Regenerative drive

A method of operating a regenerative elevator drive arranged to receive power from an external power supply, the method comprising:

• receiving at an input of an inverter a DC voltage, derived from the external power supply;
• converting the DC voltage to an AC voltage for output to an external motor;
• directing regenerative energy to the external power supply, wherein excess regenerative energy is directed through a dynamic braking resistor;
• operating a circuit breaker unit in a first state which provides a connection between the inverter and the external power supply;
• and
• operating the circuit breaker unit in a second state which disconnects the inverter from the external power supply, wherein the circuit breaker unit is arranged such that the circuit breaker unit provides a discharge path from the DC link capacitor via the dynamic braking resistor only in the second state.

A regenerative elevator drive arranged to receive power from a battery, the regenerative elevator drive comprising:

• an inverter arranged to receive at an input thereof a DC voltage, derived from a DC voltage produced by the battery, and to convert the DC voltage to an AC voltage for output to an external motor;
• and
• a dynamic braking resistor;
• wherein the regenerative elevator drive is arranged to direct regenerative energy to the battery, said regenerative elevator drive being further arranged to direct excess regenerative energy through said dynamic braking resistor;
• and
• the regenerative elevator drive being arranged such that:
• in a first diagnostic step, a first measurement of the DC voltage produced by the battery is measured while no current is supplied by the battery;
• in a second diagnostic step, a second measurement of the DC voltage produced by the battery is measured while a current supplied by the battery is passed through the dynamic braking resistor;
• wherein an internal resistance of the battery is determined from a ratio between a voltage difference and the current supplied by the battery in the second diagnostic step, said voltage difference being the difference between the first and second measurements of the DC voltage produced by the battery.

A method of operating a regenerative elevator drive arranged to receive power from a battery, the method comprising:

• receiving at an input of an inverter a DC voltage, derived from the battery;
• converting the DC voltage to an AC voltage for output to the motor;
• directing regenerative energy to the battery, wherein excess regenerative energy is directed through a dynamic braking resistor;
• in a first diagnostic step, taking a first measurement of the DC voltage produced by the battery while no current is supplied by the battery;
• in a second diagnostic step, taking a second measurement of the DC voltage produced by the battery while a current supplied by the battery is passed through the dynamic braking resistor;
• and
• determining an internal resistance of the battery from a ratio between a voltage difference and the current supplied by the battery in the second diagnostic step, said voltage difference being the difference between the first and second measurements of the DC voltage produced by the battery.