An apparatus for reducing nitrogen oxide emissions in a genset said genset having: an engine, an engine controller, a generator, a generator controller, and a shaft coupled to the engine and the generator, wherein the engine controller is operably configured to control energy transfer between the engine and the shaft, and wherein the generator controller is operably configured to control energy transfer between the generator and the shaft; the apparatus being characterised in that it further comprises: a system controller in communication with the engine controller and the generator controller, wherein the system controller is operably configured to: receive a shaft speed correction signal representing a shaft speed correction to reach a desired energy transfer between said engine and said generator; and responsive to the received shaft speed correction signal, communicate with the engine controller and with the generator controller to cause the generator to reduce load on the shaft while causing the engine to seek a steady state shaft speed for said desired energy transfer to the shaft when the shaft speed correction signal meets a criterion. an engine, an engine controller, a generator, a generator controller, and a shaft coupled to the engine and the generator, wherein the engine controller is operably configured to control energy transfer between the engine and the shaft, and wherein the generator controller is operably configured to control energy transfer between the generator and the shaft; the apparatus being characterised in that it further comprises: a system controller in communication with the engine controller and the generator controller, wherein the system controller is operably configured to: receive a shaft speed correction signal representing a shaft speed correction to reach a desired energy transfer between said engine and said generator; and responsive to the received shaft speed correction signal, communicate with the engine controller and with the generator controller to cause the generator to reduce load on the shaft while causing the engine to seek a steady state shaft speed for said desired energy transfer to the shaft when the shaft speed correction signal meets a criterion. a system controller in communication with the engine controller and the generator controller, wherein the system controller is operably configured to: receive a shaft speed correction signal representing a shaft speed correction to reach a desired energy transfer between said engine and said generator; and responsive to the received shaft speed correction signal, communicate with the engine controller and with the generator controller to cause the generator to reduce load on the shaft while causing the engine to seek a steady state shaft speed for said desired energy transfer to the shaft when the shaft speed correction signal meets a criterion. receive a shaft speed correction signal representing a shaft speed correction to reach a desired energy transfer between said engine and said generator; and responsive to the received shaft speed correction signal, communicate with the engine controller and with the generator controller to cause the generator to reduce load on the shaft while causing the engine to seek a steady state shaft speed for said desired energy transfer to the shaft when the shaft speed correction signal meets a criterion.