DC / DC converter parallel control method and device

Abstract

The application discloses a DC / DC converter parallel control method and device, and belongs to the technical field of converter control. The method collects voltage signals and current signals of DC / DC converters and current signals of energy storage units, and calculates the state of charge of the energy storage units; the state of charge of the energy storage units is used to correct droop coefficients, and finally the corresponding voltage signals of the converters are obtained, and PWM signals are generated to control the on-off of power switches in the corresponding converters. According to the state of charge of the energy storage units, the droop coefficients are corrected, the power of the energy storage units is reasonably distributed, and mode switching is realized, the switching frequency between the shutdown mode and the droop control mode of the energy storage units is reduced, the loss caused by switching is reduced, and the service life of the energy storage units is prolonged. Meanwhile, a secondary voltage compensation method is introduced in the voltage output process, and the problem of large voltage overshoot during parallel connection is solved through voltage-current double-loop control.

Description

Technical Field

[0001] This invention relates to the field of converter control technology, and in particular to a method and apparatus for parallel control of DC / DC converters. Background Technology

[0002] Distributed generation of new energy sources is of great significance to building my country's energy security strategy, and energy storage systems play a crucial role in distributed generation systems. In DC microgrids, energy storage systems significantly improve system stability and reliability. Most energy storage units are connected to the DC microgrid via DC / DC converters, but often multiple DC / DC converters need to be connected in parallel to improve capacity, redundancy, and security. Figure 1 As shown, a key technology for parallel operation of DC / DC converters is droop control. Domestic and international experts and scholars have conducted a series of studies on improving droop control strategies based on traditional droop control. Commonly used methods include: droop curve shifting method, fuzzy algorithm compensation method, and low-speed communication adjustment of droop coefficient method. However, most of these methods do not consider the actual state of charge of the energy storage unit on the adjustment of the droop coefficient, fail to fully realize the rational allocation of energy storage unit power, and cannot reduce the switching frequency between energy storage unit shutdown mode and droop control mode, thus failing to reduce the losses caused by switching. Furthermore, the problems of output voltage accuracy of the DC / DC converter in islanded mode and large voltage overshoot during parallel operation have not been effectively solved.

[0003] While patent CN110649590A, "A Networked DC Microgrid Energy Coordination Control Method," uses an adaptive adjustment method for the droop coefficient, it fails to consider situations where the initial State of Charge (SOC) of the energy storage unit is not within the limits mentioned in the paper, or where the instantaneous change in SOC during the switching between shutdown and droop modes causes the SOC to deviate from the limits. For example, when the SOC is above 90%, charging should not be performed, but discharging should be; when the SOC is below 20%, discharging should not be performed, but charging should be. However, the improved droop coefficient method in this patent results in a negative droop coefficient in these situations, leading to extreme instability of the system and causing different energy storage units within the same system to have positive droop coefficients. Negative values ​​can cause system crashes; patent CN111864852A, "A Method and System for Controlling the Charging and Discharging of Lithium Batteries in a Photovoltaic Power Generation System," does not consider incorporating the droop coefficient into the control strategy and fails to achieve reasonable power distribution when multiple converters are connected in parallel; patent CN113394804A, "A Method for SOC Equalization and Power Sharing Control of DC Microgrid Energy Storage System," introduces the droop coefficient, but the energy storage units it considers must have the same capacity; patent CN115588977A, "An Improved Power-Oriented SOC Coordination Control Method Based on Model Predictive Control," combines SOC with the droop coefficient, but has high communication requirements and does not reduce the losses caused by mode switching of energy storage units.

[0004] Furthermore, for the droop control method of parallel DC / DC converters, it is required that the instantaneous change of the SOC of the energy storage unit is small when the DC / DC converters are connected in parallel. Traditional droop control methods cannot meet the requirements, that is, the dynamic performance of the system is poor, and the output voltage quality is also reduced.

[0005] Therefore, existing parallel control methods for DC / DC converters suffer from problems such as large instantaneous changes in the SOC of the energy storage unit during parallel operation, low accuracy of the DC / DC converter output voltage, non-adaptive adjustment of power distribution, low output voltage quality, and poor system dynamic performance. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a parallel control method and apparatus for DC / DC converters, thereby solving the problem of large instantaneous changes in the SOC of energy storage units during parallel operation in islanded mode using traditional droop control methods.

[0007] To achieve the above objectives, this invention provides a parallel control method for a DC / DC converter, applied to a DC / DC converter N. j The positive and negative input terminals and the energy storage unit ESU j Connecting the positive and negative terminals involves the following steps:

[0008] (1) Acquire DC / DC converter N j The first voltage signal U at both ends dcj DC / DC converter N j The first output current signal i dcj and energy storage unit ESU j The output second current signal i Lj And calculate the ESU of the energy storage unit. j SOC signal j ;

[0009] (2) Based on the energy storage unit ESU j SOC signal j Calculate the droop coefficient correction amount and perform adaptive correction on the droop coefficient;

[0010] (3) Based on the first voltage signal U dcj First current signal i dcj Second current signal i Lj And with the corrected droop coefficient, the corresponding DC / DC converter N is obtained. j The output voltage signal is used to generate the first PWM signal;

[0011] (4) Determine the energy storage unit ESU jOperating mode, and according to the energy storage unit ESU j The operating mode and the first PWM signal generate a second PWM signal, i.e., a drive signal, which is output to the corresponding DC / DC converter N. j The switching transistor in the middle controls its on / off state.

[0012] Furthermore, step 2 specifically includes:

[0013] (2.1) Calculate the output power P of the total energy storage unit ESU_ref That is, the third power signal;

[0014]

[0015] (2.2) Based on the energy storage unit ESU j SOC signal j Calculate the droop coefficient correction amount;

[0016] (2.2.1) When SOC j <SOC j_min At this time, it is located in the lower discharge limit region, and the energy storage unit ESU j Charging is allowed only;

[0017] If P ESU_ref <0, at this time the energy storage unit ESU j If it is charging, then:

[0018] ΔR j (SOC j )=-R SOC

[0019] If P ESU_ref If the value is >0, then the energy storage unit ESU is disabled. j Discharge;

[0020] (2.2.2) When SOC j_min <SOC j <SOC j_low At this time, the energy storage unit ESU is controlled according to the basic principle of minimizing discharge and maximizing charging, while remaining in the discharge warning zone. j The output of [the system] slows down its SOC. j decline;

[0021] If P ESU_ref <0, then:

[0022]

[0023] If P ESU_ref >0, then:

[0024]

[0025] (2.2.3) When SOC j_low <SOC j <SOC j_high If the system is in the normal operating range at this time, then the energy storage unit ESU will not be activated. j After adjusting the initial droop coefficient, then:

[0026] ΔR j (SOC j ) = 0

[0027] (2.2.4) When SOC j_high <SOC j <SOC j_max At this time, the energy storage unit ESU is located in the charging warning zone and is controlled according to the basic principle of discharging more and charging less. j The output of [the system] slows down its SOC. j The rise;

[0028] If P ESU_ref <0, then:

[0029]

[0030] If P ESU_ref >0, then:

[0031]

[0032] (2.2.5) When SOC j_max <SOC j At this time, it is located in the upper limit charging zone, and the energy storage unit ESU j Discharge is permitted only;

[0033] If P ESU_ref If the value is less than 0, then the energy storage unit ESU is disabled. j Charge;

[0034] If P ESU_ref If the value is greater than 0, the energy storage unit is discharging at this time. Therefore:

[0035] ΔR j (SOC j )=-R soc

[0036] (2.2.6) The droop coefficient correction amount is compared with the initial droop coefficient R. 0j Summing yields the corrected droop coefficient R. j .

[0037] (2.3) Based on the calculated droop coefficient correction amount ΔR j (SOC jAdaptive correction to the droop coefficient:

[0038] R j =R 0j +ΔR j (SOC j )

[0039] Where: P DCPS The power of the DC power supply that injects power into the system, SOC j_max For the energy storage unit ESU j SOC j Charging limit, SOC j_high For the energy storage unit ESU j SOC j Charging warning value, SOC j_min For the energy storage unit ESU j SOC j Lower discharge limit, SOC j_low For the energy storage unit ESU j SOC j Discharge warning value, R soc R is the maximum correction magnitude of the droop coefficient. 0j This is the initial droop coefficient.

[0040] Furthermore, step 3 specifically includes:

[0041] (3.1) Given the rated voltage signal U of the bus dcref Combine it with the first voltage signal U dcj The difference between the two error signals is then subjected to proportional-integral control to obtain the second voltage signal.

[0042] (3.2) The corrected droop coefficient R j The third voltage signal is obtained by multiplying the first current signal by the voltage signal.

[0043] (3.3) The rated voltage signal U of the busbar dcref Subtracting the third voltage signal from the fourth voltage signal yields the fourth voltage signal.

[0044] (3.4) The signal obtained by adding the fourth voltage signal and the second voltage signal is compared with the first voltage signal U. dcj The error signal is subjected to proportional-integral control to output a fifth voltage signal; the fifth voltage signal is then compared with the second current signal i. Lj The error signal is used for proportional-integral control to output a sixth voltage signal;

[0045] (3.5) Generate a PWM1 signal based on the sixth voltage signal, and generate a complementary signal PWM2 signal from the PWM1 signal. The PWM1 signal and the PWM2 signal are combined to form the first PWM signal.

[0046] Furthermore, in step 4, the energy storage unit ESU is determined. j The specific methods for the working mode are as follows:

[0047] When the energy storage unit ESU j The system is in a shutdown state under the following three conditions:

[0048] When the third power signal P ESU_ref Less than 0, and the energy storage unit ESU j SOC j Greater than or equal to SOC j_max hour;

[0049] When the third power signal P ESU_ref Greater than 0, and the energy storage unit ESU j SOC j Less than or equal to SOC j_min hour;

[0050] When the first current signal i dcj When the current exceeds the preset current threshold;

[0051] In addition, the energy storage unit ESU j All are in operation;

[0052] The specific output PWM second signal, i.e., the drive signal, is as follows:

[0053] When the energy storage unit ESU j When in working condition, the output PWM second signal is equal to the PWM first signal;

[0054] When the energy storage unit ESU j When the machine is in a stopped state, the output PWM second signal is equal to a constant 0, which controls the switching transistor to turn off.

[0055] This invention also provides a parallel control device for a DC / DC converter, comprising a common-side constant power load, several sets of control drive units, and several sets of DC / DC converter controlled units; the output terminals of the several sets of DC / DC converter controlled units are connected in parallel and all connected to the common-side constant power load; each set of control drive units is connected to each set of DC / DC converter controlled units in a one-to-one correspondence; the DC / DC converter N j The positive and negative input terminals and the energy storage unit ESU jThe positive and negative terminals are connected together. The control and drive unit includes a sensor assembly, a SOC and total energy storage unit output power calculation module, an adaptive droop coefficient calculation module, a PWM signal generation module, and a DSP control and energy storage unit working mode selection module.

[0056] The sensor assembly is used to collect data from the DC / DC converter N. j The first voltage signal U at both ends dcj DC / DC converter N j The first output current signal i dcj and energy storage unit ESU j The output second current signal i Lj ;

[0057] The SOC and total energy storage unit output power calculation module is connected to the sensor assembly and is used to calculate the energy storage unit ESU. j SOC signal j and total energy storage unit output power P ESU_ref ;

[0058] The adaptive droop coefficient calculation module is connected to the SOC and the total energy storage unit output power calculation module, and is used to adaptively correct the droop coefficient based on the calculated droop coefficient correction amount.

[0059] The PWM signal generation module is connected to the sensor component and the adaptive droop coefficient calculation module to generate a first PWM signal;

[0060] The DSP control and energy storage unit operating mode selection module is connected to the sensor assembly, the SOC and total energy storage unit output power calculation module, and the drive signal generation module, and is used to determine the energy storage unit ESU. j Operating mode, and according to the energy storage unit ESU j The operating mode modifies the first PWM signal to obtain the second PWM signal, which is the drive signal.

[0061] Furthermore, the sensor assembly includes a voltage sensor, a first current sensor, and a second current sensor; the voltage sensor is connected to the corresponding DC / DC converter N in the DC / DC converter controlled unit. j Parallel connection, used to acquire the DC / DC converter N j The output voltage signal at both ends, i.e., the first voltage signal; the first current sensor is connected in series in the corresponding DC / DC converter controlled unit converter N. j The first output terminal is used to acquire the corresponding DC / DC converter N. jThe output current signal, i.e., the first current signal; the second current sensor is connected in series in the corresponding energy storage unit ESU of the DC / DC converter controlled unit. j Positive terminal and DC / DC converter N j Between the positive input terminals, the energy storage unit ESU in the controlled unit of the DC / DC converter is collected. j The output current signal, i.e. the second current signal.

[0062] Furthermore, the SOC and total energy storage unit output power calculation module includes a DSP control and SOC calculation module and a total energy storage unit output power calculation module.

[0063] The DSP control and SOC calculation module is connected to the second current sensor and is used to control the energy storage unit (ESU) in the corresponding controlled unit of the DC / DC converter. j The second current signal output is used for calculation to obtain the corresponding energy storage unit ESU in the controlled unit of the DC / DC converter. j SOC signal;

[0064] The total energy storage unit output power calculation module is connected to the voltage sensor, and calculates the power P of the DC power supply based on the first voltage signal, the given common-side constant power load impedance R, and the given system injection power. DCPS The total output power of the energy storage unit is calculated.

[0065] Furthermore, the adaptive droop coefficient calculation module includes a DSP control and droop coefficient correction calculation module and an initial droop coefficient setting submodule;

[0066] The DSP control and droop coefficient correction calculation module is connected to the SOC and total energy storage unit output power calculation module, and is used to calculate the droop coefficient correction; the initial droop coefficient setting submodule is used to set the corresponding DC / DC converter N. j The initial droop coefficient R 0j ;R 0j The corrected droop coefficient output by the adaptive droop coefficient calculation module is obtained by summing the output of the DSP control and droop coefficient correction calculation module.

[0067] The specific amount of the droop coefficient correction is:

[0068] (1) When SOC j <SOC j_min At this time, it is located in the lower discharge limit region, and the energy storage unit ESU j Charging is allowed only;

[0069] If P ESU_ref <0, at this time the energy storage unit ESUj If it is charging, then:

[0070] ΔR j (SOC j )=-R SOC

[0071] If P ESU_ref If the value is >0, then the energy storage unit ESU is disabled. j Discharge;

[0072] (2) When SOC j_min <SOC j <SOC j_low At this time, the energy storage unit ESU is controlled according to the basic principle of minimizing discharge and maximizing charging, while remaining in the discharge warning zone. j The output of [the system] slows down its SOC. j decline;

[0073] If P ESU_ref <0, then:

[0074]

[0075] If P ESU_ref >0, then:

[0076]

[0077] (3) When SOC j_low <SOC j <SOC j_high If the system is in the normal operating range at this time, then the energy storage unit ESU will not be activated. j After adjusting the initial droop coefficient, then:

[0078] ΔR j (SOC j ) = 0

[0079] (4) When SOC j_high <SOC j <SOC j_max At this time, the energy storage unit ESU is located in the charging warning zone and is controlled according to the basic principle of discharging more and charging less. j The output of [the system] slows down its SOC. j The rise;

[0080] If P ESU_ref <0, then:

[0081]

[0082] If P ESU_ref >0, then:

[0083]

[0084] (5) When SOC j_max <SOC j At this time, it is located in the upper limit charging zone, and the energy storage unit ESU j Discharge is permitted only;

[0085] If P ESU_ref If the value is less than 0, then the energy storage unit ESU is disabled. j Charge;

[0086] If P ESU_ref If the value is greater than 0, the energy storage unit is discharging at this time. Therefore:

[0087] ΔR j (SOC j )=-R soc

[0088] (6) The droop coefficient correction amount is compared with the initial droop coefficient R. 0j Summing yields the corrected droop coefficient R. j .

[0089] Where: P ESU_ref The total output power of the energy storage unit, SOC j_max For the energy storage unit ESU j SOC j Charging limit, SOC j_high For the energy storage unit ESU j SOC j Charging warning value, SOC j_min For the energy storage unit ESU j SOC j Lower discharge limit, SOC j_low For the energy storage unit ESU j SOC j Discharge warning value, R soc This is the maximum correction magnitude for the droop coefficient.

[0090] Furthermore, the PWM signal generation module includes a bus rated voltage submodule, a first voltage PI control submodule, a second voltage PI control submodule, a current PI control module, and the PWM generation submodule;

[0091] The bus rated voltage submodule is used to provide the bus rated voltage signal U of the DC / DC converter parallel control device. dcref ;

[0092] The bus rated voltage signal U dcrefThe error signal obtained by subtracting the first voltage signal output by the voltage sensor is input to the first voltage PI control submodule for proportional-integral control, and the second voltage signal is output.

[0093] The first current signal output by the first current sensor is multiplied by the corrected droop coefficient output by the adaptive droop coefficient calculation module to obtain the third voltage signal; the bus rated voltage signal U of the bus rated voltage submodule. dcref The difference between the voltage signal and the third voltage signal is used to obtain the fourth voltage signal; the error signal between the fourth voltage signal and the second voltage signal and the first voltage signal is input to the second voltage PI control submodule for proportional-integral control, and the fifth voltage signal is output.

[0094] The error signal between the fifth voltage signal and the second current signal is input to the current PI control module for proportional-integral control, and a sixth voltage signal is output.

[0095] The PWM generation submodule is connected to the current PI control module. The PWM generation submodule is used to generate a PWM1 signal based on the sixth voltage signal; and to generate a complementary signal PWM2 signal from the PWM1 signal. The PWM1 signal and the PWM2 signal are combined to form the first PWM signal.

[0096] Furthermore, the DSP control and energy storage unit operating mode selection module determines the energy storage unit ESU. j The specific working mode is as follows:

[0097] When the energy storage unit ESU j The system is in a shutdown state under the following three conditions:

[0098] When the third power signal P ESU_ref Less than 0, and the energy storage unit ESU j SOC j Greater than or equal to SOC j_max hour;

[0099] When the third power signal P ESU_ref Greater than 0, and the energy storage unit ESU j SOC j Less than or equal to SOC j_min hour;

[0100] When the first current signal i dcj When the current exceeds the preset current threshold;

[0101] In addition, the energy storage unit ESU j All are in operation;

[0102] The generation of the second PWM signal is specifically as follows:

[0103] When the energy storage unit ESU j When in operation, the second PWM signal is equal to the first PWM signal;

[0104] When the energy storage unit ESU j When the machine is in a stopped state, the second PWM signal is equal to a constant 0, which controls the switching transistor to turn off.

[0105] The beneficial effects of this invention are:

[0106] This invention acquires the output voltage and current signals of the converter and the output current signal of the energy storage unit in the controlled unit of the corresponding DC / DC converter. It calculates the state of charge (SOC) of the energy storage unit based on its output current signal, calculates the droop coefficient based on the SOC, corrects the droop coefficient, and finally obtains the corresponding converter output voltage signal. A PWM signal is generated from this voltage signal and used to control the on / off state of the power switches in the corresponding converter. Simultaneously, a secondary voltage compensation device is introduced in the process of calculating the converter output voltage signal based on the droop coefficient and generating the PWM signal to improve output voltage accuracy and ensure output voltage quality. Furthermore, adaptive droop coefficient setting enables reasonable power allocation of the energy storage unit, and adaptive operating mode switching allows the energy storage unit to switch between shutdown and droop control based on its SOC, improving its lifespan. The use of dual-loop voltage and current control solves the problem of large voltage overshoot during parallel operation. Attached Figure Description

[0107] Figure 1 This is a structural block diagram of the parallel control device for DC / DC converters according to an embodiment of the present invention.

[0108] Figure 2 This is a circuit topology diagram of the controlled unit of the DC / DC converter according to an embodiment of the present invention.

[0109] Figure 3 This is a circuit topology diagram of a DC / DC converter according to an embodiment of the present invention.

[0110] Figure 4 This is a flowchart illustrating the parallel control method for DC / DC converters according to an embodiment of the present invention.

[0111] Figure 5 This is a schematic diagram illustrating the principle of the SOC droop coefficient correction strategy in an embodiment of the present invention.

[0112] Figure 6 This is a circuit topology diagram of the control drive unit according to an embodiment of the present invention.

[0113] Figure 7 This is a waveform diagram of a supercapacitor (with a high SOC) connected in parallel with a lead-acid battery according to an embodiment of the present invention.

[0114] Figure 8 This is a waveform diagram of the output current during the switching of the supercapacitor (high SOC) mode in an embodiment of the present invention.

[0115] Figure 9 This is a waveform diagram of a supercapacitor (low SOC) / lead-acid battery connected in parallel according to an embodiment of the present invention.

[0116] Figure 10 This is a waveform diagram of the output current during the switching of the supercapacitor (low SOC) mode in an embodiment of the present invention.

[0117] Figure 11 The waveform diagram for parallel connection of supercapacitor / lead-acid battery in an embodiment of the present invention is shown in the traditional droop control waveform diagram.

[0118] Figure 12 The diagram shows the overall waveform of two DC / DC converters connected in parallel (when the supercapacitor has a high SOC) according to an embodiment of the present invention.

[0119] Figure 13 The diagram shows the voltage waveform of the parallel bus of two DC / DC converters (when the supercapacitor has a high SOC) in an embodiment of the present invention. Detailed Implementation

[0120] The following describes this embodiment in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0121] The present invention will be further explained below with reference to the accompanying drawings and embodiments.

[0122] Currently, most energy storage units are connected to DC microgrids via DC / DC converters, and often multiple DC / DC converters need to be connected in parallel to improve capacity, redundancy, and security. Parallel control of DC / DC converters is a key technology in this regard. For example... Figure 1 As shown, the output terminals of several groups of DC / DC converter controlled units 20 are connected in parallel and all connected to the common side constant power load 10; each group of control drive units 30 is connected to each group of DC / DC converter controlled units 20 in a one-to-one correspondence.

[0123] Figure 2 This is an equivalent circuit diagram of multiple DC / DC converters connected in parallel. As shown in the figure, each group of DC / DC converter controlled units 20 includes: an energy storage unit (ESU). jDC / DC converter N j Filter capacitor C j and line impedance L linej Among them, the filter capacitor C j The capacitor is non-polarized, the constant power load on the common side is 10, and the variable load is L. line1 To L linej The value of j is relatively small, and j takes a value greater than 1 and is an integer.

[0124] Energy Storage Unit (ESU) j The positive and negative terminals of the DC / DC converter N j Connect the positive and negative input terminals of the DC / DC converter N. j First output terminal and line impedance L linej The first end is connected to the filter capacitor C j The first terminal is connected to the DC / DC converter N. j The second output terminal and the filter capacitor C j The second terminal connection; the line impedance L in each group of DC / DC converter controlled units 20 linej The second end is connected to the filter capacitor C in each group of DC / DC converter controlled units 20, which has a first node. j The second end is connected to the second node, and the two ends of the common side constant power load 10, i.e., load R, are connected to the first node and the second node respectively.

[0125] like Figure 3 As shown, DC / DC converter N j Includes: Inductor L j Two metal-oxide-semiconductor field-effect transistors (MOSFETs) or insulated-gate bipolar transistors (IGBTs) Q1 and Q2, and two diodes D1 and D2; DC / DC converter N. j The positive and negative input terminals are connected to the energy storage unit ESU in the controlled unit 20 of the DC / DC converter. j Connect the positive and negative terminals, inductor L j The first terminal is connected to the DC / DC converter N j Connect the positive input terminal to the inductor L. j The second terminal is connected to the first terminal of switch Q1 and the second terminal of switch Q2, the second terminal of diode D1 and the first terminal of diode D2, and the second terminal of switch Q1 is connected to the first terminal of diode D1 and the DC / DC converter N. j The negative input terminal and its negative output terminal are connected together. The first terminal of the switch Q2 is connected to the second terminal of the diode D2 and the DC / DC converter N. j Connect the positive output terminal.

[0126] Taking two DC / DC converters as an example, the energy storage units ESU1 and ESU2 in the main circuit can be connected first, and then the control drive unit 30 can be powered on. The control drive unit 30 controls the corresponding switching transistors Q1 and Q2 to turn on and off, thereby realizing the parallel connection of multiple DC / DC converters.

[0127] This invention provides a parallel control method for DC / DC converters, such as... Figure 4 As shown, the specific steps include the following:

[0128] S101, Acquisition DC / DC converter N j The first voltage signal U at both ends dcj DC / DC converter N j The first output current signal i dcj and energy storage unit ESU j The output second current signal i Lj And calculate the ESU of the energy storage unit. j SOC signal j ;

[0129] Among them, the energy storage unit ESU j SOC signal j The calculation is as follows:

[0130]

[0131] Among them, SOC j For energy storage unit ESU j Current state of charge, SOC j0 For energy storage unit ESU j The initial state of charge, C bat For energy storage unit ESU j The capacity.

[0132] S102, Based on the energy storage unit ESU j SOC signal j Calculate the droop coefficient correction amount and perform adaptive correction on the droop coefficient;

[0133] First, we need to calculate the output power P of the total energy storage unit. ESU_ref That is, the third power:

[0134]

[0135] Where: P DCPS The power of the DC power supply that injects power into the system.

[0136] like Figure 5 As shown, through the energy storage unit ESU j SOC signalj Calculate the droop coefficient correction amount ΔR j (SOC j Specifically:

[0137] (1) When SOC j <SOC j_min At this time, it is located in the lower discharge limit region, and the energy storage unit ESU j Charging is permitted, and during charging, the energy storage unit should absorb as much power as possible.

[0138] If P ESU_ref <0, at this time the energy storage unit ESU j While charging, to minimize the sag coefficient and accelerate the charging speed, the following should be considered:

[0139] ΔR j (SOC j )=-R SOC

[0140] If P ESU_ref If the value is >0, then the energy storage unit ESU is disabled. j During discharge, the power release task is undertaken by other energy storage units;

[0141] (2) When SOC j_min <SOC j <SOC j_low At this time, the energy storage unit ESU is controlled according to the basic principle of minimizing discharge and maximizing charging, while remaining in the discharge warning zone. j The output of [the system] slows down its SOC. j decline;

[0142] If P ESU_ref If the droop coefficient is less than 0, the droop factor should be reduced.

[0143]

[0144] If P ESU_ref If the droop coefficient is greater than 0, the droop coefficient should be increased.

[0145]

[0146] (3) When SOC j_low <SOC j <SOC j_high If the system is in the normal operating range at this time, then the energy storage unit ESU will not be activated. j If the initial droop factor is adjusted to maintain its original droop factor during power distribution, then:

[0147] ΔR j (SOC j ) = 0

[0148] (4) When SOC j_high <SOC j <SOC j_max At this time, the energy storage unit ESU is located in the charging warning zone and is controlled according to the basic principle of discharging more and charging less. j The output of [the system] slows down its SOC. j The rise;

[0149] If P ESU_ref If the droop coefficient is less than 0, the droop factor should be increased.

[0150]

[0151] If P ESU_ref If the droop coefficient is greater than 0, the droop factor should be reduced.

[0152]

[0153] (5) When SOC j_max <SOC j At this time, it is in the upper limit charging zone, and the energy storage unit ESU j Discharge is permitted, and during discharge, the energy storage unit should output as much power as possible.

[0154] If P ESU_ref If the value is less than 0, then the energy storage unit ESU is disabled. j Charging is handled by other parallel energy storage units that absorb power.

[0155] If P ESU_ref If the droop coefficient is greater than 0, the energy storage unit is discharging. Therefore, the droop coefficient should be minimized to accelerate its discharge rate.

[0156] ΔR j (SOC j )=-R soc

[0157] Where: P ESU_ref The total output power of the energy storage unit, SOC j_max For energy storage unit ESU j SOC j Charging limit, SOC j_high For energy storage unit ESU j SOC j Charging warning value, SOC j_min For energy storage unit ESU j SOC j Lower discharge limit, SOC j_low For energy storage unit ESU j SOC jDischarge warning value, R soc This represents the maximum correction magnitude for the droop coefficient.

[0158] Based on the calculated droop coefficient correction amount ΔR j (SOC j Adaptive correction to the droop coefficient:

[0159] R j =R 0j +ΔR j (SOC j )

[0160] Where: R 0j This is the initial droop coefficient.

[0161] S103, based on the first voltage signal U dcj First current signal i dcj Second current signal i Lj And with the corrected droop coefficient, the corresponding DC / DC converter N is obtained. j The output voltage signal is used to generate the first PWM signal;

[0162] (1) Given the rated bus voltage signal U dcref Combine it with the first voltage signal U dcj The difference between the two error signals is then subjected to proportional-integral control to obtain the second voltage signal.

[0163] (2) The corrected droop coefficient R j The third voltage signal is obtained by multiplying the first current signal by the voltage signal.

[0164] (3) The rated voltage signal U of the busbar dcref Subtracting the third voltage signal from the fourth voltage signal yields the fourth voltage signal.

[0165] (4) The signal obtained by adding the fourth voltage signal and the second voltage signal is compared with the first voltage signal U. dcj The error signal is subjected to proportional-integral control to output a fifth voltage signal; the fifth voltage signal is then compared with the second current signal i. Lj The error signal is used for proportional-integral control to output a sixth voltage signal;

[0166] (5) Generate a PWM1 signal based on the sixth voltage signal, and generate a complementary signal PWM2 signal from the PWM1 signal. The PWM1 signal and the PWM2 signal are combined to form the first PWM signal.

[0167] S104, Determine the energy storage unit ESU j Operating mode, and according to the energy storage unit ESU jThe operating mode and the first PWM signal generate a second PWM signal, i.e., a drive signal, which is output to the corresponding DC / DC converter N. j The switching transistor in the middle controls its on / off state.

[0168] When the energy storage unit ESU j The system is in a shutdown state under the following three conditions:

[0169] When the third power signal P ESU_ref Less than 0, and the energy storage unit ESU j SOC j Greater than or equal to SOC j_max hour;

[0170] When the third power signal P ESU_ref Greater than 0, and the energy storage unit ESU j SOC j Less than or equal to SOC j_min hour;

[0171] When the first current signal i dcj When the current exceeds the preset current threshold;

[0172] In addition, the energy storage unit ESU j All are in operation;

[0173] According to the energy storage unit ESU j The specific output PWM second signal, i.e., the drive signal, in the working mode is as follows:

[0174] When the energy storage unit ESU j When in working condition, the output PWM second signal is equal to the PWM first signal;

[0175] When the energy storage unit ESU j When in the shutdown state, the output PWM second signal is equal to a constant 0.

[0176] This invention also provides another embodiment of a parallel control device for DC / DC converters, including a common-side constant power load 10, a plurality of control drive units 30, and a plurality of DC / DC converter controlled units 20; the output terminals of the plurality of DC / DC converter controlled units 20 are connected in parallel and are all connected to the common-side constant power load 10; each control drive unit 30 is connected to each DC / DC converter controlled unit 20 in a one-to-one correspondence; DC / DC converter N j The positive and negative input terminals and the energy storage unit ESU j Connect the positive and negative terminals.

[0177] like Figure 6As shown, the control drive unit 30 includes a sensor assembly 31, a SOC and total energy storage unit output power calculation module 32, an adaptive droop coefficient calculation module 33, a PWM signal generation module 34, and a DSP control and energy storage unit operating mode selection module 35.

[0178] Sensor assembly 31 includes a voltage sensor 311, a first current sensor 312, and a second current sensor 313, used to collect data from the DC / DC converter N. j The first voltage signal U at both ends dcj DC / DC converter N j The first output current signal i dcj and energy storage unit ESU j The output second current signal i Lj .

[0179] Specifically, the voltage sensor 311 and the corresponding filter capacitor C in the controlled DC / DC converter 20 j In parallel connection, the voltage sensor 311 is used to acquire the voltage of the filter capacitor C in the corresponding DC / DC converter controlled unit 20. j The first voltage signal at both ends; the first current sensor 312 is connected in series in the corresponding DC / DC converter controlled unit 20 converter N. j First output terminal and line impedance L linej Between these points, the first current sensor 312 is used to acquire the current of the intermediate converter N in the corresponding DC / DC converter controlled unit 20. j The output current signal, i.e., the first current signal; the second current sensor 313 is connected in series in the corresponding DC / DC converter controlled unit 20, in the energy storage unit ESU. j Positive terminal and DC / DC converter N j Between the positive input terminals, the second current sensor 313 is used to collect data from the energy storage unit ESU in the corresponding DC / DC converter controlled unit 20. j The output current signal, i.e., the second current signal;

[0180] The SOC and total energy storage unit output power calculation module 32 includes a DSP control and SOC calculation module 321 and a total energy storage unit output power calculation module 322. The DSP control and SOC calculation module 321 is connected to the second current sensor 313. This DSP control and SOC calculation module 322 is used to calculate the output power of the energy storage unit ESU in the corresponding DC / DC converter controlled unit 20. j The output second current signal is digitally processed and calculated to obtain the corresponding energy storage unit ESU in the controlled unit 20 of the DC / DC converter. j SOC signal jThe total energy storage unit output power calculation module 322 is connected to the voltage sensor 311. Based on the first voltage signal, the given common-side constant power load impedance R, and the given system injected power, the DC power supply power P is calculated. DCPS The total output power of the energy storage unit was calculated.

[0181] The adaptive droop coefficient calculation module 33 includes: a DSP control and droop coefficient correction calculation module 331 and an initial droop coefficient setting submodule 332. The DSP control and droop coefficient correction calculation module 331 is connected to the output of the DSP control and SOC calculation module 32, and is used to determine the ESU of different energy storage units. j Different SOC j Sag correction ΔR under signal j (SOC j The initial droop coefficient is given by submodule 332, which is used to give the corresponding DC / DC converter N. j The initial droop coefficient R 0j The initial droop coefficient given by submodule 332 is R. 0j The droop correction amount ΔR output by the DSP control and droop correction calculation module 331 j (SOC j The sum of these values ​​yields the output of the adaptive droop coefficient calculation module 33, which is the corrected droop coefficient R. j .

[0182] Specifically, this module is mainly based on different energy storage units (ESU). j Different SOC j Calculate the corresponding DC / DC converter N j The droop coefficient R j And according to the energy storage unit ESU j SOC j The change in the droop coefficient R in real time j Make corrections. ESU j Different SOCs j It is divided into 5 working zones: the upper limit charging zone, the charging warning zone, the normal discharge zone, the discharge warning zone, and the lower limit discharge zone. When the SOC... j When in the normal discharge region, the correction amount ΔR to the droop coefficient j (SOC j When the initial droop coefficient R is 0, the power distribution of different energy storage units is related to their initial droop coefficient R. 0j Size is inversely proportional; when SOC j When located in the charging and discharging warning zones, the SOC of different energy storage units should be considered. j Real-time correction of the droop coefficient; when SOCj When the battery is in the upper limit of the charging range and the lower limit of the discharging range, the correction for the droop coefficient is the largest.

[0183] In traditional droop control methods, the droop coefficient R j It is fixed and cannot be linked to the actual power source's SOC, thus it cannot control the energy storage unit (ESU). j The adaptive droop coefficient calculation module 33 added in this embodiment of the invention provides a reasonable allocation of power to the energy storage unit ESU. j SOC j Introduced into the droop coefficient R j In real-time correction, the energy storage unit ESU j Adaptive and rational power allocation can reduce the frequency of switching between the shutdown mode and droop control mode of energy storage units, reduce losses caused by mode switching, and improve their utilization rate. Although the patent "CN110649590A A Networked DC Microgrid Energy Cooperative Control Method" uses an adaptive adjustment of the droop coefficient, it does not consider the situation where the initial SOC of the energy storage unit is not within the limit range mentioned in the paper, or the instantaneous change in SOC when the energy storage unit switches from shutdown mode to droop mode, causing the SOC to be outside the limit range. The improved droop coefficient method of this patent results in a negative droop coefficient in this case, which makes the system extremely unstable. This leads to different energy storage units in the same system having positive and negative droop coefficients, thereby causing system collapse. In this embodiment, the traditional droop coefficient is not directly modified. Instead, a new correction term is added to modify the traditional droop coefficient term. Within a suitable range, a combination of fixed and variable droop coefficients is used to reduce the computational load. This addresses the issue in patent CN110649590A, "A Networked DC Microgrid Energy Coordination Control Method," where the initial SOC of the energy storage unit is not within the limits mentioned in the paper. Specifically, when the SOC is higher than the upper limit, charging is not performed, but discharging is still possible; when the SOC is lower than the lower limit, discharging is not performed, but charging is still possible. The droop coefficient will never be less than 0, improving the system's operating range and stability. Furthermore, this embodiment, through the proposed adaptive droop coefficient adjustment strategy, can also reduce the frequency of switching between the energy storage unit's shutdown mode and droop control mode, reducing losses caused by mode switching.

[0184] The PWM signal generation module 34 includes a bus rated voltage submodule 341, a first voltage PI control submodule 342, a second voltage PI control submodule 343, a current PI control module 344, and a PWM generation submodule 345.

[0185] Bus rated voltage submodule 341 is used to provide the bus rated voltage signal U of the DC / DC converter parallel control device. dcref Bus rated voltage signal Udcref The error signal obtained by subtracting the first voltage signal output by the voltage sensor 311 is input to the first voltage PI control submodule 342 for proportional-integral control, and outputs the second voltage signal.

[0186] The first current signal output by the first current sensor 312 is multiplied by the corrected droop coefficient output by the adaptive droop coefficient calculation module 33 to obtain the third voltage signal; the bus rated voltage signal U of the bus rated voltage submodule 341. dcref The difference between the fourth voltage signal and the third voltage signal is used to obtain the fourth voltage signal; the error signal between the fourth voltage signal and the second voltage signal and the first voltage signal is input to the second voltage PI control submodule 343 for proportional-integral control, and the fifth voltage signal is output; the error signal between the fifth voltage signal and the second current signal is input to the current PI control module 344 for proportional-integral control, and the sixth voltage signal is output.

[0187] Specifically, the load current distribution method mainly adopts IV droop control, which uses the DC bus voltage as a signal. IV droop control involves introducing current feedback and a virtual resistance (droop coefficient) into the control of the DC bus voltage to correct the given voltage command value. This compromises the accuracy of differential control and the current sharing effect. When the line impedance is low, it is ignored.

[0188] In this embodiment, the fifth voltage signal U dcj *Designed as:

[0189]

[0190] Where dU is the second voltage signal, U dcj U is the first voltage signal. dcref -R j ·i dcj For the fourth voltage signal, K vp and K vi These are the parameters for the second voltage PI control submodule.

[0191] In this embodiment, the DC / DC converter N considers line impedance. j The transfer function G from the control to the converter output voltage vdj (s) is:

[0192]

[0193] DC / DC converter N considering line impedance j The transfer function G from the control to the output inductor of the energy storage unit idj (s) is:

[0194]

[0195] Where D is the DC / DC converter N j Duty cycle, U ESUj For energy storage unit ESU j The voltage. Based on the transfer function, the crossover frequency is designed to be 15-20 times the power frequency to select the parameter K of the current PI control module. ip and K ii Furthermore, to ensure that the phase margin satisfying the phase frequency characteristic curve is within 30 to 60 degrees, and to set the voltage ride-through frequency to one-fifth of the current ride-through frequency, the parameter K of the second voltage PI control submodule is selected. vp and K vi .

[0196] In this embodiment, the introduction of dual closed-loop control of voltage and current can effectively improve the overshoot of the DC / DC converter output voltage, thereby avoiding system paralysis caused by excessive instantaneous power of parallel operation in islanded mode and improving the stability of bus voltage.

[0197] The PWM generation submodule 345 is connected to the current PI control module 344. The PWM generation submodule 345 is used to generate a PWM1 signal based on the sixth voltage signal, and generate a complementary signal PWM2 signal from the PWM1 signal. The PWM1 signal and the PWM2 signal are combined to form the first PWM signal.

[0198] The DSP control and energy storage unit operating mode selection module 35 is connected to the PWM generation submodule 345, the first current sensor 312, the DSP control and SOC calculation module 322, and the total energy storage unit output power calculation module 323, respectively. It is used to determine the operating mode of the energy storage unit and output the second PWM signal, i.e., the drive signal. The second PWM signal is divided into two signals, PWM3 and PWM4, which are output to the corresponding switching transistors Q1 and Q2 respectively to control their on / off state.

[0199] In this embodiment, taking two DC / DC converters as an example, the energy storage units ESU1 and ESU2 in the main circuit can be connected first, and then the drive unit 30 can be powered on. The first set of control drive units 30 is used to acquire the first voltage signal U across the filter capacitor C1 in the controlled unit 20 of the corresponding DC / DC converter. dc1 The first current signal i output by converter N1 dc1 and the second current signal i output by the energy storage unit ESU1 L1 And based on the second current signal i output by the energy storage unit ESU1 L1 The state of charge (SOC1) of the energy storage unit ESU1 is calculated. Similarly, the second set of control drive units 30 is used to acquire the first voltage signal U across the filter capacitor C2 in the corresponding DC / DC converter controlled unit 20.dc2 The first current signal i output by converter N2 dc2 and the second current signal i output by the energy storage unit ESU2 L2 And based on the second current signal i output by the energy storage unit ESU2 L2 The state of charge (SOC2) of the energy storage unit ESU2 is calculated. If energy storage units ESU1 and ESU2 are discharging at this time, when the SOC1 (or SOC2) of one of the energy storage units ESU1 (or ESU2) reaches the lower discharge limit, the DSP in the control drive unit 30 will cut off the sixth voltage signal of the DC / DC converter N1 (or N2), transmitting 0 to the PWM generation submodule, causing the DC / DC converter N1 (or N2) to disconnect, while the other converter N2 (or N1) continues to operate normally. If energy storage units ESU1 and ESU2 suddenly charge at this time, the disconnected converter N1 (or N2) will be put back into operation. If energy storage units ESU1 and ESU2 are charging at this time, when the SOC1 (or SOC2) of one of the energy storage units ESU1 (or ESU2) reaches the upper limit of charging, the DSP in the control drive unit 30 cuts off the sixth voltage signal of the DC / DC converter N1 (or N2), transmitting 0 to the PWM generation submodule, causing the DC / DC converter N1 (or N2) to disconnect, while the other converter N2 (or N1) continues to operate normally. If energy storage units ESU1 and ESU2 suddenly start charging at this time, the disconnected converter N1 (or N2) will resume operation. Therefore, the DSP in the control drive unit 30 controls the DC / DC converter N... j Whether or not the sixth voltage signal is transmitted allows for the parallel connection of multiple DC / DC converters. Various system parameters can be observed using an oscilloscope, such as the voltage change at the load end during parallel operation and the energy storage unit (ESU). j SOC j Transient situations, etc.

[0200] To verify the role of the adaptive droop coefficient calculation module in the parallel control method of the DC / DC converter in this embodiment, simulations were conducted. Since lead-acid batteries have large capacity but slow response, while supercapacitors have high power and fast response, this simulation chose to connect supercapacitors and lead-acid batteries in parallel to compensate for their respective shortcomings. The simulation process is as follows: During system operation, to prevent deep charging and discharging of the energy storage unit, the power distribution of the hybrid energy storage system was readjusted based on the current SOC of the energy storage device. An improved droop control based on supercapacitor SOC partitioning was studied in detail. To simultaneously observe the charging and discharging modes of the energy storage unit, a 200W DC power supply was connected to the system. This DC power supply only serves to inject power into the system and is not analyzed. The energy storage unit is discharging when the load is greater than 200W and charging when the load is less than 200W.

[0201] Typically, lead-acid batteries have an energy density of 20–50 Wh / kg, while supercapacitors have an energy density of 1–15 Wh / kg. By comparing the energy densities of lead-acid batteries and supercapacitors, it can be determined that under normal operating conditions, the power distribution between supercapacitors and lead-acid batteries of the same mass should be 1:2. The constant power load on the common side is designed as a variable load, fluctuating between 0 and 400 W. Under these conditions, the supercapacitor under normal operating conditions can receive a maximum power of 133.4 W, based on the rated DC bus voltage U. dcref Given 200V, calculate the maximum output current of the supercapacitor DC / DC converter as i. dcj The current is 0.67A. To ensure the stability of the bus voltage, the bus voltage can only fluctuate to a maximum of 2% of its rated value, i.e., 4V. The load current distribution method mainly adopts a DC bus voltage distribution.

[0202] Line voltage is controlled by the IV droop of the signal, according to equation U. dcj =U dcref -R j ·i dcj The initial droop coefficient R of the supercapacitor was calculated. 01 Given a value of 6, to achieve a power distribution ratio of 1:2 between the supercapacitor and the lead-acid battery, the initial droop coefficient R of the lead-acid battery can be obtained. 02 The value is 3.

[0203] In order to improve the service life of energy storage units, a droop control management strategy based on state of charge partitioning is studied. Due to the low energy density of supercapacitors, their state of charge (SOC) changes faster than that of lead-acid batteries during simulation, so the simulation process mainly observes the SOC change of supercapacitors. The SOC of the supercapacitor is divided into 5 zones, namely the lower discharge limit zone (0%<SOC<20%), the discharge warning zone (20%<SOC<40%), the normal operation zone (40%<SOC<60%), the charging warning zone (60%<SOC<80%) and the upper charging limit zone (80%<SOC<100%). Since the power density of the supercapacitor is higher than that of the lead-acid battery, in order to enable the supercapacitor to discharge as much as possible when its SOC is large, when the supercapacitor is in the upper charging limit zone, the output power distribution ratio of the supercapacitor to the lead-acid battery is set to 4:1. At this time, since the lead-acid battery is still in the normal operation zone, its droop coefficient R2=R 02 =3 remains unchanged, while the supercapacitor's R1 should be changed to 0.75. At this time, the correction amount of the supercapacitor droop coefficient ΔR1(SOC1)=R1-R 01 =-5.25 can be determined, that is, the amplitude of the maximum correction amount of the droop coefficient is R SOC =5.25. In this case, if the supercapacitor is charged when it is in the charging warning zone, the minimum power distribution ratio of the supercapacitor to the lead-acid battery can reach 3:11.25, and charging stops until the supercapacitor reaches the upper charging limit zone.

[0204] The following is a simulation example of two parallel DC / DC converters, and the simulation parameters are shown in the table:

[0205] Table 1

[0206]

[0207] Reference Figure 7 , which is the overall waveform diagram of parallel connection of supercapacitor (with high SOC) / lead-acid battery, Figure 7 (a) is the waveform change diagram of load power. Since the energy density of lead-acid batteries is much higher than that of supercapacitors, the SOC of supercapacitors changes greatly, so the SOC of supercapacitors is observed. Figure 7 (b) and Figure 7 (c) are respectively the SOC waveform transformation diagrams of the supercapacitor under traditional droop control and improved droop control. Except for the different control strategies, other conditions are the same, that is, the SOC of the supercapacitor both starts from 57%, and the load change diagram is both Figure 7 (a). Through Figure 7 (b), it can be observed that under the same conditions, in the traditional droop control mode, the supercapacitor has switched between shutdown mode and droop mode 4 times at t=2s, 2.3s, 4.2s and 5.6s, and according to Figure 7(c) It can be seen that under the improved droop control mode, the supercapacitor switched between shutdown mode and droop mode s = 0 times. The supercapacitor always operated in the improved droop mode. Furthermore, the supercapacitor in this figure operated at a high SOC (charging warning zone). During charging in this zone, as the supercapacitor's SOC increased, its allocated power gradually decreased, with the lead-acid battery, which has a higher energy density, handling the excess energy. During discharging in this zone, the supercapacitor's SOC dropped rapidly, allowing it to quickly return to the normal operating range, improving its utilization and lifespan. Observation Figure 7 (d) Figure 7 (e) It can be seen that when the improved droop control is adopted, the rate of change of the bus voltage is reduced to a certain extent, and the impact of the bus voltage change on the system is reduced to a certain extent.

[0208] like Figure 8 As shown, it is Figure 7 The output current change diagram of a supercapacitor during mode switching under certain conditions (high SOC). Figure 8 (a) shows the output current variation of the supercapacitor under the traditional droop control mode. At t = 2.3s, the supercapacitor switches from shutdown mode to droop mode. Although the switching can be successfully achieved through parameter design, the output current fluctuates during the switching process, resulting in some power loss during the switching mode. Figure 8 (b) is a graph showing the output current variation of the supercapacitor under the improved droop control mode. Since the frequency of mode switching is reduced, the supercapacitor always operates in the improved droop mode. It only switches from charging to discharging. The output current does not oscillate near 0, which reduces the loss caused by the switching process, improves the utilization rate of the supercapacitor, and protects the supercapacitor to a certain extent.

[0209] and Figure 7 Correspondingly, Figure 9 The waveform diagram shows the parallel connection of a supercapacitor (low SOC) and a lead-acid battery. Load variations are shown in the diagram. Figure 9 (a) The system is still connected to a 200W DC power supply. Figure 9 (b) and Figure 9 (c) These are waveform transformation diagrams of the supercapacitor's SOC under traditional droop and improved droop conditions, respectively. Except for the different control strategies, all other environmental conditions are the same; that is, the supercapacitor's SOC starts at 47% in both cases, and the load change diagrams are identical. Figure 9 (a). Through Figure 9 (b) It can be observed that under the same conditions, in the traditional droop control mode, the supercapacitor switched between shutdown mode and droop mode a total of 4 times at t = 1.8s, 2.2s, 4.6s, and 5.5s, respectively. Figure 9(c) It can be seen that under the improved droop control mode, the supercapacitor switched between shutdown mode and droop mode s = 0 times. The supercapacitor always operated in the improved droop mode. Furthermore, the supercapacitor in this figure operated in a low SOC (discharge warning zone). During discharge in this zone, as the supercapacitor's SOC decreased, its allocated power gradually decreased, with the excess energy being distributed to the lead-acid battery, which has a higher energy density. During charging in this zone, the supercapacitor's SOC rose rapidly, allowing it to quickly return to the normal operating range, thus improving its utilization rate and lifespan. Observation Figure 9 (d) Figure 9 (e) It can be seen that when the improved droop control is adopted, the rate of change of the bus voltage is reduced to a certain extent, and the impact of the bus voltage change on the system is reduced to a certain extent.

[0210] like Figure 10 As shown, it is Figure 9 The output current change of a supercapacitor during mode switching under certain conditions (low SOC). Figure 10 (a) shows the output current variation of the supercapacitor under the traditional droop control mode. At t = 5.5s, the supercapacitor switches from shutdown mode to droop mode. Although the switching can be successfully achieved through parameter design, the output current fluctuates during the switching process, resulting in some power loss during the switching mode. Figure 10 (b) is a graph showing the output current variation of the supercapacitor under the improved droop control mode. Due to the reduced frequency of mode switching, the supercapacitor always operates in the improved droop mode. It only switches from discharging to charging. The output current does not oscillate near 0, which reduces the losses caused by the switching process, improves the utilization rate of the supercapacitor, and protects the supercapacitor to a certain extent.

[0211] like Figure 11 As shown, it is a waveform diagram of a supercapacitor / lead-acid battery connected in parallel using traditional droop control. Figure 11 (a) shows the SOC variation of the supercapacitor in the traditional droop mode. It can be seen that, with a constant load, the rate of SOC decrease gradually accelerates during supercapacitor discharge. This is because under low-voltage conditions with very high current, the Joule loss is greater, resulting in significantly lower efficiency. Therefore, when the supercapacitor is in a region with a low SOC, the proposed improved droop coefficient strategy reduces the discharge amount in the discharge warning region and strengthens the charging amount during charging in this region. This allows the supercapacitor to quickly return to the normal operating region, improving its efficiency and lifespan.

[0212] The simulation shows that under the same load variation, charging and discharging reduces the frequency of switching between the supercapacitor's shutdown mode and droop mode, reduces the losses caused by the switching process, improves the utilization and efficiency of the supercapacitor, and protects the supercapacitor to a certain extent, so that the supercapacitor's SOC is within the normal operating range (40-60%) as much as possible, avoiding overcharging and over-discharging.

[0213] Furthermore, the parallel control method of the DC / DC converter in this embodiment was simulated. The simulation process was as follows: the rated voltage of the DC bus was designed to be 200V, and the constant power load on the common side was a variable load, fluctuating between 0 and 400W. To simultaneously observe the charging and discharging modes of the energy storage unit, a 200W DC power supply was connected to the system. This DC power supply only served to inject power into the system and was not analyzed. When one of the energy storage units reached the upper limit of charging or the lower limit of discharging, the DSP control and energy storage unit operating mode selection module disconnected the DC / DC converter corresponding to that energy storage unit. When the energy storage unit that reached the upper limit of charging suddenly discharged, or the energy storage unit that reached the lower limit of discharging suddenly charged, the DC / DC converter corresponding to that energy storage unit was connected in parallel to the system. Similarly, a supercapacitor and a lead-acid battery were connected in parallel to observe the external characteristics of the output voltage and the power distribution of the two DC / DC converters.

[0214] Figure 12This diagram illustrates the parallel waveforms of two DC / DC converters (with a high SOC for the supercapacitor) provided in this embodiment. The waveforms primarily represent the normal operating range, charging warning range, and charging upper limit range for the supercapacitor, as well as the normal operating range for the lead-acid battery. The initial SOC of the supercapacitor is 77%, and the SOC of the lead-acid battery is 50%. The diagram consists of five waveforms from top to bottom: the common-side load power, the supercapacitor SOC, the lead-acid battery SOC, the output current of the supercapacitor and lead-acid battery over time, and the ratio of the output power of the supercapacitor to the lead-acid battery. To simultaneously observe the charging and discharging modes of the energy storage units, a 200W DC power supply was connected to the system. This DC power supply only serves to inject power into the system and is not analyzed. Therefore, when the load power is greater than 200W, both energy storage units charge; when the load power is less than 200W, both energy storage units discharge. During the period from 0 to 1 second, when the load power is less than 200W, both the supercapacitor and the lead-acid battery are charged. When the supercapacitor's SOC reaches 80%, its corresponding DC / DC converter is disconnected from the system, and the load power is borne by the lead-acid battery. During the period from 1 to 2.3 seconds, when the load power reaches 400W, the supercapacitor's corresponding DC / DC converter is connected to the system, and both energy storage units discharge. During the parallel operation, the instantaneous change in the SOC of the energy storage units is small, and the dynamic performance of the system is good. As the supercapacitor's SOC1 decreases from 80% to 60%, the slope of the SOC curve gradually decreases, and the power distribution gradually decreases. When the SOC1 drops to 60%, it enters the normal operating range, and the output power ratio of the supercapacitor to the lead-acid battery reaches the set value of 1:2. During the period from 2.5 to 7.5 seconds, when the load power is less than 200W, the supercapacitor and lead-acid battery are charged. As the SOC of the supercapacitor changes from 60% to 80%, the slope of its SOC curve gradually decreases, and the power distribution gradually decreases. Until the time is 4.95 seconds, the SOC of the supercapacitor reaches 80%, and its corresponding DC / DC converter is disconnected from the system, with the load power being borne by the lead-acid battery. During the period from 7.5 to 8.5 seconds, the DC / DC converter corresponding to the supercapacitor is put back into operation. The instantaneous change of the SOC of the energy storage unit is small, and the dynamic performance of the system is good.

[0215] Figure 13 The waveform diagram of the parallel bus voltage of two DC / DC converters (when the supercapacitor has a high SOC) provided for implementation of this application is shown in the figure. Figure 11 The bus voltage waveform under the same changing SOC of the load and energy storage unit. Figure 12 (a) shows the bus voltage diagram without compensation. Figure 12(b) shows the bus voltage diagram with compensation added. By introducing a secondary voltage compensation device, the output voltage accuracy and quality of the DC / DC converter are improved, allowing the bus voltage to be maintained at around 200V. Without secondary voltage compensation, voltage drop would always exist and affect system stability.

[0216] In summary, this invention acquires the first voltage signal across the constant power load on the common side, the output current signal of the corresponding DC / DC converter controlled unit, and the output current signal of the energy storage unit. Based on the output current signal of the energy storage unit, the state of charge (SOC) of the energy storage unit is calculated. The droop coefficient is then calculated based on the SOC, corrected, and finally the voltage signal output by the corresponding converter is obtained. A PWM signal is generated from this voltage signal, and the PWM signal is used to control the on / off state of the power switching transistors in the corresponding converter. During the process of calculating the voltage signal output by the converter based on the droop coefficient and generating the PWM signal, a secondary voltage compensation device is introduced to improve the output voltage accuracy and ensure output voltage quality. Furthermore, through adaptive droop coefficient setting, the power of the energy storage unit is rationally allocated. Adaptive operating mode switching allows the energy storage unit to switch between shutdown and droop control based on its SOC, improving the lifespan of the energy storage unit. The use of dual-loop voltage and current control solves the problem of large voltage overshoot during parallel operation, reducing the instantaneous adjustment time of the DC / DC converter during parallel operation. The proposed improved droop coefficient method, through adaptive adjustment of the droop coefficient, reduces the frequency of switching between the energy storage unit's shutdown mode and droop control mode, thereby reducing losses caused by mode switching. Simultaneously, it improves the efficiency of the supercapacitor under high current and low voltage conditions, reduces the probability of the supercapacitor operating at low capacity, and ensures that the supercapacitor's state of charge (SOC) is within the maximum possible normal operating range (40-60%), i.e., the linear operating range of the supercapacitor curve, thus protecting the supercapacitor and improving its utilization rate.

[0217] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0218] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A parallel control method for a DC / DC converter, applied to a DC / DC converter, wherein the DC / DC converter... N j Positive and negative input terminals and energy storage unit ESU j The positive and negative terminals are connected, characterized in that, Includes the following steps: (1) Acquiring data from the DC / DC converter N j The first voltage signal at both ends DC / DC converter N j The first output current signal and energy storage units ESU j The second current signal output And calculate the energy storage unit ESU j SOC signal SOC j ; (2) Based on the energy storage unit ESU j SOC signal SOC j Calculate the droop coefficient correction amount and perform adaptive correction on the droop coefficient; (2.1) Calculate the total output power of the energy storage unit That is, the third power signal; (2.2) Based on the energy storage unit ESU j SOC signal SOC j Calculate the droop coefficient correction amount; (2.2.1) When < At this time, the energy storage unit is located in the lower discharge limit region. ESU j Charging is allowed only; like <0, at this time the energy storage unit ESU j If it is charging, then: like If the value is >0, then the energy storage unit is disabled. ESU j Discharge; (2.2.2) When < < At this time, the energy storage unit is located in the discharge warning zone, and is controlled according to the basic principle of minimizing discharge and maximizing charging. ESU j The output of [the resource] is slowed down. decline; like <0, then: like >0, then: (2.2.3) When < < If the energy storage unit is in the normal operating range at this time, then no action will be taken. ESU j After adjusting the initial droop coefficient, then: (2.2.4) When < < At this time, the energy storage unit is located in the charging warning zone and is controlled according to the basic principle of discharging more and charging less. ESU j The output of [the resource] is slowed down. The rise; like <0, then: like >0, then: (2.2.5) When < At this time, the energy storage unit is located in the upper limit charging zone. ESU j Discharge is permitted only; like If the value is less than 0, then the energy storage unit is disabled. ESU j Charge; like If the value is greater than 0, the energy storage unit is discharging at this time. Therefore: (2.2.6) The droop coefficient correction amount is compared with the initial droop coefficient R. 0j Summing yields the corrected droop coefficient R. j ; (2.3) Correction amount based on the calculated droop coefficient Adaptive correction to the droop coefficient: in: The power of the DC power supply that injects power into the system. For the energy storage unit ESU j of SOC j Charging limit, For the energy storage unit ESU j of SOC j Charging warning value, For the energy storage unit ESU j of SOC j Lower limit of discharge, For the energy storage unit ESU j of SOC j Discharge warning value, This represents the maximum correction magnitude for the droop coefficient. R 0j This is the initial droop coefficient; (3) Based on the first voltage signal First current signal Second current signal And with the corrected droop coefficient, the corresponding DC / DC converter is obtained. N j The output voltage signal is used to generate the first PWM signal; (4) Determine the energy storage unit ESU j Operating mode, and according to the energy storage unit ESU j The operating mode and the first PWM signal generate a second PWM signal, i.e., a drive signal, which is output to the corresponding DC / DC converter. N j The switching transistor in the middle controls its on / off state.

2. The parallel control method for DC / DC converters according to claim 1, characterized in that, The specific steps (3) are as follows: (3.1) Given the rated voltage signal of the busbar Combine it with the first voltage signal The difference between the two error signals is then subjected to proportional-integral control to obtain the second voltage signal. (3.2) The corrected droop coefficient R j The third voltage signal is obtained by multiplying the first current signal by the voltage signal. (3.3) The rated voltage signal of the busbar Subtracting the third voltage signal from the fourth voltage signal yields the fourth voltage signal. (3.4) The signal obtained by adding the fourth voltage signal and the second voltage signal is compared with the first voltage signal. The error signal is subjected to proportional-integral control to output a fifth voltage signal; the fifth voltage signal is then compared with the second current signal. The error signal is used for proportional-integral control to output a sixth voltage signal; (3.5) Generate a PWM1 signal based on the sixth voltage signal, and generate a complementary signal PWM2 signal from the PWM1 signal. The PWM1 signal and the PWM2 signal are combined to form the first PWM signal.

3. The parallel control method for DC / DC converters according to claim 2, characterized in that, In step (4), the energy storage unit is determined. ESU j The specific methods for the working mode are as follows: When the energy storage unit ESU j The system is in a shutdown state under the following three conditions: When the third power signal Less than 0, and the energy storage unit ESU j of SOC j Greater than or equal to hour; When the third power signal Greater than 0, and the energy storage unit ESU j of SOC j Less than or equal to hour; When the first current signal When the current exceeds the preset current threshold; In addition, the energy storage unit ESU j All are in operation; The specific details of the second PWM signal, i.e., the drive signal, are as follows: When the energy storage unit ESU j When in working condition, the output PWM second signal is equal to the PWM first signal; When the energy storage unit ESU j When the machine is in a stopped state, the output PWM second signal is equal to a constant 0, which controls the switching transistor to turn off.

4. A parallel control device for a DC / DC converter, used to implement the parallel control method for a DC / DC converter according to any one of claims 1-3, comprising a common-side constant power load (10), a plurality of control drive units (30), and a plurality of DC / DC converter controlled units (20); the output terminals of the plurality of DC / DC converter controlled units (20) are connected in parallel and are all connected to the common-side constant power load (10); each group of control drive units (30) is connected to each group of DC / DC converter controlled units (20) in a one-to-one correspondence; the DC / DC converter N j Positive and negative input terminals and energy storage unit ESU j The positive and negative terminals are connected, characterized in that: The control drive unit (30) includes a sensor assembly (31), a SOC and total energy storage unit output power calculation module (32), an adaptive droop coefficient calculation module (33), a PWM signal generation module (34), and a DSP control and energy storage unit working mode selection module (35). The sensor assembly (31) is used to collect data from the DC / DC converter. N j The first voltage signal at both ends DC / DC converter N j The first output current signal and energy storage units ESU j The second current signal output ; The SOC and total energy storage unit output power calculation module (32) is connected to the sensor assembly (31) and is used to calculate the output power of the energy storage unit. ESU j SOC signal SOC j and total energy storage unit output power ; The adaptive droop coefficient calculation module (33) is connected to the SOC and total energy storage unit output power calculation module (32) and is used to adaptively correct the droop coefficient based on the calculated droop coefficient correction amount. The PWM signal generation module (34) is connected to the sensor component (31) and the adaptive droop coefficient calculation module (33) to generate a first PWM signal; The DSP control and energy storage unit operating mode selection module (35) is connected to the sensor assembly (31), the SOC and total energy storage unit output power calculation module (32), and the drive signal generation module, and is used to determine the operating mode of the energy storage unit. ESU j Operating mode, and according to the energy storage unit ESU j The operating mode modifies the first PWM signal to obtain the second PWM signal, which is the drive signal.

5. The parallel control device for DC / DC converters according to claim 4, characterized in that: The sensor assembly (31) includes a voltage sensor (311), a first current sensor (312), and a second current sensor (313); the voltage sensor (311) is associated with the corresponding DC / DC converter N in the DC / DC converter controlled unit (20). j Parallel connection, used to acquire the DC / DC converter N j The output voltage signal at both ends, i.e., the first voltage signal; the first current sensor (312) is connected in series in the corresponding DC / DC converter controlled unit (20) converter N. j The first output terminal is used to acquire the corresponding DC / DC converter N. j The output current signal, i.e., the first current signal; The second current sensor (313) is connected in series with the energy storage unit ESU in the corresponding DC / DC converter controlled unit (20). j Positive terminal and DC / DC converter N j Between the positive input terminals, the energy storage unit ESU in the controlled unit (20) of the DC / DC converter is collected. j The output current signal, i.e. the second current signal.

6. The DC / DC converter parallel control device according to claim 5, characterized in that: The SOC and total energy storage unit output power calculation module (32) includes a DSP control and SOC calculation module (321) and a total energy storage unit output power calculation module (322). The DSP control and SOC calculation module (321) is connected to the second current sensor (313) and is used to control the energy storage unit (ESU) in the corresponding DC / DC converter controlled unit (20). j The second current signal output is used for calculation to obtain the corresponding energy storage unit ESU in the controlled unit (20) of the DC / DC converter. j SOC signal; The total energy storage unit output power calculation module (322) is connected to the voltage sensor (311) and calculates the power of the DC power supply based on the first voltage signal, the given common-side constant power load impedance R, and the given system injection power. The total output power of the energy storage unit is calculated.

7. The parallel control device for DC / DC converters according to claim 4, characterized in that: The adaptive droop coefficient calculation module (33) includes a DSP control and droop coefficient correction calculation module (331) and an initial droop coefficient setting submodule (332). The DSP control and droop coefficient correction calculation module (331) is connected to the SOC and total energy storage unit output power calculation module (32) and is used to calculate the droop coefficient correction; the initial droop coefficient setting submodule (332) is used to set the corresponding DC / DC converter N. j The initial droop coefficient R 0j ;R 0j The corrected droop coefficient output by the adaptive droop coefficient calculation module (33) is obtained by summing the output of the DSP control and droop coefficient correction calculation module (331); The specific amount of the droop coefficient correction is: (1) When < At this time, the energy storage unit is located in the lower discharge limit region. ESU j Charging is allowed only; like <0, at this time the energy storage unit ESU j If it is charging, then: like If the value is >0, then the energy storage unit is disabled. ESU j Discharge; (2) When < < At this time, the energy storage unit is located in the discharge warning zone, and is controlled according to the basic principle of minimizing discharge and maximizing charging. ESU j The output of [the resource] is slowed down. decline; like <0, then: like >0, then: (3) When < < If the energy storage unit is in the normal operating range at this time, then no action will be taken. ESU j After adjusting the initial droop coefficient, then: (4) When < < At this time, the energy storage unit is located in the charging warning zone and is controlled according to the basic principle of discharging more and charging less. ESU j The output of [the resource] is slowed down. The rise; like <0, then: like >0, then: (5) When < At this time, the energy storage unit is located in the upper limit charging zone. ESU j Discharge is permitted only; like If the value is less than 0, then the energy storage unit is disabled. ESU j Charge; like If the value is greater than 0, the energy storage unit is discharging at this time. Therefore: (6) The droop coefficient correction amount is compared with the initial droop coefficient R. 0j Summing yields the corrected droop coefficient R. j ; in: This represents the total output power of the energy storage unit. For the energy storage unit ESU j of SOC j Charging limit, For the energy storage unit ESU j of SOC j Charging warning value, For the energy storage unit ESU j of SOC j Lower limit of discharge, For the energy storage unit ESU j of SOC j Discharge warning value, This is the maximum correction magnitude for the droop coefficient.

8. The parallel control device for DC / DC converters according to claim 5, characterized in that: The PWM signal generation module (34) includes a bus rated voltage submodule (341), a first voltage PI control submodule (342), a second voltage PI control submodule (343), a current PI control module (344), and a PWM generation submodule (345). The bus rated voltage submodule (341) is used to provide the bus rated voltage signal of the DC / DC converter parallel control device. ; The bus rated voltage signal The error signal obtained by subtracting the first voltage signal output by the voltage sensor (311) is input to the first voltage PI control submodule (342) for proportional-integral control, and outputs the second voltage signal. The first current signal output by the first current sensor (312) is multiplied by the corrected droop coefficient output by the adaptive droop coefficient calculation module (33) to obtain the third voltage signal; the bus rated voltage signal of the bus rated voltage submodule (341) The difference between the fourth voltage signal and the second voltage signal is used to obtain the fourth voltage signal; the error signal between the fourth voltage signal and the second voltage signal and the first voltage signal is input to the second voltage PI control submodule (343) for proportional-integral control, and the fifth voltage signal is output. The error signal between the fifth voltage signal and the second current signal is input to the current PI control module (344) for proportional-integral control, and the sixth voltage signal is output. The PWM generation submodule (345) is connected to the current PI control module (344). The PWM generation submodule (345) is used to generate a PWM1 signal based on the sixth voltage signal; and to generate a complementary signal PWM2 signal from the PWM1 signal. The PWM1 signal and the PWM2 signal are combined to form the first PWM signal.

9. The parallel control device for DC / DC converters according to claim 4, characterized in that: The DSP control and energy storage unit operating mode selection module (35) determines the energy storage unit. ESU j The specific working mode is as follows: When the energy storage unit ESU j The system is in a shutdown state under the following three conditions: When the third power signal Less than 0, and the energy storage unit ESU j of SOC j Greater than or equal to hour; When the third power signal Greater than 0, and the energy storage unit ESU j of SOC j Less than or equal to hour; When the first current signal When the current exceeds the preset current threshold; In addition, the energy storage unit ESU j All are in operation; The generation of the second PWM signal is specifically as follows: When the energy storage unit ESU j When in operation, the second PWM signal is equal to the first PWM signal; When the energy storage unit ESU j When the machine is in a stopped state, the second PWM signal is equal to a constant 0, which controls the switching transistor to turn off.

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