Insulation resistance monitoring device for optical storage DC flexible DC power distribution system

Abstract

The invention provides a DC micro-grid insulation resistance monitoring device for an optical storage DC flexible system. The DC micro-grid insulation resistance monitoring device comprises a detection circuit and a controller communicating with the detection circuit. The device is connected to multiple paths of positive direct current buses including distributed photovoltaic branches and energy storage system branches in a direct current micro-grid through a Y-shaped connecting circuit, and relay logic is switched by utilizing a controller to obtain an output voltage signal. The core judgment logic is to compare whether the output voltage is in a reasonable interval defined by a coefficient gamma (the value can be dynamically adjusted according to the energy storage voltage grade) and the bus voltage, so that the insulation abnormity of the direct current micro-grid system under the flexible interaction working condition is quickly identified, and an alarm is given. According to the device, the operation process of multi-branch complex impedance is simplified, and the detection efficiency of the ground insulation state of the direct current end is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of DC power distribution and building integrated energy security, and specifically relates to a DC bus insulation impedance monitoring device in a photovoltaic-storage-DC-flexible system. Background Technology

[0002] In a photovoltaic-storage-direct-current-flexible (PEDF) system, the insulation resistance to ground of the DC microgrid bus (positive and negative poles) is a key indicator for ensuring the safe operation of the building's integrated energy system. Due to the long-term operation of photovoltaic modules, energy storage facilities, and power electronic equipment, their insulation performance is easily degraded by changes in ambient temperature and humidity, electrical aging, or physical friction, which can lead to leakage or fire risks.

[0003] Existing detection technologies primarily rely on the traditional bridge method, which determines impedance by switching resistor networks and calculating voltage values. However, this approach suffers from drawbacks such as redundant computational logic and slow response speed, making it difficult to meet the demands of efficient protection. Especially in a photovoltaic-storage-DC-flexible environment, the system integrates distributed photovoltaics, energy storage batteries, and flexible power consumption equipment. The internal branch topology of the DC microgrid is complex, and the bus voltage fluctuates frequently with flexible scheduling. The traditional single-point bridge method struggles to achieve high-frequency, high-precision rapid monitoring while simultaneously handling the switching of charging and discharging conditions in the energy storage system. Therefore, a high-performance insulation monitoring solution adaptable to dynamic DC operating conditions is urgently needed. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a DC bus insulation impedance monitoring device for a photovoltaic-storage-DC-flexible system. The device includes a detection circuit and a controller that communicates bidirectionally with the detection circuit. The input terminals of the detection circuit are respectively connected to the positive DC bus of the first power branch (e.g., photovoltaic branch) and the positive DC bus of the second power branch (e.g., energy storage branch) of the DC microgrid. Internally, it contains three detection circuits connected in a Y-type configuration. The controller performs the following steps to determine the insulation impedance:

[0005] Send a first control signal to the detection circuit to turn on the third relay (RY3) connected to the common terminal.

[0006] Send a second control signal and simultaneously activate the first relay (RY1) and the second relay (RY2) to collect the output voltage signals after the two positive DC buses are connected to the Y-type circuit;

[0007] The relationship between the product of the judgment coefficient γ and the output voltage of the power supply branch and the output voltage of the detection circuit to the controller (the value of γ can be dynamically adjusted according to the energy storage voltage level) is determined. If the output voltage is not within the range defined by γ1×output voltage and γ2×output voltage, an insulation fault alarm is issued.

[0008] A further insulation impedance monitoring device for photovoltaic-storage DC-DC flexible power distribution systems, wherein the calculation logic of the coefficient γ is as follows: With relays RY1 and RY simultaneously activated, acquire the output voltage V1 of the first power supply branch, the output voltage V2 of the second power supply branch, and the output voltage signal V3 of the detection circuit; based on the relationship that the sum of currents in the Y-connected circuit is 0, establish the relationship between the output voltage V3 and the input voltages V1, V2, and the detection resistor R. V1 R V2 The functional proportional relationship between them;

[0009] The method for configuring the coefficient γ includes: pre-setting the extreme value R of the insulation resistance determination. min and R max Substitute these values ​​into the detection resistance term in the proportional relationship of the function to calculate the upper limit proportional coefficient γ1 and the lower limit proportional coefficient γ2 used for determining the insulation fault range.

[0010] A further insulation impedance monitoring device for a photovoltaic-storage DC-DC flexible power distribution system, wherein the detection circuit includes a first, second, and third switching circuit, and a first, second, and third detection circuit connected in parallel with it; the first, second, and third detection circuits are connected in a Y-type configuration; the first and second switching circuits detect the positive DC bus voltage signals of the first and second power supply branches respectively, and output them to the controller through the third switching circuit.

[0011] Further, an insulation impedance monitoring device for a photovoltaic-storage-DC-flexible power distribution system is provided, wherein the first switching circuit includes a relay RY1, resistors R1-R2, capacitor C1, MOSFET Q1, diode D1, and Zener diode ZD1; pin 1 of RY1 is connected to PV1_ISO_TEST, pin 2 is connected to the first detection circuit, and pin 5 is connected to the control signal line through MOSFET Q1 and resistor R1.

[0012] Further, an insulation impedance monitoring device for a photovoltaic-storage DC-DC flexible power distribution system is provided, wherein the second switching circuit includes a relay RY2, resistors R4-R5, capacitor C2, MOSFET Q2, diode D2, and Zener diode ZD2; pin 1 of RY2 is connected to PV2_ISO_TEST, pin 2 is connected to the second detection circuit, and pin 5 is connected to the control signal line through MOSFET Q2.

[0013] Further, an insulation impedance monitoring device for a photovoltaic-storage-DC-flexible power distribution system is provided, wherein the third switching circuit includes a relay RY3, resistors R7-R8, capacitor C3, MOSFET Q3, diode D3, and Zener diode ZD3; pin 1 of RY3 outputs a PV_ISO signal to the controller, and pin 2 is connected to the third detection circuit.

[0014] Further insulation impedance monitoring device for a photovoltaic-storage-direct-soft DC power distribution system. Among them, the first detection circuit includes a parallel combination of a resistor R3 and a detection resistor RV1. One end of R3 is connected to the 2-pin of the relay RY1, and the other end is connected to the ground FGND.

[0015] Further insulation impedance monitoring device for a photovoltaic-storage-direct-soft DC power distribution system. Among them, the second detection circuit includes a parallel combination of a resistor R6 and a detection resistor RV2. One end of R6 is connected to the 2-pin of the relay RY2, and the other end is connected to the ground FGND.

[0016] Further insulation impedance monitoring device for a photovoltaic-storage-direct-soft DC power distribution system. Among them, the third detection circuit includes a resistor R9. One end of it is connected to the 2-pin of the relay RY3, and the other end is connected to the ground FGND.

[0017] The present invention also provides a method for detecting the insulation impedance of a photovoltaic inverter based on the aforementioned device, which is characterized by including the following steps:

[0018] The controller sends a first control signal to the detection circuit to turn on the relay RY3;

[0019] After the first threshold time, a second control signal is sent, and at the same time, RY1 and RY2 are turned on, and wait for the second threshold time;

[0020] Receive the voltage signal V3 fed back by the detection circuit, and obtain the output voltage V1 of the power supply branch according to the logic of claim 3;

[0021] Judge whether the output voltage V3 satisfies the judgment interval: γ2×V1<V3<γ1×V1; if not, it is determined that there is a problem with the insulation and an alarm is issued.

[0022] The beneficial effects achieved by the present invention include:

[0023] 1. Significantly improve the detection efficiency: Simplify the impedance calculation through the voltage ratio coefficient γ;

[0024] 2. Fast response speed: Utilize the relay action timing to achieve high-speed acquisition;

[0025] 3. Precise judgment logic: Construct a scientific fault judgment boundary;

[0026] 4. Optimize the hardware structure: Adopt a Y-shaped topology, which can better adapt to the access of multiple distributed energy sources and energy storage branches in the photovoltaic-storage-direct-soft system;

[0027] 5. Strong system protection performance: Ensure that the detection signal fed back to the controller is stable and reliable. Description of the Drawings

[0028] Figure 1 It is a schematic diagram of the insulation impedance detection circuit in the prior art;

[0029] Figure 2 This is a schematic diagram of the insulation impedance monitoring device for the photovoltaic-storage DC-DC flexible power distribution system in this invention;

[0030] Figure 3 This is a block diagram of the detection circuit in this invention;

[0031] Figure 4 This is a circuit diagram of the detection circuit in this invention;

[0032] Figure 5 This is a circuit diagram of the Y-type connection circuit in this invention;

[0033] Figure 6 This is a schematic diagram of the second conditioning circuit of the present invention;

[0034] Figure 7 This is a circuit diagram of the first conditioning circuit of the present invention. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments. The following embodiments are only used to explain the invention and are not intended to limit the scope of protection of the present invention.

[0036] like Figure 1 As shown, existing technologies typically connect capacitors C1 and C2 in parallel between the positive DC bus BUS+, the negative DC bus BUS-, and ground PE, and include an insulation resistance detection circuit 201. This circuit determines the insulation resistance to ground between the photovoltaic module 01 and the photovoltaic inverter 20 based on the ground voltage of the positive and negative buses by switching the internal resistor network, but its detection efficiency is relatively low.

[0037] The present invention will be further described below with reference to the accompanying drawings and embodiments. The following embodiments are only used to explain the invention and are not intended to limit the scope of protection of the present invention.

[0038] 1. Overall System Connection Architecture

[0039] This invention provides a DC microgrid insulation impedance monitoring device for photovoltaic-storage DC-flexible systems, such as... Figure 2 As shown, the system includes a detection circuit and a controller that communicates bidirectionally with the detection circuit. The input terminals of the detection circuit are respectively connected to the positive DC bus of the first power branch (e.g., a distributed photovoltaic branch) and the positive DC bus of the second power branch (e.g., an energy storage system branch) of the DC microgrid, and the ground terminal (FGND) of the detection circuit is grounded. Figure 3 , Figure 4As shown, the detection circuit in this embodiment includes first, second, and third switching circuits, and first, second, and third detection circuits connected in parallel with them. The first, second, and third detection circuits are connected in a Y-type configuration and converge at a common output terminal PV_ISO.

[0040] like Figure 3 , Figure 4 As shown, the detection circuit in this embodiment includes first, second, and third switching circuits (corresponding to the reference numerals PV1, PV2, and PV3), and first, second, and third detection circuits connected in parallel with them. The first, second, and third detection circuits are connected in a Y-type configuration and converge at a common output terminal PV_ISO.

[0041] 2. Detection Operation Logic and Steps

[0042] The controller switches the relay on and off by sending control signals to the detection circuit and acquires the output voltage signal of the positive DC bus. The specific steps are as follows:

[0043] 1) Open the common circuit: The controller sends the first control signal RELAY_ISO3 to control the MOSFET Q3 and thus open the third relay RY3.

[0044] 2) Multi-channel synchronous access: After the first threshold time, a second control signal is sent, controlling MOSFET Q1 to turn on the first relay RY1 via RELAY_ISO1, and simultaneously controlling MOSFET Q2 to turn on the second relay RY2 via RELAY_ISO2. At this time, both positive DC bus signals are simultaneously connected to the Y-type detection network.

[0045] 3) Signal Acquisition and Judgment: After the second threshold time, the output voltage signal V3 on the PV_ISO node is received. The controller determines the insulation status by judging the relationship between the product of the coefficient γ (which can be dynamically adjusted according to the voltage level under the current charging and discharging conditions of the energy storage battery) and the output voltage of the power supply branch, and the output voltage V3.

[0046] 3. Mathematical Model and Formula Derivation

[0047] like Figure 5 As shown, when relays RY1, RY2, and RY3 are all in the open state, based on the relationship that the sum of the currents at the center point of the Y-type connection circuit is 0 (Kirchhoff's Current Law), formula (1) is derived:

[0048]

[0049] Where RV1 and RV2 are the equivalent insulation resistances to ground of the photovoltaic branch and the energy storage branch, respectively, and R3, R6, and R9 are known detection resistors. Since V1=V2 under balanced operating conditions, formula (1) is simplified to obtain formula (2):

[0050]

[0051] The expression for V3 is further extracted using formula (2), which is formula (3):

[0052]

[0053] Therefore, the proportional coefficient γ is defined as the ratio of the output voltage to the input voltage, i.e., formula (4):

[0054]

[0055] Wherein, in formula (4), γ is the passive bridge arm ratio γ bridge .

[0056] 4. Derivation and Formula Correction of Hardware Gain

[0057] According to the conditioning circuit (see Figure 3 and Figure 4 The topology of the signal output to the controller, G, consists of two parts:

[0058] • First-stage gain (G1): The first conditioning circuit uses an integrating operational circuit, which is essentially a voltage parallel negative feedback. The first operational amplifier 21111 and resistor R3 convert the current signal collected by the bridge into a voltage signal.

[0059] • Second-stage gain (G2): The second conditioning circuit uses a non-inverting proportional amplifier circuit with voltage series negative feedback. Based on the second operational amplifier 22121 and resistors R6 and R7, its proportional gain formula is:

[0060]

[0061] 5. Complete judgment formula after completion

[0062] Introducing the aforementioned total hardware gain G into the original Y-bridge model, the expression for the final output voltage V3 (DSP) to the controller should be modified as follows:

[0063]

[0064] Where, γ bridge G represents the passive bridge arm ratio, while G is the hardware amplification term.

[0065] 6. Numerical Alignment Instructions

[0066] This device achieves numerical alignment through the following calculations:

[0067] • When the impedance to be measured is Rmax, the passive bridge arm ratio γ bridge It is approximately 0.69.

[0068] • If the resistor values ​​of the second-stage proportional amplifier circuit are set such that G2≈3 (e.g., R6=20kΩ, R7=10kΩ), then the final determination coefficient is:

[0069]

[0070] The result perfectly matches the preset judgment threshold of 2.04 in this embodiment. Through this conditioning structure, the system not only achieves signal amplification, but also uses a voltage regulator circuit to ensure that the signal input to the DSP remains stable within a safe range.

[0071] To achieve the physical mapping of the determination coefficient γ and ensure the signal stability of the input controller, this embodiment uses a conditioning circuit to perform linear transformation and conditioning on the original voltage signal V3 output by the Y-bridge, as detailed below:

[0072] • First conditioning circuit ( Figure 6 The weak signal output from the common terminal PV_ISO first enters the first conditioning circuit. The first amplification circuit 211 adopts an integrating operation circuit (voltage parallel negative feedback topology) composed of the first operational amplifier 21111, which is responsible for converting the original current signal into a stable initial voltage signal.

[0073] • Second conditioning circuit ( Figure 7 The signal then enters the second conditioning circuit. Its core, the second amplifier circuit 221, employs a non-inverting proportional amplifier circuit (voltage series negative feedback topology) composed of the second operational amplifier 22121. The gain of this stage is determined by the formula G2=1+R6 / R7.

[0074] • Gain closed-loop: Through the amplification of the above two-stage hardware gain G, combined with the passive proportional gain γ of the bridge arm itself. bridge This ensures that the total proportional coefficients received by the controller meet the previously set values ​​of γ1=2.04 and γ2=0.25. Furthermore, the clamping effect of the first and second voltage regulator circuits at the circuit's end ensures the safety of the DSP input.

[0075] While this specification contains numerous specific implementation details, these should not be construed as limiting the scope of any invention or the scope of the claims, but rather as descriptions of features that can embody specific embodiments of a particular invention. Specific features described in this specification within the context of an independent embodiment may also be implemented in combination with a single embodiment. Conversely, various features described within the context of a single embodiment may also be implemented independently in multiple embodiments, or in any suitable sub-combination. Furthermore, while features may be described for combination and even initially claimed in this way, one or more features from a claimed combination may be removed from that combination in some cases, and the claimed combination may be redirected to a sub-combination or a variation thereof.

Claims

1. An insulation impedance monitoring device for a photovoltaic-storage DC-DC flexible power distribution system, characterized in that, The system includes a detection circuit and a controller that communicates bidirectionally with the detection circuit. The input terminals of the detection circuit are respectively connected to the positive DC bus of the first power branch and the positive DC bus of the second power branch of the DC microgrid. It internally contains three detection circuits, which are connected in a Y-type configuration. The controller is used to perform the following steps to determine the insulation impedance: Send a first control signal to the detection circuit to turn on the third relay (RY3) connected to the common terminal. Send a second control signal and simultaneously activate the first relay (RY1) and the second relay (RY2) to collect the output voltage signals after the two positive DC buses are connected to the Y-type circuit; The relationship between the product of the judgment coefficient γ and the output voltage of the power supply branch and the output voltage of the detection circuit to the controller is determined. If the output voltage is not within the range defined by γ1×output voltage and γ2×output voltage, an insulation fault alarm is issued.

2. The insulation impedance monitoring device for a photovoltaic-storage DC-DC flexible power distribution system as described in claim 1, characterized in that, The calculation logic for the coefficient γ is as follows: when relays RY1 and RY2 are turned on simultaneously, the output voltage V1 of the first power supply branch, the output voltage V2 of the second power supply branch, and the output voltage signal V3 of the detection circuit are obtained. Based on the relationship that the sum of currents is zero in a Y-connected circuit, the relationship between output voltage V3 and input voltages V1, V2, and sensing resistor R is established. V1 R V2 The functional proportional relationship between them; The method for configuring the coefficient γ includes: pre-setting the extreme value R of the insulation resistance. min and R max Substitute these values ​​into the detection resistance term in the proportional relationship of the function to calculate the upper limit proportional coefficient γ1 and the lower limit proportional coefficient γ2 used for determining the insulation fault range.

3. The insulation impedance monitoring device for a photovoltaic-storage DC-DC flexible power distribution system as described in claim 2, characterized in that, The detection circuit includes a first, second, and third switching circuit, and a first, second, and third detection circuit connected in parallel with it; the first, second, and third detection circuits are connected in a Y-type configuration; the first and second switching circuits detect the positive DC bus voltage signals of the first and second power supply branches respectively, and output them to the controller through the third switching circuit.

4. The insulation impedance monitoring device for a photovoltaic-storage DC-DC flexible power distribution system as described in claim 3, characterized in that, The first switching circuit includes a relay RY1, resistors R1-R2, capacitor C1, MOSFET Q1, diode D1, and Zener diode ZD1; pin 1 of RY1 is connected to PV1_ISO_TEST, pin 2 is connected to the first detection circuit, and pin 5 is connected to the control signal line through MOSFET Q1 and resistor R1.

5. The insulation impedance monitoring device for a photovoltaic-storage DC-DC flexible power distribution system as described in claim 4, characterized in that, The second switching circuit includes a relay RY2, resistors R4-R5, capacitor C2, MOSFET Q2, diode D2, and Zener diode ZD2; pin 1 of RY2 is connected to PV2_ISO_TEST, pin 2 is connected to the second detection circuit, and pin 5 is connected to the control signal line through MOSFET Q2.

6. The insulation impedance monitoring device for a photovoltaic-storage DC-DC flexible power distribution system as described in claim 5, characterized in that, The third switching circuit includes a relay RY3, resistors R7-R8, capacitor C3, MOSFET Q3, diode D3, and Zener diode ZD3; pin 1 of RY3 outputs the PV_ISO signal to the controller, and pin 2 is connected to the third detection circuit.

7. The insulation impedance monitoring device for a photovoltaic-storage DC-DC flexible power distribution system as described in claim 3, characterized in that, The first detection circuit includes a parallel resistor R3 and a detection resistor RV1. One end of R3 is connected to pin 2 of relay RY1, and the other end is connected to ground FGND.

8. The insulation impedance monitoring device for a photovoltaic-storage DC-DC flexible power distribution system as described in claim 7, characterized in that, The second detection circuit includes a parallel resistor R6 and a detection resistor RV2. One end of R6 is connected to pin 2 of relay RY2, and the other end is connected to ground FGND.

9. The insulation impedance monitoring device for a photovoltaic-storage DC-DC flexible power distribution system as described in claim 8, characterized in that, The third detection circuit includes resistor R9, one end of which is connected to pin 2 of relay RY3, and the other end is connected to ground FGND.

10. A method for monitoring the insulation impedance of a photovoltaic-storage DC-flexible microgrid based on the device described in any one of claims 1-9, characterized in that, Includes the following steps: The controller sends a first control signal to the detection circuit to activate relay RY3; After the first threshold time, send a second control signal, and at the same time turn on RY1 and RY2, and wait for the second threshold time; Receive the voltage signal V3 fed back by the detection circuit, and obtain the output voltage V1 of the power supply branch according to the logic of claim 2 or 4; Judge whether the output voltage V3 satisfies the determination interval: γ2×V1<V3<γ1×V1; if not, it is determined that there is a problem with insulation and an alarm is issued.

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