Photovoltaic water pumping system is designed to solve the water problem in remote areas and dispersed residential populations. With the electric tricycle as the mobile carrier, the photovoltaic panel, charge and discharge and inverter controller are integrated.
According to the changeable characteristics of practical applications, the battery pack equipped with the standard electric tricycle is used as the energy storage unit of the small. The photovoltaic panel can not only charge the battery pack or drive the water pump when the electric tricycle is stopped, but also directly provide driving power during the electric tricycle.
The photovoltaic water pumping system is simple to control, has good performance, and can meet the multi-purpose needs of water intake, travel and transportation only by relying on solar energy, and has broad application prospects.
1. What is a photovoltaic water pumping system
The photovoltaic water pumping system is mainly composed of photovoltaic modules, pumps, controllers and other supporting equipment, usually using fixed installation methods, nearby water intake and utilization. In the early stages of promotion, it is difficult to attract consumers due to the high initial investment cost of photovoltaic water pumping system.
In recent years, with the sharp decline in the price of photovoltaic modules, the cost of photovoltaic water pumping system has been significantly reduced. Currently, this technology mainly used in public facilities, relatively few home energy storage. Its market size is also increasing, and it has been promoted and applied in more than 100 countries and regions around the world.
2. Design of photovoltaic water pumping system
● Structural design
The structural design of the photovoltaic water pumping system depends on the choice of mobile carrier. First, you need to decide whether the movement is automatic or drag-and-drop. Taking into account the system's own weight and the actual road conditions, if the type of drag manpower or other power is used, the on-site operation is difficult.
The choice of automatic mobile carriers requires full multi-functional compatibility. Based on this, the photovoltaic water pumping system chose an electric tricycle as the mobile carrier. Electric tricycles have the following advantages:
- The compact structure makes it easy to install photovoltaic modules, and it is flexible in operation and simple to operate.
- The standard battery is complemented by photovoltaic power generation, and photovoltaic modules charge the battery pack to provide power for the electric tricycle.
- The battery pack can assist the photovoltaic module to provide stable electrical energy to the water lifting equipment.
- The price is low, the use is wide, and the photovoltaic water lifting equipment can flexibly take water from the water source.
- After removing the water lifting equipment, it is transformed into a photovoltaic electric tricycle, which can be used for short-distance transportation and transportation.
● Device configuration
The maximum operating power of a small photovoltaic water pumping system depends on the external dimensions of the electric tricycle and the capacity of the battery pack. The equipment selection for the photovoltaic water pumping system design scheme is:
- PV modules and battery packs
Although the weight-energy ratio, volume-energy ratio and number of charge and discharge cycles of colloidal lead-acid batteries are not as good as lithium battery. However, it has a wide operating environment temperature range, low price, high safety and convenient maintenance.
- Water pump
Due to the uncertainty of water sources and water points, the requirements are wide range, high motor efficiency, and stable water lifting efficiency, which are limited by the capacity of photovoltaic modules and battery packs.
- Charger and inverter controllers
The charger, battery pack, drive and motor are all original configurations of electric tricycles. The controller of the mobile photovoltaic water pumping system is composed of a control circuit, a power supply circuit, a photovoltaic control circuit and a pump driving circuit.
- Control policies
The photovoltaic water pumping system has three operating states: loading, driving and water lifting. The control of photovoltaic power generation and water inverter is based on the state of charge of the battery pack and remains relatively independent. Therefore, it is only necessary to design the control strategy of photovoltaic power generation and water inverter separately.
3. Control strategy of photovoltaic water pumping system
According to the maximum operating voltage of the battery pack (corresponding to the fully charged state), the upper limit value of the DC bus voltage of the photovoltaic power generation control is set to be approximately equal. When the DC voltage is less than the photovoltaic power generation control, it means that the output power of the photovoltaic panel can be fully absorbed.
When the DC link voltage is greater than or equal to the upper limit of the DC bus voltage of the photovoltaic power generation control, it indicates that the battery pack is nearing full charge. The output power of photovoltaic panels is excessive.
● Inverter control strategy
Implement variable voltage inverter speed regulation control for the brushless DC motor of the water pump. According to the minimum operating voltage of the battery pack (corresponding to the power loss state), the DC voltage of the water inverter control is set to be greater than that of the battery.
When the DC link voltage is greater than the water inverter, the pump is controlled to run at full power (high) or full speed (low) by adjusting the inverter output voltage of the controller. When less than or equal to time, reduce the pump operating speed and power by reducing the inverter output voltage of the controller until the pump stops running.
Since the lower limit of the DC bus voltage controlled by the water inverter is set to maintain the corresponding margin, the battery pack reasonably conserves the electric energy required for the electric tricycle to continue driving.
4. Performance explanation of photovoltaic water pumping system
● Driving performance
The small mobile photovoltaic water pumping system must first have good handling characteristics, and the electric tricycle is simple to control. There are two modes of power supply during driving. One is the battery pack power supply mode alone, and the other is the photovoltaic power generation and battery pack power supply mode at the same time.
The cruising range after the battery pack is fully charged determines the range of activity of the photovoltaic water pumping system. As the driving range increases, the no-load voltage of the battery pack decreases until it drops to its minimum operating voltage. The battery pack has a range of about 43 km when powered alone, while on sunny days the top 500 WP PV modules can be increased to about 60 km when powered simultaneously with the battery pack.
● Water pump performance
With the increase of the pump head, the pump power increases linearly and the pump flow decreases linearly. Since the maximum head in practical applications is usually less than 50 m, the pump is mainly operated at full capacity. Slow down operation only when the PV panel output power and battery capacity are undercharged.
● PV power generation characteristics
There are three operating modes of the system: charging mode, driving mode and water mode. Charging mode In charging mode, the photovoltaic water pumping system stops and the water pump stops. The battery pack is charged by the photovoltaic module, and MPPT control or constant voltage control is implemented according to the state of charge of the battery pack.
● Driving mode
In driving mode, the pump stops and the small mobile photovoltaic water pumping system moves. For driving safety, the PV modules on both sides are not turned on, and only the 2 PV modules on the top are used as auxiliary power supply. When driving in sunny conditions, the driving power disturbance is performed, although the voltage will change accordingly. However, the output voltage of the PV module remains stable, and the output current of the PV module fluctuates slightly.
While the electric tricycle is driving, the sunlight is temporarily blocked by the surrounding buildings and trees. With short-term changes in sunlight, MPPT control responds quickly, although there is a jump in solar irradiance. Therefore, the output voltage of the photovoltaic panel remains basically stable, while the output current of the photovoltaic panel changes significantly.
● Pumping mode
In water mode, the electric tricycle stops and the pump runs, supplying power to the pump simultaneously by 4 photovoltaic modules and a battery pack. Due to the loss of the friction head in the water pipe and the loss of the speed head of the water outlet, the full head is much larger than the net head, coupled with the loss of the long cable, the input power of the pump drive circuit is significantly increased compared to pump performance.
This paper introduces the overall design scheme of photovoltaic water pumping system from three aspects: structural design, equipment configuration and charging, discharge and inverter controller. The operating characteristics of the photovoltaic water pumping system are described, and the benefits and feasibility of the system are verified.
The charge, discharge and inverter controller realizes automatic and intelligent control of photovoltaic power generation, battery pack charging and discharging and water pump operation. The MPPT accuracy is greater than 99%, and the low voltage DC configuration is adopted, and the safety of the small mobile photovoltaic water pumping system is high.
The simultaneous power supply of photovoltaic power generation and battery pack enables the range of photovoltaic water pumping system to reach 60 km, which is also suitable for daily short-distance traffic and transportation, which greatly improves the cost performance of system investment.
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