CN106058930A - Automatic detecting system and automatic detecting method for capacitance of photovoltaic grid-connected inverter bus capacitor - Google Patents

Abstract

The invention relates to an automatic detecting system and an automatic detecting method for capacitance of a photovoltaic grid-connected inverter bus capacitor. At night, an inverter is in a standby state; voltage of a DC bus reduces; a soft starting loop of the inverter is started for charging a bus capacitor, so that the voltage of the bus capacitor of the inverter is equal with the DC voltage. After charging is finished, soft starting is stopped. Hereon, an auxiliary resistance testing loop is started. The bus capacitor performs discharging through an auxiliary testing resistor, and the bus capacitor is in zero-state response. The capacitance of the capacitor can be obtained through bus voltage integration in a discharging time period and dividing the integrated result by the bus voltage drop and the auxiliary testing resistance. Furthermore the calculated capacitance is compared with a preset capacitance lower limit, thereby determining whether the capacitance of the capacitor is qualified. If the capacitance is unqualified, fault alarm is performed for reminding change of the bus capacitor, thereby preventing further damage caused by performance reduction or failure of the bus capacitor.

Description

Photovoltaic combining inverter bus capacitor capacitance automatic checkout system and method

Technical field

The present invention relates to parallel network power generation field, particularly photovoltaic combining inverter bus capacitor capacitance and automatically detect system System and method.

Background technology

Solar energy as one of regenerative resource, has rich reserves, widely distributed, cleanliness without any pollution, environmental protection Advantage, the alternative energy source being well recognized as.The unidirectional current that solar panel sends through inverter be converted into line voltage constant amplitude, with Frequently, the alternating current of homophase, be transported to electrical network.

Photovoltaic combining inverter is made up of key components such as switching device unit, dc-link capacitance unit, and direct current is female Line capacitance is the vital unit of photovoltaic combining inverter, its act as photovoltaic combining inverter DC side with exchange During top-cross is changed, absorb and the most required transient current is provided, safeguarding the voltage stabilization of dc bus, it is also possible to absorb IGBT Turn off peak voltage etc..Photovoltaic combining inverter requires the service life possessing 25 years, but due to many reasons, dc bus electricity The performance held will reduce, and mainly shows as capacitor's capacity and reduces, thus cause DC bus-bar voltage ripple to increase, exports electric current THD increases, and when DC bus-bar voltage ripple exceedes photovoltaic combining inverter tolerance value, IGBT also will be caused to demolish, and accident expands Greatly, a lot of situations, are all other component wear such as IGBT, are just the discovery that the reason that dc-link capacitance capacitance reduces, the most directly Automatically the detection of stream bus capacitor capacitance is the most particularly significant.

The detection method of photovoltaic combining inverter dc-link capacitance capacitance at present, necessarily affects system when implementing normal Run.Prior art does not the most affect the simple and effective detection method that system is run, for this situation, set forth herein A kind of photovoltaic combining inverter bus capacitor capacitance automatic testing method, the method is simple, effective, stable, reliable.

Summary of the invention

It is an object of the invention to provide a kind of photovoltaic combining inverter bus capacitor capacitance automatic checkout system, and utilize The detection method of this system, affects, in order to solve prior art detection, the problem that system is properly functioning.

For achieving the above object, the solution of the present invention includes:

Photovoltaic combining inverter bus capacitor capacitance automatic checkout system, including for connecting photovoltaic apparatus (such as photovoltaic panel Deng) DC terminal, DC terminal connect dc bus, dc bus by current transformer, soft starting circuit connect ac terminal, Ac terminal is used for connecting AC network；Connect on dc bus and have bus capacitor and voltage sensor；On described dc bus Connect and have subtest loop, subtest loop include the subtest resistance of series connection and control switch.

Present invention also offers a kind of photovoltaic combining inverter bus capacitor capacitance automatic testing method, step is as follows:

When the evening draws on, DC bus-bar voltage is less than setting value in detection, disconnect the connection of photovoltaic apparatus and dc bus, Connect AC network, bus capacitor is charged；

After charging, disconnecting AC network, put into subtest loop, is discharged in subtest loop by bus capacitor；

At least the start-stop voltage in detection discharge process and discharge time, the difference according to electricity is equal with electric parameters integration Relation, calculates bus capacitor capacitance.

Further, the difference of described electricity is the product of voltage difference and bus capacitor, and electricity difference is equal with electric parameters integration Relation beThe computing formula of bus capacitor capacitance:

Wherein, U_c(t1)、U_c(t2) being respectively start-stop voltage, t1, t2 are start/stop time, R₄₁For subtest resistance, C is bus capacitor.

Further, when the bus capacitor capacitance calculated is compared with the bus capacitor capacitance of setting, and gap exceedes limit value Shi Ze alerts, and bus capacitor is changed in prompting.

The invention has the beneficial effects as follows, this capacitance determining method can detect automatically at night every day, it is possible in time The performance indications grasping bus capacitor, and the normal power generation not affecting daytime is grid-connected, and therefore the method does not affect system and runs, And it is high to detect frequency, simple, effectively, it is simple to realize in Practical Project and promote.

Voltage Hall additionally by inverter self i.e. can detect that accurate bus voltage value, it is not necessary to increases extra Detection device, calculate through voltage integrating meter the most again and i.e. can get the capacitance of electric capacity.Relative to utilizing based on current integration carries out Calculate, not only reduce detection variable, and can avoid owing to electric current is less, detect the inaccurate detection error brought thus drop Low calculating error.

Accompanying drawing explanation

Fig. 1 is a kind of photovoltaic combining inverter bus capacitor capacitance automatic checkout system of the embodiment of the present invention；

Fig. 2 is a kind of photovoltaic combining inverter bus capacitor capacitance automatic testing method of the embodiment of the present invention.

Detailed description of the invention

The present invention will be further described in detail below in conjunction with the accompanying drawings.

As it is shown in figure 1, photovoltaic combining inverter bus capacitor capacitance automatic checkout system, including for connecting photovoltaic apparatus The DC terminal of (such as photovoltaic panel etc.), DC terminal connects dc bus, and dc bus is connected by current transformer, soft starting circuit Ac terminal.Ac terminal is used for connecting AC network；Connect on dc bus and have bus capacitor.Use it is additionally provided with on dc bus Voltage sensor in detection busbar voltage.

Soft starting circuit includes main contactor and soft opens catalyst, soft opens resistance, for grid-connected and reduce startup The impact of electric current.Current transformer uses power bridge in bridge-type current transformer, i.e. figure.

Foregoing circuit part belongs to the grid-connected part of prior art.The present invention being improved by structure division, Being also associated with subtest loop on dc bus, subtest loop includes the subtest resistance of series connection and corresponding control System switch.In the present embodiment, voltage sensor is Hall voltage sensor.As other embodiments, it would however also be possible to employ other The voltage sensor of type.

The present invention carries out the principle of bus capacitor capacitance test:

The every night of gradually dying down along with sunray, cell panel port voltage is gradually lowered, and inverter stops Work, after treating that DC voltage is reduced to 0V, inverter startup exchange is soft, and to open loop (soft open catalyst and soft open resistance) right Dc-link capacitance is charged, and complete stopping to be charged is soft opens loop, then starts subtest loop and discharges, utilizes The capacity of bus capacitor is detected by direct-current discharge process.Capacitance detecting mainly utilize AC network therein, soft open loop, Power bridge, subtest loop, bus capacitor and Hall voltage sensor, wherein AC network provide power supply, soft open loop and Power bridge constitutes commutating circuit, is charged to bus capacitor, and subtest loop is bus capacitor electric discharge, voltage hall sensing Device carries out busbar voltage detection.Then inverter utilizes own controller to carry out capacitance calculation.

According to the character of electric capacity, there is an expressions below:

$i_c\left(t\right)=\frac{u_c\left(t\right)}{R_{41}}=C\frac{{\mathrm{du}}_c}{dt}---\left(1\right)$

R₄₁For subtest resistance.

(1) formula both sides integration can be obtained:

${\∫}_{t_1}^{t_2}\frac{u_c\left(t\right)}{R_{41}}dt=C{\∫}_{t_1}^{t_2}{\mathrm{du}}_c---\left(2\right)$

I.e.Thus can get the computing formula of capacitor's capacity, i.e. capacity:

$C=\frac{{\∫}_{t1}^{t2}{u}_c\left(t\right)dt}{\left(U_c\right(t2)-U_c(t1\left)\right)R_{41}}---\left(3\right)$

Can be seen that it is known that the change in voltage △ U at t1～t2 moment bus capacitor C two ends and bus capacitor two from formula (3) The voltage u of end_cT () can calculate capacitance value according to formula (3).

Specifically test process is as shown in Figure 2:

After detecting that inverter at night is shut down, (i.e. some is close to the setting value of 0V, originally less than 20V for DC voltage Skilled person can select according to practical situation) time, start soft loop of opening and electric capacity is charged.

(it is charged to set a magnitude of voltage can stop) after to be charged to stop soft opening loop, starts auxiliary simultaneously and survey Examination resistance (starts subtest loop by the control switch of Guan Bi with subtest resistant series), in busbar voltage from U_c (t1) is to U_c(t2) during, DC bus-bar voltage is integrated, when detecting that busbar voltage is less than U_c(t3) will auxiliary time Test loop excision (controls switch realization excision by disconnecting), wherein U_c(t3)<U_c(t2)<U_c(t1), formula is then utilized (3) bus capacitor capacitance is calculated, the capacitor's capacity of the result of calculating with setting is compared, when the bus electricity calculated Hold capacitance compared with the capacitor's capacity of setting (by being divided by or subtracting each other), suggest that bus capacitor problem tight when gap is excessive Weight, needs the information being replaced.

In above-described embodiment, carrying out period of bus capacitor detection is after the evening draws on, does not thus interfere with photovoltaic Normal work.It is therefore desirable to judge that the evening draws on；The judgement to night can be realized by the way of timing, such as control Device self-clocking chip or by master control system activity clocking information；Accurately judge that the evening draws on it can be avoided that black clouds on daytime blocks Shutdown situation is caused to be also carried out bus capacitor detection.As other embodiments, it is also possible to combine judgement with the information shut down The evening draws on.

Frequency as required, can select detect night every day, or detection in some days is once.

In above-described embodiment, use detection busbar voltage, utilize electricity poor (i.e. voltage difference is with electric capacity long-pending) to amass with voltage The relation detection capacitance of split-phase etc..As other embodiments, it is also possible to by sealing in current sense in subtest loop Device (such as current transformer) detects discharge current, detects appearance by the poor equal relation of the integration of discharge current and electricity Value, the concrete formula calculated will change current integration (resistance removing on denominator) into by voltage integrating meter in formula (3), therefore no longer Repeat.But owing to Hall voltage sensor belongs to the equipment inherently having on dc bus, therefore, use voltage integrating meter to enter Row calculates and need not introduce extra equipment, and relative to the scheme of current integration, cost is lower.

Above-described embodiment, in Fig. 1, DC terminal is the outfan of photovoltaic apparatus, therefore puts into the charging of subtest loop During with electric discharge, need to disconnect photovoltaic apparatus and the connection of DC terminal in Fig. 1, it is to avoid photovoltaic apparatus participates in filling bus capacitor Electricity and the electric discharge to subtest resistance.

It is presented above the detailed description of the invention that the present invention relates to, but the present invention is not limited to described embodiment. Under the thinking that the present invention provides, use the mode being readily apparent that to those skilled in the art to the skill in above-described embodiment Art means carry out converting, replace, revise, and the effect played is essentially identical with the relevant art means in the present invention, realize Goal of the invention the most essentially identical, so formed technical scheme above-described embodiment is finely adjusted formation, this technology Scheme still falls within protection scope of the present invention.

Claims (4)

1. photovoltaic combining inverter bus capacitor capacitance automatic checkout system, including the DC terminal for connecting photovoltaic apparatus, DC terminal connects dc bus, and dc bus connects ac terminal by current transformer, soft starting circuit, and ac terminal is for even Connect AC network；Connect on dc bus and have bus capacitor and voltage sensor；It is characterized in that, described dc bus connects Subtest loop, subtest loop is had to include the subtest resistance of series connection and control switch.

2. the detection method of detecting system as claimed in claim 1, it is characterised in that step is as follows:

When the evening draws on, DC bus-bar voltage is less than setting value in detection, disconnect the connection of photovoltaic apparatus and dc bus, connect AC network, charges to bus capacitor；

After charging, disconnecting AC network, put into subtest loop, is discharged in subtest loop by bus capacitor；

At least start-stop voltage in detection discharge process and discharge time, according to the pass that the difference of electricity is equal with electric parameters integration System, calculates bus capacitor capacitance.

Detection method the most according to claim 2, it is characterised in that the relation that the difference of electricity is equal with electric parameters integration isThe computing formula of bus capacitor capacitance:

Wherein, U_c(t1)、U_c(t2) being respectively start-stop voltage, t1, t2 are start/stop time, R₄₁For Subtest resistance, C is bus capacitor.

Detection method the most according to claim 2, it is characterised in that as the mother of the bus capacitor capacitance calculated Yu setting Line capacitance capacitance is compared, and gap then alerts when exceeding limit value, and bus capacitor is changed in prompting.