POWER TRANSFORMER DESIGN FOR THE ELECTRONIC CONVERTERS

Abstract: The electronic converters that supply the required power to the vibrators which are used in construction industries, the transformers of these converters which are functioning purely as voltage transformers and designed not according to PWM modulation frequency but carrier frequency that causes a significant decrease in size and weight of converters.

Description: DESCRIPTION POWER TRANSFORMER DESIGN FOR THE ELECTRONIC CONVERTERS In construction industries the vibrators are being used in order to have more solid and resistant concrete redundant water and air out of the mixture. Vibrators help to have homogenous mixture by creating movement between the particles of the mixture in order to get rid of the lighter elements such as air and water which are inside the mixture so that the concrete will be stiff and high resistant. Vibrators run according to the simple principle of rotating with certain turning speed of an eccentric weight. The rotating eccentric weight creates centrifugal force and circular vibration. As a result of this vibration, the lighter particles such as water and air will be taken out of the mixture and the concrete is compacted. Vibrators are classified mainly into two classes; one of them is a internal vibrator which are put directly into the concrete and the other one is external vibrators which are fixed to the mould and vibrates the mould. The high frequency electric motor of the electrical internal vibrator is inside the vibrator head. In these type of vibrators squirrel cage asynchronous induction motors are used due to its mechanical simplicity, easiness of the production, high reliability and low cost. On the other hand, the motors are produced as three-phase one pair of pole because of the easy winding and simple motor structure. According to the tests and experiences, the ideal turning speed per minute for the internal vibrators used in construction industry is 12000 rpm. Because of the environmental conditions of the construction industries: mainly wet and low level of education of the workers using 220 V or 380 V is vitally dangerous. Therefore, for safety reason motors are designed for 42-48 V. Due to the reason stated above high frequency vibrators are designed for three-phase, 200 Hz. and 42 V. However, the frequency and voltage value of the mains are different. Because of this difference, devices which converts the frequency of the mains to 200 Hz. and the voltage of the mains to 42 V are needed in order to run the high frequency vibrators. These kinds of devices are called as frequency and voltage converters. The most important factor that determines the size and weight of the converters is the size and structure of the transformers. The low frequency transformers are generally made of iron sheets and this creates difficulties to the users of vibrators due to the its weight and size. Therefore, it is very important to manufacture lighter and smaller converters. The studies are going on this but there are some attempts to decrease the volume and weight by changing the form of the converters. After the improvements in power semiconductor technologies, the electronic converters were designed and manufactured. Electronic converters have achieved the flexibility and benefits which rotative converters do not have. As it will be seen from the block diagram of an electric converter given in Figure 1 , the three-phase current 380 V, 50 Hz / mono -phase 220 V, 50 Hz available from the power source (1) is converted to 200 Hz, three-phase PWM by means of frequency inverter (2). 380 or 220 V PWM signal is transformed to 42 V (5) by a transformer (4) connected to the output of the inverter and then 42 V signal applied to the vibrator (6). In electronic converters, PWM (Pulse Width Modulation) technique is used. In PWM signal that is used commonly among the pulse modulation techniques, the amplitude is not a definable parameter but determined by the power source voltage. The power source voltage is first rectified and then connected to the out put modules for switching. Therefore, pulse amplitude is the peak value of the power source voltage after rectification to direct current (D.C). The carrier frequency being a selectable parameter is the main switching frequency. There are pulses at the output depending on the samples of modulation signal within the periods determined by the carrier frequency. Any signal can be used as modulation frequency in PWM. In electronic converters, the modulation signal is the sinusoidal signal at 200 Hz frequency. In PWM technique, the mean value of the PWM signal is equal to the modulation signal. The motor will see only the modulated section of the PWM signal. The reason for this, demodulation of PWM signals made by the motor windings. The working principle of the electronic converters based on converting the supply voltage to D.C. by a rectifier and switching of the output stages by means of three-phase PWM signal produced by a microprocessor. By this way, PWM pulses, which have amplitude that is the same with the voltage of the rectified power supply, are generated at the output stages. The pulses are transformed to the desired level by means of a transformer. The main point is the frequency that will be taken as design criteria when designing transformer. In the state of art, the transformers of the converters produced for the vibrators are used as demodulator and designed according to the modulation frequency. In this type of transformers, the transformers carry out PWM demodulation process. In the present invention, the transformers of the converters are designed according to the carrier frequency and used as purely voltage transformers. By this way, dramatic decrease of the weight and volume of the converters can be achieved. Transformers designed according to the present invention are functioning as purely voltage transformers and have no effect on the demodulation process. The motor carries out demodulation process. The core section area of the transformers is determined according to the transformer equation, which is in the state of art given below; V α = 4FJNB Where, α - core cross section area; V- voltage; F - form factor; f- frequency; N - number of winding; B- flux density. As it will be from the equation, there is an inverse proportionality between frequency and core cross section area. The core cross section area will be smaller when the frequency is higher if the other variables are constant. Smaller core area will help to design smaller and lighter transformers. Designing transformers according to the to the present invention i.e. carrier frequency, the motor will work only with the modulated signal. Motor will see only the modulated section of the PWM signal. That is why the PWM signals demodulated by the motor windings. According to the present invention, the size and the weight of the transformers will be decreased due to reduction of the core cross section area. Significant decrease of the size and weight of the converters will be achieved since the smaller transformers will be used in the converters. In this context, it is possible to produce smaller and lighter converters, which are used to supply the required voltage and frequency for the vibrators.

Claims: CLAIMS Claim 1. Design of the transformers according to the PWM carrier frequency and used purely voltage transformers since the windings of the motor will demodulate PWM signals. Claim 2. The transformers according to Claim 1 and designed according to the PWM carrier frequency will be used in the converters for the vibrators of construction industry and will work only as voltage transformers. Claim 3. The transformers according to Claim 1 and Claim 2 and designed according to the PWM carrier frequency, the core of the transformers can produced different materials. Claim 4. The transformers according to Claim 1 and designed according to PWM carrier frequency can be used in different fields.

Inventors: KUM HAMDI ERHAN, TEKIN ILYAS, KUM, HAMDI, ERHAN, TEKIN, ILYAS
Applicants: KUM HAMDI ERHAN, TEKIN ILYAS, KUM, HAMDI, ERHAN, TEKIN, ILYAS
Application year: 1999
Main classification: H02M5
IPC codes: E04G21, H02M5