Series Configuration

28.2.4.1 Series Configuration

In the conventional series hybrid systems shown in Fig. 28.28, when the PV power exceeds the load demand and the batter- all power generators feed DC power into a battery. Each com- ies are fully charged. It may include MPPT to improve the ponent has therefore to be equipped with an individual charge utilization of the available PV energy, although the energy controller and in the case of a diesel generator with a rectifier. gain is marginal for a well-sized system. The system can be

To ensure reliable operation of series hybrid energy systems operated in manual or automatic mode, with the addition of both the diesel generator and the inverter have to be sized appropriate battery voltage sensing and start/stop control of to meet peak loads. This results in a typical system opera- the engine-driven generator.

tion where a large fraction of the generated energy is passed Advantages:

through the battery bank, therefore resulting in increased cycling of the battery bank and reduced system efficiency. AC

• The engine-driven generator can be sized to be optimally power delivered to the load is converted from DC to regulated

loaded while supplying the load and charging the battery AC by an inverter or a motor generator unit. The power gener-

bank, until a battery SOC of 70–80% is reached. ated by the diesel generator is first rectified and subsequently

• No switching of AC power between the different energy converted back to AC before being supplied to the load, which

sources is required, which simplifies the electrical output incurs significant conversion losses.

interface.

The actual load demand determines the amount of electrical • The power supplied to the load is not interrupted when power delivered by the PV array, wind generator, the battery

the diesel generator is started.

bank, or the diesel generator. The solar and wind charger pre- • The inverter can generate a sine-wave, modified square- vents overcharging of the battery bank from the PV generator

wave, or square-wave depending on the application.

28 Power Electronics for Renewable Energy Sources 737

Disadvantages:

Advantages:

• The inverter cannot operate in parallel with the engine- • The inverter can generate a sine-wave, modified square- driven generator, therefore the inverter must be sized to

wave, or square-wave, depending on the particular supply the peak load of the system.

application.

• The battery bank is cycled frequently, which shortens its • The diesel generator can supply the load directly, there- lifetime.

fore improving the system efficiency and reducing the • The cycling profile requires a large battery bank to

fuel consumption.

limit the depth-of-discharge (DOD).

Disadvantages:

• The overall system efficiency is low, since the diesel cannot supply power directly to the load.

• Power to the load is interrupted momentarily when the • Inverter failure results in complete loss of power to the

AC power sources are transferred. load, unless the load can be supplied directly from the

• The engine-driven alternator and inverter are typically diesel generator for emergency purposes.

designed to supply the peak load, which reduces their efficiency at part load operation.