A method and device for coordinated control of a cascade hybrid energy storage system

Abstract

The application discloses a kind of cascade type hybrid energy storage system coordinated control method, comprising: based on the output voltage and current of the hybrid energy storage system collected, determine the actual output power of system, determine power difference value in combination with the power reference value of pre-setting or dispatching;According to the positive and negative of output current, judge whether the system is in discharge or charging mode, mode is used to limit virtual parameter adjustment boundary;Based on power difference value and mode, self-adaptive calculation and update virtual resistance and virtual capacitance;The updated virtual resistance and virtual capacitance are respectively used as the virtual impedance parameter of battery branch and other type energy storage unit branch, generate corresponding voltage deviation instruction;Voltage deviation instruction is input into double closed loop controller, generate the PWM duty cycle signal of each DC-DC converter, realize dynamic coordinated control to battery and other type energy storage unit according to PWM duty cycle signal.The method can make the energy storage system of H bridge inverter reduce overshoot and oscillation, quickly reach steady state.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system control, and in particular to a cascaded hybrid energy storage system coordination control method and device. BACKGROUND

[0002] In order to achieve the target, the grid-connected capacity of distributed power supply is continuously rising, but due to the randomness and volatility of the output of the distributed power supply, these characteristics are not conducive to large-scale consumption of the distributed power supply in the power system. In order to reduce the negative impact of large-scale distributed power supply access, the energy storage system (ESS) as a kind of energy storage system that can rely on charging and discharging to compensate for the randomness and volatility of the output of the distributed power supply, the installed capacity continues to increase, but for a single form of energy storage system, such as a battery or a super capacitor, the energy density and power density cannot be considered, so the hybrid energy storage system (HESS) combining different forms of energy storage is introduced and studied, and the control strategy of HESS also attracts the attention of researchers. In addition, multi-level cascaded inverters such as cascaded H-bridge inverters have become the research direction of large-capacity HESS because they can output high voltage and thus output considerable power. How to fully utilize the advantages of various energy storage devices has become a technical problem to be solved. SUMMARY

[0003] In order to solve the problems in the prior art, the embodiments of the present application provide a cascaded hybrid energy storage system coordination control method and device, a method, a device, a computing device, a computer storage medium, and a product containing a computer program, which can reduce overshoot and oscillation of the energy storage system of the H-bridge inverter and quickly reach a steady state.

[0004] In a first aspect, the embodiments of the present application provide a cascaded hybrid energy storage system coordination control method, the cascaded hybrid energy storage system comprising at least one battery unit, at least one other type of energy storage unit, and each energy storage unit being connected to a corresponding cascaded H-bridge inverter module through an independent bidirectional DC-DC converter. The method comprises: determining the actual output power of the system based on the collected output voltage and current of the hybrid energy storage system, and determining the power difference value in combination with the pre-set or scheduled power reference value; determining whether the system is in discharging or charging mode according to the positive and negative of the output current, and the mode is used to limit the virtual parameter adjustment boundary; adaptively calculating and updating the virtual resistance and virtual capacitance based on the power difference value and the mode; taking the updated virtual resistance and virtual capacitance as the virtual impedance parameters of the battery branch and the other type of energy storage unit branch respectively, and generating the corresponding voltage deviation instruction; inputting the voltage deviation instruction into a double closed-loop controller to generate the PWM duty cycle signal of each DC-DC converter, and realizing dynamic coordination control of the battery and the other type of energy storage unit according to the PWM duty cycle signal.

[0005] In some possible implementation manners, the adaptive calculation and updating of the virtual resistance and the virtual capacitance based on the power difference and the mode comprises: calculating and updating the virtual resistance and the virtual capacitance by a non-linear function according to the power difference and preset upper and lower limit values of the virtual resistance and the virtual capacitance; and wherein the function for calculating the virtual resistance and the virtual capacitance is different in the discharging mode and the charging mode.

[0006] In some possible implementation manners, the initial value of the virtual resistance and the virtual capacitance is a middle value of the preset upper and lower limit values, and the formula is as follows:

[0007]

[0008]

[0009] wherein, and are preset upper and lower limit values of the virtual resistance, and are preset upper and lower limit values of the virtual capacitance.

[0010] In some possible implementation manners, in the discharging mode, the formula for updating the virtual resistance and the virtual capacitance is as follows:

[0011]

[0012]

[0013] wherein, represents the initial value of the virtual resistance, represents the initial value of the virtual capacitance, represents a dynamic acceleration factor, represents the power difference, represents an intermediate quantity in calculation of the virtual resistance represents an intermediate quantity in calculation of the virtual capacitance.

[0014] In some possible implementation manners, in the charging mode, the formula for updating the virtual resistance and the virtual capacitance is as follows:

[0015]

[0016]

[0017] wherein, represents the initial value of the virtual resistance, represents the initial value of the virtual capacitance, represents a dynamic acceleration factor, represents the power difference, represents an intermediate quantity in calculation of the virtual resistance characterizing the virtual capacitance calculation intermediate quantity.

[0018] In some possible implementation manners, the double closed-loop controller comprises a voltage outer loop and a current inner loop; the voltage outer loop is configured to track a voltage deviation instruction and output a current reference value; and the current inner loop is configured to output a PWM duty cycle signal after superimposing an offset through a PI controller in response to the current reference value.

[0019] In some possible implementation manners, the current reference value is represented as:

[0020]

[0021] wherein, V is a voltage reference value, V is a single-phase output voltage of the cascade type hybrid energy storage, R is a virtual resistance, I is an output current of the battery, and D is a duty cycle signal. , respectively represent a proportional coefficient and an integral coefficient of a voltage loop PI element, and s is a Laplace operator, V is a single-phase output voltage of the cascade type hybrid energy storage, R is a virtual resistance, I is an output current of the battery.

[0022] In some possible implementation manners, the duty cycle signal is represented as

[0023]

[0024] wherein, V is a voltage reference value, V is a single-phase output voltage of the cascade type hybrid energy storage, R is a virtual resistance, I is an output current of the battery, and D is a duty cycle signal. , respectively represent a proportional coefficient and an integral coefficient of a current loop PI element, I is a current reference value, I is an output current of a DC-DC converter connected with the battery.

[0025] In some possible implementation manners, the method further comprises quantitatively evaluating a dynamic response performance, specifically comprising: calculating a power oscillation equivalent value, an overshoot equivalent value, and a steady-state time, wherein the power oscillation equivalent value is used to quantitatively evaluate a fluctuation degree of an output power in a dynamic response process, the overshoot equivalent value is used to quantitatively evaluate a maximum instantaneous deviation value of the output power from a target power in the dynamic response process, and the steady-state time is used to quantitatively evaluate a time required for the system to recover to be stable; and performing weighted summation on a result of normalization to obtain a comprehensive evaluation score.

[0026] In a second aspect, the embodiment of the present application provides a cascade type hybrid energy storage system coordinated control device, comprising: an acquisition module configured to acquire output terminal voltage and current of the hybrid energy storage system; a processing module configured to determine actual output power of the system based on the acquired output terminal voltage and current of the hybrid energy storage system, and determine a power difference value in combination with a power reference value preset or dispatched; the processing module is further configured to determine whether the system is in a discharging mode or a charging mode according to positive and negative output current, and the mode is used to limit virtual parameter adjustment boundaries; the processing module is further configured to adaptively calculate and update virtual resistance and virtual capacitance based on the power difference value and the mode; the processing module is further configured to generate corresponding voltage deviation instructions by taking the updated virtual resistance and virtual capacitance as virtual impedance parameters of a battery branch and a branch of other types of energy storage units respectively; and the processing module is further configured to input the voltage deviation instructions into a double closed-loop controller to generate PWM duty cycle signals of each DC-DC converter, and realize dynamic coordinated control of the battery and the other types of energy storage units according to the PWM duty cycle signals.

[0027] In a third aspect, the embodiment of the present application provides a computer readable storage medium comprising computer readable instructions, which, when read and executed by a computer, cause the computer to perform the method of any one of the first aspect.

[0028] In a fourth aspect, the embodiment of the present application provides a computing device comprising a processor and a memory, wherein the memory stores computer program instructions, and the computer program instructions are executed by the processor to perform the method of any one of the first aspect.

[0029] In a fifth aspect, the embodiment of the present application provides a product comprising a computer program, which, when executed on a processor, causes the processor to perform the method of any one of the first aspect. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort.

[0031] Figure 1 is a cascade type hybrid energy storage system topology schematic diagram provided by the embodiment of the present application;

[0032] Figure 2 is a hybrid energy storage system DC-DC converter topology schematic diagram provided by the embodiment of the present application;

[0033] Figure 3A virtual impedance control physical device control schematic diagram provided by an embodiment of the application;

[0034] Figure 4 A flowchart of a cascade type hybrid energy storage system coordinated control method provided by an embodiment of the application;

[0035] Figure 5 A virtual impedance control equivalent structure schematic diagram provided by an embodiment of the application

[0036] Figure 6 A DC-DC converter control structure schematic diagram provided by an embodiment of the application

[0037] Figure 7 A dynamic response process power curve schematic diagram of a single battery energy storage not using virtual impedance control provided by an embodiment of the application;

[0038] Figure 8 A dynamic response process power curve schematic diagram of a hybrid energy storage system using traditional droop control provided by an embodiment of the application;

[0039] Figure 9 A dynamic response process power curve schematic diagram of a hybrid energy storage using virtual impedance control provided by an embodiment of the application;

[0040] Figure 10 A cascade type hybrid energy storage system coordinated control device structure schematic diagram provided by an embodiment of the application. DETAILED DESCRIPTION

[0041] To make the objectives, technical solutions and advantages of the embodiments of the application clearer, the technical solutions in the embodiments of the application will be described below in connection with the drawings in the embodiments of the application. Obviously, the described embodiments are some but not all of the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the application.

[0042] The term "and / or" in this document is a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. The symbol " / " in this document represents an or relationship of associated objects, for example, A / B represents A or B.

[0043] The terms "first" and "second" and the like in the description and claims of this application are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. For example, the first response message and the second response message are used for distinguishing between similar messages and not necessarily for describing a particular sequential or chronological order.

[0044] In the embodiments of the present application, the words "exemplary" and "for example" are used to mean serving as an example, instance, or illustration, at 99 2 any point in the manufacturing or processing. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be construed as being superior to other embodiments or designs. Rather, use of the words "exemplary" or "for example" is intended to present concepts in a concrete manner.

[0045] In the description of the embodiments of the present application, unless otherwise specified, "a plurality of" means two or more, for example, a plurality of processing units means two or more processing units, and the like; a plurality of elements means two or more elements, and the like.

[0046] For the purpose of clarity, further explanations shall be made as follows in connection with specific embodiments with reference to the accompanying drawings, but the embodiments do not constitute limitations to the embodiments of the present application.

[0047] Load fluctuation in the system requires timely response of the energy storage system to prevent voltage and frequency deviation from exceeding the limit, thereby adversely affecting the overall stability of the system. Compared with the battery energy storage system (BESS), the hybrid energy storage system (HESS) has greater advantages in dealing with load fluctuation. For the cascaded H-bridge hybrid energy storage system, due to the different roles played by different forms of energy storage devices, in order to fully play the advantages of various forms of energy storage devices, it is necessary to realize a coordinated control method with high-performance dynamic response and simple control structure. In view of this, the embodiments of the present application provide a cascaded hybrid energy storage system coordinated control method, which calculates power by collecting physical quantities such as output current and output voltage and current of the hybrid energy storage system; then the virtual resistance and virtual capacitance values are obtained through the power deviation value; and then the trigger signals of the fully controlled devices are obtained through double-loop control and PWM modulation, so as to finally realize the coordinated control with high-performance dynamic response.

[0048] Exemplarily, Figure 1 A cascaded hybrid energy storage system topology schematic diagram provided by the embodiments of the present application is shown. As shown in FIG. 1, the cascaded hybrid energy storage system topology schematic diagram provided by the embodiments of the present application includes a plurality of energy storage devices, a plurality of DC / DC converters, a plurality of DC / AC converters, and a plurality of AC / DC converters. Figure 1As shown, the system is cascaded by multiple independent, same structure H-bridge inverter units. Each H-bridge unit can generate -U, 0, +U three levels by controlling the turn-on and turn-off of 4 fully-controlled power devices (such as IGBT or MOSFET). By connecting the output voltages of n such H-bridge units in series, the system can synthesize 2n+1 level step waves, thereby approaching a sine wave, effectively improving the output voltage quality and reducing harmonics. Figure 2 The DC-DC converter topology of the hybrid energy storage system is shown. As shown in Figure 2 , as a DC power converter in the H-bridge inverter, its function is to realize the conversion of DC power through control signals. It is worth noting that, Figure 1 and Figure 2 The fully-controlled power devices in the H-bridge inverter are IGBTs, which are only used as an example of fully-controlled devices. In actual operation, the embodiments of the present application also support a variety of fully-controlled devices including MOSFETs, Figure 2 The hybrid energy storage system in the hybrid energy storage system adopts a combination of batteries and hybrid energy storage. In actual operation, the embodiments of the present application can also support the coordinated control of a variety of other types of energy storage devices (such as diesel generators, methanol internal combustion engines, etc.), and the illustration does not constitute a limitation on the present application.

[0049] Based on the cascaded hybrid energy storage system as shown in Figures 1-2 , Figure 3 A virtual impedance control physical device control schematic diagram provided by an embodiment of the present application is shown. As shown in Figure 3 , the main function of the physical device is to output and collect voltage and current values, and it also needs to receive the trigger pulse of the fully-controlled device to realize the coordinated control of the hybrid energy storage and improve the dynamic response performance. The coordinated control strategy of the hybrid energy storage is mainly responsible for and realized by the coordinated control center, and the purpose is to separate the data collection and calculation processes from each other, to improve the system efficiency and to avoid the control accuracy decline caused by communication asynchronization. As shown in Figure 3 , the current I bat between BAT and DC-DC, bat_out the current I out between DC-DC and H-bridge inverter, sc the current I sc_out between SC and DC-DC, and the current I sc_out between DC-DC and H-bridge inverter are collected.The physical quantity collection is directly sent to the coordination control center. The coordination control center first performs power calculation, and then sends the power value and the remaining physical quantity to the virtual impedance control link. The virtual impedance control obtains the virtual resistance and virtual capacitance values. The virtual resistance and virtual capacitance values and the collected output voltage and current values are sent to the double-loop control. Through the voltage loop and the current loop in the double-loop control, the duty cycle of the full-controlled device can be obtained. Finally, through PWM modulation, the specific full-controlled device trigger signal can be obtained, which is sent to the signal receiving side of the physical device, so that the hybrid energy storage coordination control strategy based on the physical device can be realized.

[0050] Specifically, Figure 4 A flowchart of a cascade type hybrid energy storage system coordination control method provided by the embodiment of the application is shown. The method can be used to realize dynamic and intelligent power distribution of batteries and supercapacitors in a hybrid energy storage system. The battery and other types of energy storage units (for example, supercapacitor units, or flywheel energy storage units, etc., without loss of generality, in the embodiment of the application, the supercapacitor unit is taken as an example for introduction, but it does not constitute a limitation to the application) can intelligently divide the work according to the system transient demand, guarantee the dynamic response performance, and prolong the battery life, solving the poor adaptability problem of the traditional fixed parameter virtual impedance control under complex working conditions. As shown in Figure 4 The method can include the following steps:

[0051] S41: Based on the collected output voltage and current of the hybrid energy storage system, the actual output power of the system is determined, and the power difference value is determined in combination with the power reference value preset or scheduled and issued.

[0052] In the embodiment, the voltage signal and the current signal of the output end of the hybrid energy storage system are first collected in real time by a sensor. The output end is located at the connection between the DC bus and the input end of the H-bridge inverter, representing the physical interface of the entire hybrid energy storage system for delivering power to the subsequent inverter link. The voltage value and the current value collected are multiplied, and the power actually output by the hybrid energy storage system at the current time can be obtained. This power value reflects the total power level provided by the battery branch and the supercapacitor branch to the subsequent inverter link. At the same time, the system receives the power reference value preset or issued by the external controller. The reference value can be generated according to load demand prediction, grid scheduling instructions, etc., and represents the target power that the hybrid energy storage system should output at the current time. The actual output power calculated and the power reference value received are algebraically subtracted, and a power difference value representing the deviation between the current system power and the target power can be obtained. It is expressed as , wherein, represents the actual power value, represents the power reference value.

[0053] S42: Determine whether the system is in discharging or charging mode according to the positive or negative of the output current, and the mode is used to limit the virtual parameter adjustment boundary.

[0054] In this embodiment, the system determines whether the system is in discharging or charging mode according to the positive or negative of the output current, and the current direction is defined as the positive direction from the DC bus to the H-bridge inverter. By judging the sign of the total output current, the current system overall operation state can be determined. When the total output current is greater than zero, it indicates that the hybrid energy storage system is releasing energy to the load or the grid, and the system is in discharging mode; when the total output current is less than zero, it indicates that external energy is being fed back to the DC bus through the inverter, and the system is in charging mode. The identification result of the operation mode is not directly involved in power calculation or error generation, but is used as a boundary constraint condition in the adaptive adjustment process of the virtual impedance parameter. Specifically, in the discharging mode, in order to protect the battery from bearing too high frequency or too large transient impact current, the value of the virtual resistance is limited in a higher interval, and the value of the virtual capacitance is limited in a lower interval, so as to strengthen the low-pass filtering characteristic and guide the steady-state power to be borne by the battery more; while in the charging mode, in order to preferentially utilize the super capacitor to absorb high-frequency feedback energy and reduce the impact charging to the battery, the value of the virtual resistance is limited in a lower interval, and the value of the virtual capacitance is limited in a higher interval, so as to enhance the high-pass response capability.

[0055] S43: Based on the power difference and the mode, the virtual resistance and the virtual capacitance are adaptively calculated and updated.

[0056] In this embodiment, the virtual impedance control in the control structure is used as a preprocessing link of the output current, and the difference of the output voltage is obtained by multiplying or integrating the output current and the set virtual impedance. Under steady state, the battery current is equivalent to the output current passing through a low-pass filter, and the super capacitor current is equivalent to the output current passing through a high-pass filter, so that the battery and the super capacitor bear different frequency components of the output current, which corresponds to the slow response speed of the battery and the fast response speed of the super capacitor. Under the action of the virtual impedance control, the power distribution of the battery and the super capacitor is reasonable. In addition, by reasonably controlling the values of the virtual resistance and the virtual capacitance, the cutoff frequency can be conveniently selected, so as to realize more accurate power distribution. Please refer to Figure 5 , Figure 5 An equivalent structure diagram of the virtual impedance control provided by the embodiment of the application is shown. As shown in Figure 5 , represents the virtual resistance. The impedance of the capacitor C is represented as 1 / Cs in the s domain, so that 1 / represents the equivalent impedance of the virtual capacitance, Z loadrepresents the load impedance. It can be seen that after the virtual impedance control is adopted, the battery and the super capacitor are equivalent to a series connection of a voltage source and a virtual impedance respectively, and according to the circuit KCL and KVL laws, there are:

[0057]

[0058]

[0059] In the formula, represents the virtual resistance, represents the virtual capacitance, represents the output current of the hybrid energy storage system.

[0060] In the traditional control, the virtual resistance and the virtual capacitance can change according to the power deviation. However, when the power deviation is very small and close to zero, the change of the virtual impedance will also be very slow, resulting in that the dynamic response of the system becomes sluggish and cannot quickly respond to new power fluctuations. Therefore, in the embodiment of the present application, in order to prevent the dynamic response performance from being degraded due to the fact that the actual value of the power approaches the theoretical value of the power, a dynamic acceleration factor is introduced, denoted as F. The initial values of the virtual resistance and the virtual capacitance are respectively:

[0061]

[0062]

[0063] In the formula, and are the upper limit value and the lower limit value of the virtual resistance, and are the upper limit value and the lower limit value of the virtual capacitance.

[0064] When the battery and the super capacitor are discharged, the virtual resistance and the virtual capacitance values are constructed as follows:

[0065]

[0066]

[0067] In the formula, represents the initial value of the virtual resistance, represents the initial value of the virtual capacitance, represents the dynamic acceleration factor, represents the power difference value, represents the virtual resistance calculation intermediate quantity, which is equal to in the embodiment, represents the virtual capacitance calculation intermediate quantity, which is equal to in the embodiment.

[0068] In the discharging state, when the system power is not equal to the target power, a power difference is generated. When the power difference is less than 0, it indicates that the actual power is less than the target power, and the discharge needs to be increased. The system will increase the virtual resistance and reduce the virtual capacitance to guide more low-frequency components to flow to the battery, and at the same time make the super capacitor quickly supplement the instantaneous gap. When the power difference is greater than 0, it indicates that the actual power is greater than the target power, and the discharge needs to be reduced. Then, the virtual resistance is appropriately reduced, and the virtual capacitance is increased, so that the super capacitor absorbs the excess high-frequency energy and reduces the burden on the battery.

[0069] When the battery and the super capacitor are charging, the virtual resistance and the virtual capacitance values are constructed as follows:

[0070]

[0071]

[0072] In the charging state, the parameter adjustment direction is opposite: when the power difference is positive, it indicates that the feedback energy needs to be absorbed, and the system reduces the virtual resistance and increases the virtual capacitance to preferentially let the super capacitor bear the impact charging; when the power difference is negative, it indicates that the charging is insufficient, and then the virtual resistance is appropriately increased and the virtual capacitance is reduced to guide the battery to participate in the steady-state energy recovery.

[0073] It is worth noting that, regardless of the charging mode or the discharging mode, the adjustment process of the virtual resistance and the virtual capacitance is constrained by the boundary defined by the operation mode, which ensures that the virtual resistance always changes between the preset maximum value and the minimum value, and the virtual capacitance is also adjusted within its allowed range, avoiding parameter out-of-limit leading to control instability or device overload.

[0074] S44: The updated virtual resistance and virtual capacitance are taken as the virtual impedance parameters of the battery branch and the super capacitor branch respectively to generate a corresponding voltage deviation instruction.

[0075] In this embodiment, the virtual resistance and virtual capacitance obtained by the above calculation are respectively assigned to the battery branch and the super capacitor branch to construct an equivalent virtual impedance network, and based on the interaction between the network and the real-time obtained total output current, a voltage deviation instruction signal for driving the subsequent double closed-loop controller is generated. This process is not directly controlling the current or power of the energy storage unit, but imposing an artificially constructed voltage offset on the voltage control loop, thereby indirectly guiding the branch current to be automatically distributed in the desired proportion. Specifically, the system takes the updated virtual resistance as the series virtual impedance of the battery branch and the updated virtual capacitance as the parallel virtual impedance of the super capacitor branch. The system uses the total output current of the hybrid energy storage system collected at the current time as the excitation source, and performs mathematical operations with the virtual resistance and the virtual capacitance respectively to generate two independent voltage deviation instructions, one for the battery branch and the other for the super capacitor branch.

[0076] S45: input the voltage deviation instruction into the double closed-loop controller to generate the PWM duty cycle signal of each DC-DC converter, and realize dynamic coordinated control of the battery and the super capacitor according to the PWM duty cycle signal.

[0077] In this embodiment, after generating the voltage deviation instructions of the battery branch and the super capacitor branch respectively, the system inputs the two voltage instructions into the double closed-loop controller of the corresponding DC-DC converter to finally generate the PWM duty cycle signal for driving the power switching device (such as IGBT or MOSFET), thereby realizing accurate and dynamic coordinated control of the battery and the super capacitor output. Exemplarily, Figure 6 The schematic diagram of the DC-DC converter control structure is shown. Please refer to Figure 6 and Figure 2For each DC-DC converter (whether connected to the battery or the super capacitor), its controller adopts a double closed-loop structure of voltage outer loop plus current inner loop. The voltage outer loop is used to track the voltage command generated by the virtual impedance link, and the current inner loop is used to quickly respond to the current reference value output by the voltage outer loop and suppress the inductance current fluctuation, thereby improving the dynamic performance. The entire control process starts from the voltage command, and is passed down layer by layer, and finally outputs the duty ratio. Next, the control principle of the battery side double-loop control is described, and the super capacitor side is the same. Based on the virtual resistance constructed in the foregoing, first, it is multiplied by the original output current of the battery, and is added or subtracted with the corresponding voltage, and after PI control, the reference value of the battery output current is obtained. PI control as a kind of direct flow without static control is very important to realize the tracking of voltage and current physical quantities in the voltage loop and current loop. In the voltage loop, the actual value and the reference value of the voltage are compared, and after PI control, the value obtained is used as the reference value of the inner loop current. In the current loop, the actual value and the reference value of the current are compared, and after PI control, the value obtained is the duty ratio. This voltage loop process is represented as:

[0078]

[0079] In the formula, , respectively represent the proportional coefficient and the integral coefficient of the voltage loop PI link, and s is the Laplace operator, represents the single-phase output voltage of the cascade type hybrid energy storage. Since the output voltage of the hybrid energy storage in the application is selected as 380V, the peak value of the single-phase is 311V, and the reference value of the single-phase output voltage is set as 311 / 3V.

[0080] The battery output current reference value will be compared with the actual output current in the current loop, and after PI control, a constant 0.5 is added to obtain the final duty ratio. This current loop process is represented as:

[0081]

[0082] In the formula, , respectively represent the proportional coefficient and the integral coefficient of the current loop PI link.

[0083] In the formula, the duty ratio obtained through the current loop control is centered on 0, while the duty ratio of the full-controlled device varies from 0 to 1, with the center being 0.5, so 0.5 needs to be added.

[0084] The PWM modulation link in the control structure obtains the duty cycle, and a series of 0-1 signals corresponding to the fully controlled device is obtained through PWM. The working principle of PWM is as follows: the default duty cycle is 0, that is, the output is always 0; after receiving the value of the duty cycle, the output in a certain time limit is set to 1 in a fixed period, and the level signal is still 0 in the remaining time. The final 0-1 signal is used as the trigger signal of the system output to the fully controlled device, so as to realize the coordinated control of the cascade hybrid energy storage system. By adjusting the duty cycle, the DC-DC converter can change the input / output voltage ratio or the current transmission capability, so as to accurately control the energy size flowing from the battery or super capacitor to the DC bus. When the virtual impedance link updates R_v or C_v due to the change of the power difference, the voltage deviation changes, resulting in a new current reference value output by the voltage outer loop, and then the duty cycle is changed through the current inner loop, and finally the actual output current is adjusted. The whole process forms a closed loop negative feedback, so that the system can automatically track the power command and realize dynamic coordination.

[0085] Figures 7-9 The power curves in the dynamic response processes of the single-battery energy storage without using virtual impedance control, the hybrid energy storage system using traditional droop control, and the hybrid energy storage using virtual impedance control are shown respectively. It can be clearly seen from Figures 7-9 that without introducing the super capacitor, the super capacitor cannot make up for any power difference, and the battery alone bears the power difference of the load fluctuation, showing obvious overshoot and oscillation, and the time to reach steady state is relatively long. Without using virtual impedance control, the super capacitor can make up for part of the power difference, but the dynamic response process can still observe relatively obvious overshoot and oscillation, and the time to reach steady state is also relatively long, which obviously does not achieve the optimal dynamic response performance. With the introduction of the super capacitor and the use of the virtual impedance control method of the present invention, the oscillation is eliminated, the overshoot is greatly reduced, the time to reach steady state is relatively short, and the optimal dynamic response performance is achieved.

[0086] In addition, it is not enough to qualitatively describe the dynamic response performance of the cascade hybrid energy storage, and it is necessary to quantitatively construct a comprehensive evaluation system of the dynamic response process. First, for the power oscillation phenomenon, the power oscillation equivalent value is constructed to quantitatively evaluate the fluctuation degree of the output power in the dynamic response process, which is expressed as follows:

[0087]

[0088] In the formula, P i is the actual output power of the hybrid energy storage system, and P i-refP is the power reference value that the system needs to track. The cumulative amount of all instantaneous power deviations is calculated from the dynamic process starting time t0 to the evaluation time t. t-t0 is the total time of the dynamic response. The total deviation area obtained by integration is divided by the total time to obtain the average power deviation per unit time. P eval The smaller the value, the closer the power curve to the target straight line, the stronger the power tracking ability of the system, the smaller the oscillation, and the more stable the control effect.

[0089] For the overshoot phenomenon, the overshoot equivalent value is taken to quantify the maximum instantaneous deviation value of the output power exceeding the target power in the dynamic response process. The formula is expressed as:

[0090]

[0091] In the formula, P i-max is the maximum value of the actual output power of the system, P i-ref is the power reference value that the system needs to track. ΔP eval The smaller the value, the less the overshoot phenomenon, the closer the power peak value to the target value, and the control system can effectively suppress the overshoot.

[0092] For the steady-state time, the total time required from the start of the dynamic process to the system output power re-entering and remaining within the allowable error range can be accurately measured, which can indicate the time required for the system to recover to stability, and its formula is expressed as follows:

[0093]

[0094] t0 is the starting time of the dynamic response process, t sd is the time when the system enters the steady state. t eval The smaller the value, the faster the dynamic response speed of the system, and the faster the system can quickly calm the impact of the disturbance and quickly track the new power command.

[0095] Then normalize the three evaluation indexes. For the three evaluation indexes, the smaller the better, and the normalization formula is as follows:

[0096]

[0097] The weighted sum of the three indexes is obtained, that is, the final evaluation score, which is expressed as:

[0098]

[0099] In the formula, , , is the weight coefficient of power oscillation, overshoot, and steady-state time.

[0100] The comprehensive evaluation system of the dynamic response process is constructed, the comprehensive evaluation system realizes the process from qualitative to quantitative, the physical quantity is normalized and the final evaluation score is obtained, and the dynamic response performance finally realized by the coordination control method can be judged according to the size of the final evaluation score.

[0101] The above is the introduction of the cascade type hybrid energy storage system coordination control method provided by the embodiment of the application, which is applied to a system composed of multiple H-bridge structures. The power supply of each H-bridge unit includes a group of batteries and super capacitors. A DC-DC converter is connected to each battery group and super capacitor, respectively, and the DC-DC converter is connected to the H-bridge inverter. When the system detects fluctuations in the total output current, the controller will calculate a virtual resistance value and a virtual capacitance value in real time according to the size and direction of the current. Then, using the two virtual values, the system will "create" a virtual voltage deviation for the battery and the super capacitor. This deviation is not a real voltage drop, but is used to guide the current to be allocated as needed by making the two "feel" different voltages in the control logic. The voltage loop calculates the required current reference value according to the virtual voltage deviation, and then compares the reference value with the actual current using the inner loop (current loop) to finally generate the duty cycle signal for controlling the switching devices of the DC-DC converter. Finally, the duty cycle is converted into specific switching pulses through PWM modulation and sent to the physical device for execution. Compared with the hybrid energy storage system using only batteries or using the traditional control method, the overshoot and oscillation of the system when responding to power fluctuations will be greatly reduced, the time to reach a stable state will be shortened, and the overall dynamic response performance will be significantly improved.

[0102] It can be understood that the size of the serial number of each step in the above embodiments does not mean the order of execution, and the execution order of each process should be determined according to its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the application. In addition, in some possible implementations, the steps in the above embodiments can be selectively executed, partially executed, or fully executed according to actual conditions, which is not limited here. All or part of any feature of any embodiment of the application can be freely combined in any way without contradiction. The combined technical solution is also within the scope of the application.

[0103] Based on the method in the above embodiments, the embodiment of the application further provides a cascade type hybrid energy storage system coordination control device. An exemplary, Figure 10 A structure schematic diagram of a cascade type hybrid energy storage system coordination control device provided by an embodiment of the application is shown. As Figure 10 shown, the device 1000 can include an acquisition module 1001 and a processing module 1002.

[0104] The acquisition module is configured to acquire an output voltage and an output current of the hybrid energy storage system.

[0105] The processing module 1002 is configured to determine an actual output power of the system based on the acquired output voltage and output current of the hybrid energy storage system, and determine a power difference value in combination with a power reference value preset or dispatched.

[0106] The processing module 1002 is further configured to determine whether the system is in a discharging mode or a charging mode according to the positive or negative of the output current, and the mode is used to limit an adjustment boundary of the virtual parameter.

[0107] The processing module 1002 is further configured to adaptively calculate and update the virtual resistance and the virtual capacitance based on the power difference value and the mode.

[0108] The processing module 1002 is further configured to generate a corresponding voltage deviation instruction by taking the updated virtual resistance and virtual capacitance as virtual impedance parameters of the battery branch and the super capacitor branch, respectively.

[0109] The processing module 1002 is further configured to input the voltage deviation instruction into a double closed-loop controller to generate a PWM duty cycle signal of each DC-DC converter, and realize dynamic coordinated control of the battery and the super capacitor according to the PWM duty cycle signal.

[0110] It should be understood that the above device is used to execute the method in the above embodiments, and the corresponding program modules in the device have similar implementation principles and technical effects to those described in the above method, and the working process of the device can refer to the corresponding process in the above method, which will not be described here.

[0111] Based on the method in the above embodiments, the embodiments of the present application provide a computer readable storage medium, which stores a computer program, and when the computer program runs on a processor, the processor executes the method in the above embodiments.

[0112] Based on the method in the above embodiments, the embodiments of the present application provide a computer program product, and when the computer program product runs on a processor, the processor executes the method in the above embodiments.

[0113] It is appreciated that the processor in the embodiments of the present application can be a central processing unit (CPU), and can also be other general-purpose processors, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic devices, transistor logic devices, hardware components or any combination thereof. The general-purpose processor can be a microprocessor or any conventional processor.

[0114] The method steps in the embodiments of the present application can be realized by hardware or by the processor executing software instructions. The software instructions can be composed of corresponding software modules, and the software modules can be stored in a random access memory (RAM), a flash memory, a read-only memory (ROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), an electrically EPROM (EEPROM), a register, a hard disk, a mobile hard disk, a CD-ROM or any other form of storage medium well known in the art. An exemplary storage medium is coupled to the processor, so that the processor can read information from and write information to the storage medium. Of course, the storage medium can also be an integral part of the processor. The processor and the storage medium can be located in an ASIC.

[0115] In the above embodiments, all or part of the embodiments can be implemented by software, hardware, firmware or any combination thereof. When implemented by software, all or part of the embodiments can be implemented in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of the present application are generated. The computer can be a general purpose computer, a special purpose computer, a computer network, or other programmable devices. The computer instructions can be stored in or transmitted by a computer readable storage medium. The computer instructions can be transmitted from one website, computer, server or data center to another website, computer, server or data center through a wired (such as coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (such as infrared, wireless, microwave, etc.) manner. The computer readable storage medium can be any available medium accessible by a computer or a data storage device such as a server, data center, etc. integrated with one or more available media. The available media can be a magnetic medium (for example, a floppy disk, a hard disk, a magnetic tape), an optical medium (for example, a DVD), or a semiconductor medium (for example, a solid state disk (SSD)) and the like.

[0116] It can be understood that various numerical numbers involved in the embodiments of the present application are only distinguished for convenience of description, and are not used to limit the scope of the embodiments of the present application.

Claims

1. A method for coordinating control of a cascade hybrid energy storage system, characterized in that, The cascade hybrid energy storage system comprises at least one battery unit, at least one other type of energy storage unit, and each energy storage unit is connected to a corresponding cascade H-bridge inverter module through an independent bidirectional DC-DC converter, and the method comprises: Based on the collected output voltage and current of the hybrid energy storage system, the actual output power of the system is determined, and the power difference value is determined in combination with the power reference value preset or scheduled and issued; According to the positive and negative of the output current, it is judged whether the system is in discharging mode or charging mode, and the mode is used to limit the virtual parameter adjustment boundary; Based on the power difference value and the mode, the virtual resistance and the virtual capacitance are adaptively calculated and updated, including: according to the power difference value and the upper and lower limit values of the preset virtual resistance and virtual capacitance, the virtual resistance and virtual capacitance values are respectively calculated and updated through a nonlinear function; wherein, in the discharging mode and the charging mode, the functions for calculating the virtual resistance and the virtual capacitance are different; The updated virtual resistance and virtual capacitance are respectively used as the virtual impedance parameters of the battery branch and the other type of energy storage unit branch to generate a corresponding voltage deviation instruction; The voltage deviation instruction is input into a double closed-loop controller to generate a PWM duty cycle signal of each DC-DC converter, and the dynamic coordination control of the battery and the other type of energy storage unit is realized according to the PWM duty cycle signal.

2. The method of claim 1, wherein, The initial value of the virtual resistance and the virtual capacitance is the middle value of the preset upper and lower limit values, and the formula is: In the formula, and are upper and lower limit values of a preset virtual resistance, and are upper and lower limit values of a preset virtual capacitance.

3. The method of claim 2, wherein, In the discharging mode, the formula for updating the virtual resistance and the virtual capacitance is: in which an initial value characterizing a virtual resistance, an initial value characterizing a virtual capacitance, a dynamic acceleration factor, a power difference value, a virtual resistance calculation intermediate quantity a virtual capacitance calculation intermediate quantity.

4. The method of claim 2, wherein, In the charging mode, the formula for updating the virtual resistance and the virtual capacitance is: in which an initial value characterizing the virtual resistance, an initial value characterizing the virtual capacitance, a dynamic acceleration factor, a power difference value, a virtual resistance calculation intermediate quantity a virtual capacitance calculation intermediate quantity.

5. The method of claim 1, wherein, The double closed-loop controller comprises a voltage outer loop and a current inner loop; The voltage outer loop is used to track the voltage deviation instruction and output a current reference value; The current inner loop is used to respond to the current reference value, superimpose an offset through a PI controller, and output a PWM duty cycle signal.

6. The method of claim 5, wherein, The current reference value is represented as: In the formula, , respectively represent the proportional coefficient and the integral coefficient of the voltage loop PI link, s is the Laplace operator, represents the single-phase output voltage of the cascade hybrid energy storage, is a virtual resistance, is the output current of the battery.

7. The method of claim 5, wherein, The duty cycle signal is represented as In the formula, , respectively represent the proportional coefficient and the integral coefficient of the current loop PI element, is the current reference value, is the output current of the DC-DC converter connected to the battery.

8. The method of claim 1, wherein, The method further comprises quantitatively evaluating the dynamic response performance, specifically comprising: Calculating the power oscillation equivalent value, the overshoot equivalent value, and the steady state time, wherein the power oscillation equivalent value is used to quantitatively evaluate the fluctuation degree of the output power in the dynamic response process, the overshoot equivalent value is used to quantitatively evaluate the maximum instantaneous deviation value of the output power exceeding the target power in the dynamic response process, and the steady state time is used to quantitatively evaluate the time required for the system to recover to stable state; After normalizing the calculated results, a weighted sum is obtained to obtain a comprehensive evaluation score.

9. A device for coordinating control of a cascade hybrid energy storage system, characterized in that, The device comprises: An acquisition module for acquiring the output voltage and current of the hybrid energy storage system; A processing module for determining the actual output power of the system based on the collected output voltage and current of the hybrid energy storage system, and determining the power difference value in combination with the power reference value preset or scheduled and issued; The processing module is also used to judge whether the system is in discharging mode or charging mode according to the positive and negative of the output current, and the mode is used to limit the virtual parameter adjustment boundary; The processing module is further configured to adaptively calculate and update the virtual resistance and the virtual capacitance based on the power difference and the mode, including: calculating and updating the virtual resistance and the virtual capacitance values by a non-linear function according to the power difference and preset upper and lower limit values of the virtual resistance and the virtual capacitance; wherein, in the discharging mode and the charging mode, functions for calculating the virtual resistance and the virtual capacitance are different; The processing module is further configured to take the updated virtual resistance and the virtual capacitance as virtual impedance parameters of the battery branch and the other type of energy storage unit branch respectively, and generate a corresponding voltage deviation instruction; The processing module is further configured to input the voltage deviation instruction into a double closed-loop controller to generate a PWM duty cycle signal of each DC-DC converter, and realize dynamic coordination control of the battery and the other type of energy storage unit according to the PWM duty cycle signal.

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