Solar high pressure gas discharge lamp intelligent control system (1)

Abstract: in order to increase the solar high pressure gas discharge lamp lighting efficiency, extending the lighting time, charge and discharge realize intelligent control, intelligent lighting control, a new type of solar high pressure gas discharge lamp lighting control system.

System charge control strategies for maximum power point tracking technology and accurate three-stage battery charging, lighting control strategy using variable switching frequency control and constant power control. Hardware structure using single inverter structure, reduced hardware costs, overhead, and increased energy conversion rate. Experimental results show; the system extends the battery life and lighting time and improves the efficiency of the electric light efficiency, up to 90 per cent, making solar high pressure sodium lighting system smart, efficient, stable operation.

Keywords: solar power; high pressure gas discharge lamps; Lighting; maximum power point tracking; charge-discharge

Solar energy with its pollution-free, reliable and inexhaustible, inexhaustible, the current development of a new energy.

Using high pressure gas discharge lamps for solar PV lighting, is currently the most widely used one of photovoltaic lighting technology.

The paper presents a new type of solar street lighting intelligent control system hardware design and software control strategy.

System uses the single-chip as a core for energy management, through sampling solar cell, battery and lighting power, realization of system of automatic control and run intelligent control. Control strategy on include: the charging process applied maximum power point tracking (maximum power point tracking, MPPT) maximize the absorption of solar power, and a three-stage charging technology guarantee the longevity of the battery and charge capacity. In the discharge process using frequency output control strategy, achieve high pressure sodium lamp current controllable aims to achieve high pressure sodium lighting intelligent control. Hardware design with full bridge inverter (DC-AC) circuit, combined with the lamp lighting.

1 solar high pressure sodium lighting system consisting of

This article made of solar lighting system for high pressure sodium lamp as shown in Figure 1, the system consists of solar panels (PV), batteries, lighting and controller.

　　

　　

1) solar energy as an entire system, during the day enter the charging status, battery charging process using PWM control, the control system continuously testing PV array and battery power, the different charging policy in control and switching.

When it gets dark, the solar panels voltage falls below the specified value, the quit charge.

2) batteries as solar energy storage link, the day through solar charging circuit will be stored in the battery, the battery at night through full-bridge DC-AC circuit to provide power HPS, moreover, all the control circuit of the electricity is supplied by the battery.

3) lighting generally opt for long life and high energy-saving lamps, high pressure sodium lamps in systems.

4) control system by SCM and its external circuit, through the sampling results of calculation and judgment, control of the entire system.

2 battery charging policy

To improve charging efficiency, longer battery life, battery for rechargeable battery, adopted this article introduced based on the three-section MPPT charge control strategies, a better solution to this problem.

2.1 maximum power point tracking technology

Solar cell output characteristics with nonlinear and has affected by light heat flux q and ambient temperature affect the serious characteristics, output characteristics in different light intensities of curves is shown in Figure 2.

　　

　　

In order to achieve the maximum utilization of solar energy, you need to use the maximum power point tracking (MPPT).

MPPT solar technology is on the power curve of the first order differential tracking, control objectives, through the power curve for maximum power point tracking algorithm so that the maximum output power. Specific algorithms for: solar battery voltage and current for sampling, the output power, and with the previous period calculated power values, mission score, if you meet the

So it has reached the maximum power point tracking.

In maximum power point charging stage, when the battery voltage is higher than the storage battery can accept the maximum power point voltage of no fixed value means that the solar output capacity beyond the battery capacity, then quit charge maximum power point.

2.2 battery charger of the three-section

Battery as the power of direct lighting, must take into account the attenuation of the battery capacity and service life, how to make a reasonable charge on the battery, keep the battery capacity and service life, it is very important.

Use this article following the three-stage charging policy, can be a good solution to the problem.

1) fast blanking stage: fast blanking stage with maximum power point tracking technology, maximize the solar energy into chemical energy.

When the voltage is higher than the conversion threshold, exit fast blanking stage, enter the overshoot.

2) overcharging the stage: in the fast-stage to a higher battery charging voltage, when the charging current is less than the converted threshold, i.e. battery nearly full, quit charge stage, enter floating stage.

3) floating stage: stage in floating charge to the battery with a floating charge voltage, experiments show that in appropriate floating State, for general maintenance-free battery, stable working life is 6-lO a, if no or floating charge voltage deviations larger will greatly reduce the battery life.

3 power supply circuit design

Single-stage-discharge circuit adopts the full-bridge DC-AC converter circuit with high-frequency transformer structure design principle of design, as shown in Figure 3.

　　

　　

Power supply circuits for lead-acid storage

Battery for power supply, 250 W high pressure sodium lamps to load. Battery for DC source, 3-line DC voltage range selected in 34 ~ 42 v power supply.

The relationship between the input and output voltage is

Where: q to duty, n = N1-N2/transformer ratio, R equivalent resistance for high pressure sodium lamp, ballast and reactance XL, XL for = 2 π f L.

By type (3) know by changing the output frequency, thus changing the ballasts, and change the reactance of the electric voltage divider, output voltage, current-controlled.

Due to high pressure sodium lamps in the arc discharge status, current-voltage characteristics curve is negative slope, so the circuit must concatenate a positive resistance circuit elements to balance the negative resistance characteristics.

Meanwhile, high pressure na lamp starts, since the start of HPS, making startup HPS resistance is very small, steady state at resistance values and to stabilize. Figure 4 is in different inverter voltage, high pressure sodium lamps in the startup properties and the required compensation reactor, which is the subject identity value pu said (hereinafter the same).

　　

　　

To resolve this issue, this article uses the high frequency electronic ballasts with high pressure sodium lamps work.

By changing the frequency inverter's switch, change of policy, so as to achieve the inductance ballasts for the control of high pressure sodium lamps for the purpose of the start-up current, high pressure sodium lamp start stability. In steady work, because the battery voltage decreases and high pressure sodium lamps of volt-ampere characteristic, by changing the inverter switching frequency to achieve control of partial pressure and high pressure sodium lamp current purpose, so that the stable work of HPS.

Constant switching frequency control for high pressure sodium lamp current implementation method: continuous detection ballast current, through AD sampling, feedback to the microprocessor, microcontroller by sampling values and rated the set value is compared to a change in frequency of instruction, at the same time gives the frequency of the change, when the battery voltage drops or lamp current decreases, reduces the switching frequency, the lower the partial pressure of the ballast, ensure that lamps constant-current, high pressure sodium lamp current-loop control, experiments show that the inverter output current stabilized at high pressure sodium lamps near the rated output current.

In the hardware design, the system uses as shown in Figure 3 structure of single-stage type inverter, its structure is the biggest feature only through an energy transformation link for boost, maximum power point tracking, inverter, electrical isolation, etc.

And the traditional two-stage inverter structure compared to the maximum advantage of topology simple structure, low loss, efficiency has improved significantly. At the same time using frequency transformer switching power supply replaced the volume bulky power transformer, voltage conversion and isolation, is of small size, light weight, the efficiency higher characteristic.

Because of this system for high pressure sodium lamps operating frequency is very high (30 ~ 70kHz), and the General current sensor frequency characteristics at 20 kHz, so detection current fluctuation range.

This paper presents another intelligent control programmes, through control of battery power output, indirectly controlled high pressure sodium lamp power. Control system through the sampled values battery power and set value comparisons, and constantly adjust the frequency inverter to output power-controllable.

Constant power control advantage lies in the sampled signal directly from the DC side, voltage and current measurement accuracy and high switching frequency change of more accurate.

Experiments show that takes a variable frequency output of the current control, constant power control strategy, high pressure sodium lamp running more stable.

4 system software design

The system platform run mainly by 89C51 MCU control, including energy management control, MPPT strategy, sampling, the PWM pulse.

Buck PWM pulse circuit chip directly given, fixed frequency 33 kHz.

Figure 2 gives the solar output characteristic curve, by adjusting the dutyfactor, change solar battery terminal voltage, [1] [2]