CN104716902A - Device and method for measuring maximum power of photovoltaic module and method for measuring generated energy - Google Patents

Abstract

The embodiment of the invention provides a device and a method for measuring the maximum power of a photovoltaic module and a method for measuring the power generation amount, wherein the device for measuring the maximum power of the photovoltaic module comprises the following components: one end of the voltage measuring circuit is connected with the anode of the photovoltaic module, and the other end of the voltage measuring circuit is connected with the cathode of the photovoltaic module, and the voltage measuring circuit is used for measuring the open-circuit voltage and the discharge voltage of the photovoltaic module in the current environment; and the controller is connected with the voltage measuring circuit and is used for acquiring the second maximum power of the photovoltaic module under the current environment according to the first maximum power under the standard environment, the working voltage and the working current corresponding to the first maximum power point, the open-circuit voltage and the discharge voltage. The device and the method for measuring the maximum power of the photovoltaic module and the method for measuring the generated energy can measure the maximum power and the generated energy of the photovoltaic module, improve the measurement accuracy, and have the advantages of simple structure, high reliability and low cost.

Description

The maximum power measurement mechanism of photovoltaic module, method and energy output method of measurement

Technical field

The present invention relates to technical field of photovoltaic power generation, particularly relate to a kind of maximum power measurement mechanism of photovoltaic module, method and energy output method of measurement.

Background technology

Solar energy, as a kind of new forms of energy of clean environment firendly, is subject to people and more and more pays close attention to.In the operation of photovoltaic plant, energy output is the key index evaluating its performance.In prior art, mainly contain two kinds of methods:

One is mathematical model method: utilize temperature sensor and light intensity sensor to gather environmental parameter, then in conjunction with the Mathematical Modeling of photovoltaic battery panel, calculates the output power value of photovoltaic cell under this environmental parameter.The deficiency of the method is that Mathematical Modeling is comparatively complicated, needs a large amount of site environment and electric parameter to correct wherein parameter, reduces its engineering practicability.

Two is look-up tables: the method is according to the thought of piece-wise linearization, first set up photovoltaic cell peak power output and temperature and light strong between relation table, then method by experiment, record each temperature and light in relation table and descend by force the peak power output of photovoltaic cell, and insert in table, as the reference of power prediction in future.The deficiency of the method is, when setting up photovoltaic cell peak power output and the strong relation table of temperature and light, need to gather the power output under various environment, its workload is larger, the foundation of relation table carries out gathering and testing in photovoltaic cell site in addition, and when photovoltaic cell site changes, the relation table set up no longer is applicable to current location, therefore the method adaptability is not strong, as still gone to obtain peak power output based on the relation table established, the peak power output accuracy of acquisition will be caused not high.

Summary of the invention

Embodiments of the invention provide a kind of maximum power measurement mechanism of photovoltaic module, method and energy output method of measurement, can improve and measure the maximum power of photovoltaic module and the accuracy of energy output.

For achieving the above object, The embodiment provides a kind of maximum power measurement mechanism for photovoltaic module, described device comprises: tension measuring circuit, described tension measuring circuit one end is connected with the positive pole of described photovoltaic module, the other end is connected with the negative pole of described photovoltaic module, for measuring open circuit voltage and the discharge voltage of the described photovoltaic module of current environment; Controller, be connected with described tension measuring circuit, for according to the first maximum power under standard environment and operating voltage corresponding to the first maximum power point and operating current, described open circuit voltage and discharge voltage, obtain the second maximum power of the described photovoltaic module under current environment.

Embodiments of the invention additionally provide a kind of maximum power method of measurement for photovoltaic module, and described method comprises: open circuit voltage and the discharge voltage of measuring the described photovoltaic module of current environment; According to the first maximum power under standard environment and operating voltage corresponding to the first maximum power point and operating current, described open circuit voltage and discharge voltage, obtain the second maximum power of the described photovoltaic module under current environment.

Embodiments of the invention additionally provide a kind of energy output method of measurement for photovoltaic module, described method comprises: in predetermined time section, the maximum power method of measurement for photovoltaic module of above-described embodiment is utilized, the maximum power that each time interval under acquisition current environment is corresponding with setting-up time interval; Calculated the energy output of described photovoltaic module by following formula according to maximum power corresponding to the length of predetermined time section, the time interval of setting and described each time interval:

$W_{\mathrm{PV}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}(\mathrm{\ΔT}\·P_{\mathrm{MPP}}^{\′}\left(i\right)),$

Wherein, W _pVfor the energy output of described photovoltaic module, Δ T is setting-up time interval, and i is the sequence number in the time interval, and N is the number comprising the time interval in predetermined amount of time, P ' _mPPi () is maximum power corresponding in i-th time interval.

The maximum power measurement mechanism of the photovoltaic module that the embodiment of the present invention provides, method and energy output method of measurement, have following technique effect:

On the one hand, the present invention is the maximum power based on measuring open circuit voltage and the discharge voltage acquisition photovoltaic module obtained, for mathematical model method in prior art, open circuit voltage in the present invention and discharge voltage measured value accuracy is high, error is little, thus improve the accuracy measuring photovoltaic module maximum power, and engineering practicability is strong;

On the other hand, open circuit voltage and discharge voltage belong to the electric signal parameter of photovoltaic module inside, the relation table of external environment condition parameter (temperature and light is strong) and power output is utilized compared to prior art, the power output of photovoltaic module is done and indirectly predicts, its parameter form is more close to the power output of photovoltaic module, and as internal electrical signal parameter, it more can embody the electrology characteristic of tested photovoltaic module, therefore, the power output of the photovoltaic module obtained based on this open circuit voltage and discharge voltage can be more accurate, and workload is little, strong adaptability.

Accompanying drawing explanation

Fig. 1 is the schematic diagram of the volt-ampere characteristic of photovoltaic module;

Fig. 2 is the structural representation of the maximum power measurement mechanism for photovoltaic module of the embodiment of the present invention one;

Fig. 3 is the structural representation of the maximum power measurement mechanism for photovoltaic module of the embodiment of the present invention two;

Fig. 4 is the schematic flow sheet of the maximum power method of measurement for photovoltaic module of the embodiment of the present invention three;

Fig. 5 is the schematic flow sheet of the energy output method of measurement for photovoltaic module of the embodiment of the present invention four.

Embodiment

Be used for the maximum power measurement mechanism of photovoltaic module, method and energy output method of measurement below in conjunction with accompanying drawing to the embodiment of the present invention to be described in detail.

Maximum power measurement mechanism for photovoltaic module of the present invention, method and energy output method of measurement know-why are the open circuit voltage and the discharge voltage that utilize tension measuring circuit to measure photovoltaic module under current environment, again based on the first maximum power under this open circuit voltage and discharge voltage, standard environment and operating voltage corresponding to the first maximum power point and operating current, calculate the maximum power of photovoltaic module.

For the ease of understanding the embodiment of the present invention, be used for the embodiment of the present invention by reference to the accompanying drawings before the maximum power measurement mechanism of photovoltaic module, method and energy output method of measurement be described in detail, explaining following technical term.

[I. photovoltaic module]

Photovoltaic module (also claiming solar panel) is the core in solar power system, is also most important part in solar power system.Its effect converts solar energy into electrical energy.

[II. the volt-ampere characteristic of photovoltaic module]

Fig. 1 is the schematic diagram of the volt-ampere characteristic of photovoltaic module, with reference to Fig. 1, by the photovoltaic module of illumination, under certain irradiance and temperature and different external circuit loads, and the electric current of inflow and the relation curve of photovoltaic module terminal voltage.

(i) short circuit current (I _sC), under certain irradiance and temperature conditions, the output current of photovoltaic module when terminal voltage is zero.

(ii) open circuit voltage (V _oC), under certain irradiance and temperature conditions, photovoltaic module terminal voltage in the case of an open circuit.

(iii) maximum power (P _m), under certain irradiance and temperature conditions, the maximum power value on the power vs. voltage curve of photovoltaic module; Or the maximum of electric current and voltage product in the volt-ampere characteristic of photovoltaic module.

(iv) maximum power point (maximum power point, MPP), in the volt-ampere characteristic of photovoltaic module, the point of corresponding maximum power, also claims best operating point.

V operating current (I that () maximum power point is corresponding _mPP), the electric current in the volt-ampere characteristic of photovoltaic module corresponding to maximum power point.

(vi) operating voltage (V that maximum power point is corresponding _mPP), the voltage in the volt-ampere characteristic of photovoltaic module corresponding to maximum power point.

Embodiment one

Fig. 2 is the structural representation of the maximum power measurement mechanism for photovoltaic module of the embodiment of the present invention one, as shown in Figure 2, the maximum power measurement mechanism for photovoltaic module of the embodiment of the present invention comprises: tension measuring circuit 11, tension measuring circuit one end is connected with the positive pole of photovoltaic module, the other end is connected with the negative pole of photovoltaic module, for measuring open circuit voltage and the discharge voltage of the photovoltaic module of current environment; Controller 12, be connected with tension measuring circuit 11, for according to the first maximum power under standard environment and operating voltage corresponding to the first maximum power point and operating current, open circuit voltage and discharge voltage, obtain the second maximum power of the photovoltaic module under current environment.

Concrete, this tension measuring circuit is nonpolarity, only need draw two ends, is connected respectively with the positive pole of photovoltaic module, negative pole.Controller control voltage measuring circuit records open circuit voltage and the discharge voltage of photovoltaic module under current environment, and feed back to controller, controller is according to the open circuit voltage of feedback and discharge voltage, refer again to the first maximum power under standard environment and operating voltage corresponding to the first maximum power point and operating current, thus the second maximum power of photovoltaic module under getting current environment.

The maximum power measurement mechanism for photovoltaic module that the embodiment of the present invention provides, measuring the open circuit voltage of current environment and discharge voltage by connecting tension measuring circuit at the both positive and negative polarity of photovoltaic module, just can obtain the maximum power of photovoltaic module based on the first maximum power under this open circuit voltage and discharge voltage, standard environment and operating voltage corresponding to the first maximum power point and operating current.And prior art generally adopts temperature sensor and light intensity sensor to obtain temperature, light intensity parameter, these environmental parameters are utilized to predict the maximum power of photovoltaic module.

Can show that the technical scheme of the present embodiment has following technique effect by comparative analysis:

1) the present embodiment is the maximum power based on measuring open circuit voltage and the discharge voltage acquisition photovoltaic module obtained, for mathematical model method in prior art, open circuit voltage in the present invention and discharge voltage measured value accuracy is high, error is little, thus the accuracy measuring photovoltaic module maximum power can be improved, and improve engineering practicability.A large amount of site environment of contrary prior art and measurement of electric parameter difficulty are comparatively large, and error is also very high, poor practicability, based on the very difficult guarantee of accuracy of the photovoltaic module maximum power that these parameters obtain.

2) open circuit voltage and discharge voltage belong to the electric signal parameter of photovoltaic module inside, compared to look-up table in prior art, parameter form of the present invention is more close to the power output of photovoltaic module, and as internal electrical signal parameter, it more can embody the electrology characteristic of tested photovoltaic module, therefore, the power output of the photovoltaic module obtained based on this open circuit voltage and discharge voltage can be more accurate, and workload is little, strong adaptability.Contrary prior art needs to gather the power output under various environment when setting up photovoltaic cell peak power output and the strong relation table of temperature and light, workload is comparatively large, and adaptability is strong, causes the peak power output accuracy that obtains low.

Embodiment two

Fig. 3 is the structural representation of the maximum power measurement mechanism for photovoltaic module of the embodiment of the present invention two, as shown in Figure 3, the maximum power measurement mechanism for photovoltaic module of the embodiment of the present invention comprises: tension measuring circuit 21, tension measuring circuit one end is connected with the positive pole of photovoltaic module, the other end is connected with the negative pole of photovoltaic module, for measuring open circuit voltage and the discharge voltage of the photovoltaic module of current environment; Controller 22, be connected with tension measuring circuit 21, for according to the first maximum power under standard environment and operating voltage corresponding to the first maximum power point and operating current, open circuit voltage and discharge voltage, obtain the second maximum power of the photovoltaic module under current environment.

With reference to Fig. 3, shown in dotted line frame is tension measuring circuit, tension measuring circuit 21 can comprise discharge resistor 211, switching device 212 and voltmeter 213, wherein, discharge resistor 211 and switching device 212 are composed in series series arm, voltmeter 213 is in parallel with series arm, the control signal that switching device 212 sends in response to controller 22, control the disconnection or closed of series arm, when series arm disconnects, the open circuit voltage of photovoltaic module measured by voltmeter 213, and send to controller 22, when series arm closes, discharge voltage when photovoltaic module discharges to discharge resistor 211 measured by voltmeter 213, and send to controller 22.The simple and reliable property of this tension measuring circuit structure is high.

Concrete, switching device can be specially, but is not limited to, relay or contactor.Also other switching device can be used to replace, and for example, controller sends control signal, and control relay disconnects, and the open circuit voltage of photovoltaic module measured to obtain by voltmeter; Controller sends control signal, and control relay closes, and after current stabilization, the discharge voltage of photovoltaic module when discharging to discharge resistor measured to obtain by voltmeter.

Further, tension measuring circuit can also comprise inductance, and one end of this inductance is connected with discharge resistor, and the other end of inductance is connected with switching device, the moment impact electric current produced when closing for avoiding switching device.

In embodiments of the present invention, discharge resistor is the resistance that resistance is enough little, after series arm is closed, photovoltaic module is discharged by this discharge resistor, thus will voltage be produced at these discharge resistor two ends, after current stabilization, voltmeter can record voltage when photovoltaic module discharges to discharge resistor, i.e. discharge voltage, because the resistance of discharge resistor is enough little, can be similar to and think that the electric current flowing through resistance is short circuit current, the computing the resistor value therefore by discharge voltage value and discharge resistor obtains short-circuit current value.

Tension measuring circuit in this device of the present embodiment is simply made up of inductance, resistance and voltmeter etc., does not need to configure the external equipments such as relatively expensive temperature sensor and light intensity sensor, therefore, reduces the complexity of structure, reduce cost simultaneously.

Further, after obtaining short-circuit current value, utilize the Practical model of photovoltaic module known by analysis, the ratio of the operating current that the ratio of the short circuit current under varying environment condition is corresponding with maximum power point is equal, the ratio of the operating voltage that the ratio of the open circuit voltage under varying environment condition is corresponding with maximum power point is equal, concrete as formula (1) and formula (2):

I ' _sC/ I " _sC=I ' _mPP/ I " _mPPformula (1)

V ' _oC/ V " _oC=V ' _mPP/ V " _mPPformula (2)

Wherein, I ' _sCfor the short circuit current under the first environment, I ' _mPPfor the operating current that the maximum power point under the first environment is corresponding, V ' _oCfor the open circuit voltage under the first environment, V ' _mPPfor the operating voltage that the maximum power point under the first environment is corresponding, I " _sCfor the short circuit current under the second environment, I " _mPPfor the operating current that the maximum power point under the second environment is corresponding, V " _oCfor the open circuit voltage under the second environment, V " _mPPfor the operating voltage that the maximum power point under the second environment is corresponding.

Here, it should be noted that different environmental conditions generally refers to irradiance and the ambient temperature of photovoltaic module, the power of photovoltaic module is mainly subject to the impact of irradiance and ambient temperature.

So, suppose that the first environment is current environment, the second environment is standard environment, and namely irradiance is 1000W/m ²ambient temperature is 25 DEG C, the first maximum power under standard environment and operating voltage corresponding to the first maximum power point and operating current are known numeric value, controller just by following formula (3) and formula (4) according to the first maximum power under standard environment and operating voltage corresponding to the first maximum power point and operating current, open circuit voltage and discharge voltage, can obtain the second maximum power of the photovoltaic module under current environment:

$I_{\mathrm{SC}}^{\′}=\frac{V_{\mathrm{SC}}^{\′}}{R}$ Formula (3)

$P_{\mathrm{MPP}}^{\′}=P_{\mathrm{MPPN}}\frac{V_{\mathrm{OC}}^{\′}{I}_{\mathrm{SC}}^{\′}}{V_{\mathrm{OCN}}{I}_{\mathrm{SCN}}}$ Formula (4)

Wherein, V ' _sCfor the discharge voltage of photovoltaic module under the current environment that measurement obtains, R is discharge resistance, I ' _sCfor the short circuit current of photovoltaic module under current environment, V ' _oCfor the open circuit voltage of photovoltaic module under the current environment that measurement obtains, P ' _mPPfor the second maximum power of photovoltaic module, P _mPPNfor the first maximum power under standard environment, V _oCNfor the operating voltage that the first maximum power point under standard environment is corresponding, I _sCNfor the operating current that the first maximum power point under standard environment is corresponding.

In the present embodiment, the discharge voltage directly recorded based on tension measuring circuit calculates short circuit current, and using standard environment as under the prerequisite of wherein a kind of environmental condition, under utilizing varying environment condition, the parameter of photovoltaic module under the proportionate relationship of the proportionate relationship of the operating current that short circuit current is corresponding with maximum power point, operating voltage that open circuit voltage is corresponding with maximum power point and standard environment, just can obtain the maximum power of current environment photovoltaic module, its account form is easy, and the accuracy of the photovoltaic module maximum power finally obtained is high.Below in conjunction with concrete example, carry out further the embody rule of the illustratively embodiment of the present invention more intuitively.

Choose 5 kinds of photovoltaic battery panels, power grade is 210W-300W.The use specifications of photovoltaic battery panel give the maximum power value P under reference condition (1000W/m2,25 DEG C) and non-standard condition (800W/m2,20 DEG C) these two kinds of conditions _mPPNand P _mPP.

Adopt this device of the embodiment of the present invention, measure the open circuit voltage under non-standard condition and discharge voltage, short circuit current is calculated by the discharge voltage recorded, the maximum power of photovoltaic battery panel under non-standard condition can be obtained by aforementioned computing formula (4), then the maximum power of photovoltaic battery panel under the non-standard condition provided in the maximum power of photovoltaic battery panel under acquisition non-standard condition and specifications contrasted, result is as shown in table 1 below:

Table 1

Sequence number

P MPPN

P MPP

V′ OC

I′ SC

P′ MPP

Error (%)

1

210W

152.1W

28.6V

7.13A

157.85W

3.78

2

220W

160.5W

28.1V

7.19A

164.35W

2.40

3

240W

175.1W

34.8V

6.81A

178.68W

2.04

4

250W

182.4W

34.2V

7.01A

186.50W

2.25

5

260W

189.7W

34.4V

7.25A

194.27W

2.41

6

280W

204.2W

36.7V

7.76A

209.36W

2.53

7

290W

211.5W

41.9V

7.16A

216.85W

2.53

8

300W

218.8W

42.7V

7.10A

223.40W

2.10

From the error result in table 1, the maximum power of the photovoltaic battery panel adopting this device of the embodiment of the present invention to obtain control errors within 5%, can meet the standard of engineer applied completely.

Embodiment three

Fig. 4 is the schematic flow sheet of the maximum power method of measurement for photovoltaic module of the embodiment of the present invention three, and as shown in Figure 4, the maximum power method of measurement for photovoltaic module comprises:

Step 301: open circuit voltage and the discharge voltage of measuring the photovoltaic module of current environment.

Step 302: according to the open circuit voltage under the first maximum power under standard environment and operating voltage corresponding to the first maximum power point and operating current, current environment and discharge voltage, obtain the second maximum power of the photovoltaic module under current environment.Concrete, according to the open circuit voltage under the first maximum power under standard environment and operating voltage corresponding to the first maximum power point and operating current, current environment and discharge voltage, obtain processing and utilizing following formula (5) and formula (6) realization of the second maximum power of the photovoltaic module under current environment:

$I_{\mathrm{SC}}^{\′}=\frac{V_{\mathrm{SC}}^{\′}}{R}$ Formula (5)

$P_{\mathrm{MPP}}^{\′}=P_{\mathrm{MPPN}}\frac{V_{\mathrm{OC}}^{\′}{I}_{\mathrm{SC}}^{\′}}{V_{\mathrm{OCN}}{I}_{\mathrm{SCN}}}$ Formula (6)

Wherein, V ' _sCfor the discharge voltage of photovoltaic module under the current environment that measurement obtains, R is discharge resistance, I ' _sCfor the short circuit current of photovoltaic module under current environment, V ' _oCfor the open circuit voltage of photovoltaic module under the current environment that measurement obtains, P ' _mPPfor the second maximum power of photovoltaic module, P _mPPNfor the first maximum power under standard environment, V _oCNfor the operating voltage that the first maximum power point under standard environment is corresponding, I _sCNfor the operating current that the first maximum power point under standard environment is corresponding.

The maximum power method of measurement for photovoltaic module that the embodiment of the present invention provides, by measuring the open circuit voltage of current environment and discharge voltage, the maximum power of photovoltaic module just can be obtained based on the first maximum power under this open circuit voltage and discharge voltage, standard environment and operating voltage corresponding to the first maximum power point and operating current.Compared with prior art, there is following technique effect:

1) the present embodiment is the maximum power based on measuring open circuit voltage and the discharge voltage acquisition photovoltaic module obtained, for mathematical model method in prior art, open circuit voltage of the present invention and discharge voltage measured value accuracy is high, error is little, thus improve the accuracy measuring photovoltaic module maximum power.

2) open circuit voltage that obtains of the present embodiment measurement and discharge voltage directly can reflect the electrology characteristic of tested photovoltaic module, relative to look-up table in prior art, and utilize the relation table of external environment condition parameter and power output, do the power output of photovoltaic module and indirectly predict, the present embodiment does further power calculation based on this open circuit voltage and discharge voltage can be more accurate.

3) the present embodiment calculates short circuit current based on the discharge voltage directly recorded, and under utilizing varying environment condition, the parameter of photovoltaic module under the proportionate relationship of the proportionate relationship of the operating current that short circuit current is corresponding with maximum power point, operating voltage that open circuit voltage is corresponding with maximum power point and standard environment, thus obtain the maximum power of current environment photovoltaic module, its accuracy of measurement is high, and account form is easy.Improve engineering practicability, and strong adaptability.

Embodiment four

Fig. 5 is the schematic flow sheet of the energy output method of measurement for photovoltaic module of the embodiment of the present invention four, and as shown in Figure 5, the energy output method of measurement for photovoltaic module comprises:

Step 401: in predetermined time section, utilizes the maximum power method of measurement for photovoltaic module as described in embodiment three with setting-up time interval, obtains maximum power corresponding to each time interval under current environment.

Step 402: pass through the energy output that following formula (7) calculates photovoltaic module according to the maximum power that the length of predetermined time section, the time interval of setting and each time interval are corresponding:

$W_{\mathrm{PV}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}(\mathrm{\ΔT}\·P_{\mathrm{MPP}}^{\′}\left(i\right))$ Formula (7)

Wherein, W _pVfor the energy output of photovoltaic module, Δ T is setting-up time interval, and i is the sequence number in the time interval, and N is the number comprising the time interval in predetermined amount of time, P ' _mPPi () is maximum power corresponding in i-th time interval.Concrete, for example, if predetermined amount of time is one day, namely 24 hours, with the maximum power that 5 seconds Fixed Time Interval acquisition each time intervals are corresponding, so, with Fixed Time Interval, cumulative summation is carried out to energy output, energy output on the same day can be obtained.

Energy output method of measurement for photovoltaic module of the present invention, by in predetermined time section, the maximum power method of measurement for photovoltaic module described in embodiment three is utilized with setting-up time interval, the maximum power that each time interval under acquisition current environment is corresponding, with Fixed Time Interval, cumulative summation is carried out to the energy output of being tried to achieve by maximum power again, thus calculate the energy output of photovoltaic module, improve the accuracy measuring photovoltaic module energy output.

The above; be only the specific embodiment of the present invention, but protection scope of the present invention is not limited thereto, is anyly familiar with those skilled in the art in the technical scope that the present invention discloses; change can be expected easily or replace, all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection range of described claim.

Claims (8)

1. for a maximum power measurement mechanism for photovoltaic module, it is characterized in that, described device comprises:

Tension measuring circuit, described tension measuring circuit one end is connected with the positive pole of described photovoltaic module, and the other end is connected with the negative pole of described photovoltaic module, for measuring open circuit voltage and the discharge voltage of the described photovoltaic module of current environment;

Controller, be connected with described tension measuring circuit, for according to the first maximum power under standard environment and operating voltage corresponding to the first maximum power point and operating current, described open circuit voltage and discharge voltage, obtain the second maximum power of the described photovoltaic module under current environment.

2. maximum power measurement mechanism according to claim 1, it is characterized in that, described tension measuring circuit comprises discharge resistor, switching device and voltmeter, and the resistance of described discharge resistor is enough little, makes the electric current flowing through described discharge resistor close to short circuit current;

Described discharge resistor and described switching device are composed in series series arm, described voltmeter is in parallel with described series arm, the control signal that described switching device sends in response to described controller, control the disconnection or closed of described series arm, when described series arm disconnects, described voltmeter is measured the open circuit voltage of photovoltaic module and is sent to described controller, when described series arm closes, described voltmeter is measured discharge voltage when photovoltaic module discharges to described discharge resistor and is sent to described controller.

3. maximum power measurement mechanism according to claim 2, it is characterized in that, described tension measuring circuit also comprises inductance, one end of described inductance is connected with described discharge resistor, the other end of described inductance is connected with described switching device, the moment impact electric current produced when closing for avoiding described switching device.

4. the maximum power measurement mechanism according to Claims 2 or 3, is characterized in that, described switching device is specially relay or contactor.

5. maximum power measurement mechanism according to claim 1, it is characterized in that, described controller is performed according to the first maximum power under standard environment and operating voltage corresponding to the first maximum power point and operating current, described open circuit voltage and discharge voltage by following formula, obtains the process of the second maximum power of the described photovoltaic module under current environment:

$I_{\mathrm{SC}}^{\′}=\frac{V_{\mathrm{SC}}^{\′}}{R},P_{\mathrm{MPP}}^{\′}=P_{\mathrm{MPPN}}\frac{V_{\mathrm{OC}}^{\′}{I}_{\mathrm{SC}}^{\′}}{V_{\mathrm{OCN}}{I}_{\mathrm{SCN}}},$

Wherein, V ' _sCfor the discharge voltage of photovoltaic module under the current environment that measurement obtains, R is discharge resistance, I ' _sCfor the short circuit current of photovoltaic module under current environment, V ' _oCfor the open circuit voltage of photovoltaic module under the current environment that measurement obtains, P ' _mPPfor the second maximum power of described photovoltaic module, P _mPPNfor the first maximum power under standard environment, V _oCNfor the operating voltage that the first maximum power point under standard environment is corresponding, I _sCNfor the operating current that the first maximum power point under standard environment is corresponding.

6. for a maximum power method of measurement for photovoltaic module, it is characterized in that, described method comprises:

Measure open circuit voltage and the discharge voltage of the described photovoltaic module of current environment;

According to the first maximum power under standard environment and operating voltage corresponding to the first maximum power point and operating current, described open circuit voltage and discharge voltage, obtain the second maximum power of the described photovoltaic module under current environment.

7. maximum power method of measurement according to claim 6, it is characterized in that, described according to the first maximum power under standard environment and operating voltage corresponding to the first maximum power point and operating current, described open circuit voltage and discharge voltage, the processing and utilizing following formula obtaining the second maximum power of the described photovoltaic module under current environment realizes:

$I_{\mathrm{SC}}^{\′}=\frac{V_{\mathrm{SC}}^{\′}}{R},P_{\mathrm{MPP}}^{\′}=P_{\mathrm{MPPN}}\frac{V_{\mathrm{OC}}^{\′}{I}_{\mathrm{SC}}^{\′}}{V_{\mathrm{OCN}}{I}_{\mathrm{SCN}}},$

Wherein, V ' _sCfor the discharge voltage of photovoltaic module under the current environment that measurement obtains, R is discharge resistance, I ' _sCfor the short circuit current of photovoltaic module under current environment, V ' _oCfor the open circuit voltage of photovoltaic module under the current environment that measurement obtains, P ' _mPPfor the second maximum power of described photovoltaic module, P _mPPNfor the first maximum power under standard environment, V _oCNfor the operating voltage that the first maximum power point under standard environment is corresponding, I _sCNfor the operating current that the first maximum power point under standard environment is corresponding.

8. for an energy output method of measurement for photovoltaic module, it is characterized in that, described method comprises:

In predetermined time section, utilize the maximum power method of measurement for photovoltaic module as claimed in claims 6 or 7 with setting-up time interval, obtain maximum power corresponding to each time interval under current environment;

Calculated the energy output of described photovoltaic module by following formula according to maximum power corresponding to the length of predetermined time section, the time interval of setting and described each time interval:

$W_{\mathrm{PV}}=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}(\mathrm{\ΔT}\·P_{\mathrm{MPP}}^{\′}\left(i\right)),$

Wherein, W _pVfor the energy output of described photovoltaic module, Δ T is setting-up time interval, and i is the sequence number in the time interval, and N is the number comprising the time interval in predetermined amount of time, P ' _mPPi () is maximum power corresponding in i-th time interval.