Control method and system for bidirectional DC / DC converter of energy storage system

Abstract

The invention provides a control method and system for a bidirectional DC / DC converter of an energy storage system, the energy storage system comprises a PCS unit, a DC / DC converter, a battery and a DC / DC control unit, one end of the PCS unit is connected to a power grid / load, the other end of the PCS unit is connected with the battery through the DC / DC converter, the DC / DC converter is also connected with the DC / DC control unit, and the DC / DC converter is connected with the DC / DC control unit. The control method comprises the following steps: detecting battery voltage, battery current and NTC temperature in a DC / DC converter chip during charging / discharging operation of a battery; when the battery voltage is in a low voltage interval, the dead time, the switching frequency and the bus voltage of the DC / DC converter are controlled to work in a fixed value mode; and when the battery voltage is in a high voltage interval, the dead time, the switching frequency and the bus voltage of the DC / DC converter are controlled to work in a dynamic change mode respectively. Therefore, the utilization rate of battery voltage is effectively improved, and battery capacity loss is reduced.

Description

Technical Field

[0001] This invention relates to a control method and system for a bidirectional DC / DC converter in an energy storage system, belonging to the field of chemical energy storage control technology. Background Technology

[0002] With the increasing installed capacity of renewable energy, energy storage systems are receiving high attention from countries around the world. Energy storage systems typically offer design options for single-stage and two-stage architectures, such as... Figure 1 As shown, in the primary structure scheme, the energy storage system includes a PCS unit and a battery. One end of the PCS unit is connected to the grid / load, and the other end is connected to the battery. The voltage between the PCS unit and the power grid / load. This refers to the battery voltage, which changes during charging and discharging.

[0003] like Figure 2 As shown, in the two-stage structure scheme, the energy storage system includes a PCS unit, a battery, and a DC / DC converter. One end of the PCS unit is connected to the power grid, and the other end of the PCS unit is connected to the battery via the DC / DC converter. The voltage between the PCS unit and the power grid / load; This is the voltage between the PCS unit and the DC / DC converter, also known as the bus voltage. This refers to the battery voltage. In the aforementioned energy storage system, a battery typically refers to a battery pack formed by connecting several battery cells in series, parallel, or a combination of series and parallel connections; the PCS unit is a power conversion system, which can be simply referred to as a PCS unit; the battery voltage during charging / discharging operation... Changes over time.

[0004] Energy storage systems are primarily designed to meet the system's requirements for voltage, capacity, and power. The efficiency of an energy storage system usually refers to the efficiency of energy conversion, which is the ratio of the effective output energy to the input energy during the process of storing and releasing energy.

[0005] Figure 1 The single-stage structure shown features a simple system structure, low investment cost, and high energy conversion efficiency, with overall energy conversion efficiency typically superior to the two-stage structure. However, its disadvantages include the requirement that the battery output voltage must strictly match the DC input voltage range of the PCS unit, limiting the flexibility of series-parallel battery configuration. Furthermore, it has weak resistance to voltage fluctuations; if the battery voltage changes with the battery's state of charge (SOC) and exceeds the input voltage range of the PCS unit, the system may malfunction.

[0006] Figure 2The two-stage architecture shown features high voltage flexibility, allowing the DC / DC converter to boost / buck, decoupling the battery voltage from the PCS unit input voltage, and support for a wide range of battery configurations. By optimizing the operating efficiency and power of the PCS unit, the DC / DC converter can adjust the battery voltage to the optimal operating point of the PCS unit, such as the PCS's highest input voltage, while simultaneously increasing the PCS's grid connection point voltage. This approach increases the power output of the PCS unit while keeping the input current constant, thus reducing the cost per unit power density of the PCS. The downside is increased system control complexity.

[0007] Because DC / DC converters require bidirectional energy flow to charge and discharge batteries, bidirectional Buck / Boost converters are used as DC / DC converters in energy storage systems. The topology of the DC / DC converter is as follows: Figure 3 As shown.

[0008] In traditional methods, the control method for DC / DC converters in energy storage systems is as follows: Figure 4 As shown, a fixed switching frequency is used in the control process, based on the battery voltage. The changes in voltage are stabilized by adjusting the on / off times of switching transistors S1 and S2. The relationship between battery voltage and bus voltage is as follows:

[0009] ;

[0010] In the formula, Battery voltage, Where is the bus voltage, D is the duty cycle of switch S1, and the duty cycle of switch S2 is 1-D.

[0011] The theoretical range of D is 0~100%. If D=100%, then the bus voltage can theoretically be equal to the battery voltage, i.e. In practical applications, the actual control duty cycle of switch S1 cannot reach its maximum value of 100%, causing the bus voltage to be greater than the battery voltage. Furthermore, to avoid a short circuit caused by simultaneous switching of switches S1 and S2, a switching dead time exists between switches S1 and S2 in actual use. Dead time The duty cycle loss leads to voltage loss.

[0012] Figure 4 The formula for calculating the maximum value of the bus voltage is as follows:

[0013] ;

[0014] In the formula, This represents the maximum value of the bus voltage. This refers to the voltage loss at the highest point of the battery voltage. This represents the maximum battery voltage.

[0015] The voltage drop is the difference between the bus voltage and the battery voltage required to maintain bus voltage stability, after considering duty cycle voltage loss, and is set with a 10% control margin, as shown in the following formula:

[0016] ;

[0017] In the formula, The voltage drop caused by the duty cycle loss due to dead time. Calculated using the following formula:

[0018] ;

[0019] In the formula, Duty cycle loss due to dead time. Calculated using the following formula:

[0020] ;

[0021] In the formula, When it is a dead zone, The switching cycle.

[0022] The presence of voltage loss affects the actual energy utilization rate of the battery. Therefore, a method is needed to minimize the voltage loss between the battery voltage and the bus voltage in order to improve the energy utilization rate of the battery. Summary of the Invention

[0023] This invention proposes a control method and system for a bidirectional DC / DC converter in an energy storage system.

[0024] To solve the above problems, the specific technical solution of the present invention is as follows:

[0025] A control method for a bidirectional DC / DC converter in an energy storage system, the energy storage system comprising a PCS unit, a DC / DC converter, a battery, and a DC / DC control unit, wherein one end of the PCS unit is connected to the power grid / load, and the other end is connected to the battery via the DC / DC converter, and the DC / DC converter is also connected to the DC / DC control unit, the control steps being as follows:

[0026] Detects battery voltage, battery current, and NTC temperature inside the DC / DC converter chip during charging / discharging.

[0027] When the battery voltage is in the low voltage range, the control bus voltage, the dead time of the DC / DC converter, and the switching frequency all operate in a fixed value mode.

[0028] When the battery voltage is in the high voltage range, the control bus voltage, the dead time of the DC / DC converter, and the switching frequency operate in dynamic changing modes. Specifically, the dynamic changing modes are the dynamic changing modes of the DC / DC converter dead time relative to the battery current and the NTC temperature inside the DC / DC converter chip, the dynamic changing modes of the switching frequency relative to the battery voltage, and the dynamic changing modes of the bus voltage relative to the battery voltage.

[0029] Furthermore, when the battery voltage is in the low voltage range, the control bus voltage, the dead time of the DC / DC converter, and the switching frequency all operate in a fixed value mode, specifically as follows:

[0030] When the battery voltage is in the low voltage range Bus voltage Dead time of DC / DC converter and switching frequency The working mode is controlled as follows:

[0031]

[0032] When the battery voltage is in the high voltage range The control bus voltage, the dead time of the DC / DC converter, and the switching frequency operate in a dynamic changing mode, specifically as follows:

[0033] a. The dynamic variation mode of the dead time of the DC / DC converter is expressed as:

[0034] ;

[0035] b, The dynamic mode of the switching frequency of the DC / DC converter is expressed as:

[0036] ;

[0037] c. The dynamic change pattern of the bus voltage is represented as follows:

[0038] ;

[0039] In the formula, This is the lowest possible battery charge. These are inherent values; This is the battery's first voltage; This is the battery's highest voltage. The first switching frequency; This is the second switching frequency; The first voltage of the busbar; This is the highest voltage of the busbar; Set the dead time value; This refers to the internal NTC temperature of the DC / DC converter chip. for The baseline value; This is the inverse proportionality coefficient of the battery current; This is the battery current calibration bias value; α is the temperature proportionality coefficient. This is a temperature calibration reference value; The first voltage of the battery after considering a 10% design margin Voltage loss; To account for the battery's maximum voltage after a 10% design margin Voltage loss;

[0040] Among them, the first switching frequency Take the maximum value of the switching frequency; second switching frequency Take the minimum switching frequency; the minimum battery voltage. This is an inherent value; the highest voltage of the busbar. It is a constant value;

[0041] In the above formula, the highest voltage of the battery is... Calculated using the following formula:

[0042] ;

[0043] ;

[0044] In the formula, the highest voltage of the busbar Determined based on the maximum design value of the DC / DC converter; Calculated according to the formula in a;

[0045] First voltage of the bus Calculated using the following formula:

[0046] :

[0047] The first voltage of the battery Calculated using the following formula:

[0048] ;

[0049] ;

[0050] Furthermore, the first switching frequency The second switching frequency The relationship is as follows: .

[0051] Furthermore, the first voltage The value ranges from 1.2 to 1.45. .

[0052] Furthermore, the DC / DC control unit includes a DSP digital processor, an FPGA chip, and a drive circuit. The control process of the DC / DC control unit is as follows:

[0053] DSP digital processor acquires battery voltage Battery current Feedback signal of bus voltage and NTC temperature inside DC / DC converter chip Output switch management theoretical duty cycle Switching frequency and dead zone time To FPGA chip;

[0054] The FPGA chip receives the signal, performs digital conversion to generate two center-aligned complementary PWM signals, and realizes the control of switching frequency, bus voltage and dead time.

[0055] Furthermore, the duty cycle of the switch management theory , Bus voltage This refers to the battery voltage.

[0056] An energy storage system, and a control method for implementing the bidirectional DC / DC converter of the above-mentioned energy storage system.

[0057] The present invention has the following advantages over the prior art:

[0058] The present invention discloses a voltage configuration control method for an energy storage system. This method dynamically allocates the switching frequency and dead time of the DC / DC converter according to the voltage variation range of the battery during charging / discharging operation, thereby minimizing the voltage loss at both ends of the DC / DC converter and improving the energy utilization rate of the battery.

[0059] This invention implements zoned control of the switching frequency of the DC / DC converter. When the battery voltage is in the low-voltage range, the switching frequency, bus voltage, and dead time are controlled at fixed values. When the battery voltage is in the high-voltage range, the switching frequency, dead time, and bus voltage are controlled in a variable control mode, such as using a linear function control mode. This zoned control mode improves the actual battery capacity utilization. This control method can further reduce the input-output voltage loss of the DC / DC converter by more than 70% and improve the actual battery capacity utilization by about 8%. Attached Figure Description

[0060] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0061] Figure 1 This is a circuit topology diagram of an existing Level 1 energy storage system;

[0062] Figure 2 The circuit topology diagram of an existing two-stage energy storage system is shown below.

[0063] Figure 3 This is a topology diagram of a DC / DC converter in an existing two-stage energy storage system.

[0064] Figure 4 A schematic diagram of a traditional voltage configuration control method for energy storage systems;

[0065] Figure 5 This is a schematic diagram of the voltage configuration control method for the energy storage system of the present invention;

[0066] Figure 6 A schematic diagram of the hardware circuit for implementing the control method of this invention;

[0067] Figure 7 This is a diagram illustrating the dead time of an application instance. Detailed Implementation

[0068] The specific technical solutions of the present invention will now be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention.

[0069] The two-stage energy storage system used in this invention is as follows: Figure 2 As shown, the circuit structure of the DC / DC converter is as follows: Figure 3 As shown, the improved control method of the present invention is as follows: Figure 5 As shown.

[0070] During battery charging / discharging operation, the voltage... With current Changes in the NTC temperature inside the switching transistor chip of the DC / DC converter Changes, and the switching frequency of the DC / DC converter Synchronous dynamic changes, and the dead time of the DC / DC converter. It also changes dynamically in sync; the dead time of the DC / DC converter The change is the same as the battery current. The relationship changes inversely with the NTC temperature inside the switching transistor chip of the DC / DC converter. The changes are directly proportional.

[0071] The control method of the present invention is based on the input battery voltage of the DC / DC converter. Dynamically allocate the switching frequency of the DC / D converter C. and adjusting the output voltage ,

[0072] The switching frequency of a DC / DC converter changes with the input voltage. The change is linear, consisting of two segments.

[0073] The first segment, the low-voltage segment, has a fixed switching frequency. Dead time The first interval remains unchanged as ;

[0074] The second segment, the high-voltage segment, has a switching frequency equal to the input voltage. function Dead time Input battery current to DC / DC converter and the NTC temperature inside the switching transistor chip function And the switching frequency of the first segment greater than the switching frequency of the second segment interval ;

[0075] bus voltage Also with battery voltage The change is linear and occurs in two segments. In the first segment, the bus voltage is fixed. The second section, bus voltage Battery voltage function The bus voltage in the second section The bus voltage is greater than that of the first section. ;

[0076] Based on the input battery current of the DC / DC converter and the NTC temperature inside the switching transistor chip Dynamically allocate DC / DC dead time The output voltage is adjusted in conjunction with the switching frequency and output voltage of the DC / DC converter in the energy storage system. .

[0077] Dead Time With battery current The dead time exhibits a negative correlation and must cover the reverse recovery charge and turn-off delay time of the power device, both of which are affected by current. The impact of high current on diode reverse recovery time. Because carrier recombination is accelerated, the dead time is shortened, and the junction capacitance of the device discharges faster at high currents, reducing the turn-off delay by approximately 15-30%. Therefore, the higher the current, the shorter the dead time required by the DC / DC converter. Dead Time With respect to the NTC temperature inside the switching transistor chip There is a positive correlation: as temperature increases, carrier mobility decreases, leading to an increase in turn-on delay time and a prolonged turn-off tail current duration. At high temperatures, minority carrier lifetime increases, diode reverse recovery deteriorates, and reverse recovery time increases. Therefore, increased temperature worsens the switching characteristics of semiconductor devices, requiring increased safety margins and a longer dead time for DC / DC converters.

[0078] Example 1:

[0079] This invention discloses a control method for a bidirectional DC / DC converter in an energy storage system, such as... Figure 5 As shown, the energy storage system includes a PCS unit, a DC / DC converter, a battery, and a DC / DC control unit. One end of the PCS unit is connected to the power grid / load, and the other end is connected to the battery through the DC / DC converter. The DC / DC converter is also connected to the DC / DC control unit. The method includes the following steps:

[0080] Detects battery voltage, battery current, and NTC temperature inside the DC / DC converter chip during charging / discharging.

[0081] When the battery voltage is in the low voltage range, the control bus voltage, the dead time of the DC / DC converter, and the switching frequency all operate in a fixed value mode.

[0082] When the battery voltage is in the high voltage range, the control bus voltage, the dead time of the DC / DC converter, and the switching frequency operate in dynamic changing modes. Specifically, the dynamic changing modes are the dynamic changing modes of dead time relative to battery current and NTC temperature inside the DC / DC converter chip, the dynamic changing modes of switching frequency relative to battery voltage, and the dynamic changing modes of bus voltage relative to battery voltage.

[0083] Example 2:

[0084] The control method for the bidirectional DC / DC converter of the energy storage system of the present invention includes the following steps:

[0085] When the battery voltage is in the low voltage range, the control bus voltage, the dead time of the DC / DC converter, and the switching frequency all operate in a fixed value mode, specifically as follows:

[0086] When the battery voltage is in the low voltage range Bus voltage Dead time of DC / DC converter and switching frequency The working mode is controlled as follows:

[0087]

[0088] When the battery voltage is in the high voltage range The control bus voltage, the dead time of the DC / DC converter, and the switching frequency operate in a dynamic changing mode, specifically as follows:

[0089] a. The dynamic variation mode of the dead time of the DC / DC converter is expressed as:

[0090] ;

[0091] b, The dynamic mode of the switching frequency of the DC / DC converter is expressed as:

[0092] ;

[0093] c. The dynamic change pattern of the bus voltage is represented as follows:

[0094] ;

[0095] In the formula, This is the lowest possible battery charge. These are inherent values; This is the battery's first voltage; This is the battery's highest voltage. The first switching frequency; This is the second switching frequency; The first voltage of the busbar; This is the highest voltage of the busbar; Set the dead time value;

[0096] This refers to the internal NTC temperature of the DC / DC converter chip. for The baseline value, This is the measured value of the switching transistor when the battery current is close to 0 at room temperature (25℃). For example, take the minimum measured value of the dead zone when it is 0.05~0.2A. It is the inverse proportionality coefficient of the battery current, determined through calibration experiments; The bias value is used to calibrate the battery current. The value is 0.05~0.2A; α is a temperature proportionality coefficient, which is determined through calibration experiments. According to the differences in the characteristics of the switching transistor, the value of α is usually 0.001~0.005 / ℃. The temperature calibration reference value is 25℃. ≥ , usually take ;

[0097] The first voltage of the battery after considering a 10% design margin Voltage loss; To account for the battery's maximum voltage after a 10% design margin Voltage loss;

[0098] Among them, the first switching frequency Take the maximum value of the switching frequency; second switching frequency Take the minimum switching frequency; the minimum battery voltage. This is an inherent value; the highest voltage of the busbar. It is a fixed value;

[0099] In the above formula, the highest voltage of the battery is... Calculated using the following formula:

[0100] ;

[0101] ;

[0102] In the formula, the highest voltage of the busbar Determined based on the maximum design value of the DC / DC converter; Calculated according to the formula in a;

[0103] First voltage of the bus Calculated using the following formula:

[0104] :

[0105] The first voltage of the battery Calculated using the following formula:

[0106] ;

[0107] .

[0108] Example 3:

[0109] This example uses the method from Example 2 for control, as detailed below:

[0110] According to battery voltage The difference in DC / DC converter control Piecewise linear control, and the DC / DC switching frequency also varies piecewise linearly across different battery ranges.

[0111] The first segment, namely the low-voltage segment:

[0112] ;

[0113] ;

[0114] ; ;

[0115] The second segment, namely the high-voltage segment:

[0116] ;

[0117] ;

[0118] ; ;

[0119] First segment:

[0120] ; ;

[0121] ; ;

[0122] ; ;

[0123] For the first switching frequency For 10kHz, the corresponding switching period Dead time is 100µs. The 4µs dead zone corresponds to the duty cycle loss. It is 4%, corresponding to voltage drop. It is 60V.

[0124] Second segment:

[0125] The first switching frequency is taken as the maximum switching transistor frequency. The second switching frequency is set to 10kHz, and the minimum switching frequency of the transistor is taken as the second switching frequency. The corresponding switching period is 5kHz. It is 200us. .

[0126] ; ;

[0127] Consider T NTC = 95℃, with = For example, 100A corresponds to the battery's highest voltage and dead time. The corresponding duty cycle loss due to the dead zone is 2.3µs. It is 1.15%. It is 17.25V.

[0128] in, , , α = 0.002 / ℃ The value is 25℃.

[0129] Voltage drop after considering a 10% design margin It is 66V. It is 19V.

[0130] In this example, the battery's minimum charge... The first voltage of the battery is 1000. 1415; First voltage Take 1.415 The highest voltage of the battery The value is 1481.

[0131] The maximum value of the function of bus voltage is the second maximum value of bus voltage, that is... Take 1500V; the highest voltage of the battery is the first voltage of the bus, that is... The minimum battery voltage is 1481V. =1000V, the first voltage of the battery If we take 1415V, then:

[0132] ; ;

[0133] ; .

[0134] Example 4:

[0135] Figure 6 In this invention, the DC / DC control unit in the control method includes a DSP digital processor, an FPGA chip, and a drive circuit. The control process of the DC / DC control unit is as follows:

[0136] DSP digital processor acquires battery voltage Battery current Feedback signal of bus voltage and NTC temperature inside DC / DC converter chip Output switch management theoretical duty cycle Switching frequency and dead zone time To FPGA chip;

[0137] The FPGA chip receives the signal, performs digital conversion to generate two center-aligned complementary PWM signals, and realizes the control of switching frequency, bus voltage and dead time.

[0138] Switching Theory Duty Cycle , Bus voltage This refers to the battery voltage.

[0139] DSP digital signal processor samples battery voltage Current and bus voltage and the internal NTC temperature of the DC / DC converter chip, including the bus voltage. This is the output voltage controlled by the DC / DC converter after calculation by the DSP. (Bus voltage) It is related to the battery voltage Related functions, switching frequency of DC / DC converter Also related to battery voltage Related functions. Through calculation and The ratio of DC / DC can be used to obtain the theoretical duty cycle. As shown in the following formula: .

[0140] The DSP digital signal processor, model TMS320F28335, is responsible for sampling battery voltage, battery current, and the internal NTC temperature of the DC / DC converter chip, as well as data processing, closed-loop control algorithms, and duty cycle. and switching frequency and dead zone time The calculation. Via SPI or parallel bus. Switching frequency and dead zone time The data is transmitted to the FPGA chip, model Xilinx Artix-7, with a data transmission delay of less than 1μs. The FPGA chip receives data from the inverted DSP digital signal processor, generates a complementary PWM signal with a programmable dead time, and implements the dead time. The insertion and dynamic switching frequency adjustment are also considered. The PWM system generated by the FPGA chip is amplified by the driver and then drives the DC / DC converter to adjust the bus voltage. adjust.

[0141] The DSP digital signal processor module processes input signals, including the input battery voltage. Battery current Output voltage And the internal NTC temperature of the DC / DC converter chip. Run the DC / DC voltage loop calculation and output the theoretical duty cycle. and calculate in real time Real-time calculation of switching frequency and transmit data in the form of data frames via the SPI bus. , and The data is sent to the FPGA. The DSP and FPGA are connected via a high-speed serial bus (SPI), with a data transmission delay of less than 1µs. The FPGA is based on the DSP output. , , Two center-aligned complementary PWM signals are generated, and a dead time is inserted. The rising edge interval between the two PWM signals is hard-wired to be no less than 1.5µs. The FPGA outputs the signals to the driver circuit via I / O ports. The driver circuit internally uses hardware interlocking to generate two complementary drive PWM signals for output to the DC / DC converter.

[0142] The DC / DC topology in the energy storage system can be a bidirectional Boost circuit or a Buck-boost circuit. Its key feature is enabling bidirectional energy flow, allowing for both charging and discharging of the battery.

[0143] Comparative Example 1:

[0144] This example is as follows: Figure 2 The two-stage energy storage system shown adopts existing technologies such as... Figure 4 The control method for the bidirectional DC / DC converter of the energy storage system is shown, in which the DC / DC converter controls the bus voltage. The switching frequency of the DC / DC converter is constant at 1500V. 10kHz, switching cycle Dead time is 100µs. It is 4µs. When the bus voltage At 1500V, the duty cycle loss due to dead time According to the following formula, the calculated value is 4%:

[0145] ;

[0146] Voltage drop caused by duty cycle loss due to dead time The value is calculated using the following formula, and the calculated value is 60V:

[0147] ;

[0148] Voltage loss at the highest battery voltage The value is calculated to be 66V using the following formula:

[0149] ;

[0150] When the bus voltage Set the minimum battery voltage value at 1500V. The maximum battery voltage is 1000V. The calculated value is 1434V using the following formula:

[0151] .

[0152] In this example, the voltage drop at the battery's highest voltage... It is 66V.

[0153] Conclusion: Compared with Comparative Example 1, the highest voltage of the battery in Embodiment 3 of the present invention is higher. Increasing the voltage from 1434V in Comparative Example 1 to 1481V reduces the voltage drop at the battery's maximum voltage from 66V in Comparative Example 1 to 19V. In Example 3, the voltage drop at the battery's maximum voltage is reduced by 71%, as detailed in Table 1 below. Meanwhile, the switching frequency in Example 3... and With battery voltage The frequency changes are linearly adjusted to make the frequency switching more natural, smooth and gentle.

[0154] Table 1: .

Claims

1. A control method for a bidirectional DC / DC converter in an energy storage system, the energy storage system comprising a PCS unit, a DC / DC converter, a battery, and a DC / DC control unit, wherein one end of the PCS unit is connected to the power grid / load, and the other end is connected to the battery via the DC / DC converter, and the DC / DC converter is also connected to the DC / DC control unit, characterized in that: The control steps are as follows: Detects battery voltage, battery current, and NTC temperature inside the DC / DC converter chip during charging / discharging. When the battery voltage is in the low voltage range, the control bus voltage, the dead time of the DC / DC converter, and the switching frequency all operate in a fixed value mode. When the battery voltage is in the high voltage range, the control bus voltage, the dead time of the DC / DC converter, and the switching frequency operate in dynamic changing modes. Specifically, the dynamic changing modes are the dynamic changing modes of the DC / DC converter dead time relative to the battery current and the NTC temperature inside the DC / DC converter chip, the dynamic changing modes of the switching frequency relative to the battery voltage, and the dynamic changing modes of the bus voltage relative to the battery voltage.

2. The control method for the bidirectional DC / DC converter of the energy storage system according to claim 1, characterized in that: When the battery voltage is in the low voltage range, the control bus voltage, the dead time of the DC / DC converter, and the switching frequency all operate in a fixed value mode, specifically as follows: When the battery voltage is in the low voltage range Bus voltage Dead time of DC / DC converter and switching frequency The working mode is controlled as follows: ； When the battery voltage is in the high voltage range The control bus voltage, the dead time of the DC / DC converter, and the switching frequency operate in a dynamic changing mode, specifically as follows: a. The dead time variation pattern of the DC / DC converter is expressed as follows: ； b, The dynamic mode of the switching frequency of the DC / DC converter is expressed as: ； c, The variation pattern of the bus voltage is represented as follows: ； In the formula, This is the lowest possible battery charge. These are inherent values; This is the battery's first voltage; This is the battery's highest voltage. The first switching frequency; This is the second switching frequency; The first voltage of the busbar; This is the highest voltage of the busbar; Set the dead time value; This refers to the internal NTC temperature of the DC / DC converter chip. for The baseline value; This is the inverse proportionality coefficient of the battery current; This is the battery current calibration bias value; α is the temperature proportionality coefficient. This is a temperature calibration reference value; The first voltage of the battery after considering a 10% design margin Voltage loss; To account for the battery's maximum voltage after a 10% design margin Voltage loss; Among them, the first switching frequency Take the maximum value of the switching frequency; second switching frequency Take the minimum switching frequency; the minimum battery voltage. This is an inherent value; the highest voltage of the busbar. It is a constant value; In the above formula, the highest voltage of the battery is... Calculated using the following formula: ； ； In the formula, the highest voltage of the busbar Determined based on the maximum design value of the DC / DC converter; Calculated according to the formula in a; First voltage of the bus Calculated using the following formula: ： The first voltage of the battery Calculated using the following formula: ； 。 3. The control method for the bidirectional DC / DC converter of the energy storage system according to claim 2, characterized in that, The first switching frequency The second switching frequency The relationship is as follows: .

4. The control method for the bidirectional DC / DC converter of the energy storage system according to claim 2, characterized in that, The first voltage The value ranges from 1.2 to 1.

45. .

5. The control method for the bidirectional DC / DC converter of the energy storage system according to claim 1, characterized in that, The DC / DC control unit includes a DSP digital processor, an FPGA chip, and a drive circuit. The control process of the DC / DC control unit is as follows: DSP digital processor acquires battery voltage Battery current Feedback signal of bus voltage and NTC temperature inside DC / DC converter chip Output switch management theoretical duty cycle Switching frequency and dead zone time To FPGA chip; The FPGA chip receives the signal, performs digital conversion to generate two center-aligned complementary PWM signals, and realizes the control of switching frequency, bus voltage and dead time.

6. The control method for the bidirectional DC / DC converter of the energy storage system according to claim 5, characterized in that, Switching Theory Duty Cycle , Bus voltage This refers to the battery voltage.

7. An energy storage system, characterized in that, A control method for implementing the bidirectional DC / DC converter of the energy storage system described in claims 1-6.

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