System and method to control energy supply to an electrically heated zone

Control system to control supply of electrical energy from a supply battery source (U.sub.Batt) to an electrical heater (11) having

• a controlled switch (10) serially connected between the heater and the supply voltage source, and
• means (15, 30) connected to the controlled switch and controlling periodic switching of the controlled switch between closed (ON) and open (OFF) position, comprising
• means for controlling the periodic switching cycle of the controlled switch as a function of voltage across the electrical heater (11) required to maintain the heater at a predetermined temperature, said means being responsive to the supply source voltage level and varying the periodic switching of the controlled switch to maintain the average voltage across said electrical heater at the level required to maintain the heater at said predetermined temperature,
• said means to maintain the voltage across the heater at a predetermined level (U.sub.KEM) to maintain the heater at said predetermined temperature comprising
• means (30) for providing a predetermined reference signal representative of said voltage across the electrical heater (11) required to maintain the heater at said predetermined temperature;
• and comparator means (20, 21, 22, 23) receiving said reference signal and a signal representative of the voltage of the supply battery source (U.sub.Batt) and providing an output control signal to said switch control means (15, 30), said comparator comparing the respective input signals thereto and said output control signal controlling the controlled switch for switching operation between closed and open position in dependence on equality or non-equality of the predetermined reference signal and the signal representative of the supply source voltage (U.sub.Batt) to provide to said heater (11) an average heater supply voltage (U.sub.KEM) which will maintain said heater at said predetermined temperature.

Method of controlling the supply of electrical energy from a supply voltage source (U.sub.Batt) to an electrical heater (11) having

• a controlled switch (10) serially connected between the heater and the supply voltage source (U.sub.Batt), and
• means (15, 30) connected to and controlling the controlled switch (10) for periodically switching the controlled switch between closed (ON) and open (OFF) position,
• comprising the steps of
• determining the average supply voltage (U.sub.KEM) required to maintain the heater at a predetermined temperature;
• providing said supply source voltage at a level at least as high as said average supply voltage;
• and
• controlling the periodic switching cycle of the controlled switch as a function of the required average supply voltage (U.sub.KEM), said controlling step including
• controlling the periodic switching cycle of the controlled switch (10) approximately in accordance with the relationship:
• ##EQU2## wherein U.sub.KEM is the average supply voltage required to maintain the heater at the predetermined temperature;
• U.sub.Batt is the voltage level of the supply source voltage;
• t.sub.ON is the time duration of closed position of said controlled switch (10);
• and
• t.sub.C is the duration of the overall cycle or period of switching of the controlled switch, including the time interval of closed and open position thereof.

Control system to control supply of electrical energy from a supply battery source (U.sub.Batt) to an electrical heater (11) having

• a controlled switch (10) serially connected between the heater and the supply voltage source, and
• means (15, 30) connected to the controlled switch and controlling periodic switching of the controlled switch between closed (ON) and open (OFF) position, comprising
• means for controlling the periodic switching cycle of the controlled switch as a function of voltage across the electrical heater (11) required to maintain the heater at a predetermined temperature, said means being responsive to the supply source voltage level and varying the periodic switching of the controlled switch to maintain the average voltage across said electrical heater at the level required to maintain the heater at said predetermined temperature,
• said means to maintain the voltage across the heater at a predetermined level (U.sub.KEM) to maintain the heater at said predetermined temperature comprising
• an operational amplifier (15);
• a pulse generator (30) providing periodically rising and dropping output signals to the operational amplifier in accordance with a predetermined repetition frequency;
• and means (20, 21, 22, 23) connected to a second input of the operational amplifier and providing a voltage thereto representative of said supply source voltage (U.sub.Batt), said operational amplifier being connected to compare the respective inputs thereto and control the controlled switch for switching operation between closed and open position in dependence on equality of the voltage signal derived from the pulse generator (30) and voltage representative of the supply source voltage (U.sub.Batt).