Here is an example floe you can play with - the first function creates the payload of the five variables and passes it to the CSV node and then to your function.
[{"id":"5f9ea95e.7eb188","type":"function","z":"757d259f.63e454","name":"`","func":"var voltage = 25;\nvar current= 30;\nvar power = 1024;\nvar frequency = 66;\nvar energy = 98.4;\n\nmsg.payload = {\n \"voltage\":voltage,\n \"current\":current,\n \"power\":power,\n \"frequency\":frequency,\n \"energy\":energy\n};\n//msg.payload = voltage+','+current+','+power+','+frequency+','+energy;\nreturn msg;","outputs":1,"noerr":0,"x":310,"y":132,"wires":[["595ac32c.7f55ac","3ef5c90b.4e8846"]]},{"id":"1b546429.ed86bc","type":"debug","z":"757d259f.63e454","name":"","active":true,"console":"false","complete":"true","x":769,"y":312,"wires":[]},{"id":"73a6c75f.ca6f98","type":"inject","z":"757d259f.63e454","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"x":128,"y":132,"wires":[["5f9ea95e.7eb188"]]},{"id":"79638adc.516cfc","type":"function","z":"757d259f.63e454","name":"","func":"var now = new Date(); \nvar now = new Date(); \nvar year = now.getFullYear();\nvar month = now.getMonth()+1; \nvar day = now.getDate();\nvar hour = now.getHours();\nvar minute = now.getMinutes();\nvar second = now.getSeconds(); \nif(month.toString().length == 1) {\nvar month = '0'+month;\n}\nif(day.toString().length == 1) {\nvar day = '0'+day;\n} \nif(hour.toString().length == 1) {\nvar hour = '0'+hour;\n}\nif(minute.toString().length == 1) {\nvar minute = '0'+minute;\n}\nif(second.toString().length == 1) {\nvar second = '0'+second;\n} \nmsg.timestamp = day+'-'+month+'-'+year+' '+hour+':'+minute;\nif (msg.filename === undefined) {\n msg.filename = \"/home/pi/data/nairnformat.csv\";\n }\n//msg.payload = msg.timestamp + \"
\\t\" + msg.payload;\nreturn msg;","outputs":1,"noerr":0,"x":666,"y":131,"wires":[["1b546429.ed86bc"]]},{"id":"595ac32c.7f55ac","type":"debug","z":"757d259f.63e454","name":"","active":true,"console":"false","complete":"true","x":325,"y":325,"wires":[]},{"id":"3ef5c90b.4e8846","type":"csv","z":"757d259f.63e454","name":"","sep":",","hdrin":"","hdrout":true,"multi":"mult","ret":"
\\n","temp":"voltage, current, power, frequency, energy","x":490,"y":132,"wires":[["79638adc.516cfc","ec14897a.15501"]]},{"id":"ec14897a.15501","type":"debug","z":"757d259f.63e454","name":"","active":true,"console":"false","complete":"true","x":625,"y":313,"wires":[]}]