CN105140966B - A kind of modulation strategy for suppressing non-isolation type photovoltaic system leakage current - Google Patents

A kind of modulation strategy for suppressing non-isolation type photovoltaic system leakage current Download PDF

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CN105140966B
CN105140966B CN201510656641.7A CN201510656641A CN105140966B CN 105140966 B CN105140966 B CN 105140966B CN 201510656641 A CN201510656641 A CN 201510656641A CN 105140966 B CN105140966 B CN 105140966B
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CN105140966A (en
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李国栋
陈培育
闫海云
王旭东
刘云
贝太周
韩富强
纪明
苏靖宇
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State Grid Corp of China SGCC
State Grid Tianjin Electric Power Co Ltd
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    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Abstract

The present invention relates to a kind of modulation strategy for suppressing non-isolation type photovoltaic system leakage current, its technical characterstic is to comprise the following steps：H bridge tandem photovoltaic systems are divided into first half cycle mode of operation and later half cycle operating mode, under first half cycle mode of operation, inverter output voltage is 0, Vpv and 2Vpv, wherein, subordinate's on off state is to maintain constant, switch S21With switch S24Shut-off, switchs S23With switch S22It is open-minded；Under later half cycle operating mode, inverter output voltage is 0 ,+Vpv and+2Vpv, and wherein higher level's on off state is to maintain constant, switch S11With switch S14It is open-minded, switch S13With switch S12Shut-off.The present invention is based on H bridge cascaded multilevel inverters, on the premise of not changing system architecture, not increasing system cost, from modulation strategy, wanted carrier number is set to reduce half compared with conventional modulated strategy, greatly reduce amount of calculation, and common-mode voltage is controlled in certain scope, reach the effect for suppressing leakage current.

Description

A kind of modulation strategy for suppressing non-isolation type photovoltaic system leakage current
Technical field
The invention belongs to technical field of photovoltaic power generation, especially a kind of modulation for suppressing non-isolation type photovoltaic system leakage current Strategy.
Background technology
Photovoltaic generating system due to the cost of its great number, make photovoltaic gross generation with respect to other common energy resources compared with It is small.Photovoltaic system cost is reduced, improving efficiency turns into key, and the method for one of which reduces cost is exactly not use transformer, Because non-isolation type photovoltaic DC-to-AC converter and power network are without electrical isolation, can be formed with more low-impedance leakage current circulating path, produced The problems such as raw leakage current can not only cause the distortion of electromagnetic interference, grid-connected current, while can also be made to equipment and personal safety Into harm.The method for solving non-isolation type inverter output common mode current problems both at home and abroad mainly has hardware approach and software approach Two classes.Hardware approach increases wave filter come filtering common mode voltage by inverter output end, or using improved topology knot Structure, this kind of method has the disadvantage：Addition hardware increased the volume and weight of inverter, and Control System Design is complicated, while needing Parameter to wave filter used or transformer is redesigned, and reduces the reliability of system.Software approach is from control strategy Start with, in the case where other elements are not increased, common mode current is reduced using suitable pulse modulation technology.
H bridge cascaded multilevel inverter circuits be it is in series by multiple two level H-bridges inverter structure units, it is this Inverter have flexible design, be easy to modularization, easily extension, DC side dc source it is separate, be more suitable for high power, Output level number many advantages, such as can be more flexible of high voltage circuit, inverter, based on These characteristics, HB-CMI be applied to compared with There is certain advantage in large power photovoltaic grid-connection system.As based on how H bridges cascaded multilevel inverter circuit and used It is problem in the urgent need to address at present that software suppresses non-isolation type photovoltaic system leakage current.
The content of the invention
It is an object of the invention to overcome the deficiencies in the prior art, there is provided a kind of reasonable in design, efficiency high, the suppression of low cost The modulation strategy of non-isolation type photovoltaic system leakage current processed.
The present invention solves its technical problem and takes following technical scheme to realize：
A kind of modulation strategy for suppressing non-isolation type photovoltaic system leakage current, preceding half cycle is divided into by H bridge tandem photovoltaic systems Phase mode of operation and later half cycle operating mode, and process in the steps below：
Step 1, first half cycle mode of operation
Under first half cycle mode of operation, inverter output voltage is 0,-Vpv and -2Vpv, wherein, subordinate's on off state It is to maintain constant, switch S21With switch S24Shut-off, switchs S23With switch S22It is open-minded, it is considered to the on off state of higher level's H bridges, carry Ripple is divided into three kinds with the relation of modulating wave：
(1) V is worked as1>Vref<V2When, switch S11With switch S14It is open-minded, switch S13With switch S12Shut-off, Va1N1=Vpv, Vb1N1 =0, Va1b1=+Vpv, Va2b2=-Vpv；
(2) V is worked as1>Vref>V2When, switch S14With switch S12It is open-minded, switch S11With switch S13Shut-off, Va1N1=0, Vb1N1= 0, Va1b1=0, Va2b2=-Vpv；
(3) V is worked as1<Vref>V2When, switch S13With switch S12It is open-minded, switch S11With switch S14Shut-off, Va1N1=0, Vb1N1= +Vpv, Va1b1=-Vpv, Va2b2=-Vpv；
Step 2, later half cycle operating mode
Under later half cycle operating mode, inverter output voltage is 0 ,+Vpv and+2Vpv, and wherein higher level's on off state is Keep constant, switch S11With switch S14It is open-minded, switch S13With switch S12Shut-off, only considers the on off state of subordinate's H bridges, carries Ripple is divided into three kinds with the relation of modulating wave：
(1) V is worked as1>Vref<V2When, switch S23With switch S22It is open-minded, switch S21With switch S24Shut-off, Va1N1=Vpv, Vb1N1 =0, Va2N2=+Vpv,Vb2N2=+Vpv, Va2b2=-Vpv；
(2) V is worked as1>Vref>V2When, switch S21With switch S23It is open-minded, switch S24With switch S22Shut-off, Va1N1=Vpv, Vb1N1 =0, Va2N2=+Vpv, Vb2N2=+Vpv, Va2b2=0；
(3) V is worked as1<Vref>V2When, switch S21With switch S24It is open-minded, switch S23With switch S22Shut-off, Va1N1=Vpv, Vb1N1 =0, Va2N2=+Vpv, Vb2N2=0, Va2b2=+Vpv；
Wherein, V1And V2The carrier voltage after modulation, V are represented respectivelypvRepresent photovoltaic battery panel output voltage, VrefRepresent Modulation voltage after modulation, Va1N1, Vb1N1Higher level's H bridge bridge arms midpoint a is represented respectively1、b1To reference point N1Voltage, Va2N2, Vb2N2Subordinate H bridge bridge arms midpoint a is represented respectively2、b2To reference point N2Voltage, Va1b1,Va2b2Represent higher level H bridges and subordinate's H bridges Bridge arm midpoint a1、b1And a2、b2Between voltage, switch S11,S14, S13,S12Represent each switch element of higher level's H bridges, S21,S24, S23,S22Represent each switch element of subordinate's H bridges.
And, the H bridges tandem photovoltaic system is two unit H bridge tandem photovoltaic systems.
Advantages and positive effects of the present invention are：
1st, the present invention is not being changed system architecture, is not being increased system cost based on H bridge cascaded multilevel inverters Under the premise of, from modulation strategy, wanted carrier number is reduced half compared with conventional modulated strategy, greatly reduce calculating Amount, and common-mode voltage is controlled in certain scope, reach the effect for suppressing leakage current.
2nd, based on inverter without transformer, its system architecture is simple, efficiency high, small volume, low cost for the present invention.
3rd, present invention selection H bridge cascaded multilevel inverters, it has flexible design, is more suitable for high power, high voltage Circuit, inverter output voltage flexibly, are conducive to wave filter volume to reduce.
Brief description of the drawings
Fig. 1 is H bridge cascaded multilevel inverter circuit diagrams；
Fig. 2 is schematic diagram of the invention.
Specific embodiment
The embodiment of the present invention is further described below in conjunction with accompanying drawing：
A kind of modulation strategy for suppressing non-isolation type photovoltaic system leakage current, is directed to non-isolation type photovoltaic system and there is leakage Current problems, on the premise of system architecture is not changed, using software approach, propose a kind of control method for suppressing leakage current. Because traditional modulation strategy preferably can not suppress to leakage current, and carrier wave needed for conventional modulated strategy is with level Connection inverter unit increases and increases, and can also increase amount of calculation.The present invention is right to study with two unit H bridge tandem photovoltaic systems As, as shown in figure 1, and be improved on the basis of conventional modulated strategy and obtain a kind of new modulation strategy, as shown in Fig. 2 V1 and V2 represent the carrier wave of modulation technique after improving respectively, and carrier wave is all more than zero axle, modulation strategy proposed by the present invention Under on off state and common-mode voltage it is as shown in table 1.
Table 1
The modulation strategy to this suppression non-isolation type photovoltaic system leakage current is described further below：
Fig. 1 gives two unit H bridge tandem photovoltaic systems, is divided into upper and lower two H-bridge units, L1, L2It is filter inductance, it is right Each H-bridge unit is analyzed, and can be obtained according to Kirchhoff's law：
Vcm+Va1N1-Vs-Vac=0 (1)
Vcm+Vb1N1+Vs-Va2b2=0 (2)
Because line voltage has little to no effect to leakage current, therefore ignore Vac, equation (1) is added with (2)：
2Vcm+Va1N1+Vb1N1-Va2b2=0 (3)
And then obtain the equation of common-mode voltage and be：
Modulation strategy proposed by the present invention as shown in Fig. 2 under this modulation strategy, on off state and common-mode voltage such as table Shown in 1, it is divided into two mode of operations：First half cycle and later half cycle.
1st, first half cycle (0-T/2)
In such a mode, inverter output voltage is 0,-Vpv, -2Vpv, and wherein subordinate's on off state is to maintain constant , S21, S24Shut-off, S23, S22It is open-minded, only consider the on off state of higher level's H bridges, carrier wave is divided into three kinds with the relation of modulating wave：
(1) V is worked as1>Vref<V2When, switch S11With switch S14It is open-minded, switch S13With switch S12Shut-off, Va1N1=Vpv, Vb1N1 =0, Va1b1=+Vpv, Va2b2=-Vpv；
(2) V is worked as1>Vref>V2When, switch S14With switch S12It is open-minded, switch S11With switch S13Shut-off, Va1N1=0, Vb1N1= 0, Va1b1=0, Va2b2=-Vpv；
(3) V is worked as1<Vref>V2When, switch S13With switch S12It is open-minded, switch S11With switch S14Shut-off, Va1N1=0, Vb1N1= +Vpv, Va1b1=-Vpv, Va2b2=-Vpv。
2nd, later half cycle (T/2-T)
In such a mode, inverter output voltage is 0 ,+Vpv ,+2Vpv, and wherein higher level's on off state is to maintain constant , S11 is switched, S14 is open-minded, S13, S12 shut-offs, only considers the on off state of subordinate's H bridges, and carrier wave is divided into the relation of modulating wave Three kinds：
(1) V is worked as1>Vref<V2When, switch S23With switch S22It is open-minded, switch S21With switch S24Shut-off, Va1N1=Vpv, Vb1N1 =0, Va2N2=+Vpv,Vb2N2=+Vpv, Va2b2=-Vpv；
(2) V is worked as1>Vref>V2When, switch S21With switch S23It is open-minded, switch S24With switch S22Shut-off, Va1N1=Vpv, Vb1N1 =0, Va2N2=+Vpv, Vb2N2=+Vpv, Va2b2=0；
(3) V is worked as1<Vref>V2When, switch S21With switch S24It is open-minded, switch S23With switch S22Shut-off, Va1N1=Vpv, Vb1N1 =0, Va2N2=+Vpv, Vb2N2=0, Va2b2=+Vpv。
V in above-mentioned formula1And V2The carrier voltage after modulation, V are represented respectivelypvPhotovoltaic battery panel output voltage is represented, VrefRepresent the modulation voltage after modulation, Va1N1, Vb1N1Higher level's H bridge bridge arms midpoint a is represented respectively1、b1To reference point N1Voltage, Va2N2,Vb2N2Subordinate H bridge bridge arms midpoint a is represented respectively2、b2To reference point N2Voltage, Va1b1,Va2b2Represent higher level H bridges with Level H bridge bridge arms midpoint a1、b1And a2、b2Between voltage, switch S11,S14, S13,S12Each switch element of higher level's H bridges is represented, S21,S24,S23,S22Represent each switch element of subordinate's H bridges.
From the above analysis as can be seen that the maximum changing value of common-mode voltage is Vpv/ 2, so that common mode variations are limited in In certain scope, the effect for suppressing leakage current is reached.
In order to verify the correctness of above-mentioned modulation strategy, we are based on PSIM emulation platform buildings simulation model, emulation Parameter is as follows：Unit photovoltaic panel capacity 1kW, unit DC voltage is equal and Vdc=120V, parasitic capacitance Cpv=100nF, output Filter inductance L=1.8mH, triangular carrier frequency is 3kHz, and the frequency of modulating wave sine wave is 50Hz, and line voltage is 240V/ 50Hz, the system emulation time is 0.06s, and simulation step length is 100ns.Simulation result is as shown in table 2, PD (phase Disposition), APO (alternative phase opposition), PO (phase opposition) represent three kinds of biographies The modulation strategy of system, respectively with phase carrier modulation, adjacent carrier back-modulation, reverse carrier modulation.
The leakage current virtual value of table 2, inverter output voltage THD and variable number
Result shows that wanted carrier number of the invention reduces half.
It is emphasized that embodiment of the present invention is illustrative, rather than limited, therefore present invention bag The embodiment for being not limited to described in specific embodiment is included, it is every by those skilled in the art technology according to the present invention side The other embodiment that case draws, also belongs to the scope of protection of the invention.

Claims (2)

1. it is a kind of suppress non-isolation type photovoltaic system leakage current modulator approach, it is characterised in that：By H bridge tandem photovoltaics system point It is first half cycle mode of operation and later half cycle operating mode, and processes in the steps below：
Step 1, first half cycle mode of operation
Under first half cycle mode of operation, inverter output voltage is 0,-Vpv and -2Vpv, wherein, subordinate's on off state is to protect Hold constant, switch S21With switch S24Shut-off, switchs S23With switch S22It is open-minded, it is considered to the on off state of higher level's H bridges, carrier wave with The relation of modulating wave is divided into three kinds：
(1) V is worked as1>Vref<V2When, switch S11With switch S14It is open-minded, switch S13With switch S12Shut-off, Va1N1=Vpv, Vb1N1=0, Va1b1=+Vpv, Va2b2=-Vpv；
(2) V is worked as1>Vref>V2When, switch S14With switch S12It is open-minded, switch S11With switch S13Shut-off, Va1N1=0, Vb1N1=0, Va1b1=0, Va2b2=-Vpv；
(3) V is worked as1<Vref>V2When, switch S13With switch S12It is open-minded, switch S11With switch S14Shut-off, Va1N1=0, Vb1N1=+Vpv, Va1b1=-Vpv, Va2b2=-Vpv；
Step 2, later half cycle operating mode
Under later half cycle operating mode, inverter output voltage is 0 ,+Vpv and+2Vpv, and wherein higher level's on off state is to maintain Constant, switch S11With switch S14It is open-minded, switch S13With switch S12Shut-off, only considers the on off state of subordinate H bridges, carrier wave with The relation of modulating wave is divided into three kinds：
(1) V is worked as1>Vref<V2When, switch S23With switch S22It is open-minded, switch S21With switch S24Shut-off, Va1N1=Vpv, Vb1N1=0, Va2N2=+Vpv,Vb2N2=+Vpv, Va2b2=-Vpv；
(2) V is worked as1>Vref>V2When, switch S21With switch S23It is open-minded, switch S24With switch S22Shut-off, Va1N1=Vpv, Vb1N1=0, Va2N2=+Vpv, Vb2N2=+Vpv, Va2b2=0；
(3) V is worked as1<Vref>V2When, switch S21With switch S24It is open-minded, switch S23With switch S22Shut-off, Va1N1=Vpv, Vb1N1=0, Va2N2=+Vpv, Vb2N2=0, Va2b2=+Vpv；
Wherein, V1And V2The carrier voltage after modulation, V are represented respectivelypvRepresent photovoltaic battery panel output voltage, VrefAfter representing modulation Modulation voltage, Va1N1, Vb1N1Higher level's H bridge bridge arms midpoint a is represented respectively1、b1To reference point N1Voltage, Va2N2,Vb2N2Respectively Represent subordinate H bridge bridge arms midpoint a2、b2To reference point N2Voltage, Va1b1,Va2b2Represent higher level H bridges and subordinate H bridge bridge arms midpoint a1、b1And a2、b2Between voltage, switch S11,S14, S13,S12Represent each switch element of higher level's H bridges, S21,S24,S23,S22Table Show each switch element of subordinate's H bridges；
The switch S11, switch S12, switch S13, switch S14Between annexation be：Switch S11One end with switch S13's One end is commonly connected to photovoltaic battery panel output voltage VpvOne end, switch S11The other end with switch S12One end connect jointly It is connected to higher level's H bridge bridge arms midpoint a1On, switch S13The other end with switch S14One end be commonly connected to higher level's H bridge bridge arms midpoint b1On, switch S12The other end with switch S14The other end be commonly connected to photovoltaic battery panel output voltage VpvThe other end；
The switch S21, switch S22, switch S23, switch S24Between annexation be：Switch S21One end with switch S23's One end is commonly connected to photovoltaic battery panel output voltage VpvOne end, switch S21The other end with switch S22One end connect jointly It is connected to subordinate H bridge bridge arms midpoint a2On, switch S23The other end with switch S24One end be commonly connected to subordinate H bridge bridge arms midpoint b2On, switch S22The other end with switch S24The other end be commonly connected to photovoltaic battery panel output voltage VpvThe other end；
The higher level H bridge bridge arms midpoint b1With subordinate H bridge bridge arms midpoint a2It is connected.
2. it is according to claim 1 it is a kind of suppress non-isolation type photovoltaic system leakage current modulator approach, it is characterised in that： The H bridges tandem photovoltaic system is two unit H bridge tandem photovoltaic systems.
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