Chap 11 by HadeedAhmedSher on Scribd
Chap 2a by HadeedAhmedSher on Scribd
Chap 2b by HadeedAhmedSher on Scribd
Chap 9 by HadeedAhmedSher on Scribd
Chap 7 by HadeedAhmedSher on Scribd
Chap 5 by HadeedAhmedSher on Scribd
Thew following list of commercially available MI was tabulated in Table 1.
Reference :
Sher, H.A. and Addoweesh, K.E., 2012. Micro-inverters—Promising solutions in solar photovoltaics. Energy for Sustainable Development, 16(4), pp.389-400.
Reference :
Sher, H.A. and Addoweesh, K.E., 2012. Micro-inverters—Promising solutions in solar photovoltaics. Energy for Sustainable Development, 16(4), pp.389-400.
There are two kinds of resonant switching schemes known as zero voltage switching (ZVS) and zero current switching (ZCS). The former makes the voltage across the switching device zero before the switching transition and the later makes the current through the switching device zero. They are highly efficient because by forcing the voltage or current zero makes the power product in each switching transient zero. The voltage and/or current are made zero by using an additional LC tank. This means that any conventional hard-switched power electronic circuit can be operated at resonant conditions with LC tank circuit.These converters are also categorized on the basis of resonance cycle therefore, the one in which a complete cycle of resonance is allowed is known as a full-wave circuit and the circuit in which only positive half cycle of resonance is allowed is called as a half-wave mode. In the half wave resonant circuit the negative cycle of resonance is blocked using a diode[2].
The resonant converters require high voltage/ current stress, therefore the device rating for such converters is higher than those of hard switched converters. Also, the resonant converters have more components requirement compared with the conventional converters.
Points to ponder about ZVS
- In ZVS a capacitor is connected in shunt with the active switch. In full wave operation, the same is connected across the switch diode combination.
- They are naturally recommended for metal oxide semiconductor MOSFET up to kW power rating[1].
- It eliminates the turn on losses (caused by the energy stored in the drain-source capacitance that is dissipated in the switch during turn on) but offers high turn-off losses (caused by the switch having simultaneous non-zero current and voltage while it is turning off).
- ZVS is dependent on load current and input voltage.
- The operation of ZVS is difficult at low load and high input voltage. This is because the energy stored in the inductor at light load is not sufficient to discharge the resonant capacitor before the active switch is turned on[2].
- Compared with ZCS it has high voltage stress proportional to load voltage[2].
- The auxiliary switch in a duty cycle controlled ZVS converter will experience ZCS [2].
- In this method, an inductor is connected in series with the active switch.
- This method is preferred for IGBT because of the low turn-off losses.
- This method eliminates the turn-off losses.
- In the half-wave mode, a diode is connected in series with the switch to make the power flow unidirectional [2].
- It has high current stress and capacitive turn-on the loss.
- The auxiliary switch in a duty cycle controlled ZCS converter will experience ZVS [2].
[1] Canesin, C.A. and, Barbi, I., 1999. A novel single-phase ZCS-PWM high-power-factor boost rectifier. IEEE Transactions on Power Electronics, 14(4), pp.629-635.
[2] Divakar, B.P. and Sutanto, D., 1999. Optimum buck converter with a single switch. IEEE Transactions on Power Electronics, 14(4), pp.636-642.
Basic electric circuits notes
Electricity and magnetism | Interesting points from Walter Lewin lecture.
Electricity and magnetism is a classical field in the modern world. In this interesting lecture, Dr. Walter Lewin explained the very basics of electricity and magnetism in his unique style. I chalked out some interesting points and decided to log those in this post.
Full lecture
- Electrons are so small that if 6B are lined up together it only makes 60 cm.
- In 600BC it was known that if amber is rubbed it attracts dry leaves. Amber in greek is called electron. Thats the reason electricity was named for.
- In 18th century two types of electricity was discovered. One if you rub glass and the other if rubber/amber is rubbed.
- Berjamin Franklin presented the idea of positive and negative charges. Stating the like charges repel each other and opposite charges attract.
- If a glass tube is rubbed and then taken near the conductor, the electrons present in the conductor will move towrads the direction of glass. This is called indudction or polarization.
- Even in non conducting elements the polariation or induction happens.
- Friction charges the surface and hence creates electricity.
- 1 columb charge is an enormous quantity.
- Electric force is 365 times stronger than the gravitational force.
Full lecture
Lecture 12 by PhD EE on Scribd
| Do's | Don’ts | Page length | More information | |
| IEEE Transactions on Sustainable energy | IEEE Double colum. Latex also possible | 8 | http://www.ieee-pes.org/part-4-preparation-of-a-formatted-technical-work-for-the-ieee-power-energy-society | |
| IEEE Transactions on Power Electronics | Latex is possible using IEEE templete If you choose not to use one of the available templates, prepare your technical work in single-spaced, double-column format, on paper | 8 | http://www.ieee-pes.org/part-2-preparation-and-submission-of-transactions-papers | |
| IEEE Transactions on Industrial Electronics | IEEE double column format | do NOT include authors' names, their biographies, affiliation, cover letter, signed copyright form, identifying footnotes, acknowledgments, etc. If a significant portion of your manuscript was already published at a conference, the paper must hide the identity all of the authors, so the conference paper can be cited as if it were written by different authors. NO survey papers. The file maximum size cannot exceed 40MB | 8.5 | http://www.ieee-ies.org/pubs/transactions-on-industrial-electronics/71-initial-sub#submission-checklist |
| IEEE Transactions on Industrial Informatics | IEEE double column format with single space 10p fonts and figures included in the text | authors' names, footnotes, acknowledgement, bios or photos, cover letters, copyright form | 8 | http://tii.ieee-ies.org/o/SubNM.pdf |
Course Outline | EE-355
Interleaving is one type of parallelling method. It is a well known method for high power applications. It offers several advantages the foremost among all is the input current sharing. Besides, the interleaving allows more reliability and ease in maintenance, repairing, fault tolerance and hence increases the reliability. In interleaved converters phase difference is applied to the control signals of several cells connected in parallel and operated on the the same switching frequency. Therefore, the summed up input and output current have a good performance in terms of THD, conduction losses, EMI, and has less current ripple. Because of the low THD and cancellation of low frequency harmonics the filter requirement is much smaller with less size and weight.
In this blogpost i will explain the importance of snubber circuits in power electronic applications. Additionally, the types of snubber circuits will also be discussed and some of the circuits that were published in past years.
Snubber circuits snubs the extra stress on the power semiconductors either during turn on or in turn off condition. They can be classified in various forms. For example , based on efficiency they can be classified as lossy snubber and lossless snubbers. They can also be classified on the basis of components used. In this case there are two classes namely passive and active snubbers. Based on the switching time period they are called as turn on snubber and turn off snubber.
Snubber circuits are primarily used in circuits with inductance either in the form of inductor or leakage inductance. They are very useful in reducing power dissipation due to switching loss and electromagnetic compatibility (EMC) effects [1].
The losses in a semiconductor switch occur either at turn on or at turn off because it is the time when a transition of voltage across and current through the device occurs. The turn on losses are dependent on the load current, the supply voltage, diode reverse recovery effects, rate of rise of current di/dt and the frequency of operation.
Passive snubber : The most common type of passive snubber to control the turn on loss is an inductor. The use of inductor slows down the di/dt in a switch. Moreover, it also compensates the effects of diode reverse recovery. However, this method inherits the issue of inductor reset i.e this inductor has to release the stored energy (1/2 Li2). This counts for a loss if the operation is at high frequency. Therefore this kind of snubber is a passive lossy snubber. However, this kind of snubber can be made losseless by using resonant tank, auxiliary commutation and passive energy recovery snubbers [1] . Another passive lossless snubber circuit is presented in [2]. These methods are more complex.
Another way is to use a saturable core snubber circuit that is reported by [1] as an effective method. This method when used with a bridge leg requires two saturable inductors. This is because these saturable inductors are only effective when used in high inductance unsaturated region (click here to read more on saturable inductor).
Active snubber circuits use auxiliary switch to reduce the stress on power semiconductor. They are lossless snubbers because they do not waste energy. However, these snubber circuits add complexity to not only the topology but also to the control structure and
[1] Finney, S.J., Tooth, D.J., Flethcer, J.E. and Williams, B.W., 1999. The application of saturable turn-on snubbers to IGBT bridge-leg circuits. Power Electronics, IEEE Transactions on, 14(6), pp.1101-1110.
[2] Fujiwara, K. and Nomura, H., 1999. A novel lossless passive snubber for soft-switching boost-type converters. Power Electronics, IEEE Transactions on, 14(6), pp.1065-1069.
Snubber circuits snubs the extra stress on the power semiconductors either during turn on or in turn off condition. They can be classified in various forms. For example , based on efficiency they can be classified as lossy snubber and lossless snubbers. They can also be classified on the basis of components used. In this case there are two classes namely passive and active snubbers. Based on the switching time period they are called as turn on snubber and turn off snubber.
Snubber circuits are primarily used in circuits with inductance either in the form of inductor or leakage inductance. They are very useful in reducing power dissipation due to switching loss and electromagnetic compatibility (EMC) effects [1].
The losses in a semiconductor switch occur either at turn on or at turn off because it is the time when a transition of voltage across and current through the device occurs. The turn on losses are dependent on the load current, the supply voltage, diode reverse recovery effects, rate of rise of current di/dt and the frequency of operation.
Passive snubber : The most common type of passive snubber to control the turn on loss is an inductor. The use of inductor slows down the di/dt in a switch. Moreover, it also compensates the effects of diode reverse recovery. However, this method inherits the issue of inductor reset i.e this inductor has to release the stored energy (1/2 Li2). This counts for a loss if the operation is at high frequency. Therefore this kind of snubber is a passive lossy snubber. However, this kind of snubber can be made losseless by using resonant tank, auxiliary commutation and passive energy recovery snubbers [1] . Another passive lossless snubber circuit is presented in [2]. These methods are more complex.
Another way is to use a saturable core snubber circuit that is reported by [1] as an effective method. This method when used with a bridge leg requires two saturable inductors. This is because these saturable inductors are only effective when used in high inductance unsaturated region (click here to read more on saturable inductor).
Active snubber circuits use auxiliary switch to reduce the stress on power semiconductor. They are lossless snubbers because they do not waste energy. However, these snubber circuits add complexity to not only the topology but also to the control structure and
[1] Finney, S.J., Tooth, D.J., Flethcer, J.E. and Williams, B.W., 1999. The application of saturable turn-on snubbers to IGBT bridge-leg circuits. Power Electronics, IEEE Transactions on, 14(6), pp.1101-1110.
[2] Fujiwara, K. and Nomura, H., 1999. A novel lossless passive snubber for soft-switching boost-type converters. Power Electronics, IEEE Transactions on, 14(6), pp.1065-1069.
A saturable inductor is an inductor which is designed to saturate. This kind of inductor is particularly used in snubber circuits. In [1] a typical B-H curve is shown that forms the two properties of the saturable inductor as shown in Fig.1.
First property : There is a finite time required for the core to saturate. This is governed by the Faraday's law. This implies that the the core has high permeability and hence high inductance and therefore the rate of change of current is low.
Second property : Once in saturation the core permeability decreases towards Uo. This means that the rate of change of current will increase but the core stored energy does not increase significantly.
Reference:
[1] Finney, S.J., Tooth, D.J., Flethcer, J.E. and Williams, B.W., 1999. The application of saturable turn-on snubbers to IGBT bridge-leg circuits. Power Electronics, IEEE Transactions on, 14(6), pp.1101-1110.
 |
| Fig.1 : B-H curve for saturable core |
First property : There is a finite time required for the core to saturate. This is governed by the Faraday's law. This implies that the the core has high permeability and hence high inductance and therefore the rate of change of current is low.
Second property : Once in saturation the core permeability decreases towards Uo. This means that the rate of change of current will increase but the core stored energy does not increase significantly.
Reference:
[1] Finney, S.J., Tooth, D.J., Flethcer, J.E. and Williams, B.W., 1999. The application of saturable turn-on snubbers to IGBT bridge-leg circuits. Power Electronics, IEEE Transactions on, 14(6), pp.1101-1110.
The authors of [1] have presented a mathematical model of four pole permanent magnet synchronous motor (PMSM). They made some usual assumptions like neglecting the saturation effect, sinusoidal emf and negligible losses.The stator d-q reference equations written in a rotor reference frame is given as
Testing power supplies using Oscilloscope
Consider Fig. 1 where a voltage source / current source is applied to a load (A box is shown and it is assumed to be a resistance R). If we do not use power electronics for amplitude shift then efficiency apart, we can only step down the amplitude.
Both of these two methods exhibits low efficiency when the ratio between the input and output is low.
Efficiency = (Po/Pin)= (VoIo)/(VinIo). For the current source the (Vo/Vin) is constant therefore, the efficiency= (Io/Iin). Same is the case with the voltage source.
Now, since the output is always less than 1 and that if the network has to step down the input current of 10A to 1A, the efficiency is only 10% as shown in Fig.2. The red part accounts for the power loss.
 |
| Figure 1 Resistance based dc-dc voltage converter (click to zoom) |
For voltage source the output voltage can be expressed as
Vo= (Vs R)/(Rs+R)
Therefore, the value of series resistance Rs can be calculated as
Rs= R((Vin/Vo)-1)
Therefore, in order to have a real value of Rs the output voltage Vo can never be greater than the input voltage.
Similarly, for the current source network shown , the output current can be expressed as
Io=Iin((Rsh/Rsh )+R)
Therefore, the value of shunt resistance Rshcan be written as
Rsh=R/((Iin/Io)-1)
This shows that in order to have the value of Rsh greater than zero the output current amplitude cannot be greater than the input current.
Both of these two methods exhibits low efficiency when the ratio between the input and output is low.
Efficiency = (Po/Pin)= (VoIo)/(VinIo). For the current source the (Vo/Vin) is constant therefore, the efficiency= (Io/Iin). Same is the case with the voltage source.
Now, since the output is always less than 1 and that if the network has to step down the input current of 10A to 1A, the efficiency is only 10% as shown in Fig.2. The red part accounts for the power loss.
 |
| Figure 2 Ratio of input and output (Click to zoom) |
A front-end power electronic converter is a term used when a converter is connected to an ac mains/source either using a transformer or without using a transformer.
A back-end power electronic converter is one which is connected to the load. Such converter term is used frequently in a two stage power converter system.
In a two stage PV inverter system the inverter is called back-end power electronic converter whereas, the dc-dc converter connected with the solar PV module is called as front-end converter.
A back-end power electronic converter is one which is connected to the load. Such converter term is used frequently in a two stage power converter system.
In a two stage PV inverter system the inverter is called back-end power electronic converter whereas, the dc-dc converter connected with the solar PV module is called as front-end converter.
For viewers in Pakistan
For Worldwide viewers
A Maximum power point tracking (MPPT) system is essential for enhancing the efficiency of the PV system. There are various algorithms for the MPPT system that includes the traditional hill climbing MPPT, AI based MPPT and fixed voltage based algorithms. The testing of these algorithms is important to evaluate their performance under various kinds of environmental conditions. In the research community following are the test conditions applied on the MPPT system for its evaluation.
- Standard testing condition. The MPPT system is provided a standard testing condition of a PV module with 1000 W/m2 irradiance and temperature of 25 C.
- Step change in irradiance: To simulate the behavior of MPPT under dynamic weather condition the environmental parameters are changed in step mode. Usually irradiance is changed because in reality the change in temperature is slow. So the irradiance is changed from say 1000 W/m2 to 500 W/m2 and then to 200 W/m2 . This step change evaluates the system response under abrupt changes. It is pertinent to mention that in this testing condition not only the step change is applied in decreasing fashion but can also be applied in increasing mode i.e at starting from 500 W/m2 to 1000 W/m2 with step values of 100 or 50 or whatever. The step change increment and decrements are two different things and the algorithms particularly the hill climbing behaves differently. Therefore, the MPPT must be tested for both increasing irradiance as well as for decreasing irradiance.
Condition 2 for the testing of four different MPPT methods - The environmental conditions are changed gradually in ramp function. This testing condition simulates the normal weather condition with sunlight increasing linearly from sunrise to noon and then stays constant for few hours and then begins to descend in the same manner.
- Another weather condition can be simulated by merging point 2 and 3 to have a normal day scenario with abrupt changes in between. This simulates the birds or some building shade on the PV panel.
 |
| Condition 4 |
For worldwide viewers
For viewers in Pakistan
For viewers in Pakistan