User Configurable Gate Drives


Richard Varney and Bryn Parry at Amantys Power Electronics Limited

User configurable gate drives offer the power converter stack designer faster turnaround time on testing and control over the optimization of the performance of the power stack assembly. Maintenance engineers can benefit by configuring the gate drive to be compatible with legacy systems. 

Testing and commissioning a new converter power stack design can be a lengthy process due to the requirements to change the configuration of gate drive characteristics such as the turn on and turn off resistors (Rgon and Rgoff) and the soft turn off resistor (Rgsoft). The usual method of changing the gate resistors requires the user to disassemble the converter power stack, unsolder and replace the gate resistors, reassemble and then re-run the test. For a large power converter with multiple gate drives this process could take several hours if not days. 

User configurable gate drives also deliver an advantage in the retrofit market where an older piece of equipment requires a replacement IGBT that is no longer in production, or is difficult to source. This maybe because the gate drive is now obsolete or contains components that are obsolete. 

The options for the maintenance team are to scrap the piece of equipment or attempt to repair the existing gate drive which can be costly and time consuming.

A user configurable gate drive offers the power converter stack designer the option to quickly optimize a gate drive in a new power converter stack design. In maintenance applications the maintenance engineer may need to replace an obsolete gate drive with a compatible design or replace both the IGBT and the gate drive to take advantage of the greater performance of new generations of power semiconductor technology.

Taking advantage of a two way communications protocol called Power Insight makes the process of optimisation or replacement easier.

User Configurable Gate Drives

The advances in microcontroller and complex programmable logic (CPLD) technology have made it possible to integrate advanced functionality into a product such as a gate drive cost effectively. 

One such application of this technology is to create a two way communications protocol that runs over the same fibre as the traditional PWM and ACK signals. The two way communications protocol can be used to configure the gate drive in situ over the fibre optic link.

The architecture of gate drive is shown in Figure 1.

Figure 1: Gate Drive Architecture

The communications drive interfaces directly to the control logic which stores the configuration in memory on board the gate drive. The operation of the gate drive is determined by the parameters stored in the configuration memory. The user configurable parameters are shown in Figure 2.

Figure 2: Configuration Table

The most important configurable parameters are the gate resistors Rgon and Rgoff. The gate drive has four gate resistor values that are arranged in parallel to form the effective gate resistance. Each of the four gate resistors are controlled by a MOSFET drive stage that is controlled from the CPLD on board the gate drive. The configuration thus allows for fifteen choices of Rgon and fifteen choices of Rgoff.

The soft turn off resistor Rgoffsoft is again controlled by the selection of gate drive resistor from the CPLD on the gate drive.

A further advantage of the configurable gate resistors is that the same gate drive can be used to target IGBTs from different vendors. The user can optimize the configuration for each IGBT then program the required configuration on the production line. This gives the supply chain managers in the OEM the option of sourcing multiple IGBTs for the same design giving options on cost, and supply chain security.

In situations where the maintenance engineer needs to find a compatible drive for one that is obsolete it is sometimes required to reconfigure the protocol between the gate drive and the central controller. In the configurable gate drive this is straightforward as the protocol is controlled by the CPLD which can be programmed to be compatible with a legacy protocol. Common legacy protocols can be included as standard which allow the user to switch between the standard and alternative protocols.

Some application require that the fault lock out time, i.e. the time during which the gate drive will not respond after a fault, is as short as possible to allow the central controller to continue controlling the power converter stack. Making this a configurable parameter allows the converter designer to choose the appropriate value to protect the converter.

Gate drives used in two level or three level inverter designs require a different response to a fault in the converter. The gate drive needs to know where it is in a power converter phase leg and respond accordingly. This behaviour can also be configured in the gate drive over the fibre optic link.

Configuration Made Easy

Whilst user configuration of the gate drive is beneficial to the converter power stack designer it needs to be easy to use in order to get the full benefits. To achieve this, an interface box called the Power Insight Adapter and a software tool called the Power Insight Configurator have been developed by Amantys to make the process as easy as possible.

The Power Insight Adapter

The Power Insight Adapter (Figure [3]) enables a Windows PC to communicate with the gate drives using a USB or local area network (LAN) connection. . The Power Insight Adapter can be used in two different ways: i) direct mode, where the PC is used to control the test pulses to the gate drives directly or, ii) gateway mode where the Power Insight Adapter will pass through PWM and ACK pulses from an existing central controller and gate drive but still allow 

Figure 3: Power Insight Adapter

Power Insight Configurator

The Power Insight Configurator is a Windows application that will discover and communicate with Power Insight enabled gate drives attached to the Power Insight Adapter. Each gate drive that the Power Insight Configurator finds is displayed as a button with the name of the gate drive, serial number and IP address.

The Configuration Pane

Clicking the gate drive button will open the Configuration Pane for the associated gate drive. An example of the Configuration Pane is shown in Figure 4. 

Figure 4: Configuration Pane

The Configuration pane will show all of the parameters that can be configured on the gate drive. 

The user can select a parameter and enter a new value which will be displayed in red until it has applied the new configuration to the gate drive. Programming a new configuration into the target gate drive takes a few seconds.

The user also has the option to programme the same configuration into all of the attached gate drives or revert to the original configuration and start again. 

Configurations can be stored to a file and retrieved at a later date by using the “Save to File” and “Load from File” buttons. The user can develop the optimum configuration for the target converter power stack and send the configuration file to Amantys for programming into a production batch of gate drives.

Conclusion

User configurable gate drives along with the appropriate support infrastructure make it easy for the converter power stack designer or the maintenance engineer to optimize the performance of the converter power stack or retrofit an existing power converter with a compatible gate drive and the latest generation of power semiconductors.

 

More information: Amantys    Source: Bodo's Power Systems, May 2016