Control method for avoiding voltage interference in variable frequency transmission of industrial important plant station

Abstract

The invention discloses a control method for avoiding voltage interference electricity in variable-frequency transmission of an industrial important plant station, which comprises the following steps of: firstly, constructing a voltage interference electricity avoiding energy storage configuration structure embedded in a direct current side for the industrial important plant station comprising N variable-frequency transmission devices, and then monitoring the bus voltage Vdc of the direct current side; and when the absolute value delta Vdc of the voltage variation is greater than a set threshold value delta, the compensation current value Idc is calculated according to the voltage variation delta Vdc, and the energy storage unit is further controlled according to the voltage variation delta Vdc and the state of charge SOC of the energy storage unit, so that the DC side bus voltage Vdc is kept constant or the rising or falling rate of the DC side bus voltage Vdc is limited. According to the invention, the output of the energy storage unit can be adjusted in time, and when voltage interference occurs and the voltage of the direct current link transiently fluctuates, the voltage can be recovered to a rated value within 0.5 s, that is, the purposes of avoiding voltage interference in variable frequency transmission of an industrial important plant station and maintaining the voltage stability of the direct current link can be achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of voltage fluctuation in industrial plants and stations, and more specifically, relates to a control method for avoiding voltage fluctuation in a variable frequency drive of an important industrial plant and station. Background Art

[0002] The industrial power grid is the most important infrastructure for industrial production and life, and the power supply system that directly provides energy to important factories and stations on the front line of industrial production has become the lifeline of industrial production. The quality of power supply is directly related to whether the production of industrial factories and stations can operate safely, normally and smoothly, and it is also related to the competitive survival ability of industrial enterprises and whether they can develop long-term, sustainably and healthily.

[0003] At present, the power supply system of industrial plants and stations mainly has problems such as voltage fluctuation, voltage rise, voltage drop, short interruption, long interruption, etc. Serious power supply grid quality problems may directly lead to major industrial production accidents and huge property losses. Take the more typical experimental thermal recovery industrial boiler softening water station as an example. It undertakes the important task of centralized supply of softened water for hundreds of industrial steam injection boilers. Once the variable frequency feed water pump stops operating, it will cause a low feed water pressure alarm, which will cause a large area of ​​boiler shutdown and cause a series of possible major events. It can be seen that the power supply quality of the power supply system of industrial plants and stations is not small. The reason is that the power grid line fault (grounding, etc.) or the instability of the upper substation power grid, as well as the failure of power equipment in the adjacent area, lead to problems such as second-level power shaking and voltage drop in the power supply system in the station, and finally cause the inverter to stop operating due to low voltage alarm.

[0004] At present, the main method to solve the voltage fluctuation problem is the online AVC (Active Voltage Conditioner), but it still has the following problems:

[0005] First, online AVC can only control 40% of shallow voltage fluctuations, and electrical equipment can only avoid being affected by shallow voltage sags and voltage swells.

[0006] Second, the online AVC method cannot compensate for deep sags. Shallow sags can only be compensated for more than 10 seconds, but voltage sag events are all within 2 seconds. It is more important to control sags over the entire sag depth range.

[0007] Third, the energy of the online AVC method during compensation is taken from the power grid, which will inevitably lead to a large increase in the current of the front-end power grid. If the upper circuit breaker, relay protection, transformer and other equipment have insufficient margin, it will cause equipment damage and power outages, that is, online AVC has a greater impact on the reliability of peripheral equipment.

[0008] Fourth, the online AVC method has an efficiency of 98-99% at full load, and has large losses. Summary of the invention

[0009] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a control method for avoiding voltage fluctuations in variable frequency drives of important industrial plants to control deep voltage fluctuations.

[0010] To achieve the above-mentioned purpose, the control method of the variable frequency drive of an important industrial plant to avoid voltage fluctuations of the present invention is characterized by comprising the following steps:

[0011] (1) For an important industrial plant with N variable frequency transmission devices, a voltage-swing-avoiding energy storage configuration structure embedded on the DC side is constructed, wherein the voltage-swing-avoiding energy storage configuration structure comprises an energy storage unit, a bidirectional DC-DC converter, and a controller, wherein the positive and negative ends of one side of the bidirectional DC-DC converter are respectively connected to the positive and negative ends of the energy storage unit, and the positive and negative ends of the other side are respectively connected to the positive and negative ends of the DC side busbars of the N variable frequency transmission devices;

[0012] (2) Monitor the DC bus voltage V of N variable frequency drive devices dc , calculate its voltage change ΔV dc :

[0013]

[0014] in, is the rated value of the DC bus voltage;

[0015] (3) The absolute value of the voltage change |ΔV dc | is compared with the set threshold δ. If the absolute value |ΔV dc | is less than or equal to the threshold δ, then return to step (2) and continue to adjust the DC bus voltage V dc Monitor, if the absolute value |ΔV dc | is greater than the threshold δ, then go to step (4);

[0016] (4) According to the voltage change ΔV dc Calculate the compensation current value I dc , and further according to the voltage change ΔV dc And the state of charge SOC of the energy storage unit to control the energy storage unit:

[0017] 4.1) If the voltage change ΔV dc <0, and the state of charge SOC is less than the high state of charge SOC high , the controller controls the bidirectional DC-DC converter to obtain electric energy from the DC bus of N variable frequency drive devices at a higher rate to charge the energy storage unit to maintain the DC bus voltage V dc Constant;

[0018] 4.2) If the voltage change ΔV dc <0, and the state of charge SOC is greater than or equal to the high state of charge SOC high But less than the upper limit state of charge SOC max , the controller controls the bidirectional DC-DC converter to obtain electric energy from the DC bus of N variable frequency drive devices at a lower rate to charge the storage unit energy, limiting the DC bus voltage V dc Ascent rate;

[0019] 4.3) If the voltage change ΔV dc >0, and the state of charge SOC is greater than the low state of charge SOC low , the controller controls the bidirectional DC-DC converter to discharge the energy storage unit at a higher rate, obtains electrical energy and outputs it to the DC bus to maintain the DC bus voltage V dc Constant;

[0020] 4.4) If the voltage change ΔV dc >0, and the state of charge SOC is less than or equal to the low state of charge SOC low But it is greater than the lower limit SOC min , the controller controls the bidirectional DC-DC converter to discharge the energy storage at a lower rate, discharge the energy storage unit, obtain electrical energy and output it to the DC bus to limit the DC bus voltage V dc rate of descent;

[0021] The controller controls the bidirectional DC-DC converter by obtaining a duty cycle signal through current loop control, and controlling the bidirectional DC-DC converter with the duty cycle signal to control the charging and discharging behavior of the energy storage unit until the DC side bus voltage V dc The monitoring result is lower than the threshold value, i.e. the absolute value |ΔV dc | is less than or equal to the threshold δ.

[0022] The object of the invention of the present invention is achieved in this way:

[0023] The control method for avoiding voltage swing of variable frequency transmission of industrial important plants and stations of the present invention first constructs a voltage swing avoidance energy storage configuration structure embedded in the DC side for industrial important plants and stations including N variable frequency transmission devices, and then monitors the DC side bus voltage V dc , when the absolute value of the voltage change |ΔV dc |When it is greater than the set threshold δ, the voltage change ΔV dc Calculate the compensation current value I dc , and further according to the voltage change ΔV dc The energy storage unit is controlled by the state of charge SOC of the energy storage unit to maintain the DC bus voltage V dc Constant or limited DC bus voltage Vdc The present invention can timely adjust the output of the energy storage unit. When a voltage fluctuation occurs, the voltage of the DC link can recover to the rated value within 0.5s after a brief fluctuation. That is, the present invention can achieve the goal of avoiding voltage fluctuations and maintaining DC link voltage stability through variable frequency transmission of important industrial plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flow chart of a specific implementation method of the control method for avoiding voltage swing in the variable frequency drive of an important industrial plant of the present invention;

[0025] Figure 2 This is a schematic diagram of the control principle of the variable frequency drive to avoid voltage fluctuations in important industrial plants and stations;

[0026] Figure 3 yes Figure 2 The schematic diagram of the principle of the voltage swing avoidance energy storage configuration structure is shown;

[0027] Figure 4 According to the voltage change ΔV dc A flow chart of controlling the energy storage unit according to the state of charge SOC of the energy storage unit;

[0028] Figure 5 It is a principle block diagram of a specific implementation method of controlling the energy storage unit when the voltage fluctuates according to the present invention;

[0029] Figure 6 This is a specific example result diagram of the voltage simulation of the energy storage unit when voltage fluctuation occurs;

[0030] Figure 7 This is a specific example result diagram of the DC side bus voltage simulation when voltage fluctuation occurs. DETAILED DESCRIPTION

[0031] The specific implementation of the present invention is described below in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when the detailed description of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0032] Figure 1 It is a flow chart of a specific implementation method of the control method for avoiding voltage fluctuations in variable frequency transmission of important industrial plants and stations of the present invention.

[0033] In this embodiment, if Figure 1 As shown, the control method for avoiding voltage fluctuations in the variable frequency drive of an important industrial plant of the present invention comprises the following steps:

[0034] Step S1: Construct a voltage-swing-avoiding energy storage configuration structure embedded on the DC side

[0035] like Figure 2 As shown, for an important industrial plant including N variable frequency transmission devices, based on the characteristics of the variable frequency transmission devices using AC-DC-AC converters, a voltage swing-avoiding energy storage configuration structure embedded on the DC side is constructed, wherein the voltage swing-avoiding energy storage configuration structure comprises an energy storage unit, a bidirectional DC-DC converter, and a controller, wherein the positive and negative ends on one side of the bidirectional DC-DC converter are respectively connected to the positive and negative ends of the energy storage unit, and the positive and negative ends on the other side are respectively connected to the positive and negative ends of the DC side busbars of the N variable frequency transmission devices, that is, the positive and negative ends of the DC side busbars of the N variable frequency transmission devices are respectively connected in parallel to the positive and negative ends on the other side of the bidirectional DC-DC converter.

[0036] The energy storage unit can be a supercapacitor or a high-rate battery. The amount of charge it stores changes with the charge and discharge process. This change can be described by the state of charge (SOC). SOC represents the parameter of the energy storage unit's charge storage degree. It is usually expressed in percentage form, from 0% (fully discharged) to 100% (fully charged). In addition, in order to ensure the performance and life of the energy storage unit, SOC sets an upper limit SOC max and lower limit SOC min , which means that the energy storage unit will not be charged beyond its upper limit nor discharged below its lower limit during use, thereby optimizing its operating efficiency and maintenance safety.

[0037] The bidirectional DC-DC converter realizes a bidirectional connection of a DC bus, allowing current and voltage to flow bidirectionally between the high-voltage side and the low-voltage side. The topology mainly includes the following key components: IGBT switching device, inductor, and voltage stabilizing capacitor. When the switch tube is turned on, the inductor stores energy; when the switch tube is turned off, the inductor releases the stored energy and supplies the current to the load through the diode and the output filter capacitor. Figure 3 The basic topology of a bidirectional converter for absorbing or delivering power to a DC bus is shown.

[0038] The inductor stores and transfers energy according to the working state of the IGBT. When the grid voltage is abnormal such as power fluctuation, the DC bus voltage of the inverter changes accordingly. When the voltage is below the preset value, the IGBT is forward-conducted, and the DC-DC will quickly respond to power output and control the energy storage unit to discharge according to the load current to maintain the DC output voltage of the device stable at the preset value to ensure the normal operation of the system; when the grid voltage returns to normal, the inverter bus is restored to normal value by its own rectification, at which time the IGBT will be reverse-cut off and the energy storage unit will be on standby.

[0039] The control objective of the controller is to keep the DC link voltage constant, and the PI control method is used to achieve voltage and current dual closed-loop control.

[0040] Step S2: Monitor the DC bus voltage V dc And calculate the voltage change ΔV dc

[0041] Monitor the DC bus voltage V of N variable frequency drive devices dc , calculate its voltage change ΔV dc :

[0042]

[0043] in, is the rated value of the DC bus voltage.

[0044] Step S3: Determine the absolute value of the voltage change |ΔV dc |Is it greater than the set threshold δ

[0045] The absolute value of the voltage change |ΔV dc | is compared with the set threshold δ. If the absolute value |ΔV dc | is less than or equal to the threshold value δ, then return to step S2: continue to adjust the DC bus voltage V dc Monitor, if the absolute value |ΔV dc | is greater than the threshold δ, then proceed to step S4.

[0046] Step S4: According to the voltage change ΔV dc Calculate the compensation current value I dc , and further according to the voltage change ΔV dc The energy storage unit is controlled by the state of charge SOC of the energy storage unit, as shown in the following example: Figure 4 As shown, the following steps are included:

[0047] Step S4.1: If the voltage change ΔV dc <0, and the state of charge SOC is less than the high state of charge SOC high , the controller controls the bidirectional DC-DC converter to obtain electric energy from the DC bus of N variable frequency drive devices at a higher rate to charge the energy storage unit to maintain the DC bus voltage V dc Constant;

[0048] Step S4.2: If the voltage change ΔV dc <0, and the state of charge SOC is greater than or equal to the high state of charge SOC high But less than the upper limit state of charge SOC max , the controller controls the bidirectional DC-DC converter to obtain electric energy from the DC bus of N variable frequency drive devices at a lower rate to charge the storage unit energy, limiting the DC bus voltage V dc Ascent rate;

[0049] Step S4.3: If the voltage change ΔV dc >0, and the state of charge SOC is greater than the low state of charge SOC low , the controller controls the bidirectional DC-DC converter to discharge the energy storage unit at a higher rate, obtains electrical energy and outputs it to the DC bus to maintain the DC bus voltage V dc Constant;

[0050] Step S4.4: If the voltage change ΔV dc >0, and the state of charge SOC is less than or equal to the low state of charge SOC low But it is greater than the lower limit SOC min , the controller controls the bidirectional DC-DC converter to discharge the energy storage at a lower rate, discharge the energy storage unit, obtain electrical energy and output it to the DC bus to limit the DC bus voltage V dc rate of descent;

[0051] The controller controls the bidirectional DC-DC converter by obtaining a duty cycle signal through current loop control, and controlling the bidirectional DC-DC converter with the duty cycle signal to control the charging and discharging behavior of the energy storage unit until the DC side bus voltage V dc The monitoring result is lower than the threshold value, i.e. the absolute value |ΔV dc |Less than or equal to the threshold δ.

[0052] In this embodiment, if Figure 5 As shown, the voltage change ΔV dc Calculate the compensation current value I dc for:

[0053] The DC bus voltage V dc The voltage change ΔV dc (i.e. error signal) is sent to the voltage controller (PI controller). The voltage controller is designed to quickly and accurately calculate the required compensation current value I according to the size and change trend of the error signal. dc :

[0054]

[0055] in, and are the proportional and integral coefficients respectively.

[0056] In this embodiment, step S4.1: if the voltage change ΔV dc <0, and the state of charge SOC is less than the high state of charge SOC high, the controller controls the bidirectional DC-DC converter to obtain electric energy from the DC bus of N variable frequency drive devices at a higher rate to charge the energy storage unit to maintain the DC bus voltage V dc Constant is:

[0057] In this case, the DC bus voltage V dc Increases, and the energy storage unit has a large charging capacity, charging the energy storage at a higher rate to maintain a constant DC side voltage. At this time, the reference current of the energy storage unit for:

[0058]

[0059] In the formula, τ f is the time constant of the energy storage system.

[0060] In this embodiment, if the voltage change ΔV dc <0, and the state of charge SOC is greater than or equal to the high state of charge SOC high But less than the upper limit state of charge SOC max , the controller controls the bidirectional DC-DC converter to obtain electric energy from the DC bus of N variable frequency drive devices at a lower rate to charge the storage unit energy, limiting the DC bus voltage V dc The rate of ascent is:

[0061] In this case, the DC bus voltage V dc Increase, and the energy storage unit has a small charging capacity, charging the energy storage at a lower rate, limiting the DC side voltage rise rate. At this time, the reference current of the energy storage unit for:

[0062]

[0063] Among them, 0 <k ESS <1 is a constant.

[0064] In this embodiment, the step S4.3: if the voltage change ΔV dc >0, and the state of charge SOC is greater than the low state of charge SOC low , the controller controls the bidirectional DC-DC converter to discharge the energy storage unit at a higher rate, obtains electrical energy and outputs it to the DC bus to maintain the DC bus voltage V dc Constant is:

[0065] In this case, the DC bus voltage V dc The energy storage unit has a large discharge capacity and discharges the energy storage at a higher rate to maintain a constant DC side voltage. At this time, the energy storage unit reference current for:

[0066]

[0067] In this embodiment, the step S4.4: if the voltage change ΔV dc >0, and the state of charge SOC is less than or equal to the low state of charge SOC low But it is greater than the lower limit SOC min , the controller controls the bidirectional DC-DC converter to discharge the energy storage at a lower rate, discharge the energy storage unit, obtain electrical energy and output it to the DC bus to limit the DC bus voltage V dc The rate of descent is:

[0068] In this case, the DC bus voltage V dc The energy storage unit has a smaller discharge capacity, and discharges the energy storage at a lower rate to limit the DC side voltage drop rate. At this time, the energy storage unit reference current for

[0069]

[0070] In this embodiment, the controller in the voltage swing avoidance energy storage configuration structure aims to stabilize the DC side voltage of the variable frequency transmission device, obtains a duty cycle signal through current loop control, controls the bidirectional DC-DC converter with the duty cycle signal, and controls the charging and discharging behavior of the energy storage unit until the DC side bus voltage V dc The monitoring result is lower than the threshold value, i.e. the absolute value |ΔV dc | is less than or equal to the threshold δ, such as Figure 5 Specifically,

[0071] The energy storage unit reference current and the energy storage unit measures the current I ESS The difference is passed into the current controller, and the PI control strategy is also adopted to obtain the duty cycle signal D ESS , as shown in the formula:

[0072]

[0073] in, and are the proportional and integral coefficients respectively.

[0074] The duty cycle signal D ESS The current to duty cycle transfer function G ESS,ID , get the actual current of the energy storage unit at this time

[0075]

[0076] Among them, Cdc is the DC link capacitance, R L is the load resistance, L ESS is the converter inductor.

[0077] Actual current of energy storage unit Through the transfer function G f (s) Get the energy storage unit measurement current I ESS :

[0078]

[0079] The actual current of the energy storage unit is obtained The actual voltage of the DC bus is obtained through the current-to-voltage transfer function.

[0080]

[0081] Actual DC bus voltage Through the transfer function G f (s) to get the DC bus voltage V dc :

[0082] According to the above steps, the charging and discharging behavior of the energy storage unit is controlled until the DC bus voltage V dc The monitoring result is lower than the threshold δ.

[0083] In order to verify the correctness of the control method of the variable frequency drive of industrial important plants and stations to avoid voltage fluctuations, a simulation model was established in MATLAB software and simulation verification was performed. The simulation time was set to 9s, and the AC bus voltage fluctuated at 2.5s, 4s, 5.5s, and 7s, making the absolute value of the DC bus voltage change |ΔV dc | is greater than the set threshold δ. At this time, in order to maintain the DC link voltage stability, according to step S4: control the charging and discharging of the energy storage unit, and monitor the voltage of the energy storage unit when the voltage fluctuation occurs. The result is as follows Figure 6 As shown; while monitoring the DC bus voltage V dc , the results are as follows Figure 7 shown.

[0084] from Figure 6 , 7 It can be seen that the present invention can timely adjust the output of the energy storage unit. When voltage fluctuation occurs, the DC bus voltage V dc After a short fluctuation, it can recover to the rated value within 0.5s, that is, the present invention can realize the variable frequency transmission of important industrial plants to avoid voltage fluctuations and maintain the DC side bus voltage V dc Stable target.

[0085] Although the above describes the illustrative specific embodiments of the present invention to facilitate those skilled in the art to understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A control method for avoiding voltage fluctuations in variable frequency transmission of important industrial plants, characterized in that: The following steps are involved: (1) For an important industrial plant with N variable frequency transmission devices, a voltage-swing-avoiding energy storage configuration structure embedded on the DC side is constructed, wherein the voltage-swing-avoiding energy storage configuration structure comprises an energy storage unit, a bidirectional DC-DC converter, and a controller, wherein the positive and negative ends of one side of the bidirectional DC-DC converter are respectively connected to the positive and negative ends of the energy storage unit, and the positive and negative ends of the other side are respectively connected to the positive and negative ends of the DC side busbars of the N variable frequency transmission devices; (2) Monitor the DC bus voltage V of N variable frequency drive devices dc , calculate its voltage change ΔV dc : in, is the rated value of the DC side bus voltage; (3) The absolute value of the voltage change |ΔV dc | is compared with the set threshold δ. If the absolute value |ΔV dc | is less than or equal to the threshold δ, then return to step (2) and continue to adjust the DC bus voltage V dc Monitor, if the absolute value |ΔV dc | is greater than the threshold δ, then go to step (4); (4) According to the voltage change ΔV dc Calculate the compensation current value I dc , and further according to the voltage change ΔV dc And the state of charge SOC of the energy storage unit to control the energy storage unit: 4.1) If the voltage change is ΔV dc <0, and the state of charge SOC is less than the high state of charge SOC high , the controller controls the bidirectional DC-DC converter to obtain electric energy from the DC bus of N variable frequency drive devices at a higher rate to charge the energy storage unit to maintain the DC bus voltage V dc Constant; 4.2) If the voltage change ΔV dc <0, and the state of charge SOC is greater than or equal to the high state of charge SOC high But less than the upper limit state of charge SOC max , the controller controls the bidirectional DC-DC converter to obtain electric energy from the DC bus of N variable frequency drive devices at a lower rate to charge the storage unit energy, limiting the DC bus voltage V dc Ascent rate; 4.3) If the voltage change ΔV dc >0, and the state of charge SOC is greater than the low state of charge SOC low , the controller controls the bidirectional DC-DC converter to discharge the energy storage unit at a higher rate, obtains electrical energy and outputs it to the DC bus to maintain the DC bus voltage V dc Constant; 4.4) If the voltage change ΔV dc >0, and the state of charge SOC is less than or equal to the low state of charge SOC low But it is greater than the lower limit SOC min , the controller controls the bidirectional DC-DC converter to discharge the energy storage at a lower rate, discharge the energy storage unit, obtain electrical energy and output it to the DC bus to limit the DC bus voltage V dc rate of descent; The controller controls the bidirectional DC-DC converter by obtaining a duty cycle signal through current loop control, and controlling the bidirectional DC-DC converter with the duty cycle signal to control the charging and discharging behavior of the energy storage unit until the DC side bus voltage V dc The monitoring result is lower than the threshold value, i.e. the absolute value |ΔV dc |Less than or equal to the threshold δ.

2. The control method for avoiding voltage fluctuations in variable frequency transmission of important industrial plants according to claim 1 is characterized in that: According to the voltage change ΔV dc Calculate the compensation current value I dc for: The DC bus voltage V dc The voltage change ΔV dc (i.e. error signal) is sent to the voltage controller (PI controller). The voltage controller is designed to quickly and accurately calculate the required compensation current value I according to the size and change trend of the error signal. dc : in, and are the proportional and integral coefficients respectively.

3. The control method for avoiding voltage fluctuations in variable frequency transmission of important industrial plants according to claim 1 is characterized in that: In step 4.1), the reference current of the energy storage unit for: In step 4.2), the reference current of the energy storage unit for: Among them, 0 <k ESS <1 is a constant. In step 4.3), the energy storage unit reference current for: In step 4.4), the energy storage unit reference current for:

4. The control method for avoiding voltage fluctuations in variable frequency transmission of important industrial plants according to claim 1 is characterized in that: The duty cycle signal is obtained by current loop control, and the bidirectional DC-DC converter is controlled by the duty cycle signal to control the charging and discharging behavior of the energy storage unit until the DC side bus voltage V dc The monitoring result is lower than the threshold value, i.e. the absolute value |ΔV dc | is less than or equal to the threshold δ: The energy storage unit reference current and the energy storage unit measures the current I ESS The difference is passed into the current controller, and the PI control strategy is also adopted to obtain the duty cycle signal D ESS , as shown in the formula: in, and are the proportional and integral coefficients respectively. The duty cycle signal D ESS The current to duty cycle transfer function G ESS,ID , get the actual current of the energy storage unit at this time Among them, C dc is the DC link capacitance, R L is the load resistance, L ESS is the converter inductor. Actual current of energy storage unit Through the transfer function G f (s) Get the energy storage unit measurement current I ESS : The actual current of the energy storage unit is obtained The actual voltage of the DC bus is obtained through the current-to-voltage transfer function. Actual DC bus voltage Through the transfer function G f (s) to get the DC bus voltage V dc : According to the above steps, the charging and discharging behavior of the energy storage unit is controlled until the DC bus voltage V dc The monitoring result is lower than the threshold δ.

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