['Reducing', 'a', 'certain', 'voltage', 'can', 'improve', 'the', 'power', 'factor', 'and', 'efficiency', 'of', 'the', 'beam', 'pumping', 'unit', 'when', 'in', 'light', 'load', '.We', 'can', 'change', 'the', 'voltage', 'by', 'changing', 'the', 'thyristor', 'trigger', 'angle', '.']