###### Abstract
[11; 12] numerically investigated a 3-kW straight-bladed Darrieus type VAWT with a designed J-shaped profile. Their results showed that the J-shaped profile could suppress the vortices and improve the self-starting of the turbine. The hybrid wind turbine, comprising two vertical co-axial rotors, is normally constructed as a Darrieus with drag-type blades in the middle [13]. The primary purpose of the hybrid design is to promote the lack of torque when self-starting and at low tip speed ratios (TSRs) [4]. They can self-start normally, but after starting, they are less efficient than a turbine with normal lift due to the negative drag created at the middle [14]. It has been found that the above approaches hardly provide a way to promote both the self-starting ability and the peak power coefficient of the VAWTs at same time. A particular method to address those issues is to develop a variable pitch (VP)-straight-bladed VAWT to control the pitch angles of the blades on each azimuthal angle in order to maximize turbine torque and start up easily [15]. A reduction of stall is the main mechanism whereby VP-technology produces significant improvement of the torque at start up and low TSRs [16]. Besides offering the greatest potential for achieving significantly increased torque at low and intermediate TSRs, VP-technology is also used to promote peak efficiency [17; 18; 19]. VP-VAWTs consist of active and passive-type turbines. The active designs are defined as those systems that produce blade pitch change through means other than the direct action of the aerodynamic forces acting on them in passive designs [16]. [PERSON] et al. [7] introduced three modifications for the increased power output of a straight-bladed VAWT by varying its pitch. The third modification proposed a continuous variation in the local AoA correction during the rotation cycle using a sinusoidal function. Although the power output obtained by using such a modification is less than the other two, it has the inherent advantage of being practically feasible. Also, [PERSON] et al. [4] described a micro VP-VAWT that varies the pitch angle according to the azimuthal angle. The performance of the VP-VAWT was measured in an open-circuit wind tunnel, and the results were better than those of the fixed pitch (FP)-VAWT. [PERSON] et al. [20] tested the effects of cyclic blade pitch actuation on the efficiency and operability of a high-solidity VAWT with a cam and control rod mechanism to prescribe the pitch dynamics in the wind tunnel over a wide range of design and operational variables. The results revealed that a tuned first-order sinusoidal actuation system could achieve a maximum absolute power coefficient of 0.436, which is an increase of 35% over the optimal fixed-blade configuration, with self-starting capabilities and drastically improved performance at a wide range of suboptimal operating conditions. [PERSON] et al. [21] investigated the performance of a VP-turbine controlled by a cycloidal strategy. Compared with the FP-turbine, the performance at the upwind half-cycle of the VAWT with the optimized blade pitch angle was greatly improved, particularly at the azimuth region from 90\({}^{\circ}\) to 180\({}^{\circ}\); the effective region was expanded, and was nearly twice as large as that of the FP-case. [PERSON] et al. [17] designed a 500-W VAWT to implement the pitch control mechanism using the cyclic VP-technology. Its aerodynamics were predicted using the double multiple stream tube (DMST) model, and their results showed that only a 5\({}^{\circ}\) increase of the pitch angle amplitude increased the power coefficient of the VAWT by 12%. Despite the improvement of the self-starting ability and power coefficient, the above VP-approaches have the same limitation, which is mainly about the performance enhancement of azimuths with high AoAs in the case of the FP. In FP-VAWTs, each blade is constantly subjected to a variation of the AoA.