**7.1 DC/DC and DC/AC circuit simulation**

The hardware parts of the electric circuits are modelled using Simulink power block set. The power block set consists of the power electronic elements. Each element in this block set has its own block window which allows for the selection for the key parameters. At the bottom of the block parameter window is a pull down menu, which allows for the key voltage and current to be easily measured. In the first stage, the electrical circuit was modeled in an open loop system to determine the performance of each circuit separately. The PWM generation block was modeled for both DC/DC converter stage and DC/AC inverter stage. For example, the PWM model in the MTU microprocessor unit is illustrated in Figure 17. The PWM block compares both the sin wave signal with the required output frequency and the sawtooth signal with the carrier frequency equal to 10 kHz. Then the dead time is generated using the delay block and finally, the PWM pulse is generated and fed into the gates of the full bridge transistors.

Potential of Grid Technology for Embedded Systems and Applications 345

Where: m: modulation index, VC: amplitude of the reference voltage, Vcarrier: amplitude of

In the DC/AC stage, the carrier frequency is set equal to 10kHz and the reference frequency equal to the desired output frequency of 60 Hz. By changing the modulation factor, the duty of the PWM pulse is changed. The electric circuit specification of the two stages of the inverter power supply is described in Table 2. The signal is monitored using the scope and

Parameter Value Unit Output frequency 60 Hz Output Voltage 100 RMS Battery Voltage 24 V Switching frequency 10 kHz Filter inductor DC/DC 29 mH Filter capacitor DC/DC 47 µF

Filter inductor DC/AC 3 mH Filter capacitor DC/AC 25 µF

In the inverter power supply applications, the microprocessor is used to control the switching period of the transistors as a digital controller. This microprocessor has two main units which are used to control both the DC/DC and DC/AC stages of the inverter power supply. Each unit is controlled by a software program; this embedded software function can be divided into two main parts which are the control program (control algorithm) and the

Traditionally, the implementation of switching type inverter power supply has been accomplished by using the analog technique. However, the analog technique has some drawbacks such as a number of parts required in the system and its susceptibility to ageing and environment variations, which lead to high cost of maintenance. Further, analog control once designed is inflexible and its performance cannot be optimized for various utility distortions. Now with the advent of high speed, lower cost digital signal processing (DSP) ICs, and microprocessors, digital control has become one effective candidate for inverter

Using a DSP or microprocessor has many benefits that make it attractive for use in control

 Flexibility of Control: When using analog circuits to perform control, the control algorithm is fixed, and is not easily modified. Using a microprocessor allows the designer to change the control code very quickly. It is often helpful to implement

display blocks which allow us to figure the circuit outputs.

Transformer turns ratio 7.2

Table 2. Specifications of the inverter circuits

**7.2 Microprocessor simulation** 

PWM generation program.

**7.2.1 Control algorithm** 

power supply.

systems, such as:

the carrier signal.

Fig. 16. Circuit schematic of inverter power supply

Fig. 17. PWM model in the MTU microprocessor unit

The modulation ratio, the carrier frequency, the reference frequency were changed manually. Equation (1) describes the relation among all three parameters.

$$\mathbf{m} = \mathbf{V} \mathbf{C} / \mathbf{V} \text{carrier} \tag{1}$$

Where: m: modulation index, VC: amplitude of the reference voltage, Vcarrier: amplitude of the carrier signal.

In the DC/AC stage, the carrier frequency is set equal to 10kHz and the reference frequency equal to the desired output frequency of 60 Hz. By changing the modulation factor, the duty of the PWM pulse is changed. The electric circuit specification of the two stages of the inverter power supply is described in Table 2. The signal is monitored using the scope and display blocks which allow us to figure the circuit outputs.


Table 2. Specifications of the inverter circuits
