A coordinated control method of a cascade type common direct current bus type optical storage system

Abstract

The application discloses a kind of cascade type co-DC bus type light storage system's synergic control method, comprising:1, each photovoltaic array voltage and current are collected, and the output power of each array is calculated;2, the input voltage and current of each H bridge circuit are collected, and the input power, average value and difference value of each H bridge circuit are calculated;3, the compensation modulation wave of each H bridge circuit is calculated;4, the voltage and current of common coupling point are collected, and the active and reactive power transmitted between system and power grid are calculated;5, the active and reactive power reference value is calculated;6, the phase angle and amplitude of virtual internal electric potential are calculated;7, the modulation wave of each H bridge circuit is calculated, and the output driving signal is modulated after being added with compensation modulation wave;8, the reference value of each bidirectional DC / DC converter voltage outer ring is calculated;9, the modulation signal is calculated and the output driving signal is modulated.The application can realize the coordinated control of photovoltaic equipment and energy storage equipment of cascade type co-DC bus type light storage system, and improve safety and reliability.

Description

Technical Field

[0001] The present invention relates to the fields of power electronics technology and photovoltaic storage technology, and in particular to a coordinated control method for a cascaded common DC bus photovoltaic storage system. Background Art

[0002] As the installed capacity of distributed power generation systems increases, the corresponding transmission voltage levels of distributed electric fields must also rise to improve transmission efficiency. Consequently, power electronics are increasingly being used in medium-, high-, and high-power applications. However, due to the voltage resistance of power switching transistors, the cascaded H-bridge structure, which allows low-voltage devices to transmit medium-, high-, and high-power, is widely used in medium-voltage direct-mounted grid-connected inverters. Each DC side of a cascaded H-bridge grid-connected inverter requires an independent DC source, which perfectly aligns with the characteristics of photovoltaic power generation. Therefore, cascaded medium-, high-voltage direct-mounted inverters, with photovoltaic modules as the front-end, are the most widely used. Furthermore, the increasing proportion of distributed power generation from renewable energy sources, coupled with the predominance of power electronics in these power plants, will impact the inertia of the power system, thereby reducing the grid's ability to withstand power fluctuations. Therefore, to improve the voltage resistance of high-power grid-connected inverters, they must be able to support the grid's active power. Currently, the mainstream technical solution is to adopt a virtual synchronous generator (VSG) control strategy for grid-connected inverters. VSGs, with their inertia and damping, can improve the operational performance of distributed generation systems under grid voltage and frequency disturbances, and will play a crucial role in future power systems. However, distributed photovoltaic power generation is characterized by intermittent output and power fluctuations. Directly applying photovoltaic virtual synchronization technology can easily lead to DC bus voltage deviations, causing inverter control errors. When large fluctuations at the source and load ends cause grid frequency fluctuations, the inverter requires additional output power. While performing maximum power point tracking (MPPT), it also provides inertia and damping support to the grid. This leads to frequent energy exchange on the DC side, which can easily cause DC bus voltage fluctuations. When the DC side energy is insufficient to supply the output power, the DC side voltage drops, causing inverter failure and compromising system stability. Ensuring effective and feasible grid-connected control of cascaded photovoltaic grid-connected inverters is a challenge.

[0003] Existing solutions to the feasibility of grid-connected control using cascaded photovoltaic grid-connected inverters primarily involve equipping the photovoltaic power generation system with energy storage batteries and bidirectional converters to provide additional energy for simulating virtual inertia. There are three main types of photovoltaic power generation systems equipped with energy storage: common DC bus, common AC bus, and centralized. Common AC bus and centralized systems share similar structures, with the energy storage located on the AC side of the photovoltaic power generation system, supplying energy solely through the AC side. This simplifies control and allows for relatively independent control of each unit. The common DC bus topology, on the other hand, places energy storage on the DC side, providing some energy for the inverter and allowing for a buffer on the DC side to ensure stable power supply to the load. Due to the bidirectional energy flow mechanism, the bidirectional converter facilitates energy exchange between the energy storage battery and the DC bus, playing a dual role in the photovoltaic system: providing energy support for the DC bus and absorbing excess energy from the DC bus. Energy storage photovoltaic virtual synchronous generators have broad prospects. However, the current price of energy storage is still relatively expensive, and the cost of transforming traditional photovoltaic power stations is high. Moreover, when the energy storage system is insufficient in capacity or is isolated due to a fault, the entire system will not be able to operate normally, which places high demands on the safe and reliable operation of the energy storage system. In addition, the prior art has also proposed some solutions, such as the photovoltaic grid-connected inverter control method based on active standby disclosed in patent document CN108667072A. The use of a photovoltaic power generation system working in active standby mode can not only alleviate the waste of light energy, but also provide frequency support for the power grid. The cascaded common DC bus type photovoltaic storage system adopted by the present invention, how to ensure the balance and reliability between the photovoltaic storage system and VSG control, and at the same time ensure the balance between photovoltaic and energy storage is also a problem worthy of study. At the same time, how to adopt a virtual synchronous machine control strategy and photovoltaic storage collaborative control for the converter in the cascaded common DC bus type photovoltaic storage system while considering the transmission power balance between the power conversion modules in the system is also a problem worthy of study. Summary of the Invention

[0004] In order to overcome the shortcomings of the existing technology, the present invention proposes a collaborative control method for a cascaded common DC bus photovoltaic storage system, so as to achieve coordinated control of the photovoltaic equipment and energy storage equipment of the cascaded common DC bus photovoltaic storage system, thereby improving its safety and reliability.

[0005] In order to achieve the above-mentioned object, the present invention adopts the following technical solutions:

[0006] The collaborative control method of a cascaded common DC bus solar-storage system of the present invention is characterized by comprising:

[0007] Collect the voltage and current of the photovoltaic array in the cascaded common DC bus photovoltaic storage system to calculate the output power of each photovoltaic array;

[0008] Collect the input voltage and input current of the H-bridge circuit in each power conversion module of the cascaded common DC bus solar storage system, and calculate the input power of each H-bridge circuit and its average value;

[0009] Calculate the difference between the input power of each H-bridge circuit and its average value;

[0010] Calculate the compensation modulation wave with power balancing capability for each power conversion module;

[0011] Collect the voltage and current at the common coupling point, and calculate the active power and reactive power transmitted between the cascaded common DC bus solar storage system and the grid;

[0012] Determine the active power reference value and reactive power reference value of the cascaded common DC bus photovoltaic storage system;

[0013] According to the active power reference value and reactive power reference value, the phase angle and amplitude of the virtual internal potential of the cascaded common DC bus photovoltaic storage system are calculated through the virtual synchronous machine control strategy.

[0014] According to the phase angle and amplitude of the virtual internal potential, a voltage-current dual closed-loop control strategy is used to process the cascaded common DC bus photovoltaic storage system. The d-axis and q-axis components of the modulation voltage in the rotating coordinate system are obtained, and the three-phase modulation voltage is calculated.

[0015] Calculate the modulation wave of each H-bridge circuit, add it to the compensation modulation wave respectively, and then output the driving signal of each switch tube to drive the corresponding switch tube after carrier phase shift modulation;

[0016] Based on the voltage and current of the photovoltaic array, the classical perturbation observation method is used to process each power conversion module to obtain the reference value of the voltage outer loop of the bidirectional DC / DC converter in each power conversion module;

[0017] According to the voltage of the photovoltaic array in each power conversion module, it is input into the PI controller together with the reference value of the voltage outer loop for processing, thereby obtaining the current reference value of the bidirectional DC / DC converter;

[0018] After the current reference value is processed by the current loop, the modulation signal of each switch tube in the bidirectional DC / DC converter is obtained through PWM modulation to control the corresponding switch tube.

[0019] The collaborative control method of the present invention is also characterized in that the photovoltaic voltage u of the photovoltaic array contained in the i-th power conversion module in the x-phase of the cascaded common DC bus type photovoltaic storage system is collected. pv,x,i and photovoltaic current i pv,x,i , and thus use formula (1) to obtain the output power P of the photovoltaic array contained in the i-th power conversion module in phase xpv,x,i ;

[0020] (1)

[0021] In formula (1), ω c is the cutoff frequency of the low-pass filter, represents the Laplace operator.

[0022] Furthermore, the input voltage U of the H-bridge circuit contained in the i-th power conversion module in the x-phase of the cascaded common DC bus solar storage system is collected. dc,x,i and input current I x,i , and thus use formula (2) to obtain the input power P of the H-bridge circuit contained in the i-th power conversion module in phase x x,i , and use formula (3) to get the average input power P of the H-bridge circuit contained in all power conversion modules in phase x x , so the input power P of the H-bridge module contained in the i-th power conversion module in phase x is x,i With the average input power P x The difference ΔP x,i ;

[0023] (2)

[0024] (3)

[0025] In formula (3), ∑ is the summation function.

[0026] According to the difference ΔP x,i , set the maximum deviation between the input power of the H-bridge circuit contained in the i-th power conversion module in phase x and the average value to be ΔP max , and dynamically select the compensation coefficient λ, so as to use formula (4) to obtain the compensation modulation wave Δd with power balancing capability of the H-bridge circuit contained in the i-th power conversion module in the x-phase x,i ;

[0027] (4)

[0028] In formula (4), |ΔP x,i | is ΔP x,i The absolute value of .

[0029] Furthermore, the three-phase voltage V at the common coupling point is collected. pcc and phase current I pcc , and thus the voltage and current components of the common coupling point in the dq coordinate system are obtained according to equations (5) and (6):

[0030] (5)

[0031] (6)

[0032] In formula (5) and formula (6), V d is the d-axis component of the voltage at the common coupling point in the dq coordinate system, V q is the q-axis component of the voltage at the common coupling point in the dq coordinate system, I d is the d-axis component of the current at the common coupling point in the dq coordinate system, I q is the q-axis component of the current at the common coupling point in the dq coordinate system, θ v is the phase angle of the virtual internal potential;

[0033] Using formula (7), we can get the real-time active power P transmitted between the cascaded common DC bus photovoltaic storage system and the power grid: e and reactive power Q e ;

[0034] (7).

[0035] Furthermore, the given active power reference value P is determined according to the following process: ref and reactive power reference value Q ref :

[0036] According to the input power P of the H-bridge circuit contained in the i-th power conversion module in the x-phase x,i , using formula (8) to obtain the total DC side input power P of the cascaded common DC bus solar storage system m ;

[0037] (8)

[0038] In formula (8), represents the input power of the H-bridge circuit contained in the i-th power conversion module in phase a, represents the input power of the H-bridge circuit contained in the i-th power conversion module in phase b, represents the input power of the H-bridge circuit contained in the i-th power conversion module in phase c, and n represents the total number of power conversion modules;

[0039] Set the DC bus capacitor voltage to the minimum value allowed by U lit , according to the input voltage U of the H-bridge circuit contained in the i-th power conversion module in the x-phase dc,x,i , will U dc,x,i with U lit Make the difference and input it into the PI controller. dc,x,i Higher than U lit When the current value output by the PI controller is 0, otherwise, the current value output by the PI controller is negative, and the negative value is compared with U dc,x,iAfter multiplication, the regulated power P of the H-bridge circuit contained in the i-th power conversion module in the x-phase is obtained. lit,x,i ;

[0040] According to P litxi and P m , using formula (9) to obtain the active power reference value P ref , and the reactive power reference value Q ref Directly issued according to the upper-level instructions;

[0041] (9)

[0042] In formula (9), represents the regulated power of the H-bridge circuit contained in the i-th power conversion module in phase a, represents the regulated power of the H-bridge circuit contained in the i-th power conversion module in phase b, It represents the regulated power of the H-bridge circuit contained in the i-th power conversion module in phase c.

[0043] Furthermore, the phase angle θ of the virtual internal potential is obtained by formula (10): v , and the amplitude of the virtual internal potential V is obtained by formula (11) ref ;

[0044] (10)

[0045] (11)

[0046] In formula (10), J is the virtual moment of inertia coefficient, D is the active damping coefficient, ω is the angular velocity of the virtual internal potential, ω0 is the rated angular velocity of the system, k m is the active power-frequency droop coefficient, t is the time;

[0047] In formula (11), k n is the reactive power-voltage droop coefficient, U0 is the amplitude reference value of the virtual internal potential;

[0048] V ref As the input reference value, and with V d After making the difference and processing it through the PI controller, the system's d-axis current reference value I is obtained. d * ;

[0049] Take 0 as the input reference value and compare it with V q After making the difference and processing it through the PI controller, the system's q-axis current reference value I is obtained. q * ;

[0050] Take I d* As the input reference value, and with I d After the difference is made and processed by the PI controller, the d-axis modulation voltage V of the system is obtained. d0 ; V d0 With V d After adding, the system's d-axis modulation voltage reference value V is obtained. d * ;

[0051] Take I q * As the input reference value, and with I q After the difference is made and processed by the PI controller, the q-axis modulation voltage V of the system is obtained. q0 , V q0 With V q After adding, we get the system's q-axis modulation voltage reference value V q * ;

[0052] Using formula (12) to get the three-phase modulation voltage reference value V a * 、V b * 、V c * ;

[0053] (12).

[0054] Furthermore, the three-phase modulation voltage reference value V a * 、V b * 、V c * , divided by the reference voltage V0, the modulation wave d of the H-bridge circuit contained in the i-th power conversion module in the x-phase is obtained. x,i , d x,i and compensation modulation wave Δd x,i After addition, the signals are modulated by carrier phase shift, thereby outputting a switch driving signal for the H-bridge circuit contained in the i-th power conversion module in the x-phase, so as to drive the switch of the H-bridge circuit contained in the i-th power conversion module in the x-phase;

[0055] Formula (13) is used to construct the constraints of the transmission power and modulation ratio of the i-th power conversion module in phase x;

[0056] (13)

[0057] In formula (14), P m is the maximum active power allowed by the H-bridge circuit, d m is the maximum carrier phase shift modulation ratio allowed by the H-bridge circuit.

[0058] Furthermore, the reference value u of the voltage outer loop of the bidirectional DC / DC converter in the i-th power conversion module in the x-phase is MPPTx,i and u pv,x,i The difference is made, and then after processing by the PI controller, the current reference value of the bidirectional DC / DC converter is obtained. Then, after processing by the current loop control link and further after PWM modulation, the switching tube driving signal for driving the switching tube of the bidirectional DC / DC converter in the i-th power conversion module in the x-phase is output.

[0059] An electronic device of the present invention includes a memory and a processor, and is characterized in that the memory is used to store a program that supports the processor to execute the collaborative control method, and the processor is configured to execute the program stored in the memory.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] This invention proposes a coordinated control strategy for a cascaded, common-DC-bus solar-to-storage system, ensuring maximum power tracking for the energy storage device and virtual synchronous control for the cascaded converter. Furthermore, the energy storage device and inverter functions are further decoupled, preventing interference between them. This increases the fault tolerance of the coordinated control. Furthermore, by smoothing power commands, photovoltaic power fluctuations can be mitigated, effectively improving the stability of the cascaded, common-DC-bus solar-to-storage system.

[0062] 2. The present invention adopts a virtual synchronous machine control strategy and photovoltaic storage collaborative control for the converter in the cascaded common DC bus photovoltaic storage system, which can effectively provide inertial support for active power to the power grid. Under this control strategy, it further ensures the balanced transmission power between the power conversion modules of each phase of the system, thereby effectively improving the reliability of the cascaded common DC bus photovoltaic storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 This is a topological diagram of the cascaded common DC bus solar storage system of the present invention;

[0064] Figure 2 This is a diagram showing the control structure of a virtual synchronous machine of a converter in a cascaded common DC bus solar storage system according to the present invention;

[0065] Figure 3 This is a voltage and current dual closed-loop control structure diagram of the converter in the cascaded common DC bus solar storage system of the present invention;

[0066] Figure 4 This is a control block diagram of the virtual synchronous machine control of the converter and the photovoltaic-storage coordinated control in the cascaded common DC bus photovoltaic-storage system of the present invention;

[0067] Figure 5 This is a topological diagram of a bidirectional DC / DC converter in a cascaded common DC bus solar storage system according to the present invention;

[0068] Figure 6 This is a control block diagram of the bidirectional DC / DC converter photovoltaic storage coordinated control in the cascaded common DC bus photovoltaic storage system of the present invention. DETAILED DESCRIPTION

[0069] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0070] In this embodiment, a collaborative control method for a cascaded common DC bus photovoltaic storage system is applied to the cascaded common DC bus photovoltaic storage system, and the photovoltaic storage system includes: a power conversion module, an LC filter module, a grid-connected inductor module and a power grid module.

[0071] The power conversion module includes 3n photovoltaic arrays, 3n energy storage batteries, 3n bidirectional DC / DC converters, 3n DC bus capacitors and 3n H-bridge circuits. Any power conversion module is denoted as #x i , denote any DC bus capacitor as C x,i , x represents the phase sequence of the three phases, x=a, b, c, i represents the serial number of the power conversion module in each phase, i=1, 2, ..., n, n is a positive integer. The LC filter module consists of three inductors and three capacitors. Any filter inductor is denoted as L fx , denote any filter capacitor as C fx The grid-connected inductor module consists of three inductors, and any one of the grid-connected inductors is denoted as L gx ;

[0072] Connect the positive pole of any photovoltaic array to a DC bus capacitor C x,i The positive pole is connected to form a DC positive bus, and the negative pole of any photovoltaic array is connected to a DC bus capacitor C x,i The negative pole is connected to form a DC negative bus. Connect the two ends of any energy storage battery to the input of any bidirectional DC / DC converter. Then connect the output of the bidirectional DC / DC converter in parallel between the DC positive bus and the DC negative bus. At the same time, connect the two bridge arms of the H-bridge circuit in parallel between the DC positive bus and the DC negative bus. Connect the AC output side of each H-bridge circuit in each phase in series. Finally, connect one end of the three-phase output in star shape, with the common point marked as N; connect the other end of the A-phase output in the three-phase to the filter inductor L. fa After concatenation with o a Dots connected, o a Point filter capacitor C fa Connecting with the earth, a The grid-connected inductor Lga Then connect to the grid in series; connect the other end of the B phase output in the three-phase to the filter inductor L fb After concatenation with o b Dots connected, o b Point filter capacitor C fb Connecting with the earth, b The grid-connected inductor L gb Then connect to the grid in series; connect the other end of the C phase output in the three-phase to the filter inductor L fc After concatenation with o c Dots connected, o c Point filter capacitor C fc Connecting with the earth, c The grid-connected inductor L gc After connecting to the grid in series, Figure 1 shown. Figure 1 This is the topological structure diagram of the cascaded common DC bus type photovoltaic storage system of the present invention. Figure 1 A photovoltaic array is a DC power generation unit composed of several photovoltaic modules or photovoltaic panels mechanically and electrically assembled in a certain way and having a fixed support structure. The photovoltaic voltage and photovoltaic current of a photovoltaic array refer to the terminal voltage of the entire power generation unit and the current flowing to the DC bus capacitor, rather than the electrical parameters of a single photovoltaic module. Figure 1 The medium energy storage battery is a complete battery system formed by connecting several battery cells in series and parallel. The relevant electrical parameters also refer to the parameters of the battery system, not the battery cells. Figure 1 The midpoint of the first bridge arm of the H-bridge circuit in the first power conversion module in phase A is connected to the output point marked as A, and the voltage between point A and point N is recorded as u a The midpoint of the first arm of the H-bridge circuit in the first power conversion module in phase B is connected to the output point marked as B, and the voltage between point B and point N is recorded as u b The midpoint of the first arm of the H-bridge circuit in the first power conversion module in phase C is connected to the output point marked as C, and the voltage between point C and point N is recorded as u c ; Other device names are marked near the device or on the corresponding arrows.

[0073] In this embodiment, a collaborative control method for a cascaded common DC bus solar-storage system is performed according to the following steps:

[0074] Step 1: Collect the photovoltaic voltage u of the photovoltaic array contained in the i-th power conversion module in the x-phase of the cascaded common DC bus photovoltaic storage system. pv,x,i and photovoltaic current i pv,x,i , and thus use formula (1) to obtain the output power P of the photovoltaic array contained in the i-th power conversion module in phase x pv,x,i ;

[0075] (1)

[0076] In formula (1), ω c is the cutoff frequency of the low-pass filter, represents the Laplace operator.

[0077] Step 2: Collect the input voltage U of the H-bridge circuit contained in the i-th power conversion module in the x-phase of the cascaded common DC bus solar storage system. dc,x,i and input current I x,i , and thus use formula (2) to obtain the input power P of the H-bridge circuit contained in the i-th power conversion module in phase x x,i , and use formula (3) to get the average input power P of the H-bridge circuit contained in all power conversion modules in phase x x , so the input power P of the H-bridge module contained in the i-th power conversion module in phase x is x,i With the average input power P x The difference ΔP x,i ;

[0078] (2)

[0079] (3)

[0080] In formula (3), ∑ is the summation function.

[0081] Step 3: According to the difference ΔP x,i , set the maximum deviation between the input power of the H-bridge circuit contained in the i-th power conversion module in phase x and the average value to be ΔP max , and dynamically select the compensation coefficient λ, the purpose is to ensure that the transmission power balance of the H-bridge module contained in each power conversion module in each phase is better, and at the same time improve the adjustment speed of power balance, so as to use formula (4) to obtain the compensation modulation wave Δd with power balance capability of the H-bridge circuit contained in the i-th power conversion module in the x-phase x,i ;

[0082] (4)

[0083] In formula (4), |ΔP x,i | is ΔP x,i The absolute value of .

[0084] Step 4: Collect the three-phase voltage V at the common coupling point pcc and phase current I pcc ,like Figure 1 As shown, according to equations (5) and (6), the voltage and current components of the common coupling point in the dq coordinate system are obtained. Here is the Park transformation, as shown in Figure 2 As shown, Figure 2 This is a diagram showing the virtual synchronous machine control structure of the converter in the cascaded common DC bus solar storage system of the present invention:

[0085] (5)

[0086] (6)

[0087] In formula (5) and formula (6), V d is the d-axis component of the voltage at the common coupling point in the dq coordinate system, V q is the q-axis component of the voltage at the common coupling point in the dq coordinate system, I d is the d-axis component of the current at the common coupling point in the dq coordinate system, I q is the q-axis component of the current at the common coupling point in the dq coordinate system, θ v is the phase angle of the virtual internal potential.

[0088] Using formula (7), we can get the real-time active power P transmitted between the cascaded common DC bus photovoltaic storage system and the power grid: e and reactive power Q e ,like Figure 2 As shown;

[0089] (7)

[0090] Step 5: Determine the given active power reference value P ref and reactive power reference value Q ref :

[0091] Step 5.1: According to the input power P of the H-bridge circuit contained in the i-th power conversion module in the x-phase, x,i , using formula (8) to obtain the total DC side input power P of the cascaded common DC bus solar storage system dc ;

[0092] (8)

[0093] In formula (8), represents the input power of the H-bridge circuit contained in the i-th power conversion module in phase a, represents the input power of the H-bridge circuit contained in the i-th power conversion module in phase b, represents the input power of the H-bridge circuit contained in the i-th power conversion module in phase c, and n represents the total number of power conversion modules.

[0094] Step 5.2: Set the minimum allowable value of the DC bus capacitor voltage to U litWhen the bus capacitor voltage is lower than Ulit, there is a greater risk of inverter failure. This is because when the sunlight is insufficient for a long time or the energy storage battery is insufficient, the inverter output power is higher than the sum of the photovoltaic and energy storage powers, and the DC capacitor voltage will drop. When the voltage drops to a certain value, it may cause inverter failure. Therefore, the minimum allowable voltage on the DC side is set as a warning value, which is generally higher than the inverter failure voltage. According to the input voltage U of the H-bridge circuit contained in the i-th power conversion module in the x-phase, dc,x,i , will U dc,x,i with U lit Make the difference and input it into the PI controller. dc,x,i Higher than U lit When the current value output by the PI controller is 0, otherwise, the current value output by the PI controller is negative, and the negative value is compared with U dc,x,i After multiplication, the regulated power P of the H-bridge circuit contained in the i-th power conversion module in the x-phase is obtained. lit,x,i ; This is equivalent to a DC voltage controller with a limiter. When this regulated power is added to the given value, the power output can be appropriately reduced to stabilize the DC side voltage. The control block diagram is as follows Figure 4 shown.

[0095] Step 5.3: According to P litxi and P dc , using formula (9) to obtain the active power reference value P ref When the active power reference value is given by this method, it is necessary to calculate the photovoltaic module power at all times and pass it through a low-pass filter with a large time constant. This can make the power output smooth and reduce the power fluctuation caused by the MPPT algorithm and environmental factors. ref Directly issued according to the upper-level instructions;

[0096] (9)

[0097] In formula (9), represents the regulated power of the H-bridge circuit contained in the i-th power conversion module in phase a, represents the regulated power of the H-bridge circuit contained in the i-th power conversion module in phase b, It represents the regulated power of the H-bridge circuit contained in the i-th power conversion module in phase c.

[0098] Step 6: According to the active power reference value and the reactive power reference value, the phase angle θ of the virtual internal potential is obtained by formula (10): v , and the amplitude of the virtual internal potential V is obtained by formula (11) refHere, the virtual synchronous machine control strategy is used. According to the given power command and the real-time output power, the control loop is used to increase the system inertia, thereby supporting the power grid and improving the stability of the system when the power grid is weak. The block diagram of the virtual synchronous machine control is shown in the figure below. Figure 4 shown.

[0099] (10)

[0100] (11)

[0101] In formula (10), J is the virtual moment of inertia coefficient, D is the active damping coefficient, ω is the angular velocity of the virtual internal potential, ω0 is the rated angular velocity of the system, k m is the active power-frequency droop coefficient, t is the time;

[0102] In formula (11), k n is the reactive power-voltage droop coefficient, U0 is the amplitude reference value of the virtual internal potential;

[0103] V ref As the input reference value, and with V d After making the difference and processing it through the PI controller, the system's d-axis current reference value I is obtained. d * , with 0 as the input reference value, and with V q After making the difference and processing it through the PI controller, the system's q-axis current reference value I is obtained. q * ; Here is the control of the voltage outer loop, the output is the reference value of the d-axis and q-axis current respectively. The existence of the voltage outer loop can ensure the stability of the system output voltage. The control structure diagram is as follows Figure 3 shown.

[0104] Take I d * As the input reference value, and with I d After the difference is made and processed by the PI controller, the d-axis modulation voltage V of the system is obtained. d0 ; V d0 With V d After adding, the system's d-axis modulation voltage reference value V is obtained. d * , with I q * As the input reference value, and with I q After the difference is made and processed by the PI controller, the q-axis modulation voltage V of the system is obtained. q0 , V q0 With V q After adding, we get the system's q-axis modulation voltage reference value V q* Here is the control of the current inner loop, and the outputs are the reference values ​​of the d-axis and q-axis modulation voltages. The existence of the current inner loop can improve the rapidity of the control system response. The control structure diagram is as follows Figure 3 shown.

[0105] Using formula (12) to get the three-phase modulation voltage reference value V a * 、V b * 、V c * , here is the Park inverse transform, such as Figure 3 As shown;

[0106] (12).

[0107] Step 7: Set the three-phase modulation voltage reference value V a * 、V b * 、V c * , divided by the reference voltage V0, the modulation wave d of the H-bridge circuit contained in the i-th power conversion module in the x-phase is obtained. x,i , the control structure diagram is as follows Figure 3 As shown. x,i and compensation modulation wave Δd x,i After addition, the signals are modulated by carrier phase shift, thereby outputting the switch drive signal of the H-bridge circuit contained in the i-th power conversion module in phase x to drive the switch of the H-bridge circuit contained in the i-th power conversion module in phase x. The compensation modulation wave here can effectively ensure the balance of the transmission power of each H-bridge module in each phase, thereby ensuring the reliability of system operation and effectively improving the service life of the cascade inverter. The control structure diagram is shown in FIG. Figure 3 shown.

[0108] Formula (13) is used to construct the transmission power and modulation ratio constraints of the i-th power conversion module in phase x;

[0109] (13)

[0110] In formula (14), P m is the maximum active power allowed by the H-bridge circuit, d m is the maximum carrier phase shift modulation ratio allowed by the H-bridge circuit; meeting this constraint can, on the one hand, improve the reliability of system operation, and on the other hand, avoid overmodulation during the modulation process, thereby ensuring the safety of system operation.

[0111] Step 8: Based on the photovoltaic voltage u of the photovoltaic array contained in each power conversion module of the cascaded common DC bus photovoltaic storage system pv,x,i and photovoltaic current i pv,x,i The bidirectional DC / DC converters in each power conversion module of the present invention all adopt the maximum power tracking method, wherein the bidirectional DC / DC converter topology is shown in FIG. Figure 5 As shown, Figure 5 This is a topological diagram of the bidirectional DC / DC converter in the cascaded common DC bus solar storage system of the present invention. Figure 5 Medium V in For the input side, connect the positive and negative poles of the energy storage battery, V out The output side is connected to the positive and negative poles of the DC bus capacitor. The names of other related components are marked near the components. By controlling the voltage of the DC side capacitor of the H-bridge module, the photovoltaic module works in the MPPT state. Therefore, the classic perturbation observation method is selected to obtain the reference value u of the voltage outer loop of the bidirectional DC / DC converter in each power conversion module. MPPTx,i The reference value u of the voltage outer loop of the bidirectional DC / DC converter in the i-th power conversion module in the x-phase is MPPTx,i and u pv,x,i The difference is then processed by the PI controller to obtain the current reference value of the bidirectional DC / DC converter, which is then processed by the current loop control link and then modulated by PWM to output the switch tube drive signal for driving the switch tube of the bidirectional DC / DC converter in the i-th power conversion module in the x-phase. The control block diagram is shown in the figure. Figure 6 shown.

[0112] In this embodiment, an electronic device includes a memory and a processor, wherein the memory is used to store a program that supports the processor to execute the above method, and the processor is configured to execute the program stored in the memory.

[0113] In this embodiment, a computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the above method are executed.

Claims

1. A collaborative control method for a cascaded common DC bus solar-storage system, characterized in that: include: Collect the voltage and current of the photovoltaic array in the cascaded common DC bus photovoltaic storage system to calculate the output power of each photovoltaic array; Collect the input voltage and input current of the H-bridge circuit in each power conversion module of the cascaded common DC bus solar storage system, and calculate the input power of each H-bridge circuit and its average value; Calculate the difference between the input power of each H-bridge circuit and its average value; Calculate the compensation modulation wave with power balancing capability for each power conversion module; Collect the voltage and current at the common coupling point, and calculate the active power and reactive power transmitted between the cascaded common DC bus solar storage system and the grid; Determine the active power reference value and reactive power reference value of the cascaded common DC bus photovoltaic storage system; According to the active power reference value and reactive power reference value, the phase angle and amplitude of the virtual internal potential of the cascaded common DC bus photovoltaic storage system are calculated through the virtual synchronous machine control strategy. According to the phase angle and amplitude of the virtual internal potential, a voltage-current dual closed-loop control strategy is used to process the cascaded common DC bus photovoltaic storage system. The d-axis and q-axis components of the modulation voltage in the rotating coordinate system are obtained, and the three-phase modulation voltage is calculated. Calculate the modulation wave of each H-bridge circuit, add it to the compensation modulation wave respectively, and then output the driving signal of each switch tube to drive the corresponding switch tube after carrier phase shift modulation; Based on the voltage and current of the photovoltaic array, the classical perturbation observation method is used to process each power conversion module to obtain the reference value of the voltage outer loop of the bidirectional DC / DC converter in each power conversion module; According to the voltage of the photovoltaic array in each power conversion module, it is input into the PI controller together with the reference value of the voltage outer loop for processing, thereby obtaining the current reference value of the bidirectional DC / DC converter; After the current reference value is processed by the current loop, the modulation signal of each switch tube in the bidirectional DC / DC converter is obtained through PWM modulation to control the corresponding switch tube.

2. The collaborative control method according to claim 1, characterized in that: Collect the photovoltaic voltage u of the photovoltaic array contained in the i-th power conversion module in the x-phase of the cascaded common DC bus photovoltaic storage system pv,x,i and photovoltaic current i pv,x,i , and thus use formula (1) to obtain the output power P of the photovoltaic array contained in the i-th power conversion module in phase x pv,x,i ; (1) In formula (1), ω c is the cutoff frequency of the low-pass filter, represents the Laplace operator.

3. The collaborative control method according to claim 1, characterized in that: Collect the input voltage U of the H-bridge circuit contained in the i-th power conversion module in the x-phase of the cascaded common DC bus solar storage system dc,x,i and input current I x,i , and thus use formula (2) to obtain the input power P of the H-bridge circuit contained in the i-th power conversion module in phase x x,i , and use formula (3) to get the average input power P of the H-bridge circuit contained in all power conversion modules in phase x x , so the input power P of the H-bridge module contained in the i-th power conversion module in phase x is x,i With the average input power P x The difference ΔP x,i ; (2) (3) In formula (3), ∑ is the summation function.

4. The collaborative control method according to claim 3, characterized in that: According to the difference ΔP x,i , set the maximum deviation between the input power of the H-bridge circuit contained in the i-th power conversion module in phase x and the average value to be ΔP max , and dynamically select the compensation coefficient λ, so as to use formula (4) to obtain the compensation modulation wave Δd with power balancing capability of the H-bridge circuit contained in the i-th power conversion module in the x-phase x,i ; (4) In formula (4), |ΔP x,i | is ΔP x,i The absolute value of .

5. The collaborative control method according to claim 4, characterized in that: Collect the three-phase voltage V at the common coupling point pcc and phase current I pcc , and thus the voltage and current components of the common coupling point in the dq coordinate system are obtained according to equations (5) and (6): (5) (6) In formula (5) and formula (6), V d is the d-axis component of the voltage at the common coupling point in the dq coordinate system, V q is the q-axis component of the voltage at the common coupling point in the dq coordinate system, I d is the d-axis component of the current at the common coupling point in the dq coordinate system, I q is the q-axis component of the current at the common coupling point in the dq coordinate system, θ v is the phase angle of the virtual internal potential; Using formula (7), we can get the real-time active power P transmitted between the cascaded common DC bus photovoltaic storage system and the power grid: e and reactive power Q e ; (7)。 6. The collaborative control method according to claim 4, characterized in that: The given active power reference value P is determined by the following process: ref and reactive power reference value Q ref : According to the input power P of the H-bridge circuit contained in the i-th power conversion module in the x-phase x,i , using formula (8) to obtain the total DC side input power P of the cascaded common DC bus solar storage system m ; (8) In formula (8), represents the input power of the H-bridge circuit contained in the i-th power conversion module in phase a, represents the input power of the H-bridge circuit contained in the i-th power conversion module in phase b, represents the input power of the H-bridge circuit contained in the i-th power conversion module in phase c, and n represents the total number of power conversion modules; Set the DC bus capacitor voltage to the minimum value allowed by U lit , according to the input voltage U of the H-bridge circuit contained in the i-th power conversion module in the x-phase dc,x,i , will U dc,x,i with U lit Make the difference and input it into the PI controller. dc,x,i Higher than U lit When the current value output by the PI controller is 0, otherwise, the current value output by the PI controller is negative, and the negative value is compared with U dc,x,i After multiplication, the regulated power P of the H-bridge circuit contained in the i-th power conversion module in the x-phase is obtained. lit,x,i ; According to P litxi and P m , using formula (9) to obtain the active power reference value P ref , and the reactive power reference value Q ref Directly issued according to the upper-level instructions; (9) In formula (9), represents the regulated power of the H-bridge circuit contained in the i-th power conversion module in phase a, represents the regulated power of the H-bridge circuit contained in the i-th power conversion module in phase b, It represents the regulated power of the H-bridge circuit contained in the i-th power conversion module in phase c.

7. The collaborative control method according to claim 6, characterized in that: The phase angle θ of the virtual internal potential is obtained by formula (10): v , and the amplitude of the virtual internal potential V is obtained by formula (11) ref ; (10) (11) In formula (10), J is the virtual moment of inertia coefficient, D is the active damping coefficient, ω is the angular velocity of the virtual internal potential, ω0 is the rated angular velocity of the system, k m is the active power-frequency droop coefficient, t is the time; In formula (11), k n is the reactive power-voltage droop coefficient, U0 is the amplitude reference value of the virtual internal potential; V ref As the input reference value, and with V d After making the difference and processing it through the PI controller, the system's d-axis current reference value I is obtained. d * ; Take 0 as the input reference value and compare it with V q After making the difference and processing it through the PI controller, the system's q-axis current reference value I is obtained. q * ; Take I d * As the input reference value, and with I d After the difference is made and processed by the PI controller, the d-axis modulation voltage V of the system is obtained. d0 ; V d0 With V d After adding, the system's d-axis modulation voltage reference value V is obtained. d * ; Take I q * As the input reference value, and with I q After the difference is made and processed by the PI controller, the q-axis modulation voltage V of the system is obtained. q0 , V q0 With V q After adding, we get the system's q-axis modulation voltage reference value V q * ; Using formula (12) to get the three-phase modulation voltage reference value V a * 、V b * 、V c * ; (12)。 8. The collaborative control method according to claim 7, characterized in that: The three-phase modulation voltage reference value V a * 、V b * 、V c * , divided by the reference voltage V0, the modulation wave d of the H-bridge circuit contained in the i-th power conversion module in the x-phase is obtained. x,i , d x,i and compensation modulation wave Δd x,i After addition, the signals are modulated by carrier phase shift, thereby outputting a switch driving signal for the H-bridge circuit contained in the i-th power conversion module in the x-phase, so as to drive the switch of the H-bridge circuit contained in the i-th power conversion module in the x-phase; Formula (13) is used to construct the constraints of the transmission power and modulation ratio of the i-th power conversion module in phase x; (13) In formula (14), P m is the maximum active power allowed by the H-bridge circuit, d m is the maximum carrier phase shift modulation ratio allowed by the H-bridge circuit.

9. The collaborative control method according to claim 8, characterized in that: The reference value u of the voltage outer loop of the bidirectional DC / DC converter in the i-th power conversion module in the x-phase is MPPTx,i and u pv,x,i The difference is made, and then after processing by the PI controller, the current reference value of the bidirectional DC / DC converter is obtained. Then, after processing by the current loop control link and further after PWM modulation, the switching tube driving signal for driving the switching tube of the bidirectional DC / DC converter in the i-th power conversion module in the x-phase is output.

10. An electronic device comprising a memory and a processor, characterized in that: The memory is used to store a program that supports the processor to execute the collaborative control method according to any one of claims 1 to 9, and the processor is configured to execute the program stored in the memory.

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