Utilization of solar water pump

Solar energy reserves are large, widely distributed, clean and safe. Photovoltaic water pump technology is such a technology that can make full use of solar energy and does not consume fuel and other organic energy. It is pollution-free, beneficial to environmental protection and energy conservation, and solar cells have a long service life and low maintenance costs. This technology has broad application prospects in domestic water supply and irrigation in arid areas. Photovoltaic water pumps have many advantages such as no noise, full automation, high reliability, good adaptability of water supply and evaporation. The production of solar cells in my country is far greater than the use. Various forms of water pumps are energy-consuming products. The electricity consumed by pump products in the world accounts for about 20% of the total power generation. In order to save energy, vigorously promoting photovoltaic water pump systems is a need and an important way to develop.

1. Principle of photovoltaic water pumps

The photovoltaic water pump system is a relatively typical "light energy, machine, and electricity integration" system. It involves the collection and conversion of solar energy and multiple disciplines such as power electronics, motors, water machines, and computer control, and is of great significance to energy conservation. The basic working principle of the photovoltaic water pump system is to use the electrical energy converted from solar energy, and then drive the photovoltaic water pump to operate by controlling the drive motor.

From the circuit point of view, the basic structure of the photovoltaic water pump system can be divided into four parts: photovoltaic array, maximum power point tracker, power electronic inverter and motor water pump. Among them, the photovoltaic array is composed of a large number of photovoltaic cells connected in series and parallel, and its function is to directly convert solar energy into DC electrical energy. The system uses monocrystalline silicon photovoltaic cells, and its volt-ampere characteristics must be adjusted and controlled to be optimized: the maximum power point tracker is the core of the entire system. Its function is to make the entire system always operate at the optimal working point, and convert as much solar energy as possible into electrical energy under different solar conditions, so that the power supply and load can achieve a harmonious, efficient and stable working state; the power electronic inverter is the power execution unit of the maximum power point tracker. According to the control signal of the maximum power point tracker, it sends out PWM voltage waveforms of different frequencies to drive the motor water pump to work, and at the same time has corresponding protection functions; the motor water pump is the final execution unit of the system, completing stable and reliable water discharge. The motor water pump in this system is designed according to the user's requirements for head and water output, taking into account the voltage and power level requirements of the photovoltaic array.

2. Operation and control of photovoltaic water pumps

At present, solar photovoltaic water pump control systems mostly use maximum power point tracking technology to optimize the matching between solar cells and loads. The main circuit adopts a BUCK soft switching structure, and the single-chip microcomputer realizes the duty cycle of the PWM modulation converter, changes the charging current, and optimizes the maximum power output of the solar cell array. While making full use of the output energy of the solar cell array, this type of controller makes the charging current a pulse current, reduces the polarization of the battery, and the main circuit soft switching structure enables the switch tube to achieve ZVS shutdown and ZCS opening, thereby improving the charging efficiency.

The basic characteristics of solar cells are similar to those of diodes, which can be explained by simple PN junctions. The battery unit is the smallest unit of photoelectric conversion and is generally not used as a power source alone. After the solar cell units are connected in series, parallel and packaged, they become solar cell modules with a power of several watts, tens of watts, and hundreds of watts. After many solar cell modules are connected in series and parallel, they form a solar cell display to form a "solar motor".

The solar cells currently used are all silicon solar cells, including single crystal silicon, polycrystalline silicon and amorphous silicon solar cells. They can be connected in series and parallel and can be used as solar batteries. Since the output volt-ampere characteristic curve of the photovoltaic array is strongly nonlinear and closely related to solar irradiance, ambient temperature and meteorological conditions. Therefore, in order to make the photovoltaic water pump system work in a relatively ideal working condition, a relatively ideal control link is required. The most important part of the entire control link is the control of the motor. The control operation of the motor requires not only good stability, but also good dynamic characteristics, so the phase tracking of the phase-locked loop should have good dynamic performance, that is, it must be able to achieve fast phase tracking, otherwise it will affect the acceleration and deceleration performance of the system, or under sudden load conditions, the electronic commutation error is too large, causing the motor to lose step.

For the photovoltaic water pump system, since the load of the motor is a water pump, its load torque is proportional to the square of the speed. The lower the speed, the smaller the load resistance torque. Therefore, the starting torque required for the ice pump motor is very small, as long as the friction torque is overcome. Therefore, the characteristics of the position sensorless commutation method are very suitable for the requirements of the photovoltaic water pump system for motor drive control. As for the maximum speed limit of the pump, the motor overload current limit, the pump no-load current setting, the pump shutdown low speed limit setting, the shutdown restart delay time setting, the fault shutdown number limit setting and other related controls, intelligent control must be carried out, and the power must also be changed when the flow changes, so that the solar battery, motor and water pump can achieve the best match.

3. The prospect of photovoltaic water pumps

In short, the photovoltaic water pump system is an optomechanical integration system that has developed rapidly in recent years. It uses the power generated by solar cells to drive DC, permanent magnet, brushless, position sensorless, stator-rotor double plastic-sealed motors or high-efficiency asynchronous motors or high-speed switched reluctance motors to drive high-efficiency water pumps through maximum power point tracking, conversion, control and other devices to bring water from deep on the surface to the ground for farmland irrigation or drinking for people and livestock. From design to manufacturing, modern technologies involving multiple disciplines such as electrical, mechanical, power electronics, computers, and control provide extremely good means for the development of modern agriculture, energy conservation, and environmental protection. This system has good long-term economic performance, especially compared with the common diesel engine pumping, it has an overwhelming economic advantage. The development of this new type of environmentally friendly and energy-saving product will undoubtedly bring great economic and social benefits to the development of industry and economy, especially the development of modern agriculture in arid areas. It is particularly in line with the development strategy of building a "resource-saving" and "environmentally friendly" society. Photovoltaic water pumps use solar energy and can be used flexibly for farmland irrigation, providing clean drinking water for humans and livestock, developing courtyard economy, beautifying parks, constructing colorful fountains, oxygenating fish and shrimp ponds, and supplying and draining water for seaside salt fields without any external energy.