In this paper, an enhanced five-segment space vector modulation (SVM) approach is proposed for five-phase current-source converter (CSC) to simultaneously reduce its output current harmonics and common-mode voltage (CMV). To realize proper output current harmonics mitigation, the reference current vector is synthesized by adjacent four large vectors and one zero vector in the fundamental plane. At the same time, the dwell times of four adjacent large vectors are calculated to actively control the corresponding current projection in 3rd sequence plane. In addition, the zero vector is selected according to the ranking of the instantaneous filter capacitor voltage absolute value to reduce peak CMV. Comparing to voltage-source converter (VSC) counterparts where the CMV is not affected by the AC output voltage and current harmonic components, it is interesting to find that the CMV enveloping of CSC has a strong connection with its 3rd harmonic output current. Then, a sequence arrangement for the five-segment space vector modulation approach is proposed to ensure only one switch action during vector states transition. Finally, a transformer-like loss model is established to evaluate the loss performance of the CSC with different modulation approach and vector sequence selection method.

In this paper, an enhanced fault-tolerant operation approach is developed to maintain continued operation of five-phase grid-tied current-source converters (CSCs) during one-phase supplying wire broken. First, the instantaneous power flow of this system is analyzed based on the sequence decomposition method. It is found that through proper arrangement of positive-, negative-, and pseudozero-sequence components of line current reference and compensation of filter CL current offset, the CSC system can achieve reduction of instantaneous active power fluctuation and minimization of line current magnitude at the same time. Accordingly, multiphase CSCs are able to operate with smaller dc rail current ripples and to obtain more active power transfer capability during fault tolerant operation. In addition, this paper also briefly discusses the control of multiphase systems in the case of complex grid faults with simultaneous wire broken and imbalanced grid voltage dips. It is found that an intentional constant reactive power injection can help to reduce the peak current of the five-phase grid-tied system. Furthermore, it should be noted that the proposed method is realized in a direct current modulation manner. Thus, a large number of line current acquisition devices for conventional multiphase grid-tied converters are removed. Finally, this paper also discusses the modulation method of five-phase CSC with one-phase wire broken. A modified “ampere-second balance” principle is applied to direct obtain the gating signals that can satisfy the constraints of CSCs.

In this paper, a bypass pulse injection based PWM approach is proposed for mitigating line current harmonics of grid-tied current source converters (CSCs) operating at low switching frequency. Firstly, the relationship between CSC output harmonic current and the format of bypass pulse is analyzed. Then, through online adjustment of both bypass pulse location and width, the 7th harmonic component of output current is actively regulated to mitigate the corresponding 7th line harmonic current. Meanwhile, this action may be associated with additional amplification of 5th output current. To deal with this issue, the unsymmetrical selective harmonic elimination (SHE) modulation with online adjustable switching angles is applied to further mitigate the 5th harmonic line current. It has been experimentally validated that with the application of both the bypass pulse injection and the unsymmetrical SHE based modulation approaches, both the 5th and the 7th harmonic line currents can be simultaneously suppressed with ultra-low switching frequency below 1kHz.

Parallel operation of current source converters (CSCs) is an attractive approach for medium voltage high power conversion applications. In order to achieve proper DC rail current balancing of parallel CSCs while maintaining a good control of AC line current quality at low switching frequency (typically at a few hundred Hz), an improved quasi-selective harmonic elimination (Q-SHE) modulation method with online delay angle and by-pass band adjustment is proposed. At first, each CSC positive rail DC current is regulated by tuning the delay angle of the corresponding line reference current with respect to the grid voltage. At the same time, the negative rail DC currents balancing errors are compensated by injecting small by-pass pulses into the conventional SHE pattern. By the coordinated control of the aforementioned methods, an accurate DC rail currents balancing and an enhanced line current quality can be achieved at both the steady and the transient states.

As the penetration of wind energy is being dramatically increased, the impact of wind energy on the power system should be roundly studied, especially for the fault characteristics analysis and applicability analysis of low voltage ride-through (LVRT) requirements for a whole wind farm (WF) and an individual wind turbine generator (WTG). This paper firstly describes a detailed modeling of a permanent magnet synchronous generator (PMSG)-based WF and analyzes the fault characteristics of the WF under various fault conditions. The validation of the fault characteristics analysis is carried out with the EMTP-RV generated data, with the consideration of different fault positions, fault types, and wind speeds. The relay protection and the related grid code are also taken into account. In addition, the applicability analysis of LVRT requirements for a WF and a WTG is also implemented, from the points of minimal grid-connection time and minimal dynamic reactive current support ability. The fault characteristic analysis of a PMSG-based WF could be helpful for developing new control or protection methods for a PMSG-based WF. Meanwhile, the applicability analysis of LVRT requirements could serve as a reference for WTG manufacturers, WF administrators, and grid operator.

Grid-connected inverters are widely used to interface renewable energy and energy storage resources into the grid. Voltage-controlled inverters have attracted more and more attention due to their grid-friendly characteristics. The mathematical models of the voltage and current loops are developed in this paper, considering especially the discrete control delay caused by calculation and modulation. In order to suppress the resonance peak in the current loop, the frequency characteristics of the current loop are analyzed in detail. The optimum design flow of the current controller and voltage controller parameters are presented based on numerical analysis, and the stability, dynamic performance and the resonance peak suppression in voltage loop are also considered. Finally, the validity of the mathematical model and the effectiveness of the controller parameters design method are verified by simulation and experimental results.