Grounding detection circuit, energy storage converter and grounding detection method

Abstract

A grounding detection circuit comprises a sampling circuit, the first input end (the left end of R6) of the sampling circuit is connected to a neutral terminal (INVN) of a three-phase energy storage converter, and the second input end (the left end of R5) of the sampling circuit is connected to a shell of the three-phase energy storage converter; the bus balancing circuit is arranged between a direct-current bus positive electrode and a direct-current bus negative electrode of the three-phase energy storage converter and is configured to adjust the voltage of the direct-current bus positive electrode to a neutral terminal (INVN) of the three-phase energy storage converter and adjust the voltage of the direct-current bus negative electrode to the neutral terminal (INVN) of the three-phase energy storage converter; the first switch assembly is configured to be arranged between a neutral terminal of the three-phase energy storage converter and a neutral terminal of a power grid; and the control circuit is connected to the output end of the sampling circuit.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of energy storage converters, and particularly relates to a grounding detection circuit, an energy storage converter and a grounding detection method. BACKGROUND

[0002] The TN-S system refers to a neutral point direct grounding system with a dedicated protective zero line. For the TN-S power grid system, the power grid N line is connected to the ground PE at the power grid side, and the voltage between the power grid N line and the ground PE is close to 0V. Therefore, in the related art, whether the energy storage PCS is grounded is often judged by detecting the voltage difference between the power grid N line and the shell of the energy storage PCS. When the energy storage PCS is well grounded, the shell and the ground PE are at the same potential, and the voltage difference between the power grid N line and the shell of the energy storage PCS is 0V. Therefore, when it is detected that the voltage difference between the power grid N line and the shell of the energy storage PCS is close to 0V, it is determined that the energy storage PCS is normally grounded. SUMMARY

[0003] In actual application scenarios, because of the symmetry of the parameters of the three-phase energy storage PCS, the insulation impedance of the L line of the three-phase power grid to the shell of the energy storage PCS is almost consistent, which leads to the fact that in some cases, even if the energy storage PCS is not grounded, the voltage difference between the power grid N line and the shell of the energy storage PCS is very small, and is almost close to 0V, thereby causing the fact that the above-mentioned way of judging whether the shell is grounded by judging whether the voltage difference between the power grid N line and the shell of the energy storage PCS is 0V cannot accurately identify whether the line is grounded.

[0004] The application provides a grounding detection circuit and a grounding detection method, which can identify the grounding state of a three-phase energy storage converter, the detection result is accurate, and the missed detection and false detection can be reduced.

[0005] In a first aspect, the application provides a grounding detection circuit, which comprises: a sampling circuit, a first input end of the sampling circuit being connected to a neutral terminal of a three-phase energy storage converter, and a second input end of the sampling circuit being connected to a shell of the three-phase energy storage converter; a bus balancing circuit, the bus balancing circuit being arranged between a positive DC bus and a negative DC bus of the three-phase energy storage converter, and being configured to adjust the voltage of the positive DC bus to the neutral terminal of the three-phase energy storage converter and adjust the voltage of the negative DC bus to the neutral terminal of the three-phase energy storage converter; a first switch assembly, the first switch assembly being configured to be arranged between the neutral terminal of the three-phase energy storage converter and a neutral terminal of a power grid; and a control circuit, the control circuit being connected to an output end of the sampling circuit.

[0006] In the technical solution, the ground detection circuit comprises a sampling circuit, a bus balancing circuit and a control circuit. When the ground detection is performed on the three-phase energy storage converter, the bus balancing circuit is used to adjust the voltage of the positive bus to the shell of the three-phase energy storage converter and the voltage of the negative bus to the shell of the three-phase energy storage converter, i.e. to adjust the potential through the shell of the three-phase energy storage converter. The sampling circuit collects the voltage difference between the neutral terminal and the shell of the three-phase energy storage converter before and after the adjustment of the bus balancing circuit. The control circuit determines whether the shell of the three-phase energy storage converter is grounded based on the two collected voltage differences. The shell potential of the three-phase energy storage converter is adjusted by the bus balancing circuit. When the shell is not grounded, there is a voltage difference between the shell and the ground. Thus, the shell of the three-phase energy storage converter can be accurately identified as not grounded, the detection result is accurate, and the false detection and missed detection are effectively reduced.

[0007] In combination with the first aspect, in a possible implementation manner, the bus balancing circuit comprises a first switch, a second switch and an inductor. The first end of the first switch is connected to the positive DC bus, the second end of the first switch is connected to the first end of the second switch, the second end of the second switch is connected to the negative DC bus, the third end of the first switch is connected to the control circuit, the third end of the second switch is connected to the control circuit, the first end of the inductor, the second end of the first switch and the first end of the second switch are connected to a node, and the second end of the inductor is connected to the neutral terminal of the three-phase energy storage converter through the midpoint of the DC bus.

[0008] In the technical solution, the shell potential of the three-phase energy storage converter is adjusted by adjusting the duty cycle of the first switch and the duty cycle of the second switch through the control circuit. The circuit structure is simple and the cost is low.

[0009] In combination with the first aspect, in a possible implementation manner, the first switch comprises an N-type FET, the first end of the first switch is a drain, the second end of the first switch is a source, and the third end of the first switch is a gate. The second switch comprises an N-type FET, the first end of the second switch is a drain, the second end of the second switch is a source, and the third end of the second switch is a gate.

[0010] In combination with the first aspect, in a possible implementation manner, the sampling circuit comprises an operational amplifier, a first resistor, a second resistor and a third resistor. The first end of the first resistor is connected to the shell of the three-phase energy storage converter, the second end of the second resistor is connected to the inverting input end of the operational amplifier, the first end of the second resistor is connected to the neutral terminal of the three-phase energy storage converter, the second end of the second resistor is connected to the non-inverting input end of the operational amplifier, the first end of the third resistor is connected to the inverting input end of the operational amplifier, the second end of the third resistor is connected to the output end of the operational amplifier, and the output end of the operational amplifier is connected to the control circuit.

[0011] In this technical solution, the sampling circuit uses a differential method to acquire the voltage difference, amplifying only the difference between the two voltage signals, which can suppress the same common-mode components and improve the signal-to-noise ratio.

[0012] Secondly, this application provides a three-phase energy storage converter, comprising: a DC-DC converter circuit, the input terminal of which is connected to a DC power supply interface; a DC-AC converter circuit, the positive output terminal of which is connected to a first input terminal of the DC-AC converter circuit via a positive DC bus, and the negative output terminal of which is connected to a second input terminal of the DC-AC converter circuit via a negative DC bus; a positive bus capacitor and a negative bus capacitor, which are connected in series between the positive and negative terminals of the DC bus. Between the negative terminals of the busbars, the midpoint of the DC busbar is connected to the neutral terminal of the three-phase energy storage inverter, and the midpoint of the DC busbar is located between the positive busbar capacitor and the negative busbar capacitor; and as in the grounding detection circuit of the first aspect, the first switching assembly includes a first relay, a second relay and a third relay, the first terminal of the first relay is connected to the neutral terminal of the three-phase energy storage inverter, the second terminal of the first relay and the first terminal of the second relay are configured to be connected to the neutral terminal of the load, the second terminal of the second relay is connected to the first terminal of the third relay, and the second terminal of the third relay is configured to be connected to the neutral terminal of the power grid.

[0013] Thirdly, this application provides a grounding detection method, which is applied to the grounding detection circuit as described in the first aspect. The grounding detection method includes: controlling a first switching component to conduct; controlling a bus balancing circuit to operate such that the absolute value of the voltage between the positive terminal of the DC bus and the midpoint of the DC bus is consistent with the absolute value of the voltage between the negative terminal of the DC bus and the midpoint of the DC bus; sampling a first voltage difference between the casing of the three-phase energy storage converter and the neutral terminal of the three-phase energy storage converter, and generating a first voltage signal based on the first voltage difference; controlling the bus balancing circuit to operate such that the absolute value of the voltage between the positive terminal of the DC bus and the midpoint of the DC bus is inconsistent with the absolute value of the voltage between the negative terminal of the DC bus and the midpoint of the DC bus; sampling a second voltage difference between the casing of the three-phase energy storage converter and the neutral terminal of the three-phase energy storage converter, and generating a second voltage signal based on the second voltage difference; and determining whether the casing of the three-phase energy storage converter is grounded based on the first voltage signal and the second voltage signal.

[0014] In conjunction with the third aspect, in one possible implementation, determining whether the casing of the three-phase energy storage converter is grounded based on a first voltage signal and a second voltage signal includes: comparing a first voltage value represented by the first voltage signal and a second voltage value represented by the second voltage signal with a voltage threshold, respectively; determining that the casing of the three-phase energy storage converter is grounded in response to the first voltage value being less than or equal to the voltage threshold and the second voltage value being less than or equal to the voltage threshold; or, determining that a grounding fault has occurred in the casing of the three-phase energy storage converter in response to the first voltage value being greater than the voltage threshold and / or the second voltage value being greater than the voltage threshold.

[0015] In conjunction with the third aspect, in one possible implementation, the bus balancing circuit includes: a first switch, a second switch, and an inductor; the first terminal of the first switch is connected to the positive terminal of the DC bus, the second terminal of the first switch is connected to the first terminal of the second switch, the second terminal of the second switch is connected to the negative terminal of the DC bus, the third terminal of the first switch is connected to a control circuit, the third terminal of the second switch is connected to a control circuit, the first terminal of the inductor, the second terminal of the first switch, and the first terminal of the second switch are connected to a node, and the second terminal of the inductor is connected to the neutral terminal of the three-phase energy storage converter via the midpoint of the DC bus; controlling the operation of the bus balancing circuit to make the absolute value of the voltage between the positive terminal of the DC bus and the midpoint of the DC bus consistent with the absolute value of the voltage between the negative terminal of the DC bus and the midpoint of the DC bus includes: controlling the duty cycle of the drive signal of the first switch to be D1, so that the voltage between the positive terminal of the DC bus and the midpoint of the DC bus is... The duty cycle of the drive signal controlling the second switch is (1-D1), so that the voltage between the negative terminal of the DC bus and the midpoint of the DC bus is... ;in, This is the voltage difference between the positive and negative terminals of the DC bus.

[0016] In conjunction with the third aspect, in one possible implementation, the bus balancing circuit includes: a first switch, a second switch, and an inductor; the first terminal of the first switch is connected to the positive terminal of the DC bus, the second terminal of the first switch is connected to the first terminal of the second switch, the second terminal of the second switch is connected to the negative terminal of the DC bus, the third terminal of the first switch is connected to a control circuit, the third terminal of the second switch is connected to a control circuit, the first terminal of the inductor, the second terminal of the first switch, and the first terminal of the second switch are connected to a node, and the second terminal of the inductor is connected to the neutral terminal of the three-phase energy storage converter via the midpoint of the DC bus; controlling the operation of the bus balancing circuit to make the absolute value of the voltage between the positive terminal of the DC bus and the midpoint of the DC bus inconsistent with the voltage between the negative terminal of the DC bus and the midpoint of the DC bus includes: controlling the duty cycle D2 of the drive signal of the first switch to make the voltage between the positive terminal of the DC bus and the midpoint of the DC bus equal to the absolute value of the voltage between the positive terminal of the DC bus and the midpoint of the DC bus. The duty cycle of the drive signal controlling the second switch is (1-D2), so that the voltage between the negative terminal of the DC bus and the midpoint of the DC bus is ( ); where D2 is not equal to (1-D2), and the value of a is not 1. This is the voltage between the positive and negative terminals of the DC bus.

[0017] In this technical solution, the casing potential of the three-phase energy storage converter can be adjusted simply by adjusting the duty cycle of the first switch and the duty cycle of the second switch. The adjustment method is simple and easy to implement.

[0018] In conjunction with the third aspect, in one possible implementation, the range of values ​​for 'a' is: .

[0019] In this technical solution, the range of values ​​for 'a' is set to... This ensures that the grounding detection sensitivity is maintained while preventing the difference between the positive and negative bus voltages from becoming too large. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below.

[0021] Figure 1 This is a schematic diagram of grounding detection for a conventional three-phase energy storage converter provided in an embodiment of this application; Figure 2 This is a schematic diagram of a conventional three-phase energy storage converter provided in an embodiment of this application; Figure 3 This is a schematic diagram of a three-phase energy storage converter equipped with a grounding detection circuit provided in some embodiments of this application; Figure 4 This is a schematic flowchart of a grounding detection method provided in some embodiments of this application; Figure 5 This is a schematic diagram of a sampling circuit provided in some embodiments of this application; Figure 6 This is a schematic diagram of the structure of the electronic device provided in the embodiments of this application. Detailed Implementation

[0022] The features and examples of various aspects of this application will be described in detail below. To make the purpose, technical solution, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and specific examples. It should be understood that the examples in this application are intended to provide a better understanding of this application, and are only intended to explain this application, not to limit it.

[0023] Understandably, in this document, relational terms such as first and second are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any such actual relationship or order between these entities or operations.

[0024] Before providing further detailed explanation of this application, the nouns and terms used in this application will be explained.

[0025] TN-S system: The full name is a neutral point directly grounded system with a dedicated protective neutral conductor. This system belongs to a type of TN grounding system specified by the International Electrotechnical Commission (IEC). "T" indicates that the power system is directly grounded at one point; "N" indicates that the exposed conductive parts of the equipment are directly electrically connected to the grounding point of the power system; and "S" indicates that the neutral conductor and the protective conductor are separate.

[0026] Three-phase energy storage converter: abbreviated as three-phase energy storage PCS (Power Conversion System), is a device used to realize bidirectional conversion of electrical energy between energy storage system and three-phase AC power grid or load.

[0027] Before further explaining this application, a grounding detection scheme for three-phase energy storage PCS in related technologies will be introduced. In related technologies, whether the casing is grounded is determined by directly judging whether the voltage difference between the grid's neutral (N) line and the casing of the three-phase energy storage PCS is 0V. For example... Figure 1 As shown, due to the parameter symmetry of the three-phase energy storage PCS, the insulation resistances R1, R2, and R3 of the three-phase live wires of the three-phase power grid to the casing of the three-phase energy storage PCS are almost identical. This results in a situation where, even if the casing of the three-phase energy storage PCS is not grounded, the voltage difference between the grid N line and the casing of the three-phase energy storage PCS is very small, almost close to 0V. This makes it impossible to accurately identify whether the three-phase energy storage PCS is grounded, leading to missed detections or false detections.

[0028] In view of this, in order to improve the accuracy of grounding detection in three-phase energy storage PCS, this application provides a grounding detection circuit and its grounding detection method.

[0029] Figure 2 For a system block diagram of a three-phase energy storage PCS, see [link / reference]. Figure 2A three-phase energy storage PCS includes a DC-DC conversion circuit and a DC-AC conversion circuit. The input side of the three-phase energy storage PCS includes DC power interfaces, such as photovoltaic input terminals PV+, PV- and / or battery input terminals BAT+, BAT-. The output side of the three-phase energy storage PCS is connected to the grid-side three-phase live wire connection terminals GRID_L1, GRID_L2, GRID_L3 and neutral wire connection terminal GRID_N, and the load-side three-phase live wire connection terminals LOAD_L1, LOAD_L2, LOAD_L3 and neutral wire connection terminal LOAD_N.

[0030] The photovoltaic input terminal PV+ and / or the battery input terminal BAT+ are connected to the positive input terminal of the DC-DC converter circuit, and the photovoltaic input terminal PV- and / or the battery input terminal BAT- are connected to the negative input terminal of the DC-DC converter circuit.

[0031] The positive output terminal of the DC-DC converter circuit is connected to the positive bus capacitor C3, and is also connected to the first input terminal of the DC-AC converter circuit.

[0032] The negative output terminal of the DC-DC converter circuit is connected to the negative bus capacitor C4, and is also connected to the second input terminal of the DC-AC converter circuit.

[0033] The connection point between the positive bus capacitor C3 and the negative bus capacitor C4 is called the DC bus midpoint. The DC bus midpoint is connected to the neutral terminal INV_N of the three-phase energy storage PCS, and the two are at the same potential. The neutral terminal INV_N of the three-phase energy storage PCS is connected to the third input terminal of the DC-AC conversion circuit.

[0034] See Figure 2 and Figure 3 The three-phase energy storage PCS includes a first switching assembly. The first switching assembly is configured to be located between the neutral terminal INV_N of the three-phase energy storage PCS and the neutral terminal GRID_N of the power grid. The first switching assembly can be used to control the connection between the neutral terminal INV_N of the three-phase energy storage PCS and the neutral terminal GRID_N of the power grid, and to control the connection between the neutral terminal INV_N of the three-phase energy storage PCS and the neutral terminal LOAD_N of the load.

[0035] The first switching assembly includes a first relay K1, a second relay K2, and a third relay K2. The first terminal of the first relay K1 is connected to the neutral terminal INV_N of the three-phase energy storage converter. The second terminal of the first relay K1 and the first terminal of the second relay K2 are configured to be connected to the neutral terminal LOAD_N of the load. The second terminal of the second relay K2 is connected to the first terminal of the third relay K2. The second terminal of the third relay K2 is configured to be connected to the neutral terminal GRID_N of the power grid.

[0036] The three-phase energy storage PCS includes a second switching assembly. The second switching assembly is configured to be located between the A-phase terminal of the three-phase energy storage converter (i.e., the A-phase terminal INV_L1 of the DC-AC conversion circuit) and the A-phase terminal GRID_L1 of the power grid. The second switching assembly can be used to control the connection between the A-phase terminal INV_L1 of the three-phase energy storage converter and the A-phase terminal GRID_L1 of the power grid, as well as to control the connection between the A-phase terminal INV_L1 of the three-phase energy storage converter and the A-phase terminal LOAD_L1 of the load.

[0037] The second switching assembly includes a fourth relay K10, a fifth relay K11, and a sixth relay K12. The first terminal of the fourth relay K10 is connected to the A-phase terminal INV_L1 of the three-phase energy storage converter. The second terminal of the fourth relay K10 and the first terminal of the fifth relay K11 are configured to be connected to the A-phase terminal LOAD_L1 of the load. The second terminal of the fifth relay K11 is connected to the first terminal of the sixth relay K12. The second terminal of the sixth relay is configured to be connected to the A-phase terminal GRID_L1 of the power grid.

[0038] The three-phase energy storage PCS includes a third switching assembly. This third switching assembly is configured to be located between the B-phase terminal of the three-phase energy storage converter (i.e., the B-phase terminal INV_L2 of the DC-AC conversion circuit) and the B-phase terminal GRID_L2 of the power grid. The third switching assembly can be used to control the connection between the B-phase terminal INV_L2 of the three-phase energy storage converter and the B-phase terminal GRID_L2 of the power grid, as well as to control the connection between the B-phase terminal INV_L2 of the three-phase energy storage converter and the B-phase terminal LOAD_L2 of the load.

[0039] The third switching assembly includes a seventh relay K7, an eighth relay K8, and a ninth relay K9. The first terminal of the seventh relay K7 is connected to the B-phase terminal INV_L2 of the three-phase energy storage converter. The second terminal of the seventh relay K7 and the first terminal of the eighth relay K8 are configured to be connected to the B-phase terminal LOAD_L2 of the load. The second terminal of the eighth relay K8 is connected to the first terminal of the ninth relay K9. The second terminal of the ninth relay is configured to be connected to the B-phase terminal GRID_L2 of the power grid.

[0040] The three-phase energy storage PCS includes a fourth switching assembly. This fourth switching assembly is configured to be located between the C-phase terminal of the three-phase energy storage converter (i.e., the C-phase terminal INV_L3 of the DC-AC conversion circuit) and the C-phase terminal GRID_L3 of the power grid. The fourth switching assembly controls the connection between the C-phase terminal INV_L3 of the three-phase energy storage converter and the C-phase terminal GRID_L3 of the power grid, as well as the connection between the C-phase terminal INV_L3 of the three-phase energy storage converter and the C-phase terminal LOAD_L3 of the load.

[0041] The fourth switching assembly includes a tenth relay K4, an eleventh relay K5, and a twelfth relay K6. The first terminal of the tenth relay K4 is connected to the C-phase terminal of the three-phase energy storage converter (i.e., the C-phase terminal INV_L3 of the DC-AC conversion circuit). The second terminal of the tenth relay K4 and the first terminal of the eleventh relay K5 are configured to be connected to the C-phase terminal LOAD_L3 of the load. The second terminal of the eleventh relay K5 is connected to the first terminal of the twelfth relay K6. The second terminal of the twelfth relay K6 is configured to be connected to the C-phase terminal GRID_L3 of the power grid.

[0042] In a three-phase energy storage PCS, the DC-DC converter circuit converts the photovoltaic input voltage... or battery voltage Boost to bus voltage The DC-AC conversion circuit inverts the bus voltage into AC voltage and outputs it to the load or power grid.

[0043] This application is as follows: Figure 2 Based on the block diagram of the three-phase energy storage PCS system shown, a grounding detection circuit and its detection method are proposed to detect whether the casing of the three-phase energy storage PCS is connected to the ground wire.

[0044] In related technologies, when the first switching component is turned on, the neutral terminal INV_N of the three-phase energy storage PCS is connected to the neutral terminal GRID_N of the power grid, and the two are at the same potential. Because GRID_N is grounded on the power grid side, that is, GRID_N is at the same potential as the earth (PE), therefore, after the first switching component is turned on, the neutral terminal INV_N of the three-phase energy storage PCS is also at the same potential as the earth (PE). Based on this, when the casing of the three-phase energy storage PCS is grounded, the casing of the three-phase energy storage PCS should be at the same potential as the earth (PE), and the voltage difference between the casing of the three-phase energy storage PCS and the midpoint INV_N of the positive and negative busbars is close to 0V. This voltage difference is not affected by external circuits.

[0045] Assuming the ground PE is at zero potential, the voltage difference between the positive terminal BUS+ and the negative terminal BUS- of the bus is: The positive and negative bus voltages are symmetrically balanced, that is, the positive bus voltage is The negative bus voltage is Therefore, the potential of the negative terminal BUS- is The potential of the positive terminal BUS+ of the bus is When the three-phase energy storage PCS casing is not grounded, the potential of the three-phase energy storage PCS casing... As shown in equation (1):

[0046] In the above formula (1), resistor R6 represents the insulation resistance between the positive terminal BUS+ of the busbar and the outer casing, and resistor R7 represents the insulation resistance between the negative terminal BUS- of the busbar and the outer casing. It will be understood by those skilled in the art that R6 and R7 can be regarded as virtual impedances. Considering factors such as aging of insulation materials, moisture, dust, and capacitive coupling, the impedance values ​​of R6 and R7 are usually between 1MΩ and 500MΩ.

[0047] From equation (1) above, it can be seen that when the resistance R7 is much smaller than the resistance R6, the potential of the casing of the three-phase energy storage PCS is... Approximately equal to When resistor R7 is much larger than resistor R6, the potential of the casing of the three-phase energy storage PCS is... Approximately equal to That is, when resistor R7 is much larger than resistor R6 or much smaller than resistor R6, the voltage difference between the three-phase energy storage PCS casing and ground PE is much greater than 0V. Based on this, when resistor R7 is much larger than resistor R6 or much smaller than resistor R6, the voltage difference collected by the sampling circuit is compared with a set voltage threshold. By comparison, it can be determined whether the three-phase energy storage PCS is grounded. The voltage difference collected by the sampling circuit is greater than the voltage threshold. In the case where the three-phase energy storage PCS is not grounded, and the voltage difference collected by the sampling circuit is less than or equal to the voltage threshold, it can be determined that the PCS is not grounded. In this case, it is determined that the three-phase energy storage PCS is grounded, where the voltage threshold is... It is a voltage value close to 0V.

[0048] Combining the above equation (1), when resistor R7 equals resistor R6, the potential of the casing of the three-phase energy storage PCS is... The voltage is 0V, even if the three-phase energy storage PCS is not grounded. It is also 0V, at the same potential as ground (PE). That is, when resistor R7 equals resistor R6, regardless of whether the three-phase energy storage PCS is grounded, the voltage difference collected by the sampling circuit is always less than or equal to the voltage threshold. Therefore, when resistor R7 equals resistor R6, the voltage difference acquired by the sampling circuit is compared with the set voltage threshold. By comparison, it is impossible to accurately identify whether the three-phase energy storage PCS is grounded.

[0049] Therefore, in order to accurately identify whether a three-phase energy storage PCS is grounded, whether the resistors R6 and R7 are equal or unequal, this application provides a grounding detection circuit and detection method for a three-phase energy storage PCS.

[0050] like Figure 3As shown, the grounding detection circuit provided in this application includes: a sampling circuit, a bus balancing circuit, and a control circuit. Figure 3 (Not shown in the image).

[0051] The first input terminal of the sampling circuit is connected to the neutral terminal INV_N of the three-phase energy storage PCS, and the second input terminal of the sampling circuit is connected to the housing of the three-phase energy storage PCS. The sampling circuit is used to sample the voltage difference between the housing of the three-phase energy storage PCS and the neutral terminal INV_N of the three-phase energy storage PCS.

[0052] The control circuit is connected to the output of the sampling circuit. The control circuit is configured to determine whether the casing of the three-phase energy storage PCS is grounded based on the voltage difference acquired by the sampling circuit, that is, to determine whether a grounding fault has occurred in the three-phase energy storage PCS.

[0053] As mentioned earlier, when resistors R6 and R7 are equal, even if the three-phase energy storage PCS is not grounded, the potential Vcase of the three-phase energy storage PCS casing is 0V, which is at the same potential as the earth PE. Therefore, it is difficult to accurately identify whether the casing of the three-phase energy storage PCS is grounded based on the voltage difference between the casing and the neutral terminal INV_N of the three-phase energy storage PCS. In view of this, the grounding detection circuit of this application includes a bus balancing circuit. The bus balancing circuit is located between the positive DC bus BUS+ and the negative DC bus BUS- of the three-phase energy storage PCS. It is configured to adjust the voltage between the positive DC bus and the neutral terminal INV_N of the three-phase energy storage converter, and to adjust the voltage between the negative DC bus and the neutral terminal INV_N of the three-phase energy storage converter. For ease of description, the voltage between the positive terminal of the DC bus and the neutral terminal INV_N of the three-phase energy storage converter will be referred to as the positive bus voltage, and the voltage between the negative terminal of the DC bus and the neutral terminal INV_N of the three-phase energy storage converter will be referred to as the negative bus voltage.

[0054] Based on the above-described grounding detection circuit, this application provides a grounding detection method for detecting whether the casing of a three-phase energy storage PCS is grounded. This method can be executed using the grounding detection circuit provided in this application. See also Figure 4 The grounding detection method provided in this application includes the following steps 410-440.

[0055] Step 410. Control the first switch assembly to turn on.

[0056] When performing grounding detection on a three-phase energy storage PCS, the control circuit first controls the first switching component to conduct, so that the connection between the neutral terminal INV_N of the three-phase energy storage PCS and the neutral terminal GRID_N of the power grid is established, thereby making the potential of the neutral terminal INV_N of the three-phase energy storage PCS consistent with the potential of the ground PE.

[0057] Optionally or additionally, such as Figures 1-3As shown, the first switch assembly may include a first relay K1, a second relay K2, and a third relay K3 disposed on the N line. Based on this, controlling the first switch assembly to be turned on may include controlling the first relay K1, the second relay K2, and the third relay K3 to be closed.

[0058] Step 420. Control the bus balance circuit to work so that the absolute value of the voltage between the positive terminal of the DC bus and the midpoint of the DC bus is consistent with the absolute value of the voltage between the negative terminal of the DC bus and the midpoint of the DC bus. Sample the first voltage difference between the casing of the three-phase energy storage converter and the neutral terminal of the three-phase energy storage converter, and generate a first voltage signal based on the first voltage difference.

[0059] With the first switching assembly turned on, the bus balancing circuit can be controlled by the control circuit to operate, thereby adjusting the positive and negative bus voltages to ensure that the positive and negative bus voltages are of equal magnitude, i.e., the bus voltage is... Then the positive bus voltage is The negative bus voltage is .

[0060] When the positive bus voltage and the negative bus voltage are of the same magnitude, the sampling circuit acquires the first voltage difference between the casing of the three-phase energy storage converter and the neutral terminal INV_N of the three-phase energy storage converter, generates the first voltage signal Vsamp1 based on the first voltage difference, and transmits the first voltage signal Vsamp1 to the control circuit.

[0061] Optionally or additionally, in some optional examples of this application, considering the possibility of ripple, the consistency of the positive bus voltage and the negative bus voltage is not absolute. In this application, the difference between the absolute value of the positive bus voltage and the absolute value of the negative bus voltage is less than a deviation threshold, which indicates that the positive bus voltage and the negative bus voltage are of the same magnitude. The deviation threshold can be set according to actual needs. For example, when there is a deviation of less than 10% between the absolute value of the positive bus voltage and the absolute value of the negative bus voltage, the positive bus voltage and the negative bus voltage are considered to be of the same magnitude.

[0062] Step 430. Control the bus balance circuit to work so that the absolute value of the voltage between the positive terminal of the DC bus and the midpoint of the DC bus is inconsistent with the absolute value of the voltage between the negative terminal of the DC bus and the midpoint of the DC bus. Sample the second voltage difference between the casing of the three-phase energy storage converter and the neutral terminal of the three-phase energy storage converter, and generate a second voltage signal based on the second voltage difference.

[0063] Based on the conduction of the first switching component, the control circuit further controls the bus balancing circuit to work, so as to adjust the positive bus voltage and the negative bus voltage through the bus balancing circuit, so that the magnitude of the positive bus voltage is inconsistent with the magnitude of the negative bus voltage, so that when the three-phase energy storage PCS is not grounded, there is a certain voltage difference between the shell of the three-phase energy storage PCS and the ground PE.

[0064] When the positive bus voltage and the negative bus voltage are inconsistent, the sampling circuit collects the second voltage difference between the casing of the three-phase energy storage converter and the neutral terminal INV_N of the three-phase energy storage converter. Based on the second voltage difference, a second voltage signal Vsamp2 is generated and transmitted to the control circuit.

[0065] For example, the positive bus voltage is adjusted to [value] by a bus balancing circuit. Adjust the negative bus voltage to 'a' represents the bias coefficient, and in step 430, 'a' is a value other than 1. At this time, the positive potential of the busbar (BUS+) is... The bus negative terminal BUS-potential is When the three-phase energy storage PCS casing is not grounded, the potential of the three-phase energy storage PCS casing... This can be expressed as the following formula (2):

[0066] From equation (2) above, it can be seen that when resistor R6 equals resistor R7, the potential of the three-phase energy storage PCS casing is... As shown in equation (3):

[0067] As can be seen from the above formula (3), by setting the value of the pull coefficient a, the second voltage difference sampled by the sampling circuit in step 430 can be made greater than the voltage threshold. Thus, the system determines whether the three-phase energy storage PCS casing is grounded based on the second voltage difference. When the three-phase energy storage PCS casing is not grounded, the second voltage difference will be greater than the set voltage threshold. .

[0068] Optionally or additionally, in some optional examples of this application, when R6=R7, The magnitude of the voltage depends on the magnitude of |a-1|. The larger |a-1| is, the greater the voltage. The larger the value of a, the more sensitive the detection, but the more unbalanced the voltage of the positive and negative buses will be. Under the normal operating conditions of a three-phase energy storage PCS, the positive and negative buses need to be kept as balanced as possible. Therefore, in order to meet the detection sensitivity while ensuring that the voltage of the positive and negative buses does not differ too much, the value range of a is set to [0,2]. Preferably, a=1.1.

[0069] It is understood that the order of steps 420 and 430 can be reversed, that is, step 420 can be executed first or step 430 can be executed first. This application does not make a specific limitation in this regard.

[0070] Step 440. Based on the first voltage signal and the second voltage signal, determine whether the casing of the three-phase energy storage converter is grounded.

[0071] After acquiring the first voltage difference and the second voltage difference, the control circuit can determine whether the casing of the three-phase energy storage PCS is grounded based on the first voltage signal and the second voltage signal transmitted by the sampling circuit.

[0072] Optionally or additionally, in some optional examples of this application, it can be determined whether the casing of the three-phase energy storage PCS is grounded by the following steps 4401-4403.

[0073] Step 4401. Compare the first voltage value represented by the first voltage signal and the second voltage value represented by the second voltage signal with the voltage threshold, respectively.

[0074] Here, the first voltage value represented by the first voltage signal is the value of the first voltage difference, and the second voltage value represented by the second voltage signal is the value of the second voltage difference.

[0075] The control circuit compares the first voltage value and the second voltage value with the set voltage threshold, respectively, to obtain the relationship between the first voltage value and the voltage threshold, and the relationship between the second voltage value and the voltage threshold.

[0076] For three-phase energy storage PCS, the voltage threshold can be set to 30V. The voltage threshold can be adjusted according to the detection sensitivity and false alarm rate; this application does not specify its value.

[0077] Step 4402. In response to a first voltage value being less than or equal to a voltage threshold and a second voltage value being less than or equal to a voltage threshold, determine that the casing of the three-phase energy storage converter is grounded.

[0078] After the first switching component is turned on, the neutral terminal INV_N of the three-phase energy storage PCS is connected to the neutral terminal GRID_N of the power grid, and the two are at the same potential. The grid side GRID_N is grounded, and GRID_N is at the same potential as the earth (PE). Therefore, at this time, the neutral terminal INV_N of the three-phase energy storage PCS is at the same potential as the earth (PE). When the casing of the three-phase energy storage PCS is grounded, the casing of the three-phase energy storage PCS is at the same potential as the earth (PE). Therefore, after the casing of the three-phase energy storage PCS is grounded, the voltage difference between the casing of the three-phase energy storage PCS and the neutral terminal INV_N of the three-phase energy storage PCS is close to 0V, and this voltage difference is not affected by external circuits. Based on this, after steps 420 and 430, when the voltage values ​​represented by Vsamp1 and Vsamp2 are both less than the set voltage threshold, it is determined that the casing of the three-phase energy storage PCS is grounded.

[0079] Step 4403. In response to a first voltage value being greater than a voltage threshold, and / or a second voltage value being greater than a voltage threshold, determine that a ground fault has occurred in the casing of the three-phase energy storage converter.

[0080] As mentioned earlier, after the three-phase energy storage PCS casing is grounded, the voltage difference between the three-phase energy storage PCS casing and the neutral terminal INV_N of the three-phase energy storage PCS is close to 0V. Therefore, regardless of how the bus balancing circuit operates, the voltage difference between the three-phase energy storage PCS casing and the neutral terminal INV_N of the three-phase energy storage PCS should be less than the voltage threshold. Otherwise, it indicates that the three-phase energy storage PCS casing is not grounded. Based on this, if either the first voltage value or the second voltage value is greater than the voltage threshold, it indicates that the three-phase energy storage PCS casing is not grounded. For example, if the first voltage value is greater than the voltage threshold, it is determined that the three-phase energy storage PCS casing is not grounded; if the second voltage value is greater than the voltage threshold, it is determined that the three-phase energy storage PCS casing is not grounded; if both the first and second voltage values ​​are greater than the voltage threshold, it is determined that the three-phase energy storage PCS casing is not grounded.

[0081] By means of the above method, when grounding detection is performed on a three-phase energy storage PCS, the positive bus voltage and negative bus voltage are adjusted by the bus balancing circuit so that when the three-phase energy storage PCS casing is not grounded, the voltage difference between the casing and the ground is greater than the voltage threshold, thereby accurately identifying whether the casing of the three-phase energy storage PCS is grounded.

[0082] Optionally or additionally, in some alternative examples of this application, the bus balancing circuit employs a buck-boost circuit, such as a buck-boost converter. The buck-boost circuit raises or lowers the positive bus voltage as needed, while maintaining the voltage between the positive and negative DC buses at a constant level. Therefore, the negative bus voltage decreases as the positive bus voltage increases, or the negative bus voltage increases as the positive bus voltage decreases.

[0083] Optionally or additionally, the bus balancing circuit is a BUCK-BOOST circuit composed of a first switch Q1, a second switch Q2, and an inductor L1. Specifically, the first terminal of the first switch Q1 is connected to the positive terminal of the DC bus, the second terminal of the first switch Q1 is connected to the first terminal of the second switch Q2, the second terminal of the second switch Q2 is connected to the negative terminal of the DC bus, the third terminal of the first switch Q1 is connected to the control circuit, the third terminal of the second switch Q2 is connected to the control circuit, the first terminal of the inductor L1, the second terminal of the first switch Q1, and the first terminal of the second switch Q2 are connected to a neutral node, and the second terminal of the inductor is connected to the neutral terminal INV_N of the three-phase energy storage converter via the midpoint of the DC bus.

[0084] Optionally or additionally, the first switch Q1 and the second switch Q2 can be switches with adjustable duty cycles, and the first switch Q1 and the second switch Q2 are complementary in conduction.

[0085] For example, the first switch Q1 and the second switch Q2 can be MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), BJT (Bipolar Transistor), etc.

[0086] For example, the first switch Q1 is an N-type FET, with the first terminal of the first switch Q1 being the drain, the second terminal of the first switch Q1 being the source, and the third terminal of the first switch Q1 being the gate, i.e., the control terminal. The second switch Q2 is also an N-type FET, with the first terminal of the second switch Q2 being the drain, the second terminal of the second switch Q2 being the source, and the third terminal of the second switch Q2 being the gate, i.e., the control terminal.

[0087] The first switch Q1 and the second switch Q2 are complementary and conduct. The duty cycle of the first switch Q1 is D, and the duty cycle of the second switch Q2 is (1-D). The positive bus voltage and the negative bus voltage can be adjusted by adjusting the duty cycles of the first switch Q1 and the second switch Q2 in the bus balancing circuit. The adjustment principle is shown in the following equation (4):

[0088] in, This represents the voltage across capacitor C4 on the negative bus, i.e., the negative bus voltage. This represents the voltage across the positive bus capacitor C3, i.e., the positive bus voltage.

[0089] During the normal operation of the three-phase energy storage PCS and in step 420 above, the duty cycle of the first switch Q1 can be adjusted to D and the duty cycle of the second switch Q2 (1-D) by the control circuit to make the magnitudes of the positive bus voltage and the negative bus voltage equal. For example, the duty cycle of the drive signal controlling the first switch can be D1, such that the voltage between the positive terminal of the DC bus and the midpoint of the DC bus is... The duty cycle of the drive signal controlling the second switch is (1-D1), so that the voltage between the negative terminal of the DC bus and the midpoint of the DC bus is... Where D1 is a value close to or equal to 50%, such that D1≈(1-D1). In step 430 above, the duty cycle D of the first switch Q1 and the duty cycle (1-D) of the second switch Q2 can be adjusted by the control circuit to make the magnitudes of the positive bus voltage and the negative bus voltage unequal, so that the positive bus voltage is... The negative bus voltage is For example, the duty cycle D2 of the drive signal controlling the first switch makes the voltage between the positive terminal of the DC bus and the midpoint of the DC bus equal to... The duty cycle of the drive signal controlling the second switch is (1-D2), so that the voltage between the negative terminal of the DC bus and the midpoint of the DC bus is ( ); where D2 is not equal to (1-D2), and the value of a is not 1.

[0090] By using the above method, the positive and negative bus voltages can be adjusted simply by adjusting the duty cycle of the first switch Q1 and the duty cycle of the second switch Q2. The circuit structure is simple and the cost is low.

[0091] Understandably, the control circuit can employ a microcontroller unit (MCU) or a digital signal processor (DSP).

[0092] Alternatively or additionally, in some alternative examples in this application, see [link to relevant documentation]. Figure 5 The sampling circuit is a differential sampling circuit, which includes: an operational amplifier, a fifth resistor R5, a sixth resistor R6, and a seventh resistor R7; The first end of the fifth resistor R5 is connected to the casing of the three-phase energy storage converter, and the second end of the fifth resistor R5 is connected to the inverting input terminal of the operational amplifier; the first end of the sixth resistor R6 is connected to the neutral terminal INV_N of the three-phase energy storage converter, and the second end of the sixth resistor R6 is connected to the non-inverting input terminal of the operational amplifier; the first end of the seventh resistor R7 is connected to the inverting input terminal of the operational amplifier, and the second end of the seventh resistor R7 is connected to the output terminal of the operational amplifier, which is then connected to the control circuit.

[0093] In this way, the sampling circuit uses a differential method to acquire the voltage difference, amplifying only the difference between the two voltage signals, which can suppress the same common-mode components and improve the signal-to-noise ratio.

[0094] Optionally, see Figure 3 The grounding detection circuit may also include a first Y capacitor C1 and a second Y capacitor C2. Common-mode interference can be suppressed by setting the first Y capacitor C1 and the second Y capacitor C2.

[0095] Based on the grounding detection circuit provided in this application, this application also provides a three-phase energy storage converter, which includes: a DC-DC converter circuit, the input terminal of which is connected to a DC power interface; a DC-AC converter circuit, the positive output terminal of which is connected to the first input terminal of which is connected to the positive terminal of which is connected to the DC bus, and the negative output terminal of which is connected to the second input terminal of which is connected to the negative terminal of which is connected to the DC bus; a positive bus capacitor and a negative bus capacitor, which are connected in series between the positive and negative terminals of which is connected to the DC bus, and the midpoint of which is connected to the neutral terminal of the three-phase energy storage converter, and the midpoint of which is located between the positive bus capacitor (C3) and the negative bus capacitor (C4); and the grounding detection circuit provided in any of the above embodiments. A schematic diagram of the three-phase energy storage converter is shown below. Figure 2 and Figure 3 As shown.

[0096] Figure 6 A schematic diagram of the hardware structure of the electronic device provided in this application is shown.

[0097] Electronic device 600 may include processor 601 and memory 602 storing computer program instructions.

[0098] Specifically, the processor 601 may include a central processing unit (CPU), an application-specific integrated circuit (ASIC), or one or more integrated circuits that can be configured to implement the embodiments of this application.

[0099] Memory 602 may include a large-capacity memory for data or instructions. For example, and not limitingly, memory 602 may include a hard disk drive (HDD), a floppy disk drive, flash memory, optical disk, magneto-optical disk, magnetic tape, or a Universal Serial Bus (USB) drive, or a combination of two or more of these. Where suitable, memory 602 may include removable or non-removable (or fixed) media. Where suitable, memory 602 may be internal or external to electronic device 600. In a particular embodiment, memory 602 is a non-volatile solid-state memory. Memory 602 may include read-only memory (ROM), random access memory (RAM), disk storage media devices, optical storage media devices, flash memory devices, electrical, optical, or other physical / tangible memory storage devices. Thus, generally, memory 602 includes one or more tangible (non-transitory) computer-readable storage media (e.g., memory devices) encoded with software including computer-executable instructions, and when the software is executed (e.g., by one or more processors), it performs the operations described in any of the ground detection methods in the above embodiments.

[0100] The processor 601 implements any of the grounding detection methods described in the above embodiments by reading and executing computer program instructions stored in the memory 602.

[0101] In one example, electronic device 600 may further include communication interface 603 and bus 610. For example, Figure 6 As shown, the processor 601, memory 602, and communication interface 603 are connected through bus 610 and complete communication with each other.

[0102] The communication interface 603 is mainly used to realize communication between various modules, devices, units and / or equipment in the embodiments of this application.

[0103] Bus 610 includes hardware, software, or both, that couples components of electronic device 600 together. For example, and not limitingly, the bus may include Accelerated Graphics Terminal (AGP) or other graphics buses, Enhanced Industry Standard Architecture (EISA) buses, Front Side Bus (FSB), HyperTransport (HT) interconnects, Industry Standard Architecture (ISA) buses, Infinite Bandwidth Interconnects, Low Pin Count (LPC) buses, memory buses, Microchannel Architecture (MCA) buses, Peripheral Component Interconnect (PCI) buses, PCI-Express (PCI-X) buses, Serial Advanced Technology Attachment (SATA) buses, Video Electronics Standards Association Local (VLB) buses, or other suitable buses, or combinations of two or more of these. Where appropriate, bus 610 may include one or more buses. Although specific buses are described and illustrated in embodiments of this application, any suitable bus or interconnect is contemplated herein.

[0104] Furthermore, in conjunction with the XX method in the above embodiments, this application embodiment can provide a computer storage medium for implementation. The computer storage medium stores computer program instructions; when these computer program instructions are executed by a processor, they implement any of the grounding detection methods in the above embodiments.

[0105] It should be clarified that this application is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of this application is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of this application.

[0106] The functional blocks shown in the above-described structural diagram can be implemented as hardware, software, firmware, or a combination thereof. When implemented in hardware, they can be, for example, electronic circuits, application-specific integrated circuits (ASICs), appropriate firmware, plug-ins, function cards, etc. When implemented in software, the elements of this application are programs or code segments used to perform the required tasks. Programs or code segments can be stored on a machine-readable medium or transmitted over a transmission medium or communication link via data signals carried on a carrier wave. "Machine-readable medium" can include any medium capable of storing or transmitting information. Examples of machine-readable media include electronic circuits, semiconductor memory devices, ROM, flash memory, erasable ROM (EROM), floppy disks, CD-ROMs, optical disks, hard disks, fiber optic media, radio frequency (RF) links, etc. Code segments can be downloaded via computer networks such as the Internet, intranets, etc.

[0107] It should also be noted that the exemplary embodiments mentioned in this application describe methods or systems based on a series of steps or apparatus. However, this application is not limited to the order of the above steps; that is, the steps can be performed in the order mentioned in the embodiments, or in a different order, or several steps can be performed simultaneously.

[0108] The aspects of this disclosure have been described above with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this disclosure. It should be understood that each block in the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus to produce a machine such that these instructions, executable via the processor of the computer or other programmable data processing apparatus, enable the implementation of the functions / actions specified in one or more blocks of the flowchart illustrations and / or block diagrams. Such a processor can be, but is not limited to, a general-purpose processor, a special-purpose processor, a special application processor, or a field-programmable logic circuit. It is also understood that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can also be implemented by special-purpose hardware performing the specified functions or actions, or can be implemented by a combination of special-purpose hardware and computer instructions.

[0109] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

Claims

1. A ground detection circuit, characterized by, The ground detection circuit comprises: a sampling circuit, a first input end of the sampling circuit being connected to a neutral terminal (INV_N) of a three-phase energy storage converter, and a second input end of the sampling circuit being connected to a shell of the three-phase energy storage converter; a bus balancing circuit, the bus balancing circuit being arranged between a positive DC bus and a negative DC bus of the three-phase energy storage converter, and being configured to adjust a voltage of the positive DC bus to the neutral terminal of the three-phase energy storage converter, and to adjust a voltage of the negative DC bus to the neutral terminal of the three-phase energy storage converter; a first switch assembly, the first switch assembly being arranged between the neutral terminal of the three-phase energy storage converter and a neutral terminal of a power grid; a control circuit, the control circuit being connected to an output end of the sampling circuit.

2. The ground detection circuit according to claim 1, wherein the bus balancing circuit comprises a first switch, a second switch and an inductor, a first end of the first switch is connected to the positive DC bus, a second end of the first switch is connected to a first end of the second switch, and a second end of the second switch is connected to the negative DC bus, a third end of the first switch is connected to the control circuit, and a third end of the second switch is connected to the control circuit, a first end of the inductor, the second end of the first switch and the first end of the second switch are connected to a node, and a second end of the inductor is connected to the neutral terminal of the three-phase energy storage converter through the DC bus midpoint.

3. The ground detection circuit according to claim 2, wherein the first switch comprises an N-type FET, the first end of the first switch is a drain, the second end of the first switch is a source, and the third end of the first switch is a gate, the second switch comprises an N-type FET, the first end of the second switch is a drain, the second end of the second switch is a source, and the third end of the second switch is a gate.

4. The ground detection circuit according to any one of claims 1 to 3, wherein the sampling circuit comprises an operational amplifier, a first resistor, a second resistor and a third resistor, a first end of the first resistor is connected to the shell of the three-phase energy storage converter, and a second end of the second resistor is connected to an inverting input end of the operational amplifier, a first end of the second resistor is connected to the neutral terminal of the three-phase energy storage converter, and a second end of the second resistor is connected to a non-inverting input end of the operational amplifier, a first end of the third resistor is connected to the inverting input end of the operational amplifier, and a second end of the third resistor is connected to an output end of the operational amplifier, and the output end of the operational amplifier is connected to the control circuit.

5. A three-phase energy storage converter, comprising: a DC-DC conversion circuit, an input end of the DC-DC conversion circuit being connected to a DC power supply interface; ​ a DC-AC conversion circuit, a positive output terminal of the DC-DC conversion circuit is connected to a first input terminal of the DC-AC conversion circuit through a positive DC bus, and a negative output terminal of the DC-DC conversion circuit is connected to a second input terminal of the DC-AC conversion circuit through a negative DC bus; a positive bus capacitor and a negative bus capacitor, the positive bus capacitor and the negative bus capacitor are connected in series between the positive DC bus and the negative DC bus, a DC bus midpoint is connected to a neutral terminal of the three-phase energy storage converter, and the DC bus midpoint is located between the positive bus capacitor and the negative bus capacitor; and The grounding detection circuit according to any one of claims 1-4; wherein the first switch assembly comprises a first relay, a second relay, and a third relay, a first end of the first relay is connected to a neutral terminal of the three-phase energy storage inverter, a second end of the first relay and a first end of the second relay are configured to be connected to a neutral terminal of a load, a second end of the second relay is connected to a first end of the third relay, and a second end of the third relay is configured to be connected to a neutral terminal of the power grid.

6. A ground detection method characterized by comprising: The grounding detection method is applied to the grounding detection circuit according to any one of claims 1-4, and the grounding detection method comprises: controlling the first switch assembly to be turned on; controlling the bus balancing circuit to work so that the absolute value of the voltage of the positive DC bus to the DC bus midpoint is consistent with the absolute value of the voltage of the negative DC bus to the DC bus midpoint, sampling a first voltage difference between the shell of the three-phase energy storage converter and the neutral terminal of the three-phase energy storage converter, and generating a first voltage signal based on the first voltage difference, controlling the bus balancing circuit to work so that the absolute value of the voltage of the positive DC bus to the DC bus midpoint is inconsistent with the absolute value of the voltage of the negative DC bus to the DC bus midpoint, sampling a second voltage difference between the shell of the three-phase energy storage converter and the neutral terminal of the three-phase energy storage converter, and generating a second voltage signal based on the second voltage difference, determining whether the shell of the three-phase energy storage converter is grounded based on the first voltage signal and the second voltage signal.

7. The ground detection method according to claim 6, wherein The determination of whether the shell of the three-phase energy storage converter is grounded based on the first voltage signal and the second voltage signal comprises: comparing a first voltage value represented by the first voltage signal and a second voltage value represented by the second voltage signal with a voltage threshold value, respectively; in response to the first voltage value being less than or equal to the voltage threshold value and the second voltage value being less than or equal to the voltage threshold value, determining that the shell of the three-phase energy storage converter is grounded; or in response to the first voltage value being greater than the voltage threshold value and / or the second voltage value being greater than the voltage threshold value, determining that the shell of the three-phase energy storage converter has a grounding fault.

8. The grounding detection method according to claim 6 or 7, wherein the bus balancing circuit comprises a first switch, a second switch, and an inductor. a first end of the first switch is connected to the positive pole of the DC bus, a second end of the first switch is connected to a first end of the second switch, and a second end of the second switch is connected to the negative pole of the DC bus, a third end of the first switch is connected to the control circuit, and a third end of the second switch is connected to the control circuit, a first end of the inductor, the second end of the first switch, and the first end of the second switch are connected to a node, and a second end of the inductor is connected to a neutral terminal of the three-phase energy storage converter through a DC bus midpoint; the control of the operation of the bus balancing circuit makes the absolute value of the voltage of the positive pole of the DC bus to the DC bus midpoint consistent with the absolute value of the voltage of the negative pole of the DC bus to the DC bus midpoint, and includes: The duty cycle of the drive signal for controlling the first switch is D1, so that the voltage of the positive pole of the DC bus to the midpoint of the DC bus is ; The duty cycle of the driving signal for controlling the second switch is (1-D1), so that the voltage of the negative pole of the DC bus to the midpoint of the DC bus is ; wherein is the voltage difference between the positive DC bus pole and the negative DC bus pole.

9. The ground detection method of any one of claims 6-8, wherein, the bus balancing circuit includes a first switch, a second switch, and an inductor; a first end of the first switch is connected to the positive pole of the DC bus, a second end of the first switch is connected to a first end of the second switch, and a second end of the second switch is connected to the negative pole of the DC bus, a third end of the first switch is connected to the control circuit, and a third end of the second switch is connected to the control circuit, a first end of the inductor, the second end of the first switch, and the first end of the second switch are connected to a node, and a second end of the inductor is connected to a neutral terminal of the three-phase energy storage converter through a DC bus midpoint; the control of the operation of the bus balancing circuit makes the absolute value of the voltage of the positive pole of the DC bus to the DC bus midpoint inconsistent with the absolute value of the voltage of the negative pole of the DC bus to the DC bus midpoint, and includes: The duty cycle D2 of the drive signal for controlling the first switch is such that the voltage of the DC bus positive pole to the DC bus midpoint is , The duty cycle of the driving signal for controlling the second switch is (1-D2), so that the voltage of the negative pole of the DC bus to the midpoint of the DC bus is (Vbus / 2-Vbus / 2*D2) ); Wherein, D2 is not equal to (1-D2), a is not equal to 1, is the voltage between the positive pole of the DC bus and the negative pole of the DC bus.

10. The ground detection method of claim 9, wherein, a has a value in the range of .

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