CN102403888B - Photovoltaic grid connected inverter with reverse connection prevention function and control method therefor - Google Patents
Photovoltaic grid connected inverter with reverse connection prevention function and control method therefor Download PDFInfo
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- CN102403888B CN102403888B CN 201110380147 CN201110380147A CN102403888B CN 102403888 B CN102403888 B CN 102403888B CN 201110380147 CN201110380147 CN 201110380147 CN 201110380147 A CN201110380147 A CN 201110380147A CN 102403888 B CN102403888 B CN 102403888B
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- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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Abstract
The invention discloses a photovoltaic grid connected inverter with a reverse connection prevention function. The photovoltaic grid connected inverter comprises an inverter unit, a control unit, a filter capacitor and a reverse connection prevention unit; the reverse connection prevention unit is connected with an input end of the inverter unit; and the filter capacitor is bridged between two input ends of the inverter unit. The photovoltaic grid connected inverter also comprises a voltage sampling circuit which is connected with the control unit by signal and is used for sampling voltages at the two ends of the filter capacitor and transmitting the sampling results to the control unit; the reverse connection prevention circuit comprises a current limiting resistor, a reversion prevention diode and a bypass controllable switch; the current limiting resistor is connected in series with the reversion prevention diode; the bypass controllable switch is connected in parallel with a series circuit formed by the current limiting resistor and the reversion prevention diode; and the control end of the bypass controllable switch is connected with the control unit by a signal. The invention also discloses a control method for the photovoltaic grid connected inverter. Compared with the prior art, the photovoltaic grid connected inverter has the advantages of simple structure, safety, high reliability, low requirement on components, and the like.
Description
Technical field
The present invention relates to a kind of photovoltaic combining inverter, relate in particular to a kind of photovoltaic combining inverter and control method thereof with anti-reverse function.
Background technology
Along with the continuous minimizing of the resources such as oil, coal, and the severe situation of global warming, the renewable natural energy resources such as the solar energy that environmental protection and reserves are extremely abundant, wind energy more and more are subject to people's favor.In the recent period along with the progress of technology, utilize solar energy to carry out photovoltaic generation also more and more extensive.In the photovoltaic application of solar energy, parallel network power generation is the important development trend of photovoltaic application, and oneself becomes the principal mode of photovoltaic application.Along with the extensive use of photovoltaic DC-to-AC converter on market, its fail safe also becomes one of focus of concern.Photovoltaic combining inverter is mainly that the direct current of photovoltaic module output is converted into and the alternating current of the same frequency of electrical network with identical amplitude, if the direct current input reverse-connection can cause the inverter internal damage, in design, need to take certain measure to prevent the generation of this situation.Generally we can adopt in DC side and add the counnter attack diode, utilize the unilateral conduction of diode to prevent the damage that reversal connection brings.Its structure as shown in Figure 1.It can utilize unilateral conduction protection system in the direct current input reverse-connection of diode; but after the normal operation of inverter; the counnter attack diode has certain tube voltage drop; below low power 1V; powerful may reaching about 2V; it not only causes the reduction of the busbar voltage of inverter; control to inverter exerts an influence; after electric current flows through this diode; also can produce a large amount of power losses; cause the entire system Efficiency Decreasing, also can generate heat at the diode place, during design, must consider its heat dissipation problem.Also having a kind of improvement design is to utilize contactor or relay bypass counnter attack diode when inverter works, as shown in Figure 2.The impacts such as the power loss that the tube voltage drop that this kind of mode eliminated the counnter attack diode is brought, heating, but still there is very large drawback in it, first: when the photovoltaic input powers on, due to the existence of rear class filter capacitor, can produce very large charging current, especially for powerful inverter, the appearance value of filter capacitor is very large, it can produce in the capacitor charging process in a large amount of thermal lossess, causes that the temperature of electric capacity raises, and reduces the life-span of electric capacity.Second: inverter can not guarantee that whether contactor or relay are in normal operating conditions, once it breaks down and normally adhesive, operating current still flows through diode, diode must be considered the problem of heat radiation and capacity, its type selecting must meet the rated current requirement of inverter, has caused the rising of cost.
Summary of the invention
Technical problem to be solved by this invention is to overcome the existing deficiency with anti-reverse function photovoltaic combining inverter, provide a kind of simple in structure, security reliability is high, the lower photovoltaic combining inverter with anti-reverse function and the control method thereof to the components and parts requirement.
Photovoltaic combining inverter with anti-reverse function of the present invention, comprise inversion unit, control unit, filter capacitor, anti-reverse unit, described anti-reverse unit is connected with an input of inversion unit, described filter capacitor is connected across between two inputs of inversion unit, described photovoltaic combining inverter also comprises the voltage sampling circuit be connected with the control unit signal, for the voltage to the filter capacitor two ends, is sampled and sampled result is transferred to control unit; Described reverse-connection preventing circuit comprises current-limiting resistance, counnter attack diode, bypass gate-controlled switch, current-limiting resistance is connected with the counnter attack diode, the bypass gate-controlled switch is in parallel with the series circuit that current-limiting resistance and counnter attack diode form, and the control end of bypass gate-controlled switch is connected with the control unit signal.
Described bypass gate-controlled switch can be relay or contactor.
A kind of control method that has as mentioned above the photovoltaic combining inverter of anti-reverse function comprises the following steps:
Step 1, photovoltaic combining inverter power on, and control unit is detected the filter capacitor both end voltage by voltage sampling circuit, and when the filter capacitor both end voltage reaches stable state, control unit is controlled the conducting of described bypass gate-controlled switch;
Step 2, control unit detect the voltage at filter capacitor two ends after the conducting of bypass gate-controlled switch by voltage sampling circuit, and whether the change in voltage that judges filter capacitor two ends before and after the conducting of bypass gate-controlled switch is between (Δ U-ε) ~ (Δ U+ ε), in this way, controlling described inversion unit starts, otherwise, do not start inversion unit and report to the police; Wherein, ε is default error correction values, and Δ U obtains according to following formula:
ΔU=
+VD ，
In formula,
pfor the power loss under described photovoltaic combining inverter Light Condition,
u1for the voltage at filter capacitor two ends before the conducting of bypass gate-controlled switch,
rfor the resistance of current-limiting resistance, the conduction voltage drop that VD is the counnter attack diode.
Described filter capacitor both end voltage reaches stable state, can adopt following two kinds of methods judgement:
First method: whether the variation that judges the filter capacitor both end voltage that the voltage sampling circuit sampling obtains is less than a default threshold value, in this way, judges that the filter capacitor both end voltage reaches stable state; As no, do not reach stable state.
Second method: from photovoltaic combining inverter powers on, through one default period, the filter capacitor both end voltage reaches stable state.
Compared to existing technology, the present invention has following beneficial effect:
1, larger charging current when powering on, direct current is arranged to capacitor charging due to inverter, cause the temperature rise of electric capacity, reduced the life-span of electric capacity, adopt the power resistor current-limiting charge, not only reduced the impact of charging current to electric capacity, can also select the counnter attack diode than low capacity, reduce costs.
2, when inverter is controlled bypass gate-controlled switch closure after direct current powers on, if because certain reason or gate-controlled switch fault cause gate-controlled switch there is no normally closed, after inverter work, can produce at counnter attack diode place power consumption, the counnter attack diode radiating is bad will cause its damage, cause the unreliable work of system, utilize the variation of measuring closed bypass gate-controlled switch front and back filter capacitor terminal voltage, judge whether contactor or relay work, thereby can the judgement inverter normally start, and improved the reliability of system.
3, circuit structure is simple, controls easily and realizes.
The accompanying drawing explanation
Fig. 1 is a kind of existing structural representation with photovoltaic combining inverter of anti-reverse function;
Fig. 2 is the another kind of existing structural representation with photovoltaic combining inverter of anti-reverse function;
Fig. 3 is the structural representation with photovoltaic combining inverter of anti-reverse function of the present invention;
The schematic flow sheet that Fig. 4 is control method of the present invention.
Embodiment
Below in conjunction with accompanying drawing, technical scheme of the present invention is elaborated:
Photovoltaic combining inverter with anti-reverse function of the present invention, its structure as shown in Figure 3, comprise inversion unit, control unit, filter capacitor C1, anti-reverse unit, anti-reverse unit is connected (situation for being connected with positive input terminal shown in figure) with an input of inversion unit, described filter capacitor C1 is connected across between two inputs of inversion unit, described photovoltaic combining inverter also comprises the voltage sampling circuit be connected with the control unit signal, for the voltage to filter capacitor C1 two ends, is sampled and sampled result is transferred to control unit; Described reverse-connection preventing circuit comprises current-limiting resistance R, counnter attack diode D, bypass controllable switch S, current-limiting resistance R connects with counnter attack diode D, the bypass controllable switch S is in parallel with the series circuit that current-limiting resistance R and counnter attack diode D form, and the control end of bypass controllable switch S is connected with the control unit signal.
Control unit is monitored the voltage at filter capacitor C1 two ends by voltage sampling circuit, and according to monitoring result, the bypass gate-controlled switch in inversion unit and anti-reverse unit is controlled, and control procedure as shown in Figure 4, comprises the following steps:
Step 1, photovoltaic combining inverter power on, and control unit is detected filter capacitor C1 both end voltage by voltage sampling circuit, and when filter capacitor C1 both end voltage reaches stable state, control unit is controlled the conducting of described bypass controllable switch S;
Step 2, control unit detect the voltage at filter capacitor C1 two ends after the conducting of bypass controllable switch S by voltage sampling circuit, and whether the change in voltage that judges filter capacitor C1 two ends before and after the conducting of bypass controllable switch S is between (Δ U-ε) ~ (Δ U+ ε), in this way, controlling described inversion unit starts, otherwise, do not start inversion unit and report to the police; Wherein, ε is default error correction values, and Δ U obtains according to following formula:
ΔU=
+VD ，
In formula,
pfor the power loss under described photovoltaic combining inverter Light Condition,
u1 voltage for filter capacitor two ends before the conducting of bypass gate-controlled switch,
rfor the resistance of current-limiting resistance, the conduction voltage drop that VD is the counnter attack diode.
This controlling party ratio juris is as follows:
Photovoltaic combining inverter powers on, by current-limiting resistance R and counnter attack diode D, to filter capacitor C1 charging, if photovoltaic panel input error-polarity connection, due to the existence of counnter attack diode D, can prevent that inverter from causing damage because of DC reverse connection to it.Current-limiting resistance R can be limited charging current in the filter capacitor C1 charging stage, there is no else if current-limiting resistance R, due to the existence of the equiva lent impedance ESR of filter capacitor C1, on ESR between charge period, can produce
energy loss (wherein C is filter capacitor C1 capacity, and U is input voltage), cause the temperature rise of filter capacitor C1, and very large peak current arranged
, after adding current-limiting resistance (resistance is R), energy loss during charging
most of just consumption is on current-limiting resistance R, and peak value is limited in
in, one: can protect filter capacitor C1, its two: counnter attack diode D just can select the model that rated current is less, cutting down cost.
When filter capacitor C1 charging reaches inverter built-in system starting resistor, the inverter built-in system starts the generation operating current, when filter capacitor C1 both end voltage reaches stable state, now photovoltaic combining inverter to produce stable power loss P(be the power loss under its Light Condition), if the terminal voltage that now control unit records filter capacitor C1 by voltage sampling circuit is U1, the pressure drop Δ U=produced on the series circuit that is easy to obtain forming at current-limiting resistance (resistance is R) and counnter attack diode (conduction voltage drop is VD)
+ VD.Now by control unit, control the closed conducting of bypass controllable switch S.It is U2 that control unit records filter capacitor C1 terminal voltage again, before and after the controllable switch S closure, filter capacitor C1 terminal voltage is changed to Δ U '=U2-U1, consider that internal electric source in different situations consumes the error of difference and measurement aspect to some extent, Δ U ' should be between (Δ U-ε) ~ (Δ U+ ε) (ε is error correction values), if in this scope, think that the bypass controllable switch S is reliably closed, but the operation of inverter normal power generation, otherwise inverter is not worked.Thereby prevent from causing the unreliable operation of inverter due to the unreliable closure of bypass controllable switch S.Wherein, whether filter capacitor C1 both end voltage reaches stable state, can judge by following two kinds of methods:
First method: whether the variation that judges the filter capacitor both end voltage that the voltage sampling circuit sampling obtains is less than a default threshold value, in this way, judges that the filter capacitor both end voltage reaches stable state; As no, do not reach stable state.
Second method: from photovoltaic combining inverter powers on, through one default period, the filter capacitor both end voltage reaches stable state.This default time can be determined by experiment in advance.
Claims (4)
1. the control method with photovoltaic combining inverter of anti-reverse function, described photovoltaic combining inverter comprises inversion unit, control unit, filter capacitor, anti-reverse unit, described anti-reverse unit is connected with an input of inversion unit, described filter capacitor is connected across between two inputs of inversion unit, described photovoltaic combining inverter also comprises the voltage sampling circuit be connected with the control unit signal, for the voltage to the filter capacitor two ends, is sampled and sampled result is transferred to control unit; Described reverse-connection preventing circuit comprises current-limiting resistance, counnter attack diode, bypass gate-controlled switch, current-limiting resistance is connected with the counnter attack diode, the bypass gate-controlled switch is in parallel with the series circuit that current-limiting resistance and counnter attack diode form, and the control end of bypass gate-controlled switch is connected with the control unit signal; It is characterized in that, comprise the following steps:
Step 1, photovoltaic combining inverter power on, and control unit is detected the filter capacitor both end voltage by voltage sampling circuit, and when the filter capacitor both end voltage reaches stable state, control unit is controlled the conducting of described bypass gate-controlled switch;
Step 2, control unit detect the voltage at filter capacitor two ends after the conducting of bypass gate-controlled switch by voltage sampling circuit, and whether the change in voltage that judges filter capacitor two ends before and after the conducting of bypass gate-controlled switch is between (Δ U-ε) ~ (Δ U+ ε), in this way, controlling described inversion unit starts, otherwise, do not start inversion unit and report to the police; Wherein, ε is default error correction values, and Δ U obtains according to following formula:
ΔU=
+VD ，
In formula,
pfor the power loss under described photovoltaic combining inverter Light Condition,
u1for the voltage at filter capacitor two ends before the conducting of bypass gate-controlled switch,
rfor the resistance of current-limiting resistance, the conduction voltage drop that VD is the counnter attack diode.
2. the control method of photovoltaic combining inverter as claimed in claim 1, is characterized in that, described bypass gate-controlled switch is relay or contactor.
3. the control method of photovoltaic combining inverter as claimed in claim 1, it is characterized in that, described filter capacitor both end voltage reaches stable state, according to following methods, judge: whether the variation that judges the filter capacitor both end voltage that the voltage sampling circuit sampling obtains is less than a default threshold value, in this way, the filter capacitor both end voltage reaches stable state; As no, do not reach stable state.
4. the control method of photovoltaic combining inverter as claimed in claim 1, it is characterized in that, described filter capacitor both end voltage reaches stable state, according to following methods, judges: from photovoltaic combining inverter powers on, through one default period, the filter capacitor both end voltage reaches stable state.
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| CN104158154B (en) * | 2014-09-01 | 2017-10-27 | 阳光电源股份有限公司 | Photovoltaic DC-to-AC converter and its protection device |
| CN104333319B (en) * | 2014-11-10 | 2017-12-22 | 许继电气股份有限公司 | Input reverse-connection protection circuit for photovoltaic combining inverter |
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| CN112596000A (en) * | 2020-12-02 | 2021-04-02 | 爱士惟新能源技术(江苏)有限公司 | Method and device for detecting reverse connection of PV input ends of photovoltaic inverters |
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