DC-to-ground insulation impedance detection circuit and method suitable for multi-channel DC input

Abstract

The present invention relates to the technical field of power supply, and in particular to a DC-to-ground insulation impedance detection circuit and method applicable to multiple DC inputs, comprising a controller and a DC-to-ground insulation impedance detection component, characterized in that the DC-to-ground insulation impedance detection circuit component comprises: DC side insulation impedance, a relay S0, and a resistor R0; the DC side insulation impedance of the multiple DC inputs comprises an equivalent total impedance Riso of all DC inputs to ground and a two-terminal network open-circuit voltage Vx, and the equivalent total impedance Riso of all DC inputs to ground is an equivalent total impedance of a plurality of DC bus positive electrodes BUS+ to earth / casing PE impedances and a plurality of DC bus negative electrodes BUS‑ to earth / casing PE impedances; the key point of the present invention is that the power switch tube originally existing in the DC / AC converter is utilized, the use of relays is saved, the cost is reduced, and the present invention is applicable to multiple DC inputs and detects the equivalent impedances of all DC inputs.

Description

Technical Field

[0001] The invention relates to the technical field of power supply, in particular to a direct current to ground insulation impedance detection circuit and method suitable for multi-channel direct current input. Background Art

[0002] As a commonly used electrical device, the converter can change the voltage, frequency, number of phases and other electrical quantities or characteristics of the power system, and its application is very extensive. According to the actual application occasions, some occasions need to convert AC power into DC power, which is defined as a rectifier circuit; in other occasions, it is necessary to convert DC power into AC power, which corresponds to the reverse process of rectification and is defined as an inverter circuit. Under certain conditions, a set of thyristor circuits can be used as both a rectifier circuit and an inverter circuit. This device is called a converter.

[0003] Converter types include rectifiers (AC to DC), inverters (DC to AC), AC converters (AC frequency converters) and DC converters (DC choppers). For non-isolated grid-connected DC / AC converters, such as photovoltaic grid-connected inverters, if the DC connection insulation impedance is too low, it may cause personal injury or equipment damage, so it is necessary to detect the DC side to ground insulation impedance before grid connection.

[0004] A DC insulation impedance detection scheme commonly used in the prior art is as follows: Figure 1 As shown in the figure, the schematic diagram of the DC side insulation impedance in the dotted box includes the DC side power supply and the DC bus positive pole (BUS+) to the earth / casing (PE) impedance Rp, and the DC bus negative pole (BUS-) to the earth / casing (PE) impedance Rn. By changing the voltage of BUS+ / BUS- to PE by turning on and off relays S1 and S2, two equations about Rp and Rn are obtained, and Rp and Rn are solved. This technology requires two relays and other auxiliary circuits, which is costly and is not suitable for use with multiple DC inputs at the same time. Summary of the invention

[0005] The present invention provides a high-precision DC-to-ground insulation impedance detection circuit and method to solve the problem that the existing DC insulation impedance detection cost is too high and the efficiency needs to be improved.

[0006] To achieve the above objectives, a first aspect of the present invention provides a DC-to-ground insulation impedance detection component suitable for multiple DC inputs, comprising a controller, a DC / AC converter, and a DC-to-ground insulation impedance detection component.

[0007] The power topology of the DC / AC converter has a bridge arm characteristic topology, and is provided with a bridge arm upper power switch tube group and a bridge arm lower power switch tube group;

[0008] The DC-to-ground insulation impedance detection component includes: DC-side insulation impedance, relay S0, and resistor R0; according to Thevenin theorem, all DC-side power supplies and insulation impedances to ground are equivalent to a two-terminal network, the two-terminal network includes all DC inputs to ground equivalent total impedance Riso, and the two-terminal network open-circuit voltage Ux, and all DC inputs to ground equivalent total impedance Riso is the equivalent total impedance of several DC bus positive poles BUS+ to ground / casing PE impedance, and several DC bus negative poles BUS- to ground / casing PE impedance;

[0009] One end of the earth / casing PE is connected to the DC side insulation impedance, and the other end is connected to one of the midpoints of the bridge arms of the existing power topology of the DC / AC converter through a series circuit of a relay S0 and a resistor R0. The controller changes the voltage on the resistor R0 and detects the voltage on the resistor R0 by controlling the opening and closing of the power switch tube group on the upper bridge arm and the power switch tube group on the lower bridge arm.

[0010] Preferably, an inductor L1 may be connected in series in the series circuit of the relay S0 and the resistor R0.

[0011] Preferably, the relay S0 and the resistor R0 can exchange positions.

[0012] Preferably, it is applicable to topologies with bridge arm characteristics in DC / AC topologies, including but not limited to single-phase H4 full bridge, H5 topology, H6 topology, Heric topology, three-phase NPC topology, multi-level topology, etc.

[0013] Preferably, the power switch tube group at the upper part of the bridge arm includes a first switch tube Q1; and the power switch tube group at the lower part of the bridge arm includes a second switch tube Q2.

[0014] Preferably, the power switch tube group at the upper part of the bridge arm includes a first switch tube Q1, a second switch tube Q2 and a third switch tube Qm connected in series; and the power switch tube group at the lower part of the bridge arm includes a fourth switch tube Qn.

[0015] Preferably, when used in a three-level or multi-level topology, one end of the relay S0 and the resistor R0 can be connected to any point in the middle of the bridge arm; or can be connected to any other point with the same potential as the middle point of the bridge arm.

[0016] To achieve the above object, another aspect of the present invention provides a DC-to-ground insulation impedance detection method applicable to multiple DC inputs, which is applied to the insulation impedance detection circuit. The specific implementation method is as follows:

[0017] S1, the controller controls the relay S0 to close, controls the upper power switch tube group of the bridge arm to turn on, and the lower power switch tube group of the bridge arm to turn off, and measures the voltage of the negative pole of the DC bus BUS- to the chassis PE, recorded as Viso1, and obtains the equation

[0018] Viso1=Ux*R0 / (Riso+R0)+Vbus*Riso / (Riso+R0)①

[0019] Among them, Viso1 is the voltage between the negative pole of the S1 DC bus BUS- and the chassis PE, Ux is the open circuit voltage of the two-terminal network, Riso is the equivalent total impedance of the DC input to the ground, R0 is the resistance, and Vbus is the voltage between the sampling chassis PE and the negative pole of the bus;

[0020] S2, the controller controls the relay S0 to close, controls the upper power switch tube group of the bridge arm to turn off, and the lower power switch tube group of the bridge arm to turn on. The voltage between the negative pole of the DC bus BUS- and the chassis (PE) is measured, recorded as Viso2, and equation ② is obtained.

[0021] Viso2=Ux*R0 / (Riso+R0)②

[0022] Among them, Viso2 is the voltage between the negative pole BUS- of S2 DC bus and the chassis PE, Ux is the open circuit voltage of the two-terminal network, Riso is the equivalent total impedance of DC input to ground, and R0 is the resistance;

[0023] S3, combined equations ①②, the insulation resistance is calculated as:

[0024] Riso=R0 / [Vbus / (Viso1-Viso2)-1] ③

[0025] Wherein, Riso is the equivalent total impedance of DC input to ground, Vbus is the voltage between the sampling case PE and the negative pole of the bus, Viso1 is the voltage between the negative pole BUS- of the S1 DC bus and the case PE, and Viso2 is the voltage between the negative pole BUS- of the S2 DC bus and the case PE.

[0026] The present invention has the following beneficial effects:

[0027] The present invention is a low-cost DC insulation impedance detection solution, which is suitable for multi-channel DC inputs and detects the equivalent impedance of all DC inputs. The circuit is simple and the cost is low. It is also suitable for all topologies with bridge arm characteristics in DC / AC topologies, including but not limited to single-phase H4 full bridge, H5 topology, H6 topology, Heric topology, three-phase NPC topology, multi-level topology, etc. The key is to use two relays to switch on and off to obtain two equations about Ux and Riso. The present invention uses one of the bridge arms of the existing power topology of the DC / AC converter. When the DC bus voltage remains unchanged, only one relay is needed, the circuit is simple and the cost is low. The key to the present invention is to use the power switch tube that originally existed in the DC / AC converter, which saves the use of relays, simplifies the circuit structure, and effectively reduces the manufacturing cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0029] Figure 1 It is a structural schematic diagram of an insulation impedance detection circuit provided in the prior art;

[0030] Figure 2 The structure of a DC-to-ground insulation impedance detection circuit suitable for multiple DC inputs provided in an embodiment of the present application is schematically shown. Figure 1 .

[0031] Figure 3 The structure of a DC-to-ground insulation impedance detection circuit suitable for multiple DC inputs provided in an embodiment of the present application is schematically shown. Figure 2 .

[0032] Figure 4 It is a flow chart of a DC-to-ground insulation impedance detection method applicable to multi-channel DC inputs provided in an embodiment of the present application. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0034] The terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions.

[0035] The technical solution of the present application is described in detail with specific embodiments below. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments.

[0036] The DC-to-ground insulation impedance detection circuit and method of the present application are used to detect whether the DC input terminal of the inverter is short-circuited to the ground or has low impedance. The insulation impedance detection circuit can prevent the DC input terminal of the inverter from being short-circuited to the ground or having low impedance before the inverter is connected to the grid and when the casing is not grounded, thereby preventing grid insulation failure. The insulation impedance detection circuit can be applied to solar panel grid-connected systems, and can also be applied to other DC-to-AC and AC-to-DC systems.

[0037] In an embodiment of the present application, the relay switch of the relay in the inverter circuit is connected in parallel with the impedance device, and the change in the measured value between the DC input terminal of the inverter and the grounding point is detected by switching the switching state of the relay switch of the relay. If the DC input terminal of the inverter and the grounding point are short-circuited to the ground or have low impedance, the measured value changes little or does not change, thereby determining whether the DC input terminal of the inverter is short-circuited to the ground or has low impedance. Example

[0038] like Figure 2 As shown, a DC-to-ground insulation impedance detection circuit suitable for multiple DC inputs includes a controller, a DC / AC converter, and a DC-to-ground insulation impedance detection component.

[0039] The power topology of the DC / AC converter has a bridge arm characteristic topology, and is provided with a bridge arm upper power switch tube group and a bridge arm lower power switch tube group;

[0040] The DC-to-ground insulation impedance detection circuit assembly includes: DC side insulation impedance, relay S0, and resistor R0;

[0041] This embodiment takes the DC side insulation impedance of multiple DC inputs as an example, which is applicable to multiple DC inputs and detects the equivalent impedance of all DC inputs. According to Thevenin's theorem, Figure 1 The two-terminal network in the dashed box is equivalent to Figure 2 The two-terminal network in the dotted box includes the equivalent total impedance Riso of all DC inputs to ground and the open-circuit voltage Ux of the two-terminal network. The equivalent total impedance Riso of all DC inputs to ground is the equivalent total impedance of the positive pole BUS+ of several DC buses to the ground / casing PE impedance and the negative pole BUS- of several DC buses to the ground / casing PE impedance.

[0042] One end of the earth / casing PE is connected to the DC side insulation impedance, and the other end is connected to one of the midpoints of the bridge arms of the existing power topology of the DC / AC converter through a series circuit of a relay S0 and a resistor R0. The controller changes the voltage on the resistor R0 and detects the voltage on the resistor R0 by controlling the opening and closing of the power switch tube group on the upper bridge arm and the power switch tube group on the lower bridge arm.

[0043] Preferably, the power switch tube group at the upper part of the bridge arm includes a first switch tube Q1; and the power switch tube group at the lower part of the bridge arm includes a second switch tube Q2.

[0044] Preferably, the power switch tube group at the upper part of the bridge arm includes a first switch tube Q1, a second switch tube Q2 and a third switch tube Qm connected in series; and the power switch tube group at the lower part of the bridge arm includes a fourth switch tube Qn.

[0045] like Figure 4 As shown, a DC-to-ground insulation impedance detection method applicable to multiple DC inputs is applied to an insulation impedance detection circuit, and the specific implementation method is as follows:

[0046] S1, the controller controls the relay S0 to close, controls the upper power switch tube group of the bridge arm to turn on, and the lower power switch tube group of the bridge arm to turn off, and measures the voltage of the negative pole of the DC bus BUS- to the chassis PE, recorded as Viso1, and obtains the equation

[0047] Viso1=Ux*R0 / (Riso+R0)+Vbus*Riso / (Riso+R0) ①

[0048] Among them, Viso1 is the voltage between the negative pole of the S1 DC bus BUS- and the chassis PE, Ux is the open circuit voltage of the two-terminal network, Riso is the equivalent total impedance of the DC input to the ground, R0 is the resistance, and Vbus is the voltage between the sampling chassis PE and the negative pole of the bus;

[0049] S2, the controller controls the relay S0 to close, controls the upper power switch tube group of the bridge arm to turn off, and the lower power switch tube group of the bridge arm to turn on. The voltage between the negative pole of the DC bus BUS- and the chassis (PE) is measured, recorded as Viso2, and equation ② is obtained.

[0050] Viso2=Ux*R0 / (Riso+R0) ②

[0051] Among them, Viso2 is the voltage between the negative pole BUS- of S2 DC bus and the chassis PE, Ux is the open circuit voltage of the two-terminal network, Riso is the equivalent total impedance of DC input to ground, and R0 is the resistance;

[0052] S3, combined equations ①②, the insulation resistance is calculated as:

[0053] Riso=R0 / [Vbus / (Viso1-Viso2)-1] ③

[0054] Wherein, Riso is the equivalent total impedance of DC input to ground, Vbus is the voltage between the sampling case PE and the negative pole of the bus, Viso1 is the voltage between the negative pole BUS- of the S1 DC bus and the case PE, and Viso2 is the voltage between the negative pole BUS- of the S2 DC bus and the case PE. Example

[0055] Figure 2 It is just a schematic diagram of one embodiment of the present invention. Figure 3 As shown, the relay S0 and the resistor R0 can exchange positions; the inductor L1 can also be connected in series in the series circuit of the relay S0 and the resistor R0. When used in a three-level or multi-level topology, one end of the relay S0 and the resistor R0 can be connected to any point in the middle of the bridge arm; or it can be connected to any other point with the same potential as the middle point of the bridge arm.

[0056] Regardless of the first or second embodiment, it is applicable to topologies with bridge arm characteristics in DC / AC topologies, including but not limited to single-phase H4 full bridge, H5 topology, H6 topology, Heric topology, three-phase NPC topology, multi-level topology, etc. of photovoltaic inverters. When used in a three-level or multi-level topology, one end of the relay S0 and the resistor R0 can be connected to any point in the middle of the bridge arm; or it can be connected to any other point with the same potential as the midpoint of the bridge arm.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A DC-to-ground insulation impedance detection circuit suitable for multiple DC inputs, comprising a controller, a DC / AC converter, and a DC-to-ground insulation impedance detection component, characterized in that: The power topology of the DC / AC converter has a bridge arm characteristic topology, and is provided with a bridge arm upper power switch tube group and a bridge arm lower power switch tube group; The DC-to-ground insulation impedance detection component includes: DC-side insulation impedance, relay S0, and resistor R0; according to Thevenin theorem, all DC-side power supplies and insulation impedances to ground are equivalent to a two-terminal network, the two-terminal network includes all DC input equivalent total impedance to ground Riso, and the two-terminal network open-circuit voltage Ux, and all DC input equivalent total impedance to ground Riso is the equivalent total impedance of several DC bus positive poles BUS+ to the earth / casing PE impedance, and several DC bus negative poles BUS- to the earth / casing PE impedance; one end of the earth / casing PE is connected to the DC-side insulation impedance The other end is connected to the midpoint of one of the bridge arms of the existing power topology of the DC / AC converter through a series circuit of a relay S0 and a resistor R0. The controller changes the voltage on the resistor R0 and detects the voltage on the resistor R0 by controlling the opening and closing of the power switch tube group on the upper part of the bridge arm and the power switch tube group on the lower part of the bridge arm. The inductor L1 can also be connected in series in the series circuit of the relay S0 and the resistor R0. The power switch tube group on the upper part of the bridge arm includes a first switch tube Q1, a second switch tube Q2 and a third switch tube Qm connected in series; the power switch tube group on the lower part of the bridge arm includes a fourth switch tube Qn.

2. A DC-to-ground insulation impedance detection circuit suitable for multiple DC inputs as claimed in claim 1, characterized in that: Applicable to topologies with bridge arm characteristics in DC / AC topologies, including but not limited to single-phase H4 full bridge, H5 topology, H6 topology, Heric topology, three-phase NPC topology, multi-level topology, etc.

3. A DC-to-ground insulation impedance detection circuit suitable for multiple DC inputs as claimed in claim 1, characterized in that: When used in a three-level or multi-level topology, one end of the relay S0 and the resistor R0 is connected to any point in the middle of the bridge arm, or to any other point with the same potential as the middle point of the bridge arm.

4. A DC-to-ground insulation impedance detection method applicable to multiple DC inputs, characterized in that: Applied to the insulation impedance detection circuit as described in any one of claims 1 to 3, the specific implementation is as follows: S1, the controller controls the relay S0 to close, controls the upper power switch tube group of the bridge arm to turn on, and the lower power switch tube group of the bridge arm to turn off, and measures the voltage of the negative pole of the DC bus BUS- to the chassis PE, recorded as Viso1, and obtains the equation Viso1=Ux*R0 / (Riso+R0)+Vbus*Riso / (Riso+R0)① Among them, Viso1 is the voltage between the negative pole of the S1 DC bus BUS- and the chassis PE, Ux is the open circuit voltage of the two-terminal network, Riso is the equivalent total impedance of the DC input to the ground, R0 is the resistance, and Vbus is the voltage between the sampling chassis PE and the negative pole of the bus; S2, the controller controls the relay S0 to close, controls the upper power switch tube group of the bridge arm to turn off, and the lower power switch tube group of the bridge arm to turn on. The voltage between the negative pole of the DC bus BUS- and the chassis (PE) is measured, recorded as Viso2, and equation ② is obtained. Viso2=Ux*R0 / (Riso+R0)② Among them, Viso2 is the voltage between the negative pole BUS- of S2 DC bus and the chassis PE, Ux is the open circuit voltage of the two-terminal network, Riso is the equivalent total impedance of DC input to ground, and R0 is the resistance; S3, combined equations ①②, the insulation resistance is calculated as: Riso=R0 / [Vbus / (Viso1-Viso2)-1]③ Wherein, Riso is the equivalent total impedance of DC input to ground, Vbus is the voltage between the sampling case PE and the negative pole of the bus, Viso1 is the voltage between the negative pole BUS- of the S1 DC bus and the case PE, and Viso2 is the voltage between the negative pole BUS- of the S2 DC bus and the case PE.

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