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STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTOR OR A JOINT INVENTOR
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The present disclosure generally relates to a solid state transformer power conversion system and, more specifically, to a single stage synchronous solid state transformer resonant power converter system and methods of controlling the same.
Solid state transformers are used to convert isolated AC/AC voltages, similarly to conventional transformers, with potential added benefits of smaller size, improved voltage regulation and filtering, and power factor correction. In some applications, solid state transformers may be part of a system which has AC and DC connections to support bidirectional power storage and generative loads. A prior art (
Prior implementations of solid state transformers may have lower efficiency than conventional transformers due to series losses of multiple power stages. It is desirable to develop a single stage solid state transformer with a current controlled connection for power line interface, an isolated regulated voltage controlled line connection, and isolated DC ports.
In one aspect, the objective of this invention is to implement a single stage solid state transformer with isolated current and voltage controlled line connections, and isolated DC bus connections. This objective is accomplished in the present invention by using a current controlled bridge and a voltage controlled bridge coupled by a transformer and resonant impedance to result in a single stage transformer module shown in
These and additional objects and advantages provided by the embodiments described herein will be more fully understood in view of the following detailed description, in conjunction with the drawings.
Embodiments described herein generally relate to a solid state power transformer and methods of forming a single stage synchronous solid state transformer system with synchronous average harmonic current control. As shown and described herein, new embodiments of solid state transformers with synchronous average harmonic current control are provided. The presently invented system controls the synchronous harmonic current between two isolated bridges to implement power factor corrected input line connection and regulated output line connection in a single stage.
An embodiment of a single stage synchronous solid state transformer module is illustrated in
The voltage controlled bridge (201) is illustrated in
A current controlled bridge (202) is illustrated in
The respective voltage controlled (201) and current controlled (201) bridges are illustrated in the embodiment shown in
An embodiment of a single stage synchronous solid state transformer (S5X) is illustrated in
An embodiment of an internal dynamic model of a single stage synchronous solid state transformer (S5X (DETAIL)) is illustrated in
A mathematical description for one or more embodiments, similar to the internal model shown in
where ILEQ[f] represents current flow across an equivalent harmonic inductance element due to harmonically weighted (VMULT1 and VMULT2 in
where the equivalent harmonic resistance is
and the equivalent harmonic inductance is
R0 represents switch and resonant network internal resistance, and LR represents inductance of the resonant network. The impedance is the frequency dependent relationship which predicts voltage as an output due to current as an input, and the admittance is the inverse of impedance (or current due to voltage). The admittance (or inverse of impedance) is used in EQ1 to predict current flow due to a weighted input voltage.
Bus current transfer as a result of linearized harmonic current flow is given by:
where the current into each bus, I1X[f] and I2X[f], is modulated by the first switching harmonic of respective bridge gate signals resulting in a weight related to the sine of each respective duty cycle.
Power transfer between each respective DC bus and its line connected voltage is illustrated in
where a full bridge duty cycle is amplified by DC bus voltage, V2,f=DC, and projected through the admittance associated with a series inductor, YLs[f], to convert from voltage to current, and projected through a compensator gain, k[f], to command a duty cycle. The series inductor (such as L2 in
The modulated feedback signal path of the synchronous average harmonic current compensator acts to linearize the harmonic coupling admittance as shown in
where I1:V1[f] is the first bus current flow due to first bus voltage perturbations, and I1:V2[f] is the first bus current flow due to second bus voltage perturbations, whose sum is illustrated in
The subtracted active admittance due to control simplifies over the bandwidth where the loop gain of the modulated feedback path, LG1[f], is greater than one. The controlled admittance equations (EQ5A, EQ5B, EQ5C, EQ5D) reproduce the linearized model equations used in
where g is a linearized gain constant relating to the duty cycle operating point, sin (π·d2), and V2,f=DC is the DC bus voltage (V2). The SAHC compensator frequency dependent gain is k[f]. The compensator gain may be modeled using an integrator with time constant given by R11 and double C1 (as shown in
Open loop modulated admittance terms (used in EQ5A, EQ5B, EQ5C and EQ5D) are:
where each term is a superposition of conjugate resonant network admittances at two frequencies weighted by gate signals. The gate signals, gAB,k1 and gCD,k1, represent the first harmonic of the switching frequency for pulse width modulation processes illustrated in
The controller cross admittance terms (used in EQ5A, EQ5B, EQ5C and EQ5D) are:
where gS,k1 is the first harmonic of the square wave (SQ), whose integral is the triangle wave (TRI) used for pulse width modulation. The triangle wave is 90 degrees out of phase with the square wave due to the mathematical properties of integration. Assuming a small phase command, the gate signals, gAB,k1 and gCD,k1, may be modeled as is in phase with the triangle waveform due to the pulse width modulation process. As a result, the gates signals, gAB,k1 and gCD,k1, are 90 degrees out of phase with the synchronous square wave. Therefore, each first harmonic combination of gS,k1 and gate signals, gAB,k1 and gCD,k1, is an imaginary number. The imaginary numbers which weight the cross admittance terms are conjugate symmetric resulting in sign reversal so that the weighted equations subtract
The open loop plant auto admittance term (used to calculate the loop gain of EQ6B) is:
where Y(S,S) is the modulated current response due to modulated phase command. The natural frequency associated with the resonant network. fn, is modulated by the switching frequency, fc, to result in an apparent resonance of the open loop plant auto admittance at |fc−fn|. For frequencies below |fc−fn| the open loop plant auto admittance is capacitive, and for frequencies above |fc−fn| the auto admittance is inductive. The inductive auto admittance term dominates the frequency response when |fc−fn| is small relative to the control bandwidth. Given that an inductive impedance trends proportionally with increasing frequency, and an inductive admittance trends with one over frequency, the open loop plant auto admittance term has an integrating characteristic. The open loop plant admittance is combined with the compensator to calculate loop gain (EQ6B). An integrating compensator response, as embodied by the SAHC compensator in
Embodiments of the resonant power converter, such as illustrated in
where V1 is related by V2 by the ratio of the sines of respective bridge duty cycles.
The voltage controlled bridge regulates both VAB and V1 relative to V2, where VAB is a function of bus voltage, V1, and duty cycle, d1:
where EQ11 equation assumes duty cycle sensitivity for a full bridge. Combining EQ10 and EQ11 results in the average line attached voltage response:
where the line voltage, VAB, has a sensitivity to d1 in the numerator and sin (πd1) in the denominator. For a system where a linear combination of feedforward and feedback signals is utilized, the sensitivity of VAB to d1 is expanded as:
where d1 is expanded to d2+dx to represent feedforward and feedback regulation. Assuming small perturbations in feedback, dx, the derivative of EQ13 is:
where the derivative given in EQ14 is a linear constant for d2=0.5 where both (2·d2−1) and cotangent (πd2) are zero, and becomes relatively more nonlinear for d2≠0.5. The relationship in EQ14 is sufficient to design a feedback regulator where clipping is used to ensure feedback gain is bounded. A clipping circuit (such as VHTRIM,
An embodiment of a single stage synchronous solid state transformer system is illustrated in
Voltage regulation is performed in the embodiment shown in
An embodiment of a multi-module single stage synchronous solid state transformer system is illustrated in
The embodiment illustrated in
While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications may be made without departing from the spirit and scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. It is therefore intended that the appended claims cover all such changes and modifications that are within the scope of the claimed subject matter.
This application is a continuation of prior application Ser. No. 18/336,984, filed Jun. 17, 2023, which is incorporated by reference herein in its entirety.
Number | Date | Country | |
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Parent | 18336984 | Jun 2023 | US |
Child | 18483086 | US |