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Analysis of the principle of space voltage vector svpwm control
Space Vector Pulse Width Modulation (SVPWM) is an advanced control technique that has been widely applied in inverters, uninterruptible power supplies (UPS), and reactive power compensators. In recent years, with the continuous development of industrial technology and the increasing demand for high-power, high-quality inverters, especially in China, SVPWM has gained significant attention. The advancement in power electronics, microelectronics, and control theory has laid a solid foundation for the maturity of inverter technology. As a result, SVPWM has emerged as a more efficient and effective method compared to traditional modulation techniques.
Unlike conventional Sinusoidal Pulse Width Modulation (SPWM), SVPWM focuses on optimizing the overall performance of the three-phase output by controlling the space voltage vectors. This approach aims to generate a rotating magnetic field that closely resembles a perfect circle, which leads to reduced torque ripple and improved motor efficiency. Additionally, SVPWM allows for better utilization of the DC bus voltage, resulting in higher energy efficiency and easier digital implementation.
Pulse Amplitude Modulation (PAM) is another modulation technique that adjusts the amplitude of a pulse train according to specific rules to control the output waveform. It builds upon PWM by varying both the pulse width and the modulation pattern, allowing for smoother and more accurate waveforms after filtering.
**Basic Principle of SVPWM**
The fundamental concept behind SVPWM is based on the principle of average equivalence. By combining basic voltage vectors within a single switching cycle, the average value can be made equal to the desired reference vector. This involves dividing the voltage space into six sectors, each defined by two adjacent non-zero vectors and one zero vector. Within each sector, the action times of these vectors are calculated to approximate the ideal circular trajectory of the voltage space vector.
Assuming the DC bus voltage is Udc, the three-phase output voltages UA, UB, and UC are represented as vectors in a stationary coordinate system. These vectors rotate at a constant angular frequency, forming a balanced three-phase sinusoidal waveform. The magnitude of the resultant space vector is 1.5 times the peak phase voltage, ensuring optimal performance and minimal harmonic distortion.
The inverter's switching states determine the voltage vectors generated. With six switches in the three-phase bridge, there are eight possible combinations of switch positions, including six non-zero vectors and two zero vectors. Each combination produces a unique voltage vector, which can be used to synthesize any desired reference vector within a given sector.
By calculating the time durations for each vector, the system ensures that the synthesized vector closely follows the reference. This process is repeated continuously, resulting in a smooth and efficient PWM waveform. The use of SVPWM not only improves the quality of the output but also enhances the overall performance of the inverter in various applications.