(1) Basic principle of photovoltaic controller
Figure 1 shows the basic principle diagram of a most basic photovoltaic controller. The circuit is mainly composed of solar cell components, control circuits, control switches, batteries and loads.
In the figure, switch 1 is a charging switch, and switch 2 is a discharging switch. The opening and closing of switch 1 and switch 2 are determined by the control circuit according to the charging and discharging state of the system. When the battery is full, the circuit will automatically open the charging switch 1. Disconnect the discharge switch when discharging 2.
2) Principle of parallel controller circuit
Parallel controller is also called bypass controller, which uses mechanical or electronic switching devices connected in parallel at both ends of the battery to control the charging process. Generally used in low-power systems
Figure 2 shows the single-channel parallel charging and discharging controller circuit, VD1 is the anti-reverse charging diode, VD2 is the anti-reverse diode, S1 is the controller charging circuit switch, S2 is the battery discharge switch, R is the discharge load, FU For the fuse detection control circuit to detect the voltage of the battery at any time, when it is detected that the storage S1 is closed, the circuit is overcharged and protected, otherwise S1 is disconnected; when the battery polarity is reversed, VD2 is turned on, and the battery is discharged through the VD2 circuit. Fuse the fuse.
(3) Series controller circuit
On the basis of Figure 2, connect S1 in series in the branch circuit. As shown in Figure 3, when the battery voltage reaches the full voltage, S1 is automatically disconnected, and the solar panel will stop charging the battery to play a role in overcharge protection.
(4) PWM controller circuit
Pulse width modulation (Pulse Width Modulation, PWM) technology refers to the equivalent of obtaining the desired waveform (including shape and amplitude) by modulating the width of a series of pulses.
As shown in Figure 4, the photovoltaic module input is switched on and off in a pulse mode (using field effect transistors to realize on and off). When the battery gradually becomes full, its terminal voltage gradually rises, and the frequency and time of the PWM circuit output pulse All changes make the on-time of the switch prolonged, the interval is shortened, and the charging current gradually approaches zero; when the battery voltage gradually drops, the on-time of the switch becomes shorter, and the interval is prolonged, and the charging current will gradually increase. The pulse width modulation charge and discharge control method does not have a fixed overcharge voltage point, but the circuit samples the terminal voltage of the battery to adjust its charging current in a timely manner, and finally tends to zero. This charging process can increase the charging efficiency of the photovoltaic power generation system and extend the life of the battery. In addition, the pulse width modulation controller can also realize the maximum power tracking function of the photovoltaic power generation system, so it can be used as a high-power controller.
(5) Multi-channel control type controller circuit
Divide the solar cell array into multiple branches to connect to the controller. When the battery is full, the controller disconnects each branch of the solar cell array one by one; when the battery voltage drops to a certain value, the controller connects the solar cell array one by one to realize the charging voltage and current of the battery pack. This kind of controller is generally used for high-power photovoltaic power generation systems above kW level. Its circuit principle block diagram is shown as in Figure 5.
(6) Intelligent controller circuit
The intelligent controller uses microprocessors such as CPU or MCU to collect the operating parameters of the solar power system at a high speed. In addition to the protection functions of anti-overcharge, anti-over-discharge, anti-short circuit, anti-overload and anti-reverse connection, it is controlled by a single-chip microcomputer. The intelligent control of switching off and on single-channel or multi-channel photovoltaic modules can control the discharge rate of the battery with high accuracy, and has a high-precision temperature compensation function, as shown in Figure 6.
(7) Maximum power point tracking controller circuit
The principle of the Maximum Power Point Tracking (MPPT) controller is to multiply the voltage and current of the solar cell array to obtain the power after detection, and determine whether the output power of the solar cell array reaches the maximum at this time, if not at the maximum When the power point is running, the pulse width is adjusted, the duty cycle is modulated, the charging current is changed, real-time sampling is performed again, and a judgment is made whether to change the duty cycle.
The function of the maximum power point tracking controller is to use the DC conversion circuit and the optimization tracking program, no matter how the solar irradiance, temperature and load characteristics change, always make the solar cell array near the maximum power point, and give full play to the solar cell. The efficiency of the array, while adopting the PWM method, makes the charging current a pulse current, reduces the polarization of the battery, and improves the charging efficiency.
Figure 7 shows the P-U curve of the solar cell array. The curve is bounded by the maximum power point and divided into left and right sides. When the solar cell works at point D on the right side of the maximum power point voltage, because it is far from the maximum power point, the voltage value can be reduced, that is, the power increases; when the solar cell works on the left side of the maximum power point voltage, if the voltage is lower The voltage is smaller, in order to obtain the maximum power, the voltage value can be adjusted to a larger value.
(8) MPPT charge and discharge controller circuit composed of single-chip microcomputer
Figure 8 shows a functional block diagram of a charge and discharge controller with MPPT function, which is mainly composed of a single-chip microcomputer and its control acquisition software, a measurement circuit (voltage and current acquisition) and a DC/DC conversion circuit. Among them, the DC/DC conversion circuit realizes DC boost and step-down functions; the measurement circuit mainly measures the input side voltage and current value, the output side voltage value and temperature of the DC/DC conversion circuit.