**6.1 DC-DC conversion**

332 Grid Computing – Technology and Applications, Widespread Coverage and New Horizons

Generally, it can be concluded that the Model Based Design method will reduce the number of the development stages by combining the design, implementation and testing into one process. The reduction of the required step comparing to the traditional method of design will result in better project management and mitigate the system development risk. The system design using this approach will reach the market faster and will cost less than that of the system designed using the traditional method. Subsequently, the use of the MBD method can provide numerous advantages over the traditional design method. Therefore, this study investigates how the Model Based Design method can provide such advantages by applying and building a new virtual environment for the embedded system design. Inverter power supply is used as a case study of the embedded system in

The development of new useful energy sources is the key to continued industrial progress. Discovering new sources of energy, obtaining an essentially inexhaustible energy source, making it available everywhere and converting it from one form to another without polluting or destroying the environment are some of the great challenges in the world today. One of the techniques to tackle these challenges is to produce AC (Alternative Current) from DC (Direct Current) generated by fuel cells or solar panels and such device is called an inverter power supply. An inverter power supply is a device which can convert DC to AC that can be used in various AC applications. Many topologies are considered to be candidates for the inverter design and there are many factors affecting the choice of such topology, such as the size and the required efficiency as well as the cost of the inverter. In this study, an inverter power supply configuration is broken into two stages. The first stage is to step up the DC voltage level by using DC/DC converter and the second stage is to invert DC to AC through a DC/AC inverter. The block diagram of the inverter power

DC/DC Circuit DC/AC Circuit

Microprocessor Control Circuit

Analog Signals

this research.

supply is shown in Figure 4.

Digital Signals

Fig. 4. Block diagram of inverter power supply

**6. Description of the inverter power supply** 

The first step of the inverter power supply is to step up the DC voltage level which comes from a battery to higher DC level by using the DC/DC converter. DC/DC conversion revolves around the conversion of DC voltage level which comes from sources such as batteries, solar panels, fuel cells, or wind generations to a higher DC level. There are many different types of DC/DC converters, and each of which tends to be more suitable for some types of application than for others. For convenience, we can classify them into various groups. For example, some converters are only suitable for stepping down the voltage while others are only suitable for stepping it up; a third group can be used for both cases of stepping up and stepping down the voltage. Another important distinction among converters is which one offers full dielectric isolation between their input and output circuits. Dielectric isolation behavior may be important for some applications, although it may not be significant in many others. In this section we are going to look briefly at each of the main types of DC/DC converter in the current use as presented below:

	- 1. Buck converter;
	- 2. Boost converter;
	- 3. Buck-boost converter;
	- 4. Cuk converter; and
	- 5. Charge-pump converter.
	- a. Half Bridge;
	- b. Push-Pull; and
	- c. Full Bridge DC-DC converter.

In this study, the isolation type DC/DC converter is used in the inverter power supply implementation. Figure 5 shows examples of the isolated converter.

The full-bridge is a popular design for both buck and boost applications. It is one of the simplest and most cost-effective configurations. Another advantage for using the full bridge converter is the fact that when higher power application are requested the full bridge converter can act as a modular block and that it is possible to stack up. For this purpose, the chosen topology for the converter to be used in this application is a full bridge phase shifted PWM converter (Mohan. N, 1995).

Potential of Grid Technology for Embedded Systems and Applications 335

The main purpose of this full bridge converter is to chop up the DC voltage so that AC is seen by the transformer. The current is forced across the primary side of the transformer when Q1 and Q4 are on and Q2 and Q3 are off, and the current in the primary of the transformer changes its polarity when Q2 and Q3 are on and Q1 and Q4 are off, as shown in

The transformer is a part of the DC/DC circuit that is responsible for boosting the voltage V1 by means of a ferrite core, a primary winding and a secondary winding. It is important to note that the transformer does not create any power, and it only transforms or transfers the voltage. The transformer operates by inducing a magnetic flux on the core from the current flowing through the primary winding. The flux passing through the core is induced onto the secondary winding and the current flows out of the device. The transformer output will apply to the full bridge rectifier and the low pass filter, respectively, to get the stepped up DC voltage V2. The DC voltage is converted to a square wave signal due to the switching

Fig. 6. Circuit schematic of DC/DC converter

Fig. 7. Switching operation of DC/DC converter

operation of the full bridge, as shown in Figure 8.

Figure. 7.

A schematic of DC/DC converter is shown in Figure 6. The major components are the four transistors (full bridge converter).

Fig. 5. Examples of the isolated DC/DC converter

334 Grid Computing – Technology and Applications, Widespread Coverage and New Horizons

A schematic of DC/DC converter is shown in Figure 6. The major components are the four

a) Half bridge

**N1**

•

(b) Push-Pull

(c) Full bridge

• **N1**

**N2**

•

•

**D1**

**D2**

**ID1 <sup>V</sup><sup>g</sup>**


**Io**

+ -

**Ig** +

> - **Vo**

**N2**

transistors (full bridge converter).

+


**S1 S2**

Fig. 5. Examples of the isolated DC/DC converter

**Vd**

Fig. 6. Circuit schematic of DC/DC converter

The main purpose of this full bridge converter is to chop up the DC voltage so that AC is seen by the transformer. The current is forced across the primary side of the transformer when Q1 and Q4 are on and Q2 and Q3 are off, and the current in the primary of the transformer changes its polarity when Q2 and Q3 are on and Q1 and Q4 are off, as shown in Figure. 7.

Fig. 7. Switching operation of DC/DC converter

The transformer is a part of the DC/DC circuit that is responsible for boosting the voltage V1 by means of a ferrite core, a primary winding and a secondary winding. It is important to note that the transformer does not create any power, and it only transforms or transfers the voltage. The transformer operates by inducing a magnetic flux on the core from the current flowing through the primary winding. The flux passing through the core is induced onto the secondary winding and the current flows out of the device. The transformer output will apply to the full bridge rectifier and the low pass filter, respectively, to get the stepped up DC voltage V2. The DC voltage is converted to a square wave signal due to the switching operation of the full bridge, as shown in Figure 8.

Potential of Grid Technology for Embedded Systems and Applications 337

input signals to the gates of the MOSFETs. This will be covered in the next section which

The PWM pulses which are generated by a microcontroller are fed into the gates of a full bridge inverter. Programming the microcontroller allows the transistors Q1 and Q4 to be on while Q2 and Q3 to be off and vice versa. Due to the limited response time and delay time of the transistors, two switches in one leg may be switched on at the same time then shoot through will occur and the switches may be damaged due to high short circuit current then

Figure 11 shows the ideal switching patterns and the drive signals containing the dead time for the inverter leg. The Sp and Sn are the ideal switching pattern of the positive device and the negative device of the full bridge DC/AC inverter, respectively. As mentioned before, the short time delay is used to avoid shoot-through, where the actual gate drive signals must be delayed by the dead time. The gate drive signals containing the dead time are denoted as Spd and Snd since the gate drive signals are shifted from the center of the sampling interval by the dead time. The generated phase voltage is also shifted as much as the delay time. It had been reported that the generated voltage pulses residing in the middle of the sampling interval contain the least amount of harmonics (Choi et al., 1999). Although the produced voltage pulses resulting from each of the gate drive signals during the sampling intervals are not much affected, the resultant voltage during an entire cycle is significantly reduced due to the dead time. In addition, those cumulated delays may distort

In fact, the addition of the dead time can improve the performance of inverter power supply by preventing the short circuit current. However, the instability and harmonic distortion problem can be arising due to the incorrect selection of the sufficient dead time value.

the dead time is introduced in order to avoid the occurrence of the short circuit.

focuses on microprocessor control systems and PWM.

Fig. 10. Circuit schematic of DC/AC inverter

the output waveform of the inverter.

Fig. 8. DC/DC switching operation

The output of the transformer is rectified using the full bridge rectifier circuit and then filtered using low path filter. all the signals are shown in Figure 9.

Fig. 9. DC/DC rectification and filtering operation
