Up until now, no suitably sophisticated hardware has been available that enables generators in commercial vehicles, agricultural and construction machinery as well as other vehicles with internal 24-V on-board electrical systems to be operated at maximum efficiency. To address this, EBV Elektronik collaborated with STMicroelectronics to develop the Epona generator regulator as part of the EBVchips line.
Designed for vehicles with 24-V on-board electrical systems, the component is also suitable for use in 12-V on-board electrical systems in passenger cars. Although a number of application-specific standard products (ASSPs) are already available for regulating generators, each individual ASSP is specifically adapted in line with the individual requirements of a single OEM. With Epona, however, suppliers now have a basic design for regulating generators and so are able to cover the requirements of all vehicle manufacturers - a first in the industry.
The basic idea behind Epona was to offer as many degrees of freedom as possible in order to enable a highly efficient system design on the one hand and to implement the necessary control algorithms on the other. Although it would theoretically have been possible to create a system like this as a highly efficient controller, the numerous different vehicle manufacturer specifications means that the control loop must be user-programmable to avoid the need to develop an individual ASSP for each solution.
- User-programmable: the heart of Epona is a user-programmable microcontroller in which a state machine can, in principle, be mapped. To help program the microcontroller, EBV supplies a tool that allows simulation of the control loop and the setting of all the other parameters quickly and easily. Thanks to their system expertise, the developers no longer have to worry about creating, for example, a standard P-controller. Now all they have to do is set the relevant control parameters in their software. A generator regulator ensures - usually by means of normal proportional control - that the generator is operating at the optimum control point.
- Universal component: We are in a position to create an entire product range at reasonable cost. In partnership with STMicroelectronics, EBV is currently developing a 12- and 24-V range with different bus interfaces, which will soon result in four different components: one 12-V and one 24-V version of Epona, each with and without a LIN interface.
- Interfaces: Epona is highly universal as offering interfaces like LIN 2.1, RVC (Regulated Voltage Control), PWM, C-Term and a bit-serial interface. There is currently no uniform design direction in the development of the generator systems and LIN is still far from being available in all new designs, which means that the concepts of tomorrow will still use different interface solutions and protocols; this is particularly the case for 24-V applications.
- Load response control: In most cases, the generator is mechanically attached directly to the motor shaft. Through appropriate excitation of the rotor windings, output variables such as speed can be determined automatically. During a cold start, the electronic system has to decide whether the battery still has sufficient capacity or whether electricity needs to be immediately generated, which would increase the speed of the motor. This is the task of the 'load response control' (LRC), which controls the load when starting torque occurs. In conventional solutions, this takes place as part of a strictly defined LRC scheme during a cold start. Epona allows you to completely redefine the LRC properties, which means that for example other load torques can be set. Epona performs normal battery recharging in P-controller mode, whereby quasi-recuperation mode is also possible here. These functions can be programmed directly or controlled via the relevant interfaces.
- Protection controllers: Epona can respond to different events in the on-board electrical system and in the controller itself. The component is equipped with protected output drivers, which allow for a simplified design. Different trigger levels can also be introduced by means of software to allow a more flexible response to the current situation in the vehicle. These include the ability to connect and shut-down loads as well as to compensate for and respond to large loads. When powerful 'consumers' are switched on and off in a 24-V on-board electrical system, for example, this can lead to major disturbances in the electrical system. With the right software, however, these peaks can be stabilised relatively quickly. The solution also features Control Fault Diagnosis as well as systems for increasing operational safety and reliability, with a watchdog being just one of a multitude of such systems. Epona is a 'system in a package' containing two semiconductor chips - one highvoltage component and one CMOS component. This separation means that the state machine can be woken by the hardware or a reset can be carried out, which offers improved safety over a monolithically integrated solution.
- Positive or negative control: Epona was originally designed exclusively for the European market. But since the excitation coil is available on the global market in both a high-side and low-side configuration, EBV designed the control output in such a way that it can actuate the MOSFET switch for the excitation coil winding both directly to earth and directly to the positive supply voltage. Epona therefore features a suitable gate driver that can drive the MOSFET in both the high-side and low-side configuration. A sensor input can then be used to clearly establish whether or not the MOSFET has switched through. The component can also measure the current flowing through the excitation coil as well as the voltage currently applied. For this measurement, variable gain amplifiers that are suitably buffered depending on the input or output are fitted on the chip.
- Universal inputs: Epona also offers functions to prevent individual batteries from becoming overloaded in systems containing multiple generators. For this purpose, the component features universal inputs that can be connected differently depending on the application. To ensure that raised current levels in this circuit can also be utilised, load-dependent relays that only function when the generator is running can be controlled.
- GUI: software tool featuring a GUI, the developers can run initial experimentation modes and familiarise themselves with Epona-based systems to provide a good starting point for developing the customised overall system. The tool's GUI generates parameter records and sections of the C-Code, which can then be loaded directly with the offline tool chain of the microcontroller.
Epona - Made For the Aftermarket As Well
Epona is not only of interest for new vehicle designs, but also for the spare parts market when generators need to be replaced. Many companies specialise in reconditioning old generators, for example replacing the bearings or the electrical and electronic systems in the generator. Thanks to Epona , these companies can now even boost the efficiency of generators. But in order for efficiency-increasing measures to be implemented sensibly and rationally, a universal concept is needed. And this is exactly what Epona offers.
Even older cars can be made to run more efficiently if a reconditioned generator with Epona is installed - and that even applies to vehicles without a battery or engine management system. The acceleration vector, even for older vehicles, can be determined using software by measuring the change in speed of the generator. Since the engine is to deliver power to the driven wheels with minimum deterioration as the speed increases, it is not a good idea to charge the battery while the vehicle is accelerating because this would represent an additional load.
If the acceleration vector is zero or even negative (decelerating, braking), however, it makes sense to charge the battery during this phase. With some clever programming, this results in a type of small-scale recuperation effect. In modern cars, an external controller is usually responsible for load-dependent generator control as part of battery management. EBV Elektronik assumes that around 20% of the Epona supply volume will enter the aftermarket segment. The structure of the 'alpha' customers also reflects this: of the five 'alpha' customers, one is in the aftermarket business while the others supply new vehicles.