IMPROVEMENT OF DISTURBANCE OBSERVATION
Author: Source: Datetime: 2016-10-05 01:15:06
A Perturbation Method Based on Variable Step
From the analysis of the oscillation problem, we can see that the fixed step-length perturbation observation method can not set the step length too small in order to ensure the fastness of the system tracking. Therefore, there is a certain amplitude oscillation in the vicinity, which makes it difficult to meet the requirement of high accuracy However, reducing the step size of the voltage perturbation will inevitably lead to the long search time. The proposed method is effective to reduce the amplitude of the disturbance. Obviously, there is a contradiction between the accuracy and the speed of the perturbation method. In order to reconcile this contradiction solar power generator, a perturbation method based on variable step size can be used. The basic idea is that in the region far away from the region, a large voltage disturbance step length is adopted to improve the tracking speed and reduce the low power The time of the output area; in the vicinity of the elbow area, the use of smaller voltage perturbation step size to ensure tracking accuracy. Several variable step perturbation observations are presented below.
Optimal gradient method
Gradient method is a kind of traditional and widely used method to get the extremum of function. Its basic idea is to select the positive (negative) gradient direction of the objective function as the search direction of each iteration, and gradually approach the maximum (small) value of the function. Since the characteristic curve of photovoltaic cells has a typical unimodal nonlinear characteristic, the purpose of the maximum power tracking method is to obtain the maximum value of the curve on the characteristic curve, which can be achieved by the optimal gradient method. We should choose the positive gradient direction, and gradually approach the maximum value of the function can be seen, based on the optimal gradient method% control is actually according to the photovoltaic cell factory "characteristic curve slope automatically change the voltage disturbance step. Considering the boundedness of the characteristic curve terminal voltage, when the gradient method is applied to the tracking of the maximum power point of the solar power generator, the maximum power point is global.
The above analysis shows that the optimal gradient method is a variable step-size perturbation observation method, the size of the step size is proportional to, that is: at the beginning of the maximum power tracking, due to large changes, and therefore a larger step size To meet the rapidity requirements; and when close to the maximum solar powered portable generator, because the change is small, so a smaller step size to meet the stability requirements. Obviously, the optimal gradient method solves the contradiction between the fastness and the stability of the perturbation observation method with fixed step length.
Stepwise approximation method
The calculation of the perturbation step in the optimal gradient method involves the mathematical model of the photovoltaic cell, and the relevant parameters in the mathematical model are difficult to obtain in practice. In view of this, a more practical perturbation observation method based on the variable step- The basic idea is to start the search by first selecting a larger step size to search for the region where the maximum power point is located, and then to scale the search step every time while changing the search direction, while narrowing the search area proportionally solar powered portable generator , The next round of search, so that the search for the maximum power in the region will be reduced by half, twice the accuracy, and then the cycle continues until the approximation of the maximum power point. Stepwise approximation method in the search process to adjust the search step, each adjustment makes accuracy doubled, thereby greatly improving the accuracy. This is also a variable step size algorithm, the specific variable step search process outlined below:
Assuming that the initial operating point is on the left side of the maximum power point of the characteristic curve and is far from the maximum power point, a search should be performed with a larger step size, and when 8 is satisfied, the current operating point is at the maximum power point Then it is possible to estimate the range of the maximum power point to be within the range of two initial steps. Then the direction of the search should be changed and the searching step will be performed until the search direction changes for the second time , Then the maximum power point range should be within a range of initial step length claw, so that the tracking accuracy - times. The search direction is changed again and the search is carried out in steps of claws. The range of the maximum power point of the cable should be within the range of the step length, so that the tracking accuracy can be doubled again. And so on, until the search to a given range of accuracy for solar powered portable generator, the search that the maximum power point. Obviously, the accuracy of the stepwise approximation method is improved exponentially in the search process, and it also solves the contradiction between the velocity and precision of the river tracking. TAG: Duke 100Ah 48V telecom Malta Battery-Box Passenger NTPC Containerized Off-Grid Code Building California Korean SolarEdge
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