthroughs in battery technology in a short period of time, the use of supercapacitors and batteries to form a composite power supply to avoid frequent charging and discharging of battery packs came into being.

With the deepening of research, the composite power structure has been continuously improved to meet the needs of high-performance electric vehicles. Among them, the semi-active supercapacitor/battery pack composite power supply uses the battery pack to be directly connected to both ends of the motor inverter in parallel. The supercapacitor is connected in series with a bidirectional DC converter and then the battery pack is connected in parallel; The voltage of the super capacitor can be higher or lower than the voltage of the battery pack, and the choice is more flexible. Although an appropriate control strategy can be used to make the output power of the supercapacitor follow the power demand of the motor inverter, the battery pack is directly connected to both ends of the motor inverter in parallel, which will be impacted by high-frequency charge and discharge currents and shorten the working life of the battery pack; If a bidirectional DC converter is used to connect the supercapacitor and the battery pack, there will be a certain time delay in the bidirectional DC converter during the alternating current and reverse operation, which will affect the stability and safety of the entire composite power system.

In order to effectively prevent the battery pack from being impacted by frequent charging currents, it is necessary to design a one-way output circuit of the battery pack. When recovering the braking energy of the electric vehicle, the one-way output circuit can prevent the energy from flowing back to the battery pack, and the supercapacitor will give priority to recovering the energy. However, the unidirectional output circuit cannot recover the energy of the battery pack. It is necessary to consider the orderly charging of the battery pack after the supercapacitor is fully charged. Therefore, it is necessary to supplement the design of circuits or components for the supercapacitor to charge the battery pack. In addition, when the working mode of the traditional composite power supply changes, the controller changes the PWM control signal according to the voltage and current signals to realize the working mode change of the DC converter. The program is complicated, and the delay of the program will cause the system to temporarily stop working during the delay period. Stable or even out of control.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a composite power supply including two unidirectional DC converters and a control method thereof to solve the above problems.

To achieve the above object, the present invention adopts the following technical solutions:

A composite power supply containing two unidirectional DC converters, comprising a battery pack, a switch, a power diode integrated box, a motor inverter, a unidirectional Buck-Boost converter, a supercapacitor and a unidirectional Buck converter; The positive pole is connected to the input port A of the switch, the output port B of the switch is connected to the anode integrated input terminal of the power diode integrated box, and the cathode output terminal of the power diode integrated box is respectively connected to the positive terminal of the motor inverter and the one-way Buck-Boost converter. The positive input port a ₁ of the motor inverter is respectively connected to the negative input port b ₁ of the unidirectional Buck-Boost converter and the negative electrode of the battery pack; the positive output port c ₁ and the negative electrode of the unidirectional Buck-Boost converter are respectively connected _The output interface d1 is respectively connected to the positive pole and the negative pole of the supercapacitor; the positive pole and the negative pole of the supercapacitor are also connected to the positive pole input interface a2 and the negative pole input interface b2 of the one _- way Buck converter respectively _; the positive pole output interface c of the one-way Buck converter ₂ and the negative output interface d ₂ are respectively connected to the positive and negative electrodes of the battery pack.

Further, the output circuit where the battery pack, the switch, and the power diode integrated box are located is the main circuit, and the switch located in the main circuit can control the output of the super capacitor and the battery pack at the same time.

Further, the battery pack realizes unidirectional output through a power diode integrated box, and the power diode integrated box is composed of a plurality of diodes.

Further, the unidirectional Buck-Boost converter is a digital DC converter with high and low level control, and is only used for unidirectional boost or buck charging of the supercapacitor, and cannot discharge the supercapacitor.

Further, the unidirectional Buck converter is a digital DC converter controlled by high and low levels, and is only used for unidirectional step-down and discharge of the supercapacitor, and cannot charge the supercapacitor.

Further, the one-way Buck-Boost converter, the supercapacitor and the one-way Buck converter constitute an auxiliary circuit for orderly charging the battery pack with braking energy, and the battery pack can charge the supercapacitor through the one-way Buck-Boost converter , and the supercapacitor can charge the battery pack through the unidirectional Buck converter; at the same time, the supercapacitor can provide energy to the motor inverter through the unidirectional Buck converter.

Further, a method for controlling a composite power supply containing two unidirectional DC converters, based on the composite power supply containing two unidirectional DC converters described in any one of the above, includes the following steps:

Step 1, respectively control the high and low level inputs of the digital interfaces D ₁ and D ₂ of the one-way Buck-Boost converter and the digital interfaces D ₃ and D ₄ of the one-way Buck converter according to the operating state of the electric vehicle and the voltage of the super capacitor;

Step 2, judge the value of the digital interface of the one-way Buck-Boost converter and the one-way Buck converter, and determine the working state of the one-way Buck-Boost converter and the one-way Buck converter;

Further, in step 2, when D ₁ =0, D ₂ =0, the one-way Buck-Boost converter does not work; when D ₁ =0, D ₂ =1, the one-way Buck-Boost converter is directed to the input The buck-boost converter performs step-down constant-current work at the input end; when D ₁ =1, D ₂ =0, the unidirectional Buck-Boost converter performs step-up constant-current work for the input end.

Further, in step 2, when D ₃ =0, D ₄ =0, the one-way Buck converter does not work; when D ₃ =0, D ₄ =1, the one-way Buck converter performs constant voltage on the output end Work; when D ₃ =1, D ₄ =0, the unidirectional Buck converter performs constant current work for the output end.

Further, the high and low level switching of the digital interface D1 of the one-way Buck _- Boost converter and the digital interfaces _D3 and D4 of the _one -way Buck converter adopts hysteresis control.

Compared with the prior art, the present invention has the following technical effects:

Compared with the supercapacitor/battery pack composite power supply with semi-active structure, the electric vehicle composite power supply with two unidirectional DC converters of the present invention adds a switch to the battery output main circuit, which can control the battery pack and the supercapacitor at the same time. The output of the capacitor; the power diode integrated box makes the energy output in one direction in the main circuit, avoiding the direct impact of the disordered braking current on the battery pack, effectively ensuring the safety of the battery pack and prolonging the service life of the battery pack; through more efficient digital The unidirectional Buck-Boost converter charges the supercapacitor or recovers the braking energy, which effectively solves the delay problem of the bidirectional DC converter when the current is switched between the forward and reverse currents, and helps to improve the stability of the system; A digital one-way Buck converter is connected in series between the capacitor and the battery pack, which can not only ensure that the supercapacitor is fully charged and then charge the battery pack with constant current, but also can realize the supercapacitor to provide auxiliary energy to the motor inverter, ensuring that the supercapacitor can effectively Recover braking energy and provide high-power auxiliary output to improve the utilization efficiency of super capacitors.

Description of drawings

1 is a circuit topology diagram of a composite power supply according to an embodiment of the present invention;

Fig. 2 is the internal structure of the power diode integrated box of the embodiment of the present invention;

FIG. 3 is a semi-active structure supercapacitor/battery pack composite power supply according to an embodiment of the present invention.

Fig. 4 is the working mode selection flow chart of two unidirectional DC converters according to the embodiment of the present invention;

5(a) to 5(c) are schematic diagrams of hysteresis control of working modes of two unidirectional DC converters according to an embodiment of the present invention;

Detailed ways

The present invention will be further described below with reference to the accompanying drawings. The embodiments are used to illustrate the present invention but not to limit the scope of the present invention. Some parameters can be matched and adjusted according to the specific parameters of the components and specific usage conditions. For example: the number of diodes in the power diode integrated box is related to the maximum power of the braking energy recovery of the composite power supply; the upper and lower limits of the hysteresis interval of the working mode hysteresis control of the two digital one-way DC converters can be determined according to the actual application. Adjustment.

This embodiment describes an electric vehicle composite power supply including two unidirectional DC converters and a method for controlling the working mode of the DC converter. The specific circuit topology is shown in Figure 1. The system is integrated by a battery pack 1, a switch 7, and a power diode. Box 2, motor inverter 3, one-way Buck-Boost converter 4, super capacitor 5 and one-way Buck converter 6; the positive pole of battery pack 1 is connected to the input port A of switch 7, and the output port B of switch 7 is connected The anode input end of the power diode integrated box 2 and the cathode output end of the power diode integrated box 2 are respectively connected to the anode port of the motor inverter 3 and the anode input interface a ₁ of the unidirectional Buck-Boost converter 4 , and the motor inverter 3 The negative terminal of the unidirectional Buck-Boost converter 4 is respectively connected to the negative input interface b ₁ of the one-way Buck-Boost converter 4 and the negative pole of the battery pack 1; the positive output interface c ₁ and the negative output interface d ₁ of the one-way Buck-Boost converter 4 are respectively connected to the super capacitor The positive pole and the negative pole of 5; the positive pole and negative pole of the super capacitor 5 are also respectively connected to the positive input interface a ₂ and the negative input interface b ₂ of the one-way Buck converter 6; the positive output interface c ₂ and the negative pole output of the one-way Buck converter 6 The interface d ₂ is respectively connected to the positive electrode and the negative electrode of the battery pack 1 .

The internal structure of the power diode integrated box in this embodiment is shown in Figure 2. The power diode integrated box 2 is composed of multiple power diodes connected in parallel, and the anodes of the diodes are connected together to form the anode integrated terminal of the power diode integrated box 2; It is connected to the cathode integrated terminal of the power diode integrated box 2 , and is respectively connected to the anode port of the motor inverter 3 and the anode input interface a ₁ of the unidirectional Buck-Boost converter 4 .

The semi-active structure of the supercapacitor/battery pack composite power supply is shown in Figure 3. Compared with the semi-active structure of the supercapacitor/battery pack composite power supply, an electric vehicle composite power supply containing two unidirectional DC converters of the present invention A switch 7 is added to the output main circuit of the battery pack 1, which can control the output of the battery pack 1 and the supercapacitor 5 at the same time; the power diode integrated box 2 makes the energy output in one direction in the main circuit to avoid the battery pack 1 being directly affected by disordered control. The impact of the dynamic current can effectively ensure the safety of the battery pack 1 and prolong the service life of the battery pack 1; the one-way Buck-Boost converter 4, the super capacitor 5, and the one-way Buck converter 6 constitute the orderly direction of the braking energy to the battery pack. 1 is an auxiliary circuit for charging, and the battery pack 1 can charge the supercapacitor 5 through the one-way Buck-Boost converter 4, and the supercapacitor 5 can charge the battery pack 1 through the one-way Buck-Boost converter 6. At the same time, the super capacitor 5 can also provide energy to the motor inverter through the one-way Buck converter 6 .

The standard voltage of the battery pack 1 is set to be 50% of the maximum working voltage of the supercapacitor 5, thereby ensuring that the maximum discharge energy of the supercapacitor 5 is 75%.

Operating mode control of two unidirectional DC converters:

The specific working mode selection flow chart of the two unidirectional DC converters is shown in Figure 4. After the composite power supply is started, first determine whether the voltage of the super capacitor 5 is lower than the voltage of the battery pack 1. If it is lower than the voltage of the battery pack 1, further control the single voltage. To the working mode of Buck-Boost converter 4 and unidirectional Buck converter 6, until the voltage of super capacitor 5 is greater than or equal to the voltage of battery pack 1. When the voltage of the supercapacitor 5 is greater than the voltage of the battery pack 1, it is then judged whether the demanded power is positive. If the demanded power is not positive, the operation mode of the electric vehicle is braking, and the unidirectional Buck-Boost converter 4 is further controlled in combination with the supercapacitor voltage. and the working mode of the unidirectional Buck converter 6. If the demanded power is positive and the electric vehicle is operating in the driving mode, it is necessary to further judge whether the demanded power is greater than 5kW, and then combine the voltage of the super capacitor 5 to further control the working modes of the one-way Buck-Boost converter 4 and the one-way Buck converter 6;

The digital control interface level signal corresponding to the working mode

After the composite power supply starts to work, firstly check whether the voltage of the super capacitor 5 is lower than the voltage of the battery pack 1. When it is lower than the voltage of the battery pack 1, the level signal of the digital interface of the unidirectional Buck-Boost converter 4 is D ₁ = 0, D ₂ =1, step-down constant current operation is performed on the input end of the unidirectional Buck-Boost converter 4; the level signal of the digital interface of the unidirectional Buck converter 6 is D ₃ =0, D ₄ =0, the single Buck converter 6 does not work. At this time, the battery pack 1 alone supplies energy and charges the supercapacitor 5 .

When the required power of the electric vehicle is negative, that is, when the operation mode of the electric vehicle is braking, the supercapacitor 5 preferentially uses the one-way Buck-Boost converter 4 to boost the constant current at the input terminal to recover energy, corresponding to D ₁ =1, D ₂ =0; at this time, it is necessary to further select the working mode of the unidirectional Buck converter 6 in combination with the supercapacitor voltage. When the voltage of the supercapacitor 5 rises to 99% of the rated voltage, the digital interface D of the unidirectional Buck converter The level signal of ₃ is converted from 0 to 1, and the one-way Buck converter 6 works with constant current at the output end. When the voltage of the supercapacitor 5 is reduced to 95% of the rated voltage, the level signal of the digital interface _D3 of the one-way Buck converter 6 is converted from 1 to 0, and the one-way Buck converter 6 does not work; when the required power is negative, The signal conversion of the digital interface _D3 adopts hysteresis control, as shown in Fig. 5(a), to avoid frequent switching of the working mode of the one-way Buck converter 6. In order to ensure the safety of the super capacitor, it is stipulated that the boost constant current working power of the unidirectional Buck-Boost converter 4 is smaller than the constant current working power of the Buck converter 6 .

When the electric vehicle demand power is positive, that is, when the electric vehicle operation mode is driving, the working mode of the one-way Buck-Boost converter 4 and the one-way Buck converter 6 is further controlled in combination with the demanded power and the voltage of the super capacitor 5 . If the required power is greater than 5kW, the one-way Buck-Boost converter 4 does not work, at this time D ₁ =0, D ₂ =0. It is necessary to judge whether the voltage of the supercapacitor 5 is greater than 75%. When the voltage of the supercapacitor 5 is greater than 75%, the one-way Buck converter 6 works with a constant voltage on the output end, at this time D ₃ =0, D ₄ =1; when the super capacitor 5 When the voltage is less than 75%, the unidirectional Buck converter 6 works with a constant current at the output end, at this time D ₃ =1, D ₄ =0. If the required power is less than 5kW and the voltage of the supercapacitor 5 is lower than 85% of the rated voltage, the unidirectional Buck-Boost converter 4 works on the input terminal to boost the constant current, and the unidirectional Buck converter 6 does not work, at this time D ₁ =1 , D ₂ =0, D ₃ =0, D ₄ =0, at this time, the battery pack 1 supplies energy alone, and the excess energy charges the super capacitor 5 . When the supercapacitor voltage 5 is higher than 95% of the rated voltage, the unidirectional Buck-Boost converter 4 does not work, and the unidirectional Buck converter 6 works with constant voltage on the output terminal, at this time D ₁ =0, D ₂ =0, D ₃ =0, D ₄ =1, at this time, the battery pack 1 and the supercapacitor 5 jointly output, the battery pack 1 provides constant power, and the supercapacitor 5 provides peak power. When the required power is less than 5kW, the signal conversion of digital interfaces D ₁ and D ₄ adopts hysteresis control, as shown in Figure 5(b) and 5(c), to avoid unidirectional Buck-Boost converter 4 and unidirectional Buck conversion Frequent switching of the working mode of the device 6.

The above embodiments are only intended to reflect the technical concept and characteristics of the present invention, and are not intended to limit the protection scope of the present invention. For example, the upper and lower limits of the three hysteresis control hysteresis intervals can be adjusted according to the actual situation. Equivalent replacements or modifications within the spirit and principles are all included within the protection scope of the present invention.

Claims (7)

1. A composite power supply containing two unidirectional direct current converters is characterized by comprising a battery pack (1), a switch (7), a power diode integration box (2), a motor inverter (3), a unidirectional Buck-Boost converter (4), a super capacitor (5) and a unidirectional Buck converter (6); the positive pole of the battery pack (1) is respectively connected with an input port A of a switch (7), an output port B of the switch is connected with an anode integrated input end of a power diode integrated box (2), and a cathode output end of the power diode integrated box (2) is respectively connected with a positive pole port of a motor inverter (3) and a positive pole input interface a of a unidirectional Buck-Boost converter (4)₁The negative port of the motor inverter (3) is respectively connected with the negative input interface b of the unidirectional Buck-Boost converter₁And a negative electrode of the battery (1); positive output interface c of unidirectional Buck-Boost converter₁And a negative output interface d₁The anode and the cathode of the super capacitor (5) are respectively connected; the anode and the cathode of the super capacitor (5) are respectively connected with the anode input interface a of the unidirectional Buck converter (6)₂And a negative input interface b₂(ii) a Positive output interface c of unidirectional Buck converter (6)₂And a negative output interface d₂The positive electrode and the negative electrode of the battery pack (1) are respectively connected;

the unidirectional Buck-Boost converter (4) is a digital direct-current converter controlled by high and low levels, is only used for unidirectional boosting or step-down charging of the super capacitor, and cannot discharge the super capacitor;

the unidirectional Buck converter (6) is a digital direct-current converter controlled by high and low levels, is only used for unidirectional voltage reduction and discharge of the super capacitor, and cannot charge the super capacitor;

the unidirectional Buck-Boost converter (4), the super capacitor (5) and the unidirectional Buck converter (6) form an auxiliary circuit for orderly charging the battery pack with braking energy, the battery pack can charge the super capacitor through the unidirectional Buck-Boost converter, and the super capacitor can charge the battery pack through the unidirectional Buck converter; meanwhile, the super capacitor can provide energy for the motor inverter through the unidirectional Buck converter.

2. The hybrid power supply comprising two unidirectional direct current converters according to claim 1, wherein the output circuit where the battery pack (1), the switch (7) and the power diode integration box (2) are located is a main circuit, and the switch (7) located in the main circuit can control the output of the super capacitor and the battery pack at the same time.

3. A hybrid power supply comprising two unidirectional dc converters according to claim 1, wherein the battery pack (1) achieves unidirectional output through the power diode pack (2), and the power diode pack (2) is composed of a plurality of diodes.

4. A control method of a hybrid power supply including two unidirectional dc converters, characterized in that, based on any one of claims 1 to 3, a hybrid power supply including two unidirectional dc converters includes the following steps:

step 1, respectively controlling a digital interface D of a one-way Buck-Boost converter according to the running state of the electric automobile and the voltage of a super capacitor₁And D₂And a digital interface D of the unidirectional Buck converter₃And D₄High and low level input of (1);

and 2, judging the values of the digital interfaces of the unidirectional Buck-Boost converter and the unidirectional Buck converter, and determining the working states of the unidirectional Buck-Boost converter and the unidirectional Buck converter.

5. According to claim4 the control method of the hybrid power supply comprising two unidirectional dc converters, characterized in that in step 2, when D is reached₁＝0，D₂When the voltage is equal to 0, the unidirectional Buck-Boost converter does not work; when D is present₁＝0，D₂When the input voltage is 1, the unidirectional Buck-Boost converter performs voltage reduction and constant current work aiming at the input end; when D is present₁＝1，D₂When the input voltage is 0, the unidirectional Buck-Boost converter performs boosting constant current work aiming at the input end.

6. The method as claimed in claim 4, wherein in step 2, when D is reached₃＝0，D₄When the voltage is equal to 0, the unidirectional Buck converter does not work; when D is present₃＝0，D₄When the output end of the unidirectional Buck converter is equal to 1, the unidirectional Buck converter performs constant-voltage work aiming at the output end; when D is present₃＝1，D₄When the output end of the unidirectional Buck converter is equal to 0, the unidirectional Buck converter performs constant current operation on the output end.

7. The method for controlling the hybrid power supply comprising two unidirectional direct current converters according to claim 4, wherein the digital interface D of the unidirectional Buck-Boost converter₁And a digital interface D of the unidirectional Buck converter₃And D₄The hysteresis control is adopted for high-low level switching.

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