Wave transformation method and device

An AC-AC waveform transformation method, including the following steps:

• setting a sine-wave voltage to be output, and dividing the sine-wave according to time interval t0, t1, t2, t3, . . . ti, and selecting the voltage waveform during time t0˜t1 as the given reference voltage;
• selecting j groups from n groups of m phases AC power supplies that are electrically insulated to each other as the current input voltage, where j≦n;
• performing bi-directionally controlled current rectification on the rest n-j groups of m phases AC power supplies so that its output voltage is 0;
• for the selected j groups of m phases AC power supplies that are electrically insulated to each other, selecting one voltage waveform for each group from all voltage waveforms output during t0˜t1 obtained after carrying out bi-directionally controlled rectification on j groups of m phases AC voltage so that j voltage waveforms are obtained by bi-directionally controlled rectification on the j group of m phases AC voltage that are electrically insulated to each other;
• finding the sum of said j voltage waveforms and get a total calculated output voltage;
• comparing the calculated output voltage during t0˜t1 with said given reference voltage;
• selecting m-phase AC power supplies of different groups from the above-mentioned n groups of m phase AC power supplies that are electrically insulated to each other as current input voltage;
• among each group of the m-phase AC power supplies, selecting different voltage waveforms on which gone through bi-directionally controlled rectification has been performed, so that the difference between the calculated output voltage and given reference voltage is made as low as possible at any time, and the total harmonics in the output voltage is made the smallest or some high-order harmonics is made as low as possible, or the total harmonics in the sum of current for n groups of AC power supplies is made the smallest or some high-order harmonics is made as low as possible;
• or the average leading or lagging power factors of each supply in the n input groups is make as large as possible;
• determining the working status of each bi-directionally controlled rectifying circuit based on the voltage waveform corresponding to each selected m-phase AC power supply, and performing bi-directionally controlled rectification in accordance to the working status determined;
• selecting the given expected voltage waveforms during time t1˜t2, t2˜t3, . . . ti−1˜ti as given reference voltages respectively, repeating step 2˜8, and obtain the desired AC output voltage.