CN104533806A - Group control water yield maximization control algorithm of high-power photovoltaic water pump system - Google Patents

Abstract

The invention discloses a high-power photovoltaic water pump system group control water output maximization control algorithm, which is a high-power photovoltaic water pump system group with the advantages of operation in a wide illumination range, less light rejection, large water output, easy redundancy, and high reliability. Control algorithm for maximizing water output. The beneficial effect of the present invention is that it is suitable for a high-power photovoltaic water pump water pumping system, and by adopting redundant matching of small-power photovoltaic water pump units to share the power output of a high-power photovoltaic array, it is ensured that the system can still carry out water pumping under low light intensity , so as to improve the operating efficiency of the system and the utilization rate of solar energy, and reduce or even avoid the occurrence of light abandonment as much as possible. In addition, the water output optimization control algorithm is adopted to ensure that the system maintains the maximum water output under different working conditions.

Description

A control algorithm for maximizing water output by group control of high-power photovoltaic water pump system

technical field

The invention relates to a group control water output maximization control algorithm of a high-power photovoltaic water pump system.

Background technique

The photovoltaic water pump system uses solar energy as energy input, and can work independently without relying on the power grid. The system is applied to those remote areas with abundant sunlight resources and far away from the large power grid, which can well solve the local domestic water and agricultural and animal husbandry water problems. For agricultural irrigation and other situations where the water demand is large and the groundwater is buried deep, it is often necessary to use a high-power photovoltaic water pump system to meet the demand. In a high-power photovoltaic water pump system, in order to obtain the required voltage and power level, a photovoltaic array composed of solar cells connected in series and parallel is generally used to provide DC power, and the power conversion device adopts a single power unit structure or a multi-power unit structure. The system structure of a single power unit is shown in Figure 1. The system is powered by a photovoltaic array 1, equipped with a frequency converter 2 matching its power as a power conversion device, and drives a motor of the same power level to drive a photovoltaic water pump 3 to extract groundwater. The advantage of this system is that the system configuration structure is simple, the control method is simple, and the automatic operation control of the system can be completed only by the frequency converter itself. However, this system structure also has the following disadvantages: 1) The light is seriously discarded. Due to the high power level of the system, the system needs more power to overcome the no-load running torque of its own motor and water pump. Due to the use of high-power inverters as power conversion devices, the high-power level power devices and transformers in the inverter have relatively large losses. In this way, when the light is low, the system will stop working due to the insufficient output power of the photovoltaic array to overcome the starting torque of the photovoltaic water pump, resulting in light abandonment. The higher the unit power level, the more serious the light abandonment. 2) The water output is not high; affected by the light abandonment, the system only operates to lift water during the period of strong light, which makes the system overly dependent on the light intensity and the system water output is low. 3) Poor redundancy. The high-power photovoltaic water pump system structure using a single power conversion device, when the required power level changes, the inverter, photovoltaic water pump and drive motor need to be changed accordingly to match the power level requirements. Once the power level requirements change, the system power conversion device and water pump must be redesigned, and the system scalability is weak. 4) The reliability is not high. Since the system adopts a single frequency converter and photovoltaic water pump structure, as long as a fault occurs in one of the intermediate links, the system will have to stop working. For example, the frequency converter, water pump motor or water pump, any damage to any part will cause the system to fail to operate, and the system will stop water supply.

For multi-power unit photovoltaic water pump systems, in order to obtain the maximum power output of the photovoltaic array under different lighting conditions, the unit inverter generally has the maximum power tracking function of the photovoltaic array. By controlling the output voltage of the photovoltaic array, the system can operate under different lighting conditions for maximum power operation. However, if all the units of the system work at the same time and perform maximum power tracking, that is, each unit adjusts the voltage of the photovoltaic array so that the unit can achieve the maximum power tracking of the photovoltaic array, which may cause large fluctuations in the output voltage of the photovoltaic array. Even cause the instability of the whole system. In addition, in the case of weak light, all the units work at the same time, the output power of the photovoltaic array is mainly used to overcome the self-loss of the units, and the water cannot be lifted, resulting in the phenomenon of light abandonment, and the water output of the system is small.

Contents of the invention

The technical problem to be solved by the present invention is to provide a high-power photovoltaic water pump system group control water output maximization control algorithm, which has less light rejection, large water output, good redundancy and high reliability, and can be easily increased or decreased by simply increasing or decreasing the power unit. To meet the requirements of different power levels, the system can work under a wide range of light conditions, and when a unit fails, the system can still complete the water lifting work. Moreover, through the optimal control algorithm of water output, the system can achieve the maximum water output under different power conditions, ensuring efficient operation of the system and greatly increasing the water extraction capacity of the system.

The present invention is achieved through the following technical solutions.

A high-power photovoltaic water pump system group control water output maximization control algorithm, the steps include:

(1) Determine the minimum operating number k _min and the maximum operating number k _max of the number of k photovoltaic water pumps;

(2) Calculate the water output of the Q _pv system in the case of k _min ;

(3) Increase the number of units k on the basis of k _min until k _max , calculate the Q _pv at this time and compare it with the previous Q _pv ;

(4) Find the k corresponding to the maximum Q _pv ;

(5) The high-power photovoltaic water pump system is controlled according to k obtained in (4).

Further, the above k _min and k _max are determined according to k _min ≤ k ≤ k _max , Where ceil and floor represent upward and downward rounding respectively, P _pv is the output power of the photovoltaic array, P _s is the output constrained power of a single water pump, and P _min is the minimum output power of a single water pump.

Further, the water pump speed n is proportional to the cube of a single water pump power P _u ie n=f(P _u ), and the minimum water pump speed n _min is determined.

Further, n _min =max(n _min1 , n _min2 ), n _min1 =0.6n _mp , where n _mp is the rated speed of the water pump; n _min2 is the minimum speed corresponding to the minimum lift of the water pump in actual operation.

Beneficial effects of the present invention:

1. The system of the present invention has a larger water output under the same output power condition.

2. The system of the present invention can work and operate under wider lighting conditions, and the system has high operating efficiency.

3. The system of the present invention is easy to be redundant, and according to the requirements of different power levels, it only needs to increase or decrease the number of units to meet the requirements.

Description of drawings

Figure 1 is a schematic diagram of the structure of a high-power photovoltaic water pump system;

Fig. 2 is a schematic diagram of the control scheme of the high-power photovoltaic water pump system of the present invention;

Fig. 3 is a schematic diagram of the group control strategy of the photovoltaic water pump system of the present invention;

Fig. 4 is a schematic diagram of the working characteristic curve of the water pump when the speed is adjusted;

Fig. 5 is a schematic diagram of the optimization algorithm for the maximum water output of the photovoltaic water pump group according to the present invention.

Detailed ways

The present invention will be described in further detail below according to the drawings and embodiments.

The photovoltaic water pump system uses solar energy as the energy input, and after the photoelectric conversion of the solar cell and the power conversion of the power electronic device, the drive motor drives the pump to pump groundwater. As a photovoltaic water pump system for the purpose of extracting groundwater, in order to make the system operate efficiently, two main points need to be met: one is to convert as much solar energy into electrical energy as possible; the other is to maximize the water output of the system under a certain power.

The configuration scheme of the high-power photovoltaic water pump system of the present invention is shown in Figure 2. The system adopts the redundancy of small-power water pump units to match the structure of high-power photovoltaic arrays, and realizes unified control of all units by increasing the monitoring of the upper computer. The control strategy block diagram of the photovoltaic water pump system group is shown in Figure 3. The host computer monitors the voltage and current of the photovoltaic array to realize the tracking control of the maximum output power of the array, and the maximum power tracking controls the output unit pump frequency. In addition, the water output optimization algorithm calculates the number of photovoltaic water pump units required to operate according to the output power of the photovoltaic array, and the output controller controls the number of units to operate based on this, so as to maintain the maximum water output of the system under different power outputs. The optimal control algorithm for maximizing water output is shown in Figure 5, and the implementation process of the optimal control algorithm for water output is introduced below.

In the case of a certain output power of the photovoltaic array, there can be different numbers of unit water pumps to match the power input, which can be expressed by the mathematical expression (1).

P _pv = kP _u (1)

In the formula, P _pv is the output power of the photovoltaic array, P _u is the output power of the unit, and k is the number of operating photovoltaic water pumps.

From the formula (1), it can be obtained that the output power of the photovoltaic water pump unit P _u =P _pv /k, when the output power of the photovoltaic array P _pv is constant, the unit output power P _u is determined by the number of operating units k. In other words, in order to match the output power P _pv of the photovoltaic array, the system can have different combinations of units, so how to choose a method to maximize the water output of the system? Next, by considering the system constraints, a control algorithm with the maximum water output as the goal is deduced.

In the photovoltaic water pump system, the pump speed is generally not lower than 60% of its rated speed, that is, the speed regulation range is:

n _min1 ≤n≤n _mp (2)

Where n _mp is the rated speed of the water pump, n _min1 = 0.6n _mp .

In order to ensure the normal pumping of water by the photovoltaic water pump system, the system must not only meet the speed requirements of the pump itself, but also meet certain head conditions and pump piping system requirements. The schematic diagram of the relationship curve between the water output Q and the head H of the photovoltaic water pump at different speeds n is shown in Figure 4. Curves 1 and 2 in the figure are characteristic curves of the pump at speeds n ₁ and n ₂ respectively, and curve 3 is the characteristic curve of the pump piping system. The intersection point of this curve and the water output-lift relationship curve of the pump is the operating point of the pump. In order to make the head of the photovoltaic water pump not lower than the required minimum head, the actual running speed n of the water pump should be greater than the minimum speed n _min2 corresponding to the minimum head, that is, the speed of the water pump needs to meet the constraints

n≥n _min2 (3)

Therefore, in order to ensure that the system can lift water under the head condition, it is necessary to meet the pump working within the allowable speed regulation range and meet the head requirements. Therefore, the minimum speed of the pump is:

n _min ＝max(n _min1 ,n _min2 ) (4)

In the photovoltaic water pump system, the speed of the water pump is proportional to the cubic power of the power, which is expressed by the functional relationship (5):

n=f(P _u ) (5)

For the water pump system, the corresponding relationship between speed and power can be obtained through experiments, as shown in Table 1:

Table 1 n=f(P) function table

P _{P1 P2} P ₃ ··· P _s no n ₁ n ₂ n ₃ ··· n _s

According to the speed power function table n=f(P), the _unit power P min1 , P _min2 corresponding to the minimum speed n _min1 , n _min2 corresponding to the pump's own characteristic requirements and the minimum head requirement can be obtained. At the same time, P _u ≤ P _s is constrained by the unit power level. In other words, in order to ensure the normal pumping of water in the system, the power P _u of the pump unit must meet the following conditions:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\\ {\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; \&le;</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Let P _min ＝max(P _min1 ,P _min2 ), then formula (6) is equivalent to:

P _min ≤ P _u ≤ P _s (7)

When the output power P _pv of the photovoltaic array is constant, the unit power P _u =P _pv /k can be obtained from formula (1), and it can be substituted into formula (7) to obtain the relationship between the number of operating units and the power:

$\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; PV</span>}}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; \&le;</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; PV</span>}}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

At the same time, in order to meet the requirement that the number of units k is an integer, let ceil and floor represent upward and downward rounding respectively, then

k _min ≤ k ≤ k _max (9)

Based on the power balance principle above, the range of the number of photovoltaic water pump units that can be put into operation is deduced under the condition of a certain output power of the photovoltaic array. Among the number k of operable photovoltaic water pump units that satisfy the power conservation condition, how many units are selected to have the largest water output? From the point of view of the water output of the system, the functional relationship between the water volume and the number of photovoltaic pump units is deduced below.

Assuming that the power levels of the photovoltaic water pump units in the system are the same, and the water output of the units is _Qu , the water output Q _pv of the system with k units running is:

Q _pv = kQ _u (10)

Based on the principle characteristics of the water pump, the water output _Qu of the water pump is proportional to the pump speed n. Assuming that the proportional coefficient is α, the relationship between the water output of the unit water pump and the speed can be expressed by formula (11),

Q _u =α n (11)

From equations (5), (10) and (11), it can be concluded that the functional relationship between water volume and power is:

Q _pv ＝αkf(P _u ) (12)

Combined with formula (1), we can get,

${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; PV</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&alpha;kf</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; PV</span>}}}{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; )</span>$

It can be seen from the above formula that when the output power P _pv of the photovoltaic array and the proportional coefficient α are constant, the water output is a function of the number k of the units turned on. To achieve the maximum water output Q _pv is to find a k such that Q _pv maximum, ie

stK _min ≤ k ≤ K _max , k∈int (14)

The flow of the optimal control algorithm for maximizing the water output of the present invention is shown in Figure 5. Firstly, the unit minimum power P _{min1 and P min2 are determined based on the minimum speed n min1 and n min2} of the water pump according to the speed power meter of the unit water pump and the proportional coefficient α of the water output of the speed , and then calculate the boundary k _min , k _{max of} the number of open units according to the output power P _pv of the photovoltaic array. In order to ensure the normal operation of the system, the minimum unit power of the unit is P _min = max(P _min1 , P _min2 ), and the minimum power P _min1 and P _min2 correspond to the maximum number of units respectively k _max1 = P _pv /P _min1 , k _max2 = P _pv /P _min2 , then the maximum number of operating units is k _max =min(k _max1 , k _max2 ). If the unit is running at the maximum output power, that is, when the unit is running at the rated power P _s , the corresponding number of activated units is minimum k _min . Therefore, the range of operating number of photovoltaic water pump units in the system is k _min ≤ k ≤ k _max . Based on the range of the number of operable units, combined with the functional relationship between the water output and the output power of the photovoltaic array, the optimal calculation of the maximum water output Q can be performed. The specific process is as follows: first calculate the water output based on the minimum number of units running k _min , then increase the number of units k in turn to calculate the water output Q, and compare it with the previous calculated value of the water output until the unit corresponding to the maximum water output is found The number k, the optimization calculation ends. Then, the system is controlled according to the number of units obtained by the optimization calculation, so as to ensure the maximum water output under different photovoltaic array output power conditions.

The above-mentioned embodiments are only for illustrating the technical concept and features of the present invention. The purpose is to enable those skilled in the art to understand and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention shall fall within the protection scope of the present invention.

Claims (4)

1. high-power photovoltaic water pump system team control water-outlet quantity maximizes a control algorithm, and it is characterized in that, step comprises:

(1) determine that k photovoltaic water pump runs the minimum operation number k of number of units _minwith maximum operation quantity k _max;

(2) k is calculated _minq in situation _pvsystem water-outlet quantity;

(3) at k _minbasis increases unit number k until k _max, calculate Q now _pvand an and front Q _pvcontrast;

(4) Q is found _pvk corresponding time maximum;

(5) k that high-power photovoltaic water pump system obtains according to (4) controls.

2. high-power photovoltaic water pump system team control water-outlet quantity according to claim 1 maximizes control algorithm, it is characterized in that, above-mentioned k _min, k _maxdetermination be according to k _min≤ k≤k _max, wherein ceil and floor represents respectively and rounds up and down, P _pvfor photovoltaic array output power, P _sfor single water pump output constraint power, P _minfor single water pump exports lowest power.

3. high-power photovoltaic water pump system team control water-outlet quantity according to claim 2 maximizes control algorithm, it is characterized in that, pump rotary speed n and single pump power P _uit is n=f (P that cube is directly proportional _u), determine water pump minimum speed n _min.

4. high-power photovoltaic water pump system team control water-outlet quantity according to claim 3 maximizes control algorithm, it is characterized in that, n _min=max (n _min1, n _min2), n _min1=0.6n _mp, n _mpfor water pump rated speed; n _min2for the minimum speed that the minimum lift of water pump actual motion is corresponding.