Standby power supply with load-current harmonics neutralizer

A standby power supply system comprising:

• a single inverter having an AC side and a DC side, with the AC side for coupling in parallel with a load normally powered by an AC source, the inverter supplying emergency AC power to said load during failure of the AC source, with the load drawing a load current having harmonic distortion;
• a back-up power source coupled to the DC side of the inverter;
• a harmonic distortion sensor for sensing the load current harmonic distortion during normal operating conditions, said harmonic distortion sensor including
• a load current sensor for sensing the load current including the harmonic distortion to produce, a load current source signal comprising a line current component and a harmonic distortion current component;
• and
• an inverter current sensor for sensing the AC current produced by the inverter;
• and
• a controller responsive to the load current sensor and the inverter current sensor, said controller including a line frequency notch filter which receives the load current sensor signal and removes the line current component therefrom to produce a distortion signal, causing the inverter to produce a harmonic neutralizing current to substantially neutralize the harmonic distortion and isolate the harmonic distortion from the AC source to draw only sinusoidal current therefrom.

A standby power supply system comprising:

• a single inverter having an AC side and a DC side, with the AC side for coupling in parallel with a load normally powered by an AC source, the inverter supplying emergency AC power to the load during failure of the AC source, with the load drawing a load current having harmonic distortion;
• a back-up power source coupled to the DC side of the inverter;
• a harmonic distortion sensor for sensing the load current harmonic distortion during normal operating conditions;
• and
• a controller producing an inverter control signal responsive to the harmonic distortion sensor for causing the inverter to produce a harmonics neutralizing current to substantially neutralize the harmonic distortion and isolate the harmonic distortion from the AC source to draw only sinusoidal current therefrom;
• wherein the inverter comprises a bridge type inverter having four legs with each leg having a switching device in parallel with a diode, with each switching device being responsive to the inverter control signal to neutralize the harmonic distortion and charge the back-up power source during normal operating conditions, and generate the emergency AC power for the load.

A method to claim 22 wherein of supplying AC power to a load during normal and emergency operating conditions, the method comprising the steps of:

• coupling a standby power supply system in parallel with the load and an AC source, the system including:
• a power conversion device having an AC side and a DC side, with the AC side in parallel with the AC source and the load, the power conversion device responsive to a control signal;
• a back-up power source coupled to the DC side of the power conversion device;
• a harmonic distortion sensor;
• and
• a controller;
• during normal operating conditions:
• powering the load with the AC source, with the load drawing a load current having harmonic distortion;
• charging the battery bank with a charging current produced by the power conversion device;
• sensing the harmonic distortion with the harmonic distortion sensor;
• controlling the power conversion device with the controller in response to the harmonic distortion sensor, said controlling step including the steps of:
• producing a distortion signal corresponding to the harmonics harmonic distortion and a charging current signal corresponding to the charging current;
• and
• producing a reference signal corresponding to a desired power conversion device current by removing the charging current signal from the distortion signal;
• sensing the power conversion device current and producing a conversion current sensor signal in response thereto;
• and
• producing an error signal by removing the conversion current sensor signal from the reference signal;
• and
• isolating the harmonic distortion from the AC source to draw only sinusoidal current therefrom by producing an AC harmonics neutralizing current with the power conversion device in response to the controller;
• during emergency operating conditions:
• isolating the standby power supply system and the load from the AC source when the AC power source voltage collapses below a predetermined acceptable value;
• controlling the power conversion device with the controller;
• and
• inverting back-up power from the back-up power source with the power conversion device in response to the controller to supply emergency AC power to the load.

A standby power supply system comprising:

• a single converter having an AC side and a DC side, with the AC side for coupling in parallel with a load normally powered by an AC source, the converter supplying emergency AC power to the load during failure of the AC source, with the load drawing a load current having harmonic distortion;
• a back-up power source coupled to the DC side of the converter;
• a harmonic distortion sensor for sensing the load current harmonic distortion during normal operating conditions, said harmonic distortion sensor including
• a converter current sensor for sensing AC current produced by the converter, and
• a load current sensor for sensing the load current drawn by the load;
• a controller responsive to the harmonic distortion sensor for causing the converter to produce a harmonics neutralizing current to substantially neutralize the load current harmonic distortion and isolate the harmonic distortion from the AC source to draw only sinusoidal current therefrom;
• a first isolation transformer located between the AC source and the converter;
• a second isolation transformer located between the converter and the converter current sensor;
• and
• a third isolation transformer located between the load current sensor and the load.

A standby power supply system comprising:

• a single converter having an AC side and a DC side, with the AC side for coupling in parallel with a load normally powered by an AC source, the converter supplying emergency AC power to the load during failure of the AC source, with the load drawing a load current having harmonic distortion;
• a back-up power source coupled to the DC side of the converter, wherein the back-up power source comprises a battery bank that receives a charging current from the converter for charging the battery bank during normal operating conditions;
• a harmonic distortion sensor for sensing the load current harmonic distortion during normal operating conditions;
• and
• a controller responsive to the harmonic distortion sensor for causing the converter to produce a harmonics neutralizing current to substantially neutralize the load current harmonic distortion and isolate the harmonic distortion from the AC source to draw only sinusoidal current therefrom.