A new lithium battery + supercapacitor hybrid energy storage topology and its control design method

Abstract

The present invention discloses a novel lithium battery + supercapacitor hybrid energy storage topology and its control design method, which includes an energy-type lithium battery energy storage device, a power-type supercapacitor energy storage device, a DC power supply, a smoothing reactor and an anti-reverse diode. Through the system steady-state assumption, a steady-state mean model of the lithium battery energy storage device with respect to the duty cycle is constructed, thereby obtaining a basis for selecting the smoothing reactor parameters. Through the system transient assumption, a transient mean model of the lithium battery energy storage device with respect to the duty cycle is constructed, thereby constructing a system control model, obtaining closed-loop control parameters, and designing a voltage loop and current loop switching control method. The present invention greatly improves the charging and discharging flexibility and reliability of the hybrid energy storage system, achieves the control goals of lithium battery not over-rate charging and discharging, and bus voltage not over-voltage, and has broad application prospects in the fields of rail transit, renewable energy grid connection, and high-speed drive.

Description

Technical Field

[0001] The present invention belongs to the field of energy storage technology, and specifically relates to a novel lithium battery + supercapacitor hybrid energy storage topology and a control design method thereof. Background Art

[0002] Hybrid energy storage technology is a new type of energy storage technology that combines energy storage devices with different characteristics for mixed discharge through a multi-port topology. It has the advantages of both power density and energy density and is widely used in rail transit, renewable energy grid connection, and high-speed drive.

[0003] Energy storage devices are primarily categorized into two types: power-type and energy-type. Power-type devices are supercapacitors, while energy-type devices are lithium batteries. Lithium batteries have high energy density, but low power density, making them incapable of providing instantaneous high-power electricity. They also have short cycle life and poor temperature and environmental adaptability, and are typically used for large-scale power storage. Supercapacitors, on the other hand, have high power density, long cycle life, strong temperature and environmental adaptability, and fast response speed, but they have low energy density and are typically used to absorb and provide high-frequency, high-power electricity.

[0004] Hybrid energy storage systems typically employ passive, active, and semi-active topologies. A passive topology involves lithium batteries and supercapacitors connected directly in parallel. This topology automatically distributes power during discharge based on the internal resistance of the energy storage devices, lacking flexibility and requiring passive energy flow. An active topology involves both lithium batteries and supercapacitors connected in parallel via a DC / DC converter. This topology actively controls the energy flow between the energy storage device and the load, improving the flexibility and discharge performance of the energy storage system. However, multiple DC / DC converters increase system cost, weight, and volume, and complicate control methods. The currently more commonly used semi-active topology utilizes only a single DC / DC converter to regulate the output power of the hybrid energy storage system. Compared to passive and active topologies, this topology offers a comprehensive balance between system cost and discharge performance. However, this topology suffers from high output current ripple and poor system stability. Summary of the Invention

[0005] In response to the above defects or improvement needs of the prior art, the present invention provides a novel lithium battery + supercapacitor hybrid energy storage topology and its control design method, which improves the flexibility, stability and reliability of the hybrid energy storage system.

[0006] To achieve the above objectives, the present invention provides the following technical solutions: a novel lithium battery + supercapacitor hybrid energy storage topology, including an energy-type lithium battery energy storage device, a power-type supercapacitor energy storage device, a DC power supply, a smoothing reactor, and an anti-reverse diode. The energy-type lithium battery energy storage device, the smoothing reactor, and the switch Q1 are sequentially connected in series and then connected in parallel with the DC power supply. The power-type supercapacitor energy storage device, the anti-reverse diode, and the switch Q2 are sequentially connected in series and then connected in parallel with the DC power supply.

[0007] The energy-type lithium battery storage device is composed of an adjustable battery pack and a fixed battery pack connected in series, wherein the adjustable battery pack is composed of m battery packs connected in series, and the fixed battery pack is composed of n battery packs connected in series; each battery pack includes a battery pack unit and a bidirectional DC / DC conversion circuit, wherein the battery pack unit is composed of b battery modules connected in parallel, and each battery module is composed of a single battery cell connected in series, and the bidirectional DC / DC conversion circuit is composed of two IGBTs and two diodes, wherein the two IGBTs are connected in series and then connected in parallel with the battery pack unit, and each IGBT is connected in parallel with a diode;

[0008] The power type supercapacitor energy storage device is composed of y groups of capacitor modules connected in parallel, and each group of capacitor modules is composed of x single capacitors connected in series.

[0009] Furthermore, the rated operating voltage of each battery pack is V=v b *a. Internal resistance R=r b *a / b,v b is the rated voltage of a single battery, r b is the internal resistance of a single battery; the rated storage energy of each battery pack is Q = a*b*AH*v b , the total stored energy of the energy-type lithium battery energy storage device is Q*(m+n)≥the maximum energy consumption demand of the load, and AH is the ampere-hour of the available capacity of a single battery;

[0010] The number of battery groups in the adjustable battery group is m=round[(U max -U min ) / V], the number of battery groups in the fixed battery group n=ceil(U min / V), round() is the upward rounding function, ceil() is the downward rounding function, U max is the output voltage U of the hybrid energy storage system out The maximum fluctuation range, U min is the output voltage U of the hybrid energy storage system out The minimum fluctuation range.

[0011] Furthermore, the rated operating voltage U sc is x*v sc 、Internal resistance R sc For rsc *x / y, capacitance C sc c sc *y / x,v sc is the rated voltage of a single capacitor, r sc is the internal resistance of a single capacitor, c sc is the capacitance of a single capacitor; the maximum discharge power P of the power type supercapacitor energy storage device is U sc *y*i sc_max ≥ Maximum instantaneous power demand of the load, output voltage of the hybrid energy storage system U out Satisfy [U min , U max ] constraints, U max is the output voltage U of the hybrid energy storage system out The maximum fluctuation range, U min is the output voltage U of the hybrid energy storage system out The minimum fluctuation range, i sc_max is the maximum discharge current of a single capacitor.

[0012] A control design method for the hybrid energy storage system as described above is also provided, wherein the control design method comprises: constructing a steady-state mean value model of the hybrid energy storage device with respect to the duty cycle D, and calculating the fluctuation value Δi of the output current of the energy-type lithium battery energy storage device according to the steady-state mean value model. b ; According to the fluctuation value Δi of the output current of the energy type lithium battery energy storage device b Calculate the inductance L of the smoothing reactor; construct a transient mean model of the hybrid energy storage system based on the transient changes of the hybrid energy storage system and the inductance L of the smoothing reactor; obtain the small signal model of the hybrid energy storage system according to the transient mean model; obtain the closed-loop control parameters and switching control method of the hybrid energy storage system according to the small signal model.

[0013] Furthermore, the steady-state mean value model of the hybrid energy storage device with respect to the duty cycle D is constructed, and the fluctuation value Δi of the output current of the energy-type lithium battery energy storage device is obtained according to the steady-state mean value model. b The specific process is:

[0014] When the hybrid energy storage system is in discharge mode, the upper tube S of the bidirectional DC / DC conversion circuit corresponding to the adjustable battery pack is i_1 The corresponding topological equivalent circuits are obtained by simplifying different switching states. Under the two switching states, the voltage equation of the hybrid energy storage system is shown in formula (1):

[0015]

[0016] Where, L represents the inductance of the smoothing reactor; i b Indicates the output current of the energy type lithium battery energy storage device; U outrepresents the output voltage of the hybrid energy storage system; t represents the system operating time;

[0017] Integrating the voltage equations in the two switching states in equation (1), we can obtain:

[0018]

[0019] Where T is the switching period and D is the duty cycle;

[0020] First, make a steady-state assumption: the output current i of the energy-type lithium battery energy storage device is b And the hybrid energy storage system output voltage U out The mean change in adjacent switching cycles is 0, that is, for i b and U out In terms of the upper tube S of the bidirectional DC / DC conversion circuit corresponding to the adjustable battery pack i_1 Rise Δi at opening b1 With S i_1 Drop Δi when turning off b2 Same; in a single switching cycle, it is S i_1 The mean value at opening and S i_1 The mean value at turn-off is also the same and equal to the mean value during the entire switching cycle. Assuming steady state, we can get:

[0021]

[0022]

[0023] Where Δi b Indicates the fluctuation value of the output current of the energy-type lithium battery energy storage device; i b_ave Indicates the average output current of the energy-type lithium battery energy storage device; U out_ave Represents the average output voltage of the hybrid energy storage system.

[0024] Solve equations (2) to (4) simultaneously to construct a steady-state mean value model of the hybrid energy storage system with respect to the duty cycle D, as shown in equation (5). Substitute equation (5) into equation (2) to obtain the fluctuation value Δi of the output current of the energy-type lithium battery energy storage device: b As shown in formula (6);

[0025]

[0026]

[0027] Where, f s Indicates the switching frequency.

[0028] Furthermore, the fluctuation value Δi of the output current of the energy type lithium battery energy storage device is bThe specific process of calculating the inductance L of the smoothing reactor is:

[0029] From formula (6), we can see that as the inductance L of the smoothing reactor increases, the current fluctuation gradually decreases. As the duty cycle D increases, the current fluctuation first increases and then decreases. Simplified, when D is taken as the extreme point D0 of formula (6), the current fluctuation reaches the maximum value. D0 is shown in formula (7):

[0030]

[0031] Therefore, the maximum value Δi is constrained according to the current fluctuation b_max , Equations (6) and (7), calculate the minimum value of the inductance L of the smoothing reactor, as shown in Equation (8), to ensure that the fluctuation of the output current of the energy-type lithium battery energy storage device meets the constraint requirements and achieve the stability target of the hybrid energy storage system output;

[0032]

[0033] Furthermore, the specific process of constructing the transient mean value model of the hybrid energy storage system based on the transient changes of the hybrid energy storage system and the inductance L of the smoothing reactor is as follows:

[0034] Transient assumption: Two adjacent switching cycles i b and U out The fluctuation changes are approximately the same, that is, the transient assumption can be deduced:

[0035]

[0036] ΔI=I2-I1=i b_ave (k+1)-i b_ave (k) (10)

[0037] Where, I1 represents the switching period i b The initial current; I2 represents the current in one switching cycle b Final state current; I max Indicates that i b Peak current; ΔI represents i b The average change in adjacent switching cycles; U1 represents the average change in U out U2 represents the initial voltage of U in one switching cycle. out The final state voltage; U max Indicates U in one switching cycle out Peak voltage; indicates U out The mean change in adjacent switching cycles; k represents the kth control cycle;

[0038] Combining equations (2) and (9), we can simplify and obtain:

[0039] L(I2-I1)=U b1 DT+U b TU out_ave Ti b_ave (k)R b2 T-(I max +I1)R b1 DT / 2 (11)

[0040] I max +I1=2i b_ave +(1-D)(I1-I2) (12)

[0041] Substituting equations (10) and (12) into equation (11), we can obtain the following simplified formula:

[0042]

[0043] Since φ is much smaller than L when the switching frequency is high, it is ignored and i b The change of is written in the form of differential, and the transient mean model of the hybrid energy storage system is obtained as follows:

[0044]

[0045] Furthermore, the specific process of obtaining the small signal model of the hybrid energy storage system based on the transient mean model is as follows:

[0046] According to the hybrid energy storage system discharge equivalent circuit and the transient mean value model of formula (14), the circuit equation of the hybrid energy storage system is derived as shown in formula (15):

[0047]

[0048] Where U c0 Represents the initial voltage of the power supercapacitor energy storage device; i sc Indicates the output current of the power supercapacitor energy storage device;

[0049] According to formula (15), the small signal model of the hybrid energy storage system can be deduced as shown in formula (16):

[0050]

[0051] Where, and They represent the fluctuation of the output current of the energy-type lithium battery energy storage device, the fluctuation of the duty cycle, the fluctuation of the output current of the hybrid energy storage system, and the fluctuation of the bus voltage respectively; I b and D * They respectively represent the steady-state value of the output current and the steady-state value of the duty cycle of the energy-type lithium battery energy storage device.

[0052] Furthermore, the control method of the hybrid energy storage system obtained according to the small signal model is: first designing the current loop, then designing the voltage loop, and finally designing the switching rule;

[0053] According to formula (16), we can deduce that i b The open-loop transfer function G to D id (s) is:

[0054]

[0055] U out to i b The open-loop transfer function G vi (s) is:

[0056]

[0057] The system adopts current loop control i b The size of the supercapacitor output current i sc It is equal to the total output current i of HESS out with i b The difference between the current loop PI regulator transfer function G ci (s) is:

[0058]

[0059] Where k p1 and k i1 are the proportional and integral control parameters of the current loop respectively;

[0060] Then the open-loop transfer function W1(s) of the current loop is:

[0061]

[0062] To write W1(s) in the form of a standard Type I system, define the following variables:

[0063]

[0064] Where K1 and T2 are the inherent parameters of the system; T1 is the ratio of the current loop proportional and integral control parameters;

[0065] Substituting formula (21) into formula (20), we can simplify it and get:

[0066]

[0067] Let the control parameter k of the current loop be p1 and k i1If equation (23) is satisfied, the current loop control system can be simplified to a standard I-order system, at which point the system's dynamic and steady-state response performance is optimal.

[0068]

[0069] Voltage loop design, transfer function G of voltage loop PI regulator cv (s) is:

[0070]

[0071] Where k p2 and k i2 are the control parameters of the voltage loop PI regulator respectively.

[0072] The open-loop transfer function W2(s) of the voltage loop can be expressed by G cv (s), G vi (s) and G id (s) is derived and expressed as:

[0073]

[0074] Substituting the variables of formula (22) into formula (26), we can get:

[0075]

[0076] From Equation (26), we can see that the voltage loop control system is a type II system, with the poles and zeros located on the real axis and the left half plane of the real axis. It can be deduced that when the phase margin is 90°, the voltage loop control parameters and the cutoff frequency w are cv The relationship is as follows:

[0077]

[0078] When the voltage loop control parameter k p2 and k i2 When equation (27) is satisfied, the dynamic steady-state performance of the voltage loop is optimal.

[0079] Design of switching control rules:

[0080] The principle of the switching control strategy is: when k p1 ΔI≤k p2 When ΔU, the current loop is used to control i b Stable output, ensuring i b However, the power type supercapacitor energy storage device outputs a matching current according to the load power; when k p1 ΔI>k p2 When ΔU, the voltage loop is used to control U outQuickly and accurately stabilize at the rated operating voltage to avoid overvoltage or failure to meet the initial voltage requirements for the next transmission; where ΔI is i b With the current reference value i b_ref The error, ΔU is the output voltage U of the hybrid energy storage system out With the voltage reference value U ref error.

[0081] Furthermore, the basis for switching between the current loop and the voltage loop is shown in formula (28):

[0082]

[0083] Compared with the prior art, the present invention has the following beneficial effects:

[0084] 1) Inventing a new lithium battery + supercapacitor hybrid energy storage topology. Through the control of a bidirectional DC / DC converter circuit, it achieves both power density and energy density while greatly improving the flexibility, safety, and reliability of the hybrid energy storage system.

[0085] 2) The control design method of the present invention adopts a universal mean value modeling method, provides a basis for selecting smoothing reactor parameters, and provides a theoretical model foundation for the design of hybrid system control methods;

[0086] 3) The discharge control method in the control design method of the present invention ensures that the lithium battery does not discharge at an excessive rate and the bus voltage does not exceed the control target. BRIEF DESCRIPTION OF THE DRAWINGS

[0087] Figure 1 This is a schematic diagram of the new lithium battery + supercapacitor hybrid energy storage topology of the present invention;

[0088] Figure 2 for Figure 1 The middle is the battery pack structure diagram;

[0089] Figure 3 for Figure 1 Structural diagram of a medium-power supercapacitor energy storage device;

[0090] Figure 4 for Figure 1 Equivalent circuit diagram of a medium-energy lithium battery energy storage device with the upper tube turned on and the lower tube turned off;

[0091] Figure 5 for Figure 1 Equivalent circuit diagram of a medium-energy lithium battery energy storage device with the upper tube turned off and the lower tube turned on;

[0092] Figure 6 This is a voltage and current fluctuation diagram of the hybrid energy storage system under the steady-state assumption of the present invention;

[0093] Figure 7 This is the voltage and current fluctuation diagram of the hybrid energy storage system under the transient assumption of the present invention. DETAILED DESCRIPTION

[0094] In order to make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0095] like Figure 1 The new lithium battery + supercapacitor hybrid energy storage topology shown here includes an energy-type lithium battery energy storage device, a power-type supercapacitor energy storage device, a DC power supply, a smoothing reactor, and an anti-reverse diode. The energy-type lithium battery energy storage device, the smoothing reactor, and switch Q1 are connected in series and then in parallel with the DC power supply. The power-type supercapacitor energy storage device, the anti-reverse diode, and switch Q2 are connected in series and then in parallel with the DC power supply. The smoothing reactor boosts the DC voltage during charging and suppresses current ripple during discharge. The energy-type lithium battery energy storage device outputs in the positive direction, and the anti-reverse diode prevents the load or the power-type supercapacitor energy storage device from overfeeding energy to the energy-type lithium battery energy storage device.

[0096] Energy type lithium battery storage device stores the electrical energy required by the load, such as Figure 2 As shown, the energy-type lithium battery storage device consists of an adjustable battery pack and a fixed battery pack in series. The adjustable battery pack consists of m battery packs in series, and the fixed battery pack consists of n battery packs in series. Each battery pack includes a battery pack unit and a bidirectional DC / DC conversion circuit (the bidirectional DC / DC conversion circuit is used to control the charge and discharge of the battery pack unit). The battery pack unit is composed of b battery modules in parallel, and each battery module is composed of a single battery in series. The bidirectional DC / DC conversion circuit consists of 2 IGBTs and 2 diodes. The 2 IGBTs are connected in series and then connected in parallel with the battery pack unit. Each IGBT is connected in parallel with a diode. The rated operating voltage of each battery pack is V = v b *a. Internal resistance R=r b *a / b, where v b is the rated voltage of a single battery, r b is the internal resistance of a single battery.

[0097] like Figure 3 As shown, the power supercapacitor energy storage device is composed of y groups of capacitor modules connected in parallel, and each group of capacitor modules is composed of x single capacitors connected in series. The rated working voltage U sc is x*v sc 、Internal resistance R sc For rsc *x / y, capacitance C sc c sc *y / x, where v sc is the rated voltage of a single capacitor, r sc is the internal resistance of a single capacitor, c sc is the capacitance of a single capacitor; the power supercapacitor energy storage device is directly connected in parallel to the DC bus to provide the instantaneous pulse power required by the load.

[0098] Again Figure 2 As shown, the lower tube S in the bidirectional DC / DC conversion circuit i_2 (i=1,2…m,m+1…m+n) is turned off, upper tube S i_1 When the duty cycle D is turned on, the battery pack works in the discharge mode. At this time, the duty cycle D is in the range of (0, 1], the switch Q1 is turned off, and the switch Q2 is turned on; the upper tube S i_1 Shut off, lower tube S i_2 When the duty cycle D is turned on, the battery pack works in the charging mode. At this time, the duty cycle D is in the range of [0, 1), the switch Q1 is turned on, and the switch Q2 is turned off. It should be noted that the upper tube S of the bidirectional DC / DC converter circuit i_1 and down tube S i_2 Cannot be turned on at the same time.

[0099] m+n bidirectional DC / DC conversion circuits divide the high-voltage, large-capacity lithium battery energy storage into m+n battery packs with a rated operating voltage of V and an internal resistance of R, greatly improving the safety of battery use:

[0100] In discharge mode, if a battery pack fails, the upper tube S of the corresponding bidirectional DC / DC converter circuit can be kept i_1 Shut down (i.e. duty cycle D = 0) to bypass the faulty battery;

[0101] In charging mode, if a battery pack fails or is fully charged, the lower tube S of the corresponding bidirectional DC / DC converter circuit can be kept i_2 The battery is turned on (ie, duty cycle D=1) so that a faulty or fully charged battery is bypassed.

[0102] m+n bidirectional DC / DC conversion circuits divide the high-voltage, large-capacity lithium battery energy storage into m+n battery packs with a rated operating voltage of V and an internal resistance of R, greatly improving the flexibility of battery use:

[0103] In the discharge mode, the m battery packs of the adjustable battery pack correspond to the upper tube S of the bidirectional DC / DC converter circuit. i_1 With D∈(0,1) as the duty cycle, the chopped output; the n battery packs of the fixed battery pack correspond to the upper tube S of the bidirectional DC / DC conversion circuit i_1Keep it on, the battery pack has a constant output; the rated working voltage of the battery pack can be adjusted U b1 =m*V, internal resistance R b1 =m*R, fixed battery pack rated operating voltage U b2 =n*V, internal resistance R b2 =n*R;

[0104] In charging mode, all battery packs can correspond to the lower tube S of the bidirectional DC / DC conversion circuit. i_2 The duty cycle is D∈(0,1) to realize constant current charging of lithium battery energy storage. Due to the inconsistency in the charging and discharging process of lithium battery packs, when part of the battery pack is fully charged, the lower tube S of the corresponding bidirectional DC / DC converter circuit can be controlled. i_2 Keep it open, bypass it, and continue to charge the remaining battery pack with constant current.

[0105] The energy type lithium battery energy storage device configuration must meet the load energy requirements. The rated storage energy of each battery pack is Q = a*b*AH*v b , the total stored energy of the energy-type lithium battery energy storage device is Q*(m+n)≥the maximum energy consumption demand of the load, and AH is the ampere-hour of the available capacity of a single battery;

[0106] In discharge mode, the energy type lithium battery storage device is divided into adjustable battery pack and fixed battery pack. The configuration rule is based on the output voltage U out The fluctuation range [U min , U max ], the number of battery groups in the adjustable battery pack m=round[(U max -U min ) / V], the number of battery groups in the fixed battery group n=ceil(U min / V), round() is the upward rounding function, ceil() is the downward rounding function, U max For U out The maximum fluctuation range, U min For U out The minimum fluctuation range of

[0107] The power type supercapacitor energy storage device is configured to meet the load power requirements. The maximum discharge power of the power type supercapacitor energy storage device is P = U sc *y*i sc_max ≥The maximum instantaneous power demand of the load, while ensuring that the output voltage U of the hybrid energy storage system is out Satisfy [U min , U max ] constraints, i sc_max is the maximum discharge current of a single capacitor.

[0108] The design method of hybrid energy storage device control is as follows: construct a steady-state mean model of the hybrid energy storage device with respect to the duty cycle D, and calculate the fluctuation value Δi of the output current of the energy-type lithium battery energy storage device based on the steady-state mean model. b ; According to the fluctuation value Δi of the output current of the energy type lithium battery energy storage device b Calculate the inductance L of the smoothing reactor; construct a transient mean model of the hybrid energy storage system based on the transient changes of the hybrid energy storage system and the inductance L of the smoothing reactor; obtain the small signal model of the hybrid energy storage system according to the transient mean model; obtain the closed-loop control parameters and switching control method of the hybrid energy storage system according to the small signal model.

[0109] When the hybrid energy storage system is in discharge mode, the upper tube S of the bidirectional DC / DC conversion circuit corresponding to the adjustable battery pack is i_1 The corresponding topological equivalent circuits are simplified to different switching states, such as Figure 4 、 5 As shown, in the two switching states, the voltage equation of the hybrid energy storage system is shown in formula (1):

[0110]

[0111] Where, L represents the inductance of the smoothing reactor; i b Indicates the output current of the energy type lithium battery energy storage device; U out represents the output voltage of the hybrid energy storage system; t represents the system operating time.

[0112] Integrating the voltage equations in the two switching states in equation (1), we can obtain:

[0113]

[0114] Where T is the switching period and D is the duty cycle;

[0115] First, make a steady-state assumption: the output current i of the energy-type lithium battery energy storage device is b And the hybrid energy storage system output voltage U out The mean change in adjacent switching cycles is 0, that is, for i b and U out In terms of the upper tube S of the bidirectional DC / DC conversion circuit corresponding to the adjustable battery pack i_1 Rise Δi at opening b1 With S i_1 Drop Δi when turning off b2 Same; in a single switching cycle, it is S i_1 The mean value at opening and S i_1 The mean value at turn-off is also the same and is equal to the mean value during the entire switching cycle. The voltage and current fluctuation diagram of the hybrid energy storage system under the steady-state assumption is as follows: Figure 6shown.

[0116] according to Figure 6 And the steady-state assumption can be obtained:

[0117]

[0118]

[0119] Where Δi b Indicates the fluctuation value of the output current of the energy-type lithium battery energy storage device; i b_ave Indicates the average output current of the energy-type lithium battery energy storage device; U out_ave Represents the average output voltage of the hybrid energy storage system.

[0120] Solve equations (2) to (4) simultaneously to construct a steady-state mean value model of the hybrid energy storage system with respect to the duty cycle D, as shown in equation (5). Substitute equation (5) into equation (2) to obtain the fluctuation value of the output current of the energy-type lithium battery energy storage device, as shown in equation (6).

[0121]

[0122]

[0123] Where, f s Indicates the switching frequency.

[0124] From formula (6), we can see that as the inductance L of the smoothing reactor increases, the current fluctuation gradually decreases. As the duty cycle D increases, the current fluctuation first increases and then decreases. Simplified, when D is taken as the extreme point D0 of formula (6), the current fluctuation reaches the maximum value. D0 is shown in formula (7):

[0125]

[0126] Therefore, the maximum value Δi is constrained according to the current fluctuation b_max , Equations (6) and (7), calculate the minimum value of the inductance L of the smoothing reactor, as shown in Equation (8), to ensure that the fluctuation of the output current of the energy-type lithium battery energy storage device meets the constraint requirements and achieve the stability target of the hybrid energy storage system output.

[0127]

[0128] Since the inductance L and i of the smoothing reactor are not considered in the premise assumption b and U outThe steady-state mean model of the hybrid energy storage system cannot accurately describe the instantaneous state changes of the system's energy storage devices during dynamic transformations. Therefore, in order to derive the system's control model and control parameters, it is necessary to consider the system's transient changes based on the steady-state mean model, make new assumptions, and derive the system's dynamic model under transient conditions.

[0129] Therefore, it is necessary to make a new transient assumption: two adjacent switching cycles i b and U out The fluctuations of the voltage and current of the hybrid energy storage system under transient assumptions are shown in the figure below: Figure 7 shown.

[0130] according to Figure 7 And the transient assumption can be deduced:

[0131]

[0132] ΔI=I2-I1=i b_ave (k+1)-i b_ave (k) (38)

[0133] Where, I1 represents the switching period i b The initial current; I2 represents the current in one switching cycle b Final state current; I max Indicates that i b Peak current; ΔI represents i b The average change in adjacent switching cycles; U1 represents the average change in U out U2 represents the initial voltage of U in one switching cycle. out The final state voltage; U max Indicates U in one switching cycle out Peak voltage; indicates U out The mean change in adjacent switching cycles; k represents the kth control cycle.

[0134] Combining equations (2) and (9), we can simplify and obtain:

[0135] L(I2-I1)=U b1 DT+U b TU out_ave Ti b_ave (k)R b2 T-(I max +I1)R b1 DT / 2 (39)

[0136] I max +I1=2i b_ave +(1-D)(I1-I2) (40)

[0137] Substituting equations (10) and (12) into equation (11), we can obtain the following simplified formula:

[0138]

[0139] Since φ is much smaller than L when the switching frequency is high, it is ignored and i b The change of is written in the form of differential, and the transient mean model of the hybrid energy storage system is obtained as follows:

[0140]

[0141] Compared with the steady-state mean value model, the transient mean value model reduces the inductance L of the smoothing reactor to b The voltage changes caused by sudden changes are taken into account. Therefore, regardless of whether the system is in steady state or transient state, the transient mean model can accurately characterize the dynamic changes of various variables in the hybrid energy storage topology, providing a model analytical basis for the design of control methods for hybrid energy storage topologies.

[0142] according to Figure 1 The hybrid energy storage system discharge equivalent circuit and the transient mean value model of formula (14) are used to derive the circuit equation of the hybrid energy storage system as shown in formula (15):

[0143]

[0144] Where U c0 Represents the initial voltage of the power supercapacitor energy storage device; i sc Indicates the output current of the power supercapacitor energy storage device.

[0145] According to formula (15), the small signal model of the hybrid energy storage system can be deduced as shown in formula (16):

[0146]

[0147] Where, and They represent the fluctuation of the output current of the energy-type lithium battery energy storage device, the fluctuation of the duty cycle, the fluctuation of the output current of the hybrid energy storage system, and the fluctuation of the bus voltage respectively; I b and D * They respectively represent the steady-state value of the output current and the steady-state value of the duty cycle of the energy-type lithium battery energy storage device.

[0148] According to the small signal model, the closed-loop control parameters and switching control method of the hybrid energy storage system are obtained. First, the current loop is designed, then the voltage loop is designed, and finally the switching rules are designed.

[0149] First, according to formula (16), we can deduce that i bThe open-loop transfer function G to D id (s) is:

[0150]

[0151] U out to i b The open-loop transfer function G vi (s) is:

[0152]

[0153] The system adopts current loop control i b The size of the supercapacitor output current i sc It is equal to the total output current i of HESS out with i b The transfer function G of the current loop PI regulator is ci (s) is:

[0154]

[0155] Where k p1 and k i1 are the proportional and integral control parameters of the current loop respectively;

[0156] Then the open-loop transfer function W1(s) of the current loop is:

[0157]

[0158] To write W1(s) in the form of a standard Type I system, define the following variables:

[0159]

[0160] Where K1 and T2 are inherent parameters of the system; T1 is the ratio of the current loop proportional and integral control parameters.

[0161] Substituting formula (21) into formula (20), we can simplify it and get:

[0162]

[0163] Let the control parameter k of the current loop be p1 and k i1 If equation (23) is satisfied, the current loop control system can be simplified to a standard I-order system, at which point the system's dynamic and steady-state response performance is optimal.

[0164]

[0165] Then, the voltage loop is designed. The transfer function of the voltage loop PI regulator G cv (s) is:

[0166]

[0167] Where k p2 and k i2 are the control parameters of the voltage loop PI regulator respectively.

[0168] The open-loop transfer function W2(s) of the voltage loop can be expressed by G cv (s), G vi (s) and G id (s) is derived and expressed as:

[0169]

[0170] Substituting the variables of formula (22) into formula (26), we can get:

[0171]

[0172] From Equation (26), we can see that the voltage loop control system is a type II system, with the poles and zeros located on the real axis and the left half plane of the real axis. It can be deduced that when the phase margin is 90°, the voltage loop control parameters and the cutoff frequency w are cv The relationship is as follows:

[0173]

[0174] When the voltage loop control parameter k p2 and k i2 When equation (27) is satisfied, the dynamic steady-state performance of the voltage loop is optimal.

[0175] Finally, the switching control rules are designed.

[0176] In order to compare i b With the current reference value i b_ref The error ΔI and the output voltage U of the hybrid energy storage system out With the voltage reference value U ref The magnitude relationship of the error ΔU is to convert ΔI and ΔU into proportional parameters k p1 and k p2 Multiply them and convert them into the same dimension as the duty cycle D, and then compare them to serve as the basis for switching between the current loop and the voltage loop, as shown in formula (28):

[0177]

[0178] The principle of the switching control strategy is: when k p1 ΔI≤k p2 When ΔU, the current loop is used to control i b Stable output, ensuring i bHowever, the power type supercapacitor energy storage device outputs a matching current according to the load power; when k p1 ΔI>k p2 When ΔU, the voltage loop is used to control U out Quickly and accurately stabilize at the rated operating voltage to avoid overvoltage or failure to meet the initial voltage requirements for the next transmission.

[0179] During the operation of the current loop, the integral link of the voltage loop is set to be inoperative to prevent the integral saturation of the voltage loop, which may result in a large overshoot when switching to the voltage loop; during the operation of the voltage loop, the integral link of the current loop is set to be inoperative to prevent the integral saturation of the current loop, which may result in a large overshoot when switching to the current loop.

[0180] At this point, the system's control parameters, i.e., the proportional and integral control parameters of the current and voltage loops, are known, and the control rules, i.e., the switching basis, are known, thus completing the design of the entire control method.

[0181] It is easy for those skilled in the art to understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A new lithium battery + supercapacitor hybrid energy storage topology, characterized by: It includes an energy-type lithium battery energy storage device, a power-type supercapacitor energy storage device, a DC power supply, a smoothing reactor and an anti-reverse diode. The energy-type lithium battery energy storage device, the smoothing reactor and the switch Q1 are sequentially connected in series and then connected in parallel with the DC power supply. The power-type supercapacitor energy storage device, the anti-reverse diode and the switch Q2 are sequentially connected in series and then connected in parallel with the DC power supply. The energy-type lithium battery storage device is composed of an adjustable battery pack and a fixed battery pack connected in series, wherein the adjustable battery pack is composed of m battery packs connected in series, and the fixed battery pack is composed of n battery packs connected in series; each battery pack includes a battery pack unit and a bidirectional DC / DC conversion circuit, wherein the battery pack unit is composed of b battery modules connected in parallel, and each battery module is composed of a single battery cell connected in series, and the bidirectional DC / DC conversion circuit is composed of two IGBTs and two diodes, wherein the two IGBTs are connected in series and then connected in parallel with the battery pack unit, and each IGBT is connected in parallel with a diode; The power type supercapacitor energy storage device is composed of y groups of capacitor modules connected in parallel, and each group of capacitor modules is composed of x single capacitors connected in series.

2. The novel lithium battery + supercapacitor hybrid energy storage topology according to claim 1 is characterized by: The rated operating voltage of each battery pack is V = v b *a. Internal resistance R=r b *a / b,v b is the rated voltage of a single battery, r b is the internal resistance of a single battery; the rated storage energy of each battery pack is Q = a*b*AH*v b , the total stored energy of the energy-type lithium battery energy storage device is Q*(m+n)≥the maximum energy consumption demand of the load, and AH is the ampere-hour of the available capacity of a single battery; The number of battery groups in the adjustable battery group is m=round[(U max -U min ) / V], the number of battery groups in the fixed battery group n=ceil(U min / V), round() is the upward rounding function, ceil() is the downward rounding function, U max is the output voltage U of the hybrid energy storage system out The maximum fluctuation range, U min is the output voltage U of the hybrid energy storage system out The minimum fluctuation range.

3. The novel lithium battery + supercapacitor hybrid energy storage topology according to claim 1 is characterized by: The rated working voltage U of the power type supercapacitor energy storage device sc is x*v sc 、Internal resistance R sc For r sc *x / y, capacitance C sc c sc *y / x,v sc is the rated voltage of a single capacitor, r sc is the internal resistance of a single capacitor, c sc is the capacitance of a single capacitor; the maximum discharge power P of the power type supercapacitor energy storage device is U sc *y*i sc_max ≥ Maximum instantaneous power demand of the load, output voltage of the hybrid energy storage system U out Satisfy [U min , U max ] constraints, U max is the output voltage U of the hybrid energy storage system out The maximum fluctuation range, U min is the output voltage U of the hybrid energy storage system out The minimum fluctuation range, i sc_max is the maximum discharge current of a single capacitor.

4. A control design method for the novel lithium battery + supercapacitor hybrid energy storage topology as claimed in claim 1, characterized in that: The control design method is as follows: constructing a steady-state mean value model of the hybrid energy storage device with respect to the duty cycle D, and calculating the fluctuation value △i of the output current of the energy-type lithium battery energy storage device according to the steady-state mean value model b ; According to the fluctuation value △i of the output current of the energy type lithium battery energy storage device b Calculate the inductance L of the smoothing reactor; construct a transient mean model of the hybrid energy storage system based on the transient changes of the hybrid energy storage system and the inductance L of the smoothing reactor; obtain the small signal model of the hybrid energy storage system according to the transient mean model; obtain the closed-loop control parameters and switching control method of the hybrid energy storage system according to the small signal model.

5. The control design method of the novel lithium battery + supercapacitor hybrid energy storage topology according to claim 4 is characterized by: The steady-state mean value model of the hybrid energy storage device with respect to the duty cycle D is constructed, and the fluctuation value △i of the output current of the energy-type lithium battery energy storage device is obtained according to the steady-state mean value model. b The specific process is: When the hybrid energy storage system is in discharge mode, the upper tube S of the bidirectional DC / DC conversion circuit corresponding to the adjustable battery pack is i_1 The corresponding topological equivalent circuits are obtained by simplifying different switching states. Under the two switching states, the voltage equation of the hybrid energy storage system is shown in formula (1): Where, L represents the inductance of the smoothing reactor; i b Indicates the output current of the energy type lithium battery energy storage device; U out represents the output voltage of the hybrid energy storage system; t represents the system operating time; U b1 is the rated operating voltage of the adjustable battery pack; U b2 is the rated operating voltage of the fixed battery pack; R b1 、R b2 All are internal resistance; Integrating the voltage equations in the two switching states in equation (1), we can obtain: Where T is the switching period and D is the duty cycle; First, make a steady-state assumption: the output current i of the energy-type lithium battery energy storage device is b And the hybrid energy storage system output voltage U out The mean change in adjacent switching cycles is 0, that is, for i b and U out In terms of the upper tube S of the bidirectional DC / DC conversion circuit corresponding to the adjustable battery pack i_1 Rise amount △i when opening b1 With S i_1 Drop △i when turning off b2 Same; in a single switching cycle, it is S i_1 The mean value at opening and S i_1 The mean value at turn-off is also the same and equal to the mean value during the entire switching cycle. Assuming steady state, we can get: Where, △i b Indicates the fluctuation value of the output current of the energy-type lithium battery energy storage device; i b_ave Indicates the average output current of the energy-type lithium battery energy storage device; U out_ave Represents the average output voltage of the hybrid energy storage system; Solve equations (2) to (4) simultaneously to construct a steady-state mean value model of the hybrid energy storage system with respect to the duty cycle D, as shown in equation (5). Substitute equation (5) into equation (2) to obtain the fluctuation value △i of the output current of the energy-type lithium battery energy storage device: b As shown in formula (6); Where, f s Indicates the switching frequency.

6. The control design method of the novel lithium battery + supercapacitor hybrid energy storage topology according to claim 5 is characterized by: The fluctuation value △i of the output current of the energy type lithium battery energy storage device b The specific process of calculating the inductance L of the smoothing reactor is: From formula (6), we can see that as the inductance L of the smoothing reactor increases, the current fluctuation gradually decreases. As the duty cycle D increases, the current fluctuation first increases and then decreases. Simplified, when D is taken as the extreme point D0 of formula (6), the current fluctuation reaches the maximum value. D0 is shown in formula (7): Therefore, the maximum value △i is constrained according to the current fluctuation b_max , Equations (6) and (7), calculate the minimum value of the inductance L of the smoothing reactor, as shown in Equation (8), to ensure that the fluctuation of the output current of the energy-type lithium battery energy storage device meets the constraint requirements and achieve the stability target of the hybrid energy storage system output; 7. The control design method of the novel lithium battery + supercapacitor hybrid energy storage topology according to claim 6 is characterized by: The specific process of constructing the transient mean model of the hybrid energy storage system based on the transient changes of the hybrid energy storage system and the inductance L of the smoothing reactor is as follows: Transient assumption: Two adjacent switching cycles i b and U out The fluctuation changes are approximately the same, that is, the transient assumption can be deduced: △I=I2-I1=i b_ave (k+1)-i b_ave (k) (10) Where I1 represents the i in one switching cycle b The initial current; I2 represents the current in one switching cycle b Final state current; I max Indicates that i b Peak current; △I represents i b The mean change in adjacent switching cycles; U1 represents the U out U2 represents the initial voltage of U in one switching cycle. out The final state voltage; U max Indicates U in one switching cycle out Peak voltage; indicates U out The mean change in adjacent switching cycles; k represents the kth control cycle; Combining equations (2) and (9), we can simplify and obtain: L(I2-I1)=U b1 DT+U b T-U out_ave T-i b_ave (k)R b2 T-(I max +I1)R b1 DT / 2 (11) I max +I1=2i b_ave +(1-D)(I1-I2) (12) Substituting equations (10) and (12) into equation (11), we can obtain the following simplified formula: Since φ is much smaller than L when the switching frequency is high, it is ignored and i b The change of is written in the form of differential, and the transient mean model of the hybrid energy storage system is obtained as follows:

8. The control design method of the novel lithium battery + supercapacitor hybrid energy storage topology according to claim 7 is characterized by: The specific process of obtaining the small signal model of the hybrid energy storage system based on the transient mean model is as follows: According to the hybrid energy storage system discharge equivalent circuit and the transient mean value model of formula (14), the circuit equation of the hybrid energy storage system is derived as shown in formula (15): Where U c0 Represents the initial voltage of the power supercapacitor energy storage device; i sc Indicates the output current of the power supercapacitor energy storage device; According to formula (15), the small signal model of the hybrid energy storage system can be deduced as shown in formula (16): Where, and They represent the fluctuation of the output current of the energy-type lithium battery energy storage device, the fluctuation of the duty cycle, the fluctuation of the output current of the hybrid energy storage system, and the fluctuation of the bus voltage respectively; I b and D * They respectively represent the steady-state value of the output current and the steady-state value of the duty cycle of the energy-type lithium battery energy storage device.

9. The control design method of the novel lithium battery + supercapacitor hybrid energy storage topology according to claim 8 is characterized by: The control method of the hybrid energy storage system obtained according to the small signal model is as follows: first design the current loop, then design the voltage loop, and finally design the switching rule; According to formula (16), we can deduce that i b The open-loop transfer function G to D id (s) is: U out to i b The open-loop transfer function G vi (s) is: The system adopts current loop control i b The size of the supercapacitor output current i sc It is equal to the total output current i of HESS out with i b The difference between the current loop PI regulator transfer function G ci (s) is: Where k p1 and k i1 are the proportional and integral control parameters of the current loop respectively; Then the open-loop transfer function W1(s) of the current loop is: To write W1(s) in the form of a standard Type I system, define the following variables: Where K1 and T2 are the inherent parameters of the system; T1 is the ratio of the current loop proportional and integral control parameters; Substituting formula (21) into formula (20), we can simplify it and get: Let the control parameter k of the current loop be p1 and k i1 If equation (23) is satisfied, the current loop control system can be simplified to a standard I-order system, at which point the system's dynamic and steady-state response performance is optimal. Voltage loop design, transfer function G of voltage loop PI regulator cv (s) is: Where k p2 and k i2 are the control parameters of the voltage loop PI regulator respectively; The open-loop transfer function W2(s) of the voltage loop can be expressed by G cv (s), G vi (s) and G id (s) is derived and expressed as: Substituting the variables of formula (22) into formula (26), we can get: From Equation (26), we can see that the voltage loop control system is a type II system, with the poles and zeros located on the real axis and the left half plane of the real axis. It can be deduced that when the phase margin is 90°, the voltage loop control parameters and the cutoff frequency w are cv The relationship is as follows: When the voltage loop control parameter k p2 and k i2 When formula (27) is satisfied, the dynamic steady-state performance of the voltage loop is optimal; Design of switching control rules: The principle of the switching control strategy is: when k p1 △I≤k p2 When △U, the current loop is used to control i b Stable output, ensuring i b However, the power type supercapacitor energy storage device outputs a matching current according to the load power; when k p1 △I>k p2 When △U, the voltage loop is used to control U out Quickly and accurately stabilize at the rated operating voltage to avoid overvoltage or failure to meet the initial voltage requirements for the next transmission; where △I is i b With the current reference value i b_ref The error, △U is the output voltage U of the hybrid energy storage system out With the voltage reference value U ref error.

10. The control design method of the novel lithium battery + supercapacitor hybrid energy storage topology according to claim 9 is characterized in that: The basis for switching between the current loop and the voltage loop is shown in formula (28):

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