Measurement of energy by means of a frequency converter

1. A method for the measurement of energy in an alternating-current motor drive containing a frequency converter provided with semiconductor switches,

comprising the steps of:

determining in the frequency converter, the power taken by the motor drive from the mains,

determining the energy taken from the supply mains, based on the power taken by the motor drive from the mains, especially the accumulated energy consumption after a given instant; and

wherein in the power taken from the mains is determined on the basis of measured load power.

2. A method according to claim 1 , further comprising:

determining the power taken from the supply mains on the basis of measured load power by performing a series of calibration measurements with different loads, measuring the ratio (k) between the power (Pv) taken from the mains as measured by external measuring devices and the load power (Pm) indicated by the regulator, which ratio (k) is then specified as a correction factor

the power taken from the supply mains being thus

Pv=k×Pm.   (4)

3. A method according to claim 1 or 2 ,

wherein the energy measurement determines the consumption difference as compared to a reference situation, e.g. a situation where the rotational speed of an electric motor is not regulated.

4. A method according to claim 1 or 2 ,

wherein, to measure energy savings, the motor drive fed by a frequency converter is at first operated at constant speed to measure a reference consumption, and

next the motor drive is operated under rotational speed regulation, with its internal energy measurement calculating the consumption difference directly as compared to constant-speed regulation.

5. A system for the measurement of energy in an alternating-current motor drive comprising:

a frequency converter provided with semiconductor switches and a control unit,

the control unit measuring the power taken by the motor drive from the mains,

the control unit determining the energy taken from the supply mains, based on the power taken by the motor drive from the mains, especially the accumulated energy consumption after a given instant; and

wherein the power taken from the mains is determined on basis of measured load power.

6. A system according to claim 5 , further comprising:

output current and voltage measuring elements (IU, IV, IW) for the measurement of load power taken by the motor drive,

wherein the control unit determines the power taken from the supply mains on the basis of a series of calibration measurements performed with different loads, in which measurement series the ratio (k) between the power (Pv) taken from the mains as measured by external measuring devices and the load power (Pm) indicated by the regulator, which ratio (k) is specified as a correction factor, the power taken from the supply mains being

Pv=k×Pm.   (4)