CN112379170A - Direct current to ground insulation impedance detection circuit and method suitable for multi-path direct current input - Google Patents

Abstract

The invention relates to the technical field of power supplies, in particular to a direct current to ground insulation impedance detection circuit and a method suitable for multi-path direct current input, which comprises a controller and a direct current to ground insulation impedance detection assembly, and is characterized in that the direct current to ground insulation impedance detection circuit assembly comprises: a DC side insulation resistance, a relay S0 and a resistor R0; the direct current side insulation impedance of the multi-path direct current input comprises all direct current input earth equivalent total impedance Riso and two-end network open circuit voltage Vx, wherein all direct current input earth equivalent total impedance Riso is equivalent total impedance of a plurality of paths of direct current BUS positive electrodes BUS + to earth/casing PE impedance and a plurality of paths of direct current BUS negative electrodes BUS-to earth/casing PE impedance; the key point of the invention is that the power switch tube originally existing in the DC/AC converter is utilized, the use of the relay is saved, the cost is reduced, and the invention is suitable for multi-path direct current input and detects the equivalent impedance of all direct current input.

Description

Direct current to ground insulation impedance detection circuit and method suitable for multi-path direct current input

Technical Field

The invention relates to the technical field of power supplies, in particular to a direct current to ground insulation impedance detection circuit and method suitable for multi-path direct current input.

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. This technique requires two relays and other auxiliary circuits, is costly, and is not suitable for use with multiple dc simultaneous inputs.

Disclosure of Invention

The invention provides a high-precision direct current ground insulation impedance detection circuit and method, which aim to solve the problems that the existing direct current insulation impedance detection is overhigh in cost and needs to be improved in efficiency

In order to achieve the above object, a first aspect of the present invention provides a DC-to-ground insulation resistance detection circuit suitable for multiple DC inputs, comprising a controller, a DC/AC converter, and a DC-to-ground insulation resistance detection module,

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 resistance detection circuit assembly comprises: a DC side insulation resistance, a relay S0 and a resistor R0; according to the Thevenin theorem, all direct current side power supplies and earth insulation impedances are equivalent to form a two-end network, the direct current side insulation impedances of the multipath direct current inputs comprise all direct current input earth equivalent total impedances Riso and two-end network open-circuit voltage Ux, and all direct current input earth equivalent total impedances Riso are equivalent total impedances of a plurality of paths of direct current BUS positive electrodes BUS + impedance to earth/machine shell PE and a plurality of paths of direct current BUS negative electrodes BUS-impedance to earth/machine shell PE;

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 middle point of one bridge arm of the existing power topology of the DC/AC converter through a series circuit of a relay S0 and a resistor R0, and the controller changes the voltage on the resistor R0 and detects the voltage on the resistor R0 by controlling the on and off of a power switch tube on the upper part of the bridge arm and a power switch tube on the lower part of the bridge arm.

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

Preferably, relay S0 and resistor R0 may be switched in position.

Preferably, the topology with the bridge arm feature is suitable for DC/AC topology, including but not limited to single-phase H4 full bridge, H5 topology, H6 topology, Heric topology, three-phase NPC topology, multi-level topology, and the like.

Preferably, the bridge arm upper power switch tube group comprises a first switch tube Q1; the bridge arm lower power switch tube group comprises a second switch tube Q2.

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

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

In order to achieve the above object, another aspect of the present invention provides a dc-to-ground insulation resistance detection method suitable for multiple dc inputs, which is applied to the insulation resistance detection circuit according to any one of claims 1 to 7, and the embodiments are as follows:

s1, the controller controls the relay S0 to be closed, controls the switch tube Q1 on the upper part of the bridge arm to be opened, controls the switch tube Q2 on the lower part of the bridge arm to be closed, measures the voltage of the negative electrode BUS-pair shell PE of the direct current BUS, records the voltage as Viso1, and obtains an equation

Viso1＝Vx*R0/(Riso+R0)+Vbus*Riso/(Riso+R0) ①

Wherein Viso1 is the voltage of the S1 DC BUS negative BUS-to-case PE, Vx is the two-terminal network open circuit voltage, Riso is the DC input equivalent total impedance to ground, R0 is the resistance, and Vbus is the voltage of the sampling case PE to the BUS negative;

s2, the controller controls the relay S0 to be closed, controls the switch tube Q1 on the upper part of the bridge arm to be turned off, controls the switch tube Q2 on the lower part of the bridge arm to be turned on, measures the voltage of a direct current BUS negative electrode BUS-pair shell (PE), records the voltage as Viso2, and obtains an equation

Viso2＝Vx*R0/(Riso+R0) ②

Wherein Viso2 is the voltage of S2 DC BUS negative BUS-to-casing PE, Vx is the open circuit voltage of two-terminal network, Riso is the equivalent total impedance of DC input to ground, R0 is the resistance;

s3, simultaneous equation (r), calculates the insulation resistance as:

Riso＝R0/[Vbus/(Viso1-Viso2)-1] ③

where Riso is the dc input to ground equivalent total impedance, Vbus is the voltage of the sampling enclosure PE to the BUS cathode, Viso1 is the voltage of S1 dc BUS cathode BUS-to enclosure PE, Viso2 is the voltage of S2 dc BUS cathode BUS-to enclosure PE.

The invention has the following beneficial effects:

the invention is a low-cost DC insulation impedance detection scheme, is suitable for multi-path DC input, detects the equivalent impedance of all DC input, and has simple circuit and lower cost; and is applicable to 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, multilevel topology, etc.; the key point is that two relays are switched on and off to obtain two equations of Vx and Riso. The invention utilizes one of the existing power topology bridge arms of the DC/AC converter, only needs one relay under the condition of unchanged DC bus voltage, and has simple circuit and lower cost. The key point of the invention is to utilize the power switch tube originally existing in the DC/AC converter, save the use of the relay, simplify the circuit structure and effectively reduce the manufacturing cost.

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 dc-to-ground insulation resistance detection circuit suitable for multiple dc inputs according to an embodiment of the present application.

Fig. 3 is a schematic structural diagram of a dc-to-ground insulation resistance detection circuit suitable for multiple dc inputs according to an embodiment of the present application.

Fig. 4 is a schematic flowchart of a dc-to-ground insulation resistance detection method suitable for multiple dc inputs according to an embodiment of the present disclosure.

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 DC-to-ground insulation resistance detection circuit suitable for multiple DC inputs comprises a controller, a DC/AC converter, a DC-to-ground insulation resistance detection component,

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 resistance detection circuit assembly comprises: a DC side insulation resistance, a relay S0 and a resistor R0;

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 Vx. 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.

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 middle point of one bridge arm of the existing power topology of the DC/AC converter through a series circuit of a relay S0 and a resistor R0, and the controller changes the voltage on the resistor R0 and detects the voltage on the resistor R0 by controlling the on and off of a power switch tube on the upper part of the bridge arm and a power switch tube on the lower part of the bridge arm.

Preferably, the bridge arm upper power switch tube group comprises a first switch tube Q1; the bridge arm lower power switch tube group comprises a second switch tube Q2.

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

As shown in fig. 4, a dc-to-ground insulation resistance detection method suitable for multiple dc inputs 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 S0 to be closed, controls the switch tube Q1 on the upper part of the bridge arm to be opened, controls the switch tube Q2 on the lower part of the bridge arm to be closed, measures the voltage of the negative electrode BUS-pair shell PE of the direct current BUS, records the voltage as Viso1, and obtains an equation

Viso1＝Vx*R0/(Riso+R0)+Vbus*Riso/(Riso+R0) ①

Wherein Viso1 is the voltage of the S1 DC BUS negative BUS-to-case PE, Vx is the two-terminal network open circuit voltage, Riso is the DC input equivalent total impedance to ground, R0 is the resistance, and Vbus is the voltage of the sampling case PE to the BUS negative;

s2, the controller controls the relay S0 to be closed, controls the switch tube Q1 on the upper part of the bridge arm to be turned off, controls the switch tube Q2 on the lower part of the bridge arm to be turned on, measures the voltage of a direct current BUS negative electrode BUS-pair shell (PE), records the voltage as Viso2, and obtains an equation

Viso2＝Vx*R0/(Riso+R0) ②

Wherein Viso2 is the voltage of S2 DC BUS negative BUS-to-casing PE, Vx is the open circuit voltage of two-terminal network, Riso is the equivalent total impedance of DC input to ground, R0 is the resistance;

s3, simultaneous equation (r), calculates the insulation resistance as:

Riso＝R0/[Vbus/(Viso1-Viso2)-1] ③

where Riso is the dc input to ground equivalent total impedance, Vbus is the voltage of the sampling enclosure PE to the BUS cathode, Viso1 is the voltage of S1 dc BUS cathode BUS-to enclosure PE, Viso2 is the voltage of S2 dc BUS cathode BUS-to enclosure PE.

Example two

Figure 2 is a schematic view of only one embodiment of the present invention. As shown in fig. 3, wherein relay S0 and resistor R0 may be switched in position; an inductor L1 can be further connected in series in the series circuit of the relay S0 and the resistor R0, and when the relay S0 and the resistor R0 are used for three-level or multi-level topology, one end of the relay S0 and one end of the resistor R0 can be connected to any point in the middle of a bridge arm; any other point having the same potential as the midpoint of the bridge arm may be connected.

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

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 direct current to ground insulation impedance detection circuit suitable for multi-path direct current input comprises a controller, a DC/AC converter and a direct current to ground insulation impedance detection assembly, and is 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 resistance detection circuit assembly comprises: a DC side insulation resistance, a relay S0 and a resistor R0; according to the Thevenin theorem, all direct current side power supplies and earth insulation impedances are equivalent to form a two-end network, the direct current side insulation impedances of the multipath direct current inputs comprise all direct current input earth equivalent total impedances Riso and two-end network open-circuit voltage Ux, and all direct current input earth equivalent total impedances Riso are equivalent total impedances of a plurality of paths of direct current BUS positive electrodes BUS + impedance to earth/machine shell PE and a plurality of paths of direct current BUS negative electrodes BUS-impedance to earth/machine shell PE; 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 middle point of one bridge arm of the existing power topology of the DC/AC converter through a series circuit of a relay S0 and a resistor R0, and the controller changes the voltage on the resistor R0 and detects the voltage on the resistor R0 by controlling the on and off of a power switch tube on the upper part of the bridge arm and a power switch tube on the lower part of the bridge arm.

2. The DC-to-ground insulation resistance detection circuit suitable for the multi-path DC input as claimed in claim 1, wherein an inductor L1 is further connected in series in the series circuit of the relay S0 and the resistor R0.

3. The DC-to-ground insulation resistance detection circuit suitable for multiple DC inputs as claimed in claim 1, wherein the relay S0 and the resistor R0 can exchange positions.

4. The DC-to-ground insulation resistance detection circuit suitable for the multi-path DC input is characterized in that the DC-to-ground insulation resistance detection circuit is suitable for the topologies with bridge arm characteristics in the DC/AC topology, and the topologies include but are not limited to single-phase H4 full bridge, H5 topology, H6 topology, Heric topology, three-phase NPC topology, multi-level topology and the like.

5. The direct current-to-ground insulation impedance detection circuit suitable for the multi-path direct current input is characterized in that the bridge arm upper power switch tube group comprises a first switch tube Q1; the bridge arm lower power switch tube group comprises a second switch tube Q2.

6. The DC-to-ground insulation impedance detection circuit suitable for the multi-path DC input is characterized in that the bridge arm upper power switch tube group comprises a first switch tube Q1 and a second switch tube Q2 which are connected in series; the power switch tube group at the lower part of the bridge arm comprises a third switch tube Qm and a fourth switch tube Qn which are connected in series.

7. The DC-to-ground insulation impedance detection circuit suitable for the multi-path DC input is characterized in that when the circuit is used for a three-level or multi-level topology, one end of a relay S0 and one end of a resistor R0 can be connected to any point in the middle of a bridge arm; any other point having the same potential as the midpoint of the bridge arm may be connected.

8. A DC-to-ground insulation resistance detection method suitable for multi-path DC input 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 S0 to be closed, controls the switch tube Q1 on the upper part of the bridge arm to be opened, controls the switch tube Q2 on the lower part of the bridge arm to be closed, measures the voltage of the negative electrode BUS-pair shell PE of the direct current BUS, records the voltage as Viso1, and obtains an equation

Viso1＝Vx*R0/(Riso+R0)+Vbus*Riso/(Riso+R0) ①

Wherein Viso1 is the voltage of the S1 DC BUS negative BUS-to-case PE, Vx is the two-terminal network open circuit voltage, Riso is the DC input equivalent total impedance to ground, R0 is the resistance, and Vbus is the voltage of the sampling case PE to the BUS negative;

s2, the controller controls the relay S0 to be closed, controls the switch tube Q1 on the upper part of the bridge arm to be turned off, controls the switch tube Q2 on the lower part of the bridge arm to be turned on, measures the voltage of a direct current BUS negative electrode BUS-pair shell (PE), records the voltage as Viso2, and obtains an equation

Viso2＝Vx*R0/(Riso+R0) ②

Wherein Viso2 is the voltage of S2 DC BUS negative BUS-to-casing PE, Vx is the open circuit voltage of two-terminal network, Riso is the equivalent total impedance of DC input to ground, R0 is the resistance;

s3, simultaneous equation (r), calculates the insulation resistance as:

Riso＝R0/[Vbus/(Viso1-Viso2)-1] ③

where Riso is the dc input to ground equivalent total impedance, Vbus is the voltage of the sampling enclosure PE to the BUS cathode, Viso1 is the voltage of S1 dc BUS cathode BUS-to enclosure PE, Viso2 is the voltage of S2 dc BUS cathode BUS-to enclosure PE.

Images