DC-to-ground insulation impedance detection circuit and method for variable bus voltage

Abstract

The present invention relates to the field of power supply technology, specifically a circuit and method for detecting DC-to-ground insulation impedance with variable bus voltage. The circuit comprises a topology with a variable DC bus voltage; components of the DC-to-ground insulation impedance detection circuit include: DC-side insulation impedance, a relay S0, a resistor R0, and a measured voltage Viso between the DC bus negative electrode BUS- and the housing PE; one end of the earth / housing PE is connected to the DC-side insulation impedance, and the other end is connected to the DC bus negative electrode BUS- in an existing power topology of a DC / AC converter with variable DC bus voltage via a series circuit comprising a relay S0 and a resistor R0. The present invention is a low-cost DC insulation impedance detection solution suitable for multiple DC inputs, capable of detecting the equivalent impedance of all DC inputs. The circuit is simple and low-cost. The key to the present invention is that it utilizes the variable DC bus voltage, requiring only a single relay, resulting in a simple circuit, saving relays and reducing costs.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply, and in particular to a circuit and method for detecting direct current-to-ground insulation impedance with variable bus voltage. Background Art

[0002] Converters are common electrical devices that can alter the voltage, frequency, number of phases, and other electrical quantities or characteristics of a power system, and they are widely used. Depending on the application, some applications require converting AC power to DC power, defined as a rectifier circuit; others require converting DC power to AC power, corresponding to the reverse process of rectification, defined as an inverter circuit. Under certain conditions, a thyristor circuit can function as both a rectifier 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, low DC-to-ground insulation resistance can cause personal injury or equipment damage. Therefore, it is necessary to test the DC-side insulation resistance before grid connection.

[0004] A DC insulation impedance detection solution commonly used in the prior art is Figure 1 The dashed box shows the DC-side insulation impedance diagram, including the DC-side power supply and DC bus positive (BUS+) impedance to earth / chassis (PE), Rp, and the DC bus negative (BUS-) impedance to earth / chassis (PE), Rn. By switching relays S1 and S2 on and off to change the voltages between BUS+ and BUS- relative to PE, two equations for Rp and Rn are derived, allowing Rp and Rn to be solved. This technique requires two relays and other auxiliary circuitry, resulting in high cost and unsuitable for applications with multiple DC inputs. Summary of the Invention

[0005] The present invention provides a high-precision DC-to-ground insulation impedance detection circuit and method, so as to solve the problem that the existing DC insulation impedance detection is too costly and has a low efficiency.

[0006] To achieve the above object, a first aspect of the present invention provides a DC-to-ground insulation impedance detection circuit for a variable bus voltage, comprising a controller, a DC / AC converter, and a DC-to-ground insulation impedance detection component, characterized in that:

[0007] The power topology of the DC / AC converter has a topology with a variable DC bus voltage;

[0008] The DC-to-ground insulation impedance detection circuit assembly includes: DC side insulation impedance, relay S0, resistor R0, and measurement voltage Viso of DC bus negative pole BUS- to chassis PE;

[0009] One end of the earth / chassis PE is connected to the DC side insulation impedance, and the other end is connected to one of the DC bus voltage variable topologies in the existing power topology of the DC / AC converter through a series circuit of relay S0 and resistor R0 to the DC bus negative electrode BUS-. The controller controls the DC bus voltage change to detect the voltage between the DC bus negative electrode BUS- and the chassis PE.

[0010] Preferably, the relay S0 and the resistor R0 can be exchanged.

[0011] Preferably, the topology with variable DC bus voltage is a BOOST circuit topology.

[0012] Preferably, the DC side insulation impedance of a single DC input includes the DC side power supply, the DC bus positive pole BUS+, the DC bus negative pole BUS-, the DC bus positive pole (BUS+) to earth / casing (PE) impedance Rp, and the DC bus negative pole (BUS-) to earth / casing (PE) impedance Rn.

[0013] Preferably, according to Thevenin's theorem, all DC side power supplies and insulation impedances to ground are equivalent to a two-terminal network, and the DC side insulation impedance of multiple DC inputs includes the equivalent total impedance Riso of all DC inputs to ground and the open-circuit voltage Ux of the two-terminal network.

[0014] Preferably, the equivalent total impedance Riso of all DC inputs to ground is the equivalent total impedance of the impedances of several DC bus positive poles BUS+ to ground / casing PE and several DC bus negative poles BUS- to ground / casing PE.

[0015] To achieve the above object, another aspect of the present invention provides a method for detecting DC-to-ground insulation impedance with variable bus voltage, which is applied to the above insulation impedance detection circuit. The specific implementation is as follows:

[0016] S1, the controller controls the relay S0 to close, the DC bus voltage is Vbus1, and the voltage between the DC bus negative pole BUS- and the chassis PE is measured and recorded as Viso1. Equation ① is obtained.

[0017] Viso1=Ux*R0 / (Riso+R0)+Vbus1*Riso / (Riso+R0) ①

[0018] Where 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, Vbus1 is the S1 DC bus voltage, Riso is the equivalent total impedance of the DC input to ground, and R0 is the resistance;

[0019] S2, the controller controls the relay S0 to close, changing the DC bus voltage to Vbus2, and measuring the voltage between the DC bus negative pole BUS- and the chassis PE, recorded as Viso2. Equation ② is obtained.

[0020] Viso2=Ux*R0 / (Riso+R0)+Vbus2*Riso / (Riso+R0) ②

[0021] Where Viso2 is the voltage between the negative pole of the S2 DC bus BUS- and the chassis PE, Ux is the open-circuit voltage of the two-terminal network, Vbus2 is the change in DC bus voltage, Riso is the equivalent total impedance of the DC input to ground, and R0 is the resistance;

[0022] S3, using equations ① and ②, the insulation resistance is calculated as:

[0023] Riso=R0 / [(Vbus1-Vbus2) / (Viso1-Viso2)-1] ③

[0024] Wherein, Riso is the equivalent total impedance of the DC input to ground, Vbus1 is the DC bus voltage of S1, Vbus2 is the changed DC bus voltage, Viso1 is the voltage between the negative pole BUS- of the DC bus of S1 and the chassis PE, and Viso2 is the voltage between the negative pole BUS- of the DC bus of S2 and the chassis PE.

[0025] The present invention has the following beneficial effects:

[0026] The present invention is a low-cost DC insulation impedance detection solution suitable for multi-channel DC inputs. It can detect the equivalent impedance of all DC inputs, has a simple circuit and low cost. The key to the present invention is that it utilizes the variable voltage characteristic of the DC busbar. Only one relay is required, the circuit is simple, the use of relays is saved, and the cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 any creative labor.

[0028] Figure 1 This is a structural diagram of an insulation impedance detection circuit provided in the prior art;

[0029] Figure 2 This is a schematic diagram of a DC-to-ground insulation impedance detection circuit suitable for multiple DC inputs provided in an embodiment of the present application. Figure 1 .

[0030] Figure 3 This is a flow chart of a DC-to-ground insulation impedance detection method applicable to multiple DC inputs provided in an embodiment of the present application. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0032] The terms "first," "second," "third," "fourth," and so forth (if any) in the specification and claims of this application and in the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the application described herein can be implemented in orders other than those illustrated or described herein. In addition, the terms "including," "having," and any variations thereof are intended to cover non-exclusive inclusions.

[0033] The following specific embodiments are used to describe the technical solution of the present application in detail. 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.

[0034] The DC-to-ground insulation impedance detection circuit and method disclosed herein are used to detect whether the DC input terminal of an inverter is short-circuited to ground or exhibits low impedance. This insulation impedance detection circuit can prevent short-circuit or low impedance at the DC input terminal of the inverter before the inverter is connected to the grid and when the inverter housing is ungrounded, thereby preventing grid insulation failure. This insulation impedance detection circuit can be applied to solar panel grid-connected systems, as well as other DC-to-AC and AC-to-DC systems.

[0035] 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 switching state of the relay switch of the relay is switched to detect the change of the measured value between the DC input terminal of the inverter and the grounding point. 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

[0036] like Figure 2 As shown, a DC-to-ground insulation impedance detection circuit for variable bus voltage includes a controller, a DC / AC converter, and a DC-to-ground insulation impedance detection component, characterized in that:

[0037] The power topology of the DC / AC converter has a topology with a variable DC bus voltage. In this embodiment, the topology with a variable DC bus voltage is a BOOST circuit topology.

[0038] The DC-to-ground insulation impedance detection circuit assembly includes: DC side insulation impedance, relay S0, resistor R0, and measurement voltage Viso of DC bus negative pole BUS- to chassis PE;

[0039] One end of the earth / chassis PE is connected to the DC side insulation impedance, and the other end is connected to one of the DC bus voltage variable topologies in the existing power topology of the DC / AC converter through a series circuit of relay S0 and resistor R0 to the DC bus negative electrode BUS-. The controller controls the DC bus voltage change to detect the voltage between the DC bus negative electrode BUS- and the chassis PE.

[0040] In this embodiment, the DC side insulation impedance of a single DC input is taken as an example, including the DC side power supply, the DC bus positive electrode BUS+, the DC bus negative electrode BUS-, the DC bus positive electrode (BUS+) to the ground / chassis (PE) impedance Rp, and the DC bus negative electrode (BUS-) to the ground / chassis (PE) impedance Rn.

[0041] Preferably, the relay S0 and the resistor R0 can be exchanged. Example

[0042] In this embodiment, using the DC-side insulation impedance of multiple DC inputs as an example, according to Thevenin's theorem, all DC-side power supplies and their insulation impedance to ground are equivalent to a two-terminal network, comprising the equivalent total impedance of all DC inputs to ground, Riso, and the open-circuit voltage of the two-terminal network, Ux. The equivalent total impedance of all DC inputs to ground, Riso, is the equivalent total impedance of the impedances of the positive DC bus electrodes (BUS+) to ground / the chassis (PE), and the negative DC bus electrodes (BUS-) to ground / the chassis (PE).

[0043] like Figure 3 As shown, a method for detecting DC-to-ground insulation impedance with variable bus voltage is applied to the above insulation impedance detection circuit. The specific implementation method is as follows:

[0044] S1, the controller controls the relay S0 to close, the DC bus voltage is Vbus1, and the voltage between the DC bus negative pole BUS- and the chassis PE is measured and recorded as Viso1. Equation ① is obtained.

[0045] Viso1=Ux*R0 / (Riso+R0)+Vbus1*Riso / (Riso+R0) ①

[0046] Where 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, Vbus1 is the S1 DC bus voltage, Riso is the equivalent total impedance of the DC input to ground, and R0 is the resistance;

[0047] S2, the controller controls the relay S0 to close, changing the DC bus voltage to Vbus2, and measuring the voltage between the DC bus negative pole BUS- and the chassis PE, recorded as Viso2. Equation ② is obtained.

[0048] Viso2=Ux*R0 / (Riso+R0)+Vbus2*Riso / (Riso+R0) ②

[0049] Where Viso2 is the voltage between the negative pole of the S2 DC bus BUS- and the chassis PE, Ux is the open-circuit voltage of the two-terminal network, Vbus2 is the change in DC bus voltage, Riso is the equivalent total impedance of the DC input to ground, and R0 is the resistance;

[0050] S3, using equations ① and ②, the insulation resistance is calculated as:

[0051] Riso=R0 / [(Vbus1-Vbus2) / (Viso1-Viso2)-1] ③

[0052] Wherein, Riso is the equivalent total impedance of the DC input to ground, Vbus1 is the DC bus voltage of S1, Vbus2 is the changed DC bus voltage, Viso1 is the voltage between the negative pole BUS- of the DC bus of S1 and the chassis PE, and Viso2 is the voltage between the negative pole BUS- of the DC bus of S2 and the chassis PE.

[0053] 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 them. 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 make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A DC-to-ground insulation impedance detection circuit for variable bus voltage, 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 topology with a variable DC bus voltage, and the topology with a variable DC bus voltage is a BOOST circuit topology; The DC-to-ground insulation impedance detection component includes: DC side insulation impedance, relay S0, resistor R0, and the measured voltage Viso of the DC bus negative pole BUS- to the earth / casing PE; the DC side insulation impedance of a single DC input includes the DC side power supply, the DC bus positive pole BUS+, the DC bus negative pole BUS-, 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; One end of the earth / chassis PE is connected to the DC side insulation resistance, and the other end is connected to one of the DC bus voltage variable topologies in the existing power topology of the DC / AC converter through a series circuit of relay S0 and resistor R0 to the DC bus negative electrode BUS-. The controller controls the DC bus voltage change to detect the voltage of the DC bus negative electrode BUS- relative to the earth / chassis PE.

2. A DC-to-ground insulation impedance detection circuit for variable bus voltage according to claim 1, characterized in that: Relay S0 and resistor R0 can swap positions.

3. A DC-to-ground insulation impedance detection circuit for variable bus voltage according to claim 1, characterized in that: According to Thevenin's theorem, all DC-side power supplies and insulation resistances to ground are equivalent to a two-terminal network. The DC-side insulation resistance of multiple DC inputs includes the equivalent total resistance Riso of all DC inputs to ground and the open-circuit voltage Ux of the two-terminal network.

4. A DC-to-ground insulation impedance detection circuit for variable bus voltage according to claim 1 or 3, characterized in that: The equivalent total impedance Riso of all DC inputs to ground is the equivalent total impedance of the impedances of several DC bus positive poles BUS+ to ground / casing PE, and the impedances of several DC bus negative poles BUS- to ground / casing PE.

5. A method for detecting DC-to-ground insulation impedance with variable bus voltage, characterized in that: The insulation impedance detection circuit according to any one of claims 1 to 4 is specifically implemented as follows: S1, the controller controls the relay S0 to close, the DC bus voltage is Vbus1, and the voltage between the negative pole of the DC bus BUS- and the earth / chassis PE is measured, recorded as Viso1, to obtain equation ① Viso1=Ux*R0 / (Riso+R0)+Vbus1*Riso / (Riso+R0) ① Where Viso1 is the voltage between the negative pole of the S1 DC bus BUS- and the earth / chassis PE, Ux is the open-circuit voltage of the two-terminal network, Vbus1 is the S1 DC bus voltage, Riso is the equivalent total impedance of the DC input to ground, and R0 is the resistance; S2, the controller controls relay S0 to close, changing the DC bus voltage to Vbus2, and measuring the voltage of the DC bus negative pole BUS- to the ground / case PE, recorded as Viso2, to obtain equation ② Viso2=Ux*R0 / (Riso+R0)+Vbus2*Riso / (Riso+R0) ② Where Viso2 is the voltage between the negative pole of the S2 DC bus BUS- and the earth / chassis PE, Ux is the open-circuit voltage of the two-terminal network, Vbus2 is the change in the DC bus voltage, Riso is the equivalent total impedance of the DC input to ground, and R0 is the resistance; S3, using equations ① and ②, the insulation resistance is calculated as: Riso=R0 / [(Vbus1-Vbus2) / (Viso1-Viso2)-1] ③ Where Riso is the equivalent total impedance of the DC input to ground, Vbus1 is the DC bus voltage of S1, Vbus2 is the changed DC bus voltage, Viso1 is the voltage between the negative electrode BUS- of the DC bus of S1 and the ground / case PE, and Viso2 is the voltage between the negative electrode BUS- of the DC bus of S2 and the ground / case PE.

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