Off-grid power generating apparatus and frequency and voltage control method thereof

A control method of an off-grid power generating apparatus for powering an electrical load, the apparatus including an engine and an alternator that includes a stator with a single phase winding configured to generate an induced voltage and a rotor with a plurality of symmetric phase windings, wherein the rotor is coaxially coupled to the engine, and the single phase winding of the stator is configured to be connected to the electrical load and the phase windings of the rotor respectively and provide an output voltage to the electrical load and an excitation voltage to the phase windings of the rotor, the method comprising:

• measuring an amplitude of the output voltage provided to the electrical load;
• measuring an amplitude of an alternating current provided to the electrical load;
• measuring a rotation speed of the rotor or the engine;
• calculating a load power of the electrical load at least in accordance with the measured amplitudes of the output voltage and the alternating current;
• determining a desired rotation speed of the engine at least in accordance with the calculated load power;
• modulating the speed of the engine at least in accordance with the desired rotation speed of the engine;
• determining a slip angle at least in accordance with the measured rotation speed of the rotor or the engine and the synchronous speed of the alternator;
• determining a target voltage of the rotor at least in accordance with the amplitude of the measured output voltage;
• generating a modulating signal at least in accordance with the target voltage of the rotor and the slip angle;
• and
• modulating a frequency and an amplitude of an excitation current in the phase windings of the rotor with the modulating signal.

An off-grid portable generator set for powering an electrical load, comprising:

• an engine;
• an induction alternator including:
• a rotor coaxially coupled to the engine, the rotor including a plurality of symmetric phase windings;
• a stator with a single phase winding configured to generate an induced voltage, the single phase winding being configured to be connected with the electrical load and the phase windings of the rotor respectively and provide an output voltage to the electrical load and an excitation voltage to the phase windings of the rotor;
• a voltage sensor configured to measure an amplitude of the output voltage;
• a current sensor configured to measure an amplitude of an alternating current applied by the single phase winding to the electrical load;
• and
• a speed sensor configured to measure a rotation speed of the rotor or the engine;
• and
• an excitation control device operatively connected to the engine and the alternator, wherein the excitation control device is configured to control the induced voltage generated in the single phase winding of the stator by regulating the rotating magnetic field generated in the phase windings of the rotor;
• the excitation control device includes:
• a first calculating element configured to calculate a load power of the electrical load at least in accordance with the measured amplitudes of the output voltage and the alternating current, and determine a desired rotation speed of the engine at least in accordance with the calculated load power;
• a first modulating element configured to modulate the speed of the engine at least in accordance with the desired rotation speed of the engine;
• a second calculating element configured to determine a slip angle at least in accordance with the rotation speed of the rotor or the engine measured by the speed sensor;
• a third calculating element configured to determine a target voltage of the rotor at least in accordance with the amplitude of the output voltage measured by the voltage sensor;
• and
• a second modulating element configured to generate a modulating signal at least in accordance with the target voltage of the rotor and the slip angle, and modulate a frequency and an amplitude of an excitation current in the phase windings of the rotor with the modulating signal.