Electric working machine

An electric working machine including a brushless motor as a power source, the machine comprising:

• an inverter including:
• switching elements separately disposed in conduction paths between a direct-current power source and terminals of the brushless motor, the inverter being configured to control electric conduction to windings of the brushless motor and a direction of the electric conduction via the switching elements;
• a current detector configured to detect an electric current flowing through the brushless motor;
• and
• a controller configured to:
• perform a PWM control of a conduction current to the windings by switching switching patterns to conduct electricity to the windings via the inverter for every given commutation timing of the brushless motor and by turning on and off the switching elements of the inverter in accordance with the switching patterns, the switching patterns including different on and off states for each of the switching elements;
• sequentially switch a switching pattern for controlling on and off states of the switching elements to one of the switching patterns synchronously with a period of the PWM control, and detect a rotational position of the brushless motor from a magnitude relation between inductances of the brushless motor, which are produced in different current paths by switching the switching pattern, thereby to set the given commutation timing;
• obtain a current value detected in the current detector when electricity is conducted to the brushless motor with each of the switching patterns as a parameter representing an inductance of the brushless motor, and detect the rotational position from a magnitude relation between the obtained current values;
• and
• obtain a difference between a conduction-start current at an initiation of conduction and a conduction-stop current at an end of the conduction as a parameter representing an inductance value of the brushless motor when electricity is conducted to the brushless motor with the switching pattern.

An electric working machine including a brushless motor as a power source, the machine comprising:

• an inverter including:
• switching elements separately disposed in conduction paths between a direct-current power source and terminals of the brushless motor, the switching elements including six transistors (Q1, Q2, Q3, Q4, Q5, and Q6);
• Q1 being on a high side of a U-phase node and is controlled by a first signal (UH);
• Q2 being on a high side of a V-phase node and is controlled by a second signal (VH);
• Q3 being on a high side of a W-phase node and is controlled by a third signal (WH);
• Q4 being on a low side of the U-phase node and is controlled by a fourth signal (UL);
• Q5 being on a low side of the V-phase node and is controlled by a fifth signal (VL);
• and
• Q6 being on a low side of the W-phase node and is controlled by a sixth signal (WL),
• the inverter being configured to control electric conduction to windings of the brushless motor and a direction of the electric conduction via the switching elements;
• and
• a controller configured to:
• perform a PWM control of a conduction current to the windings by switching switching patterns to conduct electricity to the windings via the inverter for every given commutation timing of the brushless motor and by turning on and off the switching elements of the inverter in accordance with the switching patterns, the switching patterns including different on and off states for each of the switching elements;
• and
• sequentially switch a switching pattern for controlling on and off states of the switching elements to one of the switching patterns synchronously with a period of the PWM control, and detect a rotational position of the brushless motor from a magnitude relation between inductances of the brushless motor, which are produced in different current paths by switching the switching pattern, thereby to set the given commutation timing,
• wherein the switching patterns are each configured to generate a rotational torque on a rotor of the brushless motor when the on and off states of the switching elements are controlled with the switching patterns in order to detect the rotational position of the brushless motor,
• a first switching pattern is UL=on, VH=on, WL=on, UH=off, VL=off, and WH=off when a rotor position is between 0 and 60 degrees, and a rotational direction is positive, and
• a second switching pattern is UL=on, VH=on, WH=on, UH=off, VL=off, and WL=off when the rotor position is between 0 and 60 degrees, and the rotational direction is positive.