Controlling charge-balance and transients in a multi-level power converter
Circuits and methods that more effectively and efficiently solving the charge-balance problem for multi-level converter circuits by establishing a control method that selects an essentially optimal pattern or set of switch states that moves the fly capacitors towards a charge-balance state or maintains the current charge state every time a voltage level at an output node is selected regardless of what switch state or states were used in the past. Accordingly, multi-level converter circuit embodiments of the invention are free to select a different switch state or output voltage level every switching cycle without needing to keep track of any prior switch state or sequence of switch states. Additional benefits include improved transient performance made possible by the novel charge-balance method.
1 . A method of setting output level and charge-balancing a set of fly capacitors during a switching cycle of a multi-level converter circuit that includes (1) a set of switches configured to be coupled between a first terminal and a second terminal, and (2) the set of fly capacitors, wherein each fly capacitor of the set of fly capacitors is coupled between a respective inner low-side switch among the set of switches and a respective outer low-side switch among the set of switches and between a respective inner high-side switch among the set of switches and a respective outer high-side switch among the set of switches, the method including:
(a) selecting an outward-most fly capacitor among the set of fly capacitors that has not previously been selected;
(b) if a voltage on the selected outward-most fly capacitor is above an associated target voltage and there are remaining low-side switches among the set of switches that are currently closable, then: (1) setting the outer low-side switch of the selected outward-most fly capacitor to be closed to discharge the selected outward-most fly capacitor, and otherwise (2) setting the outer high-side switch of the selected outward-most fly capacitor to be closed to charge the selected outward-most fly capacitor;
(c) repeating steps (a) and (b) until all fly capacitors among the set of fly capacitors have been selected; and
(d) for a remaining pair of left-over inward-most inner switches among the set of switches, setting an associated high-side switch among the set of switches or an associated low-side switch among the set of switches to a closed state based on a set of switch count rules.
2 . The method of claim 1 , wherein each fly capacitor among the set of fly capacitors is initially assigned a target level, and the method further including:
(e) if the outer low-side switch of the selected outward-most fly capacitor is set to discharge the selected outward-most fly capacitor, then the target level of the selected outward-most fly capacitor is assigned to a next inner fly capacitor among the set of fly capacitors;
(f) if the outer low-side switch of the selected outward-most fly capacitor is set to charge the selected outward-most fly capacitor, then decrementing the target level of the selected outward-most fly capacitor by one and assigning the decremented target level to the next inner fly capacitor;
(g) if the target level assigned to the selected outward-most fly capacitor is one, then setting the outer low-side switch of the selected outward-most fly capacitor to be closed;
(h) if the target level for the selected outward-most fly capacitor is a maximum voltage level for a lower-complexity substructure of the multi-level converter circuit corresponding to the selected outward-most fly capacitor, then setting the outer high-side switch of the selected outward-most fly capacitor to be closed; and
(i) repeating steps (e), (f), (g), and (h) until all switches among the set of switches have been set to an open state or a closed state.
3 . The method of claim 2 , further including setting each target level as a function of a deviation of an output voltage or current of the multi-level converter circuit from a desired target value.
4 . The method of claim 1 , wherein if a next inner fly capacitor among the set of fly capacitors requires charge balancing while the selected outward-most fly capacitor does not require charge balancing, then restricting the selected outward-most fly capacitor to switch states that allow the next inner fly capacitor to charge balance.
5 . The method of claim 1 , wherein if two cycles of the steps (a) and (b) in succession selects the same switch state for their corresponding fly capacitors among the set of fly capacitors, and the selected outward-most fly capacitor requires charge balancing, then forcing a next inner fly capacitor among the set of fly capacitors to select the opposite switch state relative to the selected outward-most fly capacitor.
6 . A method of setting output level and charge-balancing a set of fly capacitors during a switching cycle of a multi-level converter circuit that includes (1) a set of switches configured to be coupled between a first terminal and a second terminal, and (2) the set of fly capacitors, wherein each fly capacitor of the set of fly capacitors is coupled between a respective inner low-side switch among the set of switches and a respective outer low-side switch among the set of switches and between a respective inner high-side switch among the set of switches and a respective outer high-side switch among the set of switches, the method including:
(a) selecting an outward-most fly capacitor among the set of fly capacitors that has not previously been selected;
(b) if a voltage on the selected outward-most fly capacitor is above an associated target voltage and there are remaining high-side switches among the set of switches that are currently closable can be closed, then: (1) setting the inner high-side switch of the selected outward-most fly capacitor to a closed state to discharge the selected outward-most fly capacitor, and otherwise (2) setting the inner low-side switch of the selected outward-most fly capacitor to a closed state to charge the selected outward-most fly capacitor;
(c) repeating steps (a) and (b) until all fly capacitors among the set of fly capacitors have been selected; and
(d) for a remaining pair of left-over outward-most outer switches among the set of switches, setting an associated high-side switch among the set of switches or an associated low-side switch among the set of switches to a closed state based on a set of switch count rules.
7 . The method of claim 6 , wherein each fly capacitor among the set of fly capacitors is initially assigned a target level, and the method further including:
(e) if the inner low-side switch of the selected outward-most fly capacitor is set to charge the selected outward-most fly capacitor, then the target level of the selected outward-most fly capacitor is assigned to a next inner fly capacitor among the set of fly capacitors;
(f) if the inner low-side switch of the selected outward-most fly capacitor is set to discharge the selected outward-most fly capacitor, then decrementing the target level of the selected outward-most fly capacitor by one and assigning the decremented target level to the next inner fly capacitor;
(g) if the target level assigned to the selected outward-most fly capacitor is one, then setting the inner low-side switch of the selected outward-most fly capacitor to be closed;
(h) if the target level for the selected outward-most fly capacitor is a maximum voltage level for a lower-complexity substructure of the multi-level converter circuit corresponding to the selected outward-most fly capacitor, then setting the inner high-side switch of the selected outward-most fly capacitor to be closed; and
(i) repeating steps (e), (f), (g), and (h) until all switches among the set of switches have been set to an open state or a closed state.
8 . The method of claim 7 , further including setting each target level as a function of a deviation of an output voltage or current of the multi-level converter circuit from a desired target value.
9 . The method of claim 6 , wherein if a next inner fly capacitor among the set of fly capacitors requires charge balancing while the selected outward-most fly capacitor does not require charge balancing, then restricting the selected outward-most fly capacitor to switch states that allow the next inner fly capacitor to charge balance.
10 . The method of claim 6 , wherein if two cycles of the steps (a) and (b) in succession selects the same switch state for corresponding fly capacitors among the set of fly capacitors, and the selected outward-most fly capacitor requires charge balancing, then forcing a next inner fly capacitor among the set of fly capacitors to select the opposite switch state relative to the selected outward-most fly capacitor.
11 . A method of setting output level and charge-balancing a set of fly capacitors during a switching cycle of a multi-level converter circuit that includes (1) a set of switches configured to be coupled between a first terminal and a second terminal, and (2) the set of fly capacitors, wherein each fly capacitor of the set of fly capacitors is coupled between a respective inner low-side switch among the set of switches and a respective outer low-side switch among the set of switches and between a respective inner high-side switch among the set of switches and a respective outer high-side switch among the set of switches, the method including:
(a) selecting an inward-most fly capacitor among the set of fly capacitors that has not previously been selected;
(b) if a voltage on the selected inward-most fly capacitor is above an associated target voltage and there are remaining high-side switches among the set of switches that are currently closable, then: (1) setting the inner high-side switch of the selected inward-most fly capacitor to a closed state to discharge the selected inward-most fly capacitor, and otherwise (2) setting the inner low-side switch of the selected inward-most fly capacitor to a closed state to charge the selected inward-most fly capacitor;
(c) repeating steps (a) and (b) until all fly capacitors among the set of fly capacitors have been selected; and
(d) for a remaining pair of left-over outward-most outer switches among the set of switches, setting an associated high-side switch among the set of switches or an associated low-side switch among the set of switches to a closed state based on a set of switch count rules.
12 . The method of claim 11 , wherein each fly capacitor among the set of fly capacitors is initially assigned a target level, and the method further including:
(e) initializing a high-side switch counter to L−1, and a low-side switch counter to M−L, where M=total number of levels in the multi-level converter circuit, and L=the target level;
(f) each time a low-side switch among the set of switches is set to be closed, then decrementing the low-side switch counter by one;
(g) each time a high-side switch among the set of switches is set to be closed, then decrementing the high-side switch counter by one;
(h) if the high-side switch counter reaches zero, then setting the inner low-side switches among the set of switches of all remaining fly capacitors among the set of fly capacitors to be closed; and
(i) if the low-side switch counter reaches zero, then setting the inner high-side switches among the set of switches of all remaining fly capacitors among the set of fly capacitors to be closed.
13 . The method of claim 12 , further including setting each target level as a function of a deviation of an output voltage or current of the multi-level converter circuit from a desired target value.
14 . The method of claim 11 , wherein if a next outer fly capacitor among the set of fly capacitors requires charge balancing while the selected inward-most fly capacitor does not require charge balancing, then restricting the selected inward-most fly capacitor to switch states that allow the next outer fly capacitor to charge balance.
15 . The method of claim 11 , wherein if two cycles of the steps (a) and (b) in succession selects the same switch state for corresponding fly capacitors among the set of fly capacitors, and the selected inward-most fly capacitor requires charge balancing, then forcing a next outer fly capacitor among the set of fly capacitors to select the opposite switch state relative to the selected inward-most fly capacitor.
16 . A method of setting output level and charge-balancing a set of fly capacitors during a switching cycle of a multi-level converter circuit that includes (1) a set of switches configured to be coupled between a first terminal and a second terminal, and (2) the set of fly capacitors, wherein each fly capacitor of the set of fly capacitors is coupled between a respective inner low-side switch among the set of switches and a respective outer low-side switch among the set of switches and between a respective inner high-side switch among the set of switches and a respective outer high-side switch among the set of switches, the method including:
(a) selecting an inward-most fly capacitor among the set of fly capacitors that has not previously been selected;
(b) if a voltage on the selected inward-most fly capacitor is above an associated target voltage and there are remaining low-side switches among the set of switches that are currently closable, then: (1) setting the outer low-side switch of the selected inward-most fly capacitor to a closed state to discharge the selected inward-most fly capacitor, and otherwise (2) setting the outer high-side switch of the selected inward-most fly capacitor to a closed state to charge the selected inward-most fly capacitor;
(c) repeating steps (a) and (b) until all fly capacitors among the set of fly capacitors have been selected; and
(d) for a remaining pair of left-over inward-most inner switches among the set of switches, setting an associated high-side switch among the set of switches or an associated low-side switch among the set of switches to a closed state based on a set of switch count rules.
17 . The method of claim 16 , wherein each fly capacitor among the set of fly capacitors is initially assigned a target level, and the method further including:
(e) initializing a high-side switch counter to L−1, and a low-side switch counter to M−L, where M=total number of levels in the multi-level converter circuit, and L=the target level;
(f) each time a low-side switch among the set of switches is set to be closed, then decrementing the low-side switch counter by one;
(g) each time a high-side switch among the set of switches is set to be closed, then decrementing the high-side switch counter by one;
(h) if the high-side switch counter reaches zero, then setting the inner low-side switches among the set of switches of all remaining fly capacitors among the set of fly capacitors to be closed; and
(i) if the low-side switch counter reaches zero, then setting the inner high-side switches among the set of switches of all remaining fly capacitors among the set of fly capacitors to be closed.
18 . The method of claim 17 , further including setting each target level as a function of a deviation of an output voltage or current of the multi-level converter circuit from a desired target value.
19 . The method of claim 16 , wherein if a next outer fly capacitor among the set of fly capacitors requires charge balancing while the selected inward-most fly capacitor does not require charge balancing, then restricting the selected inward-most fly capacitor to switch states that allow the next outer fly capacitor to charge balance.
20 . The method of claim 16 , wherein if two cycles of the steps (a) and (b) in succession selects the same switch state for corresponding fly capacitors among the set of fly capacitors, and the selected inward-most fly capacitor requires charge balancing, then forcing a next outer fly capacitor among the set of fly capacitors to select the opposite switch state relative to the selected inward-most fly capacitor.