Publish Date: Nov 08, 2013 | 2 Bewertung(en) | 5,00 von 5 |  PDF

The National Instruments Power Electronics Fundamentals series is designed to provide an overview of power electronics concepts used in research and taught throughout worldwide institutions.

Using advanced simulation models and analyses used in industry, but wrapped in an intuitive, pedagogical environment Multisim enables students to characterize power circuits concepts before the laboratory.

The power capabilities of Multisim means that students have access to the same technology that they will use for research and industry to prototype power electronics circuit designs. However in learning power electronics in a simulated environment optimized for education, students have the ability to experiment safely before the laboratory.

Rectification systems are primarily designed for converting sinusoidal AC input signals into a DC voltage signals.  They are most commonly used in domestic power supplies and power transmission systems. Single wave rectification can be achieved by using either a half wave or full wave rectification circuit.

 

1. Half Wave Rectifier

Half-wave rectification systems utilise a single diode, removing half of the sinusoidal source. This produces a single directional signal with a pulsating characteristic.

 

 

As a result of the heavy pulsating nature of the signal, more filtering is required to eliminate any harmonies from the AC source and provide a constant DC signal. The efficiency of the half wave rectifier is also  limited because only half the sinusoidal waveform is being converted to the DC signal. Losing this half of the signal can be comparable to losing energy..

 

2. Full Wave Rectifier

Full-wave (full bridge) rectifiers construct a bridge of diodes to convert the whole of the input voltage to one of constant polarity. This is more efficient than the half wave rectifier as it allows both the positive and negative components of the input voltage to be utilised in building the DC voltage.

 

 

Once the signal has a single polarity we can apply a simple filter to provide a DC voltage source. This filter applies a smoothing effect allowing the DC output to be maintained.

 

 

3. Tutorial Questions

Why is it important to select an appropriate capacitor value? What is the effect of using a larger or a smaller capacitor?

The bridge circuit above provides us with a positive DC voltage, using NI Multisim identify how this can be modified to develop a negative DC voltage level?

Publish Date: Nov 05, 2013 | 2 Bewertung(en) | 5,00 von 5 |  PDF | Submit your review

The National Instruments Power Electronics Fundamentals series is designed to provide an overview of power electronics concepts used in research and taught throughout worldwide institutions.

Using advanced simulation models and analyses used in industry, but wrapped in an intuitive, pedagogical environment Multisim enables students to characterize power circuits concepts before the laboratory.

The power capabilities of Multisim means that students have access to the same technology that they will use for research and industry to prototype power electronics circuit designs. However in learning power electronics in a simulated environment optimized for education, students have the ability to experiment safely before the laboratory.

1.     Three Phase Inverter

Electrical power inversion is the process of converting DC voltages into AC power sources. This is most commonly used when supplying AC power from DC sources such as batteries and DC power supplies. This can be achieved using Switching and Control circuits to produce a signal of the required amplitude and frequency. Multisim allows the modelling of the circuit and PWM signal, so that the required output can be generated. This is most commonly achieved by a three-phase inverter, which is essentially the combination of three single phase converters. The switch operation of a three-phase inverter is controlled so that they act at each 60 deg point of the output waveform. In the example below we have used a three-phase PWM supply to generate PWM signals at the required phase.

 

 

2. Transient Analysis

NI Multisim comes with a range of pre-built analysis models. The transient analysis allows us to understand the operation of the inverter and how this leads to the development of the AC signal.

The analysis models built into Multisim allows for the characterization of circuits ensuring the optimum circuit design is chosen. The analysis results are based on the industry standard SPICE simulation models, more details of which can be found within the SPICE Simulation Fundamentals Whitepaper series.

Publish Date: Okt 04, 2013 | 0 Bewertung(en) | 0,00 von 5 |  PDF | Submit your review

The National Instruments Power Electronics Fundamentals series series is designed to provide an overview of power electronics concepts used in research and taught throughout worldwide institutions.

Using advanced simulation models and analyses used in industry, but wrapped in an intuitive, pedagogical environment Multisim enables students to characterize power circuits concepts before the laboratory.

The power capabilities of Multisim means that students have access to the same technology that they will use for research and industry to prototype power electronics circuit designs. However in learning power electronics in a simulated environment optimized for education, students have the ability to experiment safely before the laboratory.

When considering DC to DC power electronics we are referring mainly to the conversion of one DC voltage to another DC voltage. There are different options for achieving this that vary in complexity and efficiency.

 

1. Potential Divider

A very simple example of regulating voltage is with a potential divider.

However the output across a voltage divider is not constant and varies according to the load. To be effective, changes in the output current must remain small in comparison to the input current. This highlights the inefficiency of this technique as the input current is dissipated as heat.  An example of a potential divider is a potentiometer.

 

2. Zener Diode Regulator

We can improve on the potential divider method by using a zener diode. A zener diode allows current to flow in one direction as well as in the reverse direction when the voltage is above a certain breakdown voltage. The diode is setup so that it operates in reverse bias and conducts when the reverse bias breakdown voltage is met.

 In Multisim we can easily measure the regulated output using Virtual Multimeter  Instrument whilst also monitoring the current flow.

3. Power Switching

The buck converter is a form of power switch which dramatically increases the  efficiency of the regulator circuit. Its core functionality is built upon switching a voltage to control the output voltage allowing us to step down the input voltage to that needed by the output. A capacitor is required to smooth the output voltage and remove the steps created by the switching.

 

 

To achieve this, a Pulse Width Modulated (PWM) signal is used to control the switching of the voltage allowing regulation of the output voltage. When the switch is closed, the inductor will begin to charge and there will be a voltage drop across it causing the output voltage to drop. When the switch is open, the charge within the inductor is released, supplying the output voltage.

Below is an example of a simple Buck Converter. A PWM signal is being used to control the switch, allowing the charge in the inductor to build up. Care needs to be taken when selecting the most suited frequency for the PWM signal in order to maintain the required DC voltage level.

 

 

To help with determining the correct frequency and component values, Multisim provides interactive components which are capable of having their parameters changed during execution. The use of interactive components allows us to adjust the duty cycle, impedance and resistance during simulation.

 

 

The example above shows an open loop implementation of a buck converter. This can be taken a stage further and translated into a closed loop system by taking the output voltage and comparing it to a reference voltage to produce the appropriate PWM signal for the switch.

This can be fully modelled in Multisim alongside LabVIEW using co simulation. 

 

Multisim gives you the tools to simulate a schematic prior to the circuit creation whilst LabVIEW assists in creation of the FPGA code. Co-simulation allows these two systems to be integrated allowing full testing of the power switch prior to deployment. You can learn more about co-simulation in Simulation Fundamentals: Cosimulation In NI Multisim tutorial.

 

4. Tutorial Questions

What happens to the zener voltage if a minimum value of reverse current is being reached and what if the reverse current exceeds its maximum?

What is the disadvantage of a zener diode regulator?

Here we have an example of a Buck Converter, research and gain an understanding through Multisim of a Boast Converters operation .

Publish Date: Nov 22, 2013 | 1 Bewertung(en) | 5,00 von 5 |  PDF

Analog designers rely on datasheets to define the specification of their circuit designs. Although datasheets include the specifications of a component and remain an indispensable resource, they lack information of how parts will behave within different configurations. This is why circuit simulation is a critical tool in the design flow to complement datasheets to provide the insight needed to improve design performance and reduce iterations. In this series of application notes, we review how NI Multisim and devices from semiconductor industry partners can use simulation to improve design performance.

1. Introduction

Efficient Power Conversion (EPC) is the first to market enhancement mode Gallium Nitride (eGAN) devices. eGaN FETs are used in power conversion topologies and are able to achieve significant performance enhancements compared with silicon power FETs.

EPC and National Instruments collaborated to include these accurate models for these eGAN FETs within the NI Multisim simulation environment. This advanced and innovative model model is included in a compreshensive library and powered by the Multisim simulation, analysis, and visualization tools to enable the exploration and implementation of novel design configurations.

This document highlights different features of the EPC components in the Multisim database as well as application examples where circuit simulation plays a vital role in making accurate design decisions.

2. How to Use an EPC Model in Multisim

A complete set of the EPC eGAN FET models are located in the database under the “Power MOSFET” family  as seen in Figure 1.

 

Figure 1. EPC components inside the Multisim database

 

The EPC models are a hybrid of physics-based and behavioral functions to achieve a compact SPICE model with acceptable simulation and convergence characteristics. Temperature effects are included for conductivity and threshold parameters. Although quantum-based effects are not incorporated, the models accurately reproduce the basic response of the devices under circuit operation conditions. Device transfer and output characteristics reported in the component datasheet are easily reproduced in Multisim by running a simple sweep analysis. This can be seen in graph X of the DC transfer characteristics.

Figure 2. EPC FET used for the analysis of the transfer characteristics using the DC sweep in Multisim

 

 

   

 

Figure 3. I-V curves of the FET component 

 

 

3. Optimizing a Design with Parametric Sweeps

Novel Switch Mode Power Supply (SMPS) applications require higher switching frequencies driving power switches such as the EPC eGANs. At higher frequencies, stray inductances on the PCB have a stronger impact on the switching performance. Unwanted resonance in the transient response at switching edges may occur. To evaluate the effect of PCB traces and pads, they are modeled as series stray inductances at the gate and drain of the switching element.

A simple circuit is built for the purpose of this evaluation. The circuit consists of a voltage source charging a 13uF cap through a 10kOhm resistor used to isolate the voltage source from the device under test. The FET is driven with a 5V pulse and the capacitor is discharged through an 800 mOhm resistor and the device with a 100 mOhm stray resistance.

 

 

Figure 4. Simple voltage charging topology using the EPC2001 model

 

It is worth mentioning that Multisim includes a library of non-ideal passive components that model parasitic effects to capacitors, inductors, resistors, and transformers. This library saves a lot of time when building such circuits and reduces the number of components on a schematic while maintaining the same level of accuracy.

A step pulse with a period of 200ns is applied to the gate of the EPC2001 and the response is depicted for multiple values of drain and gate inductances by using the transient analysis.

 

 

 

 

Figure 5. Simulation results of the drain voltage vs. different inductance values

 

 

 

Figure 6. Simulation results of the gate voltage vs. different inductance values

 

4. Efficiency Matters – Buck Boost Application

The eGAN FETs are characterized by lower capacitance than silicon MOSFETs and have body diode functionality with no reverse recovery charge. Also their low on-resistance enables a high efficiency for power conversion applications at higher switching frequencies.

Efficiency is a critical design parameter in every power supply application from low-power portable devices requiring a longer battery life-time, to medium and high power applications, wanting to minimize power consumption.

The example below is a buck-boost circuit built in Multisim to demonstrate how any circuit topology using the EPC eGAN FET models can be accurately evaluated.

 

 

Figure 7. Buck-boost topology

The circuit parameters feature (learn more about circuit parameters here) allows us to define expressions in the design that are used to calculate various parameters in our circuit including TH and TL. TH and TL are different timing parameters based on the specified dead-time and switching frequency.

Let's begin by viewing a transient simulation of the design to verify the DC-DC conversion operation and the filter response.

 

 

Figure 8. Transient response simulation

 

Different filter and load configurations can be simulated to optimize the transient response. Typically the efficiency of a power supply is load-dependent. A calculation is made in Multisim for the efficiency versus different load values is shown in the following graph.

 

Figure 9. Efficiency calculation for different load values

 

5. Conclusion

The EPC eGAN FETs performance improvements can be leveraged to improve system efficiency, reduce system cost, reduce size, or a combination of all three.

The innovation represented by the EPC enhancement mode Gallium Nitride devices represent a quantum leap in the types of applications we are able to simulate with frequency capability coupled with high voltage and low on-resistance.

The collaboration between National Instruments and EPC is an example of two critical players in design working to provide the most advanced models with a truly intuitive, yet powerful simulation engine. The best-in-class circuit simulation environment of Multisim enables accurate evaluation of rransient overshoots, efficiency and power dissipation. .

The result is a more efficient design process and optimized power converter designs.

 

6. Additional Resources

• Download NI Multisim
• Learn more about EPC
• View EPC GaN Library