Multifunctional grid connected converter

Introduction

In renewable energy and storage applications that require high power density, the use of half-bridge converter is more preferable than the full bridge converter. Also, smart converters need to be equipped with multiple functionalities. Some advantages of this application are:

  1. Converter can be operated in seven different modes using only one simple topology
  2. All seven operating modes are embedded in one controller
This application demonstrates seven possible modes of operation with control strategy based on conservative power theory. The Bidirectional Multifunctional Converter is able to operate in the following modes:
  • Active Power Injection
  • Full Active Power
  • Reactive Compensation
  • Harmonic Compensation
  • Active Power Injection and Reactive Compensation
  • Active Power Consumption and Reactive Compensator
  • Stand-by.

Model description

The electrical part of the model is shown in Figure 1. An IGBT leg was used. Switches and diodes are modeled as ideal switches. In this model, we have three measurements (Grid voltage – Vgrid, Load current- iload and inverter current- iout). The load is implemented using a Single Phase Diode Rectifier. Suggested parameters of the filter for this model are: R=0.01Ω, C= 0.25 mF, L=4.8e-3 µH. Grid is modeled as single phase at 50Hz. The inverter DC-side is a battery-based storage element.

Figure 1: Multifunctional grid-connected converter

Figure 2: Converter controller

The gains and signal transition components behind iload and vgid signal input ports are used to emulate the sensor and ADC converter of a DSP used in a real laboratory setup. The current controller is based on a PI control with feedforward compensation, which is sufficient to make the current follow the reference disregarding the operation mode. The core of the controller is represented by a single Discrete Transfer Function. The decision of which mode the Bidirectional Multifunctional Converter will operate in is supplied by the user via Mode Selector SCADA Input. In a real application instead of manual selector the modes are handled by an additional decision-making algorithm or a superior hierarchical controller. Each operation mode has its own current reference as follows. References ref_1 and ref_2 are references from active power injection mode.In this mode, there are two options: when the energy is taken from VS1 and sent to the grid and this represents ref_1. The second case is when energy from the grid is stored in VS1 and this represents ref_2. Both references are sinusoidal but opposite in phase. References ref_3, ref_4 and ref_5 are used for the power compensation. Reference ref_4 represents active power compensation, while ref_5 and ref_6 represents reactive power compensation and harmonic compensation. References ref_6 and ref_7 are combinations of some of the previous options. Reference ref_6 means that converter can simultaneously work in active power injection mode and harmonic compensation mode. Reference ref_7 means that converter can simultaneously work in active power consumption mode and reactive compensation mode. Reference ref_8 represents the stand-by mode. In this mode converter current is set to be null.

Table 1. HIL device resource utilization
No. of processing cores 1
Max. matrix memory utilization 8.69%
Max. time slot utilization 45.33%
Simulation step, circuit solver 1e-6 µs
Signal processing execution rate 100e-6 µs

Simulation

Following figures describes how control is working when converter operate in each operation mode. Inverter current follows referent current as is shown. The control error signal is approximately zero. Waveform of the load current is also shown. Sum of the inverter current and load current is grid current which form is also shown. The results presented are experimentally verified on a real laboratory setup at UFSC Campus Blumenau, Brazil. For domain-specific questions the original authors of the application can be contacted directly: Prof. Dr. Tiago Davi Curi Busarello [email protected], Prof. Dr. Daniel Martins Lima [email protected]

Figure 3: SCADA_ panel

Figure 4: Active Power Injection mode

Figure 5: Full active power

Figure 6: Reactive power compensation

Figure 7: Harmonic compensation

Figure 8: Active power injection and reactive compensation

Figure 9: Active power consumption and reactive compensation

Figure 10: Stand-by mode

Table 2. Minimum requirements
Files
Typhoon HIL files

examples\models\grid-connected converters\multifunct grid-connected converter

multifunct grid-connected converter.tse,

multifunct grid-connected converter.cus

Minimum hardware requirements
No. of HIL devices 1
HIL device HIL402
Device configuration 1

Test automation

We don’t have a test automation for this example yet. Let us know if you wish to contribute and we will gladly have you signed on the application note!

Authors

[1] Jovana Markovic