Cooperative control strategy of distributed energy storage system based on voltage correction

Abstract

The application discloses a kind of based on voltage correction's distributed energy storage system collaborative control strategy, mainly including communication module, SOC equalization module, virtual voltage regulating module, voltage correction module and voltage current double-loop control module.Communication module is passed through, and each parallel energy storage unit only needs to communicate with adjacent unit node to obtain energy storage system SOC average value;Through SOC equalization module and virtual voltage regulating module, different capacity energy storage unit SOC equalization and output current are accurately distributed according to unit capacity in proportion are realized;Through voltage correction module, effectively solve the problem of DC bus voltage deviation, and bus voltage is stably maintained to the vicinity of rated value, and the application only needs energy storage system SOC average value one state variable, and the SOC equalization of different capacity energy storage unit and output current are accurately distributed according to unit capacity in proportion, and bus voltage is maintained to rated value, improve the stability of system operation.

Description

Technical Field

[0001] The present invention relates to the field of DC microgrid distributed energy storage systems, and in particular to a coordinated control strategy for distributed energy storage systems based on voltage correction. Background Art

[0002] To address the impact of the uncertainty of distributed power output on the power grid and load, microgrids have been proposed as a solution. Among them, DC microgrids are widely used due to their reliability, scalability, and high efficiency. Due to the dispersion of distributed power sources and the randomness of output power, a distributed energy storage system of a certain capacity is required to ensure the power balance of the DC microgrid. Currently, distributed energy storage systems usually use droop control to achieve accurate distribution of the output current of each power source. Although droop control has the advantages of being simple, reliable, and independent of communication, it also has the limitation of not being able to simultaneously maintain bus voltage stability and evenly distribute the output current between each energy storage unit according to capacity. At the same time, the energy storage unit uses a DC-DC converter for charging and discharging. In order to avoid the imbalance of the state of charge (SOC) of each energy storage unit, resulting in overcharging or over-discharging of a certain energy storage unit, thereby affecting the service life of the energy storage unit and the stability of the DC microgrid, the present invention designs a distributed energy storage system collaborative control strategy based on voltage correction to ensure that the output current of each energy storage unit is accurately distributed according to the capacity ratio and the SOC is balanced. Summary of the Invention

[0003] To achieve the above objectives, the technical solutions provided by the present invention are:

[0004] Step S1: The four energy storage units are connected through the corresponding DC-DC converters and the corresponding line resistors R Linei Connected in parallel to the DC bus, and connected to the load resistor R Load Power supply, at the start of each sampling period, the DC side inductor current i Li , DC side output voltage u oi , DC side output current i oi , energy storage unit state of charge SOC i , DC bus voltage u bus Sampling was carried out separately;

[0005] Step S2: In the communication module, the four energy storage units use a ring communication, and only need to exchange information with the adjacent energy storage units, and the state of charge (SOC) of each energy storage unit in the system can be obtained without going through the central controller. i The global information of the energy storage unit state of charge SOC i As input, the average state of charge SOC of the energy storage system can be obtained by using the dynamic diffusion algorithm. avg ;

[0006] Step S3: In the SOC equalization module, the energy storage system state of charge average value SOC avg and the energy storage unit state of charge SOC i are subtracted to obtain the energy storage unit state of charge standard deviation dSOC i The energy storage unit state of charge standard deviation dSOC i is then selected for output according to the positive and negative of the DC side output current i oi If the DC side output current i oi is greater than zero, it indicates that the energy storage system is in a discharging working mode, and the energy storage unit state of charge standard deviation dSOC i is output at this time. If the DC side output current i oi is less than zero, it indicates that the energy storage system is in a charging working mode, and the energy storage unit state of charge standard deviation dSOC i is output at this time. The obtained result is then multiplied by a process coefficient λ to obtain an intermediate coefficient β, wherein the process coefficient λ expression is:

[0007]

[0008] In formula (1), ε is an equalization acceleration factor, η is an equalization adjustment index factor, θ is an equalization precision factor, dSOC k is the state of charge standard deviation of the kth energy storage unit adjacent to the ith energy storage unit in the ring communication, equal to the energy storage system state of charge average value SOC avg minus the kth energy storage unit state of charge SOC k , and dSOC j is the state of charge standard deviation of the jth energy storage unit adjacent to the ith energy storage unit in the ring communication, equal to the energy storage system state of charge average value SOC avg minus the jth energy storage unit state of charge SOC j ;

[0009] The intermediate coefficient β expression is:

[0010]

[0011] The intermediate coefficient β is taken as an inverse hyperbolic tangent function arctanh, multiplied by and then added to an initial virtual resistance R v0 , multiplied by the inverse of the energy storage unit rated capacity C bat to obtain a virtual resistance R vi , wherein the virtual resistance R vi expression is:

[0012]

[0013] Step S4: In the virtual voltage regulation module, the virtual resistor R vi Multiply by the DC side output current i oi , get the virtual voltage Δu of the energy storage unit vi , and then the virtual voltage Δu of the energy storage unit vi As input, the virtual voltage Δu of the kth energy storage unit adjacent to the i-th energy storage unit in the ring communication is taken as input. vk Subtract the virtual voltage Δu of the energy storage unit vi , get the virtual voltage deviation Δu between the i-th energy storage unit and its adjacent k-th energy storage unit vki , and also the virtual voltage Δu of the jth energy storage unit adjacent to the i-th energy storage unit in the ring communication vj Subtract the virtual voltage Δu at the energy storage unit vi , get the i-th

[0014] The virtual voltage deviation Δu between the energy storage unit and its adjacent j-th energy storage unit vkj , and then the virtual voltage deviation Δu between the i-th energy storage unit and its adjacent k-th energy storage unit vki The virtual voltage deviation Δu between the i-th energy storage unit and its adjacent j-th energy storage unit vkj Add together to get the total virtual voltage deviation Δu Ti , and then multiply it by an adjustment coefficient Q to get the virtual voltage adjustment amount Δu ii , where the virtual voltage regulation value Δu ii The expression is:

[0015] Δu ii =Q(Δu vj +Δu vk -2Δu vi ) (4)

[0016] Step S5: In the voltage correction module, the voltage reference value u ref and DC bus voltage u bus Subtract and get the bus voltage deviation Δu b , the bus voltage deviation Δu b and virtual voltage regulation Δu ii Add them together, multiply them by an integral gain K, and then pass through an integrator to get the voltage correction u i , where voltage correction u i The expression is:

[0017] u i =∫(K(u ref -u bus +Δu ii ))dt (5)

[0018] Step S6: In the voltage and current double-loop control module, the voltage correction amount u i is added to the voltage reference value u ref , and then the DC side output voltage u oi is subtracted, and the result is subjected to voltage outer loop PI controller G vPI (s) to obtain the current inner loop reference value i refi , which is subtracted from the DC side inductance current i refi , and the result is subjected to current inner loop PI controller G Li (s) to obtain the driving voltage u iPI , which is subjected to PWM modulation to output a reliable modulation signal. si si

[0019] Further, in step S3, the value range of the equalization acceleration factor ε is 0.2<ε<0.9, the value range of the equalization adjustment index factor η is 0<η<1, the value range of the equalization accuracy factor θ is 0.0001<θ<0.01, and the value range of the initial virtual resistance R v0 is 0<R v0 <4; in step S4, the value range of the adjustment coefficient Q is 1<Q<6; and in step S5, the value range of the integral gain K is 10<K<25.

[0020] Compared with the prior art, the principle and advantages of the scheme are as follows:

[0021] The application discloses a distributed energy storage system cooperative control strategy based on voltage correction, mainly comprising a communication module, an SOC equalization module, a virtual voltage adjustment module, a voltage correction module and a voltage and current double-loop control module. Through the communication module, each parallel energy storage unit only needs to communicate with adjacent unit nodes to obtain the average value of the energy storage system SOC; through the SOC equalization module and the virtual voltage adjustment module, the SOC equalization of energy storage units with different capacities and the accurate proportional distribution of output currents according to the unit capacity are realized; through the voltage correction module, the problem of DC bus voltage deviation is effectively solved, and the bus voltage is stably maintained near the rated value. The application only needs one state quantity of the average value of the energy storage system SOC to realize the SOC equalization of energy storage units with different capacities and the accurate proportional distribution of output currents according to the unit capacity, and to maintain the bus voltage to the rated value, thereby improving the stability of system operation. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is the main circuit diagram of the distributed energy storage system in the embodiment of the application.

[0023] Figure 2 It is the control block diagram of the distributed energy storage system cooperative control strategy based on voltage correction in the embodiment of the application.​​

[0024] Figure 3 The ring communication diagram of the energy storage unit in the embodiment of the application;

[0025] Figure 4 The state of charge SOC in the embodiment of the application i Waveform diagram;

[0026] Figure 5 The DC bus voltage u in the embodiment of the application bus Waveform diagram;

[0027] Figure 6 The DC side output current i in the embodiment of the application oi Waveform diagram. DETAILED DESCRIPTION

[0028] The application will be further described below in combination with specific embodiments:

[0029] Figure 1 The main circuit diagram of the distributed energy storage system is shown, which is composed of four energy storage units in parallel through corresponding DC-DC converters, wherein i = 1, 2, 3, 4, DESU i represents the i th energy storage unit, i Li represents the DC side inductance current of the i th energy storage unit, u oi represents the DC side output voltage of the i th energy storage unit, i oi represents the DC side output current of the i th energy storage unit, R Linei represents the line resistance corresponding to the i th energy storage unit, the line resistances R Line1 , R Line2 , R Line3 and R Line4 are 0.6Ω, 0.7Ω, 0.65Ω, 0.5Ω respectively, R Load is a load resistance of 20Ω, the capacities of the four energy storage units are 6F, 6F, 4F and 4F respectively, the inductances L i are all 0.002H, the capacitances C i are all 0.003F, u bus is a DC bus voltage, u ref is a voltage reference value set to 400V.

[0030] Figure 2 The control block diagram of the collaborative control strategy of the distributed energy storage system based on voltage correction is shown, and the specific content is as follows:

[0031] Step S1: The four energy storage units are connected in parallel to the DC bus through corresponding DC-DC converters and corresponding line resistances R Linei , and together supply the load resistance R LoadPower supply, at the starting point of each sampling cycle, the DC side inductance current i Li , DC side output voltage u oi , DC side output current i oi , energy storage unit state of charge SOC i , DC bus voltage u bus are sampled respectively;

[0032] Step S2: In the communication module, four energy storage units adopt ring communication, only need to exchange information with adjacent energy storage units, without the need of passing through the central controller, the global information of each energy storage unit state of charge SOC i in the system can be obtained, taking the energy storage unit state of charge SOC i as the input quantity, and using the dynamic diffusion algorithm, the energy storage system state of charge average value SOC avg can be obtained;

[0033] Step S3: In the SOC equalization module, the energy storage system state of charge average value SOC avg is subtracted from the energy storage unit state of charge SOC i , the energy storage unit state of charge standard deviation dSOC i is obtained, and the energy storage unit state of charge standard deviation dSOC i is selected and output according to the positive and negative of the DC side output current i oi , if the DC side output current i oi is greater than zero, it indicates that the energy storage system is in discharging mode, at this time the energy storage unit state of charge standard deviation dSOC i is output, if the DC side output current i oi is less than zero, it indicates that the energy storage system is in charging mode, at this time the energy storage unit state of charge standard deviation dSOC i is output after inversion, and the obtained result is multiplied by the process coefficient λ, to obtain the intermediate coefficient β, wherein the process coefficient λ expression is:

[0034]

[0035] In formula (6), ε is the equalization acceleration factor, η is the equalization adjustment index factor, θ is the equalization accuracy factor, dSOC k is the state of charge standard deviation of the adjacent kth energy storage unit of the ith energy storage unit in the ring communication, equal to the energy storage system state of charge average value SOC avg minus the kth energy storage unit state of charge SOC k , dSOC j is the state of charge standard deviation of the adjacent jth energy storage unit of the ith energy storage unit in the ring communication, equal to the energy storage system state of charge average value SOC avgSubtract the jth energy storage unit state of charge SOC j ;

[0036] The intermediate coefficient β is expressed as:

[0037]

[0038] Take the inverse hyperbolic tangent function arctanh of the intermediate coefficient β, and multiply it by Add the initial virtual resistance R v0 , and multiply it by the reciprocal of the rated capacity C bat of the energy storage unit to obtain the virtual resistance R vi , where the virtual resistance R vi is expressed as:

[0039]

[0040] Step S4: In the virtual voltage adjustment module, multiply the virtual resistance R vi by the direct current side output current i oi to obtain the virtual voltage Δu vi of the energy storage unit, and subtract the virtual voltage Δu vi of the energy storage unit as input from the virtual voltage Δu vk of the kth energy storage unit adjacent to the ith energy storage unit in the ring communication to obtain the virtual voltage deviation Δu vi of the ith energy storage unit and the kth energy storage unit adjacent thereto. vki At the same time, subtract the virtual voltage Δu vj of the jth energy storage unit adjacent to the ith energy storage unit in the ring communication from the virtual voltage Δu vi of the energy storage unit to obtain the virtual voltage deviation Δu

[0041] of the ith energy storage unit and the jth energy storage unit adjacent thereto. vkj Add the virtual voltage deviation Δu vki of the ith energy storage unit and the kth energy storage unit adjacent thereto and the virtual voltage deviation Δu vkj of the ith energy storage unit and the jth energy storage unit adjacent thereto to obtain the total virtual voltage deviation Δu Ti , and multiply it by an adjustment coefficient Q to obtain the virtual voltage adjustment Δu ii , where the expression of the virtual voltage adjustment Δu ii is:

[0042] Δu ii = Q(Δu vj + Δu vk - 2Δu vi ) (9)

[0043] Step S5: In the voltage correction module, the voltage reference value u ref is subtracted from the DC bus voltage u bus to obtain the bus voltage deviation Δu b , and the bus voltage deviation Δu b is added to the virtual voltage adjustment amount Δu ii , multiplied by an integral gain K, and then passed through an integrator to obtain the voltage correction amount u i , wherein the voltage correction amount u i is expressed as:

[0044] u i =∫(K(u ref -u bus +Δu ii ))dt (10)

[0045] Step S6: In the voltage and current double-loop control module, the voltage correction amount u i is added to the voltage reference value u ref , and the DC side output voltage u oi is subtracted, and then passed through a voltage outer loop PI controller G vPI (s) to obtain the current inner loop reference value i refi , and the current inner loop reference value i refi is subtracted from the DC side inductance current i Li , and the result is passed through a current inner loop PI controller G iPI (s) to obtain the drive voltage u si , and the drive voltage u si is passed through PWM modulation to output a reliable modulation signal.

[0046] Further, in step S3, the value range of the equalization acceleration factor ε is 0.2<ε<0.9, the value range of the equalization adjustment index factor η is 0<η<1, the value range of the equalization accuracy factor θ is 0.0001<θ<0.01, and the value range of the initial virtual resistance R v0 is 0<R v0 <4; in step S4, the value range of the adjustment coefficient Q is 1<Q<6; and in step S5, the value range of the integral gain K is 10<K<25.

[0047] Figure 3 As shown in the ring-shaped communication diagram of the energy storage unit, four energy storage units are connected in the order of DESU i -DESU k -DESU q -DESU j -DESU i to form a ring-shaped communication, wherein DESUi represents the i-th energy storage unit, DESU k represents the i-th energy storage unit in the ring communication adjacent to the k-th energy storage unit, DESU j represents the i-th energy storage unit in the ring communication adjacent to the j-th energy storage unit, DESU q represents the i-th energy storage unit in the ring communication not adjacent to the q-th energy storage unit.

[0048] Figure 4 SOC of the energy storage unit is shown i The waveform diagram shows that four energy storage units are in discharging mode, and the initial state of charge SOC1, SOC2, SOC3 and SOC4 are 91%, 88%, 86% and 84% respectively. It can be seen that the four energy storage units can realize SOC equalization through the SOC equalization control module in the application, and the four SOC curves converge at a certain rate. SOC2 and SOC3 complete equalization at 2.9s, SOC1 and SOC2 and SOC3 complete equalization at 3.8s, and the four SOC curves complete equalization at 4.7s, and continue to discharge at the same rate.

[0049] Figure 5 The DC bus voltage u of the distributed energy storage system is shown bus The waveform diagram shows that the energy storage system is in discharging mode. Since the voltage correction module is added, even if the system has certain voltage fluctuations at the initial stage of starting, it will recover to the voltage reference value 400V after 0.18s, and will also be stable to 400V at other times.

[0050] Figure 6 The DC side output current i of the distributed energy storage system is shown oi The waveform diagram shows that four energy storage units are in discharging mode, and the corresponding rated capacity ratio is 3:3:2:2. Under the joint action of the SOC equalization module and the virtual voltage regulation module, the energy storage unit with larger rated capacity and initial state of charge discharges more current, and the energy storage unit with smaller rated capacity and initial state of charge discharges less current. Finally, the four energy storage units realize current equalization at about 4.7s, and the output currents of the four energy storage units are 6A, 6A, 4A and 4A respectively, which satisfies the accurate distribution principle of output current according to 3:2:2:2, and the output current of each energy storage unit remains stable during the simulation.

[0051] From the above analysis, the application designs a distributed energy storage system cooperative control strategy based on voltage correction, through designing an improved SOC equalizer, virtual voltage regulation and voltage correction controller, completing SOC equalization of different capacity energy storage units and accurate distribution of output current according to unit capacity, and maintaining the bus voltage to the rated value target, so as to prolong the service life of the energy storage unit and ensure the stability of the system operation.

[0052] The above-mentioned embodiments are only the preferred embodiments of the present application, and are not intended to limit the scope of the application. Any changes made in accordance with the shape and principle of the present application should be covered within the scope of protection of the present application.

Claims

1. A coordinated control strategy for distributed energy storage systems based on voltage correction, characterized by: The following steps are involved: Step S1: The four energy storage units are connected through the corresponding DC-DC converters and the corresponding line resistors R Linei Connected in parallel to the DC bus, and connected to the load resistor R Load Power supply, at the start of each sampling period, the DC side inductor current i Li , DC side output voltage u oi , DC side output current i oi , energy storage unit state of charge SOC i , DC bus voltage u bus Sampling was carried out separately; Step S2: In the communication module, the four energy storage units use a ring communication, and only need to exchange information with the adjacent energy storage units, and the state of charge (SOC) of each energy storage unit in the system can be obtained without going through the central controller. i The global information of the energy storage unit state of charge SOC i As input, the average state of charge SOC of the energy storage system can be obtained by using the dynamic diffusion algorithm. avg ; Step S3: In the SOC balancing module, the energy storage system state of charge average SOC avg and the energy storage unit state of charge SOC i Subtract and get the standard deviation of the state of charge of the energy storage unit dSOC i , and then the standard deviation of the state of charge of the energy storage unit dSOC i According to the DC side output current i oi The positive and negative values ​​are selected for output. If the DC side output current i oi If it is greater than zero, it means that the energy storage system is in the discharge mode. At this time, the standard deviation of the state of charge of the energy storage unit dSOC i For output, if the DC side output current i oi If it is less than zero, it means that the energy storage system is in charging mode. At this time, the standard deviation of the state of charge of the energy storage unit dSOC i Take the inverted output and multiply the result by the process coefficient λ to obtain the intermediate coefficient β, where the process coefficient λ is expressed as: In formula (1), ε is the equilibrium acceleration factor, η is the equilibrium adjustment index factor, θ is the equilibrium precision factor, and dSOC k The standard deviation of the state of charge of the kth energy storage unit adjacent to the i-th energy storage unit in the ring communication is equal to the average state of charge SOC of the energy storage system. avg Subtract the state of charge SOC of the kth energy storage unit k , dSOC j The standard deviation of the state of charge of the jth energy storage unit adjacent to the i-th energy storage unit in the ring communication is equal to the average state of charge SOC of the energy storage system. avg Subtract the state of charge SOC of the jth energy storage unit j ; The expression of the intermediate coefficient β is: Take the inverse hyperbolic tangent function arctanh for the intermediate coefficient β and multiply it by Plus the initial virtual resistance R v0 , then multiply by the rated capacity C of the energy storage unit bat The reciprocal of the virtual resistance R vi , where the virtual resistance R vi The expression is: Step S4: In the virtual voltage regulation module, the virtual resistor R vi Multiply by the DC side output current i oi , get the virtual voltage Δu of the energy storage unit vi , and then the virtual voltage Δu of the energy storage unit vi As input, the virtual voltage Δu of the kth energy storage unit adjacent to the i-th energy storage unit in the ring communication is taken as input. vk Subtract the virtual voltage Δu of the energy storage unit vi , get the virtual voltage deviation Δu between the i-th energy storage unit and its adjacent k-th energy storage unit vki , and also the virtual voltage Δu of the jth energy storage unit adjacent to the i-th energy storage unit in the ring communication vj Subtract the virtual voltage Δu at the energy storage unit vi , get the virtual voltage deviation Δu between the i-th energy storage unit and its adjacent j-th energy storage unit vkj , and then the virtual voltage deviation Δu between the i-th energy storage unit and its adjacent k-th energy storage unit vki The virtual voltage deviation Δu between the i-th energy storage unit and its adjacent j-th energy storage unit vkj Add together to get the total virtual voltage deviation Δu Ti , and then multiply it by an adjustment coefficient Q to get the virtual voltage adjustment amount Δu ii , where the virtual voltage regulation value Δu ii The expression is: Thu ii =Q(Δu vj +D vk -2Du vi ) (4) Step S5: In the voltage correction module, the voltage reference value u ref and DC bus voltage u bus Subtract and get the bus voltage deviation Δu b , the bus voltage deviation Δu b and virtual voltage regulation Δu ii Add them together, multiply them by an integral gain K, and then pass through an integrator to get the voltage correction u i , where voltage correction u i The expression is: he i =∫(K(u ref -he bus +Δu ii ))dt (5) Step S6: In the voltage and current dual-loop control module, the voltage correction value u i With the voltage reference value u ref Add, then subtract the DC side output voltage u oi , and through the voltage outer loop PI controller G vPI (s) Get the current inner loop reference value i refi , the current inner loop reference value i refi and the DC side inductor current i Li Subtract the result and pass it through the current inner loop PI controller G iPI (s) Get the driving voltage u si , the driving voltage u si A reliable modulation signal can be output through PWM modulation.

2. The coordinated control strategy for distributed energy storage systems based on voltage correction according to claim 1 is characterized in that: In step S3, the value range of the equalization acceleration factor ε is 0.2<ε<0.9, the value range of the equalization adjustment index factor η is 0<η<1, the value range of the equalization precision factor θ is 0.0001<θ<0.01, and the initial virtual resistance R v0 The value range is 0 <R v0 <4.

3. The coordinated control strategy for distributed energy storage systems based on voltage correction according to claim 1 is characterized in that: In step S4, the value range of the adjustment coefficient Q is 1 <Q<6。 4. The coordinated control strategy for distributed energy storage systems based on voltage correction according to claim 1 is characterized in that: In step S5, the value range of the integral gain K is 10 <K<25。

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