Electrical appliances testing platform

Transcription

1 Electrical appliances testing platform E. ANTONIDAKIS 1, J. CHATZAKIS 1, M. VOGIATZAKI 1, H. RIGAKIS 1, M. MANITIS 1, D. KOLOKOTSA 2 Department of Electronics 1, Department of Natural Resources and Environment 2 Technological Educational Institute of Crete Romanou 3, Halepa, GR Chania GREECE Abstract: -This paper presents the design and implementation of a platform for testing the endurance and behavior of electrical appliances in fluctuations of their input supply voltage. The proposed platform design produces similar voltage fluctuations as the power network. The platform that is presented, uses a DC/AC inverter that can produce variable frequency and variable voltage up to a maximum voltage level. A Spike Production Circuit is added to the design to produce spikes at levels higher than that of the inverter. An electronic relay circuit is responsible for switching between the inverter and the Spike Production Circuit. The inverter, the Spike Production Circuit and the relay are microprocessor controlled in order to produce the desired output waveform to the Device Under Test. The platform is interfaced with a PC where an application program was developed in order different testing patterns to be able to be generated and stored. This way the platform will have the ability to cause electrical distress at the appliance in a programmable and repeated fashion. Results are presented. Keywords: -electrical appliance, testing platform, inverter, spike 1 Introduction Power networks experience many abnormalities, which are unavoidable and most of the times, are harmful and reduce the lifetime of the electric appliances. This paper presents the design of a programmable platform, which have the ability to cause voluntary electrical distress on the appliances in a similar way with the power network. There is the ability to store the testing patterns, make corrections on the type of programmed disturbances (different frequency, voltage, current, or energy of the spike) and then implement the new pattern into electrical appliances. In order to see the results of the power network abnormalities, the platform will be able to be interfaced with a PC [1]. The function problems of the electric appliances, caused by the abnormalities of power network voltage, mainly depend on the nature of the appliance [2]. The construction of such a platform helps in the acquisition of the knowhow around the requirements of each appliance in power supply. In this way, appliances can be designed to embody effective protection from the abnormalities of the power network. The platform will also offer the ability to classify the electric appliances depending on their internal structure. Finally, the classification of the requirements for each electric appliance group will be able to be performed. The problems that appear in the electrical appliances from the abnormalities of the power network are of different kinds and depend mainly from the type of the appliance. Many manufacturers knowing the problem install different kinds of special circuits to protect their appliances from some type of abnormalities. The block diagram of the Appliance Testing Platform is shown in fig. 1. Power Network High Voltage Relays Capacitor Bank AC/DC DC/AC Inverter SPC Electronic Relay Device Under Test Fig. 1: Block Diagram of Appliance Testing Platform. PC MCUs

2 The platform supports the operation of the Device under Test (DUT) with the DC/AC inverter that can produce a variable frequency and variable voltage output. The inverter has a wide bandwidth design [3] and is able to distort one or both the peaks of its output sinewave. This way the main abnormalities of the power network can be produced. A Spike Production Circuit (SPC), consisted of a High Voltage, a number of relays and a capacitor bank, is added to the design to produce spikes. The SPC can produce spikes with controllable energy at levels higher than that of the inverter and with higher slew rate, by charging a number of capacitors from the capacitor bank. An electronic relay circuit is responsible for switching between the inverter and the SPC. The inverter, the SPC and the relay are microprocessorcontrolled (MCU) in order to produce the desired output waveform to the Device under Test (DUT). The microcontroller unit is able to communicate with a Personal Computer (PC). A special developed program running on the PC helps the programmable and repeated testing on the DUT. 2 The Inverter An experimental single-phase, three level phase voltage and five-level SPWM line-to-line voltage prototype inverter was constructed. The inverter is designed like a high bandwidth amplifier that amplifies a reference sinusoidal waveform with controllable amplification. The experimental design uses one-cycle control [4], in order to be immunized from input voltage variations and to achieve a stable open loop gain and thus to have the ability to be controlled of a high-speed feedback loop. The effect of using one-cycle control and fast negative feedback in PWM inverters reduces the output internal resistance and the output harmonic distortion significantly [5,6]. Using one-cycle control in PWM inverters additionally increases the output voltage regulation against the input voltage variations and thus improving significantly the performance of the cycloconverter inverters. The multilevel SPWM signal of the inverter output is shown in fig. 2. The feedback loop that is used is minimum-time (O-type). The output waveform under 600W load is shown in fig. 3. The result is very close to pure sinewave and the most distorted part is around the zero crossings. This crossover-like distortion is caused mainly by the dead-time. Fig. 2: The five level SPWM voltage waveform at the inverter output. Fig. 3: The inverter output waveform with 600W load. The frequency of the input reference signal is digitally controlled from the Microcontroller. The amplification of the inverter is also controlled digitally using a digital potensiometer. This way frequency and voltage variations can easily produced. The microprocessor algorithm has the ability to change the amplification rapidly near the peaks and produce peak distortion at the output waveform. 3 The Spike Production Circuit and the Electronic relay The inverter has the ability to produce high voltage with high bandwidth but it has always limited slew rate in spike production. This is caused from the inverter output demodulation L-C filter. To overcome this problem the platform utilizes a special Spike Production Circuit (SPC). The SPC is consisted of a High Voltage, a number of relays and a capacitor bank. The SPC and the Electronic Relay board photograph is shown in Fig. 4. The small board on the right shows the MCU. The MCU is able to control the operation and the voltage of the High Voltage. This voltage determines the spike amplitude. The MCU is able to also control the relays and this way it changes the connected capacitance of the Capacitor Bank. The connected capacitance is possible to control the total energy of the spike. A

3 diagram of the relays connection and the Capacitor Bank is shown in Fig 5. Power Supply SPC Control1 Fig. 4: SPC and Electronic Relay board. DUT Control2 Relay 1 Relay 2 Relay 3 Relay 4 C 2xC 4xC 8xC Inverter Fig. 5. Relays and Capacitor Bank connection. An Electronic Relay switches the DUT between the inverter and the SPC. The electronic relay is consisted of four electronic switches. Each switch is consisted of two fast, high voltage and current IGBTs connected back-to-back from their emitters [7]. The gates of the IGBTs are connected together and their drive voltage is applied from an isolated converter between the emitters and the gates. The collectors are the edges of the switch. The control of the switch is the enable input of the isolated converter. The Electronic Relay and the connections around it are shown in Fig. 6. Using this method to construct an electronic relay, faster switching between inverter and SPC is achieved, than using a normal relay from the market. Also the price of a market relay switching in 1KV is very high. That is why an electronic relay is preferred. Fig. 6. The electronic relay. 4 The Microcontrollers Unit The microcontrollers unit (MCU) is based on two microcontrollers, an 89C420 that is responsible for the control of the inverter and a DS2250 that is responsible for all the other blocks. The use of a dedicated microcontroller for the inverter allows its operation also as a stand-alone device. The whole platform (Inverter and SPC) is controlled by PC s serial port. The algorithm of the main microcontroller is shown in Fig. 7. The variable CommB stores the communication string that comes to the microcontroller from the PC.

4 5 The Application Program A PC application program was developed to interface the platform with a PC. The program is able to generate and store different testing patterns. This way the platform has the ability to cause electrical distress at the appliance in a programmable and repeated fashion. The application program has three main parts. In the first part, the user can manually control the output waveform while the platform is in operation. In the second part the output waveform of the inverter can be programmed and in the third part the spikes from the SPC can be programmed. The screen of the program that controls manually the output waveform of the inverter is shown in Fig. 8. Fig. 8. The real time control screen of the output waveform of the inverter. Fig. 7: Algorithm of the main microcontroller. The error messages give feedback to the PC and help the user of the platform to know if everything is OK during the testing process or where the problem exists. A similar algorithm is running in the inverter microcontroller. In this screen, it is possible to set the voltage and the frequency of the inverter and also to distort the peaks of the inverter output waveform with spikes. The real time control of the platform is helpful when is desirable to test the platform. Respectively, the screen of the programmable output waveform of the program is shown in Fig. 9. The user can assemble a testing waveform consisting of different patterns. On the left side of the screen the user can give the parameters for inserting a pattern. The patterns will be executed in order. The stored data of the inserted patterns are shown in the white area of the screen where each row represents one pattern. The first number is the RMS Volts of the inverter output, the second is the frequency multiplied by 100. The symbol in the third position represents the type of the peak spike and the number that follows is the peak value of the spike. The + sign designates positive spikes, the - sign designates negative spikes, the = sign

5 designates both positive and negative spikes, X sign designates no spikes. In the last position the number represents how many seconds will be the duration of the pattern. A typical spike on an AC volage is shown in Fig. 11. In this figure the operation of the electronic relay is visible. The switching dead time of the relay causes some ringing at the edges of the spike. Fig. 9. The programming screen of the output waveform of the inverter Fig. 11. Typical spike from the SPC. 6 Experimental Results The operation of the platform was verified with many tests in the laboratory. Some typical waveforms were recorded with a resistive load to explain the platform s basic operation. In Fig. 10 there is no AC voltage from the inverter and it is clear how the energy from the SPC spike can vary with different capacitance. 7 Conclusions An Electrical Appliances Testing Platform was designed, constructed and tested on the laboratory. This platform is able to produce the most typical abnormalities of the electric power network and can be used to bring knowledge about the sensitivity of the appliances to them. This way more sufficient protection against the power network absnormalities can be utilized in the appliances and people will have less problems with them. Acknowledgments This work is co-funded by the European Social Fund (75%) and National Resources of Greece (25%) through the framework of Archimedes II program with title Electrical appliance testing platform for testing the endurance and behavior of electrical appliances in fluctuations of their input voltage signal by the General Secretary of Research and Technology of Greece. The authors thank Prof. Dr. David Perreault and the Laboratory for Electromagnetic and Electronic Systems of the Massachusetts Institute of Technology for taking measurements and testing the power electronics circuitry of the Testing Platform. The authors also thank Prof. Dr. Stefanos Manias and the laboratory of Laboratory of Electric Machines and Power Electronics of the National Technical University of Athens. Fig. 10: Diferrent energy Spikes.

6 References [1] D. Lin, E.F. Fuchs, M. Doyle, Computer-aided testing of electrical apparatus supplying nonlinear loads, Power Systems, IEEE Transactions on Power Systems, Volume: 12, Issue: 1, Feb.1997 Pages: [2] A. Vamvakari, A. Kandianis, A. Kladas, S. Manias, J. Tegopoulos, Analysis of supply voltage distortion effects on induction motor operation, Energy Conversion, IEEE Transactions on, Volume: 16, Issue: 3, Sept. 2001, Pages: [3] J. Chatzakis, M. Vogiatzaki, H. Rigakis, M. Manitis, E. Antonidakis, A novel High Bandwidth Pulse-Width Modulated Inverter, WSEAS Transactions on Circuits. [4] K. Smedley, S. Cuk, One-Cycle control of switching converter, Power Electronics Specialists Conference, 1991, pp [5] Chatzakis, K. Kalaitzakis and N. C. Voulgaris, A NEW METHOD FOR THE DESIGN OF A CLASS-D DC TO AC INVERTER, Proceedings of the 31 st Universities Power Engineering Conference 1996, Vol. 3, Sep. 1996, p [6] E. Koutroulis, J. Chatzakis, K. Kalaitzakis and N. C. Voulgaris, A New Bidirectional, High- Frequency Inverter Design, IEE Proceedings on Electric Power Applications, Vol. 148, No. 4(2001) [7] J. Chatzakis, K. Kalaitzakis, N. C. Voulgaris and S. Manias, Designing a New Generalized Battery Management System, IEEE Trans. on Industrial Electronics, vol. 50, No. 5, Oct. 2003, p