Vacuum cleaner

1. A vacuum cleaner comprising:

a suction source comprising an impeller and a first motor for driving the impeller;

a cleaner head comprising an agitator and a second motor for driving the agitator;

a controller configured to generate control signals for controlling simultaneously the excitation of the first motor and the second motor; and

a voltage sensor that provides the controller with a measure of the magnitude of a supply voltage used to excite the first motor and the second motor,

wherein the first motor is a brushless motor and the second motor is a brushed motor, and the controller generates the controls signals such that the output power of the first motor is constant and the input voltage to the second motor is constant in response to changes in the supply voltage.

2. The vacuum cleaner of claim 1 , wherein the cleaner head is interchangeable with a further cleaner head, the further cleaner head comprises a further agitator and a third motor for driving the further agitator, the third motor is a brushed motor, and the controller is configured to generate control signals for controlling simultaneously the excitation of the first motor and the third motor.

3. The vacuum cleaner of claim 1 , wherein the controller generates at least one first control signal for controlling the excitation of the first motor and at least one second control signal for controlling the excitation of the second motor, the first control signal causes a winding of the first motor to be excited for a conduction period over an electrical half-cycle of the first motor, the second control signal is a PWM signal having a constant period, and the controller adjusts the conduction period and the duty cycle of the PWM signal in response to changes in a supply voltage used to excite the first motor and the second motor.

4. The vacuum cleaner of claim 3 , wherein the controller increases the conduction period and increases the duty cycle of the PWM signal in response to a decrease in the supply voltage.

5. The vacuum cleaner of claim 1 , wherein the vacuum cleaner comprises a battery pack that provides a supply voltage, and the first motor and the second motor are excited using the supply voltage.

6. The vacuum cleaner of claim 1 , wherein the first motor is a single-phase permanent-magnet motor.

7. A vacuum cleaner comprising:

a suction source comprising an impeller and a first motor for driving the impeller;

a cleaner head comprising an agitator and a second motor for driving the agitator; and

a controller configured to generate control signals for controlling simultaneously the excitation of the first motor and the second motor,

wherein the controller generates at least one first control signal for controlling the excitation of the first motor and at least one second control signal for controlling the excitation of the second motor, the first control signal causes a winding of the first motor to be excited for a conduction period over an electrical half-cycle of the first motor, the second control signal is a PWM signal having a constant period, and the controller adjusts the conduction period and the duty cycle of the PWM signal in response to changes in a supply voltage used to excite the first motor and the second motor.

8. The vacuum cleaner of claim 7 , wherein the controller increases the conduction period and increases the duty cycle of the PWM signal in response to a decrease in the supply voltage.

9. The vacuum cleaner of claim 7 , wherein the vacuum cleaner comprises a battery pack that provides the supply voltage.

10. The vacuum cleaner of claim 7 , wherein the first motor is a single-phase permanent-magnet motor.