Modified natural frame control of single‐phase cascaded H‐bridge multilevel converter under distorted grid voltage

Abstract

Cascaded H-bridge multilevel converter is widely applied in flexible AC transmission and grid connection of renewable energy, but its current quality decreases as the grid voltage distortion continues to deteriorate. A modified natural frame control method to enhance the harmonic elimination ability of converters is proposed in this paper. A single-phase cascaded delayed signal cancellation operator is applied to deal with the distorted grid voltage signals. Benefit from a system structure without any feedback loops or integral items, the transient response of single-phase cascaded delayed signal cancellation operator is faster than commonly-used second-order generalised integrator. The settling time of single-phase cascaded delayed signal cancellation operator facing grid voltage phase jump is less than one grid period. After immunising the synchronisation reference against harmonic distortion by using the single-phase cascaded delayed signal cancellation operator, the modified natural frame control method can then generate high-quality sinusoidal current. Phaselocked loop and coordinate transformation are unnecessary for the proposed method, which decreases the system complexity. Various simulations and experimental tests based on a down-scaled platform demonstrate the performance of the proposed modified natural frame control method under distorted grid voltage.

A whole control strategy for cascaded H‐bridge rectifiers under distorted grid voltage and unbalanced load

“…Note that the trigonometric function on the right-hand side of ( 11) is the transformation from the αβto the dq coordinate. By (12), one has…”

“…Various VBC approaches have also been developed to maintain the dc‐side capacitor voltages balancing, including the modulation‐based strategies [13, 14] and the duty cycle compensation methods [1, 2, 4–7, 10, 12, 15–19]. The modulation‐based methods are attractive and perform well for voltage balancing [13, 14].…”

“…The abovementioned control schemes were developed under ideal grid voltage, and the performance requirement in distorted grid voltage is often beyond the capabilities of these methods. Actually, it is difficult to avoid the harmonic components of the grid voltage (distorted grid voltage) due to the increasing usage of non‐linear power electronic devices, the saturation of magnetic elements, and so on [11, 12]. Under the distorted grid voltage, the existing methods will present highly distorted grid current, which degrades the power quality on the grid side [4–7, 9, 10].…”

Control strategy without phase‐locked loop based on power estimation and natural frame for single‐phase cascaded H‐bridge converter

“…The comparison of the steady‐state experimental results and current harmonic content of other control methods in grid‐connected mode for the same distorted grid is given in Figure 16. Figure 16A–D shows the steady‐state waveforms in grid‐connected mode for method 1 in Yang et al, 21 the method without PLL in Yang et al 26 (noted as method 2), the improved NFC method in Yang et al 32 (noted as method 3), and the voltage‐sensorless NFC method in Shao et al 33 (noted as method 4), respectively. Figure 16 gives a comparison of the steady‐state experimental results of other methods in grid‐connected mode.…”

Voltage-Sensorless Natural Frame Control for Single-Phase CHB Converter under Distorted Grid Conditions

“…The different filter schemes adopted by the synchronization method are roughly divided into the low-pass filter (LPF), notch filter, band-pass filter, comb filter, and others [3][4][5]. Cascaded delay signal cancellation (CDSC) has become a popular alternative due to its enhanced harmonic filtering performance, simple calculation, and better linear phase characteristics [6][7][8].…”