**1. Overview**
Space Vector Pulse Width Modulation (SVPWM) is a modern control technique that has gained popularity in recent years. It is a pulse width modulated signal generated by a specific switching pattern using the six power switches of a three-phase inverter. This method allows the output current waveform to closely resemble an ideal sinusoidal waveform. Unlike traditional Sinusoidal PWM (SPWM), SVPWM focuses on the overall effect of the three-phase output voltage, aiming to achieve an ideal circular flux linkage in the motor. Compared to SPWM, SVPWM produces lower harmonic content in the winding current, reducing torque ripple and making the rotating magnetic field more circular. Additionally, it improves the utilization of the DC bus voltage and is easier to implement digitally.
**2. Basic Principle of SVPWM**
The theoretical foundation of SVPWM is based on the principle of average equivalence. By combining basic voltage vectors within a single switching cycle, the average value is made equal to the reference voltage vector. In an inverter circuit, the DC bus voltage is denoted as Udc, and the three-phase voltages are UA, UB, and UC, which form a rotating space vector with constant amplitude and angular frequency ω = 2πf. The objective of the SVPWM algorithm is to represent this rotating vector using the switching states of the three-phase bridge.
There are eight possible combinations of the switching states (Sa, Sb, Sc), including six non-zero vectors (U1 to U6) and two zero vectors (U0 and U7). Each switching state corresponds to a specific voltage vector, and by selecting appropriate vectors and their durations, the reference voltage can be synthesized. For example, when Sa=1, the phase voltage UA(t) equals Udc, and similar logic applies to other phases. The line voltage between two phases, such as Uab = UA - UB, can also be derived.
By placing these vectors in a sector map, we observe that the six non-zero vectors have equal magnitude and are spaced 60 degrees apart, while the zero vectors are at the center. When synthesizing a reference vector Uref, the algorithm determines the sector it belongs to and uses the adjacent vectors to approximate it. The selection of zero vectors plays a key role in minimizing switching losses and ensuring symmetrical PWM waveforms.
To generate the actual PWM signal, the time durations of the selected vectors are calculated and distributed symmetrically. The switching sequence is optimized to reduce the number of transitions and avoid switching during high-current moments. This approach ensures efficient operation and reduces harmonic distortion in the output.
The calculation of the reference vector’s position involves determining its sector based on the α-β components of the voltage. Once the sector is identified, the action times of the adjacent vectors are computed, and the duty cycles for the three-phase PWM signals are determined. This process is repeated for each carrier cycle, allowing real-time modulation of the output.
In cases where the reference vector exceeds the maximum allowable amplitude (i.e., outside the inscribed circle of the hexagon), overmodulation occurs, leading to waveform distortion. To address this, scaling algorithms are applied to bring the vector back within the acceptable range, maintaining the quality of the output.
Overall, SVPWM offers improved performance in terms of efficiency, harmonic reduction, and DC bus utilization compared to traditional SPWM methods. Its implementation requires careful analysis of vector positions, timing, and switching sequences to ensure optimal operation.
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