Background The compensated pulsed alternator (CPA) is a pulsed power source that integrates rotor inertial energy storage, electromechanical energy conversion and power regulation. It connects the prime mover and the electromagnetic launch load directly as a “unit component”, reducing many intermediate links. It has the advantages of high output voltage, high power density, high frequency of repetition and long service life, and is regarded as the most promising pulsed power source for electromagnetic launch systems.

Purpose The air-core CPA (ACCPA) overcomes the limitations of ferromagnetic material saturation on magnetic field strength and rotational speed, significantly improving the motor’s energy storage density and power density. The Halbach permanent magnet array (HPMA) possesses a magnetic shielding, eliminating the need for a rotor core while generating an air-gap magnetic flux density (AGMFD) waveform with good sinusoidal characteristics. Therefore, this paper investigates the application of a double-layer HPMA rotor, which is simple in structure, strong in integrity, and easy to optimize, in the topological structure of ACCPA.

Methods Without considering magnetic saturation, an analytical calculation model for the no-load electromagnetic field in an ACCPA was established using the subdomain model method in polar coordinates. Starting from the basic theory of electromagnetic fields, this method used the vector magnetic potential method to establish Laplace’s equations (for no- curl fields) or Poisson’s equations (for curl fields) for four subdomains respectively. By combining the boundary conditions between adjacent subdomains, the equations were solved jointly to obtain the mathematical expression for the no-load AGMFD of the motor, and the distribution of the no-load AGMFD was analyzed.

Results This analytical model could directly reflect the relationship between the no-load AGMFD distribution of the motor and its design parameters. The analytical model’s calculation results were highly consistent with the results of finite element analysis, verifying the accuracy of the analytical model. Its calculation results could relatively accurately reflect the static and steady-state performance of the motor.

Conclusions The relationship between the four main parameters of the motor and the amplitude and sinusoidal characteristics of the radial and tangential components of the no-load AGMFD is studied, which can provide technical support for the subsequent optimization of the motor’s no-load air-gap magnetic field and further calculation design.