FIELD OF THE INVENTION

[001] The present invention relates to a single phase brushed generator and more particularly to a method and a system for starting the single phase brushed generator.

BACKGROUND OF INVENTION

[002] Single phase brushed generator is generally used to provide power supply in locations where utility electric supply from power grid is either temporarily, or permanently, not available. A typical single phase brushed generator is equipped with an Internal Combustion (IC) engine, and an alternator mounted on engine crankshaft. The alternator coupled to the crankshaft is used to generate electric power to provide alternating-current power to substitute utility supply when utility supply is not available.

[003] The alternator comprises of a rotor with a field winding, which can be excited by applying voltage to the field winding using contact between stationary brushes and rotating slip rings. The alternator also comprises a stator disposed with a main winding and a phase shifted auxiliary winding. The main winding provides electric power to external electric loads and is the primary output of the generator set. The auxiliary winding is typically connected to input of an Automatic Voltage Regulator (AVR) unit, and the output of the AVR unit is connected to field winding of rotor using contact between stationary brushes and rotating slip rings. The AVR unit, through the field winding, regulates voltage across the main winding when the generator is generating electric power.

[004] For starting the generator described hereinbefore, the IC engine needs to be rotated at sufficiently high speed before self-sustaining combustion process can commence. For this purpose, generators are equipped with an electric starter system. The electric starter system typically consists of a brushed DC motor powered by a battery, the motor being connected to crankshaft of generator set engine through a suitable power driving mechanism such as a gear train.

[005] Such a starting system results in significant wear and tear in starter motor resulting in reduced reliability of the starting system.

[006] Thus, there is a need in the art for a starting mechanism for a single phase brushed generator which addresses at least the aforementioned problems.

SUMMARY OF THE INVENTION

[007] In one aspect, the present invention is related to a method for starting a single phase brushed generator having an IC engine coupled with an alternator, the alternator having a field excitation winding disposed on a rotor, and a stator with a main winding and a phase shifted auxiliary winding. The method comprising the steps of receiving a start signal at an Electronic Control Unit (ECU) connected to the field excitation winding, the main winding and the auxiliary winding; determining, by the ECU, initial position of the rotor with respect to the main winding; applying a first voltage, by a voltage source connected to the ECU, to the field excitation winding; applying a second voltage and a third voltage, by the voltage source, to the main winding and the auxiliary winding respectively depending on the initial position of the rotor, such that magnetic field generated by the field excitation winding is out of phase with respect to magnetic field resulting from the main winding and the auxiliary winding whereby a torque is applied on the rotor causing the rotor to rotate; determining speed of rotation of the rotor by the ECU; determining whether speed of the rotor is above a threshold value; if speed of the rotor is below the threshold value, determining updated position of the rotor and varying the second voltage and the third voltage depending on the updated position of the rotor to maintain the magnetic field generated by the field excitation winding out of phase with respect to magnetic field resulting from the main winding and the auxiliary winding thereby increasing speed of rotation of the rotor; and if speed of the rotor is above the threshold value, removing the application of the first voltage, the second voltage and the third voltage.

[008] In an embodiment of the invention, the method includes the step of varying the first voltage if speed of the rotor is below the threshold value.

[009] In another embodiment of the invention, the first voltage, the second voltage and the third voltage are varied to maintain the magnetic field generated by the field excitation winding 90° out of phase with respect to the magnetic field resulting from the main winding and the auxiliary winding.

[0010] In another aspect, the present invention is directed to a system for starting a single phase brushed generator having an IC engine coupled with an alternator, the alternator having a field excitation winding disposed on a rotor, and a stator with a main winding and a phase shifted auxiliary winding. The system comprising: a voltage source; and an electronic control unit (ECU) connected to the voltage source and configured to apply a first voltage to the field excitation winding, a second voltage to the main winding and a third voltage to the auxiliary winding. The ECU is further configured to: receive a start signal; determine initial position of the rotor with respect to the main winding; apply the first voltage to the field excitation winding; apply the second voltage and the third voltage to the main winding and the auxiliary winding respectively depending on the initial position of the rotor, such that magnetic field generated by the field excitation winding is out of phase with respect to magnetic field resulting from the main winding and the auxiliary winding whereby a torque is applied on the rotor causing the rotor to rotate; determine speed of rotation of the rotor; determine whether speed of the rotor is above a threshold value; if speed of the rotor is below the threshold value, determine updated position of the rotor and vary the second voltage and the third voltage depending on the updated position of the rotor to maintain the magnetic field generated by the field excitation winding out of phase with respect to magnetic field resulting from the main winding and the auxiliary winding thereby increasing speed of rotation of the rotor; and if speed of the rotor is above the threshold value, remove the application of the first voltage, the second voltage and the third voltage.

[0011] In an embodiment of the invention, the electronic control unit includes a DC to DC converter for supplying the first voltage, the second voltage and the third voltage by the electronic control unit. [0012] In another embodiment of the invention, the electronic control unit comprises a processor; and a plurality of switches connected with the field excitation winding, the main winding and the auxiliary winding, the processor configured to control operation of the switches.

[0013] In a further embodiment of the invention, the voltage source is a DC battery.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.

Figure 1 shows a schematic representation of an alternator of a single phase brushed generator connected to an Electronic Control Unit (ECU) in accordance with an embodiment of the present invention.

Figure 2 shows a block diagram of the ECU and a schematic representation of the alternator connected to the ECU in accordance with an embodiment of the present invention.

Figure 3 illustrates power switches for connecting a field excitation winding or a main winding or an auxiliary winding of an alternator with a voltage source according to an embodiment of the invention. Figure 4 shows power switches for connecting an automatic voltage regulator with to a field excitation winding of an alternator according to an embodiment of the invention.

Figure 5 shows a method for starting a single phase brushed generator according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention relates to a method and a system for starting a single phase brushed generator.

[0016] As shown in Figure 1, the system has a voltage source 300 and an

Electronic Control Unit (ECU) 200 connected to the voltage source 300. In an embodiment of the invention, the voltage source 300 is a DC battery. The ECU 200 is connected to an alternator 100 of a single phase brushed generator (not shown). The single phase brushed generator has an IC engine (not shown) coupled with the alternator 100. The alternator 100 has a field excitation winding 110 disposed on a rotor, a stator with a main winding 130 and a phase shifted auxiliary winding 120. The field excitation winding 110, the main winding 130 and the auxiliary winding 120 are connected to the ECU 200.

[0017] As shown in Figure 2, the ECU 200 has a DC to DC converter 260 connected to the voltage source 300, a processor 210 and plurality of power switches 220, 230, 240, 250. The first power switch 220 is connected between the processor 210 and the field excitation winding 110 of the alternator 100. In this regard, the alternator 100 has slip rings 140 mounted on the rotor and rotates along with the rotor. Further, a plurality of brushes 150 are provided between slip rings 140 and supply lines from the first switch 220. Thus, the excitation winding 110 can be excited by a contact between the slip rings 140 and plurality of brushes 150 connected to the slip rings 140. The second power switch 230 is connected between the processor 210 and the main winding 130 of the alternator 100. The third power switch 240 is connected between the processor 210 and the phase shifted auxiliary winding 120 of the alternator 100. Further, the processor 210 may be configured to achieve functionalities of an Automatic Voltage Regulator (AVR). Accordingly, the fourth power switch 250 is connected between the processor 210 and the field excitation winding 110 of the alternator 100. In this regard, the power switch 250 is also connected to the auxiliary winding 120 to regulate the voltage being supplied to electrical loads 500 by the main winding 130.

[0018] In an embodiment of the invention, power switches 220, 230, 240 for field excitation winding 110, main winding 130, and auxiliary winding 120 can be realized by using MOSFET bridge or IGBT bridge as illustrated in Figure 3. The set of power switches 220, 230, 240 may also include an optional set of switches A, B to disconnect the set of power switches 220, 230, 240 from the respective winding being excited.

[0019] In another embodiment of the invention, the power switch 250 for AVR can be realized by using a Silicon Controlled Resistor (SCR) and diode bridge as illustrated in Figure 4. In an embodiment of the invention, the AVR can use power switches shown in Figure 3. Thus, the MOSFET or IGBT bridge shown in Figure 3 can be used to excite the field excitation winding 110 during starting of the generator and can be continued to be used for field excitation winding 110 during generation mode of the generator for regulating voltage across the main winding 130.

[0020] Further, as shown in Figure 1, the ECU 200 receives signal 400 from a set of sensors and switches, such as a position sensor to identify position of the rotor of the alternator 100 and a start switch to start the generator. The ECU 200 also drives the electrical loads 500 such as ignition coil and auto-choke solenoid.

[0021] According to an embodiment of the invention, the field excitation winding 110, the main winding 130 and the auxiliary winding 120 are supplied with necessary voltages to rotate the standing rotor when the generator is required to be started. The application of voltages are such that magnetic field generated by the field excitation winding 110 is out of phase with respect to magnetic field resulting from the main winding 130 and the auxiliary winding 120 whereby a torque is applied on the rotor causing the rotor to rotate. Accordingly, for optimal operation of the alternator 100, appropriate alternator winding terminals need to be connected to voltage source 300 based on rotor position alternator 100. In this regard, the ECU 200 is configured to apply a first voltage to the field excitation winding 110 through the first switch 220, a second voltage to the main winding 130 through the second switch 230 and a third voltage to the auxiliary winding

120 through the third switch 240. The first voltage, second voltage and third voltage required to start the generator are supplied by the DC to DC converter 260 to step-up or step-down the voltage received from the voltage source 300. In this regard, the DC to DC converter 260 is connected to the power switches 220, 230, 240 and selectively actuated by the processor 210 via DC bus link 260’ to provide a required voltage.

[0022] In operation, as shown in Figure 5, when a start signal 400 is received by the ECU 200 at step 610, the ECU 200 at step 620 determines initial position of the rotor with respect to the main winding 130 based on signal 400 received from the position sensor. Thereafter, at step 630, the ECU 200 actuates the first switch 220 to apply a first voltage to the field excitation winding 110. At step 640, the ECU 200 actuates the second 230 and the third switch 240 to apply a second voltage and a third voltage to the main winding 130 and the auxiliary winding 120 depending on the initial position of the rotor. In this regard, the second voltage and the third voltage are such that magnetic field generated by the field excitation winding 110 due to application of first voltage is out of phase with respect to magnetic field resulting from the main winding 130 and the auxiliary winding 120. As a result, a torque is applied on the rotor causing the rotor to rotate. At step

650, the ECU 200 determines speed of rotation of the rotor of based on signals 400 received from a speed sensor. At step 660, the ECU 200 determines whether speed of the rotor is above a threshold value. In an embodiment of the invention, the threshold value is predetermined on various factors. Typically, the predetermined threshold value of the speed of the rotor will be a value at which the generator starts and operation of the IC engine can be self-sustained thereafter. If speed of the rotor is below the threshold value, the ECU 200 at step 670, determines updated position of the rotor and vary the second voltage and the third voltage depending on the updated position of the rotor to maintain the magnetic field generated by the field excitation winding 110 out of phase with respect to magnetic field resulting from the main winding 110 and the auxiliary winding 120 thereby increasing the speed of rotation of the rotor. In an embodiment of the invention, if speed of rotor is below the threshold value, step 670 also includes the step of varying the first voltage. In a further embodiment of the invention, at step 670, the first voltage, the second voltage, and the third voltage are varied to maintain the magnetic field generated by the field excitation winding 110 90° out of phase with respect to magnetic field resulting from the main winding 130 and the auxiliary winding 120. If speed of the rotor is above the threshold value, the ECU at step 680, removes the application of the first voltage, the second voltage and the third voltage. At this stage, the generator enters into power generation mode providing power to electrical loads, while the AVR regulates output across main winding 130.

[0023] Advantageously, the present invention eliminates requirement of a starter motor which is typically required for starting a single phase brushed generator. The invention thus results in efficient usage of electrical machines already present in generator and reduces redundancy.

[0024] While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.