CN104765402A - Pendulum type MPPT (Maximum Power Point Tracking) algorithm of single-stage photovoltaic grid-connected inverter - Google Patents
Pendulum type MPPT (Maximum Power Point Tracking) algorithm of single-stage photovoltaic grid-connected inverter Download PDFInfo
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Abstract
The invention discloses a pendulum type MPPT (Maximum Power Point Tracking) algorithm of a single-stage photovoltaic grid-connected inverter. 0.8 times of open-circuit voltage is used as command voltage for system start-up, so the voltage close to the maximum power point (MPP) output voltage can be achieved quickly, and the tracking speed of the maximum power point is improved. A novel variable step size perturbation and observation method is adopted close to the maximum power point, and the main idea of the algorithm is that the characteristic of voltage difference change before and after the voltage is analyzed on the two sides of MPP; since the given voltage of the MPPT algorithm is a group of step waves, the step length of the maximum power point tracking is changed through the characteristic of difference change of a current voltage moment and a previous moment. The algorithm has a simple structure, is easy to implement, hardly has any oscillation close to the maximum power point and is low in energy loss. The algorithm has broad application prospect in the fields such as new energy power generation.
Description
Technical field
The present invention relates to grid-connected maximal power tracing to control, the particularly pendulum model MPPT algorithm of stage photovoltaic single combining inverter, belongs to power electronics parallel network power generation control field.
Background technology
The efficiency that stage photovoltaic single grid-connected system overcomes the multilevel energy conversion of the photovoltaic synchronization inverter system of traditional two-stage type is low, power consumption high shortcoming.Stage photovoltaic single grid-connected system forms primarily of photovoltaic battery array, dc-link capacitance Cpv, DA/AC current transformer, output filter and electrical network.Its principle of work is: the voltage of DC side, by connection in series-parallel, raises to guarantee that inverter can normally work by photovoltaic cell component.Meanwhile, realized the tracking of grid-connected current and line voltage same homophase and maximum power point frequently with this by control DC/AC current transformer.Visible, stage photovoltaic single combining inverter just can complete these two functions of control of MPPT maximum power point tracking and grid-connected current only by inverter.It is simple that it has circuit, and required components and parts are few; Without energy storage link, decrease risk capital; Relative to the photovoltaic combining inverter of two-stage type, owing to being one-level energy conversion, its efficiency is high, low in energy consumption, and reliability is high.
Can luminous energy be made to greatest extent to be converted to electric energy for stage photovoltaic single combining inverter in any environment to make photovoltaic cell, improve the utilization factor of photovoltaic cell, make the work that it still can be efficient, stable under changeable external environment, need control photovoltaic system being carried out to MPPT maximum power point tracking (MPPT) algorithm.Determine these the three kinds of MPPT algorithm application of voltage-tracing method, disturbance observation and conductance increment method at present relatively many.MPPT maximum power point tracking algorithm respectively has relative merits.One, determine voltage-tracing method control simply and easily realize, but accurately can not follow the tracks of maximum power point; Two, disturbance observation method is simple, realize also more for convenience, but near maximum power point both sides, produce vibration, cause power loss to system, its oscillation amplitude is relevant with choosing of step-length, and step-length is less, oscillation amplitude is less, and choosing with the tracking velocity of system of step-length is closely related, it is little that step-length is chosen, and tracking velocity is slow; And can erroneous judgement be caused when environment is undergone mutation; Three, the control degree of stability of conductance increment method is high, but higher to the requirement of sensor in hardware circuit, and corresponding design cost is also high.
Summary of the invention
The maximum power tracking and controlling method that the object of the invention is to solve known stage photovoltaic single combining inverter realizes complicated, simply effectively can not solve the problem producing vibration near maximum power point both sides, proposition simply and reliably can realize stage photovoltaic single combining inverter pendulum model MPPT algorithm.
For solving the problems of the technologies described above, the technical solution used in the present invention is:
Pendulum model MPPT algorithm is similar to the swing of clock and watch, and 12 is the equal of maximum power point, and clock and watch swing back and forth at every turn, often swing amplitude just to compare the last time and decrease, to the last be stabilized in 12 points, be maximum power point, this kind of method is referred to as pendulum model MPPT algorithm.
The pendulum model MPPT algorithm of stage photovoltaic single combining inverter comprises the following steps:
(1) according to current environment temperature T and open-circuit voltage U (k), command voltage Uref=N*U (k) that system starts, described command voltage Uref is the set-point of DC input voitage;
(2) system cloud gray model t
1stable after moment, now start to reduce command voltage Uref, adopt variable step disturbance observation to calculate;
(3) sample current time command voltage Uref (k), previous moment command voltage Uref (k-1) and front two time instructions voltage U ref (k-2);
(4) define s=x1*x2, wherein x1=Uref (k-1)-Uref (k-2), x2=Uref (k)-Uref (k-1), namely x1 is the x2 in last cycle;
(5) as s>0, before and after disturbance voltage, pressure reduction symbol does not change, and represents that system is in the vibration of MPP homonymy, so with fixed step size disturbance; As s<0, pressure reduction sign modification before and after disturbance voltage, represents that system is vibrated in MPP both sides, so reducing step-length and continue disturbance, often there is a negative value in s, then reduce a step-length, to the last step-length is reduced to 0, stablizes to maximum power point place; As s=0, disturbance step-length d is 0, and stablize to maximum power point place, disturbance terminates, and command voltage Uref is definite value.
As preferably, the N in step (1) gets empirical value 0.8.
Pendulum model MPPT algorithm adopts in photovoltaic system start-up course determines voltage-tracing method, namely the command voltage started using 0.8 of open-circuit voltage times as system, can arrive fast near maximum power point output voltage like this, improve the tracking velocity of maximum power point.Near maximum power point, adopt a kind of disturbance observation of novel variable step, its main thinking is exactly in MPP both sides, and front and back this characteristic of pressure reduction reversion of voltage is analyzed.
Because the given voltage of MPPT algorithm is one group of staircase waveform, at maximum power point place, by this characteristic of difference reversion in current voltage moment and a upper moment, changed the step-length of MPPT maximum power point tracking.
Definition s, s=x1 × x2, wherein x2=Uref-Uref_, x1=x2; At MPP place, s=0, and contrary at its symbol of MPP two ends.That is at MPP place, utilize pressure reduction reversion before and after voltage, utilize this characteristic to realize variable step, wherein Uref is the voltage of sampling current time, and Uref_ was the voltage in a upper moment.
In the same side of peak power, namely s > 0, does not at this moment change step-length.As s < 0, namely during s reversion, reduce step-length, often become a sub-symbol, reduce a step-length, to the last step-length reduces, and makes given voltage be a definite value.
Pendulum model MPPT algorithm, determines voltage-tracing method because system have employed in start-up course, near the arrival maximum power point that its system can be very fast, is also adapted to quick startup under various circumstances while improving MPPT maximum power point tracking speed.Variable step utilizes this characteristic of pressure reduction reversion before and after maximum power point place, avoids the vibration produced at maximum power point place, searches for always, until step-length is reduced to zero, therefore greatly reduce the energy loss of system near maximum power point.
Beneficial effect of the present invention is:
The present invention is by implementing pendulum model MPPT algorithm to stage photovoltaic single combining inverter, both the problem producing vibration near maximum power point can be eliminated, the energy loss of minimizing system, also can arrive near maximum power point output voltage fast, improves the tracking velocity of maximum power point.This algorithm structure is simple, is easy to realize, and almost do not vibrate near maximum power point, energy loss is little.Contribute to grid-connected extensive popularization, be particularly suited for the fields such as new forms of energy and use.
Accompanying drawing explanation
Below in conjunction with the drawings and specific embodiments, the present invention is further detailed explanation.
The stage photovoltaic single combining inverter citing of Fig. 1 mentioned by the present invention.
Fig. 2 is pendulum model MPPT algorithm variable step schematic diagram of the present invention.
Fig. 3 is pendulum model MPPT algorithm process flow diagram of the present invention.
Fig. 4 is the given voltage analogous diagram of pendulum model MPPT algorithm photovoltaic array of the present invention.
Embodiment
Stage photovoltaic single combining inverter mentioned by the present invention as shown in Figure 1.This stage photovoltaic single combining inverter, it forms primarily of photovoltaic battery array, dc-link capacitance Cpv, DA/AC current transformer, output filter and electrical network.
Its principle of work is: the voltage of DC side, by connection in series-parallel, raises to guarantee that inverter can normally work by photovoltaic cell component.Meanwhile, realized the tracking of grid-connected current and line voltage same homophase and maximum power point frequently with this by control DC/AC current transformer.Visible, stage photovoltaic single combining inverter just can complete these two functions of control of MPPT maximum power point tracking and grid-connected current only by inverter.
Fig. 2 is pendulum model MPPT algorithm variable step schematic diagram of the present invention.Pendulum model MPPT algorithm adopts in photovoltaic system start-up course determines voltage-tracing method, namely the command voltage started using 0.8 of open-circuit voltage times as system, can arrive fast near maximum power point output voltage like this, improve the tracking velocity of maximum power point.Near maximum power point, adopt a kind of disturbance observation of novel variable step, its main thinking is exactly at maximum power point place, by this characteristic of difference reversion in current voltage moment and a upper moment, changes the step-length of MPPT maximum power point tracking.
Fig. 3 is pendulum model MPPT algorithm process flow diagram of the present invention.In the same side of peak power, namely s > 0, does not at this moment change step-length.As s < 0, namely during s reversion, reduce step-length, often become a sub-symbol, reduce a step-length, to the last step-length reduces, and makes given voltage be a definite value.Wherein d is disturbance step-length, and A is for often to change a sub-symbol, and the value that step-length reduces, carries out disturbance to it after running t1 time representation system stability, adopt constant-voltage method in start-up course.
Fig. 4 is the given voltage analogous diagram of pendulum model MPPT algorithm photovoltaic array of the present invention.The initial disturbance step-length of voltage given is 10, often changes a sub-symbol, and step-length reduces 2, and by that analogy, the output voltage stabilization of last photovoltaic cell on the maximum power point voltage 720V arranged, and does not produce vibration in maximum power point both sides.
Be only the specific embodiment of this patent above, but this patent is not limited thereto, for the person of ordinary skill of the art, under the premise without departing from the principles of the invention, the distortion made should be considered as belonging to scope.
Claims (2)
1. the pendulum model MPPT algorithm of stage photovoltaic single combining inverter, is applied to stage photovoltaic single grid-connected system, it is characterized in that comprising the following steps:
(1) according to current environment temperature T and open-circuit voltage U (k), command voltage Uref=N*U (k) that system starts, described command voltage Uref is the set-point of DC input voitage;
(2) system cloud gray model t
1stable after moment, now start to reduce command voltage Uref, adopt variable step disturbance observation to calculate;
(3) sample current time command voltage Uref (k), previous moment command voltage Uref (k-1) and front two time instructions voltage U ref (k-2);
(4) define s=x1*x2, wherein x1=Uref (k-1)-Uref (k-2), x2=Uref (k)-Uref (k-1), namely x1 is the x2 in last cycle;
(5) as s>0, before and after disturbance voltage, pressure reduction symbol does not change, and represents that system is in the vibration of MPP homonymy, so with fixed step size disturbance; As s<0, pressure reduction sign modification before and after disturbance voltage, represents that system is vibrated in MPP both sides, so reducing step-length and continue disturbance, often there is a negative value in s, then reduce a step-length, to the last step-length is reduced to 0, stablizes to maximum power point place; As s=0, disturbance step-length d is 0, and stablize to maximum power point place, disturbance terminates, and command voltage Uref is definite value.
2. the pendulum model MPPT algorithm of stage photovoltaic single combining inverter according to claim 1, is characterized in that: the value of the N in step (1) is 0.8.
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| CN105159387A (en) * | 2015-08-31 | 2015-12-16 | 江苏金智科技股份有限公司 | Maximum power point implementation method and device base on three-level step length |
| CN105259971A (en) * | 2015-11-26 | 2016-01-20 | 北京京仪绿能电力系统工程有限公司 | Optimized MPPT algorithm |
| CN109901660A (en) * | 2019-03-25 | 2019-06-18 | 吉林大学 | The maximum photovoltaic power point method for tracing of power prediction and stepped variable step disturbance |
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Application publication date: 20150708 |