Research On Remanufacturing Low-efficiency Induction Machines To Permanent Magnet Synchronous Machines And Control Techniques

Due to the rapid development of global electrification,electricity has ranked up to the second most consumed energy in the world following the oil.As a result,increasing attentions are being paid by governments and organizations worldwide on the rational exploitation and utilization of electricity.On one hand,electric generation projects based on clean and renewable energies,such as the nuclear,the wind power,and the photovoltaics etc.are being promoted every year.On the other hand,compulsory standards and bills have been put forward by various countries and organizations to enhance the efficiency of electric appliances.Electric machines are usually defined as the devices that convert one kind of electric energy to another,or electric energy from/to mechanical energy.Reports reveal that electric machines consume almost half of the global electricity every year,which is more than twice of that consumed by the second runner,i.e.lightening.Therefore,improving the efficiency of electric machine systems is extremely significant to the optimal utilization of electricity,and,hence,energy saving.To better promote high efficiency electric machine systems,we need to not only increase the system efficiency,but also reduce the cost as much as possible.This dissertation remanufactures the three phase Induction Machines(IMs)which take the largest proportion in the market to Permanent Magnet Synchronous Machines(PMSMs)so that the device efficiency can be enhanced with very small cost,and investigates corresponding high efficiency control strategies to fully exert the merits of PMSMs in efficiency and dynamic performance.To reduce the system cost,this dissertation also studies the high-performance position sensorless control strategies and the smooth switching technics between inverter and grid drives,which is also beneficial to increase the system efficiency.The specific contents can be summarized as follows:Firstly,motor efficiency enhancement is achieved by replacing the squirrel cage rotors of the existing low efficiency three phase IMs to permanent magnet rotors,meanwhile the stator assemblies and the winding arrangements are not changed.With synthetic considerations of different losses in the machine,the relationship between the efficiency of remanufactured machines and their magnetic load is derived,where the permanent magnet consumptions can be estimated.Special considerations are paid to the tooth and the triple harmonic reductions for the commonly used wye-and delta-connected windings,respectively,and corresponding Electro Motive Force(EMF)optimization methods are proposed.The benefits of delta-connected windings in efficiency and Constant Power Speed Range(CPSR)are also discussed.Totally 10 low efficiency IMs of 7 frame sizes are remanufactured,and the efficiency enhancement is proved by various tests.The technic procedure of remanufacturing and the return period evaluation are also provided.Secondly,for the PMSM inductances,a novel parameter is proposed as the air gap specific permeance,which is only dependent on the slot-pole combinations and the winding arrangements.With the help of this parameter,the influence of slot-pole combinations and physical dimensions on PMSM inductances are decoupled,and the relationship between PMSM inductances and slot-pole combinations is derived.The Finite Element Analysis(FEA)is carried out for verifications.For the PMSM iron loss,based on the Bertotti iron loss theory,this dissertation proposes a novel analytical approach to expressing the iron loss in the form of d-and q-axis flux linkages,which is beneficial to the PMSM design and the online efficiency optimization.This is also verified by the FEA.To fully exert the high efficiency and dynamic performance of PMSMs,this dissertation proposes the Maximum Efficiency Per Ampere(MEPA)control algorithm based on the PMSM loss model and the above derivations,and comparisons among different efficiency control algorithms are carried out with experiments.Then,the full speed range position sensorless control of PMSMs is adopted to reduce the drive system cost and enhance its reliability.For the low speed operation,several commonly used high frequency voltage injection methods in the stationary and rotary reference frames are discussed respectively,and the influences on the position estimation error caused by the neglected resistance and rotational voltage drops along with the inverter nonlinearities are analyzed.To improve the robustness to the injection voltage errors,this dissertation proposes a modified pulse square-wave voltage injection method.The position estimation error adopting high frequency injection methods caused by the magnetic field distortion is deliberated,and specific expressions between the position estimation error and the high order harmonics of PMSM phase inductances are derived and verified.Furthermore,the influence of SVPWM harmonics on the position estimation error is also studied and verified by simulations.For the high-speed operation,the PMSM model based position sensorless control algorithm and the sliding mode observer are adopted.For the intersection between low and high speed ranges,both methods work and the estimated rotor position is obtained from a weight function.Experimental results are provided along with the discussions.Finally,for applications where constant speed operations are preferred,the system cost and efficiency can be further optimized by switching PMSMs from inverter to grid drives.However,the remanufactured PMSMs cannot start on line because of the absence of damping windings.Therefore,this dissertation studies the inverter-aided smooth switching technics for PMSMs without position sensors.For switching from inverter to grid drives,the digital Phase Locked Loops(PLLs)are adopted to detect and adjust the grid and the inverter voltage phases,and the safe switching condition is achieved by regulating the PMSM velocity and the inverter output voltage.For switching from grid to inverter drives,an additional open loop control is introduced for the smooth switching without position sensors.Experiments are carried out on 5 remanufactured PMSMs,and their efficiencies under inverter and grid drives are compared.