DC to AC converter and control method thereof

A direct current (DC) to alternating current (AC) converter in accordance with an embodiment includes a battery array module, a battery control module and a polarity converter, wherein the battery array module and the magnetic converter are respectively coupled to the battery control module. The battery array module is used to receive DC signals. The battery array module is controlled by the battery control module to reconfigure and generate a multi-phase step signal. The multi-phase step signal is sent to the polarity converter. The multi-phase step signal is converted into an AC signal output by the polarity converter.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 107108587, filed on Mar. 14, 2018. The entirety of the above-mentioned patent application is hereby incorporated by reference herein.

TECHNICAL FIELD

The technical field generally relates to a DC to AC (direct current to alternating current) converter and a control method thereof.

BACKGROUND

Nowadays, the issue of green energy is becoming increasingly important. In particular, related industries such as electric cars and electric motor vehicles of electric vehicles continue to flourish. There is a considerable demand of power supplies for electric vehicles. Lithium batteries are widely used products today, which will drive lithium batteries to replace the current lead-acid batteries in the future. With the use of cloud computing and the popularity of network storage devices, power array systems have also been adopted in order to enhance endurance. However, the use of a power array system will result in its corresponding high output voltage. Novel and complex control strategies are needed to be incorporated with the high output voltage. In order to continuously improve the efficiency and the practicality of power management, the design of energy conversion converters plays an important role and needs to be fully considered in the design of the overall system.

The realization of a general multi-level inverter system requires a DC-bus voltage source. The DC bus voltage source is divided by a plurality of series capacitors and is spliced with a plurality of semiconductor switches, and switches the semiconductor switches to achieve multi-phase voltage output. When the order of the required multi-level inverter increases, the number of switching elements and capacitors required by this system increases, resulting in increased cost and complicated control.

Working modes of multi-level inverters are, for example, a grid connected mode, a line interactive mode, or a stand-alone mode. There may be a problem of energy loss for the multi-level inverters under the working modes. Therefore, how to incorporate with a power management system and a power transfer system to maintain the system's optimal application state and integration of energy storage and energy transfer is one of the important issues today.

SUMMARY OF THE DISCLOSURE

According to an embodiment of the disclosure, a direct current (DC) to alternating current (AC) converter comprises a battery array module used to receive a DC signal; a battery control module used to control the battery array module to reconfigure and generate a multi-phase step signal; and a polarity converter used to convert the multi-phase step signal into an AC signal output.

According to an embodiment of the disclosure, a control method for a direct current (DC) to alternating current (AC) converter comprises receiving a DC signal by using a battery array module; reconfiguring and generating a multi-phase step signal by controlling the battery array module with a battery control module; and converting the multi-phase step signal into an AC signal output by using a polarity converter.

The foregoing will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

FIG. 1shows a functional block diagram of a direct current (DC) to alternating current (AC) converter100according to an embodiment of this disclosure. As shown inFIG. 1, the DC to AC converter100comprises a battery array module110, a battery control module120and a polarity converter130. The battery array module110and the polarity converter130are coupled to the battery control module120, respectively. The battery array module110is used to receive a DC signal. The battery control module120is used to control the battery array module to reconfigure out a multi-phase step signal which is transmitted to the polarity converter130. The polarity converter130converts the multi-phase step signal into an AC signal output.

FIG. 2shows a block diagram of the battery array module110according to an embodiment of this disclosure. The battery array module110comprises one or multiple battery modules110_i_j, where i=1, 2, . . . , n, j=1, 2, . . . , m, and n and m are positive integers greater than or equal to 1. A plurality of battery string modules110_1˜110_min series formed by the one or multiple battery modules110_i_jare controlled by a current mode switching converter110_m_t. The battery string modules110_1˜110_mare electrically connected in parallel to form the battery array module110.

Referring toFIG. 1andFIG. 2, when the battery array module110receives a DC signal through a DC receiving terminal, the battery control module120generates the multi-phase step signal by increasing the quantity of the plurality of battery string modules110_1˜110_mand decreasing the quantity of the plurality of battery string modules110_1˜110_m. An enable mode or a bypass mode could be used to switch the battery string modules110_1˜110_mfor increasing or decreasing the quantity of the battery string modules110_1˜110_m. The multi-phase step signal could be generated by a smooth analog signal approximating the original input signal with an integral processing or a low-pass filter. According to an embodiment, a 4-phase step signal could be generated by the battery control module120which controls the battery array module110to increase and decrease any five of battery modules110_1_1˜110_n_1. The abovementioned method could be used to generate other different multi-phase step signals and will not be repeated here. The multi-phase step signal is then transmitted to the polarity converter130for converting the multi-phase step signal into an AC signal output.

FIG. 3Ashows a circuit schematic diagram of the polarity converter130according to an embodiment of this disclosure. The polarity converter130comprises a first power switch Q1, a second power switch Q2, a third power switch Q3, a fourth power switch Q4, an inductor L, a capacitor C, diodes D1˜D4(a first diode, a second diode, a third diode and a fourth diode), and a control unit101. The first power switch Q1and the second power switch Q2are connected to each other in series. The third power switch Q3and the fourth power switch Q4are connected to each other in series. The first power switch Q1and the second power switch Q2are connected to the third power switch Q3and the fourth power switch Q4in parallel. The first power switch Q1, the second power switch Q2, the third power switch Q3and the fourth power switch Q4are connected to the control unit101, respectively. Therefore, the control unit101could respectively controls the operations of the first power switch Q1, the second power switch Q2, the third power switch Q3and the fourth power switch Q4. For example, the control unit101controls the turn-on time or the turn-off time of each power switch.

In detailed, each of the first power switch Q1, the second power switch Q2, the third power switch Q3and the fourth power switch Q4has a control terminal, a first terminal and a second terminal. The cathode of the diode D1is electrically connected to the first terminal of the first power switch Q1. The anode of the diode D1is electrically connected to the second terminal of the first power switch Q1. The cathode of the diode D2is electrically connected to the first terminal of the second power switch Q2. The anode of the diode D2is electrically connected to the second terminal of the second power switch Q2. The cathode of the diode D3is electrically connected to the first terminal of the third power switch Q3. The anode of the diode D2is electrically connected to the second terminal of the third power switch Q3. Similarly, the cathode of the diode D4is electrically connected to the first terminal of the fourth power switch Q4. The anode of the diode D4is electrically connected to the second terminal of the fourth power switch Q4. In addition, the second terminal of the first power switch Q1is electrically connected to the first terminal of the second power switch Q2. The second terminal of the third power switch Q3is electrically connected to the first terminal of the fourth power switch Q4. The first terminal of the first power switch Q1is electrically connected to the first terminal to the third switch Q3. The second terminal of the second power switch Q2is electrically connected to the second terminal of the fourth power switch Q4. Therefore, the first power switch Q1and the second power switch Q2are electrically connected to each other in series. The third power switch Q3and the fourth power switch Q4are electrically connected to each other in series.

The control terminals of the first power switch Q1, the second power switch Q2, the third power switch Q3and the fourth power switch Q4are electrically connected to the control unit101, respectively. That is, the control unit101could output control signals to the control terminals of the first power switch Q1, the second power switch Q2, the third power switch Q3and the fourth power switch Q4, so as to control the operation of overall circuit by controlling the turn-on time or the turn-off time for each of the first power switch Q1, the second power switch Q2, the third power switch Q3and the fourth power switch Q4.

According to an embodiment, the first power switch Q1, the second power switch Q2, the third power switch Q3and the fourth power switch Q4could be insulated gate bipolar transistors (IGBTs). Accordingly, the control terminals of the first power switch Q1, the second power switch Q2, the third power switch Q3and the fourth power switch Q4are the gates of the insulated gate bipolar transistors. The first terminals of the first power switch Q1, the second power switch Q2, the third power switch Q3and the fourth power switch Q4are collectors of the insulated gate bipolar transistors. The second terminals of the first power switch Q1, the second power switch Q2, the third power switch Q3and the fourth power switch Q4are emitters of the insulated gate bipolar transistors. However, the first power switch Q1, the second power switch Q2, the third power switch Q3and the fourth power switch Q4could be implemented by other types of power transistors such as metal oxide semiconductor field effect transistor (MOSFET).

As shown inFIG. 3B, a multi-phase step signal is converted into an AC signal output by a signal A (shown inFIG. 3A) from the first terminal of the first power switch Q1and a signal B (shown inFIG. 3A) from the first terminal of the fourth power switch Q4.

Referring toFIG. 4andFIG. 4A, the DC to AC converter further comprises a signal compensating module150for optimizing the multi-phase step signal according to another embodiment of this disclosure. The signal compensating module150comprises an operating unit150_2and a signal compensating unit150_1, wherein a first signal4A-3is obtained by the operating unit150_2which subtracts a predetermined signal4A-2from the multi-phase step signal4A-1. As shown inFIG. 4A, the first signal4A-3is represents the portion needed to be compensated. The first signal4A-3compensated by the signal compensating unit150_1is transmitted to the current mode switching converter are110_m_tof the battery array module110.

Referring toFIGS. 1, 3 and 4, the according to yet another embodiment of this disclosure, the DC to AC converter further comprises a sensing module140, wherein the sensing module140comprises a current sensing unit140_1and a voltage sensing unit140_2. The voltage sensing unit140_2is used to control each battery module110_n_1in the battery string module110_1, and so on. The current sensing unit140_1receives the signal A in the polarity converter130while the voltage sensing unit140_2receives the signal B in the polarity converter130. The current sensing unit140_1respectively transmits the signal A to the plural battery string modules110_1˜110_mto control the battery string modules110_1˜110_maccording to the loading characteristic. The battery string modules110_1˜110_mconnected in parallel could be adjusted to avoid the power consumption of the circuit.

In detailed, the current sensing unit140_1and the voltage sensing unit140_2are respectively connected to the control unit101. The signal A received by current sensing unit140_1could be used to detect the change of the current Io passing through an inductor (that is, the change of the input current). The change of the current Io is transmitted to the control unit101for further calculation analysis. The signal B received by the voltage sensing unit140_2could be used to detect an output voltage Vc and transmit this output voltage Vc to the control unit101for further calculation analysis. The control unit101generates control signals with the same frequency to respectively control the turn-on operations or the turn-off operations of the first power switch Q1, the second power switch Q2, the third power switch Q3and the fourth power switch Q4, according to the change of the circuit current Io detected by the current sensing unit140_1and the output voltage Vc detected by the voltage sensing unit140_2, respectively.

In other words, the control unit101controls the operations of the third power switch Q3and the fourth power switch Q4according to a current change of an inductor L detected by the current sensing unit104_1during a period, a DC voltage level of an output detected by the voltage sensing unit104_2, and the first signal4A-3to be compensated. Please note that this disclosure does not limit the actual implementation of the control unit101and the actual control of the third power switch Q3and the fourth power switch Q.

The current sensing unit could be implemented by a Hall Effect sensing element140_1or a resistor. The voltage sensing unit140_2could be implemented by a voltage sensor or a voltage divider circuit. The control unit101could be is implemented by a programmable microprocessor, such as a digital signal processor (DSP). The load could be changed according to the system architecture applied. For example, in the case of an electric vehicle, the load could be a motor or another alternative load.

According to an embodiment of this disclosure,FIG. 5shows a flowchart of a control method for a direct current (DC) to alternating current (AC) converter, comprising: receiving a DC signal by using a battery array module (step S501); reconfiguring and generating a multi-phase step signal by controlling the battery array module with a battery control module (step S502); and converting the multi-phase step signal into an AC signal output by using a polarity converter (step S503).

According to another embodiment of this disclosure, referring toFIG. 6, the component symbols and partial content of the embodiment inFIG. 5are used. The same elements are denoted by the same reference numerals. The description of the same technical content is omitted and will not be repeated here. Step S502further comprises a step of utilizing an operating unit to subtract a predetermined signal from the multi-phase step signal to obtain a first signal (step S502_1). The first signal compensated by the signal compensating unit is transmitted to a current mode switching converter of the battery array module (step S502_2). The polarity converter converts the multi-phase step signal into the AC signal output (step S503).

According to yet another embodiment of this disclosure, referring toFIG. 7, step S502further comprises a step of utilizing a voltage sensing unit to control each battery module in battery string modules with the multi-phase step signal. A current sensing unit controls the multi-phase step signal required by the battery string modules according to the loading characteristic (step S502_1_1) and subtracts a predetermined signal to obtain a first signal (step S502_1). The first signal compensated by the signal compensating unit is transmitted to a current mode switching converter of the battery array module (step S502_2). The polarity converter converts the multi-phase step signal into the AC signal output (step S503).

According to yet another embodiment of this disclosure, referring toFIG. 8, when the DC to AC converter100is applied in a hybrid power generation system, a Wind801and a photovoltaic (PV) system802could act as the DC to AC converter100to provide power to a load804and to charge the battery array module110with excess power. When the power provided by the Wind801and the PV system is less than the requirement of the load804, the battery array module110could discharge to make up the requirement to form a bi-directional DC to AC DC converter100and achieve the integration of energy storage and energy transfer.

In other words, the battery array module110is used to replace the existing DC to AC converters803to avoid power consumption. The battery array module100in the present disclosure could reconfigure voltage energy to be needed.

Therefore, according to the disclosed embodiments of the disclosure, the DC to AC DC converter100and the control method thereof are based on the control of the battery array module110at the DC end, and with the cooperation of power management, the DC to AC DC converter100have the advantages of low cost and simple control due to the easy generation of multiple phases.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the disclosed embodiments. It is intended that the specification and examples be considered as exemplars only, with a true scope of the disclosure being indicated by the following claims and their equivalents.