產學計畫研究成果


DSP控制單相在線式UPS

DSP-Controlled Single-Phase On-Line UPS

200281

鄒應嶼 教 授

交通大學 電機與控制工程系 

Abstract

      This research proposes a DSP-controlled transformerless common-neutral single-phase on-line UPS with balanced charging/discharging control. All the control functions for an on-line UPS, which includes power-on start-up control, input stage power factor control, battery charging and boosting control, output stage ac voltage regulation, and shut-down control, were realized by using a single-chip DSP controller. A multiple rate digital controller generates all the PWM control signals for the power stage by using a set of detected feedback signals. Software current control scheme with nonlinear pulsewidth compensation has been developed to eliminate the nonlinearity caused by the dead-lock protected PWM converters. A nonlinear digital control scheme with lower switching frequency has been developed for the power factor control of the ac-dc converter. Computer simulation and experimental results have been given to verify the proposed digital control scheme. The constructed DSP-controlled UPS system can achieve fast dynamic response for nonlinear loads and high power factor under various loading conditions.
 

I. INTRODUTION

      Application of microprocessors and DSP in high-performance power electronic systems has been a long term pursuing goal in development of control techniques for power converting systems [1]-[6]. However, due to the complicated control functions required in a UPS system, most of the previous works were focused on the digital control of the PWM inverter for ac voltage regulation. There are many control functions in an on-line UPS system, such as power on/off sequence control, frequency synchronization, power factor control, PWM inverter control. Battery charging control, battery voltage booster control, and many other diagnostic and monitoring functions.

       Implementation of a fully digital-controlled UPS has many advantages, such as more sophisticated control functions can be added into a UPS system, a software-controlled UPS can be more flexible, advanced robust control schemes can be implemented to accommodate stringent and versatile application requirements. Many research works have been carried out on the closed-loop regulation of PWM inverters using various feedback control schemes to achieve both good dynamic response and low harmonic distortion. Microprocessor-based deadbeat control technique has been applied to the closed-loop regulation of PWM inverters. Deadbeat control has been developed for the voltage regulation of the PWM inverter by employing a minor current loop and a major voltage loop. However, deadbeat control scheme has the disadvantages of highly sensitive to parameter and load variations and requiring large peak-to-average ratio of control signals to achieve deadbeat effect.

       With the great advances in microelectronics and VLSI technology, high-performance microprocessor and digital signal processors (DSPs) can be effectively used to realize advanced control schemes [7]. Most instructions of a DSP can be accomplished within one instruction cycle and complicated control algorithms can be executed with fast speed, therefore, more control functions can be realized by using software. Attempts have been made to realize a fully DSP-controlled UPS [8]-[9]. However, only limited functions have been realized using software. In this paper, a single-chip DSP controller, the TMS320F240 from Texas Instruments, has been used to realize all the control functions required in an on-line UPS system.

       With the availability of 16-bit high-performance DSP chips, most of its instructions can be accomplished within one instruction cycle, complicated control algorithms can be realized efficiently. This paper describes the design and implementation of a DSP-embedded fully digital-controlled single-phase on-line uninterruptible power supply (UPS) system. All the control functions for an on-line UPS, which includes power-on start-up control, input stage power factor control, dc-link voltage regulation, battery charging and voltage boosting control, output stage ac voltage regulation, and shut-down control, were realized by using a single-chip DSP controller.
   

II. DIGITAL CONTROL OF AN ON-LINE UPS

Fig. 1. System block diagram of a DSP-based intelligent UPS system.

       Fig. 1 shows the system block diagram of the proposed DSP-controlled on-line UPS system. The system consists of two major parts: a power conversion unit and a DSP-based UPS control unit. The power stage performs all the power converting functions and its major design goal is high-efficiency with constraints of low cost and small volume. The DSP-based UPS controller performs all the real-time control functions required by the power stage and its major design goal is fast dynamic response with robust performance. The core of this digital-controlled on-line UPS is the DSP-based UPS controller. The UPS controller must execute all the control functions for the power converters to achieve stable and robust performances.

Fig. 2. Transformerless common-neutral UPS with balanced charging/discharging control.

       Fig. 2 shows the circuit topology of the power stage of the single-phase on-line UPS. The power circuit consists of four sub-circuits: a boost PFC ac-dc converter, and half-bridge dc-ac inverter, and a charger and a booster with balanced common-neutral control. The proposed single-phase on-line UPS circuit has characteristics of sharing a common-neutral voltage from utility to load. The circuit is symmetric in nature and balancing control for asymmetric load can be realized by adjusting control duties of the upper and lower switches.

A. Digital Control of the PFC Boost Converter

       Regulations on line current harmonics have made power factor control a basic requirement for power electronic equipment [14]. The main purpose of the PFC converter is to shape the input current to be linear proportional to its input voltage so that it behaves as a resistor. Another purpose of the PFC converter is to regulate its output dc voltage under line and load variations.

       Conventional PFC control schemes focus on the shaping of the line current in proportional to the voltage and therefore, a current loop controller with wide bandwidth is required. However, in order to minimize the current distortion resulted from the dc-link voltage regulation, a low-pass filter is required to smooth the double line frequency ripples in the dc-link voltage. This results a slow response of the UPS front-stage power converter. The slow response of the PFC converter will result a large voltage drop under a step load change and further deteriorate the UPS output waveform.

       One major design challenge in synthesizing a digital PFC controller is that we must make a compromise between the line current distortion and a fast response of the dc-link voltage regulation. The PFC controller consists of three sub-controllers: an inner current loop controller, an outer voltage loop controller, and an adaptive ripple estimator.

       The inner current loop controller is required to regulate the line current with a high sampling rate, usually from 10 to 20 kHz. The outer voltage loop controller is used to regulate the dc-link voltage and at the same time to generate a current reference for the current loop. A lower sampling rate from 1 to 2 kHz is an appropriate choice for the voltage loop. The adaptive voltage ripple estimator is used to generate a compensated signal to cancel the line ripple voltage occurred in the dc-link.

B. Digital Control of the PWM Inverter

       A variety of control schemes have been developed for the closed-loop regulation of a PWM dc-ac converter [10]-[13]. The instantaneous feedback control with adaptive hysteresis regulates the PWM inverter with direct current and voltage feedback [10]. This control scheme changes the hysteresis width as a function of the voltage reference, but its dynamic responses to large loads change or rectifier types of load are left unsolved. Instantaneous voltage feedback with an inner current loop was also developed for the control of PWM inverters. Microprocessor-based deadbeat control technique has been applied to the closed-loop regulation of a PWM inverter [11]. However, the dead-beat control scheme has the disadvantages of highly sensitive to parameter and load variations and requiring large peak-to-average ratio of control signals to achieve dead-beat effect.

       In order to improve the dynamic response of the PFC boost converter, various feedback control schemes have been analyzed in [15]. Analog notch filter to eliminate measured output voltage ripples can achieve a better dynamic response compared with other approaches. Development of fast response control schemes for the PFC boost converter has become a technical pursuing goal in recent years [16]-[19]. These control techniques break the bandwidth barrier of double line frequency by using sophisticated control techniques in elimination the influences of output voltage ripples. All these control schemes are applied to the PFC boost converter and using analog controller or analog current-loop controller with microprocessor-based voltage-loop controller.

       Reference [12] has made a comparison study of five different approaches in synthesis of the digital control for PWM inverters. The conclusion is that no satisfactory results can be obtained by using the conventional design approach. In order to improve the dynamic responses and at the same time to provide a low THD output of the PWM inverter under nonlinear load conditions, Jung and Tzou have developed a discrete sliding mode control scheme [13]. However, this control scheme needs a high sampling rate digital controller to keep a low chattering trajectory. To implement a fully digital-controlled UPS, we need to devise a low sampling rate controller so that the computation resources can be reserved for other control functions.

       A first-order auto-regressive moving-average (ARMA) model with feedforward compensation has been used in synthesis the voltage loop controller. The DSP controls the inverter switches so that the output voltage can track the sinusoidal reference at each sampling instant. In the proposed system, the dc-link voltage, inductor current, output voltage, and output current are sensed as feedback variables, and the control algorithm computes the required pulsewidths for the dc-ac converter.

       The feedforward controller is used to synthesize predictive control action for the sinusoidal reference. The voltage loop controller is a first-order digital filter with its pole and zero to be tuned to reach a fastest step response under rated resistive load condition. An inner current loop controller, the inductor current controller, is used to regulate the current flow through the output filter indictor. Another outer current loop controller, the load current controller, is devised to improve transient responses of nonlinear loads.

C. Digital Control of the Battery Charger

       The battery charger in the designed UPS system is symmetric common-neutral flyback converter. A proportional controller is used for the current regulation and a simple PI controller is used for the voltage regulation. Constant current with battery voltage profile control is adopted as the battery charging scheme. The charging profile is stored in the EEPROM of the UPS controller and can be reloaded when a new set of battery are installed. The software control approach provides great flexibility in implementing various intelligent battery charging and discharging control schemes.

D. Digital Control of the DC-DC Booster

       The booster in a UPS system is used to convert the battery output voltage to a much more high dc-link voltage. The battery booster in the designed UPS system is a common-neutral flyback converter with a coupled transformer. The PI control scheme has been applied for the inner current loop control of the boost converter. Because the booster output is connected to the dc-link and is activated when the utility is failed, its dynamic response behaves as an important performance index. The flyback converter is voltage regulated by an outer voltage loop controller using PI control with dc-link voltage feedforward compensation.

III. CONTROLLER REALIZATION

 

Fig. 2.  Flowchart of the DSP main program for UPS control.

Fig. 3.  Setting of the DSP control registers for the PWM generation.

FEATURES
DSP-based digital controller hardware design
Programmable PWM generation 40 kHz

IV. DSP-BASED UPS CONTROLLER

Fig. 4.  A DSP-based controller for on-line UPS systems.

FEATURES
TMS320F240 DSP controller with 32k flash memory
CPLD for PWM generation and I/O decoding
Standard power bus (P-BUS) for UPS control
Standard status bus (S-BUS) for UPS monitoring
RS-232/422 computer interface

V. PROTOTYPE IMPLEMENTATION

Fig. 5.  Realization of a fully DSP-controlled 2 kVA on-line UPS.

FEATURES
True on-line UPS using single-chip DSP control technology
Digital power factor control
Digital PWM inverter control with nonlinear compensation
Programmable battery charging control
Programmable UPS controller adapted to various power stages
On-line interactive remote monitoring and control
Standard power interface bus for power conversion control


SPECIFICATIONS
Input voltage range: 80-140V (160-280 for 220V nominal line)
Frequency:50/60 Hz ±5% auto-synchronization
Output Voltage Regulation (Line): 115 (230) ±2%
Output Voltage Regulation (Battery): 115 (230) ±3%
Power Factor >0.98 @ full load

VI. PERFORMANCE MEASUREMENT

Fig. 6. (a) Simulation and (b) experimental results of the steady-state responses of the PFC converter.

Fig. 7. Experimental results of the PWM inverter with a step change of resistive load at 90°. (a) Output voltage and current and (b) harmonic spectrum of the output voltage.

PERFORMANCE MEASURES

Rated output power: 2kVA
Input power factor > 0.98
Output voltage THD < 2% under linear resistive load
Output voltage THD < 5% under nonlinear rectifier load
maximum line to output efficiency: 85%
Tach output senses commutation of the motor

 

VII. CONCLUSION

        This research has completed the design and implementation of a DSP-embedded fully digital-controlled single-phase on-line uninterruptible power supply (UPS) system. The applications of high-performance DSP in complicated power electronic systems will find great potential in synthesis of sophisticated control algorithms and PWM switching schemes. This paper has applied a single-chip DSP controller, the TMS320F240, in realizing all the required control functions for a single-phase on-line UPS. Experimental results show the designed 2 kVA UPS can reach very good dynamic responses both in utility interface and output voltage regulation.

REFERENCES

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PEMCLAB的相關研究成果

  1. Che-Hung Lai (賴哲宏) and Ying-Yu Tzou, "DSP-embedded UPS controller for high-performance single-phase on-line UPS systems," IEEE IECON Conf. Rec., Sevilla, Spain, Nov. 5-8, 2002. 

  2. Che-Hung Lai (賴哲宏) and Ying-Yu Tzou, "快速動態響應UPS換流器的DSP控制器之設計與實現," 第二十二屆電力工程研討會, 高雄, 台灣, pp. 695-700, Nov. 22-23, 2001.

  3. Kuo-Lung Tsai (蔡國隆), Yo-Ming Chen (陳佑民), Shiu-Yung Lin (林栩永), and Ying-Yu Tzou, "單相全橋式PWM AC-DC轉換器數位控制之模擬分析," 第二十二屆電力工程研討會, 高雄, 台灣, pp. 689-694, Nov. 22-23, 2001.

  4. Ya-Tsung Feng (馮雅聰) and Ying-Yu Tzou, "DSP全數位快速響應單相功率因數修正器之研製," 第二十二屆電力工程研討會, 高雄, 台灣, pp. 943-948, Nov. 22-23, 2001.

  5. Ya-Tsung Feng (馮雅聰), Che-Hung Lai (賴哲宏), Shiu-Yung Lin (林栩永), Eric Chen (陳建國), and Ying-Yu Tzou, "DSP-based fully digital control of an on-line UPS," IEEE PEDS Conf. Rec., pp. 301-305, Bali, Indonesia, Oct. 22-25, 2001.

  6. Ya-Tsung Feng (馮雅聰), Gow-Long Tsai (蔡國隆), and Ying-Yu Tzou, "Digital control of a single-stage single-switch flyback PFC AC/DC converter with fast dynamic response," IEEE PESC Conf. Rec., pp. 1251-1256, Vancouver, Canada, June 17-22, 2001.

  7. Che-Hung Lai (賴哲宏), Ya-Tsung Feng (馮雅聰), Yuan-Haur Sheu (許元豪) and Ying-Yu Tzou, "DSP控制UPS正弦穩壓的分析、設計與實現," 第二十一屆電力工程研討會, 台北, 台灣, pp. 1016-1021, Nov. 18-19, 2000.

  8. Ya-Tsung Feng (馮雅聰), Che-Hung Lai (賴哲宏), Ming-Shung Wu (吳明璇), and Ying-Yu Tzou, "DSP全數位控制在線式UPS之系統模擬," 第二十一屆電力工程研討會, 台北, 台灣, pp. 947-952, Nov. 18-19, 2000.

  9. Ya-Tsung Feng (馮雅聰), Yo-Ming Chen (陳佑民), and Ying-Yu Tzou, "DSP控制具有備用電源之48V電源供應器之研製," 第二十一屆電力工程研討會, 台北, 台灣, pp. 1040-1045, Nov. 18-19, 2000. 

  10. Ya-Tsung Feng and Ying-Yu Tzou, "DSP control of a single-stage DC-UPS with power factor correction," PCIM Proc., pp. 424-431, Boston, USA, Oct. 1-5, 2000.

  11. Ming-Tsai Kao (高明才) and Ying-Yu Tzou, "應用於UPS的高頻柔切脈寬調變換流器之研製," 第二十屆電力工程研討會, 台北, 台灣, pp. 1-6, Nov. 20-21, 1999.

  12. Yung-Hiang Liu (劉永祥) and Ying-Yu Tzou, "零電壓轉換昇壓型功因修正器設計與實現," 第二十屆電力工程研討會, 台北, 台灣, pp. 13-18, Nov. 20-21, 1999.

  13. Ying-Chuan Chiou (邱穎川) and Ying-Yu Tzou, "多功能電池充電控制實驗系統之研製," 第二十屆電力工程研討會, 台北, 台灣, pp. 7-12, Nov. 20-21, 1999.

  14. Shih-Liang Jung (榮世良), Hsiang-Sung Huang (黃湘松) and Ying-Yu Tzou, "A three-phase PWM AC-DC converter with low switching frequency and high power factor using DSP-based repetitive control technique," IEEE PESC Conf. Rec., pp. 517-523, Fukuoka, Japan, May 17-22, 1998.

  15. Hsiang-Sung Huang (黃湘松), Shih-Liang Jung (榮世良) and Ying-Yu Tzou, "應用反覆控制理論於三相交直流轉換器功率因數控制之研究," 1998自動控制研討會, pp. 565-570, 雲林, 台灣, April 9-10, 1998.

  16. 葉禮嘉, 榮世良, 張盟岳, 江晉毅, 鄒應嶼, " CPLD 為基礎的單相 UPS 脈寬調變換流器穩壓控制 IC 之研製," 第十八屆電力工程研討會, pp. 146-150, 新竹, 台灣, Nov. 8-9, 1997. 

  17. Shih-Liang Jung (榮世良) and Ying-Yu Tzou, "Multiloop control of an 1-phase PWM inverter for ac power source," IEEE PESC Conf. Rec., pp. 706-712, June 22-26, 1997. 

  18. Shih-Liang Jung (榮世良), Meng-Yueh Chang (張盟岳), and Ying-Yu Tzou, "FPGA-based control IC for an 1-phase PWM inverter used for UPS," IEEE PEDS Conf. Rec., pp. 344-349, May 26-29, 1997. 

  19. 黃湘松, 榮世良, 張盟岳, 鄒應嶼, "UPS脈寬調變換流器之單晶片DSP全數位式多迴路控制之研製," 第十七屆電力工程研討會, 新竹, 台灣, Nov. 8-9, 1996. 

  20. Ying-Yu Tzou and Hsing-Chung Yeh (葉信忠), "DSP-based adaptive repetitive control of a PWM Inverter for UPS with very low harmonic distortion," IEEE IECON Conf. Rec., pp. 1122-1127, Taipei, Taiwan, Aug. 5-9, 1996. 

  21. Shih-Liang Jung (榮世良), Hsiang-Sung Huang (黃湘松), and Ying-Yu Tzou, "Self-tuning discrete sliding mode control of a closed-loop regulated PWM inverter with optimal sliding surface," IEEE PESC Conf. Rec., pp. 1506-1512, Baveno, Italy, June. 24-26, 1996. 

  22. Shih-Liang Jung (榮世良) and Ying-Yu Tzou, "Discrete sliding mode control of a closed-loop regulated PWM inverter for sinusoidal output waveform synthesis," 自動控制研討會暨兩岸機電及控制技術交流學術研討會, pp. 503-508, Feb. 26, 1996. 

  23. Shing-Chung Yeh (葉信忠) and Ying-Yu Tzou, "Adaptive repetitive control of a PWM inverter for ac voltage regulation with low harmonic distortion," IEEE PESC Conf. Rec., pp. 157-163, June, 1995. 

  24. Y. Y. Tzou, "DSP-based fully digital control of a PWM dc-ac converter for ac voltage regulation," IEEE PESC Conf. Rec., pp. 138-144, June, 1995. 

  25. 榮世良、何濂洵、葉信忠、鄒應嶼, 具有最佳回授增益之數位控制架構於脈寬調變換流器之應用, 第十五屆電力工程研討會, pp. 36-41, 1994. 

  26. Rong-Shyang Ou (歐榮祥) and Ying-Yu Tzou, "Design and implementation of a DSP-based programmable ac power source with low harmonic distortion using repetitive control technique," 第十五屆電力工程研討會, 台南, 台灣, pp.139-145, Dec. 15-16, 1994. 

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