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

Abstract

The invention provides a micro-grid on-load soft start control method and an energy storage converter parallel system, and relates to the technical field of energy storage converter soft start. The control method comprises the following steps: randomly selecting one energy storage converter as a host, selecting the other energy storage converters as slaves, and sending a soft start instruction to the host by a control unit; and the host broadcasts a soft start instruction to each slave through the data bus. After the host and the slaves receive the soft start instruction, the relays are kept disconnected, constant-voltage and constant-frequency alternating-current soft start is synchronously executed, and the inversion voltage of the relays is constructed. The inverter voltage is detected in real time, and whether the AC soft start is completed is judged according to the inverter voltage; if so, the host broadcasts a relay closing signal to each slave; and closing each relay according to the relay closing signal to finish the on-load soft start of the micro-grid. The structure and the size of the energy storage converter parallel system are simplified, the stability of the micro-grid system is enhanced, and the service life of the micro-grid system is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of soft starting of energy storage converters, and in particular to a microgrid on-load soft starting control method and an energy storage converter parallel system. Background Art

[0002] When the energy storage inverter operates in an isolated island in an independent AC microgrid, it can provide stable voltage and frequency for the load and other distributed power sources, while improving the consumption capacity of renewable energy. In the prior art, multiple energy storage inverters are usually used to form an energy storage inverter parallel system, and on the basis of the energy storage inverter parallel system, a master-slave control method is adopted to achieve flexible configuration of the capacity of the independent AC microgrid system and other distributed power sources, such as refined management between battery units.

[0003] However, when the energy storage inverter parallel system is used as the main power source of the microgrid, there is a problem of soft start with load, that is, when the energy storage inverter parallel system is started with load, due to the asynchronous start time between the energy storage inverters and the low overload capacity of a single energy storage inverter, the energy storage inverter that is started first may experience overpower and overcurrent due to the load at the rated frequency of the entire energy storage inverter parallel system, thereby triggering protection and causing soft start failure. Among them, the so-called soft start is the recovery after the power system is completely shut down, that is, after the entire power grid suffers a large disturbance or failure and a large-scale power outage occurs, the system is gradually restored by using the units with self-starting capabilities within the power system or the power supply outside the system, that is, the interconnection line support of the adjacent power grid, and finally the entire power system is restored to normal operation.

[0004] There are two main types of existing microgrid on-load soft-start schemes. One is to remove all loads before the power supply of the energy storage inverter parallel system is started, and then the loads are put into operation in stages after the power supply is started; the other is to set a total load switch in series between the output end of the energy storage inverter parallel system and the microgrid bus, so that the total load switch can be closed after all energy storage inverters in the energy storage inverter parallel system are started.

[0005] However, for solution 1, when the independent microgrid is located in a remote area, the distribution of load switches is relatively scattered, making it difficult to control independently, and the load classification takes a long time. For solution 2, due to the application of the total load switch, the cost and volume of the energy storage inverter parallel system will be greatly increased, and the control complexity of the energy storage inverter parallel system will also be increased, thereby increasing the failure rate of the energy storage inverter parallel system and reducing the stability and service life of the microgrid system.

[0006] Based on this, a control scheme for microgrid soft start with load is urgently needed to simplify the structure and volume of the energy storage inverter parallel system, enhance the stability of the microgrid system and extend its service life. Summary of the invention

[0007] The objectives of the present invention include, for example, providing a microgrid load soft start control method and an energy storage inverter parallel system, which can simplify the structure and volume of the energy storage inverter parallel system, enhance the stability of the microgrid system and extend its service life.

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

[0009] On the one hand, the present invention provides a microgrid load soft start control method, which is applied to an energy storage converter parallel system composed of multiple energy storage converter units, wherein the energy storage converter units include energy storage batteries and energy storage converters connected in sequence, and the AC output end of each energy storage converter is connected to the AC bus through a relay; the energy storage converter parallel 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. The microgrid load soft start control method includes the following steps:

[0010] One energy storage converter is selected as the host, and the other energy storage converters are selected as slaves. The control unit sends a soft start instruction to the host; the host broadcasts the soft start instruction to each of the slaves through the data bus;

[0011] 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;

[0012] The host and each of the slaves detect their own inverter voltages in real time, and determine whether the AC soft start is completed according to the inverter voltage;

[0013] 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;

[0014] Each of the relays is closed according to the relay closing signal to end the soft start of the microgrid with load.

[0015] Preferably, the step of the host and each of the slaves synchronously performing constant voltage and constant frequency AC soft start includes:

[0016] The host and each of the slaves use the rated voltage as the target voltage and the rated frequency as the target power, and form their own inverter voltage from zero with a preset slope;

[0017] When each of the slaves forms the inverter voltage, the host sends a phase angle synchronization signal to each of the slaves via the data bus in real time to achieve phase synchronization between the master and slaves.

[0018] Preferably, when the host generates a first inverter voltage and each of the slaves generates a second inverter voltage, the step of the host sending a phase angle synchronization signal to each of the slaves in real time when each of the slaves forms the inverter voltage includes:

[0019] The host 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;

[0020] 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;

[0021] Each of the slaves 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.

[0022] Preferably, the host and each of the slaves detect the inverter voltage in real time, and the step of judging whether the AC soft start is completed according to the inverter voltage includes:

[0023] Real-time detection of the amplitude and frequency corresponding to its own inverter voltage;

[0024] 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.

[0025] Preferably, after the step of the host and each of the slaves determining in real time whether the AC soft start is completed, the step further includes:

[0026] 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;

[0027] When the AC soft start corresponding to the host is completed, a success flag signal is generated;

[0028] The host generates a pre-closing flag setting signal according to each of the first success flag signals and its own success flag signal.

[0029] Preferably, the step of the host broadcasting a relay closing signal to each of the slaves comprises:

[0030] 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.

[0031] Preferably, 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 host and each of the slaves use the corresponding rated voltage as the target voltage, 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:

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

[0033] 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;

[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] 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.

[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] Determine a modulation reference signal according to a preset modulation ratio and the final modulation reference signal;

[0041] The driving signal is determined according to the preset carrier signal and the modulated reference signal.

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

[0043]

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

[0045] In a second aspect, the present invention further provides an energy storage converter parallel system, which is used to execute the microgrid load soft start control method as described in any one of the first aspects above.

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

[0047] A microgrid on-load soft start control method and an energy storage converter parallel system, wherein the microgrid on-load soft start control method is applied to the energy storage converter parallel system. The above system is composed of multiple energy storage converter units, and the energy storage converter units include energy storage batteries and energy storage converters connected in sequence. The AC output end of each energy storage converter is connected to the AC bus through a relay; and each energy storage converter is connected through the data bus. The above microgrid on-load soft start control method includes the following steps: select one energy storage converter as the host, and the remaining energy storage converters as slaves, and the control unit sends a soft start instruction to the host; the host broadcasts the soft start instruction to each slave through the data bus. After receiving the soft start instruction, each relay remains disconnected, and the host and each slave synchronously execute constant voltage and frequency AC soft start to build their own inverter voltage. The host and each slave detect their own inverter voltage in real time, and judge whether the AC soft start is completed based on the inverter voltage; if all are completed, the host broadcasts a relay closing signal to each slave; each relay is closed according to the relay closing signal to end the soft start of the microgrid with load. In the present invention, before the relay is closed, all energy storage converters in the energy storage converter parallel system have completed the same amplitude, frequency and phase control of the AC inverter voltage, and the control logic is used to make the relays corresponding to all energy storage converters close at the same AC phase angle zero crossing as much as possible, thereby minimizing the current impact and power fluctuation, and ensuring the stability of the soft start with load under the microgrid. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0049] Figure 1 A system structure diagram of an energy storage converter parallel system provided by the present invention;

[0050] Figure 2 A flowchart of the steps of a microgrid load soft start control method provided by the present invention;

[0051] Figure 3 It is a step-by-step flow chart of step 300 in the microgrid on-load soft start control method of the present invention;

[0052] Figure 4 It is a step-by-step flow chart of step 302 in the microgrid on-load soft start control method of the present invention;

[0053] Figure 5 It is a control flow chart of AC soft start of each energy storage converter in the present invention;

[0054] Figure 6 It is a step-by-step flow chart of step 301 in the microgrid on-load soft start control method of the present invention;

[0055] Figure 7 It is a step-by-step flow chart of step 3015 in the microgrid on-load soft start control method of the present invention;

[0056] Figure 8 It is a step-by-step flow chart of step 400 in the microgrid on-load soft start control method of the present invention;

[0057] Fig. 9 It is a step-by-step flow chart of step 500 in the microgrid on-load soft start control method of the present invention;

[0058] Fig.10 This is a diagram showing the effect of soft starting of a microgrid with load in one embodiment of the present invention.

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

[0060] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0061] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0063] In the description of the present invention, it should be noted that if the terms "upper", "lower", "inside", "outside", etc. appear to indicate an orientation or position relationship, they are based on the orientation or position relationship shown in the accompanying drawings, or are the orientation or position relationship in which the product of the invention is usually placed when used. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0064] In addition, the terms “first”, “second”, etc., if used, are merely used to distinguish between the descriptions and should not be understood as indicating or implying relative importance.

[0065] It should be noted that, in the absence of conflict, the features in the embodiments of the present invention may be combined with each other.

[0066] As described in the background technology, when the energy storage inverter parallel system is used as the main power source of the microgrid, due to the asynchronous startup time between the energy storage inverters and the low overload capacity of a single energy storage inverter, the energy storage inverter that is started first will experience overpower and overcurrent due to the load under the rated power of the entire energy storage inverter parallel system.

[0067] The prior art provides two technical solutions: Solution 1: before the energy storage converter parallel system power supply is started, all loads are removed, and the loads are put into operation in stages after the power supply is started; Solution 2: a total load switch is set in series between the output end of the energy storage converter parallel system and the microgrid bus, so that the total load switch is closed after all energy storage converters in the energy storage converter parallel system are started. However, both solutions cannot enhance the stability of the microgrid system and extend its service life on the basis of simplifying the structure and volume of the energy storage converter parallel system.

[0068] Based on the above considerations, the present invention provides a control scheme for soft starting with load in a microgrid.

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

[0070] Please refer to Figure 1The present embodiment provides a parallel energy storage converter system 100, which is used to execute the following microgrid load soft start control method. The parallel energy storage converter system 100 is composed of a plurality of single energy storage converters 101, and the single energy storage converter 101 includes a sequentially connected energy storage battery 102 and a power conversion system (PCS) 103. The AC output end of each energy storage converter 103 is connected to the AC bus through a relay; the AC bus is connected to the microgrid load after passing through an industrial frequency transformer.

[0071] The energy storage converter parallel system 100 further includes a control unit 104, which is used to send control signals to each energy storage converter 103 to control the start and stop of the energy storage converter 103. When any one energy storage converter is selected as a host and the other energy storage converters are slaves, the control unit 104 can be connected to the host to broadcast control signals or control instructions to each slave through the host.

[0072] Each energy storage converter 103 is connected via a data bus. Each energy storage converter 103 in the energy storage converter parallel system 100 performs microgrid on-load soft start according to the microgrid on-load soft start control method, so as to enhance the stability of the microgrid system and extend its service life on the basis of simplifying the structure and volume of the energy storage converter parallel system 100.

[0073] Please refer to Figure 2 This embodiment also provides a microgrid load soft start control method, including steps 200 to 600.

[0074] Step 200: select one energy storage converter as the host and the other energy storage converters as slaves; the control unit sends a soft start instruction to the host; the host broadcasts the soft start instruction to the slaves through the data bus.

[0075] Step 300: After receiving the soft start instruction, each relay remains disconnected, and the host and each slave simultaneously perform constant voltage and constant frequency AC soft start to build their own inverter voltage.

[0076] Step 400: The host and each slave detect their own inverter voltage in real time, and determine whether the AC soft start is completed based on the inverter voltage.

[0077] Step 600: If the AC soft starts of the host and each slave are completed, the host broadcasts a relay closing signal to each slave.

[0078] Step 700: Each relay is closed according to the relay closing signal to end the microgrid on-load soft starting.

[0079] In this embodiment, when the microgrid is in the state of soft start with load but not started, the relays corresponding to all energy storage inverters in the energy storage inverter parallel system are in the disconnected state. When the microgrid is soft started with load, all energy storage inverters in the parallel system independently establish their own inverter voltage from scratch. At the same time, each energy storage inverter 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 inverter has completed the soft start based on the inverter voltage corresponding to each energy storage inverter.

[0080] In order to realize the data interaction between the master and the slave, the host can be preset in the energy storage converter parallel system. In one possible implementation method, one energy storage converter can be selected as the host, and the other energy storage converters can be selected as slaves. In this embodiment, all slaves will send the judgment results to the host in real time through the CAN communication bus. After the soft start of the host and all slaves is completed, the host 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 condition of an independent microgrid. In addition, before closing the relay, the host 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] The control unit can select one energy storage converter as the master among all energy storage converters according to the master-slave configuration instructions sent by the user side, and the rest of the energy storage converters are slaves. After the control unit receives the soft start instruction, the control unit will feedback the soft start instruction to the master, and the master will broadcast the soft start instruction to the rest of the slaves through 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 host 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 host and each slave use the rated voltage as the target voltage and the rated frequency as the target power, and form their own inverter voltage from zero with a preset slope.

[0086] Step 302: When each slave generates an inverter voltage, the master sends a phase angle synchronization signal to each slave via the data bus in real time to achieve phase synchronization between the master and slaves.

[0087] In a possible implementation method, after receiving the power-on instruction, all energy storage converters in the energy storage converter parallel system 100 are powered on at a rated voltage V rate As the target voltage, with the rated frequency F rate As the target frequency, the inverter voltage is gradually established from zero with a fixed slope to perform AC soft start control. At the same time, the slaves continuously synchronize the phase of the industrial frequency voltage output by the host, that is, the host broadcasts a phase synchronization signal to each slave, so that after the slave receives the phase synchronization signal, it makes the phase angle corresponding to each slave consistent with the phase angle corresponding to the host according to the phase synchronization signal.

[0088] Please refer to Figure 4 In this embodiment, when the host generates a first inverter voltage and each slave generates a second inverter voltage, when each slave forms an inverter voltage, the step of the host sending a phase angle synchronization signal to each slave in real time includes steps 3021 to 3023.

[0089] Step 3021: The host 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.

[0090] Step 3022: When the phase angle value is equal to the preset phase angle value, the host broadcasts a phase angle synchronization signal to each slave through the data bus.

[0091] Step 3023: Each slave 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.

[0092] In a possible implementation method, when the host synchronizes 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, the host can monitor the phase angle value corresponding to the first inverter voltage in real time. When the phase angle value is zero, the host broadcasts the phase angle synchronization signal to each slave with the highest priority through the data bus. Each slave can receive the phase angle synchronization signal by means of CAN receive interrupt. After receiving the phase angle synchronization signal, each slave sets the corresponding phase angle to zero in the receive interrupt.

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

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

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

[0096] In this embodiment, when the energy storage converter includes an inverter full-bridge circuit and an inverter output filter circuit connected in sequence; the inverter output filter circuit is used to provide an inverter voltage sampling value V inv , inductor current sampling value I inv Please refer to Figure 6 The host and each slave use the corresponding rated voltage as the target voltage, the rated frequency corresponding to the microgrid as the target power, and form their own inverter voltage from zero with a preset slope in step 301, including steps 3011-3015.

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

[0098] Step 3012: construct its own 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 based on the amplitude and 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 a drive signal according to the current inner loop reference value and the inductor current sampling value to drive each energy storage converter to perform constant voltage and constant frequency AC soft start.

[0102] In a possible implementation method, according to the rated frequency F corresponding to the energy storage converter rate With rated operating frequency f sThe angular frequency ω0 is determined by the ratio of the angular frequency ω0 (or the execution frequency of the control algorithm in the energy storage converter). Then, the phase angle θ is determined according to the angular frequency ω0 during the working cycle, and the range of the phase angle θ satisfies: (0, 2π). When the phase angle corresponding to the master is zero, that is, θ=0, the phase angle synchronization signal is immediately sent 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 achieving accurate synchronization of the power frequency phase of the master and slave.

[0103] The above-mentioned master-slave power frequency synchronization is performed synchronously with the off-grid constant voltage and frequency control between the master and slave machines. The process of the master and each slave machine performing constant voltage and frequency control in this embodiment will be described in detail below, that is, the corresponding rated voltage is used as the target voltage, the rated frequency corresponding to the microgrid is used as the target power, and the inverter voltage is formed from zero with a preset slope. It should be noted that in this embodiment, the rated frequency and rated voltage corresponding to the master and each slave machine are consistent.

[0104] In one possible implementation method, the phase angle θ determined in step 3011 may be subjected to a sine operation to obtain a processed phase angle sin(θ), and then the processed phase angle sin(θ) is superimposed on the slowly changing inverter voltage as a reference value of the voltage outer loop controller, i.e., the voltage outer loop reference value Among them, 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 to avoid voltage step in the voltage outer loop control process, resulting in overshoot and impact on the back-end inverter filter. In this embodiment, the rated voltage V rate As the target, determine the preset slope. At the same time, considering the soft start waiting time, it can be 10s time interval from 0 to the rated voltage V rate Determine a preset slope, which satisfies: (Vrate / 10s)-(Vrate / 0.02s). In this embodiment, the preferred preset slope is (Vrate / 1s).

[0105] Determine the reference value of the voltage outer loop controller, that is, the voltage outer loop reference value After that, the inverter voltage sampling value V inv , determine the inverter voltage sampling value V inv and voltage outer loop reference value The difference between the voltage and the external loop controller G v (s) Determine the current inner loop reference value Should satisfy: In this embodiment, the voltage outer loop controller is a proportional-integral controller, and its transfer function G v(s) means: Among them, K p_v is the voltage outer loop proportional coefficient, K i_v is the voltage outer loop integral coefficient.

[0106] Similarly, the current inner loop reference value can be determined and the inductor current sampling value I inv The current inner loop controller determines the driving signal. i (s) is a proportional-integral controller, and its transfer function G i (s) is expressed as: Among them, K p_i is the voltage outer loop proportional coefficient, K i_i is the voltage outer loop integral coefficient.

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

[0108] Step 1501: Determine an initial modulation reference signal according to a current inner loop reference value and an inductor current sampling value.

[0109] Step 1502: Determine a final modulation reference signal according to the inverter voltage sampling value and the initial modulation reference signal.

[0110] Step 1503: Determine a modulation reference signal according to a preset modulation ratio and a final modulation reference signal.

[0111] Step 1504: determine a driving signal according to a preset carrier signal and a modulated reference signal.

[0112] In this embodiment, the final modulation reference signal V mod_ref satisfy: Please continue to refer to Figure 5 , the above final modulation reference signal V mod_ref After that, the final modulated reference signal is modulated by a preset modulation ratio to modulate the transmission reference signal. In this embodiment, the expression of the modulated transmission reference signal is: Among them, V pwm_ref is the amplitude of the modulation reference signal, V Tri is the amplitude of the preset carrier signal, V bus is the DC bus voltage sampling value, is the modulation ratio, V mod_ref is the final modulation reference signal.

[0113] The modulated wave reference signal then enters the PWM modulator to be modulated by a preset carrier signal inside the PWM modulator to generate a drive signal, which in turn drives the energy storage inverter to achieve off-grid constant voltage and frequency control to ensure that before the microgrid load soft start is completed, that is, before the relay is closed, the inverter voltages output by each energy storage inverter have completed the same amplitude, frequency and phase settings.

[0114] In this embodiment, continue 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 is connected to the first end of the second inductor L2 and the first end of the filter capacitor C; the second end of the first inductor L1 and the second end of the filter capacitor C are connected to the output end of the inverter full-bridge module; the second end of the second inductor L2 is connected to the relay. The above inverter voltage sampling value V inv It is the voltage across the filter capacitor in the inverter filter; the above inductor current sampling value I inv That is, the current output by the first inductor L1 in the inverter filter.

[0115] like Figure 2 As shown, each energy storage inverter performs constant voltage and constant frequency according to the method provided in the above embodiment to construct an inverter voltage. In this embodiment, please refer to Figure 8 The master and each slave detect their own inverter voltage in real time, and step 400 of judging whether the AC soft start is completed according to the inverter voltage includes step 401-step 402.

[0116] Step 401: Detect the amplitude and frequency corresponding to the inverter voltage in real time.

[0117] Step 402, determine whether the difference between the amplitude and the target amplitude is less than or equal to the 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 the second preset error; if less than or equal to, determine that the AC soft start is completed.

[0118] In this embodiment, each energy storage converter in the energy storage converter parallel system collects the amplitude V corresponding to its own inverter voltage in real time when executing soft start. inv and frequency F inv , and judge whether the target value is reached. In one possible implementation, when the amplitude V of the inverter voltage is detected inv With the target amplitude V rate The error is within ±5V, and the inverter voltage V inv The inverter voltage frequency F inv With the target frequency Frate If the error is within ±0.5Hz, the AC soft start corresponding to the current energy storage converter is judged to be completed, and the AC soft start success flag is set. At the same time, all slaves send the AC soft start success flag to the host in real time through the CAN communication bus. inv The instantaneous sampling value of the inverter voltage V inv Calculated.

[0119] The host and each slave detect their own inverter voltage in real time, and determine whether the AC soft start is completed based on the inverter voltage in step 400, and then include step 500, the host generates a pre-closing flag setting signal based on its own AC soft start state and the AC soft start state corresponding to each slave, so that each energy storage converter drives its corresponding relay to close after the phase angle corresponding to the host and each slave meets a specific condition, so as to end the soft start.

[0120] In one possible implementation, please refer to Fig. 9 , the step 500 includes steps 501 to 503.

[0121] Step 501: After the AC soft start corresponding to each slave is completed, each slave sends a first success flag signal to the host through the data bus.

[0122] Step 502: When the AC soft start corresponding to the host is completed, a success flag signal is generated.

[0123] Step 503: The host generates a pre-close flag setting signal according to each first success flag signal and its own success flag signal.

[0124] In one possible implementation, after the host and each slave complete the soft start, the host generates a pre-closing flag setting signal to inform the host that each energy storage converter in the energy storage converter parallel system has completed the soft start. At this time, the host 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, the phase angle synchronization execution method in the above embodiment can be used to make each energy storage converter close its output relay at the same AC zero crossing point at the same time.

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

[0126] When the AC soft start of the host and each slave is completed, the host monitors the time difference between the current phase angle value of its 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 slave through the data bus. Among them, the relay closing delay value is the delay between the relay drive signal being sent and the relay actually closing.

[0127] After each energy storage converter receives the relay closing signal, it drives its corresponding relay to close, so as to end the microgrid on-load soft starting.

[0128] This embodiment also provides a comparative experiment, please refer to Fig.10 In this embodiment, a parallel energy storage converter system is constructed using multiple energy storage converters controlled by a master and a slave. The rated output power of each energy storage converter is 2000W, the rated voltage is 230V, the rated frequency is 50Hz, and the rated current is 8.7A. A is the voltage waveform corresponding to the load, B is the output current waveform corresponding to the master, and C is the output current waveform corresponding to any slave.

[0129] You can continue to refer to Fig.10 In this embodiment, the energy storage converter parallel system is as follows Figure 1 Under the structure shown, according to Figure 2 The steps of the microgrid on-load soft start control method shown in the figure perform on-load soft start, and each energy storage converter completes the closing of the relay near the AC voltage zero crossing point, and the closing time difference of the corresponding relays between the master and the slave is within 2ms. It can be seen that this embodiment can make the relays corresponding to all energy storage converters close at the same AC phase angle zero crossing as much as possible, thereby minimizing the current impact and power fluctuation, and ensuring the stability of the on-load soft start under the microgrid.

[0130] In summary, this embodiment provides a microgrid on-load soft start control method and an energy storage converter parallel system, wherein the microgrid on-load soft start control method is applied to the energy storage converter parallel system. The above system is composed of multiple energy storage converter units, and the energy storage converter unit includes energy storage batteries and energy storage converters connected in sequence. The AC output end of each energy storage converter is respectively connected to the AC bus through a relay; and each energy storage converter is connected through the data bus. The above microgrid on-load soft start control method includes the following steps: select one energy storage converter as the host, and the remaining energy storage converters as slaves, and the control unit sends a soft start instruction to the host; the host broadcasts the soft start instruction to each slave through the data bus. After receiving the soft start instruction, each relay remains disconnected, and the host and each slave synchronously execute constant voltage and frequency AC soft start to build their own inverter voltage. The host and each slave detect their own inverter voltage in real time, and judge whether the AC soft start is completed based on the inverter voltage; if both are completed, the host broadcasts a relay closing signal to each slave; each relay closes according to the relay closing signal to end the microgrid on-load soft start.

[0131] Before the relay in the present invention is closed, all energy storage converters in the energy storage converter parallel system have completed the same amplitude, frequency and phase control of the AC inverter voltage, and through the control logic, the relays corresponding to all energy storage converters are closed at the same AC phase angle zero crossing as much as possible, thereby minimizing current impact and power fluctuation to the greatest extent and ensuring the stability of soft starting with load in the microgrid.

[0132] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A microgrid on-load soft start control method, applied to an energy storage converter parallel system composed of multiple energy storage converter units, wherein the energy storage converter units include energy storage batteries and energy storage converters connected in sequence, and the AC output end of each energy storage converter is connected to the AC bus through a relay; the energy storage converter parallel 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 load soft start control method comprises the following steps: One energy storage converter is selected as the host, and the other energy storage converters are selected as slaves. The control unit sends a soft start instruction to the host; the host broadcasts the soft start instruction to each of the slaves through 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 according to the inverter voltage; 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 with load.

2. The microgrid load soft start control method according to claim 1, characterized in that: The step of synchronously performing constant voltage and constant frequency AC soft start on the host and each of the slaves comprises: The host and each of the slaves use the rated voltage as the target voltage and the rated frequency as the target power, and form their own inverter voltage from zero with a preset slope; When each of the slaves forms the inverter voltage, the host sends a phase angle synchronization signal to each of the slaves via the data bus in real time to achieve phase synchronization between the master and slaves.

3. The microgrid load soft start control method according to claim 2, characterized in that: When the host generates a first inverter voltage and each of the slaves generates a second inverter voltage, the step of the host sending a phase angle synchronization signal to each of the slaves in real time when each of the slaves forms the inverter voltage comprises: The host 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 slaves 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.

4. The microgrid load soft start control method according to claim 1 or 2, characterized in that: The host and each of the slaves 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.

5. The microgrid load soft start control method according to claim 4, 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-closing flag setting signal according to each of the first success flag signals and its own success flag signal.

6. The microgrid load soft start control method according to claim 1 or 2, characterized in that: The step of broadcasting a relay closing signal from the host 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.

7. The microgrid load soft start control method according to claim 2, 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 host and each of the slaves use the corresponding rated voltage as the target voltage, 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 according to 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.

8. The microgrid load soft start control method according to claim 7, characterized in that: The step of determining the driving signal according to the current inner loop reference value and the inductor current sampling value comprises: 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; Determine a modulation reference signal according to a preset modulation ratio and the final modulation reference signal; The driving signal is determined according to the preset carrier signal and the modulated reference signal.

9. The microgrid load soft start control method according to claim 8, characterized in that: The expression of the modulated wave reference signal is: Among them, V pwm_ref is the amplitude of the modulation reference signal, V Tri is the amplitude of the preset carrier signal, V bus is the DC bus voltage sampling value, is the modulation ratio, V mod_ref is the final modulation reference signal.

10. A parallel energy storage converter system, characterized in that: The energy storage converter parallel system is used to execute the microgrid load soft start control method as described in any one of claims 1 to 9.

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