A method and system for detecting AC synchronization of energy storage converter

Abstract

The present invention provides a method and a detection system for AC synchronization detection of an energy storage converter. Based on an energy storage converter including a circuit breaker, a grid-side filter, an inverter, a DC disconnector, and a controller, the detection method includes: the controller collects grid voltages U a , U b , and U c , and obtains voltages U α and U β in the αβ coordinate system through coordinate transformation; sets the given amplitude of the reference voltage to be U gRef_pu ; obtains the α and β components of the control voltage for controlling the energy storage converter; the controller detects the three-phase current on the energy storage converter side to determine the successful closing of the switch; the present invention determines the closing state of the grid-side circuit breaker of the energy storage converter by detecting the magnitude of the current on the grid side of the converter, omits the detection of the closing signal feedback of the circuit breaker, and can avoid the overcurrent problem caused by the delay of the closing signal at the same time.

Description

Technical Field

[0001] The invention belongs to the field of energy storage converter control, and in particular relates to an energy storage converter AC synchronization detection method and detection system. Background Art

[0002] With the gradual depletion of fossil energy such as coal, oil, and natural gas, and the increasingly serious global warming problem caused by the greenhouse effect, new energy technologies, mainly photovoltaic and wind power generation, are gradually developing. However, new energy has the characteristics of changing with the seasons, time, and climate, which makes it unstable and discontinuous, affecting the stable operation of the power system. The energy storage system can effectively solve the problems of large fluctuations and poor stability in new energy power generation, and at the same time it can also improve the user's power utilization rate and reduce production and operation costs. In the energy storage system, its energy conversion system undertakes the important task of power conversion and is the core component of the energy storage system.

[0003] Power Conversion System (PCS) is a device that realizes bidirectional conversion of electric energy in an electrochemical energy storage system, connected between the battery system and the power grid (and / or load). It can control the charging and discharging process of the battery, perform AC / DC conversion, and directly supply power to the AC load without a power grid. PCS consists of a DC / AC bidirectional converter, a control unit, etc. The PCS controller receives background control instructions through communication, and controls the converter to charge or discharge the battery according to the sign and size of the power instruction, thereby adjusting the active power and reactive power of the power grid. At the same time, PCS can obtain battery pack status information through CAN interface communication with BMS, dry contact transmission, etc., and can realize protective charging and discharging of the battery to ensure safe battery operation.

[0004] In order to filter out the output current harmonics of the energy storage converter, an LC filter is used on the grid side of the converter, which is connected to the grid through an AC circuit breaker. In the standby state, the energy storage converter usually needs to be disconnected from the grid, and when it is connected to the grid, it is connected to the grid by closing the AC circuit breaker. If the AC filter capacitor is directly connected to the grid, it may cause grid current shock and grid voltage distortion. In severe cases, it may trigger overcurrent or overvoltage faults, causing the energy storage converter to fail and shut down. Therefore, before the AC circuit breaker is closed, an AC synchronization link is usually used to establish the filter capacitor voltage, and then the AC circuit breaker is closed. Usually, the closed state of the AC circuit breaker is obtained through the feedback signal of the circuit breaker, but because the feedback signal usually has a delay, the converter control is not timely, which is prone to overcurrent faults. Invention content

[0005] In view of this, the invention aims to propose an AC synchronous detection method and detection system for an energy storage converter. It is not necessary to detect the circuit breaker feedback closing signal. The closing state of the circuit breaker on the grid side of the energy storage converter can be judged by detecting the current size on the converter grid side. This method eliminates the need for circuit breaker feedback closing signal detection and can avoid overcurrent problems caused by closing signal delay.

[0006] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0007] A method for detecting AC synchronization of an energy storage converter is based on an energy storage converter including a circuit breaker, a grid-side filter, an inverter, a DC disconnect switch and a controller. The detection method includes:

[0008] S1. When the energy storage converter receives an AC synchronization command, the controller collects the grid voltage U a , U b and U c , the voltage U in the αβ coordinate system is obtained by coordinate transformation α and U β , the coordinate transformation calculation formula is:

[0009]

[0010] S2, set the reference voltage given amplitude to U gRef_pu , whose value is in the range of [0,1], and it rises to the maximum value 1 at a given slope. Suppose the voltage given slope is U gSlop_pu , the voltage given output can be expressed as:

[0011] U gRef_pu =U gSlop_pu t (2)

[0012] Where, t is time;

[0013] S3, the maximum value of the reference voltage given amplitude UgRef_pu is 1, and after rising to 1 according to formula (2), a delay of a period of time SW1Delay is performed. During this process, the control voltage output of the energy storage converter is:

[0014]

[0015] Where U ctl_α and U ctl_β They are control voltage αβ components respectively, used for controlling the energy storage converter;

[0016] S4. When the delay SW1Delay reaches the set time, the controller sends a closing command to the circuit breaker. At this time, the energy storage converter is still performing wave control. During this process, the controller detects the three-phase current i on the energy storage converter side.a ,i b and i c When the amplitude of the three-phase current is greater than the set threshold, the closing is considered to be successful; if it is not detected that the amplitude of the three-phase current is greater than the set threshold, timing is performed. When the timing is greater than the set threshold and still not detected, it is considered that the closing has failed.

[0017] Furthermore, the detection method comprises the following steps:

[0018] The first step is to detect whether the circuit breaker is closed. If the circuit breaker is closed, the process ends; otherwise, an AC synchronization command is sent to the energy storage converter;

[0019] Step 2: Use the formulas (1), (2) and (3) to obtain the control voltage α and β components, and control the voltage to rise according to a given slope. When the voltage setting is greater than 1 and the condition is not met, the control voltage continues to increase. When the voltage setting is greater than 1 and the condition is met, the delay begins.

[0020] Step 3: Check whether the delay time is greater than the set threshold. If it is satisfied, the controller sends a closing command to the circuit breaker. If not, it continues to delay until it is satisfied.

[0021] Step 4: Detect the three-phase current i on the converter side a ,i b and i c And judge whether it is greater than the set threshold. When the current is greater than the set threshold, it indicates that the closing is successful and the end is made. Otherwise, a delay is performed. When the delay is greater than the set threshold and the current is still not greater than the set threshold, it is considered that the closing has failed.

[0022] The detection system established by using the energy storage converter AC synchronous detection method includes a power grid, an energy storage converter and a battery. The energy storage converter includes a circuit breaker, a grid-side filter, an inverter, a DC isolating switch and a controller. The circuit breaker is used to disconnect the energy storage converter from the power grid; the DC isolating switch is used to disconnect the energy storage converter from the battery; the power grid is connected to the inverter via the grid-side filter, and the inverter is a three-phase inverter.

[0023] The controller is used to control the output voltage of the energy storage inverter using the detection methods S1 to S3, to send a control signal to the circuit breaker using the detection method S4, to collect the grid voltage and the three-phase current on the energy storage inverter side, and to determine whether the circuit breaker is closed successfully using the detection method S4.

[0024] Compared with the prior art, the energy storage converter AC synchronous detection method and detection system created by the present invention have the following advantages:

[0025] The present invention does not need to detect the circuit breaker feedback closing signal, and realizes the closing state judgment of the circuit breaker on the grid side of the energy storage converter by detecting the current size on the grid side of the converter. This method eliminates the need for circuit breaker feedback closing signal detection and can avoid overcurrent problems caused by closing signal delay. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings:

[0027] Figure 1 A topological structure diagram of the energy storage converter described in the embodiment of the present invention;

[0028] Figure 2 The present invention creates an AC synchronous control flow chart described in an embodiment.

[0029] Description of reference numerals:

[0030] 1-circuit breaker; 2-grid-side filter; 3-inverter; 4-DC disconnect switch; 5-controller. DETAILED DESCRIPTION

[0031] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0032] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0033] like Figure 1 As shown, a method for detecting AC synchronization of an energy storage converter is based on an energy storage converter including a circuit breaker 1, a grid-side filter 2, an inverter 3, a DC disconnect switch 4 and a controller 5. The detection method includes:

[0034] S1. When the energy storage converter receives the AC synchronization command, the controller 5 collects the grid voltage U a , U b and U c , the voltage U in the αβ coordinate system is obtained by coordinate transformation α and U β , the coordinate transformation calculation formula is:

[0035]

[0036] S2, set the reference voltage given amplitude to U gRef_pu , whose value is in the range of [0,1], and it rises to the maximum value 1 at a given slope. Suppose the voltage given slope is U gSlop_pu , the voltage given output can be expressed as:

[0037] U gRef_pu =U gSloP_pu t (2)

[0038] Where, t is time;

[0039] S3, the maximum value of the reference voltage given amplitude UgRef_pu is 1, and after rising to 1 according to formula (2), a delay of a period of time SW1Delay is performed. During this process, the control voltage output of the energy storage converter is:

[0040]

[0041] Where U ctl_α and U ctl_β They are control voltage α and β components respectively, used for controlling the energy storage converter;

[0042] S4. When the delay SW1Delay reaches the set time, the controller 5 sends a closing command to the circuit breaker 1. At this time, the energy storage converter is still performing wave control. In this process, the controller 5 detects the three-phase current i on the energy storage converter side. a ,i b and i c When the amplitude of the three-phase current is greater than the set threshold, the closing is considered to be successful; if it is not detected that the amplitude of the three-phase current is greater than the set threshold, timing is performed. When the timing is greater than the set threshold and still not detected, it is considered that the closing has failed.

[0043] like Figure 2 As shown, the AC synchronous detection method of the energy storage converter specifically includes the following steps:

[0044] The first step is to detect whether the circuit breaker is closed. If the circuit breaker is closed, the process ends; otherwise, an AC synchronization command is sent to the energy storage converter;

[0045] Step 2: Use the formulas (1), (2) and (3) to obtain the control voltage α and β components, and control the voltage to rise according to a given slope. When the voltage setting is greater than 1 and the condition is not met, the control voltage continues to increase. When the voltage setting is greater than 1 and the condition is met, the delay begins.

[0046] Step 3: Check whether the delay time is greater than the set threshold. If it is satisfied, the controller sends a closing command to the circuit breaker. If not, it continues to delay until it is satisfied.

[0047] Step 4: Detect the three-phase current i on the converter side a ,i b and i cAnd judge whether it is greater than the set threshold. When the current is greater than the set threshold, it indicates that the closing is successful and the end is made. Otherwise, a delay is performed. When the delay is greater than the set threshold and the current is still not greater than the set threshold, it is considered that the closing has failed.

[0048] like Figure 1 As shown, a detection system established by using the AC synchronous detection method of the energy storage converter includes a power grid, an energy storage converter and a battery. The energy storage converter includes a circuit breaker 1, a grid-side filter 2, an inverter 3, a DC disconnect switch 4 and a controller 5. The circuit breaker 1 is used to disconnect the connection between the energy storage converter and the power grid; the DC disconnect switch 4 is used to disconnect the connection between the energy storage converter and the battery; the power grid is connected to the inverter 3 via the grid-side filter 2, and the inverter 3 is a three-phase inverter;

[0049] The controller 5 is used to control the output voltage of the energy storage inverter using the detection methods S1 to S3, to send a control signal to the circuit breaker 1 using the detection method S4, to collect the grid voltage and the three-phase current on the energy storage inverter side, and to determine whether the circuit breaker 1 is closed successfully using the detection method S4.

[0050] The purpose of the present invention is to overcome the deficiencies in the prior art and provide an AC synchronous detection method for an energy storage converter. The working principle of the AC synchronous detection method and detection system of the energy storage converter of the present invention is: including an inverter, a controller and a circuit breaker; first, the AC filter capacitor voltage is established through the energy storage converter control, and when the capacitor voltage is consistent with the grid voltage after a delay of a period of time, the controller sends a closing command to the AC circuit breaker, and then after detecting that the converter current is greater than the set threshold, it can be judged that the closing is successful, and then the converter stops the wave control to complete the AC synchronous control.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for detecting AC synchronization of energy storage converters. It is characterized in that Based on an energy storage converter comprising a circuit breaker (1), a grid-side filter (2), an inverter (3), a DC disconnect switch (4) and a controller (5), the detection method comprises: S1. When the energy storage converter receives an AC synchronization command, the controller (5) collects the grid voltage U a , U b and U c , the voltage U in the αβ coordinate system is obtained by coordinate transformation α and U β , the coordinate transformation calculation formula is: S2, set the reference voltage given amplitude to U gRef_pu , whose value is in the range of [0,1], and it rises to the maximum value 1 at a given slope. Suppose the voltage given slope is U gSlop_pu , the voltage given output can be expressed as: U gRef_pu =U gSlop_pu t (2) Where, t is time; S3, the maximum value of the reference voltage given amplitude UgRef_pu is 1, and after rising to 1 according to formula (2), a delay of a period of time SW1Delay is performed. During this process, the control voltage output of the energy storage converter is: Where U ctl_α and U ctl_β They are control voltage α and β components respectively, used for controlling the energy storage converter; S4. When the delay SW1Delay reaches the set time, the controller (5) sends a closing command to the circuit breaker (1). At this time, the energy storage converter is still performing wave control. During this process, the controller (5) detects the three-phase current i on the energy storage converter side. a ,i b and i c When the amplitude of the three-phase current is greater than the set threshold, the closing is considered to be successful; if it is not detected that the amplitude of the three-phase current is greater than the set threshold, timing is performed. When the timing is greater than the set threshold and still not detected, it is considered that the closing has failed.

2. The energy storage converter AC synchronous detection method according to claim 1, It is characterized in that The detection method comprises the following steps: The first step is to detect whether the circuit breaker is closed. If the circuit breaker is closed, the process ends; otherwise, an AC synchronization command is sent to the energy storage converter; Step 2: Use the formulas (1), (2) and (3) to obtain the control voltage α and β components, and control the voltage to rise according to a given slope. When the voltage setting is greater than 1 and the condition is not met, the control voltage continues to increase. When the voltage setting is greater than 1 and the condition is met, the delay begins. Step 3: Check whether the delay time is greater than the set threshold. If it is satisfied, the controller sends a closing command to the circuit breaker. If not, it continues to delay until it is satisfied. Step 4: Detect the three-phase current i on the converter side a ,i b and i c And judge whether it is greater than the set threshold. When the current is greater than the set threshold, it indicates that the closing is successful and the end is made. Otherwise, a delay is performed. When the delay is greater than the set threshold and the current is still not greater than the set threshold, it is considered that the closing has failed.

3. A detection system established by using the energy storage converter AC synchronous detection method according to claim 1, It is characterized in that The invention comprises a power grid, an energy storage converter and a battery, wherein the energy storage converter comprises a circuit breaker (1), a grid-side filter (2), an inverter (3), a DC isolating switch (4) and a controller (5), wherein the circuit breaker (1) is used to disconnect the connection between the energy storage converter and the power grid; the DC isolating switch (4) is used to disconnect the connection between the energy storage converter and the battery; the power grid is connected to the inverter (3) via the grid-side filter (2), and the inverter (3) is a three-phase inverter; The controller (5) is used to control the output voltage of the energy storage converter using the detection methods S1 to S3, to send a control signal to the circuit breaker (1) using the detection method S4, to collect the grid voltage and the three-phase current on the energy storage converter side, and to determine whether the circuit breaker (1) is closed successfully using the detection method S4.

Images