Stationary-frame current control strategy for transverse flux permanent-magnet machine.Wang Jian kuan(王建宽)，CUI Wei(崔巍)，JIANG JianZhong(江建中）School of Electromechanical Engineering and Automation, Shanghai University, Shanghai 200072, P. R. ChinaAbstract A new stationary-frame AC current control strategy that can eKminate steady-state errors is discussed and applied to the control of transverse flux permanent-magnet machine (TFPM). Based on the principle of modulation and demodulation, this AC controller can achieve the same frequency response characteristic as the equivalent DC controller. VaHdity of the TFPM control system using this current control strategy is confirmed with simulation results.Keywords transverse flux permanent-magnet machine (TFPM), current controller, stationary frame, modulation.1. IntroductionOver the last decades, with the rapid developments in power electronics, permanent magnetic materials, and manufacturing and applications of modern permanent magnet motors have been made significant progress. Among them, transverse flux permanent-magnet machine (TFPM) with relatively high torque density and low speed, which can avoid gearing configurations, is especially suited for direct drive such as full electric ship, electric vehicle, and industrial robots. Compared with conventional machines, TFPM has a number of favorable featurest: (1) It has unique three-dimensional flux pattern leading to decoupling of space requirements of the flux carrying core iron path and the space occupied by armature winding. This permits applications of small pole pitches， leading to high current loading and high force density.(2) Each of the machine phases is entirely separated, and therefore does not couple electromagnetically with other phases.(3) Low vibration signature and high reliability are achieved by increasing the number of machine phases.Due to these advantages, design work is carried out to maximize the torque density for these machines. However, in order to make full use of these machines, their control also needs to be optimized.As a novel invert-fed synchronous permanent-magnet (PM) machine, the design of current controller is an important issue for high-performance motor drivers. Over the iast few decades research on current control for power inverters has been intensive. When the reference current is a direct signal as in DC motor drives, zero steady-state error can be secured by using a conventional proportional-integral (PI) controller. When the reference current is a sinusoidal signal as in AC motor drives, however, straightforward use of the conventional PI controller would lead to steady-state errors due to finite gain at the operating frequency. Appling the Park transform, a synchronous-frarae PI controller was then proposed which guarantees zero steady-state error in a three-phase system.However, transverse flux PM machine can not meet the Park transform due to the fact that the machine phases axe entirely decoupled. To solve the problem, this paper introduces and applies a new P+Resonant stationary frame current controller in the TFPM control system which achieves zero steady-state error since it has an infinite gain at the resonant frequency. The resonant frequency is adjusted in term of the output current fundamental frequency. In the TFPM control system, control error between the input current and its reference is applied to this current controller and its output signal is applied to the pulse width modulation (PWM) pattern generator as the reference signal for input phase voltage of the transverse flux PM machine.2. Model of transverse flux PM machineA single phase TFPM proposed by Weh is illustrated in Fig.l. The stator is composed of several U-shape cores. The stator windings lie transverse to the axial length in parallel with rotor, whereas in the conventional machines the windings lie in the longitudinal plane. The rotor is composed of several vertical blades and PM with opposite polarity.Modeling is one of the most important steps in analytical analysis and control design in TFPM. BecauseTFPM phases are entirely separated, the per-phase voltage equation is the same and given as follows, from which the saturation effect and loss of the iron are excluded: （1）where x is phase number, ux is phase voltage, R is armature resistance, ix is armature current, Xpx is armature flux linkage. where Lx and are armature inductance and PM flux linkage respectively.Suppose that the predominant component of the PM flux linkage is very close to a cosine shape and the rotor position 0 with respect to the aligned position of stator. Thus, the armature flux linkage equation becomes (2)where and are the maximum PM flux linkage value and the electrical angle of rotor respectively.When the armature inductance Lx is not change with the rotor position, substitute (2) into (1). The voltage equation can be expressed as (3)With the ro