VOLTAGE CONVERSION DEVICE AND VOLTAGE CONVERSION METHOD THEREOF

A voltage conversion device includes a filter circuit, a first inductor, a second inductor a first conversion module, a second conversion module, and a control circuit. The filter circuit is electrically connected to a first AC terminal and a second AC terminal. The first inductor is electrically connected to the first AC terminal and a first conversion terminal. The second inductor is electrically connected to the second AC terminal and a second conversion terminal. The first conversion module is electrically connected to a first DC voltage terminal, a second DC voltage terminal, and the first conversion terminal. The second conversion module is electrically connected to the first DC voltage terminal, the second DC voltage terminal, and the second conversion terminal. The control circuit transmits switch-control signals to the first conversion module and the second conversion module. A voltage conversion method is used with the voltage conversion device.

This application claims the benefit of Taiwan application Serial No. 111144396, filed Nov. 21, 2022, the disclosure of which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The disclosure relates to a voltage conversion device and a voltage conversion method, and more particularly to a bidirectional voltage conversion device and a bidirectional voltage conversion method.

BACKGROUND

With the development of green technology, power conversion systems (PCS) have wider and wider applications.FIG.1Ais a schematic diagram showing that a power conversion system is installed between a power generation circuit and an electrical grid. The power conversion system13can convert the DC voltage (DC) obtained from the power generation circuit11(for example, wind turbine or solar panel) into AC voltage (AC) and then supply the AC voltage (AC) to the electrical grid15. Also, the power conversion system13can be used for energy storage and backup power supply.

FIG.1Bis a block diagram illustrating the architecture of the power conversion system in the prior arts. The power conversion system23can perform bidirectional voltage conversion to selectively convert the DC voltage (DC) into the AC voltage (AC) or convert the AC voltage (AC) into the DC voltage (DC) as desired.

The power conversion system23converts the DC voltage (DC) into the AC voltage (AC) as follows. At first, the battery module231stores the high DC voltage DC(hV) received from the power generation circuit, and then transmits the high DC voltage DC(hV) to a step-down circuit (buck circuit)233. The step-down circuit233steps down the high DC voltage DC(hV) to obtain the low DC voltage DC(IV). Subsequently, the step-down circuit233transmits the low DC voltage DC(IV) to the dc-to-ac conversion module237a, which then converts the low DC voltage DC(IV) into output AC voltage AC(out) to be supplied to the electrical grid.

The power conversion system23converts the AC voltage (AC) into the DC voltage (DC) as follows. At first, the ac-to-dc conversion module237creceives the input AC voltage AC(in) from the electrical grid, and then converts it into the low DC voltage DC(IV). Subsequently, a step-up circuit (boost circuit)235steps up the low DC voltage DC(IV) to obtain the high DC voltage DC(hV). Afterward, the step-up circuit235supplies the high DC voltage DC(hV) to the battery module231for energy storage.

FromFIG.1B, the power conversion system23in the prior parts needs both the dc-to-ac conversion module237aand the ac-to-dc conversion module237cto support bidirectional power conversion. Such implementation consumes more power, and the cost involving the circuits of the dc-to-ac conversion module237aand the ac-to-dc conversion module237cis much high.

SUMMARY

The disclosure is directed to a voltage conversion device configured to convert the DC voltage into the AC voltage and convert the AC voltage into the DC voltage, and further directed to an associated voltage conversion method. According to the voltage conversion device of the disclosure, it is not required to provide two sets of circuits for two voltage conversion modes, respectively. Such a design can significantly reduce the cost of the circuits. Furthermore, the voltage conversion device of the disclosure adopts power transistors to switch on/off the circuits and thus considerably reduces the power consumption.

According to one embodiment, a voltage conversion device is provided. The voltage conversion device includes a filter circuit, a first inductor, a second inductor, a first conversion module, a second conversion module, and a control circuit. The filter circuit is electrically connected to a first AC terminal and a second AC terminal. The first inductor has a terminal electrically connected to the first AC terminal, and the second inductor has a terminal electrically connected to the second AC terminal. The first conversion module includes a first DC stage circuit, a first conversion stage circuit, and a first inner stage circuit. The first DC stage circuit is electrically connected to a first DC voltage terminal and a second DC voltage terminal. The first conversion stage circuit is electrically connected to another terminal of the first inductor. The first inner stage circuit is electrically connected between the first DC stage circuit and the first conversion stage circuit. The second conversion module includes a second DC stage circuit, a second conversion stage circuit, and a second inner stage circuit. The second DC stage circuit is electrically connected to the first DC voltage terminal and the second DC voltage terminal. The second conversion stage circuit is electrically connected to another terminal of the second inductor. The second inner stage circuit is electrically connected between the second DC stage circuit and the second conversion stage circuit. The control circuit is electrically connected to the first conversion module and the second conversion module. The control circuit transmits first switch-control signals to the first conversion module and transmits second switch-control signals to the second conversion module. A first current path in the first DC stage circuit, the first conversion stage circuit, and the first inner stage circuit is selected in response to the first switch-control signals, and a second current path in the second DC stage circuit, the second conversion stage circuit and the second inner stage circuit is selected in response to the second switch-control signals.

According to another embodiment, a voltage conversion method used with a voltage conversion device is provided. The voltage conversion device includes a filter circuit, a first conversion module, and a second conversion module. The first conversion module includes first switch units, and the second conversion module includes second switch units. The voltage conversion method includes the following steps. The first conversion module and the second conversion module receive a DC voltage from a battery module. The first conversion module and the second conversion module generate a modified sine wave between a first conversion terminal and a second conversion terminal. The filter circuit filters the modified sine wave to generate an AC voltage. The modified sine wave has a voltage equal to a positive DC voltage value when the first switch units and the second switch units enter a first conversion state. The modified sine wave has a voltage equal to half the positive DC voltage value when the first switch units and the second switch units enter a second conversion state or a third conversion state. The modified sine wave has a voltage equal to a ground voltage when the first switch units and the second switch units enter a fourth conversion state or a fifth conversion state. The modified sine wave has a voltage equal to half a negative DC voltage value when the first switch units and the second switch units enter a sixth conversion state or a seventh conversion state. The modified sine wave has a voltage equal to the negative DC voltage value when the first switch units and the second switch units enter an eighth conversion state. The first switch units and the second switch units being switched on and configured for receiving a first PWM signal in the first conversion state are switched off in the eighth conversion state. The first switch units and the second switch units being switched on and configured for receiving a second PWM signal in the second conversion state are switched off in the seventh conversion state. The first switch units and the second switch units being switched on and configured for receiving a third PWM signal in the third conversion state are switched off in the sixth conversion state. The first switch units and the second switch units being switched on and configured for receiving a fourth PWM signal in the fourth conversion state are switched off in the fifth conversion state. The first switch units and the second switch units being switched on and configured for receiving a fifth PWM signal in the fifth conversion state are switched off in the fourth conversion state. The first switch units and the second switch units being switched on and configured for receiving a sixth PWM signal in the sixth conversion state are switched off in the third conversion state. The first switch units and the second switch units being switched on and configured for receiving a seventh PWM signal in the seventh conversion state are switched off in the second conversion state. The first switch units and the second switch units being switched on and configured for receiving an eighth PWM signal in the eighth conversion state are switched off in the first conversion state.

According to an alternative embodiment, a voltage conversion method used with a voltage conversion device is provided. The voltage conversion device includes a first inductor, a second inductor, a first conversion module, and a second conversion module. The voltage conversion method includes the following steps. An AC voltage is received between a first AC terminal and a second AC terminal. The first inductor is electrically connected between the first conversion module and the first AC terminal, and the second inductor is electrically connected between the second conversion module and the second AC terminal. A first lower conversion circuit, a first lower inner circuit and a first lower middle circuit of the first conversion module, and a second upper middle circuit, a second upper inner circuit, and a second upper conversion circuit of the second conversion module receive a first PWM signal when the AC voltage is rising from a ground voltage to a positive DC voltage value. A first current from the first AC terminal flows to the second AC terminal through the first inductor, the first conversion module, a third DC voltage terminal, the second conversion module, and the second inductor sequentially to generate a DC voltage between a first DC voltage terminal and a second DC voltage terminal. A first upper conversion circuit, a first upper inner circuit and a first upper DC circuit of the first conversion module and a second lower DC circuit, a second lower inner circuit, and a second lower conversion circuit of the second conversion module receive a second PWM signal when the AC voltage is decreasing from the positive DC voltage value to the ground voltage. A second current from the first AC terminal flows to the second AC terminal through the first inductor, the first conversion module, the first DC voltage terminal, a battery module, the second DC voltage terminal, the second conversion module, and the second inductor sequentially to generate the DC voltage. The second lower conversion circuit, the second lower inner circuit and a second lower middle circuit of the second conversion module and a first upper middle circuit, the first upper inner circuit, and the first upper conversion circuit of the first conversion module receive a third PWM signal when the AC voltage is decreasing from the ground voltage to a negative DC voltage value. A third current from the second AC terminal flows to the first AC terminal through the second inductor, the second conversion module, the first conversion module, and the first inductor sequentially to generate the DC voltage. The second upper conversion circuit, the second upper inner circuit and a second upper DC circuit of the second conversion module and a first lower DC circuit, the first lower inner circuit, and the first lower conversion circuit of the first conversion module receive a fourth PWM signal when the AC voltage is rising from the negative DC voltage value to the ground voltage. A fourth current from the second AC terminal flows to the first AC terminal through the second inductor, the second conversion module, the first DC voltage terminal, the battery module, the second DC voltage terminal, the first conversion module, and the first inductor sequentially to generate the DC voltage.

DETAILED DESCRIPTION

The disclosure provides a voltage conversion device with a bidirectional conversion function. In other words, the hardware circuit can convert the DC voltage (DC) into the AC voltage (AC) and convert the AC voltage (AC) into the DC voltage (DC) by using a single circuit structure.

FIG.2is a block diagram of a voltage conversion device according to an embodiment of the disclosure. The voltage conversion device3is electrically connected to a loading43and a battery module41. The two terminals electrically connected to the voltage conversion device3and the loading43are defined as AC terminals Np, Nn in the description. Also, the two terminals electrically connected to the voltage conversion device3and the battery module41are defined as DC voltage terminals Ndc_p, Ndc_n. A DC voltage (DC) is formed between the two DC voltage terminals Ndc_p and Ndc_n; and an AC voltage (AC) is formed between the two AC terminals Np and Nn. The DC voltage (DC) has a fixed and stable DC voltage value Vdc. In a concise manner, the symbol Ndc_p may represent the AC voltage terminal Ndc_p or the voltage at the terminal Ndc_p; and the symbol Ndc_n may represent the AC voltage terminal Ndc_n or the voltage at the terminal Ndc_n according to the context.

The voltage conversion device3converts the DC voltage (DC) supplied by the battery module41into the AC voltage (AC), and then outputs the AC voltage (AC) to the loading43. Alternatively, the voltage conversion device3receives the AC voltage (AC) from the AC terminals Np, Nn, converts the AC voltage (AC) into the DC voltage (DC), and charges the battery module41with the DC voltage (DC). During either process of converting the DC voltage (DC) into the AC voltage (AC) or converting the AC voltage (AC) into the DC voltage (DC), the voltage conversion device3is switched among several conversion states dynamically.

The voltage conversion device3includes a voltage-conversion module31, a detection circuit38, a control circuit33, and a storage circuit35. The voltage-conversion module31is electrically connected to the loading43and the battery module41. The detection circuit38and the control circuit33are electrically connected to the voltage-conversion module31. The control circuit33is further electrically connected to the detection circuit38and the storage circuit35.

The voltage-conversion module31includes inductors La, Lb, a filter circuit31e, and conversion modules31a,31c. The detection circuit38, the loading43, the inductor La and the filter circuit31eare jointly electrically connected to the AC terminal Np. The detection circuit38, the loading43, the inductor Lb and the filter circuit31eare jointly electrically connected to the AC terminal Nn. The inductor La and the conversion module31aare jointly electrically connected to the conversion terminal Na. The inductor Lb and the conversion module31care jointly electrically connected to the conversion terminal Nb.

The control circuit33is implemented by a central processing unit (CPU) or a digital signal processor (DSP), which can perform the algorithm. The control circuit33decides and generates proper switch-control signals Ssw_g1, Ssw_g2according to the current conversion state, and then transmits the switch-control signals Ssw_g1, Ssw_g2to the conversion modules31a,31c. The switch-control signals Ssw_g1, Ssw_g2are pulse width modulation (PWM) signals, for example, carrier phase-shifted-sinusoidal PWM (CPS-SPWM) signals or phase disposition SPWM (PD-SPWM) signals. The control circuit33generates the switch-control signals Ssw_g1, Ssw_g2based on the CPS-SPWM and PD-SPWM technology can increase the operation efficiency of the voltage-conversion module31.

The storage circuit35stores a lookup table. The control circuit33accesses the lookup table according to the conversion state of the voltage-conversion module31to generate the switch-control signals Ssw_g1, Ssw_g2with specific waveforms to control interior circuits of the conversion modules31a,31e. The lookup table may have information (but not exclusively) of enabled elements and PWM waveforms associated with respective conversion states. When the voltage conversion device3is converting the DC voltage (DC) into the AC voltage (AC), the control circuit33generates the switch-control signals Ssw_g1, Ssw_g2for performing the dc-to-ac conversion according to the lookup table to control the conversion states of the conversion modules31a,31c. Alternatively, when the voltage conversion device3is converting the AC voltage (AC) into the DC voltage (DC), the control circuit33generates the switch-control signals Ssw_g1, Ssw_g2for performing the ac-to-dc conversion according to the lookup table to control the conversion states of the conversion modules31a,31c.

The control circuit33reads the lookup table stored in the storage circuit35according to the voltage conversion type, and then dynamically decides the switch-control signals Ssw_g1, Ssw_g2according to the information in the lookup table so as to select and establish a proper current path in the conversion modules31a,31c. The dynamic control details of the process of converting the DC voltage (DC) into the AC voltage (AC) with the control circuit33will be given inFIGS.5and6A-6Hand the associated description. The dynamic control details of the process of converting the DC voltage (DC) into the AC voltage (AC) with the control circuit33will be given inFIGS.7and8A-8D.

FIG.3is a block diagram of a voltage-conversion module according to an embodiment of the disclosure. In addition to the inductors La, Lb, the filter circuit31e, and the conversion modules31a,31c, the voltage-conversion module31further includes a precharge switch unit preUNT and voltage divider capacitors Cd1, Cd2. The voltage divider capacitor Cd1is electrically connected between the DC voltage terminal Ndc_p and a half-DC voltage terminal Ndc_h; and the voltage divider capacitor Cd2is electrically connected between the half-DC voltage terminal Ndc_h and the DC voltage terminal Ndc_n. In a concise manner, the symbol Ndc_h may represent the half-DC voltage terminal Ndc_h or the voltage at the terminal Ndc_h according to the context.

When the voltage conversion device3is activated, the voltage divider capacitors Cd1, Cd2are charged through the precharge switch unit preUNT. The voltage divider capacitors Cd1, Cd2have equal capacitance so that the cross-voltage of the voltage divider capacitor Cd1is equal to the cross-voltage of the voltage divider capacitor Cd2(VCd1=VCd2). Therefore, the voltage difference (Ndc_p−Ndc_n) between the DC voltage terminal Ndc_p and the DC voltage terminal Ndc_n is equivalent to two times of the voltage difference (Ndc_h−Ndc_n) between the half-DC voltage terminal Ndc_h and the DC voltage terminal Ndc_n (that is, Ndc_p−Ndc_n=2(Ndc_h−Ndc_n)).

The conversion module31aincludes a flying capacitor Cf1, an upper DC circuit dcCKTu1, an upper middle circuit mCKTu1, a lower DC circuit dcCKTd1, a lower middle circuit mCKTd1, an upper inner circuit inCKTu1, a lower inner circuit inCKTd1, an upper conversion circuit vCKTu1, and a lower conversion circuit vCKTd1. To define the circuits based on their relative positions, the conversion module31ais a combination of a DC stage circuit located near the DC voltage terminals Ndc_p, Ndc_n, a conversion stage circuit located near the conversion terminals Na, Nb, and an inner stage circuit located between the DC stage circuit and the conversion stage circuit.

The conversion module31cincludes a flying capacitor Cf2, an upper DC circuit dcCKTu2, an upper middle circuit mCKTu2, a lower DC circuit dcCKTd2, a lower middle circuit mCKTd2, an upper inner circuit inCKTu2, a lower inner circuit inCKTd2,an upper conversion circuit vCKTu2, and a lower conversion circuit vCKTd2. To define the circuits based on their relative positions, the conversion module31cis a combination of a DC stage circuit located near the DC voltage terminals Ndc_p, Ndc_n, a conversion stage circuit located near the conversion terminals Na, Nb, and an inner stage circuit located between the DC stage circuit and the conversion stage circuit.

Table 1 shows the circuits in the DC stage circuits, the conversion stage circuits, and the inner stage circuits of the conversion modules31a,31c.

FromFIG.3and Table 1, the interior circuits and their connections in the conversion module31aare virtually corresponding to those in the conversion module31c(that is, mirror images of each other). The interior circuits and their connections in the conversion module31aare described sequentially as follows. In the upper half of the conversion module31aas shown inFIG.3, the upper DC circuit dcCKTu1is electrically connected to the DC voltage terminal Ndc_p and a quarter-DC voltage terminal Nqd_u1; the upper middle circuit mCKTu1is electrically connected to the quarter-DC voltage terminal Nqd_u1and the half-DC voltage terminal Ndc_h; the upper inner circuit inCKTu1is electrically connected to the quarter-DC voltage terminal Nqd_u1and a modulation terminal Npwm_p1; and the upper conversion circuit vCKTu1is electrically connected to the modulation terminal Npwm_p1and the conversion terminal Na. Similarly, in the lower half of the conversion module31aas shown inFIG.3, the lower DC circuit dcCKTd1is electrically connected to the DC voltage terminal Ndc_n and a quarter-DC voltage terminal Nqd_d1; the lower middle circuit mCKTd1is electrically connected to the quarter-DC voltage terminal Nqd_d1and the half-DC voltage terminal Ndc_h; the lower inner circuit inCKTd1is electrically connected to the quarter-DC voltage terminal Nqd_d1and a modulation terminal Npwm_n1; and the lower conversion circuit vCKTd1is electrically connected to the modulation terminal Npwm_d1and the conversion terminal Na. The flying capacitor Cf1is located between the two halves of the conversion module31a, wherein a positive terminal and a negative terminal of the flying capacitor Cf1are electrically connected to the modulation terminals Npwm_p1and Npwm_n1, respectively. When the flying capacitor Cf1is fully charged, the cross-voltage VCf1of the flying capacitor Cf1is equal to one-quarter of the voltage difference between the DC voltage terminals Ndc_p, Ndc_n, that is,

Subsequently, the interior circuits and their connections in the conversion module31care described sequentially as follows. In the upper half of the conversion module31cas shown inFIG.3, the upper DC circuit dcCKTu2is electrically connected to the DC voltage terminal Ndc_p and a quarter-DC voltage terminal Nqd_u2; the upper middle circuit mCKTu2is electrically connected to the quarter-DC voltage terminal Nqd_u2and the half-DC voltage terminal Ndc_h; the upper inner circuit inCKTu2is electrically connected to the quarter-DC voltage terminal Nqd_u2and a modulation terminal Npwm_p2; and the upper conversion circuit vCKTu2is electrically connected to the modulation terminal Npwm_p2and the conversion terminal Nb. Similarly, In the lower half of the conversion module31cas shown inFIG.3, the lower DC circuit dcCKTd2is electrically connected to the DC voltage terminal Ndc_n and a quarter-DC voltage terminal Nqd_d2; the lower middle circuit mCKTd2is electrically connected to the quarter-DC voltage terminal Nqd_d2and the half-DC voltage terminal Ndc_h, the lower inner circuit inCKTd2is electrically connected to the quarter-DC voltage terminal Nqd_d2and a modulation terminal Npwm_n2; and the lower conversion circuit vCKTd2is electrically connected to the modulation terminal Npwm_d2and the conversion terminal Nb. The flying capacitor Cf2is located between the two halves of the conversion module31c, wherein a positive terminal and a negative terminal of the flying capacitor Cf2are electrically connected to the modulation terminals Npwm_p2and Npwm_n2, respectively. When the flying capacitor Cf2is fully charged, the cross-voltage VCf2of the flying capacitor Cf2is equivalent to one-quarter of the voltage difference between the DC voltage terminals Ndc_p, Ndc_n, that is,

The subsequent description will provide further circuit details of the conversion modules31a,31cofFIG.3.FIG.4is a circuit diagram of the voltage-conversion module according to the embodiment of the disclosure. Please refer to bothFIGS.3and4for the description.

In the conversion module31a, the upper DC circuit dcCKTu1includes DC switch units dsu11, dsu21; the upper middle circuit mCKTu1includes middle switch units msu11, msu21; the lower DC circuit dcCKTd1includes DC switch units dsd11, dsd21; and the lower middle circuit mCKTd1includes middle switch units msd11, msd21. The upper inner circuit inCKTu1includes an inner switch unit inf_u1; and the lower inner circuit inCKTd1includes an inner switch unit inf_d1. The upper conversion circuit vCKTu1includes a conversion switch unit cvtf_u1; and the lower conversion circuit vCKTd1includes a conversion switch unit cvtf_d1.

In the conversion module31c, the upper DC circuit dcCKTu2includes DC switch units dsu12, dsu22; the upper middle circuit mCKTu2includes middle switch units msu12, msu22; the lower DC circuit dcCKTd2includes DC switch units dsd12, dsd22; and the lower middle circuit mCKTd2includes middle switch units msd12, msd22. The upper inner circuit inCKTu2includes an inner switch unit inf_u2; and the lower inner circuit inCKTd2includes an inner switch unit inf_d2. The upper conversion circuit vCKTu2includes a conversion switch unit cvtf_u2; and the lower conversion circuit vCKTd2includes a conversion switch unit cvtf_d2.

FromFIG.4, each conversion module31a,31cshows up-down symmetry in view of circuit blocks and switch units, which are shown in Table 2.

InFIG.4, each of the inner switch units (inf_u1, inf_d1, inf_u2, inf_d2) and the conversion switch units (cvtf_u1, cvtf_d1, cvtf_u2, cvtf_d2) includes more than one transistor, a diode and a series resistor-capacitor connected in parallel. Each of the DC switch units (dsu11, dsu21, dsu12, dsu12, dsd11, dsd21, dsd12, dsd22) and the middle switch units (msu11, msu21, msu12, msu22, msd11, msd21, msd12, msd22) includes more than one transistor, a diode and a resistor connected in parallel. In the conversion module31a, gate terminals of the transistors of the switch units (that is, the DC switch units dsu11, dsu21, dsd11, dsd21, the middle switch units msu11, msu21, msd11, msd21, the inner switch units inf_u1, inf_d1and the conversion switch units cvtf_u1, cvtf_d1) receive the switch-control signals Ssw_g1generated by the control circuit33. Similarly, in the conversion module31c, gate terminals of the transistors of the switch units (that is, the DC switch units dsu12, dsu22, dsd12, dsd22, the middle switch units msu12, msu22, msd12, msd22, the inner switch units inf_u2, inf_d2and the conversion switch units cvtf_u2, cvtf_d2) receive the switch-control signals Ssw_g2generated by the control circuit33. During the process of converting the DC voltage (DC) into the AC voltage (AC) with the voltage-conversion module31, the inductor L can smooth the current, and the capacitor C can smooth the voltage.

FIG.4gives a simplified drawing showing only one transistor in each switch unit. In real practice, each switch unit may include a plurality of transistors to withstand higher currents. Such modifications for various applications can be made without further explanation or details. In the description, the transistors used in the switch units are NMOS transistors, but are not limited to this kind of power transistors. The current direction in the transistor(s) is opposite to that in the diode in each switch unit. Table 3 shows the circuits and their corresponding switch units and the components of the switch units.

FIG.5shows waveforms of related signals when the voltage-conversion module converts the DC voltage (DC) into the AC voltage (AC). Please refer to bothFIGS.3and5. The battery module41provides the DC voltage (DC) having a constant positive DC voltage value Vdc. After the conversion modules31a,31creceive the DC voltage (DC), a modified sine wave Vab is generated between the conversion terminals Na, Nb. The modified sine wave Vab has PWM waveform property, and the voltage value is time-dependent. The filter circuit38filters the modified sine wave Vab, and then outputs the AC voltage (AC) at the AC terminals Np, Nn. In the disclosure, the symbols Va and Vb represent the voltages at the conversion terminals Na and Nb, respectively.

The waveforms inFIG.5are the DC voltage (DC), the modified sine wave Vab and the AC voltage (AC) in a top-to-bottom order. The pulse width of the modified sine wave Vab varies with the frequency of the carrier wave. According to the definition in the disclosure, the voltage of the modified sine wave Vab is the output voltage corresponding to the modified sine wave Vab. The DC voltage (DC) has a constant positive DC voltage value Vdc. The modified sine wave Vab and the AC voltage (AC) continue to rise from the ground voltage Gnd to the positive DC voltage value Vdc, decrease from the positive DC voltage value Vdc to the negative DC voltage value −Vdc, and rise from the negative DC voltage value −Vdc to the ground voltage Gnd cyclically.

One cycle Tcyc of the AC voltage (AC) is the interval between time points t1and t9, wherein a duration between the time points t1, and t5is defined as a positive half-cycle Tpos of the AC voltage (AC), and a duration between the time points t5and t9is defined as a negative half-cycle Tneg of the AC voltage (AC). The AC voltage (AC) is generated by filtering the modified sine wave Vab with the filter circuit38, so the AC voltage (AC) and the modified sine wave Vab have an equal period, and the voltage of the AC voltage (AC) depends on the voltage of the modified sine wave Vab. According to the disclosure, when the voltage conversion device3is converting the DC voltage (DC) into the AC voltage (AC), the control circuit33determines the switch-control signals Ssw_g1, Ssw_g2to control the switch units of the conversion modules31a,31caccording to the voltage of the modified sine wave Vab.

According to the disclosure, during the dc-to-ac conversion process, the control circuit33controls the voltage-conversion module31in eight conversion states. The waveforms of the switch-control signals Ssw_g1, Ssw_g2generated by the control circuit33and the combination of elements to be enabled in the voltage-conversion module31vary with the conversion states. Also, the modified sine wave Vab varies with the conversion states.

Subsequently, the dc-to-ac conversion process performed by the voltage-conversion module31is described inFIGS.6A-6H. In these diagrams, no electrical signal passes through the elements in thinner lines. On the contrary, electrical signals pass through the elements in thicker lines, including the switch units receiving the switch-control signals Ssw_g1, Ssw_g2, and other elements having current flow therein. Therefore, the elements in thicker lines are in the selected current path, but the elements in thinner lines are not. The dashed arrows indicate the directions of the electrical signals. Table 4 briefly lists the voltage of the modified sine wave Vab and the corresponding time period in each conversion state.

The voltages of the modified sine wave Vab and the dc-to-ac conversion states of the voltage-conversion module31corresponding to the time periods between the time points t1and t9given in Table 4 will be described inFIGS.6A-6H. The details of how the control circuit33controls the voltage-conversion module31between the time points t1and t2shown inFIG.5can be derived from the description regarding the time periods T2, T2a, T2bwithout further explanation. Similarly, the details of how the control circuit33controls the voltage-conversion module31between the time points t8and t9shown inFIG.5can be derived from the description regarding the time periods T3, T3a, T3bwithout further explanation.

The voltage-conversion module31enters the first dc-to-ac conversion state d2aST_p during the time period T1inFIG.5. Please refer toFIGS.3,5,6A, and Table 4 together. InFIG.6A, the control circuit33transmits the switch-control signals Ssw_g1with a PWM waveform to the gate terminals of the transistors of the DC switch units dsu11, dsu21, the inner switch unit inf_u1, and the conversion switch unit cvtf_u1of the conversion module31a, and transmits the switch-control signals Ssw_g2with a PWM waveform to the gate terminals of the transistors of the conversion switch unit cvtf_d2, the inner switch unit inf_d2and the DC switch units dsd22, dsd12of the conversion module31c. The current can flow through these switch units receiving the switch-control signals Ssw_g1, Ssw_g2, and such switch units are called enabled switch units in the disclosure. Other non-mentioned switch units are switched off and disabled.

As shown inFIG.6A, the current supplied by the battery module41sequentially flows through the DC voltage terminal Ndc_p, the transistors of the DC switch units dsu11, dsu21, the transistor of the inner switch unit inf_u1, the transistor of the conversion switch unit cvtf_u1, the inductor La, the filter circuit31e, the inductor Lb, the transistor of the conversion switch unit cvtf_d2, the transistor of the inner switch unit inf_d2, the transistors of the DC switch units dsd22, dsd12, and the DC voltage terminal Ndc_n.

According to the current path corresponding to the first dc-to-ac conversion state d2aST_p, the voltage value of the modified sine wave Vab is equal to the voltage difference between the voltages at the DC voltage terminals Ndc_p and Ndc_n, as derived in equation (1).

The voltage-conversion module31enters the second dc-to-ac conversion state d2aST_pml during the time period T2ainFIG.5. Please refer toFIGS.3,5,6B, and Table 4 together. InFIG.6B, the control circuit33transmits the switch-control signals Ssw_g1with a PWM waveform to the gate terminals of the transistors of the DC switch units dsu11, dsu21, the inner switch unit inf_u1, and the conversion switch unit cvtf_d1of the conversion module31a, and transmits the switch-control signals Ssw_g2with a PWM waveform to the gate terminals of the transistors of the conversion switch unit cvtf_u2, the inner switch unit inf_d2and the DC switch units dsd22, dsd12of the conversion module31c. Other non-mentioned switch units are switched off and disabled.

As shown inFIG.6B, the current supplied by the battery module41sequentially flows through the DC voltage terminal Ndc_p, the transistors of the DC switch units dsu11, dsu21, the transistor of the inner switch unit inf_u1, the flying capacitor Cf1, the diode of the conversion switch unit cvtf_d1, the inductor La, the filter circuit31e, the inductor Lb, the diode of the conversion switch unit cvtf_u2, the flying capacitor Cf2, the transistor of the inner switch unit inf_d2, the transistors of the DC switch units dsd22, dsd12, and the DC voltage terminal Ndc_n.

The current flows to and charges the flying capacitors Cf1, Cf2. The cross-voltage VCf1, VCf2of each flying capacitor Cf1, Cf2is equal to one-quarter of the positive DC voltage value Vdc

According to the current path corresponding to the second dc-to-ac conversion state d2aST_pml, the voltage value of the modified sine wave Vab is equal to half the positive DC voltage value Vdc

as derived in equation (2).

It is shown that the current paths inFIGS.6A and6Bare similar. Concretely speaking, inFIG.6A, the DC switch units dsu11, dsu21, dsd22, dsd12, the inner switch units inf_u1, inf_d2and the conversion switch units cvtf_u1, cvtf_d2among the switch units receive the PWM signals. InFIG.6B, the conversion switch units cvtf_d1, cvtf_u2, instead of the conversion switch units cvtf_u1, cvtf_d2, receive the PWM signals. Furthermore, the current does not flow to the flying capacitors Cf1, Cf2inFIG.6A, but flows to the flying capacitors Cf1, Cf2inFIG.6B. Therefore, the control circuit33can rapidly change the target switch units for receiving the PWM signals in response to the switching from the first dc-to-ac conversion state d2aST_p to the second dc-to-ac conversion state d2aST_pml. Hence, the conversion efficiency of the voltage conversion device3and the quality of the output waveforms are increased.

The voltage-conversion module31enters the third dc-to-ac conversion state d2aST_pmd during the time period T2binFIG.5. Please refer toFIGS.3,5,6C, and Table 4 together. InFIG.6C, the control circuit33transmits the switch-control signals Ssw_g1with a PWM waveform to the gate terminals of the transistors of the middle switch units msd21, msd11, the inner switch unit inf_d1and the conversion switch unit cvtf_u1of the conversion module31a, and transmits the switch-control signals Ssw_g2with a PWM waveform to the gate terminals of the transistors of the conversion switch unit cvtf_d2, the inner switch unit inf_u2and the middle switch units msu12, msu22of the conversion module31c. Other non-mentioned switch units are switched off and disabled.

As shown inFIG.6C, the current from the voltage divider capacitor Cd2sequentially flows through the half-DC voltage terminal Ndc_h, the transistors of the middle switch units msd21, msd11, the diode of the inner switch unit inf_d1, the flying capacitor Cf1, the transistor of the conversion switch unit cvtf_u1, the inductor La, the filter circuit31e, the inductor Lb, the transistor of the conversion switch unit cvtf_d2, the flying capacitor Cf2, the diode of the inner switch unit inf_u2and the transistors of the middle switch units msu12, msu22.

When the voltage-conversion module31is in the third dc-to-ac conversion state d2aST_pmd, the cross-voltage VCf1, VCf2of each flying capacitor Cf1, Cf2is equal to one-quarter of the positive DC voltage value Vdc

At this time, the flying capacitors Cf1, Cf2are discharged. According to the current path corresponding to the third dc-to-ac conversion state d2aST_pmd, the voltage value of the modified sine wave Vab is equal to half the positive DC voltage value Vdc

as derived in equation (3).

The voltage-conversion module31enters the fourth dc-to-ac conversion state d2aST_gp during the time period T2inFIG.5. Please refer toFIGS.3,5,6D, and Table 4 together. InFIG.6D, the control circuit33transmits the switch-control signals Ssw_g1with a PWM waveform to the gate terminals of the transistors of the middle switch units msd21, msd11, the inner switch unit inf_d1and the conversion switch unit cvtf_d1of the conversion module31a, and transmits the switch-control signals Ssw_g2with a PWM waveform to the gate terminals of the transistors of the conversion switch unit cvtf_u2, the inner switch unit inf_u2and the middle switch units msu12, msu22of the conversion module31c. Other non-mentioned switch units are switched off and disabled.

In the fourth dc-to-ac conversion state d2aST_gp, the middle switch units msd21, msd11, msu12, msu22, the inner switch units inf_d1, inf_u2, and the conversion switch units cvtf_d1, cvtf_u2are switched on. At this time, the half-DC voltage terminal Ndc_h receives the ground voltage (Ndc_h=Gnd), and no current is generated in the conversion modules31a,31c. Therefore, the voltage value of the modified sine wave Vab is equal to the ground voltage Gnd, that is, Vab=Gnd.

Please refer toFIGS.5and6B-6Dtogether. The time period T2is divided into the time periods T2aand T2b. The conversion state of the voltage-conversion module31inFIG.6Bpresents, within the time period T2a; the conversion state of the voltage-conversion module31inFIG.6Cpresents within the time period T2b; and the conversion state of the voltage-conversion module31inFIG.6Dpresents within the time period T2. During the time period T2a, the voltage-conversion module31is switched between the second dc-to-ac conversion state d2aST_pml and the fourth dc-to-ac conversion state d2aST_gp. During the time period T2b, the voltage-conversion module31is switched between the third dc-to-ac conversion state d2aST_pmd and the fourth dc-to-ac conversion state d2aST_gp.

It is to be noted that although the voltage value of the modified sine wave Vab alternates between half the positive DC voltage value Vdc

and the ground voltage (Vab=Gnd) in both of the time periods T2aand T2b, the control circuit33transmits the switch-control signals Ssw_g1, Ssw_g2with different PWM waveforms to the conversion modules31a,31cin different dc-to-ac conversion states (that is, the second dc-to-ac conversion state d2aST_pml and the third dc-to-ac conversion state d2aST_pmd). The pulse width of the modified sine wave Vab in the time period T2ais different from that in the time period T2b.

The voltage-conversion module31enters the fifth dc-to-ac conversion state d2aST_gn during the time period T3inFIG.5. Please refer toFIGS.3,5,6E, and Table 4 together. InFIG.6E, the control circuit33transmits the switch-control signals Ssw_g1with a PWM waveform to the gate terminals of the transistors of the middle switch units msu21, msu11, the inner switch unit inf_u1and the conversion switch unit cvtf_u1of the conversion module31a, and transmits the switch-control signals Ssw_g2with a PWM waveform to the gate terminals of the transistors of the conversion switch unit cvtf_d2, the inner switch unit inf_d2and the middle switch units msd12, msd22of the conversion module31c. Other non-mentioned switch units are switched off and disabled.

In the fifth dc-to-ac conversion state d2aST_gn, the middle switch units msd12, msd22, msu11, msu21, the inner switch units inf_d2, inf_u1, and the conversion switch units cvtf_d2, cvtf_u1are switched on. At this time, the voltage of half-DC voltage terminal Ndc_h is equal to the ground voltage (Ndc_h=Gnd), so no current is generated in the conversion modules31a,31c. Therefore, the voltage value of the modified sine wave Vab is equal to the ground voltage Gnd, that is, Vab=Gnd.

The voltage-conversion module31enters the sixth dc-to-ac conversion state d2aST_nmd during the time period T3ainFIG.5. Please refer toFIGS.3,5,6F, and Table 4 together. InFIG.6F, the control circuit33transmits the switch-control signals Ssw_g1with a PWM waveform to the gate terminals of the transistors of the middle switch units msu21, msu11, the inner switch unit inf_u1and the conversion switch unit cvtf_d1of the conversion module31a, and transmits the switch-control signals Ssw_g2with a PWM waveform to the gate terminals of the transistors of the conversion switch unit cvtf_u2, the inner switch unit inf_d2and the middle switch units msd12, msd22of the conversion module31c. Other non-mentioned switch units are switched off and disabled.

As shown inFIG.6F, the current from the voltage divider capacitor Cd1sequentially flows through the half-DC voltage terminal Ndc_h, the transistors of the middle switch units msd22, msd12, the diode of the inner switch unit inf_d2, the flying capacitor Cf2, the transistor of the conversion switch unit cvtf_u2, the inductor Lb, the filter circuit31e, the inductor La, the transistor of the conversion switch unit cvtf_d1, the flying capacitor Cf1, the diode of the inner switch unit inf_u1and the transistors of the middle switch units msu11, msu21.

When the voltage-conversion module31is in the sixth dc-to-ac conversion state d2aST_nmd, the cross-voltage VCf1, VCf2of each flying capacitor Cf1, Cf2is equal to one-quarter of the positive DC voltage value Vdc

At this time, the flying capacitors Cf1, Cf2are discharged. According to the current path corresponding to the sixth dc-to-ac conversion state d2aST_nmd, the voltage value of the modified sine wave Vab is equal to half the negative DC voltage value −Vdc

as derived in equation (4).

The voltage-conversion module31enters the seventh dc-to-ac conversion state d2aST_nml during the time period T3binFIG.5. Please refer toFIGS.3,5,6G, and Table 4 together. InFIG.6G, the control circuit33transmits the switch-control signals Ssw_g1with a PWM waveform to the gate terminals of the transistors of the DC switch units dsd11, dsd21, the inner switch unit inf_d1, and the conversion switch unit cvtf_u1of the conversion module31a, and transmits the switch-control signals Ssw_g2with a PWM waveform to the gate terminals of the transistors of the conversion switch unit cvtf_d2, the inner switch unit inf_u2and the DC switch units dsu22, dsu12of the conversion module31c. Other non-mentioned switch units are switched off and disabled.

As shown inFIG.6G, the current supplied by the battery module41sequentially flows through the DC voltage terminal Ndc_p, the transistors of the DC switch units dsu12, dsu22, the transistor of the inner switch unit inf_u2, the flying capacitor Cf2, the diode of the conversion switch unit cvtf_d2, the inductor Lb, the filter circuit31e, the inductor La, the diode of the conversion switch unit cvtf_u1, the flying capacitor Cf1, the transistor of the inner switch unit inf_d1, the transistors of the DC switch units dsd21, dsd11, and the DC voltage terminal Ndc_n.

The current flows to and charges the flying capacitors Cf1, Cf2. The cross-voltage VCf1, VCf2of each flying capacitor Cf1, Cf2is equal to one-quarter of the positive DC voltage value Vdc

At this time, the flying capacitors Cf1, Cf2are charging. According to the current path corresponding to the seventh dc-to-ac conversion state d2aST_nml, the voltage value of the modified sine wave Vab is equal to half the negative DC voltage value −Vdc

as derived in equation (5).

Please refer toFIGS.5and6E-6Gtogether. The time period T3is divided into the time periods T3aand T3b. The conversion state of the voltage-conversion module31inFIG.6Epresents, within the time period T3; the conversion state of the voltage-conversion module31inFIG.6Fpresents within the time period T3a; and the conversion state of the voltage-conversion module31inFIG.6Gpresents within the time period T3b. During the time period T3a, the voltage-conversion module31is switched between the sixth dc-to-ac conversion state d2aST_nmd and the fifth dc-to-ac conversion state d2aST_gn. During the time period T3b, the voltage-conversion module31is switched between the seventh dc-to-ac conversion state d2aST_nml and the fifth dc-to-ac conversion state d2aST_gn.

It is to be noted that although the voltage value of the modified sine wave Vab alternates between half the negative DC voltage value −Vdc

and the ground voltage (Vab=Gnd) in both of the time periods T3aand T3b, the control circuit33transmits the switch-control signals Ssw_g1, Ssw_g2with different PWM waveforms to the conversion modules31a,31cin different dc-to-ac conversion states (that is, the sixth dc-to-ac conversion state d2aST_nmd and the seventh dc-to-ac conversion state d2aST_nml). The pulse width of the modified sine wave Vab in the time period T3ais different from that in the time period T3b.

The voltage-conversion module31enters the eighth dc-to-ac conversion state d2aST_n during the time period T4inFIG.5. Please refer toFIGS.3,5,6H, and Table 4 together. InFIG.6H, the control circuit33transmits the switch-control signals Ssw_g1with a PWM waveform to the gate terminals of the transistors of the DC switch units dsd11, dsd21, the inner switch unit inf_d1, and the conversion switch unit cvtf_d1of the conversion module31a, and transmits the switch-control signals Ssw_g2with a PWM waveform to the gate terminals of the transistors of the conversion switch unit cvtf_u2, the inner switch unit inf_u2and the DC switch units dsu22, dsu12of the conversion module31c. Other non-mentioned switch units are switched off and disabled.

As shown inFIG.6H, the current supplied by the battery module41sequentially flows through the DC voltage terminal Ndc_p, the transistors of the DC switch units dsu12, dsu22, the transistor of the inner switch unit inf_u2, the transistor of the conversion switch unit cvtf_u2, the inductor Lb, the filter circuit31e, the inductor La, the transistor of the conversion switch unit cvtf_d1, the transistor of the inner switch unit inf_d1, the transistors of the DC switch units dsd21, dsd11, and the DC voltage terminal Ndc_n.

According to the current path corresponding to the eighth dc-to-ac conversion state d2aST_n, the voltage value of the modified sine wave Vab is equal to the voltage difference between the voltages at the DC voltage terminals Ndc_n and Ndc_p, as derived in equation (6).

It is shown that the current paths inFIGS.6G and6Hare similar. Concretely speaking, inFIG.6G, the DC switch units dsu12, dsu22, dsd21, dsd11, the inner switch units inf_u2, inf_d1and the conversion switch units cvtf_d2, cvti_u1among the switch units receive the PWM signals. InFIG.6H, the conversion switch units cvtf_u2, cvti_d1, instead of the conversion switch units cvtf_d2, cvtf_u1, receive the PWM signals. Furthermore, the current flows to the flying capacitors Cf1, Cf2inFIG.6G, but does not flow to the flying capacitors Cf1, Cf2inFIG.6H. Therefore, the control circuit33can rapidly change the target switch units for receiving the PWM signals in response to the switching from the seventh dc-to-ac conversion state d2aST_nml to the eighth dc-to-ac conversion state d2aST_n. Hence, the conversion efficiency of the voltage conversion device3and the quality of the output waveforms are increased.

ComparingFIGS.6A and6H, viewed from the positions of the switch units, the arrangement of the enabled switch units (receiving the PWM signal) in the conversion module31ainFIG.6Ais a mirror image of the arrangement of the enabled switch units (receiving the PWM signal) in the conversion module31cinFIG.6H. Similarly, the arrangement of the enabled switch units (receiving the PWM signal) in the conversion module31cinFIG.6Ais a mirror image of the arrangement of the enabled switch units (receiving the PWM signal) in the conversion module31ainFIG.6H. Such mirror copy arrangement of the enabled switch units in the conversion modules31a,31ccan be observed inFIGS.6Bvs.6G,FIGS.6Cvs.6F, andFIGS.6Dvs.6E.

Please see Table 5 showing, based on the above description with reference toFIGS.5and6A-6H, that the control circuit33selects the current paths in the conversion modules31a,31caccording to the voltage value of the modified sine wave Vab when the voltage conversion device3is converting the DC voltage (DC) into the AC voltage (AC).

From Table 5, the PWM signals are transmitted to different switch units (enabled switch units) in different dc-to-ac conversion states. The enabled switch units in respective paths are analyzed as follows.

Regarding the upper/lower DC circuits of the DC stage circuits, the upper DC circuit dcCKTu1or the lower DC circuit dcCKTd1of the conversion module31aand the upper DC circuit dcCKTu2or the lower DC circuit dcCKTd2of the conversion module31creceive the corresponding PWM signals just in the first dc-to-ac conversion state d2aST_p, the second dc-to-ac conversion state d2aST_pml, the seventh dc-to-ac conversion state d2aST_nml, and the eighth dc-to-ac conversion state d2aST_n. Regarding the upper/lower middle circuits of the DC stage circuits, the upper middle circuit mCKTu1or the lower middle circuit mCKTd1of the conversion module31aand the upper middle circuit mCKTu2or the lower middle circuit mCKTd2of the conversion module31creceive the corresponding PWM signals just in the third dc-to-ac conversion state d2aST_pmd, the fourth dc-to-ac conversion state d2aST_gp, the fifth dc-to-ac conversion state d2aST_gn, and the sixth dc-to-ac conversion state d2aST_nmd. Furthermore, it is observed from Table 5 that only one of the upper DC circuit, the lower DC circuit, the upper middle circuit, and the lower middle circuit in the same DC stage circuit receives the corresponding PWM signal in one dc-to-ad conversion state.

Regarding the upper/lower inner circuits of the inner stage circuits, the upper inner circuit inCKTu1of the conversion module31aand the lower inner circuit inCKTd2of the conversion module31creceive the corresponding PWM signals in the same dc-to-ac conversion state; and the lower inner circuit inCKTd1of the conversion module31aand the upper inner circuit inCKTu2of the conversion module31creceive the corresponding PWN signals in the same dc-to-ac conversion state. Further, the upper inner circuit inCKTu1of the conversion module31aand the upper inner circuit inCKTu2of the conversion module31cdo not receive the corresponding PWM signals in the same dc-to-ac conversion state; and the lower inner circuit inCKTd1of the conversion module31aand the lower inner circuit inCKTd2of the conversion module31cdo not receive the corresponding PWM signals in the same dc-to-ac conversion state.

Regarding the upper/lower conversion circuits of the conversion stage circuits, the upper conversion circuit vCKTu1of the conversion module31aand the lower conversion circuit vCKTd2of the conversion module31creceive the corresponding PWM signals in the same dc-to-ac conversion state; and the lower conversion circuit vCKTd1of the conversion module31aand the upper conversion circuit vCKTu2of the conversion module31creceive the corresponding PWM signals in the same dc-to-ac conversion state. Further, the upper conversion circuit vCKTu1of the conversion module31aand the upper conversion circuit vCKTu2of the conversion module31cdo not receive the corresponding PWM signals in the same dc-to-ac conversion state; and the lower conversion circuit vCKTd1of the conversion module31aand the lower conversion circuit vCKTd2of the conversion module31cdo not receive the corresponding PWM signals in the same dc-to-ac conversion state.

It is also observed from Table 5 that the control circuit33selects the circuits according to different rules in the conversion states. For example, the control circuit33changes the selected conversion circuits between two adjacent dc-to-ac conversion states in adjacent rows. The control circuit33controls the upper conversion circuit vCKTu1and the lower conversion circuit vCKTd2to be in the connection mode in the first dc-to-ac conversion state d2aST_p, the third dc-to-ac conversion state d2aST_pmd, the fifth dc-to-ac conversion state 2aST_gn, and the seventh dc-to-ac conversion state d2aST_nml. Alternatively, the control circuit33controls the lower conversion circuit vCKTd1and the upper conversion circuit vCKTu2to be in the connection mode in the second dc-to-ac conversion state d2aST_pml, the fourth dc-to-ac conversion state d2aST_gp, the sixth dc-to-ac conversion state d2aST_nmd, and the eighth dc-to-ac conversion state d2aST_n.

The control circuit33changes the selected inner circuits every two rows of the dc-to-ac conversion states. The control circuit33controls the upper inner circuit inCKTu1and the lower inner circuit inCKTd2to be in the connection mode in the first dc-to-ac conversion state d2aST_p, the second dc-to-ac conversion state d2aST_pml, the fifth dc-to-ac conversion state d2aST_gn, and the sixth dc-to-ac conversion state d2aST_nmd. Alternatively, the control circuit33controls the lower inner circuit inCKTd1and the upper inner circuit inCKTu2to be in the connection mode in the third dc-to-ac conversion state d2aST_pmd, the fourth dc-to-ac conversion state d2aST_gp, the seventh dc-to-ac conversion state d2aST_nml, and the eighth dc-to-ac conversion state d2aST_n.

The DC circuits and the middle circuits are the least selected. The control circuit33controls the upper DC circuit dcCKTu1and the lower DC circuit dcCKTd2to be in the connection mode just in the first dc-to-ac conversion state d2aST_p and the second dc-to-ac conversion state d2aST_pml; and the control circuit33controls the upper DC circuit dcCKTu2and the lower DC circuit dcCKTd1to be in the connection mode just in the seventh dc-to-ac conversion state d2aST_nml and the eighth dc-to-ac conversion state d2aST_n. Alternatively, the control circuit33controls the upper middle circuit mCKTu2and the lower middle circuit mCKTd1to be in the connection mode just in the third dc-to-ac conversion state d2aST_pmd and the fourth dc-to-ac conversion state d2aST_gp; and the control circuit33controls the upper middle circuit mCKTu1and the lower middle circuit mCKTd2to be in the connection mode just in the fifth dc-to-ac conversion state d2aST_gn and the sixth dc-to-ac conversion state d2aST_nmd.

The upper conversion circuit and the lower conversion circuit of the same conversion stage circuit alternately receive the corresponding PWM signal in the dc-to-ac conversion states. The upper DC circuit, lower DC circuit, upper middle circuit, and the lower middle circuit of the same DC stage circuit receive the corresponding PWM signals in respective two of the dc-to-ac conversion states, but any two of the upper DC circuit, lower DC circuit, upper middle circuit and the lower middle circuit of the same DC stage circuit do not receive the corresponding PWM signals in the same dc-to-ac conversion state.

FIGS.5and6A-6Hand the related description have explained how the voltage conversion device3converts the DC voltage (DC) supplied by the battery module41into the AC voltage (AC) to be transmitted to the loading43. The following description withFIGS.7and8A-8Dwill explain how the voltage conversion device3converts the AC voltage (AC) provided by the loading43into the DC voltage (DC) to be provided to the battery module41.FIG.7is a waveform diagram showing waveforms of related signals when the voltage-conversion module31converts the AC voltage (AC) into the DC voltage (DC). The waveform in the upper portion depicts the AC voltage (AC) provided by the loading43; and the waveform in the lower portion depicts the DC voltage (DC) generated by the voltage-conversion module31.

One cycle Tcyc of the AC voltage (AC) is represented by the interval between the time points t1and t5, wherein a positive half-cycle Tpos of the AC voltage (AC) is defined between the time points t1and t3, and a negative half-cycle Tneg of the AC voltage (AC) is defined between the time points t3and t5.

The positive half-cycle Tpos of the AC voltage (AC) includes the time periods Ta, Tb; and the negative half-cycle Tneg of the AC voltage (AC) includes the time periods Tc, Td. The AC voltage (AC) rises from the ground voltage 0V to the positive DC voltage value Vdc during the time period Ta, decreases from the positive DC voltage value Vdc to the ground voltage 0V during the time period Tb, decreases from the ground voltage 0V to the negative DC voltage value −Vdc during the time period Tc, and rises from the negative DC voltage value −Vdc to the ground voltage 0V during the time period Td. Table 6 briefly lists the voltage of the AC voltage (AC) and the corresponding time period in each conversion state.

Please refer toFIGS.2and7together. As described above, when the voltage conversion device3converts the AC voltage (AC) into the DC voltage (DC), the control circuit33controls the conversion module31a,31caccording to the voltage value of the AC voltage (AC). The detection circuit38detects the AC voltage (AC) at the AC terminals Np, Nn and transmits the detection result to the control circuit33. Then, the control circuit33decides the PWM waveforms of the switch-control signals Ssw_g1, Ssw_g2based on the conversion states of the voltage-conversion module31according to the detection results provided by the detection circuit38and the information in the lookup table stored in the storage circuit35.

Subsequently, the ac-to-dc conversion process performed by the voltage-conversion module31is described inFIGS.8A-8H. In these diagrams, elements in thinner lines include the switch units which do not receive the switch-control signals Ssw_g1, Ssw_g2, and the elements having no current flow therein. On the contrary, the elements in thicker lines include the switch units receiving the switch-control signals Ssw_g1, Ssw_g2, and other elements having current flow therein. Therefore, the elements in thicker lines are in the selected current path, but the elements in thinner lines are not. The dashed arrows indicate the directions of the current in the conversion states.

Please refer toFIGS.3,7,8A, and Table 6 together. The first ac-to-dc conversion state a2dST_gp inFIG.8Acorresponds to the time period Ta inFIG.7. During the procedure when the AC voltage (AC) is rising from the ground voltage Gnd to the positive DC voltage value Vdc, the control circuit33transmits the switch-control signals Ssw_g1with a PWM waveform to the gate terminals of the transistors of the middle switch units msd21, msd11, the inner switch unit inf_d1and the conversion switch unit cvtf_d1of the conversion module31a, and transmits the switch-control signals Ssw_g2with a PWM waveform to the gate terminals of the transistors of the conversion switch unit cvtf_u2, the inner switch unit inf_u2and the middle switch unit msu12, msu22of the conversion module31c. Other non-mentioned switch units are switched off and disabled.

In the first ac-to-dc conversion state a2dST_gp, the AC voltage (AC) rises from the ground voltage Gnd to the positive DC voltage value Vdc. At this time, the current from the AC terminal Np flows to the AC terminal Nn through the inductor La, the transistor of the conversion switch unit cvtf_d1, the transistor of the inner switch unit inf_d1, the diodes of the middle switch units msd11, msd21, the half-DC voltage terminal Ndc_h, the diodes of the middle switch units msu22, msu12, the transistor of the inner switch unit inf_u2and the transistor of the conversion switch unit cvtf_u2sequentially.

Please refer toFIGS.3,7,8B, and Table 6 together. The second ac-to-dc conversion state a2dST_pg inFIG.8Bcorresponds to the time period Tb inFIG.7. During the procedure when the AC voltage (AC) is decreasing from the positive DC voltage value Vdc to the ground voltage Gnd, the control circuit33transmits the switch-control signals Ssw_g1with a PWM waveform to the gate terminals of the transistors of the DC switch units dsu11, dsu21, the inner switch unit inf_u1, and the conversion switch unit cvtf_u1of the conversion module31a, and transmits the switch-control signals Ssw_g2with a PWM waveform to the gate terminals of the transistors of the conversion switch unit cvtf_d2, the inner switch unit inf_d2and the DC switch units dsd22, dsd12of the conversion module31c. Other non-mentioned switch units are switched off and disabled.

In the second ac-to-dc conversion state a2dST_pg, the AC voltage (AC) decreases from the positive DC voltage value Vdc to the ground voltage Gnd. At this time, the current from the AC terminal Np flows to the AC terminal Nn through the inductor La, the diode of the conversion switch unit cvtf_u1, the diode of the inner switch unit inf_u1, the diodes of the DC switch units dsu21, dsu11, the battery module41, the diodes of the DC switch units dsd12, dsd22, the diode of the inner switch unit inf_d2, the diode of the conversion switch unit cvtf_d2and the inductor Lb sequentially. The current flows through the battery module41and thus charges the battery module41.

Please refer toFIGS.3,7,8C, and Table 6 together. The third ac-to-dc conversion state a2dST_gn inFIG.8Ccorresponds to the time period Tc inFIG.7. During the procedure when the AC voltage (AC) is decreasing from the ground voltage Gnd to the negative DC voltage value −Vdc, the control circuit33transmits the switch-control signals Ssw_g1with a PWM waveform to the gate terminals of the transistors of the middle switch units msu21, msu11, the inner switch unit inf_u1and the conversion switch unit cvtf_u1of the conversion module31a, and transmits the switch-control signals Ssw_g2with a PWM waveform to the gate terminals of the transistors of the conversion switch unit cvtf_d2, the inner switch unit inf_d2and the middle switch units msd12, msd22of the conversion module31c. Other non-mentioned switch units are switched off and disabled.

In the third ac-to-dc conversion state a2dST_gn, the AC voltage (AC) decreases from the ground voltage Gnd to the negative DC voltage value −Vdc. As shown inFIG.8C, the current from the AC terminal Np flows to the AC terminal Np through the transistor of the conversion switch unit cvtf_d2, the transistor of the inner switch unit inf_d2, the diodes of the middle switch units msd12, msd22, the half-DC voltage terminal Ndc_h, the diodes of the middle switch units msu21, msu11, the transistor of the inner switch unit inf_u1, the transistor of the conversion switch unit cvtf_u1and the inductor La sequentially.

Please refer toFIGS.3,7,8D, and Table 6 together. The fourth ac-to-dc conversion state a2dST_ng inFIG.8Dcorresponds to the time period Td inFIG.7. During the procedure when the AC voltage (AC) is rising from the negative DC voltage value −Vdc to the ground voltage Gnd, the control circuit33transmits the switch-control signals Ssw_g1with a PWM waveform to the gate terminals of the transistors of the DC switch units dsd11, dsd21, the inner switch unit inf_d1, and the conversion switch unit cvtf_d1of the conversion module31a, and transmits the switch-control signals Ssw_g2with a PWM waveform to the gate terminals of the transistors of the conversion switch unit cvtf_u2, the inner switch unit inf_u2and the DC switch units dsu22, dsu12of the conversion module31c. Other non-mentioned switch units are switched off and disabled.

In the fourth ac-to-dc conversion state a2dST_ng, the AC voltage (AC) rises from the negative DC voltage value −Vdc to the ground voltage Gnd. As shown inFIG.8D, the current from the AC terminal Nn flows to the AC terminal Np through the diode of the conversion switch unit cvtf_u2, the diode of the inner switch unit inf_u2, the diodes of the DC switch units dsu22, dsu12, the DC voltage terminal Ndc_p, the battery module41, the DC voltage terminal Ndc_n, the diodes of the DC switch units dsd11, dsd21, the diode of the inner switch unit inf_d1, the diode of the conversion switch unit cvtf_d1and the inductor La sequentially. The current flows through the battery module41and thus charges the battery module41.

Please refer toFIGS.8A and8Ctogether. The current path in the conversion modules31a,31cinFIG.8A(the first ac-to-dc conversion state a2dST_gp) is a mirror image of the current path in the conversion modules31c,31ainFIG.8C(the third ac-to-dc conversion state a2dST_gn). In other words, the control circuit33selects similar switch units in the conversion module31aduring the conversion state corresponding toFIG.8Aand the conversion module31cduring the conversion state corresponding toFIG.8C. Also, the control circuit33selects similar switch units in the conversion module31cduring the conversion state corresponding toFIG.8Aand the conversion module31aduring the conversion state corresponding toFIG.8C. Similarly, the combination of the switch units receiving the PWM signals in the conversion modules31a,31cinFIG.8Bis a mirror image of that in the conversion modules31c,31ainFIG.8D.

Please refer to Table 7, showing, based on the above description with reference toFIGS.7and8A-8D, that the control circuit33selects the current paths in the interior elements of the conversion modules31a,31caccording to the voltage value of the AC voltage (AC) when the voltage conversion device3converts the AC voltage (AC) into the DC voltage (DC). It is observed from Table 7 that no current flows to the flying capacitors Cf1, Cf2. InFIGS.8A-8D. Therefore, the flying capacitors Cf1, Cf2are not in use (suspended) when the voltage conversion device3converts the AC voltage (AC) into the DC voltage (DC).

FIGS.5and6A-6Hand related descriptions explain how the voltage conversion device3converts the DC voltage (DC) into the AC voltage (AC) in eight dc-to-ac conversion states.FIGS.7and8A-8Dand related descriptions explain how the voltage conversion device3converts the AC voltage (AC) into the DC voltage (DC) in four ac-to-dc conversion states. Comparing the two types of the voltage conversion process, the control circuit33selects the same switch units inFIGS.6D and8A; the control circuit33selects the same switch units inFIGS.6A and8B; the control circuit33selects the same switch units inFIGS.6E and8C; and the control circuit33selects the same switch units inFIGS.6H and8D.

According to the above description, not only the dc-to-ac conversion but also the ac-to-dc conversion can be performed by switching on proper switch units in the voltage-conversion modules with the control circuit. The voltage conversion device of the disclosure can be switched between different voltage conversion states more rapidly. Based on the disclosed circuit architecture, no additional heat sink or fan is required to dissipate heat in the voltage conversion device. The power consumption of the switch units takes only 0.5% of the overall power consumption. Compared with the full-bridge architecture in the prior arts, the resistors R, the inductors L, the capacitors C and the filter circuit of the switch units of the disclosure occupy smaller space. Therefore, the voltage conversion device of the disclosure has higher conversion efficiency, smaller size, and reduced hardware cost.