Cooperative control method of cascaded common DC bus type optical storage system

Abstract

The invention discloses a cooperative control method for a cascaded common DC bus type optical storage system, and the method comprises the steps: 1, collecting the voltage and current of each photovoltaic array, and calculating the output power of each array; 2, collecting the input voltage and current of each H-bridge circuit, and calculating the input power, the average value and the difference value of each H-bridge circuit; 3, calculating a compensation modulation wave of each H-bridge circuit; 4, voltage and current of a common coupling point are collected, and active power and reactive power transmitted between the system and the power grid are calculated; 5, active and reactive power reference values are calculated; 6, calculating the phase angle and the amplitude of the virtual internal potential; 7, calculating the modulation wave of each H-bridge circuit, adding the modulation wave with the compensation modulation wave, and modulating and outputting a driving signal; 8, calculating a reference value of a voltage outer ring of each bidirectional DC / DC converter; and 9, calculating a modulation signal, modulating the modulation signal and outputting a driving signal. According to the invention, the coordination control of the photovoltaic equipment and the energy storage equipment of the cascaded common DC bus type optical storage system can be realized, and the safety and the reliability are improved.

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 direct current bus photovoltaic storage system. Background Art

[0002] With the increase of the installed capacity of a single unit of a new energy distributed power generation system, in order to improve the efficiency of power transmission, the corresponding transmission voltage level of the distributed electric field must also be increased. Therefore, power electronic equipment is increasingly widely used in medium-high voltage and high-power applications. However, due to the voltage resistance of the power switch tube, the cascade H-bridge structure with the characteristics of low-voltage devices transmitting medium-high voltage and high power is widely used in medium-voltage direct-mounted grid-connected inverters. Each DC side of the grid-connected inverter with a cascade H-bridge structure requires an independent DC source, which happens to coincide with the characteristics of photovoltaic power generation. Therefore, photovoltaic modules are used as the front stage, and the power topology is the most widely used cascaded medium-voltage direct-mounted inverter. At the same time, with the increasing proportion of new energy distributed power generation, and the dominance of power electronic equipment in these power stations, this will have a certain impact on the inertia of the power system, thereby reducing the grid's ability to support power fluctuations. Therefore, in order to improve the high-power grid-connected inverter, it is necessary for it to have support for the active power of the grid. The current mainstream technical solution is to use a virtual synchronous machine (VSG) control strategy for the grid-connected inverter. VSG has inertia and damping, which can improve the operating performance of distributed power generation systems under grid voltage and frequency disturbances, and will play an important role in future power systems. However, distributed photovoltaic power generation has the characteristics of intermittent output and power fluctuations. When photovoltaic virtual synchronization technology is directly applied, DC bus voltage deviation is prone to occur, causing inverter control disorder. When the source and load ends fluctuate greatly and cause grid frequency fluctuations, since the inverter needs additional output power, while performing maximum power tracking, it also provides inertia and damping support for the grid. The energy exchange on its DC side is frequent, which is easy to cause DC bus voltage fluctuations. When the energy on the DC side is insufficient to supply the output power, the DC side voltage decreases, causing inverter failure and affecting the stability of the system. How to ensure effective and feasible grid-type control of cascaded photovoltaic grid-connected inverters is a difficult problem.

[0003] In view of the difficulties in the feasibility of grid-type control with cascaded photovoltaic grid-connected inverters, the existing solutions mainly include: equipping photovoltaic power generation systems 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 equipment: common DC bus type, common AC bus type, and centralized type. Among them, the common AC bus type and the centralized type have similar structures. The energy storage side is located on the AC side of the photovoltaic power generation system, and energy is only provided through the AC side. Its control is simple, and the unit control is relatively independent. The common DC bus topology equips energy storage on the DC side to provide part of the energy for the inverter, and can leave a certain buffer space for the energy exchange on the DC side to ensure the stability of load power supply. Due to the existence of a bidirectional energy flow mechanism, the bidirectional converter can complete the energy exchange between the energy storage battery and the DC bus, and plays two roles in the photovoltaic system. On the one hand, it can provide energy support for the DC bus, and on the other hand, it can also absorb the surplus energy of the DC bus. Energy storage photovoltaic virtual synchronous generator has broad prospects, but the current price of energy storage is still relatively expensive, and the cost of transformation of traditional photovoltaic power stations is relatively 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 the 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 prior art, the present invention proposes a collaborative control method for a cascaded common DC bus type photovoltaic storage system, in order to achieve coordinated control of the photovoltaic equipment and energy storage equipment of the cascaded common DC bus type photovoltaic storage system, thereby improving its safety and reliability.

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

[0006] The collaborative control method of a cascaded common DC bus type photovoltaic 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 photovoltaic storage system, so as to 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] Calculating a 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 photovoltaic storage system and the power 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, the voltage and current double closed-loop control strategy is used to process the cascaded common DC bus photovoltaic storage system, and the components of the modulation voltage on the d-axis and q-axis in the rotating coordinate system are obtained, thereby calculating the three-phase modulation voltage.

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

[0016] According to the voltage and current of the photovoltaic array, each power conversion module is processed using the classical perturbation observation method 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, so as to obtain the current reference value of the bidirectional DC / DC converter;

[0018] The current reference value is processed by the current loop, and then PWM modulated to obtain the modulation signal of each switch tube in the bidirectional DC / DC converter to 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 the output power P of the photovoltaic array contained in the i-th power conversion module in phase x is obtained by using formula (1):pv,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 type photovoltaic storage system is collected. dc,x,i and input current I x,i , and thus the input power P of the H-bridge circuit contained in the i-th power conversion module in the x-phase is obtained by using formula (2): x,i , and use formula (3) to obtain 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 x,i The average input power P x The difference ΔP x,i ;

[0023] (2)

[0024] (3)

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

[0026] 4. The cooperative control method according to claim 3, characterized in that according to the difference ΔP x,i , set the maximum allowable deviation between the input power of the H-bridge circuit contained in the i-th power conversion module in the x-phase and the average value to 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] Further, 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 photovoltaic 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 lowest 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 The difference is then input into the PI controller. dc,x,i Higher than U litWhen 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 ;

[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, 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 equation (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, and 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 the difference is made and processed by the PI controller, the d-axis current reference value I of the system is obtained. d * ;

[0049] With 0 as the input reference value and V q After the difference is made and processed by the PI controller, the q-axis current reference value I of the system 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 d-axis modulation voltage reference value V of the system 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), we can 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 tube driving signal of the H-bridge circuit contained in the i-th power conversion module in the x-phase to drive the switch tube 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 the x-phase;

[0056] (13)

[0057] In formula (14), Pm 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 being processed by the PI controller, the current reference value of the bidirectional DC / DC converter is obtained, which is then processed by the current loop control link and then PWM modulated 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.

[0059] An electronic device of the present invention includes a memory and a processor, wherein 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] 1. The present invention proposes a coordinated control strategy for a cascaded common DC bus photovoltaic storage system to ensure that the energy storage device performs maximum power tracking, while the cascaded converter performs virtual synchronous control. In addition, the energy storage device and the inverter functions are further decoupled, and the two do not interfere with each other, which increases the fault tolerance of coordinated control. At the same time, the power fluctuation of photovoltaics can be smoothed by smoothing the power command setting, so that the stability of the cascaded common DC bus photovoltaic storage system is effectively improved.

[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 inter-phase 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 structure diagram of the cascaded common DC bus type photovoltaic storage system of the present invention;

[0064] Figure 2 It is a control structure diagram of a virtual synchronous machine of a converter in a cascaded common DC bus type photovoltaic storage system of the present invention;

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

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

[0067] Figure 5 It is a topological structure diagram of a bidirectional DC / DC converter in a cascaded common DC bus type photovoltaic storage system of 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 implementation modes of the present invention will be further described in detail below in conjunction with the accompanying drawings.

[0070] In this embodiment, a collaborative control method of 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 , let any DC bus capacitor be 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 , let any filter capacitor be C fx The grid-connected inductor module consists of three inductors. Any grid-connected inductor is denoted as L. gx ;

[0072] Connect the positive electrode of any photovoltaic array to a DC bus capacitor C x,i The positive poles are connected to form a DC positive bus. 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 a star shape, and the common point is marked as N; connect the other end of the A-phase output of the three-phase to the filter inductor L. fa After concatenation with o a The dots are connected, oa Point through filter capacitor C fa Connecting to the earth, a The grid-connected inductance L ga After connecting in series, connect to the grid; connect the other end of the B phase output in the three-phase to the filter inductor L fb After concatenation with o b The dots are connected, o b Point through filter capacitor C fb Connecting to the earth, b The grid-connected inductance L gb Connect the other end of the C phase output in the three-phase circuit to the filter inductor L fc After concatenation with o c The dots are connected, o c Point through filter capacitor C fc Connecting to the earth, c The grid-connected inductance L gc After connecting in series, they are connected to the grid, such as 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 The 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 supporting structure. The photovoltaic voltage and photovoltaic current of the 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 bridge 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 bridge 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 of a cascaded common DC bus photovoltaic 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 ipv,x,i , and thus the output power P of the photovoltaic array contained in the i-th power conversion module in phase x is obtained by using formula (1): 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 type photovoltaic storage system dc,x,i and input current I x,i , and thus the input power P of the H-bridge circuit contained in the i-th power conversion module in the x-phase is obtained by using formula (2): x,i , and use formula (3) to obtain 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 x,i 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 allowable deviation between the input power of the H-bridge circuit contained in the i-th power conversion module in the x-phase and the average value to 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, it is Park transformation, as shown in Figure 2 As shown, Figure 2 This is a virtual synchronous machine control structure diagram of the converter in the cascaded common DC bus type photovoltaic 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 photovoltaic 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 lit , when the bus capacitor voltage value is lower than Ulit, there is a greater risk of inverter failure. Here, it is considered that when the light 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 The difference is then input 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 limiting function. 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 shown in 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 power of the photovoltaic module at all times and pass it through a low-pass filter with a larger time constant, so that the power output can be smoothed and the power fluctuation caused by the MPPT algorithm and environmental factors can be reduced. 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, 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 system inertia is increased through the control loop, which can support the power grid and improve 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. 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, and 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 the difference is made and processed by the PI controller, the d-axis current reference value I of the system is obtained. d * , with 0 as the input reference value and with V q After the difference is made and processed by the PI controller, the q-axis current reference value I of the system is obtained. q * ; Here is the control of the voltage outer loop, and the outputs are the reference values ​​of the d-axis and q-axis currents. 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 d-axis modulation voltage reference value V of the system 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), we can 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 carrier phase shift modulation is performed to output the switch tube driving signal of the H-bridge circuit contained in the i-th power conversion module in the x-phase to drive the switch tube of the H-bridge circuit contained in the i-th power conversion module in the x-phase. 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 the system operation, and at the same time can effectively improve the service life of the cascade inverter. The control structure diagram is shown in Figure 3 shown.

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

[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 in 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 diagram is as shown in Figure 5 As shown, Figure 5 The topological structure diagram of the bidirectional DC / DC converter in the cascaded common DC bus type photovoltaic storage system of the present invention is shown in FIG. Figure 5 Medium V in The input side is connected to the positive and negative electrodes 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 devices are marked near the devices. By controlling the DC side capacitor voltage of the H-bridge module, the photovoltaic module works in the MPPT state. Therefore, the classic perturbation observation method is used 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 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 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 on the computer-readable storage medium, and the computer program executes the steps of the above method when executed by a processor.

Claims

1. A collaborative control method for a cascaded common DC bus photovoltaic 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 photovoltaic storage system, so as to 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; Calculating a 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 photovoltaic storage system and the power 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, the voltage and current double closed-loop control strategy is used to process the cascaded common DC bus photovoltaic storage system, and the components of the modulation voltage on the d-axis and q-axis in the rotating coordinate system are obtained, thereby calculating the three-phase modulation voltage. Calculate the modulation wave of each H-bridge circuit, add them to the compensation modulation wave respectively, and then output each switch tube drive signal to drive the corresponding switch tube after carrier phase shift modulation; According to the voltage and current of the photovoltaic array, each power conversion module is processed using the classical perturbation observation method 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, so as to obtain the current reference value of the bidirectional DC / DC converter; The current reference value is processed by the current loop, and then PWM modulated to obtain the modulation signal of each switch tube in the bidirectional DC / DC converter to 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 the output power P of the photovoltaic array contained in the i-th power conversion module in phase x is obtained by using formula (1): 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 photovoltaic storage system dc,x,i and input current I x,i , and thus the input power P of the H-bridge circuit contained in the i-th power conversion module in the x-phase is obtained by using formula (2): x,i , and use formula (3) to obtain 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 x,i 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 allowable deviation between the input power of the H-bridge circuit contained in the i-th power conversion module in the x-phase and the average value to 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 according to 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 photovoltaic 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 lowest 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 The difference is then input 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, 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, and 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 the difference is made and processed by the PI controller, the d-axis current reference value I of the system is obtained. d * ; With 0 as the input reference value and V q After the difference is made and processed by the PI controller, the q-axis current reference value I of the system 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 d-axis modulation voltage reference value V of the system 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), we can 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 tube driving signal of the H-bridge circuit contained in the i-th power conversion module in the x-phase to drive the switch tube 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 the x-phase; (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 MPPTx,i and u pv,x,i The difference is made, and then after being processed by the PI controller, the current reference value of the bidirectional DC / DC converter is obtained, which is then processed by the current loop control link and then PWM modulated 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.

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 any one of the collaborative control methods described in claims 1-9, and the processor is configured to execute the program stored in the memory.

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