Design of Single and Three Phase Gasoline Generator Sets

At present, it is common for instruments and equipment in our military equipment to use a combination of single-phase and three-phase electricity. Ordinary single-phase or three-phase AC generator sets cannot meet the needs well, and a single camera set cannot provide power to three-phase equipment. The single-phase load capacity of three-phase units is poor, and in the case of large three-phase load imbalance, the three-phase voltage is also extremely unbalanced, seriously threatening the safe use of electrical equipment and generator sets. In order to meet the special needs of the military, we have designed single and three-phase gasoline generators equipped with gasoline generator sets, which meet the requirements of mixed use of single and three-phase in the military and minimize the imbalance of three-phase voltage, so that all electrical appliances can be used safely and reliably. Below is an introduction to the design of various performance indicators for the 8kW single and three-phase generator sets that have passed technical appraisal.

The working principle is based on the special needs of single and three-phase AC synchronous generators. We adopt a high-performance and structurally simple reactance shunt excitation method, as shown in the electrical schematic.

Electrical schematic diagram of single-phase and three-phase AC synchronous generator. The generator stator is embedded with a set of main winding and a set of auxiliary winding. The main winding outputs three-phase AC energy and single-phase AC energy. The tail end of each phase winding is connected to the middle tap M of the three-phase shunt reactor, and the head end is the output end. The head end of the auxiliary winding is connected to one end d of each phase of the reactor, and the tail end is connected to the three-phase rectifier bridge. The other end d2 of each phase winding of the reactor is connected together as the midpoint and synchronizes outward. When the speed reaches the rated value, due to residual magnetism in the rotor, a voltage is induced in the auxiliary winding, and an excitation current of 4 (voltage component) is provided to the rotor excitation winding to enhance the magnetic flux. This continues. Going down, the motor can self excite and quickly establish no-load voltage. When loaded, relying on the load current diversion of the reactor, a portion of the current becomes the excitation current//i (current component) that is diverted to the excitation winding, compensating for the demagnetization and voltage drop effects of the generator load, so that the rotor excitation current automatically adjusts with the change of the load, achieving the effect of constant terminal voltage.

The design calculation of single and three-phase AC synchronous generators is the same as that of flexible AC synchronous generators, but attention should be paid to the coordination of single and three-phase parameters and the balance of performance indicators. Therefore, the following points need to be noted.

Due to the fact that this motor is mainly used in conjunction with a shelter, there are strict requirements for its volume, weight, and other indicators. Therefore, the stator winding design of the motor must be arranged reasonably, in a limited space, to maximize the motor output. At the same time, the mutual inductance coefficient between the phases is small to reduce the three-phase voltage imbalance during operation. The simplest and most direct method is to design both single-phase and three-phase windings as independent sets of windings, but this will inevitably increase the size and weight of the motor, and the operation during operation is also more complicated, and it is impossible to achieve mixed use of single-phase and three-phase.

The ideal solution is to design a single-phase winding with the same output power for one phase based on a three-phase generator, allowing that phase to withstand single-phase loads. This not only saves materials but also matches the actual usage situation.

Option 1: See for generator winding system. The stator coil is equipped with two sets of local phase windings, one set connected as a three-phase winding, and the other set connected in series as the phase with fewer turns in the single-phase and three-phase windings.

This is a conventional winding arrangement. After trial production and related tests, two shortcomings were found. Firstly, due to the fact that some coils in the single-phase winding are in phase with the other two phases in space, the mutual inductance coefficient between phases is high during motor operation; Secondly, the wire embedding process is complex, with some slots embedded with four types of windings. Table 1 indicates the number of turns on the primary side of U phase, V phase, and W phase, 584858, and the number of turns on the negative side, 196153196. Table 2 shows the measured standard for excellent electrical/mechanical steady-state consistency three cups. Scheme 2: See the generator winding system. The stator coil is equipped with only one set of three-phase windings, with one phase winding having twice the number of windings as the other two phases, serving as a single-phase winding. In this way, the winding arrangement is relatively neat and regular. Due to the fact that the single-phase winding and the other two phases are in phase in space, the mutual inductance coefficient between phases is small. When the generator operates in an unbalanced state, the three-phase voltage imbalance is reduced. Except for a large number of windings in one phase, the winding is completely the same as that of a three-phase AC synchronous generator. The wire embedding process is simple and the insulation is easy to handle. Compared with scheme 1, it can save about 15% of copper material and reduce the slot filling rate of some slots by about 10%. The scheme has been verified to be ideal through experiments.

This generator adopts the reactance shunt excitation method, which has a simple structure and excellent performance. However, the bridge group rectification coefficient and armature reaction are different during single-phase and three-phase operation of the motor, such as completely following.

Three-phase design results in insufficient excitation power during single-phase operation. If fully designed as a single-phase system, when the three-phase system is waiting to operate, if the resistance load voltage is too high, coordinated balancing measures must be taken. The method we adopt is to design the reactor as an unbalanced reactor, with the winding parameters on both sides of the reactor designed as a three-phase motor and the middle phase winding designed as a single-phase motor. This not only meets the requirements of single and three-phase generators but also reduces the voltage imbalance during unbalanced operation of the motor. The specific data is shown in Table 1. In order to enhance the adaptability of the motor process, improve the voltage regulation accuracy of the motor, and reduce the voltage deviation in cold and hot states, we have added an automatic voltage regulator to the excitation system. As this motor requires single and three-phase operation, the measurement signal can only take single-phase phase voltage, which has a high content of harmonics (including subharmonics), especially during single-phase operation, resulting in low voltage regulation accuracy of the regulator, generally only reaching 7% to 10%, which cannot meet the technical requirements. Therefore, compensation devices must be added. However, due to the significant changes in current during single and three-phase operation, using load current as a feedback signal is not suitable. Only motor excitation voltage can be used as a feedback signal. In the measurement circuit of the single-phase voltage regulator, we have added a feedback signal reflecting the magnitude of the excitation voltage, which is isolated by optocouplers and meets the requirements. The specific circuit is shown in.

The prototype has undergone tests in cold and hot regions, reliability, and military use, and has been tested by the National Internal Combustion Engine Power Station Quality Inspection Center. All performance indicators have met the design requirements. Specific indicators and quality grades are shown in Table 2. Single and three-phase gasoline generator sets can output single and three-phase AC power separately or simultaneously. The mixed use of single and three-phase electrical equipment not only exists in the military but also in civilian places such as construction sites. Its successful development has filled a gap in China and has wide promotion value. Currently, it has been matched with more than 500 engineering vehicles and other products. Its unique functions greatly meet the needs of military use and are highly welcomed by the troops.