Induction Machine Direct Torque Control with Space Vector Modulator

Induction machine DTC structure with SVM

Libraries:
Simscape / Electrical / Control / Induction Machine Control

Description

The Induction Machine Direct Torque Control with Space Vector Modulator implements an induction machine direct torque control structure (DTC) with space vector modulator (SVM). Use this block to generate the gate pulses for an inverter controlling an induction machine. This diagram shows the architecture of the block.

In the diagram:

You provide the reference torque, T*, and flux, ψ*.
The Flux and Torque Estimator estimates the actual torque, T, and flux, ψ from the measured phase currents, i_abc, and voltages, v_abc.
Two PI controllers determine the reference d and q voltages, v_d and v_q, from the flux and torque errors, respectively.
The SVM generates the gates pulses, G_ij, required to control an inverter driving the induction machine. Subscript i corresponds to the phase (a, b, or c). Subscript j corresponds to the high, H, or low, L, signal.

Flux and Torque Estimator

To estimate the torque and flux, the block discretizes the machine voltage equations in the stationary ɑβ reference frame using the backward Euler method. The discrete-time equations for stator fluxes in the ɑβ frame are:

$ψ_{α} = (v_{α} - i_{α} R_{s}) \frac{T_{s} z}{z - 1}$

$ψ_{β} = (v_{β} - i_{β} R_{s}) \frac{T_{s} z}{z - 1}$

Where:

v_ɑ and v_β are the ɑ- and β-axis voltages, respectively.
i_ɑ and i_β are the ɑ- and β-axis currents, respectively.
Ψ_ɑ and Ψ_β are the ɑ- and β-axis stator fluxes, respectively.
R_s is the stator resistance.

The block calculates the torque and total stator flux as:

$T = \frac{3 p}{2} (ψ_{α} i_{β} - ψ_{β} i_{α})$

$ψ_{s} = \sqrt{ψ_{α}^{2} + ψ_{β}^{2}}$

Where:

p is the number of pole pairs.
Ψ_s is the total stator flux.

Space Vector Modulator

The SVM converts the desired voltages into gate pulses, which you use to control an inverter. This figure shows possible switching states of a three-phase inverter.

The hexagon represents the space vector diagram. Each of the six vertices represents a possible switching state (G_AH,G_BH,G_CH) of the three-phase inverter. Each low gate takes the opposite state as its corresponding high gate. The inverter diagram illustrates the current state.

The rotating vector in the space vector diagram corresponds to the complex reference voltage vector, which rotates at the desired electrical frequency of the machine. In reality, the switching frequency is much faster than this electrical frequency. As a result, the inverter switches continually between the two states enclosing its current region Ri, and the zero state corresponding to (0,0,0), to generate the desired voltages.

To learn about the implementation of this method, see the PWM Generator (Three-phase, Two-level) block.

Examples

Asynchronous Machine Direct Torque Control with Space Vector Modulator

Control an asynchronous machine (ASM) using the direct-torque control method with space vector modulator. A PI-based speed controller supplies the torque reference. The direct-torque controller generates the reference voltages required by the space vector modulator. A DC voltage source feeds the ASM through a controlled average-value voltage source converter.

Open Model

Ports