Micro-grid load carrying soft start control method and energy storage converter parallel system

Abstract

The application provides a kind of micro-grid load soft start control method and energy storage converter parallel system, it is related to energy storage converter soft start technical field.The control method includes the following steps: optionally energy storage converter is host computer, the rest each energy storage converter is slave, and control unit sends soft start instruction to host computer;Host computer broadcasts soft start instruction to each slave through data bus.After host computer and each slave receive soft start instruction, each relay keeps open, and constant voltage and constant frequency AC soft start is executed synchronously, and the inverter voltage of itself is constructed.And each slave detects the inverter voltage of itself in real time, and whether AC soft start is completed is judged according to inverter voltage;If it is completed, host computer broadcasts relay closing signal to each slave;Each relay is closed according to relay closing signal, to end micro-grid load soft start.The application simplifies the structure and volume of energy storage converter parallel system, enhances the stability of micro-grid system, and prolongs its service life.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soft start of energy storage converter, in particular to a micro-grid load soft start control method and an energy storage converter parallel system. BACKGROUND

[0002] The energy storage converter can provide stable voltage and frequency for the load and other distributed power sources when it is operated in an island mode in an independent AC micro-grid, and can improve the consumption capacity of renewable energy. In the prior art, a plurality of energy storage converters are usually used to form an energy storage converter parallel system, and a master-slave control method is used on the basis of the energy storage converter parallel system to achieve flexible configuration of the capacity of the independent AC micro-grid system and fine management between battery units and other distributed power sources.

[0003] However, when the energy storage converter parallel system is used as the main power source of the micro-grid, there is a problem of load soft start, that is, when the energy storage converter parallel system starts with a load, the first started energy storage converter may have over-power and over-current due to the different starting time of each energy storage converter and the low overload capacity of the single energy storage converter under the rated frequency of the entire energy storage converter parallel system, thereby triggering protection and causing soft start failure. The so-called soft start is the recovery of the power system after a complete shutdown, that is, after a large area power failure accident occurs in the entire power grid due to a large disturbance or fault, the system is gradually restored by using the units or external power sources with self-starting capability in the power system, i.e. the tie line of the adjacent power grid, to support the system, and finally the entire power system is restored to normal operation.

[0004] The existing micro-grid load soft start scheme mainly has two kinds, one is to remove all loads before the energy storage converter parallel system starts, and then gradually put in the loads after the power supply starts; the other is to set a total load switch in series between the output end of the energy storage converter parallel system and the micro-grid bus, so as to close the total load switch after all the energy storage converters in the energy storage converter parallel system are started.

[0005] However, for scheme one, when the independent micro-grid is in a remote area, the distribution of the load switch is relatively dispersed, which is difficult to control independently, and the time-consuming of the load grading is relatively long. For scheme two, due to the application of the total load switch, the cost and volume of the energy storage converter parallel system are greatly increased, and the control complexity of the energy storage converter parallel system is also increased, thereby increasing the failure rate of the energy storage converter parallel system and reducing the stability and service life of the micro-grid system.

[0006] Therefore, there is an urgent need for a micro-grid load soft start control scheme to simplify the structure and volume of the energy storage converter parallel system, enhance the stability of the micro-grid system, and prolong the service life of the micro-grid system. SUMMARY

[0007] The present application aims to provide a micro-grid load soft start control method and energy storage converter parallel system, which can simplify the structure and volume of the energy storage converter parallel system, enhance the stability of the micro-grid system, and prolong the service life.

[0008] The embodiments of the present application can be implemented as follows:

[0009] In one aspect, the present application provides a micro-grid load soft start control method applied to an energy storage converter parallel system composed of multiple energy storage converter units, wherein each energy storage converter unit comprises an energy storage battery and an energy storage converter connected in sequence, and the AC output end of each energy storage converter is connected to an AC bus through a relay; the energy storage converter parallel system further comprises a data bus and a control unit, wherein the control unit is connected to each energy storage converter, and each energy storage converter is connected through the data bus; the micro-grid load soft start control method comprises the following steps:

[0010] Optionally, one energy storage converter is the master, and the rest are slaves, the control unit sends a soft start instruction to the master; the master broadcasts the soft start instruction to each slave through the data bus;

[0011] After receiving the soft start instruction, each relay remains open, and the master and each slave synchronously perform AC soft start with constant voltage and constant frequency to build their own inverter voltage;

[0012] The master and each slave detect their own inverter voltage in real time and determine whether the AC soft start is completed according to the inverter voltage;

[0013] If the AC soft start corresponding to the master and each slave is completed, the master broadcasts a relay closing signal to each slave;

[0014] Each relay is closed according to the relay closing signal to end the micro-grid load soft start.

[0015] Preferably, the step of the master and each slave synchronously performing AC soft start with constant voltage and constant frequency comprises:

[0016] The master and each slave form their own inverter voltage starting from zero with a preset slope, with the rated voltage as the target voltage and the rated frequency as the target power;

[0017] When each slave forms the inverter voltage, the master sends a phase angle synchronization signal to each slave in real time through the data bus to realize master-slave phase synchronization.

[0018] Preferably, when the master generates the first inverter voltage and each slave generates the second inverter voltage, the step that the master sends the phase angle synchronization signal to each slave in real time when each slave forms the inverter voltage comprises:

[0019] The master monitors the phase angle value corresponding to the first inverter voltage in real time, and judges whether the phase angle value is equal to a preset phase angle value;

[0020] When the phase angle value is equal to the preset phase angle value, the master broadcasts a phase angle synchronization signal to each slave through the data bus;

[0021] Each slave receives the phase angle synchronization signal in the form of receiving an interrupt through a local area network, and adjusts the phase angle value corresponding to each second inverter voltage to the preset phase angle value according to the phase angle synchronization signal.

[0022] Preferably, the steps that the master and each slave detect the inverter voltage in real time and judge whether the AC soft start is completed according to the inverter voltage comprise:

[0023] detecting the amplitude and frequency corresponding to the inverter voltage in real time;

[0024] judging whether the difference between the amplitude and a target amplitude is less than or equal to a first preset error, and if so, judging whether the difference between the frequency and a target frequency is less than or equal to a second preset error, and if so, determining that the AC soft start is completed.

[0025] Preferably, the steps that the master and each slave judge whether the AC soft start is completed in real time further comprise:

[0026] When the AC soft start corresponding to each slave is completed, each slave sends a first success flag signal to the master through the data bus;

[0027] When the AC soft start corresponding to the master is completed, the master generates a success flag signal of the master;

[0028] The master generates a pre-closed flag setting signal according to each first success flag signal and the success flag signal of the master.

[0029] Preferably, the step that the master broadcasts a relay closing signal to each slave comprises:

[0030] When the host and each of the slaves finishes the corresponding AC soft start, the host monitors the time difference between the current phase angle value and the next target phase value of the inverter voltage in real time, and judges whether the time difference is equal to the relay closing delay value. If yes, the host broadcasts a relay closing flag signal to each of the slaves through the data bus.

[0031] Preferably, when the energy storage converter comprises an inverter full-bridge module and an inverter filter connected in sequence, and the inverter filter is configured to provide an inverter voltage sampling value and an inductor current sampling value, the host and each of the slaves take the corresponding rated voltage as the target voltage, take the rated frequency of the microgrid as the target power, and form the inverter voltage of itself from zero with a preset slope, which comprises:

[0032] determining a target angular frequency according to the target power; converting the target angular frequency into a phase angle;

[0033] constructing the inverter voltage of itself from zero according to the preset slope and the target voltage, and determining the amplitude corresponding to the inverter voltage;

[0034] determining a voltage outer loop reference value according to the amplitude and the phase angle;

[0035] determining a current inner loop reference value according to the voltage outer loop reference value and the inverter voltage sampling value;

[0036] determining a driving signal according to the current inner loop reference value and the inductor current sampling value, so as to drive each of the energy storage converters to perform the constant voltage and constant frequency AC soft start.

[0037] Preferably, the step of determining the driving signal according to the current inner loop reference value and the inductor current sampling value comprises:

[0038] determining an initial modulation reference signal according to the current inner loop reference value and the inductor current sampling value;

[0039] determining a final modulation reference signal according to the inverter voltage sampling value and the initial modulation reference signal;

[0040] determining a modulation wave generation reference signal according to a preset modulation ratio and the final modulation reference signal;

[0041] determining the driving signal according to a preset carrier signal and the modulation wave generation reference signal.

[0042] Preferably, the expression of the modulation wave generation reference signal is:

[0043]

[0044] wherein, V pwm_refV is the amplitude of the preset carrier signal Tri V is the amplitude of the preset carrier signal nus V is the DC bus voltage sampling value V is the modulation ratio mod_ref V is the final modulation reference signal

[0045] In a second aspect, the present application also provides a storage converter parallel system, which is used to perform the micro-grid load soft start control method according to any one of the above first aspect.

[0046] The beneficial effects of the embodiments of the present application include, for example:

[0047] A micro-grid load soft start control method and a storage converter parallel system, wherein the micro-grid load soft start control method is applied to the storage converter parallel system. The system is composed of a plurality of storage converter units, each of which comprises a storage battery and a storage converter connected in sequence, and the AC output end of each storage converter is connected to an AC bus through a relay; and the storage converters are connected through a data bus. The micro-grid load soft start control method comprises the following steps: selecting one storage converter as a master and the rest as slaves, and sending a soft start instruction to the master by a control unit; the master broadcasts the soft start instruction to each slave through the data bus. After receiving the soft start instruction, each relay remains open, and the master and each slave synchronously perform constant voltage and constant frequency AC soft start to build their own inverter voltage. The master and each slave detect their own inverter voltage in real time, and determine whether the AC soft start is completed according to the inverter voltage; if it is completed, the master broadcasts a relay closing signal to each slave; each relay is closed according to the relay closing signal to end the micro-grid load soft start. In the present application, before the relay is closed, all storage converters in the storage converter parallel system have completed the same amplitude, frequency and phase control of the AC inverter voltage, and through the control logic, all relays corresponding to the storage converters are closed at the same AC phase angle zero crossing as much as possible, which maximally reduces current impact and power fluctuation, and ensures the stability of the micro-grid load soft start. BRIEF DESCRIPTION OF DRAWINGS

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0049] Figure 1 A system structure diagram of a storage converter parallel system provided by the present application;

[0050] Figure 2 A step flow chart of the micro-grid load soft start control method provided by the present application;

[0051] Figure 3 A sub-step flow chart of step 300 in the micro-grid load soft start control method of the present application;

[0052] Figure 4 A sub-step flow chart of step 302 in the micro-grid load soft start control method of the present application;

[0053] Figure 5 A control flow chart of the AC soft start of each energy storage converter in the present application;

[0054] Figure 6 A sub-step flow chart of step 301 in the micro-grid load soft start control method of the present application;

[0055] Figure 7 A sub-step flow chart of step 3015 in the micro-grid load soft start control method of the present application;

[0056] Figure 8 A sub-step flow chart of step 400 in the micro-grid load soft start control method of the present application;

[0057] Figure 9 A sub-step flow chart of step 500 in the micro-grid load soft start control method of the present application;

[0058] Figure 10 An effect diagram of the micro-grid load soft start in an embodiment of the present application.

[0059] Legend: 100-energy storage converter parallel system; 101-energy storage converter single machine; 102-energy storage battery; 103-energy storage converter; 104-control unit. DETAILED DESCRIPTION

[0060] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in connection with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0061] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application.

[0062] It should be noted that similar reference numerals and letters refer to like items in the accompanying drawings, and once an item is defined in one drawing, it need not be further defined and explained in subsequent drawings.

[0063] In the description of the present application, it should be noted that if the terms "upper", "lower", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the present application is usually placed, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0064] In addition, if the terms "first", "second" and the like appear, they are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0065] It should be noted that the features in the embodiments of the present application can be combined with each other without conflict.

[0066] As described in the background art, when the energy storage converter parallel system is used as the main power supply of the micro-grid, the different starting times of the energy storage converters and the low overload capacity of the individual energy storage converters will cause the first started energy storage converter to bear the load under the rated power of the entire energy storage converter parallel system, resulting in over-power and over-current.

[0067] The prior art provides two technical solutions, solution one: all loads are removed before the power supply of the energy storage converter parallel system is started, and the loads are then gradually put into operation after the power supply is started; solution two: a total load switch is connected in series between the output end of the energy storage converter parallel system and the micro-grid bus, so that the total load switch is closed after all the energy storage converters in the energy storage converter parallel system are started. However, both solutions cannot simplify the structure and volume of the energy storage converter parallel system while enhancing the stability of the micro-grid system and prolonging its service life.

[0068] Based on the above considerations, the present application provides a control scheme for soft starting with load under a micro-grid.

[0069] The control scheme will be described in detail below.

[0070] Please refer to Figure 1The embodiment provides a power storage converter parallel system 100 which is used for executing the micro-grid load soft start control method described below. The power storage converter parallel system 100 is composed of a plurality of power storage converter units 101, and each power storage converter unit 101 comprises a power storage battery 102 and a power conversion system (PCS) 103 which are connected in sequence. The AC output end of each power storage converter 103 is connected with an AC bus through a relay respectively; and the AC bus is connected with a micro-grid load through a power frequency transformer.

[0071] The power storage converter parallel system 100 further comprises a control unit 104 which is used for sending a control signal to each power storage converter 103 to control the start and stop of the power storage converter 103. When an optional power storage converter is a master and the rest of the power storage converters are slaves, the control unit 104 can be connected with the master to broadcast a control signal or a control instruction to each slave through the master.

[0072] The power storage converters 103 are connected through a data bus. According to the micro-grid load soft start control method, the power storage converters 103 in the power storage converter parallel system 100 perform micro-grid load soft start, so that the stability of the micro-grid system is enhanced and the service life of the micro-grid system is prolonged on the basis of simplifying the structure and volume of the power storage converter parallel system 100.

[0073] Please refer to Figure 2 The embodiment further provides a micro-grid load soft start control method which comprises steps 200-600.

[0074] In step 200, an optional power storage converter is a master, and the rest of the power storage converters are slaves, and a control unit sends a soft start instruction to the master; and the master broadcasts the soft start instruction to each slave through a data bus.

[0075] In step 300, after receiving the soft start instruction, each relay remains disconnected, and the master and each slave synchronously perform AC soft start of constant voltage and constant frequency to build an inverter voltage of itself.

[0076] In step 400, the master and each slave detect the inverter voltage of itself in real time, and determine whether the AC soft start is completed according to the inverter voltage.

[0077] In step 600, if the AC soft start corresponding to the master and each slave is completed, the master broadcasts a relay closing signal to each slave.

[0078] In step 700, each relay is closed according to the relay closing signal to end the micro-grid load soft start.

[0079] In this embodiment, when the microgrid is in the state of soft start with load not started, the relays corresponding to all energy storage converters in the energy storage converter parallel system are in the disconnected state. When the microgrid is soft started with load, all energy storage converters in the parallel system independently establish their own inverter voltage from scratch. At the same time, each energy storage converter samples and detects in real time whether the amplitude and frequency corresponding to its own inverter voltage reach the target threshold, so as to determine whether each energy storage converter has completed the soft start based on the inverter voltage corresponding to each energy storage converter.

[0080] In order to realize data interaction between the master and the slave, the master can be preset in the energy storage converter parallel system. In one possible implementation method, one energy storage converter can be selected as the master, and the remaining energy storage converters can be selected as slaves. In this embodiment, all slaves will send the judgment results to the master in real time via the CAN communication bus. After the soft start of the master and all slaves is completed, the master broadcasts the closing output relay instruction to all slaves. After receiving the instruction, all energy storage converters immediately close the relay to synchronously supply power to the load, thereby realizing the load black start control of the energy storage converter parallel system under the working condition of an independent microgrid. In addition, before closing the relay, the master will also synchronize the power frequency cycle zero crossing signal to each slave through the CAN communication bus to achieve synchronization between the power frequency phase angles corresponding to each energy storage converter in the energy storage converter parallel system.

[0081] The microgrid on-load soft start control method provided in this embodiment can simplify the structure and volume of the energy storage converter parallel system, enhance stability and extend service life.

[0082] In one possible implementation, combining Figure 2 In the method shown, step 200 is specifically as follows:

[0083] Based on the master-slave configuration command sent by the user, the control unit selects one of the energy storage converters as the master and the remaining converters as slaves. After receiving the soft-start command, the control unit feeds it back to the master, which then broadcasts it to the remaining slaves via the CAN communication bus.

[0084] After each energy storage converter receives the soft start command, it starts to perform constant voltage and constant frequency AC soft start control. Figure 3 In this embodiment, the master and each slave synchronously perform constant voltage and constant frequency AC soft start, and the steps of building their own inverter voltage include step 301-step 302.

[0085] Step 301: The master and each slave each use the rated voltage as the target voltage, the rated frequency as the target power, and form their own inverter voltage starting from zero with a preset slope.

[0086] Step 302, when the slave machines form the inverter voltage, the master machine sends the phase angle synchronization signal to the slave machines in real time through the data bus to realize the phase synchronization of the master and slave machines.

[0087] In one possible implementation, after receiving the start-up instruction, all the energy storage converters in the energy storage converter parallel system 100 start to gradually establish the inverter voltage from zero at a fixed slope as the target voltage at the rated frequency F rate as the target voltage at the rated frequency F rate The inverter voltage is gradually established from zero at a fixed slope as the target frequency, the AC soft start control is performed, and the slave machines constantly synchronize the phase of the power frequency voltage output by the master machine, i.e., the master machine broadcasts the phase synchronization signal to the slave machines, so that the slave machines adjust the phase angles corresponding to the second inverter voltages to the preset phase angle according to the phase synchronization signal after receiving the phase synchronization signal.

[0088] Please refer to Figure 4 In the embodiment, when the master machine generates the first inverter voltage and the slave machines generate the second inverter voltage, the step of the master machine sending the phase angle synchronization signal to the slave machines in real time when the slave machines form the inverter voltage includes steps 3021 to 3023.

[0089] Step 3021, the master machine monitors the phase angle value corresponding to the first inverter voltage in real time, and determines whether the phase angle value is equal to the preset phase angle value.

[0090] Step 3022, when the phase angle value is equal to the preset phase angle value, the master machine broadcasts the phase angle synchronization signal to the slave machines through the data bus.

[0091] Step 3023, the slave machines receive the phase angle synchronization signal in the form of local area network interruption, and adjust the phase angle values corresponding to the second inverter voltages to the preset phase angle value according to the phase angle synchronization signal.

[0092] In one possible implementation, when the master machine synchronizes the power frequency cycle zero signal to the slave machines through the CAN communication bus to realize the synchronization of the power frequency phase angles corresponding to the energy storage converters in the energy storage converter parallel system, the master machine can monitor the phase angle value corresponding to the first inverter voltage in real time, and when the phase angle value is zero, the master machine broadcasts the phase angle synchronization signal to the slave machines through the data bus with the highest priority. The slave machines can receive the phase angle synchronization signal in the form of CAN interruption, and set the phase angle corresponding to the slave machines to zero in the interruption after receiving the phase angle synchronization signal.

[0093] The phase angle synchronization process in the embodiment can be realized through the control process of the AC soft start. The control process will be described in detail below.

[0094] In one possible implementation, the master and each slave include a voltage outer loop controller and a current inner loop controller to control the corresponding energy storage converter to implement various control schemes. For example, in this embodiment, the corresponding energy storage converter is controlled to implement a constant voltage and constant current scheme.

[0095] Referring to Figure 5 , Figure 5 A control flowchart of the constant voltage and constant current scheme in each energy storage converter is shown. In this embodiment, each energy storage converter includes a full-bridge inverter circuit (PCS full-bridge inverter circuit) and an inverter output filter circuit (PCS output filter circuit) connected in sequence. The inverter output filter circuit is connected to a backend load through a relay.

[0096] In this embodiment, when the energy storage converter includes a full-bridge inverter circuit and an inverter output filter circuit connected in sequence, and the inverter output filter circuit is configured to provide an inverter voltage sampling value V inv and an inductor current sampling value I inv , Figure 6 Referring to , the master and each slave take the corresponding rated voltage as the target voltage, take the rated frequency of the microgrid as the target power, and take a preset slope to form the inverter voltage from zero. Step 301 includes steps 3011-3015.

[0097] Step 3011, determine the target angular frequency according to the target power; and convert the target angular frequency into a phase angle.

[0098] Step 3012, construct the inverter voltage from zero according to the preset slope and the target voltage, and determine the amplitude corresponding to the inverter voltage.

[0099] Step 3013, determine the voltage outer loop reference value according to the amplitude and the phase angle.

[0100] Step 3014, determine the current inner loop reference value according to the voltage outer loop reference value and the inverter voltage sampling value.

[0101] Step 3015, determine the drive signal according to the current inner loop reference value and the inductor current sampling value to drive each energy storage converter to implement the constant voltage and constant frequency AC soft start.

[0102] In one possible implementation, the corresponding rated frequency F rate and the rated operating frequency f sThe ratio between the frequency of the execution of the control algorithm (or the frequency of execution of the control algorithm in the energy storage converter) and the frequency of the execution of the control algorithm in the master determines the angular frequency ω0. Then, the phase angle θ is determined according to the angular frequency ω0 in the working period, and the range of the phase angle θ satisfies (0, 2π). When the phase angle corresponding to the master is zero, i.e. θ = 0, the master immediately synchronizes the phase angle synchronization signal to each slave through the CAN communication bus with the highest priority. After the slave receives the phase angle synchronization signal, each slave sets its own phase angle to zero, thereby realizing the accurate synchronization of the power frequency phase of the master and the slave.

[0103] The above master-slave power frequency synchronization is synchronized with the off-grid constant voltage constant frequency control between the master and the slave. The process of the master and each slave executing the constant voltage constant frequency control in the embodiment will be described in detail below, i.e. taking the corresponding rated voltage as the target voltage, taking the rated frequency corresponding to the microgrid as the target power, and taking the preset slope to form the inverter voltage from zero. It should be noted that the rated frequency and the rated voltage corresponding to the master and each slave in the embodiment are consistent.

[0104] In a possible implementation, the phase angle θ determined in the above step 3011 can be subjected to a sine operation to obtain a processed phase angle sin(θ). Then, the processed phase angle sin(θ) is superimposed on the slowly changing inverter voltage as a reference value of a voltage outer loop controller, i.e. a voltage outer loop reference value wherein V A_ref is the amplitude corresponding to the slowly changing inverter voltage. In this process, the amplitude of the inverter voltage slowly changes from zero to the target amplitude at a fixed slope, so as to avoid the voltage step in the voltage outer loop control process, causing the overshoot phenomenon and the impact on the rear-end inverter filter. In the embodiment, the preset slope can be determined within one power frequency period (usually 20 ms) with the rated voltage V rate as the target. Meanwhile, considering the soft start waiting time, the preset slope can be determined from 0 to the rated voltage V rate at an interval of 10 s, and the preset slope satisfies (Vrate / 10s)-(Vrate / 0.02s). In the embodiment, the preset slope is preferably (Vrate / 1s).

[0105] The reference value of the voltage outer loop controller, i.e. the voltage outer loop reference value is determined. Then, the difference between the inverter voltage sampling value V inv and the voltage outer loop reference value inv is determined, and the current inner loop reference value is determined by using the voltage outer loop controller G v (s). The current inner loop reference value satisfies: In the embodiment, the voltage outer loop controller is a proportional integral controller, and the transfer function G v(s) represents: wherein, K p_v is a voltage outer loop proportional coefficient, K i_v is a voltage outer loop integral coefficient.

[0106] Similarly, a difference between the current inner loop reference value and the inductor current sampling value I inv is determined, and a driving signal is determined by using a current inner loop controller. In this embodiment, the current inner loop controller G i (s) is a proportional-integral controller, and its transfer function G i (s) is represented as: wherein, K p_i is a voltage outer loop proportional coefficient, K i_i is a voltage outer loop integral coefficient.

[0107] In one possible implementation, in order to accelerate the response speed of the control system and enhance the dynamic performance, a sampling value V inv of the inverter voltage can be superimposed on the output value of the current inner loop controller, i.e., a sampling value feedforward is added to the output value of the current inner loop controller. Please refer to Figure 7 , and the step 3015 of determining the driving signal according to the current inner loop reference value and the inductor current sampling value comprises steps 1501-1504.

[0108] Step 1501, an initial modulation reference signal is determined according to the current inner loop reference value and the inductor current sampling value.

[0109] Step 1502, a final modulation reference signal is determined according to the sampling value of the inverter voltage and the initial modulation reference signal.

[0110] Step 1503, a modulation carrier wave reference signal is determined according to a preset modulation ratio and the final modulation reference signal.

[0111] Step 1504, a driving signal is determined according to a preset carrier signal and the modulation carrier wave reference signal.

[0112] In this embodiment, the final modulation reference signal V mod_ref satisfies: Please continue to refer to Figure 5 , after the final modulation reference signal V mod_ref , the final modulation reference signal is modulated by a preset modulation ratio to obtain a modulation carrier wave reference signal, and the expression of the modulation carrier wave reference signal in this embodiment is: wherein, V pwm_ref is the amplitude of the modulation carrier wave reference signal, V Tri is the amplitude of the preset carrier signal, and V bus is the sampling value of the DC bus voltage. is the modulation ratio, V mod_ref is the final modulation reference signal.

[0113] The modulation wave reference signal then enters the PWM modulator to be modulated by a preset carrier signal inside the PWM modulator to generate a driving signal, which in turn drives the energy storage converter to realize off-grid constant voltage and constant frequency control, so as to ensure that the output inverter voltages of each energy storage converter have been set to the same amplitude, frequency and phase before the completion of the micro-grid load soft start, i.e. before the relay is closed.

[0114] In this embodiment, continuing to refer to Figure 5 , the inverter filter includes a first inductor L1, a second inductor L2 and a filter capacitor C, wherein the first end of the first inductor L1, the first end of the second inductor L2 and the first end of the filter capacitor C are connected; the second end of the first inductor L1 and the second end of the filter capacitor C are connected with the output end of the inverter full-bridge module; and the second end of the second inductor L2 is connected with the relay. The inverter voltage sampling value V inv is the voltage corresponding to the two ends of the filter capacitor in the inverter filter; and the inductor current sampling value I inv is the current output by the first inductor L1 in the inverter filter.

[0115] As shown in Figure 2 , the constant voltage and constant frequency are performed among the energy storage inverters according to the manner provided in the above embodiment to construct the inverter voltage. In this embodiment, referring to Figure 8 , the master and each slave machine detect the inverter voltage of itself in real time, and the step 400 of judging whether the AC soft start is completed according to the inverter voltage includes steps 401-402.

[0116] The step 401 is to detect the amplitude and frequency corresponding to the inverter voltage of itself in real time.

[0117] The step 402 is to judge whether the difference between the amplitude and the target amplitude is less than or equal to a first preset error; if yes, to judge whether the difference between the frequency and the target frequency is less than or equal to a second preset error; if yes, to determine that the AC soft start is completed.

[0118] In this embodiment, each energy storage converter in the energy storage converter parallel system detects the amplitude V inv and the frequency F inv corresponding to the inverter voltage of itself in real time when performing the soft start, and judges whether the target value is reached. In one possible implementation, when it is detected that the amplitude V inv of the inverter voltage and the target amplitude V rate are within ±5V, and the inverter voltage frequency F inv of the inverter voltage V inv and the target frequency Frate If the error is within ±0.5 Hz, it is determined that the AC soft start corresponding to the current energy storage converter is completed, and an AC soft start success flag is set. Meanwhile, all the slaves send the AC soft start success flag to the master through the CAN communication bus in real time. The above frequency F inv The inverter voltage instantaneous sampling value V inv is calculated.

[0119] The master and each slave detect the inverter voltage of itself in real time, and after the step 400 of determining whether the AC soft start is completed according to the inverter voltage, the master generates a pre-closure flag setting signal according to the AC soft start state of itself and the AC soft start state of each slave. After the phase angle of the master and each slave meets a specific condition, each energy storage converter drives the relay corresponding to itself to be closed, so as to end the soft start.

[0120] In one possible implementation, referring to Figure 9 The step 500 includes steps 501-503.

[0121] In the step 501, when the AC soft start corresponding to each slave is completed, each slave sends a first success flag signal to the master through the data bus.

[0122] In the step 502, when the AC soft start corresponding to the master is completed, a success flag signal of itself is generated.

[0123] In the step 503, the master generates a pre-closure flag setting signal according to the first success flag signal of each slave and the success flag signal of itself.

[0124] In one possible implementation, when the master and each slave complete the soft start, the master generates a pre-closure flag setting signal to inform the master energy storage converter and each energy storage converter in the system that the soft start is completed. At this time, the master sends a relay closing signal to itself and each slave. In order to ensure that the relays corresponding to each energy storage converter in the energy storage converter parallel system are closed at the same time, each energy storage converter can be made to close the output relay at the same AC zero-crossing point according to the execution mode of the phase angle synchronization in the above embodiment.

[0125] In this embodiment, the step 600 of broadcasting the relay closing signal from the master to each slave can be:

[0126] When the AC soft start corresponding to the host, each slave is completed, the host real-time monitoring of its inverter voltage current phase angle value to the next target phase value between the time difference, and determine whether the time difference is equal to the relay closing delay value, if equal, the host through the data bus to each slave broadcast relay closing flag signal. Among them, the relay closing delay value is the relay drive signal to the relay actual closing between the delay.

[0127] After each energy storage converter receives the relay closing signal, then each drive its own corresponding relay closure, to end the micro-grid load soft start.

[0128] The embodiment also provides a comparative experiment, please refer to Figure 10 , the embodiment of a plurality of, master-slave control of energy storage converter single machine to build an energy storage converter parallel system, wherein the rated output power of each energy storage converter single machine is 2000W, the rated voltage is 230V, the rated frequency is 50Hz, the rated current is 8.7A, wherein A is the voltage waveform corresponding to the load, B is the output current waveform corresponding to the host, C is the output current waveform corresponding to any slave.

[0129] Please continue to refer to Figure 10 , the energy storage converter parallel system in the embodiment is executed under the structure as shown in Figure 1 , according to the steps of the micro-grid load soft start control method as shown in Figure 2 , each energy storage converter single machine completes the closure of the relay near the zero crossing of AC voltage, the time difference of the relay closure between the host and the slave is within 2ms. It can be seen that the embodiment can make all the relays corresponding to the energy storage converter close at the same AC phase angle zero crossing as possible, thereby minimizing the current impact and power fluctuation, and ensuring the stability of the micro-grid load soft start.

[0130] In summary, the embodiment provides a micro-grid load soft start control method and an energy storage converter parallel system, wherein the micro-grid load soft start control method is applied to the energy storage converter parallel system. The system is composed of multiple energy storage converter units, each of which comprises an energy storage battery and an energy storage converter connected in sequence, and the AC output end of each energy storage converter is connected to an AC bus through a relay; and the energy storage converters are connected through a data bus. The micro-grid load soft start control method comprises the following steps: selecting one energy storage converter as a master and the rest as slaves, and sending a soft start instruction to the master by a control unit; the master broadcasts the soft start instruction to each slave through the data bus. After receiving the soft start instruction, each relay remains open, and the master and each slave synchronously perform AC soft start with constant voltage and constant frequency to build their own inverter voltage. The master and each slave detect their own inverter voltage in real time, and determine whether the AC soft start is completed according to the inverter voltage; if so, the master broadcasts a relay closing signal to each slave; each relay is closed according to the relay closing signal to end the micro-grid load soft start.

[0131] In the present application, before the relay is closed, all energy storage converters in the energy storage converter parallel system have completed the control of the same amplitude, frequency and phase of the AC inverter voltage, and the relays corresponding to all energy storage converters are closed at the same AC phase angle zero crossing as much as possible through control logic, which maximally reduces current impact and power fluctuation and ensures the stability of the micro-grid load soft start.

[0132] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A microgrid on-load soft start control method, applied to a parallel energy storage converter system composed of multiple energy storage converter units, wherein the energy storage converter units include an energy storage battery and an energy storage converter connected in sequence, and the AC output end of each energy storage converter is connected to the AC bus through a relay; the parallel energy storage converter system also includes a data bus and a control unit, wherein the control unit is connected to each of the energy storage converters, and each of the energy storage converters is connected through the data bus, characterized in that: The microgrid on-load soft start control method comprises the following steps: One energy storage converter is selected as the master, and the other energy storage converters are selected as slaves. The control unit sends a soft start instruction to the master; the master broadcasts the soft start instruction to each of the slaves via the data bus. After receiving the soft start instruction, each of the relays remains disconnected, and the host and each of the slaves synchronously perform constant voltage and constant frequency AC soft start to build their own inverter voltage; The host and each of the slaves detect their own inverter voltages in real time, and determine whether the AC soft start is completed based on the inverter voltages; If the AC soft starts corresponding to the host and each of the slaves are completed, the host broadcasts a relay closing signal to each of the slaves; Each of the relays is closed according to the relay closing signal to end the soft start of the microgrid on load; The steps of synchronously performing constant voltage and constant frequency AC soft start on the host and each of the slaves include: The master and each slave each use the rated voltage as the target voltage, the rated frequency as the target power, and form their own inverter voltage starting from zero with a preset slope; When each of the slaves generates the inverter voltage, when the master generates the first inverter voltage and each of the slaves generates the second inverter voltage, the master monitors the phase angle value corresponding to the first inverter voltage in real time; and determines whether the phase angle value is equal to a preset phase angle value; When the phase angle value is equal to a preset phase angle value, the host broadcasts a phase angle synchronization signal to each of the slaves via the data bus; Each of the slave machines receives the phase angle synchronization signal by way of a local area network reception interrupt, and adjusts the phase angle value corresponding to each of its own second inverter voltages to a preset phase angle value according to the phase angle synchronization signal, so as to achieve phase synchronization between the master and slave machines.

2. The microgrid load soft start control method according to claim 1, characterized in that: The master and each slave detect the inverter voltage in real time, and the steps of judging whether the AC soft start is completed according to the inverter voltage include: Real-time detection of the amplitude and frequency corresponding to its own inverter voltage; Determine whether the difference between the amplitude and the target amplitude is less than or equal to a first preset error; if less than or equal to, determine whether the difference between the frequency and the target frequency is less than or equal to a second preset error; if less than or equal to, determine that the AC soft start is completed.

3. The microgrid load soft start control method according to claim 2, characterized in that: After the step of the host and each of the slaves determining in real time whether the AC soft start is completed, the following step further comprises: When the AC soft start corresponding to each of the slaves is completed, each of the slaves sends a first success flag signal to the host through the data bus; When the AC soft start corresponding to the host is completed, a success flag signal is generated; The host generates a pre-close flag setting signal according to each of the first success flag signals and its own success flag signal.

4. The microgrid load soft start control method according to claim 1, characterized in that: The step of the host broadcasting a relay closing signal to each of the slaves comprises: When the AC soft starts corresponding to the host and each of the slaves are completed, the host monitors the time difference between the current phase angle value of its own inverter voltage and the next target phase value in real time, and determines whether the time difference is equal to the relay closing delay value. If so, the host broadcasts the relay closing flag signal to each of the slaves through the data bus.

5. The microgrid load soft start control method according to claim 1, characterized in that: When the energy storage converter includes an inverter full-bridge module and an inverter filter connected in sequence; and the inverter filter is used to provide an inverter voltage sampling value and an inductor current sampling value, the master and each of the slaves use the corresponding rated voltage as the target voltage and the rated frequency corresponding to the microgrid as the target power, and the steps of forming their own inverter voltage from zero with a preset slope include: determining a target angular frequency according to the target power; converting the target angular frequency into a phase angle; Constructing its own inverter voltage from zero according to the preset slope and the target voltage, and determining the amplitude corresponding to the inverter voltage; determining a voltage outer loop reference value according to the amplitude and the phase angle; Determining a current inner loop reference value based on the voltage outer loop reference value and the inverter voltage sampling value; A driving signal is determined according to the current inner loop reference value and the inductor current sampling value to drive each of the energy storage converters to perform constant voltage and constant frequency AC soft start.

6. The microgrid load soft start control method according to claim 5, characterized in that: The step of determining the driving signal according to the current inner loop reference value and the inductor current sampling value includes: Determining an initial modulation reference signal according to the current inner loop reference value and the inductor current sampling value; Determining a final modulation reference signal according to the inverter voltage sampling value and the initial modulation reference signal; Determining a modulation reference signal according to a preset modulation ratio and the final modulation reference signal; The driving signal is determined according to a preset carrier signal and the modulated reference signal.

7. The microgrid load soft start control method according to claim 6, characterized in that: The expression of the modulated wave reference signal is: in, is the amplitude of the modulated reference signal, is the amplitude of the preset carrier signal, is the DC bus voltage sampling value, is the modulation ratio, is the final modulation reference signal.

8. A parallel energy storage converter system, characterized in that: The energy storage converter parallel system is used to execute the microgrid on-load soft start control method according to any one of claims 1 to 7.

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