CN205123683U - A insulating monitor cell for photovoltaic inverter - Google Patents

Abstract

The utility model provides an insulating monitor cell for photovoltaic inverter. It includes double - circuit voltage measurement device, input buffer circuit, controller, output buffer circuit, resistance configuration network, input keyboard, warning circuit, LCD, isolation CAN interface, filter circuit and isolation source transformation device. The utility model provides an insulating monitor cell for photovoltaic inverter's result of use: can be through effectual hardware sampling return circuit, improve the sampling precision of DC voltage, reach the accurate sampling frequent fluctuation under, through the efficient algorithm, improve the frequency and the required precision of monitoring, reach the monitoring purpose of real -time and high accuracy.

Description

A kind of insulating monitoring unit for photovoltaic DC-to-AC converter

Technical field

The invention belongs to technical field of new energies, particularly relate to a kind of insulating monitoring unit for photovoltaic DC-to-AC converter.

Background technology

In the prior art, in most of photovoltaic DC-to-AC converter, the insulating monitoring technology of direct-current high-voltage system has various ways, but all there are some shortcomings:

1) sensitivity of relay test mode is low;

2) balanced bridge method can not accurately and timely be reported to the police when both positive and negative polarity insulation reduces simultaneously;

3) injecting AC signal method not only can make direct current system ripple increase, and affect power supply quality, and the distributed capacitance of system directly can affect measurement result, resolution is low.

Particularly in the D.C. isolation monitoring of photovoltaic DC-to-AC converter, because its direct voltage can fluctuate continually between 0-900V, said method be difficult to reach precision, real-time, in linear requirement.

Summary of the invention

In order to solve the problem, the object of the present invention is to provide a kind of insulating monitoring unit for photovoltaic DC-to-AC converter.

In order to achieve the above object, the insulating monitoring unit for photovoltaic DC-to-AC converter provided by the invention comprises: two-way voltage measuring apparatus, input isolation circuit, controller, output isolation circuit, resistance configuration network, input keyboard, warning circuit, liquid crystal display, isolated can interface, filter circuit and insulating power supply converting means, wherein: two-way voltage measuring apparatus is connected with controller by input isolation circuit, controller respectively with input keyboard, warning circuit, liquid crystal display is connected with isolated can interface, be connected with resistance configuration network by output isolation circuit simultaneously, two signal input parts of two-way voltage measuring apparatus are connected with positive direct-current bus M+ and negative DC bus M-respectively, two reference inputs are all connected with ground wire DG, the input of filter circuit is connected with accessory power supply DY, output is connected with the input of insulating power supply converting means, three inputs of resistance configuration network respectively with positive direct-current bus M+, negative DC bus M-connects and is connected with ground wire DG, the output of insulating power supply converting means exports+5V DC power supply, for this test cell provides working power.

Described input isolation circuit is digital signal photoelectric isolating circuit, and its input is connected with the digital output end of two-way voltage measuring apparatus, output adopts asynchronous serial bus to be connected with the digital input end of controller.

Described resistance configuration network comprises: the first biasing resistor R1, the second biasing resistor R2, the first electronic switch K1 and the second electronic switch K2; Wherein: one end of the first biasing resistor R1 is connected with positive direct-current bus M+ by the first electronic switch K1, the other end is connected with ground wire DG, one end of the second biasing resistor R2 is connected with negative DC bus M-by the second electronic switch K2, the other end is connected with ground wire DG; The control end of the first electronic switch K1 is first input end I1, the control end of the second electronic switch K2 is the second input I2.

Described output isolation circuit is two-way Phototube Coupling output circuit, and two input is connected with two output control terminals of controller respectively, two outputs are connected with two inputs of resistance configuration network respectively.

Described isolated can interface is isolated form CAN communication interface circuit.

Described controller is take microcontroller chip as the controller circuitry of core.

The result of use of the insulating monitoring unit for photovoltaic DC-to-AC converter provided by the invention: can effective hardware sampling circuit be passed through, improve the sampling precision of direct voltage, reach the precision sampling under frequent fluctuation, by efficient algorithm, improve frequency and the required precision of monitoring, reach real-time and high-precision monitoring object.

Accompanying drawing explanation

Fig. 1 is photovoltaic DC-to-AC converter insulation measurement schematic diagram;

Fig. 2 is the structural representation of the insulating monitoring unit for photovoltaic DC-to-AC converter provided by the invention;

Fig. 3 is the schematic diagram of resistance configuration network in this monitoring means.

Embodiment

Below in conjunction with the drawings and specific embodiments, the insulating monitoring unit for photovoltaic DC-to-AC converter provided by the invention is described in detail.

As shown in Figure 2, the insulating monitoring unit for photovoltaic DC-to-AC converter provided by the invention comprises:

Two-way voltage measuring apparatus 1, input isolation circuit 2, controller 3, output isolation circuit 4, resistance configuration network 5, input keyboard 6, warning circuit 7, liquid crystal display 8, isolated can interface 9, filter circuit 10 and insulating power supply converting means 11, wherein: two-way voltage measuring apparatus 1 is connected with controller 3 by input isolation circuit 2, controller 3 respectively with input keyboard 6, warning circuit 7, liquid crystal display 8 is connected with isolated can interface 9, be connected with resistance configuration network 5 by output isolation circuit 4 simultaneously, two signal input parts of two-way voltage measuring apparatus 1 are connected with positive direct-current bus M+ and negative DC bus M-respectively, two reference inputs are all connected with ground wire DG, the input of filter circuit 10 is connected with accessory power supply DY, output is connected with the input of insulating power supply converting means 11, three inputs of resistance configuration network 5 respectively with positive direct-current bus M+, negative DC bus M-connects and is connected with ground wire DG, the output of insulating power supply converting means 11 exports+5V DC power supply, for this test cell provides working power.

Described two-way voltage measuring apparatus 1 is double-channel analog/digital transducer, for gathering the direct voltage of direct voltage between positive direct-current bus M+ and ground wire DG and negative DC bus M-and ground wire DG, and send controller 3 to by input isolation circuit 2 after converting these two magnitudes of voltage to digital quantity.

Described input isolation circuit 2 is digital signal photoelectric isolating circuit, and its input is connected with the digital output end of two-way voltage measuring apparatus 1, output adopts asynchronous serial bus to be connected with the digital input end of controller 3.

As shown in Figure 3, described resistance configuration network 5 comprises: the first biasing resistor R1, the second biasing resistor R2, the first electronic switch K1 and the second electronic switch K2; Wherein: one end of the first biasing resistor R1 is connected with positive direct-current bus M+ by the first electronic switch K1, the other end is connected with ground wire DG, one end of the second biasing resistor R2 is connected with negative DC bus M-by the second electronic switch K2, the other end is connected with ground wire DG; The control end of the first electronic switch K1 is first input end I1, the control end of the second electronic switch K2 is the second input I2.

Described output isolation circuit 4 is two-way Phototube Coupling output circuit, and two input is connected with two output control terminals of controller 3 respectively, two outputs are connected with two inputs of resistance configuration network 5 respectively.

Described input keyboard 6 and liquid crystal display 8 form User Interface, and warning circuit 7 is acousto-optic hint circuit, for carrying out and alarm when serious insulation fault being detected.

Described isolated can interface 9 is isolated form CAN communication interface circuit, for communicating to connect with the photovoltaic DC-to-AC converter as subscriber equipment, transmits the control command that current Insulation monitoring state and reception come from user side.

Described controller 3 is take microcontroller chip as the controller circuitry of core, and it is the control core of this device, completes corresponding function for controlling other parts.

Now the insulating monitoring cell operation principle for photovoltaic DC-to-AC converter provided by the invention is described below:

This monitoring means mainly completes following several respects function: positive and negative busbar is to the switching control of the voltage measurement of ground wire, standard bias resistance, alarm parameters setting, sound light alarming circuit, liquid crystal display and communication.

The first biasing resistor R1 in resistance configuration network 5 and the second biasing resistor R2 adopts standard bias resistance, and its selection should follow following principle: (1) does not affect the original insulation property of system under test (SUT) substantially; (2) the certainty of measurement requirement of system will be taken into account; (3) the standard resistance of different brackets is automatically configured according to system voltage grade; (4) high accuracy, Low Drift Temperature coefficient.The actual biasing resistor configuration of system is as shown in table 1.

Table 1 DC bus-bar voltage and the biasing resistor table of comparisons

Voltage/V	50～150	150～250	250～350	350～450	>450
						Resistance/K Ω	100	200	300	400	500
Power/W	2	4	6	8	10

The selection of two-way voltage measuring apparatus 1: as the above analysis, when standard bias resistance is determined, the precision of voltage detecting directly determines the precision of final result.In general, the nominal voltage of photovoltaic DC-to-AC converter is between 90 ~ 500V, in running there is certain fluctuation range in cell voltage, and insulation resistance to be measured also has certain excursion, therefore, the tension measuring circuit of universal monitoring system must ensure the measurement realizing equally accurate in gamut, and the measurement of positive and negative Bus Voltage must complete simultaneously.Adopt Low Drift Temperature precision resistance bleeder circuit in the present invention, achieve equal precision measurement in conjunction with the high-resolution A/D of biproduct somatotype, main control unit and measuring circuit adopt photoelectric coupler isolation.This kind of method, compared with adopting the measurement scheme of LEM voltage sensor, overcomes the problem such as temperature drift, null offset of the latter, and the operating current simultaneously avoiding about the 10mA that it needs affects the shortcoming of the insulation property of system under test (SUT).

The structure and parameter of the measuring circuit of positive and negative Bus Voltage is completely the same, and its gatherer process is controlled to start conversion by controller 3 simultaneously, meets the simultaneity of measurement parameter.

HCS12 series 16 MCU29S12DJ64 [4] that controller 3 selects Motorola to release, inner except central processing unit CPU 12, not only be integrated with FLASH, EEPROM and RAM memory, but also the multiple interfaces such as integrated CAN, BDLC, SCI, SPI and HSIO, feature richness, speed is high, low in energy consumption, cost performance is high, system is simple, and chip supports background debug mode and a mass storage device expansion simultaneously.FLASH memory has fast programming ability, flexibly protection and security mechanism, and wipes and write without the need to outside high voltage.

The Cleaning Principle of this monitoring means:

The problem that the technical program will solve fluctuates frequently in direct-current high-voltage system at direct current, particularly in photovoltaic DC-to-AC converter, realizes high accuracy, high-frequency insulation resistance detects, and realize the long-distance Log server, warning etc. of Monitoring Data.

For solving above-mentioned art problem, the technical program adopts: on hardware, adopt precision resistance to carry out virtual voltage to the dividing potential drop of sampled voltage change, and the isolation of high-low pressure is carried out by relay, conditioning before adopting the temperature drift amplifier very low with drift to carry out AD, adopts the AD passage of TIM3 to carry out the collection of voltage; On software, during employing base be 100us sampling module to input voltage sample, by GPIO module, hardware relay is controlled in real time, adopt software compensation and algorithm sampled data to be reduced to direct-flow positive pole over the ground and direct current negative pole insulation resistance over the ground, and realize data upload and control after transfiniting exports, instruction of reporting to the police.

One, protocol population general introduction

Insulation status weighs with direct current positive and negative busbar insulation resistance over the ground.

By measuring the voltage between DC bus and ground wire, calculate the insulating resistance value of system.Suppose that direct current system voltage (i.e. battery total voltage) is U, insulation resistance between positive and negative bus to be measured and ground wire is respectively RP, RN, voltage between positive and negative bus and ground wire is respectively UP, UN, then the equivalent model of direct current system to be measured is as shown in the dotted line frame in Fig. 1.

Fig. 1 is photovoltaic DC-to-AC converter insulation measurement principle, and in figure, RC1, RC2 are the standard resistor of measuring known resistance.Operation principle is as follows: when switch S 1, S2 all disconnect, and the voltage measured between positive and negative bus and ground wire is respectively UP0, UN0, can be obtained by circuital law [2]:

UP0/RP＝UN0/RN(1)

When switch S 1 is closed, S2 disconnects, then between positive bus-bar and ground wire, add standard bias resistance RC1, the voltage measured between positive and negative bus and ground wire is respectively UPP, UNP, can obtain equally:

$\frac{U_{pp}}{R_p}+\frac{U_{pp}}{R_{C1}}=\frac{U_{N_p}}{R_N}---\left(2\right)$

Combined by formula (1), formula (2) and solve and can obtain:

$R_P=R_{C1}(\frac{U_{P0}{U}_{NP}}{U_{N0}{U}_{PP}}-1)---\left(3\right)$

$R_N=R_{C1}\left(\frac{U_{P0}{U}_{NP}-U_{N0}{U}_{PP}}{U_{P0}{U}_{PP}}\right)---\left(4\right)$

Equally, insulation resistance also can obtain in following 2 kinds of situations:

Switch S 1, S2 all disconnect and switch S 1 disconnects, switch S 2 closes;

Switch S 1 is closed, switch S 2 disconnects and switch S 1 disconnects, switch S 2 closes.

Two, measuring result error analysis

From above-mentioned computing formula, the concrete numerical value of insulation resistance RP, RN is calculated by 4 measuring voltage values and known standard resistor, and the precision of final result is directly related with the precision of voltage measurement and standard resistor.In addition, before and after switch motion, cell voltage also should be analyzed the impact of result with the change of illumination.

(1) measurement parameter is on the impact of precision

Suppose that battery total voltage U remains unchanged, the measurement relative error of UP0, UN0, UPP, UNP is respectively γ p0, γ N0, γ pp, γ NP, the relative error of standard resistor RC1 is γ RC, the actual value of RP, RN to be measured is RP0, RN0, and remain unchanged in measuring process, exhausted according to the error of error theory

Relative error γ RP, the γ RN that can obtain RP, RN to value synthetic method [3] are respectively:

$\begin{array}{c}{\mathrm{\γ}}_{RP}={\mathrm{\γ}}_{RC}+\frac{({\mathrm{\γ}}_{P0}+{\mathrm{\γ}}_{N0}+{\mathrm{\γ}}_{NP}+{\mathrm{\γ}}_{PP})U_{P0}{U}_{NP}}{U_{P0}{U}_{NP}-U_{N0}{U}_{PP}}\\ ={\mathrm{\γ}}_{RC}+({\mathrm{\γ}}_{P0}+{\mathrm{\γ}}_{N0}+{\mathrm{\γ}}_{NP}+{\mathrm{\γ}}_{PP})(1+R_{C1}/R_{P0})\end{array}$

$\begin{array}{c}{\mathrm{\γ}}_{RN}={\mathrm{\γ}}_{RC}+\frac{({\mathrm{\γ}}_{P0}+{\mathrm{\γ}}_{N0})U_{PP}{U}_{N0}+({\mathrm{\γ}}_{NP}+{\mathrm{\γ}}_{PP})U_{P0}{U}_{NP}}{U_{P0}{U}_{NP}-U_{N0}{U}_{PP}}\\ ={\mathrm{\γ}}_{RC}+({\mathrm{\γ}}_{P0}+{\mathrm{\γ}}_{N0})(R_{C1}/R_{P0})+({\mathrm{\γ}}_{NP}+{\mathrm{\γ}}_{PP})(1+R_{C1}/R_{P0})\end{array}$

Analyze known, the overall error of system and the ratio between standard resistor resistance and measured resistance have direct relation.As RC1nRP0, the measure error of system is minimum.Now the error of tentative standard resistance is negligible, and voltage measurement error γ p0=γ N0=γ pp=γ NP=γ V, if require overall error γ≤5% of result of calculation, then the error of voltage measurement must meet γ V≤1125%.

But, the insulation resistance of photovoltaic DC-to-AC converter system in actual During Process of Long-term Operation is change, and RC1 resistance can not very little (otherwise directly reducing the insulation status of electric motor car), resistance can be selected between 100 ~ 500 Ω/V when static measurement, and therefore actual error is larger.Such as, for the photovoltaic DC-to-AC converter direct current system of nominal 300V, select RC1=30k Ω, also meet measuring result error to ask insulation resistance when minimum value 30k Ω and be less than 5%, then voltage measurement error must be made to be less than 0.625%.

(2) impact of cell voltage transition

The insulation resistance of photovoltaic DC-to-AC converter is slow varying parameter in general, and measuring process is very fast, therefore can think that actual insulation resistance resistance to be measured remains unchanged in measuring process.

Suppose the detection method utilizing formula (3), formula (4) corresponding, when switch S 1, S2 all disconnect, cell voltage is U, U=UP0+UN0, and when switch S 1 is closed, switch S 2 disconnects, cell voltage is U ', U '=U ' PP+U ' NP.Can be obtained by formula (3), formula (4):

$R_P=R_{C1}(\frac{U_{P0}{U^{\′}}_{NP}}{U_{N0}{U^{\′}}_{PP}}-1)---\left(5\right)$

$R_N=R_{C1}(\frac{{U^{\′}}_{NP}}{{U^{\′}}_{PP}}-\frac{U_{N0}}{U_{P0}})---\left(6\right)$

Formula (5), formula (6) is more known with formula (3), formula (4) respectively, correct result be obtained, must ensure that U ' NP/U ' PP=UNP/UPP sets up.When constant for actual insulation resistance, with reference to circuit shown in Fig. 1, (in formula, RP//RC1 is the parallel connection value of 2 resistance RP and RC1 can to obtain RN/ (RP//RC1) according to circuit philosophy, identical below), this value can as constant process in of short duration measuring process, but must ensure to the simultaneity of voltage U P0, UN0 sampling and the simultaneity to UPP, UNP sampling in measuring process, otherwise destroy the correct condition of above-mentioned computational methods.

Claims (6)

1. for an insulating monitoring unit for photovoltaic DC-to-AC converter, it is characterized in that: the described insulating monitoring unit for photovoltaic DC-to-AC converter comprises: two-way voltage measuring apparatus (1), input isolation circuit (2), controller (3), output isolation circuit (4), resistance configuration network (5), input keyboard (6), warning circuit (7), liquid crystal display (8), isolated can interface (9), filter circuit (10) and insulating power supply converting means (11), wherein: two-way voltage measuring apparatus (1) is connected with controller (3) by input isolation circuit (2), controller (3) respectively with input keyboard (6), warning circuit (7), liquid crystal display (8) is connected with isolated can interface (9), be connected with resistance configuration network (5) by output isolation circuit (4) simultaneously, two signal input parts of two-way voltage measuring apparatus (1) are connected with positive direct-current bus M+ and negative DC bus M-respectively, two reference inputs are all connected with ground wire DG, the input of filter circuit (10) is connected with accessory power supply DY, output is connected with the input of insulating power supply converting means (11), three inputs of resistance configuration network (5) respectively with positive direct-current bus M+, negative DC bus M-connects and is connected with ground wire DG, the output of insulating power supply converting means (11) exports+5V DC power supply, for this test cell provides working power.

2. the insulating monitoring unit for photovoltaic DC-to-AC converter according to claim 1, it is characterized in that: described input isolation circuit (2) is digital signal photoelectric isolating circuit, its input is connected with the digital output end of two-way voltage measuring apparatus (1), output adopts asynchronous serial bus to be connected with the digital input end of controller (3).

3. the insulating monitoring unit for photovoltaic DC-to-AC converter according to claim 1, is characterized in that: described resistance configuration network (5) comprising: the first biasing resistor R1, the second biasing resistor R2, the first electronic switch K1 and the second electronic switch K2; Wherein: one end of the first biasing resistor R1 is connected with positive direct-current bus M+ by the first electronic switch K1, the other end is connected with ground wire DG, one end of the second biasing resistor R2 is connected with negative DC bus M-by the second electronic switch K2, the other end is connected with ground wire DG; The control end of the first electronic switch K1 is first input end I1, the control end of the second electronic switch K2 is the second input I2.

4. the insulating monitoring unit for photovoltaic DC-to-AC converter according to claim 1, it is characterized in that: described output isolation circuit (4) is two-way Phototube Coupling output circuit, two input is connected with two output control terminals of controller (3) respectively, two outputs are connected with two inputs of resistance configuration network (5) respectively.

5. the insulating monitoring unit for photovoltaic DC-to-AC converter according to claim 1, is characterized in that: described isolated can interface (9) is isolated form CAN communication interface circuit.

6. the insulating monitoring unit for photovoltaic DC-to-AC converter according to claim 1, is characterized in that: described controller (3) is take microcontroller chip as the controller circuitry of core.