VOLTWORKS inverter servicer Grace suggests me :
microwave oven less than 700W, choose 1500W pure sine wave inverter
microwave oven between 700-900W, choose 2000W pure sine wave inverter
microwave oven more than 900W, choose 2500W pure sine wave inverter
And battery should be fully charged ,and 200Ah at least,
Their reasons as below
The power rating used with microwave ovens is the "cooking power" which refers to the power being "delivered" to the food being cooked. The actual operating power requirement rating is higher than the cooking power rating (for example, a microwave with "advertised" rating of 600 watts usually corresponds to almost 1100 watts of power consumption). The actual power consumption is usually stated on the back of the microwave. If the operating power requirement cannot be found on the back of the microwave, check the owner's manual or contact the manufacturer.