Workshop Matlab/Simulink in Drives and Power electronics Lecture 4

Transcription

1 Workshop Matlab/Simulink in Drives and Power electronics Lecture 4 : DC-Motor Chopper design SimPowerSystems Ghislain REMY Jean DEPREZ 1 / 20

2 Workshop Program 8 lectures will be presented based on Matlab/Simulink : 1 Introduction to Matlab 2 Introduction to Simulink 3 DC-Motor Control design 4 DC-Motor Chopper design SimPowerSystems 5 Introduction to Stateflow/Statechart 6 Induction Motor Inverter Control 7 Synchronous Motor Modeling 8 Synchronous Motor Control Two system applications (four quadrants electric drives of mechanical systems) will be used as "conducting lines" during the workshop. 2 / 20

3 SimPowerSystems Libraries SimPowerSystems software and other products of the Physical Modeling product family work together with Simulink software to model electrical, mechanical, and control systems. SimPowerSystems libraries contain models of: Power equipment such as transformers, lines, machines, and power electronics. These models are proven ones coming from textbooks, and their validity is based on the experience of : The Power Systems Testing and Simulation Laboratory of Hydro- Québec, a large North American utility located in Canada, The École de Technologie Supérieure and Université Laval. 3 / 20

4 SimPowerSystems main library The SimPowerSystems main library, powerlib, organizes its blocks into libraries according to their behavior. The powerlib library window displays the block library icons and names. The main powerlib library window also contains the Powergui block that opens a graphical user interface for the steadystate analysis of electrical circuits. 4 / 20

5 Building and Simulating a Simple Circuit SimPowerSystems software allows you to build and simulate electrical circuits containing linear and nonlinear elements. 5 / 20

6 Examples of SimPowerSystems Libraries Various Electrical Libraries are available: Electrical Sources Elements (Inductance, Resistance ) Power Electronics (Diode, MOSFET ) Machines (DC-motor, PM Motor ) Measurements (Voltage probe ) Application Libraries 6 / 20

7 Example: a Two-Quadrant 3ϕ Rectifier DC Drive Using SimPowerSystems: It is no more necessary to use Causal Approaches, because it is Physical Connections. 7 / 20

8 How SimPowerSystems Software Works Every time you start the simulation, a special initialization mechanism is called. This initialization process computes the state-space model of your electric circuit and builds the equivalent system that can be simulated by Simulink software. This process performs the following steps: Sorts all SimPowerSystems blocks. The blocks are separated into linear and nonlinear blocks, and all electrical nodes received a node number. Then, a state-space model (A, B, C, D matrices) of the linear part of the circuit is computed. All steady-state calculations and initializations are performed at this stage. Discrete state-space models are computed from the continuous state-space model, using the Tustin method. This matrix defines the network algebraic equations. 8 / 20

9 Power Electronics Library: Diode The diode is a semiconductor device that is controlled by its own voltage Vak and current Iak. When a diode is forward biased (Vak > 0), it starts to conduct with a small forward voltage Vf across it. It turns off when the current flow into the device becomes 0. When the diode is reverse biased (Vak < 0), it stays in the off state. The Diode block is simulated by a resistor, an inductor, and a DC voltage source connected in series with a switch. The switch operation is controlled by the voltage Vak and the current Iak. 9 / 20

10 Thyristor The thyristor is a semiconductor device that can be turned on via a gate signal. The thyristor model is simulated as a resistor Ron, an inductor Lon, and a DC voltage source representing the forward voltage Vf, connected in series with a switch. The switch is controlled by a logical signal depending on the voltage Vak, the current Iak, and the gate signal g. The Thyristor block also contains a series Rs-Cs snubber circuit that can be connected in parallel with the thyristor device. The static VI characteristic: 10 / 20

11 Universal Bridge The Universal Bridge block implements a universal three-phase power converter that consists of up to six power switches connected in a bridge configuration. The type of power switch and converter configuration are selectable from the dialog box. The Universal Bridge block allows simulation of converters using both naturally commutated (or line-commutated) power electronic devices (diodes or thyristors) and forced-commutated devices (GTO, IGBT, MOSFET). The Universal Bridge block is the basic block for building two-level voltage-sourced converters (VSC). The device numbering is different if the power electronic devices are naturally commutated or forced-commutated. 11 / 20

12 Diode and Thyristor Bridges For a naturally commutated three-phase converter (diode and thyristor), numbering follows the natural order of commutation: For the case of a two-phase diode or thyristor bridge, and for any other bridge configuration, the order of commutation is the following: 12 / 20

13 GTO-Diode and IGBT-Diode bridges GTO-Diode bridge: IGBT-Diode bridge: 13 / 20

14 MOSFET-Diode and Ideal Switch bridges MOSFET-Diode and Ideal Switch bridges 14 / 20

15 Snubber resistance and capacitance Snubber resistance Rs, in ohms (Ω). Set the Snubber resistance Rs parameter to inf to eliminate the snubbers from the model. Snubber capacitance Cs, in farads (F). Set the Snubber capacitance Cs parameter to 0 to eliminate the snubbers, or to inf to get a resistive snubber. In order to avoid numerical oscillations when your system is discretized, you need to specify Rs and Cs snubber values for diode and thyristor bridges. For forced-commutated devices (GTO, IGBT, or MOSFET), the bridge operates satisfactorily with purely resistive snubbers as long as firing pulses are sent to switching devices. 15 / 20

16 Tunning the snubbers If firing pulses to forced-commutated devices are blocked, only antiparallel diodes operate, and the bridge operates as a diode rectifier. In this condition appropriate values of Rs and Cs must also be used. When the system is discretized, use the following formulas to compute approximate values of Rs and Cs,where These Rs and Cs values are derived from the following two criteria: The snubber leakage current at fundamental frequency is less than 0.1% of nominal current when power electronic devices are not conducting. The RC time constant of snubbers is higher than two times the sample time Ts. These Rs and Cs values that guarantee numerical stability of the discretized bridge can be different from values of a physical circuit. 16 / 20

17 Interfacing SimPowerSystems with Simulink 1. The Voltage Measurement block acts as an interface between the SimPowerSystems and the Simulink blocks, and converts the measured voltages into Simulink signals. 2. Similarly, the Current Measurement block converts any measured current into a Simulink signal. 3. The Controlled Voltage Source block is use to inject a voltage in an electrical circuit 17 / 20

18 Connecting Rules for Capacitors and Inductors You have to pay particular attention when you connect capacitor elements together with voltage sources, or inductor elements in series with current sources. When you start the simulation, the software displays an error message if one of the following two connection errors are present in your diagram: To fix this problem, you can add a small resistance in series between the voltage source and the capacitors. To fix this problem, you can add a large resistance in parallel with the inductor and the capacitors. or or 18 / 20

19 The Powergui Block to Simulate The Powergui block is necessary to simulate any Simulink model containing SimPowerSystems blocks. It is used to store the equivalent Simulink circuit that represents the statespace equations of the SimPowerSystems blocks. You must follow these rules when using this block in a model: Place the Powergui block at the top level of diagram for optimal performance. However, you can place it anywhere inside subsystems for your convenience; its functionality will not be affected. Only one Powergui block per model You must name the block powergui The Most used Simulation type are: - Continous for Physical System - Discrete for Commutating system 19 / 20

20 SimPowerSystems Tools for Analysis Very useful analysis tools can be used: Use LTI Viewer (facilitate linear analysis of SimPowerSystems Model with Control System Toolbox) FFT Analysis (easy to plot FFT signal) Hysteresis Design Tool (to add hysteresis and saturation to Transformer Model) Compute RLC Line Parameters (to identify RLC value from characteristics of Grid Line) 20 / 20