The Organization of this Guide
This document is the user guide, which covers the following topics:
- Introduction - Provides an introduction to simulation and the principles behind the use of the eHS solver.
- Requirements - Software requirements for the eFPGAsim toolbox, including the eHS solver.
- Building models with the eHS solver - Describes the procedure to develop an RT-LAB model with the eHS solver.
Conventions
OPAL-RT guides use the following conventions:
Table 1: General and Typographical Conventions
| CONVENTION | DESCRIPTION |
|---|---|
| Bold | User interface elements, text that must be typed exactly as shown. |
| Note | Emphasizes or supplements parts of the text. You can disregard the information in a note and still complete a task. |
| Warning | Describes an action that must be avoided or followed to obtain desired results. |
| Recommendation | Describes an action that you may or may not follow and still complete a task. |
| Code | Sample code |
| Italics | References work titles |
| Blue Text | Cross-references (internal or external) or hypertext links |
About the OPAL-RT from the eFPGASIM Toolbox
The OPAL-RT electric Hardware Solver (eHS) is a powerful floating-point solver developed by OPAL-RT that enables users to simulate an electric circuit on an FPGA automatically, without having to write the mathematical equations.
It combines the simplicity of building electric circuit models using the SimPowerSystems Toolbox, PSIM, the PLECS Blockset, or NI Multisim software with the strength of OPAL-RT FPGA-based simulators to solve the currents and voltages within the circuit in real-time, with a sample time below 1μs.
The eHS solver uses the modified nodal analysis. It solves a conductance matrix to find the voltage at each node of the circuit, and the current in each branch.
The conductance matrix of the circuit is made independent of the switch control signals through the implementation of the Pejovic1 method representing the switch impedance. With this method, a conducting switch is represented as inductance and an open switch is represented as a capacitance so the conductance matrix does not change during the simulation.
Key Features
Configurability
The conductance matrix does not need to be re-computed since switches are represented using the Pejovic method.
All the matrices needed for solving the system are loaded onto the FPGA engine when the simulation is initiated. Reconfiguring the engine with specific firmware for each application is not necessary.
This feature makes running real-time simulations of electrical systems at high sampling rates as easy as any RT-LAB simulation.
Performance
The sample time of the electrical system solved by the eHS solver ranges from 160ns to 4μs, depending on the circuit complexity.
Compatibility
eHS solvers provide a flexible environment that allows the user to design the simulated circuit in various netlist editors such as SimPowerSystems and PLECS Simulink toolboxes, Powersim PSIM, and NI Multisim software.
Scalability
eHS exists in various form factors to accommodate low to high-end FPGA-based platforms. It is capable of simulating a Boost circuit with time step as low as 200ns, as well as a micro-grid system with outstanding resolution. Depending on the use case, it is possible to interconnect several eHS cores using a multi-FPGA system with low latency SFP 5Gbps links between chassis.
Test Scenarios
It is possible to modify the component values during simulation to apply load variations and faults using the scenario feature. Please check the scenario feature description of this manual.
Specifications
eHS Gen3
The circuit is designed using blocks in supported netlist editors.
A limited number of elements, chosen from a specific list, can be included in each circuit.
The maximum number of circuits that can be simulated in one real-time model depends on the firmware installed onto the solver hardware and the number of available eHS licenses installed onto the simulation system.
As opposed to previous generations, the 3rd Generation of eHS comes in various sizes to respond to different needs in terms of FPGA size, simulation complexity, and compatibility.
Table 1 describes the existing eHS gen3 cores followed by their associated specifications:
Table 1 -eHS Gen3 specification table
| Features | eHSx16 | eHSx32 | eHSx64 | eHSx128 |
|---|---|---|---|---|
| Targeted platforms | cRIO 7068 (Zynq 7020) | OP4200 (Zynq 7030) OP5600 (Virtex 6 240t) | OP4510 (Kintex7 325t) OP5700 (Virtex7 485t) | OP5607 (Virtex 7 485t) |
| Number of eHS core available | 1 | 1 | 1 (OP4510) 2 (OP5607 OP5700) | 1 |
| Number of inputs | 16 | 32 | 32 | 128 |
| Number of outputs | 16 | 32 | 32 | 128 |
| Number of switches | 24 | 48 | 72 | 144 |
| LCA capability2 | Yes | Yes | Yes | Yes |
| Maximum number of states3 | 60 | 100 | 150 | 300 |
| Maximum Timestep | 2.56us | 4us | ||
| Number of resistors | Unlimited | |||
| Switches type supported | IGBT/Diode, Diode, Breaker, Thyristor, Ideal Switch | |||
| Non-switching devices supported | Resistor, Inductor, Capacitor, Ideal Transformer, Mutual inductance, PI Line | |||
| Calculation power | 6.4 GFLOPS | 12.8 GFLOPS | 25.6 GFLOPS | 51.2 GFLOPS |
| Maximum number of test scenarios4 | Up to 512 scenarios | |||
| Circuit editors compatible | SimPowerSystems Simulink toolbox, PSIM, PLECS Blockset Simulink Toolbox, NI Multisim | |||
- 2 LCA stands for Loss Compensation Algorithm. This feature optimizes losses for standard topologies such as the two-level and the three-level NPC arm converters.
- 3 Estimated values. The maximum number of states depends on the number of inputs and outputs that needs to be computed as well. There is no hard coded limit. If the time step required exceeds the solver’s limit, a compilation error will occur due to overpassing the circuit size limit.
- 4 The number of scenario available for a given circuit depends on the circuit complexity. Scenarios are not currently supported on the OP4200 target.
eHS (Dual eHS) (Gen1 - Deprecated)
The circuit is designed using blocks from the SimPowerSystems library. A limited number of elements, chosen from a specific list, can be included in each circuit. The maximum number of circuits that can be simulated in one real-time model depends on the firmware installed in the solver hardware and the number of available eHS licenses in the simulation system.
The number of elements in each circuit is subject to the following limitations:
- S = 0..24 switching elements
- U = 1..16 current or voltage inputs
- Y = 1..16 current or voltage measurements
- NSD = 0..60 non-switching devices. The number of non-switching devices includes L and C. "LC" and "RLC" branches each count for two non-switching devices.
- The number of resistors is not limited.
External Tools
Simulink
Simulink is a software package developed by The MathWorks, Inc. that enables modeling, simulation and analysis of dynamic systems.
Models are described graphically, following a precise format based on a library of blocks. The eHS solver uses Simulink to define models that will be executed during an RT-LAB simulation.
Users are expected to have a clear understanding of Simulink operation, particularly regarding model definition and simulation parameters.
SimPowerSystems and PLECS Simulink Toolboxes
The SimPowerSystems and PLECS Blockset toolboxes provide libraries and analysis tools useful for modeling and simulating electrical systems.
They are used by the eHS only as circuit description environments. They can be used from within the RT-LAB environment for real-time simulation, but fail to achieve the very high sample rate that can be attained with the eHS solver.
It can be useful, though, to use these simulation tools to compare the results to those of the eHS solver.
PSIM
PSIM is a simulation environment engine. It uses a strong algorithm dedicated to electrical circuits (piecewise method, generic models, and a fixed time-step).
The fast simulation allows repetitive simulation runs and significantly shortens the design cycle. PSIM’s control library provides a comprehensive list of components and function blocks, and makes it possible to build virtually any control scheme quickly and conveniently. It is used by the eHS only as a circuit description environment. The PSIM simulation tools are also useful to compare the results to those of the eHS solver.
NI Multisim
NI Multisim is an advanced, industry-standard, best-in-class SPICE simulation environment used by educators, researchers, and engineers worldwide.
It is used by the eHS only as a circuit description environment. The NI Multisim simulation tools are also useful to compare the results to those of the eHS solver.