In-phase SOC self-adaptive rapid equalization method of angle type high-voltage direct-hanging energy storage system considering power limit and modulation degree limit

Abstract

The invention discloses an in-phase SOC (State of Charge) self-adaptive quick equalization method for an angle-type high-voltage direct-hanging energy storage system considering a power limit and a modulation degree limit, which combines two factors, namely the magnitude of system phase current and the magnitude of SOC equalization voltage. The additional SOC equalization voltage is adjusted by introducing a dynamic equalization coefficient Kp, and the SOC equalization voltage is smoothly reduced at the in-phase SOC equalization end stage. According to the method, the power limit and the modulation degree limit of the sub-modules can be fully considered, it is ensured that the system operates in a safe range, the balancing capacity of the energy storage system can be fully played, the balancing speed is increased as much as possible, and the maximum balancing speed is no longer purely pursued when SOC balancing last-stage adjustment is carried out; and instead, the additional equalization voltage is gradually reduced along with the delta SOCx, so that an additional equalization voltage error caused by an overlarge gain control coefficient is avoided, the equalization capability of the angle type high-voltage direct-hanging energy storage system is fully exerted, and the accuracy of the additional equalization voltage at the final equalization stage is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of battery energy storage conversion, and in particular to a method for adaptively fast balancing of the phase SOC of an angular high-voltage direct-mounted energy storage system taking into account power limits and modulation limits. Background Art

[0002] With the accelerated construction of new power systems and the increasing penetration of renewable energy, the short-circuit ratio and inertia of power grids have been significantly reduced. At the same time, renewable energy generation is generally characterized by volatility, randomness, and intermittency, posing a serious threat to the safe and stable operation of power systems. Electrochemical energy storage, as an effective means of integrating and accommodating renewable energy, not only reduces peak loads and smoothes fluctuations in renewable energy output, but also provides essential damping and inertial support for the power grid. Therefore, with the growing scale of renewable energy generation and the development of various energy storage technologies, electrochemical energy storage will undoubtedly become a cornerstone in ensuring the safe and stable operation of my country's new power system and achieving its "dual carbon" strategic goals. Medium-voltage direct-connected chain energy storage, with its advantages of large single-unit capacity, high operating efficiency, fast response, high output power quality, low reactive power losses, and the ability to "segment and control" battery cells, is a system solution suitable for future large-scale energy storage applications. However, the modular cascade structure typically employed in medium-voltage direct-connected chain energy storage presents significant challenges for battery management.

[0003] Due to differences in hardware technology and control parameters, maintaining consistent state of charge (SOC) across battery cells is difficult, limiting battery capacity utilization and posing the risk of overcharging and discharging. Large-capacity energy storage is often deployed near renewable energy sources, where grid strength is weak due to long transmission lines. Three-phase asymmetry in the grid voltage and negative-sequence power output from the PCS lead to imbalanced three-phase power output from the converter, further exacerbating the SOC imbalance within the BESS. This places higher demands on the performance of SOC balancing methods. Traditional intra-phase SOC balancing control strategies fail to consider submodule power and modulation constraints, lacking relevant limiting mechanisms. Furthermore, traditional intra-phase SOC balancing methods ignore the potential impact of changes in PCS power commands on the balancing process and lack the ability to adapt to power command changes. Furthermore, during the balancing process, traditional balancing strategies exhibit a gradual slowdown in balancing speed, failing to fully utilize the PCS's balancing capabilities. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an adaptive fast balancing method for the intra-phase SOC of an angular high-voltage direct-mounted energy storage system, which takes into account the power limit and modulation index limit, in view of the limitations of the traditional intra-phase SOC balancing method. The balancing voltage is dynamically controlled by real-time calculation of the balancing coefficient, and the balancing speed is dynamically maximized within the constraints of the sub-module power limit and modulation index.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A method for adaptively balancing the SOC within a phase of an angular high-voltage direct-mounted energy storage system considering power limits and modulation limits includes the following steps:

[0007] Step 1: Obtain the output phase voltage v of each phase of the energy storage converter in the angular high-voltage direct-mounted energy storage system x =V xm sinθ x , output phase current And the SOC of each phase sub-module battery cell xj ;

[0008] Where x = ab, bc, ca, j represents the jth submodule, ab represents the ab phase, bc represents the bc phase, and ca represents the ca phase; V xm represents the x-phase voltage amplitude, θ x Indicates the phase voltage of phase x, I xm represents the x-phase current amplitude, Indicates the phase of the x-phase current;

[0009] Step 2: Obtain the SOC of each phase, where the SOC of phase X is expressed as SOC xavg :

[0010]

[0011] N is the number of submodules within the phase;

[0012] Calculate the SOC deviation ΔSOC of the jth submodule xj for:

[0013] ΔSOC xj =SOC xj -SOC xavg ;

[0014] Step 3: Calculate the additional equalization voltage Δv required for the output voltage of each submodule xj :

[0015]

[0016] The additional active power ΔPxj of each submodule when performing intra-phase SOC balancing is calculated to perform intra-phase SOC balancing:

[0017]

[0018] Where: K p It is the control gain, which is used to adjust the size of the additional equalization voltage;

[0019] Among them, the fastest SOC balancing speed is K p The value of is:

[0020]

[0021] Among them, min{} means taking the minimum value; P lim Indicates the maximum active power value of the submodule, P xj represents the active power output by the jth submodule of the xth phase, ΔP xj represents the additional active power generated by the jth submodule of the xth phase;

[0022] ΔSOC x_pmax Indicates the maximum positive deviation of SOC ΔSOC x_pmax Additional active power of the corresponding submodule; ΔSOC x_nmax Indicates the maximum negative deviation of SOC ΔSOC x_pmax The additional active power of the corresponding submodule, K p_mp1 Indicates the K of the submodule corresponding to the maximum positive deviation of SOC when not modulating p The maximum value of K p_mn1 Indicates the maximum value of Kp of the submodule corresponding to the maximum negative SOC deviation when there is no overmodulation.

[0023] Further improvement, in step 3, K p The value of is obtained as follows:

[0024] Step 3.1) Ensure that the power of each submodule does not exceed the limit and the SOC balancing speed is the fastest. The corresponding K p The values ​​are:

[0025]

[0026] Step 3.2) Ensure that each submodule is not over-modulated and the SOC balancing speed is the fastest corresponding K p The value is: K p =min{K p_mp1 ,K p_mn1}

[0027] Step 3.3) combines the results of steps 3.1) and 3.2) to obtain:

[0028]

[0029] For further improvement, the specific steps of step 3.1) are as follows:

[0030] Calculate the output active power P of each phase x :

[0031] P x =v x i x

[0032] Calculate the active power P output by each submodule without considering the power redistribution caused by intra-phase SOC balance xj :

[0033] P xj =P x / N

[0034] The maximum active power value set by the submodule is P lim , to ensure that the submodule power does not exceed the limit, that is:

[0035] -P lim ≤P xj ≤P lim

[0036] Set the sub-module SOC and SOC xavg The maximum positive and negative deviations are ΔSOC x_pmax and ΔSOC x_nmax , then ΔSOC x_pmax Additional active power ΔP of the corresponding submodule x_pmax satisfy:

[0037] ΔP x_pmax ≤P lim -P xj

[0038] At the same time, ΔSOC x_nmax Additional active power ΔP of the corresponding submodule x_nmax satisfy:

[0039] ΔP x_nmax ≥-P lim -P xj

[0040] ΔSOC x_pmax and ΔSOC x_nmax The additional balanced voltage amplitude ΔV of each corresponding submodule x_pmax and ΔV x_nmax The following constraints are satisfied:

[0041]

[0042] The greater the additional active power of the submodule, the faster the SOC balancing speed in the phase. When the SOC balancing speed is fastest, K p The value of is:

[0043]

[0044] For further improvement, the specific steps of step 3.2) are as follows:

[0045] The output voltage v of the AC side submodule after the phase SOC is balanced is calculated. xj :for:

[0046]

[0047] It is required that each submodule is not over-modulated, so it is necessary to ensure that v xj The amplitude V xjm Not exceeding the DC side battery voltage U cxj ,Right now:

[0048] V xjm ≤U cxj

[0049] Let V xjm =U cxj According to the trigonometric function formula, the corresponding gain control coefficient K is obtained. p The solution is K p_1 and K p_2 :

[0050]

[0051] Among them, a1, b1, and c1 are calculated as follows:

[0052]

[0053] K p_1 , K p_2 The signs are opposite, so K satisfies the formula p The value range is:

[0054] 0≤K p ≤max(K p_1 ,K p_2 )=K p_1

[0055] ΔSOC x_pmax and ΔSOC x_nmax If the corresponding submodule is not over-modulated, the other submodules will not be over-modulated, so ΔSOC will be output. x_pmax and ΔSOC x_nmax Enter the solution formula to get the K of the corresponding submodule p Value range:

[0056]

[0057] Among them, K p_mp1 ΔSOC x_pmax The corresponding K p_1 The value of K p_mn1ΔSOC x_nma K corresponding to x p_1 The value of K p_mp ΔSOC x_pmax The corresponding K p The value of K p_mn ΔSOC x_nma K corresponding to x p The value of

[0058] The greater the additional active power of the submodule, the faster the SOC balancing speed in the phase. When the SOC balancing speed is fastest, K p The value of is:

[0059] K p =min{K p_mp1 ,K p_mn1}.

[0060] A further improvement is to reduce the balancing voltage smoothly when the intra-phase SOC balancing process enters the final stage:

[0061] Preset ΔSOC x_pmax and ΔSOC x_nmax SOC equilibrium threshold ΔSOC th , when ΔSOC x_pmax and ΔSOC x_nmax When it enters the preset equilibrium threshold,

[0062] That is |ΔSOC x_pmax |≤ΔSOC th and |ΔSOC x_nmax |≤ΔSOC th When the SOC balancing process in the phase is judged to have entered the final stage, the K p The value is set to a fixed value. When ΔSOC x_pmax and ΔSOC x_nmax Within the threshold range and K p After the set value is obtained, K is still calculated in real time according to the voltage instruction. p Value, if the calculated K p The value is less than the previously set K pf , then K pf Update to the calculated K p value, otherwise keep K pf constant.

[0063] A further improvement is that the angle-type high-voltage direct-mounted energy storage system includes an energy storage battery module, a battery-side filter capacitor, a battery-side filter inductor, an H-bridge submodule, an AC-side filter inductor, a contactor, a fuse, a sampling circuit, a main control board and a slave control board; the energy storage battery module is electrically connected to the H-bridge submodule through the battery-side filter inductor and the battery-side filter capacitor to form a cascade submodule; the cascade submodules are connected in series to form a single-phase cascade H-bridge; the single-phase cascade H-bridge is electrically connected to the AC filter inductor and forms an angle electrical connection with the other two-phase single-phase cascade H-bridges; the AC filter inductor is electrically connected to the AC power grid via a fuse and a contactor; the sampling circuit is electrically connected to the main control board; the main control board is electrically connected to the slave control board; the slave control board is electrically connected to the single-phase cascade H-bridge submodule; the main control board communicates and sends instructions and H-bridge drive signals to the slave control board, and after receiving the instructions from the main control board, the slave control board transmits the H-bridge drive signal to each single-phase cascade H-bridge.

[0064] Compared with the existing method, the present invention has the following beneficial effects:

[0065] 1. This paper proposes a method for adaptive fast balancing of phase SOC in angular high-voltage direct-mounted energy storage systems considering power limit and modulation limit. This strategy combines the two key factors of phase current and balanced voltage by introducing a dynamic balancing coefficient K. p To adjust the additional balancing voltage, it can not only fully consider the power limit and modulation limit of the sub-module to ensure that the system operates within a safe range, but also give full play to the balancing capability of the PCS and maximize the balancing speed.

[0066] 2. The present invention pre-sets the SOC balance threshold. When ΔSOC x_pmax and ΔSOC x_nmax When it enters the preset equilibrium threshold, K p Take it as a constant value, and the size of the additional balancing voltage will directly depend on ΔSOC xj The magnitude of ΔSOC xj When ΔSOC x_pmax and ΔSOC x_nmax Within the threshold range and K p After the fixed value is obtained, K still needs to be calculated in real time according to the external current instruction. p If the calculated K p The value is less than the previously set K pf , then K pf Update to the smaller value, otherwise keep K pf unchanged, so that the balanced voltage decreases smoothly. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1This is a main circuit topology diagram of an angular high-voltage direct-mounted energy storage system according to an embodiment of the present invention;

[0068] Figure 2 This is a controller block diagram of an angular high-voltage direct-mounted energy storage system according to an embodiment of the present invention;

[0069] Figure 3 This is a control structure for a method for adaptively balancing the intra-phase SOC of an angular high-voltage direct-mounted energy storage system taking into account power limits and modulation limits according to an embodiment of the present invention;

[0070] Figure 4 This is a flow chart of additional equalization voltage smoothing and transition reduction for an angular high-voltage direct-mounted energy storage system according to an embodiment of the present invention;

[0071] FIG5(a) is a waveform simulation diagram of conventional intra-phase SOC equalization when the SOC imbalance of the system according to an embodiment of the present invention is large; FIG5(b) is a waveform simulation diagram of conventional intra-phase SOC equalization when the SOC imbalance of the system according to an embodiment of the present invention is large under the same conditions as FIG5(a); FIG5(c) is a waveform simulation diagram of conventional intra-phase SOC equalization when the SOC imbalance of the system according to an embodiment of the present invention is small; FIG5(d) is a waveform simulation diagram of conventional intra-phase SOC equalization when the SOC imbalance of the system according to an embodiment of the present invention is small under the same conditions as FIG5(a);

[0072] Figure 6(a) is a waveform simulation diagram comparing the traditional intra-phase SOC balancing control strategy and the proposed intra-phase SOC balancing control strategy in an embodiment of the present invention; Figure 6(b) is a SOC waveform simulation diagram before and after switching between the traditional intra-phase SOC balancing control strategy and the proposed intra-phase SOC balancing control strategy under the same conditions as Figure 6(a) in an implementation system of the present invention. DETAILED DESCRIPTION

[0073] See attached Figure 1 , a diagram showing the main circuit topology of an angle-type high-voltage direct-mounted energy storage system according to an embodiment of the present invention. The angle-type high-voltage direct-mounted energy storage system includes an energy storage battery module, a battery-side filter capacitor, a battery-side filter inductor, an H-bridge submodule, an AC-side filter inductor, a contactor, and a fuse; the energy storage battery module is connected to the H-bridge submodule through the battery-side filter inductor and the battery-side filter capacitor, and forms a cascade submodule; the cascade submodules are connected in series to form a single-phase cascade H-bridge; the single-phase cascade H-bridge is connected to the AC filter inductor, and forms an angle connection with the other two-phase cascade H-bridges; the AC filter inductor is connected to the AC power grid through a fuse and a contactor; the sampling circuit is connected to the main control board; the main control board is connected to the slave control board; the slave control board is connected to the cascade H-bridge submodule; the main control board communicates with the slave control board to issue instructions and send H-bridge drive signals, and the slave control board transmits the H-bridge drive signal to each phase cascade H-bridge submodule circuit after receiving the instruction from the main control board. Wherein: Ucxj (x=ab, bc, ca) is the DC voltage of the jth cascaded submodule of the angular high-voltage direct-mounted energy storage system; e x (x=ab, bc, ca) is the three-phase AC output voltage of the angular high-voltage direct-mounted energy storage system; u x (x=ab, bc, ca) and i x (x=ab, bc, ca) are the AC side grid voltage and output current of the angular high-voltage direct-mounted energy storage system respectively; C dc It is the DC side capacitor of the angular high-voltage direct-mounted energy storage system; L s AC side filter inductor.

[0074] See attached Figure 2 The controller block diagram of the angle-type high-voltage direct-mounted energy storage system according to an embodiment of the present invention is mainly composed of a single-phase phase-locked loop module, an SOC balancing module, and a phase current loop module. The single-phase phase-locked loop module includes a phase, b phase, and c phase-locked loop modules. The SOC balancing module includes an inter-phase balancing module and an intra-phase balancing module. The phase current control loop module includes an active / reactive current command amplitude calculation module, a current tracking control module, and a carrier phase shift modulation module. The system control is mainly divided into five levels: single-phase phase-locked loop, active / reactive current command amplitude calculation, phase current command calculation, inter-phase SOC balancing control, and intra-phase SOC balancing control. The single-phase phase-locked loop is based on the single-phase line voltage u x (x=ab,bc,ca); construct a virtual three-phase voltage as the benchmark. According to the symmetrical component method, the virtual three-phase voltage consists of three sequence components: positive sequence, negative sequence, and zero sequence. The constructed virtual three-phase voltage components are brought into the dq transformation to filter out the zero sequence component. The dq components of the system contain DC components and double frequency components. The double frequency components are filtered out by the notch filter, and then u is controlled by the PI controller. q The phase of phase x and the voltage amplitude of phase x can be obtained by setting it to 0. x ; Active\reactive current command amplitude is calculated by giving active\reactive power command P ref \Q ref Divide by the grid voltage amplitude U x Get the active\reactive current command amplitude I xp \I xq ;(x=ab,bc,ca); The calculation of the phase current command is to first calculate the active\reactive current command amplitude to obtain the active\reactive current command amplitude I xp \I xq , and then compared with the phase of each line voltage output by the single-phase phase-locked loop θ x Construct phase link current instruction i x_ref , since the phase link current command i x_ref It is the fundamental frequency AC component, so the system current is tracked and controlled by PR control, and the grid voltage feedforward u is introducedx The inter-phase SOC balancing control adopts the zero-sequence injection method, and the average SOC value of N submodules in one phase represents the SOC of the phase, that is, SOC x Represents the SOC value of phase x. The additional power of inter-phase SOC balancing control depends on the deviation of the SOC of each phase ΔSOC x , SOC avg is the average value of the three-phase SOC, with the grid voltage u ab Phase θ ab (This θ ab The instantaneous phase of the phase-locked loop output is used as the reference phase to construct the zero-sequence current instruction, and θ ab The three-phase voltage is transformed into positive and negative sequence dq for phase reference to obtain the amplitude of positive and negative sequence active and reactive voltage components. The double frequency components in the positive and negative sequence active and reactive voltage components need to be filtered out by a notch filter. The calculated amplitude of the positive and negative sequence active and reactive voltage components is used to represent the three-phase grid voltage, and then the active power P generated by each phase after the zero sequence current is injected is calculated. 0x , where P 0x =λΔSOC x , λ is the inter-phase SOC balancing coefficient, which determines the speed of balancing. Generally, it is a constant according to the capacity. 0x =λΔSOC x Substitute the relationship between zero-sequence current and active power generated by each phase to obtain the active and reactive components of zero-sequence current I 0pref and I 0qref , and then calculate the zero-sequence current that needs to be injected, and add the calculated zero-sequence current to the current command calculated by the phase current control; add the additional balancing voltage calculated by the SOC balance within the phase to the voltage command obtained after PR tracking control, and thus calculate the voltage modulation wave of each phase.

[0075] See attached Figure 3 One embodiment of the present invention considers the power limit and modulation limit of the angular high-voltage direct-mounted energy storage system phase SOC adaptive fast balancing method control structure. The average SOC value of N submodules in a phase represents the SOC of the phase. The SOC of each phase can be expressed as:

[0076]

[0077] And the SOC deviation ΔSOC of the jth submodule can be calculated xj for:

[0078] ΔSOC xj =SOC xj -SOC x (2)

[0079] According to the SOC deviation ΔSOC of each submodule xjCalculate the additional equalization voltage Δv required in each submodule xj , and calculate the additional active power ΔP generated by each submodule xj ; According to the maximum active power value P set by the submodule hardware circuit design lim , calculate the SOC and SOC of the sub-module within the phase x Maximum positive and negative deviation ΔSOC x_pmax and ΔSOC x_nmax ; Then according to the obtained ΔSOC x_pmax and ΔSOC x_nmax Calculate the additional balanced voltage amplitude ΔV of the corresponding submodule x_pmax and ΔV x_nmax The conditions that should be met can be used to calculate the gain control coefficient K p The value range of each phase output voltage v of the energy storage system x Calculate the output voltage of each submodule The output voltage v of the AC side submodule after the phase SOC is balanced can be calculated xj * If each submodule is required to be non-overmodulated, it is necessary to ensure that v xj * The amplitude V xjm Not exceeding the DC link voltage U cxj , and calculate the corresponding gain control coefficient K p Solution; According to the obtained gain control coefficient K p The solution is combined with the maximum positive and negative SOC deviation ΔSOC x_pmax and ΔSOC x_nmax Calculate K p To ensure that the SOC balancing control within the phase does not cause overpower and overmodulation of any submodule, and at the same time maximize the SOC balancing speed within the constraints, K p It is necessary to satisfy the two calculated value ranges at the same time to obtain the gain control coefficient K that meets the conditions p ; Set the maximum positive and negative deviation of SOC ΔSOC x_pmax and ΔSOC x_nmax Compared with the preset threshold, if it is within the threshold, it is judged that the SOC balance in the phase has entered the final stage; when the SOC balance in the phase has entered the final stage, keep K p The value remains unchanged, and the additional equalization voltage amplitude is adjusted with ΔSOC xj The additional balancing voltage is reduced smoothly to prevent the additional balancing voltage from being wrong.

[0080] The gain control coefficient K of the adaptive fast equalization control method of the phase SOC of the angular high-voltage direct-mounted energy storage system considering the power limit and the modulation limit described in the present invention is pThe solution includes the following steps:

[0081] 1) At the beginning of each sampling cycle, the output phase voltage v of each phase of the energy storage converter is obtained by voltage and current sampling x =V xm sinθ x , output phase current And the SOC of each phase sub-module battery cell xj ;

[0082] 2) The SOC of each phase submodule battery cell in the current sampling period obtained by sampling in step 1) xj , taking the average SOC value of N submodules in one phase as SOC xavg Calculate the SOC of the phase. The SOC of each phase can be expressed as:

[0083]

[0084] And calculate the SOC deviation ΔSOC of the jth submodule xj for:

[0085] ΔSOC xj =SOC xj -SOC xavg (4)

[0086] 3) The SOC deviation ΔSOC of each submodule calculated according to step 2) xj And the output phase current of the current sampling period obtained by sampling in step 1) Calculate the additional equalization voltage Δv required in each submodule xj , the calculation formula is:

[0087]

[0088] Where: K p It is the control gain, which can adjust the size of the additional equalization voltage

[0089] The additional equalization voltage Δv calculated according to step 3) xj And the output phase current i of the current sampling period obtained by sampling in step 1) x Calculate the additional active power ΔP generated by each submodule xj , the calculation formula is:

[0090]

[0091] 4) The output phase voltage v of each phase of the energy storage converter in the current sampling period obtained by sampling in step 1) x =V xm sinθ x , output phase current Calculate the output active power P of each phase x , the calculation formula is:

[0092] P x =v x i x (7)

[0093] And calculate the active power P output by each submodule without considering the power redistribution caused by the intra-phase SOC balance xj , the calculation formula is:

[0094] P xj =P x / N (8)

[0095] The maximum active power value P set by the submodule hardware circuit design lim , it is necessary to ensure that the submodule power does not exceed the limit, that is:

[0096] -P lim ≤P xj ≤P lim (9)

[0097] Define the sub-module SOC and SOC within the phase xavg The maximum positive and negative deviation is ΔSOC x_pmax and ΔSOC x_nmax , then ΔSOC x_pmax Additional active power ΔP of the corresponding submodule x_pmax Should meet the following requirements:

[0098] ΔP x_pmax ≤P lim -P xj (10)

[0099] At the same time, ΔSOC x_nmax Additional active power ΔP of the corresponding submodule x_nmax Should meet the following requirements:

[0100] ΔP x_nmax ≥-P lim -P xj (11)

[0101] 5) Then, the additional equalization voltage Δv required for each submodule calculated in step 3) is xj And the additional active power ΔP generated by each submodule xj , combined with the maximum SOC deviation ΔSOC obtained in step 4) x_pmax and ΔSOC x_nmax The additional active power limit constraints of the corresponding submodules can be obtained as ΔSOC x_pmax and ΔSOC x_nmaxAdditional equalization voltage amplitude ΔV of the corresponding submodule x_pmax and ΔV x_nmax The constraint formula to be satisfied is:

[0102]

[0103] To ensure that the sum of the additional balanced voltages of all submodules is zero, K p The values ​​must be consistent, and the above constraints are taken to be the intersection. Considering K p The larger the value, the greater the additional active power of the submodule, and the faster the SOC balancing speed within the phase. Therefore, in order to maximize the SOC balancing speed within the submodule power limit constraint, K p Should be taken:

[0104]

[0105] 6) The output voltage v of each phase of the energy storage system in the current sampling period obtained by sampling in step 1) x Calculate the output voltage of each submodule Combined with the output current i of the current sampling period obtained by sampling in step 1) x , the AC side submodule output voltage v after the phase SOC is balanced can be calculated xj , the calculation formula is:

[0106]

[0107] 7) For H-bridge inverter, each submodule is required to be non-overmodulated, so it is necessary to ensure that v xj The amplitude V xjm Not exceeding the DC side battery voltage U cxj ,Right now:

[0108] V xjm ≤U cxj (15)

[0109] Combined with Vieta's theorem, the corresponding gain control coefficient K is obtained when the above formula is equal p The solution is:

[0110]

[0111] Among them, a1, b1, and c1 are calculated as follows:

[0112]

[0113] K p_1 , K p_2 The signs are opposite, so K satisfies the formula p The value range is:

[0114] 0≤Kp ≤max(K p_1 ,K p_2 )=K p_1 (18)

[0115] 8) In practical applications, only the maximum positive and negative deviations of SOC ΔSOC are required x_pmax and ΔSOC x_nmax If the corresponding submodule is not over-modulated, the other submodules will not be over-modulated, so ΔSOC x_pmax and ΔSOC x_nmax Substitute the ΔSOC obtained in step 7) into xj , and combined with K obtained in step 7) p The maximum positive and negative deviations of SOC ΔSOC can be obtained by solving x_pmax and ΔSOC x_nmax The K of the corresponding submodule p The value range of is:

[0116]

[0117] Where: K p_mp1 To convert ΔSOC x_pmax Substitute the K obtained in step 7) into p_1 The corresponding solution obtained; K p_mn1 To convert ΔSOC x_nmax Substitute the K obtained in step 7) into p_1 The corresponding solution obtained;

[0118] 9) Consider K p The larger the value, the faster the SOC balancing speed. Combined with the K obtained in step 8) p The value range of K is p The value should be:

[0119] K p =min{K p_mp1 ,K p_mn1} (20)

[0120] 9) To ensure that the intra-phase SOC balancing control does not cause overpower and overmodulation in any submodule, and at the same time maximize the SOC balancing speed within the constraints, K p It is necessary to satisfy the K obtained in step 5) and step 9) at the same time p The value of , thus finding the gain control coefficient K that meets the conditions p for:

[0121]

[0122] See attached Figure 4, an embodiment of the present invention is based on the flow chart of the additional equalization voltage smoothing transition reduction of the angular high-voltage direct-mounted energy storage system. Set the SOC equalization threshold to ΔSOC th , when the maximum SOC deviation in the phase is ΔSOC x_pmax and ΔSOC x_nmax When entering the range shown in formula (22), K p Take it as a constant value, and the size of the additional balancing voltage will directly depend on ΔSOC xj The magnitude of ΔSOC xj decreases synchronously with the decrease of .

[0123] |ΔSOC x_nmax |≤ΔSOC th and |ΔSOC x_nmax |≤ΔSOC th (twenty two)

[0124] When ΔSOC x_pmax and ΔSOC x_nmax When it is within the threshold for the first time, the K calculated at this moment is p Denoted as K pf , if in the subsequent process ΔSOC x_pmax and ΔSOC x_nmax If the voltage command remains within the threshold and the voltage command does not change, K should be maintained. p The value of K pf However, once the voltage command changes, the fixed K p It is impossible to achieve dynamic adjustment of the additional balancing voltage. Although the additional balancing voltage may be small at this time, it may still not meet the established power limit constraint and modulation index constraint conditions. Therefore, when ΔSOC x_pmax and ΔSOC x_nmax Within the threshold range and K p After the set value is obtained, K still needs to be calculated in real time according to the external voltage instruction. p If the calculated K p The value is less than the previously set K pf , then K pf Update to the smaller value, otherwise keep K pf unchanged, thereby achieving a smooth transition reduction of the additional balancing voltage at the end of the intra-phase SOC balancing period.

[0125] The effectiveness and advancement of the control method proposed in the embodiment of the present invention are verified by MATLAB / Simulink software.

[0126] See attached Figures 5(a) to 5(b), the SOC of each submodule battery in phases bc and ca is set to 80%, the SOC of the first three submodules ab1, ab2, and ab3 in phase ab are 91%, 90%, and 89% respectively, and the SOC of the remaining submodules is 90%, and the intra-phase balancing coefficient Kp is 300. A margin of 10kW is set on the rated power value of the submodule, that is, the power limit of the submodule is set to 62kW. The initial output active power of the system three phases is set to 5MW. At 0.5s, only the traditional intra-phase SOC balancing control strategy is added, and then at 1s, the inter-phase SOC balancing control strategy proposed in this paper is added. The simulation waveforms are shown in Figures 5(a) and 5(b). As can be seen from the figure, when only the traditional intra-phase SOC balancing control strategy is added, submodule ab1 is overmodulated, but no overpower phenomenon occurs. However, when inter-phase SOC balancing is added, since the average SOC value of phase ab is higher than that of the other two phases, the phase current of phase ab is at a larger value during the inter-phase SOC balancing process. At this time, under the action of traditional intra-phase SOC balancing, the power of sub-module ab1 exceeds the limit, indicating that the additional power and SOC balancing speed of the sub-module are affected by the change of phase current. This shows that the traditional balancing control strategy itself ignores the constraints of the limit values ​​such as sub-module power and modulation index, and lacks relevant restriction mechanisms.

[0127] See attached Figures 5(c) to 5(d) The SOCs of submodules ab1, ab2, and ab3 are set to 90.6%, 90%, and 89.4%, respectively, while keeping all other parameters unchanged. The simulation waveforms are shown in Figures 5(c) and 5(d). As can be seen from the figures, when the intra-phase SOC imbalance is small, the traditional intra-phase SOC balancing control strategy does not cause submodule overmodulation. However, after the inter-phase SOC balancing control strategy is implemented, the power of submodule ab1 still exceeds the limit due to the large phase current. The above simulations demonstrate that the traditional intra-phase SOC balancing control strategy lacks adaptability to varying degrees of SOC imbalance and suffers from submodule overmodulation and power overlimit issues, validating the correctness of the previous analysis.

[0128] See attached Figures 6(a) to 6(b)To verify the proposed intra-phase SOC balancing control strategy, the SOCs of sub-modules ab1, ab2, ab3 are set to 91%, 90%, 89% respectively, and the other parameters remain unchanged. At 0.5s, the proposed inter-phase SOC balancing control strategy and the traditional intra-phase SOC balancing control strategy are added, and then at 1s, the traditional intra-phase SOC balancing control strategy is switched to the proposed intra-phase SOC balancing control strategy. The simulation waveforms are shown in FIG. 6(a) and FIG. 6(b). As can be seen from the figure, in this working condition, the power constraint in the proposed intra-phase SOC balancing control strategy is stronger than the modulation degree constraint. After switching to the proposed intra-phase SOC balancing control strategy, the over-modulation phenomenon of sub-modules ab1, ab2, ab3 disappears through dynamic adjustment of the additional balancing voltage, the modulation degree of each sub-module is less than 1, and the active power output of sub-module ab1 is limited to the limit value of 62kW. At this time, the balancing capability reaches the limit within the constraint condition, proving that the proposed intra-phase SOC balancing control strategy has the ability to adapt to any SOC imbalance degree, can ensure that the power and modulation degree of any sub-module do not exceed the limit, and dynamically maximize the balancing speed within the two constraint conditions.

Claims

1. A method for adaptively balancing the phase SOC of an angular high-voltage direct-mounted energy storage system considering power limits and modulation limits, characterized in that: The steps include: Step 1: Obtain the output phase voltage v of each phase of the energy storage converter in the angular high-voltage direct-mounted energy storage system x =V xm sinθ x ,lose Output phase current And the SOC of each phase sub-module battery cell xj ; Where x = ab, bc, ca, j represents the jth submodule, ab represents the ab phase, bc represents the bc phase, and ca represents the ca phase; V xm represents the x-phase voltage amplitude, θ x Indicates the phase voltage of phase x, I xm represents the x-phase current amplitude, Indicates the phase of the x-phase current; Step 2: Obtain the SOC of each phase, where the SOC of phase X is expressed as SOC xavg : N is the number of submodules within the phase; Calculate the SOC deviation ΔSOC of the jth submodule xj for: ΔSOC xj =SOC xj -SOC xavg ; Step 3: Calculate the additional equalization voltage Δv required for the output voltage of each submodule xj : The additional active power ΔPxj of each submodule when performing intra-phase SOC balancing is calculated to perform intra-phase SOC balancing: Where: K p It is the control gain, which is used to adjust the size of the additional equalization voltage; Among them, the fastest SOC balancing speed is K p The value of is: Among them, min{} means taking the minimum value; P lim Indicates the maximum active power value of the submodule, P xj represents the active power output by the jth submodule of the xth phase, ΔP xj represents the additional active power generated by the jth submodule of the xth phase; ΔSOC x_pmax Indicates the maximum positive deviation of SOC ΔSOC x_pmax Additional active power of the corresponding submodule; ΔSOC x_nmax Indicates the maximum negative deviation of SOC ΔSOC x_pmax The additional active power of the corresponding submodule, K p_mp1 Indicates the K of the submodule corresponding to the maximum positive deviation of SOC when not modulating p The maximum value of K p_mn1 Indicates the maximum value of Kp of the submodule corresponding to the maximum negative SOC deviation when there is no overmodulation.

2. The method for adaptively balancing the intra-phase SOC of an angular high-voltage direct-mounted energy storage system considering power limits and modulation limits according to claim 1, characterized in that: In the step 3, K p The value of is obtained as follows: Step 3.1) Ensure that the power of each submodule does not exceed the limit and the SOC balancing speed is the fastest. The corresponding K p The values ​​are: Step 3.2) Ensure that each submodule is not over-modulated and the SOC balancing speed is the fastest corresponding K p The value is: K p =min{K p_mp1 ,K p_mn1 } Step 3.3) combines the results of steps 3.1) and 3.2) to obtain:

3. The method for adaptively balancing the intra-phase SOC of an angular high-voltage direct-mounted energy storage system considering power limit and modulation limit according to claim 2, characterized in that: The specific steps of step 3.1) are as follows: Calculate the output active power P of each phase x : P x =v x i x Calculate the active power P output by each submodule without considering the power redistribution caused by intra-phase SOC balance xj : P xj =P x / N The maximum active power value set by the submodule is P lim , to ensure that the submodule power does not exceed the limit, that is: -P lim ≤P xj ≤P lim Set the sub-module SOC and SOC xavg The maximum positive and negative deviations are ΔSOC x_pmax and ΔSOC x_nmax , then ΔSOC x_pmax Additional active power ΔP of the corresponding submodule x_pmax satisfy: ΔP x_pmax ≤P lim -P xj At the same time, ΔSOC x_nmax Additional active power ΔP of the corresponding submodule x_nmax satisfy: ΔP x_nmax ≥-P lim -P xj ΔSOC x_pmax and ΔSOC x_nmax The additional balanced voltage amplitude ΔV of each corresponding submodule x_pmax and ΔV x_nmax The following constraints are satisfied: The greater the additional active power of the submodule, the faster the SOC balancing speed in the phase. When the SOC balancing speed is fastest, K p The value of is:

4. The method for adaptively balancing the intra-phase SOC of an angular high-voltage direct-mounted energy storage system considering power limits and modulation limits according to claim 2, characterized in that: The specific steps of step 3.2) are as follows: The output voltage v of the AC side submodule after the phase SOC is balanced is calculated. xj :for: It is required that each submodule is not over-modulated, so it is necessary to ensure that v xj The amplitude V xjm Not exceeding the DC side battery voltage U cxj ,Right now: In xjm ≤U cxj Let V xjm =U cxj According to the trigonometric function formula, the corresponding gain control coefficient K is obtained. p The solution is K p_1 and K p_2 : Among them, a1, b1, and c1 are calculated as follows: K p_1 , K p_2 The signs are opposite, so K satisfies the formula p The value range is: 0≤K p ≤max(K p_1 ,K p_2 )=K p_1 ΔSOC x_pmax and ΔSOC x_nmax If the corresponding submodule is not over-modulated, the other submodules will not be over-modulated, so ΔSOC will be output. x_pmax and ΔSOC x_nmax Enter the solution formula to get the K of the corresponding submodule p Value range: Among them, K p_mp1 ΔSOC x_pmax The corresponding K p_1 The value of K p_mn1 ΔSOC x_nma K corresponding to x p_1 The value of K p_mp ΔSOC x_pmax The corresponding K p The value of K p_mn ΔSOC x_nma K corresponding to x p The value of The greater the additional active power of the submodule, the faster the SOC balancing speed in the phase. When the SOC balancing speed is fastest, K p The value of is: K p =min{K p_mp1 ,K p_mn1 }。 5. The method for adaptively balancing the intra-phase SOC of an angular high-voltage direct-mounted energy storage system considering power limit and modulation limit according to claim 1, characterized in that: When the intra-phase SOC balancing process enters the final stage, the method to smoothly reduce the balancing voltage is as follows: Preset ΔSOC x_pmax and ΔSOC x_nmax SOC equilibrium threshold ΔSOC th , when ΔSOC x_pmax and ΔSOC x_nmax When it enters the preset equilibrium threshold, That is |ΔSOC x_pmax |≤ΔSOC th and |ΔSOC x_nmax |≤ΔSOC th When the SOC balancing process in the phase is judged to have entered the final stage, the K p The value is set to a fixed value. When ΔSOC x_pmax and ΔSOC x_nmax Within the threshold range and K p After the set value is obtained, K is still calculated in real time according to the voltage instruction. p Value, if the calculated K p The value is less than the previously set K pf , then K pf Update to the calculated K p value, otherwise keep K pf constant.

6. The method for adaptively balancing the intra-phase SOC of an angular high-voltage direct-mounted energy storage system considering power limit and modulation limit according to claim 1, characterized in that: The angle-type high-voltage direct-mounted energy storage system includes an energy storage battery module, a battery-side filter capacitor, a battery-side filter inductor, an H-bridge submodule, an AC-side filter inductor, a contactor, a fuse, a sampling circuit, a main control board, and a slave control board; the energy storage battery module is electrically connected to the H-bridge submodule via the battery-side filter inductor and the battery-side filter capacitor to form a cascade submodule; the cascade submodules are connected in series to form a single-phase cascade H-bridge; the single-phase cascade H-bridge is electrically connected to the AC filter inductor and forms an angle electrical connection with the other two-phase single-phase cascade H-bridges; the AC filter inductor is electrically connected to the AC power grid via a fuse and a contactor; the sampling circuit is electrically connected to the main control board; the main control board is electrically connected to the slave control board; the slave control board is electrically connected to the single-phase cascade H-bridge submodule; the main control board communicates and sends instructions and H-bridge drive signals to the slave control board, and after receiving the instructions from the main control board, the slave control board transmits the H-bridge drive signal to each single-phase cascade H-bridge.

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