CN204481761U - The photovoltaic arrays ground insulation resistance on-line detecting system of high-power photovoltaic inverter - Google Patents

Abstract

The utility model provides a kind of photovoltaic arrays ground insulation resistance on-line detecting system of high-power photovoltaic inverter, photovoltaic arrays positive bus-bar PV+ and resistance R ₁one end is connected, described resistance R ₁the other end connects a MOSFET pipe Q ₁drain electrode, a described MOSFET pipe Q ₁source electrode be connected with the earth PGND, a described MOSFET pipe Q ₁drain electrode and source electrode between go back and be connected to resistance R ₃; Photovoltaic arrays positive bus-bar PV-and resistance R ₂one end is connected, described resistance R ₂the other end connects the 2nd MOSFET pipe Q ₂source electrode, described 2nd MOSFET pipe Q ₂drain electrode be connected with the earth PGND, described 2nd MOSFET pipe Q ₂drain electrode and source electrode between go back and be connected to resistance R ₄; A described MOSFET pipe Q ₁drived control end connect the first optocoupler drive circuit, described 2nd MOSFET pipe Q ₂drived control end connect the second optocoupler drive circuit; Described R ₁two ends, PV+ and PGND end, R ₂two ends and PV-and PGND end access the first voltage sampling circuit, the second voltage sampling circuit, tertiary voltage sample circuit and the 4th voltage sampling circuit respectively.Fast, loss is little, and range of application is wider in response.

Description

On-line detection system for photovoltaic square array to ground insulation resistance of high-power photovoltaic inverter

technical field

The utility model belongs to the technical field of photovoltaic power generation, and in particular relates to an on-line detection system for the ground insulation resistance of a photovoltaic square array of a high-power photovoltaic inverter.

Background technique

In high-power photovoltaic grid-connected inverters, the input voltage, that is, the voltage of the photovoltaic square array is relatively high, such as 500kW photovoltaic grid-connected inverters can be as high as 1000V. At the same time, in the photovoltaic power generation system, the on-site photovoltaic modules are affected by the sun, dust, rain, lightning strikes, construction transformation, etc., and the battery modules and their connecting cables may have problems such as aging and insulation resistance drop during long-term operation. Considering the electrical safety of power facilities, too small insulation resistance may cause the DC system to discharge to the ground; Potential imbalance and other problems, and serious problems may lead to damage to power generation system components, abnormal grid-connected inverter faults, grid-side transformer faults, etc. "Technical Specifications for Grid-connected Inverters for Power Generation" puts forward specific inspection requirements for the insulation resistance of photovoltaic square arrays to ground in grid-connected inverters. In view of the above, for high-voltage equipment such as high-power photovoltaic inverters, it is very important to design a photovoltaic array-to-ground insulation resistance detection system with fast response speed, high precision, real-time online detection, and economical and practical.

At present, the existing solutions for realizing the insulation resistance of photovoltaic square arrays mainly include: (1) Some inverters use the fixed resistance access voltage divider method, sample the divided voltage value, and compare it with the fixed predicted state to realize the insulation resistance analysis. The system is inflexible. In the case of standard changes, it is necessary to change the hardware before it can be used; (2) Some inverters use a balanced bridge detection method consisting of a relay or a single switch tube plus an adjustable resistor, and solve the insulation resistance through simultaneous equations , but this detection scheme will be different from the actual situation when both the positive and negative insulation are reduced; and the relay responds slowly, the adjustable resistance has practical problems such as the inability to automatically adapt, and there are also defects in life and cost. limited.

Utility model content

The purpose of the embodiment of the utility model is to provide an on-line detection system for the ground insulation resistance of a photovoltaic square array of a high-power photovoltaic inverter, so as to solve the problem of inflexible or inaccurate measurement in the prior art.

The embodiment of the utility model is realized in this way, an online detection system for the ground insulation impedance of a photovoltaic square array of a high-power photovoltaic inverter, in which:

The positive busbar PV+ of the photovoltaic array is connected to one end of the resistor _R1 , and the other end of the resistor _R1 is connected to the drain of the first MOSFET _Q1 , and the source of the first MOSFET _Q1 is connected to the ground PGND. A resistor _R3 is connected in parallel between the drain and the source of the MOSFET _Q1 ;

The positive busbar PV- of the photovoltaic array is connected to one end of the resistor _R2 , and the other end of the resistor _R2 is connected to the source of the second MOSFET _Q2 , and the drain of the second MOSFET _Q2 is connected to the ground PGND. A resistor _R4 is also connected in parallel between the drain and the source of the second MOSFET tube _Q2 ;

The drive control terminal of the first MOSFET _Q1 is connected to the first optocoupler drive circuit, and the drive control terminal of the second MOSFET _Q2 is connected to the second optocoupler drive circuit;

The two ends of _R1 , PV+ and PGND, _R2 and PV- and PGND are respectively connected to the first voltage sampling circuit, the second voltage sampling circuit, the third voltage sampling circuit and the fourth voltage sampling circuit.

In the first preferred embodiment of the photovoltaic array-to-ground insulation resistance online detection system of a high-power photovoltaic inverter provided by the utility model: the resistance values of the resistors R ₁ and R ₂ are greater than 10k ohms, and the resistance R The resistance value of ₃ is greater than 1 megaohm, and the resistance value of the resistor _R4 is greater than 1 megaohm.

In the second preferred embodiment of the on-line detection system for the ground insulation impedance of a photovoltaic square array of a high-power photovoltaic inverter provided by the utility model:

The PV+ and PV- terminals are connected to the fifth voltage sampling circuit.

In the third preferred embodiment of the on-line detection system for the ground insulation impedance of a photovoltaic square array of a high-power photovoltaic inverter provided by the utility model:

The voltage sampling circuit is implemented by a differential operational amplifier, including an input resistor, a matching resistor, a reference voltage resistor, a feedback resistor, a filter capacitor and an operational amplifier.

The beneficial effects of the on-line detection system for the ground insulation impedance of a photovoltaic square array of a high-power photovoltaic inverter provided by the embodiment of the utility model include:

1. Wider range of applications. For various power levels, such as 100kW-630kW high-power photovoltaic inverters, photovoltaic square array insulation resistance detection can be used; multiple switching and sampling voltages of MOSFETs can also be used to eliminate the influence of detection accuracy when the positive and negative insulation resistance values decrease ;

2. The implementation method is fast and accurate. Instead of solving the equations, the CPLD controls the switch of the MOSFET and the 10k ohm-level matching resistor voltage connected in series on the sampling bridge arm, and can solve the simple linear equation through the characteristics of the parallel branch of the resistors to obtain the insulation resistance of the positive and negative busbars to the ground;

3. Quick response and low loss. Compared with relays, adjustable resistors, etc., the switching speed of MOSFET and the sampling speed of CPLD can be very fast, and the op amp with large bandwidth can meet the needs of fast and multiple averaging, because the on-state resistance of MOSFET is very low and The switching does not need to be very frequent, so the loss is low, the power consumption is relatively small, and the power circuit design is easy, which basically guarantees the long-term reliable operation of the high-power inverter;

4. Good versatility and flexibility. Using CPLD as the main control, its program can be updated flexibly without changing the hardware.

5. High precision, real-time online detection, and cost advantages. It is mainly based on the fact that the method of the present utility model is not a system of equations, but a simple linear equation, and the calculation parameters are less than 4, without the influence of calculation errors caused by multiple parameters and complex multiplication and division operations, and can be achieved by quickly controlling the MOSFET. Multiple measurements are averaged, so the measurement accuracy is higher; in addition, the utility model realizes external communication, display and alarm I/O control, ADC sampling and MOSFET switch control, etc. through a high-level logic device such as CPLD, which is convenient for real-time online detection. Considering the selected solutions, especially low-power MOSFETs and small-capacity CPLD devices, compared with relays, adjustable resistors above 1W, multiple interface microcontrollers or DSP, the product cost will be lower and the performance will be more reliable.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the utility model, the following will briefly introduce the accompanying drawings that are required in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only the practical For some novel embodiments, those skilled in the art can also obtain other drawings based on these drawings without any creative work.

Fig. 1 is a schematic circuit diagram of a photovoltaic array-to-ground insulation impedance online detection system of a high-power photovoltaic inverter provided by the utility model;

Fig. 2 is a circuit structure diagram of the first voltage sampling circuit provided by the embodiment of the present invention;

Fig. 3 is a circuit structure diagram of a second voltage sampling circuit provided by an embodiment of the present invention;

Fig. 4 is a circuit structure diagram of a third voltage sampling circuit provided by an embodiment of the present invention;

Fig. 5 is a circuit structure diagram of a fourth voltage sampling circuit provided by an embodiment of the present invention;

Fig. 6 is a circuit structure diagram of a fifth voltage sampling circuit provided by an embodiment of the present invention;

Fig. 7 is a schematic structural diagram of the connection between the optocoupler drive circuit and the MOSFET tube provided by the embodiment of the present invention;

Fig. 8 is a schematic diagram of the ADC interface circuit provided by the embodiment of the present invention;

Fig. 9 is the signal diagram of the CPLD circuit part that the utility model embodiment provides;

Fig. 10 is a schematic diagram of the BUCK and voltage stabilizing circuit of the auxiliary power supply unit provided by the embodiment of the present invention.

Detailed ways

In order to make the purpose, technical solution and advantages of the utility model clearer, the utility model will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the utility model, and are not intended to limit the utility model.

In order to illustrate the technical solution described in the utility model, the following specific examples will be used for illustration.

As shown in Figure 1, it is a circuit schematic diagram of a photovoltaic square array ground insulation resistance online detection system of a high-power photovoltaic inverter provided by the utility model, in the system:

The positive busbar PV+ of the photovoltaic array is connected to one end of the resistor _R1 , the other end of the resistor _R1 is connected to the drain of the first MOSFET _Q1 , the source of the first MOSFET _Q1 is connected to the ground PGND, and the first MOSFET _Q1 A resistor R ₃ is connected in parallel between the drain and the source.

The positive busbar PV- of the photovoltaic array is connected to one end of the resistor _R2 , the other end of the resistor _R2 is connected to the source of the second MOSFET _Q2 , the drain of the second MOSFET _Q2 is connected to the ground PGND, and the second MOSFET _Q2 A resistor R ₄ is connected in parallel between the drain and the source.

The drive control terminal of the first MOSFET _Q1 is connected to the first optocoupler drive circuit, and the drive control terminal of the second MOSFET _Q2 is connected to the second optocoupler drive circuit.

Both ends of _R1 , PV+ and PGND, R2 _and PV- and PGND are respectively connected to the first voltage sampling circuit, the second voltage sampling circuit, the third voltage sampling circuit and the fourth voltage sampling circuit.

In specific implementation, resistors R ₁ and R ₂ are of 10k ohm level, resistor R ₃ is of mega ohm level, and resistor R ₄ is of 2M ohm level. The value of the matching resistance in series is tens of thousands of ohms, which is related to the maximum voltage of the photovoltaic array input by the high-power photovoltaic grid-connected inverter and the technical specification requirements in relevant standards; the parallel connection of megohm-level resistance is to improve the measurement accuracy It is designed because the megohm-level resistance can be ignored when the MOSFET is turned off and connected in parallel with the minimum square array DC bus-to-ground insulation resistance required by the standard.

Furthermore, in an embodiment of the on-line detection system for the ground-to-ground insulation resistance of a photovoltaic array of a high-power photovoltaic inverter provided by the present invention, the PV+ and PV- terminals are connected to the fifth voltage sampling circuit.

As shown in Figure 2-6, the circuit structure diagrams of the first voltage sampling circuit, the second voltage sampling circuit, the third voltage sampling circuit, the fourth voltage sampling circuit and the fifth voltage sampling circuit provided by the embodiment of the present invention respectively, The voltage sampling circuit is implemented by a differential operational amplifier. Taking Figure 2 as an example, the first voltage sampling circuit includes an input resistor R ₁₄ , a matching resistor R ₂₄ , a reference voltage resistor R ₃₄ , a feedback resistor R _f4 , a filter capacitor C _f4 and an operational amplifier U ₃ .

The high voltage end of the resistor _R1 passes through the resistor _R24 and then connects to the positive input end of the operational amplifier _U3 , and the low voltage end of the resistor _R1 passes through the resistor _R14 and then connects to the inverting input end of the operational amplifier _U3 . The positive input terminal of the operational amplifier _U3 is also connected to the reference voltage after passing through the resistor. A resistor R _f4 and a capacitor C _f4 are connected in parallel between the inverting input terminal and the output port of the operational amplifier U ₃ , and the real-time sampling of the voltage signal at both ends of R ₁ is completed through the differential operational amplifier.

Similarly, refer to Figure 3, Figure 4, Figure 5 and Figure 6 to complete the sampling of the voltage at both ends of _R2 , PV+ voltage sampling to ground, PV- voltage sampling to ground, and square array bus voltage sampling. The input resistors R ₁₁ , R ₁₂ , R ₁₃ , R ₁₄ and R ₁₅ and the matching resistors R ₂₁ , R ₂₂ , R ₂₃ , R ₂₄ and R ₂₅ are composed of multiple 1M European resistors in series, mainly for the consideration of electrical safety, the design According to the corresponding creepage distance specification, the feedback resistors R _f1 , R _f2 , R _f3 , R _f4 and R _f5 are 10kΩ, and the filter resistors C _f1 , C _f2 , C _f3 , C _f4 and C _f5 are 1nf. The implementation should also include voltage clamping protection through bidirectional diodes and low-pass filtering of the output voltage of the operational amplifier to eliminate the influence of AC signals and ensure the accuracy and reliability of the circuit.

As shown in Figure 7, it is a structural schematic diagram of the connection between the optocoupler drive circuit and the MOSFET tube provided by the embodiment of the utility model. The driving of the MOSFET tube _Q1 of the upper bridge arm in Figure 7 is an example, and the output control signal VT1 of the drive unit is switched with the resistor The input signal VT1 of MOSFET tube _Q1 in the unit is connected.

Embodiment one

Embodiment 1 provided by the utility model is an example of using the on-line detection system for the photovoltaic square array ground insulation impedance of a high-power photovoltaic inverter provided by the utility model. The circuit and the second optocoupler driving circuit control the turn-on or turn-off of the first MOSFET _Q1 and the second MOSFET _Q2 , including:

Step 1. Control VT1 so that the first MOSFET _Q1 is turned on, and the second MOSFET _Q2 is turned off. At this time, _R3 is short-circuited by _Q1 , and the first voltage sampling circuit measures the voltage _U1 across _R1 . The second voltage sampling circuit measures the voltage U _PV+ between PV+ and PGND terminals.

The linear equation is obtained from Kirchhoff's current law:

$\frac{u_1}{R_1}=\frac{u_{\mathrm{PV}+}}{R_{\mathrm{PV}+}}$ Formula 1);

R _PV+ is the insulation resistance of the positive busbar of the square array to the ground. In the specific implementation, _R1 can be selected as 50k, and the error can be reduced through four resistors in 2 series. Therefore, the three parameter values are known in the formula (3). get

$R_{\mathrm{PV}+}=\frac{u_{\mathrm{PV}+}}{u_1}\&Center\; Dot;R_1$ Formula (2).

Step 2. Control VT2 so that the first MOSFET _Q1 is turned off, and the second MOSFET _Q2 is turned on. At this time, _R4 is short-circuited by _Q2 , and the first voltage sampling circuit measures the voltage _U2 across _R2 . Two voltage sampling circuits measure the voltage U _PV- between PV- and PGND terminals.

The linear equation is obtained from Kirchhoff's current law:

$\frac{u_2}{R_2}=\frac{u_{\mathrm{PV}-}}{R_{\mathrm{PV}-}}$ Formula (3);

R _PV- is the insulation resistance of the negative busbar of the square array to the ground. In the specific implementation, _R2 can be selected as 50k, and the error can be reduced through four resistors 2 in series. Therefore, three parameter values are known in formula (3), namely available

$R_{\mathrm{PV}-}=\frac{u_{\mathrm{PV}-}}{u_2}\·R_2$ Formula (4).

By taking the average value of multiple measurements, the more accurate values of the positive busbar-to-ground insulation resistance R _PV+ of the square array and the negative busbar-to-ground insulation resistance R _PV- of the square array can be obtained.

Further, the first embodiment provided by the utility model is an example of using the on-line detection system for the photovoltaic square array ground insulation impedance of a high-power photovoltaic inverter provided by the utility model, and the second embodiment can also be controlled through the CPLD connection. An optocoupler driving circuit and a second optocoupler driving circuit perform actual measurement, and the output terminals of the first voltage sampling circuit, the second voltage sampling circuit, the third voltage sampling circuit, the fourth voltage sampling circuit and the fifth voltage sampling circuit are passed through the ADC Connect the CPLD after the interface circuit to collect the data.

Figure 8 is a schematic diagram of the ADC interface circuit provided by the embodiment of the utility model, and Figure 9 is a signal diagram of the CPLD circuit part provided by the embodiment of the utility model.

The drive control VT1 and VT2 of the two MOSFETs are centrally controlled by the CPLD through the I/O interface and the drive circuit shown in Figure 7. The output of the sampling signal, such as U1 and other signals, is connected to the interface of an external ADC chip (such as ADS7841); the ADC chip U9 is connected to the corresponding ADC bus interface of the CPLD through the bus output; the signal processing and communication unit of the CPLD is connected to the signal processing unit of the two bridge arms The output is also connected with the input of the MOSFET drive unit for resistance switching, connected with the output of the ADC interface circuit, and connected with the communication interface circuit; the actual implementation also includes signal indication and alarm circuits.

The PWM signal of the CPLD is amplified and driven by two push-pull triode circuits to play the role of the main switch in the BUCK circuit, and then through the isolation transformer T1, the secondary side outputs two 15V power supplies, and the secondary output AC voltage is rectified Diodes D2 and D4, Zener diodes D3 and D5, and filter capacitors C29, C30, C32 and C33 obtain stable two-way 15V output power.

As shown in Figure 10, the auxiliary power supply unit provided by the embodiment of the utility model is composed of BUCK and a schematic diagram of a voltage stabilizing circuit, which is used to supply power to each unit of the above-mentioned online detection system. Figure 10 shows part of the BUCK circuit. The PWM signal from the CPLD in Figure 9 is amplified and driven by two push-pull triode circuits to play the role of the main switch in the BUCK circuit, and then through the isolation transformer T1, the secondary side Output two 15V power supplies, and the secondary output AC voltage passes through rectifier diodes D2 and D4, Zener diodes D3 and D5, filter capacitors C29, C30, C32 and C33 to obtain stable two 15V output power supplies.

The above descriptions are only preferred embodiments of the present utility model, and are not intended to limit the present utility model. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present utility model shall be included in this utility model. within the scope of protection of utility models.

Claims (4)

1. a photovoltaic arrays ground insulation resistance on-line detecting system for high-power photovoltaic inverter, is characterized in that, in described system:

Photovoltaic arrays positive bus-bar PV+ and resistance R ₁one end is connected, described resistance R ₁the other end connects a MOSFET pipe Q ₁drain electrode, a described MOSFET pipe Q ₁source electrode be connected with the earth PGND, a described MOSFET pipe Q ₁drain electrode and source electrode between go back and be connected to resistance R ₃;

Photovoltaic arrays positive bus-bar PV-and resistance R ₂one end is connected, described resistance R ₂the other end connects the 2nd MOSFET pipe Q ₂source electrode, described 2nd MOSFET pipe Q ₂drain electrode be connected with the earth PGND, described 2nd MOSFET pipe Q ₂drain electrode and source electrode between go back and be connected to resistance R ₄;

A described MOSFET pipe Q ₁drived control end connect the first optocoupler drive circuit, described 2nd MOSFET pipe Q ₂drived control end connect the second optocoupler drive circuit;

Described R ₁two ends, PV+ and PGND end, R ₂two ends and PV-and PGND end access the first voltage sampling circuit, the second voltage sampling circuit, tertiary voltage sample circuit and the 4th voltage sampling circuit respectively.

2. the system as claimed in claim 1, is characterized in that, described resistance R ₁and R ₂resistance is greater than 10k ohm, described resistance R ₃resistance be greater than 1 megohm, described resistance R ₄resistance be greater than 1 megohm.

3. the system as claimed in claim 1, is characterized in that, described PV+ and PV-termination enters the 5th voltage sampling circuit.

4. system as claimed in claim 3, it is characterized in that, described voltage sampling circuit is realized by difference amplifier, comprises input resistance, build-out resistor, reference voltage resistance, feedback resistance, filter capacitor and amplifier.