Chapter 5 An Integrated Power Management System for Solar
5.4 Simulation Results
5.4.3 Power Efficiency Optimization
The power efficiency of proposed optimization unit compare to the constant clock supply is shown in Fig. 5.18. It shows the dynamic detection of the power efficiency optimization unit gives better power efficiency performance over the constant clock supply with different load current condition.
Fig. 5.17 The three different output voltage with variation of current from PV cell.
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
0 30 60 90 120
150 180
210 240
load current (uA)
e ff ic ie n c y (% )
180MHz66MHz Dynamic detection
Fig. 5.18 The power efficiency of 1V generator with different load current.
5.4.4 Comparison of System with CU and without CU
The difference of power management system without CU and with CU is shown in Fig. 5.19. In this simulation, the PV cell is set to output zero current and the power management system is supplied by battery.
If the power management system without control unit that is the PV cell is connected to voltage regulator, the output current of battery is 961uA in 30ns. With the control unit, the output current of battery is reduced to 200uA in 30ns.
The simulation result shows that with CU, the power consumption of battery will be reduced 80% compare to power management system without CU. This will increase the using time of battery. The specifications of power management system is summarized in TABLE I.
Fig. 5.19 Comparison of power management system with CU and without CU.
Table 5.2 Power management system for solar energy harvesting.
Technology UMC 90nm CMOS
Technology Output current of PV cell 4mA~0mA
Output voltage of PV cell 840mV~177mV Output power of PV cell 2.3mW~0mW
0.5V output 592mV~482mV
1V output 1.11V~0.9V
-0.5V output -547mV~-440mV
Maximum total power efficiency 69%
0.5 _ 1 _ 0.5 _
5.5 Summary
An integrated power management system is proposed. The power management system works with PV cell and rechargeable battery. The output current of PV cell varies from 4mA to 0mA and its output voltage varies from 840mV~177mV.
The power management system outputs voltage of 0.5V, 1V and -0.5V to loading circuitry. The 0.5V output is vary from 592mV~482mV. The 1V output is vary from 1.11V~0.9V. The -0.5V output is vary from -547mV~ -440mV.
With power efficiency optimization unit, clock switching frequency of 1V generator is slow in light loading case, thus the power consumption is less than constant high frequency (180MHz) clock. In heavy loading case, the clock switching frequency of 1V generator is fast, thus the loading capability is better than constant low frequency (66MHz) clock. The power efficiency optimization unit is co-design with Chih-Hao Kan.
With control unit and power efficiency optimization unit, the battery supplies energy efficiently and the power consumption is down to one fifth (20%). The maximum total power efficiency is 69%.
Chapter 6
Conclusions and Future Work
In this thesis, we proposed a voltage regulator with 99% current efficiency in Chapter 3. A novel connect scheme of charge pump for generating ultra high voltage is proposed in Chapter 4. In Chapter 5, we proposed an integrated power management for solar energy harvesting applications. The research results of Chapter 3 and Chapter 4 are applied to this power management system. The power management system accepts the power from PV cell and outputs 500mV, -500mV and 1V for computation circuitry and memory circuitry. The power management system also contains a rechargeable battery. Thus, the system can work in day and night. We proposed a power efficiency optimization unit to increase the power efficiency of 1V generator. A control unit is also proposed to prevent the leakage current flow back to PV cell when the PV cell do not supply energy.
Base on the MPPT concept, we can apply the MPPT mechanism to our system, as shown in Fig. 6.1. When PV cell supplies energy, the MPPT will monitor the output voltage of regulator and decide the amount of supply current to battery charger. Thus, the output power of PV cell and output voltage of voltage regulator can be controlled in our desired range.
Fig. 6.1 Efficient power management system with MPPT mechanism.
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Vita
PERSONAL INFORMATION
Birth Date: August. 31, 1984
Birth Place: Taoyuan, Taiwan, R.O.C.
Address: Department of Electronics Engineering National Chiao Tung University 1001 Ta-Hsueh Road
Hsin-chu, Taiwan 30010, R.O.C.
E-Mail Address: [email protected]
EDUCATION
B.S. [2006] Department of Control Engineering, Chiao-Tung University.
M.A. [2008] Institute of Electronics, National Chiao-Tung University.