Compound-structure Permanent-magnet Synchronous Machine Research Articles

Research on system control and energy management strategy of flux-modulated compound-structure permanent magnet synchronous machine

The flux-modulated compound-structure permanent magnet synchronous machine (CS-PMSM), composed of a brushless double rotor machine (DRM) and a conventional permanent magnet synchronous machine (PMSM), is a power split device for plug-in hybrid electric vehicles. In this paper, its operating principle and mathematical model are introduced. A modified current controller with decoupled state feedback is proposed and verified. The system control strategy is simulated in Matlab, and the feasibility of the control system is proven. To improve fuel economy, an energy management strategy based on fuzzy logic controller is proposed and evaluated by the Urban Dynamometer Driving Schedule (UDDS) drive cycle. The results show that the total energy consumption is similar to that of Prius 2012.

Investigation of the Cooling and Thermal-Measuring System of a Compound-Structure Permanent-Magnet Synchronous Machine

The compound-structure permanent-magnet synchronous machine (CS-PMSM) is a power-split device which can enable the internal combustion engine (ICE) to operate at optimum efficiency during all driving conditions by controlling its torque and speed. However, the CS-PMSM has more serious temperature rise and heat dissipation problems than conventional permanent-magnet (PM) machines, especially when the CS-PMSM is running at low speed and under full load conditions. As the thermal resistance of double-layer air gaps is quite big, the hot spot proves to be in the inner winding rotor. To ensure the safe operation of the CS-PMSM, the use of forced-air and water cooling in the inner winding rotor are investigated. The study shows that the water cooling can provide a better cooling effect, but require a complicated mechanical structure. Considering the complexity of the high efficiency cooling system, a real-time temperature monitoring method is proposed and a temperature measuring system which can accurately measure the real-time temperature of multiple key points in the machine is developed to promptly adjust the operating and cooling conditions based on the measured temperature results. Finally, the temperature rise experiment of the CS-PMSM prototype is done and the simulation results are partly validated by the experimental data.

Electromagnetic Design of a New Electromagnetic Planetary-Gear Machine

A novel brushless compound-structure permanent-magnet synchronous machine (CS-PMSM) based on the magnetic field modulation principle is proposed for hybrid electric vehicles. As the key part of the brushless CS-PMSM, the operation principle of the electromagnetic planetary-gear machine (EPGM) is investigated by analytical method. The magnetic-field distribution and torque performance of the EPGM are studied by finite-element method (FEM). To obtain the optimal design scheme, the influence of the span ratio and thickness of the magnetic block and the slot-opening on the electromagnetic performance is investigated. Finally, the core loss distribution of the EPGM is investigated and the performance of this machine is fully evaluated.

Analysis and Experiment of a Novel Brushless Double Rotor Machine for Power-Split Hybrid Electrical Vehicle Applications

A novel brushless double rotor machine (BDRM) is proposed in this paper. The BDRM is an important component in the brushless compound-structure permanent-magnet synchronous machine (CS-PMSM) system, which is a promising technology for power-split hybrid electric vehicle (HEV) applications. Compared with common double rotor machines, the brushes and slip rings required by rotating winding have been omitted in the BDRM, thus there are no such problems as maintenance, friction losses and so forth. Firstly, the torque characteristics of the BDRM are analyzed. As the stator has ring-shaped centralized windings, the size characteristics of the BDRM are different from those of conventional machines. The new sizing and torque equations are analyzed and the theoretical results are applied to determine the main dimensions. Additionally, studies of the analytical magnetic circuit and finite element method (FEM) model show that the BDRM tends to have high leakage flux and low power factor. Although the scope for improving the serious flux leakage of the BDRM is limited by the special magnetic topology, a method to obtain higher power factor is provided. Finally, a 10 kW prototype machine was manufactured, assembly of the prototype is discussed in detail and experimental tests are performed to validate the analytical and simulation results.

Investigation of a Novel Radial Magnetic-Field-Modulated Brushless Double-Rotor Machine Used for HEVs

A novel brushless compound-structure permanent-magnet synchronous machine (CS-PMSM) with six different topologies is proposed based on the magnetic field modulation principle. As the key part of the brushless CS-PMSM, the radial magnetic-field-modulated brushless double-rotor machine (MFM-BDRM) is investigated on the speed and torque relations of the first-stator magnetic field, the first-PM rotor and the modulating ring rotor by analytical method. Besides, on the basis of analyses of magnetic field distribution in the inner and outer air gap, the back electromagnetic force and torque performance of the radial MFM-BDRM are further studied by finite-element method (FEM). The results indicate that the low power factor is a major problem of the radial MFM-BDRM. Therefore, the influence of parameters, such as combinations of magnetic block number and PM pole pair number, the span ratio and radial thickness of magnetic blocks, and the length of air gap, on the power factor is analyzed. Additionally, to investigate the distribution law of core loss in the radial MFM-BDRM, amplitudes and frequencies of the magnetic fields in each part of the machine are analyzed. Furthermore, considering the weak mechanical strength of modulating ring rotor employing DW310 laminations, an attempt to use iron instead of DW310 in modulating ring rotor is investigated.

Experimental Study of Compound-Structure Permanent-Magnet Synchronous Machine Used for HEVs

A compound-structure permanent-magnet synchronous machine (CS-PMSM) system used for hybrid electric vehicles (HEVs) enables the internal combustion engine (ICE) to operate at the optimum efficiency region independent of road conditions, thus decreasing emissions and fuel consumption. The key part CS-PMSM is a high integration of two electric machines. The connection ways of the CS-PMSM in the HEV system are discussed and the better connection way is selected based on power. Different topologies of the CS-PMSM are put forward and compared on criteria, such as magnetic coupling, power match, thermal properties, etc. A downsized axial-axial flux prototype machine was designed and manufactured for the testing facilities and concept validation. The performance, magnetic coupling, efficiency, and temperature of the axial-axial flux CS-PMSM prototype are measured and analyzed to provide a reference for this kind of machine.

Topology Comparison of Compound-Structure Permanent-Magnet Synchronous Machines

A compound-structure permanent-magnet synchronous machine (CS-PMSM) system is a hybrid-electric-vehicle power-train concept. Six typical topologies of CS-PMSMs are proposed. The characteristics of different CS-PMSMs are compared and evaluated from the aspects of torque density, manufacturability, heat-dissipating capability, and magnetic coupling. The selecting principle of different topologies is proposed for practical application.

Magnetic Decoupling Design and Experimental Validation of a Radial-Radial Flux Compound-Structure Permanent-Magnet Synchronous Machine for HEVs

The radial-radial flux compound-structure permanent-magnet synchronous machine (CS-PMSM), integrated by two concentrically arranged permanent-magnet electric machines, is an electromagnetic power-splitting device for hybrid electric vehicles (HEVs). As the two electric machines share a rotor as structural and magnetic common part, their magnetic paths are coupled, leading to possible mutual magnetic-field interference and complex control. In this paper, a design method to ensure magnetic decoupling with minimum yoke thickness of the common rotor is investigated. A prototype machine is designed based on the proposed method, and the feasibility of magnetic decoupling and independent control is validated by experimental tests of mutual influence. The CS-PMSM is tested by a designed driving cycle, and functions to act as starter motor, generator and to help the internal combustion engine (ICE) operate at optimum efficiency are validated.

Performance Analysis and Simulation of a Novel Brushless Double Rotor Machine for Power-Split HEV Applications

A new type of brushless double rotor machine (BDRM) is proposed in this paper. The BDRM is an important component in compound-structure permanent-magnet synchronous machine (CS-PMSM) systems, which are promising for power-split hybrid electric vehicle (HEV) applications. The BDRM can realize the speed adjustment between claw-pole rotor and permanent-magnet rotor without brushes and slip rings. The structural characteristics of the BDRM are described and its magnetic circuit model is built. Reactance parameters of the BDRM are deduced by an analytical method. It is found that the size characteristics of the BDRM are different from those of conventional machines. The new sizing and torque equations are analyzed and the theoretical results are used in the optimization process. Studies of the analytical magnetic circuit and finite element method (FEM) model show that the BDRM tends to have high leakage flux and low power factor, and then the method to obtain high power factor is discussed. Furthermore, a practical methodology of the BDRM design is developed, which includes an analytical tool, 2D field calculation and performance evaluation by 3D field calculation. Finally, different topologies of the BDRM are compared and an optimum prototype is designed.

Modeling and Control of a Flux-Modulated Compound-Structure Permanent-Magnet Synchronous Machine for Hybrid Electric Vehicles

The compound-structure permanent-magnet synchronous machine (CS-PMSM), comprising a double rotor machine (DRM) and a permanent-magnet (PM) motor, is a promising electronic-continuously variable transmission (e-CVT) concept for hybrid electric vehicles (HEVs). By CS-PMSM, independent speed and torque control of the vehicle engine is realized without a planetary gear unit. However, the slip rings and brushes of the conventional CS-PMSM are considered a major drawback for vehicle application. In this paper, a brushless flux-modulated CS-PMSM is investigated. The operating principle and basic working modes of the CS-PMSM are discussed. Mathematical models of the CS-PMSM system are given, and joint control of the two integrated machines is proposed. As one rotor of the DRM is mechanically connected with the rotor of the PM motor, special rotor position detection and torque allocation methods are required. Simulation is carried out by Matlab/Simulink, and the feasibility of the control system is proven. Considering the complexity of the controller, a single digital signal processor (DSP) is used to perform the interconnected control of dual machines instead of two separate ones, and a typical hardware implementation is proposed.

Optimization of an 80 kW Radial-Radial Flux Compound-Structure Permanent-Magnet Synchronous Machine Used for HEVs

Compound-structure permanent-magnet synchronous machine (CS-PMSM), which is composed of a stator machine (SM) and a double-rotor machine (DRM), is a new power-split concept for hybrid electric vehicles (HEVs). To compare the CS-PMSM system with Toyota Prius based on the planetary gear unit, an 80 kW radial-radial flux prototype machine is designed. Fractional slots are employed for SM and DRM and the slot openings and pole-arc embraces of the two machines are optimized to decrease torque fluctuation. As the outer rotor is the structural and magnetic common part of SM and DRM, the magnetic circuits of the two machines are coupled. To obtain the thinner outer rotor and to decrease magnetic saturation of the outer rotor during machine design, the influences of the thickness and pole-arc embraces of permanent magnets on magnetic coupling are investigated by finite-element method. The magnetic field in the outer rotor may reach saturation, due to the impact of armature reaction on the flux distribution in the outer rotor. Under the condition of armature reaction, the flux distribution and electromagnetic torque are analyzed.

Magnetic Characteristics Investigation of an Axial-Axial Flux Compound-Structure PMSM Used for HEVs

An axial-axial flux compound-structure permanent-magnet synchronous machine (CS-PMSM) system used for hybrid electric vehicles (HEVs) enables the internal combustion engine (ICE) to operate at optimum efficiency region independent of road conditions, thus decreasing the fuel consumption and emissions remarkably. The axial-axial flux CS-PMSM is a high-degree integration of two axial-flux PMSMs. The magnetic coupling problem of the CS-PMSM is investigated based on magnetic circuit and finite-element method (FEM). The influences of the magnet rotor structures on the magnetic coupling are evaluated. Halbach structure is used for the magnet rotor, which makes the design of CS-PMSM more flexible. Further, a prototype machine of the axial-axial flux CS-PMSM was designed and manufactured. The experimental results show that the magnetic coupling problem can be solved perfectly due to special structural design, which verifies the theoretical analysis.

Experimental Evaluation of a Radial-Radial-Flux Compound-Structure Permanent-Magnet Synchronous Machine Used for HEVs

A compound-structure permanent-magnet synchronous machine (CS-PMSM) system used for hybrid electric vehicles (HEVs) enables an internal combustion engine (ICE) to operate within optimum efficiency region independent of road conditions, thus decreasing the emissions and fuel consumption. In this paper a radial-radial-flux CS-PMSM is investigated. It integrates two synchronous machines radially, one is called double-rotor machine (DRM) and the other is called Stator Machine (SM). A downsized prototype machine of the CS-PMSM was designed and manufactured, and the tests were performed. The back electromotive force (BEMF) and efficiency of the DRM and SM are measured and analyzed, respectively. The BEMFs of both machines are approximately sinusoidal, which shows a good design of the magnetic structure. The two machines have efficiencies above 85% in a wide range in both motor and generator modes, but the peak efficiency is not well-content, which is analyzed by investigating the loss distribution. The temperatures of the DRM and SM are further measured, showing a good thermal behavior of the stator but serious overheat of the inner-rotor windings, which must be improved.

Evaluation of the magnetic coupling degree and performance of an axial-axial flux compound-structure permanent-magnet synchronous machine used for hybrid electric vehicles

A novel axial-axial flux compound-structure permanent-magnet synchronous machine (CS-PMSM), which is a hybrid electric vehicle (HEV) power train concept, is integrated by two axial flux disk machines. As the two machines share a common rotor [a magnet rotor with permanent magnets (PMs) on both sides], there may be magnetic coupling between them. Three-dimensional (3D) finite-element method (FEM) calculation shows that the two machines have little magnetic coupling if they have the same pole number and consistent magnetization direction of the two layers of PMs on the common rotor. The performance of the CS-PMSM is evaluated on criteria such as power, power per unit volume and mass, torque, and torque ripple. The power and torque equations of this type of machine are deduced and verified with 3D FEM. After the optimization of diameter ratio and pole number, the power and power per unit active volume and mass are high. The torque ripple is much reduced due to the optimization of the pole arc embrace and magnet skewing angle.

Evaluation of performance and magnetic characteristics of a radial-radial flux compound-structure permanent-magnet synchronous machine used for hybrid electric vehicle

A breed of compound-structure permanent-magnet synchronous machine (CS-PMSM) is used for power-split hybrid electric vehicles (HEVs). It can help to fulfill both the speed and torque control of the internal combustion engine and, thus, realize the optimum operation of the HEV. In this paper, a radial-radial flux CS-PMSM, which is integrated by two machines radially [one stator machine (SM) and one double-rotor machine (DRM)], is designed and investigated. The machine performance is evaluated with finite-element method (FEM) and satisfactory results are obtained. The back electromotive force curves of the two machines are somewhat similar to sinusoidal ones; the average torques both meet the requirements; and due to the adoption of skewed slots, the cogging torques and torque ripples are quite small. The inductance parameter is calculated with a phasor diagram based two-dimensional FEM and the magnetic saturation and cross-magnetization effect are discussed. It is concluded that the SM is slightly saturated with no or little cross-magnetization phenomenon, whereas the DRM has deep-degree magnetic saturation and the cross-magnetization effect is notable.