Inverter

Abstract

The utility model discloses an inverter which comprises an inversion unit, and the alternating current end of the inversion unit is connected with a load and a power grid in a three-phase four-wire system wiring mode. The inverter further comprises a voltage sampling unit and a control unit. The voltage sampling unit comprises a first line voltage sampling unit, a second line voltage sampling unit and a phase voltage sampling unit, the first line voltage sampling unit is used for sampling a first line voltage, the second line voltage sampling unit is used for sampling a second line voltage, and the phase voltage sampling unit is used for sampling the phase voltage of one phase line; the control unit is configured to obtain the first line voltage, the second line voltage and the phase voltage of one phase line, and determine the phase voltages of the other two phase lines based on the first line voltage, the second line voltage and the phase voltage of one phase line. By changing the voltage sampling mode, the system impedance is improved, it is ensured that the system impedance still meets the national standard requirement under the condition that the inverters are connected in parallel, and the system safety and reliability are enhanced.

Description

Technical Field

[0001] This application relates to the field of inverter technology, and more particularly to an inverter. Background Technology

[0002] Common energy storage inverters or photovoltaic-storage inverters can be classified into three-phase three-wire and three-phase four-wire systems based on their grid connection method. Three-phase three-wire inverters are suitable for balanced load applications, while three-phase four-wire inverters are suitable for applications with high safety requirements or where there is a three-phase unbalanced load. Therefore, three-phase four-wire inverters are widely used in large-scale commercial and industrial power applications, such as factories and supermarkets.

[0003] In a three-phase four-wire topology, there is a possibility of the remote neutral line N being grounded. In this case, the neutral line N on the AC side of the inverter is also pulled to ground. Generally, inverters have phase voltage sampling units, and their system impedance will decrease due to the parallel connection of sampling resistors. Besides affecting the normal operation of the inverter, this reduced system impedance can also pose serious safety hazards, such as the inverter casing becoming electrified, thus impacting personal safety.

[0004] The national standard requires that the inverter's insulation impedance to ground be above 1MΩ, and that the inverter output voltage, grid voltage, and DC component of the voltage be detected when the inverter is off-grid. For three-phase three-wire inverters, line voltage can be sampled; however, for three-phase four-wire inverters, sampling the DC component line voltage results in a zero sum of the three phases, making it impossible to know the actual DC component value. When sampling phase voltages in a three-phase four-wire inverter, excessive sampling resistance to the neutral line N will lower the system impedance, increasing safety hazards during operation. Currently, there are two commonly used methods: one is... Figure 1 As shown, the sampling circuit is isolated from ground using an isolation device; secondly, as... Figure 2 The proposed solution involves increasing the sampling resistor value. However, the former is more expensive, while the latter occupies a larger PCB area, reducing the machine's power density. Utility Model Content

[0005] This application provides an inverter that improves system impedance by changing the voltage sampling method, ensuring that the system impedance still meets national standards when the inverter is in parallel operation, thereby enhancing system safety and reliability.

[0006] This application provides an inverter, which includes an inverter unit, wherein the AC terminal of the inverter unit is connected to the load and the power grid via a three-phase four-wire connection.

[0007] The inverter also includes a voltage sampling unit and a control unit;

[0008] The voltage sampling unit includes a first line voltage sampling unit, a second line voltage sampling unit, and a phase voltage sampling unit. The first line voltage sampling unit is used to sample the first line voltage, the second line voltage sampling unit is used to sample the second line voltage, and the phase voltage sampling unit is used to sample the phase voltage of one of the phase lines.

[0009] The control unit is configured to acquire the first line voltage, the second line voltage, and the phase voltage of one of the phase lines, and to determine the phase voltages of the other two phase lines based on the first line voltage, the second line voltage, and the phase voltage of one of the phase lines.

[0010] In one example, the voltage sampling unit includes at least one of an inverter output voltage sampling unit, a grid voltage sampling unit, and a load voltage sampling unit.

[0011] In one example, the first line voltage sampling unit includes a first line voltage sampling resistor, the second line voltage sampling unit includes a second line voltage sampling resistor, and the phase voltage sampling unit includes a phase voltage sampling resistor.

[0012] In one example, the total equivalent impedance to ground based on the first line voltage sampling resistor, the second line voltage sampling resistor, and the phase voltage sampling resistor is greater than 1 MΩ.

[0013] In one example, the resistance value of the phase voltage sampling resistor is greater than the resistance value of the first line voltage sampling resistor or the resistance value of the second line voltage sampling resistor.

[0014] In one example, at least one of an LCL filter, an AC switch, and an EMI filter is provided between the AC terminal of the inverter unit and the load or between the AC terminal of the inverter unit and the power grid.

[0015] The inverter provided in this application improves the system impedance by changing the voltage sampling method, ensuring that the system impedance still meets national standards when the inverter is in parallel operation, thereby enhancing system safety and reliability. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the equivalent impedance under an existing voltage sampling method;

[0017] Figure 2 This is a schematic diagram of the equivalent impedance under another existing voltage sampling method;

[0018] Figure 3 A schematic diagram of an inverter provided in an embodiment of this application;

[0019] Figure 4 A schematic diagram of the equivalent impedance under the voltage sampling method provided in the embodiments of this application.

[0020] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0021] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer and more understandable, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit the scope of this application.

[0022] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0023] Figure 3 A schematic diagram of an inverter provided for an embodiment of this application.

[0024] like Figure 1 As shown, the inverter includes an inverter unit (DC / AC unit in the figure). The AC terminal of the inverter unit is connected to the load and the power grid via a three-phase four-wire connection (phase A, phase B, phase C, and neutral line N in the figure). Specifically, the AC terminal of the inverter unit is connected to the load and the power grid in sequence via an LCL filter, an AC switch, and an EMI filter. The LCL filter includes the filter inductor L shown in the figure. f Filter capacitor C f and filter inductor L g The AC switch includes an AC relay, and the EMI filter can be connected to the power grid through a grid-connected transformer, etc. The remote neutral line N is grounded (PE).

[0025] In one example, the inverter further includes a voltage sampling unit and a control unit;

[0026] The voltage sampling unit includes a first line voltage sampling unit, a second line voltage sampling unit, and a phase voltage sampling unit. The first line voltage sampling unit is used to sample the first line voltage, the second line voltage sampling unit is used to sample the second line voltage, and the phase voltage sampling unit is used to sample the phase voltage of one of the phase lines.

[0027] The control unit is configured to acquire the first line voltage, the second line voltage, and the phase voltage of one of the phase lines, and to determine the phase voltages of the other two phase lines based on the first line voltage, the second line voltage, and the phase voltage of one of the phase lines.

[0028] The voltage sampling unit includes at least one of an inverter output voltage sampling unit, a grid voltage sampling unit, and a load voltage sampling unit.

[0029] For example, when the voltage sampling unit is an inverter output voltage sampling unit, it includes a corresponding first line voltage sampling unit, a second line voltage sampling unit, and a phase voltage sampling unit. The first line voltage sampling unit can sample the line voltage between phases A and B, the second line voltage sampling unit can sample the line voltage between phases B and C, and the phase voltage sampling unit can sample the phase voltage between phase C and the neutral line N. It can be understood that it can also sample the voltage between phases A, C, and BN, or the voltage between phases B, C, C, and AN.

[0030] When the voltage sampling unit is a grid voltage sampling unit or a load voltage sampling unit, it has a corresponding first line voltage sampling unit, a second line voltage sampling unit, and a phase voltage sampling unit. The sampling method can refer to the above method.

[0031] In one example, the first line voltage sampling unit includes a first line voltage sampling resistor, the second line voltage sampling unit includes a second line voltage sampling resistor, and the phase voltage sampling unit includes a phase voltage sampling resistor. The total equivalent impedance to ground based on the first line voltage sampling resistor, the second line voltage sampling resistor, and the phase voltage sampling resistor is greater than 1 MΩ.

[0032] In one example, the resistance value of the phase voltage sampling resistor is greater than the resistance value of the first line voltage sampling resistor or the resistance value of the second line voltage sampling resistor.

[0033] Thus, through the above-mentioned hybrid sampling method, relative to Figures 1-2 The sampling method of voltage between the ABC and N lines can improve the system impedance and ensure that the system impedance still meets the national standard requirements when the inverter is in parallel, thereby enhancing the system safety and reliability.

[0034] The following combination Figure 2 , Figure 4 Comparative explanation:

[0035] Since the neutral line N is grounded at the far end, the phase voltage sampling resistor is equivalent to being connected to PE, thus being incorporated into the original system impedance. The following calculations assume that the original system impedance to ground is infinite; therefore, after connecting the sampling resistor in parallel, the system impedance to ground can be equivalent to the equivalent impedance of the machine's sampling resistor.

[0036] If adopted Figure 2 The sampling method shown below results in the equivalent impedance to ground as shown in Equation 1:

[0037]

[0038] If adopted Figure 4 The equivalent impedance to ground for the hybrid sampling method shown is given by Equation 2 below:

[0039]

[0040] In the above formula, R inv R is the sampling resistor for the single-phase voltage of the inverter output; grid R is the sampling resistor for single-phase voltage of the power grid. dc This is the single-phase sampling resistor for the load voltage.

[0041] For ease of calculation demonstration, the following example uses mixed sampling with V. ab V bc V cn That is, sampling the line voltage between phases AB, sampling the line voltage between phases BC, and sampling the phase voltage between phase C and the neutral line N.

[0042] The measured values ​​of V were obtained for the inverter output voltage, grid voltage, and DC component of the load voltage. cn V was then calculated. an V bn The voltage value is as follows: (Equation 3)

[0043] V an =V ab +V bn

[0044] V bn =V bc +V cn

[0045] In the formula:

[0046] V ab V is the line voltage between A and B. bc The line voltage between B and C, V an V bn V cn These are the phase voltages between AN, BN, and CN, respectively.

[0047] As can be seen from Equations 1 and 2, if the sampling resistors remain unchanged and only the influence of the sampling resistors of the two phase voltages is removed, the system impedance can be increased by three times.

[0048] In common sampling circuits, the sampling resistor is often in the range of 2MΩ to 3MΩ. If it is a traditional phase voltage sampling scheme, the sampling resistors for the inverter output voltage sampling, grid voltage sampling, and load voltage sampling inside the inverter are connected in parallel, and the total equivalent impedance to ground is in the range of 222kΩ to 333kΩ. If a hybrid sampling method is used, the total equivalent impedance to ground is in the range of 666kΩ to 1MΩ. Even if this sampling scheme increases the system impedance by three times, it still does not meet the national standard requirement that the machine system impedance be greater than 1MΩ.

[0049] To address this issue, the sampling of one phase voltage can be further optimized. The sampling resistor for a certain phase voltage of the DC component of the inverter output voltage, grid voltage, and load voltage can be increased to 4MΩ or higher. The sampling resistors of the other two line voltage sampling circuits only need to meet the requirements of resistance withstand voltage, and there is no need to increase them. In this case, the total equivalent impedance to ground is above 1.3MΩ, which meets the national standard requirements.

[0050] The preferred embodiments of this application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and spirit of this application shall be within the scope of the claims.

Claims

1. An inverter, characterized by, The inverter comprises an inverter unit, AC ends of the inverter unit being connected with a load and a power grid through a three-phase four-wire connection mode; The inverter further comprises a voltage sampling unit and a control unit; The voltage sampling unit comprises a first line voltage sampling unit, a second line voltage sampling unit and a phase voltage sampling unit, the first line voltage sampling unit being configured to sample a first line voltage, the second line voltage sampling unit being configured to sample a second line voltage, and the phase voltage sampling unit being configured to sample a phase voltage of one phase line; The control unit is configured to acquire the first line voltage, the second line voltage and the phase voltage of the one phase line, and determine phase voltages of the other two phase lines based on the first line voltage, the second line voltage and the phase voltage of the one phase line.

2. The inverter of claim 1, wherein, The voltage sampling unit comprises at least one of an inverter output voltage sampling unit, a power grid voltage sampling unit and a load voltage sampling unit.

3. The inverter of claim 1, wherein, The first line voltage sampling unit comprises a first line voltage sampling resistor, the second line voltage sampling unit comprises a second line voltage sampling resistor, and the phase voltage sampling unit comprises a phase voltage sampling resistor.

4. The inverter of claim 3, wherein, A total equivalent impedance of the first line voltage sampling resistor, the second line voltage sampling resistor and the phase voltage sampling resistor is greater than 1 MΩ.

5. The inverter of claim 3, wherein, The resistance of the phase voltage sampling resistor is greater than the resistance of the first line voltage sampling resistor or the resistance of the second line voltage sampling resistor.

6. The inverter of claim 1, wherein, At least one of an LCL filter, an AC switch and an EMI filter is further arranged between the AC ends of the inverter unit and the load or between the AC ends of the inverter unit and the power grid.

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