Research on solar LED lighting control system based on embedded object module

Chen Jian, Zhao Zheng Zheng, Yuan Liqiang (State Key Laboratory of power system, Department of electrical engineering, Tsinghua University, Beijing 100084)

Abstract: solar LED lighting system as a new way of lighting, not only has the advantages of independent photovoltaic lighting system, such as clean, no pollution and no need of long distance transmission line, but also has high luminous efficiency LED lighting, soft light, the photovoltaic battery design capacity is small and many other advantages. However, the system needs to achieve the maximum power point tracking (MPPT) control, LED nonlinear load discharge control and battery charging and discharging control functions, which has a high demand for control. In this paper, the requirements of the control system are analyzed, the MPPT, charging strategy and LED discharge control are studied, and the main circuit and control system are simulated by using MATLAB /Simulink. Based on the simulation model, the embedded eZdsp module is used to generate the TSM320F2812 DSP control program, and the simulation model is rapidly transformed. The system has the advantages of fast dynamic response, smooth start current, high precision and so on, so as to get the control method suitable for solar LED lighting system. Key words: embedded target module maximum power point tracking LED lighting classification number: TM923. 34 document code: A article number: 1003-3076 (2010) 03-0076-05

Introduction

Solar energy as an important new energy and clean with no pollution, huge reserves, easy to use etc.; LED (light emitting diode) lighting system has the advantages of long service life, high luminous efficiency, are widely used in lighting; solar LED lighting system focused on the advantages of solar energy and LED, has good market prospects. But it has its own defects: the volt ampere characteristics of solar panel output (V-I) curve is nonlinear, only work can at a specific voltage maximum output power, the need for maximum power point tracking (MPPT) control; I-V curve of LED lamp is approximate to exponential function, so the control precision, or easy to damage; the battery as the energy storage element, need to charge and discharge management strategy is reliable and reasonable, can prolong the service life.

According to the above problems, we make MPPT control research, LED constant current research and battery charge and discharge control strategy, using MATLAB /Simulink integrated simulation of main circuit and control algorithm of the system, the control effect and the control parameters of the ideal, and the transplantation of control model, using Embedded Target for TI C2000 DSP embedded module generate the control code for the actual system controlled by TMS320F2812 DSP, and the simulation control algorithm in the actual system, fast and accurate.

2 system control requirements analysis and Implementation

The solar LED lighting system consists of photovoltaic array, battery, LED array lamp and controller. The controller to realize the whole system of charge and discharge control, real-time detection of photovoltaic array, the battery and the LED lamp working condition, and to achieve the discharge switch process, both to ensure the maximum power output of the photovoltaic array, but also to ensure the service life of the battery and the LED lamp safety work.

2.1 MPPT control optimization

At present, there are many researches on MPPT control, the methods are different, the control effect is different, so it is necessary to select a reasonable method for the actual system. According to the literature (1-3), the interference observation method which is suitable for small independent system is selected and improved.

The traditional perturbation and observation method in the photovoltaic system is the most widely used, can quickly and accurately control the MPPT, but there exists the problem of misjudgment of the maximum power point repeated oscillation and special circumstances, such as illumination changes, 3, 4.

Through the dynamic adjustment step a s disturbance to the traditional method, namely when the external conditions change rapidly, increasing the step disturbance and control cycle, when the system is running at steady state, reducing the step disturbance and control, at the same time, the variable step size method, can the change in power detection value of Delta P is large, the lock step disturbance 0, when the system is relatively stable to the maximum power point search, can effectively solve the traditional method of false judgment phenomenon.

2.2 LED lamp constant current control optimization

LED lamp load volt ampere characteristic curve is approximate to a exponential function, very large in the vicinity of rated power di /dU ratio, higher requirements on the system control 5, if a single loop control system, the low order LED load voltage and current dynamic response and steady state accuracy can not be taken into account, difficult to ensure effect. To this end, according to the actual needs of the control system, the establishment of constant current double loop control model block diagram shown in figure 1:

Set up the operating system through the Iset control system is obtained by the reference current, voltage and current sensor sampling data, the system block diagram of the final output PWM switch algorithm MOSFET gate control system to realize the function of pulse. The constant current double loop control is used to improve the order of the system, and the reference current is the final control object, which is helpful to improve the stability of LED load current.

2.3 charging and discharging strategy selection

The charging and discharging strategy has an important influence on the service life of the battery in use (6, 7). Because the system needs the maximum power output and storage in order to make full use of the photovoltaic array, the charging strategy needs to meet the needs of MPPT, but also to solve the problem of battery life. Select the following charging strategy to meet the requirements:

MPPT charge control: in the battery voltage is lower than the set value of Vset, MPPT is used to control the maximum power charging, as far as possible to ensure the output of PV array maximum power, improve the utilization rate of photovoltaic array; limit power control charging: when the battery voltage reaches Vset, the limit of power charge control, charging power set P = Pset, the the charging current is less than MPPT iP iMPP charging current, MPPT no longer control system;

Float control: when the battery voltage is close to the saturation voltage of Vf, the system further reduces the charging current, strictly control the charging voltage of Vc =Vf, the current float into the small stage, the final completion of the entire process of charging.

2.4 control program generation based on embedded object module

According to the MATLAB /Simulink simulation model, using Simu-link Embedded Target for TI C2000 module, to transplant the control algorithm, and add the eZdsp module to configure DSP resource, can quickly compile control code generation control system in TMS320F2812 DSP. Due to the use of the algorithm, the simulation results can be verified quickly and accurately in the actual system, and according to the simulation results, the control algorithm can be modified rapidly, which greatly improves the efficiency (8).

3 Simulation and experiment

In the MATLAB /Simulink simulation, the main circuit model of Figure 2 is established, which is composed of Buck main circuit, sensors and photovoltaic array model.

Fig. 3 modified step disturbance observation control model Fig. 3 for mutable step perturb and Blocks observe MPPTalgorithms

According to figure 2 and figure model for MPPT control simulation, set the rated power 300W of the PV array model at different times to change the light intensity were 900, 800, 700, 1000W /m2 as a dynamic

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Light disturbance, the ambient temperature is set to 25 DEG C, the simulation waveform is shown in Figure 4 data output PWM pulse width signal acting on MOSFET. Implement system control.

Figure 4 MPPT simulation waveform

Fig. 4 MPPT simulation waveforms

Figure 4 (a), the rapid change of light intensity, the output voltage of photovoltaic array only weak fluctuations, while the output current changes obviously, fully consistent with the ideal MPPT tracking effect; current waveform dynamic response time, steady-state fluctuation is small, reflecting the good control performance. Figure 4

(b) in the system, from the beginning of operation after a period of time that stable operation near the maximum power point, when the light intensity changes, can quickly and accurately operate at the maximum power point new; smaller change of operation waveform in the same light intensity, fully solve the disturbance observation method in near the maximum power point repeated oscillation disturbance and illumination change misjudge problem.

Simulink Figure 5 LED load discharge circuit model based on VS1, VS2, CS1 and CS2 respectively. The voltage and current sensor system, the battery circuit will boost Boost circuit and the LED control program with the load, shown in Figure 1 according to mining control algorithm

Set the LED start reference current to 0 5A, and change the reference current to 6S at 0 6A to simulate the dynamic and steady state performance of the system, and the load voltage and current waveforms are shown in figure.

In Figure 6, the LED starting current is not covered with spikes, which can protect it from damage caused by the peak voltage. After changing the reference current, the output current waveform is very small, the dynamic response is relatively fast, and the steady-state precision is high.

According to the above model, building the real system by 300W photovoltaic cells, batteries and 50W LED lamp, a system main circuit and TMS320F2812 control board, using the embedded object module to generate control code 8, finally realized by DSP control system, MPPT operating system and LED load when starting voltage and current waveforms as shown in Figure 7.

Figure 7 (a) waveform for the dramatic changes in the intensity of the time of the photovoltaic array output voltage and current waveforms. In the light of the waveform changes, the output voltage of photovoltaic array weak changes, but the current change, fully embodies the MPPT control algorithm can quickly and accurately control, fast dynamic response, small steady-state error.

LED lamp load belongs to the semiconductor device, transient overvoltage or overcurrent will lead to damage, so the experiment to control the start-up process, as far as possible

Third Chen Jian, et al. Research on solar LED lighting control system based on embedded object module

It is very important to reduce the voltage spikes and current glitches. Figure 7 (b) in the setting of LED lamp when the reference current value is 0 4A, waveform display LED load steady and smooth at startup, no peak voltage and current can produce burr, ensure the safe and stable operation of the LED lamp, the ideal control performance.

Based on the above research, the actual device of solar LED lighting controller is shown in figure 8.

1) the establishment of solar energy

Based on the simulation results, the MATLAB /Simulink simulation model of LED lighting control system is used to realize the solar LED lighting system controller.

2) simulation of the improved perturbation and observation method with variable step size, and implemented in the actual system, controlled by the MPPT system in Figure 4 shows, light mutation dynamic response speed, steady state voltage current fluctuation is small, tracking curves agree well, reflect the characteristics of high accuracy, effectively solve the traditional frequent interference the disturbance observation method and error judgment; established LED lamp constant current loop control model can effectively solve the LED load due to the overcurrent and instantaneous damage problem, higher control precision, better dynamic and steady state performance.

3) MATLAB /Simulink embedded module based on the eZdsp control program of rapid generation, simulation model and parameters used in solar LED lighting control system, improve the speed and accuracy of system development, provides a quick way for the development and Realization of control system based on DSP.

Source: China Lighting Network