CN112379172A - High-precision direct current ground insulation impedance detection circuit and method - Google Patents
High-precision direct current ground insulation impedance detection circuit and method Download PDFInfo
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Abstract
The invention relates to the technical field of power supplies, in particular to a high-precision direct current to ground insulation impedance detection circuit and a method, which are characterized in that the direct current to ground insulation impedance detection circuit comprises the following components: the device comprises a relay S1, a relay S2, a resistor R0, a constant current source Ic, a transistor Q and a current sampling circuit, wherein one end of the ground/casing PE is connected with a direct current side insulation impedance, the other end of the ground/casing PE is connected with the constant current source Ic and the current sampling circuit respectively through a three-terminal network formed by the relays S1, S2 and the resistor R0, and the constant current source Ic is connected with the current sampling circuit through the transistor Q. The key of the invention is to obtain two equations about Ux and Riso by switching on and off two relays; and a constant current source Ic is introduced to improve the current sampling precision when the Riso is smaller, thereby improving the Riso detection precision.
Description
Technical Field
The invention relates to the technical field of power supplies, in particular to a high-precision direct current ground insulation impedance detection circuit and method.
Background
The converter is used as a common electrical appliance, can change the voltage, frequency, phase number and other electric quantities or characteristics of a power supply system, and is widely applied. According to the practical application occasions, an alternating current power supply needs to be changed into a direct current power supply in some occasions, and the direct current power supply is defined as a rectifying circuit; in other cases, the dc power needs to be changed into ac power, and the inverter circuit is defined corresponding to the reverse process of rectification. Under certain conditions, a set of thyristor circuit can be used as both a rectifying circuit and an inverter circuit, and the device is called a converter.
Converter classes include rectifiers (AC to DC < AC/DC >), inverters (DC to AC < DC/AC >), AC converters (AC frequency converter < AC/AC >) and DC converters (DC Chopper < DC Chopper >). For a non-isolated grid-connected DC/AC converter, such as a photovoltaic grid-connected inverter, if the DC-to-ground insulation impedance is too low, it may cause personnel injury or equipment damage, so it is necessary to detect the DC-to-ground insulation impedance before grid-connected operation.
A scheme for detecting dc insulation resistance generally used in the prior art, as shown in fig. 1, a schematic diagram of dc side insulation resistance in a dashed line frame includes a dc side power supply, a dc BUS positive electrode (BUS +) resistance Rp to the ground/casing (PE), and a dc BUS negative electrode (BUS-) resistance Rn to the ground/casing (PE). The voltage of BUS +/BUS-to-PE is changed by switching on and off the relays S1 and S2, two equations about Rp and Rn are obtained, and Rp and Rn are solved. However, when Rp and Rn are much smaller than R1 or R2, when relays S1 and S2 are changed, Viso voltage changes little or Viso voltage approaches 0, and a small sampling error may result in a large calculation error of Riso.
Disclosure of Invention
The invention provides a high-precision direct current to ground insulation impedance detection circuit and a method, which aim to solve the problem that the existing direct current insulation impedance detection is insufficient in precision and large in error.
In order to achieve the above object, a first aspect of the present invention provides a high-precision dc-to-ground insulation resistance detection circuit, including a controller and a dc-to-ground insulation resistance detection module,
the DC-to-ground insulation resistance detection circuit assembly comprises: a DC side insulation resistance, a relay S1, a relay S2, a resistor R0, a constant current source Ic, a transistor Q, a current sampling circuit,
one end of the earth/casing PE is connected with the DC side insulation impedance, the other end of the earth/casing PE is respectively connected with the constant current source Ic and the current sampling circuit through a three-terminal network consisting of relays S1, S2 and a resistor R0, and the constant current source Ic and the current sampling circuit are connected through a transistor Q.
Preferably, the direct current side insulation impedance of the single direct current input comprises a direct current side power supply, a direct current BUS positive electrode BUS +, a direct current BUS negative electrode BUS-, a direct current BUS positive electrode (BUS +) impedance Rp to the earth/casing (PE), and a direct current BUS negative electrode (BUS-) impedance Rn to the earth/casing (PE).
Preferably, according to thevenin's theorem, the dc side power supply and the insulation impedance to ground are equivalent to a two-terminal network, and the dc side insulation impedance of the multiple dc inputs includes all dc inputs equivalent total impedance to ground Riso and two-terminal network open-circuit voltage Ux.
Preferably, all the direct current input equivalent total impedances to the ground Riso are equivalent total impedances of a plurality of direct current BUS positive electrodes BUS + to the ground/machine shell PE impedance and a plurality of direct current BUS negative electrodes BUS-to the ground/machine shell PE impedance.
Preferably, the transistor Q operates in an amplifying state.
Preferably, the three-terminal network formed by the relay S1, the relay S2 and the resistor R0 is formed by connecting a resistor R0 in series with a relay S1, one end of a tap is connected in series with a relay S2, the other end of the resistor R0 is connected with the casing PE, the other end of the relay S1 is connected with the constant current source Ic, and the other end of the relay S2 is connected with the current sampling circuit.
Preferably, the current sampling circuit consists of a sampling current Iioso and a voltage Ubus of a sampling casing PE to a negative pole of a BUS, one end of the sampling current Iioso is connected with the relay S2, the other end of the sampling current Iioso is connected with a negative pole BUS of a direct current BUS, one end of the voltage Ubus of the sampling casing PE to the negative pole of the BUS is connected with a constant current source, and the other end of the voltage Ubus is connected with the negative pole BUS of the direct current.
In order to achieve the above object, another aspect of the present invention provides a high-precision dc-to-ground insulation resistance detection method, which is applied to the insulation resistance detection circuit according to any one of claims 1 to 7, and the specific implementation manner is as follows:
s1, the controller controls the relay S1 to be closed, the relay S2 to be opened, the current Iioso 1 is sampled, and the equation (r) is obtained
(Ic-Iiso1)*(R0+Riso)＝Ubus-Ux①
The system comprises a sampling shell PE, a sampling machine shell PE, a resistor R0, a sampling machine shell PE, a bus and a two-end network, wherein Ic is a constant current source, Iioso 1 is S1 sampling current, R0 is the resistor, Riso is direct current input equivalent total impedance to ground, Ubus is the voltage of the sampling machine shell PE to the negative pole of a bus, and Ux is the open;
s2, the controller controls the relay S1 to be disconnected, the relay S2 to be closed, the current Iiso2 is sampled, and an equation is obtained
(Iiso2-Ic)*(R0+Riso)＝Ux ②
Wherein Iiso2 is S2 sampling current, Ic is constant current source, R0 is resistance, Riso is DC input equivalent total impedance to ground, Ux is two-terminal network open circuit voltage;
s3, simultaneous equation (r), calculates the insulation resistance as:
Riso＝Ubus/(Iiso2-Iiso1)-R0 ③
riso is equivalent total impedance of the direct current input to the ground, Iiso2 is S2 sampling current, Iiso1 is S1 sampling current, R0 is resistance, and Ubus is the voltage of the sampling shell PE to the negative pole of the bus.
The invention has the following beneficial effects:
the invention is a low-cost DC insulation impedance detection scheme and has the characteristic of high precision; the circuit is suitable for multi-path direct current input, detects equivalent impedance of all direct current inputs, and is simple in circuit and low in cost. The key of the invention is to obtain two equations about Ux and Riso by switching on and off two relays; and a constant current source Ic is introduced to improve the current sampling precision when the Riso is smaller, thereby improving the Riso detection precision.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without inventive exercise.
Fig. 1 is a schematic diagram of an insulation resistance detection circuit provided in the prior art;
fig. 2 is a first schematic structural diagram of a high-precision dc-to-ground insulation resistance detection circuit provided in an embodiment of the present application.
Fig. 3 is a schematic flowchart of a high-precision dc-to-ground insulation resistance detection method according to an embodiment of the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The terms "first," "second," "third," "fourth," and the like in the description and in the claims of the present application and in the above-described drawings (if any) are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the application described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," as well as any variations thereof, are intended to cover non-exclusive inclusions.
The technical solution of the present application will be described in detail below with specific examples. The following several specific embodiments may be combined with each other, and details of the same or similar concepts or processes may not be repeated in some embodiments.
The direct current to ground insulation impedance detection circuit and the method are used for detecting whether the direct current input end of the inverter is short-circuited to ground or low impedance. The insulation resistance detection circuit can prevent the direct current input end of the inverter from being short-circuited to the ground or low-resistance before the inverter is connected to the grid and when the shell is not connected to the ground, so that grid connection insulation failure is prevented. The insulation impedance detection circuit can be applied to a solar cell panel grid-connected system and can also be applied to other systems for converting direct current into alternating current and converting alternating current into direct current.
In the embodiment of the application, a relay switch of a relay in an inverter circuit is connected in parallel with an impedor, the change of a measured value between a direct current input end of an inverter and a grounding point is detected by switching the switching state of the relay switch of the relay, and if the direct current input end of the inverter and the grounding point are short-circuited to the ground or have low impedance, the change of the measured value is small or has no change, so that whether the direct current input end of the inverter is short-circuited to the ground or has low impedance is determined.
Example one
As shown in FIG. 2, a high-precision DC-to-ground insulation resistance detection circuit comprises a controller, an inverter circuit, and a DC-to-ground insulation resistance detection component,
the DC-to-ground insulation resistance detection circuit assembly comprises: the current sampling circuit comprises a direct current side insulation impedance, a relay S1, a relay S2, a resistor R0, a constant current source Ic, a transistor Q and a current sampling circuit, wherein one end of the earth/casing PE is connected with the direct current side insulation impedance, the other end of the earth/casing PE is connected with the constant current source Ic and the current sampling circuit through a three-terminal network consisting of the relays S1, S2 and the resistor R0, the constant current source Ic and the current sampling circuit are connected through the transistor Q, and the transistor Q works in an amplifying state.
In this embodiment, the dc side insulation impedance of the single dc input is used as an example, and includes a dc side power supply, a dc BUS positive electrode BUS +, a dc BUS negative electrode BUS-, a dc BUS positive electrode (BUS +) impedance Rp to the ground/casing (PE), and a dc BUS negative electrode (BUS-) impedance Rn to the ground/casing (PE).
The three-terminal network formed by the relay S1, the relay S2 and the resistor R0 is that a resistor R0 is connected with a relay S1 in series, one end of a tap is connected with a relay S2 in series, the other end of the resistor R0 is connected with the casing PE, the other end of the relay S1 is connected with the constant current source Ic, and the other end of the relay S2 is connected with a current sampling circuit.
The current sampling circuit is composed of sampling current Iioso and voltage Ubus of a sampling shell PE to a BUS cathode, one end of the sampling current Iioso is connected with a relay S2, the other end of the sampling current Iioso is connected with a DC BUS cathode BUS-, the sampling shell PE is connected with a constant current source to one end of the voltage Ubus of the BUS cathode, and the other end of the sampling shell PE is connected with the DC BUS cathode BUS-. The voltage of the shell (PE) to the negative pole of the bus is sampled by changing the voltage of the direct current bus.
Example two
In this embodiment, the dc-side insulation impedance of the multiple dc inputs is taken as an example, and the method is suitable for the multiple dc inputs and detects the equivalent impedance of all dc inputs. According to thevenin's theorem, the two-terminal network in the dashed box in fig. 1 is equivalent to the two-terminal network in the dashed box in fig. 2, including all dc input to ground equivalent total impedance Riso and two-terminal network open-circuit voltage Ux. All the direct current input equivalent total impedances to the ground Riso are equivalent total impedances of a plurality of direct current BUS positive electrodes BUS + to the ground/machine shell PE and a plurality of direct current BUS negative electrodes BUS-to the ground/machine shell PE.
As shown in fig. 3, a high-precision direct current ground insulation resistance detection method obtains two equations of Ux and Riso by using the on-off of two relays, so as to solve Ux and Riso; and a constant current source Ic is introduced to improve the current sampling precision when the Riso is smaller, thereby improving the Riso detection precision. And (3) changing the voltage of the direct current bus, and sampling the voltage of the shell (PE) to the negative pole of the bus. The specific implementation mode is as follows:
s1, the controller controls the relay S1 to be closed, the relay S2 to be opened, the current Iioso 1 is sampled, and the equation (r) is obtained
(Ic-Iiso1)*(R0+Riso)＝Ubus-Ux①
The system comprises a sampling shell PE, a sampling machine shell PE, a resistor R0, a sampling machine shell PE, a bus and a two-end network, wherein Ic is a constant current source, Iioso 1 is S1 sampling current, R0 is the resistor, Riso is direct current input equivalent total impedance to ground, Ubus is the voltage of the sampling machine shell PE to the negative pole of a bus, and Ux is the open;
s2, the controller controls the relay S1 to be disconnected, the relay S2 to be closed, the current Iiso2 is sampled, and an equation is obtained
(Iiso2-Ic)*(R0+Riso)＝Ux ②
Wherein Iiso2 is S2 sampling current, Ic is constant current source, R0 is resistance, Riso is DC input equivalent total impedance to ground, Ux is two-terminal network open circuit voltage;
s3, simultaneous equation (r), calculates the insulation resistance as:
Riso＝Ubus/(Iiso2-Iiso1)-R0 ③
riso is equivalent total impedance of the direct current input to the ground, Iiso2 is S2 sampling current, Iiso1 is S1 sampling current, R0 is resistance, and Ubus is the voltage of the sampling shell PE to the negative pole of the bus.
Finally, it should be noted that: the above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present application.
Claims (8)
1. A high-precision DC-to-ground insulation resistance detection circuit comprises a controller and a DC-to-ground insulation resistance detection component,
the DC-to-ground insulation resistance detection circuit assembly comprises: the current sampling circuit comprises a direct current side insulation impedance, a relay S1, a relay S2, a resistor R0, a constant current source Ic, a transistor Q and a current sampling circuit, wherein one end of the earth/casing PE is connected with the direct current side insulation impedance, the other end of the earth/casing PE is connected with the constant current source Ic and the current sampling circuit respectively through a three-terminal network consisting of the relays S1, S2 and the resistor R0, and the constant current source Ic is connected with the current sampling circuit through the transistor Q.
2. The high-precision direct current-to-ground insulation resistance detection circuit as claimed in claim 1, wherein the direct current side insulation resistance of the single direct current input comprises a direct current side power supply, a direct current BUS positive electrode BUS +, a direct current BUS negative electrode BUS-, a direct current BUS positive electrode (BUS +) resistance Rp to ground/casing (PE), and a direct current BUS negative electrode (BUS-) resistance Rn to ground/casing (PE).
3. The high-precision direct current-to-ground insulation resistance detection circuit as claimed in claim 1, wherein according to thevenin's theorem, a direct current side power supply and a ground insulation resistance are equivalent to form a two-terminal network, including all direct current input equivalent total resistance to ground Riso and two-terminal network open-circuit voltage Ux.
4. The high-precision DC-to-ground insulation resistance detection circuit according to claim 3, wherein the equivalent total resistance Riso of all DC inputs to ground is the equivalent total resistance of the positive electrode BUS + to ground/casing PE resistance and the negative electrode BUS-to-ground/casing PE resistance of the plurality of DC buses.
5. A high accuracy dc-to-ground isolation impedance sensing circuit as defined in claim 1 wherein transistor Q operates in an amplifying state.
6. The high-precision direct current-to-ground insulation resistance detection circuit as claimed in claim 1, wherein a three-terminal network consisting of a relay S1, a relay S2 and a resistor R0 is that a resistor R0 is connected in series with the relay S1, one end of a tap is connected in series with the relay S2, the other end of the resistor R0 is connected with the casing PE, the other end of the relay S1 is connected with a constant current source Ic, and the other end of the relay S2 is connected with a current sampling circuit.
7. The high-precision direct current-to-ground insulation resistance detection circuit as claimed in claim 1 or 6, wherein the current sampling circuit is composed of a sampling current Iioso and a voltage Ubus of the sampling casing PE to the negative pole of the BUS, one end of the sampling current Iioso is connected with the relay S2, the other end of the sampling current Iioso is connected with the negative pole BUS of the direct current BUS, one end of the voltage Ubus of the sampling casing PE to the negative pole of the BUS is connected with the constant current source, and the other end of the voltage Ubus is connected with the negative pole BUS of the direct current.
8. A high-precision direct current-to-ground insulation resistance detection method is applied to the insulation resistance detection circuit of any one of claims 1 to 7, and the specific implementation mode is as follows:
s1, the controller controls the relay S1 to be closed, the relay S2 to be opened, the current Iioso 1 is sampled, and the equation (r) is obtained
(Ic-Iiso1)*(R0+Riso)＝Ubus-Ux①
The system comprises a sampling shell PE, a sampling machine shell PE, a resistor R0, a sampling machine shell PE, a bus and a two-end network, wherein Ic is a constant current source, Iioso 1 is S1 sampling current, R0 is the resistor, Riso is direct current input equivalent total impedance to ground, Ubus is the voltage of the sampling machine shell PE to the negative pole of a bus, and Ux is the open;
s2, the controller controls the relay S1 to be disconnected, the relay S2 to be closed, the current Iiso2 is sampled, and an equation is obtained
(Iiso2-Ic)*(R0+Riso)＝Ux ②
Wherein Iiso2 is S2 sampling current, Ic is constant current source, R0 is resistance, Riso is DC input equivalent total impedance to ground, Ux is two-terminal network open circuit voltage;
s3, simultaneous equation (r), calculates the insulation resistance as:
Riso＝Ubus/(Iiso2-Iiso1)-R0 ③
riso is equivalent total impedance of the direct current input to the ground, Iiso2 is S2 sampling current, Iiso1 is S1 sampling current, R0 is resistance, and Ubus is the voltage of the sampling shell PE to the negative pole of the bus.
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Cited By (1)
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| CN116449164A (en) * | 2023-06-12 | 2023-07-18 | 苏州精控能源科技有限公司 | Insulation detection method, system and storage medium for industrial and commercial energy storage alternating current-direct current system |
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